Bone Remodeling by Rapid Maxillary Expansion (RME): Evidence from the Monitoring of Bone Turnover Biomarkers in Salivary Matrix

Background/Objectives: Orthodontic treatment with a Rapid Maxillary Expander (RME) induces stress on the mid-palatal suture and involves the surrounding craniofacial sutures, leading to significant variations in bone turnover markers (BTMs). The aim of this study was to evaluate whether monitoring biomarkers of bone resorption and deposition in saliva could provide indications for assessing RME treatment effectiveness in pediatric patients. Materials and Methods: The study was conducted at the Dental Clinic of Foggia in collaboration with the Clinical Pathology Unit of the Policlinico-Bari from January 2023 to September 2025. Salivary samples were collected using cotton swabs (SALIVETTE®, SARSTEDT, Nümbrecht-Elsenroth, Germany) from 47 patients (aged 9–13 years) presenting with Class I dental and skeletal relationships and transverse maxillary deficiency. Samples were collected at five time points: before RME application (t0), and 15 (t1), 30 (t2), 45 (t3), and 60 (t4) days after the start of expansion. For pairwise comparisons of concentrations at different time points the Wilcoxon signed-rank test was used. Analysis of Variance (ANOVA) and Ordinary Least Squares (OLS) multiple regression were used to analyze the relationships between different biomarker concentrations over time. Spearman correlation was used to assess relationships between BTM concentrations at the different time points. Results: The Wilcoxon test showed that the medians of the differences for P1NP measurements were statistically significant at all time points, except between t0 and t1. Differences in PTHrP concentrations were significant, except for the comparison of t2 and t3 relative to t4. No statistically significant differences were observed for TRAcP across any measurement times. ANOVA yielded a high F-value for P1NP (F = 3.6128; p = 0.0128), indicating significant variation, whereas the F-ratios for PTHrP (F = 1.3329; p = 0.2736) and TRAcP (F = 1.3915; p = 0.2534) were close to 1, suggesting non-significant variability. Spearman correlation indicated that P1NP showed the strongest relationships with temporal variables. Discussion and Conclusions: Rapid maxillary expansion results in a significant increase in P1NP levels, reflecting collagen deposition and the onset of bone formation. This preliminary study on saliva highlights how biochemical changes can support clinicians in monitoring and validating the effectiveness of treatment.