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126 Cards in this Set
- Front
- Back
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The primary objective of restorative dentistry
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to replace diseased or lost tooth structure with materials that restore function and esthetics
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Properties of Dental Materials
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Biocompatibility
Dimensional Changes Thermal Conductivity Electrical Properties Solubility and Sorption Wettability Mechanical Properties |
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Dimensional change is
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percent shrinkage or expansion of a material as a result of a chemical reaction
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Types of stress
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Tensile (away from each other)
Compressive (towards each other) Shear (lateral) |
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Electrical properties (3)
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1. Galvanism: electrical currents in the mouth due to different metals in the mouth that the patient can feel
2. Corrosion: Dissolution of metals in the mouth Is the result of galvanic currents 3. Tarnish: Surface reaction of metals in the mouth from components in saliva or foods resulting in corrosion |
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mechanical properties of dental materials
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-Biting force
-Stress -Strain -Elongation and compression -Resilience and toughness -Hardness |
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biting force of person with natural teeth
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77kg
patients with restorations can experience decrease of 50 to 80% |
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stress-strain curve
with elastic modulus |
The Elastic Modulus is the slope of the stress-strain curve in the initial straight-line portion.
at the upper right end (top of Y or stress axis) of curve is the fracture point |
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Proportional Limit
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Is the stress on the stress-strain curve when it ceases to be linear or vertical
the lowest point on the y axis (stress) |
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Yield Strength
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Is the stress at some arbitrarily selected value of permanent strain (each material has a different value)
-where strain begins to increase just above proportional on Y axis |
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Ultimate Strength
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is the stress at which the fracture occurs on stress strain curve (upper limit on Y axis)
(fracture point) |
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Elongation and Compression
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The amount of deformation that a material can resist before rupture is reported
The percent of elongation and compression are measures of ductility and malleability, respectively Elongation = Ductility Compression = Malleability |
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Resilience
Toughness |
Energy required to deform a material permanently
Energy necessary to fracture a material (if stress strain curve has smaller slope it is much tougher) |
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hardness
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measured in knopp hardness
-how deep the diamond goes in |
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Strain-Time Curves
Materials in which the strain is dependent on the time the load is maintained |
t0 = Compressive load is applied
0-A = Rapid increase in strain A-B = Strain gradually increase t1 = Compressive load is removed B-C = Rapid decrease in strain C-D = Gradual decrease in strain t2 = Permanent strain remained D-E = Magnitude of strain |
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The shorter the time and the less force applied to the impression means what?
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the lower the permanent strain and the more accurate the impression
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the amount of water in milliliters added to 100 g of powder
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By convention is expressed as a fraction, such as:
45/100 or 0.45 45 mL of water are added to 100 g of powder |
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Excess water mixed with model plaster does what
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1. Increases setting time
2. Reduces strength 3. Reduces expansion 4. Reduces hardness |
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If one adds too much water to a gypsum material when it is mixed, one gets a material that has
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a softer surface
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The setting reaction of a plaster material is characterized by
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the release of heat (exothermic)
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what is gypsum made of?
what is the reaction? |
Calcium sulfate dihydrate
CaSO4·½H2O + 1½ H2O ---> CaSO4·2H2O + heat |
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Increasing the water-to-powder ratio of a gypsum mix will cause the expansion of gypsum to
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decrease
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Aside from disinfection, an impression material should be rinsed thoroughly before pouring
WHY? |
Colloids on the impression will make the gypsum weak
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If one gypsum model (A) has a compressive strength twice that of model B, which will have the higher surface hardness or abrasion resistance?
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A
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Upon removal of an alginate impression from its poured model, a dentist discovers several fractured teeth on the model. What are possible causes, assuming that the dentist used the correct removal technique?
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The impression may have been removed before it reached full strength (45 to 60 minutes is required).
the impression may have been removed after the alginate dried out and became inflexible |
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model
cast dies |
-to look at structure
-for fabrications of restorations (implants,dentures) -obtained from master cast |
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An assistant fails to add surfactant to a silicone impression before pouring in high-strength die stone. What is a likely problem with the cast?
