Evaluation of physical properties of polyamide and methacrylate based denture base resins polymerized by different techniques.

AIM: This study aims to comparatively evaluate the flexural strength, internal adaptation, elastic modulus, and maximum deflection of a newly introduced, strengthened injection-molded semi-flexed polyamide resin (Deflex) and a conventional heat-cured resin containing cross-linking polymethyl methacrylate denture base polymers (QC-20). MATERIALS AND METHODS: A vinyl polysiloxane film replicating the gap between the denture base and the metallic master model of an edentulous maxilla was weighed using an analytical balance with an accuracy of 0.0001 g for the measurement of internal adaptation. The measurements were performed immediately after surface finishing. Seven rectangular test samples measuring 65 × 10 × 3.3 mm3 were set up for flexural strength test. Flexural strength test (three-point bending test) was performed using a universal machine under axial load at a crosshead speed of 5 mm/min. One-way ANOVA (α = 0.05) following by t tests was utilized in statistical analysis. RESULTS: The difference between the flexural strength of the denture base resins of Deflex and QC-20 was found to be statistically significant. The injection-molded resin demonstrated better internal adaptation compared to the conventional heat-polymerized resin. Evaluation of the physical test results revealed that the polyamide samples were more flexible than polymethyl methacrylate and did not break during flexural strength tests. CONCLUSION: Some properties of denture base resins, such as resin types, internal adaptation, and mechanical strength, may play a significant role in clinical performance of complete dentures and removable partial prostheses. Because of the superior flexural strength properties and internal adaptation characteristics, Deflex may prove to be a useful alternative to conventional denture base resin.

Effects of all-on-four implant designs in mandible on implants and the surrounding bone: A 3-D finite element analysis.

AIMS: The purpose of this study was to observe the stresses of all-on-four implant designs in an edentulous mandible in the implant, surrounding bone, and monolithic ceramics. MATERIALS AND METHODS: In mandibular all-on-four implant models, anterior implants were placed vertically, and posterior implants were differently inclined. On the full-arch fixed prosthetic restoration monolithic zirconia framework, monolithic lithium disilicate was prepared as the superstructure. Model 1M (1M-15.5); posterior implants angled at 15° to the occlusion plane and a cantilever length of 5 mm, Model 2M; (2M-15.9), Model 3M; (3M-30.5), and Model 4M; (4M-30.9) were prepared. A total of 300 N bilateral force was applied at an angle of 30° and oblique to the occlusion plane. Stress values on dental implants, abutments, the surrounding bone, and prosthetic restorations were calculated. RESULTS: The highest stress concentration was observed in the 2nd connector region between the canine and the 1st premolar tooth in the monolithic zirconia frameworks (457.21 MPa). Stress concentration in the cortical bone was 60.93 MPa in posterior implants. Stress was higher in posterior angled implants than straight implants. Stress at posterior angulation increased by 21 MPa in implants angled at 15°. CONCLUSION: In bilateral loading, the force applied to anterior implants does not have a significant effect on the bone structure. Stress concentration increases in posterior angled implants and surrounding bone. Moreover, stress concentration increases as the length of the cantilever, the weakest part in all-on-four implants, increases. As posterior implant angulation increases, stress concentration level and localization are affected.

Maxillary and mandibular all-on-four implant designs: A review.

OBJECTIVE: The objective of this review is to evaluate maxillary and mandibular all-on-four implant designs, their indications and contraindications, advantages and disadvantages. METHODS: By using Pubmed, Cochrane Library, and Google Scholar, data from January 2003 to February 2018 were scanned electronically and manually as the title, abstract, and full text. The keywords specified were determined to be the all-on-four concept, full-arch implant prostheses, 4-implant full-arch, and tilted implants. The inclusion criteria consisted of the all-on-four implant design, its use in completely edentulous maxillary and mandibular cases, advantages and disadvantages of the technique, and changes observed in the maxilla and mandible in completely edentulous cases. Clinical trials and laboratory studies on the subject using the full text and English language were evaluated. RESULTS: A total of 176 articles were found as a result of Google Scholar, Pubmed, and Cochrane Library. Thirty-seven articles were selected according to inclusion criteria; of these, 20 were related to the clinical trials. In addition, a total of 13 articles were found as a result of an additional hand search by screening the reference list of all included publications; of these, 11 was related to the clinical trials. CONCLUSIONS: It is necessary to carry out longer-term clinical and laboratory studies to determine long-term success criteria in all-on-four implant designs and to use new ceramic systems.

