Evaluation of direct pulp capping in carious primary molars: a 12-month randomized controlled clinical trial

Introduction

Direct pulp capping (DPC) of primary teeth is one of the vital pulp therapy (VPT) techniques, but is avoided by many clinicians [1] due to increased chance of clinical failure, such as internal resorption [2]. Also, pulpal inflammation and periapical bone loss have been reported [3]. However, with the arrival of newer bio- active agents, such as calcium silicate-based materials, DPC has been shown improved success rates and less complications [4].
Preservation of pulp vitality using DPC is particularly important in pediatric dentistry, as it can be less invasive treatment of choice in some instances, avoiding more complex, time-consuming, and costly procedures, such as pulpotomy or pulpectomy [5].
Direct pulp capping is “the therapeutic method for teeth with provoked pain of short duration relieved upon the removal of the stimulus and without signs or symptoms of irreversible pulpitis” [6]. This procedure includes the application of a bio-compatible radiopaque capping material, such as calcium hydroxide (CH) or mineral trioxide aggregate (MTA) on the pulp exposure [7, 8] to encourage healing by cellular re-organization and a reparative dentine-like formation over the exposure site, with the preservation of integrity and vitality of the pulp [9]. The tooth is then restored with a material that hermetically seals the cavity. For several decades, calcium hydroxide has been considered the gold standard of DPC materials. It has excellent anti-bacterial properties and a high pH that stimulates odontoblasts to initiate the production of tertiary dentin and preservation of pulp vitality [10].
MTA has similar anti-bacterial and bio-active properties [11], and allows for a better connection to the dentin providing much better long-term seal. Moreover, MTA reacts with fluids containing phosphates producing hydroxyapatite precipitate [12]. MTA stimulates the release of cytokines from bone cells, which actively promote the formation of hard tissue [13].
Frequently, pediatric dentists are confronted with deep carious lesions in primary teeth leading to pulp exposure upon excavation. Decision to proceed with a less invasive procedure of DPC is challenging, especially due to the lack of high-quality evidence in literature supporting its use for the management of deep carious lesions in primary teeth [14].

Objectives

The aim of the current study was to evaluate the clini­cal and radiographic outcomes of direct pulp capping using mineral trioxide aggregate (MTA) or hard-setting calcium hydroxide (Dycal) in carious exposed primary molars, and to assess the effect of the location of pulp exposure on this outcome.

Material and methods

Ethical consideration

The study protocol was approved by the Institutional Ethical Committee of the Faculty of Dentistry, Mansoura University, Egypt (code No.: A01071221) before starting the study. Written consent was obtained from parents or guardians of children after a brief description about the study details, including risks and benefits. Furthermore, each child’s acceptance was obtained before starting the procedures. Data of patients were confidentially protected with special codes. All procedures of the study were performed in accordance with the Code of Medical Ethics of the World Medical Association (Declaration of Helsinki) for experiments involving humans.

Study design and setting

This parallel study was carried out on 52 primary molars in 32 children, aged 4-7 years. Each molar demonstrated a deep carious lesion, with vital pulp requiring vital pulp therapy. Teeth were randomly allocated into two equal groups as per to the capping agent: group 1 (MTA) and group 2 (Dycal). According to dia­gnostic and inclusion criteria, children were chosen from the Pediatric Dental Clinic at Faculty of Dentistry, Mansoura University, between January 1, 2022 and June 6, 2023. The study was registered at Clinical Trials.gov with ID No. of NCT05530954 on September 6, 2022. The study was reported in line with the CONSORT guidelines [15].

Sample size calculation

A priori power analysis was employed for calculating the sample size. Power level of 80% and significance level of 0.05 were set, with a 70% success rate anticipated for treatment with Dycal compared with 100% with MTA, according to previous studies by Uluosy et al. [16] and Songsiripradubbon et al. [17]. The total expected sample size for each material was determined to be 22. To increase the study power due to possible dropouts, the number of teeth per group for each material was increased to 26.

