Etiology of Malocclusion PDF

Etiology of Malocclusion By: Shaho Ziyad Jamil Assistant prof. – Orth. dept. College of Dentistry /HMU B.D.S-M.Sc.- Ph.D. – Specialist Orthodontist December 2024  Occlusion Ideal occlusion Normal occlusion Molar relation Crown angulation Crown Inclination...

Etiology of Malocclusion By: Shaho Ziyad Jamil Assistant prof. – Orth. dept. College of Dentistry /HMU B.D.S-M.Sc.- Ph.D. – Specialist Orthodontist December 2024  Occlusion Ideal occlusion Normal occlusion Molar relation Crown angulation Crown Inclination No Rotation Lawrence Andrew –Six key of occlusion -1972 No Spacing Flat occlusal plane Skeletal Soft tissue Dental Habits Skeletal Factor  Specific Causes of Malocclusion Disturbances in Embryologic Development Growth Disturbances in the Fetal and Perinatal Period Progressive Deformities in Childhood Disturbances Arising in Adolescence or Early Adult Life Disturbances of Dental Development Genetic Influences Environmental Influences Equilibrium Considerations Masticatory Function Sucking and Other Habits Tongue Thrusting Respiratory Pattern Etiology in Contemporary Perspective  Specific Causes of Malocclusion It is thought that 5% of malocclusions are attributable to a specific cause. The remaining malocclusions arise due to a complex interaction between genetics and the environment ❑ Disturbances in Embryologic Development ❑ Growth Disturbances in the Fetal and Perinatal Period ❑ Progressive Deformities in Childhood ❑ Disturbances Arising in Adolescence or Early Adult Life ❑ 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. Examples of these include: Aspirin – Cleft lip and palate Smoking – Cleft lip and palate Retinoic acid – Cleft lip and palate, Treacher Collins Syndrome Alcohol – Foetal alcohol syndrome Less than 1% of children are estimated to have had a disturbance in embryological development that resulted in the need for orthodontic treatment.  Specific Causes of Malocclusion Disturbances in Embryologic Development by exposure to very high blood alcohol levels during the first trimester of pregnancy.  Specific Causes of Malocclusion Disturbances in Embryologic Development In the Treacher Collins syndrome (also called mandibulofacial dysostosis), a generalized lack of mesenchymal tissue in the lateral part of the face is the major cause of the characteristic facial appearance. Note the underdevelopment of the lateral orbital and zygomatic areas. The ears also may be affected. Patient at age 12 before (A) and immediately after (B) surgical treatment to advance the midface. Note this patient’s ear deformity, which usually is concealed by hair. (C and D) Age 16. Note the change in the lateral orbital margins.  Specific Causes of Malocclusion Disturbances in Embryologic Development In craniofacial microsomia, both the external ear and the mandibular ramus are deficient or absent on the affected side. In this patient with a relatively mild problem, note the use of the hairstyle to conceal the ear and short ramus on the affected side.  Specific Causes of Malocclusion Disturbances in Embryologic Development Typical human clefts of the lip and palate. (A) Unilateral incomplete cleft lip in an infant. Note that the cleft is not in the midline but lateral to the midline, and that there is an intact band of tissue beneath the nostril. (B) Bilateral complete cleft lip and palate in an infant. The separation of the premaxilla from the remainder of the maxilla is shown clearly. (C) Same child after lip repair  Specific Causes of Malocclusion Disturbances in Embryologic Development Crouzon’s syndrome The premature fusion frequently extends posteriorly into the cranium, producing distortions of the cranial vault as well. The fusion in the orbital area prevents the maxilla from translating downward and forward, and the result is severe underdevelopment of the middle third of the face.  Specific Causes of Malocclusion Growth Disturbances in the Fetal and Perinatal Period Injuries apparent at birth fall into two major categories: (1) intrauterine molding and (2) trauma to the mandible during the birth process, particularly from the use of forceps during delivery  Specific Causes of Malocclusion Growth Disturbances in the Fetal and Perinatal Period an arm is pressed across the face in utero, resulting in severe maxillary deficiency at birth  Specific Causes of Malocclusion Growth Disturbances in the Fetal and Perinatal Period Occasionally, a fetus’ head is flexed tightly against the chest in utero, preventing the mandible from growing forward normally. This is related to a decreased volume of amniotic fluid, which can occur for any of several reasons  Specific Causes of Malocclusion Growth Disturbances in the Fetal and Perinatal Period Birth trauma Can cause, in rare cases, facial deformity. This occurs usually because of damage to the condyles but the effects become less obvious with growth. The condylar cartilage is now thought to account for only 25% of overall growth of the mandible  Specific Causes of Malocclusion Progressive Deformities in Childhood Childhood Fractures of the Jaws The most common fracture is that of the condyle of the mandible. However, the condyle often regenerates well and 75% of children have normal mandibular growth. In the remaining cases when growth disturbances are associated with trauma the mechanism is thought to be scarring preventing normal growth and development.  