Sibylle Schneider-Feyrer

Wear performance of dental ceramics after grinding and polishing treatments.

AIM The aim of this in vitro study was to determine the two-body wear resistance of different dental ceramics after grinding and polishing treatments. MATERIAL AND METHODS Standardized specimens were prepared from three zirconia and two veneering ceramics and were subjected to different surface treatments. Zirconia ceramics were polished, ground and repolished, veneering ceramics were ground and repolished. One zirconia ceramic was investigated with a superficial glaze. Human enamel was used for reference. Surface roughness R(a) was determined using a profilometric contact surface measurement device. Two-body wear tests were performed in a chewing simulator with steatite and enamel antagonists, respectively. Specimens were loaded pneumatically in a pin-on-block design for 1.2x10(5) mastication cycles (50 N, 1.2 Hz, lateral movement: 1 mm, mouth opening: 2 mm) under simultaneous thermal cycling (600 cycles, 5/55 °C). Wear depths of specimens were determined using a 3D laser scanning device, wear areas of steatite antagonists were measured by means of light-optical micrographs. Means and standard deviations were calculated, and statistical analysis was performed using one-way analysis of variance (ANOVA) and the Bonferroni multiple comparison test for post hoc analysis (α=0.05). Scanning electron microscopy was applied for evaluating the wear performance of ceramics and antagonists. RESULTS No wear was found for polished, ground and repolished zirconia. Compared to the wear depths of the enamel reference with 274.1±187.4 μm versus steatite and 123.3±131.0 μm versus enamel, relative wear depths of porcelains ranged between 0.54±0.07 and 0.62±0.09 with steatite antagonists and between 0.66±0.26 and 1.04±0.27 with enamel antagonists. Relative wear areas of steatite antagonists (enamel reference: 1.25 mm(2)) varied between 0.84±0.13 and 1.90±0.29 for zirconia and between 1.97±0.38 and 2.47±0.40 for porcelains. Enamel antagonists generally showed wear, cracks or even fractures, but revealed smooth surfaces when opposed to polished/ground/repolished zirconia and ploughed surfaces when opposed to ground/repolished porcelains or glaze. CONCLUSIONS Zirconia ceramics yielded superior wear behavior and lower antagonistic wear compared to porcelains. A trend to higher ceramic and antagonistic wear was shown after grinding treatments.

Influence of surface properties of resin-based composites on in vitro Streptococcus mutans biofilm development

The aim of this in vitro study was to evaluate the influence of physicochemical surface properties of resin-based composites on Streptococcus mutans biofilm formation. Specimens were prepared from each of four resin-based composites by polymerization against Mylar strips. Half of the number of specimens received no further surface treatment, whereas the other half were subjected to a polishing treatment. Surface roughness (SR) and topography were assessed using profilometry and atomic force microscopy. Surface free-energy (SFE) was determined, and the chemical surface composition was analysed by X-ray photoelectron spectroscopy (XPS). S. mutans biofilms were formed on the surface of the resin-based composite specimens for either 48 or 96 h using an artificial mouth system (AMS). Polishing caused a significant decrease in SFE, and XPS analysis indicated an increase of surface silicon and a decrease of surface carbon. Only for Grandio was a significant increase in SR identified after polishing, which was probably related to the higher concentration of filler particles on its surface. Significantly less S. mutans biofilm formation was observed on polished resin-based composites than on unpolished resin-based composites. These results indicate that the proportions of resin matrix and filler particles on the surface of resin-based composites strongly influence S. mutans biofilm formation in vitro, suggesting that minimization of resin matrix exposure might be useful to reduce biofilm formation on the surface of resin-based composites.

Influence of substructure design, veneer application technique, and firing regime on the in vitro performance of molar zirconia crowns.

