An Update on Endodontic Microsurgery of Mandibular Molars: a Focused Review

medicina

Review An Update on Endodontic Microsurgery of Mandibular Molars: A Focused Review

Sun Mi Jang 1, Euiseong Kim 1 and Kyung-San Min 2,3,4,*

1 Microscope Center, Department of Conservative Dentistry and Oral Science Research Center, Yonsei University College of Dentistry, Seoul 03722, Korea; [email protected] (S.M.J.); [email protected] (E.K.) 2 Department of Conservative Dentistry, School of Dentistry, Jeonbuk National University, Jeonju 54896, Korea 3 Research Institute of Clinical Medicine, Jeonbuk National University, Jeonju 54907, Korea 4 Biomedical Research Institute, Jeonbuk National University Hospital, Jeonju 54907, Korea * Correspondence: [email protected]; Tel.: +82-63-250-2764

Abstract: Endodontic microsurgery is a highly predictable treatment option in most cases when conventional endodontic treatment is not feasible. Nevertheless, mandibular molars are still considered by clinicians to be the most difﬁcult type of teeth, with the lowest success rate. In recent years, endodontic microsurgery has been attempted more frequently with the emergence of modern cutting-edge technologies such as dental operating microscopes, various microsurgical instruments, and biocompatible materials, and the success rate is increasing. This review describes the current state of the art in endodontic microsurgical techniques and concepts for mandibular molars. Notably, this review highlights contemporary equipment, technology, and materials.

Keywords: endodontic; microsurgery; mandibular; molar; update

Citation: Jang, S.M.; Kim, E.; Min, K.-S. An Update on Endodontic 1. Introduction Microsurgery of Mandibular Molars: A Focused Review. Medicina 2021, 57, Endodontic treatment aims to disinfect the root canal system, followed by sealing 270. https://doi.org/10.3390/ this space to prevent recontamination [1]. For this purpose, nonsurgical endodontic treat- medicina57030270 ment is the first option in most cases, but a surgical approach may be indicated when peri-radicular pathosis cannot be solved by a nonsurgical method [2]. Surgical endodontic Academic Editor: Vita Maciulskiene treatment has evolved considerably owing to new technological advances such as dental operating microscopes, cone-beam computed tomography (CBCT), computer-aided Received: 28 January 2021 design/computer-aided manufacturing (CAD/CAM), and three-dimensional printing Accepted: 12 March 2021 technology. Most endodontists now consider the above equipment essential for surgical Published: 16 March 2021 endodontic treatment. Nevertheless, clinicians still consider mandibular molars to be the most difficult Publisher’s Note: MDPI stays neutral targets. The success rate for mandibular molars is lower than that for any other type of with regard to jurisdictional claims in teeth in the oral cavity [3]. The difficulty posed by mandibular molars is their anatomical published maps and institutional affil- location in the posterior areas of the oral cavity. Even in a retrospective study that used a iations. 15-year database obtained in the 21st century, molars showed a higher probability of failure than anterior teeth, and tooth type might be the only factor contributing to the outcomes of microsurgery [4]. Therefore, microsurgery of mandibular molars requires an adequate evaluation of the surgical access and the relationship of the roots to anatomical structures Copyright: © 2021 by the authors. such as the mental foramen and mandibular canal [5]. Licensee MDPI, Basel, Switzerland. However, within the limitation of our knowledge, there has been no focused review This article is an open access article regarding endodontic microsurgery of mandibular molars in the past 10 years, although distributed under the terms and considerable technical advances have occurred. Therefore, the purpose of this review was conditions of the Creative Commons to present an update on endodontic microsurgical techniques and concepts for mandibular Attribution (CC BY) license (https:// molars. creativecommons.org/licenses/by/ 4.0/).

Medicina 2021, 57, 270. https://doi.org/10.3390/medicina57030270 https://www.mdpi.com/journal/medicina Medicina 2021, 57, x FOR PEER REVIEW 2 of 15

Medicina 2021, 57, 270 to present an update on endodontic microsurgical techniques and concepts for mandibu-2 of 15 lar molars.

2.2. Anatomical ConsiderationsConsiderations 2.1.2.1. Thickness of thethe BuccalBuccal BoneBone TheThe buccalbuccal bonebone ofof thethe mandibularmandibular molarmolar areaarea isis thickerthicker thanthan inin otherother areas.areas. TheThe thicknessthickness ofof thethe posteriorposterior buccalbuccal corticalcortical plateplate isis generallygenerally 2–32–3 mmmm on average ((FigureFigure1 1a).a ). Furthermore,Furthermore, thisthis thicknessthickness maymay increaseincrease posteriorlyposteriorly (oblique(oblique ridge),ridge), limitinglimiting accessaccess toto thethe molarmolar rootsroots (Figure(Figure1 1b).b). While While the the mesial mesial root root of of the the mandibular mandibular ﬁrst first molar molar is is reasonably reasonably closeclose toto thethe buccalbuccal corticalcortical plate,plate, thethe distaldistal rootroot isis centrallycentrally locatedlocated inin thethe bonebone andand thethe rootsroots ofof thethe secondsecond molarmolar areare signiﬁcantlysignificantly closercloser toto thethe linguallingual corticalcortical plateplate [[6].6]. Therefore, mandibularmandibular molarsmolars with with a thicka thick buccal buccal bone bone plate plate pose pose a challenging a challenging problem problem in endodontic in endo- surgery,dontic surgery, especially especially for precise for root-endprecise root-end localization. localization.

FigureFigure 1.1. Anatomical features ofof thethe mandibularmandibular molar area.area. (a) Thick buccal bone of the mandible (white(white triangle).triangle). ((bb)) ObliqueOblique ridgeridge inin thethe secondsecond mandibularmandibular molarmolar areaarea (red(red triangle).triangle).

Recently,Recently, BiBi etet al.al. [[7]7] reportedreported aa sophisticatedsophisticated approachapproach thatthat reducedreduced thethe distancedistance betweenbetween thethe rootsroots andand thethe buccalbuccal corticalcortical plateplate byby orthodonticorthodontic movement.movement. ByBy orthodonticorthodontic movementmovement towardtoward the the buccal buccal aspect aspect for for 2 2 months, months, the the distance distance between between the the two two anatomical anatom- structuresical structures was decreasedwas decreased from from 4.5 mm 4.5 to mm 1.5 to mm 1.5 (mesial mm (mesial root) and root) 7.1 and mm 7.1 to mm 4.5 mm to 4.5 (distal mm root).(distal Therefore,root). Therefore, the surgical the surgical procedure procedure became became easier easier and and the the results results were were successful. success- Furthermore,ful. Furthermore, Ahn Ahn et al. et [8 al.] performed [8] performed osteotomy osteotomy and apexand apex localization localization effectively effectively using us- a CAD/CAM-guideding a CAD/CAM-guided surgical surgical template template in a mandibular in a mandibular molar molar with a with thick a buccalthick buccal bone platebone (Figureplate (Figure2). Indeed, 2). Indeed, the surgical the surgical template temp manufacturedlate manufactured by using by CAD/CAM using CAD/CAM technology tech- combinednology combined with CBCT with can CBCT determine can determine the three-dimensional the three-dimensional extent of extent the required of the required cortical bonycortical window. bony window. Therefore, Therefore, with this with guide, this the guide, surgical the approach surgical approach to the apical to regionthe apical is less re- invasivegion is less and invasive less traumatic and less so traumatic that minimizes so that boneminimizes loss in bone comparison loss in comparison to the traditional to the osteotomytraditional techniquesosteotomy techniques [9]. However, [9]. evenHowever, with thiseven static with technique, this static clinicianstechnique, may clinicians have problemsmay have regardingproblems regarding the instrumentation the instrumentation during the during surgical the procedure. surgical procedure. In this respect, In this mostrespect, recently, most recently, dynamic dynamic navigation navigation systems forsystems dental for implant dental positioningimplant positioning were applied were toapplied endodontic to endodontic microsurgery microsurgery [10]. This [10]. dynamic This dynamic navigation navigation integrates integrates surgical surgical procedure pro- andcedure radiologic and radiologic images images by using by an using optical an optical positioning positioning device device controlled controlled by a dedicated by a ded- computerizedicated computerized interface. interface. Consequently, Consequently, with the with help the of cutting-edgehelp of cutting-edge guiding guiding technologies, tech- cliniciansnologies, canclinicians perform can a safeperform and lessa safe traumatic and less surgical traumatic procedure surgical in procedure the mandibular in the molar man- area,dibular and molar unfavorable area, and complications unfavorable includingcomplications increased including postoperative increased pain,postoperative delayed healing,pain, delayed and nerve healing, damage and nerve can be damage avoided. can be avoided.

