Denture relining using digital replication method: A dental technique

The aim of this report was to digitize traditional denture relining using a digital duplication method, in addition to assessing the wear resistance of three-dimensional (3D) printed denture teeth. A complete denture was relined using light body impression. The denture with impression was scanned yielding a standard tessellation language file that was designed to print the denture base and teeth. The printed teeth were fitted into the sockets of the printed denture base and then bonded using auto-polymerized acrylic resins, followed by finishing and polishing. Dentures were inserted and fit and occlusion were adjusted as needed, and the patient was scheduled for follow-up appointments at one week, three months, and six months. At each follow-up visit, dentures were scanned using a 3Shape E3 desktop scanner and scans were superimposed. The occlusal wear was assessed in reference to the first scan after the denture insertion visit. The accuracy of the intaglio surface of dentures was within clinically acceptable limits. The clinical evaluation of inserted dentures in terms of retention, occlusion, esthetic, and patient satisfaction was encouraging. Using digital duplication, conventional dentures could be relined. The advantages of digital records include eliminating polymerization dimensional changes, and reducing cost and clinical time by minimizing the number of visits, which is particularly helpful with geriatric patients.

Influences of Different CAD/CAM Ceramic Compositions and Thicknesses on the Mechanical Properties of Ceramic Restorations: An In Vitro Study

The aim of this study was to assess the influences of different CAD/CAM ceramic compositions and thicknesses on the surface roughness and hardness of ceramic restorations. Four different ceramics were used in the current study: lithium disilicate (LD), leucite reinforced (LE), advanced lithium disilicate (ALD), and zirconia-reinforced lithium silicate (ZLS). Each group included 30 specimens subdivided into three different ceramic thicknesses (0.5, 1 and 1.5 mm thicknesses). The microhardness was measured for all the specimens using a microhardness testing machine, while the surface roughness was measured using a non-contact optical profilometer at three intervals (before toothbrushing and after toothbrushing, with and without toothpaste). Three-way and two-way ANOVA were used to determine the factors influencing the surface roughness and microhardness. There was a significant difference in the surface roughness between the studied groups for all the thicknesses. The findings showed that ALD had the lowest surface roughness, while ZLS showed the highest surface roughness. Moreover, ALD, followed by ZLS, had the highest hardness, while LD and LE had the lowest hardness values. Regarding the thicknesses, both the 0.5 and 1 mm ceramic thicknesses showed a significantly lower surface roughness than the 1.5 mm thickness, while the 1.5 mm thickness showed a significantly higher microhardness than the 0.5 mm thickness. The surface roughness and hardness were significantly affected by the ceramic composition and type of filler. It is recommended to use 1.5 mm-thick ceramic materials for the fabrication of definitive full-coverage ceramic restorations, while veneers require 0.5 mm-thick materials. ALD is a promising CAD/CAM material that can be used for the fabrication of restorations with a proper strength in both anterior and posterior regions.

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.

3D-Printable Denture Base Resin Containing SiO2 Nanoparticles: An In Vitro Analysis of Mechanical and Surface Properties

PURPOSE

To evaluate the flexural strength (FS), impact strength (IS), surface roughness (Ra), and hardness of 3D-printed resin incorporating silicon dioxide nanoparticles (SNPs).

MATERIALS AND METHODS

A total of 320 acrylic specimens were fabricated with different dimensions according to test specifications and divided into a control group of heat denture base resin, and 3 test groups (80/test (n = 10) of unmodified, 0.25 wt%, and 0.5 wt% SNPs modified 3D-printed resin. 10,000 thermal cycles were performed to half of the fabricated specimens. FS, IS (Charpy impact), Ra, and hardness were evaluated and the collected data was analyzed with ANOVA followed by Tukey's post hoc test (α = 0.05).

RESULTS

Incorporating SNPs into 3D-printed resin significantly increased the FS, IS (at 0.5%) and hardness compared to unmodified 3D-printed resin (p < 0.001). However, the FS of pure 3D-printed and 3D/SNP-0.50% resin and IS of all 3D-printed resin groups were significantly lower than the control group (p < 0.0001). Hardness of 3D/SNP-0.25% and 3D/SNP-0.50% was significantly higher than control and unmodified 3D-printed resin (p < 0.0001), with insignificant differences between them. The Ra of all 3D-printed resin groups were significantly higher than control group (p < 0.001), while insignificant difference was found between 3D-printed groups. Thermal cycling significantly reduced FS and hardness for all tested groups, while for IS the reduction was significant only in the control and 3D/SNP-0.50% groups. Thermal cycling significantly increased Ra of the control group and unmodified 3D-printed resin (p < 0.001).

CONCLUSION

The addition of SNPs to 3D-printed denture base resin improved its mechanical properties while Ra was not significantly altered. Thermal cycling adversely affected tested properties, except IS of unmodified 3D-printed resin and 3D/SNP-0.25%, and Ra of modified 3D-printed resin.

