art-5-1-21
DENTAL ERGONOMICS www.stomaeduj.com
A STANDARDIZED METHOD TO DETERMINE THE PROPER
Original Articles
WORKING DISTANCE FOR DENTAL MAGNIFICATION
UTILIZING NEUTRAL ERGONOMICS POSITIONING
Hind S. Hussein1a , Shelby Anderson1b , Melissa Matick1c , Avery Greene1d , Mark P. Zmiyiwsky1e ,
Nader F. Abdulhameed1f*
1Restorative Dentistry Department, School of Dental Medicine, Lake Erie College of Osteopathic Medicine, Bradenton, Florida, USA
a
BDS, Assistant Professor; email: Hhussein@lecom.edu; ORCIDiD: https://orcid.org/0000-0003-2850-3825
b
DMD Student; email: SAnderson24575@dmd.lecom.edu; ORCIDiD: https://orcid.org/0000-0002-6461-6651
c
DMD Student; email: MMatick37605@dmd.lecom.edu; ORCIDiD: https://orcid.org/0000-0001-7045-7055
d
DMD Student; email: AGreene91477@dmd.lecom.edu; ORCIDiD: https://orcid.org/0000-0002-4636-7364
e
DDS. MSBE, Assistant Professor; email: MZmiyiwsky@lecom.edu; ORCIDiD: https://orcid.org/0000-0002-1542-0302
f
BDS. MS.PhD, Assistant Professor; email: Nabdulhameed@lecom.edu; ORCIDiD: https://orcid.org/0000-0001-8137-2495
ABSTRACT https://doi.org/10.25241/stomaeduj.2021.8(1).art. 5
Introduction Evaluate and compare the relationship between anatomic measurements of the dental
clinician in a neutral ergonomics position with the proper working distance and test the hypothesis that
working distance can be estimated using specific anatomical measurements of the operator.
Materials and Methods Specific measurements were obtained from 134 participants utilizing a neutral
ergonomics position. Values were applied using the Pythagorean theorem to calculate a hypothesized
working distance (HWD) from lateral epicanthus (E) to antecubital fossa (F) and antecubital fossa to the tip of
the thumb (T). The actual working distance (ET) was measured from lateral epicanthus to tip of the thumb in
a neutral ergonomics position in a simulated setting.
Results The results showed a significant positive correlation between (ET) and (HWD) and a positive
correlation for all of the anatomic measurements taken in simulation: ET to height and HWD to height; (EF)
and ET, EF and HWD; antecubital fossa to the thumb (FT) and ET, FT and HWD (p<0.00). There was a marginally
significant difference when comparing vision types, corrective and non- corrective (p<0.058), with non-
corrective vision having a higher actual working distance. There was a statistical difference when comparing
gender and HWD with male participants ranking higher hypothesized and actual working distance.
Conclusion When applying the Pythagorean formula using anatomic landmark measurements, the HWD is
repeatable for most operators and may contribute to a more standardized method to measure the accurate
working distance that fits the ergonomics.
KEYWORDS
Ergonomics; Dental Education; Musculoskeletal Disorders; Dentist; Dental Hygienists.
1. INTRODUCTION and clinicians may not be aware of what constitutes
the correct ergonomics posture. The importance of
Proper ergonomics in dentistry have been viewed an early introduction to proper ergonomics may be
as contributory aspects in the prevention of beneficial to a clinician’s career, for both comfort and
musculoskeletal injury and the working distance longevity. The cause of musculoskeletal disorders
with magnification should allow the operator to (MSD) is multifactorial and can develop from as little
maintain optimum posture [1]. Many dental students as a single event, or more likely through repetitive
OPEN ACCESS This is an Open Access article under the CC BY-NC 4.0 license.
Peer-Reviewed Article
Citation: Hussein HS, Anderson S, Matick M, Greene A, Zmiyiwsky MP, Abdulhameed NF. A standardized method to determine the proper working
distance for dental magnification utilizing neutral ergonomics positioning. Stoma Edu J. 2021;8(1):45-51.
