Fixed prosthodontics: crowns, bridges and dental implants

In short

Fixed prosthodontics restores damaged teeth and replaces missing ones with restorations the patient cannot remove — crowns (single teeth), fixed partial dentures or bridges (short spans supported by prepared natural teeth), and implant-supported prostheses (titanium fixtures anchored in bone). It is the highest-revenue clinical discipline in Indian private practice, and the third- and fourth-BDS Prosthodontics papers plus the clinical/viva in Prosthodontics and Crown & Bridge examine it heavily. Entrance tests (NEET-MDS, INI-CET, AIIMS/PGI) ask preparation geometry, Ante's law, osseointegration, impression materials and cement chemistry almost every year. Clinically it demands conservative but adequate tooth reduction, correct finish-line design, accurate impressions and occlusion, and — for implants — case selection by bone volume and systemic status. Employers (corporate dental chains, hospital dental departments, dental labs, implant and CAD/CAM companies) test exactly these points.

Explained

Terminology, classification and case selection

• Crown (full veneer): an extracoronal restoration covering all axial walls and the occlusal surface. Partial veneer: covers some surfaces (3/4, 7/8 crown). Onlay: covers cusps; inlay is intracoronal only.
• Indications for a crown: extensive caries or fracture, endodontically treated posterior teeth (cuspal protection), severe attrition or erosion, hypoplasia/discolouration, abutment for an FPD or RPD rest.
• Fixed partial denture (FPD) components: retainer (restoration cemented on the abutment), abutment (tooth or implant bearing the load), pontic (artificial tooth filling the space), connector (rigid — solder/cast joint; or non-rigid — key-keyway, stress-breaking).
• FPD classification: by support — tooth-supported, implant-supported, tooth-implant hybrid (generally avoided, differing mobility); by design — conventional rigid, cantilever (abutment on one side only), spring cantilever (rare, anterior), fixed-fixed, fixed-movable, resin-bonded (Maryland/Rochette), hybrid.
• Abutment evaluation: crown-to-root ratio ideally 1:2, acceptable 1:1.5, maximum 1:1; root form (broad, curved, multirooted better than conical); periodontal attachment; absence of mobility beyond Miller grade I; angulation and parallelism.
• Ante's law: the combined pericemental (root surface) area of the abutments should equal or exceed that of the teeth being replaced. A guideline, not a proven rule, but examined as stated.
• Pontic designs: ridge-lap (unhygienic, obsolete), modified ridge-lap (standard aesthetic posterior/anterior choice — buccal contact only), sanitary/hygienic (no tissue contact, mandibular posterior), modified sanitary (Perel), conical/bullet (mandibular posterior, knife-edge ridge), ovate (into a healed socket/papilla-preserving site, best aesthetics). Tissue surface of any pontic must be highly glazed and cleansable; contact should be passive on keratinised ridge, never pressure.
• Replacement decision in India: FPD (quick, no surgery, 3-unit cost roughly ₹9,000-45,000 by material) vs implant (preserves neighbouring teeth, 4-9 month timeline, ₹25,000-60,000 per implant plus crown in most urban practices — figures vary widely by city and brand).

Principles of tooth preparation

Five classical principles (Shillingburg): preservation of tooth structure, retention and resistance, structural durability, marginal integrity, preservation of the periodontium.

• Taper/convergence angle: total occlusal convergence ideally 6° (2-3° per wall); retention falls sharply beyond 20°. Too little taper risks undercuts and seating failure.
• Retention resists removal along the path of insertion; comes from near-parallel walls, length, surface area, cement, roughness. Resistance resists oblique/tipping forces; from preparation length, box forms, grooves, pins.
• Reduction amounts (typical): occlusal 1.5-2.0 mm on functional cusps, 1.0-1.5 mm non-functional; axial 1.0-1.5 mm for PFM, 0.5 mm for full-metal crown, 1.0-1.5 mm for monolithic zirconia (0.5-0.8 mm possible with high-strength zirconia); incisal 1.5-2.0 mm; functional cusp bevel on the buccal cusps of mandibular and the lingual (palatal) cusps of maxillary posteriors.
• Finish lines: feather edge (no bulk, poor), chisel, chamfer (ideal for cast metal and zirconia — defined, conservative, stress-free), shoulder (90°, needed for all-ceramic to support porcelain, 1.0-1.5 mm), bevelled shoulder (PFM metal collar), sloped/radial shoulder.
• Finish-line position: supragingival wherever aesthetics allow (easier impression, cleansable, less inflammation); equigingival or subgingival only for aesthetics, caries extension, short clinical crown or existing restoration. Never violate the biologic width (~2.04 mm average: 1.07 mm connective tissue + 0.97 mm junctional epithelium, plus sulcus); keep the margin ≥2.5-3.0 mm from the alveolar crest or do crown lengthening.
• Path of insertion must be common to all abutments in an FPD — checked with a single-eye view at arm's length or a surveyor on the cast.
• Finishing: round all internal line angles, remove undercuts, smooth with fine diamond/carbide; sharp angles concentrate stress in ceramics.
• Pulp protection: copious water spray, intermittent light pressure, new diamonds; temperature rise above ~5.5 °C risks pulpal injury; prepare with a well-fitting provisional placed the same day.

