Human Mandibular Incisors Research Articles

Efficacy of Bacteriophage Treatment on Pseudomonas aeruginosa Biofilms

IntroductionBacterial viruses (phages) have been used successfully in the treatment of animal and human bacterial infections. This study examined the potential use of phage therapy against Pseudomonas aeruginosa strain PA14 biofilms in a root canal model. MethodsPart 1: The 24-hour and 96-hour PA14 biofilms grown in microplates were treated with phages identified as possessing potential biofilm-degrading activities, and the post-treatment bacterial biomass was quantified by using crystal violet staining. Part 2: The 24-hour and 96-hour PA14 biofilms grown in prepared root canals of extracted human mandibular incisors were treated with phages identified with potential biofilm-degrading activities. Post-treatment intracanal samples were taken by using paper points and round burs to assess phage and bacterial counts. ResultsPart 1: We identified 2 phages (JBD4 and JBD44a) with putative biofilm-degrading activities. Treatment of PA14 biofilms with these phages produced a significant reduction in the mean percentage of biomass in 24-hour (P < .05) and 96-hour (P = .08) biofilms. Part 2: In 24-hour and 96-hour PA14 biofilms in a root canal model, no significant difference was found in the number of colony-forming units after phage treatment (P > .05). ConclusionsPhage application significantly reduced the biomass of 24-hour and 96-hour PA14 biofilms grown on microplates but did not produce significant reduction of 24-hour or 96-hour PA14 biofilms grown in the extracted tooth model.

Apically Extruded Debris with Reciprocating Single-File and Full-sequence Rotary Instrumentation Systems

IntroductionThe purpose of this in vitro study was to assess the amount of apically extruded debris using rotary and reciprocating nickel-titanium instrumentation systems. MethodsEighty human mandibular central incisors were randomly assigned to 4 groups (n = 20 teeth per group). The root canals were instrumented according to the manufacturers’ instructions using the 2 reciprocating single-file systems Reciproc (VDW, Munich, Germany) and WaveOne (Dentsply Maillefer, Ballaigues, Switzerland) and the 2 full-sequence rotary Mtwo (VDW, Munich, Germany) and ProTaper (Dentsply Maillefer, Ballaigues, Switzerland) instruments. Bidistilled water was used as irrigant. The apically extruded debris was collected in preweighted glass vials using the Myers and Montgomery method. After drying, the mean weight of debris was assessed with a microbalance and statistically analyzed using analysis of variance and the post hoc Student-Newman-Keuls test. The time required to prepare the canals with the different instruments was also recorded. ResultsThe reciprocating files produced significantly more debris compared with both rotary systems (P < .05). Although no statistically significant difference was obtained between the 2 rotary instruments (P > .05), the reciprocating single-file system Reciproc produced significantly more debris compared with all other instruments (P < .05). Instrumentation was significantly faster using Reciproc than with all other instrument (P < .05). ConclusionsUnder the condition of this study, all systems caused apical debris extrusion. Full-sequence rotary instrumentation was associated with less debris extrusion compared with the use of reciprocating single-file systems.

Hydration and Dehydration Periods of Crown Fragments Prior to Reattachment

Tooth fragment bonding is an excellent treatment option in dealing with traumatic injuries of the anterior teeth. Rewetting the tooth fragment has been shown to increase restoration durability. The present study examined the effect various dry and wet storage periods had on the reattached fragment's bond to the tooth. One hundred and eight human mandibular incisors were fractured and assigned to undergo a dehydration period of 30 minutes, six hours, 24 hours, or three days before the rewetting procedure. After fracturing the teeth and drying the fragments, each of the specimens was assigned to one of the three main groups (A, B, or C) intended to evaluate the effect of different rehydration periods. Groups A and B underwent a 30-minute and a 24-hour rewetting period, respectively. Group C served as a control (without a rewetting stage). Tooth fragments were then reattached and prepared for the strength test. Force was applied on the lingual side of the tooth at a 1 mm/min rate until failure. The mean loads (N) required to fracture the restored teeth were as follows: 204.43 ± 33.48 N, 322.59 ± 34.62 N, and 253.25 ± 29.05 N for groups A, B, and C, respectively. Two-way analysis of variance (p<0.05) showed that rehydration and dehydration periods as well as their interaction caused significant differences in the strength of the final restoration. Multiple comparison tests showed that, in general, significant differences were not seen among different dehydration times prior to the rewetting stage (p>0.05), except in the case of the 30-minute dehydrated specimens (p<0.05). Compared to a 30-minute period, a 24-hour rehydration of the tooth fragment before treatment seems to salvage enough moisture to result in an increase in reattachment strength.

