Influence of apical enlargement in cleaning of curved canals using negative pressure system.

This study aimed to evaluate, by scanning electron microscopy (SEM), the cleaning of canal walls with moderate curvature subjected to biomechanical preparation with different final diameters using apical negative pressure irrigation. Thirty-two mesiobuccal roots of molars were divided into 4 groups (n=8) according to the instrument's final diameter: GI: 30.02, GII: 35.02, GIII: 40.02 and GIV: 45.02. Irrigating procedure was performed at each change of instrument with 1% NaOCl using the Endovac system. Final irrigation was conducted with 17% EDTA for 5 min. The SEM photomicrographs were evaluated under 35× and 1000× magnification, by three calibrated examiners, in a double-blind design. Data were submitted to Kruskal-Wallis and Dunn's post hoc tests (α=0.05). Canals instrumented with 30.02 and 35.02 final diameters showed more debris, statistically different from the other groups (p<0.05). Comparing each root canal third, for the cervical and apical portions no statistically significant difference (p>0.05) was found among the four groups. Regarding the presence of smear layer, canals with 30.02 final diameter showed the highest scores, statistically different from the 45.02 group (p<0.05) and similar to the 35.02 and the 40.02 groups (p>0.05). Although none of the studied diameters completely removed debris and smear layer, it may be concluded that instrumentation with higher final diameters was more effective in cleaning the root canals with moderate curvature.

Dental preparation with sonic vs high-speed finishing: analysis of microleakage in bonded veneer restorations.

PURPOSE: To compare marginal microleakage in porcelain veneer restorations following dental finishing using two types of instruments to test the hypothesis that microleakage will be less when teeth are prepared with sonic oscillating burs than when prepared with high-speed rotating burs. MATERIALS AND METHODS: Fifty-six extracted human maxillary central incisors were selected and divided randomly into two groups. Group 1 samples underwent dental finishing using high-speed rotating diamond burs, while group 2 used sonic oscillating diamond burs. Buccal chamfer preparation was carried out for both groups. Forty eight of the samples (24 per group) were restored using IPS Empress ceramic veneers. 2% methylene blue was used to evaluate microleakage at the tooth/composite veneer interface. Teeth were sectioned lengthwise into three parts and microleakage was measured at two points - cervical and incisal - on each section. Before bonding, four teeth per group underwent SEM examination. RESULTS: Evaluation of microleakage at the cervical dentin margin showed a value of 10.5% in group 1 and 6.6% in group 2, which was statistically significantly different (p < 0.05). Incisal microleakage was 1.3% for group 1 and 1.2% for group 2, which was not significantly different. SEM revealed different patterns of surface texture in both areas according to the instrument used. Group 1 exhibited parallel horizontal abrasion grooves with a milled effect and thick smear layers; group 2 showed abrasive erosion, discontinuous perpendicular depressions, and thin smear layers. CONCLUSION: Tooth preparations finished with sonic burs produced significantly less microleakage in the cervical dentin area of bonded veneer restorations. No differences were found in the incisal enamel area.

Scanning electron microscopic analysis to compare the cleaning efficiency of three different irrigation systems at different root canal levels: an in vitro study.

AIM: This study compared the efficacy of conventional, endovac and ultrasonic irrigation system for the removal of debris from root canal walls, using scanning electron microscopy (SEM) at cervical, middle and apical 3rd. MATERIALS AND METHODS: A total of 30 freshly extracted human mandibular premolars with complete root formation were selected and divided into group 1 endovac, group 2 conventional and group 3 ultrasonic. After instrumentation and irrigation, the teeth were sectioned in buccolingual direction and analyzed by SEM and the results were analyzed statistically by students unpaired 't' test. RESULTS: There was significant difference between mean values of cervical (CV), middle (M), and apical (A) when endovac compared with conventional and conventional compared with ultrasonic group (i.e. < 0.05) and no significant difference between mean values at CV, M and A when endovac compared with ultrasonic group. CONCLUSION: Among all groups ultrasonic and endovac group showed cleaner canal walls and less amount of debris than conventional group. CLINICAL SIGNIFICANCE: Application of ultrasonic and endovac can be used effectively for irrigation of canals leading to least debris and better prognosis.

