Which laser is better—Class 3b or 4a?
Therapeutic laser machines come in a wide range of powers, anywhere from 5 mW to 10 watts. The most common therapeutic lasers
fit into either Class 3b with a power range of 5 to 500 mW or Class 4a with more than 500 mW. Power has absolutely nothing
to do with depth of penetration or the targeting of specific tissues—just the speed of delivery. More powerful laser machines
are simply able to deliver laser energy more quickly.
Class 3b lasers (and low-powered Class 4a lasers) are used in direct contact with the skin. Many manufacturers and laser therapy
textbooks recommend pressing the probe firmly against or into the skin to improve penetration depth. High-powered Class 4a
lasers, on the other hand, cannot be held motionless against the skin because of the potential for cutaneous thermal damage.
This makes accurate dosage calculation impossible. Even with direct contact, a substantial amount of laser light is reflected
and refracted by the skin and subcutaneous tissues. A sweeping technique is commonly recommended with high-powered lasers,
but there's still a tremendous amount of light reflection, so there's no way of knowing exactly how much energy is reaching
the target tissues.
Manufacturers and clinicians say they see benefits with their high-powered Class 4a lasers. That's not in dispute. Light energy
has the potential to heal. However, the effectiveness of high-powered Class 4a lasers cannot be validated in research because
of this dosage-delivery dilemma. For this reason, some companies have elected to produce 750-mW and 1-watt Class 4a lasers
that can be placed directly on the skin, improving upon speed but maintaining the ability to accurately calculate the joules
Which is better—continuous or pulsed wave?
It's important to understand how pulsing the light (frequency or hertz [Hz]) comes into play. It's been proposed that low
frequencies (10 to 100 Hz) are more effective in treating pain, while higher frequencies (2,500 to 5,000 Hz) impact inflammation.
At least for now, no research has shown discernable correlation between any particular frequency and a clinical outcome.
Pulsing light can make dosage calculation more difficult, because it breaks up the laser beam, impacting the overall joules
of energy delivered. Clinically, pulsation frequency can be adjusted to diminish the energy delivered and reduce the superficial
heating properties, for example, in animals with dark hair and people with dark skin who may experience a thermal reaction
because of greater absorption of the light.