Succession of oral bacterial colonizers on dental implant materials: An in vitro biofilm model

ObjectivesOral bacterial adhesion on dental implant materials has been extensively studied using in vitro systems but has yielded results restricted to in vitro growth patterns due to limitations in species selection, sustained fastidious anaerobe growth, and mixed culture longevity. The aim of this study was to develop an oral bacterial biofilm model consisting of colonizers representative of the oral microbiome exhibiting temporal shifts characteristic of plaque development and maturation in vivo.MethodsStreptococcus oralis, Actinomyces naeslundii, Aggregatibacter actinomycetemcomitans, Veillonella parvula, Fusobacterium nucleatum, and Porphyromonas gingivalis were grown in monoculture prior to combination in mixed culture. Commercially pure titanium (cpTi) and yttria-stabilized zirconia (ZrO₂) disks with polished, acid-etched, or sandblasted surfaces were prepared to evaluate oral bacterial adhesion. After 6 h, 1, 3, 7, 14 and 21 days, genomic DNA from planktonic and adherent bacteria was isolated. Quantitative polymerase chain reaction (qPCR) was used to enumerate the amount and proportion of each species.ResultsEarly-colonizing S. oralis and A. actinomycetemcomitans, dominated after 6 h prior to secondary colonization by F. nucleatum and V. parvula in planktonic (1 day) and sessile (3 days) form. A. naeslundii maintained relatively low but stable bacterial counts throughout testing. After 14 days, late-colonizing P. gingivalis became established in mixed culture and persisted, becoming the dominant species after 21 days. The composition of adherent bacteria across all substrates was statistically similar at all timepoints with notable exceptions including lower S. oralis bacterial counts on polished cpTi (3 days).SignificanceWithin the present model’s limitations, multispecies oral bacterial attachment is similar on surface-treated cpTi and ZrO₂.     

In vivo study of the initial bacterial adhesion on different implant materials

Objective

Biofilm formation on implant materials plays a major role in the aetiology of periimplantitis. The aim of this study was to examine in vivo the initial bacterial adhesion on six different implant materials.

Methods

The implant materials Ti-m, TiUnite^®, ZiUnite^®, ATZ-m, ATZ-s, TZP-A-m were tested using bovine enamel slabs as controls. All materials, fixed on splint systems, were examined after 30 min and 120 min of oral exposure. DAPI staining was used for quantitative analysis of the initially adherent microorganisms. Initial adherent microorganisms were visualised by fluorescence In situ-hybridisation (FISH) and quantified by confocal laser scanning microscopy (CLSM). The targets of the oligonucleotide probes were Eubacteria, Veillonella spp., Fusobacterium nucleatum, Actinomyces naeslundii and Streptococcus spp.

Results

DAPI analysis showed that increasing the time of oral exposure resulted in an increasing amount of initial adherent bacteria. The highest level of colonisation was on ZiUnite^®, with the lowest occurring on the bovine enamel, followed by Ti-m. This early colonisation correlated significantly with the surface roughnesses of the materials. FISH and CLSM showed no significant differences relating to total bacterial composition. However, Streptococcus spp. was shown to be the main colonisers on each of the investigated materials.

Conclusion

it could be shown that within an oral exposure time of 30 min and 120 min, despite the salivary acquired pellicle initial biofilm formation is mainly influenced directly or indirect by the material surface topography. Highly polished surfaces should minimise the risk of biofilm formation, plaque accumulation and possibly periimplantitis.     

Soft tissue adhesion of polished versus glazed lithium disilicate ceramic for dental applications

Objective

Ceramics are widely used materials for prosthesis, especially in dental fields. Despite multiple biomedical applications, little is known about ceramic surface modifications and the resulting cell behavior at its contact. The aim of this study is to evaluate the biological response of polished versus glazed surface treatments on lithium disilicate dental ceramic.

Methods

We studied a lithium disilicate ceramic (IPS e.max^® Press, Ivoclar Vivadent) with 3 different surface treatments: raw surface treatment, hand polished surface treatment, and glazed surface treatment (control samples are Thermanox^®, Nunc). In order to evaluate the possible modulation of cell response at the surface of ceramic, we compared polished versus glazed ceramics using an organotypic culture model of chicken epithelium.

