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Unless otherwise noted, the content of this course material is licensed under a Creative Commons Attribution 3.0 License.Copyright 2008, Dr. Stephen Bayne.The following information is intended to inform and educate and is not a tool for self-diagnosis or a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional. You should speak to your physician or make an appointment to be seen if you have questions or concerns about this information or your medical condition. You assume all responsibility for use and potential liability associated with any use of the material. Material contains copyrighted content, used in accordance with U.S. law. Copyright holders of content included in this material should contact [email protected] with any questions, corrections, or clarifications regarding the use of content. The Regents of the University of Michigan do not license the use of third party content posted to this site unless such a license is specifically granted in connection with particular content objects. Users of content are responsible for their compliance with applicable law. See http://www.dent.umich.edu/license/ for more information. Mention of specific products in this recording solely represents the opinion of the speaker and does not represent an endorsement by the University of Michigan. Viewer discretion advised: Material may contain medical images that may be disturbing to some viewers.
IMPRESSION MATERIALSPart 1 and Part 2
Stephen C. BayneUniversity of Michigan School of Dentistry Ann Arbor, Michigan [email protected]
What are tolerable limits for error in indirect procedures?
PROBLEM ANALYSISa. b. c. d. e. f. g. Impressions Casts, Dies Waxing Investing Casting Finishing, Polishing Cementation = = = = = = = +/- 0 +/- 0 +/- 0 + 1.5% 1.5% +/- 0 +/- 0
Prepped Tooth Width
8 mm (=8,000 m) 8,000 m x 0.5% = 40 m = 20 m/side Typical clinical error = >100 m/side
CLASSIFICATION SYSTEMBased on Properties of Set MaterialsProperties: Reaction: Set: Irrev Rev Irrev Irrev Rev Irrev Irrev Irrev Irrev (Chem) (Phys) (Chem) (Chem) (Phys) (Chem) (Chem) (Chem) (Chem)
Rigid:1. 2. 3. Impression Plaster Impression Compound Zinc Oxide/ Eugenol Rigid Rigid Rigid Flexible Flexible Flexible Flexible Flexible Flexible
Water-Based Gel: 4. Alginate (Irreversible Hydrocolloid) 5. Agar-Agar (Reversible Hydrocolloid)Elastomers: 6. Polysulfide (Rubber Base, Thiokol) 7. Silicone (Conventional, Condensation) 8. Polyether 9. Polyvinyl Siloxane (Addition Silicone)
IMPRESSION MATERIALSKey Propertiesa. Accuracy = ability to replicate the intraoral surface details. b. Dimensional Stability = ability to retain its absolute dimensional size over time. c. Tear Resistance = ability to resist tearing in thin sections (such as through the feather-edged material within the gingival sulcus.Impression Tray Impression
Accuracy Dimensional Stability Tear ResistanceImage source: Steve Bayne, University of Michigan, 2008
GENERAL FORMULATIONFor Elastic Impression Materials
1.
Flexible Matrix (Continuous Phase): a. Multifunctional Pre-Polymer or Polymer b. Crosslinking Agent c. Curing Agent (Catalyst or Initiator) d. Modifiers (Accelerators, Retarders, Plasticizers, Flavoring Agents, Colorants)Filler or Extender (Dispersed Phase):
2.
Polymer (high shrinkage)Filled Polymer (low shrinkage)
Image source: Steve Bayne, University of Michigan, 2008
ELASTOMERIC IMPRESSIONSManagement of ShrinkageUse 2-step techniques: (a) Light-Heavy Body, OR (b) Wash-PuttyImpression Tray Impression
Load tray with heavy-bodied IM Cover prep with light-bodied IM from syringe
During setting shrinkage, distortion of impression is toward tray.
Impression
Dies tend to be oversize and so the casting is oversize.
Images source: Steve Bayne, University of Michigan, 2008
ELASTOMERIC MATERIALSMixing and Delivery SystemsPolyether, Polyvinylsiloxane
2x2x2x2x2x2x2x2 = 256 folds
Polysulfide Rubber, Silicone Rubber
Mixing Options: 2 Pastes on Mixing Pad 2 Pastes in Mixing Gun 2 Pastes in Mixing MachineGraph source: Steve Bayne, University of Michigan, 2008 Images source: Undetermined
IMPRESSION MATERIALSManagement of Distortion During Tray RemovalStrain rate sensitive elastomers !
