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Dental morphologic characteristics of normal versus delayed developing dentitions with palatally displaced canines
ORIGINAL ARTICLE
Dental morphologic characteristics of normal versus delayed developing dentitions with palatally displaced canines Stella Chaushu, DMD, MSc,a Shaltiel Sharabi, BMedSc,b and Adrian Becker, BDS, LDS, DDOc Jerusalem, Israel An earlier study reported on the delayed dental age in about 50% of patients with palatally displaced canines (PDC), suggesting the possible existence of 2 different PDC phenotypes. The present study aimed to determine whether the PDC subgroup with late dental age displays different dental features from the PDC subgroup with normal dental age, supporting the above assumption. The 3 dental parameters examined were mesiodistal and buccolingual tooth sizes, the presence of anomalous maxillary lateral incisors, and other congenitally missing teeth. Fifty-eight subjects with PDC, 37 girls and 21 boys, were divided according to dental age and compared with age- and sex-matched controls. The results revealed marked sexual dimorphism. Delayed dental development was twice as prevalent among the PDC males. The existence of 2 distinct PDC subgroups was supported for males only. One subgroup was characterized by delayed dental development, smaller-than-average teeth, and a marked increase in the prevalence of anomalous lateral incisors. The second subgroup more closely resembled the controls, presenting a timely developed dentition, a moderate and nonsignificant increase of anomalous lateral incisors, and a reduction in the dimensions of only the central incisors and the first molars. In females, although the prevalence of anomalous lateral incisors was slightly increased in the late dental age subgroup, tooth sizes were remarkably similar, negating the existence of 2 distinct subpopulations. Studying the overall PDC group as a single entity produced confusing results because important differences were obscured when the 2 sexes and the 2 dental age subgroups (in males) were combined. (Am J Orthod Dentofacial Orthop 2002;121:339-46)
D
entitions characterized by the presence of a palatally displaced maxillary canine (PDC) have been associated with a distinct group of dental abnormalities, including: 1. Small teeth. Assessment of tooth size has largely been made by qualitative clinical observation of the teeth and the presence of spacing, rather than by systematic measurement.1,2 Quantitative systematic measurement of tooth size, other than lateral incisors, has only recently been reported. Langberg and Peck3 found significantly diminished mesiodistal (MD) widths of the upper and lower incisors in a combined male/female sample of PDC patients. A similar quantitative and systematic study by the present authors4 examined males and females as From the Department of Orthodontics, Hebrew University-Hadassah School of Dental Medicine, founded by the Alpha Omega Fraternity, Jerusalem, Israel. a Clinical lecturer. b Undergraduate dental student and MSc candidate. c Clinical Associate Professor. Reprint requests to: Dr Stella Chaushu, Department of Orthodontics, Hebrew University-Hadassah School of Dental Medicine, P. O. Box 12272, Jerusalem 91120, Israel; e-mail, [email protected]. Submitted, May 2001; revised and accepted, August 2001. Copyright © 2002 by the American Association of Orthodontists. 0889-5406/2002/$35.00 ⫹ 0 8/1/121559 doi:10.1067/mod.2002.121559
separate subgroups and disclosed unexpected and unexplained findings, highlighting a sexual dimorphism not previously reported. Compared with a control group, the MD and buccolingual (BL) dimensions of all maxillary teeth in the PDC patients showed significant tooth size reduction only in the males. The BL dimension of the lateral incisor was the only parameter in which the females also showed a reduced size. When further divided into unilateral and bilateral cases, tooth size reductions were also seen in bilaterally affected females and unilaterally affected males. 2. Anomalous lateral incisors. Several investigations over the past 20 years have shown that PDCaffected dentitions feature small, peg-shaped, and missing lateral incisors in just under half the cases studied.5-12 3. Congenitally missing teeth (other than lateral incisors). Agenesis of the third molars and the second premolars has been reported in higher frequency in dentitions with PDC.10,11,13,14 It is well established that late-developing dentitions are particularly prone to individual tooth agenesis, small teeth,15,16 and teeth with a poor crown-size 339
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profile pattern.17 More than 40 years ago, it was first noticed that dentitions that exhibited late development have also been associated with PDC, although until recently, in an investigation by the present authors,19 this observation has never been substantiated experimentally. The observation was initially based on clinical experience18 and later clinically, with eruption of teeth as the criterion for dental age assessment.8 The recent study assessed dental age in a large sample of PDC patients, with more objective criteria.19 A radiographic evaluation of tooth calcification (specifically root length) showed that approximately half of the PDC subjects had a late-developing dentition. The present investigation seeks to learn whether normal and late-developing PDC dentitions differ in their association with the above anomalies. This will determine whether dental age and dental morphology characteristics, together, may support the existence of 2 distinct genetic PDC phenotypes. A null hypothesis was proposed based on the assumption that a PDC subgroup with late dental age (LDA) displays different dental features from a PDC subgroup with normal dental age (NDA). The testing hypothesis was that a higher prevalence of dental anomaly (small teeth, missing teeth, and anomalous lateral incisors) occurs in the LDA subgroup than in the NDA subgroup. MATERIAL AND METHODS
The treatment records of 58 consecutively treated patients with palatal displacement of the maxillary canine were obtained from 3 orthodontic practices in Jerusalem and Tel Aviv. The patients were between 11 and 15 years of age and included 21 boys and 37 girls; the PDC determination was made on the basis of a clinical examination and diagnostic radiographs, according to established, standardized techniques.20-22 In each case, the diagnosis was confirmed at surgical exposure, performed at an appropriate time in the overall treatment plan. The control group comprised 40 age-matched and consecutively treated patients (20 boys and 20 girls), exhibiting normally erupted and undisplaced maxillary canines, as diagnosed from their pretreatment plaster casts. Good-quality panoramic radiographs and periapical views of the incisor regions were available for each patient. These were studied, and a careful assessment of dental age23-25 was determined for each permanent tooth, erupted and unerupted. The assessments were made to an accuracy tolerance of 0.5 years, as described elsewhere.22 In the previous study,19 approximately
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half of the PDC patients showed a delay in dental age. Following a similar protocol, this group was further divided into an NDA subgroup and an LDA (over 1 year delay in dental age) subgroup. MD and BL widths of all the erupted maxillary permanent teeth, from the first molars forward, were measured directly on the plaster casts that were available for each patient of both groups. This was done to an accuracy of 0.01 mm with a dial caliper with ground tips. Partially erupted, carious, and restored teeth were excluded, and measurements were not recorded where obvious calculus or plaque obscured the true contour of the tooth. Teeth were measured on both sides of the dental arch and the results averaged, based on previous work that showed no tooth size difference between affected and unaffected sides in PDC subjects.4 Recordings were made for boys and girls separately. Anomalies of the maxillary lateral incisor (pegshaped and missing) were identified by direct observation. The incisors were defined as peg-shaped by using established criteria.5 Aplasia of the second premolars and the third molars was diagnosed from the panoramic x-rays. For third-molar aplasia, 14 years seems to be the critical age for radiologic evidence of third-molar calcification.15 Because approximately half of the PDC group showed delayed dental development, these criteria were adapted to a critical dental age of 14, rather than the more usual and, in the present context, arbitrary chronological age. As the result, only 12 control subjects and 8 with PDC were included in this part of the study, all of them belonging to the NDA subgroup. The significance of the differences between the mean tooth measurements in the examined groups was tested by Student t tests. Chi-square contingency tests were used to compare the prevalence of the lateral incisor anomalies in each group. Statistical analyses were not appropriate for the second-premolar and the third-molar aplasia prevalence because of the small numbers involved. Ten casts were randomly selected and measured on 2 separate occasions to test the reproducibility of the measurements. Experimental error was analyzed and assessed with Student t tests to assess the significance of the differences in the measurements. The experimental error was determined by calculating the standard deviation of a single parameter.26 Measurement errors ranged from 0.08 to 0.13 mm, and the 0.1 mm weighted average standard deviation of a single determination for both MD and BL dimensions was not considered significant. On this basis, experimental error was unlikely to bias the accuracy of tooth measurement.
