Assessment of the ergonomic risk from saddle and conventional seats in dentistry: A systematic review and meta-analysis

Abstract

Objective
This study aimed to verify whether the saddle seat provides lower ergonomic risk than conventional seats in dentistry.

Methods
This review followed the PRISMA statement and a protocol was created and registered in PROSPERO (CRD42017074918). Six electronic databases were searched as primary study sources. The "grey literature" was included to prevent selection and publication biases. The risk of bias among the studies included was assessed with the Joanna Briggs Institute Critical Appraisal Tool for Systematic Reviews. Meta-analysis was performed to estimate the effect of seat type on the ergonomic risk score in dentistry. The heterogeneity among studies was assessed using I² statistics.

Results
The search resulted in 3147 records, from which two were considered eligible for this review. Both studies were conducted with a total of 150 second-year dental students who were starting their laboratory activities using phantom heads. Saddle seats were associated with a significantly lower ergonomic risk than conventional seats [right side (mean difference = -3.18; 95% CI = -4.96, -1.40; p < 0.001) and left side (mean difference = -3.12; 95% CI = -4.56, -1.68; p < 0.001)], indicating posture improvement.

Conclusion
The two eligible studies for this review provide moderate evidence that saddle seats provided lower ergonomic risk than conventional seats in the examined population of dental students.

Full text

RESEARCH ARTICLE
Assessment of the ergonomic risk from
saddle and conventional seats in dentistry: A
systematic review and meta-analysis
Giovana Renata GouvêaID
1☯
*, Walbert de Andrade Vieira
2☯
, Luiz Renato Paranhos
3☯
, I
´talo
de Macedo Bernardino
4☯
, Jaqueline Vilela Bulgareli
1☯
, Antonio Carlos Pereira
1☯
1Department of Community Dentistry, School of Dentistry of Piracicaba, University of Campinas, Piracicaba,
SP, Brazil, 2Department of Dentistry, University of Sergipe, Aracaju, SE, Brazil, 3Department of Preventive
and Community Dentistry, School of Dentistry, Federal University of Uberla
ˆndia, Uberla
ˆndia, MG, Brazil,
4Postgraduate Program in Dentistry, State University of Paraı
´ba, Campina Grande, PB, Brazil
☯These authors contributed equally to this work.
*gigouvea@hotmail.com
Abstract
Objective
This study aimed to verify whether the saddle seat provides lower ergonomic risk than con-
ventional seats in dentistry.
Methods
This review followed the PRISMA statement and a protocol was created and registered in
PROSPERO (CRD42017074918). Six electronic databases were searched as primary
study sources. The "grey literature" was included to prevent selection and publication
biases. The risk of bias among the studies included was assessed with the Joanna Briggs
Institute Critical Appraisal Tool for Systematic Reviews. Meta-analysis was performed to
estimate the effect of seat type on the ergonomic risk score in dentistry. The heterogeneity
among studies was assessed using I
2
statistics.
Results
The search resulted in 3147 records, from which two were considered eligible for this review.
Both studies were conducted with a total of 150 second-year dental students who were start-
ing their laboratory activities using phantom heads. Saddle seats were associated with a sig-
nificantly lower ergonomic risk than conventional seats [right side (mean difference = -3.18;
95% CI = -4.96, -1.40; p <0.001) and left side (mean difference = -3.12; 95% CI = -4.56,
-1.68; p <0.001)], indicating posture improvement.
Conclusion
The two eligible studies for this review provide moderate evidence that saddle seats provided
lower ergonomic risk than conventional seats in the examined population of dental students.
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 1 / 14
a1111111111
a1111111111
a1111111111
a1111111111
a1111111111
OPEN ACCESS
Citation: Gouvêa GR, Vieira WdA, Paranhos LR,
Bernardino I
´dM, Bulgareli JV, Pereira AC (2018)
Assessment of the ergonomic risk from saddle and
conventional seats in dentistry: A systematic
review and meta-analysis. PLoS ONE 13(12):
e0208900. https://doi.org/10.1371/journal.
pone.0208900
Editor: Fabian Huettig, Eberhard-Karls-Universitat
Tubingen Medizinische Fakultat, GERMANY
Received: April 23, 2018
Accepted: November 26, 2018
Published: December 17, 2018
Copyright: ©2018 Gouvêa et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
files.
Funding: This work was supported by
Coordenac¸ão de Aperfeic¸oamento de Pessoal de
Nı
´vel Superior (CAPES) - process # 1595065, and
by Conselho Nacional de Desenvolvimento
Cientı
´fico e Tecnolo
´gico (CNPq) - process #
157080/2014-5.

Introduction
Occupational health has been extensively investigated in dentistry [1–4], considering that den-
tists are professionals highly vulnerable to musculoskeletal diseases [5,6], especially in the cer-
vical and lumbar spines [7]. Working posture is the main risk factor for developing
musculoskeletal disorders [8–9].
The sitting posture is the body position that dentists use most frequently [10]. The dental
stool has an influence on such posture [11–13], because it induces the use of certain postural
patterns to find a more comfortable and/or functional position [11–13]. In addition, the curva-
ture of the spine, as well as the location and correct position of the head and pelvis are crucial
for the biomechanics of the sitting position [14–16].
There is evidence that the 90˚ sitting posture (knee angle and hip angle) increases the pas-
sive tension of hamstring muscles, causing a posterior pelvic rotation and resulting in a
kyphotic sitting posture of the lumbar spine [17–18]. However, ergonomic recommendations
[19], radiographic studies [17–18], and analyses from physical therapists [20] and laypersons
[21,22] indicate that a sitting posture with a slight anterior tilt of the lumbar spine and a slight
lumbar lordosis of the lumbar spine reduces the incidence of low back pain most efficiently.
Aiming to reduce postural problems in dentistry, scientific studies have been performed to
elucidate the impact of different types of seats on the posture of students and trained profes-
sionals [16,23], as well as the importance of ergonomic seat interventions [14] in reducing
musculoskeletal symptoms [15]. However, the literature does not yet provide a consensus on
whether the saddle seat is a superior alternative to the conventional seat for maintaining opti-
mal posture.
Thus, the present study aimed to answer the following guiding question (based on the
PICO strategy): “Does the saddle seat (intervention) provide lower ergonomic risk (outcome)
to dentists and/or dental students (population) when compared with conventional seats (com-
parison)?” The authors have tested the hypothesis that using the saddle seat will promote lower
ergonomic risk than the conventional seat.
Methods
Protocol and registry
This systematic review was performed following the PRISMA (S1 PRISMA Checklist) state-
ment (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) [24] and the
Cochrane guidelines [25]. The systematic review protocol was registered in the PROSPERO
database under number CRD42017074918 (https://www.crd.york.ac.uk/PROSPERO/).
Study design and eligibility criteria
The review included only randomized controlled trials that compared the working posture of den-
tal students and/or dentists in conventional seats without ergonomic changes and in ergonomic
saddle seats. There were no restrictions of year, language, or publication status (ahead of print).
The following were excluded: 1) Studies not related to the topic; 2) Reviews, letters to the
editor, personal opinions, book/book chapters, didactic material, reports, abstracts, and pat-
ents; 3) Qualitative or prevalence studies; and 4) Studies that used other types of seats or modi-
fied seats.
Sources of information and research
The primary sources of research were the electronic databases Embase, Latin American and
Caribbean Health Sciences (LILACS), PubMed (including MedLine), SciELO, Scopus, and
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 2 / 14
Competing interests: The authors have declared
that no competing interests exist.

