TMD is one of the most common oral and maxillofacial disorders [39]. It can be treated with occlusal splints, manual therapy, physiotherapy, counselling therapy, arthrocentesis or arthroscopy, and oral or injectable pharmacotherapy. Occlusal splints are commonly used as a non-invasive treatment for patients with TMD. Among occlusal splint types, SS is one of the most effective [13], and has been shown to have an acceptable treatment effect on the signs and symptoms of TMD patients [11]. In this retrospective study, three-dimensional cephalometric analyses were performed using CBCT and primarily examined the vertical skeletal and dentoalveolar changes and secondarily the anteroposterior skeletal, dentoalveolar, and soft tissue changes after SS therapy in patients with myofascial and/or intra-articular disorders.

In terms of the primary outcome variables, this study demonstrated an increased steepness of the mandibular plan as represented by the increase in the MP-SN angle after SS treatment. Previous case study reports have shown that occlusal changes and clockwise mandibular rotation with facial profile changes often occur after splint therapy for patients with TMDs; these changes can be attributed to alterations in condylar position and morphology, and they can further worsen the condition of a retrognathic mandible and complicate subsequent orthodontic treatments [29, 31].

The comparison of the results of the Jarabak ratio before and after treatment revealed a significant decrease in the ratio of posterior facial height to anterior facial height, which is consistent with the increase in the lower facial height and the mandibular angle. In addition, the articular angle increased, and the lower gonial angle increased, indicating that the mandible shifted posteriorly in relation to the skull and that the mandible underwent clockwise rotation. These changes may explain the increased overjet, decreased overbite and open occlusion that were observed after treatment. The presence of these occlusal changes after SS treatment might be due to the restoration of the mandible to the CR position. Furthermore, the inability to achieve the same occlusion as that before SS treatment revealed that articular remodelling and adaptive changes may have occurred, as described in literature [40, 41].

The inclination of OP can be altered by various factors, such as ageing, growth, occlusal wear, tooth loss and use of dental devices [42, 43]. Changes in OP may also depend on changes in the reference planes, such as SN and FH. The findings of this study reveal a significant increase in the inclination of the functional and bisecting OPs, and these observed changes may be attributed to the clockwise rotation of the mandible after SS treatment. Additionally, the initial occlusal contact in the molar region may change with the disocclusion of the molars, which often occurs due to the posterior displacement of the mandible when the CR of the patient is taken and the condyles are seated in the CR position, which may affect the inclination of OP. In the study of Magdaleno and Ginestal [29], a patient experienced unstable occlusions with dental contacts only at the level of the wisdom teeth upon removal of a splint. Subsequently, the patient was informed of the need for orthodontic treatment to stabilise the occlusions, and the patient was referred to an orthodontist.

The current study findings revealed a significant decrease in the overbite. Alterations in the occlusal relationship induced by wearing SS may lead to the development of an anterior open bite. Intrusion of the molars is considered one of the most effective treatment methods for correcting an open bite [44]. In severe cases where patients already have an open bite before treatment and it increases further after SS treatment, orthognathic surgery may be recommended to correct such skeletal discrepancies after splint treatment [45]. When a splint is used, the condyle in the CR sits passively in the fossa, which can result in altered dental occlusion, with contact primarily on the most posterior teeth and the potential development of an anterior open bite [25, 29].

Changes in jaw position have a considerable impact on the diagnosis and treatment of dental malocclusion. These changes directly affect the diagnosis of a patient’s vertical skeletal pattern and the dentist’s analysis of the treatment mechanism. This impact can be more complex and challenging in patients with a vertical skeletal pattern than in patients with a horizontal skeletal pattern, as indicated by Shildkraut et al. [46]. The current study showed that the skeletal patterns of patients undergoing SS treatment tended to change from the original horizontal type to the average type or from the average type to the vertical type. This finding is important for determining whether an orthodontic treatment plan should include tooth extraction or orthognathic surgery to correct skeletal discrepancies, which is especially true in cases that require orthodontic treatment after SS treatment, as reported in some studies [31, 45]. In summary, the position of the mandible plays a crucial role in determining the appropriate clinical treatment plan.

Patients with a steep maxillary OP are likely to experience occlusal interference during mandibular movement and develop a convex facial profile. The steeper the maxillary OP is, the greater the impact force is during tooth contact. Early contact points on mandibular teeth may act as a fulcrum, potentially leading to condyle displacement [31, 45].

Regarding the secondary outcome variables, the current study findings revealeda significant retrusion of the mandible (decrease in SNB angle), a significant increase in the sagittal discrepancy between both jaws (↑ANB angle) and a significant increase in the overjet. No significant maxillary or mandibular dentoalveolar changes were found in this study. This result reveals that SS might not have an effect on the angulation and position of the incisors and molars. The exception is the angulation of L1-NB, which increased significantly due to the posterior displacement and clockwise rotation of the mandible. Moreover, the current study’s results showed a significant increase in LL-EP distance, which is consistent with the results of increased ANB angle due to changes in mandibular position. This change in LL-EP distance may have affected the patients’ profiles after SS treatment.

Patients undergoing single-stage treatment with occlusal splints may experience a relapse of symptoms after treatment [47]. Thus, dentists sometimes recommend that the treatment be performed in two stages. In the first stage, an occlusal splint is used, followed immediately by the second stage of orthodontic treatment to correct the position of the teeth, correct the rotation of the mandible and eliminate all occlusal disturbances. The goal is to obtain an improved long-term curative outcome, as reported by Ramachandran et al. [48]. A stable jaw after splint therapy ensures stable orthodontic treatment results [49]. However, this recommendation is not generalisable to all patients undergoing SS therapy. It applies only to patients who experience severe post-treatment effects. Therefore, post-SS treatment analyses must be performed to determine the appropriate course of action.

The study’s findings suggest crucial considerations for the management of TMD using stabilization splints. The observed possible post-treatment changes in mandibular position and occlusion emphasize the necessity for careful monitoring and individualized treatment planning. Clinicians must remain attentive to potential changes such as skeletal discrepancies and anterior open bite, which may necessitate further orthodontic interventions to achieve optimal and stable post-TMD treatment results. These changes not only have immediate implications for treatment but also carry significance for diagnosis and subsequent treatment planning if required.

Limitations of this study include its retrospective design, which prevents blinding and the inclusion of a control group. The need for a larger sample size to enhance the generalizability and validity of the findings with more males to be included to analyze the effect of gender, and the pre-treatment skeletal vertical patterns on the treatment changes. Additionally, conducting long-term follow-up studies to assess treatment effects after considerable period of time.