ABSTRACT
The aim of this study was to measure the effect of the elapsed time on micro-strain of dental structure by strain gauge test of human and bovine teeth. Ten standardized bovine incisors and ten standardized human premolars were obtained. To measure the strain it was fixed one strain gauge on the buccal of each sample and it was also performed a compression test on each of dehydration times: T0: immediately after removal from moisture; T5: after dehydration in room temperature (23 ± 1oC) for 5 minutes; T15: dehydration for 15 minutes; T45: dehydration for 45 minutes; T120: dehydration for 120 minutes; T24: dehydration for 24 hours; T24Re: dehydration for 24 hours and rehydration for 24 hours in distilled water. The results were statistically analyzed by using one-way ANOVA and Tukey’s test (p < 0.05). Mean and standard deviation values in micro-Strain (μS) of human teeth were: T0: 56.7 ± 28.5 a; T5: 56.9 ± 43.7 a; T15: 40.2 ± 29.7 ab; T45: 41.2 ± 22.1 ab; T120: 32.2 ± 22.5 ab; T24: 22.6 ± 21.7 b; T24Re: 38.5 ± 12.9 ab, and bovine teeth were: T0: 47.5 ± 15.6 a; T5: 39.2 ± 12.5ab; T15: 34.2 ± 11.5 abc; T45: 29.0 ± 7.9 bc; T120: 25.3 ± 10.5 bc; T24: 22.6 ± 10.2 bc; T24Re: 29.9 ± 13.2 bc. The μS values were decreased with increasing of the dehydration time for both teeth groups. It can be concluded that dehydration caused strain decreasing being necessary to keep the samples hydrated during strain gauge tests.
O objetivo deste estudo foi medir o efeito do tempo decorrido em microdeformação da estrutura dental por teste de extensometria de dentes humanos e bovinos. Obtiveram-se dez incisivos bovinos padronizados e dez pré-molares humanos padronizados. Para medir a deformação foram fixados extensômetros sobre a face vestibular de cada amostra, e também foi realizado um teste de compressão em cada um dos tempos de desidratação: T0: imediatamente após a remoção da umidade; T5: após desidratação em temperatura ambiente (23 ± 1°C) por 5 minutos; T15: desidratação por 15 minutos; T45: desidratação durante 45 minutos; T120: desidratação por 120 minutos; T24: desidratação por 24 horas; T24Re: desidratação por 24 horas e re-hidratação durante 24 horas em água destilada. Os resultados foram analisados estatisticamente utilizando o one-way ANOVA e teste de Tukey (p < 0,05). Os valores da média e desvio-padrão em microdeformação (μS) de dentes humanos foram: T0: 56,7 ± 28,5 a; T5: 56,9 ± 43,7 a; T15: 40,2 ± 29,7 ab; T45: 41,2 ± 22,1 ab; T120: 32,2 ± 22,5 ab; T24: 22,6 ± 21,7 b; T24Re: 38,5 ± 12,9 ab e dentes bovinos foram: T0: 47,5 ± 15,6 a; T5: 39,2 ± 12,5 ab; T15: 34,2 ± 11,5 abc; T45: 29,0 ± 7,9 bc; T120: 25,3 ± 10,5 bc; T24: 22,6 ± 10,2 bc; T24Re: 29,9 ± 13,2 bc. Os valores μS foram reduzidos com o aumento do tempo de desidratação para ambos os grupos de dentes. Pôde-se concluir que a desidratação causada promoveu maior rigidez da estrutura, sendo necessário manter as amostras hidratadas durante testes laboratoriais.
ABSTRACT
STATEMENT OF PROBLEM: Controversy exists concerning the use of fiber-reinforced posts to improve bond strength to resin cement because some precementation treatments can compromise the mechanical properties of the posts. PURPOSE: The purpose of this study was to analyze the influence of airborne-particle abrasion on the mechanical properties and microtensile bond strength (MTBS) of carbon/epoxy and glass/bis-GMA fiber-reinforced resin posts. MATERIAL AND METHODS: Flexural strength (delta(f)), flexural modulus (E(f)), and stiffness (S) were assessed using a 3-point bending test for glass fiber-reinforced and carbon fiber-reinforced resin posts submitted to airborne-particle abrasion (AB) with 50-microm Al(2)O(3), and for posts without any surface treatment (controls) (n=10). Forty glass fiber (GF) and 40 carbon fiber (CF) posts were submitted to 1 of 4 surface treatments (n=10) prior to MTBS testing: silane (S); silane and adhesive (SA); airborne-particle abrasion with 50-microm Al(2)O(3) and silane (ABS); airborne-particle abrasion, silane, and adhesive (ABSA). Two composite resin restorations (Filtek Z250) with rounded depressions in the lateral face were bilaterally fixed to the post with resin cement (RelyX ARC). Next, the specimen was sectioned with a precision saw running perpendicular to the bonded surface to obtain 10 bonded beam specimens with a cross-sectional area of 1 mm(2). Each beam specimen was tested in a mechanical testing machine (EMIC 2,000 DL), under stress, at a crosshead speed of 0.5 mm/min until failure. Data were analyzed by 2-way ANOVA followed by Tukey HSD test (alpha=.05). Failure patterns of tested specimens were analyzed using scanning electron microscopy (SEM). RESULTS: The 3-point bending test demonstrated significant differences among groups only for the post type factor for flexural strength, flexural modulus, and stiffness. The carbon fiber posts exhibited significantly higher mean flexural strength (P=.001), flexural modulus (P=.003), and stiffness (P=.001) values when compared with glass fiber posts, irrespective of surface treatment. An alteration in the superficial structure of the posts could be observed by SEM after airborne-particle abrasion. MTBS testing showed no significant effect for the surface treatment type; however, significant effects for post system factor and for interaction between the 2 factors were observed. For the carbon fiber post, the ABSA surface treatment resulted in values significantly lower than the S surface treatment. SEM analysis of MTBS-tested specimens demonstrated adhesive and cohesive failures. CONCLUSIONS: Airborne-particle abrasion did not influence the mechanical properties of the post; however, it produced undesirable surface changes, which could reduce the bond strength to resin cement. For the surface treatments studied, if silane is applied, the adhesive system and airborne-particle abrasion are not necessary.
