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Several studies have been published on the neutral zone regarding materials, techniques, and different prostheses; however, the data are incongruent, and a literature review was necessary. This review summarizes the literature on the neutral zone and identifies deficiencies suggesting future research. The English language peer-reviewed dental litera-ture was reviewed from the period January 1, 1900 to June 30, 2011. Articles were searched in Medline (PubMed) and Google scholar for the term “neutral zone” and were supplemented by a hand search in prosthodontic publications. Deficiencies in the literature were found, including materials and techniques for recording the neutral zone, the com-parison of different neutral zone dentures, and the effect of the period of edentulism on the neutral zone. (J Prosthet Dent 2013;109:129-134)

Current status of the neutral zone: A literature review

Amit Porwal, MDSa and Keiichi Sasaki DDS, PhDb Pacific Dental College, Udaipur, India; Tohoku University Graduate School of Dentistry, Sendai, Japan

The Japan Dental Association provided the fellowship which supported this research.

aReader, Department of Prosthetic Dentistry, Pacific Dental College and Hospital.bDean, Professor, Tohoku University Graduate School of Dentistry, Division of Advanced Prosthetic Dentistry.

Worldwide life expectancy at birth was 67.2 years from 2005 through 2010.1 It has been estimated that, in-ternationally, between 7% and 69% of the adult population were completely edentulous.2 However, by 2045 the number of elderly in the world is likely to surpass the number of children for the first time in history.1

Elderly patients, especially those who are long-time complete denture wearers have advanced ridge atrophy and atrophy of the musculature of the cheeks and lips.3 Adaption to com-plete dentures was less of a problem in the past probably because new den-ture wearers were younger.4 However, currently people experience tooth loss later in life, which makes it difficult for them to develop the neuromus-cular skills needed for the successful wearing of dentures. The lack of these neuromuscular skills makes denture wearing on atrophic ridges difficult.5

Because of the progressive changes that accompany edentulism,6,7 the func-tional dynamics that define the oral cav-ity,8 the loss of the patients’ capability to adapt, and increased life expectancy9 have posed a challenge for the dentist when restoring and rehabilitating the

oral cavity. After dental extraction, alveolar bone may resorb until only basal bone remains.10 Furthermore, systemic diseases such as diabetes mellitus, osteoporosis, osteosclero-sis, and osteomalacia can exacerbate the situation.11,12 Owing to this con-tinued rise in treatment complexity, other options have been suggested, such as vestibular extension proce-dures or implant-supported dentures. Vestibuloplasty procedures are less common because of involved surgical intervention, pain and edema, infec-tion, and transient paresthesia,11,13,14 whereas financial constraints and sys-temic conditions limit the availability of implants.15 Additionally, these sur-geries may also eliminate the possibili-ties for active muscular control of the mandibular denture.16

Resorption of the residual ridges is a continuous process17 and produces a flat and sometimes concave founda-tion. This has been called the difficult lower jaw.16 Following this, character-istic spaces forming the so-called den-ture space develop in the oral cavity of the edentulous patient. In edentu-lous patients, support to the lips and the cheeks is no longer available and

they tend to collapse into the oral cav-ity. Simultaneously, the tongue will try to expand into the space.18 Success in treatment with complete dentures is possible in such situations only if cer-tain anatomic and physiologic facts are considered.19

Regardless of the fabrication tech-nique used, improper tooth arrange-ment or physiologically unacceptable denture base volume or contour re-sult in poor prosthesis stability and retention,8,16,20-23 compromised pho-netics,24,25 inadequate facial tissue support,25 inefficient tongue posture and function,26 and hyperactive gag-ging.27-30 To manage such difficult situ-ations for the mandible, Fish in 193320 drew the attention of the profession towards the cameo or polished sur-faces of dentures. He highlighted the importance of the muscular function of the tongue, cheeks, and lips as be-ing critical factors for denture stability.

