Biomechanical Aspects On Overdenture Treatment

Question. Define overdenture. Mention the biomechanical rationale of over-denture prosthesis. Discuss the advantages and disadvantages of over-denture.
Answer:

Overdenture Definition

A tooth-supported complete denture is a dental prosthesis that replaces the lost or missing natural dentition and associated structures of the maxillae or mandible and receives partial support and stability from one or more modified natural teeth.

Classification of Overdenture

Based on the method of abutment preparation.

1. Noncoping
2. Coping
3. Attachments.

Read And Learn More: Complete Dentures Question and Answers

Overdenture  Noncoping Abutments

In noncoping, selected root abutments are reduced to a coronal height of 2 to 3 mm and then contoured to a convex or dome-shaped surface. These abutments commonly require endodontic therapy and are prepared conservatively to receive an amalgam or composite-type restoration.

Overdenture  Abutments with Copings

Cast metal copings with a dome-shaped surface and a chamfer finish line at the gingival margin are fabricated and cemented.

Overdenture On Natural Teeth

Two types of copings are prepared

1. Short coping
2. Long coping.

Short cast copings are 2 to 3 mm long and as coronal root reduction would expose the pulp, endodontic therapy is done. As the cast coping is small a post is fitted to the canal hence soft gutta percha-like material is used.

As long cast copings are normally 5 to 8 mm long endodontic therapy is not done. The long cast coping is ellipsoidal-shaped coronal coping and has a larger crown-root ratio hence requires good bone support.

Overdenture  Abutments with Attachments

Attachments are used to improve retention of the denture base and generally are secured to the abutment by a cast coping. As long as the tooth-supported complete dentures remain functional, the resorption rate of the remaining residual ridge is significantly reduced.

Overdenture  Goals

1. Overdenture maintains teeth as part of the residual ridge and can withstand a greater occlusal load without movement.
2. Overdenture decreases the rate of resorption as the remaining teeth support the alveolar bone.

Overdenture Indications

For young patients who face the loss of the remaining natural teeth.

Requirements of an Overdenture

1. Teeth used as over-denture abutments should be free of any periodontal diseases.
2. Good plaque control measures are to be taken to preserve the existing abutment tooth.
3. The abutment tooth should be nonmobile, some mobile teeth can be salvaged after periodontal therapy but need good attached gingiva to act as a vertical stop.
4. A well-fitting base is needed to distribute the load over a wide area and also prevent food and plaque accumulation under the base.
5. The appliance should be simple to construct and maintain.

Overdenture On Natural Teeth

Overdenture Advantages

1. The retained natural tooth in overdenture aids in providing tensile stimulation to the residual alveolar ridge preserving it.
2. Preservation of proprioceptive response.
3. The modified teeth provide a definite vertical stop for the denture base.
4. Horizontal and torquing forces are minimized.
5. Stability and support are increased.
6. The retention of only one tooth frequently makes for a more favorable prognosis.
7. Less post-insertion problems.
8. Convertibility: Can be easily relined or rebased into a conventional complete denture.

Overdenture Disadvantages

1. Caries susceptibility of the abutment teeth.
2. Periodontal disease can cause failure in overdenture functioning
3. Encroachment of the interocclusal distance when the internal attachment is used.
4. Bony undercuts adjacent to the overlaid teeth (usually buccally), prevent close adaptation of the denture flange to the underlying tissue.
5. If undercuts are blocked it causes spacing between denture and tissue creating a food trap.
6. Esthetics and bony under-cuts cause over-contouring of dentures resulting in improper lip fullness.
7. Undercontouring leads to improper retention and stability.