Prosthodontics Flashcards
shortened dental arch
dentition of no more than 20 teeth with an intact anterior region but a reduced number of occluding pairs of posterior teeth
as bone is lost what happens mandible and maxilla
maxilla - becomes narrower
mandible - becomes wider
extra oral implications of edentulousness
upper and lower lip both become more retroclined
physiological changes in the edentulous (4)
loss of proprioception due to loss of PDL
changes in musculature & support leads to decreased masticatory & biting efficiency
decreased swallowing as jaws don’t have any guidance and will possibly be problems with speech due to tongue moving differently
Atwood classification of edentulous teeth
class I - dentate - pre XLA
class II - post XLA - tooth after immediate loss
class III - broad alveolar process - alveolus refilled with newly formed bone, resorption begins
class IV - knife edge alveolar process - shape of alveolar crest starts to alter to thick knife edge but body still adequate in height & width
class V - flat ridge - loss of alveolar process - further resorption
class VI - submerged ridge - resorption into basal bone
list clinical stages in complete denture construction (8)
- assessment of ptx & current dentures
- primary imps - ask for special trays
- definitive imps - ask for occlusal rims & bases
- registration visit - ask for tooth trial
- trial insertion visit
- insertion
- maintenance
- aftercare
factors that may affect denture wearing experience (5)
xerostomia
mucosal disease
arthritis
stroke
parksinson’s
factors that may affect denture wearing experience
xerostomia
mucosal disease
arthritis
stroke
parksinson’s
freeway space
difference in OVD & RVD
space between teeth / dentures when at rest
2-4mm
what should be examined when it comes to residual ridges
ridge height, width & consistency
muscle attachments affecting denture (2)
if mentalis attachment is unusually high then this will have to be relieved as to not displace the denture
frenal attachments must be relieved if large as they can predispose denture to fracture
denture extension
should be 2/3s over the retromolar pad - both individually and with both arches together
centric jaw relation
centric jaw relation is the most retruded position of the mandible to the maxillae at an established vertical dimension which is repeatable and recordable
primary impression poured in
50:50 plaster stone combination
master impression poured in
100% dental stone
negative replica
impression on tissues of the mouth
positive replica
when impression is converted to plaster / stone
what must not be used in dentate ptx
non elastic impression materials - can be used in edentulous ptx as there is less risk of impression getting stuck in undercuts
lower special tray in edentulous ptx
close fitting (1mm) spaced non perforated light cured acrylic resin tray
ZnO eugenol or silicone can be used in this tray & there should be no bony undercuts - if there are then 2mm spacing prescribed and elastic impression material used due to undercuts i.e. silicone or alginate
upper special tray
2mm spaced light cured acrylic tray for an elastomer
handles for edentulous special trays
should be intra-oral as they do not modify the soft tissues as much to allow for a more accurate impression
on lowers there must be stub handles on premolar region as well as incisal region
extension of special tray
should be 1/2-2/3s along the retromolar pad and also extend to around 2mm from the buccal sulcus to allow for sufficient thickness of impression material to not tear
use of tracing compound in upper special tray
should be added to canine & post dam regions to allow for accurate reinsertion of tray
will also allow for pre-formed space for alginate material
rests on canine region will stop too much pressure being placed on tray
should be added to outside periphery of tray to fill width of sulci allowing peripheral seal
should also resist downward displacement forces added to handle to create accurate representation of ridges and sulci
use of tracing compound on lower special tray
closer fitting tray of lowers doesn’t need tracing compound as they can be reinserted accurately
how to deal with displaceable flabby maxillary ridge
impression should be either with an open window over the ridge and modification with green stick OR perforate a spaced tray over the ridge - these both will use a low viscosity material in these areas i.e. mucostatic to not compress tissues
flat (atrophic) mandibular ridge
Atwood class V - take impression of ridge wth greenstick impression with a light bodied silicone reline over, or using the admix impression technique (3 parts impression compound, 7 parts weight greenstick)
when to use a reline impression
problems with pain or stability associated with underside of the denture - mainly for when dentures have failed previously or conventional techniques will be unsuccessful
what is the neutral zone
zone of minimal conflict between tongue, lips and cheeks
it is more likely to be buccally placed than in pre XLA sites as post XLA tongue will expand buccally; reducing the bucco-lingual width
why a light cured base on occlusal rims
light cured bases give optimum retention & stability and is very useful when very little ridge remains
if occlusal rims don’t fit correctly then they can be used as a special tray themselves
aim of a jaw registration
to formulate the form of the maxillary rim, transfer the maxillary plane and determine the intermaxillary relationship in the retruded contact position
when adjusting upper occlusal rim the lip should be
around 90 degrees to the nose - naso labial angle
lip line
should show 2-3mm of upper teeth at rest / 4-5mm if a younger ptx
decide via common sense or old denture
centre line
centre of arch should be recorded using philtrum or nose but remember faces can be asymmetrical
occlusal plane
modified using Fox’s occlusal plane guide; should be measure to:
- pupillary line - is it parallel?
- midline - do the centres line up?
