Bernd W. Sigusch

Future perspectives of resin-based dental materials

OBJECTIVE This concise review and outlook paper gives a view of selected potential future developments in the area of resin-based biomaterials with an emphasis on dental composites. METHODS A selection of key publications (1 book, 35 scientific original publications and 1 website source) covering the areas nanotechnology, antimicrobial materials, stimuli responsive materials, self-repairing materials and materials for tissue engineering with direct or indirect relations and/or implications to resin-based dental materials is critically reviewed and discussed. Connections between these fields and their potential for resin-based dental materials are highlighted and put in perspective. RESULTS The need to improve shrinkage properties and wear resistance is obvious for dental composites, and a vast number of attempts have been made to accomplish these aims. Future resin-based materials may be further improved in this respect if, for example nanotechnology is applied. Dental composites may, however, reach a completely new quality by utilizing new trends from materials science, such as introducing nanostructures, antimicrobial properties, stimuli responsive capabilities, the ability to promote tissue regeneration or repair of dental tissues if the composites were able to repair themselves. SIGNIFICANCE This paper shows selected potential future developments in the area of resin-based dental materials, gives basic and industrial researchers in dental materials science, and dental practitioners a glance into the potential future of these materials, and should stimulate discussion about needs and future developments in the area.

Second generation LEDs for the polymerization of oral biomaterials

OBJECTIVES New blue, so called second generation light emitting diodes (LEDs) are now available with a high optical power output. These LEDs will potentially find widespread application in commercially available light curing units (LCUs). This study, therefore, investigated the curing performance of a prototype LCU containing one high power LED and a conventional halogen LCU (Polofil). METHODS The performances of the LCUs were evaluated by measuring the Knoop hardness and depth of cure of the composites. Three dental composites were selected (Z100, Admira and Revolcin Flow) in a light (A2) and a dark shade (A3.5 or A4), respectively, and were polymerized for 40 s each. RESULTS The LED prototype (irradiance=901 mW/cm2) achieved a statistically significantly greater (p<0.05) depth of cure than the halogen LCU (irradiance=860 mW/cm2) for all composites. Generally, there was no statistically significant difference in Knoop hardness on the top and bottom of a 2 mm thick disk for the composites Z100 and Admira if polymerized with the LED prototype or halogen LCU. The composite Revolcin Flow, however, showed in general a statistically significant lower Knoop hardness if polymerized with the LED LCU. SIGNIFICANCE The present study shows that second generation LEDs have the potential to replace halogen LCUs if the composites are selected carefully. Furthermore, this study confirmed that the depth of cure test does not discriminate between LCUs performance for composites containing co-initiators, but the Knoop hardness test does.

Full-Mouth Antimicrobial Photodynamic Therapy in Fusobacterium nucleatum― Infected Periodontitis Patients

BACKGROUND The purpose of this study is to clinically and microbiologically evaluate the effect of photodynamic therapy (PDT) as a full-mouth procedure in Fusobacterium nucleatum-infected patients with periodontitis. METHODS In the present study, PDT is administered adjuvantly after scaling and root planing (SRP) to patients with localized chronic periodontitis (LCP). Twenty-four patients, in whom only F. nucleatum was detected by baseline polymerase chain reaction (PCR) after SRP, were randomly assigned to PDT and control groups. PDT was carried out once as a full-mouth disinfection in the test group. The control group was treated with the photosensitizer solution, but without laser irradiation. In all subjects, the clinical parameters plaque index, reddening, bleeding on probing (BOP), probing depth (PD), gingival recession, and clinical attachment level (CAL) were determined at the baseline examination and at 1, 4, and 12 weeks after PDT. Quantitative analysis of the F. nucleatum DNA concentration was performed by competitive PCR. All clinical indices were calculated for each test and control subject as were the median and interquartile range of each group. RESULTS In patients with LCP who received PDT treatment, significant reductions in reddening, BOP, and mean PD and CAL were observed during the observation period and with respect to controls. Four and 12 weeks after PDT, the mean PD and CAL showed significant differences from baseline values and from those of the control group. In the PDT group, 12 weeks after treatment, the F. nucleatum DNA concentration was found to be significantly reduced compared to the baseline level. CONCLUSION The results of this study show that the adjuvant application of the described PDT method is appropriate to reduce periodontal inflammatory symptoms and to successfully treat infection with F. nucleatum.

