CAD/CAM-based Surgical Guide

CAD/CAM technology uses data from computerized tomography scan (CT)³³ to plan implant rehabilitation. The CT images are converted into data that are recognized by a CT imaging and planning software. This software then transfers this presurgical plan to the surgery site using stereolithographic drill guides.³⁴ CAD/CAM-based surgical guides offer many advantages. For example, the virtual 3-dimensional (3D) views of the bony morphology allow the surgeon to visualize the surgical bone site prior to implant placement; risks such as inadequate osseous support or compromise of important anatomic structures are avoided; incorporation of prosthetic planning using a scanographic template allows the treatment to be optimized from a prosthodontics and biomechanical point of view³⁵; and the technique promotes flapless surgeries, allows presurgical construction of the master cast and provisional restorations, and facilitates immediate loading.³⁶ Accuracy of CAD/CAM technology in dental implant planning and predictable transfer of the presurgical plan to the surgical site has been documented.^{37 - 46} However, the effectiveness has not yet become an established fact and still needs ongoing research. This technique has certain drawbacks. Special training for familiarity with the entire system and special equipment is necessary. Also, a considerable number of technique-related complications were observed. The various complications⁴⁷ recorded were related to inaccurate planning, radiographic stent error, intrinsic errors during scanning, software planning, the rapid prototyping of the guide stent, and the transfer of information for the prosthetics. However, if the clinician recognizes these sources of inaccuracy, efforts can be made to minimize the error and optimize patient treatment.

The procedure for fabrication of CAD/CAM-based surgical guides can be divided into the following steps:
1. Fabrication of the radiographic template,
2. The computerized tomography scan,
3. Implant planning using interactive implant surgical planning software, and
4. Fabrication of the stereolithographic drill guide.
The radiographic template must be an exact replica of the desired prosthetic end result, as it allows the clinician to visualize the location of planned implants from an esthetic and biomechanical standpoint.⁴⁸ This is followed by fabrication of an interocclusal index, to allow reproducible placement of the scan template intraorally.⁴⁹

A double scanning procedure is then followed.⁴⁹ The patient is scanned wearing the radiographic scan template and radiographic index (interocclusal index) during the first scan, whereas the second scan is performed without the index. The first scan is used to visualize the bony architecture and anatomy of the site of interest, and a second scan is performed to visualize the nonradiopaque radiographic guide. The 2 resulting sets of 2D CT data (Digital Imaging and Communication in Medicine [DICOM files]) are then superimposed over each other according to the radiographic markers and are further converted into a file format compatible with the 3D planning program.⁴⁹ Resulting from this fusion is an exact representation of the patient's bone structure and scanning denture in 3D space. At this point, the virtual surgical procedure can be performed.^49,50  A 3D implant planning software allows for simultaneous observation of both the arches and the radiographic scan template in 3 spatial planes and helps to virtually plan the location, angle, depth, and diameter of the virtual implants. It produces an axial image, a panoramic image, and a series of cross-sectional images on the screen at the same time. Various implant planning software products are available commercially, namely, SimPlant, SurgiCase (Materialise Dental Inc, Leuven, Belgium), Procera (Nobel Biocare, Göteborg, Sweden), ImplantMaster (I-Dent Imaging Ltd, Hod Hasharon, Israel), coDiagnostiX (IVS Solutions AG, Chemnitz, Germany), and Easy Guide (Keystone Dental, Burlington, MA).
Once the computer planning is accomplished, this plan is saved as a “.sim” file and sent to the processing center for fabrication of the surgical guide, using stereolithography.

Stereolithography³⁴  is a computer-guided, laser-dependent, rapid prototyping polymerization process that can duplicate the exact shape of the patient's skeletal anatomic landmarks in a sequential layer of a special polymer to produce a special 3D transparent resin model, which fits intimately with the hard and/or soft tissue surface. Once hardened, the polymeric prototype contains spaces for stainless steel or titanium drill-guiding tubes. These tubes precisely guide the osteotomy drills, precluding the need for the pilot drills.