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| | | Year : 2009 | Volume : 20 | Issue : 1 | Page : 99-106 | | | Dental caries vaccine | | | KM Shivakumar1, SK Vidya2, GN Chandu3
1 Department of Preventive and Community Dentistry, Sharad Pawar Dental College and Hospital, Datta Meghe Institute of Medical Sciences (Deemed University), Sawangi (Meghe), Wardha Maharashtra, 442 004, India
2 Department of Oral and Maxillofacial Pathology, Sharad Pawar Dental College and Hospital, Datta Meghe Institute of Medical Sciences (Deemed University), Sawangi (Meghe), Wardha Maharashtra, 442 004, India
3 Department of Preventive and Community Dentistry, College of Dental Sciences, Davangere, Karnataka - 577 004, India
Click here for correspondence address and email | Date of Submission | 26-Oct-2007 | | Date of Decision | 27-Oct-2007 | | Date of Acceptance | 09-Aug-2008 | | |      | |  Abstract | | | Dental caries is one of the most common diseases in humans. In modern times, it has reached epidemic proportions. Dental caries is an infectious microbiologic disease of the teeth that results in localized dissolution and destruction of the calcified tissue. Dental caries is a mulitifactorial disease, which is caused by host, agent, and environmental factors. The time factor is important for the development and progression of dental caries. A wide group of microorganisms are identified from carious lesions of which S. mutans , Lactobacillus acidophilus , and Actinomyces viscosus are the main pathogenic species involved in the initiation and development of dental caries. In India, surveys done on school children showed caries prevalence of approximately 58%. Surveys among the U.S. population showed an incidence of 45.3% in children and 93.8% in adults with either past or present coronal caries. Huge amounts of money and time are spent in treating dental caries. Hence, the prevention and control of dental caries is the main aim of public health, eventually the ultimate objective of public health is the elimination of the disease itself. Recently, dental caries vaccines have been developed for the prevention of dental caries. These dental caries vaccines are still in the early stages. Keywords: Dental caries, dental caries vaccine, streptococcus mutans How to cite this article:
Shivakumar K M, Vidya S K, Chandu G N. Dental caries vaccine. Indian J Dent Res 2009;20:99-106 |
Dental caries is an infectious microbiologic disease of the teeth that results in localized dissolution and destruction of the calcified tissue. [1],[2] Dental caries is one of the most common diseases in humans. [3],[4] In modern times, it has reached epidemic proportions. The prevalence of dental caries in developed countries varies greatly and can reach over 90%. The rate of Caries has been increasing in developing countries with the increase in the popularity of highly refined sugars. The development of dental caries requires the presence of cariogenic bacteria that are capable of producing acid and a sugar present in the diet which favors the colonization of these bacteria to form acid. [3],[5] Dental caries appears to be a major public health problem which if left untreated can cause considerable pain, discomfort, and treatment costs are very high. Dental caries results from the interaction between the host, the host's diet, and the microflora on the tooth surface bounded by the time factor. [6] A wide group of microorganisms are identified from carious lesions of which Streptococcus mutans  utans), Lactobacillus acidophilus, and Actinomyces viscosus are the main pathogenic species involved in the initiation and development of dental caries. [7],[8] S. mutans has been implicated as a causative organism of dental caries. [4],[9] S. mutans accounts for seven distinct species isolated from animals and humans; Streptococcus cricetus, Streptococcus ferus, Streptococcus macacae, Streptococcus rattus, Streptococcus downey, S. mutans, and Streptococcus sobrinus. S. mutans and Streptococcus sobrinus e exclusively isolated from humans and S. mutans is the most prevalent species. [10]
The traditional way of managing dental caries was by a surgical approach of "drill and fill". This approach has slowly evolved into a more conservative mode. Various preventive measures have been implicated for the prevention of dental caries, among which is immunization of the population against the disease. [7] Many studies have been conducted on the development of an effective vaccine to prevent the occurrence of dental caries. A review of literature pertaining to a dental caries vaccine is presented.
