DENT2040
What are the types of denture base materials?
Type 1: heat-processed (polymer/powder/liquid OR plastic cake) Type 2: auto-polymerised (polymer/powder/liquid OR polymer powder/liquid pour type) Type 3: thermoplastic blank or powder Type 4: light-activated Type 5: microwave-cured
What are the types of gypsum?
Type 1: impression plaster □ Compressive strength: 4-8MPa □ Expansion: 0-0.15% □ Uses: impressions only Type 2: model plaster □ Low to moderate strength □ Compressive strength: 9MPa □ Expansion: 0-0.3% □ Uses: articulation Type 3: dental stone □ Compressive strength: 20MPa □ Expansion: 0-0.2% □ Uses: edentulous casts, investments for dentures Type 4: dental stone (die stone) □ High strength □ Low expansion □ Compressive strength: 35MPa □ Expansion: 0-0.15% □ Uses: crown and bridge Type 5: dental stone (die stone) □ High strength □ High expansion □ Compressive strength: >35MPa □ Expansion: 0.16-0.3% □ Accounts for the casting shrinkage in base metals vs noble metal alloys
What are the 3 patterns of enamel etching?
Type 1: intraprismatic (within the prism) Type 2: interprismatic (between prisms) Type 3: combination (both type 1 and type 2)
In general, what should be considered when selecting a suitable restorative material?
Type and location of lesion Is aesthetics a concern? What material would suit functionally? What forces and stresses are relevant? Would chemical or micromechanical bonding be desirable? Is fluoride release necessary? Are there any treatment options beside restoring? How often will it need to be replaced? Cost
What is impression wax (dental wax)?
Used to obtain impressions of the oral structures Include corrective impression waxes (to fill small defects in ZOE and occlusal-indicator waxes) Used in the fluid wax technique for altered cast impressions
How is dimensional change relevant to dental waxes?
Waxes expand when heated and contract when cooled Coefficient of thermal expansion and contraction of waxes are greater than for any other material used in dentistry If heated too far above melting range or heated unevenly -> expansion above acceptable standards will result □ Especially important for pattern waxes (for crown and bridge) □ Smallest changes in temperature can cause a significant change in dimension to make the pattern inaccurate
What are dental waxes?
Waxes: thermoplastic materials used in many aspects of dentistry in both the clinic and laboratory Normally in a solid state at room temperature Melt without decomposition to form mobile liquids Revert back again as the temperature increases
What is the setting reaction for gypsum?
When the plaster or stone is mixed with water it forms a hard substance □ Manufacturing process reverses □ Hemihydrate converts to dihydrate □ Crystals of gypsum intermesh and become entangled with each other ® Gives strength and rigidity □ Reaction releases heat (3900 cal/gm mole) Powder mixes with water to form a thick slurry □ Hemihydrate is slightly soluble -> only a small amount can dissolve □ Hemihydrate that dissolves absorbs water and forms calcium sulphate dehydrate (gypsum) Results in 2 phase suspension □ Hemihydrate particles suspended in saturated dihydrate aqueous solution □ Aqueous phase is supersaturated -> nuclear centres appear □ Gypsum particles crystallise and grow Centres for nucleation form around impurities, particles of gypsum, or on the rough surface of undissolved hemihydrate particles □ Dehydrate particles precipitate □ Calcium and sulphate ions move from the aqueous solution □ -> allows more hemihydrate particles to dissolve
What is casting wax (dental wax)?
i.e. crown and bridge wax Made of paraffin, ceresin, beeswax and resins Supplied in sheets of various thicknesses Uses: □ Single-tooth indirect restorations □ Fixed bridges □ Casting of metal portions of a partial denture
What is utility wax (dental wax)?
i.e. orthodontic or periphery wax Supplied in: various forms depending on use Composed of beeswax, petrolatum, other soft waxes Uses: □ Extend the borders of an impression tray □ Cover brackets in orthodontic treatment
How does glass ionomer bond to mineralised tooth structure?
mineralised tooth structure + polyalkenoic acid -> release calcium and phosphate ions from hydroxyapatite Polyacrylic polymers bind This chemical union and further ion exchange binds the 2 structures together Acid + powder (base) -> salt + water No water should be added or removed while setting
What is the setting reaction for type 1 and type 2 resin denture bases?
powder (polymer) + liquid (monomer) + heat (type 1) OR chemical (type 2) activation -> polymerisation -> polymethylmethacrylate (PMA)
What are the properties of glass ionomer cement as it relates to pulp capping?
