Alpha- and beta-forms of gutta-percha in products for root canal filling

AIM: This study was undertaken to evaluate which materials were in the alpha-form of gutta-percha as claimed, and which were in the more conventional beta-form, and to explore the effect of heating on the materials. METHODOLOGY: Samples of gutta-percha without chemical additives, and dental gutta-percha formulations which included (i) two products previously studied; (ii) 12 newer products; and (iii) one newer product that had been stored at high temperature, were analysed by simultaneous differential thermal analysis and thermogravimetry. RESULTS: It was found that only four of the newer materials contained the alpha-form; all the rest comprised beta-gutta-percha. No weight loss was found for any material under the conditions of the present experiments. A typical heating cycle up to 130 degrees C caused changes in material behaviour - that is, on reheating fewer endothermic peaks were present. Storage of gutta-percha samples for 10 years under ambient temperature and storage in a heater at 80 degrees C appeared to have no effect on properties. CONCLUSIONS: It was concluded that heating dental gutta-percha to 130 degrees C causes physical changes; this was not seen with chemically pure gutta-percha. The presence of additives in the dental samples altered material behaviour.     

Brazilian gutta-percha points. Part I: chemical composition and X-ray diffraction analysis

Eight nonstandardized gutta-percha points commercially available in Brazil (Konne, Tanari, Endopoint, Odous, Dentsply 0.04, Dentsply 0.06, Dentsply TP and Dentsply FM) were analysed chemically and by X-ray diffraction, and their chemical compositions were compared. The organic fraction (gutta-percha polymer and wax/resin) of the gutta-percha points was separated from the inorganic fraction (ZnO and BaSO4) by dissolving them in chloroform. The gutta-percha polymer was precipitated with acetone. The inorganic fraction was analysed by elemental microanalysis. Energy-dispersive X-ray microanalysis (EDX) and X-ray diffraction were employed to identify the chemical elements and compounds (barium sulfate and zinc oxide). The barium sulfate content was calculated based on the percentage of sulfur found in the elemental microanalysis. All analyses were repeated three times. The means and standard deviations of the percentage by weight of gutta-percha in the points were: Konne (17.6 +/- 0.30), Tanari (15.2 +/- 0.30), Endopoint (16.7 +/- 0.23), Odous (18.8 +/- 0.20), Dentsply 0.04 (15.7 +/- 0.17), Dentsply 0.06 (16.6 +/- 0.17), Dentsply TP (21.6 +/- 0.15) and Dentsply FM (16.3 +/- 0.23). The means and standard deviations of the zinc oxide content were: Konne (79.9 +/- 0.10), Tanari (81.9 +/- 0.07), Endopoint (81.3 +/- 0.40), Odous (79.7 +/- 0.26), Dentsply 0.04 (77.9 +/- 0.03), Dentsply 0.06 (78.2 +/- 0.07), Dentsply TP (69.8 +/- 0.19) and Dentsply FM (72.6 +/- 0.70). The method utilized was appropriate to quantify gutta-percha, wax/resin, zinc oxide and barium sulfate. Cone brands without barium sulfate were found. An unusual high wax/resin percentage was detected in Dentsply FM (p = 0.0003). Dentsply TP showed the highest gutta-percha percentage.     

Differential scanning calorimetry (DSC) and temperature-modulated DSC study of three mouthguard materials

OBJECTIVES: Employ differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC) to investigate thermal transformations in three mouthguard materials and provide insight into their previously investigated energy absorption. METHODS: Samples (13-21mg) were obtained from (a) conventional ethylene vinyl acetate (EVA), (b) Pro-form, another EVA polymer, and (c) PolyShok, an EVA polymer containing polyurethane. Conventional DSC (n=5) was first performed from -80 to 150 degrees C at a heating rate of 10 degrees C/min to determine the temperature range for structural transformations. Subsequently, TMDSC (n=5) was performed from -20 to 150 degrees C at a heating rate of 1 degrees C/min. Onset and peak temperatures were compared using ANOVA and the Tukey-Kramer HSD test. Other samples were coated with a gold-palladium film and examined with an SEM. RESULTS: DSC and TMDSC curves were similar for both conventional EVA and Pro-form, showing two endothermic peaks suggestive of melting processes, with crystallization after the higher-temperature peak. Evidence for crystallization and the second endothermic peak were much less prominent for PolyShok, which had no peaks associated with the polyurethane constituent. The onset of the lower-temperature endothermic transformation is near body temperature. No glass transitions were observed in the materials. SEM examination revealed different surface morphology and possible cushioning effect for PolyShok, compared to Pro-form and EVA. SIGNIFICANCE: The difference in thermal behavior for PolyShok is tentatively attributed to disruption of EVA crystal formation, which may contribute to its superior impact resistance. The lower-temperature endothermic peak suggests that impact testing of these materials should be performed at 37 degrees C.     