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bubbles
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to much water with gypsum will cause what
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reduced strength, increased porosity,
increased setting time, decreased expansion, and decreased hardness. The mix will likely be so soupy |
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short setting time of alginate could be a result of what
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too little water
hot water too much manipulation |
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An assistant pours an alginate impression with an epoxy material. What will you predict about the quality of the cast and why?
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A poor quality cast will probably result with many bubbles and voids because epoxy (a water-hating material) is not compatible with alginate (a water-based material).
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qualities of gypsum
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1. Accuracy
2. Dimensional stability 3. Ability to produce fine details (margins) 4. Strength/resistance to abrasion 5. Ease adaptation to the impression 6. Color 7. Safety |
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type 1 gypsum (impression plaster) properties
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-setting time 2.5 to 5 min
-low expansion .15 -lowest compression strength -detail is ok |
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type 2 gypsum (model palster)
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-setting time based on package
-expansion is .30 -compression strength is low -detail is ok |
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type 3 gypsum (dental stone)
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-expansion is .20
-compression is moderate -detail is good |
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type 4 and 5 gypsum
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4. high strentgh/low expansion
5. high strength/high expansion only difference is the expansion is more on high expansion, compression is the same |
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physical form of gypsum is
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crystal
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Accelerators of gypsum
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chemicals that increase the rate of setting:
- Potassium Sulfate - Terra alba (set gypsum particles) |
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retarders of gypsum
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chemicals that decrease the rate of setting:
- Borax |
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Properties of Gypsum Materials
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Setting Time
Reproduction of Detail Strength Hardness and Abrasion Resistance Dimensional Accuracy |
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warm water does what to gypsum and working time over 37C
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it extends working time becasue heat is byproduct of reaction
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Investment
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Stone like material that can resist the high temperatures and forces experienced during burnout and casting
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Investment – Types
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1. Gypsum bonded
Resist temperatures less than 1200°c, ideal for gold Type II, III and IV good for stronger metals 2. Phosphate-bonded investments Used for higher-melting alloys, they are stronger, ideal for PFM and RPD frameworks |
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investment composition
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Binders (gypsum)
Holds investment together Refractory material (form of silica SiO2) Resists the heat of burnout and casting |
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composite resin composition
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-resin matrix
-inorganic filler particles -coupling agent -activator system -optical modifier |
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resin matrix of composites info
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bifunctional monomer called
-BIS-GMA |
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inorganic filler particles of composites info
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-improves physical, chemical, and mechanical strength
-reduces shrinkage -reduces thermal expansion |
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composite coupling agent info
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provides bonding of filler and resin matrix
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composites method of polymerization
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-light cure
-chemical cure -dual cure |
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composite particle sizes
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-macro
-small -microfill (for really smooth surfaces) great polishability -hybrid (stronger than micro but does not polish as well) |
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what is the purpose of acid etching for composites
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it decalcifies a thin outer layer of enamel
-creates mechanical undercuts -cleans surface |
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composite bonding agents objectives
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-minimize tooth prep
-reduce leakage -reinforce tooth structure -sealing |
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characteristics of dentin bonding agents
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-bond to dentin just as well as enamel
-very quick to get max. bond -biocompatable -prevents microleakage -stable in oral cavity -easy to use |
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indications (when would you use) bonding agents
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-direct composites
-indirect composites and veneers -ceramic restorations that wil be resin bonded -amalgam -post and core restorations -to densensitize dentin |
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composition of amalgam
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metal alloy and mercury
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metals in amalgam
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Silver (Ag) 40-60 wt%
Tin (Sn) 27-30 wt% Cooper (Cu) 6- 30 wt% Zinc (Zn). 0.01-2 wt% Palladium (Pd) less than 1% Indium (In) 10–15 wt% in the Hg |
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gamma phase of amalgam
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when alloy containing tin is cooled below 480 degrees C
silver + tin |
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TRITURATION
