Jan Lindhe. Clinical Periodontology

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THE TRANSMUCOSAL ATTACHMENT •

837

pared the implant (ITI O Dental Implant System) sites

in such a way that at the probing experiment some

regions were healthy, a few sites exhibited signs of

mucositis and some sites exhibited more advanced

peri-implantitis. Probes with different geometry were

inserted into the pockets using a standardized prob-

ing procedure and a small force of only 0.2 N. The

probes were anchored and block biopsies were har-

vested. The probe locations were studied in histologic

ground sections. The authors reported that the mean

histologic" probing depth at healthy sites was 1.75

mm, i.e. similar to the depth (about 2 mm) recorded

by Ericsson & Lindhe (1993). The corresponding

depth at sites with mucositis and peri-implantitis was

1.62 mm and 3.8 mm respectively. Lang et al. (1994)

further stated that at healthy and mucositis sites, the

probe tip identified "the connective tissue adhesion

level" (i.e. the base of the barrier epithelium) while at

peri-implantitis sites, the probe exceeded the base of

the ulcerated pocket epithelium by a mean distance of

0.5 mm. At such peri-implantitis sites the probe

reached the base of the inflammatory cell infiltrate.

Schou et al. (2002) compared probing measure-

ments at implants and teeth in eight cynomolgus mon

keys. Ground sections were produced from tooth and

implant sites that were (1) clinically healthy, (2)

slightly inflamed (mucositis/gingivitis), and (3) se-

verely inflamed (peri-implantitis/peridodontitis) and

in which probes had been inserted. An electronic

probe (Peri-Probe

) with a tip diameter of 0.5 mm and

a standardized probing force of 0.3-0.4 N was used. It

was demonstrated that the probe tip was located at a

similar distance from the bone in healthy tooth sites

and implant sites. On the other hand, at implants

exhibiting mucositis and peri-implantitis, the probe

tip was consistently identified at a more apical posi-

tion than at corresponding sites at teeth (gingivitis and

periodontitis). The authors concluded that (1) probing

depth measurements at implant and teeth yielded

different information, and (2) small alterations in

probing depth at implants may reflect changes in soft

tissue inflammation rather than loss of supporting

tissues.

By comparing the findings from the studies re-

ported above, it becomes apparent that meaningful —

in comparison to tooth sites — probing depth and

probing attachment level measurements at implant

sites can be obtained only if the force used during

probing is light, i.e. about 0.2—0.3 N. If a greater force

is utilized, the attachment between the mucosa and

the implant surface may be mechanically compro-

mised; the mucosa becomes dislocated in lateral, "api

cal", direction and the probe tip is allowed to end close

to the bone level. In this context it should be realized

that the probing force used by different professionals

varies between 0.5 and 1.3 N (Freed et al. 1983). Fur-

ther, in the presence of inflammation in the peri-im-

plant mucosa, the probe penetrates to a more "apical"

position than at inflamed sites at teeth.

REFERENCES

Abrahamsson, l., Berglundh, T., Glantz, P.O. & Lindhe, J. (1998).

The mucosal attachment at different abutments. An experi-

mental study in dogs.

Journal of Clinical Periodontology 25,

721-727.

Abrahamsson, I., Berglundh, T., Wennstrom, J. & Lindhe, J.

(

1996). The peri-implant hard and soft tissues at different

implant systems. A comparative study in the dog.

Clinical Oral

Implants Research

7, 212-219.

Abrahamsson, I., Zitzmann, N.U., Berglundh, T., Linder, E.,

Wennerberg, A. & Lindhe, J. (2002) The mucosal attachment

to titanium implants with different surface characteristics. An

experimental study in dogs.

Journal of Clinical Periodontology

(

in press).

Abrahamsson, I., Zitzmann, N.U., Berglundh, T., Wennerberg,

& Lindhe, J. (2001). Bone and soft tissue integration to

titanium implants with different surface topography. An ex-

perimental study in the dog.

Journal of Maxillofacial Implants

16, 323-332.

Berglundh, T. (1999). Soft tissue interface and response to micro-

bial challenge. In: Lang, N.P., Lindhe, J. & Karring, T., eds.

Implant dentistry. Proceedings from 3rd European Workshop on

Periodontology.

Berlin: Quintessence, pp. 153-174.

Berglundh, T. & Lindhe, J. (1996). Dimensions of the peri-impl an

mucosa. Biological width revisited.

