Adhesion of Streptococcus mutans and Streptococcus sanguinis on Er:YAG Laser-Irradiated Dental Enamel: Effect of Surface Roughness

Effect of a demineralization model on the microhardness, surface roughness and topography of giomers: An in vitro study

The purpose of this study is to compare the effect of a demineralization model on the microhardness, surface roughness, and topography of giomers.Seventy-two discs of six different dental materials in three different presentations (pit and fissure sealant (PFS), flowable and restorative materials) were divided into six groups (n = 12 p/g). Three experimental groups (giomers) consisted of BeautiSealant, Beautifil Flow Plus, and Beautifil II, and three control groups (resin-based materials) were formed using ClinproTM, FiltekTM Z350 XT Flow, and Filtek™ Bulk Fill materials. Vickers microhardness, surface roughness, and topographic analysis with atomic force microscopy were measured at the beginning (0) after four (1) and 7 days (2) of immersion in a demineralizing model. Statistical analysis was performed using One-way and Repeated Measures ANOVA and Pearson's correlation coefficient (p ≤ .05). The microhardness values showed significant variations, except for the G_RM group. All the groups presented significant increases in roughness through the experiment stages, except for RB_PFS in the Ra parameter. The topographic analysis showed variations in the micromorphology, especially in the experimental group at the end of the demineralization model. Finally, there was no correlation between microhardness and surface roughness. The demineralization model decreased the microhardness, with the lowest reductions in the giomers groups. The effect of the demineralizing model on the surface roughness and topography showed an increase in specific patterns for the experimental and control groups. Therefore, their clinical use is recommended. RESEARCH HIGHLIGHTS: The demineralization model decreased the microhardness property of the evaluated materials, with better performance for the giomer groups. The effect of the demineralizing model on surface roughness showed an increase with specific patterns for the experimental and control groups. Although the materials presented changes in their microhardness, roughness, and topography, their clinical use is recommended.

The impact of Er:YAG laser combined with fluoride treatment on the supragingival plaque microbiome in children with multiple caries: a dynamic study

BACKGROUND

As a minimally invasive tool for caries prevention tool, the pulsed erbium:yttrium-aluminum-garnet (Er:YAG) laser is being used in a large number of studies. Microorganisms are extremely vital in the occurrence and development of dental caries. However, the impact of Er:YAG laser irradiation combined with fluoride on the dynamic microbial changes that occur in dental plaques is still uncertain. In this study, we examined the effect of an Er:YAG laser combined with fluorine on supragingival microbial composition and diversity in children with multiple caries.

METHODS

In this study, dental plaque samples (n = 48) were collected from 12 children with over 8 filled teeth. Supragingival plaques from left mandibular molars before (CB) and after fluoride treatment (CA) and right mandibular molars before (EB) and after fluoride+Er:YAG laser treatment (EA) were collected from each patient. In CB and EB groups, the samples were collected just before the treatments. In CA and EA groups, the samples were collected 1 month after treatments. Then, all specimens were subjected to 16S rRNA high-throughput sequencing to investigate the changes in microbial composition and diversity in mandibular molar supragingival plaques before and after fluoride or fluoride+Er:YAG laser treatment.

RESULTS

The dental plaque microbial diversity was higher in the EA group than in the EB group (baseline levels), and the microbial composition changed in EA group compared with EB group (P < 0.05). The levels of microorganisms associated with caries occurrence, including Proteobacteria, Fusobacteria, and Bacteroidetes, declined, while the levels of Faecacterium, Fastidiosipila, Vibrio, and Shewanella increased in EA group compared with EB group. The declines in Firmicutes, Streptococcus, Fusobacterium, and Veillonella levels were significantly lower in the EA group than in the CA group.

CONCLUSION

The combined application of the Er:YAG laser and fluoride may be more effective than using fluoride alone in reducing the proportion of cariogenic bacteria, increasing the diversity of plaque microorganisms, and further promoting the microecological balance.

Effect of Surface Roughness of Deciduous and Permanent Tooth Enamel on Bacterial Adhesion

The adhesion of some bacteria has been attributed to critical levels of roughness in hard tissues, which increases the risk of developing caries. The objective of this work was to assess the effect of deciduous and permanent tooth enamel surface roughness on bacterial adhesion. One hundred and eight samples of deciduous and permanent enamel were divided into two groups (n = 54). G1_DE deciduous enamel and G2_PE permanent enamel. The surface roughness was measured by profilometry and atomic force microscopy (AFM). Subsequently, the evaluation of bacterial adherence was carried out in triplicate by means of the XTT cell viability test. Additionally, bacterial adhesion was observed using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The average values of the micrometric roughness in both groups were similar; however, in the nanometric scale they presented significant differences. Additionally, the G1_DE group showed the highest amount of adhered S. mutans and S. sanguinis compared to the G2_EP group. Although the roughness of deciduous and permanent enamel showed contrasting results according to the evaluation technique (area and scale of analysis), bacterial adhesion was greater in deciduous enamel; hence, enamel roughness may not be a determining factor in the bacterial adhesion phenomenon.

