Ultrasonics in Endodontics: Luxury or Necessity?

Figure 1. Inside a Satelec Handpiece. Figure 2. P5 Newtron, Satelec (ACTEON North America). Figure 3. P5 Newtron XS, Satelec.

Since the late 1950s, the use of ultrasonic technology has become a staple in endodontic practices around the world for hygiene and periodontal procedures. More recently, endodontists have introduced us to the clinical advantages of their use in root canal therapy, and we are just beginning to see their effectiveness for endo-restorative and microrestorative work.
This article will review the expanded function that ultrasonic technology has taken in root canal therapy, why piezoelectric technology is well matched to endodontics, current clinical uses and advances in both ultrasonic equipment and tips, and some of the science behind the technology.

PIEZOELECTRIC TECHNOLOGY
Ultrasonics used for operative and preventative procedures are usually divided into 2 groups: magnetorestrictive (ie, Cavitron [DENTSPLY Professional]) and piezoelectric (ie, P5 Newtron, Satelec [ACTEON North America]). Both of these classes of ultrasonics are clinically well accepted in dentistry. However, the piezoelectric ultrasonic is more conducive to endodontic use. Hence, this article will focus on piezoelectric technology.
The word "piezo" comes from the Greek piezein, which means to push, press, or squeeze. In 1880, Jacques and Pierre Curie discovered a curious characteristic of certain crystalline minerals: when subjected to a mechanical force, the crystals became electrically polarized. The converse is also true—if a voltage-generating crystal is exposed to an electric field, it lengthens or shortens, depending on the polarity of the field, and in proportion to the strength of the field. This scientific effect has therefore been used in piezoultrasonics: electrical current generates a wave in the crystals (ie, series of ceramic discs or quartz plates inside the handpiece of the ultrasonic), which is transferred to the ultrasonic tip (Figure 1). This creates a linear back-and-forth tip motion, which is ideal for many dental procedures, such as subgingival scaling, and of course, endodontic use. In the above-mentioned process, very little heat is generated in the handpiece. Unlike magnetorestrictive type ultrasonics, water is not supplied to cool the handpiece; it is simply used to cool the tooth and tip, as needed. If water is used, a low volume aerosol mist is all that is required, improving vision and patient comfort. Piezo units also do not vibrate in the operator’s hand, greatly improving the ergonomics. The following is a brief review of some of the applications of the piezoelectric ultrasonics and the associated variety of tips.

PIEZOELECTRIC ULTRASONIC EQUIPMENT
Distinguishing Features and Improved Technology
The first piezoelectric ultrasonic was introduced to the market by Satelec in the late 1970s. Since that time, there has been an evolution in the technology, operation, ergonomics, and the design of the machines. The most important feature of any ultrasonic unit is how it maneuvers the tip and adjusts to many different tip designs (each with an unique intended function). A good ultrasonic machine also must adapt to several unpredictable clinical conditions and tooth anatomy. It must be remembered that "the mechanism of ultrasonics is very different than other instruments,"1 such as a high-speed handpiece. As Dr. David Clark (Tacoma, Wash) has noted in this journal, it is somewhat "counterintuitive"; increased manual pressure or cranking up the power does not necessarily add cutting or vibrating efficiency. In many cases, it reduces efficiency. There are 2 variables of ultrasonic tip vibration: the frequency (number of times the tip moves back and forth every second) and power or intensity (the amplitude or arc of the tip movement, which is usually operator controlled). When the power is turned up, the frequency does not change; the "power" simply increases the back-and-forth arc (amplitude) of the tip. One of the latest advances in piezo "drive" technology is the Newtron (Satelec) line of ultraonics (Figures 2 and 3).
The module, which controls each unit, features "cruise control" consisting of 3 quite advanced functions:
1. Newtron type ultrasonics operate in a frequency range of 28 kHz to 36 kHz. Ideally, each tip and has its own ideal frequency. The Newtron module constantly monitors the weight and dimension of each tip, and adjusts it accordingly (in real time) to that tip’s optimal frequency.
2. With most ultrasonic units, the electronics push the tip to the farthest extent of its amplitude; the return is simply recoil action. The Newtron module controls both the push and the pull of the tip, resulting in even more precise tip control. The more tip control, the less likely the operator will break the ultrasonic tips. In the case of scaling procedures, better control results in more patient comfort.
3. As already stated, ultrasonic tips are most effective when they are passively applied to tooth structure and allowed to "dance on the surface," as opposed to being pushed. The Newtron module will adjust the power intelligently, depending on the load that it encounters in use; this is similar to torque control in electric endo motors.

