“Comparative evaluation of Fracture strength of Endodontically treated Maxillary Molars with three different Access Cavity designs and correlating it to Volume percentage of enamel and
dentin removed measured using CBCT- An In Vitro Study”
A dissertation submitted
in partial fulfillment of the requirements for the degree of
MASTER OF DENTAL SURGERY BRANCH IV
CONSERVATIVE DENTISTRY & ENDODONTICS
THE TAMILNADU DR.M.G.R. MEDICAL UNIVERSITY CHENNAI – 600 032
2017 - 2020
DECLARATION BY THE CANDIDIATE
I hereby declare that this dissertation titled“Comparative evaluation of Fracture strength of Endodontically treated Maxillary Molars with three different Access Cavity designs and correlating it to Volume percentage of enamel and dentin removed measured using CBCT- An In Vitro Study”is a bonafide and genuine research work carried out by me under the guidance of DR.P.HEMALATHA, M.D.S., Professor, Head of the Department, Department of Conservative Dentistry and Endodontics, Best Dental Science College, Madurai - 625104.
DR.G.SUDHARSAN
CERTIFICATE BY GUIDE
This is to certify that DR.G.SUDHARSAN, Post Graduate student (2017 - 2020) in the Department of Conservative Dentistry and Endodontics, Best Dental Science College, Madurai has done this dissertation titled “Comparative evaluation of Fracture strength of Endodontically treated Maxillary Molars with three different Access Cavity designs and correlating it to Volume percentage of enamel and dentin removed measured using CBCT- An In Vitro Study” under my direct guidance and supervision in partial fulfillment of the regulations laid down by the Tamil Nadu DR.M.G.R. Medical University, Chennai – 600032, for M.D.S., Conservative Dentistry and Endodontics (Branch IV) Degree Examination.
DR.P. HEMALATHA M.D.S., Professor and guide, Head of the Department,
Department of Conservative Dentistry and Endodontics, Best Dental Science College,
Madurai – 625104.
ENDORSEMENT BY HEAD OF THE DEPARTMENT AND HEAD OF THE INSTITUTION
This is to certify that the dissertation titled “Comparative evaluation of Fracture strength of Endodontically treated Maxillary Molars with three different Access Cavity designs and correlating it to Volume percentage of enamel and dentin removed measured using CBCT- An In Vitro Study ”is a bonafide research work done by DR.G.SUDHARSAN, Post Graduate student (2017 - 2020) in the Department of Conservative Dentistry and Endodontics, under the guidance of DR.P. HEMALATHA MDS., Professor and Guide, Department of Conservative Dentistry and Endodontics, Best Dental Science College, Madurai – 625104.
DR.K.S.PREMKUMAR,M .D.S.,
Principal
Best Dental Science College, Madurai-625104.
DR.P. HEMALATHA M.D.S., Professor and guide
Head of the Department
Department of Conservative Dentistry and Endodontics
“Gratitude is the fairest blossom which springs from the soul.”
– Henry Ward Beecher I take this opportunity to express my immeasurable appreciation and deepest gratitude for the Great people who have guided me in one way or the other in making this dissertation possible.
I express my sincere gratitude to our beloved Chairman and managing trustee of Ultra Trust, Prof.
K.R.Arumugam. M.Pharm., and our vice-chairman, Prof.Dr.A.Babu Thandapani.
M.Pharm.,Ph.D., for their care and support throughout my course period.
It is my extreme pleasure to extend my sincere gratitude to our respected Principal Prof.Dr.K.S.Premkumar.M.D.S., who has always been a great mentor, philosopher and pillar of support during my course period.
I extend my sincere thanks to my Guide Prof.Dr.P.HEMALATHA. M.D.S., Professor and Head of the Department, Department of Conservative Dentistry and Endodontics, Best Dental Science College, for the extreme patience to correct all my mistakes and being supportive throughout every moments to complete my dissertation work.
My sincere thanks to Dr.M.Muthalagu. M.D.S., Reader, Dr.I.PORKODI. M.D.S.,Reader, Dr.A.Velmurugan. M.D.S., Reader, Dr.M.Priyanka. M.D.S., Senior lecturer, Dr.M.Shahul Hameed.
M.D.S., Senior Lecturer ,Department of Conservative Dentistry and Endodontics, Best Dental Science College, for their support.
My sincere thanks to Mrs. Vidhya M.Sc., Biostatistician, for helping me for my statistical analysis. I extend my thanks to Library staffs, for their support in searching articles. I am grateful to my Co-PG and juniors for their extreme help and support. I also want to thank all non-teaching staffs of the Department of Conservative Dentistry and Endodontics, Best Dental Science College.
Above all I thank God Almighty for His blessings and grace
CERTIFICATE -II
This is to certify that this dissertation work titled “Comparative evaluation of Fracture strength of Endodontically treated Maxillary Molars with three different Access Cavity designs and correlating it to Volume percentage of enamel and dentin removed measured using CBCT- An In Vitro Study” of the candidate Dr.G.SUDHARSAN with registration number 241717451 for the award of Masters of Dental Surgery in the branch of Conservative Dentistry and Endodontics. I personally verified the Urkund.com website for the purpose of plagiarism check. I found that the uploaded thesis file contains from intro duction to conclusion pages and result shows 5 percentage of plagiarism in the dissertation.
Guide & Supervisor sign with seal.
DECLARATION
TITLE OF DISSERTATION
Comparative evaluation of Fracture strength of Endodontically treated Maxillary Molars with three different Access Cavity designs and correlating it to Volume percentage of enamel and dentin removed measured using CBCT- An In Vitro Study
PLACE OF STUDY BEST DENTAL SCIENCE COLLEGE, MADURAI – 625104
DURATION OF THE COURSE 3 YEARS
NAME OF THE GUIDE DR.P. HEMALATHA MDS HEAD OF THE DEPARTMENT DR.P. HEMALATHA MDS
I hereby declare that no part of the dissertation will be utilized for gaining financial assistance/any promotion without obtaining prior permission of the Principal, Best Dental Science College, Madurai – 625104. In addition, I declare that no part of this work will be published either in print or in electronic media without the guide who has been actively involved in dissertation. The author has the right to reserve for publish of work solely with the prior permission of the Principal, Best Dental Science College, Madurai – 625104.
Head of the Department Guide Signature of the candidate
COPYRIGHT
DECLARATION BY THE CANDIDATE
I hereby declare that the Tamilnadu Dr.M.G.R. Medical University, Tamilnadu shall have the rights to preserve, use and disseminate this research in print or electronic format for academic or research purpose.
