Introduction

Computer use in the medical field has increased with the numerous discoveries that the world is experiencing today. Technological field, being among the fastest growing, has been well incorporated in dentistry in the form of Computed Tomography (CT), Cone Beam CT (CBCT) scans, as well as the software processing used to maximize the utility of the CT/CBCT data. This has been the case especially with the guided surgery that is employed in dental implant cases. This process involves CT scanning of the dental arches of the patient. The scan data is then imported into computer software which is used to determine the final position of the restorations and thus the positions of the dental implants that would need to be placed during surgery. The intraoral appliance which the patient wears during the scan is vital in this process. A poor scan appliance would lead to a poor result in the treatment phase. The scan appliance therefore plays a pivotal role in the success or failure of the implant treatment. The scan appliance is used to determine the most suitable prosthetic position for each tooth that would be placed in the computerized treatment plan. After a CT scan has been done with the scan appliance in situ, the scan data is processed to plan the prosthetic and surgical phases. This makes the whole process restoratively-driven.

There are different names given to the available scan appliances but their purpose and use are basically the same. To determine which appliance to use, one needs to determine the proprietary implant system that they would employ. For example, appliance NobelGuide is used for Nobel Biocare implants whereas SimPlant software is undefined and can be used with a wide variety of implant systems. This makes it more popular and consequently more widely used.

With the improvement in the scanning appliances since their introduction, surgery in dentistry has also improved with a similar magnitude. Lately, Image Guided Surgery (IGS) has been introduced. It represents a surgical concept and set of methods, that use computer technology for pre-surgical planning, and for guiding or performing surgical interventions in real time. Image guided surgery has its roots in stereotactic surgical procedure developed at the beginning of the 20th century [1, 2]. Guided implant surgery is a process of obtaining and reformatting CT or CBCT data, planning implant placement over a virtual model, fabricating a surgical guide, and using this surgical guide during dental implant surgery. [3]. Surgeons can hardly plan anything that is not implemented in the software system. Since it is almost impossible to reconstruct the soft tissue models from patients’ CT scan data, scanning appliance is vital in the process. In some cases surgical guide can be adapted to be used as the scanning appliance [4, 5, 6].

The deviations between the planned and placed implant is the sum of the cumulative errors throughout the computer-aided implant placement cascade. A slight angular error of the placement of the scanning appliance can cause dire consequences since the final position of the patient’s teeth would be different from the one developed by the software. Missing data can be caused by effect of metals where x-ray beam is attenuated that almost no photons reach detectors. The dark and bright streaks as a result of its attenuation will show up in the CT/CBCT images. Significant errors at the apical end of the implant position will occur as a slight angular error of scanning appliance. An unstable scanning appliance result to unsatisfactory match between the scanning appliance and receptor site. The instability is often caused by poor placement or unnecessary movement of the patient during placement.

The main goal of implant dentistry is not the implant itself but the tooth that it replaces [7]. Following this concept the backward planning that starts from the implant seems acceptable, meaning that each implant is aligned along the axis of the corresponding prosthetic crown. An implant position’s planning starts with a dental impression to make a hard plaster master model and the fabrication of a scanning appliance with radiopaque teeth according to the prosthetic requirements [8]. These radiopaque teeth are made using a denture with radiopaque plastic teeth mounted in hard wax on an acrylic resin baseplate. A 1.5mm thick plastic plate in the shape of the dental arch is then fixed between the upper and lower teeth with silicone. Cross-shaped titanium markers with 2 mm long arms within the plastic plate indicate suitable implant positions. Many implant planning software support this planning method by combining other types of clinical data with the CT/CBCT scan such as a laser scan of the stone models or intraoral scan of the dentition. Additionally, virtual wax-ups can be incorporated which allows planning of implant positions with the future restoration and occlusion of opposing arch [9].

A reference guide was introduced in the early nineteen eighties in implant placement procedure. Today, almost every scanning protocol exclude CT/CBCT scanning without scanning appliance containing gutta-percha or other materials index markers.  At the beginning of new millennium American Academy of Oral and Maxillofacial Radiology recommended that evaluation of any potential implant site include cross-sectional imaging orthogonal to the site of interest [3]. The majority of CT/CBCT referrals by dentists are for implant site assessment [10]. In the future, reductions in radiation doses through improved radiographic techniques and greater accuracy might increase the number of indications for computer assisted implant placement (there is something very alarming here – if reduction in radiation dose causes more examinations, then population dose will increase). Its widespread use would prevent unsuitable cases from ever reaching surgery [11]. The use of a scanning appliance in radiographic evaluation is hard to replace in the CT examination [12].

Data about the accuracy of conventional implant placement are lacking [13, 14]. On the other hand, there has been a lot of research carried out on Image Guided Surgery (IGS). Its validity has been tested and verified by many scientists and researchers unlike conventional implant [11]. Accuracy of computer-aided oral implant surgery is not dependent on the type of implant used [15].

