A longitudinal study of facial asymmetry in a normal birth cohort up to 6 years of age and the predisposing factors.

OBJECTIVES: This prospective, population-based cohort study aimed to investigate the development of facial asymmetry up to 6 years of age using a three-dimensional (3D) soft tissue imaging method in a normal population. In addition, the study sought to identify potential predisposing factors to facial asymmetry. METHODS: A total of 102 newborns were enrolled in the study at birth. 3D stereophotogrammetric images of the head and face were analysed at the ages of 12 months (T1), 3 years (T2), and 6 years (T3). The surface-based analysis involved the calculation of the average distance (mm) and the symmetry percentage (%) between the original and mirrored surfaces. For landmark-based analysis, the distance of facial landmarks to the facial midline was examined. RESULTS: The final analysis included 70 (68.6%) subjects. Surface-based analysis showed a significant improvement of facial symmetry from T1 to T3 in all facial areas. Landmark-based analysis showed that upper facial landmarks were located, on average, slightly on the left and lower facial landmarks slightly on the right in relation to the facial midline (P < 0.001). LIMITATIONS: The size of the study population was limited. Facial posture may affect the reliability of the results, especially in younger children. CONCLUSION: Facial asymmetry is detectable in early childhood and tends to reduce with age in young children. The lower face deviates slightly to the right, and the upper face to the left in relation to the facial midline. Possible predisposing factors for facial asymmetry at the age of 6 years include deformational plagiocephaly, sleeping position, and previous facial asymmetry.

Facial asymmetry and chewing sides in twins.

OBJECTIVE: To resolve how the preferred chewing side (PCS) affects facial asymmetry in twins, whether there are differences between monozygotic (MZ) and dizygotic (DZ) twins, and whether the twins with PCS have more asymmetric faces compared to symmetrically chewing twins. MATERIAL AND METHODS: The study included 106 Lithuanian twin pairs of the same sex, 59 MZ and 47 DZ pairs. The data were analysed from facial 3D images and manually added landmarks. 3D images were analysed by Rapidform2006 software and statistical analyses were done by using the R software environment version 4.1.0. RESULTS: The contralateral effect of PCS and larger chin side was dominant among right and non-right side chewing twins. Being female increased the whole face symmetry. CONCLUSION: The volume of the chin becomes larger on the side opposite to the twins' habitual chewing side. As the results are quite similar in both twin types, functional factors are more prominent than heredity.

Exploring the midline soft tissue surface changes from 12 to 15 years of age in three distinct country population cohorts.

INTRODUCTION: Several studies have highlighted differences in the facial features in a White European population. Genetics appear to have a major influence on normal facial variation, and environmental factors are likely to have minor influences on face shape directly or through epigenetic mechanisms. AIM: The aim of this longitudinal cohort study is to determine the rate of change in midline facial landmarks in three distinct homogenous population groups (Finnish, Latvian, and Welsh) from 12.8 to 15.3 years of age. This age range covers the pubertal growth period for the majority of boys and girls. METHODS: A cohort of children aged 12 were monitored for facial growth in three countries [Finland (n = 60), Latvia (n = 107), and Wales (n = 96)]. Three-dimensional facial surface images were acquired (using either laser or photogrammetric methods) at regular intervals (6-12 months) for 4 years. Ethical approval was granted in each country. Nine midline landmarks were identified and the relative spatial positions of these surface landmarks were measured relative to the mid-endocanthion (men) over a 4-year period. RESULTS: This study reports the children who attended 95 per cent of all scanning sessions (Finland 48 out of 60; Latvia 104 out of 107; Wales 50 out of 96). Considerable facial variation is seen for all countries and sexes. There are clear patterns of growth that show different magnitudes at different age groups for the different country groups, sexes, and facial parameters. The greatest single yearly growth rate (5.4 mm) was seen for Welsh males for men-pogonion distance at 13.6 years of age. Males exhibit greater rates of growth compared to females. These variations in magnitude and timings are likely to be influenced by genetic ancestry as a result of population migration. CONCLUSION: The midline points are a simple and valid method to assess the relative spatial positions of facial surface landmarks. This study confirms previous reports on the subtle differences in facial shapes and sizes of male and female children in different populations and also highlights the magnitudes and timings of growth for various midline landmark distances to the men point.

Plagiocephaly after Neonatal Developmental Dysplasia of the Hip at School Age.

