Nonvital Pulp Therapy on Primary TeethPulpectomy in Primary TeethThe anatomic and normal physiologic features of primary teeth can present challenges to the clinician wishing to undertake pulpectomy procedures. However, with knowledge of these features and how they may impact upon clinical technique, pulpectomy and root canal obturation of primary teeth with irreversibly inflamed or necrotic pulp can be a clinically successful option.In brief, these features are:• • Root anatomy: apical positions, lateral and accessory canals.• • Root physiology: the effect of exfoliation upon root anatomy and choice

of root canal filling material.• • The permanent tooth bud: its proximity to the primary root apex.

Effect of Resorption on Canal Anatomy and Apical ForaminaIn the newly completed roots of the primary teeth, the apical foramina are located near the anatomic apices of the roots. After the deposition of additional dentin and cementum, there are multiple apical ramifications of the pulp as it exits the root, just as in the mature permanent tooth.The physiologic resorption of the roots of the primary incisors and canines starts on the lingual surfaces in the apical third because of the position of the permanent tooth bud. In primary molars, resorption usually begins on the inner surfaces of the roots near the interradicular septum ( Box 23-7 ).BOX 23-7

• Physiologic root resorption begins:◦ Soon after root-length completion.◦ In primary incisors and canines on the lingual aspect of the apical

third of the roots.◦ In primary molars on the inner surfaces of the roots next to the

interradicular septum.

Physiologic Root Resorption in Primary Teeth

As resorption progresses, the apical foramen may not correspond to the anatomic apex of the root but be coronal to it. Subsequently, radiographic establishment of the root canal length may be challenging ( Fig. 23-19 ). Resorption may extend through the roots and into the root canals, creating additional communications with the periapical tissues other than through the apical foramina or lateral and accessory canals. This has been shown to occur at all levels of the root. 244 Because of these factors, use of an apex locator is not reliable to establish canal length.

FIG. 23-19Primary maxillary canine. A, Facial view, where apical foramen appears to be at the apex of the root. B, Physiologic root resorption has occurred at the palatal aspect of the root; apical foramen is positioned more coronally and will not be coincident with the perceived radiographic apex of the tooth.

Permanent Tooth BudThe effects of primary endodontic therapy on the developing permanent tooth bud should be of paramount concern to the clinician. Manipulation through the root apex of a primary tooth and overextension of root canal instruments and filling materials are to be avoided because the permanent tooth bud lies in close proximity. If radiographic signs of resorption are visible, canal length is usually established by measurement of the diagnostic radiograph, ensuring the working length of endodontic instruments are 2 or 3 mm short of the radiographic apex. The use of the long-cone radiographic paralleling technique for maximal accuracy is recommended. Hemorrhage after pulp removal may indicate overextension into the periapical tissues.Anesthesia is usually necessary for pulp extirpation and cleaning of the canals but may be unnecessary when primary teeth are filled at a subsequent appointment. The response of the patient can sometimes be used as a guide to the proximity of the apex and as a check of the length of the canal. However, this can only be done in cooperative patients, because the discomfort caused by placing the rubber dam clamp or by the approach of the instrument to the apex might create disruptive behavior in some children.The material used to obturate root canals in primary teeth must be resorbable, so that as the tooth resorbs it offers no resistance or deflection to the eruption of the permanent tooth. Permanent obturating materials, such as gutta-percha, are contraindicated in root canal therapy for primary teeth that have permanent successors.

