Journal of Islamic Dental Association of IRAN
Volume:25 Issue: 2, 2013

Fractured ceramic crowns can sometimes be repaired with composite resin. The aim of the current study was to determine the shear bond strength of composite to feldspathic porcelain after CO2 and Er:YAG laser porcelain surface preparation. In this in-vitro study, 36 feldspathic porcelain blocksmeasuring 1*10*10 mm were divided into 3 groups of 12. Porcelain surfacesinthe first and second groupswere treated with 1.8W CO2 laser and 5W Er:YAG laserirradiation, respectively. Third group specimens were subjected to 9.5% hydrofluoric acid surface conditioning. Allgroups received application ofsilane and adhesiveafterwards. A composite cylinder with 3.5 mm diameter and 5 mm height was bonded to specimens. In order to evaluate the shear bond strength,aUniversal Testing Machine withacrosshead speed of 1 mm/min was used. Statistical analysis was performed using one-way ANOVA and Tukey’s HSD test and P<0.05 was considered statistically significant. The mean shear bond strength values (MPa) were 13.03±2.57%, 12.02 ±3.4 and 19.23±4.62, for the first, second and third groups respectively. One-way ANOVA revealed a statistically significant difference in this respect between the three groups (P< 0.001). Tukey’s HSD testdemonstratedsignificant differences betweenthefirst and third groups (P= 0.000) as well as the second and third groups (P=0.000). However, no significant difference was detected betweenthe first and second groups (P =0.778). Consideringthe study results, CO2or Er:YAG laser irradiationis not suggested as an appropriate alternative to hydrofluoric acid for surface preparationoffeldspathic porcelain.

Success of composite restorations mainly depends on their color stability when in service. The present study aimed at assessing the effect of staining solutions and repolishing on composite resin color change. In this experimental study, 200 specimens were fabricated with A2 and B2 shades of Spectrum (TPH, Dentsply) and Point 4 (Kerr, USA) composite resins (100 specimens each). Specimens were divided into 5 groups of 10 samples each and immersed in coffee, tea, coke, orange juice and distilled water for 30 days. Specimens were photographed with a digital camera (Fine Pix S9600). Color analysis was done with CS Photoshop software (CIE lab color space) at baseline, after color change and after repolishing. Obtained results were analyzed using Three-way ANOVA and LSD test. Level of significance was set at P<0.05. All specimens showed a significant color change in all solutions except for water (D E>3.3). The greatest color change occurred in B2 Spectrum composite resin in coffee while the smallest color change was observed in A2 Point 4 specimens in water. Except for water and coke, the difference in color change between the two composite resins in all solutions was statistically significant. Color changes of B2 shade were significantly higher than those of A2. Significant improvementswere observed in color of specimens after their repolishing. However, color change of specimens in coffee and tea did not improve to the clinically acceptable level by repolishing. Color change of composite restorations depends on the type and shade of composite resin as well as patient’s nutritional habits.

Determining the best restorative material to decrease microleakage in class V restorations is of great importance in operative dentistry. The aim of this in-vitro study was to evaluate the microleakage of silorane-based composites compared to low shrinkage methacrylate-based composites in class V restorations. In this in vitro study, class V cavities were prepared on the buccal and lingual surfaces of 24 human premolars and molars (48 cavities). The specimens were divided into four groups of 6(12 cavities) as follows: group 1 (LS System Adhesive, Primer & Bond + Filtek P90), group 2 (Kalore-GC+ Clearfil SE bond), group 3 (Clearfil SE bond + Grandio) and group4 (Clearfil SE bond + Aelite LS Posterior). All the specimens were thermocycled for 2000 cycles (5-50oC). The teeth were then immersed in 0.5% basic fuchsin dye for 24 hours at 370C, sectioned and observed under stereomicroscope. Data were analyzed using Kruskal-Wallis and Wilcoxon tests at a P<0.05 level of significance. There were no significant differences in microleakage among the four groups at the occlusal margin (P>0.05). But, there were statistically significant differences in microleakage between Silorane and Aelite at the gingival margin (P<0.05). Statistically significant differences were also found in microleakage between occlusal and gingival margins (except for Kalore and Silorane) (P>0.05) Silorane was not superior to the conventional low shrinkage methacrylate-based composites except for Aelite in terms of microleakage.

