Nano-bioactive glass-ionomer liner performance in stepwise versus selective caries removal: 18-month clinical trial

Introduction

Dental caries is the most prevalent disease worldwide as well as one of the major global impacts on oral health [1]. It is a frequent chronic infection caused by cariogenic bacteria, which hold onto teeth, mainly Streptococcus mutans. These bacteria break down carbohydrates into acid, de-mineralizing hard tissue of the teeth [2].
If the enamel’s de-mineralization continues, bacterial infiltration of the dentin occurs, resulting in more de-mineralization, subsequent cavitation, and possible exposure of the pulp [3]. If left untreated, deep carious lesions can lead to pulpitis, pulp necrosis, and subsequently, endodontic therapy [4].
The management of deep caries presents a difficulty to the practitioner, particularly if it is asymptomatic [5]. Deep carious lesions are a challenge in determining which course of therapy would preserve pulp vitality while providing the best possible prognosis for progression and activity [6]. In order to maximize tooth survival, the goal should be to retain pulpal vitality, stop caries’ progression and activity, preserve tooth structure, and repair tooth’s function. The dentist is confronted with the question of how much caries should be eliminated in an operational option of caries control [7].
Traditionally, the treatment of deep carious lesions involve complete caries removal by eliminating all affected dentin until reaching firm and healthy dentin in a single visit [8]. However, the application of this technique has been shown to be excessively intrusive, which may increase the risk of pulpal exposure [9]. Recent advancements in dental research introduce minimally invasive biological methods based on partial caries removal approaches (selective and stepwise caries removal), aiming to maintain pulp’s vitality whenever possible [10].
In the selective caries removal technique, the caries is excavated from dentin that is hard on probing at the cavity margins, and from dentin that appears soft but is still cuttable by excavators when being in the direction of the pulp. Following that, a final restoration is inserted instantly [5]. Moreover, the selective caries removal technique preserves the odontoblastic palisade, an important region that promotes more orderly formation of reparative tertiary dentin and at the same time, stops caries progression. Additionally, it decreases the possibility of bacteria penetrating the pulp, preserving its vitality [3].
The stepwise caries removal technique takes place over the course of two visits, with caries selectively elimi­nated and temporarily restored during first session. When the cavity is re-assessed after 6 to 12 months, any remaining caries are thoroughly eliminated before final restoration. Consequently, this management strategy must be viewed as a full caries excavation approach, although it requires two appointments [9].
The aim of conservative pulp therapies is to provide a setting that promotes pulpal health. This might entail removing infected dentin and closing cavity’s cavosurface margins, to enable the dentin-pulp system to regenerate or heal. Following the removal of tissue irritants, a medication or substance is applied on top of the dentin or in contact directly with the pulp, to encourage the odontoblasts or cells-resembling odontoblasts to build a mineralized dentin bridge [11]. Additionally, protective dental liners are placed in deep cavities to shield the pulp from various stimuli and promote the growth of reparative dentin. In addition to therapeutic benefits, re-mineralization ability, and anti-bacterial activity, these substances can block dentinal tubules and protect the pulp from microbial invasion [12].
Evidence shows that nano-bioactive glass (N-BAG) particles have anti-bacterial activity as well as the ability to exchange cations, and form a silica-rich layer, leading to the creation of hydroxyapatite or fluorapatite when fluoride is present [13]. Therefore, adding a substance to glass-ionomer cement (GIC) to strengthen its anti-bacterial capabilities and no negative impact on its mechanical qualities, such as N-BAG, would be highly favorable [14].

Objectives

The present study was conducted to compare the cli­nical performance of N-BAG/GIC liner in the selective and stepwise caries removal techniques after 18-month follow-up. The null hypothesis was that there would not be any significant difference in the prognosis using either selective or stepwise technique with N-BAG/GIC liner.

Material and methods

Nano-bioactive glass (N-BAG) was mixed with conventional glass-ionomer cement (GIC) powder to produce 20% N-BAG/ GIC liner. Final restoration was a nano-filled resin composite (Filtek Z350 XT) using a selective enamel etching technique. The materials used in the current study are shown in Table 1.

