4. Tasks for independent work during preparation to practical classes.

4.1. Recommendations for students’ independent work and album for independent work of students.

4.2 Theoretical questions to the lesson:

1. The definition of "fixation" of partial removable dentures.

2. The definition of "stabilization" of partial removable dentures.

3. Classification of methods of fixation (Boyanov).

4. Features of dentures fixing with telescopic crowns and clasps. Indications, clinical and laboratory stages of production.

5. Features of dentures fixing with attachments. Indications, clinical and laboratory stages of production.

6. Indications for fixing of removable dentures without clasps.

7. Pelota: indications for the manufactoring of dentures with pelota, features of manufacturing.

8. Conditions that provide maximum stabilization of the prosthesis.

9. Features of stabilizing the dentures on the upper and lower jaws.

10. The value of the correct definition of the limit of partial dentures, and the choice of methods of fixation in clinic of prosthetic dentistry.

4.3. Practical work (task) that are fulfilled in class:

With the help of diagnostic models and micro stands students demonstrativly consider: 1. On phantom micro stand to demonstrate stages of manufacturing of removable partial laminar dentures.

2. Using a phantom micro stand explain the sequence of clinical stages of manufacturing using various methods of fixation of partial removable dentures.

3. Using a phantom micro stand explain the sequence of laboratory stages during manufacturing clasps.

4. Give characteristic of the demonstrated sample of the partial removable denture of what basic parts it consists and explain the fixation method of it.

5. Stages of bent clasp manufacturing.

Content of the theme:

Denture retention is the quality of a denture that holds it to the tissue foundation and/or abutment teeth. Retention is the resistance to forces that tend to displace or remove the denture from the mucous membrane especially in a vertical direction.

Bojanov selected such types of retention:

1. Mechanical (by clasps, attachments).

Retainers are divided by direct and undirect. The direct retainers are disposed on a tooth and are prevented a vertical displacement of RPD.

The direct retainers can be intracoronal and extracoronal. Clasps are the extracoronal retainers. The indirect retainers prevent rotation of RPD.

2. Biomechanical retention

A) 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.

B)Ridge characteristics, Ridge relationship

1) Mandibular lingual flange:  The most desirable feature of the lingual slope of the mandible is that it approaches 90 to the occlusal plane. The extent of the contact of the lingual flange with the lingual ridge slope is thereby dictated by the functional mobility of the floor of the mouth. Any flange extension below the mylohyoid ridge must incline medially away from the mandible, to allow for the mylohyoid muscle contraction. 2) Residual ridge anatomy: 1. Residual height and conformation- large , square, broad ridges offer a greater resistance to lateral forces than do small, narrow tapered ridges. 3). Arch form- square or tapered arches tend to resist rotation of the prosthesis better than ovoid arches. 4). Palatal vault- a steep vault may enhance stability by providing greater surface area of contact, and long inclines approaching a right angle to the direction of the force

C)Condition of mucosa and submucosa

1)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".

2) Influence of orofacial musculature:  The basic geometric design of the denture base should be triangular. To direct a seating action on the mandibular denture, the tongue should rest against a lingual flange, inclined medially away from the mandible and somewhat concave. The degree of inclination depends on the balance of the muscular forces of the tongue as opposed to the mylohyoid and superior constrictor muscles. Generally, the buccal and labial flanges of the maxillary and mandibular dentures should be concave to permit positive seating by the cheeks and lips. The primary muscles of the lips and cheeks are the orbicularis oris and buccinator muscle, respectively.