Tissue-integrated prostheses for edentulous patients with normal and abnormal jaw relationships

MAXILLOFACIAL

PROSTHETICS

. DENTAL IMPLANTS

SECTION EDITORS

I. KENNETH

ADISMAN

RONALD

P. DESJARDINS

Tissue-integrated prostheses for edentulous patients with normal and abnormal jaw relationships Ronald P. Desjardins, D.M.D., M.S.D.* Mayo Clinic and Mayo Medical School, Rochester,Minn.

T

he introduction of the concept of osseointegration by Branemark and his associates’-l3 led to a renewed interest in the use of dental implants to resolve the problems associated with the fabrication and use of complete dentures. Branemark14 defines osseointegration as a “direct structural and functional connection between ordered, living bone and the surface of a load-carrying implant.” Extensive animal and laboratory research led to a 15-year clinical study in which Adell et a1.15were able to show a high percentage of successwith implants placed by using the osseointegration concept. The use of a tissue-integrated prosthesis is not indicated for all edentulous patients. A complete history, clinical examination, radiographic examination, and articulated diagnostic cast examination must be secured for every prospective patient. Laney16 described seven factors to consider in patient selection, one of which was jaw relationship. He stated, “In general patients with extreme Angle Class II or Class III jaw relationships are not good candidates for tissue-integrated prostheses without adjunctive surgery.” This article discusses problems and approaches in the use of tissue-integrated prostheses in patients with normal and abnormal jaw relationships.

THE PROBLEM The primary requisite for successful osseointegration is healthy bone. Bone must be of sufficient quantity and quality to permit integration of a stable implant fixture. A greater quantity of bone permits placement of a longer fixture with a larger surface area of integration, which should better resist forces generated by a prosthesis. However, excessive bone with minimal resorption requires fixture placement at a level that may interfere with the occlusal plane in the finished prosthesis. An incorrect level of the occlusal plane can significantly compromise esthetics, phonetics, and mastication. A reasonable harmony between cortical and trabecular bone is also needed. Dense cortical bone has a limited blood supply that delays the integration potential, and an extended time interval between surgical stages is recom-

*Consultant in Prosthodontics, Mayo Clinic, and Associate Professor of Dentistry, Mayo Medical School.

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mended. Loose trabecular bone limits early stability of the implant and also requires a longer time interval before abutment connection. Although the use of selftapping fixtures and fixtures of sufficient length to engage cortical bone will aid early stability in loose trabecular bone, development of the intimate relationship of bone to the titanium-oxide layer will be delayed. For a tissue-integrated prosthesis, there are limited sites where bone of sufficient quantity and quality are present because of anatomy and bone resorption. In the mandible the most common site for placement of osseointegrated fixtures is the anterior mandible between the mental foramina (Fig. 1). Posteriorly the inferior alveolar canal often limits the amount of bone available for placement of fixtures. In the maxillae, the most common site for placement of osseointegrated fixtures is the vertical extension of bone located between the medial wall of the antrum and the lateral wall of the nasal fossa (Fig. 1). Posteriorly the antrum and anteriorly the nasal fossa limit the amount of bone available for placement of fixtures. Although bone-grafting procedures might be considered to add bone in the posterior mandible or maxillae, the vertical relationship of the mandible to the maxillae and the intermaxillary space may pose potential problems with subsequent fabrication and placement of a tissue-integrated prosthesis. These problems include access during fabrication and placement of the level of occlusal plane. Because of anatomic and resorptive factors, osseointegrated fixtures are most commonly placed in the anterior region of the mandible and the anterior region of the maxillae. The relative relationship of these fixtures and their associated prosthesis to the opposing arch will vary with both the jaw relationship and the degree of resorption. This relationship can lead to increased problems in the opposing arch in both normal and abnormal jaw relationships.

NORMAL JAW RELATIONSHIP Edentulous patients who have had an Angle class I relationship of the natural teeth will usually have a reasonable anteroposterior and mediolateral relationship of the mandibular residual ridge to the maxillary FEBRUARY 1988

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Fig. 1. Panoramic radiograph emphasizes limited regions where sufficient bone is available in edentulous maxillae and mandible to place osseointegrated fixtures. Note limited bone present over inferior alveolar canal and antrum.

