Chlorhexidine, a Matrix Metalloproteinase Inhibitor and the Development of Secondary Caries Wall Lesions in a Microcosm Biofilm Model.

This study investigated the role of a matrix metalloproteinase (MMP) inhibitor (CHX 2%) in the development of secondary caries wall lesions in different interface conditions with small (run 1) and wider gaps (run 2). Dentin discs were restored and pretreated with or without CHX 2%. In run 1, interfaces were made with gaps of 30, 60, or 90 µm. Interfaces with composite placed directly onto the dentin were either bonded (Adper Single Bond 2) or not bonded. In run 2, interfaces were made with gaps of 100 µm, with or without adhesive on the composite side (CLEARFIL SE Bond). Interfaces were either bonded or not bonded, as in run 1. Microcosm biofilms were grown on dentin-composite samples for 14 days. Caries lesion outcomes were analyzed by transversal wavelength-independent microradiography at 3 locations: the outer surface, and the interface wall at a distance of 200 and 500 µm from the gap entrance. Linear regression analyses showed that pretreatment with MMP inhibitor did not influence progression of the wall lesion at any location (p ≥ 0.218). Interfaces with intentional gaps showed positive and significant effect on the wall lesion progression at 200 µm from the gap entrance (p ≤ 0.005). A small trend of increase in wall lesion development was observed at the 200-µm location when bonding was present on the composite side. In conclusion, the dentin pretreatment with CHX 2% was not able to slow down the development of secondary caries wall lesions in small and wide gaps in this biofilm model.

Chemical hygiene protocols for complete dentures: A crossover randomized clinical trial.

STATEMENT OF PROBLEM: Clinical evidence on the best chemical protocol for the disinfection and removal of biofilm from complete dentures is lacking. PURPOSE: The purpose of this crossover randomized clinical trial was to assess the effectiveness of various chemical hygiene clinical protocols in reducing the microbial viability of biofilm formed on complete dentures. MATERIAL AND METHODS: In this triple-blind (participants, dentist, and outcome evaluator) study, complete denture wearers without candidiasis were randomly divided into 4 groups (n=40) according to the chemical hygiene protocol: water (placebo), 0.5% sodium hypochlorite solution, 0.12% chlorhexidine gluconate solution, and 5% sodium bicarbonate solution. The biofilm formed on the palate intaglio and denture teeth was collected and assessed in each experimental phase for quantitative microbial viability at the seventh and 14th day after using the chemical protocol. RESULTS: Two participants were lost. Data were analyzed by MANOVA and Tukey HSD tests. Soaking dentures was not effective in decreasing Candida albicans, C. non-albicans, and lactobacillus counts. The use of sodium hypochlorite and chlorhexidine decreased total microorganisms and Streptococcus mutans counts for both palate and teeth compared with water and sodium bicarbonate. The intaglio of the dentures always presented higher microbial counts than did the denture teeth. CONCLUSIONS: The use of sodium hypochlorite and chlorhexidine and mechanical cleansing with a toothbrush decreased microbial viability in healthy complete denture wearers.

Secondary Caries in situ Models: A Systematic Review.

In situ caries research serves as a bridge between clinical research and laboratory studies. In this kind of research, volunteers wear a removable intraoral splint or prosthesis containing research samples. Many different in situ models exist to investigate secondary caries. This systematic review compared currently existing secondary caries models and their lesion progression per day values. MATERIALS AND METHODS: Three databases (Medline, Embase, and Cochrane) were searched for relevant literature. Bias risk was assessed and model parameters and caries-related outcomes were extracted by 2 independent researchers. Where possible, caries-related outcomes were normalized by estimating lesion progression per day by dividing lesion depth extracted from microradiographic or microhardness data by the number of days the study lasted. RESULTS: The literature search identified 335 articles. After eliminating duplicates and selection, 31 articles were included. The models differed greatly on factors such as sample location, presence of fluoride in the model, and analysis methods. Three main groups could be identified by sample placement; 68% of models placed samples palatally in the upper jaw, and the lower jaw model could be divided into the buccal (26%) and approximal (6%) areas. Average lesion progression in enamel next to composite was 4.3 ± 2.8 µm (range1.1-8.8 µm/day). DISCUSSION: Studies conducted with palatal models showed caries progression rates 2-5 times higher than the estimated clinical progression rates. Lesion progression per day could be a useful tool for future comparison of models and establishing a standardized model.

