FACE BOWS AND ARTICULATORS IN Fixed dental prosthesis

in detail explanation on facebow and articulators

1. FACEBOWS AND ARTICULATORS IN FIXED PROSTHODONTICS 1

2. Contents Definitions Introduction History Need of Facebow Need of third point of reference Importance of facebow in fixed prosthodontics Occlusal plane in relation to articulator Importance of hinge axis 2

3. Hinge axis in relation to articulator Need of articulators in fixed prosthodontics Types of articulators and selection criteria's Anterior guidance, customized AG Evaluation of Anterior guidance Review of literature Summary and conclusion References 3

4. Definitions Earbow : An instrument similar to a facebow that indexes to the external auditory meatus and registers the relation of the maxillary dental arch to the external auditory meatus and a horizontal reference plane. This instrument is used to transfer the maxillary cast to the articulator. The earbow provides an average anatomic dimension between the external auditory meatus and the horizontal axis of the mandible. 4

5. Facebow : A caliper-like instrument used to record the spatial relationship of the maxillary arch to some anatomic reference point or points and then transfer this relationship to an articulator; it orients the dental cast in the same relationship to the opening axis of the articulator. Customarily the anatomic references are the mandibular condyles transverse horizontal axis and one other selected anterior point; called also hinge bow. 5

6. Facebow fork : That component of the facebow used to attach the occlusion rim to the facebow Facebow record : The registration obtained by means of a facebow Facebow transfer: The process of transferring the facebow record of the spatial relationship of the maxillary arch to some anatomic reference point or points and transferring this relationship to an articulator 6

7. Articulator : A mechanical instrument that represents the Temporomandibular joints and jaws, to which maxillary and mandibular casts may be attached to simulate some or all mandibular movements. Hinge axis ( Okeson ) Mandibular movement around the horizontal axis is an opening and closing motion, referred to as Hinge Movement and horizontal axis around which it occurs is therefore referred to as “ HINGE AXIS ”. 7

8. Transverse horizontal axis: “ It is an imaginary line around which the mandible may rotate within the sagittal plane.” 8

9. Introduction Evaluation of occlusal disharmony, and establishment of optimum functional occlusion for both dentulous and edentulous patient is the primary goal of Prosthodontic treatment. It is mandatory that diagnostic casts and master casts be placed in an articulator approximately in the same relationship to the TMJ as exists in the patient. 9

10. In between the two end controlling factors condylar guidance and incisal guidance of articulation, the inclination of occlusal plane plays an important role while placing the maxillary cast in the articulator. Hinge axis  kinematic face bow will give the precise positional relation of the casts to each other in the articulator. 10

11. Upon removal of check bites after mounting of casts will give accurate closing of the casts in centric relation, minimizing the occlusal errors. The use of face bow gives better occlusion in centric relation and also reduces the occlusion interferences in lateral jaw movements. 11

12. History A short history of the face-bow and the period prior to its development will afford us a picture of the ideas that led to its development and the significance of its use. About ninety years ago it began to be realized that in full denture prosthesis, it was important to mount the plaster casts in the articulator in a given positional relation to the condylar mechanism. 12

13. According to Bonwill , the distance from the center of each condyle to the median incisal point of the lower teeth is 10 cm. He used this standard for mounting his casts in the articulator. 13

14. Bonwill did not mention however, at what level below the condylar mechanisms the occlusal plane should be situated. It appears that he mounted his casts with the occlusal plane in a horizontal position about midway between the upper and lower part of the articulator. It is evident that he considered this quite satisfactory. 14

15. Balkwill ,  devised methods that were an improvement on Bonwill‘s In 1866 Balkwill demonstrated an apparatus with which he could measure the angle formed by the occlusal plane of the teeth and a plane passing through the line extending from the condyles to the incisal line of the lower teeth. Avg : 22° to 30° 15

16. He too didn’t give exactly how much below the condylar mechanisms the occlusal plane should be situated. The articulating caliper however did not enable a fixed transfer or 3-dimensional orientation of the cast to the articulator. There was no control of the proper orientation of occlusal plane 16

