Ultrasonic Electric Toothbrush: How It Works

An ultrasonic toothbrush operates at frequencies above 20,000 Hz — beyond the range of human hearing — typically at 1.6 MHz (1,600,000 Hz). At these frequencies, the bristles do not visibly vibrate. Instead, the ultrasonic waves propagate through the fluid surrounding the bristles and create a phenomenon called cavitation: the rapid formation and collapse of microscopic bubbles that disrupt bacterial biofilm at a cellular level. This is fundamentally different from how sonic toothbrushes clean, and the technology exists in a much smaller niche market.

Ultrasonic vs. Sonic: The Key Differences

These two terms are frequently confused, but they describe very different technologies:

Sonic Toothbrushes (200-400 Hz)

• Bristles visibly vibrate side-to-side at 24,000-31,000 strokes/minute
• Primary cleaning through mechanical bristle contact
• Secondary cleaning through fluid dynamics
• Brands: Philips Sonicare, Burst, Waterpik, Quip
• Price range: $25-$400
• Extensive clinical evidence

Ultrasonic Toothbrushes (1.6 MHz+)

• Bristles do not visibly move from ultrasonic action alone
• Cleaning through cavitation (microscopic bubble implosion)
• Some models add sonic vibration for mechanical cleaning
• Brands: Emmi-dent, Megasonex
• Price range: $100-$250
• Limited clinical evidence

The Science: How Ultrasonic Cleaning Works

Ultrasonic cleaning is well established in industrial and medical applications — it is used to clean surgical instruments, jewelry, and electronic components. The mechanism involves cavitation: when ultrasonic waves pass through a liquid, they create alternating high-pressure and low-pressure zones. During the low-pressure phase, tiny vacuum bubbles form. When these bubbles collapse during the high-pressure phase, they release concentrated energy that dislodges contaminants from surfaces.

In the context of an ultrasonic toothbrush, the theory is that cavitation bubbles forming and collapsing in the saliva and toothpaste layer on your teeth can:

• Disrupt bacterial cell walls. The energy from collapsing bubbles can damage bacterial cell membranes, potentially killing bacteria rather than just displacing them.
• Break apart biofilm structure. The localized forces can disrupt the polysaccharide matrix that holds plaque biofilm together.
• Clean beyond direct bristle contact. Ultrasonic waves can penetrate areas that bristles cannot reach, including deep periodontal pockets and subgingival surfaces.

However, it is important to note that the energy levels in a consumer toothbrush are substantially lower than industrial ultrasonic cleaners. Whether the cavitation generated by a toothbrush at consumer-safe power levels is sufficient to deliver these theoretical benefits in a real oral environment is still debated. For more on the broader science, see how electric toothbrushes work.

Available Ultrasonic Models

Emmi-dent

The most well-known purely ultrasonic brand. Emmi-dent toothbrushes emit ultrasonic waves at 1.6 MHz through a piezoelectric chip embedded in each brush head. The bristles do not move — you hold the brush against your teeth and the ultrasonic waves do the cleaning through the special toothpaste provided (which is formulated to enhance cavitation). Price: approximately $150-200 for the handle.

Megasonex

Megasonex combines ultrasonic waves (1.6 MHz) with sonic vibration (9,000 or 18,000 strokes/minute). This dual approach provides both the theoretical ultrasonic cleaning benefits and the proven mechanical cleaning of sonic brushing. The two modes can be used together or independently. Price: approximately $100-150.

What the Clinical Evidence Shows

The evidence base for ultrasonic toothbrushes is substantially thinner than for sonic or oscillating-rotating brushes:

• A limited number of clinical studies exist, and most have small sample sizes
• Studies by C. 호 et al. have shown ultrasonic brushes can reduce plaque and gingivitis, but these studies were not included in the Cochrane systematic review due to methodology limitations
• In vitro studies demonstrate effective bacterial disruption at ultrasonic frequencies, but in vivo translation is less clear
• No large-scale, long-term studies compare ultrasonic to sonic or oscillating-rotating brushes
• The Cochrane review, which is the gold standard for electric toothbrush clinical evidence, did not have sufficient ultrasonic-specific data to draw separate conclusions about this mechanism

This does not mean ultrasonic toothbrushes are ineffective — it means we do not have the same level of evidence confidence as we do for Oral-B and Sonicare products, which have been studied in dozens of randomized controlled trials.

Who Might Benefit from Ultrasonic?

• Patients with periodontal disease. The theoretical ability of ultrasonic waves to reach below the gumline into periodontal pockets is the most compelling use case. However, this should complement, not replace, professional periodontal treatment.
• Implant patients. Ultrasonic cleaning may help maintain peri-implant health without mechanical abrasion of titanium surfaces.
• People who cannot tolerate vibration. Purely ultrasonic brushes (like Emmi-dent) produce no bristle movement, which may suit people with extreme oral sensitivity.

Practical Considerations

• Cost: Ultrasonic brushes are more expensive than comparable sonic brushes, and replacement heads are pricier due to the embedded piezoelectric chip (Emmi-dent).
• Availability: Limited compared to mainstream brands. Replacement heads and accessories may be harder to find.
• Learning curve: Purely ultrasonic brushes require a different technique — holding still rather than brushing. This feels unnatural and requires adjustment.
• Special toothpaste: Some brands recommend or require their own toothpaste formulations to optimize cavitation. This adds to ongoing costs.

For most people, a well-established sonic or oscillating-rotating toothbrush with decades of clinical validation is the more practical and proven choice. Ultrasonic technology is promising but still waiting for the body of evidence to match its theoretical potential.