Module 8 - Instrument Design and classification

Design characteristics of instrument handle

Some instruments have ergonomic design to prevent musculoskeletal injury

• Handle, shank, working end

Significance of handle design

Effect of handle shape on muscle load and pinch force

• Carpal tunnel syndrome & dental hygiene

  • Dental hygiene ranks highest for carpal tunnel syndrome cases

  • Risk factor: repetitive forceful pinching during periodontal instrumentation and non—neutral wrist positions

• Pinch force in the grasp

  • Average pinch force exerted during instrumentation is 11%—20% of clinician’s max pinch strength

  • Relaxing fingers of grasp between instrumentation strokes reduces pinch force required during instrumentation

• Variation in handle design

  • Design vary greatment according to manufacturers. Ergonomic designs may help reduce carpal tunnel syndrome.

  • Weight and diameter of instrument handle has significant effect on hand muscle load and pinch form of clinician’s performing periodontal instrumentation

Handle selection criteria

1. Weight

2. Diameter

3. Taper

4. Texture

Recommended

• Large handle diameter (10 mm)

• Lightweight hollow handle (≥15 g)

• Handle tapers near shank

• Raised texturing

Avoid

• Small handle diameter (6 mm)

• Heavy, solid metal handle

• Non—tapered handle

• No texturing or nonraised texturing

Instrument handle criteria — Weight

Instrument weight

1. Lightweight instrument is 15 grams or less — optimal

2. Less stress on hand during periodontal instrumentation. Heavy = more muscle activity

Instrument handle criteria — Diameter and taper

• Large diameter (10 mm) requires least amount of pinch force

  • Traditional handle (7 mm) have greater pinch force = muscle cramping

• Round instrument handle (instead of hexagon), reduce muscle force and compression

• Tapered handle

  • Gradualy narrows where fingers grasp the instrument

  • Improves finger grip/ contact w/ the handle

  • Reduce slipping of fingers in wet environment

  • Reduce average pinch force by 11% compared to non—tapered instrument handle

  • Round tapered and large diameter = least pinch force

Instrument handle criteria — Handle texture

Knurling pattern

• Texturing — increase static friction between fingers and handle resulting in reduced pinch force in grasp

  • Texture = more control, and reduce muscle fatigue

• No texture = decrease control in wet environment = increase muscle fatigue

• Raised texturing = easier to hold

Instrument handle criteria — Instrument balance

• Instrument is balanced if its working ends are aligned with an imaginary line that runs vertically through the center of the handle lengthwise

• Not balanced instrument = difficult to use & stress muscles of hand and arm

A is NOT balanced

B is balanced

Design characteristics of instrument shank

Simple shank design (A)

• aka straight shank

• Use on anterior teeth

Complex shank design (B)

• Bent in 2 planes (front to back or side to side) to facilitate instrumentation of posterior teeth

• Aka angled or curved shank

• Crowns of posterior teeth are rounded or overhand their roots. Complex shank is needed to reach around posterior crown onto root surface.

How to determine if shank is simple or complex?

• Hold working end towards you

Simple shank on anterior tooth

• Anterior tooth = wedge shaped

• Simple shanks can reach crown and root surface

Complex shank on lingual and proximal surface

Lingual surface w/ proximal view

• Front to back shank — working ends reach around crown and onto lingual and facial surfaces of the root

Proximal surface w/ facial view

• Side to side shank — working end reach around crown and onto proximal (mesial and distale) surfaces of the tooth

Shank’s strength

Clinician applies pressure to handle and shank

Type of diameter of metal used in a shank determines its strength

1. Rigid shank

• Withstand pressure needed to remove heavy calculus deposits

• Removed more quickly w/ less effort

2. Flexible shank

• Can’t withstand pressure to remove heavy calculus

  • Will bend or flex

• Removes small— medium sized calculus deposits

• Better tactile sensation

• Used to locate hidden calculus beneath gingival margin (Ex: Explorers)

How to detect calculus beneath gingival margin?