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Figure 2. Clinical case using a computer-aided design/computer-aided manufacturing FigureFigure 2. Clinical2. Clinical case usingcase a computer-aidedusing a computer-aided design/computer-aided design/computer-aided manufacturing (CAD/CAM)-manufacturing (CAD/CAM)-guided surgical template to localize the root apex through thick. (a) Diagnostic peri- guided(CAD/CAM)-guided surgical template surgical to localize template the to root localize apex throughthe root apex thick. through (a) Diagnostic thick. (a periapical) Diagnostic X-ray. periapical X-ray. (b) A manufactured surgical template. (c) The surgical template was positioned on the (bapical) A manufactured X-ray. (b) A manufactured surgical template. surgical (c) Thetemplate. surgical (c) The template surgical was template positioned was onpositioned the tooth. on ( dthe) tooth. (d) Postoperative radiograph. Postoperativetooth. (d) Postoperative radiograph. radiograph. 2.2. Vestibular Fornix 2.2.2.2. Vestibular Vestibular Fornix Fornix The depth of the vestibular fornix is considered a reliable predictor of the possible TheThe depth depth of of the the vestibular vestibular fornix fornix is is considered considered a a reliable reliable predictor predictor of of the the possible possible difficulty that may be encountered during periapical surgery of the mandibular posterior difﬁcultydifficulty that that may may be be encountered encountered during during periapical periapical surgery surgery of of the the mandibular mandibular posterior posterior teeth [11]. If the vestibular fornix is shallow, the buccal alveolar bone overlying the roots teethteeth [ 11[11].]. If If the the vestibular vestibular fornix fornix is is shallow, shallow, the the buccal buccal alveolar alveolar bone bone overlying overlying the the roots roots will be thick and consequently access to the root end will be limited. In some cases, there- willwill be be thick thick and and consequently consequently access access to to the the root root end end will will be be limited. limited. In In some some cases, cases, there- there- fore, the buccal cortical plate can be reduced before exploring for the periapical lesion or fore,fore, the the buccal buccal corticalcortical plateplate cancan be reduced before before exploring exploring for for the the periapical periapical lesion lesion or root end (Figure 3). In this procedure, the surgical concept of vestibuloplasty can be ap- orroot root end end (Figure (Figure 3).3). In In this this procedure, procedure, the the su surgicalrgical concept concept of of vestibuloplasty vestibuloplasty can can be be applied. However, clinicians should bear in mind that this procedure may destroy a consid- applied.plied. However, However, clinicians clinicians should should bear bear in in mind mind that this procedure maymay destroydestroy aa consid- consid- erable amount of bone. Instead of endodontic surgery, extraction and replantation/dental erableerable amount amount of of bone. bone. Instead Instead of of endodontic endodontic surgery, surgery, extraction extraction and and replantation/dental replantation/dental implantation can be a less traumatic alternative, especially for mandibular second molars. implantationimplantation can can be be a a less less traumatic traumatic alternative, alternative, especially especially for for mandibular mandibular second second molars. molars.

Figure 3. Drawings of mandibular molars and their mesiodistal supporting structures. The vestib- Figure 3. Drawings of mandibular molars and their mesiodistal supporting structures. The vestib- Figureular fornix 3. Drawings becomes of deeper mandibular by reducing molars andthe buccal their mesiodistal cortical plate. supporting structures. The vestibular ular fornix becomes deeper by reducing the buccal cortical plate. fornix becomes deeper by reducing the buccal cortical plate. 2.3. Mandibular Canal 2.3.2.3. Mandibular Mandibular Canal Canal The mandibular canal is sometimes in the proximity of the roots of all mandibular TheThe mandibular mandibular canal canal is is sometimes sometimes in in the the proximity proximity of of the the roots roots of of all all mandibular mandibular molars (Figure 4a). According to a systematic review, the shortest distances from the su- molarsmolars (Figure (Figure4 a).4a). AccordingAccording toto a systematic review, review, the the shortest shortest distances distances from from the the superior cortical bone of the mandibular canal to the first and second molars were 3.82 mm superiorperior cortical cortical bone bone of of the the mandibular mandibular canal to the ﬁrstfirst andand secondsecond molarsmolars were were 3.82 3.82 mm mm and 1.4 mm, respectively [12]. Even a direct contact relationship was found in 3.3% of the andand 1.4 1.4 mm,mm, respectivelyrespectively [[12].12]. Even Even a a direct direct co contactntact relationship relationship was was found found in in3.3% 3.3% of ofthe first molar and 16% of the second molar [13]. Furthermore, the distance from the root to thefirst ﬁrst molar molar and and 16% 16% of ofthe the second second molar molar [13]. [13 ].Furthermore, Furthermore, the the distance distance from from the the root root to to the canal was shorter in younger people (<21-year-old) than in older people [13,14].

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the canal was shorter in younger people (<21-year-old) than in older people [13,14]. Ana- the canal was shorter in younger people (<21-year-old) than in older people [13,14]. Ana- tomically, the Anatomically,mandibular canal the mandibular is situated canallingually is situated to the linguallyroots of the to themandibular roots of the first mandibular ﬁrst tomically, the mandibular canal is situated lingually to the roots of the mandibular first molars (Figuremolars 4b). (Figure4b). molars (Figure 4b).

Figure 4. Anatomical features of the mandibular canal and mental foramen. (a) Schematic illustra- Figure 4. Anatomical features of the mandibular canal and mental foramen. (a) Schematic illustration of human mandibleFigure 4. showingAnatomical the featuresinnervation of the of mandibular mandibular canal and mental and mental nerves. foramen. (b) Transverse (a) Schematic illustration tion of human mandible showing the innervation of mandibular and mental nerves. (b) Transverse section of a cone-beamof human compute mandible tomography showing the (CBCT) innervation scan through of mandibular the mandible and mental in the nerves.region (ofb )the Transverse section section of a cone-beam compute tomography (CBCT) scan through the mandible in the region of the root of the first molar. The mandibular canal (white triangle) is closely located lingual to the root ofroot a cone-beam of the first compute molar. tomography The mandibular (CBCT) canal scan (white through triangle) the mandible is closely in the located region lingual of the root to the of the root apex. firstapex. molar. The mandibular canal (white triangle) is closely located lingual to the root apex. The borders of the mandibular canal are often difficult to visualize with conventional TheThe borders borders of of the the mandibular mandibular canal canal are are often often difﬁcult difficult to to visualize visualize with with conventional conventional radiographic techniques (Figure 5a). A parallel periapical radiograph, either horizontally radiographicradiographic techniques techniques (Figure (Figure5a). 5a). A A parallel parallel periapical periapical radiograph, radiograph, either either horizontally horizontally or vertically positioned,or vertically can positioned, usually provide can usually a reasonably provide a accurate reasonably image accurate of the image relation- of the relationship or vertically positioned, can usually provide a reasonably accurate image of the relationship between thebetween superior the border superior of borderthe mand of theibular mandibular canal and canal the root and apices. the root CBCT apices. im- CBCT imaging ship between the superior border of the mandibular canal and the root apices. CBCT imaging can be verycan beuseful very for useful identifying for identifying the location the location of the mandibular of the mandibular canal and canal deter- and determining aging can be very useful for identifying the location of the mandibular canal and determining its relationshipits relationship to the toroot the apices root apices (Figure (Figure 5b) [15].5b) [ 15Martí]. Mart et al.í et [16] al. [reported16] reported that that periapical mining its relationship to the root apices (Figure 5b) [15]. Martí et al. [16] reported that periapical surgerysurgery is a isvalid a valid treatment treatment option option for mandibular for mandibular molars, molars, even eventhose thosesituated situated in close periapical surgery is a valid treatment option for mandibular molars, even those situated in close proximityproximity to the tomandibular the mandibular canal (less canal than (less 2 than mm). 2 mm). in close proximity to the mandibular canal (less than 2 mm).

