Discussion - References.
This study revealed radiographic periapical alterations in endodontically treated roots occurring more than 10 years after treatment. It confirms observations of radiographic changes in the periapical status made earlier by Strindberg (1956).However, the material, methods and findings must be analysed and discussed before conclusions are made regarding the validity of the findings and their clinical implications. The material - the observation period.
The endodontic treatments and the final coronal restorations, either by fillings or artificial crowns, had been done by undergraduate students in a dental school. Root fillings were completed in teeth with and without periapical radiolucencies, as primary treatments of inflamed and necrotic pulps or as re-treatments of root fillings made before the patients attended the dental school. The basic principles and working rules adhered to, and the technical results obtained, reflect a high standard of endodontic treatment during the period when the root- filling materials used were gutta-percha / chloro-percha (Molven1976,Molven&Halse1988).Changes in periapical status, as observed by radiographs, could therefore be studied in well-restored teeth with good root fillings. Success frequencies in such samples, presented in several investigations, are usually in the range 70-90% within a 4-year control period (for review, see Friedman1998).
Strindberg (1956) ended his observations with13% of his material followed for 9-10 years, whilst the cases in this study were first examined10-17 years after treatment and then again 10 years later. Strindberg concluded that 9% of the total material presented different results at the 4-year follow-up and the final follow-up examinations. In the present material changes were seen in 8% of the roots after more than 10 years. The latter observations support Strindberg (1956) when he doubted whether it was possible to establish an upper, definite limit for the follow-up period beyond which radiographic changes should be regarded as unlikely. The recording of later changes, both successes and failures, implies that the treatment methods were adequate and that such changes can be explained as part of the progression of events over time. The methods - the observers.
In the follow-up studies when few transitions between the diagnostic groups are expected, the quality of the diagnostic procedure is of the utmost importance (Koran 1976,WHO 1997,Wulff & Gotzsche 2000). A procedure based on an earlier suggested strategy (Halse & Molven 1986, Molven et al. 2002) was, therefore, established to minimize false recordings.
Changes were initially recorded by two observers (O.M. and A.H.) in 72 roots, which became the critical cases for assessing the reliability and validity of the recordings. With reference to the radiographic classifications (Molvenetal.2002), these cases were presented to another two experienced observers, an endodontist (I.F.) and a radiologist (D.M.). This treatment of the material should reduce the risk of error with respect to individual observations and increase the chances of obtaining correct conclusions. The supplementary recordings by I.F. and D.M. indicated a different cut-off point for disease with fewer periapical radiolucencies on both follow-up occasions. Then re-evaluation was performed by the original observers, and thereafter there were joint discussions between all four observers of all cases with disagreement. The observers knew, of course, that technical differences between radiographs increased the risk of small radiolucencies being hidden or remaining undetected, and hence they tried to avoid such pitfalls. First, the use of more than one exposure in each series would increase the chances of obtaining more reliable findings. Also a final joint evaluation of the diagnostic quality/ standard of the images for cases recorded with periapical changes would be expected to reduce false diagnoses. The approach to critical cases, first separately and then jointly by experienced examiners through discussions before consensus, satisfies reasonable methodological requirements (Koran 1976, WHO 1997).The identification of changes in the present radiographic follow-up series, therefore, should be regarded as valid. Late periapical changes - successes and failures.
The occurrence of changes after such long periods needs a biological explanation. It is recognized that microbial infection is the major factor in the prognosis of rootcanal treatment (Sundqvist & Figdor 1998). Foreign material, however, may be involved in the persistence and/or development of long-lasting lesions after conventional root-canal treatment. Filling material protruding into the periapical tissues may cause immediate tissue destruction and inflammation. A resulting asymptomatic foreign body reaction may explain some of the radiolucencies recorded after the end of the normal follow- up period (Nair et al. 1990, Ricucci & Langeland 1998, Sundqvist & Figdor1998).
In the present study, 14 of the 17 roots with late signs of periapical healing had been filled with surplus material extruding into the periapical area in necrotic cases. These cases can, therefore, be explained as healing processes disturbed by a foreign-body reaction. It is reasonable to also expect that infection and damage through over-instrumentation and extension of debris, including dentine chips into the periapical tissues, may contribute to the delay of the healing in such cases (Sundqvist & Figdor 1998). The additional three successes may be explained as infected cases with a reduction over time of the irritative effect of microorganisms and their final disappearance.
The later development of periapical radiolucencies may indicate either re-establishment of bacteria that for some time had been dormant or reduced in numbers, or contamination through coronal leakage, or both (Siqueira 2001). Clinical implications.
The clinical relevance of the present findings must be made clear, otherwise misinterpretations may easily occur regarding the relationship between over-extension of root fillings and the prognosis of root-canal treatment.
