Shoe in onlay serves as:
ONLAYS;
i) Onlays are the most indicated and universally used cast restorations for individual teeth. It is a partly intracoronal and partly extracoronal type of restoration.
ii) It has cuspal protection as the main feature.
iii) It is mainly indicated when width of the lesion exceeds one-third the intercuspal distance.
iv) In the tooth preparation, if the length : width ratio of the cusp is more than 1:1 but not exceeding 2:1, cuspal protection is to be considered.
v) If the length : width ratio of a cuspal protection is mandatory.
vi) Onlays are the ideal supporting restorations for remaining tooth structure combined with conservative tooth involvement. cusp is more than 2:1,
vii) The main designing features of onlay are coping of the functional cusps (buccal cusps of lower and lingual cusps of upper teeth) and s(Lgens of the non functional cusps.
viii) The cuspal reduction in onlays is 1.5mm deep.
ix) The bevel in the intracoronal portion of the wall constitutes the hollow ground long bevel. The bevel in the extracoronal part of the preparation is the counter or reverse bevel.
x) 'Counter bevel' is not placed on the facial cusps of maxillary premolars and first molars where the esthetic requirement dictates only a blunting and smoothing of the enamel.
xi) `Table' is the transitional area between the intracoronal and extracoronal parts of the preparation. The table should be flat and relieved from opposing cusps by atleast 1.5mm.
xii) There should be three tables prepared for each cusp, each with different directions. Table provides the resistance and retention form.
xiii) 'SHOE' serves the purpose of table on the non functional cusp. But it is less relieved than the table. It also serves as retention and resistance form.
Retention form
Resistance form
Both
Support