and Facial Aesthetic Considerations for the Contour of Fixed Prostheses

Fig. 12.1

NobelClinician® plan of atrophic maxillary quad zygoma showing implant position and prosthetic tooth replacement position

Fig. 12.2

NobelClinician® plan of maxillary All-on-4® showing implant position and prosthetic tooth replacement position

Fig. 12.3

Digital smile design simulation of prosthetic tooth replacement in terminal dentition

Fig. 12.4

Minimal loss of alveolar height and hence support for the facial tissue is largely only from the prosthetic teeth

Fig. 12.5

Compared to significant prosthetic replacement of lost tissue providing facial support

Fig. 12.6

CT scan of patient with diagnostic template in situ

Fig. 12.7

CT scan of diagnostic template in same orientation

Cawood and Howell [12] described the changes in anatomical form of the edentulous maxilla and mandible and consequences to the facial form that result from the potential atrophy. The collapse of the circumoral muscles around the mouth as well as those of the elevator and depressor muscles alters the facial form in a predictable manner. The retrusion and inversion of the upper lip follow the loss of support from the upper teeth and alveolus, and resulting mesialization of the modiolus exacerbates the visual deficiency in tissue volume. A fixed or removable dental prosthesis can be used to support the curtain of tissues and provide support to the lip and facial tissues altering the facial form. A removable denture can utilise the denture flange for this support, whereas a fixed prosthesis relies on implant position and bridge design to maximise the tissue support. Provision must be made for cleansability to ensure stability of peri-implant tissues with both fixed implant bridges and implant overdenture prostheses.

12.1 Incisor Position

The position and form of the maxillary incisors is an area more dependent on artistic and aesthetic skill than scientific rigour [13, 14]. Traditionally the incisors in complete denture patients were placed closer to the residual ridge to reduce leverage forces and hence improve stability of the tissue-supported prosthesis. As alveolar resorption is directed palatally, the position of the incisors will also move palatally as the patient ages. Lip support is reduced and coupled with an age-related loss in soft-tissue collagen; the facial profile becomes more sunken in appearance. Plumping of flanges to remove vertical lines usually has the effect of reducing vermillion display so the clinician should aim to achieve soft-tissue effects primarily from incisor position and secondarily with more subtle support from the prosthetic soft tissue.

Lip prominence , especially projection and display of the vermillion, is most dependent on incisor position. An implant-retained prosthesis does not depend on traditional concepts of denture retention so the anterior teeth can be placed in any position desired. Indeed, for a long-standing denture wearer, placing the incisors in a position similar to an age-matched patient with a natural dentition can be a dramatic change.

More recently, Coachman et al. [15] developed a process for designing the changes to a patient’s existing anterior dentition digitally. This ‘digital smile design’ protocol enables the clinician, using digital photos and presentation software, to plan changes in relation to the patient’s face for patient approval and to quantify these changes for communication to clinical and technical personnel. This enables a more accurate transfer of information and potentially better results. As always, more time spent in diagnosis and treatment planning should minimise adverse consequences and enhance the overall outcome.

Anterior tooth position , especially when teeth have been lost for many years, can be difficult to quantify and any form of smile assessment will improve diagnostic patient communication. The classic complete denture literature is invaluable [16] and the competent provision of complete dentures should be a basic requirement for the clinician embarking on extensive implant rehabilitation. The use of time-honoured phonetic tests and other diagnostic techniques can ease the transition for many patients. Even though implants can enable the placement of teeth in almost any position, if teeth are placed outside the envelope of adaptability for that particular patient, speech and comfort will always be impaired. A common example is creating a Class I incisor relationship in a significant Class II skeletal base. These patients may be used to a significant protrusion with incision and ‘s’ sounds. The ‘correction’ therefore may be too sizeable for comfortable adaptation with the patient complaining of being ‘locked in’ or restricted. A similar statement can be made for Class III relationships.

