The Occlusion Blocks & Jaw Relation PDF

THE OCCLUSION BLOCKS & JAW RELATION Dr. Omar Samy Lecturer of Prosthodontics Definition: Occlusion blocks consist of occlusion rims attached to well fitting trial denture bases. The trial denture base is that part of the occlusion block which is directly...

THE OCCLUSION BLOCKS & JAW RELATION Dr. Omar Samy Lecturer of Prosthodontics Definition: Occlusion blocks consist of occlusion rims attached to well fitting trial denture bases. The trial denture base is that part of the occlusion block which is directly adapted to the master cast. 1. BASE PLATE OR RECORD BASE: Definition: A base plate is a well adapted plate to which an occlusion rim is attached. Uses of trial denture base are: 1- Carries the occlusion rims on which maxillo-mandibular relations will be recorded. 2- Carries the artificial teeth to help the try-in stage. 3- Checks the accuracy of the final impression. Requirements of a trial denture base: I- It should be rigid. 2- It should be accurately fitted and adapted to the cast with proper extensions. 3- It should be dimensionally stable with minimal warpage during its use. 4- It should be relieved from any undercut; to avoid scrapping the cast during insertion and removal. 5- They should be neat. clean and smooth to avoid discomfort to the patient. 6- They should be of proper thickness. neither too thick nor too thin. 7- They should be easily and quickly constructed. Types of trial denture bases: There are two types of trial denture bases: a. Temporary trial denture base: They are used in recording jaw relations. arrangement of teeth and are later replaced by permanent denture base. b. Permanent trial denture base: They will ultimately become the actual base of the finished denture. Materials used for temporary trial denture base: Materials used for permanent trial denture base: 1. Hard base plate wax. 1. Heat cured acrylic resin 2. Shellac base plates. 2. Cast gold. 3. Cold curing acrylic resin. 3. Chromium-nickel alloy. 4. Swaged tin. 4. Chromium-cobalt alloy 5. Light cured acrylic resin 1- Temporary Trial Denture Bases: 1. Hard Base plate wax: Base plates constructed of hard base plate wax have the advantage of being easy, rapid and thin to gain space to set teeth. The disadvantage: Lack of dimensional stability. Although reinforced with wire base plate wax (thermoplastic) is subjected to warpage when warmed and rolled. They soften at body temperature. 2. Shellac base plates: They are thermoplastic places adapted on the final cast by heat softening and finger manipulation. Care must be exercised in the application of excessive dry heat to avoid burning the material. Advantages: They have controlled uniform minimal thickness so that they can be used in cases showing limited inter-arch space. Disadvantage: They have insufficient rigidity so that they can not be used in cases of patients with heavy biting power. Several means of reinforcement of the shellac base plates can be achieved through: Rolling the borders of the shellac trial denture base to double their thickness. Embedding a wire across the palate of the upper shellac base plate near the posterior border and on the middle lingual portion of the lower plate to strengthen this type of base plate. 3. Auto polymerizing resin (Cold cure acrylic resin denture base): It is the most commonly used material as trial denture Advantages of resin trial denture bases over shellac bases: Close and accurate tit to the cast Dimensionally stable in the mouth. high strength to withstand biting pressure. 4. Light cured acrylic resin denture base: Same advantages as the Cold cure acrylic resin denture base. No residual monomer. More dimensional stability 5. Swaged tin: Old and not used now II- Permanent Trial Denture Bases: 1. Cast metal bases: These include gold. chromium cobalt and chromium nickel alloy. Advantages: 1. No acrylic warpage. 2. More strength. 3. Increased accuracy which enables the prosthodontist to record the jaw relation under best conditions. 4. Less tissue change under the base. 5. Less porosity and therefore it is much easier to clean and keep clean. 6. Good thermal conductivity. 7. Less deformation in function. Disadvantages: 1. Cost. 2. Difficulty in relining. 3. Time consuming. 2. Heat cured resin: Advantages: 1. The base plate is strong and rigid 2. It is possible to control thickness of the base plate during the waxing up. 3. It requires minimal finishing and polishing. 4. The base constructed in this manner can serve as base plate for maxillo-mandibular relationship recording procedures and setting up of teeth and subsequently become pan of the denture. 5. Eliminates dimensional changes that occur during processing which may cause occlusal errors. Disadvantages: 1. It is much more time consuming. 2. Warpage may occur due to second processing to attach teeth. 