17. Hayes(1880’s). Used apparatus known as the “Caliper”. The median incisal point was localized in relation to its distance from the two condyles. There was no control of the proper orientation of the occlusal plane 17

18. WALKER(1890): CLINOMETER a new type of instrument Obtained the position of the lower cast in relation to the Condylar mechanism, better than with all the previous apparatus. Bulky & complicated apparatus to measure the inclination of the condylar path, Do not have the ability to be used as face-bow. 18

19. George B. Snow of Buffalo, NY,(1899) made the vital breakthrough when he introduced the first instrument and technique for recording the anatomic relationship of the maxillae to the condylar axis and transferring this relationship to the articulator. Credited for the development of the modern traditional facebow. 19

20. Gysi a little later at about the turn of the century Gysi constructed an instrument for registering the condyle path. However, he also employed his apparatus as a face-blow. 20

21. The term, “facebow,” probably evolved from a statement by A.D. Gritman , who described the “implement devised by Prof. Snow. . .as a bow of metal (that) reaches around the face. . .” It first appeared in the literature in a description for its use by Gritman and Snow in the American Textbook of Prosthetic Dentistry ( ed 2), 1900. 21

22. Snow’s new innovations were: The facebow fork for indexing the anatomic position of the maxilla to the condyles. The application of the “ala-tragus line” for establishing the orientation of the occlusal plane. 22

23. Snow: adopted the plane of orientation suggested by I.N. Broomell . Broomell : originally described it with reference to osseous structures (i.e., the center of the glenoid fossa to the anterior nasal spine). Snow used the term, “ala-tragus line,” adapting it to soft tissue structures for clinical application. 23

24. Need of Facebow "A face-bow should be used for mounting the upper cast on any articulator that has a fixed opening axis". 24

25. Need of Facebow If casts were mounted without a face-bow on a 'hinge" device where the distance between the hinge and the teeth was very close, the opening/closing arc would be different to that of the patient. 25

26. If a crown  hinge  patient whose hinge (TMJs) was farther from the tooth, the crown, when fitted, will be too high and much time will be spent adjusting it. If discrepancies are left uncorrected, occlusal interferences and associated neuromuscular disorders may result. 26

27. Hence a face-bow is used to approximate more accurately the opening/closing arc of the patient. It is most useful for saddle end teeth and for little else. Value of the face bow record in clinical practice is to fabricate the occluding surfaces of the restorations on the same radius and arc of closure which is found in the patient. 27

28. Proper alignment of the occlusal plane with relation to the end controlling factors is of great importance for the cusp inclines and cusp pathways of a prosthetic reconstruction. 28

29. Inferior error in location: Distal cusp inclines of mandibular teeth make premature contact with the Mesial cusp inclines of the maxillary teeth. Superior error in location: Mesial cusp inclines of mandibular teeth make premature contact with the distal cusp inclines of the maxillary teeth. 29

30. Though blind orientation of the maxillary cast may result in an error so slight that a face-bow appears unnecessary, however since the procedure is not complicated not time consuming when an arbitrary face-bow is used for both dentulous and edentulous patients, the chances of incorporating an error can be minimized, which improves the quality of the prosthesis and results in better physiological acceptance by the tissues. 30

31. Indications of Facebow The face-bow should be used when: Cusp form teeth are used Balanced occlusion in the centric positions is desired. A definite cusp fossa or cusp tip to cusp incline relation is desired. When interocclusal check records are used for verification of jaw positions. When the occlusal vertical dimension is subject to change, and alterations of tooth occlusal surfaces are necessary to accommodate the change. To diagnose existing occlusion in patient's mouth. 31

32. Parts of face bow: 32

33. Need of third point of reference 1. It was important to ascertain at what level in the articulator the occlusal plane determines which plane in the head will become the plane of reference when the prosthesis is being fabricated on the articulator. 33

