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 Table of Contents  
RESEARCH
Year : 2022  |  Volume : 22  |  Issue : 1  |  Page : 21-28

A comparative clinical trial for evaluating the posterior palatal seal developed from the conventional method and a novel functional swallow method


Department of Prosthodontics, Faculty of Dental Sciences, Ramaiah University of Applied Sciences, Bengaluru, Karnataka, India

Date of Submission20-May-2021
Date of Decision12-Sep-2021
Date of Acceptance12-Nov-2021
Date of Web Publication27-Jan-2022

Correspondence Address:
Ravishankar Krishna
Department of Prosthodontics, Faculty of Dental Sciences, Ramaiah University of Applied Sciences, Gnanagangothri Campus, New BEL Road, MSRIT Post, MSR Nagar, Bengaluru - 560 054, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jips.jips_235_21

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  Abstract 


Aims: The aim of this in vivo study was to compare the influence of posterior palatal seal (PPS) developed from the conventional method and a novel functional swallow method on the retention of custom tray and heat cure denture base.
Settings and Design: This was a nonrandomized crossover clinical trial.
Materials and Methods: Twenty patients requiring maxillary complete dentures were selected. In Group 1, for all twenty patients, the PPS was developed with the conventional functional method during border molding and a conventional cast scoring was performed before processing the denture base. In Group 2, for all the twenty patients, the PPS was developed with a novel functional swallow method and the master cast was “not” scored before processing the denture base. The retention was objectively measured using a dynamometer after border molding and also after processing the denture base for both groups.
Statistical Analysis Used: Independent Student's t-test and paired t-test were used for analysis.
Results: The mean retention value of Group 2 was significantly higher (P < 0.001) than Group 1 at border molding and after denture base processing. Within Group 1, the retention value significantly increased (P < 0.001) from border molding to the denture base stage, whereas within Group 2, there was no significant change (P > 0.001) between the stages.
Conclusions: Within the limitations of the study, the novel functional swallow method of establishing the PPS demonstrated higher retention than the conventional method both during border molding and after processing the denture base.

Keywords: Border molding, conventional method, denture base, functional swallow method, posterior palatal seal, retention


How to cite this article:
Mishra S, Krishna R, Mandokar RB, Agarwal S, Sharma A, Shaw M. A comparative clinical trial for evaluating the posterior palatal seal developed from the conventional method and a novel functional swallow method. J Indian Prosthodont Soc 2022;22:21-8

How to cite this URL:
Mishra S, Krishna R, Mandokar RB, Agarwal S, Sharma A, Shaw M. A comparative clinical trial for evaluating the posterior palatal seal developed from the conventional method and a novel functional swallow method. J Indian Prosthodont Soc [serial online] 2022 [cited 2022 May 25];22:21-8. Available from: https://www.j-ips.org/text.asp?2022/22/1/21/336677




  Introduction Top


Despite conflicting theories found in the literature pertaining to the method of recording the posterior palatal seal (PPS), its' importance cannot be refuted.[1],[2] Literature is abundant with a description of various methods to establish the PPS.[3],[4],[5],[6] According to education surveys conducted across the globe, the arbitrary cast scoring technique is the most commonly followed.[7],[8] However, according to Winkler, arbitrary method is considered the least accurate because the denture retention cannot be verified until the insertion appointment.[9] Winkler also proposed the conventional scoring method which involves locating and transferring the PPS boundaries using a trial denture base and scoring the PPS area on the master cast.[5] All scoring methods have the potential to overcompress the PPS area and hence considered nonphysiological.[5] A recent study investigated the efficacy of PPS obtained by employing conventional master cast scoring. The PPS retention was assessed subjectively by applying tipping forces on the palatal surface of the anterior teeth of the processed maxillary denture. The study had a small sample size and concluded that conventional scoring can be safely used to develop the PPS.[10]