Deficiency in acellular cementum and periodontal attachment in bsp null mice.

Bone sialoprotein (BSP) is an extracellular matrix protein found in mineralized tissues of the skeleton and dentition. BSP is multifunctional, affecting cell attachment and signaling through an RGD integrin-binding region, and acting as a positive regulator for mineral precipitation by nucleating hydroxyapatite crystals. BSP is present in cementum, the hard tissue covering the tooth root that anchors periodontal ligament (PDL) attachment. To test our hypothesis that BSP plays an important role in cementogenesis, we analyzed tooth development in a Bsp null ((-/-)) mouse model. Developmental analysis by histology, histochemistry, and SEM revealed a significant reduction in acellular cementum formation on Bsp (-/-) mouse molar and incisor roots, and the cementum deposited appeared hypomineralized. Structural defects in cementum-PDL interfaces in Bsp (-/-) mice caused PDL detachment, likely contributing to the high incidence of incisor malocclusion. Loss of BSP caused progressively disorganized PDL and significantly increased epithelial down-growth with aging. Bsp (-/-) mice displayed extensive root and alveolar bone resorption, mediated by increased RANKL and the presence of osteoclasts. Results collected here suggest that BSP plays a non-redundant role in acellular cementum formation, likely involved in initiating mineralization on the root surface. Through its importance to cementum integrity, BSP is essential for periodontal function.

In vitro evaluation of dentin tubule occlusion by Denshield and Neodymium-doped yttrium-aluminum-garnet laser irradiation.

INTRODUCTION: This in vitro study evaluated the efficacy of bioglass (Denshield; Novamin Technology, Alachua, FL) and Neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser irradiation on dentinal tubuli orifice occlusion (DOO) by comparing samples examined under environmental scanning electron microscope (ESEM) after applying each desensitizing approach separately and in combination. METHODS: Forty-eight human molars were collected, randomly organized in 4 equal groups, and had their cervical dentin exposed. Additionally, in half of the specimens of each experimental group, the smear layer was removed (subgroups A1, B1, C1, and D1). Group A received NovaMin paste treatment for 5 minutes (NM) to the experimental surface. Group B received Nd:YAG laser irradiation (0.5 w, 10 Hz, and 50 mJ) (L). Group C received NM followed by L. Group D was treated with L followed by NM. All specimens were stored for 24 hours and evaluated for DOO under ESEM by 4 blinded observers. RESULTS: The presence of a smear layer significantly contributed to DOO regardless of the treatment modality (ordinal logistic regression, P < .001). Compared with group A, all other treatments delivered significantly more occluded dentin orifices (P < .001 for groups B and D and P < .05 for group C). A layer formation was observed in subgroups C2 and D2. CONCLUSIONS: Under these experimental conditions, a smear layer was essential for successful DOO. Laser irradiation alone and combined with NovaMin proved superior to NovaMin alone on DOO. This combined approach has the potential to improve the outcome of treatment for cervical dentin hypersensitivity. The biological significance of this newly formed layer needs to be elucidated.

Chemical characterization of etched dentin in non-carious cervical lesions.

