Lithium Disilicate Ceramics Research Articles

Propriedades mecânicas e ópticas das cerâmicas feldspáticas e dissilicato de lítio: Revisão de literatura

Objetivo: o objetivo dessa revisão de literatura é apresentar os dados existentes sobre capacidade estética e resistência à fratura das cerâmicas feldspáticas e dissilicato de lítio confeccionadas para o uso em CAD/CAM. Material e Métodos: para realizar o estudo foram levantados artigos originais sobre as cerâmicas feldspáticas e dissilicato de lítio em periódicos na base de dados PubMed e ScienceDirect, desde 2015 até 2020 utilizando como termos de busca “lithium disilicate AND esthetic AND CAD/CAM”, “lithium disilicate AND fadigue AND CAD/CAM”, “lithium disilicate AND fracture AND CAD/CAM”, “feldspathic AND esthetic AND CAD/CAM”, “feldspathic AND fadigue AND CAD/CAM”, “feldspathic AND fracture AND CAD/CAM”. Ainda, foram selecionados artigos de relevância publicados em datas anteriores selecionados pelos autores. Constam trabalhos longitudinais, de revisão de literatura, casos clínicos e pesquisas in vitro. Resultados: no total, 209 artigos foram encontrados e somente 16 foram incluídos para comparação. Os dados apresentaram boa capacidade estética para ambos materiais, sendo o dissilicato com maior resistência à fratura. Conclusão: concluiu-se que cerâmicas feldspáticas e dissilicato de lítio para CAD/CAM apresentam capacidade ópticas satisfatórias para restaurações estéticas quando utilizado os blocos multicores, devendo-se optar pelo dissilicato de lítio em situações de maior esforço mastigatório ou menor espessura da peça protética

Repair strength and surface topography of lithium disilicate and hybrid resin ceramics with LLLT and photodynamic therapy in comparison to hydrofluoric acid.

The aim was to compare the repair bond strength and surface topography of lithium disilicate ceramics (LDC) and hybrid resin ceramics (HRC) using different surface conditioning treatments [low level laser therapy (LLLT), photodynamic therapy (PDT), hydrofluoric acid (HF) with silane and air abrasion (AA) and silane]. Sixty specimens each of LDC and HRC were used. Discs were prepared for each group (6 × 2 mm), conditioned using different regimes. Specimens in group 1 and 5 were laser irradiated using Er,Cr:YSGG (ECYL), group 2 and 6 were conditioned using methylene blue photosensitizer (PDT), group 3 and 7 surface was treated with hydrofluoric acid and silane (HFA-S), group 4 and 8 conditioned with Al2O3 air abrasion and silane (AA-S). A Porcelain Repair Kit was used according to manufacturer recommendation in all samples. Peak universal bond adhesive was rubbed on ceramic surface and then bonded with composite resin. For shear bond strength testing the specimens were placed in a universal testing machine. A stereomicroscope at 40x magnification was used to analyse failure pattern. Five specimens in each group after surface treatment were evaluated for surface changes and topography using scanning electron microscopy. The mean repair bond strength was calculated using ANOVA and Tukey's post hoc test at a significance level of (p < 0.05). The highest repair bond strength was observed in group 3 (LDC) (20.57 ± 3.58 MPa) (HFA-S), whereas, the lowest score was displayed in Group 2 (LDC) using methylene blue photosensitizer (MBPS) (12.18 ± 1.08 MPa). Similarly, in HRC the highest repair SBS was presented in group 8 (AA-S) (20.52 ± 2.51 MPa) and the lowest SBS values were exhibited by PDT treated group 6 (13.22 ± 0.62 MPa). A combination of mechanical and chemical surface treatments should be used in order to achieve adequate repair bond strength between resin composites and ceramic interface of LDC and HRC.

The effect of leachable components of resin cements and its resultant bond strength with lithium disilicate ceramics.

