| Abstract|| |
The term "work-related musculoskeletal disorders (WMSDs)," refers to musculoskeletal disorders to which the work environment contributes significantly, or to musculoskeletal disorders that are made worse or longer lasting by work conditions or workplace risk factors. In recent years, there has been an increase in reporting WMSDs for dental persons. Risk factors of WMSDs with specific reference to dentistry include - stress, poor flexibility, improper positioning, infrequent breaks, repetitive movements, weak postural muscles, prolonged awkward postures and improper adjustment of equipment. Ergonomics is the science of designing jobs, equipment and workplaces to fit workers. Proper ergonomic design is necessary to prevent repetitive strain injuries, which can develop over time and can lead to long-term disability. In this article, 20 strategies to prevent WMSDs in the dental operatory are discussed.
Keywords: Carpal tunnel syndrome, ergonomics, low back pain, musculoskeletal disorders
|How to cite this article:|
Gupta S. Ergonomic applications to dental practice. Indian J Dent Res 2011;22:816-22
| Ergonomics|| |
Ergonomics- "ergon" means work and "omics" means law. It is the science of fitting the job settings conducive to the worker. Thus, ergonomics is a science concerned with how to fit a job to man's anatomical, physiological and psychological character in such a way that it enhances human efficiency and well being. The International Ergonomics Association defines ergonomics as follows:  Ergonomics (or human factors) is the scientific discipline concerned with the understanding of interactions among humans and other elements of a system, and the profession that applies theory, principles, data and methods to design in order to optimize human well-being and overall system performance. The term ergonomics is derived from the Greek words ergon (work) and nomos (natural laws), and first entered the modern lexicon when Wojciech Jastrzêbowski used the word in his 1857 article "The Outline of Ergonomics, i.e. Science of Work, Based on the Truths Taken from the Natural Science". The coining of the term Ergonomics, however, is now widely attributed to British psychologist Hywel Murrell, at the 1949 meeting at the United Kingdom's Admiralty, which led to the foundation of The Ergonomics Society. In simple terminology, ERGONOMICS is a way to work smarter-not harder, by designing tools, equipment, work stations and tasks to fit the job to the worker-NOT the worker to the job.
Proper ergonomic design is necessary to prevent repetitive strain injuries, which can develop over time and can lead to long-term disability. Literature suggests that the prevalence of musculoskeletal pain in dentists, dental hygienists and dental students ranges between 64% to 93%.  The most prevalent regions for pain in dentists have been shown to be the back (36.3-60.1%) and neck (19.8-85%), while the hand and wrist regions were the most prevalent regions for dental hygienists (60-69.5%).  Lehto et al. surveyed musculoskeletal health in 131 professionally active dentists as part of a comprehensive health examination.  Forty two percent of dentists had experienced pain and interference with daily activities by neck-shoulder problems during the preceding year, with a tendency to greater prevalence in salaried dentists than in private practitioners. Thirty seven percent experienced lower back problems. Symptoms of stress, perceiving dentistry as physically or mentally too taxing, and a poorer general health status rating were all associated with a greater one-year prevalence of neck-shoulder and lower back pain and disability.
| Scope of Ergonomic Injuries|| |
Cumulative trauma disorders (CTDS) are health disorders arising from repeated biomechanical stress to the hands, wrist, elbows, shoulders, neck and back. Most common CTDS are Carpal tunnel syndrome and Low back pain.  Approximately 24% of all workplace injuries are back injuries. Low back pain is the most common cause of occupational and domestic disability, having a prevalence of 1:7 in general population and 1:2 in dentists. Carpal Tunnel syndrome (CTS) has been associated with both repetitive and forceful work. CTS is defined as symptomatic compression of the median nerve within the carpal tunnel, which is the space between the transverse carpal ligament on the palmar aspect of the wrist and the carpal bones on the dorsal aspect of the wrist. Symptoms of carpal tunnel compression can appear from any activity causing prolonged increased (passive or active) pressure in the carpal canal. There is evidence of an association between CTS and highly repetitive work, alone or in combination with other factors. 
