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Year: 2007

Zygoma implant-supported prosthetic rehabilitation after partialmaxillectomy using surgical navigation: a clinical report

Kreissl, M E; Heydecke, G; Metzger, M C; Schoen, R

Kreissl, M E; Heydecke, G; Metzger, M C; Schoen, R (2007). Zygoma implant-supported prosthetic rehabilitationafter partial maxillectomy using surgical navigation: a clinical report. The Journal of Prosthetic Dentistry,97(3):121-128.Postprint available at:http://www.zora.uzh.ch

Posted at the Zurich Open Repository and Archive, University of Zurich.http://www.zora.uzh.ch

Originally published at:The Journal of Prosthetic Dentistry 2007, 97(3):121-128.

Kreissl, M E; Heydecke, G; Metzger, M C; Schoen, R (2007). Zygoma implant-supported prosthetic rehabilitationafter partial maxillectomy using surgical navigation: a clinical report. The Journal of Prosthetic Dentistry,97(3):121-128.Postprint available at:http://www.zora.uzh.ch

Posted at the Zurich Open Repository and Archive, University of Zurich.http://www.zora.uzh.ch

Originally published at:The Journal of Prosthetic Dentistry 2007, 97(3):121-128.

Zygoma implant-supported prosthetic rehabilitation after partialmaxillectomy using surgical navigation: a clinical report

Abstract

The rehabilitation of patients with acquired defects of the maxilla is a challenge in terms ofreestablishing oronasal separation. In most patients these goals are met by means of prostheticrehabilitation with an obturator prosthesis. If the remaining dentition does not offer sufficient retentionand support, the placement of zygoma implants can enhance the stability of the prosthesis. Due to theanatomic intricacies of the zygomatic bone and the implant length, computer-supported navigatedimplant placement can be advantageous. In the following clinical report, a diabetic patient with a statusof posthemimaxillectomy secondary to aspergillusis infection is presented, in whom a zygoma implantwas placed using a CT scan-based navigation system. A special retentive anchoring abutment was usedto integrate the zygoma implant into a telescopic crown-retained denture on the residual dentition. Thistooth-implant-supported obturator prosthesis restored function and phonetics, as well as esthetics, forthis young patient.

17067-rev-edits 1

Zygoma implant-supported prosthetic rehabilitation after partial maxillectomy using surgical

navigation: A clinical report

ABSTRACT

The rehabilitation of patients with acquired defects of the maxilla is a challenge in terms

of re-establishing oronasal separation. In most patients these goals are met by means of

prosthetic rehabilitation with an obturator prosthesis. If the remaining dentition does not offer

sufficient retention and support, the placement of zygoma implants can enhance the stability of

the prosthesis. Due to the anatomic intricacies of the zygomatic bone and the implant length,

computer-supported navigated implant placement can be advantageous. In the following clinical

report a diabetic patient status post hemimaxillectomy secondary to aspergillusis infection is

presented, where a zygoma implant was placed using a CT-scan-based navigation system. A

special retentive anchoring abutment was used to integrate the zygoma implant into a telescopic-

crown retained denture on the residual dentition. This tooth-implant-supported obturator

prosthesis restored function, phonetics as well as esthetics for this young patient.

INTRODUCTION

Defects of the maxilla may result from trauma, disease, pathological changes or follow

surgical resection of oral neoplasms. Maxillectomy defects result in the formation of a

communication from the oral cavity into the antrum and/or the nasopharynx. This inevitably

results in problems with speech, mastication, swallowing and impaired facial esthetics.1-4

Rehabilitation is important as such functional impairments have a detrimental effect on quality of

