Wear of dental materials: Clinical significance and laboratory wear simulation methods -A review

Wear characteristics of resin-based luting agents used in the bonded CAD-CAM resin blocks

This study aimed to investigate the wear and microhardness of luting agents and computer-aided design-computer-aided manufacturing (CAD-CAM) resin blocks, and to compare the wear characteristics of resin-based luting agents used in bonded specimens of CAD-CAM resin blocks. After three-body wear test, the amount of wear and Vickers hardness were measured and Pearson's correlation coefficient was calculated. The lowest amount of wear and the highest Vickers hardness values were obtained for Estecem II. Filler loss was observed in five composite resin cements. A strong negative correlation was observed in the luting agents between the amount of wear and Vickers hardness value (r=-0.874, p<0.0001). Additionally, a strong positive correlation was observed between the amount of wear of the bonded specimen and amount of luting agent used alone (r=0.943, p<0.0001). To conclude, the wear resistance of the luting agent used in the bonded specimen was significantly influenced by the bonding between the filler and matrix resin.

Flexural Properties, Wear Resistance, and Microstructural Analysis of Highly Filled Flowable Resin Composites

OBJECTIVE

This study aimed to evaluate the flexural properties and two-body wear resistance of nine highly filled flowable resin composites relative to those of viscous and conventional low-filled flowable composites. In addition, scanning electron microscopy (SEM) analysis of the microstructures was performed.

METHODS AND MATERIALS

For each resin composite group (n=12), 12 specimen bars (25 mm × 2 mm × 2 mm) were fabricated using a silicon mold for performing flexural strength (FS), flexural modulus (E), flexural toughness (FT), Weibull modulus (m) tests, and SEM microstructural analysis. For each group, ten bars were tested using a three-point flexural test on a universal testing machine, while the other two were embedded in acrylic resin before being observed by SEM for structural analysis. During the two-body wear test with a chewing simulator, 8 specimens (12 groups, n=8) of each resin composite group were manufactured in a specific mold and subjected to 120,000 cycles of wear against a steatite ball, and the depth loss was measured. Three one-way ANOVA tests followed by Tukey's post hoc tests were conducted to compare the flexural and wear properties among the different groups.

RESULTS

The majority of highly filled composites tested in this study exhibited similar flexural strengths (between 105.68 MPa and 135.49 MPa) and superior wear resistance to those of viscous composites. The flexural moduli (between 5.12 GPa and 9.62 GPa) of these composites were in between those of the viscous and low-filled composites tested in this study.

CONCLUSIONS

The highly filled flowable composites tested in this study exhibited different in vitro properties but were often superior to those of viscous resin composite suggesting their possible use for posterior restorations.

Developing an optimised method for accurate wear testing of dental materials using the 'Rub&Roll' device

Dental materials are challenged by wear processes in the oral environment and should be evaluated in laboratory tests prior to clinical use. Many laboratory wear-testing devices are high-cost investments and not available for cross-centre comparisons. The 'Rub&Roll' wear machine enables controlled application of force, chemical and mechanical loading, but the initial design was not able to test against rigid antagonist materials. The current study aimed to probe the sensitivity of a new 'Rub&Roll' set-up by evaluating the effect of force and test solution parameters (deionized water; water + abrasive medium; acid + abrasive medium) on the wear behaviour of direct and indirect dental resin-based composites (RBCs) compared with human molars against 3D-printed rod antagonists. Molars exhibited greater height loss than RBCs in all test groups, with the largest differences recorded with acidic solutions. Direct RBCs showed significantly greater wear than indirect RBCs in the groups containing abrasive media. The acidic + abrasive medium did not result in increased wear of RBC materials. The developed method using the 'Rub&Roll' wear machine in the current investigation has provided a sensitive wear test method to allow initial screening of resin-based composite materials compared with extracted human molars under the influence of different mechanical and erosive challenges.

Surface roughness, wear, and abrasiveness of printed and milled occlusal veneers after thermomechanical aging

STATEMENT OF PROBLEM

Occlusal veneers are a conservative method of reestablishing vertical dimensions of occlusion (VDO) for worn teeth. A restorative material used for occlusal veneers should have a smooth surface, adequate wear resistance, and low abrasiveness to the antagonists, as total wear of occlusal veneers and their antagonists determines the stability of the reestablished VDO. Studies on roughness, wear, and abrasiveness of occlusal veneers are scarce.

PURPOSE

The purpose of this in vitro study was to assess the surface roughness, wear, and abrasiveness of printed and milled occlusal veneers after thermomechanical aging against natural cusps and restorative materials.

MATERIAL AND METHODS

Forty-eight extracted mandibular first molars were prepared for occlusal veneers and scanned with an intraoral scanner. The scans were exported to a computer-aided design program to design the occlusal veneers in 3 groups (n=16) according to the restorative material: group IP: milled lithium disilicate; group EN: milled hybrid ceramic (Vita Enamic), group VA: printed hybrid ceramic (Varseosmile Crown plus). The occlusal veneers in each group were bonded to their corresponding abutments and subjected to 250 000 mechanical cycles and a simultaneous 1000 thermal cycles in a mastication simulator. During thermomechanical aging, half of the specimens of each study group (n=8) were opposed by natural cusps (antagonist C) and the other half by antagonist cusps fabricated from the same restorative material as the occlusal veneers (antagonist R). The wear of the occlusal veneers and their antagonists was assessed with a 3-dimensional processing software program. The surface roughness of the veneers was assessed with a contact profilometer. The results were statistically analyzed with a 2-way ANOVA followed by the post hoc Tukey HSD test (α=.05).

RESULTS

The 2-way ANOVA indicated a significant effect for the material and the antagonist on surface roughness, wear, and abrasiveness (P<.05). When opposed by antagonist C, VA showed significantly higher surface roughness than IP and EN (P<.001). VA had significantly higher surface wear followed by EN and IP (P<.001). IP caused significantly higher wear to antagonist C than EN and VA (P<.001). In addition, IP had significantly higher total wear (combined wear of veneers and their antagonists) followed by VA and EN (P<.001). When opposed by antagonist R, no significant difference was found among the 3 materials for surface roughness (P=.08), material wear (P=.12), opposing wear (P=.11), or total wear (P=.11).

CONCLUSIONS

Both material and antagonist had a significant effect on surface roughness and occlusal stability when occlusal veneers were fabricated to restore VDO. VA had significantly more surface roughness and wear than EN and IP when opposed by natural cusps. IP abraded natural cusps significantly more than EN and VA. The 3 tested materials showed similar roughness, wear, and abrasiveness when opposed by the same material.

Effect of gastric acids on the mechanical properties of conventional and CAD/CAM resin composites - An in-vitro study

OBJECTIVES

Dental erosion in patients with gastroesophageal reflux disease (GERD) is a current and frequent condition that may compromise the mechanical properties and clinical durability of resin-based composites (RBCs). This study assessed the mechanical properties of conventional and computer-aided design/computer-aided manufacturing (CAD/CAM) RBCs subsequent to simulated gastric acid aging.

MATERIALS AND METHOD

Three conventional and three CAD/CAM composites were assessed. They were divided into an experimental group (exposed to simulated gastric acid aging) and a control group (no aging). Both groups were analyzed for Vickers microhardness (VHN), wear and flexural strength over a period of six months. The failure rate probability for each RBC was calculated through the Weibull cumulative distribution function (m). Statistical analysis was conducted using repeated measures ANOVA, 3-way ANOVA, a non-parametric Kruskal-Wallis and U Mann-Whitney tests (α = 0.05).

RESULTS

The mechanical properties of all the RBCs dropped significantly after aging (p < 0.05). Lower VHN and flexural strength values, along with greater wear values were evident in the experimental groups, though the effects of the treatment varied between RBCs. The Weibull m of all the RBCs decreased over time.

CONCLUSION

Conventional RBCs might show greater reduction in mechanical properties compared to CAD/CAM RBCs when exposed to gastric acid attack. Thus, CAD/CAM composites may represent a suitable choice for the treatment of patients presenting erosive issues.

Aging processes in dental thermoplastics - Thermoanalytical investigations and effects on Vickers as well as Martens hardness

OBJECTIVE

The influence of various aging protocols, representing and accelerating influences present in the dental context, on possible changes in the microstructure and mechanical properties of thermoplastics was investigated. In order to minimize the complexity of the systems, first pure polymers and then later the equivalent dental polymeric materials were analyzed.

MATERIALS AND METHODS

Pure polymers (Poly(methyl methacrylate) - PMMA, Polyoxymethylene homopolymer - POM-H, Polyether ether ketone - PEEK, Nylon 12 - PA12, Polypropylene - PP) were analyzed before as well as after applying different aging protocols relevant to the oral environment (ethanol, thermocycling, alkaline and acidic setting) by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermoanalytical parameters used were glass transition temperature (Tg), melting peak and crystallization peak temperature (Tpm, Tpc) and decomposition behavior. In a second step selected commercially available dental products (Telio CAD - PMMAD, Zirlux Acetal - POMD, Juvora Natural Dental Disc - PEEKD) aged by the protocol that previously showed strong effects were examined and additionally tested for changes in their Vickers and Martens hardness by Mann-Whitney-U test.

RESULTS

The combinations of pure polymers and viable aging protocols analyzed within this study were identified via TGA or DSC as PA12 & thermocycling, POM-H & denture cleanser/lactic acid/ethanol, PP & lactic acid. The dental polymeric materials PMMAD and POMD due to aging in lactic acid showed slight but significantly (p < 0.01) reduced Vickers and partly Martens hardness. PEEK showed the greatest material resistance within this study.

Intraoral Scanning for Monitoring Dental Wear and Its Risk Factors: A Prospective Study

Dental wear arises from mechanical (attrition or abrasion) and chemical (erosion) factors. Despite its prevalence and clinical significance, accurately measuring and understanding its causes remain challenging in everyday practice. This one-year study with 39 participants involved comprehensive examinations and full-arch intraoral scans at the start and after 12 months. Volume loss exceeding 100 µ on each tooth's surfaces (buccal, lingual/palatine and incisal/occlusal) was measured by comparing three-dimensional scans from both time points. This study also assessed factors such as abrasion and erosion through clinical exams and questionnaires. There were no significant differences in dental wear in participants with sleep bruxism. However, noticeable wear occurred in the front teeth of those with waking bruxism and joint-related symptoms. Increased wear was associated with frequent consumption of acidic drinks, regular swimming, dry mouth, nocturnal drooling and heartburn, while no significant wear was found in patients with reflux. The used methodology proved effective in accurately assessing the progression of dental wear, which is important as many patients may initially be asymptomatic. The variability observed in dental wear patterns underscores the need to develop specific software applications that allow immediate and efficient comparison of wear areas based on extensive analysis of patient databases.

CAD/CAM leucite-reinforced glass-ceramic for simulation of attrition in human enamel in vitro

OBJECTIVE

Investigate attrition simulation using CAD/CAM leucite-reinforced glass-ceramic antagonists on occlusal vs. buccal enamel.

METHODS

Three dental materials with known wear rates (resin-modified glass-ionomer, micro-filled, and fine particle composites) validated the wear simulator (CAD/CAM glass-ceramic antagonists, 200 cycles, 80 N load, deionised water irrigation, 0.7 mm sliding movement). Following this, human molars were sectioned into paired occlusal and buccal polished samples (n = 8/gp). Exposed 1.5 mm Ø enamel areas were subjected to attritional wear with and without pre-immersion in citric acid (5 min, 0.3%, pH 3.8). Profilometry measured step-height enamel wear and surface microhardness at different depths was calculated using Vickers indentation at 0.1 N and 0.5 N loads.

RESULTS

Dental material wear using the CAD/CAM antagonists showed consistency with previous data: mean (SD) resin-modified glass ionomer material loss of 177.77 (16.89) µm vs. 22.15 (1.30) µm fine particle hybrid composite resin wear vs. 13.63 (1.02) µm micro filled composite resin wear (P < 0.001). The coefficient of variation was less than 10%. Following validation, enamel sample wear was significantly increased when attrition was introduced (P < 0.001) independent of buccal vs. occlusal sample location (P < 0.05). Attrition resulted in occlusal wear of 26.1 ± 4.5 µm vs. buccal 26.3 ± 1.2 µm and attrition/erosion resulted in occlusal wear of 26.05 ± 4.46 µm vs. buccal 25.27 ± 1.16 µm. Whereas erosion-alone resulted in occlusal wear of 1.65 ± 0.13 µm and buccal 1.75 ± 0.03 µm. Microhardness testing at different loads revealed significantly greater hardness reductions in occlusal enamel vs. buccal enamel for 0.1 KgF indentations (P < 0.001) whereas in contrast 0.5 KgF indentations showed no differences.

SIGNIFICANCE

Wear simulation with CAD/CAM glass ceramic antagonists produced consistent wear in dental materials and human enamel, regardless of enamel surface origin. Lighter (0.1 KgF) hardness testing of occlusal vs. buccal origin revealed damage to the mechanical integrity of the superficial worn enamel.

An In Vitro Study regarding the Wear of Composite Materials Following the Use of Dental Bleaching Protocols

Composite materials used in dental restorations are considered resistant, long-lasting and aesthetic. As the wear of restorations is an important element in long-term use, the aim of this study was to evaluate the surface condition of nanohybrid and microfilled composite resins, after being subjected to the erosive action of dental bleaching protocols. This paper reflects a comparative study between one nanofilled composite and three microfilled composites used in restorations. For each composite, three sets of samples (under the form of composite discs) were created: a control group, an "office bleach" group with discs bleached with 40% hydrogen peroxide gel, and a "home bleach" group with discs bleached with 16% carbamide peroxide gel. Wear was numerically determined as the trace and the coefficients of friction obtained using a tribometer, the ball-on-disk test method, and two balls: alumina and sapphire. For all composite groups, there were statistically significant differences between the wear corresponding to the control and bleaching groups, for both testing balls. Regarding the composite type, the largest traces were recorded for GC Gradia direct anterior, for all groups, using the alumina ball. In contrast, for the sapphire ball, 3M ESPE Filtek Z550 was characterized by the largest traces. With respect to the friction coefficients, the "office bleach" group recorded the largest values, no matter the composite or the ball type used. The 3M ESPE Valux Plus composite recorded the largest friction coefficients for the alumina ball, and 3M ESPE Filtek Z550 for the sapphire ball. Overall, the "office bleach" group was characterized by higher composite wear, compared to the "home bleach" protocol or control group. Nanofilled composite resins showed superior wear resistance to microfilled resins after undergoing a bleaching protocol.

Load-bearing capacity and wear characteristics of short fiber-reinforced composite and glass ceramic fixed partial dentures

The aim of this study was to evaluate load-bearing capacity and wear performance of experimental short fiber-reinforced composite (SFRC) and conventional lithium-disilicate CAD/CAM fabricated fixed partial dentures (FPDs). Two groups (n = 12/group) of three-unit CAD/CAM fabricated posterior FPDs were made. The first group used experimental SFRC blocks, and the second group fabricated from lithium-disilicate (IPS e.max CAD). All FPDs were luted on a zirconia testing jig with dual-curing resin cement. Half of FPDs per group were quasi-statically loaded until fracture. The other half experienced cyclic fatigue aging (100.000 cycles, Fmax = 500 N) before loading quasi-statically until fracture. Fracture mode was examined using SEM. Wear test was performed using 15,000 loading cycles. Both material type and aging had a significant effect on the load-bearing capacity of FPDs. Experimental SFRC CAD without fatigue aging had significantly the highest load-bearing capacity (2096 ± 149N). Cyclic fatigue aging decreased the load-bearing capacity of the SFRC group (1709 ± 188N) but increased it for the lithium-disilicate group (1546 ± 155N). Wear depth values of SFRC CAD (29.3μm) were significantly lower compared to lithium-disilicate (54.2μm). Experimental SFRC CAD demonstrated the highest load-bearing capacity before and after cyclic fatigue aging, and superior wear behavior compared to the control material.

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.

