Wk 6: Onlay Prep #4 Flashcards
Reduction for Ceramic MOD onlay #4 prep:
1.5mm at lingual cusp, 1.5mm more axial at the margin, 1mm L margin using 6847KR-016, extended past the CG about 2mm at CG, 1mm from CEJ at D contact, 6-10’ divergence of B and L internal walls (angulation of tip of bur), 0.5mm proximal clearance, 2mm B-L width for proximal box, 1.5mm depth at proximal areas, 1.5mm BL width at center of isthmus
Bur for prep occlusal outline:
KR-018, green diamond
KR-018, green diamond width at tip:
1.3mm
Depth to reduce occlusally with green diamond:
1.8mm, 0.2mm for finishing check
Orientation of bur for prepping proximal boxes:
advance bur G then B and L, in the precise POI of the prep
Why is a 0.5mm clearance required?
for impression making
What does correct G, B, and L extension of the prep depend upon?
the contact area w the adjacent tooth
How to create additional clearance at the cusp tip:
bur more horizontal than intended resto cusp
Depth of depth grooves for lingual cusp:
1.3mm leaving 0.2mm for finishing
Depth of depth groove for the nonfunctional cusp:
0.8mm leaving 0.2mm for smoothing
Orientation of bur when reducing nonfunctional cusps:
parallel to the cusp inclines
Axial wall on functional cusp:
1mm functional cusp ledge
Bur for functional cusp ledge prep:
cylindrical carbide bur
Fxn of functional cusp ledge
gives restoration bulk in a high-stress area preventing deformation during function
Placement of functional cusp ledge in relation to opposing central contacts:
1mm apical to it
How far does axial wall on functional cusp extend?
into the proximal box, not too far apical
What would happen if the axial wall on functional cusp is placed too far apically?
resistance form from the boxes will be lost
Bur to refine outline form:
8845KR
Cavosurface angle should be:
90’
How much hygienic (at proximal contacts?) clearance is necessary?
0.5mm
Place where sharp angles are likely:
junction of the ledge and occlusal surface
how to check occlusal reduction:
Have pt close into GC pattern and measure w a thickness gauge
Is the internal outline curved more on the B or L?
B
Easy way to remember reductions:
3 1.5mm steps
Orientation of bur when shaping proximal box:
bur parallel to long axis
The proximal axial walls should be convex/ concave. B-L
concave
The internal form of the B wall of the prep should be concave/convex in the MD direction:
convex
To where should the occlusal depth extend:
just beyond enamel-dentin junction
Onlay boxes are preppe din the same manner s:
inlay preps
TF? nonfunctional cusp must always be reduced for onlays.
F
The axial wall on functional cusp extend to here:
into the proximal boxes
