Lecture 4. Endodontics. Definition. Clinical and anatomical structure of tooth’ cavities and root canals of teeth. Endodontic instruments. ISO standards. Basic endodontic procedures: tooth cavity disclosure, amputation, extirpation of the pulp. Methods of medicament and instrumental treatment of root canals (“Step-back”, “Crown-down” techniques). Treatment of instrumental not available root canals: impregnation and mummification methods. Medications. Mistakes and complications.
The word ”endodontology” is derived from the Greek language and can be translated as ”the knowledge of what is inside the tooth”. Thus, endodontology concerns structures and processes within the pulp chamber.
Endodontics it’s the science that study anatomy, pathology, and treatment of tooth cavity and root canals.
The goal of endodontic therapy is to relieve pain, control infection, and preserve the tooth so that it may functioormally during mastication. Endodontic treatment is normally preferred to extraction.
Historically, therefore, the main task of endodontic treatment has been to cure toothache due to inflammatory lesions in the pulp (pulpitis) and the periapical tissue (apical periodontitis).
Under normal, physiological conditions the pulp is well protected from injury and injurious elements in the oral cavity by the outer hard tissue encasement of the tooth and an intact periodontium. When the integrity of these tissue barriers is breached for any reason, micro-organisms and the substances they produce may gain access to the pulp and adversely affect its healthy condition. The most common microbial challenge of the pulp derives from caries. Even in its early stages substances from caries-causing bacteria may enter the pulp along the exposed dentinal tubules. Like any connective tissue, the pulp responds to this with inflammation. Inflammation has an important aim to neutralize and eliminate the noxious agents. It also organizes subsequent repair of the damaged tissue. Thus, the pulp may react in a manner that allows it to sustain the irritation and remain in a functional state. Yet, when caries has extended to the vicinity of the pulp, the response may take a destructive course and result in severe pain and death (necrosis) of the tissue.
The dentist’s knowledge of normal pulp shape, size, and depth beneath the enamel is important for proper teeth preparing, those that have deep decay.
When the dentist determines that the tooth can be restored without the need to remove the pulp, he or she must prepare the tooth in such a way to avoid disturbing or injuring the pulpal tissues. This is accomplished through knowledge of the shape of the pulp chamber and canals and a careful evaluation of the patient’s radiographs to determine the location of the pulp relative to the decay and external surface of the tooth.
The shape of pulp cavities and configuration of pulp canals
The pulp cavity is the cavity in the inner portion of the tooth containing the nerves and blood supply to the tooth. It is divided into the pulp chamber (more coronal) and the root canals (in the roots).
Pulp chamber and pulp horns
The pulp chamber is the most occlusal or incisal portion of the pulp cavity. There is one pulp chamber in each tooth. It may be located partly in the crown of anterior teeth, but in posterior teeth, it is mostly in the cervical part of the root. Its walls are the innermost surface of the dentin.
Each pulp chamber has a roof at its incisal or occlusal border often with projections called pulp horns, and the pulp chambers of multi-rooted teeth have a floor at the cervical portion with an opening (orifice) for each root canal (Fig. 8-1). The number of pulp horns found within each cusped tooth (molars, premolars, and canines) is normally one horn per functional cusp, and in young incisors, it is three (one horn in each of the three facial lobes, which is the same as one lobe per mamelon). An exception is one type of maxillary lateral incisor (called a peg lateral with an incisal edge that somewhat resembles one cusp) that has only one pulp horn. Refer to Table 8-1 for a summary of the number of pulp horns related to the number of cusps normally found within different tooth types.
ROOT CANALS (PULP CANALS)
Root canals (pulp canals) are the portions of the pulp cavity located within the root(s) of a tooth. Root canals connect to the pulp chamber through canal orifices on the floor of the pulp chamber, and pulp canals open to the outside of the tooth through openings called apical foramina (singular foramen) most commonly located at or near the root apex. The shape and number of root canals in any one root have been divided into four major anatomic configurations or types. The type I configuration has one canal, whereas types II, III, and IV have either two canals or one canal that is spilt into two for part of the root. The four canal types are defined as follows:
Type I—one canal extends from the pulp chamber to the apex.
Type II—two separate canals leave the pulp chamber, but they join short of the apex to form one canal apically and one apical foramen.
Type III—two separate canals leave the pulp chamber and remain separate, exiting the root apically as two separate apical foramina.
