Answer:

Depth of cut is a recurring issue with clinicians beginning air abrasion use. We have come to rely on the physical comparison between bur size/length and cavity preparation profile. In air abrasion, this "ruler" in the operative filed is missing. We must rely on magnification and interrupted treatment to keep track on how much tooth structure is being removed.

In addition to these steps, we can utilize several variables operationally to achieve better depth control. If the nozzle is moved back and forth repeatedly while cutting, the rate of reduction is slowed and this will reduce the depth of cut. Another easy technique to use is to move the nozzle tip very close to the pulpal/gingival floor of the preparation. This also reduces the cutting rate of the abrasive stream.

The nature of the abrasive stream is such that one must take care and observe the direction of the reflected abrasive stream. Although the energy of the particles is reduced after the primary impact, the secondary stream, particularly in dentin, will still be effective to an extent. This means that special care has to be taken when the dentist is operating in dentin. The direction and angulations of the reflected stream must be taken into consideration. The best analogy I can generate is that of a strong water stream coming from your standard garden hose. Point it into dirt or mud and you will see a graphic demonstration of what the air abrasion stream will do in dentin. You will note that if the stream is left in one position for a prolonged period of time, there will be two areas of reduction. The primary impact site primarily deepens. The reflected stream of particles rebounds and begins to generate a groove that is oriented away from the nozzle.

Air abrasion requires special operative safeguards that are unique but not difficult to master. When the overall benefits are taken into consideration, it makes sense to learn to use the technology to its fullest extent. There are many clinicians presently using air abrasion and for the most part, depth control has only been a temporary delay in the full implementation of the modality in their practice. Practice on extracted teeth, trying to simulate different clinical scenarios. Once the preparation is complete, I suggest that you serially section the tooth on a model trimmer. Analyze the cavity profile sequentially along the preparation. This will give you a "real life" idea of how the abrasive stream reduces tooth structure and how you can best approach carious lesions to best maximize the technology. Within a very brief time, you will be a master of the modality. Good luck and always keep the final goal in mind: Atraumatic Patient Care.

This issue’s article is one sent to me by a fellow colleague and it was instrumental in my understanding of the anatomical as well as biological gradation of the carious lesion. The article, Two Layers of Carious Dentin: Diagnosis and Treatment, Fusayama,T Operative Dentistry, 1979, 4, 63 - 70 is a pivotal work on the effectiveness of caries disclosing dye and on carious lesion morphology.

This seminal article by Dr. Takao Fusayama has aided my understanding of the extent of bacterial penetration within a carious lesion as well as the degree of demineralization within same.

Dr. Fusayama divides a dentinal carious lesion into two distinct layers. The outer layer is irreversibly denatured, it is infected, not remineralizable and it is the layer that we must remove. The inner carious dentin is reversibly denatured, it is not infected, it is remineralizable and we must strive to preserve it. Dr. Fusayama utilized a 0.5% solution of basic fuchsin dye in propylene glycol as a caries disclosing medium. This caries disclosing solution is particularly specific in staining only the outer dentinal layer. By so differentiating the two layers, the clinician can effectively remove only the infected layer and leave sound, remineralizable dentin behind. Dr. Fusayama goes on to explain the morphological differences between the layers and why one layer can be considered sound from a structural, biochemical as well as microbiological point of view.

He points out that the inner carious dentin bonds to conventional bonding systems as strongly as sound dentin. The preservation of as much of this dentin as possible contributes to increased pulpal protection. Pulpal response to the dye is also examined in the paper and the basic fuschin was found to be benign to pulpal tissue. At the end of the article, an added note was added mentioning that basic fuschin in very large quantities (17 million times the amount a patient might swallow during a procedure) in mice proved to be carcinogenic. With this in mind, acid red was found to be a satisfactory substitute for fuchsin as a stain for carious dentin. This is an excellent article and I encourage everyone to read it. This capacity to stain only that dentin which needs to be excised is critical for we who deal with air abrasion disclosure and removal of carious lesions. Next issue, another article on detecting carious dentin will be reviewed.

The proper metering of powder into the abrasive stream is important for two reasons. One, the abrasive stream will be most effective with a certain mixture ratio of abrasive to air volume and velocity. If you can equate this to the gasoline to air ratio in your car you can get a better idea. Today’s electronic engine management computers are expert at dialing in the correct mixture ratio for all load, temperature and speed variables. By doing this effectively, the engine generates the best power, mileage and reduced emissions.

Similarly, the air abrasion machine must also allow for the operator to adjust the mixture of abrasive to air, in order to meet his or her clinical demands; they are not always the same. A machine that accurately and reproducibly meters the abrasive will consistently give the dentist maximum efficiency, reduced abrasive use and as a result, reduced "powder mess".

