comparison between cephalometrics measure using …the introduction of cephalostat to the...

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Comparison between cephalometricsmeasure using anatomic and metallicporion point

Fábio Lourenço Romano1

Edvaldo Luiz Ramalli2

Stenyo Wanderley Tavares2

João Sarmento Pereira Neto3

Maria Beatriz Borges de Araújo Magnani3

Darcy Flávio Nouer3

1MS Orthodontics, Pediatric DentistryDepartment, University of Campinas,Piracicaba Dental School – Brazil; Professor,Department Restorative Prosthestic, AlfenasDental and Pharmacy School, Brazil2 DDS, MS, PHD student, Pediatric DentistryDepartment, University of Campinas,Piracicaba Dental School – Brazil3 DDS, MS, PHD, Professor, Pediatric DentistryDepartment, University of Campinas,Piracicaba Dental School – Brazil

Received for publication: March 04, 2004Accepted: May 02, 2005

Correspondence to:Fábio Lourenço RomanoAvenida do Café, 131 Bloco E- Ap. 16Vila Amélia - Ribeirão Preto – SPCEP: 14050-230E-mail:[email protected]

AbstractThe aim of this study was to compare the cephalometric measuresinvolving FMA (Frankfurt Mandibular Plane Angle), FMIA(Frankfurt Mandibular Incisor Angle), and occlusal plane angles(Frankfurt horizontal plane - occlusal plane) for cephalometric tracingby using anatomic and metallic porion points. Cephalometric tracingwas performed in thirty head lateral teleradiographs divided into twogroups. The anatomic porion point was marked in group 1, whereasmetallic porion point was marked regarding the Frankfurt horizontalPlane (FHP). All measures were analysed. The mean values for FMA(32.33o) and occlusal plane angles (10.77o) in group 2 were statisticallyhigher than those found in group 1 (FMA - 27.57o); occlusal planeangle - 6.23o). The mean value for FMIA angle (62.73o) in group 1was statistically higher when compared to group 2 (57,80°). Accordingto these results, one can conclude that cephalometric tracing of porionpoints (either anatomic or metallic) alter the values for FMA, FMIA,and occlusal plane angles, thus resulting in different treatment plans.

Key Words:orthodontics, cephalometrics, porion point, Frankfurt HorizontalPlane

Braz J Oral Sci. April/June 2005 - Vol. 4 - Number 13

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IntroductionThe introduction of Cephalostat to the radiographicprocedures in 1931 by Broadbent1 provided a standardizedmethod of accurately recording craniofacial structures andrelationships in living individuals. Lateral cephalometricradiography has become widely used in orthodontics as animportant descriptive, analytic and diagnostic technique2-4.Many references on radiographic cephalomtry have beenproposed and used. Some were derived from earliercraniometric studies, while others were introduced with thedevelopment of radiographic cephalometry5-6.One of thesecontributions from the craniometric studies was done byVon Ihering, in 1872, who idealized a horizontal plane whichwas selected as being the universal reference plane duringthe Frankfurt Congress of Anthropology held in 1884. Sucha horizontal plane is a tracing from the superior part of theexternal auditory meatus (anatomic porion point) to theinferior rim of the left orbital cavity (orbital point), thus beingnamed as Frankfurt Horizontal Plane (FHP). This plane isconsidered, even today, as a basic plane in certaincephalometric analysis7-10.Tweed10, in 1953, presented a diagnostic facial triangle basedon Frankfurt horizontal plane, which is composed, by theFMA (Frankfurt Mandibular Plane Angle), FMIA (FrankfurtMandibular Incisor Angle) and IMPA (Incisor MandibularPlane Angle) angles. The FMA angle formed by FHP andmandibular plane (Go - Me) has a mean value of 24.57o, theFMIA angle formed by FHP and the long axis of the inferiorincisor has a mean value of 68.20o, and the IMPA angle formedby the mandibular plane and the long axis of the inferiorincisor with mean value of 86.93o.The anatomic porion point is localized at the uppermostexternal auditory meatus, thus making difficult its lateralteleradiographic visualization. Such a difficult location is dueto the following: density of the petrous temporal bone,projection juxtaposition of the corresponding left and rightpyramids, and kilovoltage employed, which rarely allowsatisfactory visualization of such a region11-12.However, its marking should be performed despite the badvisibility since the porion may not be directly visible and asa result, it must be anatomically interpreted, that is, positionedbetween 8 and 10 mm at oblique plane of 45o, passing throughits inferior homologue13.Because of the frequent identification mistakes, whichconsequently affect the marking, the use of metallic porionpoint was conventionally adopted in order to replace theanatomic porion point. The metallic porion point is locatedat 4.5 mm above the centre of the cephalostatic radiopaqueimage of the auricular olives12,14.While most orthodontists use the anatomic porion point,others use the metallic porion for tracing the FrankfurtHorizontal Plane without worrying about the differences,which may exist involving some cephalometric measures. In