OBJECTIVES The aim of this in vitro study was to evaluate the influence of substructure design, veneer application technique, and firing regime on the failure and fracture resistance of molar zirconia crowns. METHODS Six groups (n=8/group) of zirconia crowns were fabricated in simple core (SC) or anatomically reduced (AR) design, veneered with different feldspathic or glass ceramic materials, and defined according to the application technique and firing regime (LT: layering technique; LT_L: LT with long-term cooling; PT: press technique; DV: digital veneering technique). The following groups were investigated: SCLT, ARLT, SCLT_L, SCPT, ARPT, ARDV. Crowns were adhesively bonded to polymethylmethacrylate abutment teeth and subjected to thermal cycling (TC: 2×3000×5°/55°) and mechanical loading (ML: 1.2×10(6); 50N; 1.6Hz) in a chewing simulator with metal-ceramic molar crowns as antagonists. Failures were monitored and fracture resistance determined after aging. Data were statistically analyzed (one-way analysis of variance, ANOVA; post hoc Bonferroni, α=0.05). Crowns were subjected to scanning electron microscopy for fractographic failure analysis. RESULTS Failures (chipping, cracks) during TCML were observed in groups SCLT (2×), ARDV (2×) and SCLT_L (1×). Defect sizes varied between 3.5mm (SCLT: crack) and 30.0mm(2) (SCLT_L: chipping). Mean (SD) fracture forces ranged between 1529.0 (405.2)N for SCPT and 2372.3 (351.8)N for ARDV. SIGNIFICANCE The failure frequency of veneered zirconia crowns could be reduced by using anatomically reduced substructures, the press veneering technique, and an adapted cooling protocol. Fracture resistance increased with use of anatomically reduced substructures and the digital veneering technique.

Streptococcus mutans biofilm formation and release of fluoride from experimental resin-based composites depending on surface treatment and S-PRG filler particle fraction

PURPOSE To evaluate fluoride release and biofilm formation on resin-based composites (RBCs) including surface pre-reacted glass ionomer (S-PRG) filler particles. MATERIALS AND METHODS Specimens were prepared from experimental RBCs including different fractions of S-PRG fillers (0/10/30/50/70% w/v). RBCs were light cured against mylar strips (MYL), and 50% of the specimens were additionally polished to a high gloss (POL). Surface roughness (SR), surface free energy (SFE) and fluoride release were determined. Streptococcus mutans biofilm formation (SMBF) was simulated for 48 h and 120 h; adherent viable biomass was assessed using an MTT-based assay. RESULTS The highest SR was identified for POL specimens manufactured from the RBC with a filler fraction of 70%. For all specimens and surface treatments, polishing caused an increase in surface free energy. For both MYL and POL specimens, increasing the filler fraction coincided with an increased release of fluoride; a higher release of fluoride was identified for POL specimens with filler fractions of 50% and 70% in comparison to their MYL counterparts. Release of fluoride was lower after 120 h than after 48 h. No differences in SMBF were identified between MYL and POL specimens with identical filler fractions after 48 h of biofilm formation; with increasing filler fractions, a tendency towards decreasing SMBF was observed. After 120 h, less SMBF was identified for POL specimens with filler fractions of 30%, 50% and 70% in comparison to corresponding MYL specimens. CONCLUSION The inclusion of S-PRG fillers and an effective surface treatment may reduce biofilm formation on RBCs.

Surface properties of monolithic zirconia after dental adjustment treatments and in vitro wear simulation

OBJECTIVES To investigate the surface properties (roughness, composition, phase transformation) of monolithic zirconia specimens after dental adjustment procedures (grinding, polishing) and wear simulation. METHODS Zirconia specimens (Cercon base, Cercon ht, DeguDent, G; n=10/material) were successively sintered, ground, and polished with an intraoral polishing kit in a three-step procedure. Sintered zirconia specimens with high surface roughness served as a reference. For each treatment step, wear simulations with steatite plates (d=10 mm) as antagonists were conducted as well as surface roughness tests (Ra), EDX analysis, and X-ray diffraction (XRD) measurements. SEM pictures were taken, and data were statistically analyzed (one-way ANOVA, post hoc Bonferroni, α=0.05). RESULTS Grinding significantly (p=0.000) increased the roughness of sintered zirconia up to values of 1.36±0.11 μm (Ra). Polishing significantly (p=0.000) reduced Ra. The lowest roughness value after the final polishing step was 0.20±0.03 μm. Wear testing resulted in a further slight decrease of Ra. After the grinding procedure, SEM pictures showed deep grooves that were progressively smoothed by polishing. The EDX spectra showed that magnesium was transferred from steatite antagonists to zirconia by wear. In the XRD-patterns, monoclinic (m) peaks were observed after grinding and polishing. The maximum intensity ratio between the m (11-1) peak and the tetragonal t (111) peak decreased after the completion of all polishing steps. Wear did not induce phase transformation. CONCLUSIONS Adequate polishing reduced the roughness of ground zirconia. Wear had little influence on roughness and no influence on phase transformation. CLINICAL SIGNIFICANCE Careful polishing is recommended to keep surface roughness and phase transformation low.