§ Adhesion through ion exchange □ Effective seal □ Microleakage reduced or nil § Properties: □ Antibacterial □ Biocompatible □ Cariostatic □ Stimulates remineralisation □ Low solubility □ Similar compressive strength to dentine □ Flexible § Minimum RDT 0.5mm
What are the ideal properties of pulp capping materials?
§ Bactericidal/bacteriostatic § Mildly irritant to pulp - stimulate tertiary dentine bridge formation § Adhesive § Resistant to being dissolved over time § Strong and easily applied in a thin layer § Able to infiltrate ionically into remaining dentine § Biocompatible
What is the process of pulp inflammation?
§ Initial damage □ Pulp protective mechanisms ® Seal avenues of direct pulp exposure ® Reactionary dentine forms with time (final step) □ Inflammation □ Outflow of dentinal fluid □ Dentinal tubules blocked ® Temporarily by protein molecules ® Sclerotic dentine (mineralisation) □ Reactionary dentine formation § Chronic damage □ If unrelenting inflow of microbial stimulants: ® Chronic inflammation ® Pulp eventually dies § Spread of pulpal inflammation □ Following odontoblast injury: ® Localised zone of dentinal tubules affected ® Only associated portion of pulp is inflamed ® Greater # of dentinal tubules involved = greater odontoblast injury = larger volume of pulp tissue inflamed □ If inflammation is not contained: ® New odontoblasts formed from progenitor cells (UMC) in pulp? ® Chronic inflammation may coexist with micro-abscesses ® OR gross PMNL accumulation and partial necrosis
What are the properties of mineral trioxide aggregate (MTA) as it relates to pulp capping? What is it used for?
§ Tricalcium silicate, dicalcium silicate and tricalcium aluminate w/ bismuth oxide for opacity § pH is 10.2 after mixing, 12.5 after curing § Low solubility § Low compression resistance § Can be used for: □ Retrograde fillings in endodontic surgery □ Direct pulp capping □ Repair of perforation/stripping □ Apexification Internal resorption
What are the properties of calcium hydroxide as it relates to pulp capping?
§ Very high pH (up to 12) § Highly toxic to bacteria § Causes necrosis to living tissue § Use in very small quantities only § Seal with glass-ionomer - washes out
What is vital pulp therapy? What is the rationale? What are the procedures?
• Vital pulp therapy: procedures designed to preserve or regenerate the pulp-dentine complex of compromised teeth ○ Rationale: § Remove as much of the infected hard or soft tissue as possible § Restore with a bacteria-tight restoration to preserve the health of residual pulp tissue leaving it free of inflammation ○ Procedures: § Indirect pulp capping □ For non-exposed pulps only § Direct pulp capping § Partial pulpotomy § Pulpotomy § Regenerative pulp therapy § Regenerative tooth replacement ○ Choice of procedure based on depth and extent of pulpal injury and burden of recovery
What are bases? What are their functions and disadvantages?
○ Bases: material placed in a thick layer on the floor of a cavity preparation § Placed beneath permanent restorations § Provides mechanical, thermal and chemical pulp protection § Functions: □ Reduces post-op sensitivity □ Protects pulp from thermal, chemical, bacterial stimuli □ Induces formation of tertiary dentine and pathologic sclerotic dentine § Disadvantages: □ Cannot withstand marginal infiltration □ Cement can dissolve partially or entirely over time □ May be displaced during amalgam compaction
What is indirect pulp capping? How is it done (technique)? What materials are used? What is the prognosis? What are the indications and contraindications?
