Dentalnews (en)

The basics of denture materials – tooth materials

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If you are living in an industrial country, do not rack your brain about toothmaterials.

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Terms like noble metal supply, zinc supply, titanium and Co are hyped to squeeze money out of your pocket-denture costs are getting higher unnecessarily.

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All materials, which are used in a patient´s mouth are subject to strict controls and therefore bio compatible. For you, function and aesthetic dentistry is important.

The function should fit-the bite should be ok, as well as the thickness of crowns and bridges. Function does not depend on material, but on other factors. For example, if the dentist chooses the right tooth cut-you get good results with a groove cut, but not with a tangent cut or step cut. Furthermore if the dental impression is performed properly, if the denture was biochemically well concipated and last but not least if the dentist/technician has often worked with the materials.

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If a technician mostly performs gold inlays it is more difficult for him to performm partial dentures and the other way round. A tehnician who has worked his whole life with steel is more competent to perform dentures out of steel instead of titanium.
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Costs do not depend on the material but on aesthetic. It makes a difference whether the technician is performing 10 crowns/dentures a day or just one. Tooth aesthetic is an expensive art.

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Removable dentures, denture break, loss of abutment tooth, denture extension-these are the subjects we are talking about today-especially about dentures supported by mucous membrane!

If masticatory forces are initiated on the mucous membrane it is called dentures supported by mucous membrane. You call it partial denture if there are teeth left. If there are no teeth left you call it full denture. Often teeth are used as fixation of partial dentures. You differentiate partial dentures with and without clasps (pic. 1).

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With partial dentures without clasps the clasp is substituted by different fixation elements (attachment, head abutment…)(pic.2) A part of fixation is integrated in the prosthesis; the tooth, which is used as the denture fixation, is crowned and this crown is used as the other fixation.  That is why the term clasp tooth crown is often used and means crowned fixation tooth. Sometimes it is the aim with “partial dentures with clasps” to protect the fixation tooth from clasp and abrasion and so the tooth is randomly crowned, this is called clasp tooth crown as well. The advantage of partial dentures without clasps is the better aestetics, disadvantages are higher costs and the load of the tooth by the prosthesis. The more tighter the tooth is fixed with the prosthesis, the more higher is it´s load. If  you chew, the mucous membrane is slipping, consequently the denture is moving (resilience), this movement is spread to the remaining tooth-the more tighter the fixation, the bigger the tooth dislocate. The remaining tooth can get lost after a few years!

With classical partial dentures with clasps the load is lower, but not gone. Either way a partial denture is often the entering wedge to a full denture, cause normally the remaining teeth areslipping, a denture extension has to be made.

These process is often accelerate by false constructions of partial dentures. You see a so called free end situation in pic.3, there is no tooth behind the fifth tooth left and a partial denture with clasp was made.

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Position and direction of the clasp is wrong, cause the clasp is activated while chewing (pic.4)-i.e. the tooth is levered out-this should not happen. The clasp should not be activated until the denture is stick on the opposite dentition (pic 5 and 6), but it should be deactivated whilst chewing.

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Whilst free end situation the clasp should be open backwards, as well as the lever should be constructed longer. The perfect construction would be, if the clasp along with the metallic end piece of the prosthesis (which rests on the chewing surface)is placed between the third and fourth tooth (longer lever and therefore less dislocation), as well as deactivation of the clasp whilst chewing and activation whilst removal the denture.

This would be the right way, although there would be less aesthetic and in addition this leads to break of dentures and/or break of clasp. That is why the clasps are designed wrong-the tooth is more strained, but this means the dentist/technician has no additional costs and the patient is happy for now-the aesthetic is also more advantageous.

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Dentures supported by implants-different treatment waiting times

A fixed denture is always supported by bones, which means the masticatory force is either initiated by teeth or implants.

First implants has to be set in the bones, you call this an implantation. Nowadays minimal invasive techniques are standard, for example the swage technique.

Depending on whether the implant is treated with denture, you differentiate an..

o    immediate treatment

o– –immediate loading
o    open/muted  cure

If the implant is immediately exposed to the whole masticatory forces, you call it an immediate loading. It is possible if the quality of bones is ideal-especially in the lower jaw.

If the implant is immediately treated with denture, but is not exposed to the whole masticatory forces-the tooth is made smaller-it is called immediate treatment.

