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Year : 2021  |  Volume : 9  |  Issue : 2  |  Page : 93-99

Comparative assessment of width of neutral zones recorded using two neutral zone impression methods (phonetic and swallowing) and two different materials (tissue conditioner and polyether): A crossover pilot study

1 Department of Prosthodontics, Goa Dental College and Hospital, Bambolim, Goa
2 Private Practitioner, Delhi, India

Date of Submission22-Dec-2020
Date of Decision07-Sep-2021
Date of Acceptance07-Sep-2021
Date of Web Publication30-Nov-2021

Correspondence Address:
Manjita M Parab
Department of Prosthodontics, Goa Dental College and Hospital, Bambolim - 403 202, Goa
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/dmr.dmr_67_20

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Statement of Problem: Medium body polyether impression material has been recently used as neutral zone recording material. However, there is a lack of studies comparing it with routinely used material. Purpose: The purpose of the study is to compare neutral zone width of phonetic (PNZ) and swallowing (SNZ) neutral zone impression techniques with a tissue conditioner and a polyether impression material within the same subjects. Materials and Methods: Assessments of neutral zone width were carried out in ten completely edentulous patients with advanced mandibular resorption. On each patient, four neutral zone impressions were recorded as follows: SNZ with tissue conditioner material, PNZ with tissue conditioner material, SNZ with polyether impression material, PNZ with polyether impression material. Putty indices were made of each neutral zone and traced on graph paper. The buccolingual measurements were made at five different locations, midline, right first premolar, left first premolar, right first molar, and left first molar. Statistical analysis was done using Mann–Whitney U test. Results: There was no significant difference observed when comparison was done either between materials or techniques. Conclusion: Medium body polyether can be a viable alternative to conventional tissue conditioner material and can be used with both swallowing and phonetic techniques with equal efficacy.

Keywords: Medium body polyether impression material, neutral zone recording, phonetic method, swallowing method, tissue conditioner material

How to cite this article:
Parab MM, Aras MA, Chitre V, Qanungo A. Comparative assessment of width of neutral zones recorded using two neutral zone impression methods (phonetic and swallowing) and two different materials (tissue conditioner and polyether): A crossover pilot study. Dent Med Res 2021;9:93-9

How to cite this URL:
Parab MM, Aras MA, Chitre V, Qanungo A. Comparative assessment of width of neutral zones recorded using two neutral zone impression methods (phonetic and swallowing) and two different materials (tissue conditioner and polyether): A crossover pilot study. Dent Med Res [serial online] 2021 [cited 2023 Jan 30];9:93-9. Available from: https://www.dmrjournal.org/text.asp?2021/9/2/93/331401

  Introduction Top

Severely atrophic ridges always pose a challenge to the clinician during fabrication of complete dentures in terms of compromised stability of denture. Dental implants may be considered to be used for stabilization of dentures; however, certain situations such as systemic health problems do not permit the implant treatment option or when cost is a factor.[1] Hence, a neutral zone technique can be an alternative and valuable technique in such cases. Fish (1933) highlighted that denture stability is affected by the muscular function of the tongue, cheeks, and lips.[2] Neutral zone also referred to as the dead space or zone of equilibrium is “the potential space between the lips and the cheeks on the one side and the tongue on the other side that area or position where the forces between the tongue and cheeks or lips are equal.”[3] Various techniques have been reported in the literature such as phonetic, swallowing, smiling, sucking tongue movements, blowing, and whistling. So also, various materials are being used for recording the neutral zone such as tissue conditioner material, zinc oxide eugenol impression material, silicone material, chairside relining material, and acrylic resin.[4] Swallowing and phonetic methods using tissue conditioner material are the most commonly employed techniques. Polyether impression material has been recently introduced as a neutral zone recording material.[5],[6]

There are various studies in the literature comparing the dentures fabricated in edentulous subjects using neutral zone methods and conventional methods showing superior results with neutral zones.[7],[8],[9] Furthermore, comparisons have been made among various techniques and materials used to record neutral zone. Makzoume compared phonetic neutral zone method (PNZ) recorded using tissue conditioner material and swallowing neutral zone method (SNZ) using impression compound and found that PNZ method using tissue conditioner yields narrower neutral zone.[10] Komal Ladha et al. found no significant difference in patient satisfaction by SNZ and PNZ using tissue conditioner material.[11]