Web of Science. OpenThesis and OpenGrey were used to collect the “grey literature”, avoiding
selection and publication biases. A manual search was also performed through a systematic
analysis of the references of the eligible articles.
Two eligibility reviewers conducted the research independently (GG and WAV). The DeCS
(Descriptors in Health Sciences– http://decs.bvs.br) and MeSH (Medical Subject Headings–
https://www.ncbi.nml.nih.gov/mesh) resources were used for keyword selection. The Boolean
operators “AND” and “OR” were applied to enhance the search strategy through several com-
binations (S1 Table). The bibliographical research was developed and performed in August
2017. The search strategy included the following MeSH, DeCS, and Emtree terms: ‘Dentists’,
‘Posture’, ‘Human Engineering’, ‘Odontologia’ [Portuguese], ‘Postura’ [Portuguese] associated
with the entry terms: ‘Dental students’, ‘Student of dentistry’, ‘Undergraduate student of den-
tistry’, ‘Seated Position’, ‘Sitting Position’, ‘Saddle chair’, ‘Saddle seat’. The records obtained
were exported to the software EndNote Basic/Online, desktop version (Thomson Reuters,
New York, USA) and duplicates were removed.
Selection of studies
The studies were selected in three stages. In stage 1, two reviewers (GG and WAV) performed
a systematic analysis of the titles, independently. The articles whose titles met the objectives of
the study were selected for stage 2, when both reviewers (GG and WAV) also performed a sys-
tematic analysis of the abstracts. At this time, the studies not related to the topic, reviews, let-
ters to the editor, personal opinions, book/book chapters, didactic material, reports, abstracts,
patents, qualitative or observational studies, and studies that used other types of seats or modi-
fied ones were excluded. The articles whose titles met the study objectives, but had no abstract,
were fully reviewed.
In the third stage, the full texts of the preliminary eligible studies were obtained and evalu-
ated to verify whether they met the eligibility criteria. When both reviewers could not reach an
agreement, a third reviewer (LRP) was consulted to make a final decision. Rejected studies
were recorded separately along with the explicit reasons for exclusion.
Process of data collection and extraction
After the selection, two authors (MSS and WAV) analyzed the studies, which data were
extracted for the following information: article identification (author, year, study location),
sample characteristics (number of patients in each study, mean age, sex distribution, school
year), type of intervention (seat type, training time, evaluation start time), and methods for
obtaining the results (methods used for posture evaluation, image analysis, and calibration
time). Any disagreement was discussed and a third reviewer (LRP) was consulted when
necessary.
Individual risk of bias of the studies
The risk of bias in the studies selected was assessed using the Joanna Briggs Institute Critical
Appraisal tools for use in JBI Systematic Reviews for Randomized Controlled Trials [26]. Two
authors (WAV and LRP) independently assessed each domain for the potential risk of bias.
The following questions were used for the assessment: 1) Was true randomization used for
assigning the participants to treatment groups? 2) Was the allocation to treatment groups con-
cealed? 3) Were treatment groups similar at baseline? 4) Were participants blind to treatment
assignment? 5) Were those delivering treatment blind to treatment assignment? 6) Were out-
come assessors blind to treatment assignment? 7) Were treatment groups treated identically
other than the intervention of interest? 8) Was follow-up complete, and if not, were differences
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 3 / 14

between groups in terms of their follow-up adequately described and analyzed? 9) Were partic-
ipants analyzed in the groups to which they were randomized? 10) Were outcomes measured
in the same way for treatment groups? 11) Were outcomes measured in a reliable way? 12)
Was appropriate statistical analysis used? 13) Was the trial design appropriate, and were any
deviations from the standard RCT design (individual randomization, parallel groups)
accounted for in the conduct and analysis of the trial? The risk of bias was categorized as High
when the studies reached up to 49% of “yes” score, Moderate when they reached 50% to 69%
of “yes” score, and Low when the studies reached more than 70% of “yes” score. Studies cate-
gorized as either high risk of bias or low methodological quality were eliminated.
Outcome measures and data analysis
The meta-analysis for continuous outcome was performed to estimate the effect of seat type on
the ergonomic risk score in dentistry [25]. The mean difference was used for pooling effects.
Heterogeneity among studies was assessed using I
2
statistics and classified as follows: low (I
2
<
25%), moderate (I
2
= 50%), and high (I
2
>75%) [27]. The random-effects model was selected
to minimize the effect of heterogeneity among studies [28]. Publication bias was not assessed
because there was not a sufficient number of studies to group in a funnel plot. The software
Review Manager, version 5.3 (RevMan, Cochrane Collaboration) was used to perform all sta-
tistical analyses.
Confidence in cumulative evidence
The Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) tool
[28] assessed evidence quality and grading of recommendation strength. This assessment was
based on study design, methodological limitations, inconsistency, indirectness, imprecision,
and other considerations. Evidence quality was characterized as high, moderate, low, or very
low [29].
Results
Selection of studies
The bibliographical research was developed and performed in August 2017. During the first
stage of study selections, 2993 records were found in six electronic databases. After removing
the repeated/duplicated records, 1918 articles proceeded to the analysis of titles and abstracts.
A total of 154 studies from the “grey literature” was found through the search strategy,
although only one was related to the objectives of the present review. After the analysis of titles
and abstracts, only three studies were eligible for full-text analysis. The references of the ini-
tially eligible studies were carefully assessed to verify potential articles that were absent from
the main search strategy. However, from the three studies included in this stage, one of them
was excluded for being a thesis from which an eligible article was produced. Therefore, two
articles proceeded to the analysis of results. Fig 1 reproduces the process of search, identifica-
tion, inclusion, and exclusion of articles.
Characteristics of the studies
Both eligible studies [11–12] commented on the research ethical criteria and explained the use
of consent forms for research subjects. None of the studies presented either sample calculation
or study power. The analysis resulted in a total sample of 150 dental students and there were
no studies with professional dentists. The studies were performed in the United Kingdom [11]
in 2007 and in India [12] in 2014. One study compared the Salli Saddle Chair and a
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 4 / 14

