The Effect of Remaining Coronal Tissue Height on the Fracture Strength of Over-Flared Endodontically Treated Central Incisors Restored Using a Multipost Approach.

Objectives: This study aimed to examine the effect of remaining coronal tissue height on the fracture strength of over-flared endodontically treated central incisors restored with multiple prefabricated fiberglass posts using the multipost approach. Materials and Methods: A total of 40 human central maxillary incisors were examined in this study. The samples were assigned to five groups (n = 8) based on the height of the remaining coronal tissue: with no remaining coronal tissue, 1-mm coronal tissue height (CTH1), 2-mm coronal tissue height, 3-mm coronal tissue height (CTH3), and one intact tooth (IT) group. Following endodontic treatment of an over-flared canal, the postspace depth was 10 mm, and the residual dentin thickness was 1 mm. Two prefabricated fiberglass posts were cemented into the root canal, adopting a multipost approach. The static load was applied at 0.5 mm/min and 135° concerning the tooth's longitudinal axis until a fracture occurred. One-way analysis of variance and the post hoc Tukey's test were performed to analyze the data at a significance level of p < 0.05. Results: The maximum fracture strength was recorded for IT (control group), while the minimum fracture strength was found for teeth with a coronal tissue height of 1 mm. The differences between IT group and other groups (p < 0.05), as well as the differences between the group with CTH3 and groups without coronal tissue and CTH1, were significant. Conclusion: In sum, an increase in the height of the remaining coronal tissue (≥3 mm) significantly increased the fracture strength of over-flared endodontically treated central incisors after restoration with prefabricated fiberglass posts by adopting a multipost approach.

Comparison of the effect of preheating on the flexural strength of giomer and nanohybrid composite resin.

Background. Considering the increased use of preheating and novel resin-based materials to restore teeth, the present study investigated the impact of preheating on the flexural strength of a giomer and compared it with a nanohybrid composite resin. Methods. Two restorative materials (Beautifil II giomer and Alpha III nanohybrid composite resin) were used. Thirty rod-shaped samples (adding up to 60 samples) were prepared from the materials above and divided into two subgroups: with and without preheating (n=15). Before sample preparation, the giomer and nanohybrid composite resin tubes were preheated at 68ºC for 15 minutes in the preheating subgroups. In the subgroups without preheating, the tubes were kept in a room at 25ºC. Then the flexural strength was compared between the two groups with two-way ANOVA at a significance level of P<0.05. Results. The results showed significantly higher flexural strength in the preheated subgroups than in the non-preheated subgroups (P<0.001). In addition, the mean flexural strength values were significantly higher in the giomer groups than in the nanohybrid composite resin groups (P<0.001). Conclusion. Preheating increased the studied materials' flexural strengths significantly. The flexural strength of the giomer restorative material was higher than that of the nanohybrid composite resin, irrespective of preheating.

Effect of Bleaching Method and Curing Time on the Surface Microhardness of Microhybrid Composite Resin.

Objectives: The present study aimed to evaluate the effect of curing time and bleaching agents on microhybrid composite resin surface microhardness. Material and method: A total of 180 microhybrid composite resin disks were divided into two groups in terms of curing time: 40 s, 60 s. Then, each group was divided into three subgroups: control (distilled water), home bleaching (15% carbamide peroxide) and office bleaching (40% hydrogen peroxide). Surface microhardness of the samples was determined by using Vickers hardness test both at baseline and after the completion of the tests. Two-way ANOVA and Tukey HSD tests were used to analyze and compare microhardness changes between groups. Statistical significance was defined at P<0.05. Results: Based on the two-way ANOVA, curing time, bleaching method, and cumulative effect of these two variables significantly affected composite resin microhardness (P<0.001). Tukey HSD tests showed that microhardness had significantly decreased in the bleaching groups, with the highest decrease when the office bleaching method was used (P<0.001). The samples cured for 40 s exhibited lower microhardness than those cured for 60 s and had an increased reduction in microhardness after bleaching (P<0.001). Conclusions: Application of both bleaching methods decreased the surface hardness of microhybrid composite resin. An increase in the curing time was associated with a decrease in adverse effects of bleaching agents on microhardness.

