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Endodontic treatment of teeth with apical periodontitis: Single vs. Multivisit treatment
JouRNAL OF ENDODONTICS Copyright © 1999 by The American Association of Endodontists
Printed in U.S.A. VOL. 25, No. 5, MAY 1999
Endodontic Treatment of Teeth with Apical Periodontitis: Single vs. Multivisit Treatment Martin Trope, DMD, E. Olutayo Delano, BDS, MS, and Dag •rstavik, DDS, PhD
This study was performed to evaluate radiographic healing of teeth with apical periodontitis, treated in one visit or in two visits (a) with or (b) without calcium hydroxide as an intracanal disinfecting medicament. The patients were assigned one of the three treatment groups by the throwing of a die. The Periapical Index (PAl) Scoring Method was used to compare differences in periapical status from the beginning of treatment to a 52-wk follow-up evaluation. Overall, the periapical status of the treated teeth improved significantly after 52 wk (p < 0.0001). A PAl score of 1 or 2 was considered as representing a "good" periapical status while 3, 4, or 5 was a "bad" status. When base line PAl scores were controlled for, the calcium hydroxide group showed the most improvement in PAl score (3, 4, or 5 to 1 or 2), followed by the one-step group (74% vs. 64%). The teeth that were left empty between visits had clearly inferior healing results. Power statistics were conducted to determine the numbers required for significant differences between the groups, and it was shown that large experimental groups on the order of hundreds of patients would be required to show significant differences.
NaOC1 provides disinfection in some 40 to 60% of the teeth thus treated (7). The subsequent application of a calcium hydroxide dressing brings the percentage of bacteria-negative teeth to 90 to 100% (8); this treatment regimen is thus the current standard for root canal disinfection. One issue frequently debated in recent years is whether conscientious cleaning by instrumention and irrigation may reduce the need for a dressing and effect satisfactory disinfection of the canal system (9, 10). Such single-visit treatment would, if successful, be time-saving and reduce the risk of interappointment infection. Many practitioners experience high success rates with this technique, based on patient acceptance, lack of significant flare-ups, and practice management considerations. However, whereas a favorable flare-up rate for one-step treatment is documented (11, 12), a well-designed, prospective follow-up study has not been performed on the long-term success of this technique, compared with controlled disinfection with calcium hydroxide, followed by obturation. Recently, efforts have been made to improve on the diagnostic techniques used to detect differences in response to treatment and treatment variables. An unbiased index scoring system (13) may afford improvements in the scientific aspect of radiographic interpretation in a large series of cases. Therefore, we felt that a controlled prospective study to evaluate treatment outcomes with these two treatment methods might be possible. The purpose of this study was to evaluate radiographic healing of teeth with apical periodontitis treated in (a) one visit or (b) two visits, either without or with the addition of calcium hydroxide as an intracanal disinfecting medicament.
Apical periodontitis is caused, primarily, by bacteria in the root canal space (1, 2). Therefore, a logical treatment aim is to remove as many of these bacteria as possible. If bacteria are removed to levels that are undetectable by bacteriological methods in use today, an extremely high success rate in the resolution of apical periodontitis can be expected (3, 4). The scientifically documented procedure for the best results in canal disinfection is based on complete debridement and irrigation of the root canal during the first appointment, followed by the application of a calcium hydroxide dressing for 1 wk or more. Root filling is then performed at the second or a later appointment (5). Mechanical instrumentation alone causes a 100- to a 1000-fold reduction in numbers of bacteria (6), but complete elimination in only 20 to 43% of cases. Added antibacterial irrigation with 0.5%
MATERIALS AND METHODS Patient Selection The primary criterion for inclusion of subjects in the study was the presence of radiographically demonstrable apical periodontitis on a single-rooted tooth or on one root with a single canal in one root of a multirooted tooth. Patients were excluded from the study if, (a) they had a diagnosis of diabetes, (b) they had a diagnosis of HIV infection or other immunocompromising disease, (c) they were < 16 or >80 years old, or (d) the apical two-thirds of the root canal in question had been entered and instrumented or dressed before the inclusion stage. 345
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Randomization After initial screening and registrations, the patients were assigned to a treatment group (1 of 3 treatment groups) by the throwing of a die. This ensured that each patient stood an equal chance of being treated with any method.
Consent The project was approved by the Committee on Investigations Involving Human Subjects at the University of North Carolina, School of Dentistry. All patients read and signed a consent form before initiation of the treatment.
Treatment All patients were treated by one author (D.O.) according to a standardized regimen, including elements of access, rubber dam, and establishment of asepsis. Instrumentation was also standardized with 2.5% NaOC1 used as the irrigant. All teeth were obturated with lateral condensation of gutta-percha and Roth 801 sealer (Roth Drug Co., Chicago, IL).
FIG 1. Impression of position of the radiographic mount. This enables follow-up radiographs to be taken at identical angles.
Treatment Groups GROUP1
Experimental Group (0): Treatment was completed in one appointment.
FIG 2. Reference radiographs, corresponding line drawings, and their associated PAl scores. (Reproduced with permission from the Swedish Dental Journal [1967].)
GROUP 2
Control Group (E): Instrumentation was completed at the first appointment. The canal was left empty, but closed for approximately 1 wk before the second appointment. On the second appointment, the treatment was completed. GROUP 3
Conventional Group (C): Instrumentation was completed at the first appointment. A dressing of calcium hydroxide was placed to remain for at least 1 wk. Treatment was completed at the second appointment.
interpretation designed to determine the absence, presence, or transformation of a disease state. The reference is made up of a set of five radiographs with corresponding line drawings and their associated score on a photographic print (Fig. 2). These scores are based on a correlation with inflammatory periapical status confirmed by histology (13). The 9 observers that participated in the study were made up of 4 graduate oral and maxillofacial radiology residents, 2 graduate endodontic residents, 1 oral epidemiologist, 1 general dentist, and 1 experienced endodontist. All were blinded to the u'eatment groups and aims of the study.
Observer Calibration Radiographic Technique All patients in the study had a standardized X-ray series. Pre-op, immediate post-op, and control radiographs were taken with individual bite-blocks attached to the beam-guiding device (XCP, Rinn Corp, Elgin, IL). The bite blocks were constructed in bite registration impression material (Polyvinylsiloxane, Kerr, Romulus, MI) and kept between appointments (Fig. 1). The essential radiographs in the series were all processed under similar conditions in the automatic X-ray processor.