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Table I. Mesiodistal and buccolingual crown diameters in females with PDC, according to dental age, versus female controls
Tooth number 1 2 4 5 6
MD BL MD BL MD BL MD BL MD BL
Total PDC n⫽37
NDA n⫽22
LDA n⫽15
Controls n⫽20
P PDC/C
P NDA/C
P LDA/C
8.43 ⫾ 0.82 6.58 ⫾ 0.91 6.55 ⫾ 0.61 5.31 ⫾ 0.7 6.64 ⫾ 0.68 8.73 ⫾ 0.65 6.5 ⫾ 0.65 9.2 ⫾ 0.45 10.05 ⫾ 0.88 10.52 ⫾ 0.56
8.27 ⫾ 0.88 6.59 ⫾ 0.96 6.5 ⫾ 0.57 5.31 ⫾ 0.73 6.72 ⫾ 0.77 8.77 ⫾ 0.73 6.47 ⫾ 0.74 9.13 ⫾ 0.53 10.07 ⫾ 0.78 10.47 ⫾ 0.59
8.66 ⫾ 0.68 6.57 ⫾ 0.87 6.62 ⫾ 0.69 5.31 ⫾ 0.65 6.51 ⫾ 0.66 8.66 ⫾ 0.5 6.58 ⫾ 0.93 9.31 ⫾ 0.38 10.02 ⫾ 0.49 10.6 ⫾ 0.75
8.22 ⫾ 0.32 6.8 ⫾ 0.64 6.42 ⫾ 0.54 5.82 ⫾ 0.75 6.61 ⫾ 0.37 8.89 ⫾ 0.66 6.34 ⫾ 0.31 9.25 ⫾ 0.52 9.86 ⫾ 0.45 10.42 ⫾ 0.43
NS NS NS ⬍.01 NS NS NS NS NS NS
NS NS NS ⬍.01 NS NS NS NS NS NS
⬍.05 NS NS ⬍.01 NS NS NS NS NS NS
MD, Mesiodistal; BL, buccolingual; PDC, palatally displaced canines group; NDA, normal dental age subgroup; LDA, late dental age subgroup; C, control group with undisplaced canines; NS, not significant.
Mesiodistal and buccolingual crown diameters in males with PDC, according to dental age, versus male
Table II.
controls Tooth Number 1 2 4 5 6
MD BL MD BL MD BL MD BL MD BL
Total PDC n⫽21
NDA n⫽7
LDA n⫽14
Controls n⫽20
P PDC/C
P NDA/C
P LDA/C
8.42 ⫾ 0.78 6.41 ⫾ 0.65 6.5 ⫾ 1 5.32 ⫾ 0.62 6.57 ⫾ 0.51 8.76 ⫾ 0.69 6.42 ⫾ 0.52 8.99 ⫾ 0.65 10.13 ⫾ 0.73 10.63 ⫾ 0.54
8.27 ⫾ 0.85 6.22 ⫾ 0.55 6.69 ⫾ 0.92 5.21 ⫾ 0.67 6.86 ⫾ 0.41 9.06 ⫾ 0.61 6.46 ⫾ 0.59 9.15 ⫾ 0.64 10.02 ⫾ 0.83 10.51 ⫾ 0.44
8.5 ⫾ 0.76 6.51 ⫾ 0.68 6.38 ⫾ 0.75 5.37 ⫾ 0.62 6.4 ⫾ 0.5 8.57 ⫾ 0.69 6.39 ⫾ 0.49 8.87 ⫾ 0.66 10.12 ⫾ 0.67 10.69 ⫾ 0.59
8.69 ⫾ 0.47 6.85 ⫾ 0.54 6.75 ⫾ 0.38 5.88 ⫾ 0.68 7.06 ⫾ 0.52 9.39 ⫾ 0.59 6.64 ⫾ 0.58 9.54 ⫾ 0.8 10.58 ⫾ 0.81 10.93 ⫾ 0.57
NS ⬍.05 NS ⬍.05 ⬍.01 ⬍.01 NS ⬍.01 ⬍.05 ⬍.05
⬍.05 ⬍.05 NS ⬍.05 NS NS NS NS ⬍.05 ⬍.05
NS NS ⬍.05 ⬍.05 ⬍.001 ⬍.001 NS ⬍.01 ⬍.05 ⬍.05
MD, Mesiodistal; BL, buccolingual; PDC, palatally displaced canines group; NDA, normal dental age subgroup; LDA, late dental age subgroup; C, control group with undisplaced canines; NS, not significant.
RESULTS
When dental age was determined for the entire sample of 58 persons, the distribution into normal and late dental development was precisely 50% to each group. Taking the sexes separately, 60% of the girls had a dental age corresponding with chronological age, while the remaining 40% showed delayed dental development. In boys, 33% corresponded with their chronological age, and the majority (67%) exhibited latedeveloping dentitions. In females, the MD width of most of the teeth examined did not differ from the controls in both the NDA and LDA subgroups. The only exception was the central incisor, which was larger in the LDA female subgroup (Table I). By contrast, tooth size was significantly smaller in the LDA male subgroup than in the NDA subgroup. Tooth size in NDA males was similar to the controls, except for the upper central incisor and
the first molar, which were significantly smaller. Most of the teeth in the delayed dental age male dentitions had reduced size compared with the controls, with the exception of the maxillary central incisor, which was normally sized. The lateral incisor and the first premolar were almost normally sized in the NDA subgroup but significantly reduced in the LDA subgroup (Table II). With the notable exception of the maxillary lateral incisor, which was the only tooth that was significantly narrower than the controls in both normal and late female dentitions, the BL width of teeth in the PDC females showed no variation with dental age (Table I). In males with a delay in dental age, the teeth were smaller, except for the central incisor that was again larger than in the NDA subgroup. The lateral incisor was significantly smaller than the controls on all dental age groups, by more than 0.5 mm. The first premolar
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Table III. Prevalence of anomalous lateral incisors in PDC sample, according to dental age, versus controls (females and males together) Type of anomaly
Total PDC n⫽116
NDA n⫽58
LDA n⫽58
Controls n⫽80
P PDC/C
P NDA/C
P LDA/C
Peg-shaped Missing Total
17 (14.6%) 4 (3.5%) 21 (18.1%)
6 (10.3%) 1 (1.7%) 7 (12%)
11 (18.9%) 3 (5.2%) 14 (24.1%)
1 (1.2%) 0 (0%) 1 (1.2%)
⬍.05 NS .01
NS NS NS
⬍.05 NS .001
N, Number of arch sides examined; PDC, palatally displaced canines group; NDA, normal dental age subgroup; LDA, late dental age subgroup; C, control group with undisplaced canines; NS, not significant.
