ABPros Prosthodontics cheat sheet

Prognosis is assigned per tooth, not per arch: factors include mobility, furcation involvement, crown-to-root ratio, residual bone support, and endodontic status.

A crown-to-root ratio of 1:1 is generally the minimum acceptable for a tooth intended as a fixed partial denture abutment; 2:1 or worse is a guarded-to-poor prognosis.

Ante's law: the total pericemental area of the abutment roots must equal or exceed that of the teeth being replaced; a tapered premolar abutment adjacent to a molar span frequently violates it.

Furcation involvement is classified I-IV (Glickman) or by horizontal/vertical bone loss (Hamp); Class III-IV furcations carry a guarded prognosis and are relative contraindications to FPD abutment use.

Mobility is graded 0-3 (Miller); Grade 3 (greater than 1 mm buccolingual plus vertical depression) signals loss of attachment insufficient for a load-bearing abutment.

A tooth with a questionable prognosis should be extracted before, not after, fabrication of an adjacent prosthesis, because later loss compromises the span design.

Diagnostic casts mounted in a semi-adjustable articulator with a facebow permit evaluation of occlusal plane, curve of Spee, and interocclusal space before committing to a design.

Vertical dimension of occlusion is assessed at rest minus freeway space (typically 2-4 mm anteriorly); arbitrary alteration without cephalometric or phonetic support risks phonetic and esthetic failure.

Finish line selection: chamfer (0.3-0.5 mm) for metal and metal-ceramic margins, shoulder or deep chamfer (1.0-1.2 mm) for all-ceramic, knife-edge is contraindicated for any cast or ceramic restoration.

Axial reduction for metal-ceramic is approximately 1.0-1.5 mm; for zirconia and lithium disilicate, 1.0-1.5 mm axial and 1.5-2.0 mm occlusal to resist flexure.

Taper (total occlusal convergence) for a single cast crown should be 10-20 degrees; excessive taper reduces retention, insufficient taper prevents seating.

Retention and resistance form: resistance requires a preparation height-to-width ratio of at least 0.4; short crowns need grooves, boxes, or pins to supplement.

Marginal fit standard: clinically acceptable cast or milled margins are typically within 25-40 micrometers; ceramic margins should be evaluated with an explorer and radiograph at interproximal seats.

Pontic design: modified ridge lap for esthetic anterior spans, sanitary or ovate for posterior; ovate pontics require a soft-tissue socket and 2-3 mm of tissue depth.

Connector cross-sectional area minimums: about 9 mm squared for metal-ceramic posterior, 12-16 mm squared for zirconia posterior to resist fracture.

Occlusal contacts on a single crown are adjusted in maximum intercuspation and excursive movements before cementation; heavy centric contacts cause fracture and pulpal symptoms.

Complete denture support derives from the residual ridge; stability resists horizontal forces; retention resists vertical dislodging forces.

Border molding captures the functional sulcus; the denture border should extend into the vestibule to the mucogingival junction and be 2-3 mm short of the vibrating line posteriorly.

Posterior palatal seal provides retention via a valve seal at the junction of the hard and soft palate, terminating at the fovea palatini or slightly anterior.

Balanced occlusion in complete dentures requires bilateral simultaneous contacts in centric and eccentric positions; nonbalanced contacts cause tipping and soreness.

Neutral zone: the space where forces from tongue, lips, and cheeks are in equilibrium; teeth placed in this zone improve stability and patient tolerance.

Abutment selection for RPD: only teeth with adequate crown-root ratio and periodontal support; a lone distal abutment with no cross-arch stabilization is a guarded design.

Major connector design: maxillary palatal plate or bar, mandibular lingual bar (requires 4 mm of lingual height) or lingual plate when height is insufficient; borders must be 3-4 mm from the gingival margin.

RPD clasps: circumferential (Akens) for bounded saddles and molar retention, bar (Roach) for tissue-ward approach on premolars; reciprocal arms must oppose the retentive arm.

Implant survival is enhanced by primary stability and a minimum insertion torque; immediately loaded implants generally require torque above 30-35 Ncm and adequate bone density (Type II-III).

Minimum inter-implant distance is 3 mm between adjacent implants; minimum implant-to-tooth distance is 1.5 mm to preserve the interimplant papilla and crestal bone.

Bone density classification (Lekholm and Zarb / Misch): Type I dense cortical to Type IV low-density trabecular; Type IV sites show lower primary stability and require undersized drilling or delayed loading.

Occlusal scheme for implants: flat, shallow cusp inclines, narrower occlusal tables, and no working-side contacts in lateral excursion reduce off-axis load and screw loosening.

Ceramic strength hierarchy for clinical use: zirconia (about 900-1200 MPa flexural) greater than lithium disilicate (about 360-450 MPa) greater than leucite-reinforced glass (about 100-160 MPa) greater than feldspathic (about 60-100 MPa).

Resin cement is indicated for etched glass-ceramic and for implant-supported restorations where retrievability is desired; zinc phosphate and glass ionomer are not indicated for bonded ceramic.

Implant success criteria (Buser/Albrektsson): less than 0.2 mm annual bone loss after the first year, no mobility, no pain or neuropathy, and no peri-implant radiolucency.

Screw-retained versus cement-retained: screw retention favors retrievability and posterior or multi-unit cases; cement retention favors esthetics and divergent angulation but carries retained cement risk.