Figure 5. Usefulness of CBCT for identifying the mandibular canal. (a) Unclear mandibular canal Figure 5. Usefulness of CBCTFigure for identifying 5. Usefulness the mandibular of CBCT for canal. identifying (a) Unclear the mandibularmandibular canal canal. border (a) Unclear in a conventional mandibular canal border in a conventional panoramic radiograph. Periapical bone resorption adjacent to the mandib- panoramic radiograph. Periapicalborder bone in resorptiona conventional adjacent panoramic to the mandibular radiograph. canal Peri makesapical identificationbone resorption of theadjacent upper to border the mandibular canal makes identification of the upper border of the canal difficult (white arrows). (b) A CBCT of the canal difficult (white arrows).ular canal (b) makes A CBCT identification scan shows of the the upper upper border border of of the the mandibular canal difficult canal (white remarkably arrows). well(b) A CBCT scan shows the upper border of the mandibular canal remarkably well (yellow arrows). (yellow arrows). scan shows the upper border of the mandibular canal remarkably well (yellow arrows). 2.4. Mental Nerve2.4. Mental Nerve 2.4. Mental Nerve The mental nerve,The mentala branch nerve, of the a branchinferior ofalveolar the inferior nerve, alveolar emerges nerve, with emergesthe mental with the mental The mental nerve, a branch of the inferior alveolar nerve, emerges with the mental artery throughartery the mental through foramen the mental to supply foramen the to oral supply mucosa the oraland mucosathe skin and of the the lower skin of the lower lip artery through the mental foramen to supply the oral mucosa and the skin of the lower lip and chin (Figureand chin 6). (Figure It can 6be). Itdamaged can be damaged during flap during retraction, flap retraction, and paresthesia and paresthesia may may occur. lip and chin (Figure 6). It can be damaged during flap retraction, and paresthesia may occur. The mentalThe mentalforamen foramen usually usuallyappears appears on a radiograph on a radiograph as a round as a radiolucent round radiolucent area area below occur. The mental foramen usually appears on a radiograph as a round radiolucent area the mandibular second premolar root apex. However, its location varies and it may be seen at the same level or superior to the root apices [11].

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Medicina 2021, 57, 270 5 of 15 belowbelow thethe mandibularmandibular second second premolarpremolar rootroot apex.apex. However,However, itsits location location variesvaries andand itit maymay bebe seenseen atat thethe samesame levellevel oror susuperiorperior toto thethe rootroot apicesapices [11].[11].

Figure 6. Clinical features of the mental foramen and nerve bundle (white triangle) that are detected FigureFigure 6.6. ClinicalClinical featuresfeatures ofof thethe mentalmental foramenforamen andand nervenervebundle bundle(white (white triangle) triangle) that that are are detected detected duringduring thethe surgicalsurgical procedure.procedure. during the surgical procedure. The mental foramen is most usually single in humans; when it is double or multiple, TheThe mentalmental foramenforamen isis mostmost usuallyusually singlesingle inin humans;humans; whenwhen itit isis doubledouble oror multiple,multiple, thethethe additional additionaladditional foramen foramenforamen is isis termed termedtermed an anan accessory accessoryaccessory mental mentalmental foramen. foramen.foramen. Accessory AccessoryAccessory mental mentalmental foramina foram-foram- areinaina reportedareare reported reported tobe to to rare,bebe rare, rare, with with with a prevalencea a prevalence prevalence ranging ranging ranging from from from 1.4% 1.4% 1.4% to to to 10% 10% 10% [[17–20]. 17[17–20].–20]. Moreover,Moreover, 2 IwanagaIwanagaIwanaga et etet al. al.al. [ 21 [21][21]] reported reportedreported that thatthat accessory accessoryaccessory mental mentalmental foramina foraminaforamina smaller smallersmaller than thanthan 1.3 mm 1.31.3 2mmmmwere2 werewere not clearlynotnot clearlyclearly identified identifiedidentified on surface-rendered onon surface-renderedsurface-rendered CBCT CBCTCBCT images. images.images. In this InIn respect, thisthis respect,respect, paresthesia paresthesiaparesthesia may occur maymay evenoccuroccur if eveneven the clinician ifif thethe clinicianclinician does not doesdoes recognize notnot recognizrecogniz the damageee thethe damagedamage to the mentaltoto thethe mentalmental nerve [ nerve22nerve,23]. [22,23].[22,23]. GutmannGutmann andand HarrisonHarrison [[5][5]5] suggestedsuggestedsuggested protectingprotectiprotectingng the thethe mental mentalmental nerve nervenerve by byby positioning positioningpositioning the thethe periostealperiostealperiosteal retractorretractorretractor betweenbetweenbetween thethethe mentalmentalmental foramen foramenforamen and andand the thethe intraosseous intraosseousintraosseous surgical surgicalsurgical site. site.site. More MoreMore recently,recently,recently, Kim KimKim and andand Kratchman KratchmanKratchman [ [24]24[24]] suggested suggestedsuggested an anan effective effectiveeffective tip, tip,tip, the thethe “groove “groove“groove technique”, technique”,technique”, to toto preventpreventprevent mental mentalmental nerve nervenerve damage. damage.damage. Briefly, Briefly,Briefly, a 15-mm-long aa 15-15-mm-longmm-long horizontal horizontalhorizontal groove groovegroove is prepared isis preparedprepared beyond be-be- theyondyond root the the apex root root andapex apex the and and retractor the the retractor retractor is positioned is is positi positi withinonedoned within within the groove the the groove groove (Figure (Figure (Figure7a). This 7a). 7a). technique This This tech- tech- permitsniquenique permitspermits the secure thethe retractionsecuresecure retractionretraction of the flap ofof theprotectingthe flapflap protectingprotecting the nerve thethe during nervenerve the duringduring procedure. thethe procedure.procedure. Recently, theRecently,Recently, use of thethe a piezoelectric useuse ofof aa piezoelectricpiezoelectric saw instead sawsaw of insteainstea a burdd has ofof aa been burbur shownhashas beenbeen to shownshown be useful toto bebe to useful obtainuseful to ato grooveobtainobtain a asa groovegroove narrow asas as narrownarrow is practical asas isis for practicalpractical the placement forfor thethe placementplacement of the retractor ofof thethe (Figure retractorretractor7b). (Figure(Figure By using 7b).7b). this ByBy method,usingusing thisthis excessive method,method, bone excessiveexcessive removal bonebone can removalremoval be avoided. cancan bebe avoided.avoided.

FigureFigure 7.7. The The groovegroove technique.technique. ((aa)) AA narrownarrow horizontalhorizontalhorizontal groove groovegroove is isis positioned popositionedsitioned just justjust above aboveabove the thethe mental mentalmental foramenforamenforamen (white(white (white line).line). line). (( (bb))) ClinicalClinical feature feature ofof of a a practicallypractically narrow narrow groovegroove groove mademade made usingusing using thethe the piezoelectricpiezoelectric piezoelectric saw. Note that the nerve/vessel bundle comes from the foramen (white arrow). saw.saw. Note Note that that the the nerve/vessel nerve/vessel bundlebundle comescomes fromfrom thethe foramenforamen (white(white arrow).arrow).

