Cavity Preventing Chewing Gum
PRC scientists are working to develop other calcium phosphate-based technologies that can remineralize hard tooth tissues or, at a minimum, retard caries-producing demineralization. Studies have shown that an experimental chewing gum containing a αCa3(PO4)2 can eliminate the ability of sucrose challenged plaque to demineralize tooth enamel, thus preventing a cavity from forming or progressing. Additional studies showed that separate calcium and phosphate compounds, incorporated into gums and candies, are even more effective in producing remineralizing conditions in the mouth.
For further information, contact larry.chow@nist.gov.
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Microanalytical Techniques
Dr. Gerald Vogel has developed novel analytical techniques and instrumentation to study the mechanisms of dental decay by examining the composition of microscopic samples of plaque, plaque fluid, and oral tissue recovered from the oral environment. Recently these techniques have been extensively used to develop and evaluate new anti-cavity and cavity repairing technologies. For example, as a result of these studies fluoride rinses and dentifrices have been “engineered” that produce a much greater cavity fighting effect while using a very low amount of applied fluoride.
For more information on the methods and equipment e-mail Dr. Vogel at jerry.vogel@nist.gov.
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Raisin Effects On in vitro Demineralization of Teeth
There is concern that food particles retained on the teeth will lead to demineralization and cavitation of tooth surfaces. The perception of “stickiness” of snack foods by the general population does not correlate well with actual measures of food particle retention. Though foods such as raisins are perceived as sticky, scientific research does not bear out the stickiness beliefs. In a multi-city examination of perceptions about 21 snack foods, research subjects choose jelly beans, caramels and caramel-filled chocolate bars as the most ‘sticky’ snacks. Retrieved food particles from 5 subjects just after finishing eating jelly beans (46 mg) and caramels (64 mg) were actually at the low end of the scale, though chocolate-caramel (223 mg) and chocolate-caramel-peanut (155 mg) bars were at the high end. In this study, raisins were perceived (by the general public) as the ninth stickiest food out of the twenty-one snacks listed, but actually had only 35 mg of material left on the teeth at 0 min. after swallowing (putting them in the bottom fourth). Our research has devised in vitro testing procedures to determine the potential of raisins to stimulate intraoral bacteria to demineralize human teeth. Test specimens of human teeth will be subjected to repeated insults of “raisin” in an in vitro caries model and compared to sucrose insults and to no insults. The resultant demineralization of tooth structure is evaluated using contact microradiography. With microradiography, the density of the demineralization, as well as the cross-section profile of the demineralized area is evaluated.
For more information please contact Dr. Carey at clif.carey@nist.gov.
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Calcium Phosphate Bone Cements
A calcium phosphate bone cement based on ADAHF patents was introduced to the market by an ADAHF licensee in November of 1997 under the trade name BoneSource®. The product has thus far received FDA approval for craniofacial and maxillofacial applications. This plaster-like material can be placed surgically, molded and sculpted to the correct anatomical shape, and will set to form a hard implant composed entirely of hydroxyapatite. The implant material is slowly dissolved and replaced entirely by new bone, thus repairing the original defect. Additional studies have led to significant improvements in the handling properties of the cement and development of cement formulations that would be suited for different clinical applications.
For more information on this technology, contact Dr. Larry Chow at larry.chow@nist.gov.
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Infrared Microscopy
Dr. Naomi Eidelman has been using Fourier transform infrared microspectroscopy to map cardiovascular and juvenile dermatomyositis calcified deposits, enamel and dentin of healthy and diseased teeth, narwhal tusks, dental calculi specimens, dental restorative materials, tissue engineered bone materials, calveria, nano ferroelectric polymer films, various combinatorial libraries of polymer blends and gradient polymer compositions created by temperature or UV. Understanding the chemical changes in teeth can help prevent dental caries. Determining the chemical composition of dental calculus can help to design means of preventing this pathologic calcification. Mapping the chemical constituents in the surface of experimental dental materials may lead to better understanding of their failure modes. She also applied this technology to understanding the failure mechanism of adhesive bonding to tooth tissues. The quality of the bonding and the adhesive can be assessed by mapping the fractured surface for chemical signatures of the adhesive, proteins, and mineral.
For more information contact Dr. Eidelman at naomi.eidelman@nist.gov.