Materials, impressions, provisionals, cementation

• Restorative materials: full-metal (Type III/IV gold alloys, Ni-Cr, Co-Cr — strongest, most conservative, poor aesthetics); PFM/metal-ceramic (metal coping + feldspathic veneer; strong and aesthetic; needs more reduction; metal shows at the margin); all-ceramic — feldspathic, leucite-reinforced (IPS Empress, ~120 MPa), lithium disilicate (IPS e.max, ~360-400 MPa), zirconia (Y-TZP, ~900-1,400 MPa flexural, now the commonest Indian lab crown); fibre-reinforced/PEEK and temporary acrylic/bis-acryl.
• Material choice rule of thumb: anterior single tooth with good aesthetics → lithium disilicate; posterior heavy function/bruxism or long span → zirconia or metal; minimal reduction possible → gold; short span resin-bonded with intact enamel → zirconia/metal Maryland wing.
• Impression materials: addition silicone (PVS/polyvinyl siloxane) — dimensionally most stable, hydrophobic (needs dry field), best for multiple units and implants; polyether — hydrophilic, stiff, excellent for implants; condensation silicone (alcohol by-product, shrinks); polysulfide (long setting, foul odour); agar/alginate not acceptable for fixed work.
• Techniques: one-step and two-step putty-wash, dual-arch (triple tray), custom-tray monophase; gingival displacement by retraction cord (plain or with aluminium chloride/epinephrine), paste systems, electrosurgery or rotary gingival curettage. Digital intraoral scanning replaces the impression in CAD/CAM workflows.
• Provisional restorations must protect the pulp and periodontium, maintain position and occlusion, and allow aesthetic/phonetic trial — custom (direct bis-acryl in a matrix, indirect acrylic) or preformed (polycarbonate, metal shell). Luted with non-eugenol zinc oxide or temporary resin cement.
• Luting cements: zinc phosphate (oldest benchmark, mechanical retention only, no adhesion, low initial pH); zinc polycarboxylate (chemical bond to tooth, kind to pulp); GIC (fluoride release, chemical bond, moisture sensitive while setting); resin-modified GIC (common for zirconia and metal); resin cement (highest strength, essential for resin-bonded bridges, veneers and etchable ceramics; total-etch, self-etch or self-adhesive); adhesive resin (4-META, phosphate monomer) for metal/zirconia bonding.
• Surface treatment: etchable ceramics (lithium disilicate, feldspathic) → 5-9% hydrofluoric acid + silane; zirconia (non-etchable) → airborne-particle abrasion + MDP-containing primer/cement; metal → sandblast + alloy primer.
• Trial and finish sequence: metal try-in (fit, margin, occlusion) → bisque trial (shade, contour, contacts) → glaze → cementation under rubber dam/isolation → remove excess cement completely (retained cement is a leading cause of peri-implantitis) → check occlusion in MIP and all excursions, recall.

Occlusion, aesthetics and failures in crown and bridge

• Restore to the patient's existing accepted scheme: MIP contacts on cusp tips/fossae, no interference in protrusion or lateral excursions, anterior guidance preserved, mutually protected occlusion where present.
• Articulators: semi-adjustable (Hanau Wide-Vue, Whip Mix) with facebow transfer for multi-unit work; a simple hinge is inadequate for anything beyond a single crown.
• Shade selection: Vita Classical/3D-Master or digital spectrophotometer, in daylight, early in the appointment, teeth moist, tissue-level 5-second glances; communicate a shade map and photographs to the lab.
• Common failures: secondary caries at the margin (commonest cause of failure), loss of retention/decementation, endodontic complications of the abutment, periodontal breakdown, porcelain chipping/fracture, connector or solder-joint fracture, poor aesthetics, open or high contact.
• Open margin tolerance: clinically acceptable marginal gap generally quoted as ≤120 µm, ideal <50 µm; CAD/CAM and pressed ceramics typically achieve 30-80 µm.