was smaller by almost 1 mm in the LDA males, compared with the controls (Table II). Taking the total male/female PDC sample together, peg-shaped and missing lateral incisors were 15 times more frequent in the PDC group than in the controls (Table III), with the difference highly statistically significant. This difference is mainly attributable to the large number of peg-shaped teeth in the PDC group (14.6%) versus the controls (1.2%). Additionally, twothirds of the anomalous lateral incisors were found in the LDA subgroup (24% versus 12%). The difference between the LDA subgroup and the controls was highly statistically significant, while the difference between the NDA subgroup and the controls was not statistically significant. In the females, the LDA subgroup showed a slightly higher prevalence of lateral incisor anomaly than did the NDA subgroup, which was nonsignificant. Both subgroups differed from the female controls, with a high level of statistically significance for the LDA subgroup (P ⬍ .001) and only a trend for the NDA subgroup (P ⫽ .06) (Table IV). By contrast, lateral incisor anomaly among the PDC males was twice as high in the LDA subgroup than in those with normal dental development and showed a highly significant difference from the male controls (P ⬍ .001) (Table V). Peg-shaped laterals were more frequent in the affected side (18%-8%), and missing lateral incisors more frequent in the unaffected side of PDC cases. Although the differences between these 2 subgroups did not reach statistical significance, the comparison with the control group revealed highly significant differences in the peg-shaped prevalence from the affected side only (P ⬍ .001). When the figures for peg-shaped and missing laterals were aggregated, similar values were obtained on the affected and the unaffected sides, and both sides differed from the controls (Table VI). Only 1 maxillary second premolar was missing in the PDC group, in a boy with a delayed dental age. In the control group, 2 second premolars were congenitally missing, 1 in the maxilla and 1 in the mandible.
Third molars were missing in 2 subjects (1 boy and 1 girl) with PDC, whose dental age was over 14. In the control group over 14 years of age, no subject had missing third molars. The small numbers precluded statistical analysis. DISCUSSION
The present work is the sequel to an earlier study of persons with PDC,19 that reported an approximately 50% prevalence of delayed dental development (ie, more than a 1-year discrepancy between dental age and chronological age) and no instances of accelerated dental development. This contrasted with a control group that displayed a normal distribution of timely, early, and late development of the dentition. On the basis of these findings, the authors speculated on the existence of 2 separate subgroups with PDC, with differing dental features and, perhaps, etiologies. The present study aimed to substantiate the latter suggestion by comparing specific features of the dentitions in the 2 dental age subgroups. Three parameters were selected for examination: MD and BL dimensions of the maxillary teeth, the prevalence of anomalous lateral incisors, and the prevalence of other congenitally missing teeth, each of which has a reported association with PDC. From the literature relating to random population samples, it has long been established that tooth dimensions in males are larger than in females.27 A previous work that compared tooth dimensions in dentitions with PDC revealed that teeth in PDC males are smaller than in a normal male control group, while PDC females’ teeth are similar in size to their control group.4 Moreover, the prevalence of those dental anomalies in the general population has been shown to differ according to sex.28-36 It was therefore considered mandatory to perform separate analyses of the tooth measurements for each sex and compare them with sex-matched control groups. When the present PDC group was divided according to sex, marked sexual dimorphism was observed. A different distribution of dental age was
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found for females and males. In females, the ratio of NDA to LDA dentitions was 3:2, while in the males the dominance of the LDA was expressed by a 1:3 NDA to LDA ratio. Thus, the likelihood of finding delayed dental development among PDC females is approximately half that among PDC males. The equal distribution of NDA and LDA dentitions reported in the previous study,19 in which the sexes were studied as a single PDC group, was the result of the mutual cancellation effect of these contrasting trends. Dentitions with LDA have been associated with small teeth.15,37 In the present study, tooth size also showed significant sexual dimorphism. The results presented in Table I reveal no significant differences in MD and BL tooth measurements between PDC females with normal versus delayed dental age. Paradoxically, the MD width of the central incisors was enlarged in the female LDA subgroup, a surprise finding that appears to be a notable exception to reported patterns. By contrast, in PDC males with NDA, most teeth were similar in size to the male controls, while the teeth in the LDA subgroup were significantly reduced (with the exception again of the central incisor) (Table II). The lateral incisor was the only tooth significantly smaller than those of the controls in both males and females and in both dental age subgroups. Conversely, the first premolar was exclusively affected in the LDA male subgroup, showing more than 0.5 mm reduction in the MD width and almost 1 mm in the BL dimension compared with the controls (P ⬍ .001). Thus, the high prevalence of smaller-than-average teeth in the PDC dentitions3 might be due to the especially high prevalence of delayed dentitions, particularly in males. From the point of view of the etiology of PDC, it is perhaps relevant to draw attention to the fact that reduction in size of the lateral incisors (in males and females) and the first premolars (solely in males) would appear to have the combined effect of providing more space in the canine area. It has been pointed out elsewhere that excessive spacing is strongly associated with PDC.1,2 The significant reduction in the maxillary lateral incisors in both sexes may be attributed to many peg-shaped lateral incisors in PDC cases (females and males together) compared with the controls (14.6% versus 1.2%, respectively). The explanation offered was that because peg-shaped lateral incisors are known to develop late, these teeth are probably insufficiently developed to afford the critical guidance in the early stages of canine development.5 Figures 1 and 2 might illustrate such a connection. Figure 1 shows 2 pegshaped lateral incisors, each with a markedly delayed individual dental age in a 9-year-old girl. Their roots
Chaushu, Sharabi, and Becker 343
Fig 1. Periapical radiograph of 9-year-old girl, showing 2 peg-shaped maxillary lateral incisors with severe delay in dental development. Short, nondeveloped roots cannot provide necessary guidance for canine eruption.
appear too short to provide the guidance needed for normal canine eruption. Four years later, the left canine was found to be palatally impacted (Fig 2). Others have preferred an alternative explanation in which genetics alone has dictated this abnormal eruptive path development.13,38 The highly significant increase in the lateral incisors’ anomalies in the PDC group confirms the findings of several other studies over the past 20 years.5-8,10 When PDC dentitions of both sexes were studied as a single group, the prevalence of peg-shaped and missing lateral incisors in the LDA subgroup was double that of the NDA subgroup. According to Garn et al,15 agenesis of at least 1 tooth could be considered as the extreme degree of expression of a gene or genes responsible for delayed calcification and formation. Furthermore, pegshaped incisors are considered to represent a milder expression of a gene or genes responsible for agenesis.17 It was therefore not surprising to find that the
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Fig 2. Panoramic radiograph 4 years later, showing that left maxillary canine became palatally impacted. Table IV.
