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DIAGNOSTIC IMAGING AND TECHNIQUES FOR IMPLANT PATIENTS by Dr. Smijal GM DEPT OF PERIODONTICS
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CONTENTS Introduction Imaging Objectives Imaging Modalities Presurgical Imaging- Periapical radiography Digital radiography Occlusal radiography Cephalometric Radiography Panoramic Radiography Tomography Computed Tomography MRI Imaging of vital structures Intraoperative Imaging Fabrication of Diagnostic template Radiographic signs associated with failing endosseous implants Conclusion
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INTRODUCTION Diagnostic imaging and techniques help develop and implement a cohesive and comprehensive treatment plan for the implant team and the patient. Several radiographic imaging options are available for diagnosis and treatment planning of patients receiving dental implants Options range from standard projections routinely available in the dental office to more complex radiographic techniques typically available only in radiology centers
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Standard projections include – Intraoral (periapical, occlusal) Extraoral(panoramic, lateral cephalometric) radiographs More complex imaging techniques include conventional x-ray tomography, computed tomography (CT), and cone-beam CT (CBCT)
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IMAGING OBJECTIVES Factors affecting The amount of information required Type of information required Period of treatment rendered The decision of when to image along with which imaging modality to use depends on the integration of these factors & can be organized into 3 phases – PHASE 1 [ Presurgical implant imaging] PHASE 2 [ Surgical and Intraoperative implant imaging] PHASE 3 [ Postprosthetic implant imaging]
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PHASE 1 [ Presurgical implant imaging] Involves all past radiologic examinations and new radiologic examinations to determine the patient's final and comprehensive treatment plan. Objectives To determine the quantity, quality and angulations of bone Determine relationship of critical structures to the implant site. The presence or absence of disease at the implant site.
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PHASE 2 [ Surgical and Intraoperative implant imaging] Focused on assisting in the surgical and prosthetic intervention of the patient. Objectives To evaluate the surgical site during and after surgery Assist in the optimal position and orientation of dental implants Evaluate the healing and integration phase of implant surgery To ensure that abutment position and prosthesis fabrication are correct.
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PHASE 3 [ Postprosthetic implant imaging] It commences just after the prosthesis placement and continues as long as the implant remains. Objectives To evaluate the long term maintenance of implant rigid fixation and function, including crestal bone levels To evaluate the implant complex.
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IMAGING MODALITIES Maximizing the ratio of benefit to risk for imaging examinations is a fundamental tenet of radiology Analog or digital Two or three dimensional Analog imaging - two-dimensional systems that use radiograph films or intensifying screens as the image receptors A digital two-dimensional image is described by an image matrix that has individual picture elements called pixels A digital three-dimensional image is described by an image matrix that has individual image/picture elements called voxels & is described not only by its width & height but also by its depth/ thickness
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Image receptor Direct systems: CCD (charged coupled device) and CMOS (complementary metal oxide semi-conductor) solid-state sensors contain silicon crystals converting photons to electrons. For CCDs, pixel charges are transferred to a common output source, while for CMOS conversion takes place at each pixel Indirect systems: Photostimulable storage phosphor (PSP) plates for dental imaging strongly resemble the small and especially thin intraoral ﬁlms. These plates can be designed into similar formats, including occlusal sizes, and are thus often better tolerated by patients. The major difference with ﬁlm is the absence of saturation
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Image quality characterized by Analog imaging modality: resolution/ modulation transfer function, contrast/H and curve, noise/Weiner spectrum and sensitivity Digital imaging modality: width and height of its pixels Digital three dimensional imaging: described not only by its width and height and pixels but also by its depth/thickness An imaging volume or three dimensional characterization of the patient is produced by contiguous images, which produce a three dimensional structure of volume elements (i.e computed tomography [CT], magnetic resonance imaging [MRI], and interactive computed tomography [ICT]. Each volume element has a value describing its intensity 3D modality-intensity scale of 12bits or 4096 values
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Periapical Radiography (Analog) Panoramic Radiography (Analog) Occlusal Radiography (Analog) Cephalometric Radiography (Analog) Tomographic Radiography Computed Tomography (3-D) Magnetic Resonance Imaging(3-D) Interactive Computed Tomography(3-D) The imaging modalities can be-
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Also
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PRESURGICAL IMAGING Main goals – Identify disease Determine bone quality Determine bone quantity Determine implant position Determine implant orientation While selecting the radiographic modality for the patient recommended principle is the ALARA Principle. “As Low As Reasonably Achievable”
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PERIAPICAL RADIOGRAPHY By placing the film intraorally parallel to the body of the maxillary or mandibular alveolus. The central ray of the x-ray device - perpendicular to the alveolus at the site . Produces a lateral view of the alveolus, no cross-sectional information May suffer from distortion & magnification Are two-dimensional representations of three-dimensional objects and do not provide any information of the buccal-lingual dimension of the alveolar ridge
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ADVANTAGES Low radiation dose Minimal magnification with proper alignment and positioning High resolution Inexpensive LIMITATIONS Distortion and magnification Minimal site evaluation Difficulty in film placement Technique sensitive INDICATIONS Evaluation of a small area Alignment and orientation during surgery For recall and maintenance therapy
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PARALLELING TECHNIQUE- The film, long axis of tooth, and x-ray source are all parallel, with the path the x-rays being perpendicular to all three. With this technique, you have less magnification when there is a greater distance between the x-ray source and the film with the film being as close to the tooth as possible.
