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Artificial Teeth

(artificial teeth (powerpoint




(artificial teeth (powerpoint

Requirements

1-The most important requirement of artificial teeth is good appearance.

2-There should be good attachment between the artificial teeth and the denture base. The introduction of artificial teeth into the base should not adversely affect the base material. That is, the artificial tooth and base materials should be compatible.
(artificial teeth (powerpoint



3-It is an advantage for the artificial teeth to be of low density in order that they do not increase the weight of the denture unduly.
(artificial teeth (powerpoint


4-The artificial teeth should be strong and tough in order to resist fracture.

(artificial teeth (powerpoint



5-They should be hard enough to resist abrasive forces in the mouth and during cleaning, but should allow grinding with a dental bur so that adjustments to the occlusion can be made by the dentist at the chairside.

(artificial teeth (powerpoint

Available materials

The two materials which are commonly used for the production of artificial teeth are acrylic resins and porcelain.
(artificial teeth (powerpoint


(artificial teeth (powerpoint

Acrylic resins

Acrylic resin artificial teeth are produced in reusable metal moulds using either the dough moulding technique, described for denture base construction, or by injection moulding in which the acrylic powder is softened by heating and forced into the mould under pressure.



(artificial teeth (powerpoint


(artificial teeth (powerpoint



The resins used are highly cross-linked in order to produce artificial teeth which are resistant to crazing. The main difference between the materials and those used for denture base construction is the incorporation of tooth-coloured pigments rather than pink ones.
(artificial teeth (powerpoint

Porcelain

Artificial porcelain teeth are produced to standard shapes and sizes by using moulds which are approximately 30% larger than required, in order to allow for shrinkage during firing. Small holes or metal pins are incorporated in the base of the porcelain teeth during their production. These are used to give mechanical attachment to the denture base.

properties

Both acrylic and porcelain teeth can be made to give a realistic appearance. The slightly greater translucency and depth of colour achieved with porcelain possibly gives this material a slight advantage in terms of aesthetics. Both materials are produced to a variety of shapes, sizes, and shades which enable selection of teeth to suit most individuals.

One aspect of porcelain teeth which is sometimes unpopular with patients is the ‘clicking’ sound which is made when two porcelain teeth come into contact.

Attachment of the teeth to the base is through a chemical union in the case of acrylic teeth and by mechanical retention for porcelain teeth. For both materials, adequate bonding is achieved only if all traces of wax from the trial denture are removed from the teeth during the ‘boiling out’ stage.


Acrylic resin teeth are, naturally, more compatible with the denture base than porcelain teeth. There is a serious mismatch in coefficient of thermal expansion and modulus of elasticity between porcelain and acrylic resin. This may lead to crazing and cracking of the denture base in the region around the base of the porcelain teeth.

Porcelain has a density value about twice that of acrylic resin and dentures constructed with porcelain teeth are much heavier.
Porcelain is brittle and teeth constructed from this material are more likely to chip and fracture than acrylic teeth.

There is a vast difference in hardness between acrylic resin and porcelain. Acrylic teeth are more likely to suffer abrasion than porcelain teeth.

The extreme hardness of porcelain is a disadvantage when adjustments, requiring grinding of teeth, are necessary. With acrylic teeth, such adjustments are carried out quite simply. For porcelain teeth however, the process is difficult and results in the glaze being removed from the surface of the porcelain.

It is a clinical impression that porcelain teeth transmit higher forces to the supporting soft tissues than acrylic teeth. This is a function of the greater modulus of elasticity of porcelain. The difficulties of grinding porcelain teeth combined with their tendency to transmit a greater force to the underlying tissues dictates the type of clinical case for which they can be used. They should not be used where there is diminished interocclusal distance or when there is poor ridge support.

One advantage of ceramic materials used in various aspects of medicine and dentistry is their perceived biocompatibility. This is related to their structure and lack of chemical reactivity under normal conditions.

The vast majority of artificial teeth used for denture construction are now of the acrylic type. Acceptable appearance coupled with convenient handling, greater toughness and compatibility with the acrylic denture base give the acrylic resins an advantage over the alternative porcelain materials.



رفعت المحاضرة من قبل: Sultan Alsaffar
المشاهدات: لقد قام 15 عضواً و 255 زائراً بقراءة هذه المحاضرة








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