The influence of antagonistic surface roughness on the wear of human enamel and nanofilled composite resin artificial teeth

A two-year clinical trial of enamel wear opposing 5Y-TZP and lithium disilicate crowns

STATEMENT OF PROBLEM

Clinical information on enamel wear opposing 5 mol% yttria-stabilized tetragonal zirconia polycrystal (5Y-TZP) or lithium disilicate crowns is lacking. Moreover, the effect of surface roughness on the wear of enamel antagonists remains unclear.

PURPOSE

The purpose of this clinical study was to quantify the vertical wear and total volume of wear while also measuring the surface roughness of antagonists at 6-month intervals over 2 years.

MATERIAL AND METHODS

A tooth-supported first molar 5Y-TZP Lava Esthetic Fluorescent Zirconia crown or an IPS e.max CAD lithium disilicate crown was randomly provided for 24 participants (n=12). The contralateral first molar and opposite teeth were the natural enamel controls. The crowns were fabricated using computer-aided design and computer-aided manufacturing (CAD-CAM) technology and then polished. The data were gathered every 6 months at recall appointments with an intraoral scanner and a polyvinyl siloxane impression. A 3-dimensional (3D) comparative software program was used to measure the maximum vertical and volume loss on opposing enamel, as well as on the enamel control on the opposite side of the mouth. The surface of epoxy resin replicas was analyzed using a scanning electron microscope. The surface roughness of the cusp replica was measured with a 3D laser microscope. The crown's antagonist enamel and natural enamel wear were compared using a 2-way repeated measure ANOVA (α=.05).

RESULTS

No significant difference was found in the average volume loss between the crown's antagonist enamel (ZTE 0.042 ±0.005 mm3, LTE 0.048 ±0.006 mm3) and the enamel control (ZCE 0.046 ±0.004 mm3, LCE 0.050 ±0.005 mm3) (P>.05). No significant difference was found in surface roughness between the crown's antagonist enamel (antagonist enamel of zirconia group [ZTE] 0.7 ±0.3 µm, antagonist enamel of lithium disilicate group [LTE] 0.6 ±0.3 µm) and the enamel control (enamel control of zirconia group [ZCE] 0.7 ±0.3 µm, enamel control of lithium disilicate group [LCE] 0.5 ±0.2 µm) in both zirconia and lithium disilicate groups (P>.05). Also, no correlation was found between the amount of wear and the roughness of the surface. The wear patterns observed on the opposing enamel surfaces of the monolithic zirconia and lithium disilicate materials were found to be similar to those seen on natural enamel.

CONCLUSIONS

A 2-year clinical investigation found that polished lithium disilicate and 5Y-TZP crowns did not affect enamel wear more than enamel against enamel, contrary to laboratory studies. Another finding revealed that surface roughness did not significantly affect wear.

Investigation of Bruxism wear behavior of titanium alloy biomaterials; experimental and 3D finite element simulation

Bruxism can be defined as the process of direct contact with teeth and dental materials with an involuntary jaw-tightening movement. In this process, teeth and dental materials can be exposed to various damage mechanisms. This study aims to realize the mechanism of bruxism with finite element analysis and in vitro rotating chewing movement analysis. Within the scope of the study, cp-Ti, Ti-5Zr, and Ti-5Ta materials were subjected to wear tests in the finite element analysis and in vitro rotating chewing movement method under the determined Bruxism chewing test conditions. Test specimens with cylindrical geometry were exposed to a direct every-contact wear mechanism for 30 s under 150 N bruxism chewing bite force. The bruxism chewing cycle continued for 300 min at a frequency of 2 Hz. Microanalysis of the wear surfaces of the samples after the experimental study was carried out with Scanning Electron Microscopy. The results obtained within the scope of this study showed that the Bruxism wear resistance increased by adding zirconium and tantalum to pure titanium material. This result shows that pure titanium material, which is known to have poor wear resistance, can be improved with Zr and Ta alloys. It is clinically important that the success rate in the treatment process increases with the increase in wear resistance. However, the micro-cracks observed in the microstructure may have occurred in the sub-surface, which is a show of the fatigue wear mechanism.

Effects of various beverages on characteristics of provisional restoration materials

OBJECTIVE

To investigate the effect of common beverages on four currently used provisional restoration materials: Protemp®4, Integrity®, polymethyl methacrylate (PMMA) block, and acrylic resin. Flowable resin composite is included as a control group.

MATERIALS AND METHODS

Each material was formed into disks of 10-mm diameter and 4-mm thickness (N = 40) by loading the material into acrylic molds. The exposed surface in the mold was covered using a glass slide to prevent an oxygen inhibition layer, and polymerization then proceeded. The solidified disks were placed in distilled water for 24 h. These samples (n = 8) were then immersed for 14 days in one of four different beverages: water, orange juice, cola, and coffee. Changes in color dimension, hardness, and roughness were observed and then analyzed using two-way repeated analysis of variance.

RESULTS

The provisional materials had more obvious changes in all three color dimensions than the flowable resin composite. Integrity showed the biggest changes, followed by acrylic resin and PMMA block, whereas Protemp had the smallest changes. The hardness of all the materials significantly decreased after immersion in any of the beverages for 14 days. There were no changes in surface roughness when the materials were immersed in distilled water. The surface roughness of the PMMA block significantly decreased in orange juice whereas that of Integrity and acrylic resin significantly increased in cola.

CONCLUSION

Different kinds of provisional materials had different degrees of staining due to their composition. Moisture had a significant influence on the hardness of materials, and the acidity of cola significantly roughened the surface of the provisional materials.

Effect of surface treatments on wear and surface properties of different CAD-CAM materials and their enamel antagonists

STATEMENT OF PROBLEM

Which surface treatment provides optimal surface roughness, microhardness, and wear behavior for computer-aided design and computer-aided manufacturing (CAD-CAM) materials and their enamel antagonists is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of surface treatment on the surface roughness, microhardness, and 2-body wear of different CAD-CAM materials and their enamel antagonists.

MATERIAL AND METHODS

Monolithic zirconia, polymer-infiltrated ceramic network, lithium disilicate, leucite-reinforced ceramic, zirconia-reinforced lithium silicate, and feldspathic ceramic specimens were sliced into 2-mm-thick rectangular plates and divided into polished or glazed subgroups (n=6). After surface roughness and microhardness measurements, the specimens were loaded at 49 N for 250 000 cycles and simultaneously thermocycled (5 °C and 55 °C). All specimens were scanned before and after the wear test by using a scanner. The volumetric loss and wear depth of the materials and the volumetric and height loss of the enamel were calculated, and scanning electron microscope images of the specimens were made. Multiple 2-way ANOVAs and Tukey honestly significant difference tests were used to assess the effect of material and surface treatment on surface roughness, microhardness, and wear behavior of materials and enamel (α=.05).

RESULTS

Material and surface treatment interactions affected the surface roughness (P<.001), microhardness (P<.001), volumetric loss of materials (P=.044), and height loss of enamel (P<.001).

CONCLUSIONS

Polishing resulted in higher surface roughness and microhardness than glazing. Volumetric loss depended on the material, which affected the height loss of the antagonists. Glazing and polishing had similar effects on the volumetric loss of materials and antagonists. No correlation was found between the wear of materials and the antagonists, nor between the surface roughness of materials and the volumetric loss of materials or antagonists.

The Effect of Finishing and Polishing with Proprietary Vs Interchanged Polishing Kits on the Surface Roughness of Different Ceramic Materials

PURPOSE

To evaluate the surface roughness of glazed and polished monolithic ceramic materials and to use this as a baseline for comparison after adjustment and polishing with both the recommended kit for the specific materials as well as interchanged polishing kits.

