Clinical and radiographic assessment of gummy smile patients with altered passive eruption: a cross-sectional study in a Thai population

The study aimed to evaluate the clinical crown length (CCL) among patients diagnosed with altered passive eruption (APE), the causes of a gummy smile, the prevalence of APE, and the correlation between parameters.

A total of 86 gummy smile patients (516 teeth) underwent clinical examination and assessment using cone-beam computed tomography (CBCT), photography, and intraoral scanning.

Significantly shorter CCL and distance between the cementoenamel junction and bone crest (CEJ-BC) were observed among APE-affected teeth (p < 0.05). Among the patients, 56.1% of patients were diagnosed with APE, and most of them were affected by a combination of APE and hypermobile upper lip (HUL). Based on 183 APE-affected teeth, the prevalence of APE types and subtypes was as follows: APE1A (96; 19.3%), APE1B (78; 15.9%), APE2A (8; 1.6%), and APE2B (1; 0.2%). Positive correlations were found between keratinized gingival width (KGW) and bone thickness (BT), while negative correlations were observed between gingival thickness (GT) and BT.

Shorter CCL and CEJ-BC were the highlighted features of APE. APE affected approximately half of the gummy smile patients, with most of them presenting with a combination of HUL. Almost teeth affected by APE were classified as Type I, with a nearly equal distribution between subtypes A and B.

The clinical and radiographic features of APE contribute to a better understanding of this condition and facilitate the management of patients affected by APE. Approximately half of gummy smile patients will require multidisciplinary treatment.