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Good morning. FINISHING AND POLISHING. Cementation of FPD. INTRODUCTION. Finishing, polishing of dental restorations are important aspects of clinical procedures that enhance both aesthetics and longevity.
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FINISHING AND POLISHING Cementation of FPD
INTRODUCTION • Finishing, polishing of dental restorations are important aspects of clinical procedures that enhance both aesthetics and longevity. • Residual surface roughness associated with improper finishing and polishing can cause plaque accumulation, gingival irritation, increased surface staining poor or suboptimal aesthetics. • Finishing and polishing process require a stepwise approach introducing finer scratches to the surface of the substrate in order to methodically remove the deeper scratches • Finishing and polishing are both wear processes but they differ in intent and degree
Benefits of finishing and polishing • Minimal irritation of soft and hard tissues • Simulates natural tooth surface aesthetics • Less likely to trap food debris and plaque • Reduced potential for corrosions • More hygienic
Goals of finishing and polishing • Obtain desired anatomy • Proper occlusion • Reduction of roughness, gouges and scratches • Surface should be well tolerated by oral tissue • Resist bacterial adhesion and excessive plaque accumulation • When plaque deposits exists they should
To obtain surface qualities series of procedural steps are conducted they are • Bulk reduction • Cutting • Grinding • Abrasion (finishing and polishing)
Definition :- • Bulk reduction - removal of unwanted large portion or material of the tooth or appliances quickly. This is done by cutting and grinding. • Cutting – process of removing material from the substrate by use of a bladed bur or a abrasive embedded in a binding matrix on a bur or disk. • Grinding – Process of removing material from a substrate by abrasion with relatively coarse particles.
Abrasion “A process of wear whereby a hard rough surface ( like a sand paper disk ) or hard irregular shaped particles ( like those in a slurry ) plough grooves in a softer material and cause materials from these grooves to be removed from the surface”.
Finishing and polishing are 2 abrasive procedures commonly used in dentistry • Finishing – Process of removing surface defects or scratches created during the contouring process through the use of cutting or grinding instruments or both. • Polishing – Process of providing luster or gloss on a material surface.
Other finishing methods • Electropolishing : as base metal alloy castings have very hard surface, polishing is quite tedious. • Also it is quite difficult to polish the irregular surface of cast RPDs and FPDs. In such cases electropolishing method is preferred • The finished article is suspended in an electrolyte like sulphuric acid solution. Cast metal act As the anode and a copper plate as cathode, small current of 2-5 amp is passed through it for 1-2 hr. • The projecting particles of the surface get detached due to higher potential difference and the surface become smooth and glossy
Glazing- it is not possible to polish ceramic article and composite resins easily. Self glazing and add on glazing technique are used for ceramics the glazed articles have better surface integrity ( no surface cracks). Which improves its flexure strength from 78 mpa to 138 mpa.
Purpose of finishing and polishing Provides 3 benefits of dental care- • Oral health • Oral function • Esthetics
Oral health • A well contoured and polished restoration promotes oral health by resisting the accumulation of food debris and pathogenic bacteria. • This is accomplished through reduction in total surface area and reduced roughness of the restoration. • Smoother surfaces have less retention areas and are easier to maintain in a hygienic state.
Oral function • A highly polished restoration show a very less tarnish and corrosion • Oral function is enhanced with a well polished restoration because food glides more freely over occlusal and embrasure surfaces during mastication and minimizes the wear rates • Rough surfaces will develop high contact stress that can cause the loss of functional and stabilizing contacts between teeth.
Aesthetics • Finishing and polishing gives lusture to visible surface of restoration thus increases the optical property of materials. • A high mirror like polish is preferred in highly visible areas such as the labial surfaces of the maxillary anterior teeth • These surfaces are not subject to high contact stresses and they are easily accessible for cleaning. • Important anatomic features and texture may be added to these area without affecting oral health or function.
Requirements of abrasive instrument • Have the right particle size • Not produce deep scratches, which cannot be removed easily in subsequent steps • Possess sharp edges and breakdown in a manner to expose new sharp edge particles • Not gouge substrate • Be strong enough to not permanently deform under load or high temperatures
Abrasive motion • Abrasive motion can be classified as • Rotary- burs • Planar- disk • reciprocal motion. • ROTARY • In rotary motion, the bur in a high speed hand piece rotates in a clockwise direction.
Planar motion • Are used in disks removes material along a plane. Planar motion should preferably be done in one direction to obtain a smoother surface. • Reciprocal motion • Is produced by two different motions at the same time: part cyclic and part up and down motions. • This is useful to access interproximal arears to remove overhangs, to finish sub-gingival margins without creating ditches, and to create embrasures.
Speeds used in finishing and polishing • Rotary speeds are in 3 basic ranges and are measured in revolutions per min (rpm) • 1. low speed or slow speed: speed below 12,000 rpm provides better tactile sensation and procedure lesser heat when used for cleaning teeth, caries excavation and during polishing procedure • 2. medium speed or intermediate speed: a speed of 12,000-2,00,000 rpm can be used for contouring. • 3. high speed or ultra high speed: speed above 2,00,000 rpm is used for cutting teeth and removing old restorations because these instruments remove tooth structure faster with lesser pressure, vibration and heat generation, increasing patient comfort and operator efficiency. High speeds can be used for gross finishing and countering of the restoration.
