Lecture 18 & 19 - Abrasives and Temporary Crowns Material (Slides)
Lecture 18 & 19 - Abrasives and Temporary Crowns Material (Slides)
Lecture 18 & 19 - Abrasives and Temporary Crowns Material (Slides)
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Hardness is the ability of the material to resist abrasion. If the polished surface is harder than the abrasive, minimum finishing or polishing will occur Moh scale.
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Abrasive particles are classified from coarse to fine depending on their size (grit) measured in microns
Coarse: 100 m and above Medium: 20-100 m Fine: 20-submicron size
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Loose abrasives
Powders and pastes Coarse, medium, fine, superfine grit sizes Applied by brushes, wheels, cups, soft pads The proper grit and dilution should be considered to determine the amount of polishing required
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Bonded abrasives
They are rotary instruments that have an abrasive particle uniformly incorporated in a binder to form the shape of the devise. Comes in many forms, points, disks, cups Usually used for intermediate and initial finishing
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Coated abrasives
Finishing strips and rotary disks The abrasive particles are secured to one side of the disk with an adhesive A mandrel is used to attach the disks on
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3. Silicon carbide
Hard and efficient abrasive with a 910 on the Moh scale Comes as coated disks and bonded rotary devices
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4. Aluminum oxide
Manufactured as white powder Used in:
Bonded and rotary abrasive devices Sandblasting restorations before cementation Also aluminum oxide impregnated rubber wheels are widely used (Burlew wheels)
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5. Sand
Composed of quartz and silica Rates 7 on Moh scale Coated disks and strips
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6. Silicon dioxide: mainly used in prophylaxis pastes and ranks 6-7 on Moh scale 7. Pumice: manufactured as a loose abrasive from volcanic silica and is extremely fine 8. Rouge: iron oxide found in block form run on a rag wheel to polish precious and semiprecious alloy in lab.
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9. Tin oxide: fine abrasive and used to polish enamel and restorations. Is found as powder mixed with water or glycerin. 10. Calcium carbonate: found in prophylaxis paste and dentifrices
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The paste is diluted with a lubricant to control abrasiveness and frictional heat generated, and to prevent hardening of the particles. Supplied as coarse to superfine For polishing, the hardness of the paste should be 1-2 points higher than the polished surface
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The most fine paste should be selected and well lubricated to polish and remove stains and soft deposits
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C. Denture cleansers
Cleansers used by a tooth brush are used to :
Remove stains Plaque accumulation Food debris
Some cleansers are used by soaking dentures in them to loosen debris and deposits
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Denture cleansers
Requirements:
Non toxic Non abrasive Harmless to the components of the denture
Example materials: dilute alkaline or acid preparations Prosthesis with metal parts should not be soaked in acid solutions to prevent corrosion
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Polishing: done by using bonded , coated or loose abrasives (20submicron particle sizes)
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Gold alloys: finished and polished using Burlew wheels followed by rouge on a rag wheel. Porcelain: finishing is done in the lab. Diamond burs are used to make adjustments. Rubber points and wheels designed for porcelain are used. Diamond polishing paste is also used.
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Composite (continue, ): start with fine paste, if not effective use coarser abrasives and pay attention to restoration margins and surface. use light pressure, light sweeping action under water in less than 30 seconds.
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Gold and porcelain: use porcelain polishing paste for porcelain and aluminum oxide for gold if surface of these restorations is rough or has scratches on it Resin cement interface: treated as composite.
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Air abrasion
Uses compressed air and 27-50 m particles of aluminum oxide. Not recommended for stain removal. Mainly used for:
Cast restorations before cementation Repair for porcelain and composite Tooth surface before bonding
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Preprocedure antimicrobial mouthrinses are recommended Protective eye wear for patients High volume suction Sterilize used devices and use dry and fresh pastes.
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Patient education
Effective oral hygiene practice Awareness of what causes staining Regular recall appointments Advise on appropriate abrasive agents that maybe used at home
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Requirements
Non irritant Strong Tooth colored Setting should not yield high temperatures Setting contraction not too high Sufficient working time After seating, quick initial setting (rubbery) for easy removal Quick hardening outside the mouth
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Available materials
Type
Acrylic Acrylic Higher methacrylate Composite Composite
Dispensation method
Powder/liquid Single paste (LC) Powder/liquid Paste/paste Single paste (LC)
Composition
PMMA+ peroxide MMA +activator PMMA+ monomer+ light activator PMMA+ peroxide Isobutylmethacrylate + activator Multi-functional methacrylate + fillers+ initiators + activators Multi-functional methacrylate + fillers+ light activators
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Properties
Setting characteristics:
Composite materials: have a distinct rubbery stage due to multifunctional monomer. Final setting maybe accelerated in hot water Acrylic materials: rubbery stage not as distinct
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Properties
Biocompatibility: monomer is irritant. Solution to protect freshly cut dentine? Mechanical properties: fracture is common in thin areas. Appearance: available in shades
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Reference: Dental materials, clinical applications for dental assistants and dental hygienists. Chapter 9 Applied dental materials. Chapter 26
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