Effect of Denture Disinfectants on the Mechanical Performance of 3D-Printed Denture Base Materials.

Denture care and maintenance are necessary for both denture longevity and underlying tissue health. However, the effects of disinfectants on the strength of 3D-printed denture base resins are unclear. Herein, distilled water (DW), effervescent tablet, and sodium hypochlorite (NaOCl) immersion solutions were used to investigate the flexural properties and hardness of two 3D-printed resins (NextDent and FormLabs) compared with a heat-polymerized resin. The flexural strength and elastic modulus were investigated using the three-point bending test and Vickers hardness test before (baseline) immersion and 180 days after immersion. The data were analyzed using ANOVA and Tukey's post hoc test (α = 0.05), and further verified by using electron microscopy and infrared spectroscopy. The flexural strength of all the materials decreased after solution immersion (p < 0.001). The effervescent tablet and NaOCl immersion reduced the flexural strength (p < 0.001), with the lowest values recorded with the NaOCl immersion. The elastic modulus did not significantly differ between the baseline and after the DW immersion (p > 0.05), but significantly decreased after the effervescent tablet and NaOCl immersion (p < 0.001). The hardness significantly decreased after immersion in all the solutions (p < 0.001). The immersion of the heat-polymerized and 3D-printed resins in the DW and disinfectant solutions decreased the flexural properties and hardness.

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.

Effect of treated zirconium dioxide nanoparticles on the flexural properties of autopolymerized resin for interim fixed restorations: An in vitro study.

STATEMENT OF PROBLEM: Fractures of interim fixed restorations are a common complication. The autopolymerized polymethyl methacrylate resin materials used for interim fixed restorations have limited mechanical properties, but whether adding treated zirconium dioxide nanoparticles improves mechanical properties is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effect of treated zirconium dioxide nanoparticles on the flexural strength and elastic modulus of autopolymerized polymethyl methacrylate resin. MATERIAL AND METHODS: A split-metal mold (60×10×3.3 mm) was used to fabricate 40 autopolymerized acrylic resin specimens. The specimens were divided into 4 groups (n=10) according to zirconium dioxide nanoparticle concentration: control (unmodified resin) and zirconium dioxide nanoparticle contents of 1, 2.5, and 5 wt%. The specimens were mixed and polymerized according to the manufacturer's instructions and stored in distilled water for 48 ±2 hours at 37 °C. The flexural strength and elastic modulus were evaluated based on the 3-point bend test where data were analyzed by using 1-way analysis of variance and Tukey post hoc tests (α=.05). RESULTS: The flexural strength of the 1-wt% zirconium dioxide nanoparticle specimens was significantly higher than that of the control group (P<.001) but did not significantly increase further with the higher nanoparticle content (P>.05). Elastic modulus significantly decreased with 2.5-wt% zirconium dioxide nanoparticles (P=.019), while no significant changes were found with other test groups (P>.05). CONCLUSIONS: The addition of treated zirconium dioxide nanoparticles at low concentrations increased the flexural strength of autopolymerized polymethyl methacrylate resins used in fixed interim restorations.

Students' Awareness of the Role of Phonetics in Construction of Removable Dental Prostheses: A Questionnaire-Based Cross-Sectional Study.

Phonetics plays a major role in the fabrication of prostheses. This study aimed to assess the knowledge of students regarding the role of phonetics in denture fabrication and to improve the educational process and the clinical application. The study was conducted at the College of Dentistry, Imam Abdulrahman Bin Faisal University, and involved a survey of 344 dental students and interns. The questionnaire contained 20 questions and was divided into three sections: general knowledge, clinical correlations, and clinical evaluations. The data were collected and analyzed statistically using independent t-tests, one-way ANOVA, and Tukey's post hoc tests. The response rate was 100%. Male and female students only differed significantly in terms of their scores for answers to general knowledge questions, with females achieving better results (p = 0.023). General knowledge varied significantly between fourth-year students and all other levels (p < 0.001), and fifth-year students and interns (p = 0.027). The clinical correlations varied significantly between fourth-year students and interns (p = 0.01), whereas the clinical evaluations varied between all the academic years and interns (fourth-year, p < 0.001; fifth-year, p = 0.003; and sixth-year, p = 0.017). The interns obtained the highest scores in all sections. There was a lack of awareness among dental students of some aspects of the role of phonetics in denture fabrication. The study highlights the deficiencies that need to be addressed and the need for adjustments to the curriculum related to removable prosthodontics in order to improve the knowledge of students regarding the role of speech in denture fabrication.

