Ultrasonics in Endodontics: A Review of the Literature Gianluca Plotino, DDS,* Cornelis H. Pameijer, DMD, DSc, PhD, † Nicola Maria Grande, DDS,* and Francesco Somma, MD, DDS* Abstract During the past few decades endodontic treatment has benefited from the development of new techniques and equipment, which have improved outcome and predict- ability. Important attributes such as the operating mi- croscope and ultrasonics (US) have found indispensable applications in a number of dental procedures in peri- odontology, to a much lesser extent in restorative den- tistry, while being very prominently used in endodon- tics. US in endodontics has enhanced the quality of treatment and represents an important adjunct in the treatment of difficult cases. Since its introduction, US has become increasingly more useful in applications such as gaining access to canal openings, cleaning and shaping, obturation of root canals, removal of intraca- nal materials and obstructions, and endodontic surgery. This comprehensive review of the literature aims at presenting the numerous uses of US in clinical endo- dontics and emphasizes the broad applications in a modern-day endodontic practice. (J Endod 2007;33: 81–95) Key Words Endodontics, innovations, ultrasonics T he use of ultrasonics (US) or ultrasonic instrumentation was first introduced to dentistry for cavity preparations (1–3) using an abrasive slurry. Although the tech- nique received favorable reviews (4, 5), it never became popular, because it had to compete with the much more effective and convenient high-speed handpiece (6). However, a different application was introduced in 1955, when Zinner (7) reported on the use of an ultrasonic instrument to remove deposits from the tooth surface. This was improved upon by Johnson and Wilson (8), and the ultrasonic scaler became an established tool in the removal of dental calculus and plaque. The concept of using US in endodontics was first introduced by Richman (9) in 1957. However, it was not until Martin et al. (10 –12) demonstrated the ability of ultrasonically activated K-type files to cut dentin that this application found common use in the preparation of root canals before filling and obturation. The term endosonics was coined by Martin and Cunning- ham (13, 14) and was defined as the ultrasonic and synergistic system of root canal instrumentation and disinfection. Ultrasound is sound energy with a frequency above the range of human hearing, which is 20 kHz. The range of frequencies employed in the original ultrasonic units was between 25 and 40 kHz (15). Subsequently the so-called low-frequency ultrasonic handpieces operating from 1 to 8 kHz were developed (16 –21), which produce lower shear stresses (22), thus causing less alteration to the tooth surface (23). There are two basic methods of producing ultrasound (24 –26). The first is mag- netostriction, which converts electromagnetic energy into mechanical energy. A stack of magnetostrictive metal strips in a handpiece is subjected to a standing and alternating magnetic field, as a result of which vibrations are produced. The second method is based on the piezoelectric principle, in which a crystal is used that changes dimension when an electrical charge is applied. Deformation of this crystal is converted into mechanical oscillation without producing heat (15). Piezoelectric units have some advantages compared with earlier magnetostrictive units because they offer more cycles per second, 40 versus 24 kHz. The tips of these units work in a linear, back-and-forth, “piston-like” motion, which is ideal for endodontics. Lea et al. (27) demonstrated that the position of nodes and antinodes of an unconstrained and unloaded endosonic file activated by a 30-kHz piezon generator was along the file length. As a result the file vibration displacement amplitude does not increase linearly with increasing generator power. This applies in particular when “troughing” for hidden canals or when removing posts and separated instruments. In addition, this motion is ideal in surgical endodontics when creating a preparation for a retrograde filling. A magnetostrictive unit, on the other hand, creates more of a figure eight (elliptical) motion, which is not ideal for either surgical or nonsurgical endodontic use. The magnetostrictive units also have the disadvantage that the stack generates heat, thus requiring adequate cooling (15). Applications of US in Endodontics Although US is used in dentistry for therapeutic and diagnostic applications as well as for cleaning of instruments before sterilization (28), currently its main use is for scaling and root planing of teeth and in root canal therapy (15, 28, 29). The concept of minimally invasive dentistry (30, 31) and the desire for preparations with small dimen- sions has stimulated new approaches in cavity design and tooth-cutting concepts, in- cluding ultrasound for cavity preparation (32). The following is a list of the most frequent applications of US in endodontics, which will be reviewed in detail: 1. Access refinement, finding calcified canals, and removal of attached pulp stones From the *Department of Endodontics, Catholic University of Sacred Heart, Rome, Italy; and the † School of Dental Med- icine, University of Connecticut, Farmington, CT. Address requests for reprints to Gianluca Plotino, DDS, Via Eleonora Duse, 22– 00197 Rome, Italy. E-mail address: gplotino@fastwebnet.it. 0099-2399/$0 - see front matter Copyright © 2007 by the American Association of Endodontists. doi:10.1016/j.joen.2006.10.008 Review Article JOE — Volume 33, Number 2, February 2007 Ultrasonics in Endodontics 81