Use of long implants with distal anchorage in the skull base for treatment of extreme maxillary atrophy: The remote bone anchorage concept

doi:10.4236/crcm.2013.27108

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Vol.2, No.7, 405-410 (2013) Case Reports in Clinical Medicine

http://dx.doi.org/10.4236/crcm.2013.27108

Use of long implants with distal anchorage in the

skull base for treatment of extreme maxillary atrophy:

The remote bone anchorage concept

Luc Vrielinck1*, Y i Sun1,2, Serge Schepers1,3, Constantinus Politis2,4, Sarah Van Slycke1,

Jimoh Olubanwo Agbaje1,4

1Oral and Maxillofacial Surgery, St. John’s Hospital, Genk, Belgium; *Corresponding Author: [email protected]

2Faculty of Medicine, Hasselt University, Diepenbeek, Belgium

3Oral and Maxillofacial Surgery, Faculty of Medicine, Gent University, Gent, Belgium

4Department of Oral Health Sciences, KU Leuven & Oral and Maxillofacial Surgery, University Hospitals Leuven, Leuven, Belgium

Received 14 July 2013; revised 20 August 2013; accepted 5 September 2013

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

The objectives of t his s t udy are to present a new

concept of the bone anchorage using long im-

plants in remote bone sites and to discuss four

cases treated with this method. Our patients were

treated with long implants with a distant anchor-

age in the skull bone. The planning procedure,

the construction of the drill guide, and the sur-

gical protocol are described. In the clinical

cases described, all four patients were rehabili-

tated with the remote bone anchorage concept

using long implants anchored in the skull base.

Patients were followed for 5 - 12 years and the

implants remained present and stable in these

time periods. The skull base implant is a new

concept of bone anchorage using long implants.

It can be a solution for complicated clinical si-

tuations (often failed bone reconstructions and

implant placements) or an alternative for bone

grafting and maxillary augmentation procedures.

There is effective implant retention in the skull

base, an anatomical area that is often over-

looked for implant placement.

Keywords: Long Implant; Zygomaticus Fixture;

Skull Base Implant; Sphenoid Implant; Maxillary

Rehabilitation

1. INTRODUCTION

Osseointegrated implants are commonly used in oral

and maxillofacial prosthetic rehabilitation [2,3,10]. Al-

though, advanced alveolar bone resorption combined

with increased maxillary sinus pn eumatisation, failure of

bone reconstruction, or maxillectomy procedures often

leave insufficient bone for the standard implant anchor-

age. Some bone graft augmentation methods lead to sig-

nificant patient morbidity, require lengthy healing times,

and are resource demanding [4,8]. The zygoma implant,

introduced by Brånemark, provided a new treatment al-

ternative that eliminates the need for bone grafting pro-

cedures in the lateral part of the maxilla [8,9,11,12].

However, rehabilitation of edentulous patients with

severe maxillary resorption with a fixed implant-sup-

ported prosthesis is only feasible when 2 to 4 standard

implants are placed in the anterior maxilla and splinted

with the zygomatic implants that are placed more poste-

riorly [1,7,13,16]. For patients with extensive bone loss

in the pre-maxilla and lateral bones, implant placement

in defect areas is compromised unless other bone sites

are considered. The use of long implants, which pass

through the p alate and is anchored to th e skull base, may

provide remote distal anchorage that was previously un-

attainable.

Skull Base Implants

The use of conventional implants for local anchorage

is limited to the available maxillary bone. Unfortunately,

because of bone loss or maxillary resection, these an-

chorage sites are not always suitable for the placement of

conventional implants. Subsequent investigation into the

use of remote bone anchorage led to the development of

implants with a distal anchorage in the zygomatic bone

[9,12] and the scaphoid fossa of th e pterygoid bone [15].

