Hydroxyl radical activity in thermo-catalytically bleached root-filled teeth

Fracture strength and hybrid layer formation of endodontically-treated teeth after dental bleaching photoactivated with violet LED

OBJECTIVE

To evaluate in vitro the effect of dental bleaching using high concentration hydrogen peroxide (HP) photoactivated with violet LED on fracture strength and hybrid layer formation.

METHODS

forty endodontically-treated bovine teeth were randomized into four groups (n = 10): C - Control, HP - 35% hydrogen peroxide, HP-BL - 35% hydrogen peroxide photoactivated with blue LED, HP-VL - 35% hydrogen peroxide photoactivated with violet LED. Three bleaching sessions with an interval of 7 days between them were performed. After 10 days of the last bleaching session, the dental crowns were restored and submitted to the fracture strength test. Five specimens from each group were used to evaluate the hybrid layer formation by scanning electron microscope (SEM) images. One-way ANOVA and Kruskal-Wallis test were used for parametric and non-parametric data, respectively. Significance level of 5% was adopted to all the tests.

RESULTS

No differences on fracture strength among the groups were observed (p > 0.05). HP and HP-BL showed alterations on hybrid layer formation compared to C group (p < 0.05), but not for HP-VL (p > 0.05). No differences on hybrid layer formation were observed among HP, HP-VL and HP-BL groups (p > 0.05).

CONCLUSION

Dental bleaching, photoactivated or not, did not affect the fracture strength of endodontically-treated teeth. Regardless of the protocol used, hydrogen peroxide altered the hybrid layer formation at some level when the restoration was placed after 10 days of the last bleaching session.

Applications of Antioxidants in Dental Procedures

As people are paying more and more attention to dental health, various dental treatment procedures have emerged, such as tooth bleaching, dental implants, and dental restorations. However, a large number of free radicals are typically produced during the dental procedures. When the imbalance in distribution of reactive oxygen species (ROS) is induced, oxidative stress coupled with oxidative damage occurs. Oral inflammations such as those in periodontitis and pulpitis are also unavoidable. Therefore, the applications of exogenous antioxidants in oral environment have been proposed. In this article, the origin of ROS during dental procedures, the types of antioxidants, and their working mechanisms are reviewed. Additionally, antioxidants delivery in the complicated dental procedures and their feasibility for clinical applications are also covered. Finally, the importance of safety assessment of these materials and future work to take the challenge in antioxidants development are proposed for perspective.

Present status and future directions - Managing discoloured teeth

Managing tooth discolouration involves a range of different protocols for clinicians and patients in order to achieve an aesthetic result. There is an increasing public awareness in the appearance of their teeth and management of tooth discolouration may be inter-disciplinary and involve both vital and nonvital teeth. Vital teeth can be easily treated with low concentration hydrogen peroxide products safely and effectively using an external approach and trays. For endodontically treated teeth, the walking bleach technique with hydrogen releasing peroxide products is popular. However, there is an association with external cervical root resorption with higher concentrations of hydrogen peroxide of 30%-35%. There are also regulatory considerations for the use of hydrogen peroxide in certain jurisdictions internationally. Prosthodontic treatments are more invasive and involve loss of tooth structure as well as a life cycle of further treatment in the future. This narrative review is based on searches on PubMed and the Cochrane library. Bleaching endodontically treated teeth can be considered a safe and effective protocol in the management of discoloured teeth. However, the association between bleaching and resorption remains unclear although there is likely to be a relation to prior trauma. It is prudent to avoid thermocatalytic approaches and to use a base/sealer to cover the root filling. An awareness expectations of patients and multidisciplinary treatment considerations is important in achieving the aesthetic result for the patient. It is likely that there will be an increasing demand for aesthetic whitening treatments. Bleaching of teeth has also become increasingly regulated although there are international differences in the use and concentration of bleaching agents.

