Embryo notes ch 6-7 - DHYG Embryo 341 Chapter 6 Initial teeth for both dentitions develop in the mandibular anterior region o Followed by maxillary

Embryo notes ch 6-7 - DHYG Embryo 341 Chapter 6 Initial...

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DHYG Embryo 341 Chapter 6 - Initial teeth for both dentitions develop in the mandibular anterior region o Followed by maxillary anterior region o Development progresses posteriorly in both jaw - Primary dentition develops in both embryonic and fetal period - Most of the permanent dentition is formed during the fetal period Initiation - Odontogenesis of primary dentition begins between 6 th and 7 th week of embryonic period - Ectodermal tissue must influence the mesenchymal tissue to initiate o Mesenchyme reciprocates induction to ectoderm - Beginning of 6 th week the stomodeum is lined by ectoderm o Ectoderm gives rise to oral epithelium consisting of 2 horseshoe shaped bands of tissue at surface of stomodeum These bands will make the dental arches o Deep to oral epithelium is ectomesenchyme derived from NCCs NCCs assist in formation of the cranial sensor ganglia and differentiate to form most of the connective tissue of the head o Basement membrane is an acellular structure that separates the oral epithelium and ectomesenchyme within stomodeum o During end of 7 th week, the oral epithelium grows deeper into the ectomesenchyme and produces dental lamina o Dental lamina begins to form initially in midline for both arches and progresses posteriorly Lack of initiation within dental lamina results in absence of a tooth or multiple teeth (anodontia) Adontia most common in third molar, maxillary lateral incisor, and mandibular second premolar Also associated with syndrome of ectodermal dysplasia Adontia can also result from endocrine dysfunction, systemic disease, and exposure to excess radiation Supernumerary teeth – development of one or more extra teeth can also occur Result from persisting clusters of the dental lamina and have hereditary etiology Most common in maxillary central incisors, distal to the maxillary 3 rd molars, and in the premolar region May cause dentition displacement, crowding, delayed eruption, and occlusal disruption Usually removed by surgery Bud stage - Occurs at beginning of 8 th week
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- Extensive proliferation (main part of this stage) of the dental lamina into buds – 3 dimensional oval masses penetrating into the surrounding ectomesenchyme - Max and mand will have 10 bud at the end of the proliferation process - Basement membrane remains between bud and ectomesenchyme - Bud plus ectomesenchyme will develop into tooth germ during next stage - Thus all teeth develop from both ectoderm and mesenchyme (ectomesenchyme) which is derived from NCCs - Parts of dental lamina not producing buds disintegrates - Abnormal proliferation at this stage can cause single, multiple, or entire dentition to be larger or smaller than usual o Macrodontia or microdontia o True partial microdontia common in permanent 3 rd molar and maxillary lateral incisor o Complete microdontia rarely occurs but can be associated with hypopituitarism or Down syndrome o Childhood hyperpituitarism (giantism) can produce macrodontia o
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