Oral Health Group
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The Use of Prosthodontic Principles in Managing a Compromised Implant Case

November 1, 2005
by Beatrice Leung, DDS, MPH, Cert. Prostho


Treatment planning for any complex case requires the clinician to be diligent in carrying out the clinical examination in order to arrive at a proper diagnosis. The blueprint which develops from this exercise must consider factors beyond the oral cavity, factors such as medical problems, time and cost. If these steps are performed haphazardly, the subsequent treatment may be less than ideal and it can ultimately lead to long-term complications and failure. This philosophy is especially important when using dental implants in managing partially or completely edentulous patients. Documented long-term success has recognized dental implants1 as a solution for patients with missing teeth. When dental implants are used in any partially or completely edentulous case, one must understand the surgical and restorative factors that govern the success of osseointegration. These include careful surgical techniques, careful implant site selection, and the various biomechanical factors influencing the bone-implant interface.2-4 Despite the multitude of factors that need to be considered in managing patients receiving dental implants, some basic prosthodontic principles are equally important and should not be ignored. During the diagnostic process, aside from the hard and soft tissue evaluation and the identification of the edentulous spaces, the examination should also include a detailed occlusal analysis. Such an analysis should include an evaluation of the patient’s existing occlusal vertical dimension, the state of the occlusal plane and the pattern of occlusal contacts during excursive movements. If dental implants are placed without a proper diagnostic work up, their positions and angulations may be less than ideal and the resulting prosthesis may not be able to provide proper function, aesthetics and will be susceptible to complications.

Managing a case where dental implants have been surgically placed before developing a proper diagnostic work up can be challenging. A clinical case is presented to illustrate the complications and problems encountered when proper diagnosis and treatment planning was lacking. Basic prosthodontic principles are discussed and then applied to provide a treatment solution to a treatment planning dilemma.

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A 51-year-old male presented to the clinic and his chief complaint was a desire to have an implant supported fixed prosthesis to replace missing upper front teeth. He was previously seen by another dentist for the surgical placement of dental implants and was initially treatment planned to receive a fixed implant supported prosthesis replacing the missing teeth in the maxilla. Medical history was non-contributory. Upon examination, clinical findings revealed missing teeth, #18, 17, 15, 14, 12, 11, 21, 22, 25, 27, 28 in the maxilla. Implants were placed at sites 15, 14, 12, 22 and 25 but the implant in site 22 failed to osseointegrate (Fig. 1). The patient was initially treatment planned to receive implant supported PFM crowns at sites 15, 14 and 25 and a four unit implant supported fixed partial denture with implants as abutments at site 12 and 22 (FPD 12-x-x-22). He wished to have the mandibular missing teeth replaced at a later time due to cost (Fig. 2). At the time, the patient was wearing maxillary and mandibular removable partial dentures. Further occlusal analysis revealed an irregular occlusal plane and inadequate posterior support (Figs. 3-5 & 7). Periodontal and radiographic evaluation revealed that the patient had moderate to advanced bone loss in all of the maxillary remaining teeth (Fig. 6).

OCCLUSAL PLANE

In this particular case, the uneven occlusal plane is of particular concern because it compromises the functional and aesthetic result of the final prosthesis. According to the seventh edition of the Glossary of Prosthodontic Terms, the definition of occlusal plane is the average plane established by the incisal and occlusal surfaces of the teeth.5 In an edentulous case, it is the surface established by the wax occlusal rims that are used as a guide in the arrangement of denture teeth. Historically, there are many extra oral anatomical landmarks that guide clinicians in re-establishing the occlusal plane for example, the interpupillary and ala-tragus line (Camper’s Plane). Intra-oral landmarks include the retromolar pad, the position of the tongue, and the modiolus muscle.6-8 An appropriate occlusal plane is essential for the aesthetic and functional outcome of the prosthesis. Gross discrepancy of the occlusal plane, in addition to the unpleasing smile, can also lead to interferences during mandibular excursions.9 Occlusal and incisal plane are not the only factors that influence the functional status of an implant-supported prosthesis; however, they do allow the clinician to determine the ideal position and angulation of dental implants and the need for hard and soft tissue augmentation. In this case, dental implants have been placed prior to the correction of occlusal plane and it will be evident later that the case cannot be restored with an implant supported fixed prosthesis.

OCCLUSAL VERTICAL DIMENSION

Occlusal vertical dimension is another prosthodontic concept that was not properly assessed prior to the placement of dental implants. By definition, it is the distance measured between two points in the maxilla and the mandible when the occluding surfaces are in contact.10 Reduced vertical dimension can lead to undesirable facial features such as deepening of the nasolabial groove, narrowing of the lips, increase in columnella-philtral angle and a prognathic appearance.11 There are many concepts and techniques in the literature that guide the clinician in re-establishing occlusal vertical dimension. They include physiologic concepts such as the use of interocclusal rest space, phonetics, aesthetics as well as the act of swallowing.12-16 Other mechanical concepts include pre-extraction records and other various facial measurements.17

Current scientific evidence does not support one technique as being more superior than the other.18 However, it is generally recommended to utilize more than one technique in the determination of occlusal vertical dimension and this relationship should be tested prior to the fabrication of a definitive prosthesis. Once the occlusal vertical dimension is determined, the relationship between the desired position of the teeth and the soft and hard tissue can be a guide in determining the ideal position and the angulation of dental implants. In this case study, dental implants were placed before the vertical dimension of occlusion was corrected.

