Influence of storage humidity on hardness of light-cured glass polyalkenoate cements.

The influence of storage in various environments on the hardness of four commercial light-cured glass polyalkenoate cements and one conventional glass polyalkenoate cement was investigated. Specimens with or without light exposure were stored for 7 days in different humidity conditions. A hardness tester with a diamond indenter point was used and Vickers hardness numbers under minor load conditions were determined. Non-light-exposed specimens did not increase in hardness in either dry or wet conditions. Light-exposed specimens became harder with time in dry conditions. Light-exposed specimens stored in wet conditions hardened only slightly. To investigate the effects of humidity, some light-exposed specimens stored first in wet conditions were stored another 7 days in dry conditions. They became as hard as those first stored in dry conditions for 7 days. It is concluded that the hardness of these cements corresponds with the humidity of the storage environment.

[Measurements of the elastic and permanent deflection of MOD restorations during vertical loading]. / Messung der elastischen und bleibenden Aufbiegung von mod-Füllungen bei vertikaler Belastung.

In a loading device the mesio-distal deflection of mod restorations caused by different forces is measured reproducibly with inductive transducers. The accuracy of the measurements is about +/- 1 micron. Uncemented inlays of a soft gold casting alloy deflect 40 microns under load and 25 microns permanently; for an extra hard gold casting alloy the maximum values amount to 30 and 5 microns, respectively, and for a silver palladium alloy to 15 and 2 microns, respectively. Restorations of a non-gamma-2 amalgam reveal deflections within the range of accuracy near 2 microns.

Clinical assessment of the colour stability of resin filling materials.

The clinical estimation of colour stability depends on the quality of illumination and visibility (Table I). Every observer should be aware that not only the eye but also he himself has several shortcomings. In clinical research the precision can be raised by well-defined characteristics, by recording the initial stage and by trained investigators. There are no suitable instruments for determining the colour of curved and partially hidden restorations or of the confluent shades of teeth. As indicated in Fig. 2 visual inspection renders results which characterize the resin material. For the patient minor discolourations are often hidden by not uniform illumination and reflections.

[Heat expansion of composite resins stored in water]. / Wärmeausdehnung in Wasser gelagerter Füllungskunststoffe.

Thermal expansion coefficients between 10 C and 60 C were determined in 10 degree increments with 10 plastic filling materials and two plastics used for protheses (3 specimens each). The coefficients became larger as the temperature increased. The composites with 20 to 60.10(-6)/C are closest to the thermal expansion coefficient of the tooth; unfilled plastics with 80 to 130.10(-6)/C, the farthest removed. Plastics containing less anorganic filling material demonstrated thermal expansion coefficients between 70 and 90.10(-6)/C. Water absorption did not appear to influence the expansion.

[Water retention and solubility of composite resins dependent on the mixing ratio or the irradiation time]. / Wasseraufnahme und Löslichkeit von Füllungskunststoffen in Abhängigkeit vom Mischungsverhältnis bzw. von der Bestrahlungszeit.

The deviations in the mixture ratio of 8 paste-paste-systems and 1 powder-fluid system with 50% and 100% each of both components were studied. The quality was examined in relation to the irradiation time with 7 photopolymer cured filling materials. The chemically initiated polymerization of filling material was altered so little by deviations in the mixture ratio that there was no general increase in water absorption. Six of the 9 cured filling materials however showed a significant increase in solubility. The 6 photopolymer cured filling materials tempered with ultraviolet light, in the area examined, showed no obvious alterations in water absorption; all others however with the shorter irradiation periods demonstrated a significant increase in solubility. Tempering of resin polymerized with light required disproportionately long irradiation periods. Water absorption and solubility were accordingly high for the short irradiation periods. The differences between the various materials are more striking than are the differences due to variations in processing.

Dental operating lights and illumination of the dental surgery.

The requirements laid down in national and international standards and draft standards provide helpful guidelines for optimum illumination (Fig. 1, Table I). General room illumination with 500 lx and illumination of the working area with 1000 lx are best achieved with a larger number of fluorescent lamps on the ceiling above and in front of the dental chair. Daylight white lamps with good colour rendering (e.g. Osram colour 19 or Philips colour 47) are a good combination with changing daylight and the colour of light of the operating light. The colour of external skin, mucous membrane and teeth appears natural. The eight surgical lights examined differ in quality (Figs. 2-9). The maximum illuminance is between 9000 and 21 000 lx and is thus sufficiently high. The evenness of light distribution within an ellipse 9 cm and 18 cm in diameter is between 1 : 4 and 1 : 15 (Figs. 10 and 11). Illuminance can be adjusted to the work in hand by means of controls. If the patient looks into the operating lights (Figs. 2c and 9c), maximum luminances of 5 cd/cm2-20 cd/cm2 occur 8 cm above the illuminance maximum in six operating lights. Luminances of more than 20 cd/cm2 cause squinting and running eyes. A light fitting with more than 200 cd/cm2 should not be used. A sharp fall in illuminance (distinct light/dark threshold) and low luminances to the patient's eyes can be achieved with very directed light. Very directed light leads to very heavy shadows. Similarly, less specifically directed light leads to softer shadows so that objects in the oral cavity can be discerned easily, but the patient is no longer dazzled. The following operating lights can be recommended if the patient is to suffer as little glare as possible: Den-Tel-Ez Daray, and Belmont Type 040, Faro Sunlight S 70, Ritter Super Starlite; as well as: Chirana Fax, Siemens Sirolux. The following can be recommended for good illumination of the oral cavity: Belmont Type 040, Chirana Fax, Emda Top Spot, Faro Sunlight S 70, Pelton and Crane Light Fantastic Plus, Ritter Super Starlite, Siemens Sirolux. The colour temperature, heat radiation, easy handling, stability and price are also important for qualitative assessment.

[Abrasion in modeling materials]. / Abrieb an Modellwerkstoffen.

Ten frequently used hard plasters (Types 3 and 4 in accordance with DIN 13911) and 5 current modelling plastics have been investigated. Abrasion with testing forces of 1, 2 and 5 N were determined on samples 2 mm broad and about 12 mm long. The amount of abrasion could be calculated from the loss in weight. Only Kol-Dur and the plastics Diemet, Impredur and Alpha-Die are sufficiently reliable not to become damaged by abrasion on wax modelling (abrasion less than 5 micrometer). Hard plasters are not hard enough to resist abrasion. Taking into account the bending strength and modulus of elasticity, only Kol-Dur and Diemet can be recommended. Because of the improved dimensional stability of the hard plasters, Alca Dental Stone, Begolith, Duralit, Tewstone or Ferrodur can be recommended if the bending properties and a possible slight abrasion are taken into consideration. With the hard plasters, damage of more than 10 micrometer is easily possible.