It is generally accepted that root-canal treatment should be considered as the clinical management of a microbiological problem (Sundqvist & Figdor 1998). Follow- up studies have, without exception and irrespective of the treatment and the diagnosis, shown that the best results are obtained for fillings ending at a short distance (0-2 mm) from the radiographic root apex. They have also revealed a negative influence on the prognosis from over-extension of the filling material through the apical foramen (for review, see Friedman1998).These observations are not contradicted in the present study, which is not a controlled investigation into prognostic factors, but a search for and a confirmation of the existence of late periapical changes as observed radiographically. More successes than failures were found with the long-term follow-up, thus increasing the percentage of successful cases in a selected group of roots by about 6% after more than 10 years. This increase was directly related to a number of over-extended root fillings with delayed healing - that is late disappearance of periapical areas - and underlines that tissue irritation during and after treatment should be avoided or reduced to a minimum.
Engstrom B, H Jrd af Segerstad L, Ramstrom G, Frostell G (1964) Correlation of positive cultures with the prognosis for root canal treatment. Odontologisk Revy 15, 257-70.
Friedman S (1998) Treatment outcome and prognosis of endodontic therapy. In: Krstavik D, Pitt Ford TR, eds. Essential Endodontology -Prevention and Treatment of Apical Periodontitis. London, UK: Blackwell Science, pp. 367-401.
Halse A, Molven O (1986) A strategy for the diagnosis of periapical pathosis. Journal of Endodontics12, 534-8.
Halse A, Molven O (1987) Overextended gutta-percha and Kloroperka N-K root canal fillings. Radiographic findings after 10-17 years. Acta Odontologica Scandinavica 45, 171-7.
Halse A, Molven O, Fristad I (2002) Diagnosing periapical lesions - disagreement and borderline cases. International Endodontic Journal, inpress.
Hepworth MJ, Friedman S (1997) Treatment outcome of surgical and non-surgical management of endodontic failures. Journal of Canadian Dental Association 63, 364-71.
Koran LM (1976) Increasing the reliability of clinical data and judgments.Annals of Clinical Research 8, 69-73.
Kvist T (2001) Endodontic retreatment. Aspects of decision making and clinical outcome. (Thesis). Swedish Dental Journal (Suppl.144).
Kvist T, Reit C(1999) Results of endodontic retreatment: a randomized clinical study comparing surgical and nonsurgical procedures. Journal of Endodontics 25, 814-7.
Molven O (1976) The frequency, technical standard and results of endodontic therapy.Den Norske TannlĂ¦geforenings Tidende 86,142-7.
Molven O, Halse A (1988) Success rates for gutta-percha and Kloroperka N-K root fillings made by undergraduate students: radiographic findings after 10-17 years. International Endodontic Journal 21, 243-50.
Molven O, Halse A, Fristad I (2002) Long-term reliability and observer comparisons in the radiographic diagnosis of periapical disease. International Endodontic Journal 35, 142-7.
Nair PNR, Sjogren U, Krey G, Sundqvist G (1990) Therapy-resistant foreign body giant cell granuloma at the periapex of a root-filled human tooth. Journal of Endodontics 16, 589-95.
Reit C (1987) Decision strategies in endodontics: on the design of arecallprogram. Endodontics and Dental Traumatology 3, 233-9.
Ricucci D, Langeland K (1998) Apical limit of root canal instrumentation and obturation: Part 2. A histological study. International Endodontic Journal 31, 394-409.
Saunders WP, Saunders EM (1994) Coronal leakage as a cause of failure in root canal therapy: a review. Endodontics and Dental Traumatology 10, 105-8.
Siqueira JF Jr (2001) Aetiology of root canal treatment failure: why well-treated teeth can fail. International Endodontic Journal 34, 1-10.
Sjogren U, Hagglund B, Sundqvist G, Wing K (1990) Factors affecting the long-term results of endodontic treatment. Journal of Endodontics 16, 498-504.
Strindberg LZ (1956) The dependence of the results of pulp therapy on certain factors. An analytic study based on radiographic and clinical follow-up examinations.Acta Odontologica Scandinavica 14 (Suppl. 21). Stockholm, Sweden: NO, Mauritzons Boktryckeri.
Sundqvist G, Figdor D (1998) Endodontic treatment of apical periodontitis. In: Krstavik D, Pitt FordTR, eds. Essential Endodontology Prevention and Treatment of Apical Periodontitis. London, UK: Blackwell Science, pp. 242-3, 255-6.
Torabinejad M, Ung B, Kettering JD (1990) In vitro bacterial penetration of coronally unsealed endodontically treated teeth. Journal of Endodontics16, 566-9.
Tronstad L, AsbjNrnsen K, DNving L, Pedersen I, Eriksen HM (2000) Influence of coronal restorations on the periapical health of endodontically treated teeth. Endodontics and Dental Traumatology 16, 218-21.
Weiger R, Axmann-Krcmar D, Lost C (1998) Prognosis of conventional root canal treatment reconsidered. Endodontics and Dental Traumatology 14, 1-9.
World Health Organization (1997) Oral Health Surveys, Basic Methods, 4th edn. Geneva, Switzerland: World Health Organization, pp.13-5, 62-3.
Wulff HR, Gotzsche PC (2000) Rational Diagnosis and Treatment. Evidence-Based Clinical Decision-Making. London, UK: Blackwell Science, pp.90-1.