Lower incisor position in relationship to A-Pog line, in Mexicans with ideal occlusion. Toshio Kubodera Ito, DDS, Ph.D. Chrisel Zárate Díaz DDS, MS. Ricardo Medellin Fuentes DDS, MS. Tolúca, México.

The purpose of this study was to evaluate the protrusion of the lower arch,

measuring the anteroposterior position of the lower incisor, relative to the A-Pog

Line, in a group of 192 Mexican patients with ideal occlusion. The material was a

lateral cephalometric headfilm tracing from each patient, which the perpendicular

distance from the incisal border of the lower incisor to the A-Pog line was

measured. The results were analyzed by groups of age and sex (9-11, 12-14 and

15-17 years). There was no statistical difference between the values obtained from

the different groups of age and sex, and it was observed that the protrusion of the

lower incisor to A-Pog line is reduced as the age increases. Finally, We obtained

in our sample with ideal occlusion and facial harmony a norm of the lower incisor

to A-Po line of 3.67mm in 9 – 11 year old group with a S.D. of 1.74mm , in the

group of 12 – 14 year old was 3.13mm with D.S. of 2.13mm and in the last group

of 15 – 17 year old was 2.76mm with D.S. of 2.01mm and The Main was

3.1mm.

S

Lower incisor position with relation to A-Pog plane, in mexicans with ideal occlusion. Toshio Kubodera Ito, PhD and Chrisel Zárate Díaz MOrth. Toluca, México.

The purpose was to study the protrusion of the lower arch, by means of measuring

the anteroposterior position of the lower incisor, relative to the A-Pog plane, in a

group of 192 mexican patients with ideal occlusion. The material was the lateral

cephalometric headfilm tracing from each patient, in wich the perpendicular

distance from the incisal border of the lower incisor to the A-Pog plane was

measured. The results were analyzed by groups of age and sex (9-11, 12-14 and

15-17 years). There was no stadistical difference between the values obtained

from the different groups of age and sex, and it could be observed that the

protusion of the lower incisor to A-Pog plane is reduced as the age increases.

ome of the primary goals of orthodontic treatment are to attain and preserve

optimal dental relations as well as facial attractiveness. To accomplish this, it is important

that the orthodontist performs a thorough cephalometric dentoskeletal analysis of a patient,

in which is recognized, that the denture position influences the soft-tissue profile; its

position after orthodontic treatment should be such that a harmonious soft-tissue profile is

produced. 1 There are many cephalometric norms, which consider the position of the lower

incisors, some are based on dentocranial relations as Tweed´s IMPA that relates the lower

incisor angulation to the mandibular plane, according to WilliamsError! Unknown switch argument.

it is not realistic because those dentocranial relations are not always attainable and besides

the norm proposed by Tweed, was not a common denominator in all the patients with

optimum facial aesthetics. This author recognizes, as Holdaway, Ricketts and Downs also

did, that is not the angular attitude but the linear anteroposterior position of the lower

incisor what influences upper and lower lip balance, correspondig to the distance of the

lower incisor to the A- Pog line. He points out that to create a harmonious lip balance at

the conclusion of the treatment, the tip of the lower incisor must be brougth to a position at

or near the A-Pog line (the optimum is 0 mm); both ends of this line have migrated to a

new position, point A by the relocation of upper incisors and Pog by growth.

Other application of this measurement, accordinf to WilliamsError! Unknown switch

argument. , is in diagnostic, he states that the amount of denture and skeletal change required

to place the incisal edge of the lower incisor on the A-Pog line and thereby secure a

balanced face will dictate whether any teeth are to be extracted, or wich teeth are to be

extracted.

MATERIAL AND METHODS

Sample population

3200 students who lived in Toluca and the suburbs were examined. 800 were

children from 9 to 11 years of age with late mixed dentition, to be included in this study

they should fulfill the next criteria: Angle’s class I (normal occlusion), without anterior

crowding and with pressence of temporal teeth in the buccal segments (cuspids and

premolars).2 2400 were adolescents from 12 to 17 years, they should have good facial

profile, class I normal occlusion, overbite and overjet smaller than 2.5 mm, no missing

teeth and no previous orthodontic treatment.3

192 subjects satisfied the inclussion criteria and were included in one of three

groups of age: 9 to 11 years (38 male and 32 female), 12 to 14 years (36 male and 34

female) and 15 to 17 years (18 male and 34 female).

Data acquisition

A cephalometric headfilm was taken to each subject. The tracings included the

lower incisor contour and the A-Pog line, referred as the Denture plane4 used as reference

to measure the position of the anterior teeth and define the protrusion of the lower arch.

The perpendicular distance from the incisal edge of the lower incisor to the A-Pg line, was

measured for each subject.

Statistical analysis

The mean and standar deviation of the values obtained were calculated for each of

the three groups of age, for males and females. Data was analized for each group with the

Students’s t test to reveal any significant difference between the means.

RESULTS

It was founded that the mean for the group of age 9 to 11 years, was 3.67 mm of distance

from the incisal edge of the lower incisor to the A-Pog plane and the standar deviation was

1.74. For the group 12 to 14 years, the mean was 3.13 and the standar deviation was 2.13.

For the group 15 to 17 years, the mean was 2.76 and the sd was 2.01. (Table 1)

Table 1. Distance from de lower incisor to the line A-Pog (mm).

9 to 11 years

(n=70)

12 to 14 years

(n=70)

15 to 17 years

(n=52)

Mean

Mean 3.67 3.13 2.76 3.1

Standar deviation 1.74 2.13 2.01

With the statistical analysis, it was not founded any significant difference amog the

groups.

DISCUSSION

As the results showed, the distance from the lower incisor to the Denture line (A-

Pog), diminishes with the age from 3.67 mm at 9 to 11 years old, to 2.76 at 15 to 17 years,

being no statistically significant the difference amog the values. It could be determined,

with different cephalometric values measured in this study, as the angles lower incisor-

occlusal plane, lower incisor-Franfort horizontal and lower incisor-mandibular plane, that

in mexican children and adolscents the lower incisor retroclines as the age arises. This can

be the explanation in the reduction of the distance from lower incisor to A-Pog line.

According to different norms, as Rikkets’(1mm +- 2) and Ann Arbor’s (2.3 mm),

the mexican norm (3.1) results a little more protrusive and similar to the norm proposed by

McNamara (2-3 mm).5

CONCLUSIONS

As it could be determined, in mexican children and adolescents with ideal occlusions, the lower incisor protrusion related to the Denture line (A-Pog), is reduced as the age increaces, ougth to the retroinclination of the lower incisors, having an overall mean of 3.1 mm. 1 Williams, R. The diagnostic line. AJO. 55 (5). 1969. 458-476. 2 Kubodera T., Centeno C., Esquivel G., Lara E., y Montiel N. Estudio morfológico craneofacial en dentición mixta tardía. C.I.E.A.O., U.A.E.M. 3 Kubodera T. Morphometric Study on Craniofacial Structures of Central Mexican adolescents by using cephalometric analysis. J. Meikai Univ. Sch. Dent. 21 (1). 1992. 125-144. 4 Jacobson A. and Caufield PW. Introduction to radiographic cephalometry. Pp. 72-83. 5 McNamara JA and Brudon WL. Orthodontic and orthopedic treatment in the mixed dentition. Needham press. USA. 1993.