Introduction in dental implantology. Brief historical overview. Classification of dental implants and terminology

Dental implantology focuses on replacing missing teeth with biocompatible substitutes that integrate with the bone. The substitute is typically made of titanium or zirconia. Implants restore function and aesthetics, and they act as a stable base for crowns, bridges or dentures. They also help preserve the bone structure of the jaw and improve the patient's quality of life.

Implants offer several advantages over other forms of tooth replacement.

Early developments

Early civilisations, including the Egyptians and the Mayans, experimented with tooth replacements made of shell or metal. Shell and ivory replacements have been found in Egyptian and Mayan skulls. These early replacements lacked long-term function or integration with bone.

During the 18th and 19th centuries, early attempts used gold and other alloys. These often failed because of infection and poor biocompatibility.

In the 1930s, subperiosteal frames were introduced. They sat on top of the bone, under the gum tissue. They provided some stability, but they often caused complications because they did not osseointegrate.

In 1952, a Swedish orthopaedic surgeon discovered osseointegration while studying bone healing in rabbits. Titanium chambers fused with the bone, and this led him to develop the first modern dental implants.

The titanium implant from this work was placed in 1965. It was revolutionary and laid the foundation for contemporary implantology. Osseointegration describes the direct attachment of bone to the implant without soft tissue forming between them, which gives long-term stability. The first titanium dental implants were placed successfully in the 1960s, and they showed long-term stability.

In the 1980s and 1990s, dental implants became widely accepted. Companies such as Nobelpharma (later Nobel Biocare) commercialised this research, and this era saw the development of proprietary implant systems. Improved surgical techniques and materials supported the wider adoption of implants during the 1980s.

The introduction of tapered screw implants improved primary stability, especially in softer bone, and reduced surgical complexity. The main reason is the wedge effect. A tapered implant has a conical or slightly tapered shape, so it compresses the surrounding bone as it is inserted. This creates mechanical engagement with the bone and increases the immediate primary stability of the implant. The effect is particularly important in areas of low bone density.

In the late 20th and early 21st centuries, 3D imaging, CAD/CAM technology and minimally invasive procedures further advanced the field. Today, dental implants are a standard and highly predictable solution for tooth replacement.

Dental implants are classified by their design, material, structure and surface properties. Each classification offers benefits that depend on the clinical need.

Most implants are endosseous implants, which are inserted directly into the jawbone. Endosseous implants are subdivided by their shape.

Implant surfaces are modified to enhance osseointegration, particularly in low-density bone. Two groups of techniques are used.

Subtractive processes remove material from the surface to increase its roughness. The larger surface area gives bone more contact, which accelerates osseointegration.

• Acid etching uses hydrochloric, sulfuric or hydrofluoric acid. It creates micropores that increase the surface area and give better bone anchorage. The mechanical interlocking between bone and implant improves, cellular attachment increases and bone forms faster around the implant.
• Sandblasting uses large grit particles of aluminium oxide or titanium oxide. They are blasted at the implant surface at high pressure, which creates macroscopic surface roughness.

Additive processes add materials or substances to the implant surface to improve bone-to-implant interaction.

• Plasma spraying coats the implant with bioactive titanium or hydroxyapatite using a high-temperature plasma spray. This creates a rough surface for osseointegration. Hydroxyapatite mimics the mineral content of bone, so it further improves biological fixation.
• Anodisation forms a thick oxide layer electrochemically, which produces nanoporous structures. This increases surface hydrophilicity and improves the biological response by promoting protein adsorption and cell attachment. Anodised implants are reported to have superior bone-to-implant contact rates and faster healing times.

The figure below compares two zygomatic implants, which are anchored in the zygomatic bone and pass through the maxillary sinus, with four conventional implants in the anterior maxilla.

Components of an implant restoration

Several terms describe the parts of an implant restoration, from the visible crown down to the fixture in the bone.

The exploded diagram below shows the components from the top down. The arrows are for naming the parts: the crown, the abutment screw, the abutment and the implant fixture.

The cross-section below shows the same components in bone. Labels A, B and C mark the crown, the abutment at the gum margin and the implant at the crestal bone level.

The narrower junction between the abutment and the implant neck is shown in the next figure. The circled inset magnifies the neck of the implant at the crestal bone level, where the threads sit in the bone and the bone surrounds the top of the fixture.

Implant structure and connection terms

The internal hex connection is compared with the external hex connection below.

Thread profiles vary between implant designs. The figure below shows five of them: buttress, reverse buttress, V-shape, sinusoidal and square threads.

The narrow-platform implant below illustrates platform switching, micro threads and the thread lead. It has a 2.75 mm diameter, a triple-lead thread with a 3.0 mm lead for fast, efficient insertion, and lengths from 10 mm to 18 mm.

Implant success can be graded in four groups, from success to failure.