To evaluate the leachable components of resin cements in oral simulating fluids using high performance liquid chromatography and its resultant shear bond strength with ceramics. Forty extracted permanent human mandibular molar teeth were sectioned horizontally with a disc beneath the dentino-enamel junction to expose the coronal dentin surface and later finished with 600-grit silicon carbide paper to create a uniform flat surface. Forty Lithium Di-silicate Ceramic block cylinders were sliced in a saw cutting machine at 250 rpm under water-cooling to obtain the discs. The teeth and the ceramic discs were then randomly assigned to two groups on the basis of material used for luting the ceramic disk. Group I: Ceramic disc luted with tooth surface using Variolink II Dual cure Resin Cement, Group II: Ceramic disc luted with tooth surface using multilink speed self-adhesive self-curing resin cement. All ceramic discs were etched with 5% HF acid (IPS Ceramic Etching Gel, Ivoclar, Schaan, Liechtenstein) for 20 seconds, then rinsed thoroughly for 20 seconds and dried for 20 seconds. Ceramic specimens were luted on dentin surfaces with the application of 5 kg load. The samples were stored in 75% ethanol solution for 2 weeks at 37 degree Celsius for chemical aging. HPLC Analysis were performed to analyze the eluted monomer. After HPLC Analysis, Samples were then loaded using universal testing machine for the evaluation of shear bond strength between ceramic discs and the resin cements before and after the elution of monomers. Under HPLC analysis, results showed that the peak release of monomer is Bis-GMA in both the groups. The shear force required to break the bond between the ceramic luted to tooth surface with the resin cements were more for Group I. Statistical results: The statistical analysis was done using ANOVA and paired t-test and it shows P value ≥0.05, hence the null hypothesis is rejected. The monomer eluded from all the groups are identified as Bis-GMA, The eluded monomer decreases the bond strength between the resin cement and the ceramic due to water sorption, The Variolink II (dual cure) resin cement shows improved bond strength than the Multilink (self-cure self-adhesive) resin cement.

Effect of surface finishing treatments on the color stability of CAD/CAM materials.

PURPOSEThe aim of this study was to evaluate the effect of different surface finishing processes on the color stabilities of lithium disilicate glass-ceramics, zirconia-reinforced lithium silicate ceramics, and resin nanoceramics after artificial ageing.MATERIALS AND METHODS216 samples were prepared from 3 different CAD/CAM materials (LAVA Ultimate, IPS e.max CAD, VITA Suprinity) with A1 HT color at a size of 14 × 12 mm and a thickness of 0.5 ± 0.05 mm. Color measurements of the samples were performed with a spectrophotometer using color parameters and CIE Lab color system on a gray backing between baseline color and after 5000 cycles of artificial ageing in 4 stages (i.e. the first measurement before the treatment, the second measurement after polishing, the third measurement after cement application, and the fourth measurement after artificial ageing). The results were evaluated using the Variance analysis and Fisher's LSD test.RESULTSResin nanoceramics (LU) exhibited higher color change values than zirconia-reinforced lithium silicate (VS) and lithium disilicate (EC) ceramics after artificial ageing. Manual polishing and glazing resulted in similar color change for LU and VS (P>.05). In the EC group, glazing provided statistically different results as compared to the manual polishing and control groups (P<.05). Among the ceramic groups, color change values of the subgroup, which was treated by glazing, of the zirconia-reinforced lithium silicate (VS) and lithium disilicate (EC) samples were below the clinically acceptable level (ΔE < 3.5).CONCLUSIONThe lowest color change for all stages was observed in Vita Suprinity.