conventional chair with and without back rest and flat surface [12], and the other compared a
Bambach Saddle Seat and a conventional chair with back rest and flat surface [11]. Both studies
[11–12] were performed with second-year dental students, who were starting their laboratory
activities using phantom heads.
The participants of the eligible studies [11–12] received training as to correct posture and
use of each seat type. The evaluation was performed after 10 [11] or 12 [12] weeks so the stu-
dents would get used to the seats. Table 1 presents a summary of the main characteristics of
these studies.
Fig 1. Flowchart of the process of searching and selecting the literature, adapted from the PRISMA statement.
https://doi.org/10.1371/journal.pone.0208900.g001
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 5 / 14

Risk of bias in the studies
Both studies included in this review [11–12] presented low risk of bias in the Joanna Briggs
Institute Critical Appraisal tool [26]. Table 2 shows detailed information on the risk of bias of
the studies included.
Results of individual studies and meta-analysis
The studies selected used the RULA (Rapid Upper Limb Assessment) method [30], which ana-
lyzes the overload concentrated in the neck and upper limbs during work and assesses the
static muscle work and the forces exerted by the segments analyzed. The calibration time set
by the studies ranged from 10 [11] to 15 [12] minutes so that the students could focus on their
work and be evaluated afterwards. In both studies, the students prepared a mandibular tooth
in a mannequin.
In the study by Gandavadi et al. [11], photographs were taken of both left and right sides,
while in the study by Dable et al. [12], the analysis was performed from static images captured
from videos. The results showed lower scores for the ergonomic seats (Salli Saddle Chair and
Bambach Saddle Seat) than for conventional seats. In the study by Dable et al. [12], the authors
also used image magnification lenses to compare the groups, showing even lower scores with
such system.
Table 1. Summary of the main characteristics of the eligible studies.
Author, year,
and country
Seat type Sample (n) School
period
Location Procedure
performed
Training
time
Time of
assessment
Evaluation
method
Analysis
method
Calibration
time
Gandavadi
et al., 2007,
United
Kingdom
Bambach Saddle
Seat (BSS)
Conventional
Seat (CS)
Bambach Saddle
Seat: 30
Conventional
Seat: 30
2
nd
year Preclinical
laboratory
Cavity
preparation of
mandibular teeth
in a mannequin
10 weeks 2 weeks RULA�Photos 10 minutes
Dable
et al.,2014,
India
Salli Saddle
Chair (SSC)
Conventional
chair with back
rest (CC1)
Conventional
chair without
back rest (CC2)
Salli Saddle
Chair: 30
Conventional
chair with back
rest: 30
Conventional
chair without
back rest: 30
2
nd
year Preclinical
laboratory
Cavity
preparation of the
first mandibular
premolar in a
mannequin
12 weeks 3 days RULA�Videos 15 minutes
�RULA: Rapid Upper Limb Assessment.
https://doi.org/10.1371/journal.pone.0208900.t001
Table 2. Risk of bias assessed by the Joanna Briggs Institute Critical Appraisal Tools for use in JBI Systematic Reviews for Randomized Controlled Trials” [26].
Authors Q.1 Q.2 Q.3 Q.4 Q.5 Q.6 Q.7 Q.8 Q.9 Q.10 Q.11 Q.12 Q.13 %yes/risk
Gandavadi et al., 2007 p p p —p—p p p p p p p 84.6%/Low
Dable et al., 2014 p p p —p—p p p p p p p 84.6%/Low
1) Was true randomization used for assigning the participants to treatment groups? 2) Was the allocation to treatment groups concealed? 3) Were treatment groups
similar at baseline? 4) Were participants blind to treatment assignment? 5) Were those delivering treatment blind to treatment assignment? 6) Were outcome assessors
blind to treatment assignment? 7) Were treatment groups treated identically other than the intervention of interest? 8) Was follow-up complete, and if not, were
differences between groups in terms of their follow-up adequately described and analyzed? 9) Were participants analyzed in the groups to which they were randomized?
10) Were outcomes measured in the same way for treatment groups? 11) Were outcomes measured in a reliable way? 12) Was appropriate statistical analysis used? 13)
Was the trial design appropriate, and were any deviations from the standard RCT design (individual randomization, parallel groups) accounted for in the conduct and
analysis of the trial? NA = Not Applicable; p= Yes; “–” = No.
https://doi.org/10.1371/journal.pone.0208900.t002
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 6 / 14

