Azer Flashcards
what is prosthodontics?
dental specialty that deals with restoring missing oral and paraoral structures
mandibular movements in sagittal plane
rotation and translation
where does rotation occur around?
terminal hinge axis or transverse horizontal axis (THA)- imaginary line connecting the centers of the two condyles
what distance is rotational movement limited to?
20-25mm of incisal separation before the mandible start to translate
mandibular movements in horizontal plane
whole mandible- straight protrusive
lateral movement of mandible
what happens in lateral movement of the mandible?
non-working condyle travels forward and medial
working condyle exhibits slight lateral translation (bennett movement)- may be slightly forward or backward
mandibular movements in frontal plane
straight protrusive movement- both condyles move downward as they slide along the eminences.
lateral movements- non-working condyle will move downward and medial
working condyle- rotate and move lateral and upward or lateral and downward
range of mandibular movements
envelope of motion
what is centric relation arc of closure?
when mandible is guided to centric relation, the arc traced by the point between 2 mandibular centralincisors
when is mandible in centric relation?
at any point along the centric relation arc of closure
what is the definition of centric relation?
maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective discks, with the complex in the anterior-superior position against the shapes of the articular eminencies. this position is independent of tooth contact. restricted to a purely rotary movement about the transverse horizontal axis
centric occlusion
if mandible is manipulated upward on the centric relation arc of closure until tooth contact occurs
what happens to 90% of the population?
co contact occurs between only one or two maxillary and mandibular teeth.
what are contacts points referred to as?
initial points of contact
contacting surfaces located on distal incline of the mandibular tooth and mesial inclines of maxillary teeth
what happens if the mandible closes further past centric occlusion?
it must slide out of CR along a path dictated by the inclines of the contacting posterior teeth. mandible continues to close and slide forward or laterally until all the teeth intercuspate together as best as they can.
reaches maximal intercuspation (MI)
what is centric slide? what is its significance?
slide btween CO and MI. if initial point of contact (CO) coincides with MI, restorative treatment is made relatively easy. if there is a slide- it is necessary to determine whether corrective occlusal therapy is needed before restoreative treatment is accomplished
what is protrusive movement?
starting from MI position, the mandible can be protruded keeping tooth contact. mandible has to open as mandibular anterior teeth ride down along the lingual concavity of the maxillary anterior teeth until they reach an end to end position.
tracing on sagittal plane is dictated by the shape and position of the maxillary anterior teeth (vertical and horizontal overlap)
as the mandible continues to move forward and the anterior teeth clear, the contacting posterior teeth dictates its path. the mandible continues to close and slide forward until maximum protrusive superior position is reached. from thiss position, the mandible can undergo a wide opening movement to its max opened position. max opening may range up to 50-60mm measured between maxillary and mandibular incisors. the mandible can now close back with translation and rotation to its centric relation arc of closure.
habitual arc of closure
patient is instructed to close patient close mouth from the maximum open position. line not reproducible because it is not a border position.
are border movements of the mandible reproducible?
yes
where is the physiologic rest position?
lies on habitual arc of closure. the position that the mandible assumes when all muscles are at a state of equal relaxation. characterized by the teeth being separated by the interocclusal rest distance or space
how is the interocclusal rest distance or space determined?
using two arbitrary reference points on each side of the maxlliary and mandibular teeth or attached gingiva or the skin over the mandible and cranium. distance between these two reference points with the teeth in MI is the vertical dimension of occlusion (VDO). the distance between these two points with the mandible in physiologic rest position is the vertical dimension at rest (VDR)
interocclusal rest distance=VDR-VDO
what is incisal guidance?
resultant protrusive path the lower incisors must follow due to anterior teeth contact. it is determined by the lingual concavities of the maxillary anterior teeth as well as vertical and horizontal overlap of maxillary and mandibular anterior teeth
how is the term incisal guidance widely used?
not only to define the resultant protrusive path of the mandibular incisors but also the path they must follow during lateral jaw movements
when is canine guidance used?
if relationship of the maxillary and mandibular canines determines the lateral jaw movement, the term canine guidance can be used but only in reference to the path during lateral movement
how is incisal guidance measured?
in degrees from horizontal plane
what does incisal guidance determine?
the amount the mandible must drop in the anterior region
what is determined by the angle of articular eminence?
the amount the mandible must drop in the posterior region
what are the posterior determinantsof mandibular movements?
inclination of articular eminence
medial wall of glnoid fossa
intercondylar distance
what are the anterior determinants of mandibular movement?
horizontal overlap of anterior teeth
vertical overlap of anterior teeth
what are the other determinants of mandibular movement?
