Indian Journal of Dental Research

: 2014  |  Volume : 25  |  Issue : 2  |  Page : 154--159

Early diagnostic evaluation of mandibular symmetry using orthopantomogram

Francesca Silvestrini-Biavati1, Alessandro Ugolini2, Nicola Laffi3, Carola Canevello1, Armando Silvestrini-Biavati2,  
1 Department of Orthodontics, Orthodontic Post Graduate Program, University of Cagliari, Genoa, Italy
2 Department of School of Dentistry, University of Genoa, Genoa, Italy
3 Department of Orthodontics, Orthodontic Post Graduate Program, University of Cagliari; Department of Odontostomatologia, SC Odontostomatologia, EO Galliera Hospital, Genoa, Italy

Correspondence Address:
Armando Silvestrini-Biavati
Department of School of Dentistry, University of Genoa, Genoa


Aims: The aim of this research was to complete Habets«SQ»s method on orthopantomogram, in order to measure mandibular symmetry horizontally and diagonally in mixed dentition as the first diagnostic evaluation. Settings and Design: Mixed dentition subjects were consecutively selected according to skeletal maturity. Materials and Methods: Inclusion criteria were: Mixed dentition, cervical vertebral stages 1-2, Class II or Class III malocclusions, with or without unilateral posterior cross-bite. Fourteen subjects with cross-bite (mean age 8 y, 9 m) cross group (CG) and 14 subjects with normal transverse occlusion (mean age 8y, 6m) non-cross group (NCG) were selected. Nine measurements were determined. An asymmetry index was performed for all linear variables. Statistical Analysis Used: NCG patients«SQ» data were compared with CG data using parametric t-tests. Probabilities of <0.05 were accepted as significant. Results: In CG, comparing right and left side, single values showed no significant differences up to 6% (twice if compared to the 3% threshold value). T-tests showed statistically significant differences between the groups for ramus + condyle height (index 2.5% vs 4.5%, P = 0.04), condylar height (index 3.7% vs 6.6%, P = 0.02) and mandibular length (index 1.4% vs 2.3%, P = 0.04). Overall CG group was more asymmetrical than NCG. Conclusions: In mixed dentition (CS1-2), a first appraisal of mandibular symmetry may be performed on orthopantomogram utilizing this modified Habets«SQ»s method. This tracing method provides an early evaluation about mandibular symmetry and is able to show slight asymmetries in mixed dentition thereby reducing the number of cone beam computed tomograms performed.

How to cite this article:
Silvestrini-Biavati F, Ugolini A, Laffi N, Canevello C, Silvestrini-Biavati A. Early diagnostic evaluation of mandibular symmetry using orthopantomogram.Indian J Dent Res 2014;25:154-159

How to cite this URL:
Silvestrini-Biavati F, Ugolini A, Laffi N, Canevello C, Silvestrini-Biavati A. Early diagnostic evaluation of mandibular symmetry using orthopantomogram. Indian J Dent Res [serial online] 2014 [cited 2022 Jul 5 ];25:154-159
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Full Text

Human beings are not perfectly symmetrical. Nevertheless, one of the most important aims in orthodontics is to achieve complete occlusal symmetry, correct occlusion between upper and lower teeth and facial midlines.

For the dentist and more specifically for the orthodontist it's not uncommon to see asymmetric patients; a good diagnosis of symmetry of the maxillo-facial complex is very important and the basic step, particularly when differential diagnosis between dental and skeletal problems is needed. Nowadays cone-beam computed tomography (CBCT) is the best available examination, for its 3D accuracy: Unfortunately, it is potentially dangerous for its high radiation dosage, especially in the children. [1],[2],[3],[4]

Orthopantomogram (OPG) is one of the most popular records in orthodontic diagnostic phase; it provides important bilateral dental and skeletal informations. It's a simple low radiation dosage x-ray, with magnification factors that vary from15% to 25%. [5],[6] More recently, OPG is been used also for measurements about impacted canines. [7],[8]

With the aim of avoiding the superimposition of upper and lower incisors, OPG is usually performed by using a plastic spatula between incisors: In this way the patient is forced to bite in a protrusive and/or in laterally shifted position. This fact makes it difficult to use OPG as the correct way to analyze maxillary and mandibular symmetry, [9],[10] as it is not known what the actual lateral and anterior mandibular movement is like. Moreover the midline of the face is determined by looking at the patient's face or using comprehensive maxillo-facial X-rays, such as postero-anterior or submentovertex skull radiographs.

