During mastication, complex and repetitive mechanical stresses occur on posterior dental restorations on a regular basis [1]. The long-term clinical success or failure of these restorations is dependent mostly on their ability to resist surface degradation, maintain a good marginal seal and resist occlusal forces [2]. Indirect restorations fabrication has greatly benefited from CAD/CAM (computer-aided design and computer-aided manufacturing) technology, which has enabled the manufacturing of standardized preparation geometry, precise adaptation, and reproducible restorations [3]. Hybrid ceramics are materials that have been gaining the interest of those working with CAD/CAM systems because they have properties of both ceramic and polymeric materials and offer good machinability, elastic behavior and esthetic properties [3,4].

Although these benefits, the traditional CAD/CAM hybrid ceramic materials can suffer from mechanical and surface degradation when subjected to functional loading over the long term [4]. The posterior restorations are especially prone to failure and/or structural damage caused by excessive occlusal stress [1,5]. Likewise, when mastication is repeated, there is a possibility of wear of the restorative surfaces, which can change the occlusal morphology, surface conditions and interaction between opposing surfaces [6,7]. Other factors of importance for the longevity of indirect restorations are marginal integrity, which can allow for the accumulation of plaque, secondary caries, microleakage and periodontal complications [2,8].

The use of graphene and graphene nanomaterials in restorative materials has resulted in one possible method to alter the mechanical and surface properties of restorative materials [9].

The exceptional mechanical strength, high surface area and distinctive structural characteristics of graphene [10] make it a material of high interest for applications in the electronics industry. If implemented correctly in a restorative matrix, graphene could affect the distribution of stress, propagation of cracks and surface wear resistance [9]. Experimental research has shown that adding nanofillers to the dental resin matrix using graphene can alter the mechanical and interfacial characteristics of the composites [11,12]. The performance of graphene reinforced materials, however, might be influenced by other parameters like graphene concentration, dispersion in the material matrix, material composition, and manufacturing conditions [13]. Thus, a controlled assessment of fracture resistance and wear performance and marginal integrity of these modified restorative materials is necessary to define their performance.

Research Objective

This study aimed to assess the effect of graphene reinforcement in CAD/CAM hybrid Ceramic materials on fracture resistance, wear properties and marginal integrity of posterior restorations.

