Introduction

An impacted tooth is one ‘whose eruption isconsiderably delayed, and for which there isclinical or radiographic evidence that furthereruption may not take place’ (Thilander andJakobsson, 1968). Maxillary canines are the mostfrequently impacted teeth after the third molarswith a prevalence ranging from 0.92 per cent(Dachi and Howell, 1961) to 2.56 per cent(McKay, 1978), depending on the populationexamined.

The diagnosis of an impacted maxillary canineis based on both clinical and radiographicexamination. The following clinical signs may beindicative of canine impaction:

(1) delayed eruption of the permanent canine orprolonged retention of the primary canine(Thilander and Jakobsson, 1968);

(2) absence of a normal labial canine bulge orpresence of a palatal bulge in the canineregion;

(3) delayed eruption, distal tipping, or migrationof the permanent lateral incisor;

(4) loss of vitality and increased mobility of thepermanent incisors (Kettle, 1958).

Many radiographic methods have been proposed.Two have special interest since they utilize theradiographs that are most commonly taken inorthodontic assessment.

Parallax

This was first introduced by Clark (1909). Itinvolves two radiographs taken at differenthorizontal angles with the same verticalangulation. Due to parallax, the more distant

European Journal of Orthodontics 23 (2001) 25–34 2001 European Orthodontic Society

The radiographic localization of impacted maxillary

canines: a comparison of methods

Carol Mason, Petrina Papadakou and Graham J. Roberts Department of Paediatric Dentistry, Eastman Dental Institute for Oral Health Care Sciences,University of London, UK

SUMMARY This study compared two different radiographic techniques for localization ofimpacted maxillary canines: vertical parallax (from a panoramic and a maxillary anteriorocclusal radiograph) and magnification (from a single panoramic radiograph). The radio-graphs and the information regarding the impacted canines were obtained retrospectivelyfrom records of patients treated in the Day Stay Unit of the Eastman Dental Hospital. The twodifferent radiographic techniques were tested blind and compared for localization of theimpacted canine by six examiners. The ‘gold standard’ used for the radiographic comparisonswas the true position of the canine as recorded at operation.

The results showed a wide variation between the six examiners in the prediction of thecanine position with the two different techniques. Localization with vertical parallax wasmore successful overall than with magnification, although the difference failed to reachsignificance. Seventy-six per cent of the impacted canines could be successfully locatedwith vertical parallax and 66 per cent with magnification. Further analysis showed that,while almost 90 per cent of the palatally impacted canines could be correctly detected withboth techniques, less than half of the buccal canines could be detected with parallax andonly one in 10 buccal canines could be detected with magnification. If a canine is suspectedto be buccally placed from its appearance on a panoramic film and cannot be palpated,further views are justified.

object appears to travel in the same direction asthe tube shift and the object closer to the tubeappears to move in the opposite direction [the socalled Same Lingual Opposite Buccal (SLOB)rule; this could equally be remembered as BuccalOpposite Palatal Same (BOPS)]. The parallaxtechnique may also be applied when the radio-graphs are taken at a different vertical angulations(vertical parallax). Various combinations havebeen used based on the technique of parallax:

(1) two intra-oral periapical radiographs takenat different horizontal angles (Clark, 1909).

(2) one maxillary anterior occlusal and onemaxillary lateral occlusal (Southall andGravely, 1989).

(3) one periapical and one maxillary anteriorocclusal radiograph (vertical parallax; Rayne,1969).

(4) one panoramic and one maxillary anteriorocclusal radiograph (vertical parallax; Keur,1986).

Although the tube for the panoramic radiographis actually positioned behind the patient’s headwith a vertical angle of –7 degrees, in order toexplain the shift technique it may be consideredto be in front of the head at an angle of +7degrees. Since the maxillary occlusal is taken at avertical angle in the range of 60–65 degrees,there is an effective difference ranging from53–58 degrees between the two films as shown in Figure 1 (Jacobs, 1994).

(5) one panoramic radiograph alone when aPanorex machine is used (Turk andKatzenell, 1970).

Magnification

This technique is based on the principle of ‘imagesize distortion’; that is for a given ‘focal spot’–film distance, objects further away from the imagereceptor (film) will be depicted more magnifiedthan objects closer to the film (Figure 2; Goazand White, 1982). Two methods can be used withthis technique.

Status-x radiography (Ostrofsky, 1976). Thisinvolves a special tube inserted in the patient’smouth and a film held around the face by thepatient. The hollow anode provides nearly apoint source of radiation and, therefore, the lawsof central projection apply—the object closer tothe source is magnified.