34. 2. The act of affixing a maxillary cast to an articulator relates the cast to the articulators hinge axis, to the condylar determinant to the anterior guidance and to the mean plane of the articulator. The act achieves greater importance by the use of a constant third point of reference. 34

35. 3. When three points are used the position can be repeated so that different maxillary casts of the same patient can be positioned in the articulator in the same relative position to the end controlling guidance's. 4. Visualize the anterior teeth and the occlusion in the articulator in same frame of reference that would be used when looking at the patient. 35

36. 5. Establish a baseline for comparison between patients, or for the same patient at different periods of time. This is possible only through the use of three points mounting that is constant from one patient to another or for the same patient. 36

37. Anterior reference points : Determines which plane in the head will become the plane of reference Determines the level at which the casts are mounted Orbitale (B) Hanau facebow with help of orbital pointer. Orbitale minus 7 mm. (C) represents Frankfort plane. Nasion (A) Used with quick mount facebow (Whip mix) Ala of nose (D) represents campers plane 43 mm superior from lower border of upper lip 37

38. Posterior reference points : 38

39. 39

40. 40

41. The third reference point is only a convenience point. It does NOT relate the casts to any anatomical plane (e.g. Frankfort plane, Occlusal plane etc) on the articulator. It is merely an aid to place the casts as centrally as possible between the maxillary and mandibular bows of the articulator. 41

42. It is for this reason that the Denar articulator uses a measurement of 43mm for the third reference point because its articulator bows are 86mm apart (2 x 43) when the incisal pin is at zero. Kavo's Protar face-bow uses the glabella / nasion region to rest its face-bow and compensates via its articulator design. 42

43. Hence, in this type of face-bow, there are only two usable landmarks. The position of the Maxillary teeth and its approximate relation to the TMJ’s. These two points only provide one piece of information. This is the opening arc (and hence closing arc) of the mandible against the maxilla. 43

44. Three different situations When Maxillary cast mounted in upper bow, space between bitefork and mounting plate very less. 44

45. 2. And during mounting of Mandibular cast to lower bow no enough space. 45

46. In both the cases there is a connection between the lack of space in the articulator and the previous anterior orientation of face bow on the patient. 3. After successful mounting of Maxilla –Mandible casts to articulator, a clinical discrepancy becomes evident when registration aids, occlusal splints, or extensive restorations are integrated, i.e. wedge shaped deviation either anterior / posterior. 46

47. 47

48. Patients horizontal plane: 48

49. Advocated by Guichet , how to use? The distance from the articulator’s mid-horizontal plane to the articulator’s axis-horizontal plane is measured. This same distance is measured above the existing or planned incisal edge on the patient, and its uppermost point is marked as the anterior point of reference on the face. 49

50. This point can be recorded for future use by measuring vertically downward to it from the inner canthus of the eye. The inner canthus is used because it is accessible unchanging landmark on the head Thus you select the reference points according to the articulator needs ( few articulators) 50

51. 51 Anatomic variations

52. 52

53. 53

54. Reference plane and articulators The basic principle of all type of facebow is to record in concrete dimensions the spatial relation between the patient’s maxillary teeth and a given plane of reference. This plane is a construct located bw the two hinge axis and an additional anterior reference point. Various methods differ as to the degree of accuracy of Hinge axis and in selection of anterior reference point. 54

55. Determination of ARP differs in technical details from system to system, but oriented i.r.t the orbital point in most of the cases. 55

56. Choice of plane The choice of reference plane, determined by joining the posterior reference points to the anterior one found by means of the facebow , has a direct influence on the orientation of the casts on the articulator, affecting both the esthetic and functional aspects of the restorations. To investigate this problem further we will now consider the implications of choosing between the different reference planes that can be used for the prosthetic rehabilitation 56

57. Frankfort horizontal plane: Most commonly used. Reason  it renders the ARP easily recognizable in lateral ceph x rays. ( orthodontics) Negative points: Reference point above Hinge axis Plane is in upward direction, steep masticatory and occlusal plane. Insufficient space for mounting maxillary cast. 57

