Investigation of the Association Between Upper Crossed Syndrome and Temporomandibular Joint Dysfunction in University Students: An Observational Cross-Sectional Study

Overview

This cross-sectional observational study aims to investigate the relationship between Upper Cross Syndrome (UCS), a postural imbalance characterized by forward head posture and rounded shoulders, and Temporomandibular Disorder (TMD) in university students aged 18-35 years. TMD is a musculoskeletal condition affecting the jaw joint and masticatory muscles, commonly associated with pain, limited mandibular movement, and joint sounds. Since cervical posture and jaw function are anatomically and biomechanically interconnected, postural alterations seen in UCS may be associated with temporomandibular dysfunction. In this study, participants will undergo a single-session assessment including postural angle measurements (craniovertebral angle, head-shoulder angle, thoracic kyphosis angle), temporomandibular joint clinical examination, mandibular range of motion measurements, and completion of the OHIP-14 questionnaire. No intervention will be applied. The findings are expected to contribute to understanding the association between upper body posture and jaw dysfunction in young adults and may provide guidance for interdisciplinary assessment and preventive strategies.

Temporomandibular Disorder (TMD) is a musculoskeletal condition affecting the temporomandibular joint (TMJ) and masticatory muscles, leading to pain and functional impairment. It is characterized by preauricular pain, pain in the jaw joint and masticatory muscles, mandibular movement limitation or deviation, and joint sounds such as clicking or crepitation during jaw movements. TMD is most frequently observed in adults between 20 and 40 years of age, particularly in women, and represents one of the most common causes of orofacial pain. Upper Cross Syndrome (UCS) is a postural imbalance syndrome involving the head, cervical spine, and shoulder girdle. It is characterized by forward head posture, rounded shoulders, scapular protraction or winging, and increased thoracic kyphosis. UCS is commonly associated with prolonged sitting, desk-based activities, and computer use, making it highly prevalent in modern sedentary lifestyles. Previous studies have reported that the prevalence of UCS varies between 11% and 60% across different populations. The anatomical and biomechanical interconnections between the cervical spine, shoulder girdle, and temporomandibular joint suggest a possible relationship between UCS and TMD. Muscles such as the upper trapezius, levator scapulae, sternocleidomastoid, and temporalis play roles in both postural alignment and mandibular function. Increased cervical muscle tenderness and cervical dysfunction are frequently observed in individuals with TMD, indicating a functional relationship between jaw and cervical regions. Furthermore, studies have demonstrated that individuals with temporomandibular pain exhibit significantly greater forward head posture compared to asymptomatic individuals, and the severity of TMD may correlate with the degree of postural alteration. Despite these findings, the specific association between Upper Cross Syndrome and Temporomandibular Disorder has not been sufficiently investigated, particularly in young adult and university student populations. Therefore, this study aims to examine the relationship between UCS-related postural parameters and TMD-related symptoms and functional impairments in university students. Aim The primary aim of this study is to evaluate the association between postural parameters characteristic of Upper Cross Syndrome and temporomandibular joint dysfunction findings in university students aged 18-35 years. Hypotheses H0.1: There is no statistically significant relationship between UCS-related postural angle measurements and mandibular range of motion in university students. H0.2: There is no statistically significant relationship between UCS-related postural angle measurements and pain levels associated with TMD. H0.3: There is no statistically significant relationship between UCS-related postural angle measurements and jaw functional limitations. H0.4: There is no statistically significant relationship between UCS-related postural angle measurements and OHIP-14 scores. Study Design This study is designed as a descriptive, observational, cross-sectional investigation. No intervention will be applied to participants. All data will be collected at a single time point during one assessment session. Study Setting and Timeline The study will be conducted at the Faculty of Physiotherapy and Rehabilitation, University of Health Sciences. Data collection will begin after obtaining approval from the Scientific Research Ethics Committee and is planned to take place between January 14, 2026 and April 14, 2026. Data collection is expected to be completed within approximately eight weeks, followed by manuscript preparation over four weeks. Population and Sample The study population consists of university students aged 18-35 years enrolled at the Faculty of Physiotherapy and Rehabilitation. Due to the impracticality of reaching the entire population, the study sample will consist of volunteers who meet the eligibility criteria. Convenience sampling will be used. Eligible students will be informed via telephone and invited to participate. Upon arrival, the study purpose will be explained face-to-face, questions will be answered, and written informed consent will be obtained. Sample size estimation was performed using G\*Power software based on a previously published study. Assuming an effect size of 1.55 for pain, alpha level of 0.05, and statistical power of 95%, the minimum required sample size was calculated as 24 participants. Inclusion Criteria University students aged between 18 and 35 years Voluntary participation Signed informed consent Exclusion Criteria History of jaw surgery Presence of scoliosis or spinal disorders History of shoulder or spinal surgery Botulinum toxin injection to the facial or jaw region within the past year Diagnosis of rheumatologic disease Presence of neurological, autoimmune, psychological disorders (including dementia, delirium, or significant memory impairment) Known cervical pathology within the past year Assessment Procedures All evaluations will be conducted in a single session lasting approximately 15-20 minutes. First, participants will complete a demographic information form including age, sex, health history, and current pain status. The Oral Health Impact Profile-14 (OHIP-14) will be administered face-to-face to assess the impact of oral health and jaw function on quality of life. Temporomandibular joint clinical assessment will include: Maximum mouth opening Lateral deviation (right and left) Protrusion Observation of crepitation Deviation during opening Muscle spasm Mandibular asymmetry All mandibular range of motion measurements will be obtained using a millimeter ruler. Upper Cross Syndrome evaluation will include measurement of: Craniovertebral angle (forward head posture) Head-shoulder angle (rounded shoulder posture) Thoracic kyphosis angle Participants will be positioned laterally in front of a white wall. Anatomical landmarks including tragus, C7, acromion, and T12 will be marked. A lateral photograph will be taken using the PhysioMaster® application. Craniovertebral angle and head-shoulder angle will be calculated digitally through the application. Thoracic kyphosis angle will be measured manually using the digital goniometer function within the same application. Data Collection Team Data collection will be performed by Dr. Emre Serdar Atalay, Physiotherapist Miray Uymaz, and Physiotherapist Büşra Eryiğit. Demographic and questionnaire data will be collected by Miray Uymaz. TMJ clinical assessments will be performed by Dr. Atalay. Postural measurements will be conducted by Büşra Eryiğit. Data Management and Confidentiality All data will be coded and stored electronically in accordance with confidentiality principles. Personal identifiers will not be included in the analysis dataset. Statistical Analysis Descriptive statistics will be reported as mean ± standard deviation. Normality of distribution will be assessed using the One-Sample Kolmogorov-Smirnov test. For normally distributed data, Independent Samples t-test will be used for group comparisons. For non-normally distributed data, the Mann-Whitney U test will be applied. Statistical significance will be set at p \< 0.05.