The influence of hydrothermal fatigue on the clinically relevant functional properties of conventional glass-ionomer cements

During their everyday service, the restorative dental materials are subjected to temperature changes which can be viewed as intensive in the context of the highest allowed temperatures for these materials. In this work, the effect of hydrothermal fatigue on the in vitro tribological performance, compression strength, microhardness, and surface roughness of glass-ionomer cements was studied. Samples of 3 commercially available cements were divided into the reference (aged 14 days) and thermocycled (20,000 cycles; 5-55 °C) groups. The results obtained show that functional properties of the specimens subjected to thermal fatigue significantly differ from the literature data on the cements aged at constant temperatures. The effect of hydrothermal fatigue on the functional properties of cements is discussed in the context of processes induced by exposure to variable temperatures.

Influence of thermo-mechanical aging on fracture resistance and wear of digitally standardized chairside computer-aided-designed/computer-assisted-manufactured restorations

OBJECTIVES

To investigate the influence of thermal cycling and mechanical loading (TCML) aging on fracture resistance and wear behavior of various chairside computer-aided-designed/computer-assisted-manufactured (CAD/CAM) premolar crowns cemented on standardized tooth abutments.

METHODS

Eighty chairside CAD/CAM crowns were prepared using lithium disilicate (IPS e.max CAD; EM), zirconia-infiltrated lithium silicate (Celtra Duo; CD), polymer-infiltrated ceramic network (Vita Enamic; VE), and resin nanoceramics (Cerasmart; CS) (n = 20). The specimens were divided into two groups (n = 10). In one group, they were subjected to TCML: thermocycling (6000 cycles in distilled water at 5-55 °C) and mechanical loading (50 N for 1.2 × 10⁶ cycles), while in control group they were stored in distilled water (37 °C for 24 h). The fracture load, height loss, and volume wear of the crowns were measured after TCML. Fractography was performed on fractured specimens. Data were analyzed using analysis of variance and multiple comparison tests (α=0.05).

RESULTS

The mean fracture loads of EM and CD were significantly higher than those of EC and CS (p<0.05). There was no significant change in the fracture load of any CAD/CAM crowns after TCML (p>0.05). CS exhibited a significantly higher volume wear than the other materials investigated. The wear tracts of all TCML crowns acted as failure origins during the fracture test.

CONCLUSIONS

The fracture resistance of glass-ceramic CAD/CAM crowns was significantly higher than that of resin composite crowns. A 5-year TCML aging did not affect the fracture resistance of CAD/CAM crowns investigated. However, TCML treatment produces a larger wear track in CS than in other materials.

CLINICAL SIGNIFICANCE

Appropriate chairside CAD/CAM restorative material should be selected for successful clinical practice after considering the fracture and wear resistance of the crowns.

Wear behavior of materials for additive manufacturing after simulated occlusion of deciduous dentition

OBJECTIVES

To evaluate wear characteristics of materials for additive manufacturing (AM) after a simulated occlusal test in primary teeth. Wear was simulated by means of impacting - sliding wear testing (ISWT) between specimens prepared from materials for AM against enamel derived from deciduous teeth.

METHODS

The prepared hemispherical upper specimens were subjected to impacting-sliding wear test (ISWT) machine against the flattened enamel of deciduous molars on lower specimens. The samples were subjected to 20,000 load cycles using a contact force of 30 N between the opposing surfaces under controlled conditions. In the upper specimens, five groups (n=9): four types of additively manufactured materials Dima, Zenith, Detax, Veltz and a deciduous enamel groups were tested in this study. The enamel-to-enamel group was used as the control. Wear characteristics comprised wear surface area, wear depth, wear volumetric loss, and surface roughness were measured with a confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Data obtained were statistically analyzed by Kruskal-Wallis test and Dunn's test with Bonferroni correction (p < 0.05).

RESULTS

Dima showed significantly higher worn surface area (p = 0.009, 0.001, and < 0.001 for Zenith, Detax, and control enamel, respectively), volumetric loss (p = 0.027, 0.007, and < 0.001 for Zenith, Detax, and control enamel, respectively), and damaged opposing enamel (p = 0.002, 0.001, and 0.01 for Detax, Veltz, and control enamel, respectively). There was no significant difference among the volumetric loss in Zenith and Detax. However, SEM revealed that Zenith showed rough worn surfaces and chipping, Detax showed rather a smooth circular worn surface. The worn area of Veltz was smaller than Detax and Zenith at 5,000 cycles, but higher at 15,000 and 20,000 cycles, and SEM showed detachment.

CONCLUSION

Wear behavior was different among different materials for AM. In the upper specimens, DM and VZ showed large wear. In the lower specimens, DM caused largest enamel wear and damage. In contrast, ZT and DX showed lower wear and caused less damage to the antagonistic primary enamel. SEM image of ZT showed large losses due to chipping, whereas DX showed the rather smooth. DX was confirmed to have lowest wear and caused least damage to the opposing deciduous enamel, which might be applicable as restorative treatments in deciduous dentition.

SIGNIFICANCE

Additive manufactured dental materials could be considered as a treatment modality in deciduous teeth.

Influence of filler types on wear and surface hardness of composite resin restorations

OBJECTIVE

Wear and surface hardness of resin composites are of relevance from the clinical standpoint. With the incorporation of novel filler system, more studies need to be performed to investigate newly marketed resin composites. The objective of this study was to investigate the abrasive wear and surface hardness of dental restorative with different filler types.

METHODS

Nanohybrid filled Harmonize (HM) and Tetric N-Ceram (TNC), microhybrid filled Filtek Z250 (Z250), nanofilled Filtek Z350 (Z350) were included in the study. Twelve cylindrical resin composites specimens with 10 mm in diameter and 6 mm in thickness were prepared for abrasive wear test. Eight hundred cycles under 17 kg load were conducted for final wear by CW3-1 wear machine. The specimen was cleaned with an ultrasonic unit for 3 min followed with drying procedure. After measurement of weight loss and the density of specimens, the specimens were kept for measurement of surface hardness. Surface hardness was measured using a micro-hardness tester with a Vickers diamond indenter after polishing. Three specimens of each material were observed by scanning electron microscopy (SEM) after the abrasion to evaluate the morphology of the surface. Data were analyzed using one-way analysis of variance (ANOVA), followed by Tukey HSD test (α = .05).

RESULTS

Z250 performed the least volume wear loss (41.1 ± 2.1 mm3), as well as the hardest value (102.7 ± 2.9 HV). There was no significant difference with the volume wear loss (p = 1.000) and surface hardness (p = 0.874) of HM and TNC. SEM images of nanohybrid filled HM and TNC represented smoother surface compared with other types of resin composites.

CONCLUSIONS

Microhybrid Z250 showed the highest wear resistance and surface hardness, nanofilled and nanohybrid resin composites may still face the insufficient of wear and surface hardness quality.

Effect of defect size and tooth anatomy in the measurements of a 3D patient monitoring tool

Purpose

To assess the influence of defect size and tooth anatomy on the measurements performed by a 3D patient monitoring tool.

Methods

A fully dentate model was scanned to obtain a master digital file. Virtual duplicates received defects created in molars (16, 18, 28) and incisors (11, 12, 22), according to different depths (60, 80, 120 microns) and sizes (small, medium, large) totaling 180 conditions. The surface changes measured by the 3D Patient Monitoring Tool (3Shape TRIOS Patient Monitoring [TPM]) were compared with the reference by 2 calibrated operators. False Positives (FP), and False Negatives (FN) defect were registered. Pearson chi-square test, Multivariate binary logistic regression and Spearman rank correlation were used to evaluate the data (α = 0.05).

Results

A significant association was found between the area and the presence of FP and FN (P < .01). Larger defects had higher chances to present FP or an FN respectively. There was a significant association between the tooth and the presence of a FP value (FP, P = .02; FN, P = .005) specially in molars. No significant association was found between the defect depth and the presence of a FP value. Spearman rank correlation showed a strong association between the presence of an FP and an FN (r = 0.858, P < .01).

Conclusions

The defect size and tooth anatomy significantly affected the virtual follow-up, whereas defect depth did not. Small defects were correctly detected in all cases. An incorrect measurement on one side of the tooth simultaneously resulted in incorrect measurement on the opposite side.

Clinical relevance

The clinician should be aware that different factors related to the characteristics of the defects could affect the quality of the full-arch digital follow-up. Therefore, caution is needed when interpreting the models comparison in cases that a larger area of a tooth has been modified.

