In Vitro Simulation and In Vivo Assessment of Tooth Wear: A Meta-Analysis of In Vitro and Clinical Research

Effect of the Abutment Rigidity on the Wear Resistance of a Lithium Disilicate Glass Ceramic: An In Vitro Study

Lithium disilicate (LDS) glass ceramics are among the most common biomaterials in conservative dentistry and prosthodontics, and their wear behavior is of paramount clinical interest. An innovative in vitro model is presented, which employs CAD/CAM technology to simulate the periodontal ligament and alveolar bone. The model aims to evaluate the effect of the abutment rigidity on the wear resistance of the LDS glass ceramic. Two experimental groups (LDS restorations supported by dental implants, named LDS-on-Implant, or by hybrid ceramic tooth replicas with artificial periodontal ligament, named LDS-on-Tooth-Replica) and a control group (LDS-Cylinders) were compared. Fifteen samples (n = 15) were fabricated for each group and subjected to testing, with LDS antagonistic cusps opposing them over 120,000 cycles using a dual axis chewing simulator. Wear resistance was analyzed by measuring the vertical wear depth (mm) and the volume loss (mm3) on each LDS sample, as well as the linear antagonist wear (mm) on LDS cusps. Mean values were calculated for LDS-Cylinders (0.186 mm, 0.322 mm3, 0.220 mm, respectively), LDS-on-Implant (0.128 mm, 0.166 mm3, 0.199 mm, respectively), and LDS-on-Tooth-Replica (0.098 mm, 0.107 mm3, 0.172 mm, respectively) and compared using one-way-ANOVA and Tukey's tests. The level of significance was set at 0.05 in all tests. Wear facets were inspected under a scanning electron microscope. Data analysis revealed that abutment rigidity was able to significantly affect the wear pattern of LDS, which seems to be more intense on rigid implant-abutment supports compared to resilient teeth replicas with artificial periodontal ligament.

AFM Analysis of a Three-Point Flexure Tested, 3D Printing Definitive Restoration Material for Dentistry

Background: Three-dimensional printing is a rapidly developing technology across all industries. In medicine recent developments include 3D bioprinting, personalized medication and custom prosthetics and implants. To ensure safety and long-term usability in a clinical setting, it is essential to understand material specific properties. This study aims to analyze possible surface changes of a commercially available and approved DLP 3D printed definitive restoration material for dentistry after three-point flexure testing. Furthermore, this study explores whether Atomic Force Microscopy (AFM) is a feasible method for examination of 3D printed dental materials in general. This is a pilot study, as there are currently no studies that analyze 3D printed dental materials using an AFM. Methods: The present study consisted of a pretest followed by the main test. The resulting break force of the preliminary test was used to determine the force used in the main test. The main test consisted of atomic force microscopy (AFM) surface analysis of the test specimen followed by a three-point flexure procedure. After bending, the same specimen was analyzed with the AFM again, to observe possible surface changes. Results: The mean root mean square (RMS) roughness of the segments with the most stress was 20.27 nm (±5.16) before bending, while it was 26.48 nm (±6.67) afterward. The corresponding mean roughness (Ra) values were 16.05 nm (±4.25) and 21.19 nm (±5.71) Conclusions: Under three-point flexure testing, the surface roughness increased significantly. The p-value for RMS roughness was p = 0.003, while it was p = 0.006 for Ra. Furthermore, this study showed that AFM surface analysis is a suitable procedure to investigate surface changes in 3D printed dental materials.

Effect of Different Mixing Methods on Physicochemical Properties of Mineral Trioxide Aggregate: A Systematic Review

Background

Mineral trioxide aggregate (MTA) is a commonly used endodontic biomaterial. The physicochemical properties of MTA have a crucial role in designating clinical outcome, and different factors can affect these properties. Various methods have been used for mixing MTA, including manual, mechanical, and ultrasonic. The aim of this systematic review was to evaluate the effect of different mixing methods on the physicochemical properties of MTA.

Materials and Methods

Electronic databases including PubMed, Embase, Web of Science, and Scopus were searched up to May 2022. In order to cover gray literature, the ProQuest and Google Scholar databases were also searched to detect theses and conference proceedings. For quality assessment of the included studies, we used a modified version of the Cochrane risk of bias tool for randomized controlled trials (RCTs). Experimental studies which had assessed at least one property of MTA and compared at least two different mixing methods of MTA were included in this study. All animal studies, reviews, case reports, and case series were excluded.