The PPS can also be established by functional and semi-functional methods which do not support scoring. In the functional method, the patient participates in molding of the PPS, whereas in the semi-functional method, the dentist performs the molding of the PPS.[11] Among functional methods, the fluid wax technique is considered most physiologic as it does not cause overcompression of the PPS tissues.[12] The drawbacks of the technique are it is time consuming, complex and that the waxes may not sufficiently displace the soft palate due to inadequate strength. Furthermore, waxes are not dimensionally stable during impression procedure or cast pouring.[13] The “Ah” functional technique is also used conventionally to develop the PPS during border molding.[14] However, this method may not displace the PPS area adequately as the soft palate can return to the nondisplaced position before the molding compound may have hardened. This may lead to an inadequate posterior seal.[15] Several semi-functional methods have been recommended recently. Here, the PPS is molded using materials such as wax or resin within the PPS boundaries of the completed final impression surface.[13],[15],[16] These methods can be time-consuming, technique sensitive, and also have the potential to cause excessive displacement of the posterior seal area.[16] Hence, it is clear that there is no consensus among the proponents of scoring and nonscoring methods.

A novel nonscoring “functional swallow” method can be a useful alternative to the existing methods. It utilizes a low fusing compound and the swallowing forces inherent to every individual to displace the soft palate functionally when the head is flexed forward.[17] Very few studies have assessed the magnitude of retention developed from the various PPS methods and notably those comparing scoring and nonscoring methods.[1],[18],[19]

This study aimed to evaluate and compare the conventional method (with conventional cast scoring) and a novel functional swallow method (without cast scoring) in developing the PPS by measuring the magnitude of forces required to dislodge their corresponding border molded custom trays or heat-processed denture bases. The research employed the less explored approach of applying dislodging forces through the anterior part of the denture base in an outward and upward direction using a dynamometer.

The null hypothesis was that the retention of border-molded tray or the heat-processed base fabricated from the conventional method of developing PPS will be similar to the retention of border-molded tray or the heat-processed base fabricated from the functional swallow method.


  Materials and Methods Top


The University Ethics Committee approved the trial (EC-2019/PG/31) to compare the efficacy of a conventional method versus a novel method in developing the posterior palatal seal. This clinical trial [Table 1] was conducted as per TREND (2004) guidelines for a period of 13 months from December 2018 to February 2019. The study was conducted according to the ethical principles of the Declaration of Helsinki (2013). Twenty maxillary completely edentulous patients who reported to the department of prosthodontics, crown, and bridge for complete denture treatment were selected. Informed consent was obtained from both male (11) and female (09) patients who were in the age group of 45–75 years. Inclusion criteria were patients with complete maxillary edentulous arch and at least 6 months postextraction, old denture wearers for at least 6 months, well-rounded, healed, edentulous ridges, firmly attached mucosa with no signs of inflammation, normal salivary flow, and with Class I or Class II type of soft palate anatomy based on House's classification[20] and patients who provided signed informed consent participated in the study.
Table 1: Study flowchart

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Exclusion criteria included patients with Class III type soft palate, high vaulted palate, severe hard tissue undercuts, bilateral tuberosity undercuts, presence of palatal tori, severely resorbed maxillary edentulous arch, history of neuromuscular disorders, and velopharyngeal dysfunction. Patients with the presence of irritated or abused mucosa, xerostomia, history of medication that could alter quality and quantity of saliva, and severe oral manifestations of any systematic diseases and patients with spinal problems and who could not bend forward were excluded from the study.

Based on the two interventional methods, the study had two groups. Group 1 (n = 20) comprised all twenty patients who underwent the conventional method of recording the PPS, whereas Group 2 (n = 20) comprised all twenty patients who underwent functional swallow method to record the PPS. All the clinical procedures were carried out by a single investigator.

Border molding procedure

The primary impression was made for every patient with an irreversible hydrocolloid (Neocolloid, Zhermack) and a cast obtained in plaster. On the primary cast, a 2 mm thickness of wax spacer was adapted uniformly all over with tissue stops. The spacer was kept 2 mm short of the periphery and also short of the demarcated PPS. Two autopolymerizing resin (DPI RR Cold Cure, Mumbai) custom trays were fabricated for each participant [Figure 1]. The handle was positioned symmetrically across the midline derived on the cast. The handle dimensions were standardized to 18 mm length, 12 mm width, 6 mm thickness, and tilted labial with an angle of about 45°. Using a round tungsten carbide bur, a circular vent of 4 mm diameter was made in the midline placed 5 mm from the top of the handle [Figure 2]. The maxillary border molding procedure was performed twice for each patient using a low fusing compound (DPI Pinnacle Tracing Sticks, India). The PPS was incorporated as described below.
Figure 1: Primary cast with custom trays