[External cervical tooth root resorption]

External cervical tooth root resorption is one of the most aggressive types of pathological resorption. Due to the uncontrolled growth of resorptive tissue, irreversible loss of dentin and cement occurs. To date, there is no common position regarding the etiological factor and pathogenesis of invasive cervical resorption. The histological picture is similar to some fibro-bone lesions. The treatment outcome of the pathology is difficult to predict because elimination of the causative factor is often not sufficient for resorption arrest. Only the complete elimination of resorptive tissue helps to stop the process. The report describes a clinical case of a successful treatment of invasive cervical resorption of dental hard tissues.

Effect of Antioxidant and Buffering Agent Mixture on Dentin Shear Bond Strengths of Laminate Veneer and pH Change of External Medium After Intracoronal Bleaching

Aim:

To investigate the effect of sodium ascorbate (SA), an antioxidant and calcium hydroxide (Ca(OH)2), a buffering agent mixture, on the shear bond strength of a luting resin to dentin, and pH changes of the extraradicular medium solution after intracoronal bleaching with hydrogen peroxide.

Materials and Methods:

In this in vitro study, 60 human maxillary central incisors were randomly assigned into six groups ( n: 10): Group 1: restored, no bleach; group 2: bleached, bonded immediately; group 3: bleached, treated with 10% SA applications before bonding; group 4: bleached, treated with calcium hydroxide applications before bonding; group 5: bleached, treated with CaOH2 and SA mixture applications before bonding; group 6: delay bonding by seven days. For bleach treatment in groups 2 to 6, intracoronal bleaching was performed with 35% hydrogen peroxide for four days. SA or CaOH2 or mixture of SA and CaOH2 were left in the access cavity for four days. Hybrid blocks, 4 mm × 4 mm wide × 2–mm thick, were luted with resin cements on dentin surface and then the specimens were subjected to shear bond strength testing. Analysis of variance and Tukey post hoc multiple comparison tests were applied ( P < .05).

Results:

G2 and G4 showed significantly low bond strength values and they were lower than the other groups ( P < .05). There were no significant differences between G1, G3, and G6 ( P > .05). The pH values had risen markedly in the groups containing calcium hydroxide (G4 and G5) after four days ( P < .05).

Conclusion:

The application of 10% SA or 10% SA and CaOH2 mixture were effective at reversing bleaching effects on bond strength. CaOH2 or CaOH2 and 10% SA mixture increased the external medium pH and were effective for alkalinization after intracoronal bleaching.

Pattern of Hydroxyapatite Crystal Growth on Bleached Enamel Following the Application of Two Antioxidants: An Atomic Force Microscope Study

OBJECTIVES

This study observed the topographical pattern of hydroxyapatite deposition and growth (D&G) on bleached enamel following application of two antioxidants (sodium ascorbate and catalase) using atomic force microscope.

STUDY DESIGN

Twenty enamel specimens (4×3×2mm), prepared from extracted impacted third molars, were mounted in self-cure acrylic and randomly grouped as: Group I-untreated; Group II- 35%H₂O₂; Group III- 35%H₂O₂ + artificial saliva; Group IV- 35%H₂O₂ + catalase+ artificial saliva; Group V- 35%H₂O₂ + sodium ascorbate+ artificial saliva. Groups I and II were observed immediately after treatment. Groups III-V were observed after 72 hrs. Roughness average was also calculated and analyzed with non-parametric Kruskall-Wallis ANOVA and Mann-Whitney tests.

RESULTS

H₂O₂ dissolved matrix, exposed hydroxyapatite crystals (HACs), causing dissolution on the sides of and within HACs and opening up of nano-spaces. Artificial saliva showed growth of dissoluted crystals. Antioxidants+saliva showed potentiated remineralization by D&G on dissoluted HACs of bleached enamel. Catalase potentiated blockshaped, while sodium ascorbate the needle-shaped crystals with stair-pattern of crystallization. Evidence of oxygen bubbles was a new finding with catalase. Maximum roughness average was in group V followed by group II > group IV > group III > group I.

CONCLUSION

Post-bleaching application of catalase and sodium ascorbate potentiated remineralization by saliva, but in different patterns. None of the tested antioxidant could return the original topography of enamel.