Signature of the candidate (Dr.G.SUDHARSAN) Date:
Place: MADURAI
C THE TAMILNADU DR.M.G.R MEDICAL UNIVERSITY, TAMILNADU
This agreement herein after the “Agreement” is entered into on this day of between the Best Dental Science College represented by its Principal having address at Best
Dental Science College, Madurai – 625104. (Hereafter referred to as “the college”).
And
DR.P. Hemalatha M.D.S., aged 42 years, working as Professor and Head of the Department at the college, having residence address 4/66, Sappani Kovil lane, North Masi street, Madurai-625001. (Herein after referred to as the Principal Investigator).
And
DR.G.Sudharsan, aged 27 years, studying as postgraduate student in the Department of Conservative Dentistry and Endodontics in Best dental Science College. Madurai-625104 (Herein after referred to as the PG/research student and co-investigator).
Whereas PG / Research student as part of his curriculum undertakes to research on
“Comparative evaluation of fracture strength of endodontically treated maxillary molars with three different access cavity designs and correlating it to volume percentage of enamel and dentin removed, measured using CBCT – An In Vitro study”
for which purpose PG/Principal Investigator shall act as Principal Investigator and the college shall provide requisite infrastructure based on availability and also provide facility to the PG /Research student as to the extent possible as a Co–investigator.
Whereas the parties, by this agreement have mutually agreed to the various issues including in particular the copyright and confidentiality issues that arises in this regard.
Now this agreement witnessed as follows:
1.The parties agree that all the Research material and ownership therein shall become the vested right of the college, including in particular all the copyright in the literature including the study, research and all other related papers.
2. To the extent that the college has legal right to do go, shall grant to license or assign the copyright do vested with it for medical and or commercial usage of interested persons / entities subject to a reasonable terms / conditions including royalty as deemed by the college.
3. The royalty so received by the college shall be shared equally by all the patients.
4. The PG student and Principal Investigator shall under no circumstances deal with the copyright, Confidential information and know – how generated during the course of research / study in any manner whatsoever, while shall sole vest with the college.
5. All expenses pertaining to the research shall be decided upon by the principal investigator / co-investigator or borne sole by the PG/Research student (co-investigator).
6. The college shall provide all infrastructure and access facilities within and in other institutes to the extent possible. This includes patient interactions, introductory letters, recommendation letters and such other acts required in this regard.
7. The Principal Investigator shall suitably guide the student Research right from selection of the Research Topic and Area till its completion. Howeverthe selection and conduct of research, topic and area research by the student researcher under guidance from the principal investigator shall be subject to the prior approval, recommendations and comments of the Ethical Committee of the college constituted for this purpose.
8. It is agreed that as regards other aspects not covered under this agreement, but which pertain to the research undertaken by the student Researcher, under guidance from the Principal Investigator, the decision of the college shall be binding and final.
9. If any dispute arises as to the matters related or connected to this agreement herein it shall be referred to arbitration in accordance with the provisions of the arbitration and conciliation Act, 1996. In witness whereof the parties herein above mentioned have on this day month and year herein above mentioned set their hands to this agreement in the presence of the following two witnesses.
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Witnesses
PG student
Student guide
AIM
To evaluate the fracture strength of endodontically treated extracted maxillary molars with three different access cavity designs– Traditional Endodontic Cavity (TEC), Conservative-
“TRUSS” Endodontic Cavity (CEC) and Ultra conservative “NINJA” Endodontic Cavity (NEC)access preparations and to correlate it to the volume percentage of enamel and dentin removed which was measured using CBCT.
MATERIALS AND METHODS
Sixty intact human maxillary molars extracted for periodontal reasons were selected and the samples were randomly grouped (n= 20) into Group I – Traditional (TEC), Group II – Conservative(CEC) and Ninja (NEC) endodontic access cavities. All the tooth samples were subjected to a Pre- operative CBCT imaging (NEWTOM cone beam computer tomography) with the samples mounted in a custom- made wax rim. Using Digital Imaging and Communications in Medicine data (DICOM) software the total enamel and dentin crown volume for each tooth were calculated. Then, TEC, CEC and NEC cavities access of all teeth were prepared in respected groups. The teeth samples of TEC, CEC and NEC groups were then subjected to a post-operative CBCT imaging. The volume percentage of coronal enamel and dentin removed by TEC, CEC and NEC access cavity preparations were calculated using DICOM software again. The volume percentage of coronal enamel and dentin removed in TEC, CEC, NEC were calculated using formula:(Reduction of tooth / total volume of tooth) × 100. Then, biomechanical preparations and obturation were done, followed by a post-endodontic coronal restoration with light cure composite resin for all the sixty samples.
The radicular portions of each sample were embedded in acrylic resin block and mounted in the Instron Universal Testing Machine. The coronal part of the teeth were loaded at their central fossa at a 30ᵒ angle from the long axis of the tooth. The loads at which the tooth crowns were fractured indicated by the software of the load testing machine, were recorded in Newtons. The data obtained were statistically analyzed.
RESULTS
The results showed that as the Volume of the tooth structure removed during the cavity preparation is inversely proportional to the fracture resistance of the teeth. Hence the Group III NEC group showed minimal loss of tooth structure volume (7.92%),suggesting that this can influence positively in the increase in fracture resistance (1403.08 N) of the tooth following a coronal restoration. Pairwise comparison was made among the groups which showed that the mean fracture resistance values of Group III NEC showed statistically significant mean difference values in Group I TEC followed by Group II CEC.
CONCLUSION
Within the limitations of this study it can be concluded that the Group III Ultra-conservative
”NINJA” access showed increased fracture resistance of endodontically treated maxillarymolars with the least mean volume percentage of tooth structure removed when compared to TEC and CEC groups.
Keywords:Access cavity preparation, Traditional, Truss, Ninja, Cone beam computed tomography, Post- Endodontic Restoration, Fracture resistance.
