title: Alternative methods for determining shrinkage in restorative resin composites.
abstract: OBJECTIVE
  The purpose of this study was to evaluate polymerization shrinkage of resin composites using a coordinate measuring machine, optical coherence tomography and a more widely known method, such as Archimedes Principle. Two null hypothesis were tested: (1) there are no differences between the materials tested; (2) there are no differences between the methods used for polymerization shrinkage measurements.
  
  
  METHODS
  Polymerization shrinkage of seven resin-based dental composites (Filtek Z250™, Filtek Z350™, Filtek P90™/3M ESPE, Esthet-X™, TPH Spectrum™/Dentsply 4 Seasons™, Tetric Ceram™/Ivoclar-Vivadent) was measured. For coordinate measuring machine measurements, composites were applied to a cylindrical Teflon mold (7 mm × 2 mm), polymerized and removed from the mold. The difference between the volume of the mold and the volume of the specimen was calculated as a percentage. Optical coherence tomography was also used for linear shrinkage evaluations. The thickness of the specimens was measured before and after photoactivation. Polymerization shrinkage was also measured using Archimedes Principle of buoyancy (n=5). Statistical analysis of the data was performed with ANOVA and the Games-Howell test.
  
  
  RESULTS
  The results show that polymerization shrinkage values vary with the method used. Despite numerical differences the ranking of the resins was very similar with Filtek P90 presenting the lowest shrinkage values.
  
  
  CONCLUSIONS
  Because of the variations in the results, reported values could only be used to compare materials within the same method. However, it is possible rank composites for polymerization shrinkage and to relate these data from different test methods. Independently of the method used, reduced polymerization shrinkage was found for silorane resin-based composite.
authors: Dental School, Centro Universitário de João Pessoa - UNIPÊ, João Pessoa, PB, Brazil.
authors: Gabriela Queiroz
authors: GQ
authors: de Melo Monteiro
authors: Marcos Antonio Japiassú Resende
authors: MA
authors: Montes
authors: Tiago Vieira
authors: TV
authors: Rolim
authors: Cláudia Cristina Brainer
authors: CC
authors: de Oliveira Mota
authors: Bernardo
authors: B
authors: de Barros Correia Kyotoku
authors: Anderson Stevens Leônidas
authors: AS
authors: Gomes
authors: Anderson Zanardi
authors: AZ
authors: de Freitas