Download Prediction of maxillary canine impaction using sectors and angular

ORIGINAL ARTICLE
Prediction of maxillary canine impaction using
sectors and angular measurement
John H. Warford Jr, DDS,a,b Ram K. Grandhi, BDS, Dip Perio, Cert Ortho, MS,b and Daniel E. Tira, PhDc
Bismarck, ND, and Kansas City, Mo
Maxillary canine impaction has an incidence of 1 in 100 in the general population and has been reported as
much higher in an individual orthodontic practice. Because patients with canine impactions generally have
longer treatment times, depending on the location of the impacted tooth, early identification of impaction is
of critical interest to the orthodontist. Sector location and angulation of the unerupted tooth have been
analyzed previously as predictors of canine eruption after deciduous extraction. Additionally, sector location
has been studied as an indicator of eventual impaction, resulting in good predictive success. In this study,
angulation of the unerupted tooth was measured from panoramic radiographs and added to sector location
to see whether the combination of these factors could predict impaction more accurately than sector alone.
Results verified earlier findings for sector: canines that become impacted will overlap the adjacent lateral
incisor in 82% of cases. Logistic regression analysis also determined that once the canine overlaps the
midline of the lateral incisor, there is a greater than 0.87 chance of impaction. Sector was found to be the
better predictor of impaction, with angulation adding little supplementary predictive value. (Am J Orthod
Dentofacial Orthop 2003;124:651-5)
M
axillary canine palatal impaction occurs in 1
of 100 people.1,2 In a review of the literature,
Bishara3 reported that incidence of maxillary
canine impaction ranges between 1% and 3% of patients. Although this might seem to be a relatively small
number of affected people, it is speculated that in an
individual orthodontic practice, the incidence may be
higher, with a report of 23.5% in 1 population.4 Patients
with canine impactions experience longer treatment
times than those without impactions, depending on
displacement of the tooth from the occlusal plane.5
Maxillary canine impaction is complex in its etiology, localization, response to preventive treatments,
and prediction. It is a dilemma for many orthodontists.
Determining whether impaction will occur and timing
the treatment modalities that are affected by impacted
canine(s) are paramount for a successful outcome. If, in
these cases, orthodontic treatment is not initiated at an
early age, ankylosis of the canine and detrimental
effects on incisor roots are possibilities.6-8
There are many theories as to why canine impaction
a
Former resident, Department of Orthodontics and Dentofacial Orthopedics,
University of Missouri, Kansas City; private practice, Bismarck, ND.
b
Assistant professor, Department of Orthodontics and Dentofacial Orthopedics,
University of Missouri, Kansas City.
c
Professor Emeritus, Department of Public Health and Behavioral Science,
University of Missouri, Kansas City.
Reprint requests to: John H. Warford, DDS, 1145 West Turnpike, Bismarck,
ND 58501; e-mail, [email protected].
Submitted, November 2002; revised and accepted, February 2003.
Copyright © 2003 by the American Association of Orthodontists.
0889-5406/2003/$30.00 ⫹ 0
doi:10.1016/S0889-5406(03)00621-8
occurs, but they can be separated into 2 categories:
guidance and genetics. Bishara et al9 cited abnormal
tooth bud eruption, abnormal eruption rate, and delayed
resorption of deciduous teeth as possible guidance
factors. Evidence for a genetic etiology has many
forms. Baccetti10 notes an association between canine
impactions and other dental anomalies, while Peck et
al11 report that 33% of patients with impacted canines
have other congenitally missing teeth. Sex could be
another factor, because there seem to be twice as many
palatally impacted canines in females compared with
males.12
An additional complication with regard to location
of the impaction is the preponderance of palatal impactions over buccal impactions. Although the canine
develops high near the orbit and sinus, and buccal to
adjacent tooth roots, 85% of impacted canines are
located palatally.13,14 Fournier et al15 reported a palatal-to-buccal impaction ratio of 3:1, and Jacoby16 reported a ratio of 12:1. Jacoby14 further discussed local
factors such as arch length deficiency, which may be
the most intuitive etiologic factor in canine impaction.