2.5.2.5. DistolingualDistolingual RootRoot MandibularMandibular firstfirstfirst permanentpermanent molarsmolars usuallyusually havehave twotwo rootsroots locatedlocated mesiallymesially andand dis-dis- tally,tally,tally, butbutbut ininin AsianAsianAsian populations,populations,populations, ananan additionaladditionaladditional distolingualdistolingualdistolingual rootrootroot isisis consideredconsideredconsidered aaa normalnormalnormal morphologicalmorphological variantvariant [25,26]. [[25,26].25,26]. InIn In twotwo two studiesstudies studies conductedconducted conducted inin in Korea,Korea, Korea, thethe the prevalenceprevalence prevalence ofof ofinde-inde- in- dependentpendentpendent distolingualdistolingual distolingual rootsroots roots waswas was 24.5%24.5% 24.5% andand and 22.8%,22.8%, 22.8%, respectivelyrespectively respectively [27,28].[27,28]. [27,28 TheseThese]. These separateseparate separate dis-dis- distolingual roots of mandibular first molars are considered too difficult for performing periapical surgery due to the considerable distance from the buccal cortical plate (8.63 mm) [28]. Due to this difficulty, few case reports have described surgical endodontic management of these roots. To our knowledge, only one report was found [29], and the authors

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tolingual roots of mandibular first molars are considered too difficult for performing periapical surgery due to the considerable distance from the buccal cortical plate (8.63 mm) Medicina 2021, 57, 270 [28]. 6 of 15 Due to this difficulty, few case reports have described surgical endodontic management of these roots. To our knowledge, only one report was found [29], and the authors performedperformed a reduced reduced amount amount (2 (2 mm) mm) ofof root root resection resection and and root-end root-end preparation preparation and andsug- suggestedgested that that distolingual distolingual roots roots can canbe successf be successfullyully treated treated by modifying by modifying the standard the standard pro- protocol.tocol. Nevertheless, Nevertheless, periapical periapical surgery surgery for for the the distolingual distolingual root root should bebe undertakenundertaken withwith carefulcareful deliberationdeliberation duedue toto thethe technicaltechnical difﬁculty.difficulty.

2.6.2.6. MandibularMandibular SecondSecond MolarsMolars DueDue to their location, location, endodontic endodontic microsurgery microsurgery for for mandibular mandibular second second molars molars is sel- is seldomdom attempted attempted even even by byendodontic endodontic specialists. specialists. Access Access to the to r theoot root apex apex of the of teeth the teeth is usu- is usuallyally obtained obtained by byintentional intentional replantation replantation since since the the roots roots often often have have a a convergent form. Nevertheless,Nevertheless, aa surgicalsurgical approachapproach forfor mandibularmandibular secondsecond molarsmolars isis attemptedattempted inin certaincertain situations,situations, suchsuch asas abutmentabutment ofof ﬁxedfixed prosthodonticsprosthodontics (Figure(Figure8 ).8). In In endodontic endodontic surgery surgery for for secondsecond molars,molars, thethe positionposition ofof thethe mandibularmandibular canalcanal shouldshould bebe consideredconsidered carefully.carefully. TheThe mandibularmandibular canalcanal isis locatedlocated buccalbuccal toto thethe apexapex ofof thethe secondsecond molar,molar, butbut linguallingual toto thethe apexapex ofof thethe ﬁrstfirst molarmolar inin mostmost casescases [[30].30]. Furthermore,Furthermore, itit waswas reportedreported thatthat thethe secondsecond molarsmolars hadhad aa closeclose distancedistance toto thethe canalcanal (mean,(mean, 3.73.7 mm).mm).

FigureFigure 8.8. EndodonticEndodontic surgerysurgery ofof aa mandibularmandibular secondsecond molar.molar. ((aa)) SinusSinus tracttract formedformed onon thethe buccalbuccal aspect of a left mandibular second molar. (b) Diagnostic periapical X-ray image showing that the aspect of a left mandibular second molar. (b) Diagnostic periapical X-ray image showing that tooth was an abutment for a fixed prosthodontic restoration. (c) The root apex was exposed after the tooth was an abutment for a fixed prosthodontic restoration. (c) The root apex was exposed osteotomy. (d) A five-year follow-up radiograph shows complete bony healing. Images were mod- afterified osteotomy.from Song [31] (d) Aafter five-year receiv follow-uping permission radiograph from the shows journal. complete bony healing. Images were modified from Song [31] after receiving permission from the journal.

3.3. SurgicalSurgical ConsiderationsConsiderations 3.1.3.1. FlapFlap DesignDesign FlapFlap designdesign isis ofof critical importance in endodontic surgery. It affects access, visibility, anatomicalanatomical structures,structures, repositioning,repositioning, andand suturingsuturing [[5].5]. TheThe triangulartriangular full-thicknessfull-thickness ﬂapflap withwith intrasulcularintrasulcular incisionincision hashas beenbeen widelywidely usedused inin periapicalperiapical surgerysurgery forfor thethe mandibularmandibular molarmolar area.area. However,However, thisthis incisionincision resultsresults inin recessionrecession andand shrinkageshrinkage of thethe papillapapilla [[32].32]. InIn thisthis respect,respect, currently,currently, thethe papillapapilla basebase incisionincision (PBI)(PBI) isis recommendedrecommended toto preventprevent lossloss ofof interdental papilla height height (Figure (Figure 9).9). In In the the study study by by Velvart Velvart et etal. al.[33], [ 33 no], recession no recession was wasfound found when when the healing the healing of the of PBI the was PBI wasexamined examined after afterone year. one year. In another In another study study com- comparingparing PBI PBIand and intrasulcular intrasulcular incision, incision, the the gingival gingival margin margin remained remained higher higher when aa PBIPBI was performed [34]. For this reason, the popular semilunar and Luebke-Ochsenbein ﬂap designs are no longer recommended [24].

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Medicina 2021, 57, 270 7 of 15 was performed [34]. For this reason, the popular semilunar and Luebke-Ochsenbein flap designs are no longer recommended [24].

FigureFigure 9. 9.Papilla Papilla basebase incision incision (black (black line), line), creating creating access access to to the the mandibular mandibular ﬁrst first molar. molar.

TheThe vertical vertical incision incision should should be be made made parallel parall toel theto the vessels vessels in the in attachedthe attached gingiva gingiva and submucosaand submucosa [35]. Traditionally,[35]. Traditionally, angulation angulation of the of vertical the vertical incision incision to create to acreate broad-based a broad- flap,based with flap, the with vestibular the vestibular portion ofportion the flap of wider the flap than wider the free than end, the has free been end, suggested has been [sug-36]. Thisgested design [36]. wasThis baseddesign on was the based expectation on the ex ofpectation improvement of improvement of blood supply of blood to supply the flap, to butthe thisflap, idea but isthis no idea longer is no supported longer supported scientifically. scientifically. It created It acreated lasting a scar lasting by cuttingscar by thecut- mucosalting the tissuemucosal across tissue the across fiber linesthe fiber [37]. lines [37]. AA verticalvertical incisionincision isis usuallyusually recommendedrecommended onlyonly onon thethe mesial mesial side side of of the the planned planned molar.molar. TheThe rectangularrectangular flapflap designdesign withwith twotwo vertical vertical incisions incisions isis limited limited in in the the posterior posterior portionportion of of the the mandible mandible by by anatomical anatomical considerations. considerations. A distalA distal vertical vertical incision incision provides provides no advantages,no advantages, but causesbut causes suturing suturing problems problems due todue the to extremely the extremely limited limited space space in that in area. that Whenarea. When the first the molar first ismolar treated, is treated, the vertical the vertical incision incision is commonly is commonly placed onplaced the mesial on the lineme- anglesial line of theangle first of premolar the first premolar (Figure 10 (Figure). Consequently, 10). Consequently, an incision an at incision this location at this does location not damagedoes not the damage mental the foramen mental and foramen muscle and attachment muscle attachment located around located the around second the premolar. second Onpremolar. the contrary, On the Moiseiwitsch contrary, Moiseiwitsch [38] suggested [38] suggested placing the placing vertical the incisionvertical incision distal to distal the surgicalto the surgical site to avoidsite to damageavoid damage to the mentalto the mental nerve. nerve. However, However, this approach this approach has not has been not mentionedbeen mentioned further further in the in literature. the literature.

