To evaluate root dentin pH changes using different calcium hydroxide medications in primary and permanent molar root canals.
Sixty primary and 60 permanent molar roots were prepared with Twisted files and assigned in two subgroups: Group1, nonsetting calcium hydroxide (n = 30); group 2, viscous vehicle-based material (ApexCal ® ) (n = 30). The assigned materials were delivered in root canals and then stored for 24 h, 7 days and 14 days. All specimens were transversely cut in three sections and pH change was determined by Expandable Ion Analyzer cooperating with Flat Membrane pH Electrode and Reference Half-Cell Electrode at sample root surfaces. Two-way ANOVA was used for statistical analysis.
No significant difference was observed in primary teeth at all test periods. The mean pH values of the nonsetting calcium hydroxide group (pH10.39–10.90) were greater than those in viscous vehicle-based group (pH 9.84–10.12), but significant difference was observed only at 24 h. Among permanent teeth, the highest pH values of both materials were observed at 7 days. The pH values of the nonsetting calcium hydroxide group (pH 10.40–11.10) were greater than those in the viscous vehicle-based group (pH 9.80–10.41); however, no significant difference was observed at any test period.
The peak pH of nonsetting calcium hydroxide group was at 24 h in primary teeth and 7 days in permanent teeth. The nonsetting calcium hydroxide group showed higher pH values than those in the viscous group in both primary and permanent teeth.
The goals of nonvital pulp treatment are to prevent the premature loss of primary teeth, and maintain primary teeth functions . The success rates of pulpectomy in primary teeth have been reported from 75% to 96% depends on type of root canal materials . Root canal anatomy in primary molars is quite varied and complex causing difficulty for cleaning and shaping canals while the complexity of root canal anatomy may also affect the success rate of root canal treatment . Pulpectomy in primary teeth is usually treated completely within one visit; however, two-visit pulpectomy is necessary when the root canal has remaining exudate or the tooth has acute infection. For these conditions, intracanal medication is needed to be places in root canals between visits. This helps to clear up of residual bacteria and preventing re-infection in the root canal systems .
Intracanal medicaments, which are commonly used in endodontic treatment, are volatile medicament (phenolic compound and aldehyde groups), calcium hydroxide, some antibiotics, corticosteroids, and chlorhexidine gel . Volatile medicaments are not commonly used in currently because many studies reported about their toxicities and short duration of action. Messer and Chen reported that the loss of CMCP from cotton pellets after placement into the pulp chamber of extracted molars was approximately 90–95% within 24 h. On the other hand, calcium hydroxide is the material of choice which is frequently used as intracanal dressing due to its antibacterial property and ability to induce tissue reparation . The ability of hydroxyl ions in calcium hydroxide to diffuse through dentinal tubules has benefit in halting the function of clastic cells on the root surface and promoting an environment that induces the action of hard tissue repair .
Several studies have investigated pH changes after calcium hydroxide medication through root dentin in permanent teeth. The results of root dentin pH after calcium hydroxide medication have been reported wide range from pH 7 to pH11. They found similar results that diffusion of hydroxyl ions produced peak elevated pH for 7–14 days and remained until 30 days . Nerwich et al. measured permanent root dentin pH change after dressed with calcium hydroxide over a 4-week period. The results showed that the pH raised within an hour and reached peak pH cervically at 24 h (pH 10.3) whereas reached peak pH apically at 2–3 weeks (pH 9.3) . Therefore, the recommendation of calcium hydroxide intracanal medication in permanent teeth is at least 7–14 days . Moreover, there are three types of vehicles used in calcium hydroxide intracanal medication: aqueous, viscous and oily vehicles. Previous study stated that the dissociation effect of hydroxyl ions from calcium hydroxide depends on the type of vehicle used. Calcium hydroxide mixed with distilled water and Camphorated Monoparachlorophenol (CMCP) showed higher pH values compared with those mixed with normal saline solution and propylene glycol . In addition, another study found that aqueous calcium hydroxide paste increased dentinal pH in a short period while the viscous type (Hycal ® ) gave higher pH values after seven days .
On the other hand, there was only one study in primary teeth which reported controversy result when compared with permanent teeth results. They assessed pH values through surrounding medium between thickened calcium hydroxide paste with propylene glycol paste and Calen paste (which composed of calcium hydroxide, zinc oxide, polyethylene glycol and colopony) at various times of measurement . The thickened calcium hydroxide paste with propylene glycol paste group had higher pH values than the Calen paste group while the peak of hydroxyl ion diffusion occurred at seven days in both groups. However, no study has evaluated pH values of primary root dentin directly after medication with nonsetting calcium hydroxide mixed with aqueous vehicle, the one commonly used as intracanal medication in primary teeth pulpectomy. Therefore, the objective of this study was to evaluate root dentin pH changes using different calcium hydroxide medications in primary and permanent teeth.
Materials and methods
This study was approved by the Faculty of Dentistry, Mahidol University Institutional Review Board (COE. No. MU-DT/PY-IRB 2016/005.1502) in accordance with Declaration of Helsinki. All procedures performed in this study used anonymized specimens wherein the owners were not identified.
Sample size and specimen preparation
The sample size of this study was calculated from the mean pH and standard deviation of the pilot study by using primary root dentin pH of non-setting calcium hydroxide and viscous vehicle-based material groups at 24 h, 7 days, and 14 days at cervical middle and apical root levels (data not shown). The sample size was approximately 10 per group at 92% and 99% power of test in each group. Therefore, sixty roots of extracted lower primary molars (36 mesial roots and 24 distal roots) and 60 roots of extracted lower permanent molars (32 mesial roots and 28 distal roots) were used in this study. Extracted primary molars and permanent molars were kept in 0.1% Thymol solution after extraction until the experiment started. The diagnosis, pulpal and periapical conditions before extraction were unknown. The inclusion criteria included root resorption less than 1/3 of root length, with no perforation at the lateral canal wall, no canal obliteration, no internal resorption, with canal patency and the initial apical file (IAF) size 15 could be used to determine the working length of each individual canal.
