Oral Embryology and Histology PDF 2015

Introduction Embryology is the study of prenatal development in the stages before birth Learning about the development of the oral structures is the foundation for understanding developmental problems that can occur in these structures...

Introduction Embryology is the study of prenatal development in the stages before birth Learning about the development of the oral structures is the foundation for understanding developmental problems that can occur in these structures 4  Introduction (Cont.) Histology is the study of the structure and function of the tissues on a microscopic level This includes the tissues and structures of the oral mucosa, which surrounds the teeth and lines the mouth Loading… By understanding the histology of the oral tissues, the dental assistant can understand the disease processes that occur in the oral cavity 5  Oral Embryology Pregnancy begins with conception, also known as fertilization This occurs when the sperm penetrates and fertilizes the ovum Birth occurs, on average, 38 weeks after conception, or 40 weeks after the beginning of the last menstrual period (LMP) For general descriptive purposes, this is divided into three trimesters of 3 months each In embryology, developmental age is based on the date of conception, which is assumed to have occurred 2 weeks after the LMP 6  Prenatal Development The preimplantation period is the first week The embryonic period extends from the beginning of the second week to the end of the eighth week; at this time the developing life is known as an embryo The embryonic period is the most critical time in development The fetal phase begins with the ninth week and lasts until birth 10  Primary Embryonic Layers During the third week of development, the cells of the embryo form the three primary embryonic layers: Ectoderm: skin, brain, spinal cord, hair, nails, enamel, lining of oral cavity Mesoderm: bones, muscles, circulatory system, kidneys, reproductive system, lining of abdominal cavity, dentin, pulp and cementum of teeth Endoderm: lining of digestive system, lining of lungs, parts of urogenital system 12  Embryonic Development of the Face and Oral Cavity The face and its related tissues begin to form during the fifth week of prenatal development within the embryonic period (5-8 week) During this time, the rapidly growing brain of the embryo bulges over the oropharyngeal membrane, beating heart, and stomodeum 13  Early Development of the Mouth Fourth week: The stomodeum, or primitive mouth, and primitive pharynx merge, and the stomodeum develops into part of the mouth Fifth week: The embryo is approximately 5 mm long The heart is prominent and bulging Facial development is beginning 16  Branchial Arches By the end of the fourth week, six pairs of branchial arches have formed The first branchial arch forms the lower lip, the muscles of mastication, and the anterior portion of the alveolar process of the mandible. Also known as the Mandibular arch. The second branchial arch forms the styloid process, stapes of the ear, stylohyoid ligament, and part of the hyoid bone. It also forms the side and front of the neck as well as some muscles of facial expression. 17  Development of the Hard and Soft Palates The formation of the palate in the embryo, and later in the fetus, takes several weeks The palate is formed from two separate embryonic structures: Primary palate Secondary palate Any disruption in the process may result in a cleft lip or cleft palate 18  Prenatal Tooth Development The earliest signs of tooth development are found in the anterior mandibular region when the embryo is 5 to 6 weeks old By the 17th week, development of the permanent teeth has begun At birth, there are normally 44 teeth in various stages of development Enamel formation is well under way on all primary dentition and the beginnings of the permanent first molars 21  Developmental Disturbances Disturbances at any stage of dental development may cause a wide variety of anomalies These can be caused by: Genetic factors In prenatal tooth development, the genetic factor that is most often a concern is tooth and jaw size Environmental factors Adverse environmental influences called teratogens include infections, drugs, and exposure to radiation 22  Tooth Movement Remodeling occurs in response to forces placed on the tooth within its socket When force is applied to a tooth and the tooth moves, the bone in front will be resorbed (resorption) Bone will be deposited in back of the tooth to fill the space (deposition) 26  Life Cycle of a Tooth The process of tooth formation, called odontogenesis, is divided into three primary periods: Growth Calcification Eruption 30  Growth Periods The growth period is divided into three stages: The bud stage, also known as initiation, in which the formation of the tooth begins The cap stage, also known as proliferation, in which the cells of the developing tooth increase The bell stage, also known as histodifferentiation and morphodifferentiation, in which the different tissues of the tooth form and its shape are established 31  Pits and Fissures If the tooth has several cusps, a cap of enamel forms over each cusp A fissure is a fault along a developmental groove on the occlusal surface caused by incomplete or imperfect joining of the lobes during the formation of the tooth A pit results when two developmental grooves cross each other, forming a deep area that is too small for the bristle of a toothbrush to clean 35