Types of dental implants

Classification of implants by location and installation method

Depending on which tissues and how the support for the future prosthesis is inserted, several fundamentally different designs are distinguished:

• Endosseous (intraosseous). Installed directly into the spongy bone. They are of two types: screw (cylinders with pronounced threads) and plate (flat elements with holes through which bone subsequently grows).
• Subperiosteal. These are individually cast metal frameworks. They are not inserted deep into the bone, but placed directly onto the jaw surface under the periosteum.
• Intramucosal. These are mushroom-shaped projections located on the inner side of the removable denture base. They are inserted exclusively into the oral mucosa to improve denture retention.
• Transdental (transradicular). They look like a pin on a radiograph. They pass through the tooth root canal, exiting beyond the root apex into the bone tissue. Used to stabilize a natural tooth.
• Transmandibular (transosseous). Complex structures that pass through the entire thickness of the mandible — from its lower border to the oral cavity.

Features of modern screw designs

Today, most screw implants are made self-tapping. A key design feature is the presence of an anti-rotational element (usually in the form of a hexagon or octagon). It is necessary to prevent the rotation of the abutment (the intraoral part onto which the crown is fixed) relative to the intraosseous part of the implant.

A key requirement for the implant surface is that it must be rough or microporous. This is achieved by various methods:

• Acid etching or sandblasting (as well as their dual combination);
• Using specialized lasers;
• Applying additional coatings: titanium plasma spray (T.P.S.), hydroxyapatite (HA), bone substitutes, or an additional oxide layer.

Such a surface is necessary for the proper progression of osteogenesis (bone formation). During implantation, bone tissue can regenerate through two mechanisms. In contact osteogenesis, cells migrate and form new bone directly on the implant surface (the fibrin of the blood clot actively participates in this). In distant osteogenesis, bone grows from the parent bone bed toward the implant until it reaches its surface.

Bone tissue architectonics: classification and clinical significance

To assess the structure of the jaws, the Lekholm and Zarb classification (Lekholm and Zarb, 1985) is used, which takes into account the degree of alveolar ridge resorption (from unmodified bone Shape A to extremely pronounced resorption Shape E) and the proportion between compact and spongy substance (classes 1 to 4).

Bone quality and associated problems are described in more detail by the C. Misch classification (C. Misch, 1990), where type 1 means the predominance of cortical bone, and type 4 — spongy bone:

1. Class D1 (Thick cortical bone). Most commonly found in the anterior mandible. Provides excellent stabilization and contact with the implant, but due to poor blood supply, the healing phase is prolonged. Drilling such bone is difficult due to a high risk of overheating.
2. Class D2 (Thick porous-cortical bone). Located in the mandible and the anterior maxilla. Considered optimal: provides reliable fixation, adequate blood supply for rapid healing, and is easily prepared for the osteotomy site.
3. Class D3 (Thin porous cortical bone). Characteristic of the maxilla and posterior mandible. Well-supplied with blood, but the structure is weakened. The contact area with the implant is reduced, so the clinician is forced to preserve the existing bone to the maximum and use a greater number of implants.
4. Class D4 (Compromised thin bone). Found in the maxillary tuberosity region. The worst-case scenario for work: achieving primary stability is extremely difficult. Due to critically minimal bone contact, an obligatory increase in the number of installed supports is required.

Indications and contraindications for implantation

Dental implantation is indicated for any dentition defects. For single and bounded defects, it saves adjacent teeth from turning down. For distal extension defects, it allows for a fixed prosthesis instead of a removable one, and in cases of complete edentulism, it restores fixed teeth to the patient or reliably fixes a complete removable denture.

The procedure is strictly contraindicated in decompensated chronic diseases, systemic hemostatic disorders, mental disorders, and the presence of HIV or other seropositive infections.

Temporary contraindications (when surgery needs to be postponed) include age under 18 years, pregnancy and lactation, acute infections, exacerbations of chronic diseases, as well as conditions with a high risk of bacteremia (presence of heart valve prostheses, rheumatic fever). Surgery should not be performed shortly after a myocardial infarction or stroke, or while receiving immunosuppressants, hormone therapy, or chemotherapy.

Contraindications associated with impaired osteogenesis are singled out separately. These include osteoporosis, osteomalacia, severe forms of diabetes mellitus, diseases of the thyroid, parathyroid glands, pituitary gland, adrenal glands, blood, and central nervous system, as well as oncology and systemic connective tissue diseases.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Methods for creating microporous implant surfaces (T.P.S., HA coating)
• Pathophysiology of contact and distant osteogenesis
• Classification of alveolar ridge resorption (Shape A-E) by Lekholm and Zarb
• Bone tissue osteoplasia: conversion of D3 and D4 classes into more favorable forms
• Bone bed preparation protocols in dense bone (prevention of overheating)

Other topics from the section "Chapter 17. Dental Implantology (V.I. Olesova)"

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