An alternative adhesive strategy to optimize bonding to root dentin.

INTRODUCTION: This study examined the hypothesis that the shear-bond strengths of AH Plus (AH) and Hybrid Root Seal (HRS) to root dentin might be optimized by using a powdered dentin-reinforced bonding procedure. METHODS: The surfaces of root halves obtained from extracted human premolars were ground (800-grit silicon carbide paper), treated (5.25% NaOCl 17% EDTA for 5 minutes followed by distilled water) and randomly allocated into two groups according to the sealer and then into three subgroups according to bonding procedure. Dentin particles with a maximum size of 25 µm were incorporated into the adhesive of Clearfil Liner Bond 2V, and groups were created as follows: no adhesive, adhesive alone, and with powdered dentin reinforced adhesive; 3 × 3 mm high buildups were created using sealer and allowed to set (37 °C, 100% humidity, 72 hours). Shear tests were performed (1 mm/min). Data were calculated as MPa and analyzed (two-way analysis of variance, Tukey test). RESULTS: A significant difference was found between the groups (P = .000). Adhesive or reinforced adhesive had a negative effect on the shear-bond strength of AH, but they significantly increased the shear-bond strength of HRS (P = .000). HRS showed a similar bond strength with either adhesive alone or adhesive reinforced with powdered dentin. AH group was characterized by mixed failure, whereas the predominant failure type of the HRS group was cohesive failure within the sealer. CONCLUSIONS: Reinforcing adhesive resin with powdered dentin may be considered an alternative for optimizing the bonding of methacrylate-based sealers to root dentin and might affect the shear bond strength.

The effect of cavity shape and hybrid layer on the stress distribution of cervical composite restorations.

OBJECTIVES: The aim of this finite elemental stress analysis study was to evaluate the effect of cavity shape and hybrid layer on the stress distribution of the mandibular premolar tooth under occlusal loading. METHODS: The mandibular premolar tooth was selected as the model based on the anatomical measurements suggested by Wheeler. Four different mathematical models were evaluated: 1) a saucer-shaped non-carious cervical lesion restored with a composite without a hybrid layer, 2) a saucer-shaped non-carious cervical lesion restored with a composite with a hybrid layer, 3) a wedge-shaped non-carious cervical lesion restored with a composite without a hybrid layer, and 4) a wedge-shaped non-carious cervical lesion restored with a composite with a hybrid layer. A 200 N force was applied from the buccal tubercule and central fossa of the premolar tooth. The findings were drawn by the SAPLOT program. RESULTS: In models 2 and 4, the output showed that a hybrid layer acts as a stress absorber. Additionally, when the cavity shape was changed, the stress distribution was very different. CONCLUSIONS: Cavity shape and hybrid layer play an important role in stress distribution in cervical restorations.

Effect of hybrid layer and thickness on stress distribution of cervical wedge-shaped restorations.

OBJECTIVES: The aim of this finite elemental stress analysis study was to evaluate the effect of a hybrid layer and the hybrid layer thickness on the shear stress distribution in mandibular premolar teeth under occlusal loading. METHODS: The mandibular premolar tooth was selected based on the anatomical measurements suggested by Wheeler. The analysis was performed with a computer with the SAP 2000 structural analysis program. Three different mathematical models were evaluated; 1) composite restoration without a hybrid layer 2) composite restoration with a 1.5 mum thick hybrid layer and 3) composite restoration with a 3 mum thick hybrid layer. A total of 200 N of occlusal loading force was simulated from the buccal tubercule and central fossa of the premolar tooth. The findings were drawn by the Saplot program. RESULTS: In model B, the output showed that hybrid layer reduced the shear stress concentration especially on gingival margin of the composite. Similarly shear stress intensity was decreased by a thick hybrid layer in model C, especially on the gingival margin of the composite. CONCLUSIONS: The hybrid layer and its thickness plays an important role on stress distribution and intensity in cervical restorations.

Effect of multiple consecutive adhesive coatings on microleakage of class v cavities.

