N. N. Dugas, H. P. Lawrence, P. E.Teplitsky, M. J. Pharoah & S. Friedman
Departments of Endodontics, Community Dentistry, Radiology, Faculty of Dentistry, University of Toronto,124 Edward Street, Toronto, Ontario, Canada.
Endodontics, College of Dentistry, University of Saskatchewan, 105 Wiggins Road, Saskatoon, Saskatchewan, Canada.

Introduction.
Follow-up clinical studies have shown that root canal treatment applying modern principles of practice can yield favourable outcomes, with healing rates well above 90% (Friedman1998). However, such studies are usually performed on selected patient populations treated by skilled or supervised operators; therefore, they demonstrate the potential outcome of root canal treatment rather than its realistic outcome in the general population (Eriksen 1991). The latter is more readily available from epidemiological investigations that assess the endodontic health or disease status in various populations. The majority of recent endodontic epidemiological studies (Table 1) report alarmingly high prevalences of apical periodontitis associated with root-filled teeth, in the range of 16-61% (Soikkonen 1995, Weiger et al. 1997), as well as a frequent findingof inadequate root fillings in those teeth (Eriksen et al. 1988, Odesjoet al. 1990, Imfeld 1991, de Cleen et al. 1993, Petersson 1993, Buckley & Spangberg 1995, Ray & Trope 1995, Weiger et al. 1997, Marques et al. 1998, Sidaravicius et al. 1999, de Moor et al.2000, Kirkevang et al.2000,Tronstad et al. 2000). These studies indicate that endodontic knowledge acquired individually and collectively by treatment providers is not being properly applied.
It is generally accepted that the outcome of endodontic treatment is positively correlated with the technical quality of the root filling, expected to provide an hermetic seal against bacterial ingress (Kerekes & Tronstad 1979, Sjogren et al.1990). However, it has been suggested that the quality of the coronal restoration may also have an impact on the periapical health of root-filled teeth (Ray & Trope 1995, Sidaravicius et al. 1999, Kirkevang et al. 2000, Tronstad et al.2000); when the restoration quality is good, this may allow for a favourable outcome even when the root filling quality is poor (Ray & Trope1995).
The majority of the endodontic epidemiological studies have been reported in Europe. To date, there have been two studies carried out in the USA (Ray & Trope 1995, Buckley & Spangberg 1995), and none in Canada. Endodontics in North America differs from that in Europe, mainly with regards to the greater availability of specialized endodontists. It is generally assumed that treatment provided by endodontists is characterized by better quality and treatment outcomes than treatment provided by generalists. However, there are no data to support this assumption. Therefore, it appears that further epidemiological studies on North American populations are indicated to assess the realistic outcome of endodontic treatment, and its associations with the quality of root filling and restoration, as well as the provider of treatment.
The objective of the present study was to assess the endodontic health in two Canadian populations, one from an area dense with endodontists and the other from an area with few endodontists. Specifically, the goals were to:

1. determine the prevalence of apical periodontitis in root-filled and untreated teeth, and to relate it to
2. the radiographic quality of root fillings,
3. the quality and type of the coronal restoration and
4. the treatment provider’s level of endodontic training.

Table 1. Summary of recent endodontic epidemiological studies.

The study included 610 randomly selected, 25-40-year old subjects. All subjects presented as new patients seeking routine dental care (not emergency care) at the University of Toronto Faculty of Dentistry (n = 400) and at the University of Saskatchewan Dental School in Saskatoon (n = 210) between the years 1998 and 2000. These two sites were chosen because they were considered to reflect contrasting conditions - endodontists are abundant in Toronto, whilst the yare scarce in Saskatoon. Randomization was carried out using a random numbers table. To be enrolled in the study, the patient’s chart had to contain a current full-mouth radiographic series or panoramic radiograph. Where neither was present, the patient was excluded and the next one (in the alphabetical list of all patients) selected. Where only a panoramic radiograph was present, supplemental periapical radiographs were taken of all teeth that had root fillings. Because of the nature of the radiology clinics in both institutions, the intraoral films were exposed with a variety of X-ray machines and processed in a variety of automatic processors. However, all periapical radiographs were taken using the paralleling technique.
All radiographs were viewed in a ‘blind’ manner by one investigator. The method of viewing the radiographs was standardized - they were examined in a darkened room using an illuminated viewer box with magnification (3.5x) whilst mounted in a cardboard slit to block off ambient light emanating from the viewer. To avoid the need for interexaminer calibration, the same investigator collected the data at both study sites.
The following information was recorded on a structured form for each subject:

1. number of teeth present and the location of missing teeth;
2. number and location of teeth without root fillings (untreated teeth) having identifiable apical periodontitis lesions (as observed in panoramic or periapical radiographs) and
3. number and location of root-filled teeth.

