Radiographs in prosthodontics

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Information about Radiographs in prosthodontics

Published on March 7, 2014

Author: indiandentalacademy


RADIOGRAPHS IN PROSTHODONTICS Introduction Dental radiographs are a necessary component of comprehensive patient care.In dentistry, radiographs enable the dental professional to identify many condition that may otherwise go undetected clinically. Detection is one of the most important uses of dentistry used radiographs. Many dental diseases and conditions produce no clinical signs or symptoms and are typically discovered only through use of dental radiographs. Uses of dental radiographs: 1. To detect lesions, disease and conditions of teeth and surrounding structures that cannot be identified clinically. 2. To confirm and classify or foreign objects. 3. To localize lesions or foreign objects. 4. To provide information during dental procedures. 5. T o evaluate growth and development. 6. To illustrate changes secondary to caries, periodontal disease and trauma. 7. To document the condition of patient at a specific point of time. The history of dental radiography begins with discovery of X-rays. WILHELM CONRAD ROENTGEN (pronounced ‘ren-ken’), a Bavarian physicst discovered X-ray on Nov 8,1895.This monumental discovery revolutionized the diagnostic capabilities of medical and dental profession and a result, forever changed the practice of medicine and dentistry. Roentgen named his discovery X-rays, the “X” referring to unknown nature and properties of such rays.He published a total of three scientific papers detailing the discovery, properties and characteristics of X-rays. During his life time, Roentgen was awarded many honours and distinctions including first noble prize ever awarded in Physics. For a number of years after discovery, X-rays were referred to as Roentgen rays, Radiology as Roentgenology and Radiographs were named Roentgenography.

Pioneers in dental X-ray radiation: Following the discovery of X-rays in 1895, a number of pioneers helped to shape the history of dental radiography. After announcement of discovery of X-rays in 1985, a German dentist OTTO WALKHOFF made first dental radiograph. C.Edmund Kells, a new Orleans dentist is credited with the use of radiographs dentistry in 1896. Kells dedicated to the development of Xrays ultimately cost him his fingers , later his hand and his arm. Other pioneer in dental radiography include William H.Rollins, a Boston dentist who first developed X ray unit. Frank Van Woert, a dentist from Newyork city was the first to use film in intraoral radiography. Howarth Riley Raper, an I ndiana uiversity professor established the first college course of radiography for dental students. Likewise dental x-ray film, dental radiographic techniques were developed. Present day diagnosis, treatment planning and evaluation of prognosis in the field of medicine and dentistry depends a lot on radiographic imaging and prosthodontics is no way exception to his principle. Though use of various radiographs was limited for evaluation and to reach a conclusion regarding diagnosis and treatment planning previously in Prosthodontics, present day radiographs are used to analyse even the prognosis or treatment outcome especially after advent of advanced Prosthodontic care by Implants and Maxillofacial prosthesis.

COMPLETE DENTURES Radiographic evaluation Radiographs are important aids in the evaluation of submucosal conditions in patients seeking prosthodontic care. The presence of abnormalities in edentulous jaws may be unsuspected because of absence of any clinical signs or symptoms they show the relative thickness of alveolar ridge and the mucoperiosteum, the quality of the bone. Extraoral radiographs can provide survey of the patient’s denture foundation and surrounding structures. Panoramic dental radiograph are readily available for convenient examination of edentulous patients. Knowledge of location of the anatomic structures is an essential prerequisite in the evaluation of the radiographs. Intraoral radiographs have limited role in edentulous patients. They can used in locating any localized abnormality or the examination of tuberosities. The transition from emulsion based film radiography to photostimuable phosphor based films CCD (charge couple devices) and CMOS (complementary metal oxide semiconductor) are well under way. This is limiting the exposure of patients to radiations. Other investigations tools these include Tomography, Zonography, Computed Tomography, Magnetic Resonance, Radionuclide Imaging and Ultrasounds. Radiographs in complete dentures should rule out foreign bodies, retained root tips, unerupted teeth or various pathoses of developmental, inflammatory or neoplastic origin.

Cephalometric and temporomandibular joint radiography are performed to rule out relevant abnormalities for complete denture prosthesis functioning and maintenance. Radiographs are usually taken to find out the presence of hidden abnormalities, to note the structure of cortical bone and trabeculae, sharp projections, thickness of soft tissue etc., Retained roots with no apparent pathology can often be left alone provided the patient is informed of their presence and X-rayed periodically. The interpretation of panoromic radiographs follow a 5 step analysis as outlined by Chemenko. The panoromic is also an aid in documenting the amount of ridge resorption. A very useful system of classifying the amount of ridge resorption was described by WICAL & SWOOPE .They found that the lower edge of mental foramena divides the mandible into thirds in normal dentulous panaromic radiograph. If the distance is measured from inferior border of mandible to inferior margin of mental foramina and then multiplied by 3 , the resultant product is a reliable estimate of original alveolar ridge crest height. Amount of ridge resorption can be calculated an classified as Class I (MILD RESORPTION)Loss upto 1/3 of original vertical height Class II (MODERATE RESORPTION) Loss upto 1/3 to 2/3 of vertical height. Class III (SEVERE RESOPTION) Loss of 2/3 or more of vertical height. To conclude periapical survey of edentulous jaws are acceptable but Panaromic radiographs are faster reduce patient exposure to radiation and image the entire maxilla and mandible.

