Do CAD/CAM dentures really release less monomer than conventional dentures?

Bisphenol A release from CAD/CAM splint materials

This study aimed to investigate the bisphenol A (BPA) release from four CAD/CAM splint materials: three polycarbonate-based (DD BioSplint C, Splint Plus Biostar, Temp Premium Flexible) and one polymethylmethacrylate-based (Temp Basic) material. From each material, ten cylindrical samples (n = 40) were immersed in high-performance liquid chromatography (HPLC) grade water following ISO 10993-12 and incubated for 24 h in an incubation shaker at 37°C and 112 rpm. Following BPA derivatization, analysis was performed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). After 24 h of incubation, all investigated materials released significant amounts of BPA compared to water blanks. The material-dependent elution increased in the following order: DD BioSplint C < Splint Plus Biostar < Temp Basic < Temp Premium Flexible. Subtracting extraneous BPA, the concentrations ranged between 2.27 ng/mL and 12.65 ng/mL. After extrapolating the concentrations in relation to the average surface area of occlusal splints, the amount of BPA per mL exceeded the Tolerable Daily Intake (TDI) set by the European Union for a person weighing 70 kg by 1.32-6.16 times. Contrary to the release from previously investigated materials, BPA elution from CAD/CAM splint materials was highly elevated. Considering the increasing adaptation of CAD/CAM techniques, elution from them may represent a relevant BPA source in daily dental practice.

Digital manufacturing techniques and the in vitro biocompatibility of acrylic-based occlusal device materials

OBJECTIVES

Material chemistry and workflow variables associated with the fabrication of dental devices may affect the biocompatibility of the dental devices. The purpose of this study was to compare digital and conventional workflow procedures in the manufacturing of acrylic-based occlusal devices by assessing the cytotoxic potential of leakage products.

METHODS

Specimens were manufactured by 3D printing (stereolithography and digital light processing), milling, and autopolymerization. Print specimens were also subjected to different post-curing methods. To assess biocompatibility, a human tongue epithelial cell line was exposed to material-based extracts. Cell viability was measured by MTT assay while Western blot assessed the expression level of selected cytoprotective proteins.

RESULTS

Extracts from the Splint 2.0 material printed with DLP technology and post-cured with the Asiga Flash showed the clearest loss of cell viability. The milled and autopolymerized materials also showed a significant reduction in cell viability. However, by storing the autopolymerized material in dH2O for 12 h, no significant viability loss was observed. Increased levels of cytoprotective proteins were seen in cells exposed to extracts from the print materials and the autopolymerized material. Similarly to the effect on viability loss, storing the autopolymerized material in dH2O for 12 h reduced this effect.

CONCLUSIONS/CLINICAL RELEVANCE

Based on the biocompatibility assessments, clinical outcomes of acrylic-based occlusal device materials may be affected by the choice of manufacturing technique and workflow procedures.

Flexural strength of repaired denture base materials manufactured for the CAD-CAM technique

PURPOSE

To evaluate the flexural properties of repaired poly(methylmethacrylate) (PMMA) denture base materials for computer-aided design/computer-aided manufacturing (CAD-CAM) and to compare them with heat-activated polymerized PMMA.

METHODS

A total of 288 specimens (65 × 10 × 2.5 mm) were prepared using both CAD-CAM and conventional blocks and repaired using autopolymerizing and visible-light polymerizing (VLC) materials. Microwave energy, water storage and hydroflask polymerization were applied as additional post-polymerization cycles after the repair process. The flexural strength (FS) of the specimens was evaluated using the three-point bending test. Data were evaluated statistically using 2-way ANOVA followed by Bonferroni's correction to determine the significance of differences between the groups (P ≤ 0.05).

RESULTS

The FS of the denture base materials for CAD-CAM was significantly higher than that for the heat-activated group (P ≤ 0.05). The FS was significantly highest when microwave energy was used for the post-polymerization cycle. The FS values for all groups repaired with VLC resin were significantly lower than for the autopolymerization group (P ≤ 0.05).

CONCLUSION

The flexural properties of denture base materials for CAD-CAM repaired using autopolymerizing acrylic resins can recover by 50-70%. Additional post-polymerization cycles for autopolymerizing repair resin can be suggested to improve the clinical service properties of repaired dentures.

Comparative cost-analysis for removable complete dentures fabricated with conventional, partial, and complete digital workflows

STATEMENT OF PROBLEM

Comparative cost-analysis related to different manufacturing workflows for removable complete denture fabrication is seldom performed before the adoption of a new technology.

PURPOSE

The purpose of this study was to compare the clinical and laboratory costs of removable complete dentures fabricated with a conventional (workflow C), a partial digital (workflow M), and a complete digital (workflow D) workflow and to calculate the break-even points for the implementation of digital technologies in complete denture fabrication.

MATERIAL AND METHODS

Clinical and laboratory costs for each of the investigated workflows and the manufacturing options related to denture base and denture teeth fabrication were collected from 10 private Italian dental laboratories and clinics. The selected variables included the clinical and laboratory manufacturing time needed to complete each workflow (opportunity cost); costs for materials, labor, packaging, and shipping; and capital and fixed costs for software and hardware, including maintenance fees. The effect of manufacturing workflows and their options on the outcomes of interest was investigated by using generalized estimated equations models (α=.05). Cost minimization and sensitivity analysis were also performed, and break-even points were calculated for the equipment capital costs related to the implementation of workflows M and D.

RESULTS

From a laboratory standpoint, workflows M and D and related manufacturing options significantly (P<.001) reduced manufacturing time (5.90 to 6.95 hours and 6.30 to 7.35 hours, respectively), and therefore the opportunity cost of each denture compared with workflow C. Workflow M allowed variable costs savings between 81 and 169 USD, while workflow D allowed for an additional saving of 34 USD. The sensitivity analysis showed that the break-even point related to the capital investment for the equipment needed to implement workflows M and D could be reached, depending on the manufacturing options adopted, between 170 and 933 dentures for workflow M and between 73 and 534 dentures for workflow D. From a clinical standpoint, workflows C and M were almost identical. Conversely, workflow D, which included intraoral scanning, required 1 fewer appointment, saving 0.6 hours of chairside time and about 14 USD for materials compared with M.

CONCLUSIONS

Digital workflows (partial and complete digital workflows) were more efficient and cost-effective than the conventional method of fabricating removable complete dentures, with workflow D showing the lowest opportunity and variable costs and break-even point. Savings increased when stock denture teeth were replaced with milled denture teeth and still further with the adoption of 3-dimensionally (3D) printed denture teeth. Milling equipment and materials for denture base fabrication were more expensive than those for 3D-printing. Milling monobloc dentures reduced opportunity and labor costs but increased material cost.

Challenges and Solutions in Clinical Workflow for the Rehabilitation of Completely Edentulous Patients Through CAD/CAM Dentures: A Case Study

In the field of removable prosthodontics, computer-aided design and computer-aided manufacturing (CAD/CAM) have become widely recognized. The traditional method, which uses heat-polymerized resins for injection or compression molding, necessitates up to five patient visits and laborious laboratory processes. A digital workflow combined with a CAD/CAM methodology can provide prompt prosthesis delivery for patients with time constraints. This article's goal is to outline the steps and the limitations in the fabrication of digital dentures as well as the challenges, limitations, and solutions developed while developing a clinical workflow for the rehabilitation of completely edentulous patients with the CAD/CAM System.

The Influence of Contemporary Denture Base Fabrication Methods on Residual Monomer Content, Flexural Strength and Microhardness

(1) Background: Digital technologies are available for denture base fabrication, but there is a lack of scientific data on the mechanical and chemical properties of the materials produced in this way. Therefore, the aim of this study was to investigate the residual monomer content, flexural strength and microhardness of denture base materials as well as correlations between investigated parameters. (2) Methods: Seven denture base materials were used: one conventional heat cured polymethyl methacrylate, one polyamide, three subtractive manufactured materials and two additive manufactured materials. High-performance liquid chromatography was used to determine residual monomer content and the test was carried out in accordance with the specification ISO No. 20795-1:2013. Flexural strength was also determined according to the specification ISO No. 20795-1:2013. The Vickers method was used to investigate microhardness. A one-way ANOVA with a Bonferroni post-hoc test was used for the statistical analysis. The Pearson correlation test was used for the correlation analysis. (3) Results: There was a statistically significant difference between the values of residual monomer content of the different denture base materials (p < 0.05). Anaxdent pink blank showed the highest value of 3.2% mass fraction, while Polident pink CAD-CAM showed the lowest value of 0.05% mass fraction. The difference between the flexural strength values of the different denture base materials was statistically significant (p < 0.05), with values ranging from 62.57 megapascals (MPa) to 103.33 MPa. The difference between the microhardness values for the different denture base materials was statistically significant (p < 0.05), and the values obtained ranged from 10.61 to 22.86 Vickers hardness number (VHN). A correlation was found between some results for the material properties investigated (p < 0.05). (4) Conclusions: The selection of contemporary digital denture base manufacturing techniques may affect residual monomer content, flexural strength and microhardness but is not the only criterion for achieving favourable properties.