He found, however, that 85% of palatally impacted
canines occur in patients with adequate arch length.
Regardless of the etiology, maxillary canine impactions occur with enough frequency to warrant extensive
study of possible preventive treatment modalities. Currently, the most common preventive treatment for
dealing with this quandary is to extract the deciduous
canine with the hope that the permanent canine resolves
651
652 Warford et al
its unfavorable position. Two studies have reported
good success with this treatment, finding favorable
eruption to occur 78% of the time6 and 62% of the
time,17 with the latter study finding an improved canine
position in an additional 19% of patients.
Two possible predictors of eventual treatment success are the mesiodistal location of the crown and the
angulation of the tooth. Ericson and Kurol7 found that
the more mesially located the crown, the more reduced
the likelihood of eruption after deciduous extraction.
Powers and Short17 also looked at angulation as a
predictor and found that if the tooth is angled more than
31° to the midline, its chances of eruption after deciduous extraction are decreased.
The second treatment option is to wait until the
permanent canine’s impaction is determined to be
imminent and then surgically expose and bond the tooth
or teeth in question. This procedure is followed by a
recovery technique most likely chosen by the orthodontist and accompanied by a high rate of success.
Although success rates for both treatment modes
are good, it would be desirable to have the ability to
predict maxillary canine impaction. When the patient is
referred from the general dentist with only a parent and
a panoramic radiograph, it would be reassuring to have
a reliable means to estimate the degree to which the
tooth is destined for impaction. Early detection and
prevention of impaction by deciduous extraction would
decrease the patient’s need for oral surgery and simplify orthodontic treatment.
Lindauer et al18 used an aspect of the Ericson and
Kurol6 model for predicting eruption after deciduous
extraction as a means for predicting eventual impaction
of the maxillary canine. Lindauer’s method used the
location of the cusp tip of the canine in question and its
relationship to the adjacent lateral incisor. He determined the probability for impaction based on the canine
cusp tip location in 1 of 4 sectors. Lindauer et al18
reported that this method identifies up to 78% of the
canines that are destined to become impacted, all of
which have cusp tips located in sectors II, III, and IV.
The first aim of the current study was to verify
Lindauer’s method by applying it to another sample of
patients. The second aim was to test the hypothesis that
the measurement of canine angulation will increase the
ability to estimate potential impaction beyond that
contributed by sector. Lindauer did not study canine
angulation, but it was previously noted that angulation
has been measured as an additional determinant of
successful eruption after deciduous tooth extraction.6,17
Thus, in this work, angulation was investigated as an
adjunct predictor of impaction.
American Journal of Orthodontics and Dentofacial Orthopedics
December 2003
MATERIAL AND METHODS
All patients included in the study came from 1
private practice orthodontic office. The potential study
sample was determined according to these criteria:
maxillary first molars and incisors were fully erupted,
with canines and premolars unerupted; patient’s chronological age was less than 12 years; impaction status
of the unerupted canine was unknown for either or both
teeth; no treatment was begun until impaction status
was determined; and any eventual impactions were
palatally located.
These criteria were applied to the patients’ records
by a trained member of the orthodontic practice staff.
This procedure allowed the canine’s impaction status to
remain unknown to the investigator. Records of 200
patients were selected. The investigator, still blind to
the outcomes of the canines in question, verified that
the criteria were followed, then applied 2 additional
criteria to determine the final study sample: all radiographs were taken on the same panoramic radiograph
machine (Sirona Orthophos Plus C, Bensheim, Germany), and the condyles had to be clearly distinguishable for landmark placement.
The final 2 criteria dramatically reduced the sample
size from 200 to 82, but they were deemed necessary to
reduce potential sources of variance (ie, different angular projections or focal troughs) that might have
occurred by using different panoramic radiograph machines. Additionally, clearly defined condyles were
imperative for proper landmark placement.
