Editorial Type:
Article Category: Research Article
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Online Publication Date: 06 Aug 2014

Relationship between the maxillary transverse dimension and palatally displaced canines: A cone-beam computed tomographic study

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Page Range: 440 – 445
DOI: 10.2319/032614-226.1
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ABSTRACT

Objectives: 

To examine the relationship between palatally displaced maxillary canines (PDC) and the maxillary transverse dimension using cone-beam computed tomography (CBCT).

Materials and Methods: 

Thirty-three patients (11 males and 22 females, mean age 18.2 years) with PDC were matched to 66 patients (22 males and 44 females, mean age 18.1 years) without PDC (control) by gender, age, and posterior occlusion. A CBCT image was taken on all the patients prior to any orthodontic treatment. For each patient the maxillary basal bone widths and interdental widths at the maxillary first molars and first and second premolars were measured on axial and coronal sections of CBCT images. In addition, the presence of permanent tooth agenesis and the widths of maxillary incisors were recorded.

Results: 

Similar maxillary transverse dimensions, both skeletally and dentally, were found between the PDC and control groups. In the PDC group, the number of patients with permanent tooth agenesis was six times higher than in the control group. In addition, the maxillary lateral incisors on PDC-affected sides were smaller than those of control group (P < .05).

Conclusions: 

The maxillary transverse dimension, both skeletally and dentally, had no effect on the occurrence of PDC. The higher prevalence of permanent tooth agenesis was found in the PDC group. Moreover, the mean mesiodistal width of maxillary lateral incisors in the PDC group was significantly smaller than in the control group (P < .05).

Keywords: Palatally displaced canine; Transverse dimension; CBCT

INTRODUCTION

The prevalence of permanent maxillary canine impaction is approximately 1–3% of the population.1–4 Of all permanent maxillary canine impactions, palatal impactions occur two to three times more often than do buccal impactions.1–4 The palatally impacted or displaced canine (PDC) is more prevalent in females than in males, and unilateral impactions are more common than bilateral impactions.2,5

Traditionally, the diagnosis of PDC has been based on periapical and/or panoramic radiographs. However, these methods have their limitations. The radiographs are a two-dimensional depiction of a three-dimensional object. In addition, the PDC is usually located at the most curved area of the maxillary arch. Thus, distortion of the canine area in the radiographs is difficult to avoid. More recently, dentists have been utilizing cone-beam computed tomography (CBCT) to diagnose impacted teeth because it determines the precise three-dimensional position of the impacted canine and assesses the health of neighboring roots.

The etiology of buccally impacted canines is related to space deficiency for the canine and/or a narrow maxillary arch.6,7 However, the exact cause(s) of PDC is unknown. The two respective theories on the etiology of PDC are known as the guidance theory and the genetic theory. The guidance theory suggests that the canine erupts along the root of the lateral incisor, which serves as a guide. If the root of the lateral incisor is absent or abnormal, the canine will not erupt and will become impacted.8,9 The genetic theory, however, attributes a hereditary component to PDC. It suggests that the PDC often presents with other genetic dental anomalies, such as permanent tooth agenesis and abnormally sized or shaped maxillary lateral incisors.2,10,11

In addition to these two theories, many investigators have been trying to uncover a relationship between the width of the maxilla, skeletally and dentally, and the occurrence of PDC. Some studies have shown that a posterior cross-bite or a transverse maxillary deficiency was related to canine impaction, but these studies did not differentiate whether the impactions were buccal or palatal.12,13 Langberg and Peck14 examined pretreatment dental casts of patients with PDC and found no significant difference in the arch width between the PDC and control groups. On the other hand, Al-Nimri and Gharaibeh15 examined the pretreatment dental casts of patients with PDC and reported that patients with PDC showed greater maxillary transverse dimensions than the control group. Saiar et al.16 examined the posteroanterior cephalograms of patients with PDC and reported no association between the skeletal maxillary width (measured from points J to J) with PDC. More recently, Yan et al.7 examined the pretreatment CBCT of patients with PDC and found there was no correlation between the maxillary skeletal width (measured from points J to J) and PDC. However, measurements of the maxillary skeletal widths of the first and second premolars were not completed.