MATERIAL AND METHODS

Flat ceramic specimens (n = 150) were fabricated from IPS ZirCAD Prime, IPS E.max, and Vitabloc Mark II. The specimens were adjusted and polished using either the proprietary polishing kit for the material or interchanged kits. The surface roughness was objectively assessed using Atomic Force Microscopy (AFM) and profilometer. Subjective assessment of surface finish was performed using a scanning electron microscope (SEM). Gravimetric weight loss of each sample was measured before and after polishing using a digital microscale. The mean surface roughness and standard deviation was calculated for each ceramic- polisher pair. A factorial ANOVA was used to compare the mean surface roughness values in nanometers between multiple groups (α = 0.05). The subjective results from the SEM were reported as descriptive statistics RESULTS: The zirconia polishing system produced surfaces with the lowest surface roughness regardless of the ceramic material. The polisher-ceramic combination was found to have a statistically significant effect on both Ra and RMS values when the AFM was used (p = 0.039 and 0.010, respectively).

CONCLUSION

The zirconia polishing system resulted in the lowest surface roughness values regardless of ceramic materials tested. The zirconia polishing system also did not result in significant gravimetric weight loss regardless of the ceramic material used.

The Correlation of Surface Roughness Parameters of Zirconia and Lithium Disilicate with Steatite Wear

PURPOSE

Various surface roughness parameters are utilized to describe the surface in the tooth to ceramics abrasion and to assess the resulting wear. The use of three-dimensional parameters may offer a better estimation for wear and an improved deduced clinical surface treatment. The aim of this study was to determine the influence of various surface roughness parameters of zirconia and lithium disilicate ceramics on the wear of steatite antagonists.

MATERIAL AND METHODS

Forty zirconia specimens with a diameter of 7 mm and a thickness of 3 mm and 40 lithium disilicate specimens with the dimensions 10×10×4 mm were each divided into five subgroups. Two subgroups were treated with different clinically established diamond burs; a third subgroup was treated with a silicone polishing set. Two additional subgroups were produced by glazing the surfaces after treatment. Surface roughness parameters were determined by laser scanning microscopy. All specimens underwent 1.2 million loading cycles using steatite antagonists. After regular intervals of cycles, precision impressions were made to assess the wear. The correlation between wear and different roughness parameters was evaluated using the Spearman correlation test.

RESULTS

For the glazed zirconia, unglazed zirconia, and glazed lithium disilicate specimens no significant correlations (p > 0.05) between the investigated roughness parameters and antagonist wear could be found. In the unglazed lithium disilicate groups, significant (p ≤ 0.05) correlations with steatite substance loss could be found for several roughness parameters after 1.2 million cycles.

CONCLUSIONS

For lithium disilicate, it seems not sufficient to use only one roughness parameter to indicate the wear behavior of the surface. There was no correlation between wear and the tested roughness parameters of zirconia surfaces.

Effect of Successive In-office Bleaching Sessions on the Surface Properties, Substance Loss, Biaxial Flexural Strength, and Reliability of CAD-CAM Monolithic Materials

Little is known about the effects of in-office bleaching on the surface properties and on other aspects of CAD-CAM monolithic materials, especially when successive bleaching sessions are conducted. This study evaluated the effect of up to three successive in-office bleaching sessions on the microhardness, roughness, topography, substance loss, biaxial flexural strength (BFS), and reliability of CAD-CAM monolithic materials. Disks from Lava Ultimate (LU), Vita Enamic (VE), and IPS Empress CAD (EMP) were fabricated and submitted to one, two, and three bleaching sessions. In-office bleaching was performed with 40% hydrogen peroxide and each session consisted of three applications of 20 minutes each. The analyses regarding the aforementioned parameters were assessed before and after the first, second, and third bleaching sessions, except for BFS, which was evaluated at the baseline and after the third session. Weibull modulus was calculated from the BFS data. Bleaching decreased the microhardness of LU and VE from the third and second sessions, respectively, and affected neither the roughness nor the BFS of the three materials. However, in LU, it decreased the reliability and caused topographic changes, which were accentuated by the increase in the number of sessions. In general, LU and EMP showed, respectively, the highest and the lowest substance losses. Successive in-office bleaching sessions with the use of the protocol of the present study should be avoided in LU and VE.

2D and 3D Wear Analysis of 3D Printed and Prefabricated Artificial Teeth

PURPOSE

This study aimed to assess the 3-body wear of prefabricated and 3D-printed artificial denture teeth.

MATERIALS AND METHODS

Four groups of artificial teeth were used; 3D-printed polymethylmethacrylate (PMMA) teeth (PR) and 3 prefabricated commercially available denture teeth: PMMA (Gnathostar, GN), PMMA (SR Orthotyp PE, SR), and Nanohybrid composite (SR Phonares NHC, PH). The 3-body wear test was performed using a steatite ceramic antagonist in a chewing simulator with 750,000 cycles, temperature 23 ± 2 ˚C, and force of 50 N. The abrasive medium was composed of ground millet seeds and white rice mixed with distilled water. The teeth were 3D-scanned before and after the wear test. The 3D images were assessed for teeth wear by measuring the volumetric (3D wear) and the vertical (2D wear) substance loss. The one-way analysis of variance followed by Tukey post hoc test was used to statistically obtain the data analysis.

RESULTS

Maximum 3D wear was observed in the PR (51.05 ± 4.53 mm³), followed by GN (20.22 ± 6.29 mm³) and SR (12.12 ± 6.29 mm³) artificial teeth. Minimum wear occurred in the PH teeth (6.24 ± 0.87 mm³). The analytical differences amongst the groups were statistically significant (P < .05) except between PH and SR teeth. For 2D wear measurement, the maximum was seen in the GN teeth (6.29 ± 1.64 mm), followed by PR (5.04 ± 0.83 mm) and then SR (4.53 ± 0.87 mm). The PH teeth (3.09 ± 0.68 mm) again showed minimum wear. Statistically, amongst the groups, the major observable differences (P < .05) were between PH and GN, PH and PR, and SR and GN.

CONCLUSIONS

Composite resin teeth had a greater wear resistance than acrylic resin teeth and 3D-printed resin teeth, both of which were comparable. Due to the advancement of digital workflows, manufacturers should devote effort to enhancing 3D-printed teeth.

Effect of roughness and acidic medium on wear behavior of dental resin composite

Background

The aim of the study was to investigate whether the citric acid and rough surface have a synergistic effect leading to severe wear behavior of resin composite.

Materials and methods

Disk-shaped (Ø15 × 1.5 mm) specimens of resin composite (n = 12) with different initial roughness were prepared. Reciprocating ball-on-flat wear tests were performed under distilled water and citric acid (pH = 5.5) respectively. The coefficient of friction (COF), wear volume loss, and duration of the running-in period were quantified to assess the wear performance. And the values were analyzed with one-way ANOVA (α = 0.05). Regression analysis was applied to examine the influence of Ra values and mediums on the wear data. The wear morphology was analyzed by scanning electron microscopy and a 3D profilometer.

Results

The average COF was higher in distilled water than in citric acid but was independent of the surface roughness. For the composite, the volume loss of worn area and running-in period increased with surface roughness when tested under distilled water. However, these increasing trends were not found in citric acid. All specimens exhibited mild wear behavior with low COF and less superficial abrasion in acidic medium.

Conclusions

The effect of initial roughness on wear behavior depends on the medium. In distilled water, resin composites with high initial roughness exhibit a longer running-in time, which eventually leads to a significant increase in material loss. The adverse effects of high roughness can be alleviated by the lubrication of citric acid, which can maintain a mild wear behavior regardless of initial surface roughness.