Received: January 19, 2021; Revised: February 18, 2021; Accepted: February 23, 2021; Published: February 25, 2021
*Corresponding author: Dr. Nader F. Abdulhameed, BDS, MS, PhD, Assistant Professor
Restorative Dentistry Department, LECOM School of Dental Medicine, Lake Erie College of Osteopathic Medicine
4800 Lakewood Ranch Blvd, Bradenton, FL 34211 USA
Tel: (941) 405-1508; Fax: (941) 405-1675; e-mail: nabdulhameed@lecom.edu
Copyright: © 2021 the Editorial Council for the Stomatology Edu Journal.
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Hussein HS, et al.
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Original Articles
Figure 1. Clinical position based on Module 1 Section 3 of Fundamentals of periodontal
instrumentation and advanced root instrumentation. 8th edition revised by
Gehrig JS, Sroda R, Saccuzzo D. Philadelphia, PA: Wolters Kluwer; 2019.
A B
Figure 2. The theorem application: a) The Pythagorean theorem is the formula for calculating the length of one side of a right-angled triangle (c) when
the length of the other two sides is known: a2 + b2 = c2. In this formula, c represents the hypothesized working distance, a represents the distance from
“Eye to Elbow” and b represents the distance from Elbow to Tooth; b) Investigational theorem application performed on the researcher.
occupational movements over time. However, Council on Dental Practice’s (CDP) Dental Wellness
risks for the development of MSD have been Advisory Committee (DWAC), in conjunction with the
identified among dental students with reports of ADA Health Policy Institute, stress proper diligence
pain in the back and neck regions during training when choosing loupes and the importance of the
[2]. In an earlier study on the prevalence of body magnification level, working length, field of view,
pain in a dental student population, 46-71% and the angle of declination in order to maintain
of students reported pain with the percentage good head and neck posture [6]. Measurements are
increasing with the increase of years in school [3]. individualized and unique to the clinician.
The prevalence of musculoskeletal disorders in Magnification can allow the clinician to better visu-
the dentist’s necks, backs, shoulders, and arms alize the oral cavity and to reinforce the maintenance
were higher than other areas of the body; inter- of neutral ergonomics.The use of dental magnification
vention with magnification helped to improve the in dentistry is widely utilized and continued efforts to
working conditions reducing discomfort for the support its role in maintaining work posture remains
clinicians [4]. Those who reported the regular use an area of study. Employing magnification loupes
of some type of magnification were significantly has led to a reduction in the intensity of discomfort
less likely to report MSDs compared to those who felt by dentists in areas of the “neck, shoulders and
used magnification occasionally or never [5]. There arms, back, elbow, forearm and the whole body”
is a general acceptance of the use of magnification [4]. Magnification increases a clinician’s visual acuity
by dental students and practitioners and it is widely within the oral cavity and allows the clinician to see
perceived as an adjunct, if not a standard, for dental detail without compensating with improper bending
care in the profession. Recommendations by The or positioning. If magnification is to be considered
46 Stoma Edu J. 2021;8(1): 45-51 pISSN 2360-2406; eISSN 2502-0285
Dental magnification working distance and ergonomic
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Original Articles
Table 1. Data Collection Criteria.
Participant’s Age:
Do not wish to
Participant’s Gender: Male Female
answer
D1 D2 D3 Faculty
Participant’s Educational Status:
Handedness Right Left
Standing Height (inch)
Do you wear glasses/contacts? Lasik or related Yes No
procedure?
EF
lateral epicanthus of the eye to mid-elbow fold (inch)
FT
The mid-elbow fold of the cubital fossa to the tip of
thumb and or to occlusal surface #19 or #30 (inch)
ET
Working distance without loupes
lateral epicanthus eye to typodont mandibular molar (inch)
Table 2. Correlation significance test. since it reflects an individual length impacted by an
operator’s characteristics and the ability to maintain
Pearson Sig.
r statistic proper ergonomics while working. Maintaining
Correlation (2-tailed)
proper ergonomics can be found in the curriculum
ET vs HWD 0.878 0.000 Significant of dental education as provided in a guide to neutral
ET vs Height 0 .741 0.000 Significant ergonomics [8]. Improper measurements may allow
for awkward static positions and forward bending.