It is clear that the relationship between the maxillary transverse dimensions and the occurrence of PDC requires further investigation. Thus, the purpose of this study was to utilize the CBCT technology to examine whether there was a relationship between the maxillary transverse dimensions, skeletally and dentally, and the presence of PDC. The presence of permanent tooth agenesis and the widths of maxillary incisors were also examined.

MATERIALS AND METHODS

After receiving Institutional Review Board approval from the University of Pennsylvania, the pretreatment CBCT images of 33 patients with PDC (PDC group) and 66 controls (control group) were acquired from the Oral and Maxillofacial Radiology division of the University of Pennsylvania School of Dental Medicine and two private orthodontic practices. All patients were at least 10 years old, had not received any previous orthodontic treatment, and did not present with a facial deformity. The PDC group consisted of 11 males and 22 females. The age range in the PDC group was from 10 to 41.8 years, and the mean age was 18.2 years. Palatal impactions of the canine presented both unilaterally and bilaterally. The PDC was diagnosed not only by the CBCT image but its palatal position relative to the maxillary lateral by the canine exposure surgery was confirmed. Each patient in the PDC group was matched with two controls by gender, age, and transverse dental occlusion (ie, the presence or absence of a cross-bite). The control group contained 22 males and 44 females. The age range in the control group was from 9.6 to 42.2 years, and the mean age was 18.1 years. The CBCT images were acquired using the Carestream Dental 3D extraoral imaging system (Atlanta, Ga) or an i-CAT machine (Hatfield, Pa). With both CBCT imaging systems, the voxel size was standardized at 0.4 mm.

All CBCT images were oriented and standardized using the InVivo Dental software (version 5.0, Anatomage, San Jose, Calif). In the frontal and right lateral views, each image was oriented in three planes of space.17 In the frontal view, the head was positioned with the floor of the orbits parallel to the floor. In the right lateral view, the Frankfort horizontal line (upper rim of external auditory meatus, Porion, to the inferior border of the orbital rim, Orbitale) was adjusted so that it was parallel to the floor. After these steps were completed, the skull's position was saved and set as the default position throughout this study.

All data were calculated from this new default position of the patient's three-dimensional skull. Quantitative evaluation of the parameters was based on the identification and registration of a series of points. First, points 1 and 2 were reference points that represented the level of basal bone of the maxilla. In the frontal view, these two landmarks were plotted on the right and left sides of the skull and were defined as the most superior aspect of the concavity of the maxillary bone as it joined the zygomatic process (Figure 1).18

Figure 1. Reference points 1 and 2 on the frontal view of the skull, defined as the most superior aspect of the concavity of the maxillary bone as it joined the zygomatic process. Taking points 1 and 2, a horizontal reference plane was drawn parallel to the floor.Figure 1. Reference points 1 and 2 on the frontal view of the skull, defined as the most superior aspect of the concavity of the maxillary bone as it joined the zygomatic process. Taking points 1 and 2, a horizontal reference plane was drawn parallel to the floor.Figure 1. Reference points 1 and 2 on the frontal view of the skull, defined as the most superior aspect of the concavity of the maxillary bone as it joined the zygomatic process. Taking points 1 and 2, a horizontal reference plane was drawn parallel to the floor.
Figure 1. Reference points 1 and 2 on the frontal view of the skull, defined as the most superior aspect of the concavity of the maxillary bone as it joined the zygomatic process. Taking points 1 and 2, a horizontal reference plane was drawn parallel to the floor.

