Anna Colombo

Three-dimensional dental arch curvature in human adolescents and adults

The three-dimensional arrangement of dental cusps and incisal edges in human dentitions has been reported to fit the surface of a sphere (the curve of Monson), with a radius of about 4 inches in adults. The objective of the current study was to compare the three-dimensional curvature of the mandibular dental arch in healthy permanent dentitions of young adults and adolescents. The mandibular casts of 50 adults (aged 19 to 22 years) and 20 adolescents (aged 12 to 14 years) with highly selected sound dentitions that were free from temporomandibular joint problems were obtained. The three coordinates of cusp tips excluding the third molars were digitized with a three-dimensional digitizer, and used to derive a spherical model of the curvature of the occlusal surfaces. From the best interpolating sphere, the radii of the left and right curves of Spee (quasi-sagittal plane) and of molar curve of Wilson (frontal plane) were computed. Mandibular arch size (interdental distances) was also calculated. The occlusal curvature of the mandibular arch was not significantly influenced by sex, although a significant effect of age was found (Student t, P <.005). The radii of the overall sphere, right and left curves of Spee, and curve of Wilson in the molar area were about 101 mm in adults, and about 80 mm in adolescents. Arch size was not influenced by either sex or age. The different curvatures of the occlusal plane in adolescents and adults may be explained by a progressive rotation of the major axis of the teeth moving the occlusal plane toward a more buccal position. These dental movements should be performed in a frontal plane on an anteroposterior axis located next to the dental crown.

A quantitative three-dimensional assessment of soft tissue facial asymmetry of cleft lip and palate adult patients.

The three-dimensional coordinates of 23 selected soft-tissue facial landmarks were digitized on 18 cleft lip and palate (CLP) white patients (11 male and 7 female patients aged 19–27 years) and 161 healthy controls (73 female and 89 male subjects aged 18–30 years) by an electromagnetic instrument. Facial asymmetry was quantified by detecting a plane of symmetry and the centers of gravity (CG) of the right and left hemifaces and by calculating the distance between the two CG (distance from symmetry [DFS]). Both absolute (millimeters) and percentage (of the nasion center of gravity distance) DFS was obtained. The asymmetry of single landmarks was also quantified. Overall, asymmetry in operated CLP patients appeared only moderately larger than that measured in the healthy reference population, with the largest value being only 5% larger than the maximum normal asymmetry. Female patients had a somewhat larger lateral asymmetry than male patients, and unilateral CLP patients (particularly the men) were more asymmetrical than bilateral CLP patients. Pronasale and subnasale landmarks were asymmetrical in 8 patients, whereas endocanthion, zygion, cheilion, and gonion landmarks were symmetrical in all patients. In conclusion, the facial soft-tissue structures of CLP patients operated on as adults were only moderately more asymmetrical than those measured in a reference group of the same age, sex, and ethnicity.

Morphometry of the orbital region: a soft-tissue study from adolescence to mid-adulthood.

The objective of this study was to gain information about normal sex‐related linear and angular dimensions of the orbital region; left‐right symmetry; and growth changes between adolescence and mid‐adulthood. The three‐dimensional coordinates of several soft‐tissue landmarks on the orbits and face were obtained by an electromagnetic digitizer in 40 male and 33 female adolescents aged 12 to 15 years, 73 female and 89 male young adults aged 19 to 30 years, and 41 male and 38 female adults aged 31 to 56 years. From the landmarks—binocular and intercanthal widths; paired height and inclination of the orbit relative to both the true horizontal (head in natural head position) and Frankfurt plane; length and inclination of the eye fissure; and the orbital height to eye fissure length ratio were calculated and averaged for age and sex. Comparisons were performed by factorial analysis of variance. Both the linear dimensions and the angular values were significantly larger in male subjects than in female subjects of corresponding age (p < 0.05). A significant effect of age was found (p < 0.05): while the linear distances and the orbital height‐to‐length ratio were greater in older people of the same sex, the inclination of the eye fissure decreased as a function of age. Both orbital inclinations were larger in the young adult group than in the adolescent and middle‐aged groups. On average, the paired measurements were symmetrical, with similar values within each sex and age group. Data collected in this investigation could serve as a database for the quantitative description of human orbital morphology during normal adolescent and adult growth. (Plast. Reconstr. Surg. 108: 285, 2001.)

