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REVIEW ARTICLE
Year : 2012  |  Volume : 4  |  Issue : 2  |  Page : 96-99

Anterior point of reference: Current knowledge and perspectives in prosthodontics


1 Department of Prosthodontics and Oral Implantology, Shree Bankey Bihari Dental College and Research Centre, Ghaziabad, Uttar Pradesh, India
2 Department of Prosthodontics and Oral Implantology, ITS Dental College, Modinagar, Ghaziabad, Uttar Pradesh, India
3 Department of Conservatice Dentistry and Endodontics, IDST Dental College, Modinagar, Ghaziabad, Uttar Pradesh, India
4 Private Practitioner, Pitampura, New Delhi, India

Date of Web Publication17-Jan-2013

Correspondence Address:
Prince Kumar
Department of Prosthodontics, Shree Bankey Bihari Dental College and Research Centre, N.H. 24, Masuri, Ghaziabad, Uttar Pradesh-201302
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0975-8844.106195

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  Abstract 

The opening and closing mandibular axis is not a purely theoretical postulation, but an absolutely demonstrable biomechanical entity. It is very crucial to accurately record and transfer to articulators for the purpose of maxillofacial rehabilitation. Following the Face bow record and transfer of the mandibular axis to an anatomic articulator, we can then mount the casts so that they open and close on the articulator in the same fashion as the patient's jaws. For this reason one of the fixed factors presented by the patient is taken into the consideration, which if properly considered, can be of inestimable value in all phases of dental treatment. This paper has sought to review the current concepts and practical implications regarding anterior point of reference in prosthodontics.

Keywords: Alae, anterior point of reference, nasion, orbitale


How to cite this article:
Kumar P, Kumar A, Goel R, Khattar A. Anterior point of reference: Current knowledge and perspectives in prosthodontics. J Orofac Sci 2012;4:96-9

How to cite this URL:
Kumar P, Kumar A, Goel R, Khattar A. Anterior point of reference: Current knowledge and perspectives in prosthodontics. J Orofac Sci [serial online] 2012 [cited 2017 Apr 27];4:96-9. Available from: http://www.jofs.in/text.asp?2012/4/2/96/106195


  Introduction Top


Orientation of the maxillary cast in an articulator is a crucial part of several techniques used in dentistry. Its primary objectives are the restoration of occlusion in well controlled form and position of the teeth. The maxillary cast in the articulator is the baseline from which all occlusal relationships start, and it should be positioned in space by identifying three points of different orientation which cannot be on the same line. [1],[2],[3] The plane is formed by two points located posterior to the maxillae and one point located anterior to them. Horizontal plane of reference is plane established on the face of the patient by one anterior reference point and two posterior reference points from which measurements of the posterior anatomic determinants of occlusion and mandibular motion are made. Anterior reference point is the point located on the mid face that, together with two posterior reference points, establishes a reference plane. Whereas posterior reference points are located one on each side of the face in the area of the transverse horizontal axis, which, together with an anterior reference point, establish the horizontal reference plane. [4],[5],[6],[7],[8]

Clinical significance of face bow record transfer

If the maxillary cast is positioned without the correct maxillae-hinge axis relationship, arcs of movement in the articulator will occur which differ from those of the patient. Moreover, the authentication of the mandibular cast spatial position by using interocclusal records made at increased vertical dimensions of occlusion will not be easy unless subsequent records are the same thickness. An occlusion that is restored to an incorrect arc of closure or opening axis may have interceptive and deflective tooth contacts in the hinge-closing movement if there are subsequent changes in the vertical dimension of occlusion. Deflective contacts also may be present in functional and parafunctional lateral movements from the time the restoration is initially inserted. Such contacts are undesirable in either natural or artificial occlusions and can contribute to periodontal trauma, muscle spasm and TMJ pain. [9],[10]

Prognostic role of anterior reference points

The selection of the anterior point of the triangular spatial plane determines which plane in the head will become the plane of reference when the prosthesis is being fabricated. 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 guidances. It also determines the level at which the casts are mounted which governs the future esthetic factor related to patient's denture visibility. [10],[11]

Various anterior reference points

Accurate selection of the reference point is a very critical step in oral and maxillofacial rehabilitation procedures. One should have thorough knowledge of the following anterior points and the rationale for the selection of each [12] [Figure 1].
Figure 1: Various anterior reference points

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  • Orbitale (B) Located by Hanau face bow with help of orbital pointer
  • Orbitale minus 7 mm. (C) This plane represents Frankfort plane
  • Nasion (A) minus 23mm Used with quick mount face bow (Whip mix)
  • Ala of nose (D) This plane represents campers plane
  • 43 mm superior from lower border of upper lip/lateral incisor (Denar reference plane locator/artexmeter).
  • Incisal edge plus articulator midpoint to articulator axis: Horizontal plane distance 6.