Influence of Different Types and Concentrations of Chemical Catalysts on Dental Bleaching Efficiency

The objective of this study was to evaluate the effects of different types and concentrations of chemical catalysts on the efficiency of 35% hydrogen peroxide gel on dental bleaching. Enamel-dentin disks were obtained from bovine incisors and the initial color was assessed. The groups were divided according to the type and concentration of catalyst added to an experimental gel: ferrous sulphate (FS) (0.001, 0.002 and 0.003%); ferrous gluconate (Fg) (0.01, 0.02 and 0.03%); ferric chloride (FC) (0.01, 0.02 and 0.03%); manganese gluconate (MG) (0.01, 0.02 and 0.03%); and manganese chloride (MC) (0.01, 0.02 and 0.03%). The positive control (PC) group received the bleaching gel without any catalyst, while in the negative control (NC) the specimens remained in artificial saliva. Three applications of the bleaching gels were performed for 10 minutes each, repeated after 7 days. Color assessments were performed 7 days after the first session and 7 days after the second. The specimens were stored in artificial saliva and assessed again after 1 year. The data were analyzed by parametric analysis of variance and Tukey's test. Some of the chemical catalysts tested were effective in reducing the yellowish color of the samples in relation to the positive control group after 1 and 2 applications and diminished the color relapse over time. After 1 year, the FS was the most effective catalyst tested. We concluded that some chemical catalysts increased the efficiency of dental bleaching.

Fracture resistance of endodontically-treated teeth submitted to bleaching treatment with hydrogen peroxide and titanium dioxide nanoparticles photoactivated by LED-laser

Objective: The aim of this study was evaluate the fracture resistance of endodontically-treated teeth after bleaching treatment using 15% hydrogen peroxide plus titanium dioxide nanoparticles (15HPTiO2) photoactivated by LED-laser, in comparison with protocols using 35% hydrogen peroxide (35HP), 37% carbamide peroxide (37CP) or sodium perborate (SP). Material and method: After endodontic treatment, fifty bovine extracted incisors were divided into five groups (n = 10): G1- without bleaching; G2- 35HP; G3- 37CP; G4- 15HPTiO2 photoactivated by LED-laser and G5- SP. In G2 and G4, the bleaching protocol was applied in 4 sessions, with a 7 day interval between each session. In G3 and G5, the materials were kept in the pulp chamber for 21 days, but replaced every 7 days. After 21 days, the crowns were subjected to compressive load at a cross head speed of 0.5 mm/min, applied at 135° to the long axis of the root using an eletromechanical testing machine, until fracture. The data were submitted to ANOVA and Tukey tests (p = 0.05). Result: The bleaching treatment in endodontically-treated teeth with 15HP plus TiO2 nanoparticles and photoactivated by LED-laser caused reduction of the fracture resistance similarly provided by 35HP, 37CP or SP (p>0.05). All bleaching treatments reduced the fracture resistance compared to unbleached teeth (p<0.05). Conclusion: All bleaching protocols reduced the fracture resistance of endodontically-treated teeth, but there were no differences between each other.

Fracture resistance of teeth submitted to several internal bleaching protocols

AIM

The aim of this study was to evaluate the fracture resistance of teeth submitted to several internal bleaching protocols using 35% hydrogen peroxide (35HP), 37% carbamide peroxide (37CP), 15% hydrogen peroxide with titanium dioxide nanoparticles (15HPTiO2) photoactivated by LED-laser or sodium perborate (SP).

MATERIALS AND METHODS

After endodontic treatment, fifty bovine extracted teeth were divided into five groups (n = 10): G1-unbleached; G2-35HP; G3-37CP; G4-15HPTiO2 photoactivated by LED-laser and G5-SP. In the G2 and G4, the bleaching protocol was applied in 4 sessions, with 7 days intervals between each session. In the G3 and G5, the materials were kept in the pulp teeth for 21 days, but replaced every 7 days. After 21 days, the teeth were subjected to compressive load at a cross head speed of 0.5 mm/min, applied at 135° to the long axis of the root using an eletromechanical testing machine, until teeth fracture. The data were submitted to ANOVA and Tukey tests (α = 5%).