The asymmetry of the mandible reflects different development of the right and left sides. [11] Several studies showed that early interceptive or functional therapy may lead to harmonic jaw development, particularly of the mandible [12],[13],[14],[15],[16] and even of the entire body posture. [17] It has been shown that early cross-bite treatment, starting from correction of asymmetrical condyle/ramus shapes, led to a more symmetrical dental and skeletal development. [11],[14],[18],[19] These topics underline the great importance of an early diagnosis of possible asymmetries or abnormal development of parts of the mandible. [12],[20],[21]

About mandibular skeletal symmetry, the most important structures are the condyle and the ramus, that have been studied on OPG by several authors. [11],[14],[22],[23],[24],[25],[26],[27],[28],[29],[30],[31] Many agree on using orthopantomogram in researches aiming to study mandibular symmetry in Class II, [29],[30] in Class III, [28] in unilateral [12],[13],[14] or bilateral cross-bite [4],[11] malocclusions. Others [25],[26],[27],[32] underlined that caution may be used when a mandibular asymmetry is diagnosed using OPG, because of possible distortions due to both the X-rays tube movement around the patient and head shift during long-lasting exposure. A 3% threshold value is considered as normal considering symmetry between right and left measures in the same subject. [11]

In 1987-89, Habets et al. [25],[26],[27] proposed in three articles an OPG tracing method, that aimed to investigate any correlation between temporo-mandibular joints disorders and condyle/ramus height and shape. This accurate method compared only vertical heights of the mandibular right and left condyles and rami. They also analyzed the horizontal and vertical distortion rate of OPG when compared to CT; in 31-35 years old subjects they found a significant horizontal distortion on OPG, that was not present in the vertical plane. In 1997, Ferrario et al. [22] reported, in 29 year old subjects, that the right and left condyle of the same subject have a different shape, with an high inter-individual variability.

In 2009, Uysal et al. [11] found a high rate of condylar asymmetry in young subjects with normal occlusion or with cross-bite. In 2011, Wang et al., [23] studying skulls with permanent dentition, concluded that there is a correlation between occlusal and condylar asymmetry.

In 2002, Luz et al. [24] reported significant differences in condylar heights in patients with temporo-mandibular disorders. The cited studies were done mostly on adult subjects with TMJ disorders, in permanent dentition, when the temporo-mandibular structures are completely developed.

The aim of this research was to improve and complete Habets's method, in order to measure horizontally and diagonally the condyle, ramus and mandibular symmetry, in mixed dentition, using the OPG for early diagnostic evaluation. The goal is to diagnose and intercept as early as possible small asymmetries and to reduce CBCT use for selected cases, in which it may be really necessary for planning early functional and/or orthodontic and/or surgical treatment.


The study protocol was approved by the scientific Committee of the Department of Surgical Sciences DISC, University of Genoa, Italy, and it was carried out in accordance with the ethical standards and with the Helsinki Declaration of 1975.

Subjects were consecutively selected (from January to December 2012), according to skeletal maturity as evaluated by means of the cervical vertebral maturation method. [33] All subjects presented cervical vertebral stages 1-2 (CVS 1-2) evaluated on lateral skull radiographs, and were in mixed dentition phase. Inclusion criteria were: Class II (ANB >5°) or Class III malocclusion (ANB between -1° and 2°, for early age), with or without unilateral posterior cross-bite. All the orthopantomograms were performed by the same operator, using the same X-rays system (Orthoralix S, Gendex, Hatfield, PA, USA), following standard procedures. Particular attention was given to the correct positioning of the subject during exposure.

