Effect of LED and Argon Laser on Degree of Conversion and Temperature Rise of Hybrid and Low Shrinkage Composite Resins.

OBJECTIVES: Different light curing units are used for polymerization of composite resins. The aim of this study was to evaluate the degree of conversion (DC) and temperature rise in hybrid and low shrinkage composite resins cured by LED and Argon Laser curing lights. MATERIALS AND METHODS: DC was measured using FTIR spectroscopy. For measuring temperature rise, composite resin samples were placed in Teflon molds and cured from the top. The thermocouple under samples recorded the temperature rise. After initial radiation and specimens reaching the ambient temperature, reirradiation was done and temperature was recorded again. Both temperature rise and DC data submitted to one-way ANOVA and Tukey-HSD tests (5% significance). RESULTS: The obtained results revealed that DC was not significantly different between the understudy composite resins or curing units. Low shrinkage composite resin showed a significantly higher temperature rise than hybrid composite resin. Argon laser caused the lowest temperature rise among the curing units. CONCLUSION: Energy density of light curing units was correlated with the DC. Type of composite resin and light curing unit had a significant effect on temperature rise due to polymerization and curing unit, respectively.

Effect of Mechanical Loads and Surface Roughness on Wear of Silorane and Methacrylate-Based Posterior Composites.

OBJECTIVES: Dental composite wear in posterior restorations is a concern and is affected by different factors. This study was conducted to evaluate the effect of polishing and mechanical loads on wear of silorane-based and methyl methacrylate-based composites resins. MATERIALS AND METHODS: Of each dental composite (Filtek P90 and Filtek P60), 40 samples were fabricated in a polyethylene mold (4mm diameter, 10mm height). According to the finishing and/or polishing protocols (180-grit or 2500-grit silicon carbide papers), the samples of each composite were divided into two groups. Surface roughness (R ә ) was measured and recorded using a contact profilometer. The weight of each sample was also measured in grams. The wear test was performed in a pin-on-disc device under two different loads (70N, 150N). Afterwards, samples were subjected to profilometry and their weight was measured again. Data were analyzed using t-test and univariate ANOVA. P <0.05 was considered statistically significant. RESULTS: Higher mechanical load resulted in greater weight loss (P<0.001). Samples polished with 2500-grit papers showed significantly lower Ra changes compared to those polished with 180-grit papers (P<0.001). Filtek P90 had greater weight loss than Filtek P60 except in one condition (180-grit, 70N). CONCLUSIONS: Results showed that wear of posterior composite restorations depends on mechanical load, type of composite resin and surface properties.

Comparison of Dentin Permeability After Tooth Cavity Preparation with Diamond Bur and Er:YAG Laser.

OBJECTIVES: The aim of this study was to compare the permeability of dentin after using diamond bur and Er:YAG laser. MATERIALS AND METHODS: Seventy-two recently extracted, intact, and restoration-free human permanent molars were used in this study. The samples were randomly divided into three groups of 24 each and class I cavities were prepared as follows. Group 1: High speed diamond bur with air and water spray. Group 2: Er:YAG laser. Group 3: Er:YAG laser followed by additional sub-ablative laser treatment. Each group consisted of two subgroups with different cavity depths of 2mm and 4mm. The entire cavity floor was in dentin. Two samples from each subgroup were observed under scanning electron microscope (SEM). The external surfaces of other samples were covered with nail varnish (except the prepared cavity) and immersed in 0.5% methylene blue solution for 48 hours. After irrigation of samples with water, they were sectioned in bucco-lingual direction. Then, the samples were evaluated under a stereomicroscope at ×160 magnification. The data were analyzed using two-way ANOVA and Tukey's HSD test. RESULTS: Two-way ANOVA showed significant difference in permeability between groups 2 and 3 (laser groups with and without further treatment) and group 1 (bur group). The highest permeability was seen in the group 1. There was no significant difference in dentin permeability between groups 2 and 3 and no significant difference was observed between different depths (2mm and 4mm). CONCLUSION: Cavities prepared by laser have less dentin permeability than cavities prepared by diamond bur.

Monomer release from nanofilled and microhybrid dental composites after bleaching.

OBJECTIVE: The aim of this study was to assess the effect of bleaching on elution of monomers from nanofilled and microhybrid composites. MATERIALS AND METHODS: 80 samples (5mm diameter and 3mm thickness) of each composite were prepared. After curing, half of them were randomly polished. Each group was divided into 8 subgroups and immersed in water or 10%, 20% and 30% H2O2 for 3 or 8 hours. Eluted Bis-GMA (Bis-phenol A Glycidyl Dimethacrylate), TEGDMA (Triethyleneglycol Dimethacrylate), UDMA (Urethane Dimethacrylate) and BisEMA (Bis-phenol A ethoxylate Dimethacrylate) were quantified by high performance liquid chromatography and the results were analyzed by univariate ANOVA and t-test (P<0.05). RESULTS: Bleach significantly increased the overall release of monomers (P<0.001); TEGDMA was released more than Bis-GMA (P<0.001). Supreme released more TEGDMA compared to Z250 (P<0.001). Bleaching increased the release of this monomer (P<0.001). Increasing both the concentration of H2O2, and the immersion time, increased the release of TEGDMA (P<0.001). Polishing had no effect on release of this monomer (P=0.952). Supreme released more Bis-GMA than Z250 (P=0.000). The more concentrated H2O2 caused more elution of Bis-GMA (P= 0.003); while the effect of immersion time was not significant (P=0.824). Polishing increased the release of Bis-GMA (P=0.001). Neither the type of composite nor Bleaching had any effect on release of UDMA (P=0.972) and (P=0.811) respectively. Immersion duration increased the release of UDMA (P=0.002), as well as polishing (P=0.024). CONCLUSION: Bleaching increased the release of monomers. Nanofilled composites released more monomer than the microfilled.

