materials lec 3

Finishing & polishing

Using diminishing series or order of abrasives (from rough to smooth or

fine) on surface to contour then smooth & bring shine to the surface

 Objectives (by the abrasives):

1. Smoothening of rough edges & surfaces: 1prevents accumulation

(plaque, stains & food debris) & 2minimize irritation to soft tissue

2. Esthetics: smoother surface —>  reflect light —>  shiny

3. Remove excess material (high filling)

4. Corrosion & breakdown (esp. in metallic): Smoothening —> plaque & oxidation

Abrasion

Wear process, hard & rough surface (sand-paper disk or hard irregular particles)

Plow grooves into softer materials leading to removal it from grooves

 Abrasive tools or slurries different from dental cutting instruments, HOW?:

 cutting edges or points of abrasive —> irregularly arranged —> each particle

acts on its own —> not as hard or efficient in cutting as cutting instruments

 Affected by materials (abrasives or restoration) physical & mechanical

properties (hardness, strength, thermal conductivity are imp.)

Factors affect the rate of abrasion

A. Different size, irregularity & hardness of abrasive particles:

 larger & coarser particle —>  abrasion

 new abrasives: particles wear during use & ultimately result in smooth surface finish

 very course (pumice): may remove tooth rather than polish restoration (cementum & adjacent amalgam)

 Diamonds particles:

 rate of abrasion depends on size, pressure & speed of rotating device

 most abrasive material (hardest): overcutting of composite or in enamel??

B. Number that contact the surface (esp. in powder abrasives as pumice):

 concentrated abrasive particles on surface —> abrasion

 lubricants (saliva & water): dilute abrasive —> good consistency

C. Speed of hand piece & pressure:

 Higher speed & pressure —>  abrasion

 Excessive pressure can dislodge (remove) abrasive particles &  abrasion

 Lack of proper control over speed & pressure may lead to:

 excessive & uncontrolled removal of material or tooth

 excess heat production

Surface Roughness & Gloss

 Surface Roughness (Ra or Sa):

 measured by profilometer device & in micrometers (how irregular a surface is)

 related to gloss —> affect esthetics —> indication about smoothness of surface

 Gloss (shiny of the surface restoration):

 measure of a reflection of light (GU) on surface of restoration

 zero GU —> totally no reflective surface

 mirror surface: 1000Gu at angle of 60 degrees

 <10 (low gloss), 10-70 (semi-gloss) , >70 (high gloss)

Types of Abrasives

Finishing abrasives: coarse (rough, irregular) & hard to remove excess material

 Polishing abrasives: softer, less hard, finer (smaller) particle size

 Cleansing abrasives: softer, smaller particles to remove soft deposits

Delivery designs of abrasives (A+ B+ C = Finishing, D= polishing & cleansing)

A. B. C. D. Glued on plastic or paper disks then attached to hand piece or strips

Diamond chips attached to steel wheels, disks, cylinders

Bonded by matrix material then molded into shapes & sizes (grinding wheels & stones burs)

Loose powder mixed with water or glycerin (better) to make paste or slurry:

 water evaporates & consistency changes (viscosity), so not preferred

Paper disks more durable & flexible than plastic disks

ABRASIVES USED FOR FINISHING

Aluminum oxide (bauxite)

 Coarse, medium, fine grits

 Paper & plastic discs (Reddish brown)

 Powder (27-50 micrometers) for air abrasion (air pressure to remove stain or create rough surface for bonding)

 Used to make soflex discs

Cuttle (no longer used, fish bone)

 Coarse, medium, fine

 Available now as trade name for fine grade of quartz on paper disk (Beige)

Diamond

 Hardest material (Can abrade any surface)

 Impregnated in binder to make disks & burs

 Used as bonded abrasives & can be reused several times before they wear

 Expensive & not usually disposable (can sterilize)

 Microfine particle diamond paste (powder): polish composite & porcelain

)من الارض Garnet (Mined = from nature

Extra coarse-extra fine grits

 On Paper or plastic disk (Red)

 Composed of oxides of aluminum, iron & silicon

 Used to finish & polish metal alloys & plastics

Sand

Coarse, medium, fine

 On paper or plastic disks (Beige)

 Form of quartz (SiO2)

 Cannot be used interchangeable with cuttle disks since the grit is different

Silicon carbide

Fine, extra fine, double extra fine (# on back - roughness)

 Comes as coated paper & plastic disks (Black)

 Hard & efficient abrasive (second hardest, research-sam

ABRASIVES USED FOR POLISHING & CLEANSING

1-pumice

 Polishing dentures, Prophylactic paste

 Highly siliceous volcanic glass (silica)

Kieselguhr

Polishing agent (May used as filler to add strength & viscosity)

 From remains of aquatic plants (diatoms)

 Diatomaceous earth —> coarse —> not commonly used

Rouge

Fine red powder

 Iron oxide found in block or cake form (NO colored coated disks)

 Impregnated in paper or fabric

 Run on rag or cloth wheel to polish noble, precious & semiprecious alloy i

Tin oxide

white powder abrasive mixed with water, alcohol or glycerin

 Used to polish teeth & metallic restorations

More

Silex: siliceous material - quartz , polishing

Tripoli: mined from porous rock in North Africa, polishing

Zirconium silicate: hard & abrasive, fine particles, polishing

Calcite (calcium carbonate): in prophylactic paste (powder) or in tooth paste

Amalgam

Start with fine stones & abrasive disks & strips

 Final polish: extra-fine silex followed by thin slurry of tin oxide with soft brush