Efficacy of NiTi rotary instruments in removing calcium hydroxide dressing residues from root canal walls

was to evaluate the efficacy of three rotary instrument systems (K3, ProTaper and Twisted File) in removing calcium hydroxide residues from root canal walls. Thirty-four human mandibular incisors were instrumented with the ProTaper System up to the F2 instrument, irrigated with 2.5% NaOCl followed by 17% EDTA, and filled with a calcium hydroxide intracanal dressing. After 7 days, the calcium hydroxide dressing was removed using the following rotary instruments: G1 - NiTi size 25, 0.06 taper, of the K3 System; G2 - NiTi F2, of the ProTaper System; or G3 - NiTi size 25, 0.06 taper, of the Twisted File System. The teeth were longitudinally grooved on the buccal and lingual root surfaces, split along their long axis, and their apical and cervical canal thirds were evaluated by SEM (×1000). The images were scored and the data were statistically analyzed using the Kruskall Wallis test. None of the instruments removed the calcium hydroxide dressing completely, either in the apical or cervical thirds, and no significant differences were observed among the rotary instruments tested (p > 0.05).

Incidence of two canals in extracted mandibular incisors teeth of Saudi Arabian samples

Aim: The purpose of this in vitro study is to provide clinical data on the presence of the second canal in mandibular incisor teeth of Saudi Arabian Samples. Materials and Methods: Eighty extracted human mandibular incisors were collected from Saudi patients. The teeth were accessed by small round bur then placed in 5.25% sodium hypochlorite for 24 hours to dissolve the organic debris. Indian ink was injected inside the root canal systems under negative pressure. The teeth were decalcified in 5% nitric acid for three days then dehydrated in different concentrations of ethyl alcohol. Following the decalcification process, the teeth were cleared in methyl salicylate and evaluated according to Vertucci's classification. Result: Fifty six of both mandibular central and lateral incisor teeth (70%) had type I canal configuration (one main canal and one main apical foramen), while the remaining 30% of the sample (24 teeth) had a type III canal configuration (two separate canals and merged into one canal before exiting the tooth through single apical foramen). Conclusion : The incidence of two canals in mandibular incisor teeth is about one third of the examined Saudi Arabian samples with no difference between the centrals and laterals. The clinician should deal with these teeth as if they have two canals unless it is proved otherwise.

Temperature changes on the root surfaces of mandibular incisors after an 810-nm high-intensity intracanal diode laser irradiation

Temperature changes caused by laser irradiation can promote damage to the surrounding dental tissues. In this study, we evaluated the temperature changes of recently extracted human mandibular incisors during intracanal irradiation with an 810-nm diode laser at different settings. Fifty mandibular incisors were enlarged up to an apical size of ISO No. 40 file. After the final rinse with 17% ethylenediaminetetraacetic acid, 0.2% lauryl sodium sulfate biologic detergent, and sterile water, samples were irradiated with circular movements from apex to crown through five different settings of output power (1.5, 2.0, 2.5, 3.0, and 3.5 W) in continuous mode. The temperature changes were measured on both sides of the apical and middle root thirds using two thermopar devices. A temperature increase of 7 °C was considered acceptable as a safe threshold when applying the diode laser. The results showed that only 3.5-W output power increased the outer surface temperature above the critical value. The recommended output power can be stipulated as equal to or less than 3 W to avoid overheating during diode laser irradiation on thin dentin walls.

