Mandibular asymmetry is one of the main causes of facial asymmetry. It can be caused by a deficit or excess in the size of one of its components . Patients with facial asymmetry require a clinical and radiographic analysis that allow a proper diagnosis and in that way design an appropriate treatment plan . The measurement of the size of the condyle is usually done from the highest point of the condylar head to the sigmoid notch (SN) .

During embryonic development, the mandibular body presents a membranous ossification guided by the Meckel cartilage (primary cartilage), which subsequently retrogresses and completely disappears from the mandibular body, transforming itself into two bones of the medial ear, and the sphenomandibular ligament, which will shape the mandibular lingula (ML) through traction . At the same time, the coronoid process of the mandible appears due to traction of the temporal muscle .

The sigmoid notch (SN) is the depression located between two skeletal units whose origins are secondary cartilages (condylar and coronoid cartilage) that appear on the ramus in the third month of intrauterine development . They are called secondary because they appear at a later stage of development than the Meckel cartilage, and because their growth depends on the function . The coronoid unit will develop based on the traction exercised by the tendon of the temporal muscle, whereas the condylar unit will do so based on the action of the lateral pterygoid muscle, which stimulates growth through the negative intra-articular pressure produced by suction and mandibular movements .

Thus, it can be deduced that, embryologically, the mandibular body forms, guided by the Meckel cartilage, from the mental foramen to the ML (posterior contour of the body) and the formation of the condylar cartilage are secondary, occupying the space from the ML to the glenoidal cavity of the temporal bone. In that way, the uppermost point of the condylar unit is the condylar head and its lowest point is the ML .

That is why it is proposed that the evaluation of the condylar unit ought to include the ML as it is the lowest part. The SN is the depression between two mandibular skeletal units (coronoids and condyle) and could be affected if either of these units presents with an alteration of any kind. Thus, it would not be stable when evaluating condyle length.

Unilateral condylar hyperplasia is a complex pathology that causes serious alterations to facial functions and esthetics. It typically presents itself as a progressive facial asymmetry more frequently in females . The diagnosis is essentially linked to the clinical progression of the disease. Radiological studies and the analysis of mandibular length are crucial for planning an optimal treatment .

Nuclear medicine studies, such as scintigraphy, and single photon emission computed tomography (SPECT) studies are used for diagnostic confirmation of the increased metabolic activity at the condylar affected side. Through the administration of radiomedicine (technetium Tc 99), multiplanar (SPECT) images are produced that show the distribution of this radioactive compound in the patient.

The SPECT study consists of three phases: an angiographic phase, a tissular perfusion phase, and an osseous phase. This phase measures the degree of the existing metabolism and bone formation. The normal value (nonpathologic) is an average of 50% ± 5%. .

The purpose of this study is to determine, in patients with active unilateral condylar hyperplasia (AUCH), which are the most reliable points to measure the length of the condylar unit: from the SN or from the ML to the condylar head.

Materials and Methods

An observational cross-sectional study was designed to compare, with CBCT, the development of the ML and SN in patients with AUCH, and which of those are the most reliable to measure the condylar length.

All 20 patients included in this study were selected from Dr. Rodrigo Fariña’s private practice and from Department of Maxillofacial Surgery, Hospital del Salvador, during 2013 to 2015.

All CBCT was performed at a private radiological center (Cimex) in the city of Santiago, Chile, between 2013 and 2015. The images were obtained using a Kodak 9500 Cone Beam 3D System (Carestream Health Inc, Rochester, NY) tomograph operating at 90 kV, 10 mA, with a 0.2-mm ³ voxel and a 9 × 15-cm field of vision (FOV). Volumetric reconstruction was calculated using the mathematical algorithms contained in the same company’s software. The CBCT images were visualized using Kodak Dental Imaging Software 3D module version 2.4.

A cephalometric tracing of the mandibular ramus and condyle on both sides was done on the cone beam computed tomogram to determine their lengths according to a protocol established for this study ( Fig. 1 ). All measurements were made by the same radiologist.

Outline of the protocol for determining the length of the mandibular condyle. Point 1: upper point of mandibular condyle (C). Point 2: Sigmoid notch (lowest point of the depression in the sigmoid notch) (SN). Point 3: Base of the mandibular lingula (ML). Point 4: Mandibular angle (formed by the bisector of the parotid edge and the basilar edge) (MA). Line A: Line perpendicular to plane formed by points 1−4 at point 1 (condyle). Line B: Line perpendicular to plane formed by points 1−4 at point 2 (SN). Line C: Line perpendicular to plane formed by points 1−4 at point 3 (ML).

The inclusion criteria were AUCH (mixed with vertical and horizontal pattern) corroborated with positive bone scintigraphy findings for hyperplasia (hyperuptake of over 10% compared to healthy side in SPECT ), progressive mandibular asymmetry, with a facial midline that did not coincide with the lower dental midline and with center of the chin.

Patients with negative bone scintigraphy findings were excluded, as were patients with any other asymmetry that did not correspond to AUCH.

Variables in study included the following: ramus length on both sides (affected and healthy side); condylar length on both sides, measured from the ML; condylar length on both sides, measured from the mandibular SN.

A cephalometric tracing of the mandibular ramus and condyle on both sides was done on the CBCT to determine their lengths according to a protocol established for this study.

Cephalometric points and measurement protocol

The cephalometric points and measurement protocol ( Figs. 1, 2 ) were as follows:

Cephalometric points on cone beam computed tomography (CBCT).

Point 1: Mandibular condyle (C): uppermost point of the mandibular condyle’s convexity.

Point 2: Sigmoid notch (SN): lowest point of the sigmoidal notch’s concavity.

Point 3 : Mandibular lingula (ML): base of the mandibular lingula with relation to the mandibular foramen.

Point 4 : Mandibular angle (MA): bisector formed by an angle of the tangent to the parotid edge and the tangent to the basilar edge.

With these four points identified, a connection plane is drawn from point 1 to point 4, which determines the length of the mandibular ramus. Then three lines are drawn perpendicularly to this plane, passing through points 1, 2, and 3, which are lines A, B, and C, respectively.

Once the four cephalometric points have been identified, the following measurements on both ramus sides were done and classified as the affected condyle (AC) and normal condyle (NC) measurements ( Fig. 2 ).

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  Ramus height: Distance from point C to MA

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  Condylar height from SN: Distance from line C to SN

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  Condylar height from ML: Distance from C to ML

The program Stata v 13.1 was used to analyze the results, applying a paired t test to compare results within a same group of patients. When more than two variables were compared, a Bonferroni-adjusted P value was used.

This study was approved by the Hospital del Salvador ethics board. Patient consent was not required.