Bernd W. Sigusch

Background: In adhesive dentistry, debonding-on-demand is attractive for situations where no permanent attachment is required. Due to its destructive nature, ultraviolet (UV) light may be of interest for attenuating bond forces. The aim of this study was to investigate the impact of UV light on the shear bond strength (SBS) of etch-and-rinse (n = 4) and universal adhesives (n = 3). Methods: Glass-ceramic samples were bonded to bovine enamel surfaces (n = 10/adhesive) and subjected to shear bond testing before and after exposure to UV light (320–390 nm, 126 Jcm⁻²). Data was statistically analyzed by Mann–Whitney U test. Results: Initial photopolymerized etch-and-rinse adhesives showed superior SBS compared to universal adhesives. Highest values were recorded for iBOND^® Total etch (15.48 MPa) and Syntac classic© (17.60 MPa). Lowest SBS was obtained for Ecosite Bond^® (2.63 MPa). Additional UV exposure caused a significant decrease in SBS among iBOND Total etch (5.24 MPa, p = 0.009) and Solobond M© (3.65 MPa, p = 0.005), while for Syntac classic©, an increase (24.12 MPa, p = 0.047) was recorded. Among all other tested adhesives, no significant changes were observed. Conclusions: UV radiation impacted SBS of etch-and-rinse adhesives only (decrease: iBOND Total Etch, Solobond M; enhancement: Syntac classic©). Further research should focus on introducing sufficient light-triggered debonding mechanisms.

Background/Objectives: The effect of fusidic acid on oral bacteria, especially on Gram- negative periodontopathogenic species, has not yet been investigated. This in vitro study aimed to analyze the antibacterial effect of fusidic acid alone and as an active component in electrospun poly(L-lactide-co-D/L-lactide) fiber fleeces. Methods: Minimal inhibitory concentrations (MIC) of fusidic acid and metronidazole (control) were determined for various oral bacteria. Eluates were collected from electrospun poly(L-lactide-co-D/L-lactide) fiber fleeces loaded with 10 and 20 wt% fusidic acid over a period of 28 d. Antibacterial activity was analyzed by means of a microdilution assay. Cytotoxicity was observed toward human gingival fibroblasts (HGFs). Results: All tested Gram-positive and Gram-negative oral bacteria were susceptible to fusidic acid. The lowest MIC was observed for Porphyromonas gingivalis (MIC < 0.062 µg/mL). Compared to the antibacterial activity of metronidazole, that of Porphyromonas gingivalis was suppressed by significant lower fusidic acid concentrations (p < 0.01). The eluates obtained from electrospun poly(L-lactide-co-D/L-lactide) fiber fleeces inhibited the growth of P. gingivalis, S. aureus, A. viscosus, and A. neslundii over a course of 28 days. The largest inhibition zones were detected for Porphyromonas gingivalis in case of the 20 wt% concentrations. The eluates were not cytotoxic toward HGFs. Conclusions: It was shown that fusidic acid has significant antibacterial potential. The results of the present investigation suggest that fusidic acid alone or delivered by electrospun fiber fleeces might be attractive for controlling oral pathogenic bacteria.

The actin cytoskeleton plays an important role in morphological changes of ameloblasts during the formation of enamel, which is indispensable for teeth to withstand wear, fracture and caries progression. This study reveals that the actin nucleator Cobl is expressed in ameloblasts of mandibular molars during amelogenesis. Cobl expression was particularly pronounced during the secretory phase of the enamel-forming cells. Cobl colocalized with actin filaments at the cell cortex. Importantly, our analyses show an influence of Cobl on both ameloblast morphology and cytoskeletal organization as well as on enamel composition. At P0, Cobl knock-out causes an increased height of ameloblasts and an increased F-actin content at the apical membrane. During the maturation phase, the F-actin density at the apical membrane was instead significantly reduced when compared to WT mice. At the same time, Cobl-deficient mice showed an increased carbon content of the enamel and an increased enamel surface of mandibular molars. These findings demonstrate a decisive influence of the actin nucleator Cobl on the actin cytoskeleton and the morphology of ameloblasts during amelogenesis. Our work thus expands the understanding of the regulation of the actin cytoskeleton during amelogenesis and helps to further elucidate the complex processes of enamel formation during tooth development.