RESULTS

The 35HP, 37CP, 15HPTiO2 and SP showed similar fracture resistance teeth reduction (p > 0.05). All bleaching treatments reduced the fracture resistance compared to unbleached teeth (p < 0.05).

CONCLUSION

All bleaching protocols reduced the fracture resistance of endodontically-treated teeth, but there were no differences between each other.

CLINICAL SIGNIFICANCE

There are several internal bleaching protocols using hydrogen peroxide in different concentrations and activation methods. This study evaluated its effects on fracture resistance in endodontically-treated teeth.

ESR investigation of ROS generated by H2O2 bleaching with TiO2 coated HAp

It is well known that clinical bleaching can be achieved with a solution of 30% hydrogen peroxide (H2O2) or H2O2/titanium dioxide (TiO2) combination. This study examined the hypothesis that TiO2 coated with hydroxyapatite (HAp-TiO2) can generate reactive oxygen species (ROS). ROS are generated via photocatalysis using electron spin resonance (ESR). The bleaching properties of HAp-TiO2 in the presence of H2O2 can be measured using hematoporphyrin litmus paper and extracted teeth. We demonstrate that superoxides (O2(•-)) and hydroxyl radicals (HO(•)) can be generated through excitation of anatase TiO2, rutile TiO2, anatase HAp-TiO2, and rutile HAp-TiO2 in the presence of H2O2. The combination of R HAp-TiO2 with H2O2 produced the highest level of HO(•) generation and the most marked bleaching effects of all the samples. The superior bleaching effects exhibited by R HAp-TiO2 with H2O2 suggest that this combination may lead to novel methods for the clinical application of bleaching treatments.

Coronal resistance to fracture of endodontically treated teeth submitted to light-activated bleaching

OBJECTIVES

The aim of this study was to assess the fracture resistance of endodontically treated teeth submitted to bleaching with 38% hydrogen peroxide activated by light-emitting diode (LED)-laser system.

METHODS

Fifty maxillary incisors were endodontically treated, received a zinc phosphate barrier and were embedded in acrylic resin until cemento-enamel junction. The specimens were distributed into five groups (n=10) according to the number of bleaching sessions: GI, no treatment (control); GII, one session; GIII, two sessions; GIV, three sessions and GV, four sessions. The whitening gel was applied to the buccal surface of the tooth and inside the pulp chamber for three times in each session, followed by LED-laser activation. Specimens were submitted to the fracture resistance test (kN) and data were submitted to the Tukey-Kramer multiple comparisons test.

RESULTS

No significant difference (p>0.05) was found between GI (0.71+/-0.30) and GII (0.65+/-0.13), which presented the highest strength values to fracture. Groups III (0.35+/-0.17), IV (0.23+/-0.13) and V (0.38+/-0.15) showed lower resistance to fracture (p<0.01) when compared to GI and GII.

CONCLUSIONS

The fracture resistance of endodontically treated teeth decreased after two sessions of bleaching with 38% hydrogen peroxide activated by LED-laser system.

Nonvital tooth bleaching: a review of the literature and clinical procedures

Tooth discoloration varies in etiology, appearance, localization, severity, and adhesion to tooth structure. It can be defined as being extrinsic or intrinsic on the basis of localization and etiology. In this review of the literature, various causes of tooth discoloration, different bleaching materials, and their applications to endodontically treated teeth have been described. In the walking bleach technique the root filling should be completed first, and a cervical seal must be established. The bleaching agent should be changed every 3-7 days. The thermocatalytic technique involves placement of a bleaching agent in the pulp chamber followed by heat application. At the end of each visit the bleaching agent is left in the tooth so that it can function as a walking bleach until the next visit. External bleaching of endodontically treated teeth with an in-office technique requires a high concentration gel. It might be a supplement to the walking bleach technique, if the results are not satisfactory after 3-4 visits. These treatments require a bonded temporary filling or a bonded resin composite to seal the access cavity. There is a deficiency of evidence-based science in the literature that addresses the prognosis of bleached nonvital teeth. Therefore, it is important to always be aware of the possible complications and risks that are associated with the different bleaching techniques.