Effect of support structures on the trueness and precision of 3D printing dentures: An in vitro study

Purpose Additive manufacturing has revolutionized the fabrication of complete dentures. However, this process involves support structure, which is a construction part that holds the specimen during printing, and may prove to be disadvantageous. Therefore, this in vitro study compared the effect of support structure reduction on various volume and area distributions of a 3D-printed denture base to determine optimal parameters based on accuracy.Methods A complete maxillary denture base construction file was used as reference. Twenty denture bases were 3D printed under four conditions (total n=80): no support structure reduction (control), palatal support structure reduction (Condition P), border support structure reduction (Condition B), and palatal and border support structure reduction (Condition PB). Printing time and resin consumption were also recorded. The intaglio surface trueness and precision of all acquired data were exported to a 3D analysis software, and the dimensional changes to the denture base were analyzed using the root-mean-square estimate (RMSE) to assess geometric accuracy and generate color map patterns. Nonparametric Kruskal-Wallis and Steel-Dwass tests (α=0.05) analyzed the accumulated data.Results Control had the lowest RMSE values for trueness and precision. Nevertheless, it demonstrated a significantly lower RMSE than that of Condition B (P=0.02) in precision. Owing to negative deviation at the palatal region, Conditions P and PB had higher retention than Control and Condition B regarding the color map pattern.Conclusions Within the limitations of this study, the reduction of palatal and border support structures showed optimal accuracy with resource and cost savings.

CAD/CAM full-mouth rehabilitation of an elderly patient: One-piece digital complete denture meets multilayered zirconia with gradient technology

OBJECTIVE

This article highlights a CAD/CAM complete-mouth rehabilitation in an 82-year-old patient by means of a complete maxillary prosthesis and mandibular implant- and tooth-supported fixed restorations made from multilayered zirconia.

CLINICAL CONSIDERATIONS

Comprehensive complete-mouth rehabilitations in elderly patients with adaptation of the occlusal vertical dimension (OVD) often present particular challenges. This applies especially when exacting functional and esthetic requirements are to be met and the treatment should not cause the patient too much effort, still ensuring the highest level of quality and efficiency and a low intervention rate.

CONCLUSION

The digital approach used for the present patient allowed for an efficient treatment procedure, facilitated virtual evaluations using a face-scan, and enhanced the predictability of the prosthodontic outcome. The approach enabled some steps required in the conventional protocol to be omitted, resulting in a straightforward clinical treatment with minimal strain on the patient.

CLINICAL SIGNIFICANCE

Because of the comprehensive recording of extraoral and intraoral data, for example with a facial scanner, it was possible to transfer a digital replica of the patient to the dental laboratory technician. With this protocol, many steps can be performed in the absence of the real patient.

Recent Advances in 3D Printing of Polymers for Application in Prosthodontics

Contemporary mass media frequently depict 3D printing as a technology with widespread utilization in the creation of dental prosthetics. This paper endeavors to provide an evidence-based assessment of the current scope of 3D printing's integration within dental laboratories and practices. Its primary objective is to offer a systematic evaluation of the existing applications of 3D-printing technology within the realm of dental prosthetic restorations. Furthermore, this article delves into potential prospects, while also critically examining the sustained relevance of conventional dental laboratory services and manufacturing procedures. The central focus of this article is to expound upon the extent to which 3D printing is presently harnessed for crafting dental prosthetic appliances. By presenting verifiable data and factual insights, this article aspires to elucidate the actual implementation of 3D printing in prosthetic dentistry and its seamless integration into dental practices. The aim of this narrative review is twofold: firstly, to provide an informed and unbiased evaluation of the role that 3D printing currently plays within dental laboratories and practices; and secondly, to instigate contemplation on the transformative potential of this technology, both in terms of its contemporary impact and its future implications, while maintaining a balanced consideration of traditional dental approaches.

Comparative Evaluation of the Digital Workflow and Conventional Method in Manufacturing Complete Removal Prostheses

The aging population in developed countries has increased the number of edentulous patients and, therefore, the need for prosthetic rehabilitation to improve their quality of life. Complete dentures are the main treatment option in these cases. The use of CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) in dentistry has improved clinical protocols and outcomes, achieving a reduction in work time and economic costs for the patients. The main objective of this review was to compare the characteristics of conventional and digital dentures, attempting to determine whether the use of new technologies represents an improvement in the properties of removable complete dentures. A bibliographic review was carried out in the PubMed/MEDLINE, Cochrane Library, Scielo, and Embase databases. With the initial search, 157 articles were obtained. After applying the inclusion and exclusion criteria, 64 publications were selected for this bibliographic review. The different conclusions of the studies consulted were compared regarding fit and retention, fracture resistance, surface roughness, biocompatibility, and aesthetics, taking into account the different methods of prostheses fabrication. In general, digital prostheses have shown better mechanical properties and, consequently, better biocompatibility and aesthetics than conventional prostheses. However, the obtained results were very heterogeneous, preventing a supported conclusion.

Bond strength between denture lining material and CAD-CAM denture base resin: A systematic review and meta-analysis

STATEMENT OF PROBLEM

An effective bond between a denture lining material and the denture base resin is necessary for proper function. Regarding the new technologies for manufacturing denture bases, a systematic search of the literature on this topic is lacking.

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the bond strength between denture lining material and computer-aided design and computer-aided manufacturing (CAD-CAM) denture base resin (milled and 3-dimensionally printed) versus conventional denture base resin.

MATERIAL AND METHODS

Electronic databases (PubMed/MEDLINE, Scopus, and Web of Science) were independently searched by 4 researchers for relevant studies published up to April 2023. The population, intervention, comparison, and outcome (PICO) question was: "Comparing conventional and CAD-CAM (milled and 3-dimensionally printed) denture base materials, which promote greater bond strength when associated with denture lining material?" A meta-analysis was performed based on mean ±standard deviation bond strength values between denture base resins and denture lining material with 95% confidence intervals.

RESULTS

Five in vitro studies were included. For bond strength, no difference was noted between conventional and milled denture base resin (confidence interval: -0.99 [-2.17 to 0.20]; heterogeneity: t2=0.57; Chi2:4.57; I2=78%; P=.10), and conventional resin had better values compared with those of 3-dimensionally (3D) printed (confidence interval: 3.03 [2.40-3.66]; heterogeneity: t2=0.00; Chi2:0.56; I2=0%; P<.001) when relined with soft materials. The milled denture base resin was better than the conventional (confidence interval: -0.85 [-1.33 to -0.38]; heterogeneity: Chi2:28.87; I2=93%; P<.001), with no difference between 3D printed and conventional (confidence interval: 0.18 [-4.23 to 4.59]; heterogeneity: t2=16.51; Chi2:130.99; I2=98%; P=.94) for hard liners.

CONCLUSIONS

The bond strength between resins for milled CAD-CAM denture bases and denture lining material was similar to that of conventional denture base resin, regardless of the consistency of the denture lining material. The bond strength to 3D printed CAD-CAM resin was lower than that of the milled version.

Flexural Strength Analysis of Different Complete Denture Resin-Based Materials Obtained by Conventional and Digital Manufacturing

PMMA (Polymethylmethacrylate) is the material of choice to fabricate denture bases. Recently, with the introduction of CAD-CAM and 3D printers in dentistry, new materials have been proposed for complete denture manufacturing.

AIM

This study compared the flexural strength of different resins fabricated using different technologies (conventional, CAD-CAM-milled, and 3D-printed) and polymerization techniques.

METHODS

A total of 11 different resins were tested: six PMMA conventional (Acrypol R, Acrypol LL, Acrypol HI, Acrypol Fast, Acryself and Acryslef P), two milled obtained from UDMA PMMA disks (Ivotion disk and Aadva disk, control groups), two 3D-printed PMMA resins (NextDent Denture 3D+, and SprintRayEU Denture Base), and one 3D-printed composite resin (GC Temp Print). Flexural strength was measured using a universal testing machine. One-way ANOVA and Bonferroni post hoc tests were performed; the p-value was set at 0.05 to consider statistically significant differences among the groups. Spearman test was used to evaluate the correlation between polymerization technique and the flexural strength of 3D-printed resins.

RESULTS

CAD-CAM-milled specimens showed the highest flexural strength (107.87 MPa for UDMA) followed by 3D-printed composite resins (102.96 MPa). Furthermore, 3D-printed resins polymerized for 40 min with the BB cure unit showed no statistically significant differences with conventional resin groups. Moreover, in all the 3D-printed specimens, a high correlation between polymerization technique and flexural strength was found.

CONCLUSIONS

In terms of flexural strength, the polymerization technique is a determinant for both acrylic and composite resins. Temp Print can be a potential alternative to fabricating removable dentures and showed promising results when used in combination with pink color resin powder.

The effects of different surface treatments applied to milled PMMA denture base material on repair bond strength

The high cost of CAD/CAM systems and materials is a severe economic burden. Therefore, repair of CAD/CAM PMMA, selecting appropriate repair materials, and surface modifications are clinically important. This study aims to evaluate the shear bond strength of PMMA repair materials after various surface treatments on CAD/CAM PMMA denture base material. For this purpose, a total of 480 CAD/CAM PMMA denture base test specimens were manufactured. Then all test specimens were divided into 6 groups, and different surface treatments were applied. Group A: sandblasting, Group B: 4% hydro fluoric acid, Group C: tungsten carbide bur, Group D: dichloromethane + methyl methacrylate mixture, Group E: dichloromethane and methyl methacrylate, Group F: no surface treatment. Each group is then divided into 4 different subcategories; repair processes were performed using; heat-cured acrylic resin (n:20), auto-polymerized acrylic resin (n:20), gingiva composite (n:20), and CAD/CAM PMMA tooth material (n:20). After repairs, thermal aging was applied to half of the test specimens in each subcategory. The shear bond strength value was measured with a universal test device. Sandblasting group showed the highest surface roughness value in all test specimens (p < 0.001). Heat-cured acrylic resin with sandblasting exhibited the highest bond strength, while the untreated gingiva composite resin exhibited the lowest value. Thermal aging decreased bond strength in all repair materials (p < 0.001). Among the surface treatment groups, sandblasting with Al2O3 particles exhibited the highest surface roughness value and repair bond strength. The application of organic solvents to the surface increased the surface roughness and repair bond strength. Applying dichloromethane and methyl methacrylate monomer separately is more effective than applying it as a mixture. The ideal bonding among repair materials was obtained with heat-cured acrylic resin.

