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ABSTRACT: The push-out test has been widely used in experimental endodontics but has been criticized on technical grounds particularly because the soft-core material undergoes plastic deformation under load. This study systematically evaluated the technique by comparing push-out strength and load profiles in relation to core material stiffness, canal diameter, punch diameter, sample orientation, and mode of failure.
Straight palatal roots of 90 maxillary molars were obturated with an epoxy resin-based sealer alone (10 roots) or gutta-percha (70) or epoxy resin (10) cores with a thin layer of sealer cement. Roots were embedded in mounting resin vertically or at an angle of 5° or 10° to the long axis of the root. One-millimeter sections were tested using a universal testing machine with a punch diameter corresponding to 50%, 75%, or 90% of the canal diameter. Bond strengths (MPa) were calculated, and data were analyzed using analysis of variance with post hoc Tukey multiple comparisons (P < .05). After push out, core materials and canal walls were examined using scanning electron microscopy.
Push-out strength was affected by core material stiffness. Angulation up to 10° from vertical had little effect on push-out strength, but load profiles were strongly influenced by orientation. No effect of the punch diameter was observed when the diameter was 90% of the canal diameter, but push-out strength was lower when the punch diameter was 50%-60% of the canal size.
Despite limitations, the push-out test may still be suitable for ranking the bonding of root filling materials.
Journal of endodontics 05/2013; 39(5):669-73. · 2.95 Impact Factor
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ABSTRACT: OBJECTIVES: To enumerate peri-implant bone strain pattern under quantified occlusal load and verify the bone response through comparison with the critical strain thresholds defined by Frost's bone mechanostat theory. MATERIAL AND METHODS: Mandibular unilateral recipient sites in two greyhound dogs were established with posterior teeth extractions. After 6 weeks, four titanium implants were placed in each dog mandible. Following 12 weeks of healing, successfully osseointegrated implants were placed in supra-occlusal contact via screw-retained non-splinted metal crowns. Plaque control and a dental health enhancing diet were prescribed. A bite force detection device was used to quantify in vivo occlusal load as the dogs functioned with supra-occlusal contact. After 8 weeks, the dogs were sacrificed. In vitro peri-implant bone strain under quantified occlusal load was measured using bonded stacked rosette strain gauges. RESULTS: The average and peak in vivo occlusal load measured were 434 and 795 newton (N). When individually and simultaneously loaded in vitro (≤476 N), absolute bone strains up to 1133 and 753 microstrains (με) were measured at implant apices, respectively. Bone strain reaching 229 με was recorded at distant sites. For bone strain to reach the pathological overload threshold defined by Frost's bone mechanostat theory (3000 με), an occlusal load of 1344 N (greater than peak measured in vivo) is required based on the simple linear regression model. CONCLUSION: Under the in vivo and in vitro conditions investigated in this study, peri-implant bone was not found to be under pathological overload following supra-occlusal contact function. Strain dissipation to distant sites appeared to be an effective mechanism by which implant overload was avoided.
Clinical Oral Implants Research 10/2012; · 2.51 Impact Factor
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ABSTRACT: For root canal fillings, a thin layer of sealer cement is generally recommended. However, with resin-based sealers, lower bond strength to dentin has been shown in thin layers compared to thick, contrary to typical behavior of adhesive layers between two adherents. The aim of this study was to evaluate tensile and shear bond strength of thin and thick films of three resin-based sealers (one epoxy-based and two methacrylate-based) materials and to investigate corner effects of one methacrylate-based resin sealer.
Freshly mixed sealer cements were placed between metal-to-metal surfaces of plano-parallel stainless steel aligned rods with diameter 4.7 mm. Ten samples were prepared for each type, thickness (0.1 and 1.0 mm) of sealer and test. Tensile and shear strengths were measured after 48 h for the methacrylate-based materials and after 7 days for the epoxy-based material using a universal testing machine at a crosshead speed of 1mm/min. Corner effects were investigated using one methacrylate-based resin material.