Evaluation of a combined thiourea and hydrogen peroxide regimen to bleach bloodstained teeth

BACKGROUND

Current techniques for intra-coronal bleaching of stained root-filled teeth employ oxidative bleaching with hydrogen peroxide. However, concern over the potential for invasive cervical resorption following the use of hydrogen peroxide has been expressed by many researchers, and recommendations have been made to limit the use of this agent. A reductive-oxidative bleaching process using a thiourea and hydrogen peroxide regimen is proposed as an effective and safer bleaching combination. The efficacy of this novel bleaching regimen is evaluated in this study.

METHODS

The study involved a quantitative and qualitative spectrophotometric assessment of the ability of two amine (bleaching) agents, aqueous thiourea and acidified thiourea, to alter the absorption spectra of haemoglobin and methaemoglobin compared to hydrogen peroxide. In addition, extracted premolar teeth discoloured by blood were subjected to different bleaching regimens using amine reducing agents and hydrogen peroxide. The change in the colour of the bloodstained dentine samples was measured at each stage of the bleaching process with a Photometer and Reflectance Densitometer. Comparisons of different treatments were made using a method of least significant difference and/or analysis of variance.

RESULTS

Spectrophotometric studies showed that acidified thiourea solution greatly reduced the colour of the haemoglobin and methaemoglobin in the visible range (330-760 nm). Aqueous thiourea had no effect on the presence of haemoglobin and methaemoglobin. Reflection Densitometer and Photometer scores indicate that the greatest bleaching effect was achieved by the combined acidified thiourea and hydrogen peroxide regimen.

CONCLUSION

The recognition that bleaching discoloured teeth is a chemical process, which can be achieved by both reducing and oxidizing agents, offers the possibility of developing new and safer clinical bleaching protocols. It is concluded that the bleaching regimen which employs the sequential use of 0.1 M acidified thiourea and 30% w/v hydrogen peroxide is as effective at bleaching bloodstained dentine as 30% w/v hydrogen peroxide alone. However, the addition of thiourea to the bleaching regimen has the potential benefit of reducing the level of damaging hydroxyl radicals and achieving a safer bleaching process.

The ability of thiourea to scavenge hydrogen peroxide and hydroxyl radicals during the intra-coronal bleaching of bloodstained root-filled teeth

BACKGROUND

Hydrogen peroxide, an agent used in the intra-coronal bleaching of root-filled teeth for over a century, has been shown to diffuse from the pulp chamber to the outer root surface. Furthermore, it has been demonstrated that destructive hydroxyl radicals, the by-products of the bleaching process, have been detected on the external root surface. The control of such diffusion may be of importance in minimizing the risk of invasive cervical resorption (ICR) which has been linked to intra-coronal bleaching of discoloured root-filled teeth using hydrogen peroxide. The aims of the present in vitro study are to quantify the diffusion of hydrogen peroxide and hydroxyl radicals to the outer root surface following intra-coronal bleaching, and to evaluate the ability of thiourea incorporated into the bleaching protocol to scavenge residual hydrogen peroxide and hydroxyl radicals.

METHODS

Thirty-five single rooted premolar teeth with intact cementum at the cemento-enamel junction were used in this project. Thirty teeth were stained with red blood cells and root-filled with gutta-percha and AH26. The five unstained teeth were root-filled and constituted a negative control (Group 1). The stained teeth were divided equally into the following experimental groups and subjected to various intra-coronal bleaching regimes: Group 2--'walking bleach' with 20 microl 30 per cent w/w hydrogen peroxide; Group 3--20 microl 30 per cent w/w hydrogen peroxide and thermocatalytically activated; Group 4--20 microl acidified thiourea; Group 5--20 microl acidified thiourea and 20 microl 30 per cent w/w hydrogen peroxide; Group 6--20 microl acidified thiourea and 20 microl one per cent sodium hypochlorite; Group 7--20 microl acidified thiourea, 20 microl one per cent sodium hypochlorite and 20 microl 30 per cent w/w hydrogen peroxide. The reaction products of the bleaching process were quantified at the outer root surface using high performance liquid chromatography and electrochemical detection (HPLC-ECD).