Orbitale

Orbitale is the lowest point of the infraorbital rim of skull which can be palpated on the patient through the overlying tissues and the skin. One orbitale and the two posterior points that determine the horizontal axis of rotation will define the axis - orbital plane. [11]

Clinical implications of "Orbitale"

Orbitale and the two posterior landmarks defining the plane are transferred from the patient to the articulator with the face-bow. The articulator must have an orbital indicator guide. Relating the maxillae to this plane will slightly lower the maxillary cast from the position that would be established if the Frankfort horizontal plane were used. Practically, the axis-orbital plane is used because of the ease of locating the marking orbitale and because the concept is easy to teach and understand. Orbitale is transferred from the patient to this guide by means of the orbital pointer on the anterior cross arm of the face-bow [11],[12],[13] [Figure 2].
Figure 2: Position of orbital pointer on the anterior cross arm of the face-bow during face bow transfer on Hanau semi adjustable articulator

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Alternative method

The face-bow itself is raised to the axis-orbital plane on the patient. A metal arm attached to the maxillary record base is rigidly fixed by plaster in a cup that also attaches to a vertical support arm on the face-bow and subsequently to a vertical support arm on the articulator. The relationship of these two vertical support arms to the hinge line is identical. Therefore the record base which is rigidly fixed to the vertical arm attachment can be transferred from the patient to the articulator. This will relate the maxillary cast to the axis-orbital plane or to any other plane with which the face-bow is paralleled on the patient.

Orbitale minus 7 mm

The Frankfort horizontal plane passes through both the poria and one orbital point. Because porion is a skeletal landmark, Sicher' recommended to use the midpoint of the upper border of the external auditory meatus as the posterior cranial landmark on a patient. Most articulators do not have a reference point for this landmark. Gonzalez' pointed out that this posterior tissue landmark on the average lies 7 mm superior to the horizontal axis. [1] The recommended compensation for this discrepancy is to mark the anterior point of reference 7 mm below orbitale on the patient or to position the orbital pointer 7 mm above the orbital indicator of the articulator. Later on Bergstrom developed Arcon articulator that automatically compensates for this error by placing the orbital index 7 mm higher than the condylar horizontal axis. In either technique, the Frankfort horizontal plane of the patient becomes the horizontal plane of reference in the articulator. [5]

Nasion minus 23 mm

This reference point is widely used with Whip Mix Face Bow. The nasion can be approximately located in the head as the deepest part of the midline depression just below the level of the eyebrows. The nasion guide, or positioner, or relator of the Quick Mount face-bow, which is specially designed to be used with the Whip-Mix Articulator, fits into this depression. This nasion relator can be moved only in an in and out motion and not in up and down, from its attachment to the face-bow crossbar. The crossbar is located 23 mm below the midpoint of the nasion positioner. When the face-bow is positioned anteriorly by the nasion relator, the crossbar will be in the approximate region of orbitale. [11],[12],[13],[14],[15] The face-bow crossbar and not the nasion relator is the actual anterior reference point locator. While donig the face-bow transfer, the crossbar of the face-bow supports the upper frame of the Whip-Mix articulator. The inferior surface of the frame is in the same plane as the articulator's hinge points. From this it can be concluded that the Quick Mount face-bow used with the Whip-Mix articulator employs an approximate axis-orbital plane. That is why; locating the orbital point with this method is largely dependent upon the large nasion relator, the morphologic characteristics of the nasion notch, and the inconsistency of the nasion-orbitale measurement from 23 mm in the patient. [15],[16],[17]

Incisal edge plus articulator midpoint to articulator axis-horizontal plane distance

A reasonable and consistent position for the master casts in the articulator would be one which would position the plane of occlusion near the mid-horizontal plane of the articulator. Any deviation and divergence from this scheme may position the casts high or low relative to the instrument's upper and lower arms. [14],[18] The overall deleterious effect of these positions may be inaccurate and vague occlusal relationships due to dimensional changes in the gypsum products used for cast-articulating purposes. In accordance with this concept, 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 planed incisal edges on the patient, and its uppermost point is marked as the anterior point of reference on the face. This point can be recorded for future use by measuring vertically downward to it from the inner canthus of the eye and recording this measurement. The inner canthus is used because it is accessible unchanging landmark on the head. It must be documented that this method does not relate the Frankfort plane or the axis-orbital plane parallel to the horizontal plane. Additionally, only the incisal edges or the most anterior portion of the occlusal plane will be midway between the upper and lower articulator arms. [19],[20]

