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CASE REPORT

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ESTABLISHING ZONE OF EQUILIBRIUM

FOR STABLE MANDIBULAR COMPLETE

DENTURES: A CASE REPORT

Dr. Shruti Pillai , Dr. B. Devi Parameswari , Dr. H. Annapoorni

Department of Prosthodontics, Faculty of Dentistry

Meenakshi Academy of Higher Education and Research,

Chennai, Tamil Nadu, India

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ABSTRACT

Complete denture stability and retention depends

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upon its coordination with the surrounding muscles

and oral structures. Improper position of teeth will

make the denture unstable during talking, swallowing

and mastication. Thus the denture teeth should be

placed in’ neutral zone’ where the displacing forces

of tongue, lips, cheeks and modulus are balanced.

This is a case report in which neutral zone impression

technique was used to solve the problem of denture

instability especially in patients who cannot afford

Address for Correspondence:

implant retained dentures.

Dr. B. Devi Parameswari

KEYWORDS: resorption, stability, retention,

Department of Prosthodontics,

neutral zone, mandibular denture.

Faculty of Dentistry

Meenakshi Academy of Higher Education and

Research,

Chennai, Tamil Nadu, India

e-mail id : drdeviparameswari@gmail.com

Received

: 05.08.2019

Accepted

: 03.09.2019

Published

: 27.09.2019

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Devi et al: Establishing zone of equilibrium for stable mandibular complete dentures

INTRODUCTION:

Due to financial reasons, it was planned to provide

the patient with complete dentures fabricated by

The retention and stability of mandibular

neutral zone technique.

complete dentures is challenging due to residual

alveolar resorption and proximity to the limiting

Maxillary

and mandibular

primary

structures. As the area of the impression surface

impressions were made with impression compound

decreases in ridge resorption, denture retention

(Y-Dents

Impression

Composition,

MDM

and stability becomes more dependent on correct

CORPORATION) (Fig 2).

positioning of the teeth and the contours of the

external or polished surface of the dentures. Therefore

the tooth position and the contouring of the denture

surfaces should be so that the horizontally directed

forces applied by the peridenture muscles should act

to seat the denture in well balanced muscular space

known as neutral zone.^ˡ Sir Wilfred Fish of England

described neutral zone concept in 1931. The neutral

zone is defined as the potential space between the

lips and cheeks on one side and the tongue on other;

Fig 2: Primary impressions

that area where forces between the tongue and cheeks

or lips are equal (GPT 9)¹. Positioning of teeth in

Border moulding was done with low fusing

this zone is essential for enhancing the stability and

compound (DPI Pinnacle Tracing Sticks). The lower

retention of mandibular dentures in patients who

special tray with the softened low fusing compound

cannot afford for implant retained dentures.

in a 65˚C water bath was placed in the patient’s

mouth; this tray was very carefully adjusted in

This case report describes the neutral zone

the mouth to be sure that it was not overextended

technique for fabrication of complete dentures for

and remained stable during opening, swallowing,

a patient with severely resorbed residual alveolar

and speaking. The patient was then asked to talk,

ridges.

swallow, do tongue movements etc. After 5- 10 min,

the set impression was removed from the mouth and

CASE REPORT:

examined. 1 mm of compound was scrapped from the

tray. Upper and lower master impressions were made

A 70-year old female patient reported to

using light viscosity addition silicone

(Zhermack

the Department of Prosthodontics, with the chief

elite HD+ addition silicone) (Fig 3).

complaint of difficulty in mastication due to missing

teeth. There was no relevant medical history. Intra-

oral examination revealed completely edentulous

upper and severely resorbed lower arch. (Fig1).

The different treatment options for prosthetic

rehabilitation were

-1) Conventional complete

dentures; 2) Complete dentures with neutral zone

technique (3) Implant retained prosthesis.

Fig 3: Master impressions

Wax rims were fabricated and jaw

relationship was recorded which was then mounted

on an articulator. The diagnostic articulation helped

to assess the available inter arch space. Mandibular

occlusal rim was completely removed and wire loops

were attached over the record base in accordance

with recorded vertical height. Maxillary occlusion

Fig 1: Edentulous upper and lower arch

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JIDAM/Volume:6/Issue:3/Pages 110 - 113/July-September 2019

Devi et al: Establishing zone of equilibrium for stable mandibular complete dentures

rim and modified mandibular record base with

were cut on the master cast and was covered with a

wire loops were evaluated intra-orally for their fit

silicone putty index around the impression on both

& ensured that loops do not interfere with muscle

the labial and lingual sides (Fig 5).

movement during function [Fig 4]. Maxillary rim

was left in mouth in order to provide enough support

to the facial musculature during making neutral zone

impression.

