title: Shrinkage assessment of low shrinkage composites using micro-computed tomography.
abstract: OBJECTIVE
  The aim of this study was to quantify the polymerization volumetric shrinkage of one regular and two low shrinkage bulk fill composites in class I cavities with or without an adhesive layer, using three-dimensional (3D) micro-computed tomography (μCT).
  
  
  METHODS
  Class I cavity preparations (2.5 mm depth × 4 mm length × 4 mm wide) were standardized in 36 extracted human third molars, which were randomly divided in six groups (n = 6 each) as follows: Group VIT (regular composite without bonding agent); Group SDR (low shrinkage flowable composite without bonding agent); Group TET (low shrinkage composite without bonding agent); Group VIT/P (regular composite with bonding agent); Group SDR/X (low shrinkage flowable composite with bonding agent); TET/T (low shrinkage composite with bonding agent). Each tooth was scanned via µCT at cavity preparation, immediately after cavity filling, and after light-curing. Acquired μCT data were imported into Amira software for analysis and volume values evaluated between steps from cavity preparation until light-curing.
  
  
  RESULTS
  Both low shrinkage composites showed a significantly less volumetric shrinkage than VIT. The use of dental adhesive significantly decreased the average volumetric contraction similarly for the three composites, by about 20%.
  
  
  CONCLUSIONS
  Both low shrinkage composites showed less volumetric polymerization contraction than the regular composite. The use of dental adhesive decreased the total volumetric shrinkage for all evaluated composites.
authors.affiliation: Department of Biomaterials and Biomimetics, New York University College of Dentistry, New York.
authors.forename: Ronaldo
authors.initials: R
authors.lastname: Hirata
authors.forename: Emanuele
authors.initials: E
authors.lastname: Clozza
authors.forename: Marcelo
authors.initials: M
authors.lastname: Giannini
authors.forename: Ehsan
authors.initials: E
authors.lastname: Farrokhmanesh
authors.forename: Malvin
authors.initials: M
authors.lastname: Janal
authors.forename: Nick
authors.initials: N
authors.lastname: Tovar
authors.forename: Estevam A
authors.initials: EA
authors.lastname: Bonfante
authors.forename: Paulo G
authors.initials: PG
authors.lastname: Coelho
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry*; D003737:Dental Cavity Preparation; D008422:Materials Testing / Q000379:methods*; D011140:Polyurethanes / Q000737:chemistry*; D055114:X-Ray Microtomography
chemical_list: D000180:Acrylic Resins; C029012:Composite Dental Resin; D003188:Composite Resins; D011140:Polyurethanes
keywords: 3D imaging; composite resins; polymerization; volume shrinkage; x-ray micro-computed tomography