sunitha article 1

COMPARATIVE EVALUATION OF TWO NEUTRAL ZONE IMPRESSION

TECHNIQUES : A PILOT STUDY

ABSTRACT:

Purpose : The purpose of this pilot study was to compare the outline form of the phonetic and

swallowing neutral zone impression techniques for both maxillary and mandibular arches on

same subjects and also to evaluate which prosthesis provides comfort to the patient.

Material and methods:

Five patients with advanced maxillary and mandibular ridge resorption were included in this

study. For each arch 2 trays were prepared in autopolymerizing acrylic resin. One method used

phonetics and modeling plastic impression compound followed by zinc oxide eugenol to shape

the neutral zone; the second method used swallowing and modeling plastic impression

compound followed by zinc oxide eugenol to shape the neutral zone. The resulting neutral zone

impressions were leveled to the same occlusal height by gently grinding the occlusal surface on

sandpaper until it corresponded with landmarks (corners of the mouth, two thirds of the height of

the retromolar pads, bilaterally) noted on the cast. The impression was inverted onto graph paper,

and the contour was outlined with a lead pencil. One impression was made for each technique.

The buccal contours of both neutral zones coincided at the median line.

Results: The phonetic neutral zone was narrower and found to be located lingual to the

swallowing neutral zone. The patients who are given dentures with functional method of

recording neutral zone have better satisfaction in terms of stability and chewing efficiency.

Conclusion: The location of neutral zone was not the same with the swallowing and the

phonetic technique. In general, the PNZ technique resulted in impressions where the neutral

zone appeared to be narrower as the buccal surface was located more lingual compared to

the SNZ technique.

Key words: Neutral zone, Phonetic, swallowing.

The neutral zone is defined as ‘‘the

potential space between the lips and cheeks

on one side, and the tongue on the other;

that area or position where the forces

between the tongue and cheeks or lips are

equal1. The various synonyms for neutral

zone are Dead zone, Stable, Zone of

minimal conflict, Potential denture space

zone of equilibrium, Biometric denture

space, denture space, Zone of least

interference.

All oral functions, such as speech,

mastication, swallowing, smiling, and

laughing, involve the synergistic actions of

the tongue, lips, cheeks, and floor of the

mouth which are very complex and highly

individual. Failure to recognize the cardinal

importance of tooth position and flange form

and contour often results in dentures which

are unstable and unsatisfactory, even though

they were skillfully designed and expertly

constructed.

The neutral zone concept is very

important while fabricating complete

dentures especially for patients with reduced

mandibular residual ridges3. Because the

mandibular denture is more likely to be

displaced during function than the maxillary

denture. Incorrect tooth placement and

arbitrary shaping of the polished surfaces

may have an adverse effect on the success of

the prosthesis.

So the contour of the lower denture should

be such that there is minimal interference

with the denture by the related soft tissues

during functional movements.

The aim of the neutral zone is

to construct a denture in muscle balance. A

denture which is in harmony with its

surroundings to provide optimum stability,

retention and comfort. The neutral zone

technique is most effective for patients who

had numerous unstable, un retentive lower

complete dentures.

Muscles and the neutral zone:

Dentures should occupy a position

in the mouth where all the forces during

function are neutralized2. The outer limits of

the neutral zone are determined by the

perioral musculature like Buccinator,

Masseter, Orbicularis oris, Canine muscle,

greater zygomatic muscle, risorius, mentalis

and by tongue muscles like styloglossus,

palatoglossus, hyoglossus, and genioglossus.

The purpose of this study was to

compare the outline form of the phonetic

and swallowing neutral zone impression

techniques for both maxillary and

mandibular arches on the same subjects

and also to evaluate which prosthesis

provides comfort to the patient.

MATERIALS AND METHODS :

5 Patients were selected for

treatment on the basis of those patients who

considered their dentures to be clinically

unacceptable and with advanced ridge

resorption. The preliminary impressions

were made with impression compound.

After border moulding final impressions

were made with zinc oxide euenol.

After obtaining master casts the 4 pairs of

denture bases were made for each arch. First

pair is used for recording the neutral zone

by phonetic method. Second pair is used for

recording the neutral zone by swallowing

method. Third and forth pair of denture

bases were used for obtaining wax occlusal

rims according to the pumice plaster

indexes.

In this study neutral zone was recorded

by using both phonetic and swallowing .

During recording of neutral zone to retain

material on denture bases an orthodontic

wire in the form of u shaped loops is placed

on the ridge crest.

Mandibular Maxillary

After attaching this wire to the denture

base, a thin layer of impression compound is

placed both buccal, lingual and occlusal to

this wire. This compound was softened by

immersing in warm water for 2 min and then

it is placed in the subjects mouth without

distorting the rim.

