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Craniofacial morphology in women with Class I occlusion and severe maxillary anterior crowding
ORIGINAL ARTICLE
Craniofacial morphology in women with Class I occlusion and severe maxillary anterior crowding Misa Ikoma and Kazuhito Arai Tokyo, Japan
Introduction: Our objective was to investigate craniofacial morphology in women with Class I occlusion and maxillary anterior crowding (MxAC) with bilateral palatal displacement of the lateral incisors and facial displacement of the canines. Methods: Thirty-three women with normal occlusion (mean age, 20.7 6 2.3 years) were selected as the control group, and 33 women with severe MxAC (mean age, 23.3 6 3.8 years) with bilateral palatal and facial displacement of the lateral incisors and canines, respectively, were selected as the MxAC group. Mesiodistal tooth crown diameter, arch length discrepancy, facial-palatal displacement of lateral incisors and canines, and dental arch dimensions were measured. Fourteen skeletal and 10 dental cephalometric measurements were made. Medians, interquartile ranges, means, and standard deviations were calculated for each parameter, and the nonparametric Mann-Whitney U test (P \0.05) was used to compare the 2 groups. Results: Compared with the control group, the MxAC group showed a significantly wider angle (P \0.05) and shorter length (P \0.01) in the cranial base, a smaller sagittal maxillary base (P \0.01), and a hyperdivergent skeletal pattern (P \0.01 and P \0.05). Conclusions: Women with Class I occlusion and severe MxAC exhibited a significantly wider angle and shorter length in the cranial base, a smaller sagittal maxillary base, and a hyperdivergent skeletal pattern. These skeletal and dental characteristics and cranial base dysmorphology may be helpful as potential indicators for orthodontic treatment with extractions. (Am J Orthod Dentofacial Orthop 2018;153:36-45)
P
ostadolescent female patients often seek orthodontic treatment, complaining of maxillary anterior crowding (MxAC) as a main concern in smile esthetics. MxAC is typically characterized as combined facial (often described as labial, buccal, or labiobuccal) displacement of the maxillary canines and palatal displacement of the maxillary lateral incisors.1 This malocclusion is usually considered the result of a discrepancy between a relatively larger tooth size and a shorter dental arch perimeter.2-4 The etiology of displaced maxillary canines has been investigated in relation to craniofacial morphology. Larsen et al5 analyzed sagittal, vertical, and transversal dimensions of the maxillary complex in patients with From the Department of Orthodontics, School of Life Dentistry at Tokyo, Nippon Dental University, Tokyo, Japan. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Kazuhito Arai, School of Life Dentistry at Tokyo, Nippon Dental University, 1-9-20 Fujimi, Chiyoda-ku, Tokyo 102-8159, Japan; e-mail, [email protected]. Submitted, December 2016; revised, March 2017; accepted, May 2017. 0889-5406/$36.00 Ó 2017 by the American Association of Orthodontists. All rights reserved. http://dx.doi.org/10.1016/j.ajodo.2017.05.026
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ectopic maxillary canines using cephalometric and dental cast analyses. They found that in patients with ectopic canines the size of the maxillary complex was excessive transversally and deficient sagittally and vertically. However, no distinction was considered in buccal or palatal displacement of the canines. Sacerdoti and Baccetti6 evaluated vertical craniofacial morphology in patients with palatally displaced canines and found a significantly higher prevalence of hypodivergent skeletal patterns compared with control subjects. In addition, Mucedero et al4 evaluated 49 patients with unilateral or bilateral buccally displaced canines and found a higher prevalence of hyperdivergent skeletal patterns and narrower maxillary intercanine widths in them than in the control subjects. They concluded that the etiology of buccal displacement of the maxillary canines is a result of local environmental factors, as opposed to a predominant genetic control observed in palatally displaced canines.4,7 The cranial base is generally analyzed using 4 measurements: cranial base angle (often called the saddle angle), anterior cranial base length, posterior cranial base length, and total cranial base length. Although differences in cranial base morphology among
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Angle classifications have been widely studied, their influence on dental crowding has been investigated only for the mandibular dental arch.8 Melo et al9 found a relatively short anterior cranial base length in 11 patients with mandibular crowding compared with 12 participants with no mandibular crowding in the deciduous dentition. Conversely, T€ urkkahraman and Sayin10 compared groups with and without mandibular anterior crowding in the early mixed dentition and observed no significant differences in the cranial base angle, anterior cranial base length, or posterior cranial base length. To date, there are no specific measurements to evaluate the severity of MxAC. Previous studies have used arch length discrepancy,2,10,11 which was originally proposed for the mandibular arch, or Little's irregularity index9,12 for mandibular incisors, which has been uncommonly applied to the maxillary arch. Therefore, it has been rather difficult to evaluate quantitatively the severity of facial displacement of the canines and palatal displacement of the lateral incisors in patients with MxAC.13 The purpose of this study was to investigate craniofacial morphology in Angle women with Class I occlusion and severe MxAC selected by an objective evaluation of facially displaced maxillary canines and palatally displaced lateral incisors using the fourth-order polynomial equation. MATERIAL AND METHODS
The protocol of the study was approved by the ethics committee of Nippon DentalUniversity (number T2014-34). This was designed as a retrospective cross-sectional study. The sample size was estimated to have an effect size of 0.973, which was determined based on a previous study using the G-power statistical program (version 3.1; Heinrich Heine Universitat Dusseldorf Experimentelle Psycologie, Dusseldorf, Germany).14 Power analysis indicated that the required minimum sample size for each group was 18 subjects to detect this effect size with 80% power and a significance level of 5%. Approximately 100 male and female subjects with normal occlusion who were initially selected from a total population of about 4000 students at Nippon Dental University and other related schools were evaluated by 2 orthodontists.15,16 The following inclusion criteria were used in the initial selection process. 1.
2. 3.
Age 18 years or older without previous orthodontic treatment or congenital craniofacial anomalies such as cleft lip or palate. Straight profile without strain on the lips or mentalis muscle. Normally erupted permanent teeth from second molar to second molar in the maxillary and
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4.
5.
mandibular arches with an Angle Class I relationship without anterior or posterior crossbites, and no obvious asymmetric continuous dental arch. No teeth with abnormal crowns (including fused teeth, macrodont or microdont teeth, severe tooth wear, fractured teeth, minimum restorations that cover incisal edges or cusp tips that obstruct the measurements for this study), no rotated, displaced, impacted, transposed teeth or prolonged retained deciduous teeth. Healthy periodontal tissues without gingivitis or gingival recession.
Based on these inclusion criteria, 69 women were selected. The purpose of this study, the protocol, and the potential risk due to radiation exposure during cephalographic imaging were explained in writing, and 58 subjects agreed to participate and provided informed consent. Dental casts and cephalograms of these subjects were taken. The dental casts were measured using a digital caliper (NTD12-15C; Digimatic, Mitutoyo, Kawasaki, Japan), and subjects with the following criteria were further selected: overbite and overjet, 11.0-3.0 mm; curve of Spee, \1.5 mm in the mandibular dental arch; and arch length discrepancy, 6 2.0 mm in the maxillary and mandibular arches. Furthermore, lateral cephalograms were analyzed by a software program (version 11.5; Dolphin Imaging, Chatsworth, Calif), and subjects with the following were selected: ANB angle, 2.5 6 2.0 . Accordingly, 33 women (mean age, 20.7 6 2.3 years; range, 18-29 years) were selected as the control group. For the MxAC group, dental casts, facial and intraoral photographs, lateral cephalograms, and treatment records of approximately 4200 patients diagnosed at Nippon Dental University Hospital between July 1998 and December 2015 were reviewed by 2 evaluators in the Department of Orthodontics to select female patients aged 18 years or older with the following inclusion criteria. 1. 2. 3.
4.
American Journal of Orthodontics and Dentofacial Orthopedics
No previous orthodontic treatments or congenital anomalies including cleft lip or palate. Straight facial profile without signs of lip incompetence. Completely erupted permanent teeth from second molar to second molar in the maxillary and mandibular arches except for third molars (subjects with incomplete eruption of a maxillary canine were excluded). Crowding (arch length discrepancy, \4.0 mm) in the maxillary dental arch and at least 1 maxillary canine displaced in the facial direction from the
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Fig 1. A, Reference point locations and B, dental arch measurements of 3D cast images.
Fig 2. Cephalometric measurements.
5.
6.
dental arch (ie, the tip of the canine must be displaced on the facial side from the line between the center of the lateral incisor edge and the buccal cusp tip of the first premolar observed in the occlusal plane).11 No abnormal crowns (eg, fused teeth or macrodont or microdont teeth), supernumerary teeth, transposed teeth, prolonged retained deciduous teeth, severe dental wear, occlusal attrition, fractures, minimum restorations that cover incisal edges, or cusp tips that obstruct the measurements for this study (except for the third molars). Healthy periodontal tissues without gingivitis or gingival recession.