PURPOSE: Bonding to non-carious cervical lesion (NCCL) sclerotic dentin that involves acid etching continues to be a challenging problem due to its altered chemical structure. In the present study, the objective was to investigate the chemical response of NCCL sclerotic dentin to the different acid etching times. MATERIALS AND METHODS: Extracted human premolars affected with NCCLs were selected, and a cavity matching the natural lesion with respect to size and location was prepared on the lingual surface of each tooth to serve as the control. The dentin surfaces were treated for 15 s and 30 s using 37% phosphoric acid and then analyzed by Raman microspectroscopic mapping/imaging. RESULTS: NCCL dentin substrates had dramatic effects on the chemical profile of dentin demineralization. The spectral comparison showed that the demineralized layer generated by the acid treatment was highly irregular in terms of depth and mineral component retained, especially when NCCL sclerotic dentin was etched for 15 s. When the etching time was increased to 30 s, the demineralization of NCCL sclerotic dentin was more effective and comparable to the nonsclerotic control that was treated for 15 s. Different etching times affected the depth, degree, and profile of the dentin demineralization. CONCLUSION: The shorter etching time (ie, 15 s) might not be adequate for NCCL sclerotic dentin. However, the longer etching time (ie, 30 s) would induce much deeper demineralized dentin for nonsclerotic substrates. Thus, although extended etching times can be used to remove the hypermineralized layer, further studies are required to analyze the impact this might have on the dentin bonding.

Effect of desensitizing agents on the microtensile bond strength of a two-step self-etch adhesive to dentin.

The aim of this in vitro study was to evaluate the effect of cervical hypersensitivity treatments (neodymium yttrium aluminum garnet [Nd:YAG] laser and conventional techniques) on the microtensile bond strengths of adhesives to treated dentin. The buccal cervical enamel of 42 freshly extracted human mandibular third molars was ground flat to expose the cervical dentin. The dentin surfaces were polished with a series of silicon carbide papers, and the smear was removed with an ethylenediamine tetra-acetic acid solution. The teeth were randomly divided into six groups as follows: group 1, Vivasens; group 2, BisBlock; group 3, fluoride gel; group 4, Nd:YAG laser; group 5, Clearfil SE + Nd:YAG laser; and group 6, no treatment (control). The specimens were then restored with a two-step self-etch adhesive, with the exception of group 5. Five specimens from each group were restored with a nanohybrid composite resin. The adhesive interface of two specimens from each group was examined using scanning electron microscopy. The specimens were sectioned perpendicularly to the adhesive interface to produce beams (adhesive area 1 mm(2)). The beams were then attached to a microtensile tester and stressed to failure at 1 mm/min. The data were compared using one-way analysis of variance at a significance level of 0.05. The microtensile bond strengths of the control group were significantly higher than those found for group 1, group 2, group 3, and group 4 (p< 0.05). No significant difference was found between group 5 and the control group. Most of the premature failures were seen in group 2 (80%), and the fewest premature failures were seen in group 5 (13.3%). The SEM findings verified the microtensile test findings. In conclusion, desensitizing treatment procedures (with the exception of Clearfil SE + Nd:YAG laser) reduced the microtensile bond strength of a two-step self-etch adhesive to dentin.

Effect of periodontal therapies on indirect restoration: a scanning electron microscopic analysis

The aim of this study was to evaluate the influence of different periodontal therapies on the integrity of indirect restorations by scanning electron microscopy (SEM). Sixty single-rooted bovine teeth were selected and randomly assigned to 12 groups. Inlay cavities were prepared in the cervical region on the center of the cementoenamel junction, and were restored with laboratory processed resin and luted with a resin cement. Twelve periodontal therapies were used (n= 5): C: control (no treatment); MS: manual scaling with Gracey curettes; US: ultrasonic scaling; PP: prophylaxis with prophylactic paste; PS: prophylaxis with pumice-stone; SBJ: sodium bicarbonate jet; MS/PP; MS/PS; MS/SBJ; US/PP; US/PS; US/SBJ. The specimens were prepared and analyzed by SEM. SEM micrographs at ×100 to ×1000 magnification were obtained from the surface of the laboratory resin and the interface of the indirect restorations. The images were evaluated by 3 skillful, calibrated, blinded observers as to the presence of grooves, microcavities and fracture of margins. The results showed that PS produced groves on restoration surface. MS and US produced groves and marginal fractures on the restorations. SBJ resulted in resin cement degradation. These results suggest that except for PS, all procedures had deleterious effects on the marginal integrity of indirect restorations.

