To investigate the influence of different resin composites used for sealing the screw-access hole of zirconia abutments on the fatigue behavior of lithium disilicate ceramic. Eighty 3YSZ abutment discs (IPS e.max ZirCAD MO, Ivoclar AG) (Ø = 10mm; 3mm thickness; Ø = 2.5mm access channel) and lithium disilicate restorative discs (IPS e.max CAD, Ivoclar AG) (Ø = 10mm; 1mm thickness) were obtained and randomly allocated into four groups based on the sealing protocol (2mm of thickness): Ctrl (PFTE Tape); PFTE tape + nanohybrid resin; PFTE tape + bulk-fill resin; and PFTE tape + Flow resin. After cementation procedures, monotonic (n = 5) and cyclic fatigue tests were conducted (n = 15; initial load of 100N for 5000cycles, increments of 100N every 10,000cycles at 20Hz, immersed in distilled water) until failure. Fractographic and finite element analysis were also performed. One-way ANOVA and Tukey post-hoc tests were carried out for the monotonic data, while Kaplan-Meier and Mantel-Cox tests were used for survival rates. No statistically significant effect of the presence neither the type of resin composite material was observer after the monotonic tests. For the fatigue test, the Bulk and Nano groups exhibited significantly better performance than the Ctrl and Flow (Ctrl: 1100N ≤ Flow: 1213N < Nano: 1340N ≤ Bulk: 1380N, p ≤ 0.05). Nanohybrid or bulk-fill resin composites are recommended for sealing the abutment screw-access hole and optimize the performance of lithium disilicate restorations.

This invitro study investigated the effect of a self-etching ceramic primer (Monobond Etch & Prime [MEP]), with or without aluminum oxide airborne-particle abrasion, on the surface roughness, and microtensile bond strength (μTBS) of lithium disilicate bonded to enamel, compared with the conventional hydrofluoric acid plus silane (HF + S). Lithium disilicate specimens (10 × 10 × 4 mm) were assigned to four groups: HF + S airborne-particle abraded (HF + S[a]), HF + S polished (HF + S[p]), MEP airborne-particle abraded (MEP[a]), and MEP polished (MEP[p]). Surface roughness (ΔSa) was assessed after conditioning, and specimens were bonded to bovine enamel with resin cement. μTBS was tested before and after thermo cycling (10,000 cycles, 5°C/55°C). Airborne-particle abrasion significantly increased ΔSa (HF + S[a]: 1.16 ± 0.12 μm; MEP[a]: 0.85 ± 0.02 μm) compared to polished specimens (HF + S[p]: 0.47 ± 0.04 μm; MEP[p]: 0.38 ± 0.04 μm). HF + S and MEP performed similarly in all conditions (p > 0.05). Airborne-particle abraded surfaces consistently exhibited higher μTBS than polished ones (p < 0.05). Thermo cycling significantly reduced μTBS in all groups. Mixed and cohesive failures predominated before thermo cycling, whereas adhesive failures increased after. MEP and HF + S demonstrated comparable bonding to enamel. Airborne-particle abrasion enhanced both surface roughness and μTBS, regardless of conditioning strategy. Although thermo cycling reduced adhesion in all groups, the decline was similar across treatments.

Color stability and translucency of CAD-CAM lithium disilicate ceramic materials after repeated firings using different firing modes: An in vitro study.

A comparative study of four chairside finishing/polishing protocols and their effect on the surface topography of four CAD/CAM glass-ceramic materials.

