Dental Arch Dimensions in Class II division 1 Malocclusions with Mandibular Deficiency
Objective: To test the hypothesis that there is no difference in the dimensions of the upper and lower dental arches in Class II division 1 malocclusion with a mandibular deficiency compared to normal Class I occlusion dental arches.
Materials and Methods: Photocopies of the dental arches of 48 patients exhibiting Class II division 1 malocclusion with mandibular deficiency and of 51 individuals with normal occlusion were compared. Mandibular deficiency was diagnosed clinically. All 99 individuals were in the permanent dentition. The ages of the subjects ranged from 11 years 4 months to 20 years (mean age = 12 years 5 months).
Results: When compared to subjects with normal occlusion, the upper dental arches of the Class II division 1 patients presented reduced transverse dimensions and longer sagittal dimensions while the lower arches were less influenced.
Conclusion: The hypothesis is rejected. Significant differences are present between the dimensions of the upper and lower dental arches in Class II division 1 malocclusion (with a mandibular deficiency and in the permanent dentition) compared to normal Class I occlusion dental arches.Abstract
INTRODUCTION
The real prevalence of Class II malocclusion is difficult to determine because of different methods used in studies and ethnic characteristics of the samples. Studies show that the prevalence of Class II division 1 and division 2 malocclusions varies from 8.6%1 to 33.7%2 and from 0.6%1 to 6.7%,3 respectively. An accurate occlusal analysis performed in Brazil showed that Class II constitutes almost 50% of the malocclusions in the deciduous4 and mixed5 dentitions.
Class II malocclusion can be constituted by upper dental proclination, mandibular deficiency, or both. A study relating Class II malocclusion to facial analysis showed that about 15% of the students with mixed dentition in Bauru, Brazil, present with mandibular deficiency, of which 11.5% are division 1 and 3.5% are division 2.5 Therefore, Class II malocclusion is a frequent type of malocclusion and may be associated with skeletal patterns I and II. Figure 1 shows a skeletal Class II malocclusion with mandibular deficiency.
Citation: The Angle Orthodontist 78, 3; 10.2319/022307-89.1
Prior to the use of cephalometrics in orthodontics, mandibular deficiency had already been considered part of the Class II discrepancy. Cephalometrics confirmed this idea.6–14 As a consequence, functional orthopedics and orthognathic surgery gained importance in the treatment of mandibular retropositioning. However, mandibular advancement shows the posterior crossbite that frequently appears due to the constriction of the upper dental arch in Class II malocclusions that is associated with mandibular deficiency (Figure 2).
Citation: The Angle Orthodontist 78, 3; 10.2319/022307-89.1
Some changes can be identified in the shape of the dental arches to differentiate the Class II malocclusion. Studies that refer to the morphology of the upper and lower dental arches in Class II are shown in Table 1. It is suggested that the upper dental arch is vulnerable to Class II discrepancy. The constriction of the upper arch may be interpreted as transverse compensation to mandibular retropositioning. Such constriction requires that the transverse dimensions of the upper dental arch are increased during Class II treatment81516 whenever mandibular advancement is planned. Involvement of the upper dental arch in Class II malocclusions has been shown from the time of the deciduous dentition815–18 or from 7 years of age,1819 and it does not self-correct until the individual reaches mixed816 or permanent1518 dentition.
Studies of permanent dentition demonstrate the influence of the sagittal discrepancy on the intra-arch relationship. Buschang et al20 found that the upper dental arch is narrower and longer in women with Class II division 1 who are between 17 and 68 years old. Sayin and Turkkahraman21 found constriction in only the inter–upper second premolar and inter–upper molar widths and an increase in the inter–lower canine width in Class II division 1 women in the permanent dentition at an average age of 16 years. Staley et al22 noticed constriction of the upper dental arch in the intercanine and intermolar distances in Class II malocclusions, without any dimensional change in the lower dental arch widths in young adults. Uysal et al23 found constriction in the transverse dimensions of the upper dental arch and in the widths of the inter–lower premolars and inter–lower molars of young adults with Class II division 1.