O objetivo desse estudo foi avaliar a influência de diferentes terapias periodontais na integridade de restaurações indiretas por meio de microscopia eletrônica de varredura (MEV). Sessenta raízes bovinas foram selecionadas e aleatoriamente divididas em 12 grupos. Preparos cavitários inlay foram realizados na região cervical central da junção cemento-esmalte e restaurados com resina laboratorial cimentado com cimento resinoso. Doze terapias periodontais foram usadas (n=5): C-sem tratamento (controle); MS-raspagem manual com cureta Gracey; US-raspagem com ultra-som; PP- profilaxia com pasta profilática; PS-profilaxia com pedra pomes; SBJ-jato de bicarbonato; MS/PP; MS/PS; MS/SBJ; US/PP; US/PS; US/SBJ. As amostras foram preparados e submetidas a MEV. Imagens, de ×100 a ×1000, da superfície da resina laboratorial e da interface das restaurações indiretas foram obtidas. As imagens foram avaliadas em procedimento cego por 3 observadores habilitados previamente calibrados seguindo os seguintes critérios: ranhuras, microcavidades e fratura de margem. Os resultados mostraram que a profilaxia com pedra pomes promoveu ranhuras na superfície das restaurações. Raspagem manual e ultrasônica promoveram ranhuras e fratura de margem das restaurações. Jato de bicarbonato resultou em degradação de cimento resinoso. Os resultados sugeriram que, exceto a profilaxia com pasta profilática, todos os procedimentos resultaram em efeitos deletérios na integridade da margem das restaurações indiretas.

The effect of application time of EDTA and NaOCl on intracanal smear layer removal: an SEM analysis.

AIM: To verify, under the scanning electron microscope (SEM), the influence of irrigation time with ethylenediaminetetraacetic acid (EDTA) and sodium hypochlorite (NaOCl) on intracanal smear layer removal. METHODOLOGY: Twenty-one extracted human permanent teeth with single straight root canals were included. The root canals of the teeth were instrumented and, at the end of preparation, were irrigated with 3 mL of 15% EDTA, followed by 3 mL of 1% NaOCl for 1 min (group 1), for 3 min (group 2), and for 5 min (group 3). The canals of teeth in group 4 (control) did not receive the final irrigation. The teeth were sectioned longitudinally and prepared for an SEM. The dentinal wall of cervical, middle and apical thirds was graded according to the amount of debris and smear layer remaining on the walls. The results were analysed using the Kruskal-Wallis and Conover-Inman tests. RESULTS: In all the canals of experimental groups irrigation with EDTA and NaOCl completely removed the smear layer from the cervical and middle thirds. In the apical third, the dentine surface were partially covered, particularly in the teeth of group 1, where there was significantly more smear layer when compared with the other thirds in the same group (P<0.007). However, the Kruskal-Wallis test showed overall that there were no significant differences between groups 1, 2 and 3 (P>0.05). CONCLUSION: In this limited laboratory study, canal irrigation with EDTA and NaOCl for 1, 3 and 5 min were equally effective in removing the smear layer from the canal walls of straight roots.

Glass ionomer microleakage from preparations by an Er/YAG laser or a high-speed handpiece.

OBJECTIVE: The purpose of this study was to compare microleakage of glass ionomer materials (GIC) using two different modes of cavity preparation: a high-speed hand piece and an erbium/yttrium-aluminum-garnet (Er/YAG) laser. METHODS: Eighty caries free permanent molar teeth had class V preparations cut on both the buccal and lingual surfaces. The high-speed hand piece was used to prepare a class V cavity preparation on the buccal surface and an Er/YAG laser was used to prepare a class V cavity preparation on the lingual surface. GIC or resin modified GIC was used as the restorative material. The teeth were thermocycled for 7000 cycles, placed in 2% basic fushin for 24h, sectioned in the center of each restoration, and analyzed under a stereomicroscope. RESULTS: There was no statistical difference in microleakage between the two modes of cavity preparations. The gingival margins had more microleakage than the occlusal margins for both GIC materials and the resin modified GIC showed significantly more leakage than the conventional GIC. CONCLUSIONS: The Er/YAG laser provided an equivalent method of tooth removal when evaluated for microleakage of GIC materials compared to a high-speed hand piece.