REMOVABLE PARTIAL DENTURES Planning A panoramic radiograph is of great diagnostic value and should be made wherever possible. Periapical radiographs of the remaining teeth may also be required is order to supplement the OPG.  teeth with questionable prognosis  Requiring surgical & Endodontic restoration In case OPG not there then a full month service of IOPAS have to be there. The diagnostic factors or criteria judged are. (i) Carious lesion  initial carious lesions  Recurrent caries adjacent to existing restorations  Deep lesions or extensive restorations on potential abutment teeth.  Obvious indications for endodontic therapy cast restorations are noted. (ii) Root Length, Size & Form  Large, longer roots are more favorable abutment teeth.  Form of the root is equally important tapered or conical roots are unfavorable because ever a small loss of bone height can greatly diminish the attachment area.  Multirooted teeth with divergent and curved roots are better than single rooted or Multirooted with fused roots.  Position of roots of adjacent tooth is also important, in case the roots are close with little interproximal bone separating them even a moderate irritation of force may be destructive. Crown root ratio The relationship of the length of the clinical area and the amount of root embedded is bone is a very critical factor. If the crown root ratio is greater than 1:1 then the tooth has a poor prognosis as an abutment. It is also poor when there is furcation involvement of a multi rooted teeth is present.

Lamina dura or periodontal space  The width of the periodontal ligament space is of significance in evaluating the stability of the teeth. A thin uniform ligament space and an uninterrupted Lamina dura is a more favorable sign compared to a more widened or irregular space.  A thickening of the lamina dura may occur if the tooth is mobile, has occlusal trauma or is under heavy functions occlusal trauma can cause partial or total loss of the lamina dura.  Partial or total absence of the lamina dura may be found in systemic disorders such as Hyperparathyroid and Paget’s disease. Systemic disease must be considered whenever this condition is noted; Destruction forces or the disease processes causing changes in the lamina dura must be correlated or the abutment tooth will have a poor prognosis. Bone quality & quantity Bones which has small closely grouped trabecular and small inter trabecular spaces is considered well mineralized; hence strong & healthy. This is portrayed in the radiograph as relatively radiopaque, although a certain amount of variation is size of the trabeculae is normal and to be expected. Bone height of quantity In this evaluation care must be taken to avoid any interpretation errors resulting from angulations factors with is normally used in the short cone or Bisecting angle technique. As a result of the central ray using shot at an angle results in the buccal bone to be projected higher on the crown than the lingual or palatal bone. Therefore when interpreting bone height it is imperative to follow the line of the lamina dura from the apex towards the crown of the tooth until the opacity of the lamina materially decreases. At this point of opacity charge, a less dense bone extends further towards the tooth crown.

This additional amount of bone represents false bone height. Thus the true height of the bone is ordinarily where the lamina shines a mark decrease in opacity. At this point the trabecular pattern of the bone superimposed on the tooth root is lost. And the portion of the root b/w the CEJ and the true bone height has the appearance being base as devoid of covering. BONE INDEX AREAS Index areas are those areas of alveolar support that disclose the reaction of bone to additional stress. There might be a positive Bone factor or a Negative Bone factor depending on the response of the alveolar bone to additional loading. A position or a favorable response A decrease in the trabecular pattern (bone condensation)) A heavy cortical layer. Dense lamina dura Normal bone height Normal periodontal ligament space. Retrograde or negative response  loss of lamina dura  decrease bone height  widening of periodontal ligament space  apical and furcation radioluscency Teeth that have been subjected to greater than normal stress and provide good index information are:(i) Abutment teeth of an FPD or RPD. (ii) Teeth involved in occlusal interferences. (iii) Teeth receiving greater occlusal stress due to loss of adjacent teeth. (iv) Tipped teeth with occlusal contact. Radioluscent or radioopaque lesions.  The presence of cysts, accesses, embedded teeth or roots or foreign bodies must be noted.  A surgical diagnosis and treatment must be planned so that a conditions does not flare up later on jeopardizing the prognosis of the prosthesis.

 Buried root tips or impacted teeth that show no signs of any pathosis and are encapsulated by normal appearing bone need not be surgically removed though it must be noted in the diagnosis.  It should be checked for any imparted 3 r d molars. Roentgenographic interpretation Radiographic interpretation most pertinent to partial denture construction are those relative to prognosis of remaining teeth that may be used as abutments. The quality of the alveolar support of an abutment tooth is of prime importance because the tooth will have to withstand greater stress loads when supporting a dental prosthesis, especially greater horizontal forces. Abutment teeth adjacent to distal extension bases are subjected not only to vertical and horizontal forces but to torque as well.

FIXED PARTIAL DENTURES A well defined, complete mouth radiographic series is essential. TMJ radiographs may be indicated for patients with joint dysfunction and a panoramic radiograph can also be helpful. Radiographs provide information that cannot be determined clinically, they are an adjunct, however, and not the sole or primary source of diagnostic information. The radiographic interpretation is combined with all other available findings when making a definitive diagnosis and developing a treatment plan. Radiographs used in FPD are 1. Full mouth intra-oral periapical radiographs 2. Panoramic radiographs. 3. TMJ radiographs. Full mouth intra oral radiographs An intra oral radiographic examination reveals. 1. Remaining bone support After horizontal bone loss from periodontal disease the PDL supported root surface area can be dramatically reduced. When one third of the root length has been exposed half the supporting area is lost. 2. Root number and morphology (short, long, slender, broad, bifurcated, fused dilacerated etc) and root proximity. Molar with divergent roots provide better support than a molar with little or no inter radicular bone. 3. Quality of supporting bone trabacular patterns and reaction to functional charges. 4. Width of the periodontal ligament spaces and evidence of traum from occlusion. 5. Areas of vertical and horizontal osseous resorption and furcation invasions. 6. Axial inclination of teeth (degree of non parallelism if present). A well aligned tooth will provide better support than a tilted one. 7. Continuity and integrity of the lamina dura. 8. Pulpal morphology and previous endodontic treatment with or without post and cores.

