Dental models

The role of casts in prosthetic planning

Proper prosthetic treatment with fixed partial dentures is impossible without a thorough preliminary examination. At this stage, diagnostic dental casts become an indispensable tool for the clinician. They are used to perform a comprehensive assessment of the entire dentition system before initiating intervention.

Using the casts and clinical examination data, the clinician analyzes:

• Dental arch defect: its exact size and topography.
• Supporting apparatus: the current condition of the teeth that will anchor the prosthesis, as well as the health of their periodontium.
• Alveolar ridge: the shape and condition of the edentulous site.
• Bite: the occlusal relationships of both jaws.
• Antagonists: the position and condition of the teeth in the opposite jaw that have lost their natural antagonists.

Requirements for fixed partial dentures

After the casts have been studied and a treatment plan is formulated, the fixed partial denture is designed. It must meet rigorous clinical and technical requirements.

1. Rigidity and sufficient strength. Because the structure relies on units bordering the defect, it transmits a significantly increased functional load to them. These abutment teeth are forced to do the work not only for themselves but also for the extracted teeth.
2. Aesthetic qualities. When the patient speaks or smiles, the metallic components of the structure must not be visible. Therefore, metal-ceramic restorations are recognized as the best choice for achieving high aesthetics.
3. Hygienic requirements. Hygiene depends directly on the shape of the pontic and how precisely it contacts the mucous membrane, gingiva, lips, cheeks, and tongue.

Depending on the prosthetic zone, the approach to shaping the pontic varies:

• In the anterior region, a saddle-less (ovate/tangent) design is used. The pontic should only gently touch the mucosa of the alveolar ridge without exerting any pressure on it.
• In the posterior region, a sanitary (hygienic) space must be created. A free clearance is left between the body of the fixed partial denture and the edentulous alveolar ridge. This is necessary to prevent food impaction under the prosthesis and to allow food debris to be easily washed away.

Indications and assessment of abutment teeth

Fixed partial dentures are primarily indicated for the replacement of small and medium-sized defects. For distal extension (free-end) defects of the dental arch, their use is limited and significantly less frequent.

Special, heightened requirements are placed on the teeth selected as abutments. The condition of the periodontium is of utmost importance. If a tooth is stable, this usually indicates the health of the surrounding tissues. Conversely, pathological mobility points to profound periodontal changes and requires extremely careful diagnostics.

An important factor is the height of the clinical crowns of the abutment teeth:

• Average height creates ideal conditions for denture fixation.
• High crowns harbor a hazard: their use significantly increases the risk of traumatic occlusion (in the decompensated stage).
• Low crowns create technical difficulties and significantly complicate the design of the prosthesis.

Radiological examination and complexity factors

In addition to studying casts, radiological confirmation of tooth status is necessary in a number of cases. X-rays are mandatory in the following situations:

• The tooth is stable, but there are clear signs of periodontal disease (gingivitis, exposure of the cementoenamel junction, presence of pathological bone or periodontal pockets).
• The tooth has carious lesions, fillings, artificial crowns, or exhibits wear of the coronal portion and a change in its natural color.

The success of prosthetics depends on many factors that can either facilitate or complicate the clinician's task.

Facilitate the work:

• Correct occlusal relationships.
• Healthy intact periodontium.
• Physiologically correct tooth position (when the long axes of future abutments are parallel to each other).

Significantly complicate the work:

• Any dental arch deformations.
• Inclination of abutment teeth.
• Inclination of teeth that have lost their antagonists.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Topography and classification of dental arch defects
• Traumatic occlusion in the decompensated stage
• Pathological tooth mobility and periodontal diseases
• Metal-ceramic restorations in prosthodontics
• Dental arch deformations and their prosthetic treatment

Other topics in the section "Chapter 10. Methods of restoring dental arch defects (orthopedic design)"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.