8
Contribution of Animal Models in Periodontal Research Amit Bhardwaj, Shalu V. Bhardwaj SGT Dental College, Gurgaon, Haryana; Private dental practitioner, Gurgaon Corresponding author email:[email protected] Rec.Date: Apr 03, 2012 10:05 Accept Date: Apr 21, 2012 00:24 Abstract Aim The aim of this review is to define the most pertinent animal models for periodontal research. Background In periodontal research, animal studies are complementary to in vitro experiments prior to testing new treatments. Animal models and cell cultures have contributed new knowledge in biological sciences, including periodontology. Although cultured cells can be used to study physiological processes that occur during the pathogenesis of periodontitis, the complex host response fundamentally responsible for this disease cannot be reproduced in vitro. Animal models should make possible the validation of hypotheses and prove the safety and efficacy of new regenerating approaches using biomaterials, growth factors or stem cells. Review results Among the animal kingdom, rodents, rabbits, pigs, dogs, and nonhuman primates have been used to model human periodontitis, each with advantages and disadvantages. Experimental models have been developed in order to reproduce major periodontal diseases (gingivitis, periodontitis), their pathogenesis and to investigate new surgical techniques. Conclusion A practical and highly reproducible model that truly mimics the natural pathogenesis of human periodontal disease has yet to be developed. Clinical significance The anatomy, physiology and pathogenicity of experimental models should relate as much as possible to those of patients in order to demonstrate the safety and efficacy of new biomaterials or treatments in periodontal regeneration. Key words: Biomaterials, experimental animal, periodontal disease. Background Periodontitis is an inflammatory disease of the gums, which affects all the dental supporting tissues. This immune-inflammatory disease of the periodontium results in progressive loss of Bhardwaj and Bhardwaj, IJAVMS, Vol. 6, Issue 3, 2012: 150-157 doi: 10.5455/ijavms.138 REVIEW ARTICLE

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Page 1: Contribution of Animal Models in Periodontal …ejmanager.com/mnstemps/25/25-1333472087.pdfContribution of Animal Models in Periodontal Research ... with experimental periodontitis

Contribution of Animal Models in Periodontal Research

Amit Bhardwaj, Shalu V. Bhardwaj

SGT Dental College, Gurgaon, Haryana; Private dental practitioner, Gurgaon

Corresponding author email:[email protected]

Rec.Date: Apr 03, 2012 10:05

Accept Date: Apr 21, 2012 00:24

Abstract

Aim The aim of this review is to define the most pertinent animal models for periodontal

research.

Background In periodontal research, animal studies are complementary to in vitro experiments

prior to testing new treatments. Animal models and cell cultures have contributed new knowledge

in biological sciences, including periodontology. Although cultured cells can be used to study

physiological processes that occur during the pathogenesis of periodontitis, the complex host

response fundamentally responsible for this disease cannot be reproduced in vitro. Animal models

should make possible the validation of hypotheses and prove the safety and efficacy of new

regenerating approaches using biomaterials, growth factors or stem cells.

Review results Among the animal kingdom, rodents, rabbits, pigs, dogs, and nonhuman primates

have been used to model human periodontitis, each with advantages and disadvantages.

Experimental models have been developed in order to reproduce major periodontal diseases

(gingivitis, periodontitis), their pathogenesis and to investigate new surgical techniques.

Conclusion A practical and highly reproducible model that truly mimics the natural pathogenesis

of human periodontal disease has yet to be developed.

Clinical significance The anatomy, physiology and pathogenicity of experimental models should

relate as much as possible to those of patients in order to demonstrate the safety and efficacy of

new biomaterials or treatments in periodontal regeneration.

Key words: Biomaterials, experimental animal, periodontal disease.

Background

Periodontitis is an inflammatory disease of the gums, which affects all the dental supporting

tissues. This immune-inflammatory disease of the periodontium results in progressive loss of

Bhardwaj and Bhardwaj, IJAVMS, Vol. 6, Issue 3, 2012: 150-157

doi: 10.5455/ijavms.138

REVIEW ARTICLE

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ANIMAL MODELS IN PERIODONTAL RESEARCH

IJAVMS, Vol. 6, Issue 3, 2012: 150-157 doi: 10.5455/ijavms.138

gingival tissue, the periodontal ligament, and adjacent supporting alveolar bone1. The objective of

periodontal treatment should ultimately be to regenerate the periodontal tissue by using non

surgical or surgical techniques, biomaterials for guided tissue regeneration, bone substitutes (e.g.

