When someone loses all his teeth (becomes edentulous), he also loses some of the ability to perform certain activities-eating, speaking, facial expression-and his appearance is impaired. His appearance is impaired not only by the loss of the teeth themselves but also because of the loss of support for the facial tissues lying over them. When the teeth are lost, some of the supporting them bone resorbs. The artificial substitutes-completes dentures-must not only replace the lost teeth and lost supporting bone and soft tissue, but also restore the impaired functions and appearance.
Clinical stage l.
History and examination
Clinical stage 2.
Primary impressions.
Objectives: To obtain an impression of the whole of the denture-supporting area of each jaw; to record the full extent of the sulcus; to obtain an impression in which certain landmarks on the edentulous jaws are recorded.
By achieving these objectives a model can be obtained upon which a correctly designed tray may be constructed in order to make the secondary impression. Furthermore, only impression compound has the correct properties of consistency and ability to be manipulate which are necessary in a primary impression material.
Laboratory procedures l
The preparation for the visit at which the secondary impressions will be made involves the construction of casts from the primary impressions and the construction of special trays on these casts.
Clinical stage 2 (continued)
Secondary impressions
Objective: to obtain an impression from which a retentive denture base can be constructed.
The denture base should satisfy the following requirements:
l. It must be extended until its border lies on displace able tissue where a seal can be developed.
2. The tissue adjacent to the border should be deformed enough to achieve a seal but not so much that they tend to displace the denture or suffer injury. Muscles related to the border must not be prevented from free activity.
3. It should have the closest possible contact with the surface or the mucous membrane lying beneath it.
4. Extension to provide retention ensures the maximum coverage of the jaw, and this in turn ensures that the minimum force per unit area is transmitted to the supporting tissues by the denture during function.
The advent of Vinyl-poly siloxane offers an alternative material for upper and lower impressions. It is of suitable consistency and gives an excellent surface to the cast and dentures.
Polyether materials are also used.
Laboratory procedures 2
At this stage the permanent bases are made and wax occlusion rims are added to them in preparation for the next clinical step of recording the jaw relation.
Clinical stage 3
l )Checking retention of the bases prior to
establishing jaw relationships
2) Establishing jaw relationships with permanent bases.
Objectives
l. To accurately record centric jaw relationship.
2. To take a facebow record to enable the baseplate and occlusion rims to be positioned in the articulator so that their relationship to the rotational axes of the articulator is the same as the relationship they will bear to the rotational axes of the mandible when they are in the mouth.
Procedure
Assess the lip support
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