Clinical Applications of DigitalDental Technology

Clinical Applications of DigitalDental Technology

Edited by

Radi Masri, DDS, MS, PhDAssociate Professor, Department of Endodontics, Prosthodontics, and Operative Dentistry,School of Dentistry, University of Maryland, Baltimore, Maryland, USA

Carl F. Driscoll, DMDProfessor and Director, Prosthodontic Residency, Department of Endodontics, Prosthodontics, and Operative Surgery,School of Dentistry, University of Maryland, Baltimore, Maryland, USA

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Library of Congress Cataloging-in-Publication Data

Clinical applications of digital dental technology / editors, Radi Masri, Carl F. Driscoll.p. ; cm.

Includes bibliographical references and index.ISBN 978-1-118-65579-5 (pbk.)I. Masri, Radi, 1975- , editor. II. Driscoll, Carl F., editor.[DNLM: 1. Radiography, Dental, Digital–methods. 2. Computer-Aided Design. 3. Radiation Dosage.

4. Technology, Dental. WN 230]RK309617.6′07572–dc23

2015007790

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1 2015

To family, near, and far.

Contents

Contributors ixForeword xiPreface xiii

1 Digital Imaging 1Jeffery B. Price and Marcel E. Noujeim

2 Digital Impressions 27Gary D. Hack, Ira T. Bloom, andSebastian B. M. Patzelt

3 Direct Digital Manufacturing 41Gerald T. Grant

4 Digital Application in OperativeDentistry 57Dennis J. Fasbinder and Gisele F. Neiva

5 Digital Fixed Prosthodontics 75Julie Holloway

6 CAD/CAM Removable Prosthodontics 107Nadim Z. Baba, Charles J. Goodacre, andMathew Kattadiyil

7 Digital Implant Surgery 139Hans-Peter Weber, Jacinto Cano, andFrancesca Bonino

8 Digital Design and Manufacture ofImplant Abutments 167Radi Masri, Joanna Kempler, andCarl F. Driscoll

9 Digital Applications in Endodontics 177Ashraf F. Fouad

10 From Traditional to Contemporary:Imaging Techniques for OrthodonticDiagnosis, Treatment Planning, andOutcome Assessment 193Georgios Kanavakis andCarroll Ann Trotman

11 Clinical Applications of Digital DentalTechnology in Oral and MaxillofacialSurgery 207Jason Jamali, Antonia Kolokythas, andMichael Miloro

12 The Virtual Patient 231Alexandra Patzelt and Sebastian B. M. Patzelt

Index 241

Contributors

Nadim Z. Baba, DMD, MSDProfessor, Department of Restorative Dentistry,

Loma Linda University School of Dentistry,Loma Linda, CA, USA

Francesca Bonino, DDSPostgraduate resident, Department of

Periodontology, Tufts University School ofDental Medicine, Boston, MA, USA

Jacinto A. Cano Peyro, DDSInstructor, Department of Prosthodontics &

Operative Dentistry, Tufts University School ofDental Medicine, Boston, MA, USA

Carl F. Driscoll, DMDProfessor and Director, Advanced Education in

Prosthodontics, Department of Endodontics,Prosthodontics, and Operative Dentistry, Schoolof Dentistry, Maryland, Baltimore, MD, USA

Dennis J. Fasbinder, DDSClinical Professor, Department of Cariology,

Endodontics, and Restorative Services,University of Michigan School of Dentistry,Ann Arbor, MI, USA

Ashraf F. Fouad, BDS, DDS, MSProfessor and Chair, Department of Endodontics,

Prothodontics and Operative Dentistry, Schoolof Dentistry, University of Maryland, Baltimore,MD, USA

Charles J. Goodacre, DDS, MSDProfessor, Restorative Dentistry, Loma Linda

University, School of Dentistry, Loma Linda,CA, USA

Gerald T. Grant DMD, MSCaptain, Dental Crops, United States Navy,

Service Chief, 3D Medical Applications Center,Department of Radiology, Walter ReedNational Military Medical Center, Director ofCraniofacial Imaging Research, NavalPostgraduate Dental School, Bethesda, MD,USA

Gary D. HackAssociate Professor and Director of Clinical

Stimulation, Department of Endodontics,Prosthodontics, and Operative Dentistry,School of Dentistry, University of Maryland,Baltimore, MD, USA

Julie Holloway, DDS, MSProfessor and Head, Department of

Prosthodontics, The University of Iowa Collegeof Dentistry, Iowa City, IA, USA

Jason Jamali, DDS, MDClinical Assistant Professor, Department of Oral

and Maxillofacial Surgery, University ofIllinois, Chicago, IL, USA

Georgios Kanavakis, DDS, MSAssistant Professor, Department of Orthodontics

and Dentofacial Orthopedics, Tufts University,

x Contributors

School of Dental Medicine, Boston,MA, USA

Mathew T. Kattadiyil, BDS, MDS, MS, FACPDirector, Advanced Specialty Education Program

in Prosthodontics, Loma Linda UniversitySchool of Dentistry, Loma Linda, CA, USA

Joanna Kempler, DDS, MSClinical Assistant Professor, Department of

Endodontics, Prosthodontics and OperativeDentistry, University of Maryland, Baltimore,MD, USA

Antonia Kolokythas, DDS, MScAssociate Professor, Program Director,

Department of Oral and Maxillofacial Surgery,Multidisciplinary Head and Neck CancerClinic, University of Illinois at Chicago,Chicago, IL, USA

Radi Masri, DDS, MS, PhDAssociate Professor, Advanced Education in

Prosthodontics, Department of Endodontics,Prosthodontics, and Operative Dentistry, Schoolof Dentistry, Maryland, Baltimore, MD, USA

Michael Miloro, DMD, MD, FACSProfessor and Head, Department of Oral and

Maxillofacial Surgery, University of Illinois atChicago, Chicago, IL, USA

Alexandra Patzelt, DMD, Dr med dentVisiting Scholar, Department of Periodontics,

School of Dentistry, University of Maryland,Baltimore, MD, USA

Sebastian B. M. Patzelt, DMD, Dr med dentAssociate Professor, Department of Prosthetic

Dentistry, Center for Dental Medicine, MedicalCenter – University of Freiburg, Freiburg i. Br.,Germany

Jeffery B. Price, DDS, MSAssociate Professor, Director of Oral &

Maxillofacial Radiology, Department ofOncology & Diagnostic Sciences, University ofMaryland School of Dentistry, Baltimore, MD,USA

Carroll Ann Trotman, BDS, MS, MAProfessor and Chair, Department of Orthodontics,

Tufts University School of Dental Medicine,Boston, MA, USA

Hans-Peter Weber, DMD, Dr med dentProfessor and Chair, Department of

Prosthodontics and Operative Dentistry, TuftsUniversity School of Dental Medicine, Boston,MA, USA

Foreword

Advances in technology have resulted in the devel-opment of diagnostic tools that allow cliniciansto gain a better appreciation of patient anatomythat then leads to potential improvements intreatment options. Biomechanical engineeringcoupled with advanced computer science hasprovided dentistry with the ability to incorporatethree-dimensional imaging into treatment plan-ning and surgical and prosthodontic treatment.Optical scanning of tooth preparations and dentalimplant positions demonstrates accuracy thatis similar to or possibly an improvement uponthat seen with traditional methods used to makeimpressions and create casts.