RESULTS

Results showed that hydrogen peroxide used alone in Groups 2 and 3 was able to be detected at the outer root surface in 100 per cent of the samples, and that the presence of the hydroxyl radical generated in both groups was detected in equal amounts (P < 0.05). When thiourea was incorporated into the bleaching protocols in Groups 5-7, it was shown to scavenge both hydrogen peroxide and hydroxyl radicals to a significant degree (P < 0.05).

CONCLUSIONS

Acidulated thiourea is an effective scavenger of residual hydrogen peroxide and hydroxyl radicals generated during the intra-coronal bleaching of bloodstained root-filled teeth.

Sealing capacity of a photochromatic flowable composite as protective base in nonvital dental bleaching

AIM

To evaluate microleakage of a flowable composite used as a protective isolating base, applied with different adhesive systems.

METHODOLOGY

Seventy root-filled teeth were divided into seven groups. A flowable composite base (Tetric Flow Chroma) was used with three adhesive techniques (Syntac, Excite, Excite DCS; in the three cases with and without acid etching) and in a control group without dentine conditioning or adhesive placement. A 30% hydrogen peroxide solution was applied for 24 h in the pulp chambers, followed by the placement of a dye (silver nitrate) for 4 h. Each tooth was sectioned longitudinally, and examined under 4x magnification to assess the tooth/restoration dye leakage following a four-degree scale. Percentage of dye penetration was registered. Statistical analysis was made through the Tukey and Mann-Whitney U-tests.

RESULTS

Maximum leakage (100% of specimens) was recorded in the control group without an adhesive system. In the groups subjected to acid etching, the percentage of leakage corresponded to Excite DSC (10%), followed by Syntac (20%) and Excite (30%). In the groups in which only an adhesive system was used, 50% of the teeth demonstrated dye leakage. Statistically significant differences in terms of leakage were observed between the control group and the experimental groups (P < 0.05). There were no significant differences among the experimental groups, but comparing the leakage percentages obtained between the groups in which the teeth were subjected to prior acid etching, and those in which no etching was carried out, observed differences were significant (P = 0.04).

CONCLUSIONS

There were no significant differences between the adhesive systems in terms of leakage. Acid etching significantly reduced leakage.

Role of Free Radicals and Metal Ions in Direct Current-Induced Cytotoxicity

The purpose of this study was to investigate the mechanism of direct current (DC)-induced cytotoxicity. To test the working hypothesis that electrolysis products are responsible for the DC-induced cytotoxicity, the cytotoxic effects between the direct and indirect DC treatment against human polymorphonuclear cells (PMNs) was compared. The indirect DC treatment (treatment with the culture medium exposed to DC) was comparable in cytotoxicity to the direct DC treatment, suggesting that electrolysis products have an important role in DC-induced cytotoxicity. Metal ions released from different electrodes into the culture medium were quantified by the inductively coupled plasma-mass spectroscopy. Higher concentrations of Ag, Zn, and Ni and chromium were released from Ag, Zn, and stainless steel (St) electrodes, respectively, whereas much lower concentrations of Ni and Ti were released from Ni-Ti electrode. Further, electron spin resonance spectroscopy with spin-trapping agent showed that the direct current with the following metal electrodes generated alkoxyl radical (St and Ni-Ti electrodes), hydrogen radical (Ag and Au electrodes), and both carbon and alkoxyl radicals (Zn electrode), respectively. These results suggest that free radicals and metal ions released from electrodes contribute to the cytotoxicity of DC treatment used for iontophoresis.

Inaugural Geoffrey Heithersay oration in endodontics and oral biology

Smiles are often a reflection of dental health, and as such provide great satisfaction to a dental practitioner who has successfully managed complex dental problems such as malformed, malpositioned or traumatically damaged teeth. A biological approach to the management of the pulpal and periodontal responses to dental trauma has been made possible by cumulative research, and application of this knowledge will enhance successful treatment.