LIST OF ABBREVATION USED ( IN ALPHABETICAL ORDER)
ABBREVATION WORD EXPLANATION
CBCT Cone Beam Computed Tomography
CEC Conservative Endodontic cavity
DICOM Digital Imaging and Communications in Medicine data
EDTA Ethylenediaminetetraacetic Acid
FOV Field of View
IAF Initial Apical File
MAF Master Apical File
N Newtons
NEC Ninja Endodontic Cavity
TEC Traditional Endodontic Cavity
WL Working Length
LIST OF FIGURES
FIGURE NO FIGURES PAGE NO
1 Images of sample selection 36
2 Images of Randomization 37
3 Images of pre-operative CBCT imaging 38
4 CBCT Image – Axial section (pre-op) 39
5 CBCT Image – Saggital section (pre-op) 39
6 CBCT Image – Coronal section (pre-op) 40
7 Images of Traditional Endodontic Access Cavity preparations
41
8 Images of Conservative Endodontic Access Cavity preparations
42
9 Images of Ninja Endodontic Access Cavity preparations
43
10 CBCT image of TEC (post-op) 44
11 CBCT image of CEC Buccal (post-op) 44
12 CBCT image of CEC Palatal (post-op) 45
13 CBCT image of NEC (post-op) 46
14 Images of obturation 47
15 Images of coronal composite restoration 47
16 Images of tooth moulded in acrylic block 48
17 Images of universal testing machine 48
LIST OF TABLES
TABLE NO DESCRIPTION PAGE NO
1 Repeated measures ANOVA - Fracture resistance 50
2 Repeated measures ANOVA - Volume percentage 51
3 Pairwise comparison – Fracture resistance 52
4 Pairwise comparison – Volume percentage 53
TABLE OF CONTENTS
S.NO CONTENTS PAGE NO
1 INTRODUCTION 1
2 AIMS AND OBJECTIVES 7
3 REVIEW OF LITERATURE 8
4 MATERIAL AND METHODOLOGY 36
5 FLOW CHAT 49
6 RESULTS 50
7 DISCUSSION 54
8 SUMMARY 59
9 CONCLUSION 61
10 BIBLIOGRAPHY
11 ANNEXURE
INTRODUCTION
Access cavity is defined as ‘The opening prepared in a tooth to gain entrance to the root canal system for the purpose of cleaning, shaping and obturation. The endodontic triad consists of biomechanical preparation, microbial control and complete obturation of the canal space. However, access to the canal orifices and the apical foramina are not done properly, achieving the goals of triad will be difficult and time consuming. The ultimate goal of endodontic treatment is to create an environment in which the body can heal itself. Adequate access is the key to achieving endodontic success1.
The objective of the access cavity preparation is to provide a smooth free – flowing tapered channel from the orifice to the apex that allows instruments, irrigants and medicaments to attempt cleaning and shaping of the entire length and circumference of the canal, with as minimal loss of structural integrity to the tooth as possible2.
The importance of access cavity preparation is to facilitate straight – line access which describes a preparation that provides a straight or outwardly flared, unimpeded path from the occlusal surface to the apex. Access is continually adjusted until the selected master apical file (MAF) reaches working length (WL) without undue stress upon it. The diameter of the apical preparation also effects the access preparation. To prepare a larger apical diameter, corresponding larger, stiffer files that have a stronger tendency to straighten the canal have to be taken to the apex. In order to avoid stripping on the furcal surface or transporting the apex, one must achieve straight – line access beforehand3.
The pulp complex should be conceptualized as a continuum beginning occlusally at the pulp horns and ending at the apical foramina. In order to remove pulp tissue entirely from the pulp complex, the coronal portion of the complex must be accessed in a manner that will permit pulp removal and facilitate the location and debridement of the root canals without compromising the strength of the coronal enamel and dentin4.
According to Krasner and Rankow5, laws governing access cavity preparation were:
Law of centrality:
The floor of the pulp chamber is always located in the center of the tooth at the level of the CEJ.
Law of concentricity:
The walls of the pulp chamber are always concentric to the external surface of the tooth at the level of CEJ, that is, the external root surface anatomy reflects the internal pulp chamber anatomy.
Law of CEJ:
The distance from the external surface of the clinical crown to the wall of the pulp chamber is the same throughtoutthe circumference of the tooth at the level of CEJ. The CEJ is the most consistent repeatable landmark for locating the position of the pulp chamber.
Law of symmetry 1:
Except for the maxillary molars, the orifices of the canals are equidistant from a line drawn in a mesial – distal direction, through the pulp chamber floor.
Law of symmetry 2:
Except for the maxillary molars, the orifices of the canals lie on a line perpendicular to a line drawn in a mesial – distal direction across the center of the floor of the pulp chamber.
Law of color change:
The color of the pulp chamber floor is always darker than the walls.
Law of orifice location 1:
The orifices of the root canals are always located at the junction of the walls and the floor.
Law of orifice location 2:
The orifices of the root canals are located at the angles in the floor – wall junction.
Law of orifice location 3:
The orifices of the root canals are located at the terminus of the root developmental fusion lines.
The sequence of steps for access cavity preparation:
The first objective is to penetrate through the occlusal surface
The second objective is to find the pulp chamber
The third objective is to ‘unroof’ the dentin that covers the pulp chamber
The fourth objective is to obtain uniform contact of the file with the access cavity wall
The fifth objective is to obtain straight line access6.
Various methods of access cavity design:
In traditional endodontic access cavity design centre of the pulp chamber is the target of initial penetration. The outline form is determined by shape of the pulp chamber which also determines the occlusal extent of the cavity. The convenience form is achieved by removing certain degree of dentin for specific locations and gaining straight line access to root canal orifices. This is based on Black’s concept of extension for prevention, which promotes the sacrifice of additional tooth structure to increase its resistance of fracture under functional loads7.
Recently, Clark and Khademi8 modified a new model of endodontic access cavity design, focusing on the minimal removal of tooth structure and this was known as the conservative endodontic access cavity design. Diverging from the general basic principles of traditional endodontic access cavity design, these conservative access cavity design preserve part of the pulp chamber roof and pericervical dentin. The critical zone which is roughly 4mm coronal to the crestal bone and 4mm apical to crestal bone, is crucial to transferring load from the occlusal table to the root and much of pericervical dentin is irreplaceable.
A small piece of roof around the entire coronal portion of the pulp chamber is known as soffit. The primary reason to maintain the soffit is to avoid collateral damage of the gouging of the lateral walls. This 360ºsoffit helps in maintaining dentin as it rounds corner places far from the cervical area, which is often where fracturing initiates in the endodontically accessed molar.
In conservative endodontic access cavity design, the teeth are accessed at the central fossa and they are extended only as necessary to detect canal orifices. This helps in preserving the pericervical dentin and soffit. The conservative endodontic access cavity design was considered as an alternative to the traditional endodontic access cavity design in maintaining mechanical stability which helps in the long – term survival and the function of the endodontically treated teeth8.
The orifice directed design is also known as the ‘truss’ access cavity. It is an approach to conservative access cavity where separate cavities are prepared to approach canals. In mandibular molars, two separate cavities are prepared to approach the mesial and distal canals. In maxillary molars, the mesio and distobuccal cavities are been approached in one cavity and another separate cavity for the palatal canal. The aim of preparing such conservative cavities is to preserve the dentin i.e., leaving a truss of dentin between the two cavities that has been prepared9.
