The Effect of Different Intraoral Scanners on The Accuracy of Bite Registration in Edentulous Maxillary and Mandibular Arches

OBJECTIVES

The objective of this study was to use in vitro models to examine the bite registration accuracy of four different intraoral scanners (IOS) for edentulous maxillary and mandibular arches. The objective was to assess the trueness and precision of the IOS and determine if there were significant differences between them.

METHODS

An Asiga Max UV 3D printer was used to print maxillary and mandibular edentulous models based on the shape of Frasaco models (artificial dental arch models). Four dental implants were placed symmetrically in both models using Straumann BLT RC implants. Digital impressions were taken with Primescan, Trios 3, Trios 4, and Medit i500 intraoral scanners (n = 10 for each IOS). Digital bite registrations were made, and scanning data was exported in STL format. The accuracy of the interarch distance (the distance between the metrological spheres attached to the mandibular and maxillary models) was estimated for each IOS.

RESULTS

The results showed significant differences in trueness and precision between different IOS (p <.05), except Medit i500 and Trios 3 (p >.05). Primescan provided the most accurate results, followed by Medit i500, Trios 3, and Trios 4, respectively.

CONCLUSIONS

within the limitations of this study, the IOS type affects the accuracy of interocclusal bite registration in in vitro design. Only Primescan achieved clinically acceptable accuracy for the interocclusal recording of edentulous arches.

CLINICAL RELEVANCE

The comparison of the accuracy of bite registration between different intraoral scanners will help increase the efficiency of the clinical application of digitalized interarch registration.

Influence of postprocessing rinsing solutions and duration on flexural strength of aged and nonaged additively manufactured interim dental material

STATEMENT OF PROBLEM

Additive manufacturing procedures for fabricating interim restorations include rinsing postprocessing procedures. However, the impact of different rinsing solutions and times on flexural strength is unknown.

PURPOSE

The purpose of this in vitro study was to assess the influence of the rinsing solutions and duration, as well as accelerated aging (thermocycling) procedures, on the flexural strength and Weibull characteristics of an additively manufactured interim dental material.

MATERIAL AND METHODS

A bar design (25×2×2 mm) file was used to fabricate all the specimens with 3D printing and an interim material (Nextdent C&B MFH). Five groups were created based on the rinsing solution used during the postprocessing procedures: 91% isopropyl alcohol (IPA) (control or IPA-91), 99% IPA (IPA-99 group), bio-ethyl alcohol 100% (BE group), tripropylene glycol monomethyl ether (TPM) 100% (TPM group), and water miscible formula (Resinaway) (RA group). Each group was divided into 4 subgroups depending on the total rinsing time: 5, 6, 7, and 8 minutes (5, 6, 7, and 8 subgroups). Additionally, each subgroup was distributed between nonaged and aged thermocycling procedures (n=10). Flexural strength measurements were made by using a universal testing machine. Two-parameter Weibull distribution values, including the Weibull modulus, scale (m), and shape (0), were calculated. Three-way ANOVA and pairwise multiple comparison Tukey tests were used to analyze the data (α=.05).

RESULTS

Three-way ANOVA showed that the rinsing solution (P<.001), rinsing time (P=.004), and thermocycling procedures (P<.001) were significant predictors of the flexural strength values obtained. The IPA-91 and IPA-99 groups obtained the highest flexural strength, while the RA, TPM, and BE groups obtained the lowest flexural strength. The 7- and 8-minute subgroups obtained the highest flexural strength, while the 5-minute subgroup obtained the lowest flexural strength. The nonaged specimens obtained significantly higher mean flexural strength values than the aged specimens.

CONCLUSIONS

The vat-polymerized additively manufactured interim dental material tested with differing rinsing solutions and times demonstrated significant differences in the flexural strength values measured. Accelerated artificial aging procedures significantly decreased the flexural strength of the vat-polymerized interim dental material tested.

Magnetic resonance imaging in dental implant surgery: a systematic review

PURPOSE

To comprehensively assess the existing literature regarding the rapidly evolving in vivo application of magnetic resonance imaging (MRI) for potential applications, benefits, and challenges in dental implant surgery.

METHODS

Electronic and manual searches were conducted in PubMed MEDLINE, EMBASE, Biosis, and Cochrane databases by two reviewers following the PICOS search strategy. This involved using medical subject headings (MeSH) terms, keywords, and their combinations.

RESULTS

Sixteen studies were included in this systematic review. Of the 16, nine studies focused on preoperative planning and follow-up phases, four evaluated image-guided implant surgery, while three examined artifact reduction techniques. The current literature highlights several MRI protocols that have recently investigated and evaluated the in vivo feasibility and accuracy, focusing on its potential to provide surgically relevant quantitative and qualitative parameters in the assessment of osseointegration, peri-implant soft tissues, surrounding anatomical structures, reduction of artifacts caused by dental implants, and geometric accuracy relevant to implant placement. Black Bone and MSVAT-SPACE MRI, acquired within a short time, demonstrate improved hard and soft tissue resolution and offer high sensitivity in detecting pathological changes, making them a valuable alternative in targeted cases where CBCT is insufficient. Given the data heterogeneity, a meta-analysis was not possible.

CONCLUSIONS

The results of this systematic review highlight the potential of dental MRI, within its indications and limitations, to provide perioperative surgically relevant parameters for accurate placement of dental implants.

Load bearing capacity of 3-unit screw-retained implant-supported fixed dental prostheses with a mesial and distal cantilever on a single implant: A comparative in vitro study

OBJECTIVES

To assess the mechanical durability of monolithic zirconia implant-supported fixed dental prostheses (iFDP) design on one implant, with a distal and a mesial extension cantilever bonded to a titanium base compared to established designs on two implants.

MATERIALS AND METHODS

Roxolid Tissue level (TL), and tissue level x (TLX) implants were used to manufacture screw-retained 3-unit iFDPs (n = 60, n = 10 per group), with following configurations (X: Cantilever; I: Implant, T: Test group, C: Control group): T1: X-I-X (TL); T2: X-I-X (TLX); T3: I-I-X (TL); T4: I-I-X (TLX); C1: I-X-I (TL); C2: I-X-I (TLX). The iFDPs were thermomechanically aged and subsequently loaded until fracture using a universal testing machine. The failure load at first crack (Finitial) and at catastrophic fracture (Fmax) were measured and statistical evaluation was performed using two-way ANOVA and Tukey's post-hoc tests.

RESULTS

The mean values ranged between 190 ± 73 and 510 ± 459 N for Finitial groups, and between 468 ± 76 and 1579 ± 249 N for Fmax, respectively. Regarding Finitial, neither the implant type, nor the iFDP configuration significantly influenced measured failure loads (all p > 0.05). The choice of implant type did not show any significant effect (p > 0.05), while reconstruction design significantly affected Fmax data (I-I-Xa < X-I-Xb < I-X-Ic) (p < 0.05). The mesial and distal extension groups (X-I-X) showed fractures only at the cantilever extension site, while the distal extension group (I-I-X) showed one abutment and one connector fracture at the implant/reconstruction interface.

CONCLUSION

Results suggest that iFDPs with I-X-I design can be recommended regardless of tested implant type followed by the mesial and distal extension design on one implant abutment (X-I-X).

Adhesion of tooth fragment after trauma: effect of adhesion strategy and storage in the rescue box

This study aims to investigate the impact of storage conditions for crown fragments (specifically, whether they were stored within a tooth rescue box or in tap water) on their adhesion to fractured teeth when subjected to two different adhesive systems (namely, total etch and self etch). Sixty maxillary premolars were sectioned to obtain tooth fragments. These fragments were stored briefly (2 hours) and reattached in the following groups: Group 1 (fragments stored in tooth rescue box and reattached with etch and rinse (E&R) technique), Group 2 (fragments stored in tap water and reattached with E&R technique), Group 3 (fragments stored in tooth rescue box and reattached with self-etch (SE) technique), and Group 4 (fragments stored in tap water and reattached SE technique). After reattachment, the bonded tooth fragments underwent thermal cycling (500 cycles, 5-55 °C) and bond strength testing using a universal testing machine. Two-way Analysis of Variance (ANOVA) and Tukey's tests were used for bond strength comparison (p ≤ 0.05). A two-parameter Weibull distribution was conducted to evaluate the reliability of the storage medium and adhesion modality on bond strength. The results showed that measured shear bond values (MPa ± Standard deviation (SD); arranged in descending order) for each group were: Group 2 (Tap water/E&R = 6.5 ± 2.1), Group 1 (Rescue box/E&R = 6.0 ± 2.5), Group 4 (Tap water/E&R = 5.1 ± 2.8), and Group 3 (Rescue box/SE = 3.6 ± 3.2). Significant differences were found only between Groups 2 and 3 (p = 0.002). In conclusion, storing crown fragments in a tooth rescue box did not significantly affect the shear bond strength of the restored tooth. However, fragments reattached using the self-etch technique showed comparable shear bond strength but a higher rate of adhesive failures compared to the E&R technique.

Preoperative imaging in third molar surgery - A prospective comparison of X-ray-based and radiation-free magnetic resonance orthopantomography

This study aimed to compare preoperative data relevant to third molar surgery based on radiographic orthopantomography (OPG) and orthopantomogram-like MR images (MR-OPG), using five different MR protocols. X-ray-based OPG and OPG-like MRI reconstructions from DESS, SPACE-STIR, SPACE-SPAIR, T1-VIBE-Dixon, and UTE sequences were acquired in 11 patients undergoing third molar surgery, using a 15-channel mandibular coil. Qualitative (image quality, susceptibility to artifacts, positional relationship, contact/non-contact of the inferior alveolar nerve (IAN), relationship to maxillary sinus, IAN continuity, root morphology) and quantitative (tooth length, retromolar distance, distance to the IAN, and distance to the mandible margin) parameters of the maxillary and mandibular third molars were assessed regarding inter-reader agreement and quantitative discrepancies by three calibrated readers. Radiation-free MR-OPGs generated within clinically tolerable acquisition times, which exhibited high image quality and low susceptibility to artifacts, showed no significant differences compared with X-ray-based OPGs regarding the assessment of quantitative parameters. UTE MR-OPGs provided radiographic-like images and were best suited for assessing qualitative preoperative data (positional relationship, nerve contact/non-contact, and dental root morphology) relevant to third molar surgery. For continuous and focal nerve imaging, DESS MR-OPG was superior. MR-OPGs could represent a shift towards indication-specific and modality-oriented perioperative imaging in high-risk oral and maxillofacial surgery.

