Year : 2012 | Volume
: 2 | Issue : 1 | Page : 37--41
Applications of computer-aided design/computer-assisted manufacturing technology in dental implant planning
Kathleen M D'souza, Meena A Aras
Department of Prosthodontics, Goa Dental College and Hospital, Goa, India
Kathleen M D«SQ»souza
Kel-Ken Villa, H.No. 779/4, Opp. Hill Crest Apartments, Alto-Porvorim, Bardez-Goa
Computer-aided design/computer-assisted manufacturing (CAD/CAM) technology facilitates proper diagnosis, treatment planning and fabrication of a surgical guide template that enables the clinician to plan the implant placement procedure prior to surgical intervention. This development in implant dentistry allows an interdisciplinary approach to patient treatment. The purpose of this review article is to review and analyze the current available literature published on CAD/CAM-based dental implant planning and to provide a detailed discussion on the step-wise procedures involved in using this technology for dental implant planning and placement. Literature published over the past 20 years was selected and reviewed. The advantages and disadvantages associated with CAD/CAM-based dental implant planning were analysed. The various steps involved in fabrication of a CAD/CAM-based surgical guide template, namely, the fabrication of a radiographical template, the computerized tomography scan, implant planning stage and the fabrication of a surgical drill guide, were thoroughly reviewed and discussed. CAD/CAM technology has facilitated flapless surgeries by improvising on pre-surgical planning. Moreover, they have facilitated restoration-driven surgeries by integrating the restorative determinants into the surgical planning. Various clinical reports have demonstrated the use of this system in dental implant planning and in the involved surgical procedure. However, very few studies on the accuracy and reliability of this system have been carried out. Thus, the clinical applicability of this system is still questionable and long-term longitudinal studies are certainly needed before integrating this system into routine practice.
|How to cite this article:|
D'souza KM, Aras MA. Applications of computer-aided design/computer-assisted manufacturing technology in dental implant planning.J Dent Implant 2012;2:37-41
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D'souza KM, Aras MA. Applications of computer-aided design/computer-assisted manufacturing technology in dental implant planning. J Dent Implant [serial online] 2012 [cited 2022 May 26 ];2:37-41
Available from: https://www.jdionline.org/text.asp?2012/2/1/37/96567
Prosthetic replacement of missing teeth with implants has become a predictable procedure. However, numerous clinicians are encountering difficult cases, with insufficient amount of bone. This has created an increasing demand for advanced presurgical imaging procedures, which enables the clinician to evaluate the osseous and vital anatomic structures adjacent to the implant site prior to surgical intervention.  Various cross-sectional imaging techniques  and innovative software programs  have been developed to help create an accurate presurgical plan. Thus, advancing technology permits us to make use of computer-aided design and computer-aided manufacturing (CAD/CAM) technology to overcome the above mentioned difficulties and to enable a precise surgery. 
Advantages and Disadvantages of CAD/CAM Technology
CAD/CAM technology employs a non-invasive three-dimensional (3D) imaging system.  A radiographical template employed during this procedure provides a means to integrate the restorative determinants with the presurgical plan. This allows the treatment to be optimized from a restorative point of view and further enables the implant surgeon and the restorative dentist to define the most suitable surgical requirements, to predict prosthetic outcome options and to deal more effectively with patient needs and concerns.  CAD/CAM technology facilitates minimally invasive surgical procedures. These procedures aid in reducing healing time, postoperative discomfort, swelling and pain. It also reduces impact on the patient's morbidity.  Furthermore, it aids in the preservation of hard and soft tissue, maintains blood circulation to the surgical site and facilitates immediate loading by allowing the presurgical construction of master cast and provisional restorations.  Accuracy of CAD/CAM technology in dental implant planning and predictable transfer of the presurgical plan to the surgical site has been documented. ,,, Even though, it has been established that computer-guided template-based implant placement exhibit a higher implant survival rate, a considerable number of technique-related complications were observed. Deviations were mainly related to the system and reproducibility errors. Hence, the various complications  that occur in this procedure can be related to inaccurate planning, radiographical stent error and intrinsic errors during scanning, software planning, rapid prototyping the guide stent and transferring information for the prosthetics. Nevertheless, it has been documented that if the clinician recognizes these sources of inaccuracy, efforts can be made to minimize the error and to optimize patient treatment.
The use of CAD/CAM technology in dental implant planning can be divided into the follow steps.