| Vaccines | |  |
Vaccines are an immuno-biological substance designed to produce specific protection against a given disease. It stimulates the production of a protective antibody and other immune mechanisms. Vaccines are prepared from live modified organisms, inactivated or killed organisms, extracted cellular fractions, toxoids, or a combination thereof. [11]
| The Immune Response | | |
a) The primary response
When an antigen is administered for the first time to an animal or human, there is a latent period of induction of 3 to 10 days before antibodies appear in the blood. The antibody that is elicited first is entirely of the IgM type. The IgM antibody titer rises steadily during the next 2 to 3 days, reaches a peak level, and then declines almost as fast as it developed. Meanwhile, if the antigenic stimulus was sufficient, the IgG antibody appears in a few days. IgG reaches a peak in 7 to 10 days and then gradually falls over a period of weeks or months. An important outcome of the primary antigenic challenge is the education of the reticulo-endothelial system of the body. Both B and T lymphocytes produce what are known as "memory cells" or primed cells. These cells are responsible for the immunological memory that is established after immunization. [11],[12]
b) Secondary (Booster response)
The response to a booster dose differs in a number of ways from the primary response. The secondary response also involves the production of IgM and IgG antibodies. A collaboration between B and T cells is necessary to initiate a secondary response. There is a brief production of the IgM antibody and a much larger and more prolonged production of the IgG antibody. This accelerated response is attributed to immunological memory. The immune response (primary and secondary) and immunological memory are the basis of vaccination and revaccination. [11],[12]
| Mechanism of Action of Vaccine | | |
Saliva contains approximately 1-3% of immunoglobulin concentration, a majority of which is secretary IgA. However, saliva also contains the humoral immunoglobulin IgG and IgM from the gingival sulcular fluid. In addition, cellular components of the immune system such as lymphocytes, macrophages, and neutrophils are also present in gingival sulcus. Some of the possible ways antibodies might control bacterial growth are listed below: [13],[14]
- The salivary immunoglobulin may act as a specific agglutinin interacting with the bacterial surface receptors and inhibiting colonization and subsequent caries formation. They might also inactivate surface glucosyltransferase, which would then reduce the synthesis of extra cellular glucans resulting in reducing plaque formation.
- The salivary glands produce secretory IgA antibodies by direct immunization of the gut associated lymphoid tissue (GALT), from where sensitized B-cells may be home to the salivary glands. The salivary IgA antibodies have, of course, direct access to the tooth surface. They may prevent S. mutans from adhering to the enamel surface or they may prevent formation of dextran by inhibiting the activity of glucosyltransferase (GTF). [3]
- The gingival crevicular mechanism involves all the humoral and cellular components of the systemic immune system, which may exert its function at the tooth surface. There is now sufficient evidence to postulate what may happen after subcutaneous immunization with S. mutans. The organism is phagocytosed and undergoes antigenic processing by macrophages. In the lymphoid tissue, T and B-lymphocytes are sensitized by the macrophages preventing the antigen HLA Class-II complex and releasing IL-I. This induces the CD-4 helper and CD-8 cytotoxic suppressor cell response with the activation of IL-2 receptors and the release of IL2. The interaction between the cells play an essential part in modulating the formation of IgG, IgA, and IgM classes of antibodies and B-lymphocytes. [3],[15],[16]
| Studies | | |
a) Animal studies
Rodents are attractive as experimental laboratory animals because they are inexpensive and easy to maintain. Rapid decay of their teeth can be induced by S. mutans when present during the provision of a sugar containing diet. The ability to establish large experimental groups and to arrive at an accurate diagnosis of caries by examination of the tooth surface also makes rodents a good choice for laboratory animals. [17] Immunization experiments with cells of S. mutans both in rats and monkeys have consistently resulted in a significant decrease in dental caries. Purified components of S. mutans have been used only to a limited extent. Protection has been induced by immunization with GTF in rats. Recently, immunization with purified protein antigen I/II, which resides in the cell wall of S. mutans, has induced protection against caries. The latter utilizes only one subcutaneous injection of the antigen with adjuvant, unlike all other experiments, which have not been performed in rhesus monkeys and have used from 5 to 15 injections. Immunization with whole cells of S. mutans or with purified I/II antigen produces a reduction of about 70% in both smooth surface and fissure caries when compared with controls. [18] In gnotobiotic rats, ingestion of whole S. mutans selectively produces S-IgA. The appearance of S-IgA correlated with a reduced incidence of the caries vaccine. [17],[19]