Mechanical and chemical characterization of contemporary occlusal splint materials fabricated with different methods: a systematic review

OBJECTIVE

To systematically review studies on various occlusal splint materials and describe their mechanical and chemical properties.

METHODS

MEDLINE (PubMed), Scopus, and Web of Science searches were conducted for in vitro studies focusing on occlusal splint materials. Two reviewers performed an assessment of the identified studies and data abstraction independently, and this was complimented by an additional hand search. The articles were limited to those in the English language that were published between January 1st, 2012, and December 1st, 2022.

RESULTS

The initial search yielded 405 search results of which 274 were selected for full-text review following abstract evaluation. 250 articles that did not meet the inclusion criteria were excluded, and the remaining 25 articles (with 1 article identified from the reference lists of included articles) providing mechanical and chemical values were used in this review. Poly methyl methacrylate (PMMA) -based occlusal splint materials showed the highest values in terms of hardness, wear resistance, flexural strength, flexural modulus, e-modulus, and fracture toughness. The material group with the highest water sorption and water solubility was 3D printed (PR) splint materials. In addition, the lowest degree of double bond conversion was also observed in this group of materials.

CONCLUSIONS

The outcome of this review suggests that mechanically and chemically acceptable properties can be attained with PMMA-based occlusal splint materials using both conventional and digital production methods. PR splint materials should not be considered as the primary choice for long-term treatments due to their low mechanical and chemical properties.

CLINICAL RELEVANCE

This review provides clinical recommendations for selecting the appropriate material and fabrication method for occlusal splints while taking the patients' needs and the materials´ mechanical and chemical properties into account.

Fracture strength of endocrown maxillary restorations using different preparation designs and materials

PURPOSE

This study investigated the impact of preparation design and material types on fracture strength in maxillary premolars endocrowns after thermodynamic aging.

MATERIALS AND METHODS

Eighty two-rooted maxillary premolar crowns underwent endodontic treatment (N = 80, n = 10). The teeth were categorized into ten groups (4-mm deep with no intracanal extension lithium disilicate glass ceramic & multilayer zirconia endocrowns (LE0 & ZE0); 4-mm deep with 4-mm intracanal extension in one canal (LE1 & ZE1); 4-mm deep with 2-mm intracanal extensions in both canals (LE2 & ZE2); flat overlays with no endocore (LO & ZO); glass fiber reinforced post & core and crown (LC & ZC)). After cementation, all specimens were subjected to 1500 thermocycles and 1,200,000 chewing cycles with an axial occlusal load of 49 N. A static loading test was performed at a non-axial 45° loading using a universal testing machine and failure modes (Type I: restoration debonding; Type II: restoration fracture; Type III: restoration/tooth complex fracture above bone level; Type IV: restoration/tooth complex fracture below bone level) were evaluated using a stereoscope. Data were ananalzed using 2-way ANOVA and Tukey's tests (alpha = 0.05).

RESULTS

The endocrowns manufactured from multilayered zirconia and pressed lithium disilicate glass ceramic exhibited a fracture load ranging between 1334 ± 332 N and 756 ± 150 N, with ZC presenting the highest and LE2 the lowest values. The differences were not statistically significant (p > 0.05).

CONCLUSION

All endocrowns tested in this study performed similar considering the different designs and materials tested. The distribution of fracture modes did not differ significantly depending on the design of the restoration and the type of material used.

Effects of Surface Treatments and Cement Type on Shear Bond Strength between Titanium Alloy and All-Ceramic Materials

This study aimed to evaluate the effects of surface treatments and resin cement on the adhesion of ceramic and ceramic-like materials to titanium. A total of 40 specimens (5 mm diameter) of each material (lithium disilicate glass ceramic (LDGC-IPS e.maxCAD), lithium silicate glass ceramic (LSGC-VITA Suprinity) and a polymer-infiltrated ceramic network (PICN-Vita Enamic)) were fabricated using CAD/CAM technologies. In total, 120 titanium (Ti) specimens were divided into 12 groups, and half of the titanium specimens were tribochemically coated using CoJet. The titanium and all-ceramic specimens were cemented using either Self-curing adhesive cement (SCAC-Panavia 21) or a Self-curing luting composite (SCLC-Multilink Hybrid Abutment). After 5000 cycles of thermal aging, the shear bond strength (SBS) test was conducted using a universal testing machine. The failure modes of the specimens were analyzed using stereomicroscopy, and additionally, the representative specimens were observed using Scanning Electron Microscopy. ANOVA was used for the statistical analysis (p < 0.05). The post-hoc Duncan test was used to determine significant differences between the groups. The mean SBS values (mean ± STD) ranged from 15 ± 2 MPa to 29 ± 6 MPa. Significantly higher SBS values were acquired when the titanium surface was tribochemically coated (p < 0.05). The SCLC showed higher SBS values compared to the SCAC. While the LDGC showed the highest SBS values, the PICN presented the lowest. The tribochemical coating on the cementation surfaces of the titanium increased the SBS values. The specimens cemented with the SCLC showed higher SBS values than those with the SCAC. Additionally, the SCLC cement revealed a more significant increase in SBS values when used with the LDGC. The material used for restoration has a high impact on SBS than those of the cement and surface conditioning.

Risk Factors with Porcelain Laminate Veneers Experienced during Cementation: A Review

The clinical success of porcelain laminate veneers (PLVs) depends on many clinical and technical factors, from planning to execution, among which adhesive cementation is of significant importance. This procedure carries many risk factors if not optimally executed. The objective of this study was to document the clinical parameters affecting successful cementation procedures with a focus on the adhesive strength, integrity, and esthetics of the PLVs. A literature search was conducted through MEDLINE, complemented by a hand search using predefined keywords. Articles published in English between 1995 and 2023 were selected. According to this review, the success and longevity of PLVs rely in great part on the implementation of a precise cementation technique, starting from field isolation, adequate materials selection for adhesion, proper manipulation of the materials, the seating of the veneers, polymerization, and elimination of the excess cement. Several clinical steps performed before cementation, including treatment planning, preparation, impression, and adequate choice of the restorative material, could affect the quality of cementation. Scientific evidence suggests careful implementation of this process to achieve predictable outcomes with PLVs. The short- and long-term clinical success of adhesively luted PLVs is tributary to a deep understanding of the materials used and the implementation of clinical protocols. It is also contingent upon all the previous steps from case selection, treatment planning, and execution until and after the cementation.

MR-orthopantomography in operative dentistry and oral and maxillofacial surgery: a proof of concept study

This prospective study aimed to present, compare, and evaluate the suitability of five different magnetic resonance imaging (MRI) protocols (3D double-echo steady-state (DESS), 3D fast spin echo short-tau inversion recovery (SPACE-STIR), 3D fast spin echo spectral attenuated inversion recovery (SPACE-SPAIR), volumetric interpolated breath-hold examination (T1-VIBE-Dixon), and ultrashort echo time (UTE)) and for orthopantomogram (OPG)-like MRI reconstructions using a novel mandibular coil. Three readers assessed MR-OPGs of 21 volunteers regarding technical image quality (4, excellent; 0, severely reduced), susceptibility to artifacts (3, absence; 0, massive), and visualization of anatomical structures in the oral cavity and surrounding skeletal structures (4, fine details visible; 0, no structures visible). Average image quality was good (3.29 ± 0.83) for all MRI protocols, with UTE providing the best image quality (3.52 ± 0.62) and no to minor artifacts (2.56 ± 0.6). Full diagnostic interpretability of the osseous structures is best in VIBE-Dixon and UTE MR-OPGs. DESS provided excellent visualization of the finest details of the nervous tissue (3.95 ± 0.22). Intra-reader and inter-reader agreement between the readers was good to excellent for all protocols (ICCs 0.812-0.957). MR-OPGs provide indication-specific accurate imaging of the oral cavity and could contribute to the early detection of pathologies, staging, and radiological follow-up of oral and maxillofacial diseases.

CAD-CAM complete denture resins: Effect of relining on the shear bond strength

OBJECTIVES

The aim of this study was to compare the shear bond strength of relined CAD-CAM complete removable dental prosthesis (CRDP) resins with conventional heat-polymerized polymethylmethacrylate (PMMA) resin.

METHODS

A total of 96 resin specimens in identical dimensions of 10 mm × 10 mm × 11 mm were fabricated for four study groups [#1- Conventional heat-polymerized group: n=24 (ProBase); #2- Milled#1: n=24 (Ivobase); #3- Milled#2: n=24 (Ivotion); #4- 3D-printed: n=24, (NextDent Denture 3D+)]. Twelve specimens in each group were sectioned in the middle to produce a 3 mm defect and then were relined using a conventional denture relining material. All specimens underwent thermocycling (5-55°C) for 10,000 cycles. The shear bond tests were carried out in a universal testing machine. One-way ANOVA and Tukey's test were used for statistical analysis (p<0.05). The two-parameter Weibull distribution values were calculated.

RESULTS

Relined 3D-printed specimens had a significantly lower shear bond strength when compared with conventional (p=0.0003) and milled groups (Milled#1: p=0.0004; Milled#2: p<0.0001). There were no differences in the shear bond strengths between the milled and conventional groups. Weibull distribution presented the highest shape value for the non-relined Milled#1 (22.83) group and the lowest values for the 3D-printed relined group (4.001).

CONCLUSION

The findings of this study conclude that the shear bond strength of the conventionally-relined 3D-printed resins used for fabricating CRDPs was inferior to the shear bond strength of conventionally-relined resins employed for manufacturing CRDPs using CAD-CAM milling and conventional heat-polymerization techniques.

CLINICAL SIGNIFICANCE

When considering 3D-printing for the fabrication of CRDPs, it is recommended to employ it in clinical situations where a frequent need for denture relining is not expected.

