NEET MDS Lessons
Dental Materials
COMPOSITE RESINS
Types
- Amount of filler-25% to 65% volume, 45% to 85% weight
- Filler particle size (diameter in microns)
- Macrofill 10 to 100 µm (traditional composites)
- Midi fill- 1 to 10 µm(small particle composites)
- Minifill— 0.l to 1 µm
- Microfill-: 0.01 to 0.1 µm (fine particle composites)
- Hybrid--blend (usually or microfill and midifill or minifill and microfill)
- Polymerization method
- Auto-cured (self-cured)
- Visible light cured
- Dual cured
- Staged cure
- Matrix chemistry
- BIS-GMA type
- Urethane dimethacrylate (UDM or UDMA) type
- TEGDMA-diluent monomer to reduce viscosity
Root canal sealers
Applications
Cementation of silver cone gutta-percha point
Paste filling material
Types
Zinc oxide-eugenol cement types
Noneugenol cement types
Therapeutic cement types
properties
Physical-radiopacity
Chemical-insolubility
Mechanical-flow; tensile strength
Biologic-inertness
Gingival tissue packs
Application-provide temporary displacement of gingival tissues
Composition-slow setting zinc oxide-eugenol cement mixed with cotton twills for texture and strength
Surgical dressings
1.Application-gingival covering after periodontal surgery
2. Composition-modified zinc oxide-eugenol cement (containing tannic, acid. rosin, and various oils)
Orthodontic cements
Application-cementation of orthodontic bands
Composition-zinc phosphate cement
Manipulation
Zinc phosphate types are routinely mixed with cold or frozen mixing slab to extend the working time
Enamel bonding agent types use acid etching for improved bonding
Band, bracket, or cement removal requires special care
WETTABILITY
To minimise the irregularities on the investment & the casting a wetting agent can be used .
FUNCTIONS OF A WETTING AGENT
1 . Reduce contact angle between liquid & wax surface .
2 .Remove any oily film left on wax pattern .
COMPOSITE RESINS
Components
- Filler particles-colloidal silica, crystalline silica (quartz), or silicates of various particle sizes (containing Li, AI, Zn, Yr)
- Matrix-BIS-GMA (or UDMA) with lower molecular weight diluents (e.g., TEGDMA) that correct during polymerization
- Coupling agent- silane that chemically bonds the surfaces of the filter particles to the polymer matrix
Gypsum Products
|
Characteristics |
Plaster |
Stone |
Diestone |
|
Chemical Name |
Beta-Calcium Sulfate hemihydrate |
Alpha-Calcium sulfate hemihydrate |
Alpha-Calcium sulfate hemihydrate |
|
Formula |
CaSO4 – ½ H2O |
CaSO4 – ½ H2O |
CaSO4 – ½ H2O |
|
Uses |
Plaster Models ,Impression Plasters |
Cast Stone, Investment |
Improved Stone, diestone |
|
Water(W) Reaction Water Extra Water Total water Powder (P) W/P Ratio |
18ml 32ml 50ml 100g 0.50 |
18ml 12ml 30ml 100g 0.30 |
18ml 6ml 24ml 100g 0.24 |
ACRYLIC RESINS
Use. Acrylic (unfilled) resins are used as temporary crown material. Temporary crowns are placed to protect the crown preparation and provide patient comfort during the time the permanent crown is being constructed
Physical reaction-cooling causes reversible hardening
Chemical reaction-irreversible reaction during setting