title: Volumetric polymerisation shrinkage of different dental restorative materials.
abstract: BACKGROUND
  Polymerisation shrinkage is a critical limitation of dental resins and may contribute to micro leakage.
  
  
  OBJECTIVE
  The purpose of this study is to record and compare volumetric changes of various dental composites and compomers, exposed for 40 seconds to a commercial halogen light source.
  
  
  METHODS
  Eleven light-polymerised composites and compomers were evaluated using a dilatometer that recorded the polymerisation shrinkage every 0.5 second. The mercury column pressure was measured electronically with a pressure-sensitive transducer, and the data recorded and stored in a computer. The computer also recorded the temperature, controlled the light-source and displayed the data in graphic format. Every material was tested ten times. The data were analysed by means of an ANOVA (P < 0.05).
  
  
  RESULTS
  A high rate of shrinkage occurred for all materials in the first ten seconds of polymerisation. Surefil showed the lowest rate while TPH displayed the highest. Of the higher filled materials, Surefil (0.96%) showed the least shrinkage, followed by Z250 (0.99%), Dyract AP (1.18%), Herculite (1.27%), Compoglass (1.32%), Amelogen (1.34%) and TPH-Spectrum (1.6%). Overall, the flowable materials exhibited significantly more shrinkage (P < 0.05). For this group Compoglass Flow (2.3%) showed the least shrinkage followed by Filtec Flow (2.31%). Permaflo (3.6%) exhibited the most shrinkage followed by Dyract Flow (3%).
  
  
  CONCLUSIONS
  Within the limitations of this study, it is concluded that significant differences exist among the polymerisation shrinkage of the most resins tested. An increase in the filler content of a material significantly lessens the polymerisation shrinkage while an increase in the monomer concentration causes significantly more polymerisation shrinkage.
  
  
  CONCLUSIONS
  The more flowable a composite material becomes, the more the restoration will shrink. Clinicians should take this into account when they decide on cavity design and materials to use.
authors.affiliation: University of Connecticut, School of Dental Medicine, Farmington, CT, USA. tgo@medunsa.ac.za
authors.forename: T G
authors.initials: TG
authors.lastname: Oberholzer
authors.forename: C H
authors.initials: CH
authors.lastname: Pameijer
authors.forename: S R
authors.initials: SR
authors.lastname: Grobler
authors.forename: R J
authors.initials: RJ
authors.lastname: Rossouw
mesh_terms: D000704:Analysis of Variance; D020770:Compomers / Q000737:chemistry / Q000528:radiation effects*; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D008027:Light; D008422:Materials Testing; D015394:Molecular Structure; D044367:Phase Transition; D011108:Polymers / Q000737:chemistry; D014783:Viscosity
chemical_list: D020770:Compomers; D003188:Composite Resins; D011108:Polymers