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.

Impact of thermocycling on surface roughness, microhardness and optical properties of three different lithium disilicate ceramics.

Objectives: This investigation was carried out to examine the influence of thermocycling aging on the surface roughness (Ra, µm), color parameters (L*, a*, b*), lightness change (ΔL*), chroma change (ΔC*ab), color change (ΔE), and microhardness (VH) of three lithium disilicate ceramics. Materials and methods: Forty-five specimens were prepared from three lithium disilicate materials (n = 15)-e.max CAD (EC), e.max Press (EP), and GC Initial LiSi Press (LP) ceramics-with dimensions of 6.0 × 1.2 × 16.0 ± 0.2 mm following the manufacturers' instructions. All specimens were exposed to 5000 thermal cycles with bath temperatures ranging between 5 °C and 55 °C. Data of surface roughness, color parameters, and microhardness were obtained using an optical profiler, a spectrophotometer, and a Vickers hardness tester, respectively. One-way ANOVA, a post-hoc Tukey's test, and a paired sample t-test were implemented for statistical analysis (p ≤ 0.05). Results: For surface roughness, insignificant differences were reported between the materials either before or after thermocycling (p > 0.05) while each material displayed a significant increase after being subjected to thermocycling (p < 0.05). For color parameters, LP showed significantly lower L* and b* after thermocycling while EC presented a significant reduction in a* in comparison with other materials (p < 0.05). EP showed a significant decrease in ΔL*, ΔC*ab and ΔE compared with other materials (p < 0.05). Regarding microhardness, LP showed significantly increase value in comparison with other materials (p < 0.05). Conclusions: Thermocycling had a major impact on the surface roughness, microhardness and optical characteristics of the tested materials. E.max Press displayed less changes in (ΔL*), (ΔC*ab) and (ΔE), while GC LiSi Press had better behavior in terms of microhardness.

Influence of demographic characteristics, tooth loss, and tooth wear on condylar movements: Cross-sectional study.

Objectives: The study's aim was to assess and compare the values of the sagittal condylar angle (SCA), the Bennett angle (BA), and the immediate side shift (ISS) between fully dentate and partially dentate patients, male and female patients, and Saudi and non-Saudi patients. The study also aimed to statistically analyze the correlation of the different condylar movements with tooth loss and tooth wear. Materials and Methods: Using the electronic pantograph (Cadiax Compact II), the SCA, BA, and ISS were recorded at a 10-mm condylotrack distance in dentate and partially dentate patients, from both genders, older than 20 years, medically stable, and with normal temporomandibular joint movements and normal activity of masticatory muscles. The recorded average values were compared between the groups using an unpaired t-test. Results: The average condylar movements between dentate (n = 57) and partially dentate (n = 39) groups revealed no significant differences concerning right SCA, left SCA, right BA, right ISS, and left ISS. However, the left BA showed significant differences (P = 0.011) in the dentate compared with the partially dentate group. Gender (male: n = 24, female: n = 72) showed no statistical significance between groups when measuring SCA, BA, or ISS. When comparing Saudi (n = 78) with non-Saudi patients (n = 18), it was found that the mean right SCA was significantly higher in Saudi than in non-Saudi patients (P = 0.024). Condylar inclination values in relation to tooth wear showed no statistical significance (P > 0.05), except left ISS, which was significantly higher among those who had tooth wear (P = 0.040). Conclusion: Tooth loss had a major impact on the left BA, while patients with tooth wear had a significantly increased ISS on the left side.