Translucency and mechanical behavior of partially stabilized monolithic zirconia after staining, finishing procedures and artificial aging

Partially stabilized zirconia (5Y-PSZ) has been widely used to manufacture indirect monolithic restorations, and the effect of finishing procedures on the optical and mechanical properties of these materials are still unclear. The purpose of this study was to evaluate the effect of staining, polishing and glazing on surface roughness, crystalline phase content, microhardness, fracture toughness, dynamic elastic modulus, three-point flexural strength, strain distribution, color (∆E₀₀/∆L/∆a/∆b), and translucency before and after artificial accelerated aging (water spray and ultraviolet) of 5Y-PSZ. Bar-shaped and rectangle-shaped specimens of the 5Y-PSZ were prepared and divided into six groups, according to finishing procedure: GC (control), GS (staining), GG (glazing), GSG (staining and glazing), GP (polishing), GSP (staining and polishing). There was a significant difference between groups for surface roughness (p < 0.05), dynamic elastic modulus (p = 0.007), microhardness (p =  < 0.05), ∆E₀₀ (p = 0.010), and ∆a (p = 0.008). GC presented higher cubic phase content, and the stained groups (GS, GSG and GSP) presented higher monoclinic content. The different finishing procedures affected roughness, dynamic elastic modulus, microhardness, and color of 5Y-PSZ; polishing being the finish that provides minors changes to the 5Y- PSZ. Accelerated artificial aging caused color change, regardless of finishing procedure used.

The Effect of Simulated Chewing on the Surface Roughness of Direct and Indirect Resin-Composites Opposed by Zirconia: An In Vitro Study

Purpose

To assess the surface roughness of two different light-cured resin-composites when opposed by monolithic zirconia after simulated mastication.

Materials and Methods

Materials included a direct restorative nanohybrid (n = 10) and an indirect microhybrid (n = 10) resin-composite (Tetric EvoCeram and Sinfony, respectively). The antagonist material was 3 mol% yttria-stabilized tetragonal zirconia polycrystalline ceramic. Each material was subjected to in vitro chewing against zirconia using a chewing simulator for 250,000 cycles. A 3D profilometer was used to assess the surface roughness parameters of each resin-composite before and after the simulated chewing. Independent t-test and paired sample t-test were performed to compare roughness values for both materials and to compare baseline and after chewing simulation values (p = 0.05).

Results

Sinfony showed significantly greater roughness values compared to Tetric EvoCeram (p ≤ 0.025) before and after simulated chewing, except for Sa and Sv parameters after simulated chewing where the difference between the two materials was insignificant (p = 0.06 and 0.89, respectively). Surface roughness increased for both materials after simulated chewing compared to baseline values, but the difference was insignificant (p ≥ 0.065). However, Sa (p = 0.04) and Sv (p = 0.012) for Tetric EvoCeram were significantly higher after compared to before chewing simulation.

Conclusion

Tetric EvoCeram had a smoother surface than Sinfony before and after simulated chewing. Surface roughness for both materials was higher after simulated chewing compared to baseline values which represent surface damage that was significant for Tetric EvoCeram while Sinfony showed better resistance.

Wear Behaviour of Polymer-Infiltrated Network Ceramics, Lithium Disilicate and Cubic Zirconia against Enamel in a Bruxism-Simulated Scenario

The present study aimed to evaluate the wear rate of polymer-infiltrated network composites and ceramics against enamel in a bruxism-simulated scenario. Ninety-six (n = 96) molars were divided into six groups (n = 16) according to their occlusal material: group 1—a polymer-infiltrated network ceramic (PINC); group 2—a second polymer-infiltrated network ceramic (PINC2); group 3—nanohybrid resin-based composite (CO); group 4—cubic zirconia (ZR); group 5—lithium disilicate (LS); and group 6—sound enamel (EN). A laser scanner was used to digitalize all of the occlusal surfaces before and after a fatigue test, which was conducted with a chewing simulator set at 80 N and semicircular movement in order to simulate bruxist movement and loads. Statistical analysis of volume loss was performed with a one-way ANOVA and post hoc Bonferroni test. ZR had significantly inferior wear to PINC (p ≤ 0.01) and CO (p = 0.04). LS wore the antagonist enamel significantly more than PINC, CO, PINC2 and EN (p ≤ 0.01). On the other hand, ZR wore the antagonist enamel significantly more than CO (p ≤ 0.01) and PINC2 (p = 0.05). In conclusion, PINCs better preserved antagonist enamel at the expense of a higher wear of their own. LS causes significantly higher enamel wear compared with PINCs. ZR caused significantly higher enamel wear compared with CO and PINC2, but it was wear-resistant.

Wear behavior and abrasiveness of monolithic CAD/CAM ceramics after simulated mastication

Objectives

To evaluate the wear resistance and abrasiveness of monolithic CAD/CAM ceramics.

Materials and methods

Rectangular-shaped specimens (12 mm × 6.5 mm × 1.5 mm) were sectioned from the following CAD/CAM blocks (n = 10); partially crystallized lithium disilicate (PLD), experimental fully crystallized lithium disilicate (FLD), zirconia-reinforced lithium silicate (ZLS), super-translucent monolithic zirconia (SMZ), and ultra-translucent monolithic zirconia (UMZ). Silicon carbide papers were used to mechanically flatten and polish the surfaces. PLD specimens were subjected to a combined crystallization/glazing firing cycle. Ceramic specimens were mounted to the wear device and tested for 200,000 cycles against human premolars at 20 N force and 2 mm sliding distance. Artificial saliva was used as a lubricant. The teeth were scanned using micro-CT before and after the wear test and the generated models were overlapped to determine the volumetric tooth loss. Before and after the test, specimens’ weights and surface roughness (R_a) values were measured, and the differences were calculated. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were utilized for microstructural and chemical analysis. Statistical analysis was performed using one-way ANOVA or an equivalent test for non-parametric results. Significance level was set at P ≤ 0.05.

Results

The type of ceramic material affected the ceramic and antagonist wear rates (P < 0.001). PLD and ZLS had the highest ceramic and antagonist wear, whereas UMZ and SMZ demonstrated the lowest wear values. The FLD group showed comparable antagonist wear and significantly less ceramic wear than PLD and ZLS.

Conclusions

Monolithic zirconia demonstrated the best wear resistance and least abrasiveness to the antagonist. The experimental lithium disilicate was more wear-resistant than other glass–ceramic groups.

Clinical relevance

Monolithic zirconia is wear-resistant and gentle on the antagonist. In contrast, glass–ceramics are more abrasive to enamel.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00784-022-04611-w.

Effect of different surface treatments and thermomechanical aging on the ion elution of CAD-CAM materials

STATEMENT OF PROBLEM

Dental ceramics have been reported to elute ions when subjected to nonneutral pH. However, the effect of surface treatments and thermomechanical aging on the ion elution of CAD-CAM ceramics is unclear.

PURPOSE

The purpose of this in vitro study was to compare the effect of surface treatment (glazed or polished) and thermomechanical aging on the ion elution of CAD-CAM materials before and after 2-body wear simulation.

MATERIAL AND METHODS

Specimens were prepared from 6 CAD-CAM materials-leucite (LC), feldspathic (FP), zirconia-reinforced lithium silicate (ZLS), lithium disilicate (LDS) glass-ceramics, polymer-infiltrated ceramic network (PICN), and zirconia (ZIR)-and divided into 2 groups according to the surface treatments (glazed or polished) (n=6). For baseline ion elution values, specimens were placed into polyethylene bottles containing deionized water (pH 7.4) that had been stored in an incubator for 168 hours at 37 °C. The eluted ions in the immersion solution were measured by using inductively coupled plasma-optic emission spectrophotometry. The specimens were then subjected to thermomechanical aging by using human enamel as an antagonist. After aging, the ion elution of the specimens was remeasured. Ion elution data before and after 2-body wear were analyzed by using the Mann-Whitney U test, while the effect of 2-body wear was assessed by using the Wilcoxon signed rank test (α=.05).

