Heinz Lüthy

Flexural strength of Cerec 2 machined and jointed InCeram-Alumina and InCeram-Zirconia bars.

OBJECTIVE The flexural strength of Cerec 2 InCeram-Alumina and InCeram-Zirconia bars is evaluated. The focus of the in vitro study is to identify a jointing procedure for InCeram which may be used for producing full-ceramic fixed-partial-denture frameworks. METHODS Six groups (n=15) of machined and jointed InCeram-Alumina (T1-T5) and InCeram-Zirconia (T6) bars (3x4x13mm(3)), respectively, were examined using a 3-point-bending test. InCeram-Alumina joint-free controls were: machined (C1), slip cast (C2, C3) and cut from the block (C4) bars. Machined joint-free InCeram-Zirconia bars were used as controls (C5). InCeram-Alumina slip was used for jointing T1-T5 and InCeram-Zirconia slip for bars T6. Bars were jointed in groups T1 and T2 using butt joint (S1), in T3 and T4 oblique (S2, S3) and in T5 and T6 rounded (S4) joint shapes. RESULTS Two-way analysis of variance showed significant differences between materials (p<0.001) and jointing shapes (p<0.001). The rounded (S4) shape showed the highest flexural strength of 434 (65) MPa of InCeram-Alumina (T5) and 475 (54) MPa of InCeram-Zirconia (T6) bars, respectively but machined/joint-free InCeram-Alumina (511 (59) MPa, C1) and machined/joint-free InCeram-Zirconia (624 (58) MPa, C5) were significantly (p<0.01/p<0.001) stronger. No significant differences (p>0.05) were found between machined/jointed InCeram-Zirconia (475 (54) MPa, T6), joint-free InCeram-Alumina slip cast (498 (125) MPa, C2) and joint-free InCeram-Alumina machined bars (511 (59) MPa, C1). SIGNIFICANCE Compared to conventional slip cast InCeram-Alumina the flexural strength of machined/jointed InCeram-Zirconia appears to be adequate for fixed-partial-denture frameworks.

Factors influencing metal-resin tensile bond strength to filled composites

This study evaluated the effect of metal surface conditioning, application of a silicon layer, water storage, and resin filling on tensile bond strength of a metal-resin system using three experimental composites (un-, micro-, and macrofilled) having the same self-curing resin composed of Bis-GMA and TEGDMA (2:1 wt%). Test specimens were prepared by bonding the resin between pairs of Ni-Cr-Be alloy cast disks (diameter, 8 mm) previously subjected to heat treatments simulating porcelain firing procedures. A specially constructed apparatus facilitated the absolutely parallel alignment and orientation of the disk faces to each other, maintaining a constant resin thickness of 100 microns. Before being bonded, the sand-blasted metal surfaces were either electrolytically etched and/or silicoated. Prior to being tested, assemblies were stored in water at 37 degrees C for one and 30 days. Thereafter, the specimens were processed in a universal testing machine at a cross-head speed of 2 mm/min until failure. Bond strengths ranged from 4.2 to 20.5 MPa. Data were analyzed by ANOVA with a factorial design (conf. level = 99%). The results showed that: (i) bond strength was increased when the metal was silicoated, (ii) the combination of sandblasting/silicoating produced the best values, and (iii) the 30-day water storage combined with silicoating enhanced the strength of the bond. The resin filling had no significant effect, indicating that neither its presence nor type affects bonding strengths to metal.

Corrosion considerations in the brazing repair of cobalt-based partial dentures

Cobalt-based alloys (Co-Cr-Mo) are usually used in dentistry as frameworks for removable partial dentures. In their basic form these structures function successfully. However, modifications or repairs of the frameworks may reduce their resistance to corrosion and, as a consequence, may provoke biologic reactions in the soft tissues. These reactions may be the result of different types of alloys that contact each other and, in the presence of saliva (based on potential differences), produce a galvanic cell. In this study, a clinical situation after repair of a removable partial denture was examined. The metallographic study of the prosthesis revealed a brazed zone where a gold braze was joining the Co-Cr-Mo framework with a Co-Cr-Ni type alloy (without Mo). The latter revealed signs of corrosion. Various electrochemical parameters (Ecorr, Ecouple, icorr, icouple) of these alloys were analyzed in the laboratory. The Co-Cr-Ni alloy had the lowest nobility and underwent galvanic corrosion in a galvanic couple with gold braze.

Dentalwerkstoffe und Dentalimplantate – Teil 1

Im vorliegenden Kapitel werden Dentalwerkstoffe erlautert (Tabelle 88.2), die in der Prothetik, in der konservierenden Zahnheilkunde, der Parodontologie, der Kieferchirurgie, der Kieferorthopadie und in der Kinderzahnmedizin eingesetzt werden [1]. Die Dentalwerkstoffe sind dem sehr agressiven Mundmilieu ausgesetzt. Es werden dabei folgende intraorale Einflusse wirksam:

Dentalwerkstoffe und Dentalimplantate

Im vorliegenden Kapitel werden Dentalwerkstoffe erlautert (Tabelle 69.2), die in der Prothetik, in der konservierenden Zahnheilkunde, der Parodontologie, der Kieferchirurgie, der Kieferorthopadie und in der Kinderzahnmedizin eingesetzt werden [1]. Die Dentalwerkstoffe sind dem sehr agressiven Mund milieu ausgesetzt. Es werden dabei folgende intraorale Einflusse wirksam: Speichel: Wasser (99%), organische Bestandteile (z. B. Proteine), anorganische Bestandteile (z. B. Chlorid-Ionen), geloste Gase (z. B. O2), Induktion von Korrosion [2] Nahrung: variierende chemische Zusammensetzung, Variation des pH-Werts, Temperaturwechsel Medikamente (chemische Einflusse) Karieshemmende Mittel: Fluoride Bakterien: Freisetzung von Sauren Mechanische Beanspruchungen: Kauen (Materialermudung, -abrieb) Bursten, Bruxismus usw. Hochste und geringste gemessene Kaudruckkrafte werden von 216 N bis 637 N angegeben [4, 5]. Unter Bruxismus versteht man den unbewussten Zahnkontakt mit Kaubewegungen, die zu einer Abrasion der Zahne fuhrt [3]. Bei den Metallen finden beispielsweise folgende Normen Anwendung: EN ISO 1562: 1995 „Dental-Goldgusslegierungen“, EN ISO 8891: 1995 „Dental-Gusslegierungen mit einem Edelmetallanteil von 25% bis unter 75%“, EN ISO 9693: 1994 „Metall- Keramik-Systeme fur zahnarztliche Restaurationen“.