Comparison of the effect of bleaching with 15% carbamide peroxide and 35% hydrogen peroxide on flexural strength of Cention N in selfcured and dual-cured polymerization modes.

Background. The use of bleaching agents might result in microstructural changes in tooth structure and in restorative materials. This study compared the effects of bleaching with %15 carbamide peroxide and %35 hydrogen peroxide on the flexural strength of Cention N restorative material using the self-cured and dual-cured polymerization modes. Methods. Sixty bar-shaped samples of Cention N restorative material were included in this in vitro study and assigned to three groups (n=20) randomly: control, bleaching with %15 carbamide peroxide and bleaching with %35 hydrogen peroxide. Each group was divided into two subgroups: samples polymerized in the self-cured mode and samples polymerized in the dual-cured mode. Then the flexurals trengths of the samples were determined. Two-way ANOVA was used to compare flexural strengths between the three groups in two polymerization modes, followed by post hoc Tukey test. Statisticals ignificance was defined at P<0.05. Results. The difference in the mean flexural strength was significant in terms of the bleaching regimen (P<0.001), with significantly lower flexural strength in the two bleaching groups compared to the control group. However, the mean flexural strengths were not significantly different in terms of the polymerization mode applied (P=0.14). Conclusion. The application of %15 carbamide peroxide and %35 hydrogen peroxide bleaching agents decreased the flexural strength of Cention N restorative material. Irrespective of the bleaching regimen, there was no significant difference in the flexural strength of Cention N between the self-curing and dual-curing polymerization modes.

Effect of Cavity Disinfection with Chlorhexidine on Marginal Gap of Class V Composite Restorations Bonded with a Universal Adhesive Using Self-Etch and Etch-and-Rinse Bonding Strategy.

OBJECTIVES: This in-vitro study aimed to evaluate the effect of cavity disinfection with chlorhexidine (CHX) on marginal gaps of Class V composite resin restorations bonded with a universal adhesive using self-etch and etch-and-rinse bonding strategy. MATERIALS AND METHODS: Sixty sound human premolars were randomly assigned to two groups (n=30): group 1 (CHX) and group 2 (no CHX). Each group was divided into two subgroups (n=15) according to the bonding strategy of the universal adhesive (self-etch or etch-and-rinse). Class V cavities were prepared on the buccal surfaces of the teeth. The occlusal and gingival margins of the cavities were placed in enamel and dentin, respectively. In the first and second subgroups of both groups, the All-Bond Universal adhesive was applied with self-etch and etch-and-rinse bonding strategy, respectively. After restoration and thermocycling, the samples were sectioned, and marginal gaps at the gingival margins were measured in micrometer (µm) under a stereomicroscope. Two-way analysis of variance (ANOVA) was used to compare marginal gaps between the groups and the subgroups. RESULTS: The mean marginal gap size was significantly affected by cavity disinfection (P=0.001) and bonding strategy (P=0.002). However, the interaction effect of these two factors on the mean marginal gap size was not significant (P=0.79). CONCLUSION: The use of CHX resulted in larger marginal gaps at the gingival margins of Class V composite resin restorations. Irrespective of disinfection, the self-etch bonding strategy resulted in larger marginal gaps compared to the etch-and-rinse bonding strategy.

Correction to: Comparison of the effect of bleaching with 15% carbamide peroxide and 35% hydrogen peroxide on flexural strength of Cention N in self-cured and dual-cured polymerization modes.

[This corrects the article DOI: 10.34172/joddd.2020.023.].