Film thickness had a highly significant influence on both tensile and shear strengths. For methacrylate resin-based sealers, thin films had higher bond strength than thick (p<0.001 for both tensile and shear bond strength). With the epoxy-based sealer either no difference (shear) or lower bond strength in thin films (tensile; p<0.05) was found, and appeared to result from numerous voids created during mixing. The methacrylate based sealer demonstrated typical engineering behavior for an adhesive material, with corner effects shown as a material property and in good agreement with the tensile bond strength results.
The higher tensile and shear bond strength of resin-based sealer in thin films is the opposite of that previously reported for bonding to dentin. The substrate clearly has an important role in failure behavior.
Dental materials: official publication of the Academy of Dental Materials 05/2012; 28(9):e150-9. · 2.88 Impact Factor
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ABSTRACT: The aim of this study was to measure the effect of incorporating CPP-ACP into an autocure GIC on physical and mechanical properties, ion release and enamel demineralization inhibition.
Physical and mechanical properties were evaluated using tests specified by the International Organization for Standardization (ISO). Concentrations of fluoride, calcium and inorganic phosphate in deionized water (pH 6.9) and lactic acid (pH 4.8) were measured up to five months. Cavities on human extracted molars were prepared, restored with GIC (control), CPP-ACP modified GIC or resin composite, then stored in 50mM lactic acid solution at pH 4.8 for 4 days. Sections of demineralized enamel were examined using polarized light microscopy followed by lesion area measurement.
The incorporation of up to 5% CPP-ACP into Fuji VII decreased the cements' strength and prolonged setting time. However, values remained within ISO limits. The incorporation of 3 or 5% CPP-ACP significantly decreased fluoride release, while higher calcium and inorganic phosphate release occurred. The demineralized enamel area adjacent to GIC with 3 or 5% CPP-ACP was significantly smaller compared to GIC control.
The incorporation of 3% CPP-ACP into GIC has the potential to improve its anticariogenic ability without adversely affecting its mechanical properties.
Dental materials: official publication of the Academy of Dental Materials 11/2010; 27(3):235-43. · 2.88 Impact Factor
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ABSTRACT: To measure cuspal deflection and tooth strain, plus marginal leakage and gap formation caused by polymerization shrinkage during direct resin composite restoration of root-filled premolars.
Thirty-two first and second maxillary premolars were divided into four groups (n=8). Group 1 had standardised mesio-occlusal-distal (MOD) cavities and served as the control group. Group 2 had endodontic access and root canal treatment through the occlusal floor of the MOD cavity, leaving the axial dentine intact. Group 3 had endodontic access and root canal treatment with the mesial and distal axial dentine removed. Group 4 had endodontic access and root canal treatment with axial dentine removed and a glass ionomer base (GIC). All groups were restored incrementally using a low shrink resin composite. Cuspal deflection was measured using direct current differential transformers (DCDTs), and buccal and palatal strain was measured using strain gauges. Teeth were immersed in 2% methylene blue for 24h, sectioned and scored for leakage and gap formation under light and scanning electron microscopy.
Total cuspal deflection was 4.9+/-1.3 microm for the MOD cavity (group 1), 7.8+/-3.3 microm for endodontic access with intact axial dentine (group 2), 12.2+/-2.6 microm for endodontic access without axial dentine (group 3), and 11.1+/-3.8 microm for endodontic access with a GIC base (group 4). Maximum buccal strain was 134+/-56, 139+/-61, 251+/-125, and 183+/-63 mustrain for groups 1-4 respectively, while the maximum palatal strain was 256+/-215, 184+/-149, 561+/-123, 264+/-87 mustrain respectively. All groups showed marginal leakage; however placement of GIC base significantly improved the seal (p=0.007).
Cusp deflection and strain increased significantly when axial dentine was removed as part of the endodontic access. Placement of a glass ionomer base significantly reduced tooth strain and marginal leakage. Therefore, a conservative endodontic access and placement of a glass ionomer base are recommended if endodontically treated teeth undergo direct restoration with resin composite.