Results

Fourteen studies were included. The results showed that the ultrasonic mixing method significantly improved some MTA characteristics, including microhardness, flowability, solubility, setting time, and porosity. However, the mechanical mixing method improved other properties including flowability, solubility, push-out bond strength, and hydration. The manual mixing method showed inferior results compared to other mixing methods in terms of microhardness, flowability, solubility, setting time, push-out bond strength, porosity, and hydration. Different mixing methods had a similar effect on compressive strength, sealing ability, pH and calcium ion release, volume change, film thickness, and flexural strength of MTA.

Conclusion

Mechanical and ultrasonic mixing methods are superior to the manual mixing method in terms of improving physicochemical properties of MTA. No report of selection bias and varieties in methodologies were limitations of evidence.

Wear Properties of Conventional and High-Translucent Zirconia-Based Materials

This study investigated the two-body wear resistance of a first generation 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP), a second generation 3Y-TZP, a third generation 4 mol% yttria partially stabilized zirconia (4Y-PSZ), a 5 mol% yttria partially stabilized zirconia (5Y-PSZ), and a type III gold alloy (Aurocast 8), performed using opposing antagonistic cusps made out of the same material. Eight cylindrical specimens were prepared for each material (n = 8) for a total of forty specimens (N = 40). Conical cusps were fabricated for each material. Each cylinder−cusp pair was arranged inside a two-axis chewing simulator over up to 360,000 loading cycles. The wear resistance was analyzed by measuring the vertical substance loss (mm) and the volume loss (mm3). The antagonist wear (mm) was recorded before and after the wear test to evaluate the linear difference. Statistical analysis was performed using one-way analysis of variance (ANOVA); multiple comparisons were performed according to Tukey’s method. No statistically significant differences (p > 0.05) among the first generation 3Y-TZP, second generation 3Y-TZP, and 4Y-PSZ wear were found. 5Y-PSZ showed statistically significant higher wear compared to other the zirconias. Aurocast 8 displayed the highest values in terms of vertical wear, antagonist cusp wear, and volumetric loss. Although still not statistically comparable, the wear behavior of the latest 5Y-PSZ was the closest to the widely recognized gold standard represented by the type III gold alloy.

Wear of Polymer-Infiltrated Ceramic Network Materials against Enamel

Polymer-infiltrated ceramic network materials (PICNs) have high mechanical compatibility with human enamel. However, the wear properties of PICN against natural human enamel have not yet been clarified. We investigated the in vitro two-body wear behaviors of PICNs and an enamel antagonist. Two PICNs were used: Experimental PICN (EXP) prepared via the infiltration of methacrylate-based resin into the porous silica ceramic network and commercial Vita Enamic (ENA). Two commercial dental ceramics, lithium disilicate glass (LDS) and zirconia (ZIR), were also characterized, and their wear performance was compared to PICNs. The samples were subjected to Vickers hardness tests and two-body wear tests that involve the samples being cyclically impacted by enamel antagonists underwater at 37 °C. The results reveal that the Vickers hardness of EXP (301 ± 36) was closest to that of enamel (317 ± 17). The volumetric wear losses of EXP and ENA were similar to those of LDS but higher than that of zirconia. The volumetric wear loss of the enamel antagonist impacted against EXP was moderate among the examined samples. These results suggest that EXP has wear behavior similar to that of enamel. Therefore, PICNs are mechanically comparable to enamel in terms of hardness and wear and are excellent tooth-restoration materials.

Occlusal change in posterior implant-supported single crowns and its association with peri-implant bone level: a 5-year prospective study

OBJECTIVES

This study aims to analyze the 5-year occlusal change in posterior implant-supported single crowns and the association between the relative occlusal force (ROF) and peri-implant bone level.

MATERIALS AND METHODS

Partially edentulous patients who had received implant-supported single crowns in the posterior region were included. Occlusal examinations with a computerized occlusion analysis system were conducted at 0.5, 3, 6, 12, 24, 36, 48, and 60 months after delivery of the implant-supported single crown. The ROFs of implant-supported single crowns, mesial adjacent teeth, and control natural teeth were recorded. Intraoral periapical radiographs were taken at each follow-up time to evaluate marginal bone level (MBL). Ordinary least square regression was used to analyze the association between ROF and MBL.

