Abstract
We compared polymerization stress in two commercial composites and three experimental composites made using camphorquinone (CQ) and/or phenylpropanedione (PPD) as photoinitiators. The internal surfaces of photoelastic resin discs with cylindrical cavities were roughened and treated with adhesive. Composites were divided into five groups: two commercial composites (Filtek Silorane and Filtek Z250) and three experimental composites with CQ/amine, CQ/PPD/amine, and PPD/amine. Composites were photopolymerized inside cavities, and subjected to photoelastic analysis immediately and at 24 hours and 7 days later using a plane polariscope. Stress created by Silorane (3.08 ± 0.09 MPa) was similar to that of Z250 (3.19 ± 0.13 MPa) immediately after photopolymerization (p > 0.05). After 24 hours and 7 days, Z250 (3.53 ± 0.15 and 3.69 ± 0.10 MPa, respectively) showed higher stress than Silorane (3.19 ± 0.10 and 3.16 ± 0.10 MPa, respectively). Qualitative analysis immediately after photopolymerization showed composite/CQ promoted higher stress than PPD, but stress levels at other evaluated times were statistically similar, varying between 3.45 ± 0.11 MPa and 3.92 ± 0.13 MPa. At 24 hours and 7 days, Silorane created the lowest stress. All photoinitiators created comparable tensions during polymerization.
Highlights
Dental composites are polymer-based materials that shrink during polymerization
The fringes are directly related to the deformations created in the photoelastic resin by the polymerization shrinkage process
Photoelastic resin from the group with Silorane showed the lowest stress, as characterized by a yellow fringe formation that darkened over time (Figure 1)
Summary
Dental composites are polymer-based materials that shrink during polymerization. Stress occurs when shrinkage is limited and the material is rigid and flow resistant.[1] These stresses may cause imperfections at the bond interface, allowing marginal leakage and bacterial contamination.[2] Many factors—including some that are related to material composition such as organic matrix composition, initiation system, and amount of inorganic filler—affect the degree of polymerization shrinkage, influencing contraction and strain.[3,4,5]. The organic matrices of composites contain different monomers. A new silorane-based monomer composite was introduced for use in dentistry. The silorane polymer chain is formed by cationic ring opening and involves the action of three initiator components. Ring opening results in molecular expansion that compensates for polymerization shrinkage.[6] stresses generated by polymerization processes associated with silorane are lower than those associated with methacrylate-based composites.[7]
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