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59 Cards in this Set
- Front
- Back
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What is the advantage of using metals?
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They offer strength and ductility
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How are metals cast in dentistry
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Lost Wax pattern technique
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Lost Wax Pattern Technique
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Take wax pattern and reproduce it in metal while allowing for wax and metal shrinkage
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Which metals are use?
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Noble metals because they don't oxidize
Also use titanium (not noble) because it is cheaper and has desirable biological characteristics |
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Gamma 2 phase
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Highly corrosive prone phase
Try to avoid this by adding copper to amalgam to make it less corrosion prone |
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Why is amalgam corrosion prone
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It is multiphase
It cracks It has electrotyle exposure |
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Where does corrosion usually occur
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At grain borders/ phase junctions
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Biocompatibility
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Ability of biomaterial to perform with appropriate host response in specific application
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What determines biocompatibility
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the biomaterial and host response
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Host response
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Response of host organism to the material or device
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Biomaterial
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Biomaterial is a nonviable material used in a medical device intended to interact with biological systems
AKA anything that interacts with the body and is not a drug or falls under blood, tissue |
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Class I Device
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Has general market controls
It is the least regulated device Market controls are sufficient to ensure safety and effectiveness EX: Denture and Crowns, Floss, gloves |
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What device classification is a denture
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Class I
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What device classification is a crown
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Class I
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Class II Device
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Performance Standard
Premarket notification necessary General market controls are insufficient Ex: amalgams and composites, oxygen masks, ultrasound imager AND root form dental implants |
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What device classification is a root form dental implant
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Class II
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What device classification is a amalgam
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Class II
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What device classification is a Composite
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Class II
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What device classification is a blade form dental implant
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Class III
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Class III device
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Premarket Approval
Insufficient information for reasonable safety and effectiveness Require some level of testing - most regulated Ex: orthopaedic implants, blade form dental implants, replacement heart valves |
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Acceptable and Compromised Biocompatibility depends on application - what are the classes based on?
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Class I - biomaterials in contact with gingival tissue
Class II - biomaterials in implant in teeth Class III - biomaterials implanted in soft or hard tissue |
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Things that can influence biomaterials?
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Surface characteristics like chemistry and roughness
Bulk stability of compounds Mechanical properties |
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Things that can influence host response?
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Toxicity
Inflammation Allergy Mutagenic or carcinogenic response |
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Environmental mediators affecting biomaterials
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Saliva, blood, extra cellular matrix proteins, cells, minerals
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What are the key properties of impression materials
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Accuracy
Dimensional stability Tear resistance |
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What occurs if the impression material is too thick
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Increase polymerization shrinkage
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What occurs if the impression material is too thin
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Increase percent strain during removal and more visoelastic flow possible therefore more deformation possible
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Where does shrinkage occur in impression material
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Shrinkage occurs towards the bonded surface - therefore towards the tray
Crown is short O-G Crown is wider B-L |
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Contact angle and wettability
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The lower the contact angle, the better the wettability (hydrophilic), therefore more detailed impression
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What is the purpose of the filler in impression material?
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decreases shrinkage of flexible matrix/polymer
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Working time of impression material and temperature
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Inversely proportional
If the temperature is high, you have less working and setting time If the temperature is colder, you have more working and setting time |
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Why is rapid removal important for impression techniques
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Remove tray quickly to limit strain/deformation.
keep strain in mind with periodontally compromised pts so you don’t pull their teeth out. |
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What is tear strength important for?
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Sulcus reproduction so your crown fits well with no open margins
No residual impression material left in pt which can cause inflammatory rxn. |
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What is the reason for replacement of resin based composite and amalgam restorations
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Bulk Fracture
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What should the thickness of impression material be?
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2-4mm
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What is the arrangement of time dependent properties of impression materials given that they they never recover their original dimensions
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They have a model with a dashpot in series with other parallel elements
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Why should you remove impressions fast
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You have better elastic recovery
Reduced time to activate the viscous element in the material and reduced time for polymer chains to reorient and slip |
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What is the major use of metal casting alloys in dentistry?
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In ceramometal restorations like porcelain fused to metal crowns and bridges
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What is the role of the investment in the casting process of metals?
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It compensates for heat treatment dimensional change
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What provides most of the compensation for casting shrinkage of the metal
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Heating expansion
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What is the role of the sprue in the casting process
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A path for gas escape as metal fills the investment
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What type of production has the greatest casting shrinkage associated with the casting process
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Class V inlays
This is because during the casting process, the molten metal freezes to the investment pattern walls and shrinkage is less for high surface area to volume ration patterns |
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What is the purpose of placing the wax pattern within the casting ring
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It proves gas escape during the cast process
Provide a position for relatively uniform casting investment expansion |
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Why are castings often found to have open margins after the casting process
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This is associated with non-uniform expansion of the investment
Most likely the result of setting expansion of the investment inhibited by the wax pattern |
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How do compositions of resin based sealants differ from resin based composites
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They use different ratios of the same monomers
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Chromium versus noble metal alloys
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Chromium containing alloys are stiffer than nobel
Nobel metal allows are softer than Chromium |
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What does addition of beryllium to alloys allow
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Allows it to be electrochemically etched
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What is the role of copper in high gold dental casting alloys
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Provides hardness and provides heat treatment
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What is the most important physical property in casting an alloy for inlays and onlays
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High ductility
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Dycal
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Placed on pin point exposures
Bacteriocidal - very high pH Needs a sealer like RMGI over it Sets faster in the present of moisture |
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RMGI
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Resin Modified Glass Ionomer
Liner Less then 0.5mm Can be used under Amalgam or composite Place on dentin ONLY (pulpal and axial walls) |
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Why is moist dentin bonding routine
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It promotes strong and reliable dentin bonding because the primer and resin are able to penetrate the open collagen network that exists with water
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IRM
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Intermediate Restorative Material
Used as a base Used as a temporary restoration and a sedative (due to eugenol) Moisture makes it set faster Placed on internal walls only (pulpal and axial) |
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Why are RMGI not recommended as the restorative material in Class I or II restorations?
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Because of their limited wear resistance
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What is the hardness value of abrasives used for finishing and polishing restorations
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Abrasives used for finishing have hardness values greater than restorative material
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Oxygen in the air causes what to dentin resin based composites
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Results in free radical quenching on the surface of composite
It's an unreacted layer Allows good bonding to additional layers because unreacted double bonds remains on the surface and oxygen is excluded |
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Why do dentin bonding agents have reduced bond strengths to the pulpal floor as the preparation deepens?
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Due to Increase in density of tubules near the pulp and the increase in tubule diameter near the pulp reduced bonding
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What happens to dentin bond strength of bonding agents as the prep deepens
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The bond strength reduces
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What is the weakest setting stage for amalgam
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Tin mercury phase
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