In-vitro Tissue-on-tissue Friction Model Differentiates Performance of Dry-mouth Products

Objectives: In-vitro models of mucosal friction are useful to evaluate formulations designed to ameliorate xerosis, including xerostomia. Researchers have noted that apparent efficacies of dry-mouth products depend on the surfaces used to model oral mucosa. This study aimed to determine whether an in-vitro tissue model recently successful for dry-eye formulations was effective in differentiating lubricities of over-the-counter [OTC] dry-mouth products. Methods: Bovine pericardium was used to mimic oral mucosa. One piece of saline-wet pericardium was mounted on a curved support (upper half of friction couple); another laid flat on a moist support (lower half of couple). The reciprocating friction apparatus was operated at room temperature, 32 cycles/min, and 31.5g/cm². Baseline readings were monitored for each tissue couple for 7min before applying 50μl product. Readings continued for 23min before applying 50μl saline at 5-min intervals over 20min. No fluid was added during a final 10min period. Analyses included MAIR-IR spectroscopy and contact angles on Teflon. Three replicate experiments were performed with each of three OTC products and with 99.2% glycerin (control). Results: MAIR-IR demonstrated that the OTC products were dominated by glycerin. Average contact angles were 67° (#1, Stoppers4), 72° (#2, Oasis), 93° (#3, Biotene), and 113° (control). Observations of viscosities were that #1<<control<2=3. Baseline coefficients of friction (μ) averaged 0.360. Coefficients for #1 and the control were 0.263±0.023 and 0.203±0.028, respectively, within 1min of application, and increased to baseline values 5min after application. Both #2 and #3 reduced μ to as low as 0.079 within 1min after application. Product #3's performance improved throughout the 23min period. After saline additions, #3 consistently maintained a lower μ (0.208±0.020) than #2 (0.306±0.108). Conclusions: Friction-reducing efficacies of three OTC dry-mouth products differed after application to model tissue and after saline additions. The tissue-on-tissue model is useful for evaluating lubricities and longevities of dry-mouth products.