In addition, the ‘Periapical Index’ (PAI) score (Krstavik et al.1986) was recorded for each one of the root-filled roots. The worst score of all roots was taken to represent the PAI score for multirooted teeth. The scores were then dichotomized into periapically ‘healthy’ (PAI 1 and 2) or ‘diseased’ (PAI 3- 5).The latter was considered to be consistent with apical periodontitis. The principal investigator was calibrated for the use of the PAI index. The kit of 100 reference radiographs and ‘gold standard’ observations (Krstavik et al. 1986) was used, dichotomizing the ‘gold standard’ observations as described above, and the interobserver Kappa score calculated. Observations were recorded at two different times and compared, in order to calculate the intraobserver Kappa score.
The quality of the root filling, with respect to density and length, was assessed and recorded for each root. Density was classified as follows:

1. adequate - uniform radiodensity and adaptation of the filling to the root canal walls, or
2. in adequate - visible canal space laterally along the filling or voids within the filling mass, or identifiable untreated canal.

Length was classified as follows:

1. short - ending more than 2 mm from the radiographic apex;
2. adequate - ending 0-2 mm short of the apex;
3. long - extruding beyond the apex.

The quality of the restoration was also assessed radiographically and classified as inadequate if the restoration was absent or if open margins, overhangs or secondary caries were detectable. In addition, the presence or absence of posts was noted.
All subjects identified to have at least one root-filled tooth were contacted by telephone and invited for an interview. Because the majority of the subjects had been enrolled as active patients at both institutions since their initial screening, these patients were interviewed when they arrived to undergo treatment in the university clinics. In order to increase the response rate, letters were sent to those patients who were not contacted by telephone. When contacted, the subjects were explained about the study, invited to enroll and offered a reimbursement for lost work time and travel expenses. The ethics committees of both institutions approved the study, and all enrolled subjects signed a written informed consent.
During the interview, the subjects answered a structured questionnaire that recorded reasons for extraction of missing teeth (if applicable), approximate date endodontic treatment was rendered and whether this was provided by a generalist or an endodontist. Also included were additional general questions intended to define the socio-demographic characteristics of the studied populations. In addition to the questionnaire, all root- filled teeth were clinically examined, with particular attention to detecting possible cracks or fractures of the coronal tooth structure, open margins, overhangs or secondary caries. The type of the restoration (temporary or permanent, intracoronal or extracoronal) was also noted.
Raw data were entered in Excel databases and statistical tests were carried out using the spss statistical package. Where appropriate, data were pooled for each subject and then for each of the two study populations. Chi-square and independent t-tests were used to analyse differences between and within groups. The distribution of each continuous outcome variable was checked for normality; for nonparametric distributions, Mann- Whitney U-test was used to confirm significance.
The prevalence of apical periodontitis was compared between, and within the two studied populations, between teeth treated by generalists and those treated by specialists and between teeth treated by generalists in Toronto and those treated by generalists in Saskatoon. Further comparisons were carried out between the different categories of root filling and restoration, and combinations thereof. All tests were two-tailed performed at the 5% significance level.

