title: Morphologic comparison of two neutral zone impression techniques: a pilot study.
abstract: BACKGROUND
  Several studies have compared dentures fabricated using neutral zone and conventional techniques. However, studies comparing swallowing and phonetic techniques for assessing the location and shape of the neutral zone could not be identified in the literature.
  
  
  OBJECTIVE
  The purpose of this pilot study was to compare the outline form of the phonetic and swallowing neutral zone impression techniques for the same subjects.
  
  
  METHODS
  Nine denture wearers with advanced mandibular ridge resorption were included in this study. For each subject 2 trays were prepared in autopolymerizing acrylic resin. One method used phonetics and tissue conditioner to shape the neutral zone; the second method used swallowing and modeling plastic impression compound. The resulting neutral zone impressions were leveled to the same occlusal height by gently grinding the occlusal surface on sandpaper until it corresponded with landmarks (corners of the mouth, two thirds of the height of the retromolar pads, bilaterally) noted on the cast. The impression was inverted onto graph paper, and the contour was outlined with a lead pencil. One impression was made for each subject, for each technique. The buccal contours of both neutral zones coincided at the median line. The maximum distance between the zones was measured in a buccolingual direction in the anterior, premolar, and molar regions bilaterally. When the location of the phonetic neutral zone in relation compared to the swallowing neutral zone was buccally oriented, a plus score was given. When the phonetic neutral zone was lingually located, a minus score was given. When the 2 lines coincided, a score of 0 was given. Measurements were made from direct readings on the graph paper. Statistical analysis was performed using the Sign test (alpha=.05).
  
  
  RESULTS
  Significant differences were noted buccally in the left molar (P =.031) and right molar (P =.003) regions and also in the left and right premolar regions (P =.007), where the swallowing neutral zone was found to be located buccal to the phonetic neutral zone. Significant differences were also noted lingually, in the right premolar region (P =.015), where the swallowing neutral zone was found to be located lingual to the phonetic neutral zone. There was no significant difference between the techniques for the anterior region.
  
  
  CONCLUSIONS
  Within the limits of this study, the phonetic neutral zone appears to be narrower posteriorly compared to the swallowing neutral zone, thus limiting premolar and molar positioning.
authors.affiliation: School of Dentistry, St-Joseph University, Beirut, Lebanon. makzoume@inco.com.lb
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Makzoumé
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016301:Alveolar Bone Loss; D002610:Cheek; D003679:Deglutition; D003760:Dental Impression Materials; D003761:Dental Impression Technique; D003779:Denture Design; D003826:Denture, Complete, Lower; D006801:Humans; D007575:Jaw, Edentulous; D008046:Lip; D010699:Phonation; D010865:Pilot Projects; D015203:Reproducibility of Results; D014059:Tongue
chemical_list: D003760:Dental Impression Materials