Release of metronidazole from electrospun poly(l-lactide-co-d/l-lactide) fibers for local periodontitis treatment

OBJECTIVES We aimed to achieve detailed biomaterials characterization of a drug delivery system for local periodontitis treatment based on electrospun metronidazole-loaded resorbable polylactide (PLA) fibers. METHODS PLA fibers loaded with 0.1-40% (w/w) MNA were electrospun and were characterized by SEM and DSC. HPLC techniques were used to analyze the release profiles of metronidazole (MNA) from these fibers. The antibacterial efficacy was determined by measuring inhibition zones of drug-containing aliquots from the same electrospun fiber mats in an agar diffusion test. Three pathogenic periodontal bacterial strains: Fusobacterium nucleatum, Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis were studied. Cytotoxicity testing was performed with human gingival fibroblasts by: (i) counting viable cells via live/dead staining methods and (ii) by exposing cells directly onto the surface of MNA-loaded fibers. RESULTS MNA concentration influenced fiber diameters and thus w/w surface areas: diameter being minimal and area maximal at 20% MNA. HPLC showed that these 20% MNA fibers had the fastest initial MNA release. From the third day, MNA release was slower and nearly linear with time. All fiber mats released 32-48% of their total drug content within the first 7 days. Aliquots of media taken from the fiber mats inhibited the growth of all three bacterial strains. MNA released up to the 28th day from fiber mats containing 40% MNA significantly decreased the viability of F. nucleatum and P. gingivalis and up to the 2nd day also for the resistant A. actinomycetemcomitans. All of the investigated fibers and aliquots showed excellent cytocompatibility. SIGNIFICANCE This study shows that MNA-loaded electrospun fiber mats represent an interesting class of resorbable drug delivery systems. Sustained drug release properties and cytocompatibility suggest their potential clinical applicability for the treatment of periodontal diseases.

Marginal and internal fit of pressed lithium disilicate partial crowns in vitro: A three-dimensional analysis of accuracy and reproducibility

OBJECTIVES The objective of this in vitro study was to visualize and to quantify the marginal and internal fit of heat-pressed ceramic restorations by a novel three-dimensional procedure. Accuracy and reproducibility of the employed measuring method were determined. METHODS An acrylic model of a lower left first molar was prepared to receive a partial crown and duplicated by single step dual viscosity impressions. Corresponding working casts were formed from Type IV die stone and indirect restorations were fabricated from heat-pressable lithium disilicate ceramics (IPS e.max Press, Ivoclar Vivadent AG, Schaan, Liechtenstein). The acrylic tooth model and the ceramic partial crowns were digitized by a structure light scanner with a measurement-uncertainty of 4 μm and subjected to computer-aided quality inspection. Visual discrepancies in marginal and internal fit were displayed with colors. For quantitative analysis, mean quadratic deviations (RMS) were computed and analyzed by Students t-test (n=5, α=0.05). RESULTS Mean RMS-values for accuracy (reproducibility) ranged from 34 (14) μm for internal areas to 78 (23) μm for marginal surfaces. Differences in accuracy (p=0.003) and reproducibility (p<0.001) were statistically significant. In general, areas with sharp internal line angles such as occlusal ridges and the preparation finish line exhibited oversized dimensions, whereas areas with rounded and soft internal line angles were undersized. SIGNIFICANCE The viability of a computer-aided and three-dimensional approach for assessing marginal and internal fit of indirect restorations was demonstrated. Thereby, the obtained results track complex form changes as they occur during laboratory processing.

