T m diagnosis

TWEED-MERRIFIELD
DIAGNOSIS
Identification & Classification of
Orthodontic & Orthognathic
disharmonies
www.indiandentalacademy.com

Tweed’s contribution
 IMPA:
 Tweed treated series of cases first by non extraction,
then by extracting 4’s, if necessary. The results of the
extraction cases were more gratifying and he was near
to his visualization of balance and harmony of the face.
In these successfully treated cases he observed that
the inclination of the lower incisors to the mandibular
plane was in the range of 90 (+5 or –5).
 Thus he concluded that normal range of
mandibular incisor inclination, when related
mandibular plane is 90+ 5.

 FMA
 Patients were placed in the head holder with head
oriented on FH plane using the forefinger and thumb,
he outlined and extended the mandibular plane
posteriorly to connect to FHP with the result of this
study, be concluded that the normal variation
of FMA is 16˚-35 ˚, with average of 25 ˚
 FMIA
 The sum of all the angles in a triangle is 180˚, if the
norm for IMPA is established at 90˚, norm for FMA
at 25˚, the third angle FMIA must be 65˚
 All the patients with large FMA need compensation
of mandibular incisor inclination.
 Meaning in high angle cases, the lower incisor are
slightly proclined.

Merrifield’s contribution
 Merrifield’s diagnostic philosophy outlined follows:
 Recognize and treat with the dimension of dentition.
This means non-expansion of malocclusion when the
normal muscular balance exists.
 Recognize the dimensions of lower face and treat for the
maximal facial harmony and balance.
 Recognize and understand the skeletal pattern.
Diagnose & treat in harmony with normal growth &
development

Facial
Dental
Cranial
Environmental
Diagnosis of Orthodontic and
Orthognathic disharmony
should be based on four major
areas

Facial Disharmony
 Facial proportion isoneof thegreatest challenges&
opportunitiesfor clinical orthodontist
 Most patientsdesire& demand esthetic
improvement, which includesbeautifying thesmile
& allowing normal lip postures
 Merrifield & othershavepointed out that theupper
& lower lipsarevery responsiveto maxillary incisor
tooth movements.
 Merrifield concluded that 4mm of upper incisor is
accompanied by 3mm of upper lip retraction & 1mm
of upper lip thickening

 Thechin-lip relationship can bedefined
 And also berelated to other elementsin facesuch as
thenose, naso-labial contour, thesmilelineetc.
 Lower facial contour isaresponsibility of orthodontic
specialty
 LFH isvery responsiveto proper tooth repositioning
 And in extremecasessurgical intervention supervised
by orthodontist can achievenecessary balance&
harmony of lower face
 Hence identifying & classifying facial
disharmonies must be an integral part of our
service to our patients & recognized as one
of our first responsibilities

Dental Disharmony
 Teeth, their relationship to each other 7 to the
supporting boneshavebeen theoverriding concern
of Orthodontist sinceAngle.
 Angle’ssystem isconsidered standard for morethan
100 years,.
 However disharmoniesof teeth can bebetter
understood & identified by using acomprehensive
spaceanalysissystem including all 32 teeth &
determining whether aspacedeficit or spacesurplus
existsaswell asanalysisof theocclusal relationship
of maxillary teeth to themandibular teeth

 Orthodontic treatment isaspacemanagement
procedure. Spacecan neither becreated nor
destroyed by orthodontist
 Spacemanagement must usetheelimination of
certain dental unitsto allow spatial relationship of
theremaining dental units. Thisisnot spacemaking,
but it isjudiciously using theavailablespace
 It isalso crucial to identify theareasof dentition that
havespacedeficit or surplus. In thisway the
orthodontist can most advantageously usespace
management to correct themost overriding
disharmonies

Cranial Disharmony
 To strivefor aharmoniousrelationship of maxilla&
mandibleto thecranial base& to each other isan
important responsibility of theorthodontist
 Disproportion of thesebonesor malrelationshipswith
other bonesin thecranium can befavorably
influenced by dental repositioning during growth
period.
 Orthognathic surgical intervention , supervised by
orthodontist, in extremedisharmoniescan result in re-
establishing abetter relationship between maxillato
themandibleand to thesurrounding bonesof the
cranium

Environmental
Disharmony Themost challenging areaof orthodontic treatment isto
correct environmental abnormalities.
 Henceorthodontist must understand mother nature&
knowledgeof thefunctional and static elements
associated with dentition, face& cranium.
 Bones, muscles, blood supply, nervesupply, joints&
other soft tissuesmake-up theenvironment
 Functional elements:- Joints, musclesof
expression, mastication, deglutition, speech & breathing
 Static elements:- Bone, cartilage& soft tissue

Classification of
Orthodontic &
Orthognathic
disharmonies
 Facial
 Horizontal Disharmonies
 Disharmoniesof facial convexity
 Disharmoniesof facial concavity
 Vertical Disharmonies
 Excessivefacial height
 Diminished facial height

 Dental
 Arch length disharmonies
 Mandibular arch spacedeficit
 Mandibular arch spacesurplus
 Maxillary arch spacedeficit
 Maxillary arch spacesurplus
 Arch Width disharmonies
 Mandibular arch width deficit
 Mandibular arch width excess
 Maxillary arch width deficit
 Maxillary arch width excess
 Occlusal Relation disharmonies
 Distal occlusion
 Mesial occlusions

 Cranial
Horizontal disharmonies
 Mandibular retrognathism
 Mandibular prognathism
 Maxillary retrognathism
 Maxillary prognathism
Vertical disharmonies
 Hyperdivergent cranial patterns
 Hypodivergent cranial patterns

 Environmental
Internal
 Muscles & other soft tissue disharmonies
 Bone & joint disharmonies
External
 Habits
 Trauma

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