Minimal invasive access for endodontic treatment. PAV succesvolle endodontie Wortelkanaalpreparatie 07/05/2016

Transcription

1 Minimal invasive access for endodontic treatment. PAV succesvolle endodontie Wortelkanaalpreparatie 1

2 Compromised structural or mechanical integrity of teeth results in different types of tooth fractures, which are known to be one of the most common causes for tooth extraction. Fig. 2. The accumulative removal of tooth structure undermines the resistance of the tooth to fracture, and even teeth treated under accepted endodontic and restorative protocols, despite the fact that the endodontic disease could be resolved, may fracture. It is crucial to realize that both the remaining (residual) dentin and modification of original root canal geometry play a crucial role in the biomechanical responses of tooth structures to functional forces. The remaining dentin also serves as a foundation for the restorative procedures that follow endodontic therapy. Thus, it is desirable to preserve the coronal/radicular dentin structure and maintain the geometry of the root canal anatomy so as to conserve the mechanical integrity of endodontically treated teeth.. Summary Minimally invasive concepts and procedures are currently advocated as less invasive alternatives to traditional treatments. Recent advances in the available resources and technologies (like microscopy, CBCT, Endodontic Access & Exploration & Guide burs, NiTi instrumentation) have made a significant impact on endodontic treatment procedures, allowing minimally invasive treatment procedures such as contracted endodontic cavities for preserving coronal and radicular tooth structure. The purpose of this presentation is to provide a framework for understanding the clinical reasoning for contracted endodontic cavities and their possible benefits in contemporary endodontics. A. Gluskin et al. Brit Dent J 2014, 216,

3 2010, 54, Blue arrows indicate gouges. Red arrow indicates perforation. All previously accessed molars were gouged to some degree. The third upper and lower cases have frighteningly thin pulpal floors with blushing dentin. The upper fourth case is deceptive in that it is perforated, whereas the worse-looking lower case is not, but the pulpal floor is thin. The last upper molar (with a class V resorption repair) shows what is possible with practice, high-powered loupes, microscope level magnification and the right instruments. The lower molar shows the type of access that should be routinely achieved. Introduction In recent years, restorative dentistry has been undergoing a paradigm shift toward embracing therapeutic modalities that methodically respect the original tooth tissues. The philosophy of minimally invasive dentistry acknowledges that dental caries cannot be managed merely by cavity preparations and restorations, because such treatment procedures can weaken the remaining tooth structure. Current advances in the field of adhesive dentistry, as well as progress in the diagnostics and science of cariology, have made minimally invasive dentistry possible practically. Although the paradigm of minimally invasive treatment has limited supporting evidence, it is gradually gaining acceptance in clinical dentistry. 3

4 Introduction The endodontic access cavity is considered the foremost step in root canal treatment. An adequately prepared access cavity is crucial for effective instrumentation and delivery of irrigants into the root canal system. The effective cleaning and shaping of the root canals have been linked with the overall goals of endodontic therapy. All subsequent steps which follow endodontic cavity preparation may be compromised if adequate access is lacking. An endodontic cavity that has been inadequately prepared will make locating, negotiating, debriding, disinfecting, and filling of the root canal system a challenging task. The opening in endodontics is as important as in chess play. An adequate endodontic cavity also aids in preventing iatrogenic complications during endodontic treatment procedures. 2010, 54, Traditional endodontic cavities Traditional endodontic cavities are geometrically predesigned shapes. The outline form in a traditional endodontic cavity determines the occlusal extent of the prepared cavity. The convenience form is dictated by the degree of dentin to be removed at specific locations so as to achieve a straight-line access to the root canal orifices. The extension for prevention in the endodontic cavity involves the removal of dentin obstructions to extend the straight-line access to the apical foramen or to the primary curvature of the root canal. Employing the concept of extension for prevention facilitates the treatment procedures and avoids procedural errors. Nonetheless this occurs at the expense of crucial structural dentin, which may compromise the biomechanical integrity of tooth. Ingle Endodontics 2010, 54, Eighteen-month follow-up. Despite generous access and aggressive canal enlargement, the lesion on the mesial root continues to enlarge. A more appropriate access shape is overlayed. Partial deroofing and maintenance of a robust amount of PCD is demonstrated. A soffit that includes pulp horns on mesial and distal is depicted. 4