The first report of successful immunization of monkeys against caries was by Bowen who injected whole cells S. mutans into Macaca fascicularis monkeys. [7] Rats and monkeys have been largely used in immunization studies. The principal design in most of the experiments has been to first immunize the animals with an antigen from S. mutans incorporated in an adjuvant as frequently as is necessary to attain high antibody levels, and follow this by implanting the same organism in the mouth and placing the animals on a high sucrose diet. Some of the experiments have been designed to aim for salivary immunity and others have been designed to aim for systemic immunity. [3] There have been reports of the successful use of GTF as an anticaries vaccine in rats and hamsters, but neither crude preparations, nor a highly purified GTF conferred any protection on monkeys. [20]
b) Human studies
As dental caries fulfills the criteria of an infectious disease, the possibility of preventing it by vaccination has been pursued. The rationale is that immunization with S. mutans should induce an immune response, which might prevent the organism from colonizing the tooth surface, and thereby prevent decay. As a vaccine would be administered before the deciduous dentition has erupted at about 6 months of age, it would prevent the disease in children who show the greatest incidence of caries. The vaccine could be given at the same time as the vaccines against diphtheria and tetanus. Immunity could be boosted at intervals thereafter to provide life-long protection. The existing delivery system of immunization could be used, without any financial burden being incurred. [3] Currently, clinical trials are underway to test the use of a pill of S. mutans for control of caries. There have been some conflicting results thus far in human studies. Some workers have actually reported a negative correlation between S-IgA and caries prevalence. However, this result could be the result of the experimental design. It has been shown that ingestion of capsules containing S. mutans stimulates the production of S-IgA. Stimulation of serum immunoglobulin in humans has also produced mixed results and no correlation could be made between caries experience and serum immunoglobulin stimulation. [8],[13]
| Antigenic Components of Streptococcus Mutans | | |
S. mutans posses various cell surface substances including adhesins, GTFs, and glucan binding proteins (GBP). These substances are used for vaccine preparation. Most of the recent experimental efforts have been directed toward these compounds. [21]
Adhesins: Adhesins form the two principal human pathogens of S. mutans (variously identified as antigens I/II, Pac, or P1 and Streptococcus sobrinus, Spa-A or Pag) and has been purified. Antigens I/II (Ag I/II) are found in the culture supernatant as well as in the S. mutans cell surface. This 185-KDa protein composed of a single polypeptide chain of approximately 1600 residues. Ag I/II contains an alanine-rich tandem-repeating region in the N-terminal third and a proline rich repeat region in the center of the molecule. These regions have been associated with the adhesin activity of Ag I/II. The proline-rich central portion contains an adhesin epitope basing their conclusions on adhesin inhibition assays involving the recombinant fragment of Ag I/II. The antibody directed to the intact Ag I/II molecule or to its salivary binding domain blocked adherence of S. mutans of saliva-coated hydroxyapatite. Immunization of mice with synthetic peptide (residue 301-319) from the alanine rich region of Ag I/II suppressed tooth colonization with S. mutans. [14],[22]
| Glucosyltransferase | | |
S. mutans has three forms of glucosyltransferases (GTFs):
- Water insoluble glucan synthesizing enzyme: GTF-I
- Water insoluble and water-soluble glucan synthesizingenzymes: GTF-S-I
- Water-soluble glucan synthesizing enzymes: GTF-S
The genes encoding GTF-I, GTF-SI, and GTF-S are called the GTF-B, GTF-C, and GTF-D genes, respectively. All three GTF genes are important for smooth surface caries formation in the pathogen-free rat model system. Streptococcus sobrinus produces a water insoluble glucan-synthesizing enzyme GTF-S. The GTF-I gene encoding GTF-I and the GTF-S and GTF-T genes encoding two GTF-S enzymes have been cloned. [21],[23],[24] S. mutans and Streptococcus sobrinus each synthesize several GTFs. [25]
Glucan binding protein (GBP): S. mutans secretes at least three distinct proteins with glucan binding activity: GBP-A, GBP-B, and GBP-C. Of the three S. mutans GBPs, only GBP-B has been shown to induce a protective immune response to experimental dental caries. GBP-A has a sequence of 563 amino acids. The molecular weight is 59.0 Kda. The carboxy-terminal 2/3 rd of GBP-A sequence has significant homology with a putative glucan binding region of S. mutans GTFs. The C-terminal region contains 16 repeating units, which represent the full glucan-binding domain of this protein. GBP-A has a greater affinity for water soluble glucan than for water insoluble glucan.
