Implantology

Treatment planning for implant restorations: general considerations

INTRODUCTION

The treatment plan should begin with a clear idea of the desired end result of treatment, which should fulfill the functional and aesthetic requirements of the patient. It is important that these treatment goals are realistic, predictable, and readily maintainable. Realistic means that the end result can be readily achieved and is not unduly optimistic. Predictable means that there is a very high chance of success of achieving the end result and that the prosthesis will function satisfactorily in the long term. The prosthesis should withstand normal wear and tear and not be subject to undue mechanical and technical complications . Readily maintainable means that the prosthesis does not compromise the patient’s oral hygiene and increases the patient’s susceptibility to inflammation of the peri-implant tissues and that the “servicing” implications for the patient and the dentist are acceptable.

In this ARTICLE, it will be assumed that treatment options other than implant-retained restorations have been considered and there are no relevant contraindications . Evaluation begins with a patient consultation and assessment of the aesthetic and functional requirements, and proceeds to more detailed planning with intraoral examination, diagnostic setups, and appropriate radiographic examination. At all stages in this process it is important to establish and maintain good communication (verbal and written) with the patient to ensure that they understand the proposed treatment plan and the alternatives.

Aesthetic considerations assume great importance in most patients with missing anterior teeth. This is an increasing challenge for the clinician and is related to

1. the degree of coverage of the anterior teeth (and gingivae) by the lips during normal function and smiling (Figs. 2.1A–C and 2.2A–C);

2. the degree of ridge resorption, both vertically and hori- zontally (Fig. 2.3A–C);

3. provision of adequate lip support (Fig. 2.4A,B).

The appearance of the planned restoration can be judged by producing a diagnostic setup on study casts or providing a provisional diagnostic prosthesis (Fig. 2.5A–C). The latter usually proves to be more informative for the patients as they can judge the appearance in their own mouth and even wear it for extended periods to adequately assess it. Both diagnostic casts and provisional prostheses can serve as a model for the fabrication of

1. a radiographic stent to assess tooth position in relation to the underlying ridge profile (Fig. 2.5D);

2. a surgical stent (or guide) to assist the surgeon in the optimal placement of the implants (Fig. 2.5E–H);

3. a transitional restoration during the treatment program (Fig. 2.5C).

Ideally, patients should be examined with and without their current or diagnostic prosthesis to assess

  •  facial contours;
  •  lip support;
  •  tooth position;
  •  how much of the prosthesis is revealed during function;
  •  occlusal relationships.

The diagnostic setup should then be adjusted if necessary to fulfill the requirements of the desired end result before proceeding with treatment.

Reduced or insufficient function is a common complaint for patients who have removable dentures or who have lost many molar teeth. Functional inadequacy is often a perceived problem of the patient and is assessed by interview rather than any specific clinical measure. The variation between individuals in how they perceive this problem is large. In patients who are accustomed to an intact arch of teeth from second molar to second molar, the loss of a single molar can be completely unacceptable, and replacement with a conventional fixed prosthesis or implant restoration becomes necessary. In contrast, a shortened dental arch extending to the first molar or second premolar may provide adequate function and appearance for some patients. However, missing maxillary premolars (and occasionally first molars) often present an aesthetic problem.

Provisional dentures can be used to clarify these needs, for example how many posterior units are required to satisfy both appearance and function.

Figure 2.1 (A) In normal function this patient reveals the incisal half of the anterior teeth. (B) The same patient smiling reveals most of the crowns of the teeth, but not the gingival margins. (C) The patient with the lips retracted showing a gross discrepancy of the gingival margins that is not visible in normal function and smiling.

Figure 2.2 (A) A young patient with missing maxillary lateral incisors. (B) The same patient wearing an existing partial denture allows assessment of the aesthetics and tooth position. (C) The completed result with two single tooth implants replacing the lateral incisors.

Figure 2.3 (A) A patient with missing maxillary central and lateral incisor, showing loss of vertical ridge height. (B) The occlusal view shows some loss of ridge width. (C) The patient wearing a removable prosthesis showing the discrepancy between the tooth height and the underlying ridge form.

INITIAL CLINICAL EXAMINATION

A thorough extraoral and intraoral clinical examination should be carried out on all patients to ensure diagnosis of all existing dental and oral disease. The diagnosis and management of caries, periodontal disease, and endodontic problems is not the remit of this book and the reader is referred to other more relevant texts. However, it is very important to remember that susceptibility to periodontitis is associated with more implant loss and periimplantitis, and implants placed close to apical endodontic lesions may fail. Factors of more specific relevance to implant treatment are dealt with here and in the related more detailed sections on single teeth, fixed bridges, and overdentures.

