neutral zone Flashcards
Why is the Neutral Zone (NZ) important
The oral environment changes once edentulism occurs, however these changes are not consistent withing mouth. Utilizing the zone as described
the basic concept
is the denture including base and dentition are placed in an area where the tongue and cheeks work in harmony
This is known as ‘dead space’
This goes against a temptation of placing the dentures, in a position, where the patient’s teeth may once have been.
Functions the NZ harmonizes
Speech
Mastication
Swallowing
Smiling
Laughing
These all utilize actions using:
Tongue
Cheeks
floor of the mouth
Failure to account for these areas result in unstable and unsatisfactory results
neutral zone tongue
The tongue pushing out is neutralized by the cheeks and lips- this is developed by muscular control- however as previously discussed is different in the individuals. However so are the forces
denture surface- design concepts
Occlusal surface
Impression surface
Fish proposed- The polished surface
Polished surface
The polished surface- by size can be larger than the occlusal surface and the impression surface combined. The polished surface accounts for any of the denture-based material, including the dentition that is not contacting the occlusal table
Occlusal surface
A favorable arrangement of the occlusal surface is when the overall size of the impression surface AD is equal to the overall size of the denture ABCD. In figure 2- denture A follows this pattern in denture B the overall size is less. This is due to excessive resorption of the alveolar ridge
Advanced technical consideration
The use of a neutral zone tray- many designs include
Use of neutral zone tray, with stops indicating the vertical dimension (figure 3)
Definitive base utilizing adhesive (figure 4)
Clinician recording the zone formally- this information is then transferred to the occlusal rim using matrix (figure 5) (Field & Storey, 2004). The contours of this formal recording (indicated in purple) should be incorporated into the design of the polished surface- the shape and the size
How does this impact on design- anterior
As Mandibular ridges resorb the ridge crest can fall below the origin of the mentalis muscle. This can result in a fold in the superior part of the ridge crest
This then necessitates placing the anterior dentition further back on the ridge. Figure 6 shows with the broken line the patients original placed dentition, the sold line presents proper positioning to avoid the lip dislodging the denture
Anterior arrangement
The posterior placement of the mandibular dentition can result in a more pronounced overjet as indicated in figure 7. This can impact speech and masticatory function utilizing a bite plane can help with this, the plane is indicated on the right
Posterior Dentition-
Dentition should not be placed on the slope of the retromolar pad- this can result in a smaller volume of dentition being utilized (omitting 7’s). Leaving off the 7’s provides more tounge space
posterior dentition
Teeth should be placed vertically with the occlusal surfaces contacting opposing occlusal rims
Buccal corridor should still be considered.
Posterior Dentition-
Central groves of mandible dentition and centers of marginal ridge should correspond in none neutral zone patients (figure8), it may be needed to placed posterior mandibular dentition slightly more buccal for the neutral zone patient (figure9).
Incorrect positioning can cause the denture to fracture- positioning dentition in an excessive buccal area places the masticatory forces down the buccal of the ridge rather than onto the crest- inducing a stress fracture (figure 11) (Johnson and Wood, 2012
Denture base-
Palates should be a uniform thickness in the vault of the palate- under thinned dentures lack the impact strength. Dentures thicker than 2.5mm can encourage porosity, and changes to the placement of the dentition during curing. In addition, if the palate is too thick then you have encroached in the tongue space.
Don’t overbuild the sulcus in the maxilla where there us less resorption.
Incorporating a slight concavity in areas allows muscles to ‘grip’ a fully contoured denture (figure 8) is quite complex in terms of the design