58. ORBITAL-AXIS PLANE Posterior reference: hinge axis Anterior reference: orbitale The orbital-axis plane is identified by the line that joins the individual intercondylar axis, found using the pantograph or the axiograph , to the infraorbital point ( orbitale ). 58

59. ARBITRARY PLANE Posterior reference: acoustic meatuses Anterior reference: arbitrary point The arbitrary plane is identified by the line that joins the acoustic meatuses , or other arbitrary posterior reference points, to an arbitrary point identified 43 mm above the incisal border of the maxillary lateral incisor. 59

60. CAMPERS PLANE: The bony land mark here is ANS, bony anatomical land mark, very hard to locate clinically with any degree of accuracy. Space problems encountered during the maxillary cast mounting. Mounting results in abnormally flat cast positions. Solution: Increase height of articulator. Reduce the angle of masticatory plane in the articulator and thus use less space  by changing the plane of reference on the patient 60

61. When the patient bends the head slightly FH plane is parallel. When the patient holds the head erect, the Frankfort plane lifts upward at the front to form an angle of roughly 8 degrees with the arbitrary horizontal plane, commonly defined as the esthetic plane . 61 8 degrees

62. The angle of the orbitale -axis plane is even greater: The terminal hinge axis point is at an average of 7 mm below porion , so joining it to orbitale creates a plane angled at roughly 13 degrees in relation to the esthetic plane. 62 13 degrees

63. The arbitrary plane, because the anterior reference point that identifies it is roughly 10 mm below orbitale , proves to be the most parallel with the esthetic plane when the patient's head is held in the erect position and the eyes are focused on the horizon 63 10 mm

64. Hinge axis: Hinge axis is a horizontal axis around which the condyles rotate during opening and closing movement up to a range of 20-25 mm. It is the horizontal or transverse axis where a pure rotation of condyles takes place prior to translation of the condyle. 64

65. Since the rotation of condyles occur when the mandible is in its terminal centric relation position, it was known as terminal hinge axis. Today with the changing concept of centric relation, viz , anterio -superior bracing, the term transverse horizontal axis is preferred to terminal hinge axis. The discrepancy of hinge axis between the RUM position and anterior-superior position is about 0.2 mm (Hobo). 65

66. Importance of hinge axis Allows to accurately mount the casts on articulators in CR position. It is impossible to check the accuracy of centric interocclusal record without a hinge axis transfer. It is a starting point (border movement) of lateral movements. Permits vertical dimension to be changed in the articulator. (Without change in accuracy of hinge axis) 66

67. Allows the transfer of the opening axis to the articulator so that occlusion would be on the same arc of closure as the lower jaw. 67

68. Need for an articulator Handheld casts can provide information concerning alignment of the individual arches but do not permit analysis of functional relationships. For an analysis, the diagnostic casts need to be attached to an articulator, a mechanical device that simulates mandibular movement. Articulators can simulate the movement of the condyles in their corresponding fossae. 68

69. Most articulators use mechanically adjustable posterior controls to simulate these movements, although some use plastic pre-milled or customized fossa analogs. If an articulator closely reproduces the actual border movements of a given patient, this will significantly reduce chair time because the dental laboratory can then design the prosthesis to be in functional harmony with the patient's movements. In addition, less time will be needed for adjustments at delivery. 69

70. Instrument selection depends on the type and complexity of treatment needs, the demands for procedural accuracy, and general expediency. 70

71. 71 Class I. Subdivision A Subdivision B Class II. Subdivision A Subdivision B Subdivision C Class III. Subdivision A Subdivision B Class IV. Subdivision A Subdivision B International prosthodontics workshop (University of Michigan in 1972)

72. 72 Class I. Articulator A Simple holding instrument capable of accepting a single static registration. Subdivision A : Vertical motion is possible, but only for convenience. The Corelator (Denar Corp.) The Verticulator (Jelenko)