RESULTS

The presence of some ions varied depending on the material-surface treatment pair before (Al, As, B, Ba, Ca, K, Li, Mg, Na, P, and Zn) and after (Al, B, Ba, Ca, Co, Li, Mg, and P) 2-body wear. Polished materials had higher ion elution than the glazed materials before 2-body wear (P≤.041), except for LC (P and Zn) and PICN (Ca, Cu, and K) (P≤.009). After 2-body wear, polished LC (B and Ba), FP (Al, B, and Mg), ZLS (Al, Ba, Ca, and Li), ZIR (B and Ba), glazed PICN (Ca, Mg, and P), ZLS (P), and ZIR (Co) presented higher ion elution than their counterparts (P≤.041). The effect of 2-body wear on the ion elution of polished LC (Al, K), FP (Na), ZLS (Li), LDS (K, Na), PICN (Al, Na), ZIR (Na, Y), glazed LC (Na), FP (Ba, Na), ZLS (B, Ba, Y), LDS (Na), PICN (Y), and ZIR (Na) was nonsignificant (P≥.075). However, the elution of remaining ions showed a significant difference before and after 2-body wear (P≤.046).

CONCLUSIONS

The chemical stability of tested CAD-CAM materials was affected by the 2-body wear. Glazing led to a lower ion elution except for LDS and PICN. While polishing resulted in lower ion elution for PICN, both surface treatments resulted in similar ion elution for LDS.

Enamel wear against monolithic zirconia restorations: A meta-analysis and systematic review of in vitro studies

OBJECTIVE

An assessment was performed to identify and evaluate dental enamel wear caused by monolithic zirconia restoration. Literature searches were conducted in PubMed, Science Direct, Cochrane Evidence, and the Cochrane Library up to May 2020.

MATERIAL AND METHODS

Studies were selected for systematic review according to the inclusion (articles conducted on the wear of enamel samples opposing monolithic zirconia) and exclusion (case reports, non-English articles, and monolithic zirconia samples facing other materials rather than human enamel) criteria. Of those, articles on polished and glazed monolithic zirconia subjected to a 50 N vertical load with a range of 240,000-250,000 cycles, equivalent to 1 year of in vivo mastication, were included in the meta-analysis.

RESULTS

In total, 3968 articles were pooled. Twenty-five articles met the inclusion criteria for the systematic review. Three studies were included in the meta-analysis. The results showed that the enamel wear against monolithic zirconia was within the statistically accepted level. Moreover, the polished monolithic zirconia surface caused less enamel wear than the glazed surface.

CONCLUSION

This review indicates that monolithic zirconia restorations cause acceptable antagonist enamel wear. Moreover, the meta-analysis results agreed that the final restoration's surface texture plays an essential role in the wear process.

CLINICAL SIGNIFICANCE

Monolithic zirconia restorations have been widely used in dental practice because they eliminate the chipping problems resulting from using veneered restorations. With recent technology development, monolithic zirconia has obtained more esthetic features and a more natural look. However, due to the high strength and surface roughness of monolithic zirconia, wear on the antagonist's teeth was detected. The results showed that this wear amount was statistically acceptable and lower than other ceramics such as feldspathic porcelain and enamel. Furthermore, surface treatment methods must be applied to minimize tooth wear, as polished or glazed surfaces interfere with enamel loss.

Wear Behavior of Different Generations of Zirconia: Present Literature

Objective. The wear behavior of the novel zirconia generation is less well understood and may be affected by compositional modifications compared to the conventional zirconia. Materials and Methods. Combinations of keywords such as “zirconia,” “high translucent,” and “wear” were searched in PubMed and Google Scholar databases up to May 2021. The total of 23 relevant articles was selected according to inclusion criteria. Results. Reports show comparable wear resistance of translucent zirconia to the conventional zirconia despite an increased cubic phase content and lower mean flexural strength. A meticulously polished surface creates the lowest surface roughness, producing favorable zirconia wear resistance and antagonist wear compared to a glazed surface. In comparison to other ceramic materials, zirconia produces the least wear on an enamel antagonist and almost undetectable wear when opposed by zirconia. Wear when paired against resin materials yields a favorable outcome, whereas wear behavior against a metal antagonist varies with the surface hardness of the metal. Conclusions. All zirconia generations are considered wear-friendly to all types of antagonists. Nonetheless, comparative studies on antagonist wear opposing zirconia of different compositions are still limited and further investigation is required.

Effect of alumina particle morphology used for air abrasion on loss of enamel and luting composite resin

OBJECTIVE

To evaluate the volume loss after air abrasion with alumina particles with different morphology on bovine enamel and luting composite resin.

METHODS

Air abrasion was performed on 12 unscathed bovine teeth and 72 luting composite resin discs with 85 μm round-shaped and 50 μm sharp-edged alumina particles applied for 20 s, 40 s and 60 s (n = 12). Air abrasion was standardized by uniform areas of 2 mm diameter, a pressure of 0.25 MPa and a distance of 3 mm. The volume loss was determined by using a laboratory scanner.

RESULTS

Air abrasion with round-shaped alumina particles was mostly not measurable with the laboratory scanner, while sharp-edged alumina air abrasion resulted in significant loss of enamel. The median of volume loss by sharp-edged alumina particles ranged from 0.78 mm³ (20 s) to 2.52 mm³ (60 s). In contrast to round-shaped alumina the removal caused by sharp-edged alumina increased significantly with increasing application times (p ≤ 0.05). For air abrasion on luting composite resin the median of the removed volume ranged from 2.25 mm³ (20 s) to 6.18 mm³ (60 s), while round-shaped alumina showed a range from 0.45 mm³ (20 s) to 1.40mm³ (60 s). The round-shaped alumina produced a statistically significant lower volume loss than sharp-edged alumina for all three air abrasion times.

SIGNIFICANCE

The 85 μm round-shaped alumina particles removed less composite resin than 50 μm sharp-edged alumina particles but barely any enamel, making it an option for removing composite resin residues from enamel.

Risk Indicators Affecting the Survival of the Mandibular First Molar Adjacent to an Implant at the Mandibular Second Molar Site: A Retrospective Study

This study aimed to compare the survival of mandibular first molars (MnM1s) adjacent to implants placed in mandibular second molar sites (ImM2s) with MnM1s adjacent to mandibular second molars (MnM2s) and to investigate risk indicators affecting the survival of MnM1s adjacent to ImM2s. A total of 144 patients who had MnM1s adjacent to ImM2s and MnM1s adjacent to MnM2s on the contralateral side were included in this study. Clinical variables and radiographic bone levels were evaluated. The survival of MnM1s adjacent to ImM2s or MnM2s was evaluated using a Kaplan–Meier analysis and Cox proportional hazards model. The 5-year cumulative survival rates of MnM1s adjacent to ImM2s and MnM2s were 85% and 95%, respectively. MnM1s adjacent to ImM2s of the internal implant-abutment connection type had higher multivariate hazard ratios (HR) for loss. MnM1s that had antagonists with implant-supported prostheses also had higher HR for loss. The multivariate HR for the loss of MnM1s adjacent to ImM2s with peri-implant mucositis was 3.74 times higher than MnM1s adjacent to healthy ImM2s. This study demonstrated several risk indicators affecting the survival of MnM1s adjacent to ImM2s. It is suggested that supportive periodontal and peri-implant therapy combined with meticulous occlusal adjustment can prolong the survival of MnM1s and ImM2s.

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.

