Prosthodontics II

Light chamfer

0.3-0.5mm thick, gold crowns, wide gold collars of PFM crowns

Porcelain veneer

0.3mm gingival third reduction, 0.5mm facial reduction, 1-2mm incisal reduction, intra-enamel prep

Minimum metal thickness

0.5mm at margin, 1mm at non-contact areas, 1.5mm at contact areas Min porcelain thickness = 1.5mm Min PFM thickness = 1.5mm in non-contact areas (1.2mm porcelain, 0.3mm metal), 2mm in contact areas (1.5mm porcelain, 0.5mm metal)

Heavy chamfer

1-1.5mm thick, PFM crowns and some all ceramic crowns, if not given enough room lab will be forced to over contour the crown

Shoulder

1-1.5mm thick, porcelain or PFM restorations, all ceramic crowns, maximizes esthetics - eliminate display of metal, aggressive prep - potential for pulpal embarrassment

Cobalt-chromium

2.3% shrinkage which causes irregularities and porosity Cold working - involves manipulating the metal while ambient temperature, main reason why clasps break Clasp assembly is cold worked every time it is seated and dislodged

Hygienic/sanitary

2mm, posterior mandible, good hygiene, poor esthetics, requires enough VDO/restorative space

Applegate's rules

Classification should be assigned AFTER ay extractions Missing 3rd molars are not considered Abutment 3rd molars are considered Missing 2nd molars are not considered Most posterior edentulous area determines the classification Other edentulous areas are referred to as modifications Extent of modification does not matter, only the number Class IV cannot have any modifications by definition

Maxillary major connector

Complete palatal plate = most rigid, indicated when posterior teeth are missing bilaterally, periodontally compromised teeth, shallow vault, small mouth, flat or flabby ridges Horseshoe = least rigid, only used if large palatal torus Palatal strap All major connectors should cross the midline at a right angle

Setting time

Decrease ST - hot water, less water, use of slurry water, increased spatulation Increase ST - cold water, more water, decreased spatulation

Method

Direct = made directly in pt's mouth, Indirect = made outside of pt's mouth, usually in a lab setting on a cast

All-ceramic crown

Glass-infiltrated ceramics (anterior teeth) are etched w hydrofluoric acid and treated w silane coupling agent and bonded to tooth Ceramics w no glass content (zirconia and alumina) are luted to the tooth w cement

Metal alloys

High noble = >60 noble, of which at least 40% if gold Noble = >25% noble Base metal = <35% noble (Ni-Cr, Ni-Cr-Be, Co-Cr, Ti)

Mandibular major connector

Lingual bar = when depth of lingual vestibule >7mm, simplest and most common Lingual plate = when depth of lingual vestibule <7mm OR additional tooth loss anticipated, lingual tori, all posterior teeth are missing bilaterally Labial bar = when there is a missing canine, unfavorable soft tissue contour, questionable periodontal prognosis

Biologic

Mechanical injury = thinnest gingival tissue is lingual molars and facial premolars Thermal injury = proximity to pulp (water spray, sharp cutting instruments, intermittent light pressure) Chemical injury = soaked retraction cord, certain elements Bacterial = leakage under crown

Saddle/ridge lap

NEVER use, bad hygiene, perio problems

Material

PMMA = indirect, exothermic, PEMA Bis-acryl composite (Luxatemp) = direct

Mechanical

Retention = prevents dislodgement along long axis Resistance = prevents dislodgement by apical, horizontal, oblique forces Taper = angle of convergence formed btwn 2 opposite prepared axial surfaces (6-10 degrees) Height or length = from occlusal/incisal surface to crown margin (3mm min for incisors and premolars, 4mm min for molars) Width = MD or FL dimension of base Height to base ratio = min ratio is 0.4

Connector design

Rigid = either cast in one piece or soldered Non-rigid = indicated when it is impossible to obtain a common path of insertion btwn abutments Connectors for PFM bridges should have a minimum height of 3mm

Minor connector

STABILITY, connects major connector to rests, indirect retainers, clasps

Rest

SUPPORT, rigid extension of RPD framework that contacts the occlusal, lingual, or incisal surface of an abutment tooth

Percentage elongation

ability of a material to be burnished, contact stress locally exceeds the yield strength of the material Gold is a prime example

Flexural strength

ability to resist fracture during bending

Compressive strength

ability to resist fracture during compression

Tensile strength

ability to resist fracture during pulling

Fracture toughness

ability to resist the propagation of a crack Zirconia has the best fracture toughness

Condensation silicone

alcohol byproduct, which causes shrinkage of the impression when evaporated, 30 min to pour

Dental stone HS/HE

also used for fabrication of dies, high expansion

Reduction

amount of occlusal tooth structure removed during prep (1.5-2mm)

