Endodontics Master PDF

2 Endodontics CHAPTER OUTLINE Overview, 48 2.6 Root Canal Obturation, 64 2.1 Pulpal and Periradicular Pathology, 48 2.7 Restoration of Endodontically 2.2...

2 Endodontics CHAPTER OUTLINE Overview, 48 2.6 Root Canal Obturation, 64 2.1 Pulpal and Periradicular Pathology, 48 2.7 Restoration of Endodontically 2.2 Patient Assessment, 50 Treated Teeth, 68 2.3 Vital Pulp Therapy, 53 2.8 Root Canal Retreatment, 70 2.4 Root Canal Morphology, 56 2.9 Surgical Endodontics, 75 2.5 Root Canal Preparation–Cleaning and Self-Assessment: Questions, 79 Shaping of the Root Canal System, 58 Self-Assessment: Answers, 82 Overview understand the basic pathobiology of pulpal and perira- dicular disease. Pulp and periradicular disease is common and can result in discomfort, pain and potentially premature tooth loss for patients. The understanding of endodontic disease Pulpal and periradicular diseases are inflammatory patho- and the way in which it can be managed is progressing logical conditions which result from irritation of these tis- rapidly. Although there has been a dramatic evolution in sues, generally by an infective source or, less commonly so, the technology available to make complex treatment eas- mechanical or chemical sources. ier, the field is beginning to move towards more biologi- cally based principles to diagnose and treat endodontic diseases. INFECTIVE SOURCE - BACTERIA Our understanding of pulpal disease is increasing expo- Bacteria, usually from dental caries, are the main sources nentially and while managing the injured pulp was always of injury to the pulpal and periradicular tissues. These thought to be unpredictable, such dogma is being chal- enter either directly or through dentine tubules. The link lenged. This revised chapter includes a new section on vital between bacteria and pulpal and periradicular disease is pulp therapies as modern biologically based treatments are well established as periradicular pathology does not develop shown to be far more predictable than first thought. Pulpal in the absence of bacteria. Modes of entry for bacteria – and periradicular disease is principally caused by an infec- other than caries – include periodontal disease (dentine tion which is bacterial in origin. The aim of treatment there- tubules, furcal canals and lateral canals), erosion, attrition fore is to protect pulp tissue from infection or eliminate these and abrasion (dentinal tubules), cracked teeth, trauma bacteria from within the complex anatomy of root canal with or without pulpal exposure, developmental anomalies systems if it becomes infected and then seal the canal space and anachoresis (the passage of micro-organisms into the to prevent re-entry. root canal system from the bloodstream). This chapter provides an overview of pulpal and perira- dicular disease and the methods used to examine the patient and formulate a diagnosis. A section is included on manag- MECHANICAL IRRITANTS ing the injured vital pulp, followed by a review of both tradi- Examples of mechanical irritation include trauma, operative tional and some of the more recent treatment developments procedures including iatrogenic perforations, excessive orth- that have proved useful in day-to-day practice in managing odontic forces, subgingival scaling and over instrumentation the necrotic pulp. The restoration of endodontically treated during root canal treatment. teeth is discussed before managing failed root canal treat- ment with non-surgical and surgical approaches. CHEMICAL IRRITANTS Pulpal irritation may result from bacterial toxins or some re- 2.1 Pulpal and Periradicular storative materials/conditioning agents. Periradicular irrita- Pathology tion may occur from irrigating solutions, phenol-based intra- canal medicaments or extrusion of root canal filling materials. LEARNING OBJECTIVES You should: PULP DISEASE be able to recognise conditions that may affect the dental The dentine-pulp complex (Fig. 2.1) is a unique miner- pulp and periradicular tissues caused by endodontic disease alised connective tissue that is composed of two integrated 48  2 Endodontics 49 stimulus whereas reparative dentine is deposited directly beneath the path of injured dentinal tubules as a re- sponse to strong noxious stimuli. Treatment is dependent upon the pulpal symptoms. Internal resorption: Occasionally, pulpal inflammation may cause changes that result in dentinoclastic activity. Such changes result in resorption of dentine; clinically, a pink spot may be seen in the later stages if the lesion is coro- nal. Radiographic examination reveals a punched-out outline that is seen to be continuous with the rest of the pulp cavity. Root canal therapy will result in the arrest of the resorptive process; however, if destruction is very advanced, extraction may be required (Fig. 2.2). Making an accurate diagnosis of pulp status can be chal- lenging. The information gained from an accurate patient history is supplemented with a good clinical/radiographic examination and pulp testing. It is important not to draw conclusions on one positive or negative finding. All informa- tion gathered from the examination, history and special tests Fig. 2.1 Haematoxylin and eosin staining of the dentine-pulp complex. should be assimilated and judged in context with one another (Section 2.2 and Conservative Dentistry chapter). constituents: the pulp – an underlying gelatinous soft con- PERIRADICULAR DISEASE nective tissue which has a rich vasculature and is well in- Periradicular periodontitis (also known as apical periodon- nervated, and the dentine – an outer casing of mineralised titis) is an inflammatory disease of the tissues surrounding tissue. the root of the tooth which is most frequently caused by an It is under threat from three main sources: carious attack, infection inside the root canal system. A complex polymi- trauma and iatrogenic damage. The response of the pulp crobial biofilm can become established within the root ca- depends on the severity of the insult and may result in a nal system once the pulp becomes necrotic and the tooth transient (reversible) inflammatory response or an irrevers- loses its defence system. Endodontic biofilm is mainly made ible one, which may eventually proceed to pulp necrosis. The up of Gram-negative bacteria; however Gram-positive bac- classical terms of reversible and irreversible still remain use- teria can also exist. These organisms release virulence fac- ful but are under review as our understanding of the disease tors such as lipopolysaccharides (LPS) and lipoteichoic improves and our clinical procedures are refined. Current acid (LTA) inducing a host response which leads to com- diagnostic terms for pulpal disease are: plex interactions resulting in inflammation, resorption of Normal pulp: The pulp is symptomless and responds nor- mineralised tissues surrounding the root and potential mally to a stimulus. clinical symptomology. Reversible pulpitis: Pain or discomfort initiated by a stimulus The terms periradicular periodontitis and more com- such as cold or sweet which resolves shortly after the monly used apical periodontitis can be used interchange- stimulus is removed. The pain and discomfort on occasions ably. Although a semantic point the term periradicular will may be difficult to localise. On examination suspect teeth be used here as it more accurately encompasses pathology are not tender to percussion (unless involved with occlusal that results from endodontic causes that not only exist at trauma) and have a normal radiographic appearance. Irreversible pulpitis: More intense pain that can be sponta- neous or radiating which is long lasting and lingers after removal of stimulus. It can be exacerbated or worsened by lying down. Pulp necrosis: The pulp is dead and the patient is usually unresponsive to pulp testing. Other diagnoses related to pulp pathology are: Hyperplastic pulpitis: Hyperplastic pulpitis, also known as a pulp polyp, occurs as a result of proliferation of chroni- cally inflamed young pulp tissue when exposed to the oral cavity. Pulp calcification: This results in eventual occlusion of the pulp chamber by either physiological secondary dentine A B or tertiary dentine which is laid down in response to en- vironmental stimuli as reactionary or reparative dentine. Fig. 2.2 Internal resorption of upper left central. (A) Intraoral periapical Reactionary dentine is a response to a mild noxious and (B) sagittal plane of cone beam computerised tomography scan. 50 Master Dentistry the apex of the root but on any surface of the root. Current carcinoma, osteosarcoma, chondrosarcoma and multiple diagnostic terms for periradicular disease are as follows: myeloma. These lesions are usually associated with rapid hard tissue destruction. Normal periradicular tissues: Asymptomatic tooth which responds normally on vitality testing is not sensitive to percussion or palpation testing and radiographically has continuous lamina dura and normal periodontal 2.2 Patient Assessment ligament space. LEARNING OBJECTIVES Asymptomatic periradicular periodontitis: Asymptomatic tooth that does not elucidate any positive clinical signs of You