Effects of adhesive system, thermal aging and ceramic shade on the final color and bond strength of monolithic lithium disilicate ceramics

Aim: The present study aims to observe the effects of adhesive systems and thermocycling on the final color of monolithic lithium disilicate ceramics, also impacts of ceramic shade on the bond strength of resin cement.Material and Methods: Monolithic lithium disilicate ceramic discs in VITA shades A1 and A3 and also self-adhesive, self-etch and total-etch adhesive resin cement systems that were used were investigated in this study. The same color of resin cement (A2 shade) was used for cementation. Ceramic samples of 0,5 mm in thickness were obtained from the IPS e.max CAD blocs. All specimens were distributed into two main groups and six subgroups (n=10) according to the ceramic shade and adhesive system. All specimens were exposed to thermocycling (10,000 cycles). A contact spectrophotometer measured the color differences according to the CIEL*a*b* system. The color differences between before resin cementation (1), after resin cementation procedure (2) and after thermocycling (3), were evaluated. Shear bond strength test was performed after thermocycling.Results: All L values decreased after the resin cementation. The A3-VL (total etch-A3) group had statistically significantly lowest values of L* (p0.05). A3-RX (self-adhesive-A3) group had the statistically significant highest a* and b* values (p0.05). A3-RX group had the highest bond strength results, and there were no statistically significant differences between the A1-VL group (p>0.05). Conclusions: All of the adhesive systems affected the final color of ceramics. Otherwise, the thermal aging procedure did not lead to the changes in the color of the ceramic-resin specimen. Furthermore, ceramic shade affected the bond strength of resin cement after thermocycling.

Influence of Computer-aided Design/Computer-aided Manufacturing Diamond Bur Wear on Marginal Misfit of Two Lithium Disilicate Ceramic Systems.

Marginal misfit of monolithic lithium disilicate ceramic crowns obtained from a chairside computer-aided design/computer-aided manufacturing system is affected after successive millings using a single diamond bur set. This fact can be critical for the longevity of indirect restorations.

Lithium di silicate ceramic surface treated with Er,Cr:YSGG and other conditioning regimes bonded to orthodontic bracket

AimTo assess bond integrity and modes of failure of metallic brackets to lithium disilicate ceramics (LDC) conditioned with Er,Cr:YSGG laser (ECL). Material and methodsSixty LDC were arbitrarily allocated into six groups (n = 15) according to the type of ceramic surface conditioning treatment. Group 1 surface treated with silane (S) only, group 2 surface etched with hydrofluoric acid (HF)+ S, group 3 surface conditioned with HF+ ultrasonic bath (UB)+ S, group 4 sand blasting (SB) of glass ceramic surface with 50 µm Al2O3, group 5 surface conditioned with self-etch ceramic primer (SECP) and in group 6 surface treated with ECL + S. After conditioning, the specimens were positioned in a universal testing device for shear bond strength (SBS) testing. Adhesive Remnant Index (ARI) was used to determine sites of bond failure. Among experimental groups analysis of variance (ANOVA) and Tukey multiple comparison test was used at a significance level of (p < 0.05). ResultsThe highest SBS values were observed in group 3 HF+ UB + S (18.21 ± 1.241) and the lowest SBS values were displayed group 1 surface treated with S only (5.21 ± 0.23). Specimens surface conditioned in group 2 with HF+ S (17.85 ± 1.25), group 3 HF+ UB + S (18.21 ± 1.241) and group 6 ECL + S (17.09 ± 1.114) unveiled comparable SBS values (p > 0.05). ConclusionLDC conditioned with ECL at (4.5 W and 30 Hz) has a potential to be used in clinical settings alternate to HF acid.

Effect of Hydrothermal Aging and Beverages on Color Stability of Lithium Disilicate and Zirconia Based Ceramics.