the face of the lack of standardization and the scarce literatureconcerning this subject, the aim of this work was to comparethe FHP marking based on both anatomic and metallic porionpoint by verifying the degree of variability involving FMA,FMIA, and occlusal plane angles.

Material and MethodsThis study was performed by using thirty head lateralteleradiographs selected from the Scientific DocumentationSector of the Faculty of Dentistry of Piracicaba, UNICAMP.All x-ray examinations were taken by the same professional,with the same equipment, at a distance of 1.50 m from thepatient’s face (Rotograph Plus, Villa Sistem Medical, Italy) inorder to assure the pattern and the reliability of theradiographic takings. The teleradiographs were obtained fromBrazilian leucodermic boys and girls aged between 10 and 15years who have never been submitted to orthodontictreatment before.Inside the dark room, the cephalograms were traced by oneresearcher only. The marking procedure involves thefollowing materials: negatoscope with ultraphan paper ofpersonalized size (17.5 cm x 17.5 cm and 0.07 in thickness),propelling pencil (0.3 mm lead), 0.5 mm-subdividedtransparent rule, 0.1 degree protractor, template, and adhesivetape. The standard cephalograms were traced and the anatomicstructures involving skull and face as well as the planes andlines of orientation were also delineated. The FrankfurtHorizontal Plane was used in this work as reference plane,being integral part of all the cephalometric measurements.This plane is located in the base of the cranium, beingconstituted by the porion point (anatomical or metallic) andthe orbital point. The anatomical porion point (Figure 1) islocated in the superior and posterior portions of the externalauditory meatus. The metallic porion point (Figure 2) islocated at 4.5 mm from the centre of the cefalostat’s metallicolive and the orbital point in the most inferior and posteriorareas of the orbit. The angle measurements were performedfor all cephalograms obtained from lateral cephalometricradiographs according to the both situations proposed:Group 1- The teleradiographs were delineated as previousdescription by using the anatomic porion point for FrankfurtHorizontal Plane (FHP) tracing;Group 2- The teleradiographs were delineated as previousdescription by using the metallic porion point for FrankfurtHorizontal Plane (FHP) tracing.The cephalometric measures were compared between bothgroups (Figure 3):FMA (Frankfurt Mandibular Plane Angle)- Angle formedby FHP and mandibular plane (goniometrical points).FMIA (Frankfurt Mandibular Incisor Angle)- Angle formedby FHP and the long axis of the inferior incisor.Occlusal Plane Angle (Downs, 1948)- Angle formed by FHP

Braz J Oral Sci. 4(13):730-734 Comparison between cephalometrics measure using anatomic and metallic porion point

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Fig. 1 - External acoustic meatus with demarcation of the anatomicalporion point.

Fig. 2 - Metallic olive of the cefalostato with demarcation of themetallic porion point.

and Downs’ occlusal plane (intercuspidation of molars andincisors).

