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

https://doi.org/10.1016/j.prosdent.2020.11.007Get rights and content

Abstract

Statement of problem

How 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.

Purpose

The purpose of this in vitro 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.

Material and methods

Two 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.

Results

Interim 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.

Conclusions

Interim 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.

Section snippets

Material and methods

A nickel-chromium model simulating a 2-tooth edentulous space (second premolar and first mandibular molar) with abutments on the first premolar and second mandibular molar was used to fabricate 4-unit interim prostheses (N=40) (Fig. 1). A second similar nickel-chromium mandibular model with missing second premolar and second molar with abutments on the first premolar and first molar was used to fabricate 4-unit cantilever prostheses (N=40) with a cantilevered second mandibular molar pontic. The

Results

The mean values of maximum force required to fracture the conventional and cantilever interim prostheses are shown in Table 3. The interim prostheses processed by CAD-CAM showed the highest maximum force values: VITA CAD-Temp (3136 ±7.4 N) and Telio CAD (3126 ±165 N) (P=1.0). Dentalon Plus had a mean maximum force value approximately 60% lower (1390 ±82 N) than the highest maximum force values. The bis-acrylic showed the lowest mean of maximum load (1287 ±214 N), which was approximately 29%

Discussion

The present study combines the experimental mechanical testing, microscopic inspection, and biomechanical assessment of 4-unit interim prostheses with and without cantilevers. The results of this study revealed significant differences in maximum fracture force for the processing type or cantilever design; and therefore, the null hypothesis was rejected. Within the CAD-CAM processed materials, the VITA CAD Temp 4-unit prostheses withstood the highest maximum force values of about 3136 N followed

Conclusions

Based on the findings of this in vitro study, the following conclusions were drawn:

  • 1.

    Interim fixed partial prostheses produced by CAD-CAM had higher strength than those fabricated by traditional chairside polymerization.

  • 2.

    The traditional polymerization technique is susceptible to a low degree of polymerization and the occurrence of pore-like defects that could affect the strength of the prostheses.

  • 3.

    The presence of a cantilever negatively affected the strength of the test materials, although the

Acknowledgments

The authors thank the Dentalbasto laboratory for the support on the manufacturing of the specimens. Also, the authors acknowledge Prof Luis Moreira from the Deptartment for Quality Assurance and Office of Methodological Studies and Data Processing, Institute Jean Piaget, Portugal, for the statistical analyses.

CRediT authorship contribution statement

Carolina Coelho: Data curation, Writing - original draft. Catarina Calamote: Data curation, Writing - original draft. António Correia Pinto: Conceptualization, Supervision, Project

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    Supported by FCT (Fundação para Ciência e Tecnologia) in the subject of projects: POCI-01-0145-FEDER-031035_LaserMULTICER.

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    © 2020 by the Editorial Council for the Journal of Prosthetic Dentistry.