A Comparison Between Phosphoric Acid- and Er:YAG Laser-Mediated Re-Etching of Enamel for Orthodontic Bracket Re-Bonding

Objective: This study sought to compare enamel surface morphology and orthodontic bracket re-bonding strength after phosphoric acid- or erbium-doped yttrium aluminum garnet (Er:YAG) laser-mediated re-etching. Methods: A total of 81 extracted premolars were obtained from patients undergoing orthodontic procedures. Conventional etching with 35% phosphoric acid was first used to bond brackets to the enamel surface. Then brackets were de-bonded 1 week later. These samples were then separated randomly into three groups (n = 27 teeth each group) and re-bonded with new brackets after one of the following re-etching manners: Group A-35% phosphoric acid, Group B-Er:YAG laser (200 mJ, 30 Hz), and Group C-Er:YAG laser (250 mJ, 30 Hz). The enamel surface and the interface of enamel and adhesive were then analyzed through scanning electron microscopy. Shear bond strength (SBS) and adhesive remnant index (ARI) were also measured. Results: Samples in Group A exhibited significant residual adhesive at the enamel surface, whereas samples in Groups B and C showed a cleaner surface with more distinct and evenly distributed honeycomb-like structures. Further, samples in Group C displayed a larger average SBS value between the two laser-etching groups, although there were no significant differences in SBS values or ARI scores between the acid and laser re-etching groups (p > 0.05). Conclusions: Er:YAG laser-based enamel re-etching (250 mJ, 30 Hz) produces an uniform honeycomb-like structure and a trend of similar SBS compared with 35% phosphoric acid-mediated re-etching. Er:YAG laser-mediated re-etching seems to be a promising alternative approach for bracket re-bonding.

Effect of Er:YAG laser irradiation on deciduous enamel roughness and bacterial adhesion: An in vitro study

Laser irradiation has been proposed as a preventive method against dental caries since it is capable to inhibit enamel demineralization by reducing carbonate and modifying organic matter, yet it can produce significant morphological changes. The purpose of this study was to evaluate the influence of Er:YAG laser irradiation on superficial roughness of deciduous dental enamel and bacterial adhesion. Fifty-four samples of deciduous enamel were divided into three groups (n = 18 each). G1_control (nonirradiated); G2_100 (7.5 J/cm² ) and G3_100 (12.7 J/cm² ) were irradiated with Er:YAG laser at 7.5 and 12.7 J/cm² , respectively, under water irrigation. Surface roughness was measured before and after irradiation using a profilometer. Afterwards, six samples per group were used to measure bacterial growth by XTT cell viability assay. Adhered bacteria were observed using confocal laser scanning microscopy (CLSM) and a scanning electron microscopy (SEM). Paired t-, one-way analysis of variance (ANOVA), Kruskal-Wallis and pairwise Mann-Whitney U tests were performed to analyze statistical differences (p < .05). Before treatment, samples showed homogenous surface roughness, and after Er:YAG laser irradiation, the surfaces showed a significant increase in roughness values (p < .05). G3_100 (12.7 J/cm² ) showed the highest amount of Streptococcus mutans adhered (p < .05). The increase in the roughness of the tooth enamel surfaces was proportional to the energy density used; the increase in surface roughness caused by laser irradiation did not augment the adhesion of Streptococcus sanguinis; only the use of the energy density of 12.7 J/cm² favored significantly the adhesion of S. mutans.

Predictability of Microbial Adhesion to Dental Materials by Roughness Parameters

Microbial adhesion to intraoral biomaterials is associated with surface roughness. For the prevention of oral pathologies, smooth surfaces with little biofilm formation are required. Ideally, appropriate roughness parameters make microbial adhesion predictable. Although a multitude of parameters are available, surface roughness is commonly described by the arithmetical mean roughness value (Ra). The present study investigates whether Ra is the most appropriate roughness parameter in terms of prediction for microbial adhesion to dental biomaterials. After four surface roughness modifications using standardized polishing protocols, zirconia, polymethylmethacrylate, polyetheretherketone, and titanium alloy specimens were characterized by Ra as well as 17 other parameters using confocal microscopy. Specimens of the tested materials were colonized by C. albicans or S. sanguinis for 2 h; the adhesion was measured via luminescence assays and correlated with the roughness parameters. The adhesion of C. albicans showed a tendency to increase with increasing the surface roughness—the adhesion of S. sanguinis showed no such tendency. Although Sa, that is, the arithmetical mean deviation of surface roughness, and Rdc, that is, the profile section height between two material ratios, showed higher correlations with the microbial adhesion than Ra, these differences were not significant. Within the limitations of this in-vitro study, we conclude that Ra is a sufficient roughness parameter in terms of prediction for initial microbial adhesion to dental biomaterials with polished surfaces.