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Accordingly, dental casts and lateral cephalograms of 174 patients were evaluated. Those with Angle Class I first molar relationships without posterior crossbite were selected. Additionally, patients with tooth rotation greater than 45 were excluded based on observation of the maxillary dental cast in the occlusal plane. The dental casts of the selected patients were measured using the digital caliper, and then subjects with overbite and overjet within 11.0 to 4.0 mm were selected. Maxillary dental casts of subjects in the control group were scanned using a 3-dimensional (3D) laser scanner (Surflacer model VMS-100F; UNISN, Osaka, Japan),17 and reference points were identified at the center of incisor edges, cusp tips of canines, and buccal
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Table I. Cephalometric landmarks Point Sella
S
Nasion
N
Articulare
Ar
Point A
A
Point B
B
Anterior nasal spine Posterior nasal spine Pterygomaxillary fissure
ANS PNS Ptm
Menton Gonion U6D U6M
Me Go U6D U6M
cusps of premolars using 3D point cloud evaluation software (Inspect version 7.5; GOM, Braunschweig, Germany). Three-dimensional coordinates were then converted to a file for Microsoft Office Excel 2013 (Microsoft, Redmond, Wash). Next, the fourth-order polynomial equation was fit using the least squares method to create a curve through the reference points at each tooth excluding both lateral incisors and canines in the occlusal plane.17 The horizontal distances between the curve and the reference points at the lateral incisor and canine were calculated as facial-palatal displacement of the lateral incisor and canine, respectively (Fig 1). The distance toward the facial direction was defined as a positive value, and palatal displacement was defined as a negative value. At this point, the subjects in the control group were considered unilaterally, and palatal displacement of lateral incisors was subtracted from facial displacement of the canines for 66 sides of the 33 subjects. These data were pooled, and the means and standard deviations (0.86 6 0.72 mm) was calculated. To evaluate facial-palatal displacement of the lateral incisors and canines of the 174 patients initially selected for the MxAC group, 2 SD was added to the mean value obtained in the control group and determined as the standard value (2.31 mm) for the facial-palatal positional relationship between the lateral incisors and canines. Thus, patients having values that exceeded this standard value were selected as the most severe MxAC subjects.
Location Center of the hypophyseal fossa in the midsagittal plane (sella turcica) Most anterior point of the frontonasal suture in the midsagittal plane Intersection point of the posterior border of the mandible and the inferior border of the basilar part of the occipital bone Deepest point on the midsagittal plane between the supradentale and the anterior nasal spine Deepest midline point on the mandible between pogonion and the crest of the mandibular alveolar process Most anterior point on the bony hard palate Most posterior point on the bony hard palate The contour of the pterygomaxillary fissure formed anteriorly by the retromolar tuberosity of the maxilla and posteriorly by the anterior curve of the pterygoid process of the sphenoid bone Most inferior midline point on the mandibular symphysis Most posterior inferior point at the angle of the mandible Distal contact of the maxillary first molar Mesial contact of the maxillary first molar
Consequently, patients with an ANB angle within 2.5 6 2.0 were selected by the cephalometric analysis, and 33 women (mean age, 23.3 6 3.8 years; range, 18-31 years) were selected as the MxAC group. All subjects in both groups were selected from the same ethnic population in Japan. We set the minimum age as 18 years because we considered patients aged 18 years or older to have completed growth. Patients in the MxAC group were selected to match the age range of the control group as much as possible. Mesiodistal tooth crown diameters for the maxillary central incisors, lateral incisors, canines, first and second premolars, and first molars were measured using the digital caliper, and the bilateral measurements were pooled. The median and interquartile range (IQR) with means and standard deviations were then calculated for both groups. For the central incisor relationship, overjet and overbite were measured on dental casts using the digital caliper, and medians and IQRs with means and standard deviations were calculated for both groups. Tooth size-arch size relationship was measured using the segment arch method with the digital caliper.11 Facial-palatal displacements of the lateral incisors and canines were measured (Fig 1). Medians and IQRs with means and standard deviations for these measurements were then calculated for both groups. Dental arch dimensions were measured by the 3D cloud evaluation software. Dental arch widths were measured as the distances between reference points on
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Table II. Cephalometric analysis Measurement Cranial base 1
Unit
Cranial base angle
Anterior cranial base length Posterior cranial base length Total cranial base length
mm mm mm
SNA angle SNB angle ANB angle A-Ptm distance
mm
SN-mandibular plane angle (SN-MP)
10
SN-palatal plane angle (SN-PP)
11
Palatal plane-mandibular plane angle (PP-MP) Upper anterior facial height Lower anterior facial height Anterior facial height
mm mm mm
U1-SN angle
16
U1-palatal plane angle (U1-PP)
17 18
U1-NA distance U1-NA angle
mm
19
L1-NB distance
mm
20
L1-NB angle
21
L1-MP angle
22
Interincisal angle
23
U6D-Ptm distance
mm
24
U6M-A distance
mm
2 3 4 Skeletal sagittal 5 6 7 8 Skeletal vertical 9
12 13 14 Dental 15
bilateral canines, first and second premolars, and first molars (midpoint of mesiodistal buccal cusps of the first molars). Dental arch depths were measured as the distances between the midpoint of the center of the edges of bilateral central incisors and the midpoints of bilateral reference points at the canines, first and second premolars, and first molars (Fig 1). Medians and IQRs with means and standard deviations for these measurements were then calculated for both groups. All cephalograms were taken with the same machine (CX-150SK; Asahi-Roentgen, Kyoto, Japan), and
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Description Angle formed between the S-N plane and S-Ar line. The S-N plane was formed by points S and N. This angle is also known as the saddle angle Liner distance between points S and N Liner distance between points S and Ar Liner distance between points N and Ar Angle formed between the S-N plane and N-A line Angle formed between the S-N plane and N-B line Angle formed between the lines N-A and N-B Linear distance between point A and point Ptm Angle formed between the S-N plane and mandibular plane. The mandibular plane was formed by connecting gonion and menton Angle formed between the S-N plane and palatal plane. The palatal plane was formed by connecting ANS and PNS Angle formed between the palatal plane and mandibular plane Vertical distance between point N and point ANS Vertical distance between point ANS and point Me Vertical distance between point N and point Me Angle formed by the intersection of the long axis of the maxillary central incisor (U1) and the S-N plane Angle formed by the intersection of the long axis of U1 and the palatal plane. The palatal plane was formed by points ANS and PNS Horizontal distance from the edge of U1 to the N-A line Angle formed by the intersection of the long axis of U1 and the N-A line Horizontal distance from the edge of the mandibular central incisor (L1) to the N-B line Angle formed by the intersection of the long axis of L1 and the N-B line Angle formed by the intersection of the long axis of L1 and the mandibular plane Angle formed by the intersection of the long axes of U1 and L1 Linear distance between distal contact of the maxillary first molar (U6D) and point Ptm Linear distance between mesial contact of the maxillary first molar (U6M) and point A
magnification was automatically adjusted to 1:1 by the cephalometric analyzing software program. Based on previous studies, 14 skeletal and 10 dental cephalometric measurements were conducted using the analyzing software program, and medians and IQRs with means and standard deviations were calculated for both groups (Fig 2; Tables I and II).18-20 All reference points were identified by 1 evaluator (M.I.). Articulare was used as the reference at the most posterior point of the cranial base, which is considered to be a more biometrically reliable point than basion.8,21,22
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(total, 10 casts) were also randomly selected. All measurement landmarks were identified twice with a minimum of a 2-week interval by 1 evaluator (M.I.) and once by another evaluator with a careful calibration session, since we do not use this system clinically. The maximum intraexaminer and interexaminer error values for the 3D dental cast measurements were 0.10 and 0.12 mm, respectively. Statistical analysis
All statistical analyses were performed using SPSS software for Windows (version 24.0; IBM, Armonk, NY). Because some parameters did not show normal distributions according to the Kolmogorov-Smirnov test, medians and IQRs were calculated for each parameter, and the nonparametric Mann-Whitney U test was used to compare the 2 groups. Parameters that did not show a normal distribution were displacement of lateral incisor for the control group, overbite, and sum of the displacements for 1 side for the MxAC group, and lower anterior facial height, anterior facial height, and L1-NB distance. For all statistical analyses, P values less than 0.05 were considered significant.
Fig 3. Comparison of the results of cephalometric measurements in the MxAC and control groups. Medians of reference point locations in the x-y coordinates for each group were superimposed at sella and the S-N line.
RESULTS
In addition, all x-y coordinates for each patient were exported as text data and imported into the Microsoft Office Excel program. The coordinates were superimposed at sella as the origin and on the sella-nasion line at 7 above the horizontal line for each group.23 Medians for each reference point were calculated for each group, and a graph was drawn (Fig 3). To calculate and examine intraexaminer errors with Dahlberg's formula,24 10 subjects were randomly selected from both groups (total, 20 subjects). The same cephalometric measurements were taken twice with a minimum of a 2-week interval by 1 evaluator (M.I.) and once by another evaluator (a member of the orthodontic department) using the same general clinical procedure without a calibration session. The maximum intraexaminer and interexaminer error values for the cephalometric analysis were 0.55 and 0.63 mm for linear measurements and 0.61 and 0.79 for angular measurements, respectively. For mesiodistal tooth crown diameter measurements on dental casts, the same 20 subjects were evaluated. The maximum intraexaminer and interexaminer error values were 0.17 and 0.36 mm, respectively. In addition, to analyze intraexaminer and interexaminer errors for dental cast measurements obtained by the 3D laser scanner, 5 dental casts from both groups
Mesiodistal diameters of tooth crowns of the MxAC group were significantly larger than those of the control group for all teeth except for the first molar (P \0.01). Overbite was significantly smaller in the MxAC group compared with the control group (P \0.01) (Table III). Arch length discrepancy and facial-palatal displacement of the lateral incisors and canines from the dental arch were significantly smaller and greater, respectively, in the MxAC group compared with the control group (P \0.01). Dental arch widths at the first and second premolars (P \0.01) and the first molars (P \0.01) and dental arch depths at the canine (P \0.01), the first premolar (P \0.01), and the second premolar (P \0.05) in the MxAC group were significantly smaller than in the control group. The cranial base angle was significantly greater in the MxAC group compared with the control group (P \0.05). Median cranial base length measurements for anterior cranial base length, posterior cranial base length, and total cranial base length (P \0.01) were 4.10 mm (5.89%), 3.95 mm (10.12%), and 5.16 mm (5.38%) shorter in the MxAC group compared with the control group, respectively (Fig 3; Table IV). SNA and SNB angles and the A-Ptm distance were significantly smaller in the MxAC group compared with the control group (P \0.01).