Exclusion criteria were: Previous orthodontic treatment, hypodontia in any quadrant (excluding third molars), craniofacial abnormalities, inadequate radiographs (poor quality at the mandibular area or evident distortion).

Thirty-eight patients matched the inclusion criteria (18 m, 20 f; mean age 8.7 ± 1.5 years). The available records included dental casts, panoramic and lateral skull radiographs. The lower first molar mesio-distal diameters on the right and on the left side were compared in all OPGs, in order to avoid orthopantomograms with some distortion, according to White: [34] the OPG having a difference of more than 1 mm between two sides were excluded from this study. Between the remaining 28 subjects, 14 had cross-bite (7M; 7F; mean age 8 y, 9 m) (Cross Group (CG)) and 14 had normal transverse occlusion (8M; 6F; mean age 8 y, 6 m) (Non-Cross Group (NCG)).

An asymmetry index [25],[26],[27] was performed for all linear variables, and the formula used was:

(R-L)/(R + L)*100

Tracing analysis

Orthopantomograms were all hand traced by a single examiner (FSB). Landmark location and accuracy of the anatomic outlines were checked by a second examiner (CC) and verified by two senior clinicians (ASB, NL). Data were collected in Tables (NL) and statistically processed (AU).

Habets's method [25],[26],[27] was modified, adding new landmarks and measurements [Table 1] and [Table 2].

Selected landmark points are shown in [Figure 1]. Six linear measurements (O2-C; O1-lineC through C1; O2-M; D2-C; O2-D2; Co-M) and three angular variables (M-O2-O1°; O2-M-Co°; O2-F-M°) were determined [Figure 1], [Table 1] and [Table 2].{Table 1}{Table 2}{Figure 1}

M was traced in the center of the C-shaped dimple, that is above pogonion, under the lower incisors apexes. Because of the different condylar shapes, O1 and C1 usually are not on the same plane. Therefore, the condylar width was measured from O1 perpendicularly to the opposite C line.

Statistical analysis

Descriptive statistics were calculated for each variable. The Shapiro-Wilk test demonstrated the normal distribution of data, thus parametric statistics could be applied. Patients' data were compared with data from the control group using parametric t-tests. Probabilities of < 0.05 were accepted as significant in all statistical analyses. The power of the study was adequate (>0.83), calculated a priori using the mean values and standard deviations of M-O2-O1° reported by Uysal et al. [11] at an alpha of. 05.

Method error

To analyze method error, five randomly-selected orthopantomograms were retraced. A combined error of landmark location, tracing, and measurement was determined. Intra-class correlation coefficients (ICC) were used to determine intra- and inter-operator agreement for each variable. Correlation coefficients for the skeletal measures were greater than 0.95. Linear measurement errors averaged 0.4 mm (SD 0.5 mm) and angular measurement errors averaged 0.5° (SD 0.5°).


All data were collected in [Table 3] and [Table 4].{Table 3}{Table 4}

In CG, comparing right and left side, single values showed some but no significant differences.

In CG, linear measurements O2-C and Co-M showed statistically significant differences vs NCG (t-test 0.04) [Table 3] and [Table 4].

Comparing horizontal versus vertical values, no significant differences was found.

The mandibular asymmetry indexes were calculated separately in both groups for all linear variables [Table 4]. The results of the t-tests showed statistically significant symmetry differences between the groups for ramus + condyle height (index 2.5% vs 4.5%, P = 0.04), condylar height (index 3.7% vs 6.6%, P = 0.02) and mandibular length (index 1.4% vs 2.3%, P = 0.04). Overall CG group was more asymmetrical than NCG.


