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FINISHING & POLISHING MATERIALS. By Dr K.R.Hassan Head Science of Dental Materials Department R.I.H.S Islamabad. FINISHING: Process of removing surface defects/scratches. POLISHING: Polishing is the process of providing luster or gloss on a material surface.
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Head Science of Dental Materials Department
A prosthesis or a direct restoration whose outer surface has been refined to a desired state of finish.
The goals of finishing & polishing procedures are to obtain the desired anatomy, proper occlusion & the reduction of roughness, gouges & scratches that are produced during the making of the prosthesis.
Finished & polished restorations provide 3 major benefits of dental care:
A well contoured & polished restoration resists the accumulation of food debris & pathogens.
Tarnish & corrosion activity of the restorations is reduced.
Polished restoration surfaces minimizes the wear rates of opposing & adjacent teeth.
Rough surfaces causes development of high-contact stresses which hinder functions & stabilizing contacts b/w the teeth.
Finally, to achieve the goal of patients’ demands of a polished restoration, as aesthetics play a major role in dentistry.
Is the process of wear of a material by another material through scratching, chiseling or other mechanical means.
Is a hard substance used for grinding, finishing or polishing of a less hard surface, or the material that causes wear is called abrasive.
The material being abraded is called a substrate.
P.S ABRASIVE IS HARDER THAN THE SUBATRATE.
Is caused by hard particles impacting a substrate surface, carried by a stream of either liquid or air e.g. sandblasting.
Is the process of removing excess material by cutting or grinding by a rotary instrument.
Is the process of removing material by abrasion with relatively coarse particles. CONTOURING
Is the process of producing a desired anatomical form by cutting or grinding.
The following factors causes changes in the rate of abrasion of an abrasive:
Hardness of an abrasive is directly proportional to the rate of its abrasion i.e. the harder the abrasive than the substrate the more abrasion will be produced.
The particle size of a material is
By convention, particles are classified as
Larger, coarse abrasive particles will abrade a surface more readily than smaller particles , but they tend to leave more coarser scratches in the substrate.
Sharp, irregular shaped particles will abrade a surface more rapidly than will rounded particles having dull cutting angles. However the former will produce deeper scratches than later.
Both speed & pressure are directly proportional to the rate of abrasion.
At higher speed greater friction is produced, which tends to produce higher temperatures. Similarly, greater pressure causes higher temperatures & possibly patient discomfort.
Lubricants are used during abrasion for two purposes:
but too much lubrication can reduce the abrasion rate by preventing the abrasive from coming in contact with the substrate.
Abrasives used in dentistry can be classified into the following three types:
are generally hard, coarse & used primarily to produce the desired contours of a restoration or tooth preparation.
have finer particle sizes & are less hard than the finishing abrasives, they are used
are generally soft materials with small particle sizes & are intended to remove softer materials that adhere to the enamel or restorations.
A variety of abrasives are available but the types listed below are widely used in dentistry.
is a semi translucent, light gray sedimentary rock mined in Arkansas. It is dense, hard & contains uniformly textured microcrystalline quartz. It is used for fine grinding of tooth enamel & metal alloys.
Is a white abrasive composed of CaCO3. Chalk is used as a mild abrasive paste to polish tooth enamel, gold foil, amalgam & plastic materials.
is a white mineral form of Al2O3. It is largely replaced by synthetic Al2O3 in dental
applications due to its inferior physical properties.
It is used primarily for grinding metal alloys.
is a transparent, colorless mineral composed of carbon. It is the hardest known substance & is called a super abrasive because of its ability to abrade any other known substance.
