The impact of cervical margin relocation on periodontal health using flowable resin composite and resin-modified glass ionomer: a one-year clinical trial

INTRODUCTION

Several technical factors, including esthetics, margin accuracy, occlusion function, and vitality conservation, can influence the clinical outcome of restorative denti­stry [1]. Due to the advancements in adhesive science and contemporary composite resin technologies, it is feasible to restore badly damaged teeth and minimize dental flaws utilizing direct composite resin mate­rials [2]. Sub-gingival caries and improper/restorative cervical margins can affect the health of periodontal tissues. Sub-gingival restoration margins can negatively impact the periodontal health’s outcome, and cause a disturbance in balance between periodontal tissue and bacterial colonies, potentially leading to gingivitis, bleeding on probing, and periodontal pocket formation [3]. When restoring extended cavities that reach beyond the cemento-enamel junction (CEJ), biological and technological operational issues might arise [4]. The term, “biological problems”, describes potential violations of the biological width, which calls for a minimum of 3 mm to separate the alveo­lar crest from restorative margins. Challenges in technical procedures are associated with teeth preparation, creating impressions, adhesively cementing restoration (in the case of indirect restoration), and finishing and polishing in sub-gingival areas [5, 6].
Cervical margin relocation (CMR) is a technique that elevates a sub-gingival cervical cavity to a supra-gingival level using a composite layer, addressing various issues, such as impression difficulties, margin isolation with a rubber dam, and indirect restoration cementation management [7]. Crown lengthening procedures, on the other hand, can alter gingival tissue appearance, and lead to gingival recession and root sensitivity [8]. To avoid these complications, CMR was introduced as a technique to reposition the edge of restoration supra-gingivally [9]. Moreover, as a substitute for surgical crown lengthening, CMR provides an opportunity to move deep proximal borders in steps to elevate cavity boundaries for either direct or indirect restorations [10].Establishing a base of flowable or direct resin composite is the first step in raising the margin over CEJ, while in the second step, the dentist might choose to apply an indirect or direct restoration based on the preferred restoration within better clinical circumstances [11].
Although the CMR treatment is a well-tolerated restorative therapy, randomized clinical studies are required to confirm its efficiency scientifically and therapeuti­cally [12]. Healthy periodontal tissues can be estimated via measuring the depth of probing pocket to be below or equivalent to 4 mm, with no bleeding when probing. Therefore, it is important to emphasize that the biolo­gical breadth of the alveolar bone and the cervical side of the inter-proximal composite box must both be preserved [13].

OBJECTIVES

The aim of the current trial was to comparatively evaluate the impact of CMR on periodontal health using flowable resin composite and resin-modified glass ionomer (RMGI) over one year of clinical follow-up. The null hypothesis was that there would be no statistically significant difference among the flowable resin composite and RMGI after one year pos-treatment in the mean ranks of gingival index.

MATERIAL AND METHODS

Material

Materials utilized in this study are shown in Table 1.

Methods: Study setting and ethical consideration

This randomized clinical trial was conducted at the Faculty of Dental Medicine, Al-Azhar University, Cairo, Egypt. Adult patients were recruited from outpatient clinics of the Department of Operative Dentistry. The study protocol was approved by the Research Ethics Committee (permission number: 157/167/08/06/19). All participants provided informed consent in their native language before study commencement.

Sample size calculation

Based on a previous clinical study [1], a rise in survival percentage of 0.495, having a significance level (a) of 0.05, may be detected with 80% power using a sample size of 16 in every group (two-tailed). P-value below 0.05 (two-tailed) with 80% power means statistically significant findings. The rise in survival percentage was considered not statistically significant in the remaining 20% of the studies. GraphPad StatMate v. 2.00 was employed for report producing. This number was increased to a total number of 21 in every group to compensate for losses during follow-up.