For example, with this technology, orthodontictreatment can be reevaluated to assess outcomes.Today, orthodontic treatment can be planned andexecuted differently. With CT scanning on theorthodontic patient, dentists can better understandthe boney limitation of a proposed treatment andtiming of the treatment and dental implants can beused to create anchorage to move the teeth moreeasily. Every aspect of dentistry has been affectedby digital technology, and in most instances, thishas resulted in improvements of clinical treatment.

Restorative Dentistry and Prosthodontics arelikely to experience the most dramatic changesrelative to the incorporation of digital technology.Three-dimensional imaging provides the clinicianwith an ability to analyze bone quantity and qual-ity that should lead to more effective development

of surgical guides. Likewise, hard and soft tissuegrafting may be anticipated in advance, which willallow improved site development for estheticsand function. Such planning allows more affectiveprovisionalization of the teeth and implants. Bydigitally understanding the design and toothposition, a provisional prosthesis can be fabricatedusing a monolithic premade block of acrylic,composite, or hybrid resin, thereby improving theultimate strength of these prostheses. Dental mate-rial science has responded by producing materialsthat are more esthetic and can best provide a bet-ter potential for long-term survival and stability.Dental ceramics now can be milled on machinesthat can accept ever-improving algorithms toprovide the most accurate prosthesis. Today,materials such as lithium disilicate, zirconia, andtitanium are easily milled in machines that areself-calibrating and can eliminate the cuttings, sothat accuracy is insured. In-office or in-laboratoryCAD/CAM equipment is constantly improving,and it is clear that in years to come surgical guidesand most types of ceramic restorations will ableto be produced accurately and predictably in theoffice environment. This will change some of theduties of the dental technologist but in no waywill compromise the necessity of having thesetrained and very talented professionals moreinvolved in designing, individualizing color andcharacterization, correcting marginal discrepan-cies, and refining the prosthetic occlusions that

xii Foreword

are required. The dental technologist representsthe most important function in delivering arestoration, that of quality control.

The future is exceedingly bright for all involvedin the provision of dental care; moreover,the incorporation of digital dental proce-dures promises to improve care for the mostimportant person in the treatment team, thepatient.

The authors should be commended for bring-ing such valuable information and insight to theprofession. At this point, information is whateveryone most desire and one can be very proudof all the efforts forward-thinking professionals,engineers, and material scientists are bringingto the table. An honest appraisal of where weare today and what the potential future can bewill drive the industry to create better restora-tive materials and engineered equipment andalgorithms to dentistry.

Kenneth Malament

Preface

The evolution of the art and science of dentistry hasalways been gradual and steady, driven primarilyby innovations and new treatment protocols thatchallenged the conventional wisdom such as theinvention of the turbine handpiece and the intro-duction of dental endosseous implants.

While these innovations were few and farbetween, the recent explosion in digital tech-nology, software, scanning, and manufacturingcapabilities caused an unparalleled revolutionleading to a major paradigm shift in all aspects ofdentistry. Not only is digital radiography routinepractice in dental clinics these days, but virtualplanning and computer-aided design and manu-facturing are also becoming mainstream. Digitalimpressions, digitally fabricated dentures, and thevirtual patient are no longer science fiction, butare, indeed, a reality.

A new discipline, digital dentistry, has emerged,and the dental field is scrambling to fully integrateit into clinical practice and educational curricu-lums and as such, a comprehensive textbookthat details the digital technology available anddescribes its indications, contraindications, advan-tages, disadvantages, limitations, and applicationsin the various dental fields is sorely needed.

There are a limited number of books andbook chapters that address digital radiography,digital surgical treatment planning, and digitalphotography, but none address digital dentistrycomprehensively. Although these topics will beaddressed in this book, the scope is entirely differ-ent. The main focus is the practical application ofdigital technology in all aspects of dentistry. Avail-able technologies will be discussed and criticallyevaluated to detail how they are incorporated indaily practice across all specialties. Realizing thattechnology changes rapidly, developing technolo-gies and those expected to be on the market in thefuture will also be discussed.

Thus, this book is intended for a broad audi-ence that includes dental students, generalpractitioners, and specialists of all the dentaldisciplines including prosthodontists, endodon-tists, orthodontists, oral and maxillofacialsurgeons, periodontists, and oral and maxillofacialradiologists. It is also useful for laboratory tech-nicians, dental assistants and dental hygienists,and anyone interested in recent digital advancesin the dental field. We hope that the reader willgain a comprehensive understanding of digitalapplications in dentistry.

1 Digital Imaging

Jeffery B. Price and Marcel E. Noujeim

Introduction

Imaging, in one form or another, has been availableto dentistry since the first intraoral radiographicimages were exposed by the German dentist, OttoWalkhoff (Langland et al., 1984), in early 1896, just14 days after W.C. Roentgen publicly announcedhis discovery of X-rays (McCoy, 1919; Bushong,2008). Many landmark improvements have beenmade over the more than 115-year history of oralradiography.

The first receptors were glass, however, film setthe standard for the greater part of the twentiethcentury until the 1990s, when the development ofdigital radiography for dental use was commer-cialized by the Trophy company who released theRVGui system (Mouyen et al., 1989). Other com-panies such as Kodak, Gendex, Schick, Planmeca,Sirona, and Dexis were also early pioneers of digi-tal radiography.

The adoption of digital radiography by thedental profession has been slow but steadyand seems to have been governed, at leastpartly, by the “diffusion of innovation” theoryespoused by Dr. Everett Rogers (Rogers, 2003).His work describes how various technologicalimprovements have been adopted by the end

Clinical Applications of Digital Dental Technology, First Edition. Edited by Radi Masri and Carl F. Driscoll.© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.

users of technology throughout the secondhalf of the twentieth century and the earlytwenty-first century. Two of the most impor-tant tenets of adoption of technology arethe concepts of threshold and critical mass.

