Biocompatibility of Hg/amalgam Alloy in Exposed Dental Pulps

Objectives: Many restorative materials are known to be biologically compatible with exposed dental pulps, although the stimulation of pulpal healing and dentin bridge formation have sometimes been claimed to be attributable to calcium hydroxide[Ca(OH)2]. The purpose of this study was to compare the sequence of pulpal healing and dentin bridge formation subjacent to exposed pulps when capped with a Mercury containing, high-copper amalgam alloy Dispersalloy (Hg/amalgam) and compare these responses with hard set Ca(OH)2. Methods: Class·V cavities (n=84) were placed throughout the teeth of six rhesus monkeys. Mechanical exposures (n=26) were capped with Hg/amalgam with biological sealing using Intermediate Restoration Material (IRM). Some other unsealed mechanical exposures were capped with Hg/amalgam (n=25). For comparison, the remainder of the cavities (n=33) were pulp capped with Ca(OH)2. Pulp tissues were histologically evaluated for healing using ISO criteria for inflammation, necrosis and soft-tissue organization, as well as odontoblastoid migration and dentin bridge secretion at intervals of 3, 5, 7 10, 14, 21 and 35 days. Bacteria were detected using McKay stains. Results: Little difference was observed in the sequence of pulpal healing and odontoblastoid migration and dentin bridge secretion between pulps capped with Ca(OH)2 and biologically sealed Hg/amalgam. Whereas the pulps capped with Hg/amalgam without a biological seal were associated with delayed and inferior pulp healing, showing inflammation and necrosis. Although odontoblastoid migration was observed, no dentin bridges were secreted beneath unsealed Hg/amalgam capped pulps. Conclusions: We conclude that Hg/amalgam is not toxic to direct capped pulps. However, Hg/amalgam does not provide an environment to promote dentin bridge formation in the presence of bacterial microleakage.