9. Presence of apical diseases, root resorption or root fractures. 10. Retained root fragments, radiolucent areas, calcification, foreign bodies, or impacted teeth. 11. Presence of carious lesions and restorations to the pulp and alveolar crest. 12. Proximity of carious lesions and restorations to the pulp and alveolar crest. 13. Calculus deposits. 14. Oral roentgenographic manifestation of systemic disease. 15. Edentulous areas Presence of retained root tips or other pathosis in the edentulous area should be noted. In many radiographs it is possible to trace the outline of the soft tissue in edentulous areas so that the thickness of the soft tissue overlying ridge can be determined. 16. Crown – root ratio. (Ante’s Law) This ratio is a measure of the length of tooth occlusal to the alveolar crest of bone compared with the length of root embedded in the bone. As the level of the alveolar bone moves apically, the level arm of that portion out of the bone increases and the chance for harmful lateral forces is increased. The optimum crown root ratio for a tooth to be used as a fixed partial denture abutment is 2:3. A ratio of 1:1 is the minimum ratio that is acceptable for a prospective abutment under normal circumstances. 17. Size and position of the pulp This is one of the most important factors to be assessed before preparing a tooth and may well determine the correct choice of retainer. Where the pulp is large particularly in the young patient, it may be impossible to obtain sufficient reduction of tooth tissue for adequate retainers without devitalization. This is especially true of the bonded porcelain restorations, where quite drastic reduction of tooth tissue is essential if a good esthetic result is to be obtained. On occasions where devitalization is required it is far better if this is elective rather than following an exposure. In the posterior region a bitewing X-ray is the best method of

assessing the correct position of the pulp. With anterior teeth an X-ray taken with the ray at right angles to the crown of the tooth is to be preferred to the usual apical view. Panoramic radiographs Panoramic films provide useful information as to the presence or absence of teeth. They give an overall view about the dentition. However they do not provide detailed view for assessing bone support, root morphology, or caries. Special radiographs There are needed for the assessment of TMJ disorders. A trans-cranial exposure with the help of a positioning device , will reveal the lateral third of the mandibular condyle and can be used to detect structural and positional changes. However interpretation may be difficult. More information can be obtained from serial tomography, arthrography, CT scanning or magnetic resonance imaging of the joints.

IMPLANT IMAGING Radiographic visualization of potential implant sites is an important extension of clinical examination and assessment. Radiographs help the clinician to visualize the alveolar ridges and adjacent structures in all three dimensions and guide the choice of site, number, size and axial orientation of the implants. Site selection includes consideration of adjacent anatomic structures. Pathologic conditions, that could compromise the outcome must be identified & located relative to the site of the proposed implant. A variety of radiographic techniques are available to assist the clinicians. Radiographs are useful in the Implant dentistry mainly at three levels. 1) Preprosthetic implant imaging. 2) Surgical and interventional implant imaging. 3) Post prosthetic implant imaging. IMAGING OBJECTIVES I. Preprosthetic imaging Objectives includes Information about 1. Quality, quantity and angulation of bone. 2. The relationship of critical structures to the prospective implant sites. 3. Presence or absence of disease at the proposed surgery sites. II. Surgical and Interventional imaging The objectives of this phase are 1. To evaluate the surgery sites during and immediately after surgery. 2. Assist in optimal position and orientation of dental implants. 3. Evaluate the healing and integration phase of implant surgery. 4. Ensure abutment position & prosthesis fabrication are correct.

III. Post prosthetic imaging The objectives of this phase are 1. To evaluate the long-term maintenance of implant rigid fixation and function, including the crestal bone levels around each implant. 2. To evaluate the implant complex. IMAGING MODALITIES The imaging modalities can be described as either analog or digital and two dimensional or three dimensional. a) Analog Imaging modalities  Periapical radiography.  Panoramic radiography  Occlusal radiography  Cephalometric radiography b) Three dimensional imaging modalities  Computed tomography  Magnetic resonance imaging  Interactive computed tomography. c) Quasi – three dimensional imaging modalities  X-ray tomography  Some cross – sectional panoramic imaging techniques. Periapical radiograph Peri-apical radiography provides high resolution planar images of a limited region of the jaws. They provide a lateral view of the jaws and no cross sectional information. Even with adjacent peri-apical radiographs made with limited oblique orientations, third dimensional information is of little use for the implant imaging. Periapical radiographs may suffer from both distortion & magnification. The long cone paralleling technique will eliminate distortion and limit magnification less than 10%. In order to visualize opposing cortical pate, the image most often must be foreshortened. As a result, the actual available bone height may be difficult to determine.

In terms of the objectives of preprosthetic imaging, periapical radiography is 1. A useful high – yield modality for ruling out local bone or dental diseases. 2. Of limited value in determining quality because the image is magnified, may be distorted and does not depict the third dimension of bone width. 3. Of limited value in determining bone density or mineralization. 4. Of value in identifying critical structures, but of little use in depicting the spatial relationship between the structures at the proposed implant site. In preprosthetic phase, these films are most often used for single tooth implants in regions of abundant bone width. Occlusal radiograph Occlusal radiographs produce high resolution planar images of the body of the mandible or maxilla. Maxillary occlusal radiographs are inherently oblique and so distorted they are of no quantitative use for implant dentistry for either determining the geometry or the degree of mineralization of the implant site. Mandibular occlusal radiograph is an orthogonal projection. It is a less distorted projection than the maxillary occlusal radiograph. But, the mandibular alveolus flares anteriorly and demonstrates a lingual inclination posteriorly, producing an oblique and distorted image of the mandibular alveolus, which is of little use in implant dentistry. In addition it shows the widest width at the crest, which is where the diagnostic information is needed most. As a result occlusal radiographs are rarely indicated for diagnostic preprosthetic phase in implant dentistry. Cephalometric radiographs The geometry of cephalometric imaging devices results in a 10% magnification to the image with a 60 inch focal object and a 6 inch object to film distance.