HWD vs Height 0.847 0.000 Significant
Studies have indicated that participants expressed
EF vs ET 0.854 0.000 Significant that loupes resulted in better vision, more comfort,
EF vs HWD 0.956 0.000 Significant a positive change in work posture [7], and improved
working conditions that facilitated their work [4].
FT vs ET 0.732 0.000 Significant
Of the current research available, emphasis on
FT vs HWD 0.862 0.000 Significant achieving the proper individualized working distan-
*Correlation is significant at the 0.01 level (2-tailed). ce is scarce and further research is warranted to
determine how an individual’s characteristics may
an element in maintaining proper ergonomics, the influence the necessary working distance for
ideal working distance with magnification cannot proper ergonomics positions in the selection of
be ignored. The necessary working distance needed magnification loupes.
with magnification was credited with contributing to The following null hypotheses were tested:
the positive effect and improvement among dental 1) There is a direct relationship between the specific
students by reinforcing the maintenance of proper anatomical measurements of a dental operator while
ergonomics for the head, neck, and trunk [7]. in neutral ergonomics position and a mathematical
As only one adjunct to achieving this goal, dental determination of proper working distance which
magnification has its many intricacies within can be obtained
itself. Proper alignment of declination angle and 2) No difference in working distance between the
working distance can be viewed as essential in corrective and non-corrective vision groups, and
affirming this contribution. Working distance 3) No difference in working distance between gen-
measurements may be more variable, depending ders.
on how the measurements are taken and obtained.
Although the ideal working distance needed can 2. MATERIALS AND METHODS
fall within a range dependent on the magnitude of
magnification (ie: 2.5x, 3.0x, 3.5x.etc), the working Participants were recruited through LECOM School
distance measurement/ focus point in this range of Dental Medicine by email invitation after getting
may vary. A standard to obtain the most optimal the IRB approval for the study protocol. All D1, D2,
measurement to help minimize the variation may and D3 students were asked to participate in the
be applicable and helpful in determining an ideal study. In addition, the dental faculty were invited
working distance specific for an individual. to participate. Invitation to participate was not
The working distance is measured from the clinician’s extended to the D4 students since their curriculum
eyes to the operating site. It is of critical importance places them in outreach clinics of distant locations.
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Hussein HS, et al.
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Participants were screened for exclusion factors - Step 7: Stabilize the lower back by pulling in the
Original Articles such as current musculoskeletal distress or injury stomach muscles to the spine.
preventing them from maintaining a comfortable - Step 8: Relax shoulders down and back.
ergonomics position. The exclusion characteristics - Step 9: Position arms along the long axis of the tor-
were not recorded. Experimental sessions took place so and hold elbows near the body.
in the LECOM Simulation clinic during open sim lab Student investigators and the principal investigator
hours. Upon completion of the informed consent, observed and verbally instructed changes in
the following demographic information was ergonomics keeping in mind the following reco-
recorded (Table 1): age, gender, height, handedness, mmendations:
educational year, and whether the subject wears - Head tilt of 0 to 20 degrees
- Trunk flexion of 0 to 20 degrees
Figure 3. Strong linear correlation between HWD and ET. Distance in - Torso in line with the long axis of the body
inches.
- Shoulders in a horizontal line
25
- Elbows at waist level held slightly away from the
24 body, no greater than 20 degrees from the body
23 - Forearm position held parallel to the floor, the angle
Distance in inches
22
between 100 degrees and 60 degrees
- Wrist aligned with a forearm; little finger-side of
21
the palm is slightly lower than the thumb side of the
20
palm.
