JICDRO is a UGC approved journal (Journal no. 63927)

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CASE REPORT
Year : 2020  |  Volume : 12  |  Issue : 1  |  Page : 78-83

The concept of neutral zone and rehabilitation of severely resorbed alveolar ridges: A special case file


1 Department of Prosthodontics and Crown and Bridge, Dr. Hedgewar Smruti Rugna Seva Mandal, Dental College and Hospital, Hingoli, India
2 Department of Prosthodontics and Crown and Bridge, SB Patil Dental College and Hospital, Bidar, Karnataka, India
3 Department of Prosthodontics and Crown and Bridge, Rajah Muthiah Dental College and Hospital, Annamalai University, Annamalai Nagar, Tamil Nadu, India
4 Department of Prosthodontics and Crown and Bridge, Rajas Dental College and Hospital, Kavalkinaru, Tirunelveli, Tamil Nadu, India
5 Department of Oral Medicine and Radiology, Saraswati Dhanwantari Dental College and Hospital and Post-graduate Research Institute, Parbhani, Maharashtra, India

Date of Submission05-May-2019
Date of Decision07-Jul-2019
Date of Acceptance02-Feb-2020
Date of Web Publication29-Jul-2020

Correspondence Address:
Dr. Abhishek Singh Nayyar
Department of Oral Medicine and Radiology, Saraswati-Dhanwantari Dental College and Hospital and Post-Graduate Research Institute, Parbhani, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jicdro.jicdro_11_19

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   Abstract 


Mandibular dentures often present greater difficulty in achieving retention, stability, and support than do maxillary dentures, primarily, due to a complex anatomy because of bone architecture and muscle attachments, and consequently, increased number of anatomic limitations. Long-term edentulism as well as prolonged use of ill-fitting dentures result in severe resorption of the alveolar ridges, further, worsening this situation. The present case report describes a similar case of a 90-year-old male patient who reported to the department of prosthodontics seeking replacement of his missing teeth. On examination, the lower denture was ill fitting with a severely resorbed mandibular alveolar ridge. Intraoral examination revealed an Atwood's Class III maxillary edentulous ridge with Class VI edentulous mandibular ridge. Special measures were adopted for the management of the patient through a modified impression technique along with physiologic registration of the neutral zone.

Keywords: Neutral zone, rehabilitation, severely resorbed mandibular alveolar ridge


How to cite this article:
Narayane K A, Kattimani PT, Ranganathan K, Mithran A, Raj SG, Amalorpavam V, Nayyar AS. The concept of neutral zone and rehabilitation of severely resorbed alveolar ridges: A special case file. J Int Clin Dent Res Organ 2020;12:78-83

How to cite this URL:
Narayane K A, Kattimani PT, Ranganathan K, Mithran A, Raj SG, Amalorpavam V, Nayyar AS. The concept of neutral zone and rehabilitation of severely resorbed alveolar ridges: A special case file. J Int Clin Dent Res Organ [serial online] 2020 [cited 2020 Oct 23];12:78-83. Available from: https://www.jicdro.org/text.asp?2020/12/1/78/291104




   Introduction Top


Mandibular dentures often present greater difficulty in achieving retention, stability, and support than do maxillary dentures, primarily, due to a complex anatomy because of bone architecture and muscle attachments, and consequently, increased number of anatomic limitations. Long-term edentulism as well as prolonged use of ill-fitting dentures result in severe resorption of the alveolar ridges, further, worsening this situation.[1],[2],[3] Prosthodontic management of such compromised alveolar ridges requires specialized techniques starting from the impression procedure itself.[4] Oral functions involve synergistic actions of tongue, lips, cheeks, and floor of the mouth, which are highly specific to an individual. Failure to recognize the importance of tooth position, flange form, and contour results in dentures which are unstable, howsoever, skillfully, they are constructed. Due to increased inter-ridge distance in patients with resorbed alveolar ridges, tooth positioning becomes increasingly important in aiding the stability of dentures, so that the muscle activity of the attached and surrounding muscles imparts forces to stabilize rather than displace the dentures. The teeth, therefore, should be placed in the neutral zone, that is, the potential space between the lips and cheeks on one side and the tongue on the other, while all the lateral forces are made to be in a balanced state.[5],[6] Neutral zone is, also, recognized by the terms dead zone, stable zone, zone of minimal conflict, zone of least interference, and the zone of equilibrium.[7],[8],[9],[10] The present case report describes a clinical case, wherein same measures were adopted for the management of a patient who came with severe mandibular ridge resorption through a modified impression technique along with physiologic registration of the neutral zone.


