Ranking of histologic tissue responses in the biologic evaluation of dental materials

Implantation tests are frequently used to evaluate biological properties of dental materials. The tissue reactions have been rated as no, slight, moderate and severe responses, mainly based on a quantitative assessment of the cellular response. The distinction between categories is subject to discussion, and interexaminer calibration is necessary to obtain reproducible results. This paper presents a statistical method of evaluating tissue reaction by ranking photographic prints representing histologic sections. Polyethylene tubes, carrying the materials, were implanted subcutaneously in guinea pigs. The tissue reactions at the tube ends, where the material was exposed to the tissue, were evaluated. Photographs of 20 histologic sections were selected. Five investigators from a scientific staff and five from a group of assisting personnel with minimal instruction ranked the reactions on the prints in increasing order of severity. Assisting personnel received 1 h of instruction before the ranking. Generally, the rank ordering of the different examiners showed good agreement. Qualitative histopathologic examination of the sections indicated a marked variation in the cellular response, which limits the value of the quantitative assessment.