Development and use of a mouth gag for oral experiments in rats.

OBJECTIVE: Rodent models such as mice and rats are often used in investigations of the oral cavity in the fields of periodontology and dental anesthesiology. When various treatments are performed in the oral cavity, it is very important to secure the visual field while keeping the animal's mouth fully opened, in order to ensure the consistency of experimental procedures. Therefore, we developed a standardized gag conforming to various degrees of oral cavity size of different aged rats. DESIGN: The gag was composed of a rectangular incisor-opening frame constructed from a stainless steel wire with retractors and a dial to alter the opening amounts. Wistar rats (n = 5) aged 4, 8, and 12 weeks were used to evaluate the suitability of the gag in oral cavity. As tests for application of gag in intraoral experiments, the ligature placement around the molars, drug injection into the gingiva, measurement of gingival blood flow rate, and installation of stimulation an electrode for somatosensory-evoked potentials into the molar were performed. RESULTS: Adjusting the opening dial enabled both the maintenance of open state and more favorable intraoral observation compared with tweezers as a control device in all different types of rats. Furthermore, our gag made it possible to facilitate the insertion of diverse instruments into the oral cavity and to achieve various experimental purposes. The stainless-steel gag can also be autoclaved and dry-heat sterilized. CONCLUSION: It was revealed that our mouth gag can be widely applied to various oral experiments in different old aged rats.