Results

Our results show that the surface roughness is not modified as demonstrated by equivalent R_a measurements. On the contrary, the contact angle θ in water is very different between polished (84°) and glazed (33°) samples. The culture of epithelial tissues allowed a very precise assessment of histocompatibility of these interfaces and showed that polished samples increased cell adhesion and proliferation as compared to glazed samples.

Significance

Lithium disilicate polished ceramic provided better adhesion and proliferation than lithium disilicate glazed ceramic. Taken together, our results demonstrate for the first time, how it is possible to use simple surface modifications to finely modulate the adhesion of tissues. Our results will help dental surgeons to choose the most appropriate surface treatment for a specific clinical application, in particular for the ceramic implant collar.     

Effects of different sterilization methods on surface characteristics and biofilm formation on zirconia in vitro

Objective

The current laboratory study was to investigate the effect of different sterilization treatments on surface characteristics of zirconia, and biofilm formation on zirconia surface after exposure to these sterilization treatments.

Polyspecies biofilm formation on implant surfaces with different surface characteristics

Objective:

To investigate the microbial adherence and colonization of a polyspecies biofilm on 7 differently processed titanium surfaces.

Material and Methods:

Six-species biofilms were formed anaerobically on 5-mm-diameter sterilized, saliva-preconditioned titanium discs. Material surfaces used were either machined, stained, acid-etched or sandblasted/acid-etched (SLA). Samples of the latter two materials were also provided in a chemically modified form, with increased wettability characteristics. Surface roughness and contact angles of all materials were determined. The discs were then incubated anaerobically for up to 16.5 h. Initial microbial adherence was evaluated after 20 min incubation and further colonization after 2, 4, 8, and 16.5 h using non-selective and selective culture techniques. Results at different time points were compared using ANOVA and Scheffé post hoc analysis.

Results:

The mean differences in microorganisms colonizing after the first 20 min were in a very narrow range (4.5 to 4.8 log CFU). At up to 16.5 h, the modified SLA surface exhibited the highest values for colonization (6.9±0.2 log CFU, p<0.05) but increasing growth was observed on all test surfaces over time. Discrepancies among bacterial strains on the differently crafted titanium surfaces were very similar to those described for total log CFU. F. nucleatum was below the detection limit on all surfaces after 4 h.

Conclusion:

Within the limitations of this in vitro study, surface roughness had a moderate influence on biofilm formation, while wettability did not seem to influence biofilm formation under the experimental conditions described. The modified SLA surface showed the highest trend for bacterial colonization.     

Surface properties of titanium and zirconia dental implant materials and their effect on bacterial adhesion

Objectives

Zirconia ceramic material has been widely used in implant dentistry. In this in vitro study the physiochemical properties of titanium and zirconia materials were investigated and the affinity of different bacteria to different materials was compared.

Methods

Disc samples with different surface states were used: polished partially stabilized zirconia (PZ), titanium blasted with zirconia (TBZ), titanium blasted with zirconia then acid etched (TBZA), and polished titanium (PT) as a control. Surface topography was examined using scanning electron microscopy and profilometry. Contact angle, surface free energy (SFE), surface microhardness and chemical composition were determined.Disc samples were separately incubated with Streptococcus mitis and Prevotella nigrescens, either with or without pre-coating with human saliva, for 6 h and the surface area covered by bacteria was calculated from fluorescence microscope images.

Results

PZ and TBZ exhibited lower surface free energy and lesser surface wettability than PT. Also, PZ and TBZ surfaces showed lower percentage of bacterial adhesion compared with control PT surface.

Conclusions

The zirconia material and titanium blasted with zirconia surface (TBZ surface) showed superior effect to titanium material in reducing the adhesion of the experimented bacteria especially after coating with saliva pellicle. Modifying titanium with zirconia lead to have the same surface properties of pure zirconia material in reducing bacterial adhesion.SFE appears to be the most important factors that determine initial bacterial adhesion to smooth surface.     

