DENTAL ARTICULATION, FACE-BOW AND ARTICULATORS

1. DENTAL ARTICULATION, FACE-BOW AND ARTICULATORS Dr. Waseem Bahjat Mushtaha Specialized in prosthodontics

2. 1- dental articulation Dental articulation: It means the contact relationships of maxillary and mandibular teeth as they move against each other. This is a dynamic process. Articulator: It is a mechanical instrument that represents the tempomandibular joints and jaw members, to which maxillary and mandibular cast may be attached to simulate some or all-mandibular movements. Occlusion: It is the static relation ship (process of closure) between the incising or masticating (occluding) surfaces of the maxillary and mandibular teeth when they are in contact.

3. Centric occlusion: It is the relation of opposing occlusal surfaces which provides the maximum planned contact and\or intercuspation. Centric relation: It is the relation of the mandible to the maxilla when the condyles are in uppermost and rearmost position in the glenoid fossa at a given degree of vertical dimension (jaw separation). This position may not be recorded in the presence of dysfunction of the masticatory system. Centric occluding relation: It is a term sometimes used to describe the condition in which the jaws are in centric relation and the teeth or occlusal surfaces in centric occlusion.

4. Anatomical articulation: It is an occlusal arrangement where the posterior artificial teeth have masticatory surfaces (can make normal masticatory movements with comfort and efficiency) that closely resemble those of the natural healthy dentition and articulate with similar natural or artificial surfaces. Balanced occlusion: It means that the artificial teeth are set up so that as many teeth as possible are in occlusion in any occlusal relationship. Balanced articulation: It is bilateral, simultaneous, anterior, and posterior occlusal contact of teeth in centric and eccentric positions. It means an arrangement of the teeth so that in any occlusal relationship as many teeth as possible are in occlusion, and when changing from one relationship to another they move with a smooth, sliding motion , free from cuspal interference and maintaining even contact

5. Curve of Spee (anteroposterior curve): It is the anatomic curve established by the occlusal alignment of the teeth, as projected onto the median plan, beginning with the cusp tip of the mandibular canine and following the buccal cusp tips of premolar and molar teeth, continuing through the anterior border of the mandibular ramus, ending with the anterior most portion of the mandibular condyle Curve of Menson: It is the curve of occlusion in which each cusp and incisal edge touches or conforms to a segment of the surface of a sphere 8 inches in diameter with its center in the region of the glabella

6. Curve of Wilson (mediolateral curve): It means in mandibular arch, that curve , as viewed in frontal plane, which is concave inferiorly and contacts the buccal and lingual cusps of the mandibular molars. In the maxillary arch, that curve, as viewed in frontal plane, which is convex superiorly and contacts the lingual and buccal cusps of the maxillary molars. The curved is formed by the facial and lingual cusp tips on both sides of dental arch Compensating curve: It is anteroposterior curvature (in the median plane) and the mediolateral curvature (in the frontal plane) in the alignment of occluding surfaces and incisal edges of artificial teeth that are used to develop balance articulation. These curves introduced in the construction of complete dentures to compensate for the opening influences produced by the condylar and incisal guidance during lateral and protrusive mandibular excursive movements, these curves are artificial counterparts of the curve of Spee and monsoon, which are found in the natural dentition.

7. The working side: It is the side on which the chewing is being done at the movement; it is the side to which the mandible has moved. The balancing side: It is the side opposite to the working side. It is the side on which, although there is greater separation of the teeth, there is at least one point of contact between the upper and lower teeth. It is also the side on which the grater condylar movement has occurred

8. II-FACE-BOW Def: the face-bow is a caliper-like device that is used to record the relationship of the jaws to the temporomandibular joints or the opening axis of the jaws and to orient the casts in this same relationship to the opening axis of the articulator.

9. Types of face-bow 1-the arbitrary (maxillary) face-bow 2-the kinematic (mandibular, hinge axis locator) face-bow

10. 1-the arbitrary (maxillary) face-bow A-The maxillary face-bow is one generally used in construction of complete denture B-it is used to record the position of the upper jaw in relation to the hinge axis and transferring the relation to an articulator. The maxillary face-bow is simple to use and relatively accurate, and is based on average computations of an axis opening of the jaw.

11. C-it is placed on, the face with condyle rod located approximately over the condyles. D- The condyle rods of one particular model are positioned on a line extending from the outer canthus of the eye to the top of the tragus of the ear and approximately 13mm in front of the external auditory meatus. The rods of another commonly used model (ear face bow) are designed to fit into the external auditory meatuses (as a posterior reference point). E-the fork of maxillary face bow is attached to the maxillary occlusion rim so the record is a simple measurement from the jaws to the approximate axis of the jaws.

13. 2-the kinematic (mandibular, hinge axis locator) face-bow A-it is used to locate the true terminal hinge axis and transfer this record to the articulator when mounting the maxillary cast. However, use of it can aid in recording centric relation. B-the fork of kinematic face-bow is attached to the mandibular occlusal rim. C-since this is used to orient the casts on an articulator in the same relation to the opening axis of the articulator as the jaws are to be the opening axis of jaws

15. Functions of a face-bow 1-locate the terminal hinge axis by the use of kinematic face bow. 2-relate the maxillary cast to the transfer axis of the articulator in the same relationship as the maxilla is related to the mandibular hinge axis. 3-relate the mandibular cast to the hinge axis by means of a centric relation record.

