The Pterygoid/Tuberosity Implant

The first use of an implant placed in the pterygo-maxillary region was documented by Dr. Tulasne at the suggestion of Dr. Paul Tessier in 1985,¹ only 3 years after the introduction of the concept of osseointegration to North American practitioners at the Toronto Conference in 1982. By necessity, these implants needed to be angled toward the anterior part of the mouth for access and to create the greatest possible length of implant-bone contact.

Successful placement of an implant in this area requires a volume of bone in the tuberosity region that will accommodate an implant without fenestration laterally. Due to the angulation of placement, however, it is not uncommon to have an implant length capability of 13-15 mm. There are even variants of this procedure using engagement of the sphenoid bone, through a guided approach, that allow placement of implants 20 mm or longer.²

The emergence of this implant into the oral cavity may appear to be problematic for access due to the distalized position of the fixture. In clinical practice, however, there is seldom a limitation for engaging the screw access hole with the use of angled abutments and contra-angle drivers. Occasionally, the tilt of the pterygoid implant is such that straight drivers can be used for direct screw access.

Indications

The pterygoid implant generally is used where posterior support for a full-arch prosthesis beyond the first molar is required. The placement of dentition in the area of emergence of this implant is seldom required, but the additional support gained with a beam extension can eliminate cantilever stresses that can be difficult to counter when opposing second molar occlusion is present (Figure 23-1).

Figure 23-1. A, The preoperative radiograph of a patient presenting for implant therapy in the maxillary arch shows opposing natural dentition back to the second molar. B, Provisional restoration is anchored on the anterior five implants with two pterygoid implants placed to allow extended cantilever support in the distal region. C, Provisional restoration intraorally shows the premolar occlusion is established with minimal molar contact in the areas beyond the distal implant connection. D, Completed restoration on the master cast with a bar extension of the framework to the distal implants in the pterygoid region. There is no need to add additional dentition beyond that which is already set, so the bar extensions can remain uncovered. E, The final restoration in place with radiographic evidence of adequate fit and passivity against all implants. F, Final restoration in place with first molar occlusion bilaterally supported distally to the second molar by the pterygoid extension.

This is generally a niche concept, but one that can be very valuable in prosthesis design and construction when additional cantilever support is necessary. As seen in the existing literature specific to the pterygoid approach, there are reported rates of implant success varying from the 92.7% initially seen by Tulasne to between 67% and 93% success in more recent papers.³^–⁸ Although probably not considered a mainstream approach due to a lack of universal application, it is still valuable in specifically indicated situations. When tuberosity bone is available, the use of the pterygoid implant may eliminate the necessity for sinus grafting, which is often a desirable option if the preference of the patient is to avoid a graft approach.

The Zygoma Implant

The implant was first created and used by Professor P.I. Brånemark in the late 1980s as a means of creating prosthesis stability in maxillary arches compromised by trauma or the ravages of oral cancer. It remained a specialty product for nearly 10 years, and was introduced commercially only after other more conventional applications were discovered.

The original design was a stepped, straight, hex-head implant that varied in available lengths up to 50 mm (Figure 23-2). The zygoma implant, as currently used, has an oxide enhanced surface and a premachined 45 degree angled head for improved screw access intraorally (Figure 23-3). The concept is to engage the zygomatic buttress with 11-13 mm of osseointegrated surface apically, and, after passing through the sinus, engage the alveolar and palatal bone in the first molar area coronally. Once integrated, the zygoma implant can provide significant distal support for a variety of clinical applications due to the length and strength of the fixture itself. As with the pterygoid approach, the need for sinus grafting to gain osseous volume and distal implant positioning is often eliminated.⁹^–¹⁶

Figure 23-2. The original zygoma implant was straight with a hex-head connection at the coronal surface. This was a very difficult implant to restore in its original design form due to the difficulty in creating a path of insertion against the straight head hex on the implant base as it emerged into the oral cavity at a 45-degree angle.

(Historical photo courtesy Nobel Biocare, Yorba Linda, CA.)

Figure 23-3. The modification of the head of the zygoma implant introduced in the late 1980s was machined to a 45-degree angle, which greatly facilitated intraoral access and connection to a fixed prosthesis.

(Historical photo courtesy Nobel Biocare, Yorba Linda, CA.)

Indications

Cancer

In situations of severe injury or ablative cancer surgery, the zygoma implant can play a critical role in creating a retentive base for prosthesis construction. In many presentations, these patients have minimal or no available alveolar bone, and thus are severely compromised in normal eating or speaking activities. Originally, restorations created before implant availability were only marginally successful, and were dramatically challenged in terms of retention and defect obturation.¹⁷^–¹⁹

Many oral cancer defects involve the removal of large portions of the alveolus and basal bone, creating a large fistula or communication with the maxillary sinus and associated structures (Figure 23-4, A and B). In such cases, the only available bone in the defect area is in the nasal rim, which is usually very thin, and remotely in the zygomatic buttress. The zygoma implant, in combination with conventional implants placed in any available bone sites, can often provide the basis for a retentive bar structure at the alveolar level (Figure 23-4, C and D). The obturating prosthesis can then be based entirely on the bar structure or on the bar in combination with residual dentition. The resultant restoration will then be resistant to vertical dislodgement in both the superior and inferior directions, and can provide the stability and seal to obturate the defect space effectively (Figure 23-4, E and F).