Another newer method of access cavity preparation called Ninja access design. To obtain an access ‘ninja’ outline, the oblique projection is made towards the central fossa of the root orifices in an occlusal plane. As the endodontic access is parallel with the enamel cut of 90º or more to the occlusal plane, it is easier to locate the root canal orifices even from the different visual angulations10.
A cone beam computed tomography technology can better guide conservative and ninja preparation by providing relevant information for pre – access analyses11. Clinical implications of CBCT in conservative and ultraconservative preparation are:
To enhance the accuracy of conservative and ninja access cavity design
To enhance the efficacy of conservative and ninja access cavity design for inexperienced operators
To reduce procedural errors during conservative and ninja access cavity preparation One of the most powerful applications of CBCT is its ability to provide insight as to the number of root canals and their location within a given tooth, before the treatment is even started. CBCT technology can aid in the detection of these systems and has been shown to provide a higher specificity and sensitivity when compared to intraoral radiographic assessments in the detection of the MB2 canal. Knowledge of the number root canals present in addition to their orientation within the tooth as well as their orientation relative to each other, could allow for a more precise access cavity and thus, the preservation of dentin with conservative access cavity preparation and ninja access cavity preparation. Additional information such as the presence of complex anatomy (i.e isthmus presence, broad canals buccolingually, developmental anomolies, etc.) can be planned for and taken into consideration all with the goal of increasing the efficacy and accuracy of various techniques of access cavity preparation12.
AIM
To evaluate the fracture strength of endodontically treated extracted maxillary molars with three different access cavity designs
1. Traditional
2. Conservative- “TRUSS”
3. Ultra conservative “NINJA”
Correlate to volume percentage of enamel and dentin removed measured using CBCT.
OBJECTIVES
To evaluate using CBCT, the volume percentage of tooth structure removed in the endodontically treated maxillary molars in 3 groups with different access cavity preparations.
To evaluate the fracture strength of tooth following a post endodontic restoration in the 3 groups prepared with different access designs, using Universal testing machine.
To compare the fracture strength of the coronally restored root canal treated maxillary molars in the 3 groups with the volume percentage of the dentin and enamel removed.
REVIEW OF LITERATURE:
David Assif et al., (2003) assessed the fractureresistance of endodontically treated molars with various degrees of tooth structure loss restored with amalgam underocclusal load. Ninety non carious endodontically treated teeth were divided into nine experimental groups ranging from a conservative endodontic access to removal of all cusps and restored with standardized technique to their original contour with amalgam. The specimens were subjected to fracture resistance in universal testing machine. The results of this study showed that the conservative endodontic access group and group with removal of all cusps presented higher fracture resistance when compared with other groups with no significant difference in fracture resistance under simulated load between other seven groups. It was concluded that the endodontically treated molars with conservative endodontic access that were restored to their original contour with amalgam presented highest fracture resistance13.
A L – Omiri et al., (2006) investigated the effects of retained coronal dentin restored with composite core and different post and core systems. Four groups of thirty single rooted teeth divided into three subgroups and restored with carbon fibre, glass fibre and radix titanium posts fixed with dual cure resin cement. Group A had no retained coronal dentin which was control. The Groups of B, C and D had 2, 3 and 4 mm of retained coronal dentin. The specimens were subjected to universal testing machine. The results of this study showed that teeth with retained dentin were more fracture resistance. The values was not significantly different between Groups B, C and D. In GroupAfracture mode was core and vertical oblique but combination of core, coronal dentin and root fractured occurred in other groups. It was concluded that teeth resistance to fracture was increased with retained coronal dentin. The fracture pattern of teeth was not related to the amount of retained dentin if it was greater than 2mm high14.
Ikram et al., (2009) evaluated the volume of tooth structure loss after caries removal, access cavity preparation, root canal preparation, fiber post space and cast post
preparation in carious premolar teeth. Twelve extracted human premolars with mesial or distal caries penetrating into pulp chambers were selected. The specimens were scanned in micro – computed tomography. After each operative procedures the loss of hard tooth tissue volume was calculated. The results of this study showed that percentage of preoperative hard tooth tissue volume lost after caries removal was 8.3%, 12.7% in access cavity preparation, 13.7% in root canal preparation, 15.1% in fiber post space and19.2% in cast post preparation respectively. It was concluded that access cavity and post space preparation losses largest hard tooth tissue followed by cast post preparation losses more tooth structure than fibre post15.
ElAyouti et al., (2011) assessed the influence of cusp reduction and coverage with composite on fracture resistance of premolars with prepared access cavities. Endodontic access cavities were prepared in sixty premolar divided into four test groups R1, R2, R3 and NRand the test groups were prepared with MOD cavities and extended toward one cusp. In addition R1, R2, R3 of same cusp was reduced in height to 3.5mm. composite resin cusp coverage and MOD restoration were performed. Ten intact premolars were positive control and ten MOD-prepared premolars without restoration were negative control. The specimens were subjected to fracture test. The results of this study showed that the fracture resistance of cusp-reduced groups in R1, R2 and R3 was significantly higher than the non-reduced cusp group and compared to intact-premolar group. It was concluded that cusp reduction and coverage with composite resin significantly increased the resistance to fracture of premolar teeth with MOD and endodontic access cavities16.
Marcelo Hass Villas-Boas et al.,(2011) determined mesiodistal and buccolingual diameter, apical volume and presence of isthmuses at apical level of mesial root canals of mandibular molars. Sixty extracted first and second mandibular molars were scanned using micro computed tomography. The mesiodistal and buccolingual distances of root canals were measured between 1 to 4 mm levels. The volume of root canal anatomy
between 1 to 3mm apical levels was obtained. The results of this study showed that the medians of mesiodistal diameter at 1, 2, 3 and 4mm levels in mesiobuccal and mesiolingual canals were 0.22 and 0.23mm, 0.27 and 0.27mm, 0.30 and 0.30mm, 0.36 and 0.35mm. The buccolingual length at 1, 2, 3 and 4mm levels were 0.37 and 0.35mm, 0.55 and 0.41mm, 0.54 and 0.49mm, 0.54 and 0.60mm respectively. The presence of isthumus were more prevalent at 3 to 4mm level. The mean of the volume of apical third was 0.83mm³. It was concluded that mesial root canals of mandibular molars did not present a consistent pattern. A high variability of apical diameters exists. The presence of isthmuses at the apical third was not uncommon even at 1mm apical level17.
