Microbial leakage and marginal adaptation of alkasite restorative material in Class II cavity: an in vitro study
Article information
Abstract
Objectives
This study aimed to determine the relationship between the interfacial properties of proximal cavities (microbial leakage and marginal adaptation) and restorative materials (alkasite, resin composite, and glass hybrid)
Methods
This study involved 66 human third molars that were left intact. Standardized Class II cavities were done on the mesial surface. The samples were then divided into five groups: (i) Cention N (CN, Ivoclar Vivadent), (ii) Filtek Z350XT (FZ, 3M ESPE), (iii) EQUIA Forte (GC Corporation), and (iv) two controls. For 40 days, a dual-chamber model containing Streptococcus mutans was used to study microbial leakage. Qualitative assessments of the sectioned samples were also carried out using a scanning electron microscope (SEM). Moreover, this study employed descriptive and Kaplan-Meier analyses, alongside a one-way analysis of variance for additional descriptive comparisons (p < 0.05).
Results
Across different restorative materials, notable variations in microbial leakage were recorded. From the supplementary analysis between CN and FZ, a statistically significant difference was demonstrated (p = 0.037). In comparison to other restorative systems, CN also produced a prolonged mean time before microbial leakage occurred. For the interfacial properties of the restorative systems, illustrative information was offered via the SEM images.
Conclusions
Regarding microbial leakage, all restorative systems presented their occurrence (despite the constraints of this study). When assessing CN and FZ restorative systems, a slower rate of microbial leakage was also concluded for CN. For the tooth-restoration interface, qualitative data were verified through SEM observations.
INTRODUCTION
Within the vicinity or adjacent to restorative materials and existing sealants, secondary caries (or recurrent caries) is typically observed [1]. At the restoration margin, this process has a higher likelihood of occurring, causing dental restorations to possess lower durability and effectiveness. For resin composite and amalgam restorations, failure and the need for replacement may then be necessary. Regarding the development of secondary caries, a prevalent factor contributing to this outcome is polymerization shrinkage. In this process, Streptococcus mutans, which thrives in conditions favorable to plaque accumulation, can cause bacterial infiltration and the progression of caries via marginal discrepancies [2]. Other factors have also been identified as worsening secondary caries. For example, within the resin matrices for resin composite restoration, contraction stress and hydrolytic degradation can take place [3]. Hence, optimal marginal adaptation in restorative materials must be attained to minimize microbial leakage, alongside improving clinical outcomes (lower incidence of secondary caries).
The movement or infiltration of fluids, bacteria, or molecules at the junction between restorative materials and tooth structure is denoted as microleakage. In restorative dentistry, this process is a considerable issue, in which several impacts (pulpal inflammation, tooth hypersensitivity, and restorative failure) from secondary caries may occur [4]. For resin composite-based restorative systems, antibacterial characteristics are insufficient. If the marginal sealing is compromised, these systems can be more susceptible to microbial colonization [5]. As such, viable alternatives for restorative applications have been created in response to these concerns.
For the efficient placement of materials in dental restorations, alkasite restorative materials (such as Cention N [CN]; Ivoclar Vivadent, Schaan, Liechtenstein) integrating mechanical with bioactive advantages are an optimal choice. Due to its highly reactive fillers, CN is conducive to the ion exchange of fluoride, calcium, and hydroxyl ions. With these ions, demineralization and remineralization can then be hindered, along with demonstrating antibacterial properties, as a result of pH stabilization blocking the acid [6]. For deeper cavities, polymerization can also be promoted via their dual-cure features. Thus, for resin composites that primarily necessitate incremental layering approaches, this step can be removed [7].
