Complete removable dentures

Design elements and indications for use

The choice of orthopedic design depends on the defect topography, periodontal condition, and edentulous areas. Special attention is paid to metal bases, which provide rigidity and allow the use of complex attachment systems.

Transverse palatal strap is indicated for distal and bounded defects (upon loss of premolars and molars), as well as for patients whose profession requires clear articulation. However, it cannot be used in the presence of a pronounced palatine torus due to the risk of mucosal trauma. Thinned mucosa and an elevated gag reflex also serve as limitations.

Metal base on the mandibular arch is used in the following cases:

• Significant atrophy of the alveolar ridge with distal extension defects.
• Need for anterior tooth splinting (replacement of a continuous clasp).
• Low clinical crowns and space deficiency for a standard major connector.
• Presence of bony prominences (exostoses).

Fenestrated bases are advisable only with preserved alveolar ridges and the use of multi-arm clasps.

Manufacturing technology of the cast framework

Creating an accurate metal framework is a complex multi-stage process requiring the transfer of the gypsum model into a refractory one.

1. Taking impressions and model preparation. Full anatomical impressions are taken. The working model is poured from high-strength dental stone, dried (at a temperature not exceeding 60 °C), and surveyed in a parallelometer. Undercuts of the abutment teeth are blocked out with wax and trimmed with a knife-edge rod down to the survey line.
2. Duplication. The gypsum model is fixed in a flask. Hydrocolloid material is melted at 80 °C, cooled, and poured. After the material sets, the model is removed, and refractory material is poured into the resulting mold.
3. Wax-up. The framework is modeled using special removable denture wax. The best results are achieved with ready-made silicone matrices with a pre-impressed mucosal microrelief. The wax composition is tightly pressed and sealed to the model to prevent the investment material from seeping under the framework.
4. Casting. The spruing system is installed, the wax is burned out, and the mold is baked. After metal pouring, the cooled casting is removed from the casting ring, cleaned in a sandblaster, and the sprues are cut off.

Fixation biomechanics in various defects

The problem of denture stabilization is particularly acute in distal extension defects and anterior tooth replacement.

In anterior defects, aesthetic problems often arise when using conventional clasps. In addition, the curved shape of the intermediate section creates a strong tipping moment when biting food, which can dislodge the abutment teeth. In such cases, a metal base with Roach clasps (short T-shaped arms) is indicated. They are located near the gingival margin, providing high stabilization without compromising aesthetics.

In unilateral distal extension defects, reliable fixation of a removable partial denture is extremely difficult, especially on the upper jaw, where the weight of the denture and masticatory forces contribute to its dropping. To prevent tipping, additional elements are introduced into the design:

• Finger-like extensions;
• Occlusal rests;
• Continuous clasps.

In bounded posterior defects, it is important to prevent overloading the periodontium of the abutment teeth. If the defect is large, rigid connectors are replaced with elastic (resilient) ones, and the pressure is redistributed to the mucosa using saddle areas.

Fitting and occlusion adjustment

The finished metal framework is finished with carborundum and elastic polishing wheels. It must be disinfected before intraoral try-in.

Articulating paper is used to identify areas preventing denture seating (usually in undercut areas or clasp bodies). Excess metal is carefully ground down. Critical rule: gaps must not be allowed to form at the sites of future contact between the base and artificial teeth.

Checking tooth closure (occlusal relationships) is performed only after the framework is perfectly seated on the denture foundation. If supercontacts (obstructions to the closure of natural antagonist teeth) are detected, the metal is ground down at the required points. After that, the framework is returned to the laboratory for the application of acrylic resin parts.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Classification of dental arch defects and selection of the base type
• Using a parallelometer: determination of the survey line and undercut zones
• Types of rigid and elastic connectors
• Biomechanics of precision attachments in generalized periodontitis
• Errors in modeling the wax framework composition

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.