This observational cross-sectional study aims to investigate the association between skeletal malocclusions and body posture using three-dimensional postural analysis. Patients will undergo cephalometric assessment, temporomandibular disorder evaluation using the Helkimo index, and non-invasive postural evaluation using the Spine 3D system, based on rasterstereography technology. Postural parameters, including thoracic kyphosis, lumbar lordosis, trunk inclination, pelvic asymmetry, and spinal deviations, will be analysed in relation to skeletal malocclusion classes and temporomandibular disorders. The study seeks to improve the understanding of the potential interactions between the stomatognathic system and global body posture and to support a multidisciplinary diagnostic approach in orthodontic patients.

This observational cross-sectional study aims to evaluate the association between skeletal malocclusions and postural parameters assessed through three-dimensional postural analysis. Patients will be consecutively recruited according to predefined inclusion and exclusion criteria. Written informed consent will be obtained from all participants or from parents/legal guardians in the case of minors prior to enrolment.

For each participant, demographic and clinical data will be collected using a standardized Case Report Form (CRF). Orthodontic assessment will include lateral cephalometric radiography performed as part of routine clinical practice. Cephalometric analysis will be carried out to evaluate sagittal skeletal relationships through the measurement of Sella-Nasion-A Point, Sella-Nasion-B Point, and A Point-Nasion-B Point angles, allowing classification of skeletal malocclusion into Class I, Class II, or Class III. The presence and severity of temporomandibular disorders will also be evaluated using the Helkimo index as part of the routine orthodontic diagnostic assessment.

All participants will subsequently undergo a three-dimensional postural assessment using the Spine 3D system, a rasterstereography-based technology that enables non-invasive, radiation-free evaluation of spinal alignment and global body posture. The system provides quantitative analysis of several postural parameters, including thoracic kyphotic angle, lumbar lordosis angle, cervical curvature, trunk inclination, pelvic rotation, lateral spinal deviations, scapular symmetry, and pelvic symmetry.

The primary outcome of the study will be the thoracic kyphotic angle measured with the Spine 3D system. Secondary outcomes will include the remaining postural parameters, cephalometric measurements, and temporomandibular disorder assessment scores.

No experimental intervention or modification of standard clinical practice will be performed, as all procedures are observational and non-invasive. Statistical analysis will be conducted to evaluate the association between skeletal malocclusion classes, cephalometric variables, temporomandibular disorders, and postural parameters.

Sample size was calculated considering the thoracic kyphotic angle as the primary outcome. The calculation was based on data reported by Parrini et al. (2018), with a reference population mean of 49.24, an expected mean value of 47.41, a standard deviation of 5.24, α = 0.05, and power = 80%. Therefore, a minimum of 64 participants was required for the study.

Statistical analysis will be conducted with R software (R version 3.1.3, R Foundation for Statistical Computing, Vienna, Austria). Descriptive statistics will be calculated for all variables, including mean, standard deviation, median, minimum value, and maximum value. Linear regression analyses will be performed to evaluate the association between postural parameters, skeletal malocclusions, and temporomandibular disorders. Significance for all statistical tests will be predetermined at p < 0.05.

Inclusion Criteria:

• Patients referred for orthodontic evaluation
• Presence of skeletal malocclusion
• Availability of lateral cephalometric radiograph
• Ability to undergo three-dimensional postural assessment using the Spine 3D system
• Patients of any age and sex
• Provision of written informed consent by the participant or by parents/legal guardians in case of minors

Exclusion Criteria:

• Previous orthodontic treatment
• Previous orthopaedic treatment affecting posture
• Presence of craniofacial syndromes or congenital anomalies
• History of spinal surgery
• Significant musculoskeletal disorders
• Neurological conditions affecting posture
• Use of medications affecting musculoskeletal function
• Inability to undergo postural assessment
• Lack of written informed consent

Patients referred for orthodontic evaluation at the Unit of Orthodontics and Paediatric Dentistry, Department of Clinical, Surgical, Diagnostic and Paediatric Sciences, University of Pavia, presenting skeletal malocclusion and undergoing routine orthodontic diagnostic assessment.