The PAI calibration process was concluded with inter and intraobserver Kappa scores of 0.941 and 0.985, respectively, indicating good agreement with the ‘gold standard’ and minimal variability in the PAI scoring.
Of the selected study population of 610 subjects, 328 (53.8%) were female and 282 (46.2%) were male. The sex distribution did not differ significantly between the Toronto and Saskatoon populations (P > 0.7).
Descriptive and analytic statistics regarding missing teeth, untreated teeth with apical periodontitis and root-filled teeth are summarized in Table 2. Overall, 309 subjects had at least one missing tooth (excluding third molars), 172 subjects had at least one untreated tooth with radiographic signs of apical periodontitis and 209 subjects had at least one root-filled tooth. Comparing the two study populations, the subjects in Saskatoon revealed significantly more complete, periapically healthy and endodontically untreated dentitions than the subjects in Toronto. Of the potential 17 080 teeth in the total population (28 _610), 932 teeth were missing. Thus, the total number of teeth inspected in the radiographs of all subjects was 16148, of which 10 474 were from the Toronto population and 5674 from the Saskatoon one. Of the total, 330 teeth (2.0%) were endodontically untreated and had apical periodontitis, whilst 411 teeth (2.5%) were root-filled. Because the Saskatoon population had only panoramic radiographs available, the 54 subjects with 97 root-filled teeth identified in the panoramic radiographs were invited to have periapical radiographs exposed in order to enable an appropriate determination of PAI scores for those teeth. Only 36 subjects with 69 (71.1%) root-filled teeth complied; therefore, in the following analyses only these teeth are included.
The distribution of PAI scores for the assessed 383 root-filled teeth is presented in Table 3. The most frequently assigned PAI score was ‘3’ (36.0%), whilst the most infrequent was ‘5’ (2.9%). Dichotomizing the PAI scores revealed that a total of 209 teeth were categorized as ‘healthy’, and the remaining 174 teeth were categorized as ‘diseased’, or having apical periodontitis. The difference in the proportion of ‘diseased’ root-filled teeth in the two populations was not statistically significant (chi-square, P > 0.3).
Of the total of 209 subjects with at least one root-filled tooth,119 subjects responded to the recruitment invitation and enrolled in the study, 83 in Toronto (53.5%) and 36 in Saskatoon (67.9%). The socio-demographic characteristics of the enrolled subjects are summarized in Table 4. The study populations in both sites were suitably matched, except for the significantly higher proportion of immigrants in the Toronto population.

Table 2. Numbers, mean values and prevalence of missing teeth, untreated teeth with apical periodontitis and root-filled teeth.



Table 3. Distribution of PAI scores for root-filled teeth.



Table 4. Socio-demographic characteristics of the subjects enrolled in the clinical examination and interview part of the study.



Table 5. Associations of periapical health (PAI scores1and 2) with antecedent factors in root-filled teeth. Analyses are based on all 383 teeth reviewed radiographically, unless otherwise specified.



Table 6. Odds Ratios (OR) and 95% confidence intervals (CI) estimating the risk of apical periodontitis in root-filled teeth related to treatment quality factors as assessed radiographically.

The root-filled teeth, those reviewed only radiographically (n = 383) and those examined both radiographically and clinically (n = 236), are characterized in Table 5, and the variables related to periapical health (PAI scores 1 and 2). Molars were the most prevalent amongst the root-filled teeth (42.8%), whilst the distribution amongst anteriors, premolars and molars did not differ significantly between the two populations (data not shown in table, P > 0.7). Of the 236 teeth examined clinically and addressed in patient interviews, 82.6% had been treated by generalists,87.3% had been treated over 2 years before the present examination, 16.1% were symptomatic at the time of the examination,36.4% had clinically detectable defective restorations and 19.5% had defects in coronal tooth structure. Of the total 383 teeth reviewed radiographically, the density and length of the root filling were adequate in 60.1 and 58.0%, respectively, whilst the coronal restoration was apparently adequate in only 42.3%. In 9.8% of the sample (n = 224), the restoration was either temporary or missing. The differences in periapical health related to tooth type and dental arch were borderline significant. Differences related to root filling density and length, as well as those related to the radiographic quality and type of the restoration, were all statistically significant. Differences in periapical health related to all other characteristics of the root-filled teeth were not statistically significant, including the difference between teeth treated by generalists and endodontists, and between generalists in Toronto and in Saskatoon (data not shown in table - 53.3 and 48.5%, respectively; P > 0.5).
Analysis of the agreement between the clinical and radiographic quality assessment of the coronal restorations in the 236 clinically examined teeth revealed a Kappa score of 0.235, demonstrating poor agreement between the clinical and radiographic assessments.
The likelihood of an outcome of apical periodontitis is related to radiographically assessed treatment quality factors in Table 6. The odds of developing apical periodontitis were 2.7 times higher when the root filling density was inadequate than when it was adequate, and 2.5 times higher when the root filling length was inadequate (short or long) than when it was adequate. Specifically, the root filling being short (OR = 2.4) or long (OR = 2.8) increased the odds of developing apical periodontitis, with no statistically significant difference between long and short root fillings. With regards to the quality of the coronal restoration, the odds of developing apical periodontitis were 1.7 times higher when it was inadequate than when it was adequate.
The two radiographic quality parameters of the root filling (density and length) found to be significantly associated with periapical health were analysed in various combinations (Table 7). The difference in prevalence of ‘healthy’ scores amongst the four root filling quality combinations was statistically significant (P < 0.001). The odds of apical periodontitis were 3 times higher when the root filling was inadequate (density or length) than when it was adequate. When both the root filling density and length were inadequate, the odds of apical periodontitis were 3.3 times higher than with any other root filling quality combination.
To assess the relative impacts of the apparent quality of the root filling and the restoration on periapical health, different combinations of the quality parameters were analysed (Table 8). For this analysis, the quality of the root filling was noted as inadequate if either the density or the length of the root filling was assessed as inadequate. The difference in prevalence of ‘healthy’ scores amongst the four combinations of root filling and restoration quality was statistically significant (P < 0.001). The odds of apical periodontitis were 4.6 times higher when the root filling or restoration were inadequate than when both were adequate. When both the root filling and restoration were inadequate, the odds of apical periodontitis were 2 times higher than with any other combination of root filling and restoration quality. Comparing teeth with adequate root fillings, the proportion of ‘healthy’ scores was significantly higher for those with adequate restorations than for those with inadequate restorations (P < 0.01). The odds of apical periodontitis were 2.8 times higher when an adequate root filling was coupled with an inadequate restoration than with an adequate one. In contrast, comparing teeth with inadequate root fillings, the difference between those with adequate and inadequate restorations was not statistically significant. When the root filling was inadequate, the odds of apical periodontitis were only 1.2 times higher with an inadequate restoration than with an adequate one.
Quality characteristics of the endodontic and overall treatment are related to providers of treatment in Table 9. Overall, adequate treatment on all accounts was more frequent amongst teeth treated by endodontists than teeth treated by generalists; however, the difference was statistically significant only for the length of the root fillings. Amongst teeth treated by generalists, the frequency of adequate quality of both the root filling and the restoration was significantly higher in the Saskatoon population.
Interviews of 119 subjects to determine the reasons for extraction of the 261 missing teeth revealed that 189 teeth (72.4%) were extracted because of caries and inability or refusal to receive endodontic care. A further five teeth (1.9%) were extracted because of persistence of apical periodontitis or fracture of the tooth after endodontic treatment, and eight teeth (3.1%) were extracted due to advanced periodontal disease. The remaining 59 teeth (22.6%) were extracted for a variety of other reasons, including orthodontic purposes.

Table 7. Combinations of quality of root fillings, as assessed radiographically, and their relation to periapical health (PAI scores 1 and 2) and risk of disease (N = 383 teeth).



Table 8. Combinations of quality of root fillings and restorations, as assessed radiographically, and their relation to periapical health (PAI scores1and 2) and risk for disease (N = 383 teeth).



Table 9. Quality characteristics of the treatment provided by generalists and endodontists.

