CDT common mistakes
CDT · Understand the traps and how to avoid them.
Seating the maxillary final impression with the tray border seated short of the vestibule and accepting an impression that shows no recorded peripheral roll, without first verifying extension with a PIP (pressure-indicating paste) or comparable indicator.
Candidates treat border molding as a formality and chase the impression for lack of voids rather than for correct border extension; the molded record base is usually the weak link because it is not relieved or not adapted, so the tray rides high and the borders read short.
What to do instead
Before the final wash, do a border-molding appointment with modeling plastic/elastomer tracing, then check the custom tray borders for 1–1.5 mm clearance in an unimpeded path of insertion, and inspect the finished impression for a rounded roll plus a distinct postpalatal seal (vibrating line) that was verified in the mouth.
Setting the anterior teeth by the occlusal plane and lip line on a trial denture in which centric relation was never re-verified, and then approving the wax try-in without checking bilateral simultaneous contact, phonetics of the labiodental and linguoalveolar sounds, and the patient's phonetic and aesthetic record.
Try-in is approached as only an aesthetic check; the occlusion setup is accepted from the articulator mount even though the interocclusal record from the record bases was unstable and was never re-checked on the day.
What to do instead
Re-verify CR at try-in with the teeth in wax, adjust the base for stability first, and only then correct the setup; document speech (fricative sounds 'f', 'v', 's'), the lip support with the incisal edges, and anterior tooth position relative to the retromolar pad and hamular notch before approval.
Marking the RPD design on the surveyor cast without first establishing a single path of insertion, then placing rest seats on the wrong tooth or as a surface depression rather than an occlusally facing seat adjacent to the edentulous space.
Candidates jump from the tooth list to clasp nomenclature (e.g., 'I-bar', 'circumferential') instead of working from the path of insertion and the guiding planes that the path demands, so the rests do not direct forces along the long axis or resist movement toward the tissue.
What to do instead
Survey the cast and tilt it to the position that minimizes recontouring and gives parallel guiding planes, mark the survey lines, then place each rest so its floor is perpendicular to the path of insertion and adjacent to the space it supports, and confirm the shape is a spoon/box form rather than a shallow dimple.
Ignoring framework fit and tissue support by having the patient seat the framework to the rests and then reporting 'it fits' without verifying that the framework rests fully on the rest seats and does not rock under finger pressure on the major connector, and without a bilateral/alternating pressure check.
Candidates confuse the patient's comfort for fit, and they skip the lab steps that reveal a casting that is bound on a guiding plane or that shows tissue impingement at the connector - errors visible only when checked with inspection (PIP or disclosing wax) and a finger-pressure rock test.
What to do instead
At framework try-in, check the rests with a feeler/disclosing medium, test for rocking and for a fulcrum at the major connector, verify the major connector clearance from the gingiva (relieve, do not burnish), confirm the approach arm clears the tissue, and check that the framework seats with no interference before proceeding to the jaw record and tooth arrangement.
Preparing a tooth for a full-coverage crown ending the axial reduction with a knife-edge or a shoulderless feather edge on the buccal/lingual, and then taking the impression without retraction of the gingiva at a subgingival margin.
Candidates focus on occlusal clearance and reduce only axially in the path they are drilling, leaving an undulating, under-reduced finish line in the path of insertion; a subgingival margin without cords or displacement leaves a void and a soft-tissue 'roll' in the impression that the lab reads as a supragingival margin.
What to do instead
Establish the finish line as a continuous, defined 0.8–1.2 mm chamfer (or shoulder where indicated for ceramic) around the full circumference, check clearance and taper with a bur or index, and place a retraction cord (or displacement paste) before the final wash impression, confirming the margin is recorded cleanly on both the wash and the cast.
Taking a single-arch impression or a single opposing-arch record with no interocclusal bite registration and mounting on an arbitrary hinge-axis value, then proceeding with a crown that is returned on a cast mounted by hand-articulation.
Candidates trust a maximal intercuspation record taken in a patient whose CR and MI differ, and they skip the facebow/mounting verification, so the lab-verified occlusion does not translate to the mouth and the crown shows as a heavy or light contact that is 'adjusted at insertion'.
What to do instead
Record the occlusion in the position you intend to restore to (CR or MI - pick one and document it), take a facebow or use a verified hinge-axis mounting, mount the opposing cast and confirm the record with the incisal pin, and recheck the cast-to-cast relationship before the try-in; adjust contacts at insertion against a verified seated restoration, not by articulating paper alone.
Selecting the ceramic by name (e.g., 'emax' or 'zirconia') without matching the case to the material's flexural strength, the available occlusal reduction, and the presence or absence of a supporting substructure - then prescribing a low-strength veneering porcelain over a flexing framework or on a short, thin preparation.
Candidates memorize brand names and shade guides rather than the material's fracture-mechanics requirements; they under-reduce the occlusal space and let the lab 'make it work', which leaves thin ceramic over a flexing substrate and a veneering porcelain with a mismatched coefficient of thermal expansion.
What to do instead
Start from the required minimum thickness and the occlusal load, choose a monolithic or a suitably supported core material, give the lab the measured occlusal clearance and the die spacer, and specify the core thickness and the veneering/glaze protocol so the thermal expansion and cooling regime are controlled by the lab rather than improvised.
Delivering a ceramic restoration with the internal surface contaminated by saliva or a trial-fit paste, and bonding/cementing without re-etching/silanating the fitting surface and without protecting the adjacent teeth, so the restoration is seated on a contaminated interface and shows early debonding or staining at the margin.
Candidates try in the restoration with a paste and then simply rinse and cement; they treat the try-in as a separate step and do not re-do the surface treatment that the try-in destroyed, and they forget the etched-silanated internal surface must be protected from saliva and the field isolated.
What to do instead
Do the try-in with a water-soluble medium, clean the internal surface thoroughly (and re-etch/a re-silanate for glass-ceramic), isolate the field, apply the specified cement in a thin even layer, seat with sustained pressure and remove excess before curing; verify the margin with an explorer and check the occlusion after cementation.
Starting fixed appliance therapy with the bracket slot and wire placed without first resolving the arch-length discrepancy (crowding analysis, Bolton analysis, and space analysis on the mixed dentition), and then compensating for a short arch by excessive expansion or by proclining the incisors rather than by creating space deliberately.
Candidates begin bonding before the diagnostic records are complete, so the treatment plan is a bracket-placement sequence rather than a plan to correct the specific discrepancy; they then mask an anchorage deficit with mechanics that flare incisors or intrude the arch.
What to do instead
Complete the space analysis and Bolton analysis before bonding, write down the space needed and where it will come from (extraction, IPR, distalization, expansion), plan anchorage (headgear, TADs, or a holding arch) accordingly, and record the treatment objective quantitatively so progress can be checked against it at each visit.
Applying the same force magnitude and the same wire sequence to every patient - for example, a heavy initial archwire or a continuous force to a tooth being moved into a narrow space - and not reducing force when the patient reports discomfort or when the tooth shows no movement at the expected check interval.
Candidates reason from a fixed 'sequence' (NiTi → stainless) rather than from the biology of the periodontal ligament and the anchor unit; they under-plan anchorage and over-apply force, producing hyalinization with no movement, root resorption, or an unplanned loss of anchorage.
What to do instead
Titrate force to the tooth being moved and the anchorage available, use light continuous forces for initial alignment, verify the tooth/arch status at each visit, and document the planned force and expected movement - with a specified contingency if anchorage is lost - before advancing to the next wire.