When all natural teeth have been lost, there exists within the oral cav-ity a void which is the potential den-ture space. A neutral zone is that area in the potential denture space where the forces of the tongue pressing out-ward are neutralized by the forces of

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the cheeks and lips pressing inward.31 According to the Glossary of Prosth-odontic Terms (2005)32 the neutral zone is “the potential space between the lips and the 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.”

Since these forces are developed through muscular contraction during the various functions of mastication, speaking, and swallowing, they vary in magnitude and direction in different individuals.31,33 Therefore, if the pros-thesis has not been placed in a space defined by the musculature, the chanc-es of the prosthesis failing increase.

In the literature, the neutral zone34,35 has been called the dead space,20 stable zone,16 zone of least interference,36 zone of equilibrium,37 biometric den-ture space,12 denture space,38,39 and potential denture space.40 The tech-nique for recording the same is well documented and has been referred to as the anthropoidal pouch technique,9 denture form impression technique,41 muscle formed mandibular denture technique,42 piezograph technique,43 and border molding technique.44

The term neutral zone concept31 was coined by Beresin and Schiesser in 1976. The authors suggested that the denture teeth should be arranged in the neutral zone. The neutral zone philosophy is based on the con-cept that for each individual patient there exists within the denture space a specific area where the function of the musculature will not unseat the denture and where forces generated by the tongue will be neutralized by the forces generated by the lips and cheeks. Thus, artificial teeth should be arranged in the neutral zone for denture stability. Positioning artifi-cial teeth in the neutral zone achieves 2 objectives: teeth will not interfere with the normal muscle function; and the forces exerted by the musculature against the denture are more favor-able for stability and retention.

Various authors11,16,20,21,25,31 have shown significance of the neutral zone and have suggested that teeth must

be positioned within this neutral zone for optimum stability and retention of the prosthesis. However, documenta-tion of the techniques, materials, and procedures for recording the same is incoherent and scarce. Because of the availability of newer materials, the development of more sophisti-cated techniques and an increase in the older age group, an appropriate, more evidence-based treatment is de-sired. Therefore, the purpose of this article was to summarize the existing literature concerning the neutral zone and to identify any gaps in the current research to suggest areas for further investigation.

A systematic review on this topic was not possible as related articles were few and of varied origins. Therefore, a literature search was conducted for peer reviewed dental articles published in English and limited to humans for “neutral zone”, from January 1, 1900 to June 30, 2011, in Medline (PubMed) and Google scholar.

Articles retrieved from the elec-tronic search were hand searched for the relative references and the cross references. The desired articles were obtained manually from known prosthodontic references such as The Journal of Prosthetic Dentistry, the In-ternational Journal of Prosthodontics, and the Journal of Prosthodontics. Articles that did not focus exclusively on the neutral zone or techniques, materials, or patients treated with this technique were excluded from further evaluation. The full text of all articles identified through the electronic and manual searches was reviewed and assessed for suitability.

PubMed results showed 1158 ar-ticles for neutral zone, but after ap-plying the limitations, only 32 articles remained. Of these only 25 relevant articles were reviewed. Also, Google scholar was searched for any other relevant articles.

With the neutral-zone approach the usual sequence for complete den-ture fabrication is reversed. First the individual trays are fabricated and adjusted after trial insertion in the

mouth. This is followed by making oc-clusal rims with modeling plastic im-pression compound, which, in turn, will be molded in the neutral zone by muscle function. Later, a definitive impression is made by using a closed mouth procedure at a tentative oc-clusal vertical dimension. After this procedure, the occlusal vertical di-mension and centric relation are de-termined. The shape of the polished cameo surface will determine whether the muscular forces will stabilize or dislodge the denture. Additionally, this helps patients control their den-tures even when the residual ridges have atrophied and the fit is no longer accurate.35 The proper position of the teeth is not in the center of the ridge, nor labial or buccal to it, but where the cheek pressure and tongue pres-sure balance each other.

Mahmoud et al45 found that the residual ridge type (prominent ridges and flat ridges) had no effect on the neutral zone, suggesting that mus-cular forces rather than the ridge it-self were the determining factor. The authors also demonstrated that the width of the neutral zone is smallest at the occlusal plane level (and in-creases as it goes up and down) and that as the occlusal vertical dimen-sion increases, the width of the neu-tral zone also increases and vice versa.