 It is proposed that unless we use all of the diagnostic resources available to us including the use of imaging guides in conjunction with tomography, we may be putting the patient and ourselves at needless risk for failure [16]. This view is however inaccurate since CT scan may not be important and on the contrary, not carrying out a CT scan may be appropriate for both the dentist and the patient.

History of the scanning appliance

Modern dentistry use image guided intervention which has been in use for the last over 20 years. They also use preoperative data which is in most cases in the form of CT images that relate the data to the patient. This technology is over a century old and was started in 1895 when a doctor used the then new x-ray technology to remove a sewing needle from a patient in England. This was closely followed by another incident when a doctor removed a bullet from a man’s leg using the same technology a month later. In 1908, a report was made on a device that seems very close to the modern image guided intervention. The device was named stereotactic frame and was used to affix a monkey’s head to a frame and used external markers to align it. The technology was mainly used for neuro-surgery but this later changed to include all the other parts of the body [17].

Russle Brown invented the modern CT technique in 1978. This technology allowed for the visualization of the anatomic details of the patient. It created landmarks in every topographic image using fidicials. Presently, the stereotactic image guided surgery is used.

Computer Tomography cemented its position in dentistry in 1993 after the publication of the DICOM standard in 1993, which was then followed by the increasing data speeds in the late 1990s. This enabled the process of data handling for three dimensional reconstructions a possibility using personal computers. This, in the long run, led to quick and accurate improvements in medical fields throughout preoperative examination and final diagnosis. Further, it was during this period that many companies developed and started to use CAD/ CAM systems. Once the correct diagnosis was made, the necessary preoperative preparations before the actual treatment is made became more accurate. The bone surface of the patient was well examined and drilling was properly controlled taking into account the remaining teeth, the bone surface, basal surface and any other vital part of the jaw bone. Today, there are companies that use this technology to construct pre-surgery prosthetic structures to ensure that the best implants are used.

From this technology, researchers started to develop systems, though differing in implementation, that were geared towards the achievement of tracking the surgical positions in the physical space while displaying the position in image space. The physical space would be determined from the images. Three techniques were used. They included feature based, volume based and point based. Point based registration technique was further divided into two sub-types that first used anatomic landmarks as fiducials (feature based) while the second required an attachment to extrinsic objects (marker based). Their main difference was that in marker based, the markers must be in place prior to the acquisition of images. Marker registration is said to be a prospective method. Feature based registration in general requires more computation than do marker-based methods, and they are prone to larger error. Point based registration technique is divided into two subtypes: a) uses anatomic landmarks b) uses extrinsic objects.  Conventional dental panoramic tomography and periapical radiography are often performed with the patient wearing a radiographic template simulating the preoperative prosthetic design. However, these imaging techniques do not provide complete three-dimensional (3D) information of the patient’s anatomy. In addition, conventional surgical templates have been fabricated on the diagnostic cast that will direct the bone entry point and angulations of the drill, but they neither reference the underlying anatomical structures nor provide exact 3D guidance. Conventional surgical guide does not provide 3D guidance [18, 19, 20].

The introduction of CT, 3D implant planning software, and CAD/CAM technology can provide optimal 3D implant positioning with respect to both prosthetic and anatomical parameters from where Scanning guide appliance can be used. The digital images (CT, CBCT or Optical scanner) can be converted into a virtual 3D model of the treatment area. The virtual model permits a virtual execution of the surgery in an ideal and precise prosthetically driven manner. The planned digital information can then be transferred to the clinical situation by:

  1. Mechanical positioning devices or drilling machines convert the radiographic template to a surgical template by executing a computer transformation algorithm
  2. CAD-CAM technology to generate stereo lithographic templates [21].

Materials and Method

Professional societies have to give enough guidance when using a scanning appliance. This is to ensure that the best image is obtained in order to give the patient the best match of implants. The scanning appliance used has to be scientifically and practically driven to protect the patient and yield the best results. In the recent past, CBCT technology is becoming more widely available but has to be used properly and efficiently. Since it has some weaknesses in that it does not determine the bone density of the patient, care should be taken every time this technique is put to use.

