Efficiency of ODI and APDI of Kim’s cephalometric analysis in a Latin American population with skeletal open bite

ABSTRACT Objective: The objective of this research was to demonstrate the efficiency of the overbite depth indicator (ODI) and the anteroposterior dysplasia indicator (APDI) from Kim’s cephalometric analysis, regarding the determination of the vertical and sagittal patterns of Latin American individuals. Methods: Two hundred lateral cephalometric radiographs were selected and divided into four study groups, with 50 radiographs each, for carrying out a cross-sectional study. The control group included radiographs of balanced individuals, and the other three groups had lateral cephalometric radiographs of subjects with Class I, II and III malocclusions and with skeletal open bite. After the pilot test was performed to calibrate the investigator, the ODI and APDI were measured. Descriptive statistics were performed and the one-way ANOVA with post-hoc Tukey HSD, or Kruskal-Wallis and Mann-Whitney U-test were used. Also a multiple linear regression was employed. Results: Statistically significant differences were found for the ODI of all groups (p< 0.001), except between Class I group (65.87 ± 4.26) and Class II open bite group (67.19 ± 3.58), both with similar values to each other. For APDI, statistically significant differences were also found for all groups (p< 0.001). However, no statistically significant differences were found between the balanced group (83.18 ± 1.71) and Class I group with skeletal open bite (81.78 ± 2.69). Conclusions: ODI and APDI are reliable indicators to evaluate the sagittal and vertical patterns of an individual, demonstrating their efficiency when a Latin American population was evaluated.


INTRODUCTION
An open bite has been considered as the upper, lower, anterior or posterior lack of teeth contact at the moment of occlusal closure. From an etiological point of view, an open bite can be classified as dental or skeletal. The latter is characterized by an excessive vertical dentoalveolar development on the posterior regions of the dental arches, generating an anteroinferior facial height increase and hyperdivergent maxillaries. This vertical growth can have influence on the treatment complexity and on the high frequency of relapses. 1 The Multiloop Edgewise Archwire (MEAW) orthodontic philosophy provides efficient and effective results on the skeletal open bite treatment, similar to those obtained with an orthognathic surgery treatment. 2,3 On the other hand, this philosophy is based on an integral diagnostic process using the cephalometric analysis created by Dr. Young H. Kim, who emphasizes the determination of vertical and sagittal growth patterns using the overbite depth indicator (ODI) and the anteroposterior dysplasia indicator (APDI). These indicators offer very important values in relation to the orthodontic treatment planning, mainly when deciding to perform a surgical orthodontic treatment. [4][5][6][7] It is very useful for the orthodontist to have at his disposal a simple and efficient method to diagnose a skeletal open bite (ODI) and, at the same time, that may allow him to determine whether a Class I, II or III malocclusion is present in a specific patient (APDI). Unfortunately, most cephalometric analyzes have been performed on Caucasian individuals, whose general characteristics differ from those of other populations. Therefore, standard cephalometric values should be established for each racial group, respecting the craniofacial characteristics of each population. For this reason, several investigations have been carried out in recent years to evaluate and demonstrate the diagnostic efficiency of ODI and APDI indicators on African Americans, 8 Caucasians, 7,9,10 Asians, [4][5][6]11,12 and some Latin American groups. [13][14][15] However, they did not include Class I, II and III pure skeletal open bite groups compared to a balanced group of individuals. This information would help to evaluate the effectiveness of Kim's cephalometric analysis indicators.
Currently there are no studies accurately reporting on the differential diagnosis of Class I, Class II and Class III malocclusions with skeletal open bite using ODI and APDI, nor studies had determined how af-fected these patients can be in relation to a balanced patients group . Thus, the purpose of the present study  was to evaluate the efficiency of ODI and APDI on  the differential diagnosis between Class I, Class II and  Class III malocclusions with skeletal open bite and bal-anced subjects, in a Latin American population, verifying if they are reliable indicators to evaluate the vertical and sagittal patterns.