FigureFigure 10. 10.Vertical Vertical incision incision for for endodontic endodontic microsurgery microsurgery of of the the mandibular mandibular first first molar. molar. Note Note that that the the vertical incision was placed on the mesial line angle of the mandibular first premolar and par- vertical incision was placed on the mesial line angle of the mandibular first premolar and parallel to allel to the root longitudinally. This helps to avoid mental nerve injury and the scar on the gingival the root longitudinally. This helps to avoid mental nerve injury and the scar on the gingival tissue. tissue. 3.2. Osteotomy 3.2. Osteotomy Evidence has accumulated showing that the larger the defect, the smaller the chance that completeEvidence healing has accumulated will occur. showing Furthermore, that the Rubinstein larger the and defect, Kim the [39 smaller] showed the a chance direct relationshipthat complete between healingthe will size occur. of osteotomyFurthermore, and Rubinstein the speed and of healing:Kim [39] theshowed smaller a direct the osteotomy,relationship the between faster the the healing. size of osteotomy Indeed, in an microsurgeryd the speed of of healing: the mandibular the smaller first the molar, oste- osteotomyotomy, the offaster 3 to the 4 mm healing. in diameter Indeed, suffices,in microsurgery just enough of the to mandibular provide space first formolar, a 3-mm oste- ultrasonicotomy of tip3 to (Figure 4 mm in11 ).diameter suffices, just enough to provide space for a 3-mm ultrasonic tip (Figure 11).

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Figure 11. Bone crypt (4 mm in diameter) after osteotomy, allowing an ultrasonic tip to move with- outFigureFigure interference. 11.11. BoneBone cryptcrypt (4(4 mm mm in in diameter) diameter) after after osteotomy, osteotomy, allowing allowing an an ultrasonic ultrasonic tip tip to moveto move without with- interference.out interference. Recently, the preservation of the cortical bony plate, the so-called “bone window technique”,Recently,Recently, has the thebeen preservationpreservation attempted using ofof thethe a corticalpiezoelectriccortical bonybony saw plate,plate, (Figure thethe so-calledso-called 12). With “bone“bone this conserva- windowwindow tivetechnique”,technique”, technique, hashas the beenbeen removed attemptedattempted cortical usingusing bony aa piezoelectricpiezoelectric plate can be sawsaw repositioned (Figure(Figure 1212). onto). WithWith the thisthis original conserva-conserva- site. Piezoelectrictivetive technique,technique, instruments thethe removedremoved ensure corticalcortical precise bonybony and plateplate safe cancan selective bebe repositionedrepositioned sectioning onto ontoof bone, thethe originaloriginaland the air- site.site. waterPiezoelectricPiezoelectric cavitation instrumentsinstruments effect provides ensureensure better preciseprecise visibility andand safesafe by selective selectivecreating sectioningasectioning clear and of ofblood-free bone,bone, andand surgical thethe air- fieldwaterwater [40]. cavitationcavitation With these effecteffect properties, providesprovides betterbetter osteotomy visibilityvisibility can by bybe creatingcreating performed aa clearclear safely, andand blood-freelessblood-free traumatically, surgicalsurgical andfieldfield more [[40].40]. conveniently, With these properties, especially osteotomyin the mandibular can be performed molar area. safely, In a preliminary lessless traumatically,traumatically, study, patientsandand moremore who conveniently,conveniently, underwent especially especiallya conventional inin thethe oste mandibularmandibularotomy in molar molartheir area.mandibulararea. In a preliminary molar area study, pre- sentedpatientspatients more who who swelling underwent underwent than a conventionala those conventional who were osteotomy oste treatedotomy in theirwith in their mandibulara bony mandibular window molar molartechnique area presented area [41]. pre- Recently,moresented swelling more Lee etswelling than al. [42] those reportedthan who those were a casewho treated of were periapical with treated a bonysurgery with window a onbony the technique windowmandibular technique [41 ].first Recently, molar [41]. andLeeRecently, showed et al. Lee [42 that] et reported al.the [42] repositioned reported a case of a corticalperiapicalcase of periapicalbony surgery plate surgery acted on the as on mandibular an the autologous mandibular first graft molar first for molar andthe surgicalshowedand showed site, that thethereby that repositioned the minimizing repositioned cortical bone cortical bony loss. plate bony Furthermore, acted plate as acted an this autologous as technique an autologous graft can for be graft the facilitated surgical for the bysite,surgical using thereby thesite, minimizingaforementioned thereby minimizing bone CAD/CAM-aided loss. bone Furthermore, loss. Furthermore, gu thisiding technique template this technique can [43]. be facilitatedKulakov can be etfacilitated by al. using [44] performedtheby using aforementioned the 11 aforementionedcases of CAD/CAM-aided piezoelect CAD/CAM-aidedric surgery guiding on templatethe gu mandibulariding [43 template]. Kulakov molars [43]. et with Kulakov al. [ 44repositioning] performed et al. [44] of11performed the cases cortical of piezoelectric 11 bonecases block,of piezoelect surgery and the onric therepositioning surgery mandibular on the procedure molars mandibular with was repositioning molars considered with of repositioninga thehighly cortical ac- ceptableboneof the block, cortical technique. and bone the repositioning block, and the procedure repositioning was considered procedure a was highly considered acceptable a technique.highly acceptable technique.

Figure 12. 12. TheThe “bony “bony window window technique” technique” with with a piezoelectric a piezoelectric saw. saw. (a) Bone (a) Bone preparation preparation for the for cortical the cortical window. window. (b) (b) Uncovered area of the lesion and the apices of the roots. (c) Allogenic bone was grafted and cortical bone was reposi- UncoveredFigure 12. The area “bony of the lesionwindow and technique” the apices with of the a roots.piezoelectric (c) Allogenic saw. ( bonea) Bone was preparation grafted and for cortical the cortical bone waswindow. repositioned. (b) tioned.Uncovered Images area were of the modified lesion anfromd the Kim apices et al. of [ 40]the after roots. receiving (c) Allogenic permission bone was from grafted the journal. and cortical bone was reposi- Images were modified from Kim et al. [40] after receiving permission from the journal. tioned. Images were modified from Kim et al. [40] after receiving permission from the journal. 3.3.3.3. Root-End Root-End Resection Resection 3.3. Root-EndAA consensus consensus Resection has has been been reached reached regarding regarding the the amount amount of root-end of root-end resection. resection. It is Itrec- is ommendedrecommendedA consensus that that 3 hasmm 3 mm beenshould should reached be be resected resectedregarding since since the most mostamount of of the the of ramificat ramifications/lateralroot-endions/lateral resection. It canals canalsis rec- thatthatommended may may serve serve that as as a3 microbial amm microbial should harbor harborbe resected are are thereby thereby since removed. most removed. of Furthermore,the ramificat Furthermore, ions/lateralthe modern the modern canalstech- niquetechniquethat may uses serve a uses shallow as a shallowa microbial bevel angle bevel harbor of angle 0°–10° are of thereby to 0◦ expose–10◦ removed.to fewer expose dentinal Furthermore, fewer tubules dentinal the with tubulesmodern enhanced withtech- magnificationenhancednique uses magnification a shallow and illumination bevel and angle illumination techniques of 0°–10° techniquesto [24] expose (Figure fewer [24 13).] (Figuredentinal 13 tubules). with enhanced magnification and illumination techniques [24] (Figure 13).

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FigureFigure 13. 13.A A contemporary contemporary technique technique for for root root resection. resection. (a) Clinical(a) Clinical features features of mesial of mesialmesial and distal andand rootsdistaldistal resectedroots resected perpendicular perpendicular to the to long the axis long of axis each of root.each (root.b) A ( periapicalb) A periapical X-ray X-ray image image taken taken using using the the parallel technique shows resection with a shallow bevel. Note that complete bony healing oc- parallelthe parallel technique technique shows shows resection resection with awith shallow a shallo bevel.w bevel. Note thatNote complete that complete bony healingbony healing occurred occurred with continuous lamina dura. withcurred continuous with continuous laminadura. lamina dura.