Techniques

The techniques most commonly

used for recording the neutral zone were found to be swallowing 4,35,41,42,44-

57 and phonetics.5,32,46,49,51-53,55-60 However, other techniques such as sipping water,46,49,51,56,57 lick-ing,4,46,49 smiling,46,50,57 pursing the lips,32,44,49,54 sucking, 32,42,47,48,52,53,55,57 masticating,48 mouth exercises (in-cluding tongue movements, blow-ing, protruding of the tongue, exer-cise movements of the lips, cheek, and tongue, facial expression, open-ing and closing),19,32,41,42,45,54,55,57,59 and whistling19,50 have also been reported.

To compare the outline form of swallowing and the phonetic neu-

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tral zone impression technique, Makzoumé61 conducted a study in which 1 method used phonetics and tissue conditioner to shape the neu-tral zone and another used swallow-ing and modeling plastic impression compound. It was concluded that the phonetic neutral zone appears to be narrower posteriorly, thus limit-ing premolar and molar positioning. Two factors would have resulted in this situation: either the viscosity of the modeling plastic impression com-pound was too great to be sufficiently molded by the buccinator or the ac-tivity of the muscles was increased in speaking. According to Lott and Levin,58 patients should be asked to read an interesting topic aloud and rapidly. This will cause the muscles to be increasingly strained, and in-creased saliva secretion will result in more swallowing action. Also, it will reduce patient focus on the occlu-sion rims, and more natural move-ments of the muscles will be recorded. However, the question remains which technique should be used so that the dentures remain stable during all functional activities?

Materials

Tench et al33 were the first in this

field and have proposed modeling plastic impression compound as the material to be used for recording the neutral zone. Although this advice is widely followed,31,35,47,50,51,53,61-64 other materials such as tissue con-d i t i o n e r, 4 , 5 , 3 9 , 4 4 - 4 6 , 4 8 , 4 9 , 5 6 , 5 7 , 5 9 , 6 0 , 6 5 wax,19,42,52,55,58 zinc oxide eugenol im-pression material,35,42,64,66,67 silicone material,41,51,54,67,68 chairside relining material,41,44,61 and acrylic resin60 are also described for this technique. These materials are either used for the initial recording of the neutral zone or at the evaluation appointment.

Modeling plastic impression com-pound, being a thermoplastic mate-rial, is easy to manage and has the advantages of low cost and ease of availability, whereas wax is temporar-ily stable and can be contoured over

a period of time by functional move-ments.58 A tissue-conditioning mate-rial was preferred by many authors because of the ease of mixing, elec-tive initial viscosity, and slow-setting properties that enabled capture of the movable tissue morphology in the functional state. Moreover, this ma-terial also allows for an incremental molding procedure, which is important in patients with focal neurological defi-cits and slow or false reactions to vari-ous commands.49,56 A disadvantage of this material is its relatively high cost.49 Light-polymerized acrylic resin provides sufficient working time and polishes to a high luster; however, irritation due to the monomer may be a problem.44

Whichever materials are used for recording the neutral zone, it seems that 2 factors cannot be ignored: the neutral zone should be recorded at an established occlusal vertical dimen-sion, and the material used for record-ing should be reasonably slow setting so that oral musculature shapes it into proper contour and dimension.48 A future comparative study could inves-tigate the neutral zone as recorded by different materials such as modeling plastic impression compound, silicone, tissue conditioner, denture lining mate-rials, and soft wax.