Image-based planning and the use of surgical drill guides

or navigation techniques [5,15] can be helpful in select-

ing implantation sites and in drilling distal bone [6,

14,15]. By doing this, it is possible to consider more re-

L. Vrielinck et al. / Case Reports in Clinical Medicine 2 (2013) 405-410

406

mote bone sites lying 3 - 5 cm from the entry point in the

maxilla or the palate. An example of the remote bone

anchorage concept is the skull base implant (like the zy-

goma implant), which was developed for use in patients

with severe maxillary atrophy or challenging maxillary

defects, reconstruction of failed previous bone grafts, or

maxillectomy defects.

2. MATERIALS AND METHODS

Four patients were treated with long implants with dis-

tant anchorage in the skull bone. They all presented with

extensive bone loss due to a failed bone graft, implant

placement, or maxillectomy defect. The majority of im-

plant procedures were rescue treatments following failed

standard implant or augmentation procedures in the max-

illa; while, one patient h ad a maxillectomy procedure for

a malignant tumour.

For implantation, the “zygomaticus fixture” (Nobel

Biocare, Göteborg, Sweden) was used, which is av ailab le

in different lengths, from 30 mm with increasing incre-

ments of 2.5 mm up to 52.5 mm. The head of the implant

has a built-in angulation of 45˚, which mimics the 45˚

inclination towards the occlusal plane in which the im-

plant is inserted (Figure 1). All patients were preopera-

tively evaluated with respect to jaw size, bone volume,

jaw relations, intermaxillary distance, occlusal relation,

and condition of the opposing dentition. A thorough

evaluation of the general health status was conducted to

ensure that the patient could withstand a 2 h operation

under general anaesthesia. Preoperative analysis of the

anatomical conditions and possible pathologies was

conducted with panoramic radiographs and a spiral CT

scan (Somatom Plus S®, Siemens, Erlangen, Germany).

Figure 1. The zygomati-

cus fixture from Nobel Bio-

care.

The digital data from the CT scan were transferred to a

personal computer and a treatment plan was designed to

make optimal use of the remaining bone volumes by

simulation with long implants using Simplant® software

(Materialise, Leuven, Belgium).

A step by step account of the planning procedure is

described below. An implant, represented by a cylinder

with a central axis, was defined using two points named:

the entry and end points. The cylinder diameter corre-

sponded to the diameter of the selected implant (4.5 mm

at the entry and 4.0 mm at the end point for a zygoma

implant). Using the CT-derived surface model of the

maxilla, the surgeon indicated the entry and the desired

end points for the drills. The implant and surrounding

bone was then observed in three dimensions. After plan-

ning, the implant angulation was further adjusted and its

dimensions adapted to obtain the optimal position to en-

sure maximal bone anchorage distally.

2.1. Applied Anatomy

The skull base implant enters the bone midpalatally,

and then follows an intranasal trajectory in a dorso-cra-

nial direction beside the nasal septum. Subsequently, the

implant perforates the inferior wall of the sphenoid sinu s

or body of the sphenoid bone (Figure 2). Uttermost care

has to be taken to ensure proper positioning of the im-

plant. If the apical part of the implant is placed too lateral,

it could perforate the orbit. If the inclination of the im-

plant is placed too vertical, it could enter the ethmoidal

sinus. For an implant directed too horizontally, no bony

structures will be encountered and th e implant could end

up in the nasopharynx.

2.2. Drill Guide

Using stereolithography technology (Materialise,

Leuven, Belgium), the finalized treatment plan was then

used to fabricate the jaw model and a surgical drill guide

with bone or mucosal support (SurgiGuide®, Materialise,

Figure 2. Postoperative radiographic view of a long implant

with distal skull base anchorage.

