In vitro studies and modeling of a controlled-release device for root canal therapy

Advances in hybridized nanoarchitectures for improved oro-dental health

On a global note, oral health plays a critical role in improving the overall human health. In this vein, dental-related issues with dentin exposure often facilitate the risk of developing various oral-related diseases in gums and teeth. Several oral-based ailments include gums-associated (gingivitis or periodontitis), tooth-based (dental caries, root infection, enamel erosion, and edentulous or total tooth loss), as well as miscellaneous diseases in the buccal or oral cavity (bad breath, mouth sores, and oral cancer). Although established conventional treatment modalities have been available to improve oral health, these therapeutic options suffer from several limitations, such as fail to eradicate bacterial biofilms, deprived regeneration of dental pulp cells, and poor remineralization of teeth, resulting in dental emergencies. To this end, the advent of nanotechnology has resulted in the development of various innovative nanoarchitectured composites from diverse sources. This review presents a comprehensive overview of different nanoarchitectured composites for improving overall oral health. Initially, we emphasize various oral-related diseases, providing detailed pathological circumstances and their effects on human health along with deficiencies of the conventional therapeutic modalities. Further, the importance of various nanostructured components is emphasized, highlighting their predominant actions in solving crucial dental issues, such as anti-bacterial, remineralization, and tissue regeneration abilities. In addition to an emphasis on the synthesis of different nanostructures, various nano-therapeutic solutions from diverse sources are discussed, including natural (plant, animal, and marine)-based components and other synthetic (organic- and inorganic-) architectures, as well as their composites for improving oral health. Finally, we summarize the article with an interesting outlook on overcoming the challenges of translating these innovative platforms to clinics.

Polysaccharide-Based Micro- and Nanosized Drug Delivery Systems for Potential Application in the Pediatric Dentistry

The intensive development of micro- and nanotechnologies in recent years has offered a wide horizon of new possibilities for drug delivery in dentistry. The use of polymeric drug carriers turned out to be a very successful technique for formulating micro- and nanoparticles with controlled or targeted drug release in the oral cavity. Such innovative strategies have the potential to provide an improved therapeutic approach to prevention and treatment of various oral diseases not only for adults, but also in the pediatric dental practice. Due to their biocompatibility, biotolerance and biodegradability, naturally occurring polysaccharides like chitosan, alginate, pectin, dextran, starch, etc., are among the most preferred materials for preparation of micro- and nano-devices for drug delivery, offering simple particle-forming characteristics and easily tunable properties of the formulated structures. Their low immunogenicity and low toxicity provide an advantage over most synthetic polymers for the development of pediatric formulations. This review is focused on micro- and nanoscale polysaccharide biomaterials as dental drug carriers, with an emphasis on their potential application in pediatric dentistry.

Should local drug delivery systems be used in dentistry?

In dentistry, the use of biomaterial-based drug delivery systems (DDS) aiming the release of the active compounds directly to the site of action is slowly getting more awareness among the scientific and medical community. Emerging technologies including nanotechnological platforms are offering novel approaches, but the majority are still in the proof-of-concept stage. This study critically reviews the potential use of DDS in anesthesiology, oral diseases, cariology, restorative dentistry, periodontics, endodontics, implantology, fixed and removable prosthodontics, and orthodontics with a special focus on infections. It also stresses the gaps and challenges faced. Despite numerous clinical and pharmacological advantages, some disadvantages of DDS pose an obstacle to their widespread use. The biomaterial's biofunctionality may be affected when the drug is incorporated and may cause an additional risk of toxicity. Also, the release of sub-therapeutic levels of drugs such as antibiotics may lead to microbial resistance. Multiple available techniques for the manufacture of DDS may affect drug release profiles and their bioavailability. If the benefits outweigh the costs, DDS may be potentially used to prevent or treat oral pathologies as an alternative to conventional strategies. A case-by-case approach must be followed.