Eligibility criteria

Clinical inclusion criteria [18]: 1) cooperative children and compliant parents; 2) healthy children with no systemic diseases; 3) primary molars with deep occlusal or proximal carious lesions, according to international caries detection and assessment system (ICDAS 5, ICDAS 6) [19], which upon excavation have led to pathologic pulp exposure (less than 1 mm in diameter), but without signs or symptoms of irreversible pulpitis or necrosis, e.g., history of spontaneous or severe lingering pain, pain with percussion, abnormal mobility, swelling, or presence of a sinus tract [18].
Radiographic inclusion criteria [18]: 1) deep carious lesion approximating the pulp; 2) intact lamina dura, with no widening in periodontal ligament space or radiolucency at periapical or inter-radicular region; 3) lack of pathological internal/ external root resorption, obliteration of pulp or root canal, or pulpal calcifications.

Patient recruitment

Of the treated children (n = 200), 62 were excluded due to not meeting inclusion criteria. In addition, 72 children were excluded due to unexposed pulp as well as 34 children with prolonged bleeding after pulp exposure. Using simple randomization technique, the included molars (n = 52) were allocated randomly into two main groups (26 cases in each group), according to capping material used: group 1 (MTA) and group 2 (Dycal). According to the site of pulp exposure, each group was sub-divided into two sub-groups: group A (pulpal) and group B (axial), as shown in Figure 1.

Sequencing and concealment of allocation

Fifty-two sealed opaque envelopes were employed. Computerized random sequence generator (www.random.org) with 1 : 1 allocation ratio (n = 26 per group, n = 52 in total) was used, and numbers were well-organized into 2 columns. Regarding capping material used (MTA or Dycal), the results were copied to two groups. Each piece of paper was sealed and placed in an envelope. The child was allowed to randomly choose sealed opaque envelope, and was allocated into a group. Children with more than one carious tooth were allowed to pick up one envelope for each tooth.

Protocol of clinical procedures

All clinical procedures were carried out by a well- trained principal investigator after assessment and final diagnosis for each molar established by two trained and calibrated clinicians. Children having carious primary molars presented with a pre-treatment pulpal diagnosis of a normal pulp, or reversible pulpitis along with the possibility of a direct pulp exposure due to caries excavation, were candidates for the study. Pre-operative radiographs were obtained [11, 12] in order to determine the proximity of caries to the pulp and the location of exposure as well as to exclude any signs of irreversible pulpitis or necrosis. Child management was established by communication. Topical anesthetic gel was applied, and local anesthesia was administrated with conventional standard techniques using infiltration technique for maxillary molars and inferior alveolar nerve block technique for mandibular molars.
Teeth were isolated using rubber dam. The gross carious lesion and undermined enamel were removed mechanically by sterile high-speed round bur, with copious air-water spray coolant and intermittent cutting to avoid heat generation and pulpal irritation. High-speed round bur was replaced by another sterile unit after significant removal of caries, and a sharp sterile spoon excavator was used for soft carious dentin excavation [20]. Caries removal stopped when the firm dentin was reached and resisted hand excavation with the sharp dental spoon. In cases where caries excavation did not result in pathologic pulp exposure, a glass ionomer restoration was provided, and the tooth was excluded from the study. In cases where the pulp tissue was exposed during final caries removal, hemostasis was attained by irrigating the cavity with sterile saline solution for up to 4 minutes till bleeding was controlled. If bleeding persisted, the tooth was excluded from the research, and pulpotomy was performed. Only teeth, in which the exposed pulp was less than 1 mm in diameter with controlled hemostasis [21] were candidates for DPC. After saline application, the pulp exposure was irrigated with 17% ethylenediaminetetraacetic acid (EDTA) solution for 1 minute (Prevest Direct, India) [22]. The tooth was randomly allocated to one of the two experimental groups: either group 1 (DPC with fast set MTA paste, Bio MTA, Cerkamed, Poland) or group 2 (DPC with Dycal, Promedica Urbical, Germany). According to the site of exposure, either on the pulpal wall of occlusal cavity or the axial wall of proximal cavity, the teeth were further allocated to sub-group A (n = 13) with exposure in pulpal floor, or sub-group B (n = 13) with exposure in axial wall of the cavity. After application of the capping material on the exposure site, self-cured glass ionomer restorative material (SDI Riva self-cure, Australia) was directly placed to fill the cavity for all the molars. The tooth was covered by stainless steel crown (Kids stainless steel crown, Shinghung, Seoul, Korea) in the same setting, and post-operative periapical X-ray was taken. Once each group reached 13 molars, the selection of teeth for the study stopped.