Evaluation of Impact Strength and Flexural Strength of Polyether Ether Ketone vs. Computer-Aided Design/Computer-Aided Manufacturing Polymethyl Methacrylate Denture Base Materials: An In-Vitro Study

OBJECTIVE

The objective is to comparatively assess the impact strength and flexural strength of polyether ether ketone (PEEK) vs. computer-aided design/computer-aided manufacturing (CAD/CAM) polymethyl methacrylate denture base material.

METHODS

A total of 90 samples were fabricated with traditional heat cure PMMA, PEEK, and CAD/CAM PMMA and divided into three groups of 30 samples each. The impact strength of all the samples was measured using an Izod impact tester with a pendulum in the air at 23±2°C. A three-point bending test was used in a Universal Testing Machine to assess the flexural strength of all the samples. The impact strength and flexural strength mean values were computed using a one-way ANOVA test.

RESULT

Impact strength and flexural strength of PEEK (IS=10.22±1.25 kJ/m2 and FS=120±8.0 MPa) is almost identical to CAD/CAM PMMA sample (IS=9.595±3.313 kJ/m2 and FS=118.11±5.00 MPa) whereas for conventional heat cure PMMA (IS=4.00±.011 kJ/m2 and FS=75.4±4.50 MPa) the values are least among the three.

CONCLUSION

 PEEK or CAD/CAM PMMA share almost identical and superior mechanical properties, and both can be used as better alternatives for complete denture fabrication rather than using conventional heat cure PMMA.

Impact of different chemical denture cleansers on the properties of digitally fabricated denture base resin materials

PURPOSE

To compare the impact of three different chemical denture cleansers (CDCs) (Corega, chlorhexidine, and hydrogen peroxide) on the surface roughness, microhardness, and color stability of 3D-printed, computer-aided design and computer-aided manufacturing (CAD-CAM) milled, and heat-polymerized denture base material (DBM).

MATERIALS AND METHODS

A total of 420 disc-shaped specimens (10 ± 0.1 × 2 ±0.1 mm) were fabricated using three different construction techniques: three-dimensional (3D) printing (n = 140), CAD-CAM milling (n = 140), and heat-polymerization (n = 140). Sixty specimens (20 of each DBM) were used for baseline (pre-immersion) measurements (T1 ) for the tested surface properties (hardness [n = 10/material] and roughness [n = 10/material]). The remaining 360 specimens (n = 120/material) were investigated for surface roughness, microhardness, and color change after immersion for 1 year (T2 ) in distilled water or CDCs (n = 30/solution and n = 10/test). The data were analyzed using two-way ANOVA, one-way ANOVA followed by post-hoc Tukey's test at a significance level of less than 0.05.

RESULTS

Significant differences were observed in the effects of the tested CDCs on the surface roughness, micro-hardness, and color stability of varying DBM specimens (p < 0.05). Corega showed the highest surface roughness and color change in all DBMs while H2 O2 resulted in the lowest microhardness for all DBMs. The lowest changes in all tested properties were seen with distilled water followed by chlorhexidine. A significant effect of type of cleanser, denture base material, and the interaction between the two was seen on all measured properties (p < 0.05).

CONCLUSIONS

The tested CDCs significantly affected the surface properties of all DBMs but at varying degrees. Corega produced the highest negative effect on roughness and color change while H2 O2 dramatically affected the microhardness. Prolonged use of CDCs should be cautiously followed.

Description of Poly(aryl-ether-ketone) Materials (PAEKs), Polyetheretherketone (PEEK) and Polyetherketoneketone (PEKK) for Application as a Dental Material: A Materials Science Review

Poly(aryl-ether-ketone) materials (PAEKs), a class of high-performance polymers comprised of polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), have attracted interest in standard dental procedures due to their inherent characteristics in terms of mechanical and biological properties. Polyetheretherketone (PEEK) is a restorative dental material widely used for prosthetic frameworks due to its superior physical, mechanical, aesthetic, and handling features. Meanwhile, polyetherketoneketone (PEKK) is a semi-crystalline thermoplastic embraced in the additive manufacturing market. In the present review study, a new way to fabricate high-performance polymers, particularly PEEK and PEKK, is demonstrated using additive manufacturing digital dental technology, or 3-dimensional (3D) printing. The focus in this literature review will encompass an investigation of the chemical, mechanical, and biological properties of HPPs, particularly PEEK and PEKK, along with their application particularly in dentistry. High-performance polymers have gained popularity in denture prosthesis in advance dentistry due to their flexibility in terms of manufacturing and the growing interest in utilizing additive manufacturing in denture fabrication. Further, this review also explores the literature regarding the properties of high-performance polymers (HPP) compared to previous reported polymers in terms of the dental material along with the current advancement of the digital designing and manufacturing.

Effect of adding a hard-reline material on the flexural strength of conventional, 3D-printed, and milled denture base materials

STATEMENT OF PROBLEM

Novel 3-dimensionally printed resin and milled polymethyl methacrylate materials have been marketed for computer-aided design and computer-aided manufacturing (CAD-CAM) denture base fabrication. However, information on the flexural strength of digitally fabricated denture base material is limited, and little is known about how they are affected by a hard-reline procedure.

PURPOSE

The purpose of this in vitro study was to assess the flexural strength of 6 digitally manufactured denture base materials and to assess the effect of a hard-reline procedure on their flexural strength.

MATERIAL AND METHODS

A total of 140 strips of denture base material were fabricated from a conventional heat-polymerized polymethyl methacrylate (L199), 3 brands of milled polymethyl methacrylate (IBC, DSL, and ADH), and 3 brands of 3D-printed resin (DFD, ADB, and DrFD) (n=20). Ten specimens in each group did not receive any treatment, and 10 were relined with a hard-reline material (ProBase Cold Trial Kit). Specimens were then subjected to a 3-point flexural strength test using a universal testing machine at a crosshead speed of 5.0 mm/min. A 1-way ANOVA test followed by the Tukey multiple comparison test was used to detect the difference in flexural strength and the strain at fracture of the different types of denture base materials (α=.05). The comparison of flexural strength between with and without hard-reline was analyzed using an unpaired t test (α=.05).

RESULTS

All materials, with or without the hard-reline, met the International Organization for Standardization (ISO) 20 795-1:2013 standard for flexural strength (65 MPa). The milled materials (DSL>IBC≈ADH) showed higher flexural strength than the 3D-printed or conventional materials (DrFD>DFD≈ADB≈L199) without a hard-reline. No statistical difference in flexural strength was found among the hard-relined denture base materials (P=.164). All 3 milled materials showed reduced flexural strength after relining, while the relined conventional (L199) and 3D-printed materials (DFD and ADB) showed notably higher flexural strength; printed DrFD showed no significant difference (P=.066). In terms of strain at fracture, the milled materials displayed higher values than those of the conventional or 3D-printed materials (P<.05).

CONCLUSIONS

All digitally fabricated denture base materials were within acceptable limits for clinical use, even after hard relining. Flexural strength was highly dependent on the type of material. Hard relining affected the flexural strength of most of the digitally fabricated denture base materials.

The Shear Bond Strength between Milled Denture Base Materials and Artificial Teeth: A Systematic Review

The data about bond strength between digitally produced denture base resins and artificial teeth are scarce. Several studies investigated shear bond strength values of milled denture base resins and different types of artificial teeth. The purpose of the present study was to compare and evaluate the available evidence through a systematic review. A bibliographic search was conducted in PubMed, Scopus, and Web of Science to assess adequate studies published up to 1 June 2022. This review followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. The appropriate studies that determined the shear bond strength values between milled denture base resins and artificial teeth were selected. The initial search identified 103 studies, which were included in the PRISMA 2020 flow diagram for new systematic reviews. Three studies met the inclusion criteria, and all of them present a moderate risk of bias (score 6). Two studies found no statistical differences between heat-polymerized and CAD/CAM (milled) denture base materials when attached with different types of artificial teeth, while one study showed higher values of CAD/CAM (milled) denture base materials. Bonding agents ensure bonding strength at least similar to the conventional methods. In order to improve the quality of future studies, it would be advantageous to use a larger number of specimens with standardized dimensions and a blinded testing machine operator to decrease the risk of bias.

Effect of Fiber Reinforcement on the Flexural Strength of the Transitional Implant-Supported Fixed Dental Prosthesis

PURPOSE

The aim of this in vitro study was to assess the efficacy of fiber reinforcement to enhance flexural strength of the transitional implant-supported fixed dental prosthesis (TISFDP).

MATERIALS AND METHODS

One hundred and forty denture acrylic resin plates (64 mm × 12 mm × 5 mm) with two 7 mm diameter holes were fabricated using heat-polymerized type (Lucitone 199) and CAD-CAM prepolymerized type (AvaDent) materials to simulate a chair-side reconstruction of the TISFDP. Specimens were divided into 7 groups (n = 10) according to the airborne-particle abrasion of titanium cylinder (Straumann) surface and locations of fiber reinforcement ribbons (Ribbond-ULTRA). No cylinder surface abrasion and no fiber added acrylate specimens were used as the controls. The prosthetic screws were hand-tightened on a custom fixture with analogs. Specimen hole and cylinder were joined using a 50:50 mixture of chemically polymerized resin (QYK-SET; Holmes Dental) and repair resin (Dentsply Sirona). Ten acrylate specimens with no holes were fabricated from each tested material and assigned as positive controls. A modified four-point bending test (ASTM standard-D6272) was conducted using a universal testing machine and a custom fixture with a crosshead speed 1 mm/min. The maximum failure loads were recorded. Data were statistically analyzed using 2-way ANOVA and the Tukey tests at α = 0.05.

