Prosthetic Rehabilitation of Glossectomy Patient Using Neutral Zone Technique: A Clinical Case Report

INTRODUCTION

The challenges associated with fabricating complete dentures to occupy the edentulous space optimally are quite substantial owing to the progressive changes accompanying edentulism in addition to the functional dynamics defining the oral cavity.^1,2,3 Elderly patients, especially long-time complete denture wearers, have been observed to have muscular atrophy of the perioral musculature, adding to the advanced ridge atrophy.⁴

Functionally inappropriate arrangement of teeth in a complete denture or physiologically unacceptable denture base contour and volume can have the following implications: (1) poor retention and stability^5,6 (2) inefficient posture and function of the tongue⁷ (3) inadequate tissue support⁸ (4) compromised phonetics⁹ (5) gagging.^10,11 Fish, in 1933, emphasized upon the importance of the cameo or polished denture surfaces.⁷ He highlighted the importance of the orofacial musculature for attaining denture stability.¹⁰

After the loss of the whole natural dentition, there exists a void within the oral cavity which is the potential denture space. A neutral zone is the area within the potential denture space where the outward acting forces of the tongue are neutralized by the inward acting forces of cheeks and the lips.¹² The chances of the failure of the prosthesis increase if it has not been placed in the space defined by the musculature.¹³ This case report describes a clinical case of glossectomy rehabilitated by complete denture fabrication utilizing the neutral zone technique.

CASE REPORT

A 63-year-old female reported to the Dept of Prosthodontics and Crown & Bridge with the chief complaint of difficulty in chewing due to missing teeth. Patient’s history revealed that patient had been operated twice; first for resection of squamous cell carcinoma of the right lateral border of the tongue and subsequently for the management of carcinoma in situ in respect to the same location. Intra-oral examination revealed that patient had completely edentulous maxillary and mandibular arches with resected right lateral border of the tongue. Due to imbalance of the intraoral musculature due to the glossectomy (Fig 1), it was planned to fabricate conventional complete dentures utilizing the neutral zone technique.

Primary impressions for both the arches were made using high fusing impression compound, which was followed by fabrication of custom trays. Border moulding was done with low-fusing impression compound and final impressions were made for both the arches with polyether impression material (Fig 2). Permanent denture bases were fabricated, and occlusal rims were fabricated using baseplate wax. Orientation jaw relation was recorded, to orient the maxillary cast to the opening and closing axis of TMJ, this was followed by recording of vertical and centric jaw relations. The records were then transferred to a semi-adjustable articulator (Fig 3) and the mandibular rim was replaced with impression compound. The compound was heated in water bath and placed in the patient’s mouth. The patient was asked to perform functional movements such as swallowing luke warm water, sucking, pronouncing exaggerated “eee” and “ooo” sounds followed by touching the palate (however due to scarring of left lateral region in tongue patients tongue was not able to touch the palate) and wetting the upper lips with the tongue (Fig 4). The compound rim was shaped by these movements and the neutral zone was thus identified. The mandibular denture base along with the modified compound rim was transferred to the articulator followed by fabrication of a putty index around the compound rim. The compound was then removed and the putty index was placed back in the original orientation. Molten baseplate wax was poured in the potential space and was allowed to cool down to room temperature. Teeth arrangement was done with special care being taken to place the mandibular teeth within the functionally recorded neutral zone, (Fig 5) followed by arrangement of maxillary teeth as per the mandibular teeth to develop a proper occlusion. This was followed by recording a cameo surface using zinc oxide eugenol paste (Fig 6). The dentures were then processed finished and polished following the conventional methods. The final dentures were delivered and post-insertions instructions were delivered to the patient. (Fig 7-8)

DISCUSSION

According to the Glossary of Prosthodontic Terms, tenth edition¹⁴, neutral zone is “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 equal.”

Positioning the artificial teeth in this zone fulfils the twofold objectives: (1) no interference of the teeth with normal muscular function combined with (2) enhanced stability and retention owing to the favourable forces exerted by the musculature against the denture. Proper position of the teeth is where the pressure of the cheek and tongue neutralize each other’s pressure.¹⁵

The boundaries defining the neutral zone are developed through contraction and relaxation of the muscles during various functions such as mastication, deglutition, phonation and facial expression. These neuromuscular forces differ both in magnitude as well as direction in various parts of the oral cavity, in different individuals, and during different periods of life.¹⁶ To ensure that the complete dentures reside within the neutral zone, clinicians must understand, identify, and record the neuromuscular dynamics of the functioning oral tissues with a single static registration.

The neutral zone technique usually positions the posterior denture teeth slightly facially when compared to teeth arranged over the residual ridge crest.¹⁷ This design concept has been observed to be especially effective for the mandibular removable prostheses. It is quite remarkable to observe recording of the neutral zones for patients with neuromuscular decline or dysfunction including patients with decreased facial muscle tonicity, anatomic insufficiency, such as in post cancer oral surgical resections and facial neuromuscular deficit.¹⁸ Conventional methods in such glossectomy patients may not facilitate prosthesis stability against the expected oral and perioral muscular function due to abnormal scarring and restricted movements of the musculature. Whenever glossectomy is attempted, the most common movement affected will be a lateral side-to-side movement which is crucial for sweeping and pushing food during mastication. It will also affect the swallowing due to limited tongue propulsion and causes saliva control issue.¹⁹ Denture fabricated using neutral zone technique will result in contours of denture which will fill the deficit bulk and aid in stabilizing the action of remaining musculature. As per various studies, use of the neutral zone method may result in better stability, thereby improving the prosthodontic experience for such patients.^17-18

CONCLUSION

According to various studies, dentures fabricated using the neutral zone technique are functionally more stable resulting in increased patient comfort and function, and minimal post-insertion problems.^17-18 The case discussed in this article was rehabilitated utilising the neutral zone technique for enhanced stability and patient comfort especially being a patient with post cancer glossectomy.

REFERENCES