CRITERIA FOR A GOOD OCCLUSAL RECORD
- • DIMENSIONAL ACCURACY
- • LONG TERM STABILITY
- • STRENGTH AND TOUGHNESS
- • FAST SETTING
- • SOME FLEXIBILITY
- • MUST NOT EXERT ANY INFLUENCE ON JAW POSITIONING
- • TEETH NOT PREPARED SHOULD BE IN CENTRIC OCCLUSION (ICP) WHENEVER POSSIBLE
Interocclusal record material characteristics?
- Soft at room temp
- Tenax, sheet wax, plaster, acrylic, silicon rubber, aluwax, An oxide eugenol, dead soft metal
- Filled PVS (polyviylsiloxane)
Should occlusal records capture soft tissue landmarks?
- No, trim to just cusp tips
- Remove axial and deep occlusal Vs
Should occlusal record be taken before or after die spacer?
Wait til after in order to avoid errors of thickness (pooling)
What does the facebow do?
- Approximate rotation center of the head of the condyle
- CLOSED BITE mounting in ICP, OK
- If the mounting is open bite use different technique to locate true terminal hinge or condylar rotation center?
What does the protrusive record do?
- Set semi/fully adjustable articulators to approximate ange of CONDYLAR EMINENCE
- More accurate CUSP INCLINES for jaw movements of protrusion and lateral border positions
What influences the path of the condyle?
Eminence curve (bone contour and ligaments and muscles
What innovation increased the use of double bite impressions?
ADDITION SILICON: Higher viscosity heavy body elastomerics
What are the indications for double bite impression?
- 1-2 single crowns
- Pt w/ stable bilateral occlusion, w/ at least 1 vertical stop on preparation side
- Contra: multiple, FPD, abutments, unstable, changes in VDO, can’t close mouth with tray
What are advantages of double bite?
- Prep, adj teeth and opposing in 1 impression
- Bite registration in impression
- Economic & efficient
What is the proper sprue angle?
45, smooth improved flow with less air entrapment
Where should pattern be in relation to ring?
- Margins 6-8mm from closed end
- Margins 2-4mm from open(top) end
- Sprue length 4-6mm
What is novocast w/p ratio?
- 26ml / 75g
- Hand mix 15, vacuum 30 at 27psi
- Set 1 hour
What temp is novacast patterns burnouted at?
Which area of flame should be used to melt gold?
- Ox, red, combustion, mixing
What does prevox do?
- Remove investment and dissolves surface oxides leaving higher noble content to surface metal
- Use rubber or plastic to remove from prevox
What is the contraction of gold as it shrinks?
For metal restorations what expansions and contractions should be considered?
- Gold shrinks 1.5%
- Die stone: expands when setting
- Investment: expands-> compressing ring liner, expands in oven
- Investment: setting & thermal expansion
- Net result, good fit
What are advantages of gold?
- Resists corrosion
- Tensile strength-> durable thin margins
- CTE = tooth
- Wear rates on restoration and opposing teeth similar to enamel
- High density & low oxide make predictable
Should anesthesia be used during try-in and cementation?
Typically no, patient can evaluate better
What tools can be used to remove temp?
- Backhaus towl clamp
- GC pliers
- Engage buccal/lingual and rotate
What are the limitations of radiographically detecting open margins?
Angle of beam
What is the primary component of most dental wax?
What are some modifiers of dental wax?
- Beeswax: pliability
- Carnuba: hardness, shine
- Candelilla: hardness, no m.p.
- Ceresin: reduce brittleness, increase hardness
- Gum dammar and Rosin: increase brittleness
What are the classes of dental wax?
- Pattern:inlay, casting, baseplate
- Processing: boxing, utility, stick
- Impression: low MP, Iowa wax, bite registration (Aluwax)
What are all mechanical properties of wax dependent on?
- Viscoelastic, modulus, proportional limit, strength, ductility
What are the thermal properties of wax?
- Low thermal conductivity
- High heat capacity-> long working time
- High CTE
- Melting range dependent on composition
What is the CTE?
- Coefficient of thermal expansion
- = d(L)/L(0) * d(Temp)
CTE of waxes order?
Paraffin, beeswax, hard wax, carnauba
What is the modulus?
- Elastic deformation slope of linear stress(y) strain (x) curve
- TEMP DEPENDENT
What are ways to minimize wax pattern distortion?
- Uniform heat
- Immediate investing
- Store at low temp
How much gold is needed for a wax pattern?
Weight(wax) * 16.2
What must investment material expand to compensate for?
What is refractory in investment material?
- Heat resistant, SiO2 polymorphs
- Quartz, Tridymite, Cristobalite
What is the composition of investment material?
- Refractory: heat resistant (SiO2)
- Binder: gypsum, phosphate, SiO2
- Modifiers: NaCl(regulate expansion), C, Cu reducing
What are the properties of gypsum bonded investments?
- CaSO4 hemihydrate-> dehydrate & heat
- Ultimate Setting expansion(after initial contraction) due to multidirectional crystal growth
- Heat causes thermal expansion of wax
What is hygroscopic expansion?
