Prosthesis: A prosthesis is an appliance which replaces
lost or congenitally missing tissue. Some prosthesis restore both the function & the appearance of the tissue they replace, others merely restores one of these factors.
Functions of teeth: They divide food finely so that a large surface area is available for
the action of the digestive juices. To assists the tongue & lips to form some of the sounds of speech. The teeth form an important feature of the face, and by supporting the lips and cheeks enable these structures to perform their functions of manipulating the food & expressing emotion.
Objectives of Complete Denture Prosthesis: Biological Objectives:
Restore lost part. Restore aesthetics. Restore Physical & Mental Compartments. Restore Function. Restore Health.
Mechanical Objectives: It should be strong enough to withstand various natural stresses. The stresses should be uniformly distributed. It should be well retained. It should be stable in centric & eccentric. It should be so designed so that it can take full advantages of various sources
Difference between natural teeth & artificial teeth: GENERALLY: In natural teeth: the teeth are firmly rooted in the bone of the jaws, and in consequence they can incise, tear and finally grind food of any character . In artificial teeth: They set on the gums & held their by weak forces, In addition they are subjected to powerful displacing forces, so their efficiency as a masticating apparatus is limited. AESTHETICALLY:
Artificial teeth can be distinguishable from natural teeth, and in many cases they can enhance the appearance of natural teeth were hypo plastic, grossly carious or unpleasantly irregular.
Steps in C.D. Procedure: Charting. Examination of the patient. Evaluation of the patient. Initial impression. Temporary base. Secondary impression. Permanent bases. Maxillary Mandibular relation Selection of teeth. Arrangement of teeth Trial Insertion Postinsertion complaints
The Mucous Membrane Tissue Compression: The varying thickness of mucous membrane and submucous tissue covering the bones forming the palate and alveolar ridge results in the forces which are applied to the denture during mastication being transmitted unevenly to those supporting structures.
The Alveolar Ridges:
It must be remembered that edentulous alveolar ridges are not natural structures. They are what are left of a bone after disease and surgery have been applied to it. The alveolar ridges vary greatly in size & shape and their ultimate form dependent on the following factors: The degree of Calcification. The size of the natural teeth i.e. large teeth are supported by bulky ridges & vice versa. The amount of bone lost prior to the extraction of the teeth. E.g. In diseases such as Periodontitis. The amount of alveolar process removal during the extraction of teeth. Rate & degree of absorption. The effect of previous dentures. In this (a) Ill fitting dentures (b) Dentures occluding with isolated groups of natural teeth, may cause rapid absorption of alveolar process.
Denture bearing area which is basically consisted
of: Hard bony foundation. Soft tissue covering the bony foundation. Peripheral seal.
HARD BONY FOUNDATION: The maxillary bony foundation constituted of the following: The palatine processes of the 2 maxillae anteriorly and the horizontal plate of the palatine bone posteriorly. It also rests on the alveolar processes of the 2 Maxillae extremely right upto the tuberosity. Up to pterygo-maxillary fissure. Inter-maxillary suture: It runs along the sagittal plane anterior-posteriorly. Anteriorly it is constituted by the palatine processes of the maxillae & posteriorly, by the horizontal plate of the palatine bone. If this suture is excessively prominent & is usually refers as torus palatinus. Foramina: These are: Incisive foramina : it is located in the median sagittal plane in the maxilla. (Anteriorly). Posterior palatine foramen: it is located one on each side in the region of the palatal root of the 2nd molar tooth. Fovea Palatina: There are 2 tiny depression, located approximately 1/8th of an inch or so from the posterior palatine border. (Vibrating).
Soft tissue covering the bony foundation: The soft tissue that cover the bony foundation has
got the following feature: In the oral cavity, all the bony structures are being covered by the mucoperiosteum (periosteum) toward the bony side, and mucous membrane toward the oral side; these 2 structures are separated from one another by C.T layer as to submucous tissue.
Lower Component: It is also studied under the following headings: Bony foundation Soft tissue Peripheral attatchment.