PulpectomyPulpectomy and root canal filling procedures on primary teeth have been the subject of much controversy. Fear of damage to developing permanent tooth buds and a belief that the tortuous root canals of primary teeth could not be adequately negotiated, cleaned, shaped, and filled have led to the needless sacrifice of many pulpally involved primary teeth. Much has been written regarding potential damage to the developing permanent tooth bud from root canal fillings. The extraction of pulpally involved primary teeth

and placement of space maintainers is an alternative to pulpectomy. However, there is no better space maintainer than the primary tooth. If a space maintainer is placed but adequate monitoring and preventive care is not achieved, further problems often occur.For example, with a “band and loop” design of space maintainer, loose bands and poor oral hygiene increase the risk of dental caries and gingival inflammation. Prolonged retention of the appliance may cause deflection of the erupting permanent tooth, and premature loss of the band can result in loss of space, particularly if the patient delays returning for treatment.It has been reported 126 that minor hypoplasia is increased in permanent successor teeth after root canal treatment of the primary precursors. Others 39 have reported no such increased effect and concluded that defects result from the infection existing before the pulpectomy and not the procedure itself. It is noteworthy that these studies are retrospective, involving erupted permanent teeth; findings should be viewed with caution.Economics has been advanced as an argument against endodontic treatment of primary teeth, but it is not a reasonable argument when compared with the cost of space maintainers, including the required follow-up treatment. In fact, endodontic treatment is probably the less expensive alternative when the entire treatment sequence is considered.Success of endodontic treatment on primary teeth is judged by the same criteria that are used for permanent teeth. The treated primary tooth must remain firmly attached and function without pain or infection. Radiographic signs of furcal and periapical infection should be resolved with a normal periodontal attachment. The primary tooth should resorb normally and in no way interfere with the formation or eruption of the permanent tooth.Success rates ranging from 75% to 96% have been reported. 13 123 155 327 The usual means of studying root canal filling on primary teeth have been clinical and radiographic. There exists a great need for histologic study in this area.Early reports of endodontic treatment on primary teeth usually involved devitalization with arsenic in vital teeth and the use of creosote, formocresol, or paraformaldehyde pastes in nonvital teeth. The canals were filled with a variety of materials, usually consisting of zinc oxide and numerous additives. 62 98 138 281

Rabinowitch 234 published the first well-documented scientific report of endodontic procedures on primary teeth in 1953. A 13-year study of 1363 cases of partially or totally nonvital primary molars was reported. Only seven cases were failures; most patients were followed for 1 or 2 years clinically and with radiographs. Patients underwent multiple visits to achieve root canal fillings of ZOE and silver nitrate. Periapically involved teeth required an average of 7.7 visits to complete treatment, and teeth with no periapical involvement required an average of 5.5 visits. Rabinowitch listed internal resorption and gross pathologic external resorption as contraindications to primary root canal fillings.Another well-documented study reported a success rate of 95% in vital and

infected teeth using a filling material of thymol, cresol, iodoform, and zinc oxide. 13 (See Bennett 21 for a review of the techniques of partial and total pulpectomy.)In a well-controlled clinical study of primary root canals using Oxpara paste as the filling material, 155 five preexisting factors were reported to render the prognosis less favorable:• 1. Perforation of the furcation• 2. Excessive external resorption of roots• 3. Internal resorption• 4. Extensive bone loss• 5. Periodontal involvement of the furcation

When teeth with these factors were eliminated, a clinical success rate of 96% was achieved. When all symptoms of residual infection were resolved before filling of the canals, the success rate improved.

Contraindications for Primary Root Canal FillingsMany primary teeth with pulpal involvement that has spread beyond the coronal pulp are candidates for root canal fillings, whether they are vital or nonvital. Box 23-8 lists the categories of teeth that are not good candidates for pulpectomy.BOX 23-8

• ♦ An unrestorable tooth• ♦ Internal resorption in the roots visible on radiographs• ♦ Teeth with mechanical or carious perforations of the floor of the pulp

chamber• ♦ Excessive pathologic root resorption involving more than a third of the

root• ♦ Excessive pathologic loss of bone support, with loss of the normal

periodontal attachment• ♦ Presence of a dentigerous or follicular cyst• ♦ Periapical or interradicular lesion involving the crypt of the developing

permanent successor

Contraindications for Pulpectomy in the Primary Dentition

Internal resorption usually begins just inside the root canals near the furcation area. Because of the thinness of the roots of the primary teeth, once internal resorption has become visible on radiographs, there is invariably a perforation of the root by the resorption (see Fig. 23-13 ). The short furcal surface area of the primary teeth leads to rapid communication between the inflammatory process and the oral cavity through the periodontal attachment. The end result is loss of the periodontal attachment of the tooth and, ultimately, further resorption and loss of the tooth. Mechanical or carious perforations of the floor of the pulp chamber fail for

the same reasons. It has been shown that root length is the most reliable criterion of root integrity, and at least 4 mm of root length is necessary for the primary tooth to be treatable. 244