Panoramic radiography (Wolf and Matilla, 1979;Fox et al., 1995). The principle of image dis-tortion can be applied in panoramic radiography.If a canine is relatively magnified in comparisonto the adjacent teeth in the arch or the contra-lateral canine, it will be located closer to the tube,i.e. palatally, and if it is relatively diminished itwill be located further away from the tube, i.e.labially. This method is most effective when thecanine is not rotated, not in contact with theincisor root and the latter is not tipped

Other methods reported in the radiographiclocalization of the impacted canine are the vertexocclusal radiograph (Hitchin, 1951), imagesharpness, and relationship of the canine cusp tipwith the lateral incisor root in the panoramicradiograph. The ‘right angle’ technique involvestwo films taken at right angles to each other sothat the canine can be located in three dimensions,e.g. lateral skull and postero-anterior cephalo-gram (Broadway and Gould, 1960), or lateralskull and panoramic radiograph (Coupland,1987). Tomography, e.g. polytomography (Ericsonand Kurol, 1987), and computer tomography(Ericson and Kurol, 1988) are especially useful incases of root resorption of the adjacent teeth.

26 C. MASON ET AL.

Figure 1 Vertical angulation between the orthopantomo-gram and the maxillary anterior occlusal.

Radiographic localization of the impactedcanine is very important, especially if surgicaltreatment is to be undertaken. For many cases,radiography is the only means of accuratelydetermining the position of the unerupted canine.The fact that so many radiographic localizationtechniques exist shows that none of them is ideal.A study on the radiographic prescribing habits oforthodontists and oral surgeons showed that 78 per cent used more than two radiographs and23 per cent used four or more (Southall andGravely, 1987). It may be possible that cliniciansuse the technique with which they are mostfamiliar at the cost of an increased dose ofradiation to the patient (Southall and Gravely,1987). An increase in the level of dental radio-graphy by a factor of six between 1957 and 1977has been reported (Kendall et al., 1981).

Clinicians should be encouraged to evaluatethe radiographic methods currently in use interms of the dose levels to which the patients

are exposed. If it can be shown that a singleradiographic technique provides the sameinformation as other techniques that require ahigher radiation exposure, the justification forthe use of those with higher exposure must bequestioned (Southall and Gravely, 1987).

The panoramic radiograph is widely used ingeneral practice and is the first choice radiographfor orthodontic patients (Southall and Gravely,1987). Use of the maximum amount ofinformation that can be obtained from such a radiograph would help reduce unnecessaryradiation exposure to patients.

The current study was undertaken in order toassess the validity of two different radiographictechniques in the localization of the impactedcanine: vertical parallax (from a panoramic and anterior maxillary occlusal radiograph) andmagnification (from a single panoramic radio-graph). The null hypothesis tested was that therewas no difference between the two techniques.

RADIOGRAPHIC LOCALIZATION OF CANINES 27

Figure 2 Increasing the distance between the object and the film increases themagnification.

Materials and methods

The study consisted of a retrospective analysis ofthe records of 100 patients who had undergonesurgical treatment of unerupted canines in the DayStay Unit of the Eastman Dental Institute, London.

The following criteria were used in order toselect the sample:

1. For every patient included there should beone panoramic and one maxillary anteriorocclusal radiograph of acceptable diagnosticquality (e.g. no distortions on the panoramicfilm due to incorrect patient positioning).

2. If a patient had gross distortion of the dentalarches due to a cleft palate they wereexcluded.

3. Ideally, the radiographs should have been takenon the same day, shortly before the operation.If the two radiographs were taken more than6 months apart or active orthodontic treatmenthad taken place between the two radiographicexaminations, the patient was excluded.

4. A surgical diagnosis of the position of theimpacted canine should be clearly stated inthe operation records otherwise the patientwas excluded.

