Effect of dynamic impression technique on retention of lower complete denture A thesis Submitted to Faculty of Oral and Dental Medicine Cairo University in Partial fulfillment of the Requirements of Master Degree in Prosthodontics By Mai El-sayed Hashem B.D.S. (2004) Faculty of Oral and Dental Medicine Cairo University 2012
Supervisors Dr. Alaa Aboul Ela Professor of Prosthodontics Department of Prosthodontics Faculty of Oral and Dental Medicine Cairo University Dr. Azza Farahat Lecturer of Prosthodontics Department of Prosthodontics Faculty of Oral and Dental Medicine Cairo University
Acknowledgment First of all, I thank Allah for paving the way for me to fulfill this work. I would like to express my sincere gratitude and appreciation to Dr.Alaa Aboul Ela, professor of prosthodontics, Faculty of Oral and Dental Medicine, Cairo University. I will remain grateful to her for her wise advice, scientific supervision and kind guidance throughout the entire course of this work. I am also grateful to Dr. Azza Farahat, lecturer of prosthodontics, Faculty of Oral and Dental Medicine, Cairo University, for her precious help, encouragement, guidance, valuable effort and great cooperation. Finally, many thanks to the members of prosthetic department, Faculty of Oral and Dental Medicine, Cairo University, for their kind cooperation towards achieving this work. Mai El-Sayed Hashem
Dedication I Dedicate This Work to My father and Mother for their love, care & unlimited support throughout my life My husband for his continuous support, patience and understanding. My brother and sister for their help & tender love My lovely daughter My family and my friends Mai El-said Hashem
Contents Number Title Page 1 Introduction 1 2 Review of literature 2 I. Complete denture retention 2 Factors affecting complete denture retention 2 1- Physical factors 3 2- Physiological factors 10 3- Anatomical factors 12 4- Mechanical factors 13 5- Surgical factors 14 6- Psychological factors 16 7- Clinical implications 17 8- Retentive aids 18 II. Methods of measuring retention in complete denture 21 VI
III. Complete denture impressions 24 1. Final impression techniques 26 A- Mucostatic impression technique: 25 B- Mucocompression impression technique 25 C- Selective pressure impression techniques 26 2. Impression for severely atrophied mandibular 28 ridge Dynamic impression technique: 28 Materials used for dynamic impression 31 3 Aim of the study 32 4 Materials and Methods 33 I. Patient selection criteria 33 II- Patient history 34 III. Patient Examination 34 IV. Radiographic examination 35 V. Patients grouping 35 VI. Complete denture construction 36 VII
VII. Determination of relative geometric center of the mandibular denture 46 VIII. Measuring the retention of the mandibular 49 denture 5 Results 51 6 Discussion 59 7 Summary 66 8 Conclusions 68 9 References 69 10 Arabic summary -- VIII
List of Tables No Title Page 1 Mean, standard deviation (SD) values and results of 52 Student s t-test for comparison between retention of the two groups 2 Mean differences, standard deviation (SD) values and 54 results of paired t-test for the changes by time within control group 3 Mean differences, standard deviation (SD) values and 55 results of paired t-test for the changes by time within study group 4 Mean % change, standard deviation (SD) values and results of Student s t-test for comparison between changes in retention of the two groups 58 IX
List of Figures No. Title Page 1 Alginate upper and lower 36 preliminary impression 2 special tray with stops 40 3 special tray with mandibular and 41 tongue rests 4 Dynamic, secondary impression 43 with tissue conditioning material 5 Final dynamic impression with 44 tissue conditioning material and light body rubber base. 6 Waxed-up trial dentures on a semi 45 adjustable articulator 7 Graphic illustration of the relative 47 geometric center. 8 The relative geometric center of 48 mandibular denture 9 Digital force-gauge 49 10 Measuring the retention of lower denture 11 Line chart representing changes by time in mean retention of the two groups 12 Bar chart representing mean % increase in retention of the two groups 13 Bar chart representing mean retention of the two groups 50 53 56 58 X
Introduction
Introduction Introduction Complete denture prosthesis involves the replacement of the lost natural teeth and the associated structures of the maxilla and the mandible. One of the goals that the dentist has to achieve is to produce a denture that is retentive and stable in place which in turn enhances both function and esthetics. Many edentulous patients wearing conventional complete dentures are dissatisfied with their prosthesis. This is particularly common with mandibular dentures, because of their smaller denture bearing area, unfavorable distribution of occlusal forces resulting in increased rate of bone resorption, decreased stability and retention, pain as well as patients discomfort (1). Complete denture impression is a dynamic process that involve two stages; preliminary and final impression. To