5 Traditional endodontic cavities The designs of traditional endodontic cavities have remained almost unchanged for the past several decades. This is due to existing limitations in diagnostic and imaging techniques, which have created the need to delve into the variations and complexities of root canal anatomy more clinically. Thus traditional endodontic cavity preparation usually results in the removal of dentin in order to explore the expected pulp chamber floor anatomy and canal openings. Additional alterations to the tooth anatomy, such as preflaring the coronal aspect of the root canal, are usually recommended to facilitate cleaning, shaping, and filling of the root canals. Moreover, the taper of endodontic instruments has moved from its traditional size of 0.02 to larger and even variable designs, which increases the amount of radicular dentin removed during instrumentation. C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, Traditional endodontic cavity designs rely on the convenience form and extension for prevention concepts where complete unroofing of molars is a requisite for gaining access to canals and to facilitate intracanal procedures. 5

6 C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, No less important is the constant search for variations in the anatomy, which means an ample reduction of hard tissue, justified by the statistics and what might be present in terms of isthmuses and extra canals. As an example, the literature states that the mandibular first molar has a 1-15% chance of a negotiable middle mesial canal on the mandibular first molar. Once completed, this type of approach requires a cuspal protective restoration for long-term success. Follow-up on this case is 14 years. 2010, 54,

7 Contracted endodontic cavities Recently, new designs for endodontic access cavities called conservative or contracted endodontic cavities have been advocated in order to minimize tooth structure removal. Contracted endodontic cavities are considered to be an alternative to traditional endodontic cavities in maintaining the mechanical stability and subsequently the longterm survival and function of endodontically treated teeth. Since no restorative material or technique can replace the mechanical characteristics of the lost dentin in stress-bearing areas of the tooth, treatment steps directed toward dentin conservation are essential as the primary measure to reinforce root-filled teeth. Buccal view Access overlays As well, the endodontic cavity is inevitably linked to the effectiveness of succeeding steps in the endodontic treatment. Therefore, it is normal for those changes to be judiciously assessed before being accepted into routine clinical practice. Fortunately, current advances in technology offer new possibilities in endodontics. Progress in the field of imaging, materials, instruments, and computers has considerably transformed the clinical practice of dentistry. Some of the developments in endodontic practice that make dentin conservation possible include ultra-flexible instruments, visual magnification, superior illumination, enhanced root canal irrigation systems, and three-dimensional imaging technology like cone beam computed tomography (CBCT). The emerging concept of conservative endodontic access is a shift to transform the outline of the endodontic cavity from a traditional operator-centric design to a scheme that focuses more on dentin preservation and the endodontic-restorative interface. Contracted endodontic access prioritizes the removal of: - restorative material ahead of tooth structure, - enamel ahead of dentin, and - occlusal tooth structure ahead of cervical dentin. It overlooks the traditional requirements of straight-line access and complete unroofing of the pulp chamber while emphasizing the importance of preserving the crucial pericervical dentin. Pericervical dentin is the dentin located 4 mm above and 4 mm below the crestal bone. This regional dentin is significant for the distribution of functional stresses in teeth. It is thus necessary to conserve pericervical dentin as much as possible to maintain the biomechanical response of the radicular dentin. In the case of incisors, the conservation of cingulum dentin (pericingulum dentin) is suggested to improve the functional stress distribution in teeth. These viewpoints are in direct disagreement with the principles of traditional endodontic access. 7

