Maxillary canine palatal impaction occurs in 1

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1 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, PhD c 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. 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. 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) Maxillary canine palatal impaction occurs in 1 of 100 people. 1,2 In a review of the literature, Bishara 3 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; , Warford@bis.midco.net. Submitted, November 2002; revised and accepted, February Copyright 2003 by the American Association of Orthodontists /2003/$ doi: /s (03) occurs, but they can be separated into 2 categories: guidance and genetics. Bishara et al 9 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. Baccetti 10 notes an association between canine impactions and other dental anomalies, while Peck et al 11 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 al 15 reported a palatal-to-buccal impaction ratio of 3:1, and Jacoby 16 reported a ratio of 12:1. Jacoby 14 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

2 652 Warford et al American Journal of Orthodontics and Dentofacial Orthopedics December 2003 its unfavorable position. Two studies have reported good success with this treatment, finding favorable eruption to occur 78% of the time 6 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 Kurol 7 found that the more mesially located the crown, the more reduced the likelihood of eruption after deciduous extraction. Powers and Short 17 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 al 18 used an aspect of the Ericson and Kurol 6 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 al 18 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. 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

3 American Journal of Orthodontics and Dentofacial Orthopedics Volume 124, Number 6 Warford et al 653 Fig 1. Angular measurement of unerupted canines. Fig 2. Modification of Ericson and Kurol s 6 definition of sectors, from Lindauer et al. 18 I represents area distal to line tangent to distal heights of contour of lateral incisor crown and root. II is mesial to sector I, but distal to bisector of lateral incisor s long axis. III is mesial to sector II, but distal to mesial heights of contour of lateral incisor crown and root. IV includes all areas mesial to sector III. floor would be a logical choice for a horizontal line from which to measure the canine s angulation, but Damante et al 19 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 al 18 taken from Ericson and Kurol 6 (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 for angulation and 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 sector 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.

4 654 Warford et al American Journal of Orthodontics and Dentofacial Orthopedics December 2003 Table I. Descriptive data, right and left maxillary canines RESULTS No impaction (n 125) Angle (degrees) Impaction (n 35) Angle (degrees) Mean Median Standard deviation Minimum Maximum Semi-interquartile range 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 compared with 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 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. 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 al 18 found that 78% of impacted teeth occur in sectors II, III, and IV. These results correspond Table II. Logistic regression results B df Sig OR 95% CI for OR to Angle to Constant B, Beta; df, degrees of freedom; Sig, statistical significance; OR, odds ratio. Table III. Probability of canine impaction based on sector and angle measurements I II III IV Angle (degrees) Angle not considered Table IV. locations of maxillary canines Teeth I II III IV Total Impacted Not impacted 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

5 American Journal of Orthodontics and Dentofacial Orthopedics Volume 124, Number 6 Warford et al 655 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 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. REFERENCES 1. Dachi SF, Howell FV. A study of impacted teeth. Oral Surg Oral Med Oral Pathol 1961;14: Thilander B, Jakobsson SO. Local factors in impaction of maxillary canines. Acta Odontol Scand 1968;26: Bishara SE. Clinical management of impacted maxillary canines. Semin Orthod 1998;4: Ferguson JW. Management of the unerupted maxillary canine. Br Dent J 1990;169: Stewart JA, Heo G, Glover KE, Williamson PC, Lam EW, Major PW. Factors that relate to treatment duration for patients with palatally impacted maxillary canines. Am J Orthod Dentofacial Orthop 2001;119: Ericson S, Kurol J. Early treatment of palatally erupting maxillary canines by extraction of the primary canines. Eur J Orthod 1988;10: Ericson S, Kurol J. Radiographic examination of ectopically erupting maxillary canines. Am J Orthod Dentofacial Orthop 1987;91: Ericson S, Kurol J. Resorption of maxillary lateral incisors caused by ectopic eruption of the canines. Am J Orthod Dentofacial Orthop 1988;94: Bishara SE, Kommer DD, McNeil MH, Montagano LN, Oesterle LJ, Youngquist HW. Management of impacted canines. Am J Orthod 1976;8: Baccetti T. A controlled study of associated dental anomalies. Angle Orthod 1988;68: Peck S, Peck L, Kataja M. The palatally displaced canine as a dental anomaly of genetic origin. Angle Orthod 1994;64: Bishara SE. Impacted maxillary canines: a review. Am J Orthod Dentofacial Orthop 1992;101: Hitchen AD. The impacted maxillary canine. Br Dent J 1956; 100: Jacoby H. The etiology of maxillary canine impactions. Am J Orthod 1983;84: Fournier A, Turcotte JY, Bernard C. Orthodontic considerations in the treatment of maxillary impacted canines. Am J Orthod 1982;81: Jacoby H. The ballista spring system for impacted teeth. Am J Orthod Dentofacial Orthop 1979;75: Power SM, Short MB. An investigation into the response of palatally displaced canines to the removal of deciduous canines and an assessment of factors contributing to a favourable eruption. Br J Orthod 1993;20: Lindauer SJ, Rubenstein LK, Hang WM, Anderson WC, Isaacson RJ. Canine impaction identified early with panoramic radiographs. J Am Dent Assoc 1992;123: Damante JH, Filho LI, Silva MA. Radiographic image of the hard palate and nasal fossa floor in panoramic radiography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998;85: