Nd:YAG Laser Treatment of Bioglass-coated Zirconia Surface and Its Effect on Bond Strength and Phase Transformation.

PURPOSE: To evaluate the morphological properties, phase transformation, and microshear bond strength of composite cement to bioglass-coated zirconia surfaces treated with Nd:YAG laser. MATