JADA Continuing Education
Comparison of cavity preparation quality using an electric motor handpiece and an air turbine dental handpiece
BRIAN J. KENYON, D.M.D.,
IAN VAN ZYL, B.D.S., D.D.S., M.S. and
KENNETH G. LOUIE, D.D.S., M.A.
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ABSTRACT
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Background. The high-speed high-torque (electric motor) hand-piece is becoming more popular in dental offices and laboratories in the United States. It is reported to cut more precisely and to assist in the creation of finer margins that enhance cavity preparations. The authors conducted an in vitro study to compare the quality of cavity preparations fabricated with a high-speed high-torque (electric motor) handpiece and a high-speed low-torque (air turbine) handpiece.
Methods. Eighty-six dental students each cut two Class I preparations, one with an air turbine handpiece and the other with an electric motor high-speed handpiece. The authors asked the students to cut each preparation accurately to a circular outline and to establish a flat pulpal floor with 1.5 millimeters’ depth, 90-degree exit angles, parallel vertical walls and sharp internal line angles, as well as to refine the preparation to achieve flat, smooth walls with a well-defined cavosurface margin. A single faculty member scored the preparations for criteria and refinement using a nine-point scale (range, 1–9). The authors analyzed the data statistically using paired t tests.
Results. 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 differences were not statistically significant.
Clinical Implications. The electric motor high-speed handpiece performed as well as, but not better than, the air turbine handpiece in the fabrication of high-quality cavity preparations.
Key Words: Cavity preparation; electric motor handpiece; air turbine handpiece
The need for high-quality tooth preparations has increased significantly owing to the proliferation of materials and techniques used in contemporary esthetic and restorative dentistry. The optimal selection and use of rotary instruments are key to achieving more precise preparations. The air turbine high-speed handpiece has been used in dentistry for more than 40 years (Figure 1
). It continues to be the most popular type of high-speed handpiece in the United States owing to its ability to remove tooth structure rapidly, the light touch required to operate it, its good ergonomic weight and size, the low risk of pulpal damage when it is used properly and its ease of repair.1,2
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Figure 1. Star 430 SWL air turbine high speed handpiece. Image of Star handpiece reproduced with permission of DentalEZ, Lancaster, Pa.
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The optimal selection and use of rotary instruments are key to achieving more precise cavity preparations.
A reported disadvantage of the air turbine high-speed handpiece is its low torque, which can cause a loss of speed in cutting with small lateral workloads and stall at moderate loads.3 Some consider this disadvantage to be an excellent safety feature, because it prevents excessive pressure from being applied.2 Other deficiencies of the air turbine high-speed hand-piece include a high-pitched whine, vibration, poor concentricity, and the creation of aerosols and vapors.4
The electric motor high-speed handpiece (Figure 2) was introduced as an alternative to the air turbine high-speed handpiece and is reported to have fewer undesirable properties.1 It has constant power, high torque with little stalling over the entire speed range (27–200,000 revolutions per minute), improved tactile response, a more concentric cutting performance, less atomization of airborne pathogens and increased longevity.4,5 In contrast to the high-pitched noise of some air turbine high-speed handpieces, which has been associated with possible hearing loss for dental team members,2 electric motor high-speed handpieces are quiet, run smoothly and are less irritating to patients.1 The reduced vibration of the electric motor high-speed handpiece is more comfortable for patients and decreases the likelihood of operators’ experiencing hand fatigue and cramping.6 Compared with the air turbine high-speed handpiece, the electric motor high-speed handpiece is reported to cut more precisely and to assist in the creation of finer margins (Figure 3) that enhance tooth preparation results.5,7,8 However, no published information is available to corroborate these assertions. Therefore, we conducted a study to compare the quality of cavity preparations fabricated with an electric motor high-speed handpiece and an air turbine high-speed handpiece.