RESULTS

The flexural strength values ranged from 55.4 ±8.3 to 140.9 ±15.4 MPa. The flexural strength decreased significantly when fiber was attached on the titanium cylinder surface (p < 0.05). There were no statistically significant differences in flexural strength values between specimens with and without titanium cylinder surface abrasion (p > 0.05). Statistically significant improvement in flexural strength was observed in specimens with fibers attached around the specimen holes (p < 0.05) buccally and lingually. The obtained values were not statistically significantly different from the positive controls (p > 0.05). Some fixation screw fractures were observed before catastrophic failure of specimens during testing.

CONCLUSIONS

Fiber reinforcement significantly improved the flexural strength of denture acrylic resins only if placed around the specimen holes on the tension side at the site of initiation of crack propagation. Even when the specimens underwent catastrophic failure, the segments remained attached to each other with the attached fibers.

A review on clinical use of CAD/CAM and 3D printed dentures

Aim The aim of this article was to review the current clinical application of computer-aided design/computer-aided manufacturing (CAD/CAM) and three-dimensional (3D) printed dentures in dental clinics.Methods A systematic approach for searching PubMed, Embase, Scopus, and Web of Science databases. The search was performed using a variety of keywords including clinical use AND 3D printed removable dentures OR clinical use AND CAD/CAM removable dentures OR clinical use AND digital removable dentures. Selection criteria included articles written in English and reporting information on clinical applications of digital dentures between 2010 to January 2022.Results The findings outlined the main clinical advantages of digital dentures such as saving working time, satisfying clinical results and securing patients' records, and also requirement of additional visits to secure aesthetic patient satisfaction, good retention and ideal vertical dimension. Many studies recommended performing clinical try-in with regards to providing better results. It was also established that 3D printers are less expensive than milling centres and therefore can be afforded by individual dental professionals.Conclusion Digital dentures are a promising option in treating edentulous patients, especially in remote areas where skilful technicians are rare. However, there are some limitations in their applications.

Evaluation of the Effect of Different Construction Techniques of CAD-CAM Milled, 3D-Printed, and Polyamide Denture Base Resins on Flexural Strength: An In Vitro Comparative Study

PURPOSE

To compare the flexural strength of computer-aided design and computer-aided manufacturing (CAD-CAM) milled denture base resin (DBR), 3D-printed DBR, polyamide, and conventional compression-molded DBR.

MATERIALS AND METHODS

Six denture base resins were used, one conventional heat-polymerized (Vertex), two milled CAD-CAM (AvaDent and Polident), two 3D-printed (Harz and NextDent), and one flexible polyamide (Polyamide). According to ISO 20795-1:2013, 60 specimens (65×10×3 mm) were constructed and divided into six groups (n = 10), according to DBR type. The flexural strength was measured using a universal testing machine and three-point loading test. Data were collected and analyzed using one-way ANOVA and Tukey's pair-wise post hoc tests (α = 0.05).

RESULTS

One-way ANOVA results showed significant differences in flexural strengths between the tested DBRs (p˂0.001). Milled denture base resins (AvaDent and Polident) had significantly higher flexural strength values than the other groups (p˂0.001) and were followed by Vertex and NextDent, while Polyamide and Harz had the lowest values. Polyamide and Harz denture base resins had significantly lower flexural strength values than conventional denture base resin (p˂0.001).

CONCLUSION

CAD-CAM milled DBRs showed the highest flexural strength when compared with conventional compression-molded or 3D-printed DBRs, while 3D-printed DBRs and polyamide showed the lowest flexural strengths.

CAD-CAM Fabricated Denture Base Resins: In Vitro Investigation of the Minimum Acceptable Denture Base Thickness

PURPOSE

To investigate the influence of reducing material thickness on flexural properties of computer-aided design and computer-aided manufacturing (CAD-CAM) denture base resins.

MATERIALS AND METHODS

Four CAD-CAM denture base acrylic resin materials were selected; two were made via the subtractive method (AvaDent and IvoCad) and two were made with the additive method (FormLabs and NextDent). One heat-polymerized denture base material was used as a control. Specimens were fabricated with varying thicknesses (n = 10/group): 3.3 mm, 2.5 mm, 2 mm, or 1.5 mm. Flexural strength was evaluated via a three-point bending test. One- and two-way ANOVA were used for data analysis along with Tukey's post hoc comparison (α = 0.05).

RESULTS

Reducing the thickness of materials made via the subtractive method did not influence flexural strength up to 2 mm (p > 0.05). However, the difference was significant at a 1.5 mm thickness (p ˂ 0.001). For materials made via the additive method, NextDent specimens had no significant decrease in flexural strength when the thickness was reduced to 2 mm (p = 0.58). FormLabs specimens showed a significant decrease (p ˂ 0.001), although the values of flexural strength were clinically acceptable. During testing, specimens manufactured via the additive method at a 1.5 mm thickness bent without fracturing and were therefore excluded. All materials showed a reduction in elastic modulus as the thickness decreased (p ˂ 0.001).

CONCLUSION

Heat-polymerized, AvaDent, and IvoCad materials may be used for denture base fabrication at a minimum thickness of 1.5 mm. FormLabs and NextDent may be fabricated at a 2 mm minimum thickness, with clinically acceptable flexural properties.

Evaluation of a novel 3D-printed custom tray for the impressions of edentulous jaws

PURPOSE

The purpose of this study was to evaluate a novel 3D-printed custom tray for impressions of edentulous jaws, and to compare it with conventional impression trays.

METHODS

Fifteen edentulous patients were enroled to evaluate the accuracy and border extension of a novel custom tray in the shape of a complete denture. Four impressions were made for each patient. Impressions made using novel custom trays were considered the experimental group, impressions made using conventional custom trays were considered the control group, and impressions made using final dentures and non-pressure custom trays were considered the reference groups. The experimental and control groups were compared with the reference groups using three-dimensional (3D) comparison analysis, and the impressions were further divided into regions. The root mean square (RMS) value was calculated to analyse the differences in impression morphology. Additionally, the experimental and control groups were compared to analyse border extension at standard locations.

RESULTS

Compared to the final denture impression as a reference, the diagnostic denture impression (RMS:0.146 ± 0.024 mm) was closer to the reference than the conventional impression (RMS:0.176 ± 0.047 mm), with a significant difference only in the secondary stress-bearing area. The border extension of the diagnostic denture impression was slightly longer than the conventional impression; however, the difference was not statistically significant.

CONCLUSIONS

The impressions made using the novel custom tray were similar to those made with a definitive complete denture. However, no significant differences were noted when compared with the conventional impressions.

The effect of cooling procedures on monomer elution from heat-cured polymethyl methacrylate denture base materials

OBJECTIVE

To evaluate the amount of methyl methacrylate (MMA) released in water from heat-cured polymethyl methacrylate (PMMA) denture base materials subjected to different cooling procedures.

METHODOLOGY

Disk-shaped specimens (Ø:17 mm, h:2 mm) were fabricated from Paladon 65 (PA), ProBase Hot (PB), Stellon QC-20 (QC) and Vertex Rapid Simplified (VE) denture materials using five different cooling procedures (n=3/procedure): A) Bench-cooling for 10 min and then under running water for 15 min; B) Cooling in water-bath until room temperature; C) Cooling under running water for 15 min; D) Bench-cooling, and E) Bench-cooling for 30 min and under running water for 15 min. A, B, D, E procedures were proposed by the manufacturers, while the C was selected as the fastest one. Control specimens (n=3/material) were fabricated using a long polymerization cycle and bench-cooling. After deflasking, the specimens were ground, polished and stored in individual containers with 10 ml of distilled water for seven days (37oC). The amount of water-eluted MMA was measured per container using isocratic ultra-fast liquid chromatography (UFLC). Data were analyzed using Student's and Welch's t-test (α=0.05).

RESULTS

MMA values below the lower quantification limit (LoQ=5.9 ppm) were registered in B, C, E (PA); E (PB) and B, D, E (QC) procedures, whereas values below the detection limit (LoD=1.96 ppm) were registered in A, D (PA); A, B, C, D (PB); C, D, E (VE) and in all specimens of the control group. A, B (VE) and A, C (QC) procedures yielded values ranging from 6.4 to 13.2 ppm with insignificant differences in material and procedure factors (p>0.05).

CONCLUSIONS

The cooling procedures may affect the monomer elution from denture base materials. The Ε procedure may be considered a universal cooling procedure compared to the ones proposed by the manufacturers, with the lowest residual monomer elution in water.

Digital versus conventional complete dentures: A randomized, controlled, double-blinded crossover trial

STATEMENT OF PROBLEM

The Baltic Denture System provides a digital way to fabricate complete dentures in 2 visits. Conventional dentures using injection or compression molding require additional visits and complex laboratory procedures. However, how the fabrication method affects clinical outcomes is unclear.

PURPOSE

The purpose of this clinical, randomized, controlled, double-blinded crossover trial was to evaluate the impact of the fabrication method (digital versus conventional production) of complete dentures on clinical outcomes.

MATERIAL AND METHODS

Sixteen participants received 2 pairs of new complete dentures, produced in a digital and a conventional workflow. Each complete denture was worn for an observation period of 3 months. The order of the dentures was randomized. The primary outcome was the clinical assessment of the dentures by a blinded examiner, including peripheral extension, cutout for buccal and labial frenula, denture extension, and denture thickness. Denture esthetics were evaluated by the midline, position of anterior teeth, buccal corridor, and smile arc, and occlusal relationships were evaluated by the vertical dimension, sagittal relation, the Camper plane, and occlusion. In addition, the retention of maxillary and mandibular dentures and phonetics was evaluated. Differences between the prostheses were statistically analyzed with the McNemar test (α=.05).