Fig. 2. A, Articulated diagnostic casts of patient with normal jaw relationship show that residual ridge crests are located in same anteroposterior plane even though moderate resorption has occurred. B, Cephalometric tracing of normal skeletal pattern. Red lines denote anteroposterior center of denture-bearing areas.

residual ridge if there has been a limited degree of resorption

(Fig.

2, A).

This

relationship

results

in

centering of the primary and secondary bearing regions for the maxillary and mandibular dentures opposite one another at the correct vertical dimension of occlusion (Fig. 2, B). These bearing regions are also central to the denture in both the anteroposterior and mediolateral directions for retention and stability of the maxillary and mandibular dentures during occlusal function. With vertical

increasing

resorption,

a change occurs in the

and horizontal relationship of the residual ridges. The maxillary residual ridge will resorb superiorly and medially and the mandibular residual ridge will resorb inferiorly and laterally (Fig. 3). This resorptive pattern results in a change in the centralization of the bearing regions and a decrease in retention and stability of the complete denture. Because of the more limited bearing region in the mandible and placement of a denture in close approximation to the tongue in a moving jaw, more retention and stability concerns are usually associated with mandibular dentures. Therefore, the THE JOURNAL

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Fig. 3. Cephalogram

of patient with severe mandib ular resorption sh ows that residual ridge crests (arrows) are now in progna .thic relationship to each other even though patient has

resorption and moderate maxillary

normal skeletal pattern.

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Fig. 4. A, Osseointegrated fixtures in mandibular arch oppose maxillary anterior denture bearing region. B, Occlusal relationship emphasizes potential for excessive forces to be generated to anterior maxillae.

Fig. 5. Anteroposterior relationship of stronger maxillary denture-bearing region to weaker mandibular denture-bearing region is shown with, A, articulated diagnostic casts and, B, cephalometric tracing. Red lines on tracing indicate anteroposterior location of primary denture bearing region.

placement of a tissue-integrated prosthesis is more commonly considered for the mandible. Placement of mandibular fixtures in normal jaw relationships and especially in a resorbed pattern, however, has the potential to mimic problems similar to those found in the combination syndrome.” The combination syndrome is potentially found in patients who are edentulous in the maxillae with natural anterior teeth and bilateral posterior edentulous spaces in the mandible. When present, the syndrome includes (1) resorption of the anterior region of the maxillary residual ridge with or without a resultant redundant fibrous ridge, (2) downgrowth of the maxillary tuberosities, (3) development of palatal papillary hyperplasia, (4) resorption of the posterior mandibular residual ridge, and (5) extrusion of the mandibular anterior teeth. In addition, the 182

combination syndrome might also include (1) development of epulis fissuratum in the maxillary anterior vestibule, (2) poor prosthesis adaptation, (3) a posterior slope to the orientation of the occlusal plane, (4) anterior repositioning of the mandible, (5) periodontal changes about the remaining natural teeth, and (6) loss of vertical dimension. When osseointegrated fixtures are present in the anterior mandible and a fixed prosthesis attached, most of the potential combination syndrome problems associated with the mandibular arch would not be manifested (Fig. 4, A). However, potential maxillary manifestations of the combination syndrome are of concern. Because of fixture placement, functional and parafunctional occlusal forces are generated to the anterior maxillae primarily (Fig. 4, B). This potential is further increased FEBRUARY

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Fig. 6. A, Position of osseointegrated fixtures in retrognathic mandible, suggests need to provide, B, horizontal overlap of anterior teeth in completed restoration. because the cantilevered extension posteriorly is limited to 20 mm, which usually results in deletion of the second molar tooth. This concentration of forces in the anterior maxillae could lead to resorption of this region with a resultant decrease in the vertical dimension of occlusion and a poorly fitting prosthesis. As the mandible is positioned further anteriorly, downgrowth of the maxillary tuberosities and development of palatal papillary hyperplasia and anterior vestibular epulides are all potential occurrences. Although these findings have not been reported in the literature when mandibular tissue-integrated prostheses have been used for extended periods, preventive and maintenance care must include this potential. Perhaps the rigid stability of the tissue-integrated prosthesis indirectly provides a more stable opposing denture that encourages bone maintenance instead of resorption. Nevertheless, particular importance should be placed on retention and stability of the maxillary complete denture. Certainly adaptation and border seal with maximum extension of the maxillary denture are critical factors. Of even greater importance, however, is the occlusion. A ful.ly balanced occlusal scheme with absence of anterior 0cc:lusal contact in centric relation/centric occlusion are imperative. A recall schedule that permits timely reevaluation of the denture adaptation and the occlusion must fit the needs of the patient. RETROGNATHIC

