Simple metallic compounds as pulp-capping agents

Rat molar teeth as a study model for direct pulp capping research in dentistry

The aim of this review is to evaluate the suitability of rat molar teeth in preclinical evaluation of medical devices for direct pulp capping. The ISO standard 7405 states clearly that only non-rodent mammals are suitable species for animal research in dentistry. Furthermore, without clear justification a considerable number of researchers previously rejected results of animal experiments concerning preclinical evaluation of the biocompatibility of dental materials undertaken in rat molar teeth. However, in the past 50 years about 70 studies have been published using rat molar teeth in order to evaluate direct pulp capping, pulpotomies and tissue reactions after pulp exposure. Numerous studies showed that the healing of rat molar pulp tissue after direct pulp capping is histologically comparable with humans and other animal species pulp tissue. Rat molar teeth, including pulp tissue, can be seen anatomically, histologically, biologically, and physiologically as miniature human molar teeth. Hence, the essential biological reactions of the pulp tissue and the interaction during the different stages of wound healing of rat molar teeth are comparable with that of other mammals. Rat molar teeth are a valid study model in order to provide valuable data concerning pulp tissue reaction after direct pulp capping and related questions in dentistry. Therefore, the use of rats may significantly reduce the number of currently used higher animals in research. Tests in higher developed animals should be limited to experiments which clarify inconsistent results. However, some technical difficulties, like the small size of rat molar teeth must be dealt with before undertaking any research.

Mechanisms controlling secondary initiation of dentinogenesis: a review

Dentinogenesis can be initiated secondarily as an intrinsic ability of the dental pulp to repair, or after interaction of pulp cells with specific exogenous inductive factors. In the present article the basic developmental aspects, highlighting the mechanism by which dentinogenesis is initiated during tooth development, are discussed. Furthermore, clinical and experimental observations concerning the events taking place during secondary initiation of dentine formation, as part of exposed or non-exposed pulp tissue repair, or as a result of dentine matrix or other chemical-pulp cell interactions, are reviewed. Discussion includes hypotheses relating to the crucial biological steps leading to expression of odontoblastic-like cell phenotype and secondary initiation of dentine histogenesis.

Success of pulpotomy in the management of hyperplastic pulpitis

Hyperplastic pulpitis is a variety of chronic open pulpitis which is regarded as irreversible. This condition is usually treated by root canal treatment, unless coronal damage does not permit restoration, in which case extraction is indicated. In the present study, 24 permanent teeth of individuals, aged 10-22 years and diagnosed as hyperplastic pulpitis were treated by pulpotomy using an atraumatic surgical technique with calcium hydroxide alone. The treatment was successful in 22 teeth, according to the following criteria: absence of clinical symptoms, absence of any intraradicular or periradicular radiographic pathological changes, presence of dentine bridge detected by clinical examination and sometimes observed radiographically, and sensitivity to electrical stimulation. The follow-up examination ranged from 12 to 48 months. The high frequency of clinical healing in this study appears to justify recommending pulpotomy as the treatment regime in selected cases of chronic hyperplastic pulpitis.

Bacterial contamination and the "toxicity" of materials to the exposed pulp

The role of bacterial contamination in the toxicity to the pulp of a number of metallic salts was investigated. These had been tested as pulp-capping agents in previous studies involving 228 exposed rat molars. Material from the previous investigations was stained to demonstrate bacteria. This revealed bacteria in necrotic pulp tissue and/or the cavity-restoration interface in approximately 60% of the specimens. The presence of bacteria appeared to be related to pulpal inflammation, necrosis, and failure of calcific repair.

Antibacterial activity of gutta-percha cones attributed to the zinc oxide component

Growth of several species of bacteria was inhibited by the presence of endodontic gutta-percha cones. Microbiologic analysis, measurement of osmolarity, microscopy, x-ray diffraction analysis, and scanning electron micrography were used to identify the biologically active component that slowly leaches from gutta-percha cones. This component is zinc oxide in the form of small solid particles, from which active, soluble Zn2+ ion is mobilized by hydrolysis. A hypothesis on the "depot" effect of the ZnO particles is formulated, and is used to discuss some earlier reported literature on toxic and antibacterial activity of zinc oxide-containing materials. It is concluded that zinc oxide is not to be considered an inert compound. Its widespread uses in medicine and dentistry seem to reside in its "inert," biocompatible, and astringent properties mainly. The biologically active role of zinc oxide, however, merits further investigation.

Histological considerations of direct pulp capping agents

The results from this study showed a variety of pulpal responses to various calcium hydroxide materials when placed directly on the dental pulp. Two of the materials proved to be more successful at stimulating reparative dentin bridging and healing of the underlying pulp tissue. The remainder of the pulp capping agents were ineffective at healing the pulp and forming a reparative dentin bridge. When teeth were capped with these other agents, the pulp showed necrosis and chronic inflammation.