Literature review – search strategy

The references were retrieved from PubMed database. An online search of the PubMed electronic library was performed using the following terms:

1. Bone supported stereolithographic guide.

2. CAD model guide,

3. Diagnostic template guide dental,

4. Imaging guide dental implant,

5. Mucosa supported stereo lithographic guide,

6. Radiographic guide dental,  

7. Radiographic registration device guide,

8. Radiographic scan prosthesis guide.

9. Radiographic stent guide,

10. Radiographic template guide,

11. Radiographic Templates, 

12. Radio-opaque scan-stent,

13. Radiopaque template,

14. Registration template guide,

15. Scan appliance,

16. Scan prosthesis guide,

17. Scan template appliance,

18. Scanning denture guide

19. Scanning template guide,

20. Scannographic guide,

21. Scanographic template,

22. Tooth-supported stereolithographic guide. 

By the time the research was completed, seventy seven relevant articles were found. The search included studies from January 2001 up to April 2012 and is limited to journals in published in English language. The search included papers in the 21st century since they provide the latest information that includes the CBCT technology which was only discovered in 1998. Therefore, the information will be viable and at no point will it be obsolete. Of this total study sample of 585 papers were related to scanning appliance, 402 were related to scanning appliance in other field outside the scope of this paper or same paper was appearing under differed key word research result. 77 relevant papers were analyzed.

These papers were placed in one of four groups according to their scanning protocol. Papers related to two or more groups were assigned to every relevant group. This explains why the sum of the paper in each group is larger than the total number of papers and why the sum of the separate percentage is not equal to 100.

Inclusion and exclusion criteria

No restrictions were made regarding the study design or follow-up period. Only studies performed with computer-controlled technologies or CT scanning dental implant guided surgery were included in the present systematic review. Studies using “dynamic” navigation systems were excluded as well as studies with zygoma implants, pterygoid implants or mini-implants for orthodontic purposes.

Publication types

Almost 600 articles were found to be relevant to the different points to be covered in the project. They were then downloaded and after reading their abstracts, it was found that many of them either belonged to other medical field or different implant procedure. Articles in languages other than English were excluded too. Only 77 articles were selected and referenced in this project.

Results

Names for the scanning appliance

After reading PubMed related publications and protocols for CT or CBCT scanning of many well-established companies, 32 names related to scanning appliance were found. During the PubMed search of the words the 10 of them were not found in any dental publication related to Guided Implant Surgery protocol. Therefore, 22 words were used for future examination. In PubMed database English relevant literature from Jan 2001 to Apr 2012 there are 22 different names used for scanning appliance. In some articles more than one name was used for the scanning appliance such as: “scanning template” and “radiographic template” [24].  This is a gross issue since it can mislead dentists and researchers.

The most often used key words/names are Radiographic template, Scan prosthesis guide and Radiographic guide. In the final related literature the most often used word is Diagnostic template guide, Radiographic guide and Imaging guide. In both categories the most often used key word is Radiographic guide.

One reason that the term “scanning appliance” seems to have become more accepted and adopted, is its use with a laser/optic scanner together with CT scanner in implant treatment planning process. The name of scanning appliance includes both options of scanning. The use of a standard name will help us communicate better and unambiguously.

From the literature, single scanning appliance is used more than any other, its frequency being twice as more as all other kinds of appliances put together. Double scan appliance was placed second while optical scanning came third. No scan appliance was least used. It was decided that category optical/laser scanning in combination with CT or CBCT scanning would be used regardless of the scanning appliance [25, 26].

A single scan protocol has a higher probability of getting an image with an obscured view of the vital structures because of scatter of neighboring restorations and minor scatter from barium sulphate and the radiopaque markers. Barium sulphate represents a solid radiopaque tooth [27]. Dual scan protocol is better since it merges two scans by aligning and matching the radiopaque markers so that scanning appliance will be visible over the available tissue anatomy, and metal image artifacts are minimised.

De Santis [28] presented an innovative double scanning guide solution for immediate loaded implants in postextraction sites where Guttapercha spherical markers made of oralim were used. The most often marker is Nobel Biocare type and SimPlant version which are made of silicone [29].

Procera Nobel Guide (Nobel Biocare) was the most common software used by the authors evaluated. The software used in the present review was as shown in the table with their places of origin.

Table 1: The different software used in dentistry and their companies/places of origin.

 Scanning Appliance

Place of Origin

Procera Nobel Guide

Nobel Biocare, Yorba Linda, CA

Simplant

Columbia Scientific Incorporated, Columbia, MD

Surgicase

Materialise, Leuven, Belgium

Stealth station

Spine 3Ds; Medtronic Inc

3D SENTCAD software

Media Lab Software, La Spezia, Italy

Exe-Plan software

Brussels, Belgium

Implant3D

med3D, GmbH, Heidelberg, Germany

EasyGuide Protocol

Keystone-Dental, Burlington, MA

Medicim

Sint-Niklaas, Belgium

Litorim

Leuven Information Technology, Leuven, Belgium

image-guided implantology

IGI; Denx Advanced Dental Systems, MoshavOra, Israel

MedScanII-Virtual Implant

Artma Medical Technologies AG, Vienna, Austria

 In the literature, medical CT scans were used twice as much as CBCT scans. In several cases the post-surgery procedures are done to control CT scanning. CBCT scans were on the other hand not used for a second time on the patient after the surgery. This is done in order to provide an alternative method to match planned and achieved positions of implants, after virtual planning using CBCT data and surgical guide templates, a method reducing patient radiation exposure [30, 31, 32].This method reduces radiation exposure for patients participating in scientific studies. The reduction of exposure results from the technology used where beams of light used are formed into a cone. Pre-operative cone-beam CT images were matched with post-operative images of the master cast with implant replicas. Both the pre-op and post-op were done with the involvement of the patient.

