4 - Aetiology of Malocclusion: Skeletal and Soft Tissue Factors Flashcards
Lecture Aims:
1. Understand how to examine patients and recognise skeletal soft tissue and dental
factors, and appreciate the role these play in the aetiology of malocclusion.
2. Appreciate the significance in determining tooth position and occlusion.
Define malocclusion
List 3 things malocclusion occurs as a result of
Malocclusion = appreciable deviations from the ideal considering functionally or aesthetically unsatisfactory
Malocclusion occurs as a result of:
- Genetically determined factors
- Environmental factors
- Combination of both
Aetiology of Malocclusion
List 3 Genetically determined factors:
List 2 Environmental factors
Extra - if something is in zone of balance, teeth move accordingly
Aetiology of Malocclusion
It is a combination of which factors?
The cranial base is represented by a line between sella turcica and the nasion (junction of the frontal and nasal bone
The patient on the right has a skeletal class II relationship.
The mandible is positioned further back.
The patient has proclined incisors because the patient has a lip trap.
Skeletal factors
We need to analyse patients in all 3 planes of space:
- Anterior-posterior plane
- Vertical plane
- Transverse plane
Skeletal factors
What are occlusal relationships affected by?
Occlusal relationships are affected by the A-P position of the maxilla and mandible
Both the maxilla and mandible are attached to the cranial base
Therefore, growth in the cranial base and cranial base angle can affect the occlusal relationship
Skeletal Factors: A-P Class I:
The maxilla and mandible are in a good A-P position and the skeletal pattern and occlusal relationship are class I
There may be some malalignment within the arch, but you don’t normally see larger overjet, provided the teeth have not been influenced by secondary environmental factors
(Both maxilla and mandible have normal relationship to cranial base)
Skeletal factors - A-P Class II – Maxillary Protrusion:
The class II skeletal pattern can be produced with a normal sized and a well-positioned mandible, but the maxilla being protrusive/prognathic
Sometimes the patient can have a large maxilla, which is further forwards - This brings the upper teeth further forward in relationship to the face, causing an increase in overjet.
The further back the lower jaw goes, the more likely the lower lip finds itself behind the upper incisors, further proclining them
Skeletal factors - A-P Class II – Mandibular Retrognathia:
The class II skeletal pattern can be due to the mandible being small or positioned too far posteriorly
The result of this is still an increase in overjet.
It is important to know whether the class II has been caused by a prognathic maxilla, or a retrusive mandible.
Skeletal factors- A-P Class III – Mandibular Prognathism:
The class III skeletal pattern can be due to a retrognathic maxilla, a large or prognathic mandible, or as is most common, a combination of both. The occlusion is class III
Skeletal factors: Vertical
The vertical skeletal pattern has an effect on the occlusal relationships:
- Ideally, we want the upper face height and the lower face height to be 50:50
- Increased vertical dimensions are associated with anterior open bite and incomplete overbite
- Decreased vertical dimension is associated with deep overbite
Increased or decreased vertical dimension?
Effects?
Increased or decreased vertical dimension?
Reduction in lower face height- distance between subnasale and soft tissue menton is smaller than upper face height
Deep overbite
Increased or reduced vertical?
Skeletal Factors – Transverse:
What can transverse discrepancies cause?
What radiograph commonly used to assess this?
Transverse discrepancies in the skeletal pattern will affect the occlusion and can result in posterior crossbites
The x-ray that is usually taken to check this is a skull posteroanterior (PA) view. This is to make sure that there are no skeletal problem, and that the mandible is symmetrical. It also allows you to check if the width of the mandible is the same as the width of the maxilla
Skeletal factors: transverse
What does narrow maxilla cause?
Bilateral posterior crossbite
Skeletal factors: transverse
What can wide maxilla or narrow mandible cause?
May produce a lingual buccal cross bite, which is also called a scissor bite
There is no posterior occlusion. The patients can have a big problem in terms of mastication
Radiographic Skeletal Classification:
What radiograph is used?
Lateral Skull Cephalometric Radiograph - A-P the relationship of how the maxilla is related to the mandible is described and classified as class I, II or III
Can be used to assess the position of the maxilla and the mandible, to the cranial base.