should: disease following examination apart from radiographic be able to follow a structured approach to history tak- evidence of periradicular inflammation that is of end- ing and conducting a thorough clinical examination odontic origin. understand the relevance of special tests Symptomatic periradicular periodontitis: Inflammation of appreciate the importance of patient-specific treatment the periradicular tissue produces clinical symptoms in- planning. volving a painful response to biting and/or percussion or palpation. Radiographic appearance can be varied, rang- The most common cause of orofacial pain is caused by ing from minimal widening of the periodontal ligament pulpal or periradicular disease and making an accurate di- space to a large area of destruction of periapical tissues. agnosis for such conditions can be challenging. Successful Chronic periradicular abscess: An inflammatory reaction to endodontic diagnosis requires a systematic approach to pulpal infection and necrosis characterised by gradual gathering information through a thorough history and onset, little or no discomfort and an intermittent discharge clinical examination followed by the use of appropriate di- of pus through a sinus tract or periodontal pocket. Radio- agnostic aids in order to determine the correct treatment graphically, there are frequent signs of osseous destruction strategy for the patient. Do not draw conclusions on one such as a radiolucency. positive or negative finding. All information gathered from Acute periradicular abscess: Inflammatory response to mi- the examination, history and special tests should be assimi- cro-organisms or their irritants that have leached out lated and judged in context with one another. into the periradicular tissues. Symptoms vary from mod- Diagnosis of pulpal and periradicular disease can be erate discomfort or swelling to systemic involvement, complicated because of the potential for convergence of such as raised temperature and malaise. Teeth involved nerves within the trigeminal ganglion. Pain originating are usually tender to both palpation and percussion. from other tissues such as the periodontium, paranasal si- In cases where infection is severe or where the immune nuses, temporomandibular joints, muscles of mastication, system is compromised, infection may cause systemic sepsis. ears, nose, eyes and blood vessels may also be affected by There are a number of clinical signs that are deemed high lesions that can mimic pain of endodontic origin. In some risk for sepsis, including altered mental state, rapid breath- cases, the nature of the pain is not coincident with patient’s ing and heart rate, failure to pass urine, low systolic blood symptoms or the symptoms have not changed as a result of pressure, a non-blanching rash or cyanosis of the skin. In- previous treatment, in which case there should always be a terestingly in these cases, there is often a low temperature suspicion of a non-odontogenic or neuropathic element to 36 degrees Celsius; caution should always be taken when this pain. dealing with patients who are immunocompromised. Condensing osteitis: Represents a diffuse increase in trabecular bone in response to irritation. Radiographically, PATIENT HISTORY a concentric radio-opaque area is seen around the offend- Should be considered as four components: presenting com- ing root. pliant, medical history, dental history and pain history. Although lesions noted on radiographs are usually of endodontic origin, this is not always the case. Other causes n Presenting complaint may be normal anatomic structures, benign or malignant The aim of this stage is to record the patient’s symptoms lesions. For example, certain normal anatomic structures or problems, preferably in their own words. may mimic radiolucencies (e.g. maxillary sinus, mental n Pain history foramen and nasopalatine foramen). In these situations, It is important to take the time to listen to your patient, the associated teeth will respond normally to pulp sensitiv- ask broad open questions to start with, then follow-up ity tests, and a radiograph taken from a different angle will with more direct questions once the story forms. It can reveal that the lesion is not so closely related to the root. be useful to follow a consistent pattern in questioning Benign lesions that may mimic endodontic pathology and a mnemonic such as SOCRATES below is useful. include cementoma, fibrous dysplasia, ossifying fibroma, Site – Where is the pain? primordial cyst, lateral periodontal cyst, dentigerous cyst, Onset – When did the pain start, and was it sudden or traumatic bone cyst, central giant cell granuloma, central gradual? haemangioma, odontogenic keratocyst and ameloblas- Character – What is the pain like? An ache? Stabbing? toma. In some such situations, the lamina dura will be Radiation – Does the pain radiate anywhere? intact around the teeth and final diagnosis relies on Associations – Any other signs or symptoms associated histopathological analysis following appropriate biopsy. with the pain? Malignant lesions to be aware of include squamous cell Time course – Does the pain follow any pattern?  2 Endodontics 51 Exacerbating/relieving factors – Does anything change 2 mm of circumferential supra-gingival tooth structure the pain? and not less than 30% of the original coronal tooth struc- Severity – How bad is the pain? ture remaining. n Medical history A detailed medical history should be taken for each new SPECIAL TESTS patient or be updated for previously registered pa- tients, dated and signed. Treatment planning can be All special tests have their limitations and require care in affected by the patient’s medical status. For example, the way they are performed and interpreted. The objective a patient who is at higher risk of osteonecrosis of the is to find the tooth that is causing discomfort. In general, jaw due to previous radiotherapy or taking bisphos- healthy (control) teeth are tested first. phonate drugs. n Dental history n Percussion The purpose of the dental history is to summarise cur- Percussion refers to gently tapping or pressing the oc- rent and past dental treatment. Such information may clusal or lateral surface of a tooth. A painful response provide clues as to the source of the patient’s com- indicates periradicular inflammation. The region over plaints. It is also an opportunity to establish the pa- the apices of teeth may also be palpated. Tenderness tient’s attitude towards dental health and treatment may be an indication of inflammation, although care that may affect treatment decisions/planning. should be taken in interpretation when apices are close to the surface. On occasions, it is possible to form a provisional diagnosis n Mobility based purely on the history prior to carrying out any A mirror handle is placed on either side of the tooth and clinical examination. A wise clinician has to be careful not a note made of the degree of movement: up to 1 mm to form opinions that are too fixed at this stage as it can scores 1, over 1 mm scores 2 and vertically mobile prejudice the objectivity of a clear unbiased clinical exami- teeth score 3. nation. n Occlusal analysis It is important to examine suspect teeth for interferences on CLINICAL EXAMINATION the retruded arc of closure, intercuspal position and lat- eral excursions. Interferences in any of these positions Extraoral Examination could result in occlusal trauma and initiate a symptom- As soon as a clinician first sees their patient, they are mak- atic periapical periodontitis although it may be transient. ing a subconscious assessment of their general appearance n Pulp testing and wellbeing. An assessment is made of any swelling, fa- Pulp tests determine the response to stimuli and indicate cial asymmetry, redness or extraoral sinuses. Lymph nodes if the pulp has become necrotic or is inflamed. It is are palpated for enlargement and/or tenderness. Clinicians usual to try to mimic the stimulus that initiates the should always be cautious with patients who do have a pain. Pulp testing may help to distinguish between an swelling as the extent and severity of a developing infec- infection of periodontal or endodontic origin when a tion/cellulitis is one of the few dental problems that can periodontal–endodontic communication is present. cause death. A systemic infection should be considered if Thermal tests are usually the most useful as they give the patient has general malaise or a raised body tempera- an indication not only as to whether the pulp is alive ture. If the patient has dysphagia, any compromise of but also how healthy it is. airway or there is a risk that the swelling is spreading to Numerous different methods exist in order to determine the orbit, then the patient should be managed immediately the viability of the pulp. Most commonly used thermal by an inpatient team and given appropriate intravenous and electric tests are available in general dental prac- antibiotics. tice. In the first instance, when selecting a thermal To ensure non-odontogenic causes of pain are not over- test, the practitioner should try and replicate the exac- looked, muscles of mastication