Threshold is a trait of a group and refers tothe number of individuals in a group who mustbe using a technology or engaging in an activitybefore an interested individual will adopt thetechnology or engage in the activity. Critical massis another characteristic of a group and occurs atthe point in time when enough individuals in thegroup have adopted an innovation to allow forself-sustaining future growth of adoption of theinnovation. As more innovators adopt a technol-ogy such as digital radiography, the perceivedbenefit of the technology becomes greater andgreater to ever-increasing numbers of other futureadopters until eventually the technology becomescommonplace.

Digital radiography is the most commonadvanced dental technology that patients expe-rience during diagnostic visits. According toone leading manufacturer in dental radiography,digital radiography is used by 60% of the dentistsin the United States (Tokhi, J., 2013, personalcommunication). If you are still using film, the

2 Clinical Applications of Digital Dental Technology

question should not be “Should I switch to a digitalradiography system?”, but instead “Which digitalsystem will most easily integrate into my office?”

This leads to another question, what advantagesdoes digital radiography offer the dental profes-sion as compared to simply continuing with theuse of conventional film? What are the reasons thatincreasing numbers of dentists are choosing digitalradiographic systems over conventional film sys-tems? Let us look at them.

Digital versus conventional filmradiography

The most common speed class, or sensitivity,of intraoral film has been, and continues to be,D-speed film; the prime example of this film inthe US market is Kodak’s Ultra-Speed (NCRP,2012). The amount of radiation dose requiredto generate a diagnostic image using this filmis approximately twice the amount requiredfor Kodak’s Insight, an F-speed film. In otherwords, F-speed film is twice as fast as D-speedfilm. According to Moyal, who used a randomlyselected survey of 340 dental facilities from 40states found in the 1999 NEXT data, the skinentrance dose of a typical D-speed posteriorbitewing is approximately 1.7 mGy (Moyal, 2007).Furthermore, according to the National Council onRadiation Protection and Measurements (NCRP)Report #172, the median skin entrance dose fora D-speed film is approximately 2.2 mGy whilethe typical E-F-speed film dose is approximately1.3 mGy and the median skin entrance dose fromdigital systems is approximately 0.8 mGy (NCRP,2012). According to NCRP Report #145 and others,it appears that dentists who are using F-speedfilm tend to overexpose the film and then underdevelop it; this explains why the radiation dosesavings with F-speed film is not as great as it couldbe because F-speed film is twice as fast as D-speedfilm (NCRP, 2004; NCRP, 2012). If F-speed filmwere used per the manufacturers’ instructions,the exposure time and/or milliamperage (totalmAs) would be half that of D-speed film and theradiation dose would then be half.

Why has there been so much resistance for den-tists to move away from D-speed film and embracedigital radiography? First of all, operating a dental

office is much like running a fine-tuned produc-tion or manufacturing facility; dentists spendyears perfecting all the systems needed in a dentaloffice, including the radiography system. Chang-ing the type of imaging system risks upsettingthe dentist’s capability to generate comprehensivediagnoses; therefore, in order to persuade individ-ual dentists to change, there has to be compellingreasons, and, until recently, most of the dentistsin the United States have not been persuaded tomake the change to digital radiography. It hastaken many years to reach the threshold and thecritical mass for the dental profession to makethe switch to digital radiography. Moreover, in alllikelihood, there are dentists today who will retirefrom active practice before they switch from film todigital.

There are many reasons to adopt digitalradiography: decreased environmental burdensby eliminating developer and fixer chemicalsalong with silver and iodide bromide chemicals;improved accuracy in image processing; decreasedtime required to capture and view images, whichincreases the efficiency of patient treatment;reduced radiation dose to the patient; improvedability to involve the patient in the diagnosis andtreatment planning process with co-diagnosisand patient education; and viewing software todynamically enhance the image (Wenzel, 2006;Wenzel and Møystad, 2010; Farman et al., 2008).However, if dentists are to enjoy these benefits, theradiographic diagnoses for digital systems mustbe at least as reliably accurate as those obtainedwith film (Wenzel, 2006).

Two primary cofactors seem to be moreimportant than others in driving more dentistsaway from D-speed and toward digital radiogra-phy – the increased use of computers in the dentaloffice and the reduced radiation doses seen indigital radiography. We will explore these factorsfurther in the next section.

Increased use of computers inthe dental office

This book’s focus is digital dentistry and latersections will deal with how computers interfacewith every facet of dentistry. The earliest uses ofthe computer in dentistry were in the business

Digital Imaging 3

office and accounting. Over the ensuing years,computer use spread to full-service practice man-agement systems with digital electronic patientcharts including digital image managementsystems. The use of computers in the businessoperations side of the dental practice alloweddentists to gain experience and confidence in howcomputers could increase efficiency and reliabilityin the financial side of their practices. The nextstep was to allow computers into the clinical arenaand use them in patient care. As a component ofcreating the virtual dental patient, initially, thetwo most prominent roles were electronic patientrecords and digital radiography. In the followingsections, we will explore the attributes of digitalradiography including decreased radiation dosesas compared to film; improved operator workflowand efficiency; fewer errors with fewer retakes;wider dynamic range; increased opportunity forco-diagnosis and patient education; improvedimage storage and retrievability; and communi-cation with other providers (Farman et al., 2008;Wenzel and Møystad, 2010).

Review of basic terminology

Throughout this section, we will be using severalterms that may be new to you, especially if youhave been using conventional film; therefore, wewill include the following discussion of some basicoral radiology terms, both conventional and dig-ital. Conventional intraoral film technology, suchas periapical and bitewing imaging, uses a directexposure technique whereby the X-ray photonsdirectly stimulate the silver bromide crystals tocreate the latent image. Today’s direct digital X-raysensor refers most commonly to a complementarymetal oxide semiconductor (CMOS) sensor that isdirectly connected to the computer via a USB port.At the time of the exposure, X-ray photons aredetected by cesium iodide or perhaps gadoliniumoxide scintillators within the sensor, which thenemit light photons; these light photons are thendetected within the sensor pixel by pixel, whichallows for almost instantaneous image forma-tion on the computer display. Most cliniciansview this instantaneous image formation as themost advantageous characteristic of direct digitalimaging.

