Understanding the changes in bite force and occlusal force distribution in ETT is clinically important, as it can directly influence tooth prognosis, guide restorative treatment planning, and impact the long-term survival of the treated tooth. Therefore, this study aims to further explore changes and possible correlation in maximum bite force (MBF), occlusal force distribution and patients' subjective perception of chewing function of endodontically treated teeth after non-surgical root canal treatment, subsequent restoration, and during long-term follow-up, along with comparing to contralateral vital teeth.

Methods: Patients aged 20-60 years who underwent non-surgical root canal treatment at the Graduate Endodontic Clinic, Faculty of Dentistry, Chulalongkorn University, with the following teeth indicated for endodontic treatment. Measurements of maximum bite force (MBF) of ETT and contralateral vital teeth, relative occlusal force (ROF), and questionnaire responses, are performed at the following time points: before NS-RCT, 1 month after completion of NS-RCT (before doing restoration), 3 months after crown restoration, 1, 2 and 4 years after completion of NS-RCT.

Differences in MBF and ROF over time points within subjects and differences in MBF and ROF between ETT and their contralateral vital teeth were statistically analyzed.

Inclusion Criteria:

• Premolars or molars diagnosed with pulp necrosis or previously initiate therapy with normal apical tissues, asymptomatic apical periodontitis, or chronic apical abscess without full coverage restoration.
• Adequate remaining tooth structure for cuspal coverage restoration.
• Presence of adjacent teeth and functional opposing natural teeth.
• No analgesics drug effect at the time of investigation or not have taken analgesics 6 hours ago.

Exclusion Criteria:

• Patients undergoing other dental treatments during the study period that may interfere with occlusion or bite force distribution, such as orthodontic treatment, jaw surgery, or full mouth restoration.
• Received treatments that cause weakness of the jaw and facial muscles, such as botox injections.
• History or symptoms of temporomandibular disorders (TMD)
• Periodontal disease with second- or third-degree mobility
• Teeth presenting crack lines extending into the pulp chamber floor or root canal orifices.

Patients who underwent non-surgical root canal treatment at the Graduate Endodontic Clinic, Faculty of Dentistry, Chulalongkorn University