Research Project

For a better understanding of complete maxillary retention and stability Abstract Aims of this paper 1.0 Introduction 2.0 Retentions: 2.1 What is retention? 2.2 Physiological retentions 2.2.1 Border seal 2.2.2 Accuracy of fit 2.3 Anatomical retentions 2.3.1 Bony undercut 2.3.2 Oral musculature 3.0 Stability 3.1 What is stability? 3.2 Some Stability Factors 3.2.1 Base shape and fitting surface 3.2.2 Tooth position 3.2.3 Polished surface 3.2.4 Occlusal surface 4.0 Saliva 4.1 Adhesion 4.2 Cohesion 4.3 Surface tension 4.4 Viscosity 4.5 Professional attitude towards Denture adhesion

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4.6 Patient Education 5.0 Postpalatal seal 5.1 What is Postpalatal Seal? 5.2 Objectives 6.0 Ill-fitting of the maxillary denture 6.1 Problems with the denture 6.1.1 Impression surface 6.1.2 Polished surface 6.1.3 Occlusal surface 6.2 Problems with the denture wearers 6.2.1 Poor neuromuscular control 6.2.2 Unstable foundation 6.2.3 Inadequate saliva 7.0 Conclusion 8.0 References

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Abstract: A successfully functioning maxillary and mandibular denture relies on the amalgamation of the patients’ general oral functions and the psychological acceptance of their denture. The aforementioned are dependant largely on the patients’ denture stability during mastication and general day-to-day oral functions in combination with the aesthetic affect on the patients’ facial appearance. Some edentulous people face functional problems with their complete maxillary dentures. Several factors contribute to this failure especially when it comes to the function of speech and mastication. Therefore it is imperative that during production of the denture to include features into its design that aid in improving retention and overall stability of the denture. Knowledge and implementation of techniques that take advantage of key physiological, anatomical and psychological factors will aid clinicians and technicians to create a maxillary denture with good retention and stability, giving the patient a functional and usable appliance. In addition, patient education and professional attitude will play an important role in achieving the goal of a successful prosthetic appliance. The aim of this paper is to aid the practitioner in comprehending which elements and factors are pertinent to a complete maxillary denture’s retention and stability. Border seal, accuracy of fit, bony undercut, oral musculature, base shape, fitting surface, tooth position, polished surface, occlusal surface, saliva, adhesion, viscosity, surface tension, cohesion, professional attitude towards denture adhesion, patient education, postpalatal problems with denture, and problems with denture wearers have all been considered .to have a strong relationship with retention and stability of the complete maxillary denture

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:Aims :The aims of this paper are To provide the practitioner with key characteristics that is involved in creating a -1 .complete maxillary denture with ideal retention and stability To aid and influence the complete maxillary denture’s efficiency by understanding and -2 .implementing factors that amplify retention and stability To explain the probable causes of ill-fitting dentures and to make suggestions on its -3 .administration

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1. Introduction: Although the use of dental implants is expanding, the preferred method of treating edentulous patients is still with the conventional complete denture (Celebic et la. 2003). People who wear complete maxillary and mandibular dentures will have anticipations in relation to mastication, aesthetics and confidence. Edentulous people, that use complete dentures, will have to learn the required oral motor skills to make sure that they can utilise the prostheses during common functional movements such as speech and mastication (Zarb et al. 1997). Many of these patients may incur problems during functional movements while wearing complete dentures (Garrett et al. 1996). It remains an enigma why some patients are capable of controlling their complete dentures more efficiently than others, even when the alveolar ridge morphology seems compromised (Scott and Hunter 2008). Moreover, many practitioners have treated patients who posses well designed and manufactured dentures, however some of these patients struggle to function with these appliances, on the other hand there are patients who function sufficiently with prostheses that have large amounts of damage and are supported by an inferior base. The aforementioned features stress the importance of understanding and implementing factors that affect retention and the stability of complete dentures. This paper will focus on five main factors that contribute to the retention and stability of complete maxillary dentures. First, the concept of retention, which is defined as 'the quality inherent in the prosthesis acting to resist the forces of dislodgment along the path of placement' (Driscoll et al. 2004, p. 567). Retention can be divided into two categories physiological retention, which includes border seal and accuracy of fit, and anatomical retention which includes bony undercuts and oral musculature. Second, stability which may defined as the quality of a denture to be fixed, stable, or strict, to resist displacement by functional horizontal or rotational pressures (Van Blarcom, 1999). Four stability factors are covered in detail which

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are; base shape and fitting surface, tooth position, polished surface and occlusal surface. Third, saliva which is considered to be the most important factor of complete maxillary denture retention (Husham, 2006) has been divided into six components; adhesion, cohesion, surface tension, viscosity, professional attitude towards denture adhesion and patients’ education. Fourth, the post-palatal seal has a crucial effect on the retention of the complete upper denture (Tsirmbas and Vlissidis, 1989) thus its objectives will be mentioned. Fifth, the problems and reasons that cause ill-fitting dentures will be explained. It is divided into two main areas which are problems with dentures and issues with denture wearers. Fifth, the problems and reasons that cause ill-fitting dentures will be explained. It is divided into two main areas which are problems with dentures and issues with denture .wearers

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2.0 Retentions: 2.1 What is retention? Definitions of the complete denture retention is a ‘resistance of a denture to vertical movement away from tissues’ as well as ‘that quality inherent in the prosthesis acting to resist the forces of dislodgement along the path of insertion’ (Darvell and Clark 2000, p. 248) and ‘any movement in the vertical plane’ (Rendell et al. 1995, p. 344). It is therefore obvious that retention is a feature that belongs to the denture more than to the patient (Darvell and Clark 2000). When the denture is inserted in the patient’s mouth, it should usually stay in place while the mouth is open. The maxillary complete denture ought to provide resistance when pulled in a downward direction by a finger and thumb gripping the incisors (Basker and Davenport 2002).

2.2 Physiological retentions 2.2.1 Border seal For supreme retention, the denture border must be formed so that the channel between the sulcus tissues and the denture is as minute as possible (Basker and Davenport, 2002). Because the depth of the sulcus differs during function, it is not difficult to keep a close approximation between the denture border and the reflection of the mucosa in the sulcus at all times. The construction of the denture has to be done so that the border follows the most superficial point that the sulcus reflection can reach in ordinary functions. This signifies that the denture will be moderately under-extended for some of the time while the patient is at rest. If an extended procedure is done on the denture to provide a tight seal in this spot, displacement may happen during the functional movement of the sulcus tissues. The problem of having a stable border seal can be solved by laterally extending the denture

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flanges so that the buccal and labial mucosa are contacted and marginally displaced by the flanges to create a facial seal (see Figure 1.1 below).