Volume of Material Required

Until now, the number of addi-

tions and the volume of impression materials required for recording the neutral zone have not been clarified. Heath39 demonstrated that record-ings of denture space morphology vary according to the volume of the material used. To address this volu-metric variable, a nonsetting gel - a polymer of dimethyl silicate filled with 12% calcium silicate - was used on a trial basis to estimate the optimal vol-ume of material required to record the denture space.4 Ikebe et al5 examined the effect of incremental injections of impression material on the resultant denture space. For molar and premo-lar positions, the buccolingual widths of the experimental analogs increased

significantly with each impression material. It was concluded that the denture space was regulated by the volume of material and was located slightly towards the buccal side from the crest of the residual alveolar ridge. However, the researchers included el-derly participants and did not specify their denture experience or the length of their edentulism, nor were they able to determine how many times the ma-terial should be added. Therefore, a proper technique for calculating the exact amount of material required to record the neutral zone without in-terfering with the functioning of the muscles needs to be established.

Indexing Material

Once the neutral zone has been re-

corded, its position can be preserved with the help of indexing material like plas-ter,31,41,46,53,50,58 silicone,41,44,46,48,49,51,56,57,60,64,65 stone,4,19,55 or modeling plastic impression compound.31,35

Reproducibility Studying the reproducibility of

the neutral zone, Karlsson and Hede-gard59 compared the results of 2 op-erators using 1 impression material and a spatula for application and concluded that there was no operator effect when making neutral zone impressions. They also compared the results obtained by 1 operator with 2 impression materials and 2 methods of application (spatula versus injection) and reported signifi-cant differences among impressions when different materials and differ-ent application methods of the mate-rial were used. The results confirm the variability of the neutral zone tech-niques.59,69 These findings should, how-ever, be considered carefully as sample size was limited, and interoperator and intraoperator variability of experimen-tal procedures were not assessed be-cause 1 clinician made only 1 impres-sion with each technique. Such studies need to be done with more operators using larger numbers of materials and different application techniques.

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Maxillofacial Prosthetics and Implants

Recording the neutral zone be-

comes even more difficult when the patient is not able to perform proper functional movements of the cheek, tongue, or lips because of disease or trauma to the orofacial structures. The use of dental implants to achieve improved stability and retention for the patient’s planned prosthesis is a recommended method of treat-ment.70,71 Implant-retained or sup-ported overdentures also require an appropriate polished cameo surface to prevent harmful forces from acting on the implant.72 Preparing diagnostic and surgical templates by using the neutral zone concept facilitates proper placement of implants for complete dentures54 or, after surgical recon-struction of mandible, with implants.65

However patients may refuse treat-ment with implants because of the additional surgery and cost involved. Such patients can be treated with the neutral zone concept to improve es-thetics, support of soft tissues, func-tion, and improved articulation of speech.73 Numerous articles have been published which describe prosth-odontic management with the neutral zone technique for patients undergo-ing mandibular surgical reconstruc-tion,65,73 segmental mandibulectomy,74

brain surgery,57 marginal mandibulec-tomy,64 maxillectomy,75,76 and partial glossectomy44 and for those with se-vere neurological disorders,56 Parkin-son’s disease,60 and severely resorbed residual ridge and mandibular conti-nuity defects.53 These authors have all used different materials for recording the neutral zone but have not devised any new recording techniques.

Comparative Studies

Several studies4,16,25,39,50,55,68,77 have

compared dentures fabricated by us-ing neutral zone (myodynamic) and conventional techniques, and it has been observed that neutral zone den-tures are functionally more stable

than conventional dentures, increase patient comfort and function, and experience minimum postinsertion problems.68 However, according to Fahmy and Kharat,25 comfort and speech performance were better with the neutral zone dentures than with conventional dentures, which showed better mastication results. Raja et al63 showed that in those with longer pe-riods of edentulism, neutral zone den-tures had better assessment results and success. These dentures have the advantages of improved stability and retention, sufficient tongue space, reduced food trapping adjacent to the molar teeth, and good esthetics due to facial support.46 Cineradiogra-phy has also revealed greater stability during mastication for myodynamically fabricated dentures.78 Research should be done to compare larger samples of dentures, and also to compare dentures made with and without reversal of steps to record the neutral zone.

Critically, Stromberg et al55 com-pared similar dentures whose external surfaces had been formed by manual and physiologic procedures and found that all patients preferred the manu-ally formed dentures. The reason could be that although both types of denture were properly placed, the exaggerated contours of the functionally formed den-ture base caused a slight decrease in re-tention because of the different degrees of mouth opening used during the study.

