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Neutral Zone in Complete Dentures:
Systematic Analysis of Evidence and Technique
• Ahmad A. Jum’ah, BDS(Hons), MSc/PhD (Clin) Student-Second year
Restorative Dentistry Department, Leeds Dental Institute, University of Leeds, UK
dnaahj@leeds.ac.uk
• Peter J. Nixon, Senior Consultant in Restorative Dentistry, Leeds Dental Hospital,
Leeds Teaching Hospitals Trust (LTHT), England, UK
Abstract
Neutral zone technique is a physiologic and functional approach that is widely and concisely described as a treatment
modality for unstable lower complete denture cases. It serves as a guide of where to set teeth and how to contour the
polished surface of the denture to ensure optimal stability, retention, facial support and aesthetics. In patients with
compromised support and poor denture adaptability, this technique is considered as a valuable tool in the prosthodontist’s
armoury especially where dental implants are contraindicated or unfeasible. The aim of this article is to describe the concept
and technique of neutral zone, discuss rationale, indications and to evaluate this technique from evidence-based perspective.
Abbreviations: NZ: Neutral zone, CD: complete denture, VDO: Vertical dimension at occlusion.
Introduction
Stability of lower CDs is well recognized as a potentially
difficult treatment aim to achieve. Looseness and discomfort
are the most frequent complaints reported by patients and
they are quite often difficult to manage by dentists.
Neuromuscular control is said to be the key determinant
of stability of lower CD as the area available for support is
far less than maxillary support area. Size and position of
prosthetic teeth and the contours of polished surface have
a crucial role in lower CD stability as they are subjected to
destabilizing forces from the tongue, lips and cheeks if they
are placed in hindrance with function of these structures. 1
Throughout time, many concepts and theories emerged
to describe where prosthetic teeth of CD should
be positioned. Some of them adopted mechanical
principles, 2,3 others used biometric guides 4 and a minority
advocated mathematical formulas based on natural teeth
position and dimensions. 5 These dogmatic or arbitrary
approaches have been challenged and found insufficient,
in fact not only by rigorous research, but also by failure
to restore function, aesthetic and comfort in patients with
severely atrophic mandibular ridges (Class V Atwood’s 6 ),
patients with enlarged tongue and cases of marginal or
segmental mandibulectomy. To overcome such problem,
the neutral zone technique was advocated.
The neutral zone, zone of minimal conflict, 7 zone of
equilibrium, 8 potential denture space 9 and the dead
space 10 are all terms used to describe the potential area
where forces generated in an outward direction from the
tongue are being neutralized or balanced by the inward
forces generated by lips and cheeks during functional
activities. Setting teeth and contouring polished surface
of lower CD within this zone, makes the prosthesis less
subjected to dislodging forces and adds more to stability. 11
Analysis of functional forces
Understanding the unique and synergistic interplay
and complex movements of muscles of cheeks, lips
and tongue is the first step in construction of lower
CD that is stabilized rather than being dislodged by
movements of these structures. 11,12 Description of forces
applied to the lower CD purely on the basis of direction
is an oversimplification, yet, it is quite useful for better
understanding of the concept. 12
The outward forces are principally generated by the
tongue and lingual frenum into which, genioglossus
muscle is inserted. Teeth should be set and flanges should
be contoured in harmony with tongue size, position and
shape during rest and function. In rest position, the tongue
rests on lingual cusps of posterior teeth and lingual
flanges posteriorly and anteriorly. The tongue space
determined by position of teeth is far more important
during function. Setting teeth too lingualy will encroach
on this space and the tongue tends to dislodge denture
in function. The height of posterior teeth is of a great
importance in stability of lower CD as well. Having the
tongue resting on lingual cusps will reduce the horizontal
(outward) force and apply force with vertical (downward)
component which enhances stability and retention. 11
Inward forces are generated by cheeks resulting from
contraction of the buccinator muscle that pushes food
bullous on top of occlusal surfaces of posterior teeth.
Flanges contoured and teeth set too buccal are at
increased risk of being dislodged by the action of this
muscle. Anteriorly, lip muscles (mentalis and orbicularis
oris) are the source of inward forces generated during
speaking and swallowing. Contraction of these muscles
to attain seal during these activities can destabilize lower
CD with teeth and flanges placed too far labially. The
modiolus is a knot-like structure found in corners of the
| 8 | Smile Dental Journal | Volume 6, Issue 4 - 2011