ResectionResection ofof thethe entireentire root root end end in in mandibular mandibular molars molars is is challenging. challenging. In In addition addition to to thethe thick thick cortical cortical bone, bone, the the cross-sectional cross-sectional morphology morphology of of the the root root apex apex of of the the mandibular mandibular molarmolar isis broadbroad buccolingually.buccolingually. Therefore, Therefore, careful careful inspection inspection of of the the root root end end is is mandatory mandatory toto verify verify whether whether it it is is completely completely resected. resected. For For this this purpose, purpose, methylene methylene blue blue solution solution is is helpfulhelpful for for differentiating differentiating the the root root end end from from adjacent adjacent bone bone tissue tissue by staining by staining the periodontal the perio- ligamentdontal ligament space (Figure space 14(Figurea). Sometimes, 14a). Sometimes, using a long using shank a long bur shank is necessary bur is fornecessary complete for resectioncomplete of resection the root of end. the In root some end. cases, In some the remaining cases, the remnantsremaining in remnants unfilled rootin unfilled canals canroot becanals identified can be by identified methylene by methylene blue staining blue under staining high under magnification high magnification (Figure 14 b).(Figure 14b).

Figure 14. A resected root surface stained with methylene blue solution. (a) The periodontal liga- FigureFigure 14. 14.A A resected resected root root surface surface stained stained with with methylene methylene blue blue solution. solution. (a) The (a) periodontalThe periodontal ligament ligament was stained and clearly distinguished from the adjacent bone (white triangle). The isthmus was stained and clearly distinguished from the adjacent bone (white triangle). The isthmus between between the mesio-buccal and mesio-lingual canal was also stained (yellow triangle). (b) The the mesio-buccal and mesio-lingual canal was also stained (yellow triangle). (b) The stained remnant stained remnant was identified in the unfilledilled distaldistal rootroot canalcanal (red(red triangle).triangle). was identified in the unfilled distal root canal (red triangle). 3.4. Root-End Preparation 3.4.3.4. Root-EndRoot-End PreparationPreparation Mandibular molars have an elaborate root canal anatomy, particularly in the apical MandibularMandibular molarsmolars havehave anan elaborateelaborate rootroot canalcanal anatomy,anatomy, particularly particularly in in the the apical apical portion. Mesial roots usually have two canals (buccal and lingual) and they are connected portion.portion. Mesial Mesial roots roots usually usually have have two two canals canals (buccal (buccal and and lingual) lingual) and and they they are are connected connected withwith thethe isthmus. isthmus. InIn mandibularmandibular molars,molars, anan isthmusisthmus isisfrequently frequentlyobserved observedin insections sections betweenbetween 33 andand 44 mm mm from from the the apex apex (Figure (Figure 15 15).). Karunakaran Karunakaran et et al. al. [ 45[45]] reported reported that that the the prevalenceprevalence ofof isthmuses isthmuses inin thethe mesial mesial roots roots of of mandibular mandibular first first molars molars was was 97.2%, 97.2%, while while thethe prevalence prevalence in in distal distal roots roots was was 39%. 39%. Furthermore, Furthermore, von von Arx Arx [ [46]46] analyzed analyzed the the occurrence occurrence ofof aa canalcanal isthmus isthmus inin mandibular mandibular molars molars during during endodontic endodontic surgery. surgery. HeHe reportedreported that that 83%83% ofof mesialmesial rootsroots had had two two canals canals with with an an isthmus isthmus and and that that 36% 36% of of distal distal roots roots had had two two canalscanals with with an an isthmus. isthmus. Recently,Recently, Kang Kang et et al. al. [ [47]47] inspected inspected 31 31 mesial mesial roots roots of of mandibular mandibular firstfirst molarsmolars andand foundfound thatthat 100%100% ofof rootsroots hadhad anan isthmusisthmus atat 33 mmmm levellevel fromfrom thethe apex.apex. Predictably,Predictably, thethe success success rate rate for for endodontic endodontic microsurgery microsurgery on on isthmus-absent isthmus-absent teethteeth was was higherhigher thanthan thatthat forfor isthmus-presentisthmus-present teethteeth [[4488],], whichwhich mightmight bebe duedue toto the the difference difference in in thethe level level of of difficulty difficulty for for identification identification and and instrumentation. instrumentation. InIn thisthis respect, respect, it it is is strongly strongly

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recommendedrecommended toto identifyidentify andand prepareprepare thethe isthmusisthmus asas wellwell asas rootroot canals.canals. On the contrary, recommendedifif anan isthmusisthmus isis to notnot identify present,present, and aa prepare simplesimple oval-shaped oval-shapedthe isthmus as root-endroot-end well as cavitycavityroot canals. sufﬁcessuffices On forfor the obturationobturation contrary, if(Figure(Figure an isthmus 1616).). Similar Similaris not present,to to periodontal periodontal a simple ligament ligament oval-shaped identification, identiﬁcation, root-end methylenecavity methylene suffices blue blue for is istheobturation the most most ef- (Figureeffectivefective 16).way way Similar to to stain stain to an anperiodontal isthmus isthmus during during ligament the the su surgicalidentification,rgical procedure procedure methylene (Figure blue 1414a).a). is Furthermore, the most ef- fectiveitit isis essentialessential way to thatthat stain thethe an isthmusisthmus isthmus shouldshould during bebe the preparedpr sueparedrgical toto procedure aa depthdepth ofof (Figure 33 mmmm like14a).like thethe Furthermore, rootroot canals.canals. it is essential that the isthmus should be prepared to a depth of 3 mm like the root canals.

FigureFigure 15.15. HistologicallyHistologically sectionedsectioned mesialmesial rootroot ofof thethe mandibularmandibular ﬁrstfirst molarmolar atat 33 mmmm levellevel fromfrom thethe Figureapex after 15. Histologicallycanal shaping. sectioned The whit emesial triangle root indicates of the mandibular an unprepared first middle molar atmesial 3 mm root. level The from yellow the apex after canal shaping. The white triangle indicates an unprepared middle mesial root. The yellow apextriangle after indicates canal shaping. the isth Themus whit connectinge triangle the indicates canals. an unprepared middle mesial root. The yellow triangle indicates the isthmus connecting the canals. triangle indicates the isthmus connecting the canals.

