Photodynamic Treatment of Oral Squamous Cell Carcinoma Cells with Low Curcumin Concentrations

Objective: Curcumin is known for its anti-oxidative, anti-inflammatory and anti-tumorigenic qualities at concentrations ranging from 3.7µg/ml to 55µg/ml. Therefore it is pre-destined for tumour therapy. Due to high oral doses that have to be administered and the low bioavailability of curcumin new therapy concepts have to be developed. One of these therapy concepts is the combination of low curcumin concentrations and UVA or visible light. Aim of our study was to investigate the influence of this treatment regime on oral squamous cell carcinoma cells. Materials and Methods: A human oral squamous cell carcinoma cell line (HN) was pre-incubated with low curcumin concentrations (0.01µg/ml to 1µg/ml). Thereafter cell cultures were either left un-irradiated or were irradiated either with 1J/cm² UVA or for 5min with visible light. Quantitative analysis of proliferation, membrane integrity, oxidative potential and DNA fragmentation were done. Results: It could be shown that low curcumin concentrations neither influenced proliferation, nor cell morphology, nor cell integrity nor apoptosis. When combining these curcumin concentrations with UVA or visible light irradiation cell proliferation as well as development of reactive oxygen species was reduced whereas DNA fragmentation was increased. Concentration as well as light entity specific effects could be observed. Conclusions: The present findings substantiate the potential of the combination of low curcumin concentrations and light as a new therapeutic concept to increase the efficacy of curcumin in the treatment of cancer of the oral mucosa.

Influence of Biodentine® - A Dentine Substitute - On Collagen Type I Synthesis in Pulp Fibroblasts In Vitro

Preserving a patient’s own teeth—even in a difficult situation—is nowadays preferable to surgical intervention and therefore promotes development of suitable dental repair materials. Biodentine^®, a mineral trioxide aggregate substitute, has been used to replace dentine in a bioactive and biocompatible manner in both the dental crown and the root. The aim of our study was to evaluate the influence of Biodentine^® on pulp fibroblasts in vitro. For this study, one to five Biodentine^® discs with a diameter of 5.1mm were incubated in DMEM. To obtain Biodentine^® suspensions the media were collected and replaced with fresh medium every 24h for 4 days. Primary pulp cells were isolated from freshly extracted wisdom teeth of 20–23 year old patients and incubated with the Biodentine^® suspensions. Proliferation, cell morphology, cell integrity and cell viability were monitored. To evaluate the effect of Biodentine^® on collagen type I synthesis, the secretion of the N-terminal domain of pro-collagen type I (P1NP) and the release of transforming growth factor-β1 (TGF-β1) were quantified. None of the Biodentine^® suspensions tested influenced cell morphology, proliferation or cell integrity. The cell viability varied slightly depending on the suspension used. However, the concentrations of P1NP of all pulp fibroblast cultures treated for 24h with the moderate to high Biodentine^® concentration containing suspensions of day 1 were reduced to 5% of the control. Furthermore, a significant TGF-β1 reduction was observed after treatment with these suspensions. It could be shown that Biodentine^® is biocompatible. However, dissolved particles of the moderate to high concentrated Biodentine^® suspensions 24h after mixing induce a significant reduction of TGF-β1 release and reduce the secretion of collagen type I of primary pulp fibroblasts.

Fracture resistance and failure mode of endodontically treated teeth restored using ceramic onlays with or without fiber posts-an ex vivo study

AIM

This study aimed to compare the fracture resistance and fracture modes of ceramic onlay restorations with or without fiber posts in endodontically treated premolars.

MATERIAL AND METHODS

Fifty extracted human premolars with similar anatomic features were used in this study. Four groups (n = 10) were treated endodontically. Onlay cavities extended to the buccal and palatal cusps and reached out the endodontic accesses were prepared. Ceramic onlay restorations with or without fiber posts were categorized as Group CO (ceramic onlays without posts), Group COQF (ceramic onlays and quartz fiber posts), and Group COGF (ceramic onlays and glass fiber posts). Positive control group was left as non-restored (Group NR). Ten intact teeth were stored as negative control group (Group IT). Fracture resistance was measured using a universal load-testing machine applying compressive load at a crosshead speed of 1 mm min(-1) until fracture. Fracture resistance and modes were evaluated statistically.

