title: Influence of misfit on the occurrence of veneering porcelain fractures (chipping) in implant-supported metal-ceramic fixed dental prostheses: an in vitro pilot trial.
abstract: OBJECTIVE
  Technical complications such as veneer fractures are more common in implant-supported than tooth-supported restorations. The underlying causes have not been fully identified. The aim of this study was to evaluate whether misfit between the restoration and the implant may affect the risk of veneer fractures.
  
  
  METHODS
  Twenty standardized five-unit implant-supported metal-ceramic fixed dental prostheses (FDP)s were manufactured and fixed in acrylic blocks. The test group consisted of ten FDPs fixed with a 150-μm misfit at the distal abutment. The remaining ten FDPs were fixed without misfit and acted as a control group. All FDPS underwent cyclic loading for a total of 100,000 cycles at 30-300 N. The FDPs were checked for cracks or chip-off fractures regularly. After cyclic load, the retorque value of all abutment screws was checked.
  
  
  RESULTS
  Cracks within the veneering porcelain were noted in nine FDPs in the test group and one FDP in the control group. This difference was statistically significant (P < 0.001). Fractures of the veneering porcelain occurred in three FDPs in the test group. No fractures occurred in the control group. This difference was not statistically significant. There were no significant differences in retorque values neither between the groups nor between different abutment positions in the FDPs.
  
  
  CONCLUSIONS
  Within the limitations of this in vitro pilot trial, it is suggested that misfit between a restoration and the supporting implant may increase the risk of cracking and/or chipping of the veneering porcelain for metal-ceramic FDPs.
authors.affiliation: Department of Prosthodontics, Centre for Specialist Dental Care, Public Dental Care, Lund, Sweden.
authors.forename: Nils
authors.initials: N
authors.lastname: Löfgren
authors.affiliation: Department of Materials Science and Technology, Faculty of Odontology, Malmö University, Malmö, Sweden.
authors.forename: Christel
authors.initials: C
authors.lastname: Larsson
authors.affiliation: Department of Implant Dentistry, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China.
authors.forename: Nikos
authors.identifier: http://orcid.org/0000-0001-7358-7496
authors.initials: N
authors.lastname: Mattheos
authors.affiliation: Department of Prosthodontics, Centre for Specialist Dental Care, Public Dental Care, Lund, Sweden.|Department of Implant Dentistry, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China.
authors.forename: Martin
authors.initials: M
authors.lastname: Janda
mesh_terms: D059605:Dental Implant-Abutment Design / Q000009:adverse effects*; D003776:Dental Porcelain / Q000009:adverse effects / Q000627:therapeutic use*; D019094:Dental Prosthesis, Implant-Supported / Q000379:methods*; D019232:Dental Restoration Failure; D003801:Dental Veneers / Q000009:adverse effects; D006801:Humans; D066298:In Vitro Techniques; D010865:Pilot Projects
chemical_list: D003776:Dental Porcelain
keywords: 
  FDP
  ; chipping; complication; implant; metal-ceramic