Radiographic Evaluation Radiographic evaluation was done using the Periapical Index (PAI) Scoring System (13). This is a 5-point scale radiographic
Calibration was conducted by twice scoring a set of 100 cases on individual radiographs. The "true score" was by consensus of two dentists involved with the formulation of the system. The following specific written instructions were given to the observers: 1. Find the reference radiograph where the periapical area most closely resembles the periapical area you are studying. Assign the corresponding score to the observed root. 2. When in doubt, assign a higher score. 3. For multirooted teeth, use the highest of the scores given to the individual roots. 4. All teeth must be given a score. × 2 magnification was provided for optional use. Following the first observation session, agreement with reference "true score" was assessed with kappa statistics. One of the
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Endodontic Treatment of Apical Periodontitis
TABLE 1. Weighted kappa for observers before (A) and after (B) calibration with reference true PAl scores Observers
A
B
0-OR 1 -OR 2-OR 3-ER 4-ER 5-GD 6-OR 7-OE 8-EE
0.56 0.57 0.61 0.44 0.59 0.38 0.55 0.42 0.51
0.64 0.59 0.66 0.50 0.67 0.64 0.60 0.53 0.53
OR, oral radiology resident; ER, endodontic resident; EE, experienced endodontist; OE, oral epiderniologist; GD, general dentist.
authors (E.O.D.) had a brief conference with each of the observers on all cases that had a difference of more than one from the "true score" and on other randomly selected missed cases. A second session observation was done at a time not less than 3 days after the conference. Agreement with the reference was again evaluated to determine the effectiveness of the calibration exercise. The observation session of the study radiographs then followed.
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Radiographs from 81 patients with 102 cases (Table 2) were scored with the PAI. Sixty-one patients had single cases, 18 had 2 cases, and 2 patients had 3 cases. The patients were made up of 54 females and 27 males having a mean age of 44.6 years, with a range of 19 to 79. These cases were present on 514 radiographs, and a total of 556 scores were generated. Eight patients had 2 lesions each on 1 radiograph, and 1 patient had 2 lesions each on separate radiographs.
Observer Variation and True Scores The scores from observers 6 and 8 were eliminated before the determination of the "true score." The weighted kappa (Table 3) for observers 2, 4, and 7 did not change, whereas the others did slightly. Total agreement using the threshold for model scores improved from 70% for the "silver standard" scores to 76% for the "true score." Interobserver correlation with a mixed model regression analysis shows an improvement from 0.59 to 0.64 (Table 4) with the elimination of two observers.
True Scores A silver standard of "true score" was obtained by taking the model score corresponding to agreement by five or more observers or using the mean when fewer than five were in agreement. The averaged scores were rounded off to a whole unit. The "true score" was obtained by a similar approach for a subset of scores from seven observers after eliminating the two with the lowest correlation to the silver standard. The threshold was agreement between four observers.
INTRAEXAMINER RELIABILITY A repeat observation was conducted after more than 6 wk. The sample consisted of every fourth case from the original study pool until a total of 100 cases had been read by each observer.
NUMBERS AND STATISTICAL ANALYSIS The conventional procedure should produce a success rate of - 8 0 % . Computations of necessary sample sizes for comparisons among treatments indicate that sample sizes of 55 per group would be sufficient to detect differences in rates of 5% or more, with a power o f p = 0.20 (14). In this study, 102 teeth (C = 31, E = 26, O = 45) presented for the 52-wk follow-up examination. Because these numbers were unlikely to be large enough for statistical differences between the groups, a power analysis evaluation (see Results) was performed.
RESULTS Radiographic Method CALIBRATION The observers' competence at using the PAl all improved with calibration (Table 1).
Endodontic Treatment Results Figure 3 shows the mean PAI scores for all treated teeth over the 52-wk observation period. Longitudinal A N O V A of PAl with reference to base line was significant (p < 0.001), with effective difference starting at week 12. No significant interaction between time and treatment was demonstrated. For the PAI outcome, the M U L T I L O G procedure was used to compare the three treatments while controlling for the correlation structure of the data. A replacement design was used with the patient as the primary sampling unit. The models examined predicted PAI at week 52 by base line PAl (all five levels) and treatment received. We looked at PAl at week 52 as a dichotomy of good versus bad, where good was PAI score of 1 or 2 and bad was a PAI score of 3, 4, or 5. Table 5 gives the distribution of PAl scores at base line using the same good versus bad dichotomy. At base line treatment O (one-visit teeth) began with 42% of the teeth having a good PAI score, whereas treatment C (2 visits with calcium hydroxide) had just 23% of the teeth with a good PAl score. This difference in "starting points" had to be controlled for when interpreting the healing results at week 52. At week 52 (Table 6), overall 73.5% of the teeth (75/102) ended the study with a good PAI score, whereas 26.5% of the teeth (27/102) did not. Table 6 shows how the individual treatments performed. (These do not account for base line differences seen in Table 5.) The results of treatment E (2 visits, no calcium hydroxide) were clearly inferior to the other treatment methods. For this reason, and because this group was included primarily for purposes of bacteriology, all further analysis was to compare groups C and O only. The fact that overall treatments C and O ended the study with similar proportions of good responses, but started with different base line PAl scores, emphasizes the importance of controlling for baseline in the modeling process.
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Journal of Endodontics TABLE 2. Distribution of teeth and longitudinal radiographs scored with the PAl
Tooth Maxillary incisor Maxillary canine Maxillary premolar Maxillary molar Mandibular incisor Mandibular canine Mandibular premolar Mandibular molar
Total
Cases
0
1
4
12
24
52
Total
33 32% 4 4% 15 14% 9 9% 2 2% 2 2% 19 18% 19 18%
33 32% 4 4% 15 14% 8 9% 2 2% 2 2% 19 18% 19 18%
32 32% 3 3% 15 15% 9 9% 2 2% 2 2% 17 17% 19 19%
30 31% 4 4% 13 14% 9 9% 2 2% 2 2% 17 18% 19 20%
26 20% 3 3% 12 14% 7 8% 2 2% 2 2% 16 18% 20 23%
25 30% 3 4% 12 14% 7 8% 2 2% 2 2% 15 18% 19 22%
28 33% 3 4% 13 15% 6 7% 2 2% 2 2% 15 17% 17 20%
174 31% 20 4% 80 14% 46 8% 12 2% 12 2% 99 18% 113 20%
103 100%
102 100%
99 100%
96 100%
88 100%
85 100%
86 100%
556 100%
TABLE 3. Weighted kappa for observers against "silver standard" (A) and "true score" (B) and intraobserver (C) Observers
A
B
C
0-OR 1-OR 2-OR 3-ER 4-ER 5-GD 6-OR* 7-OE 8-EE*
0.65 0.73 0.76 0.68 0.66 0.60 0.57 0.70 0.48
0.67 0.74 0.75 0.70 0.66 0.60 0.54 0.70 0.45
0.62 0.61 0.65 0.68 0.67 0.69 0.40 0.50 0.46
OR, oral radiology resident; ER, endodontic resident; EE, experienced endodontist; OE, oral epidemiologist; GD, general dentist. * Observer scores eliminated before deriving "true score."