Cervical tooth wear and sensitivity: erosion, softening and rehardening of dentine; effects of pH, time and ultrasonication.

BACKGROUND: Cervical dentine wear is commonly observed and may be associated with dentine hypersensitivity. Erosion is thought to play a part in both conditions but compared to enamel has been little studied in dentine. AIM: The aims of these studies in vitro were to: (i) determine the effects of citric acid on dentine at different pH values and over time; (ii) measure the depth of dentine demineralisation or softening using ultrasonication; (iii) determine whether softened dentine can be remineralised or rehardened using artificial saliva. METHODS: Groups of flat dentine specimens prepared from unerupted human third molar teeth were: (a) exposed to citric acid at pH 3.2 for periods up to 4 h with mineral water as control; (b) exposed to citric acid at pH 2.54, 3.2, 4.5, 5.5 and 6.0 for 2 h and then subjected to ultrasonication stepwise up to 480 s; (c) exposed to citric acid at pH 2.54, 3.2, and 4.5, placed into artificial saliva for 24 h and then subjected to ultrasonication as in (b). Loss of dentine was measured by profilometry, after, each phase of erosion, ultrasonication and immersion in artificial saliva. RESULTS: Depth of erosion significantly increased non-linearly with time and significantly decreased with increasing pH. Ultrasonication had minimal albeit significant effects on control specimens. Removal of softened dentine increased with ultrasonication time. Depth of softening significantly increased with increasing erosion time to 2 h, plateauing at 2 microm. Depth of softening increased to 2 microm from pH 2.54 to pH 3.2 and decreased at higher pH values thereafter. 24 h in artificial saliva provided no protection to the soften zone against ultrasonicaion. Citric acid at all pH values and exposure times removed the dentine smear layer to expose tubules. Ultrasonication did not remove the smear layer on control specimens but removed all deposits formed after exposure to artificial saliva. CONCLUSION: It is concluded that dentine is susceptible to erosion even at relatively high pH, the tubule system is readily exposed and dentine, unlike enamel, shows little propensity to remineralise.

Efficacy of dentin bonding to cervical defects.

The bonding efficacy of sclerotic dentin was determined by measuring the polymerization contraction gap width of a commercial light-activated resin composite in a cervical defect and by measuring the micro-Vicker's hardness at the dentin adhesive surface; morphological characteristics were observed using a scanning electron microscope in extracted human incisors and premolars. Contraction gap formation was completely prevented when the cavity wall was primed with 35 vol% glyceryl mono-methacrylate solution after 0.5 mol/L EDTA conditioning. The contraction gap width was significantly decreased when the resin composite was filled into the sclerotic dentin cavity even when priming was omitted. These results suggest that the sclerotic dentin, which is frequently observed in cervical defects, should be preserved as a substrate because it exhibits an effect of dentin priming and is suitable for bonding.

An ultrastructural study of the application of dentine adhesives to acid-conditioned sclerotic dentine.

