A comparison between anorganic bone and collagen-preserving bone xenografts for alveolar ridge preservation: systematic review and future perspectives

After tooth extraction, dimensional changes affect the alveolar socket, leading to loss in alveolar bone height and width. Histological modifications also occur, with initial formation of a blood clot that is replaced with granulation tissue and subsequently with a provisional connective tissue matrix. Spontaneous healing ends with socket filling with woven bone, which is gradually replaced with lamellar bone and bone marrow. Adequate alveolar ridge dimensions and bone quality are required to assure optimal stability and osseointegration following dental implant placement. When a tooth is extracted, alveolar ridge preservation (ARP) procedures are an effective method to prevent collapse of the post-extraction socket. Heterologous bone is widely chosen by clinicians for ARP, and anorganic bone xenografts (ABXs) made bioinert by heat treatment represents the most used biomaterial in clinical applications. Collagen-preserving bone xenografts (CBXs) made of porcine or equine bone are fabricated by less invasive chemical or enzymatic treatments to remove xenogenic antigens, and these are also effective in preserving post-extraction sites. Clinical differences between anorganic bone substitutes and collagen-preserving materials are not well documented in the literature but understanding these differences could clarify how processing protocols influence biomaterial behavior in situ. This systematic review of the literature compares the dimensional changes and histological features of ABXs versus CBXs in ridge preservation procedures to promote awareness of different bone xenograft efficacies in stimulating the healing of post-extraction sockets.

Substituted Nano-Hydroxyapatite Toothpastes Reduce Biofilm Formation on Enamel and Resin-Based Composite Surfaces

Background: Toothpastes containing nano-hydroxyapatite (n-HAp) substituted with metal ions provide calcium and phosphate ions to dental hard tissues, reducing demineralization, and promoting remineralization. Few data are available about the effect of these bioactive compounds on oral microbiota. Methods: This in vitro study evaluated the influence of two commercially-available substituted n-HAp-based toothpastes (α: Zn-carbonate substituted n-HAp; β: F, Mg, Sr-carbonate substituted n-HAp) on early colonization (EC, 12 h) and biofilm formation (BF, 24 h) by oral microbiota. Controls were brushed with distilled water. Artificial oral microcosm and Streptococcus mutans biofilms were developed using human enamel and a resin-based composite (RBC) as adherence surfaces. Two test setups, a shaking multiwell plate and a modified drip-flow reactor (MDFR), were used to simulate clinical conditions during the night (low salivary flow and clearance) and daytime, respectively. Energy-dispersive X-ray spectrometry (EDS) was used to evaluate specimens' surfaces after toothpaste treatment. Fluoride release from β toothpaste was evaluated. Viable adherent biomass was quantified by MTT assay, and biofilms' morphology was highlighted using confocal microscopy. Results: EDS showed the presence of remnants from the tested toothpastes on both adherence surfaces. β toothpaste showed significantly lower EC and BF compared to control using the artificial oral microcosm model, while α toothpaste showed lower EC and BF compared to control, but higher EC and BF compared to β toothpaste. The effect shown by β toothpaste was, to a minimal extent, due to fluoride release. Interestingly, this result was seen on both adherence surfaces, meaning that the tested toothpastes significantly influenced EC and BF even on RBC surfaces. Furthermore, the effect of toothpaste treatments was higher after 12 h than 24 h, suggesting that toothbrushing twice a day is more effective than brushing once. Conclusions: The efficacy of these treatments in reducing microbial colonization of RBC surfaces may represent a promising possibility in the prevention of secondary caries.