Figure 1.1 lateral lengthening of the buccal flange to provide a facial seal (Basker and Davenport, 2002). The facial seal along the posterior border of the maxillary denture can be possibly produced as it crosses the palate. In this spot, another approach is to produce as narrow space as possible between the denture and mucosa. A post-dam is done on the working cast so that there is a raised lip at the posterior border of the accomplished denture that becomes embedded into the palatal mucosa (Basker and Davenport, 2002).

There is a double contact of acrylic and soft tissue in the majority of the denture border such that displacing the denture in the sense of separation does not open a space along that border. There are two results from this. Firstly, the cross section that saliva should fill in is small, whereas the displacement viscous retardation is great. Secondly, the lowered

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pressure under the denture, which is caused by displacement, is likely to embrace the buccal tissues in place in close estimation.

2.2.2 Accuracy of fit It has been recommended that when a denture is positioned in place a solid seating, force be engaged as this helps retention (Darvell and Clark 2000).The forces of retention are increased when the saliva film between the denture and underlying

mucosa become

thinner (Basker and Davenport 2002). The thinnest possible saliva film and viscosity will act to prevent displacement of the denture. Nevertheless, this should also be accomplished with the sacrifice of some displacement of the sustaining soft tissue, and if this provides a superior fit, it will not remain long as that tissue elastically rebounded (Darvell and Clark 2000). Therefore, achieving the best possible an accurate fit of the denture is a very important aspect.

An inadequate fitting of the denture will increase the density of the saliva film and develop air bubbles within the film. The action of these bubbles is to minimize the retention of the denture. Moreover, the expansion of the air bubbles and their extension to the border area might cause a breaking of the border seal when the pressure of the saliva film drops due to displacing forces affecting the denture (Basker and Davenport 2002). The endurance secretion from mucosal glands will also offset any instant advantage. It might, however, be helpful for the intentional seating force to exclude air that causes problems in retention (Davell and Clark 2000).

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2.3 Anatomical retentions 2.3.1 Bony undercut The pliability of the mucosa and submucosa covering the basal bone creates some moderate undercuts that will improve retention (Zarb and Bolender 2004). The retention could be modified by supplying a prosthesis that uses these undercut spots. To be able to accomplish this without any problem on the mucosa on placement and stripping of the prosthesis, extensive consideration is needed in designing the path of insertion (Basker and Davenport 2002). In spite of overstated bony undercuts or less obvious ones overlaid by fine epithelium, they might compromise the retention of the denture by requiring broad internal modifying of the denture, less austere lateral tuberosities undercuts, premolar spots of the maxillary denture areas can be excessively useful for the retention of the dentures.

Few “undercuts” are simply undercuts regarding the path of insertion (Zarb and Bolender 2004). Even if the undercuts region is firstly placed and the reminder of the denture base can be carried into closeness with the basal seat on rotation of the denture about the undercut piece that previously placed, this “rotational path” will create vertical displacement resistance. An obvious or equal undercut anterior alveolus might determine a path of insertion that starts with placing the anterior in a posterior position and finish with rotation of the posterior border behind of the tuberosities. This concept has increased significantly as other retentive methods fail in power. For example, with a patient who has gone through waste of ordinary anatomical contours caused by tumour resection or trauma, surgically provided undercuts might imply the dissimilarity between denture triumph and failure (Zarb and Bolender 2004).

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2.3.2 Oral musculature Dentures have been worn by patients successfully, because they have learned to grasp their dentures with the muscles in their lips, cheeks and tongue. This ability may progress to a high level so that the denture which looks loose to the dentist may be quite acceptable in the patient’s opinion. In some cases, patients can eat without any problems even when the prosthesis has shattered into two or more pieces (Basker and Davenport 2002). Studies reveal that complete dentures change a few millimetres regarding the underlying structure through mastication (Basker and Davenport 2002). As a result, during chewing, loose physical retention commonly occurs; therefore, muscular control is essential. The proficient muscular control of the prosthesis is based on two elements. First, the denture shape and design and the muscles of the oral cavity (lips, cheeks and tongue) manage the bolus of food, move it around the oral cavity and put it between the teeth’s occlusal surfaces. In this way, the muscles press on the polished surfaces of the prosthesis. If these surfaces have been designed correctly, this muscular force will place the dentures on the underlying mucosa (see Figure 1.3). Besides this working muscular fixation of the dentures during mastication, there is a definite amount of passive fixation in the rest of the muscles, as the relaxed soft tissue is placed on the dentures; thus, they can be maintained in position. In contrast, an inaccurately designed prosthesis causes displacement of the denture by the force of the muscles.

The second element in the proficient muscular control of the prosthesis is the required skill that patients need, that is, the ability of the patients to attain the required abilities to manage new dentures, which is referred to as the biological age. Overall, as the patient gets older, the learning phase becomes longer. In severe cases, dentures that are technically perfect will not fit elderly or senile patients who cannot attain this skill. For this purpose, 11

denture replacement for an older patient must be performed in such a way that the skill of the patient in managing the preceding denture designs can be directly moved to the replacements. This is accomplished by duplicating the old prosthesis as closely as possible. When a patient incises, it is a particular instance of the muscular control of the prosthesis. The posterior border is fell down because of the forces that tend to tip the maxillary denture. This action is usually resisted by the dorsum of the tongue which pushes against the denture and replaces it (see Figure 1.4). Patients who suffer from obstacles when incising with dentures which look to be perfect must be inspected with caution to determine whether or not the control of the tongue exists. If it does not, the dentist must explain the problem to the patient and provide suitable training. This takes the form of teaching the main role of the tongue, lips and cheeks in managing the prosthesis and giving particular advice, such as sustaining the posterior border of the maxillary denture with the tongue during functioning. The capability of the patient to manage the dentures, which will reduce the displacement forces, can be attained by giving advice; for instance, before inserting the food into the mouth, it should be cut into small pieces, ground on both sides of the denture, and always begin with softer foods before moving on to bigger morsels. Without the patient’s awareness of muscular action, the replacement prosthesis will not address the patient’s complaint. Muscular control takes a long time to master when the denture is first fitted, which mostly causes ill fitting dentures. Therefore, the physical forces of retention are especially essential during this primary learning period. When these forces become stronger, the patient will need little effort in controlling the dentures. On the other hand, if the physical forces are poor, the dentures will be loose so that the patient will refuse to wear them (Basker and Davenport 2002).

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Figure 1.3 Influence of soft tissue forces on dentures: (a) seating the dentures when the polished surfaces are correctly shaped, (b) displacing the dentures when the polished surfaces are incorrectly shaped (Basker and Davenport 2002).

Figure 1.4 as the patient incises, the upper denture is controlled by the tongue pressing against the posterior border (Basker and Davenport 2002).

