Sveriges Tandläkarförbunds Tidning nr 4, 1966
Vital pulp extirpation and root canal filling in one sitting according to the N2-method
A follow up study of root canals made 1958-1959
By Lennart Telander
The techniques of root canal treatment in vital teeth has always been an hot topic for discussion. The clinician want to perform the operation in the safest and quickest way, with a minimum of medicaments and instruments and without discomfort for the patient.
At present, in our country, the most used technique of root canal treatment is probabbly the one proposed by Grossman (1960), Strindberg (1956), and others, the so called guttapercha method:
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(Devitalisation)
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Pulp Extirpation and intracanal medicament
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Filling of the root with gutta-percha and some kind of sealer.
This means 2 or 3 appointments (unless the pulp extirpation is made under local anaestesia). This method has in recent years been complicated with the introduction of bacteria culture, which means a minumum of three sittings.
It would be ideal if one could extirpate and fill the canal in single appointment. A clinician shoud have a material combining the tasks of the intracanal medicament and root filling material. Which properties should have such a material?
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hemostatic and antiflogistic
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Bactericidal and/or bacteriostatic
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Good adherence to the canal walls
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Be dimensionally stable (no shrinkage on setting)
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Easy to handle
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Short setting time
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Not absorbable (insoluble in tissue fluids)
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It should be radiopaque so that it can be visualized on X-ray.
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Be well tolerated by periradicular tissue
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Not stain the tooth or the periradicular tissues
Sargenti and Richter in 1954 described an edodontic material and method to be used for treating vital teeth in a single apponitment. The material and method were named N2. The method has been clinically tested since 1949 and has become widely used. The method involves something new in endodontics.
There are not many methods outlined, that allow extirpation of the pulp and filling of a root canal in one session. Nygaard Östby (1961) showed how he would clear out both vital and non vital teeth in one sitting. The pulp is totally extirpated till the apex with Hedstrom files, which gives a periapical bleeding into the root canal. Then the canal is filled to the apical third with chloropercha N-Ö and gutta-percha. Interesting is that the filling material does not reach the apex and that an intracanal blood clot is expected to form close to it. Nygaard Östby states he has abandoned his earlier opinion about how far in the direction of apex a root canal filling should end.
Strindberg (1956) states he has been getting better results in both vital and non vital cases unless the canal is filled to the apex.
Grossman (1960) fills to the apex, or close to it in vital cases. Sargenti has already in an article from 1949 pointed to the fact that periapex is preserved when the root canal filling does not reach the apex.
Technique for the N2-method
N2 is a cement available in two forms.
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Normal or Permanent hardens relatively quickly in the canal to the consistency of chalk, is x-ray contrasting and is used for root canal filling. Also suitable during the extirpation procedure.
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Medical or Temporary hardens slowly, is low contrasting on x-ray and is mainly used during cleaning and disinfecting procedure in non-vital canals.
The preparations contain the same components but in different proportions.
Powder: Zinc oxide, titanium oxide, calcium hydroxide, calcium sulphate, fenylmercuryborat, paraformaldehyde (Metal salts for coloration, adhesion capability, X-ray contrast, hardness and setting time)
Liquid: Eugenol, rose oil
N2 is a root canal filling cement. Both in Europe and the USA there are many endodontic sealers: id est cements to be used in combination with guttapercha poits or silverpoints. N2 should, according to my experience, not be regarded as a sealer of that sort. Certainly, guttapercha and silver points can be used without any problems with it, but the material is meant to be used alone.
Vital teeth
By means of reamers or files, under local anesthesia, the extirpation of the pulp is performed under local anesthesia to the apical third, or to just inside of the apex . The instrument is dipped in Normal or Medical before the extirpation. The root canal is filled with Lentulo spirals dipped in Normal. A suitable rotation speed is 1500 turns/ min. With careful technique you get a dense filling with good x-ray contrast. The setting can be accelerated with N2 Siccativ, a powder mainly consisting of calcium hydroxide. Post and filling can be made in the same sitting.
Non vital teeth
Normally treated in 2-3 apponitments. The canal is cleaned from debris with Medical, which is also used for coating the canal (without paper points) between the appointments. The root canal is filled, like above, to the apex. Canal cleaning and filling can also be made in one sitting in certain cases and with a special technique.