The Effects of Toothbrush Wear on the Surface Roughness and Gloss of Resin Composites with Various Types of Matrices

Objective: To evaluate and compare the surface roughness and gloss of a DMA-free composite and Bis-GMA-free composite with a DMA-based composite before and after toothbrushing simulation. Materials and Methods: Fifteen dimensionally standardised composite specimens of three nano-hybrid resin composites (Tetric EvoCeram, Admira Fusion, and Venus Diamond) were used. Five specimens from each composite were polished and then subjected to a toothbrushing simulator. Surface roughness (Ra) and gloss were measured before toothbrushing and after 5000, 10,000, 15,000, and 20,000 toothbrushing cycles. The data was analysed using 5 × 3 ANOVA to assess surface roughness and gloss values and pairwise comparisons in the form of Tukey post hoc tests were performed to interpret main effects. Results: For all tested materials, surface roughness increased, and gloss decreased after toothbrushing abrasion. Surface roughness (Ra) values ranged from 0.14 to 0.22 μm at baseline and increased to between 0.41 and 0.49 μm after 20,000 toothbrushing cycles. Gloss values ranged between 31.9 and 50.6 GU at baseline and between 5.1 and 19.5 GU after 20,000 toothbrushing cycles. The lowest initial Ra value was detected in Venus Diamond and the highest initial gloss value was detected in Tetric EvoCeram. Conclusions: Simulated toothbrushing abrasion led to an increase in surface roughness and a decrease in gloss for all tested materials. Venus Diamond had the smoothest surface and Tetric EvoCeram had the glossiest surface after polishing and following 20,000 cycles of toothbrushing abrasion. Admira Fusion demonstrated the roughest surface and had the lowest gloss values before and after toothbrushing abrasion.

Coating method for smooth and reinforced surface layer of highly translucent zirconia

Due to the recent evolution of dental ceramic materials, highly translucent zirconia materials have been developed. While this material has high aesthetics, there is still room for improvement in strength. In this study, we investigated to strengthen the high translucent zirconia material. In the study, monoclinic zirconia (mZrO₂) nanoparticles were used as a coating agent. The surface of the highly transparent zirconia was coated with mZrO₂ nanoparticle dispersion by dipping and sintered. Thereby, the high translucent zirconia could obtain about 1.3 times higher strength than the untreated one. The post-coating method introduced in this study would be effective as a simple and economical method for improving highly translucent zirconia strength.

Wear of feldspathic-ceramic-veneered zirconia posterior FPDs after 10 years

Background

The abrasion behavior of various ceramics is rarely investigated, though it is relevant for the clinical success of such restorations. The aim of this in vivo study was to evaluate the wear of feldspathic-ceramic-veneered zirconium oxide frameworks over a period of at least 10 years.

Methods

The abrasion behavior of 15 bridge constructions from 15 different participants was examined after a period of 3, 5, and 10 years using plaster models, which were then subjected to a scanning process on the Atos II industrial scanner and digitized for three-dimensional evaluation of the abrasion by the corresponding software (ATOS Professional 7.6). The individual post-examination models were compared to the baseline model and deviations calculated in the sense of the largest, punctual loss of material in millimeters (“minimal distance”), the average abrasion in millimeters (“mean distance”), and the volume decrease in cubic millimeters (“integrated distance”). Statistical analyses were performed using the Wilcoxon sign rank test or mixed regression models. Multiple testing was considered by Benjamini-Hochberg correction. The significance level was set at 0.05.

Results

We found steadily increasing wear of the ceramic. The average volume decrease was significant (P < 0.001) at 3 years and 10 years (− 3.25 mm³ and − 8.11 mm³, respectively).

Conclusions

The results of this study indicate that the rate of volume loss in feldspathic-ceramic-veneered zirconia frameworks in the posterior region increases significantly over time. An increasing frequency of parameters was observed, particularly in the second half of the study period. However, the use of this class of materials can be considered clinically acceptable.

Trial registration This study is registered in DRKS - German Clinical Trials Register with the register number DRKS00021743. https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00021743

Investigation of two-body wear behavior of zirconia-reinforced lithium silicate glass-ceramic for biomedical applications; in vitro chewing simulation

The aim of this work was to the investigate two-body wear behavior of zirconia-reinforced lithium silicate glass-ceramic and composite resins through in vitro chewing simulation. Two types of glass-ceramics (IPS e.max CAD; lithium disilicate, Vita Suprinity; zirconia-reinforced lithium silicate) and two types of composite resins (Filtek Supreme; nano-filled, Ivoclar Vivadent Heliomolar; micro-filled) were used. All specimens were exposed to two-body wear tests using a dual-axis computer-controlled chewing simulation. Each chewing simulation test procedure, Al2O3 ball with a diameter of 6 mm, was used as antagonist material. The mean volume loss and wear depth of all specimens after the chewing tests were determined with use non-contact 3 D profilometer. Zirconia-reinforced lithium silicate Vita Suprinity had significantly higher two-body wear resistance than lithium disilicate IPS e.max CAD glass-ceramic and other composite resins after chewing tests. While Vita Suprinity exhibited a homogeneous crystal microstructure, IPS e.max CAD glass-ceramic exhibited a structure with needle-shaped fine-grained crystals embedded in a glassy matrix. As a result, the homogeneous distribution of zirconia particles into the ceramic material will increase the two-body wear resistance through chewing simulation tests.

A State-of-the-Art Review on the Wear of the Occlusal Surfaces of Natural Teeth and Prosthetic Crowns

This review focuses on the wear mechanisms of natural and restorative dental materials, presenting a comprehensive description and analysis of the works published in the last two decades on the wear at the interface of occlusal surfaces. Different groups of tribological pairs were considered: tooth-tooth, tooth-restorative material (tooth-ceramic, tooth-resin-based-materials, and tooth-metal), and restorative-restorative materials. The lack of standardization of the wear tests impairs the direct comparison of the obtained results. However, it was possible to infer about the main wear mechanisms observed on the different classes of dental materials. Concerning ceramics, their toughness and surface finishing determines the wear of antagonist tooth. Abrasion revealed to be the main wear mechanisms at occlusal interface. In the case of resin-based composites, the cohesion of the organic matrix and the nature, shape, and amount of filler particles greatly influences the dental wear. The protruding and detachment of the filler particles are the main causes of abrasion of antagonist enamel. Metallic materials induce lower wear on antagonist enamel than the other classes of materials, because of their low hardness and high ductility. Most of the studies revealed plastic deformation and adhesive wear as the main wear mechanisms. Overall, more research in this area is needed for a better understanding of the mechanisms involved at the occlusal surfaces wear. This would be essential for the development of more suitable restoration materials.

Two-body wear test of enamel against laboratory polished and clinically adjusted zirconia

AIM

A two-body wear test experiment was performed on human enamel, in simulated chewing motion, against non-veneered zirconia ceramic. Aim-1 was to ascertain the effect of zirconia roughness on enamel wear. Aim-2 was to ascertain the relative enamel wear between enamel-zirconia wear pair and enamel-enamel control pair.

MATERIALS

Six molar and premolar human enamel cusps per group were used for a dental wear test against laboratory polished (LP) zirconia and laboratory polished and clinically adjusted (LP + CA) zirconia. Enamel antagonists were tested against incisor teeth as a control group to demonstrate laboratory enamel wear.

METHODOLOGY

Two-body wear tests were conducted in a dual-axis biomimetic dental wear simulator. 49N loading force was used for 120,000 cycles with 1 mm lateral movement of the test specimen at 1.6Hz frequency, under constant ambient temperature water flow. Surface roughness before testing was determined using 3D profilometry. Loss of enamel height and volume i.e. vertical wear and volumetric wear respectively, were measured by superimposition of before and after testing scans by 3D laser scanning. Scanning electron microscopy was used for surface morphology assessment. One-way ANOVA and Post Hoc Multiple Comparisons with Bonferroni corrections were used at the 5% significance level to determine whether surface finish affected volumetric and vertical enamel loss. The relationship between volumetric and vertical loss of enamel was assessed using Pearson's correlation test.

RESULTS

No significant difference was found between LP and LP + CA zirconia in vertical and volumetric enamel wear results. Control enamel had significantly higher vertical and volumetric enamel wear than LP and LP + CA zirconia. Pearson correlation revealed a strong relationship between vertical wear and volumetric wear of enamel.

CONCLUSION

Within the constraints of the test method in this experiment, zirconia irrespective of surface preparation, was found to cause less vertical and volumetric enamel wear compared to control enamel. No statistically significant difference was seen between LP zirconia and LP + CA zirconia.

