Abstract
The aim of this narrative literature review is to present the possibilities of using cone beam computed tomography (CBCT) and 3D dental scanners to prepare comprehensive, interdisciplinary treatment plans. Scanners are instruments whose usage seems to be a key element of modern digital dentistry. Their importance in orthodontic treatment with overlay appliances, planning modern prosthetic treatments (CAD/CAM) and implantology cannot be overestimated. These scanners allow for accurate imaging of the tooth structures and their positioning independently in the maxilla and mandible as well as in the occlusion. As a result, dentists can plan treatment, e.g., in the case of the need to implant dental implants, prosthetic crowns or orthodontic braces. Dentistry was revolutionized to a similar extent by the introduction of CBCT to everyday diagnostics, which is the most advanced imaging technology that provides even more detailed images in 3 dimensions. Its use has enabled a wider and more precise range of diagnostics, which in turn has improved the quality of multidisciplinary treatment planning. This paper explains how scanners and CBCT can be used in orthodontics and prosthetics based on the articles found in 3 databases: PubMed, Scopus and Embase. The review included 28 articles on the aforementioned topics and was presented with a brief description of the content of each article.
Key words: orthodontics, prosthodontics, CBCT, scanners, modern dentistry
Introduction
Modern dentistry provides many new tools for carrying out diagnostics allowing for the preparation of the safest, interdisciplinary treatment plans. They include, e.g., cone-beam computed tomography (CBCT) and modern intraoral scanners.1
Cone beam computed tomography can be used in almost every field of dentistry as it allows for determining the spatial conditions of the jaw bones, which is used, among others, in dental surgery, orthodontics and maxillofacial surgery, but also enables precise assessment of alveolar processes, the quality and density of their bones, the course of individual tooth structures, such as root canals, which greatly facilitates endodontic treatment or endodontic re-treatment, and also makes it possible to detect even the smallest periapical inflammatory foci or external and internal resorption2. In orthodontics, CBCT makes it possible to assess bone conditions and plan the range of possible tooth movements while avoiding complications such as fenestrations, dehiscences or recessions.3
In implant prosthetics, CBCT can be used to assess the possibility of implantation without additional procedures, such as sinus floor elevation or bone grafting, and if the procedure is necessary, to design its scope and architectonics.4 After the initial planning of the implant insertion position and path, another digital element facilitating the complicated implantation procedure is the use of a Dynamic Navigation system or specially prepared surgical templates in CAD/CAM technology.5 Cone beam computed tomography also increases the safety of performed procedures, allowing for precise determination of the location of individual nerve canals, which are anatomically variable.6
In addition to CBCT, 3D scanners are also widely used in today’s dentistry. Intraoral scanners make it possible to reproduce the patient’s occlusion without the use of impression materials.7 This ensures accurate mapping of the mutual arrangement of teeth, which is necessary for proper diagnosis before orthodontic treatment and assessment of the correctness of the treatment effects, as well as minimizes the impression-taking procedure, which is unpleasant for patients. As a result, it is also possible to avoid distortions in models cast from impressions, when they are stored under inappropriate physical conditions. Owing to scanners, this problem can also be eliminated in prosthetics. They enable to accurately map the tooth preparation border for permanent restorations (inlays, onlays, crowns) directly in the patient’s oral cavity, or indirectly, by applying extraoral scanners used in prosthetic laboratories.8 Using special computer software, it is possible to determine the insertion path, and then fabricate the finished prosthetic appliance (e.g., in CAD/CAM technology) and transfer it into the patient’s mouth.
Nowadays, CBCT and scanners are auxiliary tools commonly used in various fields of dentistry, which is the aim of this article. It presents their principles, types, and applications based on academic knowledge and provides the current knowledge contained in articles from the last 5 years available in the US National Library of Medicine National Institutes of Health (PubMed), as well as Scopus and Web of Science databases. The last search was performed on May 10, 2023. Two authors selected and described the articles (WF, AJ), and the 3rd author reviewed them in accordance with the guidelines (MM). The results of their review are presented later in the article.
