title: Relative curing degree of polyacid-modified and conventional resin composites determined by surface Knoop hardness.
abstract: OBJECTIVE
  The aim of the present study was to investigate the relative curing degree at a depth of 2 mm of several polyacid-modified composites (PAM-Cs) as a function of shade.
  
  
  METHODS
  The Knoop hardness of the irradiated top and non-irradiated bottom surfaces of 2 mm thick samples of the PAM-Cs Hytac, F2000, Glasiosite, Dyract, Dyract AP, and Compoglass F and of the resin composites Z100, Herculite Enamel XRV, and Durafill VS, were determined for shades A2 and A4.
  
  
  RESULTS
  The top and bottom hardness of F2000 and Glasiosite ranged between that of the two composites Herculite and Z100. Compoglass, Dyract and Dyract AP had a lower top and bottom hardness than the hybrid composites, but higher than that of the microfilled composite Durafill. The top hardness of Hytac compared with that of the first group, whereas the bottom hardness compared with the second group. The bottom-to-top KHN ratio reflecting the relative curing degree at a depth of 2 mm was less than 80% for the two shades of Hytac and Compoglass as well as for the A4 shade of Dyract AP and Herculite.
  
  
  CONCLUSIONS
  A hard top surface of a PAM-C is not an indication of adequate in depth polymerization. Shade A2 results in significantly greater values for the curing degree compared to shade A4, the effect depending quantitatively on the formulation of the material. Some formulations of PAM-C do not reach an adequate curing degree at a depth of 2 mm so that it is recommended to apply the incremental technique even in box-only cavities with layers of maximum 2 mm.
authors.affiliation: Department of Paediatric Dentistry, PAECAMED, Ghent University, Gent, Belgium.
authors.forename: Nikolaos S
authors.initials: NS
authors.lastname: Koupis
authors.forename: Luc C
authors.initials: LC
authors.lastname: Martens
authors.forename: Ronald M H
authors.initials: RM
authors.lastname: Verbeeck
mesh_terms: D003116:Color; D020770:Compomers / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D005899:Glass Ionomer Cements / Q000737:chemistry; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D012822:Silicon Dioxide / Q000737:chemistry; D013499:Surface Properties; D015040:Zirconium / Q000737:chemistry
chemical_list: C105428:Compoglass; D020770:Compomers; D003188:Composite Resins; D003764:Dental Materials; C088486:Dyract; C118368:F2000 cement; C515803:Glasiosite; D005899:Glass Ionomer Cements; C083568:Z100 composite resin; C105429:hytac; C083396:Herculite XR enamel; D012822:Silicon Dioxide; C039734:Durafill; D015040:Zirconium