Citation: The Angle Orthodontist 85, 3; 10.2319/032614-226.1

Taking points 1 and 2, a horizontal reference plane was drawn parallel to the floor. In the right lateral view, points S4, S5, and S6 were marked on the horizontal reference plane above the center of the clinical crowns of the maxillary first molar, second premolar (or second primary molar), and first premolar (or first primary molar), respectively (Figure 2). This same method was used to construct points S4′, S5′, and S6′ on the horizontal reference plane, but from the left lateral view. In the axial view, the maxillary basal bone width was measured at the level of the first molars (the distance between points S6 and S6′), the second premolars (the distance between points S5 and S5′), and first premolars (the distance between points S4 and S4′) (Figure 3).

Figure 2. The right lateral view of the skull. Illustrates points S4, S5, and S6 on the horizontal reference plane. Point S6 was marked directly above the midpoint of the maxillary first molar. Point S5 was marked directly above the midpoint of the second premolar (second primary molar). Point S4 was marked directly above the midpoint of the first premolar (first primary molar).Figure 2. The right lateral view of the skull. Illustrates points S4, S5, and S6 on the horizontal reference plane. Point S6 was marked directly above the midpoint of the maxillary first molar. Point S5 was marked directly above the midpoint of the second premolar (second primary molar). Point S4 was marked directly above the midpoint of the first premolar (first primary molar).Figure 2. The right lateral view of the skull. Illustrates points S4, S5, and S6 on the horizontal reference plane. Point S6 was marked directly above the midpoint of the maxillary first molar. Point S5 was marked directly above the midpoint of the second premolar (second primary molar). Point S4 was marked directly above the midpoint of the first premolar (first primary molar).
Figure 2. The right lateral view of the skull. Illustrates points S4, S5, and S6 on the horizontal reference plane. Point S6 was marked directly above the midpoint of the maxillary first molar. Point S5 was marked directly above the midpoint of the second premolar (second primary molar). Point S4 was marked directly above the midpoint of the first premolar (first primary molar).

Citation: The Angle Orthodontist 85, 3; 10.2319/032614-226.1

Figure 3. An axial section of the horizontal reference plane. S4, S4′, S5, S5′, S6, and S6′ were located on the horizontal reference plane and on the cortical outline of the maxilla. Maxillary skeletal widths were measured as S4–S4′, S5–S5′, and S6–S6′.Figure 3. An axial section of the horizontal reference plane. S4, S4′, S5, S5′, S6, and S6′ were located on the horizontal reference plane and on the cortical outline of the maxilla. Maxillary skeletal widths were measured as S4–S4′, S5–S5′, and S6–S6′.Figure 3. An axial section of the horizontal reference plane. S4, S4′, S5, S5′, S6, and S6′ were located on the horizontal reference plane and on the cortical outline of the maxilla. Maxillary skeletal widths were measured as S4–S4′, S5–S5′, and S6–S6′.
Figure 3. An axial section of the horizontal reference plane. S4, S4′, S5, S5′, S6, and S6′ were located on the horizontal reference plane and on the cortical outline of the maxilla. Maxillary skeletal widths were measured as S4–S4′, S5–S5′, and S6–S6′.

Citation: The Angle Orthodontist 85, 3; 10.2319/032614-226.1

A second set of data measured the maxillary transverse width dentally. In the frontal view, coronal sections were made through the central fossae of the maxillary first molars, second premolars (second primary molars), and first premolars (first primary molars). In order to reveal most of the dental crown structure, the thickness of each coronal section was adjusted to 5 mm. The right and left central fossae of the maxillary first molars were marked as D6 and D6′, the second premolars (or second primary molars) as D5 and D5′, and the first premolars (or first primary molars) as D4 and D4′, respectively. The maxillary dental width was measured at the level of the first molars (the distance between points D6 and D6′), the second premolars (the distance between points D5 and D5′), and first premolars (the distance between points S4 and S4′) (Figure 4).

Figure 4. Coronal section of the skull at the central fossae of the maxillary first molars. The section thickness was 5 mm to reveal most of the dental crown. D6 represents the right first molar's central fossa. D6′ represents the left first molar's central fossa. This same method was utilized for the second premolars (D5, D5′) and the first premolars (D4, D4′).Figure 4. Coronal section of the skull at the central fossae of the maxillary first molars. The section thickness was 5 mm to reveal most of the dental crown. D6 represents the right first molar's central fossa. D6′ represents the left first molar's central fossa. This same method was utilized for the second premolars (D5, D5′) and the first premolars (D4, D4′).Figure 4. Coronal section of the skull at the central fossae of the maxillary first molars. The section thickness was 5 mm to reveal most of the dental crown. D6 represents the right first molar's central fossa. D6′ represents the left first molar's central fossa. This same method was utilized for the second premolars (D5, D5′) and the first premolars (D4, D4′).
Figure 4. Coronal section of the skull at the central fossae of the maxillary first molars. The section thickness was 5 mm to reveal most of the dental crown. D6 represents the right first molar's central fossa. D6′ represents the left first molar's central fossa. This same method was utilized for the second premolars (D5, D5′) and the first premolars (D4, D4′).

Citation: The Angle Orthodontist 85, 3; 10.2319/032614-226.1

First, an axial section through the contact points of the maxillary incisors was completed to measure the mesiodistal crown widths of the maxillary central and lateral incisors. The mesiodistal widths were measured between the contact points of each incisor (Figure 5). The proportional width of the lateral incisor to the central incisor was calculated. When the maxillary lateral incisors were congenitally missing, these measurements were not performed. Also, the presence of permanent tooth agenesis, excluding the third molars, was recorded.

Figure 5. Axial section through contact points of the maxillary incisors. Measurements of mesiodistal width of upper lateral and central incisors were recorded as UR2, UR1, UL2, and UL1.Figure 5. Axial section through contact points of the maxillary incisors. Measurements of mesiodistal width of upper lateral and central incisors were recorded as UR2, UR1, UL2, and UL1.Figure 5. Axial section through contact points of the maxillary incisors. Measurements of mesiodistal width of upper lateral and central incisors were recorded as UR2, UR1, UL2, and UL1.
Figure 5. Axial section through contact points of the maxillary incisors. Measurements of mesiodistal width of upper lateral and central incisors were recorded as UR2, UR1, UL2, and UL1.

Citation: The Angle Orthodontist 85, 3; 10.2319/032614-226.1

Statistical Analysis

Descriptive statistics, including means, standard deviations, and ranges, were calculated for all measurements. The paired t-test was used to determine whether the differences in the measurements between the PDC group and the control group were significant. To test intraexaminer reproducibility, 10 images were randomly selected and remeasured 4 weeks later by the same examiner. The paired t-test was run to determine whether the initial and repeated measurements showed any significant differences. To test interexaminer reproducibility, another examiner plotted and measured the same 10 images. The paired t-test was run to determine whether the measurements by the two examiners showed any significant differences. A Student's t-test was used to determine if significant differences were present between the incisor widths in the PDC and control groups. A second Student's t-test was used to determine if significant differences were present between the ratios of the maxillary lateral incisor mesiodistal width to central incisor mesiodistal width in the PDC and control groups. Significance for all statistical tests was predetermined at P < .05.

RESULTS

The intraexaminer reproducibility test showed no statistical differences in the measurements completed at the two different time periods. The Pearson correlation coefficient was great than 0.99 in all measurements, thus indicating high reproducibility among the measurements. The magnitudes of the mean difference were less than 0.4 mm on all measurements.

The interexaminer reproducibility test showed that one (S5–S5′) out of seven measurements was statistically significant different. The mean difference in this one measurement was 0.29 mm. The Pearson correlation coefficient was greater than 0.99 in all measurements, indicating high reproducibility among the measurements.

