A soft liner is a flexible or viscoelastic substance placed on the fitting surface of a denture or obturator to minimize and better distribute occlusal forces on the underlying oral tissues. Resilient liners can be seen as a counterpart to the periodontal ligament and the compressible healthy muco-periosteum in individuals without teeth [1,2].

Resilient lining materials have established their role in complete denture prosthodontics since their initial clinical use documented by Tylman [3].

 Certain complete denture users experience extended discomfort beneath their dentures, even after all potential prosthetic adjustments. This could be due to inadequate patient tolerance, a low pain threshold, a thin mucosal layer, or uneven bone structure. The tissue under the lower denture typically experiences greater chewing pressure per unit area compared to the upper one [4].

Durable lining materials are primarily utilized for patients unable to withstand these pressures, serving as shock absorbers and diminishing the impact of force transmitted to the base of the denture [5-7]. An obturator is a prosthetic device used to seal and restore congenital and/or acquired maxillary defects, reestablishing the barrier between the oral and nasal cavities [8-11].

Significant resorption of the mandibular ridge leads to instability and discomfort associated with a traditional acrylic resin denture. In this situation, the dentures can be made effective and comfortable with a durable liner [12,13].

Storer (September 1962, October 1962) explains that the reason for employing a soft lining material is that some of the energy it transmits to the denture helps in elastically deforming the denture, thereby diminishing the direct chewing load on the atrophied region. Moreover, the soft-lining exerts uniform pressure on the ridge's bone, thus preventing obstruction from the prominent spicules when greater force is applied [14,15].

The liners facilitate alterations in the contour of damaged oral tissues when subjected to functional load16 and subsequently help to achieve a uniform distribution of functional load across the complete denture bearing surface. This approach reduces the chances of trauma to the oral mucosa under the removable denture due to its presence [16-19] Consequently, resilient liners are regarded as a counterpart to mucoperiosteum [7]. The current investigation aimed to compare the looseness of patients utilizing dental prostheses that have soft liners versus those that do not.

This forward-looking longitudinal research was carried out in the Department of Prosthodontics at Bangabandhu Sheikh Mujib Medical University in Dhaka, Bangladesh, from January 2008 until December 2010. Sixty patients of both genders participated in this study; among them, 30 patients received treatment with soft-lined dentures and obturators (Group-A), while the other 30 patients were treated with conventional dentures and obturators without soft lining (Group-B). All patients were chosen based on a comprehensive medical and dental history, clinical evaluations, diagnostic model assessments, and radiographic studies. The treatment plan was described to the patients, detailing the procedure involved. Confident in the patient's complete cooperation, they were ultimately chosen. Prior to the commencement of the procedure, each patient signed the informed consent document. Standard clinical and laboratory procedures were upheld in a sterile environment for the creation of conventional dentures and obturators. Once the prosthesis was remounted on the articulator, proper cleaning, finishing, and polishing were completed before inserting the prosthesis into the patient's mouth (group-B). Conversely, the denture or obturator made with soft-lining materials (Group-A) required additional procedures. Following insertion, the current centric occlusion and intercuspation were utilized to properly position the denture on the bearing area within the patient's mouth. The borders are trimmed by 1-2 mm, excluding the posterior border of the maxillary denture, and reshaped to their functional contours with low-fusing compound. A close mouth replication using zinc oxide-eugenol paste was made, instructing the patient to gently bring the denture teeth together in the intercuspal position. The impression was cast with rigid plaster. The denture cast was placed in a flask alongside its counterpart. Once the plaster fully set, the flask was opened, and warm water was used to extract the impression material from the denture. A grinding stone was used to reduce the tissue surface of the denture/obturator base throughout the area by approximately 1-3 mm, and several undercuts were created to ensure a secure fit for the materials. Medium was separated on the plaster surface, and a bonding agent was utilized on the resin surface. The soft lining material Molloplast-B was rolled and applied to the denture base, followed by packing using the standard method. The ultimate sealing of the flask was accomplished through metal-to-metal contact between its halves prior to beginning the curing process. The curing was done in accordance with the manufacturer's specified standard curing cycle. Following curing and bench cooling, the denture was carefully removed during deflasking and retrieval. The denture was cleaned using ultrasonic waves in a solution for removing plaster and stone. Most of the flashed materials were cut away from the denture edges and shaped using a No. 60 LG grinding wheel. Silicone rubber resilient liners were cut slowly using disks and rubber wheels. Subsequently, the polishing and finishing were executed correctly. The denture or obturator lined with Molloplast-B was subsequently placed in the patient's mouth, and usage instructions for the denture or obturator were provided to the patient (Group-A)10,20. Once the denture or obturator was placed in the mouth, the fit was assessed, and baseline data for both groups was accurately documented. Patients were instructed to return for follow-up visits after the 1st week, 3rd week, 5th week, and 5th month for assessment. During every follow-up appointment, the looseness of patients in both groups was assessed, and the findings were documented for result formulation [10,20].