Three-Dimensional Inclination of the Dental Axes in Healthy Permanent Dentitions—A Cross-Sectional Study in a Normal Population

The 3-dimensional (3-D) inclination of the facial axis of the clinical crown (FACC) and the size of the clinical crowns were measured in 100 white northern Italians. The subjects consisted of 22 girls and 21 boys, ages 13-15 years (adolescents), and 31 women and 26 men, ages 16-26 years (adults), all with a complete permanent dentition and Class I dental relationships. The 3-D coordinates of dental landmarks were obtained with a computerized electromagnetic digitizer. Clinical crowns heights and FACC inclinations in the anatomical frontal and sagittal planes relative to 2 reference planes, maxillary and mandibular (between the incisive papilla and the intersection of the palatal/lingual sulci of the first permanent molars with the gingival margin), were calculated. Ages and sexes were compared by ANOVA. On average, the frontal plane FACCs of most teeth converged toward the midline plane of symmetry. In contrast, the incisors diverged from the midline plane or were nearly vertical. Within each quadrant, the inclinations of the postincisor teeth progressively increased. In the sagittal plane, most teeth had a nearly vertical FACC. FACC inclinations showed sex- and age-related differences (P < .05). In the frontal plane, the canines, premolars, and molars were more inclined in adolescents than in adults. In the sagittal plane, a large within-group variability was observed. Clinical crown height was significantly larger in males than in females in all maxillary and mandibular canines, premolars, second molars, maxillary central incisors, and first molars. With age, some degree of dental eruption was found in maxillary and mandibular canines, maxillary second premolars, and molars. The age-related decrease in FACC inclination may be the effect of a progressive buccal and mesial drift.

Normal growth and development of the lips: a 3-dimensional study from 6 years to adulthood using a geometric model.

A 3‐dimensional computerised system with landmark representation of the soft‐tissue facial surface allows noninvasive and fast quantitative study of facial growth. The aims of the present investigation were (1) to provide reference data for selected dimensions of lips (linear distances and ratios, vermilion area, volume); (2) to quantify the relevant growth changes; and (3) to evaluate sex differences in growth patterns. The 3‐dimensional coordinates of 6 soft‐tissue landmarks on the lips were obtained by an optoelectronic instrument in a mixed longitudinal and cross‐sectional study (2023 examinations in 1348 healthy subjects between 6 y of age and young adulthood). From the landmarks, several linear distances (mouth width, total vermilion height, total lip height, upper lip height), the vermilion height‐to‐mouth width ratio, some areas (vermilion of the upper lip, vermilion of the lower lip, total vermilion) and volumes (upper lip volume, lower lip volume, total lip volume) were calculated and averaged for age and sex. Male values were compared with female values by means of Students t test. Within each age group all lip dimensions (distances, areas, volumes) were significantly larger in boys than in girls (P < 0.05), with some exceptions in the first age groups and coinciding with the earlier female growth spurt, whereas the vermilion height‐to‐mouth width ratio did not show a corresponding sexual dimorphism. Linear distances in girls had almost reached adult dimensions in the 13–14 y age group, while in boys a large increase was still to occur. The attainment of adult dimensions was faster in the upper than in the lower lip, especially in girls. The method used in the present investigation allowed the noninvasive evaluation of a large sample of nonpatient subjects, leading to the definition of 3‐dimensional normative data. Data collected in the present study could represent a data base for the quantitative description of human lip morphology from childhood to young adulthood.

The Effects of a Single Intercuspal Interference on Electromyographic Characteristics of Human Masticatory Muscles During Maximal Voluntary Teeth Clenching

In 13 healthy subjects (eight men and five women, mean age, 22 years), an aluminum intercuspal interference (height, 0.25 mm) was placed on the maxillary right first premolar to study its effect on the contractile symmetry of the right and left masseter and anterior temporalis muscles when measured through a Percentage Overlapping Coefficient (POC), derived from surface electromyographic recordings of maximum voluntary teeth clenching. Additionally, and to estimate the potential of the experimental intercuspal interference to induce lateral displacement of the mandible, a Torque Coefficient (TC) was derived from surface electromyographic recordings. The conclusion was that the experimental occlusal interference gave rise to asymmetric contractile activity in the studied mandibular elevator muscles as well as a potential to displace the mandible in a lateral direction.

Quantitative description of the morphology of the human palate by a mathematical equation.

OBJECTIVE To derive a three-dimensional mathematical description of normal human hard tissue palatal size and shape. METHODS The maxillary dental casts of 30 adolescents free from respiratory problems, who had a complete (28 teeth) permanent sound dentition with normal occlusion, were studied. The x, y, z coordinates of several standardized palatal and dental landmarks were obtained with a computerized three-dimensional digitizer. Palatal landmarks were used to derive a mathematical equation of palatal shape in the frontal and sagittal planes. Palatal width, length, frontal and sagittal heights, and sagittal slope, as well as dental arch transverse and anteroposterior dimensions, were computed. RESULTS Neither the size nor the shape of the palate was significantly influenced by gender. Only the intercanine distance was larger (p < .025) in males than in females. CONCLUSIONS Data collected in the present investigation could represent a first database for the quantitative description of normal human palatal morphology in subjects with a complete permanent dentition.

