NZ Dental Technician REX cheat sheet

Permanent dentition: 32 teeth; FDI two-digit system uses quadrant 1-4 (upper right, upper left, lower left, lower right) plus tooth number 1-8 from midline.

Primary dentition: 20 teeth; FDI quadrants 5-8; primary molars are replaced by premolars, so primary second molar sits above the second premolar.

Anterior teeth (incisors, canines) have single roots; maxillary first premolar typically has two roots; mandibular molars usually two roots, maxillary molars three.

Universal numbering runs 1-32 from maxillary right third molar to mandibular right third molar; Palmer uses quadrant brackets with 1-8.

Occlusal anatomy: mandibular first molar classically has five cusps (two buccal, two lingual, one distal); maxillary first molar has four cusps plus cusp of Carabelli on the mesiolingual surface.

Incisal edge morphology: newly erupted incisors show mamelons; perikymata and imbrication lines are incremental growth features of enamel.

Root canal counts: mandibular first molar usually three canals (two mesial, one distal); maxillary first molar usually three to four canals including MB2.

Cusp height and incline determine cusp-to-fossa relationship; the central fossa of posterior teeth is the target for occlusal contact in centric occlusion.

Saliva: 0.5-1.5 L/day; pH 6.7-7.4; buffers include bicarbonate, phosphate, and proteins; xerostomia raises caries risk and reduces denture retention.

Periodontal ligament width 0.15-0.25 mm; provides proprioception, shock absorption, and tooth support; loss of PDL means loss of physiologic mobility signal.

Gingival sulcus depth 1-3 mm clinically; junctional epithelium attaches via hemidesmosomes to enamel and connective tissue.

Muscles of mastication: masseter, temporalis, medial pterygoid (elevators); lateral pterygoid (protrusion and depression); buccinator and orbicularis oris control the denture space.

Temporomandibular joint: bilateral, ginglymoarthrodial; disc separates upper and lower compartments; translation occurs in the upper compartment.

Mandibular movements: border movements define the envelope of motion; centric relation is the uppermost anterior position of the condyles against the articular eminence.

Tongue: intrinsic and extrinsic muscles; lingual papillae include filiform, fungiform, foliate, and circumvallate; taste via cranial nerves VII, IX, X.

Bone remodelling: osteoblasts form, osteoclasts resorb; residual ridge resorption is greatest in the first year after extraction and continues lifelong, more in mandible than maxilla.

Amalgam: silver-tin-copper-mercury alloy; sets by reaction forming gamma-1 (Ag2Hg3) and gamma-2 (Sn7-8Hg) phases; gamma-2 is the weakest and most corrosion-prone phase.

Composite: resin matrix (Bis-GMA, UDMA) plus filler (silica, zirconia, barium glass); filler load raises strength and lowers polymerisation shrinkage; shrinkage stress depends on C-factor (bonded/unbonded ratio).

Glass ionomer: fluoride release, chemical adhesion to tooth via polyalkenoic acid; low fracture toughness; resin-modified GI adds light-cured HEMA-based resin.

Zirconia: transformation toughening from tetragonal to monoclinic phase; yttria-stabilised (3Y-TZP); low-temperature degradation (LTD) is a risk in humid storage; sintering shrinkage ~20-25%.

Dental ceramics: feldspathic (high aesthetics, low strength ~100 MPa), lithium disilicate (~350-450 MPa), zirconia (~900-1200 MPa); flexural strength determines indication.

Impression materials: addition silicone (polyvinyl siloxane) is hydrophobic and dimensionally stable; condensation silicone shrinks by ~0.5%; alginate is hydrocolloid and dimensionally unstable within minutes.

Dental casting alloys: high-noble (Au+Pt group >60%), noble (>25%), base metal (Co-Cr, Ni-Cr); CTE mismatch between porcelain and alloy causes cracking or chipping.

Wax and acrylic: PMMA denture base polymerised by heat (compression moulding) or auto-polymerised; residual monomer causes tissue irritation and dimensional change.

Complete denture retention: physical (adhesion, cohesion, surface tension, atmospheric pressure), muscular (polished surface contours), and mechanical (post dam, border seal).

Neutral zone: space where forces from tongue and cheeks cancel; teeth and polished surfaces placed here improve stability.

