Influência do tipo de retentor intra-radicular e nível de perda de estrutura dental coronária no comportamento biomecânico de molares tratados endodonticamente submetidos ou não à radioterapia

Abstract

The aim of this study was to evaluate the influence of dental structural loss level and intra-radicular retainer type on the fracture resistance, fracture pattern and strain in endodontically treated molars submitted or not to radiotherapy. 140 permanent mandibular human molars were selected and randomly divided into 14 groups (n=10), including 2 control groups (NiCont, intact teeth non-irradiated and ICont, intact teeth irradiated) and 12 experimental groups resulting of the interaction among 3 study factors: presence of cobalt 60 gamma radiation (Iirradiated; Ni- non-irradiated); dental structural loss level (PL- coronal partial loss, remaining 2 mm; TL- coronal total loss) and intra-radicular retainer type (Ra- retainer absence; Gfp- glass fiber post - Exacto, Angelus e Cmp- cast Ni Cr alloy post and core). For PL groups, teeth had their crowns reduced with silicon carbide papers resulting in 2 mm coronal remaining and for PT, the crown was completely removed. Then, they were endodontically treated (ET). Teeth of irradiated group were submitted to 60 Gy of cobalt 60 gamma radiation (2 Gy/day, 5 days/week). The intra-radicular retainers and metallic crowns were fixed with self-adhesive resin cement (RelyX U100, 3M-Espe). The buccal and proximal strain were measured by strain-gauges attached on external dentin, under load of 150 N at 0.5 mm/min applied with inclination of 25° on the occlusal surface. Strain data were submitted to two-way ANOVA (7X2) and Duncan test (α=.05). Fracture resistance (N) were measured in mechanical testing machine and data were submitted to two-way ANOVA (3X2) and Tukey test (α=.05). To compare fracture resistance values between teeth Ni and I for each group, t-Student test (α=.05) was performed. The pattern of fracture was analyzed based on the degree of damage to the structure and retainer. Results indicated that 2 mm ferrule presence was a determinant factor on fracture resistance and fracture pattern. Non-irradiated teeth restored with Gfp and Cmp had similar fracture resistance and higher values than teeth without post. In non-irradiated teeth with PL there were prevalence of catastrophic fractures, while in teeth with TL only the restored with Cmp resulted in catastrophic fractures. Buccal strain in non-irradiated molars was higher in intact teeth and lower in the group TLRa. Glass fiber post insertion decreased the buccal strain in non-irradiated molars compared to group PLRa. Retainer type did not influence the fracture resistance of irradiated teeth. In irradiated teeth with PL catastrophic fractures predominated, and with TL the retainer absence resulted in reparable fractures, while the restored with Gfp and Cmp resulted in catastrophic fractures. Irradiation significantly decreased the fracture resistance only in group PLGfp.