Effect of Different Fiber Reinforcement Strategies on the Fracture Strength of Composite Resin Restored Endodontically Treated Premolars

Objective: To compare the effect of three different fiber reinforcement strategies on the fracture strength of composite resin restored endodontically treated premolars. Material and Methods: Seventy-two sound human premolars extracted for orthodontic reasons were divided into 6 groups (n=12) after endodontic treatment. Group 1: intact teeth (positive control); Group 2: endodontically treated teeth without restoration (negative control); Group 3: composite resin restoration; Group 4: placement of fibers at occlusal position; Group 5: splinting the buccal and palatal walls with horizontal fiber posts; Group 6: placement of fibers at the occlusal position after splinting the buccal and palatal walls with horizontal fiber posts. Then fracture strength was measured at a crosshead speed of 0.5 mm/min in a universal testing machine. Data were analyzed using one-way ANOVA and post hoc Tukey tests at α=0.05. Results: There were significant differences between the negative and positive control groups (p<0.001) and between the negative control group and all the other study groups (p<0.001). However, there were no statistically significant differences between the positive control group and all the experimental groups and between the experimental groups (p>0.05). Conclusion: Fiber insertion had no additional reinforcing effect on the fracture strength following composite resin restoration.

The Effect of Photodynamic Therapy and Casein Phosphopeptide-Amorphous Calcium Phosphate (CPP-ACP) on the Remineralization Rate of Non-Cavitated Root: an In-vitro Study.

Using laser treatments and calcium and phosphate compounds to enhance remineralization has been investigated in this study. Seventy two premolar teeth were divided into four groups of 18: 1) control group; 2) laser therapy group; 3) CPP-ACP paste group; and 4) laser therapy and CPP-ACP group. Mineralization and remineralization of samples were investigated by Diagnodent. Data were reported using descriptive statistics (mean, standard deviation) and One Way ANOVA; they were analyzed using SPSS.16 statistical software. Statistical analysis showed that groups 3 and 4 had the highest rate of remineralization compared to groups 1 and 2. According to the results of this study, mineralization ranged decreasingly from group 4 to groups 3, 2, and 1, respectively. The antibacterial effect of laser therapy, leading to remineralization of calcium and phosphorus compounds, was the most effective on controlling root decay.

Effect of Relining with Different Composite Resins on the Push-out Bond Strength of Anatomical Fiber Posts to Root Canal Dentin.

Introduction: Relining fiber posts using composite resins helps the posts adapt to the anatomical space of the root canals. The aim of this study was to evaluate the effect of composite resin type on the push-out bond strength of anatomical fiber posts to intra canal dentin. Methods and Materials: Forty-eight bovine upper incisors were prepared for post space after root canal therapy and randomly divided in to six groups. Five different types of composite resin (GrandioSO, GrandioSO Heavy Flow, X-tra Fil, X-tra base and everX Posterior) were used for relining the prepared fiber posts. In the control group, the prepared post was cemented into the post space without relining. Cervical, middle and apical cross-sections were achieved from each root and push-out test was conducted at a crosshead speed of 0.5 mm/min. One sample from each group was scanned using a micro-CT scanner which provided views from the apical, middle and coronal thirds. Data were analyzed using Kolmogorov-Smirnov test, repeated measures ANOVA and post hoc tests using SPSS 17 (P<0.05). Results: Statistical analysis showed significant differences in terms of mean push-out bond strengths between different composite resin types and cross-sections (P<0.001). The mean push-out bond strength of the samples relined with Grandio SO composite resin (15.48±2.32) and X-tra Fil Bulk-fill composite resin (14.09±1.98) were significantly higher than that of other groups (P<0.05). The unrelined group had a mean push-out bond strength (5.94±1.45) which was significantly lower than that in other groups (P<0.05). In addition, there was a relationship between cross-sections and composite resin types (P<0.05). Conclusion: This in vitro study showed that the composite resins used for relining can affect the push-out bond strength to intra canal dentin based on their physical and mechanical properties.

Effect of surface preparation with Nd:YAG and Er,Cr:YSGG lasers on the repair bond strength of lithium disilicate glass ceramic to a silorane-based composite resin.