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Figure 2: Vent placed in the custom tray handle of specific dimensions

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Identification and development of PPS

The anterior and posterior vibrating lines were identified intraorally and marked with an indelible marker. The anterior vibrating line was marked through the Valsalva maneuver and the posterior vibrating line by asking the patient to say “Ah” in a nonvigorous fashion. These marked lines were transferred to both the custom trays. The PPS was developed employing the conventional “Ah” functional method (Group 1) with one of the custom trays and by the novel functional swallow method (Group 2) with the other [Figure 3] as described below.
Figure 3: Posterior palatal seal developed from (a) conventional method and (b) novel functional swallow method

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Conventional method

Combination of conventional functional and conventional scoring is commonly used in Asian countries.[21] It involved applying softened low fusing compound onto the demarcated PPS of the custom tray and asking the patient to say “Ah,” a few times until the compound hardened.[14] The PPS thus created was assessed by tucking the tray handle from its inner side with a finger.[22] The procedure was repeated until satisfactory PPS was obtained. The final PPS was established on the master cast by the scraping method, as described by Winkler.[5] It involved marking and transferring the anterior and posterior boundary of the PPS area using the resin trial base. The PPS was scored on the master cast with a scraper. The medial palatal raphe area was scored to about 0.5 mm and the area from the midline to hamular notch on both sides between posterior and middle thirds was scored to a depth of 1–1.5 mm.

Novel functional swallow method

Initially, the patient was trained to lean forward, bend the head down till the chin touched the chest, and then swallow, with the instruction to keep the tongue against the palate during the swallow. The angle between the Frankfort plane and horizontal plane was 45° when the head was bent forward to the trained position [Figure 4]. A stick of low fusing compound was softened using a flame and applied on the demarcated PPS section of the other custom tray. The added compound was heated uniformly using an alcohol torch, tempered in hot water, and placed in the patient's mouth. The tray was supported on either side with fingers and the patient was asked to bend forward and swallow at least two times as practiced before. The patient was instructed to return to normal posture and swallow once again. The efficacy of the PPS was assessed by tucking the tray handle on its inner side. The procedure was repeated till satisfactory PPS was achieved. The green stick that appeared beyond the boundaries of the PPS was cut and finished using a sharp B.P blade.
Figure 4: Patient position to record posterior palatal seal with novel swallow method

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Measurement of retention

The retention was evaluated using a pull-type analog dynamometer device [Figure 5]. All the retention measurements were made by a second investigator who was blinded about the study protocol. The c-shaped hook of the dynamometer engaged the vent hole of the handle snugly from its inner side. The reading was recorded in Newton.
Figure 5: Analog-type dynamometer

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Before recording the retention values, the patient was asked to wet the mouth with water and the custom tray was placed in the mouth for about 2 min. The patient's head was stabilized such that the Frankfort horizontal plane was parallel to the horizontal. The c-hook of the dynamometer was engaged into the vent of the handle and the device was pulled with one hand in an outward–upward direction perpendicular to the angulated handle [Figure 6]. Furthermore, a finger of the nonoperating hand was placed near the posterior part of the custom tray to prevent the tongue from resisting the tray dislodgment.
Figure 6: Measurement of retention

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Measuring the retention of custom tray post border molding

The border-molded custom trays with the PPS established from both methods (Group 1 and Group 2) were evaluated separately. A total of three readings were taken for each method in every patient.

