Complete denture retention

By Dr.Swathi Pai on Wednesday 7 January 2009 with 0 comments

Definition of Properties: Retention is the resistance to displacement of the denture base away from the ridge. Stability is the resistance to horizontal and rotational forces. Support is the resistance to vertical movement of the denture base toward the ridge.

Definition of Retention Factors:

1. Adhesion- attraction between unlike forces.
2. Cohesion- attraction between molecules of the same material.
3. Interfacial surface tension- refers to the forces involved in maintaining the attraction of two intimately contacted objects, by virtue of a thin fluid film in between them. Also defined as the force that maintains the surface continuity of a fluid.
4. Gravity- self-explanatory.
5. Intimate tissue contact-close adaptation of the denture base to the underlying soft tissues.
6. Border seal-involves the intimate contact of the denture borders with the surrounding tissues.
7. Atmospheric pressure- physical factor of hydrostatic pressure due to the weight of the atmosphere on the earth.
8. Neuromuscular control-refers to the functional forces exerted by the muscles of the patient, that can affect retention. Older patients have more difficulty in adjusting to new dentures, due to the progressive atrophy of their neurological systems.

Clinical Observations: Measurements made above sea level showed a decrease in denture retention. With a 70% decrease in atmospheric pressure, a 50% decrease in retention was noted. The presence of dissolved gases or air in saliva, serves to decrease the effectiveness of the atmospheric pressure. Therefore the presence of perforations in a PPS, reduces the retention of the denture.

Clinical Implications:

1. Impression material with adequate flow properties should be used to avoid uneven pressure during impression making.
2. A slight generalized pressure on the soft tissues is desirable.
3. Elimination of full arch relief spacers in the tray.
4. Use of nonperforated trays can lead to inaccurate recordings.
5. Recovery of abused oral tissues obtained by not allowing patients to wear their prostheses for a minimum of 48 hrs prior to impression taking.

Anatomical Influences on Maxillary Denture Retention: Highly tapered palatal vaults and the retrozygomatic space (buccal space), represent a problem in maintaining border seal.

Anatomic Influences on Mandibular Denture Retention: The mandibular denture presents the major problem with regard to retention. Reasons include : movable floor of the mouth, which causes difficulty in establishing border seal, and lack of ideal ridge height and conformation, which minimizes denture stability.

Adequate seal can be obtained by gently compressing the tissues of the lateral wall of the retromylohyoid fossa lingual to the retromolar pad and tucking the distolingual flange laterally against the mucosa overlying the superior constrictor muscle superiorly and the loose connective tissue of the mandible inferiorly.

The contour and inferior extension of the lingual flange are dependent on the action and anatomy of the mylohyoid muscle. The most difficult region in which to obtain a border seal is the anterior lingual border. The mylohyoid muscle acts anteriorly as well as posteriorly to raise the floor of the mouth. The superior fibers of the genioglossus muscle attach to the superior genial tubercles and function in depressing the body of the tongue. Activation of the inferior fibers serve to protect the tongue.

Conclusion: Some techniques recommend the extension of the anterior lingual flange sublingually. The flange is extended inferiorly to contact the highest level if the floor of the mouth. The flange can then be extended posteriorly to contact the sublingual folds and therefore establish a seal when the tongue is at rest.

Another technique involves adding additional softened border- molding material to the inner surface of the previously molded anterior lingual area and reseating the custom tray.

Category: Prosthodontics Notes



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