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Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion
ODW 245 No. of Pages 9
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Original article
Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion Sotaro Akiyama DDS, Kazuhito Arai DDS, DDSc * Department of Orthodontics, School of Life Dentistry at Tokyo, The Nippon Dental University, Tokyo, Japan
article info
abstract
Article history:
Purpose: The purpose of the present study was to investigate the characteristics of the antero-
Received 10 June 2016
posterior positions of teeth in subjects with Class I bimaxillary dentoalveolar protrusion
Received in revised form
(BMDP).
19 November 2016
Materials and methods: The cephalograms and dental casts of BMDP group (n=34; 21 females
Accepted 22 November 2016
with a mean age of 20.93.0years; 13 males with a mean age of 22.52.2years; interincisal
Available online xxx
angle less than 125 ) and the control group (n=39; 24 females with a mean age of 20.2 1.6years; 15 males with a mean age of 23.73.1years; balanced profile) both with Class I molar relationships were analyzed. The distances from the root apexes of the central
Keywords: Bimaxillary
dentoalveolar
protrusion Root apex Posterior available space Crown angulation
incisors to the cortical bones of the alveolar process and posterior available space in the maxilla-mandible on the cephalograms in addition to mesiodistal tooth crown diameters, dental arch dimensions, and crown angulation on the dental casts were measured and compared between groups statistically at the 5% level. Results: Greater and lesser distances of the root apex of the maxillary central incisor to the labial and palatal cortical bones, respectively, as well as greater mesial crown angulations for the maxillary canines and first premolars and the mandibular canines, first and second premolars were observed in BMDP group. Conclusion: Subjects with BMDP showed a palatally located root apex of the maxillary central incisor and mesially tipped lateral teeth when compared with subjects with normal occlusion and balanced profile from the same ethnic population. © 2016 Elsevier Ltd and The Japanese Orthodontic Society. All rights reserved.
1.
Introduction
Bimaxillary dentoalveolar protrusion (BMDP) is defined as Class I molar relationships with protruded and proclined upper and lower incisors accompanied by lip procumbency and incompetency [1]. The chief complaint of BMDP patients seeking orthodontic treatment is occasional functional problems associated with interference with lip closure; other
main concerns are facial esthetics related to protruding anterior teeth and a convex profile, which can negatively affect the quality of life during adolescence and adulthood [2,3]. Therefore, the retraction of the anterior teeth to improve the profile is an essential component of successful treatment of BMDP. Clinicians generally agree that regardless of ethnic group, the extraction of the four first premolars can be
* Corresponding author at: 1-9-20 Fujimi, Chiyoda-ku, Tokyo 102-8159, Japan. Fax: +81 3 3261 6523. E-mail address: [email protected] (K. Arai). http://dx.doi.org/10.1016/j.odw.2016.11.003 1344-0241/© 2016 Elsevier Ltd and The Japanese Orthodontic Society. All rights reserved.
Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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The sample size was estimated based on an effect size of 0.68, which was determined according to a previous study [1], and was calculated by using the G*Power 3.1 statistical power analysis program (Heinrich Heine Universitat Dusseldorf Experimentelle Psychologie, Dusseldorf, Germany). The minimum sample size of each group that was required to detect an effect of this size with 80% power at the 5% significance level was 28.
and dental casts of approximately 3800 patients at The Nippon Dental University Hospital were investigated. Patients with an Angle Class I relationship, a positive overjet, an overbite larger than 2.0mm, and an arch-length discrepancy larger than 4.0mm were selected by dental cast analysis. Cephalometric analyses of these patients were evaluated by Keating’s criteria (interincisal angle less than 125 , maxillary incisors to palatal plane angle greater than 115 , and mandibular incisors to mandibular plane angle greater than 99 ) [12] to identify BMDP patients for inclusion. Patients with congenital craniofacial anomalies, a previous history of orthodontic treatment, persistent deciduous teeth, an absence of permanent teeth except for the third molar, and crown restorations covering the cusp of a tooth were excluded. Furthermore, with consideration of growth potential, female subjects younger than 15 and male subjects younger than 18 were also excluded. Sixteen BMDP patients (9 females, with a mean age of 21.43.1years and an age range from 15.6 to 25.9 years, and 7 males, with a mean age of 23.32.3years and an age range from 21.6 to 26.7 years) were selected. To increase sample size, intraoral examinations and interviews of approximately 1400 students were conducted at The Nippon Dental University and related colleges. Based on the intraoral examinations, subjects with an Angle Class I relationship, a positive overjet, an overbite larger than 2.0mm, and an arch-length discrepancy larger than 4.0mm (mild crowding) were selected. Furthermore, subjects with congenital craniofacial anomalies, a previous history of orthodontic treatment, persistent deciduous teeth, an absence of permanent teeth except for the third molar, and crown restorations covering the cusp of a tooth were excluded. As a result of this initial selection process, 25 subjects (18 females, with a mean age of 20.22.5years and an age range from 18.5 to 28.4 years, and 7 males, with a mean age of 21.02.2years and an age range from 18.8 to 23.7 years) were selected from among the students. Next, lateral cephalograms, panoramic X-rays, and dental casts were taken of these 25 subjects. Cephalometric analyses of these 25 subjects were conducted using Dolphin Imaging software (Dolphin Imaging System, Canoga Park, CA, USA), and 18 BMDP subjects were selected based on Keating’s criteria [12]. Ultimately, 34 subjects (21 females, with a mean age of 20.9 3.0years and an age range from 15.6 to 28.4 years, and 13 males, with a mean age of 22.52.2years and an age range from 18.8 to 26.7 years) were selected as the BMDP group. To confirm the consistency of the amount of incisor proclination of the subjects in the BMDP group, the results of the cephalometric analyses of the dental students (n=18: female: male=12: 6) and the orthodontic patients (n=16: female: male=9: 7) were compared, and no statistically significant differences in interincisal angle, maxillary incisors to palatal plane angle, and mandibular incisors to mandibular plane angle were detected using the nonparametric Mann–Whitney test.
2.1.
2.2.
effective in treating BMDP in permanent dentition; however, few studies on this treatment are available in the literature [1]. In addition to various conventional methods of anchorage reinforcement, including headgear and/or a trans-palatal arch, a temporary anchorage device (TAD) has recently been used in the treatment of adult BMDP patients [4], which presents some risks [5,6]. In a case-control cephalometric study conducted by Bills et al. [1] in Chicago, the anteroposterior width of the alveolus in 48 BMDP patients with fourpremolar extractions was compared with that of normal occlusions [7]. The authors observed a narrower anteroposterior width of the alveolus in the BMDP patients and potential limitation of the posterior movement of the root apexes of the central incisors. However, the initial anteroposterior positions of the root apexes of the incisors in the alveolar processes of the maxilla and mandible in Class I BMDP have not been investigated. Furthermore, in addition to the space obtained by extracting the four first premolars to retract the protruded anterior teeth, distalizing all of the teeth using TAD has recently been applied in BMDP cases [8]. When adequate posterior space is not available, buccally displaced second molars and/or severely impacted third molars may be a risk of molar distalization in post-pubertal patients [9]. There is little scientific evidence to support this strategy; therefore, understanding the relationship between the mesiodistal tooth crown diameter and the posterior available space in both BMDP and normal occlusion is necessary to evaluate the posterior discrepancy for BMDP. Most studies of BMDP have focused on the protruded and proclined anterior teeth, whereas the crown angulation of the posterior teeth influenced by the anterior teeth has not been investigated. Compensatory changes in the angulation of molars as a result of sagittal relationships of skeletal or dental features [10] and significant mesial tipping of the mandibular molars in Class I malocclusion subjects [11] have been reported. Therefore, the angulations of the canines and molars in BMDP require investigation because of their effects on anchorage control. The purpose of the present study was to investigate the characteristics of the antero-posterior positions of teeth in subjects with Class I BMDP compared with those of subjects with normal occlusion and balanced profile from the same population.
