Healing of the guinea pig incisor after partial pulp removal

A histological and microradiographical study was made of eruption and healing of guinea pig lower incisors after endodontic treatment compared with intact incisors. One incisor per animal was cut perpendicularly at the level of the gingiva. One third to one half of the pulp was removed. The experimental periods were 0, 4, 7, 16, 21 and 31 days. Unstained, HE or Brown and Brenn stained sections were studied microscopically. Some teeth were sectioned undecalcified and studied microradiographically. In intact incisors the dentin matrix deposition and mineralization were described. In the dentin, incisally to the pulp proper, narrow canals, the walls of which consisted of mineralized material, were found opening at the occlusal surface. Histologically, in the treated teeth, a beginning of cell-rich fibrodentin deposition at the original dentin wall was present at Day 4. At Day 7 a substantial walling off of the pulp is achieved by cell-rich and some cell-poor fibrodentin. After 16 days large amounts of cell-rich and cell-poor fibrodentin were covered by some tertiary dentin. After 31 days the amount of tertiary dentin was larger than after 16 days and also covered the incisal part of the root canal walls. Further apically some vasodentin and newly formed normal, secondary, dentin was observed. In course of this period the cells of the cell-rich and cell-poor fibrodentin first showed necrobiosis, then necrosis. The cell-rich fibrodentin appeared not fully mineralized. All blood vessels and strands of soft tissue which ran in canals in the fibrodentin came to a dead end. Thus the root canal was fully obturated. Although the teeth appeared (nearly) normal to the naked eye and radiographically after 31 days, histologically they were not. Large amounts of fibrodentin still being present incisally which showed the dual potential of the guinea pig pulp to produce both fibrodentin and orthodentin.