Types of Dentures: Fixed Dental Prostheses

By Vishaal on Friday, December 7, 2007 with 0 comments

Fixed dentures transmit chewing pressure by the dental way only. Teeth fitted with those dentures (pillar teeth) are prepared properly, and constructions that attach to these teeth are called pillar constructions. This group contains inlays, crowns, fixed bridges.

Inlays replace a part of a tooth’s lost crown or the whole crown. An onlay replaces the whole occlusal part of a crown. An inlay replaces the occlusal part of a crown either totally or partially, plus one or both proximal parts of it.

Root inlay (superstructure) replaces the whole crown part of a tooth and it is attached to a treated root canal by the root pin.

Crowns replace a part or the whole damaged tooth’s clinical crown that is covered, partially or completely, by a surface jacket which reaches to, or under the marginal gingiva. Crowns are of the following types:

1. Jacket crowns, made of metal, ceramic or resin.

Metal jacket crowns are made by casting from gold, gold-palladium or silver-palladium alloys. A temporary protective band crown can be made for young patients in exceptional cases. These crowns are made of a metal sheet with cast or sheet occlusal surface (for distal teeth), or as a protective metal sheet crown made of two halves for frontal teeth.

Ceramic crowns are the oldest type of jacket crowns that still fit today’s needs well. They are used mostly at the frontal section. The base of ceramic is silicon dioxide, feldspar and kaolin that is being replaced by aluminum oxide these days. Ceramic crowns are much harder than dental tissues or prosthetic metal alloys. For this reason, a pillar tooth periodontium may get damaged by its overloading (a ceramic crown does not abrade), or a non-physiological abrasion of an antagonist tooth may occur.

Resin crowns are the most often used ones for frontal teeth. The material from which these crowns are made is a methylmetacrylate resin. A disadvantage of these crowns is their low mechanical resistance and bad color stability.

2. Veneer crowns are made of metal by casting, in combination with a resin or ceramic that form a veneer. The metal construction covers by its inner casing a treated tooth’s surface. The outer jacket completes the anatomical shape of a tooth from oral and proximal sides, whereas the facet (a part of the outer jacket) completes the crown’s shape from the visible vestibular side.

3. Pin crowns replace the whole clinical crown of a pillar tooth. They are fixed to its root by the root pin.

Fixed bridges replace gaps after one to four teeth of the dental arch that are framed by the first class abutments. If a connecting line between the abutments is straight, the bridges are referred to as linear ones. If connecting lines of the abutments enclose a plane, bridges are marked as planar (anchored to a plane). If the pillar teeth number is higher than number of replaced teeth, we call them splinting bridges. A fixed bridge consists of abutment retainers and the pontic, or so called inserts. The pontic fills the area after missing teeth and it is firmly connected abutment retainers. According to the relationship of a pontic to an alveolar ridge, there are inserts that are not in contact with the mucosa (reverse arch cleansable pontic), and contact inserts. Reverse arch cleansable pontics are used at the lower jaw’s distal parts for high abutments. The mucous surface of an insert has to be at least 3 mm clear of the alveolar ridge mucosa. Contact pontics sit at the alveolar ridge by a small oval surface that has a major part located at the vestibular slope of the alveolar ridge. The occlusal surfaces of pontics are reduced in size by about one third, so that to prevent an overload of abutments during chewing.

Category: Prosthodontics Notes



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