Soft tissue reactions to plaque formation at implant abutments with different surface topography. An experimental study in dogs

BACKGROUND: The mucosal attachment that forms to titanium implants, uncontaminated by bacterial plaque comprises, independent of the surface characteristics of the abutment, one barrier epithelium and one zone of connective tissue attachment. It was suggested that abutments with a rough surface may accumulate more plaque than abutments with a smooth surface and that such an enhanced rate of plaque build-up may favor the development of inflammatory lesions in the periimplant mucosa. OBJECTIVES: The aim of the present experiment was to study some reactions of the periimplant mucosa to plaque accumulation on implant abutments designed with either a rough or a smooth external surface. MATERIAL AND METHODS: In five beagle dogs, four fixtures were placed and submerged in the premolar region. In a second stage procedure performed after 3 months, abutments with two different types of surface topography, one rough, acid-etched (OA) and one smooth, turned abutment (TA), were installed in a random order. After 6 months of undisturbed plaque formation, the animals were sacrificed and biopsies obtained. Tissue samples were prepared for light microscopy and exposed to histometric and morphometric measurements. RESULTS: Six months of plaque accumulation resulted in the establishment of an inflammatory lesion (pl-ICT) in the connective tissue of the periimplant mucosa, the location, size and composition of which did not differ between OA and TA sites. In addition, most OA and TA sites harbored a second inflammatory cell infiltrate in the tissue lateral to the abutment/fixture junction (ab-ICT). While pl-ICT was dominated by plasma cells and lymphocytes, ab-ICT contained a comparatively large number of polymorphonuclear leukocytes. CONCLUSION: The different surface characteristics of abutment made of c.p. titanium failed to influence plaque formation and the establishment of inflammatory cell lesions in the periimplant mucosa.     

In vivo and in vitro biofilm formation on two different titanium implant surfaces

Objectives: The aim of the present in vitro and human in vivo study was twofold: first, to evaluate the initial biofilm formation on different titanium implant surfaces by means of two highly sensitive fluorescent techniques and, second, to correlate these findings to different surface properties. Materials and methods: In vivo biofilm formation was induced on purely machined (Pt) and on sand‐blasted and acid‐etched titanium (Prom) specimens, which were mounted buccally on individual splints and worn by six study participants for 12 h. In vitro bacterial adhesion was also investigated after incubation with Streptococcus sanguinis suspension (37°C, 2 h). Adherent bacteria were quantified by the following fluorescence techniques: Resazurin staining in combination with an automated fluorescence reader or live/dead cell labeling and fluorescence microscopy. Surface roughness (R_a) was determined with a perthometer, and surface free energy (SFE) was measured with a goniometer. Results: Prom showed a significantly higher median R_a (0.95 μm) and a significantly lower median SFE (18.3 mJ/m²) than Pt (R_a=0.15 μm; SFE=39.6 mJ/m²). The in vitro and in vivo tests showed a significantly higher bacterial adhesion to Prom than to Pt, and the initial biofilm formation on Pt corresponded to the circular surface modifications on the machined substratum. Both observations may be attributed to the predominant influence of surface roughness on bacterial adhesion. No significant differences in the percentage of dead cells among all adhering bacteria were found between Prom (23.7%) and Pt (29.1%). Ectopic solitary epithelial cells from the oral mucosa – strongly adhering to the substratum – were found on each Prom specimen, but not on any of the Pt surfaces. Conclusions: Initial bacterial adhesion to differently textured titanium surfaces is primarily influenced by R_a, whereas the influence of SFE seems to be of only minor importance. Therefore, the micro‐structured parts of an implant that are exposed to the oral cavity should be highly polished to prevent plaque accumulation. Both tested fluorometric techniques proved to be highly sensitive and reproducible in the quantification of biofilm formation on titanium implant surfaces. To cite this article:
Bürgers R, Gerlach T, Hahnel S, Schwarz F, Handel G, Gosau M. In vivo and in vitro biofilm formation on two different titanium implant surfaces.
Clin. Oral Impl. Res. 21 , 2010; 156–164
doi: 10.1111/j.1600‐0501.2009.01815.x     