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BISECTING ANGLE TECHNIQUE An imaginary line is visualized that splits the distance between the film and the long-axis of the tooth. The x-ray head is then moved to be parallel to this imaginary line. This technique results in decreased exposure time.
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Increasing image quality- Use smallest focal spot possible (a smaller focal spot increases the sharpness of the image)…this is controlled by the manufacturer Increase the distance between the x-ray source and the film Place the film as close as possible to the object (e.g. tooth) Make the path of the x-rays perpendicular to the film Position the film as parallel as possible to the object To reduce radiation Stand at least 6 feet away from the unit and/or stand behind a lead shield Stand at 90-135 degrees from the path of the x-rays
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CONTROLLING THE IMAGE QUALITY When taking a radiograph, you have control over these three parameters: o Kilovoltage o Milliamperes o Exposure Time.
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1. Kilovoltage (kVp) - speed at which the electrons move between the cathode and anode of an x-ray machine. Increased kVp, shortens wavelength of xrays and gives them the momentum to travel through materials better. Cause for less contrast in the image (more grey). Thus increase kVp is increased only to accomodate a denser object to pass through, such as a thick mandible. kVp range for dentistry is 65-100 kVp.
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2. The quantity, or number, of electrons is controlled instead by the temperature of the filament. A hotter filament - more electrons. The volume of electrons is measured in milliamperes (mA). Affects the intensity of the x-ray. mA range for dentistry is 7-15 mA. 3. Exposure time refers to how long x-rays are produced or how long the patient is exposed to them. Exposure is often controlled by impulses, with there being 60 impulses in 1 sec.
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BUCCAL OBJECT RULE: Used to determine the buccolingual relationship of an object (e.g. artifact) in relation to a second object (e.g tooth) i.e to determine if the object lies buccal or lingual to the second object. The protocol is to take two separate images at two different angles.
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The first image is made straight on, while the second one is made at an angle more toward the mesial or distal. By comparing the two images, you can decipher the relationship using this simple rule: SLOB = Same Lingual, Opposite Buccal If you take the second image from a more mesial angle, if the object moves more mesial as well (or in the Same direction), then the object is buccal to the second object.
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The initial radiograph (left) indicated that a metal foreign object was embedded somewhere in or near the teeth, but upon clinical examination, it could not be found anywhere in the gum tissue. Upon taking another radiograph (right) exposed at a very severe distal angulation, however, the metal fragment appeared to move a great deal to superimpose on the facial aspect of the premolar, indicating that the fragment was way more buccal than initially suspected. With the use of this second film, it was determined that the metal fragment was indeed embedded in the cheek.
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DIGITAL RADIOGRAPHY The film is replaced by a sensor that collects the data. Data is interpreted by a specialized software and the image is formed on a computer screen. Types of sensors: Charge-coupled device (CCD) (commonly used) Complementary metal oxide semiconductor / active pixel sensor (CMOS/APS) Charge injection device (CID)
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ADVANTAGES: Less radiation because the sensors are more sensitive (exposure times 50-90% less). Immediate result Ability to enhance the images (which can lead to more effective diagnoses) Patient education is better because the dentist is able to show things easier You don’t need a processor, chemicals, special rooms, film, etc.
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DISADVANTAGES: High initial start-up costs Learning curve (the staff and the doctor must be trained on how to take, view, and manipulate the radiographs) Increased thickness of the sensors & position of the connecting cord (Positioning of sensor difficult in some sites such as those adjacent to tori or tapered arch form in region of canines) Digital radiographic system that includes digital sensor and computer.
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OCCLUSAL RADIOGRAPHY Planar radiographs produced by placing the film intraorally parallel to the occlusal plane The central x-ray beam passes perpendicular to the film for mandibular image and oblique (45°) for maxillary image. Produce high resolution images.
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Maxillary occlusal view is inherently oblique and so distorted that they are of no quantitative use for implant dentistry for determining the geometry or the degree of mineralization of the implant site Critical structures such as the maxillary sinus, nasal cavity, and nasal palatine canal are demonstrated, but the spatial relationship to the implant site generally is lost in this projection Mandibular occlusal radiograph is an orthogonal projection, it is less distorted projection than the maxillary occlusal radiograph
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Maxillary full occlusal view technique
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Mandibular full occlusal view technique
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ADVANTAGE Evaluation for pathology LIMITATIONS Does not reveal true buccolingual width in mandible Difficulty in positioning
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CEPHALOMETRIC RADIOGRAPHY Oriented planar radiographs of the skull. The skull is oriented to the x-ray device and the image receptor using a cephalometer. It fixes the position of the skull with the projections into the external auditory canal. Patient's midsagittal plane oriented parallel to the image receptor.
