Musculoskeletal disorders: reducing injury risk
by Louise Madge
Louise Madge discusses musculoskeletal disorders associated with the dental hygienist, and how instrumentation design and ergonomics can prevent injuries.
Musculoskeletal disorders (MSD) are injuries or disorders that affect the muscles, nerves, tendons, joints, cartilage and spinal discs. There is a positive correlation between conditions of the neck, shoulder, elbow, hand, wrist and back, and performing receptive forceful tasks (Centres of Disease Control and Prevention, 2020).
These disorders can be an immediate result of the working environment, but they can also persist longer, even after the causative activity is ceased.
Musculoskeletal disorders are a major health concern for dental healthcare professionals (DHCP). They are the most commonly experienced health hazard, with many DHCPs developing symptoms within five years of working in the profession (Johnson et al, 2016).
Dental hygienists are at a higher risk of developing MSDs compared to dentists and dental assistants. With Leitz and colleagues (2018) reporting 60-90% of dental hygienists having some sort of MSD.
There is a strong correlation between physical workload and hand numbness that is caused by scaling and root planning (Johnson et al, 2016). Removal of heavy calculus deposits throughout the day saw an increased risk of MSD development (Akeeson et al, 2012). Hand instrumentation increased the odds of neck pain while ultrasonic instrumentation increased the odds of shoulder pain.
An in-depth study by Johnson and colleagues (2016) discovered the neck made up 80% of the total of MSDs, followed by the hands at 75%, shoulders at 71%, upper back at 64%, lower back at 59%, mid back at 45% and, lastly, arms at 40%.
The most common types of MSD injuries to occur were carpal tunnel syndrome, tendonitis, vibration-induced neuropathy, tension neck syndrome and trapezius myalgia. The signs and symptoms of MSD injuries presented as pain, tingling, spasms, numbness, and weakness.
Impact of MSDs
Musculoskeletal disorders impair productivity, leading to decreased job satisfaction and poorer quality of work.
Dental hygienists are left to take sick or unpaid leave to obtain costly and time-consuming treatment, reduce clinical hours or leaving the profession early due to premature retirement or re-education.
Occupational risk factors
The main occupational risk factors found to cause MSDs were repetitive movements, pinch-grasp forceful exertions, poor ergonomics including holding constrained and static postures for long periods of time, vibration and sociopsychological factors such as insufficient breaks (Johnson et al, 2016).
Repetitive movements
Manual scaling is considered the most straining work task as calculus removal requires precision, force and repetitive movement at the same time. This repeated flexion and extension of the wrist, placed under forceful exertion and held in awkward positions for prolonged periods, increases the risk of carpel tunnel syndrome.
This motion not only causes trouble to the wrist but hands and elbows too. Manual scaling can produce up to 30 strokes per minute on average. In addition to removal of heavy calculus deposits, there is a need for increased strength and lateral pressure for controlled function that also increases the odds of development (Johnson et al, 2016).
Pinch grasp
Both the dominant and non-dominant hands are exposed to static loads in pinch-grasp form. The dominating hand requires fine motor coordination, which is put under a lot of strain during long periods of treatment.
The non-dominating hand is used for assistance to retract the tongue and cheek for good operation view, in which during this time the non-dominating hand is placed under great force and static positioning, which increases risk of MSDs.
Instrumentation design contributes to pinch force by using small diameters around quarter-inch to 5/16-inch handles, as well as heavier weight and dull blades on the instruments increases muscle activity and pinch force (Dong et al, 2015).
Poor ergonomics
Adopting poor ergonomics is the most frequent aetiological factor in MSD development. The dental hygienist spends the majority of their working time seated and a great deal of this is spent in a forward-bent trunk posture.
Awkward twisting, neck flexion and cramped positions fixed for extended periods contributes to muscular fatigue and pain. This is created by poor circulation, insufficient removal of lactic acid and increased muscular pressure, resulting in MSD development.