Health care-associated infections: Controlled delivery of cationic antiseptics from polymeric excipients

Nowadays, the treatment of health care-associated infections represents a serious issue, due to the increasing number of bacterial strains resistant to traditional antibiotics. The use of antiseptics like quaternary ammonium salts and biguanides is a viable alternative to face these life-threatening infections. However, their inherent toxicity as well as the necessity of providing a sustained release to avoid the formation of pathogen biofilms are compelling obstacles towards their assessment in the hospitals. Within this framework, the role of polymeric drug delivery systems is fundamental to overcome the aforementioned problems. Biocompatibility, biodegradability and excipient-drug interactions are crucial properties determining the efficacy of the formulation. In this work, we provide an in-depth analysis of the polymer drug delivery systems that have been developed or are under development for the sustained release of positively charged antiseptics, highlighting the crucial characteristics that allowed to achieve the most relevant therapeutic effects. We reported and compared natural occurring polymers and synthetic carriers to show their pros and cons and applicability in the treatment of health care-associated infections. Then, the discussion is focused on a particularly relevant class of materials adopted for the scope, represented by polyesters, which gave rise, due to their biodegradability, to the field of resorbable drug delivery devices. Finally, a specific analysis on the effect of the polymer functionalization over the formulation performances for the different types of polymeric carriers is presented.

Efficacy and potential use of novel sustained release fillers as intracanal medicaments against Enterococcus faecalis biofilm in vitro

Background

Enterococcus faecalis is a bacterium frequently isolated after failed root canal therapy. This study analyzed the antibacterial and antibiofilm effects in vitro of sustained-release fillers (SRF) containing cetylpyridinium chloride (CPC) against vancomycin resistant E. faecalis.

Methods

First, the solidification capability was tested by introducing liquid SRF into phosphate buffered saline, followed by 30 s of vortexing. The antimicrobial effects of SRF-CPC against static monospecies biofilms were analyzed with a metabolic assay. Inhibition of biofilm formation was tested by exposing daily refreshed E. faecalis suspensions to SRF-CPC for 9 weeks. To evaluate the effects of SRF-CPC against preformed biofilms, biofilms were grown for 1, 3 and 7 days, and then treated with SRF-CPC for 24 h. Biofilm kill time was tested by applying SRF-CPC to a 3-day-old biofilm and measuring its viability at different time points. All experiments were compared to Placebo SRFs and to untreated control biofilms. Data were analyzed with two-way ANOVA followed by Tukey’s test. Results were considered significant at P < 0.05.

Results

The liquid SRF solidified within seconds and no structural changes were observed after 30 s of vortexing at maximum speed. SRF-CPC inhibited E. faecalis biofilm formation for 7 weeks and significantly reduced its viability in weeks 8 and 9. Mature biofilms grown for 1, 3 and 7 days were destructed by SRF-CPC in less than 24 h. Fifty percent of a 3-day-old biofilm was destructed in 2 h and complete destruction occurred in less than 12 h. (P < 0.05 in all cases, compared to SRII-Placebo).

Conclusions

SRF-CPC’s physical properties and long-lasting anti-biofilm effects make it a promising coadjuvant medication for endodontic therapy.

Electronic supplementary material

The online version of this article (10.1186/s12903-019-0879-1) contains supplementary material, which is available to authorized users.

Sustained-Release Fillers for Dentin Disinfection: An Ex Vivo Study

Enterococcus faecalis is the most commonly recovered species from failed root canal treatments. In this study, we tested the capability of a novel intracanal sustained-release filler (SRF) containing cetylpyridinium chloride (CPC) to disinfect dentinal tubules of segmented human tooth specimens. Human dental root specimens were infected with E. faecalis V583 for 3 weeks in a static environment. The tested intracanal medicaments were SRF-CPC and calcium hydroxide (CH). Each medicament was introduced into the canal of the dental specimen and incubated for 7 days. The bacteriological samples were taken by shaving the dentine surrounding the root canal with dental burs ranging in size from ISO 014-020. The obtained dentine powder was collected in test tubes containing phosphate-buffered saline, sonicated, and plated on agar plates. Colony-forming units were counted after 48 h of incubation. Random specimens were also examined under confocal laser scanning microscopy and scanning electron microscopy. A statistical difference was found in the bacterial counts obtained from all layers of infected dentin between the control and the SRF-CPC groups. CH reduced bacterial viability significantly only in the first layer of the infected dentin, up to 150 μm into the dentinal tubules. CLSM images showed that SRF-CPC killed most bacteria throughout the infected dentin up to 700 μm of penetration. SEM images demonstrated the adhesion ability of SRF-CPC to the dentinal wall. In conclusion, SRF-CPC is a potential intracanal medicament for disinfecting dentinal tubules.