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The width of bone in the symphysis region and the relationship between the buccal cortex and the roots of the anterior teeth also may be determined before harvesting this bone for ridge augmentation This technique is not useful for demonstrating bone quality and only demonstrates a cross sectional image of the alveolus where the central rays of the x-ray device are tangent to the alveolus.
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ADVANTAGES Height/width in anterior region Low magnification Skeletal relationship Evaluation of quantity of bone in anterior region LIMITATIONS Reduced resolution and magnification Technique sensitive Image information is limited to ant. region. INDICATIONS Used in combination with other techniques for anterior implants. Symphysis bone graft evaluation.
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PANORAMIC RADIOGRAPHY A curved plane tomographic radiographic technique used to depict the body of the mandible, the maxilla, and the lower half of the maxillary sinuses in a single image. The image receptor has been the radiographic film but may be a digital storage phosphor plate or a digital charge-coupled device receptor.
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Equipment consists of a horizontal rotating arm which holds an X-ray source and a moving film mechanism (carrying a film) arranged at opposed extremities. The patient's skull sits between the X-ray generator and the film. The X-ray source is collimated toward the film, to give a beam shaped as a vertical blade having a width of 4-7mm when arriving on the film, after crossing the patient's skull. Image receptor: radiographic film or digital storage phosphor plate or digital charge coupled device
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Also the height of that beam covers the mandibles and the maxilla regions. The arm moves and its movement may be described as a rotation around an instant center which shifts on a dedicated trajectory. The posterior maxillary regions are generally the least distorted regions of a panaromic radiograph.
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The tomographic section thickness of panaromic radiograph or trough of focus is thick, approximately 20mm, in the posterior regions and thin 6mm, in the anterior regions. All panoramic beam angles are approximately at 8 degrees, which gives the image inherent magnification Because of the curvature of the arch, panoramic machines have changing rotational centers.
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ADVANTAGES Easy identification of opposing landmarks. Initial assessment of vertical height of bone. Convenience, ease, and speed in performance in most dental offices. Evaluation of gross anatomy of the jaws and any related pathological findings. LIMITATIONS Distortions inherent in the panoramic system. Errors in patient positioning Does not demonstrate bone quality. Misleading quantitate because of magnification and no third dimension No spatial relationship between structures
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The x-ray source exposes the jaws from a negative angulation and produces a relatively constant vertical magnification of approximately 10 % The horizontal magnification is approximately 20% and variable depending on the anatomical location, the position of the patient and the focus object distance, and the relative location of the rotation center of the x-ray system Non-uniform magnification maybe in the range of 15%-220% More magnified as object-film distance increases and object x-ray source distance decreases
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Diagnostic templates that have 5-mm ball bearings or wires incorporated around the curvature of the dental arch and worn by the patient during the panoramic x-ray examination enable the dentist to determine the amounts of magnification in the radiography.
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Focal trough Invisible area 3D curved zone in which structures are clearly demonstrated on a panoramic radiograph Structures located within the focal trough appear reasonably well defined in the panoramic radiograph Structures inside or outside focal trough appear blurred on the panoramic film Narrow in anterior region and wide in posterior region Predetermined by manufacturer
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TOMOGRAPHY Tomography is a generic term formed from the Greek words tomo (slice) and graph(picture) Adopted in 1962 by the International Commission on Radiological Units and Measurements Describe all forms of body section radiography.
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PRINCIPLE The basic principle of tomography is that the x- ray and the film are connected by a rigid bar called the fulcrum bar, which pivots on a point called the fulcrum. When the system is energized, the x-ray tube moves in one direction with the film plane moving in the opposite direction and the system pivoting about the fulcrum. The fulcrum remains stationary and defines the section of interest, or the tomographic layer.
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Factors affecting tomographic quality Amplitude and direction of tube travel Greater amplitude of tube travel, thinner the tomographic section Linear tomography- simplest form x-ray tube and film move in a straight line One-dimensional & produces blurring of adjacent sections in one dimension, resulting in linear streak artifacts Complex motion, high quality tomography Two-dimensional motion of tube and film Uniform blurring of the regions adjacent to tomographic motion Circular, spiral and hypocycloidal tube motions used
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Structures that are in the plane (focal area) of rotation are depicted in sharp focus, while structures outside the plane of rotation are blurred The resulting image is a true cross section of the structures within the imaged plane, which is perpendicular to the x-ray beam A. Panoramic radiograph with markers indicating the five prospective implant sites.
