Posterior tooth angulations in patients with anterior open bite and normal occlusion

Introduction

The aim of this study was to compare the posterior tooth angulations in patients with open-bite malocclusion and normal occlusion.

Methods

Lateral cephalometric headfilms of 45 untreated open-bite subjects were compared with the lateral headfilms of 45 subjects with normal occlusion in the permanent dentition. The groups were matched for age and sex distribution and compared with t tests.

Results

The maxillary and mandibular premolars were more mesially angulated in relation to the bisected occlusal plane, and the first and second molars were significantly more distally angulated in the open-bite group in relation to the palatal and mandibular planes.

Conclusions

The maxillary and mandibular premolars were more mesially angulated in relation to the bisected occlusal plane and therefore do not compensate for the divergence of the palatal and mandibular planes as the molars do.

Highlights

  • We compared the posterior tooth angulations in open-bite and normal occlusions.

  • Premolars had a greater mesial angulation in the open-bite group.

  • Molars had a greater distal angulation in the open-bite group.

Malocclusion is caused by an imbalance in the complex interactions among the facial growth pattern, causative local factors, and the lack of a dentoalveolar compensation mechanism. In particular, anterior open-bite malocclusions associated with a strong vertical component are the most challenging to treat. Combinations in vertical dysplasia are various, so that a patient with a long face can have a deepbite, and a patient with a short face is not excluded from developing an anterior open bite.

The pioneer implant studies of Björk and Björk and Skieller showed the influence of the rotation of the apical bases on the final tooth positions. Solow described in more detail the dentoalveolar compensatory mechanism, and Kim stated that in skeletal open-bite subjects the posterior teeth have a marked mesial angulation when measured in relation to the bisected occlusal plane (BOP), and a major treatment objective is to upright these teeth to facilitate bite closure. Since these reports, there have been few specific studies evaluating this dental feature, which is regarded as an anterior open-bite characteristic. Much attention has been given to the compensatory vertical dentoalveolar development of the posterior and anterior teeth in open-bite malocclusions and not to the posterior tooth mesiodistal angulations.

Therefore, the aim of this study was to test the null hypothesis that there is no difference in posterior tooth angulations in patients with open-bite malocclusion and normal occlusion.

Material and methods

This study was approved by the ethics in research committee of Bauru Dental School, University of São Paulo, Brazil, with research protocol number 20303213.2.0000.5417.

The sample size calculation, considering an 80% test power at a significance level of 5%, with a minimum mean difference to be detected of 3° and a mean standard deviation of 5°, showed that 45 subjects in each of the 2 groups were the minimum for providing reliable results. The minimum mean difference to be detected and the standard deviation of the maxillary first premolar in relation to the bisected occlusal plane were based on a previous study.

The sample, consisting of lateral headfilms of 90 (43 male, 47 female) untreated subjects in the permanent dentition, selected from the files of the Department of Orthodontics at Bauru Dental School, University of São Paulo, Brazil, was divided into 2 groups, based on the amount of overbite, regardless of cephalometric characteristics. All subjects had all permanent teeth up to the second molars.

Group 1 (open bite) consisted of lateral headfilms obtained from 45 (20 male, 25 female) untreated subjects of Mediterranean ancestry, with a mean age of 13.95 years (range, 12-19.75 years); their open bites ranged from 0.5 to 8.7 mm, with a mean of 2.68 mm. Twenty-four had Class II, 17 had Class I, and 4 had Class III malocclusions.

Group 2 (normal occlusion) consisted of lateral headfilms obtained from 45 (23 male, 22 female) subjects with a mean age of 13.83 years (range, 12-15.33 years), with overbites from 0.5 to 4.7 mm, with a mean of 3.04 mm and pleasant facial profiles, of Mediterranean ancestry.

The cephalometric tracings and landmark identifications were performed on acetate paper by 1 investigator (V.L.) and then digitized with a digitizer (DT-11; Houston Instruments, Austin, Tex).

Overbite measurement was defined as the distance between the maxillary and mandibular incisor borders perpendicular to the functional occlusal plane ( Fig 1 ).

Fig 1
Overbite measurement was defined as the distance between the maxillary and mandibular incisor borders, perpendicular to the functional occlusal plane.