In 1995, Liss et al. surveyed musculoskeletal disorders among dental hygienists in Canada.  Using logistic regression models, the number of heavy calculus patients per day, "clock" position around the dental chair, and years in practice were significant predictors of CTS among hygienists. Days worked, time with the trunk rotated, and years of practice were significant predictors of reported shoulder trouble in the past 12 months. The authors emphasized the need to inform hygienists during training and continuing education about musculoskeletal problems in general and CTS in particular. They stated that attention should be directed to areas such as workstation design, posture, treating patients with heavy calculus, and scheduling rest periods. A study by Osborn et al. among dental hygienists in Minnesota reported similar findings. 
Work Related Musculoskeletal disorders (WMSDs) affect soft tissue of the body in areas like the neck, back, shoulder, elbow, hand, wrist, and fingers. These include nerves, tendons, cartilage, ligaments, and muscles. Signs and symptoms of WMSDs include decreased strength or range of motion, pain or burning, swelling or inflammation and shooting/stabbing pain into arms/legs. It has been concluded that the high frequency of symptoms from the neck, shoulders, and upper extremities of the dentists is probably related to difficult work positions with cervical flexion and rotation, abducted arms, and repetitive precision-demanding handgrips. , Burke et al. in 1997 reported WMSDs to be one the commonest reasons for early retirement among dentists.  In recent years, there has been an increase in reporting WMSDs for dental personnel which can be attributed to the below mentioned risk factors
Hence, with specific reference to dentistry, the risk factors include: Stress, poor flexibility, improper positioning, infrequent breaks, repetitive movements, weak postural muscles, prolonged awkward postures and improper adjustment of equipment.
- Force: The amount of physical effort required to maintain control of equipment or tools, or to perform a task such as heavy lifting, pushing, pulling, or carrying.
- Repetition: Performing the same motion or series of motions continually or frequently, for an extended period of time with little variation such as prolonged typing, assembling components, scaling and polishing in case of dentists and repetitive hand tool usage.
- Awkward postures: Refers to positions of the body that significantly deviate from the neutral position while performing job tasks such as working over-head, extended reaching, twisting, squatting, or kneeling.
- Static postures: Refer to holding a fixed position or posture such as gripping tools that can't be set down, standing in one place for prolonged periods.
- Contact stress: Results from occasional, repeated, or continuous contact between sensitive body tissues and hard or sharp objects like resting the wrist on the edge of a desk, or tool handles pressing into the palms.
- Age-related changes
- Reaction time lengthens
- Workload capacity decreases
- Temperature related discomfort increases
- Visual capabilities decrease ,,,
| Application of Ergonomics in Dentistry|| |
Goals of ergonomics in any workplace should include:
20 strategies to prevent work related musculoskeletal disorders and low back pain in the dental operatory are discussed below: ,,,
- Reducing the risk of CTD
- Increasing productivity
- Increasing safety
- Improving the quality of work
- Decreasing fatigue and errors
The human spine has four natural curves; Cervical lordosis, Thoracic kyphosis, Lumbar lordosis and Sacral kyphosis. Poor postural alignment accelerates wear and tear of vertebrae, discs, muscles and ligaments; leading to pain syndromes. Disc pressure dramatically increases when sitting and in bent forward and rotated positions. This is a position frequently seen among dental professionals. When a dentist sits in a chair and leans forwards towards the patient, lumbar curve flattens. The spine is not supported by bony structures, and is literally hanging on muscles, ligaments and soft tissues at the back of spine. Excess forces occur on low back, leading to muscle strain and painful trigger points. Also, sitting with thighs parallel to floor while leaning causes the pelvis to roll backward and flatten the low back curve, increases muscle strain and disc pressure. Thighs sloping downwards helps maintain the normal low back curve, decrease low back muscle strain and hence decrease low back pain.
The best way to reduce pressure in the back is to be in a standing position. However, there are times when the dentist needs to sit. When sitting, the main part of the body weight is transferred to the seat. Some weight is also transferred to the floor, back rest, and armrests. Where the weight is transferred is the key to a good seat design. When the proper areas are not supported, sitting in a seat all day can put unwanted pressure on the back causing pain.
The lumbar spine (bottom five vertebrate in the spine) needs to be supported to decrease disc pressure. Providing both a seat back that inclines backwards and has a lumbar support is critical to prevent excessive low back pressures. The combination which minimizes pressure on the lower back is having a backrest inclination of 120 degrees and a lumbar support of 5 cm. The 120 degrees inclination means the angle between the seat and the backrest should be 120 degrees. The lumbar support of 5 cm means the chair backrest supports the lumbar by sticking out 5 cm in the lower back area. ,
Operator chair ergonomic guidelines
Goal: Promote mobility and patient access;
Accommodate different body sizes
Remember- one size does not fit all!
