The central question in OSA treatment selection is not which therapy works best in the lab—it is which therapy patients will actually use. For overweight patients, this distinction determines everything.

CPAP remains the gold standard for raw efficacy, capable of reducing the apnea-hypopnea index (AHI) to near zero during hours of use. But efficacy measured in a controlled setting diverges sharply from effectiveness measured across real patients, real nights, and real years. The emerging consensus in the dental sleep medicine literature is that oral appliance (OA) therapy, through its dramatically superior compliance profile, achieves equivalent real-world disease alleviation—even in patients with higher BMI where per-hour OA efficacy is modestly reduced.

01The CPAP Compliance Crisis

Adherence Falls Far Short of Clinical Need

The standard definition of CPAP adherence—use for ≥ 4 hours on ≥ 70% of nights—is itself an alarmingly low bar, representing just half the recommended adult sleep duration. Even by this modest standard, the data are stark:

The Dose-Response Problem

The clinical consequences of subthreshold CPAP use extend well beyond simple AHI numbers. Research has identified distinct minimum usage thresholds for each meaningful outcome:

02Oral Appliance Compliance: A Different Profile

What Objective Monitoring Reveals

With the introduction of embedded temperature-sensing microchips, OA compliance can now be verified objectively rather than relying on patient self-report. The data consistently show that OA patients wear their devices for nearly the entire sleep period:

The consistency across studies is striking. Oral appliance patients routinely achieve 6–7+ hours of nightly use—the range required for meaningful blood pressure reduction, functional improvement, and objective sleepiness normalization. CPAP patients, by contrast, rarely sustain those thresholds beyond the first few months of treatment.

Why Patients Prefer Oral Appliances

Patient preference favors oral appliances in four of six crossover RCTs that asked participants to directly compare the two treatments. The reasons are practical: no mask, no hose, no machine noise, no air pressure discomfort, portability for travel, and no dependence on electricity. Critically, the gap between self-reported and objectively measured usage is smaller for OA therapy—less than 30 minutes difference versus more than one hour for CPAP—suggesting that OA compliance is more genuine and less subject to report bias.

03Efficacy vs. Effectiveness: The Core Argument

What the Head-to-Head Data Show

CPAP's per-hour superiority is not in dispute. A 2022 meta-analysis of eight RCTs found a mean AHI advantage of approximately 5.83 events/hour for CPAP over mandibular advancement devices (MADs). Complete response rates (AHI < 5/h) run roughly double with CPAP—around 73% versus 43%. These are real differences in controlled conditions.

But these numbers describe what happens during the hours of use. They say nothing about the hours of non-use—which, for the average CPAP patient, now constitute the majority of the sleep period by year five.

The SARAH Index: Measuring What Actually Happens

The Sleep Adjusted Residual AHI (SARAH Index) was developed specifically to capture real-world treatment effectiveness by combining both efficacy and actual hours of use across the total sleep period:

Mean Disease Alleviation: Equivalence Confirmed Across Studies

Mean Disease Alleviation (MDA)—the product of efficacy and adherence—is the most clinically meaningful measure of how much disease a treatment actually controls. The evidence consistently demonstrates equivalent MDA between CPAP and OA:

Vanderveken et al. (2013) calculated an OA-adjusted MDA of 51.1%, comparable to CPAP's approximately 50% adjusted effectiveness in the same population. A 2023 editorial by Vanderveken and Gagnadoux concluded that superior CPAP efficacy was being systematically offset by inferior CPAP adherence relative to higher overnight OA usage. At World Sleep 2025, presenting interim data from a 253-patient French multicenter trial, Robyn Woidtke stated plainly: "We are seeing that oral appliance therapy can be as effective in mean disease alleviation as CPAP."

04Health Outcomes: What Matters Most Confirms Equivalence

If CPAP were genuinely more effective in the real world, it would produce superior health outcomes across patient populations. The evidence shows it does not. Across every major outcome studied, OA therapy matches CPAP:

The CRESCENT trial result deserves particular attention. The MAD group achieved ≥ 6 hours of nightly use in 56.5% of patients versus just 23.2% for CPAP—crossing the 5.6-hour threshold needed for sustained blood pressure reduction far more consistently. The compliance advantage directly translated into a clinically superior cardiovascular outcome, not merely an equivalent one.