OBJECTIVE: This in vitro study examined the ultrastructure of resin-infiltrated sclerotic dentine following the application of a self-etching primer, with or without the adjunctive use of phosphoric acid pre-conditioning. MATERIALS AND METHODS: Non-carious, natural cervical sclerotic lesions were hand-cleaned with a slurry of pumice and chlorhexidine and bonded without further cavity preparation. One group was bonded using Clearfil Liner Bond 2V (Kuraray Co. Ltd, Osaka, Japan) alone. Specimens from the other group were pre-conditioned with K-etchant (40% phosphoric acid gel, Kuraray) prior to the application of the same self-etching primer. Artificially prepared wedge-shaped lesions were also made in sound bicuspids, bonded using the two methods, and used as controls for the two groups. For SEM examination, each specimen was cryofractured into two halves through a pre-formed slit made on the lingual surface, after the respective conditioning treatment. Different locations within the lesions were examined after rinsing of the phosphoric acid/self-etching primer and specimen dehydration. For TEM investigation, specimens were bonded with the adhesive. Both demineralised and undemineralised ultrathin sections were prepared from the occlusal, gingival and deepest part of the wedge-shaped bonded lesions following specimen fixation, dehydration and resin embedding. RESULTS: A hypermineralised surface layer was present on the surface of etched sclerotic dentine. This layer was thicker in the deepest part of the natural lesions, where bacterial colonisation of the lesion surface was also apparent. Both treatment protocols were unable to effectively dissolve sclerotic casts that occluded the dentinal tubules. Depending upon the thickness of the surface layers at different locations in the natural lesion, self-etching primer treatment alone resulted in reduction of the thickness of the authentic hybrid layer (i.e. hybridised intertubular dentine). This was also true of phosphoric acid pre-conditioning along the deepest part of the natural lesions. Within this region, intertubular dentine completely devoid of an authentic hybrid layer could be seen in both treatment groups. Resin tags were also sparsely observed in such regions. CONCLUSIONS: Adhesive strategies that rely mostly on micromechanical retention alone may be compromised by the sporadic absence of the hybrid layer and resin tags in sclerotic dentine. Based on the ultrastructural features presented, it is further speculated that adaptive strategies such as removal of the surface layers and extended etching time may not be completely effective in improving bonding efficacy in highly sclerotic dentine. Interdisciplinary research should be continued to develop alternative procedures for bonding resins equally well to sound and sclerotic dentine.

Enamel pearls and cervical enamel projections on 2 maxillary molars with localized periodontal disease: case report and histologic study.

Presented here is an unusual case of teeth with aberrant enamel. One small and 3 large enamel pearls were identified in 2 maxillary third molars of a patient. One long enamel projection was connected to one of the large enamel pearls, along with 2 short cervical enamel projections. The ectopic enamel was associated with advanced localized periodontal destruction. After extraction, the molars were investigated radiographically and under the scanning electron microscope. The 3 large pearls contained distinct dentinal cones. The enamel of the pearls and the long cervical projection exhibited most of the structural attributes of crown enamel but were somewhat irregular, with variable shape and course of the prisms. Morphologic considerations suggest that these enamel pearls were aberrations and should not be regarded as attempts at new cusp or new tooth formation.

Efficacy of final irrigation--a scanning electron microscopic evaluation.

The purpose of this in vitro study was to determine the degree of removal of pulpal remnants and smear layer from root canals after final irrigation with three different solutions. During instrumentation the step-back preparation and 1% NaOCl were used. The final 4-min, 30-ml irrigation varied as follows: group I, 10 ml of 1% NaOCl + 10 ml of 10% citric acid + 10 ml of distilled water; group II, 15 ml of 0.5% NaOCl + 15 ml of EDTA-T; and group III, 10 ml of 5% NaOCl + 10 ml of 3% H2O2 + 10 ml of 5% NaOCl. Scanning electron microscopic photomicrographs were evaluated for the mean number of visible open dentinal tubules by three observers. The largest number of visible tubules in the three groups was in the cervical third, followed by the middle and apical thirds. There was no statistically significant difference between groups I and II when third was compared with third; however, groups I and II had significantly more visible dentinal tubules than group III.

Micromorphological investigation of noncarious cervical lesions treated with demineralizing agents.