Impression Tray Impression
Fast removal
VERY FAST (SNAP)
Slow removal
Image and graph source: Steve Bayne, University of Michigan, 2008
IMPRESSION MATERIALSDistortion Time Related to Setting Reaction PS, Silicone
REACTION CONVERSION (%)
100
VPS Pe
log TIME (minutes)Graph source: Steve Bayne, University of Michigan, 2008
POLYSULFIDE RUBBERChemistry and Setting ReactionCONTINUOUS PHASE: Polymer Crosslinking Agent Catalysts DISPERSED PHASE: Fillers = Mercaptan Functional Polysulfide = Sulfur and/or Lead Peroxide = PbO2 or Copper Hydroxides (Type I) Zinc Peroxide or Organic Hydroperoxide (Type II) = TiO2 or Zinc Sulfate or Lithopone or Calcium Sulfate Dihydrate
SETTING REACTION: Stepwise (relatively slow), Exothermic, Affected by temperature
POLYSULFIDE RUBBERManipulation and Technique Considerationsa. Two-step techniques recommended: Reduces air entrapment and surface tension effects. Material adversely affected by H2O, saliva, and blood. Set impression should be removed quickly - do not rock tray. No syneresis or imbibition, but distortion due to continued reaction. Ideally need uniform thickness and at least 2 mm thick for accuracy. (1) Adhesive must be thin (2) Adhesive must be dry Paste-Paste Mixing Recommendations: (1) Dispense pastes at the top of the mixing pad (2) Mix pastes with tip of spatula only for 5 seconds (3) Transfer mass to fresh surface at center of mixing pad (4) Wipe spatula off with paper towel; Strop mass for 15s to constant color (5) Load syringe or tray (6) Use pad excess to monitor setting time Pouring of models: (1) Wait 20-30 minutes before pour for stress relaxation to occur (2) RB is non-reactive with model and die materials (3) Be careful of glove powder contamination of impression (4) RB can be electroplatedImages source: Steve Bayne, University of Michigan, 2008
b. c.* d. e.f.
g.
SILICONE RUBBERChemistry and Setting ReactionCONTINUOUS PHASE: Polymer Crosslinking Agent Catalysts Modifiers DISPERSED PHASE: Fillers = Polydimethyl Siloxane = Alkyl Orthosilicate or Organo H-Silane = Organo Tin Compounds (e.g., tin octoate) (but not dibutyl tin dilaurate) = Colorants, Flavorants = Silica
SETTING REACTION: Stepwise (relatively slow), Exothermic, Affected by temperature H2O by-products
SILICONE RUBBERManipulation and Technique Considerationsa. b. c. d. e. Limited shelf-life: Unstable in tubes. Requires mechanical retention or special tray adhesives No syneresis or imbibition, but continued polymerization shrinkage. Better dimensional stability than RHC but more expensive Pouring of models: (1) More flexible so more chance for distortion during removal (2) Wait 20-30 minutes before pour for stress relaxation to occur
POLYETHER RUBBERChemistry and Setting ReactionsCONTINUOUS PHASE: Polymer Crosslinking Agent Catalysts Modifiers DISPERSED PHASE: Fillers = Amine-terminated Polyether = Aromatic Sulfonate = = Colorants, Glycol Plasticizers, Flavorants = Silica
SETTING REACTION: Stepwise (relatively slow), Exothermic, Affected by temperature
POLYETHER RUBBERManipulation and Technique Considerationsa. b. c. d. e. Excellent impression accuracy and dimensional stability. Stiff and therefore difficult to remove without rocking. Break seal and rock slightly to prevent tearing: Low tear resistance. Negatively affected by H2O, saliva, and blood. (1) Since hydrophobic, moisture increases marginal discrepancy (2) Increased water absorption occurs if use thinning agents Can be dispensed from automated extruder and mixer (ESPE PentaMix)
Image source: Undetermined
POLYVINYL SILOXANEChemistry and Setting ReactionsCONTINUOUS PHASE: Polymer Crosslinking Agent Catalysts Modifiers DISPERSED PHASE: Fillers = Double-bond-functional Silicone Polymer = Chloroplatinic Acid = = Colorants, Flavorants, Plasticizers = Silica
SETTING REACTION: Chain (very fast), Exothermic, Affected by temperature Hydrogen gas released by decomposition of crosslinking agent.
POLVINYLSILOXANEManipulation and Technique Considerationsa. b. c. BEST impression material for dimensional stability: Pouring should be delayed at least 4 hours for H2 out-gassing. Pouring can be delayed up to 7-to-10 days (or indefinitely). Stiffness makes removal difficult. Most material dispensed using auto-mixing gun and mixing tips
COMMERCIAL PRODUCTS1980-1995
Predominantly POLYSULFIDE and SILICONE elastomers before 1995.
COMMERCIAL PRODUCTS1996-2004
Predominantly POLYETHER and PVS elastomers after 1996.
IMPRESSION MATERIALSComparison of Key PropertiesPoor >---------------------------------> Good
1.
Accuracy (Reproduction of Detail): a. Wetting of Tissues: b. Wetting by Dental Stone:Dimensional Stability: (Resistance to Distortion): a. Polymerization Shrinkage b. Thermal Shrinkage c. Loss of Components d. Stress Relaxation Tear Resistance (Elasticity): a. Elastic Deformation b. Strain Rate Sensitivity
ALG < SIL, PS < PE