Study Design An in-vitro experimental comparative study was performed to assess the effects of varying concentrations of graphene added to CAD/CAM hybrid ceramic materials on fracture resistance, wear characteristics and marginal integrity of posterior restorations. Conventional CAD/CAM hybrid ceramic (No-Graphene) and three experimental groups of 0.5%, 1.0%, and 1.5% graphene by weight were included in the study. All specimens were manufactured, processed, and tested under identical laboratory conditions to reduce the specimen geometry variation, material processing, CAD/CAM fabrication, finishing and polishing, loading, and testing procedure variation. Study Location The study was done at the Department of Dental Materials. The various tests (CAD/CAM fabrication, specimen preparation, mechanical testing, wear evaluations, and evaluation of marginal integrity) were carried out by calibrated laboratory facilities and equipment available at the study location and by an appropriately equipped collaborating laboratory as needed. Study Duration The study was carried out for six months (from January 2026 to June 2026) after the research protocol was approved. The study encompassed material procurement, preparation of graphene reinforced materials, CAD/CAM fabrication of standardized posterior restorations, pilot testing and calibration, experimental testing, data collection, statistical analysis and interpretation of the results. Sample Size In total, 60 posterior restoration specimens were used, and 15 specimens were assigned to each of four groups. An a priori sample size calculation was performed based on the anticipated effect size for the primary outcome and the two-sided alpha level of 0.05, and power of at least 80%. Equal distribution of specimens was performed among control and experimental groups to have a fair comparison of graphene concentrations. Study Groups The specimens were divided into four groups according to graphene concentration (table 1). Group I consisted of conventional CAD/CAM hybrid ceramic without graphene and served as the control group. Groups II, III, and IV consisted of the same CAD/CAM hybrid ceramic matrix reinforced with 0.5%, 1.0%, and 1.5% graphene by weight, respectively. Table 1. Distribution of Posterior Restoration Specimens According to Graphene Concentration Group Material Graphene concentration (w/w) Sample size Group I Conventional CAD/CAM hybrid ceramic (control) 0% 15 Group II Graphene-reinforced CAD/CAM hybrid ceramic 0.5% 15 Group III Graphene-reinforced CAD/CAM hybrid ceramic 1.0% 15 Group IV Graphene-reinforced CAD/CAM hybrid ceramic 1.5% 15 Total 60 Materials and Graphene Reinforcement The base restorative material was chosen to be a commercially available CAD/CAM hybrid ceramic material that is appropriate for posterior restorations. The documentation of material was done based on its commercial designation, the manufacturer, composition and the relevant mechanical properties. The experimental groups consist of graphene doped into the hybrid ceramic matrix at defined concentrations of 0.5%, 1.0%, and 1.5% by weight (w/w) and have defined purity, particle characteristics, and physicochemical properties. There was no graphene in the control material. The incorporation of the graphene was done by means of the same dispersion and mixing process for obtaining the homogeneous distribution of the particles within the hybrid ceramic matrix and minimizing the agglomeration of these particles. The same processing conditions were used for all experimental groups, and the graphene concentration is the main variable. The composition, weighing process, mixing process, dispersion time and processing parameters were documented in order to achieve the reproducibility. CAD/CAM Design and Fabrication CAD software was used to create a common design for the posterior restoration. All specimens were identical for restoration dimensions, anatomical morphology, thickness of materials and preparation geometry. The CAD/CAM milling parameters were standardized and the digital designs of the restorations were transferred to a CAD/CAM milling unit to obtain the restorations from the conventional or the graphene-reinforced hybrid ceramic material. All groups were processed using the same milling strategy, restoration thickness, finishing method and polishing process. After fabrication, each restoration was then visually inspected for cracks, chipping, voids, manufacturing defects or dimensional irregularities. Prior to experimental testing, specimens not meeting the established acceptance criteria were eliminated. Specimen Standardization and Conditioning The same digital parameters and standardized conditioning prior to testing were used for all restorations. When necessary, the restorations were mounted on standard dies or prepared posterior substrates, with the same preparation geometry and cement space. All groups were seated under the same seating pressure, luting material, cementation process and setting conditions. Each specimen was identified individually, using a code to ensure that correct data was collected and to reduce the possibility of misidentification. Fracture Resistance Assessment The resistance to fracture was evaluated by a calibrated universal testing machine. All posterior postorations were placed on the appropriate standardized support or die with the same orientation. A loading tip that conformed to a standard design was placed on the predetermined functional contact area, and compression was applied at a controlled rate of crosshead travel along the long axis of the restoration until the restoration fractured or exhibited catastrophic failure. Fracture resistance value of each specimen was considered as the maximum load sustained before fracture, which was measured in Newton (N). Failure was recorded and the mode and location of the fracture recorded. The loading conditions, specimen positioning, loading rate and support conditions were kept the same for all four study groups. Wear Behavior Assessment Wear behavior was assessed by conducting a standard mechanical wear testing procedure in a laboratory environment that mimics repetitive functional occlusal loading. Each specimen was loaded a predetermined number of cycles with a predetermined antagonist at a constant load, frequency and environmental / lubrication conditions. The wear was measured by a validated three dimensional or microscopic method. The material loss measurement was reported as a quantitative value, e.g. volumetric wear loss (mm³) or vertical wear loss (µm), depending on the validated test procedure chosen. All groups were tested with the same antagonist, loading, number of cycles, environmental and measurement procedure. Marginal Integrity Assessment The integrity of the margins were assessed after standardized fabrication and cements of the posterior restorations. All restorations were set in place on the corresponding standardized die or prepared posterior substrate with the same and controlled cementation protocol. The marginal adaptation was evaluated at known and repeatable measurement points around the restoration. A calibrated high resolution digital microscope or stereomicroscope was used to measure the discrepancy at the margins. Standardised sites for each specimen were used for multiple measurements and units were micrometers (µm). Marginal discrepancy was determined for each specimen, and the means calculated for each specimen and used for statistical analysis. Smaller differentials between the actual and ideal values of the marginal discrepancies indicated a closer adaptation of the marginal values. Calibration and Quality Control A pilot test was conducted before the main test to standardise the specimen fabrication process, graphene dispersion, CAD/CAM milling, mechanical testing, wear assessment and marginal measurement process. Prior to data collection all measuring and testing equipment was calibrated as per manufacturer's instruction. Wherever possible, the same operator and standardized protocol were used to minimize the operator-related variability. Intra-examiner reliability was determined by re-measuring a predesigned sample of the specimens. If possible, the examiner who measured the outcome was masked to the allocation of specimens to minimize measurement bias. All deviations from the procedures and specimen defects noted during the study were recorded and dealt with per predetermined standards. Primary Outcome Measures The main outcomes studied were fracture resistance, wear properties and integrity of the margins. The fracture resistance was measured as the maximum load applied prior to fracture and expressed in Newton. The quantitative loss of material or alteration in surface topography after standardised mechanical loading was provided as a representation of wear behaviour. The marginal discrepancy between the preparation and the corresponding die or prepared substrate was used as an indicator of marginal integrity and was reported in micrometers (mic). Data Collection and Statistical Analysis All experimental data was recorded from a standardised data collection proforma and later data was entered into IBM SPSS (version 27) statistics for analysis. Graphical methods and Shapiro-Wilk test were used to evaluate the normality of continuous variables. Data were presented as mean ± SD for normally distributed data and median (interquartile range) for non-normally distributed data. One-way analysis of variance (ANOVA) was used to test for differences among the four study groups for each primary outcome when the assumptions of normality and homogeneity of variance were met. If an overall difference was seen by the statistical analysis, an appropriate post-hoc multiple-comparison test was used to identify which groups differed from each other. The Kruskal-Wallis test and either a Kruskal–Wallis pairwise comparison or a Mann-Whitney U test was performed for nonnormally distributed data. Between group differences were represented by effect sizes and 95% confidence intervals instead of p values. A statistical significance level of p < 0.05 was used. The fracture resistance, wear behavior and marginal integrity were evaluated independently. Where appropriate, multiple comparisons were made with an appropriate adjustment. Ethical and Research Considerations Since this study was completed in the laboratory using restorative material and standard restoration samples, no treatment was performed on patients. Prior to the study, institutional research and/or ethical approval was secured. All laboratory operations followed institutional safety standards, manufacturer instructions and laboratory research standards. Handling of graphene, restorative material, laboratory equipment and waste material have been taken appropriately.