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3.0 Stability 3.1 What is stability? Denture stability is the minimum movement occurring in relation to the underlying bone throughout function. It is amazing that dentures remain seated in place at all, as they are surrounded by a very active muscular medium. They remain in place if the retention forces being applied on the dentures are more than the displacing forces and when adequate support has been provided to the denture. This support is decided on by the shape and consistency of the denture bearing tissue and the precision of fit of the denture (Basker and Davenport 2002).

Specifically, denture stability has been defined as ‘the resistance of a denture to displacement by functional forces’ (Ogden 1996, p. 71). According to this statement, the denture has been made in function. The definition of denture support is the denture resistance of the directed occlusal loads. When the patient who has no teeth at all (edentulous case), the support is achieved from the soft tissue of the denture-bearing spot and the underlying bone. Functional stability can be affected by one or more of these factors. For instance, an effective border seal may cause a good denture retainer. However, when there is an anterior fibrous maxillary ridge, the denture retainer may simply be compromised on occlusal loading during masticatory function, because the post-dam seal might break if a tipping force is applied to the denture. As a result, the following factors are essential when attempting to achieve complete dentures that are stable in function (Scott and Hunter 2008). These factors have been summarized in Figure 3.1 (Basker and Davenport 2002).

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Figure 3.1 Relationship of factors contributing to denture stability ((Basker and Davenport 2002). 3.2 Some Stability Factors 3.2.1 Base shape and fitting surface The denture fitting surface is that part which directly contacts the tissues of the denturebearing spot. The periphery of the denture may be affected due to the design of the base which is impacted by the soft tissue attachments (Scott and Hunter 2008). Consequently, these objectives should be attained by the master impression. In order to record fine details of the surface, adequate impression materials should be used.

The master cast’s

impression trays must be ideally lengthened over the entire of the denture-bearing area. The significant tissue features of the maxillary denture-bearing area are: labial fraenum, root of zygomatic arch, buccinators, and hamular notch, vibrating line, palatal rugae, incisive papilla and remnant of palatal gingival vestige (Scott and Hunter 2008). The shape of the border may be affected by a number of muscle attachments and these must be permitted for when the particular trays are evaluated in the mouth. The critical part for denture retention is the posterior border of the maxillary denture, and the shape of a postdam is included. The posterior border of the denture must be lengthened to the vibrating line (Scott and Hunter 2008). This line is defined as ‘the line of junction between the moving tissues of the soft palate and the static tissues anterior to them’ (Ogden 1996, p. 71). An inadequate posterior seal often results when the posterior border reclines short of the vibrating line. It can be broken if it extends beyond the vibrating line when the soft palate lifts during mastication. Because of that, the vibrating line, known as the ‘ah-line’, 15

must be inspected with caution, and the clinician must be convinced that it has been accurately prepared on the master cast (Scott and Hunter 2008).

The maxillary complete denture retention might be influenced by a number of elements related to the fitting surface. It might not be easy to extend the denture base ideally due to the problem of gagging that occurs with some patients. This usually affects the posterior seal (Lamb 1993). Examining the overextension of the maxillary denture is easy. If the denture is expelled by drawing the modiolus downwards and forwards, a lengthening is determined over the insertion of the buccinator into the maxilla. Drawing the modiolus downwards and backwards will check for an extension of the labial flange over the insertion of the muscles of the upper lip. During the time when the minor slips of the orbicularis oris are inserted into the maxilla and defined, the depth of the anterior sulcus can be examined by pulling the upper lip down manually, which might be simpler to permit the patient to perform the movements themselves. Any displacement of the denture should be examined, which happens when the patient contracts their lips and protrudes them in a pouting action. If an overextension is detected, the denture is laid over the suitable muscle. This is done slowly, and the patient is asked about the level of improvement to ensure that maximum stable extension is retained (Lamb 1993).

3.2.2 Tooth position The accurate positioning of the artificial teeth is crucial for accomplishing stability in mastication. Any unsuitable arrangement of the teeth of the denture can cause the prosthesis being displaced simply throughout function. Some elements that are essential in achieving greatest stability by accurate positioning of the teeth are explained in Table 1 (Scott and Hunter 2008).

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To achieve a maximum effective role of the tongue, the occlusal planes of the prostheses must be arranged at a suitable degree (Devlin and Hoad-Reddick 2001). The sitting of the maxillary occlusal planes is often carried out by alteration of an occlusal rim so that a suitable amount of tooth is observed and the occlusal plane inclination is parallel with the inter-papillary and ala-tragal planes (Scott and Hunter 2008).

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Stability points Elements to study Suitable degree of occlusal table for Degree of occlusal planes regarding effective function of the tongue.

anatomical spots; for example, vermillion border of the lip.

Occlusal vertical dimension and freeway space Suitable positioning of teeth to prevent Teeth sitting in away that will accord denture

displacement

throughout with the function of the muscle.

mastication function. Neutral zone Suitable positioning of teeth to permit the Sitting the mandibular teeth regarding the tongue

to

stabilize

the

mandibular underlying ridge.

denture. Posterior shelf of the prosthesis Table 1 The ideal points to study for ensuring greatest stability through elements related to the tooth sitting and the complete dentures occlusal surfaces (Scott and Hunter 2008).

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3.2.3 Polished surface The polished surface of the prosthesis stretches from the borders of the base to the synthetic teeth (Scott and Hunter 2008). This surface contains the form of the plate as fine as the buccal and lingual surfaces of the acrylic in touch with the tongue, lips and cheeks (Basker and Davenport 2002). Because of this, these pieces of dentures must be formed in a suitable way to permit the function of the muscles to accord with the prosthesis form. Regions of the polished surface form might affect dissimilar actions, for instance, the palatal vault of the upper prosthesis regarding speech (Scott and Hunter 2008).

The expression “neutral zone” is an area between the tongue on one side and the cheeks and the lips on the other where the muscular displacing forces playing on a denture are the least. This is also known as the zone of minimal conflict (Basker and Davenport 2002) and is usually used to illustrate the positioning of the synthetic teeth in a place in which stability is obtained. This can often be accomplished by the clinician and technician following the mentioned outlines. Nevertheless, in some stages, it might be required to register an impression of the zone to permit maximum arrangement of the synthetic teeth and the accurate forming of the polished surfaces (Gahan and Walmsley 2005). This can be obtained by fabricating a solid denture base with occlusal stops placed at the accurate vertical dimension. A tissue conditioner is an appropriate material to register a functional impression that will show the dimension of the neutral zone. The denture teeth are now formed and placed to accord with this, and the polished surfaces are also formed so that they rest within this described zone. The resulting teeth might well be very thin; however, as they are sited in a maximum location for stability, the patient might be able to manage the prosthesis throughout function more efficiently (Scott and Hunter 2008).