It has been suggested47,63,79,80 that long periods of edentulism modify the position of the neutral zone and that the duration of edentulism influ-ences residual ridge resorption.81-85 Fahmy47 in 1992 concluded that the longer the period of edentulism, the more buccally or labially located was the neutral zone. Lammie3 reported that the direction of mandibular ridge resorption allows the mentalis muscle attachments to fold over the alveolar ridge, which results in the posterior positioning of the neutral zone. Fah-my47 proposed that Lammie’s find-ings were true only for patients who were edentulous for less than 2 years. However, another study by Raja et al63

in 2010 found that Lammie’s find-ings were true for patients who were edentulous for more than 2 years and concluded that the neutral zone may be shifted lingually in relation to the alveolar ridge crest in patients with prolonged edentulism. This was also in agreement with a study by Demirel and Oktemer,80 who suggested the lingual placement of mandibular pre-molars and molars. Lingual position-ing of the neutral zone may result because of facial changes due to age. Prolonged periods of edentulism may result in sagging of the facial muscu-lature. In the mandibular molar area, adjacent buccinator fibers run hori-zontally downwards and forwards. Edentulism eliminates the tooth and alveolar bone support of the bucci-nator fibers. Watt and MacGregor12 suggested shortening the buccina-tor fibers in the absence of a dental bulge. This may distort the facial cur-tain, and, on contraction, the buc-cinators will direct the forces further lingually. Consequently, the neutral zone may be placed more lingually in the posterior segment.47 The study done by Raja et al63 seems to be more appropriate as the number of partici-pants was greater, and the procedure was standardized, and the accuracy level of measurements was up to 0.05 mm. However, whether to place teeth lingually or labially in relation to the ridge crest remains unclear and re-quires additional research.

Limitations to this review may have influenced the outcome. Although the electronic searches were supplemented with manual searches with an attempt made to include all the articles related to the neutral zone, some articles might have been omitted either because they did not focus directly on the topic or because of the filters applied.

In future studies, different materi-als and quantity, application meth-ods and techniques, number of oper-ators, and varied edentulous periods could be compared.

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SUMMARY Within the limitations of this re-

view, it is suggested that the neutral zone technique for fabricating pros-theses should be considered on a more regular basis rather than as an approach for complex treatments. Reviewing the literature revealed few articles which describe the most ap-propriate use of materials and tech-niques for recording the neutral zone, and comparative data are still missing.

REFERENCES

1. United Nations, Department of Economic and Social Affairs, Population Division (2011). World population prospects: The 2010 revision, highlights and advance tables. Available at: www.unpopulation.org.

2. Petersen PE, Bourgeois D, Ogawa H, Estupinan-Day S, Ndiaye C. The global bur-den of oral diseases and risks to oral health. Bull World Health Organ 2005;83:661-9.

3. Lammie GA. Aging changes and the complete lower denture. J Prosthet Dent 1956;6:450-64.

4. Miller WP, Monteith B, Heath MR. The effect of variation of the lingual shape of mandibular complete dentures on lingual resistance to lifting forces. Gerodontology 1998;15:113-9.

5. Ikebe K, Okuno I, Nokubi T. Effect of add-ing impression material to mandibular den-ture space in Piezography. J Oral Rehabil 2006;33:409-15.

6. Atwood DA. Reduction of residual ridges: a major oral disease entity. J Prosthet Dent 1971;26:266-79.

7. Tallgren A. The continuing reduction of the residual alveolar ridges in complete denture wearers: a mixed-longitudinal study covering 25 years. J Prosthet Dent 1972;27:120-32.

8. Weinberg LA. Tooth position in relation to the denture base foundation. J Prosthet Dent 1958;8:398-405.

9. Jagger D, Harrison A. Complete dentures: problem solving. London: British Dental Association; 1999. p. 1-15.

10.McCord JF, Smith P, Grey N. Treatment of edentulous patients. Edinburgh: Ed Churchill Livingstone; 2004. p. 32-3.