In the recent years, inlay-retained fixed partial dentures(FPDs)have gained attention due to the preservation of tooth structure and their conservative tooth preparation. The wettability of IPS2 ceramic surfaces can be increased by acid etching enhancingtheir bond to resin cement. High-strength ceramics cannot be etched due to the high resistance of alumina and zirconia. Inadequate bond between the zirconia and resin cement in zirconia-based FPDs leads to unequal stress distribution on the surface and consequent debonding and failure of the inlay-retainer. This study aimed to evaluate the effect of a trenched zirconia bar on the flexural strength of IPS-Empress 2 ceramic core. In this experimental study, 21 ceramic specimens measuring 3x4x25 mm were divided into three groups: Group 1 was the control group and fabricated from In-Ceram alumina ceramic Group 2 specimens were fabricated from IPS-Empress 2 ceramic Group 3 specimens were fabricated from IPS-Empress 2 and had an embeddedtrenched zirconia bar at the bottom Specimens were subjected to three point flexural test with 15 mm support span at a cross head speed of 0.5 mm/min. The fracture forces were recorded and data were statistically analyzed using ANOVA and Tukey’s test. The fracture surfaces were evaluated with an electron microscope. The flexural strength of specimens was 302.66 in group 1, 187.25 in group 2 and 247.89 MPa in group 3. Flexural strength of In-Ceram specimens was significantly higher than that of IPS2 (P<0.019) but no difference existed between In-Ceram and IPS2 with an embeddedtrenched zirconia bar. Therefore, use of trenched zirconia bar at the bottom of specimens had limited effects on increasing their flexural strength). Flexural strength of IPS-Empress 2 specimenswith an embeddedtrenched zirconia bar was equal to that of the other two groups. Although the flexural strength value of the mentioned group was higher than that of IPS-Empress 2 specimens without the bar and lower than that of In-Ceram alumina specimens, these differences were not statistically significant.

Full-scale demonstration of treatment phases on actual patients by an instructor is currently the conventional technique for practical instruction on endodontics. In this method, most students do not get the chance to closely observe the clinical procedure due to the small size of oral cavity. This study aimed at assessing the efficacy of an instructional multimedia program in endodontics for enhancing the knowledge and skills of dental students. In this randomized interventional trial, students taking the course of clinical endodontics were divided into two groups receiving conventional live demonstration alone or in combinationwith an instructional multimedia (DVD). Baseline knowledge of students and their level of knowledge and skills after the intervention regarding practical endodontics were assessed by a pre-test and post-test, respectively. Data were compared between the two groups using Kruskal Wallis test. No significant differenceswere noted between the two groups in terms of knowledge or practical skills of students. However, the multimedia instruction significantly reduced the number of studentinquiries to instructors for troubleshooting (P<0.001). Due to the lack of a significant difference between the two instructional techniques, the multimedia instruction technique may be successfully used as a complement to current conventional techniques for practical instruction on endodontics.

Futura Gen and GC Reline Hard denture chairside reline materialshave recently been introduced to the dental market. Although yet to be scientifically proven, these products are claimed to have optimal characteristics. This study aimed to compare the adherence of Candida strains and bacteria to denture base acrylic resins. In this in-vitro experimental study, 24 discs were fabricated of Futura Gen, GC Reline Hard and Meliodent reline acrylic resins. Specimens were inoculatedwith three Candida strains and Streptococcus mutans at three time points and after staining,their optical absorbance (microbial adhesion and biofilm formation) was calculated using spectrophotometry. Two-way ANOVA and Tukey’s HSD test were applied for statistical analysis. Absorbance (optical density)of C. albicans strains on Futura Gen, GC Reline and Meliodent hard reline acrylic resins was 0.022, 0.011 and 0.028 at one hour, 0.057, 0.022 and 0.062 at 24 hours and 0.101, 0.051 and 0.11 at one week, respectively. Absorbance of C. glabrata on the mentioned resins was 0.012, 0.008 and 0.016 at one hour, 0.039, 0.029 and 0.044 at 24 hours and 0.075, 0.068 and 0.081 at one week, respectively. Absorbance of C. dubliniensis on these resins was 0.026, 0.035 and 0.027 at one hour, 0.064, 0.066 and 0.067 at 24 hours and 0.11, 0.12 and 0.13 at one week, respectively. Absorbance of standard strain of S. mutans was 0.027, 0.014 and 0.035 at one hour, 0.064, 0.026 and 0.064 at 24 hours and 0.11, 0.05 and 0.11 at one week, respectively. Candidal and bacterial adhesion to denture base acrylic resins was not significantly different at the understudy time points (P>0.05). Except for C. dubliniensis, the lowest absorbance belonged to Meliodent. However, absorbance increased over time. Optical absorbance of S. mutans was lower in Meliodent. Among yeast strains, the highest absorbance belonged to C. dubliniensis.