The other choice for digital radiography todayis an indirect digital technique known as photo-stimulable phosphor or PSP plates; these platesresemble conventional film in appearance andclinical handling. During exposure, the latentimage is captured within energetic phosphorelectrons; during processing, the energetic phos-phors are stimulated by a red laser light beam;the latent energy stored in the phosphor electronsis released as a green light, which is captured,processed, and finally digitally manipulated bythe computer’s graphic card into images relayedto the computer’s display. The “indirect” termrefers to the extra processing step of the platesas compared to the direct method when usingthe CMOS sensor. The most attractive aspectof PSP may be that the clinical handling of thephosphor plates is exactly like handling film; so,most offices find that the transition to PSP to bevery manageable and user-friendly.

Panoramic imaging commonly uses direct digi-tal techniques as well. The panoramic X-ray beamis collimated to a slit; therefore, the direct digitalsensor is several pixels wide and continually cap-tures the signal of the remnant X-ray beam as thepanoramic X-ray source/sensor assembly continu-ally moves around the patient’s head; the path ofthe source/sensor assembly is the same whetherthe receptor is an indirect film, PSP, or direct digitalsystem. Clinicians who are using intraoral directdigital receptors generally opt for a direct digitalpanoramic system to avoid the need to purchase aPSP processor for their panoramic system.

Orthodontists require a cephalometric systemand when moving from film to digital, again havetwo choices: direct digital and indirect digital. Thelarger flat panel digital receptor systems providethe instantaneous image but are slightly morecostly than the indirect PSP systems; however, thedirect digital systems obviate the need to purchaseand maintain PSP processors. The higher thevolume of patients in the office, the quicker isthe financial payback for the direct digital X-raymachine.

4 Clinical Applications of Digital Dental Technology

Image quality comparison between directand indirect digital radiography

Some dentists will make the decision of whichsystem to purchase based solely on the speed ofthe system, with the direct digital system beingthe fastest. There are other factors as well: dentistsoften ask about image quality. Perhaps the betterquestion to ask may be, “Is there a significantdifference between the diagnostic capability ofdirect and indirect digital radiography systems?”One of the primary diagnostic tasks facing dentistson a daily basis is caries diagnosis, and there areseveral studies that have evaluated the efficacyof the two systems at this common task. Theanswer is that there is no difference between thetwo systems in diagnostic efficacy – either directdigital or indirect digital with PSP plates willdiagnose caries equally well, in today’s modernsystems (Wenzel et al., 2007; Berkhout et al., 2007;Li et al., 2007).

One important consideration to consider whencomparing systems is to make sure that the imageshave the same bit depth. Bit depth refers to the num-bers of shades of gray used to generate the imageand are expressed exponentially in Table 1.1.

The early digital systems had a bit depth of8 with 256 shades of gray, which may seem finebecause the human eye can only detect approx-imately 20 to 30 shades of gray at any one timein any one image; however, most digital systemstoday generate images at 12 or even 16 bit depth,that is, images that have 4,096 to 65,536 shades ofgray (Russ, 2007). Proper image processing is askill that must be learned in order to fully utilizeall of the information contained in today’s digitalimages. Conventional film systems do not havediscrete shades of gray; rather, film systems areanalog and have an infinite number of possibleshades of gray depending only on the numbersof silver atoms activated in each cluster of silveratoms in the latent image within the silver halidelattice of the film emulsion. Therefore, whencomparing systems, ensure that the bit depthof the systems is comparable; and, rememberthat over time, the higher bit depth systems willrequire larger computer storage capacities due tothe larger file sizes associated with the increasedamount of digital information requirements ofthe larger bit depth images. It is expected that

Table 1.1 Bit depth table that gives the relation of theexponential increase in the number of shades of grayavailable in images as the bit depth increases.

Bit depth Expression Number of shades of gray

1 21 2

2 22 4

3 23 8

4 24 16

5 25 32

6 26 64

7 27 128

8 28 256

9 29 512

10 210 1024

11 211 2048

12 212 4096

13 213 8192

14 214 16384

15 215 32768

16 216 65536

in the future, most systems will use images of aminimum of 12 bit depth quality and many arealready using images of 16 bit depth quality.

Amount of radiation required to usedirect and indirect digital radiography

One other factor that dentists should considerwhen evaluating which system to use is howmuch radiation is required for each system togenerate a diagnostic image. In order to determinethe answer to this question, clinicians should befamiliar with the term dynamic range, which refersto the performance of a radiographic receptor sys-tem in relation to the amount of radiation requiredto produce a desired amount of optical densitywithin the image. The Hurter and Driffield (H&D)characteristic curve chart was initially developedfor use with film systems and can also be usedwith direct digital and indirect digital systems

Digital Imaging 5

(Bushong, 2008; Bushberg et al., 2012). The indirectdigital system with PSP plates has the widestdynamic range, even wider than film, whichmeans that PSP plates are more sensitive to lowerlevels of radiation than either conventional film ordirect digital CMOS detectors; and, at the upperrange of diagnostic exposures, the PSP platesdo not experience burnout as quickly as filmor direct digital until very high radiation dosesare delivered. This means that the PSP systemcan handle a wider range of radiation dose andstill deliver a diagnostic image, which may be agood feature, but for patient safety, this may be anegative feature because dentists may consistentlybe unaware that the operator of the equipmentis delivering higher radiation doses than are nec-essary simply because their radiographic systemhas not been calibrated properly (Bushong, 2008;Bushberg et al., 2012; Huda et al., 1997; Hildeboltet al., 2000).

Radiation safety of digital radiography

There are several principles of radiation safety:ALARA, justification, limitation, optimization,and the use of selection criteria. We will brieflyreview these and then discuss how digital radiog-raphy plays a vital role in the improved safety ofmodern radiography.

The acronym ALARA stands for As Low AsReasonably Achievable and, in reality, is verystraightforward. In the dental profession, dentalauxiliaries and dental professionals are requiredto use medically accepted radiation safety tech-niques that keep radiation doses low and thatdo not cause an undue burden on the operatoror clinician. An example from the NCRP Report#145 Section 3.1.4.1.4 states “Image receptors ofspeeds slower than ANSI Speed Group E shallnot be used for intraoral radiography. Fasterreceptors should be evaluated and adopted iffound acceptable” (NCRP, 2004). This meansthat offices do not have to switch to digital butrather could switch to E- or F-speed film butmust switch to at least E-speed film in order tobe in compliance with this report. This is butone example of practicing ALARA. In the UnitedStates, federal and nationally recognized agenciessuch as the Food and Drug Administration (FDA)

and the NCRP issue guidelines and best practicerecommendations; however, laws are enforcedon the state level, which results in a confusingpatchwork of various regulations, and dentistssometimes confuse what must be done with whatshould be done, especially because a colleague ina neighboring state must follow different laws.For example, although it is recommended by theNCRP but not legally required in many states,the state of Maryland now legally requires dentistto practice ALARA (Maryland, 2013), althoughthe neighboring state of Virginia does not specif-ically require this in their radiation protectionregulations(Commonwealth of Virginia, 2008).Therefore, in the state of Maryland, in order tosatisfy legal requirements, dentists will soon bereplacing D-speed film with either F-speed filmor digital systems. Internationally, groups suchas the International Commission on RadiologicalProtection (ICRP), the United Nations ScientificCommittee on the Effects of Atomic Radiation(UNSCEAR), and the Safety and Efficacy in DentalExposure to CT (SEDENTEXTCT) have providedwell-researched recommendations on the use ofimaging in dentistry and guidance on the infor-mation of the effects of ionizing radiation on thehuman body (ICRP, 1991; Valentin, 2007; Ludlowet al., 2008; UNSCEAR, 2001; Horner, 2009).

