Cast gold – historical misunderstandings
The idea that cast gold inlays cause teeth to fracture has been
propagated over the last 30 or 40 years in dental school textbooks,
although recent evidence strongly suggests otherwise.
Much of the faulty opinion regarding tooth fractures caused by
gold inlay was based on clinical observations of individual experiences.
During this time procedures for dental castings were evolving, and
only a basic understanding of tooth composition and structure existed.
More formalized science eventually allowed a greater appreciation
of the many intricacies involved in developing castings. However, lack
of universal acceptance of exact casting control is evident in much
published literature. For example:
Similar water:liquid ratios were utilized regardless of the
casting design studied; a factor that cause significant variability in
the fit and potential stresses in the tooth and casting.
Photoelastic studies supported the notion that inlays behave as
wedges. This conclusion is fundamentally flawed as it misrepresents the
tooth structure and resultant photoelastic stress/strain relationships.
For decades, reference books stated that cast inlays are retained
by a “wedging” effect. In actuality, the bonding agent binds the
casting and complex together, supporting remaining tooth structure and
distributing stress.
Studies utilizing a mathematical technique for determining the
effect of various stress loads have overlooked the role of the
Dentino-Enamel Junction (DEJ) in providing the natural tooth with a
measure of flexibility.
Evaluations of the resilience of a tooth after the removal of
controlled portions of facial enamel dismissed important findings,
attributing them to the tendency of enamel to crack under the strain
gauge, thus affecting its signal.
These classic studies emphasize historical flawed observations
contributing to erroneous concepts in dental textbooks. Books used, at
least in part, to indoctrinate students into the profession. A thorough
understanding of the behavior of the tooth structure is necessary if
the dentist is to replace it with a substitute that affords predictable,
long-term function.
Choice of restoration must consider resistance to fracture, wear
caused to the opposing teeth, and aesthetics. The exclusion of any of
these factors may compromise the clinical outcome in favor of the
patient’s cosmetic values.
