————————————————- 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 . 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 ———————————————— 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. 5 – 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 ) Penetration Test: a needle should penetrate into the said mask a. Gillmore needles – small & big needle Small needle: weighs ? lb; determines Initial ST Big needle: 1 lb; determines Final ST The moment the small needle does not penetrate, you are in initial setting time. The moment the big needle does not penetrate, you are in final setting time b. Vicat needle – only takes the initial setting time. The Initial ST is important to the dentist so that he can start working into the cast 2) Loss of gloss – harden (starts to gloss); disappearance of gloss marks the use of Gilmore and vicat needle
Factors Affecting Setting Time (UNDER THE CONTROL OF THE DENTIST) 1) Water-Powder Ratio a. High – more water added b. Low – less amount of water Setting Time a. Low – decrease setting time (shorten, faster, hasten) b. High – increase setting time (prolong, slower) 2) Mixing – done for 1 minute Overmixing – destroying the crystals (known as spherullites) c. Slow – increase ST d. Fast – decrease ST (more friction) 3) Temperature – environment of doing the mixing e. Cold – increase ST f. Hot – decrease ST 4) Chemical Modifiers – addition of accelerator & retarder
Accelerator – decrease ST; NaCl (not common) Retarder – increase ST; borax g. K2SO4 – common accelerator (potassium sulfate); all sulfates h. Borax – common retarder; citrates, acetate, alum, oil, gel (UNDER THE CONTROL OF THE MANUFACTURER) 1) Fineness – refers to particle size (bigger – more H2O; smaller – less H2O) 2) Incomplete Calcination – presence of impurities increases ST 95 – 100°C – mixture of hemihydrates and remaining dihydrates impurities not converted 100 – 110°C 3. Setting Expansion – no change in set mask/appearance. Due to the outward thrust of the needles during growth.
The contact of particles during the setting if dental plaster Factors 1) Water/powder Ratio a. High – crystals are scattered – lesser SE – weaker b. Low – crystals are closer – greater SE – stronger 2) Mixing c. Fast – greater d. Slow – lesser 3) Chemical Modifiers – always an obstruction to the contact of particles e. Accelerator f. Retarder (both lesser SE – weaker) 4) Particle Size g. Small – greater – needs less amount of water h. Big – lesser – more water – less contact of particle – weaker 5) Impurities – lesser setting expansion Dihydrates – set mask on the plaster spatula.
Just the powder. Goes back to dihydrate Types 1) Normal SE – the plaster was allowed to set in (air dry). Less contact of particles – lesser SE – study models 2) Hygroscopic SE – allowed to set under water – continuous, still wet – greater in magnitude – important during the method of casting of metal – refractory models USES OF DENTAL PLASTER 1. Medical Use – plaster cast (fractures of leg) 2. Commercial Use – statues, figurines 3. Dental Use – mounting of the cast to the articulator, for investing of the wax for processing dentures, for models (study models)
Dental Stone – used as working cast or master cast. Model for constructing dentures Dental Investment – used for refractory model, used in casting Impression – negative copy of the tissue Cast – positive copy of the impression DENTAL STONE * Made up of a-hemihydrate with 2-3% chemical modifiers * Balanced dental stone – a-hemidydrate with equal amt of chemical modifiers According to Particle Size 1. Type III (Class 1) – hydrocal, bigger 2. Type IV (Class 2) – densite or improved stone; smaller Setting TimeSetting ExpansionStrength 1. Type IIIincrease (more H2O) lesserweaker . Type IVdecrees (less H2O) greaterstronger According to Use in Dentistry 1. Hydrocal – construction of cast; touches the soft tissues of the mouth; for Full/Partial Denture 2. Densite – construction of die; with prepared cavity – cemented Dental Plaster – study model Dental Stone – master model Dental Investment SIGNS OF DETERIORATION OF GYPSUM 1. Sets very fast 2. Does not set at all HOW TO PREVENT DETERIORATION * Place in a closed, metal container * Can be plastic, as long as it is closed ————————————————-
IMPRESSION • MATERIALS * Negative copy of soft tissue * Positive copy – cast & die IMPRESSION MATERIALS| FORMS| 1. Impression Plaster| Powder| 2. Impression Compound| Cakes of different design (modeling plastic compound)| 3. Zinc Oxide Eugenol Paste (ZnO)| Paste (tube)| 4. Reversible Hydrocolloid| Stick of agar – agar| 5. Irreversible Hydrocolloid| Powder – alginate| 6. Elastomeric Impression Material| Paste – rubber| CLASSIFICATION OF IMPRESSION MATERIALS According to Manner of Hardening a. Chemical Reaction Powder (Impression plaster, Irregular hydrocolloid)
Paste (ZnO, Elastomeric impression material) b. Thermoplastic / Physical Change Impression compound and Reversible hydrocolloid * Thermoplastic material – softens when heated and solidifies when cooled * Agar – liquefies when boiled, hardens when cooled Use in Dentistry a. Edentulous mouth only (rigid impression materials) b. Both edentulous and non-edentulous (flexible impression materials) State and Condition a. Rigid (impression plaster, impression compound, ZnO) b. Flexible (hydrocolloid-reversible & irreversible, elastomeric impression material) IMPRESSION PLASTER Good for edentulous mouth. Powder form. W:P = 0. 6 (30/50) – 0. 7 (35/50) * Corrective lining material – used in final impression * W:P – more water because it is rigid due to the dental plaster Matrix – main ingredient / essential components (Dental plaster) Core – other ingredients a. Potato Starch – swells in hot water, to render the impression plaster soluble in hot water, for easy removal b. Chemical Modifiers – addition of accelerator (K2SO4) and retarders (citrate and acetates) Purpose: * To regulate the setting time * To control setting expansion c.