Grapefruit consumption improves vitamin C status in periodontitis patients.

Objective Previous studies demonstrate a relationship between a lack of vitamin C and increased risk of periodontal disease. In the present study we examine the vitamin C plasma levels and inflammatory measures in periodontitis patients before and after the consumption of grapefruit.Subjects and methods Fifty-eight patients with chronic periodontitis were assigned to the test group (non-smokers n=21, smokers n=17) and a diseased control group (non-smokers n=11, smokers n=9). Furthermore, 22 healthy subjects were recruited to compare vitamin C plasma levels between periodontally diseased and healthy subjects. Clinical evaluations, including plaque index (PI), sulcus bleeding index (SBI), probing pocket depths (PPD) and plasma vitamin C levels, were performed at baseline, and after two weeks of grapefruit consumption.Results At baseline, we observed significantly reduced plasma vitamin C levels in the test group and diseased controls in comparison with the healthy controls. On principle, smokers showed lower levels of vitamin C (mean 0.39 ± 0.17 mg dl−1) than non-smokers (mean 0.56±0.29 mg dl−1). After grapefruit consumption, the mean plasma vitamin C levels rose significantly in the test group compared to the diseased controls (non-smokers: 0.87±0.39 mg dl−1, smokers: 0.74±0.30 mg dl−1). Furthermore the SBI was reduced in the test group (non-smokers: from 1.68±0.6 to 1.05±0.6, p<0.001), whereas PI and PPD were unaffected.Conclusion The present results show that periodontitis patients are characterised by plasma vitamin C levels below the normal range, especially in smokers. The intake of grapefruit leads to an increase in plasma vitamin C levels and improves sulcus bleeding scores. Longer term studies are necessary to determine whether other periodontal outcomes improve with such supplementation especially in smokers.

Quantification of dental erosion--a comparison of stylus profilometry and confocal laser scanning microscopy (CLSM).

OBJECTIVES Since stylus profilometry applies a force on the sample surface, it is logical to hypothesize that the profilometer penetrates the surface of the enamel softened by acid solutions. The aims of the present study were, therefore, to test the hypothesis that surface profilometry measurements of eroded enamel alter the surface of the enamel, to quantify the potential effect of the surface alteration (scratches) on the measured values of enamel erosion by atomic force microscopy and to compare the values of enamel loss caused by erosion as measured by profilometry and non-contact confocal laser scanning microscopy (CLSM). METHODS Enamel samples, cut from unerupted human third molars were treated with Volvic Mineral Water and citric acid solutions of different pH values. The enamel material loss was measured by two different contact profilometers and a reflection mode CLSM. The scratches depth was analyzed by atomic force microscopy. RESULTS Our study demonstrated that the tip of the profilometer penetrated the surface of eroded enamel during the profilometry measurements, leading to clearly visible surface scratches on the enamel samples. The profilometers created surface scratches of a depth ranging from 57.6 (47.1)nm to 577.1 (157.6)nm on the surface of the eroded enamel and led, therefore, to a larger measured value of erosion. It was shown that the depth of the scratches depends on the pH value, the erosion time and the profilometer used. SIGNIFICANCE With few exceptions profilometers deliver reliable values of erosive enamel material loss, although they create surface scratches on eroded enamel. Reflection mode CLSM is a non-tactile, fast and precise method for analyzing enamel erosion quantitatively in vitro.