L. Vrielinck et al. / Case Reports in Clinical Medicine 2 (2013) 405-410

407

Leuven, Belgium). The aim was to create an individual-

ized drill guide that is suited to the patient’s anatomy. A

CAD/CAM program used the shape of the bone and the

3D information of the planned drill paths to design the

drill guide, which is then produced by stereolithography

(Figure 3(a)). Its special design consists of a resin (USP

Class 6 approved) backbone with cylindrical openings

into which stainless steel tubes can be fitted (Figure

3(b)). The inner diameter of the steel tubes is 0.2 mm

greater than the diameter of the corresp onding drill. Each

cylinder’s position and direction corresponds exactly to

the position and direction of the planned implants. Drill-

ing into the bone is performed as a two-step procedure

using two drills of different diameters (2.9 mm and 3.5

mm). Consequently, two sets of 10 mm steel tubes are

provided (3.1 mm and 3.7 mm), 0.2 mm wider than the

diameter of the corresponding twist drill. Prior to surgery,

simulation of the intended operation is carried out on the

stereolithographic maxillary model using the surgical

drill guide. Since the designed drill guide can only be

used to drill the implant trajectories, theoretically the

implant must be placed freehand. In reality, it is very

difficult to find the distal entry point into the sphenoid

sinus or skull base when the distal entry point cannot be

(a)

(b)

Figure 3. (a) Surgical drill guide with mucosa sup-

port in place; (b) Steel tubes with different internal

diameters (3.1 and 3.7 mm) used for drilling the

implant trajector ies.

visualised directly; therefore a second guide was de-

signed with exactly the same supporting surface as the

drill guide, but with larger tubes for insertion of the im-

plant (Figure 4).

2.3. Surgical Protocol

All patients were treated under general anaesthesia

with nasal intubation. The surgical drill guide was fitted

in the jaw and fixated with four or five 20 mm osteosyn-

thesis screws (Leibinger, Freiburg, Germany). Following

installation of the steel tubes in the drill guide, drilling

was performed until the burr penetrated the basilar part

of the spheno id bone. Ho wever, care must be taken not to

drill deeper than originally planned. The surgical drill

guide was then removed before implants were placed and

replaced by the implant insertion guide. The tubes in the

guide were of sufficient width to allow passage of the

implant and implant insertion tool (Figure 4). After the

implant was placed at the correct depth, the implant in-

serting tool was detached and the implant inserting guide

was removed, leaving the implant in place. The implants

used in treating our patients were Branemark zygoma

fixtures, which varied in length from 30 to 52.5 mm. The

fixture head had to b e p os itioned accurately by ob serving

the screw that locked the fixture mount to the fixture.

The screw position duplicated the future abutment screw

position exactly. Finally, the fixture mounts were re-

moved and replaced by cover screws. Antibiotics (clin-

damycin, 900 mg/day) were prescribed for 10 days post-

operatively. To minimize postoperative pain, analgesics

(codeine phosphate and paracetamol) were prescribed for

all patients. In the majority of cases, the need for pain

medication was limited to one or two days. Patients were

instructed to carefully rinse their mouth with chlorhexi-

dine after each meal. After one to two weeks, a clinical

examination was conducted to evaluate the healing pro-

gress. After wound healing, the existing prosthesis of th e

patient was adapted or relined, avoiding contact between

the prosthesis and the coronal part of the implant. After a

healing period of 6 months, the implants were exposed

under local anaesthesia and healing abutments were placed

Figure 4. Implant insertion guide.

L. Vrielinck et al. / Case Reports in Clinical Medicine 2 (2013) 405-410

408

on the implants. Prosthetic rehabilitation was performed

as with regular platform implants. No special compo-

nents were needed. The prostheses connecting the skull

base and other implants were constructed with a passive

fit and all implants were joined together as soon as pos-

sible after they were exposed.

During the last fifteen years four patients have been

treated with long implants and skull base anchorage. An

overview of these patients is presented in Table 1 and

described below.

2.4. Case 1

The first patient was a 62-year-old female with an

atrophic upper jaw. Her first treatment occurred in 1995

and consisted of placing 4 regular implants in the maxil-

lary bone. After 2 years, all the implants failed. In 1999,

the patient underwent a secondary surgery containing

maxillary bone augmentation with iliac crest bone and

simultaneous placement of 4 regular implants, 2 zygoma

implants, and 2 tuberosity implants.

