April 26, 2019 0 Comment


In history, animal research and experimentation has played a pivot role in biomedical research. However, due to various impressions, it has been an intense topic and centre of discussion for many centuries. Numerous controversies, both ethical and social, surrounding the animal research has limited its resources and experimentation. Hence, the moral and social implications should be taken into consideration along with the historical abundance to evaluate the present-day ideologies and practices of animal research1
Animal experiments have contributed to understand of mechanisms of disease, but estimating the effectiveness of treatment plan in clinical trials has remained controversial . In fact, clinical trials are essential because animal studies do not predict what will happen in humans exactly. The difference between the results of animal models and clinical trials may be explained by limitations of the clinical trials, there may be insufficient statistical power to detect a true advantage of the treatment under study2. For practical purposes, the designs of some clinical trials have also failed to recognise the limitations of efficacy observed in animal studies,. Secondly, the failure to translate the results to clinic obtained from inadequate animal data and overestimated conclusions about efficacy from methodologically flawed animal studies. A third possible explanation is that they may not reflect disease in humans2.
Harvold was the lead author on one of the most famous animal experiments in the history of orthodontics. Most orthodontic treatment questions require scientific synthesis of the information available from a variety of sources including animal experimentation3
In orthodontics, animal research models are used to study fundamental biological processes such as bone growth, biomechanics, new technics and movement acceleration methods, especially dental movement biology at the alveolar bone is explained through an animal model made over 100 years ago. In turn, this knowledge has provided the rationale for making informed clinical decisions. Techniques such as cell labelling with radioactive amino acids to quantitate protein formation or radioactive nucleotides to measure cell division provide data that just cannot be gathered from human subjects under most circumstances. Animal models has increased our understanding of what happens at the tissue and cellular levels3.
What kind of models4 ?
The standard claim is that “Virtually every medical achievement of the last century has depended directly or indirectly on research with animals.”
In such a case, what is there significance in human medicine and how are they used as models?
Researchers try to replicate the symptoms in human disorders to animals to gets the intended results. For instance, during the research of multiple sclerosis, the rodents were injected with protein extracts from brains of various animals to cause inflammation of central nervous system and demyelination of neuron to resemble the characteristics of multiple sclerosis. In our evolutionary history with other species, it is probable that some experiments on animals may propose some useful theories about human medical conditions. Other than animal studies, the only way to prove the model-generated medical theories of humans is possible only by clinical studies, volunteering or population-based studies which is a time-consuming process. Hence, animal studies have been adapted for such purposes.
Selecting an Animal Model for Research:
Animals are generally used as models in research in two contexts:
1. For the study of phenomena and procedures which cannot be studied directly.
2. To investigate a problem particular to the specific species.

1. Melsen et al7 1968 conducted a study to investigate the tissue reaction related to orthodontic intrusion of teeth with a reduced periodontium and further to evaluate the influence of oral hygiene on this reaction. The study was performed on five Macaca fascicularis monkeys, periodontal tissue breakdown was induced around the premolars and the upper incisors by placing orthodontic elastic ligatures around the teeth. Flap operation was performed ,epithelium and granulation tissue excised. Histologic sections were produced and stained alternatively with hematoxylin and eosin, and van Gieson’s solution. The histologic analysis showed that new cementum formation and new collagen attachment were observed following the surgical if oral hygiene was maintained. Intrusion improved quantity of new attachment if carried out under healthy conditions.

2. Sandy et al5 in 1978 evaluated the effect of flurbiprofen , a prostaglandin inhibitor on the tooth movement on New Zealand white rabbits.Springs were ligated between lower first molars and incisors. Experimental animals were administered flurbiprofen daily.It was concluded that remarkable decrease in the number of osteoclast in the bone adjacent to induced tooth movement in experimental animals.It suggests that NSAIDS can partially inhibit tooth movement.

3. Midgett et al34 in 1981 investigated to evaluate the effect of nutritional hyperparathyroidism on tooth movement through alveolar bone via inducing changes in bone remodelling .The study was conducted in 1 year old twelve beagle dogs. Decreased calcium and phosphorous diet was given to experimental dogs. At the end of 10th week after extraction of 3rd premolar and 2nd and 4th premolars moved towards each other with 100gm of force.12 weeks later they were killed and mandibles prepared for laboratory evaluation. They concluded that more rapid tooth movement is seen in experimental animals. Increased bone remodelling changes and decreased bone density is seen in hyperparathyroid animals.