and temporomandibular erbating factor the patient identifies with most com- joints are also palpated for tenderness and a note made of monly, be that hot or cold. the degree of mouth opening. Readers are directed to the n Cold test diagnostic criteria for temporomandibular disorders (DC- Ethyl chloride (5°C) has been used for many TMD) for further information in this area. Whilst carrying years but non-polluting hydrochlorofluorocar- out the extraoral examination, it is important to note the bons (HCFCs) refrigerant spray such as tetrafluo- extent of tooth display on maximum smiling. roethane (TFE) at approximately 26°C or pro- pane/butane mix at 50°C are now considered Intraoral Examination more effective. Cold tests are effective for testing The oral mucosa and gingival tissues are examined for dis- vital and non-vital teeth and generally should be coloration, inflammatory change and sinus tract forma- used as a first line test. tion. A basic periodontal examination is performed to n Hot test screen for periodontal disease and the amount of attach- Hot gutta-percha or hot water after the application ment around suspect teeth. Teeth are examined for caries, of dental dam may be used to mimic hot stimuli. large restorations, crowns, discoloration, fracture, attrition, n Electric pulp test abrasion, erosion and restorability. In order to make the Electric instruments can provide an indication as to restoration of the tooth predictable, there should be at least whether or not there is vital nerve tissue in the 52 Master Dentistry tooth; they do not give an indication of different n proximity of restorations to pulp chamber stages of degeneration. Electric pulp tests are ac- n quality of restorations, including coronal seal curate when testing vital teeth but poor when n the size of the pulp chamber 6 calcifications testing non-vital teeth. n crown root ratio n Test cavity n the number of roots Occasionally, as a last resort, an access cavity is cut n root anatomy into dentine without local anaesthesia as an ad- n canal anatomy ditional way of pulp testing. n canal calcification n Sinus tract exploration n root end proximity to important structures Where a sinus tract is present, it may be possible to insert n presence of lesions of endodontic origin periradicularly a small gutta-percha point. A radiograph is then taken or furcally to see which root the tract/point leads to. n root fractures n Transillumination n extra root canals Transillumination with a fibre-optic light can be useful n resorptive defects in the diagnosis of cracks in teeth. n quality and effectiveness of previous treatment n Periodontal probing n root filling materials used Detailed periodontal probing around suspect teeth may n iatrogenic complications reveal a sulcus within normal limits. However, on oc- n presence of pins/posts. casions, deeper pocketing will be noted. A narrow de- Following conventional radiography there may be indica- fect may be an indication of a root fracture or an tions for three-dimensional (3D) imaging techniques to be endodontic lesion draining through the gingival crev- utilised to improve diagnostic yield (Fig. 2.3), inform prog- ice. Broader-based lesions are usually an indication of nosis to aid treatment planning and provide information to disease of periodontal origin. plan execution of treatment. Indications for cone-beam n Selective anaesthesia computer tomography include the following: Selective anaesthesia can be useful in cases of referred pain to distinguish whether the source of pain is man- n Assessment and/or management of root resorption dibular or maxillary in origin. It is less useful for dis- n Determine anatomically complex root canal systems tinguishing pain from adjacent teeth, as the anaes- prior to endodontic management (e.g. dens invaginatus) thetic solution may diffuse laterally. n Presurgical assessment prior to complex periradicular n Directed cusp loading test surgery (e.g. proximity to sensitive anatomical struc- A plastic bite stick (e.g. tooth sleuth) which allows tures such as the maxillary antrum or inferior dental directed loads to specific cusp tips can be used to aid nerve) diagnosis of cracked tooth syndrome (CTS). With CTS n Detection of radiographic signs of pathology or dentoal- it is typical, but not always, for the pain to occur on veolar trauma when plain film imaging is inconclusive release of biting pressure. and the diagnosis is unclear n Radiographs n Non-surgical retreatment of cases where prognosis and Radiographs should be taken with a paralleling tech- treatment strategy is not clear from two-dimensional nique using film holders and an associated beam- imagining aiming device. Digital radiography is superseding n Identification of the spatial location of extensively oblit- traditional film radiographs and has the advantage erated canals. of using software which can enlarge and manipu- late the image easily to improve interpretation. If DIAGNOSIS traditional films are used they should be viewed using an appropriate viewer with magnification. Following this systematic approach to history taking and Radiographs may provide much important informa- the application of appropriate special tests, it will usually be tion to help to confirm a diagnosis, but they should possible to make a diagnosis of the pulpal or periradicular not be used alone. Radiographic findings may in- problems. Such diagnoses are covered in Section 2.1. After clude the loss of lamina dura (laterally or apically) taking a thorough history and performing appropriate spe- or a frank periradicular radiolucency indicative of cial tests, the clinician may be unsure as to whether the pulp necrosis. Radiographs may show pulp chamber pain is of odontogenic origin. Endodontic treatment is inva- or root canal calcification, which can explain re- sive and should not be performed on an ad hoc or ‘hit and duced responses to pulp testing, and emphasises miss’ basis. In cases of difficult diagnosis, a referral to an the need for considering the results of more than orofacial pain clinic, a neurosurgeon or an ear, nose and one test. More rarely, radiographs may reveal tooth/ throat specialist may be considered. root resorptive defects. CASE SELECTION AND TREATMENT Checklist for Radiographic Assessment Once a diagnosis has been reached, an endodontic treat- All the following can be assessed: ment plan needs to be formulated. The difficulty of an end- n periodontal bone support odontic case can be modified by a number of factors at a n caries patient and diagnostic level. Some of these, such as the n crown shape and size medical history and emergency presentations, have been  2 Endodontics 53 A B Fig. 2.3 (A) Intraoral periapical showing sound periradicular health of left mandibular second molar and (B) sagittal plane cone beam computerised tomography image of same tooth showing bone loss around apex of mesial and distal roots. already discussed. However, limitation of opening, the posi- 2.3 Vital Pulp Therapy tion of the tooth in the arch and the ease of which routine radiography can be taken should not be underestimated. At LEARNING OBJECTIVES a tooth level, the following may complicate treatment: presence of large restorations or crowns, significant root You should: curvature, unusual canal anatomy, presence of pulp stones, be able to recognise conditions that may affect the den- calcifications, pathological resorption and previous root tal pulp canal treatment. understand the relationship between pulpal diagnosis The fact that an endodontic procedure is feasible is not and appropriate treatment. sufficient justification for performing it. Endodontic treat- ment must be considered as part of an overall treatment The principles of minimally invasive treatment approaches plan in such a way that it represents the patient’s best inter- are becoming more established as the importance of con- ests and wishes. Case selection is key to a successful out- serving dental tissue once the integrity of a tooth is bro- come and not all cases will be manageable let alone success- ken is becoming more fully appreciated. Preserving a vital ful. The past dental history will have provided information pulp is fundamental to such strategies and has numerous as to the patient’s attitude towards treatment. Good end- benefits: odontic treatment takes time, requiring a commitment from both clinician and patient. n Preservation of the tooth’s defence system. On occasions it may be necessary to perform endodontic n Preservation of full proprioceptive function of the tooth. treatment on teeth which would normally be considered n Root canal treatment is technically demanding and not unrestorable due to the patient’s medical history. There are always predictable. an increasing number of patients with a history of radio- n Permits normal growth of the tooth and dento-alveloar therapy or prescription of bisphosphonate drugs which complex during development. puts them at a high risk of osteonecrosis of the jaw if a n Avoids root filled teeth that are weakened are more prone tooth was extracted. In these cases extra efforts may to fracture. be warranted to save the tooth