8 A contracted endodontic cavity preserves a portion of the roof around the entire coronal aspect of the pulp chamber. This dentin is known as dentin roof strut or soffit. A soffit is described as the underside of an architectural feature such as the ceiling, the corner of the ceiling, and the wall. The long-term strength attributes of dentin preservation in the contracted endodontic cavity are not clearly established at this time, but it is presumed to provide some degree of structural bracing, which in turn would minimize cuspal flexure during chewing. 2010, 54, Buccal view Normal pulp Buccal view CK access Soffit (arrows) Buccal view Various extensions Mesial view Various extensions Aids to preserve dentin in contracted endodontic cavities Operating microscopes and other visual enhancers It is well recognized that operating microscopes and other aids for magnification improve clinical performances in endodontics. The minuscule dimensions of root canal orifices/lumen make it an extremely difficult anatomy to perform precise clinical procedures on without magnification. In recent years, there has been wide-ranging development and application of technologies in endodontics. Most important are the operating microscopes, loupes, and increased light levels, all of which result in improvements in the precision with which endodontic procedures are routinely practiced. 8

9 C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, Visual enhancers, such as loupes and clinical microscopes, increase the precision and efficacy of clinical endodontics, providing detailed visualization of the tooth to be treated and allowing the clinician to conservatively solve complex situations such as calcified teeth. Treatment under Magnification. The nonmutilated lower first molar to receive a direct composite onlay. D. Clark & J. Khademi. 2010, 54,

10 D. Clark & J. Khademi. 2010, 54, , 54,

11 2010, 54, , 54,

12 D. Clark & J. Khademi. 2010, 54, Conserve the pericervical dentin. The access and restorative technique for an upper molar deemed suitable for final restoration with a bonded porcelain onlay or composite onlay restoration. 2010, 54,

13 CK endodontic Munce access Discovery bur & Bur surgical length round bur SS White Burs, Inc. Conserve the pericervical dentin. 2010, 54, , 54,

14 2010, 54, Dental radiology Radiological examination is an indispensable part of the diagnosis and management of apical periodontitis. Generally, radiological examinations are limited to intraoral and panoramic radiography. These methods are usually limited to a twodimensional representation of three-dimensional structures. The presence of complex anatomy and surrounding structures can make the interpretation of such images very difficult. Most essentially, information about the three-dimensional anatomy of the tooth and the adjacent supporting structures is not visible, even with the best intentions and paralleling techniques. Root canal morphology and configuration might present the clinician with a complex anatomy to work on during root canal treatment. To successfully localize, negotiate, disinfect, and seal the root canal system without debilitating the remaining tooth structure, a precise diagnostic approach that acquires this anatomy completely, prior to endodontic cavity preparation, without depending upon the clinical skills of the operator becomes mandatory. CBCT has enabled the practitioner to assess the endodontic anatomy and disease process in a new way. CBCT aids in visualizing the precise anatomical configurations of the tooth and supporting structures. 14

15 C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, CBCT can be quite useful in understanding and knowing in advance the exact configuration of each tooth and root to be treated. As an example, mandibular premolars and the distal root of mandibular molars might show complex configurations, not possibly detailed on a conventional x-ray, but easily seen on the adequate CBCT slice, guiding the clinician on the procedure and avoiding extensive exploratory hard structure removal. 15

16 CBCT images appear to be a reliable, noninvasive measuring tool that can be used in all spatial planes to explore root canal anatomy. With high-resolution CBCT, we are able to obtain a detailed identification of the root canal system, its variations, and anomalies; the position and size of the pulp chamber; calcifications; the number, position, size, extent, and curvatures of the roots and their canals; the tri-dimensional shape of each canal: whether it is round, oval, or has any other form at any specific level of the root; as well as the status of the surrounding bone. Preoperative cone beam volumetric tomography (CBVT) imaging provides additional diagnostic information when compared with preoperative periapical radiographs, which may lead to diagnostic and/or treatment plan modifications in approximately 62% of cases. C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, CBCT as a necessary resource to run precise procedures with minimum wear of dental structures. A preoperative high-resolution focalized CBCT provides detailed information on the exact anatomy of this mandibular incisor to be endodontically treated, not visible on the conventional x-ray, allowing the practitioner to design and individualize an extremely conservative approach, understanding that an incisal cavity is convenient, and as small as the instrument shank used to shape the canals. 16

