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Maxillary Canines in Patients With Multiple Congenitally Missing Teeth: A Roentgenographic Study
Maxillary Canines in Patients With Multiple Congenitally Missing Teeth: A Roentgenographic Study Yocheved Ben-Bassat and Ilana Brin A group of 122 patients with multiple (at least 3) congenitally missing teeth was screened roentgenographically for the condition of their maxillary canines (missing, malposed, impacted, and normally erupted). Full information was available for 89 patients of the original group, who were divided into 2 subgroups, one with maxillary lateral incisors present (A) and the other with missing lateral incisors (B). Their chronologic age was found to be 12.4 ⴞ 2.9 years, which was close to their dental age, 12.4 ⴞ 2.1 years. The position of the maxillary canines was determined by a modified sector method. Of the expected number of maxillary canines, 20.4% were missing. In the group with full documentation, 42.4% were mesially displaced (most of them adjacent to a missing lateral incisor), whereas 5.6% were distally displaced. Of the mesially displaced canines, 5.7% were eventually impacted. Altogether, only 26.4% of the expected canines were positioned in their correct locations at the time of examination, mostly adjacent to a lateral incisor. It is concluded that the prevalence of affected maxillary canines (impacted, displaced) among patients with multiple congenitally missing teeth is relatively high. Because of the small number of impacted canines in each category of severity of absence no meaningful conclusions could be drawn in this regard. (Semin Orthod 2010;16:193-198.) © 2010 Published by Elsevier Inc.
he maxillary canine is second only to the wisdom tooth in the hierarchy of impacted teeth. Local and genetic factors are mentioned regarding the etiology underlying this phenomenon. The proponents of the local factors theory point to agenesis1,2 and/or to small lateral maxillary incisors,3,4 occurrences, which may deprive the erupting canine of the guidance needed to successfully align itself within the maxillary den-
T
Clinical Senior Lecturer, Department of Orthodontics, Hebrew University, Hadassah, School of Dental Medicine, founded by the Alpha Omega Fraternity, Jerusalem, Israel. Clinical Associate Professor, Department of Orthodontics, Hebrew University, Hadassah, School of Dental Medicine, founded by the Alpha Omega Fraternity, Jerusalem, Israel. Address correspondence to Dr. Y. Ben-Bassat, Department of Orthodontics, HU-Hadassah SDM, PO Box 12272, Jerusalem 91120, Israel. E-mail: [email protected] © 2010 Published by Elsevier Inc. 1073-8746/10/1603-0$30.00/0 doi:10.1053/j.sodo.2010.05.006
tal arch. By contrast, the proponents of the genetic theory consider the impacted maxillary canine as one of several associated dental malpositions5 or anomalies6 originating from the same genetic aberration that often occur concomitantly. A possible combined etiology, genetic and local, may be the case in reality, for example: small maxillary lateral incisors caused by a genetic aberration affect the path of eruption of the adjacent canine locally.4 It would be therefore interesting to evaluate the prevalence of the impaction of maxillary canines in patients with hypodontia which has a proven genetic background.7,8 A high prevalence of impacted canines in Down syndrome patients with congenital absence of teeth was reported by Shapira et al in 2000.9 The prevalence of maxillary canine impaction and malposition in patients with multiple congenitally missing teeth, but otherwise-healthy population, may
Seminars in Orthodontics, Vol 16, No 3 (September), 2010: pp 193-198
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Maxillary Canines in Patients With MCMT
shed some additional light on this phenomenon. On the basis of the literature, the high percentage of lateral maxillary incisor absence in our sample10,11 and agenesis in general could be a predisposing factor for other anomalies and deviations in the eruption pattern. It was our hypothesis that the more mesially inclined the orientation of the canine bud, the greater will be the risk of impaction. It was therefore the aim of this study to (1) determine the prevalence of impacted maxillary canines in patients with multiple congenitally missing teeth (MCMT) and to relate it to the severity of the condition and the presence of the adjacent lateral incisor; (2) define the position of the maxillary canines in a group of patients with MCMT and to relate it to the severity of the condition and the presence of the adjacent lateral incisor; and (3) relate the anatomical position of the canine bud to its eventual impaction.
Methods The pretreatment orthodontic records of 122 patients with MCMT collected from orthodontic clinics in Israel served as the database for this study. The skeletal and dental patterns of this group have been reported previously10,11 on the basis of cephalograms, panoramic roentgenograms, and full-mouth series. The frequency of missing or impacted maxillary canines was calculated by the original group (n ⫽ 122), whereas all other variables were calculated from a limited group of 89 patients for whom panoramic radiographs remained available at this stage, ie, 33 sets of records had been returned earlier to the referring orthodontists. The inclusion criterion for the present study was at least 3 CMT (excluding third molars). Children with cleft lip and palate, craniofacial anomalies, and diagnosed syndromes were excluded from the study group. The following parameters were recorded: 1. Personal data (age and sex). 2. Dental age (estimation was made based on the method of Gustafson and Koch12). 3. Absence of teeth. The number of missing teeth in each patient was determined from orthopantomograms or full-mouth series. In children younger than 9 years of age, verifi-
cation of the number of missing teeth was based on a roentgenographic follow-up. The sample was partitioned by: (a) severity of absence. Three categories by severity (number of missing teeth) were established according to Nodal et al13: 3-6, 7-9, 10 and more, as in our previous publication.10 (b) The presence or absence of lateral incisors: subgroup A and subgroup B, respectively. 4. Position of the maxillary canines on the panoramic roentgenograms was determined according to the method of Ericson and Kurol14 by a modified sector method (Fig 1). (a) For cases with existing lateral incisors (subgroup A), a slightly modified categorization of sectors was used: sector 5 denotes normal position, whereas sectors 4 through 1 denote a progressively mesial position of the canine to the midline and thus presumably more likely to become impacted. Sector 6 was added to the original method denoting distal position of the canine in relation to its primary predecessor. (b) For cases with missing lateral incisors (subgroup B), a similar classification of canine position was used with the digit 1 preceding the sector number. Sector 15 was considered as a normally erupting canine in its original position. Sectors 11, 12, 13, and 14 were considered as canines possibly erupting in the position of the missing lateral incisors. Sectors 11 and 12 were considered as clearly “suspected” for impaction. Sector 16 denotes distal eruption in relation to its primary predecessor. 5. Canines were considered as definitively impacted if positive documentation of surgical exposure and orthodontic traction existed. To reduce the possible method error, the authors reviewed the roentgenographic material and determined the canine sector position and dental age independently. Discrepancies were resolved by discussion.
Results The original group with MCMT comprised 47 male and 75 female patients. The maxillary canine was the fourth most frequently missing
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tooth in the upper arch and the sixth in the whole mouth (Fig 2). Altogether 50 maxillary canines were missing, which corresponds to 20% of the expected number of canines (21% in boys and 20% in girls). Most of the missing canines (n ⫽ 37) were found in subgroup B, in association with lateral incisor aplasia.
Figure 2. The distribution of congenitally missing teeth by tooth type, jaw and gender. The vertical scale on the left indicates the number of missing teeth in the maxilla (upper part of the figure) and mandible (lower part of the figure). The numbers on the horizontal scale correspond to the missing teeth in the maxilla (upper row) and mandible (lower row), right and left teeth depicted in the same column.
Figure 1. (A) Modified sector method in cases with existing lateral maxillary incisors. Sector 5 denotes normal position, whereas sectors 4 through 1 denote a progressively mesial position of the canine to the midline, and thus presumably more likely to become impacted. Sector 6 was added to the original method denoting distal position of the canine in relation to its primary predecessor. (B) Modified sector method in cases with missing lateral maxillary incisors. A similar classification of canine position to that Group A was used with the digit 1 preceding the sector number. Sector 15 was considered as a canine in its normally erupted position. Sectors 13 and 14 were considered as canines possibly erupting in the position of the missing lateral incisors. Sectors 11 and 12 were considered as clearly “suspected” for impaction. Sector 16 denotes distal eruption in relation to its primary predecessor. (Color version of figure is available online.)
Table 1 presents the distribution of the impacted maxillary canines in the study group. Fourteen maxillary canines in 10 patients (8.2%) had been surgically exposed and treated for impaction. The impacted canines comprised 5.7% of Table 1. Impacted Maxillary Canines in a Group of Patients With MCMT (n ⫽ 122)
Maxillary Canine
No. of Impacted Canines
Subgroup A Subgroup B Total
6 8 14
% of Impacted % of Impacted Canines of Canines of Expected Number Existing Number of Canines of Canines (n ⫽ 244) (n ⫽ 194) 2.4 3.3 5.7
3.1 4.1 7.2
“Expected canines” relates to the 244 maxillary canines that the 122 patients were expected to have. “Existing canines” relates to the maxillary canines actually present in this group. MCMT, multiple congenitally missing teeth.