Developmental dysplasia of the hip (DDH) may require early abduction treatment with infants sleeping on their back for the first few months of life. As sleeping on back is known to cause deformational plagiocephaly, we assessed school age children treated for dislocation or subluxation of the hip-joint in infancy. Plagiocephaly was analyzed by using cephalic index (CI) and oblique cranial length ratio (OCLR) as anthropometric measurements from 2D digital vertex view photographs. Six of the 58 (10.3%) DDH children and only one of the 62 (1.6%) control children had plagiocephaly (p = 0.041). Furthermore, cross bite was found in 14 (24.1%) of the DDH children and in 7 (10.3%) of the control children. Developmental dysplasia of the hip in infancy was associated with cranial asymmetries and malocclusions at school age. Preventive measures should be implemented.

A 3D Follow-Up Study of Cranial Asymmetry from Early Infancy to Toddler Age after Preterm versus Term Birth.

Preterm infants are at higher risk for both symmetrical and asymmetrical head molding. This study involved 3D stereophotogrammetry to assess the cranial growth, molding, and incidence of deformational plagiocephaly (DP) in preterm children compared to term born children. Thirty-four preterm infants and 34 term born controls were enrolled in this study from Oulu University Hospital, Finland. Three-dimensional head images were obtained at the age of 2-4 months (T1), 5-7 months (T2), 11-13 months (T3), and 2.5-3 years (T4) from the term equivalent age (TEA). There was no statistically significant difference in oblique cranial length ratio (OCLR), cephalic index (CI), or weighted asymmetry score (wAS) between the two groups. Occipital flattening, defined by flatness score (FS) was statistically significantly greater in the preterm group than in the term group at T1-T4 (p < 0.05). In both groups, OCLR improved gradually over time. There were no instances, in either group, of severe DP and no moderate DP after T2. Results indicate that DP affects preterm and full-term children almost equally during the first three years of life, and cranial asymmetry resolves at a similar rate in both preterm and term groups after three months of corrected age. Preterm infants present with more occipital flattening than full-term children.

Relations of laterality and chewing sidedness in twins.

OBJECTIVES: To study, whether there are associations between chewing side preference and other lateralities, whether there is a genetic origin for preferred chewing side (PCS), relations to sex, birth order and orthodontic treatment. MATERIALS AND METHODS: The study included 113 twin pairs, 57 pairs monozygotic, 47 pairs same sex dizygotic and 9 pairs of opposite sex. The lateralities of preferred chewing side, footedness and eyedness were assessed by functional tests and handedness was checked by asking. RESULTS: Right-handed, -footed and -eyed as separated groups, and true-right sided (combined), were evenly distributed by preferred chewing side. By contrast, left-handed, -footed, -eyed and non-right sided used more left or both sides when chewing. Birth order affected preferred chewing side among monozygotic: the first-born twin was more likely to have the preferred chewing side on the non-right, whereas second-born twins used right side. Gender, zygosity and orthodontic treatment were not statistically significant factors. LIMITATIONS: Examination of chewing sidedness could have been done in several different ways to provide a definite result. Sample size of opposite sex twins was very small. CONCLUSIONS: Preferred chewing side generally seemed to follow the side where other lateralities occur; however, monozygotic twins seemed to be more receptive to it. True-right sided were more evenly distributed than non-right sided by the preferred chewing side.

Craniofacial Asymmetry from One to Three Years of Age: A Prospective Cohort Study with 3D Imaging.

Deformational plagiocephaly (DP) is considered a risk factor for facial asymmetry. This cohort-based, prospective, follow-up study used three-dimensional (3D) stereophotogrammetry to assess the development of facial asymmetry in a normal birth cohort and to investigate the impact of DP on facial asymmetry for the age range of one to three years. The study sample consisted of 75 children: 35 girls (47%) and 40 (53%) boys recruited from Oulu University Hospital. A total of 23 (31%) subjects had a history of DP in infancy. 3D facial images were obtained at the mean (SD) age of 1.01 (0.04) year old at T1 and 3.02 (0.14) years old at T2. To determine facial asymmetry, both landmark-based and surface-based facial symmetry methods were used. As measured with the surface-based methods, upper facial symmetry improved from T1 to T2 (p < 0.05). As measured with the landmark-based methods, facial symmetry improved on the upper and lower jaw from T1 to T2 (p < 0.05). The asymmetric effect of DP on the upper parts of the face tends to correct spontaneously during growth. Results indicate that previous DP does not seem to transfer to facial or occlusal asymmetry at the age of three years old.