Sample size

The least needed sample size (n) was 7 teeth in each group, with overall 14 teeth. However, in order to compensate for a 25% rate of possible withdrawal, the number was increased. Consequently, the needed sample size was at least 9 teeth in each group, providing an overall 18 teeth. Computation of the sample size was performed according to Singhal et al. [15], employing an a level of 0.05 (5%) and a b level of 0.20 (20%), i.e., power = 80%. To calculate the sample size, IBM SPSS Power Release version 3.0.1 was employed.

Study design and setting

The study consisted of two parallel-armed rando­mized clinical trials with an identical allocation ratio (1 : 1), which were single-centered and double-blinded (assessor and participant). Eighteen adult patients aged 18-50 years were chosen for the study during their routine dental check-ups at the Faculty of Dental Medicine, Department of Operative Dentistry, Al-Azhar University, Cairo, Egypt.

Ethical approval and consent form

Al-Azhar University Faculty of Dental Medicine’s organizational committee on ethics provided approval for this study (No. 615/2922). Each patient received information about the purpose of the research, provided consent to participate, and signed a permission form (in the local language) prior to the study’s beginning.

Initial visit (diagnosis)

Before conducting the study, the main researcher (MAR) trained and calibrated one dentist, who served as the assessor, to identify eligible lesions and perform follow-up observations. The assessor was a staff member of the same department (Operative Dentistry). Subsequently, the main researcher (MAR) verified the teeth evaluation for eligibility screening.

Considerations for eligibility

Inclusion criteria: 1) adult patients (aged, 18-50 years) with class I deep caries that reached the dentin’s inner third (D3) in permanent molars (except for third molars) [16], according to the American Dental Association Caries Classification System (2015) [17], determined with digital sensor (Woodpecker, i-Sensor H1, China); 2) teeth that had a normal reading on electrical pulp tester (DY 310, Denjoy Dental Co., Ltd., Changsha, China), with no percussion sensitivity, immobility, lack of periapical pathosis, and spontaneous pain; 3) patients maintaining good overall health and oral hygiene by consistently adhering to proper hygiene measures; 4) patients who declared completing follow-up procedures and signed consent form.
Exclusion criteria: 1) presence of previous restoration; 2) teeth with periodontal disease, any swelling, fistulas, indications of irreversible pulpitis, or necrotic pulp; 3) pre­gnant women; 4) presence of any systemic disease [18].

Enrollment of patients

A total of 40 patients were diagnosed, out of whom 18 fulfilled the inclusion criteria and were enrolled in the current study.

Grouping

A total number of 18 Class I deep caries in permanent molars were collected from 18 patients and divided randomly into two equal groups (n = 9) based on the technique of caries removal: group 1 – selective (SE), and group 2 – stepwise (SW) caries removal techniques.

Randomization processes and blinding

Patients were randomly divided into SE or SW groups by utilizing sealed, consecutively numbered envelopes, opened at the time of procedure and containing the method of treatment, i.e., SW or SE. Since the main researcher (MAR) was aware of the type of decaying dentin excavation, blinding was not possible. The assessor (who was not involved in procedures), and participants were blinded to treatment allocation. In order to maintain the method of treatment anonymous, identical restorative substance was applied in both groups.

Preparation of nano-bioactive glass-ionomer

In this investigation, conventional GIC was employed (Medicem). A digital electronic sensitive balance (Sigma-Aldrich, Germany) was used to weigh N-BAG and GIC powders. In a sealed capsule, 10 grams of nano-BAG and 50 grams of GIC powders were blended for two minutes in a high-speed amalgamator (De Gotzen Amalgamator Softly 8, Italy; mixing frequency 4000 RPM/min ± 50 RPM/min) to create a homogenous mixture of 20% N-BAG/GIC. The 20% N-BAG/GIC powder was mixed with polyacrylic acid (PAA) liquid of GIC according to the manufacturer’s instruction just before restoration [13].