Effect of green gold nanoparticles synthesized with plant on the flexural strength of heat-polymerized acrylic resin.

PURPOSE: The aim of this study was to investigate the effect of gold nanoparticle on the flexural strength of polymethyl methacrylate (PMMA). MATERIALS AND METHODS: PMMA specimens (65 mm × 10 mm × 3.3 mm) containing different sizes (45 nm, 55 nm, and 65 nm) and concentrations (0.05% and 0.2%) of gold nanoparticles were prepared, along with a control group containing no added nanoparticles. Flexural strength of all specimens was measured, and one-way ANOVA and Tukey-Kramer post hoc multiple comparisons tests were performed to identify statistical differences between groups. RESULTS: The addition of gold nanoparticles increased the flexural strength of acrylic resin. Significantly greater increases were obtained with lower concentrations (0.05%) when compared to higher concentrations (0.20%). CONCLUSION: Differences in concentrations of gold nanoparticles added to PMMA have significantly different effects on PMMA flexural strength, whereas differences in sizes of gold nanoparticles added to PMMA do not significantly affect its flexural strength. Accordingly, adding gold nanoparticles to PMMA may enhance the mechanical properties of denture bases used in clinical practice.

Comparison of mechanical and dynamic mechanical behaviors of different dental resins polymerized by different polymerization techniques.

PURPOSE: The aim of the present investigation was to evaluate the effect of autoclave polymerization method on the mechanical and dynamic mechanical properties of different polymethylmethacrylate denture base materials. MATERIALS AND METHODS: Three different denture materials were used during the study, two of them were heat polymerizable denture base material (Meliodent and Paladent) and one was microwave polymerizable denture base material (Acron MC). Duncan test was used for the statistical analysis. Statistical analyses were completed using a two-way analysis of variance. Statistical analysis of test results was carried out with a 95% confidence level. RESULTS: Tensile strength was increased with autoclave polymerization regardless of the denture base material type. Paladent specimens with autoclave polymerization (30 min at 60°C and 10 min at 130°C) have the highest average impact strength value. Acron MC specimens have the highest average flexural strength and modulus. Flexural strength improved with autoclave polymerization for both of 10 and 20 min polymerizations for each of Meliodent and Paladent specimens. CONCLUSIONS: Autoclave polymerization provided higher polymerization temperatures compared with the conventional heat polymerization. Autoclave-polymerized acrylic resin specimens showed higher tensile strength values; however, this was not the case for the impact test results. Flexural strength of specimens was improved with autoclave polymerization. Glass transition temperature was increased with autoclave polymerization.

Effect of cavity design on the fracture resistance of zirconia onlay ceramics.

OBJECTIVE: The purpose of this study was to evaluate the fracture resistance and failure modes of onlay restorations prepared with different preparation designs. MATERIALS AND METHODS: A total of 42 extracted, mandibular first molars (36, 46) were used and divided into six groups according to preparation design, as follows 1A: Anatomic preparation of cusps/rounded shoulder margin/occlusal groove; 1B: Flat preparation of cusps/rounded shoulder margin/occlusal groove; 2A: Anatomical preparation of cusps/occlusal groove; 2B: Flat preparation of cusps/occlusal groove; 3A: Complete anatomical reduction of cusps/rounded shoulder margin; 3B: Complete flat reduction of cusps/rounded shoulder margin groups; intact tooth: No preparation. Onlays were constructed with 0.5-mm copings of Zirconia ceramic. The copings were veneered with porcelain (IPS e. max Ceram). All samples were subjected to fracture resistance testing. Data were analyzed with Kruskal-Wallis and Bonferroni-Dunn tests. RESULTS: Fracture resistance varied significantly according to preparation design. Among the anatomic occlusal preparation designs, fracture resistance was significantly lower in Group 3 when compared to Groups 1 and 2 (P < 0.05). Among the flat occlusal preparation designs, fracture resistance was significantly higher in Group 1 when compared to Groups 2 and 3 (P < 0.05). CONCLUSION: Preparation design affected the fracture resistance of onlay restorations. Cavities with flat occlusal preparation designs, a groove and shoulder margins (1B) resulted in the highest fracture resistance, whereas teeth prepared with a complete reduction of cusps and shoulder margins (3A) had the lowest fracture resistance.