Rest seat and abutment preparation Flashcards
Sequence for Abutment Corrections (6)
- Occlusal plane correction
- guide plane correction
- lowering height of contour
- moving undercuts gingivally
- increasing or creating undercuts
- rest seat preparation
analysis of the occlusal plane requires?
MOUNTED casts
what to check for in determining if plane needs correcting? solutions if needed?
same arch
opoosing arch
retromolar pad
radiograph
solutions
- emamoplasty
- restoration
- endodontics
- extraction
what do all unopposed teeth have?
EXTRUSION potential
- which will interfere with an ideal plane of occlusion
occlusal plane must be determined when?
during the diagnostic stage
incoorect bi-planar occlusion will cause?
Occlusal problem
when does the occlusal plane affect occlusion?
Centric -NO
Lateral - YES with curve of WILSON
Protrusion - YES with curve of SPEE
how do you correct the occlusal plane?
Check teeth in same or opposing arch
Retromolar pad if no teeth
Radiograph for enamel thickness
why do you correct the occlusal plane?
improved function in protrusion and lateral and increased room for tooth setting
where you correct the occlusal plane?
if enamel present - okay
if in dentin - restoration
if pulp – endo and crown
when do you correct the occlusal plane?
If first – before restorative treatment - must maintain the position
if last – must do by final impression (so it does not alter rest seats/ adjustments made
what / where is the ideal guide plane
occlusal 1/3 of the tooth on the PROXIMAL SURFACE
with a FLAT CONTACT WITH SLIGHT SPACE BELOW
- tooth and tissue contact
- if too short = guide point
what do anterior tissue undercuts result in?
how do you eliminate tissue undercuts?
will result in a space between tissue and denture base
tail down tilt
how do you turn a guide point into a guide plane?
by disking enamel PARALLEL to the path of insertion – to create the guide plane
where is path of insertion drawn? relationship to where you disk?
on the facial surface of the tooth and the the occlusal 1/3 is disked parallel to path of insertion
align the bur with with path on the facial and disk occlusal 1/3 of proximal parallel to the path on the facial
0 degree tilt confirmed by?
analyzing rod is parallel to midline
where does the height of contour have to be for a type 1 clasp?
in the gingival 1/3rd OR the clasp will be TOO HIGH
how do you lower height of contour?
disk the tooth to lower the height of contour
- lowering height of contour permits lowering of type 1 clasp
describe disking tooth for lowering height of contour
what does this result in?
PATH IS ON PROXIMAL
- shank of bur is aligned with path
- bur is TAPERED
- Taper of bur will create taper on tooth
- bur on facial is aligned with path on proximal
- ONLY cutting on the facial (or lingual aspect) NOT proximal
- use only the belly of the bur or undercut / chamfer will result
- bur must extend with full length of the crown or a chamfer will result
LOWERING OF SURVEY LINE
disk where to lower the height of contour?
Disk NON-parallel to path to lower height of contour
where should the bracer be?
in the gingival 1/3 rd - DIRECTLY OPPOSITE THE RETAINER
usually buccal and lingual heights of contour are?
opposite – so need to disk to lower height of contour
if use taper bur for loweiring height of contour alignment is what?
if use straight bur alignment is what?
tapered – hold it parallel
non-tapered - hold it non-parallel
problems created by bulbous teeth
- large cervical convergence angle
- retentive undercut NOT in gingival 1/3rd
- approach arm too far from tissue
options if angle of cervical convergence is too large?
- tilt away
- enamolplastly
- change to combo
- restore tooth
if bulbous tooth creates a tissue undercut.. it can be reduced by tilting how?
TAIL DOWN (A/P) TILT or by tilting ‘away’ laterally
if tilting does not remove undercut what is next option?
Enamoplasty
what does tail down tilt usually elminate that we may need?
MB undercuts may be eliminated
undercuts used correspond to?
types of metal we will use
.01 undercut uses what material? .02? .03?
Cromium cobalt -.01
Gold - .02
wroute wire - .03
what surface do you need to be able to create an undercut?
usually can from a flat surface or some type of height of contour
- if have a surface that diverges from the surveying rod- you are unable to
what bur creates a .01 undercut?
a #2 round bur – which will go about 1/3 rd into the tooth to create this
what part of the bur limits the depth of the cut?
SHANK of the bur
location of increasing an undercut
above free gingival margin (approx. 2mm) and BELOW the height of contour
profile view shows what when looking at undercut?
depth cut limited by shank of bur
direct view shows what when looking at an undercut?
does NOT permit depth determination
location of dimple?
BELOW - when looking relative to the survey line (below height of contour)
and ABOVE free gingival margin (approx. 2mm)
FLAT GINGIVAL 1/3 RD OF TOOTH
maximum depth of any dimple is?