Patient chair ergonomic guidelines
- Stability (5 legged base w/casters)
- Lumbar support
- Hands-free seat height adjustment
- Adjustable foot rests
- Adjustable, wrap-around body support
- Seamless upholstery
- Hydraulic controls
- Cylinder height
- Adjustable backrest
Tilting seat pan
- Textured seat material
- Correct wheel type
- Armrests (optional)
Goal: Promote patient comfort; maximize patient access
- Pivoting or drop-down arm rests (for patient ingress/egress)
- Supplemental wrist/forearm support (for operator)
- Articulating head rests
- Hands-free operation
- Small, thin headrest: Allows for greater leg room
- Narrow upper back: Allows closer positioning
- Swivel feature: Allows chair to rotate in the operatory
- Sling or low profile arm rests: Helps the dentist to work in 8:00-10:00 positions without hitting their knees on a fixed metal arm rest.
Large knobs: Should be absent. They hit the edge of operator chair, preventing close positioning.
- Adjustable chair height
- Instruments, materials, medications, etc. Are accessible while seated
- Hoses are positioned away from the body
- Set-up can be adapted for different operators
Another key to reducing lumbar disc pressure is the use of armrests which decreases stress on low back, neck and shoulder. They help by putting the force of your body not entirely on the seat and back rest, but putting some of this pressure on the armrests. They move the fulcrum to the elbow, hence moving the workload to the smaller motor muscles for precision work. Armrest needs to be adjustable in height to assure that shoulders are not overstressed.
Open the hip angle: By using
Tilted seat plan
It opens the hip angle by 110 degrees Retrofit a non-tilting seat such as the commercially available Fit-sit ergonomic cushion for accomplishing this.
Another way to keep the body from falling forward is with a saddle seat. This type of seat is generally seen in some sit stand stools, which seek to emulate the riding or saddle position of a horseback rider, the first "job" involving extended periods of sitting. It opens the hip angle by 135 degrees. It is ideal for confined operatory spaces. The Doctor is now half way between standing and sitting, so low back pressure is even less than when seated in traditional operator chairs.
Always adjust the backrest forward
Adjust its height so that the most convex portion nestles in your low back curve. By doing this back muscle activity is significantly reduced. It allows body's rate of repair to exceed the rate of damage or micro trauma [Figure 1].
|Figure 1: Adjust the backrest forward so that the most convex portion nestles the low back curve|
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Avoid: Too short cylinder
If doctors stool is adjusted too low, hip and knee angle becomes acute, weight is transferred to a small area under the sit bones, rather than spreading out over the back of the legs, leading to a compression of abdominal organs and flattening of spine and low back pain [Figure 2] and [Figure 3].
|Figure 2: If stool is adjusted too low, the hip and knee angle becomes acute, transferring the weight to a small area under the sit bones, leading to low back pain|
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|Figure 3: Proper height of the stool for the dentist: Weight spread out over a larger area|
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Avoid: Short working distance
Working distance is the distance between the doctors' eye and the occlusal surface of the patient. Low back pain occurs if the patient is placed too high or if the Dentist hunches over the patient. Use indirect vision to avoid awkward positions
Properly adjust the head rest (flat head rest)
If head rest is too long, the dentist is forced to hunch forward over the dead head rest space, leading to low back pain. Always ask the patient to scoot to the end of the head rest.
Selection of instruments
Tool/instrument design should be such that it reduces force exertion and maintains hand/wrist in neutral posture.
