Implants in anatomical buttresses of the upper jaw
Implantes en arbotantes anatómicos del maxilar superior

 

Marco Sorní ⁽¹⁾, Juan Guarinos ⁽²⁾, Miguel Peñarrocha ⁽³⁾

(1) Odontólogo. Master de Cirugía e Implantología Bucal. Facultad de Odontología de la Universidad de Barcelona
(2) Profesor Asociado de Cirugía Bucal. Profesor del Master de Cirugía e Implantología Oral.
Facultad de Medicina y Odontología de la Universidad de Valencia
(3) Profesor Titular de Estomatología. Director del Master de Cirugía e Implantología Oral.
Facultad de Medicina y Odontología de la Universidad de Valencia

Address:
Miguel Peñarrocha Diago
Clínica Odontológica
Gascó Oliag, 1
46021 Valencia - Spain
Tel. 963864175
Miguel.peñarrocha@uv.es

Received: 12-05-2003. Accepted: 14-03-2004

 

 

INTRODUCTION

The atrophic upper jaw may pose serious difficulties for conventional implant placement, due to pneumatization of the maxillary sinuses, the presence of the nasal fossae and centripetal maxillary reabsorption often associated with type III or IV quality bone according to Lekholm and Zarb (1). The solutions proposed for rehabilitating such regions comprise sinus lifting with bone grafts (2-5), the use of short implant lengths (6), increased implant diameters (7,8), and the placement of implants in anatomical buttresses. This latter technique has undergone considerable development particularly in recent years. The present study presents a review of the literature on implant insertion in anatomical buttresses of the upper jaw.

ANATOMICAL BUTTRESSES

The skull presents a series of dense bony buttresses that conform a protective frame around the different craniofacial cavities (orbit, nasal fossae or passages, oral cavity and paranasal sinuses) with mostly fragile walls. These buttresses distribute forces through the solid facial bone structure, and are distributed strategically throughout the three facial thirds of the skull. In this context, the middle third portion presents two anterior buttresses (frontomaxillary and frontozygomatic) and a posterior buttress (pterygomaxillary).

FRONTOMAXILLARY OR CANINE BUTTRESS

This support or abutment originates in the alveolus of the upper canine, following along the lateral margin of the piriform aperture, forming the frontal process of the upper jaw and merging with the medial margin of the supraorbital arch. The lower portion is interpositioned between the nasal cavity and the maxillary sinus, and is triangular in shape. This region normally presents a compact cortical layer and dense medullary bone - thus allowing the placement of long implants with parasinusal angulation (9). The surgical process consists of implant positioning with distal angulation, seeking bicorticalization with the floor of the maxillary sinus or nasal fossa. In these cases osteodilators are of great help in preparing the implant bed - particularly in patients presenting narrow alveolar crests (10). Krekmanov and Rangert (11) introduced implants parallel to the anterior wall of the sinus, combined with vertical implants in the anterior region, in a series of 20 patients. This procedure made it possible to extend the fixed prosthesis more than 9 mm. No implants were lost during the two years of follow-up.

Mattsson et al. (12) conducted a similar study in which anterior implants were placed in combination with tilted implants positioned in the canine region in 15 edentulous patients. To this effect the authors opened a window in the maxillary sinus to explore the anterior wall of the sinus, and introduced the implant in the zone of the canine or first premolar, adopting a mesiodistal angulation and slightly palatal orientation - leaving a few implant threads exposed in the coronal portion. Four to 6 implants were placed in each patient. After an average follow-up period of 45 months, only one implant was lost, and all the fixed prostheses remained stable.

Guarinos et al. (13) described a variant of this technique based on the use of osteotomes, in three clinical cases. According to the authors, the main advantage of this approach was that it allows upper jaw expansion in patients presenting narrow alveolar crests or concavities.

Krekmanov et al. (14) positioned 138 implants in 22 atrophic upper jaws. Forty of these implants presented a parasinusal angulation, following the curvature of the maxillary sinus. The implants were exposed after 6 months, with the positioning of fixed prostheses in all cases. Over a four-year period 5 non-angulated and a single angulated implant were lost - yielding a success rate of 92.5% and 95.7%, respectively. The authors commented that the technique offers the advantage of reducing the prosthesis cantilever, with increased corticalization, superior primary stability, and the application of longer implants.

FRONTOZYGOMATIC BUTTRESS

This support is located in the region of the upper first molar, forming the so-called zygomaticoalveolar crest, which continues laterally along a concave trajectory to the zygomatic process of the maxillary bone and, posteriorly, to the zygomatic bone. The lower portion of this buttress is formed by the lateral wall of the maxillary sinus, which usually consists of compact bone. Two management options exist in this region:

a) Implant placement in the palatal vault

This techniques involves positioning a tilted implant in the region of the first molar, using as anchorage palatal bone - which is entirely composed of cortical bone. Krekmanov (15) published a series of 75 implants in 22 atrophic upper jaws. Fifty-four implants were tilted: 19 in the palatal concavity, 11 in the anterior sinus wall, 10 in the posterior wall and 14 in the pterygoid process. After 4-5 months of follow-up, three non-angulated implants failed to osseointegrate (one positioned in the palatal vault) and another was lost upon loading. The global implant survival rate was 94.7% after an average follow-up of 18 months.