Dextranases: Dextran is an important constituent of early dental plaque. Dextranase is an enzyme produced by mutans Streptococcus. They destroy dextran and thus the bacteria can invade dextran-rich early dental plaque. Dextranase, when used as an antigen, can prevent the colonization of the organism in early dental plaque. [7]
| Routes of Immunization | | |
In general, 4 routes of immunization have been used with S. mutans:
- Oral
- Systemic (subcutaneous)
- Active gingivo-salivary
- Passive dental immunization
Common mucosal immune system
Mucosal applications of dental caries vaccines are generally preferred for the induction of secretory IgA antibodies in the salivary compartment, since this immunoglobulin constitutes the major immune component of major and minor salivary gland secretions. Many investigators have shown that exposure of an antigen to a mucosally associated lymphoid tissue in the gut, nasal, bronchial, or rectal site can give rise to immune responses not only in the region of induction but also in remote locations. This has given rise to the notion of a "common mucosal immune system". Consequently, several mucosal routes have been used to induce protective immune responses to dental caries vaccine antigens. [22],[26]
1. Oral route
Many of the earlier studies relied on oral induction of immunity in the GALT to elicit protective salivary IgA antibody responses. In these studies, an antigen was applied by oral feeding, gastric intubation, or in vaccine containing capsules or liposome. [22] Killed S. mutans was administered to germ-free rats in drinking water for 45 days before implantation of live S. mutans and then throughout the experimental period. A significant reduction in caries was related to an increased level of salivary IgA antibodies to S. mutans, as the serum antibody titer was minimal. Oral immunization with S. mutans did not induce significant secretory IgA in monkeys. Daily administration of 10 [11] cells of S. mutans in capsules produced a small increase in secretory IgA. The oral route failed to reduce caries significantly, as compared with subcutaneous immunization. The rise in secretory antibodies produced was small and of short duration, even after secondary immunization. Experiments in humans of the ingestion of S. mutans in gelatins capsules resulted in an increase in secretory IgA antibodies in saliva, although for a limited time only. Immunological memory in secretory IgA responses is rather limited and this may curtail the value of oral immunization. [3] Although the oral route was not ideal for reasons including the detrimental effects of stomach acidity on antigen, or because inductive sites were relatively distant, experiments with this route established that induction of mucosal immunity alone was sufficient to change the course of infection with S. mutans and disease in animal models and in humans. [22],[26],[27],[28]
2. Intranasal route
More recently, attempts have been made to induce protective immunity in mucosal inductive sites that are in closer anatomical relationship to the oral cavity. Intranasal installation of the antigen, the nasal associated lymphoid tissue (NALT), has been used to induce immunity to many bacterial antigens including those associated with mutans Streptococcal colonization and accumulation. Protective immunity after infection with cariogenic mutans streptococci could be induced in rats by the intranasal route with many S. mutans antigens or functional domains associated with these components. Protection could be demonstrated with S. mutans Ag I/II, the SBR of Ag I/II, a 19-mer sequence within the SBR, the glucan binding domain of S. mutans, GBP-B, and fimbrial preparations from S. mutans with antigen alone or combined with mucosal adjuvants. [22],[23],[27]
3. Tonsillar route