Discussion

Scanning appliance

The scanning appliance used in pre-implant assessment is a vital aspect since it gives the anatomy of the patient’s dental form. It is the image that is obtained from the scan that is then used in the computer software to provide the correct anatomy of the replacement teeth with the original teeth/tooth. The scanning appliance introduces the intended tooth set-up and soft tissue surface during the CT/CBCT scan for later reference during digital diagnostics and enables a prosthetic driven planning. Use of Scanning appliance relates tooth-to-bone relationship, though the underlying bony anatomy can be visualized in direct relationship to desire tooth position. Scanning guide has to be firmly supported by the jaw during the CT scanning procedure. This is even more difficult to provide when a removable denture is sitting on the opposing jaw [33]. The scanning appliances used during CBCT can be classified by generation, scanning procedure, composing material but neither is perfect or include every possible situation.

It is essential to have a scan appliance or radiographic template of an overall even thickness of at least 2.5–3.0 mm (as also mentioned in the NobelGuide protocol) [34]. Thin template in some area will be seen in planning software as whole/missing. The process of obtaining radiological guides used alongside the scanning appliances has been long and has been developed in three generations as elaborated below.

Generation 1: Barium-coated silhouette of the proposed %uFB01nal tooth positions

Generation 2: The hollow portion of the vacuum-formed template is completely filled with an acrylic resin/barium (30% barium sulphate by weight), which will represent a solid radiopaque tooth.

Generation 3:The Tardieu Scannoguide; it is a differential barium-gradient scanning appliance, which not only transfer the prosthetic outcome but also define the soft tissue boundaries on the CT study [35, 36, 37]. This third generation device is currently in the market and use.

As stated earlier, there are different types of scan appliances. Some are better than others while others are more widely used than others. Below is a brief description on the use of the different scan appliances available today.

Single scan appliance

Barium sulphate is mixed with acrylic to identify various structures radiographically. The teeth to be replaced contain a 20 percent barium sulphate mix. If the goal is to perform a flapless procedure on a fully edentulous case, the teeth are made with a 20 percent BaSO4 mix and the base a 10 percent mix [38, 39]. This allows the teeth to be identified as well as the soft tissue in the CT study [40]. For partially edentulous cases, the scan appliance can be a flipper-type design or it can overlay the remaining teeth, depending on the clinician’s preference.

Dual-Scan Appliance

The dual-scan appliance is typically fabricated from clear acrylic (optically clear, and radiolucent) with approximately eight 1 mm to 1.5 mm spherical markers [4, 21, 36]. The dual scan appliance overcomes the problem of scatter from neighboring restorations and barium sulphate (minor amount). The patient is scanned with the scan appliance, and then the scan appliance is scanned alone. The planning software converts the CT scan files and merges the two scans by matching the markers (hence the need for up to eight markers), aligning the radiopaque markers so that the prosthesis will be visible over the available osseous anatomy.

The way of surgical guide production determinates the elements of the scanning guide. No updated publication in PubMed data compares the differences of the procedure. There have been debates on whether a patient would be limited to the company from which the use their scan appliance for the first time, during the subsequent implants. It has also been posed to the dentists if they would work with the same appliance from a certain company in case they start to use it. Gutta-percha as a marker in scanning appliance was most often used. When several experiments were carried out, in only one case sorter was barium sulphate used instead [41]. The barium sulphate powder was used in 10% a mixture for the base and for the teeth in 20% usually also in several cases was used as varnish to cover surface of the teeth or base of the appliance. Metal as marker in the acrylic base was used in 11 cases while glass spheres twice and once surgical foil, lipiodol, porcelain, putty and temp-Bond or temporary filling {zinc oxide}) material [42].

Disadvantages of dual scan techniques can be seen as low stability if scanning appliance is not covering residual teeth, low visibility of residual teeth if scanning appliance is covering them and also gingival contour of neighboring teeth and edentulous area can be only estimated under the base of scanning appliance.

From these weaknesses, critics question whether the dual scan appliance markers should still remain in use. Evolution of the markers has always tried to develop a marker that will be perfect to the axis of the implant suprastructure which can be superimposed in the computer virtual image [43]. During image matching by software it is good to have perfect surface of the marker. In this case gutta-percha placed in holes created in acrylic plate will not have an even, perfect surface. Therefore, it is suggested that porcelain or glass balls, maybe, can be a better solution. They however are not very convenient to use, thus leaving gutta-percha with a bigger advantage. Barium sulphate (BaSO4) is good but can cause a minor amount of scatter and potentially obscure the view of vital structures [44, 45].