Shear bond strength of restorations applied to un‐complicated crown fractures: an in vitro study

Study was designed to evaluate shear bond strengths of different restorative techniques of uncomplicated enamel-dentin fractures in permanent incisors. Forty human mandibular incisors were divided into four groups. One-third of their anatomical crowns from the incisal edges were cut off in three groups, representing an uncomplicated enamel-dentin fracture. Intact teeth in group 1 were used as control. In group 2, edge fragments were reattached by flowable composite (Filltek Flowable Supreme XT). In group 3, teeth were restored with universal resin composite (Filtek Z 250). In group 4, pre-impregnated glass fiber sheet (everStickNet) was positioned onto fractured surface, and then restorations were completed with resin composite. Three-step etch-and-rinse adhesive system (Adper Scotchbond Multi Purpose) was used in all test groups. Shear bond strengths of all samples were determined in universal testing machine, and data were analyzed with Kruskal-Wallis followed by Mann-Whitney U tests. Failure types were observed by light microscope. Shear bond strength of sound teeth was significantly higher than those of restored teeth (P < 0.05). Mean shear bond strengths of the reattached teeth were lower than the other two restoration types; however, differences were not statistically significant (P > 0.05). Load-bearing capacity of restored teeth was not as high as sound teeth in the uncomplicated crown fracture. However, shear bond strength of different types of restorations seems close to each other.

Effects of chelating agents on the mineral content of root canal dentin

The objective of this in vitro study was to assess the effect of several chelating agents on the mineral content of root dentin. Extracted human mandibular incisor roots were prepared and divided into groups according to the following irrigation protocols: 1) 17% ethylenediaminetetraacetic acid (EDTA); 2) 10% citric acid solution; 3) 18% etidronate; 4) 2.25% peracetic acid; 5) and deionized water (control). Dentin chips were obtained (Gates-Glidden nos. 3, 4, and 5). The levels of different minerals were analyzed with the use of inductively coupled plasma-atomic emission spectrometry (ICP-AES). 1) Peracetic acid significantly decreased P, K, Mg, Na, and S levels compared with the other groups (P < .05). 2) S decreased by different levels in all of the chelating solutions (P < .05), and the greatest decrease was observed in peracetic acid. 3) Ca levels significantly decreased in peracetic acid, citric acid, and EDTA (P < .05). 4) Mn levels significantly decreased in the citric acid and peracetic acid groups (P < .05). 5) Na and Zn levels significantly decreased in the peracetic acid, citric acid, and etidronate groups (P < .05). The chelation agents can create different effects on mineral contents of root dentin, so it is important to know what effects each solution will have on root dentin before their clinical use. In addition, according to the results of this in vitro study, it might be recommended that peracetic acid, in particular, should be used with caution.

Influence of Hero Apical instruments on cleaning ovoid-shaped root canals

The cleaning capacity of Hero 642 nickel-titanium files, complemented by the Hero Apical instruments in flattened roots, was determined by histological analysis, considering the area of action of the instruments on the coronal walls and the presence of remaining debris. Twenty-four single-canal, human mandibular incisors were divided into three groups and prepared as follows: GI, instrumented with Hero 642 NiTi files 30/.06, 25/.06, 20/.06, 25/.06, and 30/.06; GII, instrumented as GI followed by Hero Apical size 30/.06; GIII, instrumented as GI followed by Hero Apical sizes 30/.06 and 30/.08, then returning to 30/.06 with pendulum movements. The apical thirds were prepared for histological processing, analyzed at 40× magnification and the images were examined morphometrically. Statistical analysis showed that GIII presented the best results for removing debris (5.22% ± 4.13), with more contact between the instruments and the root canal walls (19.31% ± 0.15). This differed statistically from GI (14.04% ± 4.96 debris removal, with 42.96% ± 7.11 instrument contact) and GII (12.62% ± 5.76 debris removal, with 35.01% ± 0.15 instrument contact). Root canal preparation with Hero 642, complemented by Hero Apical instruments (30/.06 and 30/.08, then re-instrumented with Hero Apical 30/.06 using pendulum movements), was more efficient for debris removal and allowed more contact of the instruments with the root canal walls. GII presented the worst results.

