Influence of piston material on the fatigue behavior of a glass-ceramic

doi:10.1016/j.prosdent.2021.08.001

The Journal of Prosthetic Dentistry

Volume 129, Issue 6, June 2023, Pages 931-937

https://doi.org/10.1016/j.prosdent.2021.08.001 Get rights and content

Abstract

Statement of problem

The lack of standardization regarding the loading piston material used in fatigue tests could limit the interpretation of study findings.

Purpose

The purpose of this in vitro study was to evaluate the effect of the piston material on the fatigue behavior of a lithium disilicate glass-ceramic.

Material and methods

Plate-shaped, 1.2-mm-thick, lithium disilicate glass-ceramic specimens were cemented onto a dentin analog substrate with resin cement. The specimens were divided into 4 groups according to the piston material used in the fatigue test (n=30): metal, glass fiber-reinforced epoxy resin, ceramic, and human tooth. The fatigue test was performed in a mechanical cycling machine by using the boundary technique at 2 Hz in distilled water at 37 °C. The fatigue data were analyzed by using the Weibull distribution and a lifetime-inverse power law relationship. Failures were evaluated with fractography and transillumination.

Results

The Weibull modulus (β) was similar among groups. The exponent of crack growth (n) was significantly greater for glass fiber-reinforced epoxy resin and tooth groups than for metal and ceramic; therefore, the probability of failure (P_f) of glass-ceramic specimens loaded by resin and tooth pistons depended more on load amplitude. Specimens tested with tooth showed the highest value of K (characteristic lifetime), which is an indication of greater survival. Radial crack was the only failure mode observed for all experimental groups.

Conclusions

The piston material influenced the fatigue survival of the lithium disilicate glass-ceramic. The glass fiber-reinforced epoxy resin piston closely simulated the fatigue behavior induced by the human tooth on the evaluated glass-ceramic.

Section snippets

Material and methods

The study was approved by the local ethics in research committee (no. 2404475). Lithium disilicate glass-ceramic specimens were cemented onto a dentin analog substrate with resin cement and divided into 4 groups according to the piston material used for the fatigue test (n=30): M (stainless steel), R (glass fiber-reinforced epoxy resin), C (lithium disilicate glass-ceramic), and T (human tooth).

The glass-ceramic specimens were produced from prefabricated and precrystallized computer-aided

Results

Table 2 presents the fatigue parameters for the glass-ceramic specimens tested with the different pistons. The Weibull modulus (β) was similar among the experimental groups, considering that the 95% confidence intervals (95% CI) overlapped. Specimens tested with T piston showed the greatest value for the characteristic lifetime parameter (K−number of cycles for 63.2% P_f), which indicates a higher survival. Specimens tested with T and R pistons showed significantly higher values of n (exponent

Discussion

Understanding how different types of loading pistons affect the mechanical behavior of bonded glass-ceramic structures can assist researchers in choosing the best material for their experimental designs and assist clinicians in interpreting laboratory studies. In the present investigation, 3 piston materials were evaluated: lithium disilicate–based glass-ceramic (C), a popular restorative material¹^,10, 11, 12; stainless steel (M), which has been the most frequently used material for loading

Conclusions

Based on the findings of this in vitro study, the following conclusions were drawn:

1.
The type of piston material used in the mechanical test influenced the fatigue behavior of the lithium disilicate glass-ceramic.
2.
The fatigue behavior of the glass-ceramic structures was similar when tested with the tooth and glass fiber-reinforced epoxy resin pistons.
3.
The probability of fatigue failure was more sensitive to load changes when tooth and epoxy resin pistons were used.
4.
Glass-ceramic specimens survived

Acknowledgments

The authors thank CNPq and CAPES (Finance Code 001) for the predoctoral and graduate students’ scholarships.

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Citation Excerpt :
Another relevant point to note about piston is the tip shape. Spherical tip pistons were used in the present study, which were different from 3 mm diameter flat tip pistons used by Weber et al. (2021, 2018). The main negative point of using flat tip pistons is the edge-loading that occurs when the ceramic deforms slightly beneath the piston (Kelly, 1999).
This study evaluated the influence of the piston material (glass fiber-reinforced epoxy resin or stainless steel) and the piston tip diameter (6 or 40 mm) on the fatigue mechanical behavior, failure mode, and stress distribution of feldspathic ceramic simplified restorations. Pistons were machined in glass fiber-reinforced epoxy resin (ER) and in stainless steel (SS), with active tips simulating the curvature radius of 6- or 40-mm diameter spheres. A total of sixty (N= 60) feldspathic ceramic discs (Ø= 10 mm; thickness= 1.0 mm) were adhesively luted onto supporting substrate discs (Ø= 10 mm; thickness= 2.5 mm) and allocated into 4 groups (n= 15) according to the piston used for fatigue testing: ER_6, ER_40, SS_6, SS_40. Afterwards, the specimens were submitted to the cyclic fatigue test (20 Hz frequency; initial load= 100 N; step= 50 N; 10,000 cycles/step, upon specimen failure detection). The collected data were analyzed by two-way ANOVA (α= 0.05) to verify differences by considering ‘piston material’ and ‘piston diameter’ as factors, and their association. In addition, a survival analysis (Kaplan Meier with Mantel-Cox log-rank post-hoc tests) was conducted (α= 0.05). Fractographic and finite element (FEA) analyzes were also performed. ‘Piston material’ (p= 0.040, F= 4.43) and ‘piston diameter’ (p < 0.000, F= 563.21) had a significant influence on the fatigue failure load (FFL) and the number of cycles for failure (CFF) values. Feldspathic restorations showed higher FFL and CFF (p < 0.05) when tested with a 40 mm diameter piston compared to a 6 mm diameter piston (ER_40 and SS_40 > ER_6 > SS_6). In relation to the piston material, ER and SS pistons with 40 mm diameter promoted similar fatigue performance (ER_40: 946.67 N/179,333 cycles = SS_40: 936.67 N/177,333 cycles), while 6 mm diameter groups presented different fatigue performance (ER_6: 440 N; 78,000 cycles > SS_6: 353.3 N; 60,667 cycles). Hertzian cone crack failures were only observed in the groups tested with 6 mm pistons, regardless of piston material. Higher stress concentration on the ceramic surface was observed when using 6 mm diameter pistons, whereas the SS_6 group showed a slight increase in stress concentration in comparison to the ER_6 group. The piston diameter showed an influence on the fatigue behavior, failure mode, and stress distribution of feldspathic ceramic simplified restorations. However, the influence of piston material is only observed when 6 mm diameter pistons are used. The 40 mm diameter pistons led to radial crack, being more appropriate for fatigue test of simplified feldspathic ceramic restorations with a thickness ≤ 1 mm. Whilst the 6 mm diameter pistons should be avoided, once tend to induce Hertzian cone crack failures and to underestimate fatigue performance.
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: Supported in part by the National Council for Scientific and Technological Development of Brazil (CNPq, research grant no. 461178/2014-1) and by the U.S. National Institutes of Health (NIH, research grant no. DE024333).

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Research and EducationInfluence of piston material on the fatigue behavior of a glass-ceramic

Abstract

Statement of problem

Purpose

Material and methods

Results

Conclusions

Section snippets

Material and methods

Results

Discussion

Conclusions

Acknowledgments

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Research and Education
Influence of piston material on the fatigue behavior of a glass-ceramic