Fig 2 presents the forest plots. The mean differences in ergonomic risk score and their
respective 95% confidence intervals are represented by squares for the individual studies. The
S2 Table shows the risk score of individual studies. The diamonds at the bottom represent the
pooled mean ergonomic risk score with 95% confidence interval. The meta-analysis results
showed that saddle seats are associated with significantly lower ergonomic risk scores when
compared with conventional seats [right side (mean difference = -3.18; 95% CI = -4.96, -1.40;
p<0.001) and left side (mean difference = -3.12; 95% CI = -4.56, -1.68; p <0.001)], indicating
posture improvement. The overall mean difference in ergonomic risk score was -3.16 (95%
CI = -4.02, -2.30; p <0.001). Between-study heterogeneity was high (I
2
= 95%; p <0.001).
Confidence in cumulative evidence
Overall, the quality of evidence from the outcomes evaluated by the GRADE system [29] was
assessed as moderate (Table 3).
Discussion
This study aimed to compare the ergonomic risk of saddle and conventional seats used in
work practices of dentists and/or dental students. Both eligible studies [11–12] were performed
with a convenience sample (dental students). Studies with trained professionals may result in
Fig 2. Effect of seat type (saddle versus conventional) on ergonomic risk score in dentistry, assessed usingthe RULA scale.
https://doi.org/10.1371/journal.pone.0208900.g002
Table 3. Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) summary of results table for the outcomes of the systematic review
and meta-analysis [29].
Quality Assessment Summary of Results Importance
Number of
studies
Study Design Methodological
Limitations
Inconsistency Indirectness Imprecision Publication
Biases
Number of participants General
Quality
Intervention Comparison
2Randomized
controlled trials
X
1
p p p p 60 60 +++
MODERATE
Critical
GRADE factors: = p, no serious limitations; X, serious limitation. General quality of evidence: +, very low; ++, low; +++, moderate; ++++, high.
1
Absence of blinding of outcome assessors and participants.
https://doi.org/10.1371/journal.pone.0208900.t003
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 7 / 14

bias due to the different situations of the clinical routine. Forming a control group for this type
of study, paired with the experimental group for age and time of profession, would represent
another challenge. These variables may reflect especially in existing musculoskeletal diseases
and in the resistance for changing usual postural practices [31–32]. Thus, the results of the
present meta-analysis with studies performed with dental students significantly favor saddle
seats over conventional seats, which confirms the initial hypothesis.
In both eligible studies [11–12], dental students were instructed to prepare a cavity in the man-
dibular teeth of a mannequin, at the preclinical laboratory. It is known that a procedure performed
in a dental mannequin does not reproduce the actual reality of a dentist’s routine. This is because a
real patient presents variables such as age (elderly people or children), anatomical structures (ton-
gue, cheek, and mouth opening limitation), special care (physical and/or mental disabilities),
altered psychological states (fear and/or anxiety), obesity, and pregnancy, which may change and
complicate the operational procedure. However, in the preclinical laboratory during procedures in
mannequins, students experience the first body postures, adapting their body to seat, static posture,
reduced field of vision, dental procedure, precision of fine movements, and especially to the fear
and insecurity of dealing with something new [33].
One of the methods for verifying ergonomic risks is the Rapid Upper Limb Assessment
(RULA) [30], which is the most cited in the literature and used in both eligible studies [11–12]
of this review. In this method, the positions of individual body segments are observed and
assessed with increasing scores according to the growing deviation of the neutral posture [30].
Different studies [30–34] have assessed the validity and reliability of the RULA, which is con-
sidered an adequate method to assess the body posture of dentists [35] and dental students
[36]. The observations of evaluators regarding the static image may be associated with the
uncertainty regarding camera angle [37].
Gandavadi et al. [11] observed the working postures of both right and left sides using digital
photographs. Dable et al. [12], in turn, used videos that were paused at every postural position and
at every body movement of both right and left sides. However, the assessment and final score of
both studies [11–12] were based on a static image. The assessment of the body posture images of
the research participants started after 10 to 15 minutes in a familiar environment. Given the long
time for capturing the images, the participants were likely focused on the activity proposed and
kept the postural habits of their usual routine, which canceled the Hawthorne effect [38]—a phe-
nomenon in which participants change their behavior when they are aware of being watched.
In this study, the ergonomic risk was assessed in groups that used conventional and saddle
seats. The results indicated an intermediate to high score for ergonomic risk in the group
using the conventional seat, which is consistent with other studies [36,39]. Over the last
decade, research has been intensified, designing the effects of different seats on the clinical
practice of dentists and dental students [11–13,40–42]. Among such studies, three have investi-
gated the ergonomically modified stool [40–42] and three have investigated the saddle seat
[11–13]. All studies showed an improvement in the experimental group when compared to the
control group, especially for presenting a lumbar lordosis seated posture [11–13].
There is a consensus among several studies [17–21,43–49] that the lumbar lordosed seated
posture is optimal for favoring a neutral lumbar posture, minimizing the painful symptomatol-
ogy of low back pain. It is also associated with high muscular activity and the increase in spinal
load due to the posterior pelvic tilt, which is then balanced by muscle contractions in the dorsal
spine, representing a dynamic posture [50]. This posture is obtained by positioning the lower
lumbar spine in a slight forward tilt and slight lumbar lordosis, while maintaining the relaxa-
tion of the muscles surrounding the thoracic spine [20].
In occupational science, a static body posture is defined as a posture held for more than
four seconds [51–52]. Static work procedures prevent the blood flow required for tissue
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 8 / 14