make an accurate final impression, it s important to thoroughly examine the patient s mouth and select the most suitable impression technique. In this study, dynamic impression technique was used. In dynamic impression technique the patient was asked to make specific muscular movements to register the border areas to provide satisfactory border sealing zone, tissue conditioning material could be used for this technique. Tissue conditioners are soft resilient materials which can be used as functional impression materials. There has been continuous search for the best method for recording all available denture-bearing surfaces to provide a stable and retentive prosthesis. The question raised in this study is, which technique of final impression (Conventional or dynamic impression technique) provides more retention in lower complete denture? 1
Review of literature
Review of literature Review of literature I- Complete denture retention According to the Academy of prosthodontics (2005), denture retention is defined as "The resistance to vertical stresses, or the resistance of the denture to removal in direction opposite to that of its insertion" (2). Zarb et al (1) had explained the retention as the quality inherent in a denture that resists the force of gravity, the adhesiveness of food and the forces associated with opening of the Jaws. Factors affecting complete denture retention: The recognition, understanding, and incorporation of certain mechanical, biological and physical factors are necessary to ensure optimal complete denture retention. These factors are the determinants that promote the properties of retention in the finished prosthesis through their influence on the relationship between the tissue surface of the denture and the mucosal surface of the edentulous ridge (3).. surface area of contact between the denture and the supporting tissue, the adaptation of the denture base, surface tension factors, peripheral seal, and neuromuscular control (4). 2
Review of literature These factors varied within and between patients and cannot be quantified. Clinically, base tissue contact, base extension, and the border seal were the factors that may be influenced by the clinician (4). Denture retention is a dynamic issue dependent on the control of the flow of interposed fluid and thus its viscosity and film thickness, while the timescale of displacement loading affects the assessment. Surface tension forces at the periphery contribute to retention, but the most important concerns are good base adaptation and border seal. These must be achieved if full advantage is to be taken of the saliva flow-related effects (5). Retention is affected by physical, physiological, anatomical, mechanical, psychological, surgical factors and retentive aids (6). 1- Physical factors: Many physical factors interact together for enhancing retention. Adhesion, cohesion, interfacial forces, atmospheric pressure and gravity acting either individually or in combination (7). A-Adhesion B- Cohesion C- Surface tension D- Surface area E- Capillary attraction F- Viscosity G- Wettability 3
Review of literature H- Atmospheric pressure I- Gravity J- Peripheral seal and base adaptation A- Adhesion: Adhesion is the property of remaining in close proximity, as that resulting from the physical attraction of molecules to a substance or molecular attraction existing between the surfaces of bodies in contact.(2). De Majistris (8) summarized the facts involved in the denture retention as ; negative pressure under the denture, capillary attraction, adhesion,cohesion,interfacial surface tension, viscosity of saliva and shape and surface roughness of the denture base. Emphasis was placed on the importance of the adhesive forces and the role of fixatives. The amount of retention supplied by adhesion is directly proportional to the area covered by the denture. The dentures must be extended within the limits of health and function of the oral tissue if the dentures are to have their maximum adhesion and retention (1). The effectiveness of adhesion depends on the close adaptation of the denture to the supporting tissue and the fluidity of saliva. Watery saliva is quite effective provided that the denture base material can be wetted. The thicker and more viscous the saliva, the less the adhesion and vice versa (4). 4
Review of literature Adhesion of saliva to the mucus membrane and denture base is achieved through ionic forces between charged salivary glycoproteins and surface epithelium or acrylic resin. (9) B- Cohesion: Cohesion is the force where molecules of a matter adheres to one another, or the attraction of aggregation. (2). According to Rendell et al. (10) cohesion works to maintain the integrity of interposed fluid film between denture base and soft tissue. Normally, saliva is not cohesive; therefore most of the retention force of the denture mucous membrane interface comes from adhesion and interfacial factors unless the interposed saliva is modified by the use of denture adhesives. C- Surface tension: Surface tension is the property of a liquid in which the exposed surface tends to contract to the smallest possible area. This phenomenon is attributed to the attractive forces, or cohesion between the molecules of the liquid (2). This property was found in the thin layer of saliva between the denture base and the mucosa and is quite similar in its action to cohesion and capillary attraction.it was also effective in direct proportion to the size of the basal seat of the denture (1). D- Surface area: One of the important factors influencing the support, retention and stability of the complete dentures was the ridge and size. A U shaped well developed ridge 5