Background. This study was undertaken to evaluate the repair bond strength of lithium disilicate glass ceramic to a silorane-based composite resin after surface preparation with Nd:YAG and Er,Cr:YSGG lasers. Methods. A total of 102 lithium disilicate glass ceramic samples (IPS e.max Press), measuring 5 mm in diameter and 4 mm in thickness, were randomly assigned to 6 groups (n=17): group 1, no surface preparation (control); group 2, acid etching with 9.5% hydrofluoric acid (HF); group 3, surface preparation with 4.5-W Nd:YAG laser; group 4, surface preparation with 6-W Nd:YAG laser; group 5, surface preparation with 1.5-W Er,Cr:YSGG laser; and group 6, surface preparation with 6-W Er,Cr:YSGG laser. After preparation of surfaces and application of silane, all the samples were repaired with the use of a silorane-based composite resin, followed by storage in distilled water at a temperature of 37°C for 24 hours and thermocycling. Finally, the samples were subjected to a shearing bond strength test; the fracture modes were determined under a stereomi-croscope. Results. There were significant differences between the HF group and the other groups (P=0.000). Two-by-two comparisons of the other groups revealed no significant differences (P>0.05). Conclusion. Use of HF proved the most effective surface preparation technique to increase the repair bond strength between lithium disilicate glass ceramic and silorane-based composite resin; compared to the control group.

Effect of hemostatic agent on marginal gaps of class V giomer restorations.

BACKGROUND: Contamination of dentin with hemostatic agents might exert a deleterious effect on adhesive procedures on dentin. The present study was undertaken to investigate the effect of aluminum chloride hemostatic agent on marginal gaps in Cl V giomer restorations. MATERIAL AND METHODS: Fifty sound bovine permanent incisors were selected for the purpose of this in vitro study and Cl V cavities were prepared on their buccal surfaces; the gingival margins of the cavities were placed in dentin. The tooth samples were randomly assigned to two groups (n=25). The samples in groups 1 and 2 underwent a restorative procedure without and with the application of aluminum chloride hemostatic agent in the cavity, respectively, before application of the adhesive. BeautiBond one-step self-etch adhesive and Beautifil II giomer restorative material were used for the restoration of the cavities in both groups. The samples were thermocycled and sectioned, followed by measuring the gap sizes at gingival margins in µm under a stereomicroscope. The marginal gaps were compared with Mann-Whitney U test. Statistical significance was set at P<0.05. RESULTS: The results showed significant differences in the mean marginal gaps between the two groups under study (P<0.001); the mean marginal gaps were higher in group 2 (with hemostatic agent) compared to those in group 1 (without hemostatic agent) (P<0.0005). CONCLUSIONS: Contamination with aluminum chloride hemostatic agent in giomer restorations gave rise to higher gingival margin gaps. Key words:Dental adhesives, giomer restorative material, hemostatic agent, marginal adaptation.

Effect of an extra layer of hydrophobic resin on the microleakage of Cl V composite resin restorations with a universal adhesive system.

AIM: The aim of the present study was to evaluate the effect of the application of a hydrophobic resin on the microleakage of Cl V composite resin restorations using a universal adhesive system applied in the self-etch (SE) and etch-and-rinse (ER) modes. METHOD: Cl V cavities were prepared on the buccal surfaces of 64 human premolar teeth and divided into four groups (n = 16): ER, ER with hydrophobic resin (ERH), SE, and SE with hydrophobic resin (SEH). Microleakage at occlusal and gingival margins was evaluated using 0.5% methylene blue dye penetration technique under stereomicroscope at 40 × magnification. Data were analyzed using Kruskal-Wallis and Mann-Whitney U-tests (P < 0.05). RESULTS: At the enamel margins, the ER group had significantly less microleakage than the SE and SEH groups (P < 0.001), but had no significant difference compared with the ERH group (P > 0.05). There was also no statistically-significant difference between the SE and SEH groups (P > 0.05). At the dentinal margins, the SE group had significantly less microleakage compared with the ER (P < 0.001) and ERH groups (P = 0.005). Furthermore, microleakage of the SEH group was significantly less than the SE group (P < 0.001). CONCLUSION: Applying an extra layer of hydrophobic resin significantly decreased microleakage in the SE mode at the dentinal margin, but had no significant effect in the ER mode.

Effect of pre-heating on the mechanical properties of silorane-based and methacrylate-based composites.

