Prosthodontics Lectures PDF

BASIC PRINCIPLES OF OCCLUSION WHY DO WE NEED TO UNDERSTAND OCCLUSAL CONCEPTS? Minimise errors while transmitting information from the patient’s mouth to the articulator, meaning fewer visits and less adjustments. We need an organised approach which leads to restoring the patients: Estheti...

BASIC PRINCIPLES OF OCCLUSION WHY DO WE NEED TO UNDERSTAND OCCLUSAL CONCEPTS? Minimise errors while transmitting information from the patient’s mouth to the articulator, meaning fewer visits and less adjustments. We need an organised approach which leads to restoring the patients: Esthetics Masticatory e ciency Phonetics (Speech) Most of occlusion theories are derived from Removable Prosthodontics. DEFINITION Occlusion: The relationship between all of the components of the masticatory system in normal function, dysfunction, and parafunction The static relationship between the incising or masticating surfaces of the maxillary or mandibular teeth. Articulation: Every possible position of the mandible in relation to the maxilla carried out by means of muscles of mastication. The contact relationship of the occlusal surfaces of the teeth while in action. TEMPOROMANDIBULAR JOINT / TMJ MOTION The temporomandibular Joint is made up of three primary units: Glenoid Fossa (Temporal Bone) Interarticular Disc (meniscus) Condyle (Mandible) Interarticular Disk (Meniscus) Fibrocartilage, as opposed to hyaline cartilage found in other joints of the body. Thicker posteriorly (3mm) than anterior (2mm) and thinnest at the middle (1mm). Superior head of lateral pterygoid has bers that insert in the disk to allow it to move independently of the condyle. The disk divides the joint into two separate cavities: Superior cavity (meniscotemporal) - translatory movement Inferior cavity (meniscocondylar) - rotational movement Glenoid Fossa (Temporal Bone) - Provides a seat for the condyle-disc assembly. - From Dawson: Superior (or roof) of glenoid fossa is very thin - anterior wall and medial portion are substantially thicker. (Load-bearing) Ligaments Capsular ligament is made of: - Medial ligament - Diskal ligament - Lateral ligament - Posterior ligament Capsular ligament keep the disk articulated with the condyle and glenoid fossa. Temporomandibular ligament: Prevents posterior displacement of the mandible; assists in the transition from rotational to translatory movement. Stylomandibular ligament: Accessory ligament to the TMJ; limits excessive opening and protrusive movements. Sphenomandibular ligament: Limits inferior movement of the mandible (excessive opening) 1 of 12 ffi fi 2 of 12 ARTICULATION Non-Adjustable Articulators: - Class I (Hinge-Motion): Simple holding instruments capable of accepting a single static registration. Vertical motion is possible, but only for convenience. - Class II (Mean-Value): Instruments that permit horizontal as well as vertical motion but do not orient the motion to the temporomandibular joint. - They have a xed intercondylar distance. - The condylar path is xed in 30° angle - Cast is mounted in an average position. Adjustable Articulators: - Class III: Instruments that simulate condylar pathways by using averages or mechanical equivalents for all or part of the motion. These instruments allow for joint orientation of the casts and may be ArCon or NonArCon instruments. - Subdivision A: Instruments that accept static protrusive registrations and use equivalents for the rest of the motion. - Subdivision B: Instruments that accept static lateral protrusive registrations and use equivalents for the rest of the motion. - Class IV: Instruments that will accept dimensional dynamic registrations. These instruments allow for true joint orientation of the casts. ARCON VS. NON-ARCON Arcon (Arc = Articulation + Con = Condylar): Represents the anatomy of the patient. MECHANICAL FOSSA ON UPPER / CONDYLAR SPHERES ON LOWER. Angulation of mechanical fossa is FIXED relative to the occlusal plane. Non-arcon: The reverse of arcon. DO NOT REPRESENT ANATOMY OF PATIENT MECHANICAL FOSSA ON LOWER/CONDYLAR SPHERE ON UPPER Angulation of the mechanical fossa relative to occlusal plane is NOT FIXED. (Angle changes when you open the articulator.) Class IV: Instruments that will accept dimensional dynamic registrations. Accepts Face-Bow using True (Kinematic) Hinge Axis. These instruments allow for joint orientation of the casts. 