CONTROVERSIA II

 

Alternatives to maxillary sinus lift: posterior area of the atrophic maxilla rehabilitation by means pterigoideal implants

Alternativas a la elevación de seno maxilar: rehabilitación del sector posterior del maxilar atrófico mediante implantes pterigoideos

 

 

X. Rodríguez-Ciurana¹, X. Vela Nebot², V. Mendez³, M. Segalá⁴

1 Cirujano Oral y Maxilofacial. Práctica privada en Barcelona. España
2 Odontólogo. Practica privada en Barcelona. España
3 Odontólogo. Practica privada en Madrid. España
4 Estomatóloga. Practica privada en Barcelona. España

Dirección para correspondencia

 

 

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ABSTRACT

The first and second molar are the teeth most commonly lost in the maxilla, mainly due to periodontal disease and excessive occlusal force. 1 Although partial edentulism of the posterior maxilla is common, implants are seldom placed distal to the premolars because failure rates in the posterior maxilla have historically been high. Poor volume and low density of bone are the worst conditions for long-term anchorage in the maxilla. 7 Moreover, bone under the maxillary sinus, in the atrophic maxilla, is usually insufficient to enable placement of 10 mm implants.
Several techniques have been proposed to restore the atrophic posterior maxilla: short implants, prosthetic cantilevers, sinus bone graft, zigomatic fixtures. Pterygoid implants are other possible treatment of the atrophic edentulous posterior maxilla. Anchored in the cortical bone of the pterygoid process, such implants avoid the need for bone grafting and/or prosthetic cantilevering. The aim of this article is to analyst indications, surgical procedure, complications and survival rates of pterygoid implants in the posterior atrophic maxilla.

Key words: Pterygoid implant; Atrophic maxilla; Pterygo-maxilla buttress.

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RESUMEN

El primer y segundo molar son los dientes que se pierden más a menudo debido a la enfermedad periodontal y al exceso de fuerzas oclusales. A pesar de la frecuencia del edentulismo parcial del sector posterior raramente se ubican los implantes más allá de los premolares debido al aumento del índice de fallos. El escaso volumen óseo y la pobre mineralización del sector posterior del maxilar comprometen la viabilidad de las rehabilitaciones con implantes a largo plazo. Además, la cresta ósea a nivel del seno maxilar, en el maxilar atrófico, no suele permitir el anclaje de implantes de 10 mm.
Se han propuesto varias técnicas para rehabilitar el sector posterior del maxilar atrófico: implantes cortos, extensiones protésicas, injerto sinusal, implante cigomático. El implante pterigoideo es otro de los posibles tratamientos para rehabilitar el sector posterior del maxilar atrófico. Anclado en el hueso cortical de la apófisis del esfenoides el implante pterigoideo evita la necesidad de injertar o utilizar extensiones protésicas. El objetivo de este artículo es analizar las indicaciones, la técnica, complicaciones y supervivencia del implante pterigoideo en el sector posterior del maxilar atrófico.

Palabras clave: Implante pterigoideo; Maxilar atrófico; Arbotante pterigomaxilar.

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Introduction

The loss of teeth implies progressive bone resorption that occasionally complicates or prevents the immediate collocation of implants. This fact becomes more accentuated in the posterior maxilla. This area is considered one the most difficult area for rehabilitation.¹

The main anatomic characteristics that complicate the rehabilitation of the atrophic maxilla are: the sinus of the maxilla, the resorption of the bone crest, and the reduction of the bone trabecula. The functional characteristic that makes the rehabilitation of the posterior maxilla more difficult is the big intensity of the chewing forces generated during the mastication. Even a 10mm fixture in a well-developed tuberosity cannot provide long-term osseointegration.²

In order to solve the important anatomic deficiencies and to withstand the forces applied over the posterior area, nowadays we can use different surgical and prosthetic techniques to rehabilitate these patients.

The use of short implants, cantilevers, zygomatic implant or pterygoid one and allows the rehabilitation of the posterior maxilla in a short period of time.^3-8

Bone graft apposition, interposition and sinus bone graft achieve to restore the posterior area of atrophic maxilla increasing the time due to the healing process and the osseointegration.^9,10

The purpose of this article is to define, taking into account the literature and our experience, the indications, contraindications, to describe the surgical technique and the complications of the pterygoid implant.