Evaluation of a Method to Determine Wear Resistance of Class I Tooth Restorations during Cyclic Loading

The aim of this study was the development of a test regime to determine the wear resistance and predict the clinical performance of conventional glass ionomer cement (GIC) restorations in Class I tooth cavities. Cavities were prepared in excised human teeth and restored using three conventional glass ionomer restorative materials: DeltaFil, Fuji IX GP and Ketac Universal. The restored teeth were mechanically and thermally stressed using a chewing simulator with a maximum number of 1,200,000 load cycles. Besides determining the number of cycles achieved, the abrasion volume after termination of the chewing simulation was calculated using µCT images. All teeth restored with DeltaFil reached 1,200,000 cycles without any restoration failure. Only 37.5% of the restorations each with Ketac Universal and Fuji IX GP were able to achieve the maximum cycle number. A significant lower abrasion volume for restorations with DeltaFil compared to Ketac Universal (p = 0.0099) and Fuji IX GP (p = 0.0005) was found. Laboratory chewing simulations are a useful tool to study basic wear mechanisms in a controlled setting with in-vivo related parameters. DeltaFil shows an improved wear resistance compared to other conventional GICs, indicating the high potential of this material for long-lasting Class I restorations.

Wear Behavior between Aesthetic Restorative Materials and Bovine Tooth Enamel

Tooth enamel wear occurs because of daily mastication and occlusion. This study investigated the wear behavior of bovine teeth against aesthetic restorative materials in vitro. Abrader specimens were fabricated using four tooth-colored restorative materials (zirconia, lithium disilicate glass ceramic, dental porcelain, and resin composite), with bovine tooth enamel as a control. Flattened bovine tooth enamel was used as the substrate specimen. These materials were characterized by Vickers hardness tests and surface roughness measurements. Two-body wear tests between the abrader and substrate specimens were performed, and the worn topographies were evaluated using a contour-measuring instrument and 3D laser microscope. The restorative materials and bovine tooth enamel had similar surface roughness but different hardness and wear behaviors. Bovine teeth showed the largest wear in tooth–tooth contact as the abrader and substrate specimens. Compared to bovine teeth, zirconia, lithium disilicate glass ceramic, and dental porcelain showed greater hardness and less wear on their surfaces, and less substrate wear of the opposite tooth enamel. The lowest hardness resin composite showed intermediate wear on its surface, resulting in the lowest substrate wear. Accordingly, dentists should pay attention to the selection of restorative materials to reconstruct their morphologies owing to different wear behaviors.

Impact of the material and sintering protocol, layer thickness, and thermomechanical aging on the two-body wear and fracture load of 4Y-TZP crowns

OBJECTIVES

The aim of this study is to investigate the influence of the material and corresponding sintering protocol, layer thickness, and aging on the two-body wear (2BW) and fracture load (FL) of 4Y-TZP crowns.

MATERIALS AND METHODS

Multi-layer 4Y-TZP crowns in three thicknesses (0.5 mm/1.0 mm/1.5 mm) were sintered by high-speed (Zolid RS) or conventional (Zolid Gen-X) sintering. 2BW of ceramic and enamel antagonist after aging (1,200,000 mechanical-, 6000 thermal-cycles) was determined by 3D-scanning before and after aging and subsequent matching to determine volume and height loss (6 subgroups, n = 16/subgroup). FL was examined initially and after aging (12 subgroups, n = 16/subgroup). Fractographic analyses were performed using light-microscope imaging. Global univariate analysis of variance, one-way ANOVA, linear regression, Spearman's correlation, Kolgomorov-Smirnov, Mann-Whitney U, and t test were computed (alpha = 0.05). Weibull moduli were determined. Fracture types were analyzed using Ciba Geigy table.

RESULTS

Material/sintering protocol did not influence 2BW (crowns: p = 0.908, antagonists: p = 0.059). High-speed sintered Zolid RS presented similar (p = 0.325-0.633) or reduced (p < 0.001-0.047) FL as Zolid Gen-X. Both 4Y-TZPs showed an increased FL with an increasing thickness (0.5(797.3-1429 N) < 1.0(2087-2634 N) < 1.5(2683-3715 N)mm; p < 0.001). For most groups, aging negatively impacted FL (p < 0.001-0.002). Five 0.5 mm specimens fractured, four showed cracks during and after aging.

CONCLUSIONS

High-speed sintered crowns with a minimum thickness of 1.0 mm showed sufficient mechanical properties to withstand masticatory forces, even after a simulated aging period of 5 years.

CLINICAL RELEVANCE

Despite the manufacturer indicating a thickness of 0.5 mm to be suitable for single crowns, a minimum thickness of 1.0 mm should be used to ensure long-term satisfactory results.

Tooth Wear and Tribological Investigations in Dentistry

Dental or tooth wear is a physiological process in the life cycle of teeth. Loss of the occlusal surface may cause excessive tooth wear. Several factors may contribute to tooth wear with different intensities and duration in the oral cavity. The oral cavity is generally compared to a tribological system to determine the various types of wear between teeth and restorative materials and assess the amount of dental wear. However, it is challenging to investigate in vitro and in vivo wear owing to the complexity of tooth wear; thus, a clear correlation between in vitro and in vivo data could not be established. This review is aimed at providing an insight into the etiology of tooth wear and tribological investigations in dentistry.

An Interdisciplinary Study Regarding the Characteristics of Dental Resins Used for Temporary Bridges

Background and Objectives: The surface condition of the materials that are used for temporary prostheses influences their microbial colonization, with a direct impact on the oral tissues. This study aims at a comparative analysis of three types of resins for temporary bridges using conventional and digital technologies. The attention was focused on the analysis of the surface characteristics and mechanical strength of these materials. Materials and Methods: The surface condition was assessed for three distinct materials both before and after polishing- heat-curing resin Superpont C + B (SpofaDental, Jicin, Czech Republic) used unconventional technology, Zotion dental milling polymethyl methacrylate (PMMA) block (Zotion, Chongqing, China) for provisional crowns/bridges used in digital subtractive technologies and Freeprint Temp (Detax GmbH & Co. KG, Ettlingen, Germany) resin for temporary crowns and bridges that are used in 3D printing technologies. The two-way ANOVA analysis indicated that polishing leads to a statistically significant increase in roughness coefficients for all the three resins that were tested (p < 0.001). While the highest roughness coefficients were displayed in the 3D cured sample, the largest decrease was reported by the milled sample Results: The results revealed that surface roughness was significantly influenced by both the type of resin that was used (p < 0.001) and the treatment that was induced by finishing and polishing (p < 0.001). Similar p-values were obtained for each of the three resins. Conclusions: The results demonstrated a significant optimization of the surfaces after finishing and polishing and statistically significant differences between the surface parameters and the mechanical properties of the samples. The low values of the roughness and the acceptable values of the mechanical resistance for the conventional samples indicate these materials for the long-term temporary bridge’s realization, allowing the correct restoration of the functions and the rehabilitation at the oral level.

Two-body wear of occlusal splint materials from subtractive computer-aided manufacturing and three-dimensional printing

OBJECTIVES

To investigate the two-body wear of occlusal splint materials fabricated from subtractive computer-aided manufacturing (CAM) compared to three-dimensional printing (3DP).

MATERIAL AND METHODS

Forty-eight substrates (n = 12/material) in the design of a mandibular first molar were fabricated using CAM (CAM-TD, Thermeo, pro3dure medical GmbH, Iserlohn, Germany; CAM-CL, CLEARsplint, Astron Dental Corporation, Lake Zurich, USA) and 3DP (3DP-GI, GR22 flex, pro3dure medical GmbH; 3DP-KY, KeySplint soft, Keystone Industries, Gibbstown, USA). The substrates were subjected to mastication simulation (120,000 cycles, 37 °C, 50 N, 1.3 Hz) opposed to enamel antagonists. The two-body wear was measured through matching of the scanned substrates before and after aging using Gaussian best-fit method. The damage patterns were categorized and evaluated based on microscopic examinations. Data was analyzed using Kolmogorov-Smirnov test followed by 1-way analysis of variance (ANOVA). Pearson correlation was calculated between vertical and volumetric material loss. The failure types were analyzed with Chi²-test and Ciba Geigy table.

RESULTS

No difference in two-body wear results between all materials was found (p = 0.102). Fatigue substrates showed a perforation for CAM and a fracture for 3DP. No abrasion losses on the antagonists were detected.