TABLE 4. Logistic regression analysis for interobserver correlation of PAl scores for the 9 observers (A) and subset of 7 observers used to determine "true score" (B) Week
A
B
0 1 4 12 24 52 Overall
0.60 0.59 0.61 0.52 0.57 0.44 0.59
0.63 0.65 0.65 0.59 0.62 0.51 0.64
Time in weeks 4
8
12
16
20
24
28
32
36
40
44
48
52
I
I
I
I
I
]
I
I
I
I
I
I
P
..._.._._---*
2
4-
5 -
FrG 3. Mean PAl scores for all treated teeth over the 52-wk observation period.
degrees of freedom. W h e n the model parameters are translated into odds ratios (Table 10), teeth treated with C are 1.39 (confidence interval = 0.35, 5.50) times more likely to have a good score than teeth treated with O, controlling for base line PAI score.
Power Analysis RESULTS WITH A WEIGHT OF ONE FOR EACH TOOTH (Table 7) The test for a difference among the treatments is not significant, with a p value of 0.1166 from a X2 of 2.21 with 2 degrees of freedom. When the model parameters are translated into odds ratios (Table 8), teeth treated with C are 1.15 (confidence interval = 0.31, 4.21) times more likely to have a good score than teeth treated with O, controlling for base line PAI score. RESULTS WITH EACH PATIENT ONLY CONTRIBUTING ONE TOOTH (Table 9) The overall test for a difference among the treatments is not significant, with a p value of 0.4587 from a )(2 of 0.79 with 2
This analysis was performed to determine if clinical significance between groups C and O would be attained at a number that was relevant to the practicing endodontist. Each patient contributed only one tooth to the power analysis, with preference given to the first tooth entered in the dataset. Each patient was limited to only one tooth for the most general sample size calculations for future studies, where number of teeth per patient is as yet unknown. Based on numbers from a generhl linear model from SAS, a 95% confidence interval for the difference in treatments C and O was found at DELTA--0.63018((1.96)(0.2649) = [ - 1 , 1 4 9 4 , -0.0826].
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TABLE 5. Distribution of PAl scores at baseline for the different treatment groups
Good PAl (1 or 2) Bad PAl (3, 4, 5)
C
E
O
Total
n = 7 (23 %) n = 2 4 (77%)
n = 8 (31%) n = l 8 (69%)
n = 19 (42 %) n = 2 6 (58%)
n = 34 (33 %) n = 6 8 (67%)
C, calcium hydroxide; E, empty between visits; O, one step.
TABLE 6. Distribution of PAl scores at week 52
Good PAl (1 or 2) Bad PAl (3, 4, 5)
C
E
O
Total
n = 2 5 (81%) n = 6 (19%)
n = 1 4 (54%) n - 1 2 (46%)
n = 3 6 (80%) n = 9 (20%)
n = 7 5 (73.5%) n = 2 7 (26.5%)
TABLE 7. Results with the weight of one for each tooth
Overall model Model minus intercept Base line PAl Treatment
df
Wald F
p Value
7 6 4 2
340.23 167.32 242.68 2.21
0.0000 0.0000 0.0000 0.1166
P A I >3 at start 4.5
3.5 TABLE 8. Model parameters as odds ratios
Odds of good PAl vs. bad PAl
Lower 95% limit Odds ratio Upper 95% limit
C
E
O
0.31 1.15 4.2t
0.10 0.33 1.10
1.00 1.00 1.00
"---..-"%.
3
2
0 TABLE 9. Results with each patient contributing one tooth
Overall model Model minus intercept Base line PAl Treatment
df
Wald F
p Value
7 6 4 2
361.53 152.41 219.04 0.79
0.0000 0.0000 0.0000 0.4587
TAeLE 10. Model parameters as odds ratios
Odds of good PAt vs. bad PAl
Lower 95% limit Odds ratio Upper 95% limit
C
E
O
0.35 1.39 5.50
0.15 0.57 2.16
1.00 1.00 1.00
TABLE 11. Sample sizes required per group to achieve 80%, 85%, 90%, and 9 5 % power for given deltas Delta
80%
85%
90%
95%
-0.6 -0.63018 -0.7 -1.0
44.8989 40.7014 32.9870 16.1636
51.3602 46.5586 37.7340 18.4897
60.1067 54.4874 44.1600 21.6384
74.3348 67.3854 54.6133 26.7605
Table 11 shows that, at this DELTA, the sample size of 67.3854 per group would be required for significance to be achieved.
Analysis Adjusted for Base Line: Improved Versus Not
Improved Figure 4 shows PAl scores versus time for the three treatment groups when the base line has been adjusted to those teeth that started the study with a PAI score above 3. Again, because of the
i
i
i
i
i
1
4
12
26
52
FIG 4. PAl scores versus time for the three treatment groups when the base line has been adjusted to those teeth that started the study with a PAl score above 3.
poor results of group E, further analysis was limited to C versus O. We compared groups O and C when base line at the start of the treatment of PAI > 3. Limiting to treatments C and O and to just one record per patient, there were 41 patients who began in the "bad category" with P A I > 3. Of the 41 patients who began the study with a good PAI score (1 or 2), none moved to a higher score at the end. Of the 19 patients in treatment C, 14 (74%) improved, whereas 14 of 22 (64%) patients of treatment O improved. In a clinical situation with similar trends in improvement for treatments C and O, the needed sample size per group for a significant difference between the treatments at the 0.05 level are: 354 with 80% power, 401 with 85% power, 466 with 90% power, and 571 with 95% power. DISCUSSION Traditional follow-up prognosis studies have been of large series of patients treated with one specified protocol (15, 16), with the results measured as success rates. It is difficult or impossible to use these studies to compare treatment protocols due to the variability and subjectivity of the data in the different studies (17). This study was a prospective study on teeth with similar pathology (apical periodontitis), making the comparison between treatment protocols viable. An important added advantage, in our opinion, was the use of the PAI radiographic scoring system. This method allowed an improved radiographic interpretation over the subjective radiographic evaluations used in most previous studies. The PAI developed by Orstavik et al. (13) appears to have the potential for early, objective detection of healing with good repro-
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Trope et al.