Journal of Clinical Perio-

dontology

23,

971-973.

Berglundh, T., Lindhe, J., Ericsson, I, Marinello, C.P., Liljenberg,

& Thomsen, P. (1991). The soft tissue barrier at implants

and teeth.

Clinical Oral Implants Research 2,

81-90.

Berglundh, T., Lindhe, J., Jonsson, K. & Ericsson, 1. (1994). The

topography of the vascular systems in the periodontal and

peri-implant tissues dog.

Journal of Clinical Periodontology

21,

189-193.

Buser, D., Weber, H.P., Donath, K., Fiorellini, J.P., Paquette, D.W.

& Williams, R.C. (1992). Soft tissue reactions to non-sub-

merged unloaded titanium implants in beagle dogs.

Journal

Periodontology

63,

226-236.

Ericsson, I. & Lindhe, J. (1993). Probing depth at implants and

teeth.

Journal of Clinical Periodontology

20, 623-627.

Freed, H.K, Capper, R.L, & Kalkwarf, K.L. (1983). Evaluation of

periodontal probing forces.

Journal of Periodontology

54, 488-

492.

Gould, T.R.L., Westbury, L. & Brunette, D.M. (1984). Ultrastruc-

tural study of the attachment of human gingiva to titanium

vivo.

Journal of Prosthetic Dentistry 52,

418-420.

Lang, N.P, Wetzel, A.C., Stich, H. & Caffesse, R.G. (1994). His-

tologic probe penetration in healthy and inflamed peri-im-

plant tissues.

Clinical Oral Implants Research 5,

191-201.

Moon, LS, Berglundh, T., Abrahamsson, I., Linder, E. & Lindhe,

(1999). The barrier between the keratinized mucosa and the

dental implant. An experimental study in the dog.

Journal of

Clinical Periodontology 26,

658-663.

Schou, S., Holmstrup, P., Stolze, K., Hjorting-Hansen, E., Fien,

E. & Skovgaard, L.T. (2002). Probing around implants and

teeth with healthy or inflamed marginal tissues. A histologic

comparison in cynomolgus monkeys

(Macaca fascicularis).

Clinical Oral Implants Research

13, 113-126.

CHAPTER 36

Radiographic Examination

HANS-GORAN GRONDAHL

Basic radiologic principles

Special requirements in the periodontally

compromised patient

Radiographic techniques for primary

preoperative evaluations

Radiographic techniques for secondary

preoperative evaluations

Postoperative radiography

Digital intraoral radiography

BASIC RADIOLOGIC PRINCIPLES

Whenever radiographic methods are used to acquire

information in a clinical context it is of great impor-

tance that one makes sure that the benefit of using

them exceeds the costs involved. When radiographic

methods are employed, the costs are not only of a

monetary nature. Not least important are those which

comprise radiation risks. With the growing number of

subjects for whom implant treatment is considered,

there is a risk that the population dose will increase.

This is because both preoperatively and postopera-

tively, more radiographs are often required when im-

plant treatment is performed than when conventional

prosthetic treatment is done. In addition, radiographic

methods which deliver higher radiation doses to the

patient than do conventional methods are sometimes

used.

It must thus be remembered that radiography

should be based on a comprehensive clinical exami-

nation from which is determined the clinically indis-

pensable information that can only be obtained

through radiographic methods. Furthermore, the re-

quired information should be obtained with tech-

niques yielding the smallest possible radiation dose.

SPECIAL REQUIREMENTS IN THE

PERIODONTALLY COMPROMISED

PATIENT

The placement of implants in the partially dentate

patient and, particularly, in the periodontally compro

mised patient, requires careful attention to both the

remaining teeth and the potential implant sites. The

state of the remaining teeth in a patient in whom

implant treatment is contemplated must be thor-

oughly evaluated to enable necessary treatment to be

performed and a long-term prognosis to be made

before the implant treatment is initiated. Failures to

diagnose and treat pathologic conditions in and

around remaining teeth can seriously compromise the

results of implant therapy in both the short-term and

the long-term perspective. Hence, the partially den-

tate patient must be subjected to a detailed clinical and

radiographic examination of the teeth and surround-

ing alveolar hone. The examination should include the

potential implant sites to determine the presence of

pathologic conditions, root remnants, foreign bodies

and other factors which may require surgical interven

tion and a subsequent healing period before a decision

to insert implants can be made.

