Jaw - Geometry

“Jaw - Geometry”
www.indiandentalacademy.com

Lay - out……!
Introduction
Historical Perspective
Mandibular Rotation…! Why?
Types of Rotation….! Classification
Study Done
Aims & Objective
Materials & Methods
Case Reports
Conclusion
Future scope

Face is a complex structure that has always challenged
the orthodontist for a very long time.
The face (Profile) is considered largely during treatment
planning, which is determined predominantly by
the rotation of mandible.
It was “Bjork” (1969) with his studies opened new
vistas on understanding the rotation of mandible,
which he said that it is a complex phenomena
and rightly published an article “Rotation A
Puzzle”
It was after this eye opener, treatment was focused on
the “Face” than the “Base” .
In this presentation an effort has be made, not only to
understand the the rotation of mandible but also
its effects on treatment.
Introduction….

Lay - out……!
Introduction
Historical Perspective
Mandibular Rotation…! Why?
Types of Rotation….! Classification
Study Done
Aims & Objective
Materials & Methods
Case Reports
Future Scope
Conclusion

Historical Perspective….
“BELCHIER & DUHAMMEL” (1736 to 1740 )
Investigated bones with the help of “Madder Root Die”
& published an article “Root which stains bone Red”
“DUHAMMEL”(1750) implanted wires to bones.
Phase of Transition Die to Implant.
“JOHN HUNTER”(1754) began work on mandible
“JOHN HUNTER”(1764) proved mandibular remodeling is
possiblewww.indiandentalacademy.com

1st implant study by
“G.Humphry”,boring hole
in the pigs mandible & tying
wire to it .
This was published in an
article “Growth of the
Jaws” (1871)

“JOHN HUNTER”(1771) “Natural History of Human
Teeth”describing “Ideal Occlusion”&“Mandibular Growth”
“LUCE” (1889 – 1900) worked on condyle & termed
“HINGE AXIS”
“BENNETT” (1908) Gave “ROTATIONAL THEORY”
“KEITH & CAMPION”(1922) studied growth of craniofacial
structures

An illustration
showing the
lengthening of the
Mandible occurring
Dorsally form the
published article
“The Natural
History Of The
Human teeth”by
“HUNTER” (1771)

“BRASH”(1924) proved condylar hinge movement
(1930) Ceph studies were done - not very reliable
“BJORK”(1951) started implant studies on the jaws
“POSSELT et al” (1952) did studies on Mandibular Motion

Historical
Perspective….
“BJORK”(1955) Phrased the term “Growth Rotation”
“BJORKS & Co Workers”(1960)
Longitudinal studies with implants
(1969) Orthodontic Specialty focused attention on
“Mandibular Rotations”
(1983) SKIELLER & Co Workers gave importance to jaws
especially to Mandible during treatment planning

Mandibular rotation …! Why?
Normally changes that occur in the facial complex
helps the clinician to identify & diagnose a
problem correctly so as to provide the optimal
treatment.
It is therefore essential for us to be aware of, How the
face changes ,Where & When it occurs & How
it takes place ?.
So sound understanding of growth of the Maxilla &
Mandible is necessary to understand the rotation
of the mandible,which predominantly determines
the facial type of an individual.www.indiandentalacademy.com

Mandibular rotation …!
Why? Maxillary Growth

Mandibular Growth

Total Growth Effect

Possible Maxilo-Mandibular Skeletal
Combinations

Types Of Rotation……! Classification
It is mandatory that growth follows “Cephalocaudal
Growth” trend & hence it is inevitable for the
mandible to compensate more than the maxilla to
derive at an acceptable compromised profile.
The compensation of the mandible is more because it is
the only mobile bone in the entire Cranio Facial
Complex.
The basic movements of the mandible are
Upwards & Forwards (Anti Clockwise)
Downwards & Backwards (Clockwise)
Lateral Excursions

Classification….!
Mandibular Rotation can be broadly classified into:-
 During Growth
 During Treatment
During growth:-
1. “PROFFIT”
 Internal Rotation
 Total Rotation
 External Rotation
Total Rotation = Internal Rotation – External rotationwww.indiandentalacademy.com

Classification….!
2. “SOLOW & HUSTON”
 True Rotation
 Apparent Rotation
 Angular remodeling of lower border
Apparent Rotation = Total Rotation – Angular Remodeling Of
Lower Border
3. “SHUDDY”
 Clockwise rotation
 Counterclockwise Rotation

Classification….!
4. “BJORK”
Forward Rotation
Type - I - around the condyle.
Type - II - around the incisors.
Type - III - around the premolars.
I II
III

Classification….!
Backward Rotation
Type - I - around the condyle.
Type - II - around the most distally occluding
molar
I II

5. “BJORK & SKIELLER”
Matrix Rotation – around the condyle (A)
Intra Matrix Rotation – centered within the body (B)
Total Rotation
Classification….!
Total rotation = Matrix rotation + intra matrix rotation
A
B

During Treatment:-
Classification….!
Treatment mechanics inevitably changes the position
of the mandible.
These Mechanics can be either “SKELETAL or DENTAL”
SKELETAL
During Growth Period:-
Head Gear Therapy
Myo functional Therapy…..ect !