RESULTS

Ceramic onlay restorations (Groups CO, COQF, COGF) increased the fracture resistance significantly, when compared with non-restored teeth (P < 0.05). However, no significant differences were found in the groups with fiber posts in terms of fracture resistance (P > 0.05). Negative control group (IT) had significantly higher fracture resistance than all others (P < 0.05). Fracture types had significant differences among the groups (P < 0.01).

CONCLUSIONS

Within the limitations of this ex-vivo study, partial coverage with ceramic onlays resulted in a significant improvement of the fracture resistance of endodontically treated premolars. However, insertion of glass or quartz fibers did not increase the fracture resistance significantly.

Vertical root fracture: prevalence, etiology, and diagnosis

A vertical root fracture (VRF) is a frustrating complication that may occur following root canal treatment, and in almost every case leads to the extraction of the affected tooth. This type of fracture is usually diagnosed by secondary symptoms that develop some time after primary treatment, often when prosthodontic restoration has already been completed. The fracture line itself is often not directly visible, and therefore clinical and radiographic signs and symptoms indicate the diagnosis indirectly. Knowledge of the condition and pathogenesis of VRF is required in order to avoid hopeless trials of periodontal and/or endodontic therapy. Several etiologic factors are discussed that make teeth susceptible to VRF, such as the loss of substance due to restorative and endodontic therapy and stress factors associated with root canal debridement, and filling.

Syntheses and characterization of salts with the [Al(D)4F2]+ cation (D = pyridine or water)

Our approach for preparation of tetrakis-(pyridine)-difluoro-aluminum chloride was successfully deployed for the synthesis of corresponding Br and I compounds, respectively. By reacting AlX(3)·3Py (X = Cl, Br, I) with Me(3)SiF in pyridine, two of the three halogens X were substituted by fluorine atoms forming the "aluminum mixed halide" complexes AlF(2)X·4Py with the ionic solid-state structures [Al(Py)(4)F(2)]X. Whereas the (27)Al solid state NMR spectra of AlX(3)·3Py (X = Cl, Br) confirmed the existence of the expected singular σ(6)λ(3)-Al centers in their structures, the corresponding spectrum of AlI(3)·3Py does not contain any signal that belongs to a 6-fold coordinated Al atom. The elemental analysis data strongly support the 1:2-stoichiometry of the complex (AlI(3)·2Py), which in accord to the (27)Al MAS NMR spectra possessed only one σ(4)λ(3)-Al side as in the ionic structure [Al(Py)(2)I(2)]I. AlBr(3)·3Py was also transformed by pyridine into the ionic complex [Al(Py)(4)Br(2)]Br. The later was isolated from pyridine solutions, and its structure was determined by X-ray single crystal analysis. On the basis of our results, solvated [Al(Py)(n)X(2)](+) cations are most probably the dominating species in pyridine solutions of AlX(3). Thus, only two Al-X covalent bonds underwent X/F- exchange and the halogen exchange reactions were terminated at " [Al(Py)(4)F(2)](+) stage". The hydrolysis of [Al(Py)(4)F(2)]Cl by very diluted hydrochloric acid in methanol proceeded smoothly under preservation of the Al-F bonds and displacement of pyridine by water. The formation of the stable helical trans-octahedron [Al(H(2)O)(4)F(2)](+) cation was confirmed by single-crystal XRD analysis. By reacting [Al(Py)(4)F(2)]Cl with the cyclo-n-propyl-phosphonic acid anhydride [CH(3)CH(2)CH(2)-PO(2)](3), an unexpected F-migration from Al- to P- atoms was observed.

