The influence of cement filler load on the radiopacity of various fibre posts ex vivo.

AIM: To verify whether the filler load of luting agents influences the radiopacity of intraradicularly placed posts. METHODOLOGY: Digital radiographs of the following posts were taken: RelyX Fiber Post (3M ESPE), GC Fiber Post (GC Corporation), DT Light Post Illusion (RTD), DT Light SL Post (RTD), Endo-Composipost (RTD), FibreKleer Parallel Post (Jeneric Pentron Incorporated), FRC Postec (Ivoclar Vivadent), Parapost Taper Lux (Còltene/Whaledent AG), Radix Fiber Post (Dentsply Maillefer), EverStick Post (Stick Tech Ltd), Dentin Post X (Komet), Tech 21 X-op (Isasan), ENA Post (Micerium). Post radiopacity was measured in millimetres of aluminium (mmAl) with reference to an aluminium step wedge. Two extracted contralateral premolars were root filled. After post space preparation, taking the midpoint of the post hole as a reference, each tooth was cut longitudinally into two halves in a mesiodistal direction. On each half, the exposed root dentine was ground flat to the deepest point of the post space, and an even layer of cement was placed and light-cured. To obtain a clinically relevant layer of cement, the material thickness was reduced to 75 µm by grinding with wet abrasive paper. A cement formulation with 30 wt% of filler was tested in one premolar, whilst a formulation with 70 wt% of filler was utilized in the contralateral tooth. Posts were then placed between the two facing root halves of each premolar, and radiopacity was measured in mmAl. Data were analysed using t-test for paired samples (P < 0.05). RESULTS: Radiopacity of posts ranged between 1.44 (ENA Post) and 5.78 mmAl (FibreKleer). In the presence of the more heavily filled cement, significantly higher values of post radiopacity were measured (P < 0.001). CONCLUSION: The radiopacity of the luting agent contributed to the overall post radiovisibility within the root. Even when the cement with lower filler content was used in combination with the least radiodense dowels, the post was detectable within the root.

Bond strength to unground enamel and sealing ability in pits and fissures of a new self-adhering flowable resin composite.

OBJECTIVE: To evaluate the applicability as a sealant of a new self-adhering flowable resin composite (Vertise Flow, Kerr, VF) by assessing shear bond strength (SBS) to unground enamel and microleakage (microLKG) in sealed pits and fissures. STUDY DESIGN: Marketed sealants to be used in combination with phosphoric acid (Guardian Seal, Kerr, GS) or with a self-etch adhesive (Adper Prompt-L-Pop/Clinpro Sealant, 3M ESPE, CS) were compared to VF. For SBS testing on unground enamel 10 molars per group were used. For microLKG assessment, pits and fissures sealing was performed in 12 molars per group. The sealed teeth were immersed in a 50% weight silver nitrate solution for 24 hours and the extent of interfacial leakage was measured. Between-group differences in SBS were assessed using One-Way Analysis of Variance (ANOVA), followed by Tukey test (p < 0.05). microLKG data were analyzed with Kruskall-Wallis ANOVA (p > 0.05). RESULTS: SBS of VF was statistically similar to that measured by CS and higher than that of GS. Interfacial leakage was similar in the three groups. CONCLUSIONS: The finding of satisfactory bond strength and sealing ability of VF when compared to the marketed sealants encourages the use of VF in pit and fissure sealing.

Color correspondence of different batches of TriLuxe CAD/CAM ceramic blocks.

TriLuxe ceramic blocks for chairside CAD/CAM procedures are color layered to allow natural esthetics, and only require subsequent glazing. The purpose of this study was to compare color repeatability of different batches of TriLuxe blocks. The three commercially available shades (1M2C, 2M2C, 3M2C) of TriLuxe blocks for the Cerec CAD/CAM system were examined. For each of the three colors, three different batches were tested, 5 blocks each. The measurements were made using a spectrophotometer equipped with an integrating sphere using the CIELab* colorimetric system. One-way ANOVA showed that the factor "Production Batch" was not statistically significant. Regarding deltaE, none of the 315 color comparisons (neither within the same shade, nor between specimens of the same batch, nor between specimens from different batches) exceeded the proposed deltaE = 3.3 threshold for clinical acceptability. All the different batches of the different shades of VITA TriLuxe blocks for the Cerec system showed the high degree of color correspondence necessary in industrially prefabricated CAD/CAM blocks.