Comparative Effect of Incorporation of ZrO2, TiO2, and SiO2 Nanoparticles on the Strength and Surface Properties of PMMA Denture Base Material: An In Vitro Study.

Objective: This study aimed to investigate the effects of nanoparticles (zirconium dioxide (ZrO2), titanium dioxide (TiO2), and silicon dioxide (SiO2)) on the flexural strength, impact strength, hardness, and wear resistance of the acrylic resin denture base material. Materials and Methods: Acrylic resin specimens were fabricated in dimensions according to American Dental Association (ADA) specifications per test. Specimens were divided according to nanofiller into four groups; unmodified as control, ZrO2 (Z), TiO2, (T), and SiO2 (S) groups. Each one was subdivided into two subgroups according to nanoparticle concentrations; 3% and 7% (Z3, Z7, T3, T7, S3, and S7). A 3-point bending test, Charpy impact test, and Vickers hardness test were used for flexural strength, impact strength, and hardness measurements, respectively. Wear resistance was measured by the differences in surface roughness of tested specimens before and after the wear test. A scanning electron microscope was used to assess nanoparticle specifications and distributions and for fracture surfaces analysis. ANOVA, Bonferroni's post hoc test, and the Kruskal-Wallis test were applied for data analysis (α = 0.05). Results: Regarding the flexural and impact strength, there was a statistically remarkable increase for all tested groups compared with the control group, except for the T7 and S7 groups (P value <0.001, effect size = 0.893) and (P value <0.001, effect size = 0.759), respectively. There was a statistically significant improvement in the hardness of all tested groups compared with the control group (P value <0.001, effect size = 0.67) except T3 and S3. Regarding wear, a statistically significant enhancement was noticed in the wear resistance of all tested groups (P value <0.001, effect size = 0.685), except for the T7 and S7 groups. Conclusion: The flexural strength, impact strength, and wear resistance improved with both concentrations of ZrO2 and low TiO2 and SiO2 concentrations. The hardness increased with both concentrations of ZrO2 and high TiO2 and SiO2 concentrations.

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.

Comparative Study of the Effectiveness of Laboratory-Formulated Polishing Pastes for Two CAD/CAM Ceramic Restorative Materials.

PURPOSE: To evaluate the effect of different polishing pastes with different particle sizes on the surface finish of two different CAD/CAM ceramics. MATERIALS AND METHODS: A total of 128 specimens were prepared of two CAD/CAM ceramics: lithium disilicate (12.4 × 14.5 × 2 mm) and monolithic zirconia (17.5 × 12.5 × 2.5 mm). They were divided randomly into 8 groups according to surface treatment (n = 8). Group 1 (control) was left as received after crystallization or sintering with no further surface treatment; Group 2 (glazed); Group 3 (positive control), where specimens were polished using standardized surface treatment (medium grit silicon carbide discs, rubber cup and pumice slurry, then rubber cup and toothpaste). For groups 4 to 8, in addition to silicon carbide and pumice slurry polishing, specimens were further polished using a diamond paste (DP), and polishing pastes of microzirconia (MZ), nanosilica (NS), nanodiamond (ND), and nanozirconia (NZ), respectively. Surface roughness (Ra ) was measured using noncontact profilometer. The mean values were compared using ANOVA and Post Hoc Tukey's test (α = 0.05). Specimens' surfaces were studied using a scanning electron microscope (SEM). RESULTS: Positive control group and MZ exhibited significant Ra of lithium disilicate compared to control (p ˂ 0.001), glazed (p = 0.001), DPs (p = 0.002), NS (p ˂ 0.001), ND (p ˂ 0.001), and NZ (p = 0.002). In the case of zirconia, positive control showed a significantly higher Ra compared to all other groups (p ˂ 0.001). No statistical difference was found between all other polishing techniques (positive control, glazed, DPs, NS, ND, MZ, and NZ) (p > 0.05). CONCLUSION: Polishing with ND, NZ, and NS lab-formulated pastes produced surfaces with comparable smoothness to control and glazed specimens for lithium disilicate and zirconia ceramic materials.