17 Limited field-of-view (FOV) CBCT should be considered the imaging modality of choice for the initial treatment of teeth with the potential for extra canals, suspected complex morphology (mandibular anterior teeth, maxillary and mandibular premolars and molars), and dental anomalies. High-resolution CBCT slices provide information for precise procedures without an exploratory search and/or wide removal of dental structures. See how the mesial root of this second mandibular molar splits from 1 canal to 2 at the mid-level root. The conventional x-ray and clinical view might make the clinician presume a single canal configuration on this root, thereby missing part of the anatomy. 17

18 CBCT provides detailed information about anatomical characteristics and dimensions undetectable by conventional radiography. Historically, there has been a lack of studies that define the original horizontal width of root canals and the optimum horizontal dimensions for prepared root canals. This limitation forces clinicians to make decisions on canal widening without any scientific literature support. Yi-Tai Jou et al. 2004, 48, C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, CBCT as an aid in conventional root canal treatment provides detailed information on the horizontal dimensions of roots and canals, allowing clinicians to make decisions in accordance with these dimensions, thereby avoiding sub- and over-preparations. 4-year follow-up. 18

19 By taking into account these anatomical dimensions, clinicians can minimize the removal of root dentin while maintaining the dentin thickness as much as possible, especially in the proximal areas or in the thin part of root dentin. Maintaining dentin aids in minimizing the additional tooth bending response and stress distribution in these locations. By knowing in advance the sizes and anatomical details of the tooth to be treated, access cavities can even be diminished to the level where a cuspal protection is not restoratively indicated, by maintaining the occlusal isthmus not larger than onethird of the intercuspal distance. C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, Step 1: three-dimensional imaging The goal of the three-dimensional image assessment is to preclude clinically exploring the anatomy by removing dentin structure while focusing on the actual anatomy and practicing a precise approach for dentin conservation. Three-dimensional imaging is used to provide a detailed assessment of the root canal and root anatomy via a highdefinition localized CBCT scan. It is used to determine the number of roots, canals, sizes, curvatures, and characteristics in order to establish a customized strategy with which to approach the canal anatomy in the most conservative way. Sagital view Axial view C. Bóveda & A. Kishen. Endodontic Topics 2015, 33,

20 Step 2A: preparation of the contracted access cavity The goal is to prepare a contracted endodontic access cavity. The contracted endodontic access cavity is suggested in order to minimize changes in cuspal deformation and decrease cuspal bending by maintaining the bulk dentin structure without significant restorative requirements. In anterior teeth, it is recommended to shift the approach as incisal as possible. In posterior teeth, an attempt should be made to create a small cavity centered in between the roots and existing root canals. Endo Access Endo-Z 20

21 EndoGuide Anterior/Bicuspid Kit (#18052) For Endodontic Access & Exploration Contains all instrumentation to create endodontic access through metal, porcelain and zirconia, #2 metal cutting bfeaturing SS White Great White ur, Great White Z Diamonds along with four EndoGuide Burs ideally suited for locating and accessing single root canals in anterior/bicuspid teeth. EndoGuide Molar Kit (#18051) For Endodontic Exploration Contains seven EndoGuide Burs designed to increase visibility and control during endodontic exploration in molars when locating hidden canals, navigating deeply calcified canals and troughing between canals. 21

22 Even anterior teeth with no complex anatomy, variations, or unusual pathologies can benefit from preoperative CBCT, by certainty of its configuration, with no need for further exploratory structure removal, and by exact determination of the convenience point of approach - generally more incisal and round than traditionally described. This central maxillary incisor with a metal-free crown is a clear example. Conventional x-ray does not show the apical periodontitis present, nor can it be used to guide the approach through the reduced ceramic. 5-year follow-up. C. Bóveda & A. Kishen. Endodontic Topics 2015, 33,

23 C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, The endodontic cavity should be as small as possible while still achieving the biological objectives of the root canal treatment and as wide as the anatomy permits in a particular case. Generally, a contracted cavity is suggested to be slightly wider than the coronal extension of the root canal. This permits the maintenance of some of the roof (dentin soffit) around the entire coronal portion of the pulp chamber. 23

24 The angle of entry to the Palatal canal is out to the MB The angle of entry to the DB canal is out to the MP The MB1 angles of entry are generally from the distal side The MB2 angles of entry can also be from the palatal side 2010, 54, C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, An endodontically treated mandibular molar through constricted access and limited shaping, highlighting its guidelines by area: (A) coronal, (B) pericervical, (C) radicular body, and (D) apical. 24

25 Step 2B: preparation of contracted access cavity using a lesion-guided approach The aim of this phase is to approach the pulp chamber through discontinuities in the crown (caries, restorations, etc.) Caries-leveraged access in a lower first molar. 2010, 54, Individual approach and conservative procedure due to CBCT information. This left central maxillary incisor previously restored with a veneer suffered trauma and, when root canal treatment was needed, CBCT slices showed the viability and opportunity to be less invasive by a vestibular approach. 1-year follow-up. 25

26 C Individual approach and conservative procedure due to CBCT information. This left central maxillary incisor previously restored with a veneer suffered trauma and, when root canal treatment was needed, CBCT slices showed the viability and opportunity to be less invasive by a vestibular approach. Individual approach and conservative procedure due to CBCT information. This left central maxillary incisor previously restored with a veneer suffered trauma and root canal treatment was needed. 26

27 C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, CBCT slices showed the viability and opportunity to be less invasive by a vestibular approach. 1-year follow-up. C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, Lesion-driven approach intended to take advantage of the already absent hard structures due to caries in order to modify the approach as possible through this area and by limiting the restorative needs of the treated tooth. 27

28 It is important to recognize the limiting factors in this approach, which may be beyond the operator s control. For instance tooth position, inclination, mouth-opening capabilities of the patient, anatomical complexity, degree of calcification, and other patient-related factors, all of which would result in increased time required for the endodontic treatment. This phase warrants considerable training and technical competency. Magnification CBCT Cases where coronal hard structures have been affected to the level where a constricted access does not offer the advantage of avoiding a cuspal protective restoration, where the postoperative structural bracing of the coronal remains do not seem significant, or those cases where the individual limitations of the patient do not allow a reduced access cavity can be treated through a conventionally deroofed one. However, by limiting the removal of hard structures at the pericervical, radicular, and apical zones of those teeth, longterm success should improve. An example is this c-shaped second mandibular molar with a deep and wide restoration that results in symptomatic apical periodontitis. Even though the access and the restoration may be considered conventional, the conservative shape retains most of the structural behavior of the original tooth at this level. 6-year follow-up. C. Bóveda & A. Kishen. Endodontic Topics 2015, 33,

29 C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, C. Bóveda & A. Kishen. Endodontic Topics 2015, 33,

30 Cases where coronal hard structures have been affected to the level where a constricted access does not offer the advantage of avoiding a cuspal protective restoration, where the postoperative structural bracing of the coronal remains do not seem significant, or those cases where the individual limitations of the patient do not allow a reduced access cavity can be treated through a conventionally deroofed one. However, by limiting the removal of hard structures at the pericervical, radicular, and apical zones of those teeth, long-term success should improve. An example is this c-shaped secondmandibular molar with a deep and wide restoration that results in symptomatic apical periodontitis. Even though the access and the restoration may be considered conventional, the conservative shape retains most of the structural behavior of the original tooth at this level. 6-year follow-up. Step 3: cervical procedures The goal is to respect and conserve the pericervical dentin. This step is suggested in order to allow better transfer of occlusal forces to the radicular portion of the tooth. In young patients, this goal can be achieved by maintaining the natural funnel shape of the canals. In calcified teeth, attempts to mechanically recreate this cone shape in a meticulous manner by staying away from the furcal area are required. To establish the original horizontal dimensions of the root canal at the pericervical area such that the final preparation size can be established by removing no more than approximately 10% of the dentin at this level. Thus a proposed taper for shaping procedures can be achieved. 30

