In Vitro Tensile Bond Strengths of Amalgam to Treated Dentin

Since amalgam traditionally relies on undercuts in the tooth preparation for retention, extensive tooth structure must be removed for amalgam core build-ups. In contrast, the ideal build-up material would achieve its retention by directly bonding to tooth structure. This study compared tensile bond strengths of amalgam to dentin using All-Bond Liner-FX with three different dentin pretreatment conditions and Amalgambond according to the manufacturer's directions. One hundred and twenty dentin samples were tested. Groups 1-3 used All-Bond Liner-FX as a bonding agent. Group 1 received a 15-second application of 10 percent phosphoric acid on the dentin; Group 2 received the recommended dentin conditioner; and Group 3 received no dentin pretreatment. Group 4 used Amalgambond as the bonding agent after a 10-second application of 10 percent citric acid/3 percent ferric chloride. Analysis of the data was conducted using both ANOVA and the Welbull statistic. Results of the analysis of variance Indicate that there were no statistical differences among mean tensile bond strengths for the three dentin pretreatment conditions using All-Bond. All (30) of the Amalgambond specimens debonded prior to testing. The All-Bond fracture data was well described by the Welbull function as evidenced by the high coefficient of determination (R²= 0.98 −0.99). Fracture analysis indicated that all of the Amalgambond failures were adhesive at the Amalgambond-amalgam interface. All-Bond fractures were mixed cohesive/adhesive failures indicating similar bonding to amalgam and dentin.     

Shear Bond Strengths of Resin Adhesive Cements to Dentin and Ni-Cr-Be Alloy

Two adhesives, Super Bond and Panavia, were evaluated for shear bond strength to dentin. Twenty human teeth were used for each adhesive. Bonding sites were prepared in dentin (600 grit) and the adhesives applied according to the manufacturers'instructions. Bond strengths were determined with an Instron testing machine at 24 hours. Super Bond developed the strongest bond of 21.59 ± 3.91 MPa. Panavia produced a lower bond strength of 2.68 ± 1.45 MPa. Statistically, Super Bond was found to have a stronger bond than Panavia. The same two adhesives were applied to Ni-Cr-Be specimens and compared to Comspan. Twenty Rexillium III specimens were used for each adhesive at 24 hours and 20 for thermocycling. The metal specimens were ground flat (600 grit) and then air abraded with 50-micron aluminous oxide. The adhesives were applied to the metal surface in accordance with the manufacturers'instructions. One group was tested at 24 hours while the second group was tested after thermocycling (2,500 cycles at 6°C to 60°C). At 24 hours, Super Bond had a significantly stronger bond than the other materials. Comparison of the 24-hour to thermocycled bond strengths found Comspan had a significant increase in bond strength, Panavia had no significant change and Super Bond had a significant decrease in bond strength. After 2,500 thermocycles, Comspan, Panavia, and Super Bond were not significantly different in bond strength.     

Shear Bond Strengths of Two Composite Core Materials After Using All-in-One and Single-Bottle Dentin Adhesives

PURPOSE: The purpose of this study was to compare the shear bond strengths of 2 composite core materials after using all-in-one and single-bottle dentin bonding materials. MATERIAL AND METHODS: The occlusal surfaces of 100 extracted, intact human third molars were ground to expose a flattened area of dentin and polished with 600-grit silicon carbide paper. Specimens were divided into 5 main groups (n= 20). Three all-in-one (AQ Bond, One-Up Bond, Xeno-CF Bond) and 2 single-bottle adhesives (Single Bond, One-Step Plus) were used. Each group was further divided into 2 subgroups. Ti-Core and Built-it F.R. core materials were applied using a translucent plastic ring (diameter: 3 mm, height: 5 mm). After storage in 37 degrees C water for 24 hours, shear bond strengths were measured using a Universal testing machine with a crosshead speed of 0.5 mm/min. Debonded dentin surfaces were examined with SEM. Two-way analysis of variance (ANOVA) and multiple comparison (Tukey) tests were used for statistical analysis of data. RESULTS: Two-way ANOVA revealed that the type of core material did not significantly influence the shear bond strength (p > 0.05), whereas there were significant differences in shear bond strength among the types of bonding agents (p < 0.0001). Shear bond strengths for single-bottle adhesive systems were significantly higher than those for all-in-one adhesive systems (p < 0.05). Furthermore, the interaction of these 2 parameters was not significant (p > 0.05). The fracture modes were predominantly adhesive for all-in-one adhesives and cohesive for single-bottle adhesives. CONCLUSION: Bonding of composite core materials with the newly developed all-in-one dentin adhesives produced lower shear bond strengths as compared with single-bottle adhesives.     

四种粘接系统的微拉伸粘接强度

目的 评价四种粘接系统的微拉伸粘接强度（SingleBond;Bond-1;Prime＆Bond　NT;One-Step）。方法 新鲜拔除的无龋坏人磨牙（拔除1个月以内,贮存于37℃生理盐水中）,高速涡轮机金钢砂车针在喷水降温下磨切咬合面,暴露牙本质。分别用四种粘接剂按使用说明进行粘接处理。牙齿贮存于37℃生理盐水24h后,制备成沙漏状试件。粘接界面面积控制在1mm2左右。测试其拉伸强度,并作统计学处理。结果 四种粘接系统的微拉伸强度分别为:（25.80±2.41）MPa（SingleBond）;（29.92±3.04）MPa（Bond-1）;（28.97±2.73）MPa（Prime＆BondNT）;（30.03±2.96）MPa（One-Step）。结论 微拉伸方法测得的粘接强度明显高于传统较大粘接面积时的测试值。更为客观、真实地反应了各粘接系统的粘接强度。     

Shear Bond Strengths of One-Bottle Adhesives to Oil-Contaminated Enamel

Purpose: To evaluate resin bond strength to enamel contaminated with handpiece oil. Materials and Methods: Bovine teeth were randomly assigned to six groups of 20 teeth each for treatment with one of six different bonding systems (five one‐bottle and one multibottle). For each system, 10 enamel specimens were contaminated with handpiece oil before acid‐etching and 10 were contaminated after acid‐etching. The enamel was etched for 15 seconds using 35% phosphoric acid. Following adhesive application, composite resin was bonded using a gelatin capsule technique. Shear bond strengths from the two contaminated groups were compared to bond strengths to uncontaminated enamel obtained from a previous study that was performed by the same group of investigators, using the same facility, materials, and methods. Results: Two‐way analysis of variance (ANOVA) showed that the factor “surface contamination” did not have a significant effect on bond strength (p > .542). The type of adhesive and the interaction of adhesive and surface contamination were significant (p <.0001 and p <.003, respectively). When oil was applied before etching, mean bond strengths ranged from 18.0 ± 4.8 MPa for OptiBond SOLO (Kerr Corp., Orange, California) to 25.3 ± 5.6 MPa for Tenure Quik with Fluoride (Den‐Mat Corp., Santa Maria, California). With oil applied after etching, bond strengths ranged from 18.4 ± 8.0 MPa for Tenure Quik with Fluoride to 27.4 ± 5.4 MPa for Single Bond (3M Dental Products, St. Paul, Minnesota). For the same adhesive, comparing uncontaminated and “oil‐before‐etch” contaminated groups, the only statistically significant difference in bond strengths was for OptiBond SOLO: 21.8 ± 4.0 MPa (uncontaminated) versus 18.0 ± 4.8 MPa (oil before etch). Comparing uncontaminated and “oil‐after‐etch” groups, the only statistically significant difference was for Tenure: 24.5 ± 5.7 MPa (uncontaminated) and 18.4 ± 8.0 MPa (oil after etch). CLINICAL SIGNIFICANCE Surface contamination with handpiece lubricant oil does not impair appreciably the efficacy of the adhesives used in this study when bonding composite resin to enamel.     

Shear Bond Strengths of One-Bottle Adhesives to Moist Enamel

Abstract: Purpose: This study evaluated bond strengths of six one-bottle bonding agents and a control (primer plus unfilled resin) to moist enamel.
Materials and Methods: One-hundred and five bovine teeth were randomly assigned to seven groups of 15. Enamel was etched for 15 seconds with 35% phosphoric acid. Etched enamel was rinsed, and excess water was blotted with tissue paper. Following application of the adhesive, composite resin was bonded using a gelatin capsule technique. Shear bond strengths to enamel were determined using a universal testing machine (Instron Corp., Canton, Massachusetts).
Results: Mean bond strengths ranged from 21.9 MPa for OptiBond Solo (Kerr Corp., Orange, California) to 29.6 MPa for Prime & Bond 2.1 (Dentsply/Caulk, Milford, Delaware). Prime & Bond 2.1 had a significantly higher mean bond strength than the other adhesives.
CLINICAL SIGNIFICANCE: The results of this study suggest that all of the one-bottle systems tested should provide clinically acceptable bonding to moist enamel.     

