Influência do tipo de contato oclusal, técnica restauradora e ciclagem mecânica em pré-molares superiores com lesões cervicais não cariosas

Abstract

A non-carious cervical lesion (NCCL) is the loss of dental structure on cementum-enamel junction (CEJ) cervical region caused by stress, biocorrosion and attrition. The variation of occlusal loads promotes different stress and strain pattern on CEJ. The NCCL restorative process is part of management of the lesion; however, there is no fixed restorative protocol. The propose of this study was evaluate the effect of occlusal loading direction, cyclic load aging and the restorative technique of the NCCL on stress distribution and strain pattern in maxillary. The investigation was conducted by using 3D finite element analysis (FEA) and strain-gauge test. Fourteen 3D-FEA, orthotropic/isotropic and elastic models were generated: Sound tooth (SO), Non-carious cervical lesions not restored (NR), Glass ionomer (GI), Flowable resin (FR), Composite Resin (CR), Lithium disilicate (LD) and Composite resin core + 0,5mm Lithium disilicate (CR+LD). A compressive static load of 150N was applied: axially (AL) and 45° angle to the long axis on the palatine cusp (OL). The displacement was conducet on the base and the lateral of cortical an medular bone. For the Strain gauge test, two strain gauges were bonded in teeth: 2mm above the enamel/cementum junction and the ohter 2mm under the enamel/cementum juntciton. 30 sound samples were submitted in a mechanical testing machine, being load as the FEA. After that, the mechanical fatigue of these samples was performed (200 to 000 cycles 50N, 2 Hz). At the end of aging, sound teeth samples were retested by the strain gauge test. Then, on these same samples were simulated a NCCL with dimensions of 2.5 mm width and depth with # 3118 burn. The sample groups were prepared as implemented in the finite element analysis (n = 5) and made the measurement of strain prior and posterior to the second stage of mechanical aging (200 000 cycles of 50N, 2 Hertz). The specimens were mounted in a mechanical testing machine and submitted to mechanical load (200 000 cycles, 50N). After the aging, the specimens were again submitted to the strain gauge test. As result, Equivalent Stress (Von Mises) showed that the NCCL associated with oblique loading presented higher stress values. For both loads, CR and CR+LD showed biomechanical behavior closer to SO. For Maximum Principal Criteria, GI and FR presented higher tensile stress on the bootton of the lesion; and DL showed compressive stress on gingival wall. For strain gauge test, OL after the fatigue showed the highest strain values on the materials. CR and CR+DL presented the strain pattern closer to SO. The results of the strain obtained by FEA and the strain gauge test were equivalent for both regions. Analyzing the strain gauge on dentin, after restored, just GI showed higher strain for axial load. It can be conclude that CR and CR+LD promoted similar biomechanical behavior compared to SO; and AL concentrate lower stress and strain than oblique load.