Fracture resistance, failure mode and stress concentration in a modified endocrown design

Figures & data

Figure 1. 3D model and milled in vitro restorations: (A) conventional endocrown preparation design and (B) modified endocrown preparation design.

Figure 2. Compressive test using universal testing machine: (A) axial loading, (B) lateral loading for in vitro and in silico test respectively.

Figure 3. Type I: Cohesive failure; Type II: Adhesive failure; Type III: Cohesive-adhesive failure; Type IV: Fracture of the restoration/tooth complex above the cemento-enamel junction (CEJ); Type V: Fracture of the restoration/tooth complex below the cemento-enamel junction (CEJ).

Table 1. Classification of the failure modes.

Type	Failure mode	Description
I	Cohesive failure	Fracture of the endocrown without displacement (loss of adhesion)
II	Adhesive failure	Debonding of the endocrown without fracture
III	Cohesive-adhesive failure	Fracture of the endocrown with displacement (loss of adhesion)
IV	Fracture of the restoration/tooth complex above CEJ	Fracture of the endocrown and the tooth above CEJ
V	Fracture of the restoration/tooth complex below CEJ	Fracture of the endocrown or/and the tooth below CEJ, which require tooth extraction

CEJ: Cemento-enamel Junction.

Figure 4. Stress maps according to each group: (A) in the conventional endocrown restorations with axial loading, (B) in the conventional endocrown restorations with lateral loading, (C) in the modified endocrown design with axial loading and (D) in the modified endocrown design with lateral loading.

Figure 5. Tensile stress peaks recorded for each structure during the four different simulations. E: Endocrown tensile stress; R: Root dentin tensile stress; SS: Cement shear stress; TS: Cement tensile stress.

Table 2. Distribution of load (N) to failure by preparation design and loading type (n = 40).

					95% confidence interval
	Mean	SD	Minimum	Maximum	Lower bound	Upper bound
Conventional preparation design
Axial	2914	205	2607	3278	2768	3061
Lateral	1516	202	1235	1794	1371	1660
Modified Preparation design
Axial	3329	134	3098	3509	3233	3425
Lateral	1871	99	1725	2054	1800	1941

Table 3. Distribution of load (N) to failure by 2-way ANOVA main effects of preparation design and loading (n = 40).

			Difference
	Mean	SE	Mean	SE	F	p
Main effects of design
Conventional	2215	37	−385	53	53.481	<.001**
Modified	2600	37
Main effects of loading
Axial	3122	37	1429	53	736.865	<.001**
Lateral	1693	37

No statistically significant interaction present between preparation design and loading (p = .570).

**Statistically significant, p < .001; SE: standard Error.

Table 4. Distribution of failure modes by groups and loading type (n = 40).

Failure mode n (%)
	I	II	III	IV	V
Conventional preparation
Axial	1 (10)	0 (0)	4 (40)	0 (0)	5 (50)
Lateral	1 (10)	1 (10)	1 (10)	1 (10)	6 (60)
Modified preparation
Axial	1 (10)	0 (0)	1 (10)	0 (0)	8 (80)
Lateral	0 (0)	1 (10)	1 (10)	0 (0)	8 (80)

Type I: Cohesive failure; Type II: Adhesive failure; Type III: Cohesive-adhesive failure; Type IV: Fracture of the restoration/tooth complex above the cemento-enamel junction (CEJ); Type V: Fracture of the restoration/tooth complex below the cemento-enamel junction (CEJ).

Figure 6. Features of fractographic analysis.