Access Openings for PulpectomyAnterior Primary TeethAccess openings for endodontic treatment on primary or permanent anterior teeth have traditionally been through the lingual surface. This continues to be the surface of choice except for discolored maxillary primary incisors, in which it is recommended that the clinician use a facial approach followed by an acid-etched composite restoration to improve aesthetics ( Fig. 23-20 ). 170

FIG. 23-20Primary anterior root canal treatment using a facial approach. A, Discolored primary central incisor with a necrotic pulp. B, Tooth during root canal cleansing. C, Root canal filling with zinc oxide eugenol (ZOE) has been completed. ZOE was removed to the cervical line, and a Dycal liner was placed over the dentin. Tooth has been acid etched. D, Composite resin has been bonded over the facial surface to achieve esthetics. E, Postrestorative radiograph showing completed procedures.

Posterior Primary TeethAccess openings into the posterior primary root canals are essentially the same as those for the permanent teeth. Important differences between the primary and permanent teeth are the length of the crowns, the bulbous shape of the crowns, and the very thin dentinal walls of the pulpal floors and roots. The depth necessary to penetrate into the pulpal chamber is much less than that in the permanent teeth. Likewise, the distance from the occlusal surface to the pulpal floor of the pulp chamber is much less than in permanent teeth. In primary molars, care must be taken not to overinstrument the relatively thin pulpal floor, owing to the high risk of perforation ( Fig. 23-21 ).

FIG. 23-21Illustration to show the safe removal of the roof of a pulp chamber in a primary molar. A non-end cutting bur ensures that the relatively thin floor to the pulp chamber is not perforated inadvertently by rotary cutting instruments.

When the roof of the pulp chamber is breached and the pulp chamber

identified, the entire roof should be removed. Because the crowns of the primary teeth are more bulbous, less extension toward the exterior of the tooth is necessary to uncover the openings of the root canals than in the

permanent teeth.TechniqueAs in permanent endodontic therapy, the main objective of the chemical and mechanical preparation of the primary tooth is débridement of the canals. Although an apical taper is desirable, it is not necessary to have an exact shape to the canals because obturation is achieved using a resorbable paste. Fig. 23-22 provides a schematic overview of the procedure.

FIG. 23-22Illustration to show the stages of pulpectomy and root canal filling in a mandibular second primary molar. A, Extensive approximal caries. Note the irreversible inflammation present in coronal and radicular pulp. B, Following caries removal and unroofing of the pulp chamber, the coronal pulp is amputated. Irreversibly inflamed tissue will bleed profusely. A premeasured hand file is placed approximately 2 mm from the radiographic apex; canals are gently cleaned with minimal shaping. C, Irrigation with sodium hypochlorite or chlorhexidine digluconate solution should be undertaken during the cleaning phase. D, If root canals are not to be obturated at the same visit, they may be dressed with nonsetting calcium hydroxide, or canals can be left empty and the tooth restored with a small cotton wool pledget and an interim intracoronal restoration. E, At the subsequent visit, root canals can be obturated with a resorbable root-filling material such as zinc oxide eugenol (ZOE). This can be applied using various methods; shown here is the ZOE being tamped down the canal by the piston action of a cotton pledget held in tweezers. F, Following root canal filling, the tooth is restored definitively using a

preformed metal (stainless steel) crown.

Canal Preparation

• 1. A preliminary working length is determined by measurement of a radiograph taken with a paralleling technique.

