The practice and theoretical basis of pain measurement is reviewed and critically examined in the areas of animal research, human subjects laboratory investigation and clinical study. The advantages and limitations of both physiological and behavioral methods are discussed in each area, and subjective report procedures are evaluated in human laboratory and clinical areas. The need for procedures that bridge these areas is emphasized and specific issues are identified. Progress in the technology of pain measurement over recent decades is reviewed and directions for future work are suggested.

Pain measurement: an overview

Sealing ability of a mineral trioxide aggregate for repair of lateral root perforations.

Apical periodontitis is a sequel to endodontic infection and manifests itself as the host defense response to microbial challenge emanating from the root canal system. It is viewed as a dynamic encounter between microbial factors and host defenses at the interface between infected radicular pulp and periodontal ligament that results in local inflammation, resorption of hard tissues, destruction of other periapical tissues, and eventual formation of various histopathological categories of apical periodontitis, commonly referred to as periapical lesions. The treatment of apical periodontitis, as a disease of root canal infection, consists of eradicating microbes or substantially reducing the microbial load from the root canal and preventing re-infection by orthograde root filling. The treatment has a remarkably high degree of success. Nevertheless, endodontic treatment can fail. Most failures occur when treatment procedures, mostly of a technical nature, have not reached a satisfactory standard for the control and elimination of infection. Even when the highest standards and the most careful procedures are followed, failures still occur. This is because there are root canal regions that cannot be cleaned and obturated with existing equipments, materials, and techniques, and thus, infection can persist. In very rare cases, there are also factors located within the inflamed periapical tissue that can interfere with post-treatment healing of the lesion. The data on the biological causes of endodontic failures are recent and scattered in various journals. This communication is meant to provide a comprehensive overview of the etio-pathogenesis of apical periodontitis and the causes of failed endodontic treatments that can be visualized in radiographs as asymptomatic post-treatment periapical radiolucencies.

Pathogenesis of Apical Periodontitis and the Causes of Endodontic Failures

Preparation of root canal systems includes both enlargement and shaping of the complex endodontic space together with its disinfection. A variety of instruments and techniques have been developed and described for this critical stage of root canal treatment. Although many reports on root canal preparation can be found in the literature, definitive scientific evidence on the quality and clinical appropriateness of different instruments and techniques remains elusive. To a large extent this is because of methodological problems, making comparisons among different investigations difficult if not impossible. The first section of this paper discusses the main problems with the methodology of research relating to root canal preparation while the remaining section critically reviews current endodontic instruments and shaping techniques.

Mechanical preparation of root canals: shaping goals, techniques and means

The results of an in vivo histological study involving apical and periapical tissues following root canal therapy after different observation periods demonstrated the most favourable histological conditions when the instrumentation and obturation remained at or short of the apical constriction. This was the case in the presence of vital or necrotic pulps, also when bacteria had penetrated the foramen and were present in the periapical tissues. When the sealer and/or the gutta-percha was extruded into the periapical tissue, the lateral canals and the apical ramifications, there was always a severe inflammatory reaction including a foreign body reaction despite a clinical absence of pain.

Apical limit of root canal instrumentation and obturation, part 2. A histological study.

Flare-ups in endodontics: I. Etiological factors

Periodontal tissue reactions to root perforations in the teeth of dogs and humans have been studied by Euler,l KUbler,2 Ruchenstein,3 Kaufmann,4 Taatz and Stiefel,5 and Lantz and Persson.6,7 In general, inflammatory reactions were more severe when the perforated regions were left open to saliva or when the entrance regions were closed with zinc phosphate cement. Reactions were less severe when the perforation canals were sealed with gutta-percha immediately after the perforations were made or soon thereafter. In a clinical and histologic investigation of endodontically treated teeth that had failed, Seltzer et a18 found that some of them had perforations of the floor of the pulp chamber, presumably made by improper access openings. Should such perforations occur without the operator's knowledge, the failures of endodontically treated teeth might be attributed unjustly to some other factors. Therefore, knowing the outcome of endodontically treated teeth with perforated roots should contribute to an informed prognosis for such teeth. During endodontic experiments on monkeys,9-11 a number of teeth were accidentally perforated before or during treatment.

Samuel Seltzer

Papers

Flare-ups in endodontics: I. Etiological factors

Periodontal Effects of Root Perforations Before and During Endodontic Procedures

The effect of periodontal disease on the pulp

Microbiologic factors in endodontology

A scanning electron microscope examination of silver cones removed from endodontically treated teeth.