Implantology and Prosthetics: Types of Dental Prosthesis and Implant Fixations

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What do the terms “fixed artificial teeth”, “conditionally removable dental prosthesis” and “removable dentures” really mean?

Fixed means that you cannot take the artificial teeth out of your mouth; they are firmly affixed in the mouth. In this case, the proper term is not “dental prosthesis,” but “artificial teeth.” A classic example of fixed artificial teeth is a crown. Another example of fixed artificial teeth is a bridge. Like the crown, it is cemented onto tooth stumps. The only difference with the crown is that one or more “interlink(s)” connect two “crowns” with one another.

Single crowns are often fused together without interlinks. This is done in order to save time because the dental technician has fewer sides to shape on the artificial teeth and thus the dentist pays less for the work. For you, however, such a fusing only has disadvantages!

If there is no longer a tooth stump present, an implant takes over the function of the dental root. In most cases, prostheses on implants are also cemented in, but with temporary dental cement. Therefore, this constitutes a “conditionally removable prosthesis.” If the dentist can remove the prosthesis, e.g., by loosening the screws, then this is called a “conditionally removable prosthesis.” Conditionally removable thus means that you cannot remove the prosthesis from your mouth, but the dentist can do so “simply” and without destroying it.

A classic example of a conditionally removable prosthesis would be a screwed bar solution. As previously mentioned, implant crowns (as opposed to normal crowns) are fixed with temporary cement, i.e., the dentist can remove the implant crown if necessary. Contrary to that, a crown placed on your tooth stump is a fixed artificial tooth because the dentist has to destroy the crown in order to get it off your tooth.

In the past, the use of screwed prostheses was not unusual. Today, the trend is clearly towards cemented solutions.

There are a number of reasons for this:

  • The development and improvement of cements (permanent and also temporary cements)
  • The lower costs of devices compared to elaborate screwed solutions
  • Easier to clean
  • Less prone to problems
  • More comfortable for the patient because screwed prostheses are usually bigger and thus, bulkier in the mouth
  • Positive developments in implantology in the area of bone graft surgery

In fixed/conditionally removable prostheses, the chewing forces are always guided into the bone, either via the dental root or through implants. In case of removable dentures, this is also possible. Alternatively, the dentures can utilize parts of the mucous membrane as a “rest,” and thus transmit the chewing forces to the mucous membrane. Depending on whether the chewing forces are guided into the bone (as with natural teeth) or onto the mucous membrane, removable dentures are classified as “bone-supported” or “mucous membrane-supported” dentures!

When chewing forces are guided into the bone and dentures are merely resting on the mucous membrane, they are referred to as “bone-supported” dentures. However, when the chewing forces are primarily guided into the mucous membrane and the remaining teeth and/or implants (referred to as anchoring elements) only serve the higher stability of the dentures, then they are referred to as “mucous membrane-supported” dentures.

There is a clear trend in industrialized countries towards more and more bone-supported dentures due to the following reasons:

  • Increased comfort for the patient
  • Prevention of damages on the anchoring teeth (partial prostheses – a classic example of mucous membrane-supported dentures – are anchored on the remaining teeth by means of various anchoring elements)
  • Prevention of bone resorption at the alveolar bone (“Use it, or loose it!”)

 

Bone Resorption Due to Prostheses?

In cases of dentures supported by the mucous membrane, bone resorption is often accelerated, as the stress applied to the bone is no longer natural. This leads to ill fitting dentures as well as to physical changes in the face (large lower jaw, small upper jaw). You can recognize the bone resorption due to recurring bruises and/or the deteriorating fit of the dentures. This results in a lining of the dentures in order to compensate for bone loss.

Animation von transparentem Schädelmodell mit Zahnimplantat

Even if there is very little bone left, bone augmentation surgery is able to recreate a bed for implants. Partial dentures and full dentures are often placed as temporary prostheses for the duration of the healing process for tooth implants until loads can be applied.

Artificial Teeth on Implants – Differing Waiting Times for the Provisions

Fixed artificial teeth are always bone-supported, i.e., the chewing forces are guided into the bone either via your teeth or via implants.

Implants have to be placed into the bone first. This process is referred to as an implantation. Today, minimally invasive techniques are the standard, e.g., the so-called stamping technique.

Depending on how long it takes for the implant to be provided with an artificial tooth, one differentiates between:

  • Immediate provision
  • Immediate loading
  • Open/covered healing

When the implant is immediately exposed to the full chewing forces, this is referred to as “immediate loading.” This is possible when there is optimal bone quality, particularly in the lower jaw.

When the implant is immediately provided with an artificial tooth but not exposed to the full chewing forces because the tooth is simply being prepared in a little bit smaller size, this is referred to as an “immediate provision.”

Whether loads can be applied to the implant immediately or only later on depends on various factors, but primarily on the quality of the bone. Another factor is the extent of the implantation. For example, if a bone graft surgery is performed in the same session, then the healing process takes place in a closed fashion, i.e., the mucous membrane above the implant is tightly sewn up.

Sometimes, good bone quality is not even sufficient for an immediate provision since the danger of the implant (including the tooth) loosening due to food and/or the tongue would be too big. In such a case, the implant is either left to heal in a closed fashion or a so-called gingiva former is affixed. The gingiva former spares the patient from having to undergo an uncovering procedure after the healing. This is called open healing.

Covered, healing then means that the implants are left to heal under the mucous membrane so that e.g., the bone graft material doesn’t get infected. A loss of the bone graft would be the consequence. By closing the mucous membrane, the area where the surgery was performed is protected from the bacteria located in the oral cavity. The disadvantage of this procedure versus the immediate provision, immediate loading, and open healing is that the mucous membrane has to be reopened after the implants heal. This is called an uncovering procedure.

Click here to see the video: Implantology

 

This post is also available in: German

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