Calcium phosphates or others), growth factors (e.g. enamel matrix derivatives) or, as more

recently proposed, mesenchymal stem cells2. Research in periodontology involves different

strategies, principally the etiology of periodontal diseases using experimental models of

periodontitis, and the regeneration of damaged periodontal tissues by surgically creating bone

defects in combination, or not, with experimental periodontitis. Animal models have contributed

to the generation of new knowledge in biological sciences, including periodontology3.

Periodontal disease can occur naturally or be experimentally induced in animals. Various species

have been used to study the pathogenesis of periodontitis and to assess therapeutic modalities

against the disease. Appropriate experimental animal models are required for testing and

validating new regenerative therapies for damaged periodontal tissues. Animal studies are

effectively complementary to in vitro experiments prior to testing new clinical treatments where

biopsy harvesting for histology is generally not accepted in human. Different animal species

could be used for modeling periodontitis and treatments, but primates, dogs, rats, rabbits, pigs,

hamsters and ferrets are the most commonly employed. Experimental animal models should be

used with care, particularly primates and canines, for ethical reasons4,5

. Concerning

etiopathologic studies, non-human primates are preferred but large series are not ethically and

economically acceptable. Small animal models (e.g. rats or hamsters) have been developed for

periodontal research but these studies mainly focus on bacteriology and immune response.

Depending on species, periodontal diseases could be induced spontaneously, experimentally or

both. In the context of regenerative medicine using biomaterials, large animal models have been

preferred due to the reproducibility and surgical accessibility of experimental defects. Apart from

monkeys, which are the ideal model in pre-clinical studies, dogs have been widely used for

modeling the regeneration of periodontal defects with biomaterials. Some studies have also used

rats, mini-pigs, sheep, rabbits and cats. The aim of this review is to summarize the experimental

animal models used for periodontal research.

Review results

The selection of an experimental model is determined by research objectives, as well as

laboratory constraints such as housing of large or non standard animals. In most cases, small

animal models such as rats or hamsters will be sufficient to assess the role of bacteria, diet or

other factors in periodontal inflammation at the histological level, providing sufficient statistical

significance and pre-clinical relevance. The use of large animals with ethical and social issues

such as monkeys and dogs should be reserved for last phase validation of new treatments prior to

use in human clinical practice. Experimental studies conducted in monkeys are highly relevant for

human clinical practice as they present comparable anatomy and develop similar periodontal

diseases with similar clinical symptoms. However, experimental research in monkeys requires a

strong ethical justification of their care and use and should take into account the purchasing,

transportation and housing expenses of these animals over long periods. The selection of these

animals was based on similar pathologies and the ease of surgically created clinically relevant

defects. Experimental periodontal defects may be obtained in three different ways6:

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ANIMAL MODELS IN PERIODONTAL RESEARCH

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(i) The acute defect model

(ii) The chronic defect model

(iii) The acute/chronic defect model.

In the acute model, all defects are surgically-induced by removing surgically all the periodontal

components (bone, cementum and periodontal ligament). Reproducible defects in experimental

and control sites are created. In the chronic model, lesions are obtained by placing orthodontic

elastics, silk sutures or ligatures around teeth during 12 to 20 weeks, depending on the type of

animal studied. These defects are deeper in the interproximal spaces than in the buccal or lingual

surfaces. In the combined acute/chronic model, the defects are surgically-created and ligatures are

placed to ensure calculus accumulation and to prevent spontaneous regeneration of the defects.

Different animal models used in periodontal research based on pathogenesis of periodontal

disease are non-human primates, dogs, minipigs, ferrets and hamsters. They all have showed

excellent results during experimental studies. These animal models are also used in periodontal

research based on periodontal treatment modalities.