BACKGROUND: The use of composites in dental restoration has been commonly criticized, due to their underwhelming mechanical properties. This problem may be solved partially by preheating. The present research aims to determine the effect of preheating on the mechanical properties of two different classes of composites. MATERIAL AND METHODS: A Silorane-based (Silorane) and a Methacrylate-based (Z250) composite were preheated to different temperatures (25, 37, and 68 °C) and afterwards were tested with the appropriate devices for each testing protocol. The material's flexural strength, elastic modulus, and Vickers microhardness were evaluated. Two-way ANOVA, and Tukey's post hoc were used to analyze the data. RESULTS: Microhardness and elastic modulus increased with preheating, while flexural strength values did not increase significantly with preheating. Furthermore the methacrylate-based composite (Z250) showed higher values compared to the Silorane-based composite (Silorane) in all the tested properties. CONCLUSIONS: Preheating Silorane enhances the composite's microhardness and elastic modulus but does not affect its flexural strength. On the other hand, preheating Z250 increases its microhardness but does not change its flexural strength or elastic modulus. In addition, the Z250 composite shows higher microhardness and flexural strength than Silorane, but the elastic modulus values with preheating are similar. Therefore Z250 seems to have better mechanical properties making it the better choice in a clinical situation. Key words:Composite, elastic modulus, flexural strength, microhardness, preheating.

Effect of different bleaching strategies on microhardness of a silorane-based composite resin.

Background. Dentists' awareness of the effects of bleaching agents on the surface and mechanical properties of restorative materials is of utmost importance. Therefore, this in vitro study was undertaken to investigate the effects of different bleaching strategies on the microhardness of a silorane-based composite resin. Methods. Eighty samples of a silorane-based composite resin (measuring 4 mm in diameter and 2 mm in thickness) were prepared within acrylic molds. The samples were polished and randomly assigned to 4 groups (n=20). Group 1 (controls) were stored in distilled water for 2 weeks. The samples in group 2 underwent a bleaching procedure with 15% carbamide peroxide for two weeks two hours daily. The samples in group 3 were bleached with 35% hydrogen peroxide twice 5 days apart for 30 minutes each time. The samples in group 4 underwent a bleaching procedure with light-activated 35% hydrogen peroxide under LED light once for 40 minutes. Then the microhardness of the samples was determined using Vickers method. Data were analyzed with one-way ANOVA and post hoc Tukey tests (P < 0.05). Results. All the bleaching agents significantly decreased microhardness compared to the control group (P < 0.05). In addition, there were significant differences in microhardness between groups 2 and 4 (P = 0.001) and between groups 3 and 4 (P<0.001). However, no significant differences were detected in microhardness between groups 2 and 3 (P > 0.05). Conclusion. Bleaching agents decreased microhardness of silorane-based composite resin restorations, the magnitude of which depending on the bleaching strategy used.

Shear Bond Strengths of Methacrylate- and Silorane-based Composite Resins to Feldspathic Porcelain using Different Adhesive Systems.

Background and aims. Use of porcelain as inlays, laminates and metal-ceramic and all-ceramic crowns is common in modern dentistry. The high cost of ceramic restorations, time limitations and difficulty of removing these restorations result in delays in replacing fractured restorations; therefore, their repair is indicated. The aim of the present study was to compare the shear bond strengths of two types of composite resins (methacrylate-based and silorane-based) to porcelain, using three adhesive types. Materials and methods. A total of 156 samples of feldspathic porcelain surfaces were prepared with air-abrasion and randomly divided into 6 groups (n=26). In groups 1-3, Z250 composite resin was used to repair porcelain samples with Ad-per Single Bond 2 (ASB), Clearfil SE Bond (CSB) and Silorane Adhesive (SA) as the bonding systems, afterapplication of silane, respectively. In groups 4-6, the same adhesives were used in the same manner with Filtek Silorane composite resin. Finally, the shear bond strengths of the samples were measured. Two-way ANOVA and post hoc Tukey tests were used to compare bond strengths between the groups with different adhesives at P<0.05. Results. There were significant differences in the mean bond strength values in terms of the adhesive type (P<0.001). In addition, the interactive effect of the adhesive type and composite resin type had no significant effect on bond strength (P=0.602). Conclusion. The results of the present study showed the highest repair bond strength values to porcelain with both composite resin types with the application of SA and ASB.