Direct scanning appliance

When using this form of a scanning appliance, the preparation of a stone model to fabricate a scanning appliance is eliminated. The direct scanning appliance should only be used for one or two missing teeth when the visualization in the 3D scan of a prosthetic proposal via radiopaque acrylic is not necessary or done via a virtual prosthetic proposal [46, 47]. The utilization of a bite registration material allows the immediate fabrication of a radiographic template directly in the patient's mouth. Radiographic characteristics (radiolucent) of the bite material have to be in line with planning and surgical guide manufacturing process. However, a stone model still needs to be prepared at a later time and sent to factory for the surgical guide manufacturing process and to verify the fit of the surgical guide after fabrication [48, 49]. The direct scanning guide is the basis for the surgical guide and its stable fit on the patient’s jaw is of critical importance.

Prefabricated radiographic guide plate is a method that has been applauded by many scientists.  However, its first picture is from SICAT, which many people are uncertain whether it can be used with other systems. Another is N-sequence and it can be used will any system that uses fiducials.  Clear Bite from Discus is used by many people as well. Typically there are a few fiducials on the palate and a few on the buccal.  Since it is a pre-configured arrangement one only needs to command the software where a few of the fiducials are and the software locates the rest, in a case where Radiographic Registration device practitioner can eliminate custom made scanning guide, yet the restoration is still not accepted by the  patient.

No-scan appliance technique

The process is quite simple. One only needs to capture a CBCT of the patient with the arches separated with cotton rolls. Any metal-based removable appliances are removed prior to the scan and the DICOM images are uploaded to www.dentalimplantplanning.com. The master casts of both arches are then sent, a bite registration, and study model (if available) are also sent to ROE. A diagnostic work up on the model to idealize tooth location is then completed. The work-up would then be visualized in the CT plan for ideal implant placement during planning [50, 51]. The Implant-planning report would then be given within three days. The indications of a complete and well executed procedure include a flapless or flapped surgery and immediate extraction and implant placement in the report

Contraindications include edentulous patients where patients must be scanned with a radiographic guide. Patients will also show an excessive metal-based crown and bridge (metal produces scatter in the DICOM). The no-scan appliance technique is a breakthrough that offers many benefits to dentistry practice. Surgical guides offer a high degree of accuracy, and since acceptance may increase due to the lower cost, turn-around is much quicker and significantly less coordination between the restorative dentist, surgeon, laboratory and patient would be experienced [52].

Scanning appliance transformed to surgical guide

Bioprototyping techniques are based on computer-aided design and computer-aided manufacturing (CAD/CAM) technology. They have proven to be valuable aids in diagnosis, treatment planning, and surgical intervention. One process of Bioprototyping techniques can be used as first step of implant planning. Biomedical prototypes, or biomodels, provide faithful reproductions of the patient’s bone condition, thus enabling this type of assessment. The process of obtaining and reformatting  computed tomography (CT) data, planning implant placement over a virtual model, fabricating a surgical guide with prototyping methods, and using this guide or template during dental implant surgery with specifically designed systems may be referred to as Guided Implant Surgery (GIS) [53, 54]. Rapid prototyping can be defined as a set of technology-based processes that enable fabrication of three-dimensional, concrete objects from a computer aided design (CAD) project. The objective of rapid prototyping is to create a real model with the same geometric features of the virtual model, which can then undergo real-world manipulation for a variety of purposes [55, 56].

Hybrid method for dental implant treatment planning has also been used in several occasions. The core of the approach is to create digital anatomical models of jaw bone and soft tissues with implant holes added, and manufacture these models as a base for making a surgical guide [57]. The combination of these models integrates the patient's anatomy and treatment plan information. It is called master model in this invention. For mandible (lower jaw) cases, the model will also include nerve channels. Also made are inserts corresponding to the planned implants. An insert is a kind of replica of an implant. It is inserted into the master model and has a part standing out of the soft tissue, so that the surgical guides can be made to match the insert [56]. 
Two technologies scanning

Hard tissues such as bone and teeth are well differentiated on CT scan but soft tissue is not. By integration of data from computed tomography with the optical scan data, planning software creates virtual image of both, allowing dentist to work up implant cases from hard tissue, soft tissue and prosthetic perspectives.

The use of the optical scanner, having a higher resolution and accuracy than CT scanning, has demonstrated to be a valid support to evaluate the precision of the various physical models adopted and to point out possible error sources [58].

For tooth-supported CAD/CAM surgical guides, a stone model must also be mailed together with the file because a separate optical scanning of the model is necessary [59].Tooth or tooth/mucosa supported surgical drilling guides would have benefit when the hard stone cast is optically scanned and data superimposed over the CT image to merge data [60, 61].

