Clinical efficacy of mandibular complete dentures with a resilient liner: Study protocol for a multicenter randomized controlled trial

doi:10.21203/rs.3.rs-1770080/v1

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Clinical efficacy of mandibular complete dentures with a resilient liner: Study protocol for a multicenter randomized controlled trial

https://doi.org/10.21203/rs.3.rs-1770080/v1

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Background

During restoration of poorly fitting complete dentures (CDs) in edentulous patients, liners are used to reconstruct the concave surfaces of CDs with a new base material. These relining materials are classified as resilient liners (RLs) or non-resilient liners (NRLs), but the clinical effects of and selection criteria for these liners remain unknown. The purpose of this study is to evaluate the clinical efficacy of relining mandibular CDs using RL and NRL, and to conduct a follow-up study.

Methods

The study is being conducted at eight centers, and a parallel-group randomized controlled trial (RCT) is underway. One hundred thirty-two edentulous patients with poorly fitting mandibular CDs will be assigned to two groups (with RL or NRL). Participants will receive an RL or NRL for relining their CDs by using an indirect method of dynamic impressions. Data will be recorded at 1 week and 3, 6, and 12 months after denture delivery. The primary outcome will be assessment of the patients’ general satisfaction by using a 100-mm visual analog scale (VAS). Secondary outcomes will be measured as patient-reported outcomes, including food intake status and oral hygiene-related quality of life. Masticatory performance and the number of sore spots on the oral mucosa will also be recorded. Comparisons between the two groups and within-subject comparisons of pre- and post-intervention measurements will be conducted.

Discussion

For dentists and prosthetic researchers in Japan, this RCT will provide information on the clinical efficacy of RL materials in CD wearers. We are convinced that new evidence regarding the use of RL materials in an aging population will also be useful to dentists in other countries in their routine clinical practice.

Trial registration

: This clinical trial has been registered at the University Hospital Medical Information Network (UMIN) Center (UMIN000041950).

complete denture

edentulism

resilient liner

reline

patients' general satisfaction

masticatory performance

oral health-related quality of life

The aging of the global population, especially in developed countries, has led to an increase in the number of edentulous patients [1, 2]. In dental treatment, complete dentures (CDs) are generally the first choice to restore the routine masticatory function of edentulous patients. However, because of the significant alveolar bone resorption and mucosal thinning caused by many oral diseases in the elderly, in clinical practice, mandibular CDs cannot be used satisfactorily in many cases due to movement and pain. Recently, implant- supported overdentures have been considered as one of the options for maintaining and stabilizing dentures [3, 4], but due to systemic diseases, inability to visit the hospital, and cost issues, most patients often choose to repair their existing CDs [5]. The reline method is generally used for repairing a ‘non-retentive CD. According to the Glossary of Prosthodontic terms-9 [6], relining is defined as a procedure of resurfacing the concave surface of a CD with a new base material to precisely fit the denture base. Relining materials are classified as resilient liners (RLs) and non-resilient liners (NRLs) according to their chemical structure.

Randomized clinical trials (RCTs) have been conducted to investigate the clinical effects of newly fabricated CDs with RL materials in edentulous patients. These trials reported that the cushioning effect reduced pain and pressure ulcers during occlusion, improved patient satisfaction and masticatory performance, and reduced the number of denture adjustments [7–13]. However, no studies have investigated the superiority of CDs with RL materials over conventional CDs with NRL materials in cases of poorly fitting CDs, and the subsequent progress is unknown. Therefore, we plan to conduct an RCT covering the following centers throughout Japan: Tokyo Medical and Dental University, Nihon University School of Dentistry at Matsudo, Tsurumi University, Kanagawa Dental University, Aichi Gakuin University, Tokushima University, Nagasaki University, and Kagoshima University. This eight-center RCT has external validity, and is named the ‘mandibular CDs with resilient liner trial II (MCORT II)’. The purpose of MCORT II is to evaluate patients’ general satisfaction with relining of mandibular CDs using an RL material versus relining of mandibular CDs using an NRL material, and to conduct a follow-up study.

Trial design

This trial is being organized by the Japanese Society for Denture Care, developed by KK, the principal investigator of the study, and conducted at eight centers (university hospitals). The trial is designed as a multicenter randomized parallel trial comparing patients' general satisfaction with mandibular CDs with RLs and that with mandibular CDs with NRLs.

