Durability of bonds and clinical success of adhesive restorations

Resin-dentin bond strength durability testing has been extensively used to evaluate the effectiveness of adhesive systems and the applicability of new strategies to improve that property. Clinical effectiveness is determined by the survival rates of restorations placed in non-carious cervical lesions (NCCL). While there is evidence that the bond strength data generated in laboratory studies somehow correlates with the clinical outcome of NCCL restorations, it is questionable whether the knowledge of bonding mechanisms obtained from laboratory testing can be used to justify clinical performance of resin-dentin bonds. There are significant morphological and structural differences between the bonding substrate used in in vitro testing versus the substrate encountered in NCCL. These differences qualify NCCL as a hostile substrate for bonding, yielding bond strengths that are usually lower than those obtained in normal dentin. However, clinical survival time of NCCL restorations often surpass the durability of normal dentin tested in the laboratory. Likewise, clinical reports on the long-term survival rates of posterior composite restorations defy the relatively rapid rate of degradation of adhesive interfaces reported in laboratory studies. This article critically analyzes how the effectiveness of adhesive systems is currently measured, to identify gaps in knowledge where new research could be encouraged. The morphological and chemical analysis of bonded interfaces of resin composite restorations in teeth that had been in clinical service for many years, but were extracted for periodontal reasons, could be a useful tool to observe the ultrastructural characteristics of restorations that are regarded as clinically acceptable. This could help determine how much degradation is acceptable for clinical success.     

Relationship between nanoleakage and long-term durability of dentin bonds

This study tested the hypothesis that long-term durability of resin bonds to dentin would directly relate to the nanoleakage of dentin bonding systems. Twenty extracted third molars were ground flat with #600 grit SIC paper under running water to expose middle dentin. One-Step or Single Bond was applied to the dentin surface according to the manufacturer's instruction. A crown was built-up with Clearfil AP-X resin composite and the specimens were stored in water for 24 hours at 37 degrees C. The bonded assemblies were cut mesio-distally perpendicular to the interface in approximately 0.7 mm thick slabs and trimmed for microtensile bond strength testing. All slabs were immersed in individual bottles containing 37 degrees C water that was changed daily. Specimens were randomly assigned to four groups (one day, three, six and nine months), and at the specified time period, the specimens to be tested were randomly divided into two subgroups for testing: 50% AgNO3 and the control. In the 50% AgNO3 subgroup, the slabs were coated with fingernail varnish except for approximately 0.5 mm around the bonded interface and immersed for one hour in 50% AgNO3, followed by exposure in a photo developing solution for 12 hours just prior to debonding. The specimens in the control subgroup were soaked in water until they were debonded. Then, all specimens were subjected to microtensile bond testing. Micrographs of the fractured surfaces of the debonded specimens in the AgNO3 subgroup were taken using light microscopy. They were then subjected to image analysis by NIH Image PC (Scion, Fredrick, MD, USA), and the area of silver penetration was quantitated. The fractured surface was further analyzed under the SEM. Bond strength data and the silver penetration areas were subjected to two and three-way ANOVA and Fisher's PLSD test at the 95% level of confidence. Regression analysis was used to test the relationship between bond strengths and the silver penetra tion area at each time period. The tensile bond strength of both materials gradually decreased over time. Specimens bonded with One-Step showed less silver nanoleakage at one day compared to three, six and nine months (p<0.05), but there were no significant differences between the nanoleakage measured at three, six and nine months. In contrast, for specimens bonded with Single Bond, there were no statistically significant differences in the silver nanoleakage among the four time periods tested (p>0.05). No correlation was observed between bond strength and nanoleakage for either bonding system. Nanoleakage occurred in both adhesive systems, and bond strengths gradually decreased over time. However, there was no correlation between bond strength and nanoleakage for either adhesive system in this study.     

Retentiveness of enamel-resin bonds using unfilled and filled resins

The shear strength of composite resin from etched enamel surfaces was tested using five different techniques for placing composite resin and/or unfilled resin. The results did not show significant shear strength differences among the various methods of placing unfilled resins before filled resin or placing filled resin alone.     

Durability of resin-dentin bonds related to water and oil storage

PURPOSE: To evaluate the long-term effects of etching time, adhesive system and storage condition on resin bond strength to dentin. METHODS: Twenty-five extracted human third molars had a flat dentin surface exposed. Two total-etch adhesives, Single Bond (SB) and One-Step (OS), and one self-etching adhesive system, Clearfil Liner Bond 2V (CL), were used. The adhesives were bonded to dentin according to their respective manufacturer's instructions. Additional groups of SB and OS systems were created, in which the phosphoric acid etching time was doubled (30 seconds). After bonding, build-up crowns were constructed incrementally with Z250 resin composite and the teeth were stored for 24 hours in distilled water at 37 degrees C. The teeth were serially and vertically sectioned to obtain several bonded beams with approximately 0.8 mm2 of cross-sectional area. Beams were tested in microtensile (0.6 mm/minute) either immediately (control) or after storage for 6 months or 1 year in either distilled water or mineral oil. Data were analyzed by ANOVA and Tukey's multiple comparison tests. RESULTS: Significant reductions (P< 0.05) in bond strength were observed after both long-term storage periods in water for all the materials, regardless of the etching time for SB and OS. Bond strengths were either preserved or increased in specimens stored in oil.     