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B. Conventional tomography of the same five prospective implant sites in the anterior and posterior maxilla. Note the tooth-shaped markers used that allow the clinician to evaluate bone dimensions in the jaw relative to the planned prosthetic tooth position
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Single-site evaluation Vital structures evaluation Cross-sectional views Constant Magnification CONVENTIONAL TOMOGRAPHIC IMAGES Indications- Advantages- Limitations Availability Cost Multiple Images Technique sensitive Blurred images High radiation dose
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COMPUTED TOMOGRAPHY CT is a digital and mathematical imaging technique that creates tomographic sections where the tomographic layer is not contaminated by blurred structures from adjacent anatomy. CT enables differentiation and quantification of soft and hard tissues.
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Invented by Hounsfield (1972). CT produces axial images of a patients anatomy. The x-ray source is attached rigidly to a fan-beam geometry detector array, which rotates 360 degrees around the patient and collects data. The image detector is gaseous or solid state, producing electronic signals that serve as input data for a dedicated computer. The original imaging computer can create secondaryimages from almost any perspective by reprojecting or reformatting the original 3D voxel data When secondary computer is used to perform reformatting or image processing of original CT data, it is called workstation
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The computer processes the data using back-projection Fourier algorithm techniques first developed by Hounsfield to produce CT images. CT images are inherently three-dimensional digital images, typically 512X512 pixels with a thickness described by the slice spacing of the imaging technique.
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The individual element of the CT image is called a voxel, which has a value, referred to in Hounsfield units, that describes the density of the CT image. The density of structures within the image is absolute and quantitative and can be used to differentiate tissues in the region and characterize bone quality.
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CT enables the evaluation of proposed implant sites and provides diagnostic information that other imaging or combinations of imaging techniques cannot provide. Access to this diagnostic information required a radiologist to communicate with the referring doctors in detail about prospective surgery and then to sit at the imaging computer or a workstation for a considerable length of time to reformat the study, interpret the resulting images The advantages of this type of imaging were evident and the limitations of delivery clear, which spawned the development of a number of techniques referred to generically as DentaScan imaging.
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DENTASCAN Dentascan imaging provides programmed reformation, organization, and display of the imaging study. The radiologist or technologist simply indicates the curvature of the mandibular or maxillary arch, and the computer is programmed to generate referenced cross- sectional and tangential/panoramic images of the alveolus along with three- dimensional images of the arch. Axial CT view of the mandible showing the potential crosssectional slices that can be reformatted by Dentascan.
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Limitations of DentaScan Include images that may not be true to size and require compensation for magniﬁcation Determination of bone quality that requires use of the imaging computer or workstation Hard-copy dentascan images that only include a limited range of the diagnostic grayscale of the study Tilt of the patient’s head during the examination, which is critical because all the cross-sectional images are perpendicular to the axial imaging plane
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COMPUTED TOMOGRAPHY INDICATIONS Interactive treatment planning Determination of bone density Vital structure location Subperiosteal implant fabrication Determination of pathology Preplanning for bone augmentation ADVANTAGES Negligible magnification Relatively high-contrast image Various views Three-dimensional bone models Interactive treatment planning LIMITATIONS Cost Technique sensitive
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A. Scout view of the patient's head; axial sections through the area of interest are indicated
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C. Panoramic views through the alveolar ridge demonstrate the relation of the markers to adjacent teeth B. Axial slice through the markers is used to display the orientation of the panoramic and cross-sectional images through the alveolar ridge
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E. Three-dimensional reconstructions provide an overall impression of the bone contours and shape of the alveolar ridge D. Cross-sectional slices through the area of the markers reveal the height and buccolingual dimension of the alveolar ridge, as well as the relation of the markers to the ridge
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Types of CT Scanners MEDICAL - These CT scanning units are tomographic machines that are classified as 4-, 8-, 12-, 16-, 32-, and 64-slice machines. The number of slices corresponds to the number of times the x-ray beam rotates around the patient’s head CT spiral slices produce “average” reconstructed images based on multiple x-rays transversing the scanning area. With this reconstruction of images, a small gap between each slice is present, which contributes to an inherent error within medical scanners.
