Background and aims. Polymethyl methacrylate (PMMA) is widely used for the fabrication of removable prostheses. Silver nano-particles (AgNps) have been added to PMMA because of their antimicrobial properties, but their effect on the mechanical properties of PMMA is unknown. The aim of this study was to investigate the effects of AgNps on the tensile strength of PMMA.Materials and methods. For this study, 12 specimens were prepared and divided into two groups. Group 1 included PMMA without AgNps and group 2 included PMMA mixed with 5 wt% of AgNps. Tensile strength of the specimens was measured by Zwick Z100 apparatus. Statistical analysis was carried out by SPSS using t-test. Statistical significance was defined at P<0.05.Results. This study showed that the mean tensile strength of PMMA in group 2 was significantly lower than that in group 1. Therefore, the tensile strength decreased significantly after incorporation of silver nano-particles.Conclusion. Within the limitations of this study, tensile strength of acrylic resin specimens was influenced by silver nano-particles.

Background. For esthetic considerations in anterior regions, abutments with high-strength ceramics such as alumina and zirconia have been developed as substitutes for titanium abutments. The present study was designed to investigate the distribution of stress in prosthesis and bone components of an implant-supported FPD with different abutments by using 3D finite element analysis. Methods. Ceramic FPDs were made from the canine to the upper left second premolar with titanium fixtures. In order to investigate the stress distribution, forces of 100 and 300 N were applied at angles of 0, 15 and 35 degrees to the central fossa of the second premolar and pontic, as well as the cingulum of the canine crown. Force loading was static. After analyzing the mechanical properties of the materials, boundary conditions and loading were performed according to the existing averages, and subsequently, the results obtained from this analysis were analyzed. Results. The highest level of stress was observed in the distal crest of the posterior implant (23.20 MPa) under lateral forces (15 and 35 degrees) in a model with both titanium abutments. Conclusion. Lateral forces induced higher accumulation of stress in the implant and surrounding bone, while abutment change did not affect the distribution of stress.

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Background:This in vitro study investigated the marginal fit of two porcelain laminate veneers to help the selection of more accurate veneers in discolored teeth.Materials and Methods:Thirty impressions of metal master die created from the prepared labial surface of an acrylic maxillary central incisor were made and poured with Type IV stone. The dies were distributed into test groups (n = 15) for the construction of DuCeram and InCeram laminate veneers. An image-analysis program was used to measure the gap between the veneers and the master die at the labial, lingual, and proximal margins. Statistical analysis was performed with repeated measures ANOVA. Independent t-test was used to compare the mean values between the two groups. Values of P < 0.05 were judged to be significant.Results:Differences between marginal fit of two groups were significant (P < 0.001). The overall mean marginal gap values (μm) for InCeram and DuCeram were, respectively, 114.4 ± 40.81 and 282.3 ± 82.82. Independent t-test revealed significant differences between the marginal gaps of two materials at different predetermined points.Conclusion:Within the limitations of this study, the marginal gap in InCeram laminate veneer was within the clinically acceptable standard set at 120 μm.

Objectives:The present study aimed to evaluate the bond strength of heat-cure denture base resin to newly designed Iranian artificial acrylic teeth.Materials and Methods:In this in-vitro experimental study, shear bond strengths of Ivoclar acrylic, Apple composite, and B-Star nanocomposite teeth to heat-cure acrylic denture base resin were compared. A total of 18 samples were selected from each group of teeth. The samples were attached to heat-cure resin according to ISO 10477 standard. For the assessment of bond strength, the samples were placed in a universal testing machine and were subjected to shear forces at a speed of 1 mm/minute to record the fracture load. Descriptive statistics, including frequency, mean, and standard deviation, were calculated using SPSS 20 software. Two-way analysis of variance was used to compare the shear bond strength of the groups with and without monomers and the studied artificial teeth.Results:The mean shear bond strengths of Ivoclar acrylic teeth were 392.22±23.76 MPa and 337.11±32.18 MPa with and without adding monomers to the tooth surface, respectively. The mean shear bond strengths were 250.44±29.84 MPa and 238.33±27.28 MPa (without monomers) and 438.33±24.16 MPa and 311.56±32.78 MPa (with monomers) for Apple composite and B-Star nanocomposite artificial teeth, respectively.Conclusion:The greatest shear bond strength was attributed to Ivoclar acrylic teeth followed by Apple composite and B-Star nanocomposite artificial teeth. Addition of monomers to the tooth surface significantly strengthened the shear bonding of acrylic base resin to the teeth.

Objectives. This study aimed to evaluate the effect of sandblasting on the bond strength of denture base resin to soft liners. Materials and Methods. This report follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. PubMed, Embase, Cochrane, Scopus, and OpenGrey databases were searched for in vitro studies that compared sandblasting with no treatment in terms of the tensile, shear, and peel bond strength of resilient lining materials (acrylic-based or silicone-based) to polymethyl methacrylate denture base resin. Based on the outcome, the analysis was carried out in three groups of tensile, shear, and peel bond strength. Subgroup analysis was done for the effect of size of particles on sandblasting, blasting pressure, and type of soft liner whenever possible. Heterogeneity was evaluated among the studies, and meta-analysis was performed with random effect models ( p < .05 ). Results. After screening, 16 articles met the inclusion criteria for meta-analyses. No treatment showed significantly higher tensile ( p < 0.001 ) or peel ( p = 0.04 ) bond strength, although shear bond strength of sandblasted resin was significantly better ( p = 0.008 ). Results of subgroup analyses of particle size favored the control group in 50 µ Al2O3 particle size ( p < 0.001 ). In analyses of blasting pressure, the control group had significantly better tensile bond strength than specimens with blasting pressure ≤1 bar ( p < 0.001 ) while specimens with blasting pressure beyond 1 bar showed significantly more tensile strength than control group ( p = 0.03 ). In silicon-based liners, groups without any surface treatment had significantly higher tensile bond strength ( p < 0.001 ). Conclusion. According to the in vitro studies, sandblasting would not lead to significant increase in bond strength of soft liner to the denture base resin.

Statement of the Problem: The thickness and height of the facial wall of the alveolar bone in anterior part of maxilla is a critical factor to achieving esthetic and success of   implant insertion. Objectives:The aim of  present study was evaluating the anterior maxillary bone by cone beam computed tomography (CBCT) images.Methods :In this in vitro study, 200 CBCT images of the anterior maxillary teeth were examined. Each tooth was classified according to the sagittal root position and the measurements were done by one practitioner. Results:The following variables were significantly associated with gender (male predilection): tooth-ridge angulation (TRA )in the right lateral teeth; concavity angulation (CA)in the right central and lateral teeth; concavity depth (CD ) in the right lateral teeth and both canines; concavity location (CL)in the right canine; buccal bone height (BH)and palatal bone height ( PH) in the left canine.Age was associated with CLand ridge angulation in none of the teeth; with TRA and CD in all anterior teeth; bone density in the right lateral teeth; with CA in both  lateral teeth; with BH in both central teeth; with PHin the right central and left lateral teeth; and with TA in both lateral teeth and canines.