L2 -Prep Design Flashcards
implications of a flat occlusal surdace
may over shorten the preparation
turning point on reduction of number 8
over reduction
principle number wo of prep
preservation of the periodontium
biological width is..
dimension of space that the healthy gingival tissues occupy above the alveolar bone
evaluate the bio width with
- radiographs
- probing
- bone sounding
biological width is..
dimension of space that the healthy gingival tissues occupy above the alveolar bone
normal is 2.0mm to 3.00
evaluate the bio width with
- radiographs
- probing
- bone sounding
why important to not violate biological width
the attachment complex will be damanged
- some distance of unpreparaed tooth structure should remain between the finished line and juncitonal epithelium and this distance is ideally 0.5mm
why important to not violate biological width
the attachment complex will be damanged
- some distance of unpreparaed tooth structure should remain between the finished line and juncitonal epithelium and this distance is ideally 0.5mm
amunt of tooth structure that should remain between finish line and junctional epithelium
ideally .5mm
no difference in location of margins if supra and sub-gingival
*only when?
- in health of the gingiva
- in the change of sulcus depth
- in the gingval contour
- in plaque accumulaion
*when the crown margins are well fitted and well contoured
principle number 3 of prep
retention and resistance
retention stops from
up and down
- the quality inherent in the dental prosthesis acting to resist the forces of dislodgment along the path of placement
factors affecting retention form
- magnitude of dislodging forces: sticky foods, floss under connectors
- path of insertion
- geometry of tooth prep
- materials being cemented
- type of luting agent and film thickness of luting agent
factors affecting retention form
- magnitude of dislodging forces: sticky foods, floss under connectors
- path of insertion
- geometry of tooth prep
- materials being cemented
- type of luting agent and film thickness of luting agent
path of insertion
the specific direction in which a prosthesis is placed on the abutment teeth or dental implants
two dimensions of path of insertion
- facio-lingual
2. mesio-distal
Factors affecting the Taper
1.
average taper dentist achieve in preps
from 14.3 to 22.1
- annerstad, norlander
freedom of displacement affects?
retention and resistance
freedom of displacement
associated with retention and resistance
*numbers of paths along which restoration
one path of insertion allows for
better retention
longer tooth implication
more SA - so more retention available
wider tooth?
more SA – more retention more area
resistance form
the features of a tooth prep that enhance the stability of a restoration and resist dislodgment along an axis other than the path of placement
conclusion from
3mm of height for anterior and pre-molars
with a range of 10-20 degrees
4mm for molars and have a greater convergence
T/F make sure you know the papers cited in this lecture
True
T/F make sure you know the papers cited in this lecture
True
number one failure of crowns
due to poor resistence
if prep is narrow its effect on resistence?
increase
narrow prep for resistance and retention
narrow – better resistance
narrow – worse retention
advantages of PFM
- long history of success
2.
limit of reduction use what material?
- PFM
- zirconia
both
all ceramics need what reduction?
2 mm
if aesthetics are most importnat use?
all ceramic
isolation is hard but pt. does not want metal - use what
zirconia
margin design affecting
structural durability
finish lines we will use
- chamfer
2. heavy deep chamfer
chamfer for?
for tooth prep in which gingival aspect meets the external axial surface at an obtuse angle
- uses a round end diamond
chamfer for?
for tooth prep in which gingival aspect meets the external axial surface at an obtuse angle
- uses a round end diamond
- mainly used for PFM’s and zirconia
chamfer for?
for tooth prep in which gingival aspect meets the external axial surface at an obtuse angle
- uses a round end diamond
- mainly used for PFM’s and zirconia
heavy/ deep chamfer
has a 90 degree cavo-surface angle, with a large radius
radial shoulder: same with a lesser radius
rounded tapered diamond
used with ceramics
5 principles of tooth prep
- preservation of tooth structure
- preservation of the periodontium
- retention and resistance
- structural durability
- marginal integrity
a flat occlusal surface implication
may OVER SHORTEN the preparation
convergence in terms of preservation
prep teeth with the MINIMUM practical convergence angle between axial walls
bio width usually
2-3 mm
need 2
margin has to be?
on healthy tooth structure
so caries abrasion or erosion are reasons to go sub-g
according to richter?
looked at margin location and supra- vs sub gingival
no difference between
- health of gingiva
- change in sulcus depth
- gingival contour
- plaque accumulation
geometry of tooth prep affecting?
retention form
- taper
- freedom of displacement
- surface area
- stress concentration
path of insertion dimenstion
facio-lingual
mesio-distal
mesio-distal path of insertion
must be parallel to contact areas of adjacent eeth
so if path is inclined mesially or distally - restoration will be held up at the proximal contacts and be locked out
facio-lingaul path of insertion effects?
estehtics of PFM crowns or veneers
total occlusal convergence aka
TOC – the angle of convergence between 2 opposing prepared axial surface
minimum 2-6
average is 14.3 to 22.1
TOC with specific teth?
posterior teeth > anterior teeth
mandibular teeth > maxillary
teeth with greatesst TOC?
mandibular molars
surfaces with greater TOC?
facio-lingual > mesiodistal
because cheek and tongue
FPD’s and crowns in terms of TOC?
