FINISHING POLISHING MATERIALS By Dr K R Hassan

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. • FINISHED & POLISHED RESTORATION: A prosthesis or a direct restoration whose outer surface has been refined to a desired state of finish.

GOALS 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.

BENEFITS OF FINISHING & POLISHING Finished & polished restorations provide 3 major benefits of dental care: Ø Oral health: 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.

Ø Function: Rough surfaces causes development of high-contact stresses which hinder functions & stabilizing contacts b/w the teeth. Ø Aesthetics: Finally, to achieve the goal of patients’ demands of a polished restoration, as aesthetics play a major role in dentistry.

Most finishing & polishing in dentistry are performed by ABRASION: Is the process of wear of a material by another material through scratching, chiseling or other mechanical means.

ABRASIVE Is a hard substance used for grinding, finishing or polishing of a less hard surface, or the material that causes wear is called abrasive. SUBSTRATE The material being abraded is called a substrate. P. S ABRASIVE IS HARDER THAN THE SUBATRATE.

EROSION Is caused by hard particles impacting a substrate surface, carried by a stream of either liquid or air e. g. sandblasting. BULK REDUCTION Is the process of removing excess material by cutting or grinding by a rotary instrument.

GRINDING 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.

FACTORS AFFECTING RATE OF ABRASION The following factors causes changes in the rate of abrasion of an abrasive: v HARDNESS 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. v PARTICLE SIZE The particle size of a material is

Expressed in MICROMETRES. By convention, particles are classified as ü FINE 0 - 10µm ü MEDIUM 10 - 100µm ü COARSE 100 - 1000µm Larger, coarse abrasive particles will abrade a surface more readily than smaller particles , but they tend to leave more coarser scratches in the substrate.

v PARTICLE SHAPE 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. v SPEED & PRESSURE 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.

v LUBRICATION Lubricants are used during abrasion for two purposes: ü to reduce heat buildup ü to wash away debris to prevent clogging but too much lubrication can reduce the abrasion rate by preventing the abrasive from coming in contact with the substrate.

CLASSIFICATION OF ABRASIVES Abrasives used in dentistry can be classified into the following three types: q FINISHING ABRASIVES are generally hard, coarse & used primarily to produce the desired contours of a restoration or tooth preparation. q POLISHING ABRASIVES have finer particle sizes & are less hard than the finishing abrasives, they are used

to smooth surfaces roughened by finishing abrasives. q CLEANSING ABRASIVES are generally soft materials with small particle sizes & are intended to remove softer materials that adhere to the enamel or restorations.

TYPES OF ABRASIVES A variety of abrasives are available but the types listed below are widely used in dentistry. § NATURAL abrasives include Ä ARKANSAS STONE 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.

Ä CHALK Is a white abrasive composed of Ca. CO 3. Chalk is used as a mild abrasive paste to polish tooth enamel, gold foil, amalgam & plastic materials.

Ä CORUNDUM is a white mineral form of Al 2 O 3. It is largely replaced by synthetic Al 2 O 3 in dental applications due to its inferior physical properties. It is used primarily for grinding metal alloys.

Ä DIAMOND 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.

Synthetic diamond abrasives are used far more commonly than natural diamond due to its consistent shape & size & low cost. Diamonds are mostly used on tooth structure, ceramics & resin-based composite materials.

Ä EMERY is a fine-grain grayish black corundum, used for finishing metal alloys & acrylic resin materials.

Ä GARNET 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.

Ä PUMICE is a light gray volcanic rock derivative, used in polishing tooth enamel, gold foil, dental amalgam & acrylic resins.

Ä QUARTZ is a hard, colorless, transparent & most abundant mineral. It is used mainly to finish metal alloys but can be used to grind dental enamel.

Ä SAND 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.

Ä TRIPOLI is derived from a light -weight, friable siliceous 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.

Ä ZIRCONIUM SILICATE or zircon is an offwhite mineral. It is frequently used as a component of dental prophylactic pastes.

Ä CUTTLE 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.

Ä KIESELGUHR 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.

§ SYNTHETIC abrasives include Ä SILICON CARBIDE 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.

It is available as an abrasive in coated discs, & bonded instruments.

Ä ALUMINUM OXIDE Fused aluminum oxide was the second synthetic 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.

Ä ROUGE Fe 2 O 3 is 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.

Ä TIN OXIDE Sn. O 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.

Ä 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.

Abrasive pastes have several disadvantages like > they are relatively thick & so don’t readily gain access to embrasures. > they tend to splatter off of the instruments. > heat is generated when insufficient coolant is used or when an intermittent polishing technique is not used.

DENTIFRICES Dentifrices are available as toothpastes, gels & powder.

They are used for three important functions : ü their abrasive actions provide more efficient removal of debris, plaque & stained pellicle compared with toothbrush alone. ü they polish teeth to provide increased light reflectance & superior aesthetic appearance. the high polish enables teeth to resist accumulation of microorganism & stains

more than rough surfaces. ü finally, dentifrices act as vehicles for delivery of therapeutic agents e. g. fluorides, tartar controlling agent, desensitizing agent etc.

The products advertised as whitening tooth pastes may contain an abrasive agent alone or along with a chemical agent. The former additive acts through a surface stain removal mechanism, whereas the latter acts through a combined action of abrasion & bleaching.

COMPOSITION A typical dentifrice comprises of the following components: Abrasive e. g. Ca. Co 3, 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

Colorants e. g. Food colors purpose appearance Flavoring e. g. Oils of spearmint, peppermint or cinnamon purpose flavor Humectant e. g. Sorbitol, glycerin

purpose maintains moisture content Water e. g. Deionized water purpose suspension agent Binder e. g. Carrageenan purpose thickener, prevents liquid-solid separation

Fluoride e. g. Sodium monofluorophosphate 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

tubules. 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.

TOOTHBBRUSHES 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.

Factors Affecting Dentifrice Abrasiveness: EXTRAORAL FACTORS ≈ Abrasive particle type, size, & quantity in the dentifrice. ≈ Amount of dentifrice used. ≈ Toothbrush type. ≈ Toothbrush method & force applied during brushing.

≈ Toothbrushing frequency & duration. ≈ Patient’s coordination & mental status. INTRAORAL FACTORS ≈ Saliva consistency & quantity. ≈ Xerostomia induced by drugs, gland pathology or radiation therapy.

≈ Dental deposits e. g. pellicle, plaque, calculus their presence, quantity & quality. ≈ Exposure of dental root surfaces. ≈ Presence of restorative materials, dental prostheses, & orthodontic appliances.

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