What Is The Neutral Zone And How Is It Used
Cureus. 2017 Apr; 9(4): e1189.
Improvised Neutral Zone Technique in a Completely Edentulous Patient with an Atrophic Mandibular Ridge and Neuromuscular Incoordination: A Clinical Tip
Monitoring Editor: Alexander Muacevic and John R Adler
Prathibha Saravanakumar
1 Section of Prosthodontics, Kinesthesia of Dental Sciences, Sri Ramachandra University, Porur, Chennai, India
Saravanan Thirumalai Thangarajan
one Department of Prosthodontics, Kinesthesia of Dental Sciences, Sri Ramachandra Academy, Porur, Chennai, India
Umamaheswari Mani
1 Department of Prosthodontics, Faculty of Dental Sciences, Sri Ramachandra University, Porur, Chennai, India
Anand Kumar V
1 Department of Prosthodontics, Faculty of Dental Sciences, Sri Ramachandra Academy, Porur, Chennai, Bharat
Received 2017 Apr five; Accepted 2017 Apr 24.
Abstract
Resorption of mandibular ridges is a multifactorial and biomechanical illness that is chronic, progressive, irreversible, and cumulative leading to loss of sulcular depth, vertical dimension loss, and decreased lower facial height. Some common neurological, hormonal, and metabolic disorders affect the adaptability of dentures, and this can be diagnosed past a trained prosthodontist with proper history-taking and clinical exam.The denture becomes passive due to circuitous neuromuscular control and causes difficulties in impression-making, mastication, and swallowing, which in plow leads to loss of retention and stability in complete dentures. Hence, residual ridge resorption becomes a challenging scenario for a clinician during fabrication of consummate dentures. The neutral zone concept plays a meaning role in overcoming these challenges. The neutral zone is the area where the outward forces from the tongue are neutralized or nullified by the forces of the lips and cheeks acting in during functional movements.The neutral zone technique is an culling approach for the construction of lower complete dentures. It is well-nigh effective for dentures where there is a highly atrophic ridge and history of denture instability. The technique aims to construct a denture that is shaped by muscle office and is in harmony with the surrounding oral structures. The technique is past no ways new, but information technology is a valuable ane. It is rarely used because of the extra clinical step involved and its complexity. Complete and partial denture failures are often related to non-compliance with neutral zone factors. Thus, the evaluation of the neutral zone is an important factor. Increased retention and stability with reduced chairside time are the salient features of this new approach to whatever clinically challenging situation in consummate dentures.This clinical report describes a modification of the conventional neutral zone technique using improvised procedures to minimize chairside visits for a patient with an atrophic mandibular ridge and neuromuscular incoordination.
Keywords: neutral zone, atrophic ridge, admix material, neuromuscular incoordination
Introduction
The principal concern for all patients is to retain all of their teeth comfortably throughout their lives through skillful oral health. Once a patient loses teeth, rejuvenating oral function and maintaining harmony with the muscles of the temporomandibular joints and the stomatognathic system is crucial. As the life expectancy of the population has increased, there is too a proportional increase in the complexity of complete denture cases. The unstable mandibular complete denture is a fundamental withal challenging scenario for a prosthodontist. Residual ridge resorption (RRR) is a chronic, progressive, irreversible, and disabling affliction, probably of multifactorial origin [1]. RRR is an inevitable and natural physiologic process [ii-4]. The neutral zone technique is favorable for patients with multitudinous, unstable, unretentive mandibular complete dentures. The goal of this technique is to place the teeth such that the forces exerted by the tongue and the cheek muscles are nullified, and the teeth remain in a safe, protected zone. Traditionally, the arrangement of teeth is based on the principles of teeth-setting. Even so, in the neutral zone technique, the placement of teeth is dictated by the oral musculature that varies from one patient to another. Various materials such as impression compounds [5], tissue conditioners [6], waxes [7], and impression plaster [8] have been used for recording the neutral zone, and each material has its inherent advantages and disadvantages. In this clinical technique, admix fabric was used to record the neutral zone in a patient with a neuromuscular disorder. The primary and the secondary impressions were made during the first clinical visit, and the jaw relation procedure and the neutral zone were recorded in the second clinical visit. This technique reduced the chairside time and the number of appointments or visits.
Case presentation
A 64-year-one-time man reported to the Section of Prosthodontics, Kinesthesia of Dental Sciences, Sri Ramachandra University, Chennai, Republic of india, with the primary complaint of an unstable loose mandibular denture. The medical history of the patient revealed that he was diabetic, hypertensive, and under medication. The patient presented with a history of neuromuscular incoordination for the past 4 years. He too complained of difficulty moving his jaws, normally being a consummate denture wearer for the past seven years, leading to difficulty in chewing and speech, primarily due to loose lower dentures. His past medical history was establish relevant for this case study. Manipulation with removable dentures, particularly with complete ones, is based on a very complex design of neuromuscular coordination. The denture, in itself a lifeless and passive implement, is completely useless unless operated by the neuromusculature. Diabetes mellitus is known to produce tenderness of the mucosa, rendering it prone to infections and dryness of the oral mucosa and glossodynia. The patients will mutter of a burning sensation beneath the dentures, which they usually aspect to the dentures and futilely attempt to relieve the symptoms by making new ones. On clinical examination, the maxillary rest alveolar ridge was rounded and well formed, but the mandibular residuum ridge was unfavorable due to a high degree of resorption (classified as Atwood's Gild V - low and well-rounded) [ii] (Figure one).
Highly Resorbed Mandibular Ridge
The treatment approach for this patient was to construct a mandibular denture using the conventional neutral zone technique and to use improvised procedures to minimize the chairside visits for the patient.
Objectives of the handling
The objectives of the treatment are rehabilitation with consummate denture therapy in a patient with poor neuromuscular coordination using an improvised neutral zone technique to attain maximum prosthesis stability, comfort, and role; locating the neutral zone and arranging the denture teeth accordingly; and minimizing the ongoing diminution of the residual alveolar ridges. Effigy ii reveals an orthopantograph of a severely resorbed mandibular arch.
The orofacial musculature plays a substantial role in developing the external polished surface of the denture and teeth arrangement. Forces adult during various muscular functions like chewing, speaking, and swallowing vary in direction and magnitude in each individual and in dissonant periods of time [nine]. This is particularly notable in patients with neuromuscular incoordination, which is recorded by the neutral zone impression.
Clinical Visit one
During the patient's first visit, as described in the conventional neutral zone technique, a preliminary impression of the maxillary and mandibular edentulous residue ridges was fabricated with irreversible hydrocolloid impression textile (Zhermack Grit-free Thixotropic Tropicalgin, Zhermack SpA, Badia Polesine [RO], Italy). The impressions were immediately cast in dental plaster (Mumbai Burmah Trading Corporation, Ltd., Mumbai, India), and chief casts were prepared. Custom trays were fabricated with DPI (Dental Products of India) - RR cold cure acrylic material (Bombay Burmah Trading Corporation, Ltd., Bombay, Bharat). On the same day, edge molding was washed with admix cloth – three parts by weight of impression chemical compound and seven parts by weight of tracing compound (DPI - Meridian Impression Chemical compound and Tracing Sticks, The Bombay Burmah Trading Corporation, Ltd., Mumbai, India) [10].The secondary impression was also made with the admix material (Figure iii).
Secondary impression
Secondary impression of maxillary and mandibular ridges with admix fabric
The chief casts were poured in dental stone (Zhermack Elite Model Rock, Zhermack SpA, Badia Polesine [RO], Italy) and record bases were synthetic with self-cure acrylic resin for the maxillary cast and heat-cure acrylic resin for the mandibular bandage to improve record base stability. The wax occlusal rim was made for the maxillary arch. A record base over the mandibular cast was fabricated with self-cure acrylic pillars.