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Figure 2. KaVo ELECTOtorque electric motor high-speed handpiece. Image of KaVo ELECTOtorque plus reproduced with permission of KaVo Dental Corp., Lake Zurich, Ill.
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MATERIALS AND METHODS
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In the fourth quarter of the preclinical operative course at the University of the Pacific Arthur A. Dugoni School of Dentistry, San Francisco, 86 dental students volunteered to cut two Class I preparations each using an operative teaching aid used to learn about the depth and hardness differentiation of enamel and dentin. Each student cut one preparation with a Star 430 SWL air turbine high-speed handpiece (DentalEZ, Lancaster, Pa.) and cut another preparation with a KaVo ELECTOtorque electric motor high-speed handpiece with a 25LHA contra-angle attachment (KaVo America, Lake Zurich, Ill.). The decision about which handpiece to use first was made randomly.
We gave students five minutes to cut identical circular Class I cavity preparations. We asked them to cut each preparation accurately to a circular outline and to establish a flat pulpal floor with 1.5 millimeters’ depth, 90-degree exit angles, parallel vertical walls and sharp internal line angles. We also asked them to refine the preparation to achieve flat, smooth walls with a well-defined cavosurface margin. The students used a new bur for each preparation.
A single faculty member (K.G.L.) scored the preparations for criteria and refinement using a nine-point scale (range, 1–9) (Table 1). We analyzed the data statistically using t tests for paired samples.
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RESULTS
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The dental students prepared and finished 172 Class I cavities using a high-speed high-torque (electric motor) handpiece and a high-speed low-torque (air turbine) handpiece. For preparation criteria, the electric motor high-speed handpiece had a higher average grade than the air turbine high-speed handpiece (5.07 and 4.90, respectively). For refinement, the average grade for the air turbine high-speed hand-piece was greater than that for the electric motor high-speed handpiece (5.72 and 5.52, respectively). The differences in preparation criteria and refinement scores between the two hand-pieces were not statistically significant (Table 2).
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TABLE 2 RESULTS OF STATISTICAL ANALYSIS (PAIRED t TESTS) OF CRITERIA AND REFINEMENT SCORES FOR THE ELECTRIC MOTOR AND AIR TURBINE HIGH-SPEED HANDPIECES.
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DISCUSSION
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Our in vitro study presented an original model to evaluate different ways of cutting cavity preparations. Our objective was to compare the quality of cavity preparations fabricated with high-speed high-torque (electric motor) handpiece and high-speed low-torque (air turbine) handpiece. The electric motor high-speed handpiece performed as well as, but not better than, the air turbine high-speed handpiece in the fabrication of quality cavity preparations (Figure 4).
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Figure 4. Cavity preparations created by the electric motor high-speed handpiece (A) and the air turbine high-speed handpiece (B) that received the same score (5 and 5, respectively) for criteria and refinement.
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The electric motor high-speed handpiece performed as well as, but not better than, the air turbine high-speed handpiece in the fabrication of quality cavity preparations.
Atraumatic preparation, a rational preparation system and optimal work results are three major preparation technique objectives used to ensure the quality of work conditions and performances when preparing cavities.9
Atraumatic preparation involves the careful use of dental instruments to avoid iatrogenic damage to the tooth or surrounding tissues. Considerable heat and friction are generated between a rotary instrument and the tooth surface being prepared, and the prevention of pulpal damage necessitates the selection of techniques and instruments that will reduce the risk of damage.10 When used correctly, air turbine high-speed handpieces cause minimal trauma to tooth structure.1 It also has been demonstrated that electric motor high-speed handpieces have no adverse pulpal effects compared with air turbine high-speed handpieces.11 When used properly, both handpiece types could result in an atraumatic preparation.
