Knowledge specification DN22
The skull consists of 28 bones, 22 of which form the framework of the head and provide protection for the brain, eyes, and ears; six are ear bones. With the exception of the lower jaw bone and the ear bones, all skull bones are joined together and fixed in one position. The seams where they join are known as sutures. The bones of the skull are classified as either cranial or facial bones.
The cranium is formed by eight major bones, most of which are in pairs. The frontal bone forms the forehead and the roof of each orbit (or eye socket) and the nasal cavity. The parietal bones form the roof of the skull. The temporal bones help form the sides and base of the skull and also house the auditory and hearing organs. The occipital bone forms part of the base and back of the skull, and contains a large hole called the foramen magnum. This opening permits passage of the spinal cord from the cranium into the spinal column. The sphenoid bones are wedged between several other bones in the anterior portion of the skull. These bones help form the base of the cranium, the sides of the skull, and the floors and sides of the orbits. The ethmoid bones are located in front of the sphenoid bone. They form sections of the nasal cavity roof, the cranial floor, and the orbital wall.
The facial bones of the skull consists of 14 bones: 13 immovable bones and a movable lower jawbone. The facial bones give the face its basic shape and provide attachment sites for various muscles that move the jaw and control facial expressions
NERVE SUPPLY OF THE JAWS AND TEETH
Twelve pairs of cranial nerves arise in the brain and give off branches to the structures of the head and face. These nerves leave the cranial cavity through foramina in the base of the cranium. The fifth cranial nerve (the trigeminal nerve) is the largest of the twelve pairs.It is of particular importance in dentistry since it provides the nerve supply to the jaws and the teeth. The fifth cranial nerve contains both motor and sensory fibers. Thus, it has a motor root supplying motor impulses to the muscles of mastication and a sensory root supplying sensory impulses from the structures of the head and face. Before leaving the cranial cavity, the sensory root divides into three branches or divisions.
The face, teeth and jaws are supplied by branches of the external carotid artery.Veins draining these parts eventuly join the superior vena cava and enter the right side of the heart where the deoxygenated blood will pass to the lungs for the reoxyenation.
All people have two sets of teeth. The first, deciduous teeth, and the second, permanent teeth. Deciduous teeth and permanent teeth have different appearances, or morphology, both between sets and within each other, and this is how they can be identified.
The deciduous dentition is made up of central incisors, lateral incisors, canines, first molars, and secondary molars; there is one in each quadrant, making a total of four of each tooth. All of these are replaced with a permanent counterpart except for the first and second molars; they are replaced by premolars. The deciduous teeth will remain until the age of six. At that time, the permanent teeth start to appear in the mouth resulting in mixed dentition. The erupting permanent teeth causes root resorption, where the permanent teeth push down on the roots of the deciduous teeth causing the roots to be dissolved and become absorbed by the forming permanent teeth. The process of shedding deciduous teeth and the replacement by permanent teeth is called exfoliation. This may last from age six to age twelve. By age twelve there usually are only permanent teeth remaining.
Teething age of deciduous teeth:
Central incisors : 6-12 months
Lateral incisors : 9-16 months
Canine teeth : 16-23 months...
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