Comparison between calcium hydroxide mixtures and mineral trioxide aggregate in primary teeth pulpotomy: a randomized controlled trial

Abstract Objectives: To evaluate the effect of calcium hydroxide (CH) associated with two different vehicles as a capping material for pulp tissue in primary molars, compared with mineral trioxide aggregate (MTA). Methodology: Forty-five primary mandibular molars with dental caries were treated by conventional pulpotomy using one of the following materials: MTA only (MTA group), CH with saline (CH+saline group) and CH with polyethylene glycol (CH+PEG group) (15 teeth/group). Clinical and periapical radiographic examinations of the pulpotomized teeth were performed 3, 6, and 12 months after treatment. Data were tested by chi-squared analysis and a multiple comparison post-test. Results: The MTA group showed both clinical and radiographic treatment success in 14/14 teeth (100%), at all follow-up appointments. By clinical evaluation, no teeth in the CH+saline and CH+PEG groups had signs of mobility, fistula, swelling or inflammation of the surrounding gingival tissue. However, in the CH+saline group, radiographic analysis detected internal resorption in up to 9/15 teeth (67%), and inter-radicular bone resorption and furcation radiolucency in up to 5/15 teeth (36%), from 3 to 12 months of follow-up. In the CH+PEG group, 2/11 teeth (18%) had internal resorption and 1/11 teeth (9%) presented bone resorption and furcation radiolucency at all follow-up appointments. Conclusion: CH with PEG performed better than CH with saline as capping material for pulpotomy of primary teeth. However, both combinations yielded clinical and radiographic results inferior to those of MTA alone.


Introduction
Pulpotomy is a vital pulp therapy for deciduous teeth in which the coronal pulp tissue is surgically removed and a suitable material is placed on the remaining radicular pulp to protect it from further injury. 1,2,3,4,5 Pulpotomy aims to retain a functional tooth with a vital radicular pulp in the oral cavity until its exfoliation. 1,2,6,7,8 Although formocresol was considered the gold standard for pulpotomies in primary teeth, its toxicity and carcinogenic potential have emerged as serious limitations of this capping material. 9 Numerous studies have investigated the mechanism of action, clinical indication, advantages and disadvantages of different capping materials, but no consensus has yet been reached on the ideal pulpotomy material for the treatment of primary teeth. 1,4,6,8,10,11 Calcium hidroxide (CH) has been indicated as the most appropriate material in many clinical situations aiming to promote healing. However, the results obtained from pulpotomy using CH-based materials were inconclusive, as long-term clinical trials revealed an increase in failure rates along the follow-up appointments. 6,12 The success rate of CH as a pulpotomy material in primary teeth is poor in comparison to that observed in permanent teeth.
The caustic action of the high-pH formulations of CH reduces the size of the underlying dental pulp by up to 0.7 mm. 13 In addition to the widespread clinical use of CH, studies have tested various CH formulations and mixtures of CH powder with different substances in an attempt to improve CH performance. 12,14 Typically, CH dressing is prepared with either an aqueous (distilled water, saline, anesthetic solution) or viscous (polyethylene glycol, propylene glycol, methylcellulose, glycerin) vehicle. 14,15 When in direct contact with tissues, CH paste prepared with an aqueous vehicle rapidly dissociates into calcium (Ca +2 ) and hydroxyl (OH -) ions, promoting high solubility and becoming easily resorbed by macrophages. In contrast, when CH is mixed with a viscous vehicle, its dissociation is slower, probably because of the high molecular weight of the vehicle, thus minimizing the dispersion of CH into the underlying tissue and maintaining the paste in the desired place for longer. 14 MTA is considered the gold standard material for pulpotomy of primary teeth. 3,5,7,9 Its indication is based on its adequate physiochemical and biological properties such as good sealing ability, hydroxyapatite formation and favorable biocompatibility. 8,16,17 MTA   induces hard tissue formation when used for pulp   capping, pulpotomy, perforated furcations, root canal   filling and root-end fillings in animals; 12,15,17 however, it is costly and causes dental pigmentation. 11,18,19 Considering the scarcity of randomized controlled trials testing CH associated with different vehicles as a dressing agent for primary teeth, this study aimed to evaluate the effect of CH prepared with either an aqueous (saline) or a viscous (polyethylene glycol) vehicle as a capping material for the pulpotomy of primary molars. Of note, the effects of CH mixtures were compared with those of MTA, which represents the current standard of treatment for primary teeth pulpotomy.