RESULTS

Thirty-seven posterior implant-supported single crowns in 33 participants (23.9 to 70.0 years) were followed up for 0.5 to 60 months [(42.4 ± 26.0) months]. The ROF of implant-supported single crowns increased from 2 weeks to 3 months (P < 0.01) and increased continuously between all two sequential time points from 6 to 36 months, with significant differences (P < 0.05). Then ROFs of implant-supported single crowns were significantly higher than those of control teeth at 48 and 60 months (P < 0.05). Regression analysis showed that ROF was significantly associated with MBL with a coefficient of 0.008 (P < 0.05).

CONCLUSION

The ROFs of posterior implant-supported single crown have significant change during 5 years' follow-up. The association between ROF and MBL has limited clinical significance.

TRIAL REGISTRATION

Chinese Clinical Trial Registry: ChiCTR-ROC-17012240.

CLINICAL RELEVANCE

The occlusion of implant-supported single crowns should be carefully monitored during follow-up examinations, and occlusal adjustment should be considered to prevent overloading.

Wear Behavior and Surface Quality of Dental Bioactive Ions-Releasing Resins Under Simulated Chewing Conditions

Bioactive materials can reduce caries lesions on the marginal sealed teeth by providing the release of ions, such as calcium, phosphate, fluoride, zinc, magnesium, and strontium. The presence of such ions affects the dissolution balance of hydroxyapatite, nucleation, and epitaxial growth of its crystals. Previous studies mostly focused on the ion-releasing behavior of bioactive materials. Little is known about their wear behavior sealed tooth under mastication. This study aimed to evaluate the wear behavior and surface quality of dental bioactive resins under a simulated chewing model and compare them with a resin without bioactive agents. Three bioactive resins (Activa, BioCoat, and Beautifil Flow-Plus) were investigated. A resin composite without bioactive agents was used as a control group. Each resin was applied to the occlusal surface of extracted molars and subjected to in vitro chewing simulation model. We have assessed the average surface roughness (Ra), maximum high of the profile (Rt), and maximum valley depth (Rv) before and after the chewing simulation model. Vickers hardness and scanning electron microscopy (SEM) also analyzed the final material surface quality). Overall, all groups had increased surface roughness after chewing simulation. SEM analysis revealed a similar pattern among the materials. However, the resin with polymeric microcapsules doped with bioactive agents (BioCoat) showed increased surface roughness parameters. The material with Surface Pre-reacted Glass Ionomer (Beautifil Flow-Plus) showed no differences compared to the control group and improved microhardness. The addition of bioactive agents may influence surface properties, impairing resin composites' functional and biological properties. Future studies are encouraged to analyze bioactive resin composites under high chemical and biological challenges in vitro with pH cycles or in situ models.

Presence of SARS-CoV-2 and Its Entry Factors in Oral Tissues and Cells: A Systematic Review

Background and Objectives: The aim of this systematic review is to summarize the current data about the presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its entry factors in oral tissues and cells. Materials and Methods: This systematic review was carried out based on the Preferred Reporting Items for a Systematic Review and Meta-Analysis (PRISMA). Three databases were analyzed (Pubmed, Web of science and Scopus) by three independent researchers. From the 18 identified studies, 10 of them met the inclusion criteria. The presence of SARS-CoV-2 or its entry factors (angiotensin-converting enzyme II (ACE2), transmembrane serine proteases (TMPRSS), and furin) was analyzed in these 10 studies during the pandemic. Results: ACE2 expression was analyzed in 9 of the 10 studies. ACE2 is expressed mainly in the tongue, oral mucosa, salivary glands and epithelial cells. The expression of the TMPRSS2 gene or protein was analyzed in 6 studies. These studies reported that the expression of TMPRSS2 was mainly in the salivary glands, tongue, sulcular epithelium and oral mucosa; as well as in cells of the salivary glands (ductal, acinar and myoepithelial cells) and the tongue (the spinous-based cell layer, horny layer and the epithelial surface). Other TMPRSS were also reported. The expression of TMPRSS3, TMPRSS4, TMPRSS5, TMPRSS7 and TMPRSS11D was reported mainly in salivary glands and in epithelial-type cells. Furan expression was analyzed in three studies. The expression of furin was detected mainly in epithelial cells of the tongue. A variety of methods were used to carry out the detection of SARS-CoV-2 or its input molecules. Conclusions: These results show that SARS-CoV-2 can infect a wide variety of oral tissues and cells, and that together with the theories dedicated to explaining the oral symptoms present in SARS-CoV-2 positive patients, it provides us with a good scientific basis for understanding the virus infection in the oral cavity and its consequences.

