Aetiology of malocclusion - skeletal pattern and soft tissues Flashcards
How does the relationship of the jaws to each other determine the position of teeth?
Tooth forms from dental lamina
so the relative positions of the teeth to each other will depend on the position if the dental follicle, which will be determined by the relationship of the jaws to each other - skeletal pattern
How do soft tissues affect the position of teeth in the mouth?
When teeth emerge into the mouth they will come under the influence of the surrounding muscles, lips, cheeks and tongue
The forces exerted by these soft tissues will result in the guidance of the teeth during their eruption into the position of balance and stability
Teeth in malocclusion are in a stable position, what does this mean for when carrying out treatment?
Successful treatment will mean preserving the position of balance or moving the teeth into a new stable position
What dental factors affect the tooth position?
Tooth-tissue ratio, the number of teeth, relative position and paths of eruption
What are the local factors that affect tooth position?
Habits,
Effect of the labial fraenum
Pathological conditions
What is the only connection between the mandible and maxilla?
occlusion of teeth
Since the mandible is attached to the cranial base via the squamous part of the temporal bone
and the maxilla is attached via the sphenoid bone
What is the skeletal classification based on?
The relationship of the deepest points in the incisor segment of the maxilla and the mandible
What is a class I skeletal relationship?
The basal bone of the mandible is normal in relation to the maxilla
What is a class II skeletal relationship?
The basal bone of the mandible is post-normal in relation to the maxilla
What is a class III skeletal relationship?
Basal bone of the mandible is pre-normal to the maxila
What are the 3 planes of space to consider the skeletal pattern?
Antero-posterior
Vertical
Lateral
What is the most common cause of class II in antero-posterior position?
A retrusive mandible - the mandible joint is set further back on the cranial base
What effect does an increased lower face height have on the vertical relation?
Reduced overbite
Anterior openbite
What effect does a decreased lower face height have on the vertical relation?
Deep overbite
What can an imbalance in lateral relation result in?
Crossbite
Defined as buccal or lingual
May be a result of antero-posterior discrepancy in class III skeletal pattern
What are the soft tissue factors you need to consider?
Lips and cheeks
Tongue
Muscles of mastication
What are incompetent lips?
Are apart at rest - little evidence of muscular or electro-muscular activity
80% children have incompetent lips, may gradually become competent in time due to differential growth rates of skeletal and soft tissue elements
What is the aetiology of incompetent lips?
Size - may have short upper lip
Skeletal discrepancy - lips are muscles, related to the bones of the facial skeleton, so skeletal pattern may determine whether lips are brought together
What can the skeletal discrepacy that causes incompent lips be affected by?
Antero-posterior discrepancy or vertical discrepancy
What can an oral seal do?
Exert extra forces on the teeth
How is a lip seal obtained?
Muscular effort
Mandibular posture
Lip/tongue contact
What does lip/tongue contact depend on?
the lip-line
The relationship of the lower lip to the upper incisors
How can having a high lip line affect the incisor relationship?
With a severe antero-posterior skeletal discrepancy and class II div I incisor relationship - lower lip placed behing the upper incisors on the palate or teeth Or High lip line with reduced lower face height will produce a class II div II incisor relationship since the lower lip will be on the labial side of the upper incisors
How can having a low lip line affect the incisor relationship?
The lower lip contacts the tongue thus dispersing the upper incisors
Strap lower lip - rare, hyperactive lower lip
What is the significance of a strap lower lip?
the overjet must be fully resduced in order to be stable
What is a sign of a hyperactive lower lip?
the presence of a deep mentalis fold
What are the extrinsic muscles of the tongue?
Hyoid
Styloid and palatal bones
How can having a large tongue improve as grow?
Large tongue may improve as child matures since there is an increase in lower face height with growth and the tongue somes to rest lower in the mouth
How can discrepancy in the size of maxilla and mandible affect the tongue and then affect tooth development?
If the maxilla is larger than the mandible, the tongue may rest between them and prevent the vertical development of the posterior teeth
How can a large tongue cause problem in cases treated with orthognathic surgery?
A large tongue may be a factor in relapse
What are the functions of the tongue?
mastication, SWALLOWING, and speech
At birth what is the position of the of the mandible and tongue compared to when older?
Mandible is held in a lower position, and the tongue lower and further forwards from the pharyngeal wall
How does feeding of an infant take place (suckling of milk) - INFANTILE SWALLOW
Milk ducts are surrounded by smooth muscle and are stimulated by suckling of the infant
Milk is directed into the tongue which is over the lower lip
At what age do 50% of children have an adult swallow?