Effect of Occlusal Splint Therapy on Condylar Movements Recorded Using an Electronic Pantograph: A Prospective Clinical Study

AIMS AND OBJECTIVE

The effect of occlusal splint therapy on the muscle activity has been addressed in the literature. However, its effect on condylar movements in subjects with normal and abnormal occlusions has not yet been investigated. This prospective clinical study addressed the effect of occlusal splint therapy on condylar movements in subjects with normal and abnormal occlusions using an electronic pantograph.

MATERIALS AND METHODS

Two groups of subjects were included in this study. The first group included subjects with normal occlusion, whereas the subjects in the other group were diagnosed with abnormal occlusion. The occlusal splint was fabricated, adjusted clinically, and delivered for each subject. Condylar movements were recorded using a Cadiax Compact II electronic pantograph at baseline, 2-, 4-, and 6-month follow-up periods to assess sagittal condylar inclination (SCI), immediate mandibular lateral translation (IMLT), and progressive mandibular lateral translation (PMLT). The t-test, one-way analysis of variance (ANOVA), and two-way ANOVA were used to compare the parameters between the groups and to assess the time effect on these parameters (α = 0.05).

RESULTS

Twenty subjects were recruited for this study (n = 10). Among them, 12 were women and eight were men, with a mean age of 34 years. In each group, insignificant differences were reported for each tested parameter at baseline and during the follow-up periods (P > 0.05). However, when comparing the two groups, the only significant difference was found in the SCI during the 6-month follow-up period (P = 0.014).

CONCLUSIONS

Occlusal splints had an insignificant effect on the parameters SCI, IMLT, and PMLT up to 6 months of follow-up for subjects with normal or abnormal occlusion. SCI increased substantially in normal occlusion subjects compared with abnormal occlusion subjects during the 6-month follow-up period.

The Effect of Salivary pH on the Flexural Strength and Surface Properties of CAD/CAM Denture Base Materials

OBJECTIVES

 This study aimed to evaluate the influence of different salivary pH on flexural strength, hardness, and surface roughness of computer-aided design and computer-aided manufacturing (CAD/CAM) milled and three-dimensional (3D)-printed denture base resins.

METHODS

 One heat-polymerized, two CAD/CAM milled (IvoCad, AvaDent), and two 3D-printed (FormLabs, NextDent) denture base resins were fabricated and divided into five groups (n = 10) according to the solutions: three groups were immersed in different salivary pH (5.7, 7.0, or 8.3), one group was immersed in distilled water (DW) as a positive control, and one group had no immersion (negative control). All immersions were performed at 37°C for 90 days. Flexural strength, hardness, and surface roughness were measured before and after immersion. Data was analyzed with analysis of variance and post hoc Tukey's test (α = 0.05).

RESULTS

 After immersion, all specimens had lower flexural strength values when compared with those with no immersion. Comparing the immersion groups, the highest flexural strength value (93.96 ± 3.18 MPa) was recorded with IvoCad after immersion in DW while the lowest value (60.43 ± 2.66 MPa) was recorded with NextDent after being immersed in 7.0 pH saliva. All specimens had significant decrease in hardness except IvoCad and AvaDent specimens where both presented the highest surface hardness (53.76 ± 1.60 Vickers hardness number [VHN]) after immersion in DW while NextDent showed the lowest hardness value (24.91 ± 2.13 VHN) after being immersed in 8.3 pH saliva. There was statistically significant difference between the baseline and different artificial salivary pH solutions in terms of surfaces roughness, with the highest surface roughness were found in 3D-printed resin materials.

CONCLUSION

 After exposure to artificial saliva with different salivary pH, the milled CAD/CAM denture base resins showed higher flexural strength, hardness, and lesser surface roughness than conventional and 3D-printed denture base 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.

The post-pandemic era: will physical distancing be a perceived way of life?

Background: This study aimed to determine whether people living in the Eastern Region of Saudi Arabia would prefer to continue the practice of physical distancing after the coronavirus disease 2019 (COVID-19) pandemic or to return to their previous way of life. Methods: This cross-sectional study was conducted from August 2020 to October 2020 in the Eastern Region of Saudi Arabia. A pre-tested questionnaire was sent electronically through social media. Data on participants' demographics and their perspectives regarding post-pandemic physical distancing were collected. The calculated sample size was 1,066; however, the total number of responses included in the analysis was 989. Results: The average age of the participants was 31.15±11.93 years. There were 435 men and 554 women in the study. Participants showed significantly high levels of disagreement with statements indicating that they were willing to use public transportation (61%), attend social gatherings (36%), and hug relatives or colleagues (40%) after the pandemic ( p<0.001); however, 43% agreed that they would spend time with family or friends ( p<0.001). The level of education was also found to be significantly related to the responses, and the level of disagreement increased as the level of education increased ( p<0.001). Conclusions: One-third of the study participants planned to continue engaging in physical distancing even after the current pandemic and if the COVID-19 related restriction will remain in place for longer, there is chance to increase in this proportion. However, it cannot be concluded whether or not this behavior will prevail in the long run, after the ease in restrictions. If so, it may greatly affect some businesses and perhaps some social norms and values as well.