JAW RELATIONSHIP

Edentulous patients with retrognathic (Angle class II) jaw relationships often exhibit mandibular complete denture problerns (Fig. 5, A). In retrognathia, the center THE JOURNAL

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of the stronger maxillary denture bearing region opposes the anterior portion instead of the center of the weaker mandibular denture-bearing region (Fig. 5, B). This relationship results in the potential for increasing resorption in the anterior mandible with a resultant unstable mandibular denture. The increased resorption of the mandible may improve the residual ridge relationship because of the inferior and anterior movement of the mandibular residual ridge caused by the resorptive pattern. A mandibular tissue-integrated prosthesis would resolve retention and stability concerns in retrognathic patients (Fig. 6, A). Consideration might also be given to surgical orthognathic procedures to improve the residual ridge relationship even further. Caution must be exercised, however, because retrognathic patients often have a severe vertical and horizontal overlap of the natural anterior teeth. To adequately function phonetically, the mandible is positioned anteriorly to produce adequate speech. In addition, the severe canine guidance often present encourages the use of vertical masticatory strokes. If the dentist routinely attempts to establish a normal occlusal relationship in a retrognathic patient, esthetics, phonetics, and function may be unacceptable. Even though a mandibular tissue-integrated prosthesis resolves retention and stability problems, the retrognathic patient may still tend to position the mandible anteriorly. If a normal occlusal relationship has been provided, a prognathic relationship may be evident that would be unacceptable esthetically and speech would be poor. Although use of a tissue-integrated prosthesis can be a distinct advantage in retrognathic patients, reestablish183

DES JARDINS

Fig. 7. Anteroposterior relationship of maxillae to mandible in prognathic patient are illustrated with A, articulated diagnostic casts and B, cephalometric tracing. Red lines on tracing emphasize potential for increased stress to maxillary anterior ridge if osseointegrated fixtures are placed in anterior mandible.

ing some degree of vertical and horizontal overlap of the anterior teeth with an increased buccolingual overlap of posterior teeth should be considered (Fig. 6, B). The vertical and horizontal overlap that can be provided with a tissue-integrated prosthesis often permits development of a more acceptable occlusal scheme than that found with the natural teeth. The wax trial denture must be critically evaluated to achieve optimal esthetic, phonetic,

and functional relationships tissue-integrated prosthesis.

PROGNATHIC

before finalization

of a

JAW RELATIONSHIP

1

Edentulous patients with prognathic (Angle class III) jaw relationships may exhibit either maxillary or mandibular complete denture problems (Fig. 7, A). Mandibular problems may’ result from the same degree and

Fig. 8. A, Cephalogram shows mandibular relationship following repositioning of mandible. Note that intermaxillary fixation is in place and that fixtures have been placed in anterior mandible. Postoperative results illustrate, B, normal anteroposterior occlusal relationship and, C, mandibular prosthesis that opposes center of maxillary denture bearing region (radiopaque bar emphasizes importance of tissue-integrated prosthesis rigidity). Fig. 9. A, Osseointegrated fixtures are placed lingual to residual ridge crest in prognathic patient, which permits, B, more lingual placement of replacement teeth and, C, occlusal scheme that generates less stress to anterior edentulous maxillae. Fig. 10. A, Maxillary complete denture in prognathic patient is unstable even though reverse labiolingual relationship of anterior teeth is present. B, Osseointegrated fixtures with attached bar splint permits, C, secure retention of maxillary denture with normal occlusal scheme that, D, improves esthetics of lower third of face. 184