Considerations to be kept in mind are:
While buying Hand instruments, look for:
- Overall shape/size
- Handle shape/size
- Ease of operation
- Ease of maintenance
While buying Automatic hand pieces for your operatory, look for:
- Hollow or resin handles
- Round, knurled or compressible handles
- Carbon steel construction (for instruments with sharp edges)
In Syringes and dispensers, look for:
- Lightweight, balanced models (cordless preferred)
- Sufficient power
- Built-in light sources
- Angled vs. Straight-shank
- Pliable, lightweight hoses
- Swivel mechanisms
- Easy activation
- Easy maintenance
Training of dental personnel
- Adequate lumen size
- Ease in cleaning
- Knurled handles (no finger cut-outs)
- Easy activation and placement
Training is recognized as an essential element for any effective safety and health program. For ergonomics, the overall goal of training is to enable managers, supervisors, and employees to identify aspects of job tasks that may increase a worker's risk of developing work-related MSDs, recognize the signs and symptoms of the disorders, and participate in the development of strategies to control or prevent them. Training employees ensures that they are well informed about the hazards so they can actively participate in identifying and controlling exposures
Place it close to the operator so that the knee is at about 90-100 degree angle. If placed outside this zone, the dentist must shift weight to one side, leading to asymmetrical stresses on back, hence low back pain. Switch it from one foot to another 2-3 times a day [Figure 4].
|Figure 4: Place the rheostat close to the operator so that the knee is at about 90-100 degree angle|
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Stretches are a must. They can be easily performed, by the chair side with gloves on and need minimum amount of time (10-15 seconds). Perform primarily towards the tightest side throughout the day. Consult physician first if suffering from injury or any medical condition.
Be careful while exercising
- The un-twister
Legs in tripod position; bend to left side.
Rest your left elbow on left knee.
Stretch right arm overhead and look towards the ceiling.
Hold for 2-4 breath cycles
Repeat [Figure 5].
- Trunk rotation
Sit tall. Cross right leg over left leg.
Place left forearm on right thigh and turn trunk to the right.
Hold for 2-4 breath cycles.
Repeat [Figure 6].
- The reversal
Support wrists on hips and slowly lean backward.
Do not overextend the head.
Hold for 2-4 breath cycles [Figure 7].
Avoid sit ups as they over strengthen rectus abdominus muscle, which in turn leads to flattening of low back curve, hence low back pain. Instead do abdominal crunches which utilize internal oblique and avoid over strengthening rectus abdominus.
Avoid twisting the trunk
Rear delivery systems encourage extensive trunk twisting and can result in low back pain. Try to retrieve items with the closest hand and then transfer them to the dominant hand. Position patient so that operator's elbows are elevated no more than 30 degrees [Figure 8] and [Figure 9].
|Figure 8: Rear delivery systems encourage extensive trunk twisting; can cause low back pain|
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|Figure 9: Retrieve items with the closest hand and transfer it to the dominant hand|
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For each additional 10 pounds of weight you carry, 100 pounds of force is generated to the low back [Figure 10]!
|Figure 10: Excess weight leads to weak postural muscles and low back pain|
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Goal would be to provide sufficient recovery time for staff to avoid chronic muscular fatigue.
Dentist micro breaks
- Increase treatment time for more difficult patients
- Alternate heavy and light calculus patients within a flexible scheduling system
- Vary procedures within the same appointment
- Shorten patient's recall interval
- Alternate tough and easy patients.
Take frequent breaks to relax. A dentist can take a break to do stretches' while the assistant light cures, while waiting for local anesthesia to act, while the assistant mixes cements or applies periodontal dressings etc. [Figure 11].
The human body has been made to move. Due to sedentary lifestyles of today, number of MSDs has skyrocketed. Static prolonged muscle contractions must be avoided. Alternate between standing and sitting as they use different muscle groups; allowing one group to rest while the other is working. For example, the dentist can stand during impression taking, extractions etc. Frequently move the workload from one area in the body to another.
Change positions frequently
Regularly changing positions around the head of the patient is an important strategy for moving the muscle workload from one area to another. Rest forearms on dental chair if possible.
Dentists must focus on improving the endurance of the specific trunk stabilizing muscles to prevent low back pain. Trunk stabilizing muscles are:
Transverse abdominus muscle (the ability to contract this muscle is closely linked to patients' reports of decreased pain levels); Erector spinae, which helps extend back, (In unsupported sitting, it is constantly under stress and can become painful and ischemic); Internal oblique, which move upper ½ of trunk; and, external oblique, which work lower ½ of trunk. Both the obliques must work together in rotation. Quadratus lumborum also helps side bend the body. Back and trunk strengthening can be done using Swiss balls which are easily available.