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the expected (122 patients ⫻ 2 ⫽ 244 expected canines) and 7.2% of the existing maxillary canines (244 expected ⫺ 50 missing canines ⫽ 194 existing canines). At the time of the present study panoramic roentgenograms were available for 89 patients, thus the canine sector and dental age were determined for these patients only. Their chronologic ages ranged between 7 and 27 years, mean 12.4 ⫾ 2.9 years, whereas their mean dental age was 12.1 ⫾ 2.9 years. Within this group, 42 children were missing 3-5 teeth, 25 were missing 6-9 teeth, and 22 were missing 10 teeth or more (excluding third molars). The malposed canines were determined by a modified sector method and a distinction was made between canines with adjacent permanent lateral incisor and those without (Fig. 1). Table 2 presents the distribution of the different canine positions in the group with full documentation. Altogether, 19 (14.7%) maxillary canines (out of the number of existing canines n ⫽ 129) were mesially malposed, whereas 10 (7.8%) were distally malposed. Distribution of impacted and/or mesially displaced canines in relation to the number of missing teeth is presented in Table 3. In patients with lateral incisors (subgroup A), all the impacted canines (n ⫽ 6) were in the group with least missing teeth.3-5 In subgroup B the distribution of impacted canines was similar in the 3 missing categories. The distribution of the impacted canines by subgroup and sector is presented in Table 4. Four of the impacted canines were positioned in sectors 13 and 14, which originally have been considered as a favorable sector in case of a missing lateral incisor.13 Table 2. Position of Maxillary Canines in a Group of Patients with MCMT (n ⫽ 89) Maxillary Canine Sector 1, 2, 3, and 4 Sector 11 and 12 Sector 13 and 14 Sector 6 and 16 Sector 5 and 15 Subtotal Missing Total
Subgroup A, Subgroup B, n (%) n (%) Total, n (%) 9 (5.1)
NA
9 (5.1)
NA NA 6 (3.4) 39 (21.9) 54 (80.6) 13 (7.3) 67
10 (5.6) 53 (29.8) 4 (2.2) 8 (4.5) 75 (67.6) 36 (20.2%) 111
10 (5.6) 53 (29.8) 10 (5.6) 47 (26.4) 129 (72.5) 49 (27.5) 178 (100)
For explanation of sectors, see Methods section and Figure 1. MCMT, multiple congenitally missing teeth; NA, not applicable.
Discussion Agenesis of canines is relatively rare,15,16 but disturbance in its path of eruption is a common phenomenon. Although individual variation in tooth development and eruption seems to be wide without its being considered pathologic,13 the situation is different in patients with MCMT. Our results indicated that 20.4% of the expected canines were missing in MCMT and were the sixth in the hierarchy of absence in this group of patients. There was no difference between boys (20%) and girls (21%) in the prevalence of missing canines (Fig 2) nor in the prevalence of all other missing teeth except for the second maxillary premolars (33% in boys and 51% in girls). Absence of maxillary canines in this sample was greater than that found by Kirkham et al17 for a hypodontia group in the UK (14.7%). In a smaller group of Israeli patients with Down syndrome and hypodontia, the prevalence of missing maxillary canines was only 2.9%.9 The relatively greater degree of agenesis of maxillary canines in our group might be related to the fact that these are patients with a severe absence of teeth, and thus a significant disturbance of the dental lamina. It was found that in cases with hypodontia, the odds that the antimere was also missing in the horizontally opposite quadrant was some 23 times higher than if the tooth were present,17 thus increasing the chance for missing teeth, including the canines. In the present sample 73.5% (36/49) of the missing canines were in subgroup B, thus apparently linked to a missing adjacent lateral incisor (Table 2). The dental age of patients with congenitally missing teeth is considered younger than their chronologic age.18 In this study the mean chronologic age (12.4 ⫾ 2.9 years) was only slightly higher than the dental age (12.1 ⫾ 2.9 years). This concordance between the dental and chronologic ages permits greater confidence in the determination of missing teeth in our sample. Impacted maxillary canines were found in 5.7% of the expected and 7.2% of the existing maxillary canines. This is a considerably greater prevalence than that of maxillary canine impaction in random population which is 1% to 3%, depending on the population studied.16,19-21 These impacted teeth were somewhat more frequent (Table 1) in patients with a missing adjacent lateral incisor (n ⫽ 8 canines of 244 ex-
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Table 3. Distribution of Patients With Impacted and/or Mesially Displaced Maxillary Canines by the Number of Missing Teeth (n ⫽ 89 Patients With Existing 129 Maxillary Canines) Number of Missing Teeth
Number of Patients
Existing Canines, n (%)
3-5 6-9 10⫹ Total
42 25 22 89
69 (100) 39 (100) 21 (100) 129 (100)
Canines in Subgroup A Impacted/ Displaced, n
Canines in Subgroup B Impacted/ Displaced, n
6 0 0 6
2 3 3 8
pected canines) than in those with the adjacent lateral incisor present (n ⫽ 6 canines of 244 expected canines). It should be kept in mind however that in this study plaster casts were not available to allow measurement of the existing lateral incisors, thus the risk of a small and latedeveloping lateral incisor which could not properly guide the erupting canine, is still possible in subgroup A. Another possible explanation to this phenomenon of relatively frequent maxillary canine impaction may be found in the arch dimensions of patients with hypodontia. Bu et al22 found that although there is no crowding in most patients with MCMT, their arch length and width are reduced, and a mean reduction in the maxillary intercanine width of 2.82 mm, and length of 3.4 mm was recorded. Such diminution in the arch size might affect the normal path of eruption of the maxillary canine. Although arch dimensions were not measured in the present sample, the finding of a retrognathic maxilla, especially in the cases of severe absence of teeth in our sample,10 may reflect the reduction in the maxillary size, and become a factor in the aberrant pattern of eruption of the maxillary canine. Table 4. Distribution of the Impacted Canines by Sector and Subgroup Case No
Number of Missing Teeth
Impacted Canine
Subgroup
Sector
5 9 11 85 88 90 91 96 97 104
9 5 6 3 3 3 6 14 10 4
13 13 13, 23 13 13, 23 13, 23 23 13, 23 13 13
B B B A A A B B B A
13 11 12, 12 4 2, 2 * 13 13, 14 11 2
*The panoramic X-ray of the patient was not available for sector evaluation.
