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