11.Zarb GA, Bolender CL, Eckert SE, Fenton AH, Jacob RF, Merickske-Stern R. Prosth-odontic treatment for edentulous patients: Complete dentures and implant supported prostheses. 12th ed: St. Louis: Mosby; 2004. p. 252-61; 100-22.

12.Watt DM, MacGregor AR. Designing com-plete dentures. 2nd ed: Oxford: Butter-worth-Heinemann; 1986. p. 54-69.

13.Yrastorza JA. Vestibuloplasty with skin grafting. J Oral Surg. 1976;34:29-33.

14.Kethley JL, Gamble JW. The lipswitch: a modification of Kazanjian’s labial vestibulo-plasty. J Oral Surgery 1978;36:701-5.

15.Hwang D, Wang HL. Medical contra-indications to implant therapy: part I: absolute contraindications. Implant Dent 2006;15:353-60.

16.Brill N, Tryde G, Cantor R. The dynamic na-ture of the lower denture space. J Prosthet Dent 1965;15:401-18.

17.Campbell RL. A Comparative study of the resorption of the alevolar ridges in denture-wearers and non-denture-wearers. J Am Dent Assoc 1960;60:143-53.

18.Rahn AO, Ivanhoe JR, Plummer KD. Text-book of complete dentures. 6th ed. New York: People’s Medical Publishing House USA; 2009. p. 56.

19.Russell AF. The reciprocal lower complete denture. J Prosthet Dent 1959;9:180-90.

20.Fish EW. Principles of full denture prosthe-sis. London: John Bale, Sons & Danielsson, Ltd; 1933. p. 1-8.

21.Wright CR. Evaluation of the factors neces-sary to develop stability in mandibular dentures. J Prosthet Dent 1966;16:414-30.

22.Sheppard IM. Denture base dislodge-ment during mastication. J Prosthet Dent 1963;13:462-8.

23.Kuebker WA. Denture problems: causes, diagnostic procedures, and clinical treat-ment. I. Retention problems. Quintessence Int Dent Dig 1984;15:1031-44.

24.Pound E. Lost--fine arts in the fallacy of the ridges. J Prosthet Dent 1954;4:6-16.

25.Fahmy FM, Kharat DU. A study of the importance of the neutral zone in complete dentures. J Prosthet Dent 1990;64:459-62.

26.Wright CR, Swartz WH, Godwin WC. Man-dibular denture stability - a new concept. Ann Arbor: The Overbeck Co; 1961. p. 29-41.

27.Schole ML. Management of the gagging patient. J Prosthet Dent 1959;9:578-83.

28.Morstad AT, Peterson AD. Post inser-tion denture problems. J Prosthet Dent 1968;19:126-32.

29.Means CR, Flenniken IE. Gagging--a prob-lem in prosthetic dentistry. J Prosthet Dent 1970;23:614-20.

30.Kuebker WA. Denture problems: causes, diagnostic procedures, and clinical treat-ment. III/IV. Gagging problems and speech problems. Quintessence Int Dent Dig 1984;15:1231-8.

31.Beresin VE, Schiesser FJ. The neutral zone in complete dentures. J Prosthet Dent 1976;36:356-67.

32.The glossary of prosthodontic terms. J Prosthet Dent 2005;94:10-92.

33.Beresin VE, Schiesser FJ. The neutral zone in complete dentures. Principles and technique. St. Louis: The C. V. Mosby Co; 1973. p.1.

34.Matthews E. Residual problems in full den-ture prosthesis. Br Dent J 1954;97:167-73.

35.Schiesser FJ. The neutral zone and polished surfaces in complete dentures. J Prosthet Dent 1964;14:854-65.

36.Wright SM. The polished surface con-tour: a new approach. Int J Prosthodont 1991;4:159-63.

37.Grant AA, Johnson W. An introduction to removable denture prosthetics. Edinburgh: C. Livingstone; 1983. p.24-8.

38.Schlosser RO. Complete denture prosthe-sis. Philadelphia: WB Saunders Company; 1939. p.183-90.

