(Periodontology 2000)

The use of cone beam computed tomography (CBCT) in implant dentistry: current concepts, indications and limitations for clinical practice and research

Michael M. Bornstein1,2, Keith Horner3, Reinhilde Jacobs2

1Department of Oral Surgery and Stomatology, Section of Dental Radiology and Stomatology,

School of Dental Medicine, University of Bern, Bern, Switzerland2OMFS IMPATH Research Group, Department of Imaging and Pathology, Faculty of Medicine,

University of Leuven and Department of Oral and Maxillofacial Surgery, University Hospitals

Leuven, Leuven, Belgium 3University Dental Hospital of Manchester, School of Dentistry, Oral and Maxillofacial Imaging,

Higher Cambridge Street, Manchester M15 6FH, United Kingdom

Correspondence to:

Prof. Dr. Michael M. Bornstein

Department of Oral Surgery and Stomatology

Section of Dental Radiology and Stomatology

Freiburgstrasse 7, CH-3010 Bern, Switzerland

Phone: +41 31 632 25 45/66, Fax: +41 31 632 09 14

e-mail: michael.bornstein@zmk.unibe.ch

Abstract

Diagnostic radiology is an essential component of treatment planning in the field of

implant dentistry. The present narrative review will present current concepts for the use

of cone beam computed tomography (CBCT) imaging prior to and following implant

placement in daily clinical practice and research. Guidelines for the selection of 3D

imaging will be discussed, and also limitations highlighted. Current concepts of radiation

dose optimisation including novel imaging modalities using low dose protocols will be

presented. For pre-operative cross-sectional imaging, data are still not available that

CBCT results in less intraoperative complications such as nerve damage or bleeding

incidents, or that implants inserted using pre-operative CBCT data sets for planning

purposes will exhibit higher survival or success rates. The use of CBCT following the

insertion of dental implants should be restricted to specific post-operative complications

such as damage of neuro-vascular structures or post-operative infections in relation to

the maxillary sinus. Regarding peri-implantitis, the diagnosis and severity of the disease

should be evaluated primarily based on clinical parameters and radiological findings

based on periapical radiographs (2D). The use of CBCT scans in clinical research might

not yield any evident beneficial effect for the patient included. As many of the CBCT

scans performed for research have no direct therapeutical consequence, dose

optimisation measures should be implemented by using appropriate exposure

parameters and reducing the field of view (FOV) to the actual region of interest.

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Introduction

Since its initial description in 1998 by Mozzo and co-workers (99), three-dimensional

(3D) radiographic imaging using cone beam computed tomography (CBCT) has become

an established diagnostic technique in dental medicine for various indications in the

fields of orthodontics (80, 87, 116), endodontics including apical surgery (109, 129, 153),

periodontology (154), oral and maxillofacial surgery (3), and implant dentistry (17).

CBCT imaging appears to offer the potential of an improved diagnostic value for a wide

range of clinical applications, and usually at lower doses than with multislice computed

tomography (CT). However, apart from applications in implant dentistry, CT has few

uses in dentistry, and CBCT results in increased radiation doses compared with

conventional (two-dimensional / 2D) dental radiographic techniques. Although CBCT

imaging still continues to gain popularity, its use currently is primarily recommended in

cases in which clinical examination supplemented with conventional 2D intra- and extra-

oral radiography cannot supply satisfactory diagnostic information. Thus, CBCT

scanning has to be considered basically as an adjunctive diagnostic radiographic

modality (40, 41).

In 2009, the European Academy of Dental and Maxillofacial Radiology (EADMFR)

published basic principles on the use of CBCT imaging (Table 1; 69). The set of 20

principles was formulated to act as core standards for EADMFR, and to be adopted and

to be of value in national standard-setting procedures within Europe. The first eight

statements relate principally to justification of CBCT examinations, while the first four of

these implicitly condemn routine 3D examinations. Statements nine to fifteen deal

broadly with optimisation and dose limitation. The final statements (sixteen to twenty)

discuss training and competence issues as in some countries of the European Union,

CBCT equipment can be purchased, installed and used by a dentist with no specific

requirement for additional training. The EADMFR maintains the view that, with adequate

training, it is reasonable to expect dentists to perform evaluation of images in the familiar

area of teeth and their supporting structures, while advocating a specialist evaluation for

other anatomical areas. This vision is also maintained in the 2012 European evidence-

based guidelines on the use of CBCT for dental and maxillofacial radiology (44).

The present review will present current concepts for the use of CBCT imaging

prior to and following implant placement in daily practice and research. Guidelines for

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the selection of 3D imaging will be discussed, and also limitations highlighted. Current

concepts of radiation dose optimisation including novel imaging modalities using low

dose protocols will be presented. Finally, new imaging technologies under investigation

will be reviewed, and evaluated for their potential as future options for imaging in oral

implantology.

Aspects of radiation exposure when using CBCT in implant dentistry

Patient risk from radiation is a continuing concern, due to the high frequency of dental

radiographic examinations in developed countries (145). In the context of dental CBCT,

where higher radiation doses are usually seen than for conventional (2D) radiography, it

is important to consider the risks that are associated with exposure to X-radiation. These

risks are stochastic in nature; specifically cancer induction. “Stochastic” means that

there is a statistical probability (risk) of an adverse event occurring as a result of the X-

ray exposure. The risk is proportional to the dose, but it is generally accepted that there

is no “safe” dose of radiation. The risk is age-related, with children having higher risks

than adults for the same radiation dose, a fact that has particular dental relevance. It is

reassuring therefore, that in implant dentistry, the age of patients tends to be

concentrated in older adults (14, 44) and the risk is lower. Nonetheless, in the absence

of a „safe“ dose of X-rays, attention to radiation protection of patients cannot be

neglected. Pauwels et al. (111) reported that the lifetime attributable cancer risk for

CBCT, expressed as the probability to develop a radiation-induced cancer, varied

between 2.7 per million (age > 60) and 9.8 per million (for patients ranging between 8 to

11 years) with an average of 6.0 per million. On average, the risk for female patients

was 40% higher. Overall, the estimated radiation risk was primarily influenced by the

age at exposure and the gender, pointing out the continuing need for radiation

protection, particularly in younger age groups.

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Principles of radiation protection

To reduce levels of radiation-associated risk, it is essential to adhere to radiation

protection principles. These are: justification, optimisation and limitation of doses (73).

Only the first two of these apply to patients because there can be no dose limits in this

context. For staff working with radiation and the wider public (excluding patients), dose

limitation is the paramount principle of radiation protection, although optimisation of

patient dose will sometimes translate into lower doses to the clinical staff performing the

procedure.

