1. health and fitness
2. disease

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
346
Journal of Endodontics
Trope et al.
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
Vol. 25, No. 5, May 1999
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.
347
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.
348
Trope et al.
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].
Vol. 25, No. 5, May 1999
Endodontic Treatment of Apical Periodontitis
349
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-
350
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.
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