Complete Denture Rehabilitation of a Parkinsonian Patient Using Neutral Zone Technique

INTRODUCTION

To maximize the stability and retention of mandibular dentures, previous reports have

recommended that posterior denture teeth be positioned directly over the crest of the edentulous ridge. This relationship of the teeth and alveolar ridge is important for the stability of the denture in function.1,2 Although this tooth position may be desirable when adequate alveolar ridge height is available, such a position may not be suitable for severely resorbed ridges because of a lateral shift in the orientation of the ridge crest.

The importance of the polished denture surface for retention and stability has been well advocated.3,4 Fish first exposed the dental profession tothe concept of neutral zone for complete denturetreatment in 1933.

Several authors since that timehave contributed to the development of the neutralzone concept. The neutral zone is defined as thepotential space surrounding the mandibular denturebetween the lips, cheeks, and the tongue. In theory, itis that area or position where the forces between thetongue and cheeks or lips are equal.5

Whereas leverage during function is of primary concern for the conventional ‘‘teeth over ridge’’ concept, muscular forces during function are considered more crucial for the neutral zone concept. Advocates of the neutral zone do not ignore the resulting, less favorable leverage, but assume that it is counterbalanced by the controlling actions of cheeks, lips, and tongue, especially for resorbed alveolar ridges.3,5

The purpose of this article is to present the use of the neutral zone technique for the fabrication of a complete mandibular denture for a patient with parkinsonism and severely resorbed ridges.

CASE REPORT

A 70year old male patient reported to the department of Prosthodontics, with completely edentulous upper and lower arches. The patient was suffering from Parkinsonism since 7 years and was currently under medication for the same. On examination, the patient presented with compromised neuromuscular coordination and severely resorbed mandibular ridge. Patient’s economic status and general health was not conducive for an implant therapy hence, prosthodontic rehabilitation comprised of conventional upper and lower complete dentures constructed using the neutral zone technique.
Impressions were made and casts were obtained. On the final casts occlusal rims were fabricated and a tentative vertical dimension and centric relation was recorded which was transferred on to the articulator. The lower occlusal rim was now replaced with another base plate with acrylic vertical stops to contact the upper rim at the recorded vertical dimension. Anteriorly, metal struts wereattached at the ridge proximity on the denture base to help retain the green stick during the functional movement stage (fig1).

Fig 1: Metal struts attached to the base plate

Once built with green stick compound, the mandibular rim was placed in the patient’s mouth. The patient was asked to sip in warm water and perform all the functional movements like swallowing, sucking, puckering, smiling. The green stick rim got molded to the required shape (Fig 2).

Fig 2: Functional movements recorded

Following this, the green stick compound was trimmed to the required height and contoured(Fig 3).

Fig 3: Height of the rim adjusted.

A putty index was made around this green stick compound rim (Fig 4).

Fig 4: Putty index

Following this, the green stick rim is replaced by a new base plate. The index is placed over the baseplate and modeling wax poured into the index hence creating a duplicate of the previous green stick rim (Fig 5).

Fig 5: New wax rims made

Teeth arrangement was carried out in the modeling wax occlusal rims and the wax was scraped off the polished surface. Light body elastomeric impression material was adapted to the polished surface and placed in the patient’s mouth. The patient was asked to repeat all functional movements with both upper and lower denture in place. The polished surface of the denture was reproduced in the elastomeric impression material.Trial dentures were flasked.

The final dentures were processed and delivered to the patient (Fig 6).

Fig 6: Final dentures

Post insertion instructions were given to the patient. He was comfortable with the prosthesis. The patient who is on regular follow up since two years is found to be doing well.

DISCUSSION

When the patient functionally molds the mandibularrim into the area of the neutral zone, the result is amore stable record base. This technique uses the anteriorstop described by Beresin and Schiesser andsimilar to that described by Wright. The techniquediffers from Beresin and Schiesser in that the maxillaryrim is not formed into the neutral zone by the patient, and the occlusal plane is first identified in themaxillary rim.6,7 Uniformly reheating the green stick compound occlusion rim is critical forsuccess. If this step is not completed successfully, anincorrect occlusal vertical dimension may result. Theuse of an anterior stop in the record may introduceerror to the procedure because of possible displacementof the record base. When the operator observesthat the anterior stop has just made contact with themaxillary wax rim, he or she should instruct the patientto stop closing.5,6

SUMMARY

A technique has been presented that allows thepractitioner to accurately record the maxillomandibularrelationship of a patient. Because the patient functionally molds the mandibular rim into the area ofthe neutral zone, a more stable record base is created. To accurately fabricate dentures in a compromised patient is quite a challenge and the neutral zone technique helps overcome the difficulties faced in this area. The resultant denture is comfortable to use and seats snuggly on the involved tissues.

REFERENCES