   Case Report Top


A 90-year-old male patient reported to the department of prosthodontics seeking replacement of his missing teeth. The previous denture was made 10 years back with a history of continuous denture wear. On examination, the lower denture was ill fitting with a severely resorbed mandibular alveolar ridge. His vital signs were reported to be normal, while there was no significant history pertaining to his cardiac, respiratory, and metabolic status. There was no history of any kind of prolonged stay in a hospital for medical assistance in the past as well. Intraoral examination revealed an Atwood's Class III maxillary edentulous ridge with Class VI edentulous mandibular ridge[11],[12],[13],[14] [Figure 1]. No bony spicules or signs of inflammation were seen anywhere across the maxillary and mandibular alveolar ridges. The orthopantomograph of the patient although revealed marked resorption in the mandibular arch. According to Wical and Swoope analysis,[15] this ratio was found to be around 0:1 [Figure 2]. A treatment plan was formulated, which consisted of impressing the severely resorbed mandibular edentulous ridge while using the principle of neutral zone technique. Primary impressions were made using medium fusing impression compound for the maxillary arch and irreversible hydrocolloid for the mandibular arch [Figure 3]. Primary casts were poured [Figure 4]. Special tray was constructed for the maxillary arch using full spacer with tray material. A modified mandibular custom tray was prepared without any spacer over the primary cast using tray material. After evaluation in the mouth, the custom tray was adjusted 2 mm short of the physiologic depth of the labial and lingual sulci. The crest of the ridge was marked using an indelible pencil and transferred to the tray. A window was cut in the tray corresponding to the crest of the ridge [Figure 5]. The tray was, then, seated onto the cast, and softened modeling wax was placed into the window and shaped to form a handle. Tray adhesive was applied to the borders and intaglio surface of the custom tray, and it was loaded with putty consistency elastomeric impression material. The tray was, then, seated onto the ridge, and the labial and lingual borders were molded. The borders of the impression were trimmed by 0.5 mm. The wax handle was removed and the putty material over the window cut out. Light-body elastomeric impression material was loaded into the tray and seated on the ridge. In addition, the light-body material was expressed into the window. Lingual and facial borders were, then, molded ensuring the tray remains steady until the impression material sets. Master casts were poured from it [Figure 6]. Record bases were made using autopolymerizing resin, and occlusal rims were made in medium fusing impression compound.
Figure 1: severely resorbed maxillary and mandibular alveolar ridges

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Figure 2: OPG of the patient showing resorption till mental foramen

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Figure 3: maxillary and mandibular primary impressions

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Figure 4: maxillary and mandibular primary casts

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Figure 5: modified maxillary and mandibular special trays

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Figure 6: maxillary and mandibular master casts

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Concept of neutral zone and neutral zone recording technique

In neutral zone recording, the softened compound rims were tempered and placed in the patient's mouth, and the patient was asked to perform various movements such as swallowing, pursing, and sucking the lips, so that these compound rims got molded [Figure 7]. Jaw relation was made using the same compound rims and transferred to a 3-point articulator [Figure 8]. After mounting, the casts were removed preserving the indices on the casts and the articulator. Plaster indices were made on these compound rims to ensure the neutral zone at various steps [Figure 9]. Same indices were, then, used to make the wax rims by pouring molten modeling wax automatically confining them to the recorded neutral zone [Figure 10]. The wax rims were mounted on the articulator with the help of previous indices with sticky wax [Figure 11]. Teeth arrangement was done using semi-anatomic teeth and checked with the help of plaster indices [Figure 12]. At the try-in appointment, soft-tissue recording was done by performing various movements using zinc oxide eugenol (ZOE) paste [Figure 13]. Carving was done at the cervical region of each tooth [Figure 14]. The dentures were, then, flasked, packed, processed, and verified with the help of indices [Figure 15]. Subsequently, finishing and polishing was done [Figure 16], and the dentures were inserted and occlusal prematurities were removed [Figure 17].
Figure 7: neutral zone recorded in compound rims

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Figure 8: jaw relation made in compound rims

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Figure 9: plaster indices for neutral zone

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Figure 10: wax rims made with the help of same indices

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Figure 11: teeth arrangement on articulator

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Figure 12: teeth arrangement verified in plaster indices

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Figure 13: soft tissues recorded with the help of ZOE paste

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Figure 14: excess ZOE removed with the help of waxing and carving

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Figure 15: dentures verified for neutral zone

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Figure 16: processed complete dentures

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Figure 17: dentures insertion made

