Avaliação in vitro da eficiência de um novo tipo de ponta adiamantada para preparo do canal radicular na retentividade de pinos de fibra de vidro

Abstract

Endodontically treated and extensively destroyed teeth require coronal restoration combined with the use of intraradicular posts to meet retentive requirements. One of the main causes of intraradicular post failure is loss of retention, resulting in root canal detachment. Two factors are essential for post retention: adaptation, which is related to frictional retention, and adhesion to the root canal walls, which is associated with adhesive cements and their interaction with these substrates. To increase the retentiveness of these posts, new experimental tips were developed. The objective of this study was to evaluate the bond strength to displacement of prefabricated fiberglass posts and the intraradicular dentin substrate by modifying the root substrate with the new experimental tips. Bovine teeth, without apparent defects and of similar dimensions, were extracted and stored in distilled water. They were randomly divided into 9 groups (n = 10), with roots standardized to 17 mm in length. The study was divided into three phases. In phase I, the bond strength between the prefabricated post and the root canal was evaluated when prepared with the experimental diamond bur in different particle sizes (15, 30, and 45 micrometers) and in a cylindrical shape. In phase II, the smear layers produced by these burs were analyzed under a scanning electron microscope. In phase III, after analyzing the results obtained in phases I and II, the burs with the best results were selected. Thus, the bond strength between the prefabricated post and the root canal was evaluated when prepared with the experimental diamond bur in two particle sizes (30 and 15 micrometers), in a frustoconical shape and with two different tapers. The same type of post was used in all groups. All roots were prepared using Largo 1 and 2 burs prior to the corresponding bur for the test group. The roots of each group were prepared to a depth of 12 mm for post cementation. The posts were cemented according to the manufacturer's instructions using self-adhesive resin cement. The roots were then fixed in an acrylic resin base and sectioned transversely to their longitudinal axis using a precision cutting machine, resulting in three 1 mm-thick discs in each of the three thirds evaluated. The specimens were subjected to compressive loads on the post until displacement. Bond strength was calculated considering the adhesive area. In the comparative analysis of phase I, the group prepared with the 30-micrometer experimental tip presented significantly superior results compared to the groups prepared with only the Largo bur and the groups using the 45-micrometer experimental tips. Significant differences were observed between the groups prepared with 15- and 45-micrometer burs, with superior results in the group with the smaller grain size. In phase II, scanning electron microscopy images showed different aspects of the smear layer resulting from the use of the burs. The 45- micrometer bur resulted in a thicker smear layer, and the 30- and 15-micrometer burs showed thinner layers, respectively. In phase III, the results showed that the group using only Largo 1 and 2 burs had lower bond strength values than the groups using the 15- and 30-micrometer grain sizes at both tapers. However, there was no significant difference between these groups. We can conclude that the modification of theintraradicular dentin tissue through the use of experimental fine-grain diamond burs was able to improve the quality of the adhesive interface between the cement and intraradicular dentin. The increased bond strength of the adhesive interface is associated with the smear layer pattern produced by the experimental diamond burs with particle sizes of 15 and 30 micrometers.