31 3D-Endo Planner Individual shaping taper determination based on pericervical horizontal measurements of each root and canal on axial CBCT slices. Preoperative CBCT slices can be used to determine the preoperative horizontal dimensions of each root and canal in the pericervical area, measurements not possible to obtain confidently from a conventional x-ray due to superimposition of the structures and magnification due to the nature of the projected image. By knowing the initial size, a maximum point of structure removal can be proposed and then reached by determining the taper of the instruments needed to reach this size. Step 4: instrumentation through a contracted access cavity Radicular body procedures The goal of this step is to avoid any weakening of the root and/or iatrogenic perforations. In this phase, it is necessary to adjust the instruments and their taper to the limits and dimensions of the horizontal configuration of each root/root canal. 31

32 C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, Mandibular first molar with symptomatic apical periodontitis certainly diagnosed with the use of CBCT. A restricted access cavity limits the global visualization of all canals at the same time; however, it is enough to individually approach each root canal. No restorative indication of cuspal protection. 4-year follow-up. Step 4: instrumentation through a contracted access cavity Apical procedures The goal of this step is to produce the minimum tooth structural changes possible while still achieving the biological objectives of root canal treatment. This final step focuses on keeping the apical foramen as small as possible. 32

33 C. Bóveda & A. Kishen. Endodontic Topics 2015, 33, In teeth already crowned, constricted access and limited shaping provides structural advantages by maintaining key dentin, particularly in the pericervical and radicular body area, provided that the anatomy has been previously determined by the analysis of preoperative CBCT slices. The upper first molar with a PFM crown 2010, 54,

34 2010, 54, Respect and conserve the pericervical dentin. 2010, 54,

35 Maxillary first molar with a typical complexity of the MB root. Stay away from the furcal area. 2010, 54, The calcific lower first molar with a gold crown 2010, 54,

36 2010, 54, , 54,

37 2010, 54, , 54,

38 Concluding remarks. The basis for minimally invasive dentistry evolves from the fact that an artificial restoration is of less biological and functional significance when compared to the original healthy dentin tissue. Minimally invasive endodontics encompasses systematic steps to conserve natural tissue in order to benefit the patients. This concept critically hinges on the advances in science and emerging technologies. The skill and knowledge of clinicians remain the most important elements in this paradigm shift. Conservative endodontic cavities seem to satisfy the principles of minimally invasive endodontics by preserving natural dentin, but newer endodontic irrigation strategies are required before minimally invasive root canal enlargement is routinely practiced. Clinical research to evaluate the influence of this paradigm shift on the long-term prognosis of endodontically treated teeth is also warranted There is a lack of evidence about associated risks and benefits of contracted endodontic cavities. Specific investigation into CEC is necessary. Conservative endodontic cavity (CEC) may improve fracture resistance of teeth but compromise the instrumentation of canals. Traditional endodontic cavity (TEC) designs for different tooth types have remained unchanged for decades with only minor modifications. Highlighting convenience form and extension for prevention, TEC promotes the controlled removal of tooth structure beyond gaining access to canal orifices to facilitate cleaning, shaping, and filling of root canals and to prevent procedural complications. Consequent removal of tooth structure, coronal to the pulp chamber, along the chamber walls, and around canal orifices, may undermine the resistance of the tooth to fracture under functional loads. Indeed, fractures and possible subsequent extraction of root-filled teeth have undermined the confidence of dentists and patients in the long-term benefits of endodontic treatment. Clark and Khademi modified the endodontic cavity design to minimize tooth structure removal. In departure from the completely unroofed, coronally divergent, straight-line access to canal curvatures, the conservative endodontic cavity (CEC) preserves some of the chamber roof and pericervical dentin. Clinically, the smallest CEC possible for each tooth can be outlined on cone-beam computed tomographic (CBCT) images by plotting the trajectory toward each canal. Although the preserved tooth structure may offer a benefit of improved fracture resistance under functional loads, the confined CEC outline restricts cleaning, shaping, and filling of the root canals, increasing the risks of inefficient canal instrumentation and the occurrence of procedural errors. R. Krishan et al. JOE 2014, 40,

