Viscoelasticity of dental tissue conditioners during the sol-gel transition.

Formation of tissue conditioners is a process of polymer chain entanglements. This study evaluated the influence of composition and structure on dynamic viscoelasticity of concentrated polymer solutions based on poly(ethyl methacrylate) (PEMA) used as tissue conditioners through the sol-gel transition. The hypothesis was that the ethanol content is the most influential factor in determining gelation speed. Rheological parameters were determined with the use of a controlled-stress rheometer. Analysis of variance by orthogonal array L(16)(4(5)) indicated that the strong polar bonding of ethanol (contribution ratio rho = 53.8%; confirming the hypothesis) and molecular weight of polymer powders (rho = 26.7%) had a greater influence on the gelation times of PEMA-based systems than did the molar volume of plasticizers (rho = 9.0%) and concentration of polymers (i.e., powder/liquid ratio) (rho = 4.5%). The results suggest that the gelation of tissue conditioners based on PEMA can be controlled over a wide range by varying the polymer molecular weight, and especially ethanol content.

Physical properties and compatibility with dental stones of current alginate impression materials.

This study examined physical properties and compatibility with dental stones of two types of alginate impression materials. Five powder-type alginate impression materials (Alginoplast EM, Aroma Fine, Algiace Z, Coe Alginate, Jeltrate Plus) and a paste-type alginate impression material (Tokuso AP-1) were used. The dynamic viscosity immediately after mixing was measured by means of a controlled-stress rheometer. The gelation times were determined according to Japanese Industrial Standards (JIS) T6505, and recovery from deformation, strain in compression and compressive strength were determined according to the International Organization for Standardization (ISO) specification 1563. Detail reproduction and surface roughness of type III dental stones (New Plastone, New Sunstone) and a type IV dental stone (Die Stone) were evaluated using a ruled test block as specified in the ISO specification 1563 and a profilometer, respectively. The alginate impression materials evaluated in this study were all in compliance with the ISO specification 1563 and JIS T6505. The alginate impression materials had similar mechanical properties after gelation, whilst a wide range of dynamic viscosity immediately after being mixed, gelation times and compatibility with dental stones were found among the materials. The paste-type material had a higher dynamic viscosity and a shorter gelation time than the powder-type materials. The best surface quality was obtained with the paste-type material/type III dental stone cast combinations. The materials should be selected in consideration of initial flow, setting characteristics and compatibility with dental stones. The results suggested that a paste-type material would better meet the requirements of an alginate impression material.