Journal of dentistry 10/2009; 37(9):724-30. · 2.00 Impact Factor
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ABSTRACT: To investigate the role of dentinal tubules in the fracture properties of human root dentin and whether resin-filled dentinal tubules can enhance fracture resistance.
Crack propagation in human root dentin was investigated in 200 microm thick longitudinal samples and examined by light and scanning electron microscopy. 30 maxillary premolar teeth were prepared for work of fracture (Wf) test at different tubule orientations, one perpendicular and two parallel to dentinal tubules. Another 40 single canal premolars were randomly divided into four groups of 10 each: intact dentin, prepared but unobturated canal, canal obturated with epoxy rein (AH Plus/gutta percha), or with UDMA resin sealer (Resilon/RealSeal. The samples were prepared for Wf test parallel to dentinal tubules. Wf was compared under ANOVA with statistical significance set at p<0.05.
Dentinal tubules influenced the path of cracks through dentin, with micro-cracks initiated in peritubular dentin of individual tubules ahead of the main crack tip. A significant difference (p<0.001) was found between Wf perpendicular to tubule direction (254.9 J/m(2)) vs. parallel to tubule direction from inner to outer dentin (479.4 J/m(2)). Neither canal preparation nor obturation using epoxy- or UDMA-based resins as sealer cements substantially influenced fracture properties of root dentin, despite extensive infiltration of dentinal tubules by both sealer cements.
Dental materials: official publication of the Academy of Dental Materials 08/2009; 25(10):e73-81. · 2.88 Impact Factor
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ABSTRACT: The aim of this study was to investigate fluid flow in dentin after restoration of carious teeth with resin composite bonded with a total-etching adhesive, with or without glass-ionomer cement lining. The roots of extracted third molars were removed and the crowns were connected to a fluid flow-measuring device. Each carious lesion was stained with caries detector dye and caries was removed using slow-speed burs and spoon excavators. Caries-excavated teeth were divided into two groups for restoration with resin composite bonded with a total-etch adhesive: (i) without lining; and (ii) lined with glass-ionomer cement before bonding. In non-carious teeth, cavities of similar dimensions were prepared, divided into two groups, and restored in the same manner. Fluid flow was recorded, after restoration, for up to 1 month. Caries-affected dentin was examined by scanning electron microscopy (SEM), and the bonded interfaces were observed using a confocal laser scanning microscope. No significant difference in fluid flow was observed between the two restorative procedures or between the carious and non-carious groups. The SEM images showed that the dentinal tubules of acid-etched, caries-affected dentin were usually still occluded, while some were patent. Limited penetration of fluorescent dye into dentin and into the bonded interfaces of restored carious teeth was observed.
European Journal Of Oral Sciences 07/2009; 117(3):334-42. · 1.88 Impact Factor
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ABSTRACT: The purpose of this work was to investigate fluid flow after restoration using four restorative procedures. Micro-gap, internal dye leakage, and micropermeability of bonded interfaces were also investigated. Each tooth was mounted, connected to a fluid flow-measuring device, and an occlusal cavity was prepared. Fluid flow after cavity preparation was recorded as the baseline measurement, and the cavity was restored using one of four restorative procedures: bonding with total-etch (Single Bond 2) or self-etch (Clearfil SE Bond) adhesives without lining; or lining with resin-modified glass-ionomer cement (GIC) (Fuji Lining LC) or conventional GIC (Fuji IX) and then bonding with the total-etch adhesive. Fluid flow was recorded after restoration and at specific time-points up to 6 months thereafter and recorded as a percentage. Micro-gap formation was analyzed using resin replicas and scanning electron microscopy. Internal leakage of 2% methylene blue dye was observed under a light microscope. In micro-permeability testing, fluorescent-dye penetration was investigated using confocal laser microscopy. None of the restorative procedures provided a perfectly sealed restoration. Glass-ionomer lining did not reduce fluid flow after restoration, and micro-gaps were frequently detected. The self-etch adhesive failed to provide a better seal than the total-etch adhesive, and even initial gap formation was rarely observed for the former. Penetration of methylene blue and fluorescent dyes was detected in most restorations.