2.
Methods
BMDP group
The orthodontic diagnostic records, including facial and intraoral photographs, cephalograms, panoramic X-rays,
Control group
We selected 39 subjects (24 females, with a mean age of 20.21.6years and an age range from 15.6 to 23.5 years, and
Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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15 males, with a mean age of 23.73.1years and an age range from 19.2 to 29.3 years) with Class I molar relationships and balanced facial profile as the control group. These subjects were students at The Nippon Dental University and related dental colleges who met the following inclusion criteria: Angle Class I molar relationship, 2.0mm0mm and <4mm), 5.0mm
The BMDP group included a greater number of female subjects than male subjects because of differences in patient concern about facial esthetics related to protruding anterior teeth and a convex profile. Therefore, the numbers of female and male subjects in the control group were adjusted to maintain balance.
2.3.
Cephalometric measurements
To confirm the skeletal and dental pattern of the BMDP group, all cephalometric parameters were compared with those of the control group (Table 1). The antero-posterior distances from the root apexes of central incisors to the labio-palatal or lingual cortical bones of the alveolar process in the maxilla and mandible [1,6] (UA, UP, LA, LP) (Table 2, Fig. 1) were measured and compared between the groups. Additionally, the antero-posterior widths of maxilla and mandible alveolar processes at the level of the root apex (UA+UP, LA+LP) were also measured and compared between the groups [1].
Control group
Statistical analysis
Quartile deviation
Median
Quartile deviation
P-value
Horizontal
Angular parameter (degrees) SNA 82.10 80.25 SNB 2.95 ANB 7.20 Angle of convexity
2.49 2.96 1.77 3.89
83.50 80.00 2.90 5.10
2.90 2.35 2.20 4.70
0.462 0.774 1.00 0.362
Vertical
Table 1 – Comparisons of the median and quartile deviations of the cephalometric parameters between the BMDP and control groups. BMDP group
PP-SN SN-MP FMA
7.70 33.95 26.50
2.04 5.59 4.24
7.70 35.90 29.60
1.90 3.20 3.25
0.974 0.367 0.063
Linear parameter (mm) N-S Go-Pog
67.75 79.25
4.37 6.02
69.70 80.40
15.15 2.55
0.266 0.344
86.30 125.95
9.98 12.85
87.30 129.30
7.95 7.40
0.934 0.299
4.24 4.75 5.55 3.54 3.76 4.18
113.20 104.70 127.70 93.70 23.00 28.70
2.60 3.85 5.70 4.05 3.80 1.95
0.000** 0.000** 0.000** 0.000** 0.000** 0.000**
2.34 5.49
6.00 7.00
2.50 1.95
0.000** 0.000**
1.84 2.29 6.25
2.90 0.70 101.30
1.35 1.20 6.20
0.000** 0.000** 0.001**
Horizontal
Soft tissue
Dental
Vertical
Skeletal
Measurements
**
S-Go AFH
Median
Angular parameter (degrees) 125.65 U1-PP U1-SN 116.50 U1-L1 102.25 L1-MP 104.40 U1-NA 34.10 L1-NB 38.80 Linear parameter (mm) 11.95 U1-NA L1-NB 11.50 Linear parameter (mm) UL to E-line LL to E-line Nasolabial angle
0.35 4.15 93.85
P < 0.01.
Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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Table 2 – Cephalometric measurements of the antero-posterior positions of the root apex of the central incisors and the posterior available space. Measurement UA (width of maxillary anterior alveolus)
The linear distance between the apex of the maxillary central incisors and the limit of the labial cortex, along a plane parallel to the palatal plane, drawn through the apex
UP (width of maxillary posterior alveolus)
The linear distance between the apex of the maxillary central incisors and the limit of the palatal cortex, along a plane parallel to the palatal plane, drawn through the apex
U6-Ptm
Maxillary posterior available space for the second and third molars. The linear distance between the most distal point of the maxillary first molar and the perpendicular line to the palatal plane crossing the Ptm point.
A-Ptm
Antero-posterior dimension of the maxillary basal bone. The linear distance between the perpendicular lines to the palatal plane crossing the Ptm point and the A point
LA (width of mandibular anterior alveolus)
The linear distance between the apex of the mandibular central incisors and the limit of the labial cortex, along a plane parallel to occlusal plane, drawn through the apex
LP (width of mandibular posterior alveolus)
The linear distance between the apex of the maxillary central incisors and the limit of the lingual cortex, along a plane parallel to the occlusal plane, drawn through the apex
L6-Mr
Mandibular posterior available space for the second and third molars. The linear distance between the most distal point of the mandibular first molar and the perpendicular line to the palatal plane crossing the Mr point
B-Mr
Antero-posterior dimension of the mandibular basal bone. The linear distance between the perpendicular lines to the palatal plane crossing the Mr point and the A point
In addition, the total dentition space (A-Ptm, B-Mr) and the posterior available space in the maxilla and mandible [9] (U6Ptm, L6-Mr) (Table 2, Fig. 1) were measured and compared between the groups.
2.4.
Dental cast measurements
The mesiodistal tooth crown diameters from the first molar to the first molar of each arch were measured using digital
calipers (NTD12-C, Mitutoyo, Kanagawa, Japan) with an accuracy of up to 0.01mm. The dental casts were then laser scanned (Surflacer model VMS-100F, UNISN, Osaka, Japan) [13]. The facial axis (FA) point was defined as the midpoint of the FA of the clinical crown and was selected for each tooth from the first molar to the first molar (Fig. 2) [14]. The canine and molar widths and depths were also calculated (Fig. 2), and the crown angulation was measured via 3D dental cast analysis (Fig. 3) [14].
Fig. 1 – Cephalometric measurements. Measurement of the distances from the root apexes of central incisors to the labio-palatal or lingual cortical bones of the alveolar process and from the first molar to the posterior limit of the eruption spaces to define the posterior available space in the maxilla and mandible. Mr: the intersection point of the occlusal plane and the anterior border of the mandibular ramus. Ptm: the point at the base of the fissure where the anterior and posterior wall meet. Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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Fig. 2 – Dental arch dimensions: (a) maxillary dental cast; (b) mandibular dental cast.
2.5.