Fabrication of heat-processed bases

Post border molding, the maxillary final impression was made using a low viscosity elastomer (elite HD+, Zhermack S.p.A., Italy) for both the methods [Figure 7]. The master casts were poured into Type III gypsum [Figure 8]. Whereas a PPS scoring procedure on the master cast through a trial base was followed for the conventional technique (Group 1), the master cast obtained from the functional swallow technique (Group 2) was not scored [Figure 8]. A 2 mm thickness wax sheet was adapted uniformly on all master casts and heat-polymerized bases [Figure 9] were obtained by employing the compression molding technique. The bases were finished and a handle was made for each processed base using autopolymerizing acrylic resin. The handle was made to the specific dimensions and a circular vent was placed as described before.
Figure 7: Final impression with posterior palatal seal developed from (a) conventional method and (b) novel functional swallow method

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Figure 8: Posterior palatal seal area on master cast (a) scoring using conventional method and (b) nonscoring novel functional swallow method

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Figure 9: Heat-processed bases. (a) Conventional method and (b) novel functional swallow method

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Measuring the retention of heat-processed denture base

Heat-processed bases from both methods (Group 1 and Group 2) were evaluated for retention separately. Using the dynamometer, a total of three readings were taken for each method in every patient.


  Results Top


The force required to dislodge the custom tray after border molding and after processing the heat cure denture base was measured in newton. This measured force was considered as the retention value. These values were obtained for both Group 1 (PPS obtained by conventional method) and Group 2 (PPS obtained by functional swallow method). In Group 1, for each of the twenty patients, three retentive values were recorded with the custom tray and the mean was obtained. A total of 20 values were derived. The group mean was calculated which indicated retention after border molding [Table 2]. A similar mean value was calculated for Group 2 patients after border molding [Table 2]. Again three retentive values were measured with each heat cure base for each patient in Group 1 and the mean was determined, generating another twenty values. The group mean representing retention with heat cure base was computed [Table 3]. Similarly, a mean retentive value was obtained for Group 2 after processing the heat cure base [Table 3].
Table 2: Mean retentive values obtained after border molding between groups

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Table 3: Mean retentive values obtained after conversion to heat processed base between groups

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Independent Student's t-test revealed higher mean retention values of Group 2 (PPS obtained by functional swallow method) than Group 1 (PPS obtained by conventional method) both during border molding [P < 0.001, [Table 2]]and after denture base processing [P < 0.001, [Table 3]]. Student's paired t-test showed that within Group 1, the mean retention value after denture base processing was significantly higher [P < 0.001, [Table 4]] than that during border molding. Student's paired t-test within Group 2 disclosed that there was no significant change in mean retention value [P > 0.001, [Table 5]] from the stage of border molding to heat cure denture base stage.
Table 4: Mean retentive values within Group 1 obtained after border molding and subsequent conversion to heat cure bases

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Table 5: Mean retentive values within Group 2 obtained after border molding and subsequent conversion to heat cure bases

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  Discussion Top


The philosophy behind any method used for recording PPS effectively lies in its ability to create sufficient displacement of the soft tissues within the physiological limits which will aid in creating a seal between the denture and the soft tissue during functional movements.[23] The “Ah” sound is not only used to mark the vibrating lines but also used frequently as a functional method to displace the soft palate during border molding with low fusing compound among Asian countries. In spite of its popularity, the “Ah” functional method has not been documented as a technique. Since the “Ah” functional method may not be consistent in developing a posterior seal, it is augmented by the conventional scoring procedure on the master cast. For the same reason, the conventional method in the present study combined the two. The nonscoring functional swallow method may be a simple alternative to the existing methods that are either inaccurate, cumbersome, or technique sensitive. The functional swallowing forces of the tongue that is inherent to an individual can displace the soft palate when the head is flexed forward. Due to the head flexion, the soft palate assumes a passive downward and forward position.[24] The soft palate may be easy to displace when it is passive. The swallowing function elevates the tongue to bring about an intimate contact between the custom trays carrying the softened low fusing compound with the passive soft palate. This helps to achieve a more efficient seal during border molding. Low fusing impression compound was used in this trial as it is easy to manipulate, commonly used, and also dimensionally stable during cast pouring procedures.