3 of 12 fi fi TRANSVERSE HORIZONTAL AXIS Why register the terminal hinge position? 1. All border movements start at this point 2. To program the articulator to fully reproduce mandibular movements 3. To accurately reproduce the mandibular arc of closure 4. Reduce errors in restorations fabricated at a various vertical dimensions along arc of closure. 5. To be able to increase VDO on the articulator. Arguments: Hypothetical line, more than one hinge axis exists, split axis theory, arbitrary hinge axis is satisfactory (within 5mm). ARBITRARY HINGE AXIS - Proponents of this concept felt that exact duplication of the mandibular movements is impossible and that average movements are better for programming of the articulator. - Weinberg - Tried to determine the error inherent when attempting to register a kinematic hinge axis. With a 3mm wax record at the 2nd molar, the facebow was 5mm posteriorly (Arbitrary), led to an error of 0.2 mm at the second molar. Face-bow An instrument used to transfer the relationship of the maxillary arch, the transverse horizontal axis and a third reference point from the patient’s skull to the articulation device. 1. It orients the dental casts in the same relationship to the opening axis of the articulator. 2. Uses facial landmarks to provide a horizontal and esthetic reference for the maxillary cast on the articulator. It is predominantly used to allow for an esthetic outcome. (Evaluation of an existing cant in the esthetic plane) 3. Three points of reference: - 2 posterior points (Hinge Axis) - 1 Anterior point (Na to Orb or Orb - 7 mm) JAW CLASSIFICATION Class I Angle’s Classi cation - Mesiobuccal cusp of maxillary rst molar occludes in buccal groove of mandibular rst molar. Canine Classi cation - Maxillary canine cusp tip occludes in embrasure between mandibular canine and mandibular premolar 70% of the Population Class II Angle’s Classi cation - Mesiobuccal cusp of maxillary rst molar occludes mesial to the buccal groove of mandibular rst molar. Canine Classi cation - Maxillary canine cusp tip occludes mesially to the embrasure between mandibular canine and mandibular premolar (varying degrees.) Subdivision I: Permanent maxillary central incisors are either normal or slightly protruded out toward the lips. Subdivision II: permanent maxillary central incisors are retroclined. 25% of the Population 4 of 12 fi fi fi fi fi fi fi fi  Class III Angle’s Classi cation - Mesiobuccal cusp of maxillary rst molar occludes distal to the buccal groove of mandibular rst molar. Canine Classi cation - Maxillary canine cusp tip occludes distally to the embrasure between mandibular canine and mandibular premolar (varying degrees.) FUNCTIONAL MOVEMENTS OF THE MANDIBLE Boder Movements of the Mandible - Terminal hinge movement: Rotational (Open/ Close) - Eccentric Movements: Protrusive: Pure Transitional Laterotrusive: (Working) Mediotrusive: (Non-Working) Terminal hinge movement: Rotational (Open/Close) Pure rotary movement for the rst 20mm of opening at the central incisors. Movement is by suprahyoid muscles as well as lateral pterygoid (superior and inferior bodies). Limited by the temporomandibular ligament at 20mm and then becomes a combination of rotational and translational movement reaching 45mm as maximum opening. Protrusive Relation of the mandible to the maxilla when the mandible is thrust forward Mandible translate in forward and downward action. Lateral pterygoid muscles acting simultaneously. Laterotrusive (Working) and Mediotrusive (Non- working) Working condyle rotates with-in the TM fossa (In Vertical Axis) Lateral pterygoid (Inferior belly) contracts unilaterally pulling the condyle forward, down and medially at a certain angle called Bennet Angle. (Orbiting Condyle) Habitual Positions Rest position Centric Relation Intercuspation Position (ICP) CENTRIC RELATION (CR) - De nition (GPT-5): The maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective disks with the complex in the anterior-superior position against the shapes of the articular eminencies in a healthy joint. This position is independent of tooth contact 5 of 12 fi fi fi fi fi fi  Why CR as a Tx Position? 