Certainly, OPG is not the correct way to study skeletal symmetry, as it reproduces in 2D an ovoid structure; moreover, OPG lacks adequate maxillary, nasal and inter-orbital referral points that can be used in order to identify a correct facial midline. Nowadays, the CBCT provides a 3D volumetric very accurate maxillo-facial reconstruction; it shows clearly the left and the right side and related linear or angular measurements, but is very criticized because of the high X-rays dosage for the patient, with all correlated risks, particularly in growing subjects. [35],[36] Therefore, it's required to weigh well the cases in which a CBCT is really essential. Nowadays CBCT is justified only in impacted teeth cases. [2]

About this topic, we thought that OPG, a very low dosage radiograph, might be useful also for studying mandibular symmetry in mixed dentition, at least as first assessment. This opportunity seems to be very interesting both during first diagnosis phase (in order to better direct therapy) and in the subsequent radiographic checks during the orthodontic treatment (in order to control the treatment course), because, as several authors stated, [12],[14],[15],[19],[28],[29],[30],[37],[38],[39] an early treatment may correct both dental and skeletal defects in growing patients, with a good long-term stability [39] and with lower direct and indirect costs. [38],[40]

About mandibular symmetry, Uysal et al. considered as normal [11] a 3% threshold value: A 3% index ratio can result from 1 cm change in head position; [25],[26],[27] the basic human body asymmetry may be always borne in mind.

In this preliminary research, D2-C (condylar height), O2-C (ramus + condyle height) and Co-M (mandibular diagonal length) showed significant differences between CG and NCG [Table 4]. The indexes of others linear variables showed lower not significant mean differences between 2% and 6% (up to twice compared to the 3% threshold value for ramus height, O2-D2).

This proposed tracing method was simple and useful, and showed a higher mandibular asymmetry in the cross-bite group (CBG) when compared to the control group (NCG).

All the analyzed subjects were in CS1-2 stages, still far off from the complete mandibular development, that usually has its greater vertical growth during the pubertal spurt; this may suggest that at this age a limited asymmetry may already be present, but may not always be clearly manifested.

Only few studies were performed in mixed dentition, [41] but they are not directly comparable with our results, because of a new measurement analysis used in the current research.

The results of this study are been confirmed in other researches performed in permanent dentition, on OPGs in cross-bite patients, [11],[14],[19],[28],[29],[30] on postero/anterior [18] or on lateral skull radiographs. [19]

Tracing the OPGs, shape differences led back to the skeletal pattern and to Bjork's characteristics [42] and sometimes a complete side difference was shown, both about shape and dimension. Therefore, this anatomical analysis becomes a useful diagnostic investigation, remembering that, according with Moss, [38] shape is strictly related to function.

The condyle was the most variable parameter (about length, width, shape, inclination). The drawing of a grid around the condyle head was useful; long condyles were more difficult to measure than round ones.

The first objective of this study, that was to propose a mandibular symmetry tracing method on OPG in mixed dentition, showing that this analysis can be utilized only after a previous lower first molars measurement, comparing their mesio-distal diameters. [34] Several OPGs were excluded from this study just because a horizontal distortion was recorded. This should remind clinicians or radiologists to devise an accurate face centering particularly on the transversal plane and to find methods that may keep firm the head during the tube movement.


This study, comparing cross-bite (CG) and non cross-bite (NCG) subjects, showed that:

Ramus plus condyle height (O2-C), condylar height (D2-C) and mandibular length (Co-M) were significantly different (left vs right side) in CG vs NCGThe index of other linear variables showed lower not significant mean differences between 2% and 6% (up to twice compared to the 3% threshold value); ramus height (O2-D2) was the most differentCG data were more asymmetrical than NCG, and the asymmetry is mainly due to condylar height. The use of this tracing method is able to reduce the number of CBCTs performed to safeguard our patients from not essential risks. In a second step, only in the most asymmetrical cases, it will be right and proper to carry out more suitable examinations, as postero-anterior or sub-mento-vertex skull radiographs or CBCT.


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