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ACP Remineralizing Composites
Dental materials containing amorphous calcium phosphate (ACP) have tremendous appeal due to (a) their ability to arrest demineralization and/or remineralize defective tooth structures and (b) their biocompatibility. Bioactive ACP polymeric composites may stimulate the repair of mineralized tissues through the release of calcium and phosphate ions. These ions may be incorporated into the tooth and form apatite, a natural inorganic constituent of enamel and dentin. For the last eight years Dr. Drago Skrtic has conducted systematic studies of the structure and physicochemical properties of ACP fillers in order to develop strategies for better control ACP dispersion in the polymer matrix. Additionally, polymerization-related phenomena, such as degree of vinyl conversion, polymerization shrinkage and stress development were investigated to learn more about the processes that occur at the inorganic filler/organic matrix interface. Several prototypes of ACP-based composites were successfully formulated. Moreover, ACP-based pit and fissure sealant, ACP orthodontic adhesive and ACP crown and bridge cement based on our technology are now available to dental practitioners for clinical use. Current research is aimed to extend the utility of ACP remineralizing composites to endodontic applications as a biocompatible, easy-to-manipulate root canal sealer and/or filling material.
For further information on this project, please contact Dr. Drago Skrtic at Drago.Skrtic@nist.gov
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Failure Analysis of Dental Restorations
The need for biologically compatible, aesthetically acceptable dental restorations is expected to increase during the next decade, especially among the older population. Accordingly, the last several years have seen the development and clinical use of many new environmentally-friendly restoration materials of natural appearance. While these new materials are in general advertised as durable, none have proven as robust as traditional amalgam restorations. Surprisingly, there have been few attempts to systematically relate the clinical longevity of the new dental ceramics to intrinsic material properties, and forensic studies on failed restorations are nearly nonexistent.
The main purpose of this project is to apply fractographic principles to identify and evaluate the failure mechanisms of restorations from critical failure-related properties. Newly developed fracture toughness test standards for structural ceramics can yield accurate and precise values of this important property for dental materials. One goal of this project is to obtain and correlate accurate values of strength and toughness with fractographically-determined flaw characteristics to calculate local failure stresses, and compare the susceptibility of different dental materials to different failure types and conditions and relate that information to clinically relevant observations of failures.
This project is contributing to dentistry in a number of major ways, including: providing the dental community with a scientific understanding of restoration failure; furnishing feedback to the manufacturers and laboratories to improve materials processing; providing information relevant to clinical procedures and placement; and laying the groundwork for mechanical testing and standards development. In summary, we intend to use systematic analyses and sound scientific principles to determine how and why dental materials fail. Standardized property testing and an interdisciplinary approach involving materials design, fractographic analyses and clinical outcomes are all applied to better the understanding of failure processes in dental materials.
For more information e-mail Dr. Quinn at janet.quinn@nist.gov.
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Improvement of Preventive and Restorative Materials
Because most of American dentists spend much of their time restoring teeth that have developed secondary caries at the margins of previous restorations, one of PRC’s current projects is the development of materials and methods to restore teeth esthetically in a manner that will prevent formation of secondary caries. Ongoing work in the PRC includes the synthesis and evaluation of copolymerizable polyfunctional molecules with appropriate molecular sizes and solubility parameters to rapidly infiltrate and permeate the hydrated hydrophilic organic and inorganic components of dentin and enamel. The polyfunctionality of ether-linked ligand groups on the individual molecules enables them to favorably compete with water on tissue surfaces and form numerous stronger interfacial binding interactions. Multiple ether-linked copolymerizable groups can form a densely cross-linked structure not subject to hydrolytic or chemical degradation by virtue of containing no potentially hydrolyzable ester groups, which are contained in contemporary bonding formulations. The above-described anhydrous but hydrophilic fluid composition diffuses into the hydrous tissue, it imbibes and displaces the substrate’s water, and on polymerization forms a dense, highly cross-linked hydrogel, which has higher adhesive strength than cohesive strength. The rationale for this last characteristic is that when margin gap formation occurs due to polymerization or thermal shrinkage or other stresses, the gap will comprise and expose two surfaces of cross-linked polymers rather than a space between polymer and dentin or enamel. Cariogenic bacteria can thrive so long as dentin or enamel can buffer the acids they excrete, but could not survive in a polymeric enclosure in which their acids would lower the pH to levels below their tolerance.
Although an ideal formulation as described above has not yet been tested, a similar prototypic composition gave shear bond test values that were significantly higher than that of the commercial control (p<0.05). These preliminary results are in accordance with the hypothesis that such formulations can form strong adhesive bonds to hydrated dentin surfaces. Further improvements in bonding of resins and composites to hydrated biological tissues such as dentin by means of optimized formulations are anticipated.
