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Executive | Lab Tech Talk

Lower Two Way Sagittal (with up to four clasps)

Category:

Appliance Purpose / Function:

Three-way Sagittal appliances are intended to create space in a crowded dentition, but they do so by lengthening the patient’s arch. Screws imbedded in the acrylic plate are positioned so that they open in an anterior/posterior direction. When they are activated, the posterior teeth are gradually pushed back and the anterior teeth are gradually pushed forward. An additional screw positioned on the midline so that the arch can be widened and lengthened.
Appliance Components:

  • Adams Clasp on the 1st molars
  • Ball Clasp between the 1st and 2nd bi-cuspids
  • Distalizing Screw on each side of arch
  • Acrylic Plate

Suggested Materials:
Wire: Chromium Cobalt or Stainless-Steel
Screws- 6mm vector screw

Options:
Posterior occlusal acrylic (bite blocks)

Appliance Fabrication Standards:
Clasps must be properly adapted to give maximum retention
Acrylic must fully encase the screws and be thick enough to resist breakage
The wires on the tissue side are formed about 1mm off tissue to provide clearance for the acrylic

WIRE STANDARDS:

  • The standard design has Adams clasps on the first molars and ball clasps between the first and second bicuspids. The clasping scheme may be changed according to Client preference or the teeth present in the arch.
  • Special attention must be paid to the placement of the acrylic retention portion of the clasps to avoid interfering with the cuts that must be made for the sagittal screws
  • Acrylic borne 6mm vector screws must be placed in the middle third of the sagittal walls with the long axis of the screw lined up approximately with the gingival margins of the posterior teeth on that side of the arch. The split of the screw must be positioned approximately in-line with middle of the second bicuspid or second primary molar

ACRYLIC STANDARDS:

  • Uniform overall thickness of approximately 2mm except in area of screws where there should be enough acrylic to cover the acrylic borne screws
  • All wires completely encased in acrylic on lingual portion
  • Inferior border tapered towards the tissue with a rounded edge (thin, sharp knife-like edges not acceptable)
  • Acrylic must be kept away form the lingual frenum for patient comfort
  • Acrylic must have full contact with all lingual surfaces of every posterior tooth involved in the requested plate design with the exception of the embrasures. There must be no “cupped out” areas around the teeth that can act as a food trap, instead the acrylic must butt directly against each tooth without dipping
  • The splits must begin at the embrasure between the cuspids and first bicuspids and proceed towards the midline until they are level with the superior portion of the tabs on the screws. From there the splits must be directed towards the tabs of the screws and continue on this line until they connect with the tabs. They must then continue from the inferior portion of the tabs thru the inferior border of the plate. These cuts must be very clean and straight to avoid binding when the screw is activated.
  • The tissue side of the plate is generally left alone unless otherwise requested by the Client, but it must be inspected for pits/voids or sharp areas. Pits/voids must be patched with acrylic, and sharp areas must be carefully ground smooth without removing too much acrylic. Additionally, the tissue side of the two splits must be inspected and any sharp edges carefully removed without removing too much acrylic