Angular Dependences of Reflected High-frequency Ultrasonic Signal in the Enamel Layer of Human Incisors: A Study In Vitro

The objective of this study was to obtain quantitative data on the dependence of reflected ultrasound signal on the signal incident angle in the enamel layer of the extracted human incisors. The measurements were conducted in vitro on freshly extracted human mandibular incisors by using a high-frequency focused ultrasonic transducer (PT50-3-6, Toray Engineering, Japan) in pulse-echo mode. The angle dependences of the enamel thickness measurements were studied with high accuracy using a transducer swing mechanism of the scanning acoustic microscope (Tessonics AM1103, Windsor, ON, Canada). Similar angular measurements were carried out by using the same PT50-3-6 transducer integrated into a compact hand-held probe to mimic a real dental procedure. The received thickness results were compared with the ones obtained through direct optical microscopy measurements of the teeth cross-section exposed by cutting the incisors down their long axis. Obtained results showed a close correlation between ultrasonic and optical microscopy measurements of the dental enamel thickness. The estimated difference in enamel layer thickness measured by the acoustic and optical microscopes did not exceed 12%. The dependence of reflected ultrasound signal on the signal incident angle in the enamel layer of extracted human incisors has been studied. The measurement conditions when the reflected ultrasound signals are not incident angle-dependent have been established.

Evaluation of three instrumentation techniques at the precision of apical stop and apical sealing of obturation

ObjectiveThe aim of this study was to investigate the ability of two NiTi rotary apical preparation techniques used with an electronic apex locator-integrated endodontic motor and a manual technique to create an apical stop at a predetermined level (0.5 mm short of the apical foramen) in teeth with disrupted apical constriction, and to evaluate microleakage following obturation in such prepared teeth. Material and Methods: 85 intact human mandibular permanent incisors with single root canal were accessed and the apical constriction was disrupted using a #25 K-file. The teeth were embedded in alginate and instrumented to #40 using rotary Lightspeed or S-Apex techniques or stainless-steel K-files. Distance between the apical foramen and the created apical stop was measured to an accuracy of 0.01 mm. In another set of instrumented teeth, root canals were obturated using gutta-percha and sealer, and leakage was tested at 1 week and 3 months using a fluid filtration device. ResultsAll techniques performed slightly short of the predetermined level. Closest preparation to the predetermined level was with the manual technique and the farthest was with S-Apex. A significant difference was found between the performances of these two techniques (p<0.05). Lightspeed ranked in between. Leakage was similar for all techniques at either period. However, all groups leaked significantly more at 3 months compared to 1 week (p<0.05). ConclusionsDespite statistically significant differences found among the techniques, deviations from the predetermined level were small and clinically acceptable for all techniques. Leakage following obturation was comparable in all groups.

Preflaring effects on the accuracy of three electronic apex locators

PURPOSE: To compare the accuracy of three electronic apex locators (EALs) and evaluate the influence of cervical preflaring in them. METHODS: The working length (WL) of thirty extracted human mandibular incisors was determined visually. All teeth were mounted in conducting medium and tested with: Novapex, Mini Apex Locator and Propex II. The electronic WL was determined before and after preflaring with LA Axxess burs. Differences between the electronic and visual WL were calculated and analyzed by Friedman and Wilcoxon tests. Radiographs were taken using the electronic WL of each EAL and the distance between the instrument tip and the radiographic apical vertex was measured. This value was compared to a reference or ideal value (1 mm) by one-sample t test. RESULTS: The Novapex was the most accurate EAL before and after the preflaring procedure, which was confirmed by the radiographic analysis. All EALs tested increased their accuracy after preflaring, but no significant difference was noted for the Novapex. CONCLUSION: The Novapex was more accurate compared to the Mini Apex and Propex II. Preflaring procedure was advantageous for all EALs.

Low-shrinking composites. Are they reliable for bonding orthodontic retainers?