Effect of Polymeric Microparticles Loaded With Catechin on the Physicochemical Properties of an Adhesive System

The objective of this study was to synthesize and characterize epigallocatechin-3-gallate (EGCG)-loaded/poly(D-L lactide-co-glycolide) acid (PLGA) microparticles, evaluate their effects on degree of conversion and release assay of adhesives, and subsequently to examine the resin-dentin bond strength of two EGCG formulations (free EGCG or loaded into PLGA microparticles) applied as a pretreatment or incorporated into an adhesive system. The formulations were prepared according to a PLGA:EGCG ratio of 16:1 using the spray-drying technique. The size and polydispersity index were determined by light scattering in aqueous dispersion. The degree of conversion (%DC) and release assay were assessed by Fourier transform infrared spectroscopy and ultraviolet-visible spectrophotometer, respectively. Subsequently, 45 third molars were divided into five groups (n=9) according to the different EGCG application modes and prepared for bond strength testing in a universal testing machine. Results demonstrated no statistically significant difference among the DC means after the PLGA microparticles were loaded with EGCG. For the release assay, the 1.0% PLGA/EGCG group presented better results after being elected for use in the bond strength test. The resin-dentin bond strengths of the experimental groups after 12 months of water storage were significantly higher than in the control group. EGCG could improve the durability of the resin-dentin bond over time and promote a new era for adhesive dentistry with the concept of controlled release.

Application of mathematical modeling in sustained release delivery systems

INTRODUCTION

This review, presenting as starting point the concept of the mathematical modeling, is aimed at the physical and mathematical description of the most important mechanisms regulating drug delivery from matrix systems. The precise knowledge of the delivery mechanisms allows us to set up powerful mathematical models which, in turn, are essential for the design and optimization of appropriate drug delivery systems.

AREAS COVERED

The fundamental mechanisms for drug delivery from matrices are represented by drug diffusion, matrix swelling, matrix erosion, drug dissolution with possible recrystallization (e.g., as in the case of amorphous and nanocrystalline drugs), initial drug distribution inside the matrix, matrix geometry, matrix size distribution (in the case of spherical matrices of different diameter) and osmotic pressure. Depending on matrix characteristics, the above-reported variables may play a different role in drug delivery; thus the mathematical model needs to be built solely on the most relevant mechanisms of the particular matrix considered.

EXPERT OPINION

Despite the somewhat diffident behavior of the industrial world, in the light of the most recent findings, we believe that mathematical modeling may have a tremendous potential impact in the pharmaceutical field. We do believe that mathematical modeling will be more and more important in the future especially in the light of the rapid advent of personalized medicine, a novel therapeutic approach intended to treat each single patient instead of the 'average' patient.

Interaction between chlorhexidine-impregnated gutta-percha points and several chlorine-containing endodontic irrigating solutions

AIM

To evaluate if the immersion of chlorhexidine-impregnated gutta-percha points in chlorine-containing endodontic irrigants causes colour changes and precipitate formation.

METHODOLOGY

Eighty-one size 25 chlorhexidine medicated (Activ Points, Roeko, Langenau, Germany) and 27 size 25 standard gutta-percha points (Roeko) were immersed in microtubes, containing the following solutions: 0.5 and 5.25% NaOCl or Aquatine (Optident, Ilkley, UK). The samples were visually assessed, by two independent observers, at regular intervals over 3 weeks, to detect colour changes and precipitate formation. A score system was used to grade the precipitate intensity. To compare the number of days required for a precipitate to form mean and standard differences were calculated; the means between the groups were compared using a one-way analysis of variance test. Mean intensity scores were calculated and compared between groups using Kruskal-Wallis procedure followed by the Mann-Whitney test.

RESULTS

The groups containing 5.25% NaOCl started to produce a visible precipitate after fourteen days (16.48 ± 0.98) for the Activ points; this process was first noticed with the standard gutta-percha group on day 17 (18.33 ± 1.22 days), with a statistically significant difference (P = 0.002). When looking at the intensity scores from day 17 onwards, these two groups differed statistically, with a greater amount for the AP group (P < 0.001). No other test group presented with changes.

CONCLUSION

The placement of impregnated gutta-percha points, in 5.25% NaOCl for a 2-week period, caused the formation of a precipitate in the experimental conditions of this study.

