Implants

In dentistry, implants are usually screw- or cylinder-shaped systems that serve to replace natural tooth roots and, after a healing period, are usually fitted with fixed dental prostheses in the form of crowns or bridges or improve the hold of dentures. Among a number of alloplastic implant materials (insertion of foreign material), titanium currently appears to be the most suitable, as it stands out from other materials due to quite a few material advantages:

• High mechanical stability (hardness, fracture toughness, flexural strength).
• X-ray density
• Sterilizability

Closely followed in material properties is titanium by yttrium-reinforced zirconia ceramics. However, it is crucial that despite minimal release of titanium ions on titanium and also on zirconium oxide no tissue reactions occur; both are therefore bioinert (i.e. there is no chemical or biological interaction between the implant and the tissue). The bone integrates the implant in direct and very close surface contact up to 10 nm without the formation of a connective tissue separation layer: contact osteogenesis (formation of an individual bone by contact). Although there are already bioactive implant materials that even form a physicochemical bond with the bone in the form of composite osteogenesis, their biomechanical properties do not match those of titanium and zirconium oxide. Implants are usually processed in two parts (implant body as primary part, implant abutment as secondary part). Zirconium oxide has become the material of choice for abutments because of its tooth color, which, unlike metal, does not show through a ceramic crown restoration, and because of other advantages. In addition to screw-shaped implants, the cylinder shape and so-called extension implants are also available. Extension implants are leaf-shaped, flat implants that are countersunk along the bone line of the jaws into a slot prepared there (1 mm wide; 4-14 mm long) and grow firmly there.

Indications (areas of application)

The indication for implant restoration varies in urgency depending on the anatomical conditions and the extent of tooth loss:

• Edentulous jaw: while complete dentures usually have a good hold due to the suction adhesion with the wide-surface mucosa of the upper jaw, a comparable hold on the lower jaw cannot be achieved in any case, even under optimal anatomical conditions. The edentulous mandible therefore represents the most important indication for implant restoration.
• Free-end situation: the row of teeth is shortened on one or both sides due to tooth loss and can only be supplied by removable dentures without implant treatment.
• Switching gaps: Tooth gaps that are bordered by neighboring teeth; in this case, the extent to which the gap could still be closed with a fixed bridge without an implant or whether the restoration would have to be made with removable dentures depends on the remaining teeth and the size of the gap. An implant as a strategic additional bridge abutment in a larger gap also avoids here a removable prosthesis.
• Single tooth replacement: here, without implant restoration, a fixed bridge would generally be indicated, in the anterior region possibly also as an adhesive bridge. An implant protects the adjacent teeth from crowning.

Regardless of the patient’s desire for a fixed rather than a removable prosthesis, another fact should be considered: The alveolar bone (bone portion of the jaws in which the roots of the teeth are anchored) has a tendency to regress throughout life if it is not functionally loaded by teeth. This gives implants an additional significance: because alveolar bone, in which an implant loaded by masticatory function is integrated, does not react with such a decline. Thus, an implant for which bone substance must first be sacrificed ideally serves to protect the bony alveolar process. Cheeks and lips continue to be supported. As a result, an implant restoration in the anterior region, for example, can appear more esthetic than a bridge.

Contraindications

• Children
• Adolescents who are still in the growth phase
• Wound healing disorders, for example, in diabetes mellitus (diabetes).
• Reduced general condition
• Weakened immune system
• Lack of bone substance that cannot be adequately corrected even by additional surgical procedures

Before surgery

In principle, not every patient and not every jaw is suitable for receiving implants. Pre-implantological, therefore, a thorough diagnosis must be carried out:

• General anamnesis: to exclude general medical contraindications.
• Mucosal findings: inflammation, frenulum of the lips and tongue, height of the floor and vestibule of the mouth, width of attached gingiva (synonyms: keratinized gingiva, attached mucosa), and many others

.

• Bone findings: height, width and inclination of the alveolar process (part of the jaw in which tooth roots are anchored and thus implants are placed), assessment of the regenerative capacity, e.g. by observing the healing process after a tooth extraction (tooth removal), etc.
• Models: models are used to assess the positional relationship of both jaws to each other and thus to assess the space available for the implant, as well as to produce templates for X-ray diagnostics and positioning of the implant intraoperatively.
• X-ray diagnostics: serves to exclude pathological and inflammatory changes* , the evaluation of the alveolar ridge as a future implant site in its dimensions and with regard to bone quality, the prognostic assessment of neighboring teeth and much more. Depending on the indication, X-ray techniques such as panoramic tomography (synonyms: orthopantomogram, OPG), dental films, sinus images up to computer tomography (CT) and digital volume tomography (DVT) are used. * Determination of whether reversible or irreversible contraindications (contraindications) for implantation exist – such as pathological (pathological) processes in the maxillary sinus (maxillary sinuses). If necessary, a presentation to an otolaryngologist is required.

In addition to diagnostics, the comprehensive information of the patient about alternatives, risks and contraindications, as well as the further postoperative procedure is required. Risks include, for example:

• Injury to adjacent areas, in the mandible especially the nervus alveolaris inferior (nerve running in the mandibular bone).
• Material incompatibilities
• Infection of the surgical area
• Delayed wound healing
• Risk of premature implant loss, especially in smokers.
• Poor oral hygiene

The surgical procedure

Implants can in principle be placed under local anesthesia (local anesthesia). Preparation of the surgical site under sterile procedure is a conditio sine qua non (indispensable). Intraoperative takes place:

• Determination of the implant position with the help of the positioning template.
• Incision guide
• Preparation of the bony implant site using special instruments precisely matched to the implant size.
• Checking the primary stability (strength of the implant immediately after placement).
• Placement of a closure screw for the healing phase.
• Closing the wound with sutures
• X-ray control of the implant position.

After surgery

Postoperatively, suture removal takes place after one week at the earliest, as well as regular follow-up checks during the healing phase, which lasts three to four months. Thereafter, if the procedure is performed in two stages, the implant is exposed in another operation. The cover screw in the implant post is replaced by a gingiva former, which remains in the implant until further prosthetic restoration.

Possible complications

can arise intraoperatively (during surgery), postoperatively during the healing phase, or even later when the implant is exposed to stresses due to masticatory function:

• Intraoperatively: e.g., disproportionate bleeding, injury to nerves, opening of the maxillary or nasal cavity, injury to adjacent teeth, inaccuracies of fit between implant and implant site,
• In the healing phase: e.g. disproportionate pain, hematoma (bruising), infection (inflammation) of the surgical area, postoperative bleeding,
• In the loading phase: e.g. implant fracture (breakage), problems with the prosthetic superstructure, peri-implantitis (inflammation of the bony implant environment) up to the loss of the implant.

Further notes

• New coatings on implants (heparin and hyaluronic acid) could help inhibit unwanted inflammatory response in the body. Limitation: procedures on model surfaces and in cell cultures.