design Flashcards
what are margin designs for porcelain fused metal crowns between the metal understructure and porcelain veneer
1) metal collar only
2) disappearing margin - porcelain layer is tapered, meeting metal margin together at the finish lin e
3) porcelain butt joint - when porcelain meets metal substructure on the finish line at a right angle
what is disappearing margin and its advantages
marries conservative prep of about 0.8mm heavy chamfer with aesthetics because no metal exposure will be shown
but because the design doesnt leave much space for pocelain build up, there is insufficient porcelain to mask underlying metal substructure (so not v aesthetic)
what are some differences between conventional FDP and RBB
- extensive tooth prep vs minimal tooth prep
- retention prep designs vs retention via adhesive cement
- Survival rate of FDP is 89.1% in 10 years and SR for RBB is 87.7% for 5 years
- failure for FDP is usually loss in tooth vitality and retention but failure for RBB is debonding
when are subg margins indicated
1) previous resto or decay that must be removed for margin to be placed on sound tooth structure
2) aesthetics to mask tooth/restoration interface
3) when there is a need to create adequate retention/resistance form
indications for feather edge margins
may be used for porcelain laminate veneer preps bc this conservative margin maintains enamel, which is important for the longevity of bonding
what is the chisel/ knife edge margin compared to feather edge and when is it indicated
+ its disadvantages
chisel is variation of feather - large angle between axial surfce & margin
indicated occasionally on tilted teeth
disadv:
- location of margin difficult to control
- often leads to preps with excessive taper (bc imagine it like slanting inwards)
adv, disadv and indications of chamfer margin
adv:
- distinct margin that is easily identifiable
- provides room for adequate bulk of material
- easy to prep, can be done quickly & precisely
disadv:
- easily can get unsupported lipping of enamel
indications:
- FMC, lingual margin of metal ceramic crowns
- heavy chamfer can be used for ceramic crowns
adv, disadv and indications of beveled margins
adv:
- conservation of tooth structure
- eliminate all unsupported enamel
- protct remainign tooth structure from fracture
- allow burnishing of casting
disadv:
- location of margin difficult to control
indications:
- facial margin of maxillary partial coverage restorations
- inlays and onlays
adv, disadv and indications of shoulder margins
adv:
- bulk of restorative material
- flat, smooth surface for brittle ceramics
disadv:
- less conservative of tooth structure
indications:
- facial margin of metal ceramic & complete ceramic crowns
what are some advantages of crowns
1) includes all axial surfaces of the tooth and hence has a greater retention & resistance form than partial coverage restorations
2) can facilitate modification of occlusion eg when teeth are supra erupted or when occlusal plane needs to be re established
3) allow modification of axial tooth contour so its useful for malaligned teeth
4) allow improved access for OH for furcally involved teeth eg if need fluting
5) can be used as survey crowns for RPDs
6) prep is less difficult/ demanding than partial cov restorations
7) longevity is superior to all other fixed restorations
disadvantages of all ceramic crowns
1) increased susceptibility to fracture
2) more reduction on proximal and lingual surface than PFM (bc need adequate material thickness for strength)
3) proper prep design is critical for mechanical stress
- 90 degrees
- smooth
- shoulder margin needed to prevent unfavourable stress conc & minimize risk of fracture
4) difficulties obtaining a well fitting margin
- because porcelain is unforgiving, cannot be burnished
5) appearance may be affected by colour of underlying tooth, foundation resto or cement (except zirc which is more opaque)
6) wear on opposing natural teeth by porcelain
7) increased technique sensitivity due to adhesive cementation
8) cant be used as surveyed crowns due to lack of metal substructure
contraindications of all ceramic crown
1) when a more conservative resto can be used
2) tooth with insufficient coronal structure to support resto bc porcelain cannot exceed 2mm thickness if not will be unsupported and fail
3) where occlusal loading is unfavourable
- centric contact must be in an area where porcelain is supported by tooth structure eg middle third of the lingual wall on an anterior tooth
