Jaw relationship records for orthognathic surgery

JawJaw
relationshiprelationship
records forrecords for
orthognathicorthognathic
surgerysurgery
www.indiandentalacademy.com

INTRODUCTIONINTRODUCTION
When the mandible moves as it does in
mastication & speech, the various
movements it makes & the relationship it
assumes requires description because of
their complexity.
When the mandible is motionless, definite
relationship to the cranium or maxillae
can be established.

Thus one needs to study certain static
relationships to understand the motions
made by the mandible in function.
If we know the potential limits of motions of
the mandible,we will know the confines of
the envelope of motion within which it can
move.
To understand jaw motions, it is necessary to
understand the factors involved in jaw
relations.

Jaw relation is dependent upon three
factors
 TMJ
 MUSCLES
 OCCLUSION
A thorough knowledge of above three
are essential for any orthodontist

FACTORS INVOLVED IN JAWFACTORS INVOLVED IN JAW
RELATIONRELATION
ANATOMIC FACTORS
TMJ
STRUCTURE
 mandibular fossa
 Condyle
 Ligaments
 articular disc
 Muscles
 nerve supply www.indiandentalacademy.com

The mandible is connected to the cranium at the 2
TMJ by the TM & capsular ligaments. The other
connection is between the upper & lower jaws is
through the occlusal surfaces of the teeth.For this
reason the occlusion of teeth must be in harmony
with the jaw relations when teeth are in contact.

Bony structureBony structure
Bony portion of the TMJ articulation is made up of
mandibular fossa of the temporal bone &
condyloid process of the mandible.
MANDIBULAR FOSSA
Located in front of and below the auditory
meatus.The fossa is 1 inch(2.5cm) long
anteroposteriorly & ¾ inch (19mm) in width
laterally.The styloid process leaves the bone
immediately behind the fossa.

MANDIBULAR FOSSAMANDIBULAR FOSSA

Fossa is divided into 2 portions by petrotympanic
fissure.
Anterior portion
Posterior portion
Anterior portion:Principal bearing surface upon
which the condyle presses through the disk
Posterior portion:Condyle does not bear directly on
the fossa because it is separated by the synovial
membrane & the articular disc (The meniscus)

The condyle of the healthy mandible is convex on
surfaces that bear force.It is widest mesiolaterally
and roundish anteroposteriorly.The articular
surface of the TMJ are covered with dense fibrous
connective tissue instead of hyaline cartilage.
The surfaces are non vascular & non
innervated.The cartilage accommodates
compressive force.
An articular capsule lies beneath the skin and
encloses lateral surface of the joint.

mandiblemandible
coronoid
condyle

The circular fibers are attached superiorly and
medially to the articular fossa and extend to the
eminence and neck of the mandible.
LIGAMENTS
The ligaments of the TMJ are
lateral ligament
sphenomandibular
stylomandibular

The TMJ is a synovial joint. The soft tissue
between the articular surfaces contains two
synovial compartments.
The superior compartment is largest &
contiguous with the fossa.The inferior
compartment is smallest & reinforced by
diskal attachments.
These compartments contain fluid that has
both lubricating and nutritional functions.

synovial compartmentssynovial compartments

These compartments are divided by an articular disk
composed of dense fibro elastic connective tissue.It
fuses to the capsule & lateral pterygoid muscle
anteriorly,joins the capsule mediolaterally, and
attaches to loose vascular connective tissue
posteriorly.
The disc is divided into
anterior band
intermediate zone
posterior band

Anterior band :fibers intersperse with
fibers of lateral pterygoid muscle.
Intermediate zone:Thinnest
part.During movements it forms
articulating surfaces.
Posterior band:Is the thickest and
often termed as bilaminar zone

musclesmuscles
MASSETER: Is divided into two heads.The
superficial head originates on the anterior
zygomatic arch and inserts on the angle and the
ramus.
The deep head originates from the posterior part of
the zygoma and inserts on the ramus and coronoid
process

TEMPORALIS
Arises from frontal and parietal bones, inferior to the
superior temporal line.
Fibers converge into a tendinous band;which then
divides into two parts:superficial group fibers inserts
on the superolateral surface of the coronoid process.
Deeper larger fibers form a band along the inner
coronoid process extending inferiorly to the anterior
border of ramus

Masseter and temporalis

MEDIAL PTERYGOID:
Arises from the medial surface of the lateral pterygoid
plate and from the lateral surface of the palatine bone.
Fibers run posteroinferiorly,inserting on the medial
surface of the ramus and angle.

