Journal of Islamic Dental Association of IRAN
Volume:27 Issue: 1, 2015

One of the problems of all ceramic restorations is their risk of fracture due to occlusal loads. The aim of the present study was to compare the effect of two marginal designs (shoulder and chamfer) on the fracture resistance of IPS-emax all ceramic restorations. One extracted maxillary first premolar received chamfer 50' marginal preparation (0.8 mm). Twenty impressions were made using poly vinyl siloxane. Then, chamfer was converted to shoulder 90'(1mm). After impression, epoxy resin dies were fabricated. Impressions of each epoxy resin die were made and poured with die stone. Twenty Press crowns and twenty ZirCAD crowns were made on stone dies and cemented on resin dies. Then, samples underwent a fracture test in a universal testing machine. Data were analyzed by one-way ANOVA. The mean fracture resistance was 1426N for the chamfer ZirCAD samples, 1361.3N for the shoulder ZirCAD samples, 1059.9N for the chamfer Press samples and 1295.8N for the shoulder Press samples. One-way ANOVA revealed no difference among groups. (p=0.095). After porcelain application, marginal design does not affect fracture resistance of single IPS-emax posterior crowns. Fracture resistance was approximately the same in Press and ZirPress groups probably due to porcelain application, because in ZirCAD group fractures occurred in the porcelain prior to the core.

Fluoride releasing adhesives are favorable for bracket bonding since they decrease the risk of demineralization around orthodontic brackets given that they provide acceptably high shear bond strength (SBS). The aim of this study was to evaluate the SBS of resin-modified glass ionomer cements (RMGIC) reinforced by nano-zinc oxide (NZnO) and nano-hydroxyapatite (NHA) particles in comparison with composite resins. In this experimental study, 80 extracted human premolars were used. The teeth were randomly divided into 4 groups as follows: Group 1: Transbond XT as the control group, Group 2: RMGIC (Fuji II LC), Group 3: RMGIC with 5% NHA and Group 4: RMGIC with 2% NZnO. After enamel etching, brackets were bonded. The SBS was calculated for each group. The percentage of adhesive remained on the enamel was quantified by calculating the adhesive remnant index (ARI). The data were analyzed using one-way ANOVA and the Kruskal Wallis test. According to the results of ANOVA, there were no significant differences in SBS of groups (P=0.075). The mean SBS in groups 1 to 4 was 15.43 ± 4.61, 14.95 ± 4.34, 17.97 ± 3.65 and 17.08 ± 3.59 MPa, respectively. According to the Kruskal-Wallis test, there were no significant differences in degree of ARI among groups (P=0.413). The SBS was similar among all groups and adding NZnO and NHA particles had no negative effect on SBS of RMGIC. In all groups, less than half the adhesive remained on the enamel after bond failure.

Bleaching treatments may alter the color stability of composite restorations. Silorane-based composites have shown similar or superior physical and mechanical properties compared to other types of composites. Furthermore, studies have shown variable and sometimes contradictory results regarding the effect of bleaching agents on the color stability of composite restorations. This study aimed to assess the effect of two Iranian bleaching agents on color stability of a Silorane-based (P90) composite compared with two methacrylate-based composites [nanofiller (Z350) and microhybrid. (Z250). In this in vitro study, a total of 18 disc-shaped specimens (10 × 2 mm) of Z250, Z350 and P90 composites (A3 shade) were fabricated and randomly divided into 3 groups (n=6) and subjected to bleaching treatment with 16 % carbamide peroxide, 35% carbamide peroxide and distilled water as the control group. Color parameters were measured using CIE-L*a*b* system and a spectrophotometer before and after bleaching. The factors were statistically analyzed by means of two-sided ANOVA (repeated measures ANOVA) and Tukey’s multiple comparisons tests. The mean±standard deviation of total color change (BE) in control, 16% carbamide peroxide and 35% carbamide peroxide groups was 3.48±1.43, 4.55± 1.7 and 4.17±1.9, for Z250, 4.33±2.41, 4.94±2.23 and 4.25±1.65, for Z350 and 4.97±2.47, 5.28±1.67 and 3.41±2.26 for P90, respectively. BE was clinically perceptible after bleaching treatments of all composite materials (BE>3.3).

Hepatitis B is an important infection in dentistry necessitating the use of disinfectants to prevent its transmission. This study compared the efficacy of 2/100 sodium hypochlorite disinfectants manufactured by four different manufacturers namely Ashimashi, Paknaz, Vitex and Active against hepatitis B virus (HBV). In this experimental laboratory trial, serum of 10 hepatitis B patients was poured into microtubes and Ashimashi, Paknaz, Vitex and Active disinfectants were added to them. Polymerase chain reaction (PCR) was performed with viral diagnostic kits to diagnose the virus genome. Real time PCR was performed before and after incubation with the disinfectants. The reductions occurred in the viral load of HBV were statistically analyzed by Kruskal-Wallis and Mann-Whitney U tests. No significant antiviral efficacy was noted following the application of Ashimashi 2/100 sodium hypochlorite disinfectant. Paknaz showed the highest efficacy against HBV. Vitex and Active ranked next with significant differences (P<0.0001). Under the study limitations, Paknaz 2/100 sodium hypochlorite solution was the most effective while Ashimashi 2/100 sodium hypochlorite disinfectant did not show adequate efficacy against HBV.

