Content uploaded by Amar Gandavadi
Author content
All content in this area was uploaded by Amar Gandavadi on Mar 03, 2015
Content may be subject to copyright.
Content uploaded by Amar Gandavadi
Author content
All content in this area was uploaded by Amar Gandavadi on Mar 03, 2015
Content may be subject to copyright.
EDUCATION
Objectives To assess dental students’ posture on two different seats in order to determine if one seat predisposes to
a difference in working posture. Design A between-subject experimental design was selected. Setting The study was
undertaken at the University of Birmingham School of Dentistry in 2006. Subjects (materials) and methods Sixty second
year dental students at the University of Birmingham who were attending their fi rst classes in the phantom head labora-
tory were randomly selected and allocated to two different seats (30 Bambach Saddle Seats and 30 conventional seats).
Students were trained in the use of the seats. After ten weeks, the students were observed, photographs were taken by the
researcher and these were assessed using Rapid Upper Limb Assessment (RULA). Main outcome measures The posture of
the students was assessed using the RULA. Each student was given a risk score. A Mann Whitney test was used for statisti-
cal analysis. Results The results indicated that the students using the conventional seat recorded signifi cantly higher risk
scores (p <0.05) when compared with the students using Bambach Saddle Seat, suggesting an improvement in posture
when using the Bambach Saddle Seat. Conclusion RULA has identifi ed that dental students using a Bambach Saddle Seat
were able to maintain an acceptable working posture during simulated dental treatment and this seating may reduce the
development of work-related musculoskeletal disorders.
INTRODUCTION AND BACKGROUND
In recent times, dentistry has been con-
sidered to be a demanding profession
due to the need for high concentra-
tion and precision.
1
Work-related mus-
culoskeletal disorders, especially of the
neck and upper limbs, have become
common among dentists,
2-7
most notably
with low back pain.
8
Such injuries may
lead to premature retirement.
9
Current
dental practice has the dentist working
in a sitting position at one side of the
patient, who is in a supine position.
1
The
dentist will also generally have a chair-
side assistant sitting at the other side of
the patient.
4
Because of the restricted
work area (the mouth), and the need for
dexterity, the dentist may need to adopt
infl exible work postures. This results in
static activity of the muscles in awk-
ward postures and may lead to muscu-
loskeletal disorders. For example,
Lake
10
reported that dentists who qualifi ed in
Canada spent approximately two-thirds
of each treatment hour in 19-54 degrees
of forward trunk inclination, which
increased disc pressures considerably,
11
when compared to standing.
The aim of this study was to inves-
tigate whether modifi cation of seating
improves posture in dental students.
Sitting posture
Grandjean
12
describes sitting as ‘a natu-
ral human posture’ because it relieves
the person of the need to actively main-
tain an upright posture. This reduces
the static muscular workload required
to maintain the joints of the foot, knee,
hip and spine, with a consequent reduc-
tion in energy consumption. Seating
may improve stability and perform-
ance in tasks that require fi ne or precise
upper limb movements. Sitting reduces
the weight bearing on the lower limbs,
allowing an improved posture for foot
control operations. However, sitting in a
slumped posture may contribute to the
1*
PhD student,
2
Lecturer in Physiotherapy, University of
Birmingham, School of Health Sciences, 52 Pritchatts
Road, University of Birmingham, Edgbaston, Birming-
ham, B15 2TT;
3
Professor of Primary Dental Care, The
School of Dentistry, University of Birmingham, St
Chad’s Queensway
Birmingham, B4 6NN
*Correspondence to: Mr Amar Gandavadi
Email: axg284@bham.ac.uk
Refereed Paper
Accepted 12 July 2007
DOI: 10.1038/bdj.2007.1047
©
British Dental Journal 2007; 203: 601-605
BRITISH DENTAL JOURNAL VOLUME 203 NO. 10 NOV 24 2007 601
• Emphasises the benefi ts of correct seating and good posture.
• May benefi t dental students and dentists in introducing the concept of healthy
working posture.
• Introduces the relationship between working posture and musculoskeletal disorders.
IN BRIEF
VERIFIABLE
CPD PAPER
Assessment of dental student posture in two
seating conditions using RULA methodology
– a pilot study
A. Gandavadi,
1
J. R. E. Ramsay
2
and F. J. T. Burke
3
EDUCATION
602 BRITISH DENTAL JOURNAL VOLUME 203 NO. 10 NOV 24 2007
development of musculoskeletal disor-
ders eg low back pain and neck pain.
13
Prolonged sitting may slacken the
abdominal muscles and make the spine
slump.
13,14
This, in turn, increases the
strain of spinal ligaments and stretches
the back muscles.