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Table III. Comparison of the dental cast analysis in the maxillary arches between the groups Control group (n 5 33) Measurement (mm) Mesiodistal tooth dimensionz Central incisor Lateral incisor Canine First premolar Second premolar First molar Central incisor relationship Overjet Overbite Tooth size-arch size relationship Arch length discrepancy (1) Displacement of lateral incisorz (2) Displacement of caninez Sum of the displacements for 1 sidez§ Dental arch width (3) Canine (4) First premolar (5) Second premolar (6) First molar Dental arch depth (7) Canine (8) First premolar (9) Second premolar (10) First molar
Statistical analysis
MxAC group (n 5 33)
Median
IQR
Mean
SD
Median
IQR
Mean
SD
P value
8.42 7.05 7.80 7.30 6.89 10.47
0.56 0.51 0.28 0.52 0.45 0.62
8.47 7.13 7.80 7.30 6.84 10.41
0.41 0.43 0.19 0.39 0.34 0.50
8.63 7.48 8.14 7.67 7.08 10.60
0.70 0.94 0.70 0.58 0.47 0.91
8.73 7.59 8.17 7.74 7.09 10.53
0.50 0.56 0.40 0.40 0.33 0.55
0.000 0.000 0.000 0.000 0.000 0.110
2.52 2.05
1.18 0.78
2.53 2.16
0.82 0.57
2.76 1.69
0.95 1.27
1.01 0.98
0.387 0.005
0.01 0.30
1.00 1.71
0.05 0.19k
0.77 1.55
9.71 2.72
7.51 2.69
3.94 1.94
0.000 0.000
0.44 0.76
1.13 0.79
0.48 0.86
0.95 0.72
3.03 5.61
2.45 2.74
1.64 1.72
0.000 0.000
35.37 43.60 49.80 55.20
2.54 2.21 2.89 3.17
35.62 43.67 49.86 55.38
1.43 1.91 2.43 2.44
35.52 40.55 45.34 52.66
4.04 4.06 5.38 4.08
35.61 40.18 45.61 52.42
2.33 2.78 3.55 2.83
0.954 0.000 0.000 0.000
8.33 15.44 22.23 30.66
1.23 1.98 2.04 2.67
8.34 15.61 22.11 30.52
1.03 1.40 1.59 2.03
5.67 14.11 20.80 30.00
3.82 4.42 3.82 4.33
6.04 14.01 20.87 29.79
2.12 2.44 2.57 2.76
0.000 0.006 0.038 0.267
2.65 1.72k 10.00 2.86 2.99 5.76k
y y y y y
NS NS y y y y y
NS y y y y y
* NS
IQR, Interquartile range; MxAC, maxillary anterior crowding; NS, not significant. (1) and (2), A positive number indicates displacement toward the facial direction. (1)-(10), Correspond to the numbers shown in Figure 1. *P\0.05; yP\0.01; zThe right and left side data were pooled; §The sum of the displacement was calculated as (2) – (1) for each side (ie, subtraction of lateral incisor displacement from canine displacement); kNonnormal distribution.
Significantly greater SN-mandibular plane (MP), SNpalatal plane (PP) (P \0.01), and PP-MP angles (P \0.01) were observed in the MxAC group compared with the control group, indicating a hyperdivergent skeletal pattern of this malocclusion. Regarding dental components, the MxAC group showed a significantly greater U1-PP (P \0.01) and U1-NA (P \0.05) angles, smaller interincisal angle (P \0.01), and smaller U6D-Ptm distance (P \0.05) than did the control group. DISCUSSION
In this study, the maxillary dental arch in the MxAC group exhibited narrower interpremolar and interfirst molar widths and shorter dental arch depths at the canines and premolars when compared with the control group. However, no significant difference in maxillary intercanine width was observed between the 2 groups. Therefore, the direction of canine
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displacement can be evaluated in the anterior direction, rather than the transverse, because of the short dental arch depths observed at the canines and first premolars. In the Japanese language, “yaeba” refers to the condition of multiple anterior overlapping teeth in the frontal smile. In contrast to our subjects, who were selected from the same Japanese population, Italian patients with similar malocclusion status and buccally displaced maxillary canines demonstrated significantly wider intercanine widths and no intermolar width differences.4 Therefore, heritability of cranial base morphology may explain differences in the direction of maxillary canine displacement between ethnicities.14,25,26 However, further studies in other populations are necessary to determine the effect of ethnic variation on cranial base morphology and position of ectopic maxillary canines. In orthodontics, the cranial base angle has often been investigated to identify differences among Angle
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Table IV. Comparison of the results of cephalometric and dental cast analyses between the groups Control group (n 5 33) Measurement Cranial base 1 Cranial base angle 2 Anterior cranial base length 3 Posterior cranial base length 4 Total cranial base length Skeletal sagittal 5 SNA angle 6 SNB angle 7 ANB angle 8 A-Ptm distance Skeletal vertical 9 SN-mandibular plane angle (SN-MP) 10 SN-palatal plane angle (SN-PP) 11 Palatal plane-mandibular plane angle (PP-MP) 12 Upper anterior facial height 13 Lower anterior facial height 14 Anterior facial height Dental 15 U1-SN angle 16 U1-palatal plane angle (U1-PP) 17 U1-NA distance 18 U1-NA angle 19 L1-NB distance 20 L1-NB angle 21 L1-MP angle 22 Interincisal angle 23 U6D-Ptm distance 24 U6M-A distance
Statistical analysis
MxAC group (n 5 33)
Unit
Median
IQR
Mean
SD
Median
IQR
Mean
SD
P value
122.50 69.60 39.00 96.00
5.85 3.65 3.85 6.99
122.09 69.73 38.70 96.39
3.71 3.01 3.02 4.19
124.90 65.50 35.05 90.84
7.60 4.20 4.40 8.21
124.90 66.11 34.97 90.39
5.30 3.43 3.42 5.35
0.028 0.000 0.000 0.000
mm
82.90 79.60 2.30 48.40
4.50 3.45 3.05 2.45
82.43 80.24 2.18 48.89
2.94 2.74 1.93 2.21
79.05 77.70 2.75 45.35
4.27 5.95 3.63 4.38
79.77 76.70 3.09 45.58
3.80 3.43 2.47 3.01
0.001 0.000 0.228 0.000
35.00
7.15
34.64
5.00
41.40
8.50
42.02
6.05
0.000
7.00
4.95
6.21
3.87
10.80
4.20
10.98
2.51
0.000
26.30
5.75
26.31
4.27
30.00
6.80
31.07
4.61
0.000
mm mm mm
57.90 73.40 128.10
3.70 3.95 5.95
58.06 74.08z 129.24z
2.87 4.10 5.30
56.45 72.55 125.05
5.30 5.72 7.40
56.20 72.11 124.83
3.36 4.16 5.04
0.024 0.116 0.004
* NS
106.10 115.60
6.68 5.15
106.47 114.50
4.75 4.12
108.25 119.50
7.18 7.43
107.74 118.62
4.69 4.92
0.248 0.001
NS
6.90 24.70 8.00 30.10 93.70 123.80 15.01 22.62
3.50 6.10 3.05 7.25 4.25 7.20 2.90 2.93
7.14 24.39 7.33z 28.83 93.97 124.62 15.35 22.87
2.16 4.18 2.27 4.85 5.13 5.46 2.38 2.54
7.40 26.90 8.30 31.40 92.45 116.65 13.38 22.30
4.78 8.08 4.35 12.18 10.53 15.85 4.27 3.55
7.45 27.88 8.44 31.17 92.65 117.86 13.90 21.83
3.04 5.11 3.09 6.43 6.97 9.39 3.14 3.27
0.551 0.014 0.156 0.139 0.308 0.002 0.021 0.105
NS * NS NS NS
mm mm mm
mm
mm
mm mm
*
y y y y y
NS y y y y
y
y
y
* NS
IQR, Interquartile range; MxAC, maxillary anterior crowding; NS, not significant. *P \0.05; yP \0.01; zNonnormal distribution.
