Effects of Hard Gum Chewing on Facial Soft Tissue Morphology

Inclusion Criteria: * Healthy, non-smoking adults. * Age 20 to 40 years. * Presence of a full dentition from central incisor to first molar in all four quadrants, excluding second molars. * Stable occlusion with no ongoing orthodontic treatment or myofunctional therapy. * Ability and willingness to comply with the prescribed hard-gum chewing regimen for 4 weeks and attend all study visits. * Ability to provide written informed consent. Exclusion Criteria: * Age younger than 20 years or older than 40 years. * Evident facial asymmetry from a frontal view. * Signs or symptoms of temporomandibular disorders (TMD) according to the Diagnostic Criteria for TMD (DC/TMD). * Less than the normal range of condylar motion during maximum opening and closing. * Parafunctional habits such as bruxism with pain, clenching, or habitual gum chewing for more than 1 hour per day. * History of major craniofacial trauma, orthognathic surgery, or congenital craniofacial anomalies. * Ongoing orthodontic treatment or recent removal of fixed appliances (\<6 months). * Significant malocclusion or missing teeth in the anterior or premolar-first molar region that may affect mastication. * Systemic diseases or medications affecting muscle or bone metabolism. * Previous use of botulinum toxin (Botox) within the last 6 months or anticipated use during the study period. * Pregnancy or lactation. * Allergy or intolerance to the chewing gum ingredients.