Methodology Participants and ethics
This prospective and randomized clinical trial was registered in the ISRCTN (registration number:  (Table 1).
In the CH+saline group, internal resorption indicative of treatment failure was radiographically detected in up to 9/15 teeth (67%), at 12-month follow-up (Table   2). Inter-radicular bone destruction and furcation radiolucency, which also provide evidence of treatment failure, were observed in up to 5/15 teeth (36%), at 12-month follow-up (Table 3). Consequently, the final success rate of treatment in the CH+saline group was only 33% (5/15 teeth), after 12 months of follow-up (Table 1).
Regarding inter-radicular bone destruction, no statistically significant difference between groups was found at 3 months and 6 months (p=0.190; p=0.090). CH + saline 5 (33%) a 6 (40%) a 9 (67%) a CH + PEG 2 (17%) ab 2 (18%) ab 2 (18%) b *Different superscript letters mean significant differences between groups at 3, 6 and 12 months follow-up -chi-squared analysis and a multiple comparison post-test with 5% *Different superscript letters mean significant differences between groups at 3, 6 and 12 months follow-up -chi-squared analysis and a multiple comparison post-test with 5% Table 3-Inter-radicular bone destruction radiographically observed for MTA, CH+saline and CH+PEG pulpotomies at 3-, 6-, and 12-month follow-up  11,13,17 The ability to maintain contact with the pulp tissue during the entire treatment period seems to be the main factor responsible for the excellent results with the use of MTA. 19 Although CH+saline is commonly employed as a capping material for the pulp therapy of permanent teeth, this capping mixture was tested because results are contradictory regarding its clinical and radiographic success rates for the treatment of primary teeth. 6,12,13,20,21 Moreover, CH-based materials tend to dissolve over time and leave a void underneath the restoration. 6,9 To minimize this phenomenon, CH+PEG was also tested because the association of CH with a viscous vehicle could enhance the chemical and biological potential of the paste due to the slow release of Ca 2+ and OHions. 14 Nelson-Filho, et al. 22  Internal resorption is the most frequent reason for failure following pulpotomy with CH in primary teeth, which indicates that, despite pulp vitality, a silent chronic inflammation develops after treatment with CH and remains undiagnosed, thus triggering odontoclast activity. 10,15 Inappropriate operative techniques may also result in internal resorption if a thick blood clot remains or pulp misdiagnosis occurs. 20,23,24 Thus, bleeding control after coronal pulp amputation may significantly influence the outcome of pulpotomies with CH. 23,24 Some authors suggested that avoiding blood clot formation between the pulp tissue and the CH cap prevents the occurrence of internal resorption, 11 however, this is technically difficult since the incision into vital tissue produces both haemorrhage and exudation. 17,25 In the present study, we cannot attribute the occurrence of internal resorption to differences in the operative technique, since only one investigator performed all pulpotomies.
In addition, the same method of bleeding control was employed in the three groups and no internal resorption was detected in the MTA group. It is worth mentioning that MTA has the advantage of hardening in the presence of moisture, 26 which makes it suitable for use in areas where generating a dry environment is virtually impossible, such as pulp chambers. 12,6 Following the guidelines of a prior study by Moretti, et al. 6 (2015), we categorized internal resorption as radiographic failure, and the affected teeth were monitored during follow-up. We chose not to treat the affected teeth immediately because pathological findings in primary teeth may not require intervention, as primary teeth have limited survival and the pathology may not necessarily affect the permanent successor. However, most cases of internal resorption observed in CH-treated teeth in the present study developed into osseous changes whose clinical signs and symptoms were detected later on during followup, in agreement with that reported by Moretti,et al. 6 (2015). Eventually, extraction of the affected teeth was necessary.
Dental pulp healing depends on several factors, including the presumed stimulatory effect of the capping agent, and the ability of both the capping and definitive restorative materials to seal the tooth restoration interface against immediate and longterm microleakage. 6,20 In pulpotomies with CH, zinc oxide eugenol cement is commonly used before dental restoration. 10 However, the fact that the CH paste dissolves easily could favor the contact of the healthy radicular pulp with the eugenol, which is considered aggressive, and could lead to failures. 6 To avoid this effect, a resin-based CH cement was placed over the CH pastes as an intermediate base. This material has lower solubility and water sorption than the CH paste, increasing restoration longevity. 27 Additionally, the CH cement is of low strength 28 and is highly resistant to etchant, 29 which is necessary for restorations with resin modified glass ionomer cement (RMGIC). Although stainless steel crowns provide optimal coronal seal, 6,13,17 in the present study and in several others 6,10,11,24,30 involving Class I and II cavities of primary molars in a high caries risk population, final restorations were performed with RMGIC. According to the guidelines of the American Association of Pediatric Dentistry (AAPD), there is strong evidence that RMGIC is efficient for Class I restorations, and expert opinion supports the use of RMGIC for Class II restorations in primary teeth, 31 in line with a systematic review recommending the use of RMGIC in small to moderate sized Class II cavities. 32 In support of the current recommendations, no restoration failures were observed in this study for any of the three groups throughout follow-up; thus, we can exclude restorative material as a discriminating factor between groups, in this study.
The limitations of this study are inherent to randomized clinical trials, where patients must return for follow-up and complete "blinding" may be challenging. In this study, 5 patients (one in the MTA group and four in the CH+PEG group) were lost at follow-up, because they were unwilling to travel from their hometown to report to the clinic. Moreover, it was impossible to blind the operator at the moment the material was inserted, since MTA and CH had different mixing methods. In addition, blinding the rater for the radiographic examination is not fail proof, as differences in radiopacity between materials can be identified by experienced examiners.

Conclusion
The association of CH with PEG provided better results than that of CH with saline as a capping material for pulpotomy of primary teeth. However, both associations demonstrated clinical and radiographic results inferior to those of MTA.