Marginal ridge strength of Class II tunnel restorations.

PURPOSE

To test the strength, at the marginal ridge, of the tunnel preparation vs the Class II traditional box preparation when restored with composite or glass ionomer (GI).

MATERIALS AND METHODS

Eighty-four extracted maxillary molars stored in normal saline and thymol were randomly divided into six groups of 14 each (determined by pilot study where alpha = 0.05, beta = 0.2). Group A and C were tunnel preparations. Group B and D were traditional Class II preparations. Group E-whole tooth (negative control), and Group F-tunnel preparation unrestored (positive control). Group A and B were restored with Scotchbond 2/P-50 composite. Group C and D were restored with Ketac Fil-GI. The marginal ridge of each tooth was loaded at 0.5 mm/minute on the Instron. A loading rod produced a contact point of 1.0 mm in diameter.

RESULTS

The mean compressive loads (kg) required for fracture were: (A): 42.2 +/- 11.9, (B): 53.1 +/- 10.7, (C): 52.0 +/- 10.9, (D): 23.8 +/- 8.4. (E): 79.1 +/- 16.1, (F): 27.0 +/- 10.6. A significant difference was found between whole teeth (E) and all other groups (P < 0.05). The Newman-Keuls test showed a significant difference between Class II composite (B) and tunnel composite (A) (P < 0.05), between tunnel GI (C) and tunnel composite (A) (P < 0.05) but no difference between tunnel GI (C) and Class II composite (B).