Comprehensive treatment concepts, Pterygoid implants
- Similar to the placement of zygomatic implants, the use of pterygoid implants avoids the need for sinus lift and grafting procedures
- The cumulative survival rate over a 10 year period for implants placed in the pterygoid region is reported to be 91%
- The main reason for using pterygoid implants is the availability of dense cortical bone of the pyramidal process and the pterygoid plate
In the edentulous upper jaw the placement of implants can be challenging due to limited bone quantity and the presence of the maxillary sinus. Pterygoid implants have high success rates, similar bone loss levels to those of conventional implants, minimal complications and good acceptance by patients, being an alternative to treat patients with highly atrophic maxillae and avoiding the need for extensive augmentation procedures [Candel 2012].
However, at present, pterygoid implants have mainly been studied in partial edentulism as a very attractive treatment alternative to sinus lift procedures.
The pterygoid implant is placed in the region of the former first or second maxillary molars and follows a diagonal direction posteriorly towards the pyramidal process. The implant ultimately anchors in the pterygoid fossa of the sphenoid bone. The angulation of pterygoid implants ranges from 45°-50° towards the maxillary plane [Bidra 2011].
In clinical reality, whenever pterygoid implants are described those are in reality tuberosity implants with an anchorage in the pterygoid plate and thus the treatment difficulties are very limited. As with every implant surgery the preparation of the implant bed is of high importance and treatment planning should be performed with great attention to the anatomical structures and bone availability/quality.
Due to the presence of type III or IV cancellous bone in this region, a preferred choice of implant type is the NobelActive implant given its high primary stability in soft bone.
The CSR over a 10 year period, largely due to data from one study was 91%. Evidence for long-term implant success and survival is weak in the current literature. Furthermore there is only limited evidence on immediate function on pterygoid implants [Bidra 2011].
Current definitions for pterygoid implants
Throughout literature, several terms are being used to describe pterygoid implants. The terms "pterygoid implants", "pterygomaxillary implants" and "tuberosity implants" are used interchangeably. "Pterygoid implants" have been defined by the Glossary of Oral and Maxillofacial Implants (GOMI) as "implant placement through the maxillary tuberosity and into the pterygoid plate".
There are significant differences between pterygoid and tuberosity implants including the following:
- pterygoid implants originate in the tuberosity and engage in the dense bone of the pterygoid plates and palatine bone
- tuberosity implants originate in the maxillary alveolar process and can occasionally anchor in the pyramidal process. The bone quality in this region is mainly composed of type III or IV cancellous bone
Reiser performed a cadaver study analyzing through which bony structures implants placed in the pterygomaxillary region are being supported. In cases with sufficient bone quality and quantity of the tuberosity, the implant can be placed entirely within the tuberosity. If bone is insufficient, the implants will apically anchor in the pyramidal or pterygoid processes. This leads to the conclusion that pterygoid implants do encompass the tuberosity region whereas not all tuberosity implants necessarily have to engage the pterygoid plates if enough stability is given by the tuberosity [Bidra 2011]. See also additional materials.