Evaluation of the thermoplasticity of different gutta-percha cones and Resilon

The goal of this study was to evaluate the thermoplasticity of conventional and thermoplastic gutta-percha and Resilon, a polyester polymer-based material. Specimens with standardised dimensions were made from the following materials: conventional and thermoplastic gutta-percha (Dentsply), conventional and thermoplastic gutta-percha (Endopoints) and Resilon. After 24 h, the specimens were placed in water at 70 degrees C for 60 s, and thereafter positioned between two glass slabs. Each set was compressed by a 5-kg weight. Digital images of the specimens before and after compression were obtained and analysed. The thermoplasticity of each material was confirmed by the difference between final and initial areas of each sample. The data were analysed statistically by anova and Tukey's test at a 5% significance level. Resilon had the highest thermoplasticity means (P < 0.05). Among the gutta-percha cones, Endopoints TP (thermoplastic) presented the highest thermoplasticity means and differed significantly from the other commercial brands (P < 0.05). Resilon had good thermoplasticity, endorsing its use as a thermoplastic root canal filling material.     

Effect of thermal placement techniques on some physical properties of gutta-percha

Some clinical techniques for the placement of gutta-percha root fillings involve the application of heat. This study was undertaken to assess the effects of intracanal heating techniques on the following properties of gutta-percha: coefficient of thermal expansion, softening temperature, phase transition temperature and organic content. Samples from each of four products were prepared by three different methods. The materials were studied by thermomechanical analysis, simultaneous thermogravimetry and differential thermal analysis, and by measurement of weight loss on ashing. It was shown that the techniques of gutta-percha placement involving heating in the root canal caused reversible physical changes in the materials without any apparent change in chemical composition. The average coefficient of thermal expansion was 137 x 10(-6)/degrees C, the softening temperature was 55.5 degrees C, there were two characteristic phase changes, and the organic content was 25%.     

A comparison of thermal properties between gutta-percha and a synthetic polymer based root canal filling material (Resilon)

A new polymer-based obturating material, Resilon, has been developed but there have been no studies identifying its thermal properties. The purpose of this study was to compare the melting point, specific heat, enthalpy change with melting and heat transfer between gutta-percha (GP) and Resilon (R). The first three tests were determined using a differential scanning calorimeter and the heat transfer test was determined using a split-tooth model. Results show no significant difference (t test, p > 0.05) between gutta-percha and Resilon for the melting point temperature (GP: 60.01 degrees C; R: 60.57 degrees C). There was a significant difference (t test, p < 0.05) in specific heat capacity (GP: 0.94 J/g degrees C, R: 1.15 J/g degrees C) and endothermic enthalpy change (GP: 10.88 J/g, R: 25.20 J/g) between the two materials. The heat transfer test showed a significant difference (Mann-Whitney, p < 0.05) in temperature increase between gutta-percha and Resilon within 3 mm of the heat source.     

Temperature Triggered Shape Memory Effect of Transpolyisoprene-based Polymer

Introduction

Pure gutta-percha (trans-1, 4-polyisoprene [TPI]) has been used extensively as a main component of gutta-percha for root canal filling. TPI has the interesting shape memory property by cross-linking, and this polymer was commercialized under the product name of SMP-2 (Kuraray Corp, Kashima, Japan). Therefore, the purpose of this study was to examine the thermal properties and the mechanism of the shape memory function of cross-linked SMP-2.

Methods

The crystalline of the TPI was observed by x-ray diffraction. The effects of temperature on shape recovery, recovery stress, and relaxation modulus (Er[5]) were measured in cross-linked cylindrical specimens of SMP-2. Differential scanning calorimetry was used to monitor thermal events.

Results

On heating, a pronounced increase in recovery stress, a marked decrease in Er(5), and endothermic DSC peaks were observed over the same temperature range (38°–51°C) with shape recovery. On the other hand, on cooling, a pronounced decrease in recovery stress, a marked increase in Er(5), and an exothermic DSC peak were observed over the same temperature range (27°–33°C).

