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Biomechanics of Temporo-Mandibular Joint. Articilator. Movements of Mandible Protrusion Retrusion Lateral Excursion Opening-Closing

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Biomechanics of Temporo-Mandibular Joint. Articilator. Movements of Mandible Protrusion Retrusion Lateral Excursion Opening-Closing Biomechanics of temporo-mandibular joint. Articilator. Movements of mandible Protrusion Retrusion Lateral excursion Opening-Closing Opening-Closing Translatory movement of the mandibular condyle along the posterior wall of the articular eminence. Protrusion A protrusive movement occurs when the mandible moves forward. Retrusion Retraction of the mandible from any position Lateral excurcion When the mandible moves into a left lateral excurcion the right condyle moves forward and inward (Bennett angle), while the left condyle will shift slightly in a lateroposterior direction(Bennett movement). In this example, the left side is working side and the right side is nonworking side. When the mandible moves into a right lateral excurcion the left condyle moves forward and inward (Bennett angle), while the right condyle will shift slightly in a lateroposterior direction(Bennett movement). In this example, the right side is working side and the left side is nonworking side. Border movements of the mandible The most extreme positions to which the jaw is able to move. Laterally: max 10 mm Opening: 50-60 mm Protrusion: 9mm Retrusion:1 mm Described from sagittal, frontal and horizontal planes. Usually not affected by head or body posture. Mandibular movements Most mandibular movements occur around three dimensions. They include, the transverse(horizontal), vertical(frontal) and sagittal axes. Mandibular movements can be classified as border and intraborder movements. Border movements occuring in all three planes and intraborder movements are all possible movements of the mandible occur within the border envelope. Extreme movements in the sagittal plane The patient is instructed to move the mandible from centric relation(CR) to centric occlusion(CO), then edge to edge relationship(ER), then the maximum protrusive (MP) and then arc downward to the maximum opening position. Extreme movements in the frontal plane Here the patient is instructed to move the mandible from centric occlusion (CO), then to the maximum right lateral positon, then arc downwards to the maximum mouth opening position. From this, the patient is instructed to arc upward to the maximum left lateral position and then return to centric occlusion(CO). Extreme movements in the horizontal plane Here the patient is instructed to move the mandible from the centric relation position(CR), to the maximum right lateral position, to the maximum protrusive position, to the maximum left lateral position and return to centric. Envelope of Motion When we combine the border movements of all the three planes, we get a three-dimensional space within which mandibular movement is possible. This three-dimensional limiting space is called the envelope of motion. It was first described by Posselt in 1952. Intra-border Movements Intra-border movements occur within the envelope of motion. They are chewing, speech, swallowing and yawning. Determinants movements of the mandibular movements The angle between the sagittal projection of the condylar path and the occlusion plane according to Gizi – 33°. Bennett angle- the angle formed by the sagittal plane and the path of the advancing condyle during lateral movement of the mandible, as viewed in the horizontal plane, equal average 15- 17o.This is the angle between the path of the non-working condyle and the sagittal plane. The Bennette movement (lateral shift) The bodily shift of the mandible towards the working side during lateral excursion. Bites The static interarch relashionships, or bites, are the relations of two arches under the strong contraction of the masticatory muscles. All bates are distinguished into two types: 1.the physiological (normal) bites 2. the pathological bites Orthognatia is characterized by: 1. The overbite, the characteristic of maxillary anterior teeth to overlap the mandibular anterior teeth in a vertical direction by 1-2 mm 2. The overjet the characteristic of maxillary anterior teeth to overlap the mandibular anterior teeth in a horizontal direction by 1-2 mm 3. the interdigitation, the characteristic of each tooth to articulate with two opposing teeth (except for the mandibular central incisors and the maxillary last molars) 4. The distal surface of the upper and lower third molars are situated on one frontal plane 5. The buccal cusps of the lower teeth occlude with the mesiodistal grooves of the upper teeth or, to reverse the description that the lingual cusps of the upper teeth are in contact with the mesiodistal grooves of lower teeth. Functional and nonfunctional cusps 1: functional cusps 2: nonfunctional cusps Buccal upper and Lingual lower cusps do not support occlusion they are the nonfunctional cusps The articulator The articulator is a mechanical instrument designed to simulate the movements of the mandibular arch in relation to the maxillary arch. These movements are directed and limited by the elements of the articulator that simulates the anatomical determinant of mandibular movement. DEFINITION An articulator may be defined as a mechanical device that represent the temporomandibular joint and jaw members to which maxillary and mandibular casts may be attached to simulate jaw movement. PURPOSES 1.To hold the maxillary and mandibular casts in a determined fixed relationship 2.Mounting of dental casts for diagnosis treatment planning and patient presentation. 