FPD’s»_space; crowns
b/c of path of insertion
maximum retetnion schieved by?
of only one path exists
a long parallel axis walla and grooves has high retentive values
short occluso-gingival height results in
more displacement
SA and retention
more SA more retention
more tapered prep how does it affect retention?
decreases
wide prep with retention?
increases
major factors affecting resistance
magnitude and direction of forces : mastication and parafunctional habits, interference’s, andterior guidance
leverage
length and width
taper
type of prep
luting agent
leverage is
occurs when the line of action of a force passes OUTSIDE the supporting tooth structure
forces outside the margin are caused by
wide occlusal table
crowns on tippeed teeth
cantilevers
small prep with large restoration?
poor resistance as compared to small prep and smallrestoration
OC dimension for premolars and anterior?
3mm is MINIMUM
- need this amount along with the recommended TOC (taper) range of 10-20 degrees
OC dimension for molars?
4mm is MINIMUM
- need this amount along with the recommended TOC (taper) range of 10-20 degrees
- usually have a greater convergence than anterior teeth and greater diameter than other teeth
prep width with resistance
wider - less resistance
*example when factor is opposite for retention and resitence form
use of axial grooves / boxes?
routinely when MANDIBULAR MOLARS are prepared for FIXED PARTIAL DENTURES and they should be located on the PROXIMAL SURFACES
Facioproximal and linguoproximal corners?
prepared so that they are preserved sustaining variation in the curcumferential morphology that enhances resistance form
prep is narrow, how is resitstnce?
good – increases
structural durability - general
the ability of a restoration to withstand destruction due to external forces
factors affecting the structural durability
- adequate tooth reduction
- occlusal reduction
- axial reduction - alloy selection
- metal-ceramic frameowrk
- margin design
occlusal / axial reduction for gold crown
occlusal - 1mm,
axial 0.5-1mm
occlusal / axial reduction for PFM
occlusal 1.5
axial 1.2 - 1.5
occlusal / axial reduction for all ceramic
occlusal - 2mm
axial 1-1.5
point and internal angles?
ROUNDED
- avoid the deep grooves in centerl of occlusal surfaces to prevent stress concentration and to distribute the forces over a larger surface area
tend to under-reduce where?
center of crown
indications for PFM
- high strength requirements
- limited interocclusal clearance
- metal occlusal surface
- discolored tooth structure
- long span RPD
- abutment to RPD’s (survey crowns)
if cant control the saliva want to be able to ___ with the final crown
cement
- like use of a PFM with cement - dont have to rely on bonding
advanatges of PFM
- long history of success
- highly versatile
- less demanding tooth preparation
- more conservative reduction
- ability to mask discolored tooth
- use of conventional cements (not worried about saliva being a problem as much)
indications for all ceramic crowns
- high strenght materials
- high esthetic expectation
- relatively opaque teeth
advantages of all ceramic
- no cast metal substructure
- excellent esthetics
- durable resotration
advantages to yttria stabalized zirconia
- fracture toughness
- esthetics / depends – more opaque
- no metal substructure
disadvantages of zirconia
- cannot bond the restoration
- esthetics , cannot match translucent
- fusion temperature
bond zirconia?
NO – cementation only
material if issue of reduction
use PFM or zirconia
can get away with less reduction with both of these
if esthetic is most important use?
all ceramic
even more so than zirconia
if isolation is impossile and dont want metal?
zirconia
all ceramic you have to bond and will be difficult if there is a lot of saliva
margin use what?
tapered round-end diamond instrument using 1/2 of its tip diameter
two margins we use
chamfer and deep chamfer (all ceramic)
PFM and zirconia
shoulder?
meets at 90 degrees
- uses a flat ended
- ceramics
shoulder with bevel?
used for PFM’s where a shoulder was prepared but because of caries or presence of restoration , a bevel is added
a bevel?
a slanting edge, the process of slanting the finish line and curve of a tooth preparation
- allows the cast metal margin to be bent or burnished against the prepared tooth structure
- minimize the marginal discrepency
- removes unsupoorted enamel
TOC
total occlusal convergance - angle of convergance between 2 opposing prepared axial surfaces
should meet the recommended 2 to 6 degree minimal angle
axial walls of the prep must taper slightly to permit the restoration to seat
why does facial - lingual have more taper?
cheek and tongue - dont want to hit them
forces outside the margin are caused by
wide occlual table
crowns on tipped teeth
cantilevers
shortening prep results in
less resistance – the lfiting force required is smaller
if mechanical properties are compromised bond or cemetn
bond