Effect of Low Nanodiamond Concentrations and Polymerization Techniques on Physical Properties and Antifungal Activities of Denture Base Resin

Background: Denture base resin has some drawbacks. This study investigated the impact of nanodiamonds (ND) and autoclave polymerization on the surface characteristics, translucency, and Candida albicans adherence in polymethyl methacrylate (PMMA) denture base resin after thermocycling. Methods: Heat-polymerized PMMA discs (15 × 2 mm) with a total sample size n = 160 were studied. Specimens were categorized into two main groups (N = 80): conventional water-bath-polymerized PMMA (CP/PMMA) and autoclave-polymerized PMMA (AP/PMMA). Each group was subdivided according to the ND concentration into four groups (n = 20): unmodified PMMA as a control, and 0.1%, 0.25%, and 0.5% ND–PMMA. Scanning electron microscopy (SEM) was used to inspect the morphology of the ND and the ND–PMMA mixtures before heat polymerization. The specimens were exposed to thermal cycling (5000 cycles at 5 and 55 °C), then surface roughness was measured with a non-contact optical interferometric profilometer, contact angle with an automated goniometer, and translucency using a spectrophotometer. Colony-forming units (CFU) were used to determine the adherence of Candida albicans cells to the specimens. ANOVA and Tukey post hoc tests for pairwise comparison were utilized for the statistical analysis (α = 0.05). Results: Surface roughness was significantly reduced with ND addition to CP/PMMA (p ˂ 0.001), while the reduction was not statistically significant in AP/PMMA (p = 0.831). The addition of ND significantly reduced the contact angle, translucency, and Candida albicans count of CP/PMMA and AP/PMMA (p ˂ 0.001). The incorporation of ND in conjunction with autoclave polymerization of PMMA showed significant reduction in all tested properties (surface roughness, contact angle and Candida albicans adherence) except translucency (p = 0.726). Conclusions: ND addition to PMMA and autoclave polymerization improved the surface properties with respect to antifungal activities, while the translucency was adversely affected.

Predominance of non-Streptococcus mutans bacteria in dental biofilm and its relation to caries progression

This study aims to assess differences in biofilm bacterial composition between patients with low and high caries. Patients without a medical problem and with no history of antibiotic use, mouth wash or fluoride application in the previous 3 months were recruited. Caries was recorded at cavitation level; score was calculated by a national mean (dmft of 4.8 and DMFT of 2.7). Pooled biofilm samples were collected from mesial, distal, buccal, lingual, and occlusal surfaces. Based on caries experience, individuals were classified into low and high caries and both groups were compared regarding bacteria identified using 16S rRNA gene sequencing, and molecular phylogenetic analysis of the isolates was performed. A total of twenty seven randomly selected samples with low (n = 13) and high (n = 14) caries. Identification of oral bacteria was performed using 16S rRNA sequence, Rothia mucilaginosa and R. aeria were identified in low caries individuals, while R. dentocariosa was detected in high caries individuals. Two Streptococcus spp. were identified only in low caries S. salivarius and S. gordonii whereas S. sanguinis, S. mitis, S. sinensis, S. rubneri, S. vestibularis, S. cristatus and S. massiliensis were identified only in individuals with high caries. This study revealed the absence of R. mucilaginosa in the high caries subjects and its coexistence with the low caries subjects. Streptococcus mutans was insignificant contributor of caries among samples, while, Streptococcus sanguinis was the main constituent of high caries Saudi patients.

Strength and Surface Properties of a 3D-Printed Denture Base Polymer

PURPOSE

This in vitro study evaluated the flexural strength, impact strength, hardness, and surface roughness of 3D-printed denture base resin subjected to thermal cycling treatment.

MATERIALS AND METHODS

According to ISO 20795-1:2013 standards, 120 acrylic resin specimens (40/flexural strength test, 40/impact strength, and 40/surface roughness and hardness test, n = 10) were fabricated and distributed into two groups: heat-polymerized; (Major.Base.20) as control and 3D-printed (NextDent) as experimental group. Half of the specimens of each group were subjected to 10,000 thermal cycles of 5 to 55°C simulating 1 year of clinical use. Flexural strength (MPa), impact strength (KJ/m² ), hardness (VHN), and surface roughness (μm) were measured using universal testing machine, Charpy's impact tester, Vickers hardness tester, and profilometer, respectively. Data were analyzed by ANOVA and Tukey honestly significant difference (HSD) test (α = 0.05).

RESULTS

The values of flexural strength (MPa) were 86.63 ± 1.0 and 69.15 ± 0.88; impact strength (KJ/m² )-6.32 ± 0.50 and 2.44 ± 0.31; hardness (VHN)-41.63 ± 2.03 and 34.62 ± 2.1; and surface roughness (μm)-0.18 ± 0.01 and 0.12 ± 0.02 for heat-polymerized and 3D-printed denture base materials, respectively. Significant differences in all tested properties were recorded between heat-polymerized and 3D-printed denture base materials (P < 0.001). Thermal cycling significantly lowered the flexural strength (63.93 ± 1.54 MPa), impact strength (2.40 ± 0.35 KJ/m² ), and hardness (30.17 ± 1.38 VHN) of 3D-printed resin in comparison to thermal cycled heat-polymerized resin, but surface roughness showed non-significant difference (p = 0.262).

CONCLUSION

3D-printed resin had inferior flexural strength, impact strength, and hardness values than heat-polymerized resin, but showed superior surface roughness. Temperature changes (thermal cycling) significantly reduced the hardness and flexural strength and increased surface roughness, but did not affect the impact strength.

Closed Repair Technique: Innovative Surface Design for Polymethylmethacrylate Denture Base Repair

PURPOSE

This study aimed to evaluate the repair strength of a newly introduced repair technique involving zero-gap repair width.

MATERIALS AND METHODS

A total of 36 rectangular prism specimens with dimensions of 64 × 10 × 3.3 mm were prepared from heat-polymerized acrylic resin. Nine specimens were kept intact. The other specimens were sectioned into halves and modified to create repair gaps of 2.5-mm beveled (2.5B) as control, 0-mm beveled (ZB), and 0-mm inverse bi-beveled (ZIBB). The ZIBB group was prepared with a V-shaped internal groove on both halves (repair tunnel), while the intaglio and cameo surfaces were kept intact except for two small holes at the cameo surface for repair resin injection. The 2.5B and ZB groups were repaired conventionally while the ZIBB group was repaired by injecting repair resin into the tunnel through one of the holes until excess material oozed from the other hole. Repaired specimens were thermally cycled at 5 and 55°C for 10,000 cycles with 1 min dwell time. A 3-point bending test was conducted using a universal testing machine for flexural strength and elastic modulus measurement. Kruskal-Wallis/Mann-Whitney tests and ANOVA/post hoc Tukey tests were applied for data analysis (α = 0.05).

RESULTS

The flexural strength of repaired specimens was substantially lower than that of intact specimens, and significant differences were present between repaired groups (p ˂ 0.05). ZB and ZIBB had higher flexural strength (p ˂ 0.001) and elastic modulus (p ˂ 0.05) than 2.5B. Among the ZB and ZIBB groups, ZB showed the highest flexural strength, and ZIBB had the highest elastic modulus.

CONCLUSION

The closed repair technique improved the flexural strength and elastic modulus of repaired acrylic denture base.

Translucency of nanoparticle-reinforced PMMA denture base material: An in-vitro comparative study

The aim of this study was to assess the translucency of denture base acrylic resin reinforced with zirconium dioxide (ZrO₂NPs), silicon dioxide (SiO₂NPs), and diamond (DNPs) nanoparticles. A total of 130 heat-polymerized acrylic discs (15×2.5 mm) were fabricated conventionally and divided into control and experimental groups according to nanoparticle type and concentration (0.5, 1, 1.5, and 2.5 wt%). Unmodified acrylic resin specimens served as control. All specimens were thermocycled (5,000 cycles). Translucency was measured using a spectrophotometer. ANOVA and post-hoc Turkeys' test were used for data analysis at α=0.05. The translucency of modified PMMA was significantly lower than control (p<0.05) except 0.5% ZrO₂NPs and SiO₂NPs (p>0.05) which exhibited the highest translucency values among modified groups. As the NPs concentration increased, the translucency decreased and the lowest value was seen with 2.5% DNPs (1.18±0.10). The addition of ZrO₂NPs, SiO₂NPs, and DNPs into denture base resin decreased the translucency.

Effects of Denture Cleansers on the Flexural Strength of PMMA Denture Base Resin Modified with ZrO2 Nanoparticles

PURPOSE

The additions of zirconium oxide nanoparticles (nano-ZrO₂ ) to denture base materials have produced nanocomposites with satisfactory properties, although there is a lack of research investigating the effects of denture cleansers on these materials. This study aimed to evaluate the effect of denture cleansers on the flexural strength of denture base materials modified with nano-ZrO₂ .

MATERIALS AND METHODS

A total of 270 specimens were fabricated from pure and nano-ZrO₂ reinforced acrylic resins at 2.5% and 5%, resulting in 3 main groups. The groups were further divided into subgroups (n = 10) according to immersion solution (distilled water, Corega, sodium hypochlorite, and Renew) and immersion duration. Flexural strength was measured at baseline (T₀ ) in distilled water and after 180 and 365 days of immersion (T₁ and T₂ ) in denture cleansers. Data were collected and analyzed using repeated measure ANOVA and Bonferroni post hoc tests (α = 0.05).

RESULTS

The flexural strength of the nano-ZrO₂ modified denture base material decreased significantly after immersion in different denture cleansers at different immersion durations in comparison to baseline (T₀ ) (p < 0.001). Sodium hypochlorite showed the highest reduction in flexural strength followed by Corega, while Renew cleansing solution resulted in the least change.

CONCLUSION

Denture cleansers can significantly affect the flexural strength of nano-ZrO₂ modified denture base materials and thus should be used cautiously.

Influence of Addition of Different Nanoparticles on the Surface Properties of Poly(methylmethacrylate) Denture Base Material

PURPOSE

To evaluate and compare the surface properties (roughness and hardness) of poly(methylmethacrylate) denture base material modified with zirconium dioxide (ZNPs), silicon dioxide (SNPs), and diamond (DNPs) nanoparticles.