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pattern of resorption noted in patients with normal and retrognathic jaw relationships. Maxillary problems are generated because the center of the mandibular denturebearing region opposes the anterior portion instead of the center of the maxillary denture-bearing region (Fig. 7, B). This relationship and the arc of mandibular closure generate excessive force to the anterior region of the maxillae that can result in increased resorption and loss of stability of the maxillary denture. With increased resorption, difficulties in retention and stability of both dentures increase because of increasing degrees of relative prognathism. If a tissue-integrated prosthesis is considered in the mandible, placement of mandibular anterior fixtures could lead to an even greater problem with the maxillary complete denture. Placement of maxillary anterior fixtures would not resolve the problems associated with a resorbed mandibular residual ridge. Several treatment options might be considered when contemplating a tissue-integrated prosthesis for prognathic patients. Surgery. Surgical respositioning of the mandible following vertical or sagittal splitting of the ramus will correct a prognathic relationship (Fig. 8, A). By altering mandibular position, the centers of the maxillary and mandibular denture-bearing regions would oppose one another although a reverse buccolingual relationship may remain posteriorly. A tissue-integrated prosthesis can then be placed in the mandible with the same concerns for potential maxillary denture problems as discussed with normal jaw relationships (Fig. 8, B and C’). If a tissue-integrated prosthesis is to be considered in the mandible, the fixtures can be placed either (1) after further evaluation and planning subsequent to removal of intermaxillary fixation or (2) at the time of mandibular repositioning (Fig. 8, A). A one-stage procedure necessitates more complex prosthodontic planning to assure proper surgical guidance before fixture’ placement. The fixtures would be placed in the predetermined position first and the Gunning splints wired to position in each arch. The mandibular splint must be relieved over the region of fixture placement so that hard and soft tissue irritation that may interfere with osseointegration during the fixation period is avoided. Once the ramus procedure is complete, intermaxillary fixation is provided for approximately an &week period. Upon the removal of fixation, abutment connection can be considered approximately 4 weeks later. Lingual positioning of mandibular fixtures. Because repositioning of the mandible is a more morbid procedure than placement of osseointegrated fixtures only, it may be wise to avoid this procedure in elderly patients or those with complex systemic diseases. If the degree of prognathism is minimal and if the size, shape, and contours of the maxillary denture-bearing region are 186

acceptable for complete denture retention and stability, positioning mandibular fixtures in a more lingual position or at a slight lingual inclination may resolve the mandibular problem without significantly influencing the maxilla (Fig. 9, A). This positioning places the fixtures and the artificial teeth in a more posterior position and decreases their potential effect on the maxillary anterior residual ridge. A lingual positioning of fixtures has the potential to create other problems. The concept of the neutral zone may be violated and the tongue crowded (Fig. 9, B). Because a tissue-integrated prosthesis is fixed, this crowding will not influence stability. The tendency for tongue biting, some tendency to displace food laterally from the occlusal table while chewing, and some speech difficulties may be noted initially. However, the ability of the tongue muscles to readapt to a changed environment can be expected (Fig. 9, C). A more lingual placement of fixtures may also result in the abutments being placed through the movable alveolar mucosa of the floor of the mouth (Fig. 9, A). Because movable mucosa adjacent to fixtures does not appear to influence soft tissue health or fixture integrity and because the prosthesis does not contact the mucosa, lingual position of fixtures does not appear to be contraindicated if needed. Placement of maxillary anterior fixtures. The presence of a full or partial complement of mandibular teeth with or without fixed or removable replacements usually encourages significant maxillary complete denture problems in prognathic patients (Fig. 10, A). The increased morbidity of mandibular repositioning surgery often deters this treatment recommendation in some patients. Placement of a tissue-integrated prosthesis in the maxillae might be an alternative treatment recommendation. Because maxillary fixtures are more commonly placed in the anterior region, force generated by the prognathic mandible would be resisted by the fixtures (Fig. 10, B). Placement of a fixed tissue-integrated prosthesis in the maxillae, however, must consider the esthetic and phonetic potential of the restoration. The space recommended for hygiene beneath a mandibular prosthesis cannot be duplicated in the maxillae without significant phonetic discrepancies, even in patients with long upper lips where esthetics may not be of concern. Use of an overdenture prosthesis is often more practical in the maxillae and has distinct benefits in prognathic patients (Fig. 10, C). Anterior tooth position might be improved in relation to the opposing arch for better esthetic as well as functional relationships (Fig. 10, D). SUMMARY Diagnosis and treatment planning are keys to successful prosthodontic rehabilitation. The increasing interest FEBRUARY

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in the use of the tissue-integrated prosthesis to resolve the problems of edentulous patients indicates caution in the selection of patients for this procedure. Even if patients are identified who could potentially benefit, application of the concept must meet the needs of the patient. The treatment planning phase must include all professionals participating in patient management and must consider the best placement of fixtures to improve patient findings to an optimal degree. Although many patient factors must be considered in treatment planning, this article discussed application of the tissue-integrated prosthesis concept as it relates to jaw relationship. The tissue-integrated prosthesis must not compound or create retention and stability problems found with complete dentures” This article suggests treatment considerations in planning the tissue-integrated prosthesis for normal and abnormal jaw relationships.

