Discussion - References.
Patients in this multicentre study were selected on the basis of radiographically discernible apical periodontitis. Initially, there were 199 teeth, with a total of 84 teeth filled with RS and 72 teeth filled with GS which were followed for the whole12-month period. The proportion of dropouts was approximately the same in both sealer groups. The recall rate of 78% compared well with previous prospective studies (Kerekes & Tronstad 1979, Friedman et al.1995).
Radiographic estimation of periapical structures is a complex task. Several criteria and different combinations of radiographic features have been developed to discriminate between healthy and diseased state (Odesjoet al.1990, Heling et al. 2001). In many studies, the success- failure analysis (Strindberg 1956) has been used to determine the outcome of endodontic treatment or to evaluate the periapical status in epidemiological studies. Another method to analyse periapical structures in follow-up (Orstavik & H Nrsted-Bindslev 1993, Trope et al.1999, Waltimo et al.2001) or epidemiological studies (Kirkevang et al. 2001, Boucher et al. 2002) is the PAI. It is based on Brynolfâ€™s (1967) comparative histopathological-radiographic studies. The reliability has also been tested using densitometric measurements (Delano et al.2001). In our study, the PAI scores were also used to calculate measures of the success rate and improvement, to document the results after 12 months of follow up.
Healing of apical periodontitis as seen on radiographs may begin shortly after endodontic treatment, in some cases as early as 1week (Kerosuo & Orstavik 1997). Bystrom et al. (1987) suggested that as long as there is a continuous decrease in the size of lesion, there is no reason to judge a case a failure. There maybe several reasons for apical periodontitis to heal at different rates or not to heal. The endodontic treatment may not have eliminated all the bacteria from the root canal, in exposed dentinal tubules, in lacunae of cellular cementum or in apical foramina. Another reason may be that infected dentine and cementum chips are forced into the periapical tissue during mechanical instrumentation (Yusuf 1982). Sometimes, the reduction of lesion size continues for 4-5 years (Bystrom et al. 1987) or even 8-9 years (Strindberg1956). From a clinical point of view it may be of interest to predict the prognosis of a tooth as early as possible after treatment. The estimation of different radiographic signs and clinical risk factors or a combination of them is a subject of future studies.
In this study, the healing of apical periodontitis related to two different root-canal sealers under similar conditions was compared. The periapical condition at the beginning was similar in both groups (Fig. 1). The process of healing, i.e. the change of PAI scores, was clearly seen at12 weeks of follow up and it continued over the whole follow-up period indicating that the dynamics of healing was similar in both sealer groups. Thus, the healing pattern seems largely unrelated to the sealer used, in accordance with previous studies using other sealers (Orstavik1996, Waltimo et al. 2001).
The prognosis of endodontic therapy has been shown to be poorer when the root-canal filling is overextended (Bergenholtz et al. 1979, Swartz et al. 1983) or underextended (Sjogren et al.1990). Nevertheless, in many cases sealer or gutta-percha have been extruded into the periapical tissues and left for years in well-obturated root canals without clinical or radiographic evidence of failure (Weine 1996). In our study, the results did not differ between different filling lengths. If the filling was overextended, it was not resorbed during the follow-up period. Unlike many sealers, extruded RS does not seem to be absorbed, and it probably becomes an â€˜implantâ€™in the periapical area. The adverse effects of root filling excess may be due to overinstrumentation, which normally precedes overfilling. This may force infected dentine chips into the periapical tissue (Yusuf 1982). Periapical granulomas from cases of failed endodontic treatment often contain foreign material such as dentine and cementum chips and/or root-canal filling material.
It is generally agreed (Sundqvist & Fidgor 1998) that the permanent root filling should be an inert, physical barrier to ingress of bacteria or toxins. However, conventional sealers all exhibit some biological and antimicrobial activity. The fact that the relatively inert, silicone-based RS sealer performed as well as the conventional GS, testifies to the validity of the supposition that the antimicrobial part of treatment is completed prior to the placement of the root filling.
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