Radiographic examinations

The estimated position of the canines with the twodifferent radiographic techniques was recordedfor six examiners: a consultant maxillofacialsurgeon (A), a consultant orthodontist (B), aconsultant in paediatric dentistry (C), a juniormember of staff (senior house officer) (D), andtwo MSc postgraduate students (E and F). Onepostgraduate (the person responsible for thestudy) assessed the whole sample, whilst the restexamined a sub-sample of 40 patients. The exam-inations were standardized: the radiographswere studied on the same conventional X-rayilluminator (Kodak Coldlight Illuminator series 2,Ostsiodern Scharnhausen, Germany). Black cardtemplates were used in order to eliminate theperipheral light from the X-ray viewer and thenames, hospital numbers, and dates of birth onthe radiographs were hidden. All radiographswere taken at the Department of Radiography,

Eastman Dental Hospital. The maxillary anteriorocclusal radiographs were taken using a PhilipsX-ray machine (50–65 KV and 7.5 mA; PhilipsMedical Systems, London UK) using an intra-oralfilm (Kodak E-speed Plus). The panoramic radio-graphs were taken by either Planmeca 2002CC-Proline (66 KV and 8 mA; Planmeca, Helsinki,Finland) or Siemens Orthopantomograph 5 (65–70KV and 15 mA; Siemens AG, Munich, Germany)using an extra-oral film AGFA HT-U (greensensitive; AGFA-Gaevert, Antwerp, Belgium).

Each of the examiners examined theradiographs on two separate occasions using the two different techniques. The familiarity ofeach examiner with the techniques was obtainedwith a questionnaire, since this could be helpfulin explaining differences in accuracy between thetwo techniques. At the first examination, thecanines were localized with vertical parallaxfrom the panoramic and the anterior occlusalradiographs. An example is given in Figure 3a,b:the impacted right maxillary canine has movedupwards (‘with the tube’) from the orthopanto-mogram to the anterior occlusal radiograph andtherefore is localized palatally. At the secondexamination (1 month later), the localization of the same canines was undertaken with themagnification method by the panoramic radio-graphs only. For example, in the previous ortho-pantomogram (Figure 3a), the impacted canine ishorizontally magnified with comparison to thecontralateral erupted canine and is thereforelocalized palatally. The following guidelines were given prior to the examination if theexaminers were unfamiliar with the magnifica-tion technique (Fox et al., 1995).

The impacted canine will be classified as:

(A) Buccal: Where relative diminution of thecrown has occurred in the hori-zontal plane, compared withadjacent teeth lying in the arch.

(B) In the arch: Where the canine has the samedegree of horizontal magnifica-tion as adjacent erupted teeth.

(C) Palatal: Where relative magnification of the crown has occurred in thehorizontal plane compared withadjacent teeth lying in the arch.

28 C. MASON ET AL.

In case of unilateral impaction the comparisonsshould be carried out with the contralateralnormally occluded canine.

Each examination was blind, i.e. the examinersdid not know the surgical outcome.

Reproducibility studies

One week after each examination a randomlypre-selected sub-sample was re-examined in orderto assess intra-examiner variation. This samplewas selected from random number tables, andconsisted of 40 patients for the whole sample and16 patients for the smaller sample of 40 patients(40 per cent).

Statistical analysis

The predicted positions of the impacted caninesfrom each radiographic technique were comparedwith the actual positions found during surgery.The overall percentages of correct diagnosis foreach technique were compared with a SND testof statistical significance. The purpose was todetermine the extent to which the two methodsdiffered. A Cohen’s Kappa statistic was also used in order to compare agreement of eachtechnique with the true position of the canine.

Validity of diagnosis (i.e. correct diagnosis) witheither the magnification or parallax techniquewas expressed as sensitivity for the palatally and

RADIOGRAPHIC LOCALIZATION OF CANINES 29

Figure 3 (a) Orthopantomogram showing an impacted right maxillary canine. (b) Maxillary anteriorocclusal radiograph of the same patient as 3(a).

buccally located canines. Sensitivity for thepalatally located canine is the probability that apalatally placed canine will be correctly detectedwith the specific technique.

The above statistical analysis was carried outconsidering each patient as a single unit and only one canine from each patient was analysed.Therefore, in the case of bilaterally impactedcanines the right or the left canine was randomlychosen for analysis. This was undertaken inorder to eliminate possible bias from a statisticalanalysis of variables that were not completelyindependent, i.e. two impacted canines thatbelong to the same patient.

Intra-examiner reproducibility for eachtechnique was also tested with a Cohen’s Kappastatistic.

Results

The records of 100 patients (71 females, 29males) with a total of 133 impacted maxillarycanines were used for the study. Thirty-threepatients had bilaterally impacted canines. Ofthe 133 canines, 87 (65 per cent) were locatedpalatally, 38 (28 per cent) buccally, and eight (6 per cent) in the line of the arch.