7 2 0 9
4 3 3 10
Total Impacted/Displaced, n (%) 8 (11.6) 3 (7.7) 3 (14.3) 14 (10.8)
11 (15.9) 5 (12.8) 3 (14.3) 19 (14.7)
In addition to the relatively high prevalence of surgically exposed and orthodontically treated (ie, presumed impacted) maxillary canines in this group, malposition of the erupted canines was found as well. Application of a modified sector method to a group of orthodontic patients supported the notion that the sector in which the maxillary canine is positioned was a statistically significant predictor of impaction.23 Sectors 1, 2, 3, 4, 11, and 12, were considered as malposed and predisposing the canine for impaction (“suspected”). It was suggested that sector 4 could be considered as borderline or mild malposition. Because not all the patients in our sample were followed-up longitudinally, we do not know the total percentage of impacted canines that were originally diagnosed as severely malposed in one of the aforementioned sectors, nor is the fate of all the canines designated to sector 4 known. Would they finally be severely malposed or impacted had no intervention, such as extraction of the deciduous predecessors, been undertaken? Thus, it is reasonable to assume that the final tally of impacted canines in the present study could be even higher than that reported. Evaluation of the “normally” erupted maxillary canines according to the sector revealed that only 36.4% of them (47 teeth out of 129 existing maxillary canines) were found in sector 5 and 15, which is the expected anatomic position of a normally erupting canine. Of these normally positioned canines, the majority had an adjacent lateral incisor (Table 2). Most of The remainder of the existing canines deviated mesially whereas a small minority migrated distally to sectors 6 or 16. A missing lateral incisor is related to the mesial migration, as it was found that canines without an adjacent lateral incisor mostly erupt in the location of the lateral incisor (sector 13 and 14). This can be considered a successful solution to the absence of the incisor;
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however, even here, 4 of the canines categorized to sector 13 or 14 were impacted (Table 4). Evaluation of the patient group by the number of the missing teeth (Table 3) revealed that all impacted canines with an adjacent lateral incisor (subgroup A) were in patients with 3 to 5 missing teeth only, whereas in subgroup B, the impacted canines were equally dispersed among the 3 categories of severity of agenesis. Because of the relatively small number of impacted canines in each category, meaningful conclusions could not be obtained. In conclusion, it would appear that in patients with MCMT normal eruption of maxillary canine in its assigned position is a relatively rare event.
