11/21 - Substructures, 63-67, 203-210 Flashcards
what condition:
sufficient length
wall thickness >/= 1.0 mm
all cusps present
moderate loss
preparation features of moderate loss
cement base block out of undercuts
classic prep
what condition:
Short preparation
50% of crown remaining
Wall thickness = 1.0 mm
Thickness/length ratio > 1.0
Excessive taper
More serious if an abutment
moderate/severe loss
preparation features of moderate/severe loss
Modified preparation
Existing features retained
New features added (boxes, grooves, pinholes, vertical walls)
what condition:
<50% of crown remaining
Short preparation-crown ratio
Wall thickness < 1.0 mm
Thickness-height ratio < 1.0
severe destruction
preparation features of severe destruction
Possible elective devitalization and dowel core
Walls with thickness-height ratio < 1:2 shortened or removed
Walls with thickness-height ratio of 1:1 to 1:2 supported with core
Ferrule effect in preparation
Pin(s) integrated into casting
what condition:
central destruction
enamel (if any) is undermined
total coronal loss
preparation features for total coronal loss
Dowel core + crown on single-rooted tooth
Pin-retained core + crown on molar
is the base a part of substructure/core/buildup? what is it’s purpose
NOT PART! purpose is to protect the pulp
T/F: large central lesion may require a full coverage restoration, but only after tooth is built up with a core
TRUE
what is intracoronal restoration that covers cusp
onlay
how many clearance needed to pulp for substructure
1 mm
if significantly less than 180 degrees of tooth circumference remains between two boxes [of PM], what is susceptible to occur
the lingual cusp is susceptible to fracture during function, upon removal of provisional restoration, or at try in of the permanent restoration
pins should always be halfway thru what
between pulp and external surface
where do you primarily want to put pins
over where cusps are normally or line angles
interproximal caries may preempt the use of what
a groove
what can be incorporated into a crown to augment retention and resistance
pin (which can also be used to retain a core which in turn will help retain a crown)
if the tooth to be prepared for a cast restoration has been only MODERATELY damaged, what can be done
standard MOD only preparation or a three quarter crown preparationwith boxes
if one cusp is destroyed, what can be done
widened box with groove augmentation
when half of the crown has been destroyed, what can be done
grooves may provide sufficient retention if the supragingival tooth structure in which they are placed has sufficient length. pinholes may be added to the preparation
if three or more cusps have been destroyed, what can be done
pin-retained core should be fabricated before proceeding to a full coverage cast restoration
T/F: extensive peripheral destruction often requires a full coverage cast restoration if caries has been controlled
TRUE
what does a widened F-L and gingivally lengthened box provide
facial and lingual walls become solid tooth structure and retention will be improved
what is a critical factor of restorations
biologic width
what is the typical distance between margin of crown and bone level
2 mm
if crown margin is put immediately on bone level, what happens? how does this occur
bone recedes 2 mm
recession is bad because it is unpredictable and you get more of a pocket which leads to bone loss
what do you do instead of putting crown margin directly onto bone?
CROWN LENGETHING
what typically accompanies crown lengethening
gingival recession
what is the normal anatomical crown-root ration for an average central incisor
11:14
what is the shortening of root
extrusion
how to determine amount of extrusion needed
adding distance of destruction extends beyond the alveolar crest, the biologic width of of 2.0 mm, and the 1.0 mm between the final sulcus bottom and the final crown margin
if destruction extends 1.00 beyond the alveolar crest, 4.0 mm extrusion necessary
do current studies show that you should put post in anterior teeth?
NO! don’t put post in anterior teeth as of recent studies
the length of the dowel should equal what? length of remaining apical fill is what
crown length or two-thirds the length of the root, whichever is GREATER. length of remaining apical fill should at least be 4 mm
crown lengthening vs extrusion
lengthening = bone down
extrusion = tooth up
what is critical purpose of ferrule
hold tooth together so it doesn’t fracture
why do you see a lot of crack on 18 + 31
since most distal tooth and they get most load
do you do the crown prep first or substructure prep first?
in lecture he said do crown prep first but in lab he said to remove the substructure
where is pin placed
0.5 mm into DEJ only in DENTIN not enamel
ferrule must be at least how many mm
2mm
what material do you use to build up substructure
amalgam or composite
what type of crown preparation for substructure exercise
FCC
what rules should be observed to avoid excessive tooth destruction while creating retention in an already weakened tooth
- central core (pulp and the 1.0 mm thick surrounding layer of dentin) must not be invaded in vital teeth
- no wall of dentin should be reduced to a thickness less than its height for the sake of retention
no retentive features should extend further into the teeth than ___ mm at the cervical line or from the central fossa
1.5 mm
if caries removal results in a deeper cavity, any part lying within the vital core should be filled with what
glass ionomer cement
instead of a groove, what can be placed to accommodate caries removal and provide retention
box forms
how deep and wide should a groove be
1 mm deep and wide
are multiple grooves as effective as box forms?
YES! but at some point too many grooves can affect the seating of a full veneer crown
what are the ways pins can be used
- pinholes parallel the path of insertion of the preparation, receiving pins that are an integral part of the cast restoration
- nonparallel pins placed in the tooth to retain an amalgam or composite resin core in which a classic prep for cast restoration can be formed
what materials are best used for a base
glass ionomer or polycarboxylate
if one-half or more of the clinical crown has been destroyed, what is placed in the tooth
amalgam or composite resin core