Childhood intelligence and early tooth wear patterns.

OBJECTIVE: The aim of this study is to explore the relationships between early dental wear patterns and preschool IQ (Intelligence Quotient, by Stanford-Binet) of the child to illuminate the historic relationship of mental queries and bruxism. METHODS: The dental study participants were 864 Euro-American preschool and school children whose IQs were tested for school maturity purposes at the age of 4 years, followed by dental data in a cross-sectional manner at the mean age of 7.8 years. Worn dentitions were classified as "symmetric" or "right-" and "left-sided," based on the faceting of the teeth. RESULTS: In general, the relationships of tooth wear and intelligence were scarce, reflecting social background factors. Statistically significant results between asymmetric wear and gender groups suggest that direction of jaw function has a role in the regulation of processes responsible for individual mental performance in childhood. DISCUSSION: Increased left-side tooth wear and early advantage in the intelligence test in girls is intriguing due to the fact that they reach maturity earlier than boys in verbal articulation, controlled in most cases by the limited area on the left side of the brain.

Accuracy of measurements used to quantify cranial asymmetry in deformational plagiocephaly.

OBJECTIVE: Various measurements are used to quantify cranial asymmetry in deformational plagiocephaly (DP), but studies validating cut-off values and comparing the accuracy of such measurements are lacking. In this study, we compared the accuracy of four different measurements in classifying children with and without DP diagnosed by visual assessment, and sought to determine their optimal cut-off values. STUDY DESIGN: Two experts rated 407 3D craniofacial images of children aged between 3 and 36 months old using the Argenta classification. We then measured the following asymmetry-related variables from the images: Oblique Cranial Length Ratio (OCLR), Diagonal Difference (DD), Posterior Cranial Asymmetry Index (PCAI), and weighted Asymmetry Score (wAS). We created receiver operating characteristic curves to evaluate the accuracy of these variables. RESULTS: All variables performed well, but OCLR consistently provided the best discrimination in terms of area under the curve values. Subject's age had no clear effect on the cut-off values for OCLR, PCAI, and wAS; however, the cut-off for DD increased monotonically with age. When subjects with discrepant expert ratings were excluded, the optimal cut-off values for DP (Argenta class ≥ 1) across all age-groups were 104.0% for OCLR (83% sensitivity, 97% specificity), 10.5% for PCAI (90% sensitivity, 90% specificity), and 24.5 for wAS (88% sensitivity, 90% specificity). CONCLUSION: We recommend using OCLR as the primary measurement, although PCAI and wAS may also be useful in monitoring cranial asymmetry. The threshold of relative asymmetry required for a deformation to appear clinically significant is not affected by the child's age, and DD has no additional utility in monitoring DP compared to using only OCLR.

The course of positional cranial deformation from 3 to 12 months of age and associated risk factors: a follow-up with 3D imaging.

Deformational plagiocephaly is reported in up to 46.6 % of healthy infants, with the highest point prevalence at around 3 months of age. Few prospective studies on the natural course of skull deformation have been conducted, and we know of no studies using 3D imaging starting from the highest point prevalence period. In this prospective, population-based cohort study, we describe the course of cranial asymmetry and shape in an unselected population using 3D stereophotogrammetry and investigate factors associated with late cranial deformation and failure to recover from previous deformation. We evaluated 99 infants at 3, 6, and 12 months of age. We acquired 3D craniofacial images and performed structured clinical examinations and parental interviews at each visit. Eight outcome variables, representing different aspects of cranial shape, were calculated from a total of 288 3D images. Scores of asymmetry-related variables improved throughout the observation period. However, the rate of correction for cranial asymmetry decreased as the infants grew older, also in relation to the rate of head growth, and a significant amount of asymmetry was still present at 12 months. Positional preference at 3 months predicted an unfavorable course of cranial asymmetry after 3 months, increasing the risk for DP persisting. What is known: • The prevalence of deformational plagiocephaly spontaneously decreases after the first months of life. • Limited neck range of motion and infant positional preference increase the risk of deformational plagiocephaly during the first months of life. What is new: • Positional preference at 3 months predicts an unfavorable spontaneous course of deformation also from three to 12 months of age, presenting a potential target for screening and treatment. • The spontaneous rate of correction for cranial asymmetry decreases after 6 months of age, also in relation to the rate of head growth.