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DISADVANTAGES: Because medical scanners were not developed for dental reformatting, there existed inherent errors such as distortion, magnification, and positioning problems that led to inaccuracies when reformatted. Radiation exposure of medical scans has been shown as excessive (equivalent to 20 panoramic radiographs.) No prosthetic information could be gathered to predict the final prosthetic outcome This was overcome with the advent of sophisticated scanning appliances, stereolithographic resin bone models, interactive software, computer generated surgical guides, and CT-based image-guided navigation systems, which allowed for ideal placement and prosthetic outcome to be established
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CONE BEAM VOLUMERIC TOMOGRAPHY To overcome some of the disadvantages of conventional medical CT scanners, a new type of CT speciﬁc for dental applications has recently been developed. This type of advanced tomography is termed cone beam volumetric tomography (CBVT) The x-ray tube on these scanners rotates 360 degrees and will capture images of the maxilla and mandible in 36 seconds, in which only 5.6 seconds is needed for exposure. The positioning of patients is similar to medical scans. The images recorded are placed onto a charge coupled device chip with a matrix of 752 x 582 pixels and are then converted into axial, sagittal, and coronal slices, and permit reformatting to view traditional radiographic images as well as three-dimensional soft tissue or osseous images
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Medical versus Cone Beam Technology Radiation Dosages. The average absorbed radiation dose from a CBVT scanner (NewTom 3G) is approximately 12.0 mSv (micro sieverts), medical scanners acquire images that use radiation doses of 40 to 60 times that of CBVT doses Image Acquisition of Medical versus Cone Beam Scanners. Medical CT scans produce images of transaxial planes by use of solid-state detectors and an x-ray source that rotates around the patient. However, between each parallel slice exists a small “gap” that contributes to a built-in error within medical scanners. These gaps are adjusted within the software’s algorithms that can result in errors of 1.0 to 1.5 mm. Using CBVT avoids the errors in medical scanners by accumulating data from one 360-degree rotation around the patient’s head. The algorithms on CBVT scanners are very predictable because they are void of any “gaps,” thus eliminating distortion and magniﬁcation. Margins of error for CBVT are less than 0.1 mm
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CONE-BEAM COMPUTED TOMOGRAPHY The primary difference between CBCT and CT is the shape of radiation beams and the mode of motion CBCT was introduced to dentistry in the late 1990s, and currently several CBCT units are commercially available for imaging of the craniofacial complex
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In contrast to the fan-beam generated by CT scanners, however, the CBCT scanner generates a cone-shaped x-ray beam, which images a larger area Thus, at the end of a single complete rotation, 180 to 500 images of the area are generated The computer uses these images to generate a digital, three-dimensional map of the face
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INTERACTIVE COMPUTED TOMOGRAPHY ICT is a technique that was developed to bridge the gap in information transfer between the radiologist and practitioner. This technique enables the radiologist to transfer the imaging study to the practitioner as a computer file and enables the practitioner to view and react with the imaging study on a personal computer. The dentist’s computer becomes a diagnostic radiologic workstation with tools to measure the length and the width of the alveolus, measure bone quality, change the window and level of the grayscale of the study to enhance the perception of critical structures. Axial, cross-sectional, and panoramic images and three-dimensional images are displayed and referenced so that the dentist can appreciate the same position or region within the patient’s anatomy in each of the images. Regions of the patient’s anatomy can be selected for display normally, with magniﬁcation, or with a number of grayscale depictions
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Interactive computer guided implantology using NobelGuide softwaresystem
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An important feature - dentist and radiologist can perform electronic surgery (ES) by selecting and placing arbitrary sized cylinders that simulate root form implants in the images. Electronic surgery and ICT enable the development of a 3-D treatment plan that is integrated with the patients anatomy and can be visualized before surgery by members of the implant team and the patient for approval.
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The first step in the ICT process is the impressions for study casts. With the casts a diagnostic wax-up is completed. A radiopaque template is fabricated from the diagnostic wax-up. This diagnostic template will allow the transfer of the ideal positioning of the teeth. Acrylic template along with the plaster model. Arrows indicate the radiopaque markers of the proposed implant area.
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For conventional and CT the positioning of the teeth is integrated into a scanning template by way of a radiopaque material. Which is accomplished by way of an acrylic template coated with barium sulfate, gutta percha markers or radiopaque denture teeth. These radiopaque templates may then be modified into use for surgical templates
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Implant placement in relation to the mandibular canal and mental foramen; all images are cross- referenced with each other. Three dimensional analysisfor the evaluation of proximity to vital structures may be generated from the same computed tomography images
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SURGICAL GUIDES Computer-generated drilling guides that are fabricated through the process of stereolithography. Based on the presurgical treatment planning using SimPlant software for ideal implant positioning. These successive diameter surgical osteotomy drill guides may be either bone-, teeth-, or mucosa-borne. Surgiguides have metal cylindrical tubes that correspond to the number of desired osteotomy preparations and specific drill diameters. The diameter of the drilling tube is usually 0.2 mm larger than the corresponding drill, thus making angle deviation highly unlikely.
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CT-Based Surgical Guidance Templates and Navigation Systems Advanced technology has introduced guidance systems to facilitate dental implant placement procedures during surgery These systems allow the transfer of the presurgical plan to the patient, thus indicating when there is deviation from the predetermined drilling parameters. Therefore the depth and trajectory of the drilling sequence is made to the exact location of the preplanned position.
