title: The effect of a nanofilled resin-based coating on water absorption by teeth restored with glass ionomer.
abstract: BACKGROUND
  A nanofilled, resin-based light-cured coating (G-Coat Plus, GC America, Alsip, Ill.) may reduce water absorption by glass ionomers. The authors investigated this possibility by measuring cuspal flexure caused by swelling of glass ionomer-restored teeth.
  
  
  METHODS
  The authors cut large mesio-occlusodistal slots (4-millimeter wide, 4-mm deep) in 12 extracted premolars and restored them with a glass ionomer cement (Fuji IX GP Extra, GC America). Six teeth were coated, and the other six were uncoated controls. The authors digitized the teeth in three dimensions by using an optical scanner after preparation and restoration and during an eight-week storage in water. They calculated cuspal flexure and analyzed the results by using an analysis of variance and Student-Newman-Keuls post hoc tests (significance level .05). They used dye penetration along the interface to verify bonding.
  
  
  RESULTS
  Inward cuspal flexure indicated restoration shrinkage. Coated restorations had significantly higher flexure (mean [standard deviation], -11.9 [3.5] micrometers) than did restorations without coating (-7.3 [1.5] μm). Flexure in both groups decreased significantly (P < .05) during water storage and, after eight weeks, it changed to expansion for uncoated control restorations. Dye penetration along the interfaces was not significant, which ruled out debonding as the cause of cuspal relaxation.
  
  
  CONCLUSIONS
  Teeth restored with glass ionomer cement exhibited shrinkage, as seen by inward cuspal flexure. The effect of the protective coating on water absorption was evident in the slower shrinkage compensation.
  
  
  CONCLUSIONS
  The study results show that teeth restored with glass ionomers exhibited setting shrinkage that deformed tooth cusps. Water absorption compensated for the shrinkage. Although the coating may be beneficial for reducing water absorption, it also slows the shrinkage compensation rate (that is, the rate that hygroscopic expansion compensates for cuspal flexure from shrinkage).
authors.affiliation: Ms. Hankins is a dental student, University of Tennessee Health Science Center, Memphis.
authors.forename: Amanda D
authors.initials: AD
authors.lastname: Hankins
authors.forename: Robert H
authors.initials: RH
authors.lastname: Hatch
authors.forename: Jarred H
authors.initials: JH
authors.lastname: Benson
authors.forename: Bernard J
authors.initials: BJ
authors.lastname: Blen
authors.forename: Daranee
authors.initials: D
authors.lastname: Tantbirojn
authors.forename: Antheunis
authors.initials: A
authors.lastname: Versluis
mesh_terms: D003188:Composite Resins / Q000627:therapeutic use*; D003793:Dental Restoration, Permanent / Q000379:methods*; D005899:Glass Ionomer Cements / Q000627:therapeutic use*; D006801:Humans; D055115:Light-Curing of Dental Adhesives; D049329:Nanostructures / Q000627:therapeutic use*; D014867:Water
chemical_list: D003188:Composite Resins; D005899:Glass Ionomer Cements; D014867:Water
keywords: Coating; cuspal flexure; glass ionomer; hygroscopic expansion; shrinkage; water absorption