diagnostic imaging techniques for implant patients

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