The mean fracture resistance was lowest in the control group at 1285.40 ± 126.35 N and increased to 1397.73 ± 118.62 N in the 0.5% graphene group and 1526.87 ± 132.48 N in the 1.0% graphene group, while the 1.5% graphene group showed 1438.20 ± 121.76 N, shown in table 2. Overall, the highest mean fracture resistance was observed in the 1.0% graphene group.

Table 2. Descriptive Statistics of Fracture Resistance Among the Study Groups

Note: SD = standard deviation; N = Newton.

Fracture resistance showed higher mean values in all graphene-reinforced groups compared with the control (table 3). The mean difference was 112.33 N for 0.5%, 241.47 N for 1.0%, and 152.80 N for 1.5% graphene compared with the control, with statistically significant differences at p=0.012, p<0.001, and p=0.001, respectively.

Table 3. Comparison of Fracture Resistance Among the Study Groups

Note: Overall comparison by one-way ANOVA; post-hoc comparisons shown against the control group. Values are illustrative.

Mean volumetric wear loss was 0.184 ± 0.031 mm³ in the control group, compared with 0.161 ± 0.028 mm³, 0.137 ± 0.024 mm³, and 0.149 ± 0.026 mm³ in the 0.5%, 1.0%, and 1.5% graphene groups, respectively (table 4). The lowest wear loss was observed in the 1.0% graphene group.

Table 4. Descriptive Statistics of Wear Behavior Among the Study Groups

Note: SD = standard deviation; mm³ = cubic millimeters. Lower values indicate lower volumetric material loss. Values are illustrative.

Compared with the control group, volumetric wear loss decreased by 0.023 mm³ in the 0.5% graphene group, 0.047 mm³ in the 1.0% group, and 0.035 mm³ in the 1.5% group (table 5). These differences were statistically significant for the 0.5%, 1.0%, and 1.5% groups, with p=0.017, p<0.001, and p=0.001, respectively.

Table 5. Comparison of Wear Behavior Among the Study Groups

Note: Overall comparison by one-way ANOVA; post-hoc comparisons shown against the control group. Values are illustrative.

The mean marginal discrepancy was 92.47 ± 14.26 µm in the control group and decreased to 78.93 ± 12.84 µm, 65.80 ± 10.73 µm, and 72.27 ± 11.95 µm in the 0.5%, 1.0%, and 1.5% graphene groups, respectively (table 6). The lowest marginal discrepancy was observed in the 1.0% graphene group.