This study evaluated the effects of different printing orientations on the mechanical properties and surface roughness of a 3D-printed definitive resin-based composite (RBC) material. Bar shaped samples were fabricated from a 3D-printed RBC (VarseoSmile TriniQ) using three different build orientations (0°, 45°, and 90°) and lithium disilicate ceramic (IPS e.max CAD). Flexural strength and elastic modulus were evaluated using a three point bending test. Surface microhardness was assessed with a Vickers hardness test, and surface roughness was measured using a contact profilometer. Following mechanical testing, the sample surfaces and fractured regions were further examined by scanning electron microscopy (SEM) for topographic and fractographic evaluation. Statistical analysis was performed at α = 0.05 using one way ANOVA, with post hoc comparisons conducted using the Tamhane test. Significant differences were observed among the tested materials for all evaluated parameters (p < 0.001). IPS group demonstrated superior mechanical properties and lower surface roughness compared to the 3D-printed RBCs. Within the 3D-printed groups, the 0° build orientation exhibited higher flexural strength, whereas the 90° orientation showed increased surface hardness. Elastic modulus and surface roughness were not significantly influenced by printing orientation (p > 0.05). SEM analyses supported the quantitative findings by revealing a homogeneous and compact microstructure in IPS group and orientation-dependent surface and fracture features in the 3D-printed RBC groups. IPS e.max CAD demonstrated superior mechanical performance. The 0° orientation improved flexural strength, while the 90° orientation enhanced surface hardness, suggesting that build orientation should be selected according to the intended clinical function.

Surface treatment enhances bonding to ceramic restorations but may alter their optical properties. Lithium disilicate and zirconia respond differently to surface treatments due to variations in their microstructure. This study evaluated how sandblasting, hydrofluoric acid with silane, and laser treatment affect the color stability and translucency of these ceramics. This study aimed to evaluate the individual and combined effects of ceramic material type and surface treatment on the color stability and translucency of lithium disilicate and zirconia ceramics. Forty samples were constructed in the form of discs form lithium disilicate and zirconia ceramic (n = 20 for each). Samples from each material were divided into four subgroups according to the surface treatment used as following: (Ctrl); control with no surface treatment, (S.B); sandblasting using AL2O3, (H.F); hydrofluoric acid etching with silane coupling agent, (L.A); laser treatment. Each subgroup from each material was undergoing color and translucency test using spectrophotometer. The data were statistically analysed using a Two-Way ANOVA, followed by multiple pairwise comparisons using Tukey's HSD for each individual factor. Among the tested surface treatments only laser showed color change within the clinical accepted range with lithium disilicate ceramic (1.04 ± 0.15), also hydrofluoric acid etching with silane application showed that with zirconia (0.41 ± 0.10). Sandblasting showed the lower translucency value with lithium disilicate and zirconia ceramic with a significant difference with the control samples (p value ˂0.001). Surface treatments affected the optical properties of both ceramics in a material-dependent manner. Laser conditioning preserved color acceptably in lithium disilicate, while hydrofluoric acid with silane did so for zirconia. Sandblasting significantly reduced translucency in both materials, indicating its potential to compromise esthetic outcomes.