Antimicrobial activity and enterococcus faecalis biofilm formation on chlorhexidine varnishes

Objective: To evaluate, in vitro, the antimicrobial activity and biofilm formation of three chlorhexidine varnishes in four Enterococcus faecalis strains: E. faecalis ATCC 29212, E. faecalis EF-D1 (from failed endodontic treatment), E. faecalis 072 (cheese) and E. faecalis U-1765 (nosocomial infection), and one Enterococcus durans strain (failed endodontic treatment). Study Design: The direct contact test was used to study the antimicrobial activity. Bacterial suspensions were exposed for one hour to EC40, Cervitec (CE) and Cervitec Plus (CEP) varnishes. “Eradication” was defined as 100% bacterial kill. The formation of enterococci biofilms was tested on the surface of the varnishes after 24 hours of incubation and expressed as percentage of biofilm reduction. Results: EC40 eradicated all strains except E. faecalis ATCC 29212, where 98.78% kill was achieved. CE and CEP showed antimicrobial activity against all the strains, but most clearly against E. durans and E. faecalis 072. EC40 completely inhibited the formation of biofilm of E. faecalis ATCC 29212, E. faecalis 072 and E. durans. CE and CEP led to over 92% of biofilm reduction, except in the case of E. faecalis U-1765 on CEP (76.42%). Conclusion: The three varnishes studied were seen to be effective in killing the tested strains of enterococci and in inhibiting the formation of biofilm, the best results being observed with EC40.

Key words:Biofilm, chlorhexidine varnish, direct contact test, Enterococcus durans, Enterococcus faecalis, intracanal medication.

The Application of Microencapsulation Techniques in the Treatment of Endodontic and Periodontal Diseases

In the treatment of intracanal and periodontal infections, the local application of antibiotics and other therapeutic agents in the root canal or in periodontal pockets may be a promising approach to achieve sustained drug release, high antimicrobial activity and low systemic side effects. Microparticles made from biodegradable polymers have been reported to be an effective means of delivering antibacterial drugs in endodontic and periodontal therapy. The aim of this review article is to assess recent therapeutic strategies in which biocompatible microparticles are used for effective management of periodontal and endodontic diseases. In vitro and in vivo studies that have investigated the biocompatibility or efficacy of certain microparticle formulations and devices are presented. Future directions in the application of microencapsulation techniques in endodontic and periodontal therapies are discussed.

Preparation and evaluation of lidocaine hydrochloride in cyclodextrin inclusion complexes for development of stable gel in association with chlorhexidine gluconate for urogenital use

Inclusions of lidocaine hydrochloride in cyclodextrins were prepared to obtain stable complexes compatible for association with chlorhexidine in a new gel formulation for use in urogenital applications. Two cyclodextrins, β-cyclodextrin and methyl-β-cyclodextrin, were used for encapsulating lidocaine hydrochloride through solubilization and kneading techniques. The lidocaine–cyclodextrin complexes were characterized by ultraviolet spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and X-ray diffraction. The results revealed that the techniques generated good yields of inclusion products that maintained the functional properties of lidocaine. In addition, the inclusion products obtained improved the compatibility of lidocaine hydrochloride with chlorhexidine in solution and a gel formulation. The gel formulation displayed desirable rheological and physicochemical properties. The results presented here are the first description of the inclusion of lidocaine with cyclodextrins, which improves compatibility with chlorhexidine in formulations for simultaneous delivery.

EVA copolymer matrix for intra-oral delivery of antimicrobial and antiviral agents

Biocompatible ethylene vinyl acetate copolymer (EVA) was utilized to study the release of an antiviral drug (acyclovir (ACY)) and an antimicrobial drug (doxycycline hyclate (DOH)). Release of both drugs from EVA was measured individually and in combination. The effect of drug combination of DOH and ACY is presented. Additionally, the release rate of DOH after coating of the matrix with a different copolymer, in drug-loading with increasing loads of DOH, and with increases in temperature are also presented. The drugs incorporated in EVA films were prepared from the dry sheet obtained by solvent evaporation of polymer casting solutions with drugs. Drug release from the films was examined for about 12 days in distilled water at 37 degrees C. Changes in optical density were followed spectrophotometrically. The combination of ACY and DOH resulted in an increased release of ACY by about three times (P < 0.001) while DOH showed a decrease in rate of about two times compared to the individual release rates (P = 0.008). Increases in drug levels of DOH resulted in increases in drug release rates (P = 0.001). The release rate of DOH increased with temperature (P = .001; 27, 32, 37 and 42 degrees C were studied) and the energy of activation (DeltaE ( not equal) = 56.69 kJ/mol) was calculated using the Arrhenius equation for the diffusion of DOH molecules. Thus, the release rates of drugs were influenced by many factors: drug combination, coating the device, drug-loading, and temperature variation. Therefore it is proposed that controlling these variables should make it possible to obtain therapeutic levels of drugs released from drug loaded polymer, which may be beneficial in treating oral infections.