As most of the alveolar ridge is lost, impression surface of the denture decreases and polished surface increases. To retain the denture stability, recording correct buccolingual width of the denture is mandatory to position the teeth and contour the poshed surface of the denture. Furthermore, there is a paucity of research when newer material like polyether impression material is considered. Hence, the present study was conducted to compare the neutral zones recorded using medium body polyether to those using commonly employed tissue conditioner material. Furthermore, the two most commonly used techniques swallowing and phonetics were compared. The null hypothesis was that there is no significant difference in neutral zone dimensions within both techniques and materials.

  Materials and Methods Top

Selection of patients

Ten completely edentulous patients (male; n = 2, female; n = 8) with ages ranging from 40 to 70 years were selected for the study. Selection of subjects was based on inclusion and exclusion criteria [Table 1]. Patients with advanced mandibular ridge resorption (class V Atwood) were included in the study.[12] Informed written consent was taken from each subject. Conventional steps of complete denture fabrication were followed till the jaw relation recording step. The protocol was approved by Ethical Committee of the Institution.
Table 1: Inclusion and exclusion criteria

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Fabrication of record bases

For each patient, four mandibular record bases were fabricated using autopolymerizing acrylic resin (DPI-RR Cold Cure, Dental Products of India, Mumbai). 21 gauge stainless steel wires was adapted in shape of vertical spurs on the crest region of the record bases supported by vertical acrylic stops touching the maxillary wax rim on the articulator [Figure 1]. The temporary denture bases were tried intraorally for the evaluation of overextention of the borders and adjusted accordingly. Two of the bases were used to mold the resilient tissue conditioner material with both phonetic and swallowing methods. Similarly, other two bases were used to mold the medium body polyether impression material using phonetic and swallowing method.
Figure 1: Modified baseplate with vertical wire spurs attached

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Hence in total 40 neutral zone records were made, 4 per patient that includes,

  1. Swallowing Neutral Zone recording method (SNZ) with tissue conditioner
  2. Swallowing Neutral Zone recording method (SNZ) with polyether
  3. Phonetic Neutral Zone recording method (PNZ) with tissue conditioner
  4. Phonetic Neutral Zone recording method (PNZ) with polyether.

Recording of neutral zones

The patient was seated upright with head supported. Maxillary wax rim was inserted and kept intraorally during the whole recording procedure. The mandibular bases were assessed in terms of stability and muscular function and adjusted to ensure that they are in contact with upper rim evenly in proper vertical dimension.

Techniques used

Phonetic technique

The mandibular denture base was placed intraorally with tissue conditioner (Visco–gel, Denstply International Ltd., UK) mixed with 1:1 ratio and applied on the spurs. For molding the lateral segments, the patient was asked to count from 1 to 10, say exaggerated “ohs,” “ahs,” and “ees,” pronounce the phoneme “sis” 5 times followed by the phoneme “so” once until the polymerization of the material was complete. The patient was asked to pronounce the sounds loudly and vigourously to ensure sufficient muscle contraction. After the material set, it was inspected and excess material was trimmed with a scissor. The same procedure was repeated for the other lateral segments. For anterior segment, the patient was asked to pronounce successively the phonemes “de, te, me, pe, se” vigorously. The records were discarded if the patient swallowed or spoke a sound any other than the phenomes. The same procedure was repeated for all patients and records were obtained.

Swallowing technique

The patient was asked to swallow, purse lips as in sucking for several times, and wet the lips with tongue until the material sets. Furthermore, to make swallowing easier, about 2 ml of warm water was administered intraorally with a syringe before swallowing. The same procedure was followed for all patients.

A putty index was fabricated around each of the four neutral zone records for each patient. This helps in tracing of the records on a graph paper by inverting the putty index on the paper.


