Effect of bleaching on fracture toughness of composite-dentin bonds.
OBJECTIVE
The effect of carbamide peroxide concentration and length of exposure on fracture toughness (KIC) of existing composite-dentin interfaces was assessed using the notchless triangular prism (NTP) specimen KIC test.


METHODS
Freshly extracted human molars and premolars were wet ground on 600-grit SiC to obtain 4 x 4 x 4 x 4 mm triangular prisms, exposing buccal or lingual dentin. Dentin surfaces were bonded using a resin composite (Z-250, 3M) and SingleBond dentin bonding system (3M) to obtain 180 8-mm-long dentin-composite NTP specimens. The bonding system was applied using the "wet-bonding" technique. The bonded specimens were randomly assigned to 20 groups. The effect of exposure to three control solutions (tap water, Carbopol, and Carbopol-urea) and to four concentrations (11%, 13%, 16%, 21%) of carbamide peroxide (Perfecta, Premier) was assessed. Testing was conducted after 1, 2, and 3 weeks representing a cumulative exposure of 14, 42, and 70 h. The maximum force recorded before fracture was used to calculate KIC. The data were statistically analysed using two-factor ANOVA followed by one-way ANOVA and Bonferroni multiple means comparisons. Selected fractured surfaces were characterized using SEM.


RESULTS
Data analysis revealed that cumulative exposure to bleaching agent for 70 h significantly (p < 0.01) decreased the interfacial KIC, regardless of concentration. For the 16% and 21% concentrations, a significant reduction was observed after 42 h.


CONCLUSIONS
The results suggest that bleaching could adversely affect the interfacial fracture toughness of dentin-resin composite adhesive interfaces.
Far
Cyrus
C
Faculty of Dentistry, The University of British Columbia, Vancouver, Canada.
Ruse
N Dorin
ND
D000180:Acrylic Resins; D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D000077463:Carbamide Peroxide; D003188:Composite Resins / Q000737:chemistry*; D001840:Dental Bonding / Q000379:methods*; D019232:Dental Restoration Failure; D003804:Dentin / Q000187:drug effects / Q000648:ultrastructure*; D017220:Dentin-Bonding Agents / Q000737:chemistry; D004338:Drug Combinations; D006801:Humans; D016877:Oxidants / Q000008:administration & dosage / Q000627:therapeutic use*; D010545:Peroxides / Q000008:administration & dosage / Q000627:therapeutic use*; D011145:Polyvinyls / Q000737:chemistry; D013314:Stress, Mechanical; D013997:Time Factors; D014073:Tooth Bleaching; D014508:Urea / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000737:chemistry / Q000627:therapeutic use*; D014867:Water / Q000737:chemistry
D000180:Acrylic Resins; D003188:Composite Resins; D017220:Dentin-Bonding Agents; D004338:Drug Combinations; C444701:Filtek Z250; D016877:Oxidants; D010545:Peroxides; D011145:Polyvinyls; C115612:single bond; D014867:Water; C006912:carboxypolymethylene; D000077463:Carbamide Peroxide; D017438:Bisphenol A-Glycidyl Methacrylate; D014508:Urea