LATERAL PTERYGOID: Has two heads.superior
head originates on the infratemporal surface of the
greater wing of the sphenoid bone.
Nearly horizontal fibers insert at the pterygoid fovea
of the medial condyle.
The inferior head arises from the lateral surface of
the lateral pterygoid plate and incline superiorly as
fibers run posterolaterally inserting into the
pterygoid fovea.

MEDIAL PTERYGOID & LATERAL PTERYGOID

Other than these we have
SUPRA HYOID MUSCLES
 Digastric
 geniohyoid
 mylohyoid
 stylohyoid
INFRAHYOID
 Sternothyroid
 thyrohyoid
 Omohyoid
 sternohyoid

functionsfunctions
Three paired muscles temporalis, masseter &
medial pterygoid provide elevation & lateral
movement of mandible.
The lateral pterygoid muscles are active during
protrusion, depression & lateral movement. The
superior belly is active during closure.
The supra hyoid muscles have dual functions:
They can elevate hyoid bone or depress mandible

Classification of jaw relationClassification of jaw relation
Jaw relation are classified as
 Orientation relation
 Vertical relation
 Horizontal relation
In this manner, the relation of the mandible to
maxillae(or cranium) can be accurately determined
in three dimensions

Orientation relationOrientation relation
Orientation relations are those that orient the
mandible to the cranium in such a way that,when the
mandible is kept in its most posterior portion ,the
mandible can rotate in the sagittal plane around an
imaginary transverse axis passing through or near the
condyles.
The axis can be located using a kinematic face-
bow(hinge bow) or by use of arbtrary type of face
bow.

Vertical relationVertical relation
The vertical jaw relations are those established by
the amount of separation of the two jaws in a
vertical direction under specified conditions
Classification
1) vertical relation of occlusion
2) vertical relation of rest position
3) others

vertical relation of occlusion
VR of occlusion is established by the the teeth
when in occlusion.
vertical relation of rest position
Also called physiologic rest position of the
mandible.the mandible is considered to be in PRP
(postural rest position)when all the muscles that
close the jaws & all the muscles that open the jaws
are in a state of minimal tonic contraction sufficient
only to maintain posture.

Maximum intercuspation of the teeth should occur
with the condyle and disc assembly seated properly
within the glenoid fossa.
This physiological centering or condyle centricity,
can be defined as that position of the mandible
whereby both its condyles are in the midmost,
rearmost, and uppermost position in the glenoid
fossa.
This seated position of the condyle could only occur
if the closure muscles are bilaterally contracted and
the depressor muscles are bilaterally relaxed.

Relaxation of both groups of these muscles would
place the mandible at rest or in the rest position.It is
established by muscles & gravity.It is postural
relationship of the mandible to the maxillae and the
teeth donot determine vertical level of this
relationship.
The head must be held in an upright position by the
patient and not be supported by headrest while these
observations are made

INTEROCCLUSAL DISTANCE:
Also called as freeway space.It is the distance or gap
existing between the upper and lower teeth when the
mandible is in postural rest position.
It is usually 2-3 mm at first premolar.

Horizontal relationHorizontal relation
The basic horizontal relationship is that of centric
relation,or centric jaw relation.
CENTRIC RELATION:Is the most posterior
relation of the mandible to the maxillae in an
established vertical relation.
centric relation & its importance:
In the current glossary of prosthodontic
terms(1994) there are 7 definitions for centric
relation

Centric relation is not a resting or postural
position of the mandible.Contraction of
muscles are necessary to move and fix the
mandible in this position.
According to ROTH,
CR is not a strained position.It is only a
strained position if attempts are made to
forcibly retrude the mandible and make the
teeth contact where they donot intercusp.

CR-CO IMPORTANCECR-CO IMPORTANCE
Many persons without any symptoms have
significant discrepancy between CR-CO(MI)
WHY SHOULD WE BE CONCERNED?
1 .Adopted them very well
2.If occlusion is altered by ortho or surgery
which deprogrammes the proprioception .