19
Once neutral ergonomics were achieved and confir-
18
WD mean Corrective Non-Corrective Female Male
med by the investigators, the participant was asked to
ET
HWD
21.7
22.6
21.4
22.4
22
23.1
20.7
21.6
22.5
23.6
maintain this position while focusing on the occlusal
Groups surface of tooth 46 within the mannequin for right-
ET HWD handed participants and the occlusal surface of 36
Figure 4. Group descriptive statistics. for left-handed participants. For every experimental
session, a minimum of three investigators were
contacts, glasses, or has had any corrected vision present to assist in measuring and recording the
operation. The measurements were collected data. Three measurements were recorded:
with a right-angle square and measuring tape in 1) EF: From the lateral epicanthus of the eye to the
inches which can measure up to one eighth of the mid-elbow fold of the cubital fossa.
inch. Following demographic data collection, the 2) FT: From the mid-elbow fold of the cubital fossa to
participant was seated at a simulation station and the tip of the thumb and or to the occlusal surface
instructed to assume the 9 o’clock position for right- of #46 for right-handed participants and #36 for left-
handed participants and 3 o’clock for left-handed handed participants.
participants. The participant was given safety 3) ET: From the lateral epicanthus of the eye to the
goggles to wear for the duration of the experimental typodont lower molar. The right-angle square was
session. The participant was asked by the student used to help maintain an angle consistent with our
investigator and principal investigator to adjust proposed hypotheses in the equation and record
the mannequin’s head to be at waist level. The measurements from EF and FT. A measuring tape
participant was instructed into neutral ergonomics was used to measure the observed working distance
based on Module 1 Section 3 of Fundamentals while the participant maintained an ergonomics
of periodontal instrumentation and advanced position. The investigator notified the participant
root instrumentation. 8th edition revised by when the working distance measurement was initia-
Gehrig JS, Sroda R, Saccuzzo D. Philadelphia, PA: ted and completed. A student investigator recorded
Wolters Kluwer; 2019. (Fig. 1). the participant’s demographics on a password-
- Step 1: Place buttock back in the chair with even protected computer within a password protected
distribution on the seat. flash drive.
- Step 2: Adjust chair height so that feet rest flat on Using the Pythagorean theorem (Fig. 2) EF measu-
the floor. Spread feet to shoulders width apart and rements were used to represent (a), FT measurements
directly in front of the hips. were used to represent (b), and (c) was solved as our
- Step 3: Tilt the seat until the back edge is one inch HWD in the formula and recorded.
higher than the front edge or utilize a wedge-shaped
ergonomics cushion. 2.1. The participant was informed of the following
- Step 4: Adjust the lumbar rest so the lower back is risks:
supported when the buttock is back in the chair. According to the Institutional Review Board (IRB)
- Step 5: Adjust lumbar rest so that the height supp- protocol, the participant was asked to maintain a
orts your natural curve. neutral ergonomics position for approximately up to
- Step 6: Raise the tail bone to establish correct spinal five minutes. The participant was informed that they
curvature. may experience minimal muscle soreness during
48 Stoma Edu J. 2021;8(1): 45-51 pISSN 2360-2406; eISSN 2502-0285
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or after the measurement session. To minimize this ergonomics and the use of magnification. Our
Original Articles
risk the participant was informed of their right to study does not attempt to explain the comparative
stop the session at any time. We asked participants effectiveness of different styles of magnification [9],
to verbally announce muscle soreness during the but to provide an emphasis on the proper working
session to both student researchers and verify that distance in conjunction with magnification. Neutral
the position we measured from was comfortable. If ergonomics is described as having the shoulders
the participant could not continue the session the parallel with the floor, elbows close to the sides, and
previously recorded information would be discarded. the patient’s mouth at elbow height of the clinician
The ruler edges were protected with a plastic tube to [8]. This picture of neutral ergonomics as viewed in
protect each participant and the student researchers. (Fig. 1) is observed to follow the geometry of a
The ruler, measuring tape, and the participant’s right triangle with the working distance projecting
eyewear was disinfected with CaviWipes (Metrex™ to be the hypotenuse. Our investigation aimed to
Research, Orange, CA, USA) surface disinfectant pre- place a participant in a simulated position in neutral
moistened wipe before and after each use. ergonomics prior to measuring working distance.