39.Heath R. A study of the morphology of the denture space. Dent Pract Dent Rec 1970;21:109-17.

40.Roberts A. The effects of outline and form upon denture stability and retention. Dent Clin North Am 1960;4:293-303.

41.McCord JF, Grant AA. Impression making. Br Dent J 2000;188:484-92.

42.Walsh JF, Walsh T. Muscle-formed com-plete mandibular dentures. J Prosthet Dent 1976;35:254-8.

43.Mersel A. Gerodontology--A contemporary prosthetic challenge. 1. Mandibular impres-sion technique. Gerodontology 1989;8:79-81.

44.Ohkubo C, Hanatani S, Hosoi T, Mizuno Y. Neutral zone approach for denture fabrication for a partial glossectomy patient: a clinical report. J Prosthet Dent 2000;84:390-3.

45.Khamis M, Razek A, Abdalla F. Two-dimen-sional study of the neutral zone at different occlusal vertical heights. J Prosthet Dent 1981;46:484-9.

46.Gahan MJ, Walmsley AD. The neutral zone impression revisited. Br Dent J 2005;198:269-72.

47.Fahmy FM. The position of the neutral zone in relation to the alveolar ridge. J Prosthet Dent 1992;67:805-9.

48.Lynch CD, Allen PF. Overcoming the unstable mandibular complete denture: the neutral zone impression technique. Dent Update 2006;33:21-2, 24-6.

49.Kursoglu P, Ari N, Calikkocaoglu S. Using tissue conditioner material in neutral zone technique. N Y State Dent J 2007;73:40-2.

50.Raja HZ, Saleem MN. Neutral zone dentures versus conventional dentures in diverse edentulous periods. Biomedica 2009;25:136-45.

51.Cagna DR, Massad JJ, Schiesser FJ. The neutral zone revisited: from historical concepts to modern application. J Prosthet Dent 2009;101:405-12.

52.Raybin NH. The Polished Surface of Complete Dentures. J Prosthet Dent 1963;13:236-9.

53.Wee AG, Cwynar RB, Cheng AC. Utilization of the neutral zone technique for a maxil-lofacial patient. J Prosthodont 2000;9:2-7.

54.Suzuki Y, Ohkubo C, Hosoi T. Implant placement for mandibular overdentures us-ing the neutral zone concept. Prosthodont Res Pract 2006;5:109-12.

55.Stromberg WR, Hickey JC. Comparison of physiologically and manually formed den-ture bases. J Prosthet Dent 1965;15:213-30.

56.Karkazis HC. Prosthodontic management of a patient with neurological disorders after resection of an acoustic neuri-noma: a clinical report. J Prosthet Dent 2002;87:419-22.

57.Sadighpour L, Geramipanah F, Falahi S, Memarian M. Using neutral zone concept in prosthodontic treatment of a patient with brain surgery: a clinical report. J Prosthodont Res 2011;55:117-20.

58.Lott F, Levin B. Flange technique: an anatomic and physiologic approach to increased retention, function, comfort, and appearance of dentures. J Prosthet Dent 1966;16:394-413.

134 Volume 109 Issue 2

The Journal of Prosthetic Dentistry Porwal and Sasaki

59.Karlsson S, Hedegard B, Odont. A study of the reproducibility of the functional denture space with a dynamic impression technique. J Prosthet Dent 1979;41:21-5.

60.Makzoume JE. Complete denture prosth-odontics for a patient with Parkinson’s disease using the neutral zone concept: a clinical report. Gen Dent 2008;56:12-6.

61.Makzoume JE. Morphologic comparison of two neutral zone impression techniques: a pilot study. J Prosthet Dent 2004;92:563-8.

62.Alfano SG, Leupold RJ. Using the neutral zone to obtain maxillomandibular relation-ship records for complete denture patients. J Prosthet Dent 2001;85:621-3.

63.Raja HZ, Saleem MN. Relationship of neutral zone and alveolar ridge with eden-tulous period. J Coll Physicians Surg Pak 2010;20:395-9.

