Avaliação da resistência à fratura de raízes bovinas estruturalmente comprometidas reconstruídas com diferentes materiais, restauradas com núcleo metálico fundido e coroa total, após teste de fadiga

Abstract

The destruction of internal regions of the root are suitable weakness dental structure remaining release more susceptible to fracture. Therefore, the preservation and restoration of severely weakened remaning radicular engaged launch a challenge for dentists. Thus, in order to avoid the extration of weakened roots is suggsted the use of restorative materials to fill defects and intraradicular reinforcement. The purpose of this study was to evalute the resistance to fracture of internally weakened bovine roots and reconstructed with three differents materials comparative the control roots, restored with cast post-core and full crown, after mechanical load cycling. Forty bovine incisors had been selected and the roots sectioned with 15 mm of length, endodontically treated, immediate removal the obturador material and distribuiton in four experimental groups (n=10). Group C (control), roots prepared with 2 mm thickness of dentine in the cervical wall and groups R (composite resin), I (glass ionomer) and Z (zinc-phosphate), whose roots were submit to wear for simulation weakned roots, so that remaining dentine in the cervical wall was of 0,5 mm and were reconstructive with the respective materials. All roots restored with cast post-core and metallic full crown, were cast in copper-aluminum league and cemented with cement zinc-phosphate. The specimens had been inclusion in block of polystyrene resin and simulated the periodontal ligament with polyether impression material. Were submit to the fatigue test, in machine of simulation of mechanical cycles, with 50 N, 2 Hz and temperature 37°C ± 1°C, until 250.000 cycles. After that, submitted to assay of loading for tangential compression, with a conpressive load, in lingual face, at an angle of 135° in relation to the long axis of the root, in universal testing machine, at a speed of 0,5 mm/min, until to fracture. The data had been analyzed by the statistical test of analysis of variance in only factor (p<.05). The fractures had been examined in stereomicroscope (magnification 10 and 40x) and classified in agreement with affected region radicular. The means (N) and standard-deviation for groups were: C) 470,7±190,5; R) 375,2±122,2; I) 381,0±152,8; Z) 364,1±97,6. There were not significant difference among experimental groups. In analysis of mode the fracture, in groups C and R the fractures were, mainly, in cervical radicular region (8), in I had extended the apical radicular region (2) and Z had concentrated in medium radicular region (7). Within the limitations imposed for the methodology applied, concluded that the weakened roots reconstructed with the tested materials offer similar resistance to fracture than control roots. Into to materials tested, de glass ionomer had presented better numerical mean of fracture resistance. However, the fractures of group I were more severity than other groups. It seems convenient if to base on the possibilities of success of the restorative treatment throught of reconstruction radicular, in order to keep the tooth in function, before condemning it due to loss of structure radicular.