This was based on the support of studies that
2.2. Analysis attribute MSD to improper ergonomics positioning
Both demographic and recorded measurements and allowed us to view a working distance that
were analyzed to determine statistical significance would be most conducive to a participant in neutral
based on individual characteristics with the ergonomics [1]. While in this position, the working
application of anatomic measurements in neutral distance was visualized and measured directly. The
ergonomics and working distance. Levene’s Test for results of our study provided data to show that our
Equality, Variances and t-test for equality of means hypothesized measurement derived indirectly from
was used for this study with Pearson’s correlation sig. measurements of anatomical relationships had a
(2-tailed). significant positive correlation with our observed
actual working distance measurement in the same
3. RESULTS position. Within that anatomic measurement, (ET)
and (HWD) were also both positively correlated to
Levene’s Test for Equality showed a significant an individual’s height. When viewed separately
difference when sig. (2-tailed) is ≤0.05. There was a each component of our equation EF, ET, and HWD
marginally significant difference in vision type by also individually showed a significant positive
“ET” to the vision; where the non-corrective vision correlation between itself and the observed actual
had higher “ET” values compared to corrective vision working distance. Our results showed a significant
values Sig.(2-tailed)= 0.058. difference in Eye to Tooth (ET) measurements by
Significant differences were found (Sig. (2-tailed) gender with males having significantly higher ET
=0.022) when comparing “HWD” between the measurements than females. This appears to be
corrective and non-corrective vision, where the non- explained by the higher average ET measurement
corrective vision had higher HWD. in males of 22.49 inches versus females with 20.73
There was a highly significant difference in “ET” inches. Similarly, there was a significant difference
values by gender with males having significantly in the Hypothesized Working Distance (HWD) with
higher “ET” values than females. Sig.(2-tailed)=0.000 males having a significantly higher HWD than fema-
There was a highly significant difference in “HWD” les. Again, the average measurements for males
by gender with males having a significantly higher was slightly higher at 23.61 inches compared to
“Hypothesized Working Distance” than females. females at 21.62 inches. The results also showed
Sig.(2-tailed)=0.000. There was a strong correlation a positive correlation of HWD and ET to height in
between HWD “Hypothesized Working Distance” both the female and male participants giving more
and ET “Actual Working Distance” (Linear regression= support that collectively an individual’s anatomic
0.775) see Fig. 3. proportions can help to determine a proper working
distance. It is unclear if the differences in male to
4. DISCUSSION female anatomic measurements is contributory to
the development of poor posture or MSDs; however,
Our study involved obtaining measurements of previous studies have cited an increase in reported
subjects in anatomic position with proper ergono- MSDs in females compared to males. In a study on
mics and using those values in the Pythagorean ergonomics in preclinical dental students, Kamal et al
theorem to hypothesize an individual’s working [10] reported differences in the postures of male and
distance as the hypotenuse. The primary purpose female participants without magnification, where
of this investigation was to analyze the relationship female students had worse ergonomic ratings than
between measurements in an anatomic ergonomics males. They also observed a positive correlation
position and the individual working distance using between posture and reported pain for both female
the geometric principles of the right triangle (Fig. and male students with 89.1% of female students
2). The core of the objectives centers on neutral and 65% of male students reporting MS pain after
Stoma Edu J. 2021;8(1): 45-51 pISSN 2360-2406; eISSN 2502-0285 49
Hussein HS, et al.
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starting preclinical training. A marginally significant operator while in neutral ergonomics position and
Original Articles difference in vision type by ET was found where non- a mathematical determination of proper working
corrective vision had a higher ET than corrective distance can be obtained. When applying the prin-
vision. This finding cannot be definitively explained ciples of the Pythagorean theorem with specified
since our measurements were derived while the anatomic measurements the hypothesized working
participant was sitting in neutral ergonomics and distance has a significant positive correlation to a
hypothesized from anatomic measurements. participant’s actual measured working distance.