RADIOGRAPHIC TECHNIQUES

FOR

PRIMARY PREOPERATIVE

EVALUATIONS

Intraoral and panoramic radiography

The radiographic technique of choice is the intraoral

paralleling technique (Fig. 36-1) with projections per-

pendicular to the tangent of the dental arch in the areas

of interest. The bisecting-angle technique should be

avoided because this distorts vertical dimensions. To

decrease doses as much as possible, fast (E or F speed)

films should be used in combination with narrowly

collimated X-ray beams. When applied also to the

edentate regions the intraoral technique provides

RADIOGRAPHIC EXAMINATION •

Fig. 36-1. The best radiographic

depiction of remaining teeth and

edentate regions is provided by

the

intraoral paralleling technique.

Fig. 36-2. In intraoral radiographs the mesiodistal dimension of the intended implant site can be evaluated. The

number of implants that can be inserted can thus be assessed. Intraoral radiographs also provide a preliminary esti

mate of the vertical bone dimension.

valuable information concerning the mesiodistal di-

about the potentially available bone height relative to,

mension of the region in which implants are consid- for example, the mandibular canal and the maxillary

ered and, thus, about the number of implants that can

sinus (Fig. 36-2). From the intraoral radiographs it can

be inserted. The radiographs also provide information therefore be determined in which cases implant treat-

840 • CHAPTER 36

Fig. 36-3. To be able to correctly es

timate horizontal distances in the

region of interest, radiographs

must be taken with the incident

beam perpendicular to the tan-

gent of the alveolar process (a).

incorrect beam angulation can

make the mesiodistal dimension

appear smaller than it is (b).

Fig. 36-4. Ideally the implant

should be surrounded by bone in

its entire length. The bone height

available for implant insertion

therefore corresponds to the dis-

tance from a bone level, where the

bone width is sufficient, to a limit-

ing anatomic structure. Bone

width is most accurately meas-

ured in tomograms. A measure of

the total bone height can be used

as a reference during surgery.

ment cannot be performed due to lack of available

bone volume unless bone augmentation procedures

are performed. It cannot, however, be determined

whether implant treatment can be made because of the

lack of information about the buccolingual bone di-

mensions.

While panoramic radiography can provide some of

the information that is necessary to determine

whether implant treatment may be contemplated, its

lack of detail often prohibits a sufficiently accurate

diagnosis of tooth-related diseases. Furthermore, in

panoramic radiographs distortions are frequently

found, above all concerning horizontal dimensions

(

Tronje 1982). This makes panoramic images less well

suited for accurate estimates of the amount of bone

available in the mesiodistal direction, particularly in

the anterior parts of the jaws. However, when the

anatomic conditions make it impossible to place in-

traoral films parallel to the vertical axis of the alveolar

process, a better estimate of the bone height can be

made in panoramic radiographs. It is important that

due account is taken of the magnification in pano-

ramic radiographs, as this can vary between pano-

ramic units.

When implants are to be inserted between teeth,

between a tooth and the mental foramen, or between

tooth and the anterior border of the maxillary sinus,

supplementary intraoral radiographs should always

be obtained. They should be taken with a direction of

the X-ray beam perpendicular to the tangent of the

alveolar arch (Fig. 36-3). Inaccurate horizontal angu-

lation of the X-ray beam can easily make the distances

of interest appear too small or, less frequently, too large

(Grondahl et al. 1996).

RADIOGRAPHIC TECHNIQUES FOR

SECONDARY PREOPERATIVE

EVALUATIONS

An important objective of the preoperative radio-

graphic evaluation of the implant patient is to deter-

mine the height and width of the bone available for

implant insertion. Ideally, the bone width should al-

low complete coverage of all implant threads on both

the buccal and the lingual sides. The available bone

height must therefore be estimated from that part of

the alveolar bone in which a sufficient bone width is

found to a site specific anatomic border in the vertical

direction, e.g. the lower border of the nasal cavity, the

lower border of the maxillary sinus or the upper bor-

der of the mandibular canal. Sufficiently accurate es-

timations of bone width and height cannot be ob-

tained without cross-sectional tomography. To obtain

RADIOGRAPHIC EXAMINATION • 841

Fig. 36-5. Cross-sectional tomography of the mandible

provides information about the position of the

mandibular canal relative to the marginal bone crest

and about the width of the mandible.

a reference measurement that can be used during

surgery in order to determine to what depth the drill-

ing can be performed, measures should also be taken

from the marginal border of the alveolar crest to the

anatomic structure that limits the depth to which the

preparation can be made (Fig. 36-4).