Fabrication of the radiographic templateThe computerized tomography scan procedureImplant planning using interactive implant surgical planning softwareFabrication of the surgical drill guide
Fabrication of the radiographical template
The radiographic template is an exact replica of the desired prosthetic end result. It allows the clinician to visualize the location of planned implants from a restorative standpoint.  It can be either fabricated de novo from a diagnostic wax up or by duplicating an existing denture. Various radiopaque markers such as gutta percha balls and stripes, metal pins and tubes, radiopaque varnishes, lead foil or barium sulfate in resin powder aid in determination of the implant location. One technique involves placing radiopaque markers in a staggered pattern at different levels to the occlusal plane on the buccal flanges and palatal/lingual surfaces of the template.  Another technique involves fabricating an acrylic or vacuum-formed thermoplastic template, with barium filled in the edentulous portion of the template.  Alternatively, barium sulphate denture teeth can also be used. , There are some basic requirements that need to be considered during the fabrication procedure, which are as follows: It should be fabricated at the patient's appropriate centric position and occlusal vertical dimension; the teeth should be appropriately positioned according to phonetics and aesthetics; it should have soft tissue adaptation with exact fit to the underlying mucosa and well-extended flanges that will help provide proper stabilization during the scanning process.
After fabrication of the template, a vinyl polysiloxane centric occlusion index (interocclusal index) is fabricated to stabilize the template during the CT scanning procedure. This can also be used to stabilize the surgical guide at a later stage. 
The computerized tomography scan procedure
Computerized tomography (CT) was founded by Sir Godfrey Houndsfield and Allen M. Cormack in 1972.  Multi-planar reformatting (MPR) CT allows to reformat a volumetric dataset in axial, coronal, and sagittal cuts and to build multiple cross-sectional and panoramic views. CT is considered to be more accurate than conventional tomography, since it exhibits uniform magnification. Furthermore, it provides multi-planar views and three-dimensional (3D) reconstruction, facilitates simultaneous study of multiple implant sites, and has shorter acquisition time.  These advantages make dental CT, the most precise and comprehensive radiological technique for dental implant planning. Nonetheless, CT exposes the patient to higher doses of radiation than conventional radiographic techniques. , It produces scatter artefacts of metal restorations; it is expensive to patients; transferring information from a surgical template is difficult and needs additional image processing software programs; the interpretation of images is difficult without prior training; and the chance of patient movement during exposure is likely. 
Introduction of helical CT  (spiral or volume acquisition CT) has dramatically improved the application of CT imaging in implant dentistry. Helical CT, along with advancements in stereolithography, has allowed for the development of a CAD/CAM processed surgical guide to be placed directly on the bony site. Helical CT scanning involves simultaneous patient translation and X-ray exposure, generating data specific to an angled plane of section with each rotation of the X-ray tube. Rapid acquisition of data set eliminates respiratory misregistration artefacts and prevents discontinuities in the reconstructions due to the minimization of motion artefacts. In addition, helical CT scanning allows production of overlapping images without additional radiation exposure.
Recently, cone beam CT ,,, has been recommended for dental implant imaging, as it presents with several advantages in the identification of anatomical landmarks, provides high accuracy and has low-radiation exposure levels. CBCT machines rotate around the patient only once, capturing the data using a cone-shaped X-ray beam and it uses a low-energy fixed anode tube. These changes allow for a less expensive, smaller machine that causes less radiation exposure as compared to a helical CT.  Furthermore, true 3D images of bone or soft tissue surfaces can be generated. Although its use seems promising in the near future, the availability of cone beam CT is still restricted in routine use  as this technology still needs research to identify its practical applications and to determine its superiority to existing modalities . Thus, cross-sectional imaging like spiral tomography continues to play an important role in clinical practice.
Double scanning procedure
A research team at the Catholic University of Leuven, under the guidance of van Steenberghe et al., proposed the use of the double scan procedure for integration of the prosthesis or radiological template within the craniofacial model.  As the term suggests, this procedure requires acquisition of two scans. During the first scan, the patient is scanned wearing the radiographical scan template and the interocclusal index. This is done to visualize the bony architecture and the anatomy of the site of interest. Whereas, the second scan is performed without the index to visualize the nonradiopaque radiographical template. The two resulting sets of Digital Imaging and Communication in Medicine (DICOM) files are then superimposed over each other according to the radiographical markers and are further converted into a file format, which is compatible with a -3D planning program.  This fusion of files results in an exact representation of the patient's bone structure and the radiographical scan denture in 3D space. At this point, the implant planning and the virtual surgical procedure can be performed.
