tys shen ti Flashcards
(11 cards)
list and discuss all clinical considerations you would take into account when indicating material and crown design for full coverage maxillary central incisor crown
classify into BIOLOGICAL, MECHANICAL and AESTHETIC
make sure to mention that need to gain information like hx taking of patients details, med hx nd dental hx like OH
clinical exam:
1) extraoral: smile line, lip support
2) teeth: occlusion
3) soft tissue: periodontal status
then mention RADIOGRAPHIC EXAM
BIOLOGICAL FACTORS
1) pulp + conservation of tooth structure
- young patient means relatively large pulp but if OLD, then need to think about the tooth might be attrited
- design: should do a more conservative design, ceramics
2) extent of caries - idk how this affects, more of must ensure that the margins end on sound tooth structure lor
3) must consider MALALIGNMENT especially if we are trying to correct the alignment then one side will be closer to pulp
4) vital vs non vital tooth. non vital allows placement of post retained cores
5) perio
- always treat first if not plaque accumulation can lead to gingival recession
- caeramics are more tissue biocompatible but also harder to achieve marginal adaptation
- design should be hygienic to allow plaquqe control. emergence profile not overcontoured
6) features of gingival biotype
- thin biotype is more susceptible to breakdown
7) biologic width
- padbury 2003: ensure 3mm betewen restorative margin and alveolar bone bc BW is 2.04mm and sulcus depth is 1mm
- Nevins and Skurow: limit margin to 0.5-1mm subg
MECHANICAL
1) occlusion
- if no heavy occlusal load then consider ceramic yada yada, if not opt for pfm because the metal substructure reinforces strength
- gnerally anterior teeth are suscptible to lowr occlusal loading although it may be involved in eccentric movements, so generally less demands on flexural strength
- DESIGN WISE: contacts should be on metal rather than ceramic layer with 1.5mm distance between metal ceramic junction and occlusal contact
2) specific malocclusion
- deep class II bite means heavier occlusal and eccentric loading
- must make sure got adequate incisal reduction
AESTHETICS
- - PFM harder to shade match because got underlying greyish hue
- anterior need to hide margins especially for high smile line
- replicate contralateral tooth to acheive symmetry
indications of subg margins and their disadvantages
indications:
- caries, cervical erosion or restorations that extend subgingivally, and crown lengthening not indicated
- aesthetics (so that margin of PFM crown is hidden)
- for additional resistance and retention form
- to control root sensitivity, if other more conservative methods dont work
DISADVS:
- major etiological factor in perio especially if encroach on epithelial attachment
- margin situated on dentine/ cementum
- potential for impingement of biologic width and its effects (Orkin 1999)
what are the benefits of onlay if the indications allow for it, compared to a full coverage crown?
1) while crowns get retention from extra coronal axial walls, onlays rely on intra coronal axial walls so can be used when limited extra coronal wall height is present
2) onlay can reduce the need for pre prosthetic surgery or ortho extrusion
3) mode of failure of onlays may be more favouravle than crowns
4) aesthetics wise, still got the buccal wall for aesthetics. So its gonna look like a PFM crown with metal occlusal
considerations regarding occlusion for anterior FP
occlusal schemes
- class II div 2 incisal rs: contact will be heavy
- class III edge to edge: occlusal contact is in area where porcelain is unsupported
(what is the method of answering)
this particular restoration (eg maxillary central incisor single crown) is described as a challenging restoration. discuss statement, and steps to ensure clinical success
split into the challenges based on different procedures, so during
1) shade selection
- how to manage: understand what constitutes shade and the systematic way to take shade
- 3 dimensions of colour (munsell colour order), Value, chroma, hue
- 6 elements affecting shade taking
a) environmental
- light source: should be balanced and neutral
- surrounding: grey/ pastel coloured surroundings, or blue which will increase ability to detect small differences in spectral composition
- should remove lipstick and bright clothes
b) operator
- sensitivity of eye: we are usin the most colour sensitive part of retina. working distance 25cm, should not take more than 5 seconds if not eye fatigue may happen
- brain interpretation
c) tooth factors
- shade should be taken at the start of session bc isolation with RDI can increase value
2) prep (this is like the procedural part)
- anterior location is easy to prep and easy to visualise
2a) PROVI
- aesthetics: provi have limited choice in shade and are oopaque so its difficult to match shade of neighbouring teeth
3) design
- talk about occlusal demands
4) Impression taking!
