Imaging in oral implantology

Anish Amin

Digital radiograph

y

Cone beam

volumetri

c tomograp

hy Imaging of vital

structures

Phases

of imaging Introductio

n

Interactive computed

tomography.

Periapical radiography

Conclusion

References

Panoramic radiography

Imaging

modalities.

Tomography &

computed tomography

Diagnostic templates

CONTENTS

› The widespread use of dental implants in partially and completely edentulous patients has brought about a need to preoperatively depict and quantify the accurate bone height and contour and location of vital anatomic structures by radiographic examination

› Multiple factors influence the selection of radiographic technique(s) for a particular case, including cost, availability, radiation exposure, and case type.

› Diagnostic imaging techniques must always be interpreted in conjunction with a good clinical examination.

› The decision is a balance between these factors and the desire to minimize risk of complications to the patient.

Introduction

Phases of imaging

1) Pre-surgical implant imaging

oTo assess the overall status of the remaining dentition

oTo identify and characterize the location and nature of the edentulous regions, particularly to determine the quantity , quality and angulations of bone o To determine the

relationship of critical structures to the proposed implant site o To detect regional anatomic abnormalities and pathologies.

2) Surgical & intraoperative implant imaging

› Evaluates the sites during and immediately after surgery

›Assist in the optimal position and orientation of dental implants

›To evaluate the healing and integration phase of implant surgery

› To ensure abutment position and prosthesis fabrication

3) Post-prosthetic imaging›To evaluate the long-term maintenance of implant rigid fixation and function

›To assess the Crestal bone levels around each implant

›To evaluate the implant complex

Imaging modalities›The decision to image the patient is based on the patients clinical needs and its availability.

› Imaging modalities can be:Analog / Digital imaging

modalities Two-dimensional /

Three –dimensional

imaging modalities

Periapical radiographyIndications: ›Evaluation of small edentulous spaces , Eg: in case of single tooth replacement

›Alignment and orientation of implants during surgery

›Recall/maintenance evaluations

Intraoral periapical radiograph displaying the implant placed at the site of 11, and its relation to adjacent structures

oAmount of bone loss and peri- implantitis can be visualized

oSubtle variations in bone activity is clearly seen

oMinimal magnification with high resolution

oThey are easy to obtain in the dental office, Inexpensive

oDeliver low radiation to the patient

Advantage

DisadvantagesoThey are susceptible to

unpredictable magnification of anatomic structures, which does not allow reliable measurements.

o Distortion is particularly accentuated in edentulous areas, where missing teeth and resorption of the alveolus necessitate film placement at significant angulation in relation to the long axis of the teeth and alveolar bone

Disadvantages›Periapical radiographs are two-dimensional representations of three-dimensional objects and do not provide any information of the buccal-lingual dimension of the alveolar ridge. Structures that are distinctly separated in the buccal-lingual dimension appear to be overlapping.

Disadvantages

›The periapical image is limited by the size of film being used

›Often, it is not possible to image the entire height of the remaining alveolar ridge, and when extensive mesial-distal areas need to be evaluated, multiple periapical films are required

Digital radiography›Process wherein the film is replaced by a sensor that collects the data

›The analog information received is then interpreted by specialized software and an image is formulated by a computer monitor

› The resultant image can be modified in terms of gray scale, brightness, contrast, inversion and color enhancement

› Computerised software programs like Dexisimplant are available that allowing for calibration of magnified images , ensuring accurate measurements

Advantages› Less radiation

› Superior resolution

› Instantaneous speed of image formation is highly useful during surgical placement of implants and the prosthetic verification of component placement

Disadvantage› Size and thickness of the film and position of the connecting cord

sometimes makes film placement difficult in some sites , such as those adjacent to tori or in case of tapered arch form in the region of canines

Panoramic radiographo They display image slices through the jaws by producing a single image of the maxilla and mandible and their supporting structures in a frontal plane

o The image receptor is either the radiograph film or can also be a digital storage phosphor plate or a digital charge – coupled device receptor

Indications:

› Indicated when multiple implant placements are planned.

› Initial assessment of vertical height of bone

›Evaluation of gross anatomy of the jaws and any related pathologic findings

oThey display anatomic structures like nasal cavity, maxillary sinus, inferior alveolar canal and mental foramen.

