بسم الله الرحمن الرحيم

Mechanisms leading to musculoskeletal disorders

in dentistry

JobCharacteristics

HumanCapabilities

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

What is What is ErgonomicsErgonomics??

WMSD Symptoms Among WMSD Symptoms Among DentistsDentists

0%10%20%30%40%50%60%70%80%

Body Part

% R

ep

ort

ing

Males

Females

Source: Finsen et al., 1998

WMSD Symptoms WMSD Symptoms Among Dental Among Dental HygienistsHygienists

01020304050607080

*DiagnosedCTS

*Hand-wristpain

*Shoulderpain

*Neck pain Low Backpain

% R

epo

rtin

g

Dental Hygienists Dental Assistants

Source: Liss et al., 1995* indicates difference is significant

musculoskeletal disorders common to dental operators are multifactorial .

seated for prolonged periods increased disk pressures and spinal hypomobility degenerative changes static (motionless) muscle contractions → muscle

ischemia or necrosis As muscles adapt by lengthening or shortening to

accommodate these postures, a muscle imbalance may result, leading to structural

damage and pain.

In a 1946 study, Biller found that 65 percent of dentists complained of back pain. Even after the evolution to seated four-handed dentistry and ergonomic equipment, studies found back, neck, shoulder or arm pain present in up to 81 percent of dental operators.

What Factors Contribute to What Factors Contribute to WMSDsWMSDs??

Static neck, back, and shoulder postures

What Factors Contribute What Factors Contribute to WMSDsto WMSDs??

Grasping small instruments for prolonged periods

What Factors Contribute What Factors Contribute to WMSDsto WMSDs??

Prolonged use of vibrating hand tools

When we compared statistics on pain experienced by standing dentists in 1946 to those of seated dentists, we found that being seated has made little difference in how frequently operators experience pain.

When operators sit, pain occurs not only in their backs, but also their necks, shoulders and arms. On the other hand,

operators who primarily stood experienced low back pain (65.7 percent), as well as neurocirculatory disease including varicose veins (66.7 percent), postural defects (77 percent) and flatfoot (60.1 percent).

pain can be attributed to numerous risk factors

prolonged static postures, or PSPs; repetitive movements; suboptimal lighting; poor positioning; genetic predisposition; mental stress; physical conditioning; and age

Each dental team member is predisposed to pain or injury in slightly different areas of the body ,

hygienists and periodontists who are seated are predisposed to neck, shoulder and hand-wrist pain largely due to static postures combined with forceful, repetitive movements that are inherent in the job.

general practitioners tend to be susceptible to lower back and neck injuries, due to PSPs, but have relatively fewer repetitive-motion injuries.

MUSCLE IMBALANCES

forward bending repeated rotation of the head, neck

and trunk to one side Over time, the muscles responsible

for rotating the body to one side can become stronger and shorter, while the opposing muscles become weaker and elongated

The stressed shortened muscles → ischemic and painful, exerting asymmetrical forces on the spine → misalignment of the spinal column & ↓decreased range of motion in one direction over the other

One study, for example, showed that for a majority of dentists, neck rotation to the right with side bending to the left is a difficult movement to perform. Most right-handed dentists repeatedly assume just the opposite position—rotating the neck to the left with side-bending to the right to gain better visibility.

Muscle imbalances

between the muscles stabilize and those that move

This can cause weakening and elongation of the "stabilizer" muscles of the shoulder blades (middle and lower trapezius, rhomboid and serratus anterior muscles).

As a result, the shoulder blades tend to move away from the spine, leading to rounded shoulder posture

. Meanwhile, anterior "mover" muscles (scalene, sternocleidomastoid and pectoralis) become short and tight, pulling the head forward. Ligaments and muscles then adapt to this new position, making it uncomfortable to assume correct posture.

The cycle of muscle imbalance perpetuates as tighter muscles become tighter and weaker muscles become weaker.