Background and Objectives: All-ceramic prosthesis is widely used in modern dental practice because of its improved physico-mechanical and optical properties. These restorations are exposed to coloring agents from various nutrition and beverages in the oral cavity. Long-term color stability is critical for the success of these restorative materials. The purpose of this in vitro study was to assess the effect of common beverages and mouthwash on the color stability of lithium disilicate (LD), monolithic zirconia (MZ) and bilayer zirconia (BZ) surfaces. Materials and Method: Thirty disc-shaped specimens from each material were fabricated; each group was subdivided (n = 10) according to coffee, green tea and chlorhexidine immersion solutions. The baseline color of ceramic discs was recorded according to the CIE L*a*b* system with a portable spectrophotometer. The second measurement was recorded after 3000 thermocycling and immersion in coloring agents for 7 days. The mean color difference was calculated and data were compared with Kruskal-Wallis and Mann-Whitney post hoc tests (0.05). Results: ΔE values for LD with the immersion of coffee, tea, and Chlorhexidine gluconate (CHG) were 1.78, 2.241 and 1.58, respectively. Corresponding ΔE values for MZ were 5.60, 5.19, and 4.86; marginally higher than the clinically acceptable level of 3.5. Meanwhile, BZ showed better color stability compared to MZ with ΔE values of 4.22, 2.11 and 1.43. Conclusions: Among the ceramics evaluated, LD ceramic was found to be more color stable, while MZ ceramics displayed a higher susceptibility to discoloration. MZ and BZ ceramic colors were significantly altered with coffee immersion, while LD ceramics were more affected by green tea.

Effects of glazing methods on the optical and surface properties of silicate ceramics

PurposeThis study aims to evaluate the effect of different glazing methods on translucency parameter (TP), contrast ratio (CR), opalescence parameter (OP), surface roughness (Ra) and topography of the silicate ceramics. MethodsSeventy specimens (10×10×1mm) were fabricated from lithium disilicate (IPS e.max CAD, abbreviated as E) and zirconia-reinforced lithium silicate (Vita Suprinity, abbreviated as VS) ceramics and divided into 7 subgroups (n=10) according to the polishing and glazing procedures: (1) mechanical polishing before-crystallization (m-BC), (2) mechanical polishing after-crystallization (m-AC), (3) glaze powder/liquid after-crystallization (pl-AC), (4) glaze-paste before-crystallization (gp-BC), (5) glaze-paste after-crystallization (gp-AC), (6) glaze-spray before-crystallization (gs-BC), (7) glaze-spray after-crystallization (gs-AC). Color and Ra measurements were performed. CIEL*a*b* and CIEXYZ parameters were recorded and TP, CR, and OP values were calculated. Data were analyzed using two-way ANOVA and Tukey HSD tests (α=0.05). ResultsIn E groups, the highest Ra value was found in gs-AC (1.66±0.14μm) while the lowest value was found in pl-AC (0.68±0.08μm). In VS groups, the highest Ra value was found in gp-BC (1.64±0.25μm) while the lowest value was found in m-AC (0.77±0.06μm) (p<0.05). The mean TP value of E (17.62±0.73) was found to be higher than VS (15.37±1.16). The CR (0.72±0.030) and OP (12.06±0.74) values of VS were found higher than CR (0.57±0.02) and OP (6.72±0.40) values of E. ConclusionsZirconia-reinforced silicate ceramics have higher opalescence and lower translucency values than lithium disilicate ceramics. Increase in surface roughness reduces translucency. Glaze powder/liquid after-crystallization is the most effective way to reduce surface roughness of lithium disilicate ceramics while that is mechanical polishing after-crystallization for zirconia-reinforced silicate ceramics.

Color stability of polymer-infiltrated-ceramics compared with lithium disilicate ceramics and composite.

