Fractures may occur in a partial denture framework because of metal fatigue, improper contour of the component parts, or faulty castings. Faulty castings may be due to inclusions of bits of investment in the metal, crystallization of the metal, or improper casting techniques. Many times it is impossible to know that these defects are present when the partial denture is delivered. When a patient is unfortunate enough to bend a lingual bar, the partial denture may need to be sectioned and the halves rejoined. The procedures involved in joining the two halves are the same as for repairing a framework.
Partial denture repairs may be done by soldering with an open flame. When the fracture is near a saddle, it is necessary to remove the teeth and saddle from the framework before the soldering operation. This is a major procedure which is not required when electro-soldering techniques are used.
Electro-soldering techniques are widely used in the jewelry industry. The same principles and techniques used in soldering jewelry are used to repair the metal portions of partial denture frameworks. The technique for soldering is the same whether the framework is made of gold or base metal alloys. Gold solder is used with base metal alloys in the same manner as for gold, with the exception that white solder is used.
There are many electro-soldering machines available. The directions for using the machine should be followed exactly. The directions must be read thoroughly to determine any variations in technique required of the individual machine.
The principles of soldering described in the Laboratory and Clinical Dental Materials Manual (in this series) are followed with electro-soldering machines. The surfaces to be joined must be cleaned and accessible to the contacts of the soldering machine. The work must be arranged so that gravity favors the flow of solder. One of the advantages of electric soldering is that intense heat is located at the site of the fracture rather than throughout the framework. However, if the fracture occurs adjacent to a resin portion of a partial denture, the resin should be protected with wet asbestos.