Eligibility criteria

Inclusion and exclusion criteria of participants
Inclusion criteria: Participants with at least one proximal caries affecting permanent molar teeth extending below CEJ; good oral hygiene; subjects aged 20 to 50 years; no periodontal disease; accepting and submitting the permission form of the current study; participants, who followed and validated clinical dental instructions; and those with a well-managed or tolerable medical conditions.
Exclusion criteria: subjects with uncontrolled para-function habits, such as clenching or nocturnal bruxism; insufficient oral hygiene and high caries index; pregnant or nursing women (hormonal fluctuations may affect their periodontal health [14] independent t-test, Pearson’s correlation coefficients, and multiple regression analysis. Multiple regression analysis revealed that age (β = −0.01, p < 0.001); mental and physical disabilities; systemic diseases, such as diabetes mellitus with complications affecting periodontal condition; and current participation in another study.
Inclusion and exclusion criteria of teeth
Inclusion criteria: Permanent molar teeth with proximal caries extending one millimeter below CEJ; teeth with moderate and medium cavities, and appropriate isolation after cavity preparations.
Exclusion criteria: Tooth mobility, pulp exposure after caries removal, hypoplasia, and amelogenesis imperfecta; teeth with previous restoration, and teeth with proximal caries extending more than one millimeter below CEJ.

Medical and dental history

Baseline data were collected and filled out via a report, which consisted of two charts of medical and dental history for each participant. Before the course of therapy, intra-oral X-rays were taken. Participants’ registrations were done based on their serial numbers, consisting of the first letters of their first and last names and their birthdates, recorded in anonymous reports. In order to facilitate future communication with a patient, complete personal data were saved on a separate page with a serial number.

Allocation and grouping of participants

Sixty-two patients were examined. Ten patients refused to participate in the investigation, and ten participants did not meet inclusion criteria. Finally, 42 patients having at least one proximal caries at their molar (upper or lower) teeth, which extended below the CEJ, and meeting inclusion criteria were enrolled. A total of 42 partici­pants with 42 proximal defects were randomly assigned into two equivalent primary groups (each group, n = 21) according to the type of restorative material used for CMR: group 1 = micro-hybrid flowable resin composite (Dynamic Flow; President Dental, Germany), and group 2 = resin-modified glass ionomer (Riva Light Cure; SDI Limited, Australia).

Randomization

Using a sealed envelope, randomization was perform­ed based on participant’s choice. The process depended on two linked factors, i.e., sequence generation and allocation concealment.
Sequence generation: Patients with at least one sub-gingival proximal caries at their molar teeth were included. Every patient randomly selected a sealed envelope containing written information on the type of restoration (Riva Light Cure or Dynamic Flow).
Allocation concealment mechanism: Patient was provided with individual number code at the setting, with an option to randomly choose an opaque sealed envelope containing designated treatment card (cards were prepared before the study). It was assured that allocation concealment was maintained by withholding the code until the patient was enrolled in the study. Enrollment was completed after all baseline assessments were finished. The sealed envelope containing designated material was opened by an operator at the time of procedure. The assigned tooth number and restorative material were entered into a computer, and all patients’ records were saved.

Blinding and assessors criteria

Double blinding was employed in the current study, meaning that neither patient nor examiners knew the restoration type assigned for CMR. Four dentists were approved and trained as assessors before the ini­tiation of the research to carefully select patients eligible for the investigation. The assessors were not participated in the restoration processes.

Preparation of selected participants

Patients were advised on oral care, and received prophylaxis from a periodontist to achieve ideal gingival health and plaque management.

Teeth preparation

A circumferential stainless-steel matrix fixed on a Tofflemire retainer was used to preserve adjacent molars. A flexible saliva ejector was always utilized to maintain ultimate workflow, avoid spit contamination, and facilitate operating procedures. After local anesthesia, the initial clinical approach was done using diamond bur (846 model; Komet Brasseler, USA) to carefully open caries while keeping enough water cooling. Traditional diamond bur (H1SEM; Komet Brasseler, USA) appropriate for cavity’s size was applied to remove all carious tissues completely, at a slow pace without bevels on the margins. Caries detector (Kuraray Medical Inc., Japan) was employed, and spoon excavators (Dental USA 2231 Excavators 32L, 2-pack) were used to remove all identified carious structures. With a periapical radiograph, the remaining dentin thickness (RDT) was measured, and teeth with RDT of less than 0.5 mm were removed [1].