Increased expansion when investing setting under water -> uninterrupted crystal growth
What does increasing spatulation time or speed do?
- Breaks up crystal nuclei-> more growth, interation, setting expansion
- Decreases setting time
What does increasing H2O temp do for investments?
- Faster setting time
- Inc thermal expansion
What does increasing the water/powder ratio do?
- Increase setting time
- Decrease setting expansion, strength
What is thixotropy?
Softening, viscosity reducing by rapid shear stress (vibrate)
What are the classifications of investments?
- I: inlay, thermal
- II: inlay, hygroscoic
- III: partial denture, thermal-> less expansion, higher compressive strength
What happens to CaSO4 bonded investments above 700C?
- Decomposition in presence of carbon
- Embrittle metal castings
What are the types of high-heat investments?
- Phosphate-bonded: higher melting alloys (PFM), stronger than gypsum, harder to work with
- silica-bonded: flammable, expensive
What does silica sol in water do to phosphate bonded investment?
Increase setting expansion and investment hardness
What is silicosis?
Reduced lung function from chronic SiO2 exposure, could be carcinogenic
What are the differences of hard and soft waxes for crowns?
- Hard: more heat, distortion (high when cooling, low when cooled), subject to fracture, easier to smooth and polish
- Soft: withdraw past small undercuts without fracture/distortion
What is the most important thing when removing crown?
Safety to patient, prevent damage to remaining tooth, pulp, periodontium
What tool is used to remove a crown?
- Richwil: adhesion
- Posterior: Centric
- Anterior: protrusion
When sectioning crown with a bur, should you cut all the way through?
- No leave 2mm to prevent aspiration
- Then use T-bar
What is silicone wash used for?
Intraoral crown fit checking
What burs should be used to adjust crown occlusion?
- Gold: 7404-012
- Porcelain: diamond stone
What is the difference between GC Fuji I and Plus?
- I: single, dowel, FPD
- Plus(Resin enforced): single
- Not for ceramics
What is the order of supragingival margin finishing?
- 1. Medium garnet (enamel only)
- 2. Fine Sand
- 3. Fine Cuttle
- 4. Brownie points (grooves)
- 5. Pumice: rubber cup
- 6. Greenie points (grooves)
- 7. 15mu Al2O3
- 8. Super greenie
- 9. 1mu AlO2
Which burs are good for crown sectioning?
What are recommendend depth of cutbacks for PFM?
- .7mm minimum
- 1.0 Ideal
- 2.0 Maximum
What are the margins in PFM?
- Porcelain butt joint
- Metal collar
- “disappearing margin
What is minimum shoulder width for PFM?
How much more wear does porcelain cause than gold?
What does insufficient cusp reduction lead too?
Thin porcelain or overcontour in final crown
How long does heavy/light body take to set?
5 mins from start of mix
What are the main differences of ceramic in/onlays?
- Bulk: strength
- Proximals: greater extension for finishing
- Internal angles: rounded
- Divergence: greater
Does bonding restoration increase strength of remaining structure?
Why ceramic vs composite?
- Easier to contour
- More durable
- More conservative than PFM
When is ceramics contraindicated?
- Heavy occlusal forces (fracture)
- Cannot isolate (dry for adhesion)
- Deep subgingival: poor bonding to cementum and hard to impress/finish
- Uncontrolled caries
What are the main differences between gold & ceramic in/onlays?
- Gold: 1-2mm occ clearance, sharp internal angeles, beveled shoulders in box and functional cusp, 6-10 occlusal divergence, minimal proximal, luted
- Ceramic: 2mm, rounded internal, 90 degree finish lines, 12-15 degree divergence, greater proximal, bonded
What is the order of all ceramic preps?
- Dam, remove caries/old rest, block out w ionomer
- Occlusal, boxes, covered cusps, margins
What are the requirements for cements?
- Good mechanics (compressive)
- Protective (thermal, electrical, chemical
- Adhere to tooth and restoration
- Obtundent to pulp
What does increasing powder/liquid ratio do?
- More viscous
- Faster setting
- High strength
- Low solubility, acidity
What factors do operator control for cements?
- P/L ratio
- Rate of powder incorporation
- Mixing temp
- Water contamination
What kind of cement is used for temps?
- ->zinc eugenolate
- Some liner applications
What are the biological effects of zinc-eugenol?
- Bland and obtundent on pulp
- Mild irritant to CT
What are the advantages of zinc-eugenol?
- Good for pulp, temporary seal
- Low strength, abrasion resistance, anticariogenic action
- Soluble in oral fluids
What is zinc-eugenol reinforced with?
- Natural/synthetic resins or AlO3
- Increases compressive strength, marginal use for permanent retention
- Can be used for temporary fillings
What are the properties of non-eugenol zinc oxide cements?
- Liquid is aromatic oil and organic acid NOT eugenol
- Used for temps where resin or resin ionomer luting will be used for permanent
What is the composition of most permanent cements?
- Glass ionomer
- Powder: aluminosilicate glass
- Acid: polyacylic(vs phosphoric)
What are the biological effects of zinc phosphate cements
- Zinc oxide & phosphoric acid
- Initial pulpal irritation from acidity, osmotic effects
- May permit marginal leakage
What are the advantages of zinc phosphate cements?
- easy handling
- moderate strength
- low film thickness
- Pulp irritation, poor adhesion to tooth, not anticariogenic, brittle, soluble long term
What is a polycarboxylate cement?
- Powder: Zn oxide
- Acid: polyacrylic
- Uses: luting temps, interim luting on sensitive teeth, luting restorations, base
- Decreased use for permanent and base
What is the composition of glass ionomer?
- Powder: Ca-F-Al-Si-ate glass
- Liquid:50% aqueous polyacrylic-itaconic acid
- ⇒ Calcium Aluminoacrylate gel
- High compressive strength for lining, luting, base
- Bonding: good w/clean enamel, dentin and stainless steel
- Good for luting metal, PFM, decreasing use as liner, base, restorative
What are the advantages/disadvantages of glass ionomer?
- High strength, low solubility than ZnPO4
- Minimal pulpal rxn(technique dependent)
- Fluoride release
- Technique, proportion sensitive
- Moisture contamination
What are resin cements?
- similar to restoratives but less filler and LOW viscosity
- BisGMA or UDMA diluted
- Setting rxn: addition polymerization
- Curing: chemical, light, dual
- Applications: bonding ceramic or resin resorations, luting metal or PFM
- Types: adhesive (MDP phosphates, 4-Meta)or non-adhesive
What are the biological effects of resin cements?
- Sensitivity: polymer contraction, marginal leakage
- Pulp protection
What are the adv/disadv of resin cements?
- Adv: high strength, low solubility
- Disadv: moisture contamination, thick film, difficult handling, pulp irritation, high wear on occlusal margins
What type of cement is Fuji Plus?
Resin Ionomer Luting cements
What is the composition of resin ionomer luting cements?
- Powder: F-Al-Si-ate glass, chemical or light initiator
- Liquid: polyacrylic acid with pendent methacrylate groups
What are the adv/disadv of resin ionomer luting cements?
- High compressive strength
- Lower solubility than GI
- Inherently adhesive
- Disadvantages: rapid set, excess difficult, cause fracture
Where is die spacer placed for inlays?
Pulpal floor and axial wall
For gypsum bonded investments list the W/P ratios from smallest to largest.
- DO,MO,O inlays (15)
- FGC (15.5)
- 7/8, 2/4, MOD onlays (18)
- MOD inlays (18.5)
What is the purpose of blockout?
Allows ideal preparation, keeping internal conservative
For a mesial box of an MO inlay which hand instruments are used to create the bevels?
- External Tucker 233 GMT
- Internal Tru-bal 232 GMT
What are the prep guidelines for PFM anterior?
- * Incisal Reduction-2 mm
- * Lingual Clearance-1.0-1.5 mm
- * Facial Reduction
- * Shoulder-1.0-1.2 mm wide
- * Axial-1.5 mm
- * Finish Lines
- * Facial-shoulder
- * Lingual-chamfer
- * Proximal-shoulder-beveled shoulder-chamfer
What are the restorative reqs for graduation?
- • Minimum Clinical Experiences (all prescriptive procedures
- • 30 Direct, 4 sealants)
- • Skills Assessment Evaluations (need 3.0 average on each)
- • Student Teaching Experiences (2nd year/4th year operative and crown)
- • RVU’s totaling 1200 points
What are the components of the ceramic tooth interface
- A. Glass ceramic
- B. Etched intaglio surface
- C. Silane primer
- D. Unfilled resin
- E. Filled resin cement
- F. Bonding resin
- G. Etched enamel
- H. Hybrid layer
Describe enamel vs dentinal bonding
- Enamel: etch 30-60 secs, micromechanical, more stable
- Dentin: smear layer removal etch 10-15 secs, keep wet, primer, hybrid layer, less constistent, stable
What are differences btwn self etch and total etch?
- Self: ONLY sealed areas, less post-op sensitivity, faster, weaker
- Total: may penetrate non-sealed->post-op sensitivity, stronger, longer time
Describe the different curing modes of resin cements
- • Auto cure
- • Appropriate for metal and opaque ceramic restorations
- • Dual cure
- • Allows accelerated clean up for posterior or full coverage ceramic restorations where light penetration is limited
- • Light cure
- • More color stable for thin translucent anterior porcelain veneers
Advantages of resin cements?
- • Essentially low viscosity composite materials with similar properties to composite:
- • Good strength
- • Resistance to wear better than acid/base cements
- • Low solubility
- • Tooth colored
- • Can optically connect tooth & overlying ceramic
- • Compatible with enamel and dentin bonding techniques
Disadvantages of resin cements?
- • Clean up can be very difficult
- • Can bond to unprotected adjacent tooth surface
- • Inhibition of set by oxygen means that proximal cement will set before cement on more accessible surfaces
- • Tooth color and adhesion make removal from root surfaces difficult
- • Contribution to periodontal disease
- • Post operative sensitivity from aggressive removal
Which types of glass ceramics are etchable?
Felspathic porcelain(60-120 secs, 7-10%), leucite reinforced glass ceramic, LiSiO4 (20 secs 4-5%)