 

Definition of pterygoid implant

Pterygoid implants are 13 to 20 mm fixtures length when located in pterygoid process allow the prosthetic rehabilitation without graft in posterior maxilla.⁶ They need mesial abutment usually located in the premolar area. This technique consists in using the near compact bone (pterygoid process – palatine bone) as a fixture support.⁷ When we use this technique its not necessary to harvest the compact bone from donor site to the sinus. The applied forces go to the pterygomaxillar buttress and they spread to the skull. Tulasne placed the first pterygomaxillary fixture in May 1985 at the suggestion of Paul Tessier.⁶ This was a rescue fixture in a patient who has lost several fixtures previously placed in a full iliac bone graft.⁶

Anatomy of the pterylo-palato-maxillar region.

In order to achieve the best fixture position, the implant needs go through the tuberosity, bone palatine and finally ends in pterygoid process.¹¹ (Fig. 1). Therefore, there are three bones implicated in this technique but only one anatomic area.

Pterygoid processes are two more compact bone columns than superior maxilla. They go down from the sphenoid bone to the lower area. The pterygoid process is compound by three parts: upper base, wing and pterygoid groove. The distance from the alveolar crest at second molar level to the medium region of pterygoid process is usually 15 mm. Due to this, at least 13 mm of length is necessary to reach the pterygomaxillar process. Only by this way the fixture will be called pterygoid implant¹¹ (Fig. 2).

Anthropometrically the position of this bone column compound by the tuberosity, the palatine bone and the pterygoid process, has been analyzed and the angulation change according to presence or absence of the dentition. In dentulous maxilla, there is no reabsortion then, the tuberopyramid- pterygoid column angulation is 76,5±SD 3,0º in mesio-distal way respect to the Frakfurt plane and 17,2º ±SD 2,7º of bucolingual angulation. ¹² In edentulous maxilla, the column angulation is 67,3º ±SD 5,0º in mesio-distal way respect to the Frankfurt plane and 14,1º ±SD 2,1º of bucolingual angulation¹² (Fig. 2).

The piramidal process conforms the pterygomaxillar suture width. Pterygomaxillar suture in the half lower part is compound by three bones: tuberosity, pyramidal process and pterygoid process. If we observe these bones in lateral view, we can find four different shapes:¹³ (Fig. 3).

• Type I: equilateral triangle shape

• Type II: rectangle triangle shape

• Type III: narrow rectangle triangle shape

• Type IV: there is no shape in lateral vision.

In caudal vision, we can distinguish three types:¹³

• Type I: equilateral triangle shape

• Type II: rectangle triangle shape

• Type III: narrow rectangle triangle shape.

According to Lee, the length of the pterygomaxilar suture or the pyramidal palatine bone process height is 13,1 mm and the antero-posterior width is 6,5mm. 45 (83%) of the 54 mesured skulls by Lee, showed higher height than 10 mm.¹³

Technique

The original technique described by Tulasne, consists in expose the maxilla tuberosity and begin a drilling by a straight handpiece in posterior direction (45º) and oblique (15º) to palate.⁶ Recently, has been proposed to put the implant in more vertical position.^14,15 In base on a prospective study in 135 pterygoid implants and the anatomical Yamakura’s study, it is propose to verticalize the implant until 70º in the mesio-distal axis^12,15 (Fig. 4). In this way, we diminish non axial forces and we situate the implant through the tubero-palatopterygoid column.¹⁴ After 10 mm of penetration it is possible to appreciate the resistance that high density bone offers and it is necessary to increase the pressure over the handpiece until reach pterygoid process. This point will be the limit of the fixture that usually is 18-20 mm of length. After 2, pilot and 3 mm drills of 20 mm of length are used the implant of correct length could be installed. The time of healing before loading is about 2 or 3 months. In second stage, it is necessary to remove the gingival until obtain 3-4 mm of width. This detail not only diminishes the periimplantitis risk but also allows the harvest of soft tissues to improve periodontal biotype where it is needed. The distal emergence of the Pterygoid implant allows establishing a prosthetic tripoidism. The success of this technique is between 88 and 98%^6-8,11,14-19 (Figs. 5 and 6). Sometimes, it is necessary to use angulated abutments in the prosthesis.

The Pterygoid implants could be indicated when a anterior pillar be present (implant or tooth) nearly to support the prosthesis mesially.⁶

Contraindications of this technique are the same as whatever standard implant rehabilitation and the lack of bone in pterygomaxillary area.

 

Complications

In our 135 implants cases, there were only three complications. The first, was a great intraoperatory bleeding that stopped with the implant location. The second was a palatine nerve hypoesthesia that was over in 4 weeks and the third was a pain that needs to remove the implant.¹⁵

Some authors related the difficult prosthetic process as a complication.¹⁰ Raspall described 2 abscesses in 238 cases of pterygoid implants.⁷

 

Discussion

The techniques to restore the posterior atrophic maxilla can classify according to bone graft was need or not.

