The influence of water storage and C-factor on the dentin-resin composite microtensile bond strength and debond pathway utilizing a filled and unfilled adhesive resin.
OBJECTIVE
To test the elastic wall concept utilizing adhesive resins of varying stiffness in a low- and high-C-factor cavity design after short- and long-term water storage.


METHODS
A flat and box-shaped cavity was restored on occlusal dentin with a resin composite using a filled and unfilled adhesive resin from which microtensile specimens with a 0.5mm(2) cross-sectional area were formed. After storage for 30- and 150-days the microtensile bond strength (muTBS) was determined in a Zwick materials testing machine and the subsequent debond pathway was examined under scanning electron microscopy. Fisher's exact test was used to determine differences in joint and substrate failure modes and a Weibull regression model with gamma frailties was used to test for differences between failure distributions. Tests for three-way and two-way interactions were also completed for storage time, C-factor and adhesive. All tests were at 95% confidence levels.


RESULTS
The characteristic strength (TBS degrees ) for the Optibond FL adhesive applied on a flat cavity was 47.57 and 20.90MPa and a box-shaped cavity was 49.26 and 17.49MPa for short- and long-term storage, respectively, while the corresponding TBS degrees for the unfilled Optibond adhesive on the flat cavity design was 36.93 and 32.68MPa and in a box-shaped cavity was 32.84 and 15.46MPa. Combining all groups according to storage time revealed a three-fold increase in the debond pathway including the bottom of the hybrid layer.


CONCLUSIONS
Evidence suggests that the durability of the bonded joint is threatened by hydrolysis and the most susceptible region is the bottom half of the hybrid layer and in low C-factor cavity designs a more flexible adhesive resin liner was more durable.
Department of Operative Dentistry, University of Iowa, Iowa City, IA, USA. steven-armstrong@uiowa.edu
S R
SR
Armstrong
J C
JC
Keller
D B
DB
Boyer
D000268:Adhesiveness; D003188:Composite Resins / Q000737:chemistry*; D016001:Confidence Intervals; D001840:Dental Bonding; D003737:Dental Cavity Preparation / Q000145:classification*; D003804:Dentin / Q000648:ultrastructure*; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D004548:Elasticity; D006801:Humans; D007101:Immersion; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D012044:Regression Analysis; D019279:Resin Cements / Q000737:chemistry; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D013997:Time Factors; D014867:Water / Q000737:chemistry*
D003188:Composite Resins; D017220:Dentin-Bonding Agents; C092987:Optibond; D019279:Resin Cements; D014867:Water