• 2. Local anesthesia is advisable.• 3. The placement of a rubber dam is mandatory.• 4. The working length is determined from a radiograph with an

endodontic file in the canal. The use of apex locators is unreliable because root resorption may create lateral openings into the periodontal tissues at any level. 244

• 5. To prevent overextension through the apical foramen, it is advisable that the working length be shortened to 2 to 3 mm short of the radiographic length, especially in teeth exhibiting signs of apical root resorption (see Fig. 23-22, B ).

• 6. After establishment of the working length, the canal is cleaned and gently shaped (as described in Chapter 9 ). Because of the thin root walls, sonic and ultrasonic cleaning devices should not be used to prepare the canals. Also, the use of Gates-Glidden (GG) or Peeso drills (Pulpdent Corp, Watertown, MA) is contraindicated because of the danger of perforation or stripping of the roots.

• 7. The more flexible nickel-titanium (NiTi) instruments are recommended rather than stainless steel (SS). Hand or rotary techniques are ideal for primary teeth. If SS files are used, the instruments must be gently precurved to help negotiate the canals.

•8. Care must be taken not to perforate the thin roots during cleaning and shaping procedures. The canals are enlarged several sizes past the

first file that fits snugly in the canal, with a minimum size of 30 to 35.

Importance of Irrigation During TreatmentBecause many of the pulpal ramifications cannot be reached mechanically, copious irrigation during cleaning and shaping must be maintained (see Chapter 9 ). Débridement of the primary root canal is more often accomplished by chemical means than by mechanical means. 130 This statement should not be misinterpreted as a de-emphasis on the importance of thorough débridement and disinfection of the canal. Initially, RC-Prep (Premier Dental Products, Norristown, PA) may be used as the canals are negotiated. It will digest and emulsify pulp tissue and is an effective lubricant. Once a working length has been established, the use of NaOCl solution to dissolve organic debris can play an important part in removal of tissue from inaccessible areas of the root canal system (see Fig. 23-22, C ).The Nonvital Discolored Primary Incisor

If a primary incisor is intrinsically discolored following loss of pulp vitality, there may be an esthetic need to improve the tooth's color. Bleaching is not advised in the primary dentition. The anatomy of the maxillary primary incisors is such that access may successfully be made from the facial surface. The only variation to the opening is more extension to the incisal edge than with the normal lingual access to give as straight an approach as possible into the root canal.The root canal is filled with ZOE (see the following section); then the ZOE is carefully removed to near the cervical line. A liner of Dycal or Life is placed over the ZOE to serve as a barrier between the composite resin and the root canal filling. The liner is extended over the darkly stained lingual dentin to serve as an opaquer. The access opening and entire facial surface are acid etched and restored with composite resin (see Fig. 23-20, C - D ).The Decision to ObturateAfter canal débridement, the canals are again copiously flushed with NaOCl and are then dried with sterile premeasured paper points. If the canals are dry and there is no exudate, obturation is performed in the same session. If the obturation cannot be done in the first appointment, a slurry paste of nonsetting Ca(OH) 2 can be injected into the canals and the tooth restored with a well-sealing temporary restoration.At a subsequent appointment, the rubber dam is placed and the canals reentered. As long as the patient is free of all signs and symptoms of inflammation, the canals are irrigated with NaOCl to remove the intracanal dressing and dried before obturation. If signs or symptoms of inflammation are present, the canals are recleaned and remedicated and the canal obturation delayed until a later time.

Root-Filling Materials for the Primary Root CanalsThe ideal root canal filling material for primary teeth should:• • Resorb at a similar rate as the primary root.• • Be harmless to the periapical tissues and the permanent tooth germ.• • Resorb readily if pressed beyond the apex.• • Be antiseptic.• • Fill the root canals easily.• • Adhere to the walls of the root canal.• • Not shrink.• • Be easily removed if necessary.• • Be radiopaque.• • Not discolor the tooth. 167

No material currently available meets all these criteria. The filling materials most commonly used for primary pulp canals are ZOE paste, iodoform paste, and Ca(OH) 2 . These will be discussed briefly in the following section.