Fig 5: Silicone index

The position of the teeth was checked by

placing the index together around the wax try in (Fig

6). The waxed up dentures were placed in the mouth

and patient was asked to repeat all the movements

previously mentioned.

Fig 4: Modified mandibular denture base

NEUTRAL ZONE IMPRESSION:

The patient was made comfortable in an

upright position with the head unsupported. Maxillary

Fig 6: Waxed up denture

wax rim was inserted in the mouth and reassessed for

support & occlusal plane. Low fusing compound was

The denture was stable after all the

softened in a 65˚ C water bath and kneaded into a roll

movements. Aesthetics, phonetics and occlusion

which was formed according to the crest and adapted

were assessed. The dentures were then processed as

it to retentive loop at established vertical dimension.

a conventional denture. Finishing and polishing of

The attached roll of compound was reheated in the

denture was done carefully so that the contour of the

water bath and was carried into the patient’s mouth.

polished surfaces remained unaltered. On insertion

With the record base firmly seated, the patient was

of denture, minor occlusal discrepancies were

asked to perform a series of actions like swallowing,

corrected.

speaking, sucking, pursing lips, pronouncing

vowels sipping water and slightly protruding the

tongue several times which simulated physiological

functioning. These actions molded the material by

muscle activity. After 10 minutes, the set impression

was removed from the mouth.

The neutral zone impression so obtained

was placed on the master model, locating grooves

Fig 7: Post-insertion photograph

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JIDAM/Volume:6/Issue:3/Pages 110 - 113/July-September 2019

Devi et al: Establishing zone of equilibrium for stable mandibular complete dentures

Post-insertion instructions were given to the patient

filled with calcium silicate, silicone, and tissue

(Fig 7). Periodic review was carried out for 1 year.

conditioners and resilient lining materials.⁵

DISCUSSION:

CONCLUSION:

Edentulousness can greatly affect the

Neutral zone technique in complete dentures

psychology of the patient. According to Devan,

is rarely used because of the complexity and extra

‘Perpetual preservation of what remains is more

clinical steps involved in the procedure.⁶ Teeth

important than the meticulous replacement of what

should be arranged as dictated by the musculature,

is missing’². So preserving the remaining healthy

and this will vary for different patients. So, neutral

teeth and providing overdentures can enhance their

zone must be evaluated as an important factor during

retention, thereby reducing the amount of ridge

the fabrication of complete dentures. Therefore this

resorption³. If none of the teeth could be saved, then

technique is one of the best alternative techniques in

the complete extraction followed by the conventional

cases of highly resorbed mandibular residual ridge

complete dentures or implant supported dentures are

where implant supported dentures are not possible or

the only options.

affordable by such patients.

The coordination of complete dentures

FINANCIAL SUPPORT AND

with neuromuscular function is the foundation of

SPONSORSHIP:

successful, stable dentures. The soft tissues that

form the internal and external boundaries of the

Nil

denture space exert forces which greatly influence

the stability of the dentures.³ The main aim of the

CONFLICT OF INTEREST:

neutral-zone approach (Fig 8) is to locate that area

in the edentulous mouth where the teeth should

There is no conflict of interest

be positioned so that the inward forces exerted by

mentalis, buccinator muscles and outward forces

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by the muscles of tongue will tend to stabilize the

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Prathyush et al : Tooth supported overdentures - a

case report. Journal of Indian Dental Association

Madras (JIDAM) 2019; 6(1):37-41.

Beresin V E & Schiesser F J. The neutral zone

in complete dentures. The Journal of Prosthetic

Fig 8: Neutral zone

Dentistry 2006;95(2):93-100.

Complete dentures fabricated by conventional

Anooj Lukram, Rajani A Dable, Piyush Tandon,

techniques result in denture borders that may not

Kuldeep. Neutral zone - a case report. TMU J.

facilitate denture stability against the existing oral

Dent 2014;1(4);152-154.

and perioral muscle forces. This will result in ill

Shekar S Chandra. Management of a severely

fitting prosthesis which might be uncomfortable for

resorbed mandibular ridge with the neutral zone

the patient for function.⁴

technique. Contemp Clin Dent 2010; 1(1); 36-39.

Many materials have been suggested for

shaping the neutral zone: modeling plastic impression

compound, soft wax, a polymer of Dimethyl siloxane

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