Figure 4. Optional LED handpiece for piezo.	Figure 5. POV Led headlight (Clinical Research Dental).

Figure 6. Irrigation port on the ultrasonic tip.

WATER, AIR, VISION, AND LIGHT
Many design elements are incorporated into a number of high-quality piezoelectric models. Optional fiber-optic or LED handpieces (Figure 4) (ie, optional on the Varios by NSK and the Satelec Newtron models) certainly enhance visibility, but may be an unnessecary expense if the operator is using a high-powered LED headlight (Figure 5) or a microscope. In any event, intense light, good magnification through loupes or a microscope, and reliable ultrasonic technology are all a must if you are doing molar endodontics. Water has always been inherent to ultrasonic use; being necessary in magnetorestrictive units to cool the handpiece, the tooth surface, and the tip. Piezoelectric units still require the use of water in periodontal and hygiene procedures, but for most endodontic applications water is discretionary. For example, in operations such as access refinement and chasing calcified canals, much dentinal dust is created. This, when mixed with water, tends to become a slurry that might bog down the ultrasonic instrument, and will certainly obscure the clinician’s vision.
However, there are advantages to intermittent water use. For example, when using an ultrasonic tip to remove a metal post by vibrating it, the heat generated can cause thermal injury to teeth and their supporting structures. In reporting on this possibility, Gluskin, et al2 recommended as part of a good protocol for post removal using ultrasonics, "Use devices that allow water to reach the working end of the ultrasonic tip to provide maximum cooling effect." Furthermore, the occasional use of water in endodontic access refinement yields a clean surface and can expose what many clinicians refer to as a "dentinal roadmap"; for instance: differentiating the pulp chamber floor from secondary dentin, possibly providing clues to the location of a hidden canal, and properly orienting the operator in order to begin achieving a good Glidepath, and getting the cleaning and shaping process off to a good start. As it would appear that intermittent water use is advantageous, it would follow that ultrasonic tips that have water ports are preferred over tips without (Figure 6). The availability of a stream of air during ultrasonic use is also necessary. It also will act as a coolant, and a steady stream of precisely directed air can help keep clear visibility, blowing away dentinal and other dust and debris. The use of a Stropko irrigator (Stropko) (Figures 7 to 10), adapted to your air-water syringe, allows your assistant to direct an optimal fine stream of air to the operative field.

THE USES
Finding and Breaking Into Hidden Canals and Access Enhancement
"Tooth retention has increased significantly in older adults, and dentists are now challenged by the need to preserve critical teeth."3 Clinicians are confronted with calcified canals, pulp stones, and hidden canals such as in maxillary molars (MB2).4,5 According to peer-reviewed literature, second mesial buccal canals are present in most maxilliary molars. Dr. John Stropko examined 1,732 conventionally treated maxillary molars over a period of several years in a very impressive clinical study. He noted, "As the operator became more experienced, scheduled sufficient clinical time, routinely employed the dental operating microscope, and used specific instruments adapted for microendodontics, MB2 canals were located in 93.0% of first molars and 60.4% in second molars."6 There are 3 key factors mentioned here: a certain level of familiarity in treating MB2s, allowing adequate time, proper magnification, and using the correct instruments (Figures 11a and 11b). For both general practitioners and endodontists, the ultrasonic is a valuable tool to treat calcified and difficult to find canals, as long as it is complemented by the proper tip, and sufficient magnification and light.7,8 It is less aggressive than a high-speed handpiece, and with high magnification the operator can always see where the tip is and where it is heading. By contrast, the high-speed handpiece affords little if any visibility in access procedures, so the dentist must constantly stop, look, and start again to avoid procedural mishaps. As Dr. L. Stephen Buchanan9 says, "Any clinician who performs molar endodontics without ultrasonics is working too hard, is experiencing more anxiety than is necessary, and is most likely not finding MB2 canals in more than 40% of their maxillary molar cases."
Dental manufacturers today have brought us a variety of tips and cutting surfaces such as smooth stainless steel, zirconium nitride, and diamond coated tips. Recent studies have suggested that diamond coated surfaces offer some of the best cutting efficiency;10 however, diamond particles can fall out and wear down rapidly, making ultrasonic tips dull and much less efficient all too soon. A newer entry to the marketplace is the BL series of tips (B&L Biotech/Clinical Research Dental) (Figure 12a). Instead of a diamond coating, BL tips have integrated sharp micro-projections (small raised bumps) on the tip surface, which engage the tooth surface precisely and efficiently. The active abrasive surface has considerably more longevity than other coated tips, and they are less expensive due to the lack of an additional coating process.

