Optimum aesthetic results using the Brånemark implant in the upper anterior segment

Amongst those patients who can benefit from implant treatment (^{Adell et al., 1985}; ^{Lekholm and Zarb, 1985}), it is those with a high lip line who are the most difficult to treat. This is particularly true in those cases where there are insufficient natural abutment teeth that could support a conventional fixed prosthesis and/or where there has been resorption of the alveolar processes following the loss of the maxillary incisors.

Anatomical obstacles to this type of treatment must be clearly identified. Patients must be capable of understanding that these are the obstacles that restrict the treatment options, and also they must have a realistic view of this type of treatment in respect of the biological factors.

Problems linked to crestal resorption

Loss of the alveolar crest accompanies the loss of the teeth, whether following a simple extraction, periodontal disease or associated with a poorly fitting removable denture (^{fig. 1}). The residual alveolar bone will then be situated in a more apical and more palatal position. These consequences of the loss of teeth will complicate the construction of implant therapy. As well as difficulty in positioning the implants in a sufficiently buccal location, misplacing them in a mesio-distal direction can lead to prosthetic problems that will have an unfavourable effect on the final aesthetic result.

These difficulties can include the access holes for the attachment screws being placed too far in a buccal or palatal direction, an inappropriate thickness of porcelain, too thin or lacking support and emergence profiles that can effect the aesthetics of the prosthetic restoration.

Keys to the optimal positioning of implants in the upper anterior segment

The coordination of the surgical stages is certainly one of the most important factors in achieving satisfactory aesthetic and biomechanical results. In the anterior segment, implants must be placed in such a way that the access holes for the screws are on the lingual or palatal aspects of the restorations. Major variations in the angulation of implants can compromise the aesthetic result.

Precise positioning is there fore essential in order to obtain a satisfactory aesthetic result. It is important for the surgeon, as it is for the prosthetist, to determine the optimal position for the implants in advance. Three factors are to be taken in to consideration.

1. A study of the models, articulated and waxed up, that will determine the final position of the teeth. From this study it will be possible to determine:

- the physiological vertical dimension;

- the inter-arch relationships;

- the shape of the teeth;

- the shape and spacing of the bridge components.

2. Clinical assessment and confirmation of the thorough pre-surgical analysis (study casts, wax up, etc.). Evaluation of the aesthetic criteria appropriate to the patient to be treated:

- psychological factors;

- lip line;

- mobility of the lips;

- condition and texture of the soft tissues.

The diagnostic wax up or the mounting of teeth on wax for a try-in in the mouth gives an idea of the objective to be achieved. The position of the teeth can be altered at this stage in relationship to:

- the desired amount of lip support;

- appropriate aesthetics for the patient;

- possible speech problems;

- future problems with oral hygiene linked to the position of the implants and the embrasures of the prosthetic restorations.

3. A detailed radiographic assessment (Scanora-Dentoscan) in order to evaluate the most desirable positions for the implants. This assessment will include:

- the amount of vertical bone loss;

- the amount of horizontal bone loss;

- the presence of anatomical obstacles (concavities, localized bone loss);

- evidence of pathology that could favour a given implant position over another that seems less favourable;

- assessment of the need to have recourse to bone augmentation (by grafts) (^{Seibert, 1983} ; ^{Seibert and Lindhe, 1997}).

As far as occlusal rehabilitation with implants is concerned, a single tooth implant (a titanium implant and post) must be considered as a substitute for the root of a tooth. From the prosthetic point of view, implants replace the roots and, as they support the superstructure, they must be placed in the best possible position. The degree of bone resorption, as well as other anatomical factors must be taken in to consideration.

In addition, it is important to bear in mind that the implant components support crowns of different sizes. The optimum result involves an informed choice of these prosthetic components as well as the accurate positioning of the implants.

Within the Brånemark system there is wide variety of prosthetic components to suit the demands of most prosthodontists. The prosthetic restorations can be cemented (Ti-Unit posts) or screwed (Multi-Unit). Different heights of post are available, permitting the practitioner to select a post in relationship to the height of the peri-implant mucosa that is available and to meet aesthetic requirements. For single posts, the Cerane post is most commonly used but in special cases the machined Procera posts, in titanium or alumina, allow better adaptation to the particular clinical situation.

The spacing of implants and their angulation

Implant success depends on two factors:

- sufficient space between the implants;

- the buccal inclination of the implants.

The space between two implants

The placement of implants is based on the anatomy and degree of crestal bone resorption. Whatever the resorption of the crest, it is necessary to allow a 3 mm space from side to side and 7 mm centre to centre. In the case of single posts, for example, this inter-implant space will be reduced to 2 mm where there is an absolute need to keep to the 7 mm figure. Where there has been no resorption, the ability to obtain 7 mm between the centres of two implants, it is eased (^{Olsson and Lindhe, 1991} ; ^{Olsson et al., 1993}). This figure of 7 mm is equivalent to the distances between the centres of the upper anterior teeth (incisors, canines and premolars), with the exception of the two upper incisors where the distance is approximately 8,5 mm. Where there has been advanced bone loss, the circumference of the arch will be reduced and, therefore, it will not be possible to replace one tooth with one implant, at the same time maintaining the space requirements. It may be necessary to reduce the number of implants in order to achieve satisfactory embrasures (^{fig. 2}).