The tuberosity implants and left zygoma implant were

not osseointegrated and were removed after 6 months.

There was no good prosthetic solution for the upper jaw

for 3 implants; therefor e, at the end of 2000, the decision

was made to replace the left zygoma implants and place

2 pterygoid and one skull base implant (Figure 5). The

patient was followed for 12 years and the implants and

supra-structure remained stab le in the jaw.

2.5. Case 2

The second patient was a 69-year-old female with an

aggressive maxillary adenoid cystic carcinoma. She un-

derwent a right hemimaxillectomy operation in 2001

followed by post-operative radiotherapy. A year later, 7

implants were placed: 1 zygoma implant and 1 pterygoid

implant on the right side and 5 regular implants in the

remaining maxilla. In 2004, the right zygoma implant

and 2 regular implants were removed due to chronic in-

flammation. To obtain good support for the prosthesis,

one pterygoid and one skull base implant were placed

(Figures 6(a) and (b)). The implants remained stable and

functional for five years when the patient died from brain

metastasis.

2.6. Case 3

The third patient was a 61-year-old woman with ex-

tremely atrophic upper and lower jaws. The treatment

plan consisted of a sandwich osteotomy of the lower jaw

and a Lefort 1 osteotomy of the upper jaw with inter-

positional bone grafting. The operation took place in

1997. After 6 months, 5 implants in the lower jaw and 6

implants in the upper jaw were placed. After 2 years,

there was continuous failure of the upper jaw implants

and she gradually lost all these implants. To restore the

prosthetic retention again, 6 implants were placed: 2 zy-

goma implants, 2 pterygoid implants, and 2 paranasal

implants. At the end of 2001, the left paranasal implant

failed. There was no longer good prosthetic retention;

therefore, 2 skull base implants were placed. After 11

years of follow-up, the prosthesis and implants remain

stable and functional.

Figure 5. Postoperative OPG of patient 1.

Table 1. An overview of the case patients.

Case Age Sex Reason for treatment Problem Date of

treatment Implant

treatment Follow-up

time Condition at last

follow-up

1 62 F

Failure of regular implants

and bone grafts

Bone defect in

premaxilla, atrophy

of lateral bones 26. 10. 20002 zygoma

2 pterygoid

1 skull base 12 years Implants present

and stable

2 69 F

Loss of regular and

zygoma implants after

hemimaxillectomy for

adenoid cystic carcinoma

Defect in

premaxilla, left

lateral bone defect 31. 01. 20054 standard

1 zygoma

1 skull base 5 years Implants present

and stable

3 61 F

Failure of regular implants

after interpositional bone

grafting

Bone defect in

premaxilla, atrophy

of lateral bones 2001 2 pterygoid

1 skull base 10 years Implants present

and stable

4 65 F

Failure of regular implants

after maxillary

augmentation

Bone defect in

premaxilla, atrophy

of lateral bones 16. 05. 20022 pterygoid

2 skull base 11 years Implants present

and stable

L. Vrielinck et al. / Case Reports in Clinical Medicine 2 (2013) 405-410

409

(a)

(b)

Figure 6. (a) Postoperative PA of patient 2; (b)

Obturator to close maxilla defect.

2.7. Case 4

The fourth patient was a 65-year-old woman. The

maxillary augmentation procedure and placement of 6

implants were performed for the patient in another centre.

The patient lost 3 left implants due to in fection. She was

informed about the poor prognosis of the prosthesis due

to the unilaterally placed implants; however, she was

satisfied with the prosthetic solution she had. In 2002,

she lost another implant on the right side due to the un-

favourable forces of the prosthesis. At that time, a new

treatment plan was made with the placement of 4 stan-

dard implants, 2 pterygoid, and 1 skull base implant. The

implants and prosthesis were stable after 10 years of fol-

low-up.