and re-establish healthy The vitality of the dental pulp can be challenged in periradicular tissues even if the crown of the tooth cannot many ways, including carious tissue loss, non-carious be restored predictably. tooth surface loss, trauma and iatrogenic damage, leading to reversible or irreversible changes. The extent of injury Treatment Planning to the pulp is very difficult to determine and clinicians rely Sequencing of treatment involves the management of on weak empirical evidence, since there is a poor correla- pulpal or periodontal pain as a priority, and the extraction tion between clinical signs and symptoms and the true of unsavable teeth. Teeth with large carious lesions should histological state of the pulp; however, this standpoint is be stabilised with pre-endodontic cores and a preventive being questioned. In 1922, not long after the pioneering regimen instituted to halt any further progress of periodon- thesis of Herman (1920) which demonstrated the regen- tal disease or caries. Endodontic and restorative procedures erative capacity of the dental pulp, the exposed pulp was can then be performed in a more stable environment and described as a ‘doomed organ’ (Rebel). Unfortunately, that more predictable results can be obtained. dogma still blights our approach and anecdotally appears 54 Master Dentistry to be followed by some undergraduate teaching pro- It is established that calcium silicate cements (CSCs) such grammes even though our understanding of the repara- as mineral trioxide aggregate (MTA) induce a more predict- tive mechanisms of the dentine–pulp complex is now able and better pulpal response compared to calcium so much greater. Following pulpal injury, the vitality of hydroxide; however, calcium hydroxide still produces good the pulp can be maintained therapeutically in one of results and is widely available to all practitioners. CSCs are three ways: indirect pulp cap, direct pulp cap and pulp yet to establish themselves as a mainstream material used amputation/pulpotomy. by all general dental practitioners and although CSCs are the material of choice for VPTs, calcium hydroxide is still considered acceptable. STRATEGIES FOR VITAL PULP TREATMENT (VPT) It is important to note that bismuth oxide containing Clinicians carrying out an operative procedure on a vital CSCs should not be used on anterior teeth or on teeth where tooth should be mindful that the heat generated by dental aesthetics is important. Although these materials have ex- handpieces, the potential damage by over dehydrating den- cellent biological characteristics, there is clear evidence tine and the use of caustic agents in tooth restoration can that such materials can discolour teeth and should be result in unnecessary iatrogenic pulp damage. Frequently avoided in these situations. CSCs that do not contain bis- prevention is better than cure and therefore care/attention muth oxide such as biodentine have not yet shown cause should be taken when removing tooth tissue/selecting ma- for concern with respect to discolouration; however, users terials to prevent injury to the pulp. Damage to the pulp will should still be cautious as such materials have not been not just occur when the surrounding dentine is breached used for long enough to clearly demonstrate that they will and thus VPTs should not just be considered as procedures not cause any form of discolouration. to manage the injured pulp but also thought of as a treat- ment step to prevent pulpal disease. The range of VPTs can INDIRECT PULP CAPPING be considered as follows with the aim of producing a posi- tive biological response so the pulp can protect itself: It could be argued that any therapeutic process for the ben- efit of pulp survival that is adopted during a restoration of Indirect pulp capping: Application of a material onto a thin a tooth with an unexposed pulp is an indirect pulp cap. layer of dentine which is close to the pulp. Classically, this procedure is carried out when dentine is lost Direct pulp capping: Application of a material directly onto due to caries, trauma or a previous iatrogenic intervention the pulp. and a cavity exists which is close to the pulp but dentine still Partial pulpotomy: Removal of a small portion of superficial remains over the pulp tissue. coronal pulp tissue followed by application of a material directly onto the pulp. Procedure Outline (Fig. 2.4) Full pulpotomy: Complete removal of the coronal pulp to the The tooth should be isolated with dental dam and the cavity root canal orifice level followed by application of a mate- preparation completed as appropriate. The cavity should be rial directly onto the remaining pulp. disinfected using cotton pellets soaked (removing gross ex- Pulpectomy: Total removal of the pulp from the root canal cess) ideally with sodium hypochlorite (0.5–5%). The deepest system followed by root canal treatment where there is part of the cavity, closest to the pulp, should be covered ideally no potential seen of producing a positive biological re- with a CSC or calcium hydroxide. If calcium hydroxide is used sponse so the pulp can protect itself. it should be sealed with glass ionomer cement (GIC) or a resin The following guidelines cover all indications and treat- glass ionomer cement (RMGIC). The tooth is then definitively ment procedures to treat the vulnerable pulp irrespective of restored with the appropriate restorative material. whether dentine is lost due to caries, trauma or previous iatrogenic intervention. In the case of treating caries, a DIRECT PULP CAPPING strong evidence base shows that when managing deep carious lesions, a selective caries removal approach should This procedure is carried out if dentine is lost due to caries, be adopted (one-stage or two-stage stepwise technique) in trauma or a previous iatrogenic intervention and a cavity order to decrease the risk of pulpal exposure. Numerous different materials have been used in VPTs. The aim of using these materials is to protect the pulp and maintain its normal function. In order to do this the pri- mary properties of such materials are: n antibacterial n create a bacterial tight seal and prevention of micro- leakage n promote tertiary dentinogenesis and controlled hard tissue barrier formation n biocompatible – prevention of ‘over’ irritation and avoid- A B C ance of induction of a severe inflammatory response Fig. 2.4 Indirect pulp capping. (A) Deep carious lesion extending close n radio-opaque to the pulp. (B) Cavity preparation adopting a selective caries removal n resistant to forces of displacement of any subsequent approach to minimise the risk of pulp exposure. (C) Calcium silicate material placed over them. cement overlying caries with definitive restoration.  2 Endodontics 55 exists where the soft tissue of the pulp is exposed (#2 mm) handpiece and bleeding controlled using cotton pellets and in most cases is bleeding. When carrying out this treat- soaked (removing gross excess) ideally with sodium hypo- ment strategy, if symptoms exist they should be relatively chlorite (0.5–5%). If bleeding is not controlled within mild and not considered to be indicative of irreversible pul- 8–10 minutes further pulp tissue should be removed. A pitis. CSC is placed onto the remaining pulp tissue; however, calcium hydroxide is still suitable if an appropriate CSC is Procedure Outline (Fig. 2.5) not available. If calcium hydroxide is used it should be As soon as a pulp exposure is realised, it is crucial that the sealed with GIC or a RMGIC. The tooth can then be de- tooth is isolated immediately with dental dam. Once the finitively restored. cavity preparation has been completed, it and the exposed pulp should be disinfected using cotton pellets soaked (re- FULL PULPOTOMY moving gross excess) ideally with sodium hypochlorite (0.5–5%). Once bleeding is controlled, the exposed pulp A full pulpotomy is carried out when there is gross loss of should be covered ideally with a CSC but calcium hydroxide dentine due to caries, trauma or previous iatrogenic inter- is still suitable if an appropriate CSC is not available. If cal- vention and a cavity exists where a large portion of the soft cium hydroxide is used it should be sealed with GIC or a tissue of the pulp is exposed and bleeding. The exposed pulp RMGIC. The tooth can then be definitively restored. appears to be inflamed/contaminated or it is not possible to get haemostasis at a superficial level. PARTIAL PULPOTOMY Procedure Outline (Fig. 2.7) This treatment strategy is used when dentine is lost due to The tooth should be isolated with dental dam. The coro- caries, trauma or previous iatrogenic intervention and a nal pulp tissue is completely removed to canal orifice cavity exists where the soft tissue of the pulp is exposed and level with high speed handpiece and bleeding controlled bleeding and in most cases 2 mm. The exposed pulp ap- using cotton pellets soaked (removing gross excess) ide- pears to be inflamed/contaminated or it is not possible to ally with sodium hypochlorite (0.5–5%). If bleeding is get haemostasis due to the inflammation. not controlled within 8–10 minutes further pulp tissue should be removed until haemostasis is achieved or it is Procedure Outline (Fig. 2.6) determined that a pulpectomy should be carried out. A The tooth should be isolated with dental dam. Superfi- CSC is placed onto the remaining pulp tissue; however, cial coronal pulp tissue is removed with a high-speed calcium hydroxide is still suitable if an appropriate CSC is not available. PULPECTOMY For completeness this procedure is considered here as it is a form of vital pulp treatment. In treating cases, where it is determined that the pulp is non-viable as it appears to be severely inflamed/contaminated/not possible to get haemostasis or appears necrotic a pulpectomy may be indicated. In such cases it has been shown that success rates are higher when the pulpectomy and root canal A B C treatment is completed in one visit and the clinician Fig. 2.5 Direct pulp capping. (A) Deep carious lesion extending to should adopt a cautious approach with length control as the pulp. (B) Carious exposure of pulp following cavity preparation. it is better to be short of the apical constriction. The (C) Calcium silicate cement directly interfacing with pulp and definitive treatment procedure is outlined in detail in Sections 2.4, restoration has been completed. 