classifications.8,27-29 Previous studies have suggested that larger and smaller cranial base angles determine the posterior and anterior positions of the condyle in the cranial base, resulting in skeletal Class II and Class III relationships, respectively.25,30,31 However, only a few studies have used the cranial base angle to compare differences between patients with and without crowding in the mandibular arch, with no significant differences in the cranial base angle observed.9,10 We found a significantly larger cranial base angle in the MxAC group with Class I dental and skeletal patterns. This finding supports the results of a previous study in Class I patients.29 These findings may be attributed to a topographic correlation between the cephalometric measurements and the reference points.32-34 The cranial base, maxilla, dental arch, and teeth are adjacent anatomic components, and thus may be associated with one another during the growth
period from the embryonic phase. Therefore, the cranial base angle may influence the establishment of MxAC. However, the precise biologic mechanisms are still not well understood and require further longitudinal studies of growing subjects.29 Larsen et al5 observed that children with either facially or palatally impacted maxillary canines that required fenestration surgery had a significantly shorter anterior cranial base length (approximately 1 mm), which was not necessarily the result of anterior crowding when compared with a reference group. Although we studied adults, we observed a larger difference for anterior cranial base length between groups than the previous study in growing patients.5 In addition, we found significantly smaller posterior cranial base length and total cranial base length in the MxAC group than in the control group. These findings suggest the possibility of early prediction of MxAC even before establishment of
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the permanent dentition according to a smaller cranial base on cephalometric analysis.25 The MxAC group demonstrated a significantly smaller anterior cranial base length and anteroposterior dimension of the maxilla (A-Ptm distance) compared with the control group. These findings support the conclusion of a recent review article, which suggested that anterior cranial base length has a stronger influence on facial growth than posterior cranial base length.35 Although the correlation between cranial base size and cleft palate remains unclear,36 it is plausible that a history of cleft palate repair greatly affects maxillary development, but this altered maxillary development has no significant influence on morphology or size of the cranial base.37 In addition, use of rapid maxillary expansion appliances in 8- to 11-year-olds resulted in limited expansion effects in spheno-occipital synchondrosis.38 Therefore, orthodontic intervention with maxillary development to resolve arch length discrepancy in patients with severe MxAC may be limited, even in growing patients. In Italy, Mucedero et al4 found a significantly higher possibility of hyperdivergent skeletal patterns using the SN-GoGn angle in cephalometric analysis in patients with buccally displaced maxillary canines. We observed similar significant hyperdivergent skeletal patterns with greater SN-MP, SN-PP, and PP-MP angles in the MxAC group than in the control group. A shorter posterior cranial base length and obtuse cranial base angle cause the glenoid fossa and condyle to have relatively higher positions, which may increase the SN-MP and PP-MP angles (Fig 3).39 In previous studies, subjects with a long face usually have narrower transverse dimensions, and those with a short face have wider transverse dimensions.25,40,41 In contrast, the MxAC group in this study showed significantly smaller maxillae as measured by upper anterior facial height, anterior facial height, and A-Ptm distance, despite exhibiting a hyperdivergent skeletal pattern. Therefore, smaller vertical and sagittal dimensions of the maxilla could be 1 characteristic of MxAC and may cause smaller dental arch dimensions. Traditionally, a hyperdivergent skeletal pattern is often attributed to functional problems including oral breathing and lower tongue posture, which is also considered to correlate with a narrower maxillary dental arch.11 Forster et al42 observed that patients with hyperdivergent patterns tend to exhibit a narrower dental arch width and suggested that lower masseter muscle function causes undergrowth of the mandible in a transverse direction. However, family and twin studies showed a strong genetic influence in the development of the cranial base.43,44 The influence of cranial base
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morphology on maxillary and mandibular growth is often observed in heritable developmental anomalies such as cleft lip and palate, Down syndrome, Turner syndrome, and craniosynostosis.36,45 Therefore, in addition to environmental factors, genetic factors may cause cranial base dysmorphology and potentially impact maxillary undergrowth, consequently establishing MxAC indirectly. Few treatment options for MxAC are currently available. Clinically, maxillary arch expansion in the mixed dentition and premolar extraction in the permanent dentition are commonly performed. As Enlow and Hans25 hypothesized and Klocke et al46 demonstrated, morphology and size of the cranial base are determined in the early stage of development (as early as 5 years of age). Clinically, a greater cranial base angle, shorter anterior cranial base length and posterior cranial base length, and larger mesiodistal width of the maxillary central incisors detected in the early mixed dentition may predict MxAC. In addition, the effect of maxillary expansion may be limited, and serial extraction may be recommended for such Class I MxAC patients. Greater arch length discrepancy and displacement of the maxillary lateral incisors and canines, smaller dental arch dimensions, and slightly labially tipped maxillary central incisors were observed in the MxAC group compared with the control group. Although these results were expected based on the selection criteria of subjects in this study, these findings suggest the necessity of premolar extractions with consideration of maximum anchorage for patients with MxAC. Although the selection criterion for overbite in the MxAC group was 1 mm larger, overbite values with a significantly smaller median, which reflects individual variation, were observed in the MxAC group compared with the control group. Moreover, overbite values for the MxAC group did not show a normal distribution (Table III). These findings suggest that subjects in the MxAC group had a skewed overbite distribution, and the peak in smaller overbite values might be caused by the hyperdivergent skeletal pattern observed when compared with the control group. CONCLUSIONS
Women with Class I occlusion and severe MxAC exhibited significantly wider angles and shorter lengths in the cranial base, smaller sagittal maxillary bases, and hyperdivergent skeletal patterns. REFERENCES 1. Peck S, Peck L. Classification of maxillary tooth transpositions. Am J Orthod Dentofacial Orthop 1995;107:505-17.
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2. Howe RP, McNamara JA, O'Connor KA. An examination of dental crowding and its relationship to tooth size and arch dimension. Am J Orthod 1983;83:363-73. 3. Chaushu S, Sharabi S, Becker A. Tooth size in dentitions with buccal canine ectopia. Eur J Orthod 2003;25:485-91. 4. Mucedero M, Rosaria M, Cozza P, Baccetti T. Prevalence rate and dentoskeletal features associated with buccally displaced maxillary canines. Eur J Orthod 2013;35:305-9. 5. Larsen HJ, Sørensen HB, Artmann L, Christensen IJ, Kjær I. Sagittal, vertical and transversal dimensions of the maxillary complex in patients with ectopic maxillary canines. Orthod Craniofac Res 2010;13:34-9. 6. Sacerdoti R, Baccetti T. Dentoskeletal features associated with unilateral or bilateral palatal displacement of maxillary canines. Angle Orthod 2004;74:725-32. 7. Peck S, Peck L, Kataja M. The palatally displaced canine as a dental anomaly of genetic origin. Angle Orthod 1994;64:250-6. 8. Gong A, Li J, Wang Z, Li Y, Hu F, Li Q, et al. Cranial base characteristics in anteroposterior malocclusions: a meta-analysis. Angle Orthod 2016;86:668-80. 9. Melo L, Ono Y, Takagi Y. Indicators of mandibular dental crowding in the mixed dentition. Pediatr Dent 2001;23:118-22. 10. T€ urkkahraman H, Sayin M. Relationship between mandibular anterior crowding and lateral dentofacial morphology in the early mixed dentition. Angle Orthod 2004;74:759-64. 11. Proffit WR, Fields HW, Sarver DM. Contemporary orthodontics. 3rd ed. St Louis: Elsevier Mosby; 2000. 12. Little RM. The irregularity index: a quantitative score of mandibular anterior alignment. Am J Orthod 1975;68:554-63. 13. Chaushu S, Bongart M, Aksoy A, Ben-Bassat Y, Becker A. Buccal ectopia of maxillary canines with no crowding. Am J Orthod Dentofacial Orthop 2009;136:218-23. 14. Ishii N, Deguchi T, Hunt NP. Morphological differences in the craniofacial structure between Japanese and Caucasian girls with Class II division 1 malocclusions. Eur J Orthod 2002;24:61-7. 15. Angle EH. Treatment of malocclusion of the teeth: Angle's system. Philadelphia: White Dental Manufacturing Company; 1907. 16. Andrews LF. The six keys to normal occlusion. Am J Orthod 1972; 62:296-309. 17. Arai K, Will LA. Subjective classification and objective analysis of the mandibular dental-arch form of orthodontic patients. Am J Orthod Dentofacial Orthop 2011;139:e315-21. 18. Steiner CC. The use of cephalometrics as an aid to planning and assessing orthodontic treatment: report of a case. Am J Orthod 1960;46:721-35. 19. Jarabak JR, Fizzell JA. Technique and treatment with light-wire edgewise appliances. Volumes 1 and 2. St Louis: Mosby; 1972. 20. Bj€ ork A, Solow B. Measurement on radiographs. J Dent Res 1962; 41:672-83. 21. Bj€ ork A. Cranial base development: a follow-up x-ray study of the individual variation in growth occurring between the ages of 12 and 20 years and its relation to brain case and face development. Am J Orthod 1955;41:198-225. 22. Chang ZC, Hu FC, Lai E, Yao CC, Chen MH, Chen YJ. Landmark identification errors on cone-beam computed tomographyderived cephalograms and conventional digital cephalograms. Am J Orthod Dentofacial Orthop 2011;140:e289-97. 23. Legan HL, Burstone CJ. Soft tissue cephalometric analysis for orthognathic surgery. J Oral Surg 1980;38:744-51. 24. Dahlberg G. Statistical methods for medical and biological students. London, United Kingdom: George Allen and Unwin; 1940. 25. Enlow DH, Hans MG. Essentials of facial growth. Philadelphia: Saunders; 1996.