OBJECTIVES: The purpose of this in vitro study was to evaluate the effect of multiple consecutive adhesive coatings of a one-step self-etch adhesive on microleakage of Class V cavities. METHODS: Standardized box shaped Class V cavities were prepared onto the buccal side of forty five non-carious human premolar teeth. The teeth were randomly divided into three groups of fifteen teeth in each and restored as: Group I- one-step self-etch adhesive resin (Clearfil S3, Kuraray Co. Ltd., Osaka, Japan) was applied according to the manufacturer's instructions, Group II- two consecutive same one-step self-etch adhesive application was performed, and Group III- three consecutive same one-step self-etch adhesive application was performed. After the adhesive applications light curing unit was activated for 20 seconds and the cavities were restored with a composite resin. The restorations were finished with aluminum oxide discs and the specimens were stored in water at room temperature for 24 hours before they were immersed in 2% methylene blue for 48 hours. The dye penetration was examined under a stereomicroscope and the asymtotic significance were analysed with Kruskall Wallis and Mann Whitney U tests and dentin-enamel margins were compared with each other with Wilcoxon Signed Rank test. RESULTS: The microleakage at the dentinal margins of Class V cavities were significantly decreased with two (Group II) and three (Group III) consecutive adhesive applications (P<.05). There was no significant difference between Group I, Group II and Group III at the enamel margins (P<.05). The microleakage at the dentinal margins were significantly higher than the enamel margins in Group I and Group II but in Group III there was no statistically significant difference (P<.05). CONCLUSIONS: Within the limitations of this in vitro study, it may be concluded that three consecutive applications of the one-step self-etch adhesive resin provided better sealing than the one coat of adhesive resin at the dentinal margins of Class V cavities.

Effect of multiple consecutive applications of one-step self-etch adhesive on microtensile bond strength.

AIM: The aim of this study was to evaluate the effects of multiple consecutive coatings of a one-step self-etch adhesive system (Clearfil Tri-S Bond) on the microtensile bond strength (MBS) to dentin. METHODS AND MATERIALS: Nine caries-free human lower third molars were sectioned perpendicular to the long axis to expose the mid-coronal dentin. The teeth were separated into three experimental groups (n=3) according to the number of adhesive resin coats applied. In Group 1 one layer of Clearfil Tri-S Bond was applied according to the manufacturer's instructions. In Group 2 and Group 3 the adhesive was applied in two and three layers, respectively. In these two groups the first layer was applied according to the manufacturer's instructions but the second and third layers of adhesive were not light cured after application. After the placement of the composite, the teeth were sectioned to obtain approximately 1 mm2 beams for testing. Eighteen beams were prepared for each group using the 'non-trimming' method. The MBS values of all specimens were tested, and fracture modes were then determined using a stereomicroscope. RESULTS: The mean MBS values (in MPa) of Group 1 (one coat of the adhesive) was significantly lower (p=0.04) than those of Group 3 (three applied coats of the adhesive). There were no statistically significant differences between Groups 1 and 2 and Groups 2 and 3. CONCLUSION: Within the limitations of this in vitro study the application of multiple coats of a one-step self-etch adhesive may provide an increase in bond strength compared to the application of only one coat of adhesive. CLINICAL SIGNIFICANCE: Three consecutive coats of one-step self-etching adhesive application can improve MBS.

Effect of surface treatments and different adhesives on the hybrid layer thickness of non-carious cervical lesions.

This in vitro study observed and compared the resin and non-carious sclerotic dentin interfaces generated by three different adhesives and two different techniques, using a scanning electron microscope (SEM). Thirty-two human premolars, with buccal, non-carious cervical lesions, were used. The teeth were randomly divided into eight groups. Group 1: Sclerotic dentin was treated with Single Bond (3M). Group 2: After superficial sclerotic dentin was removed with a diamond bur (Diatech, Coltene), the dentin surfaces were treated with Single Bond. Group 3: Sclerotic dentin was treated with Clearfil SE Bond (Kuraray). Group 4: After superficial sclerotic dentin was removed with a diamond bur, Clearfil SE Bond was applied. Group 5: Sclerotic dentin was treated with Xeno III (Dentsply). Group 6: After superficial sclerotic dentin was removed with a bur, Xeno III was applied to the dentin surfaces. For Groups 7 and 8, after the superficial sclerotic dentin was removed with a diamond bur, Clearfil SE Bond, with an additional 37% phosphoric acid gel, was used on the sclerotic dentin surfaces in Group 7 and Xeno III was used in Group 8. In all groups, the cavities were restored with Filtek Supreme (3M). All the specimens were sectioned longitudinally and polished along the cut surface. The sections were treated with 37% orthophosphoric acid for five seconds, rinsed with water and treated with 5% NaOCL for 10 minutes. The specimens were then gold-sputter coated and evaluated under SEM. The thickness of the hybrid layer was measured on the gingival, occlusal and axial dentin interfaces. ANOVA was performed to determine whether there were any statistically significant differences in hybrid layer thickness. Post-hoc multiple comparisons were done with Tukey's test. Hybrid layer thickness was increased with all adhesives when superficial dentin was removed with a bur. Hybrid layer thickness showed significant differences between total-etch and self-etch systems.