It is now evident that the case presented has some major problems. First, using the retromolar pad and the existing mandibular canine as reference points, the irregular occlusal plane is evident. Restoring the existing edentulous spaces as presented in the maxilla only perpetuates the problem of an irregular occlusal plane. Not only will the final prosthesis display poor aesthetics but the force distribution on the dental implants will also be unfavorable. Secondly, assessment of the remaining dentition in the maxilla reveals advanced bone loss in localized areas, pocket depths of 4-6mm and moderate mobility. These remaining teeth, aside from their poor periodontal status, also prevent the re-establishment of an ideal occlusal plane.

Based on the previous prosthodontic principles, the patient was advised that the remaining teeth in the maxilla needed to be extracted. The occlusal plane and occlusal vertical dimension needed to be re-established first before any definitive treatment could be delivered. Due to improper planning the patient was promised a treatment outcome which was not possible. This disappointment created an additional burden for a favourable outcome.

TREATMENT APPROACH

In this case, the objectives were to re-establish the occlusal plane and vertical dimension of occlusion and to eventually deliver a prosthesis that was both aesthetic and functional. To correct the ma
ndibular occlusal plane, tooth coloured acrylic resin (PMMA Jet) was added and contoured on the occlusal surfaces of the denture teeth on the mandibular removable partial denture. Acrylic resin was added until the mandibular occlusal plane was in line with the retromolar pad and the tip of the canine. The remaining maxillary teeth were extracted and an another implant was placed in site #22 that failed previously (Fig. 8). An interim maxillary complete denture supported by the existing dental implants was delivered. This interim denture was used to assess the patient’s acceptance of the new occlusal vertical dimension as well as an aesthetic evaluation of his smile line and the lip support.

At this point, it is evident that the option of an implant supported fixed prosthesis is inappropriate. The excessive loss of hard and soft tissue in relation to the desired position of the teeth indicates that bone augmentation should have been performed prior to the placement of dental implants. The less than ideal positions and angulations as well as the insufficient number of dental implants are reasons that full arch implant-supported fixed prosthesis would not be appropriate.19 The treatment option of a traditional fixed detachable prosthesis was considered but was later found to be inappropriate. The need for a denture flange for lip support will make it a challenge to clean under a fixed detachable prosthesis. An alternate treatment option of an overdenture supported by an implant bar was offered to the patient instead.

TREATMENT

Following healing, correcting the patient’s occlusal plane and verifying the vertical dimension of occlusion, a final impression was made at the level of the implants. A closed tray technique was used in preparation for the fabrication of an implant bar and the final maxillary overdenture (Figs. 9-11).

Using visible light cured denture resin (Triad Denture Base Material) and with three temporary non engaging abutments. (NobelBiocare Replace Select Temporary Non-engaging Titanium Abutments), a recording base with an occlusal wax rim was fabricated. The temporary abutments were positioned strategically to assist in stabilizing and retaining the occlusal wax rim during the wax try in stage (Fig. 12).

Using the interim maxillary complete denture as a guide, the occlusal wax rim was contoured to provide proper lip support and an adequate occlusal vertical dimension. Since the mandibular occlusal plane was previously corrected, the maxillary occlusal wax rim was adjusted to contact the mandibular teeth (Figs. 13-15). The teeth arrangement was tried in to verify the aesthetics and the vertical dimension of occlusion as well as to obtain the patient’s approval. A plaster matrix was made following this appointment to guide in the laboratory procedure of fabricating the implant bar pattern for the overdenture (Fig. 16).

When designing the implant bar for the overdenture, the plaster matrix is used to ensure that adequate clearance is provided between the acrylic resin and the metal implant bar. If the space provided is insufficient between the metal framework and the acrylic resin, the overdenture might run the risk of fracture as well as a possible metal showing through the thin layers of acrylic. The implant bar pattern is designed such that the surface has smooth, parallel sides with a two degree taper. The overdenture contains a metal superstructure that intimately fits into the implant bar. Such a design ensures that the prosthesis will have no freedom of rotation in any three planes and has only one path of insertion. Consequently, the prosthesis functions very much like a fixed denture. The advantage of this prosthesis is that it can be removed for cleaning under the bar as well as providing lip support through the function of the flange. With the non ideal placement of the dental implants, splinting the implants through the bar provides a more favorable stress distribution without compromising the position of the teeth.20 Horizontal ball attachments (Bredent attachment systems VKS-SG) are also added to the implant bar to provide auxiliary retention (Fig. 18). The metal housings are soldered to the metal super-structure (Fig. 17).

