الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 225 |  |  |
| | | from | 225 | | |
Abstract
The present study was conducted to evaluate the osseous response to laser biostimulation radiographically and histologically during distraction osteogenesis induced in the mandibles of mongrel dogs.
Eighteen dogs were divided into 3 groups I, II and III according to sacrifice periods, 6 animals(3 laser,3 control) in each group. The dogs were premedicated and anaesthetized by the ordinary technique of general anesthesia; mouth was scrubbed with Povidone Iodine 2% solution. In addition, skin at the right side of the mandible was prepared and painted with antiseptic solution. First, the right and left maxillary third incisor was extracted. Second, the prepared skin was incised 1cm bellow the inferior border of the mandible relevant to lower 2nd& 3rd premolar sites, then soft tissues were reflected laterally exposing the covering periosteum which were incised & reflected laterally and medially exposing bone at the inferior border of the mandible. Further reflection was made to the level of alveolar bone.
An osteotomy line was made between mandibular 2nd& 3rd premolars and the distraction device was placed and fixed along the bone segments with positional bicortical screws then the wound was closed in layers and the bone segments were maintained in neutral position for 7 days as a latency period. Then, the distractor device was activated in the rate of 1 mm per day for 10 days to achieve 10 mm distraction distance followed by consolidation period. During the period of consolidation, the test right mandibular side was laser irradiated using semiconductor Diode(Gallium Arsenide) laser in alternative five sessions in every other day with constant laser parameters (21) as follows:Wave length(λ) = 970 nm, power =2W,
total energy(E)=840j, duty cycle=100%, frequency(γ)=continuous wave CW, delivery system=optical fiber with spot size 320µm and time=420sec(7 min) in perpendicular direction buccally, crestally and at the inferior border along the distraction site while the same side in the control animal was not irradiated after mandibular distraction.
The first group was sacrificed at 2 weeks of consolidation; the second group was sacrificed at 4 weeks of consolidation while the third group was sacrificed at 8 weeks of consolidation period. The mandibles of the dogs were dissected &disarticulated then; the mandibles were split and kept in 10% buffered formalin solution. Postoperative radiographs were taken as follows:
Plain radiography in 1st postoperative day, taken at the end of activation period and at sacrifice periods to evaluate and inspect the the success of the distraction osteogenesis procedure.
Cone beam CT was performed at sacrifice periods 2, 4, and 8 weeks to evaluate formation and measure bone density of newly formed regenerate.
The specimens of regenerates were prepared & stained with Hematoxilin and Eosin and subjected to microscopic examination & histomorphometric analysis for quantitative assessment of the newly formed bone at the test and control animals.
Data were collected, stored and statistically analyzed by computer using SPSS statistical program with student T test and ANOVA tests so that comparison between groups was statistically tested for significance.
Clinical observation and findings clarified that Clinical evaluation of laser groups revealed no wound dehiscence, rapid healing, fast resolution of postdistraction inflammation, minimal postoperative pain and compared to control animals. In addition, The distractor device maintained its stability and anchorage to bone during the experiment..
Radiographic examinations revealed that low intensity laser diode (λ= 970 nm, 2 w, spot size 320 nm) had pronounced effect on the density of newly formed bone in the DO regenerate bridge in laser groups rather than control groups with statistically significant increase in density especially at early stages of bone formation(2&4weeks). On radiographic examinations of groups I, II and III, there were advanced stage of mineralization, increased radiodensity, maturation and remodeling in laser treated regenerates compared to control regenerates.In addition, there were gradual decrease of radiolucent interzone.
Results of evaluation of histopathological sections in laser groups I, II and III illustrated the biostimulatory effect of laser on neobone through increased rate of osteoblasts proliferation and differentiation, accelerated rate of intramembraneous ossification, increased neoangiogenesis, mineralization , maturation and remodeling compared to control animals. Moreover, The histomorphometric results using Computerized image analysis (CIA) revealed that the mean bone trabecular size, bone trabecular total area & the bony area fraction of the distraction regenerate were higher & statistically significant (p<0.05) in laser groups I & II compared to control animals of the same groups, while these parameters were statistically insignificant (p>0.05) in comparison of group III control & laser animals.
On the basis of the findings and results of the current study the following was concluded:
1-Low level diode laser (LLL) has a positive role as a potential bio-stimulator and local inducer factor in enhancing bone formation during distraction osteogenesis.
2-LLL diode laser resulted in early improvement of new bone regenerate quality and quantity & could be used for early removal of distractor and reduce the consolidation period leading to shortening of total treatment time.
¬
3- Laser biostimulation has promoted rapid healing & its anti-inflammatory effect enhanced accelerated resolution of inflammation.
4- Haemostatic and regenerative effects of laser were reflected in soft tissue and bone healing..
5-There were positive correlation between CBCT radiological densitometric analysis & histological histomorphometric analysis suggesting reliable use of CBCT as an accurate diagnostic & evaluation method.
6- The intramembranous ossification was the main mechanism of bone formation in the distraction gap induced in the mandible.
7- Laser biostimulation promoted and enhanced collagen synthesis, neoangiogenesis and neobone formation in the early stages of osteogenesis (2 & 4 weeks periods).