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life and self esteem.5, 6 There are several reconstructive options including prosthetic

obturation,2,3, 7-11 non-vascularized grafts, local flaps, regional flaps and microvascular free tissue

transfer.12-18 Although there have been advances in plastic surgery, surgical reconstruction of

maxillectomy defects continues to be challenging, unpredictable, and not always possible, either

due to local or systemic reasons.19 Additionally, some patients may prefer to avoid secondary

morbidity from reconstructive procedures.20 In these patients an obturator prosthesis can

reestablish the separation of the oral cavity from the sino-nasal cavities, restoring speech and

swallowing function. In dentate patients, support, stability and retention of such an obturating

removable prosthesis relies on the remaining hard and soft tissues.11, 21, 22 The larger the surgical

resection, the greater the loss of mucogingival support, which in turn results in increased

unfavorable forces acting on the remaining abutment teeth.12, 22, 23 Since the advent of

osseointegration the combination of implants and prosthetic obturators has proven to be

beneficial, especially in the rehabilitation of the edentulous maxillectomy patient.24-27 Because of

the limited amount of remaining maxillary bone following maxillectomy, implant placement for

anchoring a prosthesis has also been performed in more remote sites such as the zygomatic

bone.28-35 The zygoma implant (Zygomaticus fixture; Nobel Biocare, Göteborg, Sweden)

developed by Branemark was specifically designed to offer maximum bone anchorage while

simplifying access to the implant head, facilitating the abutment connection.36 The zygoma

implant is available in 8 lengths ranging from 30 to 52.5 mm. The head of the zygoma implant is

engineered to allow prosthesis attachment at a 45-degree angle to the long axis of the implant.

With this specific design these implants have been successfully used to support prostheses in the

atrophic edentulous maxilla,37-46 as well as in patients which have undergone maxillectomy.28, 35,

40, 47 This clinical report demonstrates the use of a zygoma implant to improve stability and

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retention of a telescopic-crown retained 48-51 obturator prosthesis and highlights the benefits of

computer-supported navigation when placing such an implant.

CLINICAL REPORT

A 23-year-old white woman presented at the dental school in the University Hospital of

the Albert-Ludwigs University (Freiburg, Germany) seeking definitive rehabilitation 18 months

following hemimaxillectomy. The medical history revealed a rare example of a fulminant

infection in a type I diabetic patient. Following extraction of the lower left second molar the

patient was treated for a paramandibular abscess and the postoperative course was further

complicated by sepsis. Microbiological tests revealed a suprainfection with candida albicans and

aspergillus. The bacterial and fungal infections proved to be therapy-resistant and disseminated

systemically. A poorly controlled diabetes control can be a risk factor for fungal infection after

tissue damage.52 The patient developed pneumonia which resulted in complete collapse of the

respiratory system (ARDS; acute respiratory decompensation syndrome). Aspergillus has a

propensity for invading blood vessels causing thrombosis and infarction.52 In the presented

patient a blocking of the internal carotid artery and the maxillary artery was diagnosed which

was supposedly caused by such an infarction of these vessels. The consequent necrosis of the left

maxilla made hemimaxillectomy inevitable. From the sinuses, the infection spread into the brain

resulting in multiple cerebral insults, which lead to a palsy of the oculomotory and abducens

muscle. The Magnetic Resonance Imaging (MRI) verified abscess-foci located in the frontal lobe

and temporobasal near the cavernosus sinus. As a side effect to the antimycotic therapy the

patient suffered from toxic hepatitis.

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At the time of the first appointment, the resection site was free of inflammation and

completely covered by respiratory mucosa. The defect extended from the palatal midline to the

distal surface of the left incisor and posteriorly onto the soft palate (Fig. 1 and 2), resulting in an

opening to the nasal as well as the antral cavity (Fig. 3). Examination of the remaining maxillary

dentition revealed extensive restorative treatment and root canal therapy of the right central

incisor. A provisional obturator inserted following the surgical resection allowed the patient to

speak and swallow. The patient desired a definitive rehabilitation to improve function and at the

same time provide a more esthetic result.

In this patient, there was no alternative to prosthetic obturation as microsurgical

rehabilitation was not considered a viable option due to the compromised vascular supply of the

defect site. Considering stability, retention, load distribution and suprastructure longevity, the

decision was made to rehabilitate the patient with a telescopic crown-retained obturator prothesis

additionally supported by one or two zygoma implants (Zygomaticusfixture; Nobel Biocare,

Göteborg, Sweden) on the defect side. To ensure a proper position and bone anchorage it was

planned to navigate the implant placement. After preliminary impressions with alginate (Alginat

Super; Pluradent, Offenbach. Germany) artificial teeth (Physiodens; Vita Zahnfabrik, Bad

Säckingen, Germany) were diagnostically arranged on trial bases of the maxillary prosthesis.