Figure 12a. BL tips (B&L Biotech/Clinical Research Dental).

The BL tip set consists of:
• BL-1: A workhorse tip with 100-µm projections and a very sharp tip enables easy penetration through calcification and obstructions, as well as for the removal of pulp stones and gutta-percha.
• BL-2: This is a more conservative and safe tip with the same tapered design, but with a rounded cutting end and 50-µm projections. This tip is ideal for the removal of secondary dentin in the search for elusive canals, and for de-roofing pulp chambers (Figures 12b to 12d).
• BL-3: A slightly larger profile than the BL-2, with 50-µm projections at the end, and 100 µm on the sides. This tip has a similar use to the BL-2: it is very efficient for removing and planning pulp stones on the canal wall and in the chamber simultaneously, as well as efficient removal of pulp horns to achieve better visibility.
• BL-4: The floor polisher, this tip is a flat end-cutting tip, which effectively grinds down pulp stones and irregular surfaces on the pulp chamber floor.
• BL-5: This is a longer tip with 50-µm projections, allowing it to reach where the BL-1 to -3 tips cannot. It is ideal for the removal of the isthmus, coronal shaping, especially in ovoid shaped canals, and the removal of canal obstructions (Figures 13a to 13c).
• BL-6: This is a traditional smooth surface tip that is used only for troughing around (not contacting) posts, separated instruments, obturation carriers, silver points, etc. If you are doing retreatment, this tip is very useful!

Passive Ultrasonic Irrigation
Advancements in canal shaping instruments and techniques have led to a much greater emphasis on root canal irrigation protocols. High volume and frequent exchange of sodium hypochlorite throughout the cleaning and shaping procedure is acknowledged to be essential to success. However, complete removal of canal organic and inorganic debris, especially from the apical third and webs, fins, and lateral canals continues to be a challenge.

Ultrasonic use to activate irrigant in the canal has shown to be a clinically proven and efficient adjunct to cleaning and shaping instrument sequences and is used by many endodontic specialists.11-13 Ultrasonic activation of irrigants produces at least 2 helpful effects: (1) cavitation, defined as the formation of thousands of tiny bubbles which rapidly implode, producing a "shock wave" removing biofilm, and (2) acoustic streaming which produces shear forces that will help extricate debris from instrumented canals. An excellent ultrasonic tip instrument to create this type of passive ultrasonic irrigation is the Irrisafe file (Satelec/ ACTEON North America). This a long, thin, parallel tip which resembles a K-type file, but with non-cutting, rounded flutes (Figures 14a to 14c). These flutes affect the aforementioned acoustic streaming, but will not engage the dentin or transport the canal. To use these tips effectively, the canal is filled with sodium hypochlorite (use the 31-gauge NaviTip [Ultradent Products] with 2 side ports offset to each other, and capped at the end) (Figures 15a and 15b). The Irrisafe tip is activated in the canal at low-to-medium power at least one mm short of working length for one minute in each canal. The irrigant may then be evacuated out with a Luer Vac Adapter (Ultradent Products) (Figure 16). This clinically and scientifically accepted method of passive ultrasonic irrigation helps push the ultrasonic from luxury into necessity status!14,1