Dental implants: biology, planning and surgery

• An endosseous dental implant is a biocompatible fixture (commercially pure titanium Grade 4 or Ti-6Al-4V, increasingly zirconia) placed in bone to support a prosthesis; components = fixture, abutment, abutment screw, prosthesis, plus healing cap/cover screw and impression coping.
• Osseointegration (Brånemark): a direct structural and functional connection between ordered living bone and the surface of a load-carrying implant, with no intervening fibrous tissue. Requires biocompatible material, atraumatic surgery (low-speed drilling with copious irrigation, bone temperature kept below ~47 °C), primary stability, undisturbed healing, controlled loading.
• Surface and design: roughened surfaces (SLA, acid-etched, HA-coated, anodised) osseointegrate faster than machined; threaded screw-form is standard; platform switching reduces crestal bone loss; tapered bodies aid immediate placement.
• Bone quality/quantity: Lekholm & Zarb classification — bone quantity A-E (A = most of ridge present, E = severe basal resorption) and quality 1-4 (1 = homogeneous cortical, 4 = thin cortex with sparse trabecular bone). CBCT is the imaging standard for planning (not OPG alone, which has magnification error ~20-25%).
• Minimum dimensions (consensus guidance): ≥1.5-2.0 mm bone buccal and lingual to the fixture, ≥1.5 mm between implant and adjacent tooth, ≥3.0 mm between adjacent implants, ≥2.0 mm safety margin above the inferior alveolar canal.
• Surgical protocols: two-stage (submerged) — fixture + cover screw, closed healing 3-6 months, second-stage uncovering; one-stage (non-submerged) — healing abutment at placement. Loading: conventional (>2 months), early (1 week-2 months), immediate (within 48-72 h, needs high primary stability, ISQ typically >70 and good bone).
• Site development: socket preservation grafting, GBR with resorbable/non-resorbable membranes, autograft/allograft/xenograft/alloplast, ridge split, block graft, direct (lateral window) and indirect (osteotome/Summers) sinus lift, nerve lateralisation (high risk), zygomatic implants for severely atrophic maxilla, All-on-4/All-on-6 tilted-implant full-arch concepts.
• Contraindications: absolute — uncontrolled diabetes, active IV bisphosphonate/antiresorptive therapy with MRONJ risk, recent head-and-neck radiotherapy to the site (high-dose), uncontrolled bleeding disorders, active malignancy, psychiatric unsuitability, growing patients (place after growth completion); relative — smoking, HbA1c above ~7-8%, bruxism, untreated periodontitis, poor oral hygiene, oral bisphosphonates (risk low but real).
• Prosthetic options: single crown, implant-supported FPD, cantilever, screw-retained vs cement-retained, hybrid/fixed-detachable full arch, implant overdenture (ball, locator, bar attachments — covered in removable prosthodontics).
• Screw-retained is retrievable, needs no cement (no cement-induced peri-implantitis), requires good implant angulation and an access hole; cement-retained is more aesthetic and passive but risks retained subgingival cement.
• Peri-implant tissue and complications: peri-implant mucositis (reversible inflammation, no bone loss) and peri-implantitis (inflammation with progressive crestal bone loss); mechanical complications — screw loosening, screw/abutment fracture, fixture fracture, prosthesis chipping; surgical — nerve injury, sinus perforation, bleeding in the floor of the mouth from lingual perforation, implant malposition. Success criteria (Albrektsson): immobility, no peri-implant radiolucency, bone loss <0.2 mm/year after the first year, no persistent pain/infection/paraesthesia, ≥85% at 5 years and 80% at 10 years.
• Stability measurement: insertion torque (Ncm) and resonance frequency analysis (ISQ 1-100; >65-70 favourable for immediate loading); a primary-stability dip at 2-4 weeks reflects remodelling.