○ Caries is excavated before anticipated pulp exposure § Avoids additional pulpal trauma due to mechanical pulp exposure § Allows pulp to heal and lay down reparative dentine ○ Technique: § Gain access to the lesion § Remove infected layer of dentine § Retain affected layer of dentine § Seal lesion with bioactive restorative material § Leave for minimum of 6 weeks § THEN make clinical decision to retain some or remove entirely § Permanent (non-temporary) restoration should be placed over the indirect pulp cap to create an adequate seal § Follow-up pulp testing and radiographic examination ○ Materials used: § Choice is immaterial □ Calcium hydroxide □ Glass ionomer cements □ MTA □ Other materials § BUT must seal carious dentine from oral fluids □ Nutrient deprivation - inhibits further bacterial metabolism, pulp is able to survive □ Prevents new bacteria from entering and infecting the pulp § Use of an antibacterial material (e.g. calcium hydroxide) may eliminate remaining bacteria ○ Prognosis: § High success rates if cases are carefully chosen □ 83-100% up to 3 years § Very few long-term studies verifying success beyond 3 years § Must use caution and long-term follow-up with radiographs and pulp testing ○ Indications: § Pulp is normal □ Not irreversibly inflamed □ No history of pulpalgia (pain) □ No signs of pulpitis □ Normal radiographic appearance § Removal of thin layer of affected dentine (not infected) may result in pulpal exposure ○ Contraindications: § Gross remaining caries § Presence of clinical symptoms
What is a partial pulpotomy? When is it indicated? What is the prognosis?
○ Extended version of direct pulp capping following traumatic pulp exposure ○ Similar procedure to direct pulp capping BUT remove 1.5-2mm of pulp ○ Indicated for traumatic injuries to otherwise healthy teeth ○ Prognosis: § High success rate if proper case selection § 91-96% reported success up to 5 years
What are the direct restorative materials and what are their properties relating to pulp protection?
○ Glass ionomer cement (GIC) § Initial low pH § Well-buffered by dentine § Seals tubules § Prevents microleakage ○ Composite § Releases chemical toxins § Adheres well to enamel § Short-term adhesion to dentine ○ Dental amalgam § Very low toxicity to pulp § Marginal seal through corrosion products ○ Luting agents - must seal tubules before luting § Zinc phosphate § Zinc polycarboxylate § Glass ionomer § Resin cements
What are the indications for direct pulp capping? What is the technique? What materials are used? What factors affect the success rate? When is it not indicated and why?
○ Indications: § Used for small breaches/exposures □ Smaller than tip of William's periodontal probe § Iatrogenic rather than carious in nature □ Direct pulp capping is followed by attempt to maintain pulpal vitality ○ Technique: § Remove infected dentine § Apply capping materials directly on top of pulp (in contact with pulp) § Wait for pulp to secrete dentine over time § THEN restore ○ Materials used: § Calcium hydroxide § Adhesive systems § MTA ○ Factors affecting success rate: § Patient age (younger) § State of pulp (previous insults) § Size of exposure (≤0.5mm) § Type of exposure (carious or iatrogenic) § Isolation during exposure (rubber dam best) § Material used ○ Not indicated during carious exposures due to: § Unpredictability § High long-term failure rate Possible compromise to conventional RCT at a later stage
How are pulp diseases clinically diagnosed?
○ Poor correlation of histology with clinical signs/symptoms § Pulp is asymptomatic in 50% of cases ○ May be radiographic evidence of coronal pulp inflammation § Usually in young patients § Occurs even with vital healthy pulp tissue in the roots § Visible periapical change ○ Pulp tests can be used to distinguish between vital and completely necrotic pulps ONLY ○ Signs and symptoms: § Reversible pulpitis: □ Increased cold sensitivity ® Subsides when stimulus is removed □ Positive response to pulp test § Irreversible pulpitis: □ Prolonged sensitivity to heat or cold □ Positive response to pulp test § Necrosis: □ No response to pulp test § Acute apical periodontitis: □ Pain with chewing or percussion □ Swelling and tenderness to palpation in nearby gums § Chronic apical periodontitis: □ Usually asymptomatic □ Diagnosed via radiograph □ Negative response to pulp and percussion test
What is a full pulpotomy? What are the indications and contraindications? What are the materials used? What are the disadvantages? What is the prognosis?
○ Removal of the entire coronal pulp to the level of the root canal orifices ○ Indicated in symptomless immature permanent teeth with open apices in an attempt to allow root formation and apical closure ○ Contraindications: § Irreversible pulpitis □ Clinical symptoms § Pulpal necrosis § Inability to control haemorrhage at the level of amputation ○ Materials used: § Calcium hydroxide □ Standard material of choice § MTA □ Used more often ○ Disadvantages: § Inability to perform pulp testing § Obliteration of canals may prevent RCT at a later stage and rule out the provision of a post space ○ Prognosis: § Accurate diagnosis is essential for success § 91% success rate with no radiographical or clinical signs of pathology existed
How are glass ionomers placed for restorations?