Mathematical definition of the curve of Spee in permanent healthy dentitions in man

The intrinsic morphology of the mandibular curve of Spee (i.e. independent from reference planes) was studied in 50 men and 45 women with sound dentitions. Left and right curves were reconstructed by a second-order quadratic interpolation of buccal cusp tips. Gender differences were found in both sides, while side differences were found only in the male sample. Male and female curves had similar concavities, but the position of the interpolating second-order quadratic curve relative to the dental arch was significantly different. The right and left male sides showed different concavities, the right-hand side being flatter than the left. Male curves appeared larger than female ones, and the left-hand side was significantly larger than the right regardless of gender. The reported second-order quadratic curves could be used as reference for prosthetic and orthodontic reconstructions.

Soft tissue facial growth and development as assessed by the three-dimensional computerized mesh diagram analysis

The normal growth and development of facial soft tissues from 6 years to adulthood has been studied by the 3D computerized mesh diagram analysis. The analysis allows independent quantifications of size and shape modifications both between different age groups, and between males and females. Normal age-related and sex-related references are provided. The three-dimensional facial morphometry method has been used for the collection of the x, y, z coordinates of 22 soft tissue landmarks in 2023 examinations performed on 1157 healthy white children and adolescents between 6 and 17 years of age and 191 young adults. The method detects the three-dimensional coordinates of retroreflective, wireless markers positioned on selected facial landmarks using two charge-coupled device cameras working in the infrared field. For each sex and age class, mean values were computed, and a standardized mesh of equidistant horizontal, vertical, and anteroposterior lines was consequently constructed. Within each age group, male meshes were superimposed on female meshes. Moreover, within each sex, the adult reference mesh was superimposed on the reference mesh of each age group. The global (size plus shape) difference was then evaluated by the calculation of the relevant displacement vectors for each soft tissue landmark. A global difference factor was calculated as the sum of the modules of all the displacement vectors. Consequently, a size normalization was performed, and the shape difference (size standardized) was then evaluated by the calculation of new relevant displacement vectors for each landmark, as well as a shape-global difference factor. When compared to the young adult situation, the largest child discrepancies were found in the soft tissue profile. After size standardization, shape differences were found in the forehead, nose, and chin. The soft tissue facial dimensions of boys and girls grow with similar characteristics and at the same rate between 6 and 11 years of age, but showed different patterns after this age. Within each age class, most of the sex-related differences were dimensional discrepancies that were corrected after size standardization. Nevertheless, before adolescence even these size differences were limited. On average, male faces had a larger forehead, longer and more vertical nose, more inferior and posterior gonia, more inferior and prominent lips, and a larger mouth than female faces of corresponding age.

Nasal dimensions in normal subjects: Conventional anthropometry versus computerized anthropometry

The aim of the current investigation was to compare computerized measurements of nasal linear distances (nasal tip protrusion, height of the cutaneous upper lip, length of the nasal bridge) collected from 705 healthy individuals from Northern Italy (age range 6–60 years) using an electromagnetic digitizer with conventional anthropometric measurements: one set obtained on individuals of central European origin (Zankl et al. [2002: Am J Med Genet 111:388‐391]), and one set collected from North American Caucasians (Farkas et al. [1994: Anthropometry of the Head and Face 241–335]). On average, the present lengths of the nasal bridge were always significantly smaller than the European data (P < 0.01, Students t for independent samples). Nevertheless, only in one sex and age group of 18 the discrepancy between the two mean values was larger than 10 mm. In other 10 groups, the mean values differed less than 5 mm. More limited differences (up to 6.5 mm) were found in comparison to the American data. For nasal tip protrusion, digital and conventional data were significantly different (up to 4 mm) in 18 instances of 30. On average, the present heights of the cutaneous upper lip were always smaller than the European data (up to 2.9 mm). The differences were statistically significant in 14 groups of 18. Minor discrepancies (less than 1 mm in nine groups of 12) were found in comparison to the American data. Statistical significance was reached only in seven comparisons. In conclusion, the conventional anthropometric and the digital data compared in the current study, though not superimposable, seemed sufficiently interchangeable, at least from a clinical point of view.