16. An arbitrary mounting of the maxillary cast without a face-bow transfer can introduce errors in the occlusion of the finished denture. A face bow transfer is essential when cusp teeth are used, allows minor changes in the occlusal vertical dimension without having to make new maxillo-mandibular records, and is also most helpful in supporting the maxillary cast while it is being mounted on the articulator.

17. ARTICULATORS DEF: is a mechanical device which represents the temporo-mandibular joint and jaw members to which maxillary and mandibular casts are attached to simulate jaw movements. The records made with occlusion rims are used to mount the master casts and to adjust to articulator. They also help in maintaining the desired jaw relationships of the casts during setting up of teeth.

18. Articulators are classified according to the instrument capability and record acceptance into: 1-simple hinge articulators. 2-mean value or fixed condylar path articulators 3-adjustable condylar path articulators A-semi-adjustable articulators. B-fully adjustable articulators.

19. 1-simple hinge articulators or plain line articulators 1-They are cold plain line articulators since they only permit vertical motion i.e. simple opening and closing or hinge-like movement 2-they accept a single interocclusal record, which is the centric occluding relation record. 3-Gariot's articulator is a representative for this type of articulator. It consist of upper and lower members joined by a simple hinge with a set of screw against a metal plate posteriorly to serve as a vertical stop to increase or decrease the distance between the two members of the articulator.

21. 2-mean value or fixed condylar path articulators 1-these articulators accept single interoclusal record the centric occluding relation record, they permit horizontal as well as vertical movements. Eccentric movements permitted are based on average value. For many patients the condylar path ranges from 30-40 from the horizontal with an average 32. The inclination of the condylar guidance of the articulator is fixed to the average value and cannot be adjusted in any manner.

23. 2-Gysi articulator, Mahdy articulator and Artek.pro are representive of these types of articulators. They consist of upper and lower members which are joined by two vertical posterior posts "condylar post support" fixed to the lower member, whereas the upper end of each post has an inclined groove representing the condylar path, through which the condylar shafts, extending from the upper member are located and moved in this groove allowing horizontal movement of the upper member.

24. 3-anterior vertical post, "the incisal post" which is attached to the upper member of the articulator by a screw , while its lower end rests on an inclined table, "the incisal guide table" which is fixed to the lower member of the articulator.Inclination of the incisal guide table is fixed at about 30 from the horizontal plane. 4-in the incisal post there is a hole, through which the incisal pin passes. The tip of this pin is designed to touch the midline of the occlusal rim labially.

25. 5-in Gysi articulator, the upper cast is mounted according to Bonwill's triangle which is a four inch (10 cm) equilateral triangle extending poseriorly from one condyle to the other and joining the lower incisor's contact point anteriorly. While the lower cast is mounted according to the recorded centric occluding relation record. 6-in Mahdy articulator and Artek pro articulator face-bow transfer is used to mount the upper cast while the lower cast is mounted on this instrument using centric occluding relation record.

27. 3-adjustable condylar path articulators This type of articulators differ from the fixed condylar path articulators in that they can accept eccentric records which are used to adjust the condylar guidance of the articulator, so that the movements of its jaw members closely resemble that produced by the patient. According to the eccentric records accepted by these types of articulators they are classified into: A-semi adjustable articulators B-fully adjustable articulators

28. A-semi adjustable articulators This type of articulators can accept the following records: 1-face-bow record to mount the upper cast. 2-centric occluding relation record to mount the lower cast. 3-protrusive record, to adjust the articulator's horizontal condylar guidance that corresponds to the patient's horizontal condylar path inclination. Where as the articulator lateral condylar guidance is adjusted according to the Hanau's formula Hanau's formula=L=H\8 + 12 L=the lateral condylar path inclination. H=the horizontal condylar path inclination

30. B-fully adjustable articulators This type of articulator can accept the following records: 1-face bow record to mount the upper cast. 2-centric occluding relation record to mount the lower cast. 3-protrosive record, to adjust the articulator's horizontal condylar guidance which corresponds to the patient's horizontal condylar bath inclination. 4-right lateral record, to adjust the left lateral condylar guidance which corresponds to the patient's lateral condylar path inclination. 5-left lateral record, to adjust the right lateral condylar guidance which corresponds to the patient's right lateral condylar path inclination.

32. Indexing the cast Indexing casts prior to mounting them on an articulator permits removal of the cast and accurate replacement to the articulator. Indexing is also important for remounting procedures made for correcting occlusal errors after curing a denture. Indexing can be accomplished by placing grooves or notches, in the cast or by using remounting plates

33. Mounting the master cast on the articulator In the process of mounting master casts on a fixed condylar path articulator the following steps should be performed: 1-the upper and lower casts are prepared for laboratory remount by cutting indices on the under surface of both casts. These indices are protected by tin-foil.