1. Record the horizontal relation of the mandible to the maxilla. 2. This position is independent of tooth contact. 3. It is a Repeatable position. 4. The condyles are in the most Load-bearing position. 5. Deprograming device is used to relieve any interferences and make the muscles go back to normal function. (Time varies among patients 5 - 30 mins). Longer periods suggest a problem exists. 6. Keep the record in a condition where it will not distort until the casts have been mounted. 7. The recording medium must not resist forces exerted by the muscles. Methods of registering CR 1. Bimanual Manipulation (Dawson) Most accurate especially when utilizing a jig. 2. Chin-point guidance (McCollum) 3. Lucia jig/Leaf gauge (Lucia) 4. Deglutition (Shanahan) 5. Extra-oral tracing (Gysi) 6. Intra-oral tracing (Sears) MAXIMAL INTERCUSPAL POSITION De nition (GPT-5): the complete intercuspation of the opposing teeth independent of condylar position, sometimes referred to as the best t of the teeth regardless of the condylar position. Also called maximal intercuspation. Treatment position of choice when a stable and secure occlusal relationship is present with the absence of occlusal pathologies. Centric Occlusion: the occlusion of opposing teeth when the mandible is in centric relation. This may or may not coincide with the maximal intercuspal position (10% of population) REQUIREMENTS OF STABLE OCCLUSION 1. Stable stops on all the teeth when the condyles are in Centric Relation (CR): Point contacts are on the functional cusps, fossas and marginal ridges. Forces exerted on the posterior teeth should be directed through the long axis of the teeth. 2. Anterior Guidance in harmony with the border movements of the Envelope of Function: Lower teeth are ‘guided’ by a gentle slanted slope of the upper lingual surfaces. A too upright tooth interferes with the “Envelope of Function”. 3. Disclusion (separation) of all the posterior teeth in protrusive movements by the most ANTERIOR Teeth (Anterior Guidance): Ideally this should be the 6 front teeth, but in some cases of an open bite for example, the most anterior tooth could be a bicuspid. 4. Disclusion of all the posterior teeth on the non-working or balancing side (Lateral forces can be destructive). (Recommended: 1 mm Bu er Space) 5. Disclusion of all posterior working side contacts during excursions. Notes: The elimination of posterior contacts by an appropriate anterior guidance reduces the elevating activity of the masseter and temporal muscles. 6 of 12 fi ff fi  VERTICAL DIMENSION OF OCCLUSION De nition of Physiological Rest Position: The mandibular position assumed when the head is in an upright position and the involved muscles, particularly the elevator and depressor groups, are in equilibrium in tonic contraction, and the condyles are in a neutral, unstrained position De nition of Vertical Dimension of Rest: The distance between two selected points (one of which is on the middle of the face or nose and the other of which is on the lower face or chin) measured when the mandible is in the physiologic rest position De nition of Vertical Dimension of Occlusion: The distance measured between two points when the occluding members are in contact De nition of Interocclusal Rest Space: : The di erence between the vertical dimension of rest and the vertical dimension while in occlusion Jaw muscle tonus adapts to extreme changes in vertical dimension. Tooth contact appears to be critical, and it can be assumed that periodontal receptor a erent discharge is the main feedback responsible for this adaptive mechanism Pretreatment records: Pro le pictures Articulated Casts Existing Dentures Physiologic rest: Soft tissue outline (not accurate) Class II >5mm. Average of 2-4mm. Class III 3 (50% of class II do not function in normal S position) Class III: no distal movement. Posterior Closest Speaking Space: Class I: 1.5-3mm Class II: 4-8 Class III: 1 7 of 12 fi fi fi fi fi fi ff ff ff  Cephalometrics: Lower Facial Height. Frankfort Mandibular Angle. (Baseline FMA normal 