Type IV—one canal leaves the pulp chamber but divides in the apical third of the root into two separate canals with two separate apical foramina. Accessory (or lateral) canals also occur, located most commonly in the apical third of the root and, in maxillary and mandibular molars, are common in the furcation area
The root canal is divided into crown, middle and apical parts.
The crown part is the widest and adjacent directly to canal orifices.
Most canals are flattened mesio-distally, but become more rounded in the apical 1/3. Lateral canals are branches of the main canal and occur in 17-30% of teeth
In the apical part near the dentinal-cement border root canal ends with a constriction (physiological apical hole), which is usually placed at a distance of 0.5-1.0 mm from the radiological and anatomical apexes.
Some authors identify anatomical apical hole – a place of transition the dentin into cement, and physiological hole – the border between pulp and periodontal ligament, placed 1 mm away from the X-ray hole.
The dentist who conducts endodontic manipulations before the start of treatment should identify options for topographic and anatomical structure of the tooth.
The first step of the endodontic procedure is for the dentist to gain access to the pulp chamber and the root canals of teeth through an access opening in the crown of the tooth. On anterior teeth, the opening is made on the lingual surface and on posterior teeth through the occlusal surface. These access openings vary considerably from cavity preparations used in operative dentistry. The shape (outline form), size, and position of the access opening are determined by studying ideal openings of maxillary and mandibular teeth shown in Diagram, and then modifying them to conform to what is evident on the initial radiograph of the tooth.
Finding the pulp may be difficult in older teeth, or teeth that have large or deep restorations, since the formation of secondary or reparative dentin may obliterate the pulp chamber, making endodontic access difficult.
Once the access opening is complete, the dentist locates the root canal orifices on the floor of the pulp chamber. Knowledge of the number of root canals present in teeth is critically important to successful endodontic treatment. Not locating and cleaning all the canals may result in continued discomfort for the patient or unsuccessful endodontic treatment with ensuing periapical disease. When the canal orifices have been located, endodontic files are used to remove the diseased pulp tissue and to begin cleaning the canals.
ENDODONTIC INSTRUMENTS
According to ISO endodontic instruments are classified:
1. Hand instruments: files(K and H), barbed broaches, spreader and plugger (vertical and lateral gutta percha condensors ).
2. Rotary instruments: H-files and K-reamers for slow handpiece, lentulo spiral filler/rotary paste filler.
3. Rotary instruments: Gates Glidden drills, Peeso reamer drills.
4. Pins: gutta percha pins, silver pins.
1. Hand instruments: files(K and H), barbed broaches, spreader and plugger (vertical and lateral gutta percha condensors ).
2. Rotary instruments: H-files and K-reamers for slow handpiece, lentulo spiral filler/rotary paste filler.
3. Rotary instruments: Gates Glidden drills, Peeso reamer drills.
4. Pins: gutta percha pins, silver pins.
Curson’s classification is as follows:
• – diagnostic instruments: root needles(Miller needles)
• – instruments for removing the soft teeth’ tissues: barbed broaches
• – instruments for passing, enlargement and shaping the root canals
• (K-reamers, K- files, H-files)
The main endodontic instruments and their use
Barbed broaches
• Functions and precautions
• • Finger instruments
• • Disposed of in the sharps’ container
• •Used to remove the intact pulp
• • ‘Barbs’ on the broach snag the pulp to facilitate removal
• • They need to be used cautiously as they can bind and break in the canal
• Varieties
• Available in different sizes and widths
• Gates Glidden drills
• Function, features and precautions
• •To enlarge the coronal third of the canal during endodontic treatment
• • Small flame-shaped cutting instrument used in the conventional handpiece
• • Different sizes – coded by rings or coloured bands on shank
• •Are slightly flexible and will follow the canal shape but can perforate the canal if used too deeply
• • Dispose of in sharps’ container
• • Should be used only in the straight sections of the canal
• Peeso reamer drills
Function, features and precautions
• •To remove gutta percha during post preparation
• • Small flame-shaped cutting instrument used in the conventional handpiece
• • Different sizes – coded by rings or coloured bands on shank
• • Peeso reamers are not flexible or adaptable, if not used with care can perforate canal
• • Dispose of in sharps’ container.