Prevalence of anomalous lateral incisors in females with PDC, according to dental age, versus female
controls Type of anomaly
Total PDC n⫽74
NDA n⫽44
LDA n⫽30
Controls n⫽80
P PDC/C
P NDA/C
P LDA/C
Peg Missing Total
10 (13.5%) 1 (1.3%) 11 (14.8%)
5 (11.4%) 0 (0) 5 (11.4%)
5 (16.6%) 1 (3.4%) 6 (20%)
0 (0) 0 (0) 0 (1.2%)
⬍.001 NS ⬍.05
.06 NS .06
⬍.01 NS .001
PDC, Palatally displaced canines group; NDA, normal dental age subgroup; LDA, late dental age subgroup; C, control group with undisplaced canines; NS, not significant.
prevalence of the anomalous lateral incisors in the LDA subgroup was increased in comparison with the controls to a highly significant degree. Although more peg-shaped laterals were also observed in the NDA subgroup, no statistically significant differences were obtained when compared with the controls. When each sex was studied separately, a marked sexual dimorphism was also discovered in this trait. It was obvious that the LDA versus the NDA distinction found in the whole group was the result of significant differences between them in males (Table V), but in the females the 2 subgroups were more closely similar (Table IV). While lateral incisor anomaly affects females in the general population to a greater degree than males,28-36 the opposite is true in the PDC population, where males are slightly more affected. Its association with delayed dental age is also significant only in males. In an earlier work, it was speculated that the
late-developing root of a peg-shaped lateral incisor could prevent the canine from rectifying its position in the latter stages of its downward migration, while excess space, as in the congenital absence of the lateral incisor, often permits the canine to ultimately erupt in the dental arch.5 More peg-shaped laterals were seen adjacent to the PDC (the affected side), and more lateral incisors were missing on the unaffected side (with a normally erupted canine), confirming earlier findings.5-9,12 Although statistically significant differences were not reached when comparing the 2 sides, a comparison with the controls revealed a highly significant increase in peg-shaped laterals in the affected side only. Garn et al15,37 have reported on the association between missing third molars and a delay in dental development. Taking into account the high incidence of delayed dental age in the PDC group, a critical dental
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Table V.
Prevalence of anomalous lateral incisors in males with PDC, according to dental age, versus male
controls Type of anomaly
Total PDC n ⫽ 42
NDA n ⫽ 14
LDA n ⫽ 28
Controls n ⫽ 80
P PDC/C
P NDA/C
P LDA/C
Peg Missing Total
7 (16.6%) 3 (7.1%) 10 (23.8%)
1 (7.1%) 1 (7.1%) 2 (14.2%)
6 (21.4%) 2 (7.1%) 8 (28.5%)
1 (1.2%) 0 (0) 1 (1.2%)
⬍.05 NS .001
NS NS NS
⬍.01 NS ⬍.001
PDC, Palatally displaced canines group; NDA, normal dental age subgroup; LDA, late dental age subgroup; C, control group with undisplaced canines; NS, not significant. Table VI. Prevalence of anomalous lateral incisors in subjects with PDC, affected (adjacent to the PDC) versus unaffected side (without PDC), versus controls (females and males together) Type of anomaly
Aff side n ⫽ 78
Unaff side n ⫽ 38
Controls n ⫽ 80
P Aff/Unaff
P Aff/Controls
P Unaff/Controls
Peg Missing Total
14 (17.9%) 1 (1.3%) 15 (19.2%)
3 (7.9%) 3 (7.9%) 6 (15.8%)
1 (1.2%) 0 (0) 1 (1.2%)
NS NS NS
⬍.001 NS ⬍.001
NS NS .05
Aff, Affected; Unaff, unaffected; NS, not significant.
age assessment is to be preferred to chronological age, to minimize the likelihood of overlooking late and uncalcified third molars and to avoid prematurely diagnosing agenesis. Surveys that do not consider dental age may exaggerate the true incidence of thirdmolar agenesis.10 That portion of the present sample with a dental age over 14 was too small to permit drawing firm conclusions, although the only 2 subjects who showed missing third molars belonged to the PDC group. Missing second premolars were also seldom found in the present sample. The findings from our present and previous studies4 highlight the sexual dimorphism in PDC cases. The null hypothesis proposing the existence of 2 distinct PDC subgroups was supported for males only. One subgroup is characterized by delayed dental development, smaller-than-average teeth, and a marked increase in the incidence of anomalous lateral incisors. The second subgroup more closely resembles the controls, presenting a timely developed dentition, a moderate and not significantly increased incidence of anomalous lateral incisors, and a reduction in the dimensions of only the central incisors and the first molars. Studying the overall male PDC group as a single entity might produce confusing results, because important differences are obscured when the 2 subgroups are combined. CONCLUSIONS
1. PDC cases showed significant sexual dimorphism in all parameters studied.
2. Delayed dental age was twice as prevalent in PDC males than in females. 3. Delayed dental age in males with PDC was associated with smaller teeth and higher frequency of anomalous, especially peg-shaped, lateral incisors. 4. PDC males with NDA had dentitions more similar to the controls. 5. The dental parameters studied were not significantly different in the 2 dental age subgroups in females, even though a slight increase in the prevalence of anomalous lateral incisors was associated with delayed development. 6. The lateral incisor was the only tooth significantly smaller in both boys and girls and in both dental age subgroups than in the controls. Conversely, the first premolar was exclusively affected in the LDA male subgroup. The present findings show that patients with PDC are a highly heterogeneous group. Further studies on dental characteristics, diagnosis, and etiology should consider sex and dental age. REFERENCES 1. Jacoby H. The etiology of maxillary canine impactions. Am J Orthod 1983;84:125-32. 2. Becker A. Etiology of maxillary canine impaction. Am J Orthod 1984;86:437-8. 3. Langberg BJ, Peck S. Tooth-size reduction associated with occurrence of palatal displacement of canines. Angle Orthod 2000;70:126-8. 4. Becker A, Sharabi S, Chaushu S. Tooth size variation in
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dentitions affected by palatal canine displacement. Eur J Orthod 2001, submitted for publication. Becker A, Smith P, Behar R. The incidence of anomalous lateral incisors in relation to palatally displaced cuspids. Angle Orthod 1981;51:24-9. Brin I, Becker A, Shalhav M. Position of the maxillary permanent canine in relation to anomalous or missing lateral incisors. Eur J Orthod 1986;8:12-6. Oliver RG, Mannion JE, Robinson JM. Morphology of the maxillary lateral incisor in cases of unilateral impaction of the maxillary canine. Br J Orthod 1989;16:9-16. Zilberman Y, Cohen B, Becker A. Familial trends in palatal canines, anomalous lateral incisors and related phenomena. Eur J Orthod 1990;12:135-9. Mossey PA, Campbell HM, Luffingham JK. The palatal canine and the adjacent lateral incisor: a study of a West of Scotland population. Br J Orthod 1994;21:169-74. Peck S, Peck L, Kataja M. Prevalence of tooth agenesis and peg-shaped maxillary lateral incisor associated with palatally displaced canine (PDC) anomaly. Am J Orthod Dentofacial Orthop 1996;110:441-3. Baccetti T. A controlled study of associated dental anomalies. Angle Orthod 1998;68:267-74. Becker A, Gillis I, Shpack N. The etiology of palatal displacement of maxillary canines. Clin Orthod Res 1999;2:62-6. Pirinen S, Arte S, Apajalahti S. Palatal displacement of canine is genetic and related to congenital absence of teeth. J Dent Res 1996;75:1742-6. Shapira J, Chaushu S, Becker A. Prevalence of tooth transposition, third molar agenesis and maxillary canine impaction in individuals with Down syndrome. Angle Orthod 2000;70:290-6. Garn SM, Lewis AB, Vicinus JH. Third molar polymorphism and its significance to dental genetics. J Dent Res 1963;42:1344-63. Sofaer JA. Dental morphologic variation and the Hardy Weinberg law. J Dent Res 1970;49(suppl):1505. Garn SM, Lewis AB. Effects of agenesis on the crown-size profile pattern. J Dent Res 1969;48:1314. Newcomb MR. Recognition and interception of aberrant canine eruption. Angle Orthod 1959;29:161-8. Becker A, Chaushu S. Dental age in maxillary canine ectopia. Am J Orthod Dentofacial Orthop 2000;117:657-62. Seward GR. Radiology in general dental practice. IX-unerupted maxillary canines, central incisors and supernumeraries. Br Dent J 1963;115:85-91.