Evaluation of Marginal and Internal Fit of Ceramic Laminate Veneers Fabricated with Five Intraoral Scanners and Indirect Digitization

The long-term success of ceramic laminate veneers (CLVs) is influenced by the marginal and internal fit of the restorations. However, studies comparing the fit of CLVs using different intraoral scanners or the indirect digitization technique are lacking. The purpose of this study was therefore to assess the marginal and internal fit of CAD/CAM-milled CLVs using different intraoral scanners and the indirect digitalization technique. An ivorine typodont maxillary left-central incisor was prepared; the tooth and the neighboring teeth were scanned and used as a template to print ninety 3D partial models. Thereafter, ceramic laminate veneers (CLVs) (N = 90) were milled from IPS-Emax CAD blocks and divided into six equal groups (15 specimens each) according to the type of intraoral scanner (IOS), as follows: Omnicam IOS, SC3600 IOS, Trios 3 IOS, Emerald IOS, I500 IOS. Fifteen further CLVs were fabricated using the conventional indirect digitalization technique. After cementation on the resin dies and embedding in clear epoxy resin, specimens were sectioned inciso-gingivally and mesio-distally. At the incisal and cervical positions, the marginal discrepancy was measured and evaluated in addition to the internal gap at six locations using SEM (200×). Differences between gap measurements among the six groups were determined using ANOVA. Games-Howell multiple comparisons for homogenous variances and LSD multiple comparisons for non-homogenous variances were used with 95% confidence intervals. The significance level was set at 0.05. The lowest mean absolute marginal gap at the incisal margins (AMGI) was recorded for Omnicam group (203.28 ± 80.14) µm, while the highest mean absolute marginal gap at the cervical margins (AMGC) was recorded for Omnicam group (147.16 ± 59.78) µm. The mean AMGC was reported to be significantly different between the conventional technique (146.75 ± 38.43) µm and Trios 3 (91.86 ± (35.51) µm; p = 0.001) and between Emerald (112.37 ± (50.31) µm; p = 0.042) and I500 (86.95 ± (41.55) µm; p < 0.001). The mean MGI was found to be significantly different between the conventional technique (114.11 ± (43.45) µm and I500 group (186.99 ± (73.84) µm) only (p = 0.035). However, no significant differences were found in the mean MGI between all types of IOSs. The means of AMG and MG were significantly different at incisal or cervical areas between the conventional technique and IOSs and within the scanner groups (p > 0.05). Marginal gaps were higher in the incisal region compared to the cervical region with both the indirect digitization technique and the IOSs. Ceramic laminate veneers (CLVs) fabricated using IOSs produced overall internal and marginal fit adaptation results comparable to CLVs fabricated from the indirect digitalization method, and both techniques produced clinically acceptable results.

Buccal bone thickness assessment for immediate anterior dental implant planning: A pilot study comparing cone-beam computed tomography and 3D double-echo steady-state MRI

PURPOSE

To evaluate image quality and diagnostic accuracy of buccal bone thickness assessment in maxillary and mandibular anterior region using cone-beam computed tomography (CBCT) and 3-dimensional double-echo steady-state (DESS) MRI for preoperative planning of immediate dental implants in healthy individuals.

METHODS

One hundred and twenty teeth in 10 volunteers were retrospectively evaluated for image quality and artifacts using Likert scale (4 = excellent to 0 = decreased). Buccal bone thickness was measured at three measurement points (M1 = 2 mm from the cementoenamel junction, M2 = middle of the root, and M3 = at the root apex) for each tooth in the maxillary (13-23) and the mandibular anterior region (33-43). Descriptive statistics and two-way ANOVA with Tukey's Post-hoc test were performed to evaluate the significant differences (α = 0.05) between both imaging modalities.

RESULTS

Image quality showed little to no artifacts and enabled confident diagnostic interpretation (CBCT (3.72 ± 0.46); MRI (3.65 ± 0.49)), with no significant differences between both imaging modalities (p > 0.05). Regarding the assessment of buccal bone thickness at M1-M3 for the teeth 13-23 and 33-43, no significant differences were noted (p > 0.05). MRI demonstrated slight, nonsignificant overestimation of thickness with the canines having mainly a thick buccal bone wall, where thin buccal wall was evident for the central incisors.

CONCLUSION

Black bone MRI sequences, such as 3D-DESS MRI, for immediate implant planning provided confidential diagnostic accuracy in bone thickness assessment without significant disadvantages compared to CBCT. Thus, the implementation of no-dose protocols for dental rehabilitation using an immediate loading approach seems promising and could further improve the treatment strategy for dental rehabilitation.

Durability of cantilever inlay-retained fixed dental prosthesis fabricated from multilayered zirconia ceramics with different designs

PURPOSE

The purpose of this in-vitro study was to investigate the effect of framework design on fracture resistance and failure modes of cantilever inlay-retained fixed partial dentures (IRFDPs) fabricated from two multilayered monolithic zirconia materials.

MATERIALS AND METHODS

Seventy-two natural premolar teeth were prepared as abutments for cantilever IRFDPs using three designs: mesial-occlusal (MO) inlay with short buccal and palatal wings (D1), MO inlay with long palatal wing (D2), MO inlay with long palatal wing and occlusal extension (D3). Full-contoured IRFDPs were fabricated from two monolithic zirconia materials; IPS e.max ZirCAD Prime and Zolid Gen-X. Adhesive surfaces were air-abraded and bonded with MDP-containing resin cement. Specimens were subjected to thermocycling (5-55 °C, 5000 cycles); then, mechanical loading (1.2 × 10⁶ cycles, 49 N). Surviving specimens were loaded until failure in the universal testing machine. All specimens were examined under stereomicroscope, and two samples from each group were evaluated using Scanning Electron Microscope.

RESULTS

Mean failure loads were not significantly different between different framework designs or between two materials. However, IPS e.max ZirCAD Prime showed significantly higher failure rate than Zolid Gen-X during dynamic fatigue (p = 0.009). Samples with D1 design showed higher debonding rate, D2 failed mainly by fracture of the palatal wing and debonding, and D3 failed mainly by fracture of the abutment tooth. Debonded restorations showed mainly mixed failures.

CONCLUSION

Cantilever IRFDPs with framework designs that maximize adhesion to enamel exhibited promising results. IPS e.max ZirCAD Prime was more susceptible to fractures with the long palatal wing design.

Load-bearing capacity of pressable lithium disilicates applied as ultra-thin occlusal veneers on molars

PURPOSE

The aim was to investigate the load bearing capacity of different pressable lithium disilicates cemented as occlusal veneers on molars.

MATERIALS AND METHODS

One control group and six test groups were formed consisting of 20 specimens each (n = 20). The six test groups differed in the utilizing pressable lithium disilicate to fabricate occlusal veneers. As a control group, "group Lis", the lithium disilicate with the highest reported flexural strength was used (initial LiSi Press, GC Europe; Leuven, Belgium / flexural strength: 508 MPa). The test groups consisted of other pressable lithium disilicates with lower flexural strength values: "Ema" (IPS e.max press), "Vit" (VITA Ambria), "Liv" (Livento Press), "Amb" (Amber Press), "Mas" (Amber Press Master) and "Ros" (Rosetta SP)". After the preparation of 140 extracted human molars, which included the removal of the central enamel, the specimens were scanned using a desktop scanner. With the aid of a design software, the occlusal veneers were designed in a standardized thickness of 0.5 mm. To fabricate the restorations, all tested materials were processed using heat-pressing technique. All restorations were adhesively cemented. Afterwards, the specimens underwent cyclic fatigue during an aging procedure in a chewing simulator (1'200'000 chewing-cycles, 49 N force, 5-55°C temperature changes). Subsequently, the specimens were statically loaded and the load which was necessary to fracture the specimen (F_max) were measured. Differences between the groups were compared applying the Kruskal-Wallis (KW) test and the Wilcoxon-Mann-Whitney-Test (WMW: p < 0.05). The two-parameter Weibull distribution values were calculated.

RESULTS

The fatigue resistance was 100% for the groups Lis, Vit, Liv, Amb, Mas and Ros, whereas the group Ema showed a fatigue resistance of 95%. The control group Lis showed median F_max values of 2'328 N. The median F_max values for the test groups ranged between 1'753 N (Vit) and 2'490 N (Ros). Statistically significant difference was observed among the groups Lis (control) and Vit (KW: p < 0.001). Weibull distribution presented the highest shape values for the group Ros (12.83) and the lowest values for the group Ema (4.71).

CONCLUSION

Regarding their load-bearing capacity different pressable lithium disilicates can be recommended to fabricate ultra-thin occlusal veneers on molars when restoring occlusal tooth wear.

Chemical Composition and Flexural Strength Discrepancies Between Milled and Lithography-Based Additively Manufactured Zirconia

PURPOSE

To evaluate the chemical composition, flexural strength, and Weibull characteristics of milled and lithography-based additively manufactured (AM) zirconia.

MATERIALS AND METHODS

A virtual design of a bar (25×4×2 mm) was completed using a software program. The standard tessellation language file was used to manufacture all the specimens: 3Y-TZP zirconia (Priti multidisc ZrO₂ monochrome) milled (M group) and 3Y-TZP zirconia (LithaCon 3Y 210) lithography-based AM (CeraFab System S65 Medical) (AM group) bar specimens (n = 20). The chemical composition of the specimens was determined by using energy dispersive X-ray (EDAX) elemental analysis in a scanning electron microscope. Flexural strength was measured in all specimens using 3-point bend test according to ISO/CD 6872.2 with a universal testing machine (Instron Model 8501). Two-parameter Weibull distribution values were calculated. The Shapiro-Wilk test revealed that the data were normally distributed (p < 0.05). Flexural strength values were analyzed using independent Student's t-test (α = 0.05).

RESULTS

There were no major chemical composition differences observed between M and AM groups. The AM specimens (1518.9 ± 253.9 MPa) exhibited a significantly higher flexural strength mean value compared to the milled (980.5 ± 130.3 MPa) specimens (DF = 13, T-value = -5.97, p < 0.001). The Weibull distribution presented the highest shape for M specimens (11.49) compared to those of AM specimens (6.95).