Indian regulation, standards and digital practice

• Practice is governed by the National Dental Commission Act, 2023 — the National Dental Commission (NDC) replaced the Dental Council of India (DCI), with its autonomous boards and the DNEXT licentiate/entrance examination; the Dentists Act, 1948 framework was superseded. Only a registered dentist may prepare teeth, place implants or cement prostheses; dental laboratories/technicians may not treat patients directly.
• Device regulation: implants, abutments, bone grafts and dental cements are regulated as medical devices under the Medical Devices Rules, 2017 (Drugs and Cosmetics Act, 1940 framework; CDSCO licensing, import licence for foreign implant systems). Dental implants are notified devices requiring registration/licence — classification and the notified list have been expanded in stages, so verify the current class and licence route on CDSCO before quoting it.
• Indian Standards for dental materials are published by BIS under the dental sectional committee (largely harmonised with ISO — e.g. ISO 22794 for bone-filling materials, ISO 4049 for polymer-based restoratives, ISO 9693 for metal-ceramic systems, ISO 14801 for implant fatigue testing). Many older IS numbers have been revised or withdrawn; cite the subject and ISO equivalent unless the current IS edition is confirmed.
• Radiation: dental X-ray and CBCT units need AERB registration/licence under the Atomic Energy (Radiation Protection) Rules, 2004; lead aprons, thyroid collars and an eLORA registration are expected in audits.
• Waste: amalgam, extracted teeth, sharps and gypsum/ceramic debris handled under the Bio-Medical Waste Management Rules, 2016 (as amended).
• Taxation/commercial: healthcare services by a clinical establishment are exempt from GST, but dental materials, implants and lab work attract GST (slabs are 5%/18%/40% from 22 September 2025; most dental devices and implants sit at the lower rate — confirm the current HSN rate before invoicing). Clinic income is taxed under the Income-tax Act, 2025 (in force from 1 April 2026), with presumptive taxation available to professionals within the prescribed turnover limit.
• Digital workflow: intraoral scanner → CAD design (exocad, 3Shape) → milling (zirconia, PMMA, lithium disilicate) or 3D printing (models, surgical guides, provisionals); guided implant surgery from merged CBCT + scan data; chairside same-day crowns are growing in Indian metros.

Key points

• Crown - extracoronal restoration covering all axial walls; FPD - prosthesis cemented to prepared abutments replacing missing teeth.
• Ante's law - abutment root surface area must equal or exceed that of the teeth replaced; a guideline, not a law of physics.
• Crown-to-root ratio - ideal 1:2, acceptable 1:1.5, 1:1 is the limit for an abutment.
• Total occlusal convergence - ideal 6°; retention drops steeply above 20°; undercuts if below ~4°.
• Chamfer vs shoulder - chamfer for metal and zirconia (conservative, less stress); shoulder 1.0-1.5 mm for all-ceramic to support porcelain.
• Biologic width - ~2.04 mm (1.07 connective + 0.97 epithelial); margins within it cause chronic inflammation and bone loss.
• Functional cusp bevel - extra 1.5 mm reduction on maxillary palatal (lingual) and mandibular buccal cusps to avoid a thin metal/ceramic area.
• Modified ridge-lap pontic - the default aesthetic design; sanitary pontic for hygiene in mandibular posteriors; ovate for best aesthetics in a prepared site.
• Addition silicone and polyether - the only acceptable impression materials for multi-unit fixed and implant work.
• Resin cement - mandatory for resin-bonded bridges, veneers and etchable ceramics; zinc phosphate retains only mechanically.
• HF acid + silane for lithium disilicate/feldspathic; sandblast + MDP primer for zirconia (HF does not etch zirconia).
• Osseointegration - direct bone-to-implant contact without fibrous tissue; needs primary stability and undisturbed healing.
• Lekholm & Zarb - bone quantity A-E, quality 1-4; type 4 bone is the poorest prognosis.
• Spacing rules - 1.5 mm implant-to-tooth, 3 mm implant-to-implant, 1.5-2 mm buccolingual bone.
• Loading - conventional >2 months, early 1 week-2 months, immediate within 48-72 h with ISQ >70.
• Peri-implant mucositis vs peri-implantitis - the second involves progressive crestal bone loss; retained cement is a major cause.
• Albrektsson success criteria - immobile, no radiolucency, <0.2 mm bone loss/year after year 1, ≥85% at 5 years.
• Regulator - National Dental Commission under the National Dental Commission Act, 2023; implants are CDSCO-regulated devices under the Medical Devices Rules, 2017.

Formulas and examples

Example 1 — Ante's law for a 3-unit bridge. Missing 36 (mandibular first molar). Abutments 35 and 37. Approximate pericemental areas (standard tables): 35 = 220 mm², 37 = 433 mm², 36 (to be replaced) = 431 mm².