Reliability of the method
To calculate the measurement error of the cephalometric measurements (UA, UP, LA, LP) (A-Ptm, B-Mr, U6-Ptm, L6-Mr), 5 cephalograms were randomly selected from the two groups. Intra-examiner error was determined for one operator and
calculated using Dahlberg’s formula [15] (SE=
qX ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi d2 =2n) as
0.620.18mm on average. Inter-examiner error was determined with a second operator and calculated in the same way as 0.680.21mm on average. In addition, we calculated the respective intra- and inter-examiner errors with regards to dental measurements as 0.250.17mm and 0.250.16mm for
Fig. 3 – Crown angulation: (a) maxillary dental cast; (b) mandibular dental cast. To measure crown angulation, the facial axis of the clinical crown of each tooth was drawn. Occlusal planes were formed by the anterior reference point, defined by the midpoint of the line segment connecting the bilateral incisal points (the center of the incisor edge), and the posterior reference points (the mesial palatal cusp tip of the bilateral first molars for the maxillary arches and the distal buccal cusp tip of the bilateral second molars for the mandibular arches). The crown angulation was calculated as the angle between the facial axis of the clinical crown for each tooth and the plane perpendicular to the occlusal plane. A positive value indicated mesial angulation, and a negative value indicated distal angulation. Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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the mesiodistal tooth crown diameter, 0.170.05mm and 0.220.07mm for the dental arch dimensions, and 0.880.08 and 0.980.14 for crown angulation.
2.6.
Statistical analysis
The normality of the data distribution was tested using the Kolmogorov–Smirnov test. The mean and standard deviation of the cephalometric measurements (UA, UP, LA, LP, UA+UP, LA+LP) (A-Ptm, B-Mr, U6-Ptm, L6-Mr) were calculated for the BMDP and control groups, and an independent t-test was used for between-group comparisons. The median and quartile deviation were calculated for the mesiodistal tooth crown diameters, dental arch dimensions, and crown angulations for each group. Nonparametric Mann– Whitney tests were used to compare the two groups because these measurements did not fit a normal distribution. All of the statistical tests were evaluated at the 5% level.
3.
Results
3.1.
Cephalometric measurements
Table 3 – Comparisons of the means and standard deviations (SDs) of the distances from the root apex of the central incisors to the cortical bones of the alveolar process and the posterior available space between the BMDP and control groups (mm). BMDP group Control group Statistical analysis Mean
SD
Mean
SD
t-Value
P-value
Maxilla UA UP UA +UP U6-Ptm A-Ptm
5.48 6.54 12.02 15.15 45.30
1.38 2.17 2.80 3.07 4.06
4.91 7.85 12.77 14.45 46.67
0.84 1.87 2.13 2.22 3.61
2.14 2.76 1.30 1.10 1.52
0.007** 0.036* 0.197 0.277 0.130
Mandible LA LP LA +LP L6-Mr B-Mr
3.40 3.88 7.28 15.42 41.40
0.81 0.83 1.38 2.84 4.42
3.14 3.57 6.71 14.35 43.18
0.72 0.91 1.52 2.39 4.20
1.45 1.54 1.69 1.73 1.76
0.153 0.128 0.096 0.089 0.081
* **
P <0.05. P <0.01.
3.2.
Dental cast measurements
Significantly greater mesiodistal tooth crown diameters were observed for all teeth in the BMDP group compared with the control group. Although there was no significant difference in the dental arch widths between the groups, the dental arch depths in the BMDP group were significantly longer than control group (Table 4). The crown angulations of the canines and first premolars in the maxillary arch and the canines and the first and second premolars in the mandibular arch were significantly greater in the BMDP group (Table 5).
4.
The BMDP group showed significantly (P<0.05) more protruded and proclined incisors and lip procumbency. However, in the skeletal parameters, no significant differences were observed between the groups (Table 1). For the antero-posterior distances from the root apex of the maxillary central incisor to the labial and palatal cortical bones of the alveolar process of the maxilla, UA and UP were significantly greater and lesser, respectively, in the BMDP group than in the control group (Table 3). For the mandibular central incisor (LA, LP), no significant differences were observed between the groups (Table 3).
Tooth
No significant differences were observed in the maxillary and mandibular widths of alveolar bone (UA+UP, LA+LP) between the groups (Table 3). No significant differences were observed between the groups for all parameters measuring the total dentition spaces (A-Ptm, B-Mr) and the posterior available spaces (U6-Ptm, L6-Mr) in the maxilla and mandible (Table 3).
Discussion
Although no worldwide epidemiological studies are available at present, malocclusion with BMDP is commonly observed in African–American [16] and East Asian populations [17,18] but can be observed in nearly every ethnic group [1], including Caucasian populations [12]. Margolis [19] proposed the distinction of bimaxillary prognathism from bimaxillary protrusion; the former is of phylogenetic origin, and the latter, as it applies in orthodontics, implies an ontogenetic influence. His hypothesis has been supported by cephalometric studies in the Japanese population [20,21]. Bills et al. [1] selected BMDP subjects representing multiple ethnic groups in consideration of racial differences, but studies of individual ethnic groups are also warranted. Several studies have used lateral cephalometric radiographs to clarify the morphological skeletal characteristics of BMDP, yet no consensus has been reached [12,22]. To confirm the skeletal pattern of the BMDP group in the present study, cephalometric analyses were conducted, including the total dentition spaces [14] such as A-Ptm for maxillary and B-Mr for mandibular dental arches. No significant differences in skeletal patterns and total dentition spaces were observed between the BMDP group and the control group, which consisted of subjects with normal occlusion and a balanced facial profile. Although four out of thirty-four BMDP subjects showed larger SNA and SNB angles than the normal range (adding the standard deviation to the mean of control group), these findings, therefore, suggested that there is no indication of necessity for orthognathic surgery in general. In addition, although no significant differences in vertical skeletal measurements were observed between the groups in the present study, a high angle tendency is often clinically observed in bimaxillary protrusion. Therefore, investigation of the vertical dental and skeletal components in more detail may be useful in future studies.
Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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Table 4 – Comparisons of the median and quartile deviations of the mesiodistal tooth crown diameter and dental arch dimensions between the BMDP and control groups (mm). Measurement
Maxillary arch Tooth crown diameter
Dental arch dimension
Mandibular arch Tooth crown diameter
Dental arch dimension
**
BMDP group
Control group
Statistical analysis
Median
Quartile deviation
Median
Quartile deviation
P-value
Central incisor Lateral incisor Canine First premolar Second premolar First molar
8.79 7.28 8.20 7.59 7.09 10.49
0.46 0.47 0.43 0.22 0.33 0.45
8.44 7.00 7.78 7.28 6.79 10.04
0.32 0.38 0.34 0.28 0.27 0.42
0.000** 0.000** 0.000** 0.000** 0.000** 0.000**
Canine width First molar width Canine depth First molar depth
39.68 58.42 9.55 33.15
1.77 1.98 1.01 1.62
38.18 57.70 8.36 31.32
1.23 1.90 0.57 1.19
0.302 0.745 0.000** 0.000**
Central incisor Lateral incisor Canine First premolar Second premolar First molar
5.66 6.26 7.09 7.55 7.40 11.67
0.21 0.19 0.31 0.33 0.33 0.36
5.35 5.94 6.84 7.27 7.09 11.23
0.21 0.20 0.29 0.30 0.29 0.35
0.000** 0.000** 0.000** 0.001** 0.000** 0.000**
Canine width First molar width Canine depth First molar depth
30.85 52.76 5.23 27.70
0.26 2.11 0.57 1.30
29.74 51.58 4.79 26.35
0.91 1.83 0.54 1.22
0.065 0.439 0.002** 0.000**
P < 0.01.