Teeth isolation

Following cavity preparation, a rubber dam was inserted, and to anchor the rubber dam sub-gingivally, a wax floss ligature was wound around the neighboring molar. Bioclear matrix system (Bioclear Evolve Matrix, Bioclear Corporation, USA) was utilized to restore the teeth’s proximal contacts and anatomical form, and to achieve the best cervical fit.

Cervical margin relocation using micro-hybrid flowable resin composite (Dynamic Flow)

The enamel was first etched using 37% phosphoric acid (selective enamel etch technique) and then, two-step self-etch adhesive (Clearfil SE Bond) was applied according to the manufacturer’s instruction. Polymerization was done for 40 sec using LED light curing device (LED blue light; Carlo De Giorgi, Woodpecker Medical Instrument Co., Italy). Micro-hybrid flowable resin composite (Dynamic Flow) was applied according to the manufacture instruction using a disposable cannula and plunger. The material slowly flowed from the cannula, extruding vertically to the cavity’s bottom surface. The composite was adjusted using a micro-brush, and visual examination was employed to prevent layering exceeding 1 mm. The composite was cured for 20 seconds, and an excess material was removed with a diamond bur (Komet Burs Expert) and high-speed handpiece under water coolant.

Cervical margin relocation using Riva Light Cure (RMGI)

Riva Light Cure (RMGI) was applied according to the manufacturer’s instruction. The capsule was activated by pushing the plunger, inserted in an amalgamator, and triturated for 10 seconds. Subsequently, the capsule was removed and inserted into a Riva applicator. The paste was extruded through a clear nozzle into the cavity and cured for 20 seconds. A water-cooled diamond bur was used to remove an excess material beyond the CEJ and to prevent layering exceeding 1 mm.

Final restoration procedure, finishing and polishing of restorations

As a final direct restoration, both groups were restored using nano-ceramic resin composite (Zenit, Presi­dent Dental, Germany), according to the manufacturer’s instruction. The restorative composite was placed incrementally in 2 mm layers using a gold-plated hand instrument (Miltex, stainless Italy). Every layer was cured for 40 seconds. The proximal surface of restorations underwent an extra 20 seconds of polymerization after the matrix was removed. Final finishing and polishing of restorations were carried out on the same visit by fine stone (Dura White Stone, Shofu, Japan), impregnated with high-quality abrasives and underwater coolant (Figure 1).

Evaluation procedure

Post-procedure, patients were telephoned after one week, six months, and a year, for data collection and evaluation of the periodontal health according to the gingival index, by two experienced operators using visual inspection and probing. Gingival bleeding on the mesial, distal, buccal, and palatal surfaces of every tooth that resulted from inserting a Williams periodontal probe (Nova, United Kingdom) within the pocket was assessed to calculate the participant’s gingival index. Löe and Silness [15] standards were applied as a guide to calculate gingival index scoring as follows: score 0 – lack of inflammation; score 1 – mild inflammation with tiny color and texture changes, and no bleeding upon probing; score 2 – mode­rate inflammation, with bleeding upon probing, sensible glazing, redness, edema, and enlargement; score 3 – severe inflammation, with a predisposition of spontaneous bleeding, and noticeable redness and edema.
The technique of gingival examination: The evaluation of tissue alterations was done using color (deep red versus coral pink), consistency (robust and firm versus edematous or fibrous), comparing rolling versus knife-edge edges of contour as well as bulbous or thickened papilla versus scalloped papilla [16]. Moreover, gingival bleeding was assessed using a Williams periodontal probe, where the gingiva was dried lightly with cotton rolls, and the tip of the probe followed anatomical configuration of the tooth to evaluate the mesial, distal, facial, and lingual surfaces [17].