39 Mechanical efficacy of canal instrumentation is routinely assessed with nondestructive micro-computed tomographic (micro- CT) imaging. Analysis of pre-and postoperative micro-ct images enables measurements of changes in root canal morphology, including volume of the dentin removed and canal wall surface areas untouched by instruments. Fracture resistance of teeth is routinely assessed by simulated functional loading in the Instron Universal Testing machine (Instron, Canton, MA) until fracture occurs. Loading point, force, and direction can be controlled and the load at fracture recorded. The objectives of this study were to assess the potential risks and benefits associated with CEC in different tooth types. The specific aims were to characterize canal instrumentation performed through CEC and TEC regarding the (1) proportion of the untouched canal wall area (UCW), (2) volume of dentin removed (VDR), and (3) load at fracture under dynamic loading. R. Krishan et al. JOE 2014, 40, R. Krishan et al. JOE 2014, 40, Fig. 1. CEC in a mandibular first molar. (A) The occlusal view; for comparison purposes, the outline of TEC is demarcated with a dotted line. (B E) Merged micro-ct images depicting the root canals pretreatment (green) and post-treatment (red) from the (B) buccal view, (C) distal view, (D) lingual view, and (E) mesial view. 39

40 R. Krishan et al. JOE 2014, 40, Fig. 2. Merged micro-ct images (mesial view) depicting root canals pretreatment (green) and post-treatment (red) in maxillary central incisors accessed and instrumented through (A) TEC and (B) CEC. R. Krishan et al. JOE 2014, 40, (Green) TEC CEC = Canal Wall Area Untouched by Instruments during Instrumentation Performed through Conservative (CEC) or Traditional (TEC) Endodontic Cavities Assessed by Micro-CT Imaging. The mean proportion of the total UCW was lowest in the distal roots of molars and highest in premolars, ranging from 36.7% ± 17.2% (distal canals of molars with TEC) to 76.1% ± 17.3% (premolars with TEC). It was statistically significantly higher (P <.04) in the distal canals of molars with CEC than with TEC. Small differences were observed between the CEC and TEC groups in the mesial canals of molars and premolars; in incisors, the difference was more substantial but not statistically significant. Comparing the groups at 3 canal levels, the proportion of UCW differed significantly only in the apical third of molar distal canals; it was higher (P <.05) for CEC than for TEC. 40

41 R. Krishan et al. JOE 2014, 40, (Red) TEC CEC Dentin Volume Removed (mean and standard deviation) by Preparation of Conservative (CEC) or Traditional (TEC) Endodontic Cavities and Root Canal Instrumentation in Extracted Teeth Assessed by Micro-CT Imaging. The mean VDR was least in premolars and greatest in molars, ranging from 8.24 ± 1.64 mm 3 (premolars with CEC) to ± mm 3 (molars with TEC). It was statistically significantly smaller (P <.003) in the CEC group than in the TEC group for all tooth types. Overall, in incisors, premolars, and molars with TEC, the DVR was 44%, 77%, and 103% larger, respectively, than in matched teeth with CEC. Comparing the groups at the crown and 3 canal levels, the DVR differed significantly only at the crown level; it was less (P <.002) for CEC than for TEC for all tooth types. R. Krishan et al. JOE 2014, 40, Load at Fracture (mean and standard deviation) for Extracted Teeth with Conservative (CEC), Traditional (TEC), or No Endodontic Cavities (negative control) Assessed in the Instron Universal Machine. The mean load at fracture was lowest in premolars across all 3 groups. In the CEC and TEC groups, it ranged from ± 56.7 N (premolars with TEC) to ± N (molars with CEC). In premolars and molars, the mean load at fracture for CEC was significantly higher (P <.05) than for TEC, and it did not differ significantly from intact teeth (negative control). Conversely, in the TEC group, the load at fracture in premolars and molars was significantly lower (P <.05) than in intact controls. For incisors, the mean load at fracture did not differ significantly among the 3 groups. 41