Modeling doxorubicin transport to improve intratumoral drug delivery to RF ablated tumors

A mathematical model of drug transport provides an ideal strategy to optimize intratumoral drug delivery implants to supplement radiofrequency (RF) ablation for tumor treatment. To simulate doxorubicin transport in non-ablated and ablated liver tumors, a one-dimensional, cylindrically symmetric transport model was generated using a finite element method (FEM). Parameters of this model, the diffusion (D) and elimination (gamma) coefficients for doxorubicin, were estimated using drug distributions measured 4 and 8 days after placing biodegradable implants in non-ablated and ablated rabbit VX2 liver carcinomas. In non-ablated tumor, values of diffusion and elimination parameters were 25% and 94% lower than normal liver tissue, respectively. In ablated tumor, diffusion near the ablation center was 75% higher than non-ablated tumor but decreased to the non-ablated tumor value at the ablation periphery. Drug elimination in ablated tumor was zero for the first four days, but by day 8 returned to 98% of the value for non-ablated tumor. Three-dimensional (3-D) simulations of drug delivery from implants with and without RF thermal ablation underscore the benefit of using RF ablation to facilitate local drug distribution. This study demonstrates the use of computational modeling and optimal parameter estimation to predict local drug pharmacokinetics from intratumoral implants after ablation.

Novel chlorhexidine releasing system developed from thermosensitive vinyl ether-based hydrogels

The aim of this study is to determine the effective concentrations of chlorhexidine on the release for prolonged periods of time from a novel hydrogel system. A hydrogel that exhibits a volume phase transition in response to temperature was synthesized by radiation copolymerization of ethylene glycol vinyl ether and butyl vinyl ether in the presence of crosslinking agent, diethylene glycol divinyl ether. Hydrogel samples in the disc form (diameter, 10 mm and height, 1.5 mm) were utilized as a matrix for the release of an antimicrobial agent, chlorhexidine diacetate. Chlorhexidine loading into the hydrogel was performed by water sorption at 4 degrees C, which allows high swelling and thus high loading capacity, i.e., approximately 36 mg drug per gram of dry gel. Chlorhexidine release was examined as short-term (24 h) and long-term (27 days) by UV spectrophotometer. Microbial studies were carried out by micro-dilution method in order to determine the effectiveness of the drug release. Minimum inhibitory concentration values for the pathogens of Streptococcus mutans and Lactobacillus casei were determined. The long-term chlorhexidine release is initially very fast. After that, the drug release reaches a slow but a steady rate. Such a release pattern provides an effective drug release. The prolonged release of chlorhexidine is continued up to the 27th day. MIC values for the two pathogens have been shown that the release rate from disc is effective to inhibit the growth of pathogens. These in vitro drug release results suggested that the thermosensitive hydrogel system developed in this study can be evaluated as a delivery system for the release of chlorhexidine.

The mathematical model of insulin desorption from the bioactive, fibrous artificial store

The aim of this study was to study insulin desorption from fibrous insulin artificial store in vitro as well as in vivo, with the intention to define a mathematical model that would describe this process. Release profile of cylindrical fibrous matrixes for various insulin concentrations, desorption temperatures, time periods, and pH were presented. Change of insulin concentration in the fibers and the effect of insulin release were discussed. This model was also used to predict the optimal conditions of the release process. Possibility of predicting the effect of the fibrous store design parameters (fibre radius, amount of bonded insulin, fiber type) on the resulting insulin release rate was the major advantage of this mathematical model. Also, taking all the relevant conditions regarding these experiments into consideration, by the application of mathematical model, the diffusion coefficient during insulin release was determined.

Poly(ethylene-co-vinyl acetate) copolymer matrix for delivery of chlorhexidine and acyclovir drugs for use in the oral environment: effect of drug combination, copolymer composition and coating on the drug release rate

OBJECTIVES

This study utilizes a bio-compatible ethylene vinyl acetate (EVA) copolymer to deliver drugs at therapeutic levels over extended periods of time. The release rate of an anti-fungal and an anti-microbial drug namely acyclovir (ACY) and chlorhexidine diacetate (CDA) from EVA was investigated individually and as a mixture. The effect of drug combination, the composition of the copolymer and the coating of the matrix with a different polymer on the rate of drug release are presented.

