[Twins and the heritability of dentofacial phenotype]

Multiple Dental Inclusion in Monozygotic Twins with Congenital Visual Impairment

The study presents two monozygotic twins (MZ) with multiple impacted teeth, affecting the upper canines and lower second molars, as well as congenital aniridia. The clinical aspect of the upper canines is peculiar because of the different positions—palatal in one and buccal in the other twin. Studies reporting different scenarios of impaction in monozygotic twins can contribute more data to the debate on tooth eruption aetiology and more so in this case because of the association with a genetic panocular disease. Patients' Concerns. The patients were referred by a general dentist, who diagnosed the presence of multiple inclusions. Diagnostic Study. Both patients showed severe malocclusion, classified as grade 5 of the Index of Orthodontic Treatment Need (IOTN). The MZ showed class I malocclusion, upper and lower crowding, and impacted lower right and left second molars. A Dentascan was prescribed for the canine impaction. The impaction of the upper canine was palatal of 2.3 in one of the MZ and buccal of 1.3 in the other one. The same altered pattern of eruption of the lower second molars was identified in both twins. The proposed treatment plan contemplated orthodontic surgical recovery of the impacted elements, followed by orthodontic treatment with multibracket appliance after the extraction of the first four premolars, given the crowding entity. The use of a retraction spring action was chosen for the recovery of the lower second molars. Many aspects of the possible genetic aetiology of tooth impaction are still under discussion. The study of diseases in twins offers decisive information. Finally, the possibility that alterations in the eruptive pattern of the dental elements may be associated with other congenital problems broadens the range of investigations related to the possible aetiological causes of the inclusions in humans.

Heritability of Craniofacial Characteristics in Twins - Cephalometric Study

Introduction:

The growth and development of the craniofacial complex are under the influence of genetic and environmental factors, which determine its morphological and functional characteristics. Twin studies provide significant insight into how many genetic and environmental factors determine dental and craniofacial characteristics.

Aim:

The aim of the study was to determine the genetic influence on craniofacial complex using a twin study model.

Methods:

The study sample comprised 52 pairs of twins who were referred to the Orthodontic Department, School of Dental medicine, University of Sarajevo. Informed consent was obtained by the parents of the children included in the study. Twenty pairs of twins were diagnosed as monozygotic while 32 pairs were diagnosed as dizygotic. Zygosity was diagnosed by physical characteristics similarity. Nineteen variables were measured: 10 dental variables, 9 cephalometric.

Results:

Based on the findings of this study, t-test showed significant genetic effect on the length of cranial base (p = 0.03), corpus of maxilla (p = 0.02) and mandibular length (p = 0.03), and also for B-angle (p = 0.04). Environmental factors are more involved in determining dental traits (e.g., the inclination of the incisors).

Conclusion:

There is a significant genetic effect on the linear cephalometric variables: the length of the cranial base, maxillary length and mandibular length.

[Do scoliotic patients need increased orthodontic treatment? A comparative study on 104 cases]

INTRODUCTION

The diagnosis of scoliosis during orthodontic treatment is often attributed to orthodontic treatment, which may be a simple confounding factor. Do scoliotic patients require increased orthodontic treatment? Is the extent of their need for orthodontic treatment correlated with the severity of their scoliosis?

MATERIAL AND METHOD

The authors conducted a comparative multicenter epidemiological study between a group of patients with a proven diagnosis of scoliosis objectified by the Cobb angle and a control group recruited from the general population. The endpoint was the Index Of Orthodontic Treatment Need (IOTN). The calculation of the number of subjects was made a priori. A statistical significance threshold of 5% was used for the statistical analysis.

RESULTS

In this study, 104 patients were included: 36 patients (10 boys, 26 girls) with an average age of 12.1 years (+/-2.3 years) in the scoliosis group (mean Cobb angle = 21°) versus 69 patients (20 boys, 49 girls) with an average age of 12 years (+/-2.7 years) in the control group. Patients with scoliosis have a significantly higher need for orthodontic treatment than the general population. The study did not correlate the severity of scoliosis with the increased need for orthodontic treatment.

DISCUSSION

Thus, the diagnosis of scoliosis during orthodontic treatment should not systematically result in the removal of the orthodontic appliance over-hastily held responsible for the scoliotic condition.

A genetic heritage; the same yet different: A comparative study in twins

Since the 19th century, and in every field of medicine, monozygotic twins have been studied to assess the involvement of genetic and environmental factors in phenotypic expression. The phenotype/genotype relationship remains the leading problem in contemporary biology. In dentofacial orthopedics, this relationship is of relevance in the three-dimensional approach to the face, in both diagnosis and treatment. The present study of two monozygotic twins presenting skeletal class III malocclusions which were genetic yet different is a clear illustration of the interaction of genotype and epigenetic factors with environmental influences. We will demonstrate that treatment can reduce phenotypic differences.

Le facteur ethnique est-il un indicateur thérapeutique?

Face au diktat de la beauté imposée par la société à travers des stéréotypes, il est devenu légitime de s’interroger sur le concept universel du “ beau ”. Est-ce que les normes esthétiques en orthodontie, établies à partir d’échantillons de Nord-Américains, peuvent être applicables à d’autres populations? Les différentes analyses céphalométriques menées chez des sujets afro-américains, africains et asiatiques en occlusion normale non traitée mettent en évidence des critères esthétiques éloignés des critères nord-américains. Leurs conclusions relatent comme principal caractère ethnique la biprotrusion alvéolo-dentaire en relation avec un angle naso-labial réduit. Pour le sujet africain, on note très fréquemment une antéro-position du maxillaire avec une position mandibulaire inchangée ou rétruse. Pour le sujet asiatique, une similitude des profils cutanés est rapportée avec une divergence quant aux profils squelettiques : les Japonais présentent une rétrognathie maxillaire plus prononcée; les Chinois montrent souvent une promaxilie et une rétromandibulie. Les Coréens se rapprocheraient des Japonais. Il semble donc nécessaire de constituer des données spécifiques à l’origine ethnique afin d’optimiser le diagnostic esthétique et les objectifs du traitement orthodontique.