Review of literature with a flat crest and parallel or nearly parallel sides was considered ideal. The greater size, the larger the surface and the greater the retention (11). E- Capillary attraction: Capillary attraction is defined as a quality or state which because of surface tension causes elevation or depression of the surface of liquid that is in contact with the solid walls of a vessel. (2) Capillary attraction was the result of several factors including the dimensions of the space, viscosity of the liquid and the wetting property of material. Narrow spaces promote capillary penetration (12). Zerb et al. (1) approved and stated that when the adaptation of the denture base to the mucosa on which it rested was sufficiently close, the resulting space was filled with a thin film of saliva acted like a capillary tube and helped to retain the denture. This force like the others was directly proportional to the area of the basal seat covered by the denture base. F- Viscosity of saliva: El-Akkad (13) and Murray and Darvell (14) concluded that viscosity of saliva playe an important role as one of the physical factors in denture retention due to its protein content especially mucin which affected the viscosity. They added that an increase in the mucin percentage was directly proportional to increase of salivary viscosity. 6
Review of literature G- Wettability: Wettability refers to the lowering of the energy of a system when a liquid wets a solid surface. (15) Processed materials display greater wettability than autocured products. (16) The thin fluid film between the denture base and the mucosa of the basal seat furnishes a retentive force by the tendency of the fluid to maximize its contact with both surfaces (17). If the denture base was not wet, there would be no force needed to separate the denture from saliva and therefore, there would be no retention. Fortunately, acrylic does wet with water. Furthermore, the proteins and mucopolysaccharides from the saliva adsorb to the acrylic rapidly and strongly and therefore present a surface which is even more wettable (5). H- Atmospheric pressure: Colon et al. (18) explained that well and properly extended denture borders will form a sealed compartment. The forces produced in this sealed environment are less than the pressure of the surrounding medium. The difference between these two pressures known as atmospheric pressure provides retentive forces. It is important to have a hermetically sealed denture. In 1983, Jacobson and Krol (19) considered atmospheric pressure as a key factor in denture retention. The authors noticed that introduction of a small palatal perforation or the presence of an inadequate posterior palatal seal markedly reduces the physical retention of most maxillary complete dentures. Such effects would not be observed if the forces of adhesion and cohesion were the critical retentive factors. 7
Review of literature The molecular forces by themselves are unable to resist dislodgement. Unless a peripheral seal is provided, these forces are not sufficient even to retain a denture at rest. This explains why an upper denture drops when its posterior seal is lost and retention is restored following post damming (20). Atmospheric pressure could only operate by way of a pressure difference, beneath the denture there must be a lower pressure, and the full effect could only be felt if there were a vacuum there (5). They added that even if a vacuum could be generated by virtue of a pull being applied that tended to increase the volume between the denture base and the tissue beneath; the requirement would be for a seal to be maintained around some area for the lowered pressure to be sustained (5). I- Gravity: When a person is in upright posture, gravity acts as a retentive force for the mandibular denture and a displacive force for the maxillary denture. In most cases, the weight of the prosthesis constitutes a gravitational force that is insignificant in comparison with the other forces acting on the denture (10). J- Peripheral seal and base adaptation: Peripheral seal is the contact of the denture border with the underlying or adjacent tissues to prevent the passage of air or other substances (2). Peripheral seal and base adaptation are not literally physical forces; however they have been mentioned by several authors among the other physical factors that affect denture retention (5, 14, 19).. 8