Fatigue of enamel bonds with self-etch adhesives

ObjectiveFatigue testing of adhesive bonds to tooth structures in conjunction with bond strength testing can provide more useful information for examining the effectiveness of dental adhesives. The purpose of this study was to determine the shear bond strength (SBS) and shear fatigue limit (SFL) of composite to enamel bonds using modern adhesive systems.MethodsTwelve specimens each were used to determine 24-h resin composite (Z100-3M ESPE) to enamel shear bond strengths with an etch-and-rinse system (ERA), Adper Single Bond Plus (SB), and four self-etch adhesives (SEA)—Adper Prompt-L-Pop (PLP), Clearfil SE (CSE), Clearfil S³ (CS3) and Xeno IV (X4). A staircase method of fatigue testing was used in a four-station fatigue cycler to determine the SFL of composite to enamel bonds with the adhesives (16–20 specimens for each adhesive) at 0.25 Hz for 40,000 cycles. ANOVA and Tukey's post hoc test were used for the SBS data and a modified t-test with Bonferroni correction was used for comparisons of the SFL.ResultsThe SBS and SFL of the etch-and-rinse system were significantly greater (p < 0.05) than those of the four self-etch adhesives. The SBS and SFL of CSE were also significantly greater than for the other three self-etch systems. The ratio of SFL to SBS was highest with the etch-and-rinse system and the ratio became increasing smaller in the same order that the values for SBS decreased with the self-etch systems.SignificanceThe lower fatigue limits for composite to enamel bonds obtained with the self-etch adhesive systems may indicate that greater enamel margin breakdown will occur with restorations where these systems are used for bonding.     

Fatigue limits of enamel bonds with moist and dry techniques

ObjectiveShear fatigue limit (SFL) testing, coupled with shear bond strength (SBS) measurements can provide valuable information regarding the ability of adhesive systems to bond to mineralized tooth structures. The clinical technique for enamel bonding with adhesive resins has shifted from bonding to a thoroughly dried acid conditioned surface to a moist surface to facilitate dentin bonding. The purpose of this study was to compare the performance of ethanol-containing etch-and-rinse adhesive (ERA) systems on moist and dry enamel by determining the resin composite to enamel SBS and SFL, and examining the relationship of SBS and SFL.MethodsTwelve specimens each were used to determine 24-h resin composite (Z100 – 3M ESPE) to enamel SBS to moist and dry surfaces with two ERA systems, Adper Single Bond Plus (SBP) and OptiBond Solo Plus (OBP). A staircase method of fatigue testing was used in a four-station fatigue cycler to determine the SFL of resin composite to enamel bonds (moist and dry) with the two ERA systems (20 specimens for each test condition) at 0.25 Hz for 40,000 cycles. ANOVA and Tukey's post hoc test were used for the SBS data and a modified t-test with Bonferroni correction was used for comparisons of SFL.ResultsThe two ERA systems each generated statistically similar SBS (p > 0.05) to moist and dry enamel and the SBS of SBP was significantly higher than OBP on dry enamel (p < 0.05). The SFL of SBP was significantly greater to dry enamel when compared to moist enamel and there was not a significant difference in the SFL of OBP on dry and moist enamel. There were no significant differences in SFL values between SBP on either moist or dry enamel and OBP on both moist and dry enamel.SignificanceFatigue testing may provide more useful information than SBS tests regarding the performance of dental adhesive systems. The chemical composition, solvents and filler components of ERA systems may influence their ability to develop long-term durable bonds to both moist and dry enamel surfaces.     

Comparative strength of metal-ceramic and metal-composite bonds after extended thermocycling

The relative strengths of ceramic-to-metal and composite-to-metal bonds were compared after prolonged thermocycling. A total of 104 cast discs were produced from a gold alloy (Pontor LFC). A ceramic material (Duceragold) was fused to 24 discs to assess the strength of the metal-ceramic bond. An indirect composite material (New Metacolor Infis) was bonded to the remaining discs after surface preparation by Rocatec tribochemical coating, tin plating and priming with a phosphate conditioner [10-methacryloyloxydecyl dihydrogen phosphate (MDP), Cesead II], priming with a thione conditioner (V-Primer) or no treatment (unprimed control). Shear bond strengths were determined before and after thermocycling at 20,000 and 100,000 cycles. Pre-thermocycling bond strengths were ranked in the order: metal-ceramic (40.5 MPa); Rocatec treatment (33.1 MPa) and tin plating-MDP (31.0 MPa); V-Primer (20.9 MPa); and control (11.9 MPa). The bond strengths of the first three groups were not significantly different after 20,000 thermocycles, whereas those of the V-Primer and control groups were significantly reduced. After extended thermocycling (100,000 cycles) the metal-ceramic group had the highest mean shear bond strength (28.5 MPa; P < 0.05), followed by the Rocatec (23.9 MPa) and tin plating-MDP (22.1 MPa) groups. The metal-ceramic bond was the most durable, although its strength was reduced by 29.6% after extended thermocycling. On the basis of these results, we recommend the Rocatec and tin plating-MDP systems for composite-to-metal bonding. Metal-ceramic bonding, however, is superior to metal-composite bonding within the limitation of the current experiment.