Advantages:

o Convenience, ease and speed in performance dental office

Disadvantages o The resolution is lesser when compared to intraoral radiograph.o Cross sectional view is not demonstrated and is of little use in depicting the spatial relationship between the structures o A10-20% image magnification occurs, which is non uniform. This magnification is undesirable for both implant selection and implant site assessments.o Geometric distortion and overlapping of images of teeth can occur.o Overlapping of anterior region by vertebral column occurs.

Tomography Tomo= slice ; Graph=picture

o Tomographic units produce cross-sectional slices of the jaws that can be as thin as 1 mm and are suitable for pre- and post-implant assessment

o This technique enables the visualization of patient’s anatomy by blurring regions above and below the section of interest.

› The basic principle of tomography is that the x-ray tube and film are connected by a rigid bar called the fulcrum bar, which pivots on a point called 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

›Different patterns of movement, including linear, circular, spiral or hypocycloidal have been attempted to reduce blurring artifacts and provide a sharper and more useful image.

›Linear tomography is the simplest form , which has a one dimensional motion and produces blurring of adjacent sections and results in linear steak artifacts in the resulting image, which may obfuscate the section of interest

›Circular, spiral and hypocycloidal are two- dimensional motions

›Hypocycloidal is generally accepted as the most effective blurring motion

›This technique is difficult to use in cases of multiple implant sites.

Transtomography / sectional tomography

› 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 thick and have adjacent structures that are blurred and superimposed on the image, limiting the usefulness of this technique for individual sites, especially in the anterior regions where the geometry of the alveolus changes rapidly.

Advantages ›Cross- sectional views

›Constant magnification

Disadvantages: ›Technique- sensitive

›Blurred images›High radiation dose›Multiple images needed

›Expensive

Computerised Tomography o CT is a digital imaging technique, which can generate 3D images using a very narrow “fan beam” that rotates around the patient, acquiring one thin slice (image) with each revolution

o It was first applied successfully in implantology in the 1980s.The dental CT can be performed with a conventional

CT, a spiral CT or a multislice CT scanner

o It allows clinicians to visualize the bony architecture, nerves, joints, sinuses and other structures much more completely than traditional flat radiographs

o CT scans have been shown to be very accurate with the magnification effect, the same for both the anterior and posterior area, from a range of 0% to 6% in horizontal as well as 0-4% in the vertical dimension.

Advantages› Negligible magnification› High contrast image› 3 dimensional bone models › Interactive treatment planning

Disadvantages:›High dose of radiation

›Technique – sensitive

›Expensive

‘FAN BEAM” Geometry

Recent advances in CTCone Beam Volumetric Tomography

Microtomograph

DentascanoDentaScan is a computed tomography (CT) software program that allows the mandible and maxilla to be imaged in three planes: axial, panoramic and cross-sectional.

o Data acquisition time for maxilla or mandible is about 15 min.o The effective dose of the standard DentaScan Protocol is around 8.16 mSv

Cone Beam Volumetric Tomography

› Because of higher radiation exposure, higher cost, huge footprint and difficulty in accessibility associated with CT, a new type of CT, CBVT was developed.

NewTom 3G by AFP

MercuRay by Hitachi

3D Accuitomo by J. Morita

The images recorded are placed onto a charge- coupled device chip and is then converted into axial, sagittal and coronal slices and permit reformatting to view traditional radiographic images as well as 3- dimensional soft tissue or osseous images

The x- ray tube on these scanners rotates around 360 degrees and will capture images of the maxilla and mandible in 36 seconds , in which only 5.6 seconds is needed for exposure

“ Cone beam” geometry

Indications:CBVT allows precise measurement of distance, area and volume.

›Assessment of the positions and states of the structures critical for adequate implant placement (e.g., inferior alveolar canal, location of the neurovascular bundle and the incisive and mental foramina, pneumatization of the maxillary sinus, floor of the maxillary sinus, nasal fossa);

Indications:

Indications › Examination after placement of implants and bone grafts;

› Evaluation of bone resorption and root retention, as well as lesions of the facial skeleton.