7. 8.

1983.

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Branemark PI. Osseointegration and its experimental background. J PROSTHETDENT 50:399-410, 1983. Kasemo B. Biocompatibility of titanium implants: surface science aspects. J PROSTHET DENT 49:832-7, 1983. Parsegian VA. Molecular forces governing tight contact between cellular surfaces and substrates. J PROSTHET DENT 49:838-42, 1983.

4.

Skalak R. Biomechanical considerations in osseointegrated prostheses. J PROSTHET DENT 49:843-g, 1983. 5. Eriksson AR, Albrektsson T. Temperature threshold levels for heat-induced bone tissue injury. A vital microscopic study in the rabbit. J PROSTHET DENT IiO:lOl-7, 1983. 6. Hansson H-A, Albrektsson T, Branemark PI. Structural aspects of the interface between tissue and titanium implants, J PROS. THET DENT 50:108-13,

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Albrektsson T. Direct bone anchorage of dental implants. J PROSTHET DENT 50:255-61, 1953. Zarb GA, Symington JM. Osseointegrated dental implants: preliminary report of a replication study. J PROSTHET DENT 50:271-6, 1983. Jemt T, Lindquist L, Hedegard B. Changes in chewing patterns of patients with complete dentures after placement of osseointegrated implants in the mandible. J PROSTHET DENT 53:578-83, 1985. Loos LB. A fixed prosthodontic technique for mandibular osseointegrated titanium implants. J PROSTHET DENT 55232-41, 1986.

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REFERENCES 1.

Lekholm U. Clinical procedures for treatment with osseointegrated dental implants. J PROSTHET DENT 50:116-20, 1983. Adell R. Clinical results of osseointegrated implants supporting fixed prostheses in edentulous jaws. J PROSTHET DENT 50:251-4,

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Jemt T, Stalblad P-A. The effect of chewing movements on changing mandibular complete dentures to osseointegrated overdentures. J PROSTHET DENT 55:357-61, 1986. Branemark PI, Zarb GA, Albrektsson T. Tissue-integrated prostheses-osseointegration in clinical dentistry. Chicago: Quintessence Publishing Co, 1985;l I. Adell R, Lekholm U, Roekler B, Branemark PI. A 15-year study of osseointegrated impiants in the treatment of the edentulous jaw. Int J Oral Surg 10:387-416. 1981. Laney WR. Selecting edentulous patients for tissue-integrated prostheses. Int J Oral and Max Imp1 1:129-38, 1986. Saunders TR, Gillis RE, Desjardins RP. The maxillary complete denture opposing the mandibular bilateral distal extension partial denture: treatment considerations. J PROSTHET DENT 41:124-g.

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Reprint requests to: DR. RONALD P. DESJARDINS DEPARTMENT OF DENTISTRY MAYO CLINIC ROCHESTER, MN 55905

In vitro biocompatibility of air-fired opaque porcelain with human gingival fibroblasts Charles M. Cobb, D.D.S., M.S., Ph.D.,* Connie L. White, D.D.S.,** Robert D. Gillahan, D.D.S.,*** and Daniel E. Tira, Ph.D.‘*** University of Missouri-Kansas City, School of Dentistry, Kansas City, MO.

fi or all dental implants there exists an analogy to the natural dentition regarding the soft tissue interface. For example, the epithelium in contact with the implant post *Professor, Department of Periodontology. **Assistant Professor, Department of Diagnosis and Radiology. ***Professor, Department of Fixed Prosthodontics. ****Associate Professor, Department of Behavioral Science. THE JOURNAL

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and/or tooth root, referred to asjunctional epitheiium, is a stratified squamous variety exhibiting only two strata, the stratum basale and stratum spinosum. The epithelial attachment in each instance can be mediated by hemidesmosome and basal lamina structures’” or involve interactions of substratum-absorbed serum protein and cell surface proteins.4 Regardless of the attachment mode, clinical studies have shown that the quality of the soft 187