4. Miller et al35 in 1982 conducted a study to investigate the neuromuscular changes occurred in rhesus monkeys with initial adaptation to oral respiration. The study was performed on 26 rhesus monkeys. obstruction of the nasal passage induced changes in EMG of both mandibular and facial muscles during first 6 months of adaptation. the results revealed that significant number of muscles became rhythmically active within first month of adaptation. The rhythmic pattern was evident in key muscles that actively depressed the mandible, protruded the tongue, altered the shape of the tongue, and raised the upper lip.

5. Nanda et al6 in 1984 conducted a study to protract mid facial complex of macaca mulatta monkeys by controlled anteriorly directed force. Cephalometrics , vital staining and histological examination was done in 9 monkeys to study type and nature of displacement of selected facial bones. The results showed that midfacial bones can be displaced anteriorly by sutural modification and with the same line of force, different midfacial bones displace in different directions because of various moments generated at sutures.
6. Wennstrom et al8 in 1993 evaluated the effect of orthodontic tooth movement on the level of the connective tissue attachment in sites with infrabony pockets. The study was conducted in four female 2 year old beagle dogs in which 2nd and 4th premolars were extracted and angular bony defect was created at the mesial aspect of 3rd premolar and notch at the bottom of the defect. Then plaque containing cotton floss ligatures were placed for 3 weeks followed by plaque accumulation for 2 months before start of the orthodontic tooth movement. In each dog, one premolar was moved away and one premolar into angular bony defect. It was concluded that orthodontic treatment involving tooth movement may intensify the rate of destruction of the connective tissue attachment at teeth with inflamed, infrabony pockets and for the tooth moved into infrabony pocket, additional attachment loss is seen.

7. Dixon et al9 in 1994 conducted a study to evaluate the effects prolonged papain administration on growth of the craniofacial complex with the help radiographic and biometric means. Fifty 21 day old male Lewis strain rats divided into 3 groups. It was concluded that body weight gain was less for papain treated group. Skull and nasal lengths, cranial base length and spenoidal lengths were shorter, whereas neurocranial height and supraoccipital height increased. The effectiveness of catch up growth was not constant and was more successful in the later injected group.
8. Brudwik et al10 in 1994 investigated to study relation between necrotic tissue and root resorption and cells that invade and remove necrotic tissue and cells that resorb cementum. The study was conducted on maxillary molars of wistar rats and mandibular molars of female white mice. It was seen that multinucleated and TRAP positive cells were involved in the removal of necrotic tissue and resorption of the root surface.Root resorption beneath hyalinised zone occurred in areas where invading cells close to root surface.

9. Leiker et al11 in 1995 evaluated long term effects of varying concentrations and frequencies of injectable exogenous prostaglandin E2 on the rate of tooth movement and amount of root resorption. The study was conducted on 132 male Sprague-Dawley rats of 8 weeks old. The results showed that injecting of PGE2 for extended time in rats enhanced the amount of orthodontic tooth movement. No statistical difference was found between single and multiple injections, but root resorption was increased with prostaglandin injections, specifically with increased concentrations and increased number of PGE2 injections.

10. Leewen et al12 in 1999 investigated the effect of two different force regimes and two different force magnitudes on tooth displacement. The study conducted on beagle dogs,in each dog, both mandibular third premolars were extracted, and orthodontic appliances were placed for bodily distalization of 2nd premolars. The forces (10 cN or 25 cN) were applied, either continuously (24 h a day) or discontinuously (active 16 h daily ). It was concluded that , force regime has more influence on the rate of orthodontic tooth movement than force magnitude.

11. Bohl et al13 in 2004 conducted a study to evaluate histological changes in the periodontal structures of beagle dogs after using low and high continuous forces during experimental tooth movement. The study was conducted on second premolar and first molar in 15 young beagle dogs by exerting continuous and constant force of 25 N on one side and 300 N on the other side of the mandible. Dogs were sacrificed for histological examination. Hematoxylin and eosin staining used for tissue survey, alkaline phosphatase staining for active osteoblasts and tartarate resistant acid phosphatase staining for osteoclasts. It was concluded that hyalinization limits tooth movement ,but there is no relationship with the force level

12. Aoki et a14 in 2005 investigated the possibility of using a bioabsorbable implant as orthodontic anchorage. The implants were placed in the mandibles of eight male beagle dogs of 8- 10 months old. It was seen that bioabsorbable implant had favorable biocompatibility and strength, and potential for use in orthodontic treatment.

