Armamentarium - II

Dr. Habiba Mumtaz Lecturer

Department of Operative Dentistry

ROATARY INSRUMENTS These are small and held in a handpiece e.g. burs,

stones, discs

The instrument is rotated in the handpiece from an external source, either compressed air or directly by an electric motor

Two main broad types of equipment used covering two speed ranges

1) The airotor

2) Low-speed handpieces

The airotor (air turbine)

Gives the highest speeds but with less torque than low-speed handpieces

Speed ranges from 250 000-500 000 rev/minute

High speeds are achieved by a small air-driven rotor or turbine mounted in bearings in the head of a contra-angle handpiece

Shank of the bur is inserted into the rotor of the handpiece and revolves with it

Handpiece contains a system which directs water spray at the cutting head of the bur

Often contains a fibre-optic light

Rotates only clockwise

Low-speed handpieces They are either:-

Contra-angle—used exclusively in the mouth

Straight—used for trimming temporary crowns or for other procedures carried out outside the mouth

Unlike the airotor, speed is less (operating over different ranges ) but torque is greater

Most are equipped with use of a water spray incase of higher speed ranges

Drive for low-speed handpieces comes from a small electric motor attached to the handpiece

Speed controlled by, foot control, OR control on the electric motor, OR on the dental unit

Alternatively, Air motor, less expensive, is directly attached to the end of the handpiece

Unlike the airotor, Low-speed handpieces can be rotated clockwise AND anti-clockwise

Maintaining and sterilizing handpieces

They are all autoclavable and should be done so in between patients

Lubricated before and after autoclave

Lubricant is delivered from an aerosol using an adapter

OR by an air-driven cleaning and lubricating machine

Burs and stones Rotary cutting instruments are retained

in the handpiece by :-

Friction—in the older type of airotors

A latch grip–in the contra-angle low speed handpieces

A quick release clamping chuck—in the straight handpiece and now in most contra-angle, low speed handpieces and airotors

Cutting end of the instrument consists of either a set of blades of tungsten carbides, or steel or abrasive material, ranging in hardness from diamond to sand

Airotor burs They have friction grip shanks

Cutting end is of a hard material like diamond or tungsten carbide due to use of high speed

They are used to cut sound enamel and dentine and to remove existing restorations

Not used to remove caries

For enamel cutting—best to use diamond and some tungsten carbide burs

For ceramic materials—best cut with diamond burs

All other restorations—best cut with tungsten carbide

Metal restorations—cut by special tungsten carbide burs (Beaver burs)

Diamond instruments cut metal very slowly and ordinary tungsten carbide burs tend to break

Low-speed burs Large selection of burs available in a range

of sizes, numbered according to the diameter of the cutting tip

Steel burs—not expensive but have a short working life as they are rapidly blunted by enamel and rust if not dried after autoclaving

Tungsten carbide—more commonly used now as they run more smoothly than steel and can be autoclaved

Round burs used to remove soft carious dentine at slow speed

Steel burs—does not cut sound dentine or enamel very quickly at slow speed allowing the clinician to feel his way around the carious lesion

Stones-shaping instruments Made of abrasives such as carborundum

(green ) and alundum (white or pink )

Moulded into a range of shapes and fixed directly to a bur shank

Uses:-

1) final stages of tooth preparation for smoothing the surfaces

2)shaping, smoothing and finishing cast metal and porcelain restorations out of the mouth

For this, they are used at medium speed in the straight handpiece

Finishing instruments1) Burs and points

Made of steel—for amalgam

Made of very fine diamond particles and or multifluted tungsten carbide—for composite

2)Discs Rigid and flexible discs available with

abrasive materials of different degrees of coarseness applied to one or both surfaces

Some discs also cut at their edges

All discs are either mounted on mandrels of screw design or snap-on mandrels

Rigid discs in a straight handpiece are used for cutting and trimming, posts and temporary crowns outside the mouth

Flexible single-sided discs commonly used for finishing composite and other restorations

3) Abrasive strips Used to finish restorations and are hand held

flexible strips with abrasive on one side

Metal strips—used to remove over hanging amalgam ledges on old restorations

However, these are not very effective and harmful to the gingival papilla

Plastic strips– used to finish composite restorations on the approximal surfaces of teeth