Studies also show that the lower dental arch is more vulnerable to Class II division 2. When Uysal et al23 compared Class II division 1 and 2 malocclusions, they found that the inter-lower canine and inter-lower premolar widths were narrower while the inter-upper molar widths were wider in the division 2 in comparison to division 1. Bushang et al20 found reduced inter-lower canine and inter-lower molar distances in the Class II division 2 related to division 1 and to Class 1. Walkow and Peck24 found narrower inter-lower canine distances in the Class II division 2 malocclusions with deep overbite when related to division 1.
Staley et al22 suggested that the reduced transverse dimension of the upper dental arch in Class II division 1 constriction is due to the apical bases, similar to the data found by Alarashi et al19 and de Lux et al18 in anteroposterior radiographs. Contrarily, Sayin and Turkkahraman21 stated that the upper constriction is due to dental positioning only, as they found no difference in the alveolar widths between women with Class I and Class II malocclusions.
The current study tests the hypothesis that there is no difference in the dimensions of the permanent dentition of upper and lower dental arches in Class II division 1 malocclusion with a mandibular deficiency compared to normal Class I occlusion dental arches.
MATERIALS AND METHODS
Before onset, this retrospective study was revised and approved by the Institutional Review Board of the Hospital for Rehabilitation of Craniofacial Anomalies (HRCA), University of São Paulo, Bauru, Brazil. All patients were consecutively selected from an orthodontic archive that belongs to our hospital (HRCA).
The experimental group was composed of models of the upper and lower dental arches of 48 patients exhibiting Class II division 1 malocclusion with mandibular deficiency, equally matched for gender and ranging in age from 11 years 4 months to 18 years 4 months. All subjects in this group were Caucasians in permanent dentition, with the second molars either erupted or erupting, and the patients demonstrated untreated Class II division 1 malocclusions with a symmetric sagittal discrepancy of at least 4 mm in the premolar relationship. The selection of individuals was clinical and based on a soft-tissue profile analysis, with special attention to the nasolabial angle, which indicates participation of the maxilla in the malocclusion. All patients of the sample presented a satisfactory nasolabial angle, showing that the Class II malocclusion was due to mandibular deficiency. To standardize the sample, patients with protrusive maxillas (ie, obtuse nasolabial angle) were not included. Figures 1 and 2 illustrate the characteristics of the Class II sample.
The control group was composed of cast models of the upper and lower arches of 29 females and 22 males (n = 51) with normal occlusion and harmonious faces ranging in age from 11 to 20 years. The mean age for the experimental and control groups was 12 years 5 months (SD = 1 year 3 months).
All cast models were selected from the archive of the HRCA. The control normal occlusion patients were selected from the normal occlusion archive of the HRCA.
The transverse and sagittal dimensions of the dental arches were measured on photocopies of the upper and lower cast models of the experimental and control groups. All dental casts were placed on the central part of the glass surface of a photocopy machine (PRO 40; Xerox, Hertfordshire, UK) with the occlusal aspects of the teeth facing the glass. Photocopies of the models were obtained in a standardized manner. Care was taken to maintain the occlusal plane of the models parallel to the glass copying surface. Previous studies have shown no distortion in images obtained from photocopies.162526
The images of the models were measured with a digital caliper. The transverse distances of the canines were measured between their cusp tips. The premolar widths were measured between their buccal cusps. The molar widths were measured between the mesiobuccal cusps of the first molars. The sagittal dimension of the models was determined by the distance from the midpoint of the central incisors to the midpoint of a line tangent to the distal aspect of the first molars (Figure 3). Means and standard deviations were obtained for the transverse (3-3, 4-4, 5-5, 6-6) and sagittal dimensions for the upper and lower dental arches in both groups.
Citation: The Angle Orthodontist 78, 3; 10.2319/022307-89.1
The measurements were repeated by two examiners in some pairs of randomly selected models within 1 week. In all measurements, the error of the method was close to 0.5 mm, which gives high reliability to the measurements obtained in this study.
Descriptive statistics were illustrated by means of tables and graphs. A Student's t-test was used to check whether gender and malocclusion influenced the dimensions of the dental arches. Significance levels were 5% (P < .05) and 1% (P < .01).
