Effects of Hard Gum Chewing on Facial Soft Tissue Morphology

Facial morphology is influenced by multiple functional factors, including masticatory muscle activity. Although hard gum chewing has been promoted as a method to improve facial definition and jawline appearance, there is limited scientific evidence demonstrating whether intentional chewing can produce measurable changes in facial soft tissues.

The purpose of this prospective pilot clinical trial is to evaluate the effect of intentional hard gum chewing on facial morphology using three-dimensional stereophotogrammetry (3dMD). Twenty healthy adults aged 20-40 years will be enrolled. Participants will complete a standardized hard-gum chewing protocol every other day for 4 weeks. Each chewing session will last approximately 16 minutes and will follow a predefined protocol designed to provide a consistent masticatory stimulus.

Three-dimensional facial images will be obtained at baseline (T0), immediately after the intervention period (T1), and after a 4-5-week washout period (T2). Facial changes will be assessed through surface registration techniques, heatmap analysis, regional displacement measurements, and linear and angular soft-tissue measurements. Participants will also complete questionnaires regarding muscle fatigue, soreness, oral behaviors, and temporomandibular symptoms.

The primary objective is to determine whether intentional hard gum chewing produces measurable changes in facial morphology. Secondary objectives include evaluating participant-reported outcomes and monitoring for adverse events or symptoms suggestive of temporomandibular disorders.

Because this is a pilot study, the results will be used to estimate effect sizes and feasibility for future larger clinical trials investigating the relationship between masticatory activity and facial soft-tissue adaptation.

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.