Obturation of root canal
The success of an endodontic restoration is based on how effectively all the portals of entry are sealed following cleaning and shaping the canals. This section covers the materials used , the various techniques and sealers and the indications for the same and the care taken for a hermetic seal.
1. Why is a prepared canal obturated?
A canal is obturated after preparation to block all the portal of entries into the root canal system through which microorganisms and their irritants can enter the canal and cause re infection, also to seal the irritants left out in the canal, which cannot be removed by cleaning and shaping procedures. So a perfect seal is needed at the apex, lateral and accessory canals and the coronal orifice.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,295
2. Why is Gutta Percha preferred for obturating the canal?
It is a solid core filling material with minimal toxicity, minimal tissue irritability and least allergenic, well tolerated by the periradicular tissues even if advertently overextended from a clean canal, can be softened by heat and chemical solvents and compacted. It is radiopaque and dimensionally stable.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,299, Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn, 272
3. Why is a proper canal preparation essential before obturating the canal with GP?
When GP is used the orifice of the canal should be enlarged sufficiently to allow easy insertion of small cones also. Proper flaring is given so that the condensing instruments reach the deeper portions of the canal. A proper apical stop and dentin matrix is maintained so that the GP is retained within the confines of the canal.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,272
4. When is a canal ready for obturation?
A canal is said to be ready for obturation when the culture test is negative, when there is no excessive seepage from the canal, no foul odour and no periapical sensitivity. When the above criteria is not satisfied, obturation should be delayed.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,266.
5. Why is a radiograph taken to verify the master cone positioning in the canal?
When a cone is selected at the predetermined working length, a radiograph is taken to verify the position because it may be at the apex, short of the apex or extending beyond the apex. When it is at the apex, or slightly short of it, no changes are needed. If it is too far short of the apex, the canal must be reprepared to an increased length. If it is extending beyond the apex, it can be due to an improper length determination or incorrect apical preparation. The amount of the GP extending beyond the apex is determined and clipped off to get a satisfactory filling.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,276
6. Why are spreaders used during condensation?
Spreaders are long tapered instruments used to compress the GP towards the apex and into the wall irregularities. It leaves a gap for the insertion of auxillary cones and for lateral condensation of GP.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,279
7. Why are sealers used along with GP for root canal obturation?
The sealers serve as filler for the canal irregularities and minor defects between the canal wall and the filling material. It allows for attaining an impervious seal. They seal the lateral and the accessory canals and assist in microbial control. Also they act as lubricants for the GP.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn, 301
8. Why should be a spreader be clean before insertion into the canal?
The sealer may form a cake on the spreader or there may be excess sealer on the spreader during condensation which is sufficient for the small cones to cling on to the spreader and pulled out of the canal. So it should be clean before starting the condensation and also prior to each re-insertion.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,292
9. Why are the auxillary cones dipped into the sealer while condensing laterally?
When spreaders are used to condense the GP laterally, after its removal, it leaves a space for the auxillary cones. For the auxillary cones to reach the rooms provided for them, they are lubricated by dipping into the sealer which is made slightly thinner by addition of the liquid. Also it acts as an interface between the GP cones for proper adaptation and sealing.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,281
10. Why do voids occur in a root canal filling?
Voids can occur due to a variety of reasons the first being lack of skill and execution in the technique along with improper canal shaping. They can also occur due to the pooling of large amount of root canal sealers or improper usage of spreaders and failure to place GP in the spaces created by the spreader. Voids should be avoided since they are again the pathways for leakage and re infection, leading to failures.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,307
11. Why does a master cone fit short of the desired length in an x ray?
The master cone may be short of the working length due to packing of dentin chips in the apical portion of the canal, ledging of the canal, a curvature in the canal that is not seen in the 2 dimensional radiograph, too large master cone and improper canal shaping three dimensionally.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,321
12. When the master cone is placed in the canal, it should be introduced slowly. WHY?
Slow insertion of the master cone is necessary for thorough distribution of the sealer, dissipating trapped air, for movement of the sealer coronally and laterally and minimizing the sealer extrusion beyond the apex.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,324
13. Why is the spreader inserted either to the working length or 0.5-1 mm short of this length?
The spreader is inserted slowly after placing the master cone to the same working length or 0.5 – 1 mm short of this length to achieve adaptation of the master cone to the prepared apical area. Failure of this can lead to improper GP adaptation and lateral condensation leading to void formation.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,325