Techniques without graft

Short implants. The use of short implants is possible where a minimum basal bone was present. Commonly there is not bone length enough to ensure putting an implant of 7 mm.²

The cantilevers use raises non-axial forces and make results get worse at middle term. Eckert highlights the fracture high risk and unadvices the use of cantilevers.²⁰ The measures already made on the prosthesis in edentulous maxilla, suggest that it is better to place the implants along the maxilla arch. It is more recommended to put the implant at the tuberosity level to avoid cantilevers than focusing them in the anterior maxilla and apply a cantilever.²¹

The cygomatic implant allow the posterior maxilla rehabilitation without bone graft and it doesn’t make the waiting time longer that it is necessary in bone graft techniques. The cigomatic implants are usually placed at premolar level. Frequently they need cantilevers to reach the necessary length.⁵

The main advantage of the non-bone graft techniques is the short healing time, lesser than 6 month. As disadvantages must be noted the minimum bone high, cantilevers dependence and the use of the general anesthesia in the cigomatic implants.

Bone graft techniques

The sinus bone graft technique is the most extended one to get the rehabilitation of the atrophic posterior maxilla. It was described by Boyne in 1980. It consists in the harvest of bone from the donor site (tuberosity, chin, ramus, calvarium, iliac crest) to the maxillary sinus through Cadwell- Luc approach.⁹

There are many studies that give as a result different success indexes of the osseointegration. It is difficult to compare the results due to the different techniques, observation period, donor sites and biomaterial. Acero presents a series of 50 sinus bone graft cases and the placing of 89 implants.¹⁰ In the group of patients where the implants were placed at the same time as the sinus bone graft the index of osseointegration success was 91%.¹⁰ In the group of patients where the implants were placed in second stage the index of osseointegration success was 97%. Johansson gets 75% of success in sinus bone graft technique.²² Chan presents a series of 105 implants observed during 5 years and obtains an 84% of success.²³ Triplett gets an 82% of success in sinus bone graft it is made in the same surgery and 90,8% in two steps.²⁴

The histomorphometric studies show that the percentage of new bone origined from the graft and the bone to implant contact are less the native bone.²⁵ The time for rehabilitation by this technique depends on volume of the bone and the kind of graft.²⁵

The sinus bone graft advantages are mainly to place the graft on it is necessary end a good success results. As disadvantages must be noted that it is necessary a greater number of surgeries, the harvest area morbility and the increasing time of healing tissues.

Pterygoid implants belong to the non-graft techniques and its main characteristics make us consider the Pterygoid implant as first choice in most cases. The osseointegration index is very high to the atrophic maxilla, a mean of 95% between different series.^6-8,11,14-19 Nowadays short healing time and low morbility are goals of modern implantology. Pterygoid implant has both characteristics. The healing time for ossseointegration is the same as the needed for cortical bone. It has been published the immediate loading and implant- tooth prosthesis associated to pterigoid implant.^17,26 The local anesthesia diminishes the morbility and the costs of the treatment, making this a very attractive technique.

The good blood supply of the pterygomaxilar area and the low antrophometric variability made that pterygoid implant can be chosen in most cases.

The pterygoid rehabilitations avoid the cantilevers and improve the results at middle- long term. Biomechanically, the forces transmitted from the Pterygoid implant through the pterygomaxillary buttress are very similar to the forces transmitted from the 2nd and 3rd molar which have a 20º to distal.²⁷ If the tuberosity has cortical bone at level crest the biomechanical behavior will be as bicortical implant.

The disadvantages of this technique are mostly pterygomaxilary area anatomic knowledge to get a good anchorage. ⁶ A CT is advised to study the region and its limits. Sometimes, a special skill is needed in the prosthetic procedure due to the emergency to the tuberosity level.⁸

For a good periodontal health a good cleaning of the abutment is highly advised.

 

Conclusions

In short, pterygoid implant is a good technique to rehabilitate the posterior area of the atrophic maxilla and shows a low morbility and complications. It doesn’t need general anesthesia and the successful index of this technique is higher than others techniques. Pterigoid implant avoids the bone graft, keep the sinus integrity and allows the second stage at 4 months.

 

 

Dirección para correspondencia:
Cambra-Clinic.
C/ Ganduxer 122
08022 Barcelona. España
E-mail: 30903xrc@comb.es

Recibido: 6.10.08
Aceptado: 20.10.08

 

 

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