3.To simulate the jaw movement like opening and closing. 4.Fabrication of occlusal surfaces for dental restoration. 5.Arrangement of artificial teeth for complete and removable partial denture. Uses 1.To diagnose the state of occlusion in both the natural and artificial dentition. 2.To plan the dental procedures based on the relationship between opposing natural and artificial teeth. 3.To aid in the fabrication of restorations and prosthodontics replacements. 4.To correct and modified complete restorations. 5.To arrange artificial teeth. ADVANTAGES 1.Properly mounted casts allow the operator to better visualize the patients occlusion, especially from lingual view. 2. Patient cooperation is not a factor when using an articulator. Once appropriate interocclusal records are obtained from the patient. 3. A reduces the chair time, patient appointment time. More procedures can be delegated to auxillary personnel. 4. The patients saliva, tongue, and cheeks are not factors when using an articulator BASIC COMPONENT OF AN ARTICULATOR Upper member – Represent maxilla Lower member – Represent mandible CONDYLAR TRACK – CONDYLAR ELEMENT- Vertical Rod (Incisal Pin) Incisal guide table SOME COMMONALY USED ARTICULATOR Mean-Value Articulator Hanau wide VUE articulator Whip – mix articulator Denar articulator Panadent articulator TMJ articulator HANUA WIDE VUE Semi adjustable ARCON type Accept Face-bow transfer Capable of hinge lateral movements. Upper member : & horizontal arm. Condylar T.Shaped with vertical guidance attached to this. Lower Member : L-Shaped with horizontal & vertical arm. Upper portion of vertical arm contains a roll pin. Which project on the outer surface. The condylar shaft attached to inner surface of the vertical arm 12-13 mm anterior to the roll pin. The condylar element (metal ball ) is attached to the free end of the condylar shaft. Condylar guidance : It is circular structure with a slot in the center The condylar element of lower member articulate with this slot also called condylar track. The posterior end of this track has a component known as centric stop. Vertical Rod or Incisal Pin : Helps to keep a fixed distance between the upper & lower member at anterior end. The pointed tip of vertical rod should rest on the center of incisal guide during articulation Incisal guide table : It has a customised incisal guide table. During articulation it should be flat & the incisal pin should be at in center. A pair of lateral wings is present around it. CLASSIFICATION OF ARTICULATORS BASED ON THE ADJUSTABILITY Three Types :- a. Non – Adjustable b. Semi – Adjustable c. Fully – Adjustable Adjustability of the articulator The capability of the articulator to closely simulate the movements of the mandible is dependent upon the adjustability of the articulator elements. NON – ADJUSTABLE Can open and close in a fixed horizontal axis. SEMI ADJUSTABLE Have adjustable sagittal condylar paths, adjustable lateral condylar path. Two Type Arcon Type Non arcon Type Arcon articulators The term “arcon”from the words articulator and condyle. The condylar element is attached to the lower member of the articulator and the condylar guidance (mechanical analog of the glenoid fossa) is attached to the upper member. This articulator resembles the temporomandibular joint. Non-Arcon articulators These articilators have the condylar elements are attached to the upper member of the articulator and the condylar guidance (mechanical analog of the glenoid fossa) is attached to the lower member. This articulator is the revers of the temporomandibular joint. FULLY ADJUSTABLE Capable of being adjusted to follow the mandibular movement in all direction. They are not used due to their complexity. Exp. Stuart Gnathoscope Simulator Casting Casting is the most commonly used method for the fabrication of metal restorations outside of the mouth. A pattern of the lost tooth structure is made in wax. This is then surrounded by an investment material. After the investment hardens the wax is removed leaving a space or mold. Molten alloy is forced into this mold. The resulting structure is an accurate duplication of the original wax pattern. Steps in casting Wax Pattern preparing
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