Cycle-dependent in vitro wear performance of dental ceramics after clinical surface treatments.

AIM To investigate the two-body wear performance of dental ceramics after different clinical surface treatments as a function of number of wear cycles. MATERIAL AND METHODS Standardized specimens (n=72/material) were prepared from two different zirconia ceramics, a veneering porcelain, and a lithiumdisilicate glass ceramic. Specimens were progressively glazed, ground, and polished. After each treatment step 24 specimens per material were kept at the obtained surface state. Steatite and human enamel specimens served as reference materials. Two-body wear tests were performed with steatite spheres as antagonists in a pin-on-block design (50N, 1.6 Hz, lateral movement: 1mm, mouth opening: 2mm) under simultaneous thermal cycling (5/55 °C, 2 min/cycle). For investigating the dynamic evolution of the wear process, 9 groups per material (n=8/group) were defined, differing in surface state (glazed, ground, and polished) and number of chewing cycles (40T, 80T, and 120T; T: ×1000): glazed 40T, glazed 80T, glazed 120T, ground 40T, ground 80T, ground 120T, polished 40T, polished 80T, polished 120T. Surface roughness, wear depth of the specimens and relative wear area of the steatite antagonists were determined using an optical 3D laser scanning microscope. SEM evaluation was done. Mean values and standard deviations were calculated and statistically analyzed (one-way ANOVA, post-hoc Bonferroni, α=0.05). RESULTS Veneering and lithiumdisilicate ceramics showed higher wear depths than zirconia ceramics (p<0.05). Wear of veneering and lithiumdisilicate ceramics and their antagonists increased with wear cycles but was only marginally influenced by the initial surface state. Wear of zirconia was not influenced by wear cycles but antagonists of zirconia showed a cycle-dependent wear increase. Polished zirconia surfaces showed lowest wear for material and antagonist. Wear mechanism of common ceramics was characterized by abrasive wear. Zirconia in contrast showed a superficial cyclic shifting of worn material of the antagonist. CONCLUSIONS Wear of zirconia and standard ceramics showed different wear performances, strongly influenced by surface treatments as well as number of wear cycles.

The Effectiveness of Polishing Kits:: Influence on Surface Roughness of Zirconia

This study investigated the effectiveness of intraoral and technical polishing kits. Zirconia specimens were sintered, ground, and polished with 14 different two-step or three-step polishing kits. Surface roughness (Ra, Rz) after each treatment step was determined, and scanning electron micrographs were made. Except for one system, all polishing kits were effective in reducing the surface roughness of ground zirconia. Differences in surface roughness were high after the first polishing step but were reduced to Ra/Rz values similar to or lower than those of the sintered reference after the final polishing step. Achieving smooth surfaces depended on a sequential application of all polishing steps.

In Vitro Shock Absorption Tests on Implant-Supported Crowns: Influence of Crown Materials and Luting Agents

