1. ‫الرحيم‬ ‫الرحمن‬ ‫ا‬ ‫بسم‬
Mechanisms leading to
musculoskeletal disorders in
dentistry

2. Job
Characteristics
Human
Capabilities
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 isWhat is
ErgonomicsErgonomics??

3. WMSD Symptoms AmongWMSD Symptoms Among
DentistsDentists
0%
10%
20%
30%
40%
50%
60%
70%
80%
Neck
ShoulderUpperBackLow
erBack
Elbow
sW
rists/Hands
Knees
Body Part
%Reporting
Males
Females
Source: Finsen et al., 1998

4. WMSD Symptoms AmongWMSD Symptoms Among
Dental HygienistsDental Hygienists
0
10
20
30
40
50
60
70
80
*Diagnosed
CTS
*Hand-wrist
pain
*Shoulder
pain
*Neck pain Low Back
pain
%Reporting
Dental Hygienists Dental Assistants
Source: Liss et al., 1995
* indicates difference is significant

5. 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.

6.  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.

8. What Factors Contribute toWhat Factors Contribute to
WMSDsWMSDs??
♦ Static neck, back, and shoulder postures

9. What Factors Contribute toWhat Factors Contribute to
WMSDsWMSDs??
♦ Grasping small instruments for prolonged periods

10. What Factors Contribute toWhat Factors Contribute to
WMSDsWMSDs??
♦ Prolonged use of vibrating hand tools

11.  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).

12. 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

13. 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.

15. 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

16.  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

17.  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.

20. Muscle imbalances
 between the muscles stabilize and
those that move

21.  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.

22.  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.

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

25. The muscle imbalance between the abdominal
and low back muscles
 Repeatedly leaning toward a patient
 transversus abdominus tends to become weaker

26. 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

27. 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.

28. 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.

29. 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.

30. 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

31. 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,

32. 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.

33.  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

35.  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.

37.  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.
 .

38.  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.

39. 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.

40.  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

41. 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.

42. 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.

43. CONCLUSIONS
Preventing 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.

44.  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

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

46.  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

48. Ergonomics in DentistryErgonomics 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

49. Ergonomics in DentistryErgonomics 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.

50. Ergonomics in DentistryErgonomics 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

51. 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.

52.  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.

54.  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.

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

57.  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.

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

61.  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.

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

63. 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.

64. 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.

66. 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.

67. 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.

68. 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.

70. 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.

71. 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 thanWorking in postures with greater than
20 degrees of neck flexion have been20 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.

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

73. 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.

74. 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.

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

77. Mahdi salari MSc
OT