Accuracy of CAD-CAM Drilling Guides in Zygomatic Implant Placement

Raymond, Anna

Zygomatic implants are a mainstay of reconstructive implantology, and are typically employed in cases of severe maxillary atrophy, or following midface resection secondary to malignancy. There are two major problems which challenge successful and predictable zygomatic implant placement: firstly, the amount of available bone for zygomatic implants is often minimal, thus precise placement is paramount, particularly if multiple fixtures are to be used. Secondly, given the length of zygomatic implants can be four times that of conventional dental implants, even a small inaccuracy in implant angulation, once extrapolated along the length of the fixture, can result significant apical deviation and subsequent iatrogenic perforation of the orbit or the infratemporal fossa.

Accurate placement of zygomatic implants is therefore extremely important, yet no widely-accepted method exists for reliable and predictable zygomatic implant placement. Previous cadaver studies have investigated the efficacy of tooth-borne and tissue-borne guides for zygomatic and conventional dental implant placement, with disparate results, but there is a paucity of literature on bone-level guides, particularly in vivo.

This study evaluated the accuracy of CAD-CAM (Computer-aided Design, Computer-aided Manufacture) stereolithographic bone-level guides for the placement of 16 zygomatic implant fixtures compared with 8 freehand-placed zygomatic implants over an 18 month period. All patients had pre- and post-operative cone-beam CT imaging, and the pre-operative planned implant position was compared with the actual post-operative position in three-dimensions using a computer modelling system (Simplant).

It was found that only 50% of freehand placed zygomatic implants conformed to an ideal position and 25% varied by more than 8 degrees from expected (7.3mm in a 52.5mm fixture). In contrast, from the CAD-CAM group, 93% of fixtures were found to be in an ideal position, and the mean apical deviation from the planned position was only 3.51 degrees (3.2mm in a 52.5mm fixture).

This study suggests that CAD-CAM bone level guided zygomatic implants are more accurately positioned than freehanded zygomatic fixtures, and can be placed reliably in a clinical setting with accuracy matching that of the best published cadaver studies.

References:

Schiroli G, Angiero F, Silvestrini-Biavati A, Benedicenti S, Zygomatic implant placement with flapless computer-guided surgery: a proposed clinical protocol. J Oral Maxillofac Surg. 2011 Dec;69(12):2979-89.
Chrcanovic B, Oliveira D, Custodio A, Accuracy Evaluation of Computed Tomography-Derived Stereolithographic Surgical Guides in Zygomatic Implant Placement in Human cadavers. J Oral Implantology 2010; 36(5):345-55.