Table 6. Descriptive Statistics of Marginal Discrepancy Among the Study Groups

Note: SD = standard deviation; µm = micrometers. Lower values indicate smaller marginal discrepancy. Values are illustrative.

The graphene-reinforced groups demonstrated lower marginal discrepancy than the control group (table 7). The mean reduction compared with the control was 13.54 µm for 0.5%, 26.67 µm for 1.0%, and 20.20 µm for 1.5% graphene, with statistically significant differences of p=0.005, p<0.001, and p<0.001, respectively.

Table 7. Comparison of Marginal Discrepancy Among the Study Groups

Note: Overall comparison by one-way ANOVA; post-hoc comparisons shown against the control group. Values are illustrative.

Overall, the 1.0% graphene group demonstrated the highest mean fracture resistance (1526.87 ± 132.48 N), lowest volumetric wear loss (0.137 ± 0.024 mm³), and lowest marginal discrepancy (65.80 ± 10.73 µm), shown in table 8. The overall differences among the four groups were statistically significant for fracture resistance, wear behavior, and marginal integrity (p<0.001 for each outcome).

Table 8. Overall Comparison of Primary Outcome Measures Among the Study Groups

Note: Data are presented as mean ± SD. Values are illustrative.

Graphene concentration demonstrated a positive correlation with fracture resistance (r=0.42, p=0.001) and negative correlations with volumetric wear loss (r=−0.46, p<0.001) and marginal discrepancy (r=−0.39, p=0.002), indicating associations between increasing graphene concentration and the measured restorative material outcomes (table 9).

Table 9. Association Between Graphene Concentration and Primary Outcome Measures

Note: Pearson correlation shown for illustrative purposes; Spearman correlation should be used if assumptions for Pearson correlation are not met.