PURPOSE To investigate the force absorption capacity of implant-supported crowns made of different restorative materials and connected to abutments with different luting agents. MATERIALS AND METHODS Molar crowns were milled of different computer-aided design/computer-aided manufacture materials (n = 8 crowns per material): polymethyl methacrylate, polyether ether ketone, composite, lithium disilicate, titanium, and zirconia. Crowns were mounted on titanium implant replicas using different luting agents: uncemented, temporarily cemented (zinc oxide-eugenol cement), conventionally cemented (zinc oxide phosphate cement), and adhesively bonded. As a reference, one implant replica was tested without a crown. Force absorptions of the different combinations of crown materials and luting agents were determined by applying an increasing force (0 to 250 N) on the occlusal crown surface and measuring the resulting force below the implant. Mean curves of applied and resulting forces up to 200 N were determined (six measurements per group), and slopes were calculated. Statistical analysis was performed (one-way analysis of variance, Bonferroni post hoc test, α = .05). RESULTS Significant (P < .001) differences in the applied and resulting forces were found between the crown materials that were uncemented, temporarily cemented, cemented, and adhesively bonded. Materials with higher moduli of elasticity (ceramics, titanium) showed steeper slopes of the force curves and lower shock-absorbing capacity than resin-based materials, but were influenced more by the luting agents. The damping effects of resin-based materials were higher in combination with all cementation and luting modes. CONCLUSION Shock absorption tests exhibited a strong material-dependent damping behavior of implant-supported crowns. The shock-absorbing capacity of crown materials with high moduli of elasticity may benefit from conventional cementation.

In vitro performance of one- and two-piece zirconia implant systems for anterior application.

OBJECTIVES To investigate the long-term in vitro performance and fracture resistance of one-piece and bonded two-piece zirconia implant systems for anterior application. METHODS Two groups of bonded two-piece zirconia (ZZB), four groups of one-piece zirconia (Z), and two groups of two-piece titanium (TTS, reference) implant systems were restored with identical monolithic zirconia crowns (n=10/group). Eight specimens per group were mounted at an angle of 135° in the chewing simulator and subjected to thermal cycling (TC:18,000 cycles; 5°/55°) and mechanical loading (ML:3.6×10(6) cycles; 100N) simulating an anterior situation. Fracture resistance and maximum bending stress were determined for specimens that survived aging and for two references per group after 24h water storage. SEM pictures were used for failure analysis. Data were statistically analysed (one-way-ANOVA, post-hoc Bonferroni, Kaplan-Meier-Log-Rank, α=0.05). RESULTS A one-piece zirconia and a two-piece titanium implant system survived TCML without failures. Both bonded two-piece zirconia implant systems and a one-piece zirconia implant system totally failed (fractures of abutment or implant). Failure numbers of the other systems varied between 1× (1 group) and 5× (2 groups). Significantly different survival rates were found (Log-Rank-test: p=0.000). Maximum fracture forces/bending stresses varied significantly ( ANOVA p=0.000) between 188.00±44.80N/381.02±80.15N/mm(2) and 508.67±107.00N/751.45±36.73N/mm(2). Mean fracture values after 24h water storage and TCML were not significantly different. CONCLUSION Zirconia implant systems partly showed material defects or connection insufficiencies. Bonded two-piece systems had higher failure rates and lower fracture resistance than one-piece implants. CLINICAL SIGNIFICANCE Individual zirconia implant systems may be applied in anterior regions with limitations.

Biofilm formation on denture base resin including ZnO, CaO, and TiO2 nanoparticles

PURPOSE This laboratory study aimed to investigate the effect of doping an acrylic denture base resin material with nanoparticles of ZnO, CaO, and TiO2 on biofilm formation. MATERIALS AND METHODS Standardized specimens of a commercially available cold-curing acrylic denture base resin material were doped with 0.1, 0.2, 0.4, or 0.8 wt% commercially available ZnO, CaO, and TiO2 nanopowder. Energy dispersive X-ray spectroscopy (EDX) was used to identify the availability of the nanoparticles on the surface of the modified specimens. Surface roughness was determined by employing a profilometric approach; biofilm formation was simulated using a monospecies Candida albicans biofilm model and a multispecies biofilm model including C. albicans, Actinomyces naeslundii, and Streptococcus gordonii. Relative viable biomass was determined after 20 hours and 44 hours using a MTT-based approach. RESULTS No statistically significant disparities were identified among the various materials regarding surface roughness and relative viable biomass. CONCLUSION The results indicate that doping denture base resin materials with commercially available ZnO, CaO, or TiO2 nanopowders do not inhibit biofilm formation on their surface. Further studies might address the impact of varying particle sizes as well as increasing the fraction of nanoparticles mixed into the acrylic resin matrix.