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

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.

Wear of Enamel Antagonist to Polished vs Glazed Zirconia-reinforced Lithium Silicate Crowns (Randomized Clinical Trial)

AIM

The purpose of this clinical study was to assess the wear on opposing enamel caused by two processing methods of ZLS (zirconium-reinforced lithium silicate) VITA SUPRINITY crowns-polished and glaze-fired-when used to restore posterior teeth.

MATERIALS AND METHODS

The study included 26 patients requiring full coverage molar crowns. Participants were divided into two groups based on the type of occlusal surface treatment applied. Group I comprised patients who received polished ZLS crowns, while group II included those treated with glaze-fired ZLS crowns. Following final cementation, intraoral scans were performed at baseline and after 6 months, and wear measurements were analyzed using superimposition software.

RESULTS

After a 6-month follow-up, polished crowns exhibited significantly lower wear compared to glaze-fired crowns for both the restoration (p = 0.013, effect size = 1.344) and the antagonist enamel (p = 0.041, effect size = 1.026).

CONCLUSION

Within the study's limitations, polished ZLS crowns exhibited minimal wear on opposing teeth, whereas glazed ZLS caused greater wear on both the restoration and antagonist enamel.

CLINICAL SIGNIFICANCE

VITA SUPRINITY crowns, particularly when polished with appropriate techniques, offer favorable wear resistance for both the restoration and opposing enamel, along with excellent biocompatibility. How to cite this article: Rady IS, Anwar EM, Elsharkawy AM, et al. Wear of Enamel Antagonist to Polished vs Glazed Zirconia-reinforced Lithium Silicate Crowns (Randomized Clinical Trial). J Contemp Dent Pract 2025;26(1):18-24.

Effect of occlusal adjustment and subsequent repolishing on the surface roughness and volumetric wear of different types of glazed monolithic zirconia after chewing simulation

The objective was to evaluate the effect of material (four monolithic zirconia) and surface condition [glazed (G) versus polished after simulation of occlusal adjustment (GAP)] on roughness and volumetric wear (VW) of dental zirconia after chewing simulation (CS). Zirconia specimens (ZS) were fabricated with an approximate diameter of 12.0 mm and a thickness of 1.0 mm. The four types of monolithic zirconia utilized were Prettau 4 Anterior (PA), Lava Plus (LP), Cercon hT (hT), and Cercon xT (xT). All specimens were coated with a thin and uniform layer of Prettau Plus glaze. Additionally, half of the ZS underwent a simulation of occlusal adjustment followed by clinical polishing. The sliding wear test was performed using a chewing simulator set at 30 N, 2 Hz, and 500,000 cycles, employing steatite specimens (SS) to simulate opposing dentition. ZS and SS underwent topographic analysis through optical profilometry to assess volumetric wear (VW) and surface roughness. The average roughness values (μm) of the zirconia ranged from 0.38h (PA-G before CS) to 2.55a (PA-GAP after CS), while for the antagonist the values ranged from 1.3b (LP-G before CS) to 2.6a (PA-GAP after CS). The VW values (mm3) of the ZS ranged from 0.7b (LP-G) to 2.5a (LP-GAP), while for the antagonist the values ranged from 0.17a (xT-GAP) to 0.33a (LP-G). The CS increased the roughness of all materials tested, regardless of the surface condition. The glazed condition showed lower roughness than the glazed/occlusal adjustment/polishing condition before the CS for three zirconia (PA, LP and xT) and after the CS for all materials. The surface condition did not significantly influence volumetric wear (VW) for three materials (PA, hT, and xT); however, for the Lava Plus (LP) group, the glazed condition resulted in reduced VW. The VW of the SS was unaffected by the material type or surface condition. In summary, zirconia specimens that underwent occlusal adjustment followed by repolishing demonstrated increased surface roughness compared to the glazed ones, while their wear behavior varied depending on the type of zirconia used.

Digital wear analysis of onlay restorations constructed from two pressable glass-based ceramics against natural enamel: An in vitro study

Background

The wear resistance of lithium disilicate glass ceramics remains inadequately understood. Therefore, the primary objective of this in vitro study was to digitally assess the wear characteristics of lithium disilicate and zirconia-reinforced lithium disilicate pressable ceramics following chewing simulation.

