James Karssiens T, Zhou R, Ritchie Gill J, et al. Clinical results and 10-year survivorship of the Synthes Epoca resurfacing total shoulder arthroplasty. Shoulder & Elbow. Epub ahead of print 20 October 2021. DOI:10.1177/17585732211038914
The authors have noted in their article that the “Copeland resurfacing head (RH) is 6 mm thick at the apex, and has been shown to sometimes result in overstuffing even without use of a glenoid implant” which they referenced to an article by Copeland. This 6mm thickness was that of the Mark 2 design of this implant introduced in 1990. Within the same paper it was noted by Copeland "Over the last few years, because ‘overstuffing’ has been recognized as a potential problem, the ‘Thin Shell’(BIOMET) prosthesis system has been developed, which is 3 mm thick in cross section" at the apex. The Copeland thin shell in fact was introduced in late 2009 with a shell thickness of 2mm.
Reference: Copeland SA and Sforza G. How I perform resurfacing shoulder replacement. Shoulder Elbow Volume 2, Issue 3 July 2010; 2: 209-214.