Tomography Imaging In Dental Implantology Health And Social Care Essay
Dental implants have exceptionally changed the enigmatic course of permanent tooth replacement. The use of advanced imaging studies has been the first rung of the ladder leading to this successful treatment protocol. Till date, Dental Computed Tomography had been the accepted procedure for characterizing the anatomy of jaws and to circumvent the dental related abnormalities. A number of other modalities like Dentascan, CBCT, and SIMPlant to name a few have opened new horizons, increasing the diagnostic potential and thereby making the diagnostic process more interactive. This article reviews the various imaging modalities available for assessing bone density, use of radio-opaque surgical guide, simulation of implant placement using computerized application of CT leading to enhanced prognostic values of the pre-operative implant site.
Key-words: Dental implants, Computed tomography, CBCT
Key Messages: Dental CT enables the analysis of quality and quantity of bone, jaw tomography and important anatomical landmarks. Interactive CT, plans both the surgical and the prosthetic phase of the treatment, thereby terming it rightly, "it’s not the SCAN, it’s the PLAN.
According to the World Health Organization, complete or partial absence of natural teeth is a public health problem with potential poor outcomes. The development of the osseointegrated type of dental implant in the l970s by Branemark was the breakthrough that made dental rehabilitation more reliable. The advent of three-dimensional imaging and surgical planning software for implant placement has profoundly affected the science of implantology. Proper implant treatment planning remains the first priority for implant success. Dental imaging is an important tool to accomplish this task. It is now possible to plan more accurately and place dental implants more precisely.1,2 This article gives an update about the role of CT imaging in dental implant treatment planning.
VARIOUS DIAGNOSTIC AIDS
Diagnostic imaging can play an important role in evaluating the dental implant patient.3,4,5 Several intraoral and extraoral radiographic methods such as periapical, occlusal, panoramic, motion tomography and reformatted cross-sectional, panoramic, and 3D imaging are commonly available for evaluation of the implant recipient site. The information obtained is a bidimensional geometric projection.6
Radiographic evaluation assesses the bone support for endosseous dental implants. Superimposition, poor visualization of other anatomic structures and distortion are some of the drawbacks of these techniques.7 Discrepancies in measurements are commonly encountered, especially if the site of interest is less than 15 mm high when compared with those from volumetric methods such as multidetector computed tomography (CT) or cone-beam CT. Dental CT has been a more accurate and reliable technique for preoperative evaluation of dental implantation. Dental CT can demonstrate the quantity of bone in three dimensions, the location of important adjacent anatomic structures (eg-:mandibular canal, dental inferior nerve, incisive foramen, mental foramen, maxillary sinus), and the quality of available bone with minimal geometric distortion.7
COMPUTED TOMOGRAPHY (CT): CT is a digital medical technique, which can generate 3-dimensional images of a patient´s anatomy by reconstructing many axial slices. Visualizing the bony architecture, nerves, joints, sinuses and other anatomical structures is much more complete with a three-dimensional scan than with a traditional two-dimensional radiograph. The newer generation of CT scans produces axial images perpendicular to the long axis of the patient by rotating a radiation source which emits fan-shaped beams 360 degrees around. The detectors capture X-rays, which transmit the subject and the data is processed by a computer. It is unique in that it provides images of a combination of soft tissues, bone and blood vessels.8 CT scans can identify most inferior alveolar canals when multiple cross-sectional views are performed.9 CT scans have been shown to be very accurate with the magnification effect, the same for both the anterior and posterior area, from a range of 0% to 6% in horizontal as well as 0% to 4% in vertical dimension.10 The technique of Dental CT also known as Denta Scan was developed by Schwartz et al.11 The Dental CT can be performed with a conventional CT, a spiral CT, or a multislice CT scanner [Figure1a-b].
