Evaluation of the effect of duration of edentulousness on the position of neutral zone in relation to residual alveolar ridge using Computed Tomography (CT) – An In-vivo Study

Purpose: To evaluate the effect of duration of edentulousness on the position of neutral zone in relation to the crest of the residual alveolar ridge in the molar, premolar and anterior region in mandibular complete denture using Computed Tomography (CT). Materials and Method: Thirty edentulous patients were categorized into three groups based on their period of edentulousnessGroup 1: 0 to 6 months of edentulousness, Group 2: 7 months to 2 years of edentulousness and Group 3: 3 years to 10 years of edentulousness. The neutral zone position in relation to the crest of the alveolar ridge was evaluated by adapting TMA wires on the center of the compound rim and on the ridge crest on the master cast. CT images of the casts and the rims were obtained and the results were compared in the right and left premolar, molar and anterior region. When the images of the rims and cast coincided, a zero score was assigned and buccal or labial locations of the neutral zone with respect to the ridge are given a positive value. Lingual locations of the neutral zone with respect to the ridge were given a negative value. The results were statistically analyzed using one way ANOVA followed by Tukey's Post Hoc test. Results: In the premolar and molar regions, neutral zone was positioned lingual to the crest in group 1 patients and there was a gradual shift to the buccal side in group 2 and 3 patients. Highly statistical significant difference was found between group 1 and 3 in the left premolar and molar region (p=.000). No statistical significant difference was seen between the groups in the anterior region. Conclusion: It was concluded that the neutral zone was found to be located lingual to crest of the ridge during the early period of edentulousness i.e., between 0-6 months. After that it starts shifting buccally and labially in relation to the crest. This shifting of neutral zone is more pronounced after 3 years of extraction. ISSN No 2277 8179 | IF : 4.176 | IC Value : 78.46 VOLUME-6 | ISSUE-6 | JUNE-2017 26 International Journal of Scientific Research The selected subjects are grouped into three categories as follows; Group 1: 0-6 months of edentulousness, Group 2: 7 Months -2 years of edentulousness and Group 3: 3 Years – 10 Years of edentulousness. The Null hypothesis was that there was no significant difference between the groups according to the period of edentulism on the position of the neutral zone in relation to the crest of the ridge. Clinical procedure: Primary impressions were made using impression compound (Aslate, India) and primary casts were made with Type II dental plaster (Asian Chemicals, India) (Fig. 1a, 1b) and custom trays were fabricated using auto-polymerizing acrylic resin (DPI, India). Fig.1a Primary impression Fig. 1b Primary cast Using green stick compound (Samit, India) and light body impression material (Coltene Whaledent, Switzerland), secondary impressions were made using selective pressure impression technique and master casts were made using Type III dental stone (Kalabhai, India). (Fig. 2a, 2b) Record bases were fabricated using auto-polymerizing acrylic resin and checked intra orally for extensions. If the record base moved during these functional movements, or if the patient was aware of the movement, then the record base was unstable. Now the record base was removed from the patient's mouth and adjusted for over extensions until the record base was stable. After the correct extensions of the record bases were determined, multiple grooves are made on the surface of the record base for retention of the impression compound. Establishing neutral zone: The neutral zone was recorded by using the swallowing method, where the impression compound was softened in the hot water bath maintained at 65 degree Celsius. The impression compound was kneaded and worked until it was uniformly soft and shaped in to a form of a bite block. To locate the neutral zone the patients are lubricated with petrolatum jelly. The patient was asked to swallow and purse the lips as in sucking repeatedly. After the compound rim was set, it was taken out and evaluated for the symmetry of the arch. (Fig.3a, 3b) Fig 3a.Initial moulding of the neutral zone Occlusal view and 3b.