34. 2-the upper and lower trial denture bases are sealed with wax to their casts, thus the upper cast, lower cast and wax rims are all attached together. The arms of the articulator to be used are lubricated with Vaseline or oil to facilate cleaning the articulator from the plaster after the case is finished. 3-the incisal guide pin of the articulator is adjusted until its top flushes with the top of the upper member. 4-a rubber band is placed on the articulator, extending from the lower mark of the incisal guide pin and around each condylar post support. Adjust the rubber band to form a plane that divides the space between the upper and lower members of the articulator equally "Bonwell triangle"

35. 5-Three lumps of modeling clay are placed on the lower mounting plate to serve as an adjustable cast support 6-with the base plate and occlusion rims sealed together, place both maxillary and mandibular casts in the correct relationship on the three clay supports in the articulators .then align them until of the occlusal plane of occlusion rim is parallel to the plane established by the rubber band 7-open the articulator, and paint the base of maxillary cast with a separating medium.

36. 8-mix, and add plaster to the base of the cast and to the upper member of the articulator. 9-close the articulator until the incisal guide pin touches the incisal guide table and then add more plaster as needed to fill any voids. 10-after the stone has set, invert the articulator, and open it. Removing the modeling clay cast supports, paint separating medium on the base of the lower cast and attach it to the articulator with plaster. 11-permit the plaster to set, then remove excess plaster with a knife.

39. Occlusion rims An occlusion rim is a wax form used to establish: 1-the proper lip and cheek support (fullness of the lips and cheeks) 2-the arch form, which is related to the activity of the lips, cheeks and tongue. 3-the level of the occlusal plane.

40. 4-accurate maxillo-mandibular jaw relations i.e. Help to determine: A-vertical dimension and an estimate of the interocclusal distance. B-horizontal jaw relations (centric occluding relation and condylar path) 5-occlusion rims help to determine the length and width of the artificial teeth: A-high and low lip lines are used for determining the length of the artificial teeth. B-canine line i.e. corners of the mouth; the distance between the canine lines determines the width of the six anterior teeth. C-the distance between the canine line and the posterior end of the occlusion rim determines the mesiodistal width of the posterior teeth. 6-position of midline of the arch for the correct placement of the central incisors. 7-arrangement of the artificial teeth to the trial denture (setting up of the teeth).

41. Base plate wax is the most commonly used occluasl rim material. Compound and a mixture of the plaster and pumice are sometimes used for constructing occlusal rims. There are four basic factors that should be considered in the proper fabrication of occlusion rims, to assist the dentist and the dental laboratory technician throughout the many phases of denture construction.

42. These factors are: 1-relationship of natural teeth to alveolar bone: Since the final goal in the treatment of the edentulous patient is to provide a functional and esthetic prosthesis, the relationship of the natural teeth to the alveolar bone must be understood. The fabrication of successful replacements can be accomplished in most cases only if the artificial teeth are placed in the same position that was occupied by the natural teeth they are replacing. The natural maxillary anterior teeth are inclined slightly forward of the alveolar bone. They contribute to the support of the upper lip With the canines providing support for the corners of the mouth. The mandibular incisors are also inclined forward and tend to support the lower lip. The maxillary posterior teeth are positioned slightly buccal to the alveolar ridge, when occluding with the mandibular molars; the maxillary buccal cusps usually project 2 to 3 mm. beyond the buccal cusps of the mandibular teeth. The crowns of the lower posterior teeth are inclined inward

43. 2-relationship of occlusion rims to edentulous ridges: The location and dimensions of the occlusion rims in relation to the edentulous ridge are basically the same as those for the crowns of the natural teeth that are to be replaced in their relation to the alveolar ridge. The occlusion rims simply replace the natural teeth both in dimension and in their relationship to anatomic structures. These relationships should be re-established by the occlusion rims even if resorption of the residual ridge has occurred following the removal of the natural teeth.

44. 3-fabrication technique and dimensions of occlusion rim: 1-base plate wax (modeling wax): A sheet of base plat wax is heated over approximately one half its length until the wax is soft and pliable. The soft wax is rolled to point to a point just short of unheated area. The wax is again heated and rolled until a soft roll has been formed. The soft wax roll is adapted to a bead of sticky wax that was previously applied to the recording base. The roll is further seated to the base. The roll is further seated to the base with spatula, with additional molten wax.

45. The edges of the roll are extended along the lateral surfaces to the border of the recording base. Additional wax is added to fill any voids in the contour of the rims. A heated broad bladed knife or plaster spatula is, used to quickly shape the labial surface of occlusion rim. The anterior surface should be inclined outward while the posterior surface is sloped slightly inward. A hot wax spatula is used to smooth the lingual surface and form a rim approximately 5mm wide in the anterior area and approximately 8-10mm in the posterior area. These basic dimensions are subjected to final chair side changes, since the dentist uses the rims to determine the proper vertical dimension, occlusal plane, facial support, as well as the midline of the arch, the length and width of the anterior teeth, the buccal eminence, the smiling (high) lip line, and the speaking(low) lip line. The occlusal surface of the occlusal rim must be smooth and flat. All surfaces of the rim should be smooth.