13
If this posture is
adopted over time, fatigue and back pain
may be reported.
15,16
This slumped pos-
ture also increases vertebral disc pres-
sure, again presenting as back pain
14
and
may eventually lead to disc herniation.
17
This back pain may also impair the acti-
vation of transversus abdominis mus-
cles
18
and oblique abdominal muscles.
19
These muscles are responsible for stabil-
ising the spine and for postural control
of the trunk during seated postures;
18
the
postural activation of these muscles may
be impaired when slumped seated pos-
tures are adopted. It has been found that
t
he activity of the oblique abdominal
muscles is signifi cantly higher in stand-
ing and seated postures when compared
to lying, suggesting an important role in
sustaining gravity loads
19
and stabilis-
ing these postures.
Pheasant
20
argued that the action of
sitting down on a seat of ‘average’ height
involves fl exion of the knees and hips to
about 90 degrees in each. The comfort-
able limit of hip joint fl exion is about 60
degrees from the vertical, beyond which
the passive tension of the hamstring
muscles increases, which, in turn, pulls
the pelvis backwards to about 30 degrees.
This results in kyphosis of the lumbar
spine (posterior pelvic tilt; Fig. 1). The
tension in the hamstring muscles alters
when the angle of knee fl exion and hip
fl exion varies in sitting. When a person
is seated w ith the h ips at 60 degrees from
the vertical with a forward sloping seat,
the tension in the hamstring muscles are
relieved and the pelvis is pulled forward.
This, in turn, results in lordosis of the
lumbar spine (anterior pelvic tilt; Fig.
1). Pynt
21
recommended lumbar lordosed
seated posture, regularly interspersed
with movement (lordosis to kyphosis)
as the optimal sitting posture, which is
necessary to maintain lumbar postural
health, and the prevention of low back
pain. The Bambach Saddle Seat (BSS) is
designed to facilitate this position.
METHODOLOGY
Research design
A between-subject experimental design
was selected. The postures in two dif-
ferent seats with different subjects per-
forming the same dental procedure were
compared. The working posture adopted
by each student was evaluated using
Rapid Upper Limb Assessment
22
(RULA;
Fig. 2). RULA is a survey method origi-
nally developed to assess posture in ergo-
nomic investigations in workplaces where
work-related upper limb disorders are
reported, such as in Visual Display Unit
(VDU) operators and operators working
in a variety of manufacturing tasks.
22
Since dentists work in a prolonged sitting
posture, which resembles some manufac-
turing tasks, it could be considered that
RULA would be a useful tool in assessing
the working posture of dentists.
Ethics
The research was approved by the School
of Health Sciences, University of Bir-
mingham ethics committee.
Participants
The aim and nature of the study was intro-
duced to all of the Year 2 dental students
at the Dental School who were attending
their fi rst classes in the phantom head
laboratory. Ninety students were pro-
vided with information sheets and con-
sent forms. The students were asked to
return the forms if they were willing to
participate in the study. Sixty students
were selected at random from the 80 stu-
dents who returned the forms and agreed
to participate in the study. The students
were randomly selected using a random
number generator
23
and allocated to two
Lordosis of Lumbar Spine
Ischial
Tuberosity
Kyphosis of
Lumbar Spine
Backward rotation of Pelvis
(Posterior Pelvic Tilt)
Forward rotation of Pelvis
(Anterior Pelvic Tilt)
Hamstring
Hamstring
Line of Gravity in Sitting
Fig. 1 Sitting posture (anterior and posterior pelvic tilt)
Muscle use
Posture
score
A
ForceUpper Arm
Neck
Trunk
Legs
Lower Arm
Wrist
Wrist twist
SCORE A
SCORE B
Muscle use
Posture
score
A
Force
A
B
Type of Operator Seat
Grand
Score
Fig. 2 RULA scoring sheet (adapted from McAtamney and Corlett
22
)
EDUCATION
BRITISH DENTAL JOURNAL VOLUME 203 NO. 10 NOV 24 2007 603
types of seats. Thirty students were pro-
vided with Bambach Saddle Seat (BSS)
and 30 students were provided with the
conventional seats (CS).
Training
The students attended a lecture on the
use of seats before commencement of
the study. The students were followed up
during the fi rst two weeks on their ses-
sions in the phantom head lab and indi-
vidually trained for fi ve to 10 minutes
on correct operating posture respective
to their seats.
Materials
• BSS (Fig. 3)
• CS (Fig. 4)
• Phantom Head Apparatus (Figs 3-4)
• Digital Camera (Nikon Coolpix 8400,
Tok yo) .