Under normal circumstances, the risk from dental radiography is very low.

Nonetheless, it is essential that every radiographic examination should show a net

benefit to the patient. The use of radiation is accepted when it is expected to do more

good than harm, weighing the total potential diagnostic benefits it produces against the

individual detriment that the exposure might cause (justification). The criteria for X-ray

imaging should be reviewed from time to time as more information becomes available

about the risks and effectiveness of the existing procedure, and as new procedures

emerge. The process of justification requires adequate knowledge of the patient’s

history and the results of the clinical examination. When acting as a referrer, the dentist

should therefore ensure that adequate clinical information about the patient is provided

to the person taking responsibility for the radiographic examination (63, 69).

Optimisation of dose in radiological procedures is often defined by the ALARA

principle. ALARA is the acronym for "As Low As Reasonably Achievable", referring to

the radiation dose (45). Implementing ALARA into practice involves consideration of

many factors, including initial equipment selection, maintenance, individualised selection

of X-ray exposures and an ongoing quality assurance programme, all aimed at

consistent production of adequate diagnostic information at the least exposure to

ionising radiation, taking into account economic and social factors. Regular quality

control tests are involved, including regular equipment testing, patient dose audit and

image quality assessment.

Radiation doses with CBCT equipment

Radiation dosimetry can be confusing to the novice, as there are several different

concepts and multiple units used. The dose metric commonly reported in literature is

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effective dose (E), defined by the International Commission on Radiological Protection

(ICRP) as the weighted sum of absorbed doses from different radiosensitive organs

(73). It is measured in sievert (Sv) or, more usually, as millisieverts (mSv) or even

microsieverts (µSv). The reason for this complicated concept is that different organs and

tissues have different radiation sensitivities; thus a specific x-ray exposure to one part of

the body, e.g. the abdomen, would give a very different dose and risk if applied to

another, e.g. the face.

Because almost all the organs and tissues for which dose measurements are

needed to calculate E are internal, it cannot be measured in patients directly, so it is

usually measured using an anthropomorphic phantom, representing an average human

(141). E provides an estimation of the stochastic risk for an average sized adult

reference patient. In practice however, patient dose will vary between individuals, with

patient size and mass as main influencing factors (25, 92). Although it is possible to

purchase different sizes of dosimetry phantoms representing females and children to

provide more appropriate measurements of E, multiple calculations of E for different

scenarios is very time-consuming. Dedicated Monte Carlo computer simulations offer a

valuable alternative which can model a wide variety of imaging systems, exposure

variables and examination of different gender and ages (134, 158, 159).

A large number of dental CBCT devices are currently available on the market

(104), and considerable variability in radiation doses has been reported for these (17,

110). In a recent systematic review by Bornstein and co-workers (17), CBCT devices

were grouped according to their FOV, resulting in three categories: CBCT devices with

small, medium, and large FOVs. When analyzing the reported E ranges for all three

groups, there were wide range of doses ranging from 11-252 µSv for small, from 28-652

µSv for medium, and from 52-1'073 µSv for large FOVs. The authors therefore

concluded that a single average E value is not a concept that should be used for the

CBCT technique as a whole, when comparing it to alternative radiographic methods. As

most devices exhibited E in the 50-200 µSv range, it can be stated that CBCT imaging

results in higher patient doses than standard 2D radiographic methods used in dental

practice but remain well below those reported for common multi-detector CT protocols. It

is important to recognise that doses in children may be different to those in adults, due

to relative sizes and different radiosensitive organ positions in the body (140). For

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example the proportionally greater thyroid dose in children was highlighted in a recent

meta-analysis (91). 

Image quality and radiation dose

When trying to practise ALARA, it is essential to recognise the close relationship

between image quality and radiation dose. It would be easy to reduce radiation doses to

extremely low levels, but this might make images diagnostically useless. In reality, we

require diagnostically adequate images rather than the highest quality. Consequently,

the ALARA principle has been recently modified to emphasise the need to give equal

weighting to image quality and dose in optimisation. This has resulted in the new

concept of ALADA / "As Low As Diagnostically Acceptable“ (75). For CBCT equipment,

a key influence on radiation dose and image quality is the selection of exposure factors,

e.g. X-ray tube current exposure time product and operating potential (55). Some CBCT

equipment offers high resolution programs; these achieve their image quality by

increasing the exposures. In contrast, some equipment offer low exposure options

through reducing exposure factors. A few manufacturers have incorporated automatic

exposure controls (AECs) into their CBCT machines. AECs have the advantage of

selecting exposures specific to each patient. The disadvantages are that the choice of

image quality is taken away from the clinician and could easily be set at the wrong level

for specific diagnostic tasks.

Several studies have considered the impact of lowering exposure factors in the

context of implant dentistry (4, 38, 135, 147, 155). All show substantial scope for

reducing exposure factors, and hence patient dose, without significant loss of image

quality. The impact of dose reduction techniques on the quality of 3D virtual models

fabricated using CBCT data should, however, be considered when performing

optimisation efforts (38).

Low dose protocols have been recommended to assist practitioners in

optimisation, such as that proposed by Harris et al. (63). A low dose protocol for

pediatric CBCT has been developed which represents as much as a 50% reduction

compared with manufacturer's recommendations for that specific piece of equipment

(65). However, in practice, dentists are likely to depend on manufacturers‘ instructions

on appropriate exposure settings, so it is encouraging that new low-dose protocols have

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also been developed by manufacturers. An example is the Ultra Low Dose protocol

proposed by Planmeca (Helsinki, Finland) which allows operators to adjust imaging

parameters individually, in particular the mA values. These can be adjusted for patient

groups by selecting the mA value of the scan according to patient size (small / medium /

large). This results in E values for CBCT scans in the range of panoramic views.

Although there is still a need to determine for which clinical indications the image quality

provided by these low-dose protocols is sufficient, these radiation doses (in the range of

those given by panoramic radiography) could allow CBCT scans to be used as primary

imaging modalities in specific circumstances (18).

Although a dose advantage is frequently cited for CBCT compared with mulitslice

CT, low-dose protocols are possible for the latter. Depending on the model and setting

used, radiation levels for multislice CTs may even be lower than for CBCT scans (67,

156). This progress in dose optimisation for 2D and 3D technologies in

dentomaxillofacial radiology demonstrates clearly that radiation dose exposure and risks

are a dynamic field, and need to be constantly monitored and updated by the clinician

for the respective radiographic device used in daily practice. Only by doing so, the

practitioner can really comply to ALADA principles and implement radiation protection

into daily routine.