Zinc Oxide Eugenol PasteMost reports in the U.S. literature have advocated the use of ZOE as the filler, whereas other parts of the world have used iodoform-containing pastes. 124 , 151 The antibacterial activity of ZOE has been shown to be greater than that of an iodoform-containing paste (KRI paste, Pharmachemic AG, Zurich, Switzerland), whereas its cytotoxicity in direct and indirect contact with cells is equal to and less than (respectively) than that of KRI paste. The filling material of choice in the United States is ZOE without a catalyst. The lack of a catalyst is necessary to allow adequate working time for filling the canals.

Iodoform PasteSeveral authors have reported the use of KRI paste, which is a mixture of iodoform, camphor, parachlorophenol, and menthol. 243 It resorbs rapidly and has no undesirable effects on successor teeth when used as a pulp canal medicament in abscessed primary teeth. Further, KRI paste that extrudes into periapical tissue is rapidly replaced with normal tissue. 124

Sometimes the material is also resorbed inside the root canal. A paste developed by Maisto has been used clinically for many years, and good results have been reported with its use. 174 , 289 This paste has the same components as the KRI paste, with the addition of zinc oxide, thymol, and lanolin.

Calcium HydroxideSeveral clinical and histopathologic investigations of Ca(OH) 2 and iodoform mixture (Vitapex, Neo Dental Chemical Products Co, Tokyo) have been published. 83 , 207 These authors found that this material is easy to apply, absorbs at a slightly faster rate than that of the roots, has no toxic effects on the permanent successor, and is radiopaque. For these reasons, one researcher 167 considers the calcium hydroxide–iodoform mixture to be a nearly ideal primary tooth root canal obtundant. Another preparation with similar composition, Endoflas, is available in the United States (Sanlor Laboratories, A.A. 7523 Cali, Colombia, South America). The results of root canal treatments using Endoflas in a students’ clinic were similar to those observed with KRI paste. 87

Obturation of the primary root canal is usually performed without a local anesthetic. This is preferable, if possible, so the patient's response can be used to indicate proximity to the apical foramen. It is, however, sometimes necessary to anesthetize the gingiva with a drop of anesthetic solution to place the rubber dam clamp without pain.

Obturation of the Root CanalThe chosen obturation technique depends upon the material employed and accessibility of the canal to relevant instruments.If using ZOE, it is mixed to a thick consistency and carried into the pulp chamber with a plastic instrument or on a Lentulo spiral. The material may be packed into the canals with pluggers or the Lentulo spiral. A cotton

pellet held in cotton pliers and acting as a piston within the pulp chambers is quite effective in forcing the ZOE into the canals (see Fig. 23-22, E ). The endodontic pressure syringe 23 , 103 is also effective for placing the ZOE in root canals. However, in a study of apical seal and quality of filling evaluated on radiographs, no statistically significant differences were reported between the Lentulo spiral, pressure syringe, or plugger. 56

When the root canal is filled with a resorbable paste such as KRI, Maisto, or Endoflas, a Lentulo spiral mounted in a low-speed handpiece can be used to introduce the material into the canal. When the canal is completely filled, the material is compressed with a cotton pellet. Excessive material is rapidly resorbed.Vitapex is packed in a convenient sterile syringe and the paste injected into the canal with disposable plastic needles. This technique is particularly easy to use for primary incisors but less practical for the narrow canals of primary molars. 210

Regardless of the method used to fill the canals, care should be taken to prevent extrusion of the material into the periapical tissues. It is reported that a significantly greater failure rate occurs with overfilling of ZOE than with filling just to the apex or slightly underfilling. 39 , 123 The adequacy of the obturation is checked by radiographs (see Fig. 23-20, E ; Fig. 23-23, A ; Fig. 23-24, C ).