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When gamma phase is mixed with mercury to produce the dental amalgam
Mercury diffuses into the gamma phase and reacts with the silver and tin portions of the particles forming tow compounds: (know these) 1. Silver-mercury (gamma1 phase: Ag2Hg3) 2. Tin-mercury (gamma2 phase: Sn7-8Hg) |
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amalgam reaction
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gamma phase (silver & tin) + mercury --->
gamma + gamma1 + Cu-Sn increases composition of Cu in amalgam = stronger & less corrosion up to 2 days to complete rxn. |
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dimensional changes of amalgam due to time
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-contraction increases first 20 minutes
- after 20 minutes expansion increases for up to 8 hours -bigger the restoration the larger the expansion -expansion from zinc -excessice expansion if zinc expossed to water |
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the problems if amalgam is not mixed properly (2-3 seconds off)
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Undermixed: dull and crumbly
Normal: shiny and separates in a single mass from the capsule. Overmixed: soupy and tends to stick to the walls of the capsule |
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tool used to insert amalgam
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condensor
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steps to fill with amalgam
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-each incriment with condensor 1/3 to 1/2 prep
-make sure to push laterally against axial walls -overpack 1mm to cover margins -finish within 3.5 minutes - |
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carving amalgam with cleoid discoid
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-Part of the edge of the carver’s blade should rest on non prepared surface
-Mesial and distal fossae slightly deeper than proximal marginal ridges -always go up with carving - |
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sequence of steps to prep for amalgam
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-Field isolation.
-Establish the outline. -Remove caries. -Smooth cavosurface angle. Must be in sound tooth structure. -Place base if deep or close to pulp. (Dycal). Follow the memo on policy of liners and bases -Etch, place Prime &Bond NT and light cure. -Insert amalgam as explained |
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what is an alloy
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metal + non metal
-formed into restorations by casting -produces better physical properties that orignal materials |
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name the ADA Classification of dental casting alloys
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-high nobel
-nobel -base metal **The alloy is determined by its yield strength and elongation |
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alloy type 1
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-soft
-restoration for low stress and some inlays -yield strength <140 -elongation 18% |
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alloy type 2
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-medium
-restorations subject to medium stress (some inlays/onlays) -yield strength 140-200 -elongation 18% |
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alloy type 3
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-hard
- high stress, crowns, short veneer crowns, short span FPD -yield strength 201-340 elongation 12% |
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alloy type 4
(test question) |
-extra hard
-very high stress restorations -thin veneer crowns, long span FPD, removable partials -yield strength >340 -elongation 10% |
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Noble metals
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○ Resist tarnish
○ Good luster when dry ○ Gold, platinum, palladium |
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Gold
(Gold content may be expressed in terms of 4 things) |
-a noble metal
-Soft, malleable, has low strength -MP 1063 -Content expressed ¨ % ¨ Karat Karat=24 x %gold/100 24 karat is 100% pure gold ¨ Fineness Multiply the % by 10 Used to determine dental solders (joining of two different metals ¨ Color |
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Platinum
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MP 1755
Hardness and strength is better than gold |
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Palladium
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MP 1555
Cheaper than platinum |
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base metals
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-are requuired in alloys for their strength,flexibility,and wear
-they corrode -copper -zinc -silver -nickel -titantium |
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zinc
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-present in gold alloys as a scavenger (deoxidizing agent)
-improves the castability and fluidity of the alloy |
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silver
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improves mechanical properties of gold alloys
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nickel
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improves mechanical properties of base metal alloys
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metal alloys are made of
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crystals and grain boundaries between crystals
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when would gold-platinium be used (high nobel)
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full cast, ceramic bonding
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when would gold-palladium be used (high nobel)
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full cast, ceramic bonding
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when would gold-copper-silver be used (high nobel)
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full cast applications
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when would siver-gold-copper be used (nobel)
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full cast applications
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when would palladium copper be used (nobel)
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full cast, ceramci bonding
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when would silver palladium be used (nobel)
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full cast, ceramic bonding
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when would nickel based be used (base metal)
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full cast, ceramic bonding, partial denture, wrought
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when would copper based be used (base metal)