Recommendations for CBCT imaging for dental implant treatment planning (pre-operative imaging)In a recent survey from Norwegian dental clinics on the use of CBCT (68), the most

common indications for this imaging modality were implant treatment planning (34% of

all clinics) and localization of impacted teeth (43% of the clinics). As implant treatment

planning is one of the most common indications for radiographic 3D imaging, accepted

recommendations and guidelines for the use of CBCT for this purpose are clearly

needed. Clinical guidelines are able to provide a framework for the use of a new

technology or technique, and are designed to assist the clinician and patient in making

appropriate decisions for certain specific clinical circumstances. There are three

fundamental approaches to guideline development. The first is to rely on the opinion of

an expert panel. The second is to employ a consensus method, and the third is to use

an “evidence based” guideline development methodology. Evidence-based methods are

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considered as being optimal to limit the influence of individual opinion and bias by using

defined and objective methods based upon a systematic review of the literature (58, 92).

In a recent review, Horner and colleagues (70) identified 26 publications containing

guidelines on the clinical use of CBCT in dental and maxillofacial radiology. The articles

selected by the authors that were specifically addressing the use of CBCT in dental

implant treatment planning were somewhat conflicting in their recommendations: three

publications recommended CBCT imaging for planning prior to all dental implant

placements (39, 105, 143), other guidelines consider a selective approach as

appropriate (10, 63), while a further group of publications gave equivocal statements (2,

34, 61).

Diagnostic imaging is an essential component of treatment planning in oral

rehabilitation by means of osseointegrated dental implants. Some authors have

demonstrated that clinical examination and panoramic radiography alone may provide

sufficient imaging for posterior mandibular implant placement (71, 137), especially when

there is a 2 mm margin of safety above the inferior alveolar canal (150). The European

Association for Osseointegration (EAO) Guidelines for the use of diagnostic imaging in

implant dentistry were published in 2002 (62). Since the publication of the EAO

Guidelines in 2002, CBCT has become available offering cross sectional imaging and

3D reconstructions at potentially lower radiation doses when compared to medical

multislice CT. Experts in both clinical practice and radiology were invited for a closed

workshop held at the Medical University of Warsaw, Poland in May 2011, to review and

update the initial EAO guidelines (63). Regarding the issue of what radiological

information does a surgeon require when planning for implant placement, the authors

stated that a clinician requires information on bone volume, structure and density,

topography and the relationship to important anatomical structures, such as nerves,

vessels, roots, nasal floor, and sinus cavities and any clinically relevant pathology. This

information is initially obtained with a clinical examination and appropriate conventional

(2D) radiographs. The decision to proceed to cross-sectional 3D imaging should be

based on clearly identified needs and the clinical and surgical requirements of the

clinicians involved. The EAO made the following specific recommendations for the use

of pre-operative cross-sectional imaging (including CBCT): when clinical examination

and conventional radiography have failed to adequately demonstrate relevant

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anatomical boundaries or the location of important anatomical structures (1); when

imaging was deemed appropriate in cases where extensive bone augmentation is

anticipated (2); for all sinus floor elevation (SFE) procedures (3) and guided implant

surgery (computer-assisted planning and placement of dental implants) cases (4); when

further information regarding intra-oral autogenous bone donor sites is needed (5); when

planning the use of special surgical techniques such as zygomatic implants or

osteogenic distraction (6).

In a recent systematic review by the International Team for Implantology (ITI)

from the consensus conference in Bern in 2013 (17), the authors have identified

numerous articles describing the importance of various anatomic structures identified on

cross-sectional imaging including the inferior alveolar (mandibular) canal, anterior loop

and mandibular incisive canal, mental foramen, lingual canal, submandibular gland

fossa / lingual undercut, maxillary incisive / nasopalatine canal and maxillary sinus and

their relation to implant placement. Although the placement of dental implants is an

important cause of iatrogenic inferior alveolar nerve injuries (51, 118, 133, 138),

especially when focusing on permanent neurosensory disturbances (88), it has to be

stated that it will be difficult to prove a clear benefit of CBCT over conventional 2D

imaging such as panoramic radiography with respect to damage prophylaxis of the IAN

or other vital neurovascular structures in prospective studies. This is simply related to

the fact that the sample sizes needed for such controlled prospective clinical trials will be

difficult to achieve (120), and furthermore, many institutional review boards and ethical

committees will not approve studies comparing complex surgical interventions

performed in a randomized fashion using 2D alone versus a group of patients that

benefits from 2D in combination with 3D imaging (CBCT; 59). Besides neurosensory

disturbances, neurovascular complications due to implant surgery can also result in

severe post-operative hemorrhage. Significant hemorrhages are mostly described after

anterior mandibular implant placement, and SFE procedures prior to or with implant

placement (for review see 74).

A scientifically proven beneficial effect of CBCT imaging over 2D radiographs

alone to decrease complications caused by anatomical constraints is still missing. Yet,

there is evidence that planning dental implants based on panoramic views versus CBCT

scans exhibits siginificant deviations from normal anatomy (139). In a recent study, the

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efficacy of observers’ prediction for the need of bone grafting and presence of

perioperative complications was evaluated on the basis of CBCT and panoramic

radiographic planning as compared to the surgical outcome (60). Patients were included

if both panoramic images and CBCT scans had been taken with a maximum interval of

four months and if the presurgical planning phase was followed by implant placement.

Four observers carried out implant planning using panoramic image datasets, and at

least one month later, using CBCT scans. The findings of the study indicated that CBCT-

based pre-operative implant planning enabled treatment planning with a higher degree

of prediction and agreement as compared to the surgical standard. In panoramic-based

surgery, the prediction of implant length was poor. There have been similar studies in

recent years that at least partially confirm these findings, but also emphasize that

importance of subjective factors such as observer opinion or experience (8, 35, 36, 47,

81, 115, 126).