Pointer dog exercise
It is the single most beneficial exercise. Start the exercise on hands and knees. Keep trunk still. Pull navel towards spine. Lift arm and opposite leg together, hold for 5-8 seconds. Then lower.
Lumbar roll with exercise ball
Extend arms on the floor at shoulder height, palms up. Without letting your shoulders lift off the ground, slowly roll the ball to the left side, and then reverse the movement to the right. Avoid home activities that aggravate your injured muscles. Wear long sleeve shirts or sweaters when the room is cold to keep muscles warm.
Goal: To improve neck posture; to provide clearer vision
Use of Normal scopes necessitates 20 degree forward head bending which leads to flattening of low back curve and hence low back pain. In contrast, procedure scope utilizes 0 degree forward head bending and an extra oral camera to display image on a Liquid-crystal display screen; hence better. When purchasing magnification systems, consider:
- Working distance
- Depth of field
- Declination angle
- Convergence angle
- Magnification factor
- Lighting needs
| Summary|| |
The successful application of ergonomics assures high productivity, avoidance of illnesses and injuries, and increased satisfaction among workers. Unsuccessful application, on the other hand, can lead to work-related musculoskeletal disorders (WMSDs). Good ergonomic design of tools, processes and furniture DOES improve personnel comfort, health, morale, productivity and readiness. It is critical to seek prompt medical aid for symptoms of ergonomic stress/detect risk factors.
So, take charge of your health and stay fit!
| References|| |
|1.||Hayes M, Cockrell D, Smith DR. A systematic review of musculoskeletal disorders among dental professionals. Int J Dent Hyg 2009;3:159-65. |
|2.||Lehto TU, Helenius HY, Alaranta HT. Musculoskeletal symptoms of dentists assessed by a multidisciplinary approach. Community Dent Oral Epidemiol 1991;19:38-44. |
|3.||Liss GM, Jesin E, Kusiak RA, White P. Musculoskeletal problems among Ontario dental hygienists. Am J Ind Med 1995;28:521-40. |
|4.||Hamann C, Werner RA, Franzblau A, Rodgers PA, Siew C, Gruninger S. Prevalence of carpal tunnel syndrome and median mononeuropathy among dentists. J Am Dent Assoc 2001;132:163-70. |
|5.||Osborn JB, Newell KJ, Rudney JD, Stoltenberg JL. Carpal tunnel syndrome among Minnesota dental hygienists. J Dent Hyg 1990;64:79-85. |
|6.||Milerad E, Ekenvall L. Symptoms of the neck and upper extremities in dentists. Scand J Work Environ Health 1990;16:129-34. |
|7.||Finsen L, Christensen H, Bakke M. Musculoskeletal disorders among dentists and variation in dental work. Appl Ergon 1998;29:119-25. |
|8.||Hill KB, Burke FJ, Brown J, Macdonald EB, Morris AJ, White DA, Murray K. Dental practioners and ill health retirement: A qualitative investigation into the causes and effects. Br Dent J 2010;209: E8. |
|9.||Rundcrantz BL, Johnsson B, Moritz U. Occupational cervico-brachial disorders among dentists. Analysis of ergonomics and locomotor functions. Swed Dent J 1991;15:105-15. |
|10.||Rundcrantz BL, Johnsson B, Moritz U. Pain and discomfort in the musculoskeletal system among dentists. A prospective study. Swed Dent J 1991;15:219-28. |
|11.||Rundcrantz BL. Pain and discomfort in the musculoskeletal system among dentists. Swed Dent J Suppl 1991;76:1-102. |
|12.||Rundcrantz BL, Johnsson B, Moritz U. Cervical pain and discomfort among dentists. Epidemiological, clinical and therapeutic aspects. Part 1. A survey of pain and discomfort. Swed Dent J 1990;14:71-80. |
|13.||Valachi B, Valachi K. Preventing musculoskeletal disorders in clinical dentistry: Strategies to address the mechanisms leading to musculoskeletal disorders. J Am Dent Assoc 2003;134:1604-12. |
|14.||Harrison D, Harrison S, Croft AC, Harrison DE, Troyanovich SJ. Sitting biomechanics, part 1: Review of literature. J Manipulative Physiol Ther 1992;22:594-609. |
Department of Periodontics, Dr. Harvansh Singh Judge Institute of Dental Sciences and Hospital, Sector 25, Chandigarh
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]