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21. Hunter SB. The radiographic assessment of the unerupted maxillary canine. Br Dent J 1981;150:151-5. 22. Becker A. The orthodontic treatment of impacted teeth. London: Martin Dunitz Ltd; 1998. 23. Nolla CM. The development of permanent teeth. J Dent Child 1960;27:254-66. 24. Moorrees CFA, Fanning EA, Gro`n AM, Lebret L. The timing of orthodontic treatment in relation to tooth formation. Trans Eur Orthod 1962;38:1-14. 25. Moorrees CFA, Fanning EA, Hunt EE Jr. Age variation of formation stages for ten permanent teeth. J Dent Res 1963;42: 1490-502. 26. Dahlberg G. Statistical methods for medical and biological students. London: Allen and Unwin; 1940. 27. Alvesalo L. Sex chromosomes and human growth. A dental approach. Hum Genet 1997;101:1-5. 28. Alvesalo L, Portin P. The inheritance pattern of missing, pegshaped and strongly mesio-distally reduced upper lateral incisors. Acta Odont Scand 1969;27:563-75. 29. Chosak A. Peg-shaped upper lateral incisor prevalence and heredity in Israel Jews. Abstracted in Proceedings of 6th Congress of the International Association of Dentistry for Children, in association with 50th Anniversary of the American Society of Dentistry for Children; 1977. 30. Eidelman E, Chosak A, Rosenzweig KA. Hypodontia: prevalence among Jewish populations of different origins. Am J Phys Anthropol 1973;39:129-34. 31. Muller TP, Hill IN, Peterson AL, Blayney JR. A survey of congenitally missing permanent teeth. J Am Dent Assoc 1970; 81:101-7. 32. Davis PJ. Hypodontia and hyperdontia of permanent teeth in Hong Kong school children. Community Dent Oral Epidemiol 1987;15:218-20. 33. Haavikko K. Hypodontia of permanent teeth. Suom Hammaslaak Toim 1971;67:219-25. 34. Ringqvist M, Thilander B. The frequency of hypodontia in an orthodontic material. Svensk Tandlak Tidskr 1969;62:535-41. 35. Niswander JD, Sujaku C. Congenital anomalies of teeth in Japanese children. Am J Phys Anthropol 1963;21:569-74. 36. Rose JS. A survey of congenitally missing teeth, excluding third molars in 6000 orthodontic patients. Dent Practit 1966;17:107-14. 37. Garn SM, Lewis AB, Kerewsky RS. Third molar agenesis and size reduction of the remaining teeth. Nature 1963;200:488-9. 38. Peck S, Peck L, Kataja M. The palatally displaced canine as a dental anomaly of genetic origin. Angle Orthod 1994;64:249-56.
Dental morphologic characteristics of normal versus delayed developing dentitions with palatally displaced canines Stella Chaushu, DMD, MSc,a Shaltiel Sharabi, BMedSc,b and Adrian Becker, BDS, LDS, DDOc Jerusalem, Israel An earlier study reported on the delayed dental age in about 50% of patients with palatally displaced canines (PDC), suggesting the possible existence of 2 different PDC phenotypes. The present study aimed to determine whether the PDC subgroup with late dental age displays different dental features from the PDC subgroup with normal dental age, supporting the above assumption. The 3 dental parameters examined were mesiodistal and buccolingual tooth sizes, the presence of anomalous maxillary lateral incisors, and other congenitally missing teeth. Fifty-eight subjects with PDC, 37 girls and 21 boys, were divided according to dental age and compared with age- and sex-matched controls. The results revealed marked sexual dimorphism. Delayed dental development was twice as prevalent among the PDC males. The existence of 2 distinct PDC subgroups was supported for males only. One subgroup was characterized by delayed dental development, smaller-than-average teeth, and a marked increase in the prevalence of anomalous lateral incisors. The second subgroup more closely resembled the controls, presenting a timely developed dentition, a moderate and nonsignificant increase of anomalous lateral incisors, and a reduction in the dimensions of only the central incisors and the first molars. In females, although the prevalence of anomalous lateral incisors was slightly increased in the late dental age subgroup, tooth sizes were remarkably similar, negating the existence of 2 distinct subpopulations. Studying the overall PDC group as a single entity produced confusing results because important differences were obscured when the 2 sexes and the 2 dental age subgroups (in males) were combined. (Am J Orthod Dentofacial Orthop 2002;121:339-46)
D
entitions characterized by the presence of a palatally displaced maxillary canine (PDC) have been associated with a distinct group of dental abnormalities, including: 1. Small teeth. Assessment of tooth size has largely been made by qualitative clinical observation of the teeth and the presence of spacing, rather than by systematic measurement.1,2 Quantitative systematic measurement of tooth size, other than lateral incisors, has only recently been reported. Langberg and Peck3 found significantly diminished mesiodistal (MD) widths of the upper and lower incisors in a combined male/female sample of PDC patients. A similar quantitative and systematic study by the present authors4 examined males and females as From the Department of Orthodontics, Hebrew University-Hadassah School of Dental Medicine, founded by the Alpha Omega Fraternity, Jerusalem, Israel. a Clinical lecturer. b Undergraduate dental student and MSc candidate. c Clinical Associate Professor. Reprint requests to: Dr Stella Chaushu, Department of Orthodontics, Hebrew University-Hadassah School of Dental Medicine, P. O. Box 12272, Jerusalem 91120, Israel; e-mail, [email protected]. Submitted, May 2001; revised and accepted, August 2001. Copyright © 2002 by the American Association of Orthodontists. 0889-5406/2002/$35.00 ⫹ 0 8/1/121559 doi:10.1067/mod.2002.121559
separate subgroups and disclosed unexpected and unexplained findings, highlighting a sexual dimorphism not previously reported. Compared with a control group, the MD and buccolingual (BL) dimensions of all maxillary teeth in the PDC patients showed significant tooth size reduction only in the males. The BL dimension of the lateral incisor was the only parameter in which the females also showed a reduced size. When further divided into unilateral and bilateral cases, tooth size reductions were also seen in bilaterally affected females and unilaterally affected males. 2. Anomalous lateral incisors. Several investigations over the past 20 years have shown that PDCaffected dentitions feature small, peg-shaped, and missing lateral incisors in just under half the cases studied.5-12 3. Congenitally missing teeth (other than lateral incisors). Agenesis of the third molars and the second premolars has been reported in higher frequency in dentitions with PDC.10,11,13,14 It is well established that late-developing dentitions are particularly prone to individual tooth agenesis, small teeth,15,16 and teeth with a poor crown-size 339
340 Chaushu, Sharabi, and Becker