(1) Carious defect removed from the tooth (2) Preparation treated with cavity/dentine conditioner if a manufacturer instructs (3) Glass ionomer is mixed, injected and contoured using a cervical matrix and protected from moisture for 24 hours
How are composite resins placed for restorations?
(1) Carious defect removed from the tooth (2) Treat with an appropriate enamel and dentine adhesive (after etching if done separately) (3) Composite material is inserted, contoured and polished
What are the benefits/advantages of restoring with composite resin?
1. High aesthetics, tooth-coloured, wide range of shades and translucency 2. Easy to achieve strong union between composite resin and etched enamel 3. High degree of polishability 4. Wide variety of viscosities and formulations 5. Cheaper than lab-based indirect aesthetic restoratives 6. Single sitting completion possible
What are the challenges/disadvantages of restoring with composite resin?
1. High degree of technique sensitivity and difficult to recreate anatomy 2. Difficult and less predictable bonding to dentine 3. Polymerisation shrinkage and possibility of void formation 4. No biological activity i.e. release of fluoride 5. High wear rate
What are the challenges/disadvantages of restoring with glass ionomers?
1. Relatively weak compared to composite resin and amalgam 2. Water-based material and will not last in dry mouths 3. Poor physical properties if not protected from water during maturation + Tooth coloured BUT not a great variety of translucencies/shades
What are the benefits/advantages of restoring with glass ionomers?
1. Simple to handle and relatively tolerant to placement technique 2. Chemically bonds to both enamel and dentine 3. Fluoride-releasing and plaque-inhibiting 4. Variety of dispensing mechanisms and powder/liquid ratio may be adjusted in hand-mixed GICs to produce varying consistencies and working times 5. Thermal diffusivity and thermal expansion is very similar to dentine
What is the wear rate of composite resin like?
250 microm average limiting wear over 5 years Worn or old composite can easily be repaired by bonding a new layer over the top
What are dental casts? What are they used for?
3D reproductions of the teeth and surrounding soft tissue of a patient's maxillary and mandibular arches ○ Uses: § Diagnosis for a fixed or removable prosthetic § Diagnosis for orthodontic treatment § Visual presentation of dental treatment § Making of custom trays § Making of orthodontic appliances § Making of provisional coverage § Making of mouth guards and splints
What are the components of dental waxes?
ALWAYS a mixture of various components May be natural (mineral/plant/animal) or synthetic waxes □ Mineral waxes: paraffin, ceresin, litene □ Plant waxes: carnauba, candela, Japan wax □ Animal waxes: beeswax □ Synthetic waxes: polyethylene, polyoxyethylene glycol Gums, fats, fatty acids, oils and various resins may be added to modify the properties Pigments may be added to give its distinctive colour Component waxes: usually organic molecules with high molecular weights □ Long chains allow flexibility and stickiness at room temperature Properties depend on amount of various waxes and molecular structure of organic molecules in the mixtures □ e.g. hardness, melting range, flow
What are accelerators and retarders for gypsum?
Accelerators and retarders can manipulate gypsum setting time Accelerators: increase time and speed of mixing □ Agents: 2% sodium chloride, 3.4% sodium sulfate, >3% potassium sulfate, powdered gypsum □ Theory: increased nuclei centres achieved or rate of solubility increased Retarders: slow reaction and elongate setting time □ Agents: citrates, acetates, borates □ Theory: coat hemihydrate particles and prevent from going into solution
What is the purpose of etching enamel?
Acid etching transforms the smooth enamel surface to an irregular surface Adhesive added to etched enamel is able to penetrate into enamel aided by capillary action Polymerises and interlocks with enamel surface Forms resin tags (macro - interprism, micro - intraprism)
What are the components of normal glass ionomer cement?
Acid: polyalkeonic acids (co-polymers of polyacrylic, itaconic and tartaric acids) - tartaric acid modulates setting times and process Powder: calcium fluoroalumino silicate glass - finely powdered
What are the differences between gypsum products?