In earlier studies, various methods for measuring microbial leakage were established that contained both benefits and limitations. A longstanding and economical technique for visualizing microbial leakage was pioneered by Alani and Toh [8]. Under a stereomicroscope, methylene blue for dye penetration was used to detect leakage. Nonetheless, several constraints have been indicated with this approach. As partial information for assessing microbial leakage is delivered, an underestimation of leakage can occur. Compared to other bacteria (S. mutans), an overestimation of microbial leakage can also happen owing to the smaller dye size [9,10]. In a separate investigation, Bagherian et al. [11] proposed the method of bacterial penetration. This strategy was based on S. mutans as a significant contributor to the development of dental caries. Given that it closely resembles the conditions found in the human oral cavity, it is currently regarded as the most clinically relevant approach. Nevertheless, this method is extremely slow, as it may take between 40 and 60 days to generate results [12].
The most effective seals are usually the most difficult to achieve. On the other hand, these seals are critical in preventing the occurrence of secondary caries for Class II restorations. Hence, this in vitro study examined the correlation between the interfacial properties of proximal cavities (microbial leakage and marginal adaptation) and various restorative materials. Based on the microbial leakage assessment technique, a comparison was made among CN, Filtek Z350XT (FZ; 3M ESPE, St. Paul, MN, USA), EQUIA Forte (EF; GC Corporation, Tokyo, Japan), and two control groups (positive and negative) concerning Class II restorations. Hence, the deficiency in research regarding microbiological methods for bacterial penetration in CN restorations could be addressed when conducting a comparative analysis for these materials on actual clinical sealing performance. Through this comparison, information concerning clinical performance and restoration longevity could then be obtained for CN, FZ, and EF. In this study, the null hypothesis (H₀) was posited as follows:
H₀: There would be no significant differences in the time to microbial leakage and marginal adaptation across Class II restorations restored with alkasite (CN), resin composite (FZ), and glass hybrid restorative systems (EF).
METHODS
Experimental materials
In Table 1, the materials, manufacturers, curing methods, types of resin, and fillers utilized for each restorative material are listed. To restore Class II cavities in the third molars, the restorative materials were employed. Examinations concerning microbial leakage and marginal adaptation were then carried out.
Types of materials evaluated
Teeth preparation
In this study, ethical approval from Jawatankuasa Etika Penyelidikan Manusia (JEPeM) Universiti Sains Malaysia was received in accordance with the Helsinki declaration (USM/JEPeM/KK/23070568). Using strict inclusion criteria, 66 human third molars with no caries, restorations, or cracks were selected. All third molars were also kept in a 0.02% thymol solution for 1 day to prevent bacterial contamination, alongside maintaining hydration. Regarding the mesial aspect, every tooth was subjected to Class II cavity preparation. For the gingival wall cavities, the buccolingual and mesiodistal widths were 4 mm and 2 mm, respectively.
To preserve the remaining enamel width of 0.5 mm to 1.0 mm, the gingival wall was situated within the enamel, which was above the cementoenamel junction. The preparations also incorporated rounded internal line angles, and to maintain uniformity, retentive grooves were omitted. A high-speed straight fissure diamond point friction grip bur with water coolant was also utilized for the cavity preparation. To maintain optimum cutting quality and uniformity, a bur was changed after five cavity preparations. Lastly, to ensure uniformity in the dimensions of the prepared cavities, one trained operator, using a digital vernier calliper, conducted all the cavity preparations.
Grouping of teeth
Once the third molar teeth were prepared, they were divided into five groups (three experimental [n = 20] and two control groups [n = 3]). In Groups 1 to 3, restoration involved employing an alkasite restorative material (CN), nanohybrid resin composite (FZ), and bulk-filled glass hybrid restorative material (EF), respectively. For bacterial penetration (positive control), Group 4 comprised unrestored teeth following cavity preparation. To prevent bacterial ingress (negative control), Group 5 consisted of unrestored teeth with all surfaces entirely covered in nail varnish. The teeth restoration process also included the use of a matrix to simulate natural contact points. The prepared teeth were secured in place on green stone, along with adjacent non-carious teeth. A sectional matrix band (Ultradent Products, Inc., South Jordan, UT, USA) was also used to assure proper contouring and adaptation during the restoration process.