Effects of Different Re-Wetting Techniques on Dentin Shear Bond Strengths

Purpose: For contemporary hydrophilic resin adhesive systems, bonding to dentin is improved if the substrate is maintained in a hydrated state following acid‐etching. The purpose of this study was to compare the dentin shear bond strengths of two single‐bottle adhesives (one acetone‐based and one ethanol‐based) applied under different etched‐dentin conditions: dry, wet, or dry and re‐wetted with different solutions. Materials and Methods: Bovine incisors (N = 120) were mounted in acrylic, polished to 600‐grit, and randomly assigned to 12 groups (n = 10). Dentin was etched for 15 seconds using 35% phosphoric acid, rinsed, and either blot‐dried, air‐dried, or air‐dried and re‐wetted with different solutions (distilled water, Gluma Desensitizer, Aqua‐Prep, and 5% glutaraldehyde in water). Two adhesives (Single Bond and Prime & Bond NT) were applied to each of the surface conditions following manufacturers' instructions. After adhesive application and curing, composite was applied in a No. 5 gelatin capsule and light‐cured. Specimens were loaded in shear, using an Instron at 5 mm per minute. Shear bond strengths were calculated by dividing the failure load by the bonded surface area. Data were subjected to analysis of variance (ANOVA) and a post hoc Tukey test. Results: Mean shear bond strengths ranged from 12.5 to 26.6 MPa for Single Bond and from 5.6 to 14.7 MPa for Prime & Bond NT. Significant differences were found in both groups of materials (p < .001). The three highest mean bond strengths were obtained (in order) on dentin that was re‐wetted with Gluma Desensitizer, re‐wetted with Aqua‐Prep, or never dried. Differences between these surface conditions were not statistically significant for either material. CLINICAL SIGNIFICANCE Different dentin surface conditions and re‐wetting techniques affected bond strengths for adhesives studied. Aqua‐Prep and Gluma Desensitizer can be successfully used as re‐wetting agents. The use of a re‐wetting agent may be beneficial when dentin is dried after acid‐etching and rinsing.     

Microtensile Bond Strength of Nonmetallic Dowels Bonded to Radicular Dentin with Self-Etch Adhesives

Purpose: The bonding potential of nonmetallic dowels to root dentin, particularly with new self-etch adhesives, has not been fully investigated. The aim of this study was to determine microtensile bond strength (μTBS) of nonmetallic dowels, including a novel glass fiber dowel, when bonded to radicular dentin with self-etch adhesives.
Materials and Methods: Crowns of extracted anterior teeth were severed, and endodontic treatment was performed. Teeth were divided into six groups according to dowel/adhesive. Teeth received dowels as follows: group I: Light Post + Clearfil-SE Bond/Panavia-F (SE/PF), group II: Light Post + Xeno III/Panavia-F (XN/PF), group III: ParaPost Fiber White + SE/PF, group IV: ParaPost Fiber White + XN/PF, group V: everStick Post + SE/PF, and group VI: everStick Post + XN/PF. Teeth were sectioned to produce 1 mm specimens from both cervical and middle thirds with the dowel at the center. Specimens were tested in a special machine, and μTBS values were determined.
Results: Mean μTBS values and SDs in MPa for the cervical region were as follows: group I: 10.36 (1.88), group II: 8.51 (1.41), group III: 11.61 (1.06), group IV: 9.37 (1.61), group V: 14.22 (1.16), and group VI: 12.97 (1.69). Group V had the highest mean value—significantly higher than the means of groups I, II, III, and IV ( p < 0.0001 to p < 0.02). For the middle region: group I, 9.72 (1.61); group II, 7.62 (1.42); group III, 10.28 (0.75); group IV, 8.48 (1.51); group V, 13.23 (1.06); group VI, 11.07 (1.49). Group V also had highest mean value—significantly higher than the means of groups I, II, III, and IV ( p < 0.0001 to p < 0.004).
Conclusions: everStick glass fiber dowel, bonded with either adhesive, showed the highest μTBS. Microtensile bond strengths were not significantly different with cervical root dentin than with middle root dentin.     

