Effect of different fiber post surface treatments on microtensile bond strength to composite resin.

STATEMENT OF PROBLEM: The interface of fiber post and composite resin is a site of potential failure of adhesion. Improving this interface adhesion through different pretreatments of the fiber post surface has been suggested, but the results are controversial. PURPOSE: The purpose of this in vitro study was to evaluate the effect on the bond strength to composite resin of pretreating glass fiber post surfaces with hydrogen peroxide, phosphoric acid, and a silane coupling agent. MATERIAL AND METHODS: Glass fiber posts were treated for 1 or 5 minutes with 30% hydrogen peroxide or 35% phosphoric acid. Treated posts were divided into silanization and no silanization groups. Control groups included no treatment or treatment with silanization alone (total of 10 groups; n=14). Composite resin was bonded to the fiber posts, and the specimens were cut into beams with the fiber post in the middle and the composite resin at both sides. The beams were attached to a mechanical testing device, and microtensile bond strength was evaluated. Fracture modes were assessed using stereomicroscopy. Statistical analysis was done with 3- and 2-way ANOVA (α=.05). Additional specimens were evaluated with a scanning electron microscope (SEM) to evaluate the effect of treatments on the characteristics of fiber post surfaces. RESULTS: The highest bond strength values were found in the group treated with phosphoric acid for 5 minutes with silanization, followed by the group treated with silanization alone. ANOVA showed a statistically significant effect for silanization (P<.05), but no statistically significant effect for surface treatment. SEM evaluation revealed cracked and dislodged superficial fibers in all groups, with no obvious difference in fiber exposure among the groups. CONCLUSIONS: The silane coupling agent had a significant effect on the bond strength of the tested glass fiber posts to composite resin, whereas 30% hydrogen peroxide or 35% phosphoric acid did not.

The effect of placement depth of platform-switched implants on periimplant cortical bone stress: a 3-dimensional finite element analysis.

PURPOSE: The purpose of this study was to evaluate periimplant bone stress distribution for platform-switched implants placed at different depths relative to the bone crest, maintaining the occlusal plane at the same level. MATERIALS AND METHODS: Sections of posterior mandibular bone blocks comprising cortical and cancellous bones were simulated in a computer-aided design software. A platform-switched implant was simulated and placed at 1.0 mm supracrestal to 1.8 mm subcrestal positions at 0.1 mm intervals. All bone and implant materials were presumed to be homogenous and isotropic. Conical gold crowns were designed for each model, maintaining the occlusal plane at the same level. Models were analyzed under axial and nonaxial loads. RESULTS: Cortical bone stress increased only slightly from equicrestal to 0.8 mm subcrestal positions, whereas supracrestal and deeper subcrestal positions resulted in higher stress values. Subcrestal positions showed maximum stress concentration away from crestal bone. CONCLUSION: It can be concluded that shallow subcrestal placement of 2-stage platform-switched implants only slightly increases the stress within the cortical bone.

The influence of ultrasound on removal of prefabricated metal post cemented with different resin cements.

BACKGROUND: Ultrasonic vibrations are used to remove a cemented post from a root canal requiring endodontic retreatment. Various results have been reported from the studies that evaluated the effect of ultrasonic instruments in removing the posts cemented with resin cements. The aim of this study was to evaluate the effect of ultrasonic energy on the retention of prefabricated metal post cemented with Panavia or Maxcem Elite cements. MATERIALS AND METHODS: In this in vitro study, forty eight extracted single root premolars were decoronated with a diamond disc leaving a 13 mm long root and endodontically treated. The root canals were obturated by gutta-percha up to 5 mm with vertical condensation method and the 8 mm post-space was prepared to receive a no. 2 long Dentorama post. The roots were placed in an incubator for 48 h in 37°C and 100% humidity. After mounting the teeth in acrylic blocks, posts were cemented in the root canals using Panavia F2.0 in 24 specimens and Maxcem Elite in 24 others. For half of the specimens in each subgroup, an ultrasonic device was applied for 4 min. Universal testing machine was used to measure the force needed to remove the posts with a crosshead speed of 1 mm/min until the post came out of the canal. Kruskal-Wallis test was used for statistical analysis at 5% level of significance. RESULTS: The removal force was not significantly different among the groups (P > 0.05). CONCLUSION: Ultrasonic energy did not decrease the retention of posts cemented with Panavia or Maxcem Elite cements. Furthermore, it seems that there is no significant difference between removal force of self-etch (Panavia) and the self-etch self-adhesive (Maxcem Elite) resin cements.

Shear bond strengths and morphological evaluation of filled and unfilled adhesive interfaces to enamel and dentine.