(1) Background: The in vitro study aimed to investigate mechanical characteristics of resin composites and their suitability in direct restauration of endodontically treated teeth (ETT). (2) Methods: 38 endodontically treated premolars with occlusal access cavities were directly restored using the following resin composites and adhesives: Tetric Evo Ceram^® + Syntac classic^® (n = 10), Venus Diamond^® + iBond Total-Etch^® (n = 10), Grandio^® + Solobond M^® (n = 9), Estelite^® Sigma Quick + Bond Force^® (n = 9). After thermocycling, the elastic modulus, shear-bond-strength, fracture load (Fmax) and fracture mode distribution were evaluated. Statistical analysis: one-way ANOVA, t-test, Kruskal–Wallis test; p < 0.05. (3) Results: Grandio^® showed the highest E-modulus (15,857.9 MPa) which was significant to Venus Diamond^® (13,058.83 MPa), Tetric Evo Ceram^® (8636.0 MPa) and Estelite^® Sigma Quick (7004.58 MPa). The highest shear-bond-strength was observed for Solobond M^® (17.28 MPa), followed by iBond^® (16.61 MPa), Syntac classic^® (16.41 MPa) and Bond Force^® (8.37 MPa, p < 0.05). The highest fracture load (Fmax) was estimated for ETT restored with Venus Diamond^® (1106.83 N), followed by Estelite^® Sigma Quick (1030.1 N), Tetric Evo Ceram^® (1029 N) and Grandio^® (921 N). Fracture-mode distribution did not show any significant differences. (4) Conclusions: The observed resin composites and adhesives show reliable mechanical characteristics and seem to be suitable for direct restoration of endodontically treated teeth.

Background: Material-dependent parameters have an important impact on the efficiency of light polymerization. The present in vitro study aimed to investigate the influence of the increment thickness and shade of nano- and nanohybrid resin composites on the transmission of curing light. Methods: Three contemporary resin composites were evaluated: Tetric EvoCeram^® (TEC); Venus Diamond^® (VD); and Filtek Supreme XTE^® (FS XTE). Light transmission (LT) was recorded in accordance with the sample thickness (0.5 to 2.7 mm) and the shade. Polymerized samples were irradiated for 10 s each using the high-power LED curing light Celalux 2 (1900 mW/cm²). LT was simultaneously recorded using the MARC Patient Simulator (MARC-PS). Results: LT was strongly influenced by the composite layer thickness. For 0.5 mm-thick samples, a mean power density of 735 mW/cm² was recorded at the bottom side. For the 2.7 mm samples, a mean power density of 107 mW/cm² was measured. Only LT was markedly reduced in the case of darker shades. From A1 to A4, LT decreased by 39.3% for FS XTE and 50.8% for TEC. Dentin shades of FS XTE and TEC (A2, A4) showed the lowest LT. Conclusions: The thickness and shade of resin composite increments strongly influences the transmission of curing light. More precise information about these parameters should be included in the manufacture manual.

Recently, our group showed that additional supplementation of Trolox™ (vitamin E analogue) can significantly enhance the antimicrobial photodynamic effect of the photosensitizer Indocyanine green (ICG). Up to now, the combined effect has not yet been investigated on Enterococcus faecalis in dental root canals. In the present in vitro study, eighty human root canals were inoculated with E. faecalis and subsequently subjected to antimicrobial Photodynamic Therapy (aPDT) using ICG (250, 500, 1000 µg/mL) and near-infrared laser light (NIR, 808 nm, 100 Jcm⁻²). Trolox™ at concentrations of 6 mM was additionally applied. As a positive control, irrigation with 3% NaOCl was used. After aPDT, root canals were manually enlarged and the collected dentin debris was subjected to microbial culture analysis. Bacterial invasion into the dentinal tubules was verified for a distance of 300 µm. aPDT caused significant suppression of E. faecalis up to a maximum of 2.9 log counts (ICG 250 µg/mL). Additional application of Trolox^TM resulted in increased antibacterial activity for aPDT with ICG 500 µg/mL. The efficiency of aPDT was comparable to NaOCl-irrigation inside the dentinal tubules. In conclusion, ICG significantly suppressed E. faecalis. Additional application of Trolox^TM showed only minor enhancement. Future studies should also address the effects of Trolox^TM on other photodynamic systems.

(1) Background: In the oral environment, sound enamel and dental restorative materials are immediately covered by a pellicle layer, which enables bacteria to attach. For the development of new materials with repellent surface functions, information on the formation and maturation of salivary pellicles is crucial. Therefore, the present in situ study aimed to investigate the proteomic profile of salivary pellicles formed on different dental composites. (2) Methods: Light-cured composite and bovine enamel samples (controls) were exposed to the oral cavity for 30, 90, and 120 min. All samples were subjected to optical and mechanical profilometry, as well as SEM surface evaluation. Acquired pellicles and unstimulated whole saliva samples were analyzed by SELDI–TOF–MS. The significance was determined by the generalized estimation equation and the post-hoc bonferroni adjustment. (3) Results: SEM revealed the formation of homogeneous pellicles on all test and control surfaces. Profilometry showed that composite surfaces tend to be of higher roughness compared to enamel. SELDI–TOF–MS detected up to 102 different proteins in the saliva samples and up to 46 proteins in the pellicle. Significant differences among 14 pellicle proteins were found between the composite materials and the controls. (4) Conclusions: Pellicle formation was material- and time-dependent. Proteins differed among the composites and to the control.

