Subjects

Seven randomly selected elementary schools from Wegrow County (70 miles east of Warsaw) were contacted, and their headmasters were informed about the planned investigation. All schools agreed to participate in the study, and lists of 4th and 5th grade children that were assumed to be approximately 10 years of age were formed. Individuals from the lists were examined by two investigators (BO and PF) at the school nurse's room during four trips to Wegrow County. The initial inclusion criteria were: (1) Class I molar relationship, (2) lack of crossbite or scissor-bite, (3) positive overjet and overbite less than 5 mm, (4) adequate amount of space in both dental arches, (5) no visible asymmetry, and (6) good facial proportions. Selected individuals and their parents were subsequently sent letters explaining the reason, methodology, and risks involved in the investigation. Children whose parents consented to participate were invited for examination at the Center for Craniofacial Disorders at the Institute of Mother and Child in Warsaw.

Intraoral examination, study models, extraoral and intraoral photographs, panoramic and lateral cephalograms were obtained from 83 participants. Table 1 demonstrates the details of the selection process.

Table 1.  Stages of Sample Selection

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Methods

All lateral cephalograms were taken under standard conditions with the subjects standing with their head positioned in the cephalostat and teeth in the maximal intercuspation. The distance from focus to the midsagittal plane (MSP) of the child's head, and from the midsagittal plane to the film was identical for each subject. Cephalograms carried magnification of 9.5%, and the adjustment for enlargement factor has been made in the linear measurements reported in the Results section. All cephalograms were scanned with PowerLook III (UMAX) scanner. Cephalometric analysis was carried out twice with NemoCeph NX 2005 program (Nemotec, Madrid, Spain) by one investigator (BO). The identified landmarks, and angular and linear measurements are presented in Figures 1 to 4.

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Error of Method

The measurement errors were calculated from the equation:

with D representing the difference between corresponding first and second measurements on all (N = 73) cephalograms made at least 1 week apart.

Statistical Analyses

Descriptive statistics (mean, standard deviation, minimum, and maximum) were calculated for all measured variables. Independent t-tests were performed to assess the intergender differences in measurements. If no intergender difference regarding a given measurement was detected, the sample was pooled and descriptive statistics were recalculated.

Subjects

Seventy-three subjects (39 boys and 34 girls) of 83 that were examined at the Institute of Mother and Child were finally selected. Ten subjects were excluded for the following reasons: cephalograms of four boys and four girls were of inadequate quality, one boy was diagnosed with an impacted canine, and one girl demonstrated dental midline asymmetry. Age characteristics of the groups are shown in Table 2. Male and female groups demonstrated a mean age of 10.4 years at the time of the collection of records. Additionally, standard deviation, median, minimum, and maximum values were also similar in the groups.

Table 2.  Age Characteristics of Male and Female Groups^a

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Method Error

Error for the angular measurements was from 0.61° for ANB angle to 2.25° for the interincisal angle. Linear measurements demonstrated error from 0.31 mm for overjet to 1.68 mm for the pogonion-nasion perpendicular variable (Table 3).

Table 3.  Error of Measurements

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Cephalometric Analysis

Results of the cephalometric analysis are presented in Table 4. Intergender comparison demonstrated that boys and girls differed regarding some measurements. Linear measurements such as sella-nasion distance, total and lower anterior facial height, and posterior facial height were larger in boys (P = .046, .009, .003, and .018, respectively). Position of point A and pogonion relative to the nasion perpendicular line was more retrusive in boys, and the difference was statistically significant (P = .02 and .018, respectively). Additionally, a few angular variables (SNA, facial axis) showed statistically significant intergender differences (P = .031 and .040, respectively). Other variables, including all dental parameters, were similar in both sexes (P > .05).

Table 4.  Skeletal and Dental Cephalometric Standards for Polish Boys and Girls. All Linear Measurements Adjusted for 9.5% Enlargement Factor^a

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Validity of the Sample

Reduction of selection bias is of primary importance when norms for populations are to be established. In some studies records of individuals from university clinics7 or other institutions8 were used to set cephalometric standards. This may pose a risk of introducing selection bias by limiting to the subjects that sought orthodontic treatment. The population of individuals seeking treatment may differ from the whole population living in a particular area; hence, the results may not be representative. In order to overcome this difficulty the sample was selected from the randomly chosen elementary schools. No contacted school refused to participate in the study. In site screening process included mostly objective criteria as Angle classification, positive overjet, or lack of crossbite and scissor-bite. The only subjective criterion used was a good facial profile.

Ethnic homogeneity was achieved by selecting the sample from a population living outside of the Warsaw metropolitan area where current migration is high. Wegrow County is a rural area with stable demographic structure. The majority of the subjects were born in the county hospital. All individuals had Polish family names.

Intergender Comparison

Only few variables showed differences between sexes. The length of the anterior cranial base (sella-nasion) was found larger in boys. This is in agreement with the results of Ursi et al9 who longitudinally followed 23 male and 28 female subjects from 6 to 18 years of age. They concluded that anterior cranial base length was the only measurement examined that showed significant dimorphism over the entire 12-year span. Similar conclusions were arrived at by Bhatia and Leighton10 who found highly significant intergender difference occurring from 4 to 20 years of age.