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Uncommonly, instability of the maxillary denture is due to the coronoid process touching an enormously thick buccal flange throughout opening. Suffering on opening is a common symptom, but might be covered by a destabilizing intervention which can be the main complaint (Lamb, 1993). The muscles of the cheeks, lips and tongue, along with being of basic significance in the retention of dentures, are also able to cause instability to the dentures. Displacement will happen if the polished surfaces have an adverse slope (see Figure 3.2) and also if the prosthesis intervenes with the normal position and functional action of the surrounding musculature. For instance, distal movement of a lower prosthesis might be created too far labially. The teeth must therefore be sited distant enough lingually to avoid this displacement, but not so far away as to permit excessive tongue pressure (Basker and Davenport 2002).

Figure 3.2 Pressure from the bolus on the posterior part of the lower occlusal table, which overlies a sloping part of the ridge, causes the lower denture to slide forwards ( Basker and Davenport 2002).

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3.2.4 Occlusal surface The occlusal surface of the denture is the portion that creates touch with the similar surface of the other prosthesis (Basker and Davenport 2002). For ideal function, the prosthesis must be fabricated at the accurate vertical dimension, making certain that a suitable freeway space is obtained. The vertical dimension of the dentures in occlusion is reliant on how the synthetic teeth are placed and, subsequently, the degree of the occlusal plane on both dentures is related to this (Scott and Hunter 2008).

All occlusal deficiency must be rectified at an earlier phase, if a check register or amount procedure has been carried out. Nonetheless, when patients have dentures on for the first time or after an extended period of wearing an imperfect denture, their normal jaw relationships may still be efficient. It can then be discussed that it is more complete to leave the check record until the recall phase when the faulty reflexes have had the chance of being missing when the occlusal error can then disclose itself in a compliant of looseness that is removed after the check register. It can also be discussed that when putting dentures on a denture-bearing area that reveals areas of erythema caused by previous ill-fitting dentures, few resolutions of inflammation might exist during the postinsertion stage. Here, too, the alterations in the denture-bearing areas may reveal previously unnoticed occlusal imperfections and looseness, which may be rectified by a check record at the recall phase (Lamb 1993).

In the exact way as at the insertion stage, occlusal modification can occasionally be made in the mouth. If an early contact exists, the symptom will be tipping of the prosthesis. Premature contacts can be determined with articulating paper. Unless the premature

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contact is great, which at this phase is improbable, a deepening of opposing fossa is the treatment required (Lamb 1993).

4.0 Saliva Saliva has four fundamental properties which are adhesion, cohesion, surface tension and viscosity (Escoe and Escoe 2008). These elements are fundamental to the oral health of denture wearers. Saliva is essential for the retention of the complete standard denture. Saliva should adhere to the denture surface. The film of saliva between the mucosa and the denture must be greatly cohesive and, as a result, tough to break. The denture’s outer surface where it joins the mucosa is wet with saliva. Because of surface tension, this outer common layer of saliva should be difficult to break. The viscosity of saliva is required so that it flows with difficulty during the displacement of denture. In fact, a whole industry of denture adhesives is based on augmenting the physical saliva attributes in the retention of denture (Escoe and Escoe 2008).

4.1 Adhesion Adhesion is described as the physical attraction of dissimilar molecules to each other (Basker and Davenport 2002). The saliva adhesion to the mucous membrane and the base of the denture is obtained through the ionic forces between charged salivary glycoproteins and surface epithelium or acrylic resin. Adhesion works to further improve the retentive force of interfacial surface tension through its promoting contact of saliva to both the oral tissue and the denture base. Adhesion that is shown between denture bases and the mucous membranes themselves is considered to be another version. The material of the denture base seems to cohere to the dry mucous membrane of the basal seat and other oral surfaces.

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Similarly, adhesion is not that efficient for retaining dentures and predisposes to mucosal abrasions and ulceration because of the deficiency of the salivary lubrication. It is irritating for patients to experience denture bases sticking to the cheeks, lips and tongue. Ethanolfree rinsing consisting of aloe or lanolin, a water-soluble lubricating jelly or saliva substitute consisting of carboxymethylcelluose (CMC) or mammalian mucin can be helpful in this condition. For patients who have a dry mouth because of irradiation or an autoimmune disorder, a salivary encourager through a prescription of 5 to 10 mg of oral pilcarpine three times daily can be very useful if the patient can bear the possible contraindication effect of increased perspiration and, sometimes, excess lacrimation (Zarb and Bolender 2004).

The retention amount given by adhesion is proportionate to the area covered by the denture. Lower jaw dentures cover less surface area than upper dentures; therefore, adhesive and other retentive forces are of less concern. Likewise, for some patients with small jaws or very flat alveolar ridges, or small basal seats , retention may not be as significant as in patients with a large jaw or obvious alveoli. Therefore, the dentures must be lengthened to the limits of the health and function of the tissues in the oral cavity, and efforts must be made at all times to maintain the alveolar height to maximize retention (Zarb and Bolender 2004).

4.2 Cohesion Cohesion is the physical attraction between similar molecules for each other (Basker and Davenport 2002). It is considered to be a retentive force due to its occurrence within the layer of fluid, mostly saliva that exists between the denture base and the mucosa, and

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works to keep the integrity of the interposed fluid. Cohesiveness is not the main character of normal saliva so that most of the retentive force of the denture-mucousa interface is obtained from adhesive and interfacial factors (Zarb and Bolender 2004).

4.3 Surface tension Surface tension is another important factor in maxillary complete denture retention. It is an interfacial force that resists division between two parallel surfaces which is conveyed by a thin layer of liquid between them (Zarb and Bolender 2004). Viscous tension is important regarding interfacial surface tension. The outcome from a film of liquid between any parallel planes of hard materials is called surface tension. It is the capability of a thin layer of the fluid to “wet” the hard surrounding material. With a substance that has a low surface tension, such as oral mucosa, the fluid will increase its contact with the substance surface, thus wetting it quickly and extending in a thin film. On the other hand, with material that has a high surface tension, fluid will reduce its contact area with the material which leads to creating beads on the material’s surface.

The surface tension of the denture base materials (also termed wettability) is varied. The surface tension of all denture base materials is higher than oral mucosa; however, their surface tension is reduced when coated by salivary pellicle which allows maximizing the contact area between the denture base and the liquid. The thin layer of liquid between the denture and the mucosa of the basal seat provides a retentive power by the disposition of the liquid to increase its contact with both surfaces (Zarb and Bolender 2004).