MATERIALS AND METHODS

Two hundred sixty heat-polymerized acrylic resin disks (15 × 2 mm) were prepared. ZNPs, SNPs, and DNPs were added in concentrations of 0%, 0.5%, 1.0%, 2.5%, and 5.0% by weight of acrylic powder. This yielded a total of 13 groups for each test according to filler type and concentration (n = 10/group). The control group was made of pure acrylic. A mechanical polisher was used to standardize specimens' surfaces before testing. A profilometer and Vickers hardness indenter were used to test the surface roughness and hardness, respectively. ANOVA and Tukey post hoc tests were used for data analysis (α = 0.05).

RESULTS

In comparison to control, results showed a nonsignificant increase in surface roughness (R_a ) of acrylic material after the addition of 0.5% nanoparticles (ZNPs p = 0.168, SNPs p = 0.166, and DNPs p = 0.177), while a significant increase was seen with all other concentrations (p ˂ 0.05). R_a values of ZNP and DNP groups were significantly higher than those of the SNPs group (p < 0.001). The addition of any of the fillers to acrylic denture base materials significantly increased the hardness (p ˂ 0.05), with ZNPs and DNPs having values lower than those of the SNPs group (p < 0.001).

CONCLUSIONS

Although nanofiller addition increased the hardness of denture base material, R_a was adversely affected when the concentration exceeded 0.5%. Therefore, 0.5% is suggested to be the most appropriate ratio to improve hardness with acceptable R_a .

Influence of artificial aging and ZrO2 nanoparticle-reinforced repair resin on the denture repair strength

Background

The purpose of this study was to evaluate the effect of aging process on the tensile strength (TS) of repaired acrylic denture base using ZrO2 nanoparticles (nano-ZrO2)-reinforced autopolymerized resin.

Material and Methods

A total of 240 heat-polymerized acrylic resin specimens (n=10) were prepared and sectioned creating 2 mm-repair-gap. Autopolymerized acrylic resin, pure and modified with 2.5, 5, and 7.5wt% nano-ZrO2 were used for specimens repair. TS of repaired specimens were measured using the universal testing machine after water immersion at 37oC for 2, 7 and 30 days. At each time interval, half the immersed specimens underwent thermo-cycling aging process (5000 cycles at 5/55°C) before TS testing. One-way ANOVA and Tukey-Kramer multiple-comparison tests were used for data analysis at α=0.05.

Results

Aging process for all groups showed significant differences in TS between unreinforced and nano-ZrO2 reinforced groups (p<0.05). Within immersed nano-ZrO2-reinforced specimens, 5% group immersed for 30-days showed the highest significant TS value (p<0.05). With regards to thermocycling, 5% group showed the highest TS values after 2-days and 30-days groups while after 7-days, significant differences were found between 2.5% group and 5% and 7.5% groups (p<0.05). SEM images analysis displayed the ductile fracture type for nano-ZrO2 reinforced groups.

Conclusions

In summary, 5.0%-nano-ZrO2 addition to repair resin showed an improvement in tensile strength of repaired acrylic resin with different aging processes. Key words:Acrylic resins, denture repair, tensile strength, thermocycling, water storage, zirconium oxide nanoparticle.

Impact of different surface treatments and repair material reinforcement on the flexural strength of repaired PMMA denture base material

This study assessed the impact of surface treatments and repair resin reinforcement with zirconium oxide nano-particles (nano-ZrO₂) on flexural strength (FS) of repaired denture base. A total of 320 heat-polymerized acrylic resin specimens were prepared and sectioned creating 2-mm gap. According to repair surface treatment, specimens were distributed into four groups: I) methyl methacrylate (M); II) alumina-blasted (AB); III) AB+silane coupling agent (SC); and IV) AB+methacrylate based composite bonding agent (MA). Groups were subdivided into 4 (n=20) according to nano-ZrO₂ concentration (0, 2.5, 5, 7.5 wt%). Half the specimens were thermo-cycled before testing. FS was determined by three-point bending test. Statistical analysis was done using ANOVA and Tukey-Kramer multiple comparison tests, with α=0.05. Alumina-blasting+(SC) or (MA) significantly increased FS of repaired specimens compared to control (p<0.05). All surface-treated specimens combined with nano-ZrO₂ reinforced repair resin significantly increased FS.

Prevalence of partial edentulism and RPD design in patients treated at College of Dentistry, Imam Abdulrahman Bin Faisal University, Saudi Arabia

This study aimed to investigate the prevalence of partial edentulism, RPD type, design, and components and their frequency of use by patients at the prosthodontic clinics of the College of Dentistry, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia. The prepared surveys, laboratory authorization forms, and images of the RPD metal frameworks on casts were used for data collection. Two calibrated investigators studied the digital photographs to identify the Kennedy classification, type of RPD, major connector, clasp assembly, and other details. Data was collected and analyzed statistically. The results showed that the most common class of partial edentulism was Kennedy class I, whereas class IV was the least (p < 0.001). Sixty two percent of fabricated RPDs had metal frameworks, whereas 37.2% were frameless. RPI was the most frequently used clasp assembly (38.9%), a significant finding in Kennedy class I(p < 0.01). The maxillary anteroposterior palatal strap and mandibular lingual plate were the most commonly used major connectors, at 41.2% and 60.8%, respectively. Conclusions: Simple RPD design that accomplishes the treatment objectives as well as proper communication with a well-trained dental technician would promote the success of RPDs.