25O +/- 5O ) FMA high > 30O FMA low < 20O Esthetics Facial Pro le (Collapse) Facial strain (Excessive) VDO Tactile Sense/ Proprioception: Instruct patient to open wide until muscle strain. Ask patient to close until the jaws reach a comfortable relaxed position at rest. Measure distance. Lytle (tap,tap,tap) (Using patient feedback, usually decreased VDO) Facial Dimensions: McGee (3 dimensions unchanged in life, 2 out of the three correlate 95% of the time), Willis gauge Deglutition: Swallowing with Wax- Rims with two facial marks, repeat and take average. (Shanahan) Tooth Wear: (Turner) There is no absolute method for measuring VDO. We have to utilize several methods to con rm the desirable VDO. The increase of VDO is Adaptive, but not all patients can tolerate a large increase of VDO. Loss of VDO not only e ects the vertical position of the mandible, in fact, the patients usually adapts to a more forward position (Horizontal position) as he/she functions. OCCLUSAL PLANE Why the orientation of the occlusal plane is important? Designing a proper esthetic smile pro le. Any changes in the occlusal plane (intentional or unintentional) during therapy will void the harmony between the maxillary and the mandible teeth. HANAU QUINT Incisal Guidance - In most cases, this is the overriding factor to produce disclusion posteriorly. When adequately steep, all other factors can be modi ed (exception of CI). (Variable) Cusp Height - To a limit, steep cusp heigh provides a patient with positive occlusal sense and a heightened proprioception. (Variable) Compensating Curve - The anteroposterior curving (in the median plane) and the mediolateral curving (in the frontal plane) within the alignment of the occluding surfaces and incisal edges of arti cial teeth that is used to develop balanced occlusion. Can be increased or decreased to provide more or less separation. Curve of Spee + Curve of Wilson. (Variable) Plane of Occlusion - The average plane established by the incisal and occlusal surfaces of the teeth. Condylar Inclination - The xed factor that can a ect the amount of cusp height and compensating curve provided to the patient. (Fixed) Curve of Spee: is de ned as the curvature of the mandibular occlusal plane beginning at the canine and following the buccal cusps of the posterior teeth, continuing to the terminal molar Curve of Wilson: the mediolateral curve that contacts the buccal and lingual cusp tips on each side of the arch. 8 of 12 fi fi fi ff fi fi fi ff fi  OCCLUSAL SCHEMES - It indicates the type and quantity of dental contacts which result when the mandible moves in the eccentric positions of protrusion and lateral excursion, from a relationship of maximal intercuspation. Types: Bilateral Balanced Occlusion Group Function Anterior Guidance Canine Guidance Anterior Group Function Mutually Protected Occlusion Mucosa-supported Prosthesis: Bilateral Balanced Occlusion - Bilateral balanced occlusion in both static occlusion and articulation to limit the tipping or rotation of dentures, reduce the resorption of underlying bone ridges. - Occlusion is a key factor for the retention and stability of the mucosa-supported prosthesis. - Loses occlusal contact due to continuous resorption of the underlying bone and the rapid wear of acrylic teeth. - Decreased tactile sensation. Unilateral Balanced Occlusion (GROUP FUNCTION): When should one consider a group function occlusal scheme? 1. Patients exhibiting a severe Class II division I occlusal relationship. (Increased Overjet) 2. Patients exhibiting a class III occlusal relationship. (Absence of AG) 3. Patients with periodontally involved or structurally compromised anterior teeth (Endodontically treated canines, or periodontally involved canines). Anterior Guidance: (Canine guidance/Mutually Protected Occlusion) - Developed by D’Amico and the gnathological group (Stuart, Stallard, McCollum) in response to the destructive trauma of restoring dentition to a bilaterally balanced occlusion. Why Anterior Guidance? - Protection of posterior teeth from eccentric/lateral forces - Anterior tooth contact (in exclusion of posterior contact) leads to reduced EMG activity in the muscles of mastication - It is a blessing (Clinician convenience) - Provides adequate masticatory function. (Number of identi ed foods that could be eaten without di culty.) OCCLUSAL TRAUMA 1. Primary Occlusal Trauma: Injury resulting from excessive occlusal forces applied to teeth with normal support. High restorations, bruxism, drifting or extrusion into edentulous spaces. 