ducibility (18). It is based on a histological correlation (13, 19) with a PAI score of 1-2 defined as healed or minimally inflamed and scores 3-5 defined as diseased. However, it is still a subjective outcome prone to observer variation. To overcome this disadvantage as much as possible, we undertook the rather tedious task of calibrating observers and excluding those with statistically determined deficient performance, followed by a consensus of the better and reliable ones to provide a consensus of "true scores." This study illustrated two common problems with acquiring meaningful results in comparing endodontic treatment protocols. Firstly, if the base line apical status is not controlled for, the results can give a false impression of the efficacy of the clinical procedures. Without controlling for baseline in this study, the one-step and calcium hydroxide treatments resulted in almost identical numbers of teeth with "good" apical periodontium (i.e. PAl scores of 1 or 2). However, the calcium hydroxide group started with teeth with many more teeth in the "bad" PAI score than the one-step group. When base line was controlled by comparing the improvement of teeth which started a PAl score of > 3 and ended the 52-wk observation period with a score of < 2 , the difference of 10% (74% for calcium hydroxide vs. 64% for one-step) is important. However, even though the difference in the number of teeth with improvement was 10% for the groups being compared, we ran into the second common problem with endodontic studies in that the sample size was not large enough for statistical significance in the study. Because even the inferior treatment protocols resulted in about 60% success, it requires a large sample size to show statistically significant differences in results for different treatment protocols. These numbers are extremely difficult to achieve in a prospective study such as this one. To compensate for this problem, we performed power statistics on the data to determine the sample size at which significance could be achieved for the observed difference. In general, a sample size of 67 teeth per group would have resulted in significant differences between the singlevisit and calcium hydroxide groups. In teeth with a PAI score of > 3 (i.e. easily discernible apical radiolucencies), a sample size of 571 per group would be needed for the observed difference for improvement of the periapical status of the tooth to be significant. Whereas this number is difficult to achieve in a prospective, controlled study, the findings may still be clinically relevant. According to the literature, calcium hydroxide disinfection after chemomechanical cleaning will result in negative cultures in most cases (5), and the improvement rate of 74% for the calcium hydroxide group appears rather low in light of success rates reported for teeth with negative cultures. However, it must be taken into account that the P M evaluation is a more specific test that requires a real transition in the periapical status for success/failure analysis. Therefore, it is not surprising that the percentages are lower than the usual subjective radiographic evaluation methods of success. Leaving the canal empty without obturation or additional disinfection was clearly and consistently the worst method of treatment. This group was included primarily to serve as a bacteriological control for the single-visit cases. These results may be explained by the findings of Bystr6m et al. (20), where regrowth of bacteria in the canals occurred to levels similar to those at the start of treatment. Thus, in most cases when the canal is re-entered, the bacteria are at a level similfir to that at the start of treatment. Therefore, the inferior results for this group are not surprising, and it appears to be unacceptable to leave a previously infected canal empty between visits in clinical practice. One-step treatment has many potential advantages. It is less expensive, very well accepted by patients, and has been shown to
Journal of Endodontics
result in a lower flare-up rate (1 l, 12). It has been shown that instrumentation and irrigation alone decrease the number of bacteria in the canal 1000-fold (6). However, the canals cannot be rendered free of bacteria by this method alone. It has been theorized that the low number of bacteria left in the canal is below the threshold to sustain the inflammation periapically or are entombed and killed due to lack of space and nutrition after effective obturation of the space in the canal. Therefore, some have assumed that the additional disinfecting action of calcium hydroxide would not result in discernibly superior results. However, according to the results of this study, the additional disinfecting action of calcium hydroxide before obturation resulted in a 10% increase in healing rates. This difference should be considered clinically important. Dr. Trope is JB Freedland professor and chair, Department of Endodontics, School of Dentistry, University of North Carolina at Chapel Hill, Chapel Hill, NC. Dr. Delano is lecturer, Oral Radiology and Diagnosis, University of West Indies School of Dentistry, Champs F/uers, Trinidad. Dr. Orstavik is senior scientist, Scandinavian Institute of Dental Materials, Haslum, Norway, and adjunct professor, Department of Endodontics, School of Dentistry, Uni versity of North Carolina at Chapel Hill, Chapel Hill, NC. Address requests for reprints to Dr. Martin Trope, Department of Endodontics, School of Dentistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-2707.
References 1. Sunclqvist G. Bacteriologic studies of necrotic dental pulps. Thesis, Ume& University, 1976. 2. Kakehashi S, Stanley HR, Fitzgerald RJ. The effects of surgical exposures of dental pulps in germ-free and conventional laboratory rats. Oral Surg 1965;20:340-9. 3. Bystr6m A, Happonen R-P, Sj6gren U, Sundqvist G. Healing of periapical lesions of pulpless teeth after endodontic treatment with controlled asepsis. Ended Dent Traumato11987;3:58-65. 4. Sjorgren U, Figdor D, Persson S, Sundqvist G. Influence of infection at the time of root filling on the outcome of endodontic treatment of teeth with apical periodontitis. Int Ended J 1997;30:397-406. 5. Sj6gren U, Figdor D, Sp&ngberg L, Sundqvist G. The antimicrobial effect of calcium hydroxide as a short-term intracanal dressing. Int Ended J 1991 ;24:119-25. 6. Bystr6m A, Sundqvist G. Bacteriological evaluation of the efficacy of mechanical root canal instrumentation in root canal therapy. Scand J Dent Res 1981;89:321-8. 7. BystrdmA, Sundqvist G. Bacteriologic evaluation of the effect of 0.5 per cent sodium hypochlorite in endodontic therapy. Oral Surg 1983;55:307-12. 8. Bystr6m A, Claesson R, Sundqvist G. The antibacterial effects of cam phorated monochlorophenol, camphorated phenol, and calcium hydroxide in the treatment of infected root canals. Ended Dent Traumato11985;1:170-5. 9. Soltanoff W. A comparative study of the single-visit and multiple-visit endedontic procedure. J Endodon 1978;4:9-14. 10. Oiler S. Single-visit endodontic therapy. J Endodon 1983;9:4-7. 11. Trope M. Flare-up rate of single-visit endodontics. Int Ended J 1991; 24:24-7. 12. ~rstavik D, Sigurdsson A, Moiseiwitsch J, Yamauchi S, Trope M. Sensory and affective characteristics of pain following treatment of chronic apical periodentitis ]Abstract 2848]. J Dent Res 1996;75(Special Issue):373. 13. ~rstavik D, Kerekes K, Eriksen HM. The periapical index: a scoring system for radfographic assessment of apical periodontitis. Ended Dent Traumatol 1986;2:20-4. 14. Schuurs AHB, Wu M-K, Wesselink PR, Duivenvoorden HJ. Endodontic leakage studies reconsidered. Part II. Statistical aspects. Int Ended J 1983; 26:44-52. 15. Grahnen H, Hansson L. The prognosis of pulp and root canal therapy. A clinical and radiographic follow-up examination. Qdontol Revy 1961 ;12:146-55. 16. Kerekes K, Tronstad L. Long-term results of endodontic treatment performed with a standardized technique. J Endodon 1979;5:83-90. 17. Reit C, Hollender L. Radiographic evaluation of endodontic therapy and the influence of observer variation. Scand J Dent Res 1983;91:205-12. 18. Kerosuo E, GIrstavik D. Application of computerized image analysis to monitoring endodontic therapy: reproducibility and comparison with visual assessment. Dento-Maxillo-Facial Radiology 1997;26:79-84. 19. Brynolf I. A histological and roentgenological study of the periapical region of human upper incisors. Qdg.ntol Rev 1967;18(suppl. 11):1-176. 20. Bystr6m A, Sundqvist G. The antimicrobial action of sodium hypochlorite and EDTA in 60 cases of endodontic therapy. Int Ended J 1985;18: 35-42.