A recent systematic review by Vogiatzi and co-workers (151) stated that one of

the main reasons for CBCT imaging in dental medicine was the assessment of the

residual ridge and maxillary sinus prior to SFE or dental implant placement. Cross-

sectional imaging (CBCT) has been recommended for pre-operative evaluation of the

avaliable bone in the posterior maxilla and assessing health or pathology of the

maxillary sinus by several professional organizations (10, 17, 63). Vogiatzi and co-

workers (151) have stated that the most common anatomic variation in the maxillary

sinus is the thickness of the Schneiderian membrane, which seems to be significantly

thicker in the mid-sagittal aspect and in males. Furthermore, septa within the maxillary

sinus are common findings and are most frequently located in the middle region of the

sinus. Their prevalence seems to be independent of age and gender. In a recent study

using CBCT images to evaluate the presence and type of septa, the authors found that

66.5% of the included patients had septa, and 56.5% of the sinuses, respectively (19). In

the majority of these cases, septa were observed in the first or second molar region of

the floor of the maxillary sinus. Furthermore, the most common orientation of the septa

was coronal (61.8%), followed by axial (7.6%), and sagittal (3.6%), but more than one

fourth of the septa could not be classified as coronal, sagittal or axial, and were grouped

as "other" septa. The authors also underlined that their study did not provide evidence

that the frequency of maxillary sinus septa was associated with age, gender or status of

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the dentition of the patients. The presence of septa has been related to an increased

risk for perforation of the Schneiderian membrane during SFE. In the study by Zijderveld

and co-workers (160) on 100 patients scheduled for SFE, the authors reported 11

membrane perforations, 5 of them directly related to the presence of septa. In a recent

investigation by von Arx et al. (152), the authors found a percentage of perforations in

patients with septa of 42.9% versus 23.8% in patients without septa. There are several

other factors than sinus septa that can influence the risk of a Schneiderian membrane

perforation during SFE such as the presence of a narrow sinus, previous sinus surgery

and absence of alveolar bone (106). Thus, detailed knowledge of the anatomic

structures of the maxillary sinus seems to be beneficial prior to SFE to avoid surgical

complications, which ideally is gained radiographically by the use of CBCT scans.

According to the literature, a mucosal thickening of > 2 mm is classified as

pathological according to the criteria defined by Cacigi and co-workers (25). If the width

of mucosal thickening is < 3 mm, the detection rate on panoramic radiographs versus

CBCT scans has been reported to be significantly decreased (127). To assess a

potential treatment need of pathological findings in the maxillary sinus based on CBCT

imaging, a classification for the morphology of the Schneiderian membrane was

proposed using sagittal and coronal CBCT scans according to criteria adapted and

modified from Soikkonen & Ainamo (128) in several studies (Figure 1; 16, 76, 114, 123):

1. Healthy Schneiderian membrane: no thickening

2. Flat: shallow thickening without well-defined outlines

3. Semi-aspherical: thickening with well-defined outlines rising in an angle of >

30° from the floor of the walls of the sinus

4. Mucocele-like: complete opacification of the sinus

5. Mixed: flat and semi-aspherical thickenings

Regarding the high incidence of antral mucosal thickening found in the studies using a

mucosal thickening of > 2 mm as a threshold value to distinguish physiological from

pathologic findings (16, 76, 114, 123), the clinical significance of this value has to be

questioned. In clinical situations when there is evidence of sinus pathology, or when the

clinician believes that sinus drainage is impaired and may jeopardize the outcome of the

prospective implant procedure to be undertaken, it seems advisable to consult an ear,

nose, and throat (ENT) specialist (66). This is especially true for maxillary sinuses with

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partial or complete mucocele-like opacification of the antrum. This is also supported by a

case series analyzing failures of SFE procedures reported that out of 13 patients

included, pre-operative chronic maxillary sinusitis had been present in 4 patients (5).

The authors therefore stated that elimination of sinusitis and other potential pathological

conditions is necessary before SFE. If findings such as mixed flat and semi-aspherical

thickening of the antral mucosa are visible, and the bony walls of the sinus are resorbed,

leading to a discontinuity of the cortical outline, and if the roots of the maxillary teeth are

resorbed, rapidly growing diseases or malignancies have to be suspected (9, 15).

A still controversial issue regarding assessment and diagnosis of the maxillary

sinus using CBCT imaging prior to SFE or dental implant placement is the adequate

FOV. Vogiatzi and co-workers (151) have reported that there was insufficient data to

comment on the effect of the FOV (small / medium versus large; one versus both

maxillary sinuses visualized) of the CBCT scans on the detection and prevalence of

maxillary sinus pathology. Therefore, they were not able to recommend an ideal FOV

scan, nor to state that both maxillary sinuses should always be visualized when

performing 3D imaging (Figures 2, 3, 4). Harris et al. (63) have stated that a pre-

operative screening of the maxillary sinuses using large FOVs is not recommended for

dental implant treatment planning. But in some clinical situations, when there is

evidence of sinus pathology that may jeopardise the outcome of the planned surgical

procedure, there may be a justification to extend the FOV to include the whole of the

sinus including the ostio-meatal complex (63, 76, 123, 151). This is further emphasized

by the high radiation doses applied to the eye lens using cross-sectional imaging

(CBCT or multislice CT) or in the area of the paranasal sinuses, and the need to adhere

to ALADA principles by always trying to implement dose reduction procedures. It needs

to be pointed out here that there is increasing attention and evidence in the literature

towards negative effects (i.e. cataract) to the eye lens even at low doses by radiographic

imaging (112, 125). Thus, to decrease eye lens doses through FOV reduction should be

kept in mind, and clinical recommendation such as visualization of the entire maxillary

sinus or even bilateral maxillary sinuses using CBCT scans with medium to large FOVs

for pre-operative treatment planning of dental implants is not supported by the literature,

and thus not justified.

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In a recent study, indications and frequency for 3D imaging for implant treatment

planning in a pool of patients referred to a specialty clinic over a three-year period was

evaluated (19). The data exhibited that 40% of the patients included were

radiographically assessed by using 2D technology alone. This demonstrated that even

in a specialty clinic patients are not routinely exposed to CBCT imaging prior to implant

placement. The authors reported that a typical patient receiving additional CBCT

scanning for dental implant treatment planning would be over 55 years old with an

extended or distal edentulous gap in the maxilla with the need for bone augmentation

(simultaneous or staged). A further interesting finding of the study regarding the

frequency of 3D imaging was that there was a significant increase in CBCTs over the

study period from 2008 (52.4% of all patients) to 2010 (65.9%). This is certainly also an

effect of the growing popularity of this radiographic methodology and its acceptance by

clinicians. Therefore, it seems realistic to predict that the percentage of 3D imaging –

primarily CBCT scans – will still increse over the next few years. Nevertheless, if

patients are limited to straightforward implant cases, with no clinically identified local

problems such as a limited horizontal ridge width, cross-sectional imaging made no

difference to the implants selected based on panoramic views alone (48). The authors

stated that the clinical examination provides sufficient information for selecting implant

diameter and the panoramic radiograph provides sufficient information for implant length

selection in standard cases.