Biomechanical effects of dental implant diameter, connection type, and bone density on microgap formation and fatigue failure: A finite element analysis

BACKGROUND AND OBJECTIVE

Understanding fatigue failure and microgap formation in dental implants, abutments, and screws under various clinical circumstances is clinically meaningful. In this study, these aspects were evaluated based on implant diameter, connection type, and bone density.

METHODS

Twelve three-dimensional finite element models were constructed by combining two bone densities (low and high), two connection types (bone and tissue levels), and three implant diameters (3.5, 4.0, and 4.5 mm). Each model was composed of cortical and cancellous bone tissues, the nerve canal, and the implant complex. After the screw was preloaded, vertical (100 N) and oblique (200 N) loadings were applied. The relative displacements at the interfaces between implant, abutment, and screw were analyzed. The fatigue lives of the titanium alloy (Ti-6Al-4V) components were calculated through repetitive mastication simulations. Mann-Whitney U and Kruskal-Wallis one-way tests were performed on the 50 highest displacement values of each model.

RESULTS

At the implant/abutment interface, large microgaps were observed under oblique loading in the buccal direction. At the abutment/screw interface, microgap formation increased along the implant diameter under vertical loading but decreased under oblique loading (p < 0.001); the largest microgap formation occurred in the lingual direction. In all cases, the bone-level connection induced larger microgap formation than the tissue-level connections. Moreover, only the bone-level connection models showed fatigue failure, and the minimum fatigue life was observed for the implant diameter of 3.5 mm.

CONCLUSIONS

Tissue-level implants possess biomechanical advantages compared to bone-level ones. Two-piece implants with diameters below 3.5 mm should be avoided in the posterior mandibular area.

Comparison of mechanical properties of different reinforced glass-ceramics

STATEMENT OF PROBLEM

Data concerning the mechanical properties of the newly developed lithium disilicate ceramic HS10PC are lacking.

PURPOSE

The purpose of this in vitro study was to investigate the flexural strength (FS), Martens hardness (HM), indentation modulus (E_IT), fracture load (FL), and wear resistance (WR) of HS10PC compared with those of the established glass-ceramics IPS e.max Press and IPS Empress Esthetic.

MATERIAL AND METHODS

Four pressable glass-ceramics were examined: HS10PC (estetic ceram ag), IPS e.max Press low translucency (LT) and high translucency (HT; Ivoclar Vivadent AG), and IPS Empress Esthetic (ES; Ivoclar Vivadent AG). For each material, a total of 85 specimens were fabricated. Specimens were subdivided into 4 groups for FS (n=30), HM, E_IT (n=10), and FL measurement according to the Voss test after artificial aging in an autoclave (n=15), artificial aging in a mastication simulator (n=15), and no artificial aging (n=15). In addition, WR (n=10) was measured after 240 000, 600 000, and 1 200 000 masticatory cycles. Data were statistically analyzed using the global univariate ANOVA, the Scheffé post hoc and paired t tests, and Weibull distribution (α=.05).

RESULTS

HT showed the highest FS, while ES presented the lowest FS of all groups (P<.001). ES showed lower values for HM (P<.001), E_IT (P<.001), and FL for specimens treated in an autoclave and mastication simulator (P<.001) compared with all other groups. An increase in the wear of the ceramic and enamel antagonist between 240 000 and 1 200 000 masticatory cycles was observed for all groups (P<.001). After 1 200 000 masticatory cycles, HS10PC presented less wear of the ceramic than the other 3 materials (P=.003).

CONCLUSIONS

The newly developed lithium disilicate ceramic HS10PC showed comparable results with the established IPS e.max Press for FS, HM, E_IT, FL, and WR. Lithium disilicate ceramics presented higher mechanical results than the leucite-reinforced ES, with all the ceramics showing similar results for the WR of the enamel antagonist.

Limited Evidence Supports Polished Monolithic Zirconia as Less Likely to Cause Antagonist Enamel Wear Compared to Other Prosthetic Materials

ARTICLE TITLE AND BIBLIOGRAPHIC INFORMATION

Antagonist enamel wear of tooth-supported monolithic zirconia posterior crowns in vivo: A systematic review. Gou M, Chen H, Kang J, Wang H. J Prosthet Dent 2019;121:598-603.

SOURCE OF FUNDING

This study was funded by the authors.

TYPE OF STUDY/DESIGN

Systematic review and meta-analysis.