To achieve ideal conditions for a successful integra

tion of the implant with the surrounding bone it is

important that good stability of the implant can be

obtained during the healing period (Sennerby et al.

1992, Ivanoff et al. 1996). The most important factor in

this respect is the presence of a sufficient amount of

compact bone in which the implant can be anchored.

The compact bone at the marginal bone crest can

provide stability of the marginal part of the implant.

Stability of its "apical" part can, in the anterior part of

the mandible, be obtained by anchoring the implant

in a layer of cortical bone at the base of the mandible.

In the maxilla the lower border of the nasal cavity or

the maxillary sinus can provide the necessary "apical"

stability. If neither of these possibilities are at hand,

stability of the "apical" part can sometimes be

achieved by placing it in a layer of buccal or, more

often, lingual bone cortex. When an apically located

cortical layer cannot be used for anchoring the im-

plant, a relatively narrow width of the jaw bone in

combination with a thick, cortical marginal border

may provide proper conditions for immediate im

plant

stability. On the other hand, a wide alveolar bone

with

a thin layer of compact bone at the alveolar crest

often

provides less than optimal conditions for im

plant

treatment. However, the presence of thick trabeculae

in the spongious bone can provide the neces

sary

conditions for good primary stability. Adequate

information about bone width and bone content con-

sequently is of importance in the planning of where

and how to place implants. While bone width can be

determined by tomography, the number and size of

bone trabeculae can be difficult to evaluate. The best

information is provided by the intraoral radiographs

(

Lindh et al. 1996a) but it must be remembered that

the trabecular pattern seen in these images primarily

reflects the conditions in the junctional area between

compact and trabecular bone (van der Stelt 1979,

Lindh et al. 1996b). Thus, the presence in the radio-

graph of a trabecular pattern is no guarantee that bone

trabeculae will be found in the interior parts of the jaw

bone. On the other hand, the absence of such a pattern

strongly indicates a definite absence of bone trabecu-

lae. In such cases, nutrient canals are frequently seen.

Absence of bone trabeculae and presence of nutrient

canals are also a frequent finding in alveolar processes

of a narrow buccolingual dimension.

An accurate estimate of the distance between the

marginal bone crest and the lower border of the nasal

cavity or the maxillary sinus is necessary in order to

select implants of appropriate lengths for placement

in the maxilla. Rather than choosing an implant that

does not reach the border, an implant should be used

that just penetrates the cortical border to obtain the

necessary anchorage.

In the mandible, the distance between the marginal

bone crest and the upper border of the mandibular

canal must be determined with great accuracy so that

the insertion of implants, or the preparation preceding

the insertion of an implant, does not interfere with the

infra-alveolar neurovascular bundle. If it does, perma

nent paresthesia may follow. Since this is a serious

complication, the risk for it must be minimized. Only

cross-sectional tomography can provide a good

enough depiction of the mandibular canal and pro-

vide a basis for the necessary measurements (Fig.

36-

5). In contrast to the maxilla, one must rather choose

an implant that is a little too short than too

long.

Radiographic measurements are neither so ac-curate

nor so precise that they can be completely

trusted (

Grondahl et al. 1991, Ekestubbe & Grondahl

1993,

Lindh et al. 1995). One must therefore decrease

the

calculated distances by 1-2 mm. Due account must

also be taken of the fact that the drilling procedure

which precedes the implant insertion goes deeper

than the implant itself. One must also take into ac-

count that the upper part of the implant cannot always

be placed at the level of the marginal bone crest, e.g.

in cases when an implant has to be placed buccal or

lingual to the upper bone margin or when a narrow

width of the marginal bone makes reduction of the

bone height necessary (Fig. 36-6). Hence, the need for

a reference measurement between the marginal bone

crest and the upper border of the mandibular canal is

obvious.

842 • CHAPTER 36

Fig. 36-6. The total height between the upper border of the mandibular canal and the marginal bone crest can be

used as a reference during surgery (a). The total bone height may have to be reduced due to too narrow a

marginal

bone width (b). To decrease the risk for nerve damage, the bone height measurements should be further

reduced (c).

