الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 151 |  |  |
| | | from | 151 | | |
Abstract
HA has osteoinductive effects on the dental supporting tissues as well as its ability to decrease alveolar bone resorption, these properties might be promising to enhance orthodontic anchorage and minimize post-orthodontic relapse. The objective of this study is to use an experimental rabbit model to evaluate the effect of local administration of HA on orthodontic tooth movement and post-orthodontic relapse. Histological analysis will help to understand the underlying biological processes which will help to enhance better control over orthodontic anchorage and minimize relapse after orthodontic tooth movement using a safe pharmacologic agent.
Forty-five rabbits were equally and randomly divided into three groups. Split mouth design was implemented in the three groups. A 12 mm NiTi closed coil was fixed between lower first premolar in each side and the incisors delivering 100 gm of force and left for 21 days to achieve proper magnitude of orthodontic tooth movement. This orthodontic appliance was used for the three groups and for 21 days.
In group I the orthodontic tooth movement was the point of concern, so injection was done before tooth movement initiation. Saline was injected on the control side (subgroup A), while HA was injected on the experimental side (Subgroup B). Animals were sacrificed after 21 days from orthodontic force application (day 21).
In groups II and III, relapse of the orthodontically moved teeth was the point of concern, so injection of HA was done after the end of the initial tooth movement (after 21 days). The rabbits were anaesthetized to remove the orthodontic appliance and the premolars were left to relapse without any retention appliance.
In group II, HA was injected after the removal of the orthodontic appliance (day 21) in the experimental side (Subgroup B) while the control side was injected by saline. The premolars were left to relapse for 21 days (3 weeks) then animals were killed (day 42). In group III Rabbits received the previously mentioned active orthodontic appliance for 21 days without any injections then left without any retention for another 21 days for relapse. Subgroup A: Injection of placebo saline twice, the first is immediately after the orthodontic appliance removal (day 21) and the second after 21 days of relapse period (day 42). Subgroup B: Injection of HA twice, the first is immediately after the orthodontic appliance removal (day 21) and the second after 21 days of relapse period (day 42). Animals were killed after 6weeks of removing orthodontic force (day 63).
Precise polyvinyl siloxane impressions of the experimental teeth were obtained then poured and the casts were scanned by a 3D scanner to create 3D models. Orthodontic tooth movement was measured in both subgroups in group I and compared. In groups II and III, amount of first premolar relapse on both experimental and control sides was measured and compared. Histological sections were prepared for descriptive and histomorphometric analysis.
In group I, the magnitude of experimental tooth movement was 1.79 ± 0.17mm in control subgroup A on the 21st day of experimental tooth movement, while in subgroup B a relative reduction of the magnitude of tooth movement was reported yielding 1.61±0.16mm. Percentage inhibition of total magnitude of tooth movement was calculated and it was about 9.44 ± 7.86 %. Results of paired samples t-test revealed the presence of a significant difference (P> 0.001). There was a reduction in number and extent of bone resorption lacuna in subgroup B comparison to subgroup A and this was confirmed by the significant reduction in osteoclasts count in subgroup B.
In group II, in control subgroup A, the magnitude of post-orthodontic relapse was 1.19 ± 0.27mm with a percentage of 69.39 ± 10.08% of the initial tooth movement. In subgroup B (injection of HA), the magnitude of post-orthodontic relapse was 0.95 ± 0.22mm with a percentage of 54.68 ± 10.67% of the initial tooth movement. The relapse in subgroup B was statistically significant less than in subgroup A. Histologic and histomorphometric analyses for group II revealed a reduction in osteoclastic counts and the areas of active bone resorptive lacunae in the experimental side which received HA injection.
In group III, after 3 weeks of relapse, in control subgroup A, there was 1.25 ± 0.23mm relapse with percentage of 69.63 ± 9.99% relapse from the original tooth movement. In subgroup B, there was less amount of relapse 0.93 ± 0.24mm with percentage of 53.74 ± 12.06%. There was statistically significant difference between the relapse in both groups in the first three weeks as showed by paired t-test (P<0.001) and also between the percentage of relapse between both groups (P<0.001).
In the second 3 weeks of relapse (from 3rd week to 6th week), the magnitude of relapse was 0.37 ± 0.13mm in control subgroup A, with percentage of 20.99 ± 7.30% from the initial tooth movement. In subgroup B, magnitude of relapse was 0.34 ± 0.12mm with percentage of 19.89 ± 6.34%. There was no statistically significant difference between the 2 groups in both magnitude of relapse or percentage of relapse with paired t-test (P=0.28) and (P=0.62) respectively.
Comparison between both groups regarding the total amount of relapse (0 to 6 weeks) showed that, the total amount of relapse for subgroup A was 1.54 ± 0.19mm which represent 86.90 ± 4.41% from the initial tooth movement, while in subgroup B the total amount of relapse was 1.39 ± 0.28mm with percentage of 73.30± 10.44% from the initial tooth movement. There was statistically significant difference between the total amounts of tooth movement in both groups.