Effect of Finishing and Polishing on Roughness and Gloss of Lithium Disilicate and Lithium Silicate Zirconia Reinforced Glass Ceramic for CAD/CAM Systems.

OBJECTIVE: To assess the efficacy of dedicated finishing/polishing systems on roughness and gloss of VITA Suprinity and IPS e.max CAD. METHOD: A total of 24 blocks of Suprinity and 24 of e.max were cut into a wedge shape using an InLab MC-XL milling unit. After crystallization, the 24 Suprinity wedges were divided into four subgroups: group A.1: Suprinity Polishing Set Clinical used for 30 seconds and group A.2: for 60 seconds; group A.3: VITA Akzent Plus Paste; and group A.4: spray. The 24 e.max wedges (group B) were divided into four subgroups according to the finishing procedure: group B.1: Optrafine Ceramic Polishing System for 30 seconds and group B.2: for 60 seconds; group B.3: IPS e.max CAD Crystall/Glaze paste; and group B.4: spray. After finishing/polishing, gloss was assessed with a glossmeter and roughness evaluated with a profilometer. Results were analyzed by applying a two-way analysis of variance for gloss and another for roughness (α=0.05). One specimen per each subgroup was observed with a scanning electron microscope. RESULTS: For roughness, materials and surface were significant factors ( p<0.001). Suprinity exhibited significantly lower roughness than e.max. Also the Material-Surface Treatment interaction was statistically significant ( p=0.026). For gloss, both material and surface treatment were significant factors ( p<0.001). VITA Suprinity showed significantly higher gloss than e.max. Also the Material-Surface Treatment interaction was statistically significant ( p<0.001). CONCLUSIONS: Manual finishing/polishing for 60 seconds and glazing paste are the most effective procedures in lowering the roughness of CAD/CAM silica-based glass ceramics. Manual finishing/polishing for 60 seconds allows milled silica-based glass ceramics to yield a higher gloss. VITA Suprinity displayed higher polishability than IPS e.max CAD.

Effect of Finishing and Polishing on the Surface Roughness and Gloss of Feldspathic Ceramic for Chairside CAD/CAM Systems.

OBJECTIVES: To evaluate surface roughness and gloss of feldspathic ceramic blocks for chairside CAD/CAM systems before and after finishing and polishing. METHODS: VITA Mark II ceramic blocks for the CEREC CAD/CAM system were cut perpendicularly in order to obtain a total of 70 specimens (14 × 18 × 3 mm). The flat surface was roughened using a grinder/polisher with dry 120-grit silicone-carbide paper. Surface roughness and gloss were measured using a digital profilometer (Ra) and a glossmeter (GU), respectively. Specimens were randomly divided into seven groups (n=10) based on the finishing/polishing system as follows: 1) Identoflex NGPorcelain Polisher (INP), 2) Identoflex Diamond Ceramic Polisher (IDP), 3) Hiluster Polishing System (HPS), 4) OptraFine (OF), 5) Identoflex Lucent (IL), 6) VITA Akzent Glaze Spray (AGS), and 7) VITA Shading Paste and Liquid (SPL). Surface analysis was repeated after the finishing/polishing treatment, and the obtained data were compared to the baseline in order to evaluate the ΔRa and ΔGU. Results were statistically analyzed. The surface morphology was observed by scanning electron microscopy. RESULTS: The mean surface roughness of polished systems increased in the order (statistical groups designated) SPLa < ILa < OFab < IDPbc < AGSbc < INPbc < HPSc and mean gloss decreased in the order AGSa > SPLa > OFab > ILabc > HPSbcd > INPcd > IDPd. CONCLUSIONS: The smoothest surface of CAD/CAM feldspathic ceramic blocks was achieved using the furnace-based glaze systems VITA Akzent Glaze Spray and VITA Shading Paste and Liquid and manual systems Identoflex Lucent and OptraFine.

ADM guidance-ceramics: Fatigue principles and testing.