To investigate the color stability of hybrid ceramics and to compare it to composite and lithium disilicate ceramics. One hundred eighty samples were fabricated and processed with a semiautomatic grinding and polishing device (final step: 1200 grit). After thermocycling, samples were immersed in a staining solution (five subgroups: water, red wine, curry, black tea, cola) for 4 weeks. A spectroradiometer was used to determine the color of the samples in CIE L*a*b*. Color measurements were performed before staining (baseline, initial color), after thermocycling, after 2 and 4 week storage in staining solution and each after a two stage repolishing approach. Discoloration of specimens was calculated by means of ΔE00 compared to baseline values. All factors (material, staining solution, aging stage) were significantly associated with the extent of discolorations (P < .001). Maximum color changes occurred after 28 days staining (EN: ΔE00 = 4.5 ± 4.0; GB: ΔE00 = 5.0 ± 4.5; LS: ΔE00 = 3.0 ± 2.3) clearly exceeding the 50:50 threshold for acceptable color deviations. Due to repolishing, discoloration of LS samples was almost completely eliminated (ΔE00 = 0.4 ± 0.3) and significantly reduced for the other two materials (EN: ΔE00 = 1.0 ± 0.9; GB: ΔE00 = 0.9 ± 0.4; P = .428). Discoloration of hybrid ceramics ranged in-between lithium disilicate and composites, however more comparable to composites. Repolishing could reduce discolorations substantially. This study should help dental practitioners to estimate the color stability of common dental materials and the effect of polishing in removal of discolorations.

Marginal Gap Distance and Fracture Resistance of Lithium Disilicate and Zirconia-Reinforced Lithium Disilicate All-Ceramic Crowns Constructed With Two Different Processing TechniquesWith Two Different Processing Techniques

Statement of problem: The microstructure and processing methods used to produce any dental restoration might affect the final mechanical outcomes as well as the clinical success. Objectives: The purpose of this study was to evaluate the fracture resistance of lithium disilicate and zirconia reinforced lithium disilicate ceramic crowns constructed using two processing techniques after fatigue loading namely, CAD/CAM technique and pressing technique. The marginal integrity of the crowns was examined before and after fatigue loading. Methods: A total number of thirty-two freshly extracted maxillary first molars were collected. The teeth were chosen to be of similar bucco-lingual and mesiodistal dimensions. The teeth were mounted vertically into epoxy resin templates. Full coverage all-ceramic preparation was performed for all samples using a standardized technique. The prepared teeth were randomly divided into four equal groups (n=8) according to the all-ceramic materials and technique used for crown fabrication as follows: Group I: IPS e-max CAD(EC): eight prepared teeth were restored with machinable lithium disilicate glass ceramics. Group II: Celtra Duo(CD): eight prepared teeth were restored with machinable zirconia-reinforced lithium disilicate glass ceramics. Group III: IPS e-max Press (EP): eight prepared teeth were restored with pressable lithium disilicate glass ceramics. Group IV: Celtra Press (CP): eight prepared teeth were restored with pressable zirconia-reinforced lithium disilicate glass ceramics. The crowns were cemented using self-adhesive resin cement (Rely X Unicem). Vertical margin gap distance of all the crowns was measured using a stereomicroscope. Following vertical marginal gap distance measurements, the samples were subjected to fatigue cyclic loading for 60000 cycles which is equivalent to six months clinical service. The vertical marginal gap distance for all samples were subsequently remeasured after the fatigue loading testing. Fracture resistance test was done using universal testing machine. The fracture load was recorded in Newton. Data was collected, tabulated and statistically analyzed. Results: One-way ANOVA test for comparison between the fracture resistance of the four types of all-ceramic crowns revealed that there was a statistically significant difference between mean fracture resistance of different all ceramic materials and techniques used in this study (P-value <0.001). For the marginal gap distance either before or after fatigue cyclic loading; there was a statistically significant difference between the four all ceramic crowns used in this study.Conclusions: CAD/CAM techniques showed better fracture resistance values than pressable techniques, even if the same material was used. The addition of zirconia to lithium disilicate ceramics did not improve the fracture resistance of all ceramic crowns. Pressable processing techniques showed better vertical marginal gap distance than CAD/CAM techniques for both ceramic materials used. Cyclic loading resulted in significant increase in the vertical marginal gap distance for all ceramic crowns using different processing techniques.

