An overlay denture is a removable partial or complete denture that covers and rests on remaining natural teeth, roots, or dental implants. It has several advantages, including increased support and stability, decreased bone resorption, maintained proprioception, improved crown-root ratio and masticatory efficiency, and better retention. However, disadvantages include potential periodontal disease, dental caries, endodontic failure, and mechanical failure. Drawbacks of titanium castings include irregular surface quality due to reactivity with investment material, internal porosity from solubility of gases in molten titanium, and suboptimal sprue designs for low density titanium. However, titanium has merits for dental use such as low density, superior mechanical properties, excellent

1. DEFINITION OF OVERLAY DENTURE:
A removable partial and complete denture that covers and rests on one or
more remaining natural teeth , roots, and / or dental implants. A prosthesis that
covers and is partially supported by natural teeth, roots, and /or dental implants.
Such overlay partial denture has the following advantages:
 Increase support and stability.
 Decrease in alveolar bone resorption
 Patients proprioception is maintained
 Improvement in the crown-root ratio of the abutment teeth
 Improvement in masticatory efficiency better retention.
DISADVANTAGES:
 Periodontal disease
 Dental caries
 Endodontic failure
 Mechanical failure.
Drawbacks of titanium castings:
1. Bessing et al 1992 showed the irregular surface quality of Ti casting
because of high chemical reactivity of titanium with investment at elevated
temperatures .
2. Hero et al 1993 suggested that the internal porosity rate of ti casting was
high because of increased solubility of gases like H O N in molten metal.

2. 3. Robert stein et al 1995 suggested that the sprue designs for the Ti castings
are to be modified because of low density of titanium .Othewise may
produce different castability and porosity effects for low density metals .
4. The high reactivity of titanium with O necessitates special low temperature
burnout procedure ,soaked temperature ,mold material and equipment
having inert medium like argon or helium during melting and casting.
Merits of Titanium for Dental Use:
1. Low density 4.5gm/cm3 in comparision with Co-Cr (8.9gm/cm3)
gold(19.3gm/cm3)
2. Superior mechanical properties .
 High strength
 Stiffness
 Ductility
 Execellent corrosion resistance
 Low modulus of elasticity cp Ti (103.4 Mpa)
3 Excellent biocompatibility
4 Economical.
All these merits documented made the researchers to overcome the
drawbacks mentioned earlier. Therefore titanium has not remained the metal for
the future dental castings but the metal for the present as well as future.