METHOD

Polymer casting solutions were prepared by homogeneously dissolving EVA copolymer and the drugs in the ratio (40:1) in dichloromethane. The drugs ACY and CDA were used individually as well as in three different weight ratios maintaining the total drug concentration in the polymer at 2.5%. Different concentrations of vinyl acetate (VA) 28, 32 and 40% in the EVA matrix were used to study the release of either ACY or CDA alone while 40% VA was used for the release study of the individual drug as well as their mixtures. Thin square films of 3cmx3cm with a thickness of 0.7mm were cut from the dry sheet obtained by solvent evaporation. Coated films were prepared by dipping ACY and CDA drug-loaded EVA films (VA 40%) into EVA copolymer of VA 32% and then dried. All of the drug-loaded samples were extracted at 37 degrees C in 10ml distilled water that was replaced daily. The rate of individual drug release was measured by UV-spectrophotometer while the mixtures of drugs were measured by high performance liquid chromatography (HPLC).

RESULTS

The release rate of ACY is higher than that of CDA both individually and in the ACY/CDA 50/50 mixture. In the other mixtures, the release of the drug is proportional to its concentration in the mixture. Total release of ACY is higher than CDA in most compositions. The effect of increasing the vinyl acetate content of the EVA matrix increased the drug release rate (p=0.02) while coating of films resulted in a decrease of the release rate of the drugs.

SIGNIFICANCE

Measurements of the in vitro rate of drug release showed that there was a sustained release of drug at an almost constant concentration over extended period of time, thus providing a basis for oral treatment modality. We show that it is possible to alter the rate of drug release in the EVA matrix to a desired value by: (1) changing the composition of the EVA copolymer, (2) altering the mixtures of drugs and (3) coating the matrix with additional polymer. The use of mixtures of drugs that can enhance or decrease the rate of drug release may prove more effective in treating persistent oral infections in immunocompromised patients.

Finite element analysis of the release of slowly dissolving drugs from cylindrical matrix systems

Drug release from matrix systems of cylindrical shape is analyzed in detail by using the finite element method. The model used combines the Noyes-Whitney and diffusion equations, and thus takes the effects of a finite dissolution rate into account. The model is valid for all drug solubilities and dissolution rates, and allows accurate predictions of the drug release to be made. Anisotropic drug transport that may result from the manufacturing process is properly accounted for. Model calculations show that a finite dissolution rate may affect the release profile significantly, producing an initial delay. The equivalence between anisotropic release and isotropic release from a matrix with different dimensions is demonstrated. Comparisons are made with the predictions of a recently proposed pseudo-steady state (PSS) analysis of drug release from cylindrical matrices [Y. Zhou, J. S. Chu, T. Zhou, X. Y. Wu, Modeling of dispersed-drug release from two-dimensional matrix tablets, Biomaterials 26 (2005) 945-952]. This comparison reveals that important discrepancies exist between the numerical and analytical results, which are attributed to the simplifying assumption made in the PSS analysis that the region containing solid drug remains cylindrical in shape throughout the release process. The proposed model is shown to describe experimental release data well.

The sustaining effect of three polymers on the release of chlorhexidine from a controlled release drug device for root canal disinfection

OBJECTIVES

The aim of this in vitro study was to evaluate the suitability of using chitosan, poly (lactide-co-glycolide) (PLGA), and polymethyl methacrylate (PMMA) to control the release of chlorhexidine digluconate (CHX) from a prototype of controlled release drug device for root canal disinfection.

STUDY DESIGN

Four different prototypes with different formulations were prepared. Group A (n = 12): the device (absorbent paper point) was loaded with CHX as control. Group B (n = 12): same as group A, but the device was coated with chitosan (Texan MedTech). In Groups C and D, the device was treated in the same way as group A and then coated 3 times with 5% PMMA (Group C, n = 12, Aldrich), or coated 3 times with 3% PLGA (Group D, n = 12, Sigma). The devices were randomly allocated to experimental groups of 12 each. All the prototypes of controlled release drug device were soaked in 3 mL distilled water. The concentrations of CHX were determined using a UV spectrophotometer. The surface characteristics of each prototype were observed using a scanning electron microscope.