Flavoring Ingredient – to make it palatable Normal Setting Time: 2 – 3 minutes d. Coloring Ingredient – to identify the distinction of cast material from impression materials. Disadvantages of Impression Plaster * Does not take areas with undercuts * Evolves heat (because of dental plaster) Advantage * Takes all the minute details (small markings) needed for construction of denture Manipulation (How to Handle) 1. Mix for 1 minute 2. Put in non-perforated tray (individual tray – constructed from resin) 3. Wait for setting in the mouth 15 – 20 minutes: without chemical modifiers – 3 minutes: with chemical modifiers 4. Needs separating medium (because both the cast material and the impression material used is a gypsum product) Varnish/ / lacquer, detergent soap 5. Usually colored pink 6. After 30 – 60 minutes: Removal of cast from impression material Immerse in hot/warm water. Impression plaster will swell because of the potato starch. IMPRESSION COMPOUND I. Type 1 (True Compound) Cakes; used for primary impression II. Type 2 (Tray Compound) Tray – used to carry another impression material to take the final or secondary impression; like an individual tray. Another impression’ – corrective lining material which is used in final impression. This includes all impression materials except impression compound because it is already used for primary impression. Uses 1. To take the primary impression of edentulous mouth Primary impression – study model Final impression – working / master model 2. To take the impression of single tooth with prepared cavity. E. g. jacket crown Use copper band to provide a little allowance for a single tooth; usu. cervical line Composition (Ingredients) of Impression Compound 1.
Matrix – waxes (beeswax) and resin (coumarone indene resin? ) 2. Core a. French chalk – filler (increases strength of compound); very important b. Oleic acid – lowers melting point c. Stearic acid – plasticizer (not too sticky to the touch of hand) d. Palmitic acid – hardener e. Coloring ingredient Requisites of Fillers 1. Filler must be smaller in particle size – stronger compound 2. Intermolecular bonding between filler and matrix 3. Uniformly distributed throughout the matrix Properties of Impression Compound 1. Flow – it can be beneficial and a source of error a.
Beneficial – (compound is in the soft condition) it takes all the necessary landmarks needed in the construction of dentures b. Source of Error – (compound is in the soft condition) when the compound is taken prematurely from the mouth. There is continuous flow of the compound. 2. Thermal property c. Thermal Conductivity (linear coefficient) * Low – because the material does not soften and harden at the same time * It is the transfer of heat to a material * Enamel & dentin – good thermal insulators to protect the pulp * Metallic substances – thermal conductivity; malleable objects d.
Thermal Expansion * Change in length of the material when the temperature is raised / lowered 1°C Requisites Expected From an Impression Compound 1. Should not contain poisonous and irritating ingredients. (any kind of impression materials should also be non-toxic) 2. Glossiness / smoothness after it has been passed through a flame (non-glossiness means that it is deteriorated) 3. Soft – take all the necessary landmarks needed in the construction of dentures 4. It should soften uniformly to avoid injury to the mouth tissues 5. It has to be dimensionally stable at all times 6.
After the compound has solidified, it should withstand trimming with a sharp knife to avoid flaking, chipping and fracture of the compound. Trim only the thick part * Tray boxing – one way of constructing a cast Manipulation (How to Handle) 1. Immerse the impression compound in more water (warm, not boiling to avoid ‘flow’) 2. Knead it with your fingers under warm water 3. Non-perforated tray (wet with water); so that the impression compound will not stick to the tray 4. Flatten in the tray 5. Trimming Two Ways of constructing Impression Compound 1. Boxing 2. Direct PouringHydrocolloids 3. Rubber Former