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Week 51 > Prosth: Sheeba > Flashcards

Flashcards in Prosth: Sheeba Deck (28)
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Goal of Tooth Preparation:

  • Creat space for the restoration material
  • create a path of insertion 
    • no undercuts


Tooth preparaiton inculdes:

  • Axial Walls
    • buccal, lingual, mesial, distal
  • Occlusal/incisal surface
  • Finish line 
    • "preparation margin
  • Funcitional Cusp Bevel


Hand pieces when preping a tooth

  • Turbine handpiece 
    • Gross tooth prep (40,000 RPM)
    • very aggresive 
    • light strokes 
    • might give rough surface
  • Electric handpiece
    • Finishing and smoothing preparation
    • 5000-10,000 RPM


Burs for Tooth Prep

  • Diamond Burs
    • easy and fast preps
    • micro roughness
    • gives excellent crown retention
    • more than one size an dshape
      • each used for specific task
    • Different abrasiveness
      • color coded
  • Carbide Burs
    • remove deeps caries
    • cutting boxes and grooves
    • cut metal crowns


Bur: Color coding scheme

  • Yellow (504)
    • super fine
  • Red (514)
    • Fine
  • Blue (524)
    • medium
  • Green (534)
    • coarse
  • Black (544) 
    • super coarse


Tapered Diamond Burs

  • Different tip shape=different finish
    • round end--Chamfer finish line
    • flat end--Shoulder Finish Line
    • fine end-- Opening Proximal Contacts


Football Diamond Burs

  • reduce:
    • occlusal surface of posterior teeth 
    • Lingual Fossa of Anterior teeth


Wheel Diamond Burrs

  • Reduce:
    • occlusal surface of posterior teeth
    • Lingual Fossa of anterior teeth
  • same as Football diamond


Preservation of Tooth structure

  • balance b/w preservation and room for the restoration to achieve adequate restoration strength and satisfractory esthetics
  • Over reduction might lead to=Poor prognosis
    • pulpal exposure
    •  weakening of the tooth


Guidelines for Preservation of Tooth Structure

  • Use partial coverage restorations
  • Avoid over tapering
  • occlusal reduction should follow occlusal anatomy
    • limit to the needed clearance
  • Avoid unnecessary subgingival extensions of prep


When are Subgingival Finish lines used:

  • Esthetic reasons
    • Hiding the margin in anterior tooth
  • Subgingival caries or restoration
    • can't put the preparation margin on caries or direct restoration
  • Short preparation
    • subgingival extension to gain more height for resistance form


Retention vs Resistance

  • Retention:
    • resistance to restoration in dislodgement along path of insertion
  • Resistance:
    • resistance to restoration in any direction other than path of insertion
  • Retention and resistance
    • are inseparable qualitites
    • are not used interchangeably


Factors affecting retention and resistance

  • Total Occlusal Convergence Taper
  • Length "preparation height


Total Occlusal Convergence Taper

  • seating VS resistance and and retention
    • prep w/parallel axis walls=negative effect on seating the restoration due to hydraulic pressure build up
    • Overtapering
      • negative impact on retentions and resistance
    • Recommended TOC
      • 10-20 degrees
  • shorter the prep the less the TOC will be required to provide resistance and retention


Path of insertion

  • Prep with parallel axial walls 
    • best resistance and tape
    • impossible to prepare without having undercuts
  • Slight taper needed to:
    • help seating of the crowns
    • decrease hydraulic pressure 


Length Preparation Height

  • Retention and resistance increase w/the increase occlusogingival height of the prep
  • To achieve a adequate prep that provides good retention and resistance a ratio b/w occlusogingival hiegh and buccolingual width should be 4:10
  • The loonger the prep
    • more surface area to lute cement (interlock)
    • provide excellent retention
  • When occlusogingival height is not adequate
    • added means rettention are added
      • pins
      • boxes 
      • grooves
  • Short preparations:
    • TOC should be kep to minimal


Structural Durability


  • give enough bulk to the restoration to provide adequate strength
  • only provided by tooth reduction
  • inadequate space leads to
    • bulky restoration or weak restoration
  • AMount of reduction depends on the material being used


Structural Durability: Occlusal Reduction

  • Occlusal Clearance allows for strength on the restoration
  • Occlusal surface is subjected to the highest stress


Structural Durability: Functional Cusp Bevel

  • Promides more room to increase the bulk of the restoration
  • No functional cusp bevel leads to:
    • weak restoration
    • bulky restoration that opens the occlusion


Structural Durability: Axial Wall reduction

  • Needs specific bulk for maximum strength=1-1.5mm
  • Axial wall reduction done with bur placed parallel to long axis 
    • automatically creates the finish line
    • results in no undercut
    • provides slight taper
  • Lack of axial wall reduction leads to:
    • overbulking the restoraiton
    • weak restoration


Marginal Integrity (marginal Adaptation)

  • most important requirements for successful resotration 
  • Lack of marginal adaptation leads to:
    • recurrent caries
    • perio disease
    • ultimately tooth loss
  • Type of finish line plays a role in marginal adaptation
  • Selecting finish line depends on:
    • type of restoration
    • tooth position
    • practitioiners preference


 Marginal Integrity (marginal Adaptation): Finish Lines

  • Type of restoration:
    • Chamfer FL and Shoulder with Bevel FL 
      • metal margins
    • Shoulder FL
      • ceramic (porecelain) margins
  • Tooth position:
    • anterior teeth ceramic margins=esthetic reaons
    • ceramic margins need shoulder FL
  •  most common finish line
    • Chamfer and Shoulder


Finish Lines: Chamfer vs Shoulder




  • Chamfer
    • advantages:
      • distinct margin
      • adequate bulk 
      • easier to control
    • disadvantage
      • care needed to avoid unsupported lip of enamel
    • Indication:
      • cast metal restorations
      • lingual margin of metal ceramic crowns
  • Shoulder
    • Advantages:
      • bulk of restoration material
    • Disadvantage:
      • less conservative of tooth structure
    • Indicaiton:
      • facial margins of metal ceramic crowns


Marginal Integrity (marginal Adaptation): Chamfer Finish Line

  • "classic" depth of reduction shoulud be 0.5mm
  • Axial depth sutiable for metal margins
  • prepared with tapered diamond w/round end
  • Only half of the bur should be in the tooth\
    • if whole bur is in the tooth=J-margin (enamel lip)


End Cutting Bur

  • aka Floor Bur
  • 5000 RPM
  • removes J margin
    • corrects Chamfer FINish line


Marginal Integrity (marginal Adaptation): Shoulder Finish Line

  • Use tapered diamond w/flat end
  • use w/ ceramic margins
  •  Regular shoulder vs Modified shoulder
    • modified shoulder FL has more round axial gingival angle
      • similar to deep chamfer


Preservation of the periodontium: Biological Width

  • location of the restoration margin could negatively affect the periodontal health of the tooth
  • Finish line could be supragingival or subgingival
    • Supragingival:preferred
      • least impact on periodontal tissue
    • Subgingival:
      • greatest impact on periodontal heealth
  • Causes chronic periodontal inflammation
    • infrabony pocket
    • gingival recession


Define Biological width

  • distance b/w depth of the sulcus and crest of the alveolar bone