Influence of femtosecond laser treatment on shear bond strength of composite resin bonding to human dentin under simulated pulpal pressure

This in vitro study evaluated the influence of femtosecond laser (fs-laser)-generated patterns on shear bond strength (SBS) of composite resin bonded to human dentin under simulated pulpal pressure. Laser treatment was used to produce two different patterns on dentin surfaces. Three test groups and a control group without laser treatment under pulpal pressure were investigated. Dentin discs of 800 nm thickness were cut from 60 extracted caries-free human molars. Using a perfusion machine, the discs were exposed to Ringer solution on their basal surfaces. Clearfil SE Bond/Herculite XRV system was used. The samples were stored in distilled water and thermocycled. Bonding failures caused by a test set-up to challenge SBS were analyzed by scanning electron microscope (SEM). An 80 μm-sized cube-shaped pattern caused more cohesive failures in dentin or resin compared with the 160 μm-sized cube-shaped pattern. Weibull statistics demonstrated a significant difference between the two laser patterns, but only the test group with small-sized laser pattern was significantly different from the control group. The Weibull moduli ranged from 4.3 to 9.6 (control group). The 160 μm-sized pattern enhanced the bonding quality and avoided dentin weakening. It was concluded that fs-laser treatment in a 160 μm-sized cube-shaped pattern enabled a simplified bonding procedure by dispensing the primer without affecting SBS, compared with the control group.

[German dental and postgraduate education in the European context]

The dental curriculum in Germany is still based on a concept from 1955 with some revisions in certain aspects. All groups involved are interested in a new and more current version. In doing this, the compatibility with European concepts should be a main goal. The Association for Dental Education in Europe (ADEE), to which about 160 of the 200 European dental education associations are members, is in charge of coordinating projects to create a network of European universities, which intends to harmonize higher education in Europe and to create a core curriculum for the dentistry program. Based on a visitation and evaluation program at more than 50 oral and maxillofacial surgery centers, a paper for the profiles and competencies for future European dentists was formulated for the creation of a modular curriculum, for the integration of the ECT (European Credit Transfer) system, and for quality assurance of the dentistry curriculum. Especially for the situation in Germany, consequences must be drawn for further dentistry and postgraduate educational concepts, which are not completely identical with the ADEE concepts, but which can use elements of the basic Bologna concepts.

Repair versus replacement of defective composite restorations in dental schools in Germany

The aim of this paper was to review the current teaching of repairs to direct composite restorations in dental schools in Germany, last surveyed ten years ago. Based on an 83% response rate, the findings indicate that most, but not all, dental schools included teaching of repair techniques; however marked variations were found to exist regarding clinical indications and repair techniques of the teaching. It is suggested that certain aspects of the existing teaching in some schools should be reviewed, specifically the lack of use of a bonding agent and the issue of flowable composites to complete repairs.

F/Cl-Exchange on AlCl3-Pyridine Adducts: Synthesis and Characterization of trans-Difluoro-tetrakis-pyridine-aluminum-chloride, [AlF2(Py)4]+Cl-

Whereas liquid CCl3F reacts with solid AlCl3 exothermically under chlorine-fluorine-exchange already above -20 degrees C, no reaction takes place between CCl3F and the pyridine complexes of AlCl3 (AlCl3.Py, AlCl3.2Py, or AlCl3.3Py) up to 100 degrees C. The desired chlorine by fluorine substitution on the monomer AlCl3-pyridine adducts occurs, however, easily using Me3SiF as fluorinating agent. By reacting AlCl3.3Py with Me3SiF (even up to 10-fold stoichiometric excess) in pyridine as a solvent, only two of the three Cl atoms can be substituted by fluorine, leading in good yield to the new "mixed aluminum halide", AlF2Cl.4Py. Actually, it represents the first example of a stable solid donor-acceptor adduct of an aluminum-III halide with two different halogens of defined stoichiometry. It was characterized by multinuclear solid-state NMR (27Al and 19F), IR spectroscopy, as well as single-crystal structure analysis. The new compound has an ionic solid-state structure with helical trans-octahedral [(Py)4AlF2]+ cations and isolated Cl- anions. The comparison of its 27Al MAS solid-state NMR spectra with those of a compound bearing the analogous [(Py)4AlCl2]+ cation reveals an extreme increase in the quadrupolar coupling constants, from 0.24 MHz in case of the chlorine cation to about 16 MHz in case of the new [(Py)4AlF2]+ cation.