不同表面处理方法对CAD/CAM氧化锆种植体表面显微形貌的影响研究

目的：：研究采用不同表面处理方法对CAD/CAM氧化锆种植体表面显微形貌特征及粗糙度的影响。方法：通过CAD/CAM技术加工氧化锆圆盘与一段式氧化锆种植体( Y-TZP, WIELAND),根据表面处理方式分为终烧结表面、喷砂表面及喷砂加热酸蚀处理表面;标准对照组选用BEGO钛种植体表面。各组圆盘试件及种植体用扫描电子显微镜及Keyence 3D激光显微形貌测量显微镜进行表面显微形貌观察与测量。采用单因素方差分析比较各组统计学差异。结果：各组CAD/CAM氧化锆试件表面显微形貌观察显示,喷砂后表面出现边缘锐利的凹坑及沟槽;喷砂加热酸蚀处理后,氧化锆表面可见纳米级的微小孔隙及沟纹。氧化锆种植体粗糙度测量结果显示：终烧结组的表面粗糙度值(Ra=0.69μm)显著低于其他3组(P<0.001),喷砂组Ra值(Ra=1.30μm)显著低于喷砂加热酸蚀组(Ra=1.49μm)及BEGO钛种植体组(Ra=1.57μm)(P<0.01),而喷砂加热酸蚀组与BEGO钛种植体组则无显著差异(P=0.196)。结论：CAD/CAM氧化锆试件终烧结后喷砂或喷砂加热酸蚀处理均可获得较为理想的表面粗糙度,热酸蚀处理能够改变氧化锆表面的纳米级微观结构。     

不同粗糙度金铂合金和镍铬合金对种植体龈下优势菌粘附性的影响

目的 研究不同粗糙度冠修复材料对种植体龈下优势菌粘附性的影响。方法 选用两种常用冠修复合金材料:金铂合金和镍铬合金。将其制成两种不同粗糙度的试件粘固于种植纯钛板上,分别与4种龈下优势菌牙龈卟啉单胞菌(Porphyromanus gingivalis,Pg)、伴放线放线杆菌(Actinobacillus actinomycetemcomitans,Aa)、中间普氏菌(Prevotella intermedia,Pi)及具核梭杆菌(Fusobacterium nuclertum,Fn)共同厌氧孵育,采用菌落形成单位(colony-forming unit,CFU)计数法量化测定培养试件表面的细菌量,并进行统计学分析。同时扫描电镜观察各种菌在试件上的附着情况。结果 经两两比较,同种合金中粗糙度大的试件四种细菌附着量均大于粗糙度小的(P<0.01);同种粗糙度的试件,金铂合金与种植体钛上各种细菌粘附量均大于镍铬合金与种植钛上的附着量(P<0.01)。结论 在相同条件下,冠修复合金抛光度越高,细菌粘附量越小。体外培养镍铬合金上四种细菌的粘附均小于金铂合金。     

Human osteoblasts response to different dental implant abutment materials: An in-vitro study

