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Inside Dentistry
September 2006
Volume 2, Issue 7

Understanding and Preventing Musculoskeletal Disorders in Dentistry

Eve Cuny, MS; A. Jeffrey Wood, DDS

Musculoskeletal disorders, including repetitive motion injuries, result in painful work, lost workdays, and, in extreme cases, disability resulting in forced retirement. Musculoskeletal disorders are not highly predictable in any single person. Individual susceptibility or predisposition and personal risk factors such as past injury and underlying medical conditions contribute to the risk for musculoskeletal disorders. There are steps every dental professional can take to reduce their risk of sustaining musculoskeletal disorders.

Collectively known as musculoskeletal disorders (MSDs), injuries to the tendons, muscles, nerves, and other structures in the musculoskeletal system are a major source of work-related injuries across professions, including dentistry. In the United States in 2004, MSDs accounted for 402,700 injuries requiring at least 1 day away from work. That number constitutes 32% of all workplace injuries in the United States that year.1 The causes of MSDs include equipment that is poorly designed or improperly used; the use of various types of force by parts of the body; awkward posture; repetition; the use of vibrating tools; and other factors, including some that are not work related (such as obesity, arthritis, autoimmune disorders, and smoking). Although there are known risk factors for MSDs, it is difficult to attribute a given disorder to a specific risk factor. It is likely that these types of injuries result from multiple risk factors, degrees of exposure to risk, and other issues (such as hereditary factors) rather than from any one single cause.

The practice of good ergonomics is a significant strategy for the prevention of MSDs. There are several recommendations for improved ergonomics specific to dentistry (Table 1). Although different groups use slightly different definitions for the term, one definition appropriate to the application of ergonomics in dentistry is that is it is the study of the relationship of humans to their working environment and the development of methods, tools, and equipment to improve working conditions, increase efficiency, and reduce injury. In realistic terms, this means selecting and appropriately using equipment that allows for comfortable postures, using instruments that minimize gripping force and vibration, positioning the patient to allow maximum access and visibility with minimal bending and leaning, maintaining good general health, and recognizing and addressing the warning signals for MSDs early in their progress. The early warning signs of MSDs include pain, tingling, and numbness. The appearance of these symptoms should always be discussed with the person’s medical care provider. More specific information regarding symptoms for many MSDs is detailed in Table 2.

Dental equipment

Most dental workers provide care in a relatively small space such as a dental operatory. During the course of a dental appointment, it may be necessary to access information on a computer or reach for equipment, paperwork, and dental materials. If these items are not easily accessible, the members of the dental team must reach, stretch, twist, and often contort their bodies to get to the items they need. Counters that are wide and close to the side of the assistant allow for placement of materials and devices within easy reach. Adjustable work surfaces, including flat platforms on swinging arms are also good tools to bring things close to the assistant and dentist, but allow for movement around the dental chair if needed by simply swiveling the platform out of the way.

Items attached to the dental cart or delivery system may provide resistance because of weight, balance, or the pull of cords. Some potential solutions to these issues include:

  • Selecting high-speed suction handles that are not awkward to hold and activate.
  • Purchasing lightweight handpieces that have a balanced feel.
  • Installing cords that are long enough to allow the operator to manipulate into a comfortable position yet not so long as to add unnecessary weight.
  • Installing handpiece swivels.
  • Any other available features that make the equipment more comfortable to operate.

Purchasing decisions should not be based on the marketing of ergonomic design alone. There are no industry standards for the ergonomic design of dental equipment, and improperly designed equipment may exacerbate MSDs rather than relieve them.2

Dental instruments

Instruments that generate vibration, require force to hold or manipulate, have small-diameter handles, or are difficult to grip can potentially contribute to MSDs.3 One well-known MSD that results from repetitive motion is carpal tunnel syndrome, which results when there is compression of the median nerve as it passes through a small opening bordered by bones and ligament. When subjected to repeated forceful motion of the wrist, the tendons that pass through the carpal tunnel with the nerve swell and compress the median nerve and limit its blood supply. The compression and/or obstruction of the vascular supply causes the symptoms associated with this painful syndrome.

Some useful strategies for reducing the risk of repetitive strain injuries are to use instruments with larger-diameter handles that require less gripping force; select instruments that are textured to allow easier gripping; avoid awkward wrist positions; take small rest breaks when performing repetitive tasks; and use mechanical scaling devices where appropriate to reduce the need to exert force when root planing and scaling. The use of mechanical scaling devices will also decrease the duration of the stressful activity.

Posture and patient positioning

Dentists often work using static body positions, such as extended elbows, for prolonged periods of time. This requires the retraction of at least 50% of the body’s muscles to allow the body to remain motionless while resisting gravity.4 This static loading of the muscles causes greater fatigue than moving forces, and may lead to MSDs in addition to chronic back, neck, or shoulder pain.5 Posture and patient positioning are two important tools in preventing the use of static body positions.

