Article
Combining Ergonomic Risk Assessment (RULA) with Inertial
Motion Capture Technology in Dentistry—Using the Benefits
from Two Worlds
Christian Maurer-Grubinger
1,†
, Fabian Holzgreve
1,
*
,†
, Laura Fraeulin
1
, Werner Betz
2
, Christina Erbe
3
,
Doerthe Brueggmann
1
, Eileen M. Wanke
1
, Albert Nienhaus
4
, David A. Groneberg
1
and Daniela Ohlendorf
1
Citation: Maurer-Grubinger, C.;
Holzgreve, F.; Fraeulin, L.; Betz, W.;
Erbe, C.; Brueggmann, D.; Wanke,
E.M.; Nienhaus, A.; Groneberg, D.A.;
Ohlendorf, D. Combining Ergonomic
Risk Assessment (RULA) with
Inertial Motion Capture Technology
in Dentistry—Using the Benefits from
Two Worlds. Sensors 2021, 21, 4077.
https://doi.org/10.3390/s21124077
Academic Editors: Pietro Picerno,
Andrea Mannini and Clive D’Souza
Received: 29 April 2021
Accepted: 10 June 2021
Published: 13 June 2021
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4.0/).
1
Institute of Occupational Medicine, Social Medicine and Environmental Medicine, Goethe-University,
60323 Frankfurt am Main, Germany; christian.maurer.cm@gmail.com (C.M.-G.);
maltry@med.uni-frankfurt.de (L.F.); brueggmann@med.uni-frankfurt.de (D.B.);
wanke@med.uni-frankfurt.de (E.M.W.); groneberg@med.uni-frankfurt.de (D.A.G.);
ohlendorf@med.uni-frankfurt.de (D.O.)
2
Institute of Dentistry, Department of Dental Radiology, Goethe-University, 60323 Frankfurt am Main,
Germany; w.betz@em.uni-frankfurt.de
3
Department of Orthodontics, Medical Center of the Johannes Gutenberg-University Mainz,
55128 Mainz, Germany; erbe@uni-mainz.de
4
Principles of Prevention and Rehabilitation Department (GPR), Institute for Statutory Accident Insurance and
Prevention in the Health and Welfare Services (BGW), 20246 Hamburg, Germany;
albert.nienhaus@bgw-online.de
* Correspondence: holzgreve@med.uni-frankfurt.de
† These authors equally contributed to the work.
Abstract:
Traditional ergonomic risk assessment tools such as the Rapid Upper Limb Assessment
(RULA) are often not sensitive enough to evaluate well-optimized work routines. An implementation
of kinematic data captured by inertial sensors is applied to compare two work routines in dentistry.
The surgical dental treatment was performed in two different conditions, which were recorded
by means of inertial sensors (Xsens MVN Link). For this purpose, 15 (12 males/3 females) oral
and maxillofacial surgeons took part in the study. Data were post processed with costume written
MATLAB
®
routines, including a full implementation of RULA (slightly adjusted to dentistry). For
an in-depth comparison, five newly introduced levels of complexity of the RULA analysis were
applied, i.e., from lowest complexity to highest: (1) RULA score, (2) relative RULA score distribution,
(3) RULA steps score, (4) relative RULA steps score occurrence, and (5) relative angle distribution.
With increasing complexity, the number of variables times (the number of resolvable units per
variable) increased. In our example, only significant differences between the treatment concepts were
observed at levels that are more complex: the relative RULA step score occurrence and the relative
angle distribution (level 4 + 5). With the presented approach, an objective and detailed ergonomic
analysis is possible. The data-driven approach adds significant additional context to the RULA score
evaluation. The presented method captures data, evaluates the full task cycle, and allows different
levels of analysis. These points are a clear benefit to a standard, manual assessment of one main body
position during a working task.
Keywords:
inertial motion units; wearable sensors; human factors; work place evaluation; er-
gonomics; kinematic analysis; dentist; dental assistant; dental treatment concept
1. Background
For the assessment of the ergonomic risk potential, various methods are available to
identify imbalances between workplace conditions and the physiological capabilities of the
employee, which are referred to as Ergonomic Risk Assessment Tools (ERATs) [
1
–
5
]. The
choice of the particular ERAT depends on the risk dimension studied. Common risk dimen-
sions result from applied forces, duration of physical work, or postural variability [
6
]. The
Sensors 2021, 21, 4077. https://doi.org/10.3390/s21124077 https://www.mdpi.com/journal/sensors