One of the outcomes of the surface tension of fluids is the tendency to reduce the zone of the free surface, producing the recognized curved surface of a raindrop and menisci

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(Darvell and Clark 2000). The curved surface provides a pressure difference over that surface. The pressure is higher within the drop than without if the surface is convex, which is described as positive pressure. In contrast, the pressure is negative if the total curvature is negative. The essential essence is that negative pressure applies a force willing to pull the fingertips together. This is the power that keeps two wet microscope slides together to resist a straight draw (not a slipping move). A very thin film of water is at the edge, with a great negative curvature, because the division of the slides is small; thus, the force is huge. As a result, trying to pull the denture which is wetted by saliva creates a fine, highly negatively-curved saliva surface along its boundary. Consequently, a retentive force and reduced pressure in the liquid filled space is tested (Darvell and Clark 2000). The pressure within the liquid film surrounded by a meniscus is smaller than the pressure of the enclosing medium, and the difference of this pressure supplies a retentive force. The significance of this power has been measured for parallel planes unconnected by a film of saliva, and it has been recommended that the retention of complete dentures can be maintained by this force (Barbenel 1971). This power is dependent on the denture base wettability by saliva, which is considered to be a factor of significance (Darvell and Clark 2000).

Capillary attraction, or capillarity, is another aspect in understanding surface tension in denture retention. When the space between the denture base and the mucosa is at maximum close, this space filled with a thin film of saliva acts as a capillary tube in that the liquid looks to maximize its contact with both the denture base and the surface of the mucosa. Hence, the denture will be maintained by capillarity (Zarb and Bolender 2004).

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4.4 Viscosity Of significant concern is the saliva’s rheology and the location of its viscosity (Darvell and Clark 2000). As a denture is drawn away from the tissues, saliva is pulled into the gap being made under the denture. As a result of the viscous properties of the saliva and the dimensions of the channel through which it flows, the generation of the retentive force is caused by a resistance of this flow of saliva. It follows that the higher the viscosity of the saliva and the narrower the channel, the more efficient must be the retention. This definitely holds true clinically for the channel dimension; however, it seems that very viscous saliva is associated with comparatively poor retention. It might be that retention is low in this case, because the enormous viscosity of the saliva ends in a thick and discontinuous film between the denture and the mucosa. All discontinuities, like air bubbles, in the saliva film decrease retention greatly, because the flow of air is present more than the saliva and therefore offers a little resistance to denture displacement (Basker and Davenport 2002).

It is essential to consider the buccal channel walls through which the saliva flows alter from each other. The flange of the denture is hard, while the soft tissues of the lips or cheeks are mobile. If displacement of the denture occurs, the pressure inside the saliva film drops and the mucosa is drawn tautly against the surface of the denture; thus, the channel between the two becomes narrow. The resistance, as a result, becomes extremely great to the flow of saliva and corresponding retention increases. Coincidentally, this will also raise retention due to surface tension, because narrowing of the channel increases the pressure difference between the saliva film and the air. If the denture is fabricated with flanges that are too thin, ending in a wide buccal channel, there will be no impaction of the buccal mucosa, and the saliva and air will be quickly pulled towards the impression surface as the

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denture is dislocated. Retention in this case will be insufficient (Basker and Davenport 2002).

The mechanism of retention from the viscosity of the saliva and the valve-like movement of the soft tissues is best to oppose large displacing forces of brief duration. Small forces acting over an extended duration of time, for example the influence of gravity on the maxillary denture, end in a little pressure differential between the saliva film and the air, because they allow saliva to be pulled gradually into the gap being made under the denture. A progressive downwards movement of the maxillary denture is likely to happen, if the effect of gravity is unopposed, until eventually all retention is lost and the denture drops. Nevertheless, in this condition, restoring the denture to its former location is done by occlusal forces. Whenever the patient occludes, for example throughout swallowing too much saliva that has accumulated under the prosthesis is squeezed out once again, the denture is re-seated and retention is re-created (Basker and Davenport 2002).

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4.5 Professional attitude towards denture adhesives Denture adhesives entered dentistry at the end of the 18th century. The first patent associated with adhesives was announced in 1913, and succeeded in the 1920s and 1930s (Grasso 2004). Research found that by using denture adhesives, the retention of a full prosthesis is enhanced (Fakhri et al. 2009). Products of denture adhesives can increase the patient’s satisfaction, comfort, fulfilment and function with dentures (Zarb and Bolender 2004). In spite of the benefits of the denture adhesives for a large number of edentulous patients, dental professionals have only been accepting them slowly as a material to improve denture retention, stability and function (Neill and Roberts 1973). Although clinical studies have revealed that denture adhesives have no effect on damaging tissue (Feller et al. 1986), many dental professionals consider that denture adhesives might increase the alveolar ridge resorption and cause hyperplasia to the soft tissue (Fakhri et al. 2009). In addition, denture adhesives are usually regarded as unpleasing and obstruct a dentist’s capability to precisely note the health of a patient’s oral tissues and the real nature of denture adaptation. The fact that poor fitting dentures are usually kept in place with a great amount of adhesive material has unfortunately driven many dentists to presume a relationship between denture adhesive and severe alveolar ridge resorption. Nonetheless, the latest surveys of denture faculties at U.S dental schools recommend that these doubts about the adhesive materials may be diminishing (Zarb and Bolender 2004). If a correspondence did in fact exist between the use of denture adhesive and the high resorption of the alveolar ridge, this would be a sound basis for warning patients against using these products, yet there is no scientific evidence for assuming this claimed correlation (Zarb and Bolender 2004).

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Denture adhesives cannot make use of the forces that would increase resorption (Zarb and Bolender 2004). Adhesives are fluid materials which are no more able to direct pressure than saliva. There is no such method through which adhesives can apply pressure to further increased resorption. As liquids, adhesives will transmit occlusal forces evenly to basal tissues, just like an intimately fitted acrylic base. If they were unsuccessful in doing so in one or more spots, the patient will undergo soreness and seek professional advice (Zarb and Bolender 2004).

Denture adhesives merely decrease the level of lateral movements that dentures, even excellently fitted ones, go through while in contact with basal tissues. In fact, this advantage can cause a patient to disregard their need for professional help when dentures really become ill fitting. This is an intrinsic risk during the use of any sort of adhesive treatment. Nevertheless, it must not prevent sensible clinical strategies. Denture adhesives are a fundamental part of a professional service, and their appendage advantages must be identified (Zarb and Bolender 2004).

4.6 Patient education The dentist must be the major and significant resource of the vital and critical information for the patients, not television advertisements and magazines or references of relatives and friends (Zarb and Bolender 2004). Nonetheless, it is not compulsory for dentists to teach and educate patients with dentures about denture adhesives: their use, maltreatment, benefits, troubles, and alternative choices. They think that well-fitting prostheses will preserve supporting tissues in excellent health and satisfy patients by enhancing oral function and self steam (Garrett et al. 1996).

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The selection between cream and powder is greatly subjective, but particular facts might underline a patient’s choice. The formulation of powder, as a rule, does not grant a similar level of “hold”, nor does their implementation remain as long as the comparable formulation of cream. Nevertheless, powders can be utilized in small quantities, are commonly easier to wash out of dentures and soft tissues, and are not regarded as “sloppy” by patients. In addition, the primary hold for powders is accomplished faster than it is with cream formulations.