Inclination of implants

One of the major problems associated with implant treatment is due to bony crests that are narrow in the bucco-palatal direction. One treatment option could be the use of small diameter implants (NP). However, whilst this option may prove to be satisfactory as far as the management of bone volume is concerned, it may not be from the point of view of the position of the implant in the arch. Such an implant will often be located in a position too far palatal and will result in an ugly appearance because of a poor emergence profile, a concavity in the area of the crest and the absence of papillae. In addition, in the case of single teeth, this solution is often not satisfactory from the biomechanical point of view.

Therefore, severe resorption or the presence of a large concavity in the apical area will compel the practitioner to consider a bone graft, so as to avoid placing the implant too far palatally at a too acute an angle (^{fig. 3} and ⁴).

Augmentation of the crest

Techniques for the augmentation of crestal bone volume allow problems associated with the inclination of implants to be overcome (^{fig. 5} and ⁶). It is often necessary to increase the height and thickness of bone in order to place the restoration in an aesthetically pleasing position (^{Beirne and Brånemark, 1980} ; ^{Lekholm and Zarb, 1985} ; ^{Tolman, 1995}).

The alveolar crest does not present a natural cavity that can contain bony particles. Therefore, it is necessary to place blocks of cortico-cancellous bone that are rigidly fixed to the recipient bed. Intra-oral donor sites are the maxillary tuberosities, the chin and the ramus (^{Wood and Moore, 1988}). The graft and the recipient bed must be prepared in such a way as to minimize any space between the two. The graft is held in place with fixation screws. A delay of four months is necessary before the implant can be inserted. The positioning of the implant will be greatly facilitated by the new architecture of the alveolar crest (^{fig. 7}, ⁸, ⁹ and ¹⁰).

The anterior maxillary classification (Palacci-Ericsson)

The use of a classification that takes into account the overall shape of the maxillary anterior region (including the soft tissues) assists the practitioner to evaluate the anatomical factors prior to implant therapy. This classification (^{Palacci and Ericsson, 2000a}, ^{Palacci and Ericsson, 2000b}) is based on the volumes of soft and hard tissues that have been lost, in both the horizontal and vertical dimensions. It includes four categories in the vertical dimension and four in the horizontal.

In the vertical dimension, class 1 corresponds to an intact papilla, or one only slightly reduced; class 2, a moderate reduction in the size of the papilla; class 3, a major reduction in the size of the papilla and class 4, absence of the papilla (^{fig. 11}).

In the horizontal dimension, class A corresponds to intact buccal tissue, or only slightly reduced; class B, a moderate reduction in buccal tissue; class C, a severe loss of buccal tissue and class D, an extreme loss of buccal tissue, often with limited amounts of attached gingivae (^{fig. 12}).

All combinations of these different classes are possible and each patient should be considered separately. The quality of the result depends upon the practitioner's understanding of the overall treatment complexity. The anterior maxillary classification is used to identify the anatomical factors before treatment and to guide the clinician to the most appropriate therapy to meet the clinical objectives. Some treatments (for example those for class 1A), normally only consist of correctly positioning the implants and a minor adjustment to the soft tissues at the re-entry stage. At the other extreme, in order to obtain satisfactory results in class 4D it will be necessary to have recourse to augmentation of the soft and hard tissues before, during or after insertion of the implants.

A good aesthetic result sometimes occurs by augmentation of the soft tissues by, for example, obtaining a sufficient quantity of soft tissue to recreate a papilla that has been lost. According to the loss in volume of the alveolar crest, the presence of an adequate quality and quantity of soft tissue available/present and the need to augment the volume of the crest, the augmentation can be undertaken during stage one surgery and/or during re-entry.

The following clinical cases illustrate the points described earlier (^{fig. 13}, ¹⁴, ¹⁵, ¹⁶, ¹⁷, ¹⁸, ¹⁹, ²⁰, ²¹, ²², ²³, ²⁴, ²⁵, ²⁶ and ²⁷

Conclusion

Early identification of the problems and a detailed analysis of treatment options in accordance with the biological requirements associated with the sequence of treatment allow us to obtain an optimal functional and aesthetic result. Four factors play a part in successful implantology:

- pre-implant surgical augmentation;

- the accuracy with which the implants are placed;

- the management of the peri-implant soft tissues;

- the quality of the prosthetic restoration.

When these have been appreciated, dental implants offer an excellent alternative for the replacement of missing maxillary anterior teeth. The practitioner must therefore consider implant treatment as a treatment option for young people, adults and even the elderly.

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