73. 73 Class I. Articulator Subdivision B : Vertical motion is joint related. The Centric relator (Denar Corp)

74. 74 Class II. Articulator An instrument that permits horizontal as well as vertical motion but does not orient the motion to the temporomandibular joints. Subdivision A : Eccentric motion permitted is based on average or arbitrary values Gysi Simplex Articulator

75. 75 Subdivision B : Eccentric motion permitted is based on theories of arbitrary motion. The Monson Maxillo-mandibular articulator Class II. Articulator

76. 76 Class II Articulator Subdivision C : Eccentric motion permitted is determined by the patient using engraving methods. The Gnathic Relator

77. 77 Class III. Articulator These instruments allow for orientation of the cast relative to the joints and may be Arcon or Nonarcon instruments, accept facebows, and have mounting plates for unlimited case load. Subdivision A : Instruments that accept static protrusive registrations and use equivalents for the rest of the motion. Hanau Nonarcon H2 Articulator

78. 78 Class III. Articulator Subdivision B : Instruments that accept static lateral protrusive registrations and use equivalents for the rest of the motion. Gysi trubyte Denar Mark II Articulator Hanau-Teledyne Panadent Model P Articulator Whip mix Articulator

79. 79 Class IV. Articulator 3- dimensional dynamic registrations. These instruments allow for orientation of the casts to the TMJ and replication of all mandibular movements. Subdivision A : The cam representing the condylar paths are formed by registration engraved by the patient. TMJ-Stereographic instrument Denar Combi articulator

80. 80 Class IV. Articulator Subdivision B : Instruments that have condylar paths that can be angled and customized either by selection from a variety of curvatures, by modification, or both. Stuart Articulator Denar D5A Articulator

81. 81   NEW SYSTEM CLASSIFICATION BY RIHANI- 1980: Can accept one or two of the following records: 1. Face bow 2. Centric jaw relation record 3. Protrusive record. Can accept all the following three records. 1. Face bow 2. Centric jaw relation record 3. Protrusive record. Can accept all the following five records. 1. Face bow 2. Centric jaw relation record 3. Protrusive record. 4. Lateral records 5. Intercondylar distance record Fully adjustable Semi adjustable Nonadjustable

82. 82

83. They are classified according to how closely they can reproduce mandibular border movements. Non adjustable Semi adjustable Fully adjustable 83

84. Nonadjustable articulators Often leads to restorations with occlusal discrepancies, because these instruments do not have the capacity to reproduce the full range of mandibular movement. Corrected intra orally,  time consuming and frustrating, leading to increased inaccuracy. Left uncorrected  Neuromuscular disorders 84

85. The distance between the hinge and the tooth to be restored is significantly less on most nonadjustable articulators than in the patient. This can lead to restorations with premature tooth contacts because cusp position is affected. This type of arcing motion on the nonadjustable articulator results in steeper travel than occurs clinically, resulting in premature contacts subsequently on fabricated restorations between the distal mandibular inclines and the mesial maxillary inclines of posterior teeth. 85

86. 86

87. Semi adjustable articulators For most routine fixed prostheses, while minimizing the need for clinical adjustment during treatment. Do not require an inordinate amount of time or expertise. They are about the same size as the anatomic structures they represent. Therefore, the articulated casts can be positioned with sufficient accuracy so that arcing errors will be minimal and usually of minimal clinical significance 87

88. Two basic designs of the semi adjustable articulator: ARCON NONARCON 88

89. Nonarcon instruments gained considerable popularity in complete denture prosthodontics because the upper and lower members are rigidly attached, permitting easier control when positioning artificial teeth. However, certain inaccuracies occur in cast restorations, which led to the development of the Arcon-type instrument. 89

90. In an Arcon articulator, the condylar spheres are attached to the lower component of the articulator, and the mechanical fossae are attached to the upper member of the instrument. Thus, the Arcon articulator is anatomically "correct," which makes understanding of mandibular movements easier, as opposed to the Nonarcon articulator. 90