Acquiring the maximum benefit of an adhesive material is reliant on its correct usage. For powder and cream materials, the amount of material that should be used by the patient is minimal. This is approximately 0.5 to 1.5 grams per denture unit (extra for a larger alveolar ridge, less for smaller ones). For powders, the cleaned prosthesis must be wetted and then a film, even coating of adhesive scattered onto the tissue surface of the denture. The overflow is eliminated and the denture is seated firmly. If the patient has insufficient or lack of saliva, the sprayed prosthesis must be wetted lightly with water before being inserted. For creams, two methods are considered to be workable. The majority of producers suggest placement of film beads of the adhesive in the depths of the moistureless denture in the incisor and molar areas. Moreover, an anteroposterior bead must be seated along the midpalate in the upper denture. However, to achieve a more even distribution of the adhesive product, small drops of cream are spread all over the fitting surface of the dried prosthesis. Irrespective of the form chosen, the prosthesis is then inserted and placed firmly. As with powders, the use of cream adhesives with xerostomia requires that the adhesive material be wetted with water before inserting the denture (Zarb and Bolender 2004).

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When the using the material, the patient must be advised to remove the adhesive product from the tissue surfaces of the prosthesis every day. Removal is simple by soaking the denture in water or a soaking solution overnight, at which time the product will be fully solubilised. New adhesive material needs to be seated again. Removal of the adhesive is facilitated by putting the denture under hot water and at the same time rubbing the tissue surface of the prosthesis with a suitable hard bristle denture brush. The best removal of an adhesive that has adhered to the alveolar ridge and palate is by firmly wiping the spot with gauze or a washcloth saturated with warm water (Zarb and Bolender 2004).

Patients should also be educated about the controls of prosthesis adhesive. Their anxiety will not be resolved by positioning a “cushioning layer” of adhesive on the prosthesis. Actually, irritation and discomfort signals the need for professional involvement.

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gradual increase in the amount of adhesive needed for a acceptable fit of the prosthesis is also a sound indicator to look for professional care. On the whole, denture patients should be recalled every twelve months for oral mucosa examination and denture assessment; however, they also need to be educated about the warning signs that must alert them to seek professional attention between check-ups (Zarb and Bolender 2004).

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5.0 Postpalatal seal 5.1 What is postpalatal seal? The postpalatal seal (PPS) is described as ‘a region of soft tissue next to the junction of the hard and soft palate on which pressure, within physiologic limits of the tissues, can be used by a denture to help in its retention’ (Ettinger and Scandrett 1980). The closeness of peripheral contact between the denture and its supporting tissues is the primary method to secure a complete maxillary denture. Alterations that occur during and after the processing of the denture may lead to deformity and an inadequate fit, especially at the vital posterior palatal border. As a result, insecurity of the complete maxillary denture is the usual cause for referral for consultant advice (Basker et al. 1988). In identifying this trouble, many researchers have tested the deformity involved in the processing of denture, particularly the important alterations at the posterior palatal border, and have applied it to a mixture of polymerization shrinkage, different thermal contractions, sorption of water and relaxation of stress (McCartney, 1984). In spite of studying many clinical elements thought to affect its importance, such examinations have been done under conditions that either failed to imitate the shape of the object being processed, or after removing and replacing the sample, a process likely to include replacement faults (Lamb et al. 2005).

5.2 Objectives: The postpalatal seal function in the maxillary complete denture involves improving retention, the denture base sealing with underlying tissue to avoid food and debris from entering, to decrease gagging, to compensate for volumetric shrinkage of the acrylic resin in this area, and to produce raised thickness of the posterior border, ending in increased strength (Boucher 1944). Although techniques in processing dentures and materials have improved, the dimensional alterations of acrylic resin from polymerization and thermal

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shrinkage end in a gap between the tissue and the dentures’ intaglio surface. Because of this, a balancing mechanism is required. The techniques for accomplishing a postpalatal seal of an upper complete denture involve arbitrarily scraping the model before processing the denture. The position and the integration of the postpalatal seal on the upper cast are usually done by a dentist or dental laboratory technician. However, these procedures must be the responsibility of the dentist, as the tissue displacement can only be identified clinically. An inadequate postpalatal seal may result in poor retention and/or irritation of tissue (Chang et al. 2006).

The aim of the post dam, or posterior palatal seal, is to make certain that the saliva film is as thin as feasible at the posterior border of the upper denture; therefore, maximum retention is obtained (Lamb 1993). Consequently, the post dam must be an area at the distal border where the soft tissues are pressurized. The perfect location has been matter of debate. All concur that the line of the pressurized tissue must pass through the hamular notches; however, experts differ as to the location of the intermediate portion and good retention being accomplished when putting the post dam at either of two defined positions. Some instruct that it be placed over the hard palate at a point where the underlying bone has the adequate soft tissue over it to permit compression of pressure ulceration of the mucosa (Lamb 1993). Others suggest that the line of the post dam must be positioned at the vibrating line that indicates the junction between the mobile and immobile regions of the functioning soft palate (Lamb 1993). It has been illustrated by ultra-sound examination that the two sites rarely coincide, and that the vibrating line is roughly 3 mm distal to the bony margin of the hard palate in the midline. The examination also affirmed that a particular amount of latitude occur in the determination of the most efficient post dam site (Lamb 1993).

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When attempting to fabricate an arbitrary post dam, the suggested location has to be identified on the palate. This could be performed by marking the palpation of the palate with an instrument that has a ball-ended shape to indicate compressible location, and if the try-in extends far enough, using it to move the mark to the cast. As another alternative, the vibrating line can be indicated by vision when the patient repeats the sound of “ah”, by marking and transferring the location in a similar way. An easier technique than both methods is to indicate the location of the palatal foveae on either side of the midline near the junction of the hard or soft palate. If obvious on the cast, the location of the post dam is marked just in front; if not obvious on the cast, they are indicated in the mouth, marked and transferred as before (Lamb, 1993).

