Abdul Mueed Zaigham
Associate Professor, Dept of Prosthodontics, CMH Lahore Medical College, Lahore, Pakistan.
Correspondence: “Dr.Abdul Mueed Zaigham”
How to CITE:
J Pak Dent Assoc 2010;19(2):120-123.
Mandibular denture instability is a common problem in patients with atrophic mandibular ridges. Various methods had been employed by the profession to overcome this problem. The objective of this study was to evaluate role of neutral zone approach in atrophic edentulous mandibular ridges.
Twenty edentulous patients with atrophic mandibles were selected. Seven evaluation factors were analyzed and compared.
Three factors stability, tongue space and position of anterior teeth were better achieved by using neutral zone technique.
Successful denture can be fabricated by using neutral zone in atrophic mandibular ridges.
Atrophic mandibular ridges; Neutral zone technique; Tongue space; Position of anterior teeth.
Successful complete denture therapy begins with a careful assessment of patient’s physical condition and determining a treatment plan that will deliver optimum results. Maxillary dentures have a better record of clinical success due to larger denture bearing area, regular parabolic form and less acquired muscular influence.1,2
Favourable mandibular ridges and denture bearing area significantly contribute towards the success of proposed complete denture. Ridge resorption leads to qualitative and quantitative reduction in denture bearing area; loss of sulcus depth and available ridge height; decrease in load bearing capacity of denture bearing area and reduced denture stability3, 4, 5. Conventional dentures may not provide desired results in these cases.
Provision of implant retained prostheses may serve the purpose. But every patient is not suitable for implants 6. To get the successful results in such cases other factors may have to be exploited. These may include improved impression techniques; proper location and arrangement of artificial teeth and appropriate form of polished surfaces.
Success of the complete denture depends largely upon the relation of the dentures to anatomic structures that support and limit them, familiarity with the location and character of these structures is essential 7. All the oral functions involve the synergistic actions of lips, cheeks, tongue and floor of the mouth. Failure to recognize the cardinal importance of tooth position and flange form and contours may result in unstable and unsatisfactory dentures. Neutral zone (NZ) is the area where the forces from the cheeks and lips are counter balanced by the forces exerted by tongue8, 9, 10. It is also referred to as dead space, the stable zone and the zone of minimal conflict11. Many unstable lower dentures are caused by the external surface not being properly formed and teeth not positioned in within the neutral zone10, 11.
The objective of this study was to evaluate the role of neutral zone approach in overall success of atrophic edentulous mandibular dentures.
This study was carried out on edentulous patients with atrophic mandibular ridges. 20 patients (Atwood order V & VI) 12 were selected. Patients were provided denture by using neutral zone concept described by Beresin and Schiesser9. All other steps of complete denture construction were also kept same to keep the variables constant. The technical quality of the mandibular dentures was evaluated by assessing the following factors
1- Retention 2- Stability
3- Border Extensions 4- Fit of the denture
5- Tongue Space 6- Position of posterior teeth
7- Anterior teeth arrangement
These factors were analyzed according to a three grade (I, II & III) criteria ranging from good, average and poor respectively (Table 1). Data was analyzed using SPSS Version 10. Descriptive statistics were used to describe data. Student’s T test was applied for results
Technical quality of the dentures for these evaluation factors was statistically analyzed individually (Table 2). Comparison revealed that out of these seven individual evaluation factors, three factors stability, tongue space and position of anterior teeth were better achieved by using neutral zone technique (Fig. 1)
The ultimate objective of prosthodontics is to restore form, function and esthetics. Patients with atrophic mandibular ridge are frequent and difficult to manage for majority of dentists. Several times a combined approach of preprosthetic surgical options, implants and careful prosthetic treatment yields successful results. However majority of patients are not suitable for these advance options due to various constraints 3.
About 16 different factors are considered to evaluate both upper and lower denture 13, 17. Out of these, seven factors (retention; stability; border extension; fit of denture; tongue space; position of posterior teeth and anterior teeth arrangement) were selected and evaluated. All these factors are directly related with the general assessment of mandibular denture. Although every factor was individually analyzed but collectively they have strong interrelation and have a direct or indirect effect on one another.
In atrophic ridges impression surface area is decreased and polished surface area relatively increases. Utilization of the neutral zone concept is beneficial to patients with a history of unstable and loose fitting dentures. Since the neutral zone also defines the exterior contour of a denture base (polished surfaces), in order to work in harmony with adjacent supporting and stabilizing muscle actions, the prosthesis has a more natural feel to the patient. Makzoume 18 in a pilot study also claimed that dentures made by neutral zone have an edge over others.
Tongue control also aids in retention and stability of mandibular denture if polished surfaces are in harmony to its functional activities. In addition correct positioning of occlusal plane and harmonious arrangement of teeth also helps the orofacial musculature to stabilize the lower denture. The tongue can be a powerful adjunct in the achievement of stability when above conditions are met
There has been disagreement about the optimum facial-lingual placement of mandibular teeth relative to the residual alveolar ridge. One of the possible reason may be that alveolar ridge does not resorb uniformly. Leverage is the major concern while placing the teeth on centre of the ridge whereas neutral zone considers muscular forces created during function. The lack of favourable leverage in neutral zone may be counterbalanced by controlling action of muscles surrounding the denture. This may have led to increased retention and stability in neutral zone technique.
In a comparative study, Fahmy11 has concluded that conventional dentures were found to be better for mastication. In spite of this, all the patients prefer to use dentures made with neutral zone.
In our study, analysis showed non-significant values. One possible reason may be small sample size. Comparison between large groups may lead to more obvious results. Hence further research may be carried out keeping in view these points
Successful dentures in patients with atrophic mandibular ridges were made by using neutral zone. This highlights the critical role of polished surfaces and arrangement of artificial teeth in denture success
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