The Bond Strength of a Universal Adhesive System with Silane to Lithium Disilicates in Comparison with an Isolated Silane Coupling Agent.

PURPOSE: The aim of this in vitro study was to evaluate the effects of different durations of silane coupling agent application compared to a universal adhesive system regarding the shear bond strength of two ceramic materials. MATERIALS AND METHODS: A total of 120 human molars were ground to the dentinal coronal third and then fixed into an acrylic resin holder. Lithium disilicate specimens were divided into two main groups according to the ceramic type: computer-aided design/computer-aided manufacturing IPS e.max CAD and heat-pressed Initial LiSi Press GC (dimensions of 4 × 3× 3 mm). Each main group was subdivided into 6 subgroups (n = 10) according to the duration of the silane and universal adhesive system application (20, 60, or 120 seconds) on the ceramic surface before cementation; then, the cementation procedures were performed. All specimens were subjected to 5000 thermal cycles at 5 and 55°C before testing. The shear bond strength was measured using a universal testing machine. ANOVA and Scheffe post hoc test multiple comparisons tests were conducted (α = 0.05). RESULTS: The shear bond strength increased as the duration of the silane and universal adhesive system application increased. The highest bond value for each material was found for the silane application at 120 seconds, with a significant difference between 120 and 60, and 20 seconds for both e. max CAD and Initial LiSi materials (p = 0.029 and p ˂ 0.001, respectively). No significant difference was found between 60 and 20 seconds when silane and universal adhesive system were applied for both e. max CAD and Initial LiSi materials (p = 0.169 and p = 0.120, respectively). All groups treated with the silane primer showed significantly higher values than the universal adhesive system for each application time (p ˂ 0.001). CONCLUSION: Increasing the duration of the silane coupling agent and universal adhesive system application to 120 seconds on the ceramic surface before cementation improved the shear bond strength of the ceramic-cement interface. Ceramic pretreatment with silane could be an essential step for bonding ceramic to dentin regardless of silane presence in the universal adhesive system.

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.

Double-layered acrylic resin denture base with nanoparticle additions: An in vitro study.

STATEMENT OF PROBLEM: Whether the addition of different antifungal nanoparticles to denture base materials may affect physical or esthetic properties of the resulting nanocomposite is unclear. PURPOSE: The purpose of this in vitro study was to determine how a new method of adding antifungal nanofiller affects the properties of the processed nanocomposite denture base material. MATERIAL AND METHODS: Heat-polymerized acrylic resin specimens were prepared according to each test specification. Zirconium dioxide nanoparticles (ZrO2NPs) and silver nanoparticles (AgNPs) were added in 0.5, 1.0, and 1.5% of acrylic resin powder. The specimens were divided into 2 groups according to the acrylic resin packing method: 1 layer packed conventionally in one step and 2 layers packed in 2 steps, first with unmodified acrylic resin and then by a thin layer of modified acrylic resin before the final closure. The control group was made of unaltered acrylic resin in 1 step. Flexural strength (FS), translucency, and surface roughness (Ra) were measured. A microbial assay was performed by using the direct culture and slide count methods. Three-way ANOVA and Tukey post hoc tests were used to identify statistical differences among groups (α=.05). RESULTS: The addition of ZrO2NPs and AgNPs in the 1- or 2-layer specimens reduced Candida albicans adhesion (P<.001). In the 1- and 2-layer specimens, FS significantly increased with ZrO2NPs. AgNPs decreased FS only in the 1-layer specimen (P<.001). Surface roughness was not changed for the 1- and 2-layer specimens with ZrO2NPs or the 1-layer specimen with 0.5% AgNPs (P>.05), while other AgNP groups exhibited increased surface roughness (P<.001). AgNPs significantly lowered translucency in the 1- and 2-layer specimens (P<.001), while ZrO2NPs decreased translucency only in the 1-layer specimen (P<.001). CONCLUSIONS: The addition of ZrO2NPs in the double-layer technique decreased Candida adhesion and improved FS without affecting surface roughness, while AgNPs decreased Candida adhesion and FS and increased surface roughness. Both nanofillers decreased the translucency except 0.5% ZrO2NPs, which did not change translucency when applied in 2 layers.