Tooth restoration and sealing
Group 1 samples were subjected to 20 seconds of acid etching with 37% phosphoric acid gel (Scotchbond; 3M ESPE), which was accompanied by a water rinse to remove residual etchant. A microbrush was also used to apply the bonding agent (Tetric N-Bond; Ivoclar Vivadent) and was light-cured for 20 seconds. In addition, to create a uniform CN mixture, 15 g of powder with 4 mL of liquid was combined. Subsequently, an incremental technique and a 20-second light-curing process were sequentially used. During the curing, a light-cured unit tip (3M Elipar DeepCure-S LED curing light; 3M ESPE) was brought close to the restorative material (wavelength, 430–480 nm). In order to achieve consistent polymerization, the curing light unit was recharged after every 10 samples.
The same procedure (37% phosphoric acid gel for 20 seconds and followed by water rinse) was done for Group 2. In this group, a single-bond universal adhesive bonding agent (3M ESPE) was applied using a microbrush. For optimal adhesion to the tooth structure, a 20-second light-curing process was performed on the material. Subsequently, the incremental layering technique was used to apply FZ (40-second light-curing for each layer). Polishing was done on the same day to achieve a smooth surface finish via a composite resin polishing kit (AZDENT RA 0309; Zhengzhou, China) and a slow-speed handpiece (NSK Ltd., Kanuma, Japan).
In Group 3, the GC Cavity Conditioner (GC Corporation) was applied for 10 seconds, after which it was rinsed off and gently dried without desiccation prior to the placement of EQUIA Forte Fil. The capsule was then initiated and triturated for 10 seconds, after which it was promptly positioned with a capsule applicator. Subsequently, the material was molded. Once prepared, improved mechanical characteristics were accomplished by applying EQUIA Forte Coat and then light-cured for 20 seconds. Likewise, bacterial penetration was permitted for the positive control group, which contained unrestored teeth following cavity preparation. Conversely, for completely preventing bacterial penetration, the negative control group had all tooth surfaces coated with nail varnish.
Thermocycling
Within a 37°C incubator (Memmert GmbH, Schwabach, Germany), all samples were kept in distilled water after restoration for 24 hours. In order to replicate oral conditions, the samples were also subjected to 1,000 thermal cycles (5°C–55°C, 30 seconds dwell time per cycle) [13]. For enhancing the consistency of specimen preparation, each sample underwent derooting, after which the dentin between the pulp chamber floor and the furcation area was removed. Across all surfaces, nail varnishes were finally applied. In this study, to ensure the margins were properly isolated, a 2-mm perimeter around the restoration was created.
Disinfection and sterilization
Using epoxy resin (Araldite; Huntsman Advanced Materials, Basel, Switzerland), the samples were firmly affixed at the ends of plastic tubes to establish a stable interface. Each sample was assigned a code that corresponded to its group number before being packed and sterilized by gamma irradiation (eliminating microbial contamination). In guaranteeing aseptic conditions, the glass tubes were also sterilized for 15 minutes through an autoclave (Systec GmbH, Wettenberg, Germany) at 121°C.
Sample preparation
For assessing microbial penetration, Figure 1 depicts the employed modified two-chamber microbial leakage model [11]. A sterile glass tube filled with brain-heart infusion broth (BHI; Oxoid Ltd., Basingstoke, UK) was used. For each sample, an immersion in the medium covering 2–3 mm was also ensured. An initial suspension of S. mutans (ATCC 25175; concentration, 1.5 × 108 colony-forming unit [CFU]/mL) was then prepared to introduce the bacterial challenge. Subsequently, to ensure that the restorative margin was continuously exposed to S. mutans, 8 mL of the bacterial suspension was utilized to fill the upper chamber of the experimental setup. To maintain a sterile environment and prevent unintended contamination, along with preserving the integrity of the experiment, all procedures were also conducted with great care within a biosafety cabinet field (Heraeus HS-12; Heraeus, Hanau, Germany).
Schematic diagram of the modified dual-chamber model used for microbial leakage assessment. BHI, brain-heart infusion.
