Which of the following is an indication of onlay cast restoration?
MOD Onlay

An indirect restoration, which is partly intracoronal and partly extracoronal that covers all the cusps of a posterior tooth.
Onlay has cuspal protection as the main feature.
The use of an onlay keeps the stresses at a low level and creates no hazard to the remaining tooth structure.

Indications

If the width of the lesion is 1/3 to 1/2 the intercuspal distance - cuspal protection is to be considered.
Width of the lesion exceeds 1/2 the intercuspal distance - cuspal protection is mandatory.
If the length : width of the cusp is more than 1:1, but not exceeding 2:1 - cuspal protection is to be considered.
If the length : width of the cusp is more than 2:1 - cuspal protection is mandatory.
When there is need to change the dimension, shape and inter relationship of the occluding tooth surfaces.
Abutment teeth for RPD and fixed prosthesis.
When wear facets that exceed the cusp tips and triangular ridge crests facially / lingually are to be included.

MDS Prep Bytes (Cast Restoration – Inlay)
Width of the lesion exceeds ½ the intercuspal distance
Strong, self-resistant cusps are there
Occlusal surfaces are not to be changed
The tooth is not to be used as an abutment