Bony Foundation: The mandible is composed of the body & the ramus. Body is the horizontal portion of the mandible. It has the alveolar process which is distinguished from the basal bone by the attachment of muscles & other structures that lies in the vicinity of the mandible. All other structures are mobile in nature, hence the alveolar process or its remnants is the only structure available for bony support of the lower denture. The following anatomical Land Marks limits the alveolar process: Anterior Labial Section: Starting in the labial section, then is the attachment of mentalis muscle and portion of orbicularis oris. Lateral to that there is depressor anguli oris (Triangular oris), proceeding laterally, a faint ridge starts taking shape which gets prominence more & more & proceeds posteriorly & ultimately become continous with the anterior border of the ramus. This ridge is called the external oblique ridge which give attachment to the buccinator muscle on the posterior aspects of the molar region, the attachment of the buccinator continous & the lingual half of it blends with the superior constructor of pharynx and the aponeurotic ptyregomandibular raphe limit the bony foundation. Anterior lingual section: On the lingual aspect in the anterior section; there is a genial tubercle which gives attachment to genioglossus & geniohyoid muscles. Laterally, In the curvature of the mandible, there is a vertical concavity for the sublingual gland. Often times lingual to the cuspid, the bone is exostosed forming in an eminence, the torus mandibularis. Posterior lingual section.
Posterior Limit: Posterior limits for lower denture is formed by the margins of the external & internal oblique ridge. Alveolar Process: It takes up varying shape in different individuals. Foramina: There are 2 foraminae, one on either side The mental foramen. Soft tissue overlying the bony foundation: Like the upper, the lower bony foundation is also covered by the mucoperiosteum; here it also shows variation in thickness & quality. The sub-mucous C.T. may be abundant in the anterior region & scanty in
the region of the molar. The peripheral tissue: The structures laying at the border of the bony foundation have already been enumerated. Any how they are: Labial fraenum Mentalis Buccal fraenum Depressor anguli oris Pterygo-mandibular ligament. Mylohyoid Palatoglossus
Ideal Impression material would be: Non-injurios to the tissue. Capable of compressing the soft tissues to any desired degree without it self being distorted. Sufficiently fluid on insertion to give accurate surface detail. Be able to produce accurately any undercuts which are present. Have a pleasant taste, smell & appearance. Have No dimensional changes at Normal degree of tepreture & humidity. Set, or harden at near mouth tempreture. Have a setting time under the control of the operator. Be capable of having additions made and of insertion in the mouth without distortion. Have a simple technique. Be compatible with all materials in general use for model making. Be cheap enough to use once only or capable of easy sterilization if used more than once.
The Primary Impression:
Since this impression will not be used directly in the construction of the denture but only for making a special tray for one individual mouth, the greatest possible accuracy is not required & it is therefore, possible to select a technique which is simple, quick & gives the P.t. the minimum of discomfort. For these reasons composition has been chosen as the impression material.
Impression technique: Muco-compressive technique or muco-functional technique: In this technique the material are able to compress the tissue e.g. Composition. Waxes Harder type of C.P. Muco-static technique : This is the one in which the soft tissue are in no way compressed or distorted & there for the impression material must flow readily & impose no pressure in the mucosa this technique is used for the final impression, the material used for this technique are: Plaster of Paris Alginate (Irreversible hydrocolloid). Zn Oxide Eugenol (CAVEX). Gutta Percha Rubber base material Selective impression technique or Combination of I & II These areas which are soft, flabby, bulbous are recorded in mucostatic and bony hard is recorded as mucofunctional. Materials: Pastes e.g. Plaster Splint. Soft areas are painted with plaster material. When set the tray is loaded & inserted in the mouth. 1st material act as splint. Modified Turner-Tuller technique. Splint method
Objectives Of Impression: The five objectives of an impression are to provide: Retention Stability Support for the denture Aesthetics for the lips
Maintenance the health of the oral tissues.
ADVANTAGES: It produces excellent surface detail. It is dimensionally accurate if used with anti-expansion solution. It does not distort