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26. Chang HP, Liu PH, Tseng YC, Yang YH, Pan CY, Chou ST. Morphometric analysis of the cranial base in Asians. Odontology 2014; 102:81-8. 27. Hopkin GB, Houston WJ, James GA. The cranial base as an aetiological factor in malocclusion. Angle Orthod 1968;38:250-5. 28. Kasai K, Moro T, Kanazawa E, Iwasawa T. Relationship between cranial base and maxillofacial morphology. Eur J Orthod 1995; 17:403-10. 29. Dhopatkar A, Bhatia S, Rock P. An investigation into the relationship between the cranial base angle and malocclusion. Angle Orthod 2002;72:456-63. 30. Sayin M, T€ urkkahraman H. Cephalometric evaluation of nongrowing females with skeletal and dental Class II, division 1 malocclusion. Angle Orthod 2005;75:656-60. 31. Alves PV, Mazuchelli J, Patel PK, Bolognese AM. Cranial base angulation in Brazilian patients seeking orthodontic treatment. J Craniofac Surg 2008;19:334-8. 32. Solow B. The pattern of craniofacial associations. Acta Odontol Scand 1966;24(Suppl 46):1-174. 33. J€arvinen S. Saddle angle and maxillary prognathism: a radiological analysis of the association between the NSAr and SNA angles. Br J Orthod 1984;11:209-13. 34. Halazonetis DJ. Permutation method for evaluating topographic craniofacial correlations. Am J Orthod Dentofacial Orthop 2011; 139:e211-7. 35. Nie X. Cranial base in craniofacial development: developmental features, influence on facial growth, anomaly, and molecular basis. Acta Odontol Scand 2005;63:127-35. 36. Mooney MP, Siegel MI. Understanding craniofacial anomalies: the etiopathogenesis of craniosynostoses and facial clefting. New York: Wiley-Liss; 2002. 37. Naqvi ZA, Shivalinga BM, Ravi S, Munawwar SS. Effect of cleft lip palate repair on craniofacial growth. J Orthod Sci 2015;4:59-64. 38. Leonardi R, Cutrera A, Barbato E. Rapid maxillary expansion affects the spheno-occipital synchondrosis in youngsters: a study with low-dose computed tomography. Angle Orthod 2010;80: 106-10. 39. Andria LM, Leite LP, Prevatte TM, King LB. Correlation of the cranial base angle and its components with other dental/skeletal variables and treatment time. Angle Orthod 2004;74:361-6. 40. Ricketts RM. Orthodontic diagnosis and planning: their roles in preventive and rehabilitative dentistry, 2. Denver, Colo: Rocky Mountain Orthodontics; 1982. 41. Wagner DM, Chung CH. Transverse growth of the maxilla and mandible in untreated girls with low, average, and high MP-SN angles: a longitudinal study. Am J Orthod Dentofacial Orthop 2005;128:716-23. 42. Forster CM, Sunga E, Chung CH. Relationship between dental arch width and vertical facial morphology in untreated adults. Eur J Orthod 2008;30:288-94. 43. Johannsdottir B, Thorarinsson F, Thordarson A, Magnusson TE. Heritability of craniofacial characteristics between parents and offspring estimated from lateral cephalograms. Am J Orthod Dentofacial Orthop 2005;127:200-7. 44. Sherwood RJ, Duren DL, Demerath EW, Czerwinski SA, Siervogel RM, Towne B. Quantitative genetics of modern human cranial variation. J Hum Evol 2008;54:909-14. 45. Carinci F, Avantaggiato A, Curioni C. Crouzon syndrome: cephalometric analysis and evaluation of pathogenesis. Cleft Palate J 1994;31:201-9. 46. Klocke A, Nanda RS, Kahl-Nieke B. Role of cranial base flexure in developing sagittal jaw discrepancies. Am J Orthod Dentofacial Orthop 2002;122:386-91.
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Craniofacial morphology in women with Class I occlusion and severe maxillary anterior crowding Misa Ikoma and Kazuhito Arai Tokyo, Japan
Introduction: Our objective was to investigate craniofacial morphology in women with Class I occlusion and maxillary anterior crowding (MxAC) with bilateral palatal displacement of the lateral incisors and facial displacement of the canines. Methods: Thirty-three women with normal occlusion (mean age, 20.7 6 2.3 years) were selected as the control group, and 33 women with severe MxAC (mean age, 23.3 6 3.8 years) with bilateral palatal and facial displacement of the lateral incisors and canines, respectively, were selected as the MxAC group. Mesiodistal tooth crown diameter, arch length discrepancy, facial-palatal displacement of lateral incisors and canines, and dental arch dimensions were measured. Fourteen skeletal and 10 dental cephalometric measurements were made. Medians, interquartile ranges, means, and standard deviations were calculated for each parameter, and the nonparametric Mann-Whitney U test (P \0.05) was used to compare the 2 groups. Results: Compared with the control group, the MxAC group showed a significantly wider angle (P \0.05) and shorter length (P \0.01) in the cranial base, a smaller sagittal maxillary base (P \0.01), and a hyperdivergent skeletal pattern (P \0.01 and P \0.05). Conclusions: Women with Class I occlusion and severe MxAC exhibited a significantly wider angle and shorter length in the cranial base, a smaller sagittal maxillary base, and a hyperdivergent skeletal pattern. These skeletal and dental characteristics and cranial base dysmorphology may be helpful as potential indicators for orthodontic treatment with extractions. (Am J Orthod Dentofacial Orthop 2018;153:36-45)
P
ostadolescent female patients often seek orthodontic treatment, complaining of maxillary anterior crowding (MxAC) as a main concern in smile esthetics. MxAC is typically characterized as combined facial (often described as labial, buccal, or labiobuccal) displacement of the maxillary canines and palatal displacement of the maxillary lateral incisors.1 This malocclusion is usually considered the result of a discrepancy between a relatively larger tooth size and a shorter dental arch perimeter.2-4 The etiology of displaced maxillary canines has been investigated in relation to craniofacial morphology. Larsen et al5 analyzed sagittal, vertical, and transversal dimensions of the maxillary complex in patients with From the Department of Orthodontics, School of Life Dentistry at Tokyo, Nippon Dental University, Tokyo, Japan. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Kazuhito Arai, School of Life Dentistry at Tokyo, Nippon Dental University, 1-9-20 Fujimi, Chiyoda-ku, Tokyo 102-8159, Japan; e-mail, [email protected]. Submitted, December 2016; revised, March 2017; accepted, May 2017. 0889-5406/$36.00 Ó 2017 by the American Association of Orthodontists. All rights reserved. http://dx.doi.org/10.1016/j.ajodo.2017.05.026
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ectopic maxillary canines using cephalometric and dental cast analyses. They found that in patients with ectopic canines the size of the maxillary complex was excessive transversally and deficient sagittally and vertically. However, no distinction was considered in buccal or palatal displacement of the canines. Sacerdoti and Baccetti6 evaluated vertical craniofacial morphology in patients with palatally displaced canines and found a significantly higher prevalence of hypodivergent skeletal patterns compared with control subjects. In addition, Mucedero et al4 evaluated 49 patients with unilateral or bilateral buccally displaced canines and found a higher prevalence of hyperdivergent skeletal patterns and narrower maxillary intercanine widths in them than in the control subjects. They concluded that the etiology of buccal displacement of the maxillary canines is a result of local environmental factors, as opposed to a predominant genetic control observed in palatally displaced canines.4,7 The cranial base is generally analyzed using 4 measurements: cranial base angle (often called the saddle angle), anterior cranial base length, posterior cranial base length, and total cranial base length. Although differences in cranial base morphology among
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Angle classifications have been widely studied, their influence on dental crowding has been investigated only for the mandibular dental arch.8 Melo et al9 found a relatively short anterior cranial base length in 11 patients with mandibular crowding compared with 12 participants with no mandibular crowding in the deciduous dentition. Conversely, T€ urkkahraman and Sayin10 compared groups with and without mandibular anterior crowding in the early mixed dentition and observed no significant differences in the cranial base angle, anterior cranial base length, or posterior cranial base length. To date, there are no specific measurements to evaluate the severity of MxAC. Previous studies have used arch length discrepancy,2,10,11 which was originally proposed for the mandibular arch, or Little's irregularity index9,12 for mandibular incisors, which has been uncommonly applied to the maxillary arch. Therefore, it has been rather difficult to evaluate quantitatively the severity of facial displacement of the canines and palatal displacement of the lateral incisors in patients with MxAC.13 The purpose of this study was to investigate craniofacial morphology in Angle women with Class I occlusion and severe MxAC selected by an objective evaluation of facially displaced maxillary canines and palatally displaced lateral incisors using the fourth-order polynomial equation. MATERIAL AND METHODS
The protocol of the study was approved by the ethics committee of Nippon DentalUniversity (number T2014-34). This was designed as a retrospective cross-sectional study. The sample size was estimated to have an effect size of 0.973, which was determined based on a previous study using the G-power statistical program (version 3.1; Heinrich Heine Universitat Dusseldorf Experimentelle Psycologie, Dusseldorf, Germany).14 Power analysis indicated that the required minimum sample size for each group was 18 subjects to detect this effect size with 80% power and a significance level of 5%. Approximately 100 male and female subjects with normal occlusion who were initially selected from a total population of about 4000 students at Nippon Dental University and other related schools were evaluated by 2 orthodontists.15,16 The following inclusion criteria were used in the initial selection process. 1.