The primary advantages of cephalometric radiographs in implantology are: a. A cross sectional image of the alveolus of both the mandible and the maxilla in the mid sagittal plane is demonstrated by this radiograph. b. With slight rotation of the cephalometer, a cross sectional image of the mandible or maxilla can be demonstrated in the lateral incisor or in the canine region as well. c. It demonstrates the spatial relationship between occlusion and esthetics with the length, width, angulation, and geometry of the alveolus. d. It is more accurate for bone quality determination, unlike panoramic or periapical images. e. It demonstrates the geometry of the alveolus in the anterior region and the relationship of the lingual plate to the patients’ skeletal anatomy. f. Together with regional periapical radiographs, quantitative spatial information is available to demonstrate the geometry of the implant site relationship with that of the critical structures. Panoromic radiography This modality is probably the most utilized diagnostic modality in implant dentistry. However for quantitative preprosthetic implant imaging, it is not the most diagnostic. This radiograph produces an image of a section of the jaws of variable thickness and magnification. Panoramic radiography is characterized by an image of the jaws that demonstrates both vertical and horizontal magnification, along with a tomographic section thickness that varies according to the anatomic position. It produces a relatively constant vertical magnification of approximately 10%. The horizontal magnification of approximately 20%. The nonuniform magnification of structures produces images with distortion that cannot be compensated for in treatment planning. The posterior maxillary regions are generally the least distorted regions of a panoramic radiograph.

Panoramic images offer the following advantages 1. Opposing landmarks are easily identified. 2. Vertical height of bone initially can be assessed. 3. The procedure is performed with convenience, ease, and speed in most dental offices. 4. Gross anatomy of the jaws and any related pathologic findings can be evaluated. Disadvantages are 1. It does not demonstrate bone quality / mineralization. 2. It is misleading quantitatively because of magnification and because of the third dimension cross sectional view is not demonstrated 3. It is only of some use in demonstrating critical structures but of little use in depicting the spatial relationship between the structures and dimensional quantization of implant site. Diagnostic templates that have 5 mm ball bearing or wires incorporated around the curvature of the dental arch and worn by patient during the panoramic X-ray examination enable the clinician to determine the amounts of magnification in the radiograph. A technique for evaluating the panoramic radiograph for mandibular posterior implants and comparing this to the clinical evaluation during surgery was developed by identifying the mental foramen and the posterior extent of the inferior alveolar canal. “Sunder Dharmar” proposed that approximately 5 degree downward tilt of the patient head with reference to the Frankfort horizontal reference plane, showed mandibular foramen, mandibular canal and mental foramen in 91% of the radiographs. Zonography Recently a modification of the panoramic X-ray machine has been developed that has the capability of making a cross sectional image of the jaws. These devices employ limited angle linear tomography (Zonography) and means of positioning the patient. The tomographic layer is of approximately 5 mm. This

technique enables the appreciation of spatial relationship between the critical structures and the implant site and quantification of the geometry of the implant site. The tomographic layers are relatively thick and have adjacent structures that are blurred and super imposed on the image, limiting the usefulness of this technique for individual sites, especially in the anterior regions. Tomography The diagnostic quality of the resulting tomographic image is determined by the type of tomographic motion, the section thickness and the degree of magnification. The type of tomographic motion is probably the most important factor in tomographic quality. Hypocycloidal motion is generally accepted as the most effective blurring motion. Large amplitude tube travel and 1 mm sections are preferred for high contrast anatomic objects whose geometry changes in a relatively short distance, such as the alveolus of the jaws. Magnification varies from approximately 10 – 30% with higher magnification generally producing higher quality images. Dense structures may persist in the tomographic image ever though they are 3 – 4 times the tomographic layer thickness and distant from the tomographic section. The use of tomography prosthetic implant imaging are 1. Enables quantification of the geometry of the alveolus. 2. Enables determination of the spatial relationship between the critical structures and the implant site. 3. Enables appreciation of the quasi three dimensional appearance of the alveolus. 4. The quantity of alveolar bone available for implant placement can be determined by compensating for magnification. 5. Post imaging digitization of tomographic implant images enables use of a digital ruler aid in the determination of alveolar bone for implant placement. 6. Image enhancement can aid in identifying critical structures such as the inferior alveolar canal.

Limitations Not used in determining bone quality or identifying dental and bone disease. Linear Tomography It has been shown to be acceptable for the evaluation of single implant sites or multiple sites within a single quadrant. For the assessment of a greater number of sites, this technique was found to be too time consuming because of the additional calculations required to locate the patients’ position relative to the central ray of the X-ray beam. Submento vertex radiograph is used to determine the correct angulation of the X-ray beam location of the cross – sectional plane of the image. Advantages Linear tomography is capable of producing tomograms with layer thickness of approximately 3 mm and a range of magnification from 6 – 10% .Accuracy in this range was found to be adequate as confirmed surgically. Multidirectional or Polydirectional Tomography This includes hypocycloidal and spiral. In theory it should provide images of superior quality to linear tomography because of more uniform blurring. However no direct comparison of the efficacy of linear tomography and complex motion tomography has been reported. Advantages Compared to panoramic radiography, they have shown to be more precise in measuring the distance between the alveolar crest and the mandibular canal. DIGITAL RADIOGRAPHY Intra Oral Radiography Direct digital intra oral imaging is a technique emerging as an alternative to film radiography. Advantages Includes 1. Reduced patients’ exposure to radiation.