WHY CT ADVANTAGEOUS OVER OTHERS
A conventional x-ray technique, such as periapical, occlusal, and panoramic radiography, is a simple, low-cost, and still frequently used method, but the information provided might be insufficient. Geometric distortion occurs in about 25% of studies, since the plane parallel to the beam superimposes structures. In addition, this method cannot demonstrate opacity differences of less than 10% and does not provide details about the adjacent anatomy.6 Quantitative computed tomography (CT) (i.e., quantitative interpretation of values derived from Hounsfield units with a suitable calibration procedure) is the modality of choice to determine bone mineral density (BMD). Quantitative CT to measure BMD by using simultaneous scanning for calibration has been extended to the jaws.12,13,14,15
High-resolution dental CT can generate panoramic, cross-sectional, and three-dimensional reformatted images of the alveolar bone and adjacent structures providing accurate information about bone height and width of the alveolar ridge to determine the alternatives for dental implantation.16,17 Elimination of superimpositions is an advantage with a dental CT. Contrast resolution is another major advantage of dental CT, that allows distinction of opacity differences between two tissues and further image projections or planar reformations can be performed.6 Dental CT can be achieved with a multidetector CT or more recently with cone-beam CT. 18,19,20,21
Cone Beam Computed Tomography (CBCT) or Cone Beam Volumetric Tomography (CBVT):
Because of higher radiation exposure, higher cost, huge footprint, and difficulty in accessibility associated with CT, a new type of CT, CBCT was developed [22, 23]. Cone beam CT (CBCT) scanners, newer generation machines specifically designed for the maxillofacial region, have allowed for reduction in the radiation absorbed by the patient. It uses a single 360 degrees rotation around the maxillofacial region and a cone beam, in comparison, a spiral CT, which makes several rotations and uses a fan beam. When matched up next to the conventional CT the lower cost, radiation exposure, and in-office feasibility of CBCT render it the ideal model for oral and maxillofacial radiology. The theoretical resolution of CBCT is higher than CT. The voxel size, an indicator of resolution, can be as small as 0.1 mm for CBCT when compared to 0.5mm for modern CT.
Indications and Contraindications
The most relevant indications for dental CT in preoperative evaluation of dental implant placement (listed in order of importance) are as follows:
(a) Assessment of height and thickness in cases of alveolar bone atrophy24
(b) Assessment of structures and their position, critical for adequate implant placement (e.g., inferior alveolar canal, incisive and mental foramina, pneumatization of the maxillary sinus, floor of the maxillary sinus, nasal floor)
(c) Diagnosis and treatment planning in maxillofacial surgery
(d) Examination after placement of implants and bone grafts
(e) Evaluation of bone resorption and root retention, as well as lesions of the facial skeleton.
The main contraindications include claustrophobia, Parkinson disease, tremors, tics and disabling conditions that might cause a patient to be uncooperative. One of the drawbacks of multidetector CT is radiation dose, which has been an issue of concern. 24
DENTAL IMPLANTS AND CT
Considering the new age tool, it blends the concept of thin layer radiography (tomography) with computer synthesis of image. It was first applied successfully in implantology in the 1980s. In computed tomography (CT), multiple thin axial slices at small distances are obtained through the jaws and data is reformatted with special software package to produce cross-sectional, panaromic and 3Dimages. As long term dental implantation becomes more successful from both a functional and a cosmetic perspective, imaging before such implantation will become the responsibility of the implantologist. Model based treatment planning with the assistance of CT images has been developed to fulfill the purpose.25 After a diagnostic cast and a preplanned wax-up, diagnostic templates are fabricated or modified from existing dentures.26 The implant position as well as direction is determined based on final restoration position using radiopaque material, such as gutta-percha27 or metal pins28 to mark the spots. Images are then evaluated for available bone height, width and related vital anatomical structures [Figure2: a-b].
