Oral Appliance Cuts Sleep Apnea Events by Half in 10-Year Study

A Separated-Type Oral Appliance Cut Apnea Events by More Than Half in a Decade-Long Japanese Study

A custom-made “separated-type” oral appliance reduced the apnea-hypopnea index (AHI) from an average of 17.4 events per hour to 8.2 in Japanese patients with mild-to-moderate obstructive sleep apnea (OSA). Researchers at Hiroshima University Hospital tracked 47 patients over ten years and found that after treatment, not a single patient with follow-up data remained in the severe category. For people who cannot tolerate CPAP machines, a small dental device may offer measurable relief — with important caveats worth understanding.

How Oral Appliances Physically Open the Airway

Obstructive sleep apnea occurs when the tongue and soft tissues of the throat collapse during sleep, repeatedly blocking airflow. Each apnea or hypopnea briefly wakes the brain — often without the sleeper noticing — fragmenting sleep and dropping blood oxygen. Over time, moderate-to-severe OSA raises risks of hypertension, cardiovascular disease, and impaired daytime function, as a 2026 review in Medical Clinics of North America by Duenas and colleagues at Northwell Health makes clear.

Oral appliance therapy attacks the mechanical problem directly. Most devices resemble retainers or thin mouthguards that grip the upper and lower teeth. By advancing the mandible slightly forward, the appliance pulls the tongue base and soft palate away from the back of the throat, enlarging the airway’s most collapsible region. The “separated-type” design studied at Hiroshima University differs from monobloc appliances: it consists of two independent upper and lower trays connected by an adjustable mechanism, allowing fine-tuned jaw positioning and more natural jaw movement.

What the Hiroshima Study Actually Found

Ikeda, Kunimatsu, and colleagues retrospectively reviewed 47 Japanese OSA patients referred for appliance therapy between March 2015 and March 2025. All patients had polysomnography-confirmed diagnoses. Among the 27 patients who completed both baseline and follow-up sleep studies, AHI fell from 17.4 ± 8.6 to 8.2 ± 5.1 events per hour (p < 0.001) — a mean reduction of 9.23 events per hour. That shift moves the average patient from the moderate-severity range into the mild range. Notably, the appliance performed this in a real clinical population, not a tightly controlled trial.

The authors are candid about limitations. The design was retrospective, and more than 40% of patients never underwent follow-up polysomnography. Patients who returned may have been those responding well, which could inflate the apparent benefit. That said, the magnitude of improvement aligns with the broader literature on mandibular advancement devices, which are an established option for mild-to-moderate OSA.

Where Appliances Fit in the OSA Treatment Toolbox

CPAP remains the first-line treatment for severe OSA because it delivers pressurized air that splints the airway open all night. But adherence is the weak point: many patients abandon the mask within months. Oral appliances offer a quieter, travel-friendly alternative, and evidence supports them mainly for mild-to-moderate disease.

The Medical Clinics of North America review emphasizes that OSA is heterogeneous — different patients have different anatomy and collapse patterns. Some people have positional OSA, where apnea occurs mainly on the back; others have tongues that crowd the airway regardless of position. This heterogeneity explains why the field is moving toward personalized therapy: hypoglossal nerve stimulation for selected patients, weight-loss medications such as incretin-based drugs, positional therapy, and oral appliances each suit different physiologies. A similar dental-device study — a splint that cut apnea severity roughly in half — supports the same conclusion. Appliances are not risk-free, however; long-term use can shift the bite, as covered in our piece on posterior open bite risk.

Practical Steps If You’re Considering an Appliance

Get a proper diagnosis first. Home sleep tests or full polysomnography establish your baseline AHI and rule out other disorders. Appliance therapy is best supported for mild-to-moderate OSA; severe OSA usually warrants CPAP first.

Insist on custom fabrication. Boil-and-bite devices sold online lack the precise jaw positioning that made the Hiroshima appliance effective. A dentist trained in dental sleep medicine takes impressions and titrates the advancement gradually — typically starting at 60–70% of maximum protrusion.

Verify it worked. The patients who benefited in this study all underwent repeat sleep testing. Objective follow-up matters: it distinguishes true responders from non-responders, who may need alternative or combination therapy.

Combine with behavioral levers. Weight loss, side sleeping, alcohol avoidance before bed, and even 30-degree bed elevation can add to appliance effects.

Frequently Asked Questions

Is an oral appliance as effective as CPAP?

No. CPAP typically produces larger AHI reductions, but oral appliances often achieve better long-term adherence. For mild-to-moderate OSA, appliances are a well-supported alternative when CPAP is not tolerated.

What is a “separated-type” oral appliance?

It consists of separate upper and lower trays with an adjustable connecting mechanism, allowing precise, incremental advancement of the lower jaw — unlike one-piece designs that fix the jaws together.

Will an oral appliance change my bite?

Long-term use can cause dental movement, including a posterior open bite. Regular dental follow-up minimizes and monitors this risk; report any bite changes promptly.

How long before I notice improvement?

Many patients report less snoring and better morning alertness within days to weeks of reaching the effective advancement setting, but objective confirmation requires a follow-up sleep study.

Conclusion

A decade of data from Hiroshima University shows that a custom, separated-type oral appliance can cut apnea events by more than half in patients with mild-to-moderate OSA. The findings are promising but come from a retrospective study with incomplete follow-up, so they should be read as supportive — not definitive. What is clear is that appliance therapy, when properly fitted and verified with sleep testing, offers a legitimate path to quieter, healthier sleep for the many patients who cannot live with a CPAP mask.

Sources:
https://pubmed.ncbi.nlm.nih.gov/42505766/
https://pubmed.ncbi.nlm.nih.gov/42498426/
https://pubmed.ncbi.nlm.nih.gov/42475493/
https://pubmed.ncbi.nlm.nih.gov/42469518/
https://pubmed.ncbi.nlm.nih.gov/42467132/