Although the efficacy of Er: YAG lasers for debonding all-ceramic restorations has been validated, further research is required to optimize the operational parameters for Er: YAG laser debonding of lithium disilicate veneers and to determine whether laser debonding alters the translucency, hardness, and rebonding strength of lithium disilicate veneers. This study aimed to evaluate the comprehensive debonding performance of an Er: YAG laser operating at a clinically prevalent power of 4.5 W with three different energy and frequency parameter combinations. The evaluation was performed on IPS e.max CAD lithium disilicate ceramic specimens with two thicknesses (0.5 mm and 1.0 mm), focusing on debonding time and intrapulpal temperature variation. Furthermore, the changes in ceramic rebonding strength, surface morphology, translucency, and Vickers hardness following laser debonding were analyzed, so as to identify the optimal parameters for clinical laser debonding of ceramic veneers. Forty freshly extracted maxillary first premolars were prepared to achieve standardized uniform enamel surfaces. CAD/CAM ceramic blocks were fabricated into two sizes of square specimens: 3 × 3 mm2 square specimens for the assessment of debonding efficiency and rebonding strength, and 10 × 10 mm2 square specimens for translucency and Vickers hardness tests. All specimens were categorized into two groups based on ceramic thickness (0.5 and 1.0 mm). Each thickness group was further subdivided into four subgroups with distinct laser parameters: a non-irradiated control group (E0), 300 mJ/15 Hz (E1), 225 mJ/20 Hz (E2), and 150 mJ/30 Hz (E3). The 3 × 3 mm2 square specimens were bonded to prepared tooth surfaces using Variolink N resin cement and subsequently debonded with an Er: YAG laser according to the corresponding subgroup parameters. After debonding, the specimens were rebonded to the tooth surfaces using the same resin cement. Debonding time and intrapulpal temperature change (∆T) were recorded throughout the procedure. The fracture modes of the veneer bonding interfaces were observed under a stereomicroscope, and shear rebonding strength was measured via a universal testing machine. The 10 × 10 mm2 ceramic specimens were irradiated with the corresponding Er: YAG laser parameters for 30 s. Post-treatment evaluations included observations of surface morphology and quantitative measurements of translucency and Vickers hardness. A two-way analysis of variance was adopted for statistical analysis. The Pearson correlation coefficient was calculated to analyze the correlation between debonding time and intrapulpal temperature variation. For specimens with the same thickness, the E3 group exhibited significantly longer debonding time and greater intrapulpal temperature elevation compared with the E1 and E2 groups, whereas no significant differences were detected between the E1 and E2 groups. For the same laser parameters, 1.0 mm-thick veneers showed significantly longer debonding time and higher temperature variation than 0.5 mm-thick veneers. A strong positive correlation was identified between debonding time and ∆T (R² = 0.739). The main failure mode of the adhesive surface was classified as type 1. No significant differences in rebonding strength were observed after debonding. In addition, laser irradiation exerted no remarkable influence on the surface morphology, translucency, or Vickers hardness of lithium disilicate ceramic specimens. At a constant laser power of 4.5 W, both E1 and E2 parameter settings are applicable for the debonding of 1.0 mm-thick lithium disilicate veneers, while the E2 setting is optimal for 0.5 mm-thick veneers. Er: YAG laser debonding treatment has no significant adverse effect on the rebonding strength, surface morphology, translucency, or hardness of lithium disilicate ceramics. The outcomes of Er: YAG laser debonding for all-ceramic veneers are affected by laser energy, frequency, and veneer thickness. Optimized Er: YAG laser parameters should be selected according to the thickness of all-ceramic veneers. Given the preservation of mechanical strength and translucency after laser debonding, the treated all-ceramic veneers are reusable for clinical application.

This article aims to evaluate and compare the fracture resistance of three CAD/CAM veneer materials-a polymer-infiltrated ceramic network (VE; Vita Enamic), a lithium disilicate glass-ceramic (LD; IPS e.max CAD), and a zirconia-reinforced lithium silicate ceramic (ZLS; Vita Suprinity)-before and after artificial accelerated aging. Sixty standardized epoxy resin replicas of a prepared maxillary central incisor were fabricated using a stereolithographic 3D printing technique and randomly allocated into three groups (n = 20): Vita Enamic (VE), IPS e.max CAD (LD), and Vita Suprinity (ZLS). Laminate veneers were designed digitally and milled using a five-axis CAD/CAM milling unit. After appropriate surface treatment, veneers were adhesively luted using light-cured resin cement. Each material group was subdivided into two subgroups (n = 10): no aging or artificial aging via thermocycling (10,000 cycles between 5 and 55°C). Fracture resistance was measured using a universal testing machine with loading at 135 degrees to the long axis at a crosshead speed of 1 mm/min. Data were analyzed using one-way ANOVA, independent t-tests, and two-way ANOVA (α = 0.05). Significant differences were observed among materials before and after aging (p < 0.05). Before aging: ZLS 191.89 ± 6.24 N, LD 182.69 ± 6.00 N, VE 159.12 ± 9.16 N. After aging: ZLS 149.64 ± 5.98 N, LD 136.09 ± 5.69 N, VE 132.44 ± 5.30 N. Two-way ANOVA demonstrated significant effects of material type, aging condition, and their interaction (p < 0.05). Artificial aging significantly reduced the fracture resistance of all tested materials. ZLS demonstrated the highest fracture resistance both before and after aging under the conditions tested. Although VE initially showed lower fracture resistance than LD, fracture resistance after aging was not significantly different between LD and VE under the single load-to-fracture conditions tested in this in vitro study (p > 0.05). ZLS remained significantly superior to both LD and VE after aging (p < 0.05).