Table 5 – Comparisons of the median and quartile deviations of the crown angulations between the BMDP and control groups (degrees). BMDP group
Tooth Median
Quartile deviation
Maxillary arch Central incisor Lateral incisor Canine First premolar Second premolar First molar
1.67 4.58 11.63 2.74 3.77 2.96
2.90 2.47 5.14 4.31 4.09 3.11
Mandibular arch Central incisor Lateral incisor Canine First premolar Second premolar First molar
1.48 0.43 3.98 4.51 6.69 4.41
2.53 3.40 3.68 3.70 3.60 3.30
* **
Control group Median
Statistical analysis
Quartile deviation
P-value
1.66 4.78 6.65 1.57 3.63 4.71
2.12 2.37 3.39 3.49 3.25 3.69
0.665 0.909 0.000** 0.034* 0.564 0.090
1.12 1.20 0.38 0.58 3.75 4.99
2.44 2.28 3.15 3.02 3.37 4.07
0.669 0.051 0.000** 0.000** 0.011* 0.970
P < 0.05. P < 0.01.
Recently, a new molar distalization technique using TAD has been proposed for the treatment of BMDP [8], in which analysis of the posterior space is conducted based on the mesiodistal tooth crown diameter and the space between the first molar and the anterior border of the ramus [9]. In the present study, no significant differences in the posterior available space in the maxilla and mandible (U6-Ptm, L6-Mr)
were observed between the two groups, whereas significantly greater mesiodistal tooth crown diameters were observed in the BMDP group. These findings indicate that the molar distalization technique presents a possibility for posterior discrepancy in both arches and potential increased risks of third molar impaction [23] and upper airway narrowing after treatment [24]. Thus, before conducting molar distalization in
Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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BMDP patients, the presence of third molars should be confirmed, the posterior space should be analyzed, and the option of tooth extraction should be presented to patients. The antero-posterior distances of the root apex of the maxillary central incisor to the palatal cortical bone of the alveolar process of the maxilla (UP) in the BMDP group were significantly smaller than those in the control group. The cephalometric and dental cast analyses showed that the maxillary central incisor in the BMDP group was 13.58 proclined in U1-PP and 5.29mm protruded in U1-NA compared with the control group (Table 1), and the obtainable space by the extraction of the maxillary first premolar was 7.59mm on average in the BMDP group (Table 4). These findings indicate the need for maximum anchorage mechanics to retract the anterior teeth to the normal position in most BMDP cases, even with mild crowding. However, in the present study, UP was 6.54mm in the BMDP group, and the antero-posterior position of the root apex of the maxillary central incisor in the alveolar process of the maxilla was 1.31mm more palatally located, on average, in the BMDP group compared with the control group, although variation was observed among individuals (Table 3). These findings suggest an increased possibility of the apical root resorption of incisors through contact between the root apex and the palatal cortical bone or the incisive canal in BMDP patients after retraction over about 6.5mm with maximum anchorage mechanics such as TAD because of the absolute retraction of the maxillary incisors that occurs through bodily movement [5]. Similarly, the limitations placed upon orthodontic treatment by a thin alveolar have been reported about Angle Class II division 1 malocclusion with large overjet [6]. Therefore, there will be value in comparing Angle Class II malocclusion with Class I bimaxillary protrusion statistically in the future. Tooth size differences among ethnic groups and occlusal categories have often been reported, and they suggest the possible role of genetic factors in malocclusion [25]. Regarding BMDP, McCann and Burden [26] compared the tooth sizes of 30 Northern Irish people with Class I BMDP with those of 30 people with other malocclusions without BMDP. They found a significantly greater tooth size in the BMDP group and hypothesized that this anatomical characteristic may contribute to the proclination of the incisors. The results of the present study confirm these previous findings [26] in another ethnic group. Although environmental factors, including lip function and tongue size, have been considered a major cause of BMDP [27], these results suggest the influence of genetic background on this malocclusion. The present study is the first to investigate the crown angulation on the dental cast in BMDP. Significantly greater mesial tipping of the maxillary canine and first premolar and the mandibular canine and premolars was observed in the BMDP group compared with the control group. These results suggest the mesial tipping of canine and premolars and relatively distal positions of roots to the crowns of those teeth [28]. In addition, greater mesiodistal tooth crown diameters and longer arch depths in BMDP patients may provide a greater amount of incisor retraction for achieving a balanced profile [26]. However, these findings also suggest a higher possibility of the loss of anchorage control, i.e., unfavorable mesial root movements of the canines and mandibular second premolars.
Therefore, clinicians should take measures to avoid the loss of anchorage during the alignment phase of the most popular modality of this malocclusion with extraction of the four first premolars [1,17,18]. However, linear measurements in cephalometric analysis or mesiodistal tooth crown diameters in dental cast analysis were compared using a mixture of male and female subjects in the present study. Female subjects were included because the number of male subjects of the BMDP group was not sufficient for statistical comparison. In future studies, comparisons of each measurement between females and males may be considered very significant if sufficient numbers of male subjects in the BMDP group could be collected. In addition, our results of reliability tests using Dahlberg’s formula showed the values close to the differences between the groups about the cephalometric measurements. In the present study, we used only cephalograms to evaluate the antero-posterior positions of the root apexes of the maxillary central incisors. Therefore, we may need to confirm these results diagnostic tools with higher accuracy, for example, using the cone beam CT.
5.
Conclusions
Comparisons between subjects with bimaxillary dentoalveolar protrusion and subjects with normal occlusion and balanced profile from the same population revealed the following: 1. A significantly more palatally located root apex of the maxillary central incisor to the cortical bone of the alveolar process of the maxilla was found in BMDP. 2. Significantly greater mesiodistal tooth crown diameters and larger canine and molar depths in the maxillary and mandibular arch were found in BMDP. 3. Significantly greater mesial crown angulations were observed for the maxillary canines and first premolars and the mandibular canines and first and second premolars in BMDP.
Conflict of interests The authors have no conflicts of interest to declare.
Ethical approval All subjects provided written informed consent to participate in this study. The experimental protocol was approved by the Ethics Committee of The Nippon Dental University (approval number: NDU-T2013-32). REFERENCES
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Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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[2] Leonardi R, Annunziata A, Licciardello V, Barbato E. Soft tissue changes following the extraction of premolars in nongrowing patients with bimaxillary protrusion. A systematic review. Angle Orthod 2010;80:211–6. [3] Huang YP, Li WR. Correlation between objective and subjective evaluation of profile in bimaxillary protrusion patients after orthodontic treatment. Angle Orthod 2015;85:690–8. [4] Upadhyay M, Yadav S, Nagaraj K, Patil S. Treatment effects of mini-implants for en-masse retraction of anterior teeth in bialveolar dental protrusion patients: a randomized controlled trial. Am J Orthod Dentofacial Orthop 2008; 134:18–29. [5] Chung CJ, Choi YJ, Kim KH. Approximation and contact of the maxillary central incisor roots with the incisive canal after maximum retraction with temporary anchorage devices: report of 2 patients. Am J Orthod Dentofacial Orthop 2015;148:493–502. [6] Edwards John G. A study of the anterior portion of the palate as it relates to orthodontic therapy. Am J Orthod 1976;69:249–73. [7] Handelman CS. The anterior alveolus: its importance in limiting orthodontic treatment and its influence on the occurrence of iatrogenic sequelae. Angle Orthod 1996; 66:95–109. [8] Kook Y-A, Park JH, Bayome M, Sa'aed NL. Correction of severe bimaxillary protrusion with first premolar extractions and total arch distalization with palatal anchorage plates. Am J Orthod Dentofacial Orthop 2015;148:310–20. [9] Merrifield LL. Dimensions of the denture: back to basics. Am J Orthod Dentofacial Orthop 1994;106:535–42. [10] Kim YE, Nanda RS, Sinha PK. Transition of molar relationships in different skeletal growth patterns. Am J Orthod Dentofacial Orthop 2002;121:280–90. [11] Cuoghi OA, Sella RC, de Mendonça MR. Mesiodistal angulations of the mandibular canines, premolars and molars with or without the presence of third molars. Eur J Orthod 2010;32:472–6. [12] Keating PJ. Bimaxillary protrusion in the Caucasian: a cephalometric study of the morphological features. Br J Orthod 1985;12:193–201. [13] Ronay V, Miner RM, Will LA, Arai K. Mandibular arch form: the relationship between dental and basal anatomy. Am J Orthod Dentofacial Orthop 2008;134:430–8. [14] Andrews LF. Straight-wire: the concept and appliance. Wells: San Diego; 1989.
