Removable partial dentures

Boundaries of the denture base

The formation of the boundaries depends on the anatomical features of the patient's jaws and the degree of tissue atrophy.

On the maxilla, the base must cover the maxillary tuberosities. In the anterior region, its extent is dictated by the length of the upper lip and the condition of the ridge. The remaining natural teeth are covered on the palatal side by 2 mm, and the posterior teeth by 2/3 of the clinical crown height. In deep bite cases, the thickness of the plastic in the occlusion zone is minimized or replaced with a metal base to prevent breakage.

A pronounced torus requires special attention. The mucosa over it is thin, so during chewing, the denture may rock and injure the tissues. For prevention, an isolation chamber is created in the base.

On the mandible, the denture covers the retromolar pads, and in the areas of dental arch defects, the boundary falls short of the deepest point of the mucobuccal fold by 0.5–1 mm. Notches are formed at the frenulum attachment sites. In the presence of sharp internal oblique lines, the lingual border is shortened by 3–5 mm, and exostoses are either surgically removed or isolated.

Setting of artificial teeth

The choice of setting technique depends on the degree of ridge atrophy and aesthetic requirements. Two main options are used:

• Ridge-lap (direct) setting. Artificial teeth are ground directly to the gingiva without using an acrylic base on the vestibular side. Indicated for a well-developed alveolar process and a short upper lip (to prevent artificial acrylic from showing when smiling).
• On an artificial gingiva. Teeth are mounted on the base. This method is ideal for pronounced process atrophy and a long lip, and is also standardly used in the posterior regions of both jaws.

The tooth shade is selected in bright daylight. In doubtful cases, darker shades are preferred. This is because when grinding an acrylic tooth from the cervical side, it loses part of the pigmented plastic and visually becomes lighter. If the tooth is ground down too much, the clasp may show through—in this case, the metal is masked with an opaquer.

Transfer of the wax reproduction to acrylic

Replacing wax with acrylic requires precise preparation and adherence to the temperature regimen.

1. Flask investing. Depending on the clinical presentation, direct (for ridge-lap teeth), indirect, or combined methods are used. The gypsum surface must be isolated for easy mold opening.
2. Wax elimination. The flask is placed in boiling water. After opening, wax residues are washed out, and the model is coated with a separating varnish (Isocol).
3. Packing and pressing. Polymer and monomer are mixed to the "soft dough" stage. The mass is placed into the mold, trial pressing is performed through moistened cellophane, excess is removed, and final pressing is carried out.
4. Polymerization. The flask is clamped in a flask clamp and heated in a water bath. The regimen is staged: first holding at 65 °C, then at 100 °C. Rapid heating is unacceptable.

After cooling, the appliance is retrieved, finished with burs, and polished. The mucosal surface and acrylic teeth are polished with soft brushes without pressure so as not to erase the relief.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Fabrication of occlusion rims and determination of central relation.
• Features of direct, indirect, and combined methods of model investing in the flask.
• Rules for grinding artificial teeth to abutment teeth and clasps.
• Creation of multiple occlusal contacts using a facebow and articulator.
• Specifics of polishing metal elements (clasps, occlusal rests).

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.