# Guiding Esthetic Crown Lengthening: A CBCT-Based Modified Classification of Altered Passive Eruption

## TL;DR

This study introduces a new classification system for altered passive eruption to guide esthetic crown lengthening surgery in patients with excessive gingival display.

## Contribution

A CBCT-based modified classification of altered passive eruption is proposed to improve treatment planning for esthetic crown lengthening.

## Key findings

- ECL is predicted to reduce gingival display below 4 mm in 66.67% of patients with altered passive eruption.
- Most patients (78.57%) had APE combined with a hyperactive upper lip and displayed gingival display ≥ 4 mm.
- The modified APE classification revealed that most patients belonged to Types II and III, requiring open-flap surgical approaches.

## Abstract

Background: Altered passive eruption (APE) is one of the etiological factors associated with excessive gingival display and is commonly treated with esthetic crown lengthening (ECL). However, existing classification systems provide limited guidance for selecting appropriate treatment approaches. Objectives: The aim of this study was to evaluate (1) the expected outcome of ECL in eliminating unattractive excessive gingival display (4 mm) based on digital smile assessment and (2) the distribution of teeth and patients according to the modified APE classification. Methods: Forty-two Thai patients with APE underwent clinical examination, digital smile assessment, intraoral scanning, and CBCT. Predicted gingival display (PGD) was calculated to assess the expected outcomes of ECL. The modified APE classification, incorporating CEJ–BC distance and buccal bone thickness, was analyzed at both the tooth and patient levels. Results: A total of 252 maxillary anterior teeth were assessed. Most patients (78.57%) presented with APE and hyperactive upper lip. The mean gingival display (GD) was 6.04 ± 1.76 mm, with GD ≥ 4 mm observed in 92.86% of patients. The mean PGD was 3.56 ± 1.71 mm, and ECL was predicted to reduce GD to < 4 mm in 66.67% of patients. Teeth were classified as Class I (28.97%), II (15.48%), III (41.27%), and IV (14.28%); only Types II (11.9%) and III (88.1%) occurred at the patient level. Conclusions: ECL performed at the CEJ level is predicted to eliminate excessive gingival display in approximately two-thirds of APE patients. The modified APE classification offers guidance for selecting surgical approaches, highlighting the necessity of open-flap procedures and the limited applicability of flapless approaches.