Clinicians should select equipment that fits their needs, not equipment they must adapt to.
WRITTEN BY Claudia Michalak-Turcotte, CDA, RDH, MSDH, MSOSH, Marcy Sanders, MA, MSOSH, OTR/L, Jeff Dussetschleger, DDS, MPH, and Melissa Ing, DMD
It has been well documented that dental professionals are at high risk for musculoskeletal disorders. Over 65 percent of dentists have experienced neck, shoulder or low back musculoskeletal disorders.1 Ergonomic risk factors such as repetitive motion, excessive force, awkward and static posture, and exposure to vibration can lead to these disorders.2-4 Some risk factors can be minimized but not totally eliminated, such as repetitive motions with sustained pinch forces.
Clinicians can implement various strategies through a well-designed ergonomic plan to reduce musculoskeletal disorders. Many, such as body mechanics, can be implemented with minimal cost. This includes positioning, stretching, and varying tasks. Dental equipment design may also impact musculoskeletal health. Manufacturers are constantly adapting equipment to help clinicians control or eliminate risk factors. There are no industry standards for ergonomic equipment for dentistry. Clinicians should select equipment that fits their needs, not equipment they must adapt to. This article focuses on equipment that meets individual needs.
Dental Chairs and Delivery Systems
One of the most prevalent musculoskeletal risk factors is awkward posture. Several things can help promote better posture. Clinicians should evaluate their chair, patient chair, and delivery system, since these three pieces must fit the clinician’s physical stature to promote proper posture. Both the height and backrest design of the patient chair should be considered to maintain a neutral position during delivery of care. The patient chair should be lowered and the back rest reclined for the clinician to move freely without thighs or knees being obstructed, and a small, thin headrest and narrow upper backrest will help maintain neutral posture and close proximity to the patient.5 The clinician should not have to lean forward to see into the oral cavity.
Dental delivery systems come in different styles: side, rear, over-the-patient, and transthorax/over-the-head. Dental delivery systems may be adapted to the patient chair or into the operatory’s cabinetry. Side delivery units place the handpieces, air/water syringe, and bracket table on the dentist’s side of the patient (8 to 9 o’clock position for right-handed clinicians and 3 to 4 o’clock for left-handed clinicians), and the high velocity evacuator (HVE) on the assistant’s side. These require the dentist to reach to retrieve instruments or change burs, whereas the assistant completes these activities and hands the equipment to the clinician during proper four-handed dentistry.
Rear delivery systems (12 o’clock position) have similar ergonomic disadvantages, as well as the twisting torso disadvantage. An over-the-patient delivery system is set up at 5 o’clock for the right-handed clinician and 7 o’clock for the left-handed clinician. This requires an assistant for four-handed dentistry, or positioning the delivery system closer to the clinician’s reach. Transthorax or over-the-head design places handpieces, HVE and air/water syringe over the top of patients, which makes it accessible to both clinician and assistant. Many manufacturers have created dental units that convert the delivery system from side to transthorax by simply swinging the delivery unit from one side to the other. This also allows for conversion from a right-handed to a left-handed unit.
When accessing the dental unit, length and material need to be evaluated as well as delivery and tubing style. The tubing needs to be heavy enough to withstand long-term use, but light enough to not add unnecessary weight to the handpiece. Straight tubing eliminates the torquing that occurs with coiled tubing. The tubing should be long enough so there is no tension on it during use. In addition, if the tubing has a retraction feature, it needs to adequately lock the tubing in place during use to prevent the dentist from having to maintain tension on it, which increases exertion and strain on the wrist.6
One should always try the clinician’s chair prior to purchasing. Things to consider are the backrest, seat contour, height, and adjustability. When seated, hips should be slightly above the knees and feet should be placed firmly on the floor. The backrest should be placed in contact with the lower back to provide support.
The dentist’s chair should be adjusted prior to adjusting the patient. Once you have yourself and your patient positioned, check your posture. You should be seated with shoulders relaxed, elbows close to your body, back supported by the backrest, head straight with no more than 15 degrees of neck flexion, and feet firmly on the floor. If you notice that you must continually lean forward or flex your neck to gain visual acuity, you may need a new prescription or magnification loupes. Magnification loupes should be personally adjusted to ensure correct working distance and posture.4
Proper illumination of the workspace is very important. Improper lighting can contribute to eye fatigue. Natural lighting or color-corrected overhead lighting will help not only in the selection of esthetic restoration shades, but also in reducing eyestrain. Clinicians may also consider digital shade-scanning technology to eliminate subjective factors in the selection of shades.