• NiTi (Nickel titanium) rotary instruments
• Function, features and directions for use
• • Used to clean and shape the canals
• • Used with endodontic handpiece and motor
• • NiTi is flexible and instruments follow the canal outline very well
• • Several varieties of systems with different sequences of instruments are used
• • Important to follow the manufacturer’s recommended speeds and instructions for use
• Varieties
• Different lengths: 21mm and 25mm
• Reamers Rarely used or indicated. Disadvantages of reamers include their inflexibility with ⇑ size, which can result in a wider canal being cut apically. Have now been replaced by files.
• Files These are used either with a longitudinal rasping or a rotary action (e.g. clockwise direction).
• The main types of file available are:
• K-type–file. Made by twisting a square metal blank.
• K-flex file. Similar to K-file but made by twisting a rhomboid shape blank alternating blades with acute and obtuse angles. More flexible than K-file but becomes blunt more quickly.
• Hedstroem file. Made by machining a continuous groove into a metal blank. More aggressive than K-file. Must never be used with a rotary action as liable to fracture.
• Endodontic K files. Also called: Root canal hand files
• Function, features and precaution
• • Finger instrument
• • Colour coded by size. The 6 colours used most often are: size 15 (white); 20 (yellow); 25 (red); 30 (blue); 35 (green); 40 (black). Also available in size 6 (pink), 8 (grey) and 10 (purple)
• • Operator gradually increases the size of the file to smooth, shape and enlarge canal
• • The larger the number of the file, the larger the diameter of the working end
• • Disposed of in the sharps’ container
• Varieties
• • Different lengths: 21mm, 25mm and 30mm
• Lentulo spiral filler/rotary paste filler
• Function and features
• • Small flexible instrument used to place materials into the canal
• • Fits into the conventional handpiece
• • Use with caution as it can be easily broken
• • Different sizes available
Geometric symbols. To facilitate doctor’s work, every instrument has its certain geometric symbol, that helps to choose the proper instrument.
Basic endodontic procedures: tooth cavity disclosure, amputation, extirpation of the pulp. Methods of medical and instrumental treatment of root canals (“Step-Back”, “Crown-down” techniques)
Pulpitis Inflammation of the dental pulp. Symptomatic and asymptomatic pulpitis, as well as irreversible and reversible pulpitis, are commonly used terms to specify lesions with and without painful symptoms. The terms total and partial pulpitis are also in use.
Pulp necrosis. Pulp death. Pulp chamber is without of a functional pulp tissue. Necrosis can be more or less complete, i.e. partial or total.
Apical periodontitis. An inflammatory reaction of the tissues surrounding the root apex of a tooth. Symptomatic/asymptomatic apical periodontitis and acute/chronic apical periodontitis, respectively, are applied to indicate lesions with and without overt clinical symptoms such as pain, swelling and tenderness. Dental or apical granuloma is a histological term for an established lesion. Apical, periapical and periradicular are interchangeable terms to state the location of the process at or near the root tip.
Tooth cavity disclosure – removal of pulp chamber roof, thus facilitating access to root canal orifices.
Pulpotomy (amputation) Treatment procedure by which the coronal pulp tissue is surgically removed with the aim of preserving the remaining tissue. The term pulpotomy is also used to describe a pain-relieving procedure in an emergency treatment of symptomatic pulpitis.
Pulpectomy (extirpation) Treatment procedure by which entire pulp tissue (often inflamed) is surgically removed and replaced with a root filling.
An inflamed or injured pulp may have to be removed and replaced with a root filling – a procedure termed pulpectomy. This measure is undertaken especially in cases when the condition of the pulp is such that an inflammatory breakdown is deemed imminent. A manifest infection may otherwise develop in the root canal system.
A pulpectomy procedure is carried out under local anesthesia and with the use of specially designed root canal instruments. These instruments remove the diseased pulp and prepare the canal system so that it can be filled properly. The purpose of the filling is to prevent microbial growth and multiplication in the pulpal chamber. Thus, pulpectomy is a measure primarily aimed at preventing the development of a manifest root canal infection and painful sequelae.
Pulpectomy may also be carried out any time a pulp is directly exposed to the oral environment. This may occur after clinical excavation of caries or after a traumatic insult or iatrogenic injury. If the exposure is fresh and the pulp judged not to be seriously inflamed it may not have to be removed. If the open wound is treated with a proper dressing and protected from the oral environment by pulp capping, healing and repair of the wound are possible.