- alar tragal line - AP plane coincide with this?
rims should be trimmed until the anterior posterior plane lies parallel to the alar tragus line
canine line
a mark on the rims that indicates the distance from canine to canine to allow technician to place teeth in these marks
measured with floss from inner canthus of eye down to occlusal rims and marked
lower before upper or upper before lower adjustments
always do upper before lower
why measure face height
to figure out how long the teeth should be
what measurements do you need for face height
OVD - occlusal vertical dimension
RVD - resting vertical dimension
(difference in the 2 is known as freeway space which is generally 2-4mm & is required for teeth function)
a reduced OVD can cause
angular cheilitis
if this is the case increase OVD by 3mm
how to measure face height
2 measures taken with willis bite gauge
- RVD; ptx asked to relax and measurement taken from nose to chin
- OVD; asked to occlude with previous dentures and same measurement taken
if no prev dentures OVD must be approximated
what is the only recordable position in an edentulous ptx
RCP - retruded contact position also known as the centric jaw registration
what is the RCP & how is it recorded
when the heads of the condyle are in their most superior and anterior position possible in the mandibular fossa
recorded by gently manipulating the mandible by hand to coax it into position, curling tongue back can help
in a tooth trial posterior teeth must be
along the alveolar ridge
what else should be checked in tooth trial
different planes checked at occlusal rim stage should be checked again i.e.
-posterior plane being parallel to ala tragus line
- anterior plane being parallel to inter-pupillary line
- RVD, OVD, freeway space
as well as balanced occlusion and balanced articulation
what is a post dam
groove cut on posterior palatal margin of denture cast which produces ridge on finished denture to form a more effective posterior seal to aid retention
imbrications
mesio distal ridges on cervical 2/3 of labial surface of anterior tooth associated with enamel incremental growth
asked for along with diastema when asking for tooth trial
2 forms of denture cleaning
mechanical action - not really recommended
chemical action
5 methods of chemical action for denture cleaning
- effervescent peroxidases
- alkaline hypochlorites e.g. milton - CoCr should not be left for more than 10mins in this
- acids
- disinfectants
- enzymes
effervescent peroxidases
powdered / tablet
acidic / alkaline / neutral
act rapidly, simple & effective, bubbles may dislodge debris
acidic peroxidases
best for cleaning but contraindicated in CoCr framework only neutral or alkaline should be used
main one used is Steradent
acrylic resin denture cleaning
soaked in alkaline hypochlorite for 20mins in the evening then rinsed and soaked in cold water overnight
acid cleaner can be used for stubborn stains/calcified deposits
metal based denture cleaning
alkaline peroxidases are suitable but prolonged soaking will cause discolouration of metal / may be corrosive
acid cleaners contraindicated as will cause corrosion
3 ways to improve impression surface
- reline denture
- remake denture if extremely poor
- adding post dam to denture
centric relation
this is the centric jaw relationship which is the retruded contact position
centric occlusion
this is the intercuspal position
indications for replica dentures (4)
- satisfactory occlusal, polished and impression surface but spare set needed
- modification is needed on existing denture to improve impression/occlusal surface but polished is satisfactory
- if they have had multiple bad dentures take the best and use as template for modification
- replacement of dentures where there has been general deterioration of denture base
contraindications of replica dentures
- polished surfaces of denture are incorrect and not in neutral zone
- previous dentures lost or unavailable
clinical stages for replica dentures
1st visit - denture impression using polysiloxane impression putty (remember to vaseline exposed putty)
1st lab stage - wax template
2nd visit - 2ndary impression
2nd lab stage - wax trial
3rd visit - wax trial
4th visit - delivery
advantages of labial flange on immediate denture
greater stability
increased retention
improved strength
no interference with sutures if present
provides more stable appearance when bone resorbs
easier to reline when required
disadvantages of labial flange
unnatural fullness of lip
bony undercuts labial to alveolar ridge may prevent use
use of partial flange can help overcome these and will retain most advantages
for new immediate dentures after primary imps ask for
3mm spaced perforated custom trays - as with RPD
requirements of denture base (5)
- physical - match oral tissues, high softening temp, high dimensional stability, be light, be radiopaque and a high TEC
- mechanical - rigid (high YM), high elastic limit, high transverse & impact strength, hard to resist abrasion
- chemical - chemically inert & insoluble to oral fluids
- biological - non toxic, non irritant and impermeable to oral fluids
- miscellaneous - inexpensive, easy to manipulate, easy to repair and have long shelf life
PMMA as denture base
colour match adequate
dimensionally stable
softening temp of 105
light
but has poor TEC and is radiolucent
clinical issues of complete dentures (4)
porosity - gaseous porosity due to monomer boiling away / contraction porosity due to insufficient pressure during processing
granularity - rough over denture base due to incorrect mixing ratio
crazing - fine cracks at junctions between different material areas or in areas of greatest stress caused by diff TEC of porcelain teeth & base or prolonged stress in function
residual monomer - insufficient terminal boil to remove it all, will be all over base & can cause irritated mucosa / burning mouth
lab prescription for special trays
please pour up imps in 50:50 plaster stone
produce special trays in light cured acrylic 2x wax spaced upper and close fitting 0.5mm lower
add intra oral handles and finger rests
lab prescription for jaw reg
please pour up 2ndary imps in 100% stone
construct upper and lower light cured bases with wax occlusal rims
lab prescription for tooth trial
please mount casts on semi adjustable articulator with jaw reg provided
set upper teeth to upper arch and lowers to occlude in balanced occlusion
see back for shade and mould
lab prescription for delivery
please refine wax work and process in heat cured PMMA
trim polish and refine occlusion
please return on articulator
facebow prescription - study models
please pour up impression in 100% stone
facebow prescription - mounting casts
please mount upper and transfer cast onto an average value articulator using facebow registration
articulate lower cast to upper in ICP
fabricate customised incisal table
what is a facebow transfer
used to measure relationship between jaws & TMJ with a special emphasis on axis of rotation. used to transfer relationship accurately to articulator to ensure correct orientation of casts
uses of facebow transfer
- diagnosis of tooth contact that hinders smooth jaw movement
- treatment in accordance with ptx’s anatomy
- clear standardised communication of functional tissues to lab
- baseline records