›Patients with claustrophobia, ›Parkinson disease›tremors › disabling conditions that might cause a patient to be uncooperative

Contraindications

Advantages

o lower cost and more feasible compared to the computerised tomography

o Radiation dose from a CBVT scanner is approx. 12.0 mSv , which is equivalent to 25 % of radiation from a typical panoramic radiograph or to five D-speed dental x-rays

o Almost 0% magnification

o No superimposition or overlapping of images, hence minimal distortion

Interactive computed tomography

› This technique enables the radiologist to transfer the imaging study to the practitioner as a computer file and enables the practitioner to view and interact with the imaging study on their own computer

› It helps to measure the length and the width of the alveolus, measure bone quality and change the window and level of the grayscale of the study to enhance the perception of critical structures

An important feature of ICT is that the dentist and radiologist can perform electronic surgery (ES) by selecting and placing arbitrary-sized cylinders that simulate root form implants in the images.

With an appropriately designed diagnostic template, ES can be performed to develop the patient’s treatment plan electronically in 3D

Superimposed on the CBVT image, electronic implants can be virtually previewed at arbitrary positions and orientations with respect to each other, the alveolus, critical structures and the prospective occlusion and esthetics.

ES and ICT enable the development of a 3D treatment plan that is integrated with the patient’s anatomy and can be visualized before surgery.

Surgical guides›Computer generated drilling guides that are fabricated through the process of stereolithography using SimPlant software for ideal implant positioning

The diameter of the drilling tube is usually 0.2 mm larger than the corresponding drill, thus making angle deviation highly unlikely

These successive diameter surgical osteotomy drill guides may be either bone, teeth or mucosa-borneSurgiguides have metal cylindrical tubes that correspond to the number of desired osteotomy preparations and specific drill diameters

CT based surgical guidance templates and navigation systems›These systems allow the transfer of the pre-surgical plan to the patient , thus indicating when there is deviation from the predetermined drilling parameters

›Therefore the depth and trajectory of drilling sequence is made to the exact location of the pre-planned position

Imaging of vital structures in oral implantology

Mental foramen and mandibular canal› While using the two-dimensional radiographs for imaging Mental foramen and mandibular canal ,it is mainly dependent on the positioning.

› The x-ray beam must be perpendicular to the tangent of the area in question between the foramen and the most anterior tooth

› If the image is taken from the mesio-oblique orientation, measurements will be fore-shortened

› If disto-obliquely oriented then measurements will be elongated

›Always the radiographic density should not increase above 2.8, after which the foramina becomes less apparent

› In edentulous mandibles, the risk of error is high because of the increased resorption of alveolar crest

Studies have shown that the location of mental foramen on periapical and panoramic radiograph are inaccurate and sometimes on panoramic radiograph it represents a portion of the mental canal as it leaves the mandibular canal

› Several studies have shown CT to be the most accurate and highly recommended when measurements are needed for the inferior alveolar canal and mental foramen

Mandibular lingual concavities ›When there is advanced atrophy of posterior mandible, lingual concavities may be present

›Within these concavities branches of facial artery may be present

›Over estimation of the amount of bone may lead to perforation of lingual plate when drilling with the osteotomy

›CT is the recommended method

Mandibular ramus›Donor site for autogenous onlay bone grafting and is extremely variable in the amount of bone present . Hence adequate assessment of host bone present is not possible

›Recommended : CT

Mandibular symphysis›Donor site for autogenous graft

› Panoramic radiographs mostly overestimate the height of the available bone in the anterior region

›An imaging technique that depicts the true bucco-lingual amount of bone is recommended

›Recommended: conventional CT

Maxillary sinus› For implant placement detailed information is needed regarding the position of septa, maxillary sinus anatomy, sinus pathologies No radiographic

modality till date gives more information on the above mentioned features than CT and hence considered as the gold standard for evaluation of sinuses

Intraoperative imaging › To verify the positioning and location of an osteotomy site or for identification of a vital structure, processing of standard radiograph film can take upto 6 minutes and hence is time- ineffcient

› Current day digital imaging system gives instant images that can be manipulated, and allows accurate measurements and maintains aseptic protocol

Immediate post operative imaging

›A periapical or panoramic radiograph should be taken post surgically so that a baseline image can be used to evaluate against future images

›Additional imaging tools may be used to evaluate a zone of safety around the vital structures

Abutment and prosthetic component imaging

› When evaluating for transfer of impressions along with the two- piece implant abutment component placement , radiographs should be taken to verify secure adaptation

› Intraoral radiographs are recommended because of their high geometric resolution to evaluate for any fit discrepancy

› X-ray beam should be directed at right angle to the longitudinal axis of the implant. Even a slight angulation may allow a slight gap to be noticed

› If periapical radiographs is difficult to place, Bitewing radiographs or panoramic radiography can also be used .