The value of examination aids in victim identification: a retrospective study of an airplane crash in Nepal in 2002

After the crash of an airplane in Nepal in the year 2002, the dental status of the 14 European victims was examined at autopsy as well as after additional removal of the soft tissue and compared with antemortem findings which were available in 11 cases. Re-examination of all jaws showed that nine composite fillings and seven root fillings as well as one parapulpal pin could not be detected during autopsy. Because tooth-coloured restorations may be overseen even by an experienced expert, the findings underline the necessity of performing a full resection of both jaws and removal of the soft tissue. Furthermore, X-ray analysis of the jaws and the use of phosphoric acid or ultra violet radiation for recognizing tooth-coloured restorations are recommended.

The repair of direct composite restorations: an international survey of the teaching of operative techniques and materials

This article reports the findings of a study on the aspects of the teaching of repair as a conservative alternative to the replacement of failing direct composite restorations (DCRs) in primary dental degree curricula in the UK and Ireland, Germany and Scandinavia. Data on teaching, including operative techniques applied in the repair of DCRs, were collected by means of a questionnaire sent to 58 dental schools in the surveyed countries. Based on the overall response rate of 83%, the findings indicate that the majority (59%) of the schools in the countries surveyed may be found to teach the repair of DCRs. However, marked variations were observed in respect of this teaching and the expected longevity of repaired DCRs. Where the repair of DCRs was not taught, views differed as to the intentions, if any, to include this teaching in the curriculum. It is concluded that the teaching of DCRs may be found to be widespread in dental schools in the UK and Ireland, Germany and Scandinavia, with this teaching being subjected to considerable variation within and between countries.

Comparison of microleakage on one composite etched with phosphoric acid or a combination of phosphoric and hydrofluoric acids and bonded with several different systems

STATEMENT OF PROBLEM

There are no data available on whether or to what extent hydrofluoric acid affects the marginal integrity of dentin-bonded composite restorations when it is used instead of phosphoric acid in the total-etch technique.

PURPOSE

This in vitro study examined the etching effects of phosphoric acid versus a combination of phosphoric and hydrofluoric acid by evaluation of microleakage in a composite restoration bonded with different dentin adhesive systems.

MATERIAL AND METHODS

Extracted teeth (n = 90) containing 2 class II preparations, mesial occlusal (MO) and distal occlusal (DO) standarized (cervical margins in dentin) were perfused with Ringer solution and etched in 1 of 2 ways: with phosphoric acid only or with phosphoric combined with hydrofluoric acid. Different dentin bonding agents were then applied (Etch & Prime 3.0, Optibond Solo, Prime & Bond NT, Scotchbond 1, Syntac Single Component, or Syntac Sprint; (n = 15 for each etching material)). The preparations were restored with a hybrid composite (Herculite XRV) and submitted to 5000 thermocycles (5 degrees C to 55 degrees C) to simulate the in vivo situation. Microleakage was assessed with 2% methylene blue diffusion for 24 hours. Dye penetration was calculated as a percentage of the total length of the gingival margins of the preparation with light microscopy at original magnification x 32. The results were analyzed with the Kruskal-Wallis multiple comparison z-value assay (alpha = .05).