Participant withdrawal

During the follow-up period, six patients withdrew from the study due to relocation to a different town, including two patients in sixth month and four patients at 1 year. The remaining 36 patients completed all follow-up evaluations. There were 18 patients within each group at the end of the study (1 year). The flow diagram of the trial is displayed in Figure 2.

Data analysis

Statistical analysis was performed with Kruskal-Wallis test, followed by Mann-Whitney test for pair-wise comparisons between groups. P-values ≤ 0.001 were considered extremely statistically significant (99% significance level), while p-values ≤ 0.05 were deemed statistically significant (95% significance level). Shapiro-Wilk test was employed to determine normality of data, and statistical program SPSS (version 23, IBM Co., USA) was utilized for data analysis.

RESULTS

Effect of observation time on each group (intra-group comparison)

According to the Mann-Whitney test, both restora­tive materials showed statistically non-significant difference in the mean ranks of gingival index between 6 months and one year. However, in using both restorative materials, there were statistically significant diffe­rences between baseline and 6 months as well as baseline and one year (Tables 2, 3 and Figures 3, 4). According to the Kruskal-Wallis’s test, there were statistically significant differences between the groups (p ≤ 0.05), especially between baseline (the lowest mean rank) and 1 year (the highest mean rank).

Effect of material within each time (inter-group comparison)

The outcomes of the current trial (Table 4) revealed that the differences between the two groups at any of time intervals were not statistically significant. Moreover, 100% of baseline samples recorded a score of 0 in both the groups. After 6 months, in the flowable resin composite group, 62.5% of the participants had a score of 0, 33.3% had a score of 1, 4.2% had a score of 2, and none had a score of 3. After 6 months, in the RMGI group, 75% had a score of 0, 25% had a score of 1, and none had scores of 2 or 3. The mean rank for the flowable resin composite group was 26.13, while for the RMGI group, it was 22.88. After one year, in the flowable resin composite group, 54.2% had a score of 0, 29.2% had a score of 1, 13% had a score of 2, and 4% had a score of 3. After one year, in the RMGI group, 62.5% had a score of 0, 29.2% had a score of 1, 8% had a score of 2, and none had a score of 3. The mean rank for the flowable resin composite group was 25.83, while for the RMGI group, it was 23.17.

