NEET MDS Lessons
Dental Anatomy
Interarch relationship can be viewed from a stationary (fixed) and a dynamic (movable ) perspective
1.Stationary Relationship
a) .Centric Relation is the most superior relationship of the condyle of the mandible to the articular fossa of the temporal bone as determined by the bones ligaments. and muscles of the temporomandibular joint; in an ideal dentition it is the same as centric occlusion
Centric occlusion is habitual occlusion where maximum intercuspation occurs
The characteristics of centric occlusion are
(1) Overjet: or that characteristic of maxillary teeth to overlap the mandibular teeth in a horizontal direction by 1 to 2 mm the maxilla arch is slightly larger; functions to protect the narrow edge of the incisors and provide for an intercusping relation of posterior teeth
(2) Overbite or that characteristic of maxillary anterior teeth to overlap the mandibular anterior teeth in a vertical direction by a third of the lower crown height facilitates scissor like function of incisors
(3) Intercuspation. or that characteristic of posterior teeth to intermesh in a faciolingual direction The mandibular facial and maxillary lingual cusp are centric cusps yhat contact interocclusally in the opposing arch
(4) Interdigitation, or that characteristic_of that tooth to articulate with two opposing teeth (except for the mandibular central incisors and the maxillary last molars); a mandibular tooth occludes with the same tooth in the upper arch and the one mesial to it; a maxillary tooth occludes with the same tooth in the mandibular arch and the one distal to it.
2. Dynamic interarch relationshjps are result of functional mandibular movements that start and end with centric occlusion during mastication
a. Mandibular movements are
(1) Depression (opening)
(2) Elevation (closing)
(3) Protrusion (thrust forward)
(4) Retrusion (bring back)
(5) Lateral movements right and left; one side is always the working side and one the balancing or nonworking side
b. Mandibular movements from centric occlusion are guided by the maxillary teeth
(1) Protrusion is guided by the incisors called incisal guidence
(2) Lateral movments are guided by the Canines on the working side in young, unworn dentitions (cuspid rise or cuspid protected occlusion); guided by incisors and posterior teeth in older worn. dentition (incisal/group guidance)
c. As mandibular movements commence from centric occlusion, posterior teeth should disengage in protrusion the posterior teeth on the balancing side should disengage in lateral movement
d. If tooth contact occurs where teeth should be disengaged, occlusal interference or premature contacts exist.
Maxillary Second Deciduous Molar.
-The notation is A or J.
-It looks like a first permanent molar
-There are three roots.
-Usually it has four well developed cusps.
-It is somwhat rhomboidal in outline.
-They often have the Carabelli trait.
- the shape the maxillary first permanent molar strongly resembles that of the adjacent deciduous second molar.
Periodontal ligament development
Cells from the dental follicle give rise to the periodontal ligaments (PDL).
Formation of the periodontal ligaments begins with ligament fibroblasts from the dental follicle. These fibroblasts secrete collagen, which interacts with fibers on the surfaces of adjacent bone and cementum. This interaction leads to an attachment that develops as the tooth erupts into the mouth. The occlusion, which is the arrangement of teeth and how teeth in opposite arches come in contact with one another, continually affects the formation of periodontal ligaments. This perpetual creation of periodontal ligaments leads to the formation of groups of fibers in different orientations, such as horizontal and oblique fibers.
Angle classified these relationships by using the first permanent molars
Normal or neutral occlusion (ideal):
Mesiobuccalgroove of the mandibular first molar align with the mesiobuccal cusp of the max laxy first permanent molar
ClassI malocclusion normal molar relationships with alterations to other characteristics of the occlusion such as versions, crossbites, excessive overjets, or overbites
Class II malocclusion a distal relation of the mesiobuccal groove of the mandibular first permanent molar to the mesiobuccal cusp of the maxillary first permanent molar
Division I: protruded maxillary anterior teeth
Division II: one or more maxillary anterior teeth retruded
Class III malocclusion a mesial relation of the mesiobuccal groove of the mandibular first permanent molar to the mesiobuccal cusp of the maxillary molar
MANDIBULAR THIRD MOLAR
Facial: The crown is often short and has a rounded outline.
Lingual: Similarly, the crown is short and the crown is bulbous.
Proximal: Mesially and distally, this tooth resembles the first and second molars. The crown of the third molar, however, is shorter than either of the other molars
Occlusal: Four or five cusps may be present. Occlusal surface is a same as of the first or second molar, or poorly developed with many accessory grooves. The occlusal outline is often ovoid and the occlusal surface is constricted. Occasionally, the surface has so many grooves that it is described as crenulated--a condition seen in the great apes
Contact Points; The rounded mesial surface has its contact area more cervical than any other lower molar. There is no tooth distal to the third molar..
Roots:-The roots, two in number, are shorter in length and tend to be fused together. they show a distinct distal curve
TYPES OF TEETH
The human permanent dentition is divided into four classes of teeth based on appearance and function or position.
Incisors, Canines, Premolars & Molars
Development of occlusion.
A. Occlusion usually means the contact relationship in function. Concepts of occlusion vary with almost every specialty of dentistry.
Centric occlusion is the maximum contact and/or intercuspation of the teeth.
B. Occlusion is the sum total of many factors.
1. Genetic factors.
-Teeth can vary in size. Examples are microdontia (very small teeth) and macrodontia (very large teeth). Incidentally, Australian aborigines have the largest molar tooth size—some 35% larger than the smallest molar tooth group
-The shape of individual teeth can vary (such as third molars and the upper lateral incisors.)
-They can vary when and where they erupt, or they may not erupt at all (impaction).
-Teeth can be congenitally missing (partial or complete anodontia), or there can be extra (supernumerary) teeth.
-The skeletal support (maxilla/mandible) and how they are related to each other can vary considerably from the norm.
2. Environmental factors.
-Habits can have an affect: wear, thumbsucking, pipestem or cigarette holder usage, orthodontic appliances, orthodontic retainers have an influence on the occlusion.
3.Muscular pressure.
-Once the teeth erupt into the oral cavity, the position of teeth is affected by other teeth, both in the same dental arch and by teeth in the opposing dental arch.
-Teeth are affected by muscular pressure on the facial side (by cheeks/lips) and on the lingual side (by the tongue).
C. Occlusion constantly changes with development, maturity, and aging.
1 . There is change with the eruption and shedding of teeth as the successional changes from deciduous to permanent dentitions take place.
2. Tooth wear is significant over a lifetime. Abrasion, the wearing away of the occlusal surface reduces crown height and alters occlusal anatomy.
Attrition of the proximal surfaces reduces the mesial-distal dimensions of the teeth and significantly reduces arch length over a lifetime.
Abraision is the wear of teeth by agencies other than the friction of one tooth against another.
Attrition is the wear of teeth by one tooth rubbing against another
3. Tooth loss leaves one or more teeth without an antagonist. Also, teeth drift, tip, and rotate when other teeth in the arch are extracted.