Purpose: The treatment course of patients with obstructive sleep apnea syndrome (OSAS) treated with an oral appliance (OA) was investigated to clarify the therapeutic effect of OA for OSAS and the factors related to efficacy.

Methods: The subjects were 62 patients who were treated with OA in Hokkaido University Hospital. Changes in apnea-hypopnea index (AHI) before and after OA treatment were compared by severity of OSAS to evaluate the therapeutic effect of OA. In addition, the patients were divided into two groups: the group with decreased AHI after the treatment and the group with no change or increased AHI. Then, logistic regression analysis was performed using the following factors as explanatory variables: mandibular position of OA (amount of mandibular protrusion, ratio of mandibular protrusion to the most anterior position, and amount of bite raising), type of OA (one-piece mono-block or two-piece appliance), baseline AHI before treatment, sex, and age.

Results: The average AHI decreased significantly after treatment (before, 23.2; after, 7.4). A significant decrease in AHI was observed even in the severe OSAS group and AHI decreased significantly in every level of severity. Based on the logistic regression analysis in the decreased group and the no change/increased group, age, baseline AHI, and amount of mandibular protrusion were selected as the final explanatory variables and the partial regression coefficients of the three variables were significant. The correlation coefficient of the regression equation was 0.60, which was significant.

Conclusion: The efficacy of OA treatment for every level of OSAS severity was demonstrated. It was suggested that OA can be a treatment option even in severe cases of OSAS. It was indicated that age, baseline AHI and amount of mandibular protrusion were factors associated with the efficacy of OA. These factors need to be taken into consideration when determining the indications for OA and the mandibular position of OA.

Disorders in occlusion can cause systemic symptoms in some cases. A patient who had systemic symptoms including those of the ears and symptoms within the oral cavity, who had shown no improvement in systemic symptoms after receiving treatments from various specialists, visited our clinic suspecting that the cause of the systemic symptoms might be occlusion. We used the hearing value measured with an audiometer as the indicator and provided dental treatments so as to equalize and stabilize the hearing values. At the same time as the dental treatments we also provided instructions on biting （mastication training） to reduce an unfavorable biting habit of masticating on only one side and allow the patient to learn to masticate with the entire jaws in a good balance. As a consequence, occlusion became stable at the proper position, and not only the symptoms inside the oral cavity but also the systemic symptoms improved. The hearing value, which had been outside the normal range before treatment, improved after the mastication training, and nearly entered the normal range after the dental treatments, resulting in favorable objective evaluation of the treatment effects.

A case of severe sleep bruxism（SB） treated with an occlusal appliance which restrains lateral movement by steep canine guidance is reported. The patient was a female in her 20 years who visited our hospital with a chief complaint of grinding sound of the teeth. Based on the clinical diagnosis of SB, treatment was initially performed using a stabilization appliance with a general form. However, no reduction in the number of SB waveforms was observed in the SB assessment by electromyography during sleep. On the other hand, when an appliance with restrained lateral motion by steep canine guidance was applied, the number of SB waveforms was significantly reduced. Even after long-term use of the appliance, there were no symptoms in teeth, periodontal tissue, temporomandibular joint, masticatory muscles, etc., and a good treatment course was obtained. From the treatment experience of this case, it is suggested that SB can be significantly reduced depending on the morphology of the occlusal appliance. Currently, however, there is no evidence that this form of appliance will be effective in all SB cases. Objective assessment of the effect using sleep electromyography needs to be performed in order to accurately determine the appropriateness of continuation of use. It is also considered necessary to carefully and regularly follow up on the condition of teeth, periodontal tissue, temporomandibular joint and masticatory muscles.