title: The effect of thermocycling on the bonding of different restorative materials to access opening through porcelain fused to metal restorations.
abstract: OBJECTIVE
  Porcelain fused to metal (PFM) crowns provide the best treatment option for teeth that have a large or defective restoration. More than 20% of teeth with PFM crowns or bridges require non-surgical root canal treatment (NSRCT). This may be due to the effect of restorative procedures and the possible leakage of bacteria and or their by-products, which leads to the demise of the tooth pulp. Thus, this study was planned to compare the ability of the restorative materials to seal perforated PFM specimens.
  
  
  METHODS
  The study evaluates the ability of amalgam, composite or compomer restorative materials to close perforated PFM specimen's in-vitro. Ninety PFM specimens were constructed using Ni-Cr alloys and feldspathic porcelain, and then they were divided into 3 groups: amalgam (A), composite + Exite adhesive bond (B) and compomer + Syntac adhesive bond (C). All the PFM samples were embedded in an acrylic block to provide complete sealing of the hole from the bottom side. After the aging period, each group was further divided into 3 equal subgroups according to the thermocycling period (one week for 70 cycles, one month for 300 cycles and three months for 900 cycles). Each subgroup was put into containers containing dye (Pelikan INK), one maintained at 5℃ and the other at 55℃, each cycle for 30 sec time. The data obtained was analyzed by SPSS, 2006 using one way ANOVA test and student t-test and significant difference level at (P<.01).
  
  
  RESULTS
  The depth of dye penetration was measured at the interfaces of PFM and filling materials using Co-ordinate Vernier Microscope. The lowest levels of the dye penetration for the three groups, as well as subgroups were during the first week. The values of dye leakage had significantly increased by time intervals in subgroups A and C.
  
  
  CONCLUSIONS
  It was seen that amalgam showed higher leakage than composite while compomer showed the lowest level of leakage.
authors.affiliation: Department of Prosthodontics, College of Dentistry, King Khalid University, Abha, Saudi Arabia.
authors.forename: Mohammed M
authors.initials: MM
authors.lastname: Al-Moaleem
authors.forename: Farhan Khalid
authors.initials: FK
authors.lastname: Shah
authors.forename: Nausheen Saied
authors.initials: NS
authors.lastname: Khan
authors.forename: Amit
authors.initials: A
authors.lastname: Porwal