2.5 and 2.6. A B C A B C Fig. 2.6 Partial pulpotomy. (A) Deep carious lesion extending to the Fig. 2.7 Full pulpotomy. (A) Deep carious lesion extending to the pulp. pulp. (B) Superficial pulp tissue which is inflamed is removed. (C) Cal- (B) The whole of the coronal portion of the pulp is removed. (C) Cal- cium silicate cement directly interfacing with pulp and definitive resto- cium silicate cement directly interfacing with pulp stumps at the canal ration has been completed. orifice and definitive restoration has been completed. 56 Master Dentistry FOLLOW-UP AND OUTCOMES FOR VPT constriction. These may harbour bacteria in niches which are difficult or impossible to instrument, further emphasis- Following VPT, teeth should be carefully monitored by history ing the importance of adequate chemical disinfection of the and clinical examination at 6 months and a periapical radio- canal system throughout treatment. graph at one year. If symptoms persist or there is uncertainty The pulp chamber and root canal orifices may be reduced regarding healing, the tooth should continue to be assessed at in size as a result of the age-related deposition of secondary, regular intervals and a further intervention should be carried or reactionary and reparative tertiary dentine. Identifica- out if indicated. Cold and electric pulp testing should be car- tion of these issues preoperatively will help inform access ried out to monitor pulpal response, noting that teeth with full cavity depth and the need for caution where pulp chamber pulpotomy will be unresponsive. volume has been decreased. If pulp irritation is severe with VPT carried out well using aseptic techniques can pro- extensive destruction of pulpal cells, then further inflam- duce predictable results with a high success rate. Direct matory changes involving the rest of the pulp will take pulp capping with either a CSC or calcium hydroxide at one place and could lead to pulp necrosis. Such pulpal degen- year shows success rates of nearly 90% with partial and full eration starts coronally and progresses apically. Necrotic pulpotomy demonstrating 98% and 99% success rates re- pulpal breakdown products may leach out of the root canal spectively at the same time point. system to form lesions of endodontic origin around the various portals of exit. Sometimes changes may be visible as widening of the periodontal membrane space lateral to 2.4 Root Canal Morphology the root before they are apparent apically. LEARNING OBJECTIVES You should: IMPORTANT GENERAL CONSIDERATIONS understand the complexity of root canal morphology OF PULPAL ANATOMY appreciate the importance of adequate access in root Pulp Chamber Anatomy canal therapy. This alters with age, irritants, attrition, caries, abrasion and periodontal disease. Generally, the pulp chamber is lo- An understanding of the expected root canal anatomy cated in the centre of the tooth at the CEJ level, and the before embarking on root canal treatment is essential. Intra- outline shape of the root canals apical to this will reflect oral preoperative radiographs will provide useful informa- the external root morphology throughout the length of the tion as to the overall anatomy. Shifts in horizontal or vertical root (Fig. 2.8). The walls of the pulp chamber are lighter in angulation of periapical radiography can also help visualise colour than the darker floor. what the likely root canal anatomy will be. In reality, root canal anatomy has significant variability from tooth to Root Canal Orifices tooth and from person to person. In cases where clinical and With the exception of maxillary molars, the root canal ori- plain film examination reveals complex anatomy, there may fices lie equidistant from the mesio-distal midline of the be an indication for a limited field cone beam computerised tooth where the walls of the pulp chamber meet the floor. tomography scan (CBCT) which will provide more informa- Developmental fusion lines on the floor of the pulp chamber tion on the morphology. Studies of cleared extracted teeth will also help to guide identification of root canal orifices. have shown that all roots enclose at least one root canal system, which frequently consists of a network of branches Root Anatomy that often interconnect. Furthermore, developmental anom- Over 90% of roots are curved but this may not be immedi- alies may also impact on the ability to deliver uncomplicated ately obvious from plain film radiography as the curvature root canal treatment; these include dens invaginatus where may be in a bucco-lingual direction. Canals with curvature folds in enamel and dentine often allow the passage of beyond 45° are extremely challenging to navigate. The only bacteria into the invagination and communication with the roots that rarely contain two canals are maxillary anteri- pulp. Similarly, childhood trauma may well have stunted ors, maxillary premolars with two roots and the distobuc- root development leaving teeth with incomplete root devel- cal and palatal roots of maxillary molars. All other (note opment, and if this were to have happened in early child- this includes all mandibular) roots may contain two canals. hood, root dilacerations (sharp bends or curves) may further complicate the anatomy seen. Roots often have communications with the periodontal ligament along their length either in the furcation (furcal canals) or laterally (lateral canals). In addition, the root ca- nal may frequently terminate not at a single point but with an array of accessory canals forming an apical delta. These furcal, lateral and apical communications have been termed ‘portals of exit’ from the root canal system. Furcal, lateral and accessory canals are created during tooth formation either when there is a break in the sheath of Hertwig or the sheath itself grows around an existing periodontal blood Fig. 2.8 Cross-sections of root canal anatomy showing the relationship vessel. On occasion, such canals can be as large as the apical between pulpal and radicular shape.  2 Endodontics 57 Apical Anatomy Changes With Age coronal third root canal modification required to obtain The apical constriction is variable and usually cannot be straight-line access detected by tactile sense, as dentine laid down in the coronal n the number of roots, degree of root curvature and canal third of root canals will frequently cause files to bind coro- patency. nally before they reach the apical third of the root canal. ENDODONTIC ACCESS OPENINGS, LENGTHS AND CONFIGURATIONS ACCESS Incisor and Canine Teeth Access to the root canal system involves both coronal ac- cess to the pulp chamber and radicular access to the root The access cavities for maxillary central and lateral incisors canals. are similar and broadly triangular in shape taking into ac- count the mesial and distal pulp horns. Straight-line access Coronal Access may require extension of the access cavity to include the The coronal access preparation in root canal therapy serves palatal aspect of the incisal edge (Fig. 2.9). Average lengths several important functions to: for maxillary central incisors are 23.5 mm and they typi- cally have a single root canal; maxillary lateral incisors av- n provide an unimpeded path to the root canal system erage 22 mm in length and often have distal curvature to n eliminate the pulp chamber roof in its entirety their single root canal. n be large enough to allow light in and enable inspection Access cavities for maxillary and mandibular canines are of the pulp chamber floor for root canal orifices or frac- almost identical and more ovoid in shape (see Fig. 2.9). Up- tures per canine root length averages at 26.5 mm with a single n have divergent walls to support a temporary dressing root canal and 23.5 mm for lower canines; around 15% of between visits lower canines have two root canals. n provide a straight-line path to each canal orifice. Access for mandibular central and lateral