The physiologic fluid wax method[5] also recommends the patient's forward head flexion of 30° and the use of mouth temperature wax to establish the PPS. Training the patient to flex the head to 30° requires the cumbersome use of an angle measuring device. Furthermore, in this method, the patient's tongue has been positioned against the lower anterior teeth during the recording procedure. This position takes the tongue away from the posterior palatal area and does not aid in establishing the seal. In the present technique, the patient's head was bent down till the chin touched the chest or was close to it. At this point, the Frankfort horizontal plane made an angle of 45° to the horizontal. This position not only placed the soft palate in a passive, downward and forward position, but was also easy to achieve during the clinical procedures for the patient without assistance from an angle measuring device. Hence, the head was flexed to 45° in the present study.

The retention efficacy of complete dentures can be measured by subjective methods, clinical-objective methods, and purely objective methods. The most reliable among them is the objective measurement of denture base retention using the dynamometer.[25]

Various studies have evaluated the influence of patient factors,[26] denture adhesives,[27] and the type of PPS[1],[19] on the magnitude of maxillary denture retention. These studies have quantified the denture retention by attaching a dynamometer to the geometric center of maxillary denture base through a metallic hook so as to generate a measurable dislodging force in a vertical or oblique direction. However, vertical pulling forces through the center of the denture may not simulate the denture dislodging pattern during function. This is due to the fact that the maxillary denture dislodgement pattern during function occurs through tipping or rotational forces causing dislodgement at the posterior end.[1],[18] This dislodgement force is in an outward and upward direction.[28] Hence, vertical dislodgement forces were avoided in the present study.

Chandu et al. studied the influence of different methods of recording PPS by directing outward–upward rotational forces to the posterior end of the denture base.[19] They attached the hook to the posterior end of the denture base and used cumbersome equipment for measuring retention. The influence of tongue reflex to resist the denture base dislodgement from the posterior end during measurement of retention was not considered. In the present study, it was ensured that the tongue was kept away from the custom tray and the denture base during retention measurements by the operator's hand. Also, in contrast to previous studies, the tipping forces from the dynamometer was applied to the anterior end of the denture base in an upward and outward direction. This is analogous to the chairside clinical verification of PPS where tipping forces are applied on the inside of the tray handle on the border molded tray.[22]

The magnitude of retention of the custom tray after border molding in Group 2 (novel functional swallow method) was higher by about one and half times (P < 0.001) than that of Group 1 (conventional method). This may be due to passive positioning of the soft palate during anterior flexion of the head and hence a more superior palatal displacement achieved by low fusing compound. The mean retention of heat cure bases after processing was also significantly greater (P < 0.001) in Group 2 than in Group 1. It may be due to a more accurate soft palate displacement achieved by functional swallowing forces when compared to hypothetical cast scoring. This was in agreement with a previous study,[19] which found higher retention of heat cure bases when the PPS was recorded with a nonscoring method as against different scoring methods. However, the study did not divulge the specifics of their functional technique.

An accurate PPS not only improves retention of the denture base but also compensates for processing shrinkage.[13] Within Group 1, the mean retention value was the least at the border molding stage which significantly increased (P < 0.001) after the base was processed. This probably proves that scoring of the master cast may be essential when the “Ah” functional method is used to create the PPS during border molding. Among Group 2, the difference in the mean retention value from the border molding stage to the denture base processing stage did not change much. This was perhaps due to the master cast not being scored in the PPS area. Despite not scoring the master cast, the retention remained unchanged and higher than Group 1 after processing. This probably confirms a better compensation of curing shrinkage by the functional swallow method when compared to the conventional method.

The limitation of this study was that the retention was assessed only by measuring the dislodging force of the denture base. Functional retention and patient satisfaction scores were not determined. The present study followed a nonrandomized crossover design. A randomized control trial comparing the efficacy of the two methods of establishing PPS along with patient satisfaction scores can further substantiate evidence and perceptions.


  Conclusions Top


Within the limitations of the study, the following conclusions were drawn:

  1. Between the two methods of recording the PPS, the nonscoring functional swallow method exhibited higher retention than the conventional method both during border molding and after conversion to heat cure denture base
  2. In the conventional method, scoring of the master cast helped to increase the degree of retention from the border molding stage to the denture base stage
  3. Although the master cast was not scored, the functional swallow method achieved greater retention
  4. The nonscoring functional swallow method can be a practical alternative to the conventional scoring method.


Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that her name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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[PUBMED]  [Full text]  
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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