Many dental hygienists work with their legs split either side of the chair, which limits free mobility in clock position, causing the torso to twist and tilt, the neck to flex, the wrists to increase flexion and extension and shoulders to abduct.
Vibration
Ultrasonic instrumentation requires precision, but much lower force is applied compared to manual instrumentation, which is supposed to decrease the risk of MSD development. However, studies found that vibration from the ultrasonic scaler increased the risk of carpel tunnel syndrome in the right hand by 1.13 times (Leitz et al, 2018).
Vibrations can also cause nerve damage and MSDs. A frequency of 25,000Hz to 30,000Hz begins to cause damage to the soft tissues and nerve receptors in the fingertips.
Psychosocial factors
Insufficient breaks are another high aetiological factor in MSD development. The lack of control of the dental hygienist diary, overbooking and the pressure by the employer to fill downtime decreases the recovery time of the repetitive and static postures.
Longer hours and number of patients seen by the dental hygienists per day contribute to MSD development. Dental hygienists who work more than 34 hours a week and treat more than 11 patients a day are at a higher risk than someone who works fewer hours and treats less patients. The average time a dental hygienist spends scaling and root planning is 5.5 to 7.5 hours a day and treating two patients or more who are difficult from instrumentation perspective also increases the risk (Johnson et al, 2016).
Interventions
Ergonomics
Ergonomics is the science behind equipment and process design, tailored to fit the operator to maximise productivity and reduce operator fatigue and discomfort. Different types of ergonomic strategies for posture, equipment and instrument design should be considered to prevent or reduce MSD development.
Adopting a good posture will lead to more working energy, less stress, increase in comfort and a decrease in pain and muscular tension. It is important for the dental hygienist to sit upright and maintain a neutral body position by keeping all body horizontal lines (eyes, shoulders, hips, and knees) parallel and perpendicular to the floor (Pirvu et al, 2013).
This is carried out by having the head straight to slightly flexed no more than 20-25°, the shoulders relaxed and not elevated or abducted, the back is straight to maintain the lumbar curve, the hips flexed at a 90° or less, the buttocks firmly supported on the stool, elbows close to the body and at 90° or slightly less, wrists in a neutral stance avoiding over flexion, extension or deviation, and lastly the feet firmly planted and supported by the floor (Sanders et al, 1997).
When selecting an operator chair some ergonomic features must be considered, such as lumbar and thoracic support. The chair should be slightly tapered forward, with adjustable height, back tilt and adequate size seat pan. The seat must be firm and have a supportive surface to prevent slipping off the stool. The legs should have five-point casters to prevent tipping over if the operator has leaned too far forward.
The stool should be tilted slightly forward no more than five to 15° to improve circulation to the legs and to reduce posterior rotation of the pelvis.
The position of the dental hygienist to the patient is critical for good posture maintenance. The relationship of position should mimic a clock. The patient’s head is located at 12 o’clock. Right-handed operators work from seven to 12 and left-handed operators work from 12 to five. The operator should sit no more than 14 to 16 inches away from the patient’s head, and the overhead light line should be no greater than 15° or else a shadow will be cast in the oral cavity causing deviation from good posture.
Instrumentation design
Handle design of periodontal instruments can have significant effects of pinch force and muscle activity of the hands. Various factors should be considered when selecting instrumentation design, such as weight, diameter, shape and padding. Lightest weight instruments (15g) with larger diameters (10mm) produce the lowest mean muscle activity (Simmer-Beck and Branson, 2010).
Instrument handles that are round, tapered shape with a large diameter of 10mm can reduce pinch force by 7.5% compared to round or hexagonal cross-sectional shape (Dong et al, 2015). Padding on instruments can increase the weight and diameter of the instrument, but ultimately reduces muscle strain on the thumb.
Other interventions
Magnification loupes are used to enhance visibility and force the dental hygienist to sit ergonomically correct. Dental hygienists who use loupes responded with lower symptoms of MSD compared to those without loupes. Early intervention of loupes can prove to be more effective in improving working posture and reducing risk of MSD development (Lietz et al, 2020).