All are chemically identical Differences in properties are related to physical differences in the particles Plaster of Paris (β-hemihydrate): larger crystal size, irregular shape, loosely packed, higher W/P ratio, low strength, higher porosity Artificial stone: (α-hemihydrate): smaller crystal size, prismatic shape, closely packed, lower W/P ratio, high strength, lower porosity, dense
What are the factors that affect pulp viability for restoration placement?
Amount of remaining dentine thickness (if too thin, vulnerable to further pulp damage) - related to size and depth of the cavity Viable odontoblasts Integrity of the neuroinflammatory and immune responses
What are the parts of a dental model/cast?
Anatomic portion: created from the alginate impression Art portion: forms base of the model
How well does composite resin bond to enamel, dentine and cementum?
Bonds best to etched enamel Dentine bonding is more difficult and technique sensitive Cementum bonding is poorest
What are the types of dental waxes? List them.
Boxing wax Utility wax Sticky wax Inlay wax Casting wax Baseplate wax Bite registration wax Impression wax
How is gypsum powder manufactured?
Calcining: process of gypsum converting to plaster of Paris and artificial stone Gypsum is ground to a fine powder of particle size □ -> plaster of Paris (β-hemihydrate): gypsum is subjected to heat in an open vat □ -> artificial stone (α-hemihydrate): gypsum is processed by steam heat under pressure Reaction: calcium sulfate dihydrate converts to calcium sulfate hemihydrate by removing 75% of the water molecules
What is calcium phosphate deposition as a pulp protective mechanism?
Calcium phosphate crystals deposited deep within the dentinal tubules Response to slowly advancing caries Mechanism not known but possibly mediated by odontoblasts
What mechanical loading forces are present in the cervical, anterior and posterior areas?
Cervical: tooth wear lesions Anterior: incisal, palatal, labial, cervical Posterior: occlusal, buccal, palatal
How does glass ionomer adhere to tooth structure?
Chemical adhesion to mineralised structure Chemical adhesion to organic (less mineralised) structure Possible additional mechanisms - micromechanical? (some penetration into dentine tubules if no smear layer but negligible role)
What are the direct adhesive restorative materials?
Composite resins Glass ionomer Resin modified glass ionomer Polyacid modified resins
Which bond strength is the strongest of the direct restorative materials?
Composites (strongest) > resin-modified GIC > glass ionomers (weakest)
What are some protective measures for the pulp that can be done during restoration placement?
Control of bacterial microleakage Liner placement Control of chemical toxicity Recovery drugs placed during restoration
Which areas of the dentine are most permeable?
Deep dentin areas over the pulp horns are much more permeable than superficial dentine
What are the challenges of bonding to dentine with composites?
Dentine is a living tissue and can't be etched for as long as enamel (15secs NOT 30secs) - has odontoblastic extensions Dentine has more water content and less mineral content (50%) than enamel Stress as the resin-dentine interface - especially if composite shrinks during polymerisation
What are dentures? What are the components?
Denture base - Part of the denture that rests on the soft tissues - Pink coloured - Individualised to each patient to avoid irritation Plastic teeth - Made of polymers - Can be purchased directly from the manufacturer
What should be considered when choosing a material to use to restore an occlusal lesion?
Depth of the lesion - proximity to pulp in the floor Extent of lesion/prep - proximity to pulp near cusp slopes Occlusal factors Dentine permeability Status of pulp (pain history, sensitivity, vitality) Caries risk Isolation
List some of the causes of pulp injury.
Direct insults - Trauma (mechanical, thermal, chemical) - Dental caries (bacteria and toxins) - Restoration microleakage) Indirect trauma through the dentine-pulp complex Interference with the blood supply
Why do dental waxes have a melting range?
Don't melt at a single temperature - have a melting range □ Starts to soften and then readily flow Due to mixture of different components which have different melting points □ Components with lower melting points soften first □ As temperature increases, more components soften ® -> viscosity decreases □ Wax eventually flows (becomes a liquid)
What is the apatite content (%) of enamel, dentine and cementum?
Enamel: 95% Dentine: 70% Cementum: 50%
Why do you condition and not etch for GIC?