Discussion.
The design of this cross-sectional study was modified from that of previous studies. Over the years, the endodontic cross-sectional study methodology has evolved, from exclusively radiographic evaluation of all teeth (Eckerbom et al.1991, Eriksen & Bjertness1991, de Cleen et al. 1993, Petersson 1993, Buckley & Spangberg 1995, Eriksen et al. 1995, Saunders et al. 1997, Marques et al. 1998, de Moor et al.2000, Kirkevang et al.2000), to radiographic evaluation of root-filled teeth only (Ray &Trope 1995,Tronstad et al. 2000), to radiographic and clinical evaluation of the root-filled teeth (Weiger et al. 1997, Sidaravicius et al.1999). In previous studies, the clinical examinationwas intended only to supplement the quality assessment of the restoration. In contrast, we were seeking to use the opportunity of the clinical examination to interview the subjects and derive further information, particularly regarding the providers of treatment and the causes for any tooth loss. Our data rely heavily on the reporting of the patients. It is conceivable that some of the reported information was inaccurate; however, because patients were interviewed rather than just handed a questionnaire, we were in a position to confirm the patients’confidence in providing accurate information. None of the patients indicated any doubt regarding the answers they provided. Therefore, we feel that the inclusion of interviews, although requiring actual patient enrolment and thus resulting in a reduced sample size, was worthwhile in allowing us to generate the data necessary to answer our research questions. In future studies, attempts may be made to actually contact some of the clinicians identified by the subjects a shaving performed endodontic treatment and extractions of missing teeth, to validate the data reported by the subjects.
To date, there have been just two endodontic cross-sectional studies reported on North American populations, one from a major city (Ray & Trope 1995) and one from a smaller community (Buckley & Spangberg 1995), and with the present study, we were aiming to augment that initial data. However, because in North America the population is not homogenous, it would appear that no single study focusingona specific population could have universal relevance to most of the population. Therefore, we chose to simultaneously study two populations, which we considered to have different characteristics. Toronto is the largest city in Canada, and is saturated with dental specialists including endodontists. In contrast, Saskatoon is a smaller city, with only two practising endodontists. By selecting these two sites for the present study, we were hoping that the results would have a larger applicability than if only one of the sites was selected.
For the past few years, the American Association of Endodontists (AAE) assigned a priority to the investigation of the ‘success of endodontic treatment performed by endodontists and generalists’. This research question would best be addressed in a prospective follow-up study, but both the design and time frame of such study would be very challenging. Because it is generally agreed that cross-sectional studies do reflect the realistic outcome of endodontic treatment in the general population (Eriksen 1998), we chose to address this research question using the cross-sectional study design. We assumed that a considerable proportion of the root-filled teeth in the Toronto population would be treated by endodontists. Indeed, the interviews indicated that 30.1% of the root- filled teeth of the subjects in Toronto and19.4% in Saskatoon had been treated by endodontists. Comparing these teeth with those treated by generalists could therefore address the research priority outlined by the AAE. We also wanted to expand the research question to address the level of undergraduate training, not just to compare generalists and endodontists. We assumed that the generalists in Saskatoon might be more adept at providing adequate endodontic treatment than their colleagues in Toronto, because the endodontic undergraduate training in Saskatoon is far more extensive than that in Toronto, and because the generalists in Saskatoon might have lesser opportunity to refer patients to endodontists.
Some of the previous cross-sectional studies have been compromised by the relatively high prevalence of missing teeth in the studied populations (Odesjoet al. 1990, Imfeld1991, Soikkonen1995, de Moor et al. 2000). Because usually there is no information available on the history of the missing teeth, it cannot be ruled out that they had been root-filled and then lost to persistent apical periodontitis. This possibility undermines the generated results regarding the outcome of endodontic treatment and renders them less conclusive. We intended therefore to minimize the prevalence of missing teeth in the study population. By focusing on the young adult age group, we were seeking a balance between the increase with age of the prevalence of root-filled teeth and that of advanced periodontal disease. Previous epidemiological studies (Odesjoet al. 1990, Eriksen 1991) have indicated that in the age group selected, the impact of advanced periodontal disease and resulting tooth loss should be limited, whereas the prevalence of root-filled teeth should be sufficient for a meaningful investigation. The lower probability of advanced periodontal disease would improve the chances that more of the missing teeth were root-filled. Consequently, the outcome of endodontic treatment would be more accurately reported. Indeed, the present study revealed that the mean number of missing teethwas1.69 teeth per subject, as compared to 3.3 in a previous study in middle-aged adults (Eriksen & Bjertness 1991), and 14 in an elderly urban population (Imfeld 1991). Furthermore, only 3% of the missing teeth in the examined population had been extracted due to advanced periodontal disease.
Our population-based study focused on first-time university patients, whom we considered to reflect treatment standards of private practices, rather than those of the university clinics. It is conceivable that this specific population seeking care in the university clinics represented a lower socio-economic status than the general population of the two sites of the study; however, the interviewed subjects’socio-demographic characteristics appear to dismiss this concern - 82.4% of the subjects were either enrolled in or had completed a postsecondary education, and 53.3% had an annual family income exceeding $30 000 (Canadian), confirming that the enrolled subjects did represent a population-based sample.
