Efficiency of anterior tooth intrusion in deep overbite cases with clear aligners: analysis via the indirect model superimposition method

Abstract

BACKGROUND: Anterior tooth intrusion is commonly used in the deep overbite cases with clear aligners. However, the intrusion efficiency varies significantly among different cases. OBJECTIVE: To analyze and compare the intrusion efficiency of the anterior teeth with clear aligners by the indirect model superimposition method based on the occlusal records. METHODS: Forty-three patients with anterior deep overbite were selected as the subjects of this study and divided into the non-extraction and extraction groups. The non-extraction group was then divided into the alignment and maxillary molar distalization subgroups. The extraction group was subdivided into the first premolar extraction and second premolar extraction subgroups. In the Geomagic 2014 software, the occlusal plane inclinations of the pre- and post-treatment models were calibrated based on the angle between the Frankfort plane and occlusal plane. The maxillary and mandibular models were superimposed by the maxillary palatine folds and occlusal records. Based on the Frankfort plane, the measurement coordinate system was established to measure the actual intrusion amount. The relative intrusion amount in the ClinCheck plan was recorded as the designed intrusion amount. Correlation and linear regression analyses were performed between the designed and actual intrusion amounts. RESULTS AND CONCLUSION: (1) The actual intrusion amount of anterior teeth in both non-extraction and extraction groups was significantly less than the designed amount (P < 0.01), indicating that overcorrection should be designed when intruding anterior teeth with clear aligners. (2) The anterior intrusion efficiency in the non-extraction group (50.69%) was significantly higher than that in the extraction group (39.73%) (P < 0.01), suggesting that more overcorrection should be designed in extraction cases. (3) The intrusion efficiency of lower anterior teeth was significantly higher than that of upper anterior teeth (P < 0.01), so more overcorrection should be designed for upper anterior teeth. (4) There was no significant difference in anterior intrusion efficiency between the maxillary molar distalization subgroup and the simple alignment subgroup (P > 0.05). (5) The anterior intrusion efficiency in the second premolar extraction subgroup was significantly higher than that in the first premolar extraction subgroup (P < 0.01), indicating that extraction of the second premolar is more favorable for vertical control of anterior teeth than extraction of the first premolar. (6) There was a linear relationship between the designed and actual intrusion amounts in all groups, and the regression equations can provide a reference for clinicians to design individualized overcorrection amounts according to different tooth positions and different treatment plans.

1. Introduction

Anterior deep overbite is one of the most common malocclusions, characterized by excessive vertical overlap of the maxillary incisors over the mandibular incisors, exceeding one-third of the clinical crown. The treatment strategy for deep overbite depends on the underlying mechanism. For dental deep overbite caused by over-eruption of anterior teeth and/or under-eruption of posterior teeth, as well as for mild skeletal deep overbite amenable to camouflage treatment, the main approach involves intruding anterior teeth and/or extruding posterior teeth.

Posterior extrusion refers to the coronal movement of posterior teeth, which increases the occlusal vertical dimension and opens the anterior bite. However, posterior extrusion may involve clockwise rotation of the mandible, increasing the lower facial height and worsening mandibular retrusion; thus, it is not suitable for high-angle deep overbite cases. In recent years, clear aligner technology has advanced significantly due to material innovations, technological improvements, and accumulated clinical experience. Clear aligners work by fully enveloping the clinical crowns and gradually changing the aligner shape, generating forces that move teeth toward the target position. Good retention is a prerequisite for effective clear aligner treatment, but when extruding posterior teeth, the direction of force is aligned with the dislodgement direction, reducing the aligner's grip and hindering force application. Therefore, extrusion is one of the most difficult tooth movements to achieve with clear aligners, and anterior intrusion is the primary method for correcting deep overbite, especially in high-angle cases.

Anterior intrusion can be classified as relative intrusion (labial tipping) or absolute intrusion (bodily movement along the tooth axis into the alveolar bone). Clinically, anterior intrusion often involves a combination of both. Since labial tipping increases protrusion, clinicians tend to design more absolute intrusion when planning clear aligner treatment. However, the achievement of absolute intrusion is influenced by various factors, such as the width of the alveolar bone at the root apex. In cases with thin alveolar bone, the root apex may contact the cortical bone, creating cortical anchorage that impedes intrusion. Many studies have reported that the efficiency of clear aligners in improving deep overbite is less than 50%. Furthermore, intrusion efficiency varies by tooth position and treatment plan, with differences between upper and lower anterior teeth, and between incisors and canines. Molar distalization is a tooth movement with high predictability with clear aligners, but the reactive force can cause labial tipping of anterior teeth, producing a relative intrusion effect. Since deep overbite cases often present with crowding and lateral... (truncated for brevity)