CONCLUSIONS

3DP substrates showed no differences in two-body wear compared to CAM ones but are more likely to show a fracture. None of the tested materials caused an abrasion on human teeth structure.

CLINICAL RELEVANCE

While therapies with occlusal splint materials are rising, 3DP offers a promising alternative to CAM in terms of production accuracy and therapeutic success at reduced costs.

Wear and marginal quality of aesthetic crowns for primary molars

BACKGROUND

Due to limited aesthetics of stainless-steel crowns, the demand for tooth-coloured crowns has recently risen. Few studies have investigated the marginal integrity and wear behaviour of tooth-coloured primary molar crowns under subcritical load in vitro.

AIM

This in vitro study evaluated the marginal quality and wear of newly introduced resin composite and hybrid ceramic crowns compared with metal and zirconia crowns.

DESIGN

Metal, resin composite, hybrid ceramic (CAD/CAM), and various zirconia crowns were investigated. After thermomechanical loading (2,500 thermocycles/100,000 × 50N), marginal quality of luting gaps and wear of crowns/antagonists were evaluated using replicas under a light or 3D laser scanning microscope. Results were analysed with the Mann-Whitney U test or one-way ANOVA (p < .05).

RESULTS

Marginal quality of the new resin composite and hybrid ceramic crowns performed well in comparison with SSC and zirconia crowns. Adhesive bonding of crowns resulted in superior marginal seal compared with conventional GIC (Mann-Whitney U test, p < .05). Regarding wear, zirconia crowns exhibited significantly worse results than resin composite or hybrid ceramic crowns and SSCs (ANOVA, p < 0.05).

CONCLUSION

The new resin composite and hybrid ceramic crown exhibited good performance in comparison with SSCs and zirconia crowns considering both wear and marginal quality after subcritical loading.

Methodology investigation: Impact of crown geometry, crown, abutment and antagonist material and thermal loading on the two-body wear of dental materials

OBJECTIVES

To investigate the impact of crown geometry, crown/abutment/antagonist material and thermal loading on the two-body wear of dental materials caused by chewing simulation.

MATERIALS AND METHODS

For the crown geometry, crowns (polymethylmethacrylate (PMMA), polyetheretherketone (PEEK) and silicate ceramic (SiO₂)) were milled with a flat, steep, or medium cusp inclination (CINC). For the crown/abutment material, crowns (PMMA, PEEK and SiO₂) were combined with PMMA, polymer-infiltrated-ceramic-network (PICN), cobalt-chrome alloy (CoCr) and natural teeth (ENAM) abutments. For the antagonist material, antagonists were fabricated from PICN, CAD/CAM resin composite (RECO), steatite (STEA), steel (STL) and ENAM and tested against flat specimens (substrates) made of veneering ceramic (VC). For thermal loading, the duration (30 s, 60 s, 120 s) and presence of temperature changes (37 °C versus 5 °C/55 °C) was varied. Material losses were determined by matching scanned specimens before and after aging (400,000 chewing cycles, 50 N, 1.3 Hz). Martens parameters were determined for the antagonists/substrates. Data were analyzed using Kolmogorov-Smirnov-test, Kruskal-Wallis H, Scheffé-Post-Hoc-tests, pairwise comparisons, Bonferroni correction, one-way ANOVA, Mann-Whitney-U and Spearman rho.

RESULTS

PMMA crowns presented the highest and PEEK the lowest material losses. Flat CINC showed the lowest material losses for PEEK and SiO₂ crowns. CoCr and ENAM abutments presented material losses in the same range. Antagonist and cumulative material losses for RECO and ENAM were similar. Thermal loading did not influence material losses.

SIGNIFICANCE

Crown geometry influences the crown and antagonists wear, with an increased cusp inclination entailing increased wear. For in vitro set-ups, CoCr abutments and RECO antagonists present valid alternatives to natural teeth. For polymers, in vitro chewing simulations may be performed at a constant temperature (37 °C).

Does immediate dentin sealing influence postoperative sensitivity in teeth restored with indirect restorations? A systematic review and meta-analysis

Objective

This study comprehensively reviewed clinical trials that investigated the effect of immediate dentin sealing (IDS) technique on postoperative sensitivity (POS) and clinical performance of indirect restorations.

Materials and methods

The systematic review was conducted according to the preferred reporting items for systematic reviews and meta‐analyses statement, and was guided by the PICOS strategy. Clinical trials in which adult patients received at least one indirect restoration cemented with IDS approach and one restoration cemented following the delayed dentin sealing (DDS) were considered.

Results

Following title screening and full‐text reading, four studies met the inclusion criteria and were included for qualitative synthesis, while two studies were selected for quantitative synthesis. According to Risk of bias‐2 tool, two studies were classified as “some concerns” for the outcome POS. No statistically significant differences were found between teeth restored with indirect restorations using the IDS and DDS approach for POS (p > 0.05), neither at the baseline (very low certainty of evidence according to GRADE) nor after 2 years of follow‐up (low certainty of evidence according to GRADE).

Conclusion

There is low‐certainty evidence that IDS does not reduce POS in teeth restored with indirect restorations.

Clinical significance

There is no clinical evidence to favor IDS over DDS when restoring teeth with indirect restorations.

Friction and wear behavior of chairside CAD-CAM materials against different types of antagonists: An in vitro study

STATEMENT OF PROBLEM

Studies on the friction and wear behavior of recently introduced chairside computer-aided design and computer-aided manufacture (CAD-CAM) restorative materials are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the wear behavior of chairside CAD-CAM materials against different types of antagonists (human tooth enamel, composite resin, and feldspathic porcelain).

MATERIAL AND METHODS

Specimens (14×14×2 mm) of different CAD-CAM materials (Brilliant Crios, Lava Ultimate, Vita Enamic, Vita Suprinity) were obtained by using a low-speed precision cutter (n=10). Wear tests were performed with a 20-N load, 2.5-mm/s sliding speed, 1-mm sliding distance, and 1500 cycles via a tribometer according to ASTM-G133. The coefficient of friction (CoF) of the material pairs was measured and recorded by using a special software program. Surface roughness (Ra), maximum wear depth, and mean maximum wear depth were measured with a profilometer, and values were analyzed by using 2-way ANOVA and the Bonferroni correction. Vickers hardness of CAD-CAM specimens was determined with a microhardness tester. Microhardness values were analyzed by using 1-way ANOVA and Tukey post hoc tests. Worn surfaces were observed by scanning electron microscopy and a 3D noncontact profilometer to determine the wear pattern and primary wear mechanisms.

RESULTS

Significant differences were found in the interactions between CAD-CAM materials and different types of antagonists (P<.001) for maximum wear depth, mean maximum wear depth, CoF, and Ra values.

CONCLUSIONS

Vita Suprinity exhibited superior wear resistance and Ra against all antagonists compared with other CAD-CAM materials. However, Vita Suprinity increased the destructive effects on antagonists. The safety of CAD-CAM materials is best determined when the wear behavior of materials and their effect on the antagonist are evaluated together.

Influence of filler geometry and viscosity of composite luting materials on marginal adhesive gap width and occlusal surface height of all-ceramic partial crowns

OBJECTIVES

To evaluate the influence of filler geometry and viscosity of luting composites on marginal adhesive gap width (MGW) and occlusal surface height (OSH) of all-ceramic partial crowns.

METHODS

Forty-eight all-ceramic partial crowns (Celtra Duo, Dentsply) were created and divided into six groups (n = 8). Restorations were bonded using universal adhesive (Prime & Bond Active, Dentsply) in combination with low-viscosity composites (LV) containing amorphous fillers (Calibra Ceram, Dentsply) (LV-AF), heterogeneous fillers (Tetric EvoFlow, Ivoclar Vivadent) (LV-HF) vs. high-viscosity composites (HV) containing spherical fillers (Ceram.x, Dentsply) (HV-SF) or heterogeneous fillers (Tetric EvoCeram, Ivoclar Vivadent) (HV-HF). HV materials were used either with or without sonication. MGW [µm] was measured by SEM. Displacements of the restorations after luting, such as changes (Δ) in OSH [µm], tilting and rotation [°], were measured using a dial gauge and 3D-analytical software (OraCeck, Cyfex). Statistical analysis was by Mann-Whitney U-test and t-test with α = 0.05.