When a clinician goes through the process ofexamining a patient and formulating a diagnosticquestion, he or she is justifying the radiographicexamination. This principle of justification is oneof the primary principles of radiation safety. Withdigital radiography, our radiation doses are verylow: so low, in fact, that if we have a diagnosticquestion that can only be answered with theinformation obtained from a dental radiograph,the risk from the radiograph is low enough thatthe “risk to benefit analysis” is always in favorof exposing the radiograph. There will always beenough of a benefit to the patient to outweigh thevery small risk of the radiographic examination, aslong as there is significant diagnostic informationto be gained from the X-rays.

The principle of limitation means that the X-raymachine operator is doing everything possibleto limit the actual size of the X-ray beam: thatis, collimation of the X-ray beam. For intraoralradiography, rectangular collimation is recom-mended for routine use by the NCRP and there are

6 Clinical Applications of Digital Dental Technology

various methods available to achieve collimationof the beam. Rectangular collimation reduces theradiation dose to the patient by approximately60%. In panoramic imaging, the X-ray beam iscollimated to a slit-shape. Moreover, in cone-beamCT, the X-ray beam has a cone shape.

In late 2012, the FDA and ADA issued thelatest recommendations for selection criteria of thedental patient. These guidelines give the dentistseveral common scenarios that are seen in practiceand offer suggestions on which radiographs maybe appropriate. This article provides an excellentreview of the topic and is best summarized by asentence found in its conclusion: “Radiographsshould be taken only when there is an expectationthat the diagnostic yield will affect patient care”(ADA & FDA, 2012).

How does digital radiography assist withmanaging radiation safety? As mentioned earlier,digital receptors require less radiation dose thanfilm receptors. In the 2012 NCRP Report #172,section 6.4.1.3, it is recommended that US dentistsadopt a diagnostic reference level (DRL) forintraoral radiographs of 1.2 mGy. This dose is themedian dose for E- and F-speed film systems,and it is higher than the dose for digital systems.This means that in order to predictably achievethis ambitious goal, US dentists who are stillusing D-speed film will need to either switchto F-speed film or transition to a digital system(NCRP, 2012).

Radiation dosimetry

The dental profession owns more X-ray machinesthan any other profession; and, we expose a lotof radiographs. Our doses are very small, buttoday our patients expect us to be able to educatethem and answer their questions about the safetyof the radiographs that we are recommendingand it is part of our professional responsibilityto our patients. Let’s review some vocabularyfirst. The International System uses the Gray(Gy) or milliGray (mGy), and microGray (μGy)to describe the amount of radiation dose thatis absorbed by the patient’s skin (skin entrancedose) or by their internal organs. This dose ismeasured by devices such as ionization chambersor optically stimulated dosimeters (OSLs). There

are different types of tissues in our body andthey all have a different response or sensitivity toradiation; for instance, the child’s thyroid glandseems to be the most sensitive tissue that is inthe path of our X-ray beams while the maturemandibular nerve may be the least sensitive tissuetype in the maxillofacial region (Hall and Giaccia,2012). Of course, we only deal with diagnosticradiation, but there are other types of radiationsuch as gamma rays, alpha particles, and betaparticles; in order to provide a way to measurethe effect on the body’s various tissues whenexposed by radiation from the various sources,a term known as equivalent dose is used. Thisterm is expressed in Sieverts (S) or milliSieverts(mSv), and microSieverts (μSv). Finally, anotherterm known as effective dose is used to comparethe risk of radiographic examinations. This is themost important term for dental professionals tobe familiar with as this is the term that accountsfor the type of radiation used (diagnostic in ourcase) and the type of tissues exposed by the X-raybeam in the examination, whether it is a bitewing,a panoramic, a cone beam CT or a chest X-ray, andso on. Using this term is like comparing appleswith apples. By using this term, we can comparethe risk of a panoramic radiograph with the riskof an abdominal CT or a head CT and so on.

When patients ask us about how safe a partic-ular radiographic examination may be, they arereally asking whether that X-ray is going to causea fatal cancer. Moreover, when medical physicistsestimate the risk of X-rays in describing effectivedose as measured in Sieverts and microSievertsfor dentistry, they are talking about the risk ofdeveloping a fatal cancer. The risk is usually givenas the rate of excess cancers per million. In orderto accurately judge this number, the clinicianneeds to know the background rate of cancer (andfatal cancer) in the population. According to theAmerican Cancer Society, the average person,male or female, in the population of the UnitedStates has a 40% chance of developing cancerduring his or her lifetime; furthermore, the rate offatality of that group is 50%; therefore, the overallfatal cancer rate in the United States is 20%, or200,000 per million people (Siegel et al., 2014).Now, when you read in the radiation dosimetry

Digital Imaging 7

table (Table 1.2) that if a million people had apanoramic exposure and the excess cancer rate inthose one million people was 0.9 per million, youwill know that the total cancer rate changed from200,000 per million to 200,000.9 per million. Ona percentage basis, that is very small indeed – a0.00045% risk of developing cancer. Of course,these are population-based numbers and are thebest estimates groups like the NCRP can comeup with, and you should also know that a verygenerous safety factor is built in. At the verylow doses of ionizing radiation seen in mostdental radiographic examinations experts such asmedical physicists and molecular biologists do notknow the exact mechanisms of how the humancell responds to radiation. So, to be safe and err onthe side of caution, which is the prudent course ofaction, we all assume that some cellular and somegenetic damage is possible due to a dose–responsemodel known as the linear no-threshold model ofradiation interaction, which is based on theassumption that in the low dose range of radiationexposures, any radiation dose will increase therisk of excess cancer and/or heritable disease in asimple proportionate manner (Hall and Giaccia,2012).