4种牙本质粘结剂剪切强度的实验研究

目的：通过4种牙本质粘结剂剪切强度的比较及粘结界面的超微结构的差异,评价并指导其临床使用。方法：选用新鲜的离体前磨牙40颗,分成4组暴露牙本质面。选用全酸蚀的粘结剂：PB（Prime ＆ bond NT）,自酸蚀的粘结剂：XN（XenoⅢ）、IB（IBond）、AP（Adper^TMPrompt^TM）,按照说明书的要求和步骤分别使用后充填复合树脂Z250,制备成4mm×3mm的圆柱型试件。所有的样本通过Instron测试剪切强度,用SPSS11.5对剪切强度测试值进行统计学分析。利用SEM观察粘结界面的超微结构。结果：方差分析显示材料AP的剪切强度最低且较材料PB差异在统计学上有显著性意义（P〈0.05）,材料PB、XN、IB的剪切强度差异上无统计学意义。SEM镜下,材料PB、XN、IB均可见有明显的树脂层、混合层、树脂突。结论：新一代的粘结剂XenoⅢ和IBond可应用于临床。     

Enterococcus faecalis Hydrolyzes Dental Resin Composites and Adhesives

Introduction

After root canal treatment, the dentin-sealer interface undergoes degradation, allowing for interfacial microbial biofilm proliferation and treatment failure. Saliva and cariogenic bacteria showed esterase-like activities (ie, cholesterol esterase [CE]-like and/or pseudocholinesterase [PCE]-like) that degrade methacrylate-based resin materials and/or the restoration-tooth interface, increasing microbial interfacial proliferation. Enterococcus faecalis is a gram-positive bacterium that is commonly detected in persistent endodontic infections. The aim of this study was to measure E. faecalis esterase-like, CE-like, and PCE-like activities and to assess the ability of the bacterium to degrade methacrylate-based resin composite (RC) and total-etch (TE) and self-etch (SE) adhesives.

Properties of Packable Dental Composites

The introduction of many new packable composites suggests that these products are rapidly gaining popularity. The purpose of this study was to evaluate the in vitro properties of a variety of packable composites and to determine if significant enhancements in physical and mechanical properties have been achieved for these materials compared with two popular nonpackable posterior composites. For the five packable and two regular composites tested (ALERT, Pyramid-Dentin, Pyramid-Enamel, Solitaire, SureFil, Heliomolar, and Z100), the values for fracture toughness, flexure strength, flexure modulus, hardness, and volumetric polymerization shrinkage were determined. In general, although the packable composites were of heavier consistency, they had mechanical properties that were intermediate to (ALERT, Pyramid, and SureFil) or lower than (Solitaire) those of the nonpackable materials. These results could have been predicted based on the similar meth-acrylate resin chemistry and filler volumes of the various composites. No composite had adequate depth-of-cure when tested in increments greater than 2 mm thick. Polymerization contraction of the packable composites was similar to or higher than that of the nonpackable composites. In addition, the radiopacity of at least one material, Solitaire, was not considered to be adequate (less than 2 mm of aluminum). The results of this study suggest that these packable composites are unlikely to offer improved clinical performance over well-placed nonpackable composites.
CLINICAL SIGNIFICANCE
Packable composites have physical and mechanical properties that are similar to those of nonpackable posterior composites and are, therefore, expected to provide equivalent clinical performance.     

不同金瓷面积比对瓷修补树脂粘结强度的影响

目的:比较树脂与不同比例金属暴露的瓷面的粘结剪切强度.方法:按常规烤瓷方法分别制作总面积8 mm×8 mm,金瓷比例分别为1:3(组1),1:1(组2),3:1(组3),8:0(组4,作为对照)的试样各10个,瓷厚度为1 mm,金瓷结合处为钝角,以避免内应力的产生,将各组试样表面按照瓷修补套装的产品说明书处理各试样的1/2的面积,粘结8 mm×4 mm×2 mm的树脂材料.用Instron力学测试仪,进行剪切强度测试.结果:组1,组2的剪切强度显著性高于组3,组4.结论:使用Ultradent修补套装对部分金属暴露的崩瓷进行修补时,金瓷面积比<1时的粘结力明显较大,修补效果较好.     