RESULTS

Differences in dye penetration were significant, both as a function of the dentin adhesive and the conditioning mode applied. In the specimen groups conditioned with phosphoric acid, Optibond Solo (54% +/- 44%) and Syntac Sprint (74% +/- 39%) demonstrated the lowest penetration values. Higher values were obtained for Prime & Bond NT (81% +/- 34%), Scotchbond 1 (83% +/- 31%), Etch & Prime 3.0 (85% +/- 33%), and Syntac Single Component (95% +/- 16%), with no significant differences (alpha=.05) between specimen groups. The best results were obtained for Syntac Sprint (24% +/- 26% dye penetration) after conditioning with a mixture of phosphoric and hydrofluoric acid. The least favorable result was obtained for Optibond Solo (65% +/- 31%). It was significantly different from Prime & Bond NT (76% +/- 37%), Scotchbond 1 (85% +/- 29%), and Etch & Prime 3.0 (88% +/- 24%). Syntac Single Component (75% +/- 32%) was significantly different from Syntac Sprint. Syntac Single Component and Syntac Sprint exhibited significantly better results when conditioned with a combination of phosphoric acid and hydrofluoric acid than with phosphoric acid only.

CONCLUSION

Within the limitations of this in vitro study, total-etching water-based (Syntac Single Component) and acetone-based (Syntac Sprint) bonding agents with a combination of phosphoric acid and hydrofluoric acid led to significant reductions (alpha=.05) in dye penetration compared to phosphoric acid conditioning only. Ethanol-based dentin bonding agents (Etch & Prime 3.0, Optibond Solo, and Scotchbond 1) were not significantly influenced by the type of conditioner used.

In vitro cytotoxicity of medicated and nonmedicated gutta-percha points in cultures of gingival fibroblasts

This investigation was designed to test the cellular toxicity of two medicated (Roeko activ point and Roeko Calcium Hydroxide) and four nonmedicated brands of gutta-percha (GP) points (Antaeos, DeTrey White, Roeko color, and Roeko Top color). The test points were transferred into a culture medium including the GP-point material with a concentration of 6 mg/ml, and eluates were obtained after 72 h. Five milliliters of each eluate were pipetted onto fibroblast cultures, incubated, and subsequently stained. Mitotic rates, cell densities, and the distribution of normal cells, pathologically altered and dead cells were determined and correlated with control cell cultures. Roeko activ point (containing chlorhexidine) resulted in the highest number of dead cells. The difference was statistically significant in comparison with all other materials. Concerning all parameters mentioned, the cytotoxicity of the points containing calcium hydroxide (Roeko Calcium Hydroxide) was not significantly different from all other points tested, with the exception of those containing chlorhexidine. All tested gutta-percha materials caused cytotoxic reactions in varying extents. Taking into consideration the limitations of an in vitro experiment, points containing calcium hydroxide and nonmedicated points seem to be the most recommendable products for clinical use.

Effect of the silicone disclosing procedure on the shear bond strength of composite cements to ceramic restorations

STATEMENT OF PROBLEM

There is no evidence-based information on how ceramic restorations with an adhesive bond between restoration material and composite cement may be influenced by a silicone disclosing agent.

PURPOSE

The aim of this study was to determine the effects of the silicone disclosing procedure on the shear bond strength of composite cements in the luting of industrial sintered and laboratory sintered ceramic restorations.

MATERIAL AND METHODS

Thirty standardized (15 x 10 x 9 mm) prefabricated ceramic specimens (Groups 1, 3, 5) and 30 standardized (15 x10 x 9 mm) conventionally sintered ceramic specimens (Groups 2, 4, 6) were roughened with sandpaper (800-grit). Each group contained 10 specimens. Groups 3 and 4 were conditioned with hydrofluoric acid and primed with silane solution after the use of a silicone disclosing procedure. Groups 1 and 2 served as the control groups, where no silicone disclosing procedure was performed. Groups 5 and 6 were insulated with glycerine before the silicone disclosing procedure. A glass tube (4.5 mm in diameter) was used to apply a cylinder of dual-polymerized composite cement to the conditioned surfaces. All specimens were submitted to 5000 thermocycles (5 degrees to 55 degrees C) to simulate the in vivo situation. The specimens were subjected to a shear-pull test at a constant crosshead speed of 5 mm/min with a universal testing machine. The comparative shear bond strengths were analyzed by use of Duncan's test (alpha=0.05).