First treatment visit

Pre-operative examinations
The main researcher (MAR) verified the eligibility criteria on the initial visit. After a visual examination, pulp vitality was evaluated with an electric pulp tester. Using the digital sensor, occlusal and retro-alveolar structures radiographs were taken to determine the depth of carious lesion, and to confirm the extension to the inner third of dentin (D3).
Clinical procedures
All procedural steps were done by the main researcher (MAR). The following method was applied for participants in both groups: anesthetic and rubber dam isolation of region to be operated, entry to the tooth decay was performed using carbide round bur (HM 1, size #018, Meisinger, Germany) with a high-speed contra-angle handpiece. A sharp, double-ended excavator was employed to selectively remove soft carious dentin. A low-speed fissure bur (HM 21, size #012, Meisinger, Germany) was used for caries removal along the margins, revealing peripheral healthy dentin. A minimum of 1.5 to 2 mm of healthy dental tissue was maintained around the periphery to ensure strong bond at the restoration margins. Final soft carious dentin layer was left on the floor of the pulp to avoid pulp exposure, evaluated by visual and tactile examinations. The last layer of carious dentin showed increased resistance to excavation. Moreover, it appeared less discolored or more similar in color to healthy dentin [19]. Additionally, an occlusal radiographic examination was done using a digital sensor to assess the remaining caries. Subsequently, the cavity was washed with air and water spray, and lightly dried with cotton, followed by the application of a highly viscous mixture of N-BAG/ GIC powder and PAA liquid. The mixture was packed into full cavity depth, and time was given to harden (5 minutes) [20], as N-BAG/ GIC liner and temporary filling. A protective coat (GC Equia Coat, GC) was applied and light cured for 20 seconds (according to the manufacturer’s instruction) using LED light curing unit (Elipar S10, 3M ESPE, St. Paul, Minnesota, USA).

Baseline (1 week) evaluation

One week later, all participants in both groups were phoned for baseline evaluation. Dental assessments with electrical pulp testing, percussion sensitivity testing, mobility testing, and digital radiography were performed again (as for pre-operative examinations). The assessor, who was not participating in the treatment at any appointments, gathered all data. In case of detecting any sign of failure, such as irreversible pulpitis, pulp necrosis, or periapical lesion, participants were sent to relevant departments for root canal treatment [16]. If a tooth was determined to be continued in the study, it was assigned to the appropriate treatment according to previous randomization.

Second visit treatment’s procedures (3-month follow-up)

After three months, all participants in both groups were phoned for a follow-up and second treatment session. The assessor performed dental assessments as for baseline to determine any sign of failure. Subsequently, the main researcher (MAR), who conducted all the operation steps, repeated the isolation and anesthetic as for the first treatment visit.
In the selective removal group (SE), the interim restoration was reduced pulpally, keeping around 2 mm of thickness to provide a base for final restoration. Cavities were etched using a 15-second selective enamel etching technique, and one coat of the universal adhesive was applied to the whole cavity. Ultimately, the manufacturer’s directions were followed for incrementally placing the nano-filled composite resin restoration, not exceeding 2 mm in thickness.
In the stepwise removal group (SW), the carious lesion was re-entered by completely removing temporary restoration and remaining carious lesion until firm dentin was left behind. Subsequently, the N-BAG/ GIC mixture was re-applied as a liner and base of 2 mm. Final composite resin restoration was applied in the same way as for the SE technique.

Outcomes and follow-up

The main outcome was to determine the success and failure rates of the caries removal approach, with clinical and radiographical assessments conducted individually by a single assessor at four distinct intervals of follow-up: baseline (1 week), 3 months, 12 months, and 18 months. Pulp vitality was the main success metric, and it was based on various features, including lack of discomfort upon palpation and percussion, abnormal reading during electrical testing, no creation of fistula or edema, lack of periapical pathosis (radiography evaluation), and abnormal mobility of the tooth. A failure was considered if a minimum of a single of the above symptoms indicated pulp necrosis [21].