Conclusions

The shape memory property of TPI is derived from its crystallinity and cross-linking ability. Fixing the deformed shape and shape recovery from the deformed shape to the original shape is relatively easy to achieve by changing the temperature of SMP-2. The shape memory function of the cross-linked SMP-2 was expected to be very useful as a root canal filling material by the modification of its some thermal properties.     

Dimensional variability of nonstandardized greater taper finger spreaders with matching gutta-percha points

AIM: The purpose of this research was to determine the compatibility and dimensional variability between nonstandardized gutta-percha points and matching finger spreaders. METHODOLOGY: The diameters of nonstandardized gutta-percha points (n = 15) and matching finger spreaders (n = 15) from different manufacturers (Kerr, Dentsply Maillefer, Vereignigte Dentalwerke and Roeko) were determined and statistically analysed using a profile projector under a magnification of 50 x (+/- 0.002 mm). RESULTS: The dimensions of the finger spreaders and gutta-percha cones were inconsistent. Of the 29 groups of nonstandardized gutta-percha cones evaluated, 22 had standard deviations larger than 0.020 at D1. The standard deviations at D11 were greater than at D1, with the exception of those manufactured by Roeko. Overall, nonstandardized gutta-percha cones made by VDW had the greatest dimensional consistency within each size group; the largest variations were seen in the Dentsply Maillefer gutta-percha points. The 13 sizes of nonstandardized finger spreaders were more consistent. CONCLUSIONS: The results of this study show that corresponding sizes of nonstandardized finger spreaders and gutta-percha cones have statistically significant differences. There were large dimensional variations within sizes and discrepancies between the nominal size and actual size. Thus, these discrepancies may cause problems during root canal filling.     

Influence of gutta-percha points on the filling of simulated lateral canals

The aim of this study was to investigate, in vitro, the percentage of filling of simulated lateral canals in teeth obturated with TP medium and standardized gutta-percha points. Twenty human mandibular canines were prepared with LA Axxess (SybronEndo) and K3 Endo rotary system (SybronEndo) up to a #50 file, according to the Free Tip Preparation Technique. During instrumentation, the root canals were alternately irrigated with 1% sodium hypochlorite and 17% EDTA. Six artificial lateral canals were prepared at the apical third of each tooth. Then, the teeth were assigned to two groups (n=10): Group 1 - filled with TP medium master gutta-percha points (Dentsply, Mailleffer); Group 2 - filled with standardized master gutta-percha points (Dentsply, Mailleffer). Root canal filling was complemented with AH Plus sealer (Dentsply, Mailleffer) and accessory gutta-percha points (Dentsply, Mailleffer), according to the classic technique. The teeth were radiographed and the images obtained were digitized. Linear measurements of the percentage of filling of the artificial lateral canals in each group were accomplished on the Image Tool 2.02 software. Statistical analysis of the data using Mann-Whitney U non-parametric test evidenced significant difference (p<0.01) between the experimental groups. The group obturated with TP medium points yielded higher percentage of filling of the lateral canals. It may be concluded that the use of master gutta-percha points with larger taper resulted in better filling of the simulated lateral canals, as compared to the use of standardized master gutta-percha points.     

Assessment of different gutta-percha brands during the filling of simulated lateral canals

AIM: To compare the ability of five different commercially available gutta-percha points to fill simulated lateral canals when subjected to warm vertical compaction. METHODOLOGY: Fifty clear plastic teeth with a lateral canal in each third of the root were used. All teeth were filled using warm vertical compaction. Backfilling was completed with a sealer and the same gutta-percha point used during the apical condensation. After this, they were horizontally sectioned using a diamond disc adapted to a low-speed saw. The resulting sections were embedded in epoxy resin. The extent of gutta-percha and sealer filling were measured in each lateral canal using an IMAGE-PRO 4.0 software system. The voids in each canal were measured using the same system. Data were ranked and analysed using the Kruskal-Wallis statistical test. RESULTS: The mean percentage of the three lateral canals filled with gutta-percha and sealer were respectively: Konne (68.23% and 24.50%), Analytic (67.90% and 25.28%), Obtura (63.80% and 29.60%), Tanari (49.42% and 45.86%) and Dentsply (44.60% and 47.05%). There was significantly (P < 0.05) more gutta-percha in the lateral canal filled with Analytic, Obtura and Konne points than with Tanari and Dentsply points. CONCLUSIONS: The brand of gutta-percha cone had an influence on the length of filling within lateral canals. This may be a reflection of the chemical formulation of the gutta-percha points.     

