International Abstracts 245

polymorphic forms occurred more readily than those between SiO, polymorphic forms. The reconstructive transformation of a B-berlinite to /%ristalphite occurred at about 900-I OOO”C, and was accompanied by volume expansion of 20 per cent Aluminium orthophosphate was neither decomposed by heat treatment (1400°C. 1 h) nor reacted with silica, alumina, magnesia, graphite and dental cast alloy. Aluminium orthophosphate was found to be suitable for use as a dental investment. (15 references) H. Hisamitsu

Studies on new dental investment containing aluminium orthophosphate. Part 2. Application of refractory material for dental investment. Kamemizu H., Takezawa Y., Imur3 I. et al. (1987) Jap. J Dent. Mater. 6. 248-254.

Two types of new dental investments were developed for low- and high-temperature castings by using AIPO, as a substitute for SiO,, which has been used as a refractory material in many commercially available investments. Heating of AIPO, at higher temperatures resulted in the formation of berlinite and cristalphite with the ratio of their phases depending on the heating temperature. The low-temperature investments prepared by mixing 20 per cent by weight of gypsum with 80 per cent by weight of the mixture of berlinite and crystalphite, i.e. gypsum- bonded investment, showed 2 per cent greater heating expansion at 900°C as the amount of crystalphite increased. Heating expansion of the high-temperature investment prepared by mixing 20 per cent by weight of NH,H,PO, and MgO with 80 per cent by weight of berlinite was more than 7 per cent at 1000°C. Using this investment with no appreciable setting expansion, it is possible to compensate for casting shrinkage by heating expansion alone, thus avoiding possible deformation of patterns during setting expansion. (5 references) H. Hisamitsu

Correlation between rigidity of adherends and bond strength of resin adhesives. Nakanura K., Kikuchi T., Sato M. et al. (1987) Jap. J Dent. Mater. 6. 327-333.

The relationship between the bond strength and rigidity of adherends was examined using commercial dental resin adhesives. The adherends were seven alloys with Vickers hardness numbers of 1 O-220, together with human and bovine teeth. The alloys were plated with tin to make the bonding activity uniform.

In the case of the alloys, there exists an obvious relation between hardness (x) of adherends and bond strength (y). The regression equations were y = 1 .O 1 x + 140 for resin cement of 4-M ETA-TBB-0 system, and y= 1-04x + 1 1 1 for that containing phosphate ester as a promotive monomer. In respect of teeth, although the strongest correlation was observed between the distance (pm) from enamel surface and bond strength, there was no correlation between bond strength and hardness. In addition, the increasing gradient of bond strength for hardness of enamel is relatively small compared to that of the alloys. As the bovine teeth were similar to human teeth in bond strength, bovine teeth were considered to be suitable substitutes for human teeth in these adhesion tests. (1 1 references) H. Hisamitsu

A short-term clinical evaluation of etched casting resin-bonded bridges fabricated utilizing CkCr alloy. Lui Li et al. (1987) Chin. J Stomatol. 22, 325-326.

Fifty cases of etched cast resin-bonded bridges fabricated utilizing cobalt-chromium alloy for posterior teeth were observed clinically. Before cementing, the fitting surface of the alloy in the control group was rinsed with water, while in the experimental group it was put in 18 per cent HCI and then rinsed with water. The results of a follow-up survey after 6 months were as follows: The retentive failure rate was 4 per cent in the experimental group, with failure at the interface between the composite resin and the etched enamel. The retentive failure rate of the control group was 24 per cent, with failure occurring at the interface between the composite resin and the alloy.

The difference between the two groups was significant. (4 references) Liao Fang-gang and Wei Yi

Directly measuring the galvanic current of different metal prostheses in the oral cavity. Guo Qing Xue et al. (1987) Chin. J. Stomato/. 22,348-350.

Different metal prostheses in the oral cavity produce galvanic irritation to the gnathostomatic system and the body. Electromotive forces of different metal prostheses of 153 cases were directly measured in the oral cavity. Results showed that there was a strong correlation between the galvanic current and the electrochemical characteristics of the metal prosthesis. The mean electromotive force between setting amalgam and gold alloy was 056 V& 007, and 0 11 Vf 003 after the amalgam had set completely (8 references) Liao Fang-gang and Wei Yi

Consideratii asupra igenarizaii protezelor acrilice. (Cleansers for acrylic resin dentures.) Pop E.. Grivu 0.. Pop M. et al. (1987) Stomatologia (Bucuresti) 34, 127-l 30.

The bacteriostatic action on acrylic resin of three representative proprietary denture cleansers (alkaline hypochlorite, perborate and dilute acid), manufactured outside Romania, were compared with two Romanian general-purpose disinfectants. Five dentures, which had been in use for up to 6 years, were tested. Each denture was immersed for 20 min in a different cleanser at 2-day intervals; smears were then taken and plated.

All the cleansers appreciably reduced bacterial activity. The general-purpose disinfectants (Perogen, Bromocet) were more effective than the specialized denture preparations (Denclen, Leodent Super Quick’s). Perogen, an oxidizing cleanser, was superior to Bromocet a cationic detergent consisting of a 10-20 per cent solution of ethyl p yridine in eth yi alcohol. However, these products may possibly cause tissue irritation, as well as deterioration of acrylic resin. (6 references) M. J. Shapiro