2. Secondary Occlusal Trauma: Injury resulting from normal occlusal forces applied to teeth with inadequate support. 3. Combined Occlusal Trauma: 4. Acute: Abrupt occlusal impact. Biting on a hard object or restorations interfering w/ direction + magnitude of occlusal force. 5. Chronic: More common. Gradual change in occlusion. Parafunctional habits, extrusion of teeth. 9 of 12 ffi fi OCCLUSAL TRAUMA Signs and Symptoms: Mobility (progressive) Bone loss (furcations; vertical; circumferential) Tooth migration Root resorption Pain on chewing or percussion Fremitus Chipped or fractured teeth. Occlusal pre- maturities. Thermal sensitivity Wear facets in the presence of other Widened PDL space Therapeutic goals and treatment considerations: Occlusal adjustment Temporary or long- term stabilization of mobile teeth Orthodontic tooth movement Occlusal reconstruction Management of para-functional habits IMPLANT OCCLUSION IMPLANT-RETAINED RESTORATIONS 1. Masticatory forces are the same on implants when compared to teeth. 2. Missing teeth —> Absence of PDL —> Less Proprioceptors —> 9x less tactile sensation than that of teeth. 3. The mean values of axial displacement of teeth in the socket vary between 25-100 microns. The range of motion of osseointegrated implants has been reported to be approximately 3-5 microns. 4. More susceptible to occlusal overloading. (In ammation, Crater-like bone defects, Screw loosening, Fracture of the screw/abutment/prosthesis/implant) IMPLANT-RETAINED RESTORATIONS 1. Natural teeth should contact rst because they tend to be displaced more. 2. Light Occlusion (Infra-occlusion by 30 microns). Utilize shim-stock to check Implant Restorations, with rm occlusion passing through. 3. No excursive contact. (Avoid Lateral forces) 4. Occlusal force must be guided along the axis of the implant. 5. Shallow cuspal inclinations. 6. Splinted restorations to manipulate stress distribution. 7. Minimize cantilevers. 8. Mutual protection and anterior disclusion have come to be considered as acceptable therapeutic modalities. 10 of 12 fi fi fl 11 of 12 12 of 12  Removable Partial Denture Indication for Removable partial denture: Multiple edentulous areas long edentulous spans Free end saddles Medical and/or nancial limitations to implants Severe residual ridge resorption Bene ts of removable partial denture: Minimally invasive Improved appearance and speech Improved masticatory e ciency Distribution of occlusal forces Prevent undesirable tooth movement Transition to complete denture Risk of removable partial prosthesis: Plaque retention Lingual plate vs. lingual bar Gingivallyvs.coronallyapproachingclasp Denture stomatitis Direct mechanical trauma Overloading of teeth and RR Technical maintenance Kennedy Classi cation: Class I: Bilateral edentulous areas located posterior to the remaining natural teeth Class II: Unilateral edentulous area located posterior to the remaining natural teeth Class III: Unilateral edentulous area with natural teeth remaining both anterior and posterior to it Class IV: Single, but bilateral (crossing the midline), edentulous area located anterior to the remaining natural teeth Rules 1. The classi cation should follow rather than precede extractions of teeth that might alter the classi cation. 2. If a third molar is missing and is not to be replaced, it is not considered in the classi cation. 3. If a third molar is present and is to be used as an abutment, it is considered in the classi cation. 4. If a second molar is missing and is not to be replaced, it is not considered in the classi cation. 5. The most posterior edentulous area always determines the classi cation. 6. Edentulous areas other than those that determine the classi cation are referred to as modi cations and are designated by their numbers. 7. The extent of the modi cation is not considered, only the number of additional edentulous areas. 