Important Points

1. The mandible is made up of the alveolar process, the condyle, the ramus and the corpus.
2. The Gonial Angle of the mandible plays an important part in the position of the lower incisor teeth.
3. Variations in the size or shape of different component parts often sums to produce the same overall result.

Lecture Notes

• Remember that displacement of bone only occurs at surfaces. Displacement cannot occur within bone.
• The maxilla grows upwards and backwards at its posterior surface (the back of the mouth or the maxillary tuberosity), but it is also displaced downwards and forwards as the face grows.
• From this we can conclude that crowded maxillary anterior teeth will not fix themselves because the maxilla does not grow in these areas. That is, there is little deposition of bone at the front of the maxilla (it even undergoes some resorption).

• In the early days, the mandible was thought to be a curved long bone. It isn't. The only thing that a mandible has in common with a long bone is that it is one continuous bone. Really, it is made up of different component parts (which have fused at the time of birth to form a continuous bone).

  Parts of the Mandible  
1. Alveolar Process ­ The less dense, more vascular (spongy) portions of the mandible that contains teeth (Remember, the teeth are embedded in the periodontium). It is induced to form by the presence of the dentition (bone-tooth interdependency). If you loose your teeth, then the alveolar bone resorbs since it is no longer stimulated to be there. It is said to undergo disuse atrophy. Disuse atrophy involves the surface activity of bone resorption. The alveolar process makes up a big portion of the middle of the face once it is present.  The alveolar process grows out of the corpus.
• Resorption never stops. This is why dentures must be relined periodically. The resorbing bone is replaced by a synthetic material in the denture. Dentures are not a replacement for teeth, they are a replacement for NO teeth.
• If someone is born without teeth, (anodontia), the development of the alveolar process is affected the most.
• When we place implants, we like to place them in alveolar bone. Implants do not move in bone as teeth do. In this case, an implant acts like an ankylosed tooth.

2. Corpus (body) ­ largely consists of cortical (dense) bone. It supports the alveolar process by forming a base for it.
• The tip of the chin experiences deposition (the nose is also another site of continuous deposition) throughout life. Both of the structures grow continuously. The chin and nose grow significantly at puberty.

3. Mandibular Condyle ­ The primary function of the condyle is to fine tune the articulation of the mandible to the maxilla. It is capable of remodeling (deposition and resorption) which permits adaptation. It is also capable of endochondral (cartilage converted to bone) growth. The condyle actually tends to adapt to changes in the maxilla. The condyles are always undergoing loading. Therefore, they will adapt to minute changes in the mandible throughout life. (fine tuning).
• BOARD QUESTION - The mandibular condyle is the primary growth site of the mandible. It is capable of both a) articulation and b) endochondral bone formation.
• Endochondral bone formation occurs at the condylar cartilage.

4. Ramus ­ Provides the functional connection between the mandibular condyle and the corpus/alveolar process. It serves as an important area for creating modifications between the mandibular condyle and the corpus. Exhibits no displacement, just remodeling (deposition and resorption).
• Large variations in the length of the mandible are often due to the ramus.

• The mandible is the only bone that's not attached (fused) to the skull.
• There is huge morphological variations in the mandible between people.
• The mandible undergoes constant remodeling.
• The tip of the chin is depository, but the rest of the anterior mandible is resorptive.
• The angle between the ramus and the corpus of the mandible is called the Gonial Angle. This angle has a large influence on the position of the upper and lower incisors with respect to each other.
• If the Gonial Angle is larger (more obtuse), (more brachycephalic), then the mandible becomes larger (more Angle's Class III). Similarly, decreasing the Gonial Angle (more acute), (more dolichocephalic) makes the mandible smaller (more Angle's Class II).
    Schematic Diagram of the Mandible The red dot represents the condyle and the two lines represent the ramus and corpus/alveolar process.  
• In part B of the figure, variations in the size of the Gonial Angle changes the position of the lower incisor teeth.  In many cases, variations of in the mandible will still produce a functional occlusion through compensations in the angles of the teeth.
• In biology, a common principle is often seen where different component parts often sum to achieve the same result. This is particularly evident in the face where different individuals have unique shapes or sizes of their face, but most people still have a functional dentition (that is, their teeth still come together in a functional way).
• Here is a simple example of how different parts can produce the same result.
 

• In each case, the sizes of boxes A, B and C are different, but together the three boxes produce a larger box of the same length.

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