In dentistry, an implant is a biocompatible alloplastic material or device that is surgically placed into orofacial tissues and used for anchorage or for functional, therapeutic, and/or esthetic purposes. Dental implants often consist of more than one part including the implant abutment, the implant-abutment junction, implant hardware, and the prosthesis. Implants may be required due to damage, illness, or trauma sustained by a patient to the teeth, gums, or other oral tissues and structures. Dental implants come in several different types and may be placed in either a single stage, or two-stage procedure. In addition, they may be located in the jawbone or on the jawbone and may or may not require bone augmentation surgery prior to placement. Implants can be used to support a single tooth prosthesis, a partial denture prosthesis, a full denture prosthesis, or a variety of other dental restorations. The type of restorative work needed will often help decide which type of implant is used.
Implant anchorage refers to the use of a dental implant as support for orthodontic tooth movement or arch expansion. In orthodontics, implant anchorage is used to resist the forces that are applied to the teeth. In the past, devices such as headgear, a transverse palatal bar, or a Nance bow were required in order to achieve strong to moderate anchorage. However, such devices had many drawbacks including lack of patient consistency, insufficient strength, and physical side effects. The use of implant anchorage methods eliminates the need for these orthodontic devices and aids in tooth movement with a less invasive approach. Though implant anchorage in dentistry requires bonding with the bone, in orthodontics, mechanical binding takes place to promote the movement of teeth. There are many types of implant anchorages available including onplants, miniplates, palatal plates, and miniscrews. Most implant anchorages are made of titanium, titanium alloys, or stainless steel.
The implant apex is the portion of a root-form dental implant that first engages an osteotomy during its insertion. It may incorporate self-tapping characteristics. A root-form dental implant, also known as an endosteal implant, is the most common type of implant with a screw base that is shaped like the root of a tooth. The implant apex of an endosteal implant is usually tapered for easier placement into the site of the osteotomy. Since a root-form implant is inserted directly into the bone of the jaw, sufficient bone depth, width, and quality must be present in the patient for the procedure to be performed. In patients that do not have enough bone, a different type of implant or a bone grafting procedure may be considered. Following the placement of the implant, it is left to heal for up to six months before being uncovered and having a new tooth attached.
A dental implant consists of four parts, top to bottom: the cover screw, the implant abutment interface, the implant collar, and the fixture. The implant collar is close to the top of the implant and sits just at the bone. One of the most important indicators of implant success is osseointegration, or the fusion of bone to the surface of the dental implant which was introduced by Branemark in 1952. In the early days of implant dentistry, the implant collar was smooth and polished to avoid irritating sensitive gum tissue which the collar may also come into contact with. In the 1980s, dental implantologists began to understand the value of implant hardware with rough surfaces. Osseointegration occurs much more consistently when a rough surface is used, even up to the implant collar. Textured implant collars are better suited for immediate loading and placement of dental implants.
There are many different components of a dental implant. The primary implant component that most people visualize when they think of dental implants is the fixture, or the screw that is surgically implanted deep into the jawbone. This is also called the implant body and can be divided into the collar, the body, and the apex, or tapered end. Other implant components the abutment, superstructure, cover screw, the gingival former, an implant analogue and an impression post. The dental crown is placed on top of the screw, which sits inside the abutment that is attached to the fixture. Essentially, there are four components that are stacked one on top of the other to create a permanent, natural-looking dental implant. Implant components vary greatly from implant to implant — some are smooth and others acid-etched or sandblasted to promote osseointegration. They may be different shapes, sizes, and designs that are suited to various types of implant procedures.
The implant-abutment interface is the surface where the dental implant and the prosthetic abutment connect. There is more than one type of implant-abutment interface and the one selected by the practitioner often depends upon the location of the implant and the type of prosthesis that will be attached. One possible implant-abutment connection option is the external hex. An advantage to this type of interface is its compatibility with many different implant systems. However, the external hex connection is known to experience a higher incidence of screw loosening, more rotational misfit, and a less adequate seal against microbes. Another interface option is the internal connection. Advantages to using an internal interface include a lower incidence of screw loosening, a more effective microbial seal, and better strength at the joints. Disadvantages to the internal implant-abutment interface include the fact that the bone is the weakest part of the implant rather than the retaining screw.
The implant-abutment junction, also known as the microgap or IAJ, is the external margin where the coronal aspect of a dental implant and its prosthetic abutment or restoration connect. The location of the IAJ as well as its unique morphology can affect how much bone resorption occurs following the placement of the implant. Recent studies have suggested that in order to prevent as much crestal bone loss following implant placement as possible, bone level implants should be placed subcrestally while tissue level implants should be placed equicrestally. In addition to the implant placement location, microbial presence can also be a concern at the implant-abutment junction. The leakage of bacteria into the microgap can cause inflammation and even infection at the implant site that can eventually lead to the loss of crestal bone. In order to prevent this further possible complication, a tight microbial seal achieved by a very precise fit between the implant and the abutment must be achieved.
An implant-assisted prosthesis is any prosthesis that is completely or partly supported by an implant or implants. Implant-assisted prosthesis generally rely on both the implant and the soft tissues upon which the implant is placed. The implant helps to evenly distribute the weight of the attached prosthesis across the surface of the soft tissue to assist with the load. The term “implant-assisted” can refer to either removable prostheses or to fixed prostheses but in both cases, the method of support is the same. In addition, an implant-assisted prosthesis may be part of a longer, more comprehensive restoration plan or the end result of the restoration. Possible benefits of using an implant-assisted prosthesis include the preservation of existing bone, the ability to add new implants if required with relative ease, and a decreased need for additional surgeries. It also offers a mode of treatment that is adjustable with patient needs over a long-term period.