Effect of contact stress on the cycle-dependent wear behavior of ceramic restoration

Effects of Streptococcus mutans and their metabolites on the wear behavior of dental restorative materials

The wear behavior of dental restorative materials is highly related to the biolubricating medium in the oral environment. Bacteria, along with their metabolic products, are essential substances in the oral cavity and have not been studied as a potential factor affecting lubrication performance during mastication. In this study, the effects of the Streptococcus mutans bacterial cells and their metabolites were investigated on the wear behavior of resin composites, polymer-infiltrated ceramic networks and zirconium-lithium silicate glass-ceramics. A reciprocating friction test and quantitative analysis of the wear morphology were utilized to determine the coefficient of friction (COF) and wear resistance of the test materials. The results showed that the bacterial metabolite medium significantly reduces the COF and wear rate of the three restorative materials and provide better protection against superficial abrasion. When tested under lactic acid medium, a key acid production in bacterial metabolites, similar wear reduction results were observed in the three materials, which confirmed that lactic acid should be accountable for the excellent lubricating property of bacterial metabolites. Furthermore, the resin composite with lower wettability exhibited a more significant wear reduction than the other two materials when lubricating with a bacterial metabolite medium. These findings provide novel insights into the biological basis of lubrication mechanisms in the oral cavity under high-loading and low-velocity conditions.

Effect of aqueous environment on wear resistance of dental glass-ceramics

Background

Wear resistance affects dental ceramics longevity and the functions of the opposing teeth. However, data for the effect of aqueous environment on wear resistance of dental ceramics are lacking. This study evaluated the effect of aqueous environment on wear resistance of typical dental glass–ceramics.

Methods

Disk specimens were prepared from lithium disilicate glass–ceramics (LD) and leucite reinforced glass–ceramics (LEU). The disk specimens paired with steatite antagonists were tested in a pin-on-disk tribometer under both wet and dry conditions with 10 N up to 500,000 wear cycles. The wear analysis of glass–ceramics was performed using a 3D profilometer after 100,000, 300,000 and 500,000 wear cycles. Wear morphologies were analyzed by employing scanning electron microscopy (SEM). The crystalline compositions of specimens stored in a dry environment and subsequently immersed in distilled water for 40 h were separately determined using X-ray diffraction (XRD). The chemical states of the wear surfaces for LD were analyzed by X-ray photoelectron spectroscopy (XPS). The data analysis and multiple pair-wise comparisons of means were performed by using one-way analysis of variance (ANOVA) and Tukey’s post-hoc test.

Results

LEU in a wet environment exhibited less wear volume loss than that in a dry environment (p < 0.05). The volume loss of LD in a wet environment was higher than that in a dry environment (p < 0.05). The wear volumes of steatite antagonists paired with two glass–ceramics under dry conditions were higher than under wet conditions.

Conclusions

XPS spectra of LD under wet conditions indicated that high wear loss might result from the effect of stress corrosion by water and reaction of water with the ionic-covalent bonds at the crack tip. XPS spectra and SEM images of LD under dry conditions showed a possible formation of tribofilm. Within the limitations of this in vitro study, water was wear-friendly to LEU and all opposing steatites but aggravated wear for LD.

An investigation of corrosive effects on zirconia with different crystal structures

This study aimed to compare the time-related corrosive resistance in different corrosive solution environments after sintering of zirconia with different crystal structures. The zirconia samples were produced in pellet form as 12.7 × 3 mm. To determine the time-related corrosion resistance of the sintered samples in sodium carbonate (Na₂ CO₃ ), sodium chloride (NaCl), and citric acid (C₆ H₈ O₇ ) solutions, the weights were measured at baseline then on the first and fifth days and the microhardness values were calculated. For the evaluation of surface appearance, images were obtained with a scanning electron microscope. The baseline microhardness values of the groups with 3 and 10 mol% yttria-stabilized zirconia samples were found to be 1,064 VHN and 1,079 VHN, respectively. The microhardness values of the groups with 3 mol% yttria-stabilized zirconia samples immersed in Na₂ CO₃ 1d (1,010 VHN) and 5d (1,060 VHN), and NaCl (1d (1,010 VHN) and 5d (1,055 VHN) were found to be affected more. The microhardness values of the sample group (1,064 VHN) with 10 mol% yttria doped zirconia which was left for 5 days in citric acid were found to be lower than the sample group (1,120 VHN) with 3 mol% yttria added. C₆ H₈ O₇ was seen to have a greater corrosive effect with increased yttria content and the microhardness value decreased. With longer duration of the samples of all the groups in C₆ H₈ O₇ , NaCl, and Na₂ CO₃ solutions, the surface characteristics of the samples were affected negatively. With prolonged immersion in the corrosive solutions, the resistance to the corrosion causing the changes in the surface topography of the samples was seen to decrease.