Review of the current status of tooth whitening with the walking bleach technique

Internal bleaching procedures such as the walking bleach technique can be used for whitening of discoloured root-filled teeth. The walking bleach technique is performed by application of a paste consisting of sodium perborate-(tetrahydrate) and distilled water (3% H2O2), respectively, in the pulp chamber. Following a critical review of the scientific literature, heating of the mixture is contra-indicated as the risk of external cervical resorption and the formation of chemical radicals is increased by application of heat. An intracoronal dressing using 30% H2O2 should not be used in order to reduce the risk of inducing cervical resorption. This review provides advice based on the current literature and discusses how the walking bleach technique can lead to successful whitening of non-vital root-filled teeth without the risks of side-effects.

Generation of free radicals and/or active oxygen by light or laser irradiation of hydrogen peroxide or sodium hypochlorite

Generation of free radical and/or active oxygen by light or laser irradiation of hydrogen peroxide (H2O2) or sodium hypochlorite (NaClO), which have been used for tooth whitening or root canal irrigation, was investigated using electron spin resonance spectroscopy combined with a spin-trapping technique. When H2O2 was exposed to light or laser radiation, the amount of hydroxyl radical generated changed according to the concentration of H2O2 and irradiation time. The amount of 5,5-dimethyl-1-pyrrolidone-(2)-oxyl-(1) (DMPO-X) also changed in accordance with irradiation time. The amounts of hydroxyl radical generated from H2O2 after irradiation were in the order: plasma lamp > halogen lamp > He-Ne laser > Yellow He-Ne laser. On the other hand, the amounts of DMPO-X generated from NaClO after irradiation were in the order: plasma lamp > Yellow He-Ne laser > halogen lamp > He-Ne laser.

Cervical external root resorption in vital teeth

External resorptions associated with inflammation in marginal tissues present a difficult clinical situation. Many times, lesions are misdiagnosed and confused with caries and internal resorptions. As a result inappropriate treatment is often initiated. This paper provides three-dimensional representations of cervical external resorption, based on X-ray microfocus-tomographical scanning of a case, which will aid the dental practitioner in recognizing characteristic features during clinical inspection. In addition, histopathological examination reveals the cellular morphology of the adjacent tissues.

Effect of calcium hydroxide as a supplementary barrier in the radicular penetration of hydrogen peroxide during intracoronal bleaching in vitro

AIM

To examine pH changes in the cervical external root surface, when calcium hydroxide was used as a supplementary barrier to the protective base material during intracoronal bleaching.

METHODOLOGY

Twenty-eight single-rooted human premolars extracted for orthodontic reasons were instrumented with K-Flex files, obturated with gutta-percha and subjected to thermocatalytic bleaching. The teeth were divided into four groups. In group A, a glass-ionomer cement barrier was placed at the cemento-enamel junction (CEJ) level and in group C, the barrier was placed 1 mm apical to the CEJ. In groups B and D, Ca(OH)2 was placed in contact and apical to the glass-ionomer cement at the CEJ and 1 mm apical to the CEJ, respectively. The teeth were placed in vials containing distilled water and the pH values of the medium surrounding the teeth were recorded after 1, 2, 4, 10 and 15 days, following renewal of the medium.

RESULTS

The pH in the medium became acidic in all groups. No statistically significant differences existed between groups for all the experimental days (P = 0.790).

CONCLUSION

The placement of Ca(OH)2 as a supplementary barrier during intracoronal bleaching did not have a significant effect in reversing the acidic pH created at the external root surface in vitro. Its potential effect during these procedures in vivo needs to be further investigated.

Cytotoxicity of intracanal bleaching agents on periodontal ligament cells in vitro