This work is being supported by the NIDCR Grant R01-DE05129, NIST, and the ADA Foundation.
For further information, contact Dr. Rafael Bowen at ray.bowen@nist.gov.
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Novel Cariostatic Cements
Novel resin-based calcium phosphate basing cements (RCPC) and composites have been developed as calcium and phosphate ion-releasing biomaterials.
The pulp-capping and basing cements consist of polymerizable a resin component and a filler phase. The fillers comprise a mixture of calcium phosphate minerals that can potentially form apatite and maintain a high pH to stimulate the formation of new dentin to repair pulp exposures. The cements provide a pulp-capping / basing material with adequate strength to be immediately restored. They can also serve as a cavity liner or base and most importantly, have shown to remineralize demineralized tooth hard tissues.
Data is available on various in vitro studies, for example, adhesion to dentin and microleakage evaluation, which showed that the RCPC has lower microleakage and better dentin adhesion than a comparable commercial pulp-capping cement. In vivo evaluation of RCPC as a pulp-capping material showed that the material due to its moderate dentin adhesion and good seal against bacterial invasion is an excellent candidate for stimulating the formation of reparative dentin bridges. Because the cement is able to seal the exposed pulp and because its ability to continuously release calcium and phosphate ions, it is a promising medicament for successful pulp-capping of healthy and inflamed pulps.
Moreover, in vitro and in vivo experiments have demonstrated that the basing cements are able to remineralize mineral deficient dentin, resulting in significantly improved mineral densities compared to Ca-PO4-free controls.
In vitro studies of other cements developed for orthodontic applications have shown that the cements bond orthodontic metal brackets to enamel similarly well as a commercial control material. In an in vivo pilot study the Ca-PO4-releasing experimental orthodontic cement was superior in preventing demineralization adjacent to the cemented brackets compared to the commercial control,.
More recently, remineralizing composites for the Atraumatic Restorative Treatment (ART) have been developed. In vitro these novel reinforced materials demonstrated superior strength and wear properties compared to resin modified glass ionomer cements. Extensive in vitro remineralization studies of artificial dentin lesions demonstrated that after 4 weeks the ART composites achieved similar remineralization of these lesions as the resin-reinforced glass ionomer cement.
For more information, contact Dr. Dickens at Sabine.dickens@nist.gov.
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Cavity Repairing Fluoride Devices
A laboratory study of a dicalcium phosphate dihydrate-forming fluoride gel that can be placed between teeth or in the pits and fissures of teeth has shown the ability to form large amounts of both loosely bound fluoride and tooth-bound fluoride in these “at risk” areas. Because the device contains a low overall quantity of fluoride, it can be left in the mouth until it dissolves away in about 2 hours. This technology could enable dentists remineralize early cavities without the need for large quantities of fluoride or frequent reapplication.
For further information, contact Dr. Larry Chow at larry.chow@nist.gov.
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Calcium Phosphate Chemistry and Remineralization
The formation and conversion of calcium phosphates are being studied for prevention and repair of dental caries and tooth sensitivity. The Foundation’s amorphous calcium phosphate patents have been licensed and in market in the fields of toothpaste (ENAMEL CARE and MENTADENT by Church & Dwight Co.), chewing gums, confections, prophylaxis paste and fluoride varnish (ENAMEL PRO series by Premier Dental), tooth whitening (Nitewhite ACP, Discus Dental), and topical desensitizers (Quell Desensitizer by Pentron Clinical Technologies and Relief ACP by Discus Dental). Other products are currently under development. The field of remineralizing temporary cement is still available for licensing. Ongoing research is concentrating on second generation ACPs and multimodal approaches to prevent caries. New compounds with antimicrobial and remineralization potential are synthesized.
For more information, contact Dr. Tung at ming.tung@nist.gov.
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Fluoride Requirements for Theraputic Efficacy
The goal of this project is to establish the minimum concentration of fluoride needed to prevent enamel and root caries. The lack of knowledge about "the target concentration of fluoride required in the oral environment to optimize its potential for caries prevention" has inspired the NIDCR to issue a call for research to answer this question indicating a high priority status for this subject. After 60 years of community water fluoridation we still do not know how much fluoride is required to prevent caries. This may be because no one has systematically performed in vitro studies that separate the significant factors under conditions that closely mimic those of the oral environment and then validated those findings in intraoral studies.
