Dental Arch Dimensions in the Mixed Dentition: A Study of Italian Children Born in the 1950s and the 1990s

Modern population are affected by characteristic diseases such as malocclusions, caries, diabetes, hypertension, and heart disease that are uncommon in underdeveloped societies.1 The changes in environment, habits, and the greater diffusion of respiratory pathologies were considered to be responsible for a progressive increase in the prevalence of malocclusions.2 Occlusal patterns follow secular trends that were described in the literature in several populations; this tendency was found not only between ancient and modern subjects but also in the comparison among cohorts of the same century separated by almost 30 years.3–8 Transverse dental arch dimensions, in particular, appear to be progressively reduced. A secular trend toward a reduction of the anterior space and an increased prevalence of crowding was also described by Lavelle9 and Brin et al,10 whereas Lindsten et al5 did not find similar results. The dimensions of posterior segment in the mixed dentition show instead a trend through an increase in contemporary people when compared with ancient populations (showing interproximal attrition) and subjects of the half of the last century (showing an higher prevalence of interproximal caries).4 The aim of this study is to compare the dental arch dimensions in the mixed dentition in two modern samples living in the same geographic area and separated by almost 35 years: a group of subjects born in 1950s and another group born in 1990s.

The 1950s group (50sG) of 83 subjects (39 boys and 44 girls) was derived from the files of patients, who were first observed at the Department of Orthodontics of the University of Florence, Italy, in the 1960s. All subjects were born between 1953 and 1959. The mean age of the 50sG was eight years and three months ±15 months for boys and seven years and 11 months ±12 months for girls. The boys presented 19 subjects with Class I, 17 subjects with Class II division 1, and three subjects with Class III malocclusions. The girls presented 21 subjects with Class I, 18 subjects with Class II division 1, two subjects with Class II division 2, and three subjects with Class III malocclusions.

The 1990s group (90sG) of 84 subjects (38 boys and 46 girls) was derived from patients observed at the same Department in the years between 1996 and 2003. These subjects were born between 1990 and 1998. The mean age of the 90sG was eight years and eight months ±12 months for boys and eight years and four months ±11 months for girls. The males presented 20 subjects with Class I, 16 subjects with Class II, and two subjects with Class III malocclusions. The females presented 21 subjects with Class I, 20 subjects with Class II division 1, two subjects with Class II division 2, and three subjects with Class III malocclusions.

The following inclusionary criteria were adopted for both groups: (1) availability of detailed clinical files; (2) absence of any previous orthodontic treatment; (3) absence of bruxism; (4) absence of unilateral posterior crossbite; (5) availability of dental casts of good quality; (6) absence of missing teeth, dental traumas, dental anomalies, deep caries, restorations; and (7) availability of panoramic radiographs.

All subjects were Caucasians belonging to the same geographic area (Tuscany). They all presented in early mixed dentition (presence of first permanent molars and upper and lower central and lateral incisors erupted or in phase of eruption). To reduce the range of variables affecting arch measurements, the two groups were matched for sex distribution and prevalence of sagittal malocclusions. Unilateral posterior crossbites (as assessed from the dental records and confirmed by the dental casts) were excluded because of the expected asymmetries between the sides with and without a crossbite. Panoramic radiographs were examined to control the absence of dental anomalies, deep caries, and restorations.

Measurements were made on dental casts by one of us (Dr. Baroni) using a sliding caliper.

The following measurements were taken (1) posterior segment (right and left): the distance between the mesial surface of the first permanent molar and the mesial surface of the deciduous canine; (2) anterior segment (right and left): the distance between the mesial surface of the deciduous canine and the mesial surface of the permanent central incisor; and (3) mesiodistal size of each permanent incisors.

These measurements were taken for upper and lower arch and for left and right sides. (1) Interincisal midline diastema (upper and lower); (2) available space was calculated as the sum of anterior segments and interincisal midline diastema minus the sum of the mesiodistal sizes of the teeth; (3) maxillary intermolar width: distance between the central fossae of right and left first maxillary molars; (4) mandibular intermolar width: distance between the tips of the distobuccal cusps of right and left first mandibular molars; (5) posterior transverse interarch discrepancy (PTID): difference between maxillary and mandibular intermolar widths; (6) maxillary intercanine width: distance between the mesial margin of right and left maxillary deciduous canine; (7) mandibular intercanine width: distance between the tips of the cusps of right and left deciduous canine. If the cusp tips were abraded, the assumed center of the abraded area was used; and (8) anterior transverse interarch discrepancy: difference between maxillary and mandibular intercanine widths.

Fifteen randomly selected models were remeasured to calculate method errors for all the variables, as described by Dahlberg.11 Any systematic error was determined by calculating the coefficients of reliability for all the variables, as suggested by Houston.12 Method errors ranged from 0.00 to 0.66 mm. Corresponding coefficients of reliability ranged from 0.81 to 1.00.

The data from cast measurements of the two groups were compared separately for boys and girls, using a nonparametric test (Mann-Whitney U-test) for independent samples (P < .05). All statistical computations were performed with a Social Science Statistical Package Software (SPSS, Version 12.0, SPSS Inc, Chicago, Ill).