Endodontic Retreatment and Comprehensive Endo-Prosthetic of Premolars: A Case Report

Background: The failure of endodontic treatment caused by failure of the restoration and bacterial invation. Alongside proper chemical and mechanical preparation and hermetic obturation of the root canal system, another essential factor is ensuring a permanent and hermetically-sealed restoration following endodontic treatment. Endodontic retreatment encompasses the efforts to salvage a failing previously endodontically treated tooth. As a result of advances in endodontic materials and adhesive systems, restorations in the form of fiber post and adhesively cemented crown are becoming a choice in cases of teeth that have extensive damage. Case: A case is presented a 45-year-old female was referred to Prof. Soedomo Dental Hospital with a complaint of pain in mandibular second premolar which was earlier endodontically treated. Clinical and radiographic examinations showed damaged restorations, gutta percha filling that are not hermetic and radiolucent on periapical. A successful endodontic retreatment premolar using rotary retreatment file and preparation with crown down technique using rotary progressive multiple tapering file, with comprehensive endo-prosthetic treatment using prefabricated fiber post and porcelain fused to metal crown. Conclusion: Clinical and radiographic evaluation after 6 months showed complete healing and good adaptation of the restoration. The outcomes of this case showed that failure of endodontic retreatment respond favorably to endodontic retreatment, with proper indication, prefabricated fiber post and porcelain fused to metal crown can provide an effective conservative and esthetic option for reinforcing endodontically treated teeth.

High-translucent yttria-stabilized zirconia ceramics are wear-resistant and antagonist-friendly

OBJECTIVES

To evaluate two-body wear of three zirconia ceramics stabilized with 3, 4 and 5mol% yttria and to compare their wear behavior with that of a lithium-disilicate glass-ceramic.

METHODS

Sixteen rectangular-shaped specimens made from three grades of zirconia ceramics and a lithium-disilicate glass-ceramic were polished and dynamically loaded in a chewing simulator (2kg vertical load, 2.1Hz) under water at 90°C for 1.2×10⁶ cycles (about 7 days) in the ball-on-plate mode against steatite antagonists. Surface roughness was measured before and after wear testing. Wear tracks were scanned with a non-contact 3D profilometer and super-impositions were used to determine wear loss of the antagonists. Wear surfaces were imaged by SEM. XRD and micro-Raman spectroscopy were used to characterize phase transformation and stress status in the worn and unworn areas of the zirconia ceramics.

RESULTS

Independent of fracture toughness, strength and aging-susceptibility, the three zirconia ceramics showed a similar and limited amount of wear (∼10μm in depth) and were more wear-resistant than the lithium-disilicate glass-ceramic (∼880μm in depth). Abrasive wear without obvious cracks was observed for all investigated zirconias, whereas the glass-ceramic with a lower fatigue threshold and high susceptibility to surface dissolution exhibited significant abrasion, fatigue and corrosion wear. All three zirconia ceramics yielded a lower antagonist wear than the glass-ceramic and no significant differences were found between the zirconia ceramics.

SIGNIFICANCE

In the context of this study, high-translucent zirconia ceramics stabilized with a higher yttria content, recently introduced in the dental field, were as wear-resistant and antagonist-friendly as conventional high-strength zirconia and suitable for monolithic restorations.

Recent advances in understanding the fatigue and wear behavior of dental composites and ceramics

Dental composite and ceramic restorative materials are designed to closely mimic the aesthetics and function of natural tooth tissue, and their longevity in the oral environment depends to a large degree on their fatigue and wear properties. The purpose of this review is to highlight some recent advances in our understanding of fatigue and wear mechanisms, and how they contribute to restoration failures in the complex oral environment. Overall, fatigue and wear processes are found to be closely related, with wear of dental ceramic occlusal surfaces providing initiation sites for fatigue failures, and subsurface fatigue crack propagation driving key wear mechanisms for composites, ceramics, and enamel. Furthermore, both fatigue and wear of composite restorations may be important in enabling secondary caries formation, which is the leading cause of composite restoration failures. Overall, developing a mechanistic description of fatigue, wear, and secondary caries formation, along with understanding the interconnectivity of all three processes, are together seen as essential keys to successfully using in vitro studies to predict in vivo outcomes and develop improved dental restorative materials.