14. Why are accessory cones placed in the canal?
Accessory cones are placed to fill the space created by the spreaders and for achieving a perfect seal apically, laterally and coronally. They are chosen based on the size of the spreader, size of the canal and the space created by the spreader in the canal.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,325
15. Why do problems occur while trying to place the accessory cones?
The accessory cone may be too large, the spreader may be too small, space created is insufficient due to poor compaction of the master cone, dislodgement of the master cone, improper taper in the canal, bent ends of the cone and a hardened sealer all of which can create problems while placing the accessory cones.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,325
16. Why should a sealer be radiopaque?
Radiopacity in a sealer will allow the visualization of the flow of the sealer into the accessory canals and the lateral canals, perforations and fractures and the shape of the apical foramen, radiographically.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,304.
17. What is the disadvantage of Rickert sealer?
The powder of Rickert’s sealer has zinc oxide and precipitated silver which makes it radiopaque. The main disadvantage of this sealer is its staining properties. The silver present in the powder may leach out and stain the tooth later. So after placement, the pulp chamber is thoroughly cleaned with a solvent to remove any excess.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,309
18. Why are silver cones not used for obturation nowadays?
With silver cones, it is not possible to obtain a good obturation since it cannot be made to conform to the pulp space like compatable GP, though it is stiffer than GP. Also silver cones contain other trace metals like copper and nickel which adds to the corrosion of silver when it comes in contact to periapical fluids.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,550
19. What is the beta phase of GP?
At room temperature, GP is said to be in the beta phase, in which the GP is a solid, compactible and elongatible material and does not stick to anything.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,270
20. What is Rickert’s sealer?
It is a ZnoE type sealer to seal the lateral and the accessory canals. The powder contains Zno and precipitated Silver and the liquid is Eugenol.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,306,307
21. How is GP disinfected?
Gutta Percha is disinfected in Sodium hypochlorite before use. It is submerged for one minute in a 5% solution of sodium hypochlorite.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,549
22. Why is the disinfected GP rinsed with ethyl alcohol?
The disinfected GP is rinsed with ethyl alcohol to remove the crystallized sodium hypochlorite on the GP cones, which may impair the obturation seal.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,549
23. What is the composition of the Gutta Percha cones?
The GP cones contain about 20% of Gutta Percha, 60-70% of Zno, which is the major content and makes it radiopaque and 5-10% of resins , waxes and metal sulfates.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,549.
24. Why is Gutta Percha not used as a sole filling material?
GP is not used as a sole filling material because, it lacks adhesive properties by which it can seal the root canal space effectively. A root canal sealer is always needed to achieve a complete sealing.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,549
25. What are the various solvents for GP?
The solvents for GP are Chloroform, Halothane and Eucalyptol and it is called Chloropercha, Halopercha and Eucapercha respectively.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,552
26. What is the role of calcium hydroxide as an Intracanal dressing?
It is slowly working antiseptic. In addition to killing the bacteria, calcium hydroxide hydrolyses the lipid moiety of bacterial lipo polysaccharides and inactivates the biological activity of lipo polysaccharides, which is a remaining cell wall material that causes root canal infection.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,548
27. Why should irrigation always support instrumentation of the canal?
Irrigation removes the pulp tissue remnants and the debris. It is essential for the effective functioning of files. It cleans the instrument and makes it more effective. Irrigation reduces the numbers of bacteria in the infected root canal. Also irrigants give some antimicrobial effect.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,544
28. Why the root canals are filled upto the apex without leaving any empty spaces?
The root canals are filled upto the apex without leaving any empty spaces as these unfilled portions of the root canal serve as a reservoir for the accumulation of tissue fluids and inflammatory exudates which would quickly be colonized by bacteria through anachoresis. This would prevent or delay the healing of the periapical lesion.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 606
29. What are cement sealers?
They are self hardening cements when used in conjunction with a solid or semi solid material.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 610
30. What are cements?
Cements are also self hardening when used to fill the entire root canal. They set and transform into a variably firm mass after their insertion in the canal.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 610
31. What is the difference between cements and pastes?
Like cements , pastes are also used to fill the entire canal but they do not harden once placed in the canal.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 610
32. What are the ideal requirements of a sealer?
An ideal sealer should be inert, easily manipulable and sets relatively quickly. It should have the property of being mixed to a consistency which enables it to be coated on the canal walls as a microfilm only a few microns in thickness, physically stable, non resorbable, insoluble in tissue fluids, bacteriostatic, easily removable, non immunogenic, mutagenic or carcinogenic.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 610,611
