Vertical Facial Morphology and Occlusal Force Changes After Masseter Botulinum Toxin Injection in Bruxism

Biruni University34 enrolled

Overview

This study investigated whether the shape of the face affects how jaw muscles respond to botulinum toxin injections in people who grind their teeth (bruxism). Participants were divided into two groups based on their facial structure: low-angle (shorter face height) and normal-angle. Each participant received botulinum toxin type A injections into the masseter (jaw) muscle. Bite force measurements were taken before and 15 days after the injection using the T-Scan computerized occlusal analysis system. The study aimed to determine whether facial structure influences the early changes in bite force balance following the injection.

Study Type

INTERVENTIONAL

Allocation

Purpose

TREATMENT

Masking

NONE

Enrollment

Conditions

Bruxism Occlusal Changes

Interventions

Botulinum toxin type A (Botox®, Allergan, Irvine, CA, USA) was injected bilaterally into the masseter muscle at a dose of 25 units per side (50 units total per patient). Injections were performed by a single experienced clinician under sterile conditions using a 30-gauge needle.

Eligibility

Sex: ALLMin age: 18 YearsMax age: 40 Years

Medical Language ↔ Plain English

Inclusion Criteria: * Age 18-40 years * Confirmed bruxism diagnosis through self-report and clinical signs * Full permanent dentition excluding third molars * Angle Class I molar relationship * No previous BTX-A injection within 6 months * GoGn/SN angle between 18° and 38° on lateral cephalometric radiograph Exclusion Criteria: * Systemic neuromuscular disorders * Known allergy to botulinum toxin or its excipients * Pregnancy or breastfeeding * Active infection at the injection site * Concurrent use of medications known to interact with BTX-A * History of orthognathic surgery or prior temporomandibular joint surgery

Outcomes

Primary Outcomes

Change in Center of Force (CoF)

The Center of Force (CoF) represents the geometric center of the total occlusal force distribution, measured using the T-Scan Novus™ computerized occlusal analysis system (version 10.0.40; Tekscan, Inc., South Boston, MA, USA). CoF values closer to zero indicate greater bilateral occlusal balance. Within-group changes (T0 to T1) and between-group differences were assessed and compared between low-angle (GoGn/SN \< 26°) and normal-angle (GoGn/SN 26-38°) subgroups.

Time frame: Baseline (T0) and day 15 post-injection (T1)

Secondary Outcomes

Change in Anterior and Posterior Force Percentage

Anterior force percentage is defined as the combined occlusal force distribution of the anterior teeth, and posterior force percentage as the combined force distribution of the posterior teeth. Both were measured using the T-Scan Novus™ system at baseline (T0) and day 15 post-injection (T1). Within-group changes and between-group differences in anterior-posterior force distribution were evaluated and compared between low-angle and normal-angle subgroups.