Objectives
The aim of this study was to present the advantages and possibilities of using CBCT and intraoral scanners in clinical practice during dental procedures, to show their usefulness in planning prosthetic and orthodontic procedures as a tool of modern digital dentistry.
Materials and methods
The present systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.9 The study took into account articles from 3 databases: PubMed, Scopus and Web of Science. The initial search took place on March 15, 2023, and included a total of 421 articles. After removing duplicates, 273 articles advanced to the next stage. Articles had to meet criteria such as being written in English and not being older than 5 years. After a deeper analysis, 214 articles were excluded due to a topic other than the main one discussed by the authors. Overall, 28 articles were included for the final description in the review if they met all the criteria, i.e., they referred to CBCT and/or dental scanners used in dentistry. A PRISMA 2022 Flow Diagram representing the study selection process is presented in Figure 1.
Cone beam tomography in dentistry
It is very interesting to observe how innovative technologies are increasingly applied in dentistry and orthodontics. Cone beam computed tomography, in particular, is becoming the imaging technique of choice in comprehensive orthodontic treatment.10
Over the past 2 decades, CBCT, a versatile 3D X-ray imaging technique, has become increasingly popular in the field of dental radiology.11 Since the development of the first CBCT device specifically for maxillofacial imaging in 1998, the variety of models has increased significantly, especially in the last 10 years.12
The CBCT technology uses a conical source of ionizing radiation and a 2-dimensional (2D) monitor.13 It offers dimensionally accurate multi-dimensional images for diagnosis and treatment planning. The isotropic voxels (volume elements) in these images provide accurate multiplanar images in any direction.14 Each volume element has equal dimensions in each of the 3 perpendicular planes.
Principles of CBCT
The principle of CBCT scanning is based on the rotation of a gantry with an X-ray tube and an image detector. The X-ray cone beam is attenuated by the patient’s tissues and the imaging area is exposed during scanning. Partial tissue exposure occurs in a rotating region around the imaging area, as the X-ray beam cone sweeps the necessary angular range to obtain the raw projection images used to reconstruct the final 3D CBCT images.15
Radiation doses from CBCT devices can be determined using an optically stimulated luminescence dosimeter (OSLD) or the Monte Carlo method. In the first method, a phantom simulating human body tissues in the maxillofacial area was equipped with OSLD and subjected to 4 different test conditions using 2 different devices. The irradiated portion of the skin, lymph nodes and muscles of the head and neck area was estimated to be 5%, and the irradiated portion of the esophagus was estimated at 10%. In both cases, the oral mucosa and salivary glands were the most frequently irradiated organs.16
The use of CBCT in prosthetics and orthodontics
The digitization of orthodontic and prosthetics procedures is increasing due to the use of the latest technologies. Currently, better and more individualized treatment planning is possible, largely due to the use of overlays, digital dental models and wider access to CBCT images.17
In addition, CBCT offers applications for surgical procedures, such as conducting CT scans with computer-generated surgical templates used in implant prosthetics, as well as enhanced in-office diagnostic capabilities. Current practice requires a thorough understanding of the basics of CBCT science and the ability to accurately and fully interpret images.18
The tables below summarize the potential applications and current knowledge on some types and selected properties of CBCT, which is increasingly used in dental prosthetics (Table 1) and orthodontics (Table 2).
Scanners in dentistry
Intraoral scanners are used to visualize the maxillary and mandibular dental processes together with their soft tissues.33 They allow for digitization of dental arches to create virtual models that replace conventional dental impressions.