Effect of SiO2 Nanoparticles Addition on the Flexural Strength of Repaired Acrylic Denture Base

Objective  The objective of this study was to evaluate the effect of nano-SiO ₂ addition on the flexural strength (FS) of repaired acrylic denture base.

Materials and Methods  Heat-polymerized acrylic resin specimens were fabricated in dimensions of (65 × 10 × 2.5 ± 0.1 mm ³ ) and then sectioned and prepared, creating repair gap with butt (90 degrees) and bevel (45 degrees) repair surface designs forming two main groups according to joint design. Further subdivision was done into four groups ( n = 10) according to nano-SiO ₂ concentration: one unmodified group and three modified groups (0.25, 0.5, and 0.75 wt %) in the autopolymerized repair resin. Each pair of a specimen was assembled in a mold and repaired according to manufacturer’s recommendations.

Statistical Analysis  Three-point bending test was done to measure FS, followed by scanning electron microscope (SEM) examination for fracture surface analysis. Data were analyzed using ANOVA and Tukey’s post hoc test (α = 0.05).

Results  The addition of nano-SiO ₂ significantly improved FS of repaired acrylic resin in comparison to the unmodified group ( p ˂ 0.05). For butt joint, significant differences between nano-SiO ₂ reinforced groups were noticed ( p ˂ 0.05), while reinforced beveled groups did not differ significantly ( p ˃ 0.05). Bevel design remarkably increased FS compared with butt design per respective filler concentration. From the SEM images, improved FS was presented with a homogeneous distribution of nano-SiO ₂ within polymethyl methacrylate.

Conclusion  Nano-SiO ₂ addition to repair resin and 45 degree-beveled repair surface increased FS of repaired acrylic resin.

Comparative Effect of Glass Fiber and Nano-Filler Addition on Denture Repair Strength

PURPOSE

To evaluate and compare the effects of glass fiber (GF), Zirconium oxide nanoparticles (nano-ZrO₂ ), and silicon dioxide nanoparticles (nano-SiO₂ ) addition on the flexural strength and impact strength of repaired denture base material.

MATERIALS AND METHODS

Heat-polymerized acrylic resin specimens were fabricated. All specimens were sectioned centrally and beveled creating 2.5 mm repair gap except for 10 controls. Specimen grouping (n = 10/group) was done according to filler concentration of 0%, 0.25%, 0.5%, and 0.75% of auto-polymerized acrylic powder. Modified resin was mixed, packed in the repair gap, polymerized, finished and polished. Three-point bending test and Charpy type impact testing were done. Data were analyzed using one-way-ANOVA and Post-Hoc Tukey test (α = 0.05).

RESULTS

All additives significantly increased flexural strength and impact strength (p < 0.05). Within the modified subgroups, no significant differences were found for GF. Significant increase for nano-ZrO₂ and significant decrease for nano-SiO₂ as the concentration of additive increased were noted for both flexural strength and impact strength. Highest flexural strength was found with 0.75%-nano-ZrO₂ (69.59 ± 2.52MPa) and the lowest was found with 0.75%-nano-SiO₂ (53.82 ± 3.10MPa). The 0.25%-nano-SiO₂ showed the highest impact strength value (2.54 ± 0.21 kJ/m² ) while the lowest impact strength value was seen with 0.75%-nano-SiO₂ (1.54 ± 0.17 kJ/m² ).

CONCLUSION

Nano-filler effect was concentration dependent and its addition to repair resin increased the flexural and impact strengths. The incorporation of 0.75%-ZrO₂ or 0.25%-SiO₂ into repair resin proved to be a promising technique to enhance repair strength and avoid repeated fractures.

The effect of nanodiamonds on candida albicans adhesion and surface characteristics of PMMA denture base material - an in vitro study

Candida albicans is the main causative pathogen of denture stomatitis, which affects many complete denture patients. Objective: To evaluate the effect of different concentrations of nanodiamonds (NDs) added to polymethyl methacrylate (PMMA) denture base material on Candida albicans adhesion as well as on surface roughness and contact angle. Methodology: Acrylic resin specimens sized 10×10×3 mm³ were prepared and divided into four groups (n=30) according to ND concentration (0%, 0.5%, 1%, 1.5% by wt). Surface roughness was measured with a profilometer, and the contact angle with a goniometer. The effect of NDs on Candida albicans adhesion was evaluated using two methods: 1) slide count and 2) direct culture test. Analysis of variance (ANOVA) and Tukey's post hoc test were used in the statistical analyses. Results: Addition of NDs decreased the Candida albicans count significantly more than in the control group (p<0.05), with a lowest of 1% NDs. Addition of NDs also significantly decreased the surface roughness (p<0.05), but the contact angle remained the same. Incorporation of NDs into the PMMA denture base material effectively reduced Candida albicans adhesion and decreased surface roughness. Conclusion: PMMA/NDs composites could be valuable in the prevention of denture stomatitis, which is considered one of the most common clinical problems among removable denture wearers.