BACKGROUND: Clinical failure of dental ceramics is usually reported as partial fracture of the restoration (chipping) or as catastrophic fracture of the whole structure. In contrast to metals, ceramics are linear-elastic, brittle materials exhibiting extremely low damage tolerance to failure. Well documented clinical and lab reports have shown this fracture event often occurs at loads far below their fracture strength due to intrinsic fatigue degradation via slow crack growth or cyclic fatigue mechanisms. The presence and development of surface flaws have a dominant role in damage accumulation and lifetime reduction of ceramic structures. AIMS: This ADM guidance document aims to summarize the aspects related to fatigue degradation of dental ceramics, reviewing the concepts of fatigue testing and furthermore aims to provide practical guidance to young scientists entering into fatigue related research. The description of fatigue strength is always accompanied by a clear understanding of the underlying fracture mechanisms.

Zirconia abutments and restorations: from laboratory to clinical investigations.

In last years the use of zirconia in dentistry has become very popular. Unfortunately, the clinical indications for a dental use of zirconia are not completely clear yet, neither are their limitations. The objective of this review was to evaluate the basic science knowledge on zirconia and to discuss some aspects of the clinical behavior of zirconia-based restorations. In particular, one of the goals was highlighting the possible correlation between in vitro and in vivo studies. The definition of concepts like success, survival and failure was still debated and the correlation between in vitro results and predictability of clinical behavior was investigated.

Effect of repeated firings on flexural strength of veneered zirconia.

OBJECTIVE: Chipping and/or delamination represent a clinical failure of porcelain fused to zirconia (PFZ) prostheses. Causes and solutions have not been completely clarified. The present study was aimed at evaluating the effects of number of firings on the flexural strength of PFZ specimen. METHODS: Forty-five zirconia specimens in shape of bars were cut, sintered and divided in 3 groups (n=15). Group 1: veneering ceramic was layered "in bulk" and fired. Group 2: veneering ceramic was layered in three layers, individually fired. Group 3: veneering ceramic was layered in five layers, individually fired. Each layer thickness was controlled by the use of calibrated molds. The total veneering ceramic thickness for all the specimens was 1.2mm, and the total thickness of the specimen of 2.0mm. Three-point bending test was performed. Fracture load was recorded in Newton and MPa value was calculated taking into account the bi-layered nature of the specimen. Data were statistically analyzed. RESULTS: Specimens obtained with on single firing cycle obtained a statistically significant (p<0.001) lower flexural strength (54.61±8.98MPa) than specimens veneered with 3 or 5 firing cycles. The last two obtained very similar results (77.63±13.17MPa and 73.62±12.38MPa respectively) and the differences was not statistically significant. SIGNIFICANCE: In bi-layered PFZ specimen, three to five layers and firings determine higher flexural resistance when compared to a single firing. Thus, a 3-layers veneering procedure is recommended to increase flexural resistance. If a 5-layer procedure is necessary to improve esthetics, it does not decrease flexural resistance.

Sealing ability of several restorative materials used for repair of lateral root perforations.

Amalgam, IRM, Vitremer, Bisfil, and Ana Norm Liner were evaluated for repair of experimentally induced lateral perforations. Eighty-five sound, mandibular, and maxillary molars, extracted for periodontal reasons, were selected for this study. The sample teeth were randomly divided in five groups with 15 specimens each. Ten teeth were used as control groups. After the perforations were filled with the above-mentioned materials, the teeth were immersed in a 2% methylene blue solution for 48 h, sectioned, and dye penetration was measured. The results indicated that Bisfil 2 B provided a significantly better seal than the other materials.

Efficacy of different adhesive techniques on bonding to root canal walls: an SEM investigation.

OBJECTIVES: Recently, several adhesives have been proposed for bonding fiber posts into root canals. The aim of this study was to evaluate the influence of four adhesive procedures in resin tag, adhesive lateral branch and resin dentin interdiffusion zone (RDIZ) formation when used to bond fiber posts. METHOD: Forty anterior teeth, extracted for periodontal reasons and endodontically treated, were selected for this study. The samples were randomly divided into four groups of ten samples each. Group 1: One Step applied with the small brush provided by the manufacturer and LC (Light-cured before resin cement application)+Dual Link resin cement; Group 2: One Step applied with a thin microbrush LC+Dual Link resin cement; Group 3: One Step applied with a small brush (Not light-cured)+Dual Link resin cement; Group 4: All Bond 2+C & B resin cement (as control). In Group 2 and 4 the adhesive system and resin cement were used strictly following manufacturers' instructions. In Group 1, One Step was applied using a thin microbrush, while in the other groups by a small brush. In Group 1 and 2 the priming-adhesive solution of the "one-bottle" system was light-cured before placing the resin cement and the post, whereas in Group 3 the adhesive/resin cement combination was light cured through the translucent post. Forty translucent posts (RTD, France) were used. A week later, the root samples were processed for SEM observations. RESULTS: Microscopic examination of restored interfaces of Group 1 showed a higher % (P<0.05) of RDIZ than those found in samples of Group 2, 3 and 4. In Group 2, 3 and 4 samples RDIZ morphology was well detectable and uniform in the first two thirds of root canals while in the apical third the RDIZ was not uniformly present. No statistically significant differences were found among the groups coronally, whereas apical and middle thirds of Group 1 showed significantly more resin tags than the other three Groups. In the apical third of Group 2, 3 and 4 samples, the resin tags showed a less uniform morphology and a shorter length than those found in the other two thirds. SIGNIFICANCE: A microbrush might clinically be used for bonding fiber posts into the root canal. When a microbrush was used, the bonding mechanism created between root canal dentin and bonding system was uniform along canal walls and more predictable.

