Sample From the 19th Century

Thirty-five skulls from the 19th century were selected from a sample of 150 skulls from the area of Florence, Italy (16 men and 19 women), now housed at the Museum of Anthropology of the University of Florence. The mean age of the sample was 26 ± 4 years (27 ± 4 years for the men and 25 ± 3 years for the women). They were a group of low social class, and they had not lived in comfortable conditions.

The skulls examined were selected on the basis of the following criteria: (1) no obvious cranial deformity, (2) no missing parts of fractures of the jaw bones or dental arches, (3) presence of the mandible, and (4) presence of sufficient teeth to provide a definite occlusion and mandibular articulation.

One lateral cephalogram was obtained for each skull with the teeth in centric occlusion. On all lateral cephalograms, anatomical structures were traced, and the midline of all contours of bilateral structures was traced to minimize the error due to positioning, differential magnification, and asymmetry.

Contemporary Sample

The contemporary sample was composed of 43 subjects (13 men and 30 women) with a mean age of 20 ± 3 years (20 ± 2 years for the men and 21 ± 3 years for the women) selected from the files of the Department of Orthodontics of the University of Florence, Italy.

The sample was selected using the following criteria:

• adult dentition including the second molars,

• skeletal maturation by morphological evaluation of the cervical vertebrae,36 and

• absence of previous or current orthodontic treatment.

All subjects were white young adults belonging to the same geographical area (Florence). They were born in this geographical area, and they belonged to a middle social class.

The matched samples were homogenous with regard to sagittal skeletal relationship.37 The sample from the 19th century was composed of 18 Class I, 9 Class II, and 8 Class III subjects, whereas the contemporary sample was composed of 22 Class I, 11 Class II, and 10 Class III subjects.

Landmarks

The cranial landmarks digitized and employed in this study are described in Figure 1. The definition of these points can be found in the works of Björk,38 Riolo et al,39 and Tollaro et al.40

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Digitization of landmark coordinates from cephalograms was achieved using the appropriate software (Viewbox, version 1.9) and a digitizing tablet (Numonics 2210; Numonics Co, Lansdale, Pa). All cephalograms were digitized by the same operator and redigitized by another operator, and the method error in the landmark identification was calculated.

The standard error deviation for each dimension was calculated from the double determinations using Dahlberg's formula REF. The mean value for the method error was 0.31 ± 0.13 mm. TPS analysis was performed using a digitizing tablet (Numonics 2210; Numonics Co), a digitizing software (Viewbox 3.0; D. Halazonetis, Athens, Greece), and a morphometric software (TPS Regr 1.28; F. J. Rohlf, Ecology and Evolution, SUNY at Stony Brook, New York, NY). A statistical analysis of shape differences was performed by means of permutation tests with 1000 random permutations on Goodall F statistics.

Cranial Base

Previous works have demonstrated that the cranial base angle is similar within the same population over a long time,4243 but it varies among different populations.4244 For instance, Anderson and Popovich44 and Argyropoulos et al42 have found a remarkable similarity in the cranial base angle between ancient Greek skulls (1800–1200 BC) and present-day Greek individuals. They suggested that the cranial base angle indicates a genetic homogeneity.

In another study, Kuroe et al4 found that there are significant differences between the cranial base angle of the European and Asian samples, while a considerable similarity was found between the European and African samples. These authors conclude that their results are insufficient to assert that the population difference or similarity of the cranial base angle in this study reflects the degree of genetic homogeneity of the samples.

In another study, Kuroe et al4 found that there are significant differences between the cranial base angle of the European and Asian samples, while a considerable similarity was found between the European and African samples. These authors concluded that their results were insufficient to assert that the population difference or similarity of the cranial base angle in their study reflected the degree of genetic homogeneity of the samples.

Our results that derive from the implementation of a morphometric approach versus a classical cephalometric approach are in accordance with those of Ingervall et al,45 who have compared the differences in two samples over a period of 160 years. Ingervall et al45 examined cranial base differences between 19th-century crania and a modern group. The modern group had a more acute saddle angle, and the study has found some skeletal differences that occurred over comparatively short time spans.

The principal differences between the two groups are graphically displayed in Figure 2. The analysis of the cranial base shows differences that demonstrate an acute cranial base angle with a posterior superior remodeling of the tuberculum sellae in the more modern sample when compared with the more ancient one.

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In the global evaluation of the differences between the two samples, the differences in the cranial base are smaller with respect to those detectable in the facial skeleton. These results confirm that the cranium-basal complex is a stable anatomic structure within the head.

Facial Skeleton

According to Enlow and Hans,20 the cranial base must be considered the bridge between the neurocranium and facial regions, the support on which the face is constructed, so that variations in the cranial base are associated with related modifications in facial shape. The results of the current investigation show how the modifications of the cranial base are associated with between-group differences in maxillary and mandibular shape. Thus, the maxillary complex revealed a tendency to relocate in a posterior direction, with an elongation toward the pterigomaxillary region. The mandibular modifications are easily discernible in the comparison between the two samples. These significant differences are mainly due to a positional change rather than dimensional changes. The condyle appears located in a more anterior position, along with an anterior relocation of the chin in contemporary young adults. The combination of these changes in maxillary and mandibular structures suggests a trend toward mandibular prognathism in more modern populations.

The interpretation of these results can be only tempting, while the comparison of the present outcomes with those of other studies is complicated, particularly by the specific method of morphometric analysis applied here. However, the findings indicate that the modern group exhibited a backward displacement of the maxilla. This modification might be related to an airway space reduction following an increase in the prevalence of atopic diseases (asthma, allergic rhinitis, and atopic dermatitis) in the past decades, especially in developed countries. The so-called hominization process46 is probably not involved because of the short time spans.

Certainly, the other factors that could have determined the differences in the two samples are the following:

• the influence of the same dietary consistency with effects on both muscle function and attrition,

• the possible effects of evolution together with dietary effects,

• the possible hybridization effects, and

• the differences in social class levels between the two groups with consequences on lifestyle, diet, and muscular stress.