Etch will dissolve superficial tooth structure - removes calcium and phosphate ions from the enamel/dentine that the GIC bonds to Condition will: - Remove the smear layer - Increase wettability of the tooth surface by decreasing the surface tension - Maintain plugging of the dentine tubules and reduce contamination of the dentine surface by dentinal fluid
What is the process of bonding composite resin to dentine?
Etch with 37% phosphoric acid for 15 seconds on enamel and then on dentine for another 15 seconds (total 30s on enamel, 15s on dentine) Wash etch away and dry enamel (but don't overdry! collagen fibrils may collapse) This removes the smear layer and plugs Apply primer (to replace water between the collagen fibrils) Apply the resin in increments and light cure
What factors affect the clinical success of glass ionomer restorations?
Excessive moisture - degrades physical properties -> protect from excess moisture contamination for 24 hours Layer of bond resin should be placed over the GIC restoration after initial hardening Water-contaminated GIC appears frosty, loses translucency and becomes porous
What are the properties of the matrix phase of composite resin?
Generally most transiently fluid during the manipulation or placement of materials Tends to have the least desirable properties in the mixture
How are cold cure resins different to heat cure resins?
Generally used for repair or relining of denture bases rather than making a completely new denture Very short working time (but same steps of setting)
What are some ways the pulp can be damaged during restoration placement and cavity preparation?
Generation of heat (from drilling with insufficient water spray) Overdrying of dentine (causes fluid to move rapidly out of the tubules with the potential for odontoblast cell bodies to be aspirated into the dentinal tubules resulting in cell death)
What is inlay wax (dental wax)?
Hard, brittle wax made from paraffin wax (40-60%), carnauba wax, resin, beeswax Uses: create a pattern of the indirect restoration on a model (for a crown or partial coverage crown) Classification: according to flow □ Type A: hard-inlay wax □ Type B: medium-inlay wax □ Type C: soft-inlay wax Desirable properties: □ Uniformity: no graininess or lumps when softened, all components should blend □ Colour: contrast to the die to allow for carving of the margins □ No flakes: when bent, should not flake or appear rough □ Precision: should not move during carving or pull away from the die □ Completely burn: should be no remaining residue during burn out □ Dimensionally stable: must maintain its state
How does the power/liquid ratio effect the denture base? What is the ideal ratio?
High ratio: reduced polymerisation shrinkage Too high: dry mix results in granular porosity Ideal ratio is 5:2 by weight which gives 5-6% shrinkage
What are the stages of embryonic tooth development?
Initiation stage Bud stage Cap stage (dental papilla forms pulp and dentine, enamel organ forms enamel) Bell stage (histodifferentiation and morphodifferentiation)
What are the factors affecting clinical success of composite restorations?
Isolation from contamination (oral fluids, other contaminants) - use rubber dam or cotton rolls -> otherwise use amalgam If tooth substrate is being adhered to (enamel/dentine/cementum) - organic vs inorganic content - tubules, water, permeability - ability to be roughened or etched to create micro-porosities for better retention - living tissue? Age changes of enamel - permeability, water content decreases - fluoridation - colour darkens (organic matter, sclerosis/staining of underlying dentine) - wear facets in areas of occlusal contact Polymerisation shrinkage (C factor) - higher C-factor (higher # of surfaces bonding to) -> greater potential for bond disruption Overdrying Depth of cure
How should plaster and stone be stored?
Keep containers tightly closed Humidity >70% causes partial conversion of hemihydrate to dihydrate Greatly increases speed of setting reaction
Why is aesthetics an issue when restoring?
Linked to patient concerns Location - esp. anterior. Is it visible? Patient occupation e.g. models Shade selection
What is baseplate wax (dental wax)?
Made of paraffin or ceresin with beeswax and carnauba wax Hard and brittle at room temperature Pink colour Supplied in sheets Three types: □ Type I: softer wax used for denture construction □ Type II: medium-hardness wax used in moderate climates □ Type III: harder wax for use in tropical climates Uses: making wax patterns of complete and partial dentures, orthodontic appliances, occlusal rims for recording maxillo-mandibular (jaw) relationships Composition: □ Paraffin wax (70-80%) - or ceresin □ Beeswax (12%) □ Carnuaba wax (2.5%) □ Resins (3%) □ Synthetic waxes (2.5%) Melting range: 44-62°C
How does glass ionomer adhere to organic content?