The influence of various light curing units on the cytotoxicity of dental adhesives

OBJECTIVES The objective of this study was to test the hypothesis that various light curing units (LCUs) have an influence on the cytotoxic action of adhesive systems. METHODS Samples of the dental adhesives (Syntac), iBondTM, Clearfil Protect Bond, Prime & Bond NT, Adper Prompt L-Pop) were prepared in microwell plates, making use of the LCUs Voco Polofil Lux (VPL), EMS Swiss Master Light (SML) and the LED prototype developed by the IMT of Jena University. To obtain extracts, the samples were topped with cell culture medium, which was changed daily on the 1st to 7th days and then on the 14th, 21st and 28th day, and stored for further use at -20 degrees C. Human gingival fibroblasts (HGFs) were cultivated in the extract-containing medium for 48 h. The viability of the HGFs was determined by the neutral red (NR) uptake test. The statistical test was performed by one-way ANOVA according to Bonferroni. RESULTS During the first few days, reduction of the viability rates of the HGFs by 85-90% were observed in all adhesives. A rise up to a plateau phase was observed at different times depending on the materials. The influence of the LCUs on the cytotoxic action of the dental adhesives was clearly evident for the adhesives Syntac and Clearfil Protect Bond. In case of the Syntac extracts, cytotoxicity after polymerization with the VPL was statistically significant reduced compared to the other LCUs used (p<0.001). A comparison between all the adhesives used proved that Adper Prompt L-Pop and Prime & Bond NT had the lowest overall cytotoxicities. SIGNIFICANCE In practice, one should use combinations of dental adhesive and LCU in which the material has the least toxic influences.

Mapping the mechanical properties of biomaterials on different length scales: depth-sensing indentation and AFM based nanoindentation

The micro- and nanomechanical properties of biomaterials are of central importance as surface elasticity, surface elastic response and adhesion play a central role in a large number of biological processes. They influence, e.g. morphogenesis, self-healing abilities and restoration processes, focal adhesion, motility, mechano-transduction, metastasis and are important for drug delivery applications, and others. These processes address fundamental questions in biology, medicine and diagnostics, pharmaceutical research, archaeology, dental as well as cosmetic applications. With nanoindentation as well as AFM force spectroscopic techniques suitable investigation tools are at hand, which can provide mechanical information on different length scales. The development of both techniques resulted in a broad applicability and the number of examples where both techniques have been used to study (soft) biomaterials rapidly increased during the last years.

Resin-composite cytotoxicity varies with shade and irradiance

OBJECTIVES The study was aimed at investigating the cytotoxicity of different composites as a function of composite shade and the light curing unit (LCU) employed. METHODS Non-polymerized and polymerized samples of the composites Grandio(®) (VOCO, Cuxhaven), Solitaire(®) (Heraeus Kulzer, Hanau) and Filtek Z 250(®) (3M/Espe, Seefeld) in two markedly differing shades (A2, C2) were prepared. Polymerization was performed with two LCUs: Heliolux II (Ivoclar/Vivadent, Ellwangen) and Swiss Master Light (EMS, Nyon, Switzerland). To obtain composite extracts, the samples were immersed in cell culture medium (DMEM--Dulbeccos Modified Eagle Medium), which was replaced daily up to the 7th day of the experiment, and then on the 14th, 21st and 28th day. After incubation of human gingival fibroblasts (HGF) with the extracts obtained, cytotoxicity was determined using the MTT test. RESULTS With the non-polymerized samples, essentially no influence of the composite shades investigated on HGF viability was detected, with the exception of the Solitaire material, where a higher cytotoxicity of the shade C2 in the non-polymerized state was found at the end of the observation period. After polymerization of the different composites, the cytotoxic reaction observed for the extracts of shade C2 was stronger than that observed for A2. After polymerization with the Heliolux II (HLX) LCU, the extracts of composites Grandio and Solitaire C2 were significantly more toxic than those of the A2 shade (p<0.01). Polymerization with the Swiss Master Light (SML) reduces this cytotoxic effect. The extracts of the Grandio composite showed the least cytotoxic effect throughout the observation period, irrespective of the LCU used. For the extracts of the Z250 specimens, the cytotoxicity observed was generally higher. SIGNIFICANCE The results show that the shade of the composite has an influence on its cytotoxicity and that this cytotoxicity is also influenced by the light curing unit used. It was observed that composites of the darker shade (C2) had a higher cytotoxicity, which varied with the LCU employed.