Y. Boucher, L. Matossian, F. Rilliard & P. Machtou
Unite de Formation et de Recherche (UFR) d’Odontologie de l’Université Paris 7, Service d’Odontologie de l’Hôtel Dieu, AP-HP, Paris, France.

Introduction.
The success rate of root canal treatment is a public health problem that has medical, economic, and ethical repercussions. The establishment of treatment objectives, the codification of procedures and the improvement of techniques enable the modern practitioner to expect a high success rate (Strindberg 1956, Kerekes & Tronstad 1979, Byström et al . 1987 Sjögren et al . 1997). However, these high rates of success were obtained with well-trained practitioners under strict operating conditions that do not reflect the situation found within the average dental clinic. Therefore, in order to evaluate the endodontic status of populations rather than that of controlled patient groups, numerous studies have focused on the prevalence and quality of root canal treatment. Various studies from Sweden reported that the prevalence of endodontic treatment was about 13% of teeth (Petersson et al . 1986, Eckerbom et al . 1987). Many subsequent studies published in international journals substantiated these initial findings, both in Europe (Allard & Palmqvist 1986, Ödesjö et al . 1990, Imfeld 1991, Eriksen & Bjertness 1991, De Cleen et al . 1993, Eriksen et al . 1995, Soikkonen 1995, Saunders et al . 1997, Weiger et al . 1997, Marques et al. 1998, De Moor et al . 2000) and in the USA (Buckley & Spångberg 1995).
Overall, these reports indicated that the prevalence of root canal treatment varies from 1.3% to 20% and increases with age (see De Moor et al . 2000 for review). They also show that when these root canal treatments are evaluated radiographically, they are judged to be insufficient, in a large proportion of cases (Ödesjö et al . 1990). In addition, 18 to 61% of the cases were associated with radiographic signs of periapical lesions.
Studies which attempt to analyse the prevalence and quality of root canal treatment in France are rare and consist of internal studies of the Caisse Nationale d’Assurance Maladie (CNAM) (Gérard 1989, Hess & Mace 1994). They indicate a high prevalence of periapical lesions associated with root canal treatment and confirm the high demand for retreatments experienced by specialized endodontic practitioners. In view of the potential local and general consequences of periapical pathology (Simon 1998), it is important to gather data about the endodontic status of the population.
The aim of this study was to determine the prevalence and assess the quality of root canal treatment in a sample of the French population.

Materials and methods.
The sample consisted of patients seeking treatment at the dental service of the Hôtel Dieu, in Paris. The criteria for inclusion in the study were that the patients should be attending for the first time, had no dental treatment during the previous year, had not been referred by colleagues and must not have consulted the dental service for orthodontic reasons. The patients were at least 18 years old, and were accepted in the order of their attendance during a period of 1 year. A student strike interrupted data collection for 3 months. The scientific committee of the Dental Faculty approved the study, and patient anonymity was strictly respected.
Periapical radiographs were taken by two experienced radiographers using the long-cone paralleling technique with Rinn angulators. Double Kodak Ektaspeed Plus films (Kodak, Rochester, NY, USA) were used, which were automatically developed and fixed (XR24, Dürr Dental, Germany), and then mounted on black holders. The X-ray films were then evaluated by four examiners, divided into two groups of two, with negatoscope light using a magnifier ( 2) and the Mattson viewer (Mattson 1953) in difficult cases. The examiners were three members of the Restorative Dentistry and Endodontics Department who participated in the predoctoral and postgraduate endodontic teaching programmes of the Dental School, and a resident in the last year of study who was trained both in endodontics and in the analysis of radiographs. The scoring system proposed by Ørstavik et al . (1986) was used for evaluating the periapical conditions of each root. Two sessions, with a one-month interval between them, were spent in calibrating the examiners before radiographic analysis. The radiographs were examined in a two-month period in order to limit the variations between observers. To reduce these variations to a minimum, the radiographs were systematically examined by both observers of each group (Reit & Hollender 1983, Reit & Gröndahl 1983).
For each tooth and root the following items were surveyed: the presence of intracoronal or extracoronal (crowns) restorations; the presence of a root filling; the presence of posts; the periapical status (PAI 1–5). A score greater than 2 (PAI > 2) was considered to be a sign of periapical pathology (Ørstavik et al . 1986). The quality of root canal treatment was evaluated according to the density of the filling and the distance between the end of the filling and the radiological apex. A filling without any voids or defects along the walls of the canal and located between 0 and 2 mm from the radiographic apex, was considered to be an acceptable filling.
Observations of the teeth and the roots were analysed using the Excel® (Microsoft Corporation, Redmond, WA, USA) software. The chi-squared test was used to determine if the periapical status was affected by the technical quality of the root filling and the type of coronal restoration.

A total of 208 subjects were examined with a mean age 45.9 12.9 years. The distribution of the subjects by age is given in Figure 1; females comprised 62% of the sample.

