Quantitative In Vivo Monitoring of Early Erosion-Associated Enamel Optical Changes Using Swept-Source Optical Coherence Tomography.

This study aims to evaluate the ability of swept-source optical coherence tomography (SS-OCT) to detect early enamel optical changes associated with erosive tooth wear under clinically relevant in vivo conditions. The study also investigates whether salivary stimulation induced by sugar-free chewing gum influences enamel optical properties following repeated erosive challenges. A prospective, longitudinal, within-subject study with a fixed-sequence design was conducted. Twenty-two healthy adults aged 23-33 years participated after meeting predefined inclusion and exclusion criteria. All participants completed two sequential experimental phases separated by a two-day washout period. A fixed-order design (Phase A followed by Phase B) was selected to standardize erosive exposure and minimize variability during repeated intraoral OCT measurements. As an exploratory study, randomization was not performed. In both phases, participants underwent repeated erosive challenges using commercially available orange juice (pH 3.4). During each challenge, participants swished 25 mL of orange juice for 30 seconds followed by a 30-second rest interval, repeated continuously for 10 minutes (total exposure: 250 mL). Erosive challenges were performed three times daily at three-hour intervals over three consecutive days under investigator supervision. Phase A consisted of repeated erosive challenges without intervention. In Phase B, participants followed the identical erosive protocol but chewed sugar-free chewing gum for 15 minutes immediately after each erosive challenge to stimulate salivary flow and enhance natural buffering and remineralization mechanisms. All participants used standardized fluoridated toothpaste and soft-bristled toothbrushes beginning two days before the study and throughout the experimental period. Unstimulated salivary flow rate was measured before enrolment, and participants with salivary flow rates below 0.2 mL/min were excluded. The primary outcome measure was enamel integrated reflectivity (IR), quantified from SS-OCT A-scan analysis as an indicator of enamel optical changes associated with early demineralization. A commercially available swept-source OCT system equipped with an intraoral probe was used for image acquisition. The middle third of the labial surface of the maxillary right central incisor (tooth 11) served as the standardized imaging site. Custom acrylic positioning devices and anatomical landmarks were used to improve reproducibility of repeated measurements. SS-OCT imaging was performed at six standardized time points during each study day: baseline before the first erosive challenge (t1), after the first challenge (t2), after the second challenge (t3), after the third challenge (t4), following a three-hour rest period (t5), and the following morning after overnight salivary exposure (t6). Image acquisition parameters, drying procedures, and positioning were standardized for all participants. Integrated reflectivity values were calculated from predefined regions of interest using established OCT image analysis methods. Five adjacent A-scans were averaged to reduce signal noise. Statistical analyses included paired sample t-tests for predefined comparisons and linear mixed-effects modelling to evaluate longitudinal changes while accounting for repeated measurements within participants. Statistical significance was set at α = 0.05. The study was approved by the appropriate institutional ethics committee, and written informed consent was obtained from all participants before enrolment. The study complied with the principles of the Declaration of Helsinki. Findings are expected to provide evidence regarding the feasibility of SS-OCT as a non-invasive clinical tool for monitoring early erosive enamel changes and evaluating preventive interventions under clinically relevant oral conditions.

Inclusion Criteria: Healthy adults aged 23-33 years. Presence of intact maxillary right central incisor (tooth 11) suitable for repeated SS-OCT imaging. Good general and oral health. Normal unstimulated salivary flow rate (≥0.2 mL/min). Willingness to comply with all study procedures, including repeated erosive challenges and SS-OCT examinations. Provision of written informed consent prior to participation.- Exclusion Criteria: Presence of active dental caries, restorations, enamel defects, cracks, or erosive lesions on the study tooth. Ongoing orthodontic treatment affecting the study tooth. History of systemic diseases or medications known to affect salivary flow or enamel mineralization. Unstimulated salivary flow rate \