CEPHALOMETRIC CHARACTERIZATION OF SKELETAL CLASS II , DIVISION 1 MALOCCLUSION IN WHITE BRAZILIAN SUBJECTS

1DDS, MSc, PhD, Full Professor. Department of Orthodontics. Bauru Dental School, University of São Paulo, Brazil. 2DDS, MSc, Orthodontic Graduate Student (Master degree). Department of Orthodontics. Bauru Dental School, University of São Paulo, Brazil. 3DDS, MSc, PhD, Orthodontic Graduate Student (Doctor Degree). Department of Orthodontics. Bauru Dental School, University of São Paulo, Brazil. 4DDS, MSc, PhD, Associate Professor. Department of Orthodontics. Bauru Dental School, University of São Paulo, Brazil. 5DDS, Graduate Student. Bauru Dental School, University of São Paulo, Brazil.


INTRODUCTION
The Class II malocclusion is characterized as skeletal when there is involvement of the jaws, and dental when there is just a dentoalveolar involvement; however, a combination of skeletal and dental factors happens in most cases 12,22 .This malocclusion can be related to a retrognathic mandible, prognathic maxilla, or a combination of both 12,22 .
The Class II division 1 malocclusion is the most frequent in particular clinics 25 , caused, in most times, by a retrognathic mandible 1,6,12 .The Class II malocclusions have a strong hereditary component as etiologic factor, both in families and in ethnic and racial groups 16 .The ethnic aspect in an important characteristic in the morphologic variation of malocclusions 16 .
The complex etiology and great variety of morphologic and functional aspects of this malocclusion motivate some studies 18,23,22 , aiming at obtaining a more accurate diagnosis and to allow appropriate and compatible treatment for the different types of Class II division 1 malocclusion 18 .
Although many studies have investigated Class II malocclusion characteristics 3,4,12,14,21 , few have studied the characteristics of skeletal Class II malocclusions in specific ethnic groups 1,16 .Therefore, in order to provide more specific information regarding this type of malocclusion in white Brazilian subjects, this comparative cephalometric study was undertaken.

Statement of the problem
The objective of this study is the cephalometric characterization of skeletal Class II, division 1 malocclusion in white Brazilian individuals with a mean age of 13.5 years that had not been previously submitted to any orthodontic treatment.The experimental group (Class II) was compared to normative cephalometric values obtained of 2 thesis studying normal occlusions at the Discipline of Orthodontics at Bauru Dental School 9,11 (control group).
Evaluation of the following characteristics of the jaws was made: angular and linear sagittal relation between maxilla and mandible, and related to the cranial base; geometric proportion between maxilla and mandible; craniofacial growth pattern and position of maxillary and mandibular incisors; presence of differences between genders.

MATERIAL
The experimental sample comprised 55 lateral cephalograms of white Brazilian individuals of both genders (22 women and 33 men), with a mean age of 13.5 years.This sample was originated from the records of a private clinic.
The criteria used for inclusion of subjects in the experimental sample were: full cusp molar Class II relation, Class II division 1 cases without previous orthodontic treatment, ANB angle equal or larger than 4.5 degrees.
The control group comprised subjects with the same age (13.5 years), presenting normal occlusion, and data on these subjects were obtained from 2 thesis of the Discipline of Orthodontics at Bauru Dental School 9,11 .

METHODS
The lateral cephalograms used were taken according to the conventional norms.Each cephalogram was digitized and measured by the software Cef-X version 2.1.31.After registering all data, the cephalometric points of interest were delineated, and measurements were supplied by the software.The magnification level of the lateral cephalograms was 6%, and it was corrected by the software.
Cephalometric data of the Steiner 24 and McNamara Jr 13 analyses were used.The angular and linear measurements of dental and skeletal structures used are presented in Figures 1 and 2. The normal values (control group) for measurements SNA (degrees), SNB (degrees), ANB (degrees), SN.GoGn (degrees), NS.Gn (degrees), 1.NA (degrees), 1-NA (mm), 1.NB (degrees) and 1-NB (mm) were obtained from the study of Martins 11 , and for the measurements A-Nperp (mm), P-Nperp (mm), Co-A (mm), Co-Gn (mm), MMD (maxillomandibular differencesubtraction of the values of Co-Gn and Co-A, in millimeters) and ENA-Me (mm), obtained from the study of Janson 9 .

Error study
Within a week interval from the first measurement, fourteen randomly selected radiographs were retraced, redigitized, and re-measured by the same examiner.The casual error was calculated according to Dahlberg's formula 7 (Se 2 = ∑d 2 /2n), and the systematic error with dependent t tests, for p<0.05.

Statistical analysis
The means and standard deviations for the data were calculated.The experimental group was compared with the control group 9,11

RESULTS
The data presented in Table 1 presents the casual and systematic errors for the studied measurements.No systematic errors were detected, and the random errors varied from 0.002 degrees for SNB to 1.04mm for 1-NA.
Comparison between genders showed that only the ANB angle presented statistically significant difference (Table 2).Table 3 presents comparison data between the experimental and control groups 9,11 .

