Viscoelastic Properties of Soft Materials as Periodontal Ligament Simulation Materials

Objectives: In laboratory models, the periodontal ligament (PDL) is usually not simulated. The purpose of this study was to define the viscoelastic properties of several materials and to verify whether these materials are appropriate to simulate the PDL in laboratory models. Materials and methods: Two impression materials (President, Prestige) and two liners (Soft-liner, Durabase) were studied. Viscoelasticity in tensile test: Strips (6x80x1 mm) were prepared and stretched via a loading machine to three different extensions while recording the forces during the stretching phase and relaxation phase for 30 min. Viscoelasticity in tooth model: A pair of teeth, with their roots covered with the tested material, was invested in acryl creating tight proximal contact. The contact-point tightness was measured by the TDCP device, according to a previously in-vivo published protocol. This measurement provides the behavior of the material simulating PDL material. Each experiment was repeated five times. ANOVA and Tukey tests were used for statistical analysis. Significance was considered for p<0.05. Results: Tensile test: Liners had a significantly (p<0.001) lower modulus of elasticity (~30%) than the impression materials. As a result, the maximal stresses were also significantly (p<0.001) lower (~30%). The liners presented a significantly (p<0.001) greater relaxation phase, resulting in lower (~15%) final stresses. Tooth model: The contact-point tightness values measured for President were the closest to the values measured in-vivo. Recovery of all materials was incomplete in accordance to previously published data. Conclusions: Liners exhibit viscoelastic behavior similar to the PDL. It is more accurate to simulate the PDL in laboratory models when long duration loading is considered using these materials. However, in laboratory models where short duration loading is considered, the use of impression materials is recommended, preferably Prestige material.