Effect of sodium ascorbate on the bond strength of all-in-one adhesive systems to NaOCl-treated dentin.

BACKGROUND: Ascorbic acid and its salts are low-toxicity products, which are routinely used in food industries as antioxidants. The aim of the present study was to evaluate the effect of 10% sodium ascorbate on the bond strength of two all-in-one adhesive systems to NaOCl-treated dentin. MATERIAL AND METHODS: After exposing the dentin on the facial surface of 90 sound human premolars and mounting in an acrylic resin mold, the exposed dentin surfaces were polished with 600-grit SiC paper under running water. Then the samples were randomly divided into 6 groups of 15. Groups 1 and 4 were the controls, in which no surface preparation was carried out. In groups 2 and 5 the dentin surfaces were treated with 5.25% NaOCl alone for 10 minutes and in groups 3 and 6 with 5.25% NaOCl for 10 minutes followed by 10% sodium ascorbate for 10 minutes. Then composite resin cylinders, measuring 2 mm in diameter and 2 mm in height, were bonded on the dentin surfaces in groups 1, 2 and 3 with Clearfil S3 Bond and in groups 4, 5 and 6 with Adper Easy One adhesive systems according to manufacturers' instructions. The samples were stored in distilled water for 24 hours at 37°C and then thermocycled. Finally, the samples underwent shear bond strength test in a universal testing machine at a strain rate of 1 mm/min. Data were analyzed with two-way ANOVA and post hoc Tukey tests at α=0.05. RESULTS: The differences between groups 1 and 2 (P=0.01), 1 and 5 (P=0.003). 1 and 6 (P=0.03) and 4 and 5 (P=0.03) were statistically significant. Two-by-two comparisons did not reveal any significant difference between other groups (P>0.05). CONCLUSIONS: Use of 10% sodium ascorbate for 10 minutes restored the decreased bond strength of the adhesive systems to that of the control groups. KEY WORDS: Sodium ascorbate, adhesive systems, all-in-one, bond strength, sodium hypochlorite.

Effect of an Extra Hydrophobic Resin Layer on Repair Shear Bond Strength of a Silorane-Based Composite Resin.

OBJECTIVES: Composite repair is a minimally invasive and conservative approach. This study aimed to evaluate the effect of an additional hydrophobic resin layer on the repair shear bond strength of a silorane-based composite repaired with silorane or methacrylate-based composite. MATERIALS AND METHODS: Sixty bar-shaped composite blocks were fabricated and stored in saline for 72 hours. The surface of the samples were roughened by diamond burs and etched with phosphoric acid; then, they were randomly divided into three groups according to the repairing process: Group 1: Silorane composite-silorane bonding agent-silorane composite; group 2: Silorane composite-silorane bonding agent-hydrophobic resin-silorane composite, and group 3: Silorane composite-silorane bonding agent-hydrophobic resin methacrylate-based composite. Repairing composite blocks measured 2.5×2.5×5mm. After repairing, the samples were stored in saline for 24 hours and thermocycled for 1500 cycles. The repair bond strength was measured at a strain rate of 1mm/min. Twenty additional cylindrical composite blocks (diameter: 2.5mm, height: 6mm) were also fabricated for measuring the cohesive strength of silorane-based composite. The data were analyzed using One-way ANOVA and the post hoc Tukey's test (α=0.05). RESULTS: Cohesive bond strength of silorane composite was significantly higher than the repair bond strengths in other groups (P<0.001). The repair bond strength of group 3 was significantly higher than that of group 1 (P=0.001). CONCLUSION: Application of an additional hydrophobic resin layer for repair of silorane-based composite with a methacrylate-based composite enhanced the repair shear bond strength.

Effect of different mechanical and chemical surface treatments on the repaired bond strength of an indirect composite resin.

