Dental Anatomy CH. 6

• tooth development which takes place in many stages
• no clear cut beginning or end point between stages
• -physiological processes that occur during these stages parallel the processes that occur in the formation of other embryonic structures (i.e. face)

teeth

embryonic and fetal

• fetal period
• continues after birth, specifically the 2nd and 3rd molars

• initiation
• bud stage
• cap stage
• bell stage

occurs during the 6th and 7th week of prenatal development

• physiological process
• an interaction between embryonic tissues

ectodermal tissues

• lining of embryo's stomodeum (primitive mouth)
• beginning of 6th week

• forms the outer portion (ectoderm)
• consists of 2 horseshoe-shaped bands of tissue at the surface of the stomodeum which become the upper/lower jaws

• forms concurrently
• originally from the ectoderm
• influenced by neural crest cells

• acellular structure which separates the oral epithelium from the ectomesenchyme
• similar to tissue separating all epithelial and connective tissues

• during the 7th week
• induced by the oral epithelium
• begins initially to form the midline and progresses posteriorly

• anodontia
• ectodermal Dysplasia
• supernumerary teeth

• lack of initiation
• common with permanent mas lateral incisors, third molars, and second man molars

syndrome associated with anodontia

• endocrine dysplasia
• systemic disease
• excessive radiation exposure

• abnormal initiation leading to the development of extra teeth
• common: max central incisors, distal to max 3rd molars, premolar region of both arches
• teeth are smaller than normal, accidentally discovered by radiographic exam
• may be erupted or not
• may cause crowding
• removal often necessary

• beginning of the 8th week
• -Extensive proliferation or growth of the dental lamina into buds penetrating into the ectomesenchyme
• -At the end of this proliferation process, both the future max and future mand arches of the primary dentition will each have 10 tooth buds.
• -Each bud will develop into a tooth germ and its supporting tissues -Basement membrane remains btw bud and growing ectomesenchyme
• -Only proliferation of the two tissues occur during this stage; no cellular structural change -Where teeth will not be forming, the dental lamina only remains thickened and later disintegrates as developing oral mucosa comes to line the oral cavity

• Macrodontia
• Microdontia

• abnormal proliferation leading to a single tooth or entire dentition to be larger than normal; splitting or fusion of enamel organ not true macrodontia
• hereditary

• single tooth or entire dentition develops smaller than normal
• hereditary
• permanent max lateral incisors (peg laterals)
• permanent 3rd molars (peg molars)

pituitary gland

• -Occurs during 9th and 10th week during fetal period
• -Unequal growth in different parts of the tooth bud leading to formation of a cap shape attached to the dental lamina
• -levels of differentiation (cytodifferentiation, histodifferentiation, morphodifferentiation) are active during this stage
• morphogenesis is predominant

• primordium of the tooth develops with a specific form
• consists of the enamel organ, dental papilla, dental sac
• develops into primary dentition

• originally derived from the ectoderm
• depression on the deepest part of the dental lamina forming a cap eventually forming enamel for outer surface of the tooth

• a mass within the concavity of the cap of the enamel organ
• will become the dentin and pulp

• still exists between the enamel organ and dental papilla
• will become the dentinoenamel junction

• condensed mass of ectomesenchyme surrounding the enamel organ
• produces periodontium: perio ligament, cementum, alveolar bone

10th week: initiation is occurring for anterior teeth of the permanenent dentition. Successional dental lamina: Each primordium of the permanent dentition is extension of the dental lamina into the ectomesenchyme lingual to the forming primary tooth germs.

-Non succedaneous teeth (permanent molars) develop from a posterior extension of the dental lamina distal the primary 2nd molar’s dental lamina

• dens in dente
• germination
• fusion
• tubercles

• enamel organ abnormally invaginates into the dental papilla
• usually leaves the tooth with a deep lingual pit, which can lead to pulpal exposure, pathology, and endo therapy

• radiographically appears as a "tooth within a tooth"
• hereditary factors involved
• commonly affects permanent max incisors, esp lateral incisor

• single tooth germ unsuccessfully attempts to divide in two
• results in single-rooted tooth with common pulp cavity
• tooth exhibits "twinning" in crown area
• usually occurs in anterior teeth in either dentition
• may be hereditary
• can create problems in spacing and appearance
• radiographically verified

