2: Embryology and Histology

CHAPTER 2 Embryology and Histology

EMBRYOLOGY

Embryology is the study of prenatal development (gestation period), which begins with fertilization and continues until birth. Divided into three periods: preimplantation, embryonic, fetal.

See Chapters 9, Pharmacology: drugs and placental barrier; 11, Clinical Treatment: pregnant patient.
B. Embryonic period (weeks 2 through 8): implanted blastocyst becomes embryo after first week.

DEVELOPMENT OF FACE AND ORAL CAVITY

Face and structures of the oral cavity begin development early in embryonic period. ALL three embryonic layers are involved in facial development (layers are discussed earlier). Depends on five facial processes (prominences) that form during fourth week and surround stomodeum (primitive mouth): (1) single frontonasal process; (2 and 3) paired maxillary processes; and (4 and 5) paired mandibular processes (Figure 2-1). In the future, the stomodeum will form the oral cavity.

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Figure 2-1 Embyro at third to fourth weeks of development.

(From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 2, St. Louis, 2006, Saunders/Elsevier.)

Branchial Apparatus Formation

Branchial apparatus consists of the branchial arches, branchial grooves and membranes, pharyngeal pouches.

Palatal Development

Formation of the palate starts in the embryo during fifth week, takes place during several weeks of prenatal development, and is completed in twelfth week in the fetus (Figure 2-2). Formed from two separate embryonic structures, primary palate and secondary palate. Palate is developed in three consecutive stages: formation of primary palate, formation of secondary palate, completion of final (definitive) palate.

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Figure 2-2 Development of palate.

(From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 2, St. Louis, 2006, Saunders/Elsevier.)

Patient with Cleft Palate and/or Cleft Lip

Cleft palate and/or cleft lip are craniofacial deformities that occur during fourth to twelfth weeks of prenatal development. Etiology is unknown; may involve genetics and exposure to environmental factors such as drugs or toxins (tobacco use, retinoic acid analogues, alcohol, anticonvulsants) during early prenatal development. MOST common class of congenital malformations in United States.

CLINICAL STUDY

Age 21 YRS SCENARIO
Sex image Male image Female Upon extraoral examination during an initial appointment, the dental hygienist notes that there is a notch in the upper lip on the left side of the patient. When asked about it, the patient says it has been there since he was born. Nothing else is noted.
Height 5’8”
Weight 150 LBS
BP 115/75
Chief Complaint None
Medical History Hay fever
Current Medications OTC allergy medications prn
Social History College student in engineering

TOOTH DEVELOPMENT

Child’s primary (deciduous) dentition develops during prenatal period and consists of 20 teeth, which erupt and are later shed (lost). As primary teeth are shed and jaws grow and mature, permanent dentition, consisting of as many as 32 teeth, gradually erupts and replaces primary dentition (Figure 2-3). Primary dentition begins on average with eruption of the mandibular central incisor at 6 to 10 months and is completed with eruption of the maxillary second molar at 25 to 33 months. Permanent dentition begins on average with the eruption of the mandibular first molar or central incisor at 6 to 7 years and is completed with the eruption of the third molars at 17 to 21 years. Discussion of tooth development will center first on the primary dentition and then include the permanent dentition.

See Chapters 4, Head, Neck, and Dental Anatomy: dentitions; 6, General and Oral Pathology: developmental dental disorders.
E. Apposition stage:

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Figure 2-3 Tooth development.

(From Fehrenbach MJ, ed: Dental anatomy coloring book, St. Louis, 2008, Saunders/Elsevier.)

Jan 1, 2015 | Posted by in Dental Hygiene | Comments Off on 2: Embryology and Histology
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