• Abutment total = 220 + 433 = 653 mm².
• Required ≥ 431 mm². 653 ÷ 431 = 1.51, so abutment area is 51% greater than needed → Ante's law satisfied; a conventional 3-unit FPD is acceptable if periodontal support is sound.
• Now extend the case: missing 35 and 36, abutments 34 (205 mm²) and 37 (433 mm²) → abutment total 638 mm², teeth replaced = 220 + 431 = 651 mm². 638 < 651 → Ante's law violated; choose implants or add 33 as a third abutment.

Example 2 — Crown-to-root ratio. On a periapical film an abutment shows clinical crown 9 mm and root-in-bone 12 mm (OPG magnification already corrected).

• Ratio = 9 : 12 = 1 : 1.33 = 0.75.
• Acceptable limit is 1:1 (ratio 1.0); ideal 1:2 (0.5). 0.75 lies between → acceptable but not ideal; use as an abutment only with healthy periodontium, light occlusion and a short span.

Example 3 — Reduction arithmetic for a PFM crown. A maxillary first premolar measures 9.0 mm buccopalatally and 8.5 mm occlusogingivally before preparation; plan 1.4 mm buccal (PFM aesthetic) and 1.0 mm palatal axial reduction, 1.5 mm occlusal, 1.5 mm functional cusp bevel on the palatal cusp (the functional cusp in the maxilla).

• Prepared buccopalatal width = 9.0 − (1.4 + 1.0) = 6.6 mm.
• Prepared occlusogingival height = 8.5 − 1.5 = 7.0 mm of axial wall — more than the 3-4 mm minimum for posterior retention, so retention is adequate.
• Shoulder of 1.4 mm buccally plus 0.3 mm bevel; chamfer 1.0 mm palatally. Check remaining dentine thickness over the pulp ≥1 mm on the radiograph before cutting.

Example 4 — Implant space check. Missing 11 with a 7.5 mm mesiodistal gap; bone width on CBCT 6.8 mm; planned implant 3.5 mm diameter.

• Space needed = 3.5 + 1.5 + 1.5 = 6.5 mm ≤ 7.5 mm available → mesiodistal space sufficient (1.0 mm spare, 0.5 mm each side).
• Buccopalatal: 6.8 − 3.5 = 3.3 mm of bone, i.e. ~1.65 mm per side ≥1.5 mm → adequate, but tight; place slightly palatal and consider simultaneous GBR.
• If a 4.3 mm implant were used: 4.3 + 3.0 = 7.3 mm < 7.5 mm just fits mesiodistally, but bone leaves only (6.8 − 4.3)/2 = 1.25 mm per side, below the 1.5 mm minimum → not advisable without grafting.

Example 5 — Survival and cost comparison. A clinic places 180 implants over 5 years; 9 fail.

• Survival = (180 − 9)/180 × 100 = 95.0% — in line with published 5-year survival of 94-97%.
• Cost comparison for one missing posterior tooth (illustrative urban Indian private-practice ranges; vary widely by city, brand and clinic):

Where it is used

• Corporate and chain dental clinics (Clove Dental, Apollo White, FMS, Sabka Dentist) — crown and bridge plus implantology are their main revenue lines; associate dentists are hired and appraised on preparation quality and implant case conversion.
• Hospital dental departments and dental colleges — AIIMS, PGIMER, government dental colleges and all BDS/MDS teaching institutions; Prosthodontics and Crown & Bridge departments run clinics, CAD/CAM and implant units.
• Dental laboratories and CAD/CAM centres — zirconia milling and 3D printing labs in Delhi, Mumbai, Ahmedabad, Bengaluru, Chennai; roles in design (exocad/3Shape), milling, ceramic layering and quality control (marginal fit, shade).
• Implant and materials companies — Nobel Biocare, Straumann, Dentsply Sirona, Osstem, Adin, and Indian manufacturers (Equinox, Dentcare, Ridge Dental) — clinical trainer, product specialist, technical support and regulatory (CDSCO/MDR 2017) roles.
• Insurance, TPA and dental tourism — claim assessment and treatment-plan vetting require judging FPD vs implant indications and abutment prognosis; India's dental tourism depends on implant and full-arch work.
• Clinical research and academics — implant surface studies, marginal-fit and cement-retention research, randomised trials on loading protocols; NEET-MDS/INI-CET coaching and dental content roles.