Border moulding with modelling compound records functional sulcus depth; final wash impression in elastomer records the denture-bearing area.

Jaw relations: record blocks establish vertical dimension at rest minus 2-4 mm freeway space; Gothic arch tracing or check bites record centric relation.

Kennedy classification: Class I bilateral edentulous posterior; Class II unilateral posterior; Class III bounded posterior edentulous; Class IV anterior crossing midline.

Applegate's rules: classification determined after extractions; most posterior edentulous area governs; third molars not counted if not to be replaced.

RPD components: major connector (palatal plate, lingual bar), minor connectors, rests, direct retainers (clasps), indirect retainers, and denture base.

Clasp design: circumferential (greater than 180 degrees engagement) for tooth-borne; bar clasp (Roach) for tissue-borne; rest seats direct occlusal load along the long axis.

Tooth preparation: occlusal reduction 1.5-2.0 mm for metal-ceramic, 1.0-1.5 mm for full zirconia, 0.3-0.5 mm for veneers; finish line chamfer or shoulder depending on material.

Taper and retention: axial taper ideally 6-10 degrees total; retention and resistance form depend on surface area, taper, and path of insertion.

Pontic design: sanitary (hygienic) pontic for posterior; modified ridge lap for aesthetics; ovate pontic requires a soft-tissue socket.

Implant: osseointegration depends on primary stability, surface roughness (SLA), and bone quality; biologic width around implants ~3 mm; platform switching reduces crestal bone loss.

Screw-retained vs cement-retained: screw-retained retrievable and avoids cement remnants; cement-retained allows more freedom in angulation but risks peri-implantitis from residual cement.

Marginal fit: accepted clinical gap typically under 120 micrometres; internal fit affects cement space and seating; die spacer controls cement thickness.

Veneer bonding: etch porcelain with hydrofluoric acid, silane coupling agent; enamel etch with phosphoric acid; resin cement provides bond and colour.

Occlusal scheme: mutually protected occlusion-posterior disclusion in excursion; group function acceptable in some implant and periodontal cases.

Removable appliances: Hawley retainer, Essix (vacuum-formed) retainer, and active plates with Adams clasp and Z-spring; effective for tipping movements only.

Fixed appliances: brackets (metal, ceramic, self-ligating), archwires (NiTi, stainless steel, beta-titanium), and auxiliaries; NiTi delivers light continuous force; steel for sliding mechanics.

Functional appliances: Twin Block, activator, Herbst; posture mandible forward to modify growth; require compliance and growth potential.

Force levels: light continuous forces for bodily movement; heavy forces cause hyalinisation and undermining resorption; optimal orthodontic force typically 50-150 g per tooth.

Anchorage: intraoral (palatal, lingual, transpalatal arch), extraoral (headgear), and temporary anchorage devices (TADs/miniscrews).

Cephalometric landmarks: SNA, SNB, ANB angles describe sagittal jaw relationship; ANB of 2-4 degrees is skeletal Class I.

Retention: relapse risk highest in first 6-12 months; lower incisor irregularity recurs; long-term or lifelong retention often needed.

Appliance fabrication: vacuum-formed retainers require 0.75-1.0 mm thermoformed sheet; wire components bent on a model with 0.7 mm stainless steel for clasps.

Standard precautions apply to all patients regardless of known status; hand hygiene is the single most effective measure; WHO 5 Moments for Hand Hygiene.

Personal protective equipment: gloves, mask, eye protection, gown; change gloves between patients and after contamination; perform hand hygiene before donning and after doffing.

Sterilisation: moist heat autoclave at 134 degrees C for 3 minutes (or 121 degrees C for 15 minutes); monitor with physical, chemical, and biological indicators (spore tests).

Spaulding classification: critical items (sterilise), semi-critical (sterilise or high-level disinfection), non-critical (low-level disinfection).

Impression disinfection: immerse or spray with appropriate disinfectant per manufacturer; alginate is sensitive to prolonged immersion and dimensional change.

Sharps: never recap by hand; use safety devices; dispose in puncture-resistant sharps container; report needlestick injury immediately per local protocol.