After Growth Period:-
Lefort surgeries
I
II
High Lefort
Upward Impaction
Downward Impaction
Classification….!
DENTAL
Distalization
Mesialisation
Molar extrusion
Molar Intrusionwww.indiandentalacademy.com

Schematic Explanation…!

= Low Angle
= Normal Angle
= High Angle
Schematic Explanation…!

Thus any treatment change alters the position of the
mandible which in turn alters the profile ( long or
short face).
Alterations in the position of the mandible due to
treatment usually takes place around the condyl ..i.e.,
rotation takes place as a mandible as a whole.
This concept of rotation of the mandible during
treatment is used for the study conducted in our
department to calculate the rotation of the
mandible.

Aims & Objective of the study…..!
To assess the rotation of the mandible for
every 1 mm of movement of the molar.
To derive on a “Calculated approach” to
assess the rotation with the help of
“Cephalometric & O.P.G “ analysis.
To apply this calculated approach,during the
planning phase of pre - surgical
orthodontics , so as to predict the rotation
of the mandible accurately.
To use the calculated value for the fabrication
of surgical splint to aid the surgeon in
easy & timely surgery.www.indiandentalacademy.com

Materials & Methods….!
20 Cases undergoing Begg mechanotherapy were
Selected.
Both Males & Females between the age group of
15yrs to 25yrs were considered.
All the patients had Bimaxillary Dental Proclinaiton
& underwent all1st Bicuspids extraction.
Begg stage - I arch wires were placed with 35 to 40
degrees of anchor bend & 2 to 21/2 Oz of force
used.
At the end of stage - I OPG & Lateral Cephalogram
were taken.

Pre treatment & End of stage - I OPG &
Cephalometric X- rays were assessed for the
following land marks,
OPG land marks:- [WEBER.J.S.URSI.et all,-
JCO - 1990 - March (166 - 173)
Right 6 to orbital plane
Left 6 to orbital plane
Right 6 to mandibular plane
Left 6 to mandibular plane

OPG - Land Marks
. .
..

Cephalometric land Marks (Angular)
FMA
GoGnSn
ArGoGn
Upper Go
Lower Go
Occl Plane to Sn
Cephalometric Land Marks (Linear)
N Ans
Ans Gn
Cd to Ptmwww.indiandentalacademy.com

CEPH - Land Marks
Linear
Cd to Ptm
NAns
AnsGn
Angular
FMA
GoGnSn
ArGoGn
UGo
LGowww.indiandentalacademy.com

The X - Rays of the 20 patients were analyzed for the
land marks mentioned & tabulated as follows:
Patient Name: I.D.No:
Protocol Pre Rx End of Stage I Inference
F.M.A
GoGnSn
ArGoGn
U.Go
L.Go
Rt 6 to Orbital plane
Lt 6 to Orbital Plane
Rt 6 to Mand Plane
Lt 6 to Mand Plane
Cd to Ptm
N Ans
Ans Gn

The readings obtained from the tabulated values
were analyzed & related as follows,
Every 1 mm of Molar Extrusion [OPG]
{Mo Ex}
Increase in Lower Anterior Facial Height
{LAFH}.
Downward Backward Rotation Of Mandible
{Ro Mad}.
Change in the condylar position
{Cd Ptm}
The readings were statistically deduced & were
given in a Ratio Format.i.e..
MoEx : LAFH : Ro Mad :Cd Ptm.www.indiandentalacademy.com

The ratio thus deduced was used in a “Reverse
Logical Sequence” to predict the auto
rotation of the mandible.
Cases having “Vertical Maxillary Excess”were
selected after necessary investigations were
done (Ceph, Model analysis.etc).
10 patients both Males & Females were selected,
between the age group of 20 to 28 yrs.
All selected cases were discussed with the oral
surgeons & presurgical orthodontics were
done .

