Tissue Reactions to Orthodontics part 2

Question 1

Frontal resorption

Answer 1

Ortho force does not occlude blood vessels in the PDL steady remodelling of the tooth socket will result in smooth continuous movement

Question 2

Undermining resorption

Answer 2

Ortho force occlude blood vessels the area becomes hyalinised.
Resorption in this area will not take place until osteoclasts remove bone adjacent to the crushed areas in the PDL.
Osteoclasts reach the PDL the tooth will move

Question 3

Biochemical and cellular responses to sustained pressure against a tooth

Answer 3

within a couple of hours of pressure and tension in the PDL, molecules such as PG and IL-1b levels increase within the PDL.
Osteoclasts appear to arrive in 2 stages implying that some osteoclasts are derived from a local population and others from distant areas via the blood flow. They attack the adjacent lamina dura, removing bone in the process and tooth movement begins.
Osteoblasts are recruited locally from progenitor cells in the PDL. They form bone on the tension side and begin remodelling activity on the compression side.

Question 4

what are the cellular reactions to the application of an optimal orthodontic force?

Answer 4

Pressure areas
- cellular proliferation within a few days
- osteoclasts migrate into PDL
- Resorption of bone and remodelling of PDL fibres
- Tooth movement
Tension areas
- stretching of PDL fibres
- cellular proliferation of fibroblasts and osteoblasts
- inc length of PDL fibres
- deposition of osteoid
- remodelling and reattachment of PDL fibres, and calcification of osteoid into mature bone

Question 5

what are the cellular reactions to the application of an excessive orthodontic force?

Answer 5

Pressure areas
- capillary blood vessels are crushed resulting in death of cells in PDL
- in areas adjacent to the hyalinised sections of PDL, cellular proliferation occurs
- Resorption occurs deep to hyalinised area from cancellous bone outwards towards the lamina dura (undermining resorption)
- tooth movement occurs

Question 6

relationship between force and tooth movement

Answer 6

6 hours in any 24 hours
20-25 g/cm2 of tooth root surface area

Question 7

duration of force

Answer 7

continuous
interrupted
intermittent

Question 8

continuous force

Answer 8

force maintained at some appreciable fraction of the original from one patient visit to the next.
fixed appliances

Question 9

interrupted force

Answer 9

intially force is high, then decays to ideal and then to zero between visits (activations) e.g., removable appliance springs
undermining resorption which repairs between visits

Question 10

intermittent force

Answer 10

force only present when appliance worn e.g., removable appliances.
force levels decline to zero when removable appliance is taken out

Question 11

crestal bone loss

Answer 11

slight reduction in bone height (0.5-1mm)

Question 12

root resorption

Answer 12

blunting and shortening of the roots
upper incisors and first permanent molars

Question 13

pulpal damage

Answer 13

pulp is already fibrotic with a poor blood supply then ortho movement may strangulate these blood vessels resulting in necrosis
upper incisors

Question 14

periodontal ligament damage

Answer 14

minimal transient damage unless excessive force has been used to pre-existing periodontal disease

Question 15

decalcification

Answer 15

fixed appliance predispose to plaque accumulation
lesions can regress following removal of the appliance but some patients may be left with scarring of the enamel