In addition, major nerves to the arm run behind certain tight muscles, and nerve entrapment syndromes may occur as a result of pressure on these nerves.

The forward-head-and-rounded-shoulder posture also increases forces on the upper neck muscles (upper trapezius and levator scapulae) and spinal vertebral disks

The muscle imbalance between the abdominal and low back muscles

Repeatedly leaning toward a patient

transversus abdominus tends to become weaker

What are the principles of Pilates?

There are six (some sources state 8) core principles of pilates. These are:

Centering - Briging the focus of all exercises to the centre or core of the body

Concentration - Maximum benefit will be achieved if full concentration and commitment is placed on each exercise

Control - Each exercise is done with complete muscular control

Precision - Awareness of each body parts positioning and movement is maintained throughout all exercises

Breath - Pilates exercises integrate breathing patterns and centre on using a full breath

Flow - Pilates exercises should be performed in a flowing manner with grace and ease

MUSCLE ISCHEMIA AND NECROSIS

Low back strain is a common diagnosis among workers who must sit in a slightly flexed forward position. static prolonged contractions of the low back extensor muscles significantly decreased oxygenation levels in the muscle

This occurred while people performed as little as 2 percent of the maximum voluntary contraction of the muscle.

In dentistry, these muscles must maintain eccentric contractions which increases the susceptibility to tearing of muscle tissue.

MUSCLE ISCHEMIA AND NECROSIS Ischemic areas are especially

susceptible to the development of trigger points, They feel like a knot or small pea.

These points may be active )painful) or latent (causing stiffness and restricting range of motion). When pressed on, trigger points may be painful locally or refer pain to a distant part of the body.

MUSCLE ISCHEMIA AND NECROSIS

damaged tissue is repaired during rest periods. the damage often exceeds the rate of repair due to

insufficient rest periods. Muscle necrosis then can occur →uses another part of

the damaged muscle → entire muscles become compromised, → different muscle groups to perform the needed task.

This is known as muscle substitution, and muscles are required to perform a task for which they are not ideally designed.

An abnormal "compensatory" motion then develops and predisposes the person to joint hypomobility (stiffness), nerve compression or spinal disk disorders.

HYPOMOBILE JOINTS During periods of PSPs or when joints are restricted

due to muscle contractions, synovial fluid production is reduced dramatically, and joint hypomobility may result.

Operators who continually lean forward toward patients may have excellent or excessive spinal flexion, but over time, the ability of the spine to extend is diminished.

The loss of mobility can lead to early degenerative changes in the joint and put the operator at risk of experiencing further injury → increased forces in the lumbar facet joints, → degenerative changes in those joints. This can contribute to low back pain syndrome

SPINAL DISK HERNIATION AND DEGENERATION

In unsupported sitting, pressure in the lumbar spinal disks increases 40 percent over pressure from standing.

During forward flexion and rotation—a position often assumed by dental operators—the pressure increases 400 percent,

SPINAL DISK HERNIATION AND DEGENERATION The posterior aspect of the annulus

fibrosus is the thinnest, and repeated forward flexion causes the nucleus pulposus to push against the posterior annulus, tearing away its layers. Eventually the annulus fibrosus can "give way", resulting in a bulging, or herniated, disk which can press on the spinal cord or peripheral nerves, causing low back, hip or leg pain.

This flattening of the lumbar curve also causes the nucleus in the spinal disk to migrate posteriorly toward the spinal cord.

Over time, the posterior wall of the disk becomes weak, and disk herniation can occur

frequent relaxing and stretching of the neck muscles, strengthening of the deep postural cervical muscles and preservation of the cervical lordosis in proper posture (ear over the shoulder) with all activities, including sleeping and driving, is essential for optimal musculoskeletal health of the neck.

A forward-head posture also can lead to muscle imbalances, contributing to a rounded shoulder posture.

This posture can predispose the operator to impingement of the supraspinous tendon in the shoulder (rotator cuff impingement) when reaching for items.