Effect of grinding and polishing on the roughness and fracture resistance of cemented CAD-CAM monolithic materials submitted to mechanical aging

STATEMENT OF PROBLEM

The effect of clinical adjustments on the strength of cemented computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic materials under aging challenge is unclear.

PURPOSE

The purpose of this in vitro study was to assess the surface roughness and fracture resistance (with or without mechanical aging) of cemented CAD-CAM monolithic materials submitted to grinding and polishing procedures.

MATERIAL AND METHODS

Disks of Lava Ultimate, Vita Enamic, crystallized Vita Suprinity, and IPS e.max CAD were analyzed for roughness after polishing by using silicon carbide papers (Lava Ultimate and Vita Enamic) or glazing (IPS e.max CAD and Vita Suprinity) (control), after grinding by using 30-μm grit diamond rotary instruments, and after grinding and polishing by using a polishing kit. For fracture resistance, a simplified trilayer model consisting of a restorative disk, an epoxy resin disk, and a steel ring was used. The bonded trilayer disks received the same treatments described for the roughness analysis. Half of the specimens underwent mechanical aging for 1×10⁶ cycles. All specimens were loaded until failure. The Weibull modulus was calculated.

RESULTS

The IPS e.max CAD and Vita Suprinity showed the highest roughness after grinding and the lowest at baseline. For the Lava Ultimate and Vita Enamic, polishing provided lower roughness than at baseline. Grinding, followed or not by polishing, and mechanical aging did not adversely affect the fracture resistance or the reliability of the materials.

CONCLUSIONS

Polishing did not recover the initial surface roughness of the glass-ceramic materials. Fracture resistance was not affected by grinding, followed or not by polishing, even after mechanical aging.

Effect of acidic pH on surface roughness of esthetic dental materials

STATEMENT OF PROBLEM

Exposure to gastric acid in patients with bulimia nervosa and gastroesophageal reflux disease (GERD) causes demineralization of hard tooth structures. This chemical attack also causes the degradation of dental ceramics, which results in increased surface roughness and reduced strength. However, studies comparing the effect of acidic pH on resin matrix ceramic with other computer-aided design and computer-aided manufacturing (CAD-CAM) esthetic materials are lacking.

PURPOSE

The purpose of this in vitro study was to compare the surface roughness changes of different CAD-CAM restorative dental materials after exposure to acidic pH by using a 3D optical interferometer.

MATERIAL AND METHODS

Five esthetic CAD-CAM block materials, a leucite glass-ceramic (IPS Empress CAD), a zirconia (BruxZir Solid Zirconia), a resin matrix ceramic (VITA Enamic), a lithium disilicate glass-ceramic (IPS e.max CAD), and a feldspathic porcelain (VITABLOCS Mark II CAD) were tested. Eighteen specimens were sectioned from CAD-CAM blocks into 2-mm-thick rectangular plates and immersed in 10 mL of 5% hydrochloric acid (HCl) with (pH=2) at 37 °C for 45 and 91 hours. The surface roughness average (Ra) of the specimens was measured by using a 3D optical interferometer before the storage period (baseline), after 45 hours, and after 91 hours of exposure to HCl. Statistical analyses were performed with the Kruskal-Wallis test and the post hoc Dunn test with Bonferroni correction (α=.05).

RESULTS

Regarding the comparison of surface roughness changes at different periods of evaluation (baseline, 45 hours, 91 hours), there were no statistically significant differences for lithium disilicate (P=.063) or zirconia (P=.513). Leucite glass-ceramic, feldspathic porcelain, and the resin matrix ceramic demonstrated statistically significant differences (P<.001). For all tests that were statistically significant, greater surface roughness was found at the time point with the longer HCl exposure. Regarding the comparison of materials in terms of change in surface roughness between baseline to 45 hours and baseline to 91 hours, the Kruskal-Wallis test indicated a statistically significant difference among the materials in both cases (P<.001). Lithium disilicate and zirconia exhibited the least change in surface roughness among the 5 materials.

CONCLUSIONS

Leucite glass-ceramic, feldspathic porcelain, and resin matrix ceramic showed statistically significant increases in surface roughness when they were exposed to simulated gastric acid for 45 and 91 hours. Lithium disilicate and zirconia showed no statistically significant change in surface roughness after exposure to HCl for 45 and 91 hours.

Improving the wear performance of feldspathic veneering porcelain by ion-exchange strengthening

OBJECTIVES

The present study examined the effects of Na⁺→K⁺ ion-exchange on the wear performance of feldspathic veneering porcelain.

METHODS

Bar and disk specimens were prepared using IPS classic as the feldspathic veneering porcelain. After ion-exchange by immersion of the specimens in melted KNO₃ at two temperatures for different time-periods, the bars were tested for flexural strength and Vickers surface hardness. The disks were paired with zirconia antagonists and tested with a pin-on-disk tribometer with 10 N for 70☓10⁴ wear cycles in artificial saliva. Wear analysis of the porcelain and zirconia was performed using 3D profilometer and analysed with one-way analysis of variance and Tukey's post-hoc pairwise comparison procedures. Worn surfaces were examined with scanning electron microscopy.

RESULTS

The feldspathic veneering porcelain exhibited strong time-dependent wear behaviour, with typical running-in and steady wear stages. Ion-exchange treatments at 380 °C and 440 °C both enhanced the mechanical properties, decreased the wear rates of running-in wear and steady wear. The wear performance of porcelain treated by ion-exchange at lower temperature (380 °C) was improved significantly, especially reducing the wear rate of the running-in stage.

CONCLUSION

A thicker ion-exchange layer with less stress relaxation may be obtained by ion-exchange at lower exchange temperature for a long processing time. Such a protocol improves the wear performance of the porcelain effectively.

CLINICAL SIGNIFICANCE

Restorations with veneering porcelain may fail prematurely due to excessive wear. It important to improve the wear performance of the porcelain. Ion-exchange has the potential to strengthen dental veneering porcelain. Understanding the effect of ion-exchange on the wear performance of porcelain provides insight improving the wear performance of these restorations.

Monolithic Zirconia: An Update to Current Knowledge. Optical Properties, Wear, and Clinical Performance

The purpose of this paper was to update the knowledge concerning the wear, translucency, as well as clinical performance of monolithic zirconia ceramics, aiming at highlighting their advantages and weaknesses through data presented in recent literature. New ultra-translucent and multicolor monolithic zirconia ceramics present considerably improved aesthetics and translucency, which, according to the literature reviewed, is similar to those of the more translucent lithium disilicate ceramics. A profound advantage is their high strength at thin geometries preserving their mechanical integrity. Based on the reviewed articles, monolithic zirconia ceramics cause minimal wear of antagonists, especially if appropriately polished, although no evidence still exists regarding the ultra-translucent compositions. Concerning the survival of monolithic zirconia restorations, the present review demonstrates the findings of the existing short-term studies, which reveal promising results after evaluating their performance for up to 5 or 7 years. Although a significant increase in translucency has been achieved, new translucent monolithic zirconia ceramics have to be further evaluated both in vitro and in vivo for their long-term potential to preserve their outstanding properties. Due to limited studies evaluating the wear properties of ultra-translucent material, no sound conclusions can be made, whereas well-designed clinical studies are urgently needed to enlighten issues of prognosis and long-term survival.

Simulated occlusal adjustments and their effects on zirconia and antagonist artificial enamel

PURPOSE

The aim of this study was to evaluate the effect of occlusal adjustments on the surface roughness of yttria-tetragonal zirconia polycrystal (Y-TZP) and wear of opposing artificial enamel.