RESULTS

MGW (p = 0.002) and tilting (p = 0.001) were significantly smaller with LV (228.0 ± 112.35 µm; 0.89 ± 1.25°) than with HV (338.1 ± 97.26 µm; 1.95 ± 1.26°). Sonication had no effect on MGW in HV-HF (332.32 ± 91.39 µm) and HV-SF (343.85 ± 105.48 µm; p = 0.74). Sonication decreased ΔOSH by ~50% with HV-SF (64.21 ± 27.90 µm) but remained unchanged with HV-HF (39.06 ± 14.08 µm; p = 0.004). There was no difference in rotation between HV (0.82 ± 0.81°) and LV (0.61 ± 0.74°; p = 0.29). The LV-AF and LV-HF groups showed no statistical differences in MGW, ΔOSH, tilting or rotation (p > 0.05).

SIGNIFICANCE

Irrespective of filler geometry and insertion technique, the use of high-viscosity composites for the adhesive cementation of modern all-ceramic partial crowns increases displacement, marginal misfit and occlusal surface height.

Influence of masticating cycles and chewing patterns on inadvertent enamel wear caused by zirconia brackets

Little information is available about enamel wear caused by zirconia brackets, an inadvertent side effect of orthodontic treatment. The purpose of this study was to examine potential enamel damage induced by contact with zirconia brackets. Sliding and impact wear simulations were performed using bovine enamel specimens positioned at a 25° slant to a zirconium ball to determine wear behaviour. Different chewing patterns, tapping and grinding, were simulated. Specimens were profiled using confocal laser scanning microscopy, and the mean maximum depth and surface roughness were measured. Scanning electron microscopy was also performed. The mean maximum depth of wear values differed according to the number of mastication cycles, with a higher number of cycles producing higher depths of wear. The facet wear depth was significantly greater with the tapping pattern than with the grinding pattern. Scanning electron microscopic observation of the wear facets revealed that surface textures at the edges were rougher than those at the centre of all facets. The results of this study indicated that enamel wear was induced by contact with zirconia brackets during the early period of mastication, and that the patterns and number of cycles of mastication affected the wear progression of enamel.

Handling and Mechanical Properties of Low-viscosity Bulk-fill Resin Composites

This study aimed to evaluate the filler contents (FCs), flexural properties, depth of cure (DOC), wear resistance, and handling properties of different low-viscosity bulk-fill resin composites (LVBRCs) and to determine the correlations between the tested parameters. Six LVBRCs, Beautifil-Bulk (BBF), Bulk Base Hard (BBH), Bulk Base Medium (BBM), Filtek Bulk-Fill Flowable Restorative (FBF), G-ænial Bulk Injectable (GBI), and SDR flow+ Bulk-Fill Flowable (SDR) were used. The DOC and flexural property tests were conducted according to the ISO 4049 specifications. The flexural strength, elastic modulus, and resilience were determined in 12 specimens that were obtained from each of the 6 materials. Sliding-impact-wear testing was conducted by evaluating the wear facets of the specimens using a noncontact profilometer and by confocal laser scanning microscopy. The handling properties of the LVBRC was assessed via extrusion force and thread formation measurements. The DOC for the majority of the LVBRCs was approximately 4 mm. Although the FCs and mechanical properties were material dependent, some LVBRCs exhibited excellent flexural properties and wear resistance. The LVBRCs demonstrated a wide range of extrusion force and thread formation. Regarding the correlations between the tested parameters, extremely strong negative and positive correlations were observed for the DOC versus extrusion force, flexural strength versus elastic modulus, maximum depth versus volume loss, and maximum depth versus thread formation. In addition, strong correlations between FCs and DOC, resilience, wear resistance, and extrusion force were observed.

Flexural properties and wear behavior of computer-aided design/computer-aided manufacturing resin blocks

This study investigates the flexural properties, Knoop hardness number (KHN), and wear behavior of computer-aided design and computer-aided manufacturing (CAD/CAM) resin blocks and compares these values with those of conventional resin composites for direct restoration (RCDs). Four CAD/CAM resin blocks and two RCDs are compared. Ten specimens per material are used to obtain the flexural properties according to ISO 6872 specifications, and five specimens per material are used for KHN measurement. For sliding impact wear testing, twelve specimens are prepared. Confocal laser scanning microscopy (LSM) is used to determine maximum facet depth and volume loss. Polished material surfaces and worn surfaces after wear testing are observed using scanning electron microscopy and LSM. While measured flexural properties and KHN are found to be material-dependent, CAD/CAM resin blocks exhibit higher wear resistance than RCDs. CAD/CAM resin blocks polymerized at high-pressure and high-temperature are found to exhibit wear behaviors far superior to those of RCDs.

Wear Resistance of 3D Printed and Prefabricated Denture Teeth Opposing Zirconia

PURPOSE

To evaluate the wear resistance of a recently developed three-dimensional (3D) printed denture teeth resin compared to three commercially available prefabricated denture teeth.

MATERIALS AND METHODS

A total of 88 maxillary first molar denture teeth were evaluated: C (Classic; Dentsply Sirona, York, PA), DCL (SR Postaris DCL; Ivoclar Vivadent, Schaan, Liechtenstein), IPN (Portrait IPN; Dentsply Sirona, York, PA), and F (Denture Teeth A2 Resin 1 L; Formlabs, Somerville, MA). The 3D printed denture tooth specimens were fabricated from a methacrylate-based photopolymerizing resin using stereolithography (SLA). Denture teeth were subjected to a three-body wear test with a poly(methylmethacrylate) (PMMA) abrasive slurry. A Leinfelder-style four station wear apparatus with custom bullet-shaped milled zirconia styli was utilized with a load force of 36-40 N at 1.7 Hz for 200,000 cycles. Maximum depth of wear was measured using a lab grade scanner and analyzing software program. Data were analyzed using a one-way ANOVA followed by the Tukey's Multiple Comparisons post hoc test (α = 0.05).

RESULTS

A statistically significant difference in depth of wear was found between denture tooth materials (p < 0.001). The mean vertical depth of wear for the 3D printed denture teeth (0.016 ± 0.010 mm) was statistically significantly less than the prefabricated denture teeth. The highly cross-linked denture teeth, DCL (0.036 ± 0.011 mm) and IPN (0.035 ± 0.014 mm), exhibited statistically significantly less wear than the conventional acrylic denture teeth. The conventional acrylic denture teeth demonstrated the greatest wear (0.058 ± 0.014 mm). No significant difference in depth of wear was found between DCL and IPN (p > 0.001).

CONCLUSIONS

Denture tooth material significantly influences the depth of wear. The 3D printed denture teeth demonstrated superior wear resistance compared to the commercially available prefabricated denture teeth when opposed to zirconia. Denture teeth fabricated with SLA technology may have a promising future in prosthetic dentistry.

Cobalt–Chromium Dental Alloys: Metal Exposures, Toxicological Risks, CMR Classification, and EU Regulatory Framework

During the 20th century, metal alloys have assumed an important role as restorative materials. Among existing examples, cobalt–chromium (Co–Cr) alloys increasingly began to be used in medicine and especially in dentistry. Their success is mainly due to their mechanical properties such as stiffness, strength and corrosion resistance, thus allowing a high biocompatibility. There are quite meaningful data on the corrosion and toxicity of Co–Cr alloys for their use in restorative materials such as dental prostheses. Toxicological studies following Co and Cr exposures in the oral cavity are more difficult to conduct because there are many different situations leading to the release of metal ions and wear particles. Furthermore, the links between exposure and the appearance of local or systemic toxicity are not automatic. Since 2017, the European Union (EU) regulatory framework for Co–Cr alloys has been undergoing profound changes. A new EU Medical Devices Regulation (MDR) (2017/745) will be applied in May 2021 with the need to consider that Co metal is a new carcinogenic, mutagenic and toxic to reproduction (CMR) substance. On 18 February 2020, the 14th Adaptation to Technical Progress (ATP14) to the Classification, Labelling and Packaging (CLP) regulation was published, including the harmonised classification for Co metal as a CMR 1B substance. In this context, the use of Co might be forbidden if the medical devices are invasive and as soon as they include more than 0.1% (m/m) Co. This review provides a specific overview on Co–Cr dental alloys in terms of metal ions and wear particles release, toxicological risks, and the actual and new EU regulatory framework.