Printed in U.S.A. VOL. 25, No. 5, MAY 1999
Endodontic Treatment of Teeth with Apical Periodontitis: Single vs. Multivisit Treatment Martin Trope, DMD, E. Olutayo Delano, BDS, MS, and Dag •rstavik, DDS, PhD
This study was performed to evaluate radiographic healing of teeth with apical periodontitis, treated in one visit or in two visits (a) with or (b) without calcium hydroxide as an intracanal disinfecting medicament. The patients were assigned one of the three treatment groups by the throwing of a die. The Periapical Index (PAl) Scoring Method was used to compare differences in periapical status from the beginning of treatment to a 52-wk follow-up evaluation. Overall, the periapical status of the treated teeth improved significantly after 52 wk (p < 0.0001). A PAl score of 1 or 2 was considered as representing a "good" periapical status while 3, 4, or 5 was a "bad" status. When base line PAl scores were controlled for, the calcium hydroxide group showed the most improvement in PAl score (3, 4, or 5 to 1 or 2), followed by the one-step group (74% vs. 64%). The teeth that were left empty between visits had clearly inferior healing results. Power statistics were conducted to determine the numbers required for significant differences between the groups, and it was shown that large experimental groups on the order of hundreds of patients would be required to show significant differences.
NaOC1 provides disinfection in some 40 to 60% of the teeth thus treated (7). The subsequent application of a calcium hydroxide dressing brings the percentage of bacteria-negative teeth to 90 to 100% (8); this treatment regimen is thus the current standard for root canal disinfection. One issue frequently debated in recent years is whether conscientious cleaning by instrumention and irrigation may reduce the need for a dressing and effect satisfactory disinfection of the canal system (9, 10). Such single-visit treatment would, if successful, be time-saving and reduce the risk of interappointment infection. Many practitioners experience high success rates with this technique, based on patient acceptance, lack of significant flare-ups, and practice management considerations. However, whereas a favorable flare-up rate for one-step treatment is documented (11, 12), a well-designed, prospective follow-up study has not been performed on the long-term success of this technique, compared with controlled disinfection with calcium hydroxide, followed by obturation. Recently, efforts have been made to improve on the diagnostic techniques used to detect differences in response to treatment and treatment variables. An unbiased index scoring system (13) may afford improvements in the scientific aspect of radiographic interpretation in a large series of cases. Therefore, we felt that a controlled prospective study to evaluate treatment outcomes with these two treatment methods might be possible. The purpose of this study was to evaluate radiographic healing of teeth with apical periodontitis treated in (a) one visit or (b) two visits, either without or with the addition of calcium hydroxide as an intracanal disinfecting medicament.
Apical periodontitis is caused, primarily, by bacteria in the root canal space (1, 2). Therefore, a logical treatment aim is to remove as many of these bacteria as possible. If bacteria are removed to levels that are undetectable by bacteriological methods in use today, an extremely high success rate in the resolution of apical periodontitis can be expected (3, 4). The scientifically documented procedure for the best results in canal disinfection is based on complete debridement and irrigation of the root canal during the first appointment, followed by the application of a calcium hydroxide dressing for 1 wk or more. Root filling is then performed at the second or a later appointment (5). Mechanical instrumentation alone causes a 100- to a 1000-fold reduction in numbers of bacteria (6), but complete elimination in only 20 to 43% of cases. Added antibacterial irrigation with 0.5%
MATERIALS AND METHODS Patient Selection The primary criterion for inclusion of subjects in the study was the presence of radiographically demonstrable apical periodontitis on a single-rooted tooth or on one root with a single canal in one root of a multirooted tooth. Patients were excluded from the study if, (a) they had a diagnosis of diabetes, (b) they had a diagnosis of HIV infection or other immunocompromising disease, (c) they were < 16 or >80 years old, or (d) the apical two-thirds of the root canal in question had been entered and instrumented or dressed before the inclusion stage. 345
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Randomization After initial screening and registrations, the patients were assigned to a treatment group (1 of 3 treatment groups) by the throwing of a die. This ensured that each patient stood an equal chance of being treated with any method.
Consent The project was approved by the Committee on Investigations Involving Human Subjects at the University of North Carolina, School of Dentistry. All patients read and signed a consent form before initiation of the treatment.
Treatment All patients were treated by one author (D.O.) according to a standardized regimen, including elements of access, rubber dam, and establishment of asepsis. Instrumentation was also standardized with 2.5% NaOC1 used as the irrigant. All teeth were obturated with lateral condensation of gutta-percha and Roth 801 sealer (Roth Drug Co., Chicago, IL).
FIG 1. Impression of position of the radiographic mount. This enables follow-up radiographs to be taken at identical angles.
Treatment Groups GROUP1
Experimental Group (0): Treatment was completed in one appointment.
FIG 2. Reference radiographs, corresponding line drawings, and their associated PAl scores. (Reproduced with permission from the Swedish Dental Journal [1967].)
GROUP 2
Control Group (E): Instrumentation was completed at the first appointment. The canal was left empty, but closed for approximately 1 wk before the second appointment. On the second appointment, the treatment was completed. GROUP 3
Conventional Group (C): Instrumentation was completed at the first appointment. A dressing of calcium hydroxide was placed to remain for at least 1 wk. Treatment was completed at the second appointment.
interpretation designed to determine the absence, presence, or transformation of a disease state. The reference is made up of a set of five radiographs with corresponding line drawings and their associated score on a photographic print (Fig. 2). These scores are based on a correlation with inflammatory periapical status confirmed by histology (13). The 9 observers that participated in the study were made up of 4 graduate oral and maxillofacial radiology residents, 2 graduate endodontic residents, 1 oral epidemiologist, 1 general dentist, and 1 experienced endodontist. All were blinded to the u'eatment groups and aims of the study.
Observer Calibration Radiographic Technique All patients in the study had a standardized X-ray series. Pre-op, immediate post-op, and control radiographs were taken with individual bite-blocks attached to the beam-guiding device (XCP, Rinn Corp, Elgin, IL). The bite blocks were constructed in bite registration impression material (Polyvinylsiloxane, Kerr, Romulus, MI) and kept between appointments (Fig. 1). The essential radiographs in the series were all processed under similar conditions in the automatic X-ray processor.
