SPECIAL COMMENT ON EXTRACTION OF THE 1ST MAXILLARY AND MANDIBULAR PREMOLARS
This extraction pattern use used to solve any orthodontic problems for more than 100 years. In many schools of thinking it is used to solve all kinds of malocclusions, no mater it is Class I, Class II or Class III malocclusion and all of its variations. The author wishes to share some opinions after 40 years of experience in orthodontics.
1. Anchorage Loss
This extraction pattern is likely to allow anchorage loss situation to occur, easier than the extraction pattern of the maxillary 1st premolars and mandibular 2nd premolars.
As a matter of fact, bony resistance against moving the molars forward in the mandible is 3 times greater than those in the maxilla. This means that the mandibular M1 has less tendency to move mesially (1-2 mm) while the maxillary M1 has higher tendency to move mesially (3-5 mm) causing in end effect a Class II end on molar relationship. Molar fulcrum and TMD is invited.
So, it requires much more intensive use of headgear and Class II elastics. If the patients cooperation and parental support are poor, the outcome is always compromise e.g. molar fulcrum situation will occur due to the extrusion of the molars.(see sheet ”Molar fulcrum”)
2. Collapse of the mandibular anterior teeth
After extraction of the 1st mandibular premolars, the dental support from distal become less than pretreatment. The lower lips itself tend to exert pressure which lead to “Collapse of the mandibular anterior teeth”. Mandibular canines will tip distally, and the mechanics used to close the extraction space will demonstrate additional effect making a cup shaped mandible and prominent pogonion.
3. Facial Vertical Dimension is not reduced as claimed by many.
This extraction pattern is to align the dental arches and close the bite. Reduction of protrusion will help facial balance but not changing facial vertical dimension.
There are several researches demonstrated that the patients vertical dimension with this type of extraction pattern are unchanged, so it is not suitable for treatment of any patients with high angle face and weak chin, where bite closing and mandibular anterior rotation –to produce chin prominence- are required.
4. Unable to open the bite or deep bite become deeper.
This is due to failure to control the vertical dimension. With time the mandibular brackets and its bases cannot be seen and the case gets worse before entering the contraction phase. Both maxillary and mandibular anterior teeth were extruded and lingually rolled. These extrusion can be well prevented by engaging the M2, and adding sweep and intrusion bend into the maxillary arch wires.
5. Overretraction and extrusion of the maxillary anterior teeth. Careless operators usually retract maxillary anterior teeth with small arch wires, which wire stiffness is obviously not enough for this objective. Bowing Effect is a good evidence – extrusion of the anterior and posterior segments, and the open bite in the middle segment will always be seen. And the worse is probably the idea of Straight Wire Appliance, which mentioned that wire bending is not necessary. In fact, compensatory bends are always compulsory. So in this case the over jet is reduced by extrusion of the maxillary anterior teeth as seen in many tracings and superimposition of pre- and post-treatment of cephalograms, resulting in “Gummy Smile”.
6. Deteriorate the function and TMD
As the result from no. 5 and the operator fails to perform proper interincisal angle, the mandible will be entrapped, the patients cannot perform protrusive mandibular movement, will feel very discomfort and TMD is preprogrammed.
7. Ruin of the facial esthetics
Over-retraction of the maxillary and mandibular anterior teeth tends to change the patient’s soft tissue profile much more than any other types of extraction patterns. In the worse case the facial profile become severely concave with weak lip support and wrinkle on the face. The chin becomes sudden changed and the patient gets old instantly. With time periodontal problem will follow as the roots of the anterior teeth are tipped into the labial cortical bone.
Schwan Somsiri, B.Sc., D.D.S.
Diplomate German Board of Dentofacial Orthopedics,
Practice limited to Orthodontics, Surgical Orthodontics,
TMD & Migraine
Orthopedic Early Treatment for Growing Class II and III
ศูนย์ทันตกรรมจัดฟัน และข้อต่อขากรรไกร Orthodontic and Jaw Joint (TMD) Center
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File: SPECIAL COMMENT ON EXTRACTION OF THE 1ST MAXILLARY AND MANDIBULAR PREMOLARS
v. 2012.03.15
v. 2020.03.06
Course No.7/2011