13. Chen et al15 in 2006 investigated increased failure rate of orthodontic mini-implants for anchorage during insertion. Seventy-two miniscrews were surgically placed in the mandibular alveolar bone of six adult mongrel dogs. They concluded that miniscrews contacting roots have higher insertion torque and are at greater failure rate. Difference in the removal torque was observed based on state of root contact and mobility of miniscrews.

14. Seifi et al16 in 2006 conducted a study to evaluate quantitative effects of a pulsed 850 nm laser (Optodan) and a continuous 630 nm laser (KLO3) on the orthodontic tooth movement in rabbits. The study was performed on 18 male albino rabbits. NiTi-closed coil springs were used on 1st mandibular molars and laser was irradiated for 9 days on experimental group and animals were sacrificed on 16th day . The mean orthodontic tooth movement of the first mandibular molars were 1.7±0.16 mm in control in group 0.69±0.16 mm in Optodan group and 0.86± 0.13 mm in KLO3 group, so they concluded that decreased tooth movement is observed in laser irradiated groups.

15. Nemcovsky et al17 in 2007 investigated whether orthodontic tooth movement affects periodontal healing. In this study,31 twelve week old male Wistar rats included and divided into 2 groups (group 1-bonydefect without PDL and group 2 with PDL). In both groups, the right first molar was moved mesially (orthodontic side) for 2 weeks. They concluded that significantly larger junctional epithelium, supracrestal connective tissue and pocket depth were found on the control side. Therefore, periodontal regenerative surgery might be indicated prior to orthodontic tooth movement. Orthodontic treatment immediately after periodontal surgery,have no deleterious effect on periodontal soft tissue healing.

16. Deguchi et al18 in 2008 conducted a study was to quantify the histomorphometric properties of alveolar bone to identify the characteristics of the changes of quantity and quality of alveolar bone between the maxilla and the mandible during orthodontic tooth movement in dogs. The study performed on 12 male beagle dogs of 8 months old, premolars were subjected to orthodontic force for 4 weeks. They concluded that more orthodontic tooth movement is observed in maxilla compared to mandible.primary histomorphometric analysis after 4 weeks as shown that increased bone resorption and decreased bone volume at tension and compression side followed by secondary histomorphometric analysis after 12 weeks shown that formation of new woven bone and increased bone rate.

17. Chen et al19 in 2008 compared the influences of different implant modalities on orthodontic microimplants and surrounding tissues biomechanically and histologically. The study was conducted on two adult female mongrel dogs by placing 56 titanium alloy microimplants(28 self drilling and 28 self tapping) on the buccal side of the maxillae and the mandibles. Constant and continuous force were applied with NiTi closed coil springs for 9 weeks. The results were seen that self drilling implants have higher success rate, higher osseointegration , higher insertion and removal torque. Self drilling miniimplants can provide higher anchorage than self tapping mini implants.

18. Kang et al in20 2009 examined a stabilility of mini screws invading the dental roots and their impact in paradental tissues by inserting 16 miniscrews in each of the 3 adult male beagle dogs. The failure rate of the mini-screws that invaded the dental roots are 79.2% and that of the miniscrews in the middle of the alveolar bone 8.3% However, minimally damaged dental roots do not adversely affect the healing process.

19. Xie et al21 in 2009 conducted a study to investigate differentiation and recruitment of osteoclasts during the early phase of experimental tooth movement in rats. The 3 maxillary molars of each ,fourty 6 week old wistar rats were moved moved mesially with NiTi coil springs of 10cN. It was concluded that force application induces osteoclast differentiation within bone marrow and these osteoclasts migrate into compressed PDL.

20. Kilic et al22 in 2011 to investigate the effects of 2 force levels on the amount of relapse and to determine whether there is a relationship between the rates of tooth movement and relapse. 20-g and 60-g forces were applied to the maxillary central incisors of 14 week old 25 New Zealand female rabbits. Relapse in group II is greater only on first day of experiment.

21. kim et al23 in 2011 conducted a study to evaluate biological effects of SSO on the teeth and periodontal structures. The experimental study was performed on 5 beagle dogs,their 6 maxillary incisors were retracted enmass by single palatal mini implant. Retraction was performed without and with perisegmental corticotomy in groups I and II. animals were killed on the 70th day, and their periodontal structures were processed for histologic analyses. Retraction was greater and lesser root resorption was observed in group II than group 1.SSO was effective for enmass retraction.

22. Franzen et al24 in 2013 evaluated the remodelling of alveolar bone and related periodontal structures during orthodontic relapse in molars of 35 six week old male wistar rats .The maxillary right moalrs moved mesially with orthodontic appliance for 10 days, then appliance was removed and allowed to relapse.The molars relapsed to 62.5 % of achieved OTM continued to 86.1% at 21 days. It was seen that relapse in rats occur at a greater rate and remodelling of alveolar bone and PDL plays a pivot role in relapse processes.