Implant planning stage
In 1986, Fellingham et al.,  first demonstrated the use of interactive graphics and 3D modeling for surgical planning, prosthesis, and implant design. Conventional presurgical planning of implant placement was typically facilitated by secondary reformatting using dedicated software.  For each of the CT brands available, separate software exists. For example, Dentascan software (GE, Medical systems, Milwaukee, WI, USA). However, recently specific software programs have been developed for planning implant surgery in the jaw bones. This implies that the above-mentioned reformatting programs are no longer needed. These specific software applications directly import DICOM data into a diagnostic and interactive treatment planning tool. Examples of such software programs are:
Simplant® , SurgiCase® (Materialise Inc., Leuven, Belgium)Procera Software® (Nobel Biocare, Göteborg, Sweden)ImplantMaster TM (I-Dent Imaging Ltd., Hod Hasharon, Israel)coDiagnostiX® (IVS Solutions AG, Chemnitz, Germany)Easy Guide (Keystone-dental, Burlington, MA, USA)
This 3D planning software allows an undistorted visualization of the jaw bone in four views: axial, cross-sectional, panoramic and 3D reformatted reconstructions.  It allows 3D visualization of all the anatomical structures situated within the bone and of the prosthetic appliance. In addition, this software permits graphic and complex 3D implant simulation. It provides options to allow an interactive manipulation of the 3D model along with the simulated implants in all directions. Exact virtual representations of the implants, abutments and other surgical accessories can be inserted into the 3D scene and positioned in the precise 3D coordinates that the clinician deems appropriate. 
Once the computer simulation is completed, it is saved as a ".sim'' file and sent to the processing centre via e-mail. This data is then used to fabricate computer-generated surgical templates that are preprogrammed with the individual depth, angulation, mesio-distal and bucco-lingual positioning of individual implants as planned during the 3D computer workup. This file helps to transfer geometrical information, in the form of numerous triangles, to another workstation which describes a volume by its boundary surface. This triangulated data is considered as the interface to the stereolithographic apparatus (SLA). ,
Fabrication of the surgical drill guide
In 1986, Dev et al.,  developed a computer-controlled, indirect milling machine for reproduction of an anatomical structure. Further development resulted in the rapid prototyping technology of stereolithography. Stereolithography  is a computer-guided laser-dependent, rapid prototyping polymerization process that can duplicate the exact shape of the patient's skeletal anatomical landmarks in a sequential layer of a special polymer to produce a special three-dimensional transparent resin model, which fits intimately with the hard and/or soft tissue surface. An above mentioned computer file is transferred to the stereolithography equipment, where a physical model of the patient's bone structure is created. The SLA consists of a vat containing a liquid photo-polymerized epoxy resin. A laser is mounted on top of this vat. The photovoltaic energy from the laser allows sequential polymerization of surface layer of the resin on contact. The thickness of the polymerized layer corresponds to the slice intervals specified during the CT formatting procedure. Once the first slice is completed, the mechanical table moves down below the surface carrying with it the previously polymerized resin layer of the model. The laser now polymerizes the next layer above the previously polymerized layer. In this manner, a complete stereolithographic model of the patient's jaw can be created. The major part of the polymerization process occurs within the vat. However, the final polymerization must be completed in a conventional ultraviolet light curing unit. The surgical templates  are then built onto the surface anatomy of these stereolithographic models. The template is connected to the model by a series of minute triangles, which are later removed during the finishing process. The SLA machine also reads the diameter and angulation of the simulated implants and selectively polymerizes resin around them. This forms a cylindrical guide, which is later fitted with surgical grade stainless steel tubes. The templates can be entirely supported either by soft tissue, bone, or remaining teeth. A number of studies , have established that surgical placement of dental implants based on stereolithographic technique is a safe procedure and has many advantages. This technology has provided a means to simplify and improvise on the implant placement procedure.
Until the late 1980s, conventional radiographic techniques were considered as an acceptable standard for preoperative assessment and planning of dental implant patients.  However, in present times, most diagnostic aids, such as, periapical and panoramic radiography or mounted study models are unable to provide complete comprehension of the dental arch anatomy. A surgical guide fabricated on a diagnostic study cast is endowed with unsatisfactory knowledge of the underlying anatomy. Moreover, the limitations of the conventional dental radiography, particularly, insufficient dimensional accuracy (magnification error, distortion error, setting error and position artefacts)  and inability to visualize anatomical structures in para-sagittal sections, further hinder accurate evaluation and result in unpredictable clinical outcomes. Thus, the limitations of the current clinical techniques often do not allow fabrication of surgical guides that are capable of accurately transferring planned implant placement intraoperatively. , The present use of CAD/CAM processed surgical guides has provided a high degree of simplicity in morphologic diagnosis, determining the surgical procedure, and establishing the subsequent prognosis. Moreover, CAD/CAM technology has facilitated flapless surgeries by improvising on pre-surgical planning. They have also facilitated restoration-driven surgeries by integrating the restorative determinants into the surgical planning. Various clinical reports have demonstrated the use of this system in dental implant planning and in the involved surgical procedure. However, very few studies on the accuracy and reliability of this system have been carried out. Thus, the clinical applicability of this system is still questionable and long-term longitudinal studies are certainly needed before integrating this system into routine practice.
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