Comparisons between true position andpredicted position from the radiographicexaminations

The results from the radiographic examinationswith the two different techniques were comparedwith the surgical results by a Cohen’s Kappastatistic. The Kappa statistic, between true canine

position and predicted position with parallax,had a range of 0.13 to 0.46 for the six differentexaminers. Similarly, the Kappa statistic betweentrue position and predicted position withmagnification had a lower range of 0.06 to 0.26for the same examiners (Figure 4).

With regard to the surgery, the ‘buccal’ and ‘in the line of the arch’ positions required abuccal flap (for surgical exposure or extractionof the impacted canine). The two positions weretherefore combined and new Kappa values werecalculated. This resulted in higher Kappa valuesfor most of the examiners for both parallax andmagnification (Table 1).

Comparisons between parallax and magnification

From the previously calculated Kappa values, a difference between the parallax and themagnification method was evident. Comparingthe percentages of agreement with the twomethods for examiner F, derived from Tables 2

30 C. MASON ET AL.

Figure 4 Kappa statistic between true position andposition predicted by parallax and magnification for the sixexaminers.

Table 1 Kappa values before and after ‘buccal’ and ‘in the arch’ positions were combined for parallax andmagnification (all examiners).

Examiner code Parallax Parallax Magnification MagnificationNormal Kappa Kappa when Normal Kappa Kappa when

buccal = arch buccal = arch

A 0.29 0.41 0.10 0.24B 0.17 0.48 0.17 0.30C 0.46 0.51 0.26 0.31D 0.25 0.32 0.06 0.07E 0.13 0.33 0.13 0.08F 0.45 0.50 0.20 0.29

and 3, the SND statistical test had a P value 0.05 < P < 0.1 and the confidence interval of thetrue difference between the two methods rangedfrom 0.016 to 20 per cent.

Sensitivity for the palatally or buccally locatedcanine

The sensitivity of both parallax and mag-nification in the detection of the palatally or

buccally located canine for examiner F, is shownin Figure 5. Both methods were less sensitive in detecting the buccal canine, especially themagnification.

Reproducibility studies

Intra-examiner reproducibility was assessed with a Kappa statistic for both parallax andmagnification, for each examiner (Table 4).

Table 5 shows the familiarity of each examinerwith the parallax technique in comparison withtheir Kappa scores. This could not be carried outfor magnification since none of the examinerswas familiar with the technique.

Discussion

The sample for the study consisted of patientswho had undergone surgery under generalanaesthesia for an impacted canine and for whoma panoramic and an upper anterior occlusalradiograph had been taken. Most of the patientshad been referred by the Department ofOrthodontics at the hospital where the tworadiographs are routinely taken for each patientwith an impacted canine.

The correct diagnosis of the impacted canineposition with the vertical parallax varied quitemarkedly between the six examiners. The bestKappa score was achieved by the consultant inpaediatric dentistry (0.46) and the worst by oneMSc student (0.13). Even for the highest scores

RADIOGRAPHIC LOCALIZATION OF CANINES 31

Table 2 A comparison between true canine positionand position predicted by parallax for examiner F.

Position predicted by parallax

Arch Palatal Buccal Total

True Arch 2 2 1 5Position Palatal 3 62 4 69

Buccal 3 11 12 26Total 8 75 17 100

Table 3 A comparison between true canineposition and position predicted by magnification forexaminer F.

Position predicted by magnification

Arch Palatal Buccal Total

True Arch 1 4 0 5Position Palatal 6 62 2 70

Buccal 7 15 3 25Total 14 81 5 100

Figure 5 Sensitivity for the palatal and buccal canine forboth parallax and magnification for examiner F.

Table 4 Kappa values from the parallax andmagnification reproducibility studies, for eachexaminer.

Examiner code Kappa value Kappa value withwith parallax magnification

A 0.35 0.81B 0.67 0.52C 0.55 0.91D 0.30 0.82E 0.49 0.33F 0.63 0.76

the agreement was only ‘moderate’ and, therefore,not entirely satisfactory.

These results are not in agreement with astudy comparing vertical parallax with threeother radiographic techniques (Southall andGravely, 1989). In that study, although the Kappastatistic was not calculated, the percentage ofagreement with the true position was 87 per cent.In the current study, the agreement was 76 percent for examiner F. It should be noted thatcomparisons between the two studies are notappropriate, since one was a laboratory studywhere a series of radiographs of a dried skullwith a radio-opaque marker placed in differentpositions, were tested.