Table 1 shows the distribution patients by looseness denture and obturator caused by denture during different study periods. The looseness of denture and obturator was found initially among group-A 13.3% patients had complaints and in group-B 6.7% patients had complaints of looseness of denture and obturator and different was not statistically significant (p>0.05). During different study period, complaints of looseness of denture and obturator increased in group-B patients and the difference was not statistically significant (p>0.05). However, at the end of 5th month, the complaints of looseness of denture and obturator remained static in group-B patients 33.3%, but no patient had complaint of looseness of denture and obturator in group-A patients.

Table 1: Distribution of patients by looseness of denture and obturator during different study period (n=60)

Chi-square test is done to determine the p value, Group-A (n=30): Patients treated with soft lining material, Group-B (n=30): Patients treated without soft lining material

This study was to compare the looseness of patients wearing denture and obturator with and without soft lining materials. A total of 60 patients were evaluated; of them 30 were treated with denture and obturator lined with soft liner (group A) and 30 were without soft liners (group B). Results showed that most of the patients relieved from looseness who were wearing denture and obturator with soft lining materials (group A) than patients wearing the prostheses without soft lining materials (group-B) and difference was statistically significant.

In this study show that at the last observation time after 5 months all patients (100%) wearing denture or obturator with soft liner presented with no looseness, whereas 33.3% patients wearing denture and obturator without soft liners presented with looseness.

The following studies in different ways showed that soft lining materials can relieve the denture or obturator wearer from looseness of denture and obturator. Denture liners can be either hard usually made of polymethylmethacrylate or soft liner (SL) (i.e., resilient) Acrylic-based SL is produced by adding plasticizers to the acrylic resin, and silicone-based SL is a mixture of siloxane and silica that remains "soft" after cross-linking/setting [21-27]. SL materials have been used in dental fields for over a century as resilient substances attached to the fitting surface of a denture to reduce localized point pressures and prevents the looseness of denture and obturator.

Due to their elastic nature, soft liners have a cushion effect as they absorb energy, so they can help heal the inflamed mucosa distribute the functional load in the support area of the prostheses and improve their adaptation and retention and prevent looseness [28,29]. Because soft-liner acts as a shock absorber during mastication and reduces discomfort, soreness of tissue and increased retention and stability and prevent looseness [6]. The results of these studies showed the similarity with the result of present study.

A denture care centre observed conventional as well as the denture with soft liners that poor fitting dentures can do more than be uncomfortable, and affect eating and speaking. Over time, severe complications can occur (like gum irritation). The resulting sores and blisters, if ignored, can cause bacterial and fungal infections which affect overall health. Soft liner reduces direct pressure to tissue and makes the dentures more stable and comfortable (especially for patients who have sensitive underlying tissue) and relieved from mucosal irritation and soreness and prevent looseness [30]. The result this observation is more or less similar to the result of the present study. So, the present study is consistent with the above-mentioned studies.

Based on the results of the present study it can be concluded that most of the patients relieved from looseness who were wearing denture and obturator with soft lining materials than patients wearing the prostheses without soft lining materials and difference was statistically significant (p<0.05)

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