The chief coordinators, SK, NH, and YS, are closely liaising with the coordinators at each center. Every center has its own coordinator and researcher. The coordinator randomly assigns as well as manages the schedules of participants and investigators. The investigators will receive training in assessing the outcomes of the trial, perform measurements, and record the data. Dentists who provided the denture treatment are not allowed to be investigators for this trial. The blinded digital data will be returned to the Chief Coordinator for analysis. This trial has been registered with the University Hospital Medical Information Network (UMIN) Center (UMIN000041950) on 10 October 2020.

Participants

The trial will be performed at the dental hospitals of eight universities in Japan. The recruitment and treatment protocols of the present trial have been approved by the ethical review committee of the following universities: Tokyo Medical and Dental University (Register No. D2020-058), Nihon University School of Dentistry at Matsudo (Register No. EC2-042), Tsurumi University (Register No. 1840), Kanagawa Dental University (Register No. 733), Aichi Gakuin University (Register No. 612), Tokushima University (Register No. 3855), Nagasaki University (Register No. 21041910), and Kagoshima University (Register No. 200313).

The inclusion criteria are as follows: (1) edentulous patients who wanted to have their mandibular CDs repaired and (2) patients who provided written informed consent for this study. The exclusion criteria are as follows: (1) patients with physical or mental problems, (2) patients who cannot hear or read Japanese, (3) patients with dietary restrictions, and (4) patients with oral dyskinesia.

Sample size calculation

The use of an RL material will be judged to be clinically effective when the general satisfaction (100 mm Visual Analog Scale [VAS] score after 3 months of relining) of patients having CDs with RL is 15 mm higher than that of patients having CDs with NRL. The difference between the means of the two groups is set to 15 mm. The sample size is calculated using α = 0.05 and β = 0.8, based on the standard deviation of the overall satisfaction obtained in a previous study (CDs with RL: 26.3, CDs with NRL: 31.4) [7]. However, assuming that 10% of the participants would drop out, the target number of participants has been set at 132.

Randomization and masking

Stratification is performed at each university hospital (Fig. 1). The assignment is performed by a block randomization method with a block size of 2. For this purpose, random numbers from 1 to 6 representing combinations of 2 RLs and 2 NRLs: 1 (NRL, NRL, RL, RL), 2 (NRL, RL, NRL, RL), 3 (NRL, RL, RL, NRL), 4 (RL, NRL, NRL, RL), 5 (RL, NRL, RL, NRL), and 6 (RL, RL, NRL, NRL) are generated in Excel (Microsoft, USA) to create an allocation table. Kanagawa Dental University will centrally manage the allocation list for each center, and the coordinator of each center will contact the Chief Coordinator of Kanagawa Dental University by e-mail with each patient’s registration details to determine the intervention method. Both patients and dentists in this trial will not be blinded to the intervention, but will be blinded to the outcome measures and analysis.

[Figure 1 near here]

Intervention

The intervention for this trial will be the application of an RL material (Reline 2 Extra Soft; GC, Tokyo, Japan) or an NRL material (Rebase III [Normal]; Tokuyama Dental, Tokyo, Japan) to the mandibular CD. The lining method in this trial is indirect with the application of dynamic impression. Tissue conditioner (Tissue Conditioner II Soft; Shofu, Kyoto, Japan; Tissue Conditioner; GC, Tokyo, Japan) will be used for recording the dynamic impression. All prosthetic procedures will be performed by a prosthodontist with at least 5 years of experience. In principle, the indirect method should be performed by a dental technician. The technique used is as follows:

A dynamic impression is made using a tissue conditioner on the CD to be indirectly relined. The dynamic impression should be recorded when the patient does not complain of pain during mastication. Considering the surface properties of the tissue conditioner, an interval of approximately one week is appropriate.

A super-hard plaster (New Fuji Rock; GC, Tokyo, Japan) is poured on the dynamic impression surface to make a plaster model, which is flasked for denture processing.

The flask is opened, the tissue conditioner is peeled off from the mucosal surface of the model, and the mucosal surface of the denture base is trimmed to create space for the reline layer. The thickness of the reline layer is approximately 2 mm.