Considering the increasing use of antibiotics in root canal therapy and the possible effects of intracanal medicaments on the bond strength of composite restorations, the aim of this study was to evaluate the effect of triple antibiotic paste on shear bond strength of three types of composite resins to dentin. In this in-vitro, experimental study, the enamel of 60 extracted premolars was ground parallel to the longitudinal axis of the teeth in order to produce flat dentin surfaces (5 mm2 minimum surface area). The samples were divided into six groups. In the control group, dentin surfaces were stored in saline solution and in the experimental groups, dentin surfaces were exposed to triple antibiotic paste for 10 days. After washing and drying, Single Bond was applied for dentin bond to Z100 and Z350 composites. Adhesive resin was used for bond to to P90 composite. Composites were applied on the dentin surfaces in six groups and cured in four directions. The shear bond strength was measured by Instron machine. The data were analyzed by t-test, one-way ANOVA and Tukey’s test. The highest mean shear bond strength was found in Z350 composite group following the use of triple antibiotic paste (38.75 MPa) and the lowest mean strength was found in Z100 composite group following the use of triple antibiotic paste (14.64 MPa). The mean shear bond strength of P90 and Z100 composites (in contrast to Z350 composite) was higher in the saline compared to the triple antibiotic paste groups (P=0.1). The differences between saline and antibiotic groups were not significant (P=0.959) but the difference in this regard among the three types of composites was significant. The results of this study showed that use of triple antibiotic paste has no effect on the shear bond strength of composite to dentin but the type of composite significantly affects the shear bond strength.

By application of casein phosphopeptide amorphous calcium phosphate (CPP-ACP) as a remineralizing agent, it may be feasible to only remove the carious dentin and better preserve the tooth structure. This study aimed to assess the shear bond strength of composite to primary enamel treated with CPP-ACP using total etch and self etch bonding systems.This in vitro experimental study was conducted on 96 sound primary teeth randomly divided into 12 groups (n=8). Four groups were demineralized and the rest remained sound. All the specimens were subjected to pH cycling. Then, GC-Tooth Mousse was applied on their surfaces. Composite resin was bonded using Clearfil SE Bond self-etch or Single Bond total-etch bonding systems. The bond strength of the specimens was measured by Instron machine and the mode of fracture was assessed by a stereomicroscope. Data were analyzed by one-way and two-way ANOVA and chi-square test. In the total etch system, the bond strength of demineralized group was significantly higher than that of sound group (P=0.009). This difference in self etch system was not significant (P=0.928). The CPP-ACP remineralizing agent decreased the bond strength in total etch and increased the bond strength in self etch group (P=0.032 and P=0.018, respectively). No difference was observed in the mode of fracture of the two bonding systems. GC Tooth Mousse decreased the bond strength to composite in total etch and increased it in self etch group. Higher bond strength to composite can be achieved in teeth with white spot lesions when total etch system is used.

The prevalence of musculoskeletal complaints is high among dentists; however, only a few studies have focused on this topic. The aim of this study was to assess the efficacy of an exercise program for treatment of neck pain in dentists practicing in Tehran. A questionnaire was administered among 46 dentists in Tehran matched by age, gender (all males) and neck pain complaints in the past six months. Subjects were randomly divided into two groups. The first group received exercise therapy while the second group was given no exercise. Pain was measured at two months after the intervention using the visual analog scale (VAS). Data were analyzed using t-test and p<0.05 was considered statistically significant. The t-test showed significant improvement of neck pain in the first group after the intervention (p<0.05). The results showed that exercise therapy can be effective for treatment of neck pain. Therefore, regular exercise by dentists can prevent neck pain and other musculoskeletal disorders.

Achieving appropriate retention and easy retrievability at the same time is challenging in implant-supported fixed partial dentures (FPDs). Researchers have always been in search of a temporary cement to improve the retentive strength. The aim of this in vitro study was to evaluate the effect of three different temporary cements and sandblasting of the abutment surface on the retentive strength of implant-supported fixed prostheses. In this experimental study, 10 DIO implant analogues were embedded in acrylic resin. Twenty abutments were divided into two groups of 10. The abutments in group one were used in their intact standard form while those in group two were sandblasted. Sixty metal copings were fabricated and cemented on abutments of each group using three types of temporary cements namely Kerr, Provy and GC. Specimens were subjected to a universal testing machine to measure their retentive strength. The results were analyzed by Tukey’s post-hoc test. The retentive strength of TempBond (Kerr) with sandblasted abutments was significantly higher than that of the other two cements (p<0.001). In standard abutments, Provy had slightly but not significantly higher retentive strength. The lowest values in both abutment groups were obtained by GC cement. Kerr TempBond cement with sandblasted abutments yields the highest retentive strength.