4) where it is not possible to provide an even shoulder margin width of at least 1mm circumferentially
defn on inlay vs onlay
inlay = a fixed intracoronal restoration made indirectly, which is then luted into the tooth
onlay = a partial coverage restoration that restores one or more cusps and adjoining occlusal surfaces or the entire occlusal surface, and is retained by mechanical or adhesive means
adv and disadv of inalys and onlyars
adv:
- excellent mechanical properties of gold alloy
- aesthetic advantage compared to amalgam as gold does not discolour the tooth, plus there will be lack of corrosion of gold
- onlay can support cusps, reduce risk of tooth fracture
disadv:
- for small carious lesions, inlays are not conservative as additional tooth removal is necessary to remove undercuts and enable impression making
- still need a bulk of tooth structure eg buccal & linugal cusps to provide R&R since inalys dont encircle the tooth
- high occlusal forces can lead to cuspal fracture due to wedging from inlays
indications and contraindications of inalys
indications:
- when size of defect is beyond what can be predictably restored with CR, but small enough not to warrant a complete crown
contra:
1) patients with excessive occlusal loading eg bruxism
2) poor OH, might just want to extract of gpt a ;pt pf caroes
4) if more than 2/3 of the occlusal table requires restoration, then a complete crown is preferred over onlay
what are the considerations of pontic design
1) BIOLOGICAL
- ridge contact (should not have blanching of soft tissues, tissue contact should be entirely passive)
- OH: gingival embrasures should not be opened excessively to prevent food entrapment, but should be wide enough to allow OH aids
- framework design: FDP should be as rigid as possible as flexure during mastication may cause pressure on mucosa and fracture of veneering material + occlusal contacts shouldnt lie on the metal ceramic junction during centric tooth contacts
- tiissue surface of pontic should be made in glazed porcelain as it is the most biocompatible
2) MECHANICAL
- proper tooth prep
- material (if occlusal is porcelain, must be wary of potential for fracture and risk of abrading opposing dentition if occlusal contacts are on enamel or metal)
- occlusal centric contacts must be placed 1.5mm away from metal ceramic junction as they can deform the metal ceramic interface
3) AESTHETICS
- the simulation of a natural tooth is most often betrayed at the tissue pontic junction and the greatest challenge is compensating for anatomic changes that occur after exo
- modified ridge lap recommended for anterior situations because it compensates for lost BL width in the rsidual ridge by overlapping what remains
when are non rigid connectors indicated
- when it is not possible to prep a common path of placement for abutment preps
- large complex FDP which benefit from segmenting into shorter components that are easier to replace individually (if the abutments prognosis is uncertain)
- in mandibular arch when complex FDP consists of anterior + posterior segmnts, the mandible flexes mediolaterally and rigid FDPs inhibit mandibular flexure and the associated stresses can be minimized with segmented non rigid connectors
disadvantages of rochette bridge
this is the cast perforated resin bonded FDP (the one lexuan did)
- purposely create holes in the lingual partial coverage retainer, throug which the resin luting agent is passed to achieve a mechanical lock
disadv:;
- perfs resulted in weakening of retainer
- exposure to wear of resin
- limited adhesion of metal
indications of AEB
1) missing anterior teeth in children
- conventional FP is contraed in young patients due to large size of pulps, inadequate plaque control so use this first
2) short edentulous span
3) teeth with minimal restorations
- smaller restorations can be incorporated into prep design
4) clinical studies have demonstrated success with AEBs in singl posterior teeth
5) perio splinting - idk how this works
contraindications of AEB
1) active caries, perio disease (this is always a contra)
2) short clinical crowns because need adequate surface area of enamel
3) extensively restored or damaged abutments
4) compromised enamel due to hypoplasia, demin, congenital AI/DI
5) deep bite for upper incisors, preventing adequate enamel reduction
6) parafunctional habits
7) where excellent moisture control cannot be achieved
8) long edentulous spans
9) in cases wher space correction is needed, AEB cant help with that
10) thin teeth faciolinugally, if enamel is too translucnt
