• Restorative Dentistry and Endodontics
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• v.40 no.4
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• pp.286-289
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• 2015

Objectives: The aim was to evaluate dentinal crack formation after root canal preparation with ProTaper Next system (PTN) with and without a glide path. Materials and Methods: Forty-five mesial roots of mandibular first molars were selected. Fifteen teeth were left unprepared and served as controls. The experimental groups consist of mesiobuccal and mesiolingual root canals of remaining 30 teeth, which were divided into 2 groups (n = 15): Group PG/PTN, glide path was created with ProGlider (PG) and then canals were shaped with PTN system; Group PTN, glide path was not prepared and canals were shaped with PTN system only. All roots were sectioned perpendicular to the long axis at 1, 2, 3, 4, 6, and 8 mm from the apex, and the sections were observed under a stereomicroscope. The presence/absence of cracks was recorded. Data were analyzed with chi-square tests with Yates correction. Results: There were no significant differences in crack formation between the PTN with and without glide path preparation. The incidence of cracks observed in PG/PTN and PTN groups was 17.8% and 28.9%, respectively. Conclusions: The creation of a glide path with ProGlider before ProTaper Next rotary system did not influence dentinal crack formation in root canals.

• Journal of Periodontal and Implant Science
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• v.27 no.3
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• pp.469-478
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• 1997

The purpose of this study was to evaluate the structural change of root surface and the occlusion of dentinal tubule following $CO_2$ laser treatment. Seven extracted healthy human premolar werw curetted, sectioned, and four specimens were randomly assigned to each of 6 different treatment groups : 1) untreated EDTA etched control: 2) root plande only: 3) $CO_2$ laser treated with 2W mode 6(10msec/pulse, 20pps) for 1 minute: 4) $CO_2$ laser treated with 2W mode 6(lOmsec/pulse, 20pps) for 2 minutes: 5) $CO_2$ laser treated with 2W mode 7(20msec/pulse, 20pps) for 1 minute: 6) $CO_2$ laser treated with 2W mode 7(20msec/pulse, 20pps) for 2 minutes. Following the prescribed treatment, the specimens were prepared for SEM evaluation. Results showed that $CO_2$ laser may be effective to occlude dentinal tubules tor dentin sensitivity treatment. The effect of dentinal tubule occlusion was enhanced with increasing the total energy level lased to specimen regardless of lasing mode. The structural changes of root surfaces were restricted to superficies, and these changes included fissuring, charring, crater formation over the smooth lava like texture. The charring and crater formation implying root damage was observed in the case of the longer duration of a pulse. The results of the present study suggests that the pulsed $CO_2$ laser with shorter pulse duration and longer exposure time can be used effectively in order to obtain the optimal dentinal tubule occlusion with minimal root damage.

• Proceedings of the KACD Conference
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• 2001.05a
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• pp.243-244
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• 2001

Root resorption is conventionally divided into internal and external varieties. Internal resorption occurs where there is loss of the internal wall of the root canal. and is usually associated with a localized area of necrotic pulp(Trope '||'&'||' Chivian 1984). External resorption occurs where there is loss of the external surface of the root and the resorption may be either transient or progressive(Tronstad 1988). External inflammatory resorption usually occurs following damage to the periodontal ligament or where there is communication between the periodontal ligament and a necrotic pulp. via open dentinal tubules or accessory canals. This type of resorption is usually progressive until root canal treatment is instituted (Barclay 1993).

• Restorative Dentistry and Endodontics
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• v.16 no.2
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• pp.155-164
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• 1991