Comparison of Shear Bonding Strength of Laminate Veneer by Lithium Disilicate Ceramics and Surface Treatment Methods

Comparison of Shear Bonding Strength of Laminate Veneer by Lithium Disilicate Ceramics and Surface Treatment Methods

Effect of self-etching ceramic primer on bond strength of zirconia-reinforced lithium silicate ceramics

This study evaluated the effect of self-etching ceramic primer (SECP) on shear bond strength (SBS) of zirconia-reinforced lithium silicate (ZLS) ceramics. Two hundred and seventy block-specimens of two types of ZLS ceramics and one type of lithium disilicate (LS) ceramics were prepared. Ninety blocks of each material were divided into three groups (n = 30), namely group 1: no surface treatment (control), group 2: hydrofluoric acid (HF), silane-based primer (S), and group 3: SECP. Resin cement was applied, and light-cured for build-up. Shear bond strength (SBS) test was used. Half of the bonded specimens (n = 15) were tested after storage in distilled water for 24 h, whereas the other half were tested after 5000 thermo-cycles. The failure modes were evaluated using scanning electron microscope (SEM). The SBS values for samples treated with SECP and HF + S within the respective materials were statistically comparable (p > 0.05). Thermocycling significantly reduced the SBS (p < 0.05) for all ceramic materials in groups 2 and 3. Mixed failure followed by adhesive failure were the most common failure modes in groups 2 and 3, whereas pretest failure was only detected in group 1. Considering the limitations of the study, with respect to in vitro bond strength, the SECP is an alternative for the conditioning of internal surface of glass ceramics.

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.

Influence of universal adhesive system application strategies on the long-term bond strength to dentin of CAD-CAM restorative materials

The objective of this study was to evaluate the influence of dentin application strategies of the universal adhesive system (Scotchbond Universal 3 M/ESPE) on the bond strength of a lithium disilicate-based ceramic and a nanoceramic resin, using the microshear test. A total of 40 healthy third molars were sectioned to expose flat occlusal medium dentin, and separated into four groups (n = 10). The molars were selected according to dentin treatments (application or nonapplication of phosphoric acid prior to universal Scotchbond Universal adhesive), and to the indirect materials obtained by CAD-CAM (lithium disilicate ceramics – IPS e.max CAD, and nanoceramic resin – Lava Ultimate), under study. Ceramic sticks of lithium disilicate and nanoceramic resin measuring 1 mm2 were cemented with Rely XTM Ultimate resin cement on the dentin surface, and stored in distilled water for 48 h or 12 months at 37 °C. The microshear test was performed using a universal testing machine, at a speed of 0.5 mm/min. The values were recorded in MPa, and submitted to three-way ANOVA with a significance level of 5%. The results indicated that the interactions among restorative material, dentin treatment and timepoint was not significant (p = 0.841). However, the 12-month storage time significantly affected the bond strength (p = 0.016) of all the groups. It was concluded that bond strength to dentin decreased over time, regardless of the mode of application of the universal adhesive system or the type of restorative material.

Photosensitization of lithium di-silicate ceramic by Er, Cr: YSGG and fractional carbon dioxide laser bonded to orthodontic bracket.

To evaluate the shear bond strength (SBS) and modes of lithium disilicate ceramics (LDC) photosensitized by Er,Cr:YSGG (ECL) and fractional carbon dioxide (CO2) laser bonded to metallic bracket compared to traditional conditioning methods. Fifty LDC discs were polished and randomly allocated into 5 groups (n = 10) each. Group 1 were photosensitized with ECL + Silane (S). Group 2 were irradiated using CO2 laser + S. In group 3 LDC discs were treated with aluminium trioxide (Al2O3) air abrasion (AA). Moreover, samples in group 4 and 5 were conditioned with Hydrofluoric acid (HFA)+ S (Control) and Self-Etch Glass Ceramic Primer (SEGCP). Following conditioning regimen fifty maxillary central incisor brackets were pasted on LDC using adhesive material. SBS testing was performed by mounting the specimens on a universal testing machine. After debonding, sheared surface was examined under stereomicroscope to classify failure mode using adhesive remnant index (ARI). Mean and standard deviation (SD) were compared by analysis of variance (ANOVA) and Tukey multiple comparison test at a significance level of p = 0.05. Among the conditioning groups the highest SBS values were presented by HFA + S (21.08 ± 1.06). The lowest SBS values were displayed by AA Al2O3 (12.61 ± 0.45). SBS of samples conditioned with SEGCP showed significant difference amongst all experimental groups (16.76 ± 0.81). LDC photosensitized with CO2 and ECL has a potential to be recommended in clinical settings alternate to HFA + S when bonded to metallic bracket.