Follow-up and evaluation

All patients were re-called for clinical evaluation after 2 weeks to exclude immediate failure. Then, they were followed up clinically and radiographically at 3-, 6-, 9-, and 12-month follow-ups according to criteria in Vafaeia et al. [23] (Figures 2 and 3). The presence of one of the following was considered failure in treatment: spontaneous pain, swelling, sinus tract, sensitivity to percussion, pathological internal or external root resorption, widening of the periodontal ligament space, inter-radicular radiolucency, and periapical lesions. The eva­luation was carried out by two independent clinicians blinded to the treatment. Furthermore, intra-examiner reliability was assessed by observing 10% of participants randomly selected for re-evaluation by the same exami­ner after a specified period. The results showed a high degree of consistency, with a Cohen’s κ coefficient of 0.80 of inter-examiner and intra-examiner reliability [24].

Statistical analysis

Data analysis was done using Statistical Package of Social Science (SPSS) program for Windows (Standard version 26). The normality of data was tested with Shapiro test. Qualitative data were described using numbers and percentages. The association between catego­rical variables was assessed using chi-square test, while Fisher exact test was employed when predictable cell counts were less than 5. Continuous variables were presented as mean ± SD (standard deviation) for normally distributed data using independent t test to compare between two groups. The results were considered significant when p ≤ 0.05.

Results

Out of two-hundred children aged 4 to 7 years, who were seeking operative dental treatment, 32 children with 52 primary molars with a mean age of 5.34 ± 1.32 years, who met the inclusion criteria were included in the study. Both the groups were age-matched, as seen in Table 1 and Figure 1.
No statistically significant differences in the overall success and failure rate were found between the primary first molars and primary second molars (p = 0.08). In addition, no statistically significant differences were reported between the maxillary primary molars and mandibular primary molars (p = 0.947).
Regarding age as a factor influencing treatment outcomes, it was found that among 4-years-old children, 2 (8%) failed out of 25 cases. For age 5, it was reported that 1 out of 4 cases of the same age failed (25%). Similar failure occurred among 6-year-old children: 1 out of 5 cases (20%). While for 7-years-old children, 9 out of 14 cases failed (64.3%).
Drop out occurred due to loss of interest or travelling to another city. All failed cases were managed by either root canal treatment, or extraction and construction of space maintainer, as needed. After one year, the clini­cal and radiographic success DPC rates were 87.5% (42 out of 52 molars) and 75% (36 out of 52 molars), respectively. The clinical and radiographic success rates among all studied groups at different follow-up periods are reported in Table 2. The MTA group with pulp exposure at pulpal site showed 100% (11 out of 11 molars) overall success rate after 12 months of follow-up. While in the axial pulp exposure group, the overall success rate was 46.2% (7 out of 13 molars), with a statistically significant difference (p = 0.004). In the axial MTA group (1B) after 12-month follow-up, 6 cases (54.5%) demonstrated failure with pathological external root resorption, 1 case (9.1%) with internal root resorption, and 1 child (9.1%) presented with PDL widening, as seen in Table 3. However, not all patients with patholo­gical external root resorption showed increased mobility, as in some cases the resorption was minimal and not involving the whole root length. Furthermore, in some cases, the resorption was presented only in one root.
Regarding the Dycal group, the overall success rate was reported 75% (n = 9) after 12-month follow-up for both axial and pulpal exposure, with no statistically significant differences (p = 1). In the pulpal Dycal (2A) sub-group after 12-month follow-up, 3 cases (25%) showed pathological external root resorption, and 1 case (8.3%) was observed with PDL widening. While in the axial Dycal (2B) sub-group, 5 cases (41.6%) demonstrated pathological external root resorption, 1 case (9.1%) showed internal root resorption, 1 case (9.1%) inter-radicular radiolucency, and 1 case (9.1%) presented with PDL widening, as seen in Table 3.
There were no significant differences between the  MTA and Dycal groups, both pulpally and axially (p > 0.05), as presented in Table 4. Moreover, there were significant differences between the axial and pulpal MTA sub-groups (p = 0.004), while no significant differences were noted between the pulpal and axial Dycal sub-groups (p = 1), as seen in Table 4. Moreover, there were no statistically significant differences in the overall success rate between the MTA and Dycal groups (p > 0.05).