recovery. Other significant factors are the frequency of occurrence, the pauses during move-
ment, and the duration (time component) for maintaining a static body posture [53]. Conse-
quently, several dental tasks are performed in static postures with the prolonged flexion and/or
rotation of the trunk, presenting a potential risk for the musculoskeletal system [53].
The interdisciplinarity between bioengineering and health sciences improves clinical rele-
vance and research [19,54–56]. Dynamic seats [57–58] with a slight forward inclination
[54,56–59], with or without a low backrest [57] to support the ischia [19,60], are the challenges
of novel seat designs. However, it is worth noting that adopting a good posture and using the
correct furniture are not enough to reduce the overload on the osteomyoarticular tissues of
dentists [61–62]. Besides seat design, the human, occupational, and organizational factors also
play an important role in terms of load conditions in the human body [63–65]. Psychosocial
factors are also major risk factors for persistent low back pain in workers, and they should be
considered along with the physical labor requirements, reducing the disability related to lum-
bar pain [66]. Such pain is also directly associated with depression and somatization [67]. Psy-
chosocial interventions may reduce the impact of low back pain in the workplace [68,69].
Four-handed dentistry, equipment organization in the workspace, correct positioning of
patients, illumination, and auxiliary components should be observed and controlled in the
dental clinical practice [61–62]. The musculoskeletal stress of a dental professional is quantifi-
able, comparable, and especially rather variable, considering that musculoskeletal disorders
may be reduced by improving the ergonomic positioning of the patient and the practitioner
[70]. Positioning should maintain the natural curves of the lumbar spine (cervical lordosis,
thoracic kyphosis, lumbar lordosis, and sacral kyphosis), allowing a neutral sitting posture
[7,59] so that muscles and intervertebral discs may alternate between relaxation and loading.
Correct positioning is beneficial for nourishing muscles [71] and intervertebral discs [72] and
for potentially reducing ergonomic risks.
The present review is original, and it has contributed to develop the scientific knowledge
from two main points. Primarily, it is the first systematic literature review to investigate the
influence of seat type on ergonomic risk among dental students. Second, the low risk of bias
observed in the eligible studies allows drawing more consistent and reliable conclusions from
the data obtained, producing major implications for the academic dental clinical practice.
Limitations
The present study is limited by the presence of only two clinical studies on the subject, with no
sample calculation or study power. In addition, the student population included only dental stu-
dents working on phantom heads and it was not sex-specific. In both studies included, the data
were collected only at the end of follow-up. It is worth noting that short-term investigations of the
sitting posture may not completely represent the biological time-dependent responses. Further
studies should be performed to determine whether the effectiveness of a saddle seat intervention is
maintained in the long-term, especially concerning the neutral lumbar posture. In addition, both
eligible articles used static images to represent the average posture of a person, which does not fit
the reality. Therefore, further studies need to employ state of the art posture measurement equip-
ment that automatically record the posture continuously. A combination of posture and Electro-
myography (EMG) measurement would provide additional insight.
Conclusion
The two eligible studies for this review provide moderate evidence that saddle seats provided
lower ergonomic risk than conventional seats in the examined population of dental students.
Follow-up studies are required to confirm this result by addressing the limitations of the
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 9 / 14

studies. For example, follow-up studies should employ state of the art posture measurement
equipment and examine whether saddle seats also provide lower ergonomic risk in a popula-
tion of professional dentists treating real patients.
Supporting information
S1 PRISMA Checklist. PRISMA checklist.
(DOC)
S1 Table. Strategies for database search.
(DOCX)
S2 Table. Main results of eligible articles.
(DOCX)
Author Contributions
Conceptualization: Giovana Renata Gouvêa, Luiz Renato Paranhos, Jaqueline Vilela Bulgareli,
Antonio Carlos Pereira.
Formal analysis: Giovana Renata Gouvêa, I
´talo de Macedo Bernardino.
Investigation: Giovana Renata Gouvêa, Luiz Renato Paranhos.
Methodology: Giovana Renata Gouvêa, Walbert de Andrade Vieira, Luiz Renato Paranhos,
Jaqueline Vilela Bulgareli, Antonio Carlos Pereira.
Resources: Giovana Renata Gouvêa.
Supervision: Giovana Renata Gouvêa, Jaqueline Vilela Bulgareli, Antonio Carlos Pereira.
Writing – original draft: Giovana Renata Gouvêa, Walbert de Andrade Vieira, Luiz Renato
Paranhos, I
´talo de Macedo Bernardino, Jaqueline Vilela Bulgareli, Antonio Carlos Pereira.
Writing – review & editing: Giovana Renata Gouvêa, Walbert de Andrade Vieira, Luiz Renato
Paranhos, I
´talo de Macedo Bernardino, Jaqueline Vilela Bulgareli, Antonio Carlos Pereira.
References
1. Presoto CD, Wajngarten D, Domingos PAS, Campos JADB, Garcia PPNS. Dental Students’ Percep-
tions of Risk Factors for Musculoskeletal Disorders: Adapting the Job Factors Questionnaire for Den-
tistry. J Dent Educ 2018; 82:47–53. https://doi.org/10.21815/JDE.018.007 PMID: 29292325
2. Moodley R, Naidoo S, Wyk JV. The prevalence of occupational health-related problems in dentistry: A
review of the literature. J Occup Health 2018; 60:111–125. https://doi.org/10.1539/joh.17-0188-RA
PMID: 29213011
3. Alyahya F, Algarzaie K, Alsubeh Y, Khounganian R. Awareness of ergonomics & work-related musculo-
skeletal disorders among dental professionals and students in Riyadh, Saudi Arabia. J Phys Ther Sci
2018; 30:770–776. https://doi.org/10.1589/jpts.30.770 PMID: 29950762
4. Shams-Hosseini NS, Vahdati T, Mohammadzadeh Z, Yeganeh A, Davoodi S. Prevalence of Musculo-
skeletal Disorders among Dentists in Iran: A Systematic Review. Mater Sociomed 2017; 29:257–262.
https://doi.org/10.5455/msm.2017.29.257-262 PMID: 29284995
5. Feng B, Liang Q, Wang Y, Andersen LL, Szeto G. Prevalence of work-related musculoskeletal symp-
toms of the neck and upper extremity among dentists in China. BMJ Open 2014; 4:e006451. https://doi.
org/10.1136/bmjopen-2014-006451 PMID: 25526795
6. Tirgar A, Javanshir K, Talebian A, Amini F, Parhiz A. Musculoskeletal disorders among a group of Ira-
nian general dental practitioners. J Back Musculoskelet Rehabil 2015; 28:755–59. https://doi.org/10.
3233/BMR-140579 PMID: 25547232
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 10 / 14

