Hypovitaminosis D, objective oral dryness, and fungal hyphae as three precipitating factors for a subset of secondary burning mouth syndrome

OBJECTIVE: Elucidating the concurrence and interdependence of three precipitating factors as contributors of a subset of secondary burning mouth syndrome (BMS), which is defined having detectable precipitating factors. DESIGN: 47 secondary BMS and 15 non-BMS cases were sourced from medical records of an Oral Pathology Specialty Clinic in Canada (2017–2021). Each case had Cytology, Hematology, and Sialometry tests to detail the state of three precipitating factors (the presence of fungal hyphae, hypovitaminosis D, and objective oral dryness). Three factors were compared between secondary BMS and non-BMS groups independently, in pairs, and as a triple-factor by Fisher's exact tests, Contingency Coefficients, and Logistic Regressions. RESULTS: Rates of objective oral dryness (89.36%) and hypovitaminosis D (74.47%) in the secondary BMS group significantly differ from the non-BMS group (p = 0.0013, p = 0.0016). No difference was found in the incidence of fungal hyphae between BMS (91.49%) and non-BMS groups (p = 0.0881). Rates of three precipitating factors in pairs and as a triple-factor within the secondary BMS group significantly differ from the non-BMS group (p-values from 0.0011 to <0.0001). Their significant correlations with secondary BMS are found independently (excluding fungal hyphae), in pairs, and as a triple-factor (C-values from 0.371 to 0.461, p-values from 0.002 to <0.001). The highest C-value belongs to the triple-factor. Objective oral dryness (p = 0.009) and hypovitaminosis D (p = 0.008) are confirmed as significant predictors for secondary BMS. CONCLUSIONS: The presence of fungal hyphae contribute to a subset of secondary BMS only when coinciding with objective oral dryness, hypovitaminosis D, or both. This interdependent relationship leads to a hypothesis that hypovitaminosis D, which is commonly called “a low value of vitamin D”, and objective oral dryness make an oral environment conducive to insidious Candida invasion, which is an intermediate status of the host-fungal interaction staying between healthy oral mucosa (non-infection) and oral candidiasis (infection).