Behavior Responses And Root Resoption To Experimental Tooth Movement In Rats By Different Orthodontic Forces

ObjectivePain and root resorption are common problems associated with orthodontictreatment. Pain makes the patients feel unwell and give up orthodontic treatment andthe damage caused by root resorption can lead to tooth mobility. These areinflammatory responses which have a relation with orthodontic force. Pain is asymptom, whereas root resorption is a pathological process. Remodeling changes inparadental tissues are considered essential in effecting orthodontic tooth movement.The force-induced tissue strain produces local alterations in vascularity, as well ascellular and extracellular matrix reorganization, leading to the synthesis and release ofvarious neurotransmitters, cytokines, growth factors, colony-stimulating factors, andmetabolites of arachidonic acid. The association can be studied between behavior,immune system and force.This study investigated the association of different magnitude of force tobehavior, state of root and expression of immune factors. Thus, can provide referencefor clinicians to judge if the orthodontic force is adequate or will cause rootresorption. Material and MethodsMaterials:78male SD rats (Age:8weeks, Weight:260.67g±20.46g),60x60x30mmexperimental chamber, Nickel titanium tension spring, orthodontic force measuringdevice, enamel resin bond (adhesive), high speed turbine, video recorder, slicingmachine, HE coloring agent and immunohistochemical kit, optical microscope,camera etc.MethodsThe experimental rats were randomly divided into blank group (n=6) andexperimental group: according to different orthodontic force. The experimental groupwas divided into50g group (36rats) and100g group (36rats). Orthodontic force of50g or100g were loaded between two maxillary incisors and left maxillary firstmolar of the experimental group to move the molar mesially whilst, the blank groupwere untreated. The behavior response was observed after the orthodontic forces wereloaded on1d,2d,3d,5d,7d,14d (n=6for each group). Executed the rats (after theorthodontic force were loaded on1d,3d,5d,7d,14d) and obtained66specimen fromthree molars of rats. The mesial specimens (stressed side) were marked, stained withHE lenses and immunohistochemical specimens were prepared along the mesio-distaldirection. The histomorphological change of the periodontal tissue and intensity ofroot resorption were observed using HE stained specimen. Immunohistochemicalspecimen observation included IL-6, PGE2, SP, cGRP and the average integral opticaldensity was recorded.Statistical analysis made by SPSS.19.0Results1. The open field behavior responseThe open field behavior response of the rats after orthodontic force loadingpresented certain regularity. Compared with the blank group (30s:20.10±8.61,5min:100.7±34.04, centerlines:13.00±11.12), the number of lines passed by in30s (50g:10.45±6.47,100g:11.35±6.86),5min (50g:31.00±21.90,100g:29.10±17.77) and the number of central lines (50g:2.10±2.81,100g:2.20±3.71) reduced severely on1dwhich indicates a statistically significant difference (p<0.05). There was a gradualincrease to the level of the blank group on14d. There was no statistically significantdifference between two experimental groups (p>0.05).2. The time of facial grooming and rearing behavior.There was statistically significant increase in time of facial grooming behavior(p=0.008) on1d compared with the blank group (31.30±27.89) and more statisticallysignificant difference (p=0.007) between100g group (60.30±18.83) than50gms(40.58±9.21), which then gradually recovered. The time of rearing behavior increasedon2d (50g:12.20±14.10,100g:10.80±10.87), was more obvious on3d (50g:24.20±24.60,100g:17.70±14.12) and did not recover to the level of the blank groupon14d. There was no statistically significant difference between two experimentalgroups (p>0.05).3. Resistance to capture test.There was a statistically significant increase in the resistance to capture behaviorof the experimental group (50g:2.90±0.88,3.10±0.99,100g:3.90±0.74,4.70±1.16)than the blank group (1.70±0.82) on1d and2d, which gradually reduced. However, itbecame less than the blank group on3d and4d. There was more apparent statisticallysignificant difference between the two experimental groups (p=0.013,0.004).4. Observation of tissue section.A large number of neutrophils and osteoclasts can be seen in the periodontalligament, and periodontal fibers broke on1d and2d along with violent reaction ofperiodontal inflammation. The surface of root became rough and osteoclasts existedin the lacunae on3d. The amount and area of lacunae’s on the surface of the rootincreased and more osteoclasts existed on7d. There was a statistically significantdifference between the two experimental groups. Formation of new cementum can beseen on14d.5. Observation of average integral optical density of immunohistochemicalfactors.The staining of SP, PGE2, IL-6, and cGRP became deeper from the first day, andpresented a different degree of stain in different periods. There was a statistically significant increase of the four immune factors on1d (50g:5.41±3.22,5.77±2.87,9.16±2.85,7.40±3.84,100g:12.27±7.22,10.42±4.22,11.46±3.72,7.47±2.83), higherthan the blank group (2.96±1.64,1.80±0.85,4.28±1.85,2.18±0.80) and reached thepeak on3d,5d,5d,7d respectively. There was a statistically significant differencebetween two experimental groups from3d to7d (p>0.05), which then did not returnto the same level of the blank group.6. The relevance between the time of facial grooming, the expression level ofSP and cGRP, and the extent of root resorption.There were statistically significant relevance between facial grooming behavior,the expression level of SP and cGRP, the extent of root resorption and forcemagnitude or time (r=-0.523, p=0.03: r=0.537, p=0.002: r=0.316, p=0.001: r=0.288,p=0.004: r=0.411, p=0.024: r=0.469, p=0.000), except the time of facial groomingand the extent of root resorption under50g force magnitude. May be the expressionlevel of SP could be used to predict if the force magnitude is so high that lead to rootresorption.Conclusion1. The establishment of orthodontic tooth movement model and open field testare scientific, reasonable, easier and practical.2. The observation of behavior response gives a quantitatively analysis on thechange of stress after the orthodontic tooth movement.3. The time of facial grooming behavior indirectly reflect that stress changes orintensity of pain after local stimulus during the orthodontic tooth movement.4. The behavior response and the degree of root resorption caused by differentorthodontic force were different. The greater the orthodontic force was the moreobvious the behavior response changed.5. The changes of the average integrated optical density ofimmunohistochemical factors can be used as an objective indicator that reflect thechanges of periodontium and reconstruction of root.There are changes occurring in a regular pattern with respect to time and force magnitude affect in the changes ofintegrated optical density of immunohistochemical factors.6. Early detection of the expression level of SP could be used to monitor theextent of root resorption in orthodontic tooth movement procedure; the change of thefacial grooming behavior response could be as early warning signal but not to beevidenced.