Ibrahim Hamouda et al., (2011) evaluated resistance to fracture of posterior teeth which restored with modern restorative materials. Fifty maxillary premolars divided into five groups; Group 1 were unprepared teeth, Group 2 were prepared without restoration, Group 3 were prepared and restored with tetricceram HB, Group 4 were prepared and restored with InTens and Group 5 were prepared and restored with Admira restorative material. The specimens were subjected to universal testing machine. The results of this study showed that the teeth restored with Admira had highest fracture resistance followed by InTens and tetricceram HB. Prepared, unrestored teeth were the weakest group. It was concluded that use of Admira and InTens restorative materials significantly strengthen maxillary premolars with MOD preparation18.
UnniEndal et a1.,(2011) evaluated three dimensional analysis of the isthmus area of mesiobuccal root cana in mandibular molars with micro-computed tomography and to calculate the amount of debris and filling material in isthmus after instrumentation and filling . Mandibular molar were imaged before and after instrumentation and after filling with thermafil filling technique. The characterstics of isthmus were quantitatively monitored during whole treatment and images were segmented and quantified. The surface area of the isthmus, volume of debris and filled space in isthmus after were
evaluated.The results of this study showed that the average Percentage of isthmus surface area and isthmus volume after instrumentation 21.4% and 94% whole root canal system respectively. It was concluded that dentin debris were packed into isthmus area during instrumentation of lower molar mesial canals despite continuous irrigation during and after instrumentation and it prevents penetration of filling material and sealer into the isthmus area19.
Xie et a1.,(2012) evaluated the fracture resistance and patterns of filled maxillary first premola with mesio-occlusal cavity restored using composite resin. One hundred extracted maxillary first premolars divided into five groups. For group one remained untreated was negative control.Traditional root canal treatment with additional mesial- occlusal cavity preparation was prepared on remaining groups and specimens were restored intracoronally with direct composite resin was positive control. In group three, palatal cusps reduced and restored with composite resin covering palatal cusp. In group four, conventional full coverage of composite resin restored buccal and palatal cusps along with distal marginal ridge.In group five,modified full coverage of composite resin restored buccal and palatal cusps and the fracture resistance analyzed using universal testing machine.The results of this study showed the group one,four and five was significantly higher than group two and three. It was concluded that direct composite resin restore in root filled maxillary first premolar teeth had greater fracture resistance than those restored with full coverage designs 20.
TsAshwiniSonam Bhandari et al., (2012) investigated the influence of cervical preflaring on apical file size determination using four different rotary instruments. Fifty maxillary premolars were divided into five groups and access opening was done and working length established with 8 no k-file for each canal. In group 1 no preflaring serves as control. Cervical and middle third preflaring of root canals were done in group 2, 3, 4 and 5 using Gates Glidden drills, Protaper instruments, Race instruments and Galaxy files
respectively. After preflaring, apical size determination was done and IAF was fixed at working length. Teeth were sectioned transversally 1mm from apex, with binding file in position. The samples were imaged under stereomicroscope with 30X magnification. The results of this study showed that preflaring with Race instruments lead to most accurate determination of the IAF followed by Protaper, Galaxy files and Gates Glidden drills. It was concluded that traditional method of apical size determination and cervical preflaring increases the accuracy of apical size determination21.
Rajesh Krishnan et al., (2014) assessed the efficacy of conservative endodontic cavity on root canal instrumentation and resistance to fracture. Extracted human maxillary incisors, mandibular premolar and molars were scanned with micro-computed tomography before access and after instrumentation of CEC and TEC. The proportion of untouched canal wall area(UCM), volume of dentin removed (VDR) and load at fracture under dynamic loading were evaluated. The results of this study showed that proportion of UCM was significantly higher in the apical third of the distal canal of lower molar.
Similarly VDR was significantly less in contracted endodontic cavity at crown level and the mean load at fracture for contracted endodontic cavity was significantly higher than for traditional endodontic cavity in premolars and molars. It was concluded that conservation of coronal dentin increased the resistance to fracture in premolars and molars but it compromised the efficacy of canal instrumentation in distal canal of molars22.
Sahin et al., (2014) evaluated the effect of fiber by using different techniques on fracture resistance of endodontically treated molars with MOD cavities. Forty extracted human molars divided into four groups. Group one was control and remaining groups were root canal treated and MOD prepared followed by restorationwith composite resin in group 2.Fiber was inserted into cavities in buccal to lingual direction by coating the occlusal one-third of buccal wall to the occlusal one-third of lingual wall in group 3 and teeth were restored with composite resin. In group 4, the flowable resin was coated inside cavities with fiber before restoring teeth with composite resin. The compressive loading
of teeth was performed at cross-head speed of 0.5mm\min. The results of this study showed that the fracture resistance values of all groups were compared. The differences between group 2 and 3 or group 2 and 4 were found statistically significant. It was concluded that the use of the fiber under composite resin with a flowable resin increased fracture strength to MOD cavities23.
Dan Zhao et al., (2014) described canal shaping properties of ProTaper Next, ProTaper Universal and WaveOne Nickel titanium instruments in mandibular first molars by using micro computed tomographic (micro – CT) scanning. Thirty six maxillary first molars with two separate mesial canals and one distal canal were scanned preoperatively and postoperatively by using micro-CT. Canals were prepared with PTU, PTN and Waveone followed by volume of untreated canal, the volume of dentin removed after preparation, the amount of uninstrumented area and transportation to the coronal, middle and apical thirds of canals were evaluated. The results of this study showed that instrumentation of canals increased their volume and surface area. The distal canals had higher proportion of unprepared surfaces than mesial canals. The PTN system produced less transportation in apical third of mesial canals with no significant difference on apical transportation in distal canals. It was concluded that PTN, PTU and Waveone instruments shaped root canals in mandibular first molars without significant shaping errors. The curved canals prepared with PTN was least apical transportation than canals prepared with Waveone and PTU24.
James A. Eaton et al., (2015) investigated micro-computed tomographic evaluation of the influence of root canal system landmarks on access outline forms and canal curvatures in mandibular molars correlated with the theoretical distance of orifice location and changes in canal primary curvature. Thirty calcified extracted mandibular molars examined by micro-computed tomography and Three-dimensional volume reconstruction were made followed by root canal landmark identification and plotted,
canal orifices, canal position at furcation level and pulp horn location. All landmark projected on occlusal surface and minimally invasive access, straight-line furcation access and straight-line radicular access were proposed. All access design were determine theoretical distance of orifice location and canal primary curvature. The results of this study showed that the orifice relocation distance in radicular-based access outline was greater than furcation access and resulted greater change in canal curvature. The canal curvature for minimally invasive access showed highest mean angle followed by straight- line furcation and straight-line radicular accesses. It was concluded that the use of different landmarks to establish access outline designs affected the primary angle of curvature in calcified mandibular molars25.
