Principles and practice of crown and bridgework : a practical, systematic and modern treatise upon the requirements and technique of artificial crown and bridgework / by Hart J. Goslee.

  • Goslee, Hart J. (Hart John), 1871-1930.
Date:
1907
Catalogue details

Licence: In copyright

Credit: Principles and practice of crown and bridgework : a practical, systematic and modern treatise upon the requirements and technique of artificial crown and bridgework / by Hart J. Goslee. Source: Wellcome Collection.

    40/540 (page 28)
    As this is obvious, and since the affinity of one metal for combining with another is increased by heat, it is only necessary to first raise the temperature of the higher fusing parts equal or near to the melting point of the most fusible, when very little further heat well directed upon both simultaneously will result in perfect union with little or no effort, and as the solder will follow the heat or flow in the direction of the great- est degree of temperature, it can be controlled accordingly. As the shrinkage of solder increases in propor- Sbrinkage. tion to the quantity of baser alloy incorporated, and manifests itself to such an appreciable extent in gold work, it is imperative to use the utmost precautions toward preventing the possible change in the relation of the parts which might thus ensue, and which may not infrequently result in jeopardizing the fit and adap- tation. To preclude this possibility it is necessary to observe the require- ments of apposition and contact very closely, and in more or less exten- sive work it may be further prevented by soldering each piece separately first, so that in the final assemblage of the parts as little solder may be used and carried to the fluid state as is immediately required to secure union and strength. Thus very large cases should be soldered in sections and afterward united. Perhaps paramount among the difficulties most fracturing Of frequently experienced is the checking or fracturing Porcelain facings, of porcelain facings, but this, while seemingly and apparently unavoidable, is in nearly all instances due to the most flagrant negligence, in so far as soldering is concerned. In this connection it is necessary to consider the fact that a porce- lain facing constitutes and presents two distinct substances, the mineral and the metal—the porcelain and the pins—each of which possesses phy- sical properties which are affected very differently by the heat to which they are subjected. The mineral, absorbing heat very slowly and gradually, retains it for a considerable length of time, while the metal absorbs it readily, and gives it off or cools with equal rapidity; consequently, in the process of soldering, the utmost care must be exercised in applying the heat so gradually and uniformly from the very outset that the porcelain, which is a friable material, will receive it either preceding or at least simultane- ously with the platinum pins, in order that the expansion which takes place in each may occur evenly and uniformly. It is invariably this uneven expansion, wherein that of the porcelain is not sufficient to accommodate that of the pins, which causes the fractures occurring across the surface of the facing, always radiating from the pins. To various other reasons.