Clinical outcome of fiber post and fiber-reinforced resin composite for the full crowns of anterior endodontically treated teeth: a 5-year randomized clinical trial.

Bomicke W, Schmitter M, Waldecker M, et al. Ceramic crowns and sleep bruxism: 3-year results of a randomized controlled trial. J Dent 2026;170:106691. https://doi.org/10.1016/j.jdent.2026.106691 . Prospective randomized controlled clinical trial with a 3-year follow-up evaluating the influence of Sleep Bruxism (SB) on the clinical performance of monolithic ceramic molar crowns. A total of 109 patients requiring a single molar crown were enrolled. SB diagnosis included a structured questionnaire, clinical examination, and portable electromyography device (BruxOFF). Participants were allocated into four groups: lithium disilicate with SB, lithium disilicate without SB, zirconia with SB, and zirconia without SB. Standardized crown preparation, fabrication, and cementation protocols were used. Outcomes assessed were technical complications, survival, and success rates. The study time points were 1 week, 6 months, and 1, 2, and 3 years. Survival was defined as restoration remaining in situ without replacement. Success is defined as restoration without biological or technical complications. Fisher's exact test was used to compare outcomes between SB and non-SB groups, with statistical significance set at = 0.05. No technical complications occurred during the 3-year observation period. Survival rates remained high across all groups (95.2-100%), while success rates ranged from 81.5% to 95.8% for both ceramic materials. No statistically significant differences were observed between SB and non-SB patients or between lithium disilicate and zirconia crowns. Monolithic lithium disilicate and zirconia molar crowns demonstrated favorable clinical performance over three years, and SB was not associated with increased failure or complication risk.

This study aimed to evaluate the effects of ceramic composition, resin cement shade, and tooth-shaded background on the optical properties and color differences of high translucent (HT) lithium-based ceramics. A total of 192 specimens were prepared from four CAD/CAM ceramics: advanced lithium disilicate, lithium disilicate, and two zirconia-reinforced lithium silicate ceramics. The relative translucency parameter (RTP) and opalescence (OP) were evaluated using a digital spectrophotometer. Specimens were evaluated using two resin cement shades (opaque and translucent) and two tooth-shaded backgrounds (A1 and A3). Color differences (ΔE₀₀) between baseline and after cementation measurements were calculated using the CIEDE2000 formula. Data were analyzed using one-way and three-way ANOVA (p < 0.05). Ceramic material significantly influenced RTP and OP values (p < 0.05). Three-way ANOVA revealed significant main effects of material and cement shade (p < 0.001), as well as a significant material × tooth-shaded background interaction (p = 0.013). Opaque cement resulted in significantly higher color differences than translucent cement across all materials and backgrounds (p < 0.05). Higher ΔE₀₀ values were found on the A3 background. The final color and optical properties of HT lithium-based ceramics were influenced by ceramic composition and resin cement shade. These findings may help clinicians optimize cement shade and material selection for improved esthetic outcomes.

Laser-assisted debonding of lithium disilicate veneers using an erbium chromium yttrium scandium gallium garnet laser: A clinical report.