2. 3. 4. 5. 6. 7. 8. Increased patient comfort while the radiographic image is taken. Instant results and eliminates the inconvenience associated with developing film. The images produced by digital technology can be manipulated. The contrast can be enhanced to facilitate immediate diagnosis. Video conversion improves visualization by allowing for switching between negative and positive or from black and while to white and black image. Color also can be enhanced. The images can be inverted and rotated to 90 degrees. The distance measurement icon allows for documentation of distance between different points of an image in 0.1 mm increments. This is most useful in implants. Computed Tomography Computed tomography has been widely advocated for implant site assessment especially in the posterior regions of the jaws and for complex cases. CT studies are planned on a lateral scout image of the selected jaw with alignment corrections made as needed. Direct axial image are acquired as thin, overlapping axial scans with approximately 30 axial sections per jaw. These images are usually acquired perpendicular to the long axis of body. The sequential axial images subsequently are manipulated to produce multiple two dimensional images in various planes, using a computer based process called multiplanar reformatting (MPR). In general three basic images are reformatted 1. Axial images with a superimposed curve 2. Cross sectional images 3. Panoramic like curved linear images. An axial scan including the full contour of the mandible (or maxilla) at a level corresponding to the dental roots is selected as a reference for the reformatting process. The computer places a series of dots on the selected scan and connects them to develop a customized arch or curve unique for each jaw. The

computer program then generates a series of lines perpendicular to be curves. These lines are made at constant intervals. Usually 1 to 2 mm and numbered sequentially on the axial image to indicate the position at which each cross sectional slice will be reconstructed. Cross sectional reconstructions are made perpendicular to the curve and panoramic (curved liner) reconstructions are made parallel with the curve. Three dimensional representations may also be constructed in various orientations. Uses In Preprosthetic Implant Imaging These reformatted images provide the clinician with two dimensional diagnostic information in all the three dimensions. Reformatted CT studies provide diagnostic information in all available implant sites within a dental arch. The reformatted images typically are presented life size on photographic prints or radiographic film. It provides information of the continuity of the cortical bone plates, residual bone in the mandible and maxilla, the relative location of soft tissues covering the osseous structures. Studies have reported that 94% of CT measurements between the alveolar crest and wall of the mandibular canal were accurate within 1mm. Three dimensional reformations are particularly useful in the planning of angumentation procedures such as a sinus lift. 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 Misch Bone density classification D1 - Dense cortical bone D2 - Thick dense to porous cortical bone on crest and coarse trabacular bone within D3 - Thin porous cortical bone on crest and fine trabacular bone within D4 - Fine trabacular bone D5 - Immature, non mineralized bone

CT Determination of bone density D1 : > 1250 Hounsfield Units D2 : 850 – 1250 Hounsfield Units D3 : 350 – 850 Hounsfield Units D4 : < 150 Hounsfield Units Thus CT is capable of determining all the radiologic objectives of preprosthetic implant imaging. Interactive computed tomography: [ICT] (SIM / Plant Software, columbia scientific, Inc.,) This addresses many of the limitations of CT. This technique enables the radiologist to transfer the imaging study to the clinician as a computer file and enables clinician to view and interact with imaging study on their own computer. The clinicians’ computer becomes a diagnostic radiologic work station with tools to measure the length and the width of the alveolus; measure bone quality, the change the window and level of the grey scale of the study to enhance the perception of critical structures. Axial, cross sectional, and panoramic images are displayed and referenced so that the clinician can appreciate the same position or region within the patients anatomy in each of the images. As important features of ICT is that the clinician and radiologist can perform “electronic – surgery” (ES) by selecting and placing arbitrary size cylinders that simulate root form implants in the images. With an appropriately designed diagnostic template, ES can be performed to electronically develop the patients’ treatment plan in three dimensions. ES & ICT enable the development of a three dimensional treatment plan that is integrated with the patients anatomy and can be visualized before surgery by the members of the implant team and the patient for approval or modification.

Limitations 1. Refinement and exact relative orientation of the implant position is difficult and cumbersome. 2. Parallelism is difficult to appreciate in ICT using orthogonal rather than three dimensional images. Magnetic Resonance Imaging: (MRI) MR used in implant imaging as a secondary imaging technique when primary imaging techniques such as complex tomography, CT or ICT fail. Failure to differentiate the inferior alveolar canal may be caused by osteoporotic trabacular bone and poorly corticated inferior alveolar canal. The uses of MR are 1. MR visualizes the fat in trabacular bone and differentiates the inferior alveolar canal and neurovascular bundle from the adjacent trabacular bone. 2. Double scout MR imaging protocols with volume and oriented cross Sectional imaging of the mandible produce orthogonal quantitative contiguous images of the proposed implant sites. Limitations MR is not useful in characterizing bone mineralization or a high – yield technique for identifying bone or dental disease. DIAGNOSTIC TEMPLATES A diagnostic radiographic template is used to incorporate the patient’s proposed treatment plan into the radiographic examination. This information can then be used to alter implant angulation and position, achieving optimal implant body placement within the available bone & preserving vital structures. The end result of this process is the fabrication of a surgical implant that will enable the surgeon to place the implants in their proper positions.