Using this arrangement, an acrylic resin (Probase; Ivoclar, Schaan, Liechtenstein) template for

the computerized tomography (CT) was generated and radioopaque marker (5 mm titanium

drilling sleeve, Straumann, Freiburg, Germany) was positioned where the implant-prothesis-

connnection would ideally be located. The marker was positioned so it would not interfere with

the palatal contours of the prosthesis nor with the buccal flange which was necessary for a good

seal. This information was transferred into the CT and enabled to generate a CT-based virtual

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model with the ideal position of implant head being visible. Using a special navigation system

(VoXim, IVS Solutions AG, Chemnitz, Germany) it was possible to preoperatively simulate and

predetermine the ideal implant position in a 3-D-reconstruction. It became evident that it would

not be possible to properly place two zygomas side by side as the zygomatic bone was very thin

in the caudal part, thus allowing the placement of only one implant in the thicker cranial part.

During surgery, there was constant visualization of the drill trajectory in the 3-dimensionally

reconstructed CT-image and in sagittal, coronal and axial views (Fig. 4). Deviation from the

planned position was immediately detected and precise implant placement was achieved. An

implant with the connecting external hexagon of the implant head facing towards the occlusal

plane was used. A postoperative CT-scan verified placement and angulation of the implant in the

remaining zygomatic bone (Fig. 5). During the 3 month-healing period, all remaining teeth were

prepared for a telescopic-crown retained prosthesis. The abutments were prepared with a

chamfer margin and definitive impressions were made (polyether material; Impregum Penta Soft,

3M Espe, Neuss, Germany), the inner telescopic-crown copings were cast with a precious alloy

(Bio MSG, Heraeus Kulzer, Hanau, Germany). A transfer impression over these telescopic

copings and the implant was made and (Nobel Biocare, Göteborg, Sweden) a definitive cast

model was manufactured (Fig. 6) for the framework design. Wax occlusal rims formed on the

acrylic resin record base were used to make an interocclusal record to transfer the interarch

relationship into the articulator and a face-bow registration was performed. The trial arrangement

of the teeth was completed and evaluated intraorally to verify tooth position, esthetics and proper

occlusion. At the time of insertion of the completed prosthesis (Fig. 7-9), a retentive attachment

(Locator; Zest Anchors Inc., Escondido CA, USA; see Fig. 8) was connected to the implant. The

matrix of the retentive abutment was attached to the obturator prothesis intraorally using

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autopolymerizing acrylic resin (Ufi Gel Hard, Voco, Cuxhaven, Germany) to ensure passive fit.

As the obturator had been processed on the definitive cast without any functional border

molding, a reline impression using a silicone impression material (Epiform Flex, Dreve-

Dentamid, Unna, Germany) was prepared simultaneously. After wearing the obturator for 3

weeks, nasal leakage reoccurred because of an imperfect seal in the soft palate area. Modelling

plastic impression compound (Ex-3-N, Schopfloch, Germany), was used to mold the borders

during functional movements. The patient was instructed to take a sip of warm water and to

perform functional movements including speaking and swallowing. After the relining, all

surfaces were polished to facilitate cleaning of the prosthesis. As there was no horizontal support

inside of the defect except lower orbita floor (see CT-reconstruction fig. 3) it was decided not to

extend the obturator bulb into the defect for additional support. However it can be expected that

the abutment teeth and the implant offer enough stability and retention. As the main function of

the obturating portion of the prosthesis was to guarantee oral-antral separation and seal, it was

possible to create a light-weight, flat and therefore easy to incorporate obturator bulb. Further

recall appointments were performed at 1 month, 3 months, 6 months and 1 year following

prothesis insertion. No complications such as sinusitis, periimplant mucositis or implant mobility

were detected. There was no loss of sensitivity noted at the abutment teeth. Excellent oral

hygiene was maintained and the patient was instructed and repeatedly motivated to use an

electric tooth brush and floss the angulated abutment head. The patient was also encouraged to

keep her diabetes under control. The patient is satisfied with the treatment result (Fig. 9 and 11)

and happy to resume normal life.