7. Szczygieł E, Zielonka K, Mętel S, Golec J. Musculo-skeletal and pulmonary effects of sitting position—a
systematic review. Ann Agric Environ Med 2017; 24:8–12. https://doi.org/10.5604/12321966.1227647
PMID: 28378964
8. Rafie F, Zamani Jam A, Shahravan A, Raoof M, Eskandarizadeh A. Prevalence of Upper Extremity
Musculoskeletal Disorders in Dentists: Symptoms and Risk Factors. J Environ Public Health 2015;
2015:517346. https://doi.org/10.1155/2015/517346 PMID: 26064141
9. De Sio S, Traversini V, Rinaldo F, Colasanti V, Buomprisco G, Perri R, Mormone F, La Torre G, Guerra
F. Ergonomic risk and preventive measures of musculoskeletal disorders in the dentistry environment:
an umbrella review. PeerJ 2018; 6:e4154. https://doi.org/10.7717/peerj.4154 PMID: 29362689
10. Endo K, Suzuki H, Nishimura H, Tanaka H, Shishido T, Yamamoto K. Sagittal lumbar and pelvic align-
ment in the standing and sitting positions. J Orthop Sci 2012; 17:682–86. https://doi.org/10.1007/
s00776-012-0281-1 PMID: 22915074
11. Gandavadi A, Ramsay JRE, Burke FJT. Assessment of dental student posture in two seating conditions
using RULA methodology—a pilot study. Br Dent J 2007; 203:601–05. https://doi.org/10.1038/bdj.
2007.1047 PMID: 18037853
12. Dable RA, Wasnik PB, Yeshwante BJ, Musani SI, Patil AK, Nagmode SN. Postural Assessment of Stu-
dents Evaluating the Need of Ergonomic Seat and Magnification in Dentistry. J Indian Prosthodont Soc
2014; 14:51–58. https://doi.org/10.1007/s13191-014-0364-0 PMID: 26199492
13. De Bruyne MA, Van Renterghem B, Baird A, Palmans T, Danneels L, Dolphens M. Influence of different
stool types on muscle activity and lumbar posture among dentists during a simulated dental screening
task. Appl Ergon 2016; 56:220–226. https://doi.org/10.1016/j.apergo.2016.02.014 PMID: 26975788
14. Driessen MT, Proper KI, van Tulder MW, Anema JR, Bongers PM, van der Beek AJ. The effectiveness
of physical and organizational ergonomic interventions on low back pain and neck pain: A systematic
review. Occup Environ Med 2010; 67:277–85. https://doi.org/10.1136/oem.2009.047548 PMID:
20360197
15. van Niekerk SMS, Louw QQA, Hillier SS. The effectiveness of a chair intervention in the workplace to
reduce musculoskeletal symptoms. A systematic review. BMC Musculoskeletal Disord 2012; 13:145.
https://doi.org/10.1186/1471-2474-13-145 PMID: 22889123
16. Curran M, O’Sullivan L, O’Sullivan P, Dankaerts W, O’Sullivan K. Does Using a Chair Backrest or
Reducing Seated Hip Flexion Influence Trunk Muscle Activity and Discomfort? A Systematic Review.
Hum Factors 2015; 57:1115–48. https://doi.org/10.1177/0018720815591905 PMID: 26175544
17. Hey HW, Wong CG, Lau ET, Tan KA, Lau LL, Liu KG, et al. Differences in erect sitting and natural sitting
spinal alignment-insights into a new paradigm and implications in deformity correction. Spine J 2017;
17:183–89. https://doi.org/10.1016/j.spinee.2016.08.026 PMID: 27562103
18. De Carvalho D, Grondinb D, Callaghanc J. The impact of office chair features on lumbar lordosis, inter-
vertebral joint and sacral tilt angles: a radiographic assessment. Ergonomics 2016; 60:1393–04. https://
doi.org/10.1080/00140139.2016.1265670 PMID: 27915585
19. Corlett EN. Background to sitting at work: research-based requirements for the design of work seats.
Ergonomics 2006; 49:1538–46. https://doi.org/10.1080/00140130600766261 PMID: 17050393
20. O’Sullivan K, O’Dea P, Dankaerts W, O’Sullivan P, Clifford A, O’Sullivan L. Neutral lumbar spine sitting
posture in pain-free subjects. Man Ther 2010; 15:557–61. https://doi.org/10.1016/j.math.2010.06.005
PMID: 20638321
21. O’Sullivan K, O’Keeffe M, O’Sullivan L, O’Sullivan P, Dankaerts W. Perceptions of sitting posture
among members of the community, both with and without non-specific chronic low back pain. Man Ther
2013; 18:551–56. https://doi.org/10.1016/j.math.2013.05.013 PMID: 23806489
22. O’Sullivan K, McCarthy R, White A, O’Sullivan L, Dankaerts W. Can We Reduce the Effort of Maintain-
ing a Neutral Sitting Posture? A Pilot Study. Man Ther 2012; 17:566–71. https://doi.org/10.1016/j.math.
2012.05.016 PMID: 22738884
23. Plessas A, Bernardes Delgado M. The role of ergonomic saddle seats and magnification loupes in the
prevention of musculoskeletal disorders. A systematic review. Int J Dent Hyg 2018. https://doi.org/10.
1111/idh.12327 PMID: 29318741
24. Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gøtzsche PC, Ioannidis JP, et al. The PRISMA statement
for reporting systematic reviews and meta-analyses of studies that evaluate healthcare interventions:
explanation and elaboration. BMJ 2009; 339:b2700. https://doi.org/10.1136/bmj.b2700 PMID:
19622552
25. Higgins JPT, Green S (editors): Cochrane Handbook for Systematic Reviews of Interventions Version
5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. Available from http://handbook.
cochrane.org. Accessed 25 Ago 2017.
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 11 / 14