Effects of different lasers and particle abrasion on surface characteristics of zirconia ceramics.

OBJECTIVE: The aim of this study was to assess the surface of yttrium-stabilized tetragonal zirconia (Y-TZP) after surface treatment with lasers and airborne-particle abrasion. MATERIALS AND METHODS: First, 77 samples of presintered zirconia blocks measuring 10 × 10 × 2 mm were made, sintered and polished. Then, they were randomly divided into 11 groups (n=7) and received surface treatments namely, Er:YAG laser irradiation with output power of 1.5, 2 and 2.5 W, Nd:YAG laser with output power of 1.5, 2 and 2.5 W, CO2 laser with output power of 3, 4 and 5 W, AL2O3 airborne-particle abrasion (50µ) and no treatment (controls). Following treatment, the parameters of surface roughness such as Ra, Rku and Rsk were evaluated using a digital profilometer and surface examination was done by SEM. RESULTS: According to ANOVA and Tukey's test, the mean surface roughness (Ra) after Nd:YAG laser irradiation at 2 and 2.5 W was significantly higher than other groups. Roughness increased with increasing output power of Nd:YAG and CO2 lasers. Treated surfaces by Er:YAG laser and air abrasion showed similar surface roughness. SEM micrographs showed small microcracks in specimens irradiated with Nd:YAG and CO2 lasers. CONCLUSION: Nd:YAG laser created a rough surface on the zirconia ceramic with many microcracks; therefore, its use is not recommended. Air abrasion method can be used with Er:YAG laser irradiation for the treatment of zirconia ceramic.

Assessing microleakage of composite restorations in class V cavities prepared by Er:YAG laser irradiation or diamond bur.

INTRODUCTION: The aim of this study was to make a comparison between microleakage of conventionally restored class V cavities using bur and acid etchant and, the ones prepared and conditioned by Er:YAG laser. MATERIALS AND METHODS: 30 recently extracted intact caries and filling free human permanent molars were used for this study. Then, Cold cure acrylic resin was used to seal the apices. The samples were randomly assigned to 5 groups of six each. Class V cavities were prepared one on buccal and one on lingual surface of each sample. Group 1: cavity preparation by diamond bur and turbine + acid etch, Group 2: cavity preparation by Er:YAG laser + acid etch, Group 3: cavity preparation by Er:YAG laser + Laser etching, Group 4: cavity preparation by diamond bur and turbine + laser etching, Group 5: cavity preparation by Er:YAG laser with no conditioning procedure. The cavities restored with restorative composite resin. Samples were then immersed in 2% methylene blue solution for 24 hours. The data were then analyzed using Wilcoxon signed ranks test and Kruskal-Wallis statistical tests. RESULTS: The Kruskal Wallis test showed a significant difference (P < 0.05) between enamel and cementum margin microleakage, while the higher microleakage was related to the cementum margin of restorations. CONCLUSION: There was no significant difference in evaluating microleakeage degree of cavities prepared by Er:YAG laser and diamond bur.

Enamel thickness after preparation of tooth for porcelain laminate.

OBJECTIVE: In this investigation the thickness of enamel in the gingival, middle, and incisal thirds of the labial surface of the anterior teeth were measured regarding preparation of the teeth for porcelain laminate veneers. MATERIALS AND METHODS: Part one, 20 extracted intact human maxillary central and lateral incisors ten of each were selected. The teeth were imbedded in autopolimerize acrylic resin. Cross section was preformed through the midline of the incisal, middle and cervical one-third of the labial surface of the teeth. The samples were observed under reflected stereomicroscope and the thickness of enamel was recorded. Part II, the effect of different types of preparation on dentin exposure was evaluated. Thirty maxillary central incisor teeth were randomly divided into two groups: A: Knife-edge preparation. B: Chamfer preparation. All samples were embedded in autopolimerize acrylic resin using a silicon mold. The samples were cut through the midline of the teeth. The surface of the samples were polished and enamel and dentin were observed under the stereomicroscope. RESULTS: Data were analyzed by ANOVA-one way test. The results of this study showed that the least enamel thickness in the central incisor was 345 and in lateral incisor is 235 µ this thickness is related to the one-third labial cervical area. Maximum thickness in maxillary central and lateral incisors in the one-third labial incisal surface was 1260 µ and 1220µ, respectively. In the second part of the study, the tendency of dentinal exposure was shown with the chamfer preparation, but no dentinal exposure was found in the knife-edge preparation. The differences between groups were significant (p<0.05). CONCLUSION: The knowledge of enamel thickness in different part of labial surface is very important. The thickness of enamel in the gingival area does not permit a chamfer preparation. The knife edge preparation is preferable in gingival area.