Discussion

Various experimental animal models in periodontal research

1. Non-Human Primates

Nonhuman primates have oral structures and teeth similar to those of humans and have naturally

occurring dental plaque, calculus, oral microbial pathogens (e.g., P. gingivalis), and periodontal

disease. In particular, rhesus monkeys (Macaca mulatta), cynomolgus monkeys (Macaca

fascicularis), and baboons (Papio anubis) are susceptible to naturally occurring periodontal

disease7. All these species are Diphyodont and have the same dental formula as human: I 2/2, C

1/1, Pm 2/2 and M 3/3. Although periodontitis in primates most closely resembles the human

disease, the expense of and special husbandry requirements for these animals limit their use in

periodontal studies.

2. Miniature Pigs

Miniature pigs have oral and maxillofacial structures similar to those of humans in terms of

anatomy, physiology, and disease development8. The Minnesota miniature pig (minipig) was

developed about 60 years ago9 and has been used extensively in biomedical research

10. After the

age of 6 months, minipigs usually develop gingivitis, manifested by inflamed gingival tissue,

accumulated plaque and calculus, and bleeding when probed8. There is infiltration of

inflammatory cells in the gingival tissue that results in progression to severe periodontal

inflammation at 16 months of age with identical histopathology to that seen in humans.

Periodontitis in minipigs is promoted in about 4–8 weeks using ligatures, and in association with

bacterial inoculations of P. gingivalis, S. mutans, and A. actinomycetemcomitans8. Minipigs can

be suitable for periodontal as well as orofacial investigations. However, minipigs are relatively

expensive, with husbandry issues and few studies to support their use.

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ANIMAL MODELS IN PERIODONTAL RESEARCH

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3. Dogs

Many experimental studies on gingival and periodontal diseases have been conducted in dogs.

The beagle is one of the most commonly used due to its size and its extremely cooperative

temperament. Globally, all periodontal tissues and the size of the teeth are quite similar to those

observed in humans. However, some major differences exist between dogs and humans as the

lack of lateral movements, no occlusal contacts for all the premolars and presence of open

contacts between teeth. The frequent lack of gingival sulci and crevicular fluid, a different

composition of periodontal plaque and calculus are other important differences between dogs and

humans11

. All dogs are diphyodont with deciduous and permanent dentition. The formula for

permanent dentition is I 3/3, C1/1, Pm 4/4, M 2/3.

4. Mice

The Baker mouse model of periodontitis has been used to measure alveolar bone resorption

caused by oral bacterial inoculums as an outcome for the clinical presentation of periodontitis in

humans12

. The dental formula of mice is typical rodent dentition: I 1/1, C 0/0, Pm 0/0, M 3/3.

Mice naturally develop periodontitis starting at about 9 months of age with further increases as a

function of age, similar to human periodontitis. This model, however, may not reproduce all

aspects of human periodontitis initiation and progression; the bacteria used are one or two of at

least 150 microbial types present in any dental plaque biofilm. However mice can be utilized to

understand the host-parasite interaction13

.

5. Rats

The rat is the most extensively-studied rodent for the pathogenesis of periodontal diseases.

Typical rodent dentition is I 1/1, C 0/0, Pm 0/0, M 3/3. The incisor is rootless.The structure of the

dental gingival area in rats is quite similar to that observed in humans14

, with a shallow gingival

sulcus and attachment of the junctional epithelium to the tooth surface. The most commonly-used

strains are Wistar or the Spraque-Dawley. In rats, periodontitis appears to be an infectious

process. Inoculations or injections of various periodontal pathogens such as Prophyromonas

gingivalis, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum,

Capnocytophaga, Eikenella corrodens, Actinomyces viscosus, and Streptococus sobrinus can

induce periodontal lesions15

. Furthermore, rats are easy to handle.

6. Hamsters

In hamsters, periodontal disease does not occur spontaneously but may be obtained

experimentally. The golden Syrian hamster is the most commonly used. The dentition formula is

identical to rodents: I 1/1, C 0/0, Pm 0/0, M 3/3. Histologically, the structure of the periodontal

tissue is very similar to that of rats16

but due to the small size of this kind of animal, the

interdental septum is narrower than in rats. Spontaneous periodontal disease was obtained using

an appropriate diet containing high concentrations of carbohydrates, particularly sucrose17

. In

summary, as in rats, the inflammatory response is very limited in hamsters and is very different

from that observed in humans. The mechanisms of alveolar bone resorption in hamsters with diet-

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ANIMAL MODELS IN PERIODONTAL RESEARCH

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dependent periodontal lesions are quite similar to those observed in rats infected with Gram-

positive bacteria.