Analyzing infant head flatness and asymmetry using kernel density estimation of directional surface data from a craniofacial 3D model.

Infant skull deformation is analyzed using the distribution of head normal vector directions computed from a 3D image. Severity of flatness and asymmetry are quantified by functionals of the kernel estimate of the normal vector direction density. Using image data from 99 infants and clinical deformation ratings made by experts, our approach is compared with some recently suggested methods. The results show that the proposed method performs competitively. Copyright © 2016 John Wiley & Sons, Ltd.

Comparing Facial 3D Analysis With DNA Testing to Determine Zygosities of Twins.

The aim of this study was to compare facial 3D analysis to DNA testing in twin zygosity determinations. Facial 3D images of 106 pairs of young adult Lithuanian twins were taken with a stereophotogrammetric device (3dMD, Atlanta, Georgia) and zygosity was determined according to similarity of facial form. Statistical pattern recognition methodology was used for classification. The results showed that in 75% to 90% of the cases, zygosity determinations were similar to DNA-based results. There were 81 different classification scenarios, including 3 groups, 3 features, 3 different scaling methods, and 3 threshold levels. It appeared that coincidence with 0.5 mm tolerance is the most suitable feature for classification. Also, leaving out scaling improves results in most cases. Scaling was expected to equalize the magnitude of differences and therefore lead to better recognition performance. Still, better classification features and a more effective scaling method or classification in different facial areas could further improve the results. In most of the cases, male pair zygosity recognition was at a higher level compared with females. Erroneously classified twin pairs appear to be obvious outliers in the sample. In particular, faces of young dizygotic (DZ) twins may be so similar that it is very hard to define a feature that would help classify the pair as DZ. Correspondingly, monozygotic (MZ) twins may have faces with quite different shapes. Such anomalous twin pairs are interesting exceptions, but they form a considerable portion in both zygosity groups.

Preventing deformational plagiocephaly through parent guidance: a randomized, controlled trial.

Deformational plagiocephaly (DP) occurs frequently in otherwise healthy infants. Many infants with DP undergo physiotherapy or helmet therapy, and ample treatment-related research is available. However, the possibility of preventing DP has been left with little attention. We sought to evaluate the effectiveness of intervention in the newborn's environment, positioning, and handling on the prevalence of DP at 3 months and to investigate the causal relationship between DP and cervical imbalance. We carried out a randomized controlled trial, with healthy newborns randomized into two groups at birth. All families received standard positioning instructions to prevent SIDS. Additionally, the intervention group received detailed instructions regarding the infant's environment, positioning, and handling, with the goal of creating a nonrestrictive environment that promotes spontaneous physical movement and symmetrical motor development. Two- and three-dimensional photogrammetry served to assess cranial shape and goniometry to measure cervical motion. At 3 months, the prevalence of DP was lower in the intervention group in both 2D (11 vs 31 %) and 3D analyses (15 vs 33 %), and the asymmetry was milder in the intervention group. Infants with DP at follow-up had also developed more torticollis. CONCLUSION: An early educational intervention reduces the prevalence and severity of DP at 3 months. WHAT IS KNOWN: •Deformational plagiocephaly, often with associated torticollis, is common in healthy infants. •Parental education is frequently recommended for preventing deformational plagiocephaly, although information regarding the effectiveness of preventive strategies is scarce. WHAT IS NEW: •Early parent guidance effectively reduces the prevalence and severity of DP and improves the cervical range of motion at three months. •Educating both parents and professionals about proper infant positioning on a national scale could help minimize public healthcare costs.

Masculinization of the eruption pattern of permanent mandibular canines in opposite sex twin girls.

The aim of this study is to explore the effect of prenatal androgenization on the clinical eruption of permanent teeth expressing dimorphism and bimaturism. The eruption curves of permanent teeth (except third molars), including those that make up the canine complex (permanent canines, lower first premolars), are compared among opposite sex twins (OS twins) relative to single-born boys and girls. The comparisons are made with regard to three phases of eruption (pierced mucosa, half- erupted, and completely erupted) from a cross-sectional sample of dental casts, using Kaplan-Meier survival and Cox regression analyzes. The casts were collected from 2159 school children from the US Collaborative Perinatal Project, including 39 pairs of OS-twins, of which 12 pairs (30.8%) were Euro-Americans and 27 pairs (69.2%) were of African-American ancestry. The eruption patterns of the incisors, upper first molars, and lower canines were found to be significantly masculinized (delayed) among OS twin girls. The differences in most other teeth were either not significant, or the number of observations of active eruption phases were too few, such as in the upper first molars and incisors, to yield strong evidence and meaningful results. The masculinization of the tooth eruption pattern in OS twin girls is intriguing because of the lower canine responses during puberty, as well as canine primordial formation during early fetal androgenization of their co-twin during the 8th to 14th gestational weeks. The present results offer a challenge for future research exploring tooth eruption mechanisms, and may also highlight some cases of delayed or ectopic canines, which are biased toward females.