Titanium Base Abutments in Implant Prosthodontics: A Literature Review.

Implant abutments are essential components in restoring dental implants. Titanium base abutments were introduced to overcome issues related to existing abutments, such as the unesthetic appearance of titanium abutments and the low fracture strength of ceramic abutments. This study aimed to comprehensively review studies addressing the mechanical and clinical behaviors of titanium base abutments. A search was performed on PubMed/MEDLINE, Web of Science, Google Scholar, and Scopus databases to find articles that were published in English until December 2020 and that addressed the review purpose. A total of 33 articles fulfilled the inclusion criteria and were included for data extraction and review. In vitro studies showed that titanium base abutments had high fracture strength, adequate retention values, particularly with resin cement, and good marginal and internal fit. Although the clinical assessment of titanium base abutments was limited, they showed comparable performance with conventional abutments in short-term evaluation, especially in the anterior and premolar areas. Titanium base abutments can be considered a feasible treatment option for restoring dental implants, but long-term clinical studies are required for a better assessment.

Polymethylmethacrylate Incorporating Nanodiamonds for Denture Repair: In Vitro Study on the Mechanical Properties.

OBJECTIVE: This study aimed to evaluate the effect of nanodiamond (ND) addition to repair resin with repair gap modifications on the flexural and impact strength of repaired polymethylmethacrylate denture base. MATERIALS AND METHODS: Heat-polymerized acrylic resin specimens (N = 100/test) were prepared and sectioned to half creating two repair gaps: 2.5- and 0 mm with 45 degrees beveling. They were further divided into subgroups (n = 20) according to ND concentration (control, 0.25%ND, and 0.50%ND), thermocycling (500 cycles) was done to half the specimens in each subgroup. Flexural strength was tested using 3-point bending test and impact strength was tested by Charpy's impact test. Analysis of variance and post-hoc Tukey's tests were performed for data analysis (α = 0.05). Scanning electron microscope was employed for fracture surface analysis and ND distribution. RESULTS: Before and after thermocycling, the addition of ND significantly increased the flexural strength and elastic modulus in comparison to control group (p ˂ 0.001), while 0 mm repair gap showed insignificant difference between ND-reinforced groups (p ˃ 0.05). Regarding impact strength, ND addition increased the impact strength with 0 mm gap in comparison to control and 2.5 mm with ND (p˂0.001), while later groups showed no significant in between (p ˃ 0.05). Comparing thermocycling effect per respective concentration and repair gap, thermocycling adversely affected all tested properties except elastic modulus with 0 mm-0.25 and 0 mm-0.5% and impact strength with 2.5 mm, 2.5 mm-0.25%, 2.5 mm- 0.5% (p ˃ 0.05). CONCLUSION: ND addition combined with decreased repair gap improved the flexural strength, elastic modulus, and impact strength of repaired denture resin, while thermocycling has a negative effect on denture repair strength.

Comparative Effect of Different Surface Treatments on the Shear Bond Strength of Two Types of Artificial Teeth Bonded To Two Types of Denture Base Resins.