profile pattern.17 More than 40 years ago, it was first noticed that dentitions that exhibited late development have also been associated with PDC, although until recently, in an investigation by the present authors,19 this observation has never been substantiated experimentally. The observation was initially based on clinical experience18 and later clinically, with eruption of teeth as the criterion for dental age assessment.8 The recent study assessed dental age in a large sample of PDC patients, with more objective criteria.19 A radiographic evaluation of tooth calcification (specifically root length) showed that approximately half of the PDC subjects had a late-developing dentition. The present investigation seeks to learn whether normal and late-developing PDC dentitions differ in their association with the above anomalies. This will determine whether dental age and dental morphology characteristics, together, may support the existence of 2 distinct genetic PDC phenotypes. A null hypothesis was proposed based on the assumption that a PDC subgroup with late dental age (LDA) displays different dental features from a PDC subgroup with normal dental age (NDA). The testing hypothesis was that a higher prevalence of dental anomaly (small teeth, missing teeth, and anomalous lateral incisors) occurs in the LDA subgroup than in the NDA subgroup. MATERIAL AND METHODS
The treatment records of 58 consecutively treated patients with palatal displacement of the maxillary canine were obtained from 3 orthodontic practices in Jerusalem and Tel Aviv. The patients were between 11 and 15 years of age and included 21 boys and 37 girls; the PDC determination was made on the basis of a clinical examination and diagnostic radiographs, according to established, standardized techniques.20-22 In each case, the diagnosis was confirmed at surgical exposure, performed at an appropriate time in the overall treatment plan. The control group comprised 40 age-matched and consecutively treated patients (20 boys and 20 girls), exhibiting normally erupted and undisplaced maxillary canines, as diagnosed from their pretreatment plaster casts. Good-quality panoramic radiographs and periapical views of the incisor regions were available for each patient. These were studied, and a careful assessment of dental age23-25 was determined for each permanent tooth, erupted and unerupted. The assessments were made to an accuracy tolerance of 0.5 years, as described elsewhere.22 In the previous study,19 approximately
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half of the PDC patients showed a delay in dental age. Following a similar protocol, this group was further divided into an NDA subgroup and an LDA (over 1 year delay in dental age) subgroup. MD and BL widths of all the erupted maxillary permanent teeth, from the first molars forward, were measured directly on the plaster casts that were available for each patient of both groups. This was done to an accuracy of 0.01 mm with a dial caliper with ground tips. Partially erupted, carious, and restored teeth were excluded, and measurements were not recorded where obvious calculus or plaque obscured the true contour of the tooth. Teeth were measured on both sides of the dental arch and the results averaged, based on previous work that showed no tooth size difference between affected and unaffected sides in PDC subjects.4 Recordings were made for boys and girls separately. Anomalies of the maxillary lateral incisor (pegshaped and missing) were identified by direct observation. The incisors were defined as peg-shaped by using established criteria.5 Aplasia of the second premolars and the third molars was diagnosed from the panoramic x-rays. For third-molar aplasia, 14 years seems to be the critical age for radiologic evidence of third-molar calcification.15 Because approximately half of the PDC group showed delayed dental development, these criteria were adapted to a critical dental age of 14, rather than the more usual and, in the present context, arbitrary chronological age. As the result, only 12 control subjects and 8 with PDC were included in this part of the study, all of them belonging to the NDA subgroup. The significance of the differences between the mean tooth measurements in the examined groups was tested by Student t tests. Chi-square contingency tests were used to compare the prevalence of the lateral incisor anomalies in each group. Statistical analyses were not appropriate for the second-premolar and the third-molar aplasia prevalence because of the small numbers involved. Ten casts were randomly selected and measured on 2 separate occasions to test the reproducibility of the measurements. Experimental error was analyzed and assessed with Student t tests to assess the significance of the differences in the measurements. The experimental error was determined by calculating the standard deviation of a single parameter.26 Measurement errors ranged from 0.08 to 0.13 mm, and the 0.1 mm weighted average standard deviation of a single determination for both MD and BL dimensions was not considered significant. On this basis, experimental error was unlikely to bias the accuracy of tooth measurement.
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Table I. Mesiodistal and buccolingual crown diameters in females with PDC, according to dental age, versus female controls
Tooth number 1 2 4 5 6
MD BL MD BL MD BL MD BL MD BL
Total PDC n⫽37
NDA n⫽22
LDA n⫽15
Controls n⫽20
P PDC/C
P NDA/C
P LDA/C
8.43 ⫾ 0.82 6.58 ⫾ 0.91 6.55 ⫾ 0.61 5.31 ⫾ 0.7 6.64 ⫾ 0.68 8.73 ⫾ 0.65 6.5 ⫾ 0.65 9.2 ⫾ 0.45 10.05 ⫾ 0.88 10.52 ⫾ 0.56
8.27 ⫾ 0.88 6.59 ⫾ 0.96 6.5 ⫾ 0.57 5.31 ⫾ 0.73 6.72 ⫾ 0.77 8.77 ⫾ 0.73 6.47 ⫾ 0.74 9.13 ⫾ 0.53 10.07 ⫾ 0.78 10.47 ⫾ 0.59
8.66 ⫾ 0.68 6.57 ⫾ 0.87 6.62 ⫾ 0.69 5.31 ⫾ 0.65 6.51 ⫾ 0.66 8.66 ⫾ 0.5 6.58 ⫾ 0.93 9.31 ⫾ 0.38 10.02 ⫾ 0.49 10.6 ⫾ 0.75
8.22 ⫾ 0.32 6.8 ⫾ 0.64 6.42 ⫾ 0.54 5.82 ⫾ 0.75 6.61 ⫾ 0.37 8.89 ⫾ 0.66 6.34 ⫾ 0.31 9.25 ⫾ 0.52 9.86 ⫾ 0.45 10.42 ⫾ 0.43
NS NS NS ⬍.01 NS NS NS NS NS NS
NS NS NS ⬍.01 NS NS NS NS NS NS
⬍.05 NS NS ⬍.01 NS NS NS NS NS NS
MD, Mesiodistal; BL, buccolingual; PDC, palatally displaced canines group; NDA, normal dental age subgroup; LDA, late dental age subgroup; C, control group with undisplaced canines; NS, not significant.
Mesiodistal and buccolingual crown diameters in males with PDC, according to dental age, versus male
Table II.
controls Tooth Number 1 2 4 5 6
MD BL MD BL MD BL MD BL MD BL
Total PDC n⫽21
NDA n⫽7
LDA n⫽14
Controls n⫽20
P PDC/C
P NDA/C
P LDA/C
8.42 ⫾ 0.78 6.41 ⫾ 0.65 6.5 ⫾ 1 5.32 ⫾ 0.62 6.57 ⫾ 0.51 8.76 ⫾ 0.69 6.42 ⫾ 0.52 8.99 ⫾ 0.65 10.13 ⫾ 0.73 10.63 ⫾ 0.54
8.27 ⫾ 0.85 6.22 ⫾ 0.55 6.69 ⫾ 0.92 5.21 ⫾ 0.67 6.86 ⫾ 0.41 9.06 ⫾ 0.61 6.46 ⫾ 0.59 9.15 ⫾ 0.64 10.02 ⫾ 0.83 10.51 ⫾ 0.44
8.5 ⫾ 0.76 6.51 ⫾ 0.68 6.38 ⫾ 0.75 5.37 ⫾ 0.62 6.4 ⫾ 0.5 8.57 ⫾ 0.69 6.39 ⫾ 0.49 8.87 ⫾ 0.66 10.12 ⫾ 0.67 10.69 ⫾ 0.59
8.69 ⫾ 0.47 6.85 ⫾ 0.54 6.75 ⫾ 0.38 5.88 ⫾ 0.68 7.06 ⫾ 0.52 9.39 ⫾ 0.59 6.64 ⫾ 0.58 9.54 ⫾ 0.8 10.58 ⫾ 0.81 10.93 ⫾ 0.57
NS ⬍.05 NS ⬍.05 ⬍.01 ⬍.01 NS ⬍.01 ⬍.05 ⬍.05
⬍.05 ⬍.05 NS ⬍.05 NS NS NS NS ⬍.05 ⬍.05
NS NS ⬍.05 ⬍.05 ⬍.001 ⬍.001 NS ⬍.01 ⬍.05 ⬍.05
MD, Mesiodistal; BL, buccolingual; PDC, palatally displaced canines group; NDA, normal dental age subgroup; LDA, late dental age subgroup; C, control group with undisplaced canines; NS, not significant.