Recommendations for CBCT imaging during and / or following dental implant placementDespite careful planning, surgical complications can arise following implant placement

including infection, intraoral haemorrhage, wound dehiscence, post-operative pain, lack

of primary implant stability, inadvertent penetration into the maxillary sinus or nasal

fossa, neurosensory disturbances, injuries to adjacent teeth, tissue emphysema, and

aspiration, or ingestion of surgical instruments (56). The evaluation of complications

includes careful clinical examinations and selected radiographic imaging. The EAO has

published clear statements on radiographic imaging during and following dental implant

surgery (63). The authors emphasized that during implant surgery conventional 2D

radiographic techniques would be adequate in most cases to confirm the position of an

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implant in relation to anatomical landmarks. Regarding follow-up examinations, the

authors stated that in the absence of symptoms, there would be no indication for cross-

sectional imaging. However, 3D imaging might be helpful for the diagnosis and

management of specific post-operative complications such as nerve damage or post-

operative infections in relation to sinus cavities close to the inserted dental implants.

Even when taken careful measures including appropriate clinical and radiographic

assessments prior to surgery, nerve injuries may occur. The literature seems to indicate

that three quarter of the neural injuries after implant placement result in permanent injury

(88, 118, 119). In general, damage to sensory nerves can result in anaesthesia,

dysaesthesia, pain or a combination of these. In case of acute nerve injury, timely nerve

and implant decompression are essential with supportive analgetic or anti-convulsant

therapy. Indeed, early removal of implants associated with mandibular nerve injury (less

than 36 hours post-injury) may assist in minimising or even resolving neuropathy (82).

The correct diagnosis of post-surgical complications based on presenting clinical

symptoms (anaesthesia, dysaesthesia, pain or a combination) using 3D imaging is

recommended to asses the extent of damage to neural structures (42). In this case

series of inferior alveolar nerve injuries, the authors could evaluate the trauma by CBCT

imaging and distinguished implant impingement, penetration, and even complete

obliteration of the canal (Figure 5). Similary, neuropathic pain following implant

placement in the interforaminal region of the mandible (86, 121) and the nasopalatine

canal in the anterior maxilla (Figure 6; 146) have been described. When suspecting

such a complication, CBCT scans can visualize the correct location of the implant. Thus,

perforation of the incisive canal and nerve during implant insertion should be considered

as a complication of implant surgery in the mandibular anterior area (86, 101).

Accidental displacement of endosseous implants into the maxillary sinus and

potential migration throughout the upper paranasal sinuses and adjacent structures is an

unusual complication in implant patients. Peri-operative displacement of implants into

the sinus is the obvious consequence of incorrect surgical planning, such as placement

of implants in sites with inadequate bone height and volume, surgical inexperience with

the anatomic landmarks of the maxillary sinus, or poor surgical performance like

overpreparation of the recipient site, application of heavy force during implant insertion,

or perforation of the sinus membrane during the drilling sequence (28, 50). Implant

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migration into the maxillary sinus may also be the more remote consequence of loss of

osseointegration due to peri-implantitis or, in the case of loaded implants, inaccurate

distribution of occlusal forces. In a review of published literature about accidental

displacement and migration of dental implants into the upper jaw, the authors identified

a total of 24 articles, the majority related to accidental displacement and migration of

dental implants to maxillary sinus, but there were also case reports with migration into

other craniofacial structures such as the ethmoid sinuses, sphenoid sinuses, orbit, and

cranial fossae (53). Invasion of the maxillary sinus or related structures with dental

implants might not be detected during implant placement. However, these complications

might cause problems in the long run, and might not be adequately diagnosed using 2D

imaging such as panoramic or periapical radiographs alone (157).

The diagnosis of peri-implantitis is based on clinical parameters and radiological

findings (122). The radiographic diagnosis of peri-implant lesions is based on periapical

radiographs (2D) due to their wide accessibility in dental practice. However, this

methodology has shown a significant variance in inter- and intraobserver reproducibility

of the acquired measurements (57) and an underestimation of bone loss (27). Thus,

CBCT scans have been proposed for diagnosis of peri-implant bone defects with the

added benefit of visualizing the buccal and lingual aspects of the dental implant, and

have shown an acceptable correlation with histological measurements (52). In an in vitro

study comparing periapical radiographs, panoramic views, CBCT and CT scanning,

CBCT showed the best image quality, and was able to visualize peri-implant bone

defects in all three planes, true to scale, and without distortion (96). In a similarly

designed more recent in vitro study, the best performance in detecting peri-implant bone

defects and correctly confirming their absence was found for periapical radiographs,

while CT scans demonstrated the lowest performance in detecting peri-implant bone

defects (85). Therefore, the authors concluded that periapicals should still be

recommended as favourable method evaluating bone loss around dental implants, and

that 3D imaging using CBCT should rather be performed as adjunctive imaging for

specific indications, where clincial and 2D radiographs have not provided sufficient

information.

The superiority to detect peri-implant bone defects of intraoral radiographs

compared to 3D imaging using CBCT was also reported in a study assessing implants

15

placed in fresh bovine ribs in osteotomy sites with varying peri-implant spaces (37). One

important issue that limits CBCT imaging for the diagnosis of peri-implant bone defects

is its association with beam hardening artefacts around metal (Figure 7; 124). It has

been shown that artefacts in CBCT were always present in the proximity of implants

made from titanium irrespective of the implant position in the jaw (12). Additionally,

patient movement during scanning - especially when occurring several times and for an

extended time period - results in motion artefacts, and may even result in a need for re-

exposure of the patient (131, 132). Therefore, it is questionable whether CBCT imaging

represents an adequate technique for the assessment of structures in direct or close

proximity of dental implants. It should be further emphasised that CBCT machines

performe differently, and only a couple of CBCT devices on the market are delivering

images that are almost free of visible artefacts in the peri-implant vicinity. Yet, the

resulting image quality will still depend on the local situation and the number and relative

density of the available metals in the FOV and/or the entire orofacial area.