Post prosthetic imaging› When investigating complications after implant placement, a panoramic radiograph is the most ideal technique

› Whenever Single implant image or a detailed information of implant viewed on panoramic image is needed, a periapical radiograph

› A post prosthetic radiograph helps in future evaluation of component fit verification and also for marginal bone level evaluation

Recall and maintenance imaging

›Follow up or recall radiographs are to be taken 1 year of functional loading and yearly for the first 3 years to asses the marginal bone levels

Radiographic sequence for dental implants imaging ›Pretreatment›Immediate post surgical (baseline) ›Healing period ( if necessary)›Second stage surgery ›Post prosthetic surgery ( baseline)›1 year postoperatively›After 1st year, every 2 years

Fabrication of diagnostic templates› The surfaces of the proposed restorations and the exact position and orientation of each dental implant should be incorporated into the diagnostic CT templates

The design may vary from a vaccuformed reproduction of the wax-up - to one processed from acrylic reproduction of the diagnostic wax-up – to a sophisticated specially 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 a gutta-percha

› While radiographic examination GP point will be seen as radiopaque and will help in determining the position and orientation of the proposed implant

The next design modifies the 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 a twist drill

The vaccuform templates involve either coating of

the proposed restorations with a thin film of

barium sulfate. This does not depict the ideal

position and orientation of the proposed implant

Another method is to blend 10% barium

sulfate and 90% cold cure acrylic , which

makes the proposed restoration

radiopaque and evident but again does

not give idea about the position and

orientation

›Recently radiographic teeth specifically designed for the fabrication of diagnostic templates have been introduced .

›These are time saving, placed easily, provide consistently high radiopacity, have molds corresponding to prosthetic teeth used in the final restoration and are bonded easily with the template-based material

Conclusion › Although many modalities are available for imaging the implant site, the correct and required technique should be adopted depending on the case and the clinician’s judgment to interpret the image acquired.

› The choice of pre-implant imaging must be considered carefully due to the radiation dose, the cost of each examination and the anticipated information that may be provided by the imaging study.

› The risk-to-benefit ratio should be determined on an individual basis so as to maximize success.

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Mosby Elsevier; 2008.Diagnostic imaging and techniques; p.38-67.

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› Spector L. Computer-aided dental implant planning. Dent Clin North Am 2008; 52: 761-75.

References › Ganz SD. Presurgical planning with CT-derived fabrication of surgical guides. J Oral Maxillofac Surg 2005; 63: 59-71.

› Reiskin AB. Implant imaging. DCNA 1998; 42: 47-56.

› Rashedi B, DMD, Tyndall DA. Tuned aperture computed tomography for cross-sectional implant site assessment in the posterior mandible. J Prosthodont 2003; 12: 176.

› Vercruyssen M, Jacobs R, Van Assche N, van Steenberghe D. The use of CT scan based planning for oral rehabilitation by means of implants and its transfer to the surgical field: A critical review on accuracy. J Oral Rehabil 2008; 35: 454-74.

› Mallya SM, Potluri A. Diagnostic imaging for implants. JIAOMR 2004; 16: 174-80.

References o Dula K, Mini R, van der Stelt PF, Buser D. The radiographic assessment of implant

patients: decision-making criteria. Int J Oral Maxillofac Implants. 2011; 16: 80-9. 2.

oChau AC, Fung K. Comparison of radiation dose for implant imaging using conventional spiral tomography, computed tomography, and cone-beam computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2009; 107: 559-65.

oTyndall DA, Price JB, Tetradis S, Ganz SD, Hildebolt C, Scarfe WC, et al. Position statement of the American Academy of Oral and Maxillofacial Radiology on selection criteria for the use of radiology in dental implantology with emphasis on cone beam computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol. 2012; 113: 817-26.

oLingam AS, Reddy L, Nimma V, Pradeep K. “Dental implant radiology” - Emerging concepts in planning implants. J Orofac Sci 2013; 5: 88-94.

Imaging in oral implantology

Anish Amin