ObjectivesThis study aimed to investigate human osteoblasts (HOB) response towards different dental implant abutment materials.MethodsFive dental implant abutment materials were investigated: (1) titanium (Ti), (2) titanium coated nitride (TiN), (3) cobalt chromium (CoCr), (4) zirconia (ZrO?), and (5) modified polyether ether ketone (m-PEEK). HOBs were cultured, expanded, and seeded according to the supplier’s protocol (PromoCell, UK). Cell proliferation and cytotoxicity were evaluated at days 1, 3, 5, and 10 using Alamar Blue (alamarBlue) and lactate dehydrogenase (LDH) colorimetric assays. Data were analysed via two-way ANOVA, one-way ANOVA and Tukey’s post hoc test (significance was determined as p < 0.05 for all tests).ResultsAll the investigated materials showed high and comparable initial proliferation activities apart from ZrO? (46.92%), with P% of 79.91%, 68.77%, 73.20%, and 65.46% for Ti, TiN, CoCr, and m-PEEK, respectively. At day 10, all materials exhibited comparable and lower P% than day 1 apart from TiN (70.90%) with P% of 30.22%, 40.64%, 37.27%, and 50.65% for Ti, CoCr, ZrO?, and m-PEEK, respectively. The cytotoxic effect of the investigated materials was generally low throughout the whole experiment. At day 10, the cytotoxicity % was 7.63%, 0.21%, 13.30%, 5.32%, 8.60% for Ti, TiN, CoCr, ZrO?, and m-PEEK. The Two-way ANOVA and Tukey’s Multiple Comparison Method highlighted significant material and time effects on cell proliferation and cytotoxicity, and a significant interaction (p < 0.0001) between the tested materials. Notably, TiN and m-PEEK showed improved HOB proliferation activity and cytotoxic levels than the other investigated materials. In addition, a non-significant negative correlation between viability and cytotoxicity was found for all tested materials. Ti (p = 0.07), TiN (p = 0.28), CoCr (p = 0.15), ZrO? (p = 0.17), and m-PEEK (p = 0.12).SignificanceAll the investigated materials showed excellent biocompatibility properties with more promising results for the newly introduced TiN and m-PEEK as alternatives to the traditionally used dental implant and abutment materials.     

In situ effects of restorative materials on dental biofilm and enamel demineralisation

Objectives

Since secondary caries is one of the main reasons for replacing restorations, this study assessed the effects of different restorative materials on the microbiological composition of dental biofilm and on enamel demineralisation around the restoration.

Methods

A randomized, double-blind, split-mouth in situ design was conducted in one phase of 14 days, during which, 20 volunteers wore palatal devices containing five human dental enamel slabs. Each slab was randomly restored with one of the following materials: Filtek-Z-250/Single Bond, control group (composite resin), Permite (amalgam), Fuji II (encapsulated resin-modified glass ionomer), Vitremer (resin-modified glass ionomer) and Ketac Molar (conventional glass ionomer). The volunteers used fluoride dentifrice, 3×/day and a 20% sucrose solution was dripped onto the slabs 8×/day. The biofilm formed on the slabs was analyzed to determine the counts of total streptococci, mutans streptococci and lactobacilli. Enamel demineralisation was determined by cross-sectional microhardness (CSMH) at 20 and 70 μm from the margin of the restoration. Kruskal–Wallis and analysis of variance, followed by least mean squares (LMS) test, were used to evaluate microbiota and CSMH among the groups. The significance level used was 5%.

Results

No statistically significant differences were found in the cariogenic microbiota grown on the slabs. At a 20-μm distance, only Fuji II statistically differed from the other groups, showing the lowest demineralisation. At 70 μm, Fuji II significantly inhibited demineralisation when compared to Permite, Filtek-Z-250 and Ketac Molar.

Conclusions

In the context of fluoride dentifrice and under the cariogenic exposure conditions of this study, only the encapsulated resin-modified glass ionomer material provided additional protection against secondary caries.     

Impact of surface roughness of gypsum materials on adaptation of zirconia cores

PURPOSE

The present study investigated the influences of various gypsum materials on the precision of fit of CAD/CAM-fabricated prostheses and analyzed their correlation with surface roughness.

MATERIALS AND METHODS

The master model of the mandibular right first molar was replicated, and four experimental groups based on two types of Type IV stone (GC Fujirock EP, Die keen) and two types of scannable stone (Aesthetic-Basegold, Everest Rock) were created to include a total of 40 specimens, 10 in each group. The surface roughness of the working models for the respective experimental groups was measured. Once the zirconia cores had been fabricated, the marginal and internal fits were measured with a digital microscope using the silicone replica technique. The mean and standard deviation of the respective points of measurement were computed and analyzed through the one-way ANOVA and Tukey''s HSD test. The correlation between surface roughness and the precision of fit of the zirconia core was analyzed using the Pearson correlation analysis (α=.05).

RESULTS

The zirconia cores fabricated from the scannable stone working models exhibited a superior precision of fit as compared to those fabricated from the Type IV stone working models. The correlation analysis results showed a clear positive correlation between surface roughness and the precision of fit of zirconia cores in all of the experimental groups (P<.05).