Objective: To evaluate the shear bond strength (SBS), fracture mode, wire pull out (WPO) resistance and microleakage between low-shrinking and conventional composites used as a lingual retainer adhesive. Methods: A total of 120 human mandibular incisor teeth, extracted for periodontal reasons, were collected. Sixty of them were separated into two groups. To determine the SBS, either Transbond-LR (3M-Unitek) or Silorane (3M-Espe) was applied to the lingual surface of the teeth by packing the material into standard cylindrical plastic matrices (Ultradent) to simulate the lingual retainer bonding area. To test WPO resistance, 20 samples were prepared for each composite where the wire was embedded in the composite materialand cured. Then tensile stress was applied until failure of the composite occurred. The remaining 60 teeth were divided into two groups and multi-stranded 0.0215-inch diameter wire was bonded with the same composites. Microleakage was evaluated by the dye penetration method. Statistical analyses were performed by Wilcoxon, Pearson chi-square, and Mann-Whitney-U tests at p ＜ 0.05 level. Results: The SBS and WPO results were not statistically significant between the two groups. Significant differences were found between the groups in terms of fracture mode (p ＜ 0.001). Greater percentages of the fractures showed mix type failure (85%) for Silorane and adhesive (60%) for Transbond-LR. Microleakage values were lower in low-shrinking composite than the control and this difference was found to be statistically significant (p ＜ 0.001). Conclusions: Low-shrinking composite produced sufficient SBS, WPO and microleakage values on the etched enamel surfaces, when used as a lingual retainer composite. (Korean J Orthod 2011;41(1):51-58)

A preliminary analysis in the preparation and obturation of oval canals

Objective: 1) to observe the appearance of uninstrumented recesses in oval canals after instrumentation using circumferential filing. 2) To determine the quality of obturation both with cold lateral compaction and thermo plasticized gutta-percha technique in these recesses Study design: Twenty non-carious, freshly extracted human mandibular incisors with single canals were divided into group I (n=10) and group II (n=10) according to the two different obturation methods. The sectioned roots were prepared with flexofiles (Dentsply, Maillefer) ranging from #15 to #40 by using circumferential filing. The obturated specimens were horizontally sectioned at 5 mm from the apex. Each section was observed under the stereomicroscope at x40 magnification. The quality of obturation in the recesses was evaluated by using 3-point scoring system; the results were subjected to statistical analysis. Results and Conclusion: The results showed that, uninstrumented recesses might be left in many oval canals, even after circumferential filing with smaller size files. In addition, the thermoplasticized obturation technique was better in filling the recesses as compared to lateral compaction but the results were statistically insignificant

Microleakage between composite/wire and composite/enamel interfaces of flexible spiral wire retainers: direct versus indirect application methods

The aim of this in vitro study was to compare the microleakage of flexible spiral wire retainers (FSWR) at composite/wire and composite/enamel interfaces produced by an indirect application method to that of a conventional direct application method. Forty freshly extracted human mandibular incisor teeth were randomly divided into two equal groups. Group 1 was bonded directly according to the manufacturer's recommendations. Group 2 consisted of 20 teeth bonded indirectly with Transbond LR as the adhesive and Sondhi Rapid Set A/B Primer (3M Unitek, Monrovia, CA, USA), a filled resin primer. After bonding, specimens were further sealed with nail varnish, stained with 0.5% basic fuchsine for 24 h, sectioned and examined under a stereomicroscope that measured microleakage at the composite/wire and composite/enamel interfaces from both mesial and distal margins. Statistical analyses were performed using Wilcoxon and Mann-Whitney U-tests with Bonferroni correction. Statistical comparisons indicated that no statistically significant differences were observed between composite/wire and composite/enamel interfaces for direct vs. indirect application procedures (Direct method p = 0.630 and Indirect method p = 0.930). Comparisons of the microleakage scores between direct and indirect FSWR application groups at composite/wire and composite/enamel interfaces indicated no statistically significant microleakage differences at mesial or distal margins (Composite/enamel interface p = 0.361 and Composite/wire interface p = 0.270). The type of FSWR application procedures (direct vs. indirect) did not significantly affect the amount of microleakage at the enamel/composite/wire complex.