Incubation and bacterial penetration monitoring
A 37°C incubator was utilized for placing all the samples for 40 days. For turbidity (bacterial penetration and microbial leakage), the lower chamber was monitored on a daily basis. When turbidity was detected, a broth sample was streaked onto blood agar plates in duplicate to incubate for 24 hours. The isolated bacteria were then examined using an Axioplan 2 imaging system (Carl Zeiss Pte. Ltd., Singapore, Singapore) with Gram staining and microscopic examination to identify S. mutans and to check for the presence of other microorganisms. To maintain a constant bacterial challenge, 8 mL of fresh S. mutans suspensions (concentration, 1.5 × 108 CFU/mL) were also added to the upper chamber every day. The occurrence of turbidity (microbial leakage) was then recorded for each sample. Lastly, data collection was conducted in a systematic manner over a span of 40 days. Statistical analysis was also performed using IBM SPSS Statistics ver. 29.0 (IBM Corp., Armonk, NY, USA) in evaluating the microbial leakage patterns, alongside comparing the efficacy of the restorative materials under study.
Marginal adaptation analysis
Each experimental group sample was sectioned mesiodistally using a hard tissue cutter (EXAKT Apparatebau GmbH & Co. KG, Norderstedt, Germany) through the middle of the restoration. This method ensured precision of cut while minimizing thermal damage. For the scanning electron microscopy (SEM) analysis, the proximal surface of the cut samples was examined using a SEM (JEOL JSM-IT100; JEOL Ltd., Tokyo, Japan). Both low and high magnifications of the SEM (500× and 1,000×) were also used to assess the quality of the sample, along with the presence and continuity of the interface between the enamel and restoration. Through this process, data regarding microgaps and interfacial discontinuities (microbial leakage and secondary caries) were obtained [14]. During the SEM assessment, a single calibrated examiner who was unaware of the group assignments was also present. There were no repeated quantitative measurements or statistical analyses due to the SEM analysis being primarily descriptive.
Statistical analysis
Using IBM SPSS Statistics ver. 29.0, data analysis was performed. In assessing the occurrence of microbial leakage throughout the 40-day observation period, the Kaplan-Meier product-limit survival analysis was employed. The mean leakage times were also described descriptively. For providing a descriptive comparison of mean leakage times across the group, one-way analysis of variance (ANOVA) with the Games-Howell post hoc test was utilized. In this study, the threshold for statistical significance was then established at p < 0.05.
RESULTS
Microbial leakage
Regarding the microbial leakage assessments of the three experimental groups, descriptive and Kaplan-Meier survival analyses were used, along with a supplementary descriptive comparison (ANOVA, p < 0.05). The minimum duration for microbial leakage in CN, FZ, and EF groups was then computed to be 3, 2, and 3 days, respectively. On the contrary, the maximum durations recorded were 36, 17, and 23 days, respectively. Concerning the mean values (± standard deviation), Table 2 reveals a decreasing value order as follows: CN (16.30 ± 9.465) > EF (12.50 ± 6.692) > FZ (10.15 ± 4.522). In Figure 2, the survival probabilities for microbial leakage over a 40-day period are also measured via the Kaplan-Meier product-limit method. Another finding that should be interpreted with caution was that across the three groups, the one-way ANOVA revealed a statistically significant difference in mean leakage times (p = 0.030). In comparing CN with FZ, the Games-Howell post hoc analysis computed a significant difference (p = 0.037). Conversely, when comparing CN with EF and EF with FZ, no significant differences were recorded (p = 0.320 and p = 0.404) (Table 2).
Microbial leakage in the three experimental groups over a 40-day period
Microbial leakage occurrence rates over 40 days among different restorative materials. CN, Cention N (Ivoclar Vivadent, Schaan, Liechtenstein); FZ, Filtek Z350XT (3M ESPE, St. Paul, MN, USA); EF, EQUIA Forte (GC Corporation, Tokyo, Japan).
Marginal adaptation
From the SEM assessment, qualitative differences in marginal adaptation and interfacial morphology were presented for all the restorative materials (Fig. 3). Notably, a more consistent enamel-restoration interface was indicated for CN. Nonetheless, a higher occurrence of interfacial discontinuities was implied in FZ and EF.