Pulp capping (lining placing) Treatment procedure aimed at preserving a dental pulp that has been exposed to the oral environment.
(RCT) Root canal treatment Treatment of teeth with necrotic pulps where root canals are often infected.
Non-surgical retreatment Treatment of root filled teeth with clinical and/or radiographic signs of root canal infection, where root fillings are removed, canals disinfected and refilled. May also be carried out to improve the technical quality of previous root fillings.
Traditional discussions of canal preparation have recognized cleaning and shaping as two distinct processes. Cleaning –refer to the debridement of the root canal space and shaping as the step to prepare the canal for obturation. All clinically accepted endodontic instruments and instrumentation techniques attempt to perform both processes simultaneously.
Debridement of the root canal space includes removal of vital and necrotic tissue, bacteria, bacterial byproducts, and dentinal debris created during the cleaning and shaping process. Irrigation and disinfection are integral parts of debridement.
THE MAIN PURPOSE OF ROOT CANAL TREATMENT IS:
ü removal of pulp;
ü removal of infected dentine from the inner wall of the root canal;
ü enlargement and shaping a root canal for its adequate filling.
The procedure of root canal treatment has such stages:
– disclosure of the tooth cavity;
– disclosure of the root canal orifices;
– the root canal passing;
– the root canal enlargement;
– the root canal shaping.
Manipulations of root canal treatment(RCT) are carried out manually or with the help of rotary instruments by several treatment methods, the most widespread among them are:
• apical-crown – envisage treatment from the apical hole to canal orifices with gradually increasing of instrument diameter( e.g. from №10 -№ 40)
• crown-apical – envisage root canal treatment that starts from canal orifices to apical hole with a gradual decrease in instrument diameter(e.g. from №40 – № 10)
• hybrid method of treatment – have been developed out of the two methods. Starting coronally with larger instruments, often power driven, one works down the straight portion of the canal with progressively smaller instruments, that is the crown-down approach. Then at this point, the procedure is reversed, starting at the apex with small instruments, and gradually, increasing in size as one works back up the canal, that is the ‘step-back’ approach. This hybrid approach could be called the crown-down – step-back technique or ‘modified double-flared technique’.
Step-back technique The apical part of the root canal is prepared first and the canal is then flared from apex to crown. Blockage of canals may occur using this technique, and irrigation can be difficult.
After coronal pre-enlargement with Gates Glidden burs (A), apical preparation to the desired master apical file (MAF) size is done with K-files to determine working length (WL) (B) and then files of ascending size to the desired apical dimension (C). Then, the WL is progressively decreased (“step-back”) by 1 or 0,5 mm to create a more tapered shape (D). Recapitulation with a small K-file is done to smooth canal and to ensure that the canal is not blocked (E). Frequent irrigation promotes disinfection and removal of soft tissue.
Crown-down technique This (along with several others) prepares the coronal part of the canal before the apical part. This has advantages and is the preferred technique.
Balanced force technique This involves using blunt-tipped files with an anticlockwise rotation whilst applying an apically directed force. It requires practise to master but is particularly useful when preparing the apical part of severely curved canals.
Anticurvature filing This was developed to minimize the possibility of creating a ‘strip’ perforation on the inner walls of curved root canals. It is used in conjunction with other techniques or preparation, and the essential principle is the direction of most force away from the curvature. The walls on the opposite side from the curve are instrumented more than the inner walls resulting in a decrease of the overall degree of canal curvature. Bottom Line: Anti-curvature approach can preserve dentinal thickness near furcation. It also gives a more straight line access deeper into the canal.
Advantages of orifice enlargement
• Effectively, ⇓ the curvature in the coronal part of the root canal, allowing straighter access for files to the apical region. It therefore reduces the likelihood of apical transportation (zipping).
• It allows improved access for the flow of irrigant solution within the canal.
• It reduces the likelihood of apical extrusion of infected material as most of the canal debris is removed before apical instrumentation takes place. This is particularly important because the majority of bacteria in an infected root canal are located in the coronal region.
Passing and enlargement of root canal (especially narrow and sclerosed) is not always possible to implement using only endodontic instruments. In such cases, additional chemical expansion is done. Such technique involves the use of different types of acids for decalcification of dentin.
In root canal treatment is often used products based on EDTA.