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   Discussion Top


To achieve stability and retention in patients with severely resorbed/atrophied maxillary and mandibular residual ridges in patients with prolonged edentulousness is a real challenge well-known to the prosthodontists.[1],[2],[3] The said challenge gets even more pronounced in case of severely resorbed mandibular ridges because of a complex anatomy and increased number of anatomic limitations.[2],[3] Chandrasekharan et al.[16] modified the impression technique, especially, for the said situations using elastomeric impression materials, which were more patient-friendly and convenient for the operator. The heavy-body elastomeric impression materials used in the said technique placed pressure on the ridge slopes, while the crest of the ridge was impressed with minimal pressure using light-body impression materials. Patients with increased alveolar ridge loss have smaller denture base areas. In such patients, denture stability and retention become even more difficult to be achieved and are actually dependent on the correct positioning of the teeth[17],[18],[19] and contours of the external surfaces of the dentures warranting the use of neutral zone technique.[20],[21] The said neutral zone was recorded in the present case with the help of ZOE impression paste. Hence, the outcome was with the correct alignment of teeth in the marked neutral zone area while recording the polished surface correctly allowed the tongue, lips, cheeks, and floor of the mouth to be in harmony with each other improving the stability of the denture and thus achieving a maximum functional efficiency.


   Conclusion Top


Mandibular dentures often present greater difficulty in achieving retention, stability, and support than do maxillary dentures, primarily, due to a complex anatomy because of bone architecture and muscle attachments. Recording of the neutral zone allows prosthodontists to fabricate a denture that is customized to the patient's musculature, and therefore, is more stable and with good retention and comfortable to the patient. The present case report describes a clinical case wherein same measures were adopted for the management of a patient who came with severe mandibular ridge resorption through a modified impression technique along with physiologic registration of the neutral zone.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Acknowledgment

We would like to acknowledge all the patients who contributed in the study without whom this study would not have been feasible.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Roberts AL. The effects of outline and form upon denture stability and retention. Dent Clin North Am 1960;4:293-303.  Back to cited text no. 1
    
2.
Wright CR, Swartz WH, Godwin WC. Mandibular Denture Stability: A New Concept. Ann Arbor: The Overbeck Co; 1961. p. 29-41.  Back to cited text no. 2
    
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Brill N, Tryde G, Cantor R. The dynamic nature of the lower denture space. J Prosthet Dent 1965;15:401-18.  Back to cited text no. 3
    
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Gahan MJ, Walmsley AD. The neutral zone impression revisited. Br Dent J 2005;198:269-72.  Back to cited text no. 4
    
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Fish EW. Using the muscles to stabilize the full lower denture. J Am Dent Assoc 1933;20:2163-9.  Back to cited text no. 5
    
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Cagna DR, Massad JJ, Schiesser FJ. The neutral zone revisited: From historical concepts to modern application. J Prosthet Dent 2009;101:405-12.  Back to cited text no. 7
    
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Fahmi FM. The position of the neutral zone in relation to the alveolar ridge. J Prosthet Dent 1992;67:805-9.  Back to cited text no. 9
    
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Fahmy FM, Kharat DU. A study of the importance of the neutral zone in complete dentures. J Prosthet Dent 1990;64:459-62.  Back to cited text no. 10
    
11.
Atwood DA. A cephalometric study of the clinical rest position of the mandible. II. The variability in the rate of bone loss following the removal of occlusal contacts. J Prosthet Dent 1957;7:544-52.  Back to cited text no. 11
    
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Atwood DA. Some clinical factors related to rate of resorption of residual ridges. 1962. J Prosthet Dent 2001;86:119-25.  Back to cited text no. 12
    
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Atwood DA. Post-extraction changes in the adult mandible as illustrated by microradiographs of midsagittal sections and serial cephalometric roentgenograms. J Prosthet Dent 1963;13:810-24.  Back to cited text no. 13
    
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Atwood DA, Coy WA. Clinical, cephalometric, and densitometric study of reduction of residual ridges. J Prosthet Dent 1971;26:280-95.  Back to cited text no. 14
    
15.
Wical KE, Swoope CC. Studies of residual ridge resorption. I. Use of panoramic radiographs for evaluation and classification of mandibular resorption. J Prosthet Dent 1974;32:7-12.  Back to cited text no. 15
    
16.
Chandrasekharan NK, Kunnekel AT, Verma M, Gupta RK. A technique for impressing the severely resorbed mandibular edentulous ridge. J Prosthodont 2012;21:215-8.  Back to cited text no. 16
    
17.
Watt DM. Tooth positions on complete dentures. J Dent 1978;6:147-60.  Back to cited text no. 17
    
18.
Murray CG. Re-establishing natural tooth position in the endentulous environment. Aust Dent J 1978;23:415-21.  Back to cited text no. 18
    
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Weinberg LA. Tooth position in relation to the denture base foundation. J Prosthet Dent 1958;8:398-405.  Back to cited text no. 19
    
20.
Wright SM. The polished surface contour: A new approach. Int J Prosthodont 1991;4:159-63.  Back to cited text no. 20
    
21.
Schiesser FJ. The neutral zone and polished surfaces in complete dentures. J Prosthet Dent 1964;14:854-65.  Back to cited text no. 21
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17]



 

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