RESULTS
When dental age was determined for the entire sample of 58 persons, the distribution into normal and late dental development was precisely 50% to each group. Taking the sexes separately, 60% of the girls had a dental age corresponding with chronological age, while the remaining 40% showed delayed dental development. In boys, 33% corresponded with their chronological age, and the majority (67%) exhibited latedeveloping dentitions. In females, the MD width of most of the teeth examined did not differ from the controls in both the NDA and LDA subgroups. The only exception was the central incisor, which was larger in the LDA female subgroup (Table I). By contrast, tooth size was significantly smaller in the LDA male subgroup than in the NDA subgroup. Tooth size in NDA males was similar to the controls, except for the upper central incisor and
the first molar, which were significantly smaller. Most of the teeth in the delayed dental age male dentitions had reduced size compared with the controls, with the exception of the maxillary central incisor, which was normally sized. The lateral incisor and the first premolar were almost normally sized in the NDA subgroup but significantly reduced in the LDA subgroup (Table II). With the notable exception of the maxillary lateral incisor, which was the only tooth that was significantly narrower than the controls in both normal and late female dentitions, the BL width of teeth in the PDC females showed no variation with dental age (Table I). In males with a delay in dental age, the teeth were smaller, except for the central incisor that was again larger than in the NDA subgroup. The lateral incisor was significantly smaller than the controls on all dental age groups, by more than 0.5 mm. The first premolar
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Table III. Prevalence of anomalous lateral incisors in PDC sample, according to dental age, versus controls (females and males together) Type of anomaly
Total PDC n⫽116
NDA n⫽58
LDA n⫽58
Controls n⫽80
P PDC/C
P NDA/C
P LDA/C
Peg-shaped Missing Total
17 (14.6%) 4 (3.5%) 21 (18.1%)
6 (10.3%) 1 (1.7%) 7 (12%)
11 (18.9%) 3 (5.2%) 14 (24.1%)
1 (1.2%) 0 (0%) 1 (1.2%)
⬍.05 NS .01
NS NS NS
⬍.05 NS .001
N, Number of arch sides examined; PDC, palatally displaced canines group; NDA, normal dental age subgroup; LDA, late dental age subgroup; C, control group with undisplaced canines; NS, not significant.
was smaller by almost 1 mm in the LDA males, compared with the controls (Table II). Taking the total male/female PDC sample together, peg-shaped and missing lateral incisors were 15 times more frequent in the PDC group than in the controls (Table III), with the difference highly statistically significant. This difference is mainly attributable to the large number of peg-shaped teeth in the PDC group (14.6%) versus the controls (1.2%). Additionally, twothirds of the anomalous lateral incisors were found in the LDA subgroup (24% versus 12%). The difference between the LDA subgroup and the controls was highly statistically significant, while the difference between the NDA subgroup and the controls was not statistically significant. In the females, the LDA subgroup showed a slightly higher prevalence of lateral incisor anomaly than did the NDA subgroup, which was nonsignificant. Both subgroups differed from the female controls, with a high level of statistically significance for the LDA subgroup (P ⬍ .001) and only a trend for the NDA subgroup (P ⫽ .06) (Table IV). By contrast, lateral incisor anomaly among the PDC males was twice as high in the LDA subgroup than in those with normal dental development and showed a highly significant difference from the male controls (P ⬍ .001) (Table V). Peg-shaped laterals were more frequent in the affected side (18%-8%), and missing lateral incisors more frequent in the unaffected side of PDC cases. Although the differences between these 2 subgroups did not reach statistical significance, the comparison with the control group revealed highly significant differences in the peg-shaped prevalence from the affected side only (P ⬍ .001). When the figures for peg-shaped and missing laterals were aggregated, similar values were obtained on the affected and the unaffected sides, and both sides differed from the controls (Table VI). Only 1 maxillary second premolar was missing in the PDC group, in a boy with a delayed dental age. In the control group, 2 second premolars were congenitally missing, 1 in the maxilla and 1 in the mandible.
Third molars were missing in 2 subjects (1 boy and 1 girl) with PDC, whose dental age was over 14. In the control group over 14 years of age, no subject had missing third molars. The small numbers precluded statistical analysis. DISCUSSION
The present work is the sequel to an earlier study of persons with PDC,19 that reported an approximately 50% prevalence of delayed dental development (ie, more than a 1-year discrepancy between dental age and chronological age) and no instances of accelerated dental development. This contrasted with a control group that displayed a normal distribution of timely, early, and late development of the dentition. On the basis of these findings, the authors speculated on the existence of 2 separate subgroups with PDC, with differing dental features and, perhaps, etiologies. The present study aimed to substantiate the latter suggestion by comparing specific features of the dentitions in the 2 dental age subgroups. Three parameters were selected for examination: MD and BL dimensions of the maxillary teeth, the prevalence of anomalous lateral incisors, and the prevalence of other congenitally missing teeth, each of which has a reported association with PDC. From the literature relating to random population samples, it has long been established that tooth dimensions in males are larger than in females.27 A previous work that compared tooth dimensions in dentitions with PDC revealed that teeth in PDC males are smaller than in a normal male control group, while PDC females’ teeth are similar in size to their control group.4 Moreover, the prevalence of those dental anomalies in the general population has been shown to differ according to sex.28-36 It was therefore considered mandatory to perform separate analyses of the tooth measurements for each sex and compare them with sex-matched control groups. When the present PDC group was divided according to sex, marked sexual dimorphism was observed. A different distribution of dental age was
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found for females and males. In females, the ratio of NDA to LDA dentitions was 3:2, while in the males the dominance of the LDA was expressed by a 1:3 NDA to LDA ratio. Thus, the likelihood of finding delayed dental development among PDC females is approximately half that among PDC males. The equal distribution of NDA and LDA dentitions reported in the previous study,19 in which the sexes were studied as a single PDC group, was the result of the mutual cancellation effect of these contrasting trends. Dentitions with LDA have been associated with small teeth.15,37 In the present study, tooth size also showed significant sexual dimorphism. The results presented in Table I reveal no significant differences in MD and BL tooth measurements between PDC females with normal versus delayed dental age. Paradoxically, the MD width of the central incisors was enlarged in the female LDA subgroup, a surprise finding that appears to be a notable exception to reported patterns. By contrast, in PDC males with NDA, most teeth were similar in size to the male controls, while the teeth in the LDA subgroup were significantly reduced (with the exception again of the central incisor) (Table II). The lateral incisor was the only tooth significantly smaller than those of the controls in both males and females and in both dental age subgroups. Conversely, the first premolar was exclusively affected in the LDA male subgroup, showing more than 0.5 mm reduction in the MD width and almost 1 mm in the BL dimension compared with the controls (P ⬍ .001). Thus, the high prevalence of smaller-than-average teeth in the PDC dentitions3 might be due to the especially high prevalence of delayed dentitions, particularly in males. From the point of view of the etiology of PDC, it is perhaps relevant to draw attention to the fact that reduction in size of the lateral incisors (in males and females) and the first premolars (solely in males) would appear to have the combined effect of providing more space in the canine area. It has been pointed out elsewhere that excessive spacing is strongly associated with PDC.1,2 The significant reduction in the maxillary lateral incisors in both sexes may be attributed to many peg-shaped lateral incisors in PDC cases (females and males together) compared with the controls (14.6% versus 1.2%, respectively). The explanation offered was that because peg-shaped lateral incisors are known to develop late, these teeth are probably insufficiently developed to afford the critical guidance in the early stages of canine development.5 Figures 1 and 2 might illustrate such a connection. Figure 1 shows 2 pegshaped lateral incisors, each with a markedly delayed individual dental age in a 9-year-old girl. Their roots
Chaushu, Sharabi, and Becker 343
Fig 1. Periapical radiograph of 9-year-old girl, showing 2 peg-shaped maxillary lateral incisors with severe delay in dental development. Short, nondeveloped roots cannot provide necessary guidance for canine eruption.
