Thirty molars extracted for periodontal reasons (Fig. 1) were prepared in a standardized manner with a circumferential chamfher of 0.7 mm and an axial reduction of 1.0 mm (Fig. 3). The specimens were divided randomly into 3 groups (n=10) with different occlusal thickness: 0.5 mm (group 1), 1.0 mm (group 2) and 1.5 mm (group 3). Thirty CAD-CAM Cerasmart crowns with different occlusal thickness, designed and built according the original anatomy of the teeth (Fig. 2-4), were cemented onto human molars with a dual-cure adhesive luting cement (Fig. 5) (GC-CEM Link Force). The specimens were loaded until fracture (Fig. 6); the fracture resistance and mode of failure were recorded and examined using scanning electron microscope (Fig. 7-10) (SEM). The data were statistically analyzed with the one-way ANOVA followed by the Fisher's Exact test with Bonferroni's correction (p=0.05)

The occlusal thickness of the composite reinforced with ceramic CAD-CAM crowns did not affect the fracture resistance [1]. The occlusal thickness has indeed influenced the failure modes of the crowns [2]. The fracture values recorded in all the experimental groups overcome the physiological chewing forces in molar regions and no fracture occurred. From a clinical point of view, Cerasmart can be used in the posterior region to preserve tooth tissue and in cases of reduced prosthetic interocclusal space.

Which is the maximum load that adhesive resin-reinforced single crowns can

withstand in molar regions? Arianna INFELISE*, Roberto SORRENTINO, Giovanni BONADEO, Marco FERRARI

(University of Siena; Department of Prosthodontics and Dental Materials)

Group 1 (0.5 mm)

Group 2 (1.0 mm)

Group 3 (1.5 mm)

Mean 925.08 1000.9 1111.14

S.D 296.29 398.06 360.84

Sig. A A A

Restorable 10% 60% 90%

Fig. 7- Layer of cement of 50 µm.

Fig. 9- Cohesive Fracture.

Fig. 10- Adhesive Fracture.

Fig. 8- Fracture Mirror.

Table 1- Averange fracture values (Mean), standard deviations (S.D), statistical significance and restorable of the experimental groups.

Fig. 1- Side view of specimens.

Fig. 2- Anatomic digitization.

Fig. 3- Tooth preparation.

Fig. 4- Anatomical design of crown with different thicknesses.

Fig. 5- Cementation of crowns.

Fig. 6- Static load at fracture.

References:

- Awada A, Nathanson D. Mechanical properties of resin-ceramic CAD/CAM restorative materials. D. J Prosthet Dent. 2015 Oct;114(4):587-93. -S. Lauvahutanon, H. Takahashi, M. Shiozawa, N. Iwasaki, Y. Asakawa, M.Oki, W.J. Finger &M. Arksornnukit. Mechanical properties of composite resin blocks for CAD/CAM. Dental Materials Jornal, 2014;33(5):705-10

-A. Awada & D. Nathanson. Mechanical Properties of New Chairside CAD/CAM Materials. Oral presentation (21/03/2014), International Association for Dental Research.

-Sorrentino R., Triulzio C., Tricarico M., Bonadeo G., Gherlone E., Ferrari M. In vitro analysis of the fracture resistance of CAD/CAM monolithic zirconia molar crowns with different occlusal thickness. ScienceDirect. April 2016.

Cement

Tooth

Crowns

OBJECTIVE

To compare the fracture resistance and mode of failure of CAD-CAM Cerasmart crowns with different occlusal thickness. The null hypotheses established that there was no association between occlusal thickness and resistance to fracture [1] and failure modes [2] of the samples with different occlusal thickness.

MATERIALS and METHOD

RESULTS

The group that showed the highest resistance to fracture was the group 3 (1.5 mm) followed, with very similar values, by the group 2 (1.0 mm) and the group 1 (0.5 mm). It is worth noticing that in group 3 ( 1.5 mm) the types of fracture that have occurred are in 90% restorable, in group 2 (1.0 mm) the types of recoverable fracture are 60%, while, in group 1 (0.5 mm) are only 10% (Table 1).

CONCLUSIONS