Comparison of CAD-CAM and traditional chairside processing of 4-unit interim prostheses with and without cantilevers: Mechanics, fracture behavior, and finite element analysis.

Abstract

STATEMENT OF PROBLEM\nHow processing by computer-aided design and computer-aided manufacturing (CAD-CAM) or traditional chairside fabrication techniques affects the presence of defects and the mechanical properties of interim dental prostheses is unclear.\n\n\nPURPOSE\nThe purpose of this in\xa0vitro study was to compare the effects of CAD-CAM versus traditional chairside material processing on the fracture and biomechanical behavior of 4-unit interim prostheses with and without a cantilever.\n\n\nMATERIAL AND METHODS\nTwo types of 4-unit interim prostheses were fabricated with abutments on the first premolar and first mandibular molar, one from a prefabricated CAD-CAM block and one with a traditional chairside polymer-monomer autopolymerizing acrylic resin (n=10). Both groups were assessed by compressive strength testing and additionally with or without a cantilevered second molar by using a universal testing machine with a 5-kN load cell. A finite element model (FEM) was built by scanning both prosthesis designs. Finite element analysis (FEA) replicated the experimental conditions to evaluate the stress distribution through the prostheses.\n\n\nRESULTS\nInterim fixed prostheses manufactured by CAD-CAM showed significantly higher mean fracture loading values (3126 N to 3136 N) than for conventionally made interim fixed prostheses (1287 N to 1390 N) (P=.001). The presence of a cantilever decreased the fracture loading mean values for CAD-CAM (1954 N to 2649 N), although the cantilever did not influence the traditional prostheses (1268 N to 1634 N). The highest von Mises stresses were recorded by FEA on the occlusal surface, with the cantilever design, and at the transition region (connector) between the prosthetic teeth.\n\n\nCONCLUSIONS\nInterim partial prostheses produced by CAD-CAM had a higher strength than those manufactured traditionally. The presence of a cantilever negatively affected the strength of the prostheses, although the structures manufactured by CAD-CAM still revealed high strength and homogenous stress distribution on occlusal loading.