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Available online at www.sciencedirect.com
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Original article
Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion Sotaro Akiyama DDS, Kazuhito Arai DDS, DDSc * Department of Orthodontics, School of Life Dentistry at Tokyo, The Nippon Dental University, Tokyo, Japan
article info
abstract
Article history:
Purpose: The purpose of the present study was to investigate the characteristics of the antero-
Received 10 June 2016
posterior positions of teeth in subjects with Class I bimaxillary dentoalveolar protrusion
Received in revised form
(BMDP).
19 November 2016
Materials and methods: The cephalograms and dental casts of BMDP group (n=34; 21 females
Accepted 22 November 2016
with a mean age of 20.93.0years; 13 males with a mean age of 22.52.2years; interincisal
Available online xxx
angle less than 125 ) and the control group (n=39; 24 females with a mean age of 20.2 1.6years; 15 males with a mean age of 23.73.1years; balanced profile) both with Class I molar relationships were analyzed. The distances from the root apexes of the central
Keywords: Bimaxillary
dentoalveolar
protrusion Root apex Posterior available space Crown angulation
incisors to the cortical bones of the alveolar process and posterior available space in the maxilla-mandible on the cephalograms in addition to mesiodistal tooth crown diameters, dental arch dimensions, and crown angulation on the dental casts were measured and compared between groups statistically at the 5% level. Results: Greater and lesser distances of the root apex of the maxillary central incisor to the labial and palatal cortical bones, respectively, as well as greater mesial crown angulations for the maxillary canines and first premolars and the mandibular canines, first and second premolars were observed in BMDP group. Conclusion: Subjects with BMDP showed a palatally located root apex of the maxillary central incisor and mesially tipped lateral teeth when compared with subjects with normal occlusion and balanced profile from the same ethnic population. © 2016 Elsevier Ltd and The Japanese Orthodontic Society. All rights reserved.
1.
Introduction
Bimaxillary dentoalveolar protrusion (BMDP) is defined as Class I molar relationships with protruded and proclined upper and lower incisors accompanied by lip procumbency and incompetency [1]. The chief complaint of BMDP patients seeking orthodontic treatment is occasional functional problems associated with interference with lip closure; other
main concerns are facial esthetics related to protruding anterior teeth and a convex profile, which can negatively affect the quality of life during adolescence and adulthood [2,3]. Therefore, the retraction of the anterior teeth to improve the profile is an essential component of successful treatment of BMDP. Clinicians generally agree that regardless of ethnic group, the extraction of the four first premolars can be
* Corresponding author at: 1-9-20 Fujimi, Chiyoda-ku, Tokyo 102-8159, Japan. Fax: +81 3 3261 6523. E-mail address: [email protected] (K. Arai). http://dx.doi.org/10.1016/j.odw.2016.11.003 1344-0241/© 2016 Elsevier Ltd and The Japanese Orthodontic Society. All rights reserved.
Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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The sample size was estimated based on an effect size of 0.68, which was determined according to a previous study [1], and was calculated by using the G*Power 3.1 statistical power analysis program (Heinrich Heine Universitat Dusseldorf Experimentelle Psychologie, Dusseldorf, Germany). The minimum sample size of each group that was required to detect an effect of this size with 80% power at the 5% significance level was 28.
and dental casts of approximately 3800 patients at The Nippon Dental University Hospital were investigated. Patients with an Angle Class I relationship, a positive overjet, an overbite larger than 2.0mm, and an arch-length discrepancy larger than 4.0mm were selected by dental cast analysis. Cephalometric analyses of these patients were evaluated by Keating’s criteria (interincisal angle less than 125 , maxillary incisors to palatal plane angle greater than 115 , and mandibular incisors to mandibular plane angle greater than 99 ) [12] to identify BMDP patients for inclusion. Patients with congenital craniofacial anomalies, a previous history of orthodontic treatment, persistent deciduous teeth, an absence of permanent teeth except for the third molar, and crown restorations covering the cusp of a tooth were excluded. Furthermore, with consideration of growth potential, female subjects younger than 15 and male subjects younger than 18 were also excluded. Sixteen BMDP patients (9 females, with a mean age of 21.43.1years and an age range from 15.6 to 25.9 years, and 7 males, with a mean age of 23.32.3years and an age range from 21.6 to 26.7 years) were selected. To increase sample size, intraoral examinations and interviews of approximately 1400 students were conducted at The Nippon Dental University and related colleges. Based on the intraoral examinations, subjects with an Angle Class I relationship, a positive overjet, an overbite larger than 2.0mm, and an arch-length discrepancy larger than 4.0mm (mild crowding) were selected. Furthermore, subjects with congenital craniofacial anomalies, a previous history of orthodontic treatment, persistent deciduous teeth, an absence of permanent teeth except for the third molar, and crown restorations covering the cusp of a tooth were excluded. As a result of this initial selection process, 25 subjects (18 females, with a mean age of 20.22.5years and an age range from 18.5 to 28.4 years, and 7 males, with a mean age of 21.02.2years and an age range from 18.8 to 23.7 years) were selected from among the students. Next, lateral cephalograms, panoramic X-rays, and dental casts were taken of these 25 subjects. Cephalometric analyses of these 25 subjects were conducted using Dolphin Imaging software (Dolphin Imaging System, Canoga Park, CA, USA), and 18 BMDP subjects were selected based on Keating’s criteria [12]. Ultimately, 34 subjects (21 females, with a mean age of 20.9 3.0years and an age range from 15.6 to 28.4 years, and 13 males, with a mean age of 22.52.2years and an age range from 18.8 to 26.7 years) were selected as the BMDP group. To confirm the consistency of the amount of incisor proclination of the subjects in the BMDP group, the results of the cephalometric analyses of the dental students (n=18: female: male=12: 6) and the orthodontic patients (n=16: female: male=9: 7) were compared, and no statistically significant differences in interincisal angle, maxillary incisors to palatal plane angle, and mandibular incisors to mandibular plane angle were detected using the nonparametric Mann–Whitney test.
2.1.