MATERIALS AND METHODS

Twenty-five Y-TZP slabs from each brand (Lava, 3M and Bruxzir, Glidewell Laboratories) with different surface conditions (Control polished - CPZ; Polished/ground - GRZ; Polished/ground/repolished - RPZ; Glazed - GZ; Porcelain-veneered - PVZ; n=5) were abraded (500,000 cycles, 80 N) against artificial enamel (6 mm diameter steatite). Y-TZP roughness (in µm) before and after chewing simulation (CS) and antagonist steatite volume loss (in mm³) were evaluated using a contact surface profilometer. Y-TZP roughness was analyzed by three-way analysis of variance (ANOVA) and teatite wear by two-way ANOVA and Tukey Honest Difference (HSD) (P=.05).

RESULTS

There was no effect of Y-TZP brand on surface roughness (P=.216) and steatite loss (P=.064). A significant interaction effect (P<.001) between surface condition and CS on Y-TZP roughness was observed. GZ specimens showed higher roughness after CS (before CS − 3.7 ± 1.8 µm; after CS − 13.54 ± 3.11 µm), with partial removal of the glaze layer. Indenters abraded against CPZ (0.09 ± 0.03 mm³) were worn more than those abraded against PVZ (0.02 ± 0.01 mm³) and GZ (0.02 ± 0.01 mm³). Higher wear caused by direct abrasion against zirconia was confirmed by SEM.

CONCLUSION

Polishing with an intraoral polishing system did not reduce the roughness of zirconia. Wear of the opposing artificial enamel was affected by the material on the surface rather than the finishing technique applied, indicating that polished zirconia is more deleterious to artificial enamel than are glazed and porcelain-veneered restorations.

In vitro wear behavior between enamel cusp and three aesthetic restorative materials: Zirconia, porcelain, and composite resin

PURPOSE

The aim of this study was to identify the effects of three aesthetic restorative materials on the wear between tooth and restoration by a pin-on-disk manner.

MATERIALS AND METHODS

Six aesthetic restorative materials were used to prepare disk specimens for wear test, which were Lava Zirconia as zirconia group, Vintage MP and Cerabien ZR as veneering porcelain group, Gradia Direct microhybrid composite containing prepolymerized fillers, Filtek Z250 microhybrid composite containing zirconia glass and colloidal silica particles, and Filtek Z350 nanocomposite as composite resin group. Vertical loss of the worn cusp, change of the surface roughness of the restoration materials, and the surface topography were investigated after wear test under 9.8-N contact load.

RESULTS

The porcelain groups (Vintage MP and Cerabien ZR) caused the largest vertical loss of teeth when compared with those of the composite resin and zirconia groups, and Filtek Z250 microhybrid composite results in the second-largest vertical loss of teeth. The surface of Filtek Z350 nanocomposite was deeply worn out, but visible wear on the surface of the zirconia and Gradia Direct microhybrid composite was not observed. When the zirconia surface was roughened by sand-blasting, vertical loss of teeth considerably increased when compared with that in the case of fine polished zirconia.

CONCLUSION

It was identified that microhybrid composite resin containing a prepolymerized filler and zirconia with reduced surface roughness by polishing were the most desirable restorative materials among the tested materials to prevent the two-body wear between aesthetic restorative material and tooth.

Wear resistance and abrasiveness of CAD-CAM monolithic materials

STATEMENT OF PROBLEM

Computer-aided design and computer-aided manufacturing (CAD-CAM) restorations are in contact with the antagonist tooth, either a natural tooth or a restoration. Therefore, clinicians should be aware of the wear resistance of CAD-CAM materials and the wear behavior of the antagonist.

PURPOSE

The purpose of this in vitro study was to evaluate the wear resistance and abrasiveness of CAD-CAM materials.

MATERIAL AND METHODS

In a 2-body wear test, the materials IPS e.max CAD (Ivoclar Vivadent AG), Vita Suprinity (Vita Zahnfabrik), Lava Ultimate (3M ESPE), Vita Enamic (Vita Zahnfabrik), and Lava Plus (3M ESPE) acted as abraders and, together with bovine enamel, also as antagonists. Each antagonist wheel ran against each abrader wheel for 200000 cycles, with a spring force of 15 N, and at a rotational speed of 1 Hz in distilled water. The wear rate was determined with a surface profilometer. The surfaces were observed with scanning electron microscopy, and their hardness, coefficient of friction, and roughness were evaluated.

RESULTS

Lava Plus and IPS e.max CAD exhibited the highest potential for wear of Lava Ultimate. These 2 materials, together with Vita Suprinity, provided the highest wear of enamel and Vita Enamic. Vita Suprinity and IPS e.max CAD had higher wear than Lava Plus, and the inverse was also true. Vita Enamic and Lava Ultimate were among the materials that caused the lowest wear of enamel and all other evaluated materials. Scanning electron microscopy images revealed that except for Lava Ultimate, all other materials damaged enamel, in which Vita Suprinity and IPS e.max CAD were more aggressive when sliding against the materials. Lava Plus had the greatest hardness, followed by Vita Suprinity and IPS e.max CAD, Vita Enamic, and then Lava Ultimate. The coefficient of friction varied from 0.42 to 0.53. The Vita Enamic and Lava Ultimate showed the highest surface roughness.

CONCLUSIONS

The nanofilled composite resin and polymer-infiltrated ceramic were more antagonist-friendly (whether enamel or CAD-CAM material) than glass-ceramics and zirconia. Care should be taken when selecting the material that will contact mainly with glass-ceramics. Hardness should also be considered when selecting a material.

The ball-on-disk cyclic wear of CAD/CAM machinable dental composite and ceramic materials

The purpose of this study was to investigate the wear volume and the principal strain of machinable dental composite and ceramics in simulated mastication. A ball-on-disk wear test was performed for 3,000 cycles in water, using nine ball/disk combinations of three commercial CAD/CAM materials: feldspathic, lithium disilicate glass ceramics, and a highly loaded composite material (n = 7 for each combination). The wear volume was optically measured using a digital scanner and analyzed for statistical differences based on the materials (α = 0.05). We used non-linear finite element analysis to calculate the principal strain. The wear volume of the ball was significantly larger than that of the disk when hardness and fracture toughness of the former was lower than that of the latter and vice versa (P < 0.05). The lithium disilicate glass ceramic constantly showed lower wear volume than the opposing antagonist. Except for the same material pairs of feldspathic and composite, the ball or disk specimen that showed a larger wear in the occluding pair coincided with the one with higher maximum strain. It was not possible to predict the magnitude of wear, whereas the result suggested a strong association between the maximum strain and wear volume of the ceramic surface.

Polishing of Monolithic Zirconia Crowns-Results of Different Dental Practitioner Groups

This pilot study evaluates the surface roughness of monolithic zirconia crowns after chairside polishing by different dental practitioner groups. Four practitioner groups (group I: dental clinical students (n = 6); group II: dentists < 2 years post-qualification experience (n = 6); group III: dentists > 2 years post-qualification experience (n = 6) and group IV: dental technicians (n = 6)) were asked to polish two CAD/CAM-fabricated full-contour zirconia crowns (48 in total). A two-step zirconia polishing kit was used in both trials. The first trial (T1) was conducted without a time limitation. In the second trial (T2), the polish was restricted to 15 seconds for each polisher. Two blinded investigators (I1 and I2) analyzed the surface roughness (Ra) before and after polishing (Alicona measuring system). No statistically significant difference in surface roughness was found between the polishing results of the dental practitioner groups. Major difference in surface finish was achieved by dental technicians, with a median value of 25.4 nm (interquartile range 10.15–35.26 nm) for I1 in T1. The lowest difference was achieved by dental students, with a median value of Ra = 6.72 nm (interquartile range 4.7–17.9 nm) in T1. In T2, experienced dentists showed the highest difference in surface finish, with a median value of 41.35 nm (interquartile range 7.77–54.11). No significant correlation was found between polishing time and polishing results. The polishing of monolithic zirconium dioxide crowns can be performed with the present polishing set directly chairside after occlusal adjustment, regardless of the practitioner’s experience level.