The cases selected were treated with 0.022’ Roth
prescription for necessary decompensations.
At the end of the pre surgical phase X-Rays (Ceph & OPG)
were taken & the prediction of the autorotation was done
to obtain a “Predicted Value”.
After face bow transfer, the cast was mounted on the
articulator (HANAU) & the “Predicted Value”
was used to do the mock surgery for the preparation
of the splint.
The splint thus made i.e. “Predicted Splint”is used
during surgery for easy & timely surgery.
After 3 wks of the surgery a Lateral Ceph was taken to check
the efficacy of the prediction

Case Report Begg….!
Boopathy 20 Yrs Male
Teeth Placed in the Front
Ectomorphic Body Type, Dolico cephalic Head,
Leptoprosophic Face.
Symmetrical Face , Average Clinical
FMA , Convex Profile,Incompetent
Lip , Acute Nasolabial Angle & Deep
Mento labial Sulcus
Class- I Molar & Canine , Plroclined Upper &
Lower Incisors,Over Jet of 10mm &Over
Bite of 4.5mm.
All Four Ist Bicuspids Extraction was planed &
strapped Up with Beggs.www.indiandentalacademy.com

PRE - Rx - INTRA ORAL & EXTRA ORAL

PRE Rx - OPG & LATERAL CEPHALOGRAM

END OF STAGE - I- INTRA ORAL

END OF STAGE -I- OPG & LATERAL CEPHALOGRAM

Pre
Stage- I
SUPERIMPOSITION…!

Patient Name: Bhoopathy 20/M I.D.No: 60857
Protocol Pre Rx End of Stage I Inference
F.M.A 23 26 >3
GoGnSn 30 33 >3
ArGoGn 125 127 >2
U.Go 52 52 0
L.Go 73 75 >2
Rt 6 to Orbital plane 28 31 >3
Lt 6 to Orbital Plane 29 31 >2
Rt 6 to Mand Plane 32 35 >3
Lt 6 to Mand Plane 33 36 >3
Cd to Ptm 28 25 <3
N Ans 49 49 0
Ans Gn 67 70 >3www.indiandentalacademy.com

The values thus obtained from the tabulation were
analyzed statistically and the following ratio was obtained.
3mm of molar extrusion
3mm increased Lower anterior Facial height.
2Deg Increase in Mandibular rotation.
3mm Reduction From Condyle to Pterygo Maxillary Fissure Point
MoEx : LAFH : Ro Mad : Cd Ptm = 3 : 3 : 1 : 3 (2deg = 1mm)

Case Report Orthognathic….!
Sundari 23 Yrs Female
Teeth Placed in the Front
Ectomorphic Body Type, Mesocephalic Head,
Leptoprosophic Face.
Symmetrical Face , High Clinical FMA ,
Convex Profile,Incompetent Lip , &
Posterior Divergent
Class- II Molar & Canine , Plroclined Upper &
Lower Incisors,6mm incisor exposure,
Gummy Smile Over Jet of 6mm
& Over Bite of 3mm.
Reverse Orthodontics (15,25,34 & 44)extn &
strapped Up with PAE Roth .022’& Lefort I 5mm
of Upward Impaction.

PRE Rx PHOTOS

PRE TREATMENT OPG & CEPH

PRE SURGICAL

PRE SURGICAL
CEPH & OPG

PREDICTED CEPH
Maxilla & Molar
moved up by 5mm.
Red Predicted Face.
Blue Pre surgical

FACE BOW TRANSFER
MOCK SURGERY &
PREDICTED SPLINT

DURING SURGERY

IMMEDIATE
POST - OP

POST SURGICAL CEPH & OPG

POST - OP
SETELLING

FACE PREDICTION
(with ratio obtained)

PROFILE-COMPARISION

Future Scope…!
This study should be conducted on large group to
check for its “Reliability Constant”.
The muscle structures around the mandible plays a
major role in its movement & hence it should
be considered ( For which a study is in
progress to assess the muscles function of the
mandible with the help of Ultrsonography).
TMJ especially condyle is a complex structure & so
are is its movements ,hence a MRI & C.T study
will be more essential to check its function.
Once these Diagnostic aids become reachable
for the common man it would be easy for
every body to opt for prediction results, which
in turn would increase the efficacy of the
orthodontist

USG - -Study…!

Left Lateral Pterygoid - Protrusion

Right Lateral Pterygoid -Protrusion

Left Lateral Pterygoid - Excursion

Right Lateral Pterygoid-Excursion

Left Temporalis - Clenching

Right Temporalis - Clenching

Left Masseter- Clenching

Right Masseter- Clenching

CT SCAN….!

TMJ - CT…!

3-D RECONSTRUCTION…!

MRI - TMJ…!

MRI-SCAN…!

MRI-SCAN Land Marks…!

Close up view of TMJ Different Positions

Conclusion…!
With this study the clinicians is able to accurately
predict the “Mandibular Rotation”.
The results of this study can be used effectively during
treatment planning of surgical cases where pre
surgical orthodontics is necessary.
The “ Truth Of Future Orthodontics” is to use this
easy calculated value, for “Nature Gave You
The Face , But you Have To provide the
Expression” www.indiandentalacademy.com

A patriot is a
man working
for his
country's
future instead
of boasting of
its past.
Before I Conclude…..!

An
orthodontist is
a man working
for his
fraternity’s
future instead
of boasting of
its past.
According To Me….!

A Big Thank’s to the…!

Jaw - Geometry

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