Alae of the nose

In most of the conventional complete denture techniques it is imperative to make tentative or the actual occlusal plane parallel with the horizontal plane. This relationship can be achieved as a line from the ala of the nose to the center of the auditory meatus that describes Camper's line. An alternative method of establishing this relationship is to make a wax occlusion rim parallel to Camper's line on the face. The desired location for the maxillary incisal edge should be marked on the wax occlusion rim as an initial step in determination of the occlusal plane. This actually assures that the tentative occlusal plane will not be too high or low. [11],[15]

Selection of anterior reference point: Practical considerations

Selection of the right anterior point of reference is highly subjective which necessitate special attention during its selection. A well designed and precise selection of the anterior reference point will allow the dentist to clearly visualize the anterior teeth and the occlusion in the articulator in the same frame of reference that would be used when looking at the patient. The objective is usually to achieve a natural appearance in the form and the position of the anterior teeth. Articulating the maxillary cast relative to the Frankfort horizontal plane will attain this goal. [20],[21],[22],[23],[24] When this reference plane is used, the teeth will be viewed as though the patient were standing in a normal postural position with the eyes looking straight ahead. One of very common dilemma occurs between the dentist and the laboratory technicians when they apply different objectives to the same patient. The dentist may very well have positioned the maxillary cast in relation to the Frankfort horizontal plane or used one of the other more superior anterior points of reference. [25],[26],[27] Laboratory personnel may then proceed to establish the occlusal plane parallel to the horizontal or parallel to the upper and lower articulator arms. The result will be an occlusal plane that drops from anterior to posterior when placed in the patient's mouth. The consequences of the contrary circumstances will also be disadvantageous to the patient. Camper's line can be used as the reference for the articulation of maxillary cast. [11],[15] The laboratory technician may then arrange the anterior teeth and the occlusal plane as though the Frankfort horizontal plane were being used. The result will be an occlusal plane that rises severely from anterior to posterior in the patient's mouth and maxillary anterior teeth that may be excessively positioned lingually. The following technique can be used as more convenient, practical and less time-consuming alternative option: [28],[29],[30],[31]

  • If the Camper's line-horizontal reference plane is used, raise the back of the articulator to achieve the effect of the Frankfort horizontal plane mounting
  • If the Frankfort horizontal plane reference is used, raise the anterior of the articulator to achieve the effect of paralleling the occlusal plane and Camper's line with the horizontal.

  Conclusion Top


As we all know that three points in space determine the position of the maxillary cast in an articulator. So the dentists especially Prosthodontists are more repeatedly concerned with selecting the posterior two of the three reference points. Though one must be aware of the relative significance of posterior reference points and should consider anterior reference point as one of the critical dimension during face bow transfer. Such assessment will definitely affect the development of normal occlusion and associated dentofacial aesthetics. Furthermore dentist must have thorough knowledge of these reference planes and points and should utilize them depending on the case without any misunderstanding with the laboratory personals.

 
  References Top

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4.Foster TD, Howat AP, Naish PJ. Variation in cephalometric reference lines. Br J Orthod 1981;8:183.  Back to cited text no. 4
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23.Downs WB. The role of cephaiometrics in orthodontics. Case analysis and diagnosis. Am J Orthod 1952;38:162.  Back to cited text no. 23
    
24.Lundstrom A. Head posture in relation to slope of the sella-nasion line. Angle Orthod 1982;5:279.  Back to cited text no. 24
    
25.Brandrup-Wognsen T. Face-bow, its significance and application. J Prosthet Dent 1953;3:618-30.  Back to cited text no. 25
    
26.Dos Santos Junior J, Nelson SJ, Nummikoski P. Geometric analysis of occlusal plane orientation using simulated ear-rod facebow transfer. J Prosthodont 1996;5:172-81.  Back to cited text no. 26
    
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29.Freitas A de. A comparison of the radiographic and prosthetic measurement of the sagittal path movement of the mandibular condyle. J Oral Surg 1970;30:631-8.  Back to cited text no. 29
    
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    Figures

  [Figure 1], [Figure 2]


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