FIG. 23-23Pulpectomy and root canal filling with zinc oxide eugenol (ZOE) paste in a primary maxillary central incisor. A, Root canal has been slightly overfilled with extrusion of ZOE paste apically. B, Same patient showing newly erupted permanent incisors. Note there are no enamel defects present on the crown, despite overfill of the root canal of the predecessor. C, Radiograph almost 5 years after pulpectomy and root canal filling of predecessor. Note normal apical development and almost total absorption of ZOE remnants.

FIG. 23-24Pulpectomy and root canal filling with zinc oxide eugenol (ZOE) in a maxillary second primary molar. A, Carious pulp exposure with a chronic abscess. Note furcal and periapical radiolucencies. B, Instruments in place establishing the working length. C, Root canal filled with ZOE. Note overfill and extrusion of the ZOE. D, At years after root canal treatment, primary tooth is near to exfoliation. E, One year later, premolar is erupted fully and

all traces of ZOE have been resorbed.

In the event a small amount of the ZOE is inadvertently forced through the apical foramen, it is left alone (because the material is absorbable). It has been reported that defects on successor teeth have no relationship to length of the ZOE filling. 39

When the canals are satisfactorily obturated, a fast-setting temporary cement is placed in the pulp chamber to seal over the root canal filling. The tooth may then be restored permanently. In primary molars, it is advisable to place a preformed (stainless steel) crown as the permanent restoration to ensure good coronal seal and prevent possible fracture of the tooth (see Fig. 23-22, F ).If a primary tooth requires pulpectomy and the permanent successor tooth is absent, the primary root canals are filled with gutta-percha and sealer in an attempt to retain the primary tooth long term ( Fig. 23-25 ).

FIG. 23-25Pulpectomy and root canal filling with gutta-percha in a retained mandibular primary second molar with no succedaneous permanent tooth. A, Carious exposure of the pulp. B, Because the permanent premolar is absent, root canals were filled with gutta-percha and sealer rather than just zinc oxide eugenol.

Follow-Up After Pulpectomy in the Primary DentitionAs previously stated, the rate of success after primary pulpectomy is high. However, these teeth should be periodically recalled to check for success of the treatment and intercept any problem associated with a failure. It has

been reported 39 , 283 that pulpectomized primary teeth may show delayed exfoliation. One study 39 described a 20% incidence of crossbites or palatal eruption of permanent incisors after pulpectomy on primary incisors. In the posterior teeth, extraction was required in 22% of cases because of ectopic eruption of the premolars or difficulty in exfoliation of the treated primary molar. 39 After normal physiologic resorption of the roots reaches the pulp chamber, the large amount of ZOE present may impair the resorptive process and lead to prolonged retention of the crown. Treatment usually consists of simply removing the crown and allowing the permanent tooth to complete its eruption.Retention of ZOE in the tissues is a common sequela to primary pulpectomy. One long-term study reported that after loss of the tooth, 50% of cases had retained ZOE. Teeth filled short of the apices had significantly less retained filler, and in time, most showed complete absorption or reducing amounts. Retention of filler was not related to success and caused no pathosis. 254

Therefore no attempt is made to remove retained filler from the tissues (see Fig. 23-23, A ; Fig. 23-24, C ).While resorbing normally without interference from the eruption of the permanent tooth, the primary tooth should remain asymptomatic, firm in the alveolus, and free of pathosis. Traditionally, root treatments were considered successful when no pathologic resorption associated with bone rarefaction was present. 95 , 124 If evidence of pathosis is detected, extraction and conventional space maintenance are recommended.Investigators 223 claim that most clinicians are prepared to accept pulp-treated primary teeth that have a limited degree of radiolucency or pathologic root resorption in the absence of clinical signs and symptoms. This is contingent on the assurance that the parent will contact the clinician if there is an acute problem, and the patient will return for review in 6 months. These criteria seem to be more suitable for pediatric dental practices and have been adopted clinically by Fuks et al 87 ; they consider such teeth to be “successfully treated.”