The purpose of this study was to evaluate the effects of bleaching agent through the dentinal tubules of cervical area in the intracoronal bleaching of pulpless teeth on cutured fibroblast cells. Extracted human incisors were enlarged to # 40 K-file and obturated with gutta-perella and AH 26 sealer. The gutta-percha was removed to 2mm below the cementoenamel junction of the root The teeth were divided into 3 experimental and control groups. Experimental groups; Experimental group 1: Temporary inlay wax filld with 30% $H_2O_2$ in pulp cavity. Experimental group 2: Temporary inlay wax filld with 30% $H_2O_2$ in pulp cavity after placement of ZOE cement to cementoenamel junction. Experimental group 3: Temporary inlay wax filld with 30% $H_2O_2$ in pulp cavity after application of Copalite to cementoenamel junction. Control group: Temporary inlay wax filled without 30% $H_2O_2$ in pulp cavity under the same condition at each experimental group. Each tooth was immersed in well of multidish cultured fibroblast cell for 48 hours. The cellular multiplication and cell viability were calculated at the interval of 1, 3, 5. 7 hours and the morphological changes in well were observed and their photographs were taken with inverted microscope. The obtained results were as follows : CD The cellurar multiplicaton and cell viability decreased in all experimental groups at 1 hour after experiment and the morphology of fibroblast cell was changed from star shape to round (2) The cell viability was lowered to 34 % in experemental group 1, 44 % in experimental group 2, and 38 % in experemental group 3 at 3 hours after experiment (3) The cell multiplication was decreased to 54% in experemental group 1. 47% in experimental group 2, and 40% in experemental group 3 at 7 hours after experiment. (4) The decrease of cell number and morphological changes of fibroblast cell were remarkable in experimental group 1, group 3 and 2 in order. These results suggest that the fibroblast cells receive severe damage by 30% $H_2O_2$ solution leaked through the dentinal tubules and the dentinal tubules are able to be obturated better by ZOE cement than by Copalite.

• Restorative Dentistry and Endodontics
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• v.8 no.1
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• pp.61-68
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• 1982

This study was undertaken to compare the histopathological effects of the fractionated doses of 2,400, 4,800 and 7,200 rads of Cobalt-60 irradiation on the teeth of the sixty eight rats (Wester strain), weighing approximately 130gm. They were devided into four groups; no irradiation as a control (Group I) and others (Group II, III, and IV) which received different doses of radiation using 1.25 Mev RAC-120 Cobalt-60 Teletherapy Unit with exposure dose rate 69 rads/min, TSD 80cm. Experimental animals received 600 rads every three days until the total dosage of their groups were reached. Experimental animals were sacrified at the 1st day, 1st, 2nd, 3rd, 4th, 5th and 6th week irradiation. The following histopathologic findings were obtained: 1. The Group II, received 2,400 rads, showed no histopamologic changes essentially same as those of the control Group. 2. In the Groups III and IV, received 4,800 rads and 7,200 rads, disarray of the normal palasading arrangement of the odontoblastic cells, vacuolar degeneration in the odontoblastic layer, osteodentin and dentinal niches in the anterior teeth were observed. 3. There were no distinct changes in the posterior teeth in the Groups III and IV. 4. The ameloblast cells seemed to be less sensitive to radiation damage than the odontoblast cells.

• Journal of Periodontal and Implant Science
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• v.27 no.3
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• pp.495-514
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• 1997

The purpose of this study was to evaluate the in vitro effects of Nd:YAG laser irradiation on removal of a root surface smear layer after root planing in comparison with Tetracycline HCl. The 60 extracted human teeth due to severe periodontal disease were vigorously scaled and root planed with Gracey curet. Thirty specimen($5{\times}5{\times}2mm$) were obtained from root planed surface of 30 human teeth and assigned randomly to one of three groups : root planed group(5 specimen), Tetracycline HCI group(5 specimen, burnished for 5 minutes), and Nd:YAG laser group(25 specimen, German Dental Laser, Fotona Twinlight). Nd:YAG laser group was divided into 4 subgroups according to power of 1W, 1.5W, 2W, 3W at frequency to 10Hz. The specimen were then fixed, and examed by Scanning electron microscopic study. 30 of 60 human teeth used to measurement of the intrapulpal temperature rise during laser irradiation. Laser-irradiated surface exhibited various surface texture from relative flat surface to irregular surface with patent dentinal tubules of various shape and size. In some area, the root surface alteration which are carbonization, pit and crater formation and melting and resolidification were observed. The number of exposed dentinal tubules per unit($100_{\mu}m^2$) on tetracycline HCI group was more than that in the laser group below 1.5W of power(150mJ/pulse) and was significantly less than that in laser group above 2W of power(200mJ/pulse)(P<0.OOl). As power increased the intrapulpal temperature rise also increased. The result suggested that the parameter which effectively remove root surface smear layer than tetracycline HCI may cause thermal damage to pulp and root surface alteration result from laser exposure would indicate need for additional instrumentation. Thus, Nd:YAG laser irradiation in these parameter may not be appropriate for clinical use as adjunct to conventional periodontal therapy.