Bonding of all-porcelain crowns: structural characteristics of the substrate.

OBJECTIVES: The aim of this in vitro study was to evaluate the morphology of dentin in teeth prepared for single-unit all-porcelain crowns (SUAPC) in terms of tubule orientation, density and increase in surface area after etching. METHODS: Twenty anterior and 20 posterior teeth from adults were prepared 1mm below the cemento-enamel junction (CEJ) for SUAPC. The samples were divided into groups based on type of tooth (anterior or posterior) and bonding system employed. The teeth were processed for evaluation of morphology of the substrate, hybrid layer thickness and resin tag formation. The observations were subdivided according to location in the preparation and tubule density was calculated. RESULTS: The observations revealed the variability in tubule density and orientation in different areas within any one preparation. The morphology of the cervical margin was less predictable with the presence of cementum and an ill-defined cemento-dentinal junction. Statistically significant differences in the density of tubules were found depending on location. Groups 2, 3, 5 and 6 samples showed that the hybrid layer thickness and resin tag morphology depended on the density and direction of tubules. In those sectors with parallel and oblique tubule orientation and with a low density of tubules, the hybrid layer was significantly thinner than in areas with cross-sectioned tubules. SIGNIFICANCE: The cementum and the peripheral intertubular dentin surface area are likely to be responsible for the bond strength after acid etching of crown preparations, but not all areas exhibited equal responses to etching. In particular, the bonding substrate at the gingival margins may contribute little in terms of micromechanical retention.

Mapping of tubule and intertubule surface areas available for bonding in Class V and Class II preparations.

OBJECTIVES AND METHODS: The aim of this in vitro study was to evaluate the morphology of dentine in Class V and the Class II preparation walls in terms of tubule orientation, density and increase in surface area after conditioning. Six circular V-shaped preparations were cut at the cementum-enamel junction (CEJ) of anterior teeth and six Class II cavities with the cervical margin 1 mm below the CEJ were prepared in posterior teeth. The preparations were conditioned with 10% maleic acid. The samples were directly studied by SEM. The observations were organized according to location in the preparation, tubule density was counted and the increase in area available for bonding after acid etching was calculated. RESULTS: Dentine morphology of Class V and Class II preparation walls was mostly regular according to predictable patterns. Between the tubules, along the walls of the cavity, the etched dentine surface exhibited a porous network of collagen fibers. More than 50% of Class V and Class II cavity surface presented oblique or parallel tubule orientation with respect to the cut surface. Because of the presence of a structureless cementum layer. the morphology of the cervical area turned out to be less predictable. The tubule density varied considerably in different regions of the preparations. The intertubular dentine surface area increased after conditioning in Class V preparations from 20.9% to 50.3% on the walls where tubules were cut parallel to their long axis, and from 5.8% to 47.8% where tubules were cut perpendicularly. These same values for Class II preparations ranged from 0.6% to 46.4% on the walls where tubules were cut parallel to their long axis, and 29.8% of the tubules were cut perpendicularly. CONCLUSIONS: Based on this morphological investigation, the increase in intertubular dentine surface area might very well be responsible for the enhanced bond strength after acid etching of dentine, but not all areas exhibited equal responses to etching. In particular, the bonding substrate at the gingival margins may contribute little in terms of micromechanical retention.

Clinical procedure for luting glass-fiber posts.