Methods

Twenty-two onlay ceramic restorations were fabricated on epoxy dies replicated from the maxillary first premolar ivory tooth master die. The onlay samples were randomly allocated to two equal groups (n=11) based on the material used: group L (lithium disilicate [IPS e.max Press]) and group Z (zirconia-reinforced lithium disilicate [Vita Ambria]). Self-adhesive resin cement was used to cement all of the samples. Each sample was occluded with the buccal cusps of healthy human upper first premolar teeth (n=22). Subsequently, all the samples were scanned using an intraoral scanner (Medit i500) at baseline and after chewing simulation. The acquired standard tessellation language (STL) files of baseline and post-chewing simulation data were superimposed, and the volumetric loss (mm3) and wear depth (μm) of the materials and their enamel antagonists were calculated. Statistical analysis was performed using independent t-test (P=0.05).

Results

There was no statistically significant difference in the wear behavior of Vita Ambria compared to IPS e.max (P<0.05). Similarly, there was no statistically significant difference in the wear behavior of their enamel antagonists (P<0.05).

Conclusion

IPS e.max Press and Vita Ambria ceramics demonstrated comparable wear behavior.

Tribological aspects of enamel wear caused by zirconia and lithium disilicate: A meta-narrative review

The contact between enamel and an antagonist surface is the primary factor in tooth wear. Loss of tooth structure can cause changes in occlusion, chewing functionality, dental sensitivity, and appearance. However, enamel wear caused by opposing restorations is multifactorial and there is a lack of consensus regarding its behavior. This meta-narrative review assesses the multiple factors that affect enamel wear when using two common indirect restorative materials, lithium disilicate and zirconia. PubMed, Google Scholar, MEDLINE, and CINAHL databases were searched using keywords "zirconia," "lithium disilicate," "antagonistic tooth wear," and "enamel wear" to identify studies related to enamel wear caused by zirconia and lithium disilicate restorations. The Realist and Meta-narrative Evidence Syntheses: Evolving Standards (RAMESES) publication standard was used to report this meta-narrative literature review. Four broad categories of influencing factors were identified and reviewed: (1) mechanical and physical properties, (2) wear behavior and microstructural characteristics, (3) surface state, and (4) environmental factors. We conclude that well-polished zirconia is a more favorable indirect restorative material than lithium disilicate in terms of tribology because of its microstructure and surface integrity during wear. This review will enable clinicians to better comprehend the intricate nature of tooth wear caused by dental restorations.

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 immune-boosting beverage, energy beverage, hydrogen peroxide superior, polishing methods and fine-grained dental prophylaxis paste on color of CAD-CAM restorative materials

BACKGROUND

The effect of an immune-boosting beverage (SAM) containing Sambucus Nigra, an energy beverage (ENE), an in-office bleaching (BLE) agent with 25% hydrogen peroxide superior, glazing (GLA) or polishing (POL) methods, and professional dental prophylaxis (PDP) on the color of CAD-CAM restorative materials is unknown.

METHODS

In total 210 specimens were prepared, consisting of CAD-CAM feldspathic (FC), zirconia-reinforced lithium disilicate ceramic (ZLS) and hybrid ceramic (HC). The ceramic specimens were divided according to the polishing methods of glazing (GLA) and mechanical polishing (POL). All materials were divided into two groups: with and without BLE. A 25% hydrogen peroxide superior (HPS) gel was used for BLE. After the baseline (BAS) measurement, the specimens were immersed in 3 different beverages (distilled water (DIS), SAM, ENE). After 28 days, a fine-grained (RDA 7) prophylaxis paste was applied. Statistical analysis of ∆E00 color difference values was performed by 3-way ANOVA and Bonferroni test (α = 0.05).