The scanner works by projecting a light source in the form of a laser or structured light to capture 2D images of the object being scanned. The scanner software then processes the captured 2D images to create point clouds, which are triangulated to create a 3D surface model (mesh) of the scanned object.34
The history of intraoral scanners dates back to 1985, when a scanner called CEREC 1 was developed by Dentsply Sirona. However, the system created over 30 years ago had its limitations – it provided a 2D view of scanned images and was only used to create posts for immediate cementation.35
Since then, the shortcomings of the scanner have been removed and the device has been improved. The current version of the system is CEREC 3D, and there is a whole list of intraoral scanners available on the market. These include, i.a., Trios 3 and Trios 4, iTero Element, iTero 2, iTero 5D Element, Dental Wings, Panda, Medit i500, Planmeca Emerald™ and Aoralscan. Of these, the Trios series shows the highest scanning accuracy. It should be noted that regardless of the type of scanner used, moving the device away from the scanned image has a negative effect and reduces the accuracy of measurements. The same happens when scanning from a different angle. It has been shown that diagonal scanning reduces the precision of mapping, so it should always be done carefully and in accordance with the manufacturer’s recommendations.36
In addition to the scanning technique, the operator’s experience is important. The more experienced the operator and the smaller the area to be scanned, the more precise the effect is.37
Orthodontic scanners are used at the beginning, during and after treatment. There is often a need to obtain an image of full dental arches together with the fixed orthodontic appliances. There may be doubts about the accuracy of the obtained scan. Studies have shown that the presence of orthodontic brackets has no clinically significant effect on the scanning precision.38
The use of scanners in prosthetics and orthodontics
For prosthetic reconstruction planning or malocclusion diagnosis, it is important to register occlusal contacts. The intraoral scanner minimizes the need to use occluding papers for this purpose, because the interocclusal record made with intraoral scanners is more accurate than the measurement using traditional physical methods.39
An important procedure in both prosthetics and orthodontics is reporting the mutual position of the maxilla and mandible at various stages of treatment. In the case of conventional methods, such registration may give false measurement results due to the deformation of the materials used. Intraoral scanners overcome this problem – there is no need for materials, so there is no deformation and the results become repeatable.40
The following tables summarize the current knowledge on the selected types as well as properties of scanners used in prosthetics (Table 3) and orthodontics (Table 4).
Discussion
Three-dimensional models designed on the basis of CBCT can be used to perform various types of procedures, such as crown lengthening, making a surgical template, or redesigning the patient’s occlusion using specialized software. This is possible by converting CBCT images from Digital Imaging and Communications in Medicine (DICOM) files to STL, which in turn can be applied to stereolithographic (STL) files from intraoral scans, and then, using 3D printers, a specific drill guide can be prepared.55, 56 Cone beam computed tomography is also helpful in implant prosthetics. The accuracy of imaging of bone defects around implants using CBCT was assessed by Song et al.57 The study showed that CBCT is more accurate and reliable than intraoral imaging in detecting, classifying and measuring peri-implant bone defects. Based on the data obtained, it is possible to take actions whose righteousness could not be confirmed with intraoral imaging alone.
Cone beam computed tomography tools also have their drawbacks as their accuracy can be affected by factors such as patient’s movement, metal artifacts, device-specific exposure parameters, software, and manual and automated procedures.58 They can reduce the precision and reliability of linear measurements in CBCT images.
The development of CBCT and CAD/CAM technologies has made it possible to create partial dentures and single crowns with precise mapping of tooth, arch and bone anatomy. Direct transfer of CBCT data to CAM software can eliminate a number of manufacturing processes. After tooth preparation, crowns can be restored directly on the prepared natural teeth, without the need to take final intraoral impressions thanks to CBCT with a voxel size of 0.125 mm, which is necessary for diagnosis and/or treatment planning.59 However, CAD/CAM technology is not without its disadvantages, because prosthetic restorations are milled from large blocks and about 90% of the prefabricated blocks are lost during their machining.60
Intraoral scanners have significantly shortened the time from the patient’s first visit to the completion of treatment. Omitting the stage of making a conventional impression shortens the time needed to send it to the prosthetic laboratory, as well as the time needed for corrections caused by a communication error between the doctor and the technician.61 Regarding the aforementioned communication, the scanner is also a tool that helps in mutual understanding between the doctor and the patient. Presentation of a prosthetic or orthodontic problem by means of a scan displayed on the monitor screen better illustrates the scale of the problem to the patient and makes it possible to avoid misunderstandings resulting in the failure to meet the patient’s expectations or irreversible damage to the patient’s tissues. In the patient–doctor–technician relationship, the mapping of the patient’s oral tissues using a scanner instead of conventional impressions reduces the risk of cross-infection, which is important given the existing problem of unsatisfactory awareness of dental technicians about infection control.62 Al-Mortadi et al. assessed the knowledge of dental technicians in Jordan about infection control and their practice of disinfection.63 Over 40% of laboratories admitted that they did not adequately disinfect both alginate and silicone impressions. Most (more than half) of the laboratory owners believe that disinfection of impressions is only the dentist’s responsibility before sending them to laboratory, and 38% of the respondents declared that they did not use gloves in the laboratory.