incisors is Examination of the tooth will provide guidance as to the triangular in shape, and a second canal may be present in position, size and angulation of the access cavity as many 40% which often merge again towards the apex. Identifi- teeth are tilted in one or more planes relative to the arch cation of the second canal may require extension of the and adjacent teeth. The ideal access cavity will achieve the access cavity towards the incisal edge and under the cin- above objectives but will preserve as much sound coronal gulum (see Fig. 2.9). Average lengths of mandibular cen- and radicular tissue as possible. Occasionally, however, it tral and lateral incisors are 21 mm. may be necessary to enlarge and deflect access to enhance Premolar Teeth the preparation of roots that are especially curved in their coronal thirds. In these situations, access preparation is Premolar teeth have more variability in their anatomy dynamic, developing as instrumentation progresses. and canal configurations. The maxillary first premolar in most individuals contains two canals and the access cav- Radicular Access ity is extended more buccolingually than in single-rooted The principle of straight-line radicular access cannot be premolars. Approximately 5% may have a third root/ca- overemphasised as it allows instruments to flow down the nal placed buccally. In such situations, the access will be cavity line angles into the apical third of the root canal triangular in outline with the base towards the buccal side system without interruption and provides maximum tac- (Fig. 2.10). Maxillary first premolars average 21 mm in tile feedback while instrumenting the most delicate apical length. portion of the root canal. Adequate straight-line access reduces the angle of curvature in the coronal third of the root canal where it exits from the floor of the pulp chamber and thus reduces the overall canal curvature. Further ad- vantages are discussed later. Access to the root canal system is aided by examination of: M D M D n coronal anatomy n tooth position and angulation n external root morphology n the preoperative radiograph (preferably more than one taken at different angles). M D Examination of the radiograph affords information on: A n the size of the pulp chamber 6 calcifications B n the distance of the chamber from the occlusal surface (overlay the access bur to determine the maximum safe depth) C n the angle of exit of root canals from the floor of the pulp Fig. 2.9 Access cavity outline for anterior teeth. (A) Upper incisor. chamber; this provides an indication of the amount of (B) Lower incisor. (C) Canine teeth. M, Mesial; D, distal. 58 Master Dentistry B B Box 2.1 Access: Prior Considerations. n Removal and replace all defective and temporary restorations where possible. D M n Ensure that all caries has been removed prior to entering the D M pulp chamber. n Assess the restorability of the tooth. n Extract unrestorable teeth. n Restorable but broken-down teeth should be repaired with L composite or amalgam; some may require an orthodontic A P B band to aid dental dam isolation and reduce the likelihood of Fig. 2.10 Access cavity outline for (A) upper and (B) lower premolar fracture between visits. teeth. M, Mesial; D, distal; P, palatal; B, buccal. n Examine radiographs carefully to assess the complexity of treat- ment, e.g. identify if the root canal anatomy is visible through- out the length of the canal, any variations including curvature, The maxillary second premolar (average length 21.5 mm), pulp chamber calcifications and existing filling materials. the mandibular first premolar (average length 21.5 mm) and n If the tooth has a full-coverage crown, be aware that the pulp second premolars (average length 22.5 mm) usually have chamber anatomy may not be orientated to the crown. one centrally located root canal but again there may be variations present. If the canal appears to be situated under either the buccal or lingual cusp, look carefully for a Dental Dam second canal under the opposite cusp. The access opening is The dental dam is essential for root canal treatment and a narrow oval shape. The maxillary second premolar access affords the following advantages: is centred over the central groove. Access for mandibular premolars should be made just buccal to the central groove n asepsis – prevention of saliva contamination (see Fig. 2.10). n improved visibility n soft tissue protection Maxillary Molars n confinement of excess irrigant The maxillary molar access is generally triangular in shape n reduced liability in the medicolegal sense. with the base to the buccal and the apex to the palatal, tak- On occasions, particularly where the coronal anatomy ing care not to overextend the access cavity beyond the has been altered or replaced with large restorations, it may transverse oblique ridge. Usually, one palatal and two buccal be deemed appropriate to initiate access prior to the place- canals are identified. However, two canals may be present in ment of dental dam as this allows better appreciation of the mesiobuccal root in 90% of cases with approximately external root contour and tooth position. The dam should half ending in two foramina (Fig. 2.11). Maxillary upper be placed as soon as the pulp chamber is identified for the molars average 21 mm in length. aforementioned reasons. Mandibular Molars Access Technique The mandibular molar access should start broadly triangu- Box 2.2 describes the technique used to achieve access. lar in shape and with the base towards the mesial and apex towards the midpoint of the occlusal. Mandibular molars usually have two roots (mesial and distal) with two canals 2.5 Root Canal Preparation – in the mesial root and one in the distal root (see Fig. 2.11). If necessary, the access cavity can be extended into more of Cleaning and Shaping of the Root a trapezoid in shape if two distal canals equidistant from Canal System the midline are identified (33% cases). LEARNING OBJECTIVES Access: Prior Considerations You should: A number of steps should be taken to prepare for access understand the technical procedures involved in (Box 2.1). combating root canal infection appreciate some of the problems that may be encoun- B tered in root canal preparation B appreciate some of the technological advancements that have made root canal preparation more predictable. D M M D Herbert Schilder’s seminal paper entitled ‘Cleaning and Shaping the Root Canal’ has been adopted as the ideological L approach to managing the infected root canal system. In A P B this, it refers to cleaning and shaping ‘as the removal of Fig. 2.11 Access cavity outline for (A) upper and (B) lower molar teeth. all organic substrate from the root canal system and the M, Mesial; D, distal; P, palatal; B, buccal. development of a purposeful form within each canal for the  2 Endodontics 59 Box 2.2 Access: Technique for Entering a Pulp Chamber. 1. Outline the standard access cavity shape using a water-cooled bur (see Figs 2.9–2.11). The authors’ preference is for a tapered diamond bur with around 8 mm of cutting diamonds over the length. Progress is then made pulpally, constantly being spatially aware of the depth of the bur and its orientation, stopping and checking where necessary. A round-ended bur is preferred as flat-ended ones tend to gouge the access cavity walls. The expected depth of the pulp chamber can be compared to the preoperative radiograph; if the cavity depth is at the full depth of the cutting diamonds, then the access may be misaligned or the chamber sclerosed. It is useful to remember that dentine is yellow/brown in colour, and the floor of the pulp chamber is grey. 2. If the canal(s) cannot be readily located, stop and check radio- graphically. 3. Once the pulp chamber has been identified, it is deroofed and Fig. 2.12 A multirooted tooth with a connecting isthmus between two smoothed using a safe, non-end cutting bur such as an endo-z of the canals, this space may be anatomically complex with various bur; it may be necessary to use a Gates–Glidden bur to remove interconnections throughout its length. It is a potential reservoir of small overhanging areas of the pulp chamber roof especially in tenacious infected biofilm. smaller teeth where use of a bur in air rotor would be overly destructive. 