DENTAL ARTICULATION, FACE-BOW AND ARTICULATORS

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DENTAL ARTICULATION, FACE-BOW AND ARTICULATORS

• Dr. Waseem Bahjat Mushtaha
• Specialized in prosthodontics

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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.

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• 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.

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• 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

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• 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

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• 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.

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• 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

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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.

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Types of face-bow

• 1-the arbitrary (maxillary) face-bow
• 2-the kinematic (mandibular, hinge axis locator)
  face-bow

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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.

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• 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.

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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

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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.

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• 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.

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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.

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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.

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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.

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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.

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• 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.

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• 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.

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• 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.

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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

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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 formulaLH\8 12
• Lthe lateral condylar path inclination.
• Hthe horizontal condylar path inclination

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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.

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