NewsletterSpeed, torque, load, and weight are defining factors
The introduction of the first dental handpieces between 1868 and 1871 transformed the industry.1,2 During that period, the forerunners of the two traditional handpieces began their evolution into the highly efficient and sophisticated instruments of today.
Developments in handpieces and their contra angle attachments now impact all aspects of dental treatment, including the removal of carious tissues and old restorations, tooth reduction prior to restoration placement, and preparation for root canals, implants, and other restorations.3 Although Sun and colleagues call the dental handpiece “the most fundamental instrument used by the dentists,” they point out that it is also the instrument most likely to cause tissue damage.3
The two traditional handpieces—electric and air-driven handpieces—each have unique characteristics with associated benefits and risks. There are also product variables both within the two types of technology and their attachments, and differences of opinion about the overall superiority of one over the other.
Air Turbine
The air turbine high-speed handpiece, which relies on an air-driven turbine to rotate the cutting instrument, continues to be the most popular type of high-speed handpiece in the United States, likely due to its relatively low cost for purchase and repair, ability to rapidly remove tooth structure, ergonomic weight and size, and reduced risk of pulpal damage when used properly.2
High-speed air-driven devices function at up to 400,000 rpm and usually operate within 180,000 rpm to 330,000 rpm. However, their main disadvantage is that despite their high speed, their relatively low torque causes the bur to slow down when forced to endure heavy loads.4 According to Kurtzman, when a bur in an air-driven handpiece contacts material to be cut, the speed can drop by 40% or more (depending on the hardness of the material) because as resistance builds during cutting, the air pressure is insufficient to maintain the speed of rotation of the turbine.5
As Little notes, efforts to increase torque by increasing turbine size and head size undermine two of the device’s major advantages.1
Electric
Electrically driven handpieces use a simple electrical supply to power the motor through a control unit.1 They are generally heavier, bulkier, and more expensive than their air-driven counterparts, and operate at a lower rpm than air-driven models—up to 200,000 rpm, depending on the specific handpiece and attachments used.1
The advantage is that their torque is constant, even under demanding loads, resulting in better cutting performance. They also typically offer a number of different motor attachments, which can be used to increase the rpm as needed, so the clinician can modify the same basic handpiece for a variety of procedures. Therefore one electric handpiece can be employed both for high-speed restorative and endodontic procedures and for low-speed restorative, hygienic, endodontic, surgical, and laboratory procedures.1
Due to the absence of air, electric handpieces are quieter and the chance of air embolism in a surgical site is eliminated.5 The power output with electric handpieces is greater than with air-driven handpieces, offering 33 to 45 watts of cutting power. Because the speed and torque are constant, Kurtzman maintains, removing difficult crowns, bridges, and restorations becomes easier.5 Kurtzman does note that those accustomed to air-driven handpieces need to adapt to the constant torque provided by an electric handpiece, meaning that “a lighter touch is required so that over-preparation does not occur when cutting tooth structure.”5
Disadvantages of electric handpieces cited by Little include their typical weight and configuration, which can contribute to operator fatigue. More worrisome, though, is the need to ensure that the handpiece head (“back cap area”) does not overheat; he notes that cases have been reported of patient burns (including third-degree) that have been linked to overheating of the electric handpiece head.1
Add-ons can expand the utility of handpieces in the dental office even more. Some offer greater intraoral visibility with LED light attachments, and those with a 360° swivel head are more comfortable for the operator. Others are designed to handle a wide variety of different heads and contra angles.4
Contra angles in particular vastly expand the function of handpieces by giving operators the ability to adjust their handpieces to reach working surfaces anywhere in the mouth—including areas that are difficult to reach—without straining or changing instruments.4
As is the case with much of the ever-changing technology and tools, clinicians’ preferences are influenced by their own comfort and facility.
This was suggested by the findings of Strassler and colleagues, who conducted an in vitro study to compare the quality of cavity preparations fabricated using a high-speed high-torque (electric motor) handpiece with those using a high-speed low-torque (air turbine) handpiece.6 The study included 86 “novices,” dental students, each of whom cut two Class I preparations, one with an air turbine handpiece and the other with an electric motor high-speed handpiece.
The results were mixed. “In preparation criteria, the electric motor high-speed handpiece had a higher average grade than did the air turbine handpiece (5.07 and 4.90, respectively). For refinement, the average grade for the air turbine high-speed handpiece was greater than that for the electric motor high-speed handpiece (5.72 and 5.52, respectively),” the authors wrote. “The differences were not statistically significant.” 6
Strassler noted, “Based on the results, there were no significant differences between the handpieces used. However, one must consider his or her own clinical practice. In my experience for routine operative dentistry preparations, I can achieve excellent results with both types of handpieces. But, for crown and bridge preparations, I prefer the efficiency of an electric motor high-speed high-torque handpiece. A practitioner should try both handpieces to make a decision on which he or she is better suited.”6
1. Little D. Rethinking the dental handpiece . Compend Cont Ed Dent. 2010;31(9):727-734.
2. Atlas AM. Handpiece and diamond selection . Inside Dentistry. 2011;7(9):88-92.
3.Sun H, Lau A, Heo YB, et al. Relationships between tissue properties and operational parameters of a dental handpiece during simulated cavity preparation . J Dent Biomech. 2013;4. doi:1758736013483747.
4. Handpieces and contra angles: transforming the dental profession . Inside Dental Products. 2013;March:14.
5. Kurtzman GM. Electric handpieces: an overview of current technology . Inside Dentistry. 2007;3(2).
6.Strassler HE, Kenyon BJ, van Zyl I, Louie KG. Comparison of cavity preparation quality using an electric motor handpiece and an air turbine handpiece . J Am Dent Assoc. 2005;136(8):1101-1105.