This RCT evaluated and compared the clinical performance of zirconia and titanium dental implants placed in the maxillary premolar region. Outcomes were assessed 3 years after prosthetic loading and included marginal bone level (MBL) changes, clinical parameters, aesthetic outcomes, and patient related outcome measures (PROMs). Fifty patients were randomly allocated to receive either a zirconia one-piece (ZrO2, n = 25) implant or a titanium bone-level (Ti, n = 25) implant, restored with a lithium disilicate crown 3 months after implant placement. Primary outcome was change in MBL. Secondary outcomes included implant survival, peri-implant tissue health, technical complications, aesthetic outcomes, and PROMs. Examinations were performed 3 years after crown placement. After 3 years, mean MBL change was -0.02 mm (SD = 0.78) for ZrO2 and -0.04 mm (SD = 0.36) for Ti; no statistically significant difference was found (p = 0.635). One ZrO2 implant failed to osseointegrate. Clinical parameters were favourable for both implant types, although slightly higher bleeding scores were observed for ZrO2. Differences in aesthetic outcomes and PROMs were found, favoring the ZrO2 implant group. None of these differences reached statistical significance. After 3 years of function, the ZrO2 and Ti implant as applied in this study showed comparable MBL changes. Survival, clinical and aesthetic parameters, and PROMs were generally favourable and largely comparable for both groups. These short-term findings indicate that both implant types represent a viable option for clinical use in this application. CCMO registration: NL58957.042.16.

This study compares the marginal and internal gaps for four restorative materials produced by two fabrication methods in both minimally invasive occlusal veneer and conventional onlay cavities. Eighty mandibular molars prepared as occlusal veneer and mesial-occlusal-distal-lingual onlays and restorations were produced using lithium disilicate glass ceramic, hybrid ceramic, nanohybrid composite, and laboratory composite materials. A silicone replica method was used to examine the marginal gap and internal gap with a stereomicroscope. Two-way analysis of variance (ANOVA) was used to analyze the effects of the material and design, and one-way ANOVA was used to analyze the effect of the fabrication method. The marginal gap significantly differed in relation to the material, and the internal gap significantly differed in relation to the material and design. Gaps were significantly smaller for the laboratory composite groups than for the other groups. Comparison of fabrication methods showed that internal and marginal gaps were significantly smaller for the conventional procedure. The less complicated designs yielded a better fit. In particular, because of the greater number of intaglio surfaces, internal gap values were worse when cavity design complexity increased.

BackgroundEndodontically Treated Teeth (ETT) have challenges in resisting fracture against occlusal forces. This study aimed to assess the fracture resistance (FR) of endodontically treated premolar teeth restored with an innovative self-adhesive bulk-fill resin-based composite (RBC) (Stela , SDI Limited, Australia), a short-fiber-reinforced composite (SFRC) (EverX flow, GC., Tokyo, Japan), a conventional nanohybrid (RBC) (Filtek Z250 XT, 3M ESPE, St. Paul, MN, USA) , and a Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) Lithium Disilicate (Emax, Dentsply Sirona, Bensheim, Germany) Endocrown. MethodsFor the FR test, 44 human extracted maxillary premolars were included in the study. Endodontic treatment was done, and a single operator prepared standardized mesio‑occlusal‑distal (MOD) cavities in the teeth and divided into four groups (n=11) according to the restorative material used. Group (F1): ETT restored with Stela resin-based composite, which was inserted into the cavity as a single 5 mm increment. Group (F2): ETT restored with (EverX Flow) composite,which was packed and light-cured for 20 seconds, leaving a 2 mm occlusal layer to be restored with nanohybrid composite (Filtek Z250 XT). Group (F3): ETT restored with Filtek Z250 XT resin-based composite only. Group (F4): ETT restored with (CAD/CAM Cerec MCXL) Lithium Disilicate endocrown, preparations were scanned with the Omnicam, and restorations were designed using CEREC Premium Software (version 4.4). For direct restoration groups the proximal walls were reconstructed by using a tofflemire matrix retainer and band. All restored teeth were subjected to FR testing using a universal testing machine ( Bluehill Lite Software on an Instron® / Each specimen’s failure load was recorded in Newton). Each specimen was individually mounted on the computer-controlled machine equipped with a 5 kN load cell, with the acrylic block secured to the lower fixed head. ResultsStatistical analyses were conducted using SPSS 27®, GraphPad Prism®, and Microsoft Excel 2016. Data normality was assessed with the Shapiro-Wilk and Kolmogorov-Smirnov tests, which indicated a nonparametric distribution. Comparison between groups revealed a significant difference (P<0.0001), with Group F4 (Endocrown) demonstrating the highest performance (1427.73 ± 156.96), compared to all direct restoration materials. In contrast, there were no significant differences among the three direct restoration groups despite slight differences in their means. Group F2 (EverX+Z250, mean: 619.87 ± 186.41) was higher than Group F1 (Stella, mean: 561.75 ± 173.74) with P = 1.000, and higher than Group F3 (Z250, mean: 452.22 ± 202.72) with P = 0.471. Group F1 (Stella) exceeded Group F3 (Z250), but this difference was not statistically significant (P = 0.838). ConclusionsWhile lithium disilicate endocrowns exhibit superior fracture resistance, direct restorative materials may serve as a clinically acceptable alternative for routine applications. Nevertheless, these findings should be interpreted with caution, given the inherent limitations of the in vitro study design.

