LASERS IN PROSTHODONTICS
Light has been employed as a curative agent for many centuries. It was used in heliotherapy or restoration of health.
Einstein is given credit for the development of the theory of spontaneous and stimulated emission.
The initial laser assembled by Maiman was a pulsed ruby laser.
The first report of laser exposure to vital human teeth appeared in 1965.
The first laser dentist was a physician, and the first laser patient was a dentist.
Laser physics
Understanding how a Laser works before knowing the role of Lasers in Prosthodontics.
A laser is a monochromatic, collimated, and coherent beam.
Monochromatic- it has a single color.
Collimate-beam has specific spatial boundaries.
Coherency-the light waves produced have a specific form of energy.
When light meets matter, it can be diverted (reflected or scattered) or consumed. If a photon is consumed, its energy is not damaged but preferably used to enhance the energy level of the absorbing atom or molecule.
This is the basic idea of laser physics and laser-tissue interactions.
An atom can absorb a photon then terminates to exist, and an electron (e) within the atom jumps to a higher level (e°). This atom is pumped up to exited state from the resting ground state. In the excited state, the atom is unbalanced and will soon immediately turn back to the ground state, discharging the collected energy in the frame of the emitted photon. This process is called spontaneous emission.
The manner of lasing happens when an excited atom can be excited to emit a photon before the process occurs immediately. When a photon of specifically the right energy (wavelength) enters the electromagnetic field of an enthusiastic atom, the incident photon triggers the breakup of the excited electron to lower energy levels. This is followed by the release of the stored energy in the form of the second photon.
The first photon is not absorbed but continues to encounter another excited atom. Stimulated emission can only occur when the incident photon has exactly the same energy as the released photon. The result of stimulated emission is two photons of identical wavelength traveling in the same direction.
If the collection of an atom includes more than that pumped into the excited state than that continue in the resting state, a population inversion exists, which is a necessary condition for lasing. Now spontaneous emission of a photon by one atom will stimulate the release of 2nd photon. Both the photons will trigger the release of 2 more photons; these 4 will yield 8, 8 yields 16, and so on. In a miniature space at the velocity of light, this photon chain reaction creates a short, sharp stream of monochromatic (same wavelength) and coherent (same phase) light.
Laser components and beam generation
Components
- The lasing medium within the optical cavity
- Energy source
- Cooling system
An optical cavity consists of two parallel placed mirrors. Energy is provided to pump atoms up to the excited state continuously, the population inversion can be maintained, and high-intensity light circulating back and forth between the 2 mirrors can be generated. The mirrors collimate the light, i.e., photons perpendicular to the mirrors reenter the active medium, while those off will leave the lasing process. The process is not 100% efficient, and some energy is converted into heat; thus, it is necessary to provide some form of cooling.
The active medium contains the homogenous population of atoms, or molecules that are pumped up to the excited state are stimulated to lase. The active medium suspended in the optical cavity as a gas, liquid or solid state (e.g. crystal). Thus stimulated emission within the optical cavity generates a coherent, collimated monochromatic beam of light. The laser is named after the active medium. E.g.Co2 argon
Power density
Power density is the concentration of photon in a unit area. Photon concentration is measured in watts and sq cm. Power density can be increased by placing a lens in the beam path.
Gating and pulsing
Surgical lasers have timing shutters positioned in the beam path. Timing circuits control the opening and closing of the shutter. Timing values are set by controls on the front panel control.
Solid state lasers
The lasing medium is dissolved in a see-through crystal.
Nd-YAG laser
Ho-YAG laser
Er-YAG laser
Lasing occurs at different wavelengths for each.
Laser interactions with biologic and hard tissue
Laser energy will communicate with tissue in four modes.
Reflected
Transmitted
Absorbed
Scattered
Thermal interactions of tissues
Temp (°c)
42-45
More than 65
70-90
More than 100
More than 200
Tissue effect
Hyperthermia
Desiccation,
Coagulation
Tissue welding
Vaporization
Carbonization and charing
Four basic types of tissue responses
- Photochemical interactions.
- Photothermal interactions.
- Photomechanical interactions.
- Photoelectrical interactions.
Photochemical communications include biostimulation, which explains the stimulatory outcomes of laser light on biochemical and molecular processes that usually occur in tissues such as healing and repair.
Photothermal interactions manifest clinically as photoablation or removal of tissue by vaporization and superheating of tissue.
Photomechanical interactions include photodisruption, which is the breaking apart of structures by laser light.
Photoelectrical interactions include photoplasmolysis, which describes how the tissue is separated through the production of electrically charged ions and particles that survive in a semi-gaseous or high energy state.
Laser safety
Laser hazard classification
Class 1: a low powered laser that is safe to view.
Class 2: low powered lasers which are hazardous if viewed more
than1000 sec.
Class 3: medium powered lasers that can be hazardous if viewed
directly
Class 4: high powered lasers that produce ocular, skin and fire
hazard.
Personal eye equipment
The light produced by class 4 beam produces ocular damage by direct viewing or reflection of the beam.
Both the patient and the dental operator should be protected by either goggles or safety devices.
Factor for selecting eyewear
- The wavelength of the laser emission.
- Maximum permissible exposure limits.
- Degradation of absorbing media or filter.
- The optical density of eyewear.
- Comfort and fit.
