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The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth. [1] [2] [3] They have at least two cusps.
This tissue contains blood vessels and nerves that enter the tooth from a hole at the apex of the root. [23] Along the border between the dentin and the pulp are odontoblasts, which initiate the formation of dentin. [16] Other cells in the pulp include fibroblasts, preodontoblasts, macrophages and T lymphocytes. [24]
The bell stage is known for the histodifferentiation and morphodifferentiation that takes place. The dental organ is bell-shaped during this stage, and the majority of its cells are called stellate reticulum because of their star-shaped appearance. The bell stage is divided into the early bell stage and the late bell stage. [1]
The tooth bud (sometimes called the tooth germ) is an aggregation of cells that eventually forms a tooth and is organized into three parts: the enamel organ, the dental papilla and the dental follicle. [3] The enamel organ is composed of the outer enamel epithelium, inner enamel epithelium, stellate reticulum and stratum intermedium. [3]
Lymphatic system: structures involved in the transfer of lymph between tissues and the blood stream, the lymph and the nodes and vessels that transport it; Musculoskeletal system: muscles provide movement and a skeleton provides structural support and protection with bones, cartilage, ligaments, tendons.
The tonsils also are lymphatic tissue and help mediate the ingestion of pathogens. Tonsils in humans include, from superior to inferior: nasopharyngeal tonsils (also known as adenoids), palatine tonsils, and lingual tonsils. Together this set of lymphatic tissue is called the tonsillar ring or Waldeyer's ring.
Cancellous bone or spongy bone, [12] [11] also known as trabecular bone, is the internal tissue of the skeletal bone and is an open cell porous network that follows the material properties of biofoams. [13] [14] Cancellous bone has a higher surface-area-to-volume ratio than cortical bone and it is less dense. This makes it weaker and more flexible.
Tooth development begins at week 6 in utero, in the oral epithelium. The process is divided into three stages: Initiation; Morphogenesis and; Histogenesis [2]; At the end of week 7 i.u., localised proliferations of cells in the dental laminae form round and oval swellings known as tooth buds, which will eventually develop into mesenchymal cells and surround the enamel organ.