title: Variable polymerisation shrinkage and the interfacial micropermeability of a dentin bonding system.
abstract: OBJECTIVE
  Adhesive bonds are subjected to competing stresses whilst a restoration is setting. This study aimed to determine the effect of these stresses on a chemically- and light-activated dentin adhesive (Scotch Bond MultiPurpose Plus: SBMP+) by assessing the morphology and micropermeability of the interfacial region.
  
  
  METHODS
  Restorative materials and techniques were selected to impart differing setting stresses to the adhesive interface. An amalgam (Dispersalloy), a light-activated composite (Z100) with a high- or low-intensity curing light, and chemically-activated composite (Adaptic) were placed either in bulk (4 mm thickness) or in one thin layer (2 mm) in occlusal cavities in 55 freshly extracted third molars. In addition, thin composite restorations were placed on 15 horizontally sectioned teeth using a glass slide as a rigid clear matrix. The pulp chambers of all samples were filled with rhodamine B dye solution for 4 hours. Samples were longitudinally sectioned and the interfacial dye leakage measured using a confocal optical microscope. Data were analysed using the Kolmogorov-Smirnov test.
  
  
  RESULTS
  In occlusal cavities, Z100 had significantly more leakage than the amalgam and Adaptic. There was no significant difference in micropermeability between large and small increments, or curing light intensity for Z100, but when placed in bulk, there was evidence of incomplete composite polymerisation near the cavity floor, especially with the low intensity curing light. Cohesive failure of the deep resin composite and gap formation were a frequent finding with the high-intensity light curing. The least leakage for Z100 was achieved with a thin layer on flat dentin. In contrast, the chemically-activated composite performed well in bulk when the surface of the restoration was freely exposed, but badly when constrained by the glass matrix.
  
  
  CONCLUSIONS
  Restoration setting stress is critical in the microscopic integrity of the adhesive bond to dentin.
authors.affiliation: Department of Prosthetic Dentistry, Eastman Dental Institute and Hospital, London, UK.
authors.forename: B M
authors.initials: BM
authors.lastname: Griffiths
authors.forename: M
authors.initials: M
authors.lastname: Naasan
authors.forename: M
authors.initials: M
authors.lastname: Sherriff
authors.forename: T F
authors.initials: TF
authors.lastname: Watson
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins; D003723:Dental Amalgam / Q000737:chemistry; D003763:Dental Leakage / Q000209:etiology*; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent / Q000009:adverse effects; D003799:Dental Stress Analysis; D003806:Dentin Permeability; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D005456:Fluorescent Dyes; D006801:Humans; D008963:Molar; D011108:Polymers / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry; D018709:Statistics, Nonparametric; D013314:Stress, Mechanical; D015040:Zirconium / Q000737:chemistry
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; D005456:Fluorescent Dyes; D011108:Polymers; D019279:Resin Cements; C425844:Scotchbond Multi-Purpose Plus; C083568:Z100 composite resin; D017438:Bisphenol A-Glycidyl Methacrylate; D012822:Silicon Dioxide; D003723:Dental Amalgam; D015040:Zirconium