gingival or movable tissues. five types of major connectors are listed below: lingual bar a lingual bar has a pear-shaped cross section tapering towards the gingival boundary. it should be positioned high enough so as to not irritate the lower movable tissue but low enough to allow for a substantial quantity of material to be used to ensure stiffness. at least 7mm of space is usually required. it sits on the soft tissue posteriorly to the dentition. along with the lingual plate it is the most commonly used type of connector in the lower arch. a lingual bar is more hygienic than a lingual plate but is difficult to add to if teeth are later extracted and require to be added to the denture. sublingual bar a sublingual bar is similar to a lingual bar but is located on the floor of the mouth posteriorly and inferiorly to its usual location. they are used when the superior border of a lingual bar would be positioned too closely to the gingival border. they are contraindicated in patients with a high lingual frenum and in situations where they may interfere with tongue movements. lingual plate a lingual plate is a thin plate contoured to the lingual surfaces of the lower anterior teeth. a lingual plate is useful when there is insufficient space for a lingual bar which would result in irritation of the gingival boundary. if the teeth are spaced out and the patient does not wish for visible metal to be seen then an interrupted lingual plate may be used where the material is cut away where it would be visible anteriorly. a disadvantage of a lingual plate is that it covers a lot of gingival margins and is less hygienic than a lingual bar. it should be used with caution in those patients with a high caries rate. a major advantage is that is easier to add teeth to a denture with a lingual plate than a lingual bar connector. in addition, it is useful in providing some additional support for mobile lower anterior teeth. buccal bar in rare cases where the inclination of the remaining anterior teeth is problematic and the use of a lingual connector inappropriate, a buccal bar can be considered. continuous clasp a continuous clasp is sometimes used in addition to a lingual bar and rarely as a sole major connector. it involves a bar of material placed along the cingulum of the anterior dentition. the continuous clasp has the added advantage of providing indirect retention when used in addition to a lingual bar. it may be used when a lingual plate is compromising aesthetics. support components that prevents displacement of the denture towards the tissues if the denture solely rests on the remaining teeth, it is termed ‘tooth borne’, and if the denture lies solely on the mucoperiosteum, it is termed ‘mucosa borne’. in some cases where parts of the denture lies on periosteum and parts on the remaining teeth, it is called ‘tooth and mucosa borne’ ‘tooth borne’ dentures offer ideal tooth support, as the force is transmitted down the long axis of the tooth into the periodontal ligament. this will allow the dentures to feel like natural dentition , therefore feel more comfortable for the patient. the soft tissues are protected and resorption of the alveolar bone at the saddle areas is likely to be slow. however, with ‘mucosa borne’ dentures . force placed on these areas dissipates into the alveolar bone and will cause resorption over time. dentures quickly begin to feel ill fitting as the shape of the alveolar ridge changes. tooth born/ tooth and mucosa borne when choosing the teeth to support the denture, they must have the following qualities. as close to the saddle as possible healthy teeth healthy periodontal status large surface area of the roots we place rests on the teeth for support. types of rests include: occlusal cingulum incisal rests placed on teeth must be an adequate size and thickness to ensure the occlusal load is directed down the long axis of the tooth, without impinging on the patient's occlusion. a periodontally healthy tooth will be able to sustain its own load in addition to 1.5 similar teeth. mucosa borne dentures covering a larger area spreads the load , reducing the magnitude of force placed on the mucosa, reducing the rate of resorption. clasp design direct retainers may come in various designs: cast circumferential clasp (suprabulge) akers' half and half back-action ring clasp wrought wire clasp roach clasp (infrabulge) i-bar t-bar y-bar 7-bar both cast circumferential and wrought wire clasps are supra bulge clasps, in that they engage an undercut on the tooth by originating coronal to the height of contour, while roach clasps are infrabulge clasps and engage undercuts by approaching from the gingival. in addition there are a couple of specific theories which include the clasp design: rpi: mesial rest, distolingual guide plate, i-bar the rpi design was made for clasping a bilateral free end extension. these clasps are unique because they have to take into account extra torque force due to being tissue borne (and not tooth borne) at the posterior. described by kratochvil in 1963 and modified by krol in 1973 kratochvil designed the abutment tooth with a long rest (from the mesial marginal ridge to the distal pit), long guide plane, and a regular i-bar clasp. krol modified this design with a short occlusal rest, short guide plane (touching only from occlusal to middle third), and a mesial-shifted i-bar. the theory behind krol's decision was to allow for movement of the partial denture without placing too much torque on the abutment tooth. an illustration of the rpi design function rpa: mesial rest, distolingual guide plate, akers' clasp-style retentive arm rpc: mesial rest, distolingual guide plate, other type of cast circumferential clasp so named in response to the rpi philosophy introduced by kratochvil and kroll indirect retention indirect retention is required to prevent displacement of saddles, such as free-end saddles or anterior saddle which is curved outside a straight line between the abutment teeth. such indirect retention can only be achieved where both claps and rests work together to form lever system (class iii lever system) to retain the free part of denture.