In wich way N2 is considered to influence the apical pulp rest? Due to its haemostatic and antiflogistic properties, it is suitable as wound dressing. The paraformaldheyde makes an etch nearest to the filling material. This etch crutch is thin, rather hard, and grayish white. It is thought to be a sterile shelter for the pulp rest. In a microscope cellular changes can be seen close to the canal filling and to the crutch. These are, according to Sargenti et al., a phase in the healing process of the pulp wound. In observation times of a year or more one can see precipitates of hard substances along the canal walls and the etch crutch and also in the pulp. At longer observation times hard tissue barriers have been observed, and they seem to completely separate the root canal material from the pulp. The pulp will thus undergo a degenerative calcification, a process that would seem to require a certain degree of vitality in the tissue. Rowe (1964), Schönherr-Brauer (1964). A lot of publications have been dealing with N2 root canals in vital teeth. The studies are 1. Clinical-radiografic, 2 Histological, 3. Bacteriological. In experiments on animals also the effect of the material on other tissues than pulp has been studied.
The majority of studies show good clinical and radiographic results using N2 method. To be mentioned are the works of Iten (1958) Motsch (1956), Bermann-Ebersberger (1958), Fulde (1960), Münch (1960, 1962, 1963), Anderes 1962), Nicholls (1963), Rowe (1964), Schönherr-Brauer (1964).
Council of Dental Therapeutic in 1962 got published a report, which mainly dealt with N2. There is shown 5 examples of incomplete root canals with major or minor periapical changes. They are said to be made in accordance with the N2-technique. No information about diagnosis and X-ray status before the treatment is given. The conclusions were:
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There is no evidence that a one sitting technique, where paraformaldehyde pastes are used, gives sterility to the root canals in a high percent of the cases.
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Pastes containing paraformaldehyde are extremely irritating and can make a real danger, if they are forced through the apex.
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There are clear indications that techniques with only partial filling of the canals and not based on aseptic procedures lead to a high percent of endodontic failures.
Own study
The question was: Does a clinical-radiological control of vital teeth, treated with N2 technique, show a higher failure rate after 6 years?
Patient material
The material consisted of all root canal treatments made in my private practice during the year 1958 and 1959 accordind to N2 method. The most of them were controlled in 1964. 29 teeth were controlled in 1965. The observational time was on average 5-6 years. Teeth with longer observation time have been assigned to the 6-year-follow-up group.
I had been treating 163 teeth in 147 patients. Of these 128 were controlled (recall rate = 86%). 19 patients (14%) were drop-outs. Of these, 10 were moved to unknown address, 4 were deceased and 5 did not show any interest to the study.
The controlled group consisted of 60 men and 68 women with 141 teeth and 301 roots. The patients were consisidere healthy to my judgement. The age distribution is shown in table 1.
|
≤ 30 |
30-49 | 50-69 |
≥ 70 |
total | |
| N | 41 | 66 | 19 | 2 | 128 |
| % | 32 | 51.5 | 15 | 1.5 | 100 |
Table 1
The distribution to jaws and different groups of teeth are presented in table 2 and 3.
| incisors | premolars | molars |
total |
|
| n | 28 |
54 |
67 |
141 |
| % |
14 |
38.5 |
47.5 |
100 |
Table 2
| lower jaw |
upper jaw |
total | |
| n |
68 |
73 |
141 |
| % | 48 |
52 |
100 |
Table 3
In relation to the clinical diagnosis of the pulp status, I distinguished two groups:
1. Clinically healthy pulp: teeth with deep cavities, but without symptoms of pain
2. Pulpitic: teeth with classis symptoms of pulpitis and/or with percussion sensitivity
tabella 4
| 1 canal | 2 canals | 3 canals | total | |
| n | 46 | 28 | 67 | 141 |
| % | 32.5 | 20 | 47.5 | 100 |
tabella 5
| clinically healthy pulp | pulptitis | tot | |
| n | 44 | 97 | 141 |
| % | 31 | 69 | 100 |
Periapical diagnosis is shown in table 6. The radiological diagnosis was established by professor Arne Forsberg at the Dental High School in Stockholm in blindness condition (without informing the examiner about the clinical diagnosis of the pulp status). The high percentage of “uncertain” depends on the scarce quality of some pre-op x-rays.
|
|
No change |
Bone resorption |
Uncertain |
Total |
|
n |
82 |
1 |
58 |
141 |
|
% |
58 |
1 |
41 |
100 |
Table 6
Technique
All root canal treatments were performed in single appointment. In 4 cases formaldehyde was placed as a pain-killer but it was not left for so long to devitalise the pulp. The extirpation of the pulp was complete (till the apex) solely in the few cases where the canal was wide and straight.