Clinical Visit two
The maxillary occlusal rim was inserted and parallelism was verified using the Fob occlusal plane. The mandibular record base was as well placed in the patient'southward rima oris and checked for extension and stability by guiding the patient to perform mandibular movements. Once the mandibular record base was stabilized, the vertical jaw relation was determined with the aid of cocky-cure acrylic resin vertical stops (3 mm × viii mm) placed on either side of the mandibular canine-premolar region.
The patient was made to sit in an upright position and ii prominent points were marked on the patient's face - ane on the olfactory organ and one on the chin. The vertical dimension at remainder (VDR) was checked between these ii points with the assistance of a divider and a 12-inch ruler. The determined VDR was 7.i mm. Vertical dimension at apoplexy (VDO) was determined with the help of self-cure acrylic stops fabricated on the mandibular record base. The patient was instructed to bite on the acrylic stops as information technology reached the early dough stage along with the maxillary occlusal rim, which was visualized and checked with the help of the divider and 12-inch ruler (Effigy 4).
Recording Vertical Dimension
Recording vertical dimension with acrylic stops
The established VDO was 6.eight mm. One time the resin was fix, the backlog resin was trimmed off, thus culminating the vertical jaw relation.
The horizontal jaw relation was recorded using the admix fabric. This admix cloth is manipulated in the patient's oral cavity at around xl° C. The patient was instructed to perform routine mandibular movements (including swallowing, sucking of the lips, and pronouncing the vowels), which aided in molding the neutral zone space (Figure 5).
Functional movements recorded with admix material
The external surface was completely contoured by the orofacial musculature.The maxillary and the mandibular rims were fused at the axial relation.
The maxillary and mandibular occlusal rims were articulated in a mean value articulator to fabricate indices surrounding the neutral zone plaster impression on the mandibular bandage ( Figure 6).
Articulated occlusal rims
3 notches were made on the bandage: one in the anterior and two in the posterior regions. This was followed past applying separating medium on the cast, the tape base of operations, and over the neutral zone record. Boxing was done with modeling wax, and plaster of Paris was poured into the boxing upwardly to the upper surface. The plaster indices were sectioned into a labial and buccal index and a lingual index in guild to guide the removal and placement of these indices. The neutral zone record is then removed, and the acrylic stops are trimmed off from the denture base of operations. Separating medium was applied on the inner surfaces of the indices which were then reassembled. Wax was poured in the infinite representing the neutral zone, forming the new occlusal rim on the mandibular record base of operations. Figure 7 shows the occlusal rim created and the plaster index.
Index made with impression plaster
The mandibular teeth were arranged post-obit the alphabetize, and the maxillary teeth were arranged following the mandibular teeth arrangement. In order to preserve the contours established by the plaster indices in the neutral zone, no additional wax added to the denture flanges.
Clinical Visit iii
A wax try-in was performed to evaluate mandibular record base of operations stability, aesthetics, and intraoral apoplexy. The patient successfully performed all the movements mentioned earlier. The trial dentures were processed with rut-cure acrylic resin. The denture was polished so that the customized contours remained unaltered.
Clinical Visit 4
The mandibular denture was again evaluated with the plaster index prior to denture insertion. (Effigy 8)
Processed denture verified with index
Teeth arrangement was done in the neutral zone. The mandibular denture was candy and finished. It was verified with the plaster index prior to denture insertion.
The denture was inserted and verified for retention, stability, and apoplexy. The patient was comfortable with the complete denture prosthesis. Periodic recall visits were scheduled to verify the retention, comfort, and function.
Discussion
In the field of oral rehabilitation, particularly in geriatric prosthodontics, many factors contribute to the overall functioning of complete dentures. Information technology'southward a general experience that the lower denture is relatively less stable than the upper 1 with increasing life expectancy, age-related reduction in adaptability, and progressive severe mandibular resorption. One of the philosophies being introduced to overcome the claiming of unstable dentures in clinics is the concept of the neutral zone. The neutral zone technique was used with few modifications to attain retention and stability in such atrophic mandibular ridges. An implant-supported over-denture is another viable treatment selection but was not pursued because the cost, duration, and the patient's age.