RESULTS
Means and standard deviations were obtained for the transverse and sagittal measurements of the upper and lower dental arches of the sample groups, separated by gender. A Student's t-test was applied to verify sexual dimorphism. Statistical values are expressed in Tables 2 and 3. Table 2 shows that all dimensions of the upper and lower dental arches with normal occlusion presented higher values for males, about 2.25 mm for the upper arch and 1.6 mm for the lower arch. Table 3 shows the results for the study group and demonstrates that the widths of the inter–upper first premolars, inter–upper molars, inter–lower canines, inter–lower first premolars, and inter–lower second premolars showed statistically significant differences related to gender. Figures 4 and 5 depict the measurements shown in Tables 2 and 3 for the upper and lower dental arches, respectively.
Citation: The Angle Orthodontist 78, 3; 10.2319/022307-89.1
Citation: The Angle Orthodontist 78, 3; 10.2319/022307-89.1
Tables 4 and 5 show the differences in the Class II and normal occlusion groups. The measurements of the upper (Table 4) and lower (Table 5) dental arches were compared separately for the groups with normal occlusion and Class II division 1. Except for the intercanine distance in the females, all measurements of the upper dental arch in patients with Class II were different from those of subjects with normal occlusion.
Table 6 presents the differences in the sagittal and transverse dimensions of the upper arch with Class II when compared to the normal occlusion group, while Table 7 shows that the average difference between the dental arch widths in the normal occlusion group gradually decreases from 8.7 mm in the canine area to 6.7 mm in the molar area. This difference is clearly smaller in the Class II group (Table 8), decreasing from 6.8 mm to 4.2 mm.
DISCUSSION
This study aimed to determine the influence that the Class II malocclusion with a mandibular deficiency has on the dimensions of the dental arches. Studies rarely include Class II patients with mandibular retropositioning; thus, we decided to standardize our sample on the basis of mandibular deficiency. All 99 cast models analyzed represented the occlusion of subjects with permanent dentition. Forty-eight subjects exhibited untreated Class II division 1, while 51 showed normal occlusion. The sample included patients in permanent dentition because the sagittal and transverse dimensions of the dental arches at this time are practically defined and because this is the age when most patients seek orthodontic treatment. Longitudinal studies suggest that the dimensions of the dental arches tend to stabilize after 13 years of age in girls and 16 years in boys,927–30 although the dimensional changes that influence the intra-arch dental positioning are unpredictable and may occur anytime in normal occlusions.31
The results in Table 2 show higher values for males and are consistent with prior studies that assessed dental arch dimensions.27–29 However, in our study, the Class II group did not show the same differences (Table 3). Only the widths of the inter–upper first premolars, inter–upper molars, inter–lower canines, inter– lower first premolars, and inter–lower second premolars showed statistically significant differences related to gender. Class II malocclusion seems to minimize the influence of gender on the dimensions of the lower and, mainly, upper dental arch. Therefore, sexual dimorphism influenced all sagittal and transverse dimensions of the dental arches in individuals with normal occlusion and some transverse dimensions in Class II individuals. Because many dimensions were influenced by gender, the normal occlusion and the Class II groups were compared according to gender. This comparison is shown in Tables 4 and 5.
Class II malocclusions seem to induce changes in the dimensions and, consequently, the upper dental arch shape. With regard to the sagittal dimensions, the findings show statistically significant differences between the normal and Class II groups. Subjects with Class II malocclusion presented with longer upper dental arches, most likely due to the proclination of the upper incisors. The upper dental arch in the Class II subjects presented with lesser transverse dimensions (Table 4) and a typical triangular shape (Figures 1 and 2). A statistically significant difference was noticed in all measurements except in the upper intercanine distance in females.