The large variation in the Kappa scoresbetween the six examiners could not beexplained from the familiarity with the verticalparallax technique. The examiners with the bestscores only used the technique ‘sometimes’, andthe examiner who used the technique ‘routinely’had the second worse score. This examiner was theconsultant orthodontist who, although diagnosingthe impacted canine, was not performing thesurgery. Nevertheless, when the ‘buccal’ and‘arch’ positions were combined, the same exam-iner scored very high. This indicates that he wasdiagnosing many of the buccally positionedcanines to be ‘in the line of the arch’ and viceversa. The combination of ‘buccal’ and ‘arch’positions improved the Kappa scores of allexaminers, but the agreement was still only‘moderate’.

It should be noted from the above that noconclusions can be extrapolated for the differentdental specialties, since the differences may be

due to individual variation, and not necessarilyto differences in training and experience.

The correct diagnosis with the magnificationmethod also varied between the six examinersand was less accurate than the diagnosis withvertical parallax for most of the examiners. Theexaminer with the best Kappa score was againthe consultant in paediatric dentistry (0.31), andthe worst score was the senior house officer (0.06).For two examiners (the consultant maxillofacialsurgeon and one MSc student), the Kappa scoreswere similar for parallax and magnification.Even for the highest scores the agreement was only ‘fair’ and therefore not satisfactory. The combination of the ‘buccal’ and ‘arch’position resulted in higher Kappa scores for themagnification for almost all examiners, but theagreement was still only ‘fair’.

In comparison with two previous investigations,the magnification method was less successful. In an earlier study (Wolf and Matilla, 1979) thepercentage of agreement was 88 per cent for thefirst and 89 per cent for the second examiner. In the present study, the agreement with themagnification method for examiner F was only66 per cent. However, the ‘gold standard’ for the previous study was another radiographictechnique (similar to the horizontal parallax)and not the true position of the canine, which, inthis study, was confirmed at operation. Variationsin the sample could also explain differences inagreement; the above study had comparativelymore palatally impacted canines for which themagnification has a high sensitivity (89 per centin the current study). In a later study (Fox et al.,1995) the percentage of agreement was 76 percent with a Kappa of 0.52, while in the currentinvestigation the results were 66 per cent and 0.2, respectively, for examiner F. Again, the ‘goldstandard’ in the later study was a ‘vertex occlusal’,which ‘have been shown to be unreliable undercertain circumstances’ (Southall and Gravely,1987). In addition, in both of the previous studieseach impacted canine was considered as a unitwith the possibility of introducing bias.

Although the Kappa statistic shows that themagnification method is less accurate thanvertical parallax, the difference in agreement did not reach a significant level of P < 0.05.

32 C. MASON ET AL.

Table 5 Relationship between clinical experienceand Kappa values for parallax for each examiner.

Examiner code Clinical Kappa experience value

A Never 0.29B Always 0.17C Sometimes 0.46D Sometimes 0.25E Often 0.13F Never 0.45

Therefore, to subject a patient to higher radiationexposure (with the inclusion of the anteriorocclusal radiograph) may not be justified in thecase of a palatally impacted canine, for which thesensitivity is the same with both techniques (89per cent).

In the study by Fox et al. (1995), the sensitivityin the detection of the palatal canine withmagnification was also high (82 per cent), whilethat for the buccal canine was lower (65 percent). In the current study, the sensitivity for thebuccal canine was very low (11 per cent).

Reproducibility studies

For the majority of the examiners, intra-examinerconsistency was greater with magnification than with parallax. This was not expected sincemagnification is considered to be more subject-ive than parallax, but the fact that the method iseasier and simpler may have contributed to ahigh reproducibility. The senior house officerachieved the highest Kappa score for magnification(0.82) and the consultant orthodontist thehighest score for parallax (0.67). In the study by Fox et al. (1995), the reproducibility score for magnification was similarly high (0.86). The reproducibility scores for parallax are notsatisfactory overall and, although the method ismore successful in predicting the true position ofthe canine, it is far from ideal.

The results are not directly related to thediagnostic ability of the examiners; the overalldiagnosis of an impacted canine is also based onclinical observations (i.e. intra-oral observationand palpation). It is encouraging that the buccallyimpacted canine, which is less successfullydetected with the two methods, can often bepalpated in the labial sulcus.

Conclusions

The following conclusions can be derived fromthis study:

1 Localization of an impacted canine withvertical parallax was more successful than withmagnification, although the difference was notsignificant (P > 0.05).

