Prevalence of altered passive eruption in orthodontically treated and untreated patients

Some authors have reported that after orthodontic treatment (OT), a "gummy smile" might develop. Nevertheless, there are no studies in the literature that investigate whether OT increases the presence of altered passive eruption (APE). The primary aim of this cross-sectional study is to evaluate the prevalence of APE after OT (OT group) and compare it with patients who never received OT (control group). A secondary aim is to identify which variables are related to APE.

The study population consisted of 190 patients (95 patients each in the control and OT groups), providing 1,140 anterior teeth for the clinical examination. The following clinical parameters were assessed: presence or absence of APE, clinical crown length, and gingival biotype, which was divided into three categories: thin-scalloped, thick-flat, and thick-scalloped.

Twenty-eight patients (29.5%) were diagnosed with APE in the control group and 40 (42.1%) in the OT group, although this difference was not statistically significant (P = 0.07). Furthermore, 34 (75.6%) patients with thick-flat biotype were diagnosed with APE, whereas 30 (31.3%) and four (8.2%) with thick-scalloped and thin-scalloped biotypes, respectively, had APE. These differences were statistically significant (P <0.001).

It was concluded that: 1) the prevalence of APE is higher after OT but not to a statistically significant degree and 2) APE is more common in individuals with a thick-flat gingival biotype.