RESULTS

Shear bond strength values for Groups 1 (9.86 +/- 4.97 MPa) and 2 (9.56 +/- 4.47 Mpa) were obtained with no significant differences. Lower but significantly undifferent values were obtained for Groups 3 (7.49 +/- 4.67 MPa) and 4 (7.62 +/- 3.49 MPa) after the use of a silicone disclosing procedure. In Groups 5 (8.21 +/- 4.75 MPa) and 6 (8.22 +/- 3.59 MPa), including insulation with glycerine before the silicone disclosing procedure, no significant differences were obtained.

CONCLUSION

Within the limitations of this study, the use of silicone disclosing procedures before conditioning the ceramic surface did not lead to a significant reduction of the shear bond strength between ceramic and composite cement. The ceramic materials used (industrial-sintered versus laboratory-sintered ceramic) had no significant influence on adhesion.

Defective direct composite restorations--replace or repair? A survey of teaching in Scandinavian dental schools

A questionnaire based survey was undertaken in Scandinavian dental schools to investigate aspects of the teaching of the repair of failing direct composite restorations, as a conservative alternative to total restoration replacement. The findings indicate that all undergraduate students in Scandinavian schools are taught and gain clinical experience in the repair of direct composite restorations. Although the findings reveal general agreement in relation to the teaching of reasons and operative procedures for the repair of direct composite restorations, variations were found in relation to the teaching of indications for, and the expected longevities of such repairs.

Repair versus replacement of defective direct composite restorations in teaching programmes in United Kingdom and Irish Dental Schools

The teaching of the repair of direct composite restorations has been surveyed in United Kingdom and Irish dental schools. Based on a 100% response rate, the findings indicate that the vast majority of undergraduate students in United Kingdom and Irish dental schools are taught and gain clinical experience in the repair of direct composite restorations. There is general conformity with respect to the teaching in relation to operative techniques and materials used.

Removal of amalgam, glass-ionomer cement and compomer restorations: changes in cavity dimensions and duration of the procedure

This study investigated changes in the dimensions of Class II cavities following the removal of amalgam, glass ionomer and compomer restorations. In 30 extracted caries-free human molars, preparation for 60 mesio-occlusal and occluso-distal cavities (two cavities per tooth) occurred. With a CEREC 3 laser triangulation sensor and software-based construction analysis, the dimensions of the cavities at seven defined sites were measured. The cavities were randomized into four groups. Group 1 was restored with Ketac-Fil glass-ionomer cement, Group 2 with amalgam and Group 3 with Compoglass F compomer. In Group 4, Compoglass F was used in combination with photochromic Tetric Flow Chroma as a cavity liner. The completed restorations were then removed using 2x magnification and the cavities were once again controlled using the laser system. The duration of the removal procedure was also recorded. Changes in cavity dimensions (depth, height and width) following removal of the restorations were significantly smaller in Groups 1 and 2. Groups 3 and 4 were characterized by a significant overextension of the cavities compared to Groups 1 and 2 in all three dimensions. Group 4, with Tetric Flow Chroma as a cavity liner, showed better results than Group 3, but this improvement was not statistically significant. The duration of the removal procedure was significantly shorter in Group 2 than in the other groups.

Hemisection for treatment of an advanced endodontic-periodontal lesion: a case report

AIM

To emphasize the importance of primary endodontic treatment when dealing with endo-perio lesions and to demonstrate the considerable healing potential of the endodontic aspect.

CASE REPORT

After several years of unsuccessful symptomatic periodontal treatment, an advanced endo-perio lesion on a right-mandibular first molar was successfully treated by root-canal treatment and hemisection after the re-evaluation of the lesion. This successful treatment appeared to have a positive effect on the patient's general well-being.

KEY LEARNING POINTS

The origin of a combined endo-perio lesion is indicated by its clinical and radiographic appearance. The periodontal situation is often misinterpreted. The prognosis for the endodontic element of treatment is excellent. Local pathologic processes in the oral cavity may affect a patient's general health.