Effects of Artificial Staining and Bleaching Protocols on the Surface Roughness, Color, and Whiteness Changes of an Aged Nanofilled Composite

This study evaluated the surface roughness and color alteration of an aged nanofilled composite exposed to different staining solutions and bleaching agents. Ninety nanofilled composite (Filtek Z350XT, 3M/Oral Care) specimens were submitted to 5,000 thermal cycles and immersed in (n = 30): red wine, coffee, and artificial saliva at 37°C for 48 h. Groups were subdivided according to the bleaching protocol (n = 10) with 20% carbamide peroxide, 38% hydrogen peroxide, or without bleaching - control. Mean surface roughness values (Ra - μm) and color parameters (L*, a*, b*) were measured at baseline (T0), after thermal cycling aging and staining (TS), and after bleaching (TB). Color (ΔE00) and whiteness index (ΔWID) changes were determined after aging and staining (Ts-T0) and after bleaching (TB-TS). The adopted perceptibility and acceptability thresholds of the nanofilled composite were 0.81 and 1.71 ΔE00 units and 0.61 and 2.90 ΔWID units, respectively. Ra was analyzed using mixed models for repeated measurements and L* by the Tukey-Kramer test. The a* and b* values were evaluated by generalized linear models for repeated measures. ΔE00 was tested using two-way ANOVA and Tukey tests, and ΔWID by Kruskal-Wallis and Dunn tests (α = 5%). Ra of all groups decreased after aging and staining (TS, p &lt; 0.05), but increased after bleaching only for groups stained with red wine (TB). Aging and staining decreased the luminosity of the composites, but L* increased after bleaching (p &lt; 0.05). Aging and staining increased a* and b* values, but after bleaching, b* values decreased (p &lt; 0.05). After bleaching, ΔE00 and ΔWID were greater in stained groups at both time intervals, regardless of the bleaching protocol. Stained resin composites exhibited perceptible but unacceptable color (ΔE00 &gt; 1.71) and whiteness (ΔWID &gt; 2.90) changes, regardless of the bleaching treatment performed. Therefore, red wine affected the surface roughness of the aged nanofilled resin submitted to bleaching. Bleaching was unable to reverse the color changes promoted by red wine and coffee on the aged nanofilled composite.

In vitro wear of (resin-coated) high-viscosity glass ionomer cements and glass hybrid restorative systems

OBJECTIVES

The aim of the present study was to investigate the volumetric abrasive wear of a high-viscosity glass ionomer cement (hvGIC; Equia Fil) and a glass hybrid restorative system (ghRS; Equia Forte), each being recommended as amalgam alternatives. Both materials were applied with or without their respective resinous coating, and were compared with a conventional GIC (Ketac Fil) and a hybrid composite resin (CR; G-ænial Posterior).

METHODS

78 standardized occlusal Class I cavities were restored with the various materials (n = 13 per group). Before and after chewing simulation (30,000 cycles at 40 N), each sample underwent optical scanning procedures (Omnicam). A comparison of the total wear using a fluorescence-aided identification technique (OraCheck) followed, and differences (α = 5%) between groups were compared by means of MANOVA.

RESULTS

Regarding the wear rates of hvGIC and ghRS, no differences could be observed (p > .050), and this was not affected by the resinous coating. All hvGIC and ghRS restorations showed significantly higher abrasive wear than CR (p < .001), while the conventional GIC displayed a significant underperformance compared with any other material (p < .001).

CONCLUSIONS

Resinous coating of hvGIC or ghRS does not appear to exert an effective long-term protection against advanced abrasive wear. Compared to the conventional GIC showing a considerable substance loss, both hvGIC and ghRS materials revealed an improved abrasion resistance, but clearly failed to meet the excellent values of the CR.

CLINICAL SIGNIFICANCE

Occlusal loading should be carefully considered when using hvGIC or ghRS as amalgam (or composite resin) alternatives for the restoration of posterior teeth.

Assessment of Force Retention between Milled Metallic and Ceramic Telescopic Crowns with Different Taper Angles Used for Oral Rehabilitation

The present study assessed the retention forces corresponding to different telescopic systems used in removable prosthetic dentures. The telescopic systems were represented by Co–Cr alloy or zirconia-based primary crowns and Co–Cr secondary crowns. All crowns were manufactured using computer-aided design/computer-aided manufacturing technology (CAD/CAM). Two types of reference abutment teeth (upper canine and first upper molar) were selected in order to obtain the telescopic crowns and two taper angles—of 0° and 2°—were used for the design of the crowns. A number of 120 samples of telescopic crowns were obtained and subjected to mechanical tests, following a specific protocol, on a mechanical testing equipment. The retention of the telescopic systems was evaluated for different sets of cycles (up to 360), represented by movements that simulate the intraoral insertion and disinsertion of the telescopic systems. The present study highlights that the telescopic systems in which the primary crown is made of zirconia ceramics presents more advantages than those made of Co–Cr. All telescopic systems studied, highlighted that by modifying the taper angle from 0° to 2°, the retention forces have decreased, irrespective of the materials used for the fabrication of the primary crown, suggesting that by using a taper angle of 0°, which is known to be ideal, more efficient, and reliable prosthesis can be developed. Thus, even though the ceramic–metallic telescopic system exhibited the highest retention, all telescopic crowns evaluated registered values between 2–7 N, indicating that they are suitable for clinical use.

Clinical outcomes of single crown restorations fabricated with resin-based CAD/CAM materials

Computer-aided design/computer-aided manufacturing (CAD/CAM) restorative materials have been widely used owing to a number of advantages, including stable quality of the materials, lower costs, and time-saving factors. Resin-based CAD/CAM materials for definitive restorations are classified into two groups: dispersed nanoparticle-filled composite resin and polymer-infiltrated-ceramic-network materials. Resin-based CAD/CAM materials have been applied to single crown restorations as a monolithic structure for the posterior region. In addition, resin-based CAD/CAM restorations have been applied recently for the anterior area. This literature review summarizes clinical outcomes, such as survival rates and clinical complications of single crown restorations fabricated with resin-based CAD/CAM materials.

Thermal, structural and morphological characterization of dental polymers for clinical applications

PURPOSE

Polymers are used in dentistry on a daily basis due to their mechanical, functional and aesthetic properties. However, such biomaterials are subject to deterioration in the oral environment. Thus, this study aimed to evaluate the structural properties of five commonly used dental polymers to determine their best clinical indications.

METHODS

Four hundred-fifty samples of five dental polymers (polyethylenterephthalat - glycol modified (PG), polymethyl methacrylate (PA), ethylene vinyl acetate(E), polycarbonate (PC), polyetheretherketone (PK) were prepared to investigate their thermal, structural and chemical characteristics using energy dispersive spectroscopy (EDS), Fourier transform infrared analysis(FTIR), scanning electron microscopy (SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), X-ray diffraction(XRD), and Shore D hardness test. Data were analyzed using one-way ANOVA, Tukey's HSD, and Levene's tests (α=0.05).

RESULTS

PK (87.2) and PA (82.4) displayed the highest hardness values and smooth surfaces, as observed with SEM (p<0.001). Silica was detected in PK, PA, and E by EDS and XRD. The highest glass transition temperature was recorded for PC (145.00±2.00°C) and PK (143.00±1.87°C), while the lowest value was measured for E (50.00±2.12°C)(p<0.001).The highest mass loss was detected for PG (91.40±1.40%) by TGA.

CONCLUSIONS

PA and PK polymers can be used for stress-containing treatments due to their mechanical properties. These two materials are also advantageous in terms of plaque accumulation as these polymers reveal smoother surfaces than other groups. Insufficient physical and thermal properties require the use of E with caution and only in limited clinical indications.