occlusal plane
curve of spee
neuromuscular response
articulators
mechanical devices that can simulate mandibular movements
small non-adjustable articulators
often lead to restorations with occlusal discrepancies as they cannot reproduce the full range of mandibular movements
semi-adjustable articulators
about the same size as the anatomic structures that they represent. using a facebow transfer, articulated casts can be positioned with sufficient accuracy that will minimize the need for clinical adjustment during treatment
fully adjustable articulators
instruments have a wide range of positions and can be set to follow the patient’s border movements
what is a pantograph?
device that is used in conjunction with fully adjustable articulators to adjust the condylar elements to follow the tracings obtained intraorally
what are articulators that have the condyles connected to the lower member?
arcon articulator
what are articulators with condyles connected to their upper members?
non-arcon articulator
what is the choice of an articulator based on?
the understanding of the biomechanical principles of occlusion which will result in a more efficient use of time and effor and deliver quality clinical results
what is the ear bow transfer?
the means you record from the patient the exact anatomical relation of the maxillary dental arch via imprints of teeth to the patients intercondylar axis. record is then used to mount maxillary cast on articulator and then mandibular cast is related to maxillary cast and mounted using centric relation record obtained from the patient
what are the significances of the ear bow transfer?
relates the maxillary cast (occlusal surface) to the terminal hinge axis
orients the maxillary cast (long axes of teeth) correctly in space using a third point of reference. important for extensive anterior restorations
is aligned parallel to the interpupillary line (horizontal reference)
permits mounting of the maxillary cast on a semi-adjustable articulator
allows the mandibular cast to be correctly mounted using a centric relation (CR) record
how to record mandible’s path of vertical movement in terminal hinge position?
all proprioceptive impulses that direct mandibular movements have to be blocked out
impulses are responsible for awareness of mandibular position in space and guide the mandible in its habitual movements.
a natural reflex action of the mandible is to close into a lateral or a lateral protruded position when something is introduced in the mouth as as wax and the patient is instructed to bite. there fore the relationship of the mandible to the maxilla in the terminal hinge position should be obtained without tooth contact
methods for recording centric relation
chin point guidance
anterior deprogrammer
bilateral (bimanual) manipulation
requirements of centric relation record
along the arc of rotation of the mandible
no teeth touching
thin
soft
fast setting
dimensionally stable
easily verifiable in the mouth and on the mounted casts
what are the uses of diagnostic casts?
diagnostic casts that are correctly mounted in CR on a semi-adjustable articulator using a face-bow transfer, provide valuable info for fixed prosthodontic work. they are generally used for diagnosis and treatment planning as well as construction of diagnostic wax-ups. in addition, diagnostic casts are used to fabricate custom trays and provisional restorations
what is occlusal equilibration?
correction of stressful occlusal contacts through selective grinding. it involves the selective reshaping of tooth surfaces that interfere with normal harmonious jaw function
is leaving malocclusion worse than poor equilibration?
no
may produce new interferences that the patient must learn to cope wih
proprioception of new interferences can create an occlusal awareness and can trigger extreme discomfort of the teeth, tmjs, and masticatory muscles.
what is mutually protected occlusion?
in maximum intercuspal position, posterior teeth come into contact and act as stops to minimize horizontal load on anterior teeth
anterior teeth guide excursive movements of the mandible so that no posterior teeth tooth contact occurs during lateral or protrusive excursions
is posterior tooth contacts that disclude anterior teeth during lateral excursive movements harmful?
yes
interferences can alter muscular patterns during lateral movements, as well as create primary occlusal trauma, fremitus, and increase the likelihood of tooth fracture and development of wear facets.
may result in unfavorable loading of the TMJs.
what are occlusal treatment goals?
to direct occlusal forces along the long axes of teeth (stable posterior contacts)
in MI, all mandibular teeth should contact their maxillary opponents at the same time and with the same intensity i.e. centric occlusion (CO) should be coincident with MI
to furnish a smooth protrusive path guided by anterior teeth without any interference from occlusal contacts between posterior teeth
working side contacts, whether canine protected or group function, should not be prevented from contacting by non working side interferences
what is incisal guidance?
immediate disclusion of posterior teeth takes place on mandibular protrusion
what is canine guidance?
immediate disclusion of posterior teeth takes place as soon as the lateral movement begins
what is group function?
the mandibular buccal working cusps travel downward, forward, and lateral in contact with the lingual inclines of the maxillary buccal cusps, simultaneously with the canine
what are equilibration procedures?
reduction of all contacting tooth surfaces that interfere with terminal hinge axis closure (centric relation)
selective reduction of tooth structure that interferes with lateral excursions
elimination of all posterior tooth structure that interferes with protrusive excursions
harmonization of anterior guidance