Discussion

Direct pulp capping as a VPT in the primary teeth has received limited acceptance from the dental profession due to lower success rate [14]. However, a recent systematic review [4] confirmed that various new biologically and compatible agents with promising success rates are currently available for pediatric dentists. In the current study, primary teeth with carious pulp exposure were included, which conflicts with Fuks [25], who did not recommend DPC in pulp exposure during caries excavation of primary teeth. However, Fallahinejad- Ghajari et al. [26] and Aminabadi et al. [9] reported that DPC in primary teeth, where carious pulp exposure is surrounded by sound dentin, seems to ensure successful outcomes without the need for more invasive therapies, such as pulpotomy, due to the predictable healing capability of primary pulp cells.
In this study, complete caries removal was done, and that was in agreement with a multinational survey from 16 countries and meta-analysis (2023) that preferred complete caries removal over partial or selective caries removal [27].
The children age varied from four to seven years to ensure enough root length of selected primary molars, and to avoid the presence of physiologic root resorption. In addition, this age range is the most reasonable for children cooperation, which is in accordance with Vafaei et al. [23] and Fallahinejad-Ghajari et al. [26]. Failures were observed more often in older children. This may be due to the age-related changes in the pulp, which is in correlation with Komatsu et al. [28], who measured pulpal blood flow (PBF) using laser Doppler blood flowmetry in primary teeth, and found that PBF decreased with age. Failure cases were observed more in the first primary molars, and no statistically significant differences in the overall failure and success rates between the first and the second primary molars were observed. However, this may be attributed to the morphological differences between the first and the second primary molars. The first primary molar has a smaller pulp chamber than the second one; therefore, the potential for pulpal healing might increase in molars with more pulpal tissue present.
In this study, peripheral infected soft dentin was carefully removed, and the case selection was restricted to less than 1 mm exposure size with controlled hemostasis.
Since accurate diagnosis of inflammatory status of the pulp is considered the key factor for expecting healing capacity and outcome of vital pulp treatment in primary teeth [6], in this study, pulpal bleeding was considered the final determining clinical marker for pulpal inflammation extension, apart from all other inclusion criteria [29].
Hemostasis time wide-ranged in different vital pulp therapy research, from 1-2 minutes up to 10 minutes [30]. In the present study, to ensure optimal pulp condition, the time till hemostasis was limited to 4 minutes, even though Zanini et al. [30] in their systematic review reported that “the time did not play an important role in the determination of dental pulp status”.
Hemostasis was achieved by continuous saline irrigation to avoid formation of blood clot, as it is considered a thick fibro purulent membrane over the pulp wound that could compromise the contact between the capping material and the pulp, thereby reducing its effectiveness [31-33]. Blood clot formation could be susceptible to secondary infection, and finally lead to complete loss of pulp vitality [32].
EDTA solution was applied for direct passive irrigation of exposure site after hemostasis was achieved, as it has been shown to release bio-active growth factors from the dentin [34], thus stimulating secretion of matrix, differentiation of odontoblasts, and formation of tertiary dentin. Conditioning of the dentin with EDTA can also encourage the adhesion, migration, and differentiation of dental pulp stem cells [35]. Moreover, Finnegan et al. [36] reported that EDTA was shown to have anti- microbial effects on Gram-positive and Gram-negative bacteria, yeasts, and fungi. In addition, EDTA has been shown to induce antioxidants and anti-inflammatory activities [37], unlike sodium hypochlorite that can kill stem cells of the dental pulpal [35].
In this study, self-cure glass ionomer was used as a core material before SSC placement. This comes in agreement with a study by Memarpour et al. [38], who employed different restorative materials to compare the marginal adaptation under SSC. They reported that cavity restoration with glass ionomer and amalgam showed the least micro-leakage and material loss compared with other materials.
All teeth were covered by stainless steel crowns as a final restoration to maintain coronal seal and improve success rate. The teeth were restored during a single-visit to prevent micro-leakage and protect bio-material layer. To our knowledge, no clinical study involving primary teeth evaluated clinical and radiographic success of DPC based on the location of pulp exposure, either pulpally or axially in primary molars.