Operator and assistant posture and patient positioning go hand in hand as a strategy for improving chairside ergonomics. Good operator position consists of the following elements:

  • Head and neck relatively erect with the focal distance 13 inches to 18 ? inches from the patient’s face.
  • Operator loupes adjusted to focus on the working field at a distance of 13 inches to 18 ? inches.
  • Shoulders should be parallel to the floor.
  • The back should be supported at approximately a 100-degree to 110-degree angle to the stool seat.
  • Elbows should be at the sides at the level of the patient’s mouth.
  • Forearms should generally be parallel to the floor.
  • Knees should be slightly below hip level.
  • The left leg should be extended under the patient’s chair with the foot flat on the floor while the right foot operates the rheostat (reverse for a left-handed operator).

The ideal position in which to place the patient while working on the maxillary arch is with the chair fully supine (Figure 1). With the patient in this position, the operator can use the mirror for indirect vision without bending, leaning or stretching. For the mandibular arch, elevate the back of the patient’s chair between 5 degrees and 30 degrees. When working on either arch lower the patient’s chair to just above the operator’s leg.

It is also helpful to use a variety of seated positions around the patient chair to access different teeth and surfaces while working. It is helpful to view the patient chair as if it were a clock, with the top being the 12:00 position. Although most procedures can be performed from the 11:00 position (1:00 position for left-handed operators), there are situations in which anywhere from 9:00 to 12:00 may provide better access and less bending and leaning of the upper body with less flexing of the wrist. Better access and visibility are provided to the assistant when seated with hips and thighs parallel to the patient’s shoulder. The ideal zones of activity and positioning of people and equipment for working with a rear delivery cart system are shown in Figure 2.

Four-handed dentistry

Working with a dental assistant not only increases the efficiency of the procedure, but also allows the dentist to maintain posture and avoid awkward positions. Effective four-handed techniques require the active participation of both the dentist and the assistant (Figure 3). The dentist must communicate adequately to the assistant the sequence of instruments so that the appointment progresses smoothly. Instrument transfers should occur in a designated transfer zone, ensuring that both the assistant and the dentist understand where and how instruments will be passed, reducing the need for unnecessary movement while also increasing efficiency and reducing the risk of accidentally dropping the instrument.

Regulations and assistance

The Occupational Safety and Health Administration (OSHA) does not have regulations specifically addressing the issue of ergonomics on the job. At least one of the 26 state OSHA plans (California) does have an ergonomics rule. However, OSHA does have the ability to cite for ergonomic hazards under the General Duty Clause.

In explaining their approach to ergonomics, OSHA states that they have a “four-pronged approach,” which includes:

  • Industry- or task-specific guidelines to reduce injuries in targeted industries based on current incidence rates and current information about effective and feasible solutions.
  • Inspections for ergonomic hazards and citations under the General Duty Clause and the issuance of ergonomic hazard alert letters when appropriate.
  • Providing assistance to businesses, particularly small business, to help them address ergonomic issues in the workplace.
  • Chartering an advisory committee that will be authorized to identify gaps in research to the application of ergonomics and ergonomic principles in the workplace.

OSHA/ADA Alliance

OSHA and the American Dental Association (ADA) signed an alliance agreement in April 2004 and renewed the agreement in May 2006. This alliance outlines the joint effort of OSHA and the ADA to develop dental-specific information regarding ergonomics. They also outlined a plan to speak or exhibit at conferences held by the other organization, to share information about best practices, provide outreach to the profession, and to work with other alliance participants on specific projects.


Many factors influence the risk of musculoskeletal disorders among dental workers. A comprehensive approach to prevention includes education, assessment of risk factors, proper equipment and instruments, posture, and personalhabits such as exercise. In the dental office, a team approach including the use of four-handed techniques can help both the dentist and the assistant work more comfortably. It is also important to be aware of the warning signs of MSDs and to seek medical intervention as early as possible.


1. US Bureau of Labor Statistics. Lost Work Time Injuries and Illnesses: Characteristics and Resulting Time Away From Work, 2004. USDL 05-2312. Dec 13, 2005. Available at Accessed July 14, 2006.

2. American Dental Association. An Introduction to Ergonomics: Risk Factors, MSDs, Approaches and Interventions. A Report of the Ergonomics and Disability Support Advisory Committee. Council on Dental Practice. 2004. Available at Accessed July 14, 2006.

3. Fredekind R, Cuny E. Instruments Used in Dentistry. In: Ergonomics and the Dental Care Worker. Murphy DC, ed. Washington DC: APHA;1998.

4. Valachi B, Valachi K. Mechanisms leading to musculoskeletal disorders in dentistry. J Am Dent Assoc. 2003;134(10): 1344-1350.

5. Valachi B, Valachi K. Preventing musculoskeletal disorders in clinical dentistry: strategies to address the mechanisms leading to musculoskeletal disorders. J Am Dent Assoc. 2003;134(12):1604-1612.

Figure 1 Correct patient positioning while working on the maxillary arch (supine).

Figure 3 Correct operator, assistant, and patient position for the mandibular arch. Note the operator and assistant are wearing masks with splash shields and other appropriate protective attire. Figure 2 Zones of activity for a right-handed operator and a left-handed operator.
About the Authors
Eve Cuny, MS
Director of Environmental
Health and Safety
Assistant Professor, Pathology and Medicine
University of the Pacific
Arthur A. Dugoni School of Dentistry
San Francisco, California
A. Jeffrey Wood, DDS
Professor and Chair
Department of Pediatric Dentistry
University of the Pacific
Arthur A. Dugoni School of Dentistry
San Francisco, California

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