Figure 16. Luer Vac Adaptor (Ultradent Products/Clinical Research Dental) used for evacuating irrigant and canal drying.	Figure 17. JET Surgical Tip (B&L Biotech/Clinical Research Dental). (Case courtesy of Dr. Marga Ree, Netherlands)

Obstruction Removal
In the natural course of the life of a dental practice, specialty or general, cases will present that will require retreatment of a previously restored, endodontically treated tooth. This will often entail disassembly of the restoration, perhaps including removal of a metal post, a silver point, gutta-percha, obturation carriers, etc. There is also the possibility of instrument separation during root canal therapy, which usually requires immediate intervention. The piezoelectric ultrasonic is also an invaluable tool for these procedures. In such situations, good case selection is very critical; frequently the endodontist has the proficiency to handle these procedures, having been well educated on the justification and protocols for retreatment, possessing valuable experience in retreating many cases over many years, and having all the instruments and tools essential to deal with the most difficult, unusual, and sometimes unforeseen conditions under which most retreatment is done.16
Metal post removal is a laborious and time consuming chore that can be made easier with the use of the proper ultrasonic tip. A tip, which will engage and fit over the post or contact directly and vibrate the post, can break up the crystalline structure of the post cement, thus loosening it enough to be removed. Sometimes the operator must take this a step further, following up with a long and more slender tip to trough around the post, steadily loosening and eventually extricating it. In these cases, water should be used periodically to keep the tooth cool to avoid the earlier stated "thermal injury." The same approach can be used to remove other obstructions such as silver points, obturation carriers, pins, and separated nikel-titanium or stainless steel files. Choice of the proper tip is paramount. For removal of obstructions in the canal, here are some guidelines to keep in mind:
• There is no such thing as a one-size-fits-all tip. Try to use the largest diameter and shortest tip possible (similar to a using a 21-mm file in a shorter canal), depending on where the top of the obstruction to be removed is located. In some cases, more than one tip size will be needed to remove a stubborn post or file. Patience is essential.
• Always use a low power setting (10% to 20% power is usually more than enough) when using a tip further down into the canal. It is a constricted area to work in, making the use of minimal tip amplitude better.
• If you are attempting to remove a threaded post or an endodontic file, sometimes using a counterclockwise motion might aid removal, as most files have a clockwise cut flute.
• Don’t be a hero. If you cannot see it, you probably cannot retrieve it.
In addition to the above, it cannot be overstated that excellent visibility, good magnification, and proper illumination are all vital for success in these ultrasonic uses. Experience and good case selection is also vitally important.

Other Miscellaneous Uses in Endodontics
Ultrasonics are also presently used in removing gutta-percha, condensing gutta-percha, vibrating perforation repair material, such as mineral trioxide aggregate, into location, and root end surgical preparation (Figure 17). Currently, there are an increasing number of restorative procedures, which are ideal for ultrasonic applications such as margin finishing, interproximal and small lingual restorations, and more advances in oral surgical applications are in development.

CONCLUSION
Less than 2 decades after the endodontic specialty introduced this as a marvelous tool for endodontics, ultrasonic use for endodontics is here to stay. Most dentists, who use ultrasonics for endodontic procedures acknowledge that this technology can help solve many clinical problems and challenges in treating complex root canal systems. As has been said, "Habit converts luxury into necessity." A growing number of clinicians performing endodontics are adding the piezoelectric ultrasonic and tips to the list of endodontic "necessities."