Figure 16. Endodontic microsurgery on an isthmus-absent mandibular molar. (a) A preoperative periapical radiograph Figureshows 16.periapical Endodontic radiolucency microsurgery and unsati on ansfactory isthmus-absent canal filling mandibular on the mesial molar. r oot( a) Adue preoperativepreoperative to an unnegotiable periapicalperiapical ledge. radiograph (b) The showsresected periapical root surface radiolucency shows mesio-buccal and unsatisfactory (white triangle)canal filling and on mesio-lingual the mesial r oot(yellow due totriangle) an unnegotiable canals, which ledge. are ( bclosely) The shows periapical radiolucency and unsatisfactory canal filling on the mesial root due to an unnegotiable ledge. (b) The resectedlocated withoutroot surface an isthmus shows mesio-buccalat 3 mm from (white the apex. triangle) (c) The an simple,d mesio-lingual oval-shaped (yellow root-end triangle) cavity. canals, (d) The which root-end are closely filling resected root surface shows mesio-buccal (white triangle) and mesio-lingual (yellow triangle) canals, which are closely locatedwith mineral without trioxide an isthmus aggregate at 3 mm (MTA). from (e the) A apex.postoperative (c) The simple, periapical oval-shaped radiograph. root-end (f) A 15-month cavity. (d )follow-up The root-end radiograph filling withlocatedshows mineral that without complete trioxide an isthmus healingaggregate at occurred. 3 (MTA). mm from (e) the A postoperative apex. (c) The simple,periapical oval-shaped radiograph. root-end (f) A 15-month cavity. ( dfollow-up) The root-end radiograph filling withshows mineral that complete trioxide healing aggregate occurred. (MTA). (e) A postoperative periapical radiograph. (f) A 15-month follow-up radiograph shows that complete healing occurred.Ultrasonic instruments are used for root-end cavity preparation. Smooth stainless steelUltrasonic was used instrumentsin the early days,are used but diamonfor root-endd-coated cavity instruments preparation. (e.g., Smooth KiS tips; stainless Young Ultrasonic instruments are used for root-end cavity preparation. Smooth stainless steelSpecialties, was used Algonquin, in the early IL, days,USA) butare diamonnow highlyd-coated recommended instruments since (e.g., the KiS coated tips; tipsYoung cut steel was used in the early days, but diamond-coated instruments (e.g., KiS tips; Young Specialties,the dentin andAlgonquin, filling material IL, USA) much are now faster hi thghlyan stainlessrecommended steel [49,50] since the(Figure coated 17a). tips Nota- cut Specialties, Algonquin, IL, USA) are now highly recommended since the coated tips cut thebly, dentin these andinstruments filling material are advantageous much faster for th anmulti-rooted stainless steel mandibular [49,50] (Figure molars, 17a). especially Nota- the dentin and filling material much faster than stainless steel [49,50] (Figure 17a). Notably, bly,when these an isthmusinstruments exists. are Most advantageous recently, ultras for multi-rootedonic tips with mandibular numerous metal molars, micro-projec- especially these instruments are advantageous for multi-rooted mandibular molars, especially when whentions anon isthmusthe cutting exists. surface Most insteadrecently, of ultras diamondonic tips coating with numerousare also available metal micro-projec- (JETip; B&L an isthmus exists. Most recently, ultrasonic tips with numerous metal micro-projections tionsBiotech, on theFairfax, cutting VA, surface USA) (Figure instead 17b). of diamond coating are also available (JETip; B&L on the cutting surface instead of diamond coating are also available (JETip; B&L Biotech, Biotech, Fairfax, VA, USA) (Figure 17b). Fairfax,The VA, most USA) important (Figure 17aspectb). of mandibular molar surgery is the angle of the instrument.The Double-angled most important instruments aspect of mandibular are strongly molar recommended surgery is thefor anglemandibular of the instru-molars ment. Double-angled instruments are strongly recommended for mandibular molars

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Medicina 2021, 57, 270 since the accessibility is much better compared to single-angled general tips. Manufactur-11 of 15 ers provide various double-angled tips suitable for buccal and lingual canals (e.g., KiS 3D and 5D for buccal canals, KiS 4D and 6D for lingual canals).

. FigureFigure 17. 17. ((aa)) Diamond-coated ultrasonic ultrasonic tips tips with with variou variouss angles angles (Microsurgical (Microsurgical KiS KiS tips). tips). 3D 3Dand and5D 5Dfor forbuccal buccal canals. canals. 4D 4D and and 6D 6D for for lingual lingual canals. canals. (Image (Image courtesy of YoungYoung Specialties,Specialties, https://www.youngspecialties.com/product/kis-ultrasonic-tips-1-cthttps://www.youngspecialties.com/product/kis-ultrasonic-tips-1-ct, ,accessed accessed on on 27 JanuaryJanuary 2021)2021) (b(b)) Retrograde Retrograde cavity cavity preparation preparation for for mesial mesial root-end root-end of of a a mandibular mandibular ﬁrst first molar molar with with JETip. JETip.

3.5. TheRoot-End most Filling important aspect of mandibular molar surgery is the angle of the instrument. Double-angled instruments are strongly recommended for mandibular molars since the An ultrasonically prepared root-end cavity must be filled with a material that guar- accessibility is much better compared to single-angled general tips. Manufacturers provide antees a bacteria-tight seal. Various materials have been suggested for this purpose. Amal- various double-angled tips suitable for buccal and lingual canals (e.g., KiS 3D and 5D for gam has been used as a retrograde filling material for many years, but the efficacy of amal- buccal canals, KiS 4D and 6D for lingual canals). gam has been questioned due to unfavorable physical properties and environmental dam- 3.5.age Root-End [51]. More Filling recently, zinc oxide eugenol (ZOE) containing materials such as intermedi- ate restorative material (IRM) and super ethoxy-benzoid acid (Super-EBA) has been An ultrasonically prepared root-end cavity must be filled with a material that guar- widely used due to its superior sealability compared to amalgam [52]. However, short- antees a bacteria-tight seal. Various materials have been suggested for this purpose. comings of the ZOE-containing materials are their toxicity and susceptibility to moisture. Amalgam has been used as a retrograde filling material for many years, but the efficacy of amalgamFinally, calcium has been silicate questioned cement, due widely to unfavorable known as mineral physical trioxide properties aggregate and environmen- (MTA), has talgained damage considerable [51]. More attention recently, for zinc the oxidepast quarter eugenol of (ZOE)a century containing due to its materials favorable such sealing as intermediateability and biocompatibility restorative material [53]. (IRM) Notably, and superthis hydrophilic ethoxy-benzoid material acid sets (Super-EBA) in an aqueous has beenenvironment widely used [54]. dueHowever, to its superiorthe main sealability disadvantage compared of MTA to is amalgam its poor handling [52]. However, proper- shortcomingsties [55]. This of is thean obstacle ZOE-containing regarding materials the application are their of toxicity MTA, andparticularly susceptibility in the tomandib- mois- ture.ular Finally,molar area, calcium which silicate has limited cement, access widely and known visibility. as mineral In this trioxide respect, aggregate efforts have (MTA), been hasmade gained to overcome considerable this problem attention by for enhancing the past the quarter application of a century method due or tohandling its favorable ability sealingof the materials. ability and biocompatibility [53]. Notably, this hydrophilic material sets in an aqueousSeveral environment instruments [54]. have However, been developed the main disadvantage to facilitate the of MTA application is its poor of MTA. handling The propertiesfirst one that [55 ].became This is available an obstacle was regarding the Dovg thean Carrier, application which of MTA,was designed particularly specifically in the mandibularfor the delivery molar of area, MTA which by Joseph has limited Dovgan. access It features and visibility. a NiTi plunger In this respect, as well efforts as a remov- have beenable madeluer-lock to overcome lumen that this can problem be removed by enhancing for cleaning the or application replacement method if it is or damaged handling or abilityclogged. of theIt offers materials. the choice of three different tip diameters. Similar instruments were then launchedSeveral by instruments several manufacturers have been developed such as the to Micro facilitate Apical the applicationPlacement (MAP) of MTA. system The first(Dentsply-Maillefer, one that became available Ballaigues was, Switzerland) the Dovgan Carrier,(Figure which18). Notably, was designed the ‘‘needles’’ specifically with for tri- theple delivery angles of of the MTA MAP by instrument Joseph Dovgan. are designed It features to place a NiTi MTA plunger in the as root-end well as a cavity removable in the luer-lockmost difficult lumen anatomical that can beregions removed such foras the cleaning mandibular or replacement molars [56]. if However, it is damaged if mixed or clogged.MTA is Itleft offers within the choicethe carrier of three after different the appointment, tip diameters. the Similar tip may instruments become clogged were then and launchedseemingly by unusable. several manufacturers Therefore, careful such management as the Micro of Apical the instruments Placement is (MAP) required. system (Dentsply-Maillefer, Ballaigues, Switzerland) (Figure 18). Notably, the “needles” with triple angles of the MAP instrument are designed to place MTA in the root-end cavity in the most difficult anatomical regions such as the mandibular molars [56]. However, if mixed MTA is left within the carrier after the appointment, the tip may become clogged and seemingly unusable. Therefore, careful management of the instruments is required.

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Figure 18. MAP system universal kit. (Image courtesy of Dentsply Sirona, FigureFigure 18. 18.MAP MAP systemsystem universaluniversal kit.kit. (Image(Image courtesycourtesy of Dentsply Sirona, https://www.maillefer. https://www.maillefer.com/products/specialty/map-system, accessed on 27 January 2021). com/products/specialty/map-systemhttps://www.maillefer.com/products/specialty/m, accessed onap-system, 27 January accessed 2021). on 27 January 2021).