Zehnder et al., (2015) presented a novel method of 3D printed templates to gain guided access to root canals and to evaluate its accuracy. Sixty human teeth were placed in six maxillary jaw models and preoperative CBCT scans were matched with intra-oral scans.
Templates were produced by 3D printer. After access cavity preparation by two operators, postoperative CBCT scan superimposed and calculated by the deviation of planned and prepared cavity. The results of this study showed that after cavity preparation with guided endodontics all root canals were accessible and deviation of planned and prepared access cavities were 0.16 to 0.21mm at base of bur and 0.17 to 0.47mm at tip of bur. It was concluded that guided endodontics allowed accurate access cavity preparation and utilizing printed templates for guidanceupto the apical third26.
Yasa et al., (2015) determined standardizing model for correlating fracture resistance of molar teeth with weight. Fifty extracted mandibular teeth measured mesiodistal, buccolingual dimensions, length and weight. Test for fracture strength were performed using a universal testing machine. The results of this study showed that no significant correlations were observed between fracture strength values and mesiodistal, buccolingual dimensions, length of the teeth.Differences were observed with the weight
of teeth. It was concluded that the fracture resistance of molar teeth increases as their weights increases. These weights should be standardized during fracture resistance studies when distributing sample molar teeth into the study groups27.
Vipin Arora et al., (2015) evaluated the effect of post obturation materials on reinforcement of pericervical dentin. Sixty extracted maxillary premolars were selected, standardized access were prepared and crowns were resected the final dimension of 4mm from 1mm below highest point of proximal cervical line. Then enamel were removed, obturated with guttapercha and AH plus sealer. Four groups were divided out of these three groups were obturated followed by nRMGIC, Silorane composite and temporary cement were restored. For group four, temporary cement were restored without obturation. Then specimens were tested for fracture resistance in universal testing machine. The results of this study showed that higher fracture resistance of specimens were restored with nRMGIC and Silorane composite resistance when compared to obturated samples with temporary followed by unobturated samples with temporary. It was concluded that the nRMGIC and Silorane composite significantly reinforced pericervical dentin. Obturation also plays an important role in reinforcement of pericervical dentin28.
NasrinSabari et al., (2015) evaluated fracture resistance, fracture patterns and fracture location of endodontically treated human maxillary premolars restored with direct and indirect composite resin and ceramic restoration. Eighty non-carious maxillary premolars were divided into four groups. Endodontic treatment and mesio-occluso-distal preparations were carried out in all groups except for control group. The prepared teeth were restored as indirect composite restoration in group II, ceramic restoration in group III and direct composite restoration in group IV. The specimens were subjected to load until fracture occurred. The results of this study showed that group I had higher fracture resistance than other groups. The group IV exhibited significantly higher values
compared to group II and III. The fracture pattern was significantly different between composite resin groups and ceramic groups. The direct composite restorations exhibited more fractures below the CEJ compared to indirect restorations. It was concluded that use of direct composite restorations resulted in higher resistance against fracture but their failure modes may be unfavourable29.
Moore et al., (2016) assessed the impacts of contracted endodontic cavities on instrumentation efficacy and biomechanical responses in upper molars. Eighteen extracted maxillary molars were scanned with micro-CT and divided to contracted endodontic cavity and traditional endodontic cavity groups. Canals were instrumented, reimaged and proportion of modified canal wall determined. Another twenty eight maxillary molars were attached with linear strain gauges to mesiobuccal and palatal roots and subjected to load cycles. Before access and after restoration the axial microstrain were recorded. The results of this study showed that no significant difference of mean in modified canal wall between contracted endodontic cavity and traditional endodontic cavity. The axial microstrain responses to load at failure was significantly lower for both contracted endodontic cavity and traditional endodontic cavity groups compared with intact maxillary molars. It was concluded that contracted endodontic cavity did not impact instrumentation efficacy and biomechanical responses compared with traditional endodontic cavity30.
Yuan et al., (2016) compared the biomechanics of teeth after minimally invasive preparation and straight-line preparation in finite element analysis. Sixmandibular first molar finite element analysis modelsdivided into two groups and two loads of 250Nwere applied, the one vertically stimulating masticatory force and the other 45ᵒ to the longitudinal axis of tooth specimen. The results of this study showed that the stress concentration areas of teeth in minimally invasive access cavities were smaller than straight-line access in coronal and cervical areas. It was concluded that minimally
invasive access preparation reduced the stress distribution in crown and cervical regions.
A smaller taper cervical enlargement caused lower stress in the cervical region31.
Vinny Sara Varghese et al., (2016) determined the effect of access cavity designs on pericervical dentin thickness before and after instrumentation with CBCT. Sixty mandibular anterior teeth were divided into two groups.Conventional access cavity preparation prepared above cingulum was group I and incisal access cavity preparation prepared in proximity to the incisal edge was group II followed by imaging CBCT in preoperatively, after access cavity preparation and post instrumentation. Images were sliced 4mm apical and coronal to CEJ. The pericervical dentin thickness were measured at facial, lingual, mesial and distal in all three scans. The results of this study showed that access cavity preparation and instrumentation significantly loss of tooth structure in group I on all surfaces but in group II loss of tooth structure only in mesial, lingual and distal surface. It was concluded that incisal access cavity preparation resulted in lesser loss of dentin in the pericervical region32.
ZeynepOzkurt-Kayahan et al., (2016) evaluated the fracture resistance of prepared maxillary incisors teeth after different endodontic access cavity location. Fourty five extracted maxillary central incisor divided into three groups; in group I, teeth with lingual access cavities (n=15); in group II, teeth with incisal access cavities (n=15) and in group III, teeth without access cavities(n=15). Endodontic treatments were completed for group I and II. All specimens were subjected to fracture test. The results of this study showed that mean fracture values of group III was significantly higher than group I and II withno significant difference was detected between lingual and incisal access groups. It was concluded that the location of endodontic access cavity of previously prepared maxillary incisors did not affect the fracture resistance33.
Ana Grasiela da silvalimoeiro et al., (2016) compared the shaping ability of two rotary file systems, BioRace and ProTaper Next during the preparation of curved root canals in extracted teeth using micro-computed tomographic imaging. Twenty, first and second human mandibular molars with two separate mesial canals were scanned before and after root canal preparations using micro-CT. Canals were prepared using BioRace and Protaper Next systems. The percentage of dentin removed after preparation, root canal volume increase, untreated canal walls, structure model index, degree of canal transportation and centering ability were also measured. The results of this study showed that were no significant differences between two groups in removed dentin after preparation and determination of the root canal volume, percentage of untreated canal walls, structure model index, degree of canal transportation and centering ability. It was concluded that moderately curved mesial roots with two independent root canals and foramina instrumented with BioRace and Protaper Next rotary file systems were equally effective. Both instrumentation systems caused negligible procedural errors with minimal apical transportation34.