CBCT imaging for clinical research purposesResearch involving human subjects is critical for advancing clinical medicine, and this is

also true in the field of radiology in general. To advance our clinical understanding and

practice in an appropriate manner, we must always be mindful of the requirements of

ethics when conducting research with humans. Although a wide variety of ethical issues

are expected to emerge in the conduct of radiology research, one ethical challenge that

may be particularly likely to occur in this context is distinguishing pure research

endeavors without evident and immediate benefit for the patients included from

innovative treatment concepts or standard practice (21). Standard clinical practice

involves interventions that are intended solely for the benefit of patients and that have a

reasonable expectation of success. Innovative therapy (also termed “off-label use”) can

be defined as an activity that lacks a formal evidence base. Regarding the use of CBCT

imaging in the context of implant dentistry, there is often no clear benefit for the patient

using 3D imaging - especially post-operatively. Therefore, justification of each additional

CBCT scan is ethically important, both with regard to the interval and the total number of

exposures. From a pure scientifc perspective, longterm data is always of greater value

than shorterm outcomes. One should consider that there is no grey level calibration, as

16

making the comparative appreciation of density values of CBCT scans over time

unreliable (113). Furthermore, bone remodelling with its de- and remineralisation

processes may take up to 6 months and more before regaining the original

mineralisation level, which renders CBCT taking with shortterm intervals to assess the

effect and durability of bone grafting procedures somewhat doubtful. If possible, CBCT

scans should be therefore rather taken with longer intervals than planning multiple

exposures during the initial postsurgical follow-up period.

In a recent review, Benic and colleagues (13) stated that in ethically approved

clinical research, 3D imaging (CT or CBCT) can be used to pre- and post-operatively to

evaluate bone and soft tissues as well as the implant position with reference to the

anatomical structures. CBCT imaging is increasingly being used for 3D assessment of

bone following ridge preservation (1, 7, 95), sinus floor elevation (54, 94, 107, 144), and

implant placement with simultaneous bone augmentation (23, 24, 32, 78, 84) or staged

procedures following block grafts (98, 99, 130). Besides visualization of bony structures,

CBCT is also used to assess the contour and dimension of the peri-implant mucosa (11,

79). This is accomplished by applying radio-opaque contrast materials such as thin foils

on the surface of the mucosa, or by displacing the lips and the cheeks from the alveolar

process by means of lip retractors or cotton rolls (13, 29, 30).

However, it is important to differentiate the use of cross-sectional imaging which

are intended to gather further basic knowledge from those that actually benefit the

patient. Research using CBCT scanning should not automatically be seen as valid

selection criteria for its clinical application. Before any imaging technique is put into

clinical use for a specific purpose, one should ideally have evidence of patient benefit

and cost effectiveness (49). Although evidence of a change in treatment plan and / or

management through the use of an imaging technique is sometimes used as evidence

for its acceptibility, it is weak evidence. This is due to the fact that a change in the

treatment plan of a patient may lead to the same, or even poorer clinical outcomes, and

may not always improve results.

Interesting data has been gathered from orthodontic research, where a study on

cadaver heads investigated the accuracy and reliability of buccal alveolar bone height

and thickness measurements derived from CBCT images (142). The authors found that

buccal bone height and buccal bone thickness was quantitatively assessed with high

17

precision and accuracy, but the buccal bone height had greater reliability and agreement

with direct measurements than did buccal bone thickness measurements. These

findings were corroborated also by another group, which stated that a thin buccal

alveolar bone covering is not depicted reliably by CBCT scans, and there is a risk of

overestimating fenestrations and dehiscence type defects on teeth (108). Regarding the

assessment of bone dimensions around implants, a study using dry mandibles

evaluated the minimum labial bone thickness surrounding dental implants detected

using CBCT images (103). The authors reported that only when the buccal bone on the

dental implant was 0.6 mm or greater, it might be visually detectable. Thus, when the

buccal bone thickness measured less, the bone plate was either underestimated or not

detectable. Nevertheless, these measurements also seem to depend on the CBCT

device used for the study (117).

Bone density has been suggested to be an important factor influencing the

success of dental implants. Areas of reduced bone density have exhibited higher failure

rates and reduced primary stability values (97). A factor complicating the use of CBCT

for clinical bone density assessment and follow-up of bone density changes is the lack

of standardized grey value distribution. Hounsfield units (HU) have been designed for

medical CT, but do not apply for CBCT (89, 90). Compared to HU units for medical CT,

the reliability of CBCT-based jaw bone density assessment has been found unreliable

over time and with significant variations influenced by CBCT devices, imaging

parameters and positioning (102). This lack of HU standardization is a major problem for

most CBCT devices, yet considering the fact that nowadays a healthy vascularized bone

structure may be more beneficial for implant placement than a sclerotic poorly

vascularized bone, the HU limits for implant treatment may be easily overcome. What

one might need instead is a structural bone analysis, like available in dedicated μCT

software. Such structural analysis has already been validated to be used for CBCT

imaging (72, 148), and thus might even have clinical potential for presurgical

assessment of bone quality.

Recommendations for communication in a digital environmentDICOM (Digital Imaging and Communication in Medicine) was originally developed by

the National Electrical Manufacturers Association (NEMA) and the American College of

18

Radiology to create a worldwide norm for digital image acquisition, storage, and display

in medicine, and also to have a standardized method for the transmission of medical

images and their associated information. "Digitization" is increasingly widespread in

dental medicine in terms of radiographic image acquisition (2D and 3D), optical surface

scanning (intra- and extraoral), CAD/CAM systems, and the electronic charting of patient

records. Unfortunately, the DICOM standard is not really fully implemented in dental

medicine today, with primarily hospital and dental school settings complying with the

standard (22). Picture archiving and communication systems (PACS) software act to

integrate image acquisition, storage, retrieval, and viewing based on the DICOM

standard. In dentistry the use of PACS is primarily limited to academic centers and

dental clinics in hospital facilities where there is need for transmission of data between

departments (31). Newer standard dental digital imaging devices including intraoral

digital radiographic systems, panoramic views, and CBCT scanners in large part are

DICOM compliant. Nevertheless, standards for DICOM compliance for some devices

including CBCT and CAD/CAM systems and their interoperability with respect to PACS

have not yet been fully established. This problem has already been pointed out by an

expert panel of the International Team for Implantology (ITI) during the consensus

conference in Bern in 2013 (18). These experts stated that to improve image data

transfer, clinicians should request radiographic devices and third-party dental implant

software applications that offer fully compliant DICOM data export.

For most CBCT systems there is a diagnostic data loss upon transfer to

DICOM/PACS and/or third party software. In addition, most third party software have

some additional filtering (e.g. smoothing) at the import phase, which may result in

additional information loss. It is therefore recommended to do presurgical diagnostics in

the dedicated CBCT-software of the imaging device, prior to export for presurgical

planning purposes. Furthermore, when performing presurgical planning, CBCT images

should be made with the recommended protocol, which is not necessarily the highest

resolution protocol, as the latter evidently creates more noise. Vandenberghe and co-

workers (147) demonstrated that for 3D segmentation and anatomical model making, a

voxel size of 200 µm (0.2 mm) is probably sufficiently low.