2.2.
effective in treating BMDP in permanent dentition; however, few studies on this treatment are available in the literature [1]. In addition to various conventional methods of anchorage reinforcement, including headgear and/or a trans-palatal arch, a temporary anchorage device (TAD) has recently been used in the treatment of adult BMDP patients [4], which presents some risks [5,6]. In a case-control cephalometric study conducted by Bills et al. [1] in Chicago, the anteroposterior width of the alveolus in 48 BMDP patients with fourpremolar extractions was compared with that of normal occlusions [7]. The authors observed a narrower anteroposterior width of the alveolus in the BMDP patients and potential limitation of the posterior movement of the root apexes of the central incisors. However, the initial anteroposterior positions of the root apexes of the incisors in the alveolar processes of the maxilla and mandible in Class I BMDP have not been investigated. Furthermore, in addition to the space obtained by extracting the four first premolars to retract the protruded anterior teeth, distalizing all of the teeth using TAD has recently been applied in BMDP cases [8]. When adequate posterior space is not available, buccally displaced second molars and/or severely impacted third molars may be a risk of molar distalization in post-pubertal patients [9]. There is little scientific evidence to support this strategy; therefore, understanding the relationship between the mesiodistal tooth crown diameter and the posterior available space in both BMDP and normal occlusion is necessary to evaluate the posterior discrepancy for BMDP. Most studies of BMDP have focused on the protruded and proclined anterior teeth, whereas the crown angulation of the posterior teeth influenced by the anterior teeth has not been investigated. Compensatory changes in the angulation of molars as a result of sagittal relationships of skeletal or dental features [10] and significant mesial tipping of the mandibular molars in Class I malocclusion subjects [11] have been reported. Therefore, the angulations of the canines and molars in BMDP require investigation because of their effects on anchorage control. The purpose of the present study was to investigate the characteristics of the antero-posterior positions of teeth in subjects with Class I BMDP compared with those of subjects with normal occlusion and balanced profile from the same population.
2.
Methods
BMDP group
The orthodontic diagnostic records, including facial and intraoral photographs, cephalograms, panoramic X-rays,
Control group
We selected 39 subjects (24 females, with a mean age of 20.21.6years and an age range from 15.6 to 23.5 years, and
Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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15 males, with a mean age of 23.73.1years and an age range from 19.2 to 29.3 years) with Class I molar relationships and balanced facial profile as the control group. These subjects were students at The Nippon Dental University and related dental colleges who met the following inclusion criteria: Angle Class I molar relationship, 2.0mm
The BMDP group included a greater number of female subjects than male subjects because of differences in patient concern about facial esthetics related to protruding anterior teeth and a convex profile. Therefore, the numbers of female and male subjects in the control group were adjusted to maintain balance.
2.3.
Cephalometric measurements
To confirm the skeletal and dental pattern of the BMDP group, all cephalometric parameters were compared with those of the control group (Table 1). The antero-posterior distances from the root apexes of central incisors to the labio-palatal or lingual cortical bones of the alveolar process in the maxilla and mandible [1,6] (UA, UP, LA, LP) (Table 2, Fig. 1) were measured and compared between the groups. Additionally, the antero-posterior widths of maxilla and mandible alveolar processes at the level of the root apex (UA+UP, LA+LP) were also measured and compared between the groups [1].
Control group
Statistical analysis
Quartile deviation
Median
Quartile deviation
P-value
Horizontal
Angular parameter (degrees) SNA 82.10 80.25 SNB 2.95 ANB 7.20 Angle of convexity
2.49 2.96 1.77 3.89
83.50 80.00 2.90 5.10
2.90 2.35 2.20 4.70
0.462 0.774 1.00 0.362
Vertical
Table 1 – Comparisons of the median and quartile deviations of the cephalometric parameters between the BMDP and control groups. BMDP group
PP-SN SN-MP FMA
7.70 33.95 26.50
2.04 5.59 4.24
7.70 35.90 29.60
1.90 3.20 3.25
0.974 0.367 0.063
Linear parameter (mm) N-S Go-Pog
67.75 79.25
4.37 6.02
69.70 80.40
15.15 2.55
0.266 0.344
86.30 125.95
9.98 12.85
87.30 129.30
7.95 7.40
0.934 0.299
4.24 4.75 5.55 3.54 3.76 4.18
113.20 104.70 127.70 93.70 23.00 28.70
2.60 3.85 5.70 4.05 3.80 1.95
0.000** 0.000** 0.000** 0.000** 0.000** 0.000**
2.34 5.49
6.00 7.00
2.50 1.95
0.000** 0.000**
1.84 2.29 6.25
2.90 0.70 101.30
1.35 1.20 6.20
0.000** 0.000** 0.001**
Horizontal
Soft tissue
Dental
Vertical
Skeletal
Measurements
**
S-Go AFH
Median
Angular parameter (degrees) 125.65 U1-PP U1-SN 116.50 U1-L1 102.25 L1-MP 104.40 U1-NA 34.10 L1-NB 38.80 Linear parameter (mm) 11.95 U1-NA L1-NB 11.50 Linear parameter (mm) UL to E-line LL to E-line Nasolabial angle
0.35 4.15 93.85
P < 0.01.
Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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Table 2 – Cephalometric measurements of the antero-posterior positions of the root apex of the central incisors and the posterior available space. Measurement UA (width of maxillary anterior alveolus)
The linear distance between the apex of the maxillary central incisors and the limit of the labial cortex, along a plane parallel to the palatal plane, drawn through the apex
UP (width of maxillary posterior alveolus)
The linear distance between the apex of the maxillary central incisors and the limit of the palatal cortex, along a plane parallel to the palatal plane, drawn through the apex
U6-Ptm
Maxillary posterior available space for the second and third molars. The linear distance between the most distal point of the maxillary first molar and the perpendicular line to the palatal plane crossing the Ptm point.
A-Ptm
Antero-posterior dimension of the maxillary basal bone. The linear distance between the perpendicular lines to the palatal plane crossing the Ptm point and the A point
LA (width of mandibular anterior alveolus)
The linear distance between the apex of the mandibular central incisors and the limit of the labial cortex, along a plane parallel to occlusal plane, drawn through the apex
LP (width of mandibular posterior alveolus)
The linear distance between the apex of the maxillary central incisors and the limit of the lingual cortex, along a plane parallel to the occlusal plane, drawn through the apex
L6-Mr
Mandibular posterior available space for the second and third molars. The linear distance between the most distal point of the mandibular first molar and the perpendicular line to the palatal plane crossing the Mr point
B-Mr
Antero-posterior dimension of the mandibular basal bone. The linear distance between the perpendicular lines to the palatal plane crossing the Mr point and the A point
In addition, the total dentition space (A-Ptm, B-Mr) and the posterior available space in the maxilla and mandible [9] (U6Ptm, L6-Mr) (Table 2, Fig. 1) were measured and compared between the groups.
2.4.
Dental cast measurements
The mesiodistal tooth crown diameters from the first molar to the first molar of each arch were measured using digital
calipers (NTD12-C, Mitutoyo, Kanagawa, Japan) with an accuracy of up to 0.01mm. The dental casts were then laser scanned (Surflacer model VMS-100F, UNISN, Osaka, Japan) [13]. The facial axis (FA) point was defined as the midpoint of the FA of the clinical crown and was selected for each tooth from the first molar to the first molar (Fig. 2) [14]. The canine and molar widths and depths were also calculated (Fig. 2), and the crown angulation was measured via 3D dental cast analysis (Fig. 3) [14].
