Authors: DR. MANU BANSAL, DR. CHEENA GUPTA.
GURU NANAK DEV DENTAL COLLEGE AND RESEARCH INSTITUTE, SUNAM.

ABSTRACT: Air abrasive technology has re-emerged in dentistry. Air abrasion devices are high-energy sandblasting and tooth cutting systems. The history, characteristics and clinical applications of this approach are reviewed, including advantages and limitations for the removal of stains, enamel, dentin and decay. Air abrasive technology is especially suited for use in bonded restorations.

INTRODUCTION: G .V. Black gave the principles of cavity preparations nearly 100 years ago, which provided an effective approach to successful amalgam restorations. Unfortunately, the extension and retentive undercuts often require the removal of healthy tooth structure. Conservation of tooth structure is paramount, rather than using EXTENSION FOR PREVENTION as a treatment guideline, emphasis now is placed on RESTRICTION WITH CONVICTION.
The ultimate goal of minimal intervention is to extend the life of restored teeth with as less intervention as possible. So, one of the technique is Air Abrasion which has been discussed below.
Air abrasion is also known as MICROABRASION or KINETIC CAVITY PREPARATION.

DEFINITION: Air abrasion is a pseudo-mechanical, non-rotary method of cutting and removing dental hard tissue. Air abrasion utilizes kinetic energy from alumina particles entrained in high velocity stream of air to remove tooth structure. Air abrasive methods are suited for restorations with current bonded resin materials and improves the longevity of restoration.

DEVELOPMENT OF AIR ABRASIVE TECHNOLOGY :
The instrument was first developed in the 1940's by Dr.Robert Black.
In 1951- S.S. White Technology introduced Air-Dent, the first commercially available unit for preparing cavities in teeth as an alternative to a slow-speed, belt-driven handpiece.
The father of concept of air-abrasive microdentistry is an American Dentist, Dr.J.Tim Rainey, from Refugio, Texas, USA. He was a student and friend of late Dr.Robert Black, who actually invented and unsuccessfully introduced the first air abrasive machine in the 1950's. Dr. Rainey was able to improve and combine this technology with the use of modern adhesive restorative material.

PHYSICAL PROPERTIES
The physics for air abrasion technology was made apparent in 1829 by Gaspard Coriolis with the discovery of the formula E = 1/2MV².
Essentially this equation underscores the fact that the cutting capability of air abrasive is attributable to the energy of mass in motion unlike conventional mechanical methods that depend on friction.
When that rapidly moving mass strikes its target, most of its energy is transferred to that material, if that material is hard the results is removal of small amount of material. If, on the other hand the material is soft, the energy is mostly absorbed by the material and then the mass rebounds. When these highly energized abrasive particles are directed at healthy enamel, dentin the kinetic energy is absorbed by the substrate and cuts or abrades rapidly. That is why the modality is sometimes referred to as KINETIC CAVITY PREPARATION (KCP).
The speed of the abrasive particles when they hit the tooth depends upon the following variables:

1. Pressure
2. Nozzle diameter
3. Tip angle
4. Tip distance
5. Particle size
6. Directing the particle steam

1. Pressure : Most available units operate between 40-140 psi (pounds per square inch). The lowest effective pressure should be used to achieve the desired tooth preparation. For fissure cleaning prior to sealant application, a brief exposure of 40 psi is sufficient.

2. Nozzle diameter:

• 0.018 inch nozzle: for large lesions and existing restorations.
• 0.014 inch nozzle : for smaller lesions.
• 0.011 inch nozzle: for precise cutting and diagnosis of occlusal pit and fissure, small class I and III lesions & redefining class IV and V lesions.