The ability of tonsillar application of antigens to induce immune responses in the oral cavity is of great interest. The tonsillar tissue contains the required elements of immune induction of secretory IgA responses although IgG, rather than IgA, response characteristics are dominant in this tissue. Nonetheless, the palatine tonsils, and especially the nasopharyngeal tonsils, have been suggested to contribute precursor cells to mucosal effector sites, such as the salivary glands. In this regard, the experiments have shown that topical application of formalin-killed Streptococcus sobrinus cells in rabbits can induce a salivary immune response, which can significantly decrease the consequences of infection with cariogenic Streptococcus sobrinus. Interestingly, repeated tonsillar application of a particulate antigen can induce the appearance of IgA antibodies producing cells in both the major and minor salivary glands of the rabbit. [22]
4. Minor salivary gland
The minor salivary glands populate the lips, cheeks, and soft palate. These glands have been suggested as potential routes for mucosal induction of salivary immune responses, given their short, broad secretory ducts that facilitate retrograde access of bacteria and their products and give the lymphatic tissue aggregates that are often found to be associated with these ducts. Experiments in which Streptococcus sobrinus GTF was topically administered onto the lower lips of young adults have suggested that this route may have potential for dental caries vaccine delivery. In these experiments, those who received labial application of GTF had a significantly lower proportion of indigenous S. mutans/total Streptococcal flora in their whole saliva during a 6-week period following a dental prophylaxis, compared with a placebo group. [22]
5. Rectal
More remote mucosal sites have also been investigated for their inductive potential. For example, rectal immunization with non oral bacterial antigens such as Helicobacter pylori or Streptococcus pneumoniae, presented in the context of toxin-based adjuvant, can result in the appearance of secretory IgA antibodies in distant salivary sites. The colo-rectal region as an inductive location for mucosal immune responses in humans is suggested from the fact that this site has the highest concentration of lymphoid follicles in the lower intestinal tract. Preliminary studies have indicated that this route could also be used to induce salivary IgA responses to mutans streptococcal antigens such as GTF. One could, therefore, foresee the use of vaccine suppositories as one alternative for children in whom respiratory ailments preclude the intranasal application of the vaccine. [22]
Systemic route of immunization
Subcutaneous administration of S. mutans was used successfully in monkeys and elicited predominantly serum IgG, IgM, and IgA antibodies. The antibodies find their way into the oral cavity via gingival crevicular fluid and are protective against dental caries. Whole cells, cell walls, and the 185 KD Streptococcal antigen have been administered on 2 to 4 occasions. A subcutaneous injection of killed cells of S. mutans in Freund's incomplete adjuvant or aluminium hydroxide elicits IgG, IgM, and IgA classes of antibodies. Studies have shown that IgG antibodies are well maintained at a high titer, IgM antibodies progressively fall and IgA antibodies increase slowly in titer. The development of serum IgG antibodies takes place within months of immunization, reaching a tire of up to 1:1280 with no change in antibodies being found in the corresponding sham-immunized monkeys. Protection against caries was associated predominantly with increased serum IgG antibodies. [3]
Active gingivo-salivary route
There has been some concern expressed regarding the side effects of using these vaccines with the other routes. In order to limit these potential side effects, and to localize the immune response, gingival crevicular fluid has been used as the route of administration. Apart from the IgG, it is also associated with increased IgA levels. [29]
The various modalities tried were as follows:
- Injecting lysozyme into rabbit gingival, which elicited local antibodies from cell response
- Brushing live S. mutans onto the gingiva of rhesus monkeys, which failed to induce antibody formation
- Using smaller molecular weight Streptococci antigen, which resulted in better performance probably due to better penetration. [29]
Passive immunization
As the name suggests, passive immunization involves passive or external supplementation of the antibodies. This carries the disadvantage of repeated applications, as the immunity conferred is temporary.
