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Dental implant
 

X-Ray picture of two dental implants inserted into the posterior mandible



A dental implant is an artificial tooth root replacement and is used in prosthetic dentistry to support restorations that resemble a tooth or group of teeth.


There are several types of dental implants. The major classifications are divided into osseointegrated implant and the fibrointegrated implant. Earlier implants, such as the subperiosteal implant and the blade implant were usually fibrointegrated .

The most widely accepted and successful implant today is the osseointegrated implant, based on the discovery by Swedish Professor Per-Ingvar Brånemark that titanium can be successfully fused into bone when osteoblasts grow on and into the rough surface of the implanted titanium . This forms a structural and functional connection between the living bone and the implant.
A variation on the implant procedure is the implant-supported bridge, or implant-supported denture.

History

The Mayan civilization has been shown to have used the earliest known examples of endosseous implants (implants embedded into bone), dating back over 1,350 years before Per-Ingvar Brånemark started working with titanium. While excavating Mayan burial sites in Honduras in 1931, archaeologists found a fragment of mandible of Mayan origin, dating from about 600 AD. This mandible, which is considered to be that of a woman in her twenties, had three tooth-shaped pieces of shell plac

Composition

A typical implant consists of a titanium screw (resembling a tooth root) with a roughened or smooth surface. The majority of dental implants are made out of commercially pure titanium, which is available in 4 grades depending upon the amount of carbon and iron contained. More recently grade 5 titanium has increased in use. Grade 5 titanium, Titanium 6AL-4V, (signifying the Titanium alloy containing 6% Aluminium and 4% Vanadium alloy) is believed to offer similar osseointegration levels as commercially pure titanium. Ti-6Al-4V alloy offers better tensile strength and fracture resistance. Today most implants are still made out of commercially pure titanium (grades 1 to 4) but some implant systems (Endopore and NanoTite) are fabricated out of the Ti-6Al-4V alloy Implant surfaces may be modified either by plasma spraying, anodizing, etching or sandblasting to increase the surface area and the integration potential of the implant.

Surgical procedure
Surgical planning

Prior to commencement of surgery, careful and detailed planning is required to indentify vital structures such as the inferior alveolar nerve or the sinus, as well as the shape and dimensions of the bone to properly orientate the implants for the most predictable outcome. Two dimensional radiographs, such as orthopantomographs or periapicals are often taken prior to the surgery. In most instances, a CT scan will also be obtained. Specialized 3D CAD/CAM computer programs may be used to plan the case.

 

Whether CT-guided or manual, a 'stent' may sometimes be required to facilitate the placement of implants. A surgical stent is an acrylic wafer that fits over either the teeth, the bone surface or the mucosa (when all the teeth are missing) with pre-drilled holes to show the position and angle of the implants to be placed. The surgical stent may be produced using stereolithography following computerized planning of a case from the CT scan.

Basic procedure

In its most basic form the placement of an osseointegrated implant requires a preparation into the bone using either hand osteotomes or precision drills with highly regulated speed  to prevent burning or pressure necrosis of the bone. After a variable amount of time to allow the bone to grow on to the surface of the implant (osseointegration) a tooth or teeth can be placed on the implant. The amount of time required to place an implant will vary depending on the experience of the practitioner, the quality and quantity of the bone and the difficulty of the individual situation.

Detail procedure

At edentulous (without teeth) jaw sites, a pilot hole is bored into the recipient bone, taking care to avoid the vital structures (in particular the inferior alveolar nerve or IAN and the mental foramen within the mandible). Drilling into jawbone usually occurs in several separate steps. The pilot hole is expanded by using progressively wider drills (typically between three and seven successive drilling steps, depending on implant width and length). Care is taken not to damage the osteoblast or bone cells by overheating. A cooling salineor water spray keeps the temperature of the bone to below 47 degrees Celsius (approximately 117 degrees Fahrenheit). The implant screw can be self-tapping, and is screwed into place at a precise torque so as not to overload the surrounding bone (overloaded bone can die, a condition called osteonecrosis, which may lead to failure of the implant to fully integrate or bond with the jawbone). Typically in most implant systems, the osteotomy or drilled hole is about 1mm deeper than the implant being placed, due to the shape of the drill tip. Surgeons must take the added length into consideration when drilling in the vicinity of vital structures.

Surgical incisions

Traditionally, an incision is made over the crest of the site where the implant is to be placed. This is referred to as a 'flap'. Some systems allow for 'flapless' surgery where a piece of mucosa is punched-out from over the implant site. Proponents of 'flapless' surgery believe that it decreases recovery time while its detractors believe it increases complication rates because the edge of bone cannot be visualized.. Because of these visualization problems flapless surgery is often carried out using a surgical guide constructed following computerized 3D planning of a pre-operative CT scan.

Healing time

The amount of time required for an implant to become osseointegrated is a hotly debated topic.. Consequently the amount of time that practitioners allow the implant to heal before placing a restoration on it varies widely. In general, practitioners allow 2–6 months for healing but preliminary studies show that early loading of implant may not increase early or long term complications. If the implant is loaded too soon, it is possible that the implant may move which results in failure. The subsequent time to heal, possibly graft and eventually place a new implant may take up to eighteen months. For this reason many are reluctant to push the envelope for healing.

One-stage, two-stage surgery

When an implant is placed either a healing abutment, which comes through the mucosa is placed or a 'cover screw' which is flush with the surface of the dental implant is placed. When a cover screw is placed the mucosa covers the implant while it integrates then a second surgery is completed to place the healing abutment.
Two-stage surgery is sometimes chosen when a concurrent bone graft is placed or surgery on the mucosa may be required for esthetic reasons. Some implants are one piece so that no healing abutment is required.
In carefully selected cases patients can be implanted and restored in a single surgery, in a procedure labeled "Immediate Loading". In such cases a provisional prosthetic tooth or crown is shaped to avoid the force of the bite transferring to the implant while it integrated into the socke

Surgical timing

There are different approaches to place dental implants after tooth extraction. The approaches are:

  1. Immediate post-extraction implant placement.
  2. Delayed immediate post-extraction implant placement (2 weeks to 3 months after extraction).
  3. Late implantation (3 months or more after tooth extraction).

According to the timing of loading of dental implants, the procedure of loading could be classified into:

  1. Immediate loading procedure.
  2. Early loading (1 week to 12 weeks).
  3. Delayed loading (over 3 months)
Immediate placement

An increasingly common strategy to preserve bone and reduce treatment times includes the placement of a dental implant into a recent extraction site. In addition, immediate loading is becoming more common as success rates for this procedure are now acceptable. This can cut months off the treatment time and in some cases a prosthetic tooth can be attached to the implants at the same time as the surgery to place the dental implants. However, the chances of the implant failing in these cases may be as high as 50%.
Most data suggests that when placed into single rooted tooth sites with healthy bone and mucosa around them, the success rates are comparable to that of delayed procedures with no additional complications.

 

Use of CT scanning

When computed tomography, also called cone beam computed tomography or CBCT (3D X-ray imaging) is used preoperatively to accurately pinpoint vital structures, the zone of safety may be reduced to 1 mm through the use of computer-aided design and production of a surgical drilling and angulation guidets of three missing lower incisor teeth.

 

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