PURPOSE: The purpose of this study was to examine the micromorphology of noncarious cervical lesions (NCCL) and the change occurring after acid conditioning. MATERIALS AND METHODS: Nine wedge-shaped lesions, 9 saucer-shaped lesions, and 5 third molars with prepared cervical cavities were used. All NCCLs exhibited a hard, smooth surface with no discoloration. The teeth were sectioned and divided into three groups, each containing the three lesion types. Teeth in Group I were not etched, and teeth in Groups II and III were etched with 35% phosphoric acid and 20% polyacrylic acid/3% aluminum chloride, respectively. Field emission SEM and atomic force microscopy were used to examine the lesion surfaces. RESULTS: The surfaces of the prepared cervical (control) lesions were covered with a smear layer. Treatment with phosphoric acid and polyacrylic acid resulted in removal of the smear layer, although some residual smear layer was found on the surface treated with polyacrylic acid. The images of the untreated surfaces of NCCL showed highly mineralized dentin with complete obliteration of the dentinal tubules. After treatment with phosphoric and polyacrylic acids, the images revealed demineralization of the surface, which was more pronounced on those treated with phosphoric acid. CONCLUSION: The mineral deposits on the surface of NCCL decreased the effect of acid conditioning. Although there was no apparent difference between the two forms of NCCL used in this study, further work is needed to better understand these lesions.

Bonding of a self-etching primer to non-carious cervical sclerotic dentin: interfacial ultrastructure and microtensile bond strength evaluation.

PURPOSE: The objectives of this study were 1) to examine the ultrastructural features of the resin-sclerotic dentin interface following the application of Clearfil Liner Bond II sigma to natural cervical wedge-shaped lesions, and 2) to evaluate the regional tensile bond strength of this self-etching primer at different locations on natural and artificially-created cervical lesions. MATERIALS AND METHODS: Deep cervical natural lesions were bonded using the self-etching primer. Micromorphology of the bonded interface at different locations within the lesions were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy/energy dispersive x-ray analysis (STEM/EDX). Ultrastructural features were further compared with the use of the same self-etching primer on artificial lesions created in sound cervical dentin. A nontrimming technique was used to evaluate the regional tensile bond strength from the occlusal, gingival, and the deepest central part of both natural and artificial cervical lesions. Beams with a mean area of 0.46 +/- 0.03 mm2 were prepared and were pulled to failure using a Bencor Multi-T testing device attached to an Instron universal tester. Bond strength results were evaluated using a two-way ANOVA design. RESULTS: A hypermineralized layer devoid of intact, banded collagen was invariably present on the surface of the natural lesions. Depending upon its thickness at different locations of the lesion, the action of a self-etching primer may be limited to this surface layer alone, producing a hybridized hypermineralized surface layer. Penetration of the self-etching primer into the underlying sclerotic dentin produced a hybridized complex containing a hybridized hypermineralized surface layer as well as a subsurface layer of hybridized intertubular dentin. Bacterial colonization of the lesion surface resulted in the formation of an additional zone of hybridized intermicrobial matrix over the surface of the lesions. Dentinal tubules remained blocked with sclerotic casts, and resin tags were rarely observed. Regional tensile bond strength results showed that the overall bond strength to natural sclerotic dentin was about 20% lower than sound cervical dentin, but was independent of the different locations within the lesions from which bond strength was evaluated. CONCLUSION: There were four factors that may have influenced the overall decrease in bond strength in natural cervical sclerotic lesions: a) the presence of a hybridized intermicrobial matrix together with entrapped bacteria may have weakened the bonds, b) inability of a self-etching primer to etch through a thick, hypermineralized surface layer, c) presence of a layer of possibly remineralized, denatured collagen at the base of the hypermineralized surface layer, and d) retention of acid-resistant sclerotic casts that obliterate the tubular lumina and prevent effective resin tag formation.

Bonding to root canal: structural characteristics of the substrate.