After applying the adhesive material according to the manufacturer's instructions, the CD is lined with the relining material (RL or NRL), cured, morphed, and polished. The relined CD is then delivered to the patient. Post-denture delivery follow-up appointments will be scheduled, and any necessary adjustments will be carried out.

Outcomes

The basic patient information recorded would include age, sex, years of denture use, and number of dentures fabricated. In addition, treatment difficulty index measurements [14, 15] and evaluation of used dentures [16] will also be performed. Since patient satisfaction with CDs is clinically important in evaluating the therapeutic effect of CDs with RL, the primary endpoint will be patients’ overall satisfaction with the CDs, which will be determined using a 100-mm VAS [17]. Patient satisfaction will be assessed comprehensively using a questionnaire containing eight assessment items: general satisfaction, ease of speaking, ease of cleaning, retention, stability, comfort, and esthetics. Participants will be asked to rate their satisfaction with each item in the questionnaire by using a 100-mm VAS to evaluate their current CDs. Data will be recorded as continuous variables at 1-mm intervals by using calipers from the left end. Overall patient satisfaction will be measured four times: at baseline, 7 days, 3 months, 6 months, and 1 year.

In addition, to comprehensively understand the clinical effect of CDs with RL material, the oral health-related quality of life [18], masticatory ability [19, 20], food intake [21, 22], and the location and number of mucosal pressure ulcers will be examined as secondary outcomes. Photographs of mucosal pressure ulcers will be shared among investigators to sufficiently calibrate assessments of the mucosal surface (Fig. 2).

[Figure 2 near here]

Response to adverse events

The principal investigator, a dentist, will carefully monitor the occurrence of adverse events. If an adverse event occurs, appropriate measures will be taken and, in principle, the patients will be observed until the events disappear. The type of event, date of occurrence (or the date of the hospital visit when the event was detected), treatment (continuation, discontinuation, etc.), course of the adverse event, and causal relationship to the resilient liners will be described in great detail. Observation will continue until one year after the resilient liner will be applied, and this also accounts for the entire duration of the trial.

Data handling

The study coordinators and dentists at each university will identify patients using registration numbers and initials during the duration of data preparation and handling. They will also take into consideration the protection of patient confidentiality. All of the personnel involved in this study will not be permitted to divulge, without justifiable cause, any confidential information about the individuals involved in the study.

The collected data from each university will be gathered and stored at the Center for the Promotion of Clinical Research (Kanagawa Dental University). The collected data will be analyzed by the chief coordinators after confirmation is given by the chief investigator. All materials used in the study will be stored for three years after the completion or discontinuation of the study.

Access to the final clinical trial data will be limited to the chief investigator and chief coordinators.

Clinical Trials Committee

A clinical trial committee will be established for this clinical trial. This committee will meet on a regular basis. The members of this committee will consist of the chief investigator, chief coordinators, and coordinators from each university. The role of this committee is to audit the progress of the clinical trial, report adverse events, and discuss and decide on important changes to the protocol.

Statistical analysis

The statistical analyses will be performed as follows:

Normality will be confirmed by the Kolmogorov–Smirnov test, and either parametric or nonparametric tests will be performed.

Between-group comparisons will be made using Student’s t-test or Mann-Whitney U test, depending on the distribution of the outcome.

Within-group comparisons will be performed using the paired t-test or Wilcoxon's signed-rank test depending on the distribution of outcomes.

Chi-square test will be used to test the proportions.

The significance level will be set at 5% on both sides, and p-values will be adjusted by Bonferroni's correction to account for multiplicity when more than three groups are compared.

The significance level will be 5% two-sided.

The efficacy of single-implant mandibular overdentures to stabilize CDs in edentulous patients has been noted recently [23]. This form of implant therapy is expected to be one of the treatments for edentulous patients because it involves the insertion of only one implant, less surgical invasion, and high convenience. However, it is difficult to apply this approach in geriatric patients who have systemic diseases or are unable to visit the hospital, and a fundamental solution to this problem has not yet been identified.