If patient is fortunate enough to adopt to CR-CO
discrepancy you are saved,so
We always should strive for most ideal CR-CO
relationship within our grasp.

Movements of the mandibleMovements of the mandible
Mandibular movements are complex in nature and
vary greatly among persons and within each
person.Many different mandibular movements occur
during mastication,speech,swallowing,respiration,&
facial expression including during Para functional
activities.
A knowledge of mand. Movements is essential to
understand various aspects of occlusion.

Voluntary movements of mand. are
 Opening
 Closing
 Protrusion
 Retrusion
 Lateral excursions
In first four, same translatory cycle occurs
simultaneously in both the joints.

Axes of mandibular rotationAxes of mandibular rotation
Rotational movements of the mandible are
made around three axes
 Transverse
 Vertical
 Sagittal
That move constantly during normal jaw
function

During opening & closing movements,the mandible moves
in the sagittal plane around a transverse axis that passes
through both condyles.This axis is used to properly orient
the maxillary cast on the articulator.This axis moves with
the mand.in lateral,protrusive,or lateroprotrusive
movements.

In a lateral excursion,the mandible rotates around a
vertical axis passing through the condyle on the working
side,as the condyle on the opposite (non-working)
/balancing, side moves forward and medially.
When mand moves in a vert.axis the condyle translates in
working side,tilting along with mandible

During a lateral mandibular movement, the condyle on the
balancing side that is moving forward & medially also
moves downward because of the slope of the articular
eminence . This downward movement of the condyle on
the balancing side causes the mandible to rotate around a
sagittal axis passing through the condyle on the working
side

Factors regulating mand. movementsFactors regulating mand. movements
Mand. Movement is the result of the interaction of
a number of biological factors,These include
 Contacts of opposing teeth
 Anatomy & physiology of TMJ
 Rotational axes of mandible
 Actions of the controlling & moving muscles.

Bennett movementBennett movement
During a lateral excursion,the mandible shifts
bodily in a lateral direction.This direct lateral
movement of mandible (bennett movement) is a
result of mesial (inward) movement of the balancing
condyles(left arrow),with a corresponding
lateral(outward) movement of the working
condyles(right arrow)

Laws of balanced occlusionLaws of balanced occlusion
 Inclination of condylar guidance
 Inclination of incisal guidance
 Orientation of the occlusal plane
 Inclination of the cusps
 Prominence of the compensating curves

Balanced occlusionBalanced occlusion
Balanced occlusion may be defined as the
distribution of occlusal forces over the greatest
possible supporting area in both the centric and the
eccentric positions.
AJO1980 Oct ,Anterior interocclusal relations. (Tuverson)
Schuyler( 1935) believed that it was more
important to have a balanced occlusion in the
natural dentition than in the artificial dentition.
Schuyler demonstrated a technique for
equilibrating (grinding) the canine teeth to
eliminate their overlap in order to establish a
balanced occlusion www.indiandentalacademy.com

D'Amico, in 1958, challenged the balanced-occlusion
concept He contended that the natural teeth of man are
not designed for the wide ranges of lateral and protrusive
movements associated with the balanced-occlusion
theory. These eccentric jaw movements could develop
detrimental horizontal vectors against the teeth,
producing traumatic occlusion and subsequent damage to
the periodontium.
D'Amico believed that the teeth of man are designed and
arranged so as to best resist vertical forces in line with
their long axes and that the natural vertical and horizontal
overlap of the upper canines prevents detrimental
horizontal movements from occurring.

The current feeling is that the anterior teeth work
as a unit (anterior guidance)to restrict the
horizontal movements of the posterior teeth during
eccentric excursions and that when the posterior
teeth are functioning properly without mandibular
slide, they protect the anterior teeth against
excessive horizontal forces in the vertical closure
position to produce a mutually protected
dentition.

ANTERIOR GUIDANCEANTERIOR GUIDANCE

Mutually protected occlusionMutually protected occlusion
An occlusal scheme in which the posterior teeth prevent
excessive contact of anterior teeth in maximum
intercuspation, and the anterior teeth disengage the
posterior teeth in all mandibular excursive movements.
In a mutually protected occlusion, the posterior teeth come
into contact only at the very end of each chewing
stroke,minimizing horizontal loading on the teeth.
Concurrently, the posterior teeth acts as stops for vertical
closure when the mandible returns to its maximum
intercuspation position

Nature provided the mandible with two
vertically inclined structures:
condyles in the rear and
lower anterior teeth in front.
Both structures serve well in separating the
posterior teeth.