In the easiest method for performing the cast, the post dam is cut first like a slit with a scalpel into the plaster from one hamular notch to the other via the indicated junction, making the slit 1 mm deep at the hamular notches and midline and deeper where there is more soft tissue mainstay (Lamb 1993). Using the chisel end of a spatula or any similar instrument, the anterior margin of the slit is bevelled into a bow form, taking the convexities of the bow further interiorly where the early slit is deeper. After the palatal margin has been processed, it is reduced from the lingual surface to a near knife-edge. The bevel is useful, because it can be reduced in depth by cutting it slightly back posteroanteriorly if the post dam causes over-compression and pain. A more sensible approach to the method of fabricating a post dam is to study the process of denture manufacture and find the actual cause for its existence. After a flask has been flasked, the acrylic dough is heated to bring about polymerization and, arising from the polymerization, volumetric shrinkage of the resin takes place. The uniform shrinkage is not even, but takes place first

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in those places where the exotherm of reaction increases the temperature and starts a more rapid reaction, namely the thicker parts of the base over the crest of the alveolus. The dough contraction takes place towards the locations of initial polymerization and, because the form of the space consisting of the dough contributes a physical constraint, a gap is made between the polymerizing dough and palate of the cast. The space in the midline is approximately 0.5 mm wide, becoming thinner as it passes laterally. On this basis, it is recommended that the cast should be relieved at the junction of the hard and soft palate by cutting a groove with a number 6 round burs to compensate for the shrinkage and reestablishing contact between the denture and palate. Tooth movement can occur due to polymerization shrinkage of this type and account for the occlusal deformities that can damage the most careful technical work. This sort of change is likely to occur in all noninjection moulded work. Although diverse methods have been explained for the production of arbitrary post dams, including changeable depths of relief and varying levels of bevelling (Avant 1973), all work to the amount that fills in the space caused by polymerization shrinkage and further thin the saliva film in the post dam area is by applying compression on the tissue. Their intricacy is difficulty to support without being able to calculate exactly the total addition required. Until it can be accurately accounted for, it is perhaps better to apply a functional post dam at the denture delivery phase (Lamb 1993).

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6.0 Ill-fitting maxillary denture Looseness of the dentures has been the most common complaint. There were important relationships between insufficient retention and incorrect intermaxillary relationships and patient complaints of looseness (Brunello and Mandikos, 1998). The reasons for looseness can be split into those ascribed to the denture and those ascribed to the patients (Jagger and Harrison 1999).

6.1 Problems with the denture 6.1.1 Impression surface If the impression surface of the denture does not accurately represent that of the denturebearing tissues, impounded air and saliva will fill up the space and denture retention will decrease as a result (Jagger and Harrison 1999). This can be prevented by ensuring the following procedures: 1. Use of a special tray that is cautiously adapted to the underlying tissues such that it provides a uniform thickness of the impression material. 2. The choice and use of suitable impression material for the working impression, such as zinc oxide eugenol, light or medium bodied silicone, or alginate. 3. Adequate support of the border of the material. 4. Pouring the impression material as soon as possible to prevent deformity. In the blemished working model, the retention and stability of the dentures are determined by the accuracy of the working models. As a result of time and effort spent on making high quality preliminary and final impressions, the models should then be carefully accurate. If the working model is blemished, this probably occurred on removal of the impression; therefore, the technician must consider sectional removal of the special tray. The

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technician should trim the casts, but make certain that reproduction of the depth and width of the borders of the impressions and the sulci are maintained (see Figure 5.1).

In a warped denture, the change of dimensions during processing can be avoided by using caution to manage the proper processing procedure to fully polymerise the poly (methyl methacrylate). When the laboratory phases are complete, the denture must be kept wet, since drying might alter the form.

Regarding extreme palatal relief chambers, relief chambers are rarely required. Nevertheless, in conditions where the mucosa is more compressible over the ridge than the midline, or where there is an obvious palatal torus, it might be required to incorporate one with the prosthesis base to avoid excessive flexing of the prosthesis. An extensive relief chamber may cause an easy break of the retentive seal and looseness of the denture. Epithelial proliferation can occur beneath the palatal relief chamber.

For a missing or inaccurate post-dam, an inadequate post dam in the form of a narrow line is usually included at the posterior border of the maxillary denture. To obtain effective function of the post dam, it should be placed at the junction line between the hard and soft palate (the vibration line) and extended laterally to the mucosa overlying the hamular notch. The post dam should be marked and carved on the working model by the dentist, because a technician cannot be conscious of its anatomical position. A missing post dam should be rectified in the laboratory following a reline impression (Zarb and Bolender, (2004

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6.1.2 Polished surface It is important to provide an efficient border seal to avoid the ingress of saliva and air and a corresponding decrease in retention (Jagger and Harrison 1999). In an under extended border in depth and width, the prosthesis must fill and shape a seal, each with the full functional depth and width of the sulci and the posterior border. Throughout prosthesis fabrication, this can be performed with the usage of:

1. Cautiously trimmed particular trays. 2. Suitable border moulding of the boundaries with impression tracing compound. 3. An adequate impression technique to register the functional depth and width of the sulci and maintenance of this detail on the working cast and following denture.

Overextended peripheries in depth and width, the peripheries should be identified by direct vision using a soft revealing cream or wax if required. Small spots can usually be rectified by cautious trimming and polishing, nevertheless, for flagrant overextension it might be required to decrease the peripheries short of the functional sulci and to border mould with tracing compound succeeded by a reline impression. Polished surface not the neutral zone, if the polished surfaces of the denture or teeth put outside the neutral zone, they are more probably to be displaced by the oral musculature and result in ill fitting denture. In these situations the prosthesis contours should either be reformed or, if required, remade using the neutral zone procedure.

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6.1.3 Occlusal surface Forces which are likely to create the prosthesis during speech and chewing are usually connected with occlusal irregularities (Jagger and Harrison 1999). A pre centric (no tooth contact) register must be done, the prosthesis mounted on an articulator and adjusted to provide a balanced occlusion with independence of movement from retruded contact location to intercuspal location. The process is done in two phases. First, the rectification of the centric occlusion at the right centric relation and vertical dimension and then the development of eccentric balancing contacts. To rectify centric occlusion (phase one):

1. Reduce the cusp if it is high in both centric and eccentric positions. 2. Deepen the fossa if a cusp is high in the centric but not in the eccentric position. 3. Go to phase two if the cusp is only high in the eccentric position.

To enhance eccentric contacts, selective grinding is done according to the BULL rule (reduction of the buccal upper/lingual lower) (phase two), which is no reduction in both of the maxillary lingual and mandibular buccal cusps, and no deepening of the fossa on any tooth. Adjusting the occlusion on the working side should be carried out by decreasing the inner inclines of the maxillary buccal cusps and the mandibular lingual cusps and on the balancing side by reducing the inner inclines of the mandibular buccal or the maxillary palatal cusps. Grinding the mesial inclines of the maxillary cusps, the distal incline of the mandibular cusp, the lingual surfaces of the lingual surfaces of the upper anterior teeth and the labial surfaces of the incisal edges of the mandibular teeth should be done to adjust the occlusion in protrusion position.

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For premature occlusal contact, small errors can be corrected by selective occlusal adjustment at the chair side. The denture base must be accurately placed and articulating paper used to record and mark premature contacts. For more significant errors, a precentric register must be taken, making certain that the teeth do not contact. The dentures are remounted on an articulator and adjustment of occlusion is done in the laboratory. For obvious inconsistencies, it might be necessary to take off the teeth, replace with wax occlusal rims and rerecord the centric jaw relationship. The teeth should then be rearranged for a new wax rim trail.

