Fourth Stage Tooth Movement Lecture Notes

Resorption of root surfaces, non-vitality, ankylosis of the tooth

Undermining indirect or rearward resorption

Tearing of blood vessels and ischemia

Due to tearing of blood vessels and ischemia

Pain, loosening of the tooth, healing by ankylosis

Addition of bone to endosteal surface under pressure areas and resorption under tension areas

The periodontal ligament forms a dense network of capillaries or plexus around the tooth, occupying up to half of the periodontal space, facilitating tooth movement.

The three phases are: 1) Pre-eruptive tooth movement, 2) Eruptive tooth movement, and 3) Post-eruptive tooth movement.

Eruptive tooth movement is primarily brought about by the periodontal ligament traction.

Eruptive tooth movement generally begins when about 2/3 portion of the root is formed.

Post-eruptive tooth movement helps maintain the teeth's position in occlusion until jaw growth is completed.

The text mentions three types of tooth movements: physiological, pathological, and orthodontic.

The optimal force for tooth movement varies depending on the type of movement:- Tipping: 35-60 grams- Bodily: 70-120 grams - Root uprighting: 50-100 grams- Rotation: 35-60 grams- Extrusion: 35-60 grams- Intrusion: 10-20 grams

When heavy forces are applied, the periodontal ligament on the pressure side becomes extremely compressed and crushed, possibly causing contact between the tooth and the alveolar bone. This leads to occlusion of blood vessels in that area, depriving the periodontal ligament of nutrients and causing regressive changes like hyalinization. Due to the ischemia and hyalinization, there is no recruitment of osteoclasts, and no resorption occurs on the periosteal surface of the socket, preventing the tooth from moving.

Although it might seem logical that heavier forces could lead to faster tooth movement, this is not the case. Heavy forces can cause compression and crushing of the periodontal ligament on the pressure side, leading to occlusion of blood vessels, ischemia, and hyalinization. This prevents the recruitment of osteoclasts and resorption on the periosteal surface, ultimately preventing the tooth from moving for a period of time.

The optimal orthodontic force depends on the area of the PDL that the applied force is spread across. For example, a low force should be used to intrude a tooth, where the force is concentrated in a small area at the apex. A higher force can be used to bodily move teeth, where the force is spread across the whole side of a tooth root.

The main consequence of the regressive changes, such as hyalinization, caused by heavy orthodontic forces is that there is no recruitment of osteoclasts on the pressure side of the periodontal ligament. This leads to no resorption occurring on the periosteal surface of the socket, preventing the tooth from moving for a period of time.

For intrusion, a low force of 10-20 grams should be used, as the force is concentrated in a small area at the tooth apex. In contrast, for bodily tooth movement, a higher force of 70-120 grams can be used, as the force is spread across the whole side of the tooth root.

The main problem mentioned in the text is to find something that primarily works locally.

The two types of drugs known to depress the response to orthodontic force are prostaglandin inhibitors for pain control and bisphosphonates used in the treatment of osteoporosis.

Orthodontic tooth movement and bone remodeling is accelerated during wound healing (via the regional acceleratory phenomenon described by Frost) after local injury to the alveolar process.

Other classes of drugs that can decrease prostaglandin levels and slow the response to orthodontic force include tricyclic antidepressants, antiarrhythmic agents, antimalarial drugs, anticonvulsant drugs, and doxycycline.

The regional acceleratory phenomenon described by Frost is what accelerates orthodontic tooth movement and bone remodeling during wound healing after local injury to the alveolar process.

The finding that drugs that inhibit tooth movement are frequently encountered, although not yet prescribed for their tooth-stabilizing effect, suggests that there is potential to utilize these drugs to control tooth movement in orthodontic treatment.

Osteoblasts release factors that recruit and activate osteoclasts, which are responsible for bone resorption during orthodontic tooth movement.

Osteoblasts lining the bone represent a physical barrier to resorption, and their retraction provides access for bone-resorbing osteoclasts.

Osteoblasts remove the unmineralized collagen or osteoid that lines the bone surface, which acts as a further physical barrier to osteoclasts.

Any one of the following: Pressure tension theory by Schwartz, Blood flow theory by Bien, Bone bending/piezoelectricity by Picton, Cochran and Grimm, or Mechanochemical theory by Justus and Luft.

There is a consensus about the general nature of the cellular reactions involving osteoblastic and osteoclastic activities that lead to bone resorption and deposition during orthodontic tooth movement.

Osteoclasts show little bone-resorbing activity in isolation, and they appear to be recruited and activated by the presence of osteoblasts.