In the current research, the evaluation of the treatment success was dependent on clinical and radiographic evaluation in the absence of histological evaluation, and this has some limitations. As the histological reactions of the pulp towards DPC may show normal odontoblasts, irregular odontoblasts, intra-pulpal calcifications, dentinal bridges, internal resorption, inflammatory infiltrations, and pulp necrosis [39], that are sufficient to accurately indicate treatment success or failure. That is line with Sanusia and Al-Bataynehbb [40].
In the present study, the overall success rate of DPC in the MTA group with pulp exposure at pulpal site after 12 months of follow-up was 100%. This is in accordance with Tuna and Ölmez [7], who recorded 100% success rate as well as with Fallahinejad et al. [41], Aminabadi et al. [9], Erfamarast et al. [42], and Vafaei et al. [23], who reported 95%, 93.8%, 94.6%, and 90.2% success rates, respectively.
The overall success rate in the Dycal group with pulpal wall exposure was 75%. This is in line with Ulusoy et al. [16] and Songsiripradubboon et al. [17], who reported 70.58% and 70% radiographic success rates, respectively.
The 100% success rate of DPC with MTA on the pulpal site comes also in accordance with Haghgoo and Ahmadvand [43]. The clinical success of MTA may also be related to the superficial formation of apatite layer in physiological-like solution [44]. This superficial apatite layer may provide an appropriate surface for cells to adhere and differentiate into odontoblasts [45] as well as to stimulate the formation of dentin bridge after DPC [46]. This is in accordance with a meta-analysis by Li et al. [47], where higher success rates for MTA were reported, and less inflammatory pulpal response and more predictable hard dentin bridge formation were shown when compared with CH.
Regarding DPC of axial wall pulp exposure, the present study reported a 12-month overall success rate of 46.2% and 75% for MTA and Dycal, respectively, with no statistically significant differences (p > 0.05). An increased failure rate in the MTA group with axial pulp exposure might be attributed to the sandy nature of material, despite using fast set MTA that initially sets within 4 minutes, according to the manufacturer’s instruction. Dycal is a fast set calcium hydroxide that hardens quickly and adheres to the cavity wall allowing placement of the restoration immediately. Unlike MTA, which might have been displaced from the exposure site during the restoration placement, especially when the exposure site was axially placed.
It is also noteworthy to mention that most failure cases in the MTA group with axial wall pulp exposure presented with pathological external root resorption (6 cases, 54.5%), which was detected as the sign of failure manifested clinically as increased mobility. This might lead to the assumption that this failure may have occurred due to pulp degeneration and infection, because of either a pre-existing irreversible pulpitis that was missed in the initial diagnosis, or it was due to microbial leakage along the deep gingival margin of the proximal cavity that might had extended deeper gingivally than the stainless steel crown margin.
In the present study, however, there were no statistically significant differences in the overall success rate between the MTA and Dycal groups (p > 0.05). This comes in accordance with ElSebaai et al. [48] and Chatzidimitriou et al. [49].
Although there may be a high-risk of pathological resorption after DPC in primary molars, the current results demonstrated that DPC with accurate case selection and a bio-compatible capping agent with proper application technique might be considered as a successful conservative treatment [50].

Limitations

The relatively small sample size (n = 52) and difficulty in accurate pulp status diagnosis clinically together with the short follow-up period of only 12 months may be reflected as limitations in the present study, which could be considered as preliminary research. Therefore, more clinical studies with larger sample size and longer follow-up, in addition to histological evaluations, are needed to reach the most accurate conclusion for the success of various capping materials in carious pulp exposure.

Conclusions

Within the limitations of this study, it can be concluded that after 12-month follow-up, both MTA and hard-setting calcium hydroxide (Dycal) showed comparable outcome results as direct pulp capping agents in carious primary molars. The site of the exposure did not have a significant effect on the success of DPC with calcium hydroxide (Dycal). However, DPC exposures occurring on the axial wall of the cavities using MTA had a lower success rate.

Disclosures

1. Institutional review board statement: The study was approved by the Institutional Ethical Committee of the Faculty of Dentistry, Mansoura University, Egypt (code No.: A01071221).
2. Assistance with the article: We would like to express our gratitude to Dr. Doaa Shokry, Assistant Professor of the Public Health and Preventive Medicine Department, Faculty of Medicine, Mansoura University, Egypt, for her assistance in the study’s statistics.
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