Data, consisting of sector, angular measurement,
age, and sex, were collected and entered into a spreadsheet. After all data were collected, the examiner
received a list of patients in the original 200 who had
eventual impacted canines. The 82 patients who had
met the second set of criteria were compared with the
list of eventual impactions from the original 200. Their
status, impaction or no impaction, was entered into the
data spreadsheet for statistical analysis.
For the 82 patients who met the criteria, the earliest
panoramic radiograph available was used. To determine the angular measurements, a reference line was
needed. Angulation as a predictor of eruption after
extraction of the deciduous canine was measured previously via a midline constructed from the perpendicular to the central incisors,17 and to a midline constructed from the mandibular central incisor
interproximal contact to the maxillary incisor interproximal contact.6 Although convenient, these measurements depend on anterior dental relationships. For
this investigation, skeletal landmarks were sought from
which to construct a measurement reference. The nasal
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 124, Number 6
Warford et al 653
Fig 1. Angular measurement of unerupted canines.
floor would be a logical choice for a horizontal line
from which to measure the canine’s angulation, but
Damante et al19 described no fewer than 7 shapes of the
hard palate and nasal fossa floor. The most superior
point of the condyle was selected as a landmark, as
alluded to in the secondary criteria. A bicondylar line
was then drawn and used as a constructed horizontal
reference line. The measurement was taken of the
mesial angle formed by using the constructed horizontal and the long axis of the unerupted tooth (Fig 1). The
sector of the unerupted canine cusp tip also was located
in accordance with the sector delineation used by
Lindauer et al18 taken from Ericson and Kurol6 (Fig 2).
The investigator underwent an intraexaminer reliability check for both angulation and sector. Ten
randomly selected panoramic radiographs were measured twice according to procedures mentioned, with 7
days separating the measurement sessions. Correlations
(Pearson r or Spearman ␳) between measurements on
these occasions were 0.999 for angulation and 1.000 for
sector. All measurements per patient were within 1°,
and sector designation did not differ between measurement sessions.
Descriptive statistics were applied to data for both
maxillary canines, which were subclassified as either
impacted or nonimpacted. The descriptive statistics
included mean, standard deviation (angular measures),
median, and semi-interquartile range (sector locations).
The Cramer V statistic and ␩ were used to determine
the zero-order correlations between impaction and sec-
Fig 2. Modification of Ericson and Kurol’s6 definition of
sectors, from Lindauer et al.18 Sector I represents area
distal to line tangent to distal heights of contour of
lateral incisor crown and root. Sector II is mesial to
sector I, but distal to bisector of lateral incisor’s long
axis. Sector III is mesial to sector II, but distal to mesial
heights of contour of lateral incisor crown and root.
Sector IV includes all areas mesial to sector III.
tor and impaction and angulation, respectively, for all
canines. Logistic regression was used to estimate of the
likelihood of impaction from sector location and angulation of canine.
654 Warford et al
Table I.
American Journal of Orthodontics and Dentofacial Orthopedics
December 2003
Descriptive data, right and left maxillary
Table II.
Logistic regression results
canines
No impaction
(n ⫽ 125)
Angle
(degrees)
Mean
Median
Standard deviation
Minimum
Maximum
Semi-interquartile range
75.12
75.00
8.47
50.00
97.00
Sector
1.00
1.00
3.00
.00
Impaction
(n ⫽ 35)
Angle
(degrees)
63.20
61.00
10.66
41.00
86.00
Sector
Sector
Angle
Constant
B
df
Sig
OR
95% CI for OR
2.167
⫺0.402
⫺3.830
1
1
1
.0001
.350
.014
8.728
.669
.022
3.752 to 20.304
0.288 to 1.553
B, Beta; df, degrees of freedom; Sig, statistical significance; OR, odds
ratio.
2.00
1.00
4.00
0.50
Probability of canine impaction based on
sector and angle measurements
Table III.