Classification of abrasives. ABRASIVE NON BONDED COATED BONDED POLISHING PASTES SINTERED BONDING RESINOID BONDING RUBBER BONDING VITREOUS BONDING DISPERSED IN WATER SOLUBLE MEDIUM
Based on the abrasive grits • Coarse (125-150μm) • Medium coarse (90-100μm) • Medium fine (88-125μm) • Fine (60-74μm) • Super fine (38-44μm) • Abrasive grits – Abrasive grits are derived from materials that have been crushed and passed through a series of mesh screens to obtain different particle size ranges. Sturdevant et al : The art and science of operative dentistry; 5th edition,Elsevier Publication
According to Hardness a) Hard abrasive - Diamond, Silicon carbide. b) Medium abrasive - Pumice, Silicates, Zirconates. c) Soft (Polishing) abrasive - calcites ( Robert g Craig)
According to use a) Finishing abrasive. b) Polishing abrasive. c) Cleansing abrasive. (Craig, Obrien, Powers) Nuckles DB: Status report on rotary diamond instruments, council on dental materials and devices. J Am Dent Assoc 97: 233-235, 1978
Based on availability • Paper / plastic coated • Stainless steel coated strips • Bonded stones • Powder form • Cake form • Rubber impregnated • Paste from
Bonded abrasive • Bonded abrasives consist of abrasive particles that are coated on a binder to form a grinding tool. The binder holds the abrasive during cutting, grinding or polishing. • It should not allow clogging of grinding debris between the particles since the particles will lose their cutting efficiency.
the methods used to bond the abrasives: • Sintering : the particles are fused together to make the whole cutting tool. Sintered abrasives have the strongest bonding and last longer. • Vitreous bonding: the abrasives are first mixed with a glassy or ceramic matrix material, then cold pressed to the shape of the instrument and fired to fuse the abrasives and the binder. • Resin-bonded abrasives: here the abrasives are cold pressed with resins and then the resin is cured. Heat curing of the resin yields a binder with low porosity. • Rubber-bonded abrasive: these are made similar to resin-bonded abrasives; here the abrasives are bonded with rubber and used for final polishing.
Non bonded abrasives • Loose abrasives are polishing pastes contain a fine particle size distribution of either aluminum oxide or diamond particles dispersed in water soluble vehicle, such as glycerin • Aluminum oxide particles pastes are designed for final polishing of composite resin materials • Particles size ranging from 0.3µm to 1µm • Diamond polishing pastes contain loose abrasive diamond particles in size range less than 10µm. • Effective particles size distributions of diamonds polishing pastes size range 0.3µm to and 1µm.
Indicated for final polishing of adjusted porcelain and ceramic materials. • Binders for diamond abrasives are manufactured specially to resist abrasive particles loss • diamond is hardest particle and bonded to metal wheels and been blanks with special heat resistant resins such as polyamides. • Super coarse and fine grades are then plated with nickel
Nickel plating provides improved properties and acts as a heat absorber. • Titanium nitride coatings are given to extend the longitivity. • Finishing diamonds for composites contain particles 40um or less in diameter. • Diamond burs should be used with copious amounts of water spray and rotational speed less than 50,000 rpm.
Disadvantages of abrasive pastes are • 1. Relatively thick and cannot gain access into embrasures. • 2. Paste tend to splatter off the instrument • 3. Heat generation occurs due to insufficient coolant used or when intermittent polishing.
Application Of Nanotechnology In Abrasives • Nanotechnology introduced nano silica abrasives by chemical- mechanical planarization process. • Particle size of nano silica ranges from 10-90nm and is spherical in shape. • It has been reported that polishing with nano-silica provides high polishing and low surface roughness . Also polishing of teeth with nano silica helps in prevention of damage caused by cariogenic bacteria. Roulet JF, Roulet-Mehrens TK: The surface roughness of restorative materials and dental tissues after polishing with prophylaxis and polishing pastes. J Periodontology 1982 Vol 53, 257-266
COATED • Abrasive disks and strips: Are fabricated by securing abrasive particles to flexible backing material (heavy weight paper, metal or nylon) with a suitable adhesive material. • Supplied as disks and finishing strips • Moisture resistant
Mechanism of grinding ABRASIVE TWO BODY WEAR THREE BODY WEAR
TWO BODY WEAR: here the abrasive is bound to the instrument and is used to polish the specimen surface. No other abrasive is used. • Eg; trimming, abrading burs, bonding abrasives, coated abrasive.
THREE BODY WEAR - here the abrasive is free a loose slurry between polishing substrate and surface of the specimen to be polished, • Eg; polishing paste as aluminun oxide, diamond. And tooth paste.
Removal of surface can also be achieved by EROSION Hard particles impacting a substance surface , carried by either a stream of liquid or a stream of air. Eg : Hard particle erosion occurs when SAND BLASTING a surface • Sandblasting - Its used to clean the alloy surface - To achieve both microretentive topography and increased surface area
- Pickling • Pickling is a procedure of heating the discoloured casting in an acid such as 50% hydrochloric acid. The HCL removes the oxide coating as well as any residual investment.
Electropolishing Electrolytes – • 1. Ethylene glycol – 80% Conc Sulphuric acid – 15% Water – 5% • 2. 3parts of Phosphoric acid 1 part of glycerine 1 part of water
