Type: Research Essays
Sample donated: Madeline Beck
Last updated: October 2, 2019
Denture retention will be a subject perplexing and perpetual until its troubles find their logical solution in under- standing its physics.
1 This understanding now in fact exists but it is obscured by repetition of long-held erroneous beliefs. Although the various issues have been analysed in detail and discussed at length, an up-to-date account based on modern research and understanding of materials science has yet to appear in an accessible form for the benefit of the practitioner. It is the aim of this article to address this deficiency. Denture retention has been defined as ‘resistance of a denture to vertical movement away from the tissues’2 and as ‘that quality inherent in the prosthesis acting to resist the forces of dislodgement along the path of insertion’.3,4 It is clear then that ordinarily retention is regarded as a property of the denture rather than of the patient. There is general acceptance among clinicians that to achieve retention in complete dentures there first needs to be an accurate fit of the denture base to the mucosa so that the space between the two is as small as possible.
Secondly, there needs to be a border seal, which is achieved by extending the denture flanges to fill the sulci. The subject of this paper is not the means by which these conditions are achieved clinically but rather the physical mechanisms by which dentures of this design are retention . Many physical forces and factors have been credited with causing or enhancing retention, eg atmospheric pressure, vacuum, adhesion, cohesion, wettability, surface roughness, gravity, surface tension, viscosity, base adaptation, border seal and muscular control. However, while the majority of this list have survived for a long time in teaching texts (and examination answers) they do not all survive scientific scrutiny.5,6 Retention is the chief factor required for complete denture, which is retained against the force of gravity. Denture retention can be obtained by many methods.
One such method is by determining the location of the posterior border of the maxillary denture, which plays an important role in its retention and patient comfort. Since the last century many researchers have evaluated techniques in obtaining the location of the posterior border of the maxillary denture. One of the commonest methods is using the anatomical land marks . 7,8 Fovea palatinae is one such anatomical landmark which may be used as reliable guidelines to the placement of the posterior palatal seal.
The relationship of fovea palatinae has been a subject of controversy, saying that fovea palatinae are located anterior to the vibrating lines or it may lie posterior to the anterior vibrating lines.9,10,11 The fovea palatinae are two small indentation that lie bilateral to the midline of the palate, at approximate junction between the soft and hard palte. They denote the sites of opening of ducts of small mucous glands of the palate.12 Post palatal seal is an another anatomical landmark which helps in retention of maxillary dentures. It is a soft tissue area at or beyond the junction of the hard and soft palates.
It is also considered to lie between anterior and posterior vibrating line.13 Anterior vibrating line is an imaginary line located at the junction of the attached tissue overlying the hard palate and the movable tissue of the immediately adjacent soft palate, visualized while the patient is instructed to say ‘;ah’ with short vigorous bursts. Posterior vibrating line is an imaginary line at the junction of the aponeurosis of the tensor veli palatine muscle and the muscular portion of the soft palate visualized, while the patient is instructed to say ‘ah’ in short bursts in a normal unexaggerated fashion. Although the vibrating lines is not truly an anatomical features, it is very important to locate for proper construction of the maxillary complete denture.9,12,14In a study the distance between the anterior and posterior vibrating lines varied between 2 and 8 mm 9,15 .The distance between the foveae palatinae and the vibrating line can vary according to the configuration of the soft palate; that is, a soft palate with a less steep slope could be expected to be longer, implying that a broader posterior palatal seal could be achieved.16,17The purpose of this study is using fovea palatinae as reference point for locating both anterior and posterior vibrating lines.