Methods of fixation and stabilization on edentulous jaws

The alveolar process of the jaw is well expressed immediately after tooth extraction, but gradually begins to atrophy. Atrophy is more pronounced the more time passes after tooth loss.

All about complete removable prosthetics for the “orthopedist - dental technician” team in the online course Complete removable prosthetics .

Schroeder classification for the edentulous maxilla

• Type I - the height of the alveolar process is not subject to atrophy, it is lined with dense mucosa, the palate is deep, the torus is absent or poorly expressed, protruding maxillary tubercles.

• Type II – average values of all characteristics: degree of atrophy, depth of the palate, maxillary tuberosities, torus.

• Type III – complete atrophy, the dimensions of the jaw body and maxillary tubercle are sharply reduced, the palate is flat, the torus is wide.

It is not difficult to guess that the best option for an orthopedist is the first type. There is an improved modification of this classification, which includes two more types of jaws.

• Type IV is a weak atrophy of the alveolar process in the anterior part against the background of strong atrophy in the lateral parts.

• Type V – severe atrophy in the anterior section against the background of a well-defined alveolar process in the distal sections.

Rice. 1. Complete removable dentures.

The fundamental characteristic that determines the reliability of fixation of the prosthesis on the upper jaw is the type of slope of the alveolar process.

The following varieties are distinguished:

• sheer,

• flat,

• with awnings.

To ensure optimal suction of the prosthesis when performing the function, the most suitable shape of the slope is vertical. The flat shape does not allow the creation and maintenance of a valve zone for a long time; the fixation of the prosthesis is not reliable.

Practicing clinicians consider the overhanging shape of the slope to be an obstacle to fixation and stabilization of the prosthesis, and consider it necessary to resort to surgical intervention - alveolotomy. But practice has proven that the presence of other anatomical retention zones on the jaw in the patient allows one to do without surgical preparation. Such retention zones include pronounced alveolar processes and the deep vault of the palate.

Keller classification for edentulous mandible

• Type I – the alveolar ridge is high, with a pronounced distance from the top of the ridge to the arch of the vestibule.

• Type II – strongly pronounced, but uniform atrophy of the ridge, the distance from the top of the ridge to the arch of the vestibule is minimal, sometimes the mobile mucosa begins at the level of the ridge.

• Type III – sufficient height of the ridge is preserved in the anterior part of the jaw, but is severely atrophied in the lateral parts.

• Type IV – severe atrophy of the alveolar ridges in the anterior part of the jaw against the background of pronounced height in the lateral parts.

Based on the above classification and clinical experience, the most favorable are the first and third types.

Rice. 2. Plaster models.

Mechanisms of fixation and stabilization of dentures on edentulous jaws

Long-term clinical observations have proven that patients adapt to the prosthesis better and faster the more stable the prosthesis design is, and their chewing function remains at a high level. For this reason, stabilization of the prosthesis is a primary task that must be addressed in practice. To solve the problem of stabilization, maintaining the stability of the prosthesis under the influence of significant loads, the maximum concentration of chewing pressure in the area of stable support, research is being carried out to this day.

In practice, it is impossible to achieve an optimal level of stabilization if there is no stable fixation of the orthopedic structure.

Fixation represents the stability of the prosthesis at rest, which in turn is observed when the masticatory muscles are in physiological balance.

The following factors influence the fixation force:

• anatomical features of the patient's jaw,

• method of obtaining an impression,

• type of mucous membrane

• mucosal moisture level.

The stability of a prosthesis is its stability in performing a function. Stabilization is maintaining stability while performing movements, chewing, or talking.

Rice. 3. Imprints.

The physical body is in a state of stability on the support area if the center of gravity is projected onto the support surface within the boundaries of the support area. In addition, stability is influenced by the frictional force that arises between the body and the support surface, as well as the shape of the latter.

There are two zones in the supporting area of the upper jaw:

1. A constant support, in front its border runs along the crest of the alveolar process, behind it is line “A”. The dome-shaped shape of the support area is optimal for maintaining the stability of the prosthesis in the event of application of chewing pressure of any force, direction and amplitude. The higher the height of the palate, the more optimal the stabilization of the prosthesis; therefore, a flat palate is the most unfavorable clinical indicator.

2. Temporary support, its boundaries: the crest of the alveolar process and the vestibular slope. The shape of this zone is conical, so reliable stabilization is possible only under certain conditions: the steeper the vestibular slope, the more reliable the stabilization.

In the supporting area of the lower jaw, two zones are distinguished:

1. A constant support, its border in front runs along the center of the crest of the alveolar process, in the back it is the inner surface of the jaw.

2. Temporary support, boundaries: the crest of the alveolar process and its vestibular slope. As with the upper jaw, the steeper the slope, the better.

Fixation methods

Classification of fixation methods:

• mechanical,

• physical,

• biomechanical,

• biophysical.

Mechanical methods involve the use of the following devices:

• retention points,

• pilots,

• gum clasps,

• all kinds of springs.

Today, springs placed in nylon elastic tubes are used only in conjunction with radical operations for traumatic lesions of the jaws, unless other methods help create reliable fixation of the prosthesis.

Rice. 4. Ready-made dentures.

Biomechanical methods involve the use of:

• intraosseous and subperiosteal implants,

• performing surgical plastic surgery to ensure anatomical retention.

When it is necessary to perform prosthetics for an edentulous jaw, the doctor must pay attention to any anatomical features of the patient in order to use them to improve the fixation of the orthopedic structure.

Physical methods to help strengthen a removable denture on a toothless jaw:

• rarefied space

• magnets,

• weighting of the lower prosthesis,

• suckers.

Biophysical methods involve improving the fixation of prostheses through the application of physical laws and the use of anatomical features of the boundaries of the prosthesis bed.

Improvement in fixation methods, which is based on the use of sparse space, has made it possible to learn how to create it under the entire base of the prosthesis, and not just in a limited area. The closing valve corresponds to the border of the prosthetic bed; the movable mucosa fits tightly to the edge of the prosthesis, preventing air from penetrating under it. The condition that allows a marginal closing valve to occur is the following: the edge of the prosthesis must push back the mucous membrane of the transitional fold. This condition is met if the mucous membrane of the transitional fold has good compliance with low mobility during function.

When performing a function under the influence of food, the prosthesis slightly shifts from its usual bed. The lumen formed by the mucous membrane of the palate and alveolar process becomes larger, but the volume of air remains unchanged if the closing valve is not broken. This creates a rarefied space under the prosthesis. Good clearance provides a significant pressure difference and improves fixation of the prosthesis.

If the marginal closure valve is disrupted, fixation of the prosthetic structure remains possible due to adhesion and anatomical retention.

Rice. 5. Checking the central ratio.

Adhesion is a force that brings together two objects through a third; it is a consequence of intermolecular interaction.

Conditions for adhesion to occur:

• accuracy of display of mucosal relief on the basis of the prosthesis,

• saliva quality,

• the size of the saliva layer.

The phenomenon of adhesion, the stickiness of a prosthesis, is based on such a physical characteristic as wettability, which appears if the forces of molecular adhesion are weaker than the forces of interaction between liquid and solid molecules. The surface of the prosthesis and the mucous membrane are perfectly wetted by saliva; a surface tension force appears along the edge of the prosthesis, also called capillarity force. This force is directed outward and works like a suction pump, ensuring the prosthesis is pressed against the mucous membrane of the palate.

Detailed digital and analog protocols for the manufacture of complete removable dentures at the clinical and laboratory stages are in the course Complete Removable Prosthetics for Doctors and Technicians .