In the present study tissue conditioner material (Dentsply viscogel tissue treatment kit) and medium body polyether impression materials (3 M ESPE, Impregum™ Soft, St. Paul, Germany) were used. For tissue conditioner material, 5 ml of tissue conditioner material was mixed in 1:1 ratio and applied on the record bases. For recording with medium body polyether, tray adhesive (3M ESPE, Seefeld, Germany) was first applied and dried on the baseplate. Equal amount of base and catalyst was mixed and applied on the record bases and placed intraorally.

To nullify the results, both materials were used with phonetic and swallowing neutral zone recording methods [Figure 2].
Figure 2: Four neutral zone recordings

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Measurement of neutral zone dimensions

On the mandibular cast, specific lines were drawn indicating median line, right premolar, left premolar, right molar, and left molar, ensuring that the same lines are followed for all the records of each patient [Figure 3]a. The records were then placed on the cast, and a putty index was fabricated around it using addition silicone material. The above five markings were transferred on the index using a marker. The index was then removed from the record and positioned with occlusal surface contacting a graph paper and tracings were made. PNZ contours were traced as solid lines whereas SNZ was traced as dashed lines with the same lead pencil [Figure 3]b.
Figure 3: (a) Five distinct markings made on the cast. (b) Tracing the zones on graph paper

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Neutral zone widths were evaluated by measuring the buccolingual dimension of the tracings using divider and scale. For each tracing, measurements were made at the five distinct locations as marked on the cast [Figure 4]a and [Figure 4]b. In this manner, 20 measurements were made for record of all patients [Figure 5].
Figure 4: (a) Evaluation of neutral zone width on graph paper. (b) Measuring the neutral zone width on a scale

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Figure 5: Tracings of neutral zone for 10 subjects

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Statistical analysis was performed using Mann–Whitney U test. The level of statistical significance was set at P less than 0.05.

  Results Top

Mean age of the participants included was in the age group of 51–60. The mean age and sex of the participants were comparable and had no effect on the four neutral zone recordings obtained.

Comparison of neutral zones obtained with swallowing technique

No statistically significant difference was noted in mean dimension of neutral zones obtained using phonetic technique for both the materials (tissue conditioner and polyether) at all the five constant areas.(P < 0.05) [Table 2].
Table 2: Neutral zone width by swallowing technique comparing tissue conditioner and polyether materials (cm)

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Comparison of neutral zones obtained with phonetic technique

Similarly, the difference in the mean dimensions of the NZ records made using swallowing technique was also statistically insignificant for all the areas (P < 0.05) [Table 3].
Table 3: Neutral zone width by phonetic technique comparing tissue conditioner and polyether materials (cm)

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Differences in mean dimension of neutral zones when compared based on both, the materials the methods also showed no significant difference (P < 0.05) [Table 4] and [Table 5].
Table 4: Statistical analysis showing comparison of techniques (Mann–Whitney U test)

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Table 5: Statistical analysis showing comparison of materials (Mann–Whitney U test)

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The result is summarized in [Graph 1] and [Graph 2].

  Discussion Top

In cases with severe resorption of the ridge, denture stability and retention are more dependent on the correct contour of external surface of denture as well as correct position of teeth. This crossover pilot study was undertaken to compare the difference in mean dimensions of neutral zone obtained using the conventionally used tissue conditioner material and the recently used medium body polyether impression material. Furthermore, the commonly used phonetic and swallowing techniques were used.

In the present study, the null hypothesis was accepted. There was no statistically significant difference within the two selected materials and the two techniques used for recording. This is in consensus with a similar study that was undertaken to compare patient satisfaction with dentures fabricated using two different neutral zone methods (SNZ and PNZ) using a single tissue conditioner material, and there was no significant difference in patient satisfaction in both the groups.[10] Furthermore, different consistency materials were used for by Makzoume to compare the swallowing and phonetic techniques of neutral zone recordings. The author noticed that there occurs a difference between the neutral zones recorded between the two techniques, phonetic technique with tissue conditioner giving a narrower zone compared to swallowing technique with impression compound.[10] However, studies to compare the conventional tissue conditioner material with the recently used materials are lacking.