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full cast, ceramic bonding, partial denture, wrought
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when would titanium based be used (base metal)
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fullc ast, ceramic bonding, partial denture, dentla implants
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High-noble Alloys
properties |
-Need at least 60% of gold, platinum, or palladium
-At least 40% of this 60% must be gold -Very low corrosion -Easy to manipulate -Most expensive |
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Noble alloys
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- 25% must be noble metal
- Silver based - Corrosion is low but not as low as high noble - Main use is for crowns and Fixed Partial Dentures (FPD) |
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Base metal alloys
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○ Nickel, cobalt, or titanium
○ Complex alloys ○ High corrosion and questionable biocompatibility § Is related primarly to their corrosion § Corrosion is based on releasing elements into mouth § Unpleasant taste ○ Very low cost |
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Wrought alloys
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○ Shaped into another form by mechanical force
○ Main structure is grain fibers not crystals ○ Used for orthodontic wires and clasps for partials |
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Ceramic bonding alloys
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○ Elements are added to high noble alloys to form oxide layer
-metal alloy can turn ceramic green -can also cause debonding of ceramic |
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Solder uses
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-Join an orthodontic wire to a band
-Join a clasp wire to a RPD -Join two units of a FPD -Add proximal contact -Repair and occlusal defect in a casting |
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solder flux
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material that cleans the alloy to be soldered and dissolves any surface oxide on the metal
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polymer use
(10 of them) |
1. CD or RPD base to support artificial teeth
2. Ortho appliance 3. Soft liners 4. Prosthetic Teeth 5. Provisionals 6. Composites and sealants 7. Impression trays 8. Impression materials 9. Maxillofacial material 10. Occlusal appliance |
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Oligomer
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Is a short polymer composed of two, three, or four "mer" units
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Copolymers
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When two or more different types of monomers are joined
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in polymerization reaction how is the initiator activated
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initiator is an organic peroxide (benzoyl peroxide)
it is decomposed into active free radicals either by -heating (use heat-curing acrylic) -addition of an organic accelerator (using amines termed chemically or self-curing acrylic) |
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Denture Base Polymers Properties
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-Good color stability
-No taste -No odor -Good biocompatibility -No allergic reactions if is properly process -Water sorption is fairly high (0.6 mg/cm2) can go up to 2% -The sorption of water causes the base to expand slightly, resulting in better fit |
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Heat-cured Acrylic Base
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Most popular of denture based polymers
Lower cost of processing Adequate strength Fairly flexible High resistance fatigue fracture Less unreacted methyl methacrylate monomer no odor or bad taste |
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Light-Cured Dimethacrylates uses
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1. Repair of acrylic dentures
2. Orthodontic appliances 3. Reline dentures 4. Impression trays 5. Fabrication of dentures |
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Soft Liner uses
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1. Severe undercuts of the ridge
2. Patients with continue sore ridges 3. Tissue treatment after oral surgery 4. Obturators for defects of the palate |
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soft liner classifications
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1. Acrylic or long-term (months)
2. Silicone or short-term (days) |
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Prosthetic Teeth indications
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1. Low-stress-bearing areas
2. Poor ridges 3. Opposing natural teeth 4. Limited interarch distance |
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purpose of a provisional
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1. Maintain abutment relationships
2. Function 3. Esthetics 4. Periodontal Health |
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two main categories of ceramics
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· Silica based/glass based
· Non silica based/high strength ceramics |
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two subcategories of silica based
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-Traditional feldspathic porcelain
-Reinforced feldspathic porcelain |
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Traditional feldspathic porcelain specifics
(know the chemical formulas) |
□ Is a very common material in dentistry
□ Feldspathic porcelin is what is fused to metal coping □ 3 main ingredients ¨ Feldspar K2O-Al2O3-6SiO2 ¨ Silica (unchanged during firing providing stability) in form of pure quartz ¨ Kaolin (clay) provides opaqueness Al2O3-2SiO2-2H2O |
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Materials that solidify without an organized crystalized structure
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glass, super cooled liquids
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what makes glass translucent
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¨ High translucency is #1 property
¨ This is associated with low structural (flexual) strength, the crack does not meet anything is the substance to stop the crack ¨ 60-90 mega pascils in strength (very low) ¨ Discoloration can show through this porcelain |
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when do you use Traditional feldspathic porcelain
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¨ Porcelain laminate veneers
¨ Single units (not common) |
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Reinforced feldspathic porcelain 2 types
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Leucite reinforced feldspathic porcelain
Lithium disilicate reinforced feldspathic |
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what did Sir John Mclean Do?