Tuomas K Niemi et al., (2016) compared the effectiveness of TRUShape (TS) instruments with ProFile Vortex Blue (VB) instruments for removal of obturation material in mandibular premolars with two access outlines. Initial root canal treatment was completed with contracted endodontic cavity (CEC) design. Specimens were divided into two groups on basis of access outline followed by retreatment by using Protaper retreatment instruments. Specimens were further divided and reinstrumented upto TS 40, 0.06 V or 40, 0.06 VB. Teeth were sectioned and percentage of obturating materials was measured. The results of this study showed that interaction between access design and instrument type showed combination of CEC-VB significantly higher amount of remaining obturating materials on canal surface when compared with TEC-VB, CEC-TS and TEC-TS. It was concluded that retreatment protocol was able to completely eliminate all obturating materials from root canal surface of mandibular premolars. However, in the
presence of CEC access design, using TS instruments removed more obturating material in single-rooted oval shaped canals35.
Noemi Bonessio et al., (2016) investigated the effect of root canal treatment procedures with a novel rotary nickel titanium instrument (TRUShape) on stress in mandibular molars. Identical plastic mandibular molars with natural anatomy had all 4 canals shaped with TRUShape and Conventional rotary vortex. Finite element analysis was used to evaluate stress distribution in untreated and treated models. Profiles of average and maximum Von mises stresses in dentin of the four treated conditions under functional loading were compared to the untreated model. The results of this study showed that the dentin sections with most changes after preparation were located in access cavity with average stress increase upto +5.7% for TRUShape#20, +8.5% for Vortex#2o, +8.9% for TRUShape #30 and +10.2% for Vortex #30 respectively, relatively to untreated model. It was concluded that preparation of access cavity resulted in increased von mises stresses under functional occlusal load. The limited retained radicular dentin in TRUShape versus the Vortex cavity proved effective in reducing masticatory stresses. The bonded restoration modeled in this study only partially counterbalance the combined effects of access cavity and root canal preparation36.
GianlucaPlatino et al., (2017) compared the fracture strength of endodontically treated teeth with traditional endodontic cavity, conservative endodontic cavity and ultraconservative “ninja“endodontic cavity access. Extracted human intact maxillary and mandibular premolars and molars divided into ten per group per access type of TEC, CEC, NEC and Intact groups. Minimal CEC and NEC were plotted on cone beam computed tomographic images. Then teeth were endodontically treated and restored.
Then specimens were subjected to fracture in universal testing machine. The maximum load at fracture and fracture pattern were recorded. The results of this study showed that the mean load at fracture for TEC was significantly lower and no differences was
observed among CEC, NEC and Intact teeth. Unrds.restorable fractures more in TEC, CEC and NEC groups than in control group. It was concluded that teeth with TEC access showed lower fracture strength than CEC and NEC. NEC did not increase the fracture strength of teeth compared with CEC. Intact teeth showed more restorable fractures than TEC, CEC and NEC37.
PrasannaNeelakantan et a1.,(2017) examined the orifice-directed dentin conservation access design debride pulp chamber (DDC) and mesial root canal systems of mandibular molars similar to traditional access design(TEC).Thirty two mandibular molars were divided into twelve samples each of TEC and DDC respectively. Eight samples were histologic control. After micro-computed tomographic scanning of experimental groups,instrumentation to a size 30/0.06 taper,specimens were processed for histologic evaluation and remaining pulp tissue was measured from pulp chamber,root canal and isthmus at all root thirds. The results of this study showed that the remaining pulp tissue in pulp chamber was significantly higher in DDC than TEC but within root canals or isthmus, there was no significant difference between DDC and TEC. It was concluded that debridement of pulp chamber was significantly compromised in DDC.The type of access cavity did not influence the amount of remaining pulp tissue in the root canals and isthmus38.
Mario Alovisi et al.,(2017) evaluated the influence of contracted endodontic access on the preservation of original root canal anatomy after shaping with nickel-titanium rotary instruments.Thirty extracted mandibular molars divided into traditional endodontic cavity(TEC) and contracted endodontic cavity.Each group was shaped using progilder and wave one gold. Samples were scanned before and after canal shapping and images were analyzed to evaluate canalvolumes,surface area and centroid shift on cross sections at 1mm and 3mm from the apex.The results of the study showed that a greater preservation of the original root canal anatomy with less apical transformation in TEC
than CEC because of absence of coronal interferences and therefore fewer pecking motions required to complete instrumentation. It was concluded that TEC lead to better preservation of the original canal anatomy during shaping compared with CEC.,particularly at the apical level39.
SonamAsopa at a1.,(2017) compared the fracture resistance of endodontically treated molars restored with resin composites. Ninenty extracted maxillary molar divided into two control groups and four test groups of fifteen samples each.In test groups class II MOD cavities with Mesio-palatal cusp cappings followed by root canal therapy and post endodontic restorartions were done. Restorative materials tested were nanohybridcomposite(Filtek Z250 XT),bulk fill composite(Tetricevoceram), fiber reinforced composite(Ribbond) and indirect composite(SR Adoro) used. Then teeth subjected to compressive loading in universal testing machine.The stress distribution in restored molars were tested by finite element analysis and made of failure was observed using stereomicroscope.The results of this study showed that post endodontic restorations using fiber reinforced composite and indirect composite exhibited fracture resistance similar to intact teeth.Most of the restorable(favourable) fractures were observed in nanohybridcomposite. It was concluded that restorations with fiber reinforced and indirect composites increased fracture resistance of endodontically treated teeth.Resin composites with good bonding ability transmit and distribute functional stresses and hold the potential to reinforce the weakned tooth structure40.
Gabriela Rover et a1.,(2017) assessed the influence of access cavity design on root canal detection,instrumentation efficacy and fracture resistance in maxillary molars.
Thirty extracted intact maxillary molars scanned with micro-computed tomographic image and divided into contracted endodontic cavity(CEC) and traditional endodontic cavity(TEC) groups. Root canal detection was performed in stage 1 was no magnification, stage 2 was under operating microscope and stage 3 was under operating
microscope(OM) and ultrasonic troughing. After root canal preparation specimens were scanned again followed by analysis of instrumented canal area, hard tissue debris accumulation, canal transportation and centering ratio. Then root canal were filled and cavity restored followed by fracture resistance test. The results of this study showed that TEC groups in stage 1 and 2 locate more root canals than CEC groups but no difference were observed after stage 3.No significant difference were observed in non-instrumented canal areas and accumulated hard tissue debris after preparation. It was concluded that access in maxillary molars resulted in less root canal detection when no ultrasonic troughing associated to an OM was used and did not increase fracture resistance41.
