Vertical Maxillary Movement Is Associated With Incisal Display in Orthognathic Surgery.

Background

Maxillary incisal display (MID) is a key feature in orthodontic and orthognathic surgical planning that critically impacts esthetics and forms the basis for the vertical positioning of the maxilla. In orthognathic surgical planning, several approaches are taken to position the maxilla to determine the MID, but little evidence exists in the relationship between maxillary movement and MID.

Purpose

The purpose of this study was to measure the association between MID and maxillary movements in maxillary orthognathic surgery.

Study design, setting, and sample

This was a retrospective cohort study of consecutive cases of maxillary orthognathic surgery at the University of Illinois Hospital and Health Sciences System, Department of Oral and Maxillofacial Surgery over a 19-month period. Inclusion criteria were age between 12 and 64 years and presence of cone-beam computed tomography scans before (T0) and at least 6 months after (Tp) surgery. Exclusion criteria were soft tissue strain or abnormalities on cone-beam computed tomography and the presence of facial clefts or syndromic craniofacial deformities.

Predictor variable

The primary predictor variable was vertical maxillary movement (VM) at the maxillary central incisor (U1). Secondary predictor variables were anteroposterior maxillary movement (APM) at U1 and maxillary pitch (MP).

Main outcome variable

The primary outcome variable was MID change from T0 to Tp, measured by a single examiner.

Covariates

Covariates included use of V-Y closure technique, age, and sex.

Analysis

Descriptive statistics and multivariable linear regression including the predictor variables and V-Y closure were performed. Level of statistical significance was P < .05.

Results

In 19 eligible subjects (78.9% [15] females, age 18.3 ± 1.6 years), the MID decreased by 1.17 ± 4.01 mm. Mean VM, APM, and MP were 0.90 mm (range, -3.70 to 10.80), 1.98 mm (range, -1.90 to 6.3), and 2.10 ° (range, -11.40 to 19.40), respectively. Regression showed a strong relationship between MID change and VM only (adjusted R2 = 0.883, P < .001), with a near 1:1 relationship (coefficient 0.921). APM, MP, and V-Y closure did not show a significant relationship (P = .5-.8).

Conclusions and relevance

MID is primarily associated with VM, which explains 88.3% of variances. APM, MP, and V-Y closure showed no such associations in this sample. Knowledge of the predictors of MID can guide the clinician in surgical planning for dentofacial deformities involving the maxilla.