Using optical scan data of the mucosa and remaining dentition instead of CT scan data enables a more precise reconstruction of the supporting side of the surgical guide, resulting in a stable seating of the surgical guide during transmucosal drilling of the implant osteotomy. The gypsum cast is scanned with and without the occlusal registration in place. The mucosal surface with remaining dentition and occlusal registration with an impression of the opposing arch are optically scanned. Black–white contrast is used for convenience [62].

Optical measurement systems are state-of-the-art in industry for 3D digitizing of surfaces. The most common systems are based on the principle of fringe projection. Non-destructive testing applications are capable to digitize 3D surfaces. Both technologies prove to have a high potential. The CT technology has the ability to gather information of internal structures without any significant influence of the object surface properties. Although the scan quality is independent of the bulk material, it highly depends on the surface properties of the object. Certain surfaces need to be treated with sprays to enable scanning. The main limitations of optical scanners are surface properties, undercuts, internal structures and resolution of small parts. The combination of both data can be helpful to overcome application limitations.Cone beam CT

Cone Beam Computed Tomography (CBCT) was developed for dental use in 1998 [63, 64] In July 2008, there were sixteen manufacturers of CBCT devices producing twenty-three different models [65]. CBCT advantage is its accuracy in both the use of computer supported implant placement and conventional free-hand method. If we compare planned and implanted position of implants by scanning the postoperative casts, radiation dose is significantly smaller. Accuracy of virtual planning position using cone beam CT is high and significant [66]. An x-ray examination is justified if there is a net gain to the patient. This gain may be diagnostic, an alteration of the treatment plan, or increased confidence for the surgeon contemplating a surgical procedure. This gain has to be balanced against the increased radiation dose; therefore, the dose has to be assessed.

Support for post surgery CT scanning cannot be found as benefit for patient, because the available alternative methods that give similar result without additional CT scanning of patient are few. Also, patient movement occurred during post-operative CT scan can compromise results particularly when patients wear a removable denture in the opposing jaw.

Radiographic Markers

Radiopaque Markers are used to facilitate the CBCT double-scan protocol and enable the subsequent correct matching of the two scans in a software program. Usually 6-8 spherical reference points must be incorporated into the scanning appliance. Bucco-orally markers should be evenly positioned and apically away from the gingival plane to avoid possible streak artifacts created by existing restorations. The proper compatibility between markers and (CB) CT scan is important to allow dentist to delineate the position and contour of the proposed restoration. Markers have to be distributed in several planes because of their superposition [67].

Markers are important and should be used to keep patient’s and his therapist’s message visible on computer image. Calibration of the CBCT seems important and nice way to minimize object/image volume difference, especially when each implant is aligned along the axis of the corresponding prosthetic crown marker positioned in the scanning guide barium fortified crowns will help implant position planning. 

Markers and scanning base are important for estimate of the mucosal tissue thickness. More inaccuracy of guided implant placement can be expected in cases with thicker supporting mucosa due to less stability of the surgical guide or scanning appliance [68]. The excess soft tissue needs to be removed prior to the fabrication of the scanning denture and the CT scanning procedure since the thickness is an important factor during the process [69].

Calibration procedure

Accurate fitting dimensions of the surgical template are crucial for predictable surgical results. The surgical template dimensions are defined through the scanning appliance which is digitized using CBCT technology. The crucial information for the surgical template comes from the second CT scan, which is the radiographic guide scan in the Double-scan procedure. Every CBCT is different and the grey value is (isovalue) is identified in the 3D volume of the scan. This value shows the physical border of the scanning appliance and once established, a border is generated in software. Correct extraction (“segmentation”) of this border (surface) data from the 3D DICOM files is necessary to produce an accurate (fitting) surgical guide. Almost every CBCT scanner has a unique way to determine isovalue to defined objects. The calibration object consists of a typical material used for fabrication of scanning guide. This high precision object allows software to identify the correct value for the scanning appliances scan by analyzing the reference scan made with the calibration object. It is important that the reference scan is acquired in the very same way and with the very same scanner setting used for the scanning appliance scan [70,71].

Software

After the scans and images have been obtained through the scanning appliance, they are then taken to the software for analysis and to design the implant. CT planning software converts CT Scans (DICOM files) to 2D and 3D imaging and provides as much information as possible to assist during surgical planning. Software also gives us ability to visualize vital anatomy in2D and 3D prior to surgery and assess the location of the implant virtually prior the surgery.

Computer applications allow creation 3D models to be located in virtually real situations. Constructed virtually templates carrying treatment plan necessary information can be transferred to the mouth of the patient through rapid prototyping or similar procedures. Computer assisted treatment planning enables rotation of scan in 3D and placement of implants around anatomical concerns and at same time view in both 2D and 3D.