Clearance

amount of space left btwn tooth prep and opposing tooth (1.5-2mm)

Clean the prep

anesthesia will make it harder to confirm occlusion, provisional cements have eugenol which inhibits polymerization of resin, so remove as much as possible w excavator, explorer, or wet cotton pellet before proceeding

Modified ridge lap

anteriors, good esthetics

Ovate

anteriors, superior esthetics, requires surgery, requires good ridge

Dental stone HS/LE

best abrasion resistance, least gauging water, least amount of expansion, used for fabrication of dies

Kennedy Class IV

bilateral bounded edentulous space which means it crosses the midline

Kennedy Class I

bilateral distal extension (all teeth distal to a tooth are missing)

3 principles of tooth preparation

biologic (health of oral tissues), mechanical (integrity and durability of restoration), esthetic (appearance)

If you have a short clinical crown prep

buccal grooves for retention, proximal grooves for resistance

Reversible hydrocolloid (agar)

changes btwn sol and gel based on temp, high accuracy

Body or dentin porcelain

contains most of the shade, builds up most of the crown

Malleability

deforms easily under compressive strength Gold is a prime example

Ductility

deforms easily under tensile strength Wires are a prime example

Provisional restoration

designed to enhance esthetics and provide fxn for a limited period of time after which it is replaced by a definitive prosthesis

Indirect retainer

distal extension area of a partial is 'loose' and not anchored posteriorly, rotational mvmt centered around an imaginary line drawn through the most distal rests, IR is directly perpendicular and anterior to the fulcrum line which provides bracing to resist rotational mvmt of distal extension area

Margin 1

edge or shelf at the base of the crown prep

Embrasure clasp

essentially 2 Akers clasps

Beading

exclusive for maxillary major connectors, involves scribing a 0.5mm rounded groove in the cast at the borders of the major connector, add strength and maintain tissue contact to prevent food impaction

Guide planes

flat parallel surfaces of abutment teeth that provide path of insertion and removal, 1/3 buccolingual width, extends 2-3mm vertically down from marginal ridge

Tissue management for impressions

fluid control, tissue displacement (retraction cords - stretch circumferential periodontal fibers), electrosurgery - contraindicated in those w medical devices like pacemakers or insulin pumps (electrode must not contact teeth)

Long span PFM bridges are subject to

fracture under flexing due to porcelain's low ductility

Brittle

fractures easily w/o substantial dimensional changes Porcelain is a prime example

Gold alloys

from lowest to highest strength, from greatest % gold to lowest Type I - soft, 98-99% gold, inlays, Class V restorations only Type II - medium, 77% gold, inlays, onlays Type III - hard, 72% gold, crowns Type IV - extra hard, 69% gold, bridges/post and cores/clasps/RPD castings

Gypsum materials

from lowest to highest strength, from most to least porous Type I = impression plaster Type II = model stone Type III = dental stone Type IV = dental stone, high strength, low expansion Type V = dental stone, high strength, high expansion

Water

gauging water - extra water needed to obtain a workable mix of material, does not chemically react w gypsum Increase water - less strength, more porosity, less expansion, increased setting time Decrease water - more strength, less porosity, more expansion, decreased setting time

Noble metals

gold = tarnish resistance, platinum = strength, increases melting temp, palladium = strength Silver is NOT a noble metal and causes greening of porcelain

Desirable mechanical properties

high yield strength, high elastic modulus, casting accuracy, CTE close to that of tooth (11.4), biologic compatibility (Ni and Be allergies), corrosion resistance, minimal wear of opposing dentition

I-bar contraindications

if there is not enough depth, if there is soft tissue undercut

Aqueous hydrocolloids

imbibition = absorption of water, syneresis = loss of water

Inlays, onlays, and partial crowns

inlay = within cusps, onlay = covers cusps 3/4 and 7/8 crowns = hybrid btwn onlay and full crown --> conserves tooth structure, less restoration margin in close proximity to gingival tissues, more easily seated during cementation

Cingulum rest

inverted V or U shape, 2.5-3mm MD length, 2mm labiolingual width (ledge), 1.5mm deep contraindicated for mandibular incisors benefits include good distribution of occlusal load, esthetics, strength from closeness to major connector

Impression plaster

low expansion, for mounting casts in articulator, sets quickly, 'no time for expansion'

Opaque porcelain

masks darker oxide color, provides porcelain-metal bond, masking must be accomplished w minimum thickness (0.1mm)

Elastic modulus

measure of stiffness or rigidity, stress divided by strain, sustain deformation w/o permanent change in size or shape

Coefficient of thermal expansion

measures the fractional change in size per degree change in temp, higher CTE = more tendency to change Composite (30 - unfilled resin is worst) > metal > tooth > ceramic Amalgam (25) Gold (14 - best) Tooth (11.4) Porcelain (6)

Proximal plate

metal plate that contacts proximal surface of abutment tooth

Gypsum

mined as calcium-sulfate dihydrate, manufactured w heat to get rid of some water to become calcium-sulfate hemihydrate, 20s vacuum mix or 30s hand spatulate, setting time is 45-60 min, disinfect w 1:10 bleach solution, glutaraldehyde, or iodophor spray

Conical

molars, similar to hygienic but marginally better esthetics

Bonding of porcelain to metal

monomolecular oxidative layer must be present for porcelain to bond to the metal

Circumferential clasp

most commonly used, retentive and reciprocal clasp arms as a unit, versatile

Incisal or enamel porcelain

most translucent layer

Model plaster

mouth guards and Essex retainers

Addition silicone (PVS)

no byproducts, best fine detail/elastic recovery/dimensional stability, inhibited by the sulfur in latex gloves and rubber dam

Metal-ceramic crown

occlusal contacts >1.5mm away from porcelain-metal junction

Occlusal schemes

occlusal point contacts preferred to be broad and flat to prevent wear Cusp-marginal ridge = seen in class I occlusion and w unworn teeth Cusp-fossa = seen in class II malocclusion

Margin 2

part of the restoration which forms its outer limit that adjoins to the cavosurface margin of the prepared tooth

Adhesive failures (btwn different materials)

porcelain-material if oxide was not formed, oxide-metal if metal is contaminated, porcelain-oxide if porcelain is contaminated

Cohesive failures (btwn same material)

porcelain-porcelain if inclusions or voids, oxide-oxide if oxide layer is too thick, metal-metal never happens

Mold

prefabricated crown (polycarbonate, aluminum, stainless steel), cellulose acetate crown form, putty or shim

Rest seat

prepared into occlusal, lingual, or incisal surface of an abutment tooth in order to receive and support a rest

Dental stone

removable prostheses and dx casts

Direct retainer (clasp assembly)

rest = support, minor connector = stability, clasp arms (retentive for retention, reciprocal for stability) Extra-coronal = most common, conventional clasp design, clasps should encircle a tooth at least 180 degrees Intra-coronal = precision attachment w key and keyway pattern, more esthetic because no clasps

RPA

rest, proximal plate, Akers clasp

RPI

rest, proximal plate, I bar (ideal Class II lever system)

RPC

rest, proximal plate, circumferential clasp (same as RPA)

Retentive clasp

retention, usually on buccal side, originates from minor connector and rest, contacts tooth below HoC/survey line Shoulder and middle should be above HoC, only the tip should be under HoC Tip is designed to engage in undercut and resist dislodging forces (seat passively unless force applied)

Major connector

rigidity, unites all other components, not placed on movable tissues

Incisal rest

rounded notch at incisal edge, 2.5mm MD length, 1.5mm deep, used as indirect retainer, less favorable leverage than lingual rest, not used often because of esthetic compromise

Occlusal rest

rounded, semicircular outline form (spoon shaped), 1/3 MD width, 1/2 intercuspal width, 1.5mm deep for base metal Floor inclines apically toward center, angle formed w vertical minor connector is <90 degrees

Irreversible hydrocolloid (alginate)

setting time is 3-4 min in pt's mouth, should be poured w gypsum within 10 min, active ingredient = potassium alginate, most inaccurate

Reciprocal clasp

stability, originates from minor connector and rest, contacts tooth above HoC/survey line, braces abutment tooth so it is not torqued by retentive clasp, usually on lingual side

Margin location

supragingival = above gingival crest equigingival = at gingival crest, subgingival = below gingival crest

Kennedy Class III

unilateral bounded edentulous space, teeth on either side of edentulous area

Kennedy Class II

unilateral distal extension

To increase setting time of alginate

use cold water, more water

To decrease setting time of alginate

use hot water, less water

Ring clasp

used when undercut is adjacent to BES, mostly used for molars where you can't get adequate undercut

Featheredge margin

very acute, thin margin, less invasive, best marginal seal, insufficient clearance for most materials, difficult to visualize

Polyether

very stable but easily influenced by water and humidity (hydrophilic, imbibition), very stiff and easy to break teeth on cast, 60 min to pour

Polysulfide rubber

water byproduct, moisture tolerant (hydrophobic, syneresis), 30-45 min to pour

Clasp selection

wrought wire used for periodontically compromised and endo teeth BES used Akers clasps w rest seats located adjacent to edentulous space Distal extension used in order of preference (RPI, RPA, and wrought wire)