Physical properties of periodontal dressing materials.

The purpose of this study was to develop standardized reproducible testing methods for evaluating physical properties of periodontal dressing materials. Three commercial compositions (Coe-Pak, Coe-Pak Hard & Fast Set and WondrPak) were studied. Working and setting times were determined by observing the continuous changes in viscosity via the oscillating rheometer. The 24-h and 1-week tensile and shear adhesive bonds to enamel were studied by luting orthodontic lingual cleats with a standard film thickness to the orientated labial surfaces of extracted incisors and pulling them to failure. Dimensional change was studied over a period of 24 h using a linear variable differential transformer (LVDT). The developed testing modalities have greater precision than those previously reported. The concept of 'bench time' was developed during which certain materials cannot be handled immediately after mixing.