CONCLUSION

The results confirmed that the surface roughness of dental working models has a decisive influence on the precision of fit of zirconia cores.     

Novel in vitro comparative model of osteogenic and inflammatory cell response to dental implants

Objectives

Roughened dental implants promote mesenchymal stem cell (MSCs) osteoblastic differentiation, and hydrophilic modifications induce anti-inflammatory macrophages activation. While the effect of different surface modifications on osseointegration of commercial dental implants have been compared in vivo and clinically, the initial cellular response to these modifications often overlooked. We aimed to characterize the macrophage inflammatory response and MSC osteogenesis across different commercially available implants in vitro.

Effect of acidic media on flexural strength and fatigue of CAD-CAM dental materials

ObjectiveTo investigate the effect of acidic media, including beverages and gastric fluids on flexural strength and fatigue of CAD-CAM materials.MethodsFour CAD-CAM materials (high-translucency zirconia (Ceramill Zolid HT+), lithium disilicate (IPS e-max CAD), hybrid ceramic (Vita Enamic), and nanohybrid resin composite (Grandio Blocs) were prepared and immersed in one of five media (gastric HCl, white wine, Coca-Cola, orange juice, and artificial saliva) in an incubator (37 ℃, 24 h). Surface topography and roughness were obtained using a scanning electron microscope (SEM) and a stylus contact profilometer, respectively. Initial 3-point flexural strength was measured for half of the bars (n = 20/gp) using a universal testing machine (0.5 mm/min). The other bars underwent 10⁶ cyclic fatigue loadings before measurement of residual 3-point flexural strength. Data were statistically analyzed (two-way and three-way ANOVA, Tukey’s post-hoc, p < 0.05). Weibull distributions were plotted for reliability analysis.ResultsZirconia bars has the highest initial flexural strengths followed by lithium disilicate, while resin composite and hybrid ceramic groups had the lowest strength regardless of the erosive medium. Cyclic fatigue significantly reduced initial flexural strengths for all materials except for hybrid ceramic and resin composite. Weibull moduli were the highest for zirconia, lithium disilicate and resin composite and lowest for hybrid ceramic.SignificanceErosive media significantly changed surface roughness of CAD-CAM materials except for zirconia and resin composite without jeopardizing the flexural strength of the CAD-CAM materials. Despite the higher flexural strengths for zirconia and lithium disilicate, resin composite and hybrid ceramic were more resistant to cyclic fatigue.     

In vivo monitoring of the bone healing process around different titanium alloy implant surfaces placed into fresh extraction sockets

Objectives

Increasing surface roughness and coating with tricalcium phosphate of titanium and titanium alloy implants has been proposed to provide better rates of osseointegration. However, how these changes in surface topography and chemistry influence the osseointegration process of immediate implants placed in fresh extraction sockets is unclear. This study investigated the influence of three clinically employed implant surfaces on the early bone healing events in vivo.

Methods

Machined smooth implants were milled from grade 5 Ti6Al4V titanium. Surfaces were moderately roughened by grit blasting, which were then coated with tricalcium phosphate. Implants were placed into freshly extracted incisor sockets of mandibles of normal Wistar rats and left for 1, 3 and 9 weeks. Healing bone tissue around the implants was examined by histochemistry and immunocytochemistry to localise PCNA proliferative cells, and osteoblast differentiation markers osteopontin and osteocalcin. Positive synthesising cells were counted using image analysis.

Results

Histology indicated no differences in the amount or pattern of bone formation within the healing tissue surrounding the different implant surfaces. Bone healing occurred predominantly on exposed bone surfaces (distance osteogenesis) and not on the implant surface (contact osteogenesis). No differences were observed in the number or timing of PCNA, osteopontin and osteocalcin positive cells within the bone healing tissue around each of the implant analysed.

Conclusion

For immediately placed implants, the surface modifications investigated appeared to have little influence on the activity of bone forming cells surrounding the implant, probably due to the high level of distance osteogenesis seen within this scenario.