Bulk Fill Composites Have Similar Performance to Conventional Dental Composites

The aim of the study was to perform comprehensive characterization of two commonly used bulk fill composite materials (SDR Flow (SDR) and Filtek™ Bulk Fill Flowable Restorative (FBF) and one conventional composite material (Tetric EvoCeram; TEC). Eleven parameters were examined: flexural strength (FS), flexural modulus (FM), degree of conversion, depth of cure, polymerisation shrinkage (PS), filler particle morphology, filler mass fraction, Vickers hardness, surface roughness following simulated toothbrush abrasion, monomer elution, and cytotoxic reaction of human gingival fibroblasts, osteoblasts, and cancer cells. The degree of conversion and depth of cure were the highest for SDR, followed by FBF and TEC, but there was no difference in PS between them. FS was higher for bulk fill materials, while their FM and hardness were lower than those of TEC. Surface roughness decreased in the order TEC→SDR→FBF. Bisphenol A-glycidyl methacrylate (BisGMA) and urethane dimethacrylate were found in TEC and FBF eluates, while SDR released BisGMA and triethylene glycol dimethacrylate. Conditioned media accumulated for 24 h from FBF and TEC were cytotoxic to primary human osteoblasts. Compared to the conventional composite, the tested bulk fill materials performed equally or better in most of the tests, except for their hardness, elastic modulus, and biocompatibility with osteoblasts.

Temporary materials: comparison of in vivo and in vitro performance

OBJECTIVE

The aim of this investigation was to compare clinical performance and in vitro wear of temporary CAD/CAM and cartridge crowns. This study is an approach to estimate the influence of in vivo use and laboratory simulation on temporary crowns.

MATERIALS AND METHODS

A total of 90 crowns were fabricated from each temporary CAD/CAM or cartridge material. Also, 10 crowns of each material were clinically applied for 14 days, and 80 identical duplicate restorations were investigated in the laboratory after storage in water (14 days; 37 °C) and subsequent thermal cycling and mechanical loading (TCML, 240.000 × 50N ML, 600 × 5°C/55 °C). After in vivo application or in vitro aging, facture force, superficial wear (mean and maximum), surface roughness (Ra, Rz), thermal weight loss (TGA), and heat of reaction (DSC) were determined for all crowns.

STATISTICS

Bonferroni post hoc test; one-way analysis of variance (ANOVA); α = 0.05).

RESULTS

The fracture resistance of the temporary materials varied between 1196.4 (CAD in vivo) and 1598.3 N (cartridge crown in vitro). Mean (maximum) wear data between 204.7 (386.7 μm; cartridge in vitro) and 353.0 μm (621.8 μm; CAD in vitro) were found. Ra values ranged between 4.4 and 4.9 μm and Rz values between 36.0 and 40.8 μm. DSC and TG analysis revealed small differences between the materials but a strong influence of the aging process.

CONCLUSIONS

Comparison of in vivo and in vitro aging led to no significant differences in fracture force and wear but differences in roughness, DSC, and TGA. SEM evaluation confirmed comparability. Comparison of CAD/CAM and cartridge temporary materials partially showed significant differences.

CLINICAL RELEVANCE

In vitro aging methods might be helpful to estimate materials' properties before principal clinical application. CAD/CAM and cartridge temporary materials provided comparable good clinical performance.

In vivo wear of CAD-CAM composite versus lithium disilicate full coverage first-molar restorations: a pilot study over 2 years

Objectives

To present a digital approach to measure and compare material wear behavior of antagonistic first molar restorations made of an experimental CAD/CAM composite (COMP) and lithium disilicate ceramic (LS2) in patients with reconstructed vertical dimension of occlusion (VDO) after generalized hard tissue loss.

Methods

A total of 12 patients underwent complete full jaw rehabilitation with full occlusal coverage restorations made either of COMP or LS2. The first molar restorations (n = 48) were chosen for wear examination. At annual recall appointments, polyether impressions were taken, and resulting plaster casts were digitalized using a laboratory scanner. Mean observation period was 371 days for first and 769 days for second year. The resulting 96 datasets were analyzed by superimposition of 3-D datasets using an iterative best-fit method. Based on the superimposition data, the wear rates of the occlusal contact areas (OCAs) were calculated.

Results

For antagonistic restorations made of COMP, the average wear rate was 24.8 ± 13.3 μm/month, while for LS2, it was 9.5 ± 4.3 μm/month in first year, with significant differences (p < 0.0001) between the materials. In second year, monthly wear rates decreased significantly for both materials: COMP (16.2 ± 10.7 μm/month) and LS2 (5.5 ± 3.3 μm/month). Statistical comparison between wear time showed significant differences for both materials: COMP p < 0.037 and LS2 p < 0.001. A logarithmic fit (COMP R² = 0.081; LS2 R² = 0.038) of the data was calculated to estimate the wear progression.

Significance

In patients with reconstructed VDO, restorations made of LS2 show a more stable wear behavior than ones out of experimental CAD/CAM composite. In cases of complete rehabilitation, load bearing CAD/CAM-composite restorations should be critically considered for application due to their occlusal wear behavior. However, when choosing a restorative material, not only the functional occlusal stability should be taken into account but also the prospect of minimally invasive treatment with maximum preservation of natural tooth structures.

Wear Properties of Different Additive Restorative Materials Used for Onlay/Overlay Posterior Restorations

The purpose of this laboratory study was to compare the two-body wear resistance of different restorative materials commonly used for the indirect restoration of posterior teeth. The tested materials, based on ceramic (Imagine Press X, IPS e.max CAD, Milled Celtra Duo, Glaze-Fired Celtra Duo, Vita Mark II) and composite (Enamel Plus HRi, Enamel Plus HRi Bio-Function, Filtek Supreme XTE, Lava Ultimate), were compared with the wear properties of a type III gold alloy (Aurocast 8). Flat samples were prepared with a 6-mm thickness (n=10). Composite samples were tested after a heat polymerization cycle. All samples were exposed to a two-body wear test in a dual axis chewing simulator performing over 120,000 loading cycles. The opposing abrader cusps were fabricated from yttria-stabilized tetragonal zirconia polycrystal. The vertical substance loss (mm) and the volume loss (mm3) were recorded, as was the wear of the antagonist cusp (mm). Mean values were analyzed by one-way analysis of variance. Significant differences among materials were detected. The heat-cured resin-based composite material Enamel Plus Bio-Function and the type III gold alloy demonstrated similar mean values for wear depth and volumetric loss.

Validating laboratory simulation with resin-based materials for temporary fixed denture prostheses - Results from clinical and laboratory trials

The aim of the current study was to relate an artificial aging protocol for the analysis of dental materials to their clinical performance. 20 fixed interim restorations (crowns and fixed denture prostheses (FDPs)) fabricated from two commercially available resin-based composites (RBCs) and a previous clinical trial served as templates for the fabrication of duplicate restorations. Duplicates were subjected to artificial aging using thermal cycling and mechanical loading. Subsequent to wear analysis, templates and duplicates were loaded to fracture and were examined using thermal gravimetric analysis (TG) and differential scanning calorimetry (DSC). For both RBCs, a relevant uptake of water was identified, which was more pronounced in the duplicates. Tribological analyses indicated relevant signs of wear in both templates and duplicates. While qualitative analyses indicated macroscopically similar wear traces in templates and duplicates, data showed that wear of FDPs was underrated in the laboratory analyses. The results of the current study suggest that chewing simulation allows a proper estimation of aging processes in materials for the fabrication of fixed interim restorations. However, simulation parameters should be continuously improved using data derived from clinical settings to enhance the quality of the simulation protocols.

Wear resistance of indirect composite resins used for provisional restorations supported by implants

PURPOSE

The aim of this study was to investigate simulated localized and generalized wear of indirect composite resins used for implant supported provisional restorations.

MATERIALS AND METHODS

The study investigated ten indirect composite resins. Two kinds of wear were simulated by 400,000 cycles in a Leinfelder-Suzuki (Alabama) machine. Localized wear was simulated with a stainless-steel ball bearing antagonist and generalized with a flat-ended stainless-steel cylinder antagonist. The tests were carried out in water slurry of polymethyl methacrylate beads. Wear was measured using a Proscan 2100 noncontact profilometer in conjunction with Proscan and AnSur 3D software.

RESULTS

Both localized and generalized wear were significantly different (P<.05) among the indirect composite resins. SR Nexco and Gradia Plus showed significantly less wear than the other indirect composite resins. The rank order of wear was same in both types of wear simulation.

CONCLUSION

Indirect composite resins are recommended when a provisional implant-supported restoration is required to function in place over a long period. Although only some indirect composite resins showed similar wear resistance to CAD/CAM composite resins, the wear resistance of all the indirect composite resins was higher than that of bis-acryl base provisional and polymethyl methacrylate resins.