Assessment procedure
After ten weeks, photographs were taken
of the students whilst working in the
phantom head lab. The positions recorded
on the photographs were assessed using
RULA.
The guidelines considered for taking
photographs were:
• Photographs were used to allow
analysis of the student’s posture at a
later date. Photographs of the student
were taken from all possible angles in
order to enable viewing of all joints
to be analysed
• Photographs were taken ten minutes
after the student had started the
dental procedure, which was consid-
ered suffi cient to allow time for the
student to become comfortable in
their operating position.
RULA
The RULA method uses diagrams of body
postures and three scoring tables to pro-
vide evaluation of exposure to risk fac-
tors by providing a risk score. The RULA
scoring sheet is schematically shown in
Figure 2. According to RULA, the body
is divided into two segments (A and B)
and assessed:
A. Upper arm, lower arm and wrist
B. Neck, trunk and legs.
The range of movement for each
body part is divided into segments and
recorded appropriately. The minimum
score (Score 1) is accorded to the ranges
of movement where the risk factors are
minimal and higher numbers (up to 6)
are given to ranges of movement with
extreme postures. An individual pos-
ture score (Score A and B calculated
from separate tables) is given to each
body segment (Segments A and B) dur-
ing analysis and these scores, along with
muscle use score (muscle use scores are
estimated for static postures held for
longer than one minute or repeated more
than four times per minute), and force
scores (force score is estimated for total
hours of work in a day), these are then
read from a separate table to reveal the
grand score (risk score).
The risk score ranges from 1 to 7 in
which a score of 1 or 2 is acceptable,
a score of 3 or 4 needs further inves-
tigation, 5 or 6 needs investigation and
changes sooner and a score of 7 needs
immediate investigation and change.
Modifi ed RULA suitable for dentists
The original RULA was developed to
assess only one side of the body at a par-
ticular time for the selected work pos-
ture. To assess the other side of the body
the assessment has to be repeated and
the selected work posture to be assessed
may have changed. To avoid this diffi -
culty and to save time the RULA record-
ing chart was modifi ed and designed to
record details of both sides of the body
at the same time. A separate RULA score
(risk score) for the right and left side was
ascribed to each posture assessed.
24
The dental procedure
Photographs were taken when the stu-
dents were operating on teeth in the
lower jaw of the phantom head whilst
preparing the teeth for a restoration.
Figures 3 and 4 show a dental student in
two different seats.
Analysis of photographs
The photographs of 60 students (30 stu-
dents using the BSS and 30 students
using the CS) were analysed by the
researcher using the modifi ed RULA
described above. Each student was given
a risk score, which was used for statisti-
cal analysis.
Data analysis
The hypotheses are two tailed. A Mann-
Whitney Test was used to test the hypoth-
e s i s t ha t t he r e w i l l b e a d i f fe re nc e b e t we e n
the RULA scores achieved between the
students using the BSS and CS. The level
of signifi cance of 0.05 was used for the
rejection of the null hypothesis.
RESULTS
The photographs of 60 students were
analysed using RULA. Figures 5 and 6
show the mean and standard errors for
the right and left total scores comparing
BSS and CS. The Mann-Whitney results
were signifi cant (Z = -6.015; p <0.01)
for the right total score and (Z = -6.197;
p <0.01) for the left total score. The results
confi rmed that there was a signifi cant
difference in RULA scores between the
Fig. 3 A dental student working on a Bambach
Saddle Seat (reproduced with permission from
Bambach)
Fig. 4 A dental student working on a conven-
tional seat
EDUCATION
604 BRITISH DENTAL JOURNAL VOLUME 203 NO. 10 NOV 24 2007
seats. Thus the null hypothesis can be
rejected and the experimental hypoth-
esis can be accepted. The results also
indicated that the students using the
CS recorded signifi cantly higher RULA
scores (mean = 5.06 for the right side;
mean = 5.03 for the left side) when com-
pared with the students using the BSS
(mean = 2.80 for the right side; mean =
2.66 for the left side) (p <0.01), suggest-
ing that there is a lower postural risk
when using the Bambach Saddle Seat.
The eta
2
has been calculated to obtain
the effect size, the eta
2
for right total
score is 0.43 and eta
2
for left total score
is 0.45 which indicates large effect size.
DISCUSSION
The results indicate that there is a sta-
tistically signifi cant difference between
the risk scores of the BSS and the CS.
The students using the BSS were able to
maintain an acceptable position on the
observed joints (upper limb, trunk and
lower limb), which may be considered
to contribute to a healthy working pos-
ture. The students using the CS appeared
less able to maintain a healthy posture
with the observed joint positions, indi-
cating a cause for concern. The results
indicate that the standard deviation
of the risk scores (right and left grand
scores) for the students using the BSS
were negligible when compared with the
CS. However, the left grand score for the
students using the BSS had indicated a
standard dev iation of 0.47 on r isk scores.