The root canal treatment was performed according to the technique described earlier. The distance to the radiographic apex was in most cases more than 2 mm. The conditions had been seldom so favorable to reach the apex with thick reamers. In very narrow canals I used EDTAC-Nygaard-Östby. The widening was obtained bey means of files of Kerr type. The distance to radiographic apex would probably not play a big role when using the right technique. It must be pointed out that N2 is not meant for amputations or overcappings in the usual sense, but a N2 canal should be considered for a deep amputation near the apex, where the healing capacity of the pulp is assumed to be the best.
Aseptic conditions were aimed, though rubber dam had not been considered a condition sine qua non. When vitality of the pulp were plain (pulp bleeding at the opening), reamers and files were dipped in Normal. If a superficial necrosis of the pulp was suspected, they were dipped in Medical.
The root canal treatments were performed with Normal, but in some cases a contamination has occurred when the cleansing had been carrying out with Medical. Medical hardens in the canal, though in slower degree than Normal. Normal show at the x-ray a good contrast. Medical, instead, give a scarce contrast at the x-ray, especially in narrow canals.
Medical is a disinfection material, though not so strong to induce necrotization of pulp, according to my experience.
Gutta-percha points were never used, being unnecessary. The root canal will be well sealed with the right technique anyway.
Culturing of bacteria had not been perfomed.
Grossman (1960) considers bacterial culture to be necessary, but Healey (1960) thinks it is unnecessary. He refers to Nygaard Östby (1958), who shows that the apical part of the pulp is bacteria-free even when the tooth is pulpitic and bacteria can be found in the crown pulp. A positive culture from the apical part of a vital pulp indicates that bacteria has been supplied from outside.
A cause of contamination is the leakage through the coronal temporary filling, as reported by Berman & Massler (1958) and Strindberg (1965).
A vital tooth should be sealed as soon as possible, and the endodontic technique should be adjusted to this goal.
Result
The control times are clear from table 7.
|
|
4 years |
5 years |
≥ 6 years |
Total |
|
n |
1 |
71 |
69 |
141 |
|
% |
1 |
50 |
49 |
100 |
Table 7.
No clinical pains have been noticed.
The periapical radiographs were examined by Professor Arne Forsberg. The results are shown in table 8. In 134 cases a reliable diagnosis was possible. “no change” means that the periodontal contour is distinctly visible around the apical third and that it has normal appearance.
|
|
No change |
Widened per. contour |
Bone resorption |
Unsure |
Total |
|
n |
130 |
3 |
1 |
7 |
141 |
|
% |
92 |
2 |
1 |
5 |
100 |
Table 8.
In the group “Unsure” there are 4 extracted teeth and 3 with unclear control radiographs. The extractions were made by other dentists. In one patient 3 teeth have been extracted. According to the patients the extractions reasons were not arised from the root canals.
The root canal filling grade is shown in table 9.
|
|
To apex
|
≥ 2 mm beyond |
< 2 mm from apex |
> 2mm from apex |
Total
|
|
n |
7 |
5 |
33 |
96 |
141 |
|
% |
5 |
3.5 |
23.5 |
68 |
100 |
Table 9.
Controlling overfills can give an idea of both possible tissue damage and the absorbability of the material.
In the table is seen that there were 5 overfills. From these 2 are relatively large, probably caused by root perforations. One case is a +4 (24) with straight roots , cleaned and shaped with a engine driven Kerr-reamer. The tooth became initially sensitive at chewing, but the symptoms disappeared later without further treatments. The other case is a 5+ (15) with a curved root. No unpleasantness afterwards. The root canal surplus in antrum? See pics 2 and 3.
Out of the 5 surplus fillings, 2 were large. One was totally resorbed at the 5 year control and the periodontal contour was only slightly widened. At the 6 year control the contour was normal. The other surplus, lying in bone tissue, was a little smaller at the 5-year control. The bone around it had normal structure. One of the 3 others had totally disappeared, one had diminished and was partly disconnected and one was unchanged. Periapex was normal in all cases.
These pictures indicate that N2 is absorbed in tissue rich of blood-vessels but slowly in bone tissue. That looks normal on x-ray and adapts to possible absorption of the surplus material. See pictures.
Complications had been registering. To these file fractures has not been assigned, 3 in all. The 2 root perforations have been related. A third case with complication is hard to evaluate. It is a +1 (21) with Silicate fillings, sensible to shift of temperature. After slightly more than half a year it became percussion sensitive. Still vital. Extirpation and root canal made it symptomless. After 4 months the patient returned. Apically a hard bone tissue could be palpitated. No sensibility either at percussion or apical pressure. The patient could feel it with the lip. Periapex normal on x-ray. The bump had been continually diminishing, but is still there at the end of 1965. No further treatment was made. See picture 1.
