Discussion - References.
The design of the present study repeated that of Ray & Trope (1995), but also included the clinical evaluation of the coronal restoration. It is not possible to score the quality of a coronal restoration from a radiograph with certainty, as it provides only a two-dimensional image. In the present study, only a weak correlation existed between radiographic and clinical coronal parameters (rS = 0.485 for quality of restoration and rS = 0.441 for the presence of caries). Because of this weak correlation, the need to score restorations radiographically as well as clinically in order to assess the impact of coronal leakage was obvious. It was, therefore, essential to complement radiographic information with clinical data.
The current study is a cross-sectional design. It is, therefore, not possible to determine whether a periapical lesion is healing or expanding, although Petersson et al. (1991) found that after a 10-year period the number of healed periapical lesions was equal to the number of newly developed lesions, indicating the reliability of cross-sectional studies for scoring the long-term success of endodontic treatments. This is also supported by data from Hugoson et al. (1995).
The incidence of apical periodontitis associated with root-filled teeth in this study was 32.5%. In a previous epidemiological study (DeMoor et al.2000), an incidence of apical periodontitis was 40.4%, based on panoramic radiographs. This figure is comparable to that of other studies, with data ranging from 20 to 60% (Bergstrom et al.1987, Eckerbomet al.1987, Odesjoet al.1990,Eriksen & Bjertness 1991, Imfeld 1991, De Cleen et al.1993, Buckley & SpLngberg1995, Eriksen et al.1995, Saunders et al. 1997,Weiger et al.1997, Marques et al.1998, Sidaravicus et al. 1999, Kirkevang et al. 2001). Seventy-eight percent of the coronal restorations were found acceptable on the radiographs. This is higher than in the studies by Tronstad et al. (2000) (66.2%), Ray & Trope (1995) (62.7%) and Kirkevang et al. (2000) (73.5%).When the coronal restoration was scored radiographically and clinically (Table 2), 67.4% were found acceptable. Adequate restorations (a) showed signs of apical periodontitis in 30.1% of the teeth. This was statistically different from the 37.4% apical periodontitis in endodontically treated teeth with inadequate restorations (u). When restorations were only scored radiographically (Table 2), this difference was more pronounced (23.8% (a) vs. 49.1% (u)). This difference was statistically significant, as indicated by the w2 test and the logistic regression. Other percentages were found by Tronstad et al. (2000) (30% (a) and 37% (u), respectively) and Ray & Trope (1995) (20%(a) and 69.8%(u), respectively) for these relationships.
In the present study, the prevalence of apical periodontitis was not influenced by the presence of a root-canal post. This is in agreement with other studies (Kvist et al. 1989,Tronstad et al. 2000). Eckerbom et al. (1991) found the opposite, but their study only included crowned teeth.
Root-canal treatment performed to high technical standards remains a prerequisite for long-term success (Strindberg1956, Bergenholtz et al.1979, Eckerbom et al. 1987,Odesjoet al. 1990, Sjogren et al. 1990). Agreement exists in the literature that the length of the root filling is an important factor in endodontic treatment success (Sjogren et al.1990, De Moor et al. 2000, Wu et al. 2000) and this is confirmed by the results of the present study. There is still some disagreement, however, about the effect of the homogeneity of the root filling on the periapical status. Odesjoet al. (1990), Sjogren et al. (1990) and Eriksen et al. (1995) found no difference between compact and poorly compacted root fillings in relation to periapical lesions. We found the homogeneity of the root filling to have a statistically significant influence on the prevalence of apical periodontitis (Tables 3-5). This is supported by others (Bergstromet al.1987, Petersson et al.1991, Kirkevang et al. 2000).
Twenty-three percent of the adequate root fillings (a) and 37.4% of the inadequate ones (u) had apical periodontitis (Table 3). Similar figures were presented by Tronstad et al. (2000) (22% (a) and 44% (u), respectively). Ray & Trope (1995) (24.3%(a) and 51.4%(u), respectively) found a more pronounced difference.
