In vivo versus in vitro microtensile bond strength of axial versus gingival cavity preparation walls in Class II resin-based composite restorations.
BACKGROUND
Gingival margins in Class II composite restorations are a site of frequent failure. The purpose of the authors' study was to compare the microtensile dentin bond strength of gingival and axial restored cavity preparation walls of Class II composite restorations under in vivo and in vitro conditions.


METHODS
After obtaining informed consent, the authors placed Class II resin-based composite restorations in 14 premolar teeth from five patients, under in vivo or in vitro conditions. The teeth were sectioned to obtain rectangular specimens from axial and gingival walls with a surface area of approximately 0.5 square millimeter. The authors tested 85 microtensile adhesive samples from the 14 teeth on a testing instrument (Universal Instron, Model 125, Instron, Canton, Mass.) until failure.


RESULTS
The mean (+/- standard deviation) mircotensile dentin bond strengths in mega-pascals were as follows: in vivo axial, 36.5 (14.9); in vivo gingival, 17.6 (11.6); in vitro axial, 49.5 (13.9); in vitro gingival, 34.0 (13.1). A two-way analysis of variance found a statistically significant difference between in vitro and in vivo conditions and between the axial and gingival walls (P < or = .001). Eighty-eight percent of the fractured samples involved the adhesive layer as observed under scanning electron microscopy up to x2,500. Seventeen of the gingival samples and two of the axial samples debonded during the preparation phase and could not be tested.


CONCLUSIONS
The dentinal microtensile strength of adhesive/resin-based composite bonded to the gingival wall was significantly weaker than the bond to the axial wall, and in vivo conditions produced significantly weaker bond strengths than did in vitro conditions.


CONCLUSIONS
The dentinal adhesive bond of resin-based composite to gingival walls is significantly weaker and thus more subject to failure than the bond to axial walls. In vitro bond strength studies may overestimate the bond strength of adhesives in in vivo applications.
University of Missouri-Kansas City, School of Dentistry, 64108, USA. purkj@umkc.edu
John H
JH
Purk
Vladimir
V
Dusevich
Alan
A
Glaros
Paulette
P
Spencer
J David
JD
Eick
D000293:Adolescent; D000328:Adult; D001641:Bicuspid; D003188:Composite Resins; D001840:Dental Bonding; D003737:Dental Cavity Preparation / Q000379:methods*; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis; D003804:Dentin; D017220:Dentin-Bonding Agents; D019234:Dentinal Fluid; D005260:Female; D006801:Humans; D008297:Male; D008855:Microscopy, Electron, Scanning; D019279:Resin Cements; D012822:Silicon Dioxide; D013718:Tensile Strength; D015040:Zirconium
D003188:Composite Resins; D017220:Dentin-Bonding Agents; D019279:Resin Cements; C084018:Scotchbond Multi-Purpose; C083568:Z100 composite resin; D012822:Silicon Dioxide; D015040:Zirconium