The technique described in this article differs from the conventional technique by minimizing the number of patient visits and offers the added reward of recording the physiological dynamics of oral and perioral musculus part in a simplified manner. Acrylic stops were used to guess the VDO, and the neutral zone was recorded using the swallowing technique. The hateful value articulator was desirable in this case due to the patient'south medical history of neuromuscular incoordination.
Border molding was done with green stick compound, and a secondary impression was made with zinc oxide impression paste. In this case, admix textile was the preferred substance for border molding and making the secondary impression as it permits the patient to mold the neutral zone with the least amount of time and effort. The admix cloth besides helps mold the peripheral tissues, removes whatever soft tissue folds, and smoothes them over the mandibular os during the impression procedure.
Over the years, a multifariousness of materials have been used to record the neutral zone such as impression compound, impression plaster, waxes, tissue conditioners, and polyether. The impression compound material is of high viscosity, and so performing oral functions such as bravado, sucking, and pursing of the lips cannot be dexterously performed. Impression plaster is chaotic and carries a gamble of the patient swallowing fragments of plaster while performing functional movements. Uniform softening of the complete wax rims is critical for recording full functional movements, and if non done properly, tin event in an inaccurate recording of the neutral zone. Tissue conditioners practise not possess sufficient trunk; hence, information technology becomes laborious to use them even when they are supported by wire loops. Polyether impression textile sets via an irreversible chemical reaction, making it difficult to perform whatsoever modification in the set material and reuse it [10].
Admix material was used for recording the neutral zone taking into consideration our patient's history of neuromuscular incoordination (where the oral musculature could not perform its part fully). It's a combination of impression compound and green stick (low-fusing) compound in the ratio of iii:vii. The mixing of a depression-fusing chemical compound with the impression compound results in a low viscosity material assuasive for ease in manipulation of the oral musculature. The admix fabric allowed better flow and an accurate impression. The improvised technique made few modifications to the conventional technique every bit discussed in Tabular array 1.
Tabular array 1
Differences Between the Conventional Technique and the Improvised Neutral Zone Technique
| S.no | Conventional neutral zone technique | Improvised neutral zone technique |
| 1 | Indicated for patients with resorbed mandibular ridges. | Indicated for patients with resorbed mandibular ridges and poor neuromuscular coordination. |
| ii | Requires more than clinical visits and permits the patient to mold into the neutral zone with more than amount of time and effort. | Clinical visits minimized in this technique and permits the patient to mold into the neutral zone with less amount of time and effort. |
| 3 | Admix cloth is used for making secondary impressions. Second clinical visit required for border molding secondary impressions. | Admix cloth used for both edge molding and the secondary impression, thus minimizing the clinical visits of the patient by making the primary and secondary impressions on the aforementioned day. |
| 4 | Facilitation of muscular control by using the conventional neutral zone technique improving the stability and control of the lower denture (past reduction of displacing forces). | Facilitation of muscular control past using the improvised neutral zone technique increasing stability and command of the lower denture (past reduction of displacing forces)for a patient with poor neuromuscular coordination. |
Conclusions
Functional and aesthetic dental treatments for patients with atrophic ridges are an inestimable service provided by a prosthodontist. This anthropoidal pouch technique is helpful in patients with atrophic ridges whose primary complaints are pain and looseness of the mandibular consummate denture. The technique has proved to exist efficient for patients who are not satisfied with mandibular dentures. Further, the admix material aided in recording the functions of the oral musculature in a patient with poor muscular coordination. The power of the dental prosthesis to withstand the various forces acting on information technology, and the balance tissues of the ridge expanse (along with a properly made prosthesis), help in counteracting these displacing forces and play a role in determining the success of the treatment. In this nowadays case, all the above methods accept been utilized to restore masticatory efficiency and ameliorate comfort and aesthetics for a completely edentulous patient with an atrophic mandibular ridge and neuromuscular incoordination.
Notes
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The authors have declared that no competing interests exist.
Human Ethics
Consent was obtained by all participants in this study
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What Is The Neutral Zone And How Is It Used,
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