Truly Invisible Braces: The Story of Serial Disking Dr Jabbarifar Associate Professor IsfahanUniversity School of Dentistry 2009
objective part 1 Discuss the transition of the primery dentition to the permanent dentition. part 2 Review a simplified Mixed Dention Analysis procedure. part 3 Discuss indications and procedures for Serial disking .
Part 1 - Transition From Primaryto Permanent Teeth • Transition of molar relationships • Transition of Incisors • Transition of Buccal Segment • Leeway Space • Late Mesial Shift
Flush Terminal Plane Distal Mesial
Mesial Step Distal Mesial
Disto Step Distal Mesial
Mesio Step Mesial Distal
Incisor Liability • Permanent incisors are larger than primary incisors • This difference in size is termed "incisor liability“ • How does the body create enough room for the larger, permanent incisors?
Overcoming Incisor Liability • Interdental spacing of primary incisors • Intercanine arch width growth • Labial positioning of the permanent incisors • Favorable size ratio between the primary and permanent incisors
Leeway Space • Sum of (c-d-e) > (3-4-5) • This allows more space for 3-4-5 • This "leeway space" averages 1.7 mm. in the mandibular buccal segment; 0.9 in the maxillary buccal segment
Late Mesial Shift • Refers to mandibular permanent molar moving mesially • Good news - if permanent molars are ETE, late mesial shift allows mandibular molar to move into a Class I occlusion • Bad news - the above reduces arch length
Late Mesial Shift (cont.) FTP Molar moves into this space... Class I
Part 2 Mixed Dentition Analysis • Purpose: predict amount of crowding after permanent teeth come in • Timing: mixed dentition • Materials: Boley gauge • Where: At the chair
4 Step Simplified MDA • Basic Steps • Mentally align incisors • In other words…. “how far over onto the primary cuspid will it take to make the incisors straight?” • Measure space left over for C, B1, B2 • Predict size of C, B1, B2 • Compare size vs. space for C, B1, B2 to determine amount of crowding
Step 1 MDA Methodology • Measure mesial-distal diameter of the mandibular incisors, sum and divide by two
Step 2 MDA Methodology • Select a midline point • Expand the Boley gauge to the amount determined in Step 1 • Mark the point on each primary cuspid from the midline point • This represents the space required for well aligned incisors
11.7 mm 11.7 mm
Step 3 MDA Methodology • Measure from the point on each cuspid (derived in Step 2) to the mesial of the first permanent molar • This represents the space available for the permanent cuspid and bicuspids (C, B1, B2)
22.4 mm 22.7 mm
Step 4 MDA Methodology • To the number derived in Step 1, add 10.5 mm for the mandibular teeth • This represents the size of the permanent cuspid and bicuspids in each quadrant • Subtract the number determined in Step 4 (the predicted size of C, B1, B2) from the number determined in Step 3 (the amount of space for C, B1, B2) for both sides of the arch
MDA Methodology • If the space available is less than the amount of tooth mass, a negative number will result • This number is the predicted amount of crowding
Allowance for Late Mesial Shift • If permanent molars are end to end, mandibular molar should move mesially to obtain Class I interdigitation. • This will decrease the arch length available for 3-4-5. • Figure 1.7 mm. per side with ETE relationship.
MDA Procedure Maxillary Arch • Mentally align the maxillary incisors as was done in the mandibular arch • Measure the space left over for the maxillary C, B1, B2 • Add 11.0 mm. to 1/2 the sum of the MANDIBULAR INCISORS to predict the size of the maxillary C, B1, B2 • Subtract the predicted size from the space available
Part 3 Serial Disking • Result without treatment • Description of Ideal Patient • Description of Technique • Steps in Serial Disking
2nd Premolar EruptionLate mesial shift of 1st molar Spaces close from posterior!!!
Result Without Disking • Same anterior crowding • Blocked out cuspids • Less arch length to work with
Ideal Patient for Serial Disking • Class I molars and cuspids (Not FTP) • Normal overbite and overjet • 3 mm or less of anterior crowding
Serial Disking Technique • 699, 169 carbide bur or tapered diamond • Anesthetic considerations • local • electronic • none • Prepare mesial surface as stainless steel crown prep • No ledges!…. Feather edge margin
Serial Disking Steps:Mandibular Arch • Lateral incisor eruption - disk mesial of primary cuspids • Permanent cuspid eruption - disk mesial of either 1st or 2nd primary molar