Marginal fit and photoelastic stress analysis of CAD-CAM and overcast 3-unit implant-supported frameworks.
BACKGROUND
Several studies have shown the superiority of computer-assisted design and computer-assisted manufacturing (CAD-CAM) technology compared with conventional casting. However, an advanced technology exists for casting procedures (the overcasting technique), which may serve as an acceptable and affordable alternative to CAD-CAM technology for fabricating 3-unit implant-supported fixed dental prostheses (FDPs).


OBJECTIVE
The purpose of this in vitro study was to evaluate, using quantitative photoelastic analysis, the effect of the prosthetic framework fabrication method (CAD-CAM and overcasting) on the marginal fit and stress transmitted to implants. The correlation between marginal fit and stress was also investigated.


METHODS
Three-unit implant-supported FDP frameworks were made using the CAD-CAM (n=10) and overcasting (n=10) methods. The frameworks were waxed to simulate a mandibular first premolar (PM region) to first molar (M region) FDP using overcast mini-abutment cylinders. The wax patterns were overcast (overcast experimental group) or scanned to obtain the frameworks (CAD-CAM control group). All frameworks were fabricated from cobalt-chromium (CoCr) alloy. The marginal fit was analyzed according to the single-screw test protocol, obtaining an average value for each region (M and PM) and each framework. The frameworks were tightened for the photoelastic model with standardized 10-Ncm torque. Stress was measured by quantitative photoelastic analysis. The results were submitted to the Student t test, 2-way ANOVA, and Pearson correlation test (α=.05).


RESULTS
The framework fabrication method (FM) and evaluation site (ES; M and PM regions) did not affect the marginal fit values (P=.559 for FM and P=.065 for ES) and stress (P=.685 for FM and P=.468 for ES) in the implant-supported system. Positive correlations between marginal fit and stress were observed (CAD-CAM: r=0.922; P<.001; overcast: r=0.908; P<.001).


CONCLUSIONS
CAD-CAM and overcasting methods present similar marginal fit and stress values for 3-unit FDP frameworks. The decreased marginal fit of frameworks induces greater stress in the implant-supported system.
Doctoral student, Department of Prosthodontics and Periodontology, Piracicaba Dental School, University of Campinas, Sao Paulo, Brazil.
Anna Gabriella Camacho
AG
Presotto
Assistant Professor, Department of Restorative Dentistry, School of Dentistry, Federal University of Minas Gerais, Minas Gerais, Brazil; and Associate Professor, School of Dentistry, Newton Paiva University Center, Minas Gerais, Brazil.
Cláudia Lopes Brilhante
CL
Bhering
Professor, Department of Prosthodontics and Periodontology, Piracicaba Dental School, University of Campinas, Sao Paulo, Brazil.
Marcelo Ferraz
MF
Mesquita
Assistant Professor, Department of Prosthodontics and Periodontology, Piracicaba Dental School, University of Campinas, Sao Paulo, Brazil. Electronic address: barao@fop.unicamp.br.
Valentim Adelino Ricardo
VA
Barão
D000180:Acrylic Resins; D000704:Analysis of Variance; D001641:Bicuspid; D002516:Ceramics; D002858:Chromium Alloys / Q000737:chemistry; D017076:Computer-Aided Design; D000044:Dental Abutments; D003735:Dental Casting Technique; D015921:Dental Implants; D003761:Dental Impression Technique; D018772:Dental Marginal Adaptation; D003764:Dental Materials; D017267:Dental Prosthesis Design; D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis / Q000295:instrumentation / Q000379:methods; D003779:Denture Design; D003830:Denture, Partial, Fixed; D008334:Mandible; D008422:Materials Testing; D008963:Molar; D013314:Stress, Mechanical; D019415:Torque; D015040:Zirconium / Q000737:chemistry
D000180:Acrylic Resins; D002858:Chromium Alloys; D015921:Dental Implants; D003764:Dental Materials; D015040:Zirconium; C028541:zirconium oxide