DISCUSSION

17067-rev-edits 7

Prosthetic obturation was the treatment of choice for this young patient. Recent

investigations have confirmed the effectiveness of obturator prostheses in terms of speech,

masticatory function, swallowing and appearance,5,28 especially for small defects.6, 12 There is

evidence that speech can be restored to a preoperative level with a maxillary obturator

prosthesis.4 Nasalance values are markedly influenced by the extent of resection respectively and

particularly by the degree of soft palate involvement.4

The presented patient corresponds to a class I (resection performed along the palatal

midline) according to the Aramany classification of defects,23 with the left central incisor being

preserved. Evaluating the remaining dentition without the supporting implant, a triangle is

formed by the fulcrum line of the prospective framework and the tooth farthest away from the

defect, the canine. Loading of the defect portion of a conventional obturator prosthesis would

have induced considerable non-axial forces on the anchoring dentition. Through placement of the

implant, a more favorable quadripodal support was achieved (see Fig. 7), and leverage was

reduced for the teeth adjacent to the defect.

The presented solution of using a telescopic-crown system offers maximum support and

stability, while offering acceptable esthetics without visible clasps. Because the telescopic

copings are completely embraced and incorporated into the rigid prosthesis framework these

anchoring teeth are loaded axially and are rigidly splinted by the prosthesis. Loading forces are

thereby evenly distributed among the anchoring teeth and the implant and tilting and tipping

forces are minimized. Moreover the teeth and prosthesis are easy to clean and in case of loss of 1

or more abutment teeth, the secondary crowns can be filled with relining material without

compromising function and esthetics. The disadvantages of this type of attachment are the loss of

tooth substance during preparation, a possible overcontouring of the crown and the unesthetic

17067-rev-edits 8

aspect of the uncovered inner golden copings when the prosthesis is not in position. Despite

these disadvantages, the telescopic-crown technique is well established and has good long-term

performance,48, 49 with the reported loss of abutment teeth averaging approximately 10% at 10

years.50, 51 A study comparing clasp-retained RPDs to telescopic-crown retained dentures

showed a higher rate of abutment tooth loss and failure for clasp-retained dentures.49 Technical

problems associated with telescopic-crowns are primarily related to loss of cementation of the

inner crowns and fracture or chipping of the veneering resin.48 As the residual dentition had a

substantial number of restorations the amount of required tooth preparation was considered

acceptable. The traditional alternative would have been to use conventional clasps and rests to

retain the obturator in place and to neutralize adverse cantilever forces. Such a design would

have been much more plaque retentive, thus increasing the risk of caries and gingival

inflammation. The telescopic-crown prosthesis might be more costly to manufacture, but more

cost-effective in the long term.

Due to the quadripodal support provided by remaining dentition and implant it was

possible to avoid complete palatal coverage. The narrow palatal bar connector was less

compromising speech, taste and sensitivity.

The report on the use of zygoma implants penetrating the nasal and antral cavity was

published by Branemark.36 Since then several reports have been published on the clinical

performance of zygoma implants.28, 29, 31, 35, 37-46 The 2 primary indications for the use of zygoma

implants are atrophic edentulous maxillae and defects after maxillary resection.28, 29, 40 Zygoma

implants are generally placed at a 30 to 60-degree angle relative to the occlusal plane.35 To

minimize the large lever arm detailed preoperative planning is mandatory. However, no implant

fractures because of the long lever arm have been reported to date. In the edentulous maxilla a

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“Quad” approach is recommended, supporting a denture with at least 2 implants in the anterior

maxilla in conjunction with one zygoma implant on each side.37, 38, 41, 46 However, unilateral

anatomic conditions unique to the maxillary defect patient might allow the placement of only 1

zygoma implant in combination with 2 to 6 conventional implants, which was reported to be

successful.40 In the presented situation, it was assumed that the stability of the remaining

dentition on the non-defect side is equivalent to what could be achieved with 2 conventional

implants and 1 zygoma implant. Hence, a single zygoma splinted rigidly but secondarily to the

remaining dentition should not be prone to overload. Two zygoma implants on the defect side

would have become a compromise in terms of bone anchorage as the bone quantity was very

limited. In the literature, a primary splinting of 1 or more zygoma implants by a rigid bar

assembly has been described to accomplish cross-arch stabilization, especially in the edentulous

maxilla.24, 29, 38, 40 In the presented patient, the benefits of splinting the zygoma implant to the

remaining dentition are questionable. In the event of failure of a single tooth of such a design or

the implant, repair would be much more complicated than with the telescopic crowns, where

single units are splinted rigidly but secondarily. In addition, the retentive abutment and the

telescopic-crown copings provide improved hygiene access and are more cost-effective when

compared to use of a bar crossing the defect. This concept has been shown to perform well in the

4-year follow-up study by Landes.28 The majority of patients were rehabilitated with prostheses

supported by unsplinted zygoma implants connected either by telescopes or ball attachments.