A rational preparation system includes rotary instruments that are characterized by satisfactory power or cutting efficiency, tolerable noise levels and aerosol production, resistance to frequent sterilizations, torque and fiber-optic lighting that do not deteriorate quickly with use, longevity and reasonable cost. The electric motor high-speed handpiece has been found to perform as well as or better than the air turbine high-speed handpiece in each of these parameters.4 The greater torque and cutting efficiency of the electric motor high-speed handpiece can be advantageous when cutting through all-ceramic, nonprecious and semiprecious metal restorations.7 A significant disadvantage of an electric motor high-speed handpiece is its increased size and weight compared with the air turbine high-speed handpiece.4 A larger head size may result in reduced visibility and access for the operator. Greater overall size and weight may cause ergonomic problems, particularly for operators with smaller hands.8
A visit to the fixed prosthodontic section of most dental laboratories would confirm that dentists could do much better in producing high-quality restorative preparations that lead to optimal work results. Few laboratory stone models resemble the ideal preparations displayed in fixed prosthodontics textbooks.12 Our study demonstrated no significant differences between the electric motor high-speed handpiece and air turbine high-speed handpiece in the fabrication of high-quality cavity preparations. The amount of tactile feedback, however, during cavity preparation is not equivalent for the electric motor high-speed handpiece and the air turbine high-speed handpiece.11 The air turbine high-speed hand-piece produces high speed and low torque compared with the electric motor high-speed handpiece. This necessitates using a feather-light touch13 and gives the air turbine high-speed handpiece an on (cutting) or off (stalled) feel and, consequently, less tactile feedback compared with the electric motor handpiece.11 In contrast, the high torque of the electric motor high-speed handpiece allows the operator to feel resistance to cutting without stalling. The operator can use vision and an improved sense of feel to prepare teeth with the electric motor high-speed handpiece. Improved tactile sense could result in improved preparations in areas of the mouth that are difficult to visualize, such as sub-gingival margins and the distobuccal surfaces of maxillary second molars. The electric motor high-speed handpiece has the feel of a slow-speed air turbine high-speed handpiece with the cutting power of a high-speed handpiece. The ability to control the speed of the handpiece also should be an advantage in areas that are difficult to prepare.
A possible reason that the electric motor high-speed handpiece was shown to perform as well as, but not better than, the air turbine high-speed handpiece in the fabrication of high-quality cavity preparations is that the student operators in our study were novices. Inexperienced clinicians may not be capable of taking advantage of the increased torque and tactile feedback provided by the electric motor high-speed handpiece. Further investigations are warranted to compare the quality of cavity preparations made by electric motor and air turbine high-speed handpieces when used by more experienced practitioners. Additional studies could include an evaluation of cavity preparation quality in easy and difficult areas of the mouth.
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CONCLUSIONS
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Within the limitations of this in vitro study that compared the quality of cavity preparations fabricated with a high-speed high-torque (electric motor) handpiece and high-speed low-torque (air turbine) handpiece, we drew the following conclusions:
- – There were no statistically significant differences in scores of cavity preparation criteria and refinement between an electric motor high-speed handpiece and an air turbine high-speed handpiece.
- – The electric motor high-speed handpiece performed as well as, but not better than, the air turbine high-speed handpiece in the fabrication of high-quality cavity preparations.
- – Practitioners should consider carefully the advantages and disadvantages of the air turbine high-speed handpiece and the electric motor high-speed handpiece to make a selection that is appropriate for their particular practices and techniques.
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FOOTNOTES
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DISCLOSURE
DentalEZ, Lancaster, Pa., and KaVo America, Lake Zurich, Ill., provided the dental handpieces used in the study reported in this article.
Dr. Kenyon is an assistant professor, Department of Restorative Dentistry, University of the Pacific School of Dentistry, 2155 Webster St., Suite 522L, San Francisco, Calif. 94115, e-mail "bkenyon{at}sf.uop.edu". Address reprint requests to Dr. Kenyon.
Dr. Van Zyl is in private practice, Middletown, Calif.
Dr. Louie is an assistant professor, Department of Restorative Dentistry, University of the Pacific School of Dentistry, San Francisco.
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REFERENCES
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