Radiographic Evaluation Radiographic evaluation was done using the Periapical Index (PAI) Scoring System (13). This is a 5-point scale radiographic
Calibration was conducted by twice scoring a set of 100 cases on individual radiographs. The "true score" was by consensus of two dentists involved with the formulation of the system. The following specific written instructions were given to the observers: 1. Find the reference radiograph where the periapical area most closely resembles the periapical area you are studying. Assign the corresponding score to the observed root. 2. When in doubt, assign a higher score. 3. For multirooted teeth, use the highest of the scores given to the individual roots. 4. All teeth must be given a score. × 2 magnification was provided for optional use. Following the first observation session, agreement with reference "true score" was assessed with kappa statistics. One of the
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Endodontic Treatment of Apical Periodontitis
TABLE 1. Weighted kappa for observers before (A) and after (B) calibration with reference true PAl scores Observers
A
B
0-OR 1 -OR 2-OR 3-ER 4-ER 5-GD 6-OR 7-OE 8-EE
0.56 0.57 0.61 0.44 0.59 0.38 0.55 0.42 0.51
0.64 0.59 0.66 0.50 0.67 0.64 0.60 0.53 0.53
OR, oral radiology resident; ER, endodontic resident; EE, experienced endodontist; OE, oral epiderniologist; GD, general dentist.
authors (E.O.D.) had a brief conference with each of the observers on all cases that had a difference of more than one from the "true score" and on other randomly selected missed cases. A second session observation was done at a time not less than 3 days after the conference. Agreement with the reference was again evaluated to determine the effectiveness of the calibration exercise. The observation session of the study radiographs then followed.
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Radiographs from 81 patients with 102 cases (Table 2) were scored with the PAI. Sixty-one patients had single cases, 18 had 2 cases, and 2 patients had 3 cases. The patients were made up of 54 females and 27 males having a mean age of 44.6 years, with a range of 19 to 79. These cases were present on 514 radiographs, and a total of 556 scores were generated. Eight patients had 2 lesions each on 1 radiograph, and 1 patient had 2 lesions each on separate radiographs.
Observer Variation and True Scores The scores from observers 6 and 8 were eliminated before the determination of the "true score." The weighted kappa (Table 3) for observers 2, 4, and 7 did not change, whereas the others did slightly. Total agreement using the threshold for model scores improved from 70% for the "silver standard" scores to 76% for the "true score." Interobserver correlation with a mixed model regression analysis shows an improvement from 0.59 to 0.64 (Table 4) with the elimination of two observers.
True Scores A silver standard of "true score" was obtained by taking the model score corresponding to agreement by five or more observers or using the mean when fewer than five were in agreement. The averaged scores were rounded off to a whole unit. The "true score" was obtained by a similar approach for a subset of scores from seven observers after eliminating the two with the lowest correlation to the silver standard. The threshold was agreement between four observers.
INTRAEXAMINER RELIABILITY A repeat observation was conducted after more than 6 wk. The sample consisted of every fourth case from the original study pool until a total of 100 cases had been read by each observer.
NUMBERS AND STATISTICAL ANALYSIS The conventional procedure should produce a success rate of - 8 0 % . Computations of necessary sample sizes for comparisons among treatments indicate that sample sizes of 55 per group would be sufficient to detect differences in rates of 5% or more, with a power o f p = 0.20 (14). In this study, 102 teeth (C = 31, E = 26, O = 45) presented for the 52-wk follow-up examination. Because these numbers were unlikely to be large enough for statistical differences between the groups, a power analysis evaluation (see Results) was performed.
RESULTS Radiographic Method CALIBRATION The observers' competence at using the PAl all improved with calibration (Table 1).
Endodontic Treatment Results Figure 3 shows the mean PAI scores for all treated teeth over the 52-wk observation period. Longitudinal A N O V A of PAl with reference to base line was significant (p < 0.001), with effective difference starting at week 12. No significant interaction between time and treatment was demonstrated. For the PAI outcome, the M U L T I L O G procedure was used to compare the three treatments while controlling for the correlation structure of the data. A replacement design was used with the patient as the primary sampling unit. The models examined predicted PAI at week 52 by base line PAl (all five levels) and treatment received. We looked at PAl at week 52 as a dichotomy of good versus bad, where good was PAI score of 1 or 2 and bad was a PAI score of 3, 4, or 5. Table 5 gives the distribution of PAl scores at base line using the same good versus bad dichotomy. At base line treatment O (one-visit teeth) began with 42% of the teeth having a good PAI score, whereas treatment C (2 visits with calcium hydroxide) had just 23% of the teeth with a good PAl score. This difference in "starting points" had to be controlled for when interpreting the healing results at week 52. At week 52 (Table 6), overall 73.5% of the teeth (75/102) ended the study with a good PAI score, whereas 26.5% of the teeth (27/102) did not. Table 6 shows how the individual treatments performed. (These do not account for base line differences seen in Table 5.) The results of treatment E (2 visits, no calcium hydroxide) were clearly inferior to the other treatment methods. For this reason, and because this group was included primarily for purposes of bacteriology, all further analysis was to compare groups C and O only. The fact that overall treatments C and O ended the study with similar proportions of good responses, but started with different base line PAl scores, emphasizes the importance of controlling for baseline in the modeling process.
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Journal of Endodontics TABLE 2. Distribution of teeth and longitudinal radiographs scored with the PAl
Tooth Maxillary incisor Maxillary canine Maxillary premolar Maxillary molar Mandibular incisor Mandibular canine Mandibular premolar Mandibular molar
Total
Cases
0
1
4
12
24
52
Total
33 32% 4 4% 15 14% 9 9% 2 2% 2 2% 19 18% 19 18%
33 32% 4 4% 15 14% 8 9% 2 2% 2 2% 19 18% 19 18%
32 32% 3 3% 15 15% 9 9% 2 2% 2 2% 17 17% 19 19%
30 31% 4 4% 13 14% 9 9% 2 2% 2 2% 17 18% 19 20%
26 20% 3 3% 12 14% 7 8% 2 2% 2 2% 16 18% 20 23%
25 30% 3 4% 12 14% 7 8% 2 2% 2 2% 15 18% 19 22%
28 33% 3 4% 13 15% 6 7% 2 2% 2 2% 15 17% 17 20%
174 31% 20 4% 80 14% 46 8% 12 2% 12 2% 99 18% 113 20%
103 100%
102 100%
99 100%
96 100%
88 100%
85 100%
86 100%
556 100%
TABLE 3. Weighted kappa for observers against "silver standard" (A) and "true score" (B) and intraobserver (C) Observers
A
B
C
0-OR 1-OR 2-OR 3-ER 4-ER 5-GD 6-OR* 7-OE 8-EE*
0.65 0.73 0.76 0.68 0.66 0.60 0.57 0.70 0.48
0.67 0.74 0.75 0.70 0.66 0.60 0.54 0.70 0.45
0.62 0.61 0.65 0.68 0.67 0.69 0.40 0.50 0.46
OR, oral radiology resident; ER, endodontic resident; EE, experienced endodontist; OE, oral epidemiologist; GD, general dentist. * Observer scores eliminated before deriving "true score."