DISCUSSION

The posterior area was shown to expand treatment recommendations for direct resin composite restorations, which is the preferred restorative material in minimally invasive restorations [18]. Prolonged clinical investigations demonstrated that large cavities can be successfully restored using minimally invasive direct restoration techniques, but complex treatment methods and operator’s expertise are needed for deep proximal lesions, which extend below the CEJ [19]. A minimally invasive pre-treatment called, CMR, has been suggested for the filling of deep class II cavities, which proximal cervical edges reach beneath the CEJ [20]. It involves a modified Tofflemire matrix application followed by immediate sealing of the dentin, and raising the deep gingival border of a cavity occlusally with flowable composite as a foundation layer. Moreover, this method facilitates installation of substantial direct composite resin restorations [21]. The CMR technique may only be carried out if certain requirements are fulfilled, i.e., when the gingival margins not interfere with the connective tissue space (biological width), and that a matrix band can be positioned to fully isolate the tooth edges in order to allow application of the composite resin base [9]. CMR patients must achieve complete operative field isolation, perfect matrix band placement, and avoid violating connective tissue space, in order to ensure a perfect seal and preventing violation of connective tissue space [22]. Indeed, posterior restorative CMR’s efficacy and bio-integration must be correlated with bleeding on probing and radiographic examination for marginal bone stability [23]. Furthermore, the bleeding on probing is a crucial clinical parameter for assessing health of periodontal tissue, influenced by margin precision, location, and patient’s oral hygiene; it is also critical for evaluating restorations around periodontal tissue [24]. Therefore, it is necessary to radiographically confirm the depth of restoration and existing caries, since it is possible to analyze future location of preparation margin that will be relocated. The margin elevation can achieve a maximum of 1 to 1.5 mm [25].
The present investigation offers brief clinical outcomes on the periodontal tissues’ reaction to the CMR process following one year of clinical service, which is a minimum period recommended for clinical trial evaluation of data collection [1]. The outcomes of the current study revealed that the difference in the mean ranks of gingival index between the two groups after 6 months and one year was not statistically significant. According to this result, the present null hypothesis, which was that there would be no significant variation among the flowable resin composite and RMGI after one year, was accepted. The present result is in line with Frese et al. study [26], who reported that the occluso-proximal restoration marginal elevation had no negative side effects, including persistent inflammation of the soft and hard tissues, loss of attachment, or resorption of the bone after 12-month follow-up. The radiographic assessment showed no clinical symptoms of inflammation, with a 0.5-1.0 mm gap within the alveolar crest and restorative border. The participants, who demonstrated a score of 0 bleeding on probing, can be explained by the ability of the CMR technique to be well-tolerated by the periodontal health, when a good bond is made with adequate isolation and participants follow oral hygiene instructions [27]. Another possible explanation could be the sub-gingival margin that was formed in the first phase of CMR, which is smooth, planned, and not irritating. This might have aided in the clinical outcome, along with specific oral hygiene regimen, specially designed inter-dental brushes, and their sufficient and consistent usage. All these factors indicated little or no sign of clinical inflammation at one year of follow-up [26]. Regarding the results of patients who demonstrated scores 1 and 2, the bleeding on probing may resulted from some patients’ inability to maintain deep margins clean, cervical resin margins becoming rough with time, and the lack of full control over the flow of adhesive and resin composite across the inter-proximal margin matrix in a quantity [1]. Moreover, following sub-gingival insertion of a resin-based composite, residual monomers from the resin-based composite may be released, potentially impeding periodontal health and wound healing [28]. Nevertheless, the current results disagreed with those of Köken et al. [6], who suggested that clinically, CMR does not successfully seal the cervical edge in root cementum-dentin, despite the use of resin-based composite. This issue may arise from isolating the field, addressing the cementum-dentin substrate, achieving a proper seal, bonding effectiveness, shrinkage of resin composites, operator skills, sensitivity of the approach, and the way that indirect resin restoration transfers occlusal forces [29]. This contradiction can be due to using different type of CMR technique as well as different materials.
The findings of the present trial demonstrated that there was no statistically significant difference in the mean ranks of gingival index between the flowable resin and RMGI after 6 months and one year post-procedure. The results of the RMGI can be explained as the restorations with fluoride release the ability to prevent pH dropping at the cavosurface edge and avoiding secondary caries, which is the primary reason of dental restorations failure [30]. While the result of the flowable resin composite might be related to its sealing ability for the dentin that account for limited polymerization in deep boxes with good adaptation due to the high flowability achieved [31]. Such results agree with Cerón-Flores et al. [32], who stated that CME is suitable for periodontal health if it does not interfere with the connective compartment of biological width. Additionally, the present results agree with those of Hammond et al. [33], who used resin-modified glass ionomer for CME. The patient was monitored for 6 years, and experienced no problems in periodontal health throughout that time.
The current study’s limitations include a short one-year follow-up period, evaluating only gingival index scores, not including other periodontal parameters, and focusing only on direct restorations. Therefore, further investigations with longer follow-up, additional periodontal parameters, and indirect restorations are needed to fully understand the long-term impact of CMR on periodontal health as well as to identify potential differences in responses to diverse materials used over time.

CONCLUSIONS

Within the limitations of the present study, the CMR technique appears suitable for periodontal health, resulting in little or no clinical signs of inflammation. Both micro-hybrid flowable resin composite and RMGI may be effective for CMR procedures in terms of their one year effects on periodontal health.

Disclosures

1. Institutional review board statement: Not applicable.
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