Figure 2.4 (A) Profile of a patient wearing a removable denture with a labial flange to provide lip support. (B) Profile of the same patient showing poorer lip support, following removal of the labial flange.

Evaluation of the Edentulous Space or Ridge

The height, width, and contour of the edentulous ridge can be visually assessed and carefully palpated (Fig. 2.6A–F). The presence of concavities/depressions (especially on the labial aspects) is usually readily detected. However, accurate assessment of the underlying bone width is difficult especially where the overlying tissue is thick and fibrous. This occurs particularly on the palate where the tissue may be very thick/dense and can result in a very false impression of the bone profile. The thickness of the soft tissue can be measured by puncturing the soft tissue with a calibrated probe after administering local anesthetic or carrying out a more detailed ridge mapping.

Figure 2.5 (A) A patient with severe hypodontia and retained deciduous teeth in the maxillary lateral incisor, canine, and premolar areas.

(B) Articulated study casts with a diagnostic wax-up. (C) The patient has been fitted with an immediate replacement partial denture based on information from the diagnostic wax-up. (D) The partial denture has been coated on the labial surfaces with a radiopaque medium (TempBond). (E) A cone-beam CT of the same patient wearing the denture with radiopaque medium. The outline of the teeth can be seen in relationship to the underlying ridge form. (F) A blowdown plastic surgical stent constructed based on the diagnostic denture. (G) Direction indicator placed in the implant site preparations at surgery. (H) The surgical stent in place showing a good relationship between the indicator post and the planned tooth position. (I) The implants inserted and cover screws placed.

However, 3D tomography to examine the bone profile is more commonly used (Fig. 2.5E).

The profile/angulation of the ridge and its relationship to the opposing dentition is also important. The distance between the edentulous ridge and the opposing dentition should be measured to ensure that there is adequate room for the prosthodontic components (Fig. 2.7). This will vary with the implant system being used and whether the prosthesis is to be cemented or screw retained. Retention of a cemented prosthesis is dependent on the abutment height and parallelism (which is more readily achieved with CAD-CAM technology), whereas a screw retained prosthesis has to have sufficient height to accommodate the abutment/abutment screw and prosthesis-retaining screw (ideally with suf- ficient place to place a protective restoration over it). These factors are dealt with in more detail in chapters 13 and 14. Proclined ridge forms will tend to lead to proclined placement of the implants that could affect loading and aesthetics, especially if a screw-retained prosthesis requires angulated abutments. Increased vertical space between opposing jaws (Fig. 2.8) will result in a prosthesis with an increased vertical height that will be subject to higher leverage forces. Large horizontal discrepancies between the jaws, for example, the pseudo class 3 jaw relationship following extensive maxillary resorption must be recognized, and management appropriately planned. This may be solved by prescription of an overdenture treatment or extensive grafting/orthognathic surgery.

Figure 2.6 (A) A patient with missing maxillary central incisors following loss of a fixed prosthesis. (B) The intraoral view showing good ridge height at tooth 11 but loss of vertical height at tooth 21. (C) The patient with a diagnostic denture in place with lips at rest. (D) The intraoral appearance of the diagnostic denture. There is no labial flange and the discrepancy in ridge height between teeth 11 and 21 is less obvious. This patient was treated without the ridge augmentation. (E) The same patient treated with single tooth implants after a period of eight years. The clinical crown heights of the central incisors are symmetrical but longer than the adjacent natural teeth. (F) The radiographs eight years following treatment showing ideal bone levels at the first thread of the Branemark implants. The abutments and crowns are ceramic.

The clinical examination of the ridge also allows assessment of the soft tissue thickness, which is important for the attainment of good aesthetics. Keratinized tissue, which is attached to the edentulous ridge, will also generally provide a better peri-implant soft tissue than nonkeratinized mobile mucosa. The mesiodistal length of the edentulous ridge can be measured to give an indication of the possible number of implants that could be accommodated (see chap. 1). This is best done with calipers and a millimeter rule. The space should be measured between the tips of the crowns, the maximum contour of the crowns, and at the level of the edentulous ridge. However, this also requires reference to

1.         radiographs to allow a correlation with available bone volume;

2.         the diagnostic setup for the proposed tooth location;

3.         the edentulous ridges bound by teeth; the available space will also be affected by angulation of adjacent tooth roots, which may be palpated and assessed radiographically.

