Please activate JavaScript!
Please install Adobe Flash Player, click here for download
ePaper created 2015-03-10, 11:16:47 | version 1.33.01
issue 1/2015 — 61EndodonticsArticle Fig.1 Fig.2 Fig.3 Fig. 1 Maxillary central incisor with slot-like access cavity that is cut short of the in- cisal edge, adequately un- der the cingulum, and has been kept narrow in its mesial-to-dimension. Fig. 2 Mandibular premolar with slot-like access cavity for a single canal root. Note how the access cavity is skewed toward the working buccal cusp tip and shy of the idling lingual cusp, yet is centered above the root structure. Fig. 3 Sagitally-dissected maxil- lary molar with mesially-in- clined access cavity, parallel to the mesial surface of the tooth and shy of the distal half of the tooth. planning and execution of an ideal access cavity preparation, the rest of the proce- durebecomesprogressivelysimplerasthe finish is approached. Radiographic Imaging We wouldn't even attempt RCT without Roentgen's invention of the dental radi- ograph, so it is not much of a stretch to claim the critical necessityof ideal preop- erative radiography. Ideal preoperative X-ray imaging must include a straight-on angle that splits the mesial and distal con- tactsperfectly–takeneitherasaperiapical or as a bitewing X-ray image, then at least one ideal off-angle view in order to cap- turedatafromtheZ-plane(bucco-lingual) of the tooth in question. In my practice, a mesial off-angle view ofanteriorsandpremolarsworkswell,be- cause it is much easier to capture than a distalangle,andinanteriorsandpremolars the mesial view reveals as much radicular anatomyas a distal view. In molars it is dif- ferent, in molars a distal view isfarprefer- able to a mesial off-angle view, as the mesial view superimposes the body of both roots over the distally curved root structure, while the distal view casts the apical root end sideways, where it can be more easily seen on the radiographic im- age. Of course, Cone Beam CT (CBCT) im- agingistheunfairendodonticimagingad- vantage. If told I could have either a mi- croscope or a CT machine, but not both, I would choose 3-D imaging every time. Only CBCT imaging can capture the mesial view of root structure–the view in which we see “The Secret Life of Root Canals”–the bucco-lingual plane contain- ingthe greatest degree of anatomic com- plexity. One ofthe greatest joys of having a CT machine in practice is knowing, for sure, before the access procedure is be- gun, that there is only a single canal in the mesiobuccal root of an uppermolar. Con- versely, one of the few negative experi- ences to be had with this technology is when the reconstructed volume shows twoorthreecanals,inarootthathasgiven up only one to the clinician's exhaustive search. The first gift of CBCT imaging to the field of endodontics has been the gift of finding all canals in a given tooth. Its sec- ond gift is the great diminution of access size possible, because the access cavity is no longer the primary viewing port into the pulp chamber and beyond. In fact, CT imaging is the ONLYview needed into the anatomic verities of root canal spaces, al- lowing access cavities to be used exclu- sively as treatment, rather than as ex- ploratory portals. Ultimately, RCT access procedures will be done with CT-gener- ated drill guides, allowing molars to be treated through 3–4 1mm pea-holes, rather than the 2–4mm access cavities used today.3 Outline Form So what are the objectives we consider when planning the invasion of a root canal space? Basically, all the best access cavi- ties are cut in a precise balance between conservation and convenience form. We cut as little tooth structure as possible, while ensuring ideal pathways into each canal. Access outline form objectives be- come fairly simple then; we demand con- venienceform,otherwisewecannotcom- plete our task, yet we always strive to preserve the structural integrity of the tooth. This boils down to three easily remembered objectives: 1. Inanteriorsandpremolars,conserva- tion form is found in the mesial-to- distal dimension. Traditionally, ante- rior access cavity outline form has beentriangularbecauseofthemesial and distal pulp horns in these teeth - logical until we consider the structural consequences, a needless weakeningofcoronaltoothstructure to insure these lateral pulp horns are cleaned out, when the smallest un- dercut with a #2 Mueller Bur or Buc- 1ultrasonictip(Spartan)couldsuffice as well. Premolars have pulp cham- bers like the shape of a hand, which is fortunately arranged in a bucco- lingualdirection,theangleoftherec- ommended slot-like access cavity outline form is bucco-lingual as well, simultaneously combining conven- ience conservation form. In anterior teeth, convenience form is harder won as the incisal edge is to be avoided, out of respect for post- endodontic esthetic objectives, thus requiring a deeper cut underthe cin- gulum, to allow a more straight-line entry path, while minding the "no-fly zone" of the incisal edge. The most dangerous anterior access cavity er- roris not cutting adequatelythrough what Dr. Schilder called the "lingual dentinaltriangle"underthecingulum, and this can be accomplished with minimal structural weakening when the mesio-distal dimension is kept to 1–1.5mm width (Fig. 1).