Dear Students
Welcome to the Orthodontics block for 2012. This block is aimed at improving your skill in orthos as well as maintaining the skill.
Please post comments forwarded to you via this media. I will also start a discussion on each of the ortho cases you have for classwork. A picture will be posted and you suggest treatment, each student will receive marks on their comments, whether you agree or disagree with another students treatment or not. You need to justify your comments.
Good luck
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ReplyDeleteTheory Question 1:
ReplyDeleteDescribe/explain the position, extension and angulation of the mandibular acrylic block and its occlusal planes of a Twin Block appliance for the correction of a Class II division I malocclusion with a deep overbite.
Answer:
The position of the occlusal inclined plane is determined by the mandibular block and is important in the treatment of a deep overbite. The inclined plane should be clear of the mesial surface contact with the mandibular molar. This would allow the mandibular molar to erupt unobstructed, thereby reducing the overbite.
The inclined plane on the mandibular acrylic block is angled from the mesial surface of the 2nd premolar or deciduous molar at 70 degrees to the occlusal plane. In cases where the mandibular forward protrusions are inconsistent, the angulation may be reduced to 45 degrees in order for the block to occlude correctly.
The inclined block should extend distally to the buccal cusp of the mandibular 2nd premolar or deciduous molar, stopping short of the distal marginal ridge (this allows the leading edge of the inclined plane of the maxillary appliance to be positioned mesial to the mandibular 1st molar, thereby not obstructing eruption).
Buccolingually the mandibular block covers the occlusal surfaces of the mandibular premolar or deciduous molars, to occlude with the inclined plane on the maxillary twin block. The flat occlusal bite block passes forward over the 1st premolar, and becomes thinner buccolingually in the mandibular canine region. The thickness of the block can be reduced in that area in order to improve speech by allowing the tongue freedom of movement in the phonetic area. In order to avoid breakage, the lingual flange in the midline should be of adequate thickness.
Clark, W.J. 2002. Appliance design and construction. Twin block functional therapy: applications in dentofacial orthopaedics. 2nd ed. London: Mosby. p80.
Material Science Question 1:
ReplyDeleteIn which way is an arrangement of forces called a "couple" related to the force called "moment"?
Answer:
When a body is rotated without translation by two moments equal, parallel, opposite and noncollinear, then this arrangement of forces are called a couple.
A moment is the tendency of a force to cause rotation of a body around a fixed axis. It is one force producing a sliding vector.
Moyers, R.E. 1980. Biomechanics of tooth movements. Handbook of orthodontics. 3rd ed. London: Year Book Medical Publishers Inc. p429.