12.2 Determination of Facial Support

12.2.1 Consequence of Jaw Atrophy

Following the extraction of a tooth , the width of the alveolar ridge is reported to be reduced by 50% during the first 12 months. Approximately two-thirds of this reduction occurs within the first 3 months after tooth extraction [17]. As more horizontal bone loss occurs especially in the anterior maxilla, there is a greater need for prosthetic support for the lips and surrounding peri-oral musculature.

The loss of occlusal vertical dimension can be exacerbated by previous dentures or dentistry that does not account for this loss. With loss of alveolar bone volume, the three-dimensional maxillomandibular relationship has a tendency for the mandible to become more prognathic and requires consideration for prosthetically directed implant placement.

12.2.2 Lip Support

When the optimal tooth position for aesthetics, phonetics and prosthetic lip and tissue support is established following diagnostic assessment and provisional mock-up, it is important that the position is replicated with the final prosthesis whether it be tissue or implant borne. Finalising of the prosthetic plan should always be performed prior to surgery for appropriate implant positioning to meet prosthetic requirements. Three-dimensional implant planning and guided surgical placement aid the clinician in achieving this [18] and the use of stereophotogrammetry provides additional control in prosthodontic diagnosis and treatment. The use of computer-guided surgical templates such as NobelGuide® enables the accurate placement of the implants according to the NobelClinician® plan [19] with a high degree of precision [20, 21]. A diagnostic workup is required with a mock-up of an idealised result for patient approval and planning for implant placement. A CT scan is taken with the diagnostic template in situ, with a second scan of the diagnostic template alone taken for software alignment of the template and anatomical structures.

Whilst challenges exist in the establishment of a single protocol using the different imaging device data formats for facial skeleton, extraoral soft tissue and dentition including the surrounding intraoral soft tissue [22], the incorporation of a non-invasive technology such as stereophotogrammetry will benefit patient outcomes. The technology can be prosthodontically utilised for fixed and removable prostheses, and as Fig. 12.8 indicates, analysing volumetric change between the patient’s original and provisional prosthesis aids in establishing the optimal lip support and facial tissue form.

Fig. 12.8

Volumetric tissue change between original and provisional prostheses recorded with three-dimensional photographs and superimposition of images

Quantifying the amount of change with thermal imaging of superimposition of the three-dimensional images helps the patient to understand the process without an intimate knowledge of anatomy or technical dental mechanics. It is advised that all changes are made with the provisional prosthesis or wax try-in prosthesis, with opportunity for the patient to request further modifications prior to a formal acceptance.

Once the design has been agreed upon by clinician and patient, this is then replicated in the final prosthesis and Fig. 12.9 highlights the minimal difference observed with superimposition of three-dimensional photographic images between diagnostic and final prostheses.

Fig. 12.9

Provisional maxillary implant prosthesis replacing teeth and alveolar tissues

Patient’s individual aesthetic requirements play a critical role in prosthodontic treatment planning [23]; however anatomical variability prevents a predetermined prescription for achieving a satisfactory outcome. Stereophotogrammetry aids assessment of lip position and tissue support, and communication of this with the patient. Figures 12.10 and 12.11 graphically show the significant volumetric change a removable maxillary prosthesis has not only to the maxillary lip, but also to the entire lower half of the face. Figure 12.10 shows a thermal image of volumetric change between presenting and trial prostheses designed to increase maxillary lip support and compensate for vertical face height loss following continued alveolar ridge atrophy. Figure 12.11 indicates some residual volumetric change between diagnostic wax-up and final prosthesis which may be acceptable to the patient, or highlights the limits of prosthodontic treatment and the need for additional facial contouring with injectable fillers.

Fig. 12.10

Definitive maxillary implant prosthesis replacing teeth and alveolar tissues following provisional prosthesis design

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Dec 6, 2018 | Posted by in General Dentistry | Comments Off on and Facial Aesthetic Considerations for the Contour of Fixed Prostheses
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