Articulators (Definitions & Classifications)
صناعة / د . هند (م 10 – 11)
اسنان ثاني موصل7 / 12 / 2015
د . هند (م 10)
Articulators
• It is a mechanical device which represents the TMJ and jaws to which maxillary & mandibular casts may be attached to simulate some or all mandibular movements.•
PURPOSES
• • To hold the maxillary and mandibular casts in a determined fixed relationship.
• • Mounting of dental casts for diagnosis, treatment planning and patient presentation.
• To simulate the jaw movement like opening and closing
• It should be able to produce border and intra border movements of the teeth similar to those in the mouth.
• Arrangement of artificial teeth for CD and RPD(in the absence of the patient).
REQUIREMENTS
Minimal requirements– It must be accurately maintain the correct horizontal
and vertical relationship of the patient’s casts.
– The patient casts must be easily removable and attachable to the articulator.
– It should have an incisal guide pin with a positive stop, that is adjustable and caliberated
--It should be able to open and closed in a hinge like fashion.
-- It should accept a face-bow transfer.
– The construction should be accurate, rigid and of non corrosive material.
– The design should be such that there is adequate distance between the upper and lower members.
–It should be stable on the laboratory bench and not too bulky and heavy.
ADDITIONAL REQUIREMENT
The condylar guides should allow right, left lateral and protrusive movements and should be adjustable horizontally.The incisal guide table should be mechanical table that can be adjusted in the sagittal and frontal planes.
CLASSIFICATION OF ARTICULATORS
• Several basis of classification, some of them are as follows.– Based on the instruments function.
– Based on theories of occlusion.
– Based on the adjustability of the articulator.
BASED ON INSTRUMENT FUNCTION
Ability to simulate the jaw movement• Class I : Hinge Type
• Class II : Arbitrary – type A, type B, type C
• Class III : Average -type A, type B
• Class IV : Special – type A, type B
CLASS I (Hinge Type)
• simple articulator
Capable of accepting a single static registration.
• Only Vertical motion possible.
• Use for crown and bridge.
• Example: Hinge joint articulator
CLASS II (Arbitary)
• ------Instruments that permit horizontal as well as vertical motion but do not orient the motion to the TMJ via a face bow transfer.• 1. Class -II A
• Eccentric motion permitted is based on average or arbitrary values
• E.g. Grittman articulator (Based on Bonewills theory ).
• 2. Class - II B
• Eccentric motion permitted is based on theories of arbitrary motion
• E.g. (Monson's Instrument) - Based on Monson's spherical theory of occlusion.
• 3. Class - II C
• Eccentric motion permitted is determined by the patient using engraving methods
• E.g. House articulator.
House art.
CLASS – III (Average)
simulate condylar pathways by using average or mechanical equivalents for all or parts of the motion.Allow for joint orientation of the casts via a face bow transfer.
E.g. Hanau model H
CLASS IV (Special)
Accept 3D dynamic registration. + utilize a face-bow transfer.Type A
Condylar pathways are formed by registration engraved by the patient. This path is non – modifyable
Exp. TMJ articulator.
Type B
• Condylar pathway can be selectively angled and customized / modified. E.g. Denar articulator (D4A).
BASED ON THEORIES OF OCCLUSIONS
Bonwill theory Articulators• anatomic/balanced occlusion
• According to this theory, teeth move in relation
to each other as guided by the condylar control and
the incisal point. It is also known as the theory
of equilateral triangle.
Conical Theory Articulators
• adjustable 3D anatomic articulator;
• universal mandibular movements, adjustable incisal guide
• According to this theory, Lower teeth move over the surface of the upper teeth as over the surface of a cone generating an angle of 45 degree.
Spherical Theory Articulators (Monsoon Spherical theory of occlusion)
• Lower teeth move over the surface of the upper teeth as over
a surface of sphere with a diameter of 8 inches. center in glabella.
E.g. Monson's maxilla mandibular instrument.
Bonwill Triangle
• A 4 inch equilateral triangle bouded by lines connecting the contact points of the mandibular central incisor’s incisal edge to each condyle &from one condyle to the other.
BASED ON THE ADJUSTABILITY
Three Types1. Non Adjustable articulator :
Can open and close in a fixed horizontal axis.
Have a fixed condylar path.
•A class I articulator is a nonadjustable articulator.
2. Semi adjustable articulator
Have adjustable condylar paths (horizontal, ateral) ,adjustable incisal guide table and adjustable inter condylar distance.
Can accept all three records: Face bow, centric jaw relation or protrusive record.
• A class II or III articulator is a semiadjustable articulator.
• Two Type:-
– Arcon Type
– Non arcon Type
ARCON Type
The term “Arcon” was derived by Bergstrom from the words Ar- Articulator & Con – Condyle• This articulator resembles the TMJ.
• The Condylar Element / analogue / sphere attached to – Lower Member (Movable)
• The Condylar Guidance (Glenoid Fossa) attached to – Upper / Cranial Member (immovable)
• Advantage: The Face Bow transfer, occlusal plane, and relationship of the opposing casts are preserved when the articulator is opened and closed.
Arcon principle
Non-Arcon type
This articulator is the reverse of the TMJ• The Condylar Element / analogue / sphere àattached to – Upper Member (Movable)
• The Condylar Guidance (Glenoid Fossa) attached to – Lower
Member (immovable)
(A) Arcon semi-adjustable articulator. (B) Nonarcon semi-adjustable articulator
3. Fully Adjustable--Capable of being adjusted to follow the mandibular movement in all direction.
--Can accept the following five records: Face bow, centric jaw relation, protrusive, lateral records, intercondylar distance record.
• They are not commonly used due to their complexity.
• A class IV articulator is a fully adjustable articulator
Parts of mean value articulator(fixed condylar path)(cl.II)
A. Upper member
• It is a triangular frame (equilateral triangle) with base of triangle placed posteriorly and apex anteriorly. Each side of triangle measures about 110 mm.
Condylar elements: Two condylar elements are present-one on either side of base of triangle posteriorly. They articulate with condylar guidance of the lower member.
Vertical rod: It determines the anterior height of articulator. It should rest on center of incisal guide table during articulation.
Thumb screw: Helps in fixing vertical rod to upper member.
Incisal pin: : Incisal edge of maxillary central incisors at the midline should touch the tip of pin during articulation.
Retentive pin: Helps in retention of casts to the articulator.
B. Lower member
• It is a 'L' shaped frame with a horizontal and vertical arm.Horizontal arm: It is triangular in shape and corresponds to the upper- member.
a. Incisal guide table- It helps in establishing the incisal guidance by maintaining incisal guide angle.
b. Retentive pin -helps in retention of casts to articulator.
Vertical arm: It is triangular in shape and connects upper member to the lower member.
a. Condylar guidance slots - present on the upper portion of both vertical arms. They guide the movement of condylar elements.
b. Horizontal rod - It should coincide with the plane of occlusion while articulation.
c. Stabilizing rod.
• Why is a mean value articulator called so?
Because fixed condylar paths, it has 3 fixed mean values:intercondylar distance- 10 cm to 11 cm
condylar guidance- 33 degrees
incisal guidance- 9-12 degrees