In total, 129 landmarks were identified, and 30 measurements were performed ( Table I ). Posterior tooth angulations were measured in the maxillary and mandibular arches and consisted of measuring the angles between the premolars’ (apex-cusp tip) and the molars’ long axes (furcation-center of the crown) to the BOP ( Fig 2 , A ) and to the palatal plane (ANS-PNS) ( Fig 2 , B ) and the mandibular plane ( Fig 3 , A ). The interpremolar and intermolar angulations were measured as well ( Fig 3 , B ). The BOP was obtained by bisection of the maxillary occlusal plane (from the distal buccal cusp of the maxillary second molar to the incisal edge of the most extruded maxillary central incisor) and the mandibular occlusal plane (from the distal buccal cusp of the mandibular second molar to the incisal edge of the most extruded mandibular central incisor).

Table I
Cephalometric variables
Maxillomandibular relationship (°)
SNA SN to NA angle
SNB SN to NB angle
ANB NA to NB angle
Growth pattern
SN.PP (°) SN to the palatal plane angle
SN.GOGN (°) SN to Go-Gn angle
PP.MP (°) Angle between the palatal plane (ANS/PNS) and the mandibular (Go/Gn) plane
FMA (°) Frankfort horizontal to the mandibular plane angle
Gonial angle (°) Ar-Go to Go-Gn angle
LAFH (mm) Lower anterior face height: distance from ANS to menton
Dental relationship (mm)
Overbite Distance between the maxillary and mandibular incisor borders perpendicular to the functional occlusal plane
Maxillary mesiodistal angulations (°)
Mx4.BOP Long axis of the maxillary first premolar to the BOP
Mx5.BOP Long axis of the maxillary second premolar to the BOP
Mx6.BOP Long axis of the maxillary first molar to the BOP
Mx7.BOP Long axis of the maxillary second molar to the BOP
Mx4.PP Long axis of the maxillary first premolar to the ANS-PNS angle
Mx5.PP Long axis of the maxillary second premolar to the ANS-PNS angle
Mx6.PP Long axis of the maxillary first molar to the ANS-PNS angle
Mx7.PP Long axis of the maxillary second molar to the ANS-PNS angle
Mandibular mesiodistal angulations (°)
Md4.BOP Long axis of the mandibular first premolar to the BOP
Md5.BOP Long axis of the mandibular second premolar to the BOP
Md6.BOP Long axis of the mandibular first molar to the BOP
Md7.BOP Long axis of the mandibular second molar to the BOP
Md4.MP Long axis of the mandibular first premolar to the mandibular plane (Go-Gn) angle
Md5.MP Long axis of the mandibular second premolar to the Go-Gn angle
Md6.MP Long axis of the mandibular first molar to the Go-Gn angle
Md7.MP Long axis of the mandibular second molar to the Go-Gn angle
Interdental angulations (°)
Mx4.Md4 Long axes of the maxillary and mandibular first premolars
Mx5.Md5 Long axes of the maxillary and mandibular second premolars
Mx6.Md6 Long axes of the maxillary and mandibular first molars
Mx7.Md7 Long axes of the maxillary and mandibular second molars

Fig 2
A, Maxillary and mandibular posterior tooth angulation measurements in relation to the BOP: 1 , Mx4.BOP; 2 , Mx5.BOP; 3 , Mx6.BOP; 4 , Mx7.BOP; 5 , Md4.BOP; 6 , Md5.BOP; 7 , Md6.BOP; 8 , Md7.BOP. B, Maxillary posterior tooth angulation measurements in relation to the palatal plane (PP): 1 , Mx4.PP; 2 , Mx5.PP; 3 , Mx6.PP; 4 , Mx7.PP.

Fig 3
A, Mandibular posterior teeth angulation measurements in relation to the mandibular plane (MP): 1 , Md4.MP; 2 , Md5.MP; 3 , Md6.MP; 4 , Md7.MP. B, Intermolar and interpremolar angulation measurements: 1 , Mx4.Md4; 2 , Mx5.Md5; 3 , Mx6.Md6; 4 , Mx7.Md7.

These data were stored in a computer and analyzed with Dentofacial Planner software (version 7.0; Dentofacial Software, Toronto, Ontario, Canada), which corrected the image magnification factors of the x-rays.

The lateral headfilms obtained in the open-bite group were taken with various x-ray machines, which produced different magnification factors of the images, ranging from 6% to 10.94%. All lateral cephalograms in the normal occlusion group were taken with the same x-ray machine, which had a magnification factor of 6%.