Fracture resistance of tooth fragment reattachment: effects of different preparation techniques and adhesive materials

The purpose of this study was to evaluate and compare the bond strengths of experimentally fractured human tooth fragments reattached with different adhesive materials and retentive techniques in vitro. Uncomplicated crown fractures were obtained on intact human mandibular permanent incisors by applying perpendicular load to the buccal aspect of tooth crowns. Fractured teeth were randomly assigned into one of three reattachment protocols: (i) Simple reattachment, (ii) Overcontour preparation, and (iii) Internal dentin groove. The first and second groups were divided into 10 subgroups, and the third group into five subgroups (n = 10 per group) with respect to five different adhesive systems (Prime&Bond NT, Adper Single Bond II, Adper Prompt L-Pop, Clearfil S(3) Bond, G Bond) used with or without a hybrid resin composite (Z250). Restored teeth were subjected to thermal cycling, and subsequently to the same loading protocol used for fracturing intact teeth. Fracture strength after reattachment procedures was recorded as a percentage of the original fracture strength. Both type of adhesive material and placement of an intermediate layer of resin composite affected the fracture resistance (P < 0.05). The highest fracture strength recovery was obtained using the internal dentin groove technique (54 +/- 0.58%, P < 0.05), followed by the overcontour and simple reattachment protocols (49 +/- 0.58% and 32 +/- 0.82%, respectively, P < 0.05). Ultramorphological evaluation of bonded specimens revealed voids and microcracks along the adhesive interface, which might contribute to postadhesive failure.

Apical extrusion of debris after hand, engine-driven reciprocating and continuous preparation

PURPOSE: This in vitro study assessed the amount of debris extruded apically after preparation with different techniques. METHODS: Sixty healthy, extracted, human mandibular incisors were randomly divided into 3 groups: Group A - hand crown-down technique; Group B - crown-down technique with enginedriven rotary reciprocating instruments; Group C - Protaper: engine-driven continuous rotary instrumentation. The roots were immersed in 2.3 mL of distilled water. After preparation, the water in each tube was filtered to collect solid material extruded, and the filters were weighed using a precision scale. Data were analyzed by Kolmogorov-Smirnov and Kruskal-Wallis tests at the 0.05 level of significance. RESULTS: The statistical analysis showed that group C had significantly higher values of debris than groups A and B. CONCLUSION: The instrumentation using a continuous rotary technique, Protaper, produced greater apical extrusion than the hand and engine-driven crown-down techniques. The direction of instrumentation, whether cervical-apical or apical-cervical, seems to be a more important factor influencing apical extrusion than whether the instrumentation was performed by hand or was engine-driven.

Microleakage between composite-wire and composite-enamel interfaces of flexible spiral wire retainers. Part 2: comparison of amorphous calcium phosphate-containing adhesive with conventional lingual retainer composite

The aim of this study was to test the hypothesis that there is no difference in the microleakage values of a newly developed amorphous calcium phosphate (ACP)-containing adhesive and a conventional lingual retainer composite at the composite-enamel and composite-wire interfaces of flexible spiral wire retainers (FSWRs). Sixty freshly extracted human mandibular incisors separated into three equal groups were used in this study. Multi-stranded 0.0215 inch diameter wire was bonded to enamel using conventional orthodontic adhesive (Transbond LR, 3M Unitek) and ACP-containing composite (Aegis Ortho, Harry J. Bosworth Co.), with or without the use of a primer. The specimens were sealed with nail varnish, stained with 0.5 per cent basic fuchsine for 24 hours, sectioned and examined under a stereomicroscope, and scored for microleakage at the composite-enamel and composite-wire interfaces from the mesial and distal margins. Statistical analyses were performed with Kruskal-Wallis and Mann-Whitney U-tests with a Bonferroni correction. Little or no microleakage was observed between the composite-enamel interface for any of the three groups, and any difference was not statistically significant. The amount of microleakage at the wire-composite interface was higher than that at the enamel-composite interface. Multiple comparison testing showed statistically significant differences in microleakage between Transbond LR and the ACP-containing adhesive used with primer at the composite-enamel and composite-wire interfaces (P < 0.001). ACP-containing adhesive used with primer showed the highest microleakage scores at the composite-enamel (mean: 0.39 +/- 0.42 mm) and composite-wire (mean: 1.66 +/- 0.47 mm) interfaces. The hypothesis is rejected. The ACP-containing composite used with or without primer showed significantly higher leakage at the composite-wire interface, while conventional lingual retainer composite showed lower microleakage scores.