Digitisers or computers will identify all he landmarks, and the distances and angles between them for you
Cephalometric analysis
Identify landmarks eg sella, naseon, point A = deepest concavity of the maxilla, angle SNA - tells us how maxilla is related to cranial base, point B - position of the mandible to the cranial base
Then draw lines that join up points and measure angles
Done with digitisers or on computers
Cephalometric skeletal classification
2 commonly used analysis to classify the skeletal pattern:
Cephalometric Skeletal classification - Identify the 3 aspects assessed:
Cephalometric skeletal classification
Eastman analysis - What is the relevant angle for class I-III? What is the value of that angle for all?
Cephalometric skeletal classification
Vertical skeletal pattern
- Maxillary Mandibular Plane Angle (MMPA):
- Maxillary Plane – ANS (Anterior limit of the maxillary bone) and PNS (Posterior limit of the maxillary bone) and join the lines up
Mandibular plane – From hard tissue menton and the angle of the mandible and join the lines up. - Lower Facial Height (LFH)
Cephalometric skeletal classification - Dental:
- Upper incisor angulation in comparison to the maxillary plane.
- Lower incisors to the mandibular plane.
You have to compare these angles with the patients ethnic norm - If they deviate from the norm, you have to figure out why eg why proclined or retroclined so you can give appropriate
Soft tissue factors
List 4
- lips
- adenoids
- tongue
- periodontal ligament
Final position of teeth is in position of equilibrium between cheeks and lips on outside and tongue inside -> Equilibrium theory
Soft tissue factors affecting Malocclusion - List 5 factors and their effects
Tongue
- Size – Enlarged tongues will likely cause very broad arches, as it is pushing out against
the dental arch.
- Rest position – The rest position of the tongue is important. If the tongue rests in a forward position between the upper and lower incisors an increase in skeletal vertical proportions will occur. This will lead to an anterior open bite.
Identify the relevant soft tissue factor affecting malocclusion and skeletal class
Identify the relevant soft tissue factor affecting malocclusion
Soft tissue factors: Habits
What does the effect on the occlusion of thumb sucking depend on: (3)
List 5 effects of a habit
Unlike anterior open bite associated with tongue, anterior open bite associated with Habit is ASSYMETRICAL
Posterior crossbites – When thumb sucking, the tongue is depressed. Therefore the
cheeks are exerting a force inwards, but the tongue is not opposing the force outwards. The cheeks will cause constriction of the maxillary arch. This leads to a cusp to cusp relationship on closure which is not comfortable for the patient.
Therefore mandibular displacement to one side occurs, leading to a unilateral posterior crossbite.
Soft tissue factors: Periodontal Ligament
Drifting of incisors in periodontal disease.
Soft tissue factors: Adenoidal facies
Typical features - (3)
Enlarged adenoids and tonsils can lead to difficulty in nasal breathing so pt become mouth breathers
Mouth breathing may affect skeletal pattern and occlusion.
- Tend to tip head upwards and lead mouth open.
- Posterior growth rotations
- Where the mandible is rotating in a backward direction.
- This leads to patients having long faces.
- Tongue descends and cannot oppose the cheek pressure.
- Patients tend to have narrow arches and posterior crossbites.
- Typical features are:
- Increased vertical dimension, backwards rotators. - Narrow maxilla, posterior crossbites - Reduced overbite - Narrow nose
Soft tissue factors: Fraenum — affecting occlusion
Fraenum
- Under tongue, inside upper and lower lip, connects cheeks to the gums.
- Connected to incisive papilla
- Thick fleshy, fibrous tissue
- Blanching papilla
- V shaped notch on radiograph.
- Fraenum is a small fold of tissue that secures or restricts the motion of a mobile organ tissue. This can cause a midline diastema, but not always
Iatrogenic Environmental Factors – Poorly designed mouth guards:
- An appliance in the mouth changes the environment of the teeth.
- The design of the appliance is extremely important if tooth movement is not desired
Aetiology of malocclusion - Dentoalveolar factors