Fifteen-year outcome of three-unit fixed dental prostheses made from monolithic lithium disilicate ceramic

ObjectivesThe purpose of this prospective study was to evaluate the clinical long-term outcome over 15 or more years of crown-retained fixed dental prostheses (FDPs) made from a lithium disilicate ceramic (IPS e.max Press, Ivoclar Vivadent AG). MethodsThirty-six three-unit FDPs replacing anterior (16%) and posterior (84%) teeth were inserted in 28 patients. Abutment teeth were prepared following a standardized protocol. The size of the proximal connector of the FDPs was 12 mm² (anterior) or 16 mm² (posterior). FDPs were cemented either conventionally with glass-ionomer cement (n = 19) or adhesively with composite resin (n = 17). The following parameters were evaluated at baseline, 6 months after cementation and then annually (at abutment and contralateral teeth): probing pocket depth, plaque index, bleeding on probing, and tooth vitality. ResultsThree FDPs were defined as drop-outs. The mean observation period of the remaining 33 FDPs was 167 months (range: 79–225 months). The survival rate (survival being defined as FDPs remaining in place either with or without complications) according to Kaplan-Meier was 48.6% after 15 years. The success rate (success being defined as free of complications and remaining unchanged) was 30.9% after 15 years. ConclusionsFatigue and crack propagation caused by clinical aging in monolithic lithium disilicate ceramics seem to take considerable time, as shown by the presented survival and success rates after 15 years. Further long-term studies are necessary to evaluate the reliability of FDPs made from other all-ceramic materials over a period of 15 or more years.

Enhanced bonding strength between lithium disilicate ceramics and resin cement by multiple surface treatments after thermal cycling.

All-ceramic restoration has become a popular technology for dental restoration; however, the relative bond strength between the ceramic and resin limits its further application. Long-term high bond strength, especially after thermal cycling, is of great importance for effective restoration. The effect of physical and/or chemical surface treatments on bonding durability is seldom reported. To overcome this problem, we investigate the bond strength between lithium disilicate ceramics (LDC) and two kinds of resin cements before and after thermal cycling for a variety of surface treatments including hydrofluoric acid, two kinds of silane and a combined effect. The shear bond strength in every group is characterized by universal mechanical testing machine averaged by sixteen-time measurements. The results show that when treated with HF and a mixed silane, the LDC surface shows maximum bonding strengths of 27.1 MPa and 23.3 MPa with two different resin cements after 5000 thermal cycling, respectively, indicating an excellent ability to resist the damage induced by cyclic expansion and contraction. This long-term high bond strength is attributed to the combined effect of micromechanical interlocking (physical bonding) and the formation of Si-O-Si and -C-C- at the interface (chemical bonding). This result offers great potential for enhancing bond strength for all-ceramic restoration by optimizing the surface treatment.