The implant planning software should contain realistic displays for all common implant systems in the form of an easily accessible database. Dedicated tomographic views are required for the actual implant planning, so that the implant bed can be checked optimally in all dimensions. The handling of software should be as intuitive as possible to produce an efficient workflow. Buttons and features in the top layer of the user interfaces should be as limited as possible in order to avoid user confusion and overload. One of the first computer software programs (SimPlant, Materialise, Columbia, MD, USA) that used CT images had the capability of planning and practicing surgery, but had no direct way to correlate computer images to the mouth [72]

Quality of input information is critical so the accuracy of the planning depends on the thickness of the slice obtained during the tomographic examination, movement of the patient during examination, and presence of artifacts in the restorations.

The slice thickness is related to the prediction of the software and the usually to cost of the CT scanner machine. The thinner the slice in the machine, the smaller the gap, the better the prediction and the more expensive the machine is.

Today, with the advancement of digital technology and imaging techniques, clinicians can evaluate the bone anatomy in greater details and determine the best position for implant placement. Many commercial systems are now available for transferring the planned implant to the surgical site. They are either using stereolithographic technology like SimPlant/SurgiGuides (Materialise, Leuven, Belgium), 5–7 Procera/NobelGuide (Nobel Biocare AB, Goteborg, Sweden), 8–10 ImplantMaster (I-Dent, Ltd., HodHasharon, Israel), 11 or applying %uFB01ducial markers like EasyGuide (Keystone Dental, Burlington, MA, USA), 12 some  manufacturers develop a combination of computer implant planning and real-time localization devices to guide drilling through the surgery like Image-Guided Implantology system (DenX Advanced Dental Systems, MoshavOra, Israel), 13 VISIT navigation system (University of Vienna, General Hospital, Vienna, Austria), and Treon navigation system (Medtronic, Minneapolis, MN, USA). 14 However, the accuracies of these systems have been shown to be varied; 15–17 furthermore, these systems are usually costly and some of them are implant speci%uFB01c, precluding their use in other implant systems[73, 74, 75].

The software makes the possible virtual planning on computer stereolithography, a CAD-CAM program was developed to create an accurate transfer from the image to the surgical site. Detailed preoperative analyses of the quantity and quality of bone as well as the ideal positioning of implant fixtures may be established with the aid of a surgical guide that is placed directly on the bone for precise implant insertion [76] on the dimensional difference of the CT based reconstruction that can turn out to be smaller or greater. The weak point of the whole procedure relies on the accuracy in transferring information derived from CT data into surgical planning; CT scan quality and processing of DICOM (Digital Imaging and Communication in Medicine) images affect the creation of the corresponding 3D digital models. Misalignment errors can also be introduced during the arrangement of the radiographic template within the maxillofacial structures by the gutta-percha markers. Therefore, inaccuracies can be introduced in manufacturing physical models by stereo-lithographic techniques. The influence of an appropriate segmentation on the final 3D representation is a matter of utmost importance. It depends on the adopted mathematical algorithm, spatial and contrast resolution of the slice images, technical skill of the operator selecting the optimal threshold value.

Metal restorations as well as tissues not belonging to the structure if interest (opposing teeth) must be cleaned up. A methodology to verify the accuracy of the 3D reconstruction CT derived images is necessary for clinical application. The radiographic template is manually manufactured and a 3D model of the radiographic template is reconstructed processing the DICOM images. The radiographic model is also acquired by optical scanner comparison between the CT reconstructed and the optically captured models. The comparison between the CT reconstructed and the optically captured models gives the information to optimize the parameters of the DICOM images segmentation process using the Singular Value Decomposition (SVD) method. The method uses all the physical models (impression, cast, radiographic template, study surgical template) that have been acquired by the optical scanner.  The 3D digital models are realigned virtually to give the best reconstruction model for the patient. The accuracy of the reconstruction of the radiological guide model by CT scanning has been verified by aligning the model obtained by processing the DICOM images with the gypsum cast. The model obtained by optical scanning is used as the anatomical truth. Optical scanning of the radiological guide, mounted on the gypsum cast, could be furthermore helpful for the integration of the prosthetic data within the bone structure. In case of not fully edentulous patients, the acquisition of teeth's shape could be used, in addition to gutta-percha markers, to optimize or verify the positioning of the radiological guide with respect to the maxillofacial structure. Moreover, the accurate digital model of the mouth impression could be the base for the direct design of the radiological guide using CAD/CAM technologies, without passing through manufacturing the gypsum cast, drastically reducing errors and planning time [76, 77].

Half of the patients at three months reported less satisfaction with speech. This is a well-known side effect of implant-supported prostheses, both fixed and removable. Implant patients reported that this was especially true soon after the installation of a fixed prosthesis on implants but unrelated to the presence of inter-dental spaces. Many of the patients in the control group of this cross-sectional study also had speech problems [74, 73].

