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DIAGNOSTIC IMAGING AND TECHNIQUES FOR IMPLANT PATIENTS
by
Dr. Smijal GMDEPT OF PERIODONTICS
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
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
• 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)
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 –
1. PHASE 1 [ Presurgical implant imaging]2. PHASE 2 [ Surgical and Intraoperative implant imaging]3. PHASE 3 [ Postprosthetic implant imaging]
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 boneDetermine relationship of critical structures to the implant site.The presence or absence of disease at the implant site.
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 surgeryAssist in the optimal position and orientation of dental implantsEvaluate the healing and integration phase of implant surgeryTo ensure that abutment position and prosthesis fabrication are correct.
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.
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
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
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
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-
• Also S no. TYPES EXAMPLES FUNCTION
1. PLANAR 2-DIMENSIONAL PERIAPICAL,BITE-WING, OCCLUSAL AND CEPHALOMETRIC IMAGING
GIVES A 2-D PROJECTION OF patient's ANATOMY
2. QUASI-3-DIMENSIONAL X-RAY TOMOGRAPHY, CROSS-SECTIONAL PANORAMIC IMAGING
GIVES A 3-D PERSPECTIVE OF patient's ANATOMY
3. 3-DIMENSIONAL CT AND MRI GIVES THE DENTIST TO VIEW THE VOLUME OF THE patient's ANATOMY.
PRESURGICAL IMAGING
• Main goals –1. Identify disease2. Determine bone quality3. Determine bone quantity4. Determine implant position5. Determine implant orientation
•While selecting the radiographic modality for the patient recommended principle is the ALARA Principle.
“As Low As Reasonably Achievable”
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
• Low radiation dose• Minimal magnification with proper alignment and positioning• High resolution• Inexpensive
ADVANTAGES
• Distortion and magnification• Minimal site evaluation• Difficulty in film placement• Technique sensitive
LIMITATIONS
• Evaluation of a small area• Alignment and orientation during surgery• For recall and maintenance therapy
INDICATIONS
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.
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.
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
CONTROLLING THE IMAGE QUALITY
•When taking a radiograph, you have control over these three parameters:
oKilovoltageoMilliamperes oExposure Time.
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.
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.
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.
• 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.
• 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.
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)
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.
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.
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.
• 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
Maxillary full occlusal view technique
Mandibular full occlusal view technique
ADVANTAGE•Evaluation for pathology
LIMITATIONS•Does not reveal true buccolingual width in
mandible•Difficulty in positioning
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.
• 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.
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.
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.
• 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
•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.
• 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.
ADVA
NTA
GES • 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.
LIM
ITAT
ION
S • 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
• 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
•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.
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
PROBLEM CAUSE CORRECTIONBlurred Magnified Patient positioned too far
posteriorMake sure anterior teeth are properly in the holder
Blurred Narrow anterior region Patient positioned too far anterior Make sure anterior teeth are in holder
Exaggerated curve of Spee anterior foreshortening Condyles not seen Spine forms “gazebo” effect
Patient chin tipped down too far Correctly align ala-tragus
Flattened curve of Spee Hard palate superimposed
Patient chin tipped too far upward
Correctly align ala-tragus
Radiopaque shadow over anterior region Patient slumped too far forward Straighten neck
Ramus larger on one side uneven pattern of blurring
Patient head rotated in machine Patient midsagittal plane should be perpendicular to the floor
Large radiolucency over maxilla Patient tongue not in floor of mouth
Patient place tongue on roof of mouth, swallows
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.
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.
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
• 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.
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
CONVENTIONAL TOMOGRAPHIC IMAGES Indications-
• Single-site evaluation
• Vital structures evaluation
Advantages-
• Cross-sectional views
• Constant Magnification
Limitations
• Availability• Cost• Multiple Images• Technique
sensitive• Blurred images• High radiation
dose
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.
• 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
• 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.
• 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.Muscle 35–70 HU
Fibrous tissue 60–90 HU
Cartilage 80–130 HU
Bone 150–1800 HU
D1 bone >1250 HU
D2 bone 750–1250 HU
D3 bone 375–750 HU
D4 bone <375 HU
• 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.
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.
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
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
A. Scout view of the patient's head; axial sections through the area of interest are indicated
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
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
Types of CT ScannersMEDICAL - • 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.
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
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
• 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
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
• 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
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
• Interactive computer guided implantology using NobelGuide softwaresystem
• 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.
• 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.
• 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
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
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.
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.
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
• 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
• 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
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
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
Modality Advantages Disadvantages
Lateral cephalometric radiography
-Easy to acquire, -predictable magnification-low exposure-inexpensive.
-Limited use in area of midline-2D representation of anatomy
Tomography
-3D representation, -predictable magnification, -sufficient detail, -low exposure, -images area of interest only.
-Requires special equipment, -for evaluation of multiple sites can be a lengthy procedure because the patient must be repositioned for each site,-expensive
Modality Advantages Disadvantages
Computed tomography (CT)
-3D representation, -predictable magnification, -sufficient detail, -digital format, -images whole arch.
-Requires special equipment, -expensive, -high-exposure dose
Cone-beam computed tomography (CBCT)
-3D representation, -predictable magnification, -sufficient detail, -digital format, -images whole arch, -low dose.
-Requires special equipment-expensive
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
(1) exclude pathology, (2) identify anatomic structures, and (3) measure the quantity, quality, and location of available bone
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
• 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
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
Anatomic Structures Pertinent to Treatment Planning of the Implant Patient
Maxilla• Maxillary sinus (floor and
anterior wall)• Nasal cavity (floor and lateral
wall)• Incisive foramen• Canine fossa
Mandible• Mandibular canal• Mental foramen• Submandibular fossa• Lingual inclination of the
alveolar ridge
RADIOGRAPHIC IMAGING OF VITAL STRUCTURES IN ORAL IMPLANTOLOGYMENTAL 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.
• 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.
•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)
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.
3D view showing significant sublingual undercut
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.
The more prominent the external oblique ridge, the better candidate for the ramus as a donor site
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.
Computed tomography images illustrate various views of the mandibular anterior region.
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
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
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 theperpendicular orientation of x-ray beam as all threads
are seen without distortion
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
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.
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.
Verification of direct transfer coping placement before final impression. Note ideal angulation from thread alignment
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.
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 .
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
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
Alveolar bone level evaluation. A, Ideal positioning showing ideal thread orientation. B, Improper angulation showing diffuse thread orientation.
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.
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.
•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
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.
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
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.
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.
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.
• 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.
• 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.
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.
• 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.
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.
Radiographic signs associated with failing endosseous implants Radiographic appearance Clinical implications
Thin radiolucent area that closely follows the entire outline
Failure of implant to integrate with adjoining bone.
Radiolucent area around coronal portion Peri-implantitis resulting from poor plaque control, adverse loading or both
Apical migration of alveolar bone one side of implant
Non axial loading resulting from improper angulation of implant
Widening of periodontal space of the nearest natural abutment
Poor stress distribution
Fracture of fixature Unfavorable stress distribution during function
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)
REFERENCES• 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
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