The effect of occlusal loading on the microleakage of class V restorations.

OBJECTIVE: This in vitro study evaluated the microleakage of Class V cavities restored with a resin composite and different adhesive systems after occlusal loading. METHODS & MATERIALS: Standardized box-shaped Class V cavities were prepared on the buccal side of 135 non-carious human premolars. The teeth were randomly divided into three groups of 45 premolars each and restored as follows: Group 1-two-step total-etch adhesive (Single Bond, 3M) + resin composite (Supreme, 3M ESPE); Group 2-two-step self-etch adhesive (Clearfil SE, Kuraray) + resin composite and Group 3-one-step self-etch adhesive (Xeno III, Dentsply) + resin composite. The restorations were finished with aluminum oxide discs (Sof-Lex, 3M). Fifteen teeth in each group received 10,000 x 100 N and 250 N occlusal loads, respectively, and the remaining 15 teeth served as the control. The premolars were immersed in 2% methylene blue for 24 hours. The dye penetration was examined under a stereomicroscope, and the results were statistically analyzed by Kruskal Wallis, Mann-Whitney U and Wilcoxon Signed Rank tests to determine differences between the groups. RESULTS: Gingival margins showed more dye penetration than occlusal margins in all the tested groups (p<0.05). In all the tested adhesive systems, 100 N occlusal loading did not change dye penetration; however, Groups 1 and 2 exhibited better marginal sealing than Group 3 at the enamel margins under 250 N occlusal loading. CONCLUSION: Within the limitations of this in vitro study, it may be concluded that enamel margins provided better marginal sealing than dentin/cementum margins and the two-step self-etch adhesive exhibited better marginal sealing than an all-in-one adhesive at the enamel margins under 250 N occlusal loading.

The effect of different finishing and polishing systems on the surface roughness of different composite restorative materials.

AIM: The purpose of this in vitro study was to examine the effect of two different finishing systems on the surface roughness of different types of composite restorative materials. METHODS AND MATERIALS: Thirty specimens, 8 mm in diameter and 3 mm in depth, were prepared using a microfill composite (Clearfil ST, Kuraray Co. Ltd., Osaka, Japan), a hybrid composite (Clearfil AP-X, Kuraray Co. Ltd., Osaka, Japan), and a packable composite (Clearfil Photo Posterior, Kuraray Co. Ltd., Osaka, Japan) cured against a Mylar matrix strip to create a baseline surface. The average surface roughness was measured using a surface profilometer (Surftest 211, Mitutoyo, Japan) in five different positions on each sample before and after finishing with one of the two finishing systems [Sof-Lex discs (3M) and Po-Go (Dentsply)]. The obtained data were analyzed by two-way analysis of variance (ANOVA) at a p=0.05 significance level. RESULTS: There were statistically significant differences in the average surface roughness (Ra, microm) between the Mylar matrix strip, Sof-Lex discs, and Po-Go discs (p<0.05). For all tested materials, the Mylar matrix strip provided smoother surfaces than both of the finishing systems (p<0.05). When the finishing discs were compared, Sof-Lex discs produced a smoother surface than Po-Go discs for all tested materials (p<0.05). CONCLUSION: The Mylar matrix strip provided a smoother surface than Sof-Lex and Po-Go discs. Furthermore, Sof-Lex discs produced smoother surfaces than Po-Go discs. Sof-Lex and Po-Go systems produced clinically acceptable surface roughness for microfill, hybrid, and packable composite resin materials. The effect of finishing and polishing systems on surface roughness was dependent on both the system and the composite resin restorative material.