Blood Flow Alterations in the Anterior Maxillary Mucosa as Induced by Implant-Retained Overdenture

PURPOSE

Blood flow disturbance from functional pressure may lead to ischemia and accumulation of metabolites leading to residual ridge resorption (RRR) underneath complete dentures. The purposes of this study were to determine the effect of mandibular complete denture (CD) and implant-retained overdenture (IRO) on blood flow disturbance in the opposing denture bearing-mucosa of maxillary CD and to compare the blood flow disturbance to RRR of the anterior maxilla.

MATERIALS AND METHODS

The test group included 9 participants rehabilitated by maxillary CD opposing mandibular IRO, while the control group consisted of 4 participants with CDs. Blood flow was measured by laser Doppler flowmetry (LDF) after denture removal for 0, 30, 60, and 90 minutes. RRR was quantified as reduction in bone volume a year post-treatment. The measurement of blood flow was then compared to the quantification of RRR.

RESULTS

The mean blood flow measure for the IRO group was significantly lower than CD after immediate denture removal and 30 minutes later. After 60 minutes, the mean difference was not significant between groups, and at 90 minutes, the mean blood flow of both groups equalized to reach a steady state of 377 BPU. The mandibular IRO had reduced the initial blood flow measure in the opposing anterior maxilla mucosa to almost a quarter (103 BPU) of the steady state value (377 BPU) compared to the CD, which reduced it to only about one half (183 BPU), suggesting greater blood flow disturbance in the IRO group. This result is in tandem with the greater reduction of bone volume observed in the IRO group, which was 7.3 ± 1.3% after a year, almost three times higher than CD group at 2.6 ± 1.7%.

CONCLUSION

IRO may cause significantly higher blood flow disturbance than CD and may have contributed to greater RRR in the anterior maxilla.

Effect of Nanodiamond Addition on Flexural Strength, Impact Strength, and Surface Roughness of PMMA Denture Base

PURPOSE

To assess the effect of addition of different concentrations of nanodiamonds (NDs) on flexural strength, impact strength, and surface roughness of heat-polymerized acrylic resin.

MATERIALS AND METHODS

120 specimens were fabricated from heat-polymerized acrylic resin. They were divided into a control group of pure polymethylmethacrylate (PMMA; Major.Base.20) and three tested groups (PMMA-ND) with 0.5%wt, 1%wt, and 1.5%wt of added ND to PMMA. Flexural strength was determined using the three-point bending test. Impact strength was recorded by using a Charpy type impact test. Surface roughness test was performed using a Contour GT machine. One-way ANOVA and Tukey's post-hoc analysis (p ≤ 0.05) were used for statistical analysis.

RESULTS

Acrylic resin reinforced with 0.5% ND displayed significantly higher flexural strength than the unreinforced heat-polymerized specimens, acrylic resin reinforced with 1% ND and the 1.5% ND (p < 0.0001). The impact strength of unreinforced heat-polymerized specimens was significantly higher than all nano-composite materials (p < 0.0001) with no significant difference between 1% ND and the 1.5% ND (p > 0.05). The addition of 0.5% ND and 1% ND significantly decreased the surface roughness in comparison to both control and the 1.5% ND groups (p < 0.0001) while no significant differences between 0.5% ND and 1% ND (p > 0.05) were reported. Nano-composite material (0.5% ND) showed significantly lower surface roughness when compared to other specimens.

CONCLUSIONS

The addition of NDs to acrylic denture base improved the flexural strength and surface roughness at low concentrations (0.5%), while the impact strength was decreased with ND addition.

The influence of simulated aging on the color stability of composite resin cements

STATEMENT OF PROBLEM

Data for the color stability of dual-polymerized and light-polymerized resin cements used in esthetic dentistry are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the color stability of 4 types of composite resin cements after water aging.

MATERIAL AND METHODS

Specimens (n=30) of each resin cement (Variolink Esthetic LC, RelyX Ultimate DC, Nexus 3 DC, Nexus 3 LC) were prepared. The shade selected was Light+ for Variolink Esthetic, B 0.5 for RelyX Ultimate, and White for both Nexus 3 DC and LC. All 120 specimens were aged by water for 30 days at 37°C under dark conditions, using a thermocycling machine. The specimens' color characteristics (L*, luminosity; a*, red-green; b*, yellow-blue) and color differences (ΔE) were measured with a spectrophotometer before day 0, after day 1, and after 30 days of immersion. Statistical analysis used ANOVA and Tukey post hoc tests (α=.05).

RESULTS

Considering ΔE<3.3 as clinically acceptable, results showed significant color variations for all cements (RelyX Ultimate=3.69; Nexus 3 LC=3.76; Nexus 3 DC=5.34), except for Variolink Esthetic (0.88). However, this variation was significantly less when day 1 was considered the baseline measurement, showing clinically acceptable ΔE values for all types of cement.