2. 3.
Age 18 years or older without previous orthodontic treatment or congenital craniofacial anomalies such as cleft lip or palate. Straight profile without strain on the lips or mentalis muscle. Normally erupted permanent teeth from second molar to second molar in the maxillary and
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4.
5.
mandibular arches with an Angle Class I relationship without anterior or posterior crossbites, and no obvious asymmetric continuous dental arch. No teeth with abnormal crowns (including fused teeth, macrodont or microdont teeth, severe tooth wear, fractured teeth, minimum restorations that cover incisal edges or cusp tips that obstruct the measurements for this study), no rotated, displaced, impacted, transposed teeth or prolonged retained deciduous teeth. Healthy periodontal tissues without gingivitis or gingival recession.
Based on these inclusion criteria, 69 women were selected. The purpose of this study, the protocol, and the potential risk due to radiation exposure during cephalographic imaging were explained in writing, and 58 subjects agreed to participate and provided informed consent. Dental casts and cephalograms of these subjects were taken. The dental casts were measured using a digital caliper (NTD12-15C; Digimatic, Mitutoyo, Kawasaki, Japan), and subjects with the following criteria were further selected: overbite and overjet, 11.0-3.0 mm; curve of Spee, \1.5 mm in the mandibular dental arch; and arch length discrepancy, 6 2.0 mm in the maxillary and mandibular arches. Furthermore, lateral cephalograms were analyzed by a software program (version 11.5; Dolphin Imaging, Chatsworth, Calif), and subjects with the following were selected: ANB angle, 2.5 6 2.0 . Accordingly, 33 women (mean age, 20.7 6 2.3 years; range, 18-29 years) were selected as the control group. For the MxAC group, dental casts, facial and intraoral photographs, lateral cephalograms, and treatment records of approximately 4200 patients diagnosed at Nippon Dental University Hospital between July 1998 and December 2015 were reviewed by 2 evaluators in the Department of Orthodontics to select female patients aged 18 years or older with the following inclusion criteria. 1. 2. 3.
4.
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No previous orthodontic treatments or congenital anomalies including cleft lip or palate. Straight facial profile without signs of lip incompetence. Completely erupted permanent teeth from second molar to second molar in the maxillary and mandibular arches except for third molars (subjects with incomplete eruption of a maxillary canine were excluded). Crowding (arch length discrepancy, \4.0 mm) in the maxillary dental arch and at least 1 maxillary canine displaced in the facial direction from the
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Fig 1. A, Reference point locations and B, dental arch measurements of 3D cast images.
Fig 2. Cephalometric measurements.
5.
6.
dental arch (ie, the tip of the canine must be displaced on the facial side from the line between the center of the lateral incisor edge and the buccal cusp tip of the first premolar observed in the occlusal plane).11 No abnormal crowns (eg, fused teeth or macrodont or microdont teeth), supernumerary teeth, transposed teeth, prolonged retained deciduous teeth, severe dental wear, occlusal attrition, fractures, minimum restorations that cover incisal edges, or cusp tips that obstruct the measurements for this study (except for the third molars). Healthy periodontal tissues without gingivitis or gingival recession.
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Accordingly, dental casts and lateral cephalograms of 174 patients were evaluated. Those with Angle Class I first molar relationships without posterior crossbite were selected. Additionally, patients with tooth rotation greater than 45 were excluded based on observation of the maxillary dental cast in the occlusal plane. The dental casts of the selected patients were measured using the digital caliper, and then subjects with overbite and overjet within 11.0 to 4.0 mm were selected. Maxillary dental casts of subjects in the control group were scanned using a 3-dimensional (3D) laser scanner (Surflacer model VMS-100F; UNISN, Osaka, Japan),17 and reference points were identified at the center of incisor edges, cusp tips of canines, and buccal
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Table I. Cephalometric landmarks Point Sella
S
Nasion
N
Articulare
Ar
Point A
A
Point B
B
Anterior nasal spine Posterior nasal spine Pterygomaxillary fissure
ANS PNS Ptm
Menton Gonion U6D U6M
Me Go U6D U6M
cusps of premolars using 3D point cloud evaluation software (Inspect version 7.5; GOM, Braunschweig, Germany). Three-dimensional coordinates were then converted to a file for Microsoft Office Excel 2013 (Microsoft, Redmond, Wash). Next, the fourth-order polynomial equation was fit using the least squares method to create a curve through the reference points at each tooth excluding both lateral incisors and canines in the occlusal plane.17 The horizontal distances between the curve and the reference points at the lateral incisor and canine were calculated as facial-palatal displacement of the lateral incisor and canine, respectively (Fig 1). The distance toward the facial direction was defined as a positive value, and palatal displacement was defined as a negative value. At this point, the subjects in the control group were considered unilaterally, and palatal displacement of lateral incisors was subtracted from facial displacement of the canines for 66 sides of the 33 subjects. These data were pooled, and the means and standard deviations (0.86 6 0.72 mm) was calculated. To evaluate facial-palatal displacement of the lateral incisors and canines of the 174 patients initially selected for the MxAC group, 2 SD was added to the mean value obtained in the control group and determined as the standard value (2.31 mm) for the facial-palatal positional relationship between the lateral incisors and canines. Thus, patients having values that exceeded this standard value were selected as the most severe MxAC subjects.
Location Center of the hypophyseal fossa in the midsagittal plane (sella turcica) Most anterior point of the frontonasal suture in the midsagittal plane Intersection point of the posterior border of the mandible and the inferior border of the basilar part of the occipital bone Deepest point on the midsagittal plane between the supradentale and the anterior nasal spine Deepest midline point on the mandible between pogonion and the crest of the mandibular alveolar process Most anterior point on the bony hard palate Most posterior point on the bony hard palate The contour of the pterygomaxillary fissure formed anteriorly by the retromolar tuberosity of the maxilla and posteriorly by the anterior curve of the pterygoid process of the sphenoid bone Most inferior midline point on the mandibular symphysis Most posterior inferior point at the angle of the mandible Distal contact of the maxillary first molar Mesial contact of the maxillary first molar
Consequently, patients with an ANB angle within 2.5 6 2.0 were selected by the cephalometric analysis, and 33 women (mean age, 23.3 6 3.8 years; range, 18-31 years) were selected as the MxAC group. All subjects in both groups were selected from the same ethnic population in Japan. We set the minimum age as 18 years because we considered patients aged 18 years or older to have completed growth. Patients in the MxAC group were selected to match the age range of the control group as much as possible. Mesiodistal tooth crown diameters for the maxillary central incisors, lateral incisors, canines, first and second premolars, and first molars were measured using the digital caliper, and the bilateral measurements were pooled. The median and interquartile range (IQR) with means and standard deviations were then calculated for both groups. For the central incisor relationship, overjet and overbite were measured on dental casts using the digital caliper, and medians and IQRs with means and standard deviations were calculated for both groups. Tooth size-arch size relationship was measured using the segment arch method with the digital caliper.11 Facial-palatal displacements of the lateral incisors and canines were measured (Fig 1). Medians and IQRs with means and standard deviations for these measurements were then calculated for both groups. Dental arch dimensions were measured by the 3D cloud evaluation software. Dental arch widths were measured as the distances between reference points on
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Table II. Cephalometric analysis Measurement Cranial base 1
Unit
Cranial base angle
Anterior cranial base length Posterior cranial base length Total cranial base length
mm mm mm
SNA angle SNB angle ANB angle A-Ptm distance
mm
SN-mandibular plane angle (SN-MP)
10
SN-palatal plane angle (SN-PP)
11
Palatal plane-mandibular plane angle (PP-MP) Upper anterior facial height Lower anterior facial height Anterior facial height
mm mm mm
U1-SN angle
16
U1-palatal plane angle (U1-PP)
17 18
U1-NA distance U1-NA angle
mm
19
L1-NB distance
mm
20
L1-NB angle
21
L1-MP angle
22
Interincisal angle
23
U6D-Ptm distance
mm
24
U6M-A distance
mm
2 3 4 Skeletal sagittal 5 6 7 8 Skeletal vertical 9
12 13 14 Dental 15
bilateral canines, first and second premolars, and first molars (midpoint of mesiodistal buccal cusps of the first molars). Dental arch depths were measured as the distances between the midpoint of the center of the edges of bilateral central incisors and the midpoints of bilateral reference points at the canines, first and second premolars, and first molars (Fig 1). Medians and IQRs with means and standard deviations for these measurements were then calculated for both groups. All cephalograms were taken with the same machine (CX-150SK; Asahi-Roentgen, Kyoto, Japan), and
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Description Angle formed between the S-N plane and S-Ar line. The S-N plane was formed by points S and N. This angle is also known as the saddle angle Liner distance between points S and N Liner distance between points S and Ar Liner distance between points N and Ar Angle formed between the S-N plane and N-A line Angle formed between the S-N plane and N-B line Angle formed between the lines N-A and N-B Linear distance between point A and point Ptm Angle formed between the S-N plane and mandibular plane. The mandibular plane was formed by connecting gonion and menton Angle formed between the S-N plane and palatal plane. The palatal plane was formed by connecting ANS and PNS Angle formed between the palatal plane and mandibular plane Vertical distance between point N and point ANS Vertical distance between point ANS and point Me Vertical distance between point N and point Me Angle formed by the intersection of the long axis of the maxillary central incisor (U1) and the S-N plane Angle formed by the intersection of the long axis of U1 and the palatal plane. The palatal plane was formed by points ANS and PNS Horizontal distance from the edge of U1 to the N-A line Angle formed by the intersection of the long axis of U1 and the N-A line Horizontal distance from the edge of the mandibular central incisor (L1) to the N-B line Angle formed by the intersection of the long axis of L1 and the N-B line Angle formed by the intersection of the long axis of L1 and the mandibular plane Angle formed by the intersection of the long axes of U1 and L1 Linear distance between distal contact of the maxillary first molar (U6D) and point Ptm Linear distance between mesial contact of the maxillary first molar (U6M) and point A
magnification was automatically adjusted to 1:1 by the cephalometric analyzing software program. Based on previous studies, 14 skeletal and 10 dental cephalometric measurements were conducted using the analyzing software program, and medians and IQRs with means and standard deviations were calculated for both groups (Fig 2; Tables I and II).18-20 All reference points were identified by 1 evaluator (M.I.). Articulare was used as the reference at the most posterior point of the cranial base, which is considered to be a more biometrically reliable point than basion.8,21,22
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(total, 10 casts) were also randomly selected. All measurement landmarks were identified twice with a minimum of a 2-week interval by 1 evaluator (M.I.) and once by another evaluator with a careful calibration session, since we do not use this system clinically. The maximum intraexaminer and interexaminer error values for the 3D dental cast measurements were 0.10 and 0.12 mm, respectively. Statistical analysis
All statistical analyses were performed using SPSS software for Windows (version 24.0; IBM, Armonk, NY). Because some parameters did not show normal distributions according to the Kolmogorov-Smirnov test, medians and IQRs were calculated for each parameter, and the nonparametric Mann-Whitney U test was used to compare the 2 groups. Parameters that did not show a normal distribution were displacement of lateral incisor for the control group, overbite, and sum of the displacements for 1 side for the MxAC group, and lower anterior facial height, anterior facial height, and L1-NB distance. For all statistical analyses, P values less than 0.05 were considered significant.