42 Discussion The CEC concept, although consistent with that of minimally invasive dentistry, has not impacted on the mainstream practice of endodontics. Benefits of tooth structure conservation and possible drawbacks have not been well supported by research data. Clinicians may use small field-of-view CBCT imaging for planning CEC outlines in clinical practice. Untouched canal wall area Because the distal canals of mandibular molars typically are oval with pronounced buccallingual tapers and a wide range of apical diameters, instrumentation efficacy is commonly compromised, especially in the apical third, resulting in over 60% of UCW. Instrumentation in oval-shaped canals might be further compromised by the restrictive CEC. Thus, the distal outline of CEC should be slightly extended buccolingually to better match the wide dimension of the distal canals. This may facilitate approaching the distal canal as 2 pathways, which is suggested to improve instrumentation efficacy. Dentin volume removed CEC consistently resulted in less dentin removal than TEC, primarily at the tooth crown level. Coronal dentin conservation was greatest in molars, moderate in premolars, and least in incisors. Fracture resistance The fracture resistance of molars and premolars with CEC was about 2.5-fold and 1.8-fold more, respectively, than in matched teeth with TEC but comparable for incisors with both cavity designs. Molars and premolars with CEC showed comparable fracture resistance to intact teeth of the same type, whereas teeth with TEC were less resistant than intact teeth. Dentin preservation through cavity size reduction improved the fracture resistance of teeth. Specifically, the removal of cervical dentin, inherent to TEC, increases cuspal deflection, which may enhance the potential for fracture even if not significantly altering the stiffness of the tooth. The removal of cervical dentin also increased the frequency and severity of cuspal fracture in clinical reports. R. Krishan et al. JOE 2014, 40, Discussion An estimated 4.6%-7.5% of root-filled teeth, predominantly molars and premolars, are extracted within 4-5 years after treatment with coronal fractures causing up to 47% of post-treatment extractions. Post-treatment fractures are frequently attributed to a pronounced loss of dental tissues; although the 5-year survival rate of root-filled molars without crowns is 36%, it increases to 78% for molars with maximum coronal tooth structure remaining. In mandibular premolars and molars, CECs improved resistance to fracture and, in premolars, presented cuspal chipping patterns less catastrophic than full cuspal fractures observed with TEC. These benefits of CEC in premolars, the most prone to fracture after endodontic treatment, were not offset by the apparent risks of compromised instrumentation, suggesting that CEC should merit consideration as a standard cavity design. In molars, the benefit of increased fracture resistance must be weighed against the risk of compromised canal instrumentation in distal canals. Although the impact of compromised instrumentation on the prognosis of healing is yet unclear, modest widening of the distal outline of CEC to better debride oval-shaped distal canals might reduce this risk. Therefore, even in molars, CEC should merit consideration as a preferable cavity design. Medicine and dentistry have been moving toward minimally invasive procedures that may benefit patients. Although technological advances such as CBCT imaging, operating microscopes, and nickel-titanium instruments enable this progress, clinicians have to adapt their skills to meet the challenge of working effectively in confined spaces. CECs are likely to benefit patients, but they challenge clinicians to address all canals, debride all pulp tissue from pulp horns, and avoid procedural complications while lacking convenience form. Individual skilled clinicians have met this challenge, suggesting the practicality of CEC. It may be appropriate for the larger endodontic community to revisit endodontic access cavities in premolars and molars to better align them with CEC. R. Krishan et al. JOE 2014, 40,

43 Discussion In conclusion, CEC afforded conservation of coronal dentin in incisors, premolars, and molars and increased resistance to fracture in molars and premolars, but it compromised the efficacy of canal instrumentation in the distal canals of molars. These results appeared to support the rationale for the revision of the guidelines for endodontic cavity design in premolars and molars focused on the conservation of coronal dentin. R. Krishan et al. JOE 2014, 40, dendo Step1 and 2 43

44 3Dendo Step 3 3Dendo Step 4 44

45 3Dendo Step 5 3Dendo Saving 45