Three-dimensional morphological characterization of malocclusions with mandibular lateral displacement using cone-beam computed tomography

A three-dimensional method to calculate mechanical advantage in mandibular function : Intra- and interexaminer reliability study

PURPOSE

Masticatory muscles are physically affected by several skeletal features. The muscle performance depends on muscle size, intrinsic strength, fiber direction, moment arm, and neuromuscular control. To date, for the masticatory apparatus, only a two-dimensional cephalometric method for assessing the mechanical advantage, which is a measure for the ratio of the output force to the input force in a system, is available. This study determined the reliability and errors of a three-dimensional (3D) mechanical advantage calculation for the masticatory system.

METHODS

Using cone-beam computed tomography images from teenage patients undergoing orthodontic treatments, 36 craniofacial landmarks were identified, and the moment arms for seven muscles and their load moment arms (biomechanical variables) were determined. The 3D mechanical advantage for each muscle was calculated. This procedure was repeated by three examiners. Reliability was verified using the intraclass correlation coefficient (ICC) and the errors by calculating the absolute differences, variance estimator and coefficient of variation (CV).

RESULTS

Landmark coordinates demonstrated excellent intra- and interexaminer reliability (ICC 0.998-1.000; p < 0.0001). Intraexaminer data showed errors < 1.5 mm. Unsatisfactory interexaminer errors ranged from 1.51-5.83 mm. All biomechanical variables presented excellent intraexaminer reliability (ICC 0.919-1.000, p < 0.0001; CV < 7%). Interexaminer results were almost excellent, but with lower values (ICC 0.750-1.000, p < 0.0001; CV < 10%). However, the muscle moment arm and 3D mechanical advantage of the lateral pterygoid muscles had ICCs < 0.500 (p < 0.05) and CV < 30%. Intra- and interexaminer errors were ≤ 0.01 and ≤ 0.05, respectively.

CONCLUSIONS

Both landmarks and biomechanical variables showed high reliability and acceptable errors. The proposed method is viable for the 3D mechanical advantage measure.

Implications of occlusal plane in diagnosis and treatment of malocclusion

Occlusal plane (OP) is one of the essential factors affecting craniofacial morphology and function. The OP not only assists in diagnosing malocclusion but also serves as an important reference for making treatment plans. Patients with different types of malocclusions have different forms of OP. Compared with patients with standard skeletal facial type, the occlusal plane of patients with skeletal class Ⅱ and high angle is steeper, while that of patients with skeletal class Ⅲ and low angle is more even. In orthodontic treatment, adjusting and controlling the OP can promote the normal growth and development of the mandible in most patients with malocclusion during the early stage of growth, while causing favorable rotation of the mandible in some adults with mild-to-moderate malocclusion. For moderate-to-severe malocclusion, the OP rotation by orthodontic-orthognathic treatment can achieve better long-term stability. This article reviews the evolution of the definition of OP and its implications for diagnosing and the guiding treatment of malocclusion.

Evaluation of horizontal condylar angle in malocclusions with mandibular lateral displacement using cone-beam computed tomography

OBJECTIVES

To evaluate the horizontal condylar angle (HCA) in mandibular lateral displacement (MLD).

MATERIALS AND METHODS

HCA in MLD malocclusions were examined using cone-beam computed tomography data in subjects with MLD and control subjects.

RESULTS

HCA in joints of control patients and contralateral side joints of MLD patients were not significantly different. The mean HCA on the shifted side was larger than on the contralateral side (P < .001) in the different HCA groups. HCA was significantly larger on the shifted side than on the contralateral side in skeletal Class I, Class II, and Class III groups (P < .001).

CONCLUSIONS

(1) There was no statistically significant difference between HCA in control patients and on the contralateral side in MLD patients. (2) HCA was significantly larger on the shifted side than on the contralateral side. (3) HCA on the shifted side and the contralateral side in MLD Class I, Class II, and Class III are significantly different.

The Law of Minimum Vertical Dimension: Evidence for Improvement of Dental Occlusion

The law of minimum vertical dimension (MVD) states that “when the mandible moves to reach the maximum intercuspal position, this always involves bringing the mandible and maxilla as close together as possible.” Therefore, after the first occlusal contact is made, the MIP will be reached through reduction of the vertical dimension. Our objective of this study, through an integrative review of the literature review, was to determine whether ignoring this law is a factor that contributes to malocclusion, temporomandibular joint dysfunction, and recurrences of functional orthodontic and orthopedic treatments.We conducted a search of the literature in five of the main electronic scientific databases. The following medical subject heading terms were used in our search: centric relation, dental occlusion, malocclusion, vertical dimension, and mastication. We cross-referenced the descriptors in the following four groups: centric relation and maximum intercuspation; occlusal plane and malocclusion; neuro-occlusal rehabilitation; and vertical dimension and unilateral chewing. From this, we selected 277 potentially eligible articles. Out of these, 209 were excluded in accordance with the exclusion criteria already described. Thus, 65 studies were included in the qualitative synthesis.The articles were also classified according to their impact factor and degree of recommendation, in conformity with the table of the Oxford Centre for Evidence-Based Medicine. The scientific interest in the scope of the articles was also assessed by using three charts developed according to year and country of publication and the percentage of publication. Unilateral chewing creates a vicious cycle of damage that leads to an ever-increasing masticatory deficiency. Most of the articles chosen for this review confirmed that noncompliance with law of MVD was a predisposing factor in cases of relapse, in functional orthodontic and orthopedic treatments, as well as a causal factor in malocclusion and in functional and morphological TMJ dysfunctions.

