| 2718 Strain in bovine incisors during cavity preparation and restoration | ||
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C. ELGIN1, G.A. LAUGHLIN2, and J.C. MITCHELL1, 1Oregon Health & Science University, Portland, USA, 2Oregon Health & Science Universty, Portland, USA Objectives: Measure the strain state of a tooth during cavity preparation and composite restoration. Methods: Permanent anterior bovine teeth (stored in Chloramine-T) were mounted in dental stone with the facial surface upward. An area at the CEJ was flattened with a grinding disk in a slow speed handpiece and a strain gage was attached with cyanoacrylate adhesive. The block containing the tooth was mounted in a CNC milling machine, which used an electric motor-driven high speed handpiece to cut a standardized 3x5x2mm Class-V cavity preparation in the tooth immediately incisal to the strain gage. This preparation was restored using Scotchbond Multipurpose adhesive (3M-ESPE), and Z250 composite (C2 shade) (3M-ESPE). Microstrain readings were taken (10/second) throughout the entire cutting and restoration process. Results: Several strain response patterns were observed, however, the prevailing pattern is illustrated in the figure: There was an initial compressive strain. When the bur was approximately 2mm deep, and the preparation began to be widened toward the strain gage, we observed a change to the tensile strain direction. There was a consistent small tensile strain seen during light curing of the adhesive, and a large rise in tensile strain associated with composite curing, followed by a secondary rise after light removal. Conclusions: Removal of tooth structure during cutting always resulted in deformation of the tooth structure, observable as surface strain. Heat produced by the curing light likely caused the transient strain rise during curing of the adhesive and the separation of the strain rise during composite polymerization into two phases. The variability observed in both the pattern and the magnitude of strain indicates that a complex set of factors determine the distribution of stresses within the tooth – and its expression as surface strain during cutting and restoration. Acknowledgement: This study was supported by an AADR Student Research Fellowship. | ||
| Seq #282 - Tooth, Biocompatibility 10:45 AM-12:00 PM, Saturday, March 24, 2007 Ernest N. Morial Convention Center Exhibit Hall I2-J | ||
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