PURPOSE: To evaluate in vitro the dentin morphology in root canals in terms of tubule orientation, density and increase in surface area after etching. MATERIALS AND METHODS: Thirty anterior teeth were divided in 3 groups at random: the samples of Group 1 were used to study tubular morphology in SEM. Groups 2 and 3 samples were etched with 32% phosphoric acid. The teeth in Group 2 were examined by SEM without further treatment. The samples in Group 3 were treated with a bonding system and fiber posts were luted into the canal. These teeth were then processed for evaluation of hybrid layer formation and resin tags in dentin tubules. The observations were made according to location in the root dentin, tubule density was estimated, and the increase in area available for bonding after etching was calculated. RESULTS: The observations revealed variability in tubule density and orientation within different areas of any one sample. Statistically significant differences in the density of tubules were found depending on location. The dentin surface area available for bonding increased by 202% after etching in the cervical third, 156% in the middle third, and 113% in the apical third of the root dentin. Group 3 samples showed that the thickness of the hybrid layer depended on the density of tubules. In the sectors with a low density of tubules, the hybrid layer was significantly thinner than in areas with a higher density of tubules. The increase in dentin surface area might be responsible for the enhanced bond strength after acid etching, but not all areas exhibited equal responses to etching.

Evidence that laminin-5 is a component of the tooth surface internal basal lamina, supporting epithelial cell adhesion.

Laminin-5 (Ln-5) is an extracellular matrix (ECM) glycoprotein found in epithelial basal laminae. We studied its expression on the surface of rat molars, in relationship to the location of the internal basal lamina (IBL) of the junctional epithelium (JE). In order to avoid disruption of the JE-tooth interface as much as possible, the surface of molars was prepared by mechanical removal of tissue debris and detergent/osmotic lysis of epithelial cell layers, and directly stained by immunohistochemistry, without sectioning. Antibodies to Ln-5 specifically stained a narrow band in the region of the cemento-enamel junction (CEJ), consistent with the expected location of the IBL. Western blotting of ECM material detergent--solubilized from the prepared tooth surfaces confirmed the molecular nature of Ln-5 identified by immunohistochemistry. By the use of a high-definition 3-D microscope, it appeared that Ln-5 coated the most apical part of the enamel and the most coronal portion of the cementum, on either side of the CEJ. In adhesion assays performed directly on tooth surfaces, epithelial cells adhered preferentially to the Ln-5 coated area of the tooth compared to the root surface, which is coated by other ECM components. Adhesion to the Ln-5 coated surface was specifically inhibited by a function-blocking monoclonal antibody to Ln-5. These results suggest that Ln-5 is a component of the IBL, and that it may be important in promoting adhesion of JE cells onto the tooth surface.

Long-term effects of CO2 laser irradiation on treatment of hypersensitive dental necks: results of an in Vivo study.

OBJECTIVE: The present in vivo study was performed to examine the long-term effects of combined CO2 laser treatment and fluoridation on hypersensitive dental necks. SUMMARY BACKGROUND DATA: Attempts have been made to treat dental hypersensitivity by sealing exposed dentinal tubules, primarily using fluoride preparations, strontium chloride, and hydroxyapatite. However, these treatment methods have the disadvantage that the preparation is effective only for a limited period of time and must be applied repeatedly, at short intervals. The CO2 laser has been shown to have an excellent sealing effect on hypersensitive dentinal surfaces. METHODS: Test subjects suffering from dentinal hypersensitivity were recruited from the patients of the Department of Conservative Dentistry, School of Dentistry of the University of Vienna, Austria and treated with combined laser irradiation and fluoridation with stannous fluoride gel. The patients were followed up for a period of 18 months. In vivo examinations were supplemented by atomic absorption spectroscopy (AAS) of tiny dentin samples obtained from the dental necks 6 weeks and 18 months after laser treatment and by scanning electron microscopy (SEM). RESULTS: Compared to conventional fluoridation, combined laser irradiation and fluoridation was shown to be effective in the treatment of hypersensitive dental necks. When success was defined as complete freedom from pain, the success rate in the laser group was 96.5%. Furthermore, examinations of irradiated teeth under the scanning electron microscope still revealed complete closure of the dentinal tubules four and six months after laser treatment. AAS showed that tin was present in the samples, which indicates that combined laser treatment and fluoridation result in permanent integration of fluoride in the dentin surface. CONCLUSIONS: Based on these results, the CO2 laser can be recommended as an ideal tool for desensitization of dental necks.