Specific Causes of Malocclusion Progressive Deformities in Childhood Rheumatoid arthritis is an uncommon cause of facial asymmetry, but in the polyarticular form of the disease (multiple joints affected), the temporomandibular joints (TMJs) often are involved, and asymmetry may develop as one side is affected more than the other  Specific Causes of Malocclusion Disturbances Arising in Adolescence or Early Adult Life Acromegaly An anterior pituitary tumour causes an excess amount of growth hormone. The manifestations include continual growth of the mandible creating a Class III skeletal relationship. This is often seen in adult life.  Genetic Influences Are malocclusions inherited? It can be seen that some malocclusions are inherited by observing families. Some features such as the famous “Hapsburg jaw” where a prognathic mandible was shown to run in the German royal family.  Genetic Influences Mandibular prognathism (Class III) has the strongest inheritable tendency followed by long-face deformity. The greater the genetic component the worse the prognosis for a successful outcome with orthodontics. It will be potentially easier to treat a malocclusion consisting of an anterior open bite caused solely by a digit habit than if the reason for the habit was due the craniofacial morphology  So what is the importance of determine the aetiology of malocclusion? A. As we know the malocclusion is multifactorial inheritance and if the genetic has more influence than environmental, then treatment will be difficult, B. but if the environment factors are more expressive then the orthodontic prognosis is better. C. However this is not easy since the diagnostic tools available to differentiate between genetic and environmental are suggestive, blunt and not precise. The role of the soft tissues Lip trap This is a secondary effect. In moderate to severe Class 2 skeletal patterns the lower lip can be trapped behind the upper incisors exacerbating the Class II division 1 incisor relationship. Upper incisors would be proclined and lower incisors retroclined Lip line The lower lip should cover 1/3 to ½ of the upper incisor in the anteriorposterior and vertical position to aid stability Competence Where the lips are incompetent, the tongue with the palate, incisors or lower lip will strive to achieve an anterior oral seal Lip to lip anterior oral seal  In-competent lip Adaptive anterior oral seal a. tongue to lower lip  In-competent lip Adaptive anterior oral seal b. Lower lip to palate Adaptive anterior oral seal Tongue to upper lip Lower Lip line High lip line High lip line Aetiology Strap-like lower lip Size  The modern viewpoint is, in short, that tongue thrust swallowing is seen primarily in two circumstances: ❖ In younger children with reasonably normal occlusion, in whom it represents only a transitional stage in normal physiologic maturation; ❖In individuals of any age, in whom it is an adaptation to the space between the teeth or to achieve anterior oral seal ❖Endogenous tongue thrust ( neurological disorder )  The total per day therefore is usually under 1000. “the duration of force is much more important than magnitude of any force acting on dental or skeletal units, based on his equilibrium theory, (Proffit WR. 1970) Forward resting position of the tongue , the duration , even if very light , could affect tooth position H or V ( Ingervall, B. and Thilander, B., 1974 ) On the other hand, if a patient has a forward resting posture of the tongue, the duration of this light pressure could affect tooth position, vertically or horizontally the tongue rests on the palatal surface of the incisors resting on the palatal surface of the upper incisors and on the incisal edges of the lower incisors the tongue assumes a lower position position very low posture of the tongue at rest, associated with a severe AOB  Specific Causes of Malocclusion Muscle Dysfunction Facial asymmetry in a boy whose masseter muscle was largely missing on the left side. The muscle is an important part of the total soft tissue matrix; in its absence growth of the mandible in the affected area also is deficient. (A) Age 4. (B) Age 11. (C) Age 17, after surgery to advance the mandible more on the left than the right side. The soft tissue deficiency from the missing musculature on the left side still is evident.  Specific Causes of Malocclusion Muscle Dysfunction 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  Specific Causes of Malocclusion Muscle Dysfunction A) Lengthening of the lower face typically occurs in patients with muscle weakness syndromes, as in this 15- year-old boy with muscular dystrophy. (B) Anterior open bite, as in this patient, usually (but not always) accompanies excessive face height in patients with muscular weakness Specific Causes of Malocclusion Disturbances in Embryologic Development Growth Disturbances in the Fetal and Perinatal Period Progressive Deformities in Childhood Disturbances Arising in Adolescence or Early Adult Life Specific Causes of Malocclusion Disturbances in Embryologic Development Growth Disturbances in the Fetal and Perinatal Period Progressive Deformities