Comparative study of fracture strength depending on the occlusal thickness of full zirconia crown

Soo-Ah Jang; Yoon-Young Kim; Won-Hee Park; Young-Soo Lee

doi:10.4047/jkap.2013.51.3.160

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Jang, Kim, Park, and Lee: Comparative study of fracture strength depending on the occlusal thickness of full zirconia crown

ORIGINAL ARTICLE

J Korean Acad Prosthodont 2013;51(3):160-166.

Published online: 18 December 2013

DOI: https://doi.org/10.4047/jkap.2013.51.3.160

Comparative study of fracture strength depending on the occlusal thickness of full zirconia crown

Soo-Ah Jang, MSD, DDS, Yoon-Young Kim, MSD, DDS, Won-Hee Park, DDS, PhD, Young-Soo Lee, DDS, PhD^∗

Major in Dentistry, Department of Medical Science, Hanyang University Graduate School, Seoul, Korea

∗Corresponding Author: Young-Soo Lee Major in Dentistry, Department of Medical Science, Hanyang University Graduate School, 17 Hangdang-dong, Sungdong-gu, Seoul, 133-792, Korea +82 2 2290 8675: e-mail, leeys@hanyang.ac.kr

Received 19 April 201311 June 2013 Accepted 3 July 2013

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

The purpose of this study was to compare the fracture strength of traditional metal-ceramic crowns and full zirconia crowns according to the occlusal thickness.

Materials and methods

A mandibular first molar resin tooth was prepared with 1.5 mm occlusal reduction, 1.0 mm rounded shoulder margin and 6^° taperness in the axial wall. Duplicating the resin tooth, 64 metal dies were fabricated. 48 full zirconia crowns were fabricated using Prettau zirconia blanks by ZIRKONZAHN CAD/CAM and classified into six groups according to the occlusal thickness (0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm). 16 metal-ceramic crowns were fabricated and classified into two groups according to the occlusal porcelain thickness (1.0 mm, 1.5 mm). All crowns were cemented on each metal die and mounted in a universal testing machine. The load was directed at the functional cusp of each specimen until catastrophic failure occurred. One-way ANOVA, Tukey multiple comparison test (α =.05) and t-test (α =.05) were used.

Results

The results were as follows. 1. The test 1 group (646.48 N) showed the lowest fracture strength (P<.05), and the value of the test 2.3.4.5 groups (866.40 N, 978.82 N, 1196.82 N, 1222.41 N) increased as thickness increased, but no significant difference were found with the groups (P>.05). The value of test 6 group (1781.24 N) was significantly higher than those of the other groups (P<.05). 2. There were no significant differences of the fracture strength of metal ceramic crowns according to occlusal porcelain thickness 1.0 mm (2515.71 N) and 1.5 mm (3473.31 N) (P<.05).

Conclusion

Full zirconia crown needs to be 1.0 mm or over in occlusal thickness for the posterior area to have higher fracture strength than maximum bite force. (J Korean Acad Prosthodont 2013;51:160-6)

Keywords: Full zirconia crown, Fracture strength

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Fig. 1.

Fabrication process of metal die.

Fig. 2.

Full zirconia crown.

Fig. 3.

Metal ceramic crown - occlusal porcelain thickness 1.0 mm (left), 1.5 mm (right).

Fig. 4.

A: Schematic illustration of the universal test machine experimental setup, B: Secured crown for testing in custom jig on universal testing machine, C: Fractured specimen after loading.

Table 1.

Fracture strength of full zirconia crown (unit: N)

	Mean	SD	Minimum	Maximum
Test 1 (0.5 mm)	646.48	300.82	140.58	932.94
Test 2 (0.6 mm)	866.40	220.98	506.74	1124.75
Test 3 (0.7 mm)	978.82	235.87	703.40	1404.36
Test 4 (0.8 mm)	1196.82	305.35	859.60	1689.08
Test 5 (0.9 mm)	1222.41	449.17	865.22	1941.44
Test 6 (1.0 mm)	1781.24	423.30	1214.38	2366.23

Table 2.

Results of one-way ANOVA

Source	Sum of squares	df	Mean square	F value	P value
Between groups	6095736.74	5	1219147.35	10.931	<.001
Within groups	4684134.40	42	111527.01
Total	10779871.14

Table 3.

Statistical comparisons of full zirconia crown (Tukey test at P=.05)

	Subgroup at P=.05
	1	2	3
Test 1 (0.5 mm)	A
Test 2 (0.6 mm)		B
Test 3 (0.7 mm)		B
Test 4 (0.8 mm)		B
Test 5 (0.9 mm)		B
Test 6 (1.0 mm)			C

Table 4.

Fracture of metal ceramic crown and results of t-test (unit: N)

	Mean	SD	Minimum	Maximum	t	df	P value
Control 1 (1.0 mm)	2515.71	388.81	823.56	4302.49	1.854	14	0.085
Control 2 (1.5 mm)	3473.31	961.13	2724.36	7667.95	1.854	14	0.085

(P=.05)

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