Three-dimensional longitudinal assessment of facial symmetry in adolescents.

Recent advances in laser scanning technology provide the opportunity to examine faces in three dimensions. The aim of this prospective clinical study was to explore facial symmetry in healthy growing individuals and determine whether asymmetric changes occur during adolescent growth. Non-invasive laser surface scanning was performed to capture facial images of 60 Caucasian Finnish adolescents (30 males and 30 females, mean 11.5 years). Facial symmetry was analysed on images obtained at the initial scanning (T1), 2.5 (T2), and 4.5 (T3) years thereafter. The final sample consisted of 39 adolescents (19 males and 20 females, mean 16 years). Three-dimensional images were processed and analysed using an in-house developed subroutine for commercial software. A mirror image was generated and superimposed on the original image to create a symmetric face and establish the midsagittal plane. The surface matching of the original face and the mirror face (amount of symmetry) was measured for the whole face, upper, middle, and lower thirds at tolerance level 0.5 mm and presented with colour maps. Three angular and 14 linear measurements were made based on 21 soft tissue landmarks, which have proven to be reliable. The results of the Friedman test showed that facial symmetry parameters did not significantly differ over time (P > 0.05). Mann-Whitney U-test did not reveal statistically significant differences between genders at any time point (P > 0.05). Facial growth of healthy individuals during adolescence is symmetric, although further investigation on larger randomized sample is suggested.

Primary tooth wear in functional lateralities.

PURPOSE: The purpose of this study was to explore the sidedness of primary tooth horizontal wear facets between the left and right sides of the dentition among 2 types of functionally lateralized (hand, foot, eye) children--those who were true right-sided (TRS), and partially or totally nonright-sided (NRS) at 4 years of age. METHODS: Study subjects were 855 children with signs of wear in deciduous teeth on the dental casts (N=1,720) of the GOS (Genetic Odontometric Study of the Collaborative Perinatal) project, carried out in the 1960s in the United States by the National Institute of Neurological Disorders and Stroke (NINDS) in a cross-sectional manner at a mean age of 8(1/2) years (40% Caucasian and 60% African-American children). The statistical method used was chi-square analysis. RESULTS: Tooth wear was identified from dental casts in approximately 50% of cases. Wear was symmetric (equal on the right and left) in 49% of these dentitions, while asymmetric wear was found in 50%. Left-sided extra wear was slightly more common (26%) than right-sided extra wear (24%), but gender and race differences appeared. Statistically significant unilateral wear was found among TRS Caucasian boys on the dentition's right side. In NRS Caucasian boys, however, the left-sided extra wear was more common than for the right-sided extra wear (P=.04). In Caucasian girls, the same relationship appeared, but the difference was not significant (P=.11). In African American TRS children, the left-sided extra wear was more common, and symmetric proportion was increased in boys. The differences between laterality and gender groups, however, were not statistically significant. CONCLUSIONS: Sidedness in the form and function of a primary dental apparatus has variation among gender and race groups that is involved with the determination of general structural and functional lateralities. Early asymmetric oral functioning (unilateral bolus placement, sucking, chewing, bruxism, etc) should be considered in registration of the various phases of occlusal development, also having craniofacial aspects due to asymmetric growth promoting function.

Primary dentition unilateral crossbite in relation to functional lateralities.

