Prosthodontics Flashcards
Ideal teeth abutments
diverging, mutlirooted, curved, broad BL roots
Anterior edentulous space with ridge resorption is best restored with what?
RPD, not an FPD
If bone height is adequate (good clinical attachment + more than half bone covering roots), a canine that is replaced should be splinted to the incisors to prevent lateral drifting of the FPD
Most destructive load on the periodontium?
Horizontal forces
Dental Investments
- Refractory material used to surround the wax pattern for metal crowns, which forms the mold in which the metal alloy will be casted
- Should expand on setting (via refractory material of either quartz or cristobalite) and heating to compensate for the alloy shrinkage
- Should be porous to allow for air to escape
Types:
- Gypsum bonded = gold alloy
- Phosphate bonded Type I = base metal alloy = PFMs
- Phosphate bonded Type II = RPDs
- Silica bonded = not used much
Follow-up veneer seating
1 week
Partial crowns
- made entirely from metal that covers 50%
7/8ths crown are effective for single teeth or abutment restoration on max. molars, but used on any posterior tooth (good abutments). For esthetics, save MB cusp.
3/4 crowns insertion:
- Anterior = parallels incisal ½ - 2.3 of the labial surface
- Posterior = parallels long axis of the tooth
A ¾ crown is a partial veneer, where B surface is left uncovered. Could be esthetic in anterior region if prepared correctly!
A reverse ¾ crown is used most on mandibular molars, where it preserves the lingual surface
Precious vs Nobel vs Base Metal Alloys
High Nobel (Precious)
- Gold
- Platinum
- Silver (can cause porcelain greening)
> 60% noble + > 40% gold
- Expensive
Nobel (semi-precious)
- Gold
- Platinum
- Palladium
> 25% noble + no gold required
- Called nobel metals based on lack of chemical reactivity
- Oxidation resistant (don’t oxidize on casting), thus metal-porcelain interface can be controlled by adding trace elements to the metal
Base metal alloys (Non-precious)
- Nickel → ductility (margin burnishing)
- Chromium → passive film for corrosion resistance
- Cobalt → rigidity
Karat vs fineness
Karat = parts of pure gold on 24 parts per until (24 K = 100% gold)
Fineness = parts of pure gold per 1,000 (1,000 finess = 100% gold)
Pure gold is only used in foil restorations
Yellow gold has >60% gold
White gold has > 50% gold
Margins
- Least marginal strength: feathered/bevel
- Ideal for gold = chamfer is ideal, but could be bevel
- Ideal for Porcelain, Ceramic =shoulder (edge strength of porcelain is low, thus you need a butt joint)
- Ideal for metals: any type (shoulder with bevel or chamfer)
- Ideal fo metal with porcelain margins = shoulder
- Butt joint (via shoulder) is poorest type for cast metal restorations. Use an acute edge is optimal.
Chamfer has a hollow ground bevel, scooped out, creating more bulk of the metal near the margin and a greater cavosurface angle.
Bevel is flat in one dimension only (Wide bevel = enamel + dentin)
Plane = flat in ALL dimensions
Categories of ceramics:
- Predominantly glass = highly esthetic in mimicking optical properties. Change optical effects via [fillers]
- Particle-filled glass = fillers (crystalline) added to glass to improve mechanical stability
- Polycrystalline = no glass = crystalline arrangement resulting in tougher material = highest strength, but not as esthetic as glass.
Ceramics in general is considered a composite material (glass matrix + crystalline/glass particle filler)
Shade matching
- Half closed eyes can increase sensitivity of retinal rods to better chose value color
- Blue fatigue accentuates yellow sensitivity (look at blue objects to discriminate yellow)
- Metamerism is increased with porcelain staining
- Fluorescence is the ability to reflect UV radiation which makes a contribution to tooth shade. (Human teeth fluoresce blue-white hues 400-450 nm)
- Opalescence is light effect of a translucent material (incisal edges) appearing blue in reflected light and red-orange in transmitted light
contraindication for electro surgery
- thin attached gingiva
- dehiscence
- Cardiac pacemakers
- insulin pump
- delayed wound healing (uncontrolled diabetes)
GOOD to obtain hemostasis and retract gingiva
non-rigid connectors
- T-shape key attached to pontic + Dovetail key way in the retainer
- Only used in one tooth replacement (short span bridge) when no equal path of withdrawl can occur without excessive tooth reduction.
- Note: when teeth are in normal alignment, connects should be solder joints (rigid connector)
Sprue
- Creates a path for the molten alloy to reach the mold
- minimum is 1.5 mm in diameter
- Sprue pin diameter is greater than the thickest portion of the pattern
- Attachment of the sprue is at the point of greatest bulk in the mold, and never attached at a right angle (must be 45 degrees)
- This will allow the metal to flow evenly throughout the mold and prevent shrink-back porosity.
Pontics
- A pontic should be in contact in CO and may/may not be in working movements, but NOT in non-working movements.
- Narrower at the expense of the lingual aspect of the ridge
- Preferred materials which are less irritating to tissue: Glazed Porcelain > gold > unglazed porcelain > polished acrylic
- F-L dimension on the occlusal table is determined by the F-L dimension of the opposing centric holding contact areas.
Types:
- Saddle ridge lap = Saddle Shape = concave = difficult hygiene = v. esthetic
- Hygienic contact = Bullet/egg shape = convex in all aspects = easiest to clean but not esthetic
- Modified ridge lap = best = convex but esthetic
- Conical pontic = round top with conical bottom = molar without esthetic
- Ovate pontic = sanitary substitute for saddle-ridge lap pontics = gives the appearance that it is growing from the tooth.
Burger should be restored using what material?
Gold > porcelain
Tooth contacts should be broad and flat to prevent wear.
Function and non-function cusp reduction
Metal = 0.5 mm Porcelain = 1.5 mm
Functional cusp = 2.0 mm
Non-functional cusp = 1.5 mm
PFMs have ___ angle at the outer junction of metal to porcelain
90 degree angle
Main cause of PFM fracture: poor metal design
The porcelain and metal must have similar coefficients of thermal expansion
The alloy should be higher proportional limit and higher modulus of elasticity to reduce the stress on the porcelain
Best measure to determine potential clinical performance of a casting alloy?
ADA certification
Ideal interocclusal distance (free way space)
3 mm
Excessive VDO
- Gagging
- Strained lips
- Posterior teeth clicking
- Muscle fatigue
- Teeth clicking
- Trouble swallowing
- Incisors touching during sibilant sounds
- Trauma to underlying supporting tissue in a denture patient
Inadequate VDO
- Angular chelitis = hurts = vitamin B deficiency = candida or staph infection in the corners
- Dimisinshed occlual force
- Aging appearance in lower facial 1/3
What does a protrusive record measure?
Registers the Anterior-inferior condyle path one point in the translation of the condyles.
- Used to determine space needed for the occlusal rims in functional movements
Christensen’s Phenomenon
Space that opens between the posterior teeth during anterior movement of the mandible.
- Amount of separation increased by an increase in incised guidance and horizontal condylar guidance
Muscles involved in:
- Protrusion
- Retrusion
- Opening
- Lateral displacement
- both lateral pterygoid
- temporalis muscle posterior fibers
- lateral pterygoids with accessory digastic, hyoid mm.
- unilateral lateral pterygoids: R lateral pterygoid contracts, mandible moves to the left
Ideal denture teeth
- Plastic teeth bond better than porcelain teeth to acrylic
- Denture teeth will have a reduced BL width (narrow occlusal table) to decrease occlusal forces and increase tongue space
- Denture teeth size is based on the characteristics of the denture-supporting tissue and the useful posterior tooth space (interarch distance)
New dentures takes ___ weeks to learn to chew properly
6-8 weeks to learn to chew properly
Denture Problems:
- Dentures that dislodge when smiling
- Dislodge when yawning
- Sore gums and muscles at bottom face
- Clicking or Trouble swallowing
- Incisors touching during sibilant sounds
- Difficult F and V sounds
- “S” sounds like “th”
- “t” sounds like “d”
- Whistle on S sounds
- Lisp on S sounds not enough air passing between palate and tongue (correct: reduce VDO)
- tingling sensation at corner of mouth or in lower lip
- over-extended buccal notch and buccal flange
- over-extended DB flange (coronoid process)
- opposing teeth have insufficient spac (must reduce VDO)
- excessive VDO
- excessive VDO
- Max anterior teeth placed too far superiorly or anteriorly. Note: children with Class III skeletal will pronounce F and V difficult
- palate is too thick OR incisors are set too far palatally
- incisors are set too far lingually
- too much air passing between palate and tongue (Correct: increase amount of palatal resin via ruggae). Other causes: vertical overlap not enough, too much horizontal overlap)
10: not enough air passing between palate and tongue (correct: reduce VDO) - pressure from lower buccal flange on mental foramen
Denture Pathology
- max tuberosity hits the retromolar pad will result in
- denture bearing mucosa has redness + burning
- I-ll fitting denture or flange over-extension result in
- candidida is mainly found where?
- Fibrous maxillary tuberosity
- Denture stomatitis (chronic inflammation of denture bearing mucosa. Trauma and secondary fungus cause most denture stomatitis)
- epulis fissuratum (hyperplastic rxn due to an irritant)
NOTE: Vestibule = flange - Hard palate, due to OHI or local irritation issue (Papillary Hyperplasia = found on palatal vault, due to poor OHI, ill fitting denture. Caused primarily by Candida)
How will a UA CD and LA Kennedy Class I RPD make the patient profile look like?
prognathic and decreased VDO
- cause combination syndrome
- from lack of posterior occlusion
Best impression technique for denture patient with loose hyper plastic tissue is ___
passive position
Preferred materials which are less irritating to tissue:
Glazed Porcelain > gold > unglazed porcelain > polished acrylic
Glazing porcelain
- Glaze is where glass grains post firing at high temp for 5 minutes flows over the surface forming a vitreous layer.
- nonporous, resists abrasion, esthetic, ST biocompatible
Types:
- Natural glaze = glaze firing (final firing in porcelain process) = most permanent type
- Overglaze = applied glaze = ceramic powders added to porcelain post firing = glossy, non-porous layer = subject to erosion in the mouth leaving a rough or porous surface
Smooth surfaces give the tooth a larger appearance
What are the metal oxides in PFM bonding to each other?
Fe = bond best to gold alloy Cr = gold-substituted alloys
Note: Opaque layer of porcelain covers the metal color and provides the bonding surface between the porcelain and the metal (not the body porcelain layer).