The preprosthetic imaging procedures enable evaluation of the proposed implant site at the ideal position and orientation identified by radiographic markers incorporated into the template. The radiopaque markers used are 1. Barium sulphate 2. Lead foil 3. Gutta percha 4. Metal sleeves (set up disks) Of this lead foil is of limited use. Because of larger lead atom causes distortion of the image at the localized site occurs. Diagnostic templates used in computed tomography. The precision of CT enables the use of complex and precise diagnostic templates. Although CT scan can accurately identify the available bone height and width for a dental implant at a proposed implant site, the exact position and orientation of implant, which many times determines the actual length and diameter of the implant, is often dictated by the prosthesis. The surfaces of the proposed restorations and exact position and orientation of each dental implant should be incorporated into the diagnostic CT template. Many designs have been proposed for diagnostic CT templates. They are basically two forms. 1. Produced from a vacuumform reproduction 2. Produced from a processed acrylic reproduction of the diagnostic wax up. Vacuumform Template A number of variations have been proposed. 1. Coating the proposed restoration with a thin film of barium sulfate. Although the proposed restoration becomes evident in the CT examination, the ideal position & orientation of the proposed implant is not identified by this design. 2. The proposed restoration sites are filled in the vacuform of the diagnostic wax up with a blend of 10% barium sulfate and 90% cold cure acrylic this results in radiopaque tooth appearance of the proposed restorations in the CT

examination which matches the density of enamel and dentin of natural teeth but does not identify the exact position and orientation of the proposed implant site. 3. Modification of previous design by drilling a 2 mm hole through the occlusal surface of the proposed restoration at the ideal position and orientation of the proposed implant site with twist drill. This results in a natural tooth like appearance to the proposed restoration in the CT examination where all the surfaces of the restoration are evident along with a 2 mm radiolucent channel through the restoration, which precisely identifies the position and orientation of the proposed implant. Processed acrylic template The processed acrylic template is modified by coating the proposed restoration 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 is identified by the radiopaque plug of gutta-percha within the proposed restoration. Diagnostic Templates used for Tomography Diagnostic templates for tomography examinations are generally less precise than those required in CT examinations. The diagnostic information available from tomography examinations is not as detailed or as precise as that available from CT examinations. 1. The simplest tomography template is produced by obtaining a vacuform of the patient’s diagnostic cast with 3 mm ball bearing 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. The ball bearing can additionally serve as a measure of the magnification of most tomographic imaging system. 2. Templates that incorporate metal cylinders or tubes at the proposed implant sites also enable evaluation of tomograms for the orientation along with the position of the proposed implant. 3. The diagnostic template used in CT examination, which is produced from a vacuform of the patients diagnostic cast

with barium coating of the proposed restoration and orthodontic wires to indicate the position and orientation of the proposed implant, can also be used for tomography and provide the most diagnostic information of templates described. Dual purpose templates Diagnostic templates can be modified and used as surgical templates. If metamorphosis from diagnostic template to surgical template is the objective of the surgeon, the diagnostic template should be selected and fabricated with that in mind. Typically bench modification of a diagnostic template to produce a surgical template does not incorporate the precision of the results of ICT or ES. CAD/CAM Stereo Tactic Surgical Templates Anatomically accurate three dimensional models of the patients’ alveolar anatomy can be produced by a number of CAD/ CAM and rapid prototyping procedures. CAD/ CAM surgical stereotactic templates can be produced from CT examinations that have used interactive CT to develop a three dimensional treatment plan for the patient of the position and orientation of dental implants. 2. Surgical and Interventional Imaging Surgical and interventional imaging involves imaging the patient during and immediately after surgery and during the placement of the prosthesis. Purpose 1. To evaluate the depth of implant placement 2. To evaluate the position and orientation of implants / osteotomies. 3. To evaluate donor or graft sites. Modalities used 1. periapical radiographs. 2. panoramic radiographs. Film based intra-oral radiography The patient can be generally imaged at chair side with periapical radiography to determine implant/osteotomy depth, position and orientation. Corrections for magnification similar to those employed in endodontics are necessary to quantify the

depth of osteotomy. The disadvantage of periapical radiography is that a dark room and approximately 5 minutes radiography for film processing is generally required. Digital periapical radiography Digital periapical image receptors enable virtually instantaneous image acquisition, produce image quality similar to that of dental film and enable the surgical procedure to proceed without undue delay. Additional features of digital imaging such as image enhancement and use of digital measuring techniques can help the surgeon in establishing the optimum depth and orientation of the implants. Panoramic radiography For extensive implant procedures that may involve the entire jaw, both jaws, large donor graft sites, or sinus argumentation, panoramic radiography will provide a more global view of the patients’ anatomy. The disadvantage of panoramic radiography is that the patient must generally leave the surgical suite and stand or sit for the panoramic procedure. A panoramic radiography has less resolution than the periapical radiography. Clinical assessment Periapical or digital periapical radiography is useful modality to determine if the implants components and prosthesis are seated or fitted appropriately. The anti rotation device of the implant body may prevent the abutment from seating in the correct position. This may be difficult to ascertain because the implant crest module is often at the bone crest and the tissue is several millimeter thick. An x-ray examination is also performed to determine of the metal frame work and / or final restoration is completely seated, and the margins are acceptable around the implants and/or teeth. The important portion to image is the crestal aspect of the implant not the apex. 3. Post Prosthetic Imaging The purpose of post prosthetic implant imaging is to evaluate the status and prognosis of the dental implant. The bone around to the dental implant should be evaluated on a routine

