Lasers in Restorative Dentistry

• Lasers are used in restorative dentistry.

Laser Ablation of Dental Hard Tissue

• Two key criteria for laser ablation are matching the incident wavelength to target chromophores and evacuating the products of ablation.

Ablation Threshold

• The minimum energy required to generate a clinical effect is the ablation or vaporization.
• When incident photonic energy is above the ablation threshold of the target, that results in the conversion of photonic energy into photothermal heat change in the target.

Laser Handpiece Tips

• As the tip diameter is reduced, the energy per exposed target area increases as well as overheating can occur.
• Quartz tips provide efficient transmission of laser energy.
  • Spallation can cause irregularity in the beam.
• Sapphire tips offer marginal improvements in energy delivery.
  • Sapphire tips have limitations, like being more expensive and having a higher fracture risk.

Advantages of Laser Cavity Preparation vs Rotary Instruments

• Lasers are more conservative.
  • They allow for the preservation of sound tissue and the removal of caries with higher water content.
• Lasers generate less heat.
  • Explosive defragmentation allows much of the heat to escape from the cavity, carried off in ablated particles.
• Lasers are less painful.
  • Lasers involve no contact, no vibration, and less heat.
• Lasers offer disinfection, providing a bactericidal effect.

Laser vs Rotary Instrumentation

Classification of Lasers Used in Dentistry

Carbon Dioxide (CO2) Laser

• Emits infrared light at wavelengths of 9300 nm for cavity preparation and 10,600 nm for soft tissue applications.
• Advantages include excellent hydrophilicity, effective in ablating soft, water-rich tissues (gingivectomy, oral ulcers).
• Disadvantages include the potential for carbonization of hard tissue.

Neodymium Yag Laser (Nd: YAG Laser)

• The 1064 nm wavelength is highly absorbed in melanin, less in hemoglobin, and slightly in water.
• Advantages include ablation of pigmented tissues and excellent hemostasis.
• Disadvantages include very low absorption in sound enamel or dentin, and the potential for unwanted heating effects like cracking and melting of mineral structures.

Erbium Lasers

• Er:YAG (2940 nm) erbium-doped yttrium aluminium garnet
• Er,Cr:YSGG (2780 nm) erbium, chromium-doped yttrium scandium gallium garnet
• Both wavelengths are highly absorbed in water, with Er:YAG being more absorbed.
• They exhibit precise and selective ablation of tooth tissue.

Waterlase (Biolase)

• Er,Cr:YSGG at 2780 nm provides optimal absorption in both water and hydroxyapatite for efficient cutting in both hard and soft tissue.
• Waterlase employs patented technology that combines laser energy and a water spray in a process called "Hydrophotonics," delivering photons into an air-water matrix system.
• This process requires minimal or no anesthesia, and involves no heat, vibration, or pressure.

Advantages of Waterlase over Conventional Methods

• For Hard Tissue:
  • Less pain during and after the procedure
  • Minimal to no anesthesia needed
  • Precise removal and conservation of sound tooth structure
• For Soft Tissue:
  • Quicker healing
  • Reduced postoperative swelling, bleeding, and discomfort

Diode Laser

• Semiconductor diode lasers are available in four different wavelengths: 810 to 830 nm, 940 nm, and 980 nm.
• They are used in bleaching and soft tissue procedures.

Argon Laser

• This laser operates at 488 nm, which is high-intensity visible blue light.
• Argon lasers are used particularly for the polymerization of restorative resin materials and teeth bleaching.

Soft Tissue Laser Applications

• Gingivectomy: Using diode lasers absorbed by melanin and hemoglobin to lead to soft tissue ablation.
• Frenectomy
• Gingival troughing for impression: To exposure of sub-gingival tooth margins for impression taking.
• Exposure of implant.
• Biopsy incision/excision.
• Pulp capping/pulpotomy: Resulting in laser hemostasis and decontamination.
• Treatment of aphthous ulcers

Light Amplification by Stimulated Emission of Radiation (LASER)

• The first dental laser was available in 1989.
• Laser light is monochromatic, directional, and coherent vs ordinary light

Basic Laser Components

• Lasers include an optical cavity that includes the active medium.
• They have an active medium, using different wavelengths for specific lasers.
• Lasers have a delivery system.
• Their controllers have software that controls the parameters of laser emission.
• Lasers have an energy source

Laser Classification by Wavelength

• Ultraviolet (100-400 nm)
• Visible laser (400-750 nm)
• Infrared laser (750 nm and above)

Laser Classification by Mode of Operation

• Pulsed laser
• Non-pulsed (continuous) laser

Laser Classification by Use

• Soft tissue laser
• Hard tissue laser

Laser Classification by Active Medium

• Gas lasers (Argon/Carbon-dioxide).
• Solid-state lasers (Nd:YAG/Er:YAG).

Laser Photonic Energy-Hard Tissue Interactions

• Hard dental tissues are different percentages of hydroxyapatite, water, and collagen matrix.
• Each compound is a target chromophore: a tissue element capable of selective absorption of photonic laser energy.
• The affinity of mid-IR lasers (erbium lasers) wavelengths for water aids absorption in demineralized tissue that is organic material with a higher percentage of water, which protects sound tissue.
• Incident laser energy converts chromophores (water or carbonated hydroxyapatite) to heat and then superheating, leading to disruptive expansion in tissue; fragments are ejected, and a hole is cut.
• This effect is spallation.

Laser Ablation

• Laser ablation is the process of removing material from a solid surface by irradiating it with a laser beam.
• The rate of dental hard tissue ablation depends on multiple factors: incident laser energy, wavelength, pulse duration, power density, delivery mode, ablation products, angle of the tip, and fluoridation of tissue.
  • Power (W) = energy (J) x pulse repetition rate (Hz or pps)

Explore laser applications in restorative dentistry, focusing on laser ablation, the ablation threshold, and laser handpiece tips like quartz and sapphire. Compare laser cavity preparation advantages to rotary instruments, and how matching wavelength to target chromophores, and evacuating the products of ablation are two key criteria for laser ablation.