General Classes of Materials PDF

# Ammar's Dental Materials ## **Lecture 2** ## **General Classes of Materials** **"Polymers - Composite - Ceramic"** ### **Contents** - **Metallurgy** - **Polymers** - Definition - Types of Bonds - Covalent Bonds - Polar Bonds - Dental Applications of Polymers...

# Ammar's Dental Materials ## **Lecture 2** ## **General Classes of Materials** **"Polymers - Composite - Ceramic"** ### **Contents** - **Metallurgy** - **Polymers** - Definition - Types of Bonds - Covalent Bonds - Polar Bonds - Dental Applications of Polymers - Impression Materials - Composite Filling Materials - Cements - Basic Nature of Polymers - The term "polymer" - Co-polymers - **Composite** - Definition - Bond - Uses - Character - Advantages - Disadvantages - **Ceramics** - Definition - Bond - Uses - Character - Advantages - Disadvantages ### **Polymers** 1. **Definition:** Polymers are materials formed of several large molecules (polymer chain) with high molecular weight. These molecules are formed when smaller molecules named monomers are connected together through covalent bonding. - **Polymers:** Long chain molecules made up pattern of many repeating units connected together. - **Monomer:** The smallest repeating unit in the polymer chain 2. **Types of Bonds:** - **Covalent bonds:** Polymers are solid molecules bonded by a strong primary covalent bonds between the monomers along the polymer chain (inter-atomic or intramolecular). - **Polar Bonds:** (Hydrogen bond): between chains (Inter-molecular). - **NB:** As these polar bonds are weak, they are responsible for 1. low strength, 2. high water sorption. 3. **Dental Applications of Polymers:** - Impression materials (Agar & alginate & Elastomer) - Composite filling materials & Pits, fissure sealant - Cements (Glass Inomer & Zincpolycarboxylate). - Acrylic denture base & artificial teeth. - Soft lining materials 4. **Basic Nature of Polymers:** - The term **polymer** denotes a molecule that is made up of many (poly) parts (mers). - The **mer**-ending represents the simplest repeating units from which the polymer is formed. - **Co-polymers:** is Polymer molecules formed of repeated mixture of monomers units. - **Ex:** Poly-methyl metgacrylate (PMMA) is a polymer having chemical structural units derived from methyl meth-acrylate. ### **Types Of Co-polymers:** It is a polymer formed when a mixture of monomers to modify the properties of polymer. 1. **Random Copolymer:** Two monomers enter in a relatively random manner along the chain. - (M-A-M-M-M-A-A-M-A) 2. **Alternating Copolymer:** Alternating sequence of different monomers. - (M-A-M-A-M-A-M-A-M) 3. **Block Copolymer:** A linear copolymer with one or more long uninterrupted sequences of each polymeric species. - (м-м-м-M-M-M-A-A-A-A-A-A) 4. **Graft Copolymer:** Is a branched copolymer with one monomer chin to which one or more side chains of another monomer are attached to it. ### **Spatial Structure** There are 3 basic types of structures: linear & branched & cross-linked. | Structural units | 1- Linear | 2- Branched | 3- Cross-linked | |---|---|---|---| | Monomers connected to another in a linear & adjacent sequence | Side branch chain connected to the main one | Adjacent linear chain are Joined one to another in a various positions by covalent bond. | Form 3-dimensional network | | Molecules | 1- Poly-ethyle. 2- Nailon | | Glycol diemethacrylate | **NB:** Effect of cross linking 1. Increases the strength. 2. Increases the hardness. 3. Increases the brittleness (extensive cross-linking may lead to brittleness of polymer) 4. Increases the glass transition temperature (Tg). 5. Decrease the water sorption 6. Decrease the solubility (the material show better resistance to organic solvents as alcohol and monomer "crazing resistance"). 7. Decrease the ductility. 8. Spatial structure of the polymer molecules is important in determining the properties of polymer. ### **Molecular Weight** - Polymers have high M.W. - The M.W of the polymers has an effect on the physical properties of polymer. - The higher M.W the higher melting range, stiffer the plastic. ### **Polymerization Process** 1. **Definition:** It is a process consist of the monomers become chemically linked together to form high molecular weight molecules. 2. **Clinical Significance:** - Polymerization is never entirely completed - There remain an amount of monomer incompletely cooked called residual monomer, which is the cause of irritation of the soft tissues of the mouth, and hypersensitivity. - (l.e. 100% polymerization is not present). 3. **Types:** | Addition Polymerization | Condensation Polymerization | |---|---| | **Def:** The reaction between two molecules to form larger molecule **Without** the elimination of a smaller molecule | **Def:** The reaction between two molecules to form larger molecule **with** the elimination of a smaller molecule such as water or alcohol as a by-product. | | **Shrinkage:** Low | **Shrinkage:** High due to by product. | | **Rapidity:** Rapid | **Rapidity:** Slow | | **Types & Example** | 1- **Free-radical:** Acrylic resin & resin composite. 2- **Ring-opening:** Poly-ether I.M & Silorane composite. | 1- **Water:** Poly-Sulphide I.M 2- **Alcohol:** Cond. Silicon I.M | ### **Steps of Polymerization reaction:** (activation ----> Initiation ----> Propagation ----> termination ----> Inhibition) 1. **Activation & Initiation (induction):** Initiator (Benzoyl peroxide or comphorquinone) is activated by activator (Chemical or Light or Heat). - Activated Initiator generates free radical (highly reactive unpaired electron). - Free radical will attack a double bond of monomer and pairs with one of the electrons, leaving the other member of pair free electron to form a new free radical. 