Microleakage between composite-wire and composite-enamel interfaces of flexible spiral wire retainers. Part 1: comparison of three composites

The aim of this investigation was to test the hypothesis that there is no difference in microleakage between composite-enamel and composite-wire interfaces, when different composites are used. Forty-five freshly extracted human mandibular incisors separated into three groups were used in the study. Multi-stranded 0.0215 inch diameter wire was bonded to enamel using two conventional (Transbond XT and Transbond LR) and a flowable (Venus Flow) orthodontic composite. The specimens were sealed with nail varnish, stained with 0.5 per cent basic fuchsine for 24 hours, sectioned and examined under a stereomicroscope, and scored for microleakage at the composite-enamel and composite-wire interfaces from the mesial and distal margins. Statistical analysis was performed using Kruskal-Wallis and Mann-Whitney U-tests with a Bonferroni correction. Little or no microleakage was observed between the composite-enamel interfaces for the three investigated composites, and any difference was not statistically significant. However, statistically significant differences were found between microleakage at the composite-wire interface for both the conventional and flowable composite groups (P < 0.001). Flowable composite showed the highest leakage (mean: 4.8 +/- 0.8 mm), while Transbond XT (mean: 0.5 +/- 0.3 mm) and Transbond LR (mean: 1.1 +/- 1.2 mm) showed significantly lower and comparable results. The amount of microleakage at the wire-composite interface was significantly greater than that at the enamel-composite interface of flexible spiral wire retainers (FSWRs). The null hypothesis is therefore rejected. Flowable composites may not be appropriate for bonding FSWRs.

Adhesive properties of bonded orthodontic retainers to enamel: stainless steel wire vs fiber-reinforced composites.

The objectives of this study were to compare the bond strength of a stainless steel orthodontic wire vs various fiber-reinforced composites (FRC) used as orthodontic retainers on enamel, analyze the failure types after debonding, and investigate the influence of different application procedures of stainless steel wires on bond strength. Caries-free, intact human mandibular incisors (N = 80, n = 10 per group) were selected and randomly distributed into 8 groups. After etching with 37% H3PO4 for 30 s, rinsing and drying, bonding agent (Stick Resin) was applied and light polymerized. Then one of the following FRC materials was applied on the flowable composite (Stick Flow) using standard molds: group 1: Angelus Fibrex Ribbon; group 2: DentaPreg Splint; group 3: ever-Stick Ortho; group 4: Ribbond. In group 5, Quad Cat Wire was applied in the same manner as in FRC groups. In group 6, after applying bonding agent (Stick Resin), Quad Cat Wire was placed directly on the tooth surface and covered with Stick Flow composite. In group 7, after bonding agent (Heliobond) was applied, Quad Cat Wire was placed directly on the tooth surface and covered with Tetric Flow composite. In group 8, after applying bonding agent (Heliobond) and polymerization, Tetric Flow composite was applied, not polymerized, and Quad Cat Wire was placed and covered with Tetric Flow again. Specimens were thermocycled for 6000 cycles between 5 degrees C and 55 degrees C and loaded in a universal testing machine under shear stress (crosshead speed: 1 mm/min) until debonding occurred. The failure sites were examined under an optical light microscope. Data were analyzed using one-way ANOVA and the Tukey-Kramer adjustment test (alpha = 0.05). Significant differences were found between the groups (p = 0.0011) (ANOVA). Bond strength results did not significantly differ either between the FRC groups (groups 1 to 4) (6.1 +/- 2.5 to 8.4 +/- 3.7 MPa) (p > 0.05) or the wire groups (groups 5 to 8) (10.6 +/- 3.8 to 14 +/- 6.7 MPa) (p > 0.05). Failure types varied within the FRC groups, but mainly composite was found left adhered on the enamel surface at varying degrees. In the stainless steel wire groups, when the retainer was applied onto the bonding agent and then covered with flowable resin, partially attached composite on the enamel was often found after debonding. When the wires were embedded in the flowable composite, the Heliobond group (group 8) showed more adhesive failures between the enamel and the composite compared to group 5, where the bonding agent was Stick Resin. Regardless of their application mode, stainless steel orthodontic bonded retainers delivered higher bond strengths than those of fiber retainers. The differences were statistically significant compared to those of Angelus Fibrex Ribbon and DentaPreg Splint.