in Childhood Disturbances Arising in Adolescence or Early Adult Life Disturbances of Dental Development  Specific Causes of Malocclusion Disturbances of Dental Development Congenitally Missing Teeth Anodontia, oligodontia hypodontia Anodontia and oligodontia are usually associated with a systemic abnormality Anodontia and oligodontia are usually associated with a systemic abnormality  Specific Causes of Malocclusion Disturbances of Dental Development Malformed and Supernumerary Teeth Disproportionately small (A) or large (B) maxillary lateral incisors are relatively common. This creates a tooth-size discrepancy that makes normal alignment and occlusion almost impossible. It is easier to build up small laterals than reduce the size of large ones, because dentin is likely to be exposed interproximally after more than 1 to 2 mm in width reduction Specific Causes of Malocclusion Disturbances of Dental Development Specific Causes of Malocclusion Disturbances of Dental Development Specific Causes of Malocclusion Disturbances of Dental Development Traumatic Displacement of Teeth Environmental Influences Equilibrium Considerations Masticatory Function Sucking and Other Habits Tongue Thrusting Respiratory Pattern  Environmental Influences Equilibrium Considerations light sustained pressures from lips, cheeks, and tongue at rest are important determinants of tooth position  Environmental Influences Equilibrium Considerations Scarring of the corner of the mouth in this child will occur as the burn from biting an electrical cord heals. From equilibrium theory, one would expect a distortion in the form of the dental arch in the region of the contracting scar, and exactly this occurs after an injury of this type.  Environmental Influences Equilibrium Considerations In this individual, a large part of the cheek was lost because of a tropical infection. Note the outward splaying of the teeth on the affected side after the restraining force of the cheek was lost. (B) After a paralytic stroke, this patient’s tongue rested against the mandibular posterior teeth. Before the stroke, the occlusion was normal; within a few months afterward, an outward splaying of the teeth occurred on the affected side because of the increase in resting tongue pressure Environmental Influences Equilibrium Considerations Masticatory Function  Environmental Influences Masticatory Function Function and Dental Arch Size Function would only have an effect on the width of the dental arches. Biting Force and Eruption biting forces have no relationship or bearing on the vertical facial development Environmental Influences Equilibrium Considerations Masticatory Function Sucking and Other Habits Environmental Influences Sucking and Other Habits From equilibrium theory, one would expect that how much the teeth are displaced would correlate better with the number of hours per day of sucking than with the magnitude of the pressure  Environmental Influences Sucking and Other Habits The main effects are : o Proclination of the upper incisors o Retroclination of the lower incisors o Maxillary constriction o Unilateral crossbite with displacement o Anterior open bite (can be asymmetric) This 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 as a distinct feature.  Environmental Influences Sucking and Other Habits Cheek pressures are greatest at the corners of the mouth, and this probably explains why the maxillary arch tends to become V- shaped, with more constriction across the canines than the molars. A child who sucks vigorously is more likely to have a narrow upper arch than one who just places the thumb between the teeth. Environmental Influences Equilibrium Considerations Masticatory Function Sucking and Other Habits Tongue Thrusting Environmental Influences Tongue Thrusting Environmental Influences Equilibrium Considerations Masticatory Function Sucking and Other Habits Tongue Thrusting Respiratory Pattern Environmental Influences Respiratory Pattern Respiratory Pattern  Environmental Influences Respiratory Pattern Nitric oxide is produced in the nasal sinuses, secreted into the nasal passages and inhaled through the nose  Environmental Influences Respiratory Pattern increased pressure from the stretched cheeks might cause a narrower maxillary dental arch.  Environmental Influences Respiratory Pattern anterior face height would increase, and posterior teeth would super-erupt; (2) unless there was unusual vertical growth of the ramus, the mandible would rotate down and back, opening the bite anteriorly 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  Environmental Influences Respiratory Pattern immediate change in head posture when the nostrils are totally blocked: The head tips back about 5 degrees, increasing the separation of the jaws. When the obstruction is relieved, head posture returns to its original position  Etiology in Contemporary Perspective Contemporary research has refuted the simplistic picture of malocclusion as resulting from independent inheritance of dental and facial characteristics, but the research findings consistently have shown also 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. At least, at this point we are more aware of how much we really do not yet know about the etiology of orthodontic problems.