Descriptive statistics and statistical comparison for the examined groups are reported in Tables 1 and 2. Both boys and girls of 90sG showed significantly smaller maxillary intermolar width when compared with 50sG. PTID was significantly minor in girls of 90sG. A reduction of the anterior segments of the upper arch in girls of 90sG on the left side was found, but the difference is clinically not relevant. No differences were found for all other examined values.

Dental conditions of many different “primitive” populations have been studied since the beginning of the last century. Price13 studied Gaelic communities in the Outer Hebrides, Eskimos and Indians of North America, Melanesian and Polynesian South Sea Islanders, African tribes, Australian Aborigines, New Zealand Maori, and the Indians of South America and observed a very low incidence of dental diseases and malocclusions. In Eskimos, he observed perfect occlusions until the contact with industrialized societies,14 and later the incidence of malocclusion increased to 50%.15 

Price13 related dental problems with the introduction of a diet based on processed foods. Begg16 in 1954 studied living and dead Australian aboriginals and noted a very low prevalence of malocclusions. He suggested that the loss of interproximal hard tissues because of attrition could be able to provide enough space for permanent teeth to achieve an adequate alignment. Corruccini and Whitley,17 extending Price's hypotheses, supported the “disuse theory,” in contrast to Begg and gave a great importance to decreased function of the masticatory system, which should be responsible of inadequate development of the jaws.

The findings of this study indicate that untreated subjects in the mixed dentition observed in the last 10 years show a significantly smaller width of the upper arch when compared with subjects observed 40 years ago in accordance with the findings of Lindsten et al.3–4,6 This can be interpreted as a sign of lack of function in modern subjects as a consequence of processed food, on the basis of the positive association between masticatory function and development of the jaws. This association has been experimentally demonstrated on animal samples by numerous studies. Beecher and Corruccini18 found association between moderate differences in the hardness of the diet and narrowing of the maxillary arch in the rats. They suggested that mediolateral maxillary growth depends on the stimulation of the muscles provided by rough elements in the diet. The same authors found the equivalent results with a population of rhesus macaques.19 Bouvier and Hylander20 microscopically examined the same sample and found fewer secondary Haversian systems in the mandibular corpus. Ciochon et al21 found a 25% greater size of the deep masseter and superficial masseter and temporalis weight in minipigs fed hard food in comparison with minipigs supplied with soft food.

Another important cause of narrowing of the upper arch in modern populations is the amplified prevalence of mouth breathing22 as a consequence of an increase in respiratory diseases such as allergy and asthma.23–27 Lindsten et al28 suggested that many contemporary children chew gum frequently, and so a change in dietary consistency cannot be ruled out as a causative factor of narrowing of the maxilla. Consequently, mouth breathing has to be considered a major cause of the narrowing of maxillary arch in the modern populations.

A tendency toward a reduction of the posterior transverse intermolar dimension was found in children born in the 1990s with respect to their coetaneous born in 1950s: PTID is an underlying sign of various malocclusions. Tollaro et al29 have shown that a negative PTID exists in dental arches with Class II malocclusion (3.4 mm on average) and seemingly normal buccal relationships. Baccetti et al30 demonstrated that a negative PTID is recorded consistently in Class II subjects with deciduous dentitions and that the negative PTID is maintained or worsened during the transition into the mixed dentition. Varrela31 confirmed that children with distal occlusions have narrower intermolar distances with respect to normal subjects since the age of three years, and this dissimilarity amplifies with age. In a previous study8 performed on the same cohort, differences between the 50sG and the 90sG were found for all deciduous teeth, which appeared to be significantly more abraded in the 50sG.

The simultaneous presence of underdeveloped jaws and unworn teeth may be a cause of dental interferences and forced guidance of the mandible in an incorrect position in the sagittal or transverse plane, with a consequential malocclusion.32,33 The stimulation of the muscular structures due to hard and fibrous foods allows a major development of the dental arches, resulting in a greater functional stimulation of the masticatory muscles and increased occlusal wear.

There was no difference between the two groups for the dimensions of the posterior segments, which contrasts with the results of Lindsten et al.34 Lindsten's group found larger spaces in the posterior segment in children born in the 1980s when compared with subjects born in the 1950s. They hypothesized that there was a change in the lateral arch space conditions during the last decades because of the decline in caries prevalence occurring in the same period. The different findings of our study may be due to a different selection of the samples because the absence of caries was an inclusionary criterion for subjects involved in this study. The other causes of loss of proximal tooth material of posterior teeth, such as interproximal wear, are lacking in modern populations and are not able to cause a reduction of the length of the posterior segments of the arch in the mixed dentition.

• Italian children born in the 1990s show a significantly reduced transverse intermolar maxillary width and a tendency to a reduction of the posterior transverse intermolar discrepancy, in comparison with a sample of children born in 1950s.

• Contemporary children have a greater probability for developing a malocclusion compared with the children living 35 years before.