RESULTS

The result showed that release rate of CHX was the greatest in the noncoated group, followed by the chitosan-coated group, the PLGA-coated group, and the PMMA-coated group (P < 0.05). Pores were observed on the surface of the prototypes that were coated with PLGA and PMMA. When the pore size was smaller, the release rate was lower.

CONCLUSION

These data indicate that polymer coating can control the release rate of CHX from the prototypes of controlled release drug device.

Modeling of dispersed-drug release from two-dimensional matrix tablets

A mathematical model was developed and analytical solutions were obtained for dispersed-drug release from two-dimensional matrix tablets in a perfect sink. This model can be used to describe kinetics of solute release from matrices with isotropic or anisotropic properties. Moving boundaries of dispersed-drug in both radial and axial directions and release kinetics were predicted by the model. Various factors influencing release kinetics were analyzed including the ratio of initial solute loading (C0) to solute solubility (Cs), the anisotropy of the matrix and the aspect ratio of tablet radius to the half-thickness. The model is also applicable to 1-D planar or 1-D cylindrical geometries when R/H is larger than 100 or smaller than 0.01.

Theoretical analysis of drug release into a finite medium from sphere ensembles with various size and concentration distributions

Release kinetics for heterogeneous sphere ensembles with a dissolved drug, i.e., initial drug loading below or equal to the drug solubility in the matrix, in a finite external medium was modeled with consideration of heterogeneity among and within spheres. Numerical solutions were obtained using the finite element method for sphere ensemble with normal or log-normal distribution of particle size or initial drug loading among spheres. Exact series solutions were derived for ensembles with various initial loading distributions within spheres, namely linear, quadratic, sigmoidal and uniform distribution, using their mean or average radii. Simplified solutions retaining only one term of the series for non-uniform distributions and three terms for uniform distribution were suggested because of their good approximation to the exact solution. The results of finite element analysis showed that the release rate of an ensemble decreased with increasing standard deviation of particle size. Using weight-average radii in the exact solution gave a prediction of release profile closer to that from the actual size distribution than using mean radii. The three non-uniform loading patterns within spheres all showed reduced initial burst and release rate, leading to more steady release rates than uniform loading, among which the sigmoidal distribution offered the best near-zero order release. Non-uniform initial loading among spheres seemed to have insignificant influence on the release profiles. The volume ratio of liquid to a sphere ensemble played an important role in release kinetics. The derived analytical solutions are applicable to multiple spheres or a single sphere in a finite medium or in a perfect sink.

In vitroantimicrobial effect of chlorhexidine-impregnated gutta percha points onEnterococcus faecalis

AIM

To evaluate the in vitro antimicrobial effect of chlorhexidine-impregnated gutta percha points, Roeko activ point (Roeko, Langenau, Germany) on Enterococcus faecalis.

METHODOLOGY

Human maxillary premolar roots were prepared with.04 rotary ProFile instruments to a master apical file size 40, autoclave-sterilized and then infected with E. faecalis (ATCC 29212) for 3 weeks. Baseline controls were carried out verifying negligible effects of plain gutta percha cones on E. faecalis. Subsequent to intracanal placement of calcium hydroxide, 'activ points' or saline (positive control) and the 2-week incubation in 54 root specimens, dentine sampling at depths of 100 and 250 micro m was carried out using.04 rotary ProFile instruments at sizes 60 and 90 to assess the quantity of bacteria present. Inactivating agents were used prior to sampling and the colony-forming units (CFU) of E. faecalis were then plate-counted after culturing. Statistical analysis was completed using the paired t-test.

RESULTS

In comparison to the positive control, treatment with calcium hydroxide (P = 0.000 and 0.000) or activ points (P = 0.000 and 0.002) produced significantly lower colony counts of E. faecalis at dentine depths of 100 and 250 micro m, respectively. Calcium hydroxide (2.10 x 102 CFU mL-1) was significantly more effective than activ points (1.58 x 103 CFU mL-1) at 100 micro m (P = 0.013), but not at 250 micro m (P = 0.353). Neither of these two medications was able to eliminate E. faecalis completely.

CONCLUSIONS

Chlorhexidine-impregnated activ points did not possess an in vitro inhibitory activity strong enough to eliminate E. faecalis completely from infected dentinal tubules.

