Effect of photodynamic therapy on the mechanical properties and bond strength of glass-fiber posts to endodontically treated intraradicular dentin.

STATEMENT OF PROBLEM: The use of photosensitizers in photodynamic therapy promotes intraradicular microbial reduction during nonsurgical endodontic therapy. However, studies are lacking on the consequences of the application of these agents on the mechanical properties of intraradicular dentin and on the bond strength of glass-fiber posts. PURPOSE: The purpose of this in vitro study was to evaluate the influence of photodynamic therapy on the bond strength of glass-fiber posts using a push-out test and, additionally, to measure the Martens hardness (MH) and elastic indentation modulus (Eit) of intraradicular dentin when different photosensitizers are used. MATERIAL AND METHODS: Eighty bovine teeth were used to simulate experimental endodontic treatments. Biomechanical instrumentation was performed for all root canals, and the teeth were distributed into 5 groups: control-deionized water; methylene blue 50 mg/L + red laser; methylene blue 100 mg/L + red laser; curcumin 500 mg/L + blue LED; and curcumin 1000 mg/L + blue LED. The MH and Eit of intraradicular dentin were measured using an ultramicrohardness tester under a load of 3 mN (n=8). The push-out bond strength of glass-fiber posts to dentin was measured using a universal testing machine (n=8). Mechanical properties and bond strength data were subjected to the Kruskal-Wallis test, ANOVA, and Fisher least significant difference test (α=.05). Images of representative specimens were obtained using a scanning electron microscope. RESULTS: The MH, Eit, and bond strength of intraradicular dentin were influenced by the photosensitizer used. In general, curcumin promoted lower mechanical properties values but higher bond strength values. CONCLUSIONS: Photosensitizers influenced the mechanical properties of intraradicular dentin and the bond strength of glass-fiber posts, and methylene blue at 50 mg/L had no marked effect on the mechanical properties of the dentin or the bond strength values.

Evaluating the bonding of two adhesive systems to enamel submitted to whitening dentifrices

The aim of this study was to evaluate by micro-shear bond strength test, the bond strength of composite resin restoration to enamel submitted to whitening dentifrices. Forty bovine teeth were embedded in polystyrene resin and polished. The specimens were randomly divided into eight groups (n= 5), according to the dentifrice (carbamide peroxide, hydrogen peroxide and conventional dentifrice) and the adhesive system (Prime & Bond 2.1 and Adper Single Bond 2). Dentifrice was applied for 15 minutes a day, for 21 days. Thirty minutes after the last exposure to dentifrice, the samples were submitted to a bonding procedure with the respective adhesive system. After that, four buttons of resin were bonded in each sample using transparent cylindrical molds. After 24 hours, the teeth were submitted to the micro-shear bond strength test and subsequent analysis of the fracture mode. Data were submitted to analysis of variance and Fisher's PLSD test (α=0.05). The micro-shear bond strength showed no difference between adhesives systems but a significant reduction was found between the control and carbamide groups (p=0.0145) and the control and hydrogen groups (p=0.0370). The evaluation of the failures modes showed that adhesive failures were predominant. Cohesive failures were predominant in group IV. The use of dentifrice with peroxides can decrease bonding strength in enamel.

O objetivo deste trabalho foi avaliar, pelo metodo de microcisalhamento, a resistencia adesiva obtida em restauracoes de resina composta realizadas sobre o esmalte dental previamente exposto a diferentes dentifricios. Para isso, quarenta dentes bovinos foram incluidos em resina de poliestireno e polidos. Os dentes foram divididos aleatoriamente em 8 grupos (n=5) de acordo com o dentifricio utilizado (cremes contendo peroxido de hidrogenio, peroxido de carbamida ou dentifricio convencional) e sistema adesivo (Prime & Bond 2.1 ou Adper single Bond 2). Os dentes foram expostos por 15 minutos por dia durante 21 dias as suspensoes dos respectivos cremes dentais. Trinta minutos apos a ultima exposicao ao dentifricio, os dentes foram restaurados empregando os 2 diferentes sistemas adesivos e resina composta. Apos 24 horas os dentes foram submetidos ao teste de microcisalhamento e posterior analise do padrao de fratura. Os resultados obtidos foram submetidos a analise de variancia e teste de Fisher's PLSD (α=0.05). Nao foi detectada diferenca estatistica entre os adesivos, porem entre os tratamentos com dentifricios, houve reducao estatisticamente significante entre os grupos controle x carbamida (p=0.0145) e entre o grupo controle x hidrogenio (p=0.0370). Na avaliacao do tipo de fratura houve predominancia de falhas adesivas, com excecao do grupo IV que apresentou maior fratura coesiva em esmalte. Assim, a utilizacao de cremes dentais, contendo peroxidos em suas formulacoes, pode provocar uma reducao na resistencia de uniao ao esmalte.