EDTA预处理硬化牙本质对树脂粘结强度的影响

目的：采用微拉伸试验比较EDTA（Ethylene Diamine Tetraacetie Acid,乙二胺四乙酸）预处理硬化牙本质前后的离体牙树脂粘结强度。方法：选择24颗具有典型楔状缺损的离体牙,12颗离体牙的楔状缺损处为Ⅲ级以上硬化牙本质,其余12颗为正常牙本质。以平分楔状缺损为标准对离体牙进行纵剖,随机分为硬化牙本质对照组A与实验组B;正常牙本质对照组C与实验组D。实验组均使用EDTA（Glyde File Prep EDTA）预处理牙本质表面,再行自酸蚀树脂粘结。测定4组样本的微拉伸粘结强度。结果：微拉伸实验显示测得A、B、C、D,4组样本的微拉伸强度分别为（9.49±2.23）MPa、（10.50±2.16）MPa、（10.89±4.76）MPa、（10.99±5.21）MPa。实验组B的粘结强度显著高于对照组A,有统计学意义（P〈0.05）;而实验组D的粘结强度略高于对照组C,但无统计学意义。结论：利用EDTA预处理能提高硬化牙本质的自酸蚀树脂粘结强度,但对正常牙本质无明显作用。     

The Effect of Endodontic Irrigants on the Microtensile Bond Strength of Dentin Adhesives

IntroductionThe purpose of this study was to evaluate the microtensile bond strength of a total etch (XP-Bond) and a self-etch (Clearfil SE Bond) adhesive system to dentine surfaces treated using endodontic irrigants.MethodsTwenty-four freshly extracted third molars were used. After creating a smear layer on the coronal midthird portion of the crowns, the teeth were divided into three groups and surfaces were irrigated with distilled water, 5.25% NaOCl + 17% EDTA, and 1.3% NaOCl + BioPure MTAD, respectively. Each group was divided into two subgroups, and a self-etching adhesive and an etch-and-rinse adhesive were applied respectively. The teeth were restored with a composite material and sectioned to produce sticks for microtensile bond testing.ResultsThe microtensile bond strength of the MTAD + Clearfil SE group was found to be significantly lower than the microtensile bond strength of the distilled water + Clearfil SE Bond group and the NaOCl, EDTA, + Clearfil SE Bond group (p = 0.0001, p = 0.009).ConclusionsBecause of the significant reduction of Clearfil SE Bond to coronal dentine after MTAD application, an etch-and rinse adhesive such as XP-Bond may be preferred if this irrigant has been chosen during endodontic treatment.     

POSS纳米填料对复合树脂与牙本质粘接强度的影响

目的：评价自制POSS纳米填料复合树脂经冷热循环后粘接强度的变化,为新型树脂的研发和应用提供参考依据。方法：160颗人类离体前磨牙随机分为5组,牙体近中面牙本质预备后选用Prime＆BondNT粘接剂分别粘接5种复合树脂（自制POSS纳米复合树脂、未添加POSS填料复合树脂、FiltekTMZ250、FiltekTMZ350、DU-RAFILLVS）。80个试件经10000次冷热循环后,万能材料试验机测试所有试件粘接强度。结果：冷热循环前后粘接强度测试结果分别为：POSS纳米树脂组（27.84±2.19,27.01±2.19）MPa,无POSS填料树脂组（26.73±3.37,20.28±3.30）MPa,FiltekTMZ250（27.56±1.95,26.77±2.74）MPa,FiltekTMZ350（27.68±2.28,24.47±3.04）MPa,DURAFILL○RVS（27.40±1.83,21.49±2.92）MPa。冷热循环前五组树脂粘接强度差异无显著性,经冷热循环各组材料粘接强度差异有显著性（P〈0.05）。结论：5种复合树脂牙本质粘接强度差异显著,添入POSS纳米树脂组冷热循环前后粘接强度均优于未添入组,其耐温度老化性能优于部分临床常用复合树脂。     