When evaluating air abrasion systems, research has demonstrated to us that powder flow capacities of from .5 gm/minute to 6 gm/minute (.008 gm/sec to .1 gm/sec) are what is necessary in order to provide efficient and consistent performance throughout a wide range of clinical applications. These values will vary depending on nozzle size, air pressure utilized and procedural application. For the most part, exceeding these values will generate unwanted excess powder and reduced system efficiency.

The automated regulation of these parameters, contrary to the automotive analogy mentioned earlier, does not allow for sufficient flexibility for the clinician to use in all clinical applications effectively. There are many times when a clinician needs to independently reduce powder flow while maintaining the air pressure constant. Independent control allows you to selectively remove the organic plug from an occlusal fissure or composite from an existing restoration. That means removing just what you want, not what the machine will allow you to.

Remember that powder mess is largely a function of the volumetric powder consumption values of the equipment. If the equipment TRULY allows the doctor to control it and not the other way around, you will find that the issue of powder management clinically all but disappears. Efficient and accurate metering of the abrasive powder allows the high velocity suction to take care of the majority of the powder used. Extra oral ejected powder becomes something of tertiary importance. Your staff and your patients will love you for that!

NEW PRODUCT:

Swiveling Handpiece

Unique in the field of air abrasion is Crystal mark's swiveling handpiece. The handpiece is designed such that the nozzle connector can swivel through an angle of 30 degrees. This gives the dentist the ultimate in access convenience.

Many times, particularly in the preparation of maxillary second molars, it is very difficult to access the distal without some pretty creative handpiece positioning. This handpiece allows the dentist easy access without the associated contortions. The design is, like all other Crystal mark designs, fully autoclavable and requires no loosening of the collar in order to move the nozzle connector. It can also be fitted to other air abrasion equipment by utilizing the correct connection attachment.

By serially sectioning these teeth, Dr. Caine has found what Dr. Fusayama and others have eluded to in various research papers. The decay process might violate the enamel through a pinpoint aperture and propagate along the DEJ to other areas of the tooth. I and others believe that this DEJ propagation is largely responsible for the delamination of the lingual enamel of mandibular anteriors we sometimes see in some patients. In posterior teeth, this propagation leads to extensive carious involvement that IS NOT radiographically evident. We have been watching these teeth until the decay becomes more pronounced ! I have several of Dr. Caine’s slides generated as evidence of his experimentation and there are some images in which he has used transillumination and caries detecting dye; the impact they have on you is unforgettable.

Dr. Caine first embraced air abrasion about 2-1/2 years ago. After 35 years of following the dental philosophy of "watch" areas, air abrasion brought him the means to no longer observe but to disclose and to treat. It was the first time in his career that he felt he was truly practicing preventive dentistry. He was now able to prevent the future fractures, the crowns and endodontic treatment on those incipiently carious teeth he was intercepting with air abrasion.

Soon after he began using air abrasion in his practice, Dr. Caine realized that much of his time was being devoted to the explanation of this new technique to his patients. This was taking time from his effective productive treatment time. Combining a former hobby of his, the making of wedding videos, Dr. Caine made and produced a 5 minute video tape developed and designed to inform and educate the dental patient with regards to air abrasion. A simple but thorough explanation of the air abrasion technique along with the obvious advantages to the patient, the tape has become an unbelievably successful internal marketing tool. Once the patients realize the benefits of no-anesthetic, no-drilling and very small restorations, they want this new treatment.

Dr. Caine is a 1962 graduate of the University of Detroit School of Dentistry. He spent two years in the Army Dental Corps at Fort Belvoir, VA before opening his general dental practice in Chardon, OH. Dr. Caine mentioned to me just recently that his use of air abrasion re-energized his practice and made him quite popular as the "painless dentist". Dr. Caine mentions how much patients value his ability to treat them without anesthesia and conservatively too. On a personal opinion note, I feel that his patient education tape is essential to anyone utilizing air abrasion. By using the tape, the dentist and staff can relegate the bulk of the patient education regarding air abrasion to the video. In this fashion, the treatment team need only answer simple questions and begin treatment.

Dr. Caine also believes one hundred percent in the use of the intraoral camera and caries disclosing solution to show the patient where the disease process is present. He then utilizes it to show how the carious dentin (stained) is removed and terminates the "show" with a close up of his final restoration. I have been extremely fortunate to know this kind practitioner and feel free if you see him to ask him about air abrasion; he is one enthusiastic proponent.