Genetic Factors In Orthodontics Question And Answers

Genetic Factors In Orthodontics

Question 1. Write short note on genetics as cause of malocclusion.
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Write short note on genetics as etiological factor of malocclusion
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Write short note on role of genetics in applied orthodontics.
Or
Discuss in brief genetics in orthodontics.
Or
Briefly describe genetics in orthodontics.
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Write short answer on genetics in orthodontics.
Answer. Genetics: Genetics is the science concerned with the structure and function of all genes in different organisms.

Role of Genetics in Etiology of Malocclusion

Genetic disorders are conditions which are caused due to disturbances in germ plasm or chromosomes or genes.

Genetic disorders can be classified into hereditary and mutational.

Hereditary Disorders

Hereditary disorders are transmitted from one generation to another.

Neel has given the criteria for considering a problem as hereditary disorder:

• Occurrence of disease in definite numerical proportions among individuals related by descent.
• Failure of disease to spread to non–related individuals.
• Onset of disease without a known precipitation acts at a characteristic age.
• Greater concordance of disorder in identical twins.

Read And Learn More: Orthodontics Question And Answers

Mutational Disorders

• These disorders arises de novo in a previously unaffected individual due to damage to the germ plasm.
• As these mutational disorders get transmitted to the future generation, they becomes hereditary.

Types or Modes of Transmission of Malocclusion

Malocclusions are transmitted by three ways i.e. repetitive, discontinuous and variable.

• Repetitive Trait: It is characterized by recurrence of a dentofacial deviation within the immediate family and its progenitors.
• Discontinuous Trait: It is characterized by the recurrence of a malocclusion trait that reappears within the family background over several generations but not continuously.
• Variable Trait: It is characterized by the occurrence of different but related types of malocclusion within several generations of the same family.

Modes of Inheritance

Modes of inheritance are:

• Autosomal dominance
• Autosomal recessive
• X-linked
• Polygenic
• Chromosomal

Genetic Influence

Malocclusions could be produced by heredity in two major possible ways:

• Inherited disproportion between size of teeth and size of jaws.
• Inherited disproportion between size or shape of upper and lower jaws, which leads to occlusal malrelationships.

Genetic Studies

There are basically 2 methods of genetic study, i.e. twin study and family study.

Twin Study

• In this study, twins are compared.
• Comparison of monozygotic twins with dizygotic twins is the best way for determination of extent of genetic effect on malocclusion.

Monozygotic Twins

• These twins happen due to early division of fertilized egg.
• Both individuals will have same DNA.
• These twins are genetically similar and are also known as identical twins.

Dizygotic Twins

• They happen when two eggs fuse with two different spermatozoa.
• These twins will have different DNA
• These twins are genetically dissimilar and are also known as fraternal twins.

Procedure

• Heritability of malocclusion is determined by comparing monozygotic twins, dizygotic twins and the ordinary siblings.
• In monozygotic twins, any change in occlusion should be attributed to environment factor as both have same DNA.
• In dizygotic twins, interplay of genetic and environmental factors is studied.

Disadvantages of Twin Studies

• There is difficulty in identifying identical twins.
• It is very difficult to establish the same environment for twins.

Family Study/Pedigree Study

• In this study, occlusal features as well as differences between mother and child, father and child as well as siblings is analyzed.
• This study helps in differentiating between dominant and recessive traits.
• Dominant traits will be expressed in all the subsequent generation.
• Recessive traits will be expressed in children born of consanguineous marriage.

Contemporary View

Contemporary views on the etiology of malocclusion contribute some of the malocclusions to hereditary or genetic causes, i.e.

• Dental Problem
  • Crowding: It has both hereditary and environment reasons
  • Individual tooth malalignments and crossbites: It is due to pressure environment
• Skeletal Problem
  • This is attributed to inherited or genetic cause such as
    • Retrognathic mandible and maxilla
    • Prognathic mandible (Habsburg jaw)
    • Skeletal deep bite.

Advances in Genetics

• Gene mapping: It is the mapping of genes to specific locations on chromosomes
• Cloning: It is a series of identical DNA.
• Gene therapy: In this there is insertion of normal genes in the bodies of individuals affected with genetic disorder.

Question 2. Write about Butler’s field theory in Genetics.
Or
Write short note on Butler’s field theory.
Answer. Human dentition is divided into four fields, i.e. incisor, canine, premolar and molar. Most distal tooth in each field is the most susceptible to changes or variations. Changes are absence of tooth, variation in size, shape and structure. Accordingly, lateral incisors, second premolars and third molars are the most variable in their group. This is known as Butler’s fild theory.

• Here, canine is the least variable tooth in the arch.
• Butler’s field theory does not apply in lower anterior region, where mandibular central incisor is more commonly missing than lateral incisor.

Example 1

Within Molar/Premolar Field: According to Butler’s fild theory, maximum variability will be seen for the third molars. Third molars are the most common teeth to be congenitally absent and to be impacted.

Variability of third molars includes:

• Variability in size
• Third molars can be small appearing as microdonts. They can have small roots and small cusps.

Variability in Form

• They may have well formed cusps or several small tubercles.
• Some maxillary third molars may not resemble any of the teeth and appear like abnormalities.
• The roots can be very short, long often fused, may be separate and sometimes an extra root can be seen.

Example 2

Within incisor field, according to Butler’s field theory, the maximum variability will be seen for the lateral incisor.

Variability of lateral incisor includes:

• Peg-shaped lateral incisor.
• Congenitally missing laterals.

Example 3

• Within canine field.
• Canines, especially in maxillary arch can be impacted or ectopically erupted.