Conclusion

A comprehensive clinical examination must precede

the radiographic examination. The latter should be

done with techniques yielding the lowest possible

doses, yet all clinically necessary information.

Failure to diagnose and treat pathologic conditions

in and around remaining teeth can seriously compro-

mise the results of implant therapy.

The intra-oral paralleling technique is recom-

mended for an estimate of horizontal dimensions of

the

intended implant site, and for a preliminary esti

mate

of its vertical dimensions.

When panoramic techniques are used, supplemen-

tary intraoral radiographs should always be obtained

when horizontal distances are critical.

For the best estimate of height and width of the

implant site, cross-sectional tomography should be

carried out.

To avoid damages of the infra-alveolar neurovascu-

lar bundle, a safety margin should be applied to the

calculated distances between the marginal bone crest

and the upper border of the mandibular canal.

Requirements for cross-sectional tomography

In cross-sectional tomography with conventional to-

mographic techniques (motion tomography) one

must

take into account the curvature of the jaws. For

each

intended implant site, the placement of the to-

mographic layers must be individualized. This is pos-

sible with some computer-operated tomographic

units

because of special software. Other units require

that

the patient is moved and his/her head rotated in

the

horizontal plane to achieve the appropriate posi

tion. A

correct position of the tomographic layer im

plies that it

is perpendicular to the tangent of the jaw

curvature

and to a horizontal reference plane (Fig.

36-7). In the

maxilla the reference plane is the hard

palate, in the

mandible the mandibular canal, which

in the premolar

to first molar region often runs paral

lell to the base of

the mandible. To obtain correct

positions of the

tomographic layer relative to one of

these horizontal

reference planes the patient's head

may have to be

slightly tilted forwards or backwards.

The latter is the

case for a tomographic examination

in the mandibular

premolar and molar regions. Incor

rect angulation of

the tomographic layer decreases the visibility of the

cortical bone plates and the mandibu-

Fig. 36-7. In cross-sectional to-

mography a proper placement of

the tomographic layers is essential

for correct estimates of bone

height and width.

RADIOGRAPHIC EXAMINATION • 843

lar canal and can lead to incorrect estimates of both

bone height and width (Grondahl et al. 1996).

Implants in the premolar and molar regions

In the maxillary premolar and molar regions, the ex-

tension of the maxillary sinus limits the amount of

bone available for implant placement both in the hori-

zontal and the vertical direction. In cases where teeth

remain in the anterior part of the jaw, but are missing

posteriorly, one must be able to determine the number

of implants that can be inserted between the most

posteriorly positioned tooth and the anterior border

the maxillary antrum. An estimate of the horizontal

dimension of the potential implant site can be made

from panoramic or intraoral radiographs. If the im-

plant site is within a curved part of the jaw, measure-

ments from panoramic radiographs can be inaccurate.

Orthoradially obtained radiographs are therefore to be

preferred. These can also be used for a preliminary

estimate of the available bone height between the

marginal bone crest and the lower border of the max-

illary sinus. When the film cannot be placed parallel

the vertical axis of the alveolar process, the vertical

measurements are best made in the panoramic image.

The bone height actually available for implant in-

sertion also depends upon the width of the alveolar

process. For example, when the bone width is too

narrow in the marginal part of the alveolar process,

the

bone height has to be surgically reduced until a

level

is reached where the bone width is sufficient for

implant placement. To determine the height of the

bone in areas with proper width, supplementary to-

mography is often needed. This can also establish

whether bone of sufficient width is present lingual to

the maxillary sinus (Fig. 36-8), which neither intraoral

nor panoramic radiographs can reveal (Grondahl et al.

1996). To be able to give as accurate information as

possible about the height and width of the jaw bone,

the tomographic layers must be perpendicular to the

hard palate and to the tangent of the jaw curvature.

Because of the shape of the dental arch, each side and

region must be examined with individual adjustments

of the direction of the X-ray beam (Eckerdal & Kvint

Fig. 36-8. Tomography can reveal whether bone of suffi

cient width for implant placement is present on the lin

gual side of the maxillary sinus.

1986). To obtain the best possible image quality the

amount of scatter radiation should be small. This is

achieved by narrowly collimated X-ray beams that

also

reduce the radiation dose to the patient.

