Christine Schille

Precision of an instrumentation-based method of analyzing occlusion and its resulting distribution of forces in the dental arch.

AbstractBackground and Objective:In practice, analysis of occlusion is reduced to depicting it with color-marking foils. Precise analysis that incorporates time resolution and plots the distribution of forces within the occlusion is not possible in the everyday clinical situation with the usual methods. T-Scan® III is a computer-assisted dental occlusion analyzer that depicts occlusion by means of pressure-sensitive foils. The aim of our study was to test the accuracy and reliability of this method.Subjects and Methods:The study population comprised 42 subjects (23 male and 19 female, aged 20–30, median age 26 years). The measurements were performed using the TScan® III from Tekscan Inc., South Boston, MA, USA. Six recordings with two foils were made for each subject and a total of 30 masticatory cycles were registered. Statistical analysis referred to the method’s measurement accuracy and reliability, as well as the influence of changing the foil and repositioning the T-Scan® III during the repeated measurements.Results:The percentage distribution of forces per tooth ranged from 0 to 41%. The mean measurement per tooth was 6.9% of the maximum total force exerted. The measurement error was 1%, the 1.96-fold measurement error calculated according to Bland & Altman (accuracy) was 2% and the 2.77-fold measurement error (reliability) was 2.8%. Neither changing the foil nor the repeated measuring had any statistically significant influences on the measured value.Conclusion:The measuring technique studied is superior to the usual methods, particularly with regard to force analysis per tooth. The level of accuracy is acceptable and no interference arising from change of foil or repeated measuring was detected. The method presented in this study therefore enhances routine diagnostics with marking foils. A combination of this method with marking foils would be ideal because the pressure-sensitive foils in this system do not produce any contact markings intraorally. This combination enables the contacts depicted on the computer to be assigned intraorally with even greater precision.ZusammenfassungHintergrund und Ziel:Die Analyse der Okklusion ist in der Praxis auf die Abbildung mit farbig markierenden Folien reduziert. Eine präzise zeitlich auflösende und die aufbauende Kraftverteilung darstellende Analyse ist mit den üblichen Methoden im klinischen Alltag nicht möglich. Ein Messverfahren, das computerunterstützt mit drucksensitiven Folien die Okklusion abbildet, ist das T-Scan®-III. Ziel unserer Untersuchung war es, Messgenauigkeit und Reliabilität dieser Methode zu prüfen.Probanden und Methodik:Die Studienpopulation bildeten 42 Probanden (23 männlich und 19 weiblich, 20–30 Jahre alt, Median 26 Jahre). Die Messungen wurden mit dem TScan® III der Firma Tekscan Inc., South Boston, MA, USA, durchgeführt. Bei jedem Probanden wurden insgesamt sechs Messaufzeichnungen mit zwei Folien und insgesamt 30 Kauzyklen aufgezeichnet. Die statistische Auswertung analysierte die Messgenauigkeit und Reliabilität der Methode sowie den Einfluss des Folienwechsels und der Repositionierung des T-Scan®-III während der Wiederholungsmessungen.Ergebnisse:Die prozentuale Kraftverteilung pro Zahn variierte von 0 bis 41%. Der mittlere Messwert pro Zahn betrug 6,9% der maximal entwickelten Gesamtkraft. Der Messfehler betrug 1%, der nach Bland & Altman berechnete 1,96fache Messfehler (Messgenauigkeit) betrug 2% und der 2,77fache Messfehler (Reliabilität) betrug 2,8%. Es wurden keine statistisch signifikanten Einflüsse am Messwert durch den Folienwechsel oder die Wiederholungsmessung festgestelltSchlussfolgerung:Das überprüfte Messverfahren ist, insbesondere aufgrund der Kraftanalyse pro Zahn, den üblichen Methoden überlegen. Die Messgenauigkeit ist akzeptabel und störende Einflüsse durch Folienwechsel oder wiederholte Messungen konnten nicht nachgewiesen werden. Das vorgestellte Verfahren stellt daher eine Ergänzung zur Routinediagnostik mit markierenden Folien dar. Ideal ist eine Kombination dieses Verfahrens mit markierenden Folien, da die drucksensitiven Folien des Messsystems keine Markierungen der Kontaktpunkte intraoral erzeugen. Durch eine Kombination sind die im Computer dargestellten Kontakte noch präziser intraoral zuzuordnen.