Other challenges in the digital data flow include the fact that there is a growing

availability of non-DICOM 3D imaging data formats required to be used for an integrated

19

virtual patient dataset (64, 77). Examples include STL and OBJ formats, respectively,

used for digital intraoral impressions and printing as well as for facial scanning.

Transferring those datasets to PACS is actually not possible, as such that the power of

the integrated virtual patient information is lost at this level. Another point of attention is

the lack of standardised grey level calibration or hounsfield scoring, making the

comparative follow-up of bone healing, grafting and implant placement rather difficult

and quite unreliable (113).

Conclusions and outlook on novel developments in dento-maxillofacial imagingIt can be concluded that CBCT imaging is not only an established radiographic modality

in treatment planning for dental implants, but its use is also becoming increasingly

popular and widespread among clinicians around the globe. This is partially due to a

new understanding of anatomic landmarks and structures at risk during implant

placement such as neuro-vascular canals and bundles. Nevertheless, that CBCT

imaging results in less intraoperative complications such as nerve damage or bleeding

incidents, or that implants inserted using pre-operative CBCT data sets for planning

purposes will exhibit higher survival or success rates has not been demonstrated yet in

the literature. It even seems at least doubtful that this will be possible to demonstrate

using a prospective and controlled trial setting for ethetical reasons. Maybe more soft

factures such as the time of surgery, the onfidence of the surgeon, or even patient

morbidity need to be evaluated in future clinical studies to demonstrate these potential

benefits of 3D imaging over 2D imaging modalities alone prior to dental implant

placement. Another reason for the growing use of CBCT scanning is the increasing

popularity of computer-guided surgery that relies on digital planning based on high-

quality CBCT images (136), but may also include the superimposition of intraoral scans

and extraoral face scans to create a 3D virtual dental patient (77). The virtual patient

concept is actually demonstrating again the need for an uniform data standard in digital

imaging in dental medicine, as creating a craniofacial virtual reality model needs image

fusion of DICOM, STL, and OBJ files.

The use of CBCT imaging following insertion of dental implants should be

restricted to specific post-operative complications such as damage to neuro-vascular

structures or post-operative infections in relation to the maxillary sinus. To confirm the

20

position of an implant in relation to anatomical landmarks after insertion, and also for

evaluation of peri-implant bone conditions during follow-up visits, conventional (2D)

radiographic techniques such as periapicals or panoramic views are sufficient.

Regarding peri-implantitis, the diagnosis and severity of the disease should be

evaluated primarily based on clinical parameters and radiological findings based on

periapical radiographs (2D). To date, the literature suggest that 3D imaging using CBCT

should should be rather performed as adjunctive imaging with a clear benefit for the

patient in terms of diagnosis or treatment strategy chosen.

Other than for daily practice, the use of CBCT scans in clinicial research might

not yield any evident beneficial effect for the patient included. CBCT imaging is used in

research to pre- and post-operatively evaluate bone and soft tissues as well as the

implant position with reference to the anatomical structures. The effect on peri-implant

hard and soft tissues of surgical techniques such as ridge preservation, SFE, implant

placement with simultaneous bone augmentation or following staged procedures using

block grafts is evaluated in a short- and long-term perspective with quite variable

frequencies between the actual CBCT scans. As many of the CBCT scans performed for

research have no direct therapeutical consequence, dose optimisation measures should

be implemented by using appropriate exposure parameters and reducing the field of

view (FOV) to the actual region of interest. To minimize dose exposure risks and effects

from cumulated effective doses over time, CBCT scans should rather be taken with

longer intervals than multiple exposures following surgery and the initial follow-up

period, if possible.

In radiation protetction, ALARA is the acronym for "As Low As Reasonably

Achievable" and is a fundamental principle for diagnostic radiology in medicine and

dentistry. This concept has been recently adapted to the ALADA ("As Low As

Diagnostically Acceptable“) principle for selection and justification of the ideal imaging

modality. Although, when cross-sectional imaging is indicated, CBCT has been

recommended to be preferable over CT (18), imaging modalities visualizing cranio-facial

hard and soft tissues without radiation exposure would be desirable. Currently, there are

two modalities that show some clinical potential for this desire: magnetic resonance

imaging (MRI) and ultrasound (6). MRI as a non-ionizing diagnostic tool in the dento-

maxillofacial region has been limited mostly due compromised visualization of hard

21

tissues and feasibility concerns such as availibility of the equipment and high costs (83).

In a recent study on an ex vivo human jaw and in vivo, a novel protocol for MRI imaging

was applied using an intraoral coil that creates an increased signal within a defined FOV

to obtain high-resolution images within an acquisition time applicable for clinical routine

3D radiography (46). The authors reported that compared with CBCT and histological

sections, MRI images exhibited dimensional accuracy, and the course of the mandibular

canal was accurately displayed. Regarding ultrasound in dento-maxillofacial radiology

and diagnosis, recent publications have reported its capability of imaging representative

features for implant treatment planning in a porcine model such as implants placed in

edentulous ridges, implants with simulated dehiscences, or mental foramina (33).

Further research for the application of ultrasound is directed towards the sensitivity and

changes of the ultrasonic response during the healing period of dental implants that

could potentially predict the amount and level of osseointegration, and also be helpful in

diagnosing peri-implant bone changes (149). Regarding only these two recent

developments in the field of dento-maxillofacial radiology, it can be stated that this field

is very dynamic and constantly changing. Thus, although CBCT currently is growing

rapidly in its popularity for imaging in the field of implant dentistry, and might even be

considered as a primary imaging modality in selected cases, future breakthroughs in

research will most likely bring new technologies that will again change the way we

visualize hard and soft tissues for pre- and post-operative evaluation of dental implants.

22

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Tables

Table 1: Basic principles on the use of CBCT imaging as proposed by the European

Academy of Dental and Maxillofacial Radiology (EADMFR; Horner et al.