This study compared the effects of two mechanical surface preparation techniques, air abrasion and Nd:YAG laser, with the use of two adhesive systems, self-etch and etch and rinse, on the repair bond strengths of an indirect composite resin. One hundred fifty cylindrical samples of an indirect composite resin were prepared and randomly divided into six groups (n = 25). In groups 1-3, the composite resin surfaces were respectively prepared as follows: no roughening, roughening by air abrasion, and roughening by Nd:YAG laser, followed by application of an etch-and-rinse adhesive. In groups 4-6, the preparation techniques were respectively the same as those in groups 1-3, followed by application of a self-etch adhesive. Subsequently, a direct composite resin was added and repair bond strengths were measured. Data were analyzed with two-way ANOVA and post hoc Tukey's test. Mean bond strength value was significant based on the preparation technique (P < 0.001), i.e., in air abrasion and Nd:YAG laser groups, bond strengths were significantly higher compared to no-preparation groups (P < 0.0005). There were significant differences in bond strength values between air abrasion and Nd:YAG laser groups, with significantly higher values in air abrasion groups (P < 0.0005). However, there were no significant differences in bond strength values between the adhesive systems. Furthermore, the cumulative effects of the adhesive system and the surface preparation technique were not significant. Surface preparation of the indirect composite resin with air abrasion and Nd:YAG laser resulted in a significant increase in the repair bond strength, with air abrasion being more effective. There were no significant differences in bond strength between the two adhesives.

Effect of Light Intensity on the Degree of Conversion of Dual-cured Resin Cement at Different Depths with the use of Translucent Fiber Posts.

OBJECTIVES: To evaluate the effect of different light intensities on the degree of conversion (DC) of dual-cured resin cement at different depths of translucent fiber posts. MATERIALS AND METHODS: Thirty translucent fiber posts were randomly assigned into three (n=10) groups. They were cemented in the simulated canal spaces using Duo-Link dual-cured resin cement. The cement was light-cured under 600, 800 and 1100 mW/cm(2) light intensities for 40 seconds. DC of the resin cement was calculated at cervical, middle and apical thirds using the spectra of FT-Raman spectrometer. Data were analyzed by repeated measurement ANOVA and Tukey's post hoc tests (α=0.05). RESULTS: In all the groups, the least DC was obtained at the apical region. There were no significant differences in the DC with different light intensities between the cervical and middle regions (p>0.05). However, in the apical region, the DC in both 800 and 1100 mw/cm(2) was similar (p>0.05), but greater with 600 mW/cm(2) light intensity (p=0.02 and p<0.001, respectively). CONCLUSION: In comparison with the light intensity of 600 mW/cm(2), the light intensity of 800 mW/cm(2) significantly increased the DC of dual-cured resin cement in the apical region. However, DC was not significantly different between 800 and 1100 mw/cm(2) light intensities. If the resin cement, especially in the apical areas is not sufficiently cured, microleakage might increase and post retention might be jeopardized. In comparison with 600 mW/cm(2) light intensity, 800 mW/cm(2) significantly increases DC at the apical third that might be clinically beneficial.

Effect of Surface Treatment with Er;Cr:YSSG, Nd:YAG, and CO2 Lasers on Repair Shear Bond Strength of a Silorane-based Composite Resin.

Background and aims. The aim of the present study was to compare the effect ofsurface treatment with Er; Cr:YSSG, Nd:YAG, and CO2 lasers on repair shear bond strength of a silorane-based composite resin. Materials and methods. Sixty eight cylindrical samples of a silorane-based composite resin (Filtek Silorane) were pre-pared and randomly divided into 4 groups as follows: group 1: without surface treatment; groups 2, 3 and 4 with surface treatments using Er; Cr:YSSG, Nd:YAG, and CO2 lasers, respectively. A positive control group (group 5) was assigned in order to measure cohesive strength. Repair shear bond strength values were measured and data was analyzed using one-way ANOVA and a post hoc Tukey test at a significance level of α=0.05. Results. There were statistically significant differences in repair shear bond strength values between group 2 and other groups (P < 0.05); and between group 1and groups 3and 4 (P < 0.001); however, there were no significant differences be-tween groups 3 and 4 (P = 0.91). Conclusion. The repair shear bond strength of silorane-based composite resin was acceptable by surface treatment with lasers.