26. Tufanaru C, Munn Z, Aromataris E, Campbell J, Hopp L. Chapter 3: Systematic reviews of effective-
ness. In: Aromataris E, Munn Z (Editors). Joanna Briggs Institute Reviewer’s Manual. The Joanna
Briggs Institute, 2017. Available from https://reviewersmanual.joannabriggs.org/
27. Higgins JP, Thompson SG. Quantifying heterogeneity in a meta-analysis. Stat Med 2002; 21: 1539–58.
https://doi.org/10.1002/sim.1186 PMID: 12111919
28. DerSimonian R, Laird N. Meta-analysis in clinical trials revisited. Contemp Clin Trials 2015; 45:139–45.
https://doi.org/10.1016/j.cct.2015.09.002 PMID: 26343745
29. Balshem H, Helfand M, Schu¨nemann HJ, Oxman AD, Kunz R, Brozek J, Vist GE, Falck-Ytter Y, Meer-
pohl J, Norris S, Guyatt GH. GRADE guidelines: 3. Rating the quality of evidence. J Clin Epidemiol
2011; 64:401–6. https://doi.org/10.1016/j.jclinepi.2010.07.015 PMID: 21208779
30. McAtamney L, Nigel Corlett E. RULA: A survey method for the investigation of work-related upper limb
disorders. Appl Ergon 1993; 24:91–9. PMID: 15676903
31. Esquirol Y, Niezborala M, Visentin M, Leguevel A, Gonzalez I, Marquie
´JC. Contribution of occupational
factors to the incidence and persistence of chronic low back pain among workers: results from the longi-
tudinal VISAT study. Occup Environ Med 2017; 74:243–51. https://doi.org/10.1136/oemed-2015-
103443 PMID: 27672181
32. Aicardi G, Alvarez J, Cotobal F, Hernandez M, Cumplido M, Lourdes Barrueco. Effect of age and body
mass index as risk factor for occupational contingencies in healthcare workers Occup Environ Med
2017; 74:A138–A139.
33. Hayes MJ, Smith DR, Taylor JA. Musculoskeletal disorders in a 3 year longitudinal cohort of dental
hygiene students. J Dent Hyg 2014; 88:36–1 PMID: 24563051
34. Levanon Y, Lerman Y, Gefen A, Ratzon NZ. Validity of the modified RULA for computer workers and
reliability of one observation compared to six. Ergonomics 2014; 57:1856–63. https://doi.org/10.1080/
00140139.2014.952350 PMID: 25205040
35. Park HS, Kim J, Roh HL, Namkoong S. Analysis of the risk factors of musculoskeletal disease among
dentists induced by work posture. J Phys Ther Sci 2015; 27:3651–54. https://doi.org/10.1589/jpts.27.
3651 PMID: 26834324
36. Movahhed T, Dehghani M, Arghami S, Arghami A. Do dental students have a neutral working posture?
J Back Musculoskelet Rehabil 2016; 29:859–64. https://doi.org/10.3233/BMR-160702 PMID:
27197705
37. Qu Y, Hwang J, Lee KS, Jung MC. The effect of camera location on observation-based posture estima-
tion. Ergonomics 2012; 55:885–97. https://doi.org/10.1080/00140139.2012.682165 PMID: 22676050
38. Gillespie R. Manufacturing knowledge: A history of the Hawthorne experiments. Cambridge: Cam-
bridge University Press; 1993.
39. Petromilli NSGP, Polli GS, Campos JA. Working postures of dental students: ergonomic analysis using
the Ovako Working Analysis System and rapid upper limb assessment. Med Lav 2013; 104:440–47.
PMID: 24640831
40. Haddad O, Sanjari MA, Amirfazli A, Narimani R, Parnianpour M. Trapezius muscle activity in using ordi-
nary and ergonomically designed dentistry chairs. Int J Occup Environ Med 2012; 3(2):76–83. PMID:
23022854
41. Custo
´dio RA, Brandão JG, Amorim JB. The influence of an abdominal support for a dental stool in the
distributions and electrical activity of the longissimus and the superior trapezius muscle in dentists.
Work 2012; 41:5652–4. https://doi.org/10.3233/WOR-2012-0908-5652 PMID: 22317641
42. Tran V, Turner R, MacFadden A, Cornish SM, Esliger D, Komiyama K, Chilibeck PD. A dental stool with
chest support reduces lower back muscle activation. Int J Occup Saf Ergon 2016; 22:301–4. https://doi.
org/10.1080/10803548.2016.1153223 PMID: 27058816
43. Scannell JP, McGill SM. Lumbar posture–should it, and can it, be modified? A study of passive tissue
stiffness and lumbar position during activities of daily living. PhysTher 2003; 83:907–917.
44. Dankaerts W, O’Sullivan PB, Burnett A, Straker LM. Differences in sitting postures are associated with
non-specific chronic low back pain disorders when subclassified. Spine (Phila Pa 1976) 2006; 31:698–
704.
45. Womersley L, May S. Sitting posture of subjects with postural backache. J Manipulative Physiol Ther
2006; 29:213–218. https://doi.org/10.1016/j.jmpt.2006.01.002 PMID: 16584946
46. Pynt J, Mackey MG, Higgs J. Kyphosed seated postures: extending concepts of postural health beyond
the office. J Occup Rehabil 2008; 18:35–5. https://doi.org/10.1007/s10926-008-9123-6 PMID:
18256905
47. Claus AP, Hides JA, Moseley GL, Hodges PW. Is ’ideal’ sitting posture real? Measurement of spinal
curves in four sitting postures. Man Ther 2009; 14:404–8. https://doi.org/10.1016/j.math.2008.06.001
PMID: 18793867
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 12 / 14