Among the 33 patients in the PDC group, 19 patients (58%) had a unilateral PDC and 14 patients (42%) had bilateral PDCs. In addition, patients with permanent tooth agenesis, excluding the third molars, were recorded. In the PDC group, six patients (18%) had presented with permanent tooth agenesis consisting of two maxillary lateral incisors, two mandibular central incisors, three maxillary premolars, and seven mandibular premolars. In the control group, two out of 66 patients (3%) presented with permanent tooth agenesis consisting of one mandibular premolar and one maxillary premolar (Table 1).

Table 1.  General Information of the Palatally Displaced Maxillary Canines (PDC) Group and Control Groupa
Table 1. 

Table 2 shows the maxillary measurements of the skeletal and dental transverse widths of both the PDC and control groups. No significant relationship was found between PDC and the maxillary skeletal transverse dimensions at the levels of the maxillary first molars, maxillary second premolars, and maxillary first premolars. Similarly, no significant relationship was found between PDC and the maxillary transverse dimensions dentally at the level of the maxillary first molars, maxillary second premolars, and maxillary first premolars.

Table 2.  Skeletal and Dental Width Measurements of Palatally Displaced Maxillary Canines (PDC) and Control Groupsa
Table 2. 

Table 3 shows the measurements of maxillary lateral incisor width and lateral incisor to central incisor ratio of patients with unilateral PDC and patients with unilateral and bilateral PDC vs controls. On these measurements, no significant difference was found between the PDC side and the non-PDC side in the patients with unilateral PDC (N  =  19). But the lateral incisor was significantly narrower and the ratio of lateral incisor to central incisor was significantly smaller in the PDC group than in the control group (P < .05).

Table 3.  Maxillary Lateral Incisor Width and Lateral Incisor to Central Incisor Ratio of Patients with Unilateral Palatally Displaced Maxillary Canines (PDC) (N  =  19) and Patients with Unilateral and Bilateral PDC (N  =  32) vs Controlsa
Table 3. 

DISCUSSION

Only patients over 10 years of age were included in this study. At dental age 10, the root of the maxillary canine starts to migrate buccally and occlusally.19 It has been suggested that radiographic examination before the age of 10 years does not provide a reliable prognosis of the maxillary canine eruption path.20,21 All the PDCs in this study were confirmed by the CBCT image and with a canine exposure surgery.

The results in this study showed that the skeletal transverse widths of the maxilla in the PDC group were similar to those in the control group on the first molar, second premolar, and first premolar levels. Therefore, it is concluded that the maxillary transverse width, skeletally, was not an etiologic factor contributing to the presence of PDC. This finding was in agreement with those of Saiar et al.16 and Yan et al.7

This study's results also illustrated no significant difference, dentally, in the intermolar and interpremolar widths between the PDC and control groups. Similar results were reported by Langberg and Peck,14 Saiar et al.,16 and Yan et al.7 In contrast, Al-Nimri and Gharaibeh15 found that PDC occurred more frequently in the Class II division 2 malocclusions and in those with larger intermolar and interpremolar widths.

Among the 33 PDC patients in this study, not one patient presented with a posterior cross-bite. Schindel and Duffy12 found a higher occurrence rate of PDC in patients with a posterior cross-bite. Langberg and Peck14 reported that patients with PDC presented with adequate size and form of the maxillary arch because the typical orthodontic treatment plan to resolve this condition did not involve palatal expansion or permanent tooth extractions. Baccetti et al.22 reported that rapid maxillary expansion in the early mixed dentition lowered the incidence of PDC. It should be noted that in their studies the mean age of the patients was younger than 10 years, specifically, 9.5 and 8.8 years. Again, it has been suggested that before the dental age of 10 may be too early to diagnose a PDC.20,21 Furthermore, in these studies panoramic radiographs and/or posteroanterior cephalograms were used to diagnose the PDC. These radiographic techniques have a higher incidence of error in diagnosing a PDC, especially when compared to CBCT.

