title: Voids and interlayer gaps in Class 1 posterior composite restorations: a comparison between a microlayer and a 2-layer technique.
abstract: OBJECTIVE
  The main objective was to compare the presence of interlayer gaps between 2 hybrid composites placed using a microlayer and a 2-layer technique.
  
  
  METHODS
  Standardized Class 1 cavities were prepared in 40 extracted posterior teeth. Two resin composite materials were used. The control group, group A, consisted of samples of the materials extruded out of the manufacturers' syringes. Group B consisted of 10 teeth restored using 2 layers per restoration. Group C consisted of 30 teeth restored using 6 microlayers per restoration. A scanning electron microscope was used to detect voids in the samples.
  
  
  RESULTS
  Round, well-defined voids were found in 85% to 100% of the samples within the bulks of the resin composite materials only. A statistically significant relationship between the type of composite and presence of bubbles (Fisher exact test, P = .04) was found among the 2-layer technique group. No statistically significant difference (Fisher exact test, P = .48) was found among the microlayer technique group. Irregular interlayer gaps were found in 5% to 15% of specimens within areas between bulks of composite, as detected by an electron microscope based on the different densities of the bulks of composite and the interlayer areas. No such statistically significant relationship was found (Fisher exact, P = .62) among the study groups.
  
  
  CONCLUSIONS
  Voids are routinely found in bulks of composite materials. Higher incidences of interlayer gaps in the 2-layer samples suggest that the use of a microlayering technique may result in fewer gaps.
authors.affiliation: Department of Restorative Dentistry and Biomaterials Sciences, Harvard School of Dental Medicine, 188 Longwood Avenue, Boston, MA 02115, USA. Nachum_samet@hsdm.harvard.edu
authors.forename: Nachum
authors.initials: N
authors.lastname: Samet
authors.forename: Kung-Rock
authors.initials: KR
authors.lastname: Kwon
authors.forename: Phoebe
authors.initials: P
authors.lastname: Good
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Weber
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry*; D001840:Dental Bonding / Q000379:methods; D003793:Dental Restoration, Permanent / Q000379:methods*; D017220:Dentin-Bonding Agents / Q000737:chemistry; D006801:Humans; D011140:Polyurethanes / Q000737:chemistry*; D018709:Statistics, Nonparametric
chemical_list: D000180:Acrylic Resins; C029012:Composite Dental Resin; D003188:Composite Resins; D017220:Dentin-Bonding Agents; D011140:Polyurethanes