2009)

1 CBCT examinations must not be carried out without a medical history and clinical examination

2 CBCT examinations must be justified for each patient to demonstrate that the benefits outweigh the risks

3 CBCT examinations should potentially add new information to aid the patient’s management

4 CBCT should not be repeated ‘‘routinely’’ on a patient without a new risk/benefit assessment

5 When accepting referrals from other dentists for CBCT examinations, the referring dentist must supply sufficient clinical information to allow for justification

6 CBCT should only be used when the question for which imaging is required cannot be answered adequately by lower dose conventional radiography

7 CBCT images must undergo a thorough clinical evaluation of the entire image data set (reporting)

8 When soft tissue evaluation is required, the appropriate imaging should be conventional medical CT or MR, rather than CBCT

9 CBCT equipment should offer a choice of volume sizes and examinations must use the smallest that is compatible with the clinical situation

10 Where CBCT equipment offers a choice of resolution, the resolution compatible with adequate diagnosis and the lowest achievable dose should be used

11 A quality assurance programme must be established and implemented for each CBCT facility, including equipment, techniques and quality control procedures

12 Aids to accurate positioning (light beam markers) must always be used

13 All new installations of CBCT equipment should undergo a examination and detailed acceptance tests before use to ensure that radiation protection for staff, members of the public and patient are optimal

14 CBCT equipment should undergo regular routine tests to ensure that radiation protection has not significantly deteriorated

15 For staff protection from CBCT equipment, the guidelines detailed in Section 6 of the European Commission document Radiation Protection 136. European guidelines on radiation protection in dental radiology should be followed

16 All those involved with CBCT must have received adequate theoretical and

40

practical training for the purpose of radiological practices and competence in radiation protection

17 Continuing education and training after qualification are required, particularly when new CBCT equipment or techniques are adopted

18 Dentists responsible for CBCT facilities who have not previously received ‘‘adequate theoretical and practical training’’ should undergo a period of additional theoretical and practical training that has been validated by an academic institution (university or equivalent). Where national specialist qualifications in DMFR exist, the design and delivery of CBCT training programmes should involve a DMF Radiologist

19 For dentoalveolar CBCT images of the teeth, their supporting structures, the mandible and the maxilla up to the floor of the nose (e.g. 8 cm x 8 cm or smaller fields of view), clinical evaluation (‘‘radiological report’’) should be made by a specially trained DMF Radiologist or, where this is impracticable, an adequately trained general dental practitioner

20 For non-dentoalveolar small fields of view (e.g. temporal bone) and all craniofacial CBCT images (fields of view extending beyond the teeth, their supporting structures, the mandible, including the TMJ, and the maxilla up to the floor of the nose), clinical evaluation (‘‘radiological report’’) should be made by a specially trained DMF Radiologist or a Medical Radiologist

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Figures

Figure 1: Schematic illustrations of the classification for the morphology of the

Schneiderian membrane as analyzed using sagittal and coronal CBCT scans

according to criteria adapted from Soikkonen & Ainamo (1995). A / B) Healthy

Schneiderian membrane: no thickening (A: sagittal view; B: coronal view). C /

D) Flat: shallow thickening without well-defined outlines (C: sagittal view; D:

coronal view). E / F) Semi-aspherical: thickening with well-defined outlines

rising in an angle of > 30° from the floor of the walls of the sinus (E: sagittal

view; F: coronal view). G / H) Mucocele-like: complete opacification of the

sinus (G: sagittal view; H: coronal view). I / J) Mixed: flat and semi-aspherical

thickenings (I: sagittal view; J: coronal view).

A B

C D

42

E F

G H

I J

43

Figure 2: Visualization of the entire right maxillary sinus using a CBCT with a small

FOV (6x6 cm) for implant treatment planning in a 54-year old female patient.

The sinus exhibits good pneumatization and open ostium without

enlargement of the Schneiderian membrane. A) Sagittal view of the CBCT

scan; B) Coronal view; C) Axial view.

A

B

C

44

Figure 3: Visualization of the basal aspects of the right maxillary sinus using a CBCT

with a small FOV (4x4 cm) for implant treatment planning in a 61-year old

male patient. The sinus exhibits good pneumatization without visualization of

the open ostium. The Schneiderian membrane exhibits a flat and shallow

thickening of the mucosa. A) Sagittal view of the CBCT scan; B) Coronal

view; C) Axial view.

A

B

C

45

Figure 4: Visualization of the basal aspects of the right maxillary sinus using a CBCT

with a small FOV (4x4 cm) for implant treatment planning in a 62-year old

male patient. The sinus exhibits radiographic signs of a sinusitis with

honeycomb like surface loculations without visualization of the ostium. This

finding makes it advisable to consult an ENT prior to sinus floor elevation

(SFE). A) Sagittal view of the CBCT scan; B) Coronal view; C) Axial view.

A

B

C

46

Figure 5: CBCT scan (small FOV: 6x5 cm) of the right mandible of a 73-year old male

patient after referral by his treating dentist following insertion of two dental

implants in regions 45 and 47. The patient reported complete anaethesia of

the lower right lip. A) Sagittal view showing proximity of the dental implant in

region 45 to the mental foramen located distally to the tooth 44; B) Coronal

view of implant penetration in region 45 into the mandibular canal and region

of the mental foramen; C) Coronal view of the implant in region 47 exhibiting

its relation to the mandibular canal; D) Axial view visualizing penetration of

the implant in region 45 into the mental foramen.

A

B

47

C

D

48

Figure 6: CBCT scan (small FOV: 4x4 cm) of the anterior maxilla of a 66-year old

female patient after referral by her treating dentist one year following insertion

of a dental implants in region 21. The patient reported persisting neuropathic

pain in the anterior mandible towards the nose. A) Sagittal view showing

penetration of the dental implant in region 21 into the nasopalatine canal; B)

Coronal view of the restored implant in region 21. There is also a slight

osteolysis visible at the apical region of tooth 11; C) Axial view of the implant

in region 21 exhibiting penetration into the nasopalatine canal.

A

B

49

C

50

Figure 7: CBCT scan (medium FOV: 8x5 cm) of the mandible of a 79-year old female

patient referred for analysis of peri-implant bone defects around implants in

the symphysis and left first premolar area. A dental implant in the right canine

region had been lost a couple of weeks ago. The beam hardening artefacts

around the metal make it difficult to assess the structures in direct or close

vicinity of the dental implants A) Axial view showing the two implants

(symphysis and left first premolar region), and a bone defect resulting from

implant loss in the right canine area; B) Sagittal view showing the two

implants in the symphysis and left first premolar region; C) Sagittal view

showing the implant in the symphysis with almost no visible bone on the

buccal and lingual aspects; D) Coronal view showing the implants in the left

first premolar region with evident bone loss on the buccal and lingual aspects.

A

B

51

C

D

52