References 1. Miller BH: The influence of congenitally missing teeth on the eruption of the upper canine. Dent Pract Dent Rec 13:497-504, 1963 2. Bass TB: Observations on the misplaced upper canine tooth. Dent Pract Dent Rec 18:25-33, 1967 3. Becker A, Smith P, Behar R: The incidence of anomalous lateral incisors in relation to palatally-displaced cuspids. Angle Orthod 51:24-29, 1981 4. Becker A: Palatally impacted canines, in The Orthodontic Treatment of Impacted Teeth (ed 2). Abingdon, Informa, 2007, p 98 5. Shalish M, Chaushu S, Wasserstein A: Malposition of unerupted mandibular second premolars in children with palatally displaced canine. Angle Orthod 79:796799, 2009 6. Peck S, Peck L, Kataja M: The palatally displaced canine as a dental anomaly of genetic origin. Angle Orthod 64:249-256, 1994 7. Vastardis H: A human MSX1 homeodomain missense mutation causes selective tooth agenesis. Nat Genet 13: 417-421, 1996 8. Stockton DW, Das P, Goldberg M: Mutation of PAX9 is associated with oligodontia. Nat Genet 24:18-19, 2000
9. Shapira J, Chaushu S, Becker A: Prevalence of tooth transposition, third molar agenesis and maxillary canine impaction in individuals with Down syndrome. Angle Orthod 70:290-296, 2000 10. Ben-Bassat Y, Brin I: Skeletodental patterns in patients with multiple congenitally missing teeth. Am J Orthod Dentofac Orthop 124:521-525, 2003 11. Ben-Bassat Y, Brin I: Skeletal and dental patterns in patients with severe congenital absence of teeth. Am J Orthod Dentofac Orthop 135:349-356, 2009 12. Gustafson G, Koch G: Age estimation up to 16 years of age based on dental development. Odontol Revy 25:297306, 1974 13. Nodal M, Kjaer I, Solow B: Craniofacial morphology in patients with multiple congenitally missing teeth. Eur J Orthod 16:104-109, 1994 14. Ericson S, Kurol J: Resorption of maxillary lateral incisors caused by ectopic eruption of the canines. Am J Orthod 94:503-513, 1988 15. Stewart RE, Witkop CJ Jr, Bixler D: The dentition and anomalies of tooth size, form, structure and eruption; Stewart RE, Barber TK, Troutman KC, et al (eds). Pediatric Dentistry. St. Louis, Mosby, 1982, p 91 16. Brin I, Becker A, Shalhav M: Position of the maxillary permanent canine in relation to anomalous or missing lateral incisors: A population study. Eur J Orthod 8:1216, 1986 17. Kirkham J, Kaur R, Stillman EC, et al: The patterning of hypodontia in a group of young adults in Sheffield, UK. Arch Oral Biol 50:287-291, 2005 18. Garn SM, Lewis AB, Vicinus JH: Third molar polymorphism and its significance to dental genetics. J Dent Res 42:1344-1363, 1963 19. Grover PS, Lorton L: The incidence of unerupted permanent teeth and related clinical cases. Oral Surg Oral Med Oral Pathol 59:420-425, 1985 20. Kramer RM, Williams AD: The incidence of impacted teeth. Oral Surg Oral Med Oral Pathol 29:237-241, 1970 21. Dachi SF, Howell FV: A survey of 3874 routine fullmouth radiographs. II. A study of impacted teeth. Oral Surg Oral Med Oral Pathol 14:1165-1169, 1961 22. Bu X, Khalaf K, Hobson RS: Dental arch dimensions in oligodontia patients. Am J Orthod Dentofac Orthop 134:768-772, 2008 23. Warford JH, Grandhi RK, Tira DE: Prediction of maxillary canine impaction using sector and angular measurements. Am J Orthod Dentofac Orthop 124:651-655, 2003
he maxillary canine is second only to the wisdom tooth in the hierarchy of impacted teeth. Local and genetic factors are mentioned regarding the etiology underlying this phenomenon. The proponents of the local factors theory point to agenesis1,2 and/or to small lateral maxillary incisors,3,4 occurrences, which may deprive the erupting canine of the guidance needed to successfully align itself within the maxillary den-
T
Clinical Senior Lecturer, Department of Orthodontics, Hebrew University, Hadassah, School of Dental Medicine, founded by the Alpha Omega Fraternity, Jerusalem, Israel. Clinical Associate Professor, Department of Orthodontics, Hebrew University, Hadassah, School of Dental Medicine, founded by the Alpha Omega Fraternity, Jerusalem, Israel. Address correspondence to Dr. Y. Ben-Bassat, Department of Orthodontics, HU-Hadassah SDM, PO Box 12272, Jerusalem 91120, Israel. E-mail: [email protected] © 2010 Published by Elsevier Inc. 1073-8746/10/1603-0$30.00/0 doi:10.1053/j.sodo.2010.05.006
tal arch. By contrast, the proponents of the genetic theory consider the impacted maxillary canine as one of several associated dental malpositions5 or anomalies6 originating from the same genetic aberration that often occur concomitantly. A possible combined etiology, genetic and local, may be the case in reality, for example: small maxillary lateral incisors caused by a genetic aberration affect the path of eruption of the adjacent canine locally.4 It would be therefore interesting to evaluate the prevalence of the impaction of maxillary canines in patients with hypodontia which has a proven genetic background.7,8 A high prevalence of impacted canines in Down syndrome patients with congenital absence of teeth was reported by Shapira et al in 2000.9 The prevalence of maxillary canine impaction and malposition in patients with multiple congenitally missing teeth, but otherwise-healthy population, may
Seminars in Orthodontics, Vol 16, No 3 (September), 2010: pp 193-198
193
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Maxillary Canines in Patients With MCMT
shed some additional light on this phenomenon. On the basis of the literature, the high percentage of lateral maxillary incisor absence in our sample10,11 and agenesis in general could be a predisposing factor for other anomalies and deviations in the eruption pattern. It was our hypothesis that the more mesially inclined the orientation of the canine bud, the greater will be the risk of impaction. It was therefore the aim of this study to (1) determine the prevalence of impacted maxillary canines in patients with multiple congenitally missing teeth (MCMT) and to relate it to the severity of the condition and the presence of the adjacent lateral incisor; (2) define the position of the maxillary canines in a group of patients with MCMT and to relate it to the severity of the condition and the presence of the adjacent lateral incisor; and (3) relate the anatomical position of the canine bud to its eventual impaction.