3. DISCUSSION

It is well known that the placement of long implants

with zygomatic or pterygoid anchorage is more complex

and difficult than conven tional oral implants. Man y max-

illofacial surgeons are not familiar with the anatomy of

the sphenoid bone and skull base region, which makes it

unlikely that these bone structures will be chosen as an-

chorage points for long implants. Implant placement in

this region demands excellent surgical skills, profound

anatomical knowledge, and good three dimensional

simulation skills using image-based implant planning

software.

As a rule of thumb, two zygoma implants are com-

bined with three or four anterior standard implants (Fig-

ure 2). When a patient presents with anterior and poste-

rior bone atrophy, the current treatment plan involves

using the quad zygoma technique, which can be used as

long as enough anch orage is present in th e zygoma bone.

When combining zygoma and pterygoid implants, 0 - 2

standard implants may be added anteriorly [1,4,5,8,10,

11]. In cases with severe anterior bone loss and failed

anterior implants, there may not be a sufficient amount of

bone to provide anchorage for new implants. In such

cases, it is possible to obtain additional anchorage by

adding 1 or 2 skull base implants.

Placing skull base implants cannot be done without the

use of computer-assisted planning and guided surgery.

The time necessary to prepare the implant planning using

the Simplant® software depends on the user ’s experience.

Actual implant planning typically took between 30 min

and 1 h. Computer-assisted planning allows the surgeon

to use the maximum amount of sphenoid bone for im-

plant placement and also to identify and avoid adjacent

anatomical structures. This technique is precise enough

but the precision depends largely on the ability to posi-

tion the drill guide accurately on the underlying tissue

[10]. This technique is also highly dependent on the

user’s experience. In this aspect, more recent develop-

ments like navigation systems are important since this

allows for an intra-operative check of the drilling direc-

tion, which is not the case with a drill guide.

The skull base implant follows an intra-nasal trajec-

tory beside or through the nasal septum. Although the

implants may partially occlude the nasal passageway, no

complication has been recorded and none of the patients

complained of a nose obstruction. This may need further

attention if a patient has breathing problems before im-

plant placement. Intra-orally, the implant emerges in a

nearly mid-palatal position, allo wing for a fixed structure

like an overdenture. As a rule these implants are rigidly

splinted to the remaining other implants to achieve good

cross arch stabilisation. In most cases, a fixed removable

overdenture is used. This not only allows the chewing

function to be restored but also provides support for the

soft tissue of the face. It can also function as an obturator

for closing intra-oral defects.

The patients presented here are examples of extremely

complicated clinical cases with many previous recon-

struction procedures including: regular implants, bone

grafting, and zygomatic and pterygoid implants. Despite

these procedures, proper maxillary rehabilitation could

L. Vrielinck et al. / Case Reports in Clinical Medicine 2 (2013) 405-410

410

not be achieve d and patie nts searched for bett er treatment

options. In one of the patients, the tumour resection left

no room for a bone graft or implants. With the aid of the

skull base implant, this complex and challenging patient

was rehabilitated. The most significant and immediate

benefit of this approach is the ability to extend the pros-

thesis anchorage points into the mid-palatal area, thus

minimizing the can tilever forces on teeth and implants in

residual ridge tissue. The skull base implant supplements

this concept by creating effective retention in an ana-

tomical area that otherwise could be overlooked for im-

plant placement.

4. CONCLUSION

A skull base implant is a new concept of bone an-

chorage using long implants. It can be a solution for pa-

tients presenting with prosthetic and implant challenges

due to sequelae of a maxillectomy, failed reconstruction

combined with scaring and fibrosis due to previous

treatments, and a lack of bone in the maxilla. In most

cases, judicious use of the remaining bone (sometimes

distant to the maxilla) may be a solution for these pa-

tients.

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