PURPOSE: This in vitro study aims to assess the impact of various surface treatments on the shear bond strength (SBS) of two types of artificial teeth and denture base resins (DBRs). MATERIALS AND METHODS: Two types of DBRs (CAD/CAM-milled and heat-polymerized) and two types of denture teeth (acrylic and composite) were investigated. Teeth were cut into slices (5 × 5 × 2 mm) and divided according to surface treatment into four subgroups (n = 10): no treatment (control), air abrasion (Alumina-blasting; AB), bur roughening, and dichloromethane (DCM) subgroups. According to manufacturer recommendations, the treated tooth slices were bonded to the acrylic disk of DBRs. The SBS test was performed using a universal testing machine. ANOVA was used for results analysis followed by Tukey's post hoc tests (α = 0.05). RESULTS: DCM and AB increased the SBS of acrylic teeth to heat-polymerized DBR compared with other groups (p < 0.001). All surface treatments showed no significant difference in CAD/CAM DBR with acrylic teeth (p = 0.059; AB, p = 0.319; bur roughening, p = 0.895; DCM), while there was a significant decrease in SBS with composite teeth (p ˂ 0.001). Between teeth, acrylic teeth showed a statistically significant increase in SBS compared to composite teeth (p < 0.001). CONCLUSION: AB and DCM application improved the SBS for acrylic teeth with the heat-polymerized DBR when compared with the untreated group, but none of the surface treatment agents showed significant improvement with CAD/CAM DBR. All surface treatment agents reduced the SBS for composite teeth with CAD/CAM DBR while AB only increased the SBS with heat-polymerized DBR.

Effect of silicon dioxide nanoparticles on the flexural strength of heat-polymerized acrylic denture base material: A systematic review and meta-analysis.

OBJECTIVE: This study evaluated the influence of silicon dioxide (SiO2) nanoparticles on the flexural strength of heat-polymerized denture base materials. BACKGROUND: Nanoparticles have been incorporated into the denture base materials in different proportions to enhance the mechanical properties. Recently, the incorporation of SiO2 nanoparticles at low concentrations has shown promising outcomes. MATERIALS AND METHODS: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) protocol, this study was designed with the following focused question: "Does the addition of SiO2 nanoparticles improve the flexural strength of heat-polymerized acrylic resins?" The inclusion criteria included in-vitro studies that assessed the flexural strength of SiO2 nanoparticle-reinforced heat-polymerized acrylic denture base resins tested according to American Dental Association specifications. The database search involved articles published from 2005 to 2020 on PubMed/MEDLINE, Web of Science, Google Scholar, and Scopus using the following keywords: SiO2, nanosilica, silica oxide, nanoparticles, denture base resin, acrylic resin, polymethyl methacrylate, PMMA, flexural strength, and mechanical properties. RESULTS: Among 167 studies, five papers fulfilled the inclusion criteria and were added for the data analysis and meta-analysis. Proportions of incorporated SiO2 nanoparticles ranged from 0.25% to 15% and the reported flexural strength values for the reinforced acrylic resin ranged from 41.25 MPa to 124.56 MPa. The meta-analysis revealed no significant effect on the flexural strength between the unmodified and the SiO2 nanoparticle-reinforced acrylic resin. CONCLUSION: Therefore, No particular concentration of SiO2 nanoparticles could be recommended for heat-polymerized denture base reinforcement.

Flexural properties of three lithium disilicate materials: An in vitro evaluation.

OBJECTIVE: The goal of this study was to investigate the flexural strength, Young's modulus and Weibull modulus of two heat-pressed and one CAD/CAM processed lithium disilicate (LD) ceramics. MATERIAL AND METHODS: A total of 45 specimens with dimensions 16 × 4 × 1.2 ± 0.2 mm were fabricated out of three LD ceramics. For heat-pressed LD specimens, acrylate polymer blocks were cut and divided into two groups (n = 15 per group); a GC LiSi Press LD group (LP) and an IPS e.max Press group (EP). Specimens for each group were pressed corresponding to the manufacturer's recommendations. For the CAD-CAM Group (EC), IPS e.max CAD blocks were cut to obtain specimens (n = 15) to the desired dimensions. Flexural strength and Young's modulus tests were executed using a universal testing machine. A one-way ANOVA and post-hoc Tuckey's tests were applied to analyze the results (p ≤ 0.05). RESULTS: Regarding flexural strength, the EC group showed higher statistically substantial difference than the EP and LP groups (p = 0.001), while there was no pronounced difference between the EP and LP groups (p = 0.065). For Young's modulus test, all the three tested groups had no statistically substantial difference (p = 0.798). CONCLUSION: The IPS e.max CAD group had higher mechanical performance than the IPS e.max Press and GC LiSi Press groups.