PURPOSE: This report presents clinical cases in which a self-activating dual-cure adhesive system was used in combination with proprietary self-curing resin cement for bonding a translucent glass-fiber post. The clinical luting procedure of a self-activating bonding/self-curing resin cement system in combination with a glass-fiber post based on fiber-reinforced technology is documented. MATERIALS AND METHODS: The glass-fiber post was placed into a root canal preparation under clinical conditions and documented. A few restored teeth were extracted after 1 week and processed for SEM observations to determine the bonding mechanism to root dentin under clinical conditions. RESULTS: The SEM observations clearly showed that the bonding mechanism between Excite Dual Cure and root dentin was based on hybrid layer, resin tag, and adhesive lateral branch formation. CONCLUSION: The luting procedure described is simple and easy, and can be proposed as a daily clinical technique.

Bond strengths of a porcelain material to different abutment substrates.

The study evaluated the bond strength values of a single-unit all-porcelain material luted with an adhesive-resin cement to different abutment substrates: amalgam, compomer, traditional glass ionomer cement, microhybrid resin composite, two resin composites for abutment build-up, gold, sandblasted gold, dentin and enamel. Syntac enamel-dentin bonding system, in combination with IPS-Empress porcelain material, was used. After thermal cycling, the samples were inserted into a Bencor jig device and sheared in a Controls testing machine. The statistical analysis of the differences between the bond strength values obtained was performed by ANOVA and the Student-Newman-Keuls multiple-comparison test. The type of failure at the interface was evaluated using scanning electron microscopy. The type of failure, such as adhesive, cohesive and adhesive-cohesive, was correlated with bond strength values. Enamel, dentin and the two resin composites for crown build-up showed the highest bond strength values, while amalgam and gold samples showed the lowest.

Clinical evaluation of fiber-reinforced epoxy resin posts and cast post and cores.

PURPOSE: This retrospective study evaluated treatment outcome of cast post and core and Composipost systems after 4 yrs of clinical service. MATERIALS AND METHODS: 200 patients were included in the study. They were divided in two groups of 100 endodontically treated teeth restored with a post. Group 1: Composipost systems were luted into root canal following the manufacturer's instructions. Group 2: Cast post and cores were cemented into root canal preparations with a traditional technique. The patients were recalled after 6 months, 1, 2 and 4 yrs and clinical and radiographic examinations were completed. Endodontic and prosthodontic results were recorded. RESULTS: Group 1: 95% of the teeth restored with Composiposts showed clinical success; 3% of these samples were excluded for noncompliance and 2% showed endodontic failure. Group 2: Clinical success was found with 84% of teeth restored with cast post and core. 2% of these samples were excluded for noncompliance, 9% showed root fracture, 2% dislodgment of crown and 3% endodontic failure. Statistical evaluation showed significant differences between Groups 1 and 2 (P < 0.001). The results of this retrospective study indicated that the Composipost system was superior to the conventional cast post and core system after 4 yrs of clinical service.

Clinical and laboratory evaluation of adhesive restorative systems.

PURPOSE: To investigate the effectiveness of Clearfil Liner Bond, Gluma 2000, and Scotchbond Multi-Purpose when applied in combination with proprietary restorative resins in V-shaped circular cavities which were cut in incisors either centrally on the labial enamel surface (Type 1) or labially crossing the cemento-enamel junction (Type 2). MATERIALS AND METHODS: Forty teeth scheduled for extraction for periodontal reasons were treated in vivo and another 40 teeth in vitro. The in vivo restored teeth were extracted after 3 months of clinical service and the in vitro treated samples were stored in water for 1 week and thermocycled 250 times between 5 degrees C and 55 degrees C, prior to a 24-hour immersion in 0.5% fuchsin tracer solution of all specimens, sectioning and scoring interfacial dye penetration. RESULTS: ANOVA revealed no significant differences between all in vivo samples sites, all in vitro enamel sites and the apical Type 2 sites of the Gluma samples. In contrast, the apical Type 2 leakage of CLB and SMP was significantly more pronounced, although not statistically different from each other. The results of the short-term clinical performance of the three systems was moderately more favorable than the laboratory microleakage test results.

Retrospective study of the clinical performance of fiber posts.

