Procedures in Implant Dentistry
Dental implants are used for the replacement of single teeth and to support fixed and removable dental prostheses replacing multiple teeth. They enjoy very high success rates and relatively few complications. Success criteria are focused on clinical/radiographic factors such as immobility, absence of radiolucencies and good maintenance of bone levels. Patient‐based criteria such as absence of pain and nerve damage and provision of a functional and aesthetic prosthesis must be achieved to satisfy most patients.
Successful treatment is highly dependent upon effective levels of diagnosis, treatment planning and execution of the surgical and prosthodontic aspects of treatment, together with long‐term maintenance care. It is imperative to consider all treatment options with the patient, and during detailed planning it may become apparent that an alternative solution is preferred. The advantages and disadvantages of the various options can be presented to the patient following careful clinical and radiographic examinations. The treatment plans should be outlined in writing. Written consent to the agreed treatment plan is essential.
Patients usually have high expectations of dental implants and it is therefore essential that their expectations are understood and that the clinician is confident that they can be met. Risk factors for implant failures and complications include by plaque‐induced inflammation, a history of periodontitis, associated endodontic lesions, smoking and parafunction. One of the most important contraindications for implant treatment is the child who has not completed growth. The ankylosed implant can become increasingly in infraocclusion following growth and eruption of the adjacent teeth.
Clinical and Radiographic Examination and Planning
It is essential that patients undergo a thorough history and examination to determine their main complaints and to avoid missing important diagnoses that will have a bearing on their overall management, especially caries, endodontic problems and periodontal status. It is important to determine the reason for tooth loss and to manage all dental conditions as part of an overall treatment plan.
Where anterior tooth replacement is planned, the coverage of the anterior teeth and gingivae by the lips during normal function and smiling should be carefully assessed. An anterior prosthesis should provide good aesthetics and adequate lip support. The appearance of the planned restoration can be judged by providing a diagnostic set up or preferably a provisional prosthesis, for example a removable partial denture. This can serve as a model for a surgical guide to assist in the optimal placement of the implants, and as a transitional restoration during the treatment programme.
The height, width and contour of the edentulous ridge should be visually assessed and palpated to evaluate the soft tissue and underlying bone profile. Plain radiographs may provide sufficient information to assess available bone height but 3D tomography may be required to assess the ridge contour. The clinician needs to gather sufficient information to determine whether there is sufficient bone for implant placement or whether the patient needs to be advised that bone augmentation is required.
The distance between the edentulous ridge and the opposing dentition should be measured to ensure that there is adequate room for the implant prosthesis. The length of the edentulous space should be measured and related to the diagnostic set‐up or denture and radiographs. In edentulous ridges bound by teeth, the proximity and angulation of adjacent teeth must be evaluated. The occlusion should be carefully assessed, in particular in all excursive movements. It may be helpful to examine the occlusion with the existing prosthesis or the provisional prosthesis to assess the type of loading to which the implant restoration will be subjected. The overall aim is to provide an adequate number of implants within sound bone beneath the proposed location of the replacement teeth.
Study casts allow detailed measurements to be made. Also, the proposed replacement teeth can be positioned on the casts by the technician using either denture teeth or teeth carved in wax. The diagnostic set‐up therefore helps to determine the number and position of the teeth to be replaced and their occlusal relationship with the opposing dentition.
The most convenient radiographic examination is the dental panoramic tomogram. Periapical radiographs using a paralleling technique are often adequate for evaluation in single tooth replacement and should be considered for all adjacent/opposing teeth that are heavily restored, with known or suspected endodontic problems and teeth with moderate to advanced periodontitis. Tomographic examinations to give cross‐sectional and three‐dimensional images have become more common with the introduction of cone beam CT. Radiographic stents with radioapaque teeth or markers are usually worn by the patient to relate proposed tooth position to the location of the underlying bone. The stents can subsequently be used to produce guides to assist in correct placement of the implants at surgery. All images should be of a known magnification so that accurate measurements can be taken. Computer‐based image software programs are available that produce images of implants and their prosthodontic components which can then be imported into the CT image. This can be developed to very high levels of sophistication using a combination of radio‐opaque diagnostic set‐ups, CT scans and stereolithic modelling to produce surgical drill guides and premade prostheses.
Implants should be placed using a careful aseptic surgical technique. Success is highly dependent upon a surgical technique which avoids heating the bone. Slow drilling speeds, the use of successive incrementally larger sharp drills and copious saline irrigation aim to keep the temperature below that at which bone tissue damage occurs (around 47 °C for 1 min). The most favourable quality of jaw bone for implant placement has a well formed cortex and densely trabeculated medullary spaces with a good blood supply. Bone which is predominantly cortical may offer good initial stability at implant placement but is more easily damaged by overheating during the drilling process.
The implants have to be placed at the correct positions, depths and angulations to allow fabrication of a functional and aesthetic prosthesis. Surgical guides can help considerably. Poorly positioned or angled implants will compromise the prosthodontic reconstruction. An adequate number of implants are required to support a given prosthesis and the distribution of load to the supporting bone can be spread by increasing the number and dimensions (diameter, surface topography, length) of the implants.
