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).
Porcelain shrinks ___ % during firing
20%
Porcelain has poor thermal conductivity. This results in cooling stresses that create surface micro-cracks
Porcelain is biocompatible with ST, but is brittle due to its high compressive strength (of all ceramics), and low shear (lack of ductility) and tensile strength (unavoidable surface defects)
Porcelain esthetics comes from powder condensation.
- Hue
- Chroma
- Value
- Metamerism
- Fluorescence
- Opalescence
- color tone = color (red, blue) = selected first
- saturation, color strength (degree of saturation of hue) = i.e. yellow staining
- brightness = intensity = amount of light and dark (is reduced by adding a complimentary color) = black and white
Value is most important in shade selection
Stains are added via metallic oxides, which reduces value. Almost impossible to increase the value.
- Teeth appear different shades under different light sources (Staining increases metamerism)
- 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
sintering
- Changes the porcelain from a powder to a solid during firing (does not melt the powder)
- Results in reduced porosity, increased density, higher strength
If fired porcelain occurs too many times, it will become milky and detrify, resulting in difficult glazing
What type of fluoride damages all ceramics?
Acidulated fluoride
Most used material in porcelain that is destined for PFMs
- Feldspathic porcelain
- most used in PFM due to its tendency to form the crystalline mineral Lucite when melted. Lucite in turn allows control of the thermal expansion.
Post crown vs post and core
Post crown is a post and crown attached to the final restoration
Solders
Gold = FPD Silver = oath
- Solders must melt at least 150 F below the fusion temp. of the alloys it is soldered with
- Solder joint must be free of electrons
- Strength is determined by surface area, not thickness, and is increased in height (not width), located circularly at the contact areas.
- The solder is joined to the metal by wetting, not by melting, thus cleanliness of the surface is the most important factor
- Fluxing is the oxidative cleaning of surface impurities on the solder to allow for wetting (and hence joining). Composed of borax, silica, and sodium pyroborate
- To reduce too much wetting, an anti-flux of soft graphite pencil is added.
Distance of parts to be joined via solder?
0.25 mm
Types of provisional restorative material:
- PMMA
- PEMA
- PVMA
- bis-acryl composite resin
- light cured urethane dimethacrylate
Stress brakers
- flexible or movable connection between a denture/pontic and direct retainer
- The stress is directed to the terminal abutments and onto the residual ridge (not PDL), and hence ridge resorption
- Ex: wrought wire retentive clasp
- Stress breakers placed at most distal pontic will become unseated when biting from the key-way
Intra-coronal retainers are used only in what RPD situation?
Precision attachments
- Used only in tooth borne partials (not Kennedy Class I or II), or must utilize stress breakers
- Require full cast crowns
Most frequent interference for mandibular major connectors?
lingually inclined PMs.
NOTE: if large lingual tori or lingually tipped teeth, use labial bar as the major connector.
Cannot use a lingual plate with severe anterior crowding
Dimensions for RPD:
- FGM to metal
- AP strap
- lingual bar
- 3 mm
- 6-8 mm wide
- 7 mm from FGM to FOM
Types of maxillary major connectors
- Palatal Plate = Kennedy Class I (all posterior teeth missing)
- Single palatal Strap = kennedy Class III
- Single palatal bar = lack rigidity. Not used for Kennedy Class III.
- AP Palatal Strap = most versatile for any situation
- AP Palatal bar = must be v. bulky → tongue interference
- Horseshoe = least rigid = only indicated when palatal tori cannot be removed
Altered Cast technique
used for RPD metal framework to see the relation to ST
RPD terms:
- supports
- brace
- retentive
- stable
- Support = resist vertical forces (main job of rest seats and edentulous ridges), doesn’t change position when forces are added.
- Bracing = resist horizontal (reciprocal arm)
- Retentive = resist occlusal direction (gravity, away from tissue) = distal parts of the retentive clasps
- Stable = Resist dislodgment horizontally. RPD stability is made via occlusion
Rest seat prep
- main job is to resist vertical forces of occlusion
- Mesial rest seat (and indirect retainers) eliminates Class I lever action and resists gingival and vertical displacement * main reason
- Base of preparation = 2.5 mm
- Marginal ridge reduction = 1.5 mm
- positive rest or acute angle (less than 90 degree) with the minor connections
Retentive arm
tip is flexible, while other components are rigid
Guide planes should be:
2/3 width of BL cusps
1/3 of BL width of tooth
Extend vertically to 2/3 of clinical crown from marginal ridge
Cingulum rests
Cingulum rest = Max. canine (due to gradual incline. Mand. Canine has too steep of a lingual incline for a proper rest)
o MD length = 2.5 – 3 mm
o FL length = 2 mm
o IA length = 1.5 mm
o These measurements prevent LA CI and LI from proper cingulum preparations
Cingulum rest is more esthetic and less torque, compared to incisal rests. But the later is used when cingulum rests cannot (LA incisors)
Incisal rests width = 2.5 mm, Depth = 1.5 mm
mesial rest eliminates what type of lever system?
Class I
Suprabulge clasps
- CC
- Ring
- Embrasure
- Reverse action
- extended arm
- half and half clasp
Supra bulge begin at rest seats, while infrabuldge come from he denture base
Infra-bulge (I-bar, T-bar, Y-bar) are known to be too tissue irritating. However, advantages include more efficient retention, less coronal contour distortion, less tooth contact (less caries prone, cleaner), greater adjustability and more esthetic in most cases, than supra bulge retainers
As the maxillary sinus enlarges, the ____ moves downward
tuberosity
Risk of using denture adhesives and pastes
May change the bite, which may alter the ridge.
Anterior teeth are placed ___ mm from incisive foramen
8 mm
Cheek biting in dentures
- posterior teeth set edge to edge
- inadequate VDO
reline immediate dentures when?
5 months and 10 months post EXT
most common reason to obtain the most extensive coverage for a mandibular CD
increase capacity of the underlying structures to withstand the stress due to biting force and to increase the effectiveness of the seal
- Under-extension of the peripheral border affects denture stability
- Marked ridge resorption will occur if the denture base terminates short of the retromolar pad
casts made from irreversible hydrocolloids are more accurately mounted with what? What about with elastomeric materials?
- wax records
2. ZOE paste or other elastomeric materials
posterior palatal seal
posterior outline: vibrating line (Ah) + haular notch (pterygomaxillary notches)
anterior outline: distal extent of the hard palate (blow line)
The seal compensates for the polymerization shrinkage of the resin during processing of the denture.
denture porosities occur from
insuffiient pressure on the flask in processing
- need to be under 20-30 psi
- Positives are found in the THICKEST part
- Self cured resins distort the denture less than heat cured resins, thus are used more for denture repairs
Edentulism leads to:
- Deep nasiolabial groove
- Narrow lips
- Increase in columella-philtral angle
- Prognathic appearance
modeling compound (plastic)
has a low thermal conductivity
Face-bow
true hinge axis
- not a mxillo-mand. record
- Used to record arc of closure
- Ear tragus to outer eye canthus
capping vs shoeing in cusp coverage for FCC
Capping = complete functional cusp coverage (1.5 mm gold)
Shoeing = veneering of non-function causp with slight bevel (1.0 mm gold). Never used on functional cusps.
Gypsum Bonded Investements
Gypsum Plaster
• Setting expansion = calcium sulfate-hemihydrate crystal growth
- Alpha hemi-hydrate = boiled gypsum in 30% CaCl= smaller, prism/rods = much harder = dental stone
- Beta hemi-hydrate = heated gypsum to 120-150 C = more porous, larger and irregularly shaped = dental plaster = weakest gypsum product
All gypsum products + water → calcium sulfate dehydrate → hemihydrate (add water to reverse the rxn)
All products are weaker in tensile strength than compression strength Weaker stones (Type I) need more water, with lesser compression strength
Main components of Gypsum Bonded Investments: Refractory, binder, modifiers
- Refractory Filler = SiO2 = Quartz = 60^ of the investment = Different thermal expansion coefficients = Thus, regulates thermal expansion of the investment
- Binder = calcium hemihydrate = hardens with water = thus adds strength to the investment. Less water = thinner mix = weaker material
- Modifiers = modify other properties
compensates for solidification shrinkage
Onlay prep
- mesial box has axiopulpal line angle longer from FL than axiogingival line angle
- M and D axial walls converge for retention (or risk undercuts)
- from F to L, the D axiopulpal line angle is longer than the M axiopulpal line angle
- Gingival bevel is required.
Ideal margin: 40 degree bevel. Gingival it is 30 degrees.
> 40 degrees it is too thick to burnish, less than 30 degrees its too thin and breaks
Acrylic curing via:
- Heat cured
- Self cured
- Heat cured = accelerator is used to decompose the acrylic initiator (benzoyl peroxide) into free radicals for polymerization
- Self cured = cold cure = auto cure = activator is added to the monomer that begins the polymerization process.
Heat cure has less residual monomer, thus stronger and more color stable.
Acrylic initiator = benzoyl peroxide
What muscle influences the buccal vestibule in a lower completed denture?
AKA buccal shelf
Buccinator m. (runs obliquely)
NOTE: distobuccal extension = masseter m. distolingual extension = superior constrictor m. buccal vestibule = buccal shelf Lingual frenum = genioglossus m.
Lingual border of mand = palatoglossus, genioglossus, mylohyoid, superor pharnyngeal constrcitor m.
Border molding with ZOE impression requires only 1 shot at insertions, while modeling compound can be used with multiple insertions
What muscles are found in the retro-mylohyoid area?
palatoglossus m.
superior constrictor m.
Ideal metal alloy for an RPD framework?
- Metal choice = gold alloys (low yield strength, low modulus of elasticity = high flex). If Chromium-cobalt is used, should incorporate wrought wire (more rigid)
- Chrom-cobalt claps engages less undercut (decrease retention)
- Gold clasps offer half the retention of chromium-cobalt when engaging identical undercut
- Bending chrome-cobalt has higher fracture due to cobalt hardens more rapidly than gold
chromium-cobalt
- tarnish resistant
- low cost
- low density
- v. stiff (low modulus of elasticity)
- low flexibility
Counter stiffness with using wrought wires.
- low yield strength + low modulus of elasticity = higher flexibility. Thus, Gold is twice as flexible as Cr-Co, and is thus better.
Wrought wire
Wrought wire = 0.02” undercut + elongation % of 6% or more. This allows the the clasp to bend without microstructure changes that could compromise its physical properties.
- Wrought wire means that the metal is cold-worked (not cast metal)
- Allowed to have a smaller diameter to have same retention than cast metal
- 25% greater strength, hardness, tensile, flexibility, ductility than the cast alloy, due to a fibrous microstructure. BUT too much heat will reduce it via recrystallization.
- Clasp will be rigid except the tip which is engaged to the undercut
- Wire gauge is selected based on its active length. So a 7 mm or less arm clasp should be made with a finer wire (20 gauge)
High vs Low fusion porcelain teeth
High fusing = denture teeth
Medium = ACC and porcelain jacket crowns
Low fusing = PFMs
Ceramic Properties
High MP High modulus of elasticity Low coeficent of thermal expansion low reactivity (absorption, solubility) Brittle solid = stronger compression than tensile strength
Primary support for dentures
MAX: Horizontal hard palate, maxillary tuberosity
MAND: Buccal shelf, retromolar pad
secondary support = palatal ruggae
Mand DB = massetter m.
Max DB = coronoid process
Register condylar path with
protrusive records
- The least reproducible record
- Protrusive interferences are found on distal inclines of facial cusps of maxillary posteriors and mesial inclines of facial cusps of mand. post.
Average measurements of:
- opening
- protrusive
- retrusive
- lateral excursions
Open = 50-60 mm (Lateral pterygoids**, digastric, mylohyoid, geniohyoid) Protrusive = 9 -10 mm (Lateral pterygoid) Retrusive = 1 mm (temporalis m. posterior fibers) Lateral = 10 mm (one lateral pterygoid, moves to opposite side in function. During trauma, its same side)
Implant types
- Endosseous = surgically inserted into bone
a. Root form = tapered
b. Blade form = flat. Used when bone width is inadequate. - Subperiosteal = framework which rides on bone, under the mucoperiosteum. Not a true osseointegrated form of implants.
- Transosseous = similar to endosseous implants, but penetrate the entire jaw. Used in atrophic jaws
CR vs MI
CR = terminal hinge position = maxillo-mandibular record = bone to bone relation = pure rotational movement MI = CO = true hinge axis
CO = tooth guided
CR = ligament guided
Rest position = muscle guided
Properties of an ideal bite registration
low resistance to teeth and low flow at mixing
Ideal placement of terminal end of retentive arm
middle 1/3 of gingival third of the crown.
But it is acceptable to have it placed at the junction of the gingival and middle 1/3 of the crown.