This proposal details such a systematic study to identify the significant factors and their interactions as related to the efficacy of fluoride to prevent caries. A predictive model that takes into account the conditions of each person is to be developed from in vitro studies and then validated through intraoral studies. In the mouth, fluoride originates either from the saliva at a relatively low and fairly constant concentration (0.1 ppm; Carey et al., 1986) or from fluoride rinses, gels, and dentifrices, which is transient and can range in concentration up to 15,000 ppm. In Aim 1 the continuous flow model is used to optimize the amount of fluoride that is needed to prevent enamel caries when there is a steady, low concentration of fluoride at all times. Aim 2 is focused on determining the amount of fluoride on a time-weighted basis that is required to prevent enamel caries when the fluoride is provided as a bolus treatment twice daily. Recognizing that root dentin is a very different substrate than enamel, Aims 3 and 4 are focused on determining the therapeutic amounts of fluoride required to prevent root caries under conditions of constant exposure (Aim 3) and periodic high concentration fluoride exposures (Aim 4). Aim 5 will establish the amount of fluoride required to prevent caries when proteins or other permselective macromolecules are adsorbed on the surfaces of the enamel or root dentin. In Aim 6, the relationships between saliva composition, salivary flow and the amount of fluoride required to prevent caries established with the continuous flow model will be tested by use of an intraoral model. In this Aim 6 the effect of fluoride exposure on the prevention of caries will be determined.
Together these studies should, for the first time, be able to demonstrate the minimum therapeutic levels of fluoride necessary to have a prophylactic effect. Additionally, the potential of this project to develop predictive models that can be used to indicate the required amount of F as a function of a specific environment is particularly significant because the profession will be able to tailor F regimes as appropriate. This is particularly important in the treatment of populations that are at higher risk.
For more information e-mail Dr. Carey at clif.carey@nist.gov.
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Anti Caries Properties of an Amorphous Calcium Phosphate (ACP) Orthodontic Adhesive
A common problem that occurs with orthodontic patients is that over the course of their treatment white spot caries lesions develop around the orthodontic brackets. A new ACP containing orthodontic adhesive has been developed that releases calcium and phosphate at the site of the bracket thus avoiding demineralization of the tooth. A two year clinical study is underway in collaboration with Howard University comparing the white spot caries incidence around orthodontic brackets attached to the tooth with either ACP containing or non-ACP containing orthodontic adhesive. Six month results show that there is a reduced amount of demineralization around the brackets. Additionally, the bonding failure rate for the ACP containing orthodontic adhesive is not different than that of the commercial non-ACP orthodontic adhesive.
For further information on this research, please contact Dr. Clif Carey at clif.carey@nist.gov.
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Nano Bioactive Materials
Nano forms of hydroxyapatite and other bioactive materials are prepared by a novel method developed under a new NIH grant, employing a spray drying technique in such a way that (1) target particle sizes over a wide range can be obtained, (2) compounds with both low and high solubilities can be prepared, and (3) the prepared particles would not be exposed to any solution environment after their formation and therefore would retain their original, highly reactive surfaces. Due to their small sizes and high reactivity, the prepared nano materials are expected to have a range of clinical applications. Ongoing studies are focused on evaluating the effectiveness of nano forms calcium fluoride as the source of fluoride for remineralizing tooth enamel carious lesions and the effectiveness of nano sized calcium phosphates and calcium fluoride in reducing dentin permeability.
Please contact Dr. Chow at larry.chow@nist.gov for further information on this technology.
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Screening Test for Oral Rinse Erosive Capacity
To establish a screening protocol to evaluate the dental erosive capacity (if any) of oral rinses to be incorporated into U.S. National and International standards on the safety and efficacy of mouth rinses.
Definitions: Dental erosion – the loss of dental hard tissue by chemical action not involving bacteria [Imfeld, Definition classification and links. Eur J Oral Sci 104:151-155, 1996]. Note that the dental definition excludes loss of dental hard tissue due to physical forces [Pickles, The Teeth and Their Environment. Monogr oral Sci. Basel, Karger, vol 19, pp 86-104, 2006].
Concepts: Dental hard tissue (enamel) is predominately Hydroxyapatite (HAp) mineral, and thus HAp is a reasonable model for erosion studies. However note that any screening test that uses only HAp in the evaluation will not account for other protective features such as pellicle. The erosive capacity of an oral rinse can be due to three factors: acidity (buffer capacity), pH, and calcium binding capacity of the solution. The test must address all of these factors to be relevant. Finally, the screening test is being validated through direct measurements of erosion on dental hard tissue.
For further information on this study, please contact Dr. Clif Carey at clif.carey@nist.gov.
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