Preliminary CT examination of the mandible or maxilla for implantation uses a bone algorithm to obtain contiguous 1-mm thick axial images of the mandible (excluding the condyles)or the maxilla parallel to the alveolar ridge. A custom- designed stent may be worn by the patient during CT examination.29,30 The volume of data acquired by the CBCT is then reformatted to synthesize three different types of two-dimensional images. The three types of two-dimensional CT reconstructions are axial scans, cross-sectional reconstructions and panoramic reconstruction [Figure3: a-c].31
The most important information to document is the location of the indicated site, bony height, width (with the cortex included) and inclination from the vertical are noted [29, 30,]. Bone atrophy and remodeling of the alveolar ridge are common after tooth removal or loss; important landmarks should be noted such as the bony depth to the mandibular canal and the distance to the inferior recess of the maxillary sinus or to the floor of the nasal cavity . If a stent is not used, similar data should be recorded from edentulous areas or at selective sites such a parasymphyseal and premolar locations. The quality of bone directly affects the success of osseointegrated implants [Figure4: a-b].
Interactive Implant Treatment Planning
An interactive computer program can be used for examination before dental implantation. With the aid of interactive software, another approach for the transfer of implant planning to the surgical site is to use Computer-aided design/Computer-aided manufacturing technique. Many software programs are currently available [Table- 1]. These programs enable the clinician to transfer CT/CBCT findings in to surgical area. Using one of these software programs, clinician uses the CT data obtained with the same displays of axial, cross-sectional, and panoramic images, allowing them for a pre-operative simulation of implant placement, prosthetic simulation and bone augmentation simulation that makes the software the state-of-the-art imaging tool for implants. Bone width and height and regional abnormalities are determined, and measurements of bony attenuation are performed. Additionally, an implantology team can manipulate graphically displayed implants to allow a more accurate selection of implant size and orientation and a better appreciation and estimation of reconstructive needs such as bone-graft augmentation [Figure-5].
Furthermore the placed implant can be evaluated from several different viewpoints as well as from 3-dimensional view. It can also be rotated and tilted on any axis to adjust its position. For multiple implant placements, the parallel relationship to simplify prosthetic reconstruction can be ascertained. Moreover, once treatment planning is determined in the computer, it can be saved and applied to surgical sites by means of image-aided template production32 or image-aided navigation.33 The primary interest in the literature is the accuracy of transferring treatment plan into surgical field. CT based implant planning and its transfer to the surgical field via a surgical guide has resulted ~1 mm of mean linear deviation and 3degrees mean angulation difference. Although computer-aided-implant placement is a promising technique, the unexpected high linear deviation which sometimes reaches 4 mm and angulation deviation 17 degrees34 can be a major concern. Hence more research is needed before this approach can be widely used. With the use of interactive CT, not only is the surgical phase of treatment planned, but the prosthetic phase is planned as well.
The dental implant team’s ability to plan, place and restore implants accurately, has been greatly enhanced by the use of computer-guided implant surgery. This level of precision was unattainable a few years ago. More than diagnosis, CBCT permits and facilitates an image-guided surgery and hence rightly quoted as "It’s not the SCAN, it’s the PLAN." 35
Table 1-Software Programs for Implant Treatment Planning
Comparison of some of commonly used Software Programs for Implant Planning
Compatible with stereolithography (SLA) technique
Noble Biocare, Sweden
Compatible with SLA technique Dual-scan technique: the patient scanned with the guide and the guide itself alone
Compatible with Five-axis milling technique Copu-Guide (Pilot and the Complete Compu-Guide)
Compatible with SLA technique Have license to make guides in the United States Dual-Sscan technique
Volumetric superimposition function 3D Stitching Plugin Create-Model (compatible with SLA)
Astra Tech, Sweden
Based on the SimPlant software
Keystone Dental, Ml
Xmmarker: allow for surgical guide manufacturing process
Patterson Dental, St. Paul, MN
Volume-to-volume superimposition 3D nerve marking
Compatible with SLA technique
Summary & Conclusion:
Dental CT enables an analysis of the state, quality, quantity of bone, jaw tomography and important anatomical landmarks. However, because of its higher radiation dose and cost, CBCT was introduced to overcome these shortfalls. With images acquired from CBCT and the assistance of software programs, clinicians may now place implants in the ideal position while avoiding vital structures so they can fulfill esthetic, functional and biologic demands. For the near future CBCT imaging can be seen as an indispensable part of dental imaging armamentarium.