Locked occlusion in some people, particularly the elderly who might be used to worn flat occlusal surfaces, is usually hard to adapt to a cusp fossa occlusal relationship or a deep anterior overbite. In this situation, it might be required to grind the occlusal surfaces to permit freedom of movement, especially in lateral excursions, and to decrease the overbite.

Reasonable wear of the occlusal surfaces often permit free jaw movement and must not cause a problem of looseness. Nevertheless, extreme wear, with a loss of occlusal vertical dimension, can cause a class III jaw relationship following the locking of the lower anterior teeth in front of the uppers. This difficulty can be corrected by recreating a suitable vertical dimension and occlusal relationship by summing up autopolymerising acrylic resin to the lower occlusal surfaces of the posterior teeth, in phases, to permit for a time of adaptation to the growth in height.

For an incorrect occlusal plane, if the occlusal plane is not parallel in relation to the ridge, pressure of forces can displace the denture. If the occlusal plane of the lower prosthesis is too high, the movement of the tongue by resting it on the teeth will be difficult and will

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lead to displacing the prosthesis rather than help keep it. In this situation, if the occlusal plane on the maxillary denture is adequate, the lower occlusal plane will be raised at the expense of the freeway space and it will be required to remark the lower denture at the accurate occlusal vertical dimension.

6.2 Problems with the denture wearers 6.2.1 Poor neuromuscular control There are many neuromuscular disorders, for example Parkinson’s disease and cerebrovascular causes which can influence the development of complete dentures because of a diminished muscular rule (Jagger and Harrison 1999). As it is important to supply dentures with maximum retention and stability, the use of non-anatomic teeth together with a neutral zone procedure must be considered.

6.2.2 Changeable foundation If the bases of the denture are adverse, for flabby ridge of the upper anterior, lower ridge atrophy, attachments of fraenal or noticeable mylohyoid ridges, it might be required to consider the use of particular impression technique or even prosthetic surgery to provide an enhanced anatomy and ideal denture. For the flabby ridge of the upper anterior, it is essential that the flabby tissue must not be displaced by the upper anterior. The might be well adapted if the flabby tissue is displaced when undergoing occlusal pressure; however, it is likely to be displaced by elastic recoil of the displaced tissue when the teeth are away. The pumping action will damage the fibrous tissue and the tooth contact causes the movement of the denture. It is possible to use a spaced particular tray with a low viscosity material if there is only minimal displacement of the flabby ridge, for example impression plaster or low viscosity alginate. It is better to use a two-part impression technique with

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marked displacement. An impression of the undisplaced mucosa can be taken in zinc oxide eugenol impression material through a close fitting special tray with a window over the flabby area. The impression is examined, replaced in the mouth, and a flabby ridge impression is taken by adding impression plasters to the window area (Pankhurst et al. 1996).

6.2.3 Inadequate saliva To reinforce retention in the denture wearer, adequate saliva is essential. For some patients with xerostomia, for example Sjogren’s syndrome, retention can be quite a problem. Dentures must be supplied which maximise retention and stability together with the provision of a synthetic saliva replacement where suitable. The use of denture fixative is an option.

Figure 5.1Examples of the similar casts; the one on the right has been adequately trimmed while the one on the left is an incorrect and over trimmed cast (Jagger and Harrison 1999).

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Conclusion This paper has been explained in detail for the practitioner some of the inessential elements for retention and stability of the complete maxillary denture. This explanation will guide both the practitioner and the technician to control the complete maxillary denture, either at clinical or laboratory procedure, with great efficiency. It is crucial to consider the aspects needed to make supreme retention and stability for a patient who has to wear complete maxillary denture. Obviously, cautious attention is needed in relation to recognizing the crucial features of the prosthesis shape to gain supreme retention and stability during function. There are many opinions regarding which factor is most involved in the retention and stability of maxillary complete denture. Some studies suggest that surface tension is a major factor in complete denture retention, whereas other studies believe that adhesion is the most important factor (Stamoulis 1962). Furthermore, this dilemma is also found in factors considered to be not important in the maxillary complete denture such as atmospheric pressure, vacuum, surface roughness and gravity (Darvell and Clark 2002). It is agreed that the factors that provide retention and stability are related. In fact, some authors have recommended that the interaction between stability and retention creates indistinguishable factors (Jacobson and Krol 1983). It is strongly suggested that researching for retention and stability in the mandibular complete denture will amalgamate the efforts for the optimal understanding of the retention and stability of maxillary and mandibular complete dentures.

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Jacobson, T. E. & Krol, A. J. (1983) A contemporary review of the factors involved in complete dentures. Part II: stability. Journal of Prosthetic Dentistry, 49, 165-72. Jagger, D. & Harrison, A. 1999, Complete Dentures - Problem Solving, London, British Dental Association. Lamb, D. J. (Ed.) 1993, Problems and Solutions in Complete Denture Prosthodontics London, Quintessence. Lamb, D. J., Samara, R. & Johnson, A. 2005, Palatal discrepancies and postdams. Journal of Oral Rehabilitation, 32, 188-92. McCartney, J. 1984, Flange adaptation discrepancy, palatal base distortion, and induced malocclusion caused by processing acrylic resin maxillary complete dentures. The Journal of prosthetic dentistry, 52, 545. Neill, D. & Roberts, B. 1973, The effect of denture fixatives on masticatory performance in complete denture patients. Journal of dentistry, 1, 219. Pankhurst, C. L., Dunne, S. M. & Rogers, J. O. (1996) Restorative dentistry in the patient with dry mouth: Part 2. Problems and solutions. Dental Update, 23, 110-14. Rendell, J., Grasso, J. E. & Gay, T. 1995, Retention and stability of the maxillary denture during function. Journal of Prosthetic Dentistry, 73, 344-7. Stamoulis, S. (1962) Physical factors affecting the retention of complete dentures. Journal of Prosthetic Dentistry, 12, 857-64. Tsirmbas, M. & Vlissidis, D. (1989) [The effect of postpalatal seal on the retention of a full upper denture]. Hellenika Stomatologika Chronika, 33, 269-73. Van blarcom, C. (1999) Glossary of prosthodontic terms, 7 th edn. Journal of Prosthetic Dentistry, 81, 39. Zarb, G., Chl, B. & GE, C. (1997) Boucher’s prosthodontic treatment for edentulous patients. 11de druk. St. Louis: The CV Mosby Company. Zarb, G. A. & Bolender, C. L. (Eds.) 2004, Prosthodontic Treatment for Edentulous Patients, Philadelphia, Mosby.

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