Further studies may be necessary to investigate the This finding may contribute to a more standardized
significance of corrective and non-corrective visi- method to measure the working distance that fits
on differences. Our interpretation of the results provi- the proper neutral ergonomics for the operator. The
des that our hypothesis was correct, and our first null hypothesis was accepted, while the second
working distance value obtained through anatomic and third hypotheses were rejected. Through this
measurements is similar to a measured working study, we are able to provide applicable information
distance in neutral ergonomics. An individualized for students to reinforce proper ergonomics through
working distance correlating to a person’s body the analysis of individual working distance values
proportions can accurately provide their expected and the relationship to individual anatomic measure-
working distance. This allows us to propose that ments in order to utilize adjuncts like magnification
ideal working distance can be reproduced consis- in dentistry.
tently through the Pythagorean formula with
measured values of the eye to the cubital fossa and CONFLICT OF INTEREST
the cubital fossa to the tooth. In addition, by using The authors declare no conflict of interest.
identifiable landmarks (ie: the outer canthus and
antecubital fossa), one may be able to obtain these ACKNOWLEDGMENTS
measurements to calculate the desired working
distance assuming ergonomics position without the None.
aid of simulation in a dental chair or with a manne-
quin. Furthermore, future applications of this study AUTHOR CONTRIBUTIONS
may assist in the development of standardized
measuring methods, thus promoting bio ergonomic HH: Take the existing design. Come up with some modifications
head and neck posture. which improve the sensitivity, and reduce the error percentage
of the previous design. Writing the manuscript; Data collection
5. CONCLUSIONS and data analysis. SA, MM, AG: Data collection and data
analysis; Writing the manuscript. MZ: Methodology, calculation
The results allow us to conclude that we can accept of modifications, writing and reviewing the manuscript.
the hypothesis that there is a direct relationship to NA: Methodology, calculation of modifications, writing and
the specific anatomical measurements of a dental reviewing the manuscript, data analysis and data interpretation.
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Dental magnification working distance and ergonomic
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Original Articles
Hind S. HUSSEIN
BDS, Assistant Professor of Restorative Dentistry
LECOM School of Dental Medicine
Bradenton, Florida 34211, USA
CV
Dr. Hind S. Hussein is a Clinical Assistant Professor at LECOM School of Dental Medicine. She is the director of Operative Dentistry
courses. In 2014 she completed her Advanced Post Graduate Multispecialty Residency. In 2014, Dr. Hussein joined the University
of Florida UF as Visiting Scientist (Restorative Dental Science and Orthodontics). In 2017, she was certified as UF Graduate
Assistant Teacher with a technology program. From 2017 to 2018, she worked as Courtesy Clinical Assistant Professor at UF, with
the Operative Dentistry and Prosthodontics, Department of Restorative Dental Sciences. Since 2014 she has been successfully
involved in many research projects in dental materials. Dr. Hussein has successfully registered 4 US patents.
Questions
1. In an earlier study on the prevalence of body pain in a dental student population,
______ of students reported pain with the percentage increasing with the increase of
years in school.
qa. 25-30 %;
qb. 10-15%;
qc. 46-71%;
qd. 32-55 %.
2. All below are the null hypotheses tested in the study except one, which one is the
exception?
qa. There is a direct relationship to the specific anatomical measurements of a dental operator while in
neutral ergonomics position, and a mathematical determination of proper working distance can be obtained;
qb. No difference in working distance between the corrective and non-corrective vision groups;
qc. No difference in working distance between genders;
qd. No difference in the working distance when using different light.
3. In the study, the investigators observed and verbally instructed changes in
ergonomics keeping in mind the following recommendation:
qa. Head tilt of 0 to 20 degrees;
qb. Head tilt 0-30 degrees;
qc. Head tilt 0-10 degrees;
qd. No head tilt.
4. In the conclusion, when applying the principles of the Pythagorean theorem with
specified anatomic measurements, the hypothesized working distance has______ to the
actual working distance.
qa. Non- significant correlation;
qb. Significant positive correlation;
qc. Significant negative correlation;
qd. Borderline significance.
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