A general impression is that the root canal fillings contrast very differently, especially in molars. Wide canals are easily seen, narrow worse. As mentioned above, the extirpations were often made with Kerr files dipped in Medical. The root filling with Normal therefore gets mixed with Medical, that is lacking of a special contrasting agent. Medical hardens however in the canal and can thus be used for filling root canals although it is not meant for that purpose. N2-root canals can thus look like amputated on x-ray. A cosmetic flaw wich can cause misunderstandings.
Discussion
Criticism has been directed against the N2-method and the N2 material, and a report from Council of Dental Therapeutic (1962) is already mentioned. Nobody would probably deny that the reported 3 points are correct in a general point of view, but they are irrelevant in their context. They have application to neither the N2-technique nor the material. A reader takes special notice of some facts.
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In the report there is shown 5 examples of incomplete root canal fillings with major or minor periapical changes. They are said to be made in accordance with the N2 technique.
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No information of diagnosis and radiological status before the treatment is available.
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From the text it is evident that the author has not been sure of what material has been used. It is apparently about “reported failures”.
With such methods it is easy to throw suspicion on any method or material.
The talk of tissue damage also comes from American experiments in rats and rabbits. Implants have been made in muscles and bonding tissue. Even eyes have been rubbed with alternating powder and liquid. Tissue cultivations have been made. All this is named “biological test methods” for root filling materials, Torneck (1961), Guttoso (1962), Rappaport et al. (1964). Such studies are of little value, since everything one wants can be proved. A reader may ask himself for instance what would happen if one eye was rubbed with chloropercha and choroform was dropped into the other?
A method for root canal can only be fairly evaluated after several years of clinical use. A few failures or dubious animal experiments should not be used as the basis of judgment.
The speak of tissue damage comes from that N2 due to its content of paraformaldehyde is thought to be necrotizing. In short term studies this opinion seems to be relevant as paraformaldehyde gives an etch crutch closest to the root filling. According to Sargenti (1953) the effect of the paraform will almost entirely cease when the filling material hardens. The effect should be neutralized by calcium hydroxide, which is a powder component. Long term studies show that N2 does not have a necrotizing effect but seems to preserve the pulp in a vital status, yet degenerative condition, leading to hard tissue production along the canal walls, in the pulp and along the root filling material. Even in the etch crutch hard tissue formation has been observed. Iten (1958), Rowe (1964), Schönherr-Brauer (1964)
In many control radiographs of the apical area in my material distinct differences to the primary pictures can be seen. There is no lumen under the root filling, while the neighbor teeth have the same appearance in both pictures. This observation is a reminder that you must be careful with statements that N2 is tissue damaging. See for instance Andersen (1962), who shows how apex in young teeth can close themselves in a normal way after N2 canals have been made. Somebody who has experience of N2 Normal must be totally unsympathetic to the statement that N2 is a paste. Such has, according to current medical terminology completely other properties than N2, which hardens in the canal and is not absorbable, as far as can be judged so far.
For a clinician who has had the opportunity to try for several years both the gutta-percha method and the N2-method it comes natural to prefer the latter, having the same high frequency of clinical and radiological success as the gutta-percha method. In the present control material, including 141 vital teeth, only one bone resorption detected. The N2 method is worth trying to a larger extent than up to now.
The author is aware of the lack of a control group in the present investigation. The value of this is however disputable within endodontics, because it is difficult to draw conclusions from possible different results. These may not imply more than that the operator had taken more interest in, or had a better command of one of the treatment methods.
The author conveys his thank to Professor Arne Forsberg, Dental High Schol, for help of great value with all the interpretation of the x-ray material.
Summary
1. The N2-method indicates a suitable method of pulpectomy and root canal filling of vital teeth in one sitting. The present paper accounts experiences from a clinical material containing 141 teeth and 301 roots. Of the total amount of teeth 86 %, 165, have been checked. Observation time 5-7 years. Grade of root filling: 7 to apex, 5 overfilled, 129 underfilled.
2. Post-op pain occurred in 3 cases. It disappeared without treatment. At the follow-up controls no troubles in any of the 141 cases.
3. On follow-up x-rays 92% showed periapical conditions compatible with health status , 2% slightly widened periodontal membrane, 1% periapical rarefaction, 5% uncertain diagnosis.
4. Of 5 overfillings two are completely disappeared and 3 diminished. Periapex was normal in all cases.
5. The N2 cement is not absorbed in the canal and is slowly absorbed in bone tissue. It seems to be rather easily absorbed in soft tissues.
6. The N2 method sould be the method of choice compared to the gutta-percha method in clinical practice for two main reasons: the success rate is about the same an the N2 technique, being simpler, needs lesser instruments and drugs than those used for the gutta-percha method.