Wave lengths used in dentistry
- Argon – 514nm
- Diode – 800 to 900nm
- Nd-YAG – 1364nm
- Co2 – 10,600nm
- Ho-YAG – 2120nm
- Eximer – 308nm
Lasers in prosthodontics
Laser Use in Fixed Prosthodontics
- Laser sulcular gingivoplasty.
- Sculpting of edentulous areas.
Sulcular gingivoplasty
- Used to develop a new, more youthful gingival sulcus and to kill just enough epithelial attachment.
- To facilitate the placement (not packing) of the retraction cord.
- Improves impression techniques and minimizes gingival recession.
Technique
A dental laser that has good absorption characteristics for hemoglobin or water and has a variety of power settings is used.
Laser tips or fibers 400 to 600µm diameter are ideal
Quartz glass fiber must be cleaved properly to permit complete transmittance.
Energy settings according to the manufacturer’s recommendations and the operator’s experience.
A feather-light stroke should be used that resembles the pressure equal to drawing a line with ink-dipped brush without bending.
The fiber should be held parallel to the long axis of the tooth as much possible.
Post-operative instructions
- Warm salt water rinses morning and night.
- Use of ultra-soft toothbrush to the affected area.
- Use of over the counter pain medications.
Sculpting of edentulous area
It is advantageous to contour the edentulous ridge to enhance the esthetics.
In the conventional gingettage, diamonds are used for the bulk removal of the tissue during crown preparation.
The laser is used to coagulate this area at the same time.
This approach saves time and reduces unnecessary laser energy to the site.
Lasers in Prosthodontics – Pre-Prosthetic Surgery
Pre-prosthetic surgeries
- Soft tissue tuberosity reduction.
- Removal of frenum
- Treatment of hyperplastic tissue.
- Removal of fibromas and papillomas.
Tuberosity reduction
It can be pendulous and not offer a stable base for a removable appliance.
Carbon dioxide laser is recommended, because of its speed and effectiveness in vaporization.
The new 600µ and 1000µ fibers and different wavelengths can be used.
The paintbrush-like stroke allows the operator to vaporize or cutaway tissue carefully.
Careful planning by using mounted casts and fabricating of splints are recommended.
The splint is used to verify sufficient removal.
Frenectomy
Carbon dioxide laser is ideal for maxillary midline and lingual frenectomies. The frenum is vaporized with the Co2 laser.
The tip of the tongue is gripped, the pressure is placed, and from the greatest concavity, the frenum is cut.
The power settings are usually 4-5 watts. The time required for the procedure is anywhere between 35 secs to 3 mins.
With the use of lasers in prosthodontics for this procedure, the patient can be guaranteed a pain-free postoperative course.
Hyperplastic tissue
Epulis fisurata (fibrous hyperplasia of alveolar mucosa.)
Papillomatosis (fibrous hyperplasia of the palatal mucosa.)
These are two hyperplastic reactions to denture irritation and poor fit. Pulsed Nd-YAG laser with 320µ fiber and 2.8 watt of laser energy is used. Co2 laser is also used with 4 watt of power setting using an 800µ tip.
Advantages
- Virtually bloodless field.
- Enhanced infection control.
- Reduced swelling and pain.
- Reduced scarring.
The special role of lasers in Prosthodontics
Laser Welding
Welding of ceramic materials
The Carbon dioxide laser is well suited for the treatment of ceramic materials because its emission wavelength is almost totally absorbed by ceramic.
After vacuum firing, an irregular wave-like structure with dendrite crystal features is found on dental ceramics. After the furnace glass firing, these structures are leveled off, but the crystal features are not removed.
With the laser gloss firing, a full leveling of the surface is achieved, and even with SEM examinations, any remaining structure is hardly noticeable.
Welding of dental alloys
Laser welding belongs to the field of melt-weld processing. The efficiency of laser beam treatment is proportional to the degree of energy absorption of the material. Nd: YAG laser, the degree of absorption of titanium, is slightly better than precious metal alloys. Laser welds are superior to soldered welds since corrosion takes place much later on laser welds.
Advantages
- High bond strength and corrosion resistance.
- Reduced oxidation when argon gas is applied during welding.
- Greater precision.
Laser Use in Implants
Titanium is material of choice for implants as it displays minimal corrosion and excellent biocompatibility. Its use for a prosthesis is hampered by difficulties in processing because of its high melting point and susceptibility to oxidation. The use of lasers in prosthodontics is a big comeback for its use in Implants.
In dentistry, soldering has generally be used to join metals. Due to its high melting point, laser welding is more practical.
Laser radiation can produce surface alterations of titanium implants in the form of pits and melted areas, which could improve osseointegration. But indiscriminate use can remove surface layers from plasma coated implants, hence Nd: YAG should not be used for peri-implant soft tissue procedures. The preferential reflection of Co2 laser energy greatly reduces the potential for damage to the metallic implant surface and thermal injury to underlying tissues. This is a major advantage for laser soft-tissue procedures involving metallic implants.
Exposure of Implants (2nd stage surgery)
Lasers can be used to remove the tissues over implants, whether they are single or multiple. Before any surgery, the healing process, the crestal bone height, and the zones of the attached gingiva should be evaluated. Carbon dioxide laser is used for uncovering of implants to access the cover screw.
Conclusion
Although there has been researching done in laser in prosthodontics since 1960, only recently has there clinical use grown. But there hasn’t been an equal flurry of research to prove the claim that laser is the more efficient and better method of treatment.