Thermal transfer in extracted incisors during thermal pulp sensitivity testing

AIM: To measure the temperature distribution within tooth structure during and after application of thermal stimuli used during pulp sensitivity testing. METHODOLOGY: Extracted intact human maxillary anterior teeth were investigated for temperature changes at the labial enamel, the dentino-enamel junction (DEJ) and pulpal surface during and after a 5-s application of six different thermal stimuli: hot water (80 degrees C), heated gutta-percha (140 degrees C), carbon dioxide dry ice (-72 degrees C), refrigerant spray (-50 degrees C), ice stick (0 degrees C) and cold water (2 degrees C). J-type thermocouples and heat conduction paste were used to detect temperature changes, together with a data acquisition system (Labview). Data were analysed using analysis of variance, with a confidence level of P < 0.05. RESULTS: Temperature change was detected more quickly at the DEJ and pulpal surface with the application of hot water, heated gutta-percha and refrigerant spray than with carbon dioxide dry ice and ice (P < 0.05). Cold water and refrigerant spray were in the same range in terms of time to detect temperature change at both the DEJ and pulpal surface. Thermal stimuli with greater temperature difference from tooth temperature created a greater thermal gradient initially, followed by a greater temperature change at the DEJ and the pulpal surface. In this regard, ice and cold water were weaker stimuli than others (P < 0.05). CONCLUSIONS: Thermal stimuli used in pulp testing are highly variable in terms of temperature of the stimulus, rate of thermal transfer to the tooth and extent of temperature change within tooth structure. Overall, dry ice and refrigerant spray provide the most consistent stimuli, whereas heated gutta-percha and hot water were highly variable. Ice was a weak stimulus.     

Chemical and X-ray analyses of five brands of dental gutta-percha cone

AIM: To determine the chemical composition of five commercially available nonstandardized gutta-percha points. METHODOLOGY: The organic fraction (gutta-percha polymer and wax/resin) of nonstandardized gutta-percha points (Dentsply, Tanari, Konne, Obtura Spartan and Analytic Endodontics) was separated from the inorganic fraction (ZnO and BaSO4) by dissolution in chloroform. Gutta-percha polymer was precipitated with acetone. Zinc oxide was partially separated from barium sulphate by reaction with HCl. Energy-dispersive X-ray microanalysis and X-ray diffraction were employed to identify the chemical elements and compounds (barium sulphate and zinc oxide). The barium sulphate content was calculated by percentage of sulphur from elemental microanalysis. All analyses were repeated three times. RESULTS: The means and standard deviations of the percentage by weight of gutta-percha in the points were: Dentsply (14.5 +/- 0.70%), Tanari (15.6 +/- 0.66%), Obtura (17.7 +/- 0.35%), Konne (18.9 +/- 0.32%) and Analytic (20.4 +/- 0.40%). The mean and SD of the zinc oxide content were: Dentsply (84.3 +/- 0.50%), Tanari (82.0 +/- 0.72%), Obtura (69.5 +/- 0.21%), Konne (78.0 +/- 0.05%) and Analytic (66.5 +/- 0.50%). CONCLUSIONS: The method was appropriate to quantify gutta-percha and resin/wax components of gutta-percha points, but not barium sulphate and zinc oxide. An alternative procedure to determine barium sulphate and zinc oxide contents has been proposed based on elemental microanalysis of sulphur. Some brands of gutta-percha did not contain barium sulphate.     

The thermomechanical properties of gutta-percha. Part V. Volume changes in bulk gutta-percha as a function of temperature and its relationship to molecular phase transformation

A variety of gutta-percha materials was subjected to dilatometric analysis to measure volume changes which take place with heating and cooling. The volume changes were found to be related directly to the molecular transformation kinetics of the polymer material and to the temperature ranges within which they take place. If the gutta-percha in the apical segment is not elevated above 45 degrees C, molecular transformation is avoided and the ultimate volume changes which accompany temperature cycling are small, predictable, and controllable.     

Temperature mediated coefficient of dimensional change of dental tooth-colored restorative materials.