• Restorative Dentistry and Endodontics
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• v.21 no.1
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• pp.19-34
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• 1996

It has been demonstrated that intracoronal bleaching of pulpless teeth may result in cervical root resorption. Several authors postulated that bleaching agents such as hydrogen peroxide penetrated through the dentinal tubules to damage the surrounding tissues that cause cervical root resorption. The purpose of this study was to suggest on in vitro model for direct determination of hydrogen peroxide penetration through CEJ during nonvital bleaching. In addition, this model permit the quantification of the amount of hydrogen peroxide penetrated during the procedure. Freshly extracted intact premolars, removed for orthodontic reasons were used. Root canal treatment was performed in each tooth. And then the outer surface and crown portion of the teeth was sealed with wax leaving the CEJ. The prepared teeth mounted on the wax laminates were placed in plastic assay tubes containing 1.5ml bidistilled water with their entire root, including the CEJ, submerged in the solution. The teeth were dividied into four groups. Thermo group : thermocatalytic bleaching with superoxol Walk group: walking bleaching with sodium perborate & superoxol Combi group : combination of thermocatalytic & walking bleaching Dw group : walking bleaching with sodium perborate & water The bleaching procedure was performed three times. The bleaching intervals were at 3 days. The hydrogen peroxide present in the assay system was added to ferrous ammonium sulfate resulting in ferric ion release. Upon the addition of potassium thiocyanate a ferrithiocyanate complex results, which absorbs light at the wavelength of 467nm. The radicular penetration of hydrogen peroxide in the four groups was assessed directly using spectrophotometer. The amount of hydrogen peroxide in the samples tested is determined by comparing them with a standard curve generated by known amounts of hydrogen peroxide. The results were obtained as follows : 1. In all experimental groups except the Dw group showed lower penetration amount in day 4 than day 1, there was statistical importance in the difference (P<0.05). 2. After 3rd treatment, Thermo group showed slightly increased value and narrow distribution. Walk group showed much more penetration amount and widely dispersed value. Value of Combi group showed wide distribution without regard to treatment time, but value of Dw group evenly distributed. 3. Thermo group, Walk group and Dw group showed a tendency of increasing penetration amount with increasing treatment times(P<0.01), but Combi group revealed no statistically important differences. 4. Combi group showed the highest degree of penetration. Walk group showed lower penetration than Combi group. Thermo group & Dw group showed lower than Walk group. 5. Cervical root permeability to hydrogen peroxide varied from 0 to 35 %.

• Journal of Oral Medicine and Pain
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• v.30 no.4
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• pp.457-464
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• 2005

The purpose of our study was to investigate whether the intrapulpal temperature during cavity preparation of enamel or dentin with Er:YAG laser still remained in range of safety for dental pulp protection when combined with appropriate water flow rate. The effect of different pulse repetition rates at the same pulse energy during ablation was evaluated as well. Caries-free, restoration-free extracted human molar teeth were prepared for the specimen and divided two experimental groups of enamel and dentin. Each group comprised 5 specimens and each of tooth specimens were embedded into a resin block each and measuring probe was placed on the irradiated pulpal walls. For experiments of dentin ablation, enamel layers were prepared to produce dentin specimen with a same dentin thickness of 2 mm. A pulse energy of Er:YAG laser was set to 300 mJ and three different pulse repetition rates of 20 Hz, 15 Hz and 10 Hz were employed. Laser beam was delivered with 3 seconds and less per application over enamel and dentin surfaces constant sized by $3\;mm{\times}2\;mm$ and water spray added during irradiation was a rate of 1.6 ml/min. Temperature change induced by Er:YAG laser irradiation was monitored and recorded While enamel was ablated, there was no significant difference of temperature related to pulse repetition rates(p=0.358) and temperature change at any pulse repetition rate was negligible. Significant statistical difference in temperature changes during cavity preparation in dentin existed among three different pulse groups(p=0.001). While temperature rise was noticeable when the dentinal wall was perforated, actual change of temperature due to Er:YAG laser irradiation was not enough to compromise safety of dental pulp when irradiation was conjugated with appropriate water spray. Conclusively, it can be said that cavity preparation on enamel or dentin with an Er:YAG laser is performed safely without pulp damage if appropriate volume of water is sprayed properly over the irradiated site.