Designing Ergonomic Dental Tools

1
Designing Ergonomic Dental Tools

• Hui Dong
• D.D.S., Ph.D. Student
• Environmental Health Science Program
• Advisor Dr. David Rempel

2
Why is it important?

• Dentists and dental hygienists have a high
  prevalence of upper-extremity musculoskeletal
  disorders, including Carpal Tunnel Syndrome
  (CTS).
• 9.2 dentists have repetitive motion disorder.
• 19 affected required surgery.
• gt40 affected reduced work hours.
• 29.5 premature retirement was due to
  musculoskeletal disorders (UK).

3
Risk Factors for CTS

• Repetitive hand motions
• Forceful pinching or gripping
• Awkward wrist postures
• Temperature
• Vibration

4
Risks Associated with Dentistry

• Holding instruments requires a high level of
  pinch force.
• Wrists are held in awkward positions for
  prolonged periods.
• Dental hygiene work tooth cleaning or scaling
  / root planing poses the highest ergonomic risk.

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Current Studies on Dental Tool Handle Design

• Non-powered hand instruments are still important
  in dentistry.
• Ultrasonic scalers can not replace hand scalers
  or curettes for tooth cleaning.
• Studies on the tools for root canal treatment
  show handles with large diameters reduce working
  time and muscle stress.
• No study has been done on hand tools for tooth
  cleaning. It is my work.

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Periodontal Curettes Tools for Tooth Cleaning
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Purpose of the Study

• Evaluate handle designs of non-powered dental
  scalers while the subjects (practicing dentists)
  work on an artificial mouth model.
• Measure pinching pressure on the thumb.
• Record EMG during the task.
• Evaluate performance of the subjects.

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Subject Selection

• 24 subjects balanced on gender
• Faculty and residents at UCSF experienced
  dental practitioners doing scaling at least 5
  hours/week
• Exclude subjects with recent hand injuries,
  previous surgeries in the hand or wrist areas.
• Exclude subjects with a dominant left hand.

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Instruments

• The same type of curette tips are fitted to 16
  different handles.
• Handle diameters range from 7.0 to 11.5 mm.
• Total weights range from 15 to 24 grams.
• 4 different shapes round, hexagonal, tapered
  round, tapered hexagonal.

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Procedures

• Subjects perform scaling on plastic teeth fitted
  in an artificial jaw.
• The plastic teeth are painted with nail polish to
  simulate plaque and calculus deposits.
• Each subject will spend 3 hours in a data
  collecting session, using all 16 instruments.

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Mouth Model and Manikin
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Procedures (continued)

• EMG will be recorded from 4 muscles FDS, FPL,
  EDC, ECR.
• Pressure sensor will be placed on the thumb.
• Scaled teeth will be photographed with a digital
  camera
• Adobe Photoshop and NIH Image are used to
  calculate the paint area that has been
  instrumented, as a measurement of subject
  performance.

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Data Analysis

• Calculate the integrated and normalized EMG
  values, median EMG, and the APDF (amplitude
  probability distribution function) 10, 50, and
  90.
• Thumb pressure will be treated in the same
  manner.
• RMANOVA will be used to compare the effects of
  different handle designs.