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ePaper created 2016-11-22, 09:52:12 | version 1.38.0
access cavities technique | 25 roots 4 2016 The first gift of CBCT imaging to the field of end- odontics has been the gift of finding all canals in a given tooth. Its second gift is the great diminution of access size possible, because the access cavity is no longer the primary viewing port into the pulp cham- ber and beyond. In fact, CT imaging is the only view needed into the anatomic verities of root canal spaces,allowingaccesscavitiestobeusedexclusively astreatment,ratherthanasexploratoryportals.Ulti- mately, RCT access procedures will be done with CT-generateddrillguides,allowingmolarstobetreated through three to four 1-mm pea-holes, rather than the 2- to 4-mm access cavities used today.3 Outline form So what are the objectives we consider when plan- ningtheinvasionofarootcanalspace?Basically,allthe best access cavities are cut in a balance between con- servationandconvenienceform.Wecutaslittletooth structure as possible, while ensuring ideal pathways intoeachcanal.Accessoutlineformobjectivesbecome fairlysimplethen;wedemandconvenienceform,oth- erwise we cannot complete our task, yet we always strive to preserve the structural integrity of the tooth. Thisboilsdowntothreeeasilyrememberedobjectives: 1) In anteriors and premolars, conservation form is found in the mesial-to-distal dimension. Tradition- ally, anterior access cavity outline form has been tri- angularbecauseofthemesialanddistalpulphornsin these teeth—logical until we consider the structural consequences,aneedlessweakeningofcoronaltooth structure to insure these lateral pulp horns are cleaned out, when the smallest undercut with a #2 Mueller Bur or Buc-1 ultrasonic tip (Spartan) could sufficeaswell.Premolarshavepulpchamberslikethe shape of a hand, which is fortunately arranged in a bucco-lingual direction, the angle of the recom- mended slot-like access cavity outline form is buc- co-lingual as well, simultaneously combining conve- nience and conservation form. In anterior teeth, convenience form is harder won as the incisal edge is to be avoided, out of respect for postendodontic aesthetic objectives, thus requiring a deeper cut under the cingulum, to allow a more straight-line entry path, while minding the “no-fly zone” of the incisal edge. The most dangerous ante- rior access cavity error is not cutting adequately throughwhatDrSchildercalledthe“lingualdentinal triangle”underthecingulum,andthiscanbeaccom- plishedwithminimalstructuralweakeningwhenthe mesio-distaldimensioniskepttoa1to1.5 mmwidth (Fig. 1). 2) In posterior teeth, premolars and molars, it is important to remember that their occlusal surfaces are not centred over the root structure, but are skewedtowardtheidlingcuspsideoftherootstruc- ture. As pulp chambers are centred in the root struc- ture, not centred under the occlusal surface, access in posterior teeth is best accomplished by cutting near working cusps, while staying 1–2 mm away from idling cusps (Fig. 2). 3) In molars, conservation form is held by avoiding the distal half of the occlusal plane, as ideal file paths from the distal canals of upper and lower molars are canted severely to the mesial, so much so that distal canals of lower molars are best referenced to the MB or ML cusp tips, and distobuccal canals of upper mo- lars are best referenced to the palatal cusp tips. Con- venience form is achieved by cutting the mesial wall of molar access cavities parallel to the mesial surface of the tooth (Fig. 3). Back from the abyss IwastaughtSchildertechniqueatUniversityofthe Pacific by Dr Michael Scianamblo and after grad schoolbyDrCliffRuddle.Iunderstoodtheclinicalim- perative Dr Schilder had placed on cutting an access adequatetotreattheentirerootcanalsysteminapre- dictable manner, and I enjoyed working through the large access cavities and the generous coronal canal shapes he recommended until I was broughtup short by Dr Carl Reider, a well-known prosthodontic lec- turer from Southern California. WhenIaskedwhathemostwantedfromtheendo- dontists he referred his patients to, he said he wished Fig.8:This restored access cavity design was opportunistic in the best sense of the word.This patient’s endodontic disease state was resolved with almost no tooth structure being cut,preserving the structural integrity of the tooth by using the cleaned out carious defect as access cavity. No need for a full-coverage crown. (Photo:ProvidedbyDrMichaelTrudeau) Fig.9:This lower molar was treated through an access opening that was less than 2 mm square,cut just behind the MB triangular ridge.Note the definitive treatment of the apical thirds of all four canals,despite the narrow entry portal. (Photo:Provided by Dr Charles Maupin) Fig.10: Postoperative radiograph of a mandibular molar treated through an alternative to the truss configuration — an‘X-entry’ access cavity — a design that minimizes removal of tooth structure in the critical trunk of the tooth (author’s case). Fig.8 Fig.9 Fig.10 42016