RESULTS

The borders of the digital dentures were significantly more often overextended at the time of insertion (P=.021), reducing the retention of the digital dentures, especially the maxillary dentures (P=.016). The borders of the dentures could be corrected so that after 2 weeks and 3 months, no significant differences could be seen between digital dentures and conventional dentures.

CONCLUSIONS

The fabrication method has a significant influence only on the dimension of the denture border. It was significantly more often overextended in digital dentures and impaired retention, especially of the maxillary dentures, at the time of insertion. As this parameter is correctable, no significant clinical differences could be observed over the observation time of 3 months between digital dentures and conventional dentures.

In Vitro Analysis of Shear Stress: CAD Milled vs Printed Denture Base Resins with Bonded Denture Tooth

PURPOSE

As the fabrication of computer-aided design (CAD) milled and 3D printed denture base resins with bonded denture teeth increase in popularity, there is a need for research comparing the shear bond stress of milled and printed denture base resins with bonded denture teeth to that of a conventional heat processed denture base.

MATERIALS AND METHODS

Denture base resin specimens (n = 9) were fabricated according to manufacturers' instructions using a novel test design. Two milled (Ivobase CAD PMMA, Ivoclar Vivadent and Polident PMMA, Polident Dental) and two 3D printed (Denture Base LP Resin, Formlabs and Lucitone Digital Print, Dentsply Sirona) materials were used. Conventional heat processed polymethylmethacrylate was used as the control (Lucitone 199, Dentsply Sirona). Denture teeth (VITA Vitapan XL T44, #8, VITA Zahnfabrik) were bonded to their respective bases using denture tooth bonding agent (Ivobase CAD bonding system, Ivoclar). Specimens were aged in water for 600 hours at 37°C and loaded until failure in a Universal testing machine. Shear bond stress was calculated. All specimens were evaluated for mode of failure and select specimens under scanning electron microscope and vertical scanning interferometry. Data were analyzed with one-way ANOVA followed by Tukey test (IBM SPSS) and fracture analysis performed.

RESULTS

Shear stress was highest for the heat processed control (mean = 180 N ±26.76) and Polident test groups (mean = 180 N ± 34.90). Milled specimens were not significantly different from the control (p = 0.076 for IvoBase CAD and 1.00 for Polident), while the printed groups were significantly different from the control (p = 0.012 for Formlabs Denture Base Resin and p = 0.00 for Carbon Lucitone Digital Print). Milled denture base resins performed similarly to heat processed denture base resin and better than 3D printed denture bases.

CONCLUSION

For complete denture wearers, all resin materials used in this study may be clinically acceptable, as the sheer stress for all groups was higher than the reported maximum biting force of complete denture patients. However, for implant retained prostheses, the incorporation of additional retentive features should be considered when bonding denture teeth to printed bases. More research is needed to evaluate methods to increase the bond strength of denture teeth to printed denture base resins.

Physical, mechanical and anti-biofilm formation properties of CAD-CAM milled or 3D printed denture base resins: In Vitro analysis

PURPOSE

To investigate surface characteristics (roughness and contact angle), anti-biofilm formation, and mechanical properties (mini-flexural strength) of computer-aided design and computer-aided manufacturing (CAD-CAM) PMMA polymer, and three-dimensional (3D) printed resin for denture base fabrication compared with conventional heat polymerized denture base resins.

MATERIALS AND METHODS

A total of 60 discs and 40 rectangular specimens were fabricated from one CAD-CAM (AvaDent), one 3D printed (Cosmos Denture), and two conventional heat polymerized (Lucitone 199 and VipiWave) materials for denture base fabrication. Roughness was determined by Ra value; the contact angle was measured by the sessile drop method; the biofilm formation inhibition behavior was analyzed through C. albicans adhesion, while mini-flexural strength test was done using a three-point bending test. The data were analyzed using descriptive and analytical statistics (α = 0.05).

RESULTS

The CAD-CAM PMMA group showed the lowest C. albicans adhesion (log CFU/mL: 3.74 ±0.57) and highest mini-flexural strength mean (114.96 ±16.23 MPa). 3D printed specimens presented the highest surface roughness (Ra: 0.317 ±0.151 μm) and lowest mini-flexural strength values (57.23 ±9.07 MPa). However, there was no statistical difference between CAD-CAM PMMA and conventional groups for roughness, contact angle, and mini-flexural strength.

CONCLUSIONS

CAD-CAM milled materials present surface and mechanical properties similar to conventional resins and show improved behavior preventing C. albicans adhesion. Nevertheless, 3D printed resins present decreased mini-flexural strength. This article is protected by copyright. All rights reserved.

Cytotoxicity of 3D‐printed, milled, and conventional oral splint resins to L929 cells and human gingival fibroblasts

Objectives

Evidence on the biocompatibility of three‐dimensional (3D)‐printed and milled resins for oral splints is limited. This in vitro study assessed the influence of the manufacturing method on the cytotoxicity of oral splint resins on L929 cells and human gingival fibroblasts (GF1).

Materials and Methods

Standardized specimens of four 3D‐printed, two‐milled, one‐thermoformed, and one‐pressed splint resin were incubated with L929 and GF1 cells for 24 h. Immunofluorescence and WST‐8 assay were performed to evaluate cytotoxic effects. One‐way analysis of variance and Tukey's multiple comparison test were applied with the variables “splint resin” and “manufacturing method” (p < .05).

Results

Immunofluorescence showed attachment of L929 and GF1 cells to the splint resins. Irrespective of the manufacturing method, the WST‐8 assay revealed significant differences between splint resins for the viability of L929 and GF1 cells. L929 cells generally showed lower viability rates than GF1 cells. The evaluation of cell viability by the manufacturing method showed no significant differences between 3D printing, milling, and conventional methods.

Conclusions

The cytotoxic effects of 3D‐printed, milled, and conventional oral splint resins were similar, indicating minor influence of the manufacturing method on biocompatibility. Cytotoxicity of the resins was below a critical threshold in GF1 cells. The chemical composition might be more crucial than the manufacturing method for the biocompatibility of splint resins.

Flexural Properties and Hardness of CAD-CAM Denture Base Materials

PURPOSE

To compare flexural strength, elastic modulus, and surface hardness of CAD-CAM milled, 3D-printed, and heat-polymerized denture base resins.

MATERIALS AND METHODS

A total of 120 specimens were fabricated from heat-polymerized acrylic resin (HP), milled resin (Avadent and IvoCad), and 3D-printed resin (ASIGA, FormLabs, and NextDent). The specimens were divided into 6 groups according to the type of denture base material n = 20/material, (10/flexural properties and 10/hardness). Flexural strength and elastic modulus of the specimens were evaluated by 3-point bending test and surface hardness by Vickers hardness test. To test flexural properties, the specimens were fabricated according to ISO 20795-1:2013 standards (64×10×3.3 ±0.2 mm). The dimensions for hardness test were 15×10×2.5 ±0.2 mm. Scanning electron microscope was used to evaluate the surface morphology of the fractured specimens. The means and standard deviations were calculated, followed by one-way ANOVA and Tukey post-hoc test (α = 0.05).

RESULTS

Milled resins showed significantly higher values for flexural strength, elastic modulus, and surface hardness, followed by HP then 3D-printed resins (P<0.001). In between milled groups, flexural strength of AvaDent was significantly higher than IvoCad (P<0.001), while elastic modulus and hardness didn't show significant difference. In between 3D-printed resins, ASIGA showed the highest flexural strength and elastic modulus, insignificantly with FormLabs (P = 0.595) and significantly with NextDent (P = 0.008). ASIGA also showed significantly the highest hardness among the 3D-printed groups. No significant difference was found between FormLabs and NextDent flexural strength (P = 0.357), elastic modulus (P = 1.00) and surface hardness (P = 0.987).

CONCLUSION

CAD-CAM milled resins had greater flexural properties and hardness compared to heat-polymerized acrylic resin and 3D-printed resins. Although 3D-printed samples showed the lowest values of tested properties, the flexural strength and modulus were above the clinically acceptable values. This article is protected by copyright. All rights reserved.

Digital Determination and Recording of Edentulous Maxillomandibular Relationship Using A Jaw Movement Tracking System

PURPOSE

To establish a direct digital method for determining and recording edentulous maxillomandibular relationship using a custom-made jaw movement tracking system and evaluate its accuracy.

MATERIALS AND METHODS

A novel jaw tracking system was used to record the trajectory of habitual opening-closing jaw movement, and mandibular rest position (MRP) in 10 edentulous patients. 3D surface scanning was performed on the conventional maxillomandibular impressions and facial structures of patients in MRP. The multi-source data were registered using a custom-made recording tool. A plane parallel to the ala-tragus and horizontal lines was constructed 2 mm above the MRP, and its vertical position was used to determine the vertical relationship. The intersections of the trajectory passing through the plane were located, and their density distributions were analyzed. The coordinates of highest density, which presented the highest repeatability of jaw movement, were used to construct the digital maxillomandibular relationship (test group). The maxillomandibular relationship of the new complete dentures with artificial teeth in the intercuspal position was defined as the control group. The displacements of the anterior reference point and 3D deviations of the entire mandibular arch were measured and compared between the test and control groups using a Wilcoxon signed-ranks test and a one-sample t-test, respectively.

RESULTS

With reference to the centric relationship position, the maximum displacements of the anterior reference points were in the horizontal anteroposterior direction for both groups, and there were no significant differences. Compared to the control group, the 3D deviations of the entire mandibular arch in the test group were significant (95% confidence interval: 0.76 mm to 1.35 mm, P < 0.001).

CONCLUSIONS

By analyzing the individual trajectory features obtained by the in-house developed jaw tracking system, a digital method for determining and recording edentulous maxillomandibular relationships was established; however, the accuracy needs to be further improved. This article is protected by copyright. All rights reserved.