Several approaches tried were:
Monoclonal antibodies to S. mutans cell surface antigen I/II have been investigated. The topical application in human subjects brought a marked reduction in the implanted S. mutans. Thus, by bypassing the system, less concern exists about the potential side effects. [3],[29]
Systemic immunization of cows with a vaccine using whole S. mutans led to the bovine milk and whey containing polyclonal IgG antibodies. This was then added to the diet of a rat model. The immune whey brought a reduction in the caries level. This whey was also used in a mouth rinse, which resulted in a lower percentage of S. mutans in the plaque. [3,29]
The novel concept of using hen egg-yolk antibodies against the cell-associated glucosyltransferase of S. mutans was introduced by Hamada. Vaccines used were formalin killed whole cells and cell associated GTFs. Caries reduction has been found with both these treatments. [3]
The latest in these developments in passive immunization is the use of transgenic plants to give the antibodies. The researchers have developed a caries vaccine from a genetically modified (GM) tobacco plant. The vaccine, which is colorless and tasteless, can be painted onto the teeth rather than injected and is the first plant derived vaccine from GM plants. [30]
The advantages are listed below:
- The genetic material can be easily exchanged.
- It is possible to manipulate the antibody structure so that while the specificity of the antibody is maintained, the constant region can be modified to adapt to human conditions, thus avoiding cross reactivity.
- Large scale production is possible as it would be quite inexpensive. [29]
| Adjuvants and Delivery Systems for Dental Caries Vaccines | | |
Various new approaches have been tried out to potentiate aspects of the immune response to induce sufficient antibodies to achieve a protective effect to overcome the existing disadvantages.
Synthetic peptides: Any antigen derived from animals or humans has the potential for hypersensitivity reaction. The chemically synthesized peptides hold an advantage in that this reaction can be avoided. This has been found to enhance the immune response. In humans, synthetic peptides elicited both IgG and T-cell proliferative responses, and the antibodies were both anti-peptide and anti-native. The synthetic peptides give antibodies not only in the GCF but also in the saliva. The synthetic peptide used is derived from the Glucosyltransferase enzyme. [23],[29]
Coupling with Cholera Toxin Subunits: Cholera toxin (CT) is a powerful mucosal immunoadjuvant, which is frequently used to enhance the induction of mucosal immunity to a variety of bacterial and viral pathogens in animals systems. Mucosal application of a soluble protein or peptide antigen alone rarely results in elevated or sustained IgA responses. However, the addition of small amounts of CT or the closely related E. coli heat-labile enterotoxins (LT) can greatly enhance mucosal immune responses to intragastrically or intranasally applied mutans Streptococcal antigens or to peptides derived from these antigens. The coupling of the protein with the nontoxic unit of the cholera toxin was effective in suppressing the colonization of S. mutans. [22],[24],[29]
Fusing with Salmonella More Details: The avirulent strains of salmonella are an effective vaccine vector; fusion using recombinant techniques have been used. [29]
Microcapsules and microparticles: Combinations of antigens in or various types of particles have been used in an attempt to enhance mucosal immune responses. The microcapsules and microparticles made of poly lactide-co-glycolide (PLGA) have been used as local delivery systems because of their ability to control the rate of release, evade preexistent antibody clearance mechanisms, and degrade slowly without eliciting an inflammatory response to the polymer. [29]
Liposomes: Liposomes, which are bilayered phospholipids membrane vesicles manufactured to contain and deliver drugs and antigens, have been used to enhance mucosal responses to mutans Streptococcal carbohydrate and GTF. Liposomes are thought to improve mucosal immune responses by facilitating M cell uptake and delivery of antigen to lymphoid elements of inductive tissue. [22],[29]
| Risks of Using Caries Vaccine | | |