8. No modi cation areas can be included in Class IV arches 1 of 8 fi fi fi fi fi fi fi fi ffi fi fi fi fi fi Saddle (Denture base): Transfers functional forces to the supporting tissues Improves aesthetics Flange vs. angeless Three surfaces Occlusal Polished Impression Base extension. How far? Saddle abutment junction open vs close Guide Planes: Two or more parallel surfaces contacting the denture Limit the path of insertion Provide reciprocation Prevent clasp deformation Improve appearance 3-4 mm long Away from from the gingival margin Support: Resistance to displacement towards the mucosa Tooth supported tooth/soft tissue supported soft tissue supported Vertical loading on long axis of the tooth is always preferred Provided by rest seats Lingual bar? Palate Residual ridge Function of the rest: Maintains components of the clasp assembly in their planned positions Maintains established occlusal relationships by preventing settling of the denture Prevents impingement of soft tissue Distributes occlusal loads to abutment teeth Prevents over-eruption Provides indirect retention Support: Why prepare the rest seat? Prepare favorable area for support Transmit forces to the long axis of the tooth Prevent occlusal interference Reduce the prominence of the rest Within enamel No sharp line angles Occlusal rest Minimum thickness of 1 mm (1.5 mm over marginal ridge) Rule of 1/3rd Rounded triangular (base at marginal ridge) Spoon shaped in cross section The rest should be inclined towards the centre of the tooth so that an acute angle is formed between the rest and minor connector to load the long axis of the tooth 2 of 8 fl  Support: Double occlusal rest (OM and OD) on mesially tilted molar Extended occlusal rest Embrasure rest Retention: Resistance to displacement along the path of withdrawal Primary source of retention —> mechanical (clasp assembly) Secondary sources of retention Neuromuscular control Proper extension of the denture base Major connector (maxilla): adhesion and cohesion Principle of encirclement: >180° of the abutment surface is engaged by the clasp assembly Factors a ecting retention of the clasp Alloy: CC, type IV gold, wrought wire SS, CC has higher modulus of elasticity compared to gold CC and gold have similar proportional limits, both lower than SS Depth and location of undercut CC 0.25mm Gold 0.5 mm SS 0.75mm Length —> Longer more exible (molars vs, premolars) Cross sectional form: Round exes in all directions Half round exes more horizontal than vertical 3 of 8 fl ff fl fl  Clasp assembly: Should provide support, stabilization, retention and reciprocation Components of clasp assembly Rest retentive arm guide plane/minor connector reciprocating arm Factors a ecting choice of clasp Position of undercut Appearance Periodontal health Occlusion Shape and depth of sulcus Circumferential clasp (C clasp) Used in most tooth supported partial dentures unless for aesthetic reasons or location of the undercut Terminal 1/3rd of the retentive arm engages undercut, the rest provides bracing Hygiene —> Occlusal approaching more hygienic Occlusion —> Occlusal clearance required Disadvantages Increased tooth coverage Aesthetics Adjustments Ring clasp: Modi cation of C clasp Mesio-lingual undercut on lower molar With or without an auxiliary rest Embrasure clasp: Placed on contralateral non-edentulous spaces in class II or III without modi cation Two retentive and two reciprocal arms Su cient space must be provided between abutment teeth High percentage of fracture caused by inadequate tooth preparation Bar clasp: The I-bar located in the gingival third engaging a 0.25mm undercut The horizontal portion of the approach arm located at least 4 mm from the gingival margin Tapered to its terminus, with no more than 2 mm of its tip contacting the abutment shape of retentive terminal T, I, or Y Improved aesthetics Hygiene: crosses gingival margin Limitations of bar clasps Deep tissue/tooth undercut Shallow visitable High frenal attachment Excessive buccal or lingual tilt of abutment teeth RPI clasp = rest (mesial) + proximal guide plate (distal) + I bar Distal guiding plate and minor connector provide the stabilization and