Analysis of the residual monomer content in milled and 3D-printed removable CAD-CAM Murali complete dentures: an in vitro study

OBJECTIVE

The study aimed to quantitatively evaluate the elution of methylmethacrylate from CAD-CAM manufactured removable complete dentures (RCDs) using high performance liquid chromatography (HPLC).

METHODS

Thirty-two RCDs were manufactured following either the CNC-milling (Milled: n=8) or the 3D-printing (n=24) protocols. The 3D-printed dentures were further categorized into three groups based on their post-production rinsing cycles [Extended wash cycle (EWC), Standard wash cycle (SWC), and SWC and additional Durécon coating (SWC2)]. HPLC was used to evaluate the methylmethacrylate concentrations (MMCs) eluted from the dentures in each group for different time periods (1, 2, 4, 8, and 24 hours). Mean and standard deviations were calculated for the MMCs; data was verified for normal distribution, ANOVA and post hoc tests were applied for statistical analyses (⍺=0.05).

RESULTS

The HPLC revealed that all the denture groups recorded some amounts of MMCs, with significant differences [F (3, 31) = 23.646, p<0.0001]. The milled denture group had the highest MMCs at 24 hours when compared to the EWC (p<0.0001), SWC (p=0.001), and SWC2 (p<0.0001) denture groups. SWC had a higher MMC than EWC (p=0.032) and SWC2 (p=0.015). No differences were found in MMCs when comparing EWC and SWC2 (p=0.989).

CONCLUSION

Methylmethacrylate concentrations were significantly lower in 3D-printed RCDs than in milled RCDs when using the resins employed in this study. Furthermore, the MMCs can be further decreased in the 3D-printed RCDs when coated with an additional thin protective layer (Durécon) by following the manufacturer-recommended rinsing protocol or when an extended isopropanol wash cycle is adopted.

Comparative analysis of leaching residual monomer and biological effects of four types of conventional and CAD/CAM dental polymers: an in vitro study

OBJECTIVES

The objective of this study is to investigate leaching residual monomer and biological effects of four types of conventional and computer-aided design/computer-aided manufacturing (CAD/CAM) dental polymers on human gingival fibroblasts (HGFs).

MATERIALS AND METHODS

A total of 540 disk-shaped specimens were fabricated from four different materials (n=135 per group): compression-molding polymethylmethacrylate (PMMA) (conventional denture polymer), CAD/CAM PMMA (CAD/CAM denture polymer), bis-acrylic composite resin (conventional temporary polymer), and CAD/CAM PMMA (CAD/CAM temporary polymer). Specimens were eluted in cell culture medium for 72 h at 37°C, and the residual monomer in eluates subsequently was measured by high-performance liquid chromatography (HPLC). The biological effects of material eluates on HGFs were analyzed by CCK-8 assay, flow cytometry, real-time quantitative PCR, Western blotting, and enzyme-linked immunosorbent assay (ELISA) to identify cell death patterns and its biological mechanism.

RESULTS

Methyl methacrylate (MMA) was detected only in compression-molding PMMA, and by-products were detected in bis-acrylic composite resin. The cell proliferation of CAD/CAM denture polymer or CAD/CAM temporary polymer was greater than that of compression-molding PMMA or bis-acrylic composite resin at 72 h in culture. No apoptosis and necrosis were detected in CAD/CAM dental polymers. Apoptosis was detected only in bis-acrylic composite resin and further confirmed by the upregulation of Bax and cleaved Caspase-3, as well as the downregulation of Bcl-2 gene. And no significant variation in inflammatory cytokines secretion was observed in all materials.

CONCLUSIONS

CAD/CAM dental polymers (including temporary and denture polymers) have favorable biocompatibility due to lower residual monomer, which provides scientific evidence to the controversy of biocompatibility of conventional and CAD/CAM dental polymers.

CLINICAL RELEVANCE

The use of CAD/CAM dental polymers is recommended in the fabrication of temporary restorations and dentures due to their favorable biocompatibility.

Flexural strength of CAD/CAM denture base materials: Systematic review and meta-analysis of in-vitro studies

Introduction:

Digital complete dentures fabrication techniques are expanding. This study aimed to review flexural strength (FS) of milled and 3D-printed denture base materials to answer the study question: is FS of computer-aided designing/computer-aided manufacturing (CAD/CAM) denture base comparable to conventional heat-polymerized materials?

Materials and Methods:

Search was done within different databases for articles published between January 2010 and June 2021 using specific keywords. Articles of in-vitro studies in English language with methods following International Standards Organization standardization/ADA specifications for flexural testing of conventional and CAD/CAM (milled or printed) polymethyl methacrylate (PMMA) materials were included.

Results:

Out of the 61 studies, 9 were processed for data extraction and only 7 underwent meta-analysis. Two, six, and one study showed high, moderate, and low risk of bias, respectively. Random-effects model was used for analysis and resulted in the average FS of 120.61 MPa [95% confidence interval (CI): 109.81−131.41] and 92.16 MPa (CI: 75.12−109.19) for CAD/CAM milled and heat-polymerized PMMA, respectively.

Conclusion:

Subtractive CAD/CAM technique of denture fabrication showed satisfactory FS values, whereas additive CAD/CAM method was comparable to conventional heat-polymerized technique with lower value, requiring further investigations and improvement. The clinical use of milled denture bases is an acceptable substitution to heat-polymerized PMMA, making the denture fabrication an easier and faster process.

Comparative evaluation of the effect of thermocycling on the mechanical properties of conventionally polymerized, CAD-CAM milled, and 3D-printed interim materials

STATEMENT OF PROBLEM

Studies on the energy absorption characteristics by means of elastic and plastic material deformation of interim materials are lacking.

PURPOSE

The purpose of this in vitro study was to compare the effect of different thermocycling periods on the flexural strength (σ_fs), resilience (U_r), and toughness (U_T) of conventionally polymerized, computer-aided design and computer-aided manufacturing (CAD-CAM) milled, and 3-dimensionally (3D) printed interim materials.

MATERIAL AND METHODS

Rectangular specimens (n=30 for each material) were fabricated from autopolymerized polymethyl methacrylate (PMMA), bis-acryl resin (Bis-acryl), CAD-CAM polymethyl methacrylate-based polymer (CAD-CAM/Milled), and 3D-printed composite resin (3D-Printed). Each material was divided into 3 groups (n=10) according to the applied thermocycling (5 °C to 55 °C) procedure: control (0 cycles), 2500, and 10 000 cycles. Parameters of the materials such as σ_fs, U_r, and U_T were tested in a 3-point bend test according to International Organization for Standardization (ISO) 10477. Data were statistically analyzed with the Shapiro-Wilk test followed by Kruskal-Wallis test, the Mann-Whitney U test, the Friedman test, and Wilcoxon signed-rank test (α=.05).

RESULTS

The tested material and thermocycling had a statistically significant influence on the σ_fs, U_r, and U_T values (P<.05). PMMA showed the lowest mean σ_fs, U_r, and U_T values (P<.05), and CAD-CAM/Milled showed σ_fs values similar to those of 3D-Printed at all thermocycling periods. CAD-CAM/Milled showed the highest U_r values at 10 000 cycles and the highest U_T values at all thermocycles. No significant differences were found in the mean change of σ_fs and U_r of CAD-CAM/Milled among different thermocycling periods.

CONCLUSIONS

The results suggested that digitally fabricated interim materials had better mechanical properties than conventionally polymerized materials and that milled materials had the highest stability in maintaining their initial capacity to absorb energy.

Removable partial dentures retained by hybrid CAD/CAM cobalt-chrome double crowns: 1-year results from a prospective clinical study: CAD/CAM cobalt-chrome double crowns: 1-year results

OBJECTIVES

Computer-aided design and manufacturing (CAD/CAM) has been successfully used to replace conventional steps in the fabrication of double crowns, creating hybrid-workflows that might facilitate the wider application of these restorations in the future. However, in-vivo data are still lacking.

METHODS

A prospective clinical trial was designed in which 20 patients (median age = 69 years; n women = 10) with 73 abutment teeth who needed a double-crown-retained removable partial denture (RPD) were consecutively recruited. While most of the work steps were done conventionally, gypsum models were digitized with a laboratory scanner to allow CAD/CAM fabrication of primary crowns and secondary structures. DentalDesigner software (3Shape) was used in combination with milling unit PrograMillPM7 and Co-Cr- blanks (Ivoclar-vivadent). Connectors were milled from wax, transferred to Co-Cr using lost-wax technique and bonded to the secondary crowns. Clinical follow-ups were scheduled 6 and 12 months after prosthesis insertion. Outcome parameters were complication-free survival of RPDs and abutment teeth after one year.

RESULTS

After 12 months, complication-free survival was 74% and 91% for the RPDs and abutment teeth, respectively. Complications comprised decementations (n = 5), abutment tooth fractures (n = 2), fracture of denture teeth (n = 1), and loss of abutment teeth (n = 1). These complications were easily manageable, resulting in 1-year survival of 100% for CAD/CAM RPDs.

CONCLUSIONS

First data on short-term complication rates of CAD/CAM double-crown-retained RPDs appear promising. To gather further evidence, prospective clinical trials over a longer follow-up time and with larger patient groups are required.

CLINICAL SIGNIFICANCE

Hybrid CAD/CAM double-crown retained RPDs showed a successful clinical application after one year of follow-up. Further research is needed to evaluate their performance in comparison to conventional manufacturing methods.

Fibroblast behavior on conventionally processed, milled, and printed occlusal device materials with different surface treatments

STATEMENT OF PROBLEM

Occlusal devices can be either conventionally processed, milled, or printed. However, little is known about the biocompatibility of 3D printing resin materials.