Interview questions

• Q: What is osseointegration and what four or five conditions are needed for it? A: A direct structural and functional connection between living bone and a load-bearing implant surface with no fibrous interface; it needs a biocompatible implant, atraumatic surgery with irrigation, primary stability, an undisturbed healing period and controlled loading.
• Q: State Ante's law and say whether you rely on it. A: The combined root surface area of the abutments should equal or exceed that of the teeth replaced; it is a useful planning guideline, but evidence shows long spans can succeed and short spans fail, so periodontal health, occlusal load and span flexure matter at least as much.
• Q: Why a shoulder for an all-ceramic crown but a chamfer for metal or zirconia? A: A 1.0-1.5 mm shoulder gives flat bulk to support brittle veneering porcelain in compression; a chamfer is adequate and more conservative for metal and high-strength monolithic zirconia, and produces less stress concentration.
• Q: What is biologic width and what happens if a crown margin invades it? A: The junctional epithelium plus connective tissue attachment above the bone, averaging about 2.04 mm; a margin inside it causes chronic gingival inflammation, bleeding, and either crestal bone loss or persistent recession.
• Q: Ideal taper for a crown preparation, and why not more or less? A: About 6° total occlusal convergence; too little creates undercuts and prevents cement escape and seating, too much (above roughly 20°) sharply reduces retention and resistance.
• Q: How do you cement a zirconia crown and how does it differ from lithium disilicate? A: Zirconia is sandblasted and primed with an MDP/phosphate-monomer primer and luted with resin-modified GIC or self-adhesive resin cement; lithium disilicate is etched with 5-9% hydrofluoric acid, silanated and bonded with resin cement, since HF does not etch zirconia.
• Q: A patient has a 9 mm gap for a single missing lower molar and 5 mm of bone above the mandibular canal. What do you do? A: Do not place a standard-length implant into 5 mm — plan a short implant if the system and bone quality permit, vertical augmentation, or an FPD; CBCT measurement and a 2 mm safety margin above the canal decide it, and the patient is consented for paraesthesia risk.
• Q: Why is retained cement a problem around implants? A: Implants lack periodontal attachment and the mucosal seal is weaker, so subgingival cement acts as a plaque-retentive foreign body and is a recognised cause of peri-implantitis and bone loss — hence the preference for screw-retained prostheses where angulation allows.
• Q: Would you ever connect an implant to a natural tooth in one FPD? A: Generally no — the tooth moves 25-100 µm while the implant is virtually ankylosed, producing intrusion of the tooth, screw loosening and cement failure; if unavoidable, a rigid connector with a splinted design and close follow-up is used.
• Q: Which impression material for a 6-unit anterior bridge and why? A: Addition silicone or polyether in a custom tray — highest dimensional accuracy and stability, with polyether's hydrophilicity helping in moist sulci; alginate and condensation silicone shrink too much for multi-unit work.
• Q: Commonest cause of long-term failure of a conventional FPD? A: Secondary caries at the abutment margins, followed by loss of retention and endodontic complications of the prepared abutments.
• Q: Which Act and which body regulate your practice of implantology in India today? A: The National Dental Commission Act, 2023 — the National Dental Commission replaced the Dental Council of India; the implants and grafts themselves are medical devices regulated by CDSCO under the Medical Devices Rules, 2017.
• Q: Patient on oral bisphosphonates for 6 years wants an implant — your approach? A: Assess MRONJ risk with the physician, consider duration, route and comorbidities; oral therapy carries a low but real risk, so consent specifically for MRONJ, keep surgery atraumatic, and prefer a non-surgical option if risk factors stack up (IV antiresorptives are a contraindication).

Common mistakes

• Over-tapering the preparation to "remove undercuts" and then blaming decementation on the cement.
• Under-reducing for an all-ceramic crown, so the lab either makes a thin fracture-prone crown or an over-contoured one.
• Placing margins deep subgingivally by habit, violating biologic width, then treating the resulting inflammation as poor hygiene.
• Quoting Ante's law without computing it, or applying it to implant abutments (where it does not apply).
• Trying to etch zirconia with hydrofluoric acid, or bonding lithium disilicate without silane.
• Planning implants on an OPG alone and ignoring its 20-25% magnification and lack of buccolingual information.
• Forgetting the functional cusp bevel, or omitting a common path of insertion check for multiple abutments, so the bridge will not seat.
• Reporting "crown cemented" without checking excursive interferences and removing all excess cement.

Related topics

Prosthodontics: complete and removable dentures · Endodontics: root canal treatment · Periodontology · Conservative dentistry: caries and restorations · Oral and maxillofacial surgery: extractions and minor oral surgery · Dental materials and occlusion.