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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
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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)
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Should occlusal records capture soft tissue landmarks?
- No, trim to just cusp tips
- Remove axial and deep occlusal Vs
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Should occlusal record be taken before or after die spacer?
Wait til after in order to avoid errors of thickness (pooling)
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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?
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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
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What influences the path of the condyle?
Eminence curve (bone contour and ligaments and muscles
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What innovation increased the use of double bite impressions?
ADDITION SILICON: Higher viscosity heavy body elastomerics
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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
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What are advantages of double bite?
- Prep, adj teeth and opposing in 1 impression
- Bite registration in impression
- Economic & efficient
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What is the proper sprue angle?
45, smooth improved flow with less air entrapment
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Where should pattern be in relation to ring?
- Entered
- Margins 6-8mm from closed end
- Margins 2-4mm from open(top) end
- Sprue length 4-6mm
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What is novocast w/p ratio?
- 26ml / 75g
- Hand mix 15, vacuum 30 at 27psi
- Set 1 hour
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What temp is novacast patterns burnouted at?
1200 F
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Which area of flame should be used to melt gold?
- REDUCING
- Ox, red, combustion, mixing
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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
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What is the contraction of gold as it shrinks?
1.5%
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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
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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
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Should anesthesia be used during try-in and cementation?
Typically no, patient can evaluate better
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What tools can be used to remove temp?
- Backhaus towl clamp
- GC pliers
- Engage buccal/lingual and rotate
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What are the limitations of radiographically detecting open margins?
Angle of beam
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What is the primary component of most dental wax?
Paraffin CnH(2n+2)
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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
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What are the classes of dental wax?
- Pattern:inlay, casting, baseplate
- Processing: boxing, utility, stick
- Impression: low MP, Iowa wax, bite registration (Aluwax)
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What are all mechanical properties of wax dependent on?
- Temperature
- Viscoelastic, modulus, proportional limit, strength, ductility
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What are the thermal properties of wax?
- Low thermal conductivity
- High heat capacity-> long working time
- High CTE
- Melting range dependent on composition
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What is the CTE?
- Coefficient of thermal expansion
- = d(L)/L(0) * d(Temp)
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CTE of waxes order?
Paraffin, beeswax, hard wax, carnauba
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What is the modulus?
- Elastic deformation slope of linear stress(y) strain (x) curve
- TEMP DEPENDENT
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What are ways to minimize wax pattern distortion?
- Uniform heat
- Immediate investing
- Store at low temp
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How much gold is needed for a wax pattern?
Weight(wax) * 16.2
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What must investment material expand to compensate for?
Gold shrinkage
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What is refractory in investment material?
- Heat resistant, SiO2 polymorphs
- Quartz, Tridymite, Cristobalite
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What is the composition of investment material?
- Refractory: heat resistant (SiO2)
- Binder: gypsum, phosphate, SiO2
- Modifiers: NaCl(regulate expansion), C, Cu reducing
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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
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What is hygroscopic expansion?
Increased expansion when investing setting under water -> uninterrupted crystal growth
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What does increasing spatulation time or speed do?
- Breaks up crystal nuclei-> more growth, interation, setting expansion
- Decreases setting time
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What does increasing H2O temp do for investments?
- Faster setting time
- Inc thermal expansion
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What does increasing the water/powder ratio do?
- Increase setting time
- Decrease setting expansion, strength
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What is thixotropy?
Softening, viscosity reducing by rapid shear stress (vibrate)
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What are the classifications of investments?
- I: inlay, thermal
- II: inlay, hygroscoic
- III: partial denture, thermal-> less expansion, higher compressive strength
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What happens to CaSO4 bonded investments above 700C?
- Decomposition in presence of carbon
- Embrittle metal castings
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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
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What does silica sol in water do to phosphate bonded investment?
Increase setting expansion and investment hardness
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What is silicosis?
Reduced lung function from chronic SiO2 exposure, could be carcinogenic
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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
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What is the most important thing when removing crown?
Safety to patient, prevent damage to remaining tooth, pulp, periodontium
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What tool is used to remove a crown?
- Richwil: adhesion
- Posterior: Centric
- Anterior: protrusion
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When sectioning crown with a bur, should you cut all the way through?
- No leave 2mm to prevent aspiration
- Then use T-bar
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What is silicone wash used for?
Intraoral crown fit checking
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What burs should be used to adjust crown occlusion?
- Gold: 7404-012
- Porcelain: diamond stone
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What is the difference between GC Fuji I and Plus?
- I: single, dowel, FPD
- Plus(Resin enforced): single
- Not for ceramics
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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
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Which burs are good for crown sectioning?
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What are recommendend depth of cutbacks for PFM?
- .7mm minimum
- 1.0 Ideal
- 2.0 Maximum
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What are the margins in PFM?
- Porcelain butt joint
- Metal collar
- “disappearing margin
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What is minimum shoulder width for PFM?
1.0mm
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How much more wear does porcelain cause than gold?
40x
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What does insufficient cusp reduction lead too?
Thin porcelain or overcontour in final crown
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How long does heavy/light body take to set?
5 mins from start of mix
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What are the main differences of ceramic in/onlays?
- Bulk: strength
- Proximals: greater extension for finishing
- Internal angles: rounded
- Divergence: greater
- Bonded
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Does bonding restoration increase strength of remaining structure?
Yes
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Why ceramic vs composite?
- Easier to contour
- More durable
- More conservative than PFM
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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
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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
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What is the order of all ceramic preps?
- Dam, remove caries/old rest, block out w ionomer
- Occlusal, boxes, covered cusps, margins
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What are the requirements for cements?
- Non-toxic
- Insoluble
- Good mechanics (compressive)
- Protective (thermal, electrical, chemical
- Adhere to tooth and restoration
- Bacteriostatic
- Obtundent to pulp
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What does increasing powder/liquid ratio do?
- More viscous
- Faster setting
- High strength
- Low solubility, acidity
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What factors do operator control for cements?
- P/L ratio
- Rate of powder incorporation
- Mixing temp
- Spatulation
- Water contamination
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What kind of cement is used for temps?
- Zinc-oxide(powder)
- Eugenol(liquid)
- ->zinc eugenolate
- Some liner applications
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What are the biological effects of zinc-eugenol?
- Bland and obtundent on pulp
- Mild irritant to CT
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What are the advantages of zinc-eugenol?
- Good for pulp, temporary seal
- Disadvantages:
- Low strength, abrasion resistance, anticariogenic action
- Soluble in oral fluids
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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
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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
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What is the composition of most permanent cements?
- Glass ionomer
- Powder: aluminosilicate glass
- Acid: polyacylic(vs phosphoric)
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What are the biological effects of zinc phosphate cements
- Zinc oxide & phosphoric acid
- Initial pulpal irritation from acidity, osmotic effects
- May permit marginal leakage
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What are the advantages of zinc phosphate cements?
- easy handling
- durable
- moderate strength
- low film thickness
- DIADVANTAGES:
- Pulp irritation, poor adhesion to tooth, not anticariogenic, brittle, soluble long term
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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
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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
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What are the advantages/disadvantages of glass ionomer?
- Adv:
- High strength, low solubility than ZnPO4
- Minimal pulpal rxn(technique dependent)
- Adhesion
- Fluoride release
- Disadvantages:
- Technique, proportion sensitive
- Moisture contamination
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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
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What are the biological effects of resin cements?
- Sensitivity: polymer contraction, marginal leakage
- Pulp protection
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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
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What type of cement is Fuji Plus?
Resin Ionomer Luting cements
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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
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What are the adv/disadv of resin ionomer luting cements?
- High compressive strength
- Lower solubility than GI
- F-release
- Inherently adhesive
- Disadvantages: rapid set, excess difficult, cause fracture
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Where is die spacer placed for inlays?
Pulpal floor and axial wall
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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)
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What is the purpose of blockout?
Allows ideal preparation, keeping internal conservative
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Which types of glass ceramics are etchable?
Felspathic porcelain(60-120 secs, 7-10%), leucite reinforced glass ceramic, LiSiO4 (20 secs 4-5%)
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