All vaccines, even if properly manufactured and administered, seem to have risks. The most serious is that sera of some patients with rheumatic fever who show serological cross-reactivity between heart tissue antigens and certain antigens from hemolytic Streptococci. [31] Experiments from antisera from rabbits immunized with whole cells of S. mutans and with a high molecular weight protein antigen of S. mutans were reported to cross react with normal rabbit and human heart tissues. Polypeptides (62-67 KDA) immunologically cross-reactive with human heart tissue and rabbit skeleton muscles myosin are found in the cell membrane of S. mutans and Streptococcus ratti. [32] On the other hand, demonstrations showed that rabbit antiserum to high molecular weight, Todd-Hewitt broth components reacted with monkey cardiac muscle with S. mutans coated with medium components. Heart cross-reactive antibodies do not develop in rhesus monkeys or rabbits immunized with purified Ag I/II from S. mutans. It is possible that increased production of heart-reactive antibody in rabbits immunized with mutans streptococci results in injury of heart tissue as a consequence of binding of this low molecular weight Streptococcal polypeptide. Because of the potential of Streptococcal whole cells to induce heart reactive antibodies, the development of a sub-unit vaccine for controlling dental caries has been the focus of intense research interest. Glucosyltransferase was also tested for cross-reactivity with human heart tissue and the results were negative. [21,33] Further research showed that the C-terminal part of Ag I/II contains an epitope, which is cross-reactive with human IgG and, although the clinical significance of this observation is unknown, it appears that this potentially harmful epitope should be excluded from a caries vaccine. The human IgG cross-reactive region is also present in other mutans streptococci such as Streptococcus sobrinus as well as in non mutans streptococci. [33]
| Public Health Aspects | | |
Although the prevalence of tooth decay has declined according to a national epidemiologic survey by the United States national institute of dental research, this oral disease is still a significant health problem that affects approximately 50% of the 5 to 17 year old children in the U.S. In fact, by the age of 17, only 16% remain free of caries. Interestingly, 25% of children and adolescents aged 5 to 17 years old account for 80% of caries in permanent teeth, indicating the existence of high-risk groups. Meanwhile, in many developing countries in Central and South America, Africa, Asia, as well as in certain European countries, dental caries is on the rise. Despite the wide spread use of fluoride (e.g., in toothpaste and drinking water) to which the decline of caries between the 1970s and 1980s is mainly attributed, this disease still remains among the most prevalent and costly in industrialized and in developing countries. Indeed, developing countries without a water fluoridation system and where access to dental health education and treatment may not be available to everyone are in great need of a vaccine. An effective, safe, and readily deliverable vaccine may not only help against pain and health issues associated with caries but also save the billions of dollars that are currently spent in the U.S. for restorative treatment. [33] An important question is whether the search for a caries vaccine is justified from a public health point of view. This question is especially critical as we already have effective means to control the disease. Given that S. mutans is not the only cariogenic microorganism and that a series of factors influence the development of the disease, the question arises as to what extent successful vaccination against S. mutans could reduce the incidence of dental caries. [31] Considerable caries reduction could be attained if colonization of S. mutans could be prevented or reduced at the time of eruption of both deciduous and permanent teeth. Thus, a successful vaccination directed against S. mutans could be a valuable adjunct to other caries-preventive measures. Some other studies also suggest that vaccination could be a supplement to antimicrobial treatment in individuals with high levels of S. mutans. In third-world countries, a rapid increase in caries has been observed both in children and adolescents. The low dentist to population ratio and the lack of organized dental health care limit the possibilities of utilizing conventional caries-preventive methods. Therefore, it was thought that vaccination against dental caries could be of great value as a preventive adjunct in some societies and as a major public health measure in others. It ought to be stressed, however, that a thorough analysis of the need, cost benefits, and risk-benefits of a vaccine against dental caries in various societies and subgroups has to be performed. [31]
| Discussion | | |
Loesche [34] stated that dental caries is one of the most widespread diseases of mankind. S. mutans is the primary etiologic agent of dental caries that are transmissible. It is also said that a strong association exists between the level of colonization with S. mutans and dental caries, although other organisms such as Lactobacilli have also been implicated in this disease. Adding to this, the studies conducted by Caufield, et al.[35] stated that under normal circumstances of diet, children become permanently colonized with S. mutans between the middle of the 2 nd year and the end of the 3 rd year of life. This period is called the window of infectivity. Many studies were conducted on active immunization. Childers, et al. [36] immunized adults orally by using enteric coated capsules filled with crude Streptoccoccus mutans Gs-5 GTF antigen preparation contained in liposome, resulting in the production of parotid salivary IgA antibodies. Similarly, the studies by Childers, et al.