Lasers used for cavity preparation are ______ systems with wavelengths of small penetration depths so no heat transfer to the pulp.

• A. CO2
• B. Nd:YAG
• C. Erbium based systems ER:YAG and ER,CR:YSGG
• D. Diode

Answer: (C)

The key idea here is that the laser used for cavity preparation should deposit energy in a very thin surface layer so heat does not reach the pulp. Erbium-based lasers (Er:YAG and Er,Cr:YSGG) operate at wavelengths that are highly absorbed by water and by the mineral components of tooth structure. This strong water absorption means the energy is confined to a superficial zone, causing rapid water vaporization and a micro-explosive removal of tissue rather than deep heating. The result is efficient ablation with a minimal heat-affected zone, which helps protect the pulp from heat transfer during cavity prep.

Other lasers, like Nd:YAG and diode types, have less water absorption at their wavelengths, so the energy penetrates deeper and increases the risk of thermal diffusion to the pulp. CO2 lasers also interact with water but can cause more surface changes and charring, making them less ideal for controlled hard-tissue cutting in routine cavity preparation. Therefore, the Er:YAG and Er,Cr:YSGG systems are preferred for their shallow penetration and reduced thermal impact on the pulp.