Clinical significance

For immediate placement of implants into fresh extraction sockets, titanium implants with roughened surfaces and coating with tricalcium phosphate have negligible influence in accelerating the early bone healing events of osseointegration.     

Resin composite blocks for dental CAD/CAM applications reduce biofilm formation in vitro

ObjectivesModern dentistry is increasingly focusing on digital procedures, including CAD/CAM technologies. New materials have to resist in a demanding environment that includes secondary caries occurrence. The current study hypothesized that the microbiological behavior of different RBCs for CAD/CAM applications is better than that of their counterparts for direct restorations due to differences in the surface characteristics.MethodsBoth direct and CAD/CAM RBCs were tested. Specimens were obtained from each group, polished, cleaned, stored in artificial saliva (1 w), then sterilized under UV (24 h). Specimens’ surface was assessed using profilometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction; resin/filler content was assessed using thermogravimetry. After pre-incubation with sterile human saliva (24 h), the microbiological behavior of the materials was assessed using four models: Streptococcus mutans adherence (2 h), S. mutans biofilm formation in an orbital shaking bioreactor (24 h), S. mutans biofilm formation in a continuous-flow bioreactor simulating shear forces (24 h), and mixed-plaque formation in the bioreactor (24 h). The viable biomass adhering to the specimens’ surfaces was measured using a tetrazolium dye-based test. Statistical analysis included verification of normality of distribution and homoscedasticity, then Oneway ANOVA and Tukey's test (α = 5%).ResultsWhen using the bioreactor setup, CAD/CAM RBCs generally yielded lower S. mutans and mixed-plaque biofilm formation compared to direct RBCs. This difference was not evidenced in the first two microbiological models. Differences in manufacturing and curing processes rather than in materials’ surface roughness and composition could explain these results.SignificanceCAD/CAM RBCs are promising materials from a microbiological point of view, featuring reduced biofilm formation on their surfaces when shear conditions similar to in vivo ones are present.     

Human epithelial tissue culture study on restorative materials

Objectives

Health condition of the gingival tissues contacting the surfaces of fixed prostheses is a result of multiple etiologic factors. The aim of the investigation discussed here was to evaluate the attachment and proliferation rate of cultured human epithelial cells on three commonly used restorative materials under in vitro conditions.

Methods

Morphological and chemical structure of polished lithium-disilicate (IPS e.max Press, Ivoclar Vivadent AG, Germany), yttrium modified zirconium dioxide (5-TEC ICE Zirkon Translucent, Zirkonzahn GmbH Srl, Germany) and cobalt chromium alloy (Remanium star, Dentaurum GmbH & Co. KG, Germany) discs were examined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and atomic force microscopy (AFM). Human epithelial cells harvested and cultured from one donor, were applied to investigate cell attachment (24 h observation) and proliferation (72 h observation) via dimethylthiazol-diphenyl tetrazolium bromide (MTT) and AlamarBlue^® (AB) assays on control surface (cell-culture plate) and on the restorative materials (n = 3 × 20 specimens/material).

Results

SEM and AFM revealed typical morphology and roughness features for the materials. Zirconia presented significantly higher R_a value. EDS confirmed typical elements on the investigated restorative materials: lithium-disilicate (Si, O); Zirconia (Zi, Y, O); CoCr (Co, Cr, W). All surfaces except CoCr exhibited significant cell proliferation according to MTT and AB assays after 72 h compared to 24 h. Among the restorative materials, CoCr samples showed the highest cell attachment as indicated by MTT assay. AB results showed that attachment and proliferation of human epithelial cells is supported more on lithium-disilicate. Both assays indicated the lowest value for zirconia.

Conclusions

The results indicate that the restorative materials examined are equally suitable for subgingival restorations. Lithium-disilicate exhibited the best biocompatibility.

Clinical significance

The examined materials are indicated for use in restorative procedures, directly contacting the sulcular epithelial tissues. Thus it is essential to monitor the biological acceptibility of these materials in order to better understand their clinical properties. The results indicate that Lithium-disilicate is a suitable material for such purposes.