Mode of failure in the dentin-adhesive resin-resin composite bonded joint as determined by strength-based (muTBS) and fracture-based (CNSB) mechanical testing.
OBJECTIVE
To determine the failure mode between dentin-adhesive resin-resin composite bonded joint produced with a chevron-notch short-bar (CNSB) and microtensile test methods.


METHODS
Forty teeth were randomly selected for microtensile and forty for CNSB specimen fabrication and stored in 0.5% chloramine T at 37 degrees C until respective static load to failure testing at 30 and 180days. Failure modes were categorized by SEM and tested with Fisher's exact test. Within respective mechanical testing methods the probability of failure curve distributions being significantly different were analyzed by the Wald chi-square statistic.


RESULTS
The characteristic fracture toughness at 30- and 180-day storage was 0.82 and 0.87MPam(1/2), while the Weibull Modulus (m) for the failure distributions, was 4.60 and 4.56, respectively. No significant difference was demonstrated in the failure distributions between these groups (p=0.45). The characteristic tensile strength (muTBS(o)) at 30- and 180-day storage was 52.53 and 14.71MPa with an m of 3.04 and 1.56, respectively. Failure distributions for muTBS groups were significantly different (p<0.001). K(IvM) failure modes, regardless of storage time, were within the adhesive joint with 30-day debonds primarily through the top region of the hybrid layer (THL) and after 180-days involving the bottom of the hybrid layer (BHL). The 30-day muTBS group demonstrated a propensity to debond in dentin or resin composite substrates but after 180-days storage debonds again involved the BHL.


CONCLUSIONS
The weak links in the dentin-adhesive resin-resin composite bonded joint may be the interphase regions between the THL and the adhesive resin and the BHL and dentin.
Department of Operative Dentistry, College of Dentistry, University of Iowa, 2295 Dental Science, Iowa City, IA 52242-1010, USA. steven-armstrong@uiowa.edu
S R
SR
Armstrong
J C
JC
Keller
D B
DB
Boyer
D000268:Adhesiveness; D016009:Chi-Square Distribution; D002700:Chloramines; D003188:Composite Resins / Q000737:chemistry*; D016001:Confidence Intervals; D001840:Dental Bonding; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis / Q000295:instrumentation; D003804:Dentin / Q000648:ultrastructure*; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D004202:Disinfectants; D004548:Elasticity; D006801:Humans; D016013:Likelihood Functions; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D019279:Resin Cements / Q000737:chemistry; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013499:Surface Properties; D016019:Survival Analysis; D013718:Tensile Strength; D013997:Time Factors; D014105:Tosyl Compounds
D002700:Chloramines; D003188:Composite Resins; D017220:Dentin-Bonding Agents; D004202:Disinfectants; C092987:Optibond; C099128:Prodigy; D019279:Resin Cements; D014105:Tosyl Compounds; C016300:chloramine-T