湿度对"单瓶"牙本质粘结系统微拉伸粘结强度的影响

目的用微拉伸强度检测法评价脱矿牙本质表面的不同"湿度"状态对酒精/水基和丙酮基"单瓶"牙本质粘结系统粘结强度的影响.方法选择40颗健康前磨牙,去除牙合面釉质,随机均分为8个实验组,在过湿、用滤纸吸干、用空气干燥1 s或用空气干燥30 s的脱矿牙本质上分别应用Single Bond或Prime&Bond NT单瓶牙本质粘结系统.将牙齿片切为粘结面积约0.9 mm×0.9 mm的长方体状样本,进行微拉伸粘结强度检测,对结果进行统计学分析.结果对于同一种粘结系统,其吸干组和1 s干燥组间的微拉伸粘结强度值无统计学差异,但均显著高于过湿组和30 s干燥组.结论脱矿牙本质表面的湿度对酒精/水基和丙酮基"单瓶"牙本质粘结系统的粘结强度有极大的影响.     

Packable Composites: Overview and Technical Considerations

Abstract: Objective: New composites, called packable or condensable composites, are being promoted as amalgam alternatives. The purposes of this review article are to identify these products, define new terminology associated with them, summarize the advertised properties for the materials, discuss the ideal properties for packable composites, review the properties of the major products, and critically evaluate the proposed handling procedures for these materials.
Review: The term packable is preferable to condensable for describing this new class of materials. All materials should be considered amalgam alternatives, not amalgam substitutes. The compositions and physical properties reported by manufacturers reveal that none of the materials represents a remarkable improvement over the properties of more traditional universal composites. The designs of Solitaire (Heraeus Kulzer), ALERT (Jeneric-Pentron), and SureFil (Dentsply/Caulk) are discussed in detail. The distinguishing characteristics of all packable compositions are less stickiness or stiffer viscosity than conventional composites, which allow them to be placed in a manner that somewhat resembles amalgam placement.
Conclusions: Packable composites may allow more convenient placement in posterior sites and may offer some technique advantages over conventional composites. However, there is no evidence that their clinical properties are consistently better than those of conventional universal composites.     

几种粘结树脂在粘结失败后的不同牙本质界面进行再粘结的微拉伸粘结强度和形态学观察

目的:研究3种不同树脂在粘结失败后的不同牙本质表面粘结的微拉伸粘结强度及形态学的观察.方法:磨除因正畸拔除的前磨(牙合)面牙釉质暴露中层牙本质,用Single Bond 2进行粘结建立再粘结模型.在打磨机上打磨再粘结模型样本,产生含有混合层的牙本质表面和去除混合层的牙本质表面.用3种粘结树脂分别在正常牙本质表面,含有混合层的牙本质表面和去除混合层的牙本质表面进行粘结.Z250树脂充填.在低速锯下切割样本进行微拉伸测试(μTBS)和扫描电镜观察粘结界面及断裂类型.结果:每种树脂在含有混合层的牙本质表面粘结的μTBS数值及所产生的混合曾的厚度显著低于在正常牙本质表面粘结的数值.而且较正常牙本质产生较多的玷污颗粒.结论:本实验表明混合层及树脂玷污层的存在降低了在牙本质表面进行再粘结的粘结强度.     

Porcelain to Dentin Bond Strength with a Dentin Adhesive

Adhesion of porcelain to dentin may be important in those cases with little remaining enamel. The purpose of this study was to determine the bond strength of porcelain to dentin using a dentin adhesive (All-Bond) and compare it to the enamel bond strength. Sixty human molar teeth had either a dentin or enamel bonding site prepared by flat grinding to a 600 grit. The teeth were divided into three groups of 20 each. Sixty porcelain cylinders were prepared, hydrofluoric acid etched on one end and silane treated. Twenty of the cylinders were bonded to enamel, 20 bonded to dentin with a dentin adhesive to be tested at 48 hours, and 20 bonded to dentin with a dentin adhesive to be tested after 24 hours of thermocycling (800 cycles at 6°C to 60°C). The specimens were tested in an Instron at a crosshead speed of 0.5 mm/minute. The following bond strengths were found: enamel (19.0 ± 2.9 MPa), dentin at 48 hours (14.4 ± 5.4 MPa), and dentin after thermocycling (10.1 ± 3.8 MPa). When this data was subjected to statistical analysis (ANOVA), there was a significant difference between the groups. A Scheffe's test found that the dentin-porcelain bond at 48 hours was stronger than the thermocycled group, and that the enamel bond was significantly stronger than the two dentin bonds.