#FIXEDPROS

Indications and Contraindications for crowns

crown vs fillings for caries

• fillings are better for primary, secondary caries
• crowns can be better for larger lesions and cusps lost

General indications for crowns

• failing restorations, lack of shape, discolouration
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  • very large restorations have unpredictable long term durability
  • lost dentine often needs to be replaced by suitable core of restorative material
  • sometimes needs endo first
• trauma
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• gross tooth wear
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• peg shaped upper lateral incisors
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• amelogenesis imperfecta
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• dentinogenesis imperfecta
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• enamel hypoplasia
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• changing shape and size of teeth/aesthetics
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Mechanical Problems

• sometimes a a filling is sufficient, but pattern of damage to tooth gives concern about retention of the restoration, strength of remaining tooth, or strength or restorative material
• if a filling fails, the next option is a larger restoration or a crown
• if a crown fails, another crown may not be possible and extraction may be the only option left
• deciding between filling and crown
  • how real is the risk of mechanical failure of the filling or surrounding tooth? what can be done to minimise this risk?
  • how much more destruction of sound tooth tissue is necessary to make a crown?
  • more conservative option first is usually better

Indications for anterior crowns

• caries and trauma
• non vital teeth
• tooth wear
  • only when cause cannot be identified or eliminated
• hypoplastic conditions

Alternatives to anterior crowns

• internal and external bleaching
• composite restorations
• composite and porcelain veneers
  • composite veneers quite reversible, porcelain are not
  • porcelain more costly

alternatives to posterior crowns

• amalgam restoration
• composite restoration
• composite inlay and onlay
• ceramic inlay and onlay

Types of Crown

types

• Anterior Complete crowns for vital teeth
  • ceramic crowns
  • metal ceramic crowns
  • other types
• Anterior crowns for root filled teeth
• Posterior complete crowns
• Posterior partial crowns

Anterior Complete crowns for vital teeth

Ceramic Crowns

• traditional fused porcelain jacket crowns
  • 1-2mm thick porcelain crown covering entire tooth
  • alumina incorporated to porcelain powder which is fired in a furnace shaped on an impression of the tooth
• pressed ceramic crowns
  • ceramic material pressed at high temperature and pressure onto a die then building up layers of traditional porcelain to create right contour and shade
• milled ceramic crowns
  • core produced with strong ceramic, then additional porcelain added to complete the crown
• zirconia cores
  • zirconia core with conventional porcelain built on top
• cast crowns
  • ceramic cast placed in ceramming oven, which it undergoes crystallisation conversion and becomes much stronger
  • then staining and porcelain in a porcelain furnace
• reinforced porcelain
  • alumina substruture formed and coated with glass fired powder, which will infilitrate the pores after firing for several hours

ceramic crowns

• advantages
  • appearance
  • stability
  • cost
  • plaque
  • brittleness
• disadvantages
  • marginal fit
  • brittleness
  • removal of tooth tissue

Metal ceramic crowns

• PFM
• 3 groups of alloys
  • precious metals containing platinum and gold
  • semi precious containing palladium or silver
  • base metal alloys containing nickel and chromium
• porcelain fired to the metal at a temperature that doesn't melt or distort the metal
• advantages
  • strength
  • minimum palatal reduction
  • adaptability (secondary retentive factors)
  • can be cast, soldered or laser welded
• Disadvantages
  • strength
    • stronger than natural dental tissues so can cause root or tooth prep to fracture in trauma
  • appearance
  • destruction of tooth tissue
  • cost

Cast metal acrylic or composite faced crowns

• usually long term provisional restorations

Fibre reinforced composite crowns

• long term provisional crowns / bridges

Anterior crowns for root filled teeth

• endo access + crown prep leaves insufficient dentine to support crown
• therefore we need retention via post fitted into enlarged root canal

types

Composite/GIC core and crown

• if sufficient dentine remains, endo access cavity can be filled with GIC or composite