4. The pulp chamber space should now be thoroughly irrigated with sodium hypochlorite solution and canal orifices identified possible to mechanically prepare the whole of the root using a straight probe or DG16 endodontic explorer. Magnifi- canal system and therefore the operator is reliant on other cation and lighting are particularly useful in helping to identify methods of cleaning this space. The biological objectives small root canal openings and to refine access. suggested by Schilder have therefore evolved but the under- 5. Further refinement of the access may now be performed to lying philosophy remains the same which is to: enable straight-line access to the canals. In addition, troughing may be performed using a long-neck or goose-neck bur; alter- n disinfect as much of the root canal system as possible natively the careful use of high powered cutting piezoelectric n remove any potential nutrient source to prevent recolo- ultrasonic inserts will remove dentine overlying canal orifices, nisation of micro-organisms in the root canal system especially in the MB2 region of upper molar teeth. n prevent recontamination of the root canal system. MECHANICAL OBJECTIVES OF CLEANING AND SHAPING THE ROOT CANAL SYSTEM reception of a dense and permanent root canal filling’. He established the broad objectives that are still relevant today Cleaning and shaping are processes that are not indepen- when carrying out root canal treatment and can be consid- dent of one another. Mechanically altering the shape of the ered separately as the biological and technical objectives of root canal system facilitates cleaning in two ways: (1) direct root canal preparation. removal of bacteria and nutrient sources from the root ca- nal system; and (2) enables active agents that are involved in the disinfection process to penetrate deeper into the root BIOLOGICAL OBJECTIVES OF CLEANING canal system. Schilder proposed design objectives in order AND SHAPING THE ROOT CANAL SYSTEM to shape the canal so that cleaning could be facilitated but Pulp death and subsequent necrosis renders the root canal also to produce a shape that would aid obturation to pro- space undefended and provides an ideal environment which duce an optimal seal. These objectives are summarised as: has an abundant nutrient source to support microbial pro- n Taper – A continuously tapered preparation should be liferation. To use a military analogy, this chamber acts as a produced. barrack to harbour micro-organisms in which they have n Canal axis – The position of the canal axis should be the opportunity to develop pathogenicity and induce in- maintained in the centre of the root. flammatory disease of the periradicular tissues. Primary n Foramen – The original position of the foramen should endodontic infections are caused by oral bacteria which are be maintained and it should not be enlarged. usually opportunistic pathogens. Once the root canal space is infected, endodontic microbiota exist in a fluid phase or, A continuously tapering preparation is required to de- as dense bacterial aggregates/coaggregates adhered to the liver and exchange chemically active fluids to the canal root canal walls forming multi-layered communities that terminus in order to remove and destroy bacteria that are resemble a biofilm (Fig. 2.12). The root canal space is a driving the inflammatory process in periradicular disease. complex environment – it is not as simple as round canals Sufficient space needs to be created to enable solutions to be passing through the centre of the roots. The anatomy is carried to the apical part of the canal. It has been suggested unique to every tooth and there may be accessory canals, that canals should be prepared to larger diameters to fins, isthumi, branches and other aberrant forms. It is not achieve this; however, larger canal preparation may lead to 60 Master Dentistry destruction of the delicate anatomy of the apical foramen important, this should never be done at the expense of compromising the ability to seal the canal. There is clearly hindering canal location, access or increase the risk of a greater risk of perforation with such an approach and it problems during preparation. There is currently little evi- can also lead to weakening of the dentine thus compromis- dence for the benefit of these very limited size occlusal ing the long-term survival of the tooth. access cavities when the marginal ridges that provide In summary, the aim of root canal preparation is to de- much of a tooth’s flexural strength remain intact. Such an bride the pulp space, rendering it as bacteria free as possible, ideology will rely even more heavily on irrigation or more producing a shape amenable to irrigation and obturation. advanced methods of disinfection of the root canal. This apparently straightforward task is clinically challeng- Our basic demands for irrigating solutions are outlined in ing through the complex anatomy of root canal systems. Table 2.1; however, in the future, more efficacious irrig- ants will be required to fulfil a minimally invasive philoso- INSTRUMENT MANIPULATION phy and an appetite for treatment modalities which are more biologically driven to improve healing. The two most commonly used motions applied to endodon- Irrigating solutions are usually delivered using a syringe tic instruments (files) are watch winding and balanced with a 27- or 28-gauge side-venting needle. Care should be force. taken to ensure that the needle tip remains free in the canal Watch winding refers to the gentle side-to-side rotation of and does not bind; if this were to happen there is a risk that a file (30° each way). This motion is useful for all stages of the canal becomes an extension of the irrigating needle with canal preparation, especially initial negotiation and finish- the risk of extrusion of irrigating solution into periapical tis- ing the apical third. sues. The role of the irrigant is to remove debris and provide Balanced forces involves rotating a file 60° clockwise to lubrication for instruments. Specifically, an irrigant such as ‘set the flutes’ and then rotating it 120° anticlockwise while sodium hypochlorite will dissolve organic remnants and, maintaining apical pressure sufficient to resist coronal most importantly, also has an antibacterial action. It may be movement of the file. Balanced forces are an efficient cut- used in a range of concentrations (0.5–5.25%), with 2.5% ting motion and have been shown to maintain a central being popular. It is important that the irrigant is changed canal position even around moderate curvatures while al- frequently; ideally irrigation should be performed between lowing a larger size to be prepared apically (compared with each file, at least every two to three files being the minimum. other hand instrumentation techniques). If removal of the smear layer is desired, then an irrigation Coronal interferences influence the forces a file will exert solution containing ethylenediamine tetra-acetic acid (EDTA) within a canal. This is of particular importance in curved should be used. There is no clinical consensus to the removal canals where files may prepare more dentine along the fur- of the smear layer although there is opinion that it may have cal (danger zone) as opposed to the outer canal wall. It is a positive effect on the outcome of retreatment cases. important to be aware of this, to limit the size of enlarge- ment in curved canals and direct files away from the furcal Enhancing Irrigant Efficacy wall to avoid a strip perforation (Fig. 2.13). Numerous suggestions have been made to enhance the ef- ficacy of irrigation solutions. For example, by intensifying the energy supplied to the irrigant by mechanical means, IRRIGATION heat or ultrasound. It is worth noting that whichever tech- Advances in preparation techniques may plateau in the nique is adopted, irrigant use carries a risk of complica- near future, and in order to improve treatment outcome, tions, especially with the use of NaOCl; controlled safe there will be more reliance on improving methods of irri- practice is therefore essential. Conventionally, irrigant is gation with enhanced biological activity. A philosophy of delivered via a syringe in a passive manner or with simple minimally invasive endodontics is developing, in which agitation. The latter is achieved by moving the needle up access cavities are limited in size in order to preserve as and down whilst dispensing the irrigant. Other simple much tooth tissue as possible, to prevent weakening the methods of manual agitation include using a gutta-percha tooth. Whilst preservation of tooth structure is of course cone with an ‘in and out’ pumping action – this has been shown to significantly improve debris removal compared to no agitation. Dange r zon Table 2.1 Summary of Desired Properties From an Irrigant Solution Used in Endodontics. Biological n High bactericidal efficacy against micro-organisms in biofilms and their planktonic state e Danger n Inactivate endotoxin zone n Nontoxic and hypoallergenic to vital tissues B Mechanical n Flush out debris n Lubricate the canal A Chemical n Dissolve organic tissue Fig. 2.13 The danger zone where care needs to be taken in order to avoid strip perforation. (A) Lateral view and (B) cross-sectional view. n Dissolve inorganic tissue and remove smear layer  2 Endodontics 61 Other methods may improve the hydrodynamic action Radicular access is the process of pre-enlargement of the of the solution through using additional devices or pieces coronal part of the canal to facilitate a pathway to the char- of equipment. Sonic agitation operating at a lower fre- acteristically and more anatomically complex apical third quency (1–6 kHz) produces smaller shear stresses than the of the canal. Typically, in multirooted teeth this means re- similarly principled ultrasonic agitation (25–30 kHz). The moving dentine to eliminate any curvature in the coronal endo activator (Dentsply Sirona, Switzerland) is a device part of the canal so that