91. The angulations of the mechanical fossae of an Arcon instrument is fixed relative to the occlusal plane of the maxillary cast. In the Nonarcon design, it is fixed relative to the occlusal plane of the mandibular cast. Most semi adjustable articulators permit adjustments to the condylar inclination and progressive and/or immediate side shift. Some have straight condylar inclined paths, although more recent instruments have curved condylar housings, which are more anatomically correct. 91

92. 92

93. The mechanical fossae on semiadjustable articulators can be adjusted to mimic the movements of the patient through the use of interocclusal records. These consist of several thicknesses of wax or another suitable material in which the patient has closed. 93

94. Because these records can be several millimeters thick, an error is introduced when setting Nonarcon articulators with protrusive wax records, because its condylar path is not fixed relative to the maxillary occlusal plane. As the protrusive record used to adjust the instrument is removed from the Arcon articulator, the maxillary occlusal plane and the condylar inclination become more parallel to each other, leading to reduced cuspal heights in subsequently fabricated prostheses 94

95. 95 Denar Mark II Articulator Hanau-Teledyne Panadent Model P Articulator Whip mix Articulator

96. Fully adjustable articulators A fully adjustable articulator has a wide range of positions and can be set to follow a patient's border movements. The accuracy of reproduction of movement depends on the care and skill of the operator, the errors inherent in the articulator and recording device, and any mal alignments due to slight flexing of the mandible and the non rigid nature of the TMJs. 96 Stuart Articulator Denar D5A Articulator TMJ-Stereographic instrument Denar Combi articulator

97. Anterior Guidance Border movements of the mandible are governed by tooth contacts and by the shape of the left and right TMJ’s. In patients with normal jaw relationships, the vertical and horizontal overlap of anterior teeth and the lingual concavities of the maxillary incisors are highly significant during protrusive movements. 97

98. In lateral excursions, the tooth contacts normally existing between the canines are usually dominant, although the posterior teeth may also be involved. Restorative procedures that change the shape of the anterior teeth can have a profound effect on excursive tooth contacts. For this reason, when preparation of anterior teeth is contemplated, the exact nature of the anterior contacts should be transferred to the articulator, where it can be studied and stored before these teeth are prepared. 98

99. Mechanical Anterior Guidance Table Most articulator manufacturers supply a mechanical anterior guidance table. Such tables can be pivoted anteriorly and posteriorly to simulate protrusive guidance, and they have lateral wings that can be adjusted to approximate lateral guidance. 99

100. However, the sensitivity of these adjustments is insufficient for successfully transferring the existing lingual contours of natural teeth to newly fabricated Restorations. Therefore, the principal use for these mechanical tables is in the fabrication of complete dentures and occlusal devices 100

101. Custom Acrylic Anterior Guidance Table This simple device is used for accurately transferring to an articulator the contacts of anterior teeth when determining their influence on border movements of the mandible. Acrylic resin is used to record and preserve this information, even after the natural lingual contours of the teeth have been altered during preparation for complete coverage restorations. The technique is similar to that for stereographic recording used in setting the posterior controls of some articulators. 101

102. 102

103. 103

104. Evaluation of CAG When the custom anterior guidance table has been completed, the incisal pin should contact the table in all excursive movements. This can be checked with thin Mylar strips (shim stock). If contact is deficient, a small mix of new resin is added and the process repeated. If too much resin has been used, the table may interfere with the hinge opening-closing arc of the articulator. Excess can be easily trimmed away. 104

105. 105

106. Summary Diagnostic casts provide valuable preliminary information and a comprehensive overview of the patient‘s needs often not apparent during the clinical examination. They are obtained from accurate irreversible hydrocolloid impressions and should be transferred to a semiadjustable articulator using a facebow transfer and interocclusal record. 106

107. For most routine fixed Prosthodontic diagnostic purposes, the use of an arbitrary hinge axis facebow is sufficient. If special concerns apply, such as a change in vertical dimension, a kinematic facebow transfer is needed. 107