Tissue reaction to primers used in the “single-step” bonding system

Abstract

A large number of direct-bonding systems have been introduced for use by orthodontists. Although these agents are used for direct bonding of brackets to enamel, contact with skin, oral mucosa, and gingiva is not uncommon. While these products have wide clinical use, their biocompatibility has not been extensively investigated. The present study was undertaken to determine the effects of the primer component of Mono-Lok and the primer component of Control on gingiva. Three adult and one juvenile Macaca mulatta monkeys were used in this investigation. In two adults and the one juvenile animal, the primer component of Mono-Lok was applied to the right buccal surfaces of teeth; in the remaining adult animal, the primer component of Control was applied to the right buccal surfaces of teeth. The excess material was extended 5.0 mm onto the gingival tissues and for 3 minutes the cheeks and saliva were kept away from the sites to be tested. Saline solution was applied to the left buccal segments in all animals. Primer and saline solution were applied at 3-day intervals for a period of 21 days. The gingival tissues were examined clinically and biopsied for histologic evaluation. The gingiva in contact with the primer component of Mono-Lok exhibited pronounced inflammatory changes and was characterized by redness, swelling, and spontaneous bleeding. Histologic observations confirmed these findings by showing a marked inflammatory cellular response characterized by eosinophils. In contrast to these findings, the gingiva that was in contact with the primer component of Control or saline solution exhibited normal gingival architecture. Histologic observations supported this appearance and showed a minimal inflammatory cell infiltrate. These results demonstrate that there are differences in the biocompatability of direct-bonding systems used by orthodontists and indicate that further studies are needed to clarify the long-term effects of such systems on patients.