To evaluate the intraexaminer errors, 14 radiographs were randomly selected, traced, digitized, and measured again by the same operator (V.L.) after a 30-day interval. The random errors were calculated according to Dahlberg’s formula (Se 2 = ∑d 2 /2n), where Se 2 is the error variance and d is the difference between 2 determinations of the same variable, and the systematic errors were calculated with dependent t tests, at P <0.05.

Statistical analyses

To assess normal distribution of the data in the sample, Kolmogorov-Smirnov tests were performed. All variables had a normal distribution in both groups.

We used t tests to evaluate the groups’ comparability regarding age, and the chi-square test was used to compare the groups regarding sex distribution.

Intergroup comparisons of all variables were performed with t tests.

The results were considered significant at P <0.05. All statistical analyses were performed with Statistica software (Statistica for Windows, version 10.0; StatSoft, Tulsa, Okla).

Results

No systematic errors were found, and the random errors were within acceptable limits, varying from 0.47° (ANB) to 3.99° (Mx7.BOP).

The 2 groups where comparable regarding age and sex distribution ( Tables II and III ).

Table II
Intergroup comparison for age ( t test)
Variable Group 1, open bite
(n = 45)
Group 2, normal occlusion
(n = 45)
P
Mean SD Mean SD
Age (y) 13.95 1.89 13.83 0.95 0.700

Table III
Sex distribution in the groups (chi-square test)
Group Sex
Boys Girls Total
Group 1, open bite 20 25 45
Group 2, normal occlusion 23 22 45
Total 43 47 90
Chi-square = 0.04; degrees of freedom = 1; P = 0.833.

The open-bite group showed significantly more retruded mandibles, greater Class II skeletal relationships, and more upward inclinations of the palatal plane than did the normal occlusion group ( Table IV ). There were also significantly more accentuated vertical growth patterns and smaller overbites in the open-bite group.

Table IV
Intergroup comparison of all variables ( t tests)
Variable Group 1, open bite (n = 45) Group 2, normal occlusion (n = 45) P
Mean SD Mean SD
Maxillomandibular relationship (°)
SNA 81.88 6.09 81.76 3.65 0.911
SNB 77.16 5.17 79.32 3.01 0.017
ANB 4.71 2.90 2.44 1.92 0.000
Growth pattern
SN.PP (°) 6.58 3.62 8.40 3.03 0.001
SN.GoGn (°) 39.52 6.64 32.38 4.72 0.000
PP.MP (°) 32.93 5.45 23.98 4.58 0.000
FMA (°) 33.68 5.15 28.32 4.61 0.000
Gonial angle (°) 129.26 5.57 125.84 6.74 0.010
LAFH (mm) 71.54 5.57 63.94 4.58 0.000
Dental relationship (mm)
Overbite −2.68 2.05 3.04 1.10 0.000
Maxillary mesiodistal angulations (°)
Mx4.BOP 75.47 5.04 79.23 4.34 0.000
Mx5.BOP 83.95 3.89 86.56 3.69 0.001
Mx6.BOP 90.78 4.72 89.94 4.28 0.378
Mx7.BOP 99.57 6.16 96.80 5.75 0.030
Mx4.PP 94.94 5.33 94.25 5.20 0.538
Mx5.PP 86.47 5.09 86.94 4.73 0.653
Mx6.PP 79.64 5.62 83.55 4.49 0.000
Mx7.PP 70.84 7.38 76.69 5.54 0.000
Mandibular mesiodistal angulations (°)
Md4.BOP 76.65 5.74 82.95 4.21 0.000
Md5.BOP 78.46 5.43 84.05 4.11 0.000
Md6.BOP 81.37 4.82 82.22 4.20 0.377
Md7.BOP 76.56 5.29 78.07 5.18 0.174
Md4.MP 79.99 5.77 79.56 5.14 0.712
Md5.MP 78.18 4.97 78.47 5.19 0.786
Md6.MP 75.27 5.41 80.30 4.23 0.000
Md7.MP 80.08 5.74 84.45 4.48 0.000
Interdental angulations (°)
Mx4.Md4 152.13 6.93 162.20 6.21 0.000
Mx5.Md5 162.40 6.66 170.61 5.10 0.000
Mx6.Md6 171.97 5.31 172.08 3.81 0.914
Mx7.Md7 175.96 7.00 174.88 4.21 0.376
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Apr 4, 2017 | Posted by in Orthodontics | Comments Off on Posterior tooth angulations in patients with anterior open bite and normal occlusion
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