In vitro evaluation of the polishing effect and optical properties of monolithic zirconia

STATEMENT OF PROBLEM

The relationship between surface roughness and the optical characteristics of zirconia prostheses may be affected by the type of shaded block.

PURPOSE

The purpose of this in vitro study was to investigate changes in surface roughness and brightness of monolithic zirconia blocks of different shades after polishing.

MATERIAL AND METHODS

The surface roughness averages of 3 different kinds of shaded zirconia blocks (Zenostarof T0 [T0], Zenostar sun [Ts], and Zenostar sun chroma [Tsc]) were compared after surface polishing. Fifteen specimens of differing thicknesses were produced per block. (1 mm and 3 mm). Surface morphology and compositions were analyzed by using filed emission scanning electron microscopy (FE-SEM) and energy dispersive spectrometry. A 1-way ANOVA and the post hoc Scheffé test were performed (α=.05). The correlations between surface roughness and brightness were determined using the Pearson correlation analysis (α=.01).

RESULTS

After phased polishing, Ts had the highest average roughness, followed by T0 and then Tsc. A statistically significant difference in roughness was observed between Ts and Tsc (P<.05). Ts exhibited multiple distinct layers in the FE-SEM image. Carbon was detected in the Ts specimens only. Brightness was highest in T0, followed by Ts and then Tsc. A positive correlation was observed between brightness and surface roughness for all specimens (P<.01). This correlation was stronger in the thicker specimens.

CONCLUSIONS

The results of this study suggest that polishing affects monolithic zirconia differently depending on shade. The polishing of monolithic zirconia reduces both surface roughness and brightness. The optical properties of monolithic zirconia vary by thickness and can be opaque or translucent.

Predictable prosthetic space maintenance during staged complete-mouth rehabilitation

Staged complete-mouth rehabilitation to accommodate a patient's financial constraints during the course of treatment is presented. Clear acrylic resin added to the anterior cameo surface of the maxillary fixed complete denture (FCD) served as a space maintainer. The restoration of the maxillary FCD addressed the patient's chief complaint. By adding the space maintainer, supraeruption of mandibular anterior teeth and encroachment of the prosthetic space, which could have resulted in additional treatment, was avoided. During the second stage of the complete-mouth rehabilitation, zirconia restorations were used to restore the mandibular arch to the maxillary FCD after straightforward removal of the space maintainer. This allowed a smooth transition after a delay in treatment without having to modify the previous treatment.

Effect of simulated chairside grinding procedures using commercially available abrasive agents on the surface properties of zirconia

Aim:

The aim of the present study was to assess the change in physical properties (surface roughness, surface hardness and phase transformation) after surface grinding of zirconia by using three commercially available abrasives.

Materials and Methods:

Thirty sintered zirconia specimens were prepared and divided into three groups namely Group M (grinded using Mani Dia diamond bur standard grit), Group T (grinded using Tri Hawk diamond bur coarse grit) and Group P (grinded using Predator carbide bur). A customised assembly was used to follow a standardised protocol for surface grinding. The surface roughness, surface hardness and phase transformation was recorded before and after the grinding procedure.

Statistical Analysis Used:

ANOVA and Bonferroni post hoc test were used to assess the values obtained after the testing the surface roughness and surface hardness.

Results:

The results of the present study revealed the average values of change in surface roughness as Group M (0.44 μm) and Group T (1.235 μm) and Group P (-0.88 μm). The average values of change in surface hardness were Group T (19.578 HV), Group M (46.722 HV) and Group P (36.429 HV). The change in surface hardness was not statistically significant. There was no phase transformation seen after the grinding procedure.

Clinical Significance:

Carbide burs along with copious water irrigation when used to grind zirconia intra-orally produces has a polishing effect, minimal change in hardness & no phase transformation. The present study advocates the use of carbides for chair-side grinding of zirconia.

Influence of the preparation design and artificial aging on the fracture resistance of monolithic zirconia crowns

PURPOSE

The aim of this study was to evaluate the fracture resistance and fracture behavior of monolithic zirconia crowns in accordance with the preparation design and aging simulation method.

MATERIALS AND METHODS

An upper first molar was prepared sequentially with three different preparation designs: shoulderless preparation, 0.4 mm chamfer and 0.8 mm chamfer preparation. For each preparation design, 30 monolithic zirconia crowns were fabricated. After cementation on Cr-Co alloy dies, the following artificial aging procedures were performed: (1) thermal cycling and mechanical loading (TCML): 5000 cycles of thermal cycling 5℃-55℃ and chewing simulation (1,200,000 cycles, 50 N); (2) Low Temperature Degradation simulation (LTD): autoclave treatment at 137℃, 2 bar for 3 hours and chewing simulation; and (3) no pre-treatment (control group). After artificial aging, the crowns were loaded until fracture.

RESULTS

The mean values of fracture resistance varied between 3414 N (LTD; 0.8 mm chamfer preparation) and 5712 N (control group; shoulderless preparation). Two-way ANOVA analysis showed a significantly higher fracture loads for the shoulderless preparation, whereas no difference was found between the chamfer preparations. In contrast to TCML, after LTD simulation the fracture strength of monolithic zirconia crowns decreased significantly.

CONCLUSION

The monolithic crowns tested in this study showed generally high fracture load values. Preparation design and LTD simulation had a significant influence on the fracture strength of monolithic zirconia crowns.

Esthetic Prosthetic Restorations: Reliability and Effects on Antagonist Dentition

Recent advances in ceramics have greatly improved the functional and esthetic properties of restorative materials. New materials offer an esthetic and functional oral rehabilitation, however their impact on opposing teeth is not welldocumented. Peer-reviewed articles published till December 2014 were identified through Pubmed (Medline and Elsevier). Scientifically, there are several methods of measuring the wear process of natural dentition which enhances the comparison of the complicated results. This paper presents an overview of the newly used prosthetic materials and their implication on antagonist teeth or prostheses, especially emphasizing the behavior of zirconia restorations.

Full-Arch, Implant-Supported Monolithic Zirconia Rehabilitations: Pilot Clinical Evaluation of Wear Against Natural or Composite Teeth

PURPOSE

To clinically evaluate the amount of contact wear generated between full-arch monolithic zirconia implant-supported restorations and natural or composite antagonists, over a 1-year period.

MATERIALS AND METHODS

Forty-seven teeth from clinically functional, full-arch monolithic zirconia screw-retained implant prostheses (FDPs) and their antagonists were investigated. The first group ("Zirconia-E") was opposed to natural teeth ("Enamel"), whereas the other one ("Zirconia-CR") was opposed to nano-hybrid composite teeth ("Composite Resin"). Replicas of the restorations and their antagonists were obtained immediately after delivery (T₀ ) and after 1 year of clinical service (T₁ ). Each tooth surface was individually evaluated three-dimensionally by software to quantify the vertical distance between the two scans (Hausdorff distance), which was considered as contact wear. Data obtained for each arch were subjected to one-way ANOVA test and a post hoc analysis (Tukey's test) at a 5% level of significance. Furthermore, the influence of the location of the teeth (anterior or posterior) was analyzed. Minimum post hoc statistical power between statistically different groups was 99.6%.

RESULTS

Mean values were 63 ± 23 μm for Zirconia-E, 76 ± 29 μm for enamel, 70 ± 38 μm for composite resin; Zirconia-CR had a mean value of 19 ± 4 μm and significantly differed from the other groups. Contact wear between anterior and posterior teeth differed significantly only in the composite resin arch, with a mean of 39 ± 22 μm for anterior teeth versus 101 ± 19 μm for posterior ones.

CONCLUSIONS

Within the limitations of this preliminary evaluation, monolithic zirconia full-arch rehabilitations induced a clinically acceptable wear on natural and composite antagonists over a 1-year period; they might be considered a viable solution for implant-supported rehabilitations.