• results from the union of 2 adjacent tooth germs, possibly due to pressure in the area
• -Two distinct pulp cavities, but enamel, dentin, and pulp are united
• -Usually occurs in crown area of tooth, but can involve both crown and root
• -Occurs in anterior teeth of primary dentition

• extra cusps or extensions of enamel
• -found mainly on permanent molars, esp 3rd molars, but can be found on any tooth
• -also lingual extension on the cingulum on perm max ant teeth, exp lateral incisors and canines
• -May be due to trauma, pressure, metabolic disease

• between week 10 and 11
• -Ongoing processes of proliferation, differentiation, and morphogenesis
• -Differentiation on all levels occurs to furthest extent and 4 different types of cells are now found within the enamel organ
• -cap shape from previous stage assumes a bell shape

• increasing amount of collagen fibers forming around enamel organ
• -will differentiate into cementum, perio ligament, alveolar bone

• outer cuboidal cells of enamel organ
• protective barrier for enamel organ

• more outer star-shaped cells in many layers, forming a network within the enamel
• supports the production of the enamel matrix

• most inner layer of flat to cuboidal cells
• supports the production of the enamel matrix

• innermost tall, columnar cells of enamel organ
• differentiates into ameloblasts that form the enamel matrix

• outer layer of cells of the dental papilla nearest the IEE
• there is a basement membrane between these two layers
• will give rise to ondontoblasts that form the dentin matrix

will differentiate into pulp tissue

• apposition
• maturation

• final stage of odonotgenesis during which the enamel, dentin, and cementum are secreted in successive layers.
• -Initially secreted as a matrix which is extracellular substance that is partially calcified yet serves as a framework for later calcification

• 1. Many inductions occur between the ectodermal tissue of the enamel organ and mesenchymal tissues of the dental papilla and dental sac. Basement membrane conveys communication btw these cells as well as acting as a boundary
• 2. These interactions are necessary for the production of enamel, dentin, and cementum by the proliferation of cellular byproducts

other final stage which is reached when the dental tissues are fully mineralized

• enamel dysplasia
• enamel hypoplasia (hutchinson's incisors, mulberry molars)
• enamel hypocalcification
• amelogenesis imperfecta
• dentinogenesis imperfecta

• results from the quantity of enamel matrix;
• teeth appear pitted and grooved

• -Hutchinson’s incisors: crown has screwdriver shape with notched incisal edge
• -Mulberry molars: have enamel tubercles on the occlusal surface

• disturbance results in the reduction of quality of enamel maturation.
• -Teeth appear more opaque, yellower, or browner due to intrinsic staining of enamel

• enamel hypoplasia
• enamel hypocalcification

• enamel dysplasia which is hereditary, can affect all teeth of both dentitions.
• -teeth have very thin enamel portions that chip off or have no enamel at all
• -crowns are yellow and composed of dentin
• -severe attrition can occur due to chewing -no tx required, but may want to place crowns for appearance and prevent further attrition

• dentinal dysplasia which may be hereditary
• -blue/gray or brown teeth with opalescent sheen.
• -enamel is normal, but chips off due to lack of dentinal support
• -results in “dentinal crown” leading to severe attrition
• -no tx required, but may want to place crowns for appearance and prevent further attrition

• During the Bell stage IEE cells grow even more columnar or elongate as they differentiate into pre-ameloblasts
• -repolarization occurs: the nuclei of all the cells move away from the center and position themselves farthest away from the basement membrane
• -In the future, the preameloblasts will differentiate into cells secreting enamel matrix; preameloblasts will also induce dental papilla cells to differentiate

1. After the IEE differentiates into preameloblasts, the outer cells of the dental papilla are induced by the preameloblasts to differentiate into odonoblasts

2. Repolarization occurs in the similar manner as the preameloblasts. However, these cells are lined up next to basement membrane in a mirror image of the preameloblasts.

3. Odonotblasts now begin dentinogensis or production of dentin matrix (predentin) on their side of the basement membrane

4. Odontoblasts start their secretory activity before the enamel matrix production begins.

5. This explains why the dentin layer is slightly thicker than the corresponding layer of enamel matrix