Deep overbite is a common malocclusion caused by abnormal vertical development of the upper and lower dental arches and jaws. Among the malocclusions of primary dentition, the most common are increased overjet and deep overbite, with the highest prevalence in Europe (33.08 %) [1]. A deep overbite poses risks to oral health and physiological functions. Treating deep overbites has always been challenging in orthodontic therapy, with treatment success largely depending on the degree of bite opening. Clinically, methods such as uprighting or extruding the posterior teeth and intruding the anterior teeth are commonly used to open the bite [2]. Treatment strategies depend on the incisor type and skeletal vertical pattern. Flatting the curve of Spee is a common strategy involving mandibular anterior tooth intrusion, posterior tooth extrusion, or a combination of both [3]. For patients with gummy smiles, maxillary anterior tooth intrusion may be appropriate [4]. In patients with hypodivergence, appropriate extrusion of the posterior teeth can be advantageous for deep overbite correction, whereas it should be avoided in those with hyperdivergence; conversely, intruding the maxillary and mandibular anterior teeth is preferable.

Clear aligner treatment (CAT) has gained in popularity recently owing to its aesthetics, comfort, and convenience, especially among adults with specific needs, making it a preferred choice. As of August 2024, over 18 million patients worldwide have received Invisalign treatment. With continuous advancements in clear aligner technology and digital orthodontics, current invisible aligner systems are suitable for various types of malocclusions. Align Technology introduced Invisalign G5 in 2014 and G8 in 2021, with the aim of enhancing deep overbite correction [5].

The primary mechanism of the use of clear aligners for bite opening involves the intrusion of both the maxillary and mandibular anterior teeth and their proclination, with minimal molar extrusion. Over the past 15 years, numerous studies [[6], [7], [8], [9]] have been published on the accuracy of CAT. In 2009, Kravitz et al. [8] conducted a prospective study. They reported the predictability of CAT, demonstrating an average accuracy of 41 % for Invisalign treatment of maxillary and mandibular anterior teeth. In 2020, Haouili et al. [6] published updated results, noting that although movement accuracy was slightly improved (reaching 50 %), weaknesses such as mandibular incisor intrusion (35 %) remained. However, since overcorrection was already included in the initial design stage, the authors stated that these percentages may underestimate the actual efficacy of the Invisalign system. A scoping review by Muro et al. [9] revealed that aligner treatment had poorer predictability for overbite correction and that intrusion was one of the least predictable movements. Kravitz et al. [7] reported that only 6 % of patients completed the treatment without any refinements, whereas 22.4 % completed with one refinement. On average, CAT patients required approximately 2–3 refinements and a treatment duration of 22.8 months.

The clinical effectiveness of clear aligners in treating deep overbites has not reached a definitive conclusion, and the predictability of incisor movement remains a topic of focus. Research on whether additional refinements provide similar treatment accuracy has not been clearly established. Therefore, the aim of this study was to comprehensively evaluate the accuracy of incisor intrusion in treating adult female patients with deep overbites using aligners, identify discrepancies in the vertical movement of individual teeth among several refinements, and assess the predictability of clear aligners for deep overbite correction to provide clinical guidance for orthodontists in treatment planning and prognosis assessment.