Specialists from all fields of dentistry, especially orthodontics and prosthetics, would not be able to fully solve the patient’s problems without imaging. Scanners are a very good clinical tool for routine assessment of treatment effectiveness. Due to the fact that data are collected in files on a computer, there is no problem with the lack of space for the required storage of plaster models for 20 years after treatment. Nevertheless, the CBCT scanner is quite large, which is its disadvantage, as is its price.64
Scanned images provide essential information needed for digitally assisted design and even fabrication of full dentures. Data obtained with scanners are often more precise and accurate than those obtained with analogue impressions.65 Al-Atyaa and Majeed proved that the impression technique had a significant impact on the marginal and internal seal of CAD/CAM monolithic zirconia crowns.66
Differences in mean values of marginal fissures caused by the impression technique were statistically significant. Zirconium oxide crowns made using an intraoral scanner showed a better marginal and internal fit than crowns made with conventional impression techniques. The authors also noted that, among conventional impressions, a better fit of the crowns is obtained with the use of a two-step rather than one-step impression-taking method. In turn, when comparing the discrepancy in the marginal seal of lithium disilicate crowns made in CAD/CAM technology using conventional impressions and with the use of intraoral scanners, it was found67 that there is no statistically significant difference in the effects between the above-mentioned impression techniques.
A similar level of accuracy is achieved in the case of crowns made using conventional and digital impressions.
In reviews with meta-analyses performed by other authors, we can find information that IOSs are precise enough to provide full-arch digital impressions that meet clinical requirements. The accuracy of IOS’s for complete arches can change depending on the clinical situation. Based on information from articles examined in another systematic review, objectives could not be precisely and objectively defined. The authors do not know which implant impression approach results in a superior passive fit of the superstructure.68, 69
Limitations
When scanners and CBCT are used, we can count on more accurate imaging of tissues and anatomical structures within the patient’s head, but unfortunately there are also limitations to this technology. A large number of studies indicate the advantages of using these devices in everyday clinical practice.
However, taking into account the opinion of many prosthetic technicians working in prosthetic laboratories, it can be noticed that not all scans allow for as accurate reflection of the patient’s oral cavity conditions as impressions taken, e.g., with silicone or polyether masses. They believe that impressions prepared with the use of scanners often need additional corrections, which extends the treatment time and causes additional visits to the dentist’s office.46
In the case of CBCT, the main limitations that may occur during the examination are the high cost of the device, which translates into a higher cost of the examination, limited access to the radiology laboratory, and exposure of the patient to ionizing radiation.14 The limitation for the physician is mainly the additional need for training, which also generates costs for the office.
Conclusions
Cone beam computed tomography is a tool for in vivo and in vitro examinations of oral cavity tissues. Despite the existing doubts and discussions regarding the safe dose of radiation, it has been proven that cone beam tomography can be applied in various fields of dentistry, from maxillofacial surgery through prosthetics to orthodontics.
Early detection of changes in the bone and its more accurate image help to plan a safe range of tooth movements and to notice early periapical changes that are a contraindication to moving the teeth.
Intraoral scanners allow for hard tissue imaging, which can be useful in prosthetics to determine the margin of preparation during tooth preparation procedures for permanent restorations, and in both prosthetics and orthodontics to determine and design the occlusion.
Despite the discussed applications for both tools, there are still many fields of dentistry and other applications that have not been described so far, and future research may enable their widespread use in everyday dentistry.