subsequent files entering the apical which is operated in the sonic frequency range. It is an region have straight-line access and an unimpeded path- untethered handpiece with a smooth polymer disposable way. Once the initial opening of the canal has been created tip that is inserted and activated in a saturated canal. It has with small stainless steel hand files, coronal curvature been reported to clean debris from lateral canals, remove can be removed with instruments such as traditional the smear layer and dislodge clumps of simulated biofilm Gates–Glidden burs, X-gates (Dentsply Sirona, Switzer- within the curved canals of molar teeth. Ultrasonic devices land), Protaper Sx (Dentsply Sirona, Switzerland) or Endo- can enhance the energy in the irrigation solution through flare (Micro-Mega, France) (Fig. 2.14) if required. This transmission from an oscillating file or smooth wire which crown-down approach allows for bulk removal of infected induces acoustic microstreaming and cavitation within material early in the preparation. This will also reduce the solution. Such a technique is known as passive ultra- stress on subsequent instruments used deeper in the canal sonic irrigation (PUI). It is suggested that ultrasonic sys- and facilitate better irrigant exchange. tems remove more dentine debris than sonic ones. A fur- Advantages of pre-enlargement and establishment of ther technique suggested to improve irrigant efficacy straight-line access are as follows: follows the principle of developing apical negative pressure n It creates sufficient space to introduce files and irrigating to ostensibly drag irrigant into the apical portion of the needles/solutions deeper in the canal. canal. One such system is known as the EndoVac system n The bacterial count in the more coronal aspects of the (Kerr, USA). Irrigant solution is dragged into the canal by a canal is reduced. macro- or micro-cannula which is positioned in the apical n A reservoir of irrigant is created that files pass through part of the canal and connected to a conventional dental as they move apically. suction system. This results in a high volume of irrigant n The increased space allows files to fit passively in the flow/replenishment and reduced risk of extrusion of irrig- canal, making inoculation of infected material into the ant solution. periapical tissues less likely. n Pressure on the coronal flutes of the file is decreased CANAL PREPARATION thereby increasing tactile sense and control when using files in the apical third. Several methods of canal preparation exist; however n Precurved files remain curved, can be easily inserted and most contemporary techniques follow this basic sequential freely pass down the canal. framework: n A greater volume of irrigant is present enhancing pulp n canal exploration digestion. n pre-enlargement (when necessary) n The bulk of pulpal and related irritants are removed n straight-line radicular access reducing debris accumulation apically. n length determination and apical patency n Working length is more accurate because there is a more n apical third preparation. direct path to the canal terminus. n Larger files may be used for the working length radio- Canal Exploration graph. Root canals are infinitely variable in their shapes and sizes. Larger canals allow easy placement of instruments and irrigating solutions whereas smaller ones require pre- enlargement coronally prior to the canal exploration. Pre- liminary assessment of the canal can be made with the smallest and most flexible instruments. It is unlikely that the operator will be able to determine the working length initially as files may be binding coronally. Pre-enlargement and Straight-Line Radicular Access Pre-enlargement may be achieved by watchwinding file, small flexible stainless steel hand file sizes 10–20 in series, gradually opening up narrow canal orifices to a size suffi- cient to take a mechanical bur (e.g. Gates–Glidden) or motor-driven endodontic file to gain radicular access. The pre-enlargement can then be developed further to produce straight-line radicular access taking care to work the bur away from furcal regions of roots. A file should stand up- Fig. 2.14 Burs designed for improving straight-line radicular access. right in the tooth and pass undeflected deep into the canal Top to bottom: ProTaper Sx (Dentsply Sirona), End of lare (Micromega), once this has been achieved. X-Gates, Gates Glidden No. 4 (Various). 62 Master Dentistry It is important to ensure that the apical region of the The working length can change during the preparation canal is not blocked with dentine debris or pulp tissue of curved canals. It is therefore important to recognise when using a crown-down technique. For this reason, it is length determination as a process and not a single stage important that small files 6 chelating agents are used to and therefore should be checked a few times during prepa- prevent blockage and ensure canal patency. Although api- ration to accommodate the likely change following removal cal preparation develops throughout canal enlargement, it of coronal interferences. The EAL lends itself well to this is not completed until the end of the procedure when approach. greater control is possible over the files in this most delicate region of the root canal. APICAL PATENCY Length Determination and Apical Patency The concept of apical patency is considered controversial To best meet the biological objectives of cleaning and shap- but is becoming increasingly accepted. A patency file is a ing the root canal system, the operator should attempt to small flexible instrument (08, 10) that will move passively prepare and obturate the whole canal. In terms of deter- through the terminus of a root canal without binding or mining root canal length, clinically, the aim is to identify enlarging the apical constriction. The aim is to prevent api- the apical constriction. This is the narrowest point of the cal blockage which will, in turn, reduce the incidence of root canal towards its terminus. Apical to this, the canal ledge formation and transportation of the root canal. The space widens to form the apical foramen and beyond is the use of a patency file also helps remove vital or necrotic periodontal ligament (in the absence of disease). pulpal remnants from the end of the canal. To use a patency The length of a root canal can be determined in many technique, therefore, infers an intention to clean to the full ways, including radiographic methods, tactile discrimina- canal length. Care should be taken not to use larger instru- tion, paper-point method and with the use of an electronic ments as patency files as these can damage the delicate apex locator (EAL). It is now widely accepted by most op- periapical region and unnecessarily enlarge or transport erators that the EAL is a mandatory tool in the armamen- the anatomical apex. tarium of the dentist. Amongst manufacturers of these electronic devices there is not always consistency about APICAL PREPARATION which anatomical point the EAL will identify. It is however recognised by users that the most reliable reference point, Once straight-line access, glide pathway, patency and the regardless of the device, is the zero reading. With modern working length of the canal have been established, the apex locators considered so reliable, a huge step forward remaining part of the root canal preparation is more has been made compared with relying on the preoperative straightforward. There are countless methods of prepar- radiograph to determine the length. In reality, this previ- ing the remainder of the root canal with the use of stain- ous method was no more than a crude estimation of the less steel hand files, ultrasonic instruments and hand/ length of the canal with the position of the apical foramen motor-driven NiTi (nickel titanium) instruments. Most in relation to the radiographic apex varying enormously recent developments in this area have focused on motor- (0–3 mm) (Fig. 2.15). It is essential that care is taken over driven NiTi instruments. identification of the correct canal length with the aim to identify the apical constriction that is the narrowest point Apical Preparation With Conventional of the root canal. Instruments Although the use of NiTi instruments is rapidly increasing, most root canals are still prepared today with conventional hand stainless steel files. Such techniques should never be discounted as they still have their place so that clinicians can develop skills to negotiate a complex canal and prepare a glide pathway. In larger, straight canals, the apical prepa- ration is accomplished by preparing the apical portion us- ing a slight rotational action of the file to an appropriate size after straight-line access has been confirmed. Apical Preparation With NiTi Instruments Since Nitinol was proposed as a material for the manufac- ture of root canal instruments in 1988 due to its increased flexibility compared to stainless steel, there has been consid- erable evolution of instrument design using NiTi alloys over the last three decades. The original NiTi files were based on a design with fixed tapered instrume