Sector
I
II
III
IV
0.11
0.08
0.05
0.04
0.06
0.53
0.43
0.33
0.25
0.38
0.91
0.87
0.81
0.75
0.87
0.99
0.98
0.98
0.96
0.99
RESULTS
Two hundred patients met the first criteria; of these,
82 met the final criteria. There were 164 total teeth, 4 of
which were determined to have an unquestionable
eruption. The remaining 160 canines resulted in 35
impactions. Six impactions were found in sector I, 12 in
sector II, 10 in sector III, and 7 in sector IV.
Descriptive statistics for the combined right and left
canines organized by impaction status are found in
Table I. Angulation was higher for nonimpacted teeth,
with a mean of 75.12° compared with 63.20° for
impacted teeth. The median sector for impacted teeth
was II compared with I for nonimpacted teeth. The
correlation of sector location with impaction (Cramer’s
V) was 0.68, and the correlation of angle and impaction
(␩) was 0.48.
Predictability of canine impaction as a function of
sector location and angulation was estimated by logistic
regression. Angulation was divided into 4 equal ranges
of 15° each, based on the maximum and minimum angles
found in the data. The 15° range was selected only for
ease of determination while viewing a radiograph.
Results of the logistic regression indicated that
sector was a statistically significant predictor of impaction. As shown in Table II, for every unit of change in
sector, the odds of indication of impaction increase by
a factor of 8.7. The probabilities of impaction for the
various combinations of sector and angle are shown in
Table III. Sector location provides the greater influence
on the prediction of impaction, with canine location in
the more mesial sectors substantially predictive. Angulation did not provide any statistically significant additional predictability. The probabilities of predicting
impaction are much the same, whether or not angulation is considered.
DISCUSSION
Lindauer et al18 found that 78% of impacted teeth
occur in sectors II, III, and IV. These results correspond
Angle (degrees)
40–54
55–69
70–84
85–99
Angle not considered
Table IV.
Sector locations of maxillary canines
Sector
Teeth
Impacted
Not impacted
I
II
III
IV
Total
6
105
12
18
10
2
7
0
35
125
with those of this study in that 82% of impacted canines
(29 of 35) were found in sectors II, III, and IV (Table
IV).
The findings in this study indicate that of the 2
factors considered for predicting maxillary canine impaction, prediction appears to rest almost solely on the
sector location of the cusp tip of the erupting canine. As
shown by the predictive values in Table III for sector
location alone, the more mesial the cusp tip location,
the greater the likelihood of impaction. The greatest
probability of impaction was found in sectors III (0.87)
and IV (0.99).
Indication of maxillary canine impaction increased
by a factor of almost 9 per sector with location of the
tooth from distal to most mesial sector. The 95%
confidence interval of the odds ratio supports this
finding in that the lower bound (3.752) is well beyond
a neutral position of 1 despite the somewhat wide range
of the interval.
Angulation does not add significantly to the predictive value of sector location. In sector I, most teeth will
not become impacted, so the role of angle in predicting
impaction is not clinically significant. Likewise, in
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 124, Number 6
sectors III and IV, where most teeth will become
impacted, the small increase that angle contributes to
probability is not clinically significant. Only in sector II
would angulation have potential significance in predicting impaction.
CONCLUSIONS
Sector location of the cusp tip of the unerupted
canine is the most important predictor of eventual
impaction. In this study, 82% of the impacted canines
had cusp tips located in sectors II, III, and IV. If the
cusp tip is located in sector III, the prediction of
eventual impaction is .87, based on sector alone. In
almost all cases, angulation did not increase the prediction of eventual impaction, though it may contribute
slightly in sector II. Despite promising results, outcomes of this study should be taken as suggestive only
and certainly not absolute. A study with a larger sample
size may be able to confirm these findings along with
the role, if any, of angulation in predicting maxillary
canine impaction.
We thank Dr John Warford Sr for providing records
from his private practice in Bismarck, ND, for this
study; Nanc Skaret for collecting the records; Dr
Edward Combe, University of Minnesota, Minneapolis,
and Dr Richard White, University of Missouri, Kansas
City, for reviewing the manuscript; and Jim Thomas,
University of Missouri, Kansas City, for technical help
with the figures.
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