Statistical analysis

Statistical analysis was carried out with SPSS Statistics, version 21. Normality of distribution was evaluated using Kolmogorov-Smirnov test. Efficacy of both techniques was distinguished with one-way ANOVA test at various intervals of follow-up. Tukey’s post hoc test was utilized for multiple contrasts within the two groups and compared at two intervals. Significance level was set at p < 0.05.

Results

Baseline data (patient allocation and follow-up)

A total of 18 patients, with a mean age of 30.2 years, participated in the current clinical study. 61.11% of patients were females (n = 11) and 38.89% were males (n = 7), with a mean age of 30.2 years for both genders. Molar teeth with deep carious lesions were treated (18 teeth included in this study). There was no loss to follow-up (Figure 1).

Success and failure rates results from the selective and stepwise caries removal techniques

The outcomes for both techniques demonstrated that after baseline (1 week) and 3 months, there were no indications of clinical or radiological failures, and the success rates were 100%. However, the selective caries removal technique showed success rates of 88.89% and 77.78% after 12 and 18 months, respectively. Nevertheless, 11.11% of cases demonstrated failure (1 case with pulp necrosis) after 12 months compared with 22.22% at 18 months (1 more case with pulp necrosis). No significant variation existed among each of the follow-up intervals according to c2 test (p = 0.261) (Table 2, Figure 2). Moreover, after 12 and 18 months, the stepwise caries removal technique revealed success rates of 77.78% and 66.67%, respectively. While 22.22% of cases displayed failure after 12 months (2 cases with pulpitis) compared with 33.33% after 18 months (1 more case with pulp necrosis). No significant variation was observed among each of the follow-up intervals according to c2 test (p = 0.099) (Table 3, Figure 3).

Comparison between the selective and stepwise caries removal techniques at different follow-up intervals

Regarding the technique, c2 test demonstrated that there was no difference among both tested groups at baseline and 3 months. Moreover, at 12 and 18 months, the results showed that there was a statistically non-significant difference between both groups (p = 0.5270 and p = 0.0815, respectively). The selective caries removal technique showed higher success rates than the stepwise caries removal technique (Table 4, Figure 4).

