Day Six: The Jaw and Teeth

Welcome to Day SIX of class!

Today we are looking the mandible and tooth structure. Despite the fact that we are reviewing teeth in this challenge, the teeth are not considered to be bones even if they do resemble them.

Facts about the Mandible:

• The mandible is also known as the jaw or jaw bone

• Gives shape to the bottom half of the face

• Is the only part of the skull that can move independently from the rest of the head. The cranium, brow and cheek bone, nasal cavity, and the upper half of the oral cavity are all stationary and can only move when the whole head is turned or tilted by the neck. This creates one large, singular structure that is separate from the structure of the mandible.

• It opens and closes with the aid of a hinge joint (to be discussed in week three), towards the center mass of the skull

• The jaw can move so we can speak, breath, and chew our food

• The jaw can open at a width of about 1.4 - 2.2 inches, or 35 - 55 millimeters

• When we are born the jaw is made up of two bones which later fuse at about two years of age

• The mandible is the only bone structure to have two individual joints, one on either side of the head

There are four types of teeth, incisors, canines, pre-molars, and molars. Incisors are teeth that are designed to cut and are the eight teeth at the front of the mouth. These front teeth help us to cut into our food and take bites. Besides these are our two canine teeth, of which we have four in total; two on top and two on the bottom. These teeth can be longer than our other teeth, and can grip onto things if it were necessary. Pre-molars and Molars make up the rest of the 16 teeth. Pre-molars are considered to be transitional teeth that are similar to both canines and molars and help get food from the front of the mouth to the back, where molars take over the job of chewing.

Humans are typically born with about 52 teeth in total. 20 baby teeth, or primary teeth, and 30 - 32 adult or permanent teeth. An infants primary teeth start to protrude between the ages of 4 and 6 months. At about the age of 6 permanent teeth start to grow in. These new adult teeth displace and replace the primary teeth, making them fall out. This process ends at around the age of 18 - 21 when all 32 adult teeth have emerged. Most people get their wisdom teeth removed as we have evolved to no longer need them due to the fact that we cook most of our foods as opposed to eating them raw. This has caused our jaws to shrink over time, leaving no room for additional teeth.

Bones

• Are made up of calcium phosphate which makes them strong

• Produce bone marrow which has the ability to create blood cells

• They grow and change as the body develops through childhood and into adult hood

• Have the ability to repair themselves when or if they break at any age