The Effect of Endocrown Ferrule Design on Cerec Crown Retention

Objectives: To evaluate the effect of ferrule on failure stress with adhesively-luted mandibular molar CADCAM Endocrowns.
Methods: Recently-extracted mandibular third molars were randomly divided into 3 groups (n=12) with the coronal tooth structure removed perpendicular to the root long axis approximately 2mm above the CEJ with a water-cooled, slow-speed diamond saw. The pulp chamber was exposed using a diamond bur in a high speed handpiece, pulpal remnants removed, and canals prepared using endodontic hand instruments. The chamber was restored with a dual-cure, resin core material (Gradia Core) after application of a two-step, self-etch adhesive (Clearfil SE) with photopolymerization accomplished with a visible light curing unit (Bluephase G2). All specimens were prepared with 2mm endocrown preparation depths. Two groups received additional features of 1- and 2mm ferrule preparations. All preparations were accomplished with a high speed handpiece with a diamond bur under air/water spray. Completed preparation surface area was determined using a digital measuring microscope (Hirox). Scanned preparations (CEREC) were fitted with e.max CAD crowns and luted with RelyX Unicem after HF acid etching and silanation. All manufacturer recommendations were followed for all materials used. Specimens were stored at 37C/98% humidity and tested after 24 hours to failure with the load applied to the buccal cusps at a 45-degree angle to the tooth long axis on a universal testing machine (Alliance RT5). Failure load (N) was converted to stress (MPa) using the available bonding surface area with mean data analyzed with Kruskal-Wallis (p=0.05).
Results: Results are listed in the table. No difference were found between the groups (p=0.41).
Conclusions:
Under this study’s conditions, ferrule addition to mandibular molar Endocrown preparations did not result in a change in failure stress.