Comparison of different in vitro tests for biocompatibility screening of Mg alloys.

Standard cell culture tests according to ISO 10993 have only limited value for the biocompatibility screening of degradable biomaterials such as Mg alloys. The correlation between in vitro and in vivo results is poor. Standard cytotoxicity tests mimic the clinical situation to only a limited extent, since in vivo proteins and macromolecules in the blood and interstitial liquid will influence the corrosion behaviour and, hence, biocompatibility of Mg alloys to a significant extent. We therefore developed a modified cytotoxicity test simulating the in vivo conditions by use of bovine serum as the extraction vehicle instead of the cell culture medium routinely used in standard cytotoxicity testing according to ISO 10993-5. The modified extraction test was applied to eight experimental Mg alloys. Cytotoxicity was assayed by inhibition of cell metabolic activity (XTT test). When extraction of the alloy samples was performed in serum instead of cell culture medium the metabolic activity was significantly less inhibited for six of the eight alloys. The reduction in apparent cytotoxicity under serum extraction conditions was most pronounced for MgZn1 (109% relative metabolic activity with serum extracts vs. 26% in Dulbeccos modified Eagles medium (DMEM)), for MgY4 (103% in serum vs. 32% in DMEM) and for MgAl3Zn1 (84% vs. 17%), resulting in a completely different cytotoxicity ranking of the tested materials when serum extraction was used. We suppose that this test system has the potential to enhance the predictability of in vivo corrosion behaviour and biocompatibility of Mg-based materials for biodegradable medical devices.

Influence of surface treatment on the wear of solid zirconia.

Abstract Objective. Recently there has been talk of the use of full-contour solid zirconia crowns or bridge restorations with no porcelain overlay. This could be a useful solution for patients with bruxism or limited interocclusal space. However, the hardness of zirconia could affect the opposite natural dentition. The aim of this in-vitro study was to investigate the role of surface treatments on the wear of a zirconia material and its antagonist. Materials and methods. Fifty plates (10 × 10 × 1 mm) made of zirconia (LavaMulti™ ZrO2, 3M ESPE), divided into five equal groups, were sandblasted and ground under standardized conditions with a fine-grit diamond bur (Komet Brasseler, Germany) to simulate clinical conditions. Group (a) was only fired, (b) was fired and sandblasted, (c) only ground, (d) was ground and additionally polished (EVE Ceramic Polishing-Set, Pforzheim) and (e) was ground and glazed. Wear behavior was measured with a pin-on-disk apparatus ABREX against 6 mm steatite balls as antagonists (45°, 5 N load, 5000 cycles, water). The amount of wear was determined topographically using a 3-D profilometer (Concept 3D, Mahr, Germany) by measuring the height loss of the antagonist and the depth of wear Pt of the zirconia. Results. In groups (a), (b), (c) and (d) the wear value Pt could not be determined (<1 μm). Wear values of the antagonists (steatite balls) revealed a similar outcome in contact with (b), (c) and (e) in the range of 81–85 μm, whereas (e) was more abrasive but not significantly. A noticeable difference in the wear of the antagonist showed group (d) to have the smallest value. Conclusion. Polished zirconia seems to have the lowest wear on the antagonists, in contrast with the other kinds of surface treatment.

Fretting Corrosion Behavior of Experimental Ti-20Cr Compared to Titanium

Experimental cast titanium alloys containing 20 mass% chromium (Ti-20Cr) show preferable mechanical properties and a good corrosion resistance. This study evaluated the fretting corrosion behavior of Ti-20Cr. Ti-20Cr (n = 4) and commercially pure titanium (CP-Ti, n = 6) disk specimens were used. The fretting corrosion test was performed by electrochemical corrosion at 0.3 V in 0.9% saline solution and mechanical damage using 10 scratching cycles with three different scratching speeds (10–40 mm/s) at 10 N. After testing, the activation peak, repassivation time and surface morphology of each specimen were analyzed. The differences between the results were tested by parametric tests (α = 0.05). The average activation peaks were significantly higher in CP-Ti than in Ti-20Cr (p < 0.01), except at 20 mm/s. In the series of scratching speeds, faster scratching speeds showed higher activation peaks. The maximum activation peaks were also higher in CP-Ti. Slight differences in the repassivation time were observed between the materials at every scratching speed; faster scratching speeds showed shorter repassivation times in both materials (p < 0.05). CP-Ti showed severe damage and significantly higher wear depth than Ti-20Cr (p < 0.05). In conclusion, adding chromium to titanium reduced surface damage and improved the fretting corrosion resistance.