Scanning electron microscope images of the enamel–restoration interface for three materials (A, Cention N [Ivoclar Vivadent, Schaan, Liechtenstein]; B, Filtek Z350XT [3M ESPE, St. Paul, MN, USA]; and C, EQUIA Forte [GC Corporation, Tokyo, Japan]) at 500× (left) and 1,000× (right) magnifications. Yellow arrows indicate the marginal gap between enamel (E) and restorative material (R).
DISCUSSION
In this study, based on a bacterial penetration method to assess microbial leakage, both microbial leakage and marginal adaptation of various restorative materials were successfully examined. What could then be observed was that CN, FN, and EF produced notable disparity in microbial leakage. In this case, a partial rejection of the null hypothesis concerning microbial leakage was suggested. This study also only performed a qualitative evaluation of the marginal adaptation. As such, for the corresponding null hypothesis, statistical rejection was precluded.
In dentistry, microleakage in dental restorations has consistently raised concerns. Specifically, several processes in the tooth have been demonstrated to cause issues via dimensional alterations of restorative materials. Such examples of these processes entail polymerization shrinkage, thermal contraction, and mechanical stress, alongside tooth-related dimensional changes [15]. For polymerization shrinkage, contraction forces are generated within the resin composite. Microbial leakage can then occur when the bonds to the cavity walls are disrupted [16]. Microbial leakage following the polymerization of resin composites can also be observed when inner cracks develop in the enamel [17].
Regarding the coefficient of thermal expansion, it has been mainly deemed as a factor causing microbial leakage [18]. In an investigation documented by McCabe and Walls [19], the authors reported that differences in this coefficient between restorative materials and teeth could produce this leakage type. This leakage has also been observed to occur under bond failure, as the restorations along cavity walls promote micromovements due to elastic modulus disparities [20]. For the samples undergoing thermocycling in this study, it was then expected that microbial leakage might be generated when repetitive contraction and expansion stress occurred on the tooth and restoration interfaces. Specifically, earlier onset of microbial leakage could occur under higher interfacial stress and gap formation owing to the rising thermal expansion of the resin composite.
In examining microbial leakage for Class II cavities, various restorative materials were employed in this study. Nevertheless, there are currently no restorative techniques or materials that can achieve an ideal marginal seal with cavity walls, along with completely preventing microbial leakage [21]. At the interface between tooth structure and restorative materials, microsurfaces are also invariably present. Thus, if the penetration of bacteria and fluids takes place, secondary caries can occur [22]. When examining the results of this study, an elevated C-factor in Class II restorations was assumed to demonstrate a larger microbial leakage than Class I restorations. In utilizing comparable restorative materials, a significant correlation was then indicated between this factor and microbial leakage [23].
Looking through earlier studies, there were multiple techniques for assessing microbial leakage (SEM, dual-chamber modification, and dye penetration). Historically, the earliest strategy employed to assess microbial leakage was dye penetration. In most investigations, the ease and practicality of this approach have rendered it frequently utilized as a gold standard [8,11,24-26]. Some dye examples that are primarily used include methylene blue, eosin, hematoxylin, aniline red, fluorescent dye, and crystal violet red [8]. Nonetheless, a number of limitations have been documented with this method.
To effectively demonstrate the adaptation of restorations, another strategy for the assessment of microbial leakage involves the SEM tool [21]. As a detailed visualization of the enamel-restoration interface (high magnification) can be obtained through this tool, a qualitative evaluation of interfacial continuity can be presented, alongside the presence of observable gaps. Therefore, the microbial leakage and bacterial infiltration along the margins can be placed in detail [27]. In readily navigating through marginal gaps, the small size of S. mutans (0.5–1 μm) also makes this process easily achieved [28]. Secondary caries can then form when bacterial infiltration is allowed, along with the movement of enzymes and saliva. For deep cavities, this outcome is evident when enamel is compromised, alongside the edges consisting of dentin and cementum (or both) [29].