There is one more column in Table 1.2 that needssome explanation – background equivalency. Welive in a veritable sea of ionizing radiation, andthe average person in the United States receivesapproximately8 μSv of effective dose of ionizingradiation per day (NCRP, 2009). Take a look at thefirst examination – panoramic exposure; it hasan effective dose of approximately16 μSv; if youdivide 16 μSv by 8 μSv per day, the result is 2 daysof background equivalency. Using this method,you now know that the amount of effective dosein the average panoramic examination equals thesame amount of radiation that the average personreceives over the course of 2 days. This sameexercise has been completed for the examinationslisted in the table; and, for examinations not listed,you can calculate the background equivalency byfollowing the aforementioned simple calculations.The intended use of effective dose is to comparepopulation risks; however, this use as describedearlier is a quick and easy patient education toolthat most of our patients can quickly understand.

Uses of 2D systems in daily practice

The use of standard intraoral and extraoral imag-ing for clinical dentistry have been available formany years and include caries and periodontaldiagnosis, endodontic diagnosis, detection, andevaluation of oral and maxillofacial pathologyand evaluation of craniofacial developmentaldisorders.

Caries diagnosis

The truth is that diagnosing early carious lesionswith bitewing radiographs is much more difficultthan it appears to be than at first impression.Most researchers have found that a predictablyaccurate caries diagnosis rate of 60% would bevery acceptable in most studies. In a 2002 study,Mileman and van den Hout compared the abilityof Dutch dental students and practicing generaldentists to diagnose dentinal caries on radio-graphs. The students performed almost as wellas the experienced dentists (Mileman and VanDen Hout, 2002; Bader et al., 2001; Bader et al.,2002; Dove, 2001). We will explore caries diagnosisand how modern methods of caries diagnosis arechanging the paradigm from the past ways ofdiagnosing caries (Price, 2013).

Caries detection is a basic task that all dentistsare taught in dental school. In principle, it is verysimple – detect mineral loss in teeth visually,radiographically, or by some other adjunctivemethod. There can be many issues that affectthis task, including training, experience, andsubjectivity of the observer; operating conditionsand reliability of the diagnostic equipment; thesefactors and others can all act in concert andoften, the end result is that this “simple” taskbecomes complex. It is important to realize thatthe diagnosis of a carious lesion is only one aspectof the entire management phase for dental caries.In fact, there are many aspects of managing thecaries process besides diagnosis. The lesion needsto be assessed as to whether the caries is limitedto enamel or if it has progressed to dentin. Adetermination of whether the lesion progressedto a cavity needs to be made because a cavitatedlesion will continue to trap plaque and will needto be restored. The activity level of the lesion

8 Clinical Applications of Digital Dental Technology

Table 1.2 Risks from various dental radiographic examinations.

Effective Doses from Dental and Maxillofacial X-Ray Techniques and Probability of Excess Fatal Cancer Risk PerMillion Examinations

Technique DoseMicrosieverts

CA Risk PerMillion Examinations

BackgroundEquivalency

Panoramic–indirect digital 16 0.9 2 days

Skull/Cephalometrics–indirect digital 5 0.3 17 hours

FMX (PSP or F-speed film-rectangular collimation) 35 2 4.3 days

FMX (PSP or F-speed film-round collimation) 171 9 21 days

FMX (D-speed film-round collimation) 388 21 47 days

Single PA or Bitewing (PSP or F-speed film-rect.collimation)

1.25 0.1 3.6 hours

Single PA or Bitewing (PSP or F-speed film-roundcollimation)

9.5 0.5 1 day

Single PA or Bitewing ( D-speed film-round collimation) 22 1.2 2.6 days

4 Bitewings (PSP or F-speed film-rectangularcollimation)

5 0.3 17 hours

4 Bitewings (PSP or F-speed film-round collimation) 38 2 4 days

4 Bitewings (D-speed film-rectangular collimation) 88 5.5 11 days

Conventional Tomogram (8 cm×8 cm field of view) 10 0.5 1 day

Cone Beam CT examination (Carestream 930010× 10 cm Full Jaw)

79 5 10 days

Cone Beam CT examination (Carestream 9300 5× 5 cm,post mand)

46 3 6 days

Cone Beam CT examination (Sirona Galileos) 70 4 8 days

Maxillo-mandibular MDCT 2100 153 256 days

Permission granted by Dr. John Ludlow.

needs to be determined; a single evaluation willonly tell the clinician the condition of the toothat that single point in time; not whether the dem-ineralization is increasing or, perhaps whetherit is decreasing; larger lesions will not require adetailed evaluation of activity, but smaller lesionswill need this level of examination and follow-up.Finally, the therapeutic or operative managementoptions for the lesion need to be considered basedon these previous findings.

One thing to keep in mind is that most of thepast research on caries detection has focused onocclusal and smooth surface caries. There are tworeasons for this – first of all, from a populationstandpoint, more new carious lesions are occlusal

lesions today than in the past (NIH, 2001; Zan-doná et al., 2012; Marthaler, 2004; Pitts, 2009) and,secondly, many studies rely on screening exami-nations without intraoral radiographic capability(Bader et al., 2001; Zero, 1999). Let look at thetraditional classification system that US dentistshave used in the past and a system that is beingtaught in many schools today.

Caries classifications

The standard American Dental Association(ADA) caries classification system designateddental caries as initial, moderate, and severe

Digital Imaging 9

Table 1.3 ADA caries classification system.

ADA Caries Classification System

No caries – Sound tooth surface with no lesion

Initial enamel caries – Visible non cavitated or cavi-tated lesion limited to enamel

Moderate dentin caries – Enamel breakdown or loss ofroot cementum with non-cavitated dentin

Severe dentin caries – Extensive cavitation of enameland dentin

(Table 1.3); this was commonly modified withthe term “incipient” to mean demineralizedenamel lesions that were reversible (Zero, 1999;Fisher and Glick, 2012). There have been manyattempts over the years to develop one universalcaries classification system that clinical dentistsas well as research dentists can use not only inthe United States, but also internationally. As theresult of the International Consensus Workshopon Caries Clinical Trials (ICW-CCT) held in 2002,the work on the International Caries Detectionand Assessment System (ICDAS) was begun inearnest, and today it has emerged as the leadinginternational system for caries diagnosis (Ismailet al., 2007; ICDAS, 2014). The ICDAS for cariesdiagnosis offers a six-stage, visual-based systemfor detection and assessment of coronal caries. Ithas been thoroughly tested and has been found tobe both clinically reliable and predictable. Perhapsits’ greatest strengths are that it is evidence based,combining features from several previously exist-ing systems and does not rely on surface cavitationbefore caries can be diagnosed (Figures 1.1 and1.2). Many previous systems relied on conflictinglevels of disease activity before a diagnosis ofcaries; but, with the ICDAS, leading cariologistshave been able to standardize definitions andlevels of the disease process. The ICDAS appearsto be the new and evolving standard for cariesdiagnosis internationally and in the UnitedStates.

