J. Adv Dental Research CASE REPORT

All Right Res

Journal of Advanced Dental Research Vol II : Issue I: January, 2011 www.ispcd.org

Enhancement of stability for mandibular

complete denture prosthesis in atrophied

ridge with neutral zone technique — A

case report

Viraj Patil* R B Hallikerimath** Shweta Magadum***

*M.D.S, Professor, **M.D.S, Professor, ***Post Graduate student, Department of Prosthodontics,

Maratha Mandal’s Nathajirao G. Halgekar Institute of Dental Sciences and Research Centre.

Belgaum. Karnataka, India. Email: drvirajpatil@gmail.com

Abstract:

The Neutral Zone technique is not a new but a very

valuable technique, it is an alternative approaches in

constructing stable complete denture in case of a

highly atrophic mandible. The main aim of the

Neutral zone technique is to construct denture in

muscle harmony, so that it does not get displaced

during the actions of the muscles surrounding as the

actions of swallowing, mastication, speech and so on.

Key words—Neutral zone, Atrophic mandible.

Introduction:

The goal of dentistry is for patients to keep all

their teeth throughout their lives in health and comfort. If

the teeth are lost despite all efforts to save them, a

restoration should be made in such a manner as to

function efficiently and comfortably in harmony with the

muscles of the stomatognathic system and the

temporomandibular joints. With the increase in the life

expectancy of the population, the numbers of complex

complete denture cases also have been increasing. The

treatment for these complex complete denture cases

should be different from those of traditional complete

dentures. In case of Atrophic mandible, Dental implants

may provide stabilization of mandibular complete

dentures, but in cases when it is not possible to provide

implants on the grounds of medical risks, economic

limitations or patients attitudes, an alternative technique

should be thought1. The Neutral Zone Technique is an

alternative approach for these cases. The Neutral zone

technique is not new, but is one that is valuable yet not

practiced. The Neutral zone has been defined as the area

in the mouth where during function, the forces of the

tongue pressing outwards are neutralized by the forces of

the cheek and lips pressing inwards.

The aim of the Neutral zone is to construct a

denture in muscle balance. If the denture is out of

harmony with the neutral zone, it will result in instability,

interference with function or some degree of discomfort.

Thus neutral zone must be evaluated as an important

factor before aligning the teeth in complete denture or

partial denture. This is the zone where the natural

dentition exists. As the mandible atrophies at a greater

rate than the maxilla and has less residual ridge for

retention and support, the lower denture commonly

presents the most difficulties with pain and looseness

being the most common complaints. The Neutral zone

technique is most effective for patients who have had

numerous unstable and nonretentive lower complete

dentures. These patients usually have a highly atrophic

mandible and there has been difficulty in positioning the

teeth to produce a stable denture. The Neutral zone

approach has been used for patients who have had a

partial glossectomy, mandibular resections or motor nerve

damage to the tongue– which have led to either atypical

movement or an unfavorable denture bearing area.

Background:

Sir Wilfred Fish in 1931 first described

the influence of the polished surface on retention and

stability. He also described how dentures should be

constructed in the ‘dead space’, which later became as the

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Journal of Advanced Dental Research Vol II : Issue I: January, 2011 www.ispcd.org

Neutral Zone1. Since then many techniques have been

described in the literature in an attempt to provide a

molding of the Neutral zone. These techniques involved

the use of soft, moldable material being placed in the

mouth and patients performing actions with their lips,

cheeks and tongue in order to capture actions with their

lips, cheek and tongue. These actions determine the tooth

position and shape of the polished surfaces. In highly

atrophic mandible muscular control over the denture is the

main retentive and stabilizing factor during function.

• The denture shaped by the Neutral zone technique

will ensure that the muscular forces are working

more efficiently and in harmony.

• Other advantages1----

• Improved retention and stability

• Posterior teeth will be correctly positioned

allowing sufficient tongue space.

• Reduced food trapping adjacent to the molar

teeth

• Good esthetics due to facial support.

Factors affecting the neutral zone: Muscles and the neutral zone: The actions of following

muscles affect.

• Muscles of cheek:

• Buccinator

• Masseter

• Muscles of lips:

• Orbicularis oris

• Caninus

• Muscles of tongue

Clinical case report:

A 55 year old male patient was referred

to the department of prosthodontics for the provision of

complete denture. He had been edentulous since 7 yrs. He

was a denture wearer and was willing for a new set of

denture due to the reduced retention and repeated fracture

of the denture. On examination it was diagnosed that the

maxillary residual ridge was favourable, but the

mandibular residual ridge was unfavorable due to

resorption. Then it was decided to provide lower complete

denture, utilizing Neutral zone impression technique.

Clinical visit 1

At the first visit primary impression of

the maxillary and mandibular edentulous residual ridge

were made with modelling plastic compound impression

material. Soon after making primary impression, the

impression was poured in plaster of paris and primary

casts were prepared. The custom trays were fabricated

with self cure resin over the primary casts keeping the

borders 2mm short of the sulcus.

Clinical visit 2

The borders of the trays were molded

with green stick impression compound and the secondary

impressions were made with zinc oxide eugenol

impression material. The master casts were poured in

dental stone plaster. In order to increase the

stability and retention of the record bases during

recording the neutral zone, the permanent bases were

prepared in heat cure resin on master casts. Wax occlusal

rims were made over the permanent record bases for

recording the jaw relations.