This may be because most of the stu-
dents operate with the right hand and
showed an acceptable risk score on the
right side, whereas their left hand was
kept at a position of reduced risk, close
to the body with joints in a safe range,
thereby decreasing the fi nal risk score
from 3 to 2. There was variation in the
position of the left hand, with some stu-
dents holding the cheek of the phantom
head in order to get an improved vision
of the teeth which were being operated
on, while others used a mirror or rested
their left hand on their thigh. The stu-
dents using the CS recorded higher risk
scores (mean of 5) with a standard devi-
ation of 1.36 on both the sides observed,
indicating poor posture. Even though
the position of their left hand was simi-
lar to that of the students using the BSS,
their slumped posture kept their joints
at extreme ranges ie their shoulders
were kept elevated and abducted with
their arm working across the midline
of their body, thereby increasing the
range of their fi nal risk scores ranging
from 3 to 7 indicating extreme concern
which requires immediate investigation
and changes.
The spine is in its natural curved posi-
tion (‘S’ shape) while standing, enabling
t he body ’s li ne of gr av it y to pass t hroug h
the trunk and feet, so requiring minimal
muscular activity to maintain the pos-
ture and to hold the trunk erect.
25
Cal-
laghan and McGill
26
found that standing
produced a uniquely different spine pos-
ture compared with sitting, and stand-
ing spine postures did not overlap with
fl exion postures adopted in sitting. Sit-
ting with a 90 degree angle between
the trunk and the thighs causes the
pelvis to rotate backwards shifting the
spine away from the line of gravity (Fig.
1). This in turn reduces the lumbar lor-
dosis,
12
causing the spine to slump and
increasing the load placed on the spine.
27
Black et al.
28
found that the movement of
the lumbar spine infl uenced the move-
ment of the cervical spine and identifi ed
the slumped sitting posture (posterior
pelvic tilt) as the poor posture for the
spine. The students using the CS may
have registered higher risk scores as a
result of sitting in posterior pelvic tilt
(kyphosis of the lumbar spine). They
recorded higher risk scores in the neck
(hyper fl exion), shoulder (raised and
abducted) and trunk
10
(slumped/forward
inclined)
(Fig. 4) since the position of
neck, shoulders and trunk are interre-
lated and an acceptable spinal posture
is necessary to maintain good sitting
Bambach
Left Total Score
Flat
Type of Operator Seat
2
3
4
5
6
7
Fig. 5 Box plot showing the left grand score
Bambach
Right Total Score
Flat
Type of Operator Seat
2
3
4
5
6
7
Fig. 6 Box plot showing the right grand score
EDUCATION
BRITISH DENTAL JOURNAL VOLUME 203 NO. 10 NOV 24 2007 605
posture.
27,28
On the other hand, the stu-
dents using the BSS were able to main-
tain an acceptable position of the neck,
shoulders and trunk, as they were able
to maintain anterior pelvic tilted posi-
tion contributing to the lower risk score
(Fig. 3). The BSS is designed to maintain
the pelvis in an anterior tilted position
in order to achieve a slight lumbar lor-
dosis
29
and the angle of hips and knees
can be adjusted so that the spinal pos-
ture simulates standing, thereby con-
tributing to a healthy spinal posture.
CONCLUSION
The RULA method applied to dental
students’ working postures allowed a
rapid evaluation of their posture dur-
ing simulated dental treatment. The
RULA scores indicate that the students
using the BSS are able to maintain an
acceptable working posture (lower risk
score), whereas for students using the
CS the posture deteriorates over time
(higher risk score). This may predispose
to the development of musculoskeletal
disorders. This study serves as a pilot
trial and further studies in other den-
tal schools and with practising dentists
is suggested.
This project was funded by Bambach Saddle Seat
Europe Ltd and undertaken independently at the
University of Birmingham. We are grateful to all
of the students who participated in this study
and also the staff members at the University Of
Birmingham who assisted in this study.
1. Finsen L, Christensen H, Bakke M. Musculoskeletal
disorders among dentists and variation in dental
work. Appl Ergon 1998; 29: 119-125.
2. Milerad E, Ekenvall L. Symptoms of the neck and
upper extremities in dentists. Scand J Work Environ
Health 1990; 16: 129-134.
3. Osborn J, Newell K, Rudney J, Stoltenberg J.
Musculoskeletal pain among Minnesota dental
hygienists. J Dent Hyg 1990; 64: 132-138.