May bind to organic collagen component of dentine Through hydrogen bonds or metallic ion bridging between the carboxylic acid end of the polyacid and collagen
What types of biomaterials are available for restorations? Which materials are used for direct restorations?
Metals and alloys Ceramics Polymers Composites Direct restorations: Dental amalgam Temporary restorative materials Composite resins Glass ionomer Resin-modified glass ionomer Polyacid modified resins
How does reparative dentine present in mild, moderate and chronic injury?
Mild injury: - Most odontoblasts survive - Regular reparative dentine - Normal tubules - Continuation of main body of dentine - At pulp-dentine interface near damaged area Moderate injury: - Odontoblasts may die - Reparative hard tissue (atubular, poorly mineralised or defects) - Depends on nature and differentiation of cells from cell-rich pulp zone Chronic injury: - Diffuse calcification may occur due to activation, differentiation and calcific matrix secretion by mesenchymally-derived cells
What is the ideal powder/water ratio for gypsum products?
Model plaster: 100g / 45-50mL Dental stone: 100g / 30-32mL High strength stone: 100g / 19-24mL
What is the effect of having a different balance between the resin and filler components of composite resin?
More resin: easy modulation, quick polyermisation More filler: rigidity, hardness, lower coefficient of thermal expansion, less setting contraction, optical properties
What is gypsum?
Naturally obtained from gypsum rock and composed mainly of calcium sulfate dihydrate Dihydrate: 2 parts water, 1 part compound Calcium sulfate dihydrate: 2 parts water, 1 part calcium sulfate CaSO4 ∙ 0.5 H2O ↔ CaSO4 ∙ 2 H2O
What are the histological zones of pulp?
Odontoblast layer Cell-free zone Cell-rich zone Pulp core
How does the coupling agent complete its function in composite resin?
One end reactive to polymer One end reactive to filler material
What are liners (in restorations)?
Only used if pulp is not exposed ○ Liners: material placed in a thin layer over exposed dentine in a cavity preparation § Suspension/dispersion of zinc oxide, calcium hydroxide or resin-modified glass ionomer § Usually medicative § Provides chemical protection, sedation and stimulation
What is sclerotic dentine? When does it occur?
Peritubular dentine formed to narrow the dentinal tubules Dense, calcific material Laid down in an active, odontoblastic, metabolic process May occur: - Beneath advancing carious lesions - Dentine exposed through abrasion/attrition/erosion - Slowly as a natural part of ageing
What are the ideal properties of denture base materials?
Physical: - Match appearance of natural tissues - Glass transition temperature 32-70degC - Dimensional stability - Low specific gravity - High thermal conductivity - Radiopaque Mechanical: - High elastic limit and modulus of elasticity in thin dentures - High flexural strength - Good fatigue life and limit - High impact strength - Abrasion resistance Chemically inert Biological: - Non-toxic and non-irritant - Impermeable to oral fluids - Non-conducive to bacterial and fungal growth Other: - Inexpensive - Long shelf life - Easy to manipulate - Easy to repair
What are the most common problems that occur with denture base resins?
Porosity Distortion Crazing Fracture Discolouration
What are the components of the liquid and powder of type 1 and type 2 denture base materials?
Powder: - Polymer: polymethylmethacrylate beads - Initiator: 0.5% peroxide - Pigments Liquid: - Monomer: methylmethacrylate - Cross-linking agent: 10% ethyleneglycoldimethacrylate - Inhibitor: hydroquinone - Activator (self-cure only): 1% N N'-dimethyl-p-toluidine
What is salivary precipitation as a pulp protective mechanism? When is it unlikely to occur?
Precipitation of salivary calcium and phosphate Occludes dentinal tubules exposed to saliva Densensitises hypersensitive dentine Unlikely in: - Active caries and acid erosion (due to low pH preventing remineralisation) - Active abrasion or attrition
What is the trimming and finishing process of a dental model?
Prepare the model by soaking in water for 5 minutes Trim the maxillary model: □ Trim base □ Trim posterior area □ Trim sides □ Trim heel cuts □ Trim angled portion from canine to canine Trim the mandibular model: □ Trim posterior portion □ Trim base □ Trim lateral cuts to match maxillary lateral cuts □ Trim back and heel cuts □ Trim from canine to canine in a rounded form
What should you consider when selecting a material to restore a cervical lesion?
