Load-bearing capacity of pressable lithium disilicates applied as ultra-thin occlusal veneers on molars.

PURPOSE: The aim was to investigate the load bearing capacity of different pressable lithium disilicates cemented as occlusal veneers on molars. MATERIALS AND METHODS: One control group and six test groups were formed consisting of 20 specimens each (n = 20). The six test groups differed in the utilizing pressable lithium disilicate to fabricate occlusal veneers. As a control group, "group Lis", the lithium disilicate with the highest reported flexural strength was used (initial LiSi Press, GC Europe; Leuven, Belgium / flexural strength: 508 MPa). The test groups consisted of other pressable lithium disilicates with lower flexural strength values: "Ema" (IPS e.max press), "Vit" (VITA Ambria), "Liv" (Livento Press), "Amb" (Amber Press), "Mas" (Amber Press Master) and "Ros" (Rosetta SP)". After the preparation of 140 extracted human molars, which included the removal of the central enamel, the specimens were scanned using a desktop scanner. With the aid of a design software, the occlusal veneers were designed in a standardized thickness of 0.5 mm. To fabricate the restorations, all tested materials were processed using heat-pressing technique. All restorations were adhesively cemented. Afterwards, the specimens underwent cyclic fatigue during an aging procedure in a chewing simulator (1'200'000 chewing-cycles, 49 N force, 5-55°C temperature changes). Subsequently, the specimens were statically loaded and the load which was necessary to fracture the specimen (Fmax) were measured. Differences between the groups were compared applying the Kruskal-Wallis (KW) test and the Wilcoxon-Mann-Whitney-Test (WMW: p < 0.05). The two-parameter Weibull distribution values were calculated. RESULTS: The fatigue resistance was 100% for the groups Lis, Vit, Liv, Amb, Mas and Ros, whereas the group Ema showed a fatigue resistance of 95%. The control group Lis showed median Fmax values of 2'328 N. The median Fmax values for the test groups ranged between 1'753 N (Vit) and 2'490 N (Ros). Statistically significant difference was observed among the groups Lis (control) and Vit (KW: p < 0.001). Weibull distribution presented the highest shape values for the group Ros (12.83) and the lowest values for the group Ema (4.71). CONCLUSION: Regarding their load-bearing capacity different pressable lithium disilicates can be recommended to fabricate ultra-thin occlusal veneers on molars when restoring occlusal tooth wear.

The Effect of SnCl2/AmF Pretreatment on Short- and Long-Term Bond Strength to Eroded Dentin.

This study investigated the effect of SnCl2/AmF pretreatment on short- and long-term bond strength of resin composite to eroded dentin mediated by two self-etch, MDP-containing adhesive systems. 184 dentin specimens were produced from extracted human molars. Half the specimens (n = 92) were artificially eroded, and half were left untreated. For both substrates, half the specimens were pretreated with SnCl2/AmF, and half were left untreated. The specimens were treated with Clearfil SE Bond or Scotchbond Universal prior to application of resin composite. Microtensile bond strength (µTBS) was measured after 24 h or 1 year. Failure mode was detected and EDX was performed. µTBS results were statistically analyzed (α = 0.05). µTBS was significantly influenced by the dentin substrate (eroded < noneroded dentin) and storage time (24 h > 1 year; p < 0.0001) but not by pretreatment with SnCl2/AmF or adhesive system. The predominant failure mode was adhesive failure at the dentin-adhesive interface. The content of Sn was generally below detection limit. Pretreatment with SnCl2/AmF did not influence short- and long-term bond strength to eroded dentin. Bond strength was reduced after storage for one year, was lower to eroded dentin than to noneroded dentin, and was similar for the two adhesive systems.