Methods The pretreatment orthodontic records of 122 patients with MCMT collected from orthodontic clinics in Israel served as the database for this study. The skeletal and dental patterns of this group have been reported previously10,11 on the basis of cephalograms, panoramic roentgenograms, and full-mouth series. The frequency of missing or impacted maxillary canines was calculated by the original group (n ⫽ 122), whereas all other variables were calculated from a limited group of 89 patients for whom panoramic radiographs remained available at this stage, ie, 33 sets of records had been returned earlier to the referring orthodontists. The inclusion criterion for the present study was at least 3 CMT (excluding third molars). Children with cleft lip and palate, craniofacial anomalies, and diagnosed syndromes were excluded from the study group. The following parameters were recorded: 1. Personal data (age and sex). 2. Dental age (estimation was made based on the method of Gustafson and Koch12). 3. Absence of teeth. The number of missing teeth in each patient was determined from orthopantomograms or full-mouth series. In children younger than 9 years of age, verifi-
cation of the number of missing teeth was based on a roentgenographic follow-up. The sample was partitioned by: (a) severity of absence. Three categories by severity (number of missing teeth) were established according to Nodal et al13: 3-6, 7-9, 10 and more, as in our previous publication.10 (b) The presence or absence of lateral incisors: subgroup A and subgroup B, respectively. 4. Position of the maxillary canines on the panoramic roentgenograms was determined according to the method of Ericson and Kurol14 by a modified sector method (Fig 1). (a) For cases with existing lateral incisors (subgroup A), a slightly modified categorization of sectors was used: sector 5 denotes normal position, whereas sectors 4 through 1 denote a progressively mesial position of the canine to the midline and thus presumably more likely to become impacted. Sector 6 was added to the original method denoting distal position of the canine in relation to its primary predecessor. (b) For cases with missing lateral incisors (subgroup B), a similar classification of canine position was used with the digit 1 preceding the sector number. Sector 15 was considered as a normally erupting canine in its original position. Sectors 11, 12, 13, and 14 were considered as canines possibly erupting in the position of the missing lateral incisors. Sectors 11 and 12 were considered as clearly “suspected” for impaction. Sector 16 denotes distal eruption in relation to its primary predecessor. 5. Canines were considered as definitively impacted if positive documentation of surgical exposure and orthodontic traction existed. To reduce the possible method error, the authors reviewed the roentgenographic material and determined the canine sector position and dental age independently. Discrepancies were resolved by discussion.
Results The original group with MCMT comprised 47 male and 75 female patients. The maxillary canine was the fourth most frequently missing
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tooth in the upper arch and the sixth in the whole mouth (Fig 2). Altogether 50 maxillary canines were missing, which corresponds to 20% of the expected number of canines (21% in boys and 20% in girls). Most of the missing canines (n ⫽ 37) were found in subgroup B, in association with lateral incisor aplasia.
Figure 2. The distribution of congenitally missing teeth by tooth type, jaw and gender. The vertical scale on the left indicates the number of missing teeth in the maxilla (upper part of the figure) and mandible (lower part of the figure). The numbers on the horizontal scale correspond to the missing teeth in the maxilla (upper row) and mandible (lower row), right and left teeth depicted in the same column.
Figure 1. (A) Modified sector method in cases with existing lateral maxillary incisors. Sector 5 denotes normal position, whereas sectors 4 through 1 denote a progressively mesial position of the canine to the midline, and thus presumably more likely to become impacted. Sector 6 was added to the original method denoting distal position of the canine in relation to its primary predecessor. (B) Modified sector method in cases with missing lateral maxillary incisors. A similar classification of canine position to that Group A was used with the digit 1 preceding the sector number. Sector 15 was considered as a canine in its normally erupted position. Sectors 13 and 14 were considered as canines possibly erupting in the position of the missing lateral incisors. Sectors 11 and 12 were considered as clearly “suspected” for impaction. Sector 16 denotes distal eruption in relation to its primary predecessor. (Color version of figure is available online.)