Teeth.
The mean number of teeth per subject was 25.8, which corresponded to a total number of 5373 teeth (Table 1); 19.1% were root-filled. The periapical status of all teeth is indicated in Table 1. Excluding the 61 teeth for which the periapical status was impossible to determine, 7.4% of the teeth had a periapical lesion (PAI > 2). The periapical status of root-filled and nonroot-filled teeth is given in Table 2. In the nonroot-filled teeth, 2% presented with a PAI > 2 vs. 29.7% for the root-filled teeth.

Figure 1. Age and gender distribution of the sample.

Roots.
The teeth included in the survey had a total number of 8899 roots, of which 156 were not included in the study because of the poor quality of the radiograph or the absence of the apex on the radiograph. Of the 8743 usable roots, 1982 had undergone root canal treatment (22.7%). Amongst these, 24.4% had radiological signs of a periapical lesion (PAI > 2). The percentage was 2.2% for the-non-filled roots. The PAI value attributed to each category of teeth is shown in Table 3. The quality of root canal treatment is outlined in Table 4. Overall, 20.8% of the roots had acceptable root filling and 15.7% of these were associated with a PAI > 2. In the roots with unacceptable fillings, 73.3% had a normal periapical status. The most frequently root-filled teeth were the mandibular first molars (41.2%) and the maxillary first molars (34.2%), followed by the mandibular second molars (32.1%) and the maxillary second premolars (30.3%). There were 514 roots with posts (25.9% of the filled roots) (Table 5), and these were associated with a PAI > 2 in 28.6% of the cases. This was statistically different from the roots filled without a post ( P < 0.001, 2 ). 30.3% of the filled roots were associated with an intracoronal restoration with a PAI > 2 in 22.5% of the cases (Table 6); 59.6% exhibited an extra-coronal restoration associated in 23.7% of the cases with a periapical lesion. The remaining 10.1% of roots with no restoration were associated with a PAI > 2 in 33.3% of the cases. Root-filled roots without coronal restoration had significantly more periapical pathology compared to those with restorations ( P < 0.001, 2 ).

Table 1. Presence/absence of teeth and periapical status.

There were 52 fractured instruments and four patients had undergone periapical surgery. Sixty-two per cent of the patients presented with at least one periapical lesion.
Figure 2 illustrates the distribution of the different scores of PAI expressed as percentages for the different categories cited.

Table 2. Periapical status of root-filled and nonroot-filled teeth.


Table 3. Periapical status of-nonroot-filled and root-filled roots.


Table 4. Quality of root canal fillings.


Table 5. Periapical status of roots with posts.

Discussion.
The sample included in this study were adult patients attending the dental service of the Hôtel Dieu for general dental treatment. The recruitment of subjects was the same as those used by others (De Cleen et al. 1993, Buckley & Spångberg 1995, Saunders et al. 1997, Weiger et al. 1997, De Moor et al. 2000). There is no information available for this patient population, which makes it difficult to extrapolate the data obtained into the population of Paris or of France. However, the dental service attracts a patient population from numerous parts of the city and its surroundings, which eliminates the risk of only including patients previously treated by a limited number of practitioners. Some patients sought care because of the expense of prosthetic treatment, which in general is less at the dental service than in the private sector. It should also be noted that there were other patients who sought care because of the reputation of the university dental service.

Figure 2. PAI distribution according to the different categories of teeth and roots. Intra R, intracoronal restoration; Extra R, extra-coronal restoration; R-F, root-filling.