- subg margins usually indicated for anterior aesthetic regions
- talk about tissue management and need to take care of not to damage tissue if not unsightly recession might be a cause for redo
- to manage challenges: use mechanical retraction like retraction cord
- need to dry teeth to prevent bubble formation
5) issue
- if its all ceramic crown then resin luting cement to be used but difficulty would be with moisture control
6) follow up - care for prosthesis
- plaque control might be hard because subg margins difficult for patient to clean
- but anterior tooth is easy for patient to visualise and access if properly taught
compare PFM vs zirc
advantages of PFM over zirc:
1) less wear of opposing teeth
2) mechanical strength: bOTH GOOD to overcome heavy load potential
- bring in how emax is not considered bc of heavy occlusal forces
3) PFM prep is more conservature
- because can use lingual chamfer for metal collar whereas zirc requires all round shoulder
4) PFM has less plaque accumulation and hence less chance of secondary caries and perio
- consider when qn stem talks about patients caries risk
5) PFM easier to polish
6) lower cost
advantages of zirc
1) aesthetic outcome is superior
- PFM might have grey substructure
- BUT consider how zirc also doesnt have the best aesthetic because it is not suitable for teeth with high value and high translucency
crown does not seat fully when first tried on prepped tooth, what are the possible causes of this problem and describe mx
split into lab error and clinical error
LAB ERRORS:
- distortion during csating
- insufficient die spacer
- blebs
- poor margination
CLINICAL ERRORS:
- poor impression, or distortion
- distortion during pouring of the cast
- note that if the crwon seats on the die but not in the mouth then theres fault in the impression/ die, nOT the fabircation process
mx:
- from when first receiving the crown back, have to ensure that the crown seats on the die, good proximal contact and occlusion
- also inspect crown for blebs and fins that could interfere with seating , determine whether these are correctable or not. if bubbles at margin then send back but if blebs on the internal surface then can be adjusted
- then talk about INTRAOP, during clinical visit, check proximal contact and internal surface
considerations for prognosis of prosthesis
what is the defn of success? - free of complications
VS “SURVIVAL” which is retaining its function in the mouth
then talk about the different types of failures
BIOLOGICAL COMPLICATIONS
1) caries of abutment
2) perio
3) loss of vitality
MECHANICAL COMPLICATIONS
PROSTHESIS itself
1) loss of retention
2) fracture of veneering porcelain
3) connector fracture
ABUTMENT tooth:
1) fracture - coronal or VRF
AESTHETICS
1) poor aesthetic match to neighbouring teeth
2) loss of veneering porcelain
but prognosis must also evaluate
- patient factors
- operator factors
- factors of other teeth (like occlusion)
and there is a TIME factor for prognosis
- when are we prognosticating? at diagnosis or pre tx or after tx
for single pontic FDP, what are the differences between a conventional bridge and resin retained bridge
then advantages and disadv
1) ABUTMENT PREP
- fdp more extensive, leads to greater risk of pulpal exposure and loss of vitality.
- rbb is more conservative tooth prep
2) RETENTION
- fdp retention is via conventional means aka luting cement, may have chemical retention if adhesive cement is used
- rbb is chemical retention
3) MAIN REASON FOR FAILURE
- fdp mainly fails via biological and mechanical
- rbb fails by mechanical (debonding)
principles of post prep
CONSERVATION OF TOOTH STRUCTURE - split into both root and coronal structure
1) root canal
- we want minimal removal, not excessive enlargement that will weaken tooth
- should only be enlarged enoguh to enable post to fit accurately and yet passively
2) coronal structure
- for cpc, might need further reduction to remove undercuts
- but the more tooth structure we save coronally, the more reduction of stress conc at gingival margin
- talk about how still need ferrule
RETENTION FORM
split into anterior and posterior teeth
1) anterior teeth
- relies on prep geometry because the teeth have circular x section with minimal taper, so can choose preform post with snug fit
- avoid threaded systems to reduce stress in dentine
- talk about how post length and diameter can give retention
2) posterior teeth
- CURved roots so retetion is better provided by 2 or more relatively short posts in divergent canals
- AR core can also consider (mayyar)
- or one post in largest canal
RESISTANCE FORM
divide into stress distribution and rotational resistance
stress distribution:
- greatest conc of stress is found at the shoulder, at inteprox and apex so DENTINE SHOULD BE CONSERVED AT THESE AREAS
- Stress redued as length increase
- parallel sided posts may distribute stress more evenly than tapered bc tapered got wedging effect but parallel sided generate high stress at apex
- avoid high stress generation during insertion, particularly with smooth parallel sided posts that have no vent for cement escape
- threaded posts can produce high stress concentrations during insertion and loading
rotational resistance:
- add anti rotational feature eg groove where root is bulkiest aka lingual
- prep geomtery to prevent rotation