33. How does gutta percha adapt to the canal walls?
Gutta percha adapts to the canal walls by its compatibility. GP is neither molecularly condensable nor compressible, but once it is softened by heat, it can be compacted against the canal walls on such a way as to eliminate and collapse any voids present in the commercial GP.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 614
34. How is GP softened?
GP is stable in size once softened .When chemically softened with chloroform, it shrinks following evaporation of the solvent and when physically softened by heat, during the cooling phase it shrinks. But chemical softening of GP is to be avoided since it creates voids and softening by physical means must be accompanied by compaction of the material to compensate the volumetric changes that occur during the cooling phase.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 615
35. Why does any technique that requires heating of GP requires compaction also?
When GP is introduced into the canal and heated, it expands and ensures a tighter seal. But on cooling, it shrinks and to compensate for the thermal shrinkage, any technique that requires heating must also require compaction.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 615
36. What is the main disadvantage of using GP?
The main disadvantage of using GP is that since it is in a semi solid or semi plastic state at the time of insertion, it cannot surpass any errors in the canal preparation. Since it lacks rigidity, it cannot be pushed to overcome a ledge that might be present.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 615
37. How is standardization of GP cones useful for obturation?
Like the root canal instruments, the cones follow the same rules for standardization. The number in the cones corresponds to the instruments of the same number. Thus during obturation, the master cone is chosen on the basis of the last instrument used.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 615
38. How is lateral condensation performed?
In lateral condensation technique, the GP cone that fits well to the apical preparation together with a small amount of sealer is introduced into the canal. Then an appropriate spreader is used cold to compress the cone against the canal wall introducing between the dentin and the GP. This creates a space for the first auxillary cone. The introduction of the spreader and placement of auxillary cones is continued till a dense, well adapted filling is obtained.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 616,617
39. What is the main drawback of lateral condensation being a cold technique?
In this method, being a cold technique, the GP cones never merge into a homogenous, compact mass and the technique will yield an obturation comprising a number of GP cones separated by a greater or lesser amount of sealer.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 617
40. What is the disadvantage of lateral condensation with respect to the apical portion of the canal?
In the most apical portion of the canal, several auxillary cones can be condensed next to the master cone with difficulty only. As a result, obturation performed with lateral condensation technique is obtained in the coronal two thirds of the canal and in the apical third obturation is represented by a single cone surrounded by a bit of sealer. Thus the critical and most important zone doesn’t have enough auxillary cones which is a main disadvantage of lateral condensation technique.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 618,619
41. What is thermoplastic GP?
The thermoplastic GP consists of injecting GP heated by an electrical device into the prepared root canal. The instrument has a gun that has small GP cylinders heated to a temperature that can be regulated. Exerting pressure on the trigger presses the heated GP towards the tip of the instrument.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 620
42. How is obturation obtained with thermoplasticized GP?
The obturations obtained were dense without air entrapment if accompanied by using sealers. Lateral canals were also filled with a good apical seal. Adaptation to the dentinal walls was also good.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 620
43. What is the main drawback of thermoplasticized GP technique?
The great drawback of using thermoplasticized GP is that it lacks apical control of obturation. To overcome this, during the shaping procedure, a good apical barrier is created to prevent the extrusion of material into the periodontium.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 620
44. What is chemical softening of Gutta percha?
Chemical softening uses chloroform to soften Gutta percha to achieve obturation of the root canal system.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 630
45. What are the drawbacks of chemical softening of GP?
When the GP is softened by chloroform and introduced into the canal, once the chloroform evaporates, the root canal is filled only upto the two thirds since the creamy mix of chloropercha has a volume three times greater than the original material. Also chloroform is toxic and hence overfilling should be avoided.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 630
46. Why is chloroform substituted with eucalyptol?
Recently chloroform is found to be carcinogenic and it is substituted by eucalyptol, an organic solvent whose toxicity is much lower than chloroform and has anti bacterial and anti inflammatory properties.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 630
47. What are the indications (or) conditions where thermoplasticized GP can be used confidently?
•Back packing, after the apical third has been obturated by schilder’s technique. •Unnegotiable canals, in which it is necessary to fill the endodontium as much as possible. •Partially unnegotiable canals. •Root canals of teeth with immature apices after having achieved closure. •Root canals of immature teeth after apical barrier technique with MTA. •Internal resorption where apical portion is obturated with traditional techniques. •Root canals with perforation in the apical third •In non surgical treatment of surgical failures.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 620,621,622,623