European Journal Of Oral Sciences 01/2009; 116(6):571-8. · 1.88 Impact Factor
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ABSTRACT: Dentinal tubules occupy a substantial proportion of total dentin volume, especially of inner dentin. Resin-based sealer cements are known to penetrate deeply into dentinal tubules, but their ability to influence root strength is controversial. In this study, the contribution of dentinal tubules to shear strength and the influence of a resin-based sealer on shear strength were evaluated. Coronal 100-microm sections of 12 single-canal premolar teeth were tested in different locations (buccal and proximal) and tubule directions (parallel and perpendicular) using the micropunch shear test (MPSS). Tests were also conducted by using 10 two-canal premolars, with one untreated canal and the other obturated using epoxy resin-based sealer (plus gutta-percha). No difference in MPSS was found because of location or tubule orientation (p > 0.05). Outer dentin had a higher MPSS than middle and inner dentin (p < 0.001). Tubule infiltration by epoxy resin did not increase MPSS.
Journal of endodontics 11/2008; 34(10):1215-8. · 2.95 Impact Factor
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ABSTRACT: The purpose of this study was to compare fluid flow rates across dentin surfaces treated with four conditioners. The effect of conditioning on the micro-shear bond strengths of glass ionomer cement (Fuji IX GP) and resin-based adhesives (Single Bond 2 or Clearfil SE Bond) were also investigated. Under a simulated pressure of 1.3 kPa, two dentin conditioners, phosphoric acid, and a self-etching primer were applied to the dentin surfaces. Dentinal fluid flows at baseline and after conditioning were recorded for 15 min each. The conditioned surfaces were examined using a scanning electron microscope. The micro-shear bond strengths of the glass ionomer cement and of the resin-based adhesives bonded to conditioned dentin surfaces were evaluated while simulated intrapulpal pressure was maintained at 0 or 1.3 kPa. Only the dentin surface etched with phosphoric acid showed a significant increase in permeability. Micro-shear bond strengths of Fuji IX GP were not affected by conditioning the dentin surfaces or by bonding at different intrapulpal pressures (0 or 1.3 kPa). The effects on bond strengths of resin-based adhesives depended on the system used. The simulated positive intrapulpal pressure during bonding significantly affected the adherence of Single Bond 2, whereas Clearfil SE Bond was unaffected.
European Journal Of Oral Sciences 01/2008; 115(6):502-9. · 1.88 Impact Factor
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ABSTRACT: The aim of this study was to correlate the rate and magnitude of dentinal fluid flow (DFF) with cuspal displacement in response to resin composite restorative procedures.
Ten extracted human maxillary premolar teeth with an extensive MOD cavity preparation were connected to an automated fluid flow measurement apparatus (Flodec), and a direct current differencial transformer (DCDT) was attached to each cusp. The rate, magnitude and direction of DFF and cuspal displacement were recorded simultaneously in response to each stage of resin composite restorative procedures.
Cuspal displacement and DFF in outward and inward directions accompanied each stage of the procedures. Drying produced rapid cuspal contraction. Bonding caused slight cuspal expansion, whereas light curing of resin induced gradual but extensive cuspal contraction, which persisted following light curing. During baseline outward DFF was low and increased slightly during etching. In contrast, substantial outward DFF occurred during drying. Light curing of the bonding agent and the resin composite produced inward DFF. Following light curing, an outward DFF began and continued for at least 15 min.
The large, rapid fluid movement and cuspal displacement during restoration, and the prolonged outward fluid flow post-curing have implications for post-operative sensitivity. While mechanical stresses within dentin associated with cuspal displacement appear capable of inducing DFF, the net fluid movement is the result of complex interactions either directly or indirectly of several stimuli (thermal, evaporation, osmotic, and possibly mechanical).