Table 6 shows the sagittal and transverse differences between both groups, which indicate the average amount of expansion needed in the upper arch to transversely fit it to the advanced mandible in Class I patients. Therefore, constriction of the upper dental arch is not generally accompanied by posterior crossbite in the Class II division 1 patients. It has been suggested that constriction of the upper arch in the Class II patients is due to constriction of the nasomaxilary complex, identified in posteroanterior radiographs.1925 Frontal cephalograms show alterations in the upper dental arch with no transverse changes in the mandible and lower dental arch.1925
Similar to other researchers (Table 1), Fröhlich32 studied a longitudinal sample of 51 children aged 6 to 12 years and noticed that the sagittal discrepancy remained during the follow-up period, with an increase of the overjet and overbite after eruption of the permanent incisors. However, no difference was found in the dimensions of the dental arches with Class II. Such a contradiction is probably explained because the Class II divisions 1 and 2 subjects were gathered together in that sample. The current research does not confirm Fröhlich's32 results. On the contrary, our results agree with several other studies that have shown changes in the shapes of dental arches with Class II malocclusion.1921–2327
Despite other factors related to the upper arch constriction, such as oral breathing, prolonged sucking habits, and inadequate positioning and function of the tongue, the transverse adaptation of the upper arch to the lower arch may not be neglected. Such adaptation happens naturally as a transverse compensation of the upper arch to the retropositioning of the lower arch and is typical of Class II division 1 malocclusions. Therefore, dental compensation in Class II is neither restricted to the sagittal dimensions nor to the incisors. An accurate orthodontic tridimensional morphologic evaluation (Figures 1 and 2) would provide a complete and correct interpretation of the sagittal, transverse, and vertical alterations found in Class II malocclusions. The current study focuses on the transverse changes and corroborates the need for expanding the upper arch prior to mandibular advancement. The clinical confirmation of the upper arch constriction is evidenced by the posterior crossbite that results when the mandible is advanced and implies the achievement of a well-balanced final lateral relationship between the upper and lower arches following mandibular advancement.
The lower dental arch in Class II malocclusion (Table 5) shows more subtle changes that are restricted to its greater length and to the smaller interpremolar and intermolar dimensions, with statistical significance for females only. The longer lower arch is due to proclination of the lower incisors, which characterizes the dental compensation in Class II. The wide variation in the positioning of the lower incisors in Class II, from proclination to retroclination, has possibly camouflaged the statistical significance in males. Therefore, even if the lower arch tends to be longer, the difference between the upper and lower arches in comparison to normal occlusion (Table 7) is greater in Class II (Table 8).
The tendency for posterior constriction of the lower arch may be interpreted as accommodation to the upper arch constriction. In our study, the characteristic of the lower arch was similar to that registered by Uysal et al,23 who found reduced interpremolar and intermolar widths. Our results are not similar to those found by Sayin and Turkkahramam21 and Fröhlich.32 The former authors noticed changes in the lower intercanine width in women (mean age = 16 years) that were greater in Class II subjects, while the latter did not find any influence of Class II on the lower dental arch in growing children.
Constriction of the upper dental arch in Class II division 1 malocclusion is reflected in the differences between the transverse dimensions of the upper and lower arches.
CONCLUSION
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The hypothesis is rejected. Significant differences are present between the dimensions of the upper and lower dental arches in Class II division 1 malocclusion (with a mandibular deficiency and in the permanent dentition) compared to normal Class I occlusion dental arches.
Orthodontic diagnosis is based on facial (1A), radiographic (1B), and occlusal (1C to 1K) analyses. Patient has Class II division 1 malocclusion with mandibular deficiency
Dental cast models representing Class II division 1 (A–E). Simulation of the malocclusion correction (F–H) with mandibular advancement shows the posterior crossbite that appears due to the maxillary transverse deficiency
Assessment of the dimensions of the upper and lower arches obtained from the measurement of the intercanines (3-3), inter–first premolars (4-4), inter–second premolars (5-5), inter–first molars (6-6), and sagittal dimensions
Sagittal and transverse dimensions of the upper arch in normal and Class II division 1 males and females
Sagittal and transverse dimensions of the lower arch in normal and Class II division 1 males and females
Contributor Notes
Corresponding author: Dr Omar Gabriel da Silva Filho, Setor de Ortodontia–HRAC/USP, Silvio Marchione, 3-20 Vl. Universitária, 17012-900 Bauru/SP, Brazil (ortoface@travelnet.com.br)