Biofilm Formation on Dental Implant Surface Treated by Implantoplasty: An In Situ Study

Peri-implantitis is a biofilm-related disease whose characteristics are peri-implant tissues inflammation and bone resorption. Some clinical trials report beneficial effects after implantoplasty, namely the surgical smoothening of the implant surface, but there is a lack of data about the development of the bacterial biofilm on those smoothened surfaces. The aim of this study is to evaluate how implantoplasty influences biofilm formation. Three implants with moderately rough surfaces (control) and three implants treated with implantoplasty (test) were set on a tray reproducing the supra- and sub-gingival environment. One volunteer wore this tray for five days. Every 24 h, plaque coverage was measured and, at the end of the period of observartion, the implant surfaces were analyzed using scanning electron microscopy and confocal laser scanning microscopy. The proportion of implant surface covered with plaque was 65% (SD = 7.07) of the control implants and 16% (SD = 0) of the test implants. Untreated surfaces showed mature, complex biofilm structures with wide morphological diversity, and treated surfaces did not show the formation of mature biofilm structures. This study supports the efficacy of implantoplasty in reducing plaque adhesion and influencing biofilm formation. These results can be considered a preliminary proof of concept, but they may encourage further studies about the effects of implantoplasty on biofilm formation.

Laser microtextured titanium implant surfaces reduce in vitro and in situ oral biofilm formation

INTRODUCTION

Micro- or nano-topography can both provide antimicrobial properties and improve osseointegration of dental implant titanium surfaces. Laser treatment is one of the best surface microtexturing techniques. The aim of this study was to evaluate in vitro and in situ biofilm formation on a laser-treated titanium surface, comparing it with two conventional surfaces, machined and grit-blasted.

METHODS

For the in vitro experiment, an oral microcosm biofilm model was developed on the surface of titanium disks and reference human enamel using a bioreactor for 48 h. For the in situ experiment, titanium implants with laser-treated, machined and grit-blasted surfaces were mounted on intraoral trays and worn by ten volunteers for 48 h. Biofilm formation was quantitatively evaluated, and surfaces were analyzed using confocal laser scanning microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy.

RESULTS–IN VITRO STUDY

Biofilm structures with a prevalence of viable cells covered most of the machined, grit-blasted and human enamel surfaces, whereas less dense biofilm structures with non-confluent microcolonies were observed on the laser-treated titanium. Laser-treated titanium showed the lowest biofilm formation, where microorganisms colonized the edges of the laser-created pits, with very few or no biofilm formation observed inside the pits.

RESULTS–IN SITU STUDY

The biofilm formation pattern observed was similar to that in the in vitro experiment. Confocal laser scanning microscopy showed complete coverage of the implant threads, with mostly viable cells in grit-blasted and machined specimens. Unexpectedly, laser-treated specimens showed few dead microbial cells colonizing the bottom of the threads, while an intense colonization was found on the threading sides.

CONCLUSION

This data suggests that laser-created microtopography can reduce biofilm formation, with a maximum effect when the surface is blasted orthogonally by the laser beam. In this sense the orientation of the laser beam seems to be relevant for the biological interaction with biofilms.

Streptococcus mutans adherence and biofilm formation on experimental composites containing dicalcium phosphate dihydrate nanoparticles

This study aimed at evaluating bacterial adhesion and biofilm formation on resin-based composites (RBC) including dicalcium phosphate dihydrate nanoparticles (nDCPD).

METHODS

Specimens were prepared from experimental RBCs with BisGMA/TEGDMA resin matrix including 20 vol% of either nDCPD (nDCPD-RBC), TEGDMA-functionalized nDPCD (F-nDCPD-RBC) or silanized silica (SiO₂-RBC). Neat resin blend (control-Resin), conventional nanohybrid RBC (control-RBC) and human enamel were used for reference. Characterization of the specimens included surface roughness (SR), surface free energy (SFE), chemical surface composition (EDS, XPS), and buffering ability of a pH = 4.00 solution. Streptococcus mutans adherence was assessed after 2 h; biofilm formation was simulated for 48 h using a bioreactor. Adherent, viable biomass was determined using tetrazolium salt assay (MTT).