When comparing the results of the present and other epidemiological studies, consideration should be given to the variability of the evaluation criteria for apical periodontitis. In several studies (de Cleen et al.1993, Buckley & Spangberg 1995, Saunders et al. 1997, Weiger et al. 1997), apical periodontitis was noted when the periodontal ligament space was widened or the lamina dura was lost, and not just when a discernible periapical radiolucency was present. It is conceivable that such criteria may allow subjectivity and bias to affect the results. In contrast, in this study, like in several others (Eriksen & Bjertness 1991, Eriksen et al. 1995, Marques et al. 1998, Sidaravicius et al.1999, Kirkevang et al.2000) the PAI system was used and scores of 3-5 were considered as evidence of apical periodontitis. The PAI system provides criteria that are measurable (scores are related to reference radiographs), mutually exclusive (when in doubt, the higher value is assigned), meaningful (based on a combined radiographic and histologic evaluation of the periradicular tissues) and reproducible (Krstavik et al. 1986, Krstavik 1988). The principal investigator demonstrated excellent consistency in the assessment of the radiographs, with Cohen’s Kappa scores in excess of 0.94, confirming the validity and reliability of the results reported herein.
The radiographic examination of all teeth was cross sectional in design; radiographs were viewed at one point in time, irrespective of the time elapsed since endodontic treatment. It is conceivable that some of the radiolucencies associated with root-filled teeth and identified as apical periodontitis may have represented healing lesions, particularly if the time elapsed since treatment was less than 2 years (Friedman 1998). The above is a recognized limitation of cross-sectional studies; however, misinterpretations and misdiagnoses are known to be fairly equally distributed so that the results remain meaningful (Altman 1991). In any event, in the present study only 12.7% of the root-filled teeth had been treated within 2 years of the interview date, minimizing the risk of misinterpretation of radiolucent lesions.
By focusing on the total 16148 teeth present in the 610 young adults aged 25-40, the prevalence of root-filled teeth (n = 411) appeared to be 2.5%. However, conducting interviews with the subjects permitted a projection of the prevalence of endodontic disease in both the present and missing teeth.The119 interviewed subjects presented with 261 missing teeth, of which 193 had a history of endodontic disease - they were either extracted without endodontic treatment, or because disease persisted after treatment. Thus, the projected total number of teeth was 16 409 (16148+ 261), of which 604 (411+193) had suffered endodontic disease, for a projected prevalence of 3.7%. This prevalence is consistent with that reported in previous endodontic epidemiological studies on different populations, ranging from 1.3 to 20.3% (Imfeld1991, Eriksen et al.1995).
The prevalence of apical periodontitis in root-filled teeth in the present study was 45.4%.This finding is consistent with the results reported in previous methodologically compatible studies. In specific studies in which the prevalence of missing teeth is relatively high, the prevalence of apical periodontitis about root-filled teeth is lower than in other studies, probably because many root-filled teeth with apical periodontitis had been extracted (Soikkonen 1995, Marques et al. 1998). These two studies should therefore be excluded from comparison with the present one. In other previous studies on young adult populations, the prevalence of apical periodontitis in root-filled teeth is approximately 38% (Eriksen et al. 1995, Sidaravicius et al. 1999); in studies on university patients it ranges from 31to 60% (Buckley & Spangberg 1995, Ray & Trope 1995, de Moor et al. 2000, Tronstad et al.2000) and in studies using the PAI system it ranges from 37 to 52% (Eriksen et al. 1988, Eriksen & Bjertness 1991, Eriksen et al. 1995, Sidaravicius et al. 1999, Kirkevang et al.2000).Thus, the present study supported the well-documented conclusion that the realistic outcome of endodontic treatment in the general population was mediocre and considerably poorer than the potential outcome demonstrated in follow-up studies (Bystrom et al.1987, S jogren et al.1990, Friedman1998). The results also indicate the relatively large need in the population to treat apical periodontitis associated with root-filled teeth, mainly by performing orthograde retreatment or apical surgery. As in the previous studies, the mediocre outcome observed herein was coupled with mediocre quality of endodontic treatment, with less than 40% of the teeth having adequate root fillings, and less than 20%having adequate root fillings and restorations.
Root filling length was found to be adequate in 57% of the teeth, and the density in 60% of the teeth. When length was adequate, 36% of the teeth were associated with apical periodontitis. This finding is consistent with the range of 10 to 46% reported in previous studies (Eriksen et al.1988, Eriksen & Bjertness 1991).When the root-filling length was inadequate, the prevalence of apical periodontitis was close to 60%, regardless of whether the filling was too short or too long. Again, this finding was consistent with the observations in previous studies (Eriksen et al.1988, Eriksen & Bjertness 1991, de Cleen et al. 1993, Saunders et al. 1997). Likewise, when the root filling density was inadequate, 60% of the teeth had apical periodontitis - slightly less than the 70% reported in previous studies (Eriksen et al.1988, Eriksen & Bjertness 1991). Most importantly, when both the length and density of the root filling were adequate, less than 30% of the teeth were associated with apical periodontitis, in stark contrast to 70% of the teeth with both quality parameters being inadequate. As in previous studies, these results clearly implicate the quality of the root filling in the outcome of treatment.
The near 30% of teeth associated with apical periodontitis in spite of adequate root fillings indicated that the periapical health of the root-filled teeth was influenced by factors other than just the quality of the root filling Because the restoration and the root filling both serve as barriers against root canal reinfection (Saunders & Saunders 1997), both were assessed in combination. Although 236 root-filled teeth were clinically examined, it was decided to base the analyses related to restoration quality mostly on the radiographic examination for the following reasons:

1. some restorations might have been altered in the interim between the radiographic and clinical examinations;
2. Cohen’s Kappa and chi-square analyses revealed poor agreement between the clinical and radiographic quality assessments of the restorations and
3. only 57.4% of the root-filled teeth were available for clinical examination.

Previous studies (Ray & Trope1995, Sidaravicius et al. 1999, Kirkevang et al.2000,Tronstad et al.2000) attempting to assess the relative impact on periapical health of the coronal restoration and root filling have reported conflicting results. The first such study (Ray & Trope 1995) suggests that the quality of the restoration has a greater impact on periapical health than the quality of the root filling. Another study (Tronstad et al.2000) suggests that a correlation exists between the quality of the restoration and periapical health, but concludes that the quality of the restoration is significantly less important than the quality of the root filling. Further studies (Sidaravicius et al. 1999, Kirkevang et al. 2000) suggest that periapical health of root-filled teeth depends equally on the quality of the root filling and the restoration. The results of the present study suggested that for teeth with adequate root fillings but inadequate restorations, the risk of developing apical periodontitis was three times greater than for teeth with both adequate root filling and restoration. In other words, when the root filling appeared to be sound, the quality of the restoration had a decisive impact on the periapical health. This maybe explained by the inadequate restoration allowing a pathway for microbial ingress into the root canal system. If, however, the root filling was inadequate, the risk of developing apical periodontitis was not affected by the quality of the restoration. Thus, if the root filling was unsound, this most likely permitted the persistence of microorganisms within the root canal system that resulted in apical periodontitis (Moller et al.1981),without being dependent on further microbial ingress through the margins of an inadequate restoration. These findings further elucidated the associations between treatment quality and the outcome of treatment. They suggested that the root filling had a more decisive impact on the outcome of treatment than the restoration, corroborating the results reported by the most recent studies (Sidaravicius et al.1999, Kirkevang et al. 2000, Tronstad et al. 2000).
There is a general perception that endodontic treatment provided by endodontists is performed to a higher technical standard than treatment provided by generalists. It is further perceived that this higher standard results in a better treatment outcome. This study appears to be the first attempt to test these perceptions. Although adequate quality was almost 20% more prevalent amongst teeth treated by endodontists, this difference in quality was not characterized by statistical significance except for the length of the root filling. Most importantly, the outcome of treatment as shown by prevalence of apical periodontitis did not differ significantly between teeth treated by endodontists and generalists. However, in this study, treatment outcomes could be related to the treatment provider only for the interviewed subjects (n = 119); thus, the lack of significance may be the result of insufficient power. Furthermore, we must consider the possibility of recall bias, especially since 87% of the root-filled teeth had been treated more than 2 years prior to the interview date. Another concern is the large percentage of immigrants, particularly amongst the examined subjects in Toronto. There is a possibility that some of the root-filled teeth captured in this study were treated in the subjects’ countries of origin, and thus do not represent the standards of treatment provided by endodontists in Canada. Nevertheless, our findings appear to corroborate those of a recent insurance database-driven study (Lazarski et al. 2001), in which ‘untoward events’ (extraction, retreatment, or apical surgery) are used as an outcome measure. The authors conclude that their findings ‘strongly support the hypothesis that the specialist practice provides similar rates of clinical success compared with other providers’.
Treatment outcome and specific quality characteristics in teeth treated by generalists in Toronto and in Saskatoon did not differ; however, the overall quality of the treatment was significantly better in the Saskatoon population. This confirms our assumption that the treatment provided by generalists in Saskatoon would be better than that provided by generalists in Toronto. However, in the present study, this better quality did not translate in to a better treatment out come. Also, as mentioned above, the large percentage of immigrants may have introduced a bias that affected the assessment of treatment quality for the examined subjects in Toronto.

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