References

1. Clark D. The operating microscope and ultrasonics; a perfect marriage. Dent Today. 2004;23:74-76, 78-81.
2. Gluskin AH, Ruddle CJ, Zinman EJ. Thermal injury through intraradicular heat transfer using ultrasonic devices: precautions and practical preventive strategies. J Am Dent Assoc. 2005;136:1286-1293.
3. Allen PF, Whitworth JM. Endodontic considerations in the elderly. Gerodontology. 2004;21:185-194.
4. Sempira HN, Hartwell GR. Frequency of second mesiobuccal canals in maxillary molars as determined by use of an operating microscope: a clinical study. J Endod. 2000;26:673-674.
5. Buhrley LJ, Barrows MJ, BeGole EA, et al. Effect of magnification on locating the MB2 canal in maxillary molars. J Endod. 2002;28:324-327.
6. Stropko JJ. Canal morphology of maxillary molars: clinical observations of canal configurations. J Endod. 1999;25:446-450.
7. Rampado ME, Tjäderhane L, Friedman S, et al. The benefit of the operating microscope for access cavity preparation by undergraduate students. J Endod. 2004;30:863-867.
8. Paz E, Satovsky J, Moldauer I. Comparison of the cutting efficiency of two ultrasonic units utilizing two different tips at two different power settings. J Endod. 2005;31:824-826.
9. Buchanan LS. Access procedures: breaking and entering safely and effectively. Pract Proced Aesthet Dent. 2006;18(suppl):6-9.
10. Lin YH, Mickel AK, Jones JJ, et al. Evaluation of cutting efficiency of ultrasonic tips used in orthograde endodontic treatment. J Endod. 2006;32:359-361.
11. Abou-Rass M, Piccinino MV. The effectiveness of four clinical irrigation methods on the removal of root canal debris. Oral Surg Oral Med Oral Pathol. 1982;54:323-328.
12. Lee SJ, Wu MK, Wesselink PR. The effectiveness of syringe irrigation and ultrasonics to remove debris from simulated irregularities within prepared root canal walls. Int Endod J. 2004;37:672-678.
13. van der Sluis LW, Versluis M, Wu MK, et al. Passive ultrasonic irrigation of the root canal: a review of the literature. Int Endod J. 2007;40:415-426.
14. van der Sluis LW, Gambarini G, Wu MK, et al. The influence of volume, type of irrigant and flushing method on removing artificially placed dentine debris from the apical root canal during passive ultrasonic irrigation. Int Endod J. 2006;39:472-476.
15. Jiang LM, Verhaagen B, Versluis M, et al. Evaluation of a sonic device designed to activate irrigant in the root canal. J Endod. 2010;36:143-146.
16. Cohen SJ, Glassman GD. Endodontic junkyard dog [editorial]. Oral Health. 2005;95:3.

Dr. Glassman graduated from the University of Toronto, Faculty of Dentistry in 1984 and graduated from the endodontology program at Temple University in 1987, where he received the Louis I. Grossman Study Club Award for academic and clinical proficiency in endodontics. The author of numerous publications, Dr. Glassman lectures globally on endodontics and is on staff at the University of Toronto, Faculty of Dentistry in the graduate department of endodontics. He is a Fellow of the Royal College of Dentists of Canada, and the endodontic editor for Oral Health. He maintains a private practice, Endodontic Specialists in Toronto, Ontario, Canada. He can be reached at (416) 963-9988 or at rootcanals.ca.

Disclosure: Dr. Glassman reports no disclosures.

Dr. Kratchman received a BS in biology and a DMD from Tufts University in Boston, Mass. He then entered the University of Pennsylvania, where he received a certificate of endodontics and currently serves as an associate professor of endodontics and the assistant director of graduate endodontics, in charge of the microsurgical portion of the program. Dr. Kratchman has authored several articles and chapters on endodontics and intentional replantation for the Microsurgery in Endodontics textbook, and the Dental Clinics of North America. He also developed a patented instrument called the S Kondenser for the obturation of root canals. He serves as the District I director for the American Association of Endodontists. Both Main Line Today and Doctor of Dentistry magazines honored Dr. Kratchman as the cover story for their "Best of" issues. Dr. Kratchman lectures on several topics relating to endodontics throughout the United States, Europe, Scandinavia, South America, and Asia. He also maintains 3 private practices, limited to endodontics, in Exton, Ardmore, and West Chester, Penn. He can be reached at (610) 524-1610.

Disclosure: Dr. Kratchman receives royalties from Obtura Spartan for gutta-percha condensers.

Reprinted with permission, Oral Health Journal, November 2010, Volume 100, Number 11.