OBJECTIVES: Restorative materials are constantly subjected to thermal challenges in the oral environment. Such challenges, if significant, can have unfavorable effects on the margins of restorations in terms of the seal between the material and the tooth structure. This study aimed to assess the Coefficient of Dimensional Change (CDC) of tooth-colored restorative materials. METHODS: Five cylindrical specimens (6 mm x 4 mm) were made (using a stainless steel mold) of each of the following: the compomers Dyract AP (Dentsply), or F2000 Compomer (3M); a resin composite, Z100 MP (3M); a resin-modified glass-ionomer, Fuji II LC Capsule (GC); the conventional glass-ionomers Fuji IX GP Fast (GC) or Ketac Fil Aplicap (ESPE). The light-cured materials were cured for 40 s at each end and also around the 'waist' after removal from the mold. All specimens were stored in distilled water at 37 degrees C for 24 h, before testing. The CDC for each specimen was determined using a thermal mechanical analyser, by heating the sample from 25 to 70 degrees C at 10 degrees C min(-1). RESULTS: All materials except the glass-ionomers showed expansion on heating. The temperature response was non-linear in each case and values of CDC were therefore calculated between 25 and 50 degrees C and between 50 and 70 degrees C. The mean values of CDC (x 10(-6) degrees C(-1)) between 25 and 50 degrees C were Dyract: 83.4, F2000: 66.1, Z100: 64.5. The glass-ionomer materials showed contraction, which was non-linear in nature and was associated with a loss of water on heating. ANOVA and Tukey's pairwise comparisons of mean CDC values for the other materials indicated significant differences between all pairs of materials. SIGNIFICANCE: The compomers and resin composite tested had similar values of CDC. The conventional and resin-modified glass-ionomers contracted on heating. For one glass-ionomer the dimensional change on heating was minimal as thermal expansion appeared to be compensated by water loss.     

Thermal analysis of experimental and commercial gutta-percha.

Differential thermal analysis and penetration analysis were used to study the effects of heat treatment and plasticizers on the structure and resistance to penetration of commercial and experimental gutta-percha formulations. Penetration of commercial cones was related to the amount of gb and y crystalline polymorphs of gutta-percha and could be changed by heat treatment. The addition of waxes to experimental formulations of gutta-percha with barium sulfate and zinc oxide lowered the resistanceto penetration more than the addition of resins.     

EVALUATION OF THE THERMOPLASTICITY OF DIFFERENT GUTTA-PERCHA CONES AND THE TC SYSTEM

Objective:

The aim of this study was to evaluate the thermoplasticity of three commercial brands of gutta-percha (Tanari, Dentsply 0.06, and Roeko), and of the TC system.

Materials and Methods:

Standardized specimens were fabricated from the materials to be evaluated. Specimens were placed in water at 70°C for 60 seconds. Following that, they were positioned between two glass slabs and each set was compressed by a 5kg weight. Images of the specimens before and after compression were digitized and analyzed by the Image Tool software. The flow capacity of each material was confirmed by the difference between the initial and final areas of each sample.

Results:

The resulting data were analyzed by ANOVA. The TC system presented the greatest thermoplasticity values (p<0.05). Among the gutta-percha cones, the Roeko brand showed higher thermoplasticity than the others (p<0.05).

Conclusion:

The gutta-percha from TC system present good thermoplasticity capacity.     

An evaluation of .06 tapered gutta-percha cones for filling of .06 taper prepared curved root canals

AIM: To compare the area occupied by gutta-percha, sealer, or void in standardized .06 tapered prepared simulated curved canals and in mesio-buccal canals of extracted maxillary first molars filled with a single .06 gutta-percha point and sealer or lateral condensation of multiple .02 gutta-percha points and sealer. METHODOLOGY: Simulated canals in resin blocks with either a 30 degrees curve and radius of 10.5 mm (n = 20) or a 58 degrees curve and 4.7 mm radius (n = 20) and curved mesio-buccal canals of extracted maxillary first molars (n = 20) were prepared using .06 ProFiles in a variable tip crown-down sequence to an apical size 35 at 0.5 mm from the canal terminus or apical foramen. Ten 30 degrees and 58 degrees curved resin canals and 10 canals in the extracted teeth group were obturated with .02 taper gutta-percha cones and AH 26 sealer using lateral condensation. The time required to obturate was recorded. The remaining canals were obturated with a single .06 taper gutta-percha cone and AH 26 sealer. Excess gutta-percha was removed from the specimens using heat and the warm mass vertically condensed. Horizontal sections were cut at 0.5, 1.5, 2.5, 4.5, 7.5 and 11.5 mm from the canal terminus or apical foramen. Colour photographs were taken using an Olympus 35 mm camera attached to a stereomicroscope set at x40 magnification, and then digitized using a flatbed scanner. The cross-sectional area of the canal contents was analysed using Adobe PhotoShop. The percentage of gutta-percha, sealer or voids to the total root canal area were derived and data analysed using unpaired Student's t-test and the Mann-Whitney U-test. RESULTS: In the 30 degrees curved canals the levels had between 94 and 100% of the area filled with gutta-percha with no significant difference (P > 0.05) between the lateral condensation and single cone techniques. In the 58 degrees curved canals the levels had 92-99% of the area filled with gutta-percha, with the single cone technique having significantly (P < 0.05) more gutta-percha fill at the 2.5 mm level only. In the mesio-buccal canals of the teeth the levels had between 72 and 96% of the area filled with gutta-percha with no significant difference (P > 0.05) between the lateral condensation and single cone technique. The time for obturation was significantly (P < 0.05) greater for lateral condensation compared with the single cone technique in all groups. CONCLUSIONS: The .06 taper single cone technique was comparable with lateral condensation in the amount of gutta-percha occupying a prepared .06 tapered canal. The .06 single cone technique was faster than lateral condensation.     