basis for changes in mineralization or bone volume. Changes in bone mineralization in the region of bone adjacent to the dental implant may indicate successful integration, fibrous tissue interfaces, inflammation or infection, loss of crestal bone volume adjacent to the dental implant, excessive functional loading or Para-functional loading. Periapical Radiography The implants bone interface is depicted only at mesial, distal, inferior or crestal aspect or where the central ray of the xray source is tangent to the implant surface, evaluating the dental implant for changes in bone mineralization or bone volume in alveolar bone adjacent to the implant requires evaluation of temporally acquired periapical radiographs. The angulation of the x-ray beam must be within a degree of the long axis of the fixture to open the threads on the image on most threaded fixtures. Angular deviations of 13 degrees or more result in complete overlap of the threads. In general periapical radiographs are appropriate for longitudinal assessments. Mesial & distal marginal bone height is measured using known inter thread measurements and comparing that with the bone level in previous periapical radiographs. Studies suggest that the rate of marginal bone loss after successful implantation is approximately 1.2mm in the first year, subsequently tapering of to about 0.1mm in succeeding years. Occasionally areas of marginal bone gain also may be noted. Bite wing radiography The short and long term evaluation of crestal bone loss around implants is best evaluated with intra oral radiographs. A vertical bite wing radiography is often ideal and much easier to position once the prosthesis is in place. Most threaded implants have a smooth crestal region that measure 0.8 – 2mm depending upon the manufacturers. There is constant distance between the threads. As a result, the amount of crestal bone loss can be determined when compared to the original implant insertion.

The image is optimal when the implant body threads can be seen clearly on both sides. Quality periapical or bite wing radiographs placed parallel to the implant body with the central ray of source oriented perpendicular to the film will enables sequential radiographs for crestal and peri implant bone loss. Radiographs produced in this manner should result in a relatively undistorted image of the body of the implant, the implant abutment connection and / or threads. Radiographic signs associated with failing endosseous implants: Radiographic Appearance Clinical Implications Thin radiolucent area that Failure of the implant to closely follows the entire integrate with adjoining bone. outline of the implant. Radiolucent area around the Peri implantitis resulting from coronal portion of the implant poor plague control, adverse loading or both. Apical migration of alveolar Non axial loading resulting bone on one side of the from improper angulation of the implant implant. Widening of periodontal Poor stress distribution ligament space of the nearest resulting from bio mechanically natural abutment. inadequate prosthesis implant system. Fracture of the fixture. Unfavorable stress distribution during function. Temporal digital subtraction radiography (SR) It is a radiographic technique that enables two radiography made at different points of time of the same anatomic region to be subtracted resulting in an image of the difference between the two original radiographs. SR requires the same orientation between the x-ray source patient and film for each radiograph which can be accomplished by the use of registration templates. Additionally, SR requires the radiography to be standardized to account for changes in exposure and processing between each radiograph. Then the radiographs can be digitized, registered and

subtracted with a resulting subtraction image that simply depicts the changes in the patient anatomy during the time period between the radiographic exposures. Advantages 1. SR has been shown to be considerably more accurate at depicting changes in bone mineralization and bone volume than simply viewing the original periapical radiographs. 2. In addition to identifying mesial and distal changes in alveolar bone, SR can also depict buccal and lingual changes in alveolar bone. 3. SR has been the modality of choice for depicting temporal changes of alveolar bone for clinical and research studies. Disadvantages 1. SR has had limited utilization in clinical practice because of the difficulty in obtaining reproducible periapical radiographs. 2. Both periapical and SR techniques have limitation in determining buccal and lingual changes in alveolar bone. 3. Absolute quantization of trabacular bone, and 4. Depiction of the three dimensional relationship between the dental implant and surrounding trabacular and cortical bone. Computed tomography The advantages of CT are 1. The resolution. 2. The quantitative gray scale evaluation. 3. Three dimensional characteristics of CT enable evaluation of the bone implant interface in all orientations. 4. Failing implants characterized by trabacular and crestal demineralization, resorption of the bone implant interface, cortical plate fenestrations and perforation of the inferior alveolar canal cortical plates and nasal cavity or maxillary sinus floor can be identified with CT. 5. CT also demonstrates the results of sinus augmentation surgery. 6. Unlike conventional imaging techniques such as periapical or panoramic anatomy, the resolution, spatial

discrimination, and the three dimensional imaging capabilities of CT enable precise evaluation of the position of dental implants relative to critical structures such as the inferior alveolar canal, the mental foramen, maxillary sinus, nasal cavity, incisive foramen, anterior loop adjacent teeth, buccal or lingual cortical plates and so on. And suffers from magnification and distortion. MAXILLOFACIAL PROSTHODONTICS Radiographs play major role in maxillofacial rehabilitation of intra and extra oral facial structures which have been congenitally malformed or lost due to trauma. Main Indications for Maxillofacial radiographing are 1. Fracture of maxillofacial skeleton 2. Embroyonic abnormalities of maxillofacial region 3. fracture of skull 4. investigations of antra 5. diseases effecting skull base and vault 6. TMJ disorders The extent of damage to tissues needed to be rehabilitated and extent of underneath supporting tissues vital for receiving maxillofacial prosthesis to be analysed by various radiographic views of maxillofacial prosthesis and treatment plan is executed. Radiographs of maxillofacial region are 1. I ntraoral radiographs – IOPA, bitewing etc 2. Extraoral radiographs – most commonly used maxillofacial imaging. Ex. P-A Projection (Granger projection ) Inclined P-A (Caldwell projection) Most maxillofacial rehabilitations in Prosthodontics include closure of developmental defects like clefts and eye , ear, nose and cranial prosthesis lost due to trauma which go best with radiographic evidence. For best visualization of clefts most preffered radiographs are 1. Occlusal radiographs. 2. Lateral Cephalogram