Influence of Different Beverages on the Color Stability of Nanocomposite Denture Base Materials.

BACKGROUND: The effect of beverages on nanocomposite denture base materials is neglected. Therefore, this study aimed to investigate the influence of different beverages (coffee, tea, cola, and mineral water) on the color stability of nanoparticles-modified denture base materials (DBMs). MATERIALS AND METHODS: A total of 280 specimens (n = 10/group) were prepared from heat-polymerized acrylic resin modified with different concentrations (3% and 7%) of zirconium dioxide (nano-ZrO2), titanium dioxide (nano-TiO2), and silicon dioxide (nano-SiO2) nanoparticles, while 0% was taken as a control. Color change (∆E) of the specimens was evaluated after simulating 6-month immersion time in four commonly used beverages, coffee, tea, cola, and mineral water, as experimental groups. Color stability was measured using a spectrophotometer, and then values were converted to National Bureau of Standards units (NBS units). The one-way ANOVA test was applied to compare color change (ΔE) results followed by Bonferroni's post hoc test (α = 0.05). RESULTS: The results showed that the heat-polymerized acrylic resin modified with different types of nanoparticles showed lower color changes after being immersed in beverage solutions compared to the unmodified group (P < 0.001), so the color stability of heat-polymerized acrylic resin was significantly enhanced by the addition of several nanoparticles; nano-ZrO2 showed the lowest ΔE followed by nano-TiO2 and then nano-SiO2. Regardless of the filler type, 3% concentration showed lower mean ΔE than 7% concentration. Regarding the beverage solutions, the greatest color change was found in the coffee group followed by tea and cola, while water showed the least changes. CONCLUSION: Modification of heat-polymerized acrylic resin with certain amounts of nano-ZrO2, nano-TiO2, and nano-SiO2 may be useful in improving color stability.

Impact of different surface treatment methods on bond strength between fiber post and composite core material.

PURPOSE: To assess the impact of different surface treatments on the push-out bond strength between fiber post and a composite resin core material. MATERIAL AND METHODS: Seventy-two glass-fiber posts were randomly assigned into six groups according to the method of surface treatment: Control (no treatment), silane, sandblasting, hydrofluoric acid, hydrogen peroxide, and hydrogen peroxide with sandblasting. Two posts from each group were inspected under a scanning electron microscope to assess the surface modifications and 10 posts were employed for the push-out test. Each post was placed vertically in the middle of a cylindrical putty matrix and a dual-cure composite resin material was applied for core build-up. Two discs of each specimen were cut using a low-speed diamond saw (total 120 discs). The push-out test was executed using a universal testing machine at a crosshead speed of 0.5 mm/min. Statistical analysis was performed using one-way ANOVA and Tukey's test (p ≤ 0.05). The mode of failure of each disc was evaluated under SEM. RESULTS: The sandblasting and hydrofluoric acid groups presented significantly higher bond strength than control and hydrogen peroxide groups. The hydrogen peroxide groups exhibited significantly the lowest bond strength of all groups. There was no significant difference between the control and silane groups. All groups showed predominantly adhesive failure except the hydrogen peroxide with sandblasting, where the cohesive failure of the post was predominant. CONCLUSIONS: Sandblasting and hydrofluoric acid surface treatments demonstrated superior results to silane and hydrogen peroxide. The combined method of hydrogen peroxide and sandblasting could weaken the fiber post and lead to clinical fractures.