Differential DiagnosisORTHODONTICS
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Differential diagnosis analysis system
Merrifield ,in his effort to establish a sound diagnostic basis for his directional force treatment using multibanded mechanotherpy ,introduced diagnostic analyses that allow clinician to determine
1)Whether & when are extractions necessary and 2)which teeth should be removed
Attainment of previously stated objectives require a through and accurate diagnosis that specifically identifies the major areas of disharmony. www.indiandentalacademy.com
Thus, Weber defines diagnosis as “ a determination of a disease from symptoms, data or tests, and the decisions and judgment made prior to treatment”.
Merrifield’s diagnostic philosophy can be outlined as follows:
1.recognise and treat within the dimensions of the dentition (non-expansion, when normal muscular balance exist.)
2 recognize the dimension of the lower face and treat for the maximal facial harmony & balance.
3.recognise and understand the skeletal pattern. Diagnose and treat in harmony with normal growth and developmental patterns.
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Any valid identification and classification of orthodontic & orthognatic disharmony should be based on the four major areas of the orthodontist responsibility
1.Facial 2.Dental 3.Cranial
4.Environmental.
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Facial disharmony
A study of the face & its balance or lack of it must be the first concern during a differential diagnosis. The clinician must have intuitive concept of a balanced face .
There are 3 factors that influences the balanced face or lack of it
1.the positions of teeth, 2.the skeletal pattern, 3.the soft tissue thickness.
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The facial balance is affected by the marked protrusion/ retrusion/ crowding of teeth. the lips are supported by the max. incisor teeth. Thus lip protrusion is the reflection of the amt. of max. incisor protrusion. Protruded teeth thus cause facial imbalance. Facial disharmonies are often the result of abnormal skeletal relationships. The clinician must understand the skeletal pattern & have the ability to compensate for abnormal skeletal relationships by changing the position of the teeth. (The FMA, is a skeletal angular value that is crucial in diff/dia. lower facial balance can be dramatically improved by using this knowledge). www.indiandentalacademy.com
Facial disharmony that are not the result of skeletal or dental distortion are generally the result of poor soft tissue distribution. this problem needs to identified during diff/dia. so that crucial dental compensations can be planned. ď Ž
Total chin thickness =upper lip thickness.
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(if it is,< ult ,the anterior teeth must be positioned upright further to facilitate a more balanced facial profile, because lip retraction follows tooth retraction.)
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Thus careful consideration of the positions of teeth, skeletal pattern, & soft tissue overlay will give crucial information about face & enable the clinician to determine whether dental compensations will improve facial balance. before initiating tooth movement.
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Its impact on the overlying soft tissue must be clearly understood.
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Whenever facial balance is present ,the ideal relationship of profile line is to be tangent to the chin & the vermilion border of both lips and should bisect the nose. This results in a pleasing & balanced profile.
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Similarly, on frontal view, the vermilion border of lower lip should bisect the distance between bottom of the chin & ala of nose. The vermilion border of upper lip should also bisect the distance between from the vermilion border of lower lip to ala of nose. These are universally accepted orthodontic standards for facial balance & harmony. www.indiandentalacademy.com
Several cephalometeric standards quantify facial balance. Two that have been found to be very useful are the1. Z angle
2.FMIA Z angle: This Angle was developed to further define facial esthetics & is an adjunct to the FMIA. It is the angle b/n the FH plane and soft tissue profile which quantifies Facial balance. NORMAL RANGE- 70o-80o. (ideal value- 75o â&#x20AC;&#x201C; 78o.) www.indiandentalacademy.com
Z angle is more indicated of the soft tissue profile than FMIA and is responsive to the maxillary incisor position.
Maxillary incisor retraction of 4 mm allows 4 mm of lower lip retraction & apprx. 3 mm of upper lip response.
It quantifies the combined abnormalities in the values of FMA, FMIA & soft tissue thickness and all have a direct bearing on facial balance.
If any of the 3 above component is not within the optimal range, differentiation can be made to determine which values are not optimum & why
It gives immediate guidance to anterior tooth reposition. www.indiandentalacademy.com
FMIA:
Tweed believed that this value was significant in establishing the harmony of the face. Tweed established a standard of 68o for individual with an FMIA of 22o – 28o. Standard should be 65o if the FMA is 30o or more, and the FMIA will increase if FMA is lower. www.indiandentalacademy.com
Cranial Disharmony:
A careful cranial analysis must include but if not be limited to study and understanding of the following information.
Skeletal Analysis Factors: FMA – It is the most significant value for skeletal analysis because it defines the direction of lower facial growth in both the horizontal and vertical dimensions. Normal Range- 22o – 28o. <FMA
>FMA
Deficient vertical growth. Excessive vertical growth.
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IMPA:
Defines axial inclination of mandibular incisors w.r.t. mandibular plane. It is a good guide to use in maintaining or positioning of the mandibular incisors in relation to the basal bone. Standard value – 88o. (indicates an upright incisors, with a normal FMA reflects optimal balance and harmony of lower facial profile) www.indiandentalacademy.com
SNA:
Indicates relative horizontal position of the maxilla to the cranial base.
Normal Range: 80o– 84o.
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SNB:
Indicates horizontal relationship of mandible to the cranial base.
Normal Range: 78o–82o.
<74o / >84o – Large maxillomandibular discrepancy. (orthognathic surgery indicated) www.indiandentalacademy.com
ANB:
It indicates horizontal relationship of maxilla to the mandible.
Normal Range- 1o - 5o.
>10o />-3o indicative of facial disproportion. (possibility of surgical assistance)
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AO-BO:
This indicates relationship of maxilla to mandible. More sensitive than ANB because it is measured at the occlusal plane. Normal Range: 0–4 mm.
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Occlusal Plane:
Occlusal plane value expresses a dentoskeletal relationship of OP to FH plane. Normal Range: 8o – 12o. Values < or > normal range indicates more difficulty in treatment. In most orthodontic corrections, the original values should be maintained or decreased. An > indicated loss of control & instability. www.indiandentalacademy.com
Facial Height Index:
Andre Horn studied the relationship of AFH to PFH, developed Facial Height Index. He found that Normal PFH is 0.69 or 69% of AFH. Normal Range: 0.65 – 0.75. If the value is < or > this range, the malocclusion is difficult to correct.
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Facial Height Ratio:
Facial height change ratio is valuable in the evaluation of treatment interval changes.
Ratio of two times as much of PFH as AFH during treatment is ideal for correction of class II div 1.
However, even more important is the volume of the change.
Merrifield and Gebeck reported 2 to 1 increase in PFH to AFH in the sample of successfully treated malocclusion.
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Jim Gramling of Jonesboro, Arkansas, research director of Tweed foundation compiled a large sample of successful & unsuccessfully treated Class II malocclusion by the foundation and compared the results.
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In the successful sample, FMA was controlled, FMIA , IMPA In the unsuccessful sample, FMA , FMIA remained same or decreased, IMPA or remained the same. There was not as much Z angle increased in unsuccessful sample. SNA reduction was similar. AO-BO reduction was unsatisfactory. Y axis & SNB remained the same for both samples. By studying the data from two samples, it can be concluded that in unsuccessful Class II treatment, the mandibular incisor position was not corrected or if corrected, the correction was subsequently compromised by excessive, unreciprocated use of Class II elastics in an attempt to estb proper AP maxillo mandibular dental relationships. www.indiandentalacademy.com
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