188 J. Dent. 1993;21:188-189

International Abstracts

Section Editor: W. R. E. Laird

Assistant Section Editor: Dr A. D. Walmsley

Inhibition of secondary caries by laminating restoration method with glass ionomer cement and composite resin. Torii Y., Kato R., lmazato S. et a/. (1990) Jap. J. Conserv. Dent. 33, 994-l 000.

The purpose of this study was to investigate the inhibition of marginal leakage and artificial secondary caries by a laminating restoration method with glass ionomer cement and resin composite. Class V cavities were prepared at the cement-enamel junction on the buccal and palatal surfaces of extracted human upper premolars. Glass ionomer cement was applied onto the dentine wall prior to light-cured composite resin restoration. Microleakage around restorations was estimated using a dye penetration test. Artificial secondary caries was formed by immersion of the teeth in acidified gelatin (pH 4.5) for 4 weeks. The depth of the lesion along the cavity wall was measured by microradiography. Glass ionomer cement restoration and resin composite restorations with bulk and two-layer incremental filling methods were also estimated. The main findings were as follows:

1. Without regard to incrementation, a resin composite presented poor sealing and severe secondary caries at the gingival margin.

2. Glass ionomer cement prevented artificial secondary caries around restorations effectively, although it presented poor sealing at the cement-enamel interface.

3. Laminated restoration with glass ionomer cement and resin composite presented the best marginal sealing and prevented artificial secondary caries effectively.

The results indicated that laminated restoration with glass ionomer and resin composite has an inhibitory effect on secondary caries. (24 references) H. Hisamitsu

Inhibition of the progress of root dentine caries in vitro by fluoride-releasing resin. Torii Y., Kato R., Ui T. et a/. (1990) Jap. J. Conserv. Dent. 33,1143-1150.

The purpose of this study was to investigate the inhibitory effect of a newly synthesized fluoride-releasing resin on the production and the progress of root dentine carious lesion. The resin contains methacryloyl fluoride- methylmethacrylate copolymer which is able to release fluoride ion through a hydrolytic reaction (F-resin). Dentine blocks were cut from the roots of extracted bovine teeth. The specimens were stored in deionized water for 7 days after application of the resin onto sound

@ 1993 Butterworth-Heinemann Ltd. 0300-5712/93/030188-02

dentine surfaces and predecalcified dentine surfaces induced by immersion in an acetate buffer solution, pH 4.0, for 12 h. Then the resin was removed mechanically and the specimen was again immersed in an acetate buffer solution (pH 4.0) for 40 h. The inhibitory effect of F-resin on the decalcification of dentine was estimated by microhardness testing, microradiography and X-ray microanalysis. C-resin without fluoride-releasing copolymer was also estimated. The following results were obtained:

1. Microradiographic observation showed that the application of F-resin onto a sound root dentine reduced the depth of lesion as compared with that of C-resin. Microhardness-testing showed that the decalcified dentine in F-resin group was harder than those in both C- resin and no-resin group.

2. As for the effect on a predecalcified dentine, microradiographic observation showed that the depth of lesions in both F-resin and C-resin groups was significantly shallower than that in no-resin group and they were almost comparable between F-resin and C- resin groups. Microhardness testing showed that the lesion in F-resin group was harder than that in C-resin group. X-ray microanalysis showed an uptake of fluoride and an increased mineral density in the lesion of F-resin group.

The results suggested that the application of fluoride- releasing resin inhibits the production and the progress of caries on an exposed root surface. (17 references) H. Hisamitsu

Studies on physical properties of bleached tooth. 1. Microstructural changes by bleaching agent. Toko T., Hisamitsu H., Wakumoto S. et a/. (1990) Jap. J. Consefv. Dent. 33, 1 102-l 1 13.

A sectioned tooth surface was treated with a 31% hydrogen peroxide solution at 37°C for 2 h or 1 week, and the microstructural change of the surface with or without treatment was examined under scanning electron microscopy.