Changes in the physical properties of the Ultrafil low-temperature (70 degrees C) thermoplasticized gutta-percha system

Three tests were used to obtain a basic understanding of the changes taking place in the physical properties of the Hygienic Ultrafil system. The materials studied were raw gutta-percha, gutta-percha points, and the two Ultrafil materials Blue (firm set) and White (regular set) gutta-percha. In the first test a differential scanning calorimeter was used to determine melting points; two crystalline forms were observed in the dental materials and only one crystalline form in the raw gutta-percha. In the second test a magnetic bearing torsional creep apparatus was used in which the rates of crystallization were observed. The differences seen in the induction times of the crystallization are related to the amount of mastication of the gutta-percha. Mastication in this usage is the manufacturers process of mixing the raw gutta-percha with its other components. The gutta-percha is masticated slightly in the points and considerably more in the Ultrafil material. Ultrafil exhibits longer periods of time required to induce nucleation at any specific temperature due to the increased mastication. Melting points were also decreased with increased mastication. In the third test a dilatometer was used to observe isothermal volumetric shrinkage of the materials during crystallization. When the Ultrafil material was compared with the gutta-percha points, the blue material had approximately the same amount of shrinkage, 2.6%; the white material shrank slightly less, 2.2%. The raw gutta-percha being 100% polymer had the greatest amount of shrinkage, 4.6%.     

How does canal taper affect root stresses?

AIM: To examine the effect of specific tapers on root stresses and thus vertical root fracture. METHODOLOGY: The effect of taper on root stresses was calculated during simulated warm vertical compaction of gutta-percha in a straight rooted premolar for three tapers (0.04, 0.06 and 0.12 mm mm(-1)) using finite element analysis. Stresses in the dentine were observed whilst the root was filled with three subsequent gutta-percha increments. Each increment was compacted at 10 or 15 N and the gutta-percha cooled down to 37 degrees C. After filling, composite was polymerized in the access space. A functional occlusal load of 50 N was then applied on the buccal cusp incline. The stress distribution in the root during the occlusal loading was compared with the stresses during filling. RESULTS: During filling, the highest stresses were found: (a) at the canal surface; (b) using the smallest taper; (c) in the apical third; and (d) during the first gutta-percha increment. The root stress distribution changed when the functional post-filling load was applied. It generated the highest stresses at the external root surface, with a tensile stress concentration at the lingual surface of the cervical third. Since the stresses during simulated masticatory loading concentrated on the external surface, an increased taper size caused only slightly higher root stress levels. CONCLUSIONS: With increasing taper, root stresses decreased during root filling but tended to increase for masticatory loading. Root fracture originating at the apical third is likely initiated during filling, whilst fracture originating in the cervical portion is likely caused by occlusal loads.     

Root surface temperature rises in vitro during root canal obturation with thermoplasticized gutta-percha on a carrier or by injection

The aim of this in vitro study was to measure the temperature rise on the outer root surfaces of teeth during four different root canal obturation techniques. Sixty extracted human maxillary and mandibular premolars with a single canal were used. After root canal cleaning and shaping, the teeth were randomly divided into four groups of 15 teeth each and obturated with Thermafil obturators or Soft-Core obturators using Ultrafil or Trifecta low-temperature thermoplasticized gutta-percha techniques. Temperature changes on the external mesial root surfaces were measured using a thermal imaging camera. Lower temperature rises were found for Ultrafil and Trifecta techniques (2.14 degrees C and 2.03 degrees C, respectively) than for Thermafil and Soft-Core techniques (3.87 degrees C and 3.67 degrees C, respectively). These findings suggest that solid core gutta-percha combined with low-temperature injectable gutta-percha obturation techniques may impose less risk for thermal damage to the surrounding periradicular tissues.