RESULTS

The effect of all other actions except material-BLE-beverage on color for BAS-Day 28 was statistically different (p < 0.05). The effect of material, material-BLE, beverage on color for Day 28-PDP was statistically different (p < 0.05). After 28 days, the lowest color change was found in FC-GLA and HC immersed in DIS (p = 0.0001) and the highest in FC-POL immersed in ENE (p = 0.0002). PDP was efficient in color recovery in HC immersed to DIS, ENE and SAM (p = 0.0010). For FC, HC and ZLS, BLE caused a higher color change (p < 0.0001). Regardless of the material, the highest color change for BLE-beverage was found in BLE-treated specimens immersed in ENE (p = 0.0496) and the lowest color change was found in non-BLE-treated specimens immersed in SAM (p = 0.0074).

CONCLUSIONS

In materials pre-exposed to 25% HPS, the effect of PDP on color recovery was lower than in unexposed materials. After 28 days, mechanical polishing produced higher color change in FC than glazing, however, in ZLS effects of glazing and mechanical polishing on color were similar. For material/polishing method, HC was the most effective. ENE caused higher color change than DIS and SAM. PDP was more effective than ENE in restoring color to DIS- and SAM-immersed specimens.

Effect of different surface treatments and adhesive cementation on the surface topography and flexural strength of translucent and ultra-translucent monolithic zirconia

PURPOSE

To evaluate the effect of different surface treatments and adhesive cementation on the miniflexural strength (MFS) of monolithic zirconia.

MATERIALS AND METHODS

Two-hundred and forty (240) sintered bars of translucent zirconia (ZT) and ultra-translucent zirconia (ZUT) were obtained (8 mm ×2 mm ×1 mm). The bars were divided into 16 groups (n = 15) according to the factors "Zirconia" (ZT and ZUT), "Cementation" (Cem) and "surface treatment" (Ctrl:Control, Al:Aluminum oxide/Al2O3 50 µm, Si:Silica/SiO2 coated alumina particles oxide 30 µm, Gl:Glazing+hydrofluoric acid). Half of the bars received an adhesive layer application, followed by application of resin cement and light curing. The surface roughness was measured in non-cemented groups. All the bars were subjected to the MFS test (1.0 mm/min; 100 kgf). Scanning electron microscopy was used for qualitative analyses. MFS data (MPa) and roughness (µm) were statistically evaluated by three-way and two-way ANOVA respectively and Tukey's test (5%).

RESULTS

The surface treatment and the interaction were significant for roughness. Glazing promoted less roughness compared to silicatization. Regarding MFS, only the zirconia and surface treatment factors were significant. For ZT, the sandblasted groups had an increase in MFS and glazing reduced it. There was no difference between the groups without cementation for the ZUT; however, ZUT.Si/Cem, and ZUT.Al/Cem obtained superior MFS among the cemented groups.

CONCLUSIONS

Sandblasting increases the flexural strength for ZT, while glaze application tends to reduce it. Applying resin cement increases the flexural strength of ZUT when associated with sandblasting. Sandblasting protocols promote greater surface roughness.

Optimized 3D printed zirconia-reinforced leucite with antibacterial coating for dental applications

OBJECTIVES

This study aims to produce by robocasting leucite/zirconia pieces with suitable mechanical and tribological performance, convenient aesthetics, and antibacterial properties to be used in dental crown replacement.

METHODS

Leucite pastes reinforced with 12.5%, 25%, and 37.5% wt. ZrO2 nanoparticles were prepared and used to print samples that after sintering were characterized in terms of density, shrinkage, morphology, porosity, mechanical and tribological properties and translucency. A coating of silver diamine fluoride (SDF) and potassium iodide (KI) was applied over the most promising material. The material's antibacterial activity and cytotoxicity were assessed.

RESULTS

It was found that the increase of ZrO2 reinforcement up to 25% enhanced both microhardness and fracture toughness of the sintered composite. However, for a superior content of ZrO2, the increase of the porosity negatively affected the mechanical behaviour of the composite. Moreover, the composite with 25% ZrO2 exhibited neglectable wear in chewing simulator tests and induced the lowest wear on the antagonist dental cusps. Although this composite exhibited lower translucency than human teeth, it was three times higher than the ZrO2 glazed material. Coating this composite material with SDF+KI conferred antibacterial properties without inducing cytotoxicity.

