The main concern with complete dentures (CD) is poor retention. Resilient linings, denture creams, and other retention aids may alleviate the problem temporarily but rarely “remedy” retention or stability issues. One approach to addressing such concerns during the 1970s and, subsequently, was the subperiosteal implant which comprised a metallic framework that closely fit and sat directly on the bone.
Subperiosteal Implants
The subperiosteal implant is designed as a metal implant framework that rests directly on the bone, subjacent to the periosteum, providing attachment posts. The posts extend across the gingival tissue for prosthesis anchorage. Hence, masticatory and other stresses were transmitted directly to the supporting bone rather than to the oral mucosa as with conventional CDs.
Fabricating a subperiosteal implant consumes a lot of time and focus.
- The mandibular mucosa had to be reflected and an impression made of the exposed bone.
- A wax pattern was then designed on the gypsum cast and used as the pattern for a chrome-cobalt cast framework.
- In a subsequent procedure, the mucosa was reflected again, and the framework was placed on the exposed bone before the mucosa was restored in position and healing was allowed to start.
- After healing, a CD could be fabricated and seated on the abutments projecting through the mucosa.
The three principal varieties of subperiosteal implants are full mandibular, full maxilla,ary, and unilateral or single‐unit implants. The latter was smaller than full arch implants and had only one protruding abutment.
The subperiosteal implant is a lengthy procedure and usually has complications. The implant causes discomfort to patients. Subperiosteal implants required close collaboration between the prosthodontist, surgeon, and dental technician with great surgical skills to guarantee optimal clinical outcomes. But if the carefully selected patient has good overlying soft tissue and no residual alveolar bone, the procedure could have a reasonably high short-term success chance.
Endodontic Implants
Endodontic pin implant, also called “endodontic stabilizer” is the most and longest established implant for years. The implant functions as a rigid anchor of a mobile tooth to the bone. Some of the consequences of a mobile tooth are gum tissue and alveolar bone recession, unbalanced occlusion, unfavorable crown-to-root ratio, and bruxism.
The basis of this approach was that a pin was inserted through the root canal into the underlying bone such that it was anchored in bone but with the upper end projecting into the mouth and upon which, a crown or RPD was fabricated. Typically, the lower end of the pin did not penetrate the cortical plate of the mandible or the antral or nasal floors of the maxilla.
Indications for endodontic implants included treatment of root fractures, external or internal root resorption, and when better support and stability were required for FPD or RPD abutments.
Endosseous Implants
Endosseous implants, also called intra-osseous and endosteal implants have been in clinical use since the 1960s. Regardless of implant design, endosseous implants are used in edentulous areas with sufficient healthy bone to accommodate the implant. The four main categories of endosseous implants are pins, spirals, blades, and screws.
In 1947, the Formiggini screw implant was the first successful endosseous implant. Later, the Cherchève spiral‐post implant in the 1960s to 1970.
Cherchève implant consisted of a double hollow spiral mounted on a square post. After the bone was surgically drilled to create a cavity, the implant was set below the alveolar ridge with the shank or post extending into the oral cavity, at which point, the final prosthesis was constructed.
The surgically drilled bone of early implants created a gap or space between the abutment post and the host’s hard and soft tissues, and this could sometimes present consequences.
In the late 1960s, the spiral implant developed modifications mostly consisted of self‐tapping screw implants, often with a vent or port for retention. While a lot of these screw implants were successful, there are still many failed implantation of these screws as the consequence of tissue irritation, frank infection, and epithelial down growth that intercept adequate retention and on occasion complete uprooting of the implant. Usually, poor bony attachment to these implants had given rise to stability issues.
A tripodal pin implant is another endosseous implant that existed at the same time as the screw-type. Thin tantalum pins fit into the bone at around 120° angulations and the exposed ends of the pins were bonded together using acrylic resin.
This type of implant could be used as a bridge abutment or to support the single‐unit prosthesis. The tripodal pin has its usefulness but it does not possess long‐term retention, usually not self‐supporting and the pins were easily displaced.
Between 1968 to 1971, Linkow designed and took part in modifying the blade or blade vent implant. Blade vent implant was a major development in endosseous implants and was originally designed for use in areas with knife‐edge alveolar ridges, and situations where screw‐type implants are contraindicated. The blade implant can be applied in almost all maxillary and mandibular edentulous areas, on the condition that there is sufficient residual alveolar process.
Several concerns were linked with blade vent implants, especially the difficulty in achieving an ideal gingival relationship to the crown when it is used to support a single crown. Another issue is the thin ridges in a manner that any bony destruction could result in implant loss. Fewer problems were found with blades used to support a denture base although stability was a problem with unilateral mandibular free‐end saddles.
The modern “screw” implant derives from the pioneering work of Stefano Tramonte in Italy and Per‐Ingvar Brånemark in Sweden, both of whom advocated the use of titanium for dental implants. The excellent physical properties and outstanding biocompatibility of titanium were the driving force for this application. In particular, Brånemark described the clinically observed close apposition and adherence of bone with titanium, which he termed osseointegration. Since then, a wide variety of “screw” or tooth root‐shaped endosseous implants have come into clinical use, and they have achieved remarkable clinical success such that they are now considered important components of the restorative dentistry armamentarium. However, the clinical success of dental implants requires good clinical technique, accurate placement, and careful patient selection with good bone quality.
The efficacy and rate of osseointegration of bone and implant have been enhanced by techniques such as designing the implant with a screw profile, providing a micro‐texture to the implant surface as well as coating the surface with hydroxyapatite (HA). More recently, a novel approach to dental implantology has been to coat the implant surface with a nanometer‐thick layer of protein containing a bisphosphonate drug. Animal studies indicate that the bone surrounding the implant becomes denser and stronger, ensuring a more durable implant‐tissue interface.
Conclusion
Dental implants have existed from the very early 1900s until the present time. Numerous successes and failures of implantation occurred, but as modifications and innovations continue to develop together with the skills and knowledge of the dental professionals, the success rate of implantations rises. The modern dental implant has become one of the best alternatives for replacing missing teeth and as a support to a crown, bridges, and other prostheses.