When the mandible moves in any direction away
from centric relation, these supporting structures
need to make only enough downward vertical
movement to separate the back teeth.

Excessive lateral stress on the cuspids may
cause lingual movement of the lower cuspids
and resultant lower anterior crowding, and/or
labial movement of the maxillary cuspids.
In addition to this, since the maxillary anterior
teeth are retracted in most cases, an improper
anterior guidance in protrusive will tend to
enhance the chances of relapse of the maxillary
anterior teeth labially.
Importance of mutual protection

A centrically related occlusion and a mutually
protective excursive occlusal scheme are dependent
upon:
 Proper individual tooth positioning.
 Knowing when the mandible is in centric and when
it is not.
 Coordination of arch form and arch width.
 Control of the vertical dimension.
 Anteroposterior correction between maxilla and
mandible.
 Clinical awareness of excursive interferences.

Canine protected occlusionCanine protected occlusion
A form of mutually protected occlusion in
which the vertical and horizontal overlap of
the canine teeth disengage the posterior teeth
in the excursive movements of the mandible

Optimum occlusionOptimum occlusion
* Uniform contact of all teeth when condyle are in
most superior position
* Stable post. Tooth contacts with vertically
directed forces
* Centric relation is coinciding with maximum
intercuspation
* No contact of post. teeth in lateral or protrusive
moments

Objective of occlusal treatmentObjective of occlusal treatment
Direct the occlusal forces along the long axis of
tooth
Attain simultaneous contact of all teeth in CR
Eliminate any occlusal contact on inclined planes
Centric relation should coincide with MI

In this I will be describing about
 Face bows,recording of
 Recording centric relation
 Mock surgery
 Pre-surgical splint

Face bowsFace bows
Face bows are rigid caliper like device.face
bows are used to record the
anteroposterior& mediolateral spatial
position of the maxillary occlusal surfaces .
The face bow is then attached to the
articulator to transfer the recorded
relationship of the maxilla
Subsequently the mand. Cast is related to
max. cast through the use of an interocclusal
record www.indiandentalacademy.com

There are basically two types of face
bows
1.kinematic hinge axis facebow
2.arbitrary hinge axis facebow
arbitrary face bows are less accurate
than the kinematic,but they suffice for
most dental procedures

Parts of face bow
Regardless of manufacturer all the face bows have
1.Side arms
Which can be - inserted into ext. acoustic meatus
Can be centered on skin over condyle
2.Bite fork which records maxilla
3.an anatomic reference pointer
Nasion
Infra orbital foramen

centered on skin
over condyle

Face bow transfer techniqueFace bow transfer technique
Add modelling compound to the bite fork &
positioned on the maxilla

Face bow attached to bite fork

Infra orbital locator
pin

Cast placed on bite fork & face
bow attached to articulator
Reference pointer

Recording the centric relationRecording the centric relation

ARTICULATORSARTICULATORS
Fully adjustable
Semi-adjustable
Arcon(articulating condyle)
Non arcon
Non adjustable

Arcon & non arconArcon & non arcon
arcon
Non-
arcon

TYPESTYPES

MODEL SURGERYMODEL SURGERY
(CAST SURGERY)(CAST SURGERY)
Successful movements by orthognathic surgery
require a stable occlusion.Model surgery is a
means of anticipating an resolving occlusal
problems.
The Models are repositioned intact or sawn along
the possible osteotomy lines to see if satisfactory
occlusion can be achieved.
Where premature cuspal interferences are noted,
these are marked on the models and spot grinding
planned. www.indiandentalacademy.com

Similarly extractions of unwanted or over erupted
non-functional teeth can be ‘carried out’.
Several osteotomies should be tried with difficult
cases.
Model surgery also gives a measure of jaw
advancement or pushback and bone removal.
Splitting or expansion of part of the whole upper
arch to accommodate the lower arch may also be
planned by this means.