In contrast, it is equally important not to place too many implants in a given space such that they are too close together. This compromises the health of the intervening bone and soft tissue and construction of the prosthesis. It is generally recommended that a space of 3 mm is left between adjacent implants and at least 1 mm between an implant and an adjacent tooth. The average implant is approximately 4 mm in diameter and between 8 and 15 mm in length.
Implants should be selected to ensure good primary stability, measured by insertion torque or resonance frequency analysis. Implant length is also limited by the need to avoid damage to important anatomical structures, such as the inferior dental nerve. The assessment of length should allow an adequate safety margin, especially as most drills are designed to prepare the implant site slightly longer than the chosen implant.
In conventional protocols a cover screw or healing abutment is attached to the head of the implant following insertion of the implant. The mucoperiosteal flaps are closed with sutures and the implant left to heal for a period of 6–12 weeks. During this period, the implant remains unloaded and bone forms on the surface of the implant to provide a union termed osseointegration. Rapid treatment protocols are also used where the prosthesis is provided on the same day or within a few weeks. If the implant is loaded during this early period the amount of movement must be below 100 μm as fibrous encapsulation rather than osseointegration could occur.
The procedure guideline (Table 13.1) describes placement of a single implant using a conventional protocol.
Table 13.1 Surgical placement of a single implant.
|Treatment plan||To check that preparatory treatment has been completed.|
|Signed consent||To ensure valid consent.|
|Radiographs||To provide information on available bone height, width of space at various levels, presence of important anatomical structures, position and angulation of adjacent tooth roots.
3D scans may be needed to give bone thickness if this was in doubt.
|Study casts||May be required to check on diagnostic set‐up and fit of surgical guide.|
|Surgical guide disinfected in chlorhexidine solution||Surgical guide helps in establishing mesiodistal and buccolingual positioning, angulation and vertical level of implant placement.|
|Straight handpiece and acrylic trimmer||To adjust surgical guide if required and temporary prosthesis at end of procedure.|
|The implant – planned design, length, diameter and appropriate alternative||Appropriate implant should have been ordered and checked against treatment plan. Shorter/longer/wider/narrower alternatives if any doubt about selection should be available.|
|Healing abutment or cover screw||To protect internal mechanism of the implant. Cover screw required for submerged surgery and healing abutment for non‐submerged surgery.|
|Sterile surgical implant instruments||Complete set of instruments compatible with planned implant type. This may also include disposable sterile drills.|
|Sterile surgical kit||Basic surgical kit to elevate mucoperiosteal flaps and closure with sutures.|
|Sterile irrigation system||To keep drills irrigated during drilling process and avoid overheating of bone.|
|Sterile drapes||To maintain appropriate surgical environment covering patients’ clothing and hair.|
|Analgesics||Either 1 g paracetamol or 400 mg ibuprofen given just before procedure to provide first line of analgesia when local anaesthesia wears off.|
|Antibiotics||Evidence that preoperative antibiotics may reduce early implant failure. However, failure rates are extremely low and evidence not particularly robust. Antibiotics more strongly indicated if systemic health problem with patient, e.g poorly controlled diabetes or procedure likely to be complicated by previous infection/need for grafting.|
|Chlorhexidine mouthwash||0.2% for 1 min to reduce bacteria in mouth. Some clinicians also use as circum‐oral skin disinfection. More stringent barrier methods such as adhesive film dressings and covering of nose used in some countries.|
|Local anaesthesia||Usually containing adrenaline to produce more profound anaesthesia and haemostasis. Lignocaine commonly used. Articaine infiltration may be more effective in mandibular sites.|
|Incision made with number 15 blade||Normally mid crestal incision to provide good wound closure around healing abutment and adequate keratinised tissue buccally and lingually.
Relieving incisions can be used to improve access – either extending around crevices of adjacent teeth or vertical relieving incision avoiding placement over adjacent prominent root surfaces.
|Elevation of full thickness buccal and lingual flaps (Figure 13.1)||Cleanly under periosteum to minimise trauma and provide good visualisation of bone ridge, any concavities or important anatomical structures, e.g. mental nerve. Adequate visualisation of ridge profile should minimise chance of implant being placed in wrong position.|
|Drilling of site to accept implant using saline irrigation (Figure 13.2)||Drilling at low speeds (1500 rpm) with low pressure and clearing of swarf from drills to prevent overheating of bone (Figure 13.2(a)). More of a problem in dense bone. Depth of site established early in sequence. Position and angulation of site checked against surgical guide with guide pin placed in prepared hole (Figures 13.2(b), (c)).|
|Modification of position and angle of drilling||Drilling is in sequence as recommended by implant system. Correction and modification in early stages is very important to ensure optimum positioning. Diameter of site gradually increased with wider diameter drills to be just smaller in diameter than the planned implant.|
|Preparation of coronal part of the site||Many implants have a head that is a different diameter or shape. A final drill is used to match this and finalise the vertical position of the head of the implant.|
|Irrigation of the site||To remove any loose bone fragments.|
|Check depth of site with measurement gauge||To check that planned implant can be inserted.|
|Mount implant on insertion device and maintain sterility of implant||Carefully connect implant to insertion device so that it can be inserted. The implant should not be touched during this procedure or allowed to touch any surface other than the osteotomy site that has been prepared in the bone.|
|Insertion of implant|