The results in this study showed that in the 19 unilateral PDC patients, the widths of maxillary lateral incisors were similar in the PDC and non-PDC sides. Similar findings have been reported in previous research studies.15,23–26 Overall, the mean mesiodistal width of the maxillary lateral incisors was significantly smaller in the PDC group than in the control group. Langberg and Peck27 found that PDC patients often presented with smaller maxillary central and lateral incisors. However, Al-Nimri and Gharaibeh15 did not find a size difference in the maxillary central incisors, maxillary lateral incisors, or maxillary premolars in patients with PDC.

This study also calculated the ratio of the mesiodistal width of the maxillary lateral incisor to the central incisor, which is an important factor with regard to maxillary anterior esthetics. This calculation was completed because, according to Langberg and Peck,27 the entire dentition could be smaller in patients with PDC. Thus, to only compare the widths of the maxillary lateral incisors in the PDC and control groups, and not the ratio of the lateral incisor to the central incisor, would have been a mistake.

There were more females than males (2:1) in the PDC group, which was consistent with previous reports.1,2,28 Previous research studies have suggested that the gender distribution of the PDC might be related to its genetic origin. Often PDC presents with other genetic anomalies, such as congenitally missing permanent teeth.2 This study showed that patients with permanent tooth agenesis occurred at a rate that was six times higher in the PDC group than in the control group. Thus, the data in this study suggested that genetics could be an etiologic factor for PDC. Previous reports10,14 have stated that transcription factors, such as MSX1 and PAX9, might be the genetic components managing canine transposition and PDC.

CONCLUSIONS

  • The maxillary transverse width, both skeletally and dentally, was not related to the occurrence of PDC.

  • There was a high incidence of agenesis of permanent teeth in patients with PDC.

  • In the PDC group, there was a higher incidence of smaller maxillary lateral incisors on the PDC side than was noted in the control group.

ACKNOWLEDGMENTS

We thank Drs Marianna Evans, Eric Howard, and Solomon Katz for their help in conducting this study.

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Copyright: © 2015 by The EH Angle Education and Research Foundation, Inc.
Figure 1.
Figure 1.

Reference points 1 and 2 on the frontal view of the skull, defined as the most superior aspect of the concavity of the maxillary bone as it joined the zygomatic process. Taking points 1 and 2, a horizontal reference plane was drawn parallel to the floor.

Figure 2.
Figure 2.

The right lateral view of the skull. Illustrates points S4, S5, and S6 on the horizontal reference plane. Point S6 was marked directly above the midpoint of the maxillary first molar. Point S5 was marked directly above the midpoint of the second premolar (second primary molar). Point S4 was marked directly above the midpoint of the first premolar (first primary molar).

Figure 3.
Figure 3.

An axial section of the horizontal reference plane. S4, S4′, S5, S5′, S6, and S6′ were located on the horizontal reference plane and on the cortical outline of the maxilla. Maxillary skeletal widths were measured as S4–S4′, S5–S5′, and S6–S6′.

Figure 4.
Figure 4.

Coronal section of the skull at the central fossae of the maxillary first molars. The section thickness was 5 mm to reveal most of the dental crown. D6 represents the right first molar's central fossa. D6′ represents the left first molar's central fossa. This same method was utilized for the second premolars (D5, D5′) and the first premolars (D4, D4′).

Figure 5.
Figure 5.

Axial section through contact points of the maxillary incisors. Measurements of mesiodistal width of upper lateral and central incisors were recorded as UR2, UR1, UL2, and UL1.

Contributor Notes

Corresponding author: Dr Chun-Hsi Chung, Chauncey M. F. Egel Endowed Chair and Associate Professor, Robert Schattner Center, Department of Orthodontics, University of Pennsylvania School of Dental Medicine, 240 South 40th Street, Philadelphia, PA 19104 (e-mail: chunc@dental.upenn.edu)
Received: 01 Mar 2014
Accepted: 01 Jun 2014
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