For chemical enlargement of a root canal a small amount of gel product is applied to endodontic instruments and mechanical treatment of root canal is performed. The procedure is repeated several times. After obtaining the required result, canal is washed with solution of sodium hypochlorite or distilled water. — brand names are available, but basic chemical component could be…
Root canal treatment should include thorough mechanical debridement and medicatment treatment as well (antiseptic solutions), these two procedures should go together.
Treatment of the necrotic pulp is by root canal treatment (RCT) and is aimed to combat the intracanal infection. The canal is cleaned with files in order to remove microbes as well as their growth substrate. Owing to the complex anatomy of the root, instruments cannot reach all parts of the canal system and therefore antimicrobial substances are added to disinfect the canal.
Irrigants. These are required to flush out debris and lubricate instruments. Dilute sodium hypochlorite is generally considered to be the best irrigant as it is bacteriocidal and dissolves organic debris. The normal concentration is 2.5% available chlorine. Chelating agents which soften dentine by their demineralizing action are particularly helpful when trying to negotiate sclerosed or blocked canals.
Prepared root canal for sealing, regardless of the method of instrumental treatment, must fulfill the following criteria as:
ü To be sufficiently enlarged;
ü To have a conical shape (tapered);
ü To have formed apical ledge;
ü Do not contain a necrotic dentine;
ü Do not have typical smell;
ü To be clean and dry;
ü Do not have a painful reaction to percussion.
COMMON ERRORS IN CANAL PREPARATION
• Incomplete debridement : working length short, missed canals.
• Lateral perforation : often occurs as a result of poor access.
• Apical perforation : makes filling difficult.
• Ledge formation : can be very difficult to bypass.
Apical transportation (zipping) A file will tend to straighten out when used in a curved canal and straightening can transport the apical part of the preparation away from the curvature. The use of flexible files reduces the likelihood of this happening.
Elbow formation When apical zipping happens, a narrowing often occurs coronal to this in the canal such that the canal is hourglass in shape. This narrowing is termed an elbow.
Strip perforation A perforation occurring in the inner or furcal wall of a curved root canal, usually towards the coronal end.
SOME ENDODONTIC PROBLEMS AND THEIR MANAGEMENT
v Fractured instruments. Sometimes it is possible to get hold of the fractured portion with a pair of fine mosquitos. If not, insertion of a fine file beside the instrument may dislodge it. Should the fractured piece be lodged in the apical portion of the canal it may be better to fill the canal below it and keep it under observation, resorting to an apicectomy as a last-ditch solution.
v Fractured instrument removal. Ultrasonic vibration may be used to facilitate fractured instrument removal.The clinician must take care to ascertain the type of metalic obstruction because nickel-titanium (NiTi) and stainless steel respond differently to ultrasonic vibration. Direct ultrasonic vibration causes NiTi to fragment, so the clinician must work carefully around the fragment. Stainless steel is more resistant to vibration and responds to it by subsequently loosening.
v Ultrasonic vibration is applied directly to stainless steel files. Fine inserts can be used to work counter-clockwise around broken instruments. This technique often results in an “unscrewing” action that assists in removal.
v Perforations can be iatrogenic or caused by resorption
In the latter case, dressing with non-setting calcium hydroxide may help to arrest the resorption and promote formation of a calcific barrier. Increasingly MTA is being used for the repair of perforations and in surgical endodontics as a retrograde filling material with excellent results. Management of traumatic perforations depends upon their size and position:
v Pulp chamber floor If small perfortion, one can cover with calcium hydroxide and fill with GP or GI, but if large, hemisection or extraction may be necessary.
v Lateral perforation If this occurs near the gingival margin it can be incorporated in the final restoration of the crown, e.g. a diaphragm post and core crown. If in the middle 1/3, the remainder of the canal may be cleaned by passing instruments down the side of the wall opposite the perforation. Then the canal can be filled with GP, using a lateral condensation technique to try and occlude the perforation as well. Larger perforations may require a surgical approach and in multirooted teeth hemisection or extraction may be unavoidable.
v Apical 1/3 It is usually worth trying a vertical condensation technique to attempt to fill both the perforation and the remainder of the canal. If this is unsuccessful an apicectomy will be required.
v Ledge formation If this occurs, return to a small file curved at the apex to the working length and use this to try and file away the ledge, using EDTA or RC– Prep as lubricants.