05The Overweight Patient: Why Compliance Matters Even More

BMI Reduces OA Efficacy—But Not Enough to Overcome the Compliance Gap

Higher BMI is consistently associated with reduced oral appliance efficacy. Suzuki et al. (2014) found OA responders had mean BMI of 23.6 versus 27.9 for non-responders. A Korean multicenter study identified BMI as the strongest single predictor of AHI percentage reduction with OA. These are real findings that should inform treatment planning.

However, the critical and often overlooked counterpoint is this: overweight patients also experience degraded CPAP compliance. Higher BMI typically requires higher treatment pressures (≥ 15 cmH₂O), which increases mask leak, aerophagia, claustrophobia, and pressure intolerance. In overweight patients, the compliance gap between CPAP and OA may actually widen—making OA's compliance advantage even more decisive for real-world effectiveness.

Approximately Two-Thirds of Overweight Patients Respond Meaningfully

Despite the BMI effect, the majority of overweight patients still achieve clinically meaningful OA responses. In a large 425-patient cohort, approximately one-third achieved complete resolution (AHI < 5/h), another third achieved > 50% AHI reduction, and only one-third showed minimal response. Even in severe OSA (AHI ≥ 30/h), 23% reached complete resolution and 42% achieved AHI < 10/h.

A case report from the AADSM documented a morbidly obese patient (BMI 36.26, baseline AHI 55.1) who was CPAP-intolerant and achieved AHI reduction to 9.1 with OA therapy. The 2025 French multicenter study of 253 patients with moderate-to-severe OSA found more than half achieved ≥ 50% AHI reduction—with over 90% all-night compliance at 12 months. When 50% efficacy is multiplied by 90% all-night compliance, the MDA calculation yields real-world effectiveness that consistently matches what typical CPAP users actually achieve.

Weight Loss as a Force Multiplier

Weight reduction amplifies OA effectiveness in a way that has no CPAP parallel. A meta-regression of 27 studies found that a 20% BMI reduction corresponded to a 57% AHI reduction; a 10% reduction yielded 36% improvement. For overweight OA patients, combining weight management with oral appliance therapy simultaneously improves the efficacy component of MDA while maintaining the compliance advantage—a dual benefit that CPAP simply cannot offer.

06Clinical Decision Framework

Guideline Positions

The AASM/AADSM 2015 clinical practice guideline recommends OA as first-line therapy for mild-to-moderate OSA and for severe OSA patients who fail CPAP or prefer an alternative. Crucially, the guideline establishes no BMI cutoff for OA candidacy, acknowledging conflicting evidence on the BMI-response relationship. Patient preference is explicitly recognized as a factor to consider before any therapy is prescribed.

Putting It Into Practice

The most important clinical consideration in every row of that table is the same: an oral appliance worn all night every night—even at 50% AHI reduction—delivers dramatically more real-world disease alleviation than a CPAP device worn for 3–4 hours or sitting untouched on the nightstand. For overweight patients who cannot or will not use CPAP consistently, OA therapy is not a compromise. It is the superior clinical choice when treatment is measured by the metrics that predict actual health outcomes.

07Key Clinical Takeaways

• Measure real-world effectiveness, not just lab efficacy: the SARAH Index and Mean Disease Alleviation consistently show OA therapy achieves equivalent disease control to CPAP when compliance is factored in.
• Oral appliance compliance runs 80–90% at 6–7+ hours per night, far exceeding CPAP's 17% long-term adherence rate—and this gap likely widens in overweight patients who require higher CPAP pressures.
• Do not use BMI as a disqualifier for oral appliance candidacy; approximately two-thirds of overweight patients achieve ≥ 50% AHI reduction, and high compliance compensates for the modest reduction in per-hour efficacy.
• Blood pressure outcomes in both the CRESCENT trial and 2025 Journal of Dental Research data favored MAD over CPAP in real-world conditions, driven entirely by the compliance advantage crossing the 5.6-hour threshold.
• For any patient who is non-compliant with CPAP, oral appliance therapy is strongly indicated: partial OA efficacy at high compliance always delivers more mean disease alleviation than full CPAP efficacy at near-zero compliance.