Cervicomental angle changes observed after mandibular advancement surgery – A systematic review

INTRODUCTION

Skeletal Class II jaw base relation is one of the most common scenarios experienced in clinical orthodontic practice. Such a jaw base relation could be due to (a) retrognathic mandible, normal maxilla (b) normal mandible, prognathic maxilla, and (c) combination of both.

Such a skeletal relationship, if found in growing children, can be corrected by growth modulation, whereas such a relation in adults can be corrected only by orthognathic surgery.

Mandibular advancement is the most frequently performed procedure for correction of skeletal Class II jaw base relation in adults with retrognathic mandible. Forward movement of mandible in orthognathic correction of skeletal dysplasia produce changes in the chin and lips that have been found in the previous studies.^[1]

Predicting soft-tissue changes in relation to surgical skeletal correction is important while deciding the treatment protocol. Several soft-tissue analyses^[2-6] have been developed to accurately predict the treatment outcome, however, focused on the region between glabella and soft-tissue chin.^[1]

The morphology of the neck and its changes with the submental region has a great effect on the aesthetics of the lower face, and the chin-throat angle (CTA) is an important determinant of facial profile attractiveness. A number of etiological factors may be involved in creating a poor aesthetic silhouette of the chin-throat region, which include the tonicity and laxity of the submental-cervical skin, the suprahyoid muscle support, excessive submental, supraplatysmal and subplatysmal fat deposits, the size of the submandibular glands, the spatial position of the hyoid bone, and the skeletal framework of the mandible and chin. Forward positioning of mandible and/or advancement osseous genioplasty tend to improve the chin-throat aesthetics.^[7]

Many experimental linear and angular measurements have been used to judge cervical and facial esthetics and to evaluate the soft tissue response to surgical correction protocol.^[8] Despite the fact that there are numerous clinical reports of patients opting for various surgical procedures to change the submental cervical contour,^[9-12] the submental cervical area has had a little consideration in radiographic analysis.

Each facial factor, such as the submental-cervical angle, has an “average” value or “norm” for a given population, which is age, gender, and racial specific. Each parameter has a range of normal variability, with the existence of a facial irregularity often subsequent to a significant deviation of one or more facial parameters from the accepted norm for that group of people. In clinical scenarios, it is important to determine at which point the deviation of a facial parameter moves from the acceptable range of variability to being perceived as a facial irregularity.^[13]

The terms submandible-neck, chin-neck region, cervical angle, cervicomental, and submental area are all terms that mean the same and point toward the same anatomical area^[1] that is formed by the cervical plane and the submental plane. The normal cervicomental angle ideally has been reported to be 90°.^[14-16] Ellenbogen and Karlin^[17] concluded that a cervicomental angle in the range of 105–120° is acceptable. Sommerville et al.^[18] found that the ideal cervicomental angle to be 126° for men and 121° for women.

The objective of the study was to evaluate the changes observed in cervicomental angle after mandibular advancement surgery.

METHODS

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RESULTS

DISCUSSION

In adult subjects having skeletal Class II malocclusions with mandibular deficiency, there traditionally are two possible treatment modalities. The first modality is camouflage orthodontics–extraction of upper premolars allowing retrusion of the upper anterior (ANT) teeth to normalize the overjet and cover the underlying skeletal problem. The second modality is orthognathic surgery to reposition the mandible anteriorly.^[19]

In this systematic review, an exhaustive literature search attempted to find studies that evaluated the changes observed in the CTA after mandibular advancement surgery. In all studies, the method used to analyze the CTA was well stated and validated. No study declared blinding of measurement or analysis. Out of the four studies included, three were retrospective studies while one was a questionnaire analysis describing the facial attractiveness as rated by clinicians and laypeople [Table 1].

Hayes et al. (1994)^[1] quantified the changes seen in CTA and the lip-CTAs in response to forward positioning of mandible and hyoid bone positional changes. They concluded that on mandibular advancement, the hyoid bone moves toward sella, basion, and posterior (POST) nasal spine by 3.7 mm, with 1 mm of superior-ANT movement of hyoid bone, cervicomental angle reduced by 1.83°. As the hyoid bone moves 1 mm toward sella or posterior nasal spine, the cervicomental angle reduces by 2.13° and 1.94°, respectively. For each degree of reduction in lip-CTA, the cervicomental angle goes down by 0.77°. According to their findings, for each millimeter that the mandible is taken ahead, the cervicomental angle will go down by approximately 1.5°.

Mommearts et al. (2004)^[20] performed a retrospective study of patients with deep bite hypoplastic mandible and evaluated the cervicomental angle, gonial angle, antegonial notch, lower lip position, and ANT mandible bowing after forward repositioning of mandible. They found that in groups with mandibular advancement/chin setback osteotomy and mandibular advancement-POST rotation, there was no significant change in the cervicomental angle in 30–40% participants but it became more acute in 50–60% participants, in dentoalveolar mandibular osteotomy group, there was slight improvement observed in cervicomental angle in 50% participants and no change observed in remaining 50% whereas, in maxillomandibular POST rotation group, cervicomental angle became more acute in all the participants post-surgery. They concluded that procedures that involve a setback of the chin along with mandibular advancement are potentially prone to create or increase submental fullness. It makes the cervicomental angle more obtuse making it difficult to manage, even with liposuction techniques.

Naini et al. (2015)^[13] evaluated the influence of the submentalcervical angle on perceived attractiveness and threshold values of desire for surgery. They included 35 clinicians and 75 laypeople to guarantee 80% in the effectiveness of this questionnaire. This investigation showed that a submental cervical angle of 90–100° is considered to be the most attractive and up to 105° is considered acceptable. Angles above this value begin to be considered as unattractive, though up to 120° is deemed only little unattractive by the layman and clinician groups, but very unattractive by the patient group. By 125–130° all groups perceive the submental-cervical angle as very/extremely unattractive. In terms of threshold values of desire for surgery, for patients the threshold value of desire for surgery was 110°, for lay people the threshold value was 115° and similarly 120° for clinicians.

Haddad and Ghafari (2017)^[21] determined if a new facial line (T), tangent to the throat, intersects the mandibular border in ANT and POST parts in proportions varying with facial configuration, and evaluated the association between chin projection and throat inclination and the potential for the T-line to reflect this association. They observed that patients with mandibular deficits are found to have a cervicomental angle of 90°. The Class II obtuse angle was less acceptable than either of the others, a conclusion agreeing with the other study done by the perception of a CTA angle of 110° as “slightly unattractive,” the “very,” and “extremely” unattractive set measured at 125° and 130°.^[14] This finding supports the concept of more geometric delineation (expansion) of hard and soft tissues as being more esthetic than the constriction of skeletal volume.^[18] A more obtuse CTA represents a constitutional limitation to ideal correction of the chin-throat zone in this dysmorphology, barring the surgical correction, whereby, on average, the post-treatment CTA (reduced by more than 15°) was closer to the Class I readings. In the younger sample, CTA decreased after treatment (from 127° to 115°), also closer the Class I values.^[22]

CONCLUSION

Adult patients with deficient mandible require mandibular advancement for skeletal correction. Such patients often have an obtuse cervicomental angle giving an anesthetic and aged look. Mandibular advancement makes the cervicomental angle more acute, bringing it toward the normal range of 95–125°, which is perceived as attractive and gives a youthful neck appearance. Therefore, while evaluating soft tissues cephalometrically and planning mandibular advancement, the amount of correction required for the cervicomental angle should be taken into consideration.