Fig 3. Comparison of the results of cephalometric measurements in the MxAC and control groups. Medians of reference point locations in the x-y coordinates for each group were superimposed at sella and the S-N line.
RESULTS
In addition, all x-y coordinates for each patient were exported as text data and imported into the Microsoft Office Excel program. The coordinates were superimposed at sella as the origin and on the sella-nasion line at 7 above the horizontal line for each group.23 Medians for each reference point were calculated for each group, and a graph was drawn (Fig 3). To calculate and examine intraexaminer errors with Dahlberg's formula,24 10 subjects were randomly selected from both groups (total, 20 subjects). The same cephalometric measurements were taken twice with a minimum of a 2-week interval by 1 evaluator (M.I.) and once by another evaluator (a member of the orthodontic department) using the same general clinical procedure without a calibration session. The maximum intraexaminer and interexaminer error values for the cephalometric analysis were 0.55 and 0.63 mm for linear measurements and 0.61 and 0.79 for angular measurements, respectively. For mesiodistal tooth crown diameter measurements on dental casts, the same 20 subjects were evaluated. The maximum intraexaminer and interexaminer error values were 0.17 and 0.36 mm, respectively. In addition, to analyze intraexaminer and interexaminer errors for dental cast measurements obtained by the 3D laser scanner, 5 dental casts from both groups
Mesiodistal diameters of tooth crowns of the MxAC group were significantly larger than those of the control group for all teeth except for the first molar (P \0.01). Overbite was significantly smaller in the MxAC group compared with the control group (P \0.01) (Table III). Arch length discrepancy and facial-palatal displacement of the lateral incisors and canines from the dental arch were significantly smaller and greater, respectively, in the MxAC group compared with the control group (P \0.01). Dental arch widths at the first and second premolars (P \0.01) and the first molars (P \0.01) and dental arch depths at the canine (P \0.01), the first premolar (P \0.01), and the second premolar (P \0.05) in the MxAC group were significantly smaller than in the control group. The cranial base angle was significantly greater in the MxAC group compared with the control group (P \0.05). Median cranial base length measurements for anterior cranial base length, posterior cranial base length, and total cranial base length (P \0.01) were 4.10 mm (5.89%), 3.95 mm (10.12%), and 5.16 mm (5.38%) shorter in the MxAC group compared with the control group, respectively (Fig 3; Table IV). SNA and SNB angles and the A-Ptm distance were significantly smaller in the MxAC group compared with the control group (P \0.01).
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Table III. Comparison of the dental cast analysis in the maxillary arches between the groups Control group (n 5 33) Measurement (mm) Mesiodistal tooth dimensionz Central incisor Lateral incisor Canine First premolar Second premolar First molar Central incisor relationship Overjet Overbite Tooth size-arch size relationship Arch length discrepancy (1) Displacement of lateral incisorz (2) Displacement of caninez Sum of the displacements for 1 sidez§ Dental arch width (3) Canine (4) First premolar (5) Second premolar (6) First molar Dental arch depth (7) Canine (8) First premolar (9) Second premolar (10) First molar
Statistical analysis
MxAC group (n 5 33)
Median
IQR
Mean
SD
Median
IQR
Mean
SD
P value
8.42 7.05 7.80 7.30 6.89 10.47
0.56 0.51 0.28 0.52 0.45 0.62
8.47 7.13 7.80 7.30 6.84 10.41
0.41 0.43 0.19 0.39 0.34 0.50
8.63 7.48 8.14 7.67 7.08 10.60
0.70 0.94 0.70 0.58 0.47 0.91
8.73 7.59 8.17 7.74 7.09 10.53
0.50 0.56 0.40 0.40 0.33 0.55
0.000 0.000 0.000 0.000 0.000 0.110
2.52 2.05
1.18 0.78
2.53 2.16
0.82 0.57
2.76 1.69
0.95 1.27
1.01 0.98
0.387 0.005
0.01 0.30
1.00 1.71
0.05 0.19k
0.77 1.55
9.71 2.72
7.51 2.69
3.94 1.94
0.000 0.000
0.44 0.76
1.13 0.79
0.48 0.86
0.95 0.72
3.03 5.61
2.45 2.74
1.64 1.72
0.000 0.000
35.37 43.60 49.80 55.20
2.54 2.21 2.89 3.17
35.62 43.67 49.86 55.38
1.43 1.91 2.43 2.44
35.52 40.55 45.34 52.66
4.04 4.06 5.38 4.08
35.61 40.18 45.61 52.42
2.33 2.78 3.55 2.83
0.954 0.000 0.000 0.000
8.33 15.44 22.23 30.66
1.23 1.98 2.04 2.67
8.34 15.61 22.11 30.52
1.03 1.40 1.59 2.03
5.67 14.11 20.80 30.00
3.82 4.42 3.82 4.33
6.04 14.01 20.87 29.79
2.12 2.44 2.57 2.76
0.000 0.006 0.038 0.267
2.65 1.72k 10.00 2.86 2.99 5.76k
y y y y y
NS NS y y y y y
NS y y y y y
* NS
IQR, Interquartile range; MxAC, maxillary anterior crowding; NS, not significant. (1) and (2), A positive number indicates displacement toward the facial direction. (1)-(10), Correspond to the numbers shown in Figure 1. *P\0.05; yP\0.01; zThe right and left side data were pooled; §The sum of the displacement was calculated as (2) – (1) for each side (ie, subtraction of lateral incisor displacement from canine displacement); kNonnormal distribution.