CONCLUSIONS

There was no significant difference in the chemical composition of milled and AM zirconia material tested. AM zirconia tested exhibited significantly higher flexural strength compared with the milled zirconia evaluated.

Effect of Cumulative Ionizing Radiation on Flexural Strength, Flexural Modulus, and Elasticity Modulus of Dentin in Unerupted Human Third Molars

Purpose

This in vitro study aimed to investigate the changes in mechanical properties in dentin of third molars after radiation therapy using variable doses and frequencies.

Methods and Materials

Rectangular cross sectioned dentin hemisections (N = 60, n = 15 per group; >7 × 4 × 1.2 mm) were prepared using extracted third molars. After cleansing and storage in artificial saliva, random distribution was performed to 2 irradiation settings, namely AB or CD (A, 30 single doses of irradiation [2 Gy each] for 6 weeks; B, control group of A; C, 3 single doses of irradiation [9 Gy each]; and D, control group of C). Various parameters (fracture strength/maximal force, flexural strength, and elasticity modulus) were assessed using a universal Testing Machine (ZwickRoell). The effect of irradiation on dentin morphology was evaluated by histology, scanning electron microscopy, and immunohistochemistry. Statistical analysis was performed using 2-way analysis of variance and paired and unpaired t tests at a significance level of 5%.

Results

Significance could be found considering the maximal force applied to failure when the irradiated groups were compared with their control groups (A/B, P < .0001; C/D, P = .008). Flexural strength was significantly higher in the irradiated group A compared with control group B (P < .001) and for the irradiated groups A and C (P = .022) compared with each other. Cumulative radiation with low irradiation doses (30 single doses; 2 Gy) and single irradiation with high doses (3 single doses; 9 Gy) make the tooth substance more prone to fracture, lowering the maximal force. The flexural strength decreases when cumulative irradiation is applied, but not after single irradiation. The elasticity modulus showed no alteration after irradiation treatment.

Conclusions

Irradiation therapy affects the prospective adhesion of dentin and the bond strength of future restorations, potentially leading to an increased risk of tooth fracture and retention loss in dental reconstructions.

Effect of Titanium-Base Abutment Height on Optical Properties of Monolithic Anterior Zirconia Crowns

The effects of different heights of ti-base abutments on the color of anterior screw-retained zirconia restorations fabricated using computer-aided design and computer-aided manufacturing (CAD-CAM) technologies may affect the optical clinical outcome. The purpose of this study was to measure and compare the color parameters of zirconia crowns in different shades on ti-base abutments. Identical specimens (N = 160) were milled to restore the screw-retained central maxillary incisor crown, using 5% mol yttria zirconia (5Y-TZP). The specimens were designed using computer design software to match 3.5 mm and 5.5-mm ti-base abutments and milled using one CAD-CAM technology. Specimens were divided into four main groups depending on zirconia shade (A1/0, A2/3, A3.5/4 and B2/3) and then assigned to two subgroups according to ti-base height. Color measurements in the CIELab coordinates were made using a spectrophotometer under room-light conditions. Color difference (ΔE*) values were calculated using the CIE76 and CIEDE2000 formula. Within the group of A0/1 and A2/3, for 5.5 mm abutment height, a significant difference was found between the means of colors ∆E00 and ∆Eab (p < 0.01). Using a 5.5 mm-height ti-base abutment may produce a clinically unacceptable outcome (ΔEab > 2) in A1/0 and A2/3 color groups.

Effect of Surface Pre-Reacted Glass Ionomer Containing Dental Sealant on the Inhibition of Enamel Demineralization

The effect of a surface pre-reacted glass ionomer (S-PRG)-containing sealant on the demineralization inhibition and remineralization of intact enamel adjacent to the sealant material was investigated. BeautiSealant (BTS, S-PRG sealant, Shofu), Teeth Mate F-12.0 (TMF, fluoride-releasing sealant, Kuraray Noritake Dental), and an experimental silica-filler sealant were investigated. After pH cycling for 10 days, the enamel surface adjacent to the sealant material was observed using confocal laser microscopy and scanning electron microscopy. The polymerized sealant disks were immersed in a demineralized solution (pH: 4.3) to measure pH change. The enamel specimens with polymerized sealant disks were additionally immersed in demineralized solution, followed by energy-dispersive X-ray spectroscopy. The demineralized area of BTS was significantly smaller than that of TMF and SS (p < 0.05). The surfaces adjacent to the sealant of TMF and SS were demineralized, while the surface of BTS was comparatively intact. An increase in pH values were observed in the BTS and TMF groups. Enamel surfaces presented an inhibition of demineralization for BTS and TMF, but not for SS. Fluoride uptake from the polymerized sealant was greater for BTS than for TMF. The S-PRG-containing sealant showed a buffering ability, demineralization inhibition, promotion of remineralization, and it can be advised for clinical applications.

Evaluation of radiodensity and dimensional stability of polymeric materials used for oral stents during external beam radiotherapy of head and neck carcinomas

Purpose

Intraoral stents protect the healthy tissues from ionizing radiation during external beam radiotherapy reducing mucositis, hyposalivation and osteoradionecrosis. This study investigated the radiodensity and dimensional stability of polymeric materials for suitability in construction of intraoral stents and aimed to provide clinical guidelines.

Methods

Specimens were fabricated using 4 material types namely, resin composite (ProTemp-PRO), polymethylmethacrylate (PMMA) (Enamel Temp Plus-ETP, Palapress-PAL, TAB 2000-TAB), polycaprolactone (Orfit-ORF) and silicone (Adisil-ADI, Lab Putty-LAB, Memosil2-MEM, Optosil-OPT, President Plus-PRE, Siolaplast A-SIA). They were randomly assigned to measure their radiodensity in Hounsfield Units (HU) (12x12x11mm³) (N_radiodensity = 66; n = 6) using a computer tomograph (CBCT, Toshiba Aquillon LB scanner) at baseline and after 6 weeks. The scanning protocol was applied with and without single energy metal artifact reduction (SEMAR) scans using a slice thickness of 1 and 5 mm. The same materials have been tested for their dimensional stability (µm³) at baseline, 1, 6, 12, 24 h, 3 and 6 weeks (14 × 4 × 2 mm³) (N_dimension = 55; n = 5 per material) using stereolithography (STL) files generated by a lab scanner (L2i, Imetric4D, Courgenay, Switzerland) and analyzed using a matching software (Geomagic ControlX 2020, 3D Systems). Data were analyzed using a paired t-test (alpha = 0.05).

Results

Radiodensity values (HU) were significantly affected by the material classification (p < 0.05). Polycaprolactone (43.6) presented significantly lower HU values followed by PMMA (91.3-414.9) than those of silicone materials (292.8-874.5). In terms of dimensional stability (µm³), PMMA materials (Δ:1.53-2.68) and resin composite (Δ:2.89) were significantly more dimensionally stable compared to those of silicone materials (Δ:13.64-6.63) and polycaprolactone (Δ:-0.76) and (p < 0.05).

Conclusion

For fabricating intraoral stents, when reduced radiodensity values are required polycaprolactone could be recommended as it fulfils the requirements for reduced radiodensity and dimensional stability. Among all silicone materials, OPT and MEM can be recommended based on the low HU and dimensional stability.

Evaluating the Bond Strength of a Polymer Infiltrated Ceramic Network to Zirconia Using the Crossbeam Push-Off Method

Porcelains and glass-ceramics have been used to produce CAD-milled veneers and crowns for zirconia copings and implant-abutments. This study evaluated the bondstrength of a polymer-infiltrated-ceramic-network to zirconia using two adhesive cement systems: Panavia 21 and Multilink Automix. Lithium disilicate and feldspathic porcelain were also tested as reference CAD-On materials. Long beams (3x6x40 mm³) of zirconia and short beams (3x6x15 mm³) of the CAD-On materials were prepared. Zirconia and each CAD-On material were bonded in a crossbeam arrangement and subjected to a modified tensile bond-strength test. Half of the samples in each group (n=10) were tested 5 days after bonding (baseline) and the remaining (n=10) underwent aging (50,000 thermocycles at 5°C and 55°C) prior to bond-strength testing. The effects of material, cement, and aging on the tensile bond-strength were tested using a three-way ANOVA. The reference lithium disilicate/Multilink system showed no significant differences in bond strength compared to polymer-infiltrated-ceramic-network and porcelain. The long-term retention of polymer-infiltrated-ceramic-network was not statistically different compared to the baseline values and the two reference materials. With comparable bond strength between all materials, polymer-infiltrated-ceramic-network is the favorable choice for CAD-On to zirconia copings and implant-abutments due to its superior resistance to fatigue fracture relative to porcelain.

Influence of the layer thickness on the flexural strength of aged and non-aged additively manufactured interim dental material

PURPOSE

To measure the flexural strength and Weibull characteristics of aged and non-aged printed interim dental material fabricated with different layer thickness.

MATERIAL AND METHODS

Bars (25×2×2 mm) were additively fabricated by using a polymer printer (Asiga Max) and an interim resin (Nexdent C&B MFH). Specimens were fabricated with the same printing parameters and postprocessing procedures, but with 7 different layer thickness: 50 (control or 50-G group), 10 (10-G group), 25 (25-G group), 75 (75-G group), 100 (100-G group), 125 (125-G group), and 150 μm (150-G group). Two subgroups were created: non-aged and aged subgroups (n = 10). A universal testing machine was selected to measure flexural strength. Two-parameter Weibull distribution values were computed. Two-way ANOVA and Tukey tests were elected to examine the data (α = .05).

RESULTS

Artificial aging methods (P<.001) were a significant predictor of the flexural strength computed. Aged specimens acquired less flexural strength than non-aged specimens. The Weibull distribution obtained the highest shape for non-aged 50-G and 75-G group specimens compared with those of other non-aged groups, while the Weibull distribution showed the highest shape for aged 125-G specimens.