Mechanical Characteristics, In Vitro Degradation, Cytotoxicity, and Antibacterial Evaluation of Zn-4.0Ag Alloy as a Biodegradable Material

Zn-based biodegradable metallic materials have been regarded as new potential biomaterials for use as biodegradable implants, mainly because of the ideal degradation rate compared with those of Mg-based alloys and Fe-based alloys. In this study, we developed and investigated a novel Zn-4 wt % Ag alloy as a potential biodegradable metal. A thermomechanical treatment was applied to refine the microstructure and, consequently, to improve the mechanical properties, compared to pure Zn. The yield strength (YS), ultimate tensile strength (UTS) and elongation of the Zn-4Ag alloy are 157 MPa, 261 MPa, and 37%, respectively. The corrosion rate of Zn-4Ag calculated from released Zn ions in DMEM extracts is approximately 0.75 ± 0.16 μg cm–2 day–1, which is higher than that of pure Zn. In vitro cytotoxicity tests showed that the Zn-4Ag alloy exhibits acceptable toxicity to L929 and Saos-2 cells, and could effectively inhibit initial bacteria adhesion. This study shows that the Zn-4Ag exhibits excellent mechanical properties, predictable degradation behavior, acceptable biocompatibility, and effective antibacterial properties, which make it a candidate biodegradable material.

Influence of Pre-Sintered Zirconia Surface Conditioning on Shear Bond Strength to Resin Cement

This study analyzed the shear bond strength (SBS) of resin composite on zirconia surface to which a specific conditioner was applied before sintering. After sintering of either conditioner-coated or uncoated specimens, both groups were divided into three subgroups by their respective surface modifications (n = 10 per group): no further treatment; etched with hydrofluoric acid; and sandblasted with 50 µm Al2O3 particles. Surfaces were characterized by measuring different surface roughness parameters (e.g., Ra and Rmax) and water contact angles. Half of the specimens underwent thermocycling (10,000 cycles, 5–55 °C) after self-adhesive resin cement build-up. The SBSs were measured using a universal testing machine, and the failure modes were analyzed by microscopy. Data were analyzed by nonparametric and parametric tests followed by post-hoc comparisons (α = 0.05). Conditioner-coated specimens increased both surface roughness and hydrophilicity (p < 0.01). In the non-thermocycled condition, sandblasted surfaces showed higher SBSs than other modifications, irrespective of conditioner application (p < 0.05). Adhesive fractures were commonly observed in the specimens. Thermocycling favored debonding and decreased SBSs. However, conditioner-coated specimens upon sandblasting showed the highest SBS (p < 0.05) and mixed fractures were partially observed. The combination of conditioner application before sintering and sandblasting after sintering showed the highest shear bond strength and indicated improvements concerning the failure mode.

Influence of Different Framework Designs on the Fracture Properties of Ceria-Stabilized Tetragonal Zirconia/Alumina-Based All-Ceramic Crowns

The aim of this study was to evaluate the fracture load and failure mode of all-ceramic crowns with different ceria-stabilized tetragonal zirconia/alumina nanocomposite (Ce-TZP/A) framework designs. Four frameworks (anatomical shape: AS, with a buccal or lingual supporting structure: BS and LS, or buccal and lingual supporting structures: BLS) were fabricated. All frameworks were veneered with porcelain to fabricate all-ceramic crowns followed by cementation to tooth analogs. The fracture load of each crown either without or with pre-loading (1.2 million cycles, 49 N) was measured. The failure mode was classified into partial or complete fracture. Differences were tested for significance (p < 0.05) by a two-way Analysis of Variance (ANOVA), followed by Tukey’s test and by Fisher’s exact test, respectively. Without pre-loading, supporting structures did not influence the fracture load or failure mode. Partial fractures were the most common failure mode. Pre-loading promoted the severity of the failure mode, although the fracture load among the framework designs was not influenced. In the AS group, prefailures were observed during pre-loading, and complete fractures were significantly increased after pre-loading. In contrast, the failure mode of the BLS group remained unchanged, showing only partial fracture even after pre-loading. This Ce-TZP/A framework design, comprised of an anatomical shape with additional buccal and lingual structures, has the potential to reduce the chipping of the veneering porcelain.

