Lecture 7

Rotary Cutting Instrument

Rotary Cutting Instrument

instruments that rotate on an axis to perform cutting and abrading on tooth structure

Parts of dental Handpieces

• working end (head)

• shank

• connection

Dental handpieces are divided into two categories:

• high-speed handpieces

  (operate up to 450,000 rpm and higher)

• low-speed handpieces

  (operate up to 30,000 rpm)

Low-speed Motor

referred to as “slow speed or straight handpiece”

High-speed handpiece

to cut tooth structure, to cut bone, to remove decay, and to modify or remove restorations

Different types of securing burs in the handpiece:

1. power level chuck

2. push button chuck

3. conventional chuck - need to secure bur and loosen bur in handpiece with wrench

Chuck

a small, metal cylinder to hold the rotary instruments (burs)

Dental bur

• part of a group of instruments referred to as rotary instruments

• rotary cutting instrument which has bladed cutting head

Stainless Steel bur

• first developed burs

• designed for slow speed

• not used often because they dull very fast

Tungsten carbide bur

• designed to withstand heavy stresses and increase shelf life

• stronger and remain sharper during cavity preparation

Classification of burs: attachment

● latch type ● friction grip type

Classification of burs: composition

● stainless steel ● carbide bur or ● combination

Classification of burs: length of head

● long ● short ● regular

Classification of burs: use

● cutting ● finishing ● polishing

Classification of burs: shape

● round ● inverted cone ● pear shaped ● tapering fissure ● straight fissure ● end cutting

Three basic parts of the bur

• head

• neck

• shank

Three important angles:

1. rake angle - most important design characteristic of a bur blade

2. edge angle

3. clearance angle

Factors affecting cutting efficiency of bur

● Rake angle ● Spiral angle and cross cuts ● Concentricity and run out ● Neck diameter ● No of teeth/blades

Abrasive instruments can be divided into:

1. diamond abrasives

2. other abrasives

Diamond Abrasive Instruments

• introduced in 1942

• greater resistance to abrasion, lower heat generation and longer life to be preferred over tungsten carbide burs.

Diamond instruments consists of three parts

1. metal blank

2. powered diamond abrasive

3. bonding agent

Hazards with cutting instruments

1. pulpal precautions

2. soft tissue precautions

3. eye protections

4. ear protections

5. inhalation precautions