All of the following features can be given in a grossly carious tooth to strengthen the tooth structure except:
In the preparation of a tooth that has been grossly weakened by caries or previous filling material and is judged to be prone to fracture under occlusal loads, the resistance form that cusp capping provides should be augmented by the use of skirts, collars, or facial (lingual) surface groove extensions.
When properly placed, these features result in onlays that distribute the occlusal forces over most or all of the tooth and not just a portion of it, reducing the likelihood of fractures of teeth.
The lingual “skirt” extension, the lingual “collar” preparation or the lingual surface groove extension on a maxillary molar protects the facial cusps from fracture.
The facial skirt extension, the facial collar preparation, or the facial surface groove extension on a mandibular molar protects the lingual cusp from fracture.

Sturdevant operative dentistry 7th Edition, Page No:e122
Skirt extension
Collar preparation
Dovetail preparation
Surface groove extension