title: The Effects of New Design of Access Hole on Porcelain Fracture Resistance of Implant-Supported Crowns.
abstract: BACKGROUND
  One disadvantage of cement-retained crowns is the lack of predictable irretrievability. This problem can be overcome through designing a screw access hole in the metal substructure of cement-retained restoration and using porcelain stain to define this area.
  
  
  OBJECTIVE
  This study aimed to evaluate the influence of existence of screw access hole on porcelain fracture resistance of metal-ceramic implant-supported crowns.
  
  
  METHODS
  Thirty six standardized metal-ceramic crowns were fabricated and divided into 3 groups (n=12); group 1 conventional cement-retained metal-ceramic crowns as control group, group 2 cement-retained MC crowns in which porcelain stain was used to define the location of screw access channel, and group 3 cement-retained metal-ceramic crowns in the metal substructure of which a hole and ledge was designed in the location of screw access channel. The specimens were cemented (TempBond, Kerr) to their dedicated abutments. A hole was made in the location of screw access channel in group 2 and 3 and filled with photo-polymerized composite resin (3M; ESPE). All specimens were thermocycled and loaded in universal testing machine at crosshead speed of 2mm/min until fracture. Mean values of load at fracture were calculated in each group and compared with One-way ANOVA (α=0.05).
  
  
  RESULTS
  Mean value of the load required to fracture the restorations was 1947±487 N in group 1, 1927±539 N in group 2, and 2170±738 N in group 3. No statistically significant difference was found between the fracture resistance values of the three groups (p> 0.05).
  
  
  CONCLUSIONS
  Presence of screw access channel in cement-retained implant restorations does not compromise fracture resistance.
authors.affiliation: Dept. of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran;
authors.forename: Reza
authors.initials: R
authors.lastname: Derafshi
authors.affiliation: Dept. of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran;
authors.forename: Mitra
authors.initials: M
authors.lastname: Farzin
authors.affiliation: Postgraduate Student of Prosthodontics, Dept. of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran;
authors.forename: Masoumeh
authors.initials: M
authors.lastname: Taghva
authors.affiliation: Postgraduate Student of Prosthodontics, Dept. of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran;
authors.forename: Hossein
authors.initials: H
authors.lastname: Heidary
authors.affiliation: Postgraduate Student of Prosthodontics, Dept. of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran;
authors.forename: Berivan
authors.initials: B
authors.lastname: Atashkar
keywords: Cement-retained; Dental Implants; Fracture Resistance; Metal Ceramic Crowns