Simulation of Drug Release from Biodegradable Polymeric Microspheres with Bulk and Surface Erosions

New models are developed to account for the kinetics of drug release from porous, biodegradable polymeric microspheres under the schemes of bulk erosion and surface erosion of the polymer matrix, respectively. Three mechanisms of drug release, namely, drug diffusion, drug dissolution, and polymer erosion jointly govern the overall release process. For bulk erosion, the model incorporates an erosion term into the dissolution and diffusion equation and is solved numerically for various boundary conditions. Dissolution and erosion are defined in the model by introducing three equations which take into account the drug concentration in the liquid phase, virtual solid phase, and effective solid phase. For surface erosion, drug concentrations in liquid and solid phases are defined and a substitution is introduced to convert the moving-boundary problem to a fixed-boundary problem. The resulting differential equations are solved simultaneously to obtain the concentration profile in the liquid and solid phases, respectively. Numerical solutions are provided to illustrate the effects of drug dissolution constant, drug diffusion coefficient, and erosion rate constant. In general, increasing erosion rate, diffusivity, dissolution, and decreasing particle radius enhance the drug release rate. Predictions from the models are also compared with experimental data to verify their validity and possible improvements are proposed.

Modeling and analysis of dispersed-drug release into a finite medium from sphere ensembles with a boundary layer

Mathematical models were developed and analytical solutions were derived for describing kinetics of dispersed-drug release into a finite external medium from multi-particulate systems, such as ensembles of matrix spheres and microcapsules with a diffusion boundary layer. The solutions can be used to compute profiles of the moving boundary of a dispersed drug and the amount of drug released for multiparticulate ensembles with various ratios of initial drug loading (C(0)) to drug solubility (C(s)) in a finite to infinite medium. They are also applicable to a single sphere without a boundary layer in a perfect sink. The determinants of release kinetics, such as the liquid volume, the initial drug loading, the boundary layer thickness, and the number of spheres in a population, were analyzed using the derived solutions. The effect of coating thickness and material on the release profiles of microcapsules was studied as well. Criteria were established for finding the conditions when drug release would stall due to saturation of the medium, which can be used to determine suitable liquid volume and time for refreshing the medium.

Theoretical analyses of dispersed-drug release from planar matrices with a boundary layer in a finite medium

Analytical solutions for the kinetics of dispersed-drug release from planar matrices with a boundary layer in a well-stirred finite external medium were derived in a general and a simplified form. The general solutions are applicable for a broad range of the ratio of initial drug loading to drug solubility (e.g. C(0)/C(s)> or =3) till all dispersed drug is dissolved, while the simplified solutions describe the entire release process for higher C(0)/C(s) ratios (e.g. C(0)/C(s)> or =10). As the C(0)/C(s) ratio increased, the general solutions approached the exact solution from the lower bound, and the simplified solution from the upper bound. This property could be useful to find the lower and upper bound of an exact solution for the sink condition without a boundary layer when it is unknown. The current solutions can cover more scenarios than the existing analytical and approximate solutions. The formulas, with explicit expressions, can be readily applied to analyze determinants of release kinetics, including volume of external medium, initial drug loading, and boundary layer thickness. With the criterion established for finding the conditions of drug saturation in a medium, minimal liquid volume and maximal time for refreshing the medium can be determined.

Substantive antimicrobial activity in chlorhexidine-treated human root dentin

OBJECTIVE

The aim of this in vitro study was to assess the substantive antimicrobial activity of different medicaments in human root dentin.

STUDY DESIGN

Canals of 98 roots were enlarged to standard size and medicated for 7 days with the following: (1) 2% chlorhexidine (CHX) gel, (2) 0.2% CHX gel, (3) 2% CHX solution, (4) Ca(OH)(2), (5) Ca(OH)(2)+ 0.2% CHX gel, (6) 2% CHX solution + a 25% CHX-containing controlled-release device, (7) saline, and (8) gel vehicle. After medication, canals were inoculated with Enterococcus faecalis for 21 days. Dentin samples were collected with Gates-Glidden burs into brain heart infusion broth, and bacterial growth was assessed with spectrophotometric analysis of optical density after 72 hours of incubation.

RESULTS

Mean optical densities were significantly lower for groups with 2% CHX (1, 3, and 6) when compared with those of the controls (P < .05, analysis of variance with the Tukey test). Other groups did not differ significantly from the controls.

CONCLUSIONS

Canal dressing for 1 week with 2% CHX may provide residual antimicrobial activity against E faecalis.