Table 1 presents the distribution of the impacted maxillary canines in the study group. Fourteen maxillary canines in 10 patients (8.2%) had been surgically exposed and treated for impaction. The impacted canines comprised 5.7% of Table 1. Impacted Maxillary Canines in a Group of Patients With MCMT (n ⫽ 122)
Maxillary Canine
No. of Impacted Canines
Subgroup A Subgroup B Total
6 8 14
% of Impacted % of Impacted Canines of Canines of Expected Number Existing Number of Canines of Canines (n ⫽ 244) (n ⫽ 194) 2.4 3.3 5.7
3.1 4.1 7.2
“Expected canines” relates to the 244 maxillary canines that the 122 patients were expected to have. “Existing canines” relates to the maxillary canines actually present in this group. MCMT, multiple congenitally missing teeth.
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Maxillary Canines in Patients With MCMT
the expected (122 patients ⫻ 2 ⫽ 244 expected canines) and 7.2% of the existing maxillary canines (244 expected ⫺ 50 missing canines ⫽ 194 existing canines). At the time of the present study panoramic roentgenograms were available for 89 patients, thus the canine sector and dental age were determined for these patients only. Their chronologic ages ranged between 7 and 27 years, mean 12.4 ⫾ 2.9 years, whereas their mean dental age was 12.1 ⫾ 2.9 years. Within this group, 42 children were missing 3-5 teeth, 25 were missing 6-9 teeth, and 22 were missing 10 teeth or more (excluding third molars). The malposed canines were determined by a modified sector method and a distinction was made between canines with adjacent permanent lateral incisor and those without (Fig. 1). Table 2 presents the distribution of the different canine positions in the group with full documentation. Altogether, 19 (14.7%) maxillary canines (out of the number of existing canines n ⫽ 129) were mesially malposed, whereas 10 (7.8%) were distally malposed. Distribution of impacted and/or mesially displaced canines in relation to the number of missing teeth is presented in Table 3. In patients with lateral incisors (subgroup A), all the impacted canines (n ⫽ 6) were in the group with least missing teeth.3-5 In subgroup B the distribution of impacted canines was similar in the 3 missing categories. The distribution of the impacted canines by subgroup and sector is presented in Table 4. Four of the impacted canines were positioned in sectors 13 and 14, which originally have been considered as a favorable sector in case of a missing lateral incisor.13 Table 2. Position of Maxillary Canines in a Group of Patients with MCMT (n ⫽ 89) Maxillary Canine Sector 1, 2, 3, and 4 Sector 11 and 12 Sector 13 and 14 Sector 6 and 16 Sector 5 and 15 Subtotal Missing Total
Subgroup A, Subgroup B, n (%) n (%) Total, n (%) 9 (5.1)
NA
9 (5.1)
NA NA 6 (3.4) 39 (21.9) 54 (80.6) 13 (7.3) 67
10 (5.6) 53 (29.8) 4 (2.2) 8 (4.5) 75 (67.6) 36 (20.2%) 111
10 (5.6) 53 (29.8) 10 (5.6) 47 (26.4) 129 (72.5) 49 (27.5) 178 (100)
For explanation of sectors, see Methods section and Figure 1. MCMT, multiple congenitally missing teeth; NA, not applicable.
Discussion Agenesis of canines is relatively rare,15,16 but disturbance in its path of eruption is a common phenomenon. Although individual variation in tooth development and eruption seems to be wide without its being considered pathologic,13 the situation is different in patients with MCMT. Our results indicated that 20.4% of the expected canines were missing in MCMT and were the sixth in the hierarchy of absence in this group of patients. There was no difference between boys (20%) and girls (21%) in the prevalence of missing canines (Fig 2) nor in the prevalence of all other missing teeth except for the second maxillary premolars (33% in boys and 51% in girls). Absence of maxillary canines in this sample was greater than that found by Kirkham et al17 for a hypodontia group in the UK (14.7%). In a smaller group of Israeli patients with Down syndrome and hypodontia, the prevalence of missing maxillary canines was only 2.9%.9 The relatively greater degree of agenesis of maxillary canines in our group might be related to the fact that these are patients with a severe absence of teeth, and thus a significant disturbance of the dental lamina. It was found that in cases with hypodontia, the odds that the antimere was also missing in the horizontally opposite quadrant was some 23 times higher than if the tooth were present,17 thus increasing the chance for missing teeth, including the canines. In the present sample 73.5% (36/49) of the missing canines were in subgroup B, thus apparently linked to a missing adjacent lateral incisor (Table 2). The dental age of patients with congenitally missing teeth is considered younger than their chronologic age.18 In this study the mean chronologic age (12.4 ⫾ 2.9 years) was only slightly higher than the dental age (12.1 ⫾ 2.9 years). This concordance between the dental and chronologic ages permits greater confidence in the determination of missing teeth in our sample. Impacted maxillary canines were found in 5.7% of the expected and 7.2% of the existing maxillary canines. This is a considerably greater prevalence than that of maxillary canine impaction in random population which is 1% to 3%, depending on the population studied.16,19-21 These impacted teeth were somewhat more frequent (Table 1) in patients with a missing adjacent lateral incisor (n ⫽ 8 canines of 244 ex-