Perales and Aparicio (16) conducted a retrospective study of 25 patients involving 101 implants - 59 in an axial position and 42 in a tilted position. In all cases rehabilitation was carried out by placing fixed partial prostheses without cantilevers. After a mean follow-up of 33 months, cumulative success rates of 95.2% and 91.3% were recorded for the tilted and axial implants, respectively. On the other hand, 55.2% of the prostheses developed mechanical complications - all such problems posteriorly being resolved. The authors concluded that it is important to interconnect the implants by means of the prosthetic superstructure, which acts as a rigid splint. On the other hand, they considered this management approach to be simpler, less costly and faster to complete than the maxillary sinus floor lifting technique.

b) Transzygomatic implants

This new technique involves insertion of an implant measuring 35-55 mm in length in the palatal region of the second premolar, anchored in the zygomatic bone after an intrasinusal trajectory. At present, such implants must always be positioned bilaterally in combination with at least two implants in the anterior region, splinted by means of a prosthetic superstructure. Aparicio and Malevez (17), in a series of 29 clinical cases, described the surgical and prosthetic elaboration characteristics of this technique.

Parel et al. (18) in turn conducted a retrospective study of 65 zygomatic implants placed in 27 patients (24 subjected to maxillectomy, and 3 with alveolopalatal fissures), obtaining a percentage survival of 100% after a minimum follow-up of 6 years.

At present this technique is also indicated in edentulous patients with intense bone resorption in the posterior zone, where the placement of two zygomatic implants can be associated to four anterior sector implants, without having to resort to grafting. It has also been used in patients with total dental agenesis attributable to some syndrome or to genetic alterations. Balshi and Wolfinger (19) reported the case of a 20-year-old patient with ectodermal dysplasia who underwent rehabilitation with two zygomatic implants in combination with four anterior implants and two implants in the pterygomaxillary zone - thus avoiding maxillary reconstruction with grafts.

Stella and Warner (20) described a variant of the technique in which the implant is positioned through the sinus via a narrow slot, following the contour of the malar bone and introducing the implant in the zygomatic process. In this way the need for fenestration of the maxillary sinus is avoided, and the implant is made to emerge over the alveolar crest at first molar level, with a more vertical angulation. The authors considered this variant to afford increased contact between bone and implant, optimum implant positioning, and a better postoperative course.

PTERYGOMAXILLARY BUTTRESS

The pterygomaxillary buttress comprises three structures: the tuberosity, pyramidal process of the palatal bone, and the pterygoid process of the sphenoid bone. The tuberosity is usually composed of scantly dense medullary bone with a very thin cortical layer - as a result of which it is normally not an ideal structure for implant placement. The pyramidal process of the palatal bone is joined to the anterior portion of the pterygoid process, and is interposed between the lower portion of the latter and the tuberosity. Both structures are located in the posterior and medial zone of the tuberosity, and are composed of corticalized bone. Above this junction lies the pterygopalatal fossa, which contains the terminal portion of the internal maxillary artery. Tulasne in 1989 described the technique for placing implants in this region (9). According to this author, the pterygomaxillary implant should anchor in the pterygoid process or even traverse the latter - avoiding the posterior portion of the sinus and major palatal duct. To this effect, the implant should be directed posterior, superior and medial. The length of the implant is normally between 15 and 20 mm. Tulasne recommended general anesthesia when performing the technique, due to the risk of damaging the posterior palatal artery and causing important bleeding. The latter ceases after placing the implant proper. This same author published a series of 52 implants placed over a period of 6 years; of these implants, 43 were exposed, yielding a single failure in a second phase and two further losses after one year of loading. There were no postoperative complications (21). Graves (22) in turn presented a series of 64 implants positioned in 49 patients, with the recording of 7 failures - all after implant loading.

Balshi et al. (23) placed 51 implants in 44 patients, with a follow-up of 1-64 months after the second surgical step. The success rate was 86.3%. There were 7 failures: 6 in a second phase, and one implant which was removed after three months of loading due to patient referred discomfort in the area - though the implant was seen to be osseointegrated. Most of the lost implants had been positioned in type IV bone. Marginal bone loss was no greater than in the case of other implants positioned in the anterior sector.

Pi (24) published the results of 177 pterygomaxillary implants in 136 patients, with a follow-up of 1-10 years. The success rate was 97.2%. Four implants were removed in the second phase, and one was removed due to fracture after three years of loading.

Fernández and Fernández (25) described the technique using osteotomes in place of surgical drills. This procedure reduced the surgical risks (particularly as regards bleeding), due to its less traumatic nature.

Balshi and Wolfinger (26) placed 356 pterygomaxillary implants in combination with 1461 anterior implants in 189 edentulous upper jaws. After an average follow-up of 4.68 years, 41 pterygomaxillary implants failed to osseointegrate, and one was lost after loading - yielding an 88.2% implant survival rate. No intraoperative complications were recorded.

Vila-Biosca et al. (27) compared pterygoid implants with the sinus lift technique. The authors explained the main indications, advantages and inconveniences of both procedures. They considered the pterygoid implant technique to be less invasive, with a usually shorter intervention time and interval to patient rehabilitation.

Other Spanish authors, concretely Mateos et al. (28), also conducted a review of the literature on pterygoid implants. On the other hand, they developed a protocol with a detailed description of the technique and prosthetic procedure.

Nocini et al. (29) presented a clinical case in which they described the placement of pterygomaxillary implants using modified osteotomes. A handle tilt angle of 20 degrees allowed better osteotome adaptation to the anatomy of the oral cavity, reducing the risk of damaging the lips or cheek mucosa, and facilitating the work of the dental surgeon. The authors considered the main advantage of these osteotomes with respect to drills to be the lesser risk of damaging the palatal artery - though this affirmation has not been clinically demonstrated.

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