Evaluation of cariogenicity of fruit juices as healthy snacks has special importance. The aim of this study was to evaluate the effect of 3 different Iranian industrial fruit juices on plaque pH. In this randomized clinical trial, 10 healthy dental students were selected based on the inclusion criteria namely the amount of streptococcus mutans and lactobacillus in the saliva, salivary secretion rate, buffering capacity of saliva, absence of active dental caries, absence of systemic disease and etc. Dental plaque pH in certain areas of the 4 mouth quadrants was measured by Ω Metrohm microelectrode and digital pH meter before and 2 to 60 minutes after the consumption of Children orange juice, orange nectar with pulp, pineapple nectar and 10% sucrose solution. The pH curve at different time points was then drawn for each product. Data were analyzed statistically by repeated measures ANOVA (P<0.05). The maximum drop in plaque pH occurred 2 minutes after consumption. The time spent below the critical pH was the longest for orange nectar with pulp (10.75 ± 2.24) and shortest for pineapple nectar (3.46 ± 1.14). At final minutes of study, plaque pH returned to its baseline value after consumption of all fruit juices except for orange nectar with pulp). After consumption of orange nectar with pulp, the mean plaque pH was significantly lower in comparison to other juices and the time spent under the critical plaque pH was the longest.

Considering the risk of cross contamination, disinfection of dental stones is essential provided that their mechanical and structural properties remain unchanged. The aim of this study was to evaluate the effect of disinfection on the hardness of dental stones. In this experimental study, 40 discs were fabricated of type III and IV dental stones and divided into three groups. The three understudy chemical disinfectants namely 1% Virkon, 0.525% hypochlorite and slurry water were sprayed on samples in each group. The hardness of sprayed samples was evaluated by measuring the width of scratch according to the Mohs scale of mineral hardness. Surfaces of sprayed samples were also inspected by optical microscopy. Data were analyzed using Kruskal-Wallis and Mann-Whitney tests (P<0.05). Mohs scale of mineral hardness revealed that the width of scratches was narrower in samples sprayed with Virkon than in those sprayed with hypochlorite and slurry water. In type III dental stone specimens, the maximum width was observed in samples sprayed with slurry water (1.35±0.02) and the minimum width was observed in Virkon group samples (0.97±0.01). For type IV, the maximum and minimum widths were observed in samples sprayed with slurry water (1.20±0.01) and Virkon (0.61±0.01), respectively. In both types of stones, no significant differences were noted between the sprayed groups, while the differences between each sprayed group and the control stones (no spraying) were significant. Surface hardness of dental stones decreased after spraying them with the three understudy disinfectants. Dental stones sprayed with Virkon exhibited the lowest reduction in hardness.

Optimal bond strength between soft liners and denture base resin is an important requirement for application of these materials. This study aimed to determine the effect of 2.5% sodium hypochlorite (NaOCl) and Corega denture cleanser solutions on tensile bond strength of Acropars, Molloplast-B, GC soft liner and Mollosil soft liners to denture base resin. In this in-vitro experimental study, 30 specimens of each of the 4 soft liners according to the manufacturer’s instructions were processed between two blocks of polymethyl methacrylate. Specimens were divided into 3 groups and after immersion in 2.5% sodium hypochlorite and Corega solutions were subjected to tensile bond strength testing using Universal Testing Machine (Zwick Roell, Z50, Germany) with a crosshead speed of 5 mm/min. Data were analyzed with two-way ANOVA, Tamhane’s post hoc test and Fisher’s exact test. The mean tensile bond strength of all three testing positions was 3.27 ± 1.04, 0.93 ± 0.35, 0.71 ± 0.31 and 0.28 ± 0.11 MPa for Acropars, Molloplast-B, GC soft liner and Mollosil, respectively. Type of soft liner material had a significant effect on the tensile bond strength of soft liner to denture base resin (P<0.0001) but type of cleansing solution had no significant influence on tensile bond strength of specimens. The 2.5% sodium hypochlorite and Corega solutions had no significant effect on tensile bond strength of soft liners to denture base.

At present, stainability and color instability of tooth-colored restorations following the consumption of colored beverages are among the problems commonly encountered in restorative dentistry. Filtek P90 composite resin comprising of Oxirane and Siloxanefunctional moietieswas recently introduced aiming at reducing the polymerization shrinkage. The aim of this study was to evaluate the effect of tea on color change of P90 and Z250 composite resins using spectrophotometry. For this experimental study, 20 composite discs were fabricated in metal molds from Z250 and P90 composite resins and light cured using LED light-curing unit. Specimens were stored in distilled water at 37 ° C for 24 hours to allow completion of polymerization. Color of specimens was then measured at baseline and after 5 days of storage in water and tea solution using spectrophotometer. Data were analyzed using independent sample t-test and two-way ANOVA. The color change of P90 and Z250 composites after storage in distilled water was not significant in comparison to their baseline color (P>0.05). However, both composite resins showed a significant change in color after storage in tea solution (P<0.05). Stainability of Z250 composite in tea was significantly greater than that of P90; but in distilled water P90 showed greater color change than Z250. Within the limitations of this study, Z250 composite demonstrated significantly greater color change in comparison to P90 after immersion in tea solution