Minimal Gap Size and Dentin Wall Lesion Development Next to Resin Composite in a Microcosm Biofilm Model.

This in vitro study investigated the development of dentin wall lesions next to resin composite containing very small gap sizes using an in vitro biofilm model, and evaluated whether a relevant threshold for the gap size could be established. Microcosm biofilms were grown for 14 days within small interfacial gaps between dentin-resin composite discs under intermittent cariogenic challenge. The factor under study was gap size: samples were either restored with composite resin without adhesive procedure (no intentional gap; no bonding [NB] group) or with intentional gaps of 30, 60, or 90 µm, or with complete adhesive procedure (no gap; bonding [B] group). Secondary caries wall lesion progression was measured in lesion depth (LD) and mineral loss (ML) using transversal wavelength independent microradiography at 3 locations: outer surface lesion and wall lesions at 200 and 500 µm distance from gap entrance. Results from linear regression analysis showed that the presence of an intentional gap (30, 60, and 90 µm) affected the secondary caries progression at 200 µm from the gap entrance (p ≤ 0.013). The NB group did not show significant wall lesion development (ML and LD, p ≥ 0.529). At 500 µm distance almost no wall caries development was observed. In conclusion, dentin wall lesions developed in minimal gap sizes, and the threshold for secondary wall lesion development was a gap of around 30 µm in this microcosm biofilm model.

Influence of the Inoculum Source on the Cariogenicity of in vitro Microcosm Biofilms.

This study investigated the cariogenic potential of biofilms originating from different types of inoculum (saliva and dental plaque) from caries-active and caries-free individuals. Ten volunteers were selected from each caries condition for the paired collection of saliva and dental plaque. Microcosm biofilms were grown in triplicate from each inoculum on enamel specimens in 24-well plates under cariogenic challenge. After 10 days, the biofilms were collected for analysis of outcome variables: percentage of surface hardness change (%SHC) and microbiological composition of biofilms. Statistical analysis was performed using the t test, the linear multivariate analysis model and Pearson's correlation coefficients (α = 0.05). A comparative analysis between microbiological baseline data showed higher counts of mutans streptococci in plaque samples within caries-active individuals; a comparative analysis of colony-forming unit (CFU) counts between individuals with different caries status showed higher counts of acid-tolerant microorganisms and mutans streptococci in dental plaque and of acid-tolerant microorganisms in saliva. After 10 days of biofilm growth, the CFU values for total microorganisms, lactobacilli, mutans streptococci and acid-tolerant bacteria, as well as for SHC, were not statistically significant, considering the type of inoculum and caries condition (p > 0.05). A positive correlation was found for %SHC and CFU counts of acid-tolerant bacteria (r = 0.406) and lactobacilli (r = 0.379). Under the limits of this study, the cariogenic potential of biofilms, formed under identical conditions in vitro, is similar, regardless of baseline differences between the source and type of inoculum.

A biofilm cariogenic challenge model for dentin demineralization and dentin bonding analysis.

OBJECTIVES: This study was designed to adapt a previously developed in vitro microcosm biofilm model to create carries-affected dentin (CAD) and establish conditions for using the model in bonding studies. MATERIALS AND METHODS: Biofilms were originated from human saliva and grown on dentin discs for 0 (sound dentin), 3, 5, 7, 14, or 21 days under intermittent cariogenic condition (n = 10). At each time point, composite cylinders were bonded to the dentin using self-etch adhesive (Clearfil SE Bond). The response variables were integrated mineral loss (ΔS), lesion depth (LD), shear bond strength (SBS), and failure mode. Data were statistically analyzed (α = 0.05). Bonded interfaces were analyzed by scanning electron microscopy (SEM), and dentin surfaces characterized by infrared spectroscopy (Fourier transform infrared spectroscopy, FTIR). RESULTS: Lower ΔS was found for sound dentin than for CAD in all experimental groups, except for the group under cariogenic challenge for 3 days. The SBS to CAD was significantly lower than control for all cariogenic challenge times. Adhesive failures were predominant in all groups. ΔS and LD had a significant negative correlation with SBS. A significant exponential decay in SBS was associated with increased ΔS values. CAD had lower mineral and amide I content and an irregular hybridization interface compared to sound dentin. CONCLUSIONS: The microcosm biofilm model was able to artificially induce CAD, which imposed challenge to the bonding of the polymeric adhesive material. CLINICAL RELEVANCE: Presence of CAD might interfere with the bonding of polymeric materials. The microcosm biofilm model proposed could be useful for preclinical dentin bonding studies.