3. Duplication of the master cast is needed to complete teeth processing because the master cast is ruined during the base processing II- Occlusion rims (Record rims): Occlusion rims are occluding surfaces fabricated on interim or final denture bases for the purpose of making maxillomandibular relation records and arranging teeth. The occlusion rims are supposed to simulate the space formerly occupied by natural teeth and related tissue. The technician builds the occlusion rims to standard, average dimensions and attaches them to the trial denture base plate. The following material are used for construction of the record rims: 1- Wax: Pink modeling wax is the most commonly used occlusion rims. Advantages: Quick and simple. Disadvantages: 1. liability to distortion if kept in the mouth for more than a few minutes without removal and chilling in water. 2. They yield inaccurate results in case of patients with heavy biting face 2. Modeling compound: They are used in recording jaw relations by the graphic tracing method and for mounting tracers. Disadvantages: 1) Modeling composition takes longer time for trimming and adjustments than wax. 2) Residual pigments can be easily left in the final denture as the modeling composition is not easily washed out during the wax elimination. 3. Plaster and pumice rims: Such rims are selected when recording the mandibular movements using the functional generating path technique. The surface of the occlusion rim is shaped according to the path taken by the mandible during function. Uses of occlusion rim: 1. Base plates and occlusion rims assist in recording the Jaw Relation, (the vertical dimension and centric relation). 2. Selection of the artificial teeth: a- High and low lip lines are determined on it to indicate the length of the teeth. b. Canine lines determine the width of the teeth. They are placed at the corner of the mouth and they represent an estimated position of the long axes of canines: The distance between the lines is used to choose a set of six anterior teeth of proper width. c- The width of posterior teeth is determined by distance between the canine line and the posterior end of the occlusion rim Occlusal Plane 3. The desired support for lips and cheeks can be indicated on the occlusion blocks. 4. Setting up of the artificial teeth: Orientation of occlusal plane. Determination of the central line. Determination of the neutral zone. General construction characteristics: Specific construction characteristics: I. Maxillary occlusion rim measurements: 1. Anterior height. 20-22min from the labial flange, beside the labial notch, to the occlusal plane. 2. Anterior width: 6-8mm. 3. Posterior height: 16-18mm from the deepest point on the buccal flange to the occlusal plane. 4. Posterior width: 8-10mm with the rim centered over the crest of the ridge. II. Mandibular occlusion rim measurement: 1. Anterior height: 16-18mm from the labial flange, beside the labial notch. to the occlusal plane. 2. Anterior width: 6-8mm. 3. Posterior height: The wax rim is flush with lines scored on both heels of the mandibular base plate, 2/3 of the way up the retromolar pads. 4. Posterior width 8-10mm with the rim centered over the crest of ridge. JAW RELATIONSHIPS: In edentulous patients, centric occlusion is re-established and recorded by means of occlusion models or blocks. The blocks are used to establish or record a plane of occlusion similar to that originally occupied by the natural teeth. Definitions: Jaw relations: are any relation of the mandible to the maxilla. Plane of occlusion: An imaginary surface which is related anatomically to the incisors and tips of the occluding surfaces of the posterior teeth. In complete denture prosthodontics, this plane is parallel to Camper's line, a line running from the inferior border of the ala of the nose to the superior border of the tragus of the ear. Physiologic rest position: The habitual postural position of the mandible when the patient is resting in an upright position and the condyles are in a neutral, unstrained position in the glenoid fossa. Vertical dimension at rest position: The length of the face when the mandible is in the physiologic rest position. The wax rims should not touch. Vertical dimension of occlusion: The distance measured between two points when the occluding members (upper and lower Occlusion rims) are in contact. It is about 2-4mm less than Vertical Relation at Rest Position. (free way space) Centric relation: It is bone to bone relationship. It is the most posterior relation of the mandible to the maxilla when the condyles are in their most posterior unstrained position in the glenoid fossae from which mandibular movements can be performed at any given degree of jaw separation. Centric occlusion: It is the relation of opposing occluding surfaces (teeth to teeth relation) when the mandible is an centric relation to maxilla. It should be in harmony with centric relation. Centric relation record: A registration of the relationship of the maxilla and the mandible in centric relation made at the established vertical relation of occlusion Maximum Intercuspation refers to the complete intercuspation of opposing teeth independent of condylar position, also known as habitual/ acquired occlusion. Eccentric relations: Any relation other than centric relation is an eccentric relation. Protrusive relation: It is the relation of the mandible to the maxilla when the mandible is in forward position. Right and left lateral maxilla-mandibular relations: These are mandible to maxilla relationship when the mandible is moved either to the right or to the left side. Christensen Phenomenon: When the mandible moves to an edge to edge position separation occurs distally between the teeth or occlusal rims. Protrusive record being taken with pink baseplate wax. The mandible is brought forward in a straight Protrusive direction about 4-6 mm distance, and the patient Closes on the softened wax. The record is then brought to the articulator, where it is used to set the condylar inclination. Then incisal inclination can be set by the dentist according to esthetics and phonetics requirements Importance of jaw relations: 1. Accurate recording of jaw relations is essential for performing the functions as mastication and phonetics as well as esthetics. 