appear too short to provide the guidance needed for normal canine eruption. Four years later, the left canine was found to be palatally impacted (Fig 2). Others have preferred an alternative explanation in which genetics alone has dictated this abnormal eruptive path development.13,38 The highly significant increase in the lateral incisors’ anomalies in the PDC group confirms the findings of several other studies over the past 20 years.5-8,10 When PDC dentitions of both sexes were studied as a single group, the prevalence of peg-shaped and missing lateral incisors in the LDA subgroup was double that of the NDA subgroup. According to Garn et al,15 agenesis of at least 1 tooth could be considered as the extreme degree of expression of a gene or genes responsible for delayed calcification and formation. Furthermore, pegshaped incisors are considered to represent a milder expression of a gene or genes responsible for agenesis.17 It was therefore not surprising to find that the
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Fig 2. Panoramic radiograph 4 years later, showing that left maxillary canine became palatally impacted. Table IV.
Prevalence of anomalous lateral incisors in females with PDC, according to dental age, versus female
controls Type of anomaly
Total PDC n⫽74
NDA n⫽44
LDA n⫽30
Controls n⫽80
P PDC/C
P NDA/C
P LDA/C
Peg Missing Total
10 (13.5%) 1 (1.3%) 11 (14.8%)
5 (11.4%) 0 (0) 5 (11.4%)
5 (16.6%) 1 (3.4%) 6 (20%)
0 (0) 0 (0) 0 (1.2%)
⬍.001 NS ⬍.05
.06 NS .06
⬍.01 NS .001
PDC, Palatally displaced canines group; NDA, normal dental age subgroup; LDA, late dental age subgroup; C, control group with undisplaced canines; NS, not significant.
prevalence of the anomalous lateral incisors in the LDA subgroup was increased in comparison with the controls to a highly significant degree. Although more peg-shaped laterals were also observed in the NDA subgroup, no statistically significant differences were obtained when compared with the controls. When each sex was studied separately, a marked sexual dimorphism was also discovered in this trait. It was obvious that the LDA versus the NDA distinction found in the whole group was the result of significant differences between them in males (Table V), but in the females the 2 subgroups were more closely similar (Table IV). While lateral incisor anomaly affects females in the general population to a greater degree than males,28-36 the opposite is true in the PDC population, where males are slightly more affected. Its association with delayed dental age is also significant only in males. In an earlier work, it was speculated that the
late-developing root of a peg-shaped lateral incisor could prevent the canine from rectifying its position in the latter stages of its downward migration, while excess space, as in the congenital absence of the lateral incisor, often permits the canine to ultimately erupt in the dental arch.5 More peg-shaped laterals were seen adjacent to the PDC (the affected side), and more lateral incisors were missing on the unaffected side (with a normally erupted canine), confirming earlier findings.5-9,12 Although statistically significant differences were not reached when comparing the 2 sides, a comparison with the controls revealed a highly significant increase in peg-shaped laterals in the affected side only. Garn et al15,37 have reported on the association between missing third molars and a delay in dental development. Taking into account the high incidence of delayed dental age in the PDC group, a critical dental
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Table V.
Prevalence of anomalous lateral incisors in males with PDC, according to dental age, versus male
controls Type of anomaly
Total PDC n ⫽ 42
NDA n ⫽ 14
LDA n ⫽ 28
Controls n ⫽ 80
P PDC/C
P NDA/C
P LDA/C
Peg Missing Total
7 (16.6%) 3 (7.1%) 10 (23.8%)
1 (7.1%) 1 (7.1%) 2 (14.2%)
6 (21.4%) 2 (7.1%) 8 (28.5%)
1 (1.2%) 0 (0) 1 (1.2%)
⬍.05 NS .001
NS NS NS
⬍.01 NS ⬍.001
PDC, Palatally displaced canines group; NDA, normal dental age subgroup; LDA, late dental age subgroup; C, control group with undisplaced canines; NS, not significant. Table VI. Prevalence of anomalous lateral incisors in subjects with PDC, affected (adjacent to the PDC) versus unaffected side (without PDC), versus controls (females and males together) Type of anomaly
Aff side n ⫽ 78
Unaff side n ⫽ 38
Controls n ⫽ 80
P Aff/Unaff
P Aff/Controls
P Unaff/Controls
Peg Missing Total
14 (17.9%) 1 (1.3%) 15 (19.2%)
3 (7.9%) 3 (7.9%) 6 (15.8%)
1 (1.2%) 0 (0) 1 (1.2%)
NS NS NS
⬍.001 NS ⬍.001
NS NS .05
Aff, Affected; Unaff, unaffected; NS, not significant.
age assessment is to be preferred to chronological age, to minimize the likelihood of overlooking late and uncalcified third molars and to avoid prematurely diagnosing agenesis. Surveys that do not consider dental age may exaggerate the true incidence of thirdmolar agenesis.10 That portion of the present sample with a dental age over 14 was too small to permit drawing firm conclusions, although the only 2 subjects who showed missing third molars belonged to the PDC group. Missing second premolars were also seldom found in the present sample. The findings from our present and previous studies4 highlight the sexual dimorphism in PDC cases. The null hypothesis proposing the existence of 2 distinct PDC subgroups was supported for males only. One subgroup is characterized by delayed dental development, smaller-than-average teeth, and a marked increase in the incidence of anomalous lateral incisors. The second subgroup more closely resembles the controls, presenting a timely developed dentition, a moderate and not significantly increased incidence of anomalous lateral incisors, and a reduction in the dimensions of only the central incisors and the first molars. Studying the overall male PDC group as a single entity might produce confusing results, because important differences are obscured when the 2 subgroups are combined. CONCLUSIONS
1. PDC cases showed significant sexual dimorphism in all parameters studied.
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