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MAGNETIC RESONANCE IMAGING Magnetic resonance imaging was first introduced by Lauterbur A CT imaging technique that produces images of thin slices of tissues with excellent spatial resolution Uses a combination of magnetic fields that generate images of tissues in the body without the use of ionizing radiation Allows complete flexibility in the positioning & angulation of image sections & can produce multiple slices simultaneously
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Digital MRI images are characterized by voxels with an in-plane resolution measured in pixels (512 x 512) and millimeters and a section thickness measured in millimeters (2 to 3 mm) for high- resolution imaging acquisitions. The images created by MRI are the result of signals created by hydrogen protons in water or fat such that cortical bone appear black (radiolucent) or as having no signal Cancellous bone will generate a signal & will appear white because it contains fatty marrow Metal restorations will not produce scattering and thus will appear as black images. MRI is a quantitatively accurate technique with exact tomographic sections & no distortion
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In cases where the inferior alveolar canal cannot be differentiated by conventional or computed tomography, MRI would be a viable alternative as the trabecular bone is easily differentiated with the inferior alveolar canal In cases of nerve impairment or infection, MRI may be used because of added advantages including differentiation of soft tissue with respect to CT MRI may be used in implant imaging as a secondary imaging technique when primary imaging techniques such as complex tomography or CT fail
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Advantages No radiation Vital structures are easily seen Uses Evaluation of vital structures when computed tomography is not conclusive Evaluation of infection Limitations Cost Technique sensitive No reformatting technique Availability Non-signal for cortical bone Not useful in characterizing bone mineralization or as a high-yield technique for identifying bone or dental disease
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Advantages and Disadvantages of the Various Radiographic Projections Modality Advantages Disadvantages Periapical and occlusal radiography High resolution and detail easy acquisition, low exposure inexpensive. -Unpredictable magnification -small imaged area, -2D representation of anatomy Panoramic radiography -Easy to acquire, images whole ridge -low exposure, -inexpensive. -Unpredictable magnification -2D representation of anatomy, not detailed
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PATIENT EVALUATION Evaluation of the implant patient should be disciplined and objective The objectives for any radiographic evaluation, regardless of imaging technique used, should include an evaluation to exclude pathology, identify anatomic structures, and measure the quantity, quality, and location of available bone
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Exclude Pathology Healthy bone - for successful osseointegration and long-term implant success The first step in evaluation of the implant site - to establish the health of the alveolar bone and other tissues imaged within a particular projection Local and systemic diseases that affect bone homeostasis can preclude, modify, or alter placement of implants
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Retained root fragments, residual periodontal disease, cysts, and tumors - identified and resolved before implant placement Areas of poor bone quality - identified and if indicated, adjustments to the treatment plan incorporated Maxillary sinusitis, polyps, or other sinus pathology - diagnosed and treated when implants are considered in the posterior maxilla, especially if sinus bone augmentation procedures are planned
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Identify Anatomic Structures Several important anatomic structures are found close to desired areas of implant placement in the maxilla and mandible Familiarity with the radiographic appearance of these structures is important during treatment planning and implant placement Their exact localization is central to prevent unwanted complication and unnecessary morbidity
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Anatomic Structures Pertinent to Treatment Planning of the Maxilla Maxillary sinus (floor and anterior wall) Nasal cavity (floor and lateral wall) Incisive foramen Canine fossa Implant Patient Mandible Mandibular canal Mental foramen Submandibular fossa Lingual inclination of the alveolar ridge
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RADIOGRAPHIC IMAGING OF VITAL STRUCTURES IN ORAL IMPLANTOLOGY MENTAL FORAMEN AND MANDIBULAR CANAL The position of the mandibular canal and mental foramen - identified to avoid trauma to the inferior alveolar nerve. Because of the curvature of the mandible, great care must be given to the angulation of the x-ray beam for intraoral radiography.
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Periapical and panoramic images are still used routinely as the sole determinate of osseous measurements with respect to these vital structures. If the image is taken from a mesio-oblique orientation, measurements will be foreshortened and if the orientation is from a distal-oblique, it will be elongated. In edentulous mandibles, the risk of error increases considerably where there is increased resorption of the alveolar crest.
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Most accurate means of identification is with conventional and computerized tomography. Studies have shown that tilting the patient’s head approximately 5 degrees downward in reference to the Frankfort horizontal plane allows these anatomical structures to be seen in 91% of radiographs.(Dharmar S)
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Mandibular Lingual Concavities Advanced atrophy in the posterior mandible is present, lingual concavities may be present. Within these concavities or submandibular gland fossa, branches of the facial artery may be present. Overestimation of the amount of bone may lead to perforation of the lingual plate when drilling the osteotomy. Lingual bleeding problems - even be life-threatening. Assessment of the posterior mandible - cross-sectional tomography is recommended.
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3D view showing significant sublingual undercut
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Mandibular Ramus (Donor Site for Autogenous Grafting) The mandibular ramus area has become a very popular donor site for autogenous onlay bone grafting. This area of the mandibular jaw is extremely variable in the amount of bone present. Usually panoramic images are taken and the location of the external oblique and the mandibular canal is noted. For accurate representation - use of computerized tomography.