For Class II restoration, this study employed a dual-chamber modification in evaluating microbial leakage. Typically, a documented count of the days during which turbidity is observed is necessary for assessing microbial leakage (quantitative data). Given that S. mutans more accurately reflects oral conditions (more reliable data), they are mainly applied via this approach [30]. Conversely, this process remains time-consuming (40–60 days) concerning the microbial penetration method. Daily observations of samples are conducted, alongside the replacement of fresh bacteria if there is no turbidity.
In the event of turbidity, it is essential to confirm the presence of bacteria through culturing, morphology assessment of the bacterial colony, Gram staining, and microscopic observation. Through these steps, no contamination from other bacterial species, aside from S. mutans, can then be confirmed. For assessing the movement of bacteria across the tooth-restoration interface, the microbial penetration method is also highly capable. Nevertheless, in understanding microbial leakage, information concerning bacterial metabolites, fluids, toxins, or ions is lacking [30]. For this study, mimicking the chemical composition of saliva within the oral cavity is another challenge, as the employed BHI broth could not completely achieve this environment [11].
For all restorations assessed in this study, microbial leakage was detected within 40 days, aligning with the outcomes reported by Nematollahi et al. [30]. What could be inferred from this observation was that at the marginal gaps at the tooth-restoration interface, the daily replacement and exposure to large fresh bacteria levels caused them to infiltrate. Further examination of the results also revealed a correlation between restorative materials and microbial leakage rates, in which a delayed onset or an earlier occurrence of this leakage was observed for CN and FZ, respectively. For the CN restorative system, the formation of an acid-resistant interface and resin-dentin interdiffusion zone might be the factors lowering the leakage when utilized alongside the suggested bonding protocol (strong sealing) [31]. Manuela Lopes [32] also published similar trends.
In reducing shrinkage stress, CN powder was suitable based on its isofiller. On the contrary, the liquid formulation contained four dimethacrylates (DMAs), along with initiators and various additives. Improved mechanical strength and durability over time were also demonstrated when tricyclodecan-dimethonal dimethacrylate (DCP), urethane dimethacrylate (UDMA), aromatic aliphatic-UDMA, and polyethylene glycol 400 (PEG-400) DMA were present to produce cross-links during polymerization. Likewise, straightforward handling was offered by DCP, alongside its low viscosity. For UDMA, it acted as the main component of the monomer matrix to improve mechanical characteristics while preserving moderate viscosity. A lower likelihood of discoloration could also be attained through the aliphatic features of aromatic aliphatic-UDMA. In enhancing stiffness, aromatic diisocynates were pivotal. Better flowability and adaptation to the smear layer could then be accomplished using PEG-400 DMA [33,34]. For both polymerization and low shrinkages, they could also be lowered via CN (containing patented filler partially functionalized with silane) and the organic/inorganic ratio with monomer composition, respectively [31].
Regarding marginal adaptation, varying interfacial morphology was observed from the SEM images for different materials. At the enamel-restoration interface, fewer noticeable discontinuities were denoted for CN, agreeing with the data published by Samanta et al. [35] and Firouzmandi et al. [36]. In another article by Mehesen et al. [14] concerning glass ionomer-based restorations, greater marginal gaps were reported. Nonetheless, qualitative observations were only presented in this study for the SEM analysis. Interestingly, the microbial leakage characteristics of CN for both this study and Sujith et al. [37] were identical, who examined the hybrid composite restorative materials and glass ionomer cement, alongside their corresponding mechanical and microbial leakage performances.
In this study, the experiment was performed under in vitro conditions for the alkasite restorative material and glass hybrid restorative materials. Conversely, other clinical studies have reported positive in vivo outcomes in posterior restorations. For alkasite restorative materials concerning stress-bearing posterior teeth, several benefits have been documented (satisfactory marginal integrity, periodontal response, and short- to medium-term survival). As such, regular clinical use can benefit from this design [7]. In terms of nanohybrid resin composites, favorable aesthetic results and mechanical strength have also been noted within long-term clinical studies. Nevertheless, issues with secondary caries and restoration replacement over time can still occur due to polymerization shrinkage and marginal degradation [22]. Regarding posterior restorations in atraumatic restorative treatment and high-caries-risk populations, glass hybrid restorative materials still remain popular owing to their fluoride release and chemical adhesion to tooth structure [38]. All these clinical observations have then suggested that under controlled laboratory conditions, microbial leakage and interfacial behavior examinations are vital, which this study successfully addressed.
