5 - Development of the Teeth

Development of the dental organ
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Terms in this set (19)
Development of the dental organ
•As early as the second month of fetal life, the development of the deciduous teeth may first become evident.

•The transition from the earliest beginnings of the dental organ through its completion will be outlined in morphologic terms.
Dental Lamina
•An epithelial thickening that occurs in the region where teeth will form

•Occurs at about six weeks of prenatal life
Image: Dental Lamina
Bud Stage
•Shortly after the dental lamina differentiates, twenty tooth buds begin to appear on the dental lamina in the approximate location of the twenty primary teeth.

•The individual tooth buds are somewhat round, or ovoid, and this stage is appropriately known as the bud stage.
Image: Bud Stage
Cap stage
•As further development takes place, the generally round form of the bud is altered.

•The basal portion invaginates, and the structure thus formed gives the appearance of a cap, and hence this phase is termed the cap stage.
Image: Cap stage
Bell stage
•As the concavity on the basal area of the cap continues to deepen, development of the tooth enters the bell stage.

•As this stage nears completion, the form of the tooth's crown can be recognized, and the dentinoenamel junction is identifiable.

•During this time, most of the crown's dentin and enamel is laid down.

•During the latter portion of the bell stage, the dental lamina connection with the deciduous tooth begins to break down, and eventually disintegrates.

•As this portion of the dental lamina disappears, the bud of the succedaneous tooth is forming from it.
Image: Bell stage
Root Development
•When enamel and dentin deposition have formed the area of the cementoenamel junction, the bell is regarded as ending, and the root development stage begins.

•The enamel organ then proliferates a structure known as Hertwig's sheath (epithelial root sheath), from which the root structure is formed.

•The dentin and the cementum of the root are then deposited.
Image: Root Development
Eruption
•Prior to the complete calcification of its root, the tooth normally originates eruption by pushing through the mucous membrane cover of the alveolar process, and into the oral cavity.

•The eruption process is considered complete when the tooth contacts its opponent(s) in the opposite jaw member.

•This term eruption involves two entities:
•Active eruption
•Passive eruption
•Active eruption
•Active eruption is the process just described, from the tooth's entry into the oral cavity, to its contact with an antagonist in the opposing arch.
•Passive eruption
•Passive eruption is the continuing process of adaptation of the tooth to changing incisal and occlusal relationships, after active eruption has ended.
•This adjustment to attritional wear and changing locations of adjacent and opposing teeth, continues throughout the life of the tooth.
Supraeruption
•When a tooth erupts past the normal occlusal plane, usually due to the loss of its antagonist tooth or teeth from the opposing arch.
Nasmyth's membrane•When the tooth erupts, a keratinous, membrane-like enamel cuticle envelopes the anatomical crown. •This structure, also known as nasmyth's membrane, is soon abraded away over most of its extent.Root Completion•As described previously, the root apex is funnel shaped shortly after eruption. •Root formation is thus not complete until additional dentin deposition reduces the funnel shaped opening to a constricted foramen. •At age 3, root formation has ended for all deciduous teeth. •The time lag between eruption and root completion for the deciduous teeth is thus about one year.Position of developing permanent teeth•All the while that the child is in the deciduous dentition stage, the permanent teeth are beginning, and continuing, their growth process. •Remember that the time when the tooth bud first differentiates from the dental lamina is always prior to the initiation of calcification. •Normally the succedaneous tooth buds exhibit a consistent relationship to the roots of the deciduous teeth they are to replace. •The permanent incisors and canine buds, are found in a position just lingual to the roots of their deciduous predecessors. •The premolar buds are located in the root furcation of the deciduous molars. •The permanent molars are not succedaneous teeth, and their buds develop from the dental lamina in the alveolar process distal to the deciduous dentition.Late deciduous stage•By approximately five years of age, growth of the mandible and maxilla has created more space for the permanent teeth which are soon to erupt. •This extra space often results in the creation of diastemas, or spaces between adjacent teeth, usually in the anterior segment of the arches. •Another suggested cause for the diastemas at this stage of development is the pressure exerted from the lingual by the developing permanent anterior teeth. •The greater space in the arches also allows room for the entry of the first molars distal to the deciduous dentition.Permanent first molars•The mandibular first molar is normally the first permanent tooth to emerge, at about age six, thus ending the deciduous dentition stage, and initiating the mixed dentition stage. •The maxillary first molars follow shortly thereafter, and the four first molars are considered to be the cornerstones in the development of occlusion of the permanent dentition.resorption•Shortly after the permanent first molars appear, the permanent mandibular central incisors are scheduled to erupt. Before this can occur, the deciduous predecessors must be shed, or exfoliated. •Generally, resorption begins at the apex and moves toward the cervical line. •The reason for the initiation and progression of resorption is ascribed to the pressure from the permanent tooth crown against the deciduous root, the actual process is due to osteoclastic activity. •The resorption phase normally begins at least a year prior to exfoliation. •Thus, the period between the completion of the root for the second deciduous molars (about 3 years of age), and the initiation of resorption for some deciduous incisors (before age 5), is less than two years.exfoliation•Exfoliation usually occurs symmetrically, with the same teeth of the right and left sides being lost at about the same time. •Mandibular teeth generally precede the same maxillary teeth in exfoliation, with the exception of the second molars, where all four are usually lost simultaneously. •The same series of events occurs for all the deciduous teeth over a range of approximately six years, when the mixed dentition period ends with the exfoliation of the deciduous second molars at about age 12.Incomplete resorption•Occasionally, root resorption is only partial, and the deciduous tooth does not exfoliate. •In this situation, the permanent tooth must erupt in an abnormal position, or be entirely blocked from entry. •If this aberrant feature is present, it is the responsibility of the practitioner to diagnose it, and perform the customary treatment, which is extraction of the offending deciduous tooth.ankylosis•Occasionally, the root surface of the deciduous tooth becomes "fused" to the surrounding alveolar bone. •When this happens, any further eruption ceases, the tooth becomes "fixed" in position, and resorption cannot progress naturally. •This condition is termed ankylosis, and occurs most often with the deciduous molars. •The presence of an ankylosed tooth precludes the proper eruption of the succedaneous tooth, and so the ankylosed tooth must be surgically removed as soon as it is diagnosed.