RoserinRatanajirasut et al.,(2017) investigated root and root canal morphology of maxillary first and second permanent molars in a thai population using cone-beam computed tomographic(CBCT) imaging. Four hundred seventy six maxillary first molars and four hundred fifty seven maxillary second molars receiving CBCT examination and determined number of roots and canal morphology according to Vertucci’s classification and prevalence of secondmesiobuccal(MB2) canal in mesiobuccalrootwas correlated with sex,age and tooth side.The results of this study showed that three roots were most commonly found in maxillary first and second molars.MB2 canals were found 63.6%
first molars and 29.4% second molars.There was significant correlation between males and prevalence of MB2 canals in first molars. It was concluded that CBCT imaging is useful to determine root canal morphology. Furthermore,bilateral MB2 canals were commonly found42.
Neha Mishra et al.,(2017) evaluated the effect of remaining dentinal wall thickness and effect of remaining cusp height of endodontically treated premolars when restored with composite resin.Ninenty premolars were divided into four test groups and two control groups.In all groups,except negative control group,standardized endodontic access cavities were prepred,mesioocclusodistal(MOD) cavity prepared and access sealed with
light cure glass ionomer cement. Test groups were divided as cusp reduction for group 1st and 2nd was 2.5mm and for groups 3rd and 4th was 1.5mm.Dentinal wall thickness for group 1st and 3rd was 1-1.5mm and group 2nd and 4th was2-3mm.The groups were further subdivided into subgroup A restored with P60 and subgroup B restored with herculiteprécis.Positive control was only access cavity with no cusp reduction and restoration.Fracture resistance was accessed using universal testing machine.The results of this study showed the highest fracture resistance were demonstrated by group 4th and least by group 5th .It was concluded that when cusp reduction was 2.5mm,dentinal wall thickness had no effect on fracture resistance for both composites.When the cusp reduction was 1.5mm and the remaining dentinal thickness was 11.5mm herculite précis showed inferior results43.
Zdenekchlup et al.,(2017) analyzed fracture behavior of teeth with conventional and mini-invasive access cavity designs. Thirty maxillary and thirty mandibular extracted premolars were divided into three groups of CEC group,TEC group and negative control group(n=10 teeth/group).Root canals were shaped with primary waveone reciprocating instruments and obturated using warm vertical compaction,restored using dual-cured resin composite with filtekultimate.All samples subjected to fracture test using universal testing machine.The results of this study showed that no significant difference between TEC and CEC in maxillary and mandibular premolars. The average loads at fracture for CEC were generally higher. It was concluded that the preservation of sound tooth tissue together with favorable effect of polymeric composite filling increases the fracture resistance of teeth.The largest reduction in the fracture resistance results from traditional preparation,especially the loss of marginal ridges.The observed fracture behavior and formed fracture patterns well correspond to those found in the clinical dentistry44.
Qianzhou Jiang et al., (2018) compared the biomechanical properties of maxillary first molars with different endodontic cavities using finite element analysis. An intact human
maxillary first molar was scanned with micro-CT. An intact tooth model was designed for comparison and three finite element analysis models of traditional endodontic cavity and an extended endodontic cavity were constructed. Each model was subjected to three different force loads directed at the occlusal surface. The stress distribution patterns and the maximum von mises (VM) stress were calculated and compared. The results of this study showed that the peak VM stress on all models was at the site of the force load. The stress was higher when force close to the access cavity margins. The peak root VM stress increased as the cavity extended and stress became concentrated in the area between the filling materials and the dentin. It was concluded that the stress distribution on the occlusal surface were similar between conservative, traditional and extended endodontic cavity and the enlargement of the access cavity dramatically increased the stress on pericervical dentin45.
GokhanSaygili et al., (2018) evaluated the relationship between endodontic access cavity (EAC) with MB2 canal detection ratio in the upper first molars. Sixty roots of extracted human maxillary first molars were divided and prepared with point endodontic access cavity (PEAC), conservative endodontic access cavity (CEAC), traditional endodontic access cavity (TEAC) respectively. Extra canal was searched and preoperative & postoperative tooth weight was calculated. The results of this study showed that EAC types were changed tooth loss quantity. Secondary mesiobuccal canal detection rate of CEAC and TEAC were significantly higher than PEAC. Eight teeth of secondary mesiobuccal canal were detected only with CBCT images. It was concluded that in upper molars conservative endodontic access cavity seems reasonable in terms of detected the secondary mesiobuccal canal and removed hard tissue46.
Mohammad Sabeti et al., (2018) evaluated the effect of access cavity design and root canal taper on fracture resistance of endodontically treated maxillary molars. For tapering assessment, thirty distobuccal roots of maxillary molars divided into three groups 0.04,
0.06 and 0.08 taper. Endodontic canal were prepared using Twisted Files rotary system.
In additionfourty eight intact maxillary molars divided into three groups of intact teeth, traditional access cavity and conservative access cavity. Fracture resistance was tested using universal testing machine. The results of this study showed that the 0.04 and 006 groups did not differ significantly but 0.08 taper groups had the lowest fracture resistance. Regarding cavity preparation approaches, no significant difference between conservative access cavity and traditional access cavity groups. It was concluded that increasing the taper of the root canal preparation can reduce fracture resistance. However, contracted access cavity in comparison with traditional access cavity had no significant impact on fracture resistance47.
TabaOzyurek et al., (2018) compared the effects of endodontic access cavity preparation design on the fracture strength of endodontically treated teeth. A hundred intact human mandibular first molars divided into five groups. They are control group, teeth prepared traditional endodontic access cavity (TEC) restored wihEverXposterior and composite resin, conservative endodontic cavity (CEC) restored withEverXposterior and composite resin, TEC restored with SDR and composite resin and CEC restored with SDR and composite resin. All specimens were subjected to universal testing machine to evaluate fracture strength. The results of this study showed that fracture strength in control group were significantly higher than experimental groups. There was no significant difference in TEC and CEC methods and restored using same composite base material. It was concluded that CEC preparation did not increase the fracture strength of teeth with class II cavities compared with TEC preparation. The fracture strength of teeth restored with the SDR bulk-fill composite was higher than that of teethrestored with EverXposterior48.
GiacomoCorsentino et al.,(2018) assessed the influence of access cavity preparation and remaining tooth substance on fracture strength of endodontically treated teeth. One