RESULTS

nDCPD-RBC yielded highest roughness and showed higher polar and lower disperse component to total SFE. EDS and XPS indicated higher amounts of calcium and phosphate on the surface of nDCPD-RBC than on F-nDCPD-RBC. nDCPD buffered the acidic solution to 5.74, while functionalization almost prevented buffering (pH = 4.26). F-nDCPD-RBC reduced adherence and biofilm formation in comparison to nDCPD-RBC. Regardless of functionalization, biofilm formation on nDCPD-containing RBCs was not significantly different from SiO₂-RBC. Control-Resin, control-RBC, and enamel surfaces showed similar adherence values as F-nDCPD-RBC, but lower biofilm formation compared to both nDCPD-containing RBCs. In conclusion, the incorporation of nDCPD did not minimize S. mutans adherence and biofilm formation as a function of the materials´ surface properties. However, results observed for the buffering capacity indicated that optimized formulations of biomimetic RBCs may be useful for modulating their interaction with microorganisms.

Influence of Light-curing Parameters on Biofilm Development and Flexural Strength of a Silorane-based Composite

Objectives: The aim of this study was to evaluate the differences in biological and mechanical performances of a silorane-based and a methacrylate-based composite. Another aim was to assess the influence of light-curing time and light-curing intensity on in vitro biofilm formation and flexural strength of the two tested composites.

Methods: Experiment 1: 432 specimens obtained from a silorane-based composite and from a standard methacrylate-based composite were divided into six groups and light-cured for 10, 20, 30, 40, 60, or 80 seconds, using one of two light-curing intensities, 400 mW/cm2 or 800 mW/cm2. At 24 hours, a monospecific Streptococcus mutans biofilm adherent to the surfaces of the samples was obtained. Then, a colorimetric technique (MTT assay) was used to evaluate the adherent viable biomass. Two samples per group were observed using confocal laser scanning microscopy. Analysis of variance (ANOVA) and Tukey tests were used to analyze the results (p<0.05). Experiment 2: 192 bar-shaped specimens were obtained and light-cured as in the previous experiment. A three-point bend test using a universal testing machine was performed to obtain flexural strength values. ANOVA and Tukey tests were used to analyze the results (p<0.05).

Results: In experiment 1, a highly significant difference (p<0.0001) in biofilm development was shown between silorane-based and methacrylate-based composites. In fact, the silorane-based composite exhibited better biological performance. Significant differences were also found between the two light-curing intensities (p<0.018) and for curing times (p<0.0001): silorane-based composite light-cured for 80 seconds at 800 mW/cm2 light-curing intensity showed the lowest biofilm development. In experiment 2, a significant difference in flexural strength (p<0.0318) was only found between the different composites. Nevertheless, both resin composites showed flexural strength values in accordance with International Organization for Standardization guidelines even after 10 seconds of light-curing time.

Conclusions: Silorane-based composite was less prone to biofilm development compared with a methacrylate-based composite. Acceptable flexural strength values for both composites were obtained after 10 seconds of light-curing time.

Surface properties of resin-based composite materials and biofilm formation: A review of the current literature

PURPOSE

To evaluate the state of art on the relations between surface properties (surface roughness, topography, surface free energy and chemistry) of resin-based composite materials and microbial adhesion and biofilm formation.

METHODS

An electronic search using Scopus and PubMed (until May 2015) was conducted applying the following search items: "Plaque OR Biofilm AND Surface chemistry", "Plaque OR Biofilm AND Surface-free energy", "Plaque OR Biofilm AND Roughness", "Surface characteristics AND Composites", "Biofilm AND Surface characteristics".

RESULTS

Surface properties of resin-based composite materials as well as surface treatments can strongly affect bacterial adhesion and biofilm formation, although the "ideal" surface features have not been identified yet. Moreover, investigations highlighted that cariogenic biofilm formation may alter materials' surface properties, thus encouraging bacterial adhesion and biofilm formation, starting a "vicious cycle" which might compromise restoration longevity.