CONCLUSIONS

The flexural strength of the additively fabricated interim material examined was not influenced by the layer thickness at which the specimens were fabricated; however, artificial aging techniques reduced its flexural strength. Aged specimens presented lower Weibull distribution values compared with non-aged specimens, except for the 125-G specimens. This article is protected by copyright. All rights reserved.

Push-Out Bond Strength Assessment of Different Post Systems at Different Radicular Levels of Endodontically Treated Teeth

This study assessed the bond strength of prefabricated post systems at different root levels of endodontically treated teeth. One-rooted human premolars (N = 70; n = 10) were cut to 2 mm above the cement-enamel junction. Root canals were treated and randomly assigned to one of the seven post systems: T: Titanium (Mooser), ZrO: Zirconia (Cosmopost), G: Fiber (FRC Postec Plus), E1: Fiber (Direct) (Everstick post), E2: Fiber (Indirect) (Everstick post), PP: Fiber (PinPost), and LP: Injectable Resin/Fiber composite (EverX Posterior). All posts were luted using a resin cement (Variolink II), and the roots were sectioned at the coronal, middle, and apical root levels. Push-out tests were performed in the Universal Testing Machine (0.5 mm/min). Data (MPa) were analyzed using two-way ANOVA and Tukey’s tests (α = 0.05). The results showed that the bond strength (mean ± SD) of E2 posts were highest (5.3 ± 2.7) followed by PP (4.1 ± 2.0); G (4.0 ± 1.6); LP (2.6 ± 1.9): T (2.2 ± 1.5) and ZrO (1.9 ± 1.0) posts systems. No significant differences were found in bond strength of all post systems. The bond strength in the coronal root level was the highest with 3.6 ± 2.2 MPa. The bond strength of FRC post systems was significantly higher than those of rigid posts of titanium or ZrO₂. Bond strength results were the highest in the coronal root level for all tested post systems but did not differ significantly from the other two root levels.

Assessing masticatory performance with a colour-mixing ability test using smartphone camera images

Background

Colour‐mixing ability tests are frequently used to assess masticatory performance, but the image acquisition process may be cumbersome and technique sensitive.

Objectives

To evaluate the reliability of smartphone camera images in assessing masticatory performance using a colour‐mixing ability test.

Methods

Participants were recruited into three groups of dental state (n = 20 each): fully dentate, removable partial denture wearers and complete denture wearers. After performing a colour‐mixing ability test, images of the gum specimens (Hue‐Check Gum©) were captured with two smartphones and compared with the images obtained from a flatbed scanner by two examiners. The images were analysed with a subjective‐ (SA) and an opto‐electronical assessment (VoH). Inter‐ and intra‐rater reliability were tested. ANOVA models with repeated measures were used for statistical analysis (⍺ = .05).

Results

All three image acquisition techniques were able to distinguish masticatory performance between different dental states. For SA, inter‐rater reliability was fair to substantial and intra‐rater reliability was substantial to almost perfect. For VoH, inter‐rater reliability with the smartphones was at times different between two examiners, but the intra‐rater assessment was reliable. The opto‐electronic analysis with smartphone images underestimated the masticatory performance significantly when compared to the flatbed scanner analysis. Seven‐day ageing of the specimens did not significantly affect the results.

Conclusions

The assessment of masticatory performance with the Hue‐Check Gum© is a reliable method. The use of smartphones may occasionally underestimate masticatory performance; image acquisition with a flatbed scanner remains the gold standard. A centralised analysis of the photographed wafer may foster the reliability of the diagnosis.

Stress Distribution on Various Implant-Retained Bar Overdentures

The purpose of this study was to evaluate the effects of various fabrication techniques and materials used in implant-supported mandibular overdentures with a Hader bar attachment over added stress distribution. Three-dimensional geometric solid models, consisting of two implants (3.3 mm × 12 mm) placed at the bone level on both mandibular canine regions and a Hader bar structure, were prepared. Model 1 simulated a bar retentive system made from Titanium Grade 5 material by Computer Numerical Control (CNC) milling technique without using any converting adapter/multi-unit element on the implants, while Model 2 simulated the same configuration, but with converting adapters on the implants. Model 3 simulated a bar retentive system made from Cobalt-Chromium material, made by using conventional casting technique with converting adapters on the implants. Static loads of 100 Newton were applied on test models from horizontal, vertical and oblique directions. ANSYS R15.0 Workbench Software was used to compare Von Mises stress distribution and minimum/maximum principal stress values, and the results were evaluated by using Finite Element Analysis method. As a result, the highest stress distribution values under static loading in three different directions were obtained in Model 1. Stress was observed intensely around the necks of the implants and the surrounding cortical bone areas in all models. In scope of the results obtained, using converting adapters on implants has been considered to decrease transmission of forces onto implants and surrounding bone structures, thus providing a better stress distribution. It has also been observed that the type of material used for bar fabrication has no significant influence on stress values in those models where converting adapters were used.

A Comparison of Microtensile Bond Strength, Film Thickness, and Microhardness of Photo-Polymerized Luting Composites

The aim of this study was to evaluate the effect of CAD/CAM composite thickness on micro-tensile bond strength (µTBS), microhardness (HV), and film thickness (FT) of different luting composites. Composite blocks (6.8 mm × 6.8 mm) were divided into 12 groups according to: CAD/CAM thickness and luting composite. For each group, 21 rods (1 mm × 1 mm) were tested in tension at crosshead speed of 1 mm/min. Fracture modes were categorized as adhesive, mixed, and cohesive. Microhardness (n = 5/group) was assessed using microhardness tester. Film thickness (12-rods/group) was evaluated using a stereomicroscope (×40). Data were analyzed using the two-way ANOVA/Tukey’s HSD test (p = 0.05). Parameters “thickness”, “cement”, and “thickness x cement” showed significant difference on µTBS and HV (p < 0.05). At 2 mm, heated x-tra fil composite showed the highest µTBS (45.0 ± 8.5 MPa), while at 4 mm thickness, Grandio Flow revealed the lowest µTBS (33.3 ± 6.3 MPa). Adhesive, mixed, and cohesive failures were reported. The HV of all composites decreased when photo-polymerized through 4 mm thickness (p < 0.05). Regardless of CAD/CAM thickness, photo-polymerized composites can be successfully used for luting CAD/CAM composite.

Micro-Computed Tomographic Assessment of Microcrack Formation before and after Instrumentation of Curved Root Canals with Neoniti Rotary Files

The aim of this study was to assess the microcrack formation of moderately and severely curved root canals following instrumentation with Neoniti rotary files using micro-computed tomography. This in vitro study evaluated 18 extracted sound mandibular molars with two separate mesial canals and foramina in two groups (n = 9) with 5−20° (moderate) and 20−40° (severe) root canal curvature. The number of microcracks in the root canal walls was counted at baseline by micro-CT. Subsequently, the root canals were instrumented with 0.20/0.06 v Neoniti files as single files with a torque of 1.5 Ncm and a speed of 400 rpm. The number of microcracks was counted again postoperatively on micro-CT images using Amira software. Statistical analysis was performed using the Shapiro−Wilk test, Levene’s test and repeated-measures ANOVA (α = 0.05). The mean number of microcracks significantly increased postoperatively in both the moderately curved (11.59 ± 9.74 vs. 8.2 ± 7.4; p = 0.001) and the severely curved (13.23 ± 5.64 vs. 7.20 ± 5.94; p < 0.001) groups. However, the differences between the two groups were not significant (p = 0.668). Based on the results obtained, it can be stated that the instrumentation of moderately and severely curved root canals with Neoniti rotary files increases the number of microcracks. However, the higher degree of curvature does not necessarily translate to a higher number of microcracks after root canal instrumentation with this specific rotary system and methodological procedures.

Adhesion of Different Resin Cements to Zirconia: Effect of Incremental versus Bulk Build Up, Use of Mould and Ageing

Bonding to zirconia presents a great challenge, as the clinical guidelines for predictable adhesion are not sufficiently validated. The aim of this study was to assess the influence of various bonding methodologies of various resin cements on zirconia, using different aging protocols. Manufactured zirconia specimens (N = 300 and n = 20 per group) were randomly assigned to three luting protocols: 1—in mould incremental build up; 2—in mould incremental build up with mould removal; 3—in mould non-incremental bulk build up. Five dual, photo- and chemical-cure resin cements were used, namely, Variolink Esthetic (Ivoclar), Tetric (Ivoclar), Panavia (Kuraray), TheraCem (Bisco), and RelyX UniCem (3M ESPE), and were applied on primed zirconia using photopolymerization protocols. Thereafter, the specimens were subjected to the following three ageing methods: 1—dry; 2—thermocycling (×5000; 5−55 °C); 3—3−6 months of water storage. Using a universal testing machine, the specimens were loaded under shear, at 1 mm/min crosshead speed. An analysis of the data was performed using three-way ANOVA and the Bonferroni method. The moulding type, ageing and luting cement significantly affected the results (p < 0.05). Among all the protocols under dry conditions, TheraCem (16 ± 3; 11 ± 1; 16 ± 3) showed the best bond strength, while, after thermocycling, TheraCem (7 ± 2) and Tetric (7 ± 2) performed the best with Protocol 1. In Protocol 2, RelyX (7 ± 3) presented the highest result, followed by TheraCem (5 ± 3) and Tetric (5 ± 1) (p < 0.05). Using Protocol 3, RelyX (10 ± 6) showed the highest result, followed by TheraCem (7 ± 2) and Panavia21 (7 ± 2) (p < 0.05). Six months after water storage, TheraCem presented the highest result (10 ± 2) in Protocol 1, while, in Protocols 2 and 3, Tetric (10 ± 2; 15 ± 5) presented the highest result, followed by TheraCem (6 ± 2; 8 ± 3). Adhesion tests using the incremental or bulk method, using moulds, showed the highest results, but removing the mould, and the subsequent ageing, caused a decrease in the adhesion of the resin cements tested on zirconia, probably due to water absorption, with the exclusion of Tetric.