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¨ Took alumina and mixed with traditional feldspathic porcelain and put it in the furnace to 1000C
¨ Feldspathic at 1000C fuse to form glass ¨ Alumina (aluminum oxide) at 2000C ◊ These become stuck in the glass (the double the flexual strength to about 160 mega pascils) ◊ There is now something for the crack to run into (it is a filler in the material) ◊ If you have a matrix and a filler the matrix determines the restoration, explained is a glass based restoration |
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Leucite reinforced feldspathic porcelain specifics
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¨ Is the most common now, leucite is glass based restoration
¨ Leucite grows during firing, it is not put in like the alumina above ¨ Preciable ceramics is the group ◊ Onlays ◊ Full coverage crowns ◊ Veneers ◊ Inlays ¨ Flexual strength is about 220 |
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Leucite reinforced feldspathic porcelain Require a substrate to bind to
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◊ A rough surface is created by applying a acidic agent like hydrofluoric acid to create porous and rough surface to apply bonding agent to. You apply this on restoration and tooth
◊ The adhesive is Bis Gma |
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Lithium disilicate reinforced feldspathic specifics
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¨ Condense particles, making it the strongest material
¨ 360 mega pascils ¨ Do not use this material for a bridge, too stiff ¨ No metal is needed |
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two sub categories of non silica based
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Alumina based
Zirconia based |
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Two categories of Alumina based
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Glass infiltrated aluminous porcelain
Densely sintered alumina |
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what was Michael Sadoul's role in Glass infiltrated aluminous porcelain
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he bipased the shrinkage of aluminum oxide (alumina)
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how is shrinkage bipassed in Glass infiltrated aluminous porcelain
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-Used pre centering temperature
► This is point where temp is high enough to make particles move and slightly fuse at the grain boundaries ► You can see some fusion but no shrinkage of alumina -Cool it down - This coping is very pourus so another stage to seal ◊ Takes glass in form of liquid and adds to coping and fires it so glass can infiltrate the coping and fill it in. ◊ The glass is a filler ◊ The alumina is the matrx ► This makes it a alumina based filler ► Has flexual strength of 450 mega pascils ► First cementable all ceramic restoration No bonding agent needed |
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indications for Glass infiltrated aluminous porcelain
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up to the first molar
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Densely sintered alumina specifics
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¨ No porosity here, it is very dense
¨ Flexual strength is 700 mega pascils ¨ Can be cemented anywhere in the dental arch ¨ You make the model big to calculate the shrinkage ¨ The use of a computer to calculate the precise shrinkage ¨ Alumina oxide can mask staining from amalgam and has a radio opacity is similar to enamel |
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Zirconia based (2nd on non silica)
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□ Zirconium oxide
□ Flexual strength is 1000 mega piscals (the strongest) □ All ceramic brides would use this □ It shrinks during firing □ Compensate for shrinkage like above in densely sintered □ Procerkrzircon is method we use in clinic |
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what is an inlay
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a restoration that is made to fit into a tapered cavity preparation and involves the occlusal and proximal surface(s) and possibly a cusp.
-prepared outside the mouth and cemented to the prepared tooth |
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what is an onlay
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a restoration that involves the occlusal and proximal surface or surfaces and covers all the cusps
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