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Advisory Committee Chair

John O Burgess

Advisory Committee Members

Jack E Lemons

Deniz Cakir-Ustun

Lance C Ramp

Amjad Javed

Document Type

Thesis

Date of Award

2013

Degree Name by School

Master of Science in Dentistry (MScD) School of Dentistry

Abstract

Polymerization shrinkage is an important property when restoring teeth with dental composites since resins shrink during polymerization creating stress and strain around the restoration. This may produce failure at the composite-tooth interface. This leads to marginal gaps, staining, post-operative sensitivity, secondary caries, and crack development within the body of a tooth. It is critical to be able to measure polymerization strain produced during composite polymerization. Objective: To measure and compare the polymerization shrinkage strain of various bulk and incrementally placed composites using a novel and recently developed model with different C-factors. Methods: Teflon molds were used to prepare Z100 composite blocks (3M ESPE), which served as a tooth analogue. Z100 was packed into the mold in 2mm increments and light cured. The base of the Teflon mold contained an extension which corresponded to the cavity. For emulating a Class I cavity the dimensions of the base extension was 2mmx4mmx4mm, while for a Class II cavity it was 2mmx7mmx4mm. The Z100 composite blocks were then embedded using self-cure acrylic in brass rings using specially fabricated Teflon molds and stored at 37 C for 24 hours. The cavity surface was treated with 50 micron alumina (45 psi,15 sec) and Rocatec Soft (3M ESPE) 30 microns silica-modified alumina (45 psi,15 sec). RelyX Silane (3M ESPE) then Adper Single Bond Plus (3M ESPE) bonding agent was applied and cured. Strain gages were attached to the outer surface of the Z100 composite block using M-Bond 200 (Vishay). The end wires of the strain gage were connected to a Model 5100 Analog to Digital Scanner (Vishay). The composite resin to be tested was placed in the cavity and cured with Bluephase 20i (Ivoclar Vivadent). Strain units were recorded on a computer using StrainSmart software (Vishay). Residual strain was graphically plotted as a function of time. The strain values were recorded for 15 minutes. Results: Significant difference between Class I and Class II residual shrinkage strain was observed for all the materials. Conclusion: All composite resins had residual strain which stresses the marginal interface in restorations and may contribute to increased marginal breakdown.

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Dentistry Commons

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