CONCLUSIONS

Water aging had a significant effect on color stability; most color variations occurred in the first 24 hours of polymerization, with relatively nonsignificant variations afterwards.

A Novel Extended Range Attachment System to Retain Implant Overdentures: A Clinical Report

Various attachment systems have been used to facilitate the retention, stability, and support of overdentures. The low profile design, pivoting technology, and durability of the Locator attachment made it one of the commonly used tissue-supported implant-retained overdentures. It has been successfully used to retain overdentures as well as partial dentures. This article describes the uses of the new Locator R-Tx abutment and illustrates both the direct and indirect techniques used to process the denture attachment housing into the prosthesis to retain overdentures and partial dentures.

Mandibular Implant-supported Overdentures: Prosthetic Overview

Implant-supported overdentures are becoming the treatment of choice for the completely edentulous mandible. They significantly improve the quality of life in edentulous patients. For this review article, the literature was searched to identify pertinent studies. No meta-analysis was conducted because of high heterogeneity within the literature. Accordingly, in this review article, the author provides an update on implant-supported mandible overdentures with regard to the number of implants, type of loading, stress-strain distribution, mode of implant-to-denture attachment, occlusal considerations and complications.

Internal Fit and Marginal Gap Evaluation of Zirconia Copings Using Microcomputed Tomography: An In Vitro Analysis

The purpose of this in vitro study was to measure the marginal and internal fit of single-unit all-ceramic zirconia copings (ZCs) fabricated through three different computer-aided design/computer-assisted manufacture (CAD/CAM) systems using microcomputed tomography (microCT). A total of 10 ZCs were produced for each experimental group. Scanning of the stainless steel (SS) model with its respective copings was conducted with a SkyScan machine. DataViewer software was used to acquire cross-sectional images. Locations of cross-sections for all specimens were standardized to reduce errors. Seven different cross-section locations were selected: four transverse and three sagittal. Adobe Photoshop CS3 was used for the measurements. One-way analysis of variance and Tukey post hoc test were used for the statistical analysis for each group. In addition, t test (α = .05) was used to compare values at each measurement location for the different groups. The results of this study show significant differences in the precision of fit of the experimental groups at the axio-occlusal transition (AOT) location, with a significant gap present in the DeguDent CAD/CAM System compared to the other two systems. Tukey test results indicate a significant difference in the marginal gap between the DeguDent CAD/CAM System and KaVo Everest Dental CAD/CAM System (P = .004). In addition, there is a significant difference in gap size values in the sagittal sections distal to the midline between the DeguDent CAD/CAM System and the Lava Ultimate CAD/CAM System (P = .002). The different CAD/CAM systems showed a clinically acceptable internal fit and marginal adaptation. Different levels of fit were found between the experimental groups. Marginal adaptation was the best in all experimental groups. The gap at the AOT area varied among the three groups, with the DeguDent CAD/CAM System showing the greatest value.

PMMA denture base material enhancement: a review of fiber, filler, and nanofiller addition

This paper reviews acrylic denture base resin enhancement during the past few decades. Specific attention is given to the effect of fiber, filler, and nanofiller addition on poly(methyl methacrylate) (PMMA) properties. The review is based on scientific reviews, papers, and abstracts, as well as studies concerning the effect of additives, fibers, fillers, and reinforcement materials on PMMA, published between 1974 and 2016. Many studies have reported improvement of PMMA denture base material with the addition of fillers, fibers, nanofiller, and hybrid reinforcement. However, most of the studies were limited to in vitro investigations without bioactivity and clinical implications. Considering the findings of the review, there is no ideal denture base material, but the properties of PMMA could be improved with some modifications, especially with silanized nanoparticle addition and a hybrid reinforcement system.

Agreement in Scoring Preclinical Dental Procedures: Impact on Grades and Instructor-Related Determinants

The aims of this study were to assess agreement among instructors in scoring preclinical dental procedures, the effect of this agreement on grades, and factors associated with agreement and grades differences. Twenty-six instructors from five clinical specialties participated in a scoring exercise at the College of Dentistry, University of Dammam, Saudi Arabia, in January 2015. Instructors blindly and independently scored 19-20 anonymous students' procedures, filling forms with rating scales as used in preclinical lab sessions. Their scores were compared to those of gold standard instructors in the same specialty. Percent agreement and having one letter grade difference from gold standard instructors were assessed, and associated factors were investigated after controlling for the effect of specialty/student. Agreement between instructors and their specialty gold standards occurred in 54.3% of decisions, with only 12.8% similar scores and 52.8% of scores representing underestimation in relation to gold standards. Instructor-related variables accounted for 40-50% of the variation in percent score as well as percent agreement and percent difference between instructors and gold standards. Educational background and teaching experience were significantly associated with less agreement among instructors and odds of one letter grade difference. Modest agreement existed among instructors in scoring various preclinical procedures, and there was a considerable percentage of one letter grade difference from gold standard instructors. Some factors associated with these outcomes are non-modifiable, but corrective measures are needed to increase agreement in scoring among instructors.