1. Visual information

• Limited vision — can’t see working end subgingivally

• Must rely on touch

2. Tactile sensitivity

• Feel vibrations transmitted through instrument or finger resting on shank and handle

3. Vibrations

• Made when working ends move over irregularities on surface of the tooth

• Vibrations transmited from working end, through shank, into handle

Instrument identification (big picture)

Handle > functional shank > lower shank > working end

Functional shank identification

Functional shank

• Portion of shank that allows working end to be adapted to the tooth surface

  • Adaptation = instrument hugging tooth
    (Last straight segment of shank nearest to working end)

• Begins below working end

• Ends at last bend nearest to handle

Functional shank length

Short functional shank

Used on…

• Tooth crowns

• Supragingival area (above gumline)

  • Ex: Removing supragingival calculus

Long functional shanks

Used on…

• Tooth crowns

• Roots

• Subgingival (below the gumline)

  • Ex: Detecting calculus below gingival margin

Lower shank importance

• Portion of functional shank nearest to the working end

Lower shank tells you….

• Select the correct working end

• If instrument angulation is correct

How to select working end

• Lower shank should be parallel to tooth surface being instrumented — mesial, distal, facial, or lingual

• If not parallel = wrong angulation, adaptation, and working end

Standard vs Extended lower shank

Standard lower shank

• Normal length

Extended lower shank

• 3 mm or longer

Used for:

• Deep periodontal pockets

• Reaching below gingival

Simple & complex Shank design overview

refer to photo

Functional and lower (terminal) shank overview

Functional shank

• Part of shank that allows working end to adapt to tooth

• Below working end, ends at last bend near handle

• Short functional shank — crowns/ supragingival

• Long functional shank — crowns, roots, subgingival

Long (terminal) shank

• Part of functional shank closest to working end

• Visual guide for working end selection

• Parallel to tooth surface

• Standard or extended length

  • Extended lower shank = 3 mm longer, used in deep periodontal pockets

Working end instrument design

Single ended instrument

• One working end

• Periodontal probes

Double ended instrument

• Two working ends

• Curets

Types of double ended instrument

Unpaired (Dissimilar) — A

• 2 different working ends

• Example: Explorer and probe combination

Paired (MIrror images) — B

• Working ends are mirror images of each other

• Example: Gracey 11/12 curet

Design name and number

Design name

• Identifies designer or institution that developed instrument

• Ex: Gracey

  • Named after Dr. Clayton H. Gracey

Number

• Identifies specific instrument within series

• Ex: Gracey 11

  • Gracey = design name

  • 11 = design number

Gracey 11/12

• One end = 11

• Other end = 12

Rule:

• Each working end is identified by number closest to it

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Gracey 11/12 vertical

• Name and number marked around handle

• First number on the left = top end of handle

• Second number on right = bottom end of handle

Parts of the working end

• Used to assess teeth, soft tissues, remove calculus.

• Be able to identify the face, back, lateral surface, cutting edge, and toe or tip of working ends

Face and back of working ends

Face

• Concave purple area

Back

• Convex gold line

Laterla surface of working end

• Side surfaces of working end (2 on either side)

• Green shaded area

Cutting edge of working end

• Edge where face and lateral surface meets

• Orange line

Toe or tip of working end

• Look directly down the instrument’s face

Curet

• Rounded end

• Called a toe

Sickle scaler

• Pointed end

• Called a tip

Working end in cross section

• Explains why curets and sickles are different

Cross section

• View obtained by cutting instrument perpendicular to its length

  • Ex: Cutting a pencil in half or cutting tree to see growth rings

  • Cross section of pencil = hexagon shaped

• Cross section of working ends = determins if it can be used subgingivally or supragingivally

A. Imagine cutting working ends of periodontal instruments

B. After cut is made — cross sections visible

• Top = semi—circular

• Bottom = triangular

Curets cross section

• Semicircular

• Round back

• Round toe

Use

• Remove calculus

• Crowns

• Roots

• Subgingivally

Sickle scaler cross section

• Triangualr

• Pointed back

• Pointed tip

Use

• Primarily supragingival calculus

Instrument classification chart

2 types of periodontal instruments

• Assessment instruments

• Calculus removal instruments

Assessment instruments

Periodontal probes

• Measures periodontal tissues

• Blunt rod shaped working end

• Circular or rectangular cross section

Explorer

• Detects

  • Calculus

  • Tooth surface irregularities

  • Defective margins on restorations

• Flexible shank

• Circular cross section

Calculus removal instruments

Sickle scalers

• Removes calculus deposits from crowns of teeth

• Pointed back

• Pointed tip

• Triangle cross section

Curets

• Removes calculus deposits from crowns and roots of teeth

• Rounded back

• Rounded toe

• Semicircular cross section

Subtypes

• Universal curet

• Area—specific curet

Periodontal files

• Crush large calculus deposits

• Multiple cutting edge on working end