[Electron microscopic study of canine dentin and odontoblast following the insertion of various composite resin monomers].

The purpose of this study was to evaluate the effect of composite resin monomer on dentinal tubules, odontoblasts and pulp with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Resin monomers of ethyleneglycol dimethacrylate (EDMA), triethyleneglycol dimethacrylate (Tri-EDMA), urethane dimethacrylate (UDMA), and 2, 2-bis [4- (3-methacryloxy-2-hydroxypropoxy) phenyl] propane (Bis-GMA) were used, and placed on a class V cavity in eighty teeth of adult dogs. Then, these treated animals were sacrificed after 30 to 120 days. The findings obtained were as follows: In the odontoblast body; 1. After 30 days, there were uneven unclear envelopes in all odontoblasts. 2. After 60 and 90 days, there were more invaginations of unclear envelope in Bis-GMA group than those in EDMA, Tri-EDMA and UDMA, and lysosomes and autophagic vacuoles increased in number. 3. In Bis-GMA group after 120 days, there were many degenerative changes of chromatin aggregation and hydropic, and many necrosis cells were seen. Uneven nucleous and lysosomes increased in EDMA, Tri-EDMA and UDMA groups. In the odontoblast process; 4. The odontoblast process disappeared in the dentinal tubule one third of cavity floor side of residual dentin with SEM and TEM after 30 days. However, after 120 days, there were few granular substances and calcified closure was not seen in dentinal tubules. In the region of central one third; 5. Microfilaments and microtubules in the odontoblast process decreased in number, and disarrangement and reticular degeneration of these fibers in all experimental groups after 30 days were seen. After 60 days, shrinkage and reticular degeneration of the odontoblast process were seen. Especially in Bis-GMA group, the odontoblast processes disappeared and the one in other three groups showed reticular degeneration after 90 and 120 days. 6. At the portion of pulp side one third on residual dentin, all odontoblast processes were almost seen normal ultrastructure after 60 days. In the group of Bis-GMA after 90 days, reticular degeneration was seen. Shrinkage of microfilaments and microtubules in EDMA, Tri-EDMA and UDMA groups were slightly seen. In the dentinal tubules after 120 days, reticular degeneration and empty in Bis-GMA group, and disarrangement of microfilaments and microtubules was seen in EDMA, Tri-EDMA and UDMA groups. The above findings indicated that composite resin monomers used in this experiment have effects on the odontoblast respectively. In the clinic, when we restore the cavity with these composite resins, we should intercept the stimulation of residual monomers with perfect dentin lining.