CH 1 handbook Flashcards
what is a preparation
THe final shape (form of the tooth produced by instrumentation) to a restoration
what is a complete veneer crown
An extracoronal preparation involving the entire clinical crown
What is the Path of Withdrawal
The imaginary line along which a casting is moved when it is separated from its prep
what should the path of withdrawal coinside with
with the tooth’s long axis
what forms the tooths long axis
opposing axial surfaces in 3rd of the tooth
what is an axial wall
The part of the crown preparation preparing in the long axis of the tooth
what are the names for the axial walls
Buccal, lingual, mesial, or distag
what is the Convergence angle
The angle or taper formed b diametrically opposed axial walls
what is the chamfer
The cervical junction of the prepared axial wall and the unprepared portion of the strucutre
where does the chamfer extend
Around the cervical portion of the tooth preparation
what are the line angle
The lines formed by the junction of any two tooth surfaces
what should the line angles be shaped like on a crown prep
Ground
Where is the occlusoaxial line angle
The junction between the occlusal surface and an axial wall
where is the cavo-surface line angle
The junction of the prepared and unprepared tooth strucutre
what are depth orientation grooves
Placed on the surface of the tooth to provide a reference to determine when sufficient tooth strucutre has been reduced
what is the functional cusp bevel
A wide bevel placed on the functional cusps
what is the role of the functional cusp bevel
the thickness of the tooth strucutre removed when preparing this bevel ensure that correct contours of the final restoration can be re-established while providnig correct convergence and adequate thickness of retorative materials
when is a crown prep seen as undercut
If a wax pattern cannot be withdrawn from its die without distorting
what cuases a crown prep to be undercut
Depression in an axial wall (can be from a carious lesion)
Diametrically opposed axial wals that do not converge
how to fix undercuts due to a depression in the axial
correct with base matterial
how to fix undercuts due to divergent walls
further tooth reduction
what is occlusal clearance
Distance between the occlusal surface of a prep and the occlusal surface of the opposing tooth
How is occlusal clearance evaluated
During excusive jaw movements as wall as intercuspal position
what is retention form
The characteristis of the tooth preparation which tends to resist the removal of a restoration allong the POW
What is retention form
Prevents dislodgement of a seated restoration by forces directed in an apical or oblique direction
prevents dislodgement by occlusal forces
advantages of CVC’s
High strength
Longevity
High restistance to displacement
Ability to modify axial contours and oclusion
Disadvantages of CVCs
display metal
remove tooth substance
Vitality testing
Margin close to gingiva
Indications for CVC
Extensive destruction by caries or trama Endo treated teeth Large existing restorations Maximum retnetion needed (long span fixed partial denture abutment) Recontouring of axial surfaces Correction of malinclination Correction of occlusal discrepancies To provide contours suitable for a removal partial denture
Contraindications for a CVC
when tooth can be adequately restored with a more conservative restoration
why would exessive reduction of tooth will occure
If too much convergance
Prep does not follow the anatomy of the tooth
POW diverges from the long axis of the tooth
V. wide margin
Excessive Gingival extension of the preparation (no further cervication than retention form and restoration and defects dictate)
where is a poteintial site of failure
the tooth restoration interface at the gingival margin
why would a restoration fail at the gingival margin tooth restoration interface
Cement dissolution or roughness
What would be a cause of inadequate marginal integrity
Chemfer is too narrow to provide sufficient bulk of restorative material without over contouring
The cavo surface line angle cannot be determined during laboratory procedures
Chamfer is rough or uneven
Prep is undercut causing distortion of the wax pattern
Causes of Inadequate retention and resistance
Excessive convergence angle (greater than 10 degrees)
Inadequate height and surface area of the axial wals
Insufficient SA to resist tipping of restoration
Recommended Bulk of prep
Functional cusp:1.5 (1.3-1.7)
central goove: 1mm (.8-1.2mm)
Non-functional cusp: 1mm (.8-1.2)
Chamber width: .5mm
what is the occlusal convergence of the burs
3-4 degrees
