title: The effect of consistency, specimen geometry and adhesion on the axial polymerization shrinkage measurement of light cured composites.
abstract: OBJECTIVE
  This study investigated the effect of the consistency, specimen geometry and adhesion on the measurements of axial polymerization shrinkage of light cured composite resins using an axial shrinkage-measuring device.
  
  
  METHODS
  Four commercially available composites were examined: an anterior posterior hybrid composite Z100, a posterior packable composite P60 and two flowable composites, Filtek flow and Tetric flow. The axial polymerization shrinkage of the composites was determined using a 'bonded disc method' and 'non-bonded' free shrinkage method at varying C-factors by altering the specimen geometry. These measured axial shrinkages were compared with the free volumetric shrinkages. The consistency of the composites was also compared using a squeeze test.
  
  
  RESULTS
  Using the non-bonded method, the axial shrinkage was approximately one third of the true volumetric shrinkage as a result of isotropic contraction. However, in the bonded disc method, the axial shrinkage increased up to the volumetric shrinkage by anisotropic contraction as the bonded surface increased. The axial shrinkage increased with the increasing C-factor. It approached the true volumetric shrinkage and reached a plateau at near a C-factor of 5-6. However, in flowable composites, a lower level of axial shrinkage was measured by the compensational radial flow.
  
  
  CONCLUSIONS
  When estimating the volumetric shrinkage from the axial shrinkage measured using the bonded disc method, the C-factor of the specimen should be higher than 5 and the consistency of the composite is also an important factor that needs to be considered.
authors.affiliation: Department of Conservative Dentistry and Dental Research Institute, College of Dentistry, Seoul National University, 28-2 Yeongeon-Dong, Jongro-Ku, Seoul 110-749, South Korea. inboglee@snu.ac.kr
authors.forename: In-Bog
authors.initials: IB
authors.lastname: Lee
authors.forename: Byeong-Hoon
authors.initials: BH
authors.lastname: Cho
authors.forename: Ho-Hyun
authors.initials: HH
authors.lastname: Son
authors.forename: Chung-Moon
authors.initials: CM
authors.lastname: Um
authors.forename: Bum-Soon
authors.initials: BS
authors.lastname: Lim
mesh_terms: D016880:Anisotropy; D003188:Composite Resins / Q000737:chemistry*; D001840:Dental Bonding; D006801:Humans; D008027:Light; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014783:Viscosity; D015040:Zirconium / Q000737:chemistry
chemical_list: D003188:Composite Resins; C467913:Filtek Flow; C443708:P60 Condensible Resin Composite; D011108:Polymers; C083568:Z100 composite resin; C452226:tetric flow composite resin; D012822:Silicon Dioxide; D015040:Zirconium