In this laboratory study shear bond strengths of three filled and one unfilled adhesive systems to enamel and dentine were compared. Forty-eight extracted intact noncarious human mandibular molars were randomly assigned to two groups of 24 one for bonding to enamel and the other for bonding to dentine. Buccal and lingual surfaces of each tooth were randomly assigned for application of each one of filled (Prime & Bond NT (PBNT), Optibond Solo Plus (OBSP), and Clearfil SE Bond (CSEB)) and unfilled (Single Bond (SB)) adhesive systems (n = 12). A universal resin composite was placed into the translucent plastic cylinders (3 mm in diameter and 2 mm in length) and seated against the enamel and dentine surfaces and polymerized for 40 seconds. Shear bond strength was determined using a universal testing machine, and the results were statistically analyzed using two-way ANOVA, one-way ANOVA, t-test, and Tukey HSD post hoc test with a 5% level of significance.There were no statistically significant differences in bond strength between the adhesive systems in enamel, but CSEB and SB exhibited significantly higher and lower bond strength to dentine, respectively, than the other tested adhesive systems while there were no statistically significant differences between PBNT and OBSP.

Comparison of shear bond strength of two veneering ceramics to zirconia.

BACKGROUND: Chip-off fracture of veneering porcelain has been described as the most frequent reason for the failure of zirconia-based fixed partial dentures. The purpose of this study was to evaluate the shear bond strength (SBS) of two commercial zirconia core ceramics to their corresponding veneering ceramics. MATERIALS AND METHODS: Zirconia disks with 7-mm diameter and 3-mm height were prepared (Cercon and Biodenta systems) and veneered with recommended layering ceramics (Cercon ceram and 2 in 1 ceramic, respectively) (n = 10). The disks were polished with diamond paste and airborne-particle abraded before layering. The specimens were mounted in a T-shaped metal holder using autopolymerized acrylic resin and stored in 37°C distilled water for one week, after which they were subjected to thermal cycling. SBS of zirconia core to veneering ceramic was measured using a universal testing machine and failure modes were determined microscopically. Data were analyzed using t test (α < 0.05). RESULTS: Mean (±SD) SBS values were 27.19(±3.43) and 28.22(±4.08) MPa for Cercon and Biodenta systems, respectively, with no significant difference. Biodenta system showed more adhesive failure compared to more combined (adhesive and cohesive) failures in Cercon system. CONCLUSION: Within the limitations of this study it can be concluded that SBS of Biodenta and Cercon specimens were nearly the same, but the fracture mode of these two systems were different. Since Biodenta fracture pattern was predominantly adhesive, it seems that maybe Biodenta porcelain was stronger than Cercon porcelain where as its adhesive bond was weaker.

Effect of casein phosphopeptide-amorphous calcium phosphate and acidulated phosphate fluoride gel on erosive enamel wear.

BACKGROUND: Some studies have shown that casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and acidulated phosphate fluoride (APF) gel can protect teeth against erosion. The aim of this study was to assess whether CPP-ACP and fluoride could reduce enamel wear rates under erosive conditions simulating abrasion and acidic diet regimen. MATERIALS AND METHODS: Enamel specimens consisted of 3 experimental groups (receiving CPP-ACP, APF or both) and a control group. Specimens were subjected to 5,000 wear cycles at a load of 30 N and a pH of 3 in a tooth wear machine. The amount of wear was determined by stereomicroscope. Data were analyzed using one-way analysis of variance and Tukey post hoc tests (α = 0.05). RESULTS: Mean wear rate (mean±SD) was 194.6±49.2 micrometers in CPP-ACP group, 197.6±39.5 in APF group, 134.6±44.7 in combination group and 266.2± 22.7 in the control group. Statistical analysis indicated significantly higher wear rate in the control group than the experimental groups and also in the CPP-ACP and APF group than the combination group (P<0.05). CONCLUSIONS: We concluded that although either CPP-ACP or APF can protect enamel against wear, their combination provides significant enamel wear reduction. These findings would lead to new strategies for the clinical management of tooth wear.

Effect of face form on maximal molar bite force with natural dentition.

OBJECTIVE: The purpose of this study was to determine mean maximum bite force in adults with normal occlusion and to evaluate effect of face form on it. DESIGN: Twenty male and 20 female students with normal dentitions and between the ages of 19 and 27 participated in the study. A strain-gauge force transducer was developed to measure bite force and was calibrated with known loads. Three measurements were performed on each side of the dentition in the first molar region and mean values used for analysis. Face form was defined as square, tapering, square-tapering or oval and determined using digital photographs. Effect of gender and face form on bite force was statistically analysed using two-way ANOVA and Duncan tests. RESULTS: Mean maximum bite force and standard deviation (S.D.) in the sample population was 64.4 (24.0) kilograms (kg). In men, the mean was 73.6 (23.8) which was statistically higher than in women (53.0 (19.6) kg) (P < 0.05). Mean maximum bite force in subjects with square face form was 93.7 kg, which was significantly higher than in subjects with other facial forms (P < 0.05). CONCLUSION: The results showed higher bite force in men and those with square face form. Square face form may contribute to higher bite force values by maintaining a higher mechanical advantage for muscles of mastication.