As in the studies of Ray & Trope (1995) and Tronstad et al. (2000), the lowest prevalence of apical periodontitis (22.5%) was found in teeth with both a good root filling and a good coronal restoration (Table 7). A comparable figure was found when the quality of the coronal restoration was poor and the quality of the root-canal treatment was good (24.3%).When the two groups with poor endodontics were compared, there was a better result when a good restoration was present, but this difference was not statistically significant. On the basis of the present data, it became clear that the quality of the coronal restoration (scored clinically and radiographically) did not have a statistically significant influence on the periapical status when it was combined with the endodontic quality (Table 9: Avs. C and B vs. D). This is in contrast to the findings of Ray & Trope (1995). Tronstad et al. (2000) found the quality of the coronal restoration scored radiographically only to be significant when combined with good endodontics.
Table 8. Periapical status of endodontically treated teeth as related to the radiographic quality of the coronal restoration combined with the quality of the root-canal treatment determined by the length and homogeneity of the root filling (n = 745)
Table 9. Periapical status of endodontically treated teeth determined by the radiographic and clinical quality of the coronal restorations combined with the quality of the root-canal treatment determined by the length and the homogeneity of the root filling (n = 745).
Table 10. Periapical status of endodontically treated teeth determined by the presence of a base combined with the quality of the root-canal treatment determined by the length and the homogenity of the root filling (n = 745).
When the endodontic status of the teeth in the present study was combined with the quality of the coronal restorations (Table 9: Avs. B and C vs. D), a statistically significant influence on the periapical status was seen. An explanation for the difference in findings in this study, as compared to the findings of Ray & Trope (1995) and Tronstad et al. (2000), is not obvious. In the latter studies, there was no information on the use and the influence of bases and filling materials. Coronal leakage of a restoration can be prevented by the placement of a base (Saunders & Saunders 1990, Heys & Fitzgerald 1991, Guerra et al. 1994). Our results confirm that the use of bases under coronal restorations is beneficial for the long-term outcome of root-canal fillings (Tables 2 and 5). Also more apical periodontitis was detected in teeth filled with composite material than with amalgam. This was confirmed by Buckley & SpLngberg (1995). Gap formation at gingival margins and subsequent bacterial colonization under the restoration is a common problem when composites are utilized (Qvist 1980, Qvist1993, Retief1994, Ciucchi et al.1997).
The technical quality of a root filling, as scored on a radiograph, can be taken as an indication of the care taken for the overall quality of treatment (especially cleaning of the root canal). Canal cleanliness cannot be scored on a radiograph, although it is very important for endodontic success. Bacteria left in the root canal at the time of canal obturation influence the success of treatment (Nair et al.1990, Sjogren et al.1997, Molander et al.1998, Sundqvist et al.1998).
A limitation of the present and other studies remains the incomplete diagnostic value of radiographs. It is commonly known that lesions limited to the cancellous bone are almost impossible to detect with conventional radiographic techniques (Le Quire et al. 1977, Bender 1982, van der Stelt1985); moreover, the microbiological status of the root canals cannot be derived from a radiograph.
The question remains as to how important a well sealed coronal restoration is for the long-term success of endodontic treatment. Studies by Ray & Trope (1995) and Kirkevang et al. (2000) found the coronal restoration to be of relatively greater importance than the root-canal filling. Tronstad et al. (2000) found the quality of rootcanal treatment to be more important; the present study found both to be of equal importance. The Odds ratios in Tables 4 and 5 for the radiographic appearance of the coronal restoration and the homogeneity of the root fillings are of the same magnitude, indicating an equal effect on the periapical condition. This is in contrast with the study by Ray&Trope (1995) who found the Odds ratio for quality of restoration to be four times higher than for endodontic quality. Ricucci et al. (2000) found no statistically different prevalence of apical periodontitis in root fillings exposed to the oral environment compared with a control group. It is clear that bacterial ingress should be avoided, but the importance of both the coronal restoration and the root filling should be emphasized as good technical quality of both is a prerequisite for long-term success.
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