Cumulative zygoma implant survival was 82% after a follow-up period of 4 years. Four factors

for failure were identified and included: overloading leverage in extensive maxillectomies,

overgrowth of local soft tissue preventing abutment connection, recurrent infection and tumour

recurrence.28

17067-rev-edits 10

Another factor described as crucial for the prognosis of the zygoma implant is soft tissue

management. Thick soft tissue overlapping the implant head can create problems when it comes

to the prosthetic phase of rehabilitation.28, 34 The situation is worse if the implants extend through

soft tissue flaps after palatal reconstruction, creating deep peri-implant pockets which are

predisposed sites for infections.28 In the presented patient, no signs of inflammation were visible

during the follow-up period. In event of implant failure the double-crown retained obturator will

have enough support and retention to function until a new implant can be placed. In the worst

case scenario of a second implantation not being possible, the patient could function with the

prosthesis without any implant at all. An extension of the major connector onto the remaining

hard palate might then be considered to increase support.

There is agreement that the placement of a zygoma implant is more complex and difficult

than conventional oral implant placement.30, 33, 34 Not only the dimensions of the implants, but

also the anatomical intricacies of the curved zygomatic bone, such as the orbital floor and the

limited intraoperative visibility make this type of surgery a demanding procedure.28, 29, 31, 35, 37-39,

41, 43, 44, 46 The surgical procedure can be simplified and facilitated by making use of computer-

assisted planning and surgery.33,42,44,46 A computer-based transfer of preplanned positioning can

be achieved by using drilling guides.33,42,44,46 However when applying this technique the

precision depends largely on the ability to position the drill guide accurately on the underlying

tissue 46. In contrast to the approach with drilling-templates, a computer-aided surgical

navigation approach offers constant intraoperative visualization of the tip of the drilling bur. This

enables the surgeon to precisely guide the drill to control the implant axis and ensure optimum

bone utilization. A cadaver study revealed an accuracy of 1.3 mm (±0.8mm) of the implant

17067-rev-edits 11

position compared to the planned position.47 This result is better than the accuracy reportedly

achieved by using drilling templates.46

SUMMARY

The presented situation demonstrates the interdisciplinary treatment of a patient with a

maxillary defect using conventional prosthetics as well as computer-supported implant surgery.

Although there is scarce data on the long-term performance of zygoma implants, the literature

provides evidence that zygoma implants can reliably anchor maxillary prostheses. This treatment

option provides additional support and retention to a conventional obturator and renders such a

procedure beneficial to the patient.

17067-rev-edits 12

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LEGENDS

Fig. 1. Preoperative situation.

Fig. 2. Preoperative situation.

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Fig. 3. CT- reconstruction showing extent of resection.

Fig. 4. Intraoperative navigation program. The drilling direction is made visible in the CT in

three different planes (upper left figure: frontal plane, lower left figure: coronal plane, upper

right figure: sagittal plane) and a three-dimensional reconstruction (lower right figure) by using a

special pointing device (green). This enables adjustment to the preoperatively simulated zygoma

position (red). The red marker represents the radioopaque marker of acrylic resin template and

indicates the ideal position of implant head.

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Fig. 5. Postoperative CT-scan with acrylic resin template in position. Implant head is ideally

situated above the marker (yellow) of template. Position and angulation of implant in zygoma

bone provide sufficient anchorage.

Fig. 6. Primary crowns on definitive cast.

Fig. 7. Completed prosthesis.

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Fig. 8. Inner telescopic crown copings after cementation

Fig. 9. Completed prosthesis in place.

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Fig. 10. OPT after insertion of the primary crowns

Fig. 11. Facial harmony with definitive prosthesis