Aging Reduces the Anticaries Effect of Antibacterial Adhesive - An In Vitro Biofilm Study.

PURPOSE: This in vitro study investigated whether aging different restorative materials influences secondary caries development using a short-term in vitro biofilm model, hypothesizing that the antibacterial adhesive employed may lose its effect over time. MATERIALS AND METHODS: Sixty enamel-dentin blocks were divided into 6 groups with n = 10 per group. The groups were restored with three different restorative materials, of which each sample contained an artificial gap: composite with conventional adhesive (CCA; negative control), composite with an antibacterial adhesive (CAA), and amalgam (A; positive control). Half of the groups were prepared fresh and half of the groups were submitted to an aging protocol consisting of water storage, thermocycling, storage in human saliva, and storage in 0.9% saline solution. All specimens were subjected to an intermittent 1% sucrose biofilm model for 20 days to create artificial caries lesions. Lesion progression in the enamel and dentin next to the different materials was measured as lesion depth (LD) and mineral loss (ML), using transverse wavelength independent microradiography (T-WIM). Regression analysis was used to evaluate the effect of aging on LD and ML per restorative material, corrected for gap size. RESULTS: In the amalgam group, aging led to shallower lesions and less mineral loss. Fresh amalgam samples showed an average lesion depth of 156.65 ± 39.18 µm at wall dentin locations. Aged amalgam samples had an average lesion depth of 73.42 ± 73.50 µm. Fresh CAA samples showed lower average surface mineral loss values (9104 ± 2631 µm•vol%) than did fresh CCA samples (13166 ± 4769 µm•vol%). After aging, this effect was absent, and the average mineral loss in the CAA group was 13382 ± 5586 µm•vol%, while in the CCA group it was 15518 ± 9283 µm•vol%. CONCLUSION: Aging can influence secondary caries development either positively or negatively depending on the kind of restorative material. Antibacterial adhesives may lose their effectiveness over time.

Failed bonded interfaces submitted to microcosm biofilm caries development.

OBJECTIVES: This study aimed to evaluate the dentin wall carious lesion development of different composite-dentin interfaces in the presence of two adhesive bonding materials in the gaps, using a microcosm biofilm model. METHODS: Dentin samples were prepared (10.4mm(2)) and restored with a composite resin using two adhesive systems (etch-and-rinse and self-etch techniques). Different conditions with respect to composite-dentin interfaces were produced with a 200µm gap: failed bonded without ageing or after mechanical ageing, or non-bonded with or without the presence of adhesive material on the dentin wall. For cariogenic challenge, specimens were subjected to a biofilm microcosm model for 14days to create caries-like wall lesions. Before and after caries development, transverse wavelength-independent microradiography images were taken, and lesion depth and mineral loss were measured. Data were analysed with linear regression models (p<0.05). RESULTS: The composite-dentin interface conditions significant influenced the caries development: lesion development was reduced by the presence of the adhesive material on dentin wall, while lesion development was increased by the mechanical ageing (p=0.019). There was no difference between the adhesive materials (p values>0.05). CONCLUSION: Different composite-dentin interfaces influence wall lesion development in gaps, with the interfaces submitted to ageing showing less carious protection than those interfaces with the presence of adhesive covering the dentin. CLINICAL SIGNIFICANCE: The presence of adhesive bonding material in the gaps plays a role on the wall caries lesion development.