TABLE 4. Logistic regression analysis for interobserver correlation of PAl scores for the 9 observers (A) and subset of 7 observers used to determine "true score" (B) Week
A
B
0 1 4 12 24 52 Overall
0.60 0.59 0.61 0.52 0.57 0.44 0.59
0.63 0.65 0.65 0.59 0.62 0.51 0.64
Time in weeks 4
8
12
16
20
24
28
32
36
40
44
48
52
I
I
I
I
I
]
I
I
I
I
I
I
P
..._.._._---*
2
4-
5 -
FrG 3. Mean PAl scores for all treated teeth over the 52-wk observation period.
degrees of freedom. W h e n the model parameters are translated into odds ratios (Table 10), teeth treated with C are 1.39 (confidence interval = 0.35, 5.50) times more likely to have a good score than teeth treated with O, controlling for base line PAI score.
Power Analysis RESULTS WITH A WEIGHT OF ONE FOR EACH TOOTH (Table 7) The test for a difference among the treatments is not significant, with a p value of 0.1166 from a X2 of 2.21 with 2 degrees of freedom. When the model parameters are translated into odds ratios (Table 8), teeth treated with C are 1.15 (confidence interval = 0.31, 4.21) times more likely to have a good score than teeth treated with O, controlling for base line PAI score. RESULTS WITH EACH PATIENT ONLY CONTRIBUTING ONE TOOTH (Table 9) The overall test for a difference among the treatments is not significant, with a p value of 0.4587 from a )(2 of 0.79 with 2
This analysis was performed to determine if clinical significance between groups C and O would be attained at a number that was relevant to the practicing endodontist. Each patient contributed only one tooth to the power analysis, with preference given to the first tooth entered in the dataset. Each patient was limited to only one tooth for the most general sample size calculations for future studies, where number of teeth per patient is as yet unknown. Based on numbers from a generhl linear model from SAS, a 95% confidence interval for the difference in treatments C and O was found at DELTA--0.63018((1.96)(0.2649) = [ - 1 , 1 4 9 4 , -0.0826].
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TABLE 5. Distribution of PAl scores at baseline for the different treatment groups
Good PAl (1 or 2) Bad PAl (3, 4, 5)
C
E
O
Total
n = 7 (23 %) n = 2 4 (77%)
n = 8 (31%) n = l 8 (69%)
n = 19 (42 %) n = 2 6 (58%)
n = 34 (33 %) n = 6 8 (67%)
C, calcium hydroxide; E, empty between visits; O, one step.
TABLE 6. Distribution of PAl scores at week 52
Good PAl (1 or 2) Bad PAl (3, 4, 5)
C
E
O
Total
n = 2 5 (81%) n = 6 (19%)
n = 1 4 (54%) n - 1 2 (46%)
n = 3 6 (80%) n = 9 (20%)
n = 7 5 (73.5%) n = 2 7 (26.5%)
TABLE 7. Results with the weight of one for each tooth
Overall model Model minus intercept Base line PAl Treatment
df
Wald F
p Value
7 6 4 2
340.23 167.32 242.68 2.21
0.0000 0.0000 0.0000 0.1166
P A I >3 at start 4.5
3.5 TABLE 8. Model parameters as odds ratios
Odds of good PAl vs. bad PAl
Lower 95% limit Odds ratio Upper 95% limit
C
E
O
0.31 1.15 4.2t
0.10 0.33 1.10
1.00 1.00 1.00
"---..-"%.
3
2
0 TABLE 9. Results with each patient contributing one tooth
Overall model Model minus intercept Base line PAl Treatment
df
Wald F
p Value
7 6 4 2
361.53 152.41 219.04 0.79
0.0000 0.0000 0.0000 0.4587
TAeLE 10. Model parameters as odds ratios
Odds of good PAt vs. bad PAl
Lower 95% limit Odds ratio Upper 95% limit
C
E
O
0.35 1.39 5.50
0.15 0.57 2.16
1.00 1.00 1.00
TABLE 11. Sample sizes required per group to achieve 80%, 85%, 90%, and 9 5 % power for given deltas Delta
80%
85%
90%
95%
-0.6 -0.63018 -0.7 -1.0
44.8989 40.7014 32.9870 16.1636
51.3602 46.5586 37.7340 18.4897
60.1067 54.4874 44.1600 21.6384
74.3348 67.3854 54.6133 26.7605
Table 11 shows that, at this DELTA, the sample size of 67.3854 per group would be required for significance to be achieved.
Analysis Adjusted for Base Line: Improved Versus Not
Improved Figure 4 shows PAl scores versus time for the three treatment groups when the base line has been adjusted to those teeth that started the study with a PAI score above 3. Again, because of the
i
i
i
i
i
1
4
12
26
52
FIG 4. PAl scores versus time for the three treatment groups when the base line has been adjusted to those teeth that started the study with a PAl score above 3.
poor results of group E, further analysis was limited to C versus O. We compared groups O and C when base line at the start of the treatment of PAI > 3. Limiting to treatments C and O and to just one record per patient, there were 41 patients who began in the "bad category" with P A I > 3. Of the 41 patients who began the study with a good PAI score (1 or 2), none moved to a higher score at the end. Of the 19 patients in treatment C, 14 (74%) improved, whereas 14 of 22 (64%) patients of treatment O improved. In a clinical situation with similar trends in improvement for treatments C and O, the needed sample size per group for a significant difference between the treatments at the 0.05 level are: 354 with 80% power, 401 with 85% power, 466 with 90% power, and 571 with 95% power. DISCUSSION Traditional follow-up prognosis studies have been of large series of patients treated with one specified protocol (15, 16), with the results measured as success rates. It is difficult or impossible to use these studies to compare treatment protocols due to the variability and subjectivity of the data in the different studies (17). This study was a prospective study on teeth with similar pathology (apical periodontitis), making the comparison between treatment protocols viable. An important added advantage, in our opinion, was the use of the PAI radiographic scoring system. This method allowed an improved radiographic interpretation over the subjective radiographic evaluations used in most previous studies. The PAI developed by Orstavik et al. (13) appears to have the potential for early, objective detection of healing with good repro-
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Trope et al.
