Removable prosthodontics

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Removable prosthodontics Powered By Docstoc
					Removable prosthodontics

    1. INTRODUCTION
       In removable prosthodontics, there are two types of substitutes: TOTAL PROSTHESIS (TP)
       and PARTIAL PROSTHESIS (PT) (in this year we will be discussing the TP).

        The TP is a prosthodontic device, which substitutes all teeth, and can be put in and out of the
        oral cavity by the patient himself.


The main problem when trying to make a prosthetic substitute is, that we try to substitute a tooth,
which is in fact a tool. Imagine a hammer: the head of the hammer (the active part) is in the mouth
the tooth crown and the root represents the handle of the hammer. The crown serves as a chopping
device, to prepare the consummed food roughly. Substituting a crown does not represent a major
problem for the dentist- the supply of confection crowns exceeds its needs.

The root, however, becomes more problematic when we try to substitute it. Normally, it is firmly
attached into the mandibule via the hanging apparatus.

    2. / 3. CHANGES IN THE ORAL CAVITY AFTER TOTAL TEETH LOSS, CONSEQUENCES OF LOSS
       OF ALL TEETH- RESORPTION, PROPRIOCEPTION

Complications arising after teeth (root!) loss:

    a.) The tooth bearing surface is 4 times smaller as before (picture!). That causes a corresponding
        fall of the effectiveness of chewing (example: we need to chew 4 times as much so as to
        reach the same effect).
    b.) Loss of dental proprioception: pressoreceptors of the periodontium are up to 200 times more
        accurate than the ones in the chewing muscles, the temporomandibular joint and the
        periosteum altogether. The load of teeth in every possible way normally excites and activates
        the afferent part of the proprioceptive arc, according to which the higher centers perform a
        very accurate motion of the mandibule. When the teeth are lost, at first the patient doesn´t
        locate the bolus accurately.
    c.) The periodontium reaches its peak resistance when forces acting upon it are directed axially,
        and the Sharpey fibers of the periodontal ligament are loaded steadily. When the forces are
        directed in the radiarly/transversially (??), the tooth moves excentrically in the alveole and,
        consequentially, one part experiences compression and the other extension. This
        phenomena represents the hardest problem to solve when trying to stabilize the TP.
        The TP reciprocates the vertical forces well enough, but on the contrary, the alongside forces
        destabilize it and cause its horisontal movement (picture 1)

        STABILISATION AND RETENTION
        Retention depends on ADHESION (Jozef Stefan´s law-picture!)
        There are two forms of the maxilla, whicha are important for the retention:
               a.) ADHESION FORM (A. Palate)
                   Only horisontal surfaces are appropriate for adhesion, not the ones with a slope.
               b.) RETENTION FORM (is based on mechanical retention)
Differences between adhesion and retention palate:

                                   Adhesion palate                     Retention palate
Course of alveolar ridges          Low                                 High
Paratuberal space                  Not underhung                       Overhanging
Shape of the palate                Flat                                Gothic


BONE RESORPTION (=bone melting)

The process begins with tooth loss, as the supporting surface is diminishing. The spongious bone is
being resorbed, not the compact!!!

To what extent does the resorption process take place? (question of the hour)

Until there is no processus alveolaris (just after birth, the newborn has only the corpus of the
mandibule developed, not the processi; the latter is linked to grown teeth). The process can continue
until it reaches the insertia of buccinator and mylohyoideus muscles (if the insertia on the bone had
been resorbed, desinsertion would have taken place) (picture!)

At what time after the extraction should the removable prosthodontic treatment begin? 6 to 8 weeks
after extraction.

Explanation: shortly after extraction the resorption takes place at its highest pace. We should wait,
because the following happens:

    -   The extraction wound is filled with coagulum,
    -   Which is then substituted with granulation tissue (fibrous cells, capillaries),
    -   It then transforms into fibrous tissue,
    -   And later into osteoid tissue (=organic matrix that doesn´t mineralize),
    -   It reconstructs the alveolar ridge during a time period lasting from a few weeks up to 1 year,
    -   At last, the mucosa epitelises.

Had the wound healed properly, we should find out that the oral and buccal periostal poles had
come together; compact bone would form under periosteum, and in this case, there wouldn´t be any
resorption at all. Unfortunately, this above described scenario takes place very rarely.

Carlsson et.al. : what happens to the mandibule/maxilla after the extraction?

    -   1. Week after: high osteoclast activity
    -   3. W: osteoclasts melt the walls of the alveole.
    -   5. W: on the X-ray, the alveole is empty.

    But in the 2. Week after the extraction, the regeneration process had already begun:
    - High osteoblast activity.

    - 4.W: unorganised osteoblast islands form and fill the alveole.

    - 6.W: the islets form an organized osteoid trabecular structure. (diagram!!!9

				
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