23. Rebeiro et al25 in 2013 conducted a study to determine bond strength of orthodontic brackets in resin restorations with surface treatment. The study was conducted on fifty one bovine lower incisors and allocated into 3 groups ( control group and experimental groups with and without surface treatment) The teeth were embedded in PVC tubes with autopolymerized acrylic resin jet. They concluded that CG (6.62 MPa) and EGT (6.82 MPa) groups presented similar results, while EGN (5.07 MPa) lower results,so best way of bonding orthodontic brackets on composite resin restorations is the performance of surface detritions.

24. Brown et al26 in 2014 compared stainless steel and titanium alloy miniscrew implants by inserting 48 stainless steel and 48 titanium alloy miniscrew implants into tibias of 12 male New Zealand white rabbits of 4- 5 months old. Both the miniscrew implants, stainless steel and titanium alloy have same mechanical stability and histological responses. No significant difference was found in microdamage burden and bone-to-implant contact regardless of loading status,the only difference found was stainless steel have higher insertion torque than titanium alloys.

25. Lu et al27 in 2014 conducted a study to establish a stable animal model of obstructive sleep apnea-hypopnea syndrome corrected by mandibular advancement device. Eighteen 6 month old male New Zealand rabbits were allocated into 3 groups(OSAHS,MAD,Control group). Group OSAHS and MAD was injected with 2 ml hydrophilic polyacrylamide gel. The rabbits in OSAHS which developed apnea-hypopnea was significantly improved with MAD.

26. Franzen et al28 in 2014 evaluated biological changes in alveolar bone occurring during orthodontic relapse.The study was conducted in maxillary first molars of fourty six week old wistar rats to move mesially. They concluded that one day after appliance removal,molars relapsed to 73% ,then continued to 93% at 21 days. During the experimental period tissue mineral density and bone volume increased but total porosity decreased. Bone tissue reactions on a molecular level are similar during OTM and orthodontic relapse. Immediate retention is required after OTM.

27. Kirschneck et al29 in 2014 determine the applicability of the osteoporosis medication strontium ranelate induced orthodontic tooth anchorage.The study was comducted first molars and incisors of 48 male Wistar rats, a constant orthodontic force of 0.25 N applied by closed coil springs.Animals treated with strontium ranelate showed 40% less tooth movement and geneexpression and histologically also smaller resorption area and less osteoclastic activity seen. Patients on strontium ranelate have prolonged orthodontic treatment.

28. Schneider et al30 in 2015 determined minimum dosage levels required forlocal inhibition of orthodontic relapse by recombinant OPG protein and also its effects on alveolar bone and long bone. The study was conducted on maxillary molars of 18 Sprague male Dawley rats by moving mesially withNiTi springs. After appliance has removed, OPG –Fc was injected distal to molar teeth. The results was observed that OPG-Fc effectively inhibits orthodontic relapse, with minimal systemic effect on bones and also OPG-Fc will effect tooth movement only in teeth close to injection site. OPG-Fc is safe and effect in to control osteoclasts locally.

29. Tang et al31 in 2015 conducted a study to investigate effect of maxillary expansion in orthodontics in eight beagle dogs. Magnetic expansion appliance used for expansion and after expansion, model was taken and executed for CBCT scanning to to measure the dental measurement indicators and width of base bone arch. They concluded that the significant difference in dental indicators between the CBCT measurement method and model measurement as well as bone indicator of width of base bone arch and spacing of implant anchorage.

30. Plut et al32 in 2015 investigated to determine effects of diabetes type 2 on bone remodelling during orthodontic tooth movement.The study was performed on 48 rats,in which distance between teeth were measured weekly and on 42nd day maxillary alveolar bone specimens were collected for histological examination and gene expression. They concluded that rats with type 2 diabetes have decreased bone formation and increased bone bone resorption during orthodontic tooth movement.

31. Utreja et al33 in 2018 to explore the more physiologic maxillary expansion with light continuous force. They conducted a study on twenty 6-week-old Sprague-Dawley rats. A custom-fabricated archwire expansion appliance made from 0.014-inch copper-nickel-titanium wire was activated 5 mm and bonded to maxillary molar segments. They concluded that application of light, continuous force resulted in maxillary osseous expansion due to bilateral sutural apposition and buccal drift of the alveolar processes and no difference in bone morphologic parameters.