Abrasive and polishing material The finishing and polishing of dental material are important in fabrication of successful restoration and the benefit of it is to: 1- promote oral hygiene by resisting accumulation of food debris and pathogenic bacteria 2- enhance oral function so the food glides through occlusal surface and embrasure of tooth 3- improve esthetic

abrasion Is the process of wear whereby of hard rough surface lick sand paper or hard irregularly shape grooves in soft material and cause grooves from these material to be removed from these surface

Wear: Is the material removal process that can occur whenever the materials slides against each other in dentistry the outer most surface of abrading instrument called abrasive the material to be finished called substrate

Abrasive wear is tow type 1- tow body: wear occur when abrasive particles are firmly attached to the surface of abrasive instrument and no other abrasive abrasive particle are used eg: diamond bur abrading teeth 2- three body wear: is when abrasive particle are free to translate and rotate between tow surface eg: dental prophylaxis past between tooth and rubber cup

Factor affecting rate of abrasive 1- size of abrasive particles: larger size greater abrasion 2- pressure of abrasion against substrate: when the abrasive particles pressed against substrate scratch are deeper and abrasion is more rapid 3- the speed at which abrasive particles travels across the work greater the speed greater would be the abrasion

Types of abrasives A- finishing abrasive : these are hard, coarse abrasive used to develop desired contour and remove off gross irregularities B- polishing abrasive : these are smaller particles size and less hard then abrasive used for finishing , these used for smoothing surfaces that are roughned by finishing abrasive

C- cleaning abrasives These are soft abrasive with small particles and intend to remove softer materials that adhere to enamel and restoration

Types of abrasive according to manufacturing: 1- natural abrasive lick : A- arkansas stone: It is semi translucence, light gray, silicon sedimentary rock It contain microcrystalline quartz Small pieces of this mineral is attached to metal and trued to various shape for fine grinding of tooth enamel and metal alloy

B- Chalk It is mineral form of calcite It is composed of calcium carbonate It is used as milled abrasive past to polish teeth enamel, amalgam

C- pumice: It is produced from volcanic activity Used in polishing teeth enamel, gold foil, amalgam, acrylic resin D- quartz: It is hard colorless , transparent It is used in finishing metal alloy and may be used in grinding enamel of the teeth

2- manufactured abrasive lick: A- silicon carbide: Two types manufactured green form and blue black form both have same physical properties The green form is preferred because substrate is more visible against green color The cutting activity of silicon carbide abrasive is higher Used in cutting metal alloy , ceramic and plastic material

B- aluminum oxide The form usually prepared are 1- white stone: used for contouring enamel and finishing metal and ceramic materials 2- various of aluminum oxide are those include chromium compound addition those obtained in pink and ruby color

C - synthetic diamond: It is used in manufacturing diamond saws, wheel and bur It is used on tooth structure, ceramic materials and resin based composed materials

D - tin oxide: It is fine abrasive used in polishing agent in polishing tooth and metallic restoration in mouth It is mixed with water, alcohol or glycerin to form mild abrasive past

Polishing: Is production of smooth mirror lick surfaces without the use of external film Importance of polishing: 1-Smooth polished surface of teeth and restoration are less respective for bacterial colonization and plaque formation 2-rough surface without polishing are uncomfortable to the patient