PURPOSE

The purpose of this in vitro study was to compare the viability and morphology of human gingival fibroblast cells (HFG-1) after cultivation on conventionally processed, milled, and printed occlusal device materials with different surface treatments.

MATERIAL AND METHODS

Disks of a conventionally processed (PalaXpress Clear [pP]), milled (Yamahachi PMMA Clear [sY]), and 2 different printed materials (Dental LT Clear Resin [aD]; Freeprint splint [aF]) were prepared. The surfaces of the specimens were finished by using 2 different treatments (unpolished and polished with P1200-grit silicon carbide paper). HGF-1 cells were cultivated on the specimens for 24 hours, and a viability assay was performed by using polystyrene disks as a control (n=9 disks per group). Cell morphology and the topography of the specimens were examined with scanning electron microscopy (n=3 disks per group). Two-way analysis of variance was applied to determine the effect of material and surface treatment followed by the post hoc Fisher least significant difference test (α=.05).

RESULTS

Overall, material (P<.001) and surface treatment (P<.001) significantly influenced the viability of HGF-1 cells. The viability of cells on all specimens displayed mean values between 0.85 and 1.01 compared with the control except for unpolished aD (0.00 ±0.07) and aF (0.02 ±0.05) that had only a few cells with a round shape.

CONCLUSIONS

The behavior of HGF-1 cells on conventionally processed and milled specimens was similar and not dependent on the surface treatment. Unpolished printed specimens had a cytotoxic effect. However, after polishing, cell behavior was similar to that of the conventionally processed and milled specimens.

Current Status of Digital Complete Dentures Technology

Fabrication of complete dentures (CDs) utilizing computer-aided design and computer-aided manufacturing (CAD/CAM) methods has attracted a lot of attention. The purpose of this paper was to summarize current knowledge about digital CDs and the relevant technology, and to present the application of the new technology in a dental geriatrics case. Initially, some of the challenges regarding digitization of the oral mucosa as a supporting surface of the CDs’ intaglio surface are listed. Next, a brief introduction of the CAD software capabilities regarding CDs is presented. The latest CAM additive and subtractive techniques for CDs are following. Subsequently, the consecutive steps for the construction of a digital CD as part of the prosthodontic treatment of a 90-year-old ambulative female patient are presented. Finally, some considerations about the digital workflow in CD manufacturing are discussed. In conclusion, the new digital technology has clear advantages; however, implementation requires careful planning. The digital workflow is applicable and versatile.

CAD-CAM removable complete dentures: A systematic review and meta-analysis of trueness of fit, biocompatibility, mechanical properties, surface characteristics, color stability, time-cost analysis, clinical and patient-reported outcomes

OBJECTIVES

This review compared Computer-aided designand Computer-aided manufactured (CAD-CAM) and conventionally constructed removable complete dentures (CDs).

DATA

Seventy-three studies reporting on CAD-CAM (milled/3D-printed) CDs were included in this review. The most recent literature search was performed on 15/03/2021.

SOURCES

Two investigators searched electronic databases [PubMed (MEDLINE), Embase, CENTRAL], online search engines (Google) and research portals. Hand searches were performed to identify literature not available online.

STUDY SELECTION

Studies on CAD-CAM CDs were included if they reported on trueness of fit, biocompatibility, mechanical, surface, chemical, color , microbiological properties, time-cost analysis, and clinical outcomes. Inter-investigator reliability was assessed using kappa scores. Meta-analyses were performed on the extracted data .

RESULTS

The kappa score ranged between 0.897-1.000. Meta-analyses revealed that 3D-printed CDs were more true than conventional CDs (p = 0.039). Milled CDs had a higher flexural-strength than conventional and 3D-printed CDs (p < 0.0001). Milled CDs had a higher flexural-modulus than 3D-printed CDs (p < 0.0001). Milled CDs had a higher yield-strength than injection-molded (p = 0.004), and 3D-printed CDs (p = 0.001). Milled CDs had superior toughness (p < 0.0001) and surface roughness characteristics (p < 0.0001) than other CDs . Rapidly-prototyped CDs displayed poor color-stability compared to other CDs (p = 0.029). CAD-CAM CDs d displayed better retention than conventional CDs (p = 0.015). Conventional CDs had a higher strain at yield point than milled CDs (p < 0.0001), and had superior esthetics than 3D-printed (p < 0.0001). Fabrication of CAD-CAM CDs required less chairside time (p = 0.037) and lower overall costs (p < 0.0001) than conventional CDs.

CONCLUSIONS

This systematic review concludes that CAD-CAM CDs offer a number of improved mechanical/surface properties and are not inferior when compared to conventional CDs.

CLINICAL SIGNIFICANCE

CAD-CAM CDs should be considered for completely edentulous patients whenever possible, since this technique offers numerous advantages including better retention, mechanical and surface properties but most importantly preserves a digital record. This can be a great advantage for older adults with limited access to dental care.

Comparison of CAD/CAM and Conventional Denture Base Resins: A Systematic Review

At present, complete dentures (CDs) remain the only treatment available for the majority of edentulous patients. CDs are primarily fabricated using a conventional method using polymethylmethacrylate (PMMA) resin. The steps involved in PMMA polymerisation directly affect the quality of the resin prosthetic base and any error reduces retention and occlusal accuracy of CDs. Furthermore, when using the conventional technique, the residual monomer alters the resin mechanical properties and may cause mucosal reactions. Recently, computer aided design and computer aided manufacture (CAD/CAM) techniques were increasingly used to fabricate CDs by machining resin discs that have been manufactured under high pressure and temperature. This systematic review compares CAD/CAM and conventional CDs according to their mechanical, physical and chemical characteristics, as well as the clinical impact of any differences between them. A review was conducted according to the preferred reporting items for systematic reviews and meta-analyses checklist on 392 publications from both PubMed and backward research. Fifteen studies have been included. Results showed that CAD/CAM resins had globally better physical and mechanical properties than conventional resins. The use of machined resin could improve the clinical performance, maintenance and longevity of CDs. Further studies in clinical use would be required to complement these results.

Comparison of Mechanical Properties of PMMA Disks for Digitally Designed Dentures

In this study, the physical properties of a custom block manufactured using a self-polymerizing resin (Custom-block), the commercially available CAD/CAM PMMA disk (PMMA-disk), and a heat-polymerizing resin (Conventional PMMA) were evaluated via three different tests. The Custom-block was polymerized by pouring the self-polymerizing resin into a special tray, and Conventional PMMA was polymerized with a heat-curing method, according to the manufacturer’s recommended procedure. The specimens of each group were subjected to three-point bending, water sorption and solubility, and staining tests. The results showed that the materials met the requirements of the ISO standards in all tests, except for the staining tests. The highest flexural strength was exhibited by the PMMA-disk, followed by the Custom-block and the Conventional PMMA, and a significant difference was observed in the flexural strengths of all the materials (p < 0.001). The Custom-block showed a significantly higher flexural modulus and water solubility. The water sorption and discoloration of the Custom-block were significantly higher than those of the PMMA-disk, but not significantly different from those of the Conventional PMMA. In conclusion, the mechanical properties of the three materials differed depending on the manufacturing method, which considerably affected their flexural strength, flexural modulus, water sorption and solubility, and discoloration.

Mechanical properties of polymethyl methacrylate as a denture base: Conventional versus CAD-CAM resin - A systematic review and meta-analysis of in vitro studies

STATEMENT OF PROBLEM

The development of polymethyl methacrylate (PMMA) computer-aided design and computer-aided manufacturing (CAD-CAM) resin blocks with reported improved mechanical properties has simplified complete denture production. However, whether the objective of improved mechanical properties has been achieved compared with conventional heat-polymerized PMMA is not yet clear.

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the mechanical properties of denture base resins manufactured by conventional heat-polymerization and by CAD-CAM in terms of flexural strength, flexural modulus, and surface roughness.

MATERIAL AND METHODS

Electronic databases (PubMed/MEDLINE, Scopus, Web of Science) were independently searched by 2 researchers for relevant studies published up to November 2020. The population, intervention, comparison, and outcome (PICO) question was, "Does the conventionally manufactured, heat-polymerized PMMA resin, as a denture base, demonstrate the same mechanical properties as the CAD-CAM resin block?" In addition, a meta-analysis was based on the inverse variance method. Flexural strength, flexural modulus, and surface roughness were analyzed through the continuous outcome evaluated by mean difference and standard deviation, with 95% confidence intervals. To evaluated heterogeneity, the I² value (≤25%=low, ≥50%=moderate and ≥75%=high) and the P value were considered. P<.10 indicated statistical difference for heterogeneity. The effects of meta-analysis were based on the results of heterogeneity as per the studies.

RESULTS

Thirteen in vitro studies were included in the analysis. A total of 507 specimens were evaluated, 222 conventional and 285 CAD-CAM. In terms of flexural strength, the data showed no significant difference when conventional heat-polymerized PMMA was compared with CAD-CAM PMMA resins (P=.06; mean difference=18.28; 95% confidence interval:-0.42 to 36.97). In terms of flexural modulus, there was a significant difference for the CAD-CAM PMMA group (P=.01; mean difference=589.22; 95% confidence interval: 117.95 to 1060.48). In terms of surface roughness, a significant difference was observed between the groups (P=.02; mean difference=-0.53; 95% confidence interval: -0.97 to -0.09) with the conventional heat-polymerized PMMA resin having higher surface roughness values.

CONCLUSIONS

The mechanical properties of CAD-CAM PMMA resins were generally improved when compared with heat-polymerized polymethyl methacrylate resin.

Accuracy of 3D printing compared with milling - A multi-center analysis of try-in dentures

OBJECTIVES

In recent years, computer-aided design/computer-aided manufacturing (CAD/CAM) has been used to produce removable complete dentures. Most workflows include fabrication of milled or 3D-printed try-in prostheses. 3D-printing accuracy is affected by laboratory-specific and operator-dependent factors. This international five-center study sought to compare the accuracy of 3D-printed and milled try-in dentures.

