Effect of in-office tooth bleaching on the microhardness of six dental esthetic restorative materials.
OBJECTIVE
The aim of this in vitro study was to evaluate the effect of the in-office bleaching technique on the microhardness of six dental esthetic restorative materials.


METHODS
Four composite resins (a hybrid, a flowable, a micro-hybrid and a nano-hybrid), an ormocer and a ceramic were tested, after the use of an in-office bleaching product. Fourteen specimens of each composite and the ormocer were fabricated and randomly divided into two groups of seven samples each. One group was polished and the other group remained unpolished. For the ceramic, seven polished samples were fabricated. Two samples of each group were used as negative controls. The specimens were bleached for 15, 30 and 45min. Five Knoop microhardness measurements were made on each sample, for each of the following periods tested: before bleaching, after 15, 30 and 45min of bleaching, 24h and 1 month after the bleaching procedure. Data were analyzed by the repeated measures analysis of variance with three between factors and one within.


RESULTS
The differences in the microhardness values between the bleached and the control samples for the composites and the ceramic, were not statistically significant (hybrid: p=0.264; flow: p=0.584; micro-hybrid: p=0.278; nano-hybrid: p=0.405; ceramic: p=0.819). For the ormocer, although bleaching did not have any significant effect on the unpolished samples (p=0.115), it caused an increase on microhardness of the polished samples.


CONCLUSIONS
Bleaching with 38% hydrogen peroxide does not reduce the microhardness of the restorative materials tested. Therefore, no replacement of restorations is required after bleaching.
Department of Operative Dentistry and Periodontology, Dental School and Hospital, Albert-Ludwigs-University, Freiburg, Germany. olga.polydorou@uniklinik-freiburg.de
Olga
O
Polydorou
Jürgen Schulte
JS
Mönting
Elmar
E
Hellwig
Thorsten M
TM
Auschill
D002516:Ceramics / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D003775:Dental Polishing; D003776:Dental Porcelain / Q000737:chemistry; D003793:Dental Restoration, Permanent; D004955:Esthetics, Dental; D006244:Hardness; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D008422:Materials Testing; D063225:Organically Modified Ceramics; D016877:Oxidants / Q000737:chemistry; D012821:Silanes / Q000737:chemistry; D012833:Siloxanes / Q000737:chemistry; D013729:Terpenes / Q000737:chemistry; D013997:Time Factors; D014073:Tooth Bleaching / Q000379:methods*
D003188:Composite Resins; C421785:Definite composite resin; D003764:Dental Materials; C474035:Filtek Supreme; D063225:Organically Modified Ceramics; D016877:Oxidants; D012821:Silanes; D012833:Siloxanes; D013729:Terpenes; C121818:Tetric ceram; C452226:tetric flow composite resin; D003776:Dental Porcelain; C074543:Cerec; D006861:Hydrogen Peroxide