Whether the implant is loaded immediately or afterwards depends on different factors, especially on the quality of bones. Another factor is the extent of the implantation. For example, if a bone set up surgery is made in the same session, the mucous membrane is sutured tightly-a muted cure.

Sometimes the bone quality is not adequate for an immediate treatment. This would be a risk, since the tooth can be loosed before it is healed by the nutrition and/or the tongue. Either the implant is cured muted, or a so called gingiva shaper is fixed. The gingiva shaper saves the clearance surgery after the cure is done. You call this an open cure.

It is called muted cure if the implants are cured below the mucous membrane, so that the bone set up material cannot be infected-a bone loss would be the result. Through the mucous membrane occlusion the area of operations is protected from bacteria in the oral. The disadvantage of immediate treatment, immediate loading and open cure is the co called clearance surgery-the mucous membrane has to be open again after implant cure.

What does “dentures-supported by bones or mucous membrane” mean?

Depending on whether the masticatory force is initiated by bones (just like with your own teeth) or by mucous membrane. You differentiate from denture “supported by bones or mucous membrane”

It is called dentures- supported by bones, if  the masticatory force is located in the bones and the denture is hardly seated on the mucous membrane.

If  the masticatory force is primarily located in the mucous membrane and help remained teeth and/or implants (so called fixation elements) it is called dentures-supported by mucous membrane.

Often no fixation elements are used-  total denture. If fixation elements are used you call it a hybrid prosthesis. Better fixation can be improved through two implants. (pic. 1)You don´t need synthetic gums, but the masticatory force is not supported by these implants-so you see a mucous membrane supported denture placed on implants in this picture.

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A denture-supported by bones is trend setting in industrial countries. The reasons are:

• better comfort for the patient
• prevention of damages on fixation teeth (partial dentures-a classical example of a mucous membrane supported denture-is fixed on remained teeth)
• prevention of bone loss from the alveolar bone (Use it-or lose it)

Often a bone is not loaded naturally through a denture supported by mucous membrane (non physiological). The result is not only a bad fitting prosthesis, but also face changes (big lower jaw, small upper jaw). You can recognize bone loss because of recurrent pressure sores and/or a prosthesis, which is not fitting well anymore. The result is a denture lining-which compensate a bone loss.

Even if there are less bones left, a bone set up surgery can be made to use implants. Partial dentures and total dentures are implanted provisionally till the implants are healed.

Advantages of partial,- and total dentures opposite to implants are lower costs.

Fixed means that you are not able to remove the dentures out of the mouth. The denture is in the mouth constantly. This is not a dental plate, but a denture.

A classic example is a dental crown (pic.1). The quality of dental crowns, a correct bite and the dental arch incorporation have to fit all the time! Differences in costs refer to the effort and the aesthetic elaboration.

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Another example of a fixed denture is the dental bridge (pic.2) Like the dental crown it is also carbonised on tooth stumps. The only difference is, that a dental bridge connects one or more interlinks together.  Separate crowns are often linked together-without interlinks. This is done to save work, cause the technician has to mold less sides on the denture and so the dentist has to pay less for the work.  But this causes disadvantages for you!

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If there is no tooth stump left you need an implant instead (pic.3). A denture with implants is mostly carbonised- but with a temporary dental cement-this is called a “partly removable denture.”

If the dentist is able to remove the denture, for example by loosen screws, it is called partly removable denture-so the dentist is able to remove your denture “easily” but you are not.

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A classic example of a partly removable denture is a screwed bridge solution (pic.4)

As said before: Implant crowns are carbonised contrary to normal crowns, so the denture can be removed by the dentist as needed.  You call it a fixed denture if the crown is placed on the tooth stump, cause the dentist has to destroy the crown to get to the tooth.

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The use of screwed dentures was not unusual in the past, today carbonised solutions are  trend setting.

Some reasons are:

• Development and improvement of dental cement (permanent and temporary cement)
• lower costs in contrast to expensive screwed solutions
• easier to clean
• less problems
• higher comfort, cause screwed dentures are usually bigger and clumsy
• positive development in the region implantology and bone structure surgery

If you have a fixed or partly removable denture the masticatory force is initiated by bones either on the dental root or with implants. This is also possible with removable dentures-the masticatory force can also be initiated by the mucous membrane. You differentiate from denture, supported by bones or mucous membrane. More on this in the next article.