In the present study, medium body polyether impression material was compared with widely used tissue conditioner material having viscosity similar to polyether impression material. The materials with low viscosity are technique sensitive since control of flow is difficult. So also, the geriatric patients may not have sufficient muscle tone to mold the impression materials with high viscosity like impression compound. Medium body polyether impression material has the advantage of ideal medium viscosity with sufficient body, good flow, easy to use, less time consuming, and no chance of fracturing or swallowing.[5] Working time of medium body polyether impression material is ideal (2 min 45 s), sufficient to carry out the whole molding procedures and hence comfortable for the patient compared to tissue conditioner material.

To eliminate any bias in the results, the whole procedure was carried out by single operator. Furthermore, both materials and both techniques were used in each patient. Since neutral zone width is affected by the occlusal plane level and alteration of vertical dimension,[13] the measurements were made on a constant plane at established vertical dimension. The buccolingual dimensions of neutral zone obtained were compared at five distinct locations for each patient (median line, right and left premolar, and molar region).

The results showed no significant difference in the mean dimension of neutral zones recorded by both the techniques and both the groups. This indicates that polyether impression material can be used as an alternative to the tissue conditioner material. However, this result should be considered carefully since sample size was less. Hence, further research is required to carry out this study with a large sample size and by taking into consideration patient satisfaction.

  Conclusion Top

The present study was carried out to evaluate if any difference occurs in neutral zone dimensions when different material and methods are used for recording the neutral zone.

Within the limitation of this study, the results indicated that there occurs no significant difference in the mean dimensions of neutral zones recorded using swallowing and phonetic techniques with tissue conditioner and polyether impression materials.

Following conclusions can be drawn as follows:

  • Polyether impression material can be viable alternative to the conventional tissue conditioner material
  • Use of polyether impression material depends on operator convenience and skill and material availability
  • Both materials can be used with swallowing, phonetic, or combination of both techniques with equal efficacy.

Ethical clearance

Study protocol has been approved by ethical committee of the Institution.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Gahan MJ, Walmsley AD. The neutral zone impression revisited. Br Dent J 2005;198:269-72.  Back to cited text no. 1
Fish EW. Principles of full denture prosthesis. London: John Bale, Sons and Danielsson, Ltd; 1933. p. 1-8.  Back to cited text no. 2
The glossary of prosthodontic terms. J Prosthet Dent 2005;94:10-92.  Back to cited text no. 3
Porwal A, Sasaki K. Current status of the neutral zone: A literature review. J Prosthet Dent 2013;109:129-34.  Back to cited text no. 4
Yeh YL, Pan YH, Chen YY. Neutral zone approach to denture fabrication for a severe mandibular ridge resorption patient: Systematic review and modern technique. J Dent Sci 2013;8:432-8.  Back to cited text no. 5
Agarwal S, Gangadhar P, Ahmad N, Bhardwaj A. A simplified approach for recording neutral zone. J Indian Prosthodont Soc 2010;10:102-4.  Back to cited text no. 6
Stromberg WR, Hickey JC. Comparison of physiologically and manually formed denture bases. J Prosthet Dent 1965;15:213-30.  Back to cited text no. 7
Barrenäs L, Odman P. Myodynamic and conventional construction of complete dentures: A comparative study of comfort and function. J Oral Rehabil 1989;16:457-65.  Back to cited text no. 8
Fahmy FM, Kharat DU. A study of the importance of the neutral zone in complete dentures. J Prosthet Dent 1990;64:459-62.  Back to cited text no. 9
Ladha K, Gupta R, Gill S, Verma M. Patient satisfaction with complete dentures fabricated using two neutral zone techniques: A within-subject cross-over pilot study. J Indian Prosthodont Soc 2014;14:161-8.  Back to cited text no. 10
Makzoumé JE. Morphologic comparison of two neutral zone impression techniques: A pilot study. J Prosthet Dent 2004;92:563-8.  Back to cited text no. 11
Atwood DA. The problem of reduction of residual ridges. In: Winkler S. Essentials of complete denture prosthodontics. 2nd ed. St. Louis: Mosby Year Book; 1988. p. 22-38.  Back to cited text no. 12
Razek M, Abdalla F. Two-dimensional study of the neutral zone at different occlusal vertical heights. The Journal of Prosthet Dentistry 1981;46:484-9.  Back to cited text no. 13


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

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


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