Fig. 1 – Cephalometric measurements. Measurement of the distances from the root apexes of central incisors to the labio-palatal or lingual cortical bones of the alveolar process and from the first molar to the posterior limit of the eruption spaces to define the posterior available space in the maxilla and mandible. Mr: the intersection point of the occlusal plane and the anterior border of the mandibular ramus. Ptm: the point at the base of the fissure where the anterior and posterior wall meet. Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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Fig. 2 – Dental arch dimensions: (a) maxillary dental cast; (b) mandibular dental cast.
2.5.
Reliability of the method
To calculate the measurement error of the cephalometric measurements (UA, UP, LA, LP) (A-Ptm, B-Mr, U6-Ptm, L6-Mr), 5 cephalograms were randomly selected from the two groups. Intra-examiner error was determined for one operator and
calculated using Dahlberg’s formula [15] (SE=
qX ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi d2 =2n) as
0.620.18mm on average. Inter-examiner error was determined with a second operator and calculated in the same way as 0.680.21mm on average. In addition, we calculated the respective intra- and inter-examiner errors with regards to dental measurements as 0.250.17mm and 0.250.16mm for
Fig. 3 – Crown angulation: (a) maxillary dental cast; (b) mandibular dental cast. To measure crown angulation, the facial axis of the clinical crown of each tooth was drawn. Occlusal planes were formed by the anterior reference point, defined by the midpoint of the line segment connecting the bilateral incisal points (the center of the incisor edge), and the posterior reference points (the mesial palatal cusp tip of the bilateral first molars for the maxillary arches and the distal buccal cusp tip of the bilateral second molars for the mandibular arches). The crown angulation was calculated as the angle between the facial axis of the clinical crown for each tooth and the plane perpendicular to the occlusal plane. A positive value indicated mesial angulation, and a negative value indicated distal angulation. Please cite this article in press as: S. Akiyama, K. Arai, Antero-posterior positions of teeth in bimaxillary dentoalveolar protrusion, Orthod Waves (2016), http://dx.doi.org/10.1016/j.odw.2016.11.003
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the mesiodistal tooth crown diameter, 0.170.05mm and 0.220.07mm for the dental arch dimensions, and 0.880.08 and 0.980.14 for crown angulation.
2.6.
Statistical analysis
The normality of the data distribution was tested using the Kolmogorov–Smirnov test. The mean and standard deviation of the cephalometric measurements (UA, UP, LA, LP, UA+UP, LA+LP) (A-Ptm, B-Mr, U6-Ptm, L6-Mr) were calculated for the BMDP and control groups, and an independent t-test was used for between-group comparisons. The median and quartile deviation were calculated for the mesiodistal tooth crown diameters, dental arch dimensions, and crown angulations for each group. Nonparametric Mann– Whitney tests were used to compare the two groups because these measurements did not fit a normal distribution. All of the statistical tests were evaluated at the 5% level.
3.
Results
3.1.
Cephalometric measurements
Table 3 – Comparisons of the means and standard deviations (SDs) of the distances from the root apex of the central incisors to the cortical bones of the alveolar process and the posterior available space between the BMDP and control groups (mm). BMDP group Control group Statistical analysis Mean
SD
Mean
SD
t-Value
P-value
Maxilla UA UP UA +UP U6-Ptm A-Ptm
5.48 6.54 12.02 15.15 45.30
1.38 2.17 2.80 3.07 4.06
4.91 7.85 12.77 14.45 46.67
0.84 1.87 2.13 2.22 3.61
2.14 2.76 1.30 1.10 1.52
0.007** 0.036* 0.197 0.277 0.130
Mandible LA LP LA +LP L6-Mr B-Mr
3.40 3.88 7.28 15.42 41.40
0.81 0.83 1.38 2.84 4.42
3.14 3.57 6.71 14.35 43.18
0.72 0.91 1.52 2.39 4.20
1.45 1.54 1.69 1.73 1.76
0.153 0.128 0.096 0.089 0.081
* **
P <0.05. P <0.01.
3.2.
Dental cast measurements
Significantly greater mesiodistal tooth crown diameters were observed for all teeth in the BMDP group compared with the control group. Although there was no significant difference in the dental arch widths between the groups, the dental arch depths in the BMDP group were significantly longer than control group (Table 4). The crown angulations of the canines and first premolars in the maxillary arch and the canines and the first and second premolars in the mandibular arch were significantly greater in the BMDP group (Table 5).
4.
The BMDP group showed significantly (P<0.05) more protruded and proclined incisors and lip procumbency. However, in the skeletal parameters, no significant differences were observed between the groups (Table 1). For the antero-posterior distances from the root apex of the maxillary central incisor to the labial and palatal cortical bones of the alveolar process of the maxilla, UA and UP were significantly greater and lesser, respectively, in the BMDP group than in the control group (Table 3). For the mandibular central incisor (LA, LP), no significant differences were observed between the groups (Table 3).
Tooth
No significant differences were observed in the maxillary and mandibular widths of alveolar bone (UA+UP, LA+LP) between the groups (Table 3). No significant differences were observed between the groups for all parameters measuring the total dentition spaces (A-Ptm, B-Mr) and the posterior available spaces (U6-Ptm, L6-Mr) in the maxilla and mandible (Table 3).
Discussion
Although no worldwide epidemiological studies are available at present, malocclusion with BMDP is commonly observed in African–American [16] and East Asian populations [17,18] but can be observed in nearly every ethnic group [1], including Caucasian populations [12]. Margolis [19] proposed the distinction of bimaxillary prognathism from bimaxillary protrusion; the former is of phylogenetic origin, and the latter, as it applies in orthodontics, implies an ontogenetic influence. His hypothesis has been supported by cephalometric studies in the Japanese population [20,21]. Bills et al. [1] selected BMDP subjects representing multiple ethnic groups in consideration of racial differences, but studies of individual ethnic groups are also warranted. Several studies have used lateral cephalometric radiographs to clarify the morphological skeletal characteristics of BMDP, yet no consensus has been reached [12,22]. To confirm the skeletal pattern of the BMDP group in the present study, cephalometric analyses were conducted, including the total dentition spaces [14] such as A-Ptm for maxillary and B-Mr for mandibular dental arches. No significant differences in skeletal patterns and total dentition spaces were observed between the BMDP group and the control group, which consisted of subjects with normal occlusion and a balanced facial profile. Although four out of thirty-four BMDP subjects showed larger SNA and SNB angles than the normal range (adding the standard deviation to the mean of control group), these findings, therefore, suggested that there is no indication of necessity for orthognathic surgery in general. In addition, although no significant differences in vertical skeletal measurements were observed between the groups in the present study, a high angle tendency is often clinically observed in bimaxillary protrusion. Therefore, investigation of the vertical dental and skeletal components in more detail may be useful in future studies.
