The goal of this clinical trial is to learn if Heart Rate Variability Biofeedback (HRVB) can reduce stress and anxiety in dentistry students during the transition from pre-clinical training to clinical practice.

The main questions this study aims to answer are:

1. Does HRVB training reduce perceived stress, measured with the Perceived Stress Scale (PSS-10), from baseline to post-intervention and to 2-month follow-up?
2. Does HRVB training reduce psychological distress, measured with the Kessler Psychological Distress Scale, 10-item version (K-10), from baseline to post-intervention and to 2-month follow-up?
3. Does HRVB training reduce anxiety, measured with the State-Trait Anxiety Inventory, Form Y, State subscale state anxiety (STAI Y-1), from baseline to post-intervention and to 2-month follow-up?

Researchers will compare an HRVB training group to a control group (no intervention) to see if HRVB leads to greater improvements in stress, distress, and anxiety across the study time points.

Participants will:

• Receive study information and provide electronic informed consent.
• Complete online baseline questionnaires (sociodemographic questionnaire, K-10, PSS-10, and STAI Y-1).
• Be randomly assigned to one of two groups: HRVB training or control (no intervention).
• If assigned to the HRVB group, complete a 5-week program with 10 sessions (twice per week; about 10 minutes per session) using an emWave2 HRVB device; participants will practice slow breathing (about 6 breaths per minute) while recalling a positive memory, with real-time feedback provided in a game format.
• If assigned to the HRVB group, practice the breathing exercise daily.
• If assigned to the control group, not receive HRVB sessions or daily breathing training as part of the study, and only complete the study assessments at the scheduled time points.
• Complete the post-intervention assessment online after the intervention period (same questionnaires as baseline except the sociodemographic questionnaire).
• Complete a follow-up assessment online about 2 months after the end of the intervention period; participants will be contacted by email to complete this follow-up questionnaire.

This study is a randomized clinical trial designed to evaluate a brief Heart Rate Variability Biofeedback (HRVB) training program to help manage stress and anxiety during a critical stage of dentistry education: the transition from pre-clinical training to clinical practice with real patients. During this transition, students may experience increased pressure and responsibility, adapt to new clinical routines and interactions, and face concerns related to performance and making mistakes. The project focuses on whether a structured HRVB training protocol can support students' adaptation during this period and whether any potential benefits are maintained after the end of the training.

Study setting and overall design:

The study will be conducted with students from the Integrated Master's in Dentistry at Egas Moniz School of Health and Science. The design is a randomized, two-arm, parallel-group clinical trial with repeated assessments over time. After enrollment, participants will be allocated to one of two groups: (1) an experimental group that will receive the HRVB training protocol or (2) a control group that will not receive an intervention during the study period. Both groups will be assessed at three time points: baseline (pre-intervention), immediately after the intervention period (post-intervention assessment), and approximately two months after the end of the intervention (follow-up). This structure allows the study to examine changes over time within each group and to explore differences between groups across the same schedule of assessments.

Recruitment and enrollment procedures:

Recruitment will occur through direct contact with students to present the study and its objectives, as well as via announcements in university social media and flyers made available in the dental clinic. Interested students will be provided with a link to access the electronic informed consent process. Only after providing informed consent will participants be given access to the baseline assessment. Throughout recruitment, students will be provided with clear information about the study's objectives, procedures, potential risks and benefits, and the confidentiality of collected data.

Assessment schedule and data collection procedures Data collection will be performed using electronic questionnaires. The baseline (pre-intervention) assessment includes a sociodemographic questionnaire and a set of standardized self-report questionnaires related to stress, psychological distress, and anxiety. The sociodemographic questionnaire is used to characterize the sample and to identify information relevant to eligibility screening and participant description.

After the intervention period is complete, all participants will complete the post-intervention assessment, which uses the same questionnaire set, as the baseline assessment, except that the sociodemographic questionnaire is not repeated. Approximately two months after the end of the intervention, a follow-up assessment will be conducted. Participants will be contacted by email and asked to complete an online questionnaire similar to the post-intervention assessment. This repeated assessment approach is intended to capture both short-term changes associated with the intervention period and whether any changes persist after the intervention has ended.

Randomization and group allocation:

After recruitment is completed, participants will be randomly distributed into the experimental (HRVB) group and the control group. Randomization is used to reduce systematic differences between groups and to help ensure that any observed differences across time are more likely to be associated with the intervention rather than pre-existing group differences.

Experimental condition, HRVB training protocol:

Participants allocated to the experimental group will complete a structured HRVB program delivered over five weeks. The program consists of 10 HRVB sessions, scheduled twice per week, with each session lasting approximately 10 minutes. During the HRVB sessions, participants are instructed to breathe slowly (approximately six breaths per minute) and to attempt to recall a memory they consider positive while practicing the breathing pattern. The feedback is provided in the form of an interactive game in which the objective is to make a hot-air balloon fly as quickly as possible, with the goal of achieving greater distance in each session. In addition to the scheduled HRVB sessions, participants in the experimental group will be asked to complete daily breathing practice. This daily practice component is intended to support skill acquisition and encourage regular application of the breathing technique beyond the supervised sessions.

Biofeedback device and feedback format The HRVB training uses a portable HRVB system (emWave2) developed for monitoring heart rate variability and training cardiac coherence. The device uses an ear sensor to capture cardiac signals in real time and provides feedback in a game-based format. At the end of each session, the software presents a final score reflecting the participant's level of cardiac coherence, which represents the degree of harmony between cardiac and respiratory rhythms. Higher values are described as indicating greater coherence and physiological balance. The game-based interface is intended to facilitate engagement and make feedback understandable and actionable during training.

Control condition, no intervention during the study period:

Participants allocated to the control group will not take part in HRVB sessions and will not be asked to perform daily breathing training as part of the study protocol. Their participation will consist of completing the same online assessments at the scheduled time points (baseline, post-intervention, and follow-up). This allows the study to compare the pattern of change in the experimental group to a group experiencing the same academic transition period without receiving the HRVB training component.

Participant experience and time commitment:

Participation involves completing online questionnaires at three time points. For those allocated to the experimental group, participation also includes attending 10 brief HRVB sessions over five weeks and completing daily breathing practice logs. For those allocated to the control group, participation is limited to completing the assessments on the same schedule. The follow-up assessment is conducted remotely, with participants contacted by email to complete the questionnaire.

Safety considerations and management of discomfort:

The protocol includes specific precautions intended to minimize potential discomfort associated with HRVB use. Although the protocol notes that the equipment has no contraindications and that adverse effects are not known, participants are informed that they have the right to interrupt participation at any time without the need to justify their decision. If any physical or emotional discomfort occurs during the intervention, the session will be promptly suspended. Any adverse event will be recorded and addressed according to the situation and the participant's needs.

Ethics oversight and start of data collection:

The project is approved by the Ethics Committee at Egas Moniz School of Health and Science. The study procedures are planned to follow applicable ethical principles for research involving human participants, including respect for autonomy, voluntariness, and confidentiality.

Voluntary participation and the right to withdraw:

Participation is voluntary. Students can refuse to participate or can stop participating at any time, without negative consequences. Participants are informed that they can request deletion of their data from this study up to the start of the data analysis phase, in line with the project's stated procedures for data handling and participant rights.

Confidentiality and data protection procedures:

The study includes multiple measures to protect participants' personal data and privacy. Data will be pseudonymized using a numerical code assigned to each participant. A separate correspondence file (linking participant identity to the pseudonymized code) will be created for situations where identification is necessary, such as a participant's request for data deletion; this file will be encrypted, password-protected, and accessible only to the research team. Study data will be stored on secure platforms (OneDrive) with access restricted to the research team.

Because email contact is needed for recruitment, scheduling, and follow-up, participants' email addresses will be collected for contact purposes. However, the email list will be stored in an independent file without any correspondence to the other study data collected. This separation is intended to reduce the risk of linking identifiable contact information to questionnaire responses and other research data.

Follow-up and participant support:

At follow-up, participants will be contacted by email to complete the online follow-up assessment approximately two months after the end of the intervention period. In any situation where a need for psychological or psychiatric follow-up is detected, participants will be advised to seek support through the Psychology clinic at Egas Moniz campus. This procedure is included to ensure that participants who may benefit from additional support are guided toward appropriate resources.

Planned approach to analysis:

The study will include descriptive analysis to characterize the sample, followed by analyses aimed at comparing patterns of change over time within and between groups across repeated assessments. The analysis plan is structured to evaluate differences across time points and to examine whether the HRVB group shows a different trajectory from the control group across the baseline, post-intervention, and follow-up assessments.

Rationale for the intervention approach:

HRVB is a form of biofeedback in which physiological signals are measured and presented in a way that helps participants learn to voluntarily influence a target response. In this project, the target response relates to heart rate variability patterns, with training focused on slow-paced breathing and the use of a positive memory during practice. The training uses real-time feedback to support learning and self-regulation, and it includes repeated practice sessions to encourage skill development and possible transfer to daily life. The protocol emphasizes a brief, structured program intended to be feasible to implement and potentially useful during a time-limited but demanding educational transition.

Operational flow of the study:

1. Students are approached through invitation-based recruitment methods (direct contact, social media announcements, flyers) and are informed about the study's goals and procedures.
2. Interested students access an electronic informed consent link and decide whether to participate.
3. After consent, students complete the baseline online assessment (including the sociodemographic questionnaire and the psychological questionnaires).
4. After recruitment is completed, participants are randomly assigned to either the HRVB training group or the control group.
5. Over the next five weeks, the HRVB group completes the scheduled HRVB sessions and daily breathing practice logs, while the control group receives no study intervention during this period.
6. After the intervention period ends, all participants complete the post-intervention online assessment.
7. Approximately two months later, participants are contacted by email to complete the follow-up assessment online.
8. Data are stored securely using pseudonymization and separation of contact information, and analyses are conducted after completion of data collection, consistent with the study's procedures and participant rights.

Inclusion Criteria:

• Enrolled in the Integrated Master's in Dentistry at Egas Moniz School of Health and Science.
• Attending the 4th year of the program for the first time (transition from pre-clinical to clinical training).
• Able to provide informed consent autonomously.

Exclusion Criteria:

• Initiation or change in the last 6 months of psychopharmacological medication or psychotherapy (including psychological support/supportive psychotherapy)
• Diagnosed psychiatric disorder.
• Regular use (more than twice per week) of psychotropic substances.

Individual participant data (IPD) will not be shared because the informed consent obtained for this study did not include permission to share de-identified participant-level data with external researchers. If an ethics/IRB amendment and participant authorization (e.g., re-consent) are obtained in the future, the study team may update this record and make a de-identified dataset available under controlled access.