64.Pekkan G, Hekimoglu C, Sahin N. Reha-bilitation of a marginal mandibulectomy patient using a modified neutral zone technique: a case report. Braz Dent J 2007;18:83-6.

65.Kokubo Y, Fukushima S, Sato J, Seto K. Ar-rangement of artificial teeth in the neutral zone after surgical reconstruction of the mandible: a clinical report. J Prosthet Dent 2002;88:125-7.

66.Barone JV. Physiologic complete denture impressions. J Prosthet Dent 1963;13:800-9.

67.Martone AL. Clinical applications of concepts of functional anatomy and speech science to complete denture prosthodontics: Part VIII. The final phases of denture con-struction. J Prosthet Dent 1963;13:204-28.

68.Barrenäs L, Odman P. Myodynamic and conventional construction of complete den-tures: a comparative study of comfort and function. J Oral Rehabil 1989;16:457-65.

69.Neill DJ, Glaysher JK. Identifying the den-ture space. J Oral Rehabil 1982;9:259-77.

70.Adell R, Eriksson B, Lekholm U, Branemark PI, Jemt T. Long-term follow-up study of osseointegrated implants in the treatment of totally edentulous jaws. Int J Oral Maxil-lofac Implants 1990;5:347-59.

71.Lewis S. Implant-retained overdentures. Compendium 1993;14:1270-74.

72.White GE. Osseointegrated dental technolo-gy: London: Quintessence;1993. p.153-168.

73.Beumer J, Curtis TA, Marunick MT. Maxil-lofacial rehabilitation: prosthodontic and surgical considerations: St. Louis: Ishiyaku EuroAmerica, Inc; 1996. p.194-206.

74.Patil PG. Conventional complete denture for a left segmental mandibulectomy patient: a clinical report. J Prosthodont Res 2010;54:192-7.

75.Raja HZ, Saleem MN. Gaining retention, sup-port and stability of a maxillary obturator. J Coll Physicians Surg Pak 2011;21:311-4.

76.Beresin V, Schiesser F. Neutral zone in complete and partial dentures. 2nd ed. St. Louis: Mosby; 1978. p. 208-20.

77.Dimmer A. A clinical assessment of a functional impression technique for the complete lower denture. Gerodontics 1985;1:217-9.

78.Karlsson S. Cineradiography in odontology. Swed Dent J Suppl 1979;4:1-63.

79.Watt DM. Tooth positions on complete dentures. J Dent 1978;6:147-60.

80.Demirel F, Oktemer M. The relations be-tween alveolar ridge and the teeth located in neutral zone. J Marmara Univ Dent Fac 1996;2:562-6.

81.de Baat C, Kalk W, van ‘t Hof M. Factors connected with alveolar bone resorp-tion among institutionalized elderly people. Community Dent Oral Epidemiol 1993;21:317-20.

82.Klemetti E, Lassila L, Lassila V. Biometric design of complete dentures related to residual ridge resorption. J Prosthet Dent 1996;75:281-4.

83.Karaagaclioglu L, Ozkan P. Changes in mandibular ridge height in relation to ag-ing and length of edentulism period. Int J Prosthodont 1994;7:368-71.

84.Narhi TO, Ettinger RL, Lam EW. Radio-graphic findings, ridge resorption, and subjective complaints of complete denture patients. Int J Prosthodont 1997;10:183-9.

85.Kordatzis K, Wright PS, Meijer HJ. Posterior mandibular residual ridge resorption in patients with conventional dentures and implant overdentures. Int J Oral Maxillofac Implants 2003;18:447-52.

Corresponding author:Dr Amit Porwal Pacific Dental College and HospitalUdaipur, RajasthanINDIA Fax: +91-294-2491508 E-mail: aporwal2000@gmail.com

Acknowledgments The authors thank Dr Anurag Satpathy, Dr Naveen Halemane, and Dr Santosh Nelogi for assistance in the preparation and editing of the manuscript.

Copyright © 2013 by the Editorial Council for The Journal of Prosthetic Dentistry.