Ethics of caries diagnosis

One of the five principles of the American DentalAssociation’s Code of Ethics is nonmaleficence,

Detection system: Each of the7 scores are illustrated with anexample

1W

2W

1B

1W2B

Sound Opacity

White,brown

Opacitywith air-drying:

White,brown

without air-drying:

Surfaceintegrity

loss

Underlyinggrey

shadow

Distinctcavity

Extensivecavity

Score0

Scores1

Scores2

Score3

Score4

Score5

Score6

Sound

Ekstrand et al., (1997) modified by ICDAS (Ann Arbor), 2002 and again in 2004 (Baltimore)

Figure 1.1 ICDAS caries classification. (Printed with permis-sion of professor Kim Ekstrand.).

ICDAS ‘0’ & ‘1’

ICDAS ‘3’ or ‘4’

ICDAS ‘6’ ICDAS ‘5’ ICDAS ‘2’

Figure 1.2 A radiographic application of the ICDAS classifi-cation for interproximal caries compiled by the author.

which states that dentists should “do no harm”to his or her patients (ADA, 2012). By enhancingtheir caries detection skills, dental practitionerscan detect areas of demineralization and caries atthe earliest possible stages; these teeth can then bemanaged with fluorides and other conservativetherapies (Bravo et al., 1997; Marinho et al., 2003;Petersson et al., 2005). This scenario for managingteeth with early caries will hopefully make someinroads into the decades old practice of restoringsmall demineralized areas because they are goingto need fillings anyway and you might as wellfill them now instead of waiting until they getbigger (Baelum et al., 2006). Continuing to stress

10 Clinical Applications of Digital Dental Technology

the preventive approach to managing early cariesbegins with early diagnosis, and what better wayto “do no harm” to our patients than to avoidplacing restorations in these teeth with earlydemineralized enamel lesions and remineralizethem instead?

Computer-aided diagnosis of radiographs

The use of computer-aided diagnosis (CAD) ofdisease is well established in medical radiology,having been utilized since the 1980s at the Uni-versity of Chicago and other medical centers forassistance with the diagnosis of lung nodules,breast cancer, osteoporosis, and other complexradiographic tasks (Doi, 2007). A major distinc-tion has been made in the medical communitybetween automated computer diagnosis andcomputer-aided diagnosis. The main differenceis that in automated computer diagnosis, thecomputer does the evaluation of the diagnosticmaterial, that is, radiographs, and reaches thefinal diagnosis with no human input, while incomputer-aided diagnosis, both a medical prac-titioner and a computer evaluate the radiographand reach a diagnosis separately. Computer-aideddiagnosis is the logic behind the Logicon CariesDetector (LCD) software marketed by CarestreamDental LLC, Atlanta, GA (Gakenheimer, 2002).

The Logicon system has been commerciallyavailable since 1998 and has seen numerousupdates since that time. The Logicon softwarecontains within its database teeth with matchingclinical images, radiographs, and histologicallyknown patterns of caries; as a tooth is radio-graphed and an interproximal region of interest isselected for evaluation, this database is accessedfor comparison purposes. The software will then,in graphic format, give the dentist a tooth densitychart and the odds ratio that the area in questionis a sound tooth or simply decalcified or franklycarious and requires a restoration. In addition,the dentist can adjust the level of false positives,or specificity, that he or she is willing to accept(Gakenheimer, 2002; Tracy et al., 2011; Gaken-heimer et al., 2005). The author used the Logiconsystem as part of his Trophy intraoral digital radi-ology installation in a solo general practice from2003 to 2005 and found the Logicon system to be

very helpful, particularly in view of its intendeduse as a computer-aided diagnosis device, whichis also known as computerized “second opinion.”

In a 2011 study, Tracy et al. describe the use ofLogicon whereby 12 blinded dentists reviewed17 radiographs from an experienced practitionerwho meticulously documented the results that heobtained from the use of Logicon. Over a periodof 3 years, he followed and treated a group ofpatients in his practice and photographed theteeth that required operative intervention fordocumentation purposes. In addition, he docu-mented those teeth that did not have evidence ofcaries or had evidence of caries only in enamelthat did not require operative treatment. Thestudy included a total of 28 restored surfaces and48 nonrestored surfaces in the 17 radiographs.His radiographic and clinical results were thencompared to the radiographic diagnoses of the 12blinded dentists on these 17 radiographs. The truepositive, or actual diagnosis of caries when cariesis present, is where the Logicon system proved tobe of benefit. With routine bitewing radiographsand unadjusted images, the dentists diagnosed30% of the caries; with sharpened images, only39% of the caries. When using Logicon, the cariesdiagnosis increased to 69%, a significant increasein the ability to diagnose carious lesions. Theother side of the diagnostic coin is specificity,or ability to accurately diagnose a sound tooth;both routine bitewing and Logicon images wereequally accurate, diagnosing at a 97% and a 94%rate (Tracy et al., 2011). These results offer evidencethat by using the Logicon system, dentists are ableto confidently double the numbers of carious teeththat they are diagnosing without affecting theirability to accurately diagnose a tooth as being freefrom decay. The Logicon system appears to be avery worthwhile technological advancement incaries detection.

Non radiographic methods of cariesdiagnosis

Quantitative light-induced fluorescence

It has been shown that tooth enamel has a naturalfluorescence. By using a CCD-based intraoralcamera with specially developed software for

Digital Imaging 11

image capture and storage (QLFPatient, InspektorResearch Systems BV, Amsterdam, The Nether-lands), quantitative light-induced fluorescence(QLF) technology measures (quantifies) the refrac-tive differences between healthy enamel anddemineralized, porous enamel with areas of cariesand demineralization showing less fluorescence.With the use of a fluorescent dye which can beapplied to dentin, the QLF system can also be usedto detect dentinal lesions in addition to enamellesions. A major advantage of the QLF system isthat these changes in tooth mineralization levelscan be tracked over time using the documentedmeasurements of fluorescence and the imagesfrom the camera. In addition, the QLF system hasshown to have reliably accurate results betweenexaminers over time as well as all around goodability to detect carious lesions when they arepresent and not mistakenly diagnose caries whenthey are not present (Angmar-Månsson and TenBosch, 2001; Pretty and Maupome, 2004; Amaechiand Higham, 2002; Pretty, 2006).