Effect of additional reference objects on accuracy of five intraoral scanners in partially and completely edentulous jaws: An in vitro study

STATEMENT OF PROBLEM

The effect of additional reference objects on the accuracy of different intraoral scanners for partially and completely edentulous patients has not been investigated sufficiently.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of an additional reference object in the form of additional artificial landmarks on the trueness and precision of different intraoral scanners in partially and completely edentulous areas.

MATERIAL AND METHODS

Partially and completely edentulous models with 2 and 4 implants (BLT, RC, Institut Straumann AG), respectively, were used in the study. For the digital scan, scan bodies (CARES Mono Scanbody) were attached, and reference data obtained by using industrial scanners. Ten digital scans of the same model were made with each intraoral scanner: PRIMESCAN, TRIOS 3, TRIOS 4, Carestream 3600, and Medit. Then, additional artificial landmarks were attached, and 10 more intraoral scans were made with each device. Computer-aided design files of the scan bodies were aligned to obtain 3-dimensional surfaces with reference and test scanners. Trueness and precision of distance, angulations, and vertical shift between scan bodies were estimated. The Mann-Whitney Wilcoxon or Student 2-sample t test was applied to estimate statistically significant differences between groups (α=.05).

RESULTS

In the partially edentulous model, distance trueness mean ±standard deviation values ranged from -46.7 ±15.4 μm (TRIOS 3) to 392.1 ±314.3 μm (Medit) in models without additional artificial landmarks. When additional artificial landmarks were applied, trueness of distance mean ±standard deviation values ranged between -35 ±13 μm (TRIOS 4) and 117.7 ±232.3 μm (CARESTREAM). Trueness mean ±standard deviation values of angulation varied from -0.0 ±0.5 degrees (CARESTREAM) to 0.2 ±0.0 degrees (PRIMESCAN) without additional artificial landmarks and from 0.0 ±0.2 degrees (TRIOS 3) to 0.4 ±0.5 degrees (CARESTREAM) with additional artificial landmarks. Vertical shift trueness measurements varied from -108 ±47.1 μm (TRIOS 4) to 107.2 ±103.5 μm (Medit) without additional artificial landmarks and from -15.0 ±45.0 μm (CARESTREAM) to -86.9 ±42.1 μm (TRIOS 4) with additional artificial landmarks. The additional artificial landmark technique improved the trueness of all measured parameters for the 5 tested intraoral scanners. No statistically significant differences were found among models with or without additional artificial landmarks, except for Medit in all parameters and PRIMESCAN in angle measurements (P<.05). The best precision for distance was found with TRIOS 3 and with PRIMESCAN for angulation and vertical shift. Larger deviations were observed in the completely edentulous situation. The effect of additional artificial landmarks was limited when the accuracy parameters of digital scans were considered.

CONCLUSIONS

Scans with and without additional artificial landmarks of partially edentulous conditions scanned by any of the intraoral scanners tested did not influence precision and trueness, except for Medit i500 in the distance and vertical shift parameters and CARESTREAM3600 in vertical shift. Precision and trueness of digital scans of completely edentulous areas were affected, except for Medit i500 for distance, PRIMESCAN and TRIOS 4 for angle, and all systems except TRIOS 4 for vertical shift precision.

Digital workflow for implant-supported fixed complete dentures based on backwards planning in an edentulous patient

AIM

This case report describes a digital workflow for prosthetically driven surgical planning, implant placement, and the fabrication of two screw-retained, complete-arch, implant-supported dentures in an edentulous patient. The purpose of this case report is to present and discuss the digital steps in the workflow, especially the scanning technique to obtain the centric relation, through a clinical case. The limitations of the workflow are also discussed.

MATERIALS AND METHODS

Static computer-aided implant surgery (s-CAIS) was planned three-dimensionally, based on cone beam computed tomography, intraoral optical scanning, and digital bite registration. Using s-CAIS, four and six implants were placed in the edentulous mandible and maxilla, respectively. The final screw-retained complete-arch monolithic zirconia restorations were manufactured based on a digital workflow, using the pre-existing modified radiologic guide for the digital maxillomandibular record.

CONCLUSIONS

The evolution of digital processing methods allows for design, processing, and fabrication of implant-supported fixed complete dentures using a surgical, prosthetic, and technical workflow based on 3D restorative backward planning. A digital prosthetic setup and CAD/CAM can be used for the fabrication of intraoral try-ins that serve as a model for the final monolithic zirconia superstructure.

An Intraoral Repair Method for Chipping Fracture of a Multi-unit Fixed Zirconia Reconstruction: A Direct Dental Technique

Fracture or chipping of veneering ceramic is one of the most frequent clinical failures in dentistry in fixed dental and implant-borne prostheses. Due to the friable nature of the ceramic material, chippings may result in an aesthetic and functional problem for the patient requiring a rapid solution. Direct repairs have been indicated for the restoration of function, aesthetics and comfort, especially in cases where the fractured prosthesis presents good adaptation and satisfactory aesthetics. This case report aims to present and discuss the techniques of the direct reveneering method, their advantages and disadvantages, as well as the importance of adhesive procedures in the success of these restorative approaches. Success in repairing the fractured area, regardless of the technique used, is fundamental to establish a strong and stable adhesion between the repaired and the fractured areas, since the longevity of the repair will depend on the quality of the interface generated.

Clinical outcomes and costs of conventional and digital complete dentures in a university clinic: A retrospective study

STATEMENT OF PROBLEM

Scientific data analyzing the clinical outcomes and costs of complete dentures fabricated by using conventional and computer-aided design and computer-aided manufacturing (CAD-CAM) processes are lacking.

PURPOSE

The purpose of this retrospective study was to compare the treatment duration, financial costs, and postdelivery adjustments of CAD-CAM and conventional removable complete dentures.

MATERIAL AND METHODS

Thirty-two edentulous participants (16 women, 16 men; age 35-85 years) who had received either CAD-CAM (n=16) or conventional (n=16) maxillary and mandibular removable complete dentures provided by prosthodontists with a minimum of 2 years of experience were evaluated. The CAD-CAM denture systems were either DDS-AV (AvaDent Digital Dental Solutions) (n=11) or DD-IV (Wieland Digital Denture) (n=5). The total treatment period (days) was recorded at 3 different time points (T0: preliminary alginate impression; T1: denture delivery; T2: last scheduled postdelivery adjustment). Adjustments during the follow-up (after T2) were noted and included the removal of areas of excessive pressure, relining, or repairs. The costs of the dental treatment and the laboratory fees were calculated. The Wilcoxon rank sum tests were used for statistical analysis (α=.05).

RESULTS

No statistically significant difference regarding the treatment duration between digitally and conventionally fabricated removable complete dentures was found: T₀-T₁ (P=.889); T₁-T₂ (P=.675); T₂- T₃ (P=.978). No significant difference was found in the number adjustments for areas of excessive pressure, relines, or repairs (P=.757, P=1.000, P=1.000) during the period. Laboratory costs of CAD-CAM removable complete dentures were significantly lower than those of conventional removable complete dentures (P<.001), but clinical fees were similar between groups (P=.596), resulting in a reduction in the overall total costs for the CAD-CAM removable complete dentures (P=.011). Regarding the number of clinical visits, neither the group (conventional/CAD-CAM (P=.945)/DDS-AV/DD-IV [P=.848]) nor the interaction group (conventional/CAD-CAM and DDS-AV/DD-IV)/period (P=.084/P=.171) showed any significant differences.

CONCLUSIONS

CAD-CAM removable complete dentures can be considered a viable alternative to conventional removable complete dentures regarding treatment duration, clinical and follow-up visits, adjustments, and maintenance requirements.

Mechanical stability of dental CAD-CAM restoration materials made of monolithic zirconia, lithium disilicate, and lithium disilicate-strengthened aluminosilicate glass ceramic with and without fatigue conditions

STATEMENT OF PROBLEM

Studies investigating the mechanical stability of lithium disilicate-strengthened aluminosilicate glass ceramic that do not require sintering after milling compared with other computer-aided design and computer-aided manufacturing (CAD-CAM) materials are lacking.

PURPOSE

The purpose of this in vitro study was to investigate the flexural strength of CAD-CAM zirconia, lithium disilicate, and lithium disilicate-strengthened aluminosilicate glass ceramics with and without fatigue conditions.

MATERIAL AND METHODS

Specimens (N=90, n=15) (12×4×3 mm) from the following CAD-CAM materials were prepared and polished: lithium disilicate glass ceramic (IPS e.max CAD); lithium disilicate-strengthened aluminosilicate glass ceramic (N!ce); and zirconium dioxide ceramic (IPS e.max ZirCAD). All specimens were divided into 2 subgroups: immediate testing without aging and simulation of aging by using a mastication simulator for 1 200 000 cycles (5 °C-55 °C). Thereafter, flexural strength testing was performed by using a universal testing machine (1 mm/min) on nonaged and aged specimens. The data were evaluated by using nonparametric 2-way ANOVA and Wilcoxon rank post hoc tests (α=.05).

RESULTS

Both the material type and aging significantly affected the results (P<.001). The interaction was not significant (P>.05). Under nonaged conditions, zirconium dioxide ceramic (1136 ±162 MPa) showed significantly higher mean ±standard deviation flexural strength (P<.001) than lithium disilicate (304 ±34 MPa) and lithium disilicate-strengthened aluminosilicate glass ceramic (202 ±17 MPa). The glass ceramic groups were also significantly different from each other (P<.001). After aging, zirconium dioxide (1087.9 ±185.3 MPa) also presented significantly higher mean ±standard deviation flexural strength (P<.001) than lithium disilicate (259 ±62 MPa) and lithium disilicate-strengthened aluminosilicate glass ceramic (172 ±11 MPa) (P<.001). Aging significantly decreased the flexural strength of lithium disilicate (14.6%) (P=.03) and lithium disilicate-strengthened aluminosilicate glass ceramic (14.5%) (P=.01) but had minimal effect on the zirconium dioxide ceramic (4.3%) (P=.29).

CONCLUSIONS

Among the tested CAD-CAM materials, the mechanical performance of lithium disilicate-strengthened aluminosilicate glass ceramic was comparable with that of lithium disilicate and considerably lower than that of zirconia. Aging decreased the flexural strength of both lithium disilicate and lithium disilicate-strengthened aluminosilicate glass ceramic.