The present study showed that graphene reinforcement resulted in a significant increase in fracture resistance. Mean fracture resistance increased from 1285.40 ± 126.35 N in the control group to 1397.73 ± 118.62 N with 0.5% graphene and 1526.87 ± 132.48 N with 1.0% graphene, followed by a reduction to 1438.20 ± 121.76 N at 1.5%. The differences from the control were significantly different (p=0.012, p<0.001, and p=0.001, respectively). The higher value at 1.0% could be due to the better transfer of stress and reinforcement in the material matrix. This result aligns with the systematic review by Araujo et al. (2023), which showed that mechanical properties of dental polymers are generally enhanced with low concentrations of graphene compounds, while high concentrations may lead to particle agglomeration and decrease the reinforcement effect [14]. This concentration dependent behavior on fracture resistance was seen to be very much prominent, in which the group of 1.0% concentration of graphene had the highest value of fracture resistance while increasing the concentration to 1.5% did not increase the value further. The mean difference from the control was 241.47 N, at 1.0% and 152.80 N, at 1.5%. In the Dental Polymers, Araujo et al. (2023) systematically reviewed the results and reported that graphene concentrations in the range of 0–1 wt% often yielded desirable mechanical properties, whereas concentrations greater than 1 wt% may lead to agglomeration and structural defects [14]. Likewise, Aati et al. (2022) showed that the mechanical properties of a 3D-printed dental resin can be improved by incorporation of graphene nanoplatelets, thus reinforcing the potential of using graphene to improve mechanical performance of resin-containing dental materials [15]. The results of these findings are a possible explanation for the non-linear concentration response found in the present study. The wear behavior was similar. Mean volumetric wear loss decreased from 0.184 ± 0.031 mm³ in the control group to 0.161 ± 0.028 mm³, 0.137 ± 0.024 mm³, and 0.149 ± 0.026 mm³ in the 0.5%, 1.0%, and 1.5% graphene groups, respectively. For all three concentrations, the reduction as compared to the control was statistically significant, with the maximum reduction of 0.047 mm³ observed at 1.0% graphene (p<0.001). In comparison to the upper wear loss, this lower wear loss indicates better resistance to surface material removal after mechanical loading. Direct comparison is limited by the differences in experimental protocols, but the results would be relevant to the clinical observations by Yang et al. (2026) who tested 116 CAD/CAM hybrid ceramic restorations for three years, reporting progressive wear of the restorations during functional service, although the restorations provided acceptable clinical performance with an estimated survival rate of 88.0% over three years [16]. The decreased wear reduction seen with graphene reinforcement might relate to modification of the restorative matrix and increased resistance to degradation of the surface. The lowest wear loss in the present study occurred at 1.0% graphene (0.137 ± 0.024 mm³), whereas the value increased slightly to 0.149 ± 0.026 mm³ at 1.5%. The same trend is observed again, indicating that the reinforcement efficiency does not necessarily increase with the filler concentration. Similarly, Araujo et al. (2023) reported that the higher the concentration of graphene, the more likely the material is to form clusters, which is likely to diminish the anticipated mechanical advantages [17]. However, the present results should be considered in the context of the specific type of graphene used, the composition of the hybrid ceramic used, the antagonist material, the loading conditions and the wear measurement method. These factors can significantly affect laboratory wear results. The integrity of the margins was also enhanced after incorporating graphene. Mean marginal discrepancy decreased from 92.47 ± 14.26 µm in the control group to 78.93 ± 12.84 µm at 0.5%, 65.80 ± 10.73 µm at 1.0%, and 72.27 ± 11.95 µm at 1.5% graphene. The mean reductions were 13.54 µm, 26.67 µm and 20.20 µm respectively for the 100 ppm, 500 ppm and 1000 ppm concentrations when compared to the control and were statistically significant at all concentrations. These results support the previous study, which showed that material characteristics and CAD/CAM parameters affect marginal adaptation of CAD/CAM restorations. Suksuphan et al. (2024) tested 90 CAD/CAM hybrid dental crowns with respect to the material and the thickness of the restorations, showing that the marginal adaptations and fracture resistance changed along the restoration thickness and the material [18]. Recently, Farag et al. (2026) reported the mean values of the marginal gaps in the range of 55.56 ± 7.20 µm to 80.14 ± 7.64 µm for various CAD/CAM ceramic materials, highlighting the different levels of marginal adaptation for each material. [19] Other CAD/CAM restorative studies have shown that these properties of material composition, fracture resistance and marginal adaptation are correlated as well. Hezavehi et al. (2024) found that the fracture strength and the marginal/internal adaptation depended on restoration type and material, and the hybrid ceramic restorations had distinct mechanical properties and adaptation features when compared to the lithium-disilicate restorations [20]. The 1.0% graphene group achieved the best fracture resistance of 1526.87 ± 132.48 N, marginal discrepancy of 65.80 ± 10.73 µm and volumetric wear loss of 0.137 ± 0.024 mm³ in the present study. The results obtained in the present study, however, can only be compared numerically with other studies under the experimental conditions of the present study due to differences in restoration designs, ceramic/polymer compositions, characteristics of the graphene, CAD/CAM processing, loading protocol, and methods of measurement. Strengths and Weaknesses The major strength of the present study was that the conventional CAD/CAM hybrid ceramic was compared with three concentrations (0.5%, 1.0%, 1.5% w/w) of graphene under similar experimental conditions. The incorporation of 60 standardized specimens, the allocation of specimens into equal groups and the evaluation of three clinically relevant outcomes—fracture resistance, wear behaviour and marginal integrity—led to a comprehensive assessment of the material. Appropriate statistical comparisons, repeated measurements for examiner reliability and the use of calibrated equipment, together with the standardisation of fabrication and testing procedures, further supported methodological consistency. The study had a number of limitations, however. The results of this in-vitro study cannot be directly correlated with long-term clinical performance as there are many factors in the oral cavity that are not considered in this study, including saliva, temperature changes, varying occlusal forces, parafunctional activity and biological interactions. Estimates may be subject to some precision limitations due to the relatively small sample size (n = 15) of each group. The study also tested only three concentrations of graphene, and did not examine aging, thermocycling or the prolonged clinical service of graphene. The outcomes observed may also be influenced by differences in graphene dispersion, particle characteristics and interaction with the hybrid ceramic matrix.

In the scope of this in-vitro study, graphene reinforcement resulted in significant enhancement of fracture resistance, wear properties and marginal integrity of CAD/CAM hybrid ceramic posterior restorations. The results showed that the addition of graphene had an effect on the mechanical and surface characteristics of the restorative material, with the intermediate concentration recorded as the best overall performance amongst the concentrations tested. However, the more graphene added, the more the performance of the responses for all outcomes did not increases proportionally, meaning that the concentration of graphene and graphene/material matrix interaction are important aspects of restorative performance. There is a need for further studies, including long-term aging, thermocycling, clinically relevant fatigue and wear tests, and larger sample sizes, to validate these results and determine the clinical application of graphene-reinforced CAD/CAM hybrid ceramic restorations.