Our sample consisted of more women (62%) than men (38%), which may constitute a recruitment bias or reflect some sociologic aspects of the French population. However, similar epidemiological studies reported that gender had no effect on the quality of root filling or the presence of periapical lesions.
Our results showed that 19.1% of the teeth had undergone root canal treatment, which is rather higher than found in studies performed on populations of comparable age (Ödesjö et al. 1990, Buckley & Spångberg 1995, Saunders et al. 1997). They resemble more closely those obtained by Imfeld (1991) on a sample of patients older than 65 years. The high percentage of root-filled teeth may reflect a selection bias with regard to the patient population of our dentistry service or to treatment habits of French dentists. Pulp extirpation for prosthetic reasons are, for example, frequent (Weiss et al. 1998). However, this high number of root-filled teeth confers a greater statistical value to the sample with regard to periapical pathologies if one compares it to other studies (De Cleen et al. 1993, Marques et al. 1998). Moreover, it should be noted that in this study, the assessment of periapical status and technical quality was determined not only by teeth but also by root.
A periapical lesion was associated with 24.4% of the root-filled roots. This figure is in the range of those found in previous studies, which vary from 18 to 61% (De Moor et al. 2000). These findings can be compared with those obtained in France by Gérard (1989), who classified 24.5% of the teeth as being pathological. However, his sample included only radiographs sent by practitioners to the CNAM, the government organization which reimburses part of the cost of the crown when the tooth involved does not present any sign of periapical pathology. These radiographs were therefore selected. It was noted that, despite the prosthetic criteria requiring no existing periapical pathology, one-quarter of the teeth had a periapical lesion. In addition, no indication of age was available in that study. Our results are also difficult to compare with the study performed in France by Hess & Mace (1994), since these authors used two series of radiographs: either radiographs which had been submitted to the CNAM with a view toward prosthetic treatment, with the same reservations as previously cited, or orthopantomograms which are less precise for assessing periapical conditions than the periapical radiographs (Muhammed & Manson-Ring 1982) and are more subject to interobserver variations (Rohlin et al. 1991).
The number of roots classified as having periapical lesions is of interest. Ørstavik et al. (1986) established a Periapical Index (PAI) in correlation with the histological work of Brynolf (1979). The PAI scoring system allows standardization of the different categories, and thus comparisons between studies. Its reliability was established by further investigations (Ørstavik 1988). However, in order to differentiate the normal from the pathologic, the authors proposed a cut-off at a score of 2, since PAI > 2 was considered to be indicative of periapical pathology. This choice was selected by some authors but is, from our point of view, debatable. It is not the purpose of this article to reconsider what can radiologically be interpreted as healthy, but a cut-off point of PAI = 1 may be more appropriate. First, a score of 2 corresponds to an image with a localized widening of the ligament and/or associated signs of bone modifications which may be interpreted as either an ongoing healing process, an established state of irritation, or an evolution toward a pathological state. Since peak incidence of healing or emerging chronic apical periodontitis is at 1 year (Ørstavik 1996), the risks of a questionable image developing a more advanced lesion are increased. Secondly, periapical lesions are in general radiographically underestimated, since the cortical bone must have a 30–50% mineral bone loss to be detectable (Bender 1982). Moreover, as the PAI system was established for maxillary anterior incisors, where the cortical bone is thin, the risk of underestimation of lesions with a PAI > 2 is increased. Thirdly, other authors who did not use the PAI scoring system (Petersson et al. 1986, Hess & Mace 1994, Buckley & Spångberg 1995, Saunders et al. 1997,Weiger et al. 1997, De Moor et al. 2000) considered a localized increase of the periodontal space as a sign of apical periodontitis if bone changes were present. Finally, interobserver agreement is greater for teeth considered to be healthy than it is for grading a pathological state (Reit 1987). It is clear that the choice of cut-off is of primary importance because the number of roots classified as pathologic is approximately doubled if one chooses a limit at grade 2 or 3 (Tables 1–6).
This study also poses the problem of absent teeth, some of which may have been extracted for periapical pathological reasons. The most root-treated teeth were mandibular molars, which were also the most frequently missing, excluding third molars. It is reasonable to suppose that some of these teeth were extracted because of periapical pathology, with or without endodontic treatment. Root-filled teeth that were most frequently associated with pathology are, respectively, the single-rooted teeth > premolars > molars. In this study, if the mandibular incisors are excluded because of low numbers, the teeth that were most often associated with periapical pathology were the maxillary lateral incisors. Another interesting result of the present study concerns the quality of root canal treatment. Only 20.8% of the roots fulfilled the criteria for an acceptable root canal filling, i.e. a radiographically dense filling with its end located between 0 and 2 mm from the apex (European Society of Endodontology 1994). These results are worse than those of most of the other published studies, which show an acceptable root canal filling rate in 30–40% of roots (Petersson et al. 1986, Allard & Palmqvist 1986, Eckerbom et al. 1987, Eriksen et al. 1991, Ödesjö et al. 1990, Imfeld 1991, Buckley & Spångberg 1995, Saunders et al. 1997, Weiger et al. 1997, De Moor et al. 2000). These results therefore indicate that the majority of root canal fillings were performed poorly, despite the fact that the technical quality of care is a key factor in the healing or prevention of periapical pathologies (Strindberg 1956, Sjögren et al. 1990, ANDEM 1996). In addition, these observations only take into account the radiographic image of the treatment. It is therefore impossible to take into account the working conditions and especially disinfection of the root canal prior to filling, which is a major factor in terms of the outcome (Sjögren et al. 1997).
On the other hand, the poor technical quality must be balanced by the fact that 73.3% of the teeth with unacceptable root canal fillings did not present with radiographic signs of pathology. These root fillings may have been completed recently with insufficient time having elapsed for lesions to develop. Poorly sealed root-fillings are likely to become reinfected due to leakage, and thus represent a high risk for future periapical inflammation. At the same time, the filling criteria are not the only factors affecting the outcome and many studies have underlined the role of bacteria in the initiation of pulpal and periapical diseases (Bergenholtz et al. 1982, Ray & Trope 1995, Katebzadeh et al. 1999, Trope et al. 1999). It is therefore necessary to consider whether other factors (tooth isolation, use of disinfecting medications such as formalin derivates, etc.) may explain the success rate, despite the poor quality of the fillings. However, almost one-quarter of the root-filled roots had apical pathology, which translates into an important health risk. The quality of the seal performed with the coronal restoration is one of the factors which is significantly associated with failure of endodontic treatment (Ray & Trope 1995). Our study confirms these results, since 33.3% of the root-filled roots without coronal restoration showed significantly more periapical pathology (P < 0.001, 2) compared to those with restorations. Overall, 28.6% of the roots having a post were associated with periapical disease (P < 0.001, 2). These findings are in the range of other studies (Kvist et al. 1989: 16%; Buckley & Spångberg 1995: 26.9%; Saunders et al. 1997: 77%).

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