CDT cheat sheet

Residual ridge resorption is fastest in the first 6 months after extraction and is greater in the mandible than in the maxilla; it continues for the life of the patient.

Freeway space averages 2–4 mm; the occlusal vertical dimension is adjusted until this interocclusal rest space is present.

The posterior palatal seal is placed at or near the vibrating line, between the fovea palatinae and the junction of the hard and soft palate.

The labial surface of the maxillary central incisors is set about 8–10 mm anterior to the incisive papilla, which lies on the midline.

The retromolar pad must be covered by the mandibular denture base; its midpoint approximates the level of the posterior occlusal plane.

Posterior teeth are arranged in the neutral zone - the space between the tongue, lips and cheeks where the muscular forces balance.

Monoplane posterior teeth are indicated for severely resorbed ridges and for patients with poor neuromuscular control because they generate less horizontal force.

PMMA denture base resin polymerizes with linear shrinkage of about 0.4–0.5%, which alters the occlusion; a laboratory remount with selective grinding corrects it.

A flabby, displaceable anterior maxillary ridge is recorded with a separate mucostatic impression and the cast is relieved over that area so the tissue is not compressed.

Kennedy Class I = bilateral distal extension; Class II = unilateral distal extension; Class III = bounded edentulous area with natural teeth posterior to it; Class IV = single edentulous area crossing the midline.

Applegate's rules: classify after all extractions are complete; the most posterior edentulous area determines the class; a modification is an additional edentulous area.

A Kennedy Class IV arch has no modification spaces, and teeth not planned for replacement (often third molars) are not counted in the classification.

An occlusal rest seat should be at least 1 mm deep at the marginal ridge, with a floor inclined toward the centre of the tooth and an angle of less than 90° to the proximal surface.

A cast circumferential clasp engages 0.25 mm of undercut; a bar (Roach) clasp also engages 0.25 mm but approaches from the gingival direction and suits undercuts in the gingival third.

A mandibular lingual bar needs at least 4 mm of height and 2 mm of thickness, with its superior border about 3 mm below the gingival margin and at least 4 mm from the floor of the mouth.

In the RPI design (mesial rest, proximal plate, I-bar) the I-bar tip contacts the mesiobuccal undercut and the mesial rest reduces torque on the distal extension abutment.

Distal extension bases are recorded with an altered cast (functional) impression so the edentulous ridge is captured under load; indirect retention is placed as far as possible from the distal extension, roughly perpendicular to the fulcrum line.

Chamfer of about 0.5 mm is used for cast metal and metal-ceramic margins; a shoulder of 1.0 mm or a beveled shoulder is used for ceramic margins; a knife-edge margin is contraindicated.

Occlusal reduction for metal-ceramic is 1.5 mm over functional cusps and 1.0 mm over non-functional cusps; all-ceramic crowns require about 2.0 mm.

Axial reduction of 1.0–1.5 mm combined with total occlusal convergence of 10–20° gives the best balance of retention, resistance form and path of insertion.

A ferrule of 1.5–2.0 mm of sound axial dentin encircling the core increases fracture resistance of endodontically treated abutments.

Ante's law: the root surface area of the abutments must equal or exceed that of the pontics; crown-root ratio should be no worse than 1:1.

A nonrigid connector is used at a pier abutment, where the lone tooth would otherwise act as a fulcrum, and in long-span fixed partial dentures.

Die spacer of 25–50 µm creates room for the luting agent; zinc phosphate cement has a film thickness of about 25 µm.

Eugenol-containing provisional cement must be completely removed before adhesive resin cementation because residual eugenol inhibits polymerization of the resin.

Flexural strength: feldspathic 60–100 MPa, leucite-reinforced 100–160 MPa, lithium disilicate 360–400 MPa, zirconia 900–1200 MPa.

Etch glass ceramics with hydrofluoric acid - 9.5% for 60–90 s on feldspathic and leucite-reinforced ceramics, 5% for 20 s on lithium disilicate - then apply a silane primer.

Zirconia and alumina cannot be etched; use airborne-particle abrasion with 50 µm alumina and an MDP-containing primer for resin bonding.

The veneering porcelain should be left in compression at the interface, so the metal framework is given a slightly higher coefficient of thermal expansion than the porcelain.

Zirconia toughening is transformation-based; sintering shrinkage is about 20–25%, and low-temperature degradation (aging) is its main long-term concern.

Lithium disilicate is adhesively bonded with resin cement; light-cured cement is used only where the ceramic is thin enough for adequate light transmission.

A bonded glass-ceramic veneer needs 0.5–0.7 mm of thickness, while an all-ceramic crown typically needs 1.0–1.5 mm of axial thickness.

Firing must exceed the glass transition temperature of the ceramic; underfiring leaves porosity and reduces both strength and esthetics.

Angle Class I: mesiobuccal cusp of the maxillary first molar in the buccal groove of the mandibular first molar; Class II: mandibular molar distal; Class III: mandibular molar mesial.

Cephalometric means: SNA 82°, SNB 80°, ANB 2°, FMA 25°, IMPA 90°, upper incisor to SN 104°.

Leeway space is about 0.9 mm per side in the maxilla and 1.7 mm per side in the mandible.

Light continuous force ranges: intrusion 10–20 g, tipping 35–60 g, translation 100–150 g; heavier forces cause hyalinization and undermine resorption.

Anchorage is classified as maximum, moderate or minimum and can be reinforced with headgear, temporary anchorage devices or palatal coverage.

Andrews' six keys: molar relationship, crown angulation, crown inclination, absence of rotations, tight contacts and a flat occlusal plane.

Cervical headgear distalizes and extrudes the maxillary molars; high-pull headgear distalizes and intrudes them.

Cervical vertebral maturation staging on a lateral cephalogram estimates the pubertal growth spurt and the timing of orthopaedic treatment.