Factors Involved In Complete Dentures

By Dr.Swathi Pai on Tuesday, January 6, 2009 with 0 comments

Nature of Supporting Tissues:

A. Soft tissues: Ideally soft tissues should be firmly bound to cortical bone, containing a resilient layer of submucosa, and be covered by keratinized mucosa. Keratin is a scleroprotein present in the stratum corneum and is the end product of epithelial degeneration. Excessive trauma to the mucosa beneath a denture base can lead to abnormal tissue changes such as development of parakeratin, localized hyperkeratosis, and epithelial ulceration or necrosis. The fatty and glandular tissue work as a "hydraulic cushion".

B. Bone factor: The bone factor appears to be related to local anatomic and physiologic variations within and between individuals. At the present time bone factor can only be determined by comparing the patient’s response to bone stress( extractions, surgery) or by radiographic observation.

Tension placed on bone on areas of bone attachment tend to preserve the quality of the bone and sometimes results in bone deposition. Cortical bone is more resistant to resorption than cancellous or medullary bone. Sharpey’s fibers ensure tension on bone, minimizing the resorptive changes otherwise be the normal response of bone to pressure. Therefore a keratinized masticatory mucosa firmly bound to underlying cortical bone through a variable zone of connective tissue and submucosa with associated muscle attachments that provides the ideal denture-bearing tissue.

Anatomic Considerations:

A. Mandibular considerations: The primary stress bearing areas of the mandible must include the pear-shaped pad and the buccal shelf. The pear-shaped pad is the most distal extent of the keratinized masticatory mucosa of the mandible. The junction of the retromolar pad and the pear-shaped area demarcate the extension of the denture base. The pear-shaped area is associated with the muscle attachments of the buccinator , superior constrictor, and temporal muscle. The muscle attachments and the overlying mucosa provide a stress-bearing area. The other regions of the mandible are not usually essential in providing denture support.
B. Maxillary considerations:

1. Keratinized masticatory mucosa overlies a submucosal layer everywhere except at the midline suture.
2. The submucosa contains fatty and glandular tissue.
3. Dense connective tissue traverse the mucosa, except the midline raphe which has little or no submucosa.
4. The cortical bone of the hard palate (palatine process and the horizontal processes of the palatine bones), resists resorptive changes.
5. The tensor veli and the levator palatini may provide the source of tension that counteract the pressure resorption.
6. The crest of the ridge has a layer of thick keratinized tissue, dense fibrous connective tissue between mucosa and bone that acts as a resilient liner. The underlying bone is cancellous bone which is subject to resorptive changes.
7. The remaining facial slopes of the maxillary ridge are not essential in the denture support.

Relief Regions: Tissues susceptible to resorption should not be subjected to functional pressures:

1. most maxillary and mandibular ridge crests,
2. regions of thin mucosa directly over hard cortical bone, these include; midline raphe, tori, exostoses, and the mylohyoid ridge,
3. regions of mucosa overlying neurovascular bundles such as the incisive papilla, and the mental foramen.

Practical Considerations
: A truly mucostatic or pressure free impression is virtually impossible to achieve. The fluid impression material contained in a rigid tray inevitably causes some tissue compression. According to Pascal’s laws of hydrostatics, the pressure exerted on a confined fluid will transmit evenly throughout the fluid. Unfortunately, the fluid in oral tissues is not confined, the tissue fluids can move freely in response to stresses placed on them.

Selective pressure impressions provide equal distribution of pressure to the supporting tissues during function. It has some disadvantages so, the ideal technique for impression taking should incorporate both pressure-free and selective-pressure procedures.

Selection of the regions that should provide primary and secondary support depends on the anatomic variations unique to each patient.

Category: Prosthodontics Notes



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