Mandibular asymmetry in young adult patients with unilateral posterior crossbite: A controlled retrospective CBCT study

OBJECTIVE

This study aimed to evaluate the mandibular skeletal asymmetry in pre-orthodontic patients with the unilateral posterior dental crossbite (UPCB).

MATERIALS AND METHODS

Using a retrospective design, 30 pre-orthodontic patients with a UPCB, (16 on the right side, 14 on the left side), 18 females and 12 males were selected (mean age: 21.2±4.92 years), along with 30 controls matched by age and sex with cl I occlusal relationship (mean age: 21.9±4.80 years). The patients were from an Orthodontic Department of Dental Faculty of Hamadan University of Medical Sciences and a private office from 2009 to 2013. In the UPCB group, at least one molar tooth was in the crossbite position. All the patients had initial CBCT¹ and pre-orthodontic study models. 10 linear and 3 angular measurements were performed to evaluate the mandibular skeletal asymmetry. repeated measure-ANCOVA² by controlling the effect of age and sex, T-test and paired-samples t-test were used for comparisons. Measurement's reliability was measured with ICC³ test.

RESULTS

There was a positional deviation of mandible to the crossbite side 95% CI⁴ (0.166 - 1.087). The intergroup analysis showed that Corpus Length (P≤0.014), Ramus Angle in frontal view (P≤0.046), and Condylar-Width in axial view (P≤0.029) in the crossbite side of the case group were significantly smaller than the control group. In the subjects with UPCB, mandibular condylar width was smaller in the crossbite side (17.31±2.50) relative to the non-crossbite side (18.06±2.18).

CONCLUSIONS

The adults with dental UPCB, in addition to deviation to crossbite side, may show smaller condylar head and Corpus length in crossbite side relative to the control group.

Three-Dimensional Analysis of the Condylar Hypoplasia and Facial Asymmetry in Craniofacial Microsomia Using Cone-Beam Computed Tomography

PURPOSE

To assess the condylar hypoplasia and its correlation with craniofacial deformities in adults with unilateral craniofacial microsomia (CFM).

METHODS

Pretreatment cone-beam computed tomography scans of consecutive adults (mean age: 20.4 ± 3.0 years; range: 17.3 to 31.4 years) with Pruzansky-Kaban type I and IIA CFM were reconstructed in 3D. Both condyles were segmented. Asymmetry ratios (affected side/contralateral side) of condylar volume were calculated to indicate the extent of condylar hypoplasia. 3D cephalometry was performed to quantify the maxillomandibular morphology and facial asymmetry. The correlations in between were assessed by using Pearson's or Spearman's correlation coefficients.

RESULTS

Thirty-six subjects were enrolled, consisting of 22 subjects with Pruzansky-Kaban type I and 14 subjects with type IIA. The condyles in type IIA group were significantly more hypoplastic in height (asymmetry ratio: 40.69 vs 59.95%, P = .006) and volume (18.16 vs 47.84%, P < .001) compared to type I group. Type IIA group had a significantly smaller SNB value than type I group (72.94° vs 77.41°, P = .012), and a significantly greater facial asymmetry (P < .05). The hypoplastic extent of condylar volume and Pruzansky-Kaban types were significantly correlated with SNB (r = 0.457 and ρ = -0.411, respectively), upper incisor deviation (r = -0.446 and ρ = 0.362), chin deviation (r = -0.477 and ρ = 0.527), upper occlusal plane cant (r = -0.672 and ρ = 0.631), and mandibular plane cant (r = -0.557 and ρ = 0.357, P < .05).

CONCLUSION

For unilateral CFM adults, greater condylar hypoplasia in volume along with more severe mandibular retrusion and facial asymmetry objectively indicated a higher scale of Pruzansky-Kaban classification (type IIA). These quantitative distinctions are expected to enhance the diagnostic reliability of CFM.

Mandibular and temporomandibular morphologic characteristics of patients with suspected unilateral condylar hyperplasia: a CT study

INTRODUCTION

Facial asymmetry associated with unilateral condylar hyperplasia (UCH) is a complicated clinical condition.

OBJECTIVE

The objective of this study was to describe morphological characteristics of the mandible and the temporomandibular joint in patients with facial asymmetry, using computed tomography and 3D reconstruction.

METHODS

A retrospective observational study was performed with patients displaying facial asymmetry evaluated by single photon emission computed tomography (SPECT)/CT analysis, for suspected UCH, between 2015 and 2018. The following variables were compared between the affected side (producing the asymmetry) and the contralateral side (side to where the jaw is deflected): condylar length, condylar medial and lateral pole length, mandibular ramus length, intra-articular spaces, articular eminence height and position of the posterior wall of the glenoid fossa.

RESULTS

Forty-three patients (21 women, mean age: 20.7 ± 7.25 years) with facial asymmetry were included, 19 patients presented right side deviation and 24 patients had left side deviation. Condylar length, lateral pole length, the sum of maximum values and articular eminence height were greater in the affected side (p< 0.05). A positive correlation was found between the position of the posterior wall of the glenoid fossa and the articular eminence height in the affected side (r = 0.442).

CONCLUSIONS

In patients with suspected UCH, evaluated through CT, craniofacial measurements showed significantly larger condylar length and the condylar sum of maximum values in the affected side. A positive correlation was found between the increased dimensions of the articular eminence and the more posterior position of the glenoid fossa in the affected side.