Scanning electron microscope evaluation of the marginal gap and internal fit of additive versus subtractive fabrication techniques for posterior lithium disilicate crowns

Statement of the problem: The wide use of digital dentistry in fixed prosthodontics using 3D printers and CAD/CAM in fabricating crowns and partial fixed dental prosthesis created a need for more information about their marginal gap and internal fit.Purpose: This study aimed to evaluate the effect of fabrication technique using CAD/CAM manufactured and heat pressed lithium dislicate crowns made from milled wax and 3D printed resin patterns on their marginal gap and internal fit.Material & Methods: A total of 50 prepared mandibular first molar resin models were used and divided into two main groups according to their fabrication phase: Patterns group and fully fabricated crowns group. Patterns group was subdivided into milled wax patterns (W) (n=10) and 3D printed resin patterns (P) (n=10). Fully fabricated crowns group was subdivided according to fabrication technique of lithium disilicate crowns into: Machinable ceramics (M), using IPS e-max CAD blocks (n=10), Pressable ceramics (Pw), using IPS e-max press ingots following wax milling (n=10) and Pressable ceramics (Pp), using IPS e-max press ingots following 3D resin printing (n=10). All patterns and ceramic crowns were cemented with Rely-X self-adhesive resin cement. Marginal and internal adaptations were measured using SEM at 300 × magnification. Kruskal-Wallis and Wilcoxon signed-rank tests were applied to compare between the groups. Data were presented as median and range values. The significance level was set at P ≤ 0.05.Results: P group showed a significant higher median total marginal gap of 111.4 μm (80.8-139.7) than W group of 51.3 μm (45.1-57.8) before heat pressing. While M group showed the significant highest median marginal gap of 138.4 μm (83.4-191.8) and no significant difference between heat pressed groups (Pw and Pp) (P ≤ .05). Regarding changes after heat pressing, Pw group showed no significant decrease, while Pp group showed a significant decrease in median total marginal gap. For internal fit, there was no significant difference between the pattern groups (W and P) before heat pressing (P ≤ .05). After heat pressing, Pp group showed the significantly highest median gap of 195 μm (138.9-441.5) with no significant difference between M and Pw groups (P ≤ .05). Pw group showed a significant decrease in median gap, and Pp group showed no significant decrease after pressing (P ≤ .05). Conclusions: Heat pressed lithium disilicate glass ceramic crowns produced from CAD/CAM waxing or resin 3D printing techniques resulted in better marginal and fit accuracy than CAD/CAM. 3D printed resin patterns yielded internal fit values higher than other groups, but with promising clinical acceptability.Clinical implications: Both the additive and subtractive production for patterning phase before heat pressing allow clinical acceptability in terms of marginal and internal adaptation when a single unit posterior ceramic lithium disilicate crown is fabricated.

The Influence of Repeated Cementation of an Old and New Glass Ceramic Lithium Disilicate Veneers on Shear Bond Strength to the Tooth Structure (In Vitro Study)

Objective: Debonding of dental veneers represents the most common problems faced the patient and the dentist. The aim of this study was to compare the bond strength of repeated bonding Glass ceramic Lithium Disilicate (LD) veneers and new veneers to the tooth structure. &#x0D; Methods: Twenty veneers from (IPS e.max CAD (LD), Ivoclar Vivadent) block (5mm length, 3mm width and 2mm thickness) were prepared. They bonded to twenty of prepared labial surfaces of bovine teeth by using Variolink resin cement (Ivoclar Vivadent) as a sample group of twenty samples. They randomly divided into two subgroups of 10 samples named as A1 and B1 and tested under the universal testing machine to measure shear bond strength (SBS). The 10 deboned veneers of A1 rebonded on the related tooth structure after conservative cleaning of both veneers and teeth structure and assigned as group A2. While for the subgroup B1, new 10 veneers bonded on the same teeth structure and assigned as group B2. The (SBS) tested for groups A2 and B2 and compared with each other and with the previous sample groups. All debonded samples evaluated under a stereomicroscope to assess the mode of failure.&#x0D; Results: There is no statistical difference between all groups and the mode of failure was mostly adhesive failure between the resin and tooth structure.&#x0D; Conclusions: There are no statistical differences in bond strength between re-bonding of debonded veneer compared with of bonding of the new veneer.