Article
Implant-supported prostheses are an option to replace missing teeth. A systematic review reported the survival rate of dental implants at 10 years was 96.4%.1 Although dental implants have high survival rates, the overall success of implant treatment depends on both aesthetic and functional outcomes. Correct implant placement influences the position and shape of the final restoration. Previously, dental implant placement was dictated by the quality and quantity of bone and protocols for placement reflected this. This bone-driven implant placement approach sometimes resulted in malpositioned implants causing aesthetic, biological and technical complications. Aesthetic complications include elongated implant crowns and disharmony of the soft tissue profile including the absence or reduction of interdental papillae.2 These complications can be caused by incorrect planning and can be reduced by an awareness of the need for prosthetically driven implant placement.
Planning for implant placement is enhanced by the use of cone beam computed tomography (CBCT) in conjunction with a diagnostic wax-up of the proposed restoration. From these diagnostic tools, a suitable surgical guide for placement can be made. The surgical guide, which is fabricated with radiopaque markers will allow the surgeon to verify the three-dimensional relationship of the implant in the mesiodistal (sagittal), corono-apical (transverse) and bucco-lingual (coronal) planes to the proposed restoration.3 Despite the advantage of using surgical guides, the conventional method of free-hand implant placement is still widely used. A systematic review reported that both guided and free-hand implant placement resulted in high implant survival rates. The number of implant failures, such as occurs when implants are not osseo-integrated or are aesthetic failures, were three times greater for those placed free hand than those with guided placement.4
Implant surgical guides are usually constructed using computer aided design (CAD) and computer aided milling (CAM) techniques, or vacuum forming. CAD/CAM surgical guides are very accurate, with as little as 0.1 mm vertical error and maximum 5.9° angle of deviation from the proposed implant position.5 These guides are expensive because of the cost of the scanning software and hardware, which may limit availability for some clinicians. If the CAD/CAM surgical guides are opaque, they do not always allow for intra-operative visualization of the implant site.
As a simpler alternative to CAD/CAM produced surgical guides, conventional vacuum-formed surgical guides may be useful in providing an accurate three-dimensional position of implant. They are relatively cheap and simple to produce.6 They can be made from polyester, and are satisfactory for a short bounded saddle area. For a free-end saddle or a long edentulous area, the guides are better made from polyacetate or polypropylene because the materials are stiffer and more resilient. These surgical guides are transparent, which allows for intra-operative visualization of the alveolar bone and implant position. This Technique Tip highlights the important features to be incorporated when constructing vacuum-formed surgical guides, which are simple, cheap and easy to make.
The surgical guide is constructed on the diagnostic wax-up that shows the intended gingival margin position of the definitive restoration. This is usually symmetrical with the gingival margin of the contralateral tooth where it is present. The labial contour and size of proposed prosthetic crown has to be as accurate as possible for a good prosthetic outcome (Figure 1).
An access hole is trimmed through the surgical guide on the palatal surface to allow straight-line access of the implant drills while maintaining material on the mesial and distal sides to limit the path of insertion (Figure 2). The buccal thickness of the surgical guide replicates the thickness of the intended crown to allow sufficient space for the fabrication of a screw-retained restoration.
On the labial surface, the guide is trimmed to the planned position of gingival margin. It can be highlighted using black marker to improve visibility during surgery (Figure 3). The mark is important to determine how deep the implant position should be in an apico-coronal plane. A mid-buccal line helps to determine mesiodistal position of implant and maintain a distance of 1.5 mm from adjacent roots.
The guide should be stable and well supported on teeth, with adequate extension that does not interfere with tissue reflection during surgery (Figure 4). The three-dimensional position during surgery can be checked to confirm the accuracy of placement using an implant depth gauge or alignment pin against the pre-drawn marks on the surgical guide (Figure 5).
Conclusion
Appropriately adjusted vacuum-formed surgical guides are useful tools for guiding correct three-dimensional implant placement. They also provide valuable interdisciplinary communication when the restorative dentist is not performing the implant surgery. They have the added benefit of being relatively easy to make and are cost efficient.