Discussion

Deep caries can be identified with clinical or radiographic methods. International caries detection and assessment system (ICDAS) specifies the most severe carious lesion as “extensive” with code 6 on a scale of 1 to 6. Such a lesion is deep and wide, and involves at least half of the tooth surface or reaching the pulp [22]. However, it is challenging to evaluate the thickness of remaining dentin and caries depth in clinical setting [23]. Radiographically, as defined by the International Caries Consensus Collaboration in 2016, deep carious lesions refer to teeth that are destructed to 1/3 or 1/4 of the dentin close to the dental pulp, or are in danger of pulp exposure [7].
A radiopaque zone between the pulp and caries lesion must be radiographically proven for stepwise caries removal to be used in patients with deep caries. This radiopaque zone shows that the pulp is not affected by the caries, preventing germs from reaching the pulp [3]. To mitigate the increased risk of failure associated with teeth undergoing multi-surface restorations, a class I cavity that had just occlusal surface caries was chosen for this clinical investigation [24]. Similarly, the selective and stepwise caries removal techniques were selected in this study, as the two alternative methods have been suggested to reduce the risk of pulp exposure and post-operative pulpal complications [25].
In fact, dental caries is infectious multi-factorial disease that can be effectively treated through biomimetic re-mineralization of non-infected carious dentin. However, micro-gaps and bacteria below restorations can lead to micro-leakage and secondary caries, requiring utilization of antibacterial re-mineralizing agents [26]. There is growing interest in using bioactive materials in dentistry to re-mineralize caries-affected dentin. N-BAG has shown a promise in promoting dentin re-minerali­zation and anti­bacterial activity, being possible effective treatment option for preventing and conserving carious lesions [27].
The easy displacement of N-BAG particles in oral environment necessitates using an appropriate carrier or matrix material, such as GIC [28]. Fluoride in GIC has a cariostatic effect by inhibiting S. mutans growth, preventing caries development, and thereby limiting the production of acids [29]. Furthermore, glycolysis is the main metabolic mechanism of saccharolytic bacteria. Fluoride’s antimicrobial activity is attributed to its ability to inhibit glycolysis, affect the disintegration and assimilation of polysaccharides, and impede the bacterium cells’ pH equilibrium [30].
Despite the benefits of GICs, they are susceptible to early moisture sensitivity, which can be reduced with resin coatings, such as varnishes, adhesive systems, and light-cured protective coatings. They shield the surface of GIC from moisture, separate it from saliva contamination, occlude cracks and porosity, and reinforce its strength during material maturation [31].
A recent trend in simplifying and streamlining adhesive systems is employing universal adhesives in either etch-and-rinse or self-etch modes [32]. Total-etch adhesive systems have been found to cause persistent inflammatory reactions, delay in pulpal healing, and inability to form dentin bridge. Nonetheless, self-etching adhesive systems may be helpful and safe when used on the dentin, applied to human pulp [33]. Moreover, the bond performance between the composite adhesive system and GIC was shown to be influenced by the type of adhesive system, and the self-etch mode produced favorable results [34]. The selective enamel etching approach was found to be an efficient technique for class I composite restorations, promoting better marginal integrity for enamel [35]. Furthermore, in a two-visit procedure, it is crucial that temporary restoration applied during treatments effectively seals the cavity. It might be appropriate to use an acceptable quality restoration, such as glass-ionomer [6]. Therefore, the self-etching mode was chosen in this present clinical study to decrease the expected inflammatory reactions of total-etch adhesive, especially in the case of deep carious lesions (as in the present study).
The 3-month recall period was selected for both techniques to decrease the risk of failure of the temporary restoration or patient drop-out [16]. Besides, the bond performance between the adhesive system and GIC was influenced by restoration time, and delayed final restoration in the selective removal technique was better than immediate restoration [34]. While in the stepwise removal technique, the critical period for the success of the capping procedure seems to be within the first 3 months. Therefore, the 3-month time was considered adequate for the effect of liner to occurs, and for the possibility of tertiary dentin formation [36].
The present findings showed no statistically signifi­cant difference among various follow-up intervals in the selective and stepwise caries removal techniques. This might be due to the short time intervals between different follow-ups; although, there was a decrease in the success rates by increasing follow-up intervals.
In the selective caries removal technique, the disruption of biofilm affects bacterial adhesion, metabolism, and reproduction, resulting in decreasing of acid generation that causes de-mineralization and pulp cytotoxi­city. Once the dentin is completely isolated from the oral environment, the residual bacteria do not support caries advancement [37]. These findings are in line with those of Singhal et al. [15], who stated that partial caries removal and tooth sealing are correlated with significant decrease in bacterial proliferation and arresting of lesion progression.