Cleaning Efficacy of Poly-ether-ether-ketone Tips in Eliminating Cement Remnants Around Implants With Different Abutment Heights

The excess cement not removed after the cementation of fixed implant-supported restorations may cause loss of peri-implant attachment or adjacent bone. The aims of this study were to evaluate the amount of residual cement at different abutment-crown connection levels and to test the cleaning efficacy of poly-ether-ether-ketone (PEEK) ultrasonic tips after cementation. One implant was placed in an anterior central tooth position 5 mm below the gingival margin in an acrylic model, and 32 stone models were obtained with implant analogs. Abutment heights of 1-2 and 2.5-4 mm were used on the vestibular and lingual sides, respectively. Crowns were cemented and cleaned, and half of the samples were cleaned again using PEEK tips. The abutment-crown suprastructure was then disconnected, and cleaning efficacy was evaluated. Varying amounts of excess cement were found on all specimens except for the PEEK group with abutment-crown connections 1 mm below the gingival margin. An increase of undetected cement remnants was observed when the restoration margins were located deeper subgingivally. Various amounts of excess cement associated with margin location were detected on the abutment-restoration complex despite meticulous cleaning efforts. Ultrasonic PEEK tips were effective at cleaning the cement remnants around implants to a certain depth.

Effect of photo-polymerization mode on the degree of conversion of resin cement under different ceramic materials

BACKGROUND

This study evaluated the effect of different polymerization modes and duration on the degree of conversion (DC) of resin cement under different types of ceramics.

METHODS

Ceramic materials were divided into 3 groups (N.=60): group 1, Cerasmart; group 2, Vita Enamic; and group 3, Vita Mark II. Each group was then divided into three subgroups (N.=20) according to the polymerization mode (A: low-intensity; B: high-intensity; and C: soft-start). Subgroups were then divided into two further groups according to the polymerization time (I: 10 s; and II: 20 s). DC of light-cured resin cement beneath different kinds of ceramics was tested using FTIR spectroscopy. Results were compared to a control group cured without overlying ceramic.

RESULTS

While the type of ceramic and mode of polymerization showed a significant effect on the DC of resin cement, polymerization duration did not. Vita Mark II group showed the highest DC of resin cement followed by Vita Enamic and Cerasmart. High- and low-intensity polymerization modes did not show significant difference, but both showed significantly lower DC when compared to soft start mode.

CONCLUSIONS

Type of ceramic and polymerization mode showed a direct effect on the DC of resin cement.

Clinical Performance of Partial and Full-Coverage Fixed Dental Restorations Fabricated from Hybrid Polymer and Ceramic CAD/CAM Materials: A Systematic Review and Meta-Analysis

The aim of this systematic review and meta-analysis was to evaluate the clinical performance of tooth-borne partial and full-coverage fixed dental prosthesis fabricated using hybrid polymer and ceramic CAD/CAM materials regarding their biologic, technical and esthetical outcomes. PICOS search strategy was applied using MEDLINE and were searched for RCTs and case control studies by two reviewers using MeSH Terms. Bias risk was evaluated using the Cochrane collaboration tool and Newcastle–Ottawa assessment scale. A meta-analysis was conducted to calculate the mean long-term survival difference of both materials at two different periods (≤24, ≥36 months(m)). Mean differences in biologic, technical and esthetical complications of partial vs. full crown reconstructions were analyzed using software package R (p < 0.05). 28 studies included in the systematic review and 25 studies in the meta-analysis. The overall survival rate was 99% (0.95–1.00, ≤24 m) and dropped to 95% (0.87–0.98, ≥36 m), while the overall success ratio was 88% (0.54–0.98; ≤24 m) vs. 77% (0.62–0.88; ≥36 m). No significance, neither for the follow-up time points, nor for biologic, technical and esthetical (88% vs. 77%; 90% vs. 74%; 96% vs. 95%) outcomes was overserved. A significance was found for the technical/clinical performance between full 93% (0.88–0.96) and partial 64% (0.34–0.86) crowns. The biologic success rate of partial crowns with 69% (0.42–0.87) was lower, but not significant compared to 91% (0.79–0.97) of full crowns. The esthetical success rate of partial crowns with 90% (0.65–0.98) was lower, but not significant compared to 99% (0.92–1.00) of full crowns.

Fracture resistance of teeth obturated with two different types of Mineral Trioxide Aggregate Cements

Objective: Endodontically obturated teeth have lower fracture resistance depending on the obturating material and technique. The purpose of this study was therefore to evaluate the influence of ProRoot MTA (Dentsply Sirona, Tulsa Division) and OrthoMTA III (BioMTA, Daejeon, Korea) as an obturating material on the fracture resistance of endodontically treated teeth. Material and Methods: Thirty extracted human maxillary central incisors were decoronated and instrumented using Protaper instruments (size F5). Irrigation was performed with 2.5% sodium hypochlorite between each instrument change followed by 7% maleic acid for one minute. Finally, canals were flushed with 5 ml of PBS solution for one minute. Samples were then divided into three groups. Group I- positive control (no root canal filling); Group II- obturation with ProRoot MTA; Group III- obturation with OrthoMTA III. Ten teeth were randomly selected as a negative control in which no treatment was performed. All the specimens were then subjected to fracture strength testing using universal testing machine. For evaluation of biomineralization, six maxillary central incisors were divided into two groups. Group I obturated with ProRoot MTA and group II obturated with OrthoMTA III. These samples were subjected to SEM analysis. Results: Positive control group demonstrated the least fracture resistance, while OrthoMTA III group showed the highest fracture resistance. There was no significant difference between negative control group and ProRoot MTA groups (p=0.821). OrthoMTA III group showed better tubular biomineralization when compared to ProRoot MTA. Conclusions: Root canals obturated with OrthoMTA III had better fracture resistance and increased tubular biomineralization compared to ProRoot MTA. Since root canals obturated with OrthoMTA III had better fracture resistance, it can be used as a promising obturating material.KeywordsBiomineralization; Fracture Resistance; OrthoMTA III; ProRoot MTA; Root Canal; Tubular.

Chemical composition, surface roughness, and ceramic bond strength of additively manufactured cobalt-chromium dental alloys

STATEMENT OF PROBLEM

Selective laser melting (SLM) additive manufacturing (AM) technology is a current option to fabricate cobalt-chromium (Co-Cr) metal frameworks for dental prostheses. However, the Co-Cr alloy composition, surface roughness, and ceramic bond strength values that SLM metals can obtain are not well-defined.

PURPOSE

The purpose of this in vitro study was to compare the chemical composition, surface roughness, and ceramic shear bond strength of the milled and SLM Co-Cr dental alloys.

MATERIAL AND METHODS

A total of 50 disks of 5 mm in diameter and 1 mm in thickness were fabricated by using subtractive (control group) and AM with each of following SLM providers: SLM-1 (EOS), SLM-2 (3D systems), and SLM-3 (Concept Laser). The milled disks were airborne-particle abraded with 100-μm aluminum oxide particles. All the specimens were cleaned before surface roughness (Ra), weight (Wt%), and atomic (At%) percentages were analyzed. Three-dimensional profilometry was used to analyze the topographical properties of the surface parameters Ra (mean surface roughness). The chemical composition of Co-Cr alloy specimens was determined by using energy dispersive X-ray (EDAX) elemental analysis in a scanning electron microscope (SEM). Thereafter, the specimens were bonded to a ceramic (Dentine A3 and Enamel S-59; Creation CC) interface. Specimens were stored for 24 hours at 23 °C. The bond strength of the SLM-ceramic interface was measured by using the macroshear test (SBT) method (n=10). Adhesion tests were performed in a universal testing machine (1 mm/min). The Shapiro-Wilk test revealed that the chemical composition data were not normally distributed. Therefore, the atomic (At%) and weight percentages (Wt%) were analyzed by using the Kruskal-Wallis test, followed by pairwise Mann-Whitney U tests between the control and AM groups (AM-1 to AM-4). However, the Shapiro-Wilk test revealed that the surface roughness (Ra) and ceramic bond strength data were normally distributed. Therefore, data were analyzed by using 1-way ANOVA, followed by the post hoc Sidak test (α=.05).

RESULTS

Significant differences were obtained in Wt%, At%, and Ra values among the Co-Cr alloys evaluated (P<.05). Furthermore, the control group revealed significantly lower mean ±standard deviation Ra values (0.79 ±0.11 μm), followed by AM-3 (1.57 ±0.15 μm), AM-2 (1.80 ±0.43 μm), AM-1 (2.43 ±0.34 μm), and AM-4 (2.84 ±0.27 μm). However, no significant differences were obtained in the metal-ceramic shear bond strength among the different groups evaluated, ranging from mean ±standard deviation 75.77 ±11.92 MPa to 83.65 ±12.21 MPa.

CONCLUSIONS

Co-Cr dental alloys demonstrated a significant difference in their chemical compositions. Subtractive and additive manufacturing procedures demonstrated a significant influence on the surface roughness of the Co-Cr alloy specimens. However, the metal-ceramic shear bond strength of Co-Cr alloys was found to be independent of the manufacturing process.

Flexural strength and Weibull characteristics of stereolithography additive manufactured versus milled zirconia

STATEMENT OF PROBLEM

Zirconia restorations can be processed by using stereolithography additive manufacturing (AM) technologies. However, whether additive manufactured zirconia could achieve flexural strength values comparable with those of milled zirconia is unclear.

PURPOSE

The purpose of this in vitro study was to compare the flexural strength and Weibull characteristics of milled and additive manufactured zirconia.

MATERIAL AND METHODS

A total of 40 zirconia bars (25×4×1.2 mm) were obtained by using 2 manufacturing procedures, subtractive (CNC group) (IPS e.max ZirCAD; Ivoclar Vivadent AG) and additive manufacturing (AM group) (3DMix ZrO₂; 3DCeram) technologies and assigned to 2 subgroups according to accelerating artificial aging procedures (mastication simulation): nonaged and aged (n=10). Flexural strength was measured in all specimens by using 3-point bend tests according to ISO/CD 6872.2 with a universal testing machine (Instron Model 8501; Instron Corp). Two-parameter Weibull distribution values, including the Weibull modulus, scale (m), and shape (0) were calculated. Flexural strength values were analyzed by using 2-way ANOVA and Student t statistical tests (α=.05).