3. Tip Angle : Tip angle can range from 40o to 120o allowing access to both straight occlusal surfaces and the distolingual grooves of upper molars.
4. Tip Distance: By keeping the tip less than 2 mm from target surface, the clinician maximizes the focus of abrasive stream. Greater distances significantly reduce the energy of the stream. For preparations which require a beveled cavosurface margin (e.g acid etch-retained adhesive restorations), the instrument tip is placed upto 5 mm from the tooth surface. For restorations requiring a butt joint the nozzle is placed closer approximately 1mm from the tooth.
5. Particle Size: 27 mm aluminium oxide powder is normal for intra oral procedure, 50 mm powder for extraoral endeavours due to its excessive cutting and the difficulty in controlling over spray. Small particles- cuts faster because surface is increased, cuts smoother. Large particle- requires higher velocity, less cutting surface.
6. Directing the particle stream: The alumina escapes from the nozzle tip in a cone shaped stream, the wall of which diverge from its long axis at an angle of approximately 3.5°. The dimensions of the cutting cone increase in proportion to the distance between the nozzle tip and the tooth surface due to increase in particle spatter. The abrasion provided by the peripheral portion of the stream is less efficient because of lower velocity and concentration of alumina particles. This causes the internal angles to be rounded.

Teeth with stained pits and fissures.	Teeth with stained pits and fissures.	Completed restoration

APPLICATIONS OF AIR - ABRASION :

1. Cavity preparations - Class I, V, VI
2. Internal cleaning of tunnel preparations
3. Removal of temporary cement from inside a crown
4. Microairabrasion of white spot enamel hypoplasia
5. Stain removal
6. Preparation of metal surfaces inside a crown for better bonding.
7. Aid in repair of acrylic, composite and porcelain : the narrow cutting path and lack of vibration and heat make air abrasion technology an alternate method for these repairs.

ADVANTAGES OF AIR-ABRASION :

1. Non - traumatic treatment
2. Biocompatibility
3. No chipping
4. No microfracturing
5. Decreased thermal build up
6. Micro-smooth margins
7. Less invasive procedure that preserves more natural tooth structure than conventional instrumentation.
8. Greater strength and longevity because of lesser preparation.
9. No anesthesia
10. Less discomfort during preparation

DISADVANTAGES :

1. Ability to accomplish only some aspects of dentistry.
2. Lack of tactile sensation when using the air abrasion handpiece, because the nozzle of air abrasion instrument does not come in actual contact with the tooth.
3. Non contact based modality, leading to significant risk of cavity over preparation and inadequate carious dentin removal.
4. Mess and spread of aluminium oxide around the dental operatory.
5. Danger of air embolism and emphysema.
6. Impaired indirect view because abrasive particles collect on mirror rapidly blocking the viewing surfaces.
7. Damage to dental mirrors, optical devices like magnifying lopes, intraoral camera lenses or photographic equipment.

CONTRAINDICATIONS TO AIR ABRASIVE TREATMENT :

1. Asthma patients
2. Severe dust allergy
3. Chronic pulmonary disease
4. Recent extraction
5. Any open wounds in oral cavity
6. Subgingival caries removal

SAFETY ISSUES:

1. To reduce respiratory exposure, the clinical staff should always use surgical face masks and use dry vacuum systems to reduce patient exposure.
2. Use rubber dam, protective eye glass and dead soft metal matrix to protect adjacent tooth structure.
3. Use disposable mouth mirrors.
4. Rinsing instead of rubbing the optical surfaces helps prevent scratches.
5. High speed suction and an external vacuum system are necessary to capture the powder that escapes into the air and to enhance practitioner vision and patient comfort.

CONCLUSION
Now that the profession has a better understanding of prevention of dental disease and use of fluoride, with the advent of adhesive and bioactive restorative materials, dentists should adopt to more conservative attitude to the treatment of the cavitation caused by demineralization of the tooth.
One should eliminate the disease first and then eliminate existing lesions as much as possible through remineralisation procedure. When all else fails, the surgical repair of lesions should be the last resort and carried out with minimal intervention into the crown of the tooth.

REFRENCES

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