Dental Materials 12/2007; 23(11):1405-11. · 3.13 Impact Factor
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ABSTRACT: The study aimed to determine fracture loads in tooth roots after canal preparation using different techniques. Mesiobuccal roots of 39 extracted mandibular molars were used. Three groups each of 13 roots were prepared by stainless steel hand files (K-files), and two rotary nickel-titanium techniques (Lightspeed and Greater Taper files). After obturation, a vertical load was applied by means of a spreader inserted into the canal until fracture occurred. The mean fracture load was 10.2 +/- 4.4 kg for K-files, 15.7 +/- 9.1 kg for Lightspeed and 13.2 +/- 6.1 kg for Greater Taper files, but differences were not statistically significant (p > 0.05). Most fracture lines were incomplete fractures on the buccal surface, followed by proximal and compound fractures. Greater apical enlargement (Lightspeed) or increased canal taper (Greater Taper files) did not increase fracture susceptibility of tooth roots.
Journal of Endodontics 07/2005; 31(7):529-32. · 2.88 Impact Factor
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ABSTRACT: The aim of the study was to determine the extent to which canal size, radius of curvature and proximal root concavity influence fracture susceptibility and pattern. A standardized cross-section of the mid-root region of a mandibular incisor was created by averaging the dimensions of 10 extracted teeth, and then the basic finite element analysis (FEA) model was created. By varying canal diameter, shape, and proximal concavity, these factors could be examined for roles in fracture susceptibility and pattern. The factors all interact in influencing fracture susceptibility and pattern, with dentin thickness not the only determining factor. The removal of dentin does not always result in an increased fracture susceptibility.
Journal of Endodontics 05/2005; 31(4):288-92. · 2.88 Impact Factor
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ABSTRACT: The purpose of the study was to determine whether rotary nickel-titanium (NiTi) canal preparation strengthens roots, and whether the fracture pattern can be predicted by finite element analysis (FEA) models. From a fracture mechanics viewpoint, structural defects, cracks or canal irregularities are likely to play a major role in fracture susceptibility of the roots, because stresses can be exponentially amplified at these sites. By incorporating defects into a smooth round canal using rotary NiTi, theoretically the roots could be strengthened. 25 teeth were prepared using hand files and another 25 using rotary NiTi. After obturation, all teeth were subject to loading until fracture; load and patterns were recorded. Four FEA models were created from fractured roots. No significant difference of fracture load between the two techniques was found. Mesio-distal fracture occurred more often in the rotary NiTi group. Stress patterns in three of the four FEA models correlated well with the observed fracture patterns.
Journal of Endodontics 05/2005; 31(4):283-7. · 2.88 Impact Factor
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ABSTRACT: This experimental study was designed to examine whether screw head design influenced the angle of application of a screwdriver at which failure of engagement or stripping of the screw head occurred.
Four different screw head designs (slot, cross, square, star) were tested in a custom-made jig that was designed to enable the screws to be tested over a range of angles of application of the respective screwdrivers, to determine whether the screw head design influenced the torque value at which the screw head stripped or failure of driver engagement occurred.
The results fell clearly into 2 groups: The slot and cross designs gave the highest torque values at all angles, while the torque values for the square and star designs dropped to a low value with increasing angulation between the screw and driver. These differences were significant (P <.001).
Although this experimental situation cannot be entirely extrapolated to the clinical situation, it indicates that the slot or cross design may offer an advantage in regions of difficult access where the angulation of the screwdriver to the screw may of necessity be increased.
Journal of Oral and Maxillofacial Surgery 05/2004; 62(4):473-8. · 1.64 Impact Factor
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ABSTRACT: Vertical root fracture seems to result from stresses generated within the root canal and typically occurs in a buccolingual direction through the thickest part of dentin. Because stresses in the canal wall are difficult to measure experimentally, we have attempted to correlate stress patterns derived from finite element models of maxillary and mandibular incisors with strain measurements on the root surfaces of extracted teeth. Finite element analysis indicated that circumferential tensile stresses were concentrated on the buccal and lingual surfaces of the canal wall, corresponding to areas of greatest canal wall curvature. Surface stresses were much lower and were consistently tensile on the proximal root surfaces but variable on the buccal and lingual surfaces. The measurement of root surface stresses does not provide a reliable picture of internal stresses in the root. Canal wall curvature is a major factor in stress concentration and hence in the pattern of fracture.