The passive fit of the implant bar was verified and the prosthesis was subsequently processed (Figs. 19 & 20). After delivering the implant bar and the overdenture, there was minimal post-delivery adjustment made and the patient was satisfied with both the functional and aesthetic outcome. He also understood that the addition of acrylic resin on the mandibular partial denture teeth served as a temporary solution to correct the occlusal plane and recognized that the partial denture would need to be replaced in the future. This temporary solution allowed the maxillary prosthesis to be fabricated without the uneven occlusal plane dictating the final case result.

In this clinical case presentation, a treatment solution and its rationale are presented to highlight the importance of some basic prosthodontic principles that should not be overlooked in treating an implant case. The surgical placement of dental implants should not take place until a proper examination and diagnosis have been made. In this case, to provide a fixed implant supported prosthesis would require additional hard and soft tissue augmentation as well as increasing the number of implants involved. The additional treatment and cost were not feasible for this patient and again brought to light the importance of diagnosis and treatment planning to avoid disappointment to the patient and to be able to provide a more predictable treatment outcome.

Beatrice Leung DDS MPH Cert. Prostho is a fellow and a diplomate of the International Congress of Implantologists, a clinical instructor in the department of Prosthodontics at the University of Toronto. Her practice in Toronto is limited to aesthetic, implant and reconstructive dentistry.

Oral Health welcomes this original article.

REFERENCES

1.Adell R., Eriksson B., Lekholm V., Branemark PI., Jemt T., long-term follow-up study of osseointegrated implants in the treatment of totally edentulous jaws. International Journal of Oral Maxillofacial Implants. 1990; 5: 347-59

2.Albrektsson T., Bone Tissue Response. In: Brnemark P.-I., Zarb G, Albrektsson T (eds). Tissue-integrated prostheses: Osseointegration in clinical dentistry. 1st ed. Chicago: Quintessence 1985. 129-143.

3.English CE., Biomechanical Concerns with Fixed Partial Dentures Involving Implants. Implant Dentistry. 1993; 2 (4); 221-242

4.Bidez MW., Misch CE., Force Transfer in Implant Dentistry: Basic Concepts and Principles. Journal of Oral Implantology. 1992;18(3):264-74

5.Glossary of Prosthodontic Terms 7th Edition. Journal of Prosthetic Dentistry, 1999: 81(1); 87

6.Zarb GA., Identification of shape and location of arch form: the recording base and occlusion rim In: Zarb GA, Bolender CL, Carlsson GE. Boucher’s prosthodontic treatment for edentulous patients. 11th ed. St. Louis: Mosby- Year book, Inc 1997. 191-194

7.Ismail YH., Bowman JF. Position of the Occlusal Plane in Natural and Artificial Teeth. Journal of Prosthetic Dentistry. 1968: 20 (5) 407-411

8.Wright CR., Evaluation of the Factors Necessary to Develop Stability in Mandibular Dentures. Journal of Prosthetic Dentistry. 1966: 16(3) 414-430

9.Mulcahy DF., Functional Modification of Acrylic Resin Monoplane Occlusions. Journal of Prosthetic Dentistry. 1987: 57(4); 465-470

10.Glossary of Prosthodontic Terms 7th Edition. Journal of Prosthetic Dentistry, 1999: 81(1); 88

11.Zarb GA., Biomechanics of the edentulous state. In: Zarb GA, Bolender CL, Carlsson GE. Boucher’s prosthodontic treatment for edentulous patients. 11th ed. St. Louis. Mosby- Year book, Inc.; 1997. 26

12.Swerdlow H., Vertical Dimension Literature Review. Journal of Prosthetic Dentistry. 1965: 15(2): 241-7.

13.Shanahan TE., Physiologic Vertical Dimension and Centric Relation. Journal of Prosthetic Dentistry. 1956; 6 (6); 741-7

14.S
ilverman MM., The Speaking Method in Measuring Vertical Dimension. Journal of Prosthetic Dentistry. 1953; 3 (2): 193-199

15.Pound E., Esthetic Dentures and Their Phonetic Values. Journal of Prosthetic Dentistry. 1951; 1 (1 & 2): 98-111.

16.Ismail YL., George AH., The Consistency of the Swallowing Technique in Determining Occlusal Vertical Relation in Edentulous Patients. Journal of Prosthetic Dentistry. 1968; 19: 230-36

17.Turrell AJW., Clinical Assessment of Vertical Dimension. Journal of Prosthetic Dentistry. 1972; 28 (3); 238-46

18.Fayz F., Eslami A., Determination of Occlusal Vertical Dimension: A literature review. Journal of Prosthetic Dentistry. 1988; 59 (3): 321-3

19.Sadowsky SJ., The Implant-Supported Prosthesis for the Edentulous Arch: Design Considerations. Journal of Prosthetic Dentistry. 1997; 78: 28-33

20.Muftu A., Karabetou S., Complications in Implant-Supported Overdentures. Compendium. 1997; 18 (5); 497-503


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