fixed prostho

8/2/2019 Fixed Prostho

http://slidepdf.com/reader/full/fixed-prostho 1/42

DR.SHIREEN HAWWARI

M.SC. IN

PROSTHODONTICS

Fixed Prosthodontics



crowns

y Definition:

A dental crown is a tooth-shaped "cap" that is placedover a tooth - covering the tooth to restore its shape

and size, strength, and/or to improve its appearance.



Indications for crowns

y Weak tooth after RCT

y Large filling

y Hold a bridge

y On an implant

y Cover mis-shaped or mal-aligned tooth



Types

y Metal

y Porcelain fused to metal

y All ceramic

y All resin



Metal crowns

y used in crowns include gold alloy, other alloys (forexample, palladium) or a base-metal alloy (forexample, nickel or chromium). Compared with othercrown types, less tooth structure needs to beremoved with metal crowns, and tooth wear toopposing teeth is kept to a minimum. Metal crowns

withstand biting and chewing forces well andprobably last the longest in terms of wear down.

Also, metal crowns rarely chip or break. The metalliccolor is the main drawback. Metal crowns are a goodchoice for out-of-sight molars



Properties of metals

y Opaque lustrous chemical subtances

y Good conductors of heat and electricity

y High fracture toughness

y More ductile

y Resist tarnish and corrosion in air at room temp.

y Most metals are opaque white



Metal alloys

y Metal alloy is a substance with metallic propertiesthat consists of two or more chemical elements,atleast one of which is metal.



Metal alloysMetal alloys%noble metal content-by weight%noble metal content-by weight

y High noble

y Noble

y Base-metal

y 60% (40% gold)

y 25%

y <25%

alloys



High noble &noble alloys

y Type 1:83%gold,for small inlays

y Type 2 :increasing amounts of silver&copper,for large inlays

y Type 3:for crowns and bridges

y Type 4:for partial denture frameworks



Base metal alloys

y Nickel chromium

y Titanium

y Progold



Porcelain-fused-to-metal

dental crowns can be color matched to your adjacentteeth (unlike the metallic crowns). However, more

wearing to the opposing teeth occurs with this crown

type compared with metal or resin crowns. Thecrown's porcelain portion can also chip or break off.Next to all-ceramic crowns, porcelain-fused-to-metalcrowns look most like normal teeth. However,

sometimes the metal underlying the crown's porcelaincan show through as a dark line, especially at the gumline and even more so if your gums recede.



A ll-resin dental crowns

less expensive than other crown types. However, they wear down over time and are more prone to fracturesthan porcelain-fused-to-metal crowns.



A ll-ceramic or all-porcelain dentalcrowns

provide the best natural color match than any othercrown type and may be more suitable for people withmetal allergies. However, they are not as strong as

porcelain-fused-to-metal crowns and they wear downopposing teeth a little more than metal or resincrowns.



Definition

y Dental ceramics :inorganic compounds with non-metallic properties, typically composed of metallic orsemi-metallic elements.

y They have composite structure (crystalline phases within a glassy matrix.

y Feldspare:the main raw ingredient of the classicalhigh fusing dental porcelains for CFM.



Feldspare

y Crystalline, opaque

y When melts, it forms leucite and moltenglass(potassium aluminum silicate)



Classification of ceramics according tocomposition

y Predominantly glassy(feldspathic glasses)

y Particle-filled glasses

y Polycrystalline



Particle-filled glasses

y Composite ceramics:crystalline filler particles areadded to the base glass composition to improvemechanical properties.(leucite,aluminium oxide,

zirconium oxide, lithium disilicate).



Moderately-filled glasses

y 17-25 mass% leucite added to feldspathic glass

y High thermal expansion/contraction coefficientcompared to feldspathic glasses



Highly-filled glasses

y Crystalline particles of al.oxide(55 mass%) orleucite(40-55mass%)are added

y Dispersion strengthening

y Ex.:Empress and Inceram ceramicsy Glass ceramics:ceramming(mica

crystals),Dicor(Dentsply),Empress2



temperature

y High fusing

y Med.fusing

both for production of denture teeth

y Low fusing

y Ultra-low

both for crown &bridge



method

y Sintered porclains

y Slip-casting

y Lost wax

y Hot-pressed,injection molded

y machined



Sintered porcelains

y Powder+water=slurry,built up in layers,then it issintered.

y It is the transformation of an originally porous

compact to a stronger denser ceramicy Used with feldspathic porcelain



technique

y In-ceram ceramic system



Lost wax technique

y Glass ceramics



Hot-pressed

y External pressure at elevated temperatures to obtainsintering of the ceramic body.

y IPS Empress,Optec pressable ceramics



Machined ceramics

y Cerec system

y Celey porcelain



ceramic ingot



Before fixed prosthodontic intervention

y History taking &clinical examination

y Diagnostic casts

y Treatment planning, taking into consideration the

patient needsy Periodontal considerations

y Mouth preparation:perio,RCT,fillings..a logicaltreatment sequence



Principles of tooth preparation

y Occlusal clearance

y Axial reduction

y Finish line

y The optimum restoration should satisfy biological,mechanical,and esthetic requirements



Biological

y Conservation of tooth structure

y Avoidance of over contouring

y Supra gingival margins when possible

y Harmonious occlusion

y Protection against tooth fracture



Indications for subgingival margins

y Dental caries,cervical erosion, or restorationextended sub-ggv.and crown-lengthening notindicated

y More retention/resistance neededy Aesthetic considerations



Aesthetic consideratios

y Min display of metal

y Max thickness of porcelain

y margins



Mechanical

y Retention form: preventing dislodgment by forcesparallel to path of placement

y Resistance form: against horizontal or obliqueforces(mastication and Para functionalforces),preventing rotation of the crown

y Prevent deformation: alloy selection, proper tooth

prep.metal-ceramic framework design



Min required clearance: buccal cusp:1.5mmlingual cusp:1mmmarginal ridges&fossae:1mm



A nterior tooth preparation

Incisal:1.5-2 mm

facial:.1-1.5 mm

Ligual:.1-1.5 mm

Chamferpreparation(1mm wide),or rounded shoulder: to

direct stresses optimally in the completedporcelain restoration,forces on crown will beparallel to its path of placement



Margin design

y Feather edge: not recommendedy Chisel edge: occasionally on tilted teethy Bevel: for onlays and inlaysy Chamfer: for cast metal restorations and lingual margins

of the metal ceramic crowns, more conservative thanshoulder, produce less stress on cementy Shoulder: facial margins of metal ceramic and all ceramicy Slopped shoulder: facial margins of metal ceramic

crownsy Shoulder with bevel: facial margin of metal ceramic

crowns with supraggv margins, reduces leakage(only bevel>70degree,extends prep.apically,cant beacommodated in the shallow sulcus of ant.teeth

fixed prostho

Documents