Journal of Endodontics 09/2003; 29(8):529-34. · 2.88 Impact Factor
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ABSTRACT: Previous studies have indicated that vertical root fracture tends to occur in a buccolingual direction, where dentin thickness is greatest. Factors potentially influencing the location and direction of root fracture include root canal shape, external root morphology, and dentin thickness. In this finite-element study, simulated root sections were varied systematically with respect to canal size and shape, external root morphology, and dentin thickness to determine their relative contribution to vertical root fracture. Similar models were constructed based on cross-sections of human tooth roots that had been fractured clinically or experimentally. Finite-element models demonstrated that canal curvature seems more important than external root morphology, in terms of stress concentration, and that reduced dentin thickness increases the magnitude but not the direction of maximum tensile stress. Models based on actual root fractures showed a strong similarity between tensile-stress distribution and fracture patterns.
Journal of Endodontics 09/2003; 29(8):523-8. · 2.88 Impact Factor
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ABSTRACT: There are several methods of determining strain in the facial skeleton on loading in vitro. This article describes an alternative photoelastic coating technique adapted from the commonly accepted method used by engineers to study surface strains in objects. In applying this method to the stomatognathic system, because the masticatory apparatus is loaded by muscular contraction an opposite reaction load should be distributed throughout the skeletal structure. This load distribution should slightly deform the bones to which the muscles of mastication are attached. An understanding of the resulting strain generated in the facial skeleton is important because strain distribution on loading reflects how the loads applied during mastication are partially dissipated. Preliminary descriptive results are presented, suggesting that anatomic structures influence the distribution of strain on loading. The technique described should allow in vitro investigation of the mechanical environment into which osseointegrated implants are placed and may aid in understanding their behavior.
Journal of Prosthetic Dentistry 08/2003; 90(1):92-6. · 1.32 Impact Factor
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ABSTRACT: The aim of this study was to investigate the creep, stress relaxation and strain rate behavior of human root dentin under compressive loading.
Cylindrical root dentin samples of 3.5mm outer diameter, 1.5mm internal canal diameter and 6-10mm long were prepared from freshly extracted teeth. The samples were tested in a closed-loop servohydraulic testing machine at constant load or displacement, and varied strain rate. In vivo strain rates were estimated using strain gauges bonded to human teeth.
A family of creep curves, determined at different loads within dentin's elastic region, was found to be consistent with a material having linear viscoelastic behavior. A positive correlation (r(2)=0.79, P<0.001) was found between creep rate and stress. Young's modulus (E) was found to be a function of the strain rate with rates of loading in the range 10-500,000Ns(-1). Loading at constant displacement showed stress to be a decreasing function of time (i.e. stress relaxation).
Dentin showed linear-viscoelastic behavior under various conditions of compressive loading. Time dependent properties of dentin should be taken into account in restorative dentistry.
Dental Materials 10/2002; 18(6):486-93. · 3.13 Impact Factor
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ABSTRACT: This study compared the ultimate tensile strength, micropunch shear strength, and microhardness of bleached and unbleached human dentin. Forty-four intact premolars were root canal treated and randomly divided into four groups. Bleaching agents were sealed in pulp chambers, as in clinical use. Group 1 (control) was treated with water, group 2 with 30% hydrogen peroxide, group 3 with sodium perborate mixed with water, and group 4 with sodium perborate mixed with 30% hydrogen peroxide. The teeth were stored in saline at 37 degrees C for 7 days. The teeth were then sectioned and biomechanical tests were carried out on dentin specimens that were obtained from all teeth. Intracoronal bleaching with 30% hydrogen peroxide and sodium perborate used either alone or in combination weakened dentin. Hydrogen peroxide alone tended to be more damaging than sodium perborate used alone or sodium perborate mixed with hydrogen peroxide.
Journal of Endodontics 03/2002; 28(2):62-7. · 2.88 Impact Factor