MATERIAL AND METHODS
This cross-sectional study was approved by the research and ethics committee of the School of Stomatology, Científica del Sur University, Lima (Peru) under the number 000289. Patients attended IDM Diagnostic Institute during 2013-2016, having an age range between 15 and 40 years. Lateral cephalograms obtained from a total of 1,714 subjects were analyzed. Sample size was calculated considering the comparison of two means using the ODI angular measurement, with a confidence level of 95%, a power of 90%, a variance of 13.03 o for the ODI of the control group and a precision of 6.78 o (obtained from a preliminary pilot study in which the mean of the ODI of the balanced group versus the open bite Class II group was assessed). This estimation showed that a sample of 7 lateral cephalograms was necessary in each group. However, to ensure the validity of comparison among different study groups, sample size was increased to 50 lateral cephalograms (in overall 200 patients) in each of the four groups (Fig 1).
» Class II group with skeletal open bite (n = 50; mean age = 19.88 years, 16 males and 34 females): subjects with ANB > 4 o , USP Projection = greater than -3 mm, FMP = greater than or equal to 30 o , and overbite = 0 mm or negative. Patients under orthodontic or orthopedic treatment, with systemic diseases, with other bone alterations or with prior history of orthognatic surgery were not considered in this investigation.

Measurements
The images were taken using a digital cephalometric panoramic equipment (ProMax ® 2D, Planmeca, Finland), which was set at 16 mA, 84 Kv and 10.9 seconds of exposure. The lateral cephalometric radiographs were taken in maximum intercuspation, with the head on a natural position and with the lips at rest. Radiographs were 1:1 calibrated, and then processed by a calibrated examiner, using the MicroDicom Viewer software.
The following measurements were performed for the sample selection: » FMP: From the Tweed cephalometric analysis, angle formed by the Frankfort FH (Po-Or) plane and the mandibular plane (Go-M) (Fig. 2). 16 » Overbite: Distance between the incisal edges of the upper and lower central incisors, measured perpendicular to the functional occlusal plane (Fig 3). 17,18 » Overjet: Distance between the incisal edges of the upper and lower central incisors measured at the level of the functional occlusal plane (Fig 3). 17 » ANB: Angle formed by the N-A and N-B planes (Fig 2). 16 » USP projection: Linear distance between A' and B' points, obtained by the orthogonal projection of A and B points to the bisector of the angle formed by the maxillary plane (PNS-P'). P' is the intersection point of the N-A line with the "p" line (floor of the nostrils, between incisor foramen and ANS) with the mandibular plane (Go-Me). 19 The location and layout of the ODI and APDI reference points and planes of Kim's cephalometric analysis were performed once the lateral cephalograms were selected for the four study groups. [5][6][7] The ODI was quantified from the arithmetic sum of the angle formed by A-B plane with the mandibular plane (MP), and the angle of the palatine plane (PP) with the Frankfort horizontal plane (FH). A positive     value was considered when the palatal plane (PP) was inclined downwards and forward, and the value obtained for the PP-FH angle was added to that of the angle formed by the A-B with the MP plane. 4 Also, when the palatal plane (PP) was inclined upwards and forward, a negative value was considered and this value was subtracted from that of the angle formed by the A-B plane with the MP plane. 7 The APDI was quantified from the angle formed between the palatine plane and the A-B plane ( Table 1, Fig 4). 13,20 Ten cephalometric tracings were performed per day and all values obtained had an approximation of 0.5 mm or 0.5°.

Calibrations
The examiner was previously trained by a recognized orthodontist specialist on the identification of different cephalometric points and planes used in the present study. Two training sessions were organized prior to the final observations, for calibration of the observer. Intraobserver reliability was assessed by performing ODI and APDI measurements. The observer undertook two viewing sessions, separated by a minimum time interval of four weeks. A pilot study was performed on 20 lateral cephalograms selected from the balanced group, and on 5 lateral cephalograms selected from each of the three skeletal open bite groups. In total, 35 lateral cephalograms were observed to calibrate the observer and to determine the efficiency of the methodology and the sample size. These calibrations were performed using ICC, mean error, Student's t-test and Dahlberg's error test -results are shown in Table 2.

Statistical analysis
The collected data were statistically analyzed using SPSS version 24 for Windows (IBM SPSS, Chicago, IL, USA). Descriptive statistics were used to summarize the ODI and the APDI of Kim's cephalometric analysis measurements ( Table 3). The normality assumption was partially satisfied according to the Shapiro-Wilk test. One-way ANOVA with post-hoc Tukey HSD for independent samples test were used for ODI. When there was no normality (APDI), the Kruskal-Wallis test was performed. In addition, the results of the latter were compared using the Mann Whitney U-test. The p-values smaller than 0.05 were considered statistically significant. Finally, two multiple linear regression analyzes were performed to determine the influence of other predictor variables on ODI and APDI.

