Malocclusion Etiology

Etiology of Malocclusion

• Occlusion refers to the way teeth fit together.
• Ideal occlusion is a perfect alignment of teeth.
• Normal occlusion is acceptable alignment, not necessarily perfect.
• Lawrence Andrew identified six keys to occlusion in 1972: molar relation, crown angulation, crown inclination, no rotation, no spacing, and a flat occlusal plane.
• Malocclusion includes conditions like crossbite (front and back teeth), crowding, open bite, protrusion, deep bite, underbite, spacing, and issues related to oral habits.
• Malocclusion etiology has skeletal, soft tissues, dental, and habits factors

Skeletal Factors

• Skeletal malocclusion includes Class I, Class II, Class III

Specific Causes of Malocclusion

• A small percentage (5%) of malocclusions have a specific cause, while the majority result from complex interactions between genetics and environmental factors.
• Specific causes include disturbances in embryologic development, growth disturbances in the fetal and perinatal periods, progressive deformities in childhood, disturbances arising in adolescence or early adult life, and disturbances of dental development.

Disturbances in utero

• The majority of defects caused in utero are incompatible with survival, however, a number of specific causes are known to exist.
• Agents capable of causing embryological defects are called teratogens i.e. Aspirin, Smoking, Retinoic acid, Alcohol
• Less than 1% of children need orthodontic treatment due to disturbances in embryological development.
• The facial features of fetal alcohol syndrome include short palpebral fissures, flat midface, short nose, indistinct philtrum, thin upper lip, low nasal bridge, epicanthal folds, micrognathia, and minor ear anomalies.
• Treacher Collins syndrome (mandibulofacial dysostosis) is caused by a lack of mesenchymal tissue in the lateral face, impacting lateral orbital and zygomatic areas. Ears may also be involved.

Growth Disturbances in the Fetal and Perinatal Period

• Injuries that are apparent at birth are typically categorized into intrauterine molding and trauma to the mandible during birth, especially from the use of forceps.
• Severe maxillary deficiency at birth could happen if an arm is pressed across the face in utero.
• Mandible growth might be prevented by a fetus’ head being tightly flexed against the chest in utero. This relates to decreased amniotic fluid volume.
• Facial deformity, in rare cases, occurs from birth trauma, usually because of damage to the condyles. Condylar cartilage now accounts for only 25% of overall mandibular growth.

Progressive Deformities in Childhood

• Condyle fractures of the mandible are the most common fracture in childhood.
• 75% of children with condyle fractures have normal mandibular growth because the condyle often regenerates well. Growth disturbances are usually associated with trauma, where scarring prevents normal growth and development.
• Rheumatoid arthritis is an uncommon cause of facial asymmetry, but multiple joints including the temporomandibular joints (TMJs) may be affected.

Disturbances Arising in Adolescence or Early Adult Life

• Acromegaly is caused by an anterior pituitary tumor, leading to an excess of growth hormone. It results in continuous mandibular growth, creating a Class III skeletal relationship, usually seen in adults.

Genetic Influences

• Malocclusions are inherited and can be seen across families like the "Hapsburg jaw" in the German royal family.
• Mandibular prognathism (Class III) is the most inheritable tendency followed by long-face deformity.
• Orthodontic success can be affected by large genetic component. A anterior open bite caused by a digit habit will be easier to treat than one caused by craniofacial morphology.

Importance when determining the etiology of malocclusion

• Malocclusion is multifactorial, an environment can make treatment more difficult to treat if the genetics have more influence
• Environmental factors are more expressive of orthodontic prognosis if its better.
• Distinguishing genetic and environmental is difficult since available diagnostic tools are suggestive, blunt, and not precise.

Role of the soft tissues

• Secondary effect in moderate to severe Class 2 skeletal patterns: Lower lip can be trapped behind the upper incisors exacerbating Class II division 1 incisor relationship, which causes upper incisors to be proclined and lower incisors to be retroclined.

Lip line and competence

• Lip line: the lower lip should cover 1/3 to 1½ of the upper incisor in the anterior-posterior and vertical position to aid stability.
• Competence of lips: Where lips are incompetent, the tongue will strive with the palate, incisors or lower lip to achieve an anterior oral seal. The adaptive anterior oral seal can be lip to lip. In-competent lip can be tongue to lower lip, or lower lip to palate.

Tongue

• In younger children with reasonably normal occlusion, tongue thrust swallowing represents only a transitional stage in normal physiologic maturation.
• In individuals of any age, tongue thrust swallowing is an adaptation to the space between the teeth or to achieve anterior oral seal.
• Endogenous tongue thrust, or a neurological disorder.
• Total force per day is usually under 1000.
• Forward resting position of the tongue, the duration, even is very light, could affect tooth position horizontal or vertical

Muscle Dysfunction

• Facial asymmetry in a boy whose masseter muscle was largely missing on the left side
• Facial asymmetry in a 6-year-old girl with torticollis: Excessive muscle contraction can restrict growth in a way analogous to scarring after an injury
• Lengthening of the lower face typically occurs in patients with muscle weakness syndromes, as in this 15-year-old boy with muscular dystrophy

Disturbances of Dental Development

• Specific causes include disturbances in embryologic development, growth disturbances in the fetal and perinatal periods, progressive deformities in childhood, disturbances arising in adolescence or early adult life, and disturbances of dental development.
• Congenitally Missing Teeth: Anodontia, oligodontia, and hypodontia, the former 2 are usually associated with a systemic abnormality.
• Disproportionately small or large maxillary lateral incisors are relatively common. It is easier to build up small laterals than reduce the size of large ones, because dentin is likely to be exposed interproximally. Other development factors include Malformed and Supernumerary Teeth and Traumatic Displacement of Teeth.

Environmental Influences

• Equilibrium Considerations: light sustained pressures from lips, cheeks, and tongue at rest are important determinants of tooth position
• Masticatory Function: Only effect on the width of the dental arches.
• Biting Force and Eruption: no relationship or bearing on the vertical facial development.
• Sucking and other habits: Thumb Sucking, Proclination of the upper incisors, Retroclination of the lower incisors, Maxillary constriction, Unilateral crossbite, Anterior open bite is caused by a combination of interference with eruption of the incisors and excessive eruption of the posterior teeth causing a step in the occlusal plane.
• Cheek pressures are greatest at the corners of the mouth, this probably explains why the maxillary arch tends to become V-shaped. A child who sucks vigorously is more likely to have a narrow upper arch than one who just places the thumb between the teeth.
• Tongue Thrusting
• Respiratory Pattern- nitric oxide is produced in the nasal sinuses, secreted into the nasal passages and inhaled through the nose . increased pressure from the stretched cheeks might cause a narrower maxillary dental arch.

Adenoid Face

• In 1872, C.V Tomes coined the term "adenoid faces” to describe the long lean id-face with high arched palate and dental crowding present in children with chronic nasal airway obstruction.
• α: craniovertebral angle: immediate change in head posture when nostrils are totally blocked: Head tips back about 5 degrees, increasing separation of jaws; head posture returns to original position when obstruction is relieved.

Etiology in Contemporary Perspective

• Contemporary research has refuted simplistic pictures of malocclusion and research findings have consistently found that there are no simple explanations for malocclusion in terms of oral function.
• Mouth breathing, tongue thrusting, soft diet, sleeping posture-none of these can be regarded as the sole or even the major reason for most malocclusions.
• Conclusions about the etiology of most orthodontic problems are difficult because several interacting factors probably played a role.