Bloodborne pathogens: HBV, HCV, HIV; HBV is the most transmissible; vaccination against HBV recommended for all dental personnel.

Zoonotic and waterline risks: dental unit waterlines can harbour biofilm; flush and use approved waterline treatment; Legionella control per building water safety plan.

Hazardous chemicals: monomer (methyl methacrylate) is flammable and a sensitiser; store in a cool, ventilated area away from ignition; use local exhaust ventilation.

Silica dust: crystalline silica from plaster and investment causes silicosis; use wet trimming, local extraction, and respiratory protection (P2/N95).

PPE in the laboratory: safety glasses with side shields, dust mask, nitrile gloves, and apron; hearing protection near model trimmers and lathes.

Waste segregation: sharps, infectious (yellow), chemical (including amalgam and monomer), and general waste; amalgam separators required on sinks.

No food or drink in the laboratory; do not store food in refrigerators used for materials; wash hands after handling impressions and prostheses.

Electrical safety: RCDs, test and tag, no water near power outlets; lathes and handpieces require guarding and routine maintenance.

Ergonomics: adjustable benches, anti-fatigue mats, regular breaks; cumulative trauma disorders from repetitive trimming and polishing.

Fire safety: know extinguisher classes (A, B, C, E, F); monomer and solvent fires require foam, CO2, or dry powder-never water on solvent fires.

Scope of practice: dental technicians work to a prescription from a registered oral health practitioner; they do not diagnose or treat patients directly.

HPCA Act 2003: registration, competence, and complaints processes; the Dental Council of New Zealand sets standards and codes of conduct.

Privacy Act 2020: personal health information must be collected, stored, and disclosed only for the purpose for which it was collected; breaches reportable to the Privacy Commissioner.

Health and Safety at Work Act 2015: PCBUs must eliminate or minimise risks; workers must be consulted and trained; notifiable events reported to WorkSafe.

Informed consent: valid consent requires capacity, adequate information, and voluntariness; the Code of Health and Disability Services Consumers' Rights (HDC Code) applies.

Cultural safety: partnership, participation, and protection under Te Tiriti o Waitangi; recognise Maori health inequities and the importance of whanau involvement.

Professional boundaries and conflicts of interest: declare any financial interest; do not accept gifts that influence prescribing; maintain confidentiality of patient records.

Record keeping: accurate, legible, contemporaneous records retained per Dental Council guidance; traceability of materials and devices for each patient.

Workflow: prescription receipt, model pouring, design, fabrication, finishing, quality check, dispatch; each stage has a documented sign-off.

Inventory control: FIFO stock rotation; track expiry of alginate, plaster, investment, and resin; minimum stock levels for critical materials.

Scheduling: identify bottleneck stations (trimming, ceramic firing); batch compatible work; track turnaround time against promised delivery dates.

Costing: price includes materials, labour time, overhead, and margin; record actual versus estimated time to refine quotes.

Staff management: role clarity, training records, competency assessment, and supervision of trainees; delegation only within competence.

Document control: SOPs version-controlled and accessible; equipment maintenance logs; incident and complaint registers reviewed regularly.

Traceability: link each prosthesis to patient, prescription, material batch, and technician; enables recall if a material defect is identified.

Business continuity: backup of digital files, contingency for equipment failure, and clear communication with dental practices during disruptions.

Quality assurance cycle: plan, do, check, act (PDCA); define measurable indicators such as remake rate, marginal fit, and on-time delivery.

Digital workflow: intraoral scan (IOS) or model scan, CAD design, CAM milling or 3D printing; STL is the standard tessellation format for surface data.

3D printing: stereolithography (SLA) and digital light processing (DLP) for resins; layer thickness affects surface finish and fit; post-cure required for biocompatibility.

Milling: subtractive; zirconia and PMMA; tool wear and chipping affect fit; nesting and sprue placement influence accuracy.

Accuracy: trueness (closeness to true value) and precision (repeatability); scanner accuracy typically 10-20 micrometres for IOS.

Validation: verify fit on a printed or milled model; check occlusion in the articulator; document deviations and corrective actions.

Data security: patient scans are personal health information; encrypted storage and transmission; access controls and audit trails.

Calibration: reference models and calibration blocks for scanners and printers; scheduled maintenance and software version control.