In the premolar and molar regions of the mandible,

the position of the mental foramen and the mandibu-

lar canal must be identified. If there is a certain mini-

mum distance between a tooth and the anterior border

of the mental foramen, it may be possible to insert an

implant between the tooth and the foramen. Because

the mental foramen on the one hand and the root of

an anteriorly positioned tooth on the other are at

different distances from the X-ray source, the horizon-

tal distance between the tooth and the foramen can be

misinterpreted. In images taken from a mesio-oblique

direction the distance can appear too long, while it can

appear too short in images taken from a disto-oblique

direction. Therefore, the X-ray beam must be perpen-

dicular to the tangent of the dental arch in the area

between the foramen and the anteriorly positioned

tooth (Fig. 36-9).

The mandibular canal often makes a more or less

Fig. 36-9. To enable a correct estimate of the distance between the mental foramen and an anteriorly positioned

tooth, a correct horizontal angulation of the X-ray beam (a) is essential. Incorrect angulations can make the

distance

appear too large (b) or too small (c).

44 • CHAPTER 36

Fig. 36-10. Cross-sectional tomography of a mandibu

lar molar region revealing a deep lingual concavity

anteriorly convex loop before it reaches the mental

foramen. To avoid damaging the nerve, the distance

between the anterior border of the mental foramen and

the tooth must allow for some safety margin

between

the foramen and an implant.

The insertion of implants above the mandibular

canal should be preceded by a radiographic evalu

ation

which provides information not only on the

width of

the jaw bone and the distance between the

upper

border of the mandibular canal and the mar

ginal

bone crest, but also of the cross-sectional shape

of the

jaw. Not infrequently, the width of the jaw is

limited by

lingual concavities, most notably the sub-

mandibular

gland fossa within which a branch from the facial

artery can be found. Failure to take account

of this

cavity can lead to a lingual perforation of the

mandible

during surgery and damage to the artery.

The

subsequent bleeding can be life threatening

(

Bruggenkate et al. 1993). Failure to observe the some-

times pronounced lingual inclination of the posterior

part of the alveolar process can also lead to uninten-

tional perforation of the lingual border of the mandi-

ble. The necessary information about lingual concavi-

ties or a marked lingual inclination of the posterior

part of the mandible can only be obtained through

cross-sectional tomography (Fig. 36-10). This not only

prevents serious complications, it also provides infor-

mation about where sufficient amount of bone can be

found in which the apical part of the implant can be

anchored (Fig. 36-11). Tomographic images which in-

clude the crowns of the teeth in the maxilla also pro-

vide guidance for an appropriate buccolingual place-

ment and inclination of the mandibular implant.

Regardless of technique used, the tomographic lay-

Fig. 36-11. Cross-sectional tomography of the posterior

parts of the mandible can reveal a lingual inclination of

the alveolar process and the presence of a lingual fossa.

It can also be used to determine proper implant place-

ment for good primary stability as well as optimal

placement and inclination relative to teeth in the max-

illa.

ers should be placed as perpendicular as possible to

the mandibular canal and to the tangent of the jaw

curvature. This provides the most distinct images of

the canal and the borders of the mandible while offer-

ing the best possibilities for reliable measurements.

Although it is true that the mandibular canal occa-

sionally can be difficult to perceive even in high quality

tomograms (Lindh et al. 1992) the combination of

intraoral, panoramic and tomographic images usually

provides a solid radiographic foundation for sub-

sequent treatment decisions.

Conclusion

The horizontal dimension of an intended implant site

can be determined from intraoral or panoramic radio-

graphs. In curved parts of the dental arch, measure-

ments in panoramic radiographs can be inaccurate

due to distortions.

Preliminary estimates of the bone height can be

made in intraoral radiographs, provided that a paral-

leling technique has been used, or in panoramic radio-

graphs.

Determination of the bone height actually available

is best made in cross-sectional tomograms in which

the width of the jaw bone also can be determined.

Cross-sectional tomography should be done per-

pendicular to the tangent of the dental arch and per-

pendicular to a horizontal reference plane, the hard

palate for maxillary examinations and the base of the

mandible for mandibular examinations.

To determine the distance between the mental fora-

men and an anteriorly positioned tooth, intraoral ra-

diographs should be obtained with an X-ray beam

RADIOGRAPHIC EXAMINATION •

Fig. 36-12. The eventual position

of the marginal part of an implant

depends on the width of the mar-

ginal bone. Tomography can re-

veal where sufficient bone width

is located and, thus, where the

marginal part of the fixture will

become placed once the necessary

bone reduction has been made.

direction perpendicular to the tangent of the dental

arch.