Recently, our group developed two different polymeric biomaterials with photodynamic antimicrobial surface activity for periodontal bone regeneration. The aim of the present study was to analyze the biocompatibility and osseointegration of these materials in vivo. Two biomaterials based on urethane dimethacrylate (BioM1) and tri-armed oligoester-urethane methacrylate (BioM2) that additionally contained ß-tricalcium phosphate and the photosensitizer mTHPC (meso-tetra(hydroxyphenyl)chlorin) were implanted in non-critical size bone defects in the femur (n = 16) and tibia (n = 8) of eight female domestic sheep. Bone specimens were harvested and histomorphometrically analyzed after 12 months. BioM1 degraded to a lower extent which resulted in a mean remnant square size of 17.4 mm², while 12.2 mm² was estimated for BioM2 (p = 0.007). For BioM1, a total percentage of new formed bone by 30.3% was found which was significant higher compared to BioM2 (8.4%, p < 0.001). Furthermore, BioM1 was afflicted by significant lower soft tissue formation (3.3%) as compared to BioM2 (29.5%). Additionally, a bone-to-biomaterial ratio of 81.9% was detected for BioM1, while 8.5% was recorded for BioM2. Implantation of BioM2 caused accumulation of inflammatory cells and led to fibrous encapsulation. BioM1 (photosensitizer-armed urethane dimethacrylate) showed favorable regenerative characteristics and can be recommended for further studies.

(1) Background: Decalcified enamel and dentin surfaces can be regenerated with non-fluoride-containing biomimetic systems. This study aimed to investigate the effect of a zinc carbonate-hydroxyapatite-containing dentifrice on artificially demineralized enamel and dentin surfaces. (2) Methods: Human enamel and dentin discs were prepared and subjected to surface demineralization with 30% orthophosphoric acid for 60 s. Subsequently, in the test group (n = 20), the discs were treated three times a day for 3 min with a zinc carbonate-hydroxyapatite-containing toothpaste (biorepair^®). Afterwards, all samples were gently rinsed with PBS (5 s) and stored in artificial saliva until next use. Samples from the control group (n = 20) received no dentifrice-treatment and were stored in artificial saliva, exclusively. After 15 days of daily treatment, specimens were subjected to Raman spectroscopy, energy-dispersive X-ray micro-analysis (EDX), white-light interferometry, and profilometry. (3) Results: Raman spectroscopy and white-light interferometry revealed no significant differences compared to the untreated controls. EDX analysis showed calcium phosphate and silicon dioxide precipitations on treated dentin samples. In addition, treated dentin surfaces showed significant reduced roughness values. (4) Conclusions: Treatment with biorepair^® did not affect enamel surfaces as proposed. Minor mineral precipitation and a reduction in surface roughness were detected among dentin surfaces only.

The goal of this study was to evaluate the effectiveness of the toothpaste Tooth Mousse compared to conventional fluoride-based versions in the prevention of enamel and dentin demineralization. Human enamel and dentin samples (n = 120 each) were exposed to artificial demineralization at pH 4.92. During the demineralization process, the samples in the test groups were periodically treated with Tooth Mousse (TM) containing casein-phosphopeptide -amorphous-calcium-phosphate (CPP-ACP) and Tooth Mousse Plus (TMP) containing amorphous-calcium-fluoride-phosphate (CPP-ACPF) to evaluate their protective properties. Fluoride toothpastes containing 1400 ppm amine fluoride (AmF) and 1450 ppm sodium fluoride (NaF) were applied in the positive control groups. Treatment with distilled water (group C-W) or demineralization without treatment (group C-D) served as negative controls. After the demineralization and treatment process, all samples were cut longitudinally and lesion depths were determined at six locations using polarized light microscopy. In TM/TMP groups (enamel: 80/86 µm, dentin: 153/156 µm) lesion depths were significantly smaller compared to the negative control groups C-W/C-D (enamel: 99/111 µm, dentin: 163/166 µm). However, TM and TMP compared to the positive controls AmF/NaF (enamel: 58/63 µm, dentin: 87/109 µm) showed higher lesion depths. The application of TM/TMP (89%/78%) during demineralization led to a reduced number of severe lesions compared to the negative controls C-W/C-D (100%/95%). In this study we demonstrate that Tooth Mousse is less effective regarding prevention of enamel and dentin demineralization compared to fluoride containing toothpastes.