Influence of a surface conditioner to pre-sintered zirconia on the biaxial flexural strength and phase transformation

OBJECTIVES To assess the influence of a surface conditioner applied to pre-sintered yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) on the biaxial flexural strength and phase transformation. METHODS Conditioner-coated specimens (12mm diameter×0.8mm thickness) were prepared by application of a slurry conditioner using a brush on pre-sintered Y-TZP discs, followed by sandblasting with 50-μm Al2O3 after sintering (C-SB) or no further treatment (C-NT). The remaining conditioner-free specimens were subjected to sandblasting before sintering (NC-SB) or were maintained without treatment (NC-NT). Surface roughness measurements and scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray spectroscopy (SEM-EDX) were performed for surface characterizations. The phase transformation of Y-TZP was identified by X-ray diffraction (XRD), and the biaxial flexural strength was measured using the piston-on-three-ball test according to ISO 6872:2015. The data were analyzed using nonparametric Kruskal-Wallis tests and Weibull distributions with the maximum likelihood estimation. RESULTS Sandblasting resulted in significantly rougher surfaces, irrespective of conditioner application. Conditioner layers were observed on surfaces in the C-NT and C-SB specimens. Monoclinic contents were present in a very small amount in the C-SB specimens. Both median biaxial flexural and characteristic strengths of all specimens exceeded ISO 6872:2015 requirements (Class 5: >800MPa), except the NC-SB specimens which showed significantly the lowest strength (p<0.001). Although no statistical difference was observed in Weibull modulus among the specimens (p=0.598), the NC-SB specimens showed the highest. SIGNIFICANCE Surface conditioner application does not affect the biaxial flexural strength and phase stability of Y-TZP and can be considered practical for clinical use.

Fracture resistance and failure modes of polymer infiltrated ceramic endocrown restorations with variations in margin design and occlusal thickness

PURPOSE The purpose of this in vitro study was to assess the effect of varying the margin designs and the occlusal thicknesses on the fracture resistance and mode of failures of endodontically treated teeth restored with polymer infiltrated ceramic endocrown restorations. METHODS Root canal treated mandibular molars were divided into four groups (n=8) and were prepared to receive Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) fabricated polymer infiltrated ceramic endocrowns (ENAMIC blocks). Group B2 represents teeth prepared with a butt joint design receiving endocrowns with 2mm occlusal thickness and the same for group B3.5 but with 3.5mm occlusal thickness. Group S2 represents teeth prepared with 1mm shoulder finish line receiving endocrowns with 2mm occlusal thickness and the same for group S3.5 but with 3.5mm occlusal thickness. After cementation and thermal aging, fracture resistance test was performed and failure modes were observed. RESULTS Group S3.5 showed the highest mean fracture load value (1.27±0.31kN). Endocrowns with shoulder finish line had significantly higher mean fracture resistance values than endocrowns with butt margin (p<0.05). However, the results were not statistically significant regarding the restoration thickness. Evaluation of the fracture modes revealed no statistically significant difference between the modes of failure of tested groups. CONCLUSIONS For the restoration of endodontically treated teeth, adding a short axial wall and shoulder finish line can increase the fracture resistance. However, further investigations, especially the fatigue behavior, are needed to ensure this effect applies with small increases of restoration thickness.

Influence of the Conditioning Method for Pre-Sintered Zirconia on the Shear Bond Strength of Bilayered Porcelain/Zirconia

This study evaluated the bond strength of veneering porcelain with an experimental conditioner-coated zirconia. Pre-sintered Y-TZP specimens (n = 44) were divided in two groups based on conditioning type. After sintering, all sample surfaces were sandblasted and layered with veneering porcelain. Additionally, half of the specimens in each group underwent thermal cycling (10,000 cycles, 5–55 °C), and all shear bond strengths were measured. After testing, the failure mode of each fractured specimen was determined. Differences were tested by parametric and Fisher’s exact tests (α = 0.05). The differences in bond strength were not statistically significant. Adhesive fractures were dominantly observed for the non-thermal cycled specimens. After thermal cycling, the conditioner-coated group showed cohesive and mixed fractures (p = 0.0021), whereas the uncoated group showed more adhesive fractures (p = 0.0021). Conditioning of the pre-sintered Y-TZP did not change the shear bond strength of the veneering porcelain, but did improve the failure mode after thermal cycling.