Operating light can be mounted on a cabinet, wall, ceiling, track or unit, and should be adjusted to eliminate shadows on the working site. Lights should not drift. Consideration should be given to the installation of X-ray machines and operating lights. Operating lights and X-ray units should not impinge on each other. In comparison, short-armed chair-based lights are awkward, as the clinician needs to reach further around to adjust lighting, causing possible strain or injury. Additionally, track lighting can be directly overhead, which allows for good illumination without shadows.
Mechanical and manual instruments
Dental instruments may be mechanical or manual, and should accomplish the task and keep the clinician’s posture neutral. Instrument design should also be considered. An angled instrument may be more appropriate than a straight instrument to promote neutral wrist posture. Dental clinicians should select mechanical instruments that effectively accomplish the task and reduce force, time, and awkward posture. Mechanical instruments include handpieces (high and low speed), lasers, ultrasonic scalers, and electrosurgical units. Clinicians need to consider instrument weight and select well-balanced instruments. A clinician may need to apply more force to grasp and activate the handpiece if it is not balanced.
Manufacturers have produced various lengths of handpieces, with short ones providing less torque on clinicians with small hands or clinicians who grasp the handpiece close to the working end. Another feature to consider is fiber optics within the handpiece, which allow for more localized light to the working area. Handpieces should also be assessed for noise level. Clinicians should evaluate the total noise level (suction and handpiece) during procedures to ensure that it does not exceed 85 A-weighted decibels, or dBA, over an eight-hour period. There are a variety of handpieces, and clinicians should select one that best fits their needs.
Dental clinicians can choose from a variety of handle designs, including diameter, surface, weight, and balance. Diameters range from 1/4 inch to 5/8 inch. Recent studies indicate that large diameter (handles up to 10mm) require less muscle loads and pinch forces to operate. Handles larger than 10mm do not elicit any additional benefits.7
Light weight handles reduce the muscle forces needed to operate the instruments.7 Handle shapes are round, octagonal, and hexagonal. Although gloves minimize the impact of longitudinal ridges, these ridges can place pressure on the nerves lateral to each finger and create discomfort. Round handles are generally considered the most comfortable for long-term use.
Handle surfaces are usually textured with serrated, longitudinal, knurled, crosscut or ribbed patterns. Generally, small textured patterns provide adequate friction between the glove and tool to promote a firm grasp. Some handle designs apply a rubber synthetic coating to increase the diameter and improve friction, which has also been related to decreased muscle force generation.
Dental mirrors have been studied with regard to handle design, hand loads, and pinch force generation. Generally, padded dental mirrors reduce thumb forces, and those that are lightweight with a large diameter decrease overall hand force. Thus, using dental mirrors that are lightweight and with large-diameter, padded
handles may minimize the cumulative hand forces. 8
There is a variety of mouth mirrors in different sizes, double-sided, and magnified. Double-sided mirrors can accomplish two tasks simultaneously, retracting tissues and indirect vision.
Dental pliers and forceps should be evaluated for fit in the clinician’s palm. These should not press against the palm of the hand or put pressure on the nerves. Locking pliers reduce the pinch force needed to transfer materials to the oral cavity. Also, there is a variety ofanesthetic syringes on the market that have different styles of thumb rings to fit different clinicians’ hands.
Dentistry presents many ergonomic risks. These can be minimized through the use of ergonomically designed instruments and equipment. This selection should be based not only on design, but on the practitioner’s physical stature and preferences. The key to selecting the best ergonomic equipment is to select equipment that will be incorporated into the practice and used regularly.
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2. Armstrong TJ, Fine LJ, Goldstein SA, et al. Ergonomic considerations in hand and wrist tendonitis. J Hand Surg 1987; 12(a):830-837.
3. Horstman SA, Horstman B, Horstman F. Ergonomic risk factors associated with the practice of dental hygiene: A preliminary study. Professional Safety 1997; April: 49-53.
4. Rucker LM, Surrel S. Ergonomic Risk Factors Associated with Clinical Dentistry. J California Dental Association 2002; 30(2):139-148.
5. Valachi B, Valachi K. Preventing Musculoskeletal Disorders in Clinical Dentistry: Strategies to Address the Mechanisms Leading to Musculoskeletal Disorders. JADA 2003; 134:1605-1612.
6. Fredeking R, Cuny E. Instruments Used in Dentistry. Ergonomics and the Dental Health Care Worker. Waldorf, MD; American Public Health Association, 1998.
7. Dong H, Barr A, Loomer P, Laroche C, Young E, Rempel D. The Effects of Periodontal Instrument Handle Design on Hand Muscle Load and Pinch Force. Am Dent Assoc. 2006;137 (8): 1123-1130.
8. Simmer-Beck M, Bray KK, Branson B, Galaros A, Weeks J. Comparison of Muscle Activity Associated with Structural Differences in Dental Hygiene Mirrors. JDH 2006; 80 (1): 1-16.