.01
3 SCENARIOUS FOR CREATING AN UNDERCUT
- to create a .01 undercut – dimple a flat surface by .01
- to create a .02 undercut , dimple a 0.1 undercut by .01
- to create a .03 undercut, dimple a .02 undercut by .01
three types of rest
occlusal rest
cingulum rest
ML (mesial lingual rests)
function of rests
- preventing cervical movement of partial
- preventing rotational movement
- maintaining or establishing occlusion
- maintaining relationship of clasp to abutment
rest seats and their functions
what you prepare on pt's teeth Functions 1. directing occlusal force along tooth long axis even without opposing tooth present 2. decreasing torque on abutment tooth 3. preventing hyperocclusion of rest
occlusal forces of teeth usually occuring where? implication on rest placement?
in the middle 1/3 are usually strongest occlusal forces present
so place the rest close to the LONG AXIS OF THE TOOTH - in the middle 1/3 prevents tippping and requires that rest seats be as large as possible
size requirements for occlusal rest seat
approx. spoon shaped
1/3rd M-D of width
1/2 to 1/3 B-L
round floor and walls
widest at marginal ridge
narrowest toward center
1mm reduction at marginal ridge
1.5 mm reduction at the center
flared at marginal ridge
round bur #6 or #8
if rest seat not prepared first or correctly?
then a rest will cause tooth movement and if not reduced enough - will end up in hyper-occlusion
what happens if rest floor slopes outward?
rest and tooth may separate
so HAS TO HOLD WATER – ask yourself this question
- so need it to slope INWARD – so that the rest and ttooth will remain together
Rest seat material
gold - best for contour control
enamel - okay if polished
amglam - okay if outline of rest > restoration
composite - okay if outline of rest is greater than restoration (not suitable for retention)
lithium disilicate - okay - not well researched yet
porcelain- NEVER - DUE TO FRACTURE
- so has to end on enamel
composite implication on rest seat?
okay if outline of rest is larger than restoration however NOT suitable for retention so if need dimple on lingual or facial – cannot do it on composite
Porcelain implication on rest seats
NEVER
- due to fracture
rest seat and undercut material composition and comparative size statemtns
- margins of rest seat must be larger than the restoration and not end in the margin of the restoration
- regardless of material of restortion already in place – the rest seat preparation must obtain support from the enamel of the tooth. so extend if needed but not larger than 1/2 in B-L direction and if this is needed - consider a crown
rest seats over restorations?
okay if amalgam or composite as long as prep outline is beyond the margins end on enamel for support
- so if MO on tooth already (not acceptable) – can do a DO rest seat prep as the marginal ridge will end in enamel
if tooth has proximal contact and need to make a rest seat? vs open embrasure?
interproximal contact provides NO room for minor connectors or clasp arms
MAY NEED A LINGUAL CHANNEL for a minor connector
BUCCAL CHANNEL - for a clasp arm
an open embrasure –> leaves plenty of room for minor connector
general reasons why channels may be necessary?
- minor connector may interfer with occlusion b/c of additional metal
- clasp arms may interfere with occlusion
* but these wont occur if have a channel
insufficient occlusal clearance implication for clasp arm?
Will interfere with occlusion and will fracture under function
if there is interproximal contact?
contact provides NO room for minor connectors or clasp arms
so will creare a lingual channel for a minor connector and a buccal channel for clasp arm
when are inter-proximal channels required?
when marginal ridges are at the same height
two types of inter-proximal channels and how you make them
- square channel - made with round bur
2. tapered bevel - made with finishing bur
direction a channel is cut in? sequence of creating?
HORIZONTAL not vertical
- AFTER REST SEAT IS PREPARED
- move to smaller bur than prepared the rest seat with
- so not touching facial aspect if just going towards the lingual of the tooth
dimensions of a channel
1mm wide by 1 mm deep
method of preparation for rest seat with clasp
- prepare rest seat
- outline is width of bur - come out horizontal for channel and outline is 1 mm
mesio-lingual rest seat is like what?
they are like a mesio-occlusal in the CINGULUM OF A CUSPID
how to locate area for mesio-lingual rest seat
- locate top bottom and middle of cingulum
- divide the cingulum into 3rds mesio-distally
- select the Mesio-lingual (or mesio-distal) as the target area
- enter
- move bur labially, then gingivally, then raise bur to remove the undercut
when creating mesio-lingual rest seat where do you ‘enter’ for the prep
enter from LINGUAL JUST ABOVE the target area
w/ #6 or #4 depending on size of cuspid
what happens if you approach mesio-lingual target area TOO LINGUALLY?
TOO LOW?
results in an OUTUWARD SLOPING FLOOR
- all rest seats need an inward sloping floor
if too low
- floor will be FLAT
- if origionally placed above the target area you can use the next smallest bur to create an inward sloping floor
6 basics for mesio-lingual rest seat
- as large as possible
- at MESIAL end of cingulum
- round seat
- floor sloped inward
- in and up movement to avoid unsupported enamel
- round bur (#4 and #6)
inward and upward movement
cingulum rest seat
-describe sequence of prep
- locate top bottom middle of cingulum
- locate the tooths long axis
- place an INVERTED CONE PARALLEL TO THE TOOTH’S LONG AXIS
- shank of bur parallel to long axis - start at the midpoint of one marginal ridge – then SWIPE until approach the opposire marginal ridge
- line angle to line angle - floor sloping inwards and PERPENDICULAR to the tooth’s lonng axis
- ends in the thickest bulk of the cingulum
describe position of bur an handpiece in a cingulum rest seat
bur held upright with shank parallel to long axis of the tooth
cut with base and side of bur – swiping mesio-distally
axial wall in a cingulum rest seat
the axil wall will initially be slightly undercut and then we will take a straight bur and reduce it so the axial wall is PARALLEL TO LONG AXIS of the tooth
pretection of abutments
rest seats do what?
DIRECT OCCLUSAL FORCES along a tooth’s long axis
sloping inward – can withhold more forces and along the long axis of the tooth
hand instrument to refine preps
gingival marginal trimmer
angle of floor in rest seat
inward at an ACUTE angle