All root specimens were obtained from the transverse section of the root at the cemento-enamel junction. Each root was separated using a diamond disc (Intensiv Swiss Dental Products, Montagnola, Switzerland) and the adherent tissue was removed with a round carbide bur (Meisinger, Neuss, Germany). Pre-operative radiographs of the root specimens in both the bucco-lingual and mesio-distal direction were taken for observing root canal anatomy and abnormality by using the Max DC70 and Dixel Mega CCD digital X-ray sensor (J Morita Mfg. Corp., Kyoto, Japan). Access to the canal was performed with a cylinder diamond bur (Meisinger, Neuss, Germany) and a steel round bur (Meisinger, Neuss, Germany). Then, pulpal tissue was removed with a barbed broach (Dentsply Maillefer, OK, USA) and determined the working length of each root by inserting a size 15 K-file past the apical foramen and defining at 1 mm short of that length. Root canal was prepared and shaped by crown down technique with the Twisted Files (TF) rotary nickel titanium file (SybronEndo, CA, USA) to the 0.06/30 file as the master apical file. Each primary root canal was rinsed with 3 mL of 1% NaOCl after changing each instrument. Final irrigation was performed with 1 mL of 17% EDTA for 3 min and 1% NaOCl. Moreover, each permanent root canal was rinsed with 3 mL of 2.5% NaOCl followed by 1 mL of 17% EDTA for 3 min and 2.5% NaOCl as final irrigation. All specimens were dried with cotton pellets and paper points before intracanal material placement.
Placement of materials
After that, root specimens of primary and permanent roots were randomly divided by stratified random sampling in six subgroups regarding different root canal filling materials and periods of measurement as follows.
Nonsetting calcium hydroxide group ( n = 30) One gram of pure calcium hydroxide powder (Merck Chemicals GmbH, Darmstadt, Germany) was mixed with 1 mL of distilled water and then inserted in the root canal by Ultradent syringe 1.2 mL and NaviTip™ (Ultradent Products, Inc., South Jordan, USA). The pH of pure calcium hydroxide/distilled water was approximately pH 12.5.
Viscous vehicle–based material group ( n = 30) ApexCal ® (Ivoclar Vivadent AG, Schaan, Liechtenstein) was inserted in the root canal by Application tip (Ivoclar Vivadent AG, Inc., Liechtenstein). The pH of Apexcal ® was approximately pH 11.
The lentulo spiral was applied in the canal under light pressure against the root canal wall and slowly rotated out of the canal. This was repeated until the paste was seen at the orifice of the root canal. Two postoperative radiographs were taken at the bucco-lingual and mesio-distal directions to access the quality of root canal medicament. When inadequate root canal medicament was found, the medicament would be added in the canal until it was completely filled. Then digital radiograph would be retaken to evaluate the quality of the filling. Access was cleaned with cotton pellets. The medicament was compressed with cotton pellet leaving 2 mm space: for Kernel ® Temporary Filling and Filtek™ Z350 XT Universal Restorative (3 M Company, St. Paul, MN, USA) collaborated with Scotchbond ™ Universal Adhesive (3 M Company, St. Paul, MN, USA). All procedures were standard performed by a single operator. The specimens were stored in each moisted glass tight bottle at 37 °C for 24 h, 7 days and 14 days respectively.
pH measurement and statistic analysis
Each specimen was transversely cut at the assigned period of measurement by IsoMet ® Low Speed Saw with water coolant (Buehler, An ITW Company, Binghamton, NY, USA) in three levels corresponding to the cervical, middle and apical areas as presented in Fig. 1 a. Each section was rinsed with 10 mL of distilled water to remove the residual medicament. Expandable Ion Analyzer EA 940 (Orion Research, Inc., Jacksonville, FL, USA) cooperating with MI-406 Flat Membrane pH Electrode (Microelectrodes, Inc., Bedford, NH, USA) and Orion™ 900100 Sure-Flow™ Reference Half-Cell Electrode (Thermo Fisher Scientific Inc., Waltham, MA, USA), were used and calibrated with standard buffer pH 4, 7 and 10 before measuring. The root dentin pH was measured by touching the MI-406 Flat Membrane pH Electrode on each root section and touching the Orion ™ 900100 Sure-Flow ™ Reference Half-Cell Electrode on a moist towel until a stable reading was obtained as the manufacturer recommendation ( Fig. 1 b). During each measurement, the electrodes were rinsed with distilled water and dried by cleaned tissue paper. The pH measurement of each section was repeated three times and then mean pH was calculated to represent mean pH of each area of measurement. After that, mean pH from the cervical, middle and apical areas of each root canal were calculated to represent the pH of the entire canal. Normal distribution of the data was proved by Kolmogorov-Smirnov test. Two-way analysis of variance was used to analyze the difference in pH values between different types of medicaments and periods of measurement. The difference among groups were identified using Bonferroni test. Statistical significant was set at P < 0.05.
Intraexaminer reliability of the quality assessments was good (Kappa and weighted Kappa C > 0.790)
Mean ± SD of primary and permanent root dentin pH values of the various calcium hydroxide types at 24 h, 7 days and 14 days were determined at different root levels. The pH values of the different areas of measurement of both primary and permanent showed that most of the cervical pH values of both materials were higher than the middle and apical pH values. Then, mean pH from the cervical, middle and apical areas of each root canal were recalculated to represent the pH of the entire canal at the last column and using for statistical analysis (as shown in Tables 1 and 2 ).