2. **Propagation:** Theoretically; the chain reaction continues until all the monomer convert into polymer. 3. **Termination:** Chain process is terminated either by - Direct coupling of two radical chain ends. - By the exchange of a hydrogen atom from one growing chain to another. - **NB:** Actually the reaction is never complete but there are residual monomers remain. ### **Inhibition of polymerization** 1. **Cause:** Any impurity in the monomer will retard the polymerization to prevent further growth. 2. **Example:** 1-hydroquinone, 2- Large amounts of oxygen 3. **Significance:** Inhibitors are added to the monomers to prevent polymerization during Storage and give adequate shelf life. ### **Factors associated with Polymerization:** 1. Evolution of heat as the reaction is strongly exothermic due to breaking of bonds. 2. Reduction in volume (polymerization shrinkage) 3. Residual monomer: the polymerization process is never complete, there is always a varying amount of residual unpolymerized monomers. ### **Thermal behavior of polymer:** **1. Thermoplastic Polymers** | Feature | Details | |---|---| | **Structure** | Linear or branched (No cross linking) | | **Bond bt. chains** | The chains bonded by 2ry bond. | | **Behavior under reheating** | Reversible (physical reaction) Soften by heat & harden by cooling | | **Shaping** | By heating and maintained their shape after cooling. | | **Properties** | 1- Soluble in organic solvent. 2- Less dimensional stability 3- Low abrasion resistance 4- Better flexure & impact strenth | | **Example** | Non-cross linked PMMA (Impression compound) | **2. Thermosetting Polymers** | Feature | Details | |---|---| | **Structure** | Cross-linked and the chains bonded by 1ry covalent bond | | **Bond bt. chains** | The chains bonded by 1ry covalent bond | | **Behavior under reheating** | Irreversible (chemical reaction) Can't remelt and reformed into another shape but undergo decomposition on heating to higher temperature by molding process into a permanent shape, so the final product is chemically different from original substance. | | **Properties** | 1- Insoluble in organic solvent. 2- More dimensional stability 3- High abrasion resistance. | | **Example** | Cross linked PMMA (Impression silicon) | **NB:** Elastomers materials is intermediate behavior of material between thermoplastic, thermosetting ### **Composite** **Definition:** Composites are combination of two or more classes of materials with different properties to produce an intermediate properties between the properties of 2 material **Uses:** - Sealant - Restoration - Veneer - Cement - Core build up - Denture teeth. **Bond:** - Various bonds - Intermediate bt the 2 compositional materials - Moderate hardness, stiffness. - Thermal and electrical insulators. - Barely soluble. - Formable, can be machinable. - Opaque or translucent. **Characteristics** - Esthetic in compare with amalgam - Moderate in stiffness, hardness - High compressive strength. - Ability to control material properties - Light in weight. **Disadvantages:** - Polymerization shrinkage. - Delamination - High cost. - Tendency to discoloration - Water sorptione & have solubility rate ### **Ceramic & Glasses** - Its refractory solid tightly packed inorganic compound (metallic & non-metallic) consist of two phases:- - **Amorphous "Glassy" phase:** (Fledspark which will softened, flow during melting allowing powder particles to coalesce together to form glass matrix which give translucency (esthetics), is amorphous in structure. - **Crystalline" Quartaz" phase:** (<span style="text-decoration: underline;">Al₂O₃</span> & ZrO2): remain unchanged during firing process, acts as a refractory skeleton (1) mechanic properties crack propagation). **Bond:** - **Ionic bond** in Feldspar (main bond) and **Covalent bond** in silica. **Uses:** - Crown, bridges. - Onlay, inlays. - Laminate veneers. **Characteristics:** - High hardness and melting temperature and modulous of elasticity - Low thermal, electrical conductivity (Insulator). - Chemical resistance and inertness (insoluble). - Brittle (has high compressive strength and low tensile strength). **Advantages:** - No discoloration due to ionic nature. - High hardness. - High compressive strength. - Biocompatible & inert to body fluid - Corrosion resistance **Disadvantages:** - Low impact strength - Low tensile strength (brittle material due to ionic nature & minimum sliding). - Susceptibility to notches or micro- cracks. - They can't shear plastically. ### **Composite Polymer** | Feature | Microstructure | Advantages | Disadvantages | |------------|----------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------| | **Metalic** | Crystalline | 1- Strong. 2- Stiff 3- Thermal conductive (with denture base) 4- Oral tissue like appearance 5- No tarnish, corrosion. 6- Light in weight. | 1- Non-esthetics. 2- Fracture. 3- Creep, Sag. 4- Fatigue. 5- Tarnish, corrosion. 6- Thermal, electrical conductive. (with filling) | | **Covalent** | Amorphous | 1- Low cost | 1- Low stiffnes (weak). 2- Low strength. 3- Creep | | **Various** | Matrix, filler...ect| 1- Esthetic in compare with amalgam 2- Moderate in stiffness, hardness 3- High compressive strength 4- Ability to control material properties 5- Light in weight. | 1- Polymerization shrinkage. 2- Delamination 3- High cost. 4- Water sorptione. 5- Tendency to discoloration 6- Still have solubility rate | | **lonic** | Crystal grains, | 1- Have esthetic appearance. 2- High hardness. 3- High compressive strength. 4- Biocompatible. 5- Inert to the body fluid 6. Corrosion resistance | 1- Low impact strength. 2- Low tensile strength (brittle material). 3- Susceptibility to notches or micro-cracks | | | amorphous | | |