Elsevier

Dental Materials

Volume 20, Issue 1, January 2004, Pages 88-95
Dental Materials

Polymerization shrinkage-strain kinetics of temporary crown and bridge materials

https://doi.org/10.1016/S0109-5641(03)00101-5Get rights and content

Abstract

Objective. The purpose of this study was to measure the polymerization shrinkage kinetics of four commercially available polymer-based temporary crown and bridge materials, including the effect of ambient temperature.

Methods. Three dimethacrylate-based materials and one monomethacrylate-based material were investigated. The polymerization shrinkage-strains were measured by using the Bonded-disk method with initial specimen temperature at both 23 and 37 °C, with values particularly noted at 5, 10, and 120 min after mixing. Five recordings were taken for each material. The progress of the setting reaction and its temperature-dependence were evaluated by the kinetic curves, and net shrinkage and total shrinkage (inclusive of expansion magnitude) of each material were compared by independent sample t-test and one-way ANOVA.

Results. Most shrinkage occurred in the first 10 min after mixing although there was an early expansion especially with the monomethacylate in the first 5 min. At 120 min, the net shrinkage-strain at 23 and 37 °C of the materials used in this test ranged from 3.54 to 4.13%. The fastest setting dimethacrylate-based material and the monomethacrylate-based material showed higher shrinkage-strain than other materials. No significant differences of net shrinkage-strain were found between 23 and 37 °C, but higher shrinkage rates were measured at 37 °C than at 23 °C.

Significance. The Bonded-disk method is a suitable method for measuring temperature-dependence of shrinkage-strain of polymer-based temporary materials. The dimethacrylate-based materials are preferable to monomethacrylates for temporary restoration as judged by the magnitude of polymerization shrinkage-strain, the majority of which is apparent within 10 min from the start of mixing and may affect the clinical outcome.

Introduction

Temporary crown and bridge (TCB) materials should have high mechanical strength, dimensional stability, biocompatibility, esthetics, marginal accuracy, no toxicity and easy handling characteristics.1 Although many materials have been used for temporary restoration, the materials of choice are tooth-colored materials when esthetics is of primary concern. All TCB tooth-colored materials, such as polymethyl methacrylate, higher (meth)acrylate and dimethacrylate, are based on polymeric structures. One of the inherent properties of polymer-based TCB materials is shrinkage during polymerization, which may cause several clinical problems. The shrinkage can cause distortion that may jeopardize the accurate fit to the prepared teeth and also internal stress within the restorations.2 Poor marginal fit allows passage of oral fluids and bacteria into the gap, and this may predispose to caries or pulpitis. This also causes mechanical irritation to the surrounding tissues, and allows the deposition of bacterial plaque. As a consequence, the periodontal health and the integrity of the prepared tooth structure may be damaged. Therefore, it is important to know the polymerization shrinkage kinetics and the amount of shrinkage-strain of the polymer-based TCB materials before using them, to reduce clinical complications.

The purpose of this study were (i) to measure the polymerization shrinkage kinetics and strain of four polymer-based TCB materials, and (ii) to investigate the effect of ambient temperature on the polymerization shrinkage kinetics and strain of the materials investigated. The null hypothesis to be tested was that there was no difference in the net polymerization shrinkage-strain between monomethacrylate-based and dimethacrylate-based TCB materials.

Section snippets

Materials and methods

The materials used in this study are presented in Table 1. One monomethacrylate-based material, (Trim) and three dimethacrylate-based materials (Protemp 3 Garant, Luxatemp, Temphase) were used. All four materials incorporated chemically activated resins. They were mixed and initiated in accordance with manufacturers' instructions. Trim was mixed manually, but the other materials were mixed automatically by dispenser tip.

The polymerization shrinkage kinetics of all materials were measured by the

Results

The polymerization shrinkage kinetic curves are presented in Fig. 2. The mean values and the standard deviations in parenthesis are shown in Table 2, and are shown graphically in Fig. 3.

Discussion

This study used the Bonded-disk method for determining polymerization shrinkage-strain. Many other methods developed are based on mercury dilatometry or water dilatometry.4., 5., 6., 7., 8., 9. Dilatometry is very sensitive to the ambient temperature during the experiment. The volume of a medium in the dilatometer can increase as the temperature of the medium increases. It may reduce the percentage volume shrinkage of the test material.7 Also, changes in temperature of the specimen may affect

Conclusions

  • 1.

    The Bonded-disk method was used successfully for measuring the volumetric polymerization shrinkage-strain of polymer-based TCB materials. Most shrinkage occurred in the first 10 min after mixing, and an increase in the ambient temperature increased the speed of polymerization shrinkage, but not always the magnitude.

  • 2.

    When the materials were compared in terms of net polymerisation shrinkage-strain after 2 h, the differences between them were not significant (range 3.54–3.94% at 23 °C; range

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