[37] have shown that nasal immunization with dehydrated liposome containing GTRF preparation induced significant IgA antibody response in nasal washes. However, the studies by Smith, et al.[38] reported that mucosal immunization with GTF could influence the re-emergence of mutans Streptococci in adults after a dental prophylaxis. Although the oral route was not ideal for reasons such as the detrimental effects of stomach acidity on antigens or because inductive sites were relatively distant, experiments with this route established that induction of mucosal immunity alone was sufficient to change the course of mutans Streptococci infection and disease in animal models by Michalek, et al.[39] and humans by Smith, et al.[38] Most recently, attempts have been made to induce protective immunity in mucosal inductive sites closes to the oral cavity. Studies conducted by Katz, et al.[40] have demonstrated that intranasal immunization of rats with AgI/II - CTB induced a protective salivary immune response, which was associated with a reduction in Streptococci mutans colonization and Streptococci mutans induced caries. The studies by Brandtzaed [41] have shown that tonsillar application of antigens to the palatine tonsils i.e., nasopharyngeal tonsils may contribute precursor cells to mucosal effectors sites such as salivary glands. The experiments performed by Schroeder, et al.[42] have shown that Streptococcus sobrinus GTF was topically administered on the lower lips of young adults and suggested that this route may have potential for dental caries vaccine delivery. Kleanthous, et al.[43] conducted experiments through rectal immunization with non oral bacteria antigens such as H. pylori resulting in secretory IgA antibodies in distant salivary sites. Filler, et al.[44] conducted experiments on passive immunization and showed that passive immune protection can be achieved with antibodies to GTF or GBPs mouth rinses containing bovine milk or hen egg yolk . Childers, et al. [45] reported that the antibody to S. mutans cells lead to a modest, short-term decrease in the number of Streptococci mutans in saliva or dental plaque.
| Conclusion | | |
Clearly, there is strong evidence that S. mutans and Streptococcus sobrinus are closely associated with dental caries. Fluoride treatment used abroad has successfully limited caries progression, but was not sufficient to control this infectious disease even when used together with professional tooth cleaning and dietary counseling in populations highly exposed to these cariogenic microbiota. Active and passive immunization strategies, which target key elements in the molecular pathogenesis of mutans Streptococci, hold promise. Integrating these approaches into broad-based public health programs may yet forestall dental caries disease in many of the world's children, among whom those of high risk might derive the greatest benefit. Despite the encouraging decline in dental caries observed in recent years in many populations, millions of children remain at risk of experiencing extensive tooth decay and it is particularly distressing that many of those suffering will be among the least likely to obtain satisfactory treatment. Along with established methods of caries prevention, caries vaccines have the potential of making a highly valuable contribution to disease control. In the meantime, basic research on the mode of action of caries vaccine and the search for new, more effective, and possibly polyvalent vaccines must continue if we are to fully explore their potential for helping us in the struggle against dental caries. Regardless of the mechanism by which immune protection against dental caries is achieved, further advances to make immunization against caries practical will depend upon clinical trials aimed at establishing whether the findings from animal experiments can be transferred to humans. Particular goals for such studies include determining whether appropriate immune responses can be safely generated in humans, especially in susceptible age groups and whether such responses will afford desirable levels of protection.
Although several methods such as topical or systemic use of fluorides, fissure sealants, and dietary control have been developed to prevent dental caries, the efficacy of these methods is not enough to eradicate dental caries in humans; however, there are a few studies on the efficacy of caries vaccines in humans.
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Correspondence Address:
K M Shivakumar
Department of Preventive and Community Dentistry, Sharad Pawar Dental College and Hospital, Datta Meghe Institute of Medical Sciences (Deemed University), Sawangi (Meghe), Wardha Maharashtra, 442 004
India
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DOI: 10.4103/0970-9290.49066 PMID: 19336869
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