Error AnalisysWith the purpose of evaluating the magnitude of the tracingerror, all the thirty x-rays were traced three times at minimuminterval of 10 days for each procedure so as the anatomicalstructures could not be memorized. Next, the mean arithmeticvalues of the three planes for each measurements werecalculated according to the methodology proposed byMitgard et al.15.

Statistic TreatmentThe measures for FMA angle were considered non-normalaccording to the statistical analysis of the results by usingMann-Whitney’s test.The angles formed by FMIA and occlusal plane angles wereconsidered normal according to the statistical evaluation ofthe data by using Student’s t test.The cephalometric measures of group 1 were compared totheir homologues of group 2.

Results and DiscussionThe mean values for FMA angle are shown in Table 1, wherestatistically significant values at 1% (P<0,01) was found forthe group using metallic porion marking.Statistically significant difference in the marking was alsofound between the groups according to the analysis of FMIAangle (P<0,05), thus revealing higher values for the anatomicporion group in relation to the metallic porion group (Table 1).Statistically significant difference between the samples wasobserved by the mean values for occlusal plane angle(P<0,01), where the mean value for metallic porion marking ishigher than that for anatomic porion marking (Table 1).

Fig. 3 - Cephalometric measurement evaluation.


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The radiographic cephalometrics is very useful fororthodontics, sometimes guiding both diagnoses andorthodontic treatment plan. Despite the great number ofcephalometric analysis with their respective angles andvalues, certain cephalometric landmarks are marked in astandardized way. The anatomic porion point may not be easily visualized onmany teleradiographs because of its location at the uppermostportion of the external auditory meatus. Such a difficulty isdue to the density of the petrous temporal bone in additionto the projection juxtaposition of the corresponding rightand left pyramids as well as the kilovoltage employed11.However, regardless of the lower visibility, if the porion isnot directly visible it must be anatomically interpreted, thatis, the porion is located at 8-10 mm with oblique plane of 45o,passing through their inferior homologue13.The Frankfurt horizontal plane (FHP) is reference for a greatnumber of cephalometric measures. This plane is traced byjoining both porion and orbital points, which along with otherlines or planes, result in angles guiding the treatment planduring the analysis.The uppermost portion of the external auditory meatus isthe correct place for marking the porion point, but in the faceof the difficulty mentioned above, many practitioners havebeen using the metallic porion point located at 4.5 mm fromthe centre of the cephalostatic image of the auricular olive12.Such a difference in the marking (anatomic or metallic porion)causes difficulties for standardizing and evaluating theresults. Consequently, the way patient is treated may besignificantly altered, mainly when the Tweed’s diagnosticfacial triangle is used10.Statistically significant differences were found in this studywhen the values of cephalometric measures for FMA, FMIAand occlusal plane angles were compared in terms of anatomicor metallic porion point.The FMA angle indicating the facial type of the patient,according to Tweed10, had a mean value of 32.33o in thetracings using the metallic porion point, whereas those usingthe anatomic porion point had mean value of 27.57o. Such a

Method

Measures Anatomic porion Metallic porion Significance (P) Mean SD Mean SD

FMA 27.57o 6.22 32.33o 5.62 1%

FMIA 62.73o 7.71 57.80o 8,02 5%

OPA 6.23o 6,54 10.77o 3.92 1%

Note: OPA = Occlusion plane angleFMA= Frankfurt Mandibular Plane AngleFMIA= Frankfurt Mandibular Plane AngleSD= Standard Deviation

Table 1 - Mean values and standard deviation (SD) for FMA, FMIA, and occlusal plane angles.