Proximity to gingival margin (bleeding of inflamed tissues, cementum, thin enamel and dentine) Moisture control - bleeding, saliva, GCF Proximity of pulp Aesthetics Caries risk
How does the pulp respond to injury?
Pulpal inflammation (pulpitis) Chronic inflammation: - Usually low grade - Increased T cells - Symptomless - Depends on bacteria involved Acute inflammation: - Foci of inflammation can develop within chronically inflamed tissue - Strong pain associated Reversible pulpitis: - Pulp actively responds to an irritant - Reverses if irritant is removed - Pulp changes after each incident (becomes less vascular, less cellular, more fibrous) Irreversible pulpitis: - Pulp is irreversibly damaged and cannot recover - Pulp may die painlessly over time OR may cause necrosis and pain
What are the challenges when restoring a cervical lesion?
Relatively easy to place (buccal aspect has good access and direct vision) Longevity is an issue Undergoes unique processes and forces - caries, abrasion, abfraction from tooth flexure, erosion What caused the lesion is likely to cause the restoration to be lost
What are the challenges when restoring an occlusal lesion?
Relatively easy to place - on occlusal aspect w/ good access and direct vision or easy indirect vision No missing wall that needs to be replaced Occlusal loading makes longevity an issue Placement of margins - marginal ditching, niches for plaque accumulation Creep and future ditching if restored with metals Flash
What are the components of composite resin? Why are they included?
Resin (Bis-GMA or UDMA, + TEGDMA): polymerisation, ability to shape Fillers (quartz, glasses, ceramics, graded filling): strength Coupling agent (organo-silanes): couples resin and filler Photoinitiator: able to 'command cure' Tints: gives range of colours
What are the differences between glass ionomer and modified glass ionomers?
Resin-modified GIC: more GIC, a little resin - Reduced bonding and fluoride release due to resin - More aesthetic Polyacid-modified resin: more composite resin, a little polyacid from GIC - Aesthetics not as good as pure composite - Provides fluoride release
How were cervical lesions traditionally prepared for restoration? Why is this unsuitable?
Restore with amalgam and cast metals which naturally adhere to tooth structure Needs retention form - more tooth structure is removed with burs and high speed handpieces Cervical lesions: Already lost tooth structure and needs to be preserved Amalgam is not aesthetic Amalgams are brittle - cervical areas may have tooth flexure, so are lost or fractured often if restored with amalgam
What are the steps in setting of resins for denture bases?
Sandy -> sticky -> stringy -> dough -> rubbery -> hard Doughing time: sticky -> stringy Working time: dough -> rubbery
List the protective mechanisms of the pulp.
Sclerotic dentine Calcium phosphate deposition Salivary precipitation Reparative dentine
Do gypsum products expanded when set?
Setting reaction associated with expansion of 0.3-0.6% If this occurs in the confines of an impression tray -> significant reduction in accuracy
What is the smear layer? Why is it removed to bond to GIC?
Smear layer: salivary pellicle (salivary glycoproteins and proteoglycans deposited on the surface of teeth generally within 30s) and debris from cavity preparation Dentine is conditioned with 10% polyacrylic acid to remove the smear layer Requirement of some pure GICs Must be removed to ensure a clean surface that GICs can chemically bind to
What is bite registration wax (dental wax)?
Soft and very similar to casting waxes Soften under warm water Patient is instructed to bite down, leaving an imprint of the teeth in the wax Includes beauty wax, aluwax
What is boxing wax (dental wax)?
Soft, pliable wax with smooth, shiny appearance Supplied in: long narrow strips 1-1.5 inches wide and 12-18 inches long Uses: form a wall or box around an impression when pouring
What is sticky wax (dental wax)?
Supplied in: bright yellow sticks or blocks Components: □ Yellow beeswax(60%) □ Resin (17%) □ Gum dammar (17%) Very brittle and adhesive at room temperature but becomes very tacky when heated □ Does not flow at room temperature □ Melting range: 60-65°C Uses: □ Creation of a wax pattern □ Joining of acrylic resin □ Glue for putting together fractured prosthesis or holding a set of dental models together
