• This study will enroll approximately 12 endodontists (primary subjects) and approximately 120 patients (secondary subjects) undergoing routine endodontic treatment (primary root canal treatment or retreatment), resulting in approximately 120 observed treatment sessions. Patients will be treated as part of standard clinical care and will not receive any experimental intervention.
• Participating endodontists will wear an Apple Watch to continuously monitor heart rate (HR) during routine endodontic procedures. The Apple Watch contains built-in physiological sensors that automatically record heart rate. HR data are stored locally in the Apple Health app on a study-designated iPhone assigned for research use and handled solely by the Principal Investigator (PI). No real-time data transmission or cloud-based sharing occurs during data recording. At designated intervals, the PI will use the Apple Health app's built-in "Export Health Data" function, which generates a ZIP file containing an export.xml file with sensor-recorded data. The ZIP file will be uploaded directly from the study iPhone to a secure, university-approved UI Box Health Data Folder designated for the study. No research-specific Apple ID, cloud account, or third-party data-sharing platform will be used.
• A trained, non-intervening observer will record start and stop timepoints of predefined endodontic treatment stages to align HR signals with procedural phases. These stages include patient presentation, examination, informed consent, local anesthesia administration, rubber dam placement, access cavity preparation, root canal instrumentation, obturation, and final radiographic assessment. The observer will document only minimal, non-identifiable procedural variables necessary for analysis, including treatment type (primary root canal treatment or retreatment), treatment difficulty level (based on the AAE Endodontic Case Difficulty Assessment), and patient age category. No patient identifiers or protected health information (PHI) will be recorded.
• Each participating endodontist will complete the Perceived Stress Questionnaire (PSQ) two times in total at baseline and at the conclusion of study participation to assess perceived stress levels and evaluate associations between baseline stress and physiological stress responses during treatment. The PSQ requires approximately 5 minutes to complete. Endodontists will not complete questionnaires for individual patient encounters. HR data and permitted procedural variables will be coded, securely stored in the UI Box Health Data Folder, and analyzed to assess HR variation across endodontic treatment stages and treatment difficulty levels. No additional patient identifiers or PHI will be collected beyond what is specified above.

Inclusion Criteria for Primary Subjects (endodontics residents) :

• Active enrollment in an accredited endodontics residency program during the data-collection period
• Routine clinical involvement in primary root canal treatment and/or retreatment
• Willingness to wear a wrist-worn heart rate monitoring device during clinical sessions
• Willingness to complete the Perceived Stress Questionnaire (PSQ) at baseline and at the conclusion of participation
• Absence of medical or dermatologic conditions that would preclude safe or accurate wrist-worn heart rate monitoring

Inclusion Criteria for secondary Subjects (Patients):

• Scheduled to receive standard endodontic care with a participating endodontics resident during the study period
• Willingness to allow the presence of a non-intervening observer
• Willingness to allow collection of minimal, approved visit-level variables
• Adult patients able to provide written informed consent
• Minor patients (under 18 years of age) with parent or legally authorized representative permission
• Assent obtained from minors as follows:
• Verbal assent for minors aged 7-12 years
• Written assent for minors aged 13-17 years
• No formal assent required for children under 7 years of age (developmentally appropriate explanation provided when feasible)
• Ability of patient or legally authorized representative to understand and communicate in English

Exclusion Criteria for Primary Subjects (endodontics residents) :

• Not engaged in clinical endodontic care during the study window
• Known dermatologic, cardiovascular, neurologic, or other medical conditions that could interfere with safe or accurate heart rate monitoring
• Unwilling or unable to provide informed consent or comply with study procedures

Exclusion Criteria for secondary Subjects (Patients):

• Decline consent, permission, or assent
• Withdraw participation at any time
• Prisoners or individuals under custodial supervision
• Pregnant patients

A total of approximately 132 subjects will be enrolled in this study, consisting of approximately 12 endodontics (primary subjects) and approximately 120 patients (secondary subjects). Each participating endodontics will be observed during approximately 10 endodontic treatment sessions, resulting in an estimated total of 120 clinical sessions for data collection. Each patient will participate in one clinical encounter only, while resident participation will continue throughout the data collection period.