title: An acoustic emission study on interfacial debonding in composite restorations.
abstract: OBJECTIVE
  This paper studied in vitro the effect of the C-factor on interfacial debonding during curing of composite restorations using the acoustic emission (AE) technique. Finite element (FE) analyzes were also carried out to evaluate the interfacial stresses caused by shrinkage of the composite resin in restorations with different C-factors.
  
  
  METHODS
  Twenty extracted third molars were divided into 4 groups of 5. They were cut to form Class-I (Groups 1 and 2) and Class-II (Groups 3 and 4) cavities with different C-factors. The average C-factors of the four groups were 3.37, 2.88, 2.00, and 1.79, respectively. The cavities were then applied with an adhesive and restored with a composite, which was cured by a halogen light for 40 s. A 2-channel AE system was used to monitor the interfacial debonding, caused by shrinkage stress, between the tooth and restoration through an AE sensor attached to the surface of the specimen. Recording of the AE started at the same time as curing of the composite and lasted 10 min. Simplified FE models were used to evaluate the interfacial stresses in restorations with different C-factors, with a thermal load (temperature decrease) being applied to the composite resin to simulate its shrinkage.
  
  
  RESULTS
  The mean and standard deviation of the total number of AE events for the four groups were 29.6±15.7, 10.0±5.8, 2.6±1.5, and 2.2±1.3, i.e. the number of AE events increased with an increase in the C-factor. The FE results also showed that, the higher the C-factor of the restoration, the higher the interfacial tensile stress between the tooth and restoration.
  
  
  CONCLUSIONS
  From the results of the AE tests and FE simulations, it can be concluded that, the higher the C-factor, the higher the shrinkage stress and the more likely is interfacial debonding.
authors.affiliation: Department of Prosthodontics, Peking University School and Hospital of Stomatology, Beijing, PR China.
authors.forename: Xiaozhou
authors.initials: X
authors.lastname: Liu
authors.forename: Haiyan
authors.initials: H
authors.lastname: Li
authors.forename: Jianying
authors.initials: J
authors.lastname: Li
authors.forename: Peijun
authors.initials: P
authors.lastname: Lu
authors.forename: Alex Siu-Lun
authors.initials: AS
authors.lastname: Fok
mesh_terms: D000162:Acoustics; D003188:Composite Resins / Q000737:chemistry*; D018772:Dental Marginal Adaptation; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis / Q000379:methods*; D003804:Dentin; D004548:Elasticity; D020342:Finite Element Analysis; D006801:Humans; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing / Q000379:methods; D058105:Polymerization; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D014783:Viscosity
chemical_list: D003188:Composite Resins