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Table 3. Distribution of Patients With Impacted and/or Mesially Displaced Maxillary Canines by the Number of Missing Teeth (n ⫽ 89 Patients With Existing 129 Maxillary Canines) Number of Missing Teeth
Number of Patients
Existing Canines, n (%)
3-5 6-9 10⫹ Total
42 25 22 89
69 (100) 39 (100) 21 (100) 129 (100)
Canines in Subgroup A Impacted/ Displaced, n
Canines in Subgroup B Impacted/ Displaced, n
6 0 0 6
2 3 3 8
pected canines) than in those with the adjacent lateral incisor present (n ⫽ 6 canines of 244 expected canines). It should be kept in mind however that in this study plaster casts were not available to allow measurement of the existing lateral incisors, thus the risk of a small and latedeveloping lateral incisor which could not properly guide the erupting canine, is still possible in subgroup A. Another possible explanation to this phenomenon of relatively frequent maxillary canine impaction may be found in the arch dimensions of patients with hypodontia. Bu et al22 found that although there is no crowding in most patients with MCMT, their arch length and width are reduced, and a mean reduction in the maxillary intercanine width of 2.82 mm, and length of 3.4 mm was recorded. Such diminution in the arch size might affect the normal path of eruption of the maxillary canine. Although arch dimensions were not measured in the present sample, the finding of a retrognathic maxilla, especially in the cases of severe absence of teeth in our sample,10 may reflect the reduction in the maxillary size, and become a factor in the aberrant pattern of eruption of the maxillary canine. Table 4. Distribution of the Impacted Canines by Sector and Subgroup Case No
Number of Missing Teeth
Impacted Canine
Subgroup
Sector
5 9 11 85 88 90 91 96 97 104
9 5 6 3 3 3 6 14 10 4
13 13 13, 23 13 13, 23 13, 23 23 13, 23 13 13
B B B A A A B B B A
13 11 12, 12 4 2, 2 * 13 13, 14 11 2
*The panoramic X-ray of the patient was not available for sector evaluation.
7 2 0 9
4 3 3 10
Total Impacted/Displaced, n (%) 8 (11.6) 3 (7.7) 3 (14.3) 14 (10.8)
11 (15.9) 5 (12.8) 3 (14.3) 19 (14.7)
In addition to the relatively high prevalence of surgically exposed and orthodontically treated (ie, presumed impacted) maxillary canines in this group, malposition of the erupted canines was found as well. Application of a modified sector method to a group of orthodontic patients supported the notion that the sector in which the maxillary canine is positioned was a statistically significant predictor of impaction.23 Sectors 1, 2, 3, 4, 11, and 12, were considered as malposed and predisposing the canine for impaction (“suspected”). It was suggested that sector 4 could be considered as borderline or mild malposition. Because not all the patients in our sample were followed-up longitudinally, we do not know the total percentage of impacted canines that were originally diagnosed as severely malposed in one of the aforementioned sectors, nor is the fate of all the canines designated to sector 4 known. Would they finally be severely malposed or impacted had no intervention, such as extraction of the deciduous predecessors, been undertaken? Thus, it is reasonable to assume that the final tally of impacted canines in the present study could be even higher than that reported. Evaluation of the “normally” erupted maxillary canines according to the sector revealed that only 36.4% of them (47 teeth out of 129 existing maxillary canines) were found in sector 5 and 15, which is the expected anatomic position of a normally erupting canine. Of these normally positioned canines, the majority had an adjacent lateral incisor (Table 2). Most of The remainder of the existing canines deviated mesially whereas a small minority migrated distally to sectors 6 or 16. A missing lateral incisor is related to the mesial migration, as it was found that canines without an adjacent lateral incisor mostly erupt in the location of the lateral incisor (sector 13 and 14). This can be considered a successful solution to the absence of the incisor;
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however, even here, 4 of the canines categorized to sector 13 or 14 were impacted (Table 4). Evaluation of the patient group by the number of the missing teeth (Table 3) revealed that all impacted canines with an adjacent lateral incisor (subgroup A) were in patients with 3 to 5 missing teeth only, whereas in subgroup B, the impacted canines were equally dispersed among the 3 categories of severity of agenesis. Because of the relatively small number of impacted canines in each category, meaningful conclusions could not be obtained. In conclusion, it would appear that in patients with MCMT normal eruption of maxillary canine in its assigned position is a relatively rare event.
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