post and core and separate crown

• crown is either ceramic or metal ceramic crown
• post and core can be made in laboratory from impression of post hole (indirect)
  • usually has core and sometimes diaphragm cast with the post
  • adaptable, can be used in very tapered root canals or elliptical shaped canals,
• ready made post can be purchased and cemented into post hole which is prepared with a matching drill of same diameter as the post (direct)
  • composite core built up directly after post cemented
  • avoids need for temp crown
  • strong and can be more retentive
• direct preferable to indirect when possible
• direct post materials
  • precious metals - little advantage over non precious unless diaphragm is needed
  • non precious metals - usually stainless steel, most common, strong
  • carbon fibre - black, difficult to disguise
  • quartz fibre
  • titanium
• post shapes
  • parallel smooth or serrated
    • preformed metal with composite core or preformed plastic post
    • more retentive than tapered smooth, serrations increase retention
  • tapered smooth or serrated
    • cast gold or other alloy
    • least retentive but if long and good fit, retention usually sufficient
    • serrations increase retention but weaken post
    • easy
    • less likely to perforate
    • diaphragm may be added to cover root face
  • parallel threaded
    • fine threaded - very retentive, self tapped
    • coarse thread - cannot be removed by techniques to remove other types of post
  • tapered threaded
    • base metal
    • considerable dentine stress, not to be used permanently
    • removal difficult and risks splitting the root
• choosing post systems
  • usually preformed serrated or cast parallel serrated post
  • preformed preferable for single uncomplicated crowns
  • cast parallel serrated preferred when core needs to be extended as a diaphragm to cover part or all of root surface when stronger core is needed
  • tapered smooth cast post and core used for very tapered or oval root canal

One piece post crown

• insufficient space within crown for both retentive core and separate crown
• crown made of metal ceramic material with post cast of crown is usually solution
• very short clinical crown or lower incisors

Posterior Complete Crowns

Cast metal crowns

• metal alloy groups
  • 1 (or I or A) soft used for small inlays
  • 2 (or II or B) medium used for large inlays
  • 3 (or III or C) hard used for crowns and bridges
  • 4 (or IV or D) extra hard used for larger bridges, implant frameworks and denture clasps
• used when patient doesn't mind metal or it wont show during normal movements of the mouth
• requires minimum reduction of tissue, occlusal surface readily adjusted and polished
• cost is least
• most convenient for rest seats, guide planes, reciprocal ledges and undercuts with partial dentures
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Metal ceramic crowns

• better appearance than cast metal
• porcelain on buccal and occlusal,
• requires more tooth tissue removed for thickness of porcelain

Ceramic crowns

• more preparation required to allow for crowns of adequate thickness
• need to be careful with occlusion
• not for bruxists

Posterior partial crowns

three quarter crowns

• cover 4/5ths of the tooth surface
  • mesial distal, occlusal lingual
• retained by grooves on MOD surfaces
• always made of cast metal, and are used when buccal surface of tooth is intact and reducing it would be unaesthetic, reduce strength of prep
• more conservative

Cores for posterior crowns

amalgam, composite or GIC

• pins can be used, not for root filled teeth, used rarely
• most common post is parallel serrated preformed metal post
• Nayyer technique can be used where pulp chamber is intact
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cast posterior cores

• pretty outdated
• can be used for single rooted premolars when post hole is tapered and when diaphragm is needed

Tooth considerations

• strategic value
  • not all teeth are equal
  • depends on other teeth and how useful this one is
• appearance
  • usually consider replacing restorations before a crown
• crown pulp and perio condition
  • deep caries or fractures will make crown difficult
  • perio surgery can be used to expose margin of the fracture
  • always vitality test
  • if recent endo and unsure of outcome
    • wait and see if symptoms settle
    • repeat if unsatisfactory
    • proceed with core and temp but wait for final crown until symptoms settle
  • treat perio first
• occlusion
  • canine guidance, group function
  • contact should be either crown or tooth, not at their junction
• root length
  • root to crown ratio
  • bone suport

Decisions to be made

• is tooth kept or extracted
  • restorable vs non restorable
• crown or filling
• any preparatory treatment needed before crown
  • ortho, perio, endo

Planning

• aesthetics
  • wax mock up, informed consent
  • modified study cast
  • shade, get bleaching done prior to shade match
• need for a core
  • sufficient tooth structure for crown prep?
  • otherwise built up via core,
  • what core material
  • decide position of crown margin
• type of crown and material
• prep design
• appointments and lab stages`