.

A forward-head posture also can lead to muscle imbalances, contributing to a rounded shoulder posture.

This posture can predispose the operator to impingement of the supraspinous tendon in the shoulder (rotator cuff impingement) when reaching for items.

Additionally, static posture of the arms in an elevated or abducted state of more than 30 degrees impedes the blood flow to the supraspinous muscle and tendon. Prolonged arm abduction also can lead to trapezius myalgia—chronic pain and trigger points in the upper trapezius muscle.

MUSCULOSKELETAL DISORDERS

chronic low back pain: pain in the low back, often referring into the hip, buttock or one leg. The cause may be muscle strains or trigger points, instability due to weak postural muscles, hypomobile spinal facet joints, or degeneration or herniation of spinal disks.

tension neck syndrome: pain, stiffness and muscle spasms in the cervical musculature, often referring pain between shoulder blades or the occiput, and sometimes numbness or tingling into one arm or hand. Forward head posture may precede this syndrome, precipitating muscle imbalances, ischemia, trigger points, or cervical disk degeneration or herniation

MUSCULOSKELETAL DISORDERS

trapezius myalgia: pain, tenderness and muscle spasms in the upper trapezius muscle. Operating with the arm elevated can predispose the operator to this syndrome, which often is seen in the trapezius muscle on the side on which the dentist holds the mirror.

rotator cuff impingement: pain in the shoulder on overhead reaching, sustained arm elevation or sleeping on the affected arm. Incorrect body mechanics and rounded shoulder posture in the operatory can lead to the impingement.

CONCLUSIONS PSPs are inherent in dentistry. Serious

detrimental physiological changes in the body can result from these abnormal postures, including muscle imbalances, muscle necrosis, trigger points, hypomobile joints, nerve compression, and spinal disk herniation or degeneration. These changes often result in pain, injury or MSDs.

CONCLUSIONSPreventing chronic pain in dentistry may

require a paradigm shift within the profession

regarding clinical work habits including proper use of ergonomic

equipment frequent short stretch breaks and regular

strengthening exercise. The second article in this series will discuss various effective prevention strategies that dental operators can use to manage discomfort and prevent MSDs.

When sitting unsupported—a frequent posture in dentistry—the lumbar lordosis flattens .The bony infrastructure provides little support to the spine, which now is hanging on the muscles, ligaments and connective tissue at the back of the spine, causing tension in these structures. Ischemia can ensue, leading to low back strain and trigger points. This flattening of the lumbar curve also causes the nucleus in the spinal disk to migrate posteriorly toward the spinal cord. Over time, the posterior wall of the disk becomes weak, and disk herniation can occur. Therefore, operators need to know about strategies they can use to maintain the essential lumbar lordosis whenever possible.

When these curves become either exaggerated or flattened, the spine increasingly depends on muscles, ligaments and soft tissue to maintain erect.

Maintaining the cervical lordosis in the proper position is equally important. Forward-head postures are common among dentists, due to years of poor posture involving holding the neck and head in an unbalanced forward position to gain better visibility during treatment

Ergonomics in Dentistry Ergonomics in Dentistry Prosthetics LabsProsthetics Labs

Naval Station Rota Spain Clinic Case Study: Lab techs mentioned chronic back, shoulder & neck discomfort / pain during periodic Industrial Hygiene survey from working at non-adjustable bench in obviously stressful static postures -- with no forearm support nor bench edge padding

Ergonomics in Dentistry Ergonomics in Dentistry Prosthetics LabsProsthetics Labs

Naval Station Rota Spain Clinic Case Study -- Post intervention improvements offered by Kavo ergonomic lab benches : Lab techs affirm GREATLY increased comfort / decrease in back, shoulder & neck discomfort / pain.