2 There was a wide variation in agreementbetween true and predicted position from bothparallax and magnification between differentexaminers and dental specialities, not neces-sarily related to familiarity with the method.

3 Seventy-six per cent of the impacted caninescould be successfully located with verticalparallax and 66 per cent with magnification.According to Kappa statistic the predictionwith parallax can only be classified ‘moderate’and with magnification ‘fair’.

4 Almost 90 per cent of the palatally impactedcanines could be correctly detected withparallax and magnification, but only 46 per centof the buccal canines with parallax and 11 percent with magnification. Therefore, magnifi-cation is only suitable for the detection ofpalatally impacted canines. If the canine isplaced buccally and cannot be palpated, anupper anterior occlusal view is necessary. Sinceboth techniques are unsatisfactory in thelocalization of a buccal canine, additional viewsmay be justified when a buccally impactedcanine is suspected and cannot be palpated.

Address for correspondence

Miss C. MasonEastman Dental Institute for Oral Health CareSciencesUniversity of London256 Gray’s Inn RoadLondon WC1X 8LD, UK

Acknowledgements

We would like to thank all the consultants, the senior house officer and the MSc studentwho carried out the radiographic examinations.Without their help this study could not havebeen completed. We would also like to thank the staff in the Day Stay Unit, the Departmentsof Radiography and Medical Records for theirco-operation.

References

Broadway R T, Gould D G 1960 Surgical requirements ofthe orthodontist. British Dental Journal 108: 1187–1190

RADIOGRAPHIC LOCALIZATION OF CANINES 33

Clark C 1909 A method of ascertaining the position ofunerupted teeth by means of film radiographs. Proceedingsof the Royal Society of Medicine 3: 87–90

Coupland M A 1987 Localization of misplaced maxillarycanines: orthopantomograph and PA skull views compared.American Journal of Orthodontics and DentofacialOrthopedics 91: 483–492

Dachi S F, Howell F V 1961 A survey of 3,874 routine full-mouth radiographs. II. A study of impacted teeth.Oral Surgery, Oral Medicine, Oral Pathology 14: 1165–1169

Ericson S, Kurol J 1987 Radiographic examination ofectopically erupting maxillary canines. American Journalof Orthodontics and Dentofacial Orthopedics 91: 483–492

Ericson S, Kurol J 1988 CT diagnosis of ectopically eruptingmaxillary canines—a case report. European Journal ofOrthodontics 10: 115–120

Fox N A, Fletcher G A, Horner K 1995 Localizingmaxillary canines using dental panoramic tomography.British Dental Journal 179: 416–420

Goaz B W, White S C 1982 Oral radiology—principles andinterpretation, 2nd edn. Mosby Co., St Louis

Hitchin A D 1951 The impacted maxillary canine. DentalPractitioner 2: 100–103

Jacobs S G 1994 Localization of the unerupted maxillarycanine: additional observations. Australian OrthodonticJournal 13: 71–75

Kendall G M, Darby S C, Rae S 1981 The level of dentalradiography in Great Britain. British Dental Journal 151: 377–379

Kettle M A 1958 Treatment of the unerupted maxillarycanine. Dental Practitioner and Dental Record 8:245–255

Keur J J 1986 Radiographic localization techniques.Australian Dental Journal 31: 86–90

McKay C 1978 The unerupted maxillary canine—anassessment of the role of surgery in 2500 treated cases.British Dental Journal 145: 207–210

Ostrofsky M K 1976 Localization of impacted canines withstatus-x radiography. Oral Surgery, Oral Medicine, OralPathology 42: 529–533

Rayne J 1969 The unerupted maxillary canine. DentalPractitioner 19: 194–204

Southall P J, Gravely J F 1987 Radiographic localization of unerupted teeth in the anterior part of the maxilla: a survey of methods currently employed. British Journalof Orthodontics 14: 235–242

Southall P J, Gravely J F 1989 Vertical parallax radiology tolocalize an object in the anterior part of the maxilla.British Journal of Orthodontics 16: 79–83

Thilander B, Jakobsson S O 1968 Local factors in impactionof maxillary canines. Acta Odontologica Scandinavica 26: 145–168

Turk M H, Katzenell J 1970 Panoramic localization. OralSurgery, Oral Medicine, Oral Pathology 29: 212–215

Wolf J E, Mattila K 1979 Localization of impacted maxillarycanines by panoramic tomography. DentomaxillofacialRadiology 8: 85–91

34 C. MASON ET AL.