RESULTS
The sample distribution did not present significant association between sex and the evaluated group (Chi square p = 0.111). Likewise, the age did not show significant differences between the groups, except for the comparison between balanced group and open bite Class II group (p = 0.044) ( Table 3).
The mean value and standard deviation obtained for the ODI of the balanced group (72. 10  showing similar values between both groups, as can be seen in Table 5. When multiple linear regression tests were evaluated, FMP and overbite were found to be significant (p < 0.05) determining the influence on ODI; for APDI, the ANB angle, USP projection, and sex were found to be significant (p < 0.05).

DISCUSSION
Kim's cephalometric analysis allows an integral diagnosis of the vertical and sagittal growth patterns of the patient, using ODI and APDI. The main objective of this study was to evaluate the efficiency of Kim's cephalometric analysis on the differential diagnosis of Class I, Class II and Class III malocclusions with skeletal open bite, and to verify how affected these individuals were in relation to a balanced group. At present, several studies have been carried out on Caucasian, 7,9,10 Asian, [4][5][6]11,12 Pakistani, 21 Iraqis, 22 African American, 8 and even Latin American populations. [13][14][15] In these studies, the diagnostic efficiency of this method has been demonstrated. However, no study on the accuracy of differential diagnosis nor comparing subjects with different skeletal open bite malocclusions performed comparisons with a balanced group of subjects.  In order to avoid measurement and sample selection biases, a pilot study was carried out, thus ensuring the reliability of the results. The operator was trained by an orthodontist and the intra-observer variability was performed with a difference of one month. ODI measurement and APDI angles were almost perfect, thus ensuring the measurements reliability. Therefore, one of the strengths of the present study was related to the distribution of the groups in relation to sex and age. Although a difference in age was found between the control group and the open bite Class II group, all cases in this condition were young adults (19.88 ± 5.59 years old) in which the amount of growth is residual -by this reason, the researchers consider that groups were matched.
The results found in the present research demonstrate Kim's analysis efficiency on the ODI and APDI assessment. 4 In this study, ODI values for the balanced group were slightly lower than the values found by Kim on Caucasian individuals -the present results were slightly hyperdivergent. This could be due to racial differences in the composition of each sample. Similar results were found by Jones 8 in an African American sample, by Freudenthaler et al 10 4,[6][7][8][9][10]12,14,15,21,24 On the other hand, the APDI is also considered an excellent parameter for the anteroposterior malocclusions evaluation. 11,13,25,26 In the present research, APDI values for the balanced group were slightly higher in relation to the values found by Kim and Vietas. 5 This could be due to racial differences in the composition of each sample, which was corroborated in the present results, similar to those found by Navarrete et al. 13 and Castañeda 15 in Latin American groups. However, Oktay 27 found lower values for the APDI than those found by Kim and Vietas. 5 A good indicator of sagittal malocclusions should yield different values for skeletal Class I, Class II and Class III malocclusions. In this sense, the APDI value complies with this requirement, since in this study significant differences were found in the groups with different malocclusions. Similar averages to those proposed by Kim were found on Class I group (balanced and with open bite). Class III group were approximately 6 degrees greater in relation to the group with open bite and Class I. Class II group reported values approximately 7 degrees lower than those of Class I with open bite. Similar results were found by different investigators. [9][10][11][12][13][14][15]21,23,25,26 Meanwhile, as expected, the skeletal open bite Class I group and the balanced group did not present statistically significant differences for APDI values.
In the present study, the multivariate analysis did not show the influence of the sex variable, nor age, except for the APDI, probably due to the fact that in general more women were evaluated in all groups, this distribution could be taken into account for future studies. However, Fatima et al 21 found no statistically significant differences between the mean values found for ODI and APDI between male and female individuals, nor between subjects in different age groups. Navarrete et al 13 also reported no statistically significant differences for APDI between genders, and Romero 14 found that the values of both indicators remained stable during growth.
This reaffirms that ODI and APDI values can be used in a Latin American population. The applicability of these values in different populations demonstrates the universal benefit of its use when evaluating different populations.

CONCLUSIONS
ODI and APDI indicators for Kim's cephalometric analysis demonstrated its efficiency when evaluated in a Latin American population. APDI and ODI are reliable indicators for evaluating an individual's sagittal and vertical patterns.