4. Rundcrantz B-L, Johnsson B, Moritz U. Cervical
pain and discomfort among dentists. Epidemio-
logical, clinical and therapeutic aspects. Part 1. A
survey of pain and discomfort. Swed Dent J 1990;
14: 71-80.
5. Oberg T, Oberg U. Musculoskeletal complaints in
dental hygiene: a survey study from a Swedish
country. J Dent Hyg 1993; 67: 257-261.
6. Akesson I, Lundborg G, Horstmann V, Skerfving S.
Neuropathy in female dental personnel exposed
to high frequency vibrations. Occup Environ Med
1995; 52: 116 -123.
7. Finsen L. Biomechanical analyses of occupational
work loads in the neck and shoulder. A study in
dentistry. PhD thesis, National Institute of Occu-
pational Health, Copenhagen, Human Physiology,
August Krogh Institute at University of Copenha-
gen, Department of Oral Function and Physiology,
School of Dentistry, 1995.
8. Shugars D, Miller D, Williams D, Fishburne C,
Strickland D. Musculoskeletal pain among general
dentists. Gen Dent 1987; 35: 272-276.
9. Burke F J T, Freeman R. The practice of dentistry:
an assessment of reasons for premature retire-
ment. Br Dent J 1997; 182: 250-254.
10. Lake J. Musculoskeletal dysfunction associated
with the practice of dentistry – proposed mecha-
nisms and management: literature review. Univ Tor
Dent J 1995; 9: 7-11.
11. Nachemson A. The lumbar spine: an orthopedic
challenge. Spine 1976; 1.
12. Grandjean E. Ergonomics in the home. London:
Taylor and Francis, 1973.
13. Beach T A C, Parkinson R J, Stothart J, Callaghan J P.
Effects of prolonged sitting on passive stiffness of
the in vivo lumbar spine. Spine J 2005; 5: 145-154.
14. McGill S M, Brown S. Creep response of the lumbar
spine to prolonged fl exion. Clin Biomech 1992;
7: 43–46.
15. Mannion A F. Fibre type characteristics and func-
tion of the human paraspinal muscles: normal
values and changes in association with low back
pain. J Electromyogr Kinesiol 1999; 9: 363-377.
16. Gunning J, Callaghan J P, McGill S M. The role of
prior loading history and spinal posture on the
compressive tolerance and type of failure in the
spine using a porcine trauma model. Clin Biomech
2001; 16: 471–480.
17. Bogduk N. Clinical anatomy of the lumbar spine
and sacrum, 4
th
ed. Edinburgh: Churchill Living-
stone, 2005.
18. Moseley G L. Impaired trunk muscle function in
sub-acute neck pain: etiologic in the subsequent
development of low back pain? Man Ther 2004;
9: 157-163.
19. Snijders C J, Bakker M P, Vleeming A, Stoeckart R,
Stam H J. Oblique abdominal muscle activity in
standing and in sitting on hard and soft seats. Clin
Biomech 1995; 10: 73-78.
20. Pheasant S. Ergonomics, work and health. UK:
Palgrave Macmillan, 1991.
21. Pynt J, Higgs J, Mackey M. Seeking the optimal
posture of the seated lumbar spine. Physiother
Theory Pract 2001; 17: 5-21.
22. McAtamney L, Corlett E N. RULA: a survey method
for the investigation of work-related musculoskel-
etal disorders. Appl Ergon 1993; 24: 91-99.
23. Random Number Generator. http://www segobit.
com/rng.htm. Accessed 27 July 2006.
24. Nguyen B D. Musculoskeletal problems and occupa-
tional stress among dentists and dental assistants
in a dental clinic. National Institute of Occupational
and Environmental Health, Vietnam. Occup Environ
Med 2004; 61: e57. http://www.occenvmed.com/
cgi/content/full/61/11/e57. Accessed 27 July 2006.
25. Corlett E N, Eklund J A E. How does a back rest
work? Appl Ergon 1984; 15: 111-114.
26. Callaghan J P, McGill S M. Low back joint loading
and kinematics during standing and unsupported
sitting. Ergonomics 2001; 44: 280-294.
27 Hedman T P, Fernie G R. Mechanical response of
the lumbar spine to seated postural loads. Spine
1997; 22: 734-743.
28. Black K M, McClure P, Polansky M. The infl uence of
different sitting positions on cervical and lumbar
posture. Spine 1996; 21: 65-70.
29. Gale M, Feather S, Jensen S, Coster G. Study of a
workseat designed to preserve lumbar lordosis.
Aust Occup Ther J 1989; 36: 92-99.
