It is known that patients who ceased to wear their dentures less than 5 years reached to more than 60%. Denture failure due to the loss of the abutment tooth or caries accounted for about 20% of the number. Abrasion of the abutment tooth with clasp is thought to be another reason for cease to wearing dentures.
Considering these data, the author undertook a study of plating on the human teeth as a means of caries prevention. The method of Electroless Nickel plated surface is acidresistant, wear-resistant, very hard, and heat-resistant.
Since these properties were desired for the tooth surface, the author decided to examine the possible application of Nickel plating for dental practice.
Following results were obtained:
1. The possible active agent for the Catalyzing (=Catalysis stage) was PdCl2 (2g/l) at pH 4.
2. The thickness of the plating film increased with plating time and reached a plateau after 10 minutes.
3. Surface roughness increased due to the etching procedure prior to Nickel plating. Although Nickel plating for 60 minutes reduced the roughness, the plated tooth surface was not so smooth as the original surface.
4. Surface hardness of the tooth decreased from the normal value of 380 Hv to about 260 Hv following etching. Five minutes after plating, the hardness returned to normal and reached to plateau at 450 Hv by 10 minutes.
5. The force of adhesion between the plating film and the teeth was approximately 140-160 kg/cm2.
6. After 3 hours of thermal shock testing between 4°C and 80°C (30 cycles), no specimen showed signs of “blistering”, “peeling off” or “cracking”.
7. The acid-resistance test was carried out in 1/1, 000 N and 1/100 N Hydrochloric acid. The plated film was not affected, whereas the control tooth surface was corroded.
8. In the wear-resistance test, the gloss of the plated tooth surface increased, but the tooth surface was not exposed after 20, 000 toothbrush strokes. But when a Co-Cr alloy plate was applied instead of brush (with a load of 2kg), the tooth surface appeared as a small round after 100 strokes followed by rapid expansion in size.
9. The interface between the plating film and the teeth was analyzed by SEM (Scanning electron microscope), EPMA (Electron probe X-ray microanalyser), ESCA (Electron spectroscopy for chemical analyser) and following observation were obtained.
At first, the inter-rod substance of surface enamel was corroded due to the etching process. Followed by dissolution of residual substance by the low pH during the Catalyzing step. The plated film was appeared as a globular granules of 1 μm in size and was intimately associated with the tooth surface when observed by SEM. Tin and palladium attached to the tooth during the Catalyzing step were observed by EPMA in a very small quantities.
After Nickel plating, tin and palladium were still present in the deeply etched areas. The Ca/P ratio was decreased due to the presence of phosphorous in the Nickel plating solution. These were ascertained with ESCA analysis of plating film.
From the above results, it appeares that the Electroless Nickel plating method will be used as a means of caries prevention and may have application in dental practice.