PURPOSE: The aim of this study was to explore primary dentition unilateral crossbite malocclusion prevalences in functionally true right-sided and nonright-sided children, with the latter having 1 or more left-sided or indeterminate functions (eye, hand, foot). METHODS: The transversal relationship of the primary teeth was determined from dental casts of 1,835 young African American (60%) and Caucasian (40%) children in a cross-sectional sample at a mean age of 8.5 years. Hand, foot, and eye preferences (right, left, or indeterminate) were recorded at the age of 4 years during the same collaborative perinatal study. The prevalences of left and right crossbites were compared between true right-sided and mixed or completely nonright-sided children using chi-square analysis. RESULTS: Unilateral crossbite occurred in 140 cases with a complete set of laterality tests: 65 were right-sided and 75 left-sided. True right-sided children had more bilaterally symmetric occlusions and less crossbite on the right side than those having nonright-sidedness in their functions, with the differences being statistically significant (P<.01). CONCLUSIONS: These results point to anatomical relationships between the structures supporting the occlusion, the asymmetric neurocranium, and the cranial base. This suggests variable unilateral compensatory growth after unbalanced fetal asymmetry, modified by sidedness and the growth-stimulating effects of early lateralized functions and oral habits.

Deciduous tooth crown size in prematurely born children.

AIM: The purpose of our study was to examine deciduous tooth crown size in preterm children. SUBJECTS AND METHODS: The subjects consisted of 328 prematurely born (< 37 gestational weeks) white and black children and 1804 controls, who participated in the cross-sectional study of the Collaborative Perinatal Project (USA) in the 1960s and 1970s. Documents of the present research consisted of dental casts of the 6-12 years old children. Tooth crown measurements on canines and molars were performed on the dental casts with an electronic measuring device according to precise definitions generally quoted in the anthropological and genetic literature. For the results, the preterm and control groups were divided by sex and race. RESULTS: There were both increased and decreased mesiodistal and labiolingual tooth crown dimensions in prematurely born children, but no significant differences between the study groups was found. CONCLUSIONS: The findings of the present research suggest that short gestation is not associated with reduced deciduous tooth crown size as suggested by earlier studies and are parallel with our previous results of permanent tooth crown dimensions in prematurely born children. Boys showed clearly larger tooth crown sizes than girls within all preterm and control groups. This indicates that sexual dimorphism is apparent in its final form beginning some months after birth.

The eruption of permanent incisors and first molars in prematurely born children.

The purpose of this work was to examine whether the clinical eruption of the permanent first molars and incisors is affected by pre-term birth. The data applied to 328 prematurely born white and black children and 1804 control children who participated in the Collaborative Perinatal Project (USA) in the early 1960s and 1970s. The dental examinations had been performed in a cross-sectional manner at ages varying from 6 to 12 years in 95 per cent of cases (range 5-14 years). Dental casts were placed in matched pairs by sex, race and conceptional age for comparison of the four clinical stages of eruption of the permanent incisors and first molars between the pre-term and control children. The results showed significantly (P < 0.05) earlier tooth eruption in the pre-term children. The findings suggest that the eruption process is earlier in those teeth that go through a sensitive period circumnatally, being at the pre-eruptive stages and entering the first phases of mineralization under the influence of various neonatal systemic factors and accelerated growth period (catch-up growth) with related unknown mechanisms, which may influence the eruption of the permanent incisors and first molars in prematurely born children.

Sagittal occlusal relationships and asymmetry in prematurely born children.

The aim of this investigation was to examine the effect of pre-term birth on sagittal occlusal relationships. The subjects were 328 prematurely born white and black children and 1804 control children who participated in the cross-sectional study of the Collaborative Perinatal Project (USA) in the early 1960s and 1970s. Dental examinations, including dental casts and photographs, were performed at the age of 6-12 years. The sagittal occlusion of the permanent molars and the canine relationship was recorded by examining and measuring the hard stone casts. The pre-term and comparison groups were divided by sex and race. A significantly greater prevalence of pre-normal canine relationships was found in the pre-term group than in the controls (P < 0.001). The incidence of a bilateral symmetrical canine relationship was 60.3 per cent in both the pre-term and control groups, but in the pre-term group the girls had better symmetry than the boys. Asymmetry occurred significantly more often on the left side (P < 0.001), especially in the control boys, but this was not so clear in the pre-term group. The prevalence of mesial molar occlusion was greater in the pre-term group. These results suggest that premature birth and the consequent exceptional adaptation from intra- to extra-uterine nutrition may influence dental occlusal development. This emphasizes the importance of early functional activity and differences in masticatory muscle activity and the largely unknown phenomenon of early catch-up growth. Individual differences in neonatal factors, in the need for intubation and other medical care are also of importance. Pre-term birth may also interfere with the development of symmetry and lateralization.