By age 6
What is the normal adult swallow?
The lips are closed
The teeth are in light occlusal contact
the tongue is elecated to the palate
The teeth are clenched tightly as the food is pressed between the palate and the floor of the mouth
What is the adaptive swallow caused by?
Teeth being apart -lip incompetence
the tongue does not move into the upper arch, there may be narrowing of the upper arch, a buccal crossbite and lack of full development of the buccal segements `
Teeth together - reduced overbite, anterior open bite- the tongue is positioned forwards
What is an endogenous tongue thrust swallow?
What is the problem with it?
This is a primary atypical neuromuscular pattern
it occurs in less than 3% of cases and is not treatable
What does the effect of soft tissue effects depend on?
the duration and intensity of the forces
What is the most significant factor of force on the soft tissues?
Continuous resting force from the soft tissues
Relaxed muscles - 10g of force for 24h/day
What are the non-occlusal mandibular positions?
Rest
Adaptive posturakl
What are the occlusal mandibular positions?
Retruded contact position
Intercuspal
Ligamentous
What is the rest position?
Endogenous postural position
Muscles are in relaxed state, condyles are retruded and the mandible is held in unstrained attitude
There is a freeway space
The rest position is controlled by feedback mechanisma and is not fixed
What is the rest position affected by?
Head posture -when head tilted back, freeway space increases, when tilted forwards = decrease in freeway space
Age
Loss of teeth - if mandibular teeth are lost, the mandible comes closer to the maxilla
What are adaptive postural positinos adapeted in order to do?
Maintain and oral seal
Acheive oral respiration
What postural positions may be adapted in class II div I incisor relationships?
where there is adequate lip length, the mandible is postured forwards - for comfort and function
What are adaptive postural positions for class III incisor?
forward posture for the teeth to meet edge-to-edge
What are the 3 occlusal positions?
Retruded contact
Intercuspal - determined by tooth position
Ligamentous
What is the retruded contact position?
The condyles are in the most posterior position
What is the ligamentous position?
this is a forced retruded position and the amount is limited by the ligaments
Usually 2mm posterior to intercuspal
What are mandibular movements under control of?
voluntary control and reflex activities governed by sensory and proprioceptive impulses
What is normal madibular movement to occlusion?
A simple hinge from rest over 3mm
What is deviation from the mandibular movement?
closure from the postured position
What is displacement mandibular movement?
Starts from rest but may displace from normal movement due to premature contact
What is lateral displacement?
Crossbite
What is an example of an antero-posterior displacement
in a mild class III where the patient acheives edge-to-edge incisal occlusion but then postures forwards to a more comfortable bite
What is a posterior displacement?
Due to overclosure with loss of posterior teeth
What is an example of an environmental factor that has led to malocclusion?
Failure of eruption of an upper central incisor as a result of dilaceration following an episode of trauma during the deciduous dentition which led to intrusion of the primary tooth
What is meant by the true vertical line?
head and neck position
not facing up or down, just straight ahead
What is the frankfort mandibular plane angle?
Frankfort mandibular plane and the tangent to the lower border of the mandible - see where they meet
What does an increase in FMP angle mean?
Anterior openbite
Meets anterior to the back of the head - significant increase in face height
What does a decrease in FMP angle mean?
deep bite, reduced anterior face height
What casues a ‘gummy smile’?
Short upper lip and top jaw set down too far
Upper jaw verically placed lower than should be
What are potentially competent lips?
Would meet if overjet is reduced
Need to get the lower lip around the teeth to meet
What is a normal lip line?
Lower lip rests in the middle of the upper incisor
What happens if the lower lip is above the crown of the upper incisors?
Class II div II incisors
Force is pushing back the upper incisors - contributing to retroclined upper incisors
What may lead you to needing an adaptive thrust?
thumb sucking - anterior open bite
when swallow need to brung tongue forwards to create a seal
What does an endogenous tongue thrust cause to happen?
What is this associated with?
tongue causes an anterior open bite by pushing the teeth forwards
Lisping and bimaxillary proclination
What are the problems with digit sucking?
Reduced overbite/incomplete Preventing eruption of upper incisors Proclining upper incisors Retroclines lower incisors Can get trasverse effect - posterior crossbite - reduced intraoral pressure
What does low labial frenum attachement cause?
diastema - causing spacing