difference of 4.76o was statistically significant and revealedfacial patterns completely different. If we consider the patient,the value found in group 2 (metallic porion point) suggestsa highly vertical pattern, whereas the value in group 1(anatomic porion point) is nearly normal, thus characterizingthe mesofacial aspect according to Tweed’s value (25o).Also, it was found that the mean values for FMIA anglewere different. In the anatomic porion the mean value was62.73o, whereas in the metallic porion group the mean valuewas 57.80o, thus characterizing the statistically significantdifference between both groups. As this angle indicates thelocation of inferior incisor in relation to the Frankfurthorizontal plane, the first group shows the closest positionto that predicted by the author (68o), whereas the secondgroup shows a highly vestibular inclination of the incisor inrelation to the reference plane.The occlusal plane angle corroborates the occlusal planeinclination (intercuspidation of molars and incisors) inrelation to FHP, whose mean value is 10o. Concerning thecephalometric tracings, a statistically significant differencewas found between the groups since the mean values for theanatomic and metallic porion tracings were, respectively, 6.23o

and 10.77 o. The latter group has values closer to thenormality, whereas the former indicates a low inclination ofthe occlusal plane.By analysing the cephalometric measures in order to describethe patient characteristics, the anatomic porion groupshowed mean values for FMA (27.56o), FMIA (62.73o), andFHP (6.23o), thus suggesting a vertical bias for facial pattern,close to normality, with labial inclination of the inferior incisorin relation to FHP and little inclination of the occlusal plane.In the metallic porion group, there was a highly verticalpattern (FMA -32.33o) with highly labial inclination of theinferior incisors in relation to FHP (FMIA - 57.80o), and properinclination of the occlusal plane (occlusal plane angle - 0.77o).In the face of this measures, we would have distinct treatmentplans for both groups because of the porion point variation.According to the analysis of the data and the results obtainedwe can conclude the following:


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1 - The marking using cephalometric tracings (eitheranatomic or metallic porion point) alters the values forFMA, FMIA, and occlusal plane angles;

2 - Alteration of some cephalometric measures throughvariation of the porion point marking may lead tocompletely different therapeutic treatment of the patient;

3 - To obtain cephalometric measures for analysis andcomparison the porion marking should be standardized,regardless of being anatomic or metallic.

References1. Broadbent HB. A new x-ray technique and its application to

orthodontia. Angle Orthod 1931; 4: 45-66.2. Bjerin RA. A comparison between the Frankfort Horizontal and

the sella turcica nasion as reference planes in cephalometricanalysis. Acta Odontol Scand 1957; 15: 1-12.

3. Koski K. Some effects of the Growth of the cranial base and theupper face. Odont Tidski 1960; 68: 344-58.

4. Tng TT, Chan TC, Cooke MS, Hagg U. Effect of head postureon cephalometric sagittal angular measures: Am J Orthod 1993;104: 337-41.

5. Nanda SK, Sassouni V. Planes of reference in roentgenographiccephalometry. Angle Orthod 1965; 35: 311-9.

6. Wei SHY The variability of roentgenographic cephalometriclines of reference. Angle Orthod 1968; 38: 74-8.

7. Wyllie WL. The assessment of anteroposterior dysplasia. AngleOrthod 1947; 17: 97-109.

8. Downs WB. Variations in facial relationship: their significancein treatment and prognosis. Am J Orthod 1948; 4: 812-40.

9. Tweed CH. The Frankfort-mandibular plane angle in orthodonticdiagnosis, classification, treatment planning and prognosis. AmJ Orthod Oral Surg 1946; 34: 175-230.

10. Tweed C. H. Evolutionary trends in orthodontics – past, presentand future. Am J Orthod 1953; 39: 81-108.

11. Lima RS. Localização anatômica do forame auditivo externoem telerradiografias. Ortodontia 1981; 14: 97-100.

12. Vilela OV. Manual de cefalometria. Rio de Janeiro: GuanabaraKoogan; 1998.

13. Vion PE. Anatomia cefalométrica. 2thed. São Paulo: Santos; 2002.14. Pereira CB, Mundstock CA, Berthold TB. Introdução à

cefalometria radiográfica. 2thed. São Paulo: Pancast; 1989.15. Mitgard, J, Björk G, Linder-Aronson S. Reproducibility of

cephalometric landmarks and errors of measurements ofcephalometric cranial distances. Angle Orthod 1974; 44: 56-61.


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