Significantly greater SN-mandibular plane (MP), SNpalatal plane (PP) (P \0.01), and PP-MP angles (P \0.01) were observed in the MxAC group compared with the control group, indicating a hyperdivergent skeletal pattern of this malocclusion. Regarding dental components, the MxAC group showed a significantly greater U1-PP (P \0.01) and U1-NA (P \0.05) angles, smaller interincisal angle (P \0.01), and smaller U6D-Ptm distance (P \0.05) than did the control group. DISCUSSION
In this study, the maxillary dental arch in the MxAC group exhibited narrower interpremolar and interfirst molar widths and shorter dental arch depths at the canines and premolars when compared with the control group. However, no significant difference in maxillary intercanine width was observed between the 2 groups. Therefore, the direction of canine
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displacement can be evaluated in the anterior direction, rather than the transverse, because of the short dental arch depths observed at the canines and first premolars. In the Japanese language, “yaeba” refers to the condition of multiple anterior overlapping teeth in the frontal smile. In contrast to our subjects, who were selected from the same Japanese population, Italian patients with similar malocclusion status and buccally displaced maxillary canines demonstrated significantly wider intercanine widths and no intermolar width differences.4 Therefore, heritability of cranial base morphology may explain differences in the direction of maxillary canine displacement between ethnicities.14,25,26 However, further studies in other populations are necessary to determine the effect of ethnic variation on cranial base morphology and position of ectopic maxillary canines. In orthodontics, the cranial base angle has often been investigated to identify differences among Angle
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Table IV. Comparison of the results of cephalometric and dental cast analyses between the groups Control group (n 5 33) Measurement Cranial base 1 Cranial base angle 2 Anterior cranial base length 3 Posterior cranial base length 4 Total cranial base length Skeletal sagittal 5 SNA angle 6 SNB angle 7 ANB angle 8 A-Ptm distance Skeletal vertical 9 SN-mandibular plane angle (SN-MP) 10 SN-palatal plane angle (SN-PP) 11 Palatal plane-mandibular plane angle (PP-MP) 12 Upper anterior facial height 13 Lower anterior facial height 14 Anterior facial height Dental 15 U1-SN angle 16 U1-palatal plane angle (U1-PP) 17 U1-NA distance 18 U1-NA angle 19 L1-NB distance 20 L1-NB angle 21 L1-MP angle 22 Interincisal angle 23 U6D-Ptm distance 24 U6M-A distance
Statistical analysis
MxAC group (n 5 33)
Unit
Median
IQR
Mean
SD
Median
IQR
Mean
SD
P value
122.50 69.60 39.00 96.00
5.85 3.65 3.85 6.99
122.09 69.73 38.70 96.39
3.71 3.01 3.02 4.19
124.90 65.50 35.05 90.84
7.60 4.20 4.40 8.21
124.90 66.11 34.97 90.39
5.30 3.43 3.42 5.35
0.028 0.000 0.000 0.000
mm
82.90 79.60 2.30 48.40
4.50 3.45 3.05 2.45
82.43 80.24 2.18 48.89
2.94 2.74 1.93 2.21
79.05 77.70 2.75 45.35
4.27 5.95 3.63 4.38
79.77 76.70 3.09 45.58
3.80 3.43 2.47 3.01
0.001 0.000 0.228 0.000
35.00
7.15
34.64
5.00
41.40
8.50
42.02
6.05
0.000
7.00
4.95
6.21
3.87
10.80
4.20
10.98
2.51
0.000
26.30
5.75
26.31
4.27
30.00
6.80
31.07
4.61
0.000
mm mm mm
57.90 73.40 128.10
3.70 3.95 5.95
58.06 74.08z 129.24z
2.87 4.10 5.30
56.45 72.55 125.05
5.30 5.72 7.40
56.20 72.11 124.83
3.36 4.16 5.04
0.024 0.116 0.004
* NS
106.10 115.60
6.68 5.15
106.47 114.50
4.75 4.12
108.25 119.50
7.18 7.43
107.74 118.62
4.69 4.92
0.248 0.001
NS
6.90 24.70 8.00 30.10 93.70 123.80 15.01 22.62
3.50 6.10 3.05 7.25 4.25 7.20 2.90 2.93
7.14 24.39 7.33z 28.83 93.97 124.62 15.35 22.87
2.16 4.18 2.27 4.85 5.13 5.46 2.38 2.54
7.40 26.90 8.30 31.40 92.45 116.65 13.38 22.30
4.78 8.08 4.35 12.18 10.53 15.85 4.27 3.55
7.45 27.88 8.44 31.17 92.65 117.86 13.90 21.83
3.04 5.11 3.09 6.43 6.97 9.39 3.14 3.27
0.551 0.014 0.156 0.139 0.308 0.002 0.021 0.105
NS * NS NS NS
mm mm mm
mm
mm
mm mm
*
y y y y y
NS y y y y
y
y
y
* NS
IQR, Interquartile range; MxAC, maxillary anterior crowding; NS, not significant. *P \0.05; yP \0.01; zNonnormal distribution.
classifications.8,27-29 Previous studies have suggested that larger and smaller cranial base angles determine the posterior and anterior positions of the condyle in the cranial base, resulting in skeletal Class II and Class III relationships, respectively.25,30,31 However, only a few studies have used the cranial base angle to compare differences between patients with and without crowding in the mandibular arch, with no significant differences in the cranial base angle observed.9,10 We found a significantly larger cranial base angle in the MxAC group with Class I dental and skeletal patterns. This finding supports the results of a previous study in Class I patients.29 These findings may be attributed to a topographic correlation between the cephalometric measurements and the reference points.32-34 The cranial base, maxilla, dental arch, and teeth are adjacent anatomic components, and thus may be associated with one another during the growth
period from the embryonic phase. Therefore, the cranial base angle may influence the establishment of MxAC. However, the precise biologic mechanisms are still not well understood and require further longitudinal studies of growing subjects.29 Larsen et al5 observed that children with either facially or palatally impacted maxillary canines that required fenestration surgery had a significantly shorter anterior cranial base length (approximately 1 mm), which was not necessarily the result of anterior crowding when compared with a reference group. Although we studied adults, we observed a larger difference for anterior cranial base length between groups than the previous study in growing patients.5 In addition, we found significantly smaller posterior cranial base length and total cranial base length in the MxAC group than in the control group. These findings suggest the possibility of early prediction of MxAC even before establishment of
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the permanent dentition according to a smaller cranial base on cephalometric analysis.25 The MxAC group demonstrated a significantly smaller anterior cranial base length and anteroposterior dimension of the maxilla (A-Ptm distance) compared with the control group. These findings support the conclusion of a recent review article, which suggested that anterior cranial base length has a stronger influence on facial growth than posterior cranial base length.35 Although the correlation between cranial base size and cleft palate remains unclear,36 it is plausible that a history of cleft palate repair greatly affects maxillary development, but this altered maxillary development has no significant influence on morphology or size of the cranial base.37 In addition, use of rapid maxillary expansion appliances in 8- to 11-year-olds resulted in limited expansion effects in spheno-occipital synchondrosis.38 Therefore, orthodontic intervention with maxillary development to resolve arch length discrepancy in patients with severe MxAC may be limited, even in growing patients. In Italy, Mucedero et al4 found a significantly higher possibility of hyperdivergent skeletal patterns using the SN-GoGn angle in cephalometric analysis in patients with buccally displaced maxillary canines. We observed similar significant hyperdivergent skeletal patterns with greater SN-MP, SN-PP, and PP-MP angles in the MxAC group than in the control group. A shorter posterior cranial base length and obtuse cranial base angle cause the glenoid fossa and condyle to have relatively higher positions, which may increase the SN-MP and PP-MP angles (Fig 3).39 In previous studies, subjects with a long face usually have narrower transverse dimensions, and those with a short face have wider transverse dimensions.25,40,41 In contrast, the MxAC group in this study showed significantly smaller maxillae as measured by upper anterior facial height, anterior facial height, and A-Ptm distance, despite exhibiting a hyperdivergent skeletal pattern. Therefore, smaller vertical and sagittal dimensions of the maxilla could be 1 characteristic of MxAC and may cause smaller dental arch dimensions. Traditionally, a hyperdivergent skeletal pattern is often attributed to functional problems including oral breathing and lower tongue posture, which is also considered to correlate with a narrower maxillary dental arch.11 Forster et al42 observed that patients with hyperdivergent patterns tend to exhibit a narrower dental arch width and suggested that lower masseter muscle function causes undergrowth of the mandible in a transverse direction. However, family and twin studies showed a strong genetic influence in the development of the cranial base.43,44 The influence of cranial base
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morphology on maxillary and mandibular growth is often observed in heritable developmental anomalies such as cleft lip and palate, Down syndrome, Turner syndrome, and craniosynostosis.36,45 Therefore, in addition to environmental factors, genetic factors may cause cranial base dysmorphology and potentially impact maxillary undergrowth, consequently establishing MxAC indirectly. Few treatment options for MxAC are currently available. Clinically, maxillary arch expansion in the mixed dentition and premolar extraction in the permanent dentition are commonly performed. As Enlow and Hans25 hypothesized and Klocke et al46 demonstrated, morphology and size of the cranial base are determined in the early stage of development (as early as 5 years of age). Clinically, a greater cranial base angle, shorter anterior cranial base length and posterior cranial base length, and larger mesiodistal width of the maxillary central incisors detected in the early mixed dentition may predict MxAC. In addition, the effect of maxillary expansion may be limited, and serial extraction may be recommended for such Class I MxAC patients. Greater arch length discrepancy and displacement of the maxillary lateral incisors and canines, smaller dental arch dimensions, and slightly labially tipped maxillary central incisors were observed in the MxAC group compared with the control group. Although these results were expected based on the selection criteria of subjects in this study, these findings suggest the necessity of premolar extractions with consideration of maximum anchorage for patients with MxAC. Although the selection criterion for overbite in the MxAC group was 1 mm larger, overbite values with a significantly smaller median, which reflects individual variation, were observed in the MxAC group compared with the control group. Moreover, overbite values for the MxAC group did not show a normal distribution (Table III). These findings suggest that subjects in the MxAC group had a skewed overbite distribution, and the peak in smaller overbite values might be caused by the hyperdivergent skeletal pattern observed when compared with the control group. CONCLUSIONS
Women with Class I occlusion and severe MxAC exhibited significantly wider angles and shorter lengths in the cranial base, smaller sagittal maxillary bases, and hyperdivergent skeletal patterns. REFERENCES 1. Peck S, Peck L. Classification of maxillary tooth transpositions. Am J Orthod Dentofacial Orthop 1995;107:505-17.
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