To evaluate and compare the fatigue performance of veneers fabricated from lithium disilicate, 3D-printed resin composite, and injection-molded direct resin composite under standardized cyclic loading. Thirty extracted human maxillary central incisors (n = 10 per group) received standardized veneer preparations. Veneers were fabricated using CAD/CAM milling (lithium disilicate), additive manufacturing (3D-printed resin composite), or injection molding (direct composite). Specimens were adhesively bonded following manufacturer protocols, thermocycled (10,000 cycles) and subjected to cyclic fatigue loading (200 N, 1.6 Hz) for up to 1,000,000 cycles. Fatigue survival was analyzed using Kaplan-Meier and log-rank tests. Significant differences in survival distributions were observed (p < 0.001). Lithium disilicate showed the highest fatigue performance, with 80% survival at 1,000,000 cycles and a mean survival of 954,060 cycles. 3D-printed resin composite showed the lowest survival (mean: 134,878 cycles), while direct resin composite exhibited intermediate performance (mean: 460,453 cycles). Failure modes varied by material, with lithium disilicate demonstrating debonding, 3D-printed resin presenting multiple failure types, and direct composite limited to incisal fractures. Lithium disilicate demonstrated superior fatigue performance compared with resin-based materials. Injection molded direct composite performed better than 3D-printed resin composite with more repairable fractures. Although lithium disilicate restorations remain the most durable material choice for anterior veneers, injection molded direct composites offer an economical option with possibly repairable fractures.

Comparative wear behavior of lithium disilicate CAD/CAM ceramics under simulated mastication.

The management of proximal cavities under porcelain laminate veneers remains a clinical challenge. Conventional strategies-such as placing an intermediate composite restoration or extending the preparation-require additional steps or sacrifice healthy tooth structure. While the literature reports conflicting findings on whether composite substrates affect veneer longevity, a comprehensive biomechanical evaluation of a monolithic veneer design that directly incorporates the proximal cavity has not been reported. This in-vitro study compared the marginal fit, internal adaptation, and fracture resistance of lithium disilicate laminate veneers fabricated for three substrate conditions: an intact tooth, a tooth with a proximal composite restoration, and a monolithic veneer with an integrated proximal cavity. Thirty-six maxillary central incisor typodont teeth were divided into three groups (n = 12): control (intact tooth), composite restoration, and integrated cavity. Standardized proximal cavities were prepared in the latter two groups; the composite restoration group received a composite restoration prior to veneer fabrication, while the integrated cavity group had the cavity incorporated directly into the veneer design. Lithium disilicate laminate veneers were fabricated using a CAD/CAM system. Marginal and internal fit were evaluated at 19 points per specimen using a silicone replica technique examined under stereomicroscopy. Fracture resistance was assessed in a universal testing machine with a load applied at a 135° angle. Data were analyzed using one-way ANOVA or Kruskal-Wallis tests (α = 0.05). The integrated cavity group exhibited a statistically significantly larger marginal gap at the proximal margin compared to the control and composite restoration groups (p<0.001). A corresponding significant increase in cement gap thickness was observed in the mesial internal region of the integrated cavity group. No significant differences were detected at any other marginal or internal measurement points. Fracture resistance did not differ significantly among the three groups (p = 0.516), and the integrated cavity group recorded the highest mean fracture resistance value. Incorporating a proximal cavity directly into a monolithic laminate veneer design compromised marginal and internal fit in the cavity region but did not negatively affect overall fracture resistance. This preliminary proof-of-concept is promising; however, validation through thermomechanical aging and clinical trials is essential before routine application.