Clinical visit 3

During this visit face- bow transfer was

made (fig 1) and centric jaw relation was recorded on

semi-adjustable (Hanau Wide view) articulator. The

mandibular rim was completely removed and wire loops

were adapted over the permanent record base in

accordance with the recorded vertical height of jaw

relation (fig 2).

Figure 1- Face-bow transfer

Clinical visit 4

The maxillary record base with wax occlusion rim and

mandibular record base with wire loops were evaluated

intra-orally for their fit (fig 3). The maxillary rim was left

in mouth in order to provide enough support to the facial

musculature during making neutral zone impression. Then

the tissue conditioning material (GC Corporation Tokyo.

Japan) was mixed and loaded over the wire loops on

buccal and lingual aspects and inserted in mouth and

patient was asked to perform the usual movements, which

included swallowing, sucking of the lips, pronouncing the

vowels, which helped in recording the neutral zone

space(fig 4).

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Journal of Advanced Dental Research Vol II : Issue I: January, 2011 www.ispcd.org

Figure 2- Adaptation of wire loops in accordance with

obtained vertical dimension

Figure 3- Evaluation of loops intra- orally

Next step was to make plaster

indices (fig 5) surrounding the neutral zone impression.

‘V’ shaped indexes were made on the mandibular cast, in

order to guide the placement and removal of the plaster

Figure 4- Recording neutral zone with tissue

conditioner

indices properly. Then the tissue conditioning material

and the adapted wire loops were removed from the

mandibular record base. Now an empty space (neutral

zone space) was evident within the plaster indices. Next

molten wax was made to flow in this empty neutral zone

space, in order to create rim for arranging the mandibular

teeth in the neutral zone. According to the neutral zone

space recorded, the mandibular teeth were arranged (fig6)

and in accordance with the mandibular teeth, maxillary

teeth arranged. The wax contours were preserved in case

of mandibular denture as derived from neutral zone

technique and no additional wax was added on denture

flanges.

Figure 5- Plaster index surrounding Neutral zone

impression

Figure 6- Teeth arrangement in Neutral zone space

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Journal of Advanced Dental Research Vol II : Issue I: January, 2011 www.ispcd.org

Clinical visit 5

Try-in was done, in order to evaluate

the stability, esthetics and occlusion intra-orally and

satisfactory results were seen. Then the dentures were

processed with heat cured acrylic.

Clinical visit 6

Denture insertion (fig 7) was done

and again it was evaluated for stability, esthetics and

occlusion. Results were found satisfactory and patient

also was satisfied with the dentures.

Figure 7- Denture insertion

Conclusion: Neutral zone technique is one of the best

alternative techniques in case of highly atrophied

mandibular residual ridge, but it is rarely used because of

the extra clinical step involved. The neutral zone

philosophy is based on the concept that for each

individual patient there exists within the denture space a

specific area where the function of the musculature will

not unseat the denture, and at the same time where the

forces generated by the tongue are neutralized by the

forces generated by the lips and cheeks. Orthodontic

relapses, postoperative problems, unsuccessful

periodontal procedures and relapses with orthognathic

surgery can be attributed to neutral zone imbalance.

Complete and partial denture failures are often related to

non compliance with neutral zone factors. Thus the

neutral zone must be evaluated as an important factor

before one rates any changes in arch form or alignment of

teeth.

References:

1. Gahan MJ, Wansley AD.The neutral zone

impression revisited. Br Dent J 2005; 198(5):

269-72

2. Lymph CD, Allen PF. Overcoming the unstable

mandibular complete denture: The neutral zone

impression technique. Dental update 2006; Jan-

Feb 33(1); 21-2, 24-6.

3. David R, Cogna et al. The neutral zone revisited:

from historical concepts to modern application. J

Prosthet Dent 2009; 101(6):405-12.

4. Kokuto Y, Fukushimas et al. Arrangement of

artificial teeth in neutral zone after surgical

reconstruction of mandible: a clinical report. J

Prosthet Dent 2002; 88(2):125-7.

5. Alfano SG, Leupold RJ. Using neutral zone to

obtain maxillomandibular relationship records

for complete denture patients. J Prosthet Dent

2001; 85(6):621-23.

6. Victor E. Beresin et al. The neutral zone in

complete dentures. J Prosthet Dent 2006;

95(2):93-101.

7. Fahmy F M, Kharat D U. A study of the

importance of the neutral zone in complete

dentures. J Prosthet Dent 1990; 64(4): 459-62.

8. Cantor R, Curtis TA. Prosthetic management of

edentulous mandibulectomy patients. Part II.

Clinical procedures. J Prosthet Dent 1971;

25:546-55.

9. Frank J, Schiesser JR. The neutral zone and

polished surfaces in complete dentures. J

Prosthet Dent 1964; 14(5): 854-65.

10. Fahmi FM. The position of the neutral zone in

relation to the alveolar ridge. J Prosthet Dent

1992; 67: 805-9.

Source of Support: Nil

Conflict of Interest: Not Declared

Received: September 2010

Accepted: December 2010