Neutral zone impression Flashcards
Neutral zone?
the potential space between the lips and cheeks on one side and the tongue on the other;
that area or position where the forces between the tongue and cheeks or lips are equal
where the denture teeth can avoid being dislodged by normal oral functions
can be used to help define tooth position and/or shape of polished surfaces
Where is the denture sitting?
neutral zone
For complete stability, where should the prosthetic teeth be arranged?
within the neutral zone
Techniques for positioning of denture teeth?
biometric guides to replicate natural tooth position
conventional shaping of wax rim
copy denture
NZ (neutral zone) technique
conventional zone technique?
produces dentures of good stability
where there is a favourable ridge
when to use neutral zone technique?
resevered for pt for proven instability
has not been able to be rectified…
resorbed ridges
enlarged tongue
poor facio-structural control
Parkinson’s/stroke
facial reconstructive structure
conventional technique used on pt with resorbed ridges?
poor denture stability
good ridges, use what technique?
conventional dentures
NZ technique reserved for what teeth?
lower anterior
what happens to the ridge with tooth loss?
degenerative changes take place and ridge flattens
what happens with flattened ridge?
has a reduced ability to resist lateral displacing forces
why is image 2 a problem?
second image has a larger distance between the ridge and occlusal surface
resulting in greater instability
consequently retention and stability of denture become more dependent on the correct positioning of teeth and the contours of the external/polished surfaces of denture
how to seat the lower denture?
more dependent on the correct positioning of teeth and the contours of the external/polished surfaces of denture
peri denture muscular should act to seat the denture rather than displace it
tongue widens after tooth loss?
lateral spread of the tongue
what is occurring here due to bone resorption?
insertion of the circum-oral musculature come to light superficially to the denture bearing area
causing denture instability
effect of age on complete dentures?
loss of facial tonicity
diminished capacity for successful neuromusculture adaptation
the age at which people become edentate is increasing
relevance to clinical tx?
poor denture bearing tissues
poor capacity for adaptation
poor tolerance of complete dentures impacts of quality of life indices an nutrition
what is the preferred minimum tx option for stabilizing lower complete dentures?
2 mandibular implants
why 2 mandibular implants?
stabilization
increase function
decrease pain
increase pt quality of life compared with conventional dentures
why would a pt no want mandibular implants?
fear of pain
post op complications
social embarrassment
financial resources
not not perceive the necessity
if pt does not want implant to stabilize denture, what is the other option?
prosthesis manufactured according to NZ principles
objectives of NZ?
define the position of the lower anterior teeth so they are in equilibrium between opposing muscular forces
sculpt the polished surface so that the forces exerted by the muscles will tend to stabilise the denture rather than unseat it
CONSORT?
guidelines for clinical trials - gold standard is CONSORT
guidelines for consort?
sample size calculation
randomisations
blinding
statistical methods
limitations
external validity
NZ vs conventional?
pts prefer NZ dentures
pts with well formed ridges prefer conventional dentures
better masticatory performance with conventional
‘muscular’ fixation of dentures better with NZ dentures
conventional dentures have better retention
where does most evidence for dentures come from?
randomised control trials rather than CONSORT
1) technique to record labio-lingual position of lower anterior denture teeth?
1) NZ tray made on the working cast after the bite registration stage
occlusal stops incorporated
- can be made form green stick or fabricated in lab
2) try-in tray
- check stability, extension, comfort
- blocks and wires not outside of neutral zone
3) load with impression material
- pt performs sequence of mouth exercises
- make sounds
4) NV the wax try-in with teeth
2) technique to define the shape of the polished surfaces?
define the polished surface
1) Vaseline added to teeth as separator
2) silicone impression material is added to the polished surface
3) pt asked to make movements to mould the polished surface
4) returned to lab
- lost wax technique for complete denture
5) NV = fit
- special care for stability
impression material?
compo (green stick)
silicone
modified waxes
viscogel
what is the neutral zone with regards to dentures?
the position of muscle balance an dis especially relevant to -/C
when to use neutral zone?
for unstable -/C cases which cannot be managed by conventional means
typical pt who benefits form NZ?
atrophic ridges
neurological conditions
post resection surgery
preferred tx option over NZ?
implant supported over denture