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Table 4 – Comparisons of the median and quartile deviations of the mesiodistal tooth crown diameter and dental arch dimensions between the BMDP and control groups (mm). Measurement
Maxillary arch Tooth crown diameter
Dental arch dimension
Mandibular arch Tooth crown diameter
Dental arch dimension
**
BMDP group
Control group
Statistical analysis
Median
Quartile deviation
Median
Quartile deviation
P-value
Central incisor Lateral incisor Canine First premolar Second premolar First molar
8.79 7.28 8.20 7.59 7.09 10.49
0.46 0.47 0.43 0.22 0.33 0.45
8.44 7.00 7.78 7.28 6.79 10.04
0.32 0.38 0.34 0.28 0.27 0.42
0.000** 0.000** 0.000** 0.000** 0.000** 0.000**
Canine width First molar width Canine depth First molar depth
39.68 58.42 9.55 33.15
1.77 1.98 1.01 1.62
38.18 57.70 8.36 31.32
1.23 1.90 0.57 1.19
0.302 0.745 0.000** 0.000**
Central incisor Lateral incisor Canine First premolar Second premolar First molar
5.66 6.26 7.09 7.55 7.40 11.67
0.21 0.19 0.31 0.33 0.33 0.36
5.35 5.94 6.84 7.27 7.09 11.23
0.21 0.20 0.29 0.30 0.29 0.35
0.000** 0.000** 0.000** 0.001** 0.000** 0.000**
Canine width First molar width Canine depth First molar depth
30.85 52.76 5.23 27.70
0.26 2.11 0.57 1.30
29.74 51.58 4.79 26.35
0.91 1.83 0.54 1.22
0.065 0.439 0.002** 0.000**
P < 0.01.
Table 5 – Comparisons of the median and quartile deviations of the crown angulations between the BMDP and control groups (degrees). BMDP group
Tooth Median
Quartile deviation
Maxillary arch Central incisor Lateral incisor Canine First premolar Second premolar First molar
1.67 4.58 11.63 2.74 3.77 2.96
2.90 2.47 5.14 4.31 4.09 3.11
Mandibular arch Central incisor Lateral incisor Canine First premolar Second premolar First molar
1.48 0.43 3.98 4.51 6.69 4.41
2.53 3.40 3.68 3.70 3.60 3.30
* **
Control group Median
Statistical analysis
Quartile deviation
P-value
1.66 4.78 6.65 1.57 3.63 4.71
2.12 2.37 3.39 3.49 3.25 3.69
0.665 0.909 0.000** 0.034* 0.564 0.090
1.12 1.20 0.38 0.58 3.75 4.99
2.44 2.28 3.15 3.02 3.37 4.07
0.669 0.051 0.000** 0.000** 0.011* 0.970
P < 0.05. P < 0.01.
Recently, a new molar distalization technique using TAD has been proposed for the treatment of BMDP [8], in which analysis of the posterior space is conducted based on the mesiodistal tooth crown diameter and the space between the first molar and the anterior border of the ramus [9]. In the present study, no significant differences in the posterior available space in the maxilla and mandible (U6-Ptm, L6-Mr)
were observed between the two groups, whereas significantly greater mesiodistal tooth crown diameters were observed in the BMDP group. These findings indicate that the molar distalization technique presents a possibility for posterior discrepancy in both arches and potential increased risks of third molar impaction [23] and upper airway narrowing after treatment [24]. Thus, before conducting molar distalization in
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BMDP patients, the presence of third molars should be confirmed, the posterior space should be analyzed, and the option of tooth extraction should be presented to patients. The antero-posterior distances of the root apex of the maxillary central incisor to the palatal cortical bone of the alveolar process of the maxilla (UP) in the BMDP group were significantly smaller than those in the control group. The cephalometric and dental cast analyses showed that the maxillary central incisor in the BMDP group was 13.58 proclined in U1-PP and 5.29mm protruded in U1-NA compared with the control group (Table 1), and the obtainable space by the extraction of the maxillary first premolar was 7.59mm on average in the BMDP group (Table 4). These findings indicate the need for maximum anchorage mechanics to retract the anterior teeth to the normal position in most BMDP cases, even with mild crowding. However, in the present study, UP was 6.54mm in the BMDP group, and the antero-posterior position of the root apex of the maxillary central incisor in the alveolar process of the maxilla was 1.31mm more palatally located, on average, in the BMDP group compared with the control group, although variation was observed among individuals (Table 3). These findings suggest an increased possibility of the apical root resorption of incisors through contact between the root apex and the palatal cortical bone or the incisive canal in BMDP patients after retraction over about 6.5mm with maximum anchorage mechanics such as TAD because of the absolute retraction of the maxillary incisors that occurs through bodily movement [5]. Similarly, the limitations placed upon orthodontic treatment by a thin alveolar have been reported about Angle Class II division 1 malocclusion with large overjet [6]. Therefore, there will be value in comparing Angle Class II malocclusion with Class I bimaxillary protrusion statistically in the future. Tooth size differences among ethnic groups and occlusal categories have often been reported, and they suggest the possible role of genetic factors in malocclusion [25]. Regarding BMDP, McCann and Burden [26] compared the tooth sizes of 30 Northern Irish people with Class I BMDP with those of 30 people with other malocclusions without BMDP. They found a significantly greater tooth size in the BMDP group and hypothesized that this anatomical characteristic may contribute to the proclination of the incisors. The results of the present study confirm these previous findings [26] in another ethnic group. Although environmental factors, including lip function and tongue size, have been considered a major cause of BMDP [27], these results suggest the influence of genetic background on this malocclusion. The present study is the first to investigate the crown angulation on the dental cast in BMDP. Significantly greater mesial tipping of the maxillary canine and first premolar and the mandibular canine and premolars was observed in the BMDP group compared with the control group. These results suggest the mesial tipping of canine and premolars and relatively distal positions of roots to the crowns of those teeth [28]. In addition, greater mesiodistal tooth crown diameters and longer arch depths in BMDP patients may provide a greater amount of incisor retraction for achieving a balanced profile [26]. However, these findings also suggest a higher possibility of the loss of anchorage control, i.e., unfavorable mesial root movements of the canines and mandibular second premolars.
Therefore, clinicians should take measures to avoid the loss of anchorage during the alignment phase of the most popular modality of this malocclusion with extraction of the four first premolars [1,17,18]. However, linear measurements in cephalometric analysis or mesiodistal tooth crown diameters in dental cast analysis were compared using a mixture of male and female subjects in the present study. Female subjects were included because the number of male subjects of the BMDP group was not sufficient for statistical comparison. In future studies, comparisons of each measurement between females and males may be considered very significant if sufficient numbers of male subjects in the BMDP group could be collected. In addition, our results of reliability tests using Dahlberg’s formula showed the values close to the differences between the groups about the cephalometric measurements. In the present study, we used only cephalograms to evaluate the antero-posterior positions of the root apexes of the maxillary central incisors. Therefore, we may need to confirm these results diagnostic tools with higher accuracy, for example, using the cone beam CT.
5.
Conclusions
Comparisons between subjects with bimaxillary dentoalveolar protrusion and subjects with normal occlusion and balanced profile from the same population revealed the following: 1. A significantly more palatally located root apex of the maxillary central incisor to the cortical bone of the alveolar process of the maxilla was found in BMDP. 2. Significantly greater mesiodistal tooth crown diameters and larger canine and molar depths in the maxillary and mandibular arch were found in BMDP. 3. Significantly greater mesial crown angulations were observed for the maxillary canines and first premolars and the mandibular canines and first and second premolars in BMDP.
Conflict of interests The authors have no conflicts of interest to declare.
Ethical approval All subjects provided written informed consent to participate in this study. The experimental protocol was approved by the Ethics Committee of The Nippon Dental University (approval number: NDU-T2013-32). REFERENCES
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