Dental implants

Not all missing teeth need to be replaced and it should be considered carefully whether an implant is indicated. The need to replace a tooth will depend on whether function is affected (for example mastication and phonation), aesthetics, or both. An advantage of implants is that they do not damage existing tooth structure, provided they are placed appropriately.

Implant placement has associated risks including:

The majority of implants are made of titanium. However, there are multiple surface modifications such as the addition of fluorides, integration of calcium phosphate microcrystals (such as calcium hydroxyl apatite coatings), to improve osseointegration of the implant. Osseointegration is the direct structural bond between the implant surface and jaw bone, with no soft tissue or periodontal ligament connections between the two.

Planning of the implant is a crucial stage of the process. As well as a thorough initial examination, imaging will be necessary, with a cone beam computed tomogram (CBCT) scan being the gold standard.

Active periodontitis and even treated periodontitis increase the risk of post-operative peri-implantitis, therefore caution should be exercised in this patient group. Ideally, all active disease in the mouth should be stabilized prior to implant treatment.

Following the decision for an implant to be placed, the type of implant needs to be chosen. Implants range in length from short (less than 9 mm), standard (10 mm) to long (more than 10 mm), with most systems providing lengths of 4 mm to over 20 mm. The length of the implant selected will depend on its purpose, bone availability and anatomical features. Most implants will include an anti-rotation device. There are advantages and disadvantages of each type of implant; this discussion is beyond the remit of this website.

The position of the implant is determined by considering occlusion, position of adjacent teeth, the planned prosthesis, anatomical features and bone levels (a bone graft, gingival graft or sinus lift may be required for example). The dental laboratory may help determine this, or the use of CT scanning and CAD/CAM three-dimensional planning and printing techniques if planning the implant digitally. A surgical guide may be produced (known as a stent). Whilst not used by all surgeons, these can help in ensuring the correct positioning of the final implant.

An intra-osseous channel is drilled into the bone, compressing the bone and creating a surface with a reduced vasculature and some cell necrosis. Constant temperature control by irrigation and the use of ultra-slow drilling speeds are crucial at this step in the process. The implant is then inserted into the prepared channel. Once the implant is screwed or pressed in to place, a healing cap is attached and the soft tissue sutured back in place.

As the compressed surface adjacent to the implant heals, a blood clot forms, with the fibrin clot eventually being replaced with granulation tissue. This is gradually replaced with woven bone then lamellar bone and marrow as the site matures. Whilst there are some circumstances where immediate loading is acceptable, in general it is advised that a few months is given for the site to heal before the implant is loaded with a prosthesis. If the implant is loaded prematurely, connective tissue may form between the implant and the bone reducing osseointegration and stability of the implant. Once the healing period has passed (2 to 6 months depending on clinical situation), the implant can be exposed and a final prosthesis attached.

Implants should be closely monitored over the life of the device. A recall interval of 6 months is recommended, following an initial year of intensive monitoring.

The treatment may be considered to be a success if the implant is present and functional (able to eat, speak, taste) with acceptable aesthetics. There should be no pain and the surgery should not have resulted in paraesthesia. From a clinical perspective the implant should not be mobile, there should not be a surrounding radiolucency in X-ray images, and there should be bone loss of no more than 1.5 mm surrounding the implant.

Radiographic review is advised at the fit of the prosthesis, one year after this, then bi-annually. Periapical radiographs should be used with a reproducible technique and a radiograph should be taken if the implant becomes symptomatic. Implants should only be debrided if clinically necessary and implant-safe instruments should be used, such as a titanium hand scaler. Ultrasonic and sonic instruments are not recommended.

In a maxillofacial context the use of implants can range from routine (as in immediate replacement of a traumatically lost upper central incisor), through demanding (such as rehabilitation of cleft lip and palate or craniofacial anomalies patients) to highly controversial (the use of implants to rehabilitate oral cancer survivors after surgical and radiotherapeutic interventions where there is a risk of doing more harm than good by attempting implant supported dental rehabilitation). A similar issue arises with the use of implants in patients taking bisphosphonates. While some regard very weak bisphosphonates such as etidronate a negligible risk factor for implant placement, very few would risk placing them in someone receiving intravenous ibandronate.

Further reading: Restorative dentistry