Posterior, total, and lower anterior facial heights demonstrated significant intergender difference. Posterior facial height was larger in males by approximately 2.2 mm, whereas total anterior facial height was larger by about 3.5 mm. This corroborates findings of Drevensek et al11 who examined 42 boys and 46 girls with ideal occlusion at the age of 9.31 years (SD = 1.52) and found highly significant intergender difference. Also, El-Batouti et al8 following examination of 35 boys and 29 girls at the age of 9 years concluded that both posterior and lower anterior facial heights were significantly larger in boys than in girls. Similar findings were presented Bhatia and Leighton.10 However, they found that posterior facial height in boys was larger than in girls from 4 to 10 years of age. In 11-, 12-, and 13-year-old individuals, the difference was not present. It reoccurred at the age of 14 and lasted until the end of observation period. The phenomenon of lack of intergender difference from 11 to 13 is likely attributable to the earlier onset of growth spurt in girls.

Maxillary protrusion, as represented by SNA and A-N perpendicular measurements, differed between genders. The maxilla in females was more protruded, the SNA angle was larger by approximately 1.8°, and the distance from point A to nasion perpendicular line was diminished by 1.8 mm. This finding disagrees with the results of Ursi et al9 who could not detect any difference in maxillary protrusion.

On the other hand, El-Batouti et al8 demonstrated that in a Norwegian population the maxilla was more protruded in boys and the difference increased with age. Also, mandibular protrusion, as measured with the position of pogonion relative to nasion perpendicular line, was found more in Polish girls as opposed to no intergender difference demonstrated in an American population.9

The possible explanation for these conflicting findings may be that more maxillary and mandibular protrusion in girls than in boys is a characteristic trait of a Polish population. However, the level of statistical significance was not very high and ranged from 0.018 to 0.031. In addition, the error of measurement for pogonion-nasion perpendicular exceeded 1.6 mm, and other variables of mandibular protrusion such as SNB angle or pogonion-NB did not show difference between sexes.

Comparison With Other White Populations

Comparison of different white populations based on the published data encounters multiple problems. Despite the use of standardized cephalometric analyses, the definitions of some landmarks are not universally used. Bhatia and Leighton10 defined condylion as the most superior point of the outer outline of condyle, whereas Riolo et al12 defined it as the most posterior superior point of condyle. Gonion landmark was defined either as the most posterior inferior point of the mandibular angle,81012 or as the point at the intersection of mandibular and ramus planes.813 Consequentially, the measurements based on differently defined landmarks cannot be directly compared.

Enlargement of the craniofacial structures may differ when different cephalostats are used. Although information about magnification factor should be clearly stated in the publication, it is not always the case. El-Batouti et al8 did not mention enlargement. When the statement by Drevensek et al11 that “magnification of 10% was taken into account” is confronted with linear measurements that are approximately 10% larger than in other populations (Table 5), one may put in question whether the linear variables were actually adjusted.

Table 5.  Comparison of Craniofacial Structure Among White Populations

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Selection of individuals with ideal or almost ideal occlusion vs inclusion of subjects presenting with different types of malocclusion poses a risk of setting two kinds of norms: ideal standards81113 and population standards1012 that are not necessarily comparable.

When the craniofacial structure of Polish and other white 10-year-old boys and girls is compared there are a few distinctive features of Poles. Only the cranial base angle (NSBa) and gonial angle were dissimilar, with the NSBa angle being larger by 4.4° to 6.5°, and the gonial angle being smaller by approximately 2° to 8° depending on the compared population. Total anterior facial height (TAFH) was larger than in Scandinavian populations and smaller than in the American population. However, the differences were rather small, in the range of about ±2.5 mm. Comparison of the posterior facial height (PFH) among populations is limited due to the different definition of gonion landmark. PFH in Poles was larger than in Swedes by about 1 mm and smaller than in Slovenians by about 4 mm. Proportion of the posterior to total anterior facial height (PFH/TAFH·100%) is similar among Polish, Swedish, and Slovenian populations, and substantially larger than in Norwegian and American populations. Maxillary and mandibular protrusion in all compared populations was similar. Small differences ranging ±1.5° may result from variance within the samples rather than from intersample differences.

Comparison of dental relationships reveals that the angle between the upper incisors and palatal plane (ILs/PP) is less than in English and American individuals. Inclination of lower incisors (Ili/MP) is similar to other populations, except for Swedish boys and Norwegian girls (smaller inclination) and Slovenian girls (larger inclination). Interincisal angle (ILs/Ili) in Polish populations is more obtuse than in American and Norwegian male populations and American female populations. Other populations show the interincisal angle similar to the Polish sample. This erratic pattern of interpopulation differences demonstrates that these data should be interpreted cautiously. To detect true difference between populations, raw data must be used.

This investigation had some limitations that might affect the results. During the selection process 24 subjects (22.4%) that met inclusion criteria did not arrive at the Institute for examination. This might have introduced bias in the sample. Although the investigators attempted to limit subjective criteria while selecting the sample, “good facial profile” used in the selection is definitely one of them. Most individuals in the sample were likely ahead of the growth spurt. Therefore, some intergender differences not found in this study may develop provided older subjects are compared.