Maintaining and sterilizing burs and stones

All burs and stones should be autoclaved

Re-usable Steel burs are dried quickly after autoclaving or they will corrode

Flexible discs and strips are disposable

Tungsten carbide burs and diamond burs should be assessed regularly and discarded if they become blunt, worn out, break or are bent

Tooth preparation with rotary instrumentsSpeed, torque and ‘feel’

Torque is the “turning moment” of the instrument

High-torque system—pressure applied to the surface by means of the bur with only minimal slowing of the drive

However, heat, vibration and increased amount of material is removed

High speed—low torque

Enamel, porcelain and metal—cut at high speed with low torque

Carious dentine or other softer material—cut at low speed with higher torque

High speed—cutting has to be controlled visually as there is very little “feel” and difficulty with water spray

Low speed—much easier to feel the cutting process

Heat generation and dissipation

Heat is generated in proportion to the work done

Potentially damaging to the vital pulp

High speed cutting always produces sufficient heat and use of cooling water spray is required

Prolonged slow-speed cutting may also produce heat

Advised to wash and dry the cavity at frequent intervals to improve visibility and cooling of the tooth

Effects on the patient Tooth preparation with rotary instruments has the

potential of producing pain

pressure

vibration

trauma and

long term-effects on the pulp

The longer time of cutting and the higher the local temperature produced, the greater is the threat of thermal trauma

Steel burs produce more heat then carbide burs due to inefficient cutting

Burs and diamonds when plugged with debris or if are dull do not cut efficiently resulting in increased heat production

Diamond instruments generate more damaging heat than carbide burs when used without coolants

Hence, instrument coolants like air or air-water spray are most commonly used

Provided that cooling is adequate, superficial enamel cutting may not be painful…however, cutting dentine in a vital tooth may be painful and local analgesics may be used

Vibration which may be produced in a rotary instrument and cause discomfort in a patient is produced less if the bur is gripped more firmly in the hand piece OR an electric motor drive is used instead of an air motor

Pressure needs to be controlled as there is greater pressure in a low speed and higher torque as compared with high speed and low pressure

Proper examination of the tooth and pre-operative radiographic assessment will cause accidental and unexpected exposure of the pulp due to careless cutting

Damage to sound adjacent teeth is common when preparing approximal surfaces

Damage to adjacent gingival margin is also very common

Particles of old restoration, tooth structure, bacteria and other debris are discharged at high speed s from the patients mouth which may cause eye damage

PrecautionsAll this can be avoided by:-

Choosing proper size and shape of bur

Use of rubber dam for isolation

Use of gingival retraction cord

Use of protective eye glasses

Finishing and polishing

For surface finish, straight burs provide a smoother finish than cross-cue designs

Tungsten carbide burs provide a smoother finish than either steel or diamond burs

Margins and surfaces of restorations should be smooth and polished

This minimizes plaque retention

All materials should be shaped when they are unset so minimal shaping is required with abrasive or finishing instruments

For increased shaping, coarser instrument used first and finest at the end of the procedure

Auxiliary instruments and equipmentFibre-optic lights

Fibre-optic lighting system provides good illumination during cavity preparation

Present at the tip of the handpiece and available with airotors and low-speed handpieces

Also available are independent fibre-optic lights and those built in some mouth mirrors

Light used for Polymerization of certain materials

May restorative materials now polymerized using intense visible light

Light is transmitted down a flexible light guide which is either a fibre-optic gel or cable

Light can also be contained in a hand held equipment connected to an electrical supply

Disadvantages:- light of such intensity may damage the retina, hence must never be shone directly in anyone’s eye

Therefore, protective screens or spectacles are used

Ultrasonic scalers

The working tip vibrates at ultrasonic frequency under voluminous water sprays

They provide a quick and efficient way of removing calculus

Also used in endodontics

And for loosening crowns or posts

Electrosurgical equipment

They remove hyperplastic gingival tissue

Gain access to cavity margins

Expose the margins of a tooth fractured below gingival level