The results were as follows:

1. Tubular structures (inner wall) in the dentinal tubule disappeared, and non-fibrous organic components of peritubular dentine were also removed by immersing in a 31 % hydrogen peroxide solution.

2. A demineralizing effect (exposed in 2.5% EDTA for 30 min) was conspicuously observed in sectioned dentine and enamel surfaces. This effect was accelerated by removing the organic substances in tooth components.

International Abstracts 189

3. The same removing effect on organic substances, as that observed by immersion in a 31% hydrogen peroxide solution, was also observed in the teeth bleached by the Walking Bleach Technique. (42 references) H. Hisamitsu

The influence of metal and different expansion coefficient of ceramic on the thermal stability of porcelain-fused-to-metal (PFM) crowns. Lei Ya-chao et a/. (199 1) Chin. J. Stomato/. 26, 329.

In this study, experimental ceramic of different thermal expansion and metal of the same thermal expansion were selected, and porcelain-fused-to-metal (PFM) crowns were made according to mutual matching. Thermo-shock test and ceramic-cracking micro-examination were applied to investigate: (i) the influence of metal-ceramic thermal expansion difference on the heat resistance of the PFM crowns, (ii) the allowance range of metal-ceramic thermal expansion difference from the thermal stability. The results showed: (i) when the difference between the ceramic thermal expansion and metal thermal expansion was beyond the range of - 0.9-l .O X 1 O”“C-‘, ceramic cracking would occur after firing, (ii) the rule of thermo- shock resistance was-the smaller the thermal expansion of ceramic compared to that of the metal, the higher the value of the thermo-shock resistance was. The authors indicated that: (i) the internal stress was the internal factor of ceramic cracking of the PFM crown, while the instantaneous external expansion stress was the external condition for ceramic cracking of the PFM crown, (ii) the optimal thermal expansion difference between metal and ceramic of the PFM crown was-the thermal expansion

of the ceramic should be 0.7 x 1 O-6oC-1 smaller than that of the ceramic. (8 references) Wei Yi

Perni moncone in resina acetalica. (Post and core restorations by using acetalyc resin.) Cantatore G., Carigliano M., and Malagnino V. (1992) Dent. Cadmos 12. 42-5 1.

Endodontically treated teeth often need coronal reconstruction, where it is necessary to prepare an endodontic post and core restoration. Materials used include amalgam, composite, glass ionomer cements, metal castings and ceramics. These can give rise to problems, however, including weight, resistance, transparency, root fracture, corrosion and electrical conductivity. In the present study endodontic post-cores in acetalyc resin were used. This resin is a thermoplastic technopolymer with a low specific weight, high fracture resistance, and a moderate elasticity. Thirty endodontically treated teeth were prepared in vivo and 15 in vitro. Root canal preparation was done with Gates burs. Posts were made using an indirect technique and cemented using Unity cement (Whaledent). In vitro prepared teeth were analysed in thin ground sections for microscopic observations (Exact cutting-grinding and Exact micro- grinding system) to evaluate the endo post accuracy of acetalyc resins, the sharpness of outlines and the contraction after polymerization.

In vivo prepared teeth showed no failures after 2 years of clinical trials. Endodontic post-cores made with this technique could be a viable alternative for the reconstruction of endodonrically treated teeth. (33 references) Mario Pezzoli

11th Postgraduate Study Day University of Sheffield Department of Restorative Dentistry Sheffield, United Kingdom 13 November 1993 The study day will feature a series of seminars delivered by invited speakers and members the department, on a variety of topics.

Invited speakers

??Mr Peter Hull ??Dr David Hussey ??Professor Ian Benington

For further details please contact:

of

Mr R B Winstanley, Head of Department of Restorative Dentistry, School of Clinical Dentistry, Claremont Crescent, Sheffield SlO 2TA, UK. Tel: 0742 670444 ext 3055.