In the stepwise caries removal technique, the initial phase seeks to change the caries activity into an environment that is ceased or moving slowly. In a clinical setting, the presence of carious dentin during two appointments transforms active deep caries setting, from a soft, discolored, and moist structure to carious dentin that is darker, tougher, and drier. Therefore, during the second phase, the residual carious dentin becomes simpler to remove, devoid of exposing the pulp [8].
The results in the current study revealed that there was no statistically significant difference in the number of failures for both techniques. This could be related to the microbial burden in the residual infected dentin, being decreased by sealing of the carious dentin tissues due to limiting the inflow of external nutrients by separating the mouth cavity’s caries activity in the partial caries removal technique [38]. The current outcomes agree with those of previous study by Labib et al. [16], who reported no significant difference in the success rates among selective and stepwise caries removal techniques during 1 year of follow-up.
Furthermore, the favorable results of utilizing selective and stepwise caries removal techniques are due to the encouragement of re-mineralization of the residual de-mineralized dentin, and the formation of tertiary or sclerotic dentin [37]. Less porous than original dentin, sclerotic dentin shields pulp from harmful substances produced by microbial metabolism, allowing the pulp to heal and regulate inflammatory response to caries. This was demonstrated through the lack of periapical lesions in radiographic assessment as well as the absence of pain in most subjects assessed over the course of 18 months [39]. Additionally, the BAG in N-BAG/GIC liner possesses antibacterial effects and play a crucial role in decreasing the amount of cariogenic bacteria [40]. BAG’s antibacterial properties are attributed to its high rate of ion release, which increases local pH from 7 to 10, creating an alkaline micro-environment [41].
The present findings are in line with those of Xu et al. study [42], who observed that the BAG exhibits antibacterial properties against S. mutans bacteria by releasing alkaline ions (Na and Ca), which elevate the solution’s pH, a crucial factor in micro-organism destruction. In addition, treatment with the N-BAG/GIC liner can re-mineralize dentin caries, as incorporation of BAG into GIC enhance its re-mineralization property [13]. The components in N-BAG, including calcium, sodium, phosphorus, and silicon oxides, exhibit surface activity and bioactivity due to their ability to form bone-like apatite [43]. Furthermore, GICs release ions, such as fluoride, calcium, and phosphate, positively impacting the biological environment, re-mineralizing tooth structure, and inhibiting bacterial growth [44]. The present study corresponds to Wu et al. [45], who assumed that bioactive glass shows potential for dentin carious lesion re-mineralization, and might serve as a treatment option for managing deep caries.
Evidently, fluoride from GIC inhibits de-mineralization and enhances re-mineralization by replacing HAp’s hydroxyl ion and forming fluorapatite on the teeth’s surface, which enhances acid resistance. The development of this ability is facilitated by sufficient calcium and phosphate ions, which enhance re-mineralization [13]. This agree with a recent systematic review by Ghilotti et al. [46], supporting the application of GICs as restoration following partial caries removal, due to their ability to re-mineralize the affected dentin.
Our findings demonstrated that at 12 and 18 months, the selective caries removal technique exhibited higher success rates (88.89% and 77.78%, respectively) compared with the stepwise caries removal technique (77.78% and 66.67%, respectively), although the difference was not statistically significant. This may be due to the mechanical techniques used to re-open the cavity and remove carious dentin in the stepwise caries removal technique, which may harm the pulp, increasing the risk of pulp exposure, and potential failure [47]. While the selective caries removal technique is a single-phase, keeping much of the carious dentin, decreases the risk of pulp exposure and encourages its physiological response [48]. The current result is in line with Abdelhamid et al. [38], who reported that the stepwise caries removal technique revealed more exposure risk than the selective caries removal technique during the entire second phase of excavation. In comparison with the single-visit selective caries removal technique, the stepwise caries removal technique increased the likelihood of pulp exposure.
The present study has limitations, which need be acknowledged. Firstly, the study group consisted of a small sample size, with only 9 patients (9 teeth) for each caries removal approach. This limited sample size could affect generalizability of the findings. Additionally, the wide age range of the participants (from 18 to 50 years) introduces variability in pulp response due to age-related differences. These limitations highlight the need for further research with larger sample sizes and more specific age ranges to validate the current findings.

Conclusions

Within the limitations of this in vivo study, it can be concluded that nano-bioactive glass-ionomer can be used after selective and stepwise caries removal techniques as a favorable dentin dressing material, and can halt carious dentin lesions for 18 months. Moreover, teeth sealing and partial caries excavation for 18 months lead to stopping lesion progression. Therefore, the entire dentin caries excavation in the second visit is not necessary.

Disclosures

1. Institutional review board statement: The study was approved by the the Ethical Committee of the Al-Azhar University Faculty of Dental Medicine’s.
2. Assistance with the article: None.
3. Financial support and sponsorship: None.
4. Conflicts of interest: The authors declare no potential conflicts of interest concerning the research, authorship, and/or publication of this article.

References