Dental Materials

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  • Topic: Chemistry, Dentures, Restorative dentistry
  • Pages : 10 (2057 words )
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  • Published : December 22, 2011
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DENTAL • MATERIALS
* Study of physical and chemical properties of the metallic and non-metallic materials used in dentistry

OBJECTIVES
1. In order to know the basic physical and chemical properties as they are related to its manipulation by the dentist. 2. To bridge the gap between the knowledge obtained in the basic courses like chemistry, physics and its relation…

Physical properties: hardness, strength, brittleness
Chemical properties: composition, ingredients

* Most of dental materials used are solids, liquids, and colloids

CLASSIFICATION OF SOLID
1. Crystalline – exhibits rigidity (hard), atoms are arranged in a regular space lattice 2. Semi-crystalline – hard but not as hard as crystalline, arranged in regular lattice, not as rigid as crystalline 3. Amorphous – no definite melting and freezing point (impression compounds/materials) thermoplastic material – melts in hot, forms in cold

SCOPE OF THE STUDY OF DENTAL MATERIALS
Restorative dentistry
Operative Dentistry – caries fillings. Erosion, attrition & abrasion (reduction of tooth tissues) acidic foods cause tooth erosion Prosthodontics
1. Fixed Partial Denture (FPD)
2. Removable Partial Denture (RPD)
3. Complete Denture (CD)
4. Maxillofacial – accident cases

MATERIALS THAT ARE NOT INCLUDED IN THE STUDY
1. Anesthesia
2. Medicament
3. Materials used in surgery
4. Materials used in orthodontics

SPACE LATTICE
* Any arrangement of atoms in space, so that atoms are situated similarly to every atom 1. Simple Cubic – cube with atoms at the corners

2. Face Centered – simple cubic but there are additional atoms at each face (6 faces) 3. Body Centered – on atom at symmetrical center of simple cubic 4. Closed-packed Hexagonal – two or more cubic space lattice

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GYPSUM
* Mineral mined, CaSO4 • 2H2O
* Dental plaster, Dental stone, Dental investment, Impression plaster

CALCINATION
* Heating of gypsum. To dry off or remove water to change it to (CaSO4)2H2O; alpha or beta hemihydrates – final product of calcining gypsum
CaSO4 • 2H2O (heat) (CaSO4)2H2O

Beta hemihydrate – dental plaster
Alpha hemihydrate – dental stone

CONVERSION OF GYPSUM PRODUCTS TO B & A

B-Hemihydrate (dental plaster)
* Calcine gypsum at 110 – 120°C temp
* Heating is done in a kettle/rotary kiln (open air)

A-Hemihydrate (dental stone)
* At a temperature 120 - 130°C, not in an open air but in an autoclave, under steam pressure * Calcine it to 120 - 130°C but with 30% calcium chloride * Also 120 - 130°C but with the presence of 0.05% sodium succinate

BetaAlpha
1. Calcination process:110 - 120°C120 - 130°C
2. Particle size:biggersmaller
3. Amount of waterto be added:moreless
4. Strength/hardness:weakerstronger
5. Appearance of mixture:porousdense/compact

PROPERTIES OF DENTAL PLASTER
1. Water/powder Ratio – quotient obtained when the volume of water is divided by the weight of the plaster a. Dental plaster: 0.45 – 0.55
b. Dental Stone III: 0.30 – 0.35
c. Dental Stone IV: 0.20 – 0.25 (needs less amount of water) d. Dental Investment: none
e. Impression Plaster:0.6 – 0.7 (used in impression making; more water) W:P = 25/50, 30/50, 35/50 (mL / g)
2. Setting Time – time elapsing from the beginning of mixing until the material hardens. There is evolution of heat f. Initial Setting Time – the moment when there is evolution of heat. When the mixture starts to harden g. Final Setting Time – disappearance of the heat, totally hardens

Test to Determine Setting Time
1) Penetration Test: a needle should penetrate into the said mask a. Gillmore needles – small & big needle
Small needle: weighs ¼ lb; determines Initial ST
Big needle: 1 lb; determines...
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