Figure 2.7 (A) A patient with missing maxillary anterior teeth in whom the lower incisors nearly touch the soft tissue ridge in centric occlusion. The space available for implant components will depend on the level of placement of the implant heads in the underlying bone. (B) The same patient with the existing partial denture. The prosthetic teeth have been ridge-lapped and no labial flange has been provided. The denture teeth produce a considerable overlap of the existing ridge. Implants would have to be placed in a submerged position to allow an emergence of the implant crowns at the cervical level of these teeth.

INITIAL RADIOGRAPHIC SCREENING

A screening radiograph should give the clinician an indication of

  1. overall anatomy of the maxilla and mandible and poten- tial vertical height of available bone;
  2. anatomical anomalies or pathological lesions;
  3. sites where it may be possible to place implants without grafting and sites that would require grafting;
  4. restorative and periodontal status of remaining teeth;
  5. length, shape, angulation, and proximity of adjacent tooth roots.

In many instances the dental panoramic tomograph (DPT) is the radiograph of choice (Fig. 2.9). It provides an image within a predefined focal trough of both upper and lower jaws that gives a reasonable approximation of bone height, the position of the inferior dental neurovascular bundle, the size and position of the maxillary antra, and any pathological conditions that may be present. It is therefore an ideal view for initial treatment planning and for providing patient information as it presents the image in a way that many patients are able to understand. Some areas may not be imaged particularly well, but this can be minimized by ensuring that the patient is positioned correctly in the machine and that the appropriate program is selected. It provides more information about associated anatomical structures than periapical radiographs but with less fine detail of the teeth. It should be remembered that all DPTs are magnified images (at approximately ×1.3). Distortion also occurs in the anteroposterior dimension reducing their usefulness when planning implant spacing/numbers. The initial screening radiograph allows selection of the most appropriate radiographic examination for definitive planning (see sections on single teeth, fixed bridgework, and overdentures) and together with the clinical examination indicates whether 3D scanning is needed.

Figure 2.8 This patient has suffered extensive loss of mandibular bone following a road traffic accident that resulted in a fractured mandible and osteomyelitis. There is now a marked vertical and horizontal discrepancy between the jaws.

Figure 2.9 A dental panoramic tomogram provides a very good radiograph to show the major anatomical features of the jaws in relation to the existing teeth. This patient has good bone height in the premolar regions of the upper and lower jaw. The maxillary sinuses do not encroach upon the maxillary premolar sites and the mental nerve and inferior dental nerve are located well apically.

STUDY CASTS AND DIAGNOSTIC SETUPS

Articulated study casts allow measurements of many of the factors considered in the previous section. The proposed replacement teeth can be positioned on the casts using either denture teeth or teeth carved in wax (Fig. 2.5B, C). The former have the advantage that they can be converted into a temporary restoration that can be evaluated in the mouth by clinician and patient. The diagnostic setup therefore determines the number and position of the teeth to be replaced and their occlusal relationship with the opposing dentition.

Once the diagnostic setup has been agreed by the patient and clinician, it can be used to construct a stent (or guide) for radiographic imaging and surgical placement of the implants (Fig. 2.5D–F). The stent/guide can be positioned on the original cast, and with reference to the radiographs the clinician can decide upon the optimum location, number, and type of implants.

BASIC TREATMENT ORDER

Deciding on the treatment order may be very straightforward in some circumstances and in others extremely difficult, particularly for those cases involving transitional restorations.

A traditional plan may include the following:

  1. Examination—clinical and initial radiographic
  2. Diagnostic setup, provisional restoration, and specialized radiographs if required
  3. Discussion of treatment options with the patient and decision on final restoration
  4. Completion of any necessary dental treatment including : Extraction of hopeless teeth, Periodontal treatment and Restorative treatment, new restorations and/or endodontics as required
  5. Construction of provisional or transitional restorations if required
  6. Construction of surgical guide or stent
  7. Surgical placement of implants
  8. Allow adequate time for healing/osseointegration according to protocol, bone quality, and functional demands
  9. Prosthodontic phase

CONCLUSION

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. In all cases the implant treatment should be part of an overall plan to ensure health of any remaining teeth and soft tissues. Once the goal or end point has been agreed it should be possible to work back to formulate the treatment sequence. The cost of the proposed treatment plan is also of great relevance. The greater the number of implants placed, the higher will be the cost, and this may therefore place limits on treatment options. In difficult cases it is better to place additional implants to the minimum number required to take account of possible failure and improved predictability and biomechanics.

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