Cytotoxicity of modern dentin adhesives--in vitro testing on gingival fibroblasts

The present investigation was designed to test cellular toxicity of modern dentin adhesives. With the use of the products Ariston Liner, Etch & Prime 3.0, Optibond Solo, Prime & Bond NT, Scotchbond 1, and Syntac Sprint, test specimens were prepared according to the manufacturers' instructions and transferred into a culture medium. Eluates were obtained and pipetted onto fibroblast cultures, incubated, and subsequently stained. The respective cell densities and the numbers of normal, altered, and dead cells were determined and compared with control cell cultures. Statistical analysis of the data showed that all materials caused cytotoxic effects. Scotchbond 1 displayed the highest number of dead cells. The difference was statistically significant compared to Etch" 3.0, Optibond Solo, Prime&Bond NT, and the control. The lowest cell density was found for Scotchbond 1 and Ariston Liner. The difference was also statistically significant in comparison with Etch" 3.0, Optibond Solo, Prime&Bond NT, and the control. To conclude, all tested dentin adhesives caused cytotoxic reactions. Taking the limitations of an in vitro experiment into consideration, Prime&Bond NT, Optibond Solo, and Etch" 3.0 appear to be the most recommendable products, and Scotchbond 1 and Ariston Liner the least.

Influence of rubber-dam on the reconstruction of proximal contacts with adhesive tooth-colored restorations

PURPOSE

To clinically measure the influence of rubber-dam on the proximal contact strength after its reconstruction with tooth-colored restorations.

MATERIALS AND METHODS

The frictional forces during the removal of a metal strip from the proximal contact area were taken as measure for the proximal contact strengths of 46 restorations (35 ceramic inlays, 11 direct composite restorations). The teeth were separated with a rubber-dam and wedged thoroughly during the complete reconstruction procedure according to the multiple wedging technique. The proximal contact strengths were measured immediately before and immediately after removing the rubber-dam.

RESULTS

The contact strengths were statistically significantly lower immediately after the removal of the rubber-dam (1.07+/-0.82N) compared to the situation with the rubber-dam (1.99+/-1.21N). The amount of the reduction after removing the rubber-dam was statistically significantly higher between the second premolar and the first molar (1.45+/-1.06N) compared to the contacts between the canines and the first premolar (0.32+/-0.44N) and the first and second premolar (0.59+/-0.77N). No influence of the restorative material, the use and localization of retainers, localization of the restoration, or number of teeth under the rubber-dam was detectable.

CONCLUSION

Rubber-dam is recommended for adhesive restorations as it is helpful for achieving good adhesion between the tooth and restorative materials. Nevertheless, the application of rubber-dam seems to be a factor which complicates the reconstruction of adequate proximal contacts.

Comparative study of composite resin placement: centripetal buildup versus incremental technique

An in vitro study was performed to evaluate the effect of two different proximal restoration techniques with different matrix systems on the marginal seal and microhardness of Class II composite restorations. Results indicated that the lowest, however, not significantly different, microleakage was achieved in totally bonded deep Class II restorations prepared with margins surrounded by enamel when using transparent matrices and reflective wedges in combination with the centripetal buildup technique. Highest surface hardness of composite resin was related to transparent matrices and reflecting wedges.

Preparation of severely curved simulated root canals using engine-driven rotary and conventional hand instruments

This in vitro study evaluated the efficacy and safety of six different nickel-titanium engine-driven instruments used with a torque-controlled engine device and nickel-titanium hand and stainless steel hand instruments in preparation of curved canals. A total of 80 curved (36 degrees) simulated root canals were prepared. Images before and after were superimposed, and instrumentation areas were observed. Time of instrumentation, instrument failure, change in working length and weight loss were also recorded. Results show that stainless steel hand instruments cause significantly less transportation towards the inner wall of the canal than do nickel-titanium hand instruments. No instrument fracture occurred with hand instruments, but 30-60% breakage of instruments was recorded during instrumentation with the engine-driven devices. The working length was maintained by all types of instruments. Newly developed nickel-titanium rotary files were not able to prevent straightening of the severely curved canals when a torque-controlled engine-driven device was used.