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The more prominent the external oblique ridge, the better candidate for the ramus as a donor site
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Mandibular Symphysis Mandibular symphysis area -very critical anatomical area for oral implantology. A common position for implants in mandibular edentulous patients and used as a donor site for autogenous grafting. When two-dimensional images are used, inherent errors may occur because of lingual concavities. Radiographs including lateral cephalometric and conventional CT, may be used.
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Computed tomography images illustrate various views of the mandibular anterior region.
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Maxillary Sinus CT, which is the gold standard for viewing the osseous structures and evaluating pathology in the sinuses. It provides detailed information regarding – Prevalence and position of septa Maxillary sinus anatomy Detection of sinus pathology
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INTRAOPERATIVE IMAGING The use of surgical imaging has dramatically changed the way that surgical implantology is completed With digital radiography technology, instantaneous images are achieved, allowing for multiple images to be completed in a fraction of the time. Additional advantages – Manipulation of images Calibration Accurate positioning Maintenance of aseptic protocol
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Initial pilot orientation with slight mesial inclination Angulation corrected and verified with final depth indicator Implant placement. Note poor angulation of radiograph leading to distorted measurements. Ideal implant placement radiograph. Due to the perpendicular orientation of x-ray beam as all threads are seen without distortion
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During symphysis bone harvesting, the beneﬁts of digital radiography can be used by placing gutta percha in the superior osteotomy site for radiographic evaluation to conﬁrm and measure adequate distance from tooth apices
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Immediate Postsurgical Imaging A plain film radiograph (periapical or panoramic) should be taken post surgically so that a baseline image may be used to evaluate against future films Additional imaging tools may be used to evaluate a zone of safety around vital structures.
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Abutment and Prosthetic Component Imaging When evaluating for transfer impressions along with two-piece abutment component placement, radiographs should be taken to verify secure adaptation. When positioning is difficult for periapical radiographs, bitewing or panoramic radiographs may be used.
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Veriﬁcation of direct transfer coping placement before ﬁnal impression. Note ideal angulation from thread alignment
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POSTPROSTHETIC IMAGING When investigating complications after implant placement, a panoramic radiograph is the most ideal imaging technique for multiple implants. If single implants - periapical radiographs are the image of choice. A postprosthetic radiograph needs to be taken for- Future evaluation of component fit verification For marginal bone level evaluation.
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RECALL AND MAINTENANCE IMAGING Immobility and Radiographic evidence of bone adjacent to the implant are the two most accurate diagnostic aids in evaluating success. Follow-up or recall radiographs should be taken after 1 year of functional loading and yearly for the first 3 years. Studies show that marginal bone loss and a higher rate of failure are seen - in the first .
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Evaluation of Alveolar Bone Changes Radiographically, lack or loss of integration is usually indicated as a radiolucent line around the implant. However, false-negative diagnoses may be made when the soft tissue surrounding an implant is not wide enough to overcome the resolution of the radiographic modality used. Also, false-positive diagnoses may be made when a “Mach band effect” results from an area of lower radiographic density adjacent to an area of high density (implant), which results in a more radiolucent area than is actually present. Digital radiography has been shown to have the advantage over conventional radiography with respect to “edge enhancement,” which is the ability to detect space between the implant and the surrounding bone
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Periapical Radiographs In recall radiographic examinations, the marginal bone level is compared with the immediate postprosthetic films. If the implant threads are not clearly seen in the radiographs, modification of the beam angle needs to be made. If diffuse threads are present on the right side of the implant, then the beam angle was positioned too much in the superior direction. If the threads are diffuse on the left side, then the beam angle was from an inferior angulation Computer-assisted measurements, rulers, calipers, and suprabony thread evaluation have been shown to have highly reproducible results in digital radiography
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Alveolar bone level evaluation. A, Ideal positioning showing ideal thread orientation. B, Improper angulation showing diffuse thread orientation.
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Bitewing Radiographs In cases where the x-ray source cannot be positioned perpendicular to the implant because of oral anatomy or existing prosthesis, horizontal or vertical bitewings may be taken to evaluate the crestal bone area. The only limitation of bitewing radiographs is that the apical portion cannot be seen.
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Subtraction Radiography Digital subtraction radiography, allows two radiographs taken at different times to be superimposed on one another, resulting in an image that exhibits the differences in the bone level. Subtraction radiography requires the use of the same positioning and imaging technique between the two radiographs with respect to the x-ray source, patient and film position, exposure, and processing variables.
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After the images are subtracted, a subtraction image will be left that depicts the osseous changes between the radiographs. This technique has been shown to be more accurate in accessing bone mineralization and volume changes
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Panoramic Radiographs Panoramic radiographs usually are not used routinely for evaluation of osseous bone levels and recall examinations. When multiple implants need to be evaluated, panoramic radiography is the imaging technique of choice.