48. De Carvalho DE, Soave D, Ross K, Callaghan JP. Lumbar spine and pelvic posture between standing
and sitting: a radiologic investigation including reliability and repeatability of the lumbar lordosis mea-
sure. J Manipulative Physiol Ther 2010; 33:48–55. https://doi.org/10.1016/j.jmpt.2009.11.008 PMID:
20114100
49. De Carvalho DE, Callaghan JP. Influence of automobile seat lumbar support prominence on spine and
pelvic postures: a radiological investigation. Appl Ergon 2012; 43:876–82. https://doi.org/10.1016/j.
apergo.2011.12.007 PMID: 22280849
50. Grooten WJ, A
¨ng BO, Hagstro
¨mer M, et al. Does a dynamic chair increase office workers’ movements?
—Results from a combined laboratory and field study. Appl Ergon 2017; 60:1–11. https://doi.org/10.
1016/j.apergo.2016.10.006 PMID: 28166867
51. Standardization ISOf. ISO 11226:2000(en): Ergonomics—Evaluation of static working postures. 2000.
https://www.iso.org/obp/ui/#iso:std:iso:11226:ed-1:v1:en. Accessed 05.10.2017.
52. Delleman NJ, Haslegrave CM, Chaffin DB. Working postures and movements: tools for evaluation and
engineering. Boca Raton, London, New York, Washington D.C: CRC Press; 2004.
53. Ohlendorf D, Erbe C, Nowak J, Hauck I, Hermanns I, Ditchen D, Ellegast R, Groneberg DA. Con-
strained posture in dentistry—a kinematic analysis of dentists. BMC Musculoskelet Disord 2017;
18:291. https://doi.org/10.1186/s12891-017-1650-x PMID: 28679450
54. Gadge K, Innes E. An investigation into the immediate effects on comfort, productivity and posture of
the Bambach saddle seat and a standard office chair. Work 2007; 29:189–03. PMID: 17942990
55. George SC, Meyerand ME, On behalf of the council of chairs of biomedical Engineering. Challenges
and Opportunities: Building a Relationship Between a Department of Biomedical Engineering and a
Medical School. Ann Biomed Eng 2017; 45:521–24. https://doi.org/10.1007/s10439-016-1785-1 PMID:
28070773
56. Zemp R, Taylor WR, Lorenzetti S. Seat pan and backrest pressure distribution while sitting in office
chairs. Appl Ergon 2016; 53 Pt A:1–9. https://doi.org/10.1016/j.apergo.2015.08.004 PMID: 26674398
57. Kingma I, Van Diee
¨n JH. Static and Dynamic Postural Loadings During Computer Work in Females: Sit-
ting on an Office Chair Versus Sitting on an Exercise Ball. Appl Ergon 2009; 40:199–05. https://doi.org/
10.1016/j.apergo.2008.04.004 PMID: 18508028
58. van Uffelen JG, Wong J, Chau JY, van der Ploeg HP, Riphagen I, Gilson ND, et al. Occupational Sitting
and Health Risks: A Systematic Review. Am J Prev Med 2010; 39:379–88. https://doi.org/10.1016/j.
amepre.2010.05.024 PMID: 20837291
59. O’Sullivan K, McCarthy R, White A, O’Sullivan L, Dankaerts W. Lumbar Posture and Trunk Muscle Acti-
vation During a Typing Task When Sitting on a Novel Dynamic Ergonomic Chair. Ergonomics 2012;
55:1586–95. https://doi.org/10.1080/00140139.2012.721521 PMID: 23009637
60. Pynt J, Higgs J, Mackey M. Seeking the optimal posture of the seated lumbar spine. Physiother Theory
Pract 2001; 17:5–21. https://doi.org/10.1080/09593980151143228
61. Presoto CD, Wajngarten D, Garcia PPNS. Risk Factors of Musculoskeletal Disorders in Dental Stu-
dents–A Qualitative Study. Br J Med Res 2016; 18:1–9. https://doi.org/10.9734/BJMMR/2016/30232
62. Garcia PP, Gottardello AC, Wajngarten D, Presoto CD, Campos JA. Ergonomics in dentistry: Experi-
ences of the practice by dental students. Eur J Dent Educ 2016; 21:175–79. https://doi.org/10.1111/eje.
12197 PMID: 26998591
63. Eriksen W, Bruusgaard D, Knardahl S. Work factors as predictors of intense or disabling low back pain;
a prospective study of nurses’ aides. Occup Environ Med 2004; 61:398–04. https://doi.org/10.1136/
oem.2003.008482 PMID: 15090659
64. Molenbroek JFM, Albin TJ, Vink P. Thirty years of anthropometric changes relevant to the width and
depth of transportation seating spaces, present and future. Appl Ergon 2017; 65:130–38. https://doi.
org/10.1016/j.apergo.2017.06.003 PMID: 28802432
65. Steenbeek R, Dam LV, Vroome ED. 0263 Determinants of occupational diseases in the Netherlands:
risks at the individual and the population level. Occup Environ Med 2017; 74:A81. https://doi.org/10.
1136/oemed-2017-104636.214
66. Matsudaira K, Konishi H, Miyoshi K, Isomura T, Inuzuka K. Potential risk factors of persistent low back
pain developing from mild low back pain in urban Japanese workers. PLoS One 2014; 9:e93924.
https://doi.org/10.1371/journal.pone.0093924 PMID: 24714616
67. Robertson D, Kumbhare D, Nolet P, Srbely J, Newton G. Associations between low back pain and
depression and somatization in a Canadian emerging adult population. J Can Chiropr Assoc 2017;
61:96–105. PMID: 28928493
68. Matsudaira K, Kawaguchi M, Isomura T, Inuzuka K, Koga T, Miyoshi K, Konishi H. Assessment of psy-
chosocial risk factors for the development of non-specific chronic disabling low back pain in Japanese
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 13 / 14

workers-findings from the Japan Epidemiological Research of Occupation-related Back Pain (JOB)
study. Ind Health 2015; 53:368–77. https://doi.org/10.2486/indhealth.2014-0260 PMID: 26051289
69. Kamper SJ, Apeldoorn AT, Chiarotto A, Smeets RJ, Ostelo RW, Guzman J, van Tulder MW. Multidisci-
plinary biopsychosocial rehabilitation for chronic low back pain. Cochrane Database Syst Rev 2014;(9):
CD000963. https://doi.org/10.1002/14651858.CD000963.pub3 PMID: 25180773
70. Blanc D, Farre P, Hamel O. Variability of musculoskeletal strain on dentists: an electromyographic and
goniometric study. Int J Occup Saf Ergon 2014; 20:295–307. https://doi.org/10.1080/10803548.2014.
11077044 PMID: 24934426.
71. Visser B, Van Diee
¨n JH. Pathophysiology of upper extremity muscle disorders. J Electromyogr Kinesiol
2006; 16:1–16. https://doi.org/10.1016/j.jelekin.2005.06.005 PMID: 16099676
72. Belavy
´DL, Albracht K, Bruggemann GP, Vergroesen PP, van Diee
¨n JH. Can Exercise Positively Influ-
ence the Intervertebral Disc? Sports Med 2016; 46:473–85. https://doi.org/10.1007/s40279-015-0444-2
PMID: 26666742
Assessment of the ergonomic risk in dentistry
PLOS ONE | https://doi.org/10.1371/journal.pone.0208900 December 17, 2018 14 / 14