When segmental surgery is to be performed the
final ‘postoperative’ planning model is also
important for fabricating occlusal wafers,
splints and arch bars.
If orthodontic treatment is necessary a
diagnostic set-up where individual teeth are
sawn from the model and are remounted in wax
enables the results of pre-surgical orthodontic
treatment to be visualized.

REQUIREMENTSREQUIREMENTS
The following equipment is required for neat
model surgery :
1. A fret saw Hand piece and motor.
2. A steel fissure bur.
3. A plaster bur or an Ash acrylic cutter pear.
4.Surgical scalpel blades,No. 10 or 20.
5.Plaster knife, spatula, 15 cm (6 inch) rubber
bowl.
6.Bunsen burner, spirit lamp, or soldering iron.www.indiandentalacademy.com

7.Wax knife and carver.
8.Soft ribbon wax, hard modeling and sticky wax.
9.15 cm (6 inch) flexible ruler.
10.Spring dividers (15 cm/6 inch).
11.a semi adjustable articulator & facebow

Basic surgical changes
In complex cases,north American
method (anatomically oriented model surgery)
ANATOMICALLY ORIENTED MODEL SURGERY
Accurate impressions of the upper & lower arches
taken,including buccal & lingual sulci.It is useful
to mark the facial midline on the gingivae & the
teeth with a felt tipped pen.This is then reproduced
on the models
METHOD

The impressions are cast in stone,& two duplicate
sets are prepared
1.master cast
2.working cast
a squash bite made and a face bow recording done
which will orient the models to the Frankfort plane.

The working models are articulated on semi
adjustable articulator using the face bow recording
and the squash bite.

when the models are dry ,horizontal & vertical
reference lines are drawn to register the pre
operative position.
Two sets of parallel horizontal lines are drawn on
the upper & lower models.The B line should be
just above the apices of teeth & not less than 15
cm from A line.The actual distance is measured &
noted on the models.
These lines are used to plan vertical movements.

parallel
horizontal lines

Three vertical lines VC,VB,VM,are drawn on the
upper baseline to lower base line on each buccal
segment.
These lines pass through the Upper cuspid,bicuspid
& the distal cusp of the last upper molar tooth,& are
extended to their occluding partners.
vertical lines

This will help to indicate the anteroposterior
movements achieved by the model surgery.
Vertical lines are also drawn to depict midlines.
Vertical distances measured from above lines are
noted on the models.
Transverse changes are recorded by measuring
intercanine & intermolar distance measured across
the palate.

Now the osteotomy lines are drawn & cut to
correspond bone cuts.The segments are sectioned &
are repositioned in planned post operative position
osteotomy lines

OCCLUSAL WAFERSOCCLUSAL WAFERS
Final step in the pre-surgical planning ,is the
fabrication of occlusal wafers fabricated on casts
mounted to an post operative position
Advantage of wafers
Solid interdigitation of teeth,no matter what the
underlying occlusion is.
Final finishing and detailing can be delayed until
fixations are removed

Stability of the occlusion seems to be enhanced.
during fixation changes in tooth position due to
loose bands or broken bonds are minimized.
The use of splints also eliminates the need for
the orthodontist to place a continuous arch wire at
the time of surgery in patients undergoing
segmental procedures.- (Jacobs and Sinclair 1983
Nov ajo)

Types of waferTypes of wafer
There are three types of wafers
Final or post-operative
Intermediate
Functional occlusal

Wafer construction techniqueWafer construction technique
French chalk is applied to the casts
Modeling wax is softened & is pressed on to the
occlusal surface of the lower cast & upper cast is
brought firmly into occlusion.
The wax is resoftened & adapted on to the labial
& lingual surfaces,no more than 2mm down
from the incisal edges.
This ensures positive location of the dentition

The thickness of occlusal wafer will vary at
different locations but as a rule it should be as thin
as possible so that the teeth penetrate completely
through the wafer at a minimum of three points.
The wax pattern is removed and processed in
either heat cured or auto polymerizing clear
acrylic resin
The wafer is trimmed,polished & fitted back on
the cast to check that it does not interfere with
wire ligatures.

conclusionconclusion
Understanding jaw relation is basic
and application of its principles is
essential, if we are to provide
optimum dental health for our
patients for their lifetime.

Jaw relationship records for orthognathic surgery

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Jaw relationship records for orthognathic surgery