Laser fluorescence

The DIAGNOdent uses the property of laserfluorescence for caries detection. Laser fluores-cence detection techniques rely on the differentialrefraction of light as it passes through soundtooth structure versus carious tooth structure. Asdescribed by Lussi et al. in 2004, a 650 nm lightbeam, which is in the red spectrum of visiblelight, is introduced onto the region of intereston the tooth via a tip containing a laser diode.As part of the same tip, there is an optical fiberthat collects reflected light and transmits it to aphoto diode with a filter to remove the higherfrequency light wavelengths, leaving only thelower frequency fluorescent light that was emittedby the reaction with the suspected carious lesion.This light is then measured or quantified, hencethe name “quantified laser fluorescence.” Onepotential drawback with the DIAGNOdent isthe increased incidence of false-positive readingsin the presence of stained fissures, plaque andcalculus, prophy paste, existing pit and fissuresealants, and existing restorative materials. Areview of caries detection technologies publishedin the Journal of Dentistry in 2006 by Pretty that

compared the DIAGNOdent technology withother caries detection technologies such as ECM,FOTI, and QLF showed that the DIAGNOdenttechnology had an extremely high specificity orability to detect caries (Lussi et al., 2004; Tranaeuset al., 2005; Côrtes et al., 2003; Lussi et al., 1999;Pretty, 2006).

Electrical conductance

The basic concept behind electrical conductancetechnology is that there is a differential conduc-tivity between sound and demineralized toothenamel due to changes in porosity; saliva soaksinto the pores of the demineralized enamel andincreases the electrical conductivity of the tooth.

There has been a long-standing interest inusing electrical conductance for caries detection;original work on this concept was published asearly as 1956 by Mumford. One of the first moderndevices was the electronic caries monitor (ECM),which was a fixed-frequency device used in the1990s. The clinical success of the ECM was mixedas evidenced by the lack of reliable diagnosticpredictability (Amaechi, 2009; Mumford, 1956;Tranaeus et al., 2005).

Alternating current impedancespectroscopy

The CarieScan device uses multiple electricalfrequencies (alternating current impedance spec-troscopy) to detect and diagnose occlusal andsmooth surface caries. By using compressed air tokeep the tooth saliva free, one specific area on atooth can be isolated from the remaining areas andone small region of interest can be examined. If anentire surface needs to be evaluated, an electrolytesolution is introduced and the tip of the probe isplaced over the larger area to allow for examina-tion of the entire surface. The diagnostic reliabilityof this device is more accurate and reliable thanthe ECM, and, according to the literature, stainsand discolorations do not interfere with the properuse of the device. It appears to have good potentialas a caries detection technology (Tranaeus et al.,2005; Amaechi, 2009; Pitts et al., 2007; Pitts, 2010).

12 Clinical Applications of Digital Dental Technology

Frequency-domain laser-induced infraredphotothermal radiometry and modulatedluminescence (PTR/LUM)

This technology has recently been approved bythe FDA and is known as the Canary system(Quantum Dental Technologies, Inc., Toronto,CA). It relies on the absorption of infrared laserlight by the tooth with measurement of the sub-sequent temperature change, which is in the 1 ∘Crange. This optical to thermal energy conversionis able to transmit highly accurate informationregarding tooth densities at greater depths thanvisual only techniques. Early laboratory testingshows better sensitivity for caries detection forthis technology than for radiography, visual, orDIAGNOdent technology; laboratory testing ofan early OCT commercial model meant for thedental office has been accomplished; and clinicaltrials were successfully completed before the FDAapproval (FDA, 2012; Amaechi, 2009; Jeon et al.,2007; Jeon et al., 2010; Sivagurunathan et al., 2010;Matvienko et al., 2011; Abrams et al., 2011; Kimet al., 2012).

Cone beam computed tomography

Dental cone beam computed tomography (CBCT)is arguably the most exciting advancement in oralradiology since panoramic radiology in the 1950sand 1960s and perhaps since Roentgen’s discoveryof X-rays in 1895 (Mozzo et al., 1998). The conceptof using a cone-shaped X-ray beam to generatethree-dimensional (3D) images has been success-fully used in vascular imaging since the 1980s(Bushberg et al., 2012) and, after many iterations,is now used in dentistry. Many textbooks offerin-depth explanations of the technical features ofcone beam CT (White and Pharoah, 2014; Miles,2012; Sarment, 2014; Brown, 2013; Zoller andNeugebauer, 2008), so, we will offer a summaryusing a full maxillofacial field of view CBCT asan example. While the X-ray source is rotatingaround the patient, most manufacturers todaydesign the electrical circuit to pulse the sourceon and off approximately 15 times per second;the best analogy to use is that the computer isreceiving a low-dose X-ray movie at a qualityof about 15 frames per second. At the end of

the image acquisition phase for most systems,the reconstruction computer then has about 200basis or projection images. These images are thenprocessed using any one of several algorithms.The original, classic algorithm is the back projectionreconstruction algorithm that was a key elementof the work of Sir Godfrey Hounsfield and AllanMcCormack who shared the Nobel Peace Prize inMedicine in 1979 (Bushberg et al., 2012). Today,many other algorithms such as the Feldkampalgorithm, the cone beam algorithm, and the iter-ative algorithm are used in various forms as wellas metal artifact reduction algorithms. In addition,manufacturers have their own proprietary algo-rithms that are applied to the CBCT volumes aswell. The end result of the processing is not only3D volumes, but also multi-planar reconstructed(MPR) images that can be evaluated in the threefollowing standard planes of axial, coronal, andsagittal images (Figure 1.3). In addition, it is agenerally accepted standard procedure to recon-struct a panoramic curve within the dental archesthat is similar to a 2D panoramic image except forthe lack of superimposed structures (Figure 1.4).In addition, any structure can be evaluated fromany desired 360 degree angle. The strength ofCBCT is the ability to view any mineralizedanatomic structure within the field of view, fromany angle. These images have zero magnification,and unless there are patient motion artifacts orpatients have a plethora of dental restorations,these anatomic structure can be visualized withoutdistortions.

Limitations of CBCT

The most significant limitation of CBCT is theincreased radiation dose to the patient whencompared to panoramic imaging. It is the duty ofthe ordering clinician to remain knowledgeableregarding the radiation doses of the CBCT exam-inations he or she orders for his or her patients.Earlier in this chapter, we referred to the risk tobenefit analysis; this concept should be applied toCBCT decision making as well when the clinicianis considering ordering a CBCT for the patient. Thedentist should consider the following questions:(i) What is the diagnostic question? (ii) Is it likelythat the information gained from the CBCT yield