 Fast set amalgam (less than 5 min to set) maybe polished 8-12 min after they set using

creamy paste of extra-fine silex or tin oxide & water on slow speed hand piece

 Finishing & polishing with water coolant, Why?:  thermal

conductivity —>  heat —> conduct heat to pulp & irritatio

Composites & compomers

Diamond stones on 12-blade carbide burs

 Abrasive disks or white stone burs depending on surface to be polished

 Final finishing: by Fine & microfine diamonds & diamond polishing pastes & disks

 The Best finish is achieved by mylar strip

Resin-modified & Conventional GICs

Finish & polish: abrasive disks (same one that is used in composite)

 Cannot be finished as smoothly as composites

 Conventional GIC produces roughest surface due to larger glass particle size, > filler

 RM- GIC is better compared to conventional: because it has resin (LC) - easier finish & polish

Denture base

Acrylic finishing bur: removal of sharp edges

 Rag wheel & felt cone with pumice: finish tongue side of upper denture

 Smaller wheels with pumice: lower denture

 Rag wheel with tripoli or tin oxide & water: polish the non tissue surface

 Beware of overheating & protect teeth from pumice to avoid their abrasion

 Infection control is important when polishing pt prosthesis

Prophylactic paste (Prophy paste)

Uses

Remove external stains, pellicle, oral debris, material alba

 Polish surface of teeth esp. after scaling (remove of plaque & calculus)

 Done before fluoride gel application to make enamel more reactive to fluoride

 Some paste contain fluoride preparations (Some studies argue their effectiveness in caries prevention, not sure)

 Over use can affect materials with low hardness values (abrade exposed dentine or cementum, esp. at cervical part)

Composition

Type of abrasive may differ among different products (pumice,

calcium sodium phosphosilicate & zirconium silicate)

 Properties:

 Pumice & quartz produce greater abrasion (coarse pumice = most abrasive)

 Zirconium is effective but influenced by particle distribution in different products

 Perlite (volcanic glass): wears with use & produce finer finish with use

Dentifrices

A. Tooth powders:

 Contain abrasive to clean tooth surface & prevent plaque accumulation

 Flavoring oil

 Sweetening agent (saccharine)

 Surface active detergent (wetting & cleansing agent) for better wettability of enamel

B. Toothpaste: contains all of the above and:

 Water, Color agent

 Humectant to prevent dehydration (sorbitol OR glycerin)

 Binder (sodium alginate with carboxymethyl cellulose)

 Preservative to prolong shelf life

 Fluoride content:

 Sodium fluoride, stannous fluoride, sodium monofluorophoshate

 Soluble tetrasodium or tetrapotassium pyrophosphate (supra-gingival calculus formation)

 Abrasives used:

o Pumice

o Calcium carbonate, silica, anhydrous dibasic calcium: claim to whiten &

brighten teeth (actually have only cleansing effect rather than whitening)

Denture cleansers

Used by tooth brush to remove stains & deposits

 Some (solution) used by soaking dentures in them to loosen debris & deposits

 Or professional re-polishing can be done by dentist

 Types: 1Abrasive creams,

2Alkaline hypochlorite,

3Alkaline perborate (oxidizing ability, 7-11.5 pH)

 Ideal requirements: 1Easy to remove & stable when stored,

2dissolve

(organic & inorganic),

3Non toxic & Harmless (to denture & to user)

Temporary crown & bridge resins

General outlines of the procedure

1. Rubber Impression is taken (prior preparation), then the tooth prepared

2. 4. Temporary crown material mixed & placed in impression or plastic crown then reseated

3. Initial setting —> impression & material is taken out

Adjustments & finishing is made then crown cemented

Requirements

 Non irritant, Strong , Tooth colored

 Low heat & Low contraction upon setting

 Sufficient WT & quick hardening outside mouth

 After seating, quick initial setting (rubbery) for easy removal

Available materials

Type Dispensation

method

Composition

 Composite compared to Acrylic:

 less shrink, less heat, more esthetic

 easy to recognize initial setting stage

 Automixing for acrylic (mixing gun):

 removes porosities so rubbery stage is

more distinct & homogeneous mixture

 Shrinkage & temp rise is highest for PMMA (Acrylic)

Acrylic powder/Liquid  PMMA + peroxide (initiator)

 MMA + activator

Acrylic Single paste

(LC)

PMMA + monomer +

light activator

Higher

methacrylate

(less irritant )

powder/Liquid  PMMA + peroxide

 Isobutylmethacrylate +

activator

Composite Paste/ paste Multi-functional methacrylate +

fillers + initiators + activators

Properties

Composite Single paste

(LC)

Multi-functional methacrylate +

fillers + light activators

 Setting characteristics:

 Exothermic

 Composite:

 Distinct initial rubbery stage due to multifunctional monomer

 Final setting maybe accelerated in hot water

 Acrylic: rubbery stage not as distinct

 Undergo shrinkage

 Biocompatibility: monomer (MMA) is irritant —> used

liner or varnish (solution to protect freshly cut dentine)

 Mechanical properties: fracture is common in thin areas

 Appearance: available in shades