Diamonds are mostly used on tooth structure, ceramics & resin-based composite materials.
is a fine-grain grayish black corundum, used for finishing metal alloys & acrylic resin materials.
consists of a group of different minerals that have the same physical properties & crystalline forms. Minerals included in this group are silicates of Al, Co, Fe, Mg & Mn. The type of garnet used in dentistry is usually dark red. It is used in grinding metal alloys & acrylic resin materials.
is a light gray volcanic rock derivative, used in polishing tooth enamel, gold foil, dental amalgam & acrylic resins.
is a hard, colorless, transparent & most abundant mineral. It is used mainly to finish metal alloys but can be used to grind dental enamel.
is a mixture of mineral particles, predominantly composed of silica. The particles represent a mixture of colors, making it distinct in appearance. They are coated onto paper disks for grinding of metal alloys & acrylic resin materials.
is derived from a light-weight, friablesiliceous sedimentary rock. Tripoli can be white, gray, pink, red or yellow. The gray & red types are mostly used in dentistry. It is used for polishing metal alloys & some acrylic resin materials.
or zircon is an off-white mineral. It is frequently used as a component of dental prophylactic pastes.
commonly referred to as cuttlefish or cuttle bone, is a white calcareous powder made from the internal shell of a Mediterranean marine mollusk. It is available as coated abrasive & used for polishing metal margins & dental amalgam restorations.
is composed of the remains of minute aquatic plants known as diatoms. Its coarser form is called diatomaceous earth & is used as a filler in many dental materials, such as hydrocolloid impression materials.
It was the first of the synthetic abrasives to be produced. It is available in green & blue-black types, having equivalent physical properties. Silicon carbide is extremely hard & brittle & results in highly efficient cutting of materials, including metal alloys, ceramics & acrylic resins.
Fused aluminum oxide was the secondsynthetic abrasive to be developed. Aluminum oxide (alumina) is much harder than corundum (natural alumina) due to its purity. Several grain sizes are available & has largely replaced emery for several abrasive uses. Alumina is largely used in dentistry to make bonded, coated & air propelled grit abrasives. It is popular for adjusting dental enamel & for finishing metal alloys, resin-based composites & ceramic materials.
Fe2O3is the fine, red abrasive component of rouge. Like tripoli, rouge is blended with various soft binders into a cake form. It is used to polish high noble metal alloys.
SnO is an extremely fine abrasive used extensively as a polishing agent for polishing teeth & metallic restorations. It is mixed with water, alcohol or glycerin to form a mildly abrasive pastes.
The most commonly used abrasive pastes contain either alumina or diamond particles.
Alumina pastes should be used with a rotary instrument & increasing amounts of water.
Diamond abrasive pastes are used in dry conditions.
Dentifrices are available as toothpastes, gels & powder.
the high polish enables teeth to resist accumulation of microorganism & stains
The former additive acts through a surface stain removal mechanism, whereas the latter acts through a combined action of abrasion & bleaching.
A typical dentifrice comprises of the following components:
Abrasive e.g. CaCo3, hydrated alumina/ silica
soda bicarb or a mixture of these.
purpose removal of plaque/stain & polish
Detergent e.g. Sodium lauryl sulfate
purpose aids in debris removal
Flavoring e.g. Oils of spearmint, peppermint or
Humectant e.g. Sorbitol, glycerin
Water e.g. Deionized water
purpose suspension agent
Binder e.g. Carrageenan
purpose thickener, prevents liquid-solid
purpose prevents dental caries
Tartar control e.g. Disodium pyrophosphate
purpose inhibits formation of calculus
above gingival margin
Desensitizing e.g. Potassium nitrate
purpose promotes occlusion of dentinal
The abrasive concentrations in paste & gel dentifrices are 50 – 75% lower than those of powder dentifrices. So powders should be used more sparingly & with greater caution to avoid excessive dentinal abrasion & pulpal sensitivity.
Toothbrush bristle stiffness alone have no effect on abrasion of hard dental tissues. However, with the use of a dentifrice, there is evidence that brush bristles bend more readily & bring more abrasive particles into contact with the tooth structure. This interaction produces more effective abrasion & cleaning action.
or radiation therapy.
their presence, quantity & quality.
prostheses, & orthodontic appliances.