RESULTS

The manufacturing procedure (P<.001), the mastication simulating aging procedure (P<.001), and the interaction between them (P<.001) significantly affected flexural strength values. The CNC group exhibited statistically higher flexural strength values than those in the AM group when the specimens were tested before performing an aging procedure (P<.001) and after mastication simulation (P<.001). Moreover, mastication simulation produced a significant reduction in flexural strength for both the CNC group (P<.039) and the AM group (P<.001).

CONCLUSIONS

The manufacturing process reported a significant effect on the flexural strength of the zirconia material tested. Mastication simulation as a means of accelerating artificial aging resulted in the significantly decreased flexural strength values of milled and additively manufactured zirconia material, with the Weibull moduli being significantly higher for the milled groups versus the milled specimens.

A digital cast-free clinical workflow for oral rehabilitation with removable partial dentures: A dental technique

The present report describes a technique for a digital cast-free clinical workflow for the fabrication of a combined tooth-implant-supported removable partial denture. This technique comprises digital intraoral scanning, computer-aided design, and subtractive computer-aided manufacturing for the denture base, denture teeth, and crowns and additive computer-aided manufacturing for the denture framework (CAD-CAM).

Salivary 8-hydroxyguanosine levels in smokers and non-smokers with chronic periodontitis

This case-controlled clinical trial was performed on the salivary 8-hydroxyguanosine (8-OHdG) levels in smokers and non-smokers with chronic periodontitis after non-surgical periodontal therapy. Subjects (N = 40) with periodontitis (smokers and non-smokers) and with clinically healthy conditions (smokers and non-smokers) were assigned to this study. At baseline, clinical periodontal parameters (plaque index, gingival index, pocket probing depth and clinical attachment levels) were evaluated. Saliva samples were obtained pre- and post-treatment to quantify the 8-OHdG levels using Elisa technique. Subjects diagnosed with chronic periodontitis with smoking habit (CPs) and non-smokers (CPns) received scaling and root planing. In clinically healthy subjects with smoking habit (CHs) and non-smokers (CHns), only oral hygiene tutoring was performed. All clinical measurements and salivary collection were repeated in a 3-month recall interval. Data were analyzed using Anova, Tukey post hoc test and Mann-Whitney 'U' tests (P < 0.05). At baseline, CPs and CPns groups showed significantly higher PI, GI, PD and CAL values than those of CHns and CHs (P < 0.001). Baseline salivary levels of 8-OHdG were significantly higher in CPs group (14.775 pg/mL) (P < 0.001) compared to the other groups. All clinical parameters in chronic periodontitis group improved at the 3rd month recall interval, however, with regards to 8-OHdG values, the CP smoker category still had a higher level compared to CP non-smoker. This study reflects an on-going periodontal destructive status in smokers and salivary 8-OHdG levels could be recognized as an oxidative biomarker for determining periodontal tissue destruction.

Effect of length of LOCATOR abutment and cement type on retention to intraradicular dentin in overdentures

STATEMENT OF PROBLEM

Limited information is available on the effect of LOCATOR abutment length and luting cement type on retention to intraradicular dentin in overdentures.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of the length of a commercially available LOCATOR abutment and cement type on retention in the root canal.

MATERIAL AND METHODS

Eighty LOCATOR abutments with a standard length of 6 mm were obtained. Half of them were shortened to 3 mm. Eighty recently extracted single-rooted teeth were divided into 2 groups. The post space was prepared to 6 mm in the first group and 3 mm in the second. After preparation, the LOCATOR abutments were luted with one of the following cements: dual-polymerized glass-reinforced resin cement (Parapost Paracore), dual-polymerized resin cement (Variolink II), self-adhesive resin cement (RelyX Unicem), and conventional cement (zinc phosphate). The tensile force required for the removal of the LOCATOR abutments from their corresponding roots was recorded. Data were statistically analyzed with 2-way ANOVA and the Tukey multiple comparison test.

RESULTS

Both the cement type (P<.001) and the length of the LOCATOR abutment (P<.001) significantly affected the mean tensile forces. Dual-polymerized glass-reinforced resin cement (Parapost Paracore) presented significantly higher mean tensile forces for the LOCATOR abutment retention among all cements (P<.05).

CONCLUSIONS

Regardless of the length, LOCATOR abutments luted with Parapost Paracore resin cement presented higher mean resistance to tensile forces compared with those luted with the other cements. LOCATOR abutments of 6 mm in length were more resistant to tensile forces than those of 3 mm in length in combination with all cements.

A review on potential toxicity of dental material and screening their biocompatibility

OBJECTIVES

A wide range of compounds are utilized in dentistry such as dental composites, resins, and implants. The successful clinical use of dental materials relies on theirm physiochemical properties as well as biological and toxicological reliability. Different local and systemic toxicities of dental materials have been reported. Placement of these materials in oral cavity for a long time period might yield unwanted reactions. An extensive variety of materials is used in dentistry including filling materials, restorative materials, intracanal medicines, prosthetic materials, different types of implants, liners, and irrigants. The increasing rate in development of the novel materials with applications in the dental field has led to an increased consciousness of the biological risks and tempting restrictions of these materials. The biocompatibility of a biomaterial used for the replacement or filling of biological tissue such as teeth always had a high concern within the health care disciplines for patients.

MATERIALS AND METHODS

Any material used in humans should be tested before clinical application. There are many tests evaluating biocompatibility of these materials at the point of in vitro, in vivo, and clinical investigations.

RESULTS

The current review discusses the potential toxicity of dental material and screening of their biocompatibility.

CLINICAL RELEVANCE

It is essential to use healthy and safe materials medical approaches. In dentistry, application of different materials in long-term oral usage demands low or nontoxic agents gains importance for both patients and the staff. Furthermore, screening tests should evaluate any potential toxicity before clinical application.

Comparison of Adhesion of a Novel Pre-sintered Cobalt-Chromium to Pre-sintered Zirconia and Cast Nickel-Chromium

AIM

This study compared the bond strength of pre-sintered Ceramill Sintron to pre-sintered zirconia and cast nickel-chromium (NiCr).

MATERIALS AND METHODS

Specimens (n = 60) (diameter: 15 mm; thickness: 2 mm) were prepared (n = 20/group) (Ceramill Sintron, Ceramill Zi, and Wirobond 99). Disks were layered with vita VM ceramic (4 mm). Specimens were randomly divided into two subgroups. Only one subgroup was thermocycled. Specimens were tested under shear strength. Energy-dispersive X-ray (EDX) mapping was done on one disk of each material before and after ceramic layering.

RESULTS

Failure types were mostly mixed failures. Significant difference was found between the three materials for Y and Z failure types (p-values: 0.032 and 0.010 respectively). Thermocycling had no major effect on the results reported. Considering Fmax (force-inducing bonding failure) registered, significant difference was found between the control group and milled alloys groups. No significant difference was found between Ceramill Sintron and Zi. The EDX mapping showed a net increase in the control group oxide layer, whereas only slight increase and decrease were reported for Zi and Sintron respectively.

CONCLUSION

When compared with cast NiCr, novel Ceramill Sintron has higher bond strength, comparable to Ceramill Zi. Thermocycling had no major effects on the results.

CLINICAL SIGNIFICANCE

Ceramic-alloy bonding is a primary factor in the prosthesis' longevity.

Marginal and internal fit of pre-sintered Co-Cr and zirconia 3-unit fixed dental prostheses as measured using microcomputed tomography

STATEMENT OF PROBLEM

Limited information is available on the precision of new metal processing technologies.

PURPOSE

The purpose of this in vitro study was to evaluate the marginal and internal fit of pre-sintered cobalt-chromium (Co-Cr) and zirconia 3-unit fixed dental prostheses using x-ray microcomputed tomography.

MATERIAL AND METHODS

Three-unit fixed dental prostheses were prepared on metal dies (N=12) using a typodont model from the maxillary first premolar to the first molar. A standardized preparation with a 1.2-mm chamfer (360 degrees) and a 2-mm occlusal reduction was prepared on abutment teeth. The dies were scanned and divided into 2 groups to receive the fixed dental prostheses (n=6) made of pre-sintered Co-Cr and pre-sintered zirconia. Each framework was seated on its cast, and marginal and internal discrepancies were measured at 9 points, starting from the most distal point from the pontic for the maxillary first premolar and the first molar (points 1-4, mesial; point 5, occlusal; points 6-9, distal) of each abutment tooth using microcomputed tomography. The data were analyzed using the Levene test, t test, and ANOVA (α=.05).

RESULTS

When overall mean discrepancy values were compared, no significant difference was observed between pre-sintered Co-Cr and pre-sintered zirconia (P=.085). Discrepancy values for points 1, 2, and 3 were significantly different for pre-sintered Co-Cr and pre-sintered zirconia, with the lowest mean values for point 1 and the highest for point 5. On the abutment tooth basis, for the maxillary first premolar and the first molar, a significant difference was found only in points 6 (P<.001) and 8 (P<.003) for both materials. When the discrepancies for the maxillary first premolar were considered for pre-sintered Co-Cr and pre-sintered zirconia, the mean values were significantly different only at points 1 (P<.001), 2 (P=.007), and 3 (P=.003) and were smaller for pre-sintered zirconia. For the tooth the first molar, a significant difference was observed at point 2 (P=.002) and point 3 (P=.008) for both materials, where the mean values were higher for pre-sintered Co-Cr than for pre-sintered zirconia. The pairwise comparison between points showed a significant difference between measurement points within each material (P<.05). The increase in values between points 1 and 5 was evident for both pre-sintered Co-Cr and pre-sintered zirconia materials.

CONCLUSIONS

Three-unit fixed dental prostheses made of pre-sintered Co-Cr or zirconia showed similar marginal and internal discrepancy values, with the highest discrepancy values at the occlusal region in both the first premolar and first molar.