Shear bond strength of the repair composite resin to zirconia ceramic by different surface treatment.

INTRODUCTION: The purpose of this study is the evaluation of the amount of surface roughness (Ra) of Zirconia Ceramic following different surface treatments as well as the assessment of its shear bond strength to composite resin. METHODS: 40 sintered zirconia ceramic block samples were randomly divided in 4 groups of 10 and underwent the following surface treatments: a) Control group without treatment b) Air abrasion with Al2O3 particles (50um) c) Er:YAG laser with 2W power for 10s d) Nd:YAG laser with 1.5W power for 2min Then the mean surface roughness (Ra) was evaluated by profilometer. In the next step, Alloy primer was used on a section of 9mm(2) on the samples following the manufacturer's instructions. After that Clearfil AP-X composite resin in cylinder shape with an internal diameter and height of 3mm were cured on the sections mentioned. At the end, all samples were tested to assess the shear bond strength by the Universal Testing Machine at a speed of 0.5mm/min until fracture occurred. The mean shear bond strengths were calculated and statistically analyzed by One Way ANOVA. RESULTS: ANOVA analysis showed that roughness (Ra) was significantly different between the groups (P≤0.05). Ra was higher in the Nd:YAG group compared to the other groups (P≤0.05). The lower Ra was related to the control group. Air abrasion group showed highest amounts of shear bond strength and Nd:YAG laser group demonstrated lower amounts of shear bond strength (P≤0.05). CONCLUSION: Various surface treatments are differently effective on bond strength. Air abrasion is the most effective method to condition zirconia ceramic surfaces.

Bond strength of resin cements to noble and base metal alloys with different surface treatments.

OBJECTIVES: The bond strength of resin cements to metal alloys depends on the type of the metal, conditioning methods and the adhesive resins used. The purpose of this study was to evaluate the bond strength of resin cements to base and noble metal alloys after sand blasting or application of silano-pen. MATERIALS AND METHOD: Cylinders of light cured Z 250 composite were cemented to "Degubond 4" (Au Pd) and "Verabond" (Ni Cr) alloys by either RelyX Unicem or Panavia F2, after sandblasting or treating the alloys with Silano-Pen. The shear bond strengths were evaluated. Data were analyzed by three-way ANOVA and t tests at a significance level of P<0.05. RESULTS: When the alloys were treated by Silano-Pen, RelyX Unicem showed a higher bond strength for Degubond 4 (P=0.021) and Verabond (P< 0.001). No significant difference was observed in the bond strength of Panavia F2 to the alloys after either of surface treatments, Degubond 4 (P=0.291) and Verabond (P=0.899). Panavia F2 showed a higher bond strength to sandblasted Verabond compared to RelyX Unicem (P=0.003). The bond strength of RelyX Unicem was significantly higher to Silano-Pen treated Verabond (P=0.011). The bond strength of the cements to sandblasted Degubond 4 showed no significant difference (P=0.59). RelyX Unicem had a higher bond strength to Silano-Pen treated Degubond 4 (P=0.035). CONCLUSION: The bond strength of resin cements to Verabond alloy was significantly higher than Degubond 4. RelyX Unicem had a higher bond strength to Silano-Pen treated alloys. Surface treatments of the alloys did not affect the bond strength of Panavia F2.

Antioxidant effect on the shear bond strength of composite to bleached bovine dentin

Several studies have shown that compromised bonding to bleached enamel can be reversed with antioxidants. Aim: The aim of this study was investigate the effect of the antioxidant treatment on themicro-shear bond strength of a composite resin with a clinically acceptable antioxidant usage timetaken into account. Methods: Using in vitro techniques, the effect of the antioxidant sodiumascorbate (SA) was evaluated on the micro-shear bond strength of a hybrid composite resin(Tetric® A2 Ivoclar Vivadent) to dentin, which was bleached with 35% carbamide peroxide(Opalescence Quick, Ultradent Products Inc). Thirty-five intact flat buccal dentin surfaces frombovine incisors were randomly assigned to five groups which were subjected to the following treatment protocols: group 1, bleached for 45 min and bonded immediately afterwards; groups 2and 3, bleached and then treated with 10% SA for 10 and 5 min before bonding, respectively; group 4, stored in distilled water for seven days after bleaching and before bonding; group 5,received no bleaching or antioxidant treatment. After the bonding procedure, specimens were subjected to a micro-shear bonding test. Data were analyzed by ANOVA and a post-hoc Tukey’stest. Results: One-way ANOVA revealed significant differences in bond strength among the five groups. Conclusions: It was found that the shear bond strength was reduced by carbamide peroxide bleaching, and that the antioxidant SA was ineffective at reversing the composite strength at the concentrations and treatment times examined.