Intracoronal bleaching of nonvital teeth is a simple and conservative procedure for esthetic restoration of discolored teeth. However it is possible that damage to the periodontal ligament may occur if the bleaching agents contact this tissue. The purpose of this study was to examine the cytotoxicity of intracanal bleaching agents on human periodontal ligament (PDL) cells in vitro. Three bleaching agents, 30% hydrogen peroxide (H2O2), 2.0 g/ml sodium perborate (SP) solution, and 2.0 g/ml SP in H2O2, were diluted from 10(-3) to 10(-7) with Eagle's minimal essential medium and incubated with PDL cells isolated and cultured from extracted teeth. Cytotoxicity was assessed quantitatively by determining the amount of lactic dehydrogenase activity released from the cells after exposure to the agents for 24 or 72 h. Dose-response curves were plotted, and TD50 values (dilution causing the release of 50% of control lactate dehydrogenase activity) and 95% confidence limits determined. The rank order of the TD50 values after exposure for 24 h was SP in H2O2 (most toxic) > H2O2 > SP solution (least toxic). After 72 h SP in H2O2 still produced the greatest cytotoxic effect. However the SP solution was more cytotoxic than H2O2 at this time point. It is concluded that the mixture of SP with H2O2 was the most toxic to the PDL cells in vitro.

Dental materials: 1997 literature review

This review of the published literature on dental materials for the year 1997 has been compiled by the Dental Materials Panel of UK. It continues a series of annual reviews started in 1973. Emphasis has been placed upon publications, which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, ceramometallic restorations and resin-bonded bridges, ceramics, denture base resins and soft lining materials, impression materials, dental implant materials, orthodontic materials, biomechanics and image processing, resin composites, and casting investment materials and waxes). Three hundred and thirty three articles have been reviewed.

Invasive cervical resorption following trauma

Invasive cervical resorption is an insidious and often aggressively destructive form of external root resorption which may occur as a late complication following dental trauma particularly where it involves damage to cementum and supporting tissues. While this resorption may be evident clinically as a pink coronal discolouration, later with cavitation of the enamel, often there are no obvious external signs and the condition is only detected radiographically. It is characterised by the invasion of the cervical region of the root by fibrovascular tissue which progressively resorbs dentine, enamel and cementum. The dental pulp remains protected by an intact layer of dentine and predentine until late in the process. Ectopic calcifications can be observed in advanced lesions both within the invading fibrous tissue and deposited directly onto the resorbed dentine surface. The aetiology of invasive cervical resorption is unknown but trauma has been documented as a potential predisposing factor. A recent study by the author of 222 patients with a total of 257 teeth which displayed varying degrees of invasive cervical resorption showed that trauma alone was a potential predisposing sole factor in 14% of patients and 15.1% of teeth. Trauma in combination with bleaching, orthodontics or delayed eruption was found in an additional 11.2% of patients or 10.6% of teeth and of these a combination of trauma and bleaching occurred in a relatively high proportion of 7.7% of patients or 7.4% of teeth. This study also revealed that of other potential predisposing factors orthodontics was the most common sole factor constituting 21.2% of patients and 24.1% of teeth examined. Successful treatment of invasive cervical resorption is dependent on the extent of the resorptive process. Teeth with invasive cervical resorption have been divided into four classes. Whilst several treatment modalities are possible, a clinical evaluation of the treatment of this condition by the topical application of a 90% aqueous solution of trichloracetic acid, curettage, endodontic therapy where necessary and restoration with a glass ionomer cement has been evaluated on 94 patients with a total of 101 teeth with a minimum follow-up period of three years. Results indicate a satisfactory treatment outcome can be anticipated in Class 1, 2 and 3 cases. In Class 4 resorption no treatment or alternative therapy is recommended. Diagnosis of lesions at an early stage of development is highly desirable and therefore the patients who have a potential for the development of this condition by virtue of a history such as trauma should be monitored radiographically at intervals throughout life.

A quantitative comparison of traditional and non-peroxide bleaching agents

Single-rooted premolar teeth, stained with blood utilizing the technique devised by Freccia & Peters (1981), were subjected to traditional and non-peroxide bleaching agents. Colour changes were recorded over a period of 7 days using a Speedmaster R75-CP Reflection Densitometer. The most efficient removal of staining occurred after the application of 30% hydrogen peroxide, with sodium perborate being 75% as effective. All bleaching agents realized their optimum efficacy within the first 3 days. A combination of three enzymes (amylase, lipase and trypsin) with disodium edetate was not as effective as the routine bleaching agents; however, the combination did have a modifying effect on the blood stains. It is suggested that other non-peroxide agents should be investigated to determine their efficacy in removing staining from experimentally induced blood-stained teeth.