DISCUSSION
In the experimental group, there was no statistically significant difference between genders.This finding is in agreement with the literature, which has stated that gender exerts little or no effect on skeletal and dental components in Class II malocclusions 18 .
The sagittal position of the maxilla (SNA) was similar to the control group, with a well positioned maxilla in relation to the cranial base, corroborating previous studies 6,8,12,15,17 .However, the linear sagittal position of the maxilla (A-NPerp) showed moderate protrusion.Interpretation of this result should be cautious, because the last measurement is linear (in millimeters), and the difference between maxilla and mandible should be considered.These diverging results between angular and linear measurements for the maxilla can be partly explained by the difficulty in the location of the reference points of the Frankfort plane.Another point could be the inclination of the oclusal plane, interfering with the results.It should remembered that the control group belonged to two theses, and each of the measurements cited was compared to a different control group, although both of normal occlusion.The effective length of the maxilla (Co-A) was similar to the control group, presenting a normal sized maxilla 6,12,15 .These characteristics found for the maxilla, well positioned and with normal size, have a direct implication in the Class II treatment 20 .The literature has been giving emphasis in these therapeutic aspects, which are scientific findings that subsidize functional orthopedics 10,20 .T h e sagittal position of the mandible (SNB) presented it retracted in relation to the cranial base.The effective length (Co-Gn) showed a small sized mandible.These results are in agreement with the literature 6,12,15,17,23,22 , demonstrating that the mandible presents great participation in this type of malocclusion.There are relevant studies 12,14,19 that accept the variations in the position of the mandible as inherent characteristics of this type of malocclusion.These cephalometric results justify the mandibular advancement for correction of the Class II malocclusion in great part of the cases 10,20 .
The sagittal discrepancy of the apical bases (ANB) presented statistically significant difference when compared to the control group.The process of craniofacial growth and development in normal conditions promote a decrease in the ANB angle, by the differential growth between maxilla and mandible, tending to flatten the profile, what would benefit this malocclusion 5 .However, when this malocclusion is analyzed in the absence of treatment, it is verified that the decrease of ANB can be minimum, and even an increase could happen 5 .It is important to emphasize that the Class II malocclusion does not present self-correction, meaning that the probable decrease in the ANB angle only happens with treatment 2,1 .
The difference between maxilla and mandible (DMM) was statistically significant when compared to the control group.In normal subjects with the same age of the sample studied, an increase in this measure is expected 3,12 .The results confirm the great discrepancy of dimensional and postural relations observed between the apical bases.
The lower anterior facial height (ENA-Me) behaved in a similar way as the control group, although it was slightly increased in the experimental group.The excessive vertical development of the craniofacial component is a consequence of the decrease in the posterior facial height and increase in the lower anterior facial height 12,15 .The behavior of the lower anterior facial height similar to the control group suggested an increase in the posterior facial height in the experimental group.
The maxillary incisors presented buccal inclination (1.NA).That finding is in consonance with the results of previous studies 6,8,12,19 .The maxillary incisors are reference for identification of the division of the Class II malocclusion.Martins 11 , when comparing a normal occlusion group to Steiner's norms 24 , noted great differences and concluded that theses norms 24 are not reliable for application in white Brazilian individuals.The linear position (1-NA) showed well-positioned maxillary incisors in relation to the cranial base.This result diverges from most studies in the literature 6,8,12,19 , but it can be due to the control group used for comparison 11 , which presented protruded maxillary incisors in Brazilian subjects with normal occlusion, when compared to the Steiner's norms 24 .
The angular measurement for the mandibular incisors (1.NB) presented statistically significant difference, showing mandibular incisors strongly buccally inclined.Previous studies showed minimum alteration of these teeth, with a buccal tendency 6,12 .The results for the linear position of mandibular incisors (1-NB) showed protrusion in relation to their apical base, indicating tooth compensation for the skeletal discrepancy.
The definition of Class II, division 1 malocclusion is based on the sagittal relation between the apical bases and their teeth, but not exclusively sagittal; the vertical and traverse involvement should also be considered.Therefore, diagnosis and treatment prognosis should be based on sagittal, vertical and traverse relations, to verify the level of dental compensation in Class II, division 1 malocclusions.

CONCLUSIONS
According to the methodology used, the cephalometric characterization of white Brazilian subjects presenting Class II, division 1 malocclusion (experimental group) was the following: 1 -The maxilla was well positioned in relation to the cranial base.
2 -The mandible was retracted in relation to the cranial base.

TABLE 1 -
Casual and systematic errors for the studied measurements

TABLE 2 -
Comparison between genders (experimental group) by the Student t test * STATISTICALLY SIGNIFICANT FOR P<0.05.

TABLE 3 -
Means, standard deviations and comparison between experimental and control group by the Student t test * STATISTICALLY SIGNIFICANT FOR P<0.05.