ducibility (18). It is based on a histological correlation (13, 19) with a PAI score of 1-2 defined as healed or minimally inflamed and scores 3-5 defined as diseased. However, it is still a subjective outcome prone to observer variation. To overcome this disadvantage as much as possible, we undertook the rather tedious task of calibrating observers and excluding those with statistically determined deficient performance, followed by a consensus of the better and reliable ones to provide a consensus of "true scores." This study illustrated two common problems with acquiring meaningful results in comparing endodontic treatment protocols. Firstly, if the base line apical status is not controlled for, the results can give a false impression of the efficacy of the clinical procedures. Without controlling for baseline in this study, the one-step and calcium hydroxide treatments resulted in almost identical numbers of teeth with "good" apical periodontium (i.e. PAl scores of 1 or 2). However, the calcium hydroxide group started with teeth with many more teeth in the "bad" PAI score than the one-step group. When base line was controlled by comparing the improvement of teeth which started a PAl score of > 3 and ended the 52-wk observation period with a score of < 2 , the difference of 10% (74% for calcium hydroxide vs. 64% for one-step) is important. However, even though the difference in the number of teeth with improvement was 10% for the groups being compared, we ran into the second common problem with endodontic studies in that the sample size was not large enough for statistical significance in the study. Because even the inferior treatment protocols resulted in about 60% success, it requires a large sample size to show statistically significant differences in results for different treatment protocols. These numbers are extremely difficult to achieve in a prospective study such as this one. To compensate for this problem, we performed power statistics on the data to determine the sample size at which significance could be achieved for the observed difference. In general, a sample size of 67 teeth per group would have resulted in significant differences between the singlevisit and calcium hydroxide groups. In teeth with a PAI score of > 3 (i.e. easily discernible apical radiolucencies), a sample size of 571 per group would be needed for the observed difference for improvement of the periapical status of the tooth to be significant. Whereas this number is difficult to achieve in a prospective, controlled study, the findings may still be clinically relevant. According to the literature, calcium hydroxide disinfection after chemomechanical cleaning will result in negative cultures in most cases (5), and the improvement rate of 74% for the calcium hydroxide group appears rather low in light of success rates reported for teeth with negative cultures. However, it must be taken into account that the P M evaluation is a more specific test that requires a real transition in the periapical status for success/failure analysis. Therefore, it is not surprising that the percentages are lower than the usual subjective radiographic evaluation methods of success. Leaving the canal empty without obturation or additional disinfection was clearly and consistently the worst method of treatment. This group was included primarily to serve as a bacteriological control for the single-visit cases. These results may be explained by the findings of Bystr6m et al. (20), where regrowth of bacteria in the canals occurred to levels similar to those at the start of treatment. Thus, in most cases when the canal is re-entered, the bacteria are at a level similfir to that at the start of treatment. Therefore, the inferior results for this group are not surprising, and it appears to be unacceptable to leave a previously infected canal empty between visits in clinical practice. One-step treatment has many potential advantages. It is less expensive, very well accepted by patients, and has been shown to
Journal of Endodontics
result in a lower flare-up rate (1 l, 12). It has been shown that instrumentation and irrigation alone decrease the number of bacteria in the canal 1000-fold (6). However, the canals cannot be rendered free of bacteria by this method alone. It has been theorized that the low number of bacteria left in the canal is below the threshold to sustain the inflammation periapically or are entombed and killed due to lack of space and nutrition after effective obturation of the space in the canal. Therefore, some have assumed that the additional disinfecting action of calcium hydroxide would not result in discernibly superior results. However, according to the results of this study, the additional disinfecting action of calcium hydroxide before obturation resulted in a 10% increase in healing rates. This difference should be considered clinically important. Dr. Trope is JB Freedland professor and chair, Department of Endodontics, School of Dentistry, University of North Carolina at Chapel Hill, Chapel Hill, NC. Dr. Delano is lecturer, Oral Radiology and Diagnosis, University of West Indies School of Dentistry, Champs F/uers, Trinidad. Dr. Orstavik is senior scientist, Scandinavian Institute of Dental Materials, Haslum, Norway, and adjunct professor, Department of Endodontics, School of Dentistry, Uni versity of North Carolina at Chapel Hill, Chapel Hill, NC. Address requests for reprints to Dr. Martin Trope, Department of Endodontics, School of Dentistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-2707.
References 1. Sunclqvist G. Bacteriologic studies of necrotic dental pulps. Thesis, Ume& University, 1976. 2. Kakehashi S, Stanley HR, Fitzgerald RJ. The effects of surgical exposures of dental pulps in germ-free and conventional laboratory rats. Oral Surg 1965;20:340-9. 3. Bystr6m A, Happonen R-P, Sj6gren U, Sundqvist G. Healing of periapical lesions of pulpless teeth after endodontic treatment with controlled asepsis. Ended Dent Traumato11987;3:58-65. 4. Sjorgren U, Figdor D, Persson S, Sundqvist G. Influence of infection at the time of root filling on the outcome of endodontic treatment of teeth with apical periodontitis. Int Ended J 1997;30:397-406. 5. Sj6gren U, Figdor D, Sp&ngberg L, Sundqvist G. The antimicrobial effect of calcium hydroxide as a short-term intracanal dressing. Int Ended J 1991 ;24:119-25. 6. Bystr6m A, Sundqvist G. Bacteriological evaluation of the efficacy of mechanical root canal instrumentation in root canal therapy. Scand J Dent Res 1981;89:321-8. 7. BystrdmA, Sundqvist G. Bacteriologic evaluation of the effect of 0.5 per cent sodium hypochlorite in endodontic therapy. Oral Surg 1983;55:307-12. 8. Bystr6m A, Claesson R, Sundqvist G. The antibacterial effects of cam phorated monochlorophenol, camphorated phenol, and calcium hydroxide in the treatment of infected root canals. Ended Dent Traumato11985;1:170-5. 9. Soltanoff W. A comparative study of the single-visit and multiple-visit endedontic procedure. J Endodon 1978;4:9-14. 10. Oiler S. Single-visit endodontic therapy. J Endodon 1983;9:4-7. 11. Trope M. Flare-up rate of single-visit endodontics. Int Ended J 1991; 24:24-7. 12. ~rstavik D, Sigurdsson A, Moiseiwitsch J, Yamauchi S, Trope M. Sensory and affective characteristics of pain following treatment of chronic apical periodentitis ]Abstract 2848]. J Dent Res 1996;75(Special Issue):373. 13. ~rstavik D, Kerekes K, Eriksen HM. The periapical index: a scoring system for radfographic assessment of apical periodontitis. Ended Dent Traumatol 1986;2:20-4. 14. Schuurs AHB, Wu M-K, Wesselink PR, Duivenvoorden HJ. Endodontic leakage studies reconsidered. Part II. Statistical aspects. Int Ended J 1983; 26:44-52. 15. Grahnen H, Hansson L. The prognosis of pulp and root canal therapy. A clinical and radiographic follow-up examination. Qdontol Revy 1961 ;12:146-55. 16. Kerekes K, Tronstad L. Long-term results of endodontic treatment performed with a standardized technique. J Endodon 1979;5:83-90. 17. Reit C, Hollender L. Radiographic evaluation of endodontic therapy and the influence of observer variation. Scand J Dent Res 1983;91:205-12. 18. Kerosuo E, GIrstavik D. Application of computerized image analysis to monitoring endodontic therapy: reproducibility and comparison with visual assessment. Dento-Maxillo-Facial Radiology 1997;26:79-84. 19. Brynolf I. A histological and roentgenological study of the periapical region of human upper incisors. Qdg.ntol Rev 1967;18(suppl. 11):1-176. 20. Bystr6m A, Sundqvist G. The antimicrobial action of sodium hypochlorite and EDTA in 60 cases of endodontic therapy. Int Ended J 1985;18: 35-42.