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Computed Tomography Two-dimensional radiographs (periapical, panoramic) have limitations in that they give no buccolingual information about the present condition of alveolar bone. Ct does allow three-dimensional information about the osseous status around an implant. Resolution and scattering has always been a problem in evaluation of implants – overcome with cone beam technology. With the advantage of bone density evaluation using hounsfield units, important information on bone maturation may be determined. This radiographic modality is the image of choice for evaluation of sinus infection or postsurgical sinusitis complications
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Reformatted cone-beam CT study for postoperative assessment of an implant cylinder displaced into the right maxillary sinus, associated with mucositis in the right antrum. The implant on the left alveolus is not well supported by bone and extends well into the antrum.
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FABRICATION OF DIAGNOSTIC TEMPLATES The purpose of diagnostic radiographic templates is to incorporate the patient’s proposed treatment plan into the radiographic examination. Ideally, mounted diagnostic casts, a diagnostic wax-up, agreement between the practitioners on the number and location of proposed dental implants, and prior authorization of the proposed treatment by the patient make the diagnostic template a useful tool of the patient. The preprosthetic imaging procedure enables evaluation of the proposed implant site at the ideal position and orientation identiﬁed by radiographic markers incorporated into the template.
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Computed Tomography The precision of CT enables use of a complex and precise diagnostic template. Although CT can identify the available bone height and width accurately for a dental implant at a proposed implant site, the exact position and orientation of the implant, which many times determine the actual length and diameter of the implant, often are dictated by the prosthesis. As such, a diagnostic template used during imaging is most beneﬁ cial.
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The surfaces of the proposed restorations and the exact position and orientation of each dental implant should be incorporated into the diagnostic CT template. Designs for diagnostic CT templates have evolved from a simple vacuform reproduction of the wax-up to one produced from a processed acrylic reproduction of the diagnostic wax-up and to more sophisticated types fabricated with specifically designed radiopaque denture teeth.
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The processed acrylic template may be modified by coating the proposed restorations with a thin film of barium sulfate and filling a hole drilled through the occlusal surface of the restoration with gutta- percha. The surfaces of the proposed restoration then become radiopaque in the CT examination, and the position and orientation of the proposed implant may be identified by the radiopaque plug of gutta-percha within the proposed restoration.
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A - A vacuum-formed imaging stent with a metal rod to indicate desired axis of insertion. B - A processed stent with metal cylinders marking the implant sites. This can also be used as a surgical stent by inserting the guide bur through the cylinders. C - A processed stent with insertion axis markers, along with a radiopaque strip outlining the buccal and lingual contours of the planned restoration. The stent provides an image of the emergence profile of the restored implant and can also be used as a surgical guide.
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Radiopaque teeth designed for the fabrication of diagnostic templates for fixed and removable implant-supported restorations have been introduced. The advantages – The diagnostic template then can be modified into a surgical template They are time saving Easily placed Provide high radiopacity Bond easily with the template.
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Tomography The simplest tomography template is produced by obtaining a vacuform of the patient’s diagnostic cast with 3-mm ball bearings placed at the proposed implant positions. A number of tomograms of the implant region are produced with the implant site identified by the one in which the ball bearing is in sharp focus. It can serve as a measure of the magnification of the imaging system, although the magnification of most tomographic imaging systems is fixed and known.
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Radiographic signs associated with failing endosseous implants Radiographic appearance Clinical implications Thin radiolucent area that closely follows the entire outline Radiolucent area around coronal portion Apical migration of alveolar bone one side of implant Widening of periodontal space of the nearest natural abutment Fracture of fixature Failure of implant to integrate with adjoining bone. Peri-implantitis resulting from poor plaque control, adverse loading or both Non axial loading resulting from improper angulation of implant Poor stress distribution Unfavorable stress distribution during function
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CONCLUSION Many radiographic projections are available for the evaluation of implant placement, each with advantages and disadvantages The clinician must follow sequential steps in patient evaluation, and radiography is an essential diagnostic tool for implant design and successful treatment of the implant patient “as low as reasonably achievable” (ALARA)
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Contemporary Implant Dentistry. Carl E. Misch – 3rd Edition Caranza's Clinical Periodontology - 11th Edition Swati S Bhosale, P Balaji Raman and Joshua Mall. Guided implant placement in the edentulous mandible: A novel approach. Journal of ICDRO 2010; Vol 2 (1): Page 30 – 34. Lingeshwar D, Dhanasekar B, Aparna IN. Diagnostic Imaging in Implant Dentistry. International Journal of Oral Implantology and Clinical Research, September-December 2010;1(3):147-153 Bart Vandenberghe Reinhilde Jacobs Hilde Bosmans, Modern dental imaging: A review of the current technology and clinical applications in dental practice. Eur Radiol 2010 20: 2637-2655