In vitro dentinal surface reaction of 9.5% buffered hydrofluoric acid in repair of ceramic restorations: a scanning electron microscopic investigation

STATEMENT OF PROBLEM

Fracture of porcelain is a relatively common clinical misfortune. Recent research has indicated that strong bonds can be formed between composite and dental porcelain. Porcelain surfaces are etched with hydrofluoric acid and treated with silane coupling agents before composite application. The question is how exposed dentin may react to etching with hydrofluoric acid.

PURPOSE

This investigation examined the effect of 9.5% buffered hydrofluoric acid, of 36% o-phosphoric acid alone and in combination on the surface structure of cut human dentin.

MATERIAL AND METHODS

Human molar teeth were sectioned in approximately 0.8-mm thick slices and treated with different acids or their combinations. Application periods were 10, 60, and 180 seconds. Specimens were processed for SEM and for energy-dispersive x-ray (EDX) microanalysis.

RESULTS

The smear layer on the surface of sectioned dentin was not completely removed by hydrofluoric acid alone and that a dense amorphous precipitate was formed on the peritubular zone. Starlike structures in dentinal tubules were visible. EDX analysis revealed different fluoride content on the treated surface, dependent on the etchant used.

CONCLUSION

Topical application of hydrofluoric acid appeared to provide a dentinal surface with an amorphous precipitate of fluoride. This layer may be important both for resistance of dental caries in dentin and for bonding reactions.

Tooth-colored restorations of posterior teeth in German dental education

Optimizing the quality of tooth-colored restorations is one of the main topics of current research. But there is only little information available about university education in this field. The aim of this study was to collect and evaluate data about the different aspects of dental education in Germany concerning tooth-colored restorations. Based on the response to a questionnaire from 90% of all German dental schools in the fall of 1997 a detailed survey is given of the utilization, indications, practical procedure, problems and limitations of both direct and indirect tooth-colored restorations done by students. The results indicate a wide-spread use of directly inserted composite for posterior teeth in the different education programs. Indeed, the preferred preparation of the cavity margin differs from school to school. Rebuilding an adequate proximal contact and a precise fit at the gingival margin are looked upon as the main problems of class II composite fillings. Ceramic inlays are mainly inserted by students in advanced clinical courses with the insertion procedure being claimed as the main problem of this technique. The findings of this study mostly show the same limitations and difficulties of tooth-colored restorations in education as found by research. Partly different teaching concepts are reflected in the differing scientific results.

Erbium:YAG laser application in caries therapy. Evaluation of patient perception and acceptance

OBJECTIVES

In previous studies it has been demonstrated that the Er:YAG laser can be used to prepare cavities efficiently and without thermal damage to the adjacent dental hard and soft tissues. To investigate the patients' response to Er:YAG laser preparation of teeth, a prospective clinical study was performed in five dental hospitals.

METHODS

To evaluate patients' perception and response to cavity preparation a direct comparison was made between conventional mechanical preparation and Er:YAG laser preparation of caries in dental hard tissues. Half of the preparations were completed by the laser alone with standardized parameters, with the other half being mechanically prepared. The sequential order of treatment was randomized, and clinical parameters such as depth and location of the cavities were carefully balanced. A three-score evaluation scheme of patient responses was used: comfortable, uncomfortable, very uncomfortable. In addition the patients were asked to decide which was the more uncomfortable form of treatment and the preferred treatment for future caries therapy.

RESULTS

The study included 103 patients with 206 preparations distributed amongst 194 teeth. All teeth gave vital responses (ice test) before and after both types of treatment. The laser treatment was found to be more comfortable than the mechanical treatment, with high statistical significance. During treatment, the need for local anaesthesia was 11% for mechanical preparation compared to 6% during laser application. It was found that 80% of the patients rated the conventional preparation as more uncomfortable than the laser treatment and 82% of the patients indicated that they would prefer the Er:YAG laser preparation for further caries treatment.

CONCLUSIONS

The application of the Er:YAG laser system is a more comfortable alternative or adjunctive method to conventional mechanical cavity preparation.