Cross-sectional tomography in the mandible is

needed to determine the distance between the mar-

ginal bone crest and the upper border of the mandibu

lar canal as well as the presence of lingual concavities

and the inclination of the alveolar process.

Conventional versus computed tomography

Conventional tomography is to be preferred for im-

plant treatment in the partially dentate patient not

least because computed tomography delivers consid-

erably larger radiation doses (Clark et al. 1990, Ekes-

tubbe et al. 1993, Fredriksen et al. 1995). For conven

tional tomography, equipment with which multidirec-

tional tomography – hypocycloidal or spiral – can be

performed provides the best image quality due to less

disturbing ghost shadows from surrounding struc-

tures (Curry et al. 1990). When computed tomography

has to be done, because of lack of conventional to-

mographic equipment, lower doses can be achieved

through a lowering of the X-ray tube current (Ekes-

tubbe et al. 1996). If possible, so-called direct com-

puted tomography should be done instead of axial

tomography, which requires subsequent reformatting

to obtain cross-sectional images. Direct computed to-

mography, in which the scan planes are positioned as

in conventional tomography, requires a careful, indi-

vidual positioning of the patient relative to each re-

gion of interest, to obtain high quality images (Lindh

et al. 1995, Grondahl et al. 1996). In many patients this

can be difficult to achieve. In addition, the presence of

metal components within the scan plane can cause

disturbing artifacts.

Conclusion

Conventional tomography delivers lower doses than

computed tomography and is therefore to be pre-

ferred.

Multidirectional tomography provides the best im-

age quality due to a smaller amount of ghost shadows

from surrounding structures.

Lower doses in computed tomography can be

achieved by a lowering of the X-ray tube current.

In computed tomography, direct techniques pro-

vide better image quality than techniques requiring

image reformatting. However, direct techniques can

be difficult to use clinically.

The single implant case

When an implant is to be inserted between neighbor-

ing teeth, the distance between the opposing root

surfaces must be determined to make sure that the

implant does not become placed too close to either

tooth. It has been shown that marginal bone loss can

occur at the approximal bone surfaces facing the im-

plant and that this bone loss becomes more pro-

nounced, the closer to the tooth the implant is placed

(

Esposito et al. 1993, Andersson et al. 1995). Another

factor which can affect the marginal bone at adjacent

teeth is the vertical position at which the most mar-

ginal part of the implant is positioned relative to the

neighboring teeth. A long vertical distance between

the level of the marginal part of the implant and the

bone level at adjacent root surfaces is unfavorable and

the more so, the smaller the horizontal distance be-

tween the implant and the root surface. In a region

with a narrow marginal width of the alveolar bone,

and therefore a need to reduce its height to reach a

bone level of sufficient width, the eventual vertical

position of the marginal part of the implant can be best

predicted through a preceding tomographic examina-

tion (Fig. 36-12).

The most accurate estimation of the distance be-

846 • CHAPTER 36

Fig. 36-13. The most correct infor-

mation about the distance be-

tween opposing root surfaces is

obtained from an orthoradially ob-

tained radiograph relative to the

region of implant placement (a). A

mesio-oblique beam direction can

make the distance appear too

small

(b).

Fig. 36-14. If the horizontal distance between a tooth

and the incisive canal appears too small for implant

placement, tomography may reveal sufficient bone

width anterior to the incisive canal.

tween neighboring root surfaces is made from or-

thoradially obtained intraoral radiographs (Fig. 36-

13).

Panoramic radiographs can easily depict such a

distance

incorrectly and make it either too large or too small. This

is especially the case in the anterior regions

of the jaws

and depends on incorrect patient position

ing in the

panoramic machine (Grondahl et al. 1996).

In the

anterior part of the maxilla, one must also take

the

proximity of the incisive canal into account. In

cases

where the mesiodistal distance between the ca-

nal and

the intended implant site appears too small in

intraoral radiograph, tomography can be used to

determine whether sufficient amount of bone is pre-

sent

buccal to the canal (Figs. 36-14, 36-15).

Tomography within a small region surrounded by

teeth can lead to disturbing ghost shadows from the

Fig. 36-15. Intraoral radiographs (a) in which the distance between the lateral incisor and the incisive canal appears

too small for implant placement. A tomographic examination (b) reveals sufficient bone width anterior to the canal.