METHODS

The construction file of a maxillary removable complete denture was selected as a reference. Eight try-in dentures were 3D printed at each of the five centers. Each center used their own printer (Objet260 Connex, Stratasys; MAX, Asiga; Anycubic Photon, Anycubic 3D; PRO2, Asiga and cara Print 4.0, Kulzer) along with their own material, printing settings, post-processing and light-curing parameters. At center 2, eight try-in dentures were milled to serve as a benchmark (PrograMill PM7, Ivoclar Vivadent). Dentures were scanned and aligned to the reference file using best-fit algorithms. Geometric accuracy was analyzed using the root mean square value (trueness) and standard deviation (precision) of the distributed absolute mesh deviations. Mean values of the five sets of printed dentures and the single set of milled dentures were compared.

RESULTS

Milled dentures showed a mean trueness of 65 ± 6 μm and a mean precision of 48 ± 5 μm. Thus, they were significantly more accurate than the 3D-printed dentures in four out of five centers. In mean absolute numbers, 3D printing was less true than milling by 17-89 μm and less precise by 8-66 μm.

CONCLUSIONS

Although milling remains the benchmark technique for accuracy, differences between milled and 3D-printed dentures were non-significant for one printing center. Furthermore, the overall performance of 3D printing at all centers was within a clinically acceptable range for try-in prostheses.

CLINICAL SIGNIFICANCE

The accuracy of 3D printing varies widely between and within laboratories but nonetheless lies within the range of accuracy of conventional manufacturing methods.

Fibrin Biopolymer Incorporated with Antimicrobial Agents: A Proposal for Coating Denture Bases

The characteristics of the denture base surface, in combination with the oral environment, promote the colonization and development of Candida albicans biofilm, which is the main cause of denture stomatitis. This study evaluated the effectiveness of fibrin biopolymer with digluconate chlorhexidine or Punica granatum alcoholic extract to prevent C. albicans biofilm. Conventional heat polymerized and pre-polymerized poly(methyl methacrylate) (PMMA) circular specimens (10 × 2 mm) were fabricated (n = 504) and randomly divided into groups: no treatment (control—CT), fibrin biopolymer coating (FB), fibrin biopolymer with P. granatum (FBPg), or digluconate of chlorhexidine (FBCh) coating. The specimens were inoculated with C. albicans SC5314 (1 × 10⁷ cells/mL) and incubated for 24, 48, and 72 h. Crystal violet and colony-forming unit assays were used to quantify the total biofilm biomass and biofilm-living cells. A qualitative analysis was performed using confocal laser scanning microscopy. Data obtained are expressed as means and standard deviations and were statistically analyzed using a three-way analysis of variance (α = 0.05). The FBPg and FBCh groups inhibited the growth of C. albicans biofilm in both PMMA materials analyzed, with FBCh performing better in all periods evaluated (p < 0.0001). The colony forming unit (CFU) assay showed that the FB group favored the C. albicans biofilm growth at 24 h and 48 h (p < 0.0001), with no differences with CT group at 72 h (p = 0.790). All groups showed an enhancement in biofilm development up to 72 h (p < 0.0001), except the FBCh group (p = 0.100). No statistical differences were found between the PMMA base materials (p > 0.050), except in the FB group (p < 0.0001). Fibrin biopolymer, albeit a scaffold for the growth of C. albicans, when combined with chlorhexidine digluconate or P. granatum, demonstrated excellent performance as a drug delivery system, preventing and controlling the formation of denture biofilm.

Clinical analysis of CAD-CAM milled and printed complete dentures using computerized occlusal force analyser

BACKGROUND

Digital complete dentures (CDs) by computer-aided designing and computer-aided manufacturing (CAD-CAM) techniques (milling and three-dimensional (3-D) printing) have been evaluated clinically and provided satisfactory results. But clinical studies assessing occlusal forces by digital dentures are lacking.

OBJECTIVES

To compare the occlusal force parameters in complete dentures (CDs) fabricated by milling, 3-D printing and conventional techniques having 3 commonly used occlusal schemes, using computerized occlusal force analysis system (Tech-Scan III- T-Scan III).

METHODS

A total of 45 CDs were fabricated for 5 patients. Nine sets of CDs were made for each patient and were divided into 3 groups: Conventional CDs (CCD), Milled CDs (MCD), and 3-D printed CDs (3-DP CD). The CDs in each group were further divided into 3 sub-groups based on occlusion schemes - bilateral balanced (BBO), lingualized (LO) and mono plane (MP). Occlusal force analysis [percentage (%) of occlusal force applied on the right and left sides of the arch difference between them, centralization of forces and % of maximum occlusal/bite force] was done using computerized occlusal analysis system (T-Scan III) at the time of denture insertion. Univariate regression analysis and logistic regression analysis were performed (p< 0.05).

RESULTS

The intergroup comparison of force distribution on right and left side in CDs fabricated by various techniques showed insignificant differences (p> 0.05) but statistically significant differences (p< 0.01) were found in right-left side force difference, maximum bite force % and centralization of forces. The maximum force difference on right and left side was observed CCD with MO (37.48 ± 1.03 N) and maximum occlusal-bite force % was observed for 3-DPCD with LO (95.40 ± 1.30 N). In comparison to 3-DP CD, the chances of centre of force out of ellipse (centralization of forces) was 3.36 and 2.15 times more in CCD and MCD techniques made CDs respectively.

CONCLUSIONS

The occlusal parameters in CDs were affected by the fabrication techniques and occlusal schemes of CDs. The digital CDs retain adjusted occlusal schemes better and 3-DP CDs with BBO and LO occlusal schemes provided centralization of forces, better distribution and high maximum occlusal force % respectively.

Computerized occlusal forces analysis in complete dentures fabricated by additive and subtractive techniques

BACKGROUND

Fabrication of complete dentures by computer-aided designing and computer-aided manufacturing (CAD-CAM) techniques are now common. Subtractive and Additive are the two principal CAD-CAM techniques used for this purpose. However, studies that evaluated the occlusal forces by CDs manufactured by these techniques are lacking.

OBJECTIVES

To compare the occlusal forces in complete dentures fabricated by additive, subtractive and conventional techniques with different occlusal schemes, using computerized occlusal force analysis system [Tech-Scan III (T-Scan III)].

METHODS

Three groups (Gr) were made on the basis of techniques of fabrication of CDs: Conventional CDs (CCD), Subtractive CDs (SCD), and Additive CDs (ACD). Each group CDs were further divided into three sub groups based on occlusion schemes: bilateral balanced occlusion (BBO), lingualized occlusion (LO) and mono plane occlusion (MO). A total of 45 CDs were made: 15 in each group with 5 CDs of each occlusal scheme. For all samples, occlusal force analysis (percentage of occlusal force applied on the right and left sides of the arch, centralization of forces and percentage of maximum occlusal force) was done using computerized occlusal analysis system: T-Scan III. Univariate regression analysis and logistic regression analysis were used to find the effects of the technique of fabrication and occlusion scheme over the occlusal forces (p< 0.05).

RESULTS

The intergroup comparison revealed statistically significant differences (p< 0.01) in right-left side force difference, maximum bite force in CDs fabricated by various techniques and with different occlusion schemes. Though the effect of occlusion scheme was more than the technique of fabrication (according to effect size estimation). The maximum force difference between right-left side was observed in combination of CCD technique and MO scheme (36.88 ± 2.82 N). Furthermore, the maximum bite force was observed for SCD technique (89.14 ± 6.08 N) and LO scheme (92.17 ± 3.22 N). In comparison to ACD, the chances of centre of force out of ellipse was 2.53 time more in CCS and 0.75 times less in SCD techniques and in comparison to MO, the chances of out of ellipse was 0.298 times less in BBO and 0.396 times less in LO schemes, though these chances were not statistically significant (p> 0.05).

CONCLUSIONS

The digital CDs fabricated by subtractive technique were proved to be superior to additive technique in terms of occlusal force analysis on tested parameters. However, further research is needed on patients to determine the exact superiority of one technique over the other.

Graphene-Doped Poly (Methyl-Methacrylate) (Pmma) Implants: A Micro-CT and Histomorphometrical Study in Rabbits

Background—the graphene-doping procedure represents a useful procedure to improve the mechanical, physical and biological response of several Polymethyl methacrylate (PMMA)-derived polymers and biomaterials for dental applications. The aim of this study was to evaluate osseointegration of Graphene doped Poly(methyl methacrylate) (GD-PMMA) compared with PMMA as potential materials for dental implant devices. Methods—eighteen adult New Zealand white male rabbits with a mean weight of approx. 3000 g were used in this research. A total of eighteen implants of 3.5 mm diameter and 11 mm length in GD-PMMA and eighteen implants in PMMA were used. The implants were placed into the articular femoral knee joint. The animals were sacrificed after 15, 30 and 60 days and the specimens were evaluated by µCT and histomorphometry. Results—microscopically, all 36 implants, 18 in PMMA and 18 in DG-PMMA were well-integrated into the bone. The implants were in contact with cortical bone along the upper threads, while the lower threads were in contact with either newly formed bone or with marrow spaces. The histomorphometry and µCT evaluation showed that the GP-PMMA and PMMA implants were well osseointegrated and the bone was in direct contact with large portions of the implant surfaces, including the space in the medullary canal. Conclusions—in conclusion, the results suggest that GD-PMMA titanium surfaces enhance osseointegration in rabbit femurs. This encourages further research to obtain GD-PMMA with a greater radiopacity. Also, further in vitro and vivo animal studies are necessary to evaluate a potential clinical usage for dental implant applications.