reciprocation Distal extension to avoid tipping forces on the abutment 4 of 8 ffi fi ff fi Altered cast impression: Free end saddle: indirect support provided by optimising extension of the base altered cast technique mesial occlusal rest Reline minimise occlusal loading by reducing the size of the occlusal table Altered cast impression technique Applegate 1937 Minimize movement of the denture base during function Functional impression of the soft tissues Pressure on rests only Indirect retention: Applies when dislodging forces are applied to the free end saddle Rotation of the denture around a fulcrum Axis of rotation passes through most distal clasps Indirect retainer placed as far as possible from the distal extension and at right angle to the fulcrum Canines and rst premolars Reciprocation: Resistance to displacement of the tooth by the direct retainer Plays an important role in the e ectiveness of the retainer Doesn’t come in contact with the tooth until the denture is seated Cross arch reciprocation Bracing: Resistance to horizontal forces acting on the denture (anterior-posterior or lateral) Provided by any rigid component of the denture maintaining contact against vertical surfaces of the teeth or the ridge Rigid portion of the clasp Flanges Plates Minor connectors Major connector 5 of 8 fi ff  Major connectors: Connects parts of the prosthesis together Provides cross arch stabilization Requirements Biocompatible alloy Rigidity No impingement on soft tissues or teeth Cover tissues as needed Don’t contribute to retention of food and plaque All borders should be free of the gingival margin (4mm mand, 6 mm max) Proper relief in areas of bony prominences (mandibular tori, median palatal suture)\ Mandibular major connectors: A. Lingual bar Most common Flat on tissue side and half pear shaped on tongue side Bulkier inferiorly and tapered towards the gingival margin Minimum 4 mm height Hygienic Superior border should be 4 mm away from gingival margin and inferior border shouldn’t impinge on the oor of the mouth (relief) B. Lingual plate Half pear shaped inferiorly with thin edge towards the teeth Cingulum rests provide indirect retention Indications Shallow lingual sulcus High frenal attachment Kennedy class I Stabilizing periodontally a ected teeth Facilitate future replacement of teeth Interrupted lingual plate C. Sublingual bar Modi ed lingual bar placed more inferior and posterior Dimensions are determined by a master impression technique that records the functional depth of the mouth D. Dental (cingulum) bar located on or slightly above the cingulum and can be added to a lingual bar Positive vertical support provided by rest seats E. Double lingual bar Dental bar and lingual bar Plaque accumulation and discomfort to the tongue F. Labial bar Excessive lingual inclination Mandibular tori Poor aesthetics 6 of 8 fi fl ff Maxillary Major connectors: A. Single palatal strap Class III with or without modi cation Short spans Tolerable B. Anterior posterior palatal straps Very versatile, used in many scenarios Rigid The posterior strap is at 8mm wide Posterior bar goes as back as possible but anterior to vibrating line Anterior strap can be extended to replace anterior teeth Incircles maxillary torus C. Palatal plate Full coverage of the palate with anatomical replica Ultimate rigidity and support Provides retention (intimate contact) Extends posteriorly to junction between hard and soft palate Anteriorly closed or open Used in bilateral distal extension or long edentulous spans D. Horseshoe Least desirable Should be used only when large maxillary torus exists Lacks rigidity, can bend No support E. Single palatal bar Lack of rigidity and support Bulky Should be avoided 7 of 8 fl fi The design: Patients needs vs over-engineering Path of insertion: path travelled by the denture from its rst contact with the tooth until it is fully seated. Coincides with path of withdrawal. Path of displacement: when the denture is displaced in function usually at a di erent angle to the path of insertion Single path of insertion found if su cient guide planes are contacted by the denture (tooth bounded saddles) Open design vs closed design saddle 8 of 8 ffi fi ff