In the late 1970s, ultrasonic scaling units began to be adapted for use in endodontics resulting in the first generation of Endosonics. Endosonic instruments work at frequencies of 25 to 40 kHz. The file undergoes a characteristic oscillatory movement of alternating nodes and antinodes with the greatest displacement occurring at the tip. The pioneering research was done by Cunningham and Martin and published in the JOE in the early 1980s. Unfortunately, these early machines were fraught with problems. When used with NaOCL irrigant, the original Dentsply "Cavi-Endo" (a converted Cavitron) frequently plugged due to crystallization of the NaOCl solution in the irrigation lines. Furthermore, tip design had not been refined or calibrated specifically for endodontic applications. The initial claims of better, faster preparations were found to be without merit and the ultrasonic concept was often relegated to the "electric swizzle stick" status. It was used most often to increase the agitation and effectiveness of endodontic irrigants and not much more.
Since that time endodontists such as Gary Carr have done a lot of research on Endosonics and the field has undergone a high level of specialization. Several manufacturers created devices and tips specifically tuned for endodontic applications. These units have now become an integral part the Endodontist's treatment armamentarium. Endosonic tips also have a distinct advantage over burs in that when using high magnification, the slender tips allow for much better vision deeper in the canal. This is not possible when a contra-angle mounted bur is used in this manner. Suffice to say that if you routinely perform endodontics your office should have one. This month's EndoFiles Fax will discuss specific applications for these units.
There are 6 basic categories where Endosonics are used in endodontics:
1. Access Refinement
Performing access preparations with burs can lead to gouging of the pulpal floor and sides of the chamber. Have you ever wondered how the endodontic access preparation photos shown by endodontists such as Steve Buchanan and Cliff Ruddle look so smooth? These smooth shapes are achieved by using the "sanding effect" of round or tapered ultrasonically activated diamond coated instrument tips. Instead of angular gouges, you end up with smooth surfaces that allow instruments to literally slide into position in the canals. While this may seen to be overkill in access design, when it comes to access preparation smart clinicians realize that a really finely prepared access actually saves you time because it allows you to insert instruments into the canal orifices without looking. (This is one of the reasons that Endodontists prefer to perform the access themselves - gouged out pulpal floors actually can increase preparation time because instruments do not easily go onto the canal orifices without effort.) Endosonic tips are also used to marry the orifice of the access to the pulpal floor, smoothing this "transition zone" to allow for better orifice visibility as well as easier instrument and irrigation insertion.
2. Troughing and Orifice Location
Ultrasonic instruments are particularly helpful in removal of chamber calcifications and pulp stones as well as "troughing" for canals in isthmuses and locating canal orifices. The troughing concept involves using an endodontic tip in a back and forth brushing motion along a groove in the pulpal floor. This is most common method of looking for MB2 in maxillary molars and for finding the "middle mesial" canal in mandibular molars. (Yes! With higher levels of magnification, not only are we seeing MB2 canals in 95% of maxillary first molars, we now are finding that 2-12% of mandibular molars have a third "middle mesial" canal that is located between the MB and ML canals!) By "Troughing out" these areas we not only remove the tissue in the isthmus between the canals, we also conserve tooth structure by not using a bur and have greater visibility during the search.
The literature has shown that activation of endodontic irrigation solutions with endosonic energy results in cleaner canals. There is a synergistic action of the physical action of the tip coupled with the chemical action of the sodium hypochlorite irrigant. Acoustic microstreaming forces within the irrigant together with the oscillation of the instrument are useful for dislodging or flushing out obstructions and debris in the canal. Endosonics cannot remove the smear layer by itself but can assist in its removal when used in combination with irrigants such as EDTA.
4. Post Removal
Post removal used to be quite a chore. With the advent of devices such as the Gonon Post Puller and the Ruddle Post Removal System, post removal has become relatively easy. Small ultrasonic tips can also be used around the post to remove any exposed cement and facilitate removal. Ultrasonic vibration can also be applied directly to the posts to assist in their removal. It is important to use water spray to cool the post when this is being done because the posts can get hot and thermal damage to the PDL can cause bone sloughing around the tooth.
5. MTA Placement
MTA (Mineral Trioxide Aggregate) is a wonderful material and has many uses. However, because of its sandy consistency, it can be difficult to apply because it does not "pack" like amalgam. Low powered ultrasonics can be used to "vibrate" the material into position and ensure that no voids are present in canal fills, retrofills or perforation repair sites. The best way to do this is to have your assistant touch a metal instrument (a Schilder plugger for example) that is in contact with the MTA. This works in the same way that your vibrator takes out the bubbles when pouring stone into an alginate impression. Minimal power is required and it is far easier to do this than to try to "condense" the MTA into position.
6. Instrument Removal
Removal of broken endodontic files remains one of the most difficult procedures performed in Endodontics. It is almost impossible to remove a file in the middle or apical third without the use of Endosonics. When considering whether to attempt instrument removal, one very important factor must be considered - visibility. That is where the SOM (Surgical Operating Microscope) comes in. If you cannot clearly see the fragment, NO ATTEMPT SHOULD BE MADE TO REMOVE IT WITH ENDOSONICS. Blindly sticking an endosonically activated tip into the canal space in the hope that you will shake the fragment free is sheer folly. File removal involves very specific procedures that create an environment that allows for retrieval or bypass of the broken fragment. If you are not sure what you are doing and you cannot see - refer the case.
Several companies sell Endosonic products. Here are some recommendations:
Satelec P5 (Tulsa Dental) (2) MTS-1 and Piezo-Electric Systems (Spartan-Obtura) (3) NSK (TDO version - only recently released for sale by TDO) (4) MiniEndo (Sybron Endo) My preferred unit is the Satelec P5. It has greater power than the two other old Spartan Piezo units that I have. I have not had a chance to use the TDO unit but Dr. Gary Carr is selling it and I'm sure its top notch. Both the MS-1 and MiniEndo are also good choices.
Endosonic Tips - It is important to remember that not all tips work in all machines. Tip nomenclature is also very confusing. Some tips are specifically tuned to work in specific manufactured units. I have found that many new tips can break easily in only a few seconds by being used at too high a setting or in the wrong device. At between $120-160 each (!), it can be an expensive to have to replace them. What's even more confusing is that some tips actually work better in rival devices.
Tips are divided into 3 categories:
(1) Zirconium coated tips (ProUltra by Tulsa) Buc tips (Sybron Endo and Obtura Spartan) CPR Tips (Obtura Spartan)
(2) Titanium Tips- (Obtura Spartan and Tulsa) Very slender and fragile but excellent for working around posts and removing broken files
(3) Specialized Tips - If you are considering a tip purchase, I strongly suggest that you consult www.eie2.com for details. Dr. Carr's tips are almost unbreakable and are a great investment. They are by far the best tips available.
(4) Surgical Tips - Specialized zirconium coated tips used for endodontic surgical retropreparation - Kis tips - (Obtura Spartan)