The purpose of this study was to assess the surface roughness, color stability, and contact angle of lithium disilicate glass-ceramic (LD) and zirconia-reinforced lithium silicate (ZLS) ceramics following surface finishing and to compare these values using both manufacturer-specific polishing and glazing procedures and alternative methods designed for other types of ceramics. LD and ZLS ceramics were used to fabricate 80 samples, which were allocated into eight groups (n = 10) according to manufacturer-specific polishing (VITA Suprinity Polishing Set Clinical and OptraGloss Ceramic Kit) and glazing protocols (VITA Akzent Plus and Ivocolor Glaze) and their interchanged applications. Measurements of surface roughness, contact angle, and color stability were made following the polishing and glazing processes. The results were evaluated using parametric statistical analysis. Glazing produced a statistically significant change with the LD ceramic, whereas polishing did not. In the ZLS group, there was a significant difference between the glazing methods, but there was no statistically significant difference between the polishing techniques. In both ceramics, the contact angle values of the glazed samples were greater than those of the polished samples. Surface finishing procedures significantly affected both the color change of the ZLS ceramic and the surface roughness of the LD ceramics. The contact angle values of the glazed samples in both ceramics were approximately two to five times greater than those of the polished samples. It may be advisable for clinicians to use nonmanufacturer-specific techniques for polishing ceramic materials, especially in areas that do not affect their appearance, such as the back of the mouth.

Catastrophic failures in lithium disilicate single-unit prostheses in the mandibular anterior region, particularly when subjected to endodontic access for root canal treatment, represent a significant clinical concern. This in vitro study evaluated the fracture resistance of CAD/CAM-fabricated lithium disilicate intact and endodontically accessed crowns, with and without aging through thermocycling. A mandibular right central incisor typodont was prepared and scanned for CAD/CAM fabrication of a lithium disilicate crown. Eighty crowns were milled, treated, etched, primed, and cemented to printed resin dies. The crowns were divided into eight groups based on endodontic access location (facial, incisal, or lingual) and thermocycling condition (presence or absence). All groups underwent vertical loading until fracture, and fracture resistance was measured. Fractured crowns were analyzed for crack patterns and failure modes using scanning electron microscopy. Two-way ANOVA assessed the effects of access type on fracture resistance, while one-way ANOVAs with Tukey's HSD post hoc tests analyzed fracture resistance across aging conditions. Fracture resistance was significantly affected by endodontic access type and thermocycling (p < 0.001). Non-thermocycled, intact crowns had the highest fracture resistance (1218.0 ± 174.8 N), while thermocycled crowns with incisal access demonstrated the lowest resistance (720.9 ± 98.3 N). Lingual access crowns displayed higher fracture resistance than facial and incisal access crowns, although resistance significantly decreased with thermocycling (p = 0.008). SEM analysis revealed that lingual access crowns visually appeared to exhibit less irregular crack patterns compared to facial and incisal access crowns, which displayed more numerous and irregular crack lines. Endodontic access reduced fracture resistance; however, thermocycling had a statistically significant effect only in the lingual access group. A conservative lingual access preserved integrity similarly to intact crowns, making it preferable for mandibular restorations. All crowns met minimum clinical fracture resistance standards, suggesting that crown replacement may not be necessary with conservative access designs. Variations between aged and non-aged specimens should be considered when interpreting in vitro data.