2. Maintaining the stability of complete denture. 3. It is also important for maintaining of the health of the supporting structures and the TMJ. 4. Jaw relation constitutes the relation of the mandible to the maxilla in vertical. anteroposterior and lateral direction. 5. In an edentulous person, it is important to record both the centric relation and the vertical dimension of occlusion to build up the occlusion of the denture (the position of maximum contact between the artificial teeth). The Plane of Occlusion: Does connecting the tips of the incisor teeth and the distobuccal cusps of the most posterior teeth on both sides of the arch form a plane called the plane of occlusion. Determination of the occlusal plan: Anterior and Posterior occlusal plane: The occlusal plane is parallel to the interpupillary line anteriorly. It is parallel to the ala-tragus line posteriorly. Factors at be considered: 1- Aesthete base 2- Functional base (chewing and speech) 3- Principle of Physics and Mechanics.  Aesthetic base: The height of the occlusal plane should be 1-2 mm below the upper lip. Functional base (chewing and speech): Chewing: The occlusal surface of the teeth should be below the greatest convexity of the tongue. This also improves the stability of lower denture. Speech: During speech, the tongue pushes against the sides of the teeth to produce a seal for better pronunciation of words. Principle of Physics and Mechanics: 1) Leverage action: The nearer the occlusal plane to the basal bone of the jaws, the less the leverage action and the better the stability. 2) Parallelism: The occlusal plane should he parallel to both supporting ridges. 3) Arch form: Both the width of the occluding surfaces and the contour of the arch form of the occlusion rims should be individually established according to the patient’s arch form. Vertical Relations: Vertical dimension: The length of the face between two selected points. one located above and the other located below the mouth usually in the midline. Two vertical relations are of importance in complete denture construction: a- Vertical dimension of physiologic rest position (V.D.R.): V.D.R. is the vertical separation of the jaws when the patient is resting comfortably in an upright position, the condyle Its are in a neutral unstrained position in the glenoid fossae and the elevator and depressor muscles of the mandible are in a state of equilibrium. This position is constant throughout life whether teeth are present or not. b- Occlusal vertical relation (V.D.O.): V.D.O. is the vertical relation of the mandible to maxilla when the teeth or occlusion rims are in contact. Difference between vertical dimension of rest and occlusal vertical dimension is referred to the interocclusal distance or freeway space. The average is 2-4mm in normal individuals: VDR-VDO = freeway space (2-4mm) Methods of centric relation registration: I. Wax registration or check bite method: 1. This procedure makes use of a suitable wax wafer interposed between occlusion rims at the previously determined occlusal vertical dimension. 2. The wax medium used must be of a uniformly softened consistency to make sure that an equalized vertical pressure is exerted on both sides. In this procedure. careful repeated checking of centric position is necessary. II- Graphic Tracing Method (Gothic arch tracer): This technique shows the horizontal movement of the mandible in the form of a tracing made by a point stylus fitted to the occlusion block on a recording plate fitted to the tracers. It is believed by some operators that this is the most accurate method for recording centric relation. III- Terminal hinge axis method: This method is based on the fact that the condyles show pure hinge move movement at the early opening and late closing of mandible, when the latter is in centric position. This technique is performed by the use of mandibular facebow. IV-Chew-in or functional generating path method: In this method, the occlusion blocks used are made of rigid bases and plaster and pumice rims. The patient is asked to perform functional grinding movements until an even gliding contact between the rims is produced. ECCENTRIC JAW RELATIONS: Eccentric jaw relations includes: a. Protrusive relation. b. Right and left lateral relations. It is generally accepted that any relation between the mandible and maxilla other than the centric is considered to be eccentric. Eccentric relations are used to adjust the articulator to reproduce the various eccentric mandibular movements. This is important for setting up of teeth in balanced occlusion.