From this study, the chemical composition and ion-releasing ability of CN were thoroughly explained. Still, to provide context for the current findings, a comparative analysis with FZ and EF properties must be carried out. When using FZ, enhanced polishability, aesthetics, and mechanical strength can generally be observed, as this nanohybrid resin composite contains high filler loading and nanoscale filler technology. Nevertheless, being a methacrylate-based composite, it is naturally prone to polymerization shrinkage stress, along with insufficient intrinsic ion release. Thus, the formation of marginal gaps, alongside a heightened vulnerability to microbial penetration as time progresses, can occur [15,16].
For EF, it represents a glass hybrid restorative system, which consists of high-viscosity glass ionomer cement and a resin-based surface coating. Based on its chemical adhesion to tooth structure and the release of fluoride, EF can diminish the risk of caries. In contrast, the marginal integrity of Class II restorations when exposed to occlusal loading can be jeopardized due to the sensitivity to moisture (initial setting phase), alongside lower fracture toughness [38]. Therefore, as the CN restorative system integrates resin-based mechanical properties and alkaline ion release, superior microbial sealing restorative systems can be attained (demonstrated in this study). It was also crucial to note that for each material, the bonding and conditioning protocols recommended by the manufacturer were followed. Thus, the results should be interpreted with respect to the system containing the materials.
From a clinical standpoint, scenarios involving critical marginal sealing and caries prevention could highly benefit from alkasite restorative systems (CN), as demonstrated in this study. In particular, in scenarios where optimal moisture control proved difficult, individuals with a high risk of caries, deep proximal cavities, or clinical circumstances could employ these Class II restorations. As this study also revealed good ion-releasing ability and qualitative interfacial properties, a more stable tooth-restoration interface, alongside minimized bacterial infiltration at the margins of the restoration, could be accomplished. Nonetheless, the differences observed were dependent on the material system used, which clinicians must take into account. Significant relationships were also exhibited between long-term clinical success, cavity design, occlusal loading, oral hygiene, and patient-related risk factors.
It was important to note that between restorative materials and the authentic oral environment, actual conditions or interactions that occurred in this study were not completely represented by the data. Some constraints observed in this methodology involved inadequate causatives (salivary enzymes, bacterial plaque, and pH fluctuations) within the oral environment. Accordingly, to confirm the clinical advantages of alkasite restorative systems in dynamic oral environments, a long-term randomized controlled clinical trial was necessary. The inferential comparisons of microbial leakage times also denoted another limitation, as they were not solely reliant on survival-specific statistical tests. Thus, it is advisable for future research to utilize survival-based comparative methods.
CONCLUSIONS
Albeit with variations in both the extent and timing of the leakage observed, this in vitro study revealed that all restorative systems demonstrated microbial leakage. Compared to FZ, delayed microbial leakage was presented by the CN restorative system. For the qualitative illustrative information on the tooth-restoration interface, it was demonstrated through the SEM observations.
Notes
CONFLICT OF INTEREST
No potential conflict of interest relevant to this article was reported.
FUNDING/SUPPORT
This research project was supported by a short-term grant from Universiti Sains Malaysia (304/PPSG/6315781).
AUTHOR CONTRIBUTIONS
Conceptualization: Ibrahim H, Yusop N. Data curation, Formal analysis, Investigation, Software, Visualization: Chew KH. Funding acquisition, Project administration, Supervision: Ibrahim H. Methodology, Validation: Mokhtar K. Resources: Yusop N. Writing - original draft: Chew KH. Writing - review & editing: Ibrahim H, Mokhtar K, Yusop N. All authors read and approved the final manuscript.