Differences between CT Scan and CBCT Scan Techniques

In the recent pas, there has been a lot of scan used in the medical field including dentistry. Computer Tomography (CT) is an older technology having been in use since 1980s. On the other hand, Cone Beam Computed Tomography (CBCT) was only used for he first time in 1998 in Europe and 2001 n the United States. Both techniques are used in dentistry and have their strengths that dentists use to determine which one to use.

Among the biggest difference between the two, CT images provide more details than CBCT images. The bone density of the patient from CBCT images can not be determined. Although some people argue that it can be done using the Honsfield Units (HU) which is also referred to as the CT number, this assertion is however wrong since there is no concrete data relating these HU values to bone quality.  This leaves CBCT as inaccurate and without any reliable way to determine the bon density of the organ under examination [56].

The inaccuracy is as a result of the fact that different areas in a scan always possess different grey-scale values. These values depend on the relative positions of the organ in observation since the organ voxel on an image value in an organ depends highly on the position in the image volume.

On the other hand, CT technique reveals the three dimensions of the organ. It can also be manipulated to show two dimensions. It gives detailed images with all dimensions, shape and even defects of the under examination. The bone density is readily available from the images. Its largest critic is the recent questioning regarding its risk to cause cancer due to the radiations involved. In one case, it was accused to have a 1.5- 2% probability to cause cancer. However, these are figures that are yet to be proven and no heavy emphasis is laid on them, leaving it in use.

The dentist who is carrying out the implant usually has certain considerations to make before he decides whether to use CT or CBCT. Among them is the density of the bone in teeth implants. When the patient has a history of weak bones, CT should be used ahead of CBCT. Therefore, the choice of technique used, to some significant extent, is determined by the weaknesses or strengths of the technique. 

Conclusions

Scanning appliances are vital in the tooth implant process. It gives the software the dental form of the patient so that there can be a successful implant of the teeth or tooth. Therefore, details on use and errors that could be related to the appliance use should be provided. If the wrong image, for whatever reasons, is forwarded to the software, a wrong implant process would follow. This would result to poor recovery by the patients. It may even lead to the conditions of poor speech or enlarged dental from. At the same time, there need to be more knowledge on the best scanning guide to use at different times and different patients. This is because, whereas dual scan appliance provides the best results, it is less widely used. This may be due to its high costs it involves as compared to the more error prone single scan appliance.

Information regarding the scanning guide is scanty and needs to be more improved. There are many names given to the different scanning guides available, and this is not very healthy to the people who use and need the services they perform. A universal name needs to be developed to avoid miscommunications which could lead to dire consequences. This universal name would be important in communicating between patients, dentists and technicians. Furthermore, with the high dynamism in the field of computer science, there is need to come up with a term that would remain and be used at all levels of treatment.

The most widely used scanning appliances are single scan scanning appliance, Dual scan scanning appliance and two technologies scanning appliances. There need to be more research to determine the ways in which they can be improved to provide better results at a relatively lower cost. Today, people go for the less expensive yet more error prone single scan appliance due to its affordability.

Markers are important yet there is no concrete answer on which should be used at any given moment. Every time the operation is conducted, the manufacturer has to be contacted for instructions. Classification should be carried out in a composition that has the scanning appliance base as well as the nature of the used marker, such as, Acrylic / metal, Acrylic / barium sulphate, Acrylic / gutta-percha, Acrylic / barium sulphate coat, Acrylic alone, Acrylic radiolucent/ teeth made of barium sulphate –acrylic or Special markers.

Further, the patient should be actively involved in the treatment planning and his massage should be implemented through scanning appliance. Somebody else can do technical part for patient but decision about final aesthetic and beauty should be conveyed through scanning appliance.

CT scanning is burning this days and many time product of this scanning is not perfect because data is missing. Computer software use data that is inputted in the file, so if data is missing the treatment plan will be less than perfect. Optimal plan provides optimal results. Somebody has to stop half planning because of rush or leaking knowledge. Advertise “no scanning appliance need” is misleading as “tooth in one hour”. The guided implant surgery procedure needs more optical scanning if not as essential but as additional procedure to keep the volume in safe desirable limits.

Bone can not be scanned optically but data of mucosa and remaining dentition is key. Accuracy of scanner is 12 micrometers (Frisardi G, 2011).

To prevent error CT scanning, an optical scanning of the radiological guide, mounted on the gypsum cast the accurate digital model of the mouth impression could be the base for the direct design of the radiological guide using CAD/CAM technologies, without passing through manufacturing the gypsum cast, drastically reducing errors and planning time.

Finally, the research has determined that it is vital that optimal patient CT scanning should never be done without information about final prosthetic restoration in several missing teeth or complete edentulous cases.

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