AnotherAnotherAnother type typetype of ofof manual manualmanual carrier, carrier,carrier, which whichwhich consists consistsconsists of ofof a aa disposable disposabledisposable Teﬂon TeflonTeflon sleeve sleevesleeve and andand plugger,plugger,plugger, is isis available availableavailable in inin the thethe endodontic endodonticendodontic market marketmarket (Dentsply (Dentsply(Dentsply Sirona) Sirona)Sirona) (Figure (Figure(Figure 19 19a).19a).a). This ThisThis instru- instru-instru- mentmentment is isis also alsoalso useful usefuluseful for forfor placing placingplacing MTA MTAMTA in inin the thethe root-end root-endroot-end cavity cavitycavity of ofof mandibular mandibularmandibular molars molarsmolars because becausebecause clinicianscliniciansclinicians can cancan push pushpush a aa relatively relativelyrelatively large largelarge amount amountamount of ofof MTA MTAMTA into intointo the thethe cavity cavitycavity with withwith smooth smoothsmooth pressure pressurepressure (Figure(Figure(Figure 19 19b).19b).b). However, However,However, the thethe use useuse of ofof the thethe manual manualmanual carrier carriercarrier is isis limited limitedlimited when whenwhen the thethe bony bonybony cavity cavitycavity is isis smallsmallsmall and andand the thethe roots rootsroots are areare located locatedlocated deep deepdeep in inin the thethe buccal buccbuccalal bony bonybony plate plateplate since sincesince the thethe vertical verticalvertical dimension dimensiondimension ofofof the thethe plugger pluggerplugger is isis relatively relativelyrelatively long. long.long.

.. Figure 19. Manual carrier for MTA application. (a) Assembled Teflon sleeve and plugger. (b) Clini- FigureFigure 19. 19.Manual Manual carrier carrier for for MTA MTA application. application. (a ()a Assembled) Assembled Teﬂon Teflon sleeve sleeve and and plugger. plugger. (b) ( Clinicalb) Clini- cal application of MTA into root-end cavity prepared in the buccal root of the mandibular first molar applicationcal application of MTA of MTA into into root-end root-end cavity cavity prepared prepared in thein the buccal buccal root root of of the the mandibular mandibular ﬁrst first molar molar using the manual carrier. A blue arrow indicates the direction of the force of the plugger. usingusing the the manual manual carrier. carrier. A A blue blue arrow arrow indicates indicates the the direction direction of of the the force force of of the the plugger. plugger.

SeveralSeveralSeveral attempts attemptsattempts have havehave also alsoalso been beenbeen made mademade to toto enhance enhanceenhance the thethe handling handlinghandling ability abilityability by byby modifying modifyingmodifying thethethe material materialmaterial properties. properties.properties. Biodentine BiodentineBiodentine (Septodont, (Septodont,(Septodont, St. St.St. Maurdes MaurdesMaurdes Foss Fossés,Fossés,és, France) France)France) is isis a aa moldable moldablemoldable MTA-basedMTA-basedMTA-based material materialmaterial that thatthat contains containscontains a aa hydro-soluble hydro-solublehydro-soluble polymer polymerpolymer in inin liquid, liquid,liquid, which whichwhich reduces reducesreduces the thethe viscosityviscosityviscosity of ofof the thethe cement cementcement and andand thereby therebythereby improves improvesimproves handling handlinghandling [ 57 [57].[57].]. Therefore, Therefore,Therefore, Biodentine BiodentineBiodentine can cancan be bebe appliedappliedapplied easily easilyeasily with withwith conventional conventionalconventional instruments instrumentsinstruments such suchsuch as stoppers, asas stoppers,stoppers, without withoutwithout the aforementioned thethe aforemen-aforemen- speciallytionedtioned speciallyspecially designed designeddesigned instruments. instruments.instruments. Furthermore, Furthermore,Furthermore, injectable injectableinjectable bio-ceramic bio-ceramicbio-ceramic root-end ﬁlling root-endroot-end materi- fill-fill- alsinging have materialsmaterials also been havehave developed alsoalso beenbeen (Figure developeddeveloped 20). They(Fig(Figureure are 20).20). premixed TheyThey areare with premixedpremixed polymeric withwith vehicles polymericpolymeric and preservedvehiclesvehicles andand in water-tight preservedpreserved inin syringes water-tightwater-tight so that syringessyringes the materials soso thatthat canthethe materials bematerials placed cancan directly bebe placedplaced by injection. directlydirectly Theybyby injection.injection. are also TheyThey moldable areare alsoalso and moldablemoldable can be delivered andand cacann be bybe delivered simpledelivered instruments. byby simplesimple instruments.instruments. Consequently, Conse-Conse- the materialsquently,quently, the canthe materialsmaterials be placed cancan more bebe conveniently placedplaced moremore conveniently inconveniently the mandibular inin thethe molar mandibularmandibular area. molarmolar area.area.

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Figure 20. CommerciallyFigure 20. Commercially available premixed available calcium premixed silicate calcium root-end silicate ﬁlling root-end materials. filling (a) Endo-sequencematerials. (a) Endo- Root Repair sequence Root Repair Material (RRM). (Image courtesy of Brasseler, https://brasseleru- Material (RRM). (Image courtesy of Brasseler, https://brasselerusadental.com/products/bc-rrm-fast-set-putty/, accessed sadental.com/products/bc-rrm-fast-set-putty/, accessed on 28 January 2021) (b) Endocem MTA Pre- on 28 January 2021) (b) Endocem MTA Premix (Image courtesy of Maruchi). mix (Image courtesy of Maruchi). 4. Conclusions 4. Conclusions Endodontic microsurgery for the mandibular molar area is challenging for clinicians Endodonticdue tomicrosurgery the difﬁculty for in the access mandibular and the molar critical area anatomical is challenging structures. for clinicians Owing to the devel- due to the difficultyopment ofin cutting-edgeaccess and the technology critical anatomical including structures. equipment Owing and materials, to the devel- the success rate opment of cutting-edgehas been increasing. technology Therefore, including clinicians equipment should and be materials, familiar withthe success up-to-date rate information has been increasing.on the current Therefore, concepts clinicians to achieve should successful be familiar outcomes, with up-to-date and this information review can be a useful on the currentguideline concepts for to the achieve preservation successful of mandibular outcomes, and molars this through review microsurgery.can be a useful guideline for the preservation of mandibular molars through microsurgery.

Author Contributions: Conceptualization, E.K. and K.-S.M.; writing—original draft preparation, Author Contributions: Conceptualization, E.K. and K.-S.M.; writing—original draft preparation, S.M.J. and K.-S.M.; writing—review and editing, E.K. and K.-S.M.; funding acquisition, K.-S.M. All S.M.J. and K.-S.M.; writing—review and editing, E.K. and K.-S.M.; funding acquisition, K.-S.M.; All authors have read and agreed to the published version of the manuscript. authors have read and agreed to the published version of the manuscript. Funding: Funding: This research Thiswas funded research by was the funded Korea Medical by the Korea Device Medical Development Device DevelopmentFund grant funded Fund grant funded by the Korea bygovernment the Korea (the government Ministry (theof Science Ministry and of ICT, Science the andMinistry ICT, of the Trade, Ministry Industry of Trade, and Industry and Energy, the MinistryEnergy, of the Health Ministry & Welfare, of Health Republic & Welfare, of Korea, Republic the Ministry of Korea, of the Food Ministry and Drug of Food Safety) and Drug Safety) (Project Number:(Project 202011C03). Number: 202011C03). Institutional ReviewInstitutional Board Review Statement: Board Not Statement: applicable.Not applicable. Informed ConsentInformed Statement: Consent Not Statement: applicable.Not applicable. Conflicts of Interest:Conﬂicts The of Interest:authors declareThe authors no conflict declare of nointerest. conﬂict of interest. References References 1. Tabassum, S.; Khan, F.R. 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