Pain management
Dental hygienists seek traditional conventional solutions (physicians, splints, medication) to manage pain, but in the last 15 years complementary and alternative medicine (CAM) therapies – such as yoga, acupuncture, massage therapy, herbal remedies – have become increasingly popular, and proven effective for managing chronic musculoskeletal pain.
Those who use CAM therapies report a reduction in work interruptions, increased job satisfaction and longevity compared to those who use conventional therapies alone (Gupta et al, 2014).
Future considerations
To prevent musculoskeletal disorders and early retirement, the dental hygienist must adapt a good neutral posture, using an ergonomic stool and magnification loupes to support this. They must choose lightweight instruments with large diameters and padding to reduce pinch force and muscle activity. They should also alternate different instrument handles throughout the day to activate and rest various muscles of the hand.
In addition, frequent breaks are required to allow stretching and getting out of the static positions.
Diary management is advised to relieve stress and is also key in reducing MSD development. Dental professionals should be working no more than 34 hours per week, seeing fewer than 11 patients per day.
Future considerations for employers and the dental hygienist are to work with a dental nurse to relieve some psychosocial and ergonomic factors for increased job satisfaction and longevity.
If pain has already developed, the use of complementary and alternative medicine therapies is proven to manage chronic pain and increase job satisfaction and longevity compared to conventional treatments alone.
References
- Akeeson I, Balogh GA (2012) Physical workload in neck. shoulders and wrists/hands in dental hygienists during a work-day. Applied Ergonomics 43(3): 803-811
- Centres of Disease Control and Prevention (2020) [Online] Available at: www.cdc.gov/workplacehealthpromotion/health-strategies/musculoskeletal-disorders/index.html
- Dong H, Barr A, Loomer P, LaRoche C, Young E, Rempel D (2006) Effects of periodontal instrument handle design on muscle load and pinch force. The Journal of the American Dental Association 137(8): 1123-30
- Dong H, Barr A, Loomer P, LaRoche C, Young E, Rempel D (2007) Effect of tool handle shape on hand muscle load and pinch force in a simulated dental scaling task. Applied Ergonomics 35(5): 525-531
- Gupta D, Bhashar DJ, Gupta KR, Larim B, Kanwar A, Jain A, Yadav A, Saini P, Arya S, Sachdawa N (2014) Use of complementary and alternative medicine for work related musculoskeletal disorders associated with job contentment in dental professionals. Ethiopian Journal of Health Science 24(2): 117-124
- International Ergonomics Association [Online] Available at: https://iea.cc/what-is-ergonomics
- Johnson CR, Kanji Z (2016) The impact of occupation-related muscoloskeletal disorders on dental hygienists. Canadian Journal of Dental Hygiene 50(2): 72-79
- Lietz J, Agnessa K, Nienhaus A (2018) Prevalence and occupational risk factors of musculoskeletal diseases and pain among dental professionals in Western countries: a systematic literature review and meta-analysis. Plos One 13(12): e028628
- Lietz J, Ulusay N, Nienhaus A (2020) Prevention of musculoskeletal diseases and pain among dental professionals through ergonomic interventions: a systematic literature review. International Journal of Environmental Reasearch and Public Health 17(10): 3482
- Pirvu C, Patrascu I, Pirvu D, Ionescu C (2013) The dentists operating posture – ergonomic aspect. Journal of Medicine and Life 7(2): 177-182
- Sanders MJ, Turcotte CA (1997) Ergonomic strategies for dental professionals. Work 8(1): 55-72
- Simmer-Beck M, Branson BG (2010) An evidence-based review of ergonomic features of dental hygiene instruments. Work 35(4): 477-85
- Suedback JR, Tolle SL, McCombs G, Walker ML, Russell DM (2017) Effects of instrument handle design on dental hygiene forearm muscle activity during scaling. Journal of Dental Hygiene 91(3): 47-54
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