In clinical dentistry, the supplementary use of RL materials in the postoperative management of CD wearers has already been recognized [24–26]. Since their introduction in the 1950s, these RL materials have been used to improve the fit of CDs, condition traumatized tissues, and provide an interim or permanent cushioning-like effect, and have undergone subsequent development and improvement. These materials have been reported to help distribute the forces of mastication more evenly and absorb energy [5, 24]. However, most of the previous studies on RL materials have focused on their material properties, such as mechanical properties, bond strength between the denture resin and RL, and bonding methods [5]. In contrast, few clinical trials have investigated the clinical effects of RL materials [7–13]. and no large clinical study has been conducted to clarify the functionality of RL materials using a multicenter RCT, as in this trial.

In Japan's rapidly aging society, many elderly CD wearers are unable to visit the dentist's office, despite the fact that poor denture quality can affect their quality of life. The application of RL materials can help some of these patients. However, the lack of sufficient evidence on RL materials has made dentists hesitant to recommend or apply RL materials.

This clinical study has several limitations. First, both the patient and the dentist cannot be blinded to the treatment because of dental treatment. In this study design, it is not possible to conduct a double-blind study. Second, the results obtained have limited generalizability because the sample included only patients who were able to visit the hospital. Since the external validity of the evidence is lacking as the aging society progresses, we believe it is necessary to conduct a clinical trial in a new population.

The RCT will provide dentists and prosthetic educators evidence regarding the effectiveness of RL materials for edentulous patients. We believe that the elucidation of this evidence will liberate dentists from the conventional notion that RL materials cause more harm than benefit, and will yield useful information while selecting treatment options for edentulous patients with ill-fitting CDs.

Trial Status And Result

January 2021 - March 2023 (Registration period until September 2022). At the time of manuscript submission (January 26, 2022), patient recruitment is ongoing.

The obtained data will be presented at conferences and submitted to academic journals to help develop diagnostic and therapeutic guidelines for the selection and use of resilient liners.

complete denture

resilient liner

NRL

non-resilient liner

MCORT II

Mandibular Complete dentures with Resilient liner Trial II

RCT

randomized controlled trial

VAS

visual analog scale

Declaration of interests

This clinical was conducted and written independently; no company, university, or institution supported it financially. There is no conflict of interest to be declared.

Ethics approval and consent to participate

All patients will be required to provide written informed consent before starting the trial. Patients wishing to withdraw may do so at any time during the trial. The recruitment and treatment protocols of the present trial have been approved by the ethical review committee of the following universities: Tokyo Medical and Dental University (Register No. D2020-058), Nihon University School of Dentistry at Matsudo (Register No. EC2-042), Tsurumi University (Register No. 1840), Kanagawa Dental University (Register No. 733), Aichi Gakuin University (Register No. 612), Tokushima University (Register No. 3855), Nagasaki University (Register No. 21041910), and Kagoshima University (Register No. 200313).

Consent for publication: Not applicable.

Availability of data and materials: Not applicable.

Competing interests: The authors declare that they have no competing interests.

Funding

This study was supported by a Grant-in-Aid for Scientific Research (C) from the Japan Society for the Promotion of Science (grant number 20K10062). The sponsor had no role in the the design of the study or collection, analysis, or interpretation of data or in writing the manuscript.

Authors' contributions:

KK drafted the trial protocol that is being used at the eight centers and is a chief investigator. YY, JT, TI, HM, MN, SN, YK and KK developed the drafted protocol. SK, NH and YS serve as chief coordinators and maintain close contact with the coordinators at each center. NH, YY, JT, TI, HM, MN, SN and YK are coordinators at each center. SK, NH and YS are collecting the data. All authors read and approved the final manuscript.

Acknowledgements: The authors acknowledge the study’s collaborators and thank all individuals participating in the trial.

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Editorial decision: Major revision
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Reviewers agreed at journal
22 Jul, 2022
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You are reading this latest preprint version

Clinical efficacy of mandibular complete dentures with a resilient liner: Study protocol for a multicenter randomized controlled trial

Status:

Version 1

Abstract

Background

Methods

Discussion

Trial registration

Figures

Background

Methods/design

Trial design

Participants

Sample size calculation

Randomization and masking

Intervention

Outcomes

Response to adverse events

Data handling

Clinical Trials Committee

Statistical analysis

Discussion

Trial Status And Result

Abbreviations

Declarations

References

Supplementary Files

Status:

Version 1