While the material in softened stage, in

phonetic method instruct the patient to

pronounce phonemes whereas in

swallowing method instruct the patient to

perform certain activities. Then buccal and

lingual to this impression compound zinc

oxide eugenol paste is added and instruct the

patient to pronounce phonemes in phonetic

method, whereas in swallowing method

instruct the patient to perform certain

activities.


After moulding

Phonetic method : In this method the

subject was instructed to pronounce

phonemes like Sis in the form of sister, So

in the form of somu, De in the form of dean,

Te in the form of tea, Me in the form of

meena, Pe in the form of pea, Se in the form

of seeta, E in the form of knee.


Swallowing method :

In this method the subject was instructed to

perform functions like Swallowing,

sucking, Grinning, whistling and pursing

the lips.

The resulting impressions were

leveled to the same occlusal height by gently

grinding the occlusal surface until it

corresponded with landmarks like anteriorly

height of lower lip, the commisures laterally,

and to a point located approximately 2/3rd of

the height of the retromolar pad posteriorly

for mandibular record. Whereas for

maxillary arch 2 mm below the upper lip

anteriorly and parallel to the ala tragus line

posteriorly.


The impressions were inverted on

the graph paper and contours of both

records were outlined. These contours were

super imposed such that buccal contours of

both records coincided with the median line.

The recording of the phonetic

neutral zone was always performed before

that of the swallowing neutral zone, and an

impression was made for each subject using

each technique.

For Mandibular arch:

Phonetic: Red Swallowing: Violet

For maxillary arch :

Phonetic : Red Swallowing: Violet

The lower anterior teeth are set to the

height of the labial matrix and to the labial

limit of the neutral zone4.

The upper anterior teeth are set against

the labial limits of the upper matrix.

The lower posterior teeth are set against

the tongue matrix and against the template

occlusally.

The upper posterior teeth are set, to the

buccal limits of the neutral zone. The

matrices are removed, and the upper bow of

the articulator is closed in order to evaluate

the relationship of the upper and lower

posterior teeth.

Try in done followed by denture

processing done by using compression

moulding technique.

First dentures made by phonetic

method were given. After one week patient

is recalled and the dentures were collected

from patient. The patient was left out

without dentures for a period of one week to

allow deprogramming of muscles. Then the

dentures made by swallowing method were

given.

RESULTS :

The location of the neutral zone was not

the same with the swallowing and phonetic

technique. The phonetic neutral zone

appeared to be narrower as the buccal

surface was located more lingual compared

to the swallowing neutral zone technique.

Visual analog scale :

It is a measurement tool that can be applied to evaluate patients perception.

It is simple to administer, reliable and valid.

Questionnaire :

1) How satisfied are you with your dentures ?

A) Dentures by phonetic method:

not pleased pleased very pleased

B) Dentures by swallowing method:


2) Which dentures are more comfortable ?





3) With which dentures are you able to speak comfortably ?



B)Dentures by swallowing method:


4) With which dentures are you chewing efficiently ?





5) Which dentures are more stable in your mouth?





6) Which dentures are esthetically pleasing ?





Analysis :

Within the limitations of the study,

the patients who are given dentures with

functional method of recording neutral zone

have expressed better satisfaction in terms of

stability, and chewing efficiency. But the

dentures made by phonetic method shows

better pronouncation.

CONCLUSION :

The location of the neutral zone was not the

same with the swallowing (functional) and

the phonetic technique. In general, the

phonetic neutral zone technique resulted in

impressions where the neutral zone appeared

to be narrower as the buccal surface was

located more lingual compared to the

swallowing neutral zone technique.

REFERENCES:

Morphologic comparison of two neutral

zone impression techniques: A pilot study.

JPD 2004; 92:563-8

The neutral zone in complete dentures.

J Prosthet Dent 2006; 95: 93-101

The neutral zone impression revisited .

British Dental Journal 2005; 198: 269–272

Neutral zone approach for denture

fabrication for a partial glossectomy patient:

A clinical report

JPD Oct 2000; Vol 84, No 4

Neutral zone dentures versus conventional

dentures in diverse edentulous periods

Biomedica 2009; Jul - Dec ; Vol.25.

Perceptions of patients’ smiles. JADA

2007; 138(12):1544-53.

Rehabilitation of a Marginal

Mandibulectomy. Patient using a Modified

Neutral Zone Technique: A Case Report.

Braz Dent J (2007) 18(1): 83-86

Using the neutral zone to obtain maxilla

mandibular relationship records for

complete denture patient. J Prosthet Dent

2001;85:621-3.

Muscle formed complete mandibular

dentures. JPD 1976; Mar : vol 35; No.3: 254

– 258.

Enhancement of stability for mandibular

complete denture prosthesis in atrophied

ridge with neutral zone technique — A case

report. Journal of advanced dental research

2011; Jan : vol 11; I1.

Identifying the denture space. JOR, 1982,

Vol 9, pg : 259-277.

sunitha article 1

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