Ergonomics in Dentistry Ergonomics in Dentistry Prosthetics LabsProsthetics Labs

Naval Station Rota Spain Clinic Case Study: Lab technicians now work in optimized ergonomic posture. In addition to forearm supports and central workpiece support (locally-ventilated for air contaminant removal !) , the table also has much improved overhead lighting, a magnifying lens and a drill speed control operated by the tech’s right knee

POSTURAL AWARENESS TECHNIQUES

Research shows that maintaining the low back curve—the lumbar lordosis—when sitting can reduce or prevent low back pain

The following practices can help maintain the low back curve.

Tilt the seat angle slightly forward five to 15 degrees to increase the low back curve.This will place your hips slightly higher than your knees and increase the hip angle to greater than 90 degrees, which may allow for closer positioning to the patient. Chairs without the tilt feature can be retrofitted with an ergonomic wedge-shaped cushion.

Consider using a saddle-style operator stool that promotes the natural low back curve by increasing the hip angle to approximately 130 degrees. Using this type of stool may allow you to be closer to the patient when the patient chairs have thick backs and headrests.

http://www.youtube.com/watch?v=e3WpN0Qh4wU

Sit close to the patient and position knees under the patient’s chair if possible. This can be facilitated by tilting the seat and using patient chairs that have thin upper backs and headrests. For some operators, this positioning may cause shoulder elevation or arm abduction. In such cases, a different working position should be assumed.

Use the lumbar support of the chair as much as possible by adjusting the lumbar support forward to contact your back.

Stabilize the low back curve by contracting the transverse abdominal muscles. To do this while sitting, sit tall with a slight curve in the low back, exhale, pull your navel toward the spine without letting the curve flatten. Continue breathing while holding the contraction for one breath cycle. Repeat five times. Strive to maintain this stabilization regularly throughout the workday.

Pivot forward from your hips, not your waist. Stabilize the low back curve by performing the previous exercise before pivoting forward.

Adjust operator chair properly

Adjust your chair first. A common mistake operatorscommon mistake operators

make is positioning patients first, and then adjusting their chairs to accommodate the patients. Allowances can be made when working with patients who are elderly or disabled.

Adjust operator chair properly

Position the buttocks snugly against the back of the chair. The edge of the seat should not contact the backs of the knees. A seat that is too deep can encourage you to perch on the edge of the seat.

Adjust operator chair properly

Place feet flat on the floor and adjust the seat height up until thighs gently slope downward while the feet remain flat on floor. This helps maintain the low back curve and enables you to position your knees under the patient more easily.

Adjust operator chair properly

Move backrest up or down until the lumbar support nestles in the natural lumbar curve of the low back. Then angle the lumbar support forward to facilitate contact with the low back.

Adjust operator chair properly

Adjust armrests, which are designed to decrease neck and shoulder fatigue and strain, to support elbows in the neutral shoulder position.

Use magnification

Proper selection, adjustment and use of magnification systems have been associated with decreased neck and low back pain, as they allow operators to maintain healthier postures.

Keep the following in mind when choosing and using a magnification system.

Use magnification Operating telescopes or loupes are

available with flip-up or through-the-lens designs. The declination angle of the scopes should allow you to maintain less than 20 degrees of neck flexion. Working in postures with greater than Working in postures with greater than 20 degrees of neck flexion have been 20 degrees of neck flexion have been associated with increased neck painassociated with increased neck pain. You should try several operating telescope models to determine which suits your needs and fits you best.

Use magnification

The working distance should allow you to maintain optimal posture, with your shoulders relaxed and your elbows close to your sides.

Use magnification

Magnification of x2 will allow you to see working field detail that is approximately identical to that you would see when hunching over the patient without scopes. Magnification greater than x2 provides enhanced visual detail but a smaller field of vision.

Use magnification

Operating microscopes allow for the highest magnification of available systems with the greatest operating detail and promote the most neutral postures by design.

http://www.youtube.com/watch?v=wlhyiWT4CYA

Mahdi salari MSc OT