SIGNIFICANCE

Robocasting of leucite reinforced with 25% ZrO2 led to best results. The obtained material revealed superior optical properties and tribomechanical behaviour compared to glazed ZrO2 (that is a common option in dental practice). Moreover, the application of SDF+KI coating impaired S. aureus proliferation, which anticipates its potential benefit for preventing pathogenic bacterial complications associated with prosthetic crown placement.

Color stability and surface roughness of resin-ceramics with different surface treatments: A systematic review and meta-analysis of in vitro studies

STATEMENT OF PROBLEM

Surface treatments for resin-ceramics have been developed to obtain a smooth surface and improve color stability. However, a consensus on the best treatment for these materials is lacking.

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the color stability and roughness of glass-ceramics versus resin-ceramics with different surface treatments.

MATERIAL AND METHODS

The preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines were followed, and the study was registered in the open science framework (OSF) for in vitro studies. The population, intervention, control, and outcome (PICO) question was "Is there a difference in color stability and roughness between resin-ceramic vs vitreous ceramics in different surface treatment protocols?" A literature search was performed in PubMed/MEDLINE, Embase, Web of Science, Scopus, Cochrane Library, and ProQuest databases up to January 2023. The Joanna Briggs Institute's critical assessment guidelines for quasi-experimental studies were used for quality assessment. The meta-analysis was based on the inverse variance (IV) method (α=.05).

RESULTS

A total of 18 laboratory studies were published between 2015 and 2022, with a total of 2160 specimens, all of which were analyzed qualitatively. The meta-analysis indicated significantly less optical alteration for lithium disilicate ceramics (P<.01; MD: 2.69; 95% CI: 2.00-3.39; I²=89%, P<.01), even when compared with resin-ceramics with polish or sealants (P<.01; MD: 2.45; 95% CI: 1.59-3.30; I²=87%, P<.01) and (P<.01; MD: 3.24; 95% CI: 2.02-4.47; I²=89%, P<.01), while there was no significant difference in surface roughness (P=.08; MD: -0.71; CI 95%: -1.52 to 0.09; I²=87%, P<.01) (P=.33; MD: -0.31; CI 95%: -0.94 to 0.32; I²=87%, P<.01), respectively.

CONCLUSIONS

Resin-ceramics that have been polished or treated with sealants have lower color stability than glazed glass-ceramics; however, they are similar in terms of surface roughness.

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.

Development of Dental Poly(methyl methacrylate)-Based Resin for Stereolithography Additive Manufacturing

Poly(methyl methacrylate) (PMMA) is widely used in dental applications. However, PMMA specialized for stereolithography (SLA) additive manufacturing (3D-printing) has not been developed yet. This study aims to develop a novel PMMA-based resin for SLA 3D-printing by mixing methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDMA), and PMMA powder in various mixing ratios. The printability and the viscosity of the PMMA-based resins were examined to determine their suitability for 3D-printing. The mechanical properties (flexural strength and Vickers hardness), shear bond strength, degree of conversion, physicochemical properties (water sorption and solubility), and cytotoxicity for L929 cells of the resulting resins were compared with those of three commercial resins: one self-cured resin and two 3D-print resins. EGDMA and PMMA were found to be essential components for SLA 3D-printing. The viscosity increased with PMMA content, while the mechanical properties improved as EGDMA content increased. The shear bond strength tended to decrease as EGDMA increased. Based on these characteristics, the optimal composition was determined to be 30% PMMA, 56% EGDMA, 14% MMA with flexural strength (84.6 ± 7.1 MPa), Vickers hardness (21.6 ± 1.9), and shear bond strength (10.5 ± 1.8 MPa) which were comparable to or higher than those of commercial resins. The resin’s degree of conversion (71.5 ± 0.7%), water sorption (19.7 ± 0.6 μg/mm³), solubility (below detection limit), and cell viability (80.7 ± 6.2% at day 10) were all acceptable for use in an oral environment. The printable PMMA-based resin is a potential candidate material for dental applications.