3. CT scan 4. Ultrasound Radiographs in maxillofacial sinuses 1. Standard occipeto mental projection( 0 degress) 2. Modified method (30 degrees mental projection) 3. P-A Waters view 4. Bregma menton view Radiographs of mandible 1. P-A mandible 2. Rotated P-A mandible 3. Lateral oblique a. Anterior body of mandible b. Posterior body of mandible c. Ramus of mandible Radiographs of Zygomatic arches 1. Jughandle view Radiographs of base of skull 1. Submentovertex projection Radiographs of skull 1. Lateral cephalogram 2. True lateral cephalogram 3. P-A cephalogram 4. P-A skull 5. TOWNES projection Radiographs of TMJ imaging 1. Panoromic radiography 2. Transcranial projection 3. Tomography 4. Arthromography 5. Arthromography with videofloroscopy 6. MRI 7. Computed tomography

TMJ interpretation Roentgenograms are of value for differential diagnosis in that other pathologic condition having signs and symptoms similar to traumatic TMJ arthritis may be distinguished by roentgenographic changes. Roentgenographic changes associated with Osteoarthritis of TMJ are 1. Lack of definition of anterior aspect of condyle 2. Peripheral lipping of bone of condyle with flattening of articular surface 3.resorption of bone at posterior aspect of articular tubercle towards glenoid fossa. 4. Fragmentation of meniscus 5. Dystrophic calcification Presence of tumor , cyst and fracture should be ruled out before a final diagnosis is made on tmj and occlusal related problems. Usually such problems can be detected from panorex radiograph. Panorex radiographs presents the entire joint region and ascending ramus in clarity and completeness, they are most practical for use in differential diagnosis of TMJ. Radiographic examination procedures for TMJ should always include periapical films. Radiographs are important third step in making differential diagnosis. Four basic radiographic techniques can be used in most dental offices for evaluating the TMJ 1. panoramic view 2. Lateral transcranial 3. Transpharangeal 4. Transmaxillary or A-P view More sophisticated techniques include 1. Tomography 2 Arthrography 3. MRI

4. Bone scanning Alternate and specialized imaging modalities Research and development have focused on manuplating and altering all three basic requirements of image production i.e the patient, image generating equipment and image receptor. New softwares are being developed to manuplate the image itself once it has been captured. Many of imaging modalities are playing increasing role in dentistry. Many of imaging modalities are playing increasing role in dentistry. Main specialized imaging modalities are 1. Contrast studies 2. Radioisotope imaging 3. Computed tomography 4. Cone beam CT (CBCT) 5. Ultrasound 6. Magnetic resonance

Conclusion Proper modality of radiographic interpretation, good technical skill in taking radiograph, thorough radiographic study, proper interpretation help to reach a perfect diagnosis and optimum treatment .Arriving at definite diagnosis and treatment plan is challenging task in Prosthodontics which is made easy by radiographic interpretation. Many of abnormalities both intraoral and facial which remain undetected by inspection for a successful prosthetic rehabilitation can be detected by radiographs. So ‘eye misses but X-ray catches’. Radiographs are an adjunct and not the sole or primary source of diagnostic information. Good understanding and sound knowledge of various radiographic modalities and their specificity help to eliminate unnecessary radiation hazards and control expense of treatment. Radiographs form final aspect of diagnostic procedure and provide Prosthodontist correlate all the facts that have been collected listening to the patient , examining the mouth and evaluating the diagnostic cast.

Reference  Imaging in Implantology, Bhat.S, Shetty.S, Shenoy K.K,2005,VOL 5,JIPS,Issue 1,page 10-14.  Basic Implant Surgery, R.Palmer, P.Palmer, Floyd, Vol 187,No 8,OCT 23,1999,BDJ  Prosthetic treatment of edentulous patients,Zarb-Bolender,12th edition,2004.  Essentials of complete denture prosthodontics, Sheldon Wrinkler,2nd edition,2004.  Syllabus of Complete dentures,Charles M.Heartwell jr, 4th edi,1984.  McCrackens Removable partial Posthodontics, 11th edi,Alan B. Care,Glen .P.Mc Givney,David T.Brown.,2005.  Clinical removable partial Prosthodontics,2nd edi,Steward,Rudd,Kuebker,2003.  Contemporary Fixed prosthodontics,Stefen F. Rosential,2001.  Tylmans theory and practice of Fixed Prosthodontics,8th edi, W.F.P.Malone,D.L. Koth,2004.  Fundamentals of Fixed Prosthodontics,3rd edi.Herbert T. Shillingberg,1997.  Functional occlusion From TMJ to SMILE DESIGN,Peter E.Dawson,1989.  Management of TM disorders and occluysion,5th edi,Jeffrey P. Okeson,1998.  Clinical maxillofacial prosthesis,Thomas D. Taylor,2004.  Dental implant prosthetics,Carl.F. Misch,1st edi,2004.  Essentials of dental radiology and radiography,4th edi,Eric Whaites,2007.  Text book of Dental and Maxillofacial Radiology,Freny R. KARJODKAR,2006.  Oral Radiology principles and interpretations,5th edi,2004.s

Contents  Introduction  Pioneers in dental radiography  Radiographs in CD prosthesis  Radiographs in RPD prosthesis  Radiographs in FPD prosthesis  Implant imaging  Radiographs in maxillofacial prosthodontics  TMJ interpretation  Alternate and specialized imaging  Conclusion  Reference

A Seminar on RADIOGRAPHS IN PROSTHODONTICS Presented by Dr.G.MANMOHAN, P.G Student, Date: 27-11-07. Signature of Prof & HOD


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