PURPOSE: To evaluate the clinical performance of C-Posts, AEstheti Posts and AEstheti Plus Posts after a period of clinical service ranging from 1-6 yrs. MATERIALS AND METHODS: 1,304 posts were included in the study: 840 Composiposts, 215 AEstheti posts and 249 AEstheti Plus posts were placed into endodontically treated teeth. Four combinations of bonding/luting materials were used. The patients were recalled every 6 months and clinical and radiographic examinations were completed. Endodontic and prosthodontic results were recorded. Actuarial Life Table statistical analysis and Mantel-Haenszel comparison of survival curve have been performed at 95% level of confidence. RESULTS: The 3.2% failure rate was due to two reasons: 25 posts debonded during removal of temporary restorations, and 16 teeth showed periapical lesions at the radiographic examination. No statistical significant differences were found among the four groups. The results of this retrospective study indicate that fiber posts in combination with bonding/luting materials can be routinely used.

Role of hybridization on marginal leakage and bond strength.

PURPOSE: To evaluate whether the hybrid layer significantly contributes to the seal of adhesive Class V restorations placed in vivo and to the bond strength obtained in vitro. MATERIALS AND METHODS: 20 periodontally severely compromised anterior teeth were selected for the leakage study. In each tooth, one round 3 mm wide V-shaped cavity with a maximum depth of 2 mm was prepared on the labial surface crossing the cementum-enamel junction. The sample teeth were randomly divided into two groups of ten samples each: in Group 1, Scotchbond Multi-Purpose Plus was applied in combination with Z-100 following the manufacturer's instructions. In Group 2 the bonding procedure was the same as in Group 1, except that after the phosphoric acid treatment, the cavities were treated with 5% NaOCl for 2 min. Following a period of clinical service of 60-90 days, the teeth were extracted and processed for the leakage test. RESULTS: At the enamel site, 30% of the samples of Group 1 and 70% of the samples of Group 2 showed dye penetration. At the dentin site, 50% of the samples of Group 1 showed leakage, while all the samples of Group 2 were severely infiltrated. Statistically significant differences between the groups both for the enamel sites (P < 0.05) and for dentin-cementum sites (P < 0.001) were found. Bond strength tests were performed on 2 mm thick dentin slides of tapered Class I cavities (n = 10 in each group). The mean bond strength value obtained from cavities treated without NaOCl was 15.23 (+/-1.40) MPa and with NaOCl treatment 20.52 (+/-1.70) MPa. Statistical analysis showed significant differences (P < 0.05) between the two groups. No hybrid layer was detected on the NaOCl-treated samples by scanning electron microscopy.

Effect of two etching times on the sealing ability of Clearfil Liner Bond 2 in Class V restorations.

PURPOSE: To investigate the sealing ability of the Clearfil Liner Bond 2 self-etching primer in Class V restorations placed under clinical and laboratory conditions. MATERIALS AND METHODS: Firstly, the influence of two etching times of the self-etching primer were tested in vitro. In 10 Class V cavities (Group 1), the self-etching primer was applied for 30 seconds on the enamel and dentin, while in another 10 Class V cavities (Group 2) the etching time was 60 seconds. Since the Group 2 samples showed the best in vitro sealing ability at both the enamel and cementum-dentin sites, the teeth of Group 3 (10 restorations) were restored as in Group 2 under clinical conditions, applying the self-etching primer for 60 seconds. The sample teeth were extracted after 65-90 days, and then processed for leakage. Two other groups of 10 samples each were prepared under laboratory conditions to investigate hybrid layer, resin tags and adhesive lateral branch formation. A flat buccal surface on each extracted tooth was prepared. Group 4 samples were conditioned for 30 seconds, and those of Group 5 for 60 seconds. RESULTS: In Group 1, 40% of the restorations showed leakage at the cementum-dentin site and 40% at the enamel site. Groups 2 and 3 showed statistically significant difference (less leakage) than Group 1. In Group 2 and 3 no leakage was found at the enamel site, and only a moderate leakage (10% and 20% of restorations, respectively) was found at the cementum-dentin site. The scanning electron microscopy observations of Group 4 samples showed a thin hybrid layer, with well-fitting and smooth resin tags and adhesive lateral branches only sporadically. Group 5 samples presented a thicker hybrid layer, rough and deep resin tags with many adhesive lateral branches. The etch enamel pattern was more uniform and rougher in Group 5 than in Group 4. The 60-second application time of the self-etching primer seems to be more reliable than a shorter conditioning time in day-to-day practice.

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.