7. Ferrets

Ferrets have a deciduous and permanent dentition. The formula is I 2/2, C 1/1, Pm 4/4, M 2/2.

Ferrets (Mustela putorius) naturally develop calculus and periodontal disease similar to

humans18,19

. Unlike rodents, calculus formation in ferrets does not depend on the diet and can be

scored in live ferrets. Ferrets are a suitable model to study calculus; however, they can easily

escape from standard cages and they need special maintenance.

8. Minks

The dentition formula of the adult mink is I 3/3, C 1/1, Pm 3/3 and M 1/2. In minks, spontaneous

periodontitis, which is age- and plaque-dependent, is observed. Nevertheless, the extent of this

periodontal disease appears to be severe only in very old animals. In minks, neutrophils play a

key role in periodontal destruction due to deficiencies in the chemotactic response and massive

release of lysosomal enzymes and proteases into periodontal tissue. Minks are therefore

interesting experimental models in research on the etiology of periodontal diseases. Nevertheless,

housing these animals may be difficult or require specific authorizations that may explain the

absence of recent publications in the literature

9. Rabbits

Characterization of the oral microorganisms in rabbits showed numerous pathogenic bacteria,

including F. nucleatum, P. heparinolytica, Prevotella spp., P. micros, S. milleri group, A. israelii,

and A. haemolyticum, which is somehow consistent with the flora related to periodontal disease in

humans20

. Rabbits have been used for creation of surgically induced periodontal defect and to

study periodontal regeneration, but they have been found less suitable for regeneration of

periodontal ligament21

.

10. Other Animals

Other animal models have been investigated for modeling periodontal diseases.

Horses- Common naturally occurring oral diseases in horses include buccal abrasions, calculus,

gingival recession,and periodontal pockets. According a recent equine survey, the prevalence of

periodontal pockets and gingival recession is highest in older horses and mostly associated with

other dental disorders and tooth loss22

. Because of their size and husbandry considerations, horses

are not a practical model for basic science studies of periodontitis or for testing of potential

therapies.

Sheep- They have also been studied in the context of periodontal diseases. The permanent

dentition of sheep consists of 32 teeth with a formula: I 0/3, C 0/1, Pm 3/3, M 3/3.

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ANIMAL MODELS IN PERIODONTAL RESEARCH

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One publication23

used the cat as animal model. In this research, class III furcation defects were

surgically created at the level of the premolars in order to study ankylosis at root level during

periodontal healing.

Few studies have reported mini-pigs for research, mainly related to dental implant surgery and

periodontal regeneration by enamel matrix derivatives24,25

, as well as the effects of dental lasers

on periodontal healing26

.

Table 1. Advantages and disadvantages of select animal models for studying

periodontal disease development

Animal Model Advantages Disadvantages

Non Human Primates Similar dental structure, microflora,

and disease to humans’. Natural or

experimentally induced

periodontitis.

Very expensive, with ethical

and husbandry issues

Dogs Develop natural or experimental

periodontitis similar to humans

Relatively expensive, need

special daily care, husbandry

issues. Dentition different

from humans.

Minipig Dental structure and periodontitis

have some similarity to humans’.

Natural or experimentally induced

periodontitis

Relatively expensive,

husbandry issues; relatively

few studies

Ferrets Naturally or experimentally

induced disease with similarity to

humans

Some husbandry issues

Rodents Experimentally induced disease.

Similar molar structure to humans’.

Inexpensive model

Naturally resistant to

periodontitis. Different

microbiota from humans’.

Small size and therefore

amount of tissue for analysis.

Large number of animals

needed

Conclusion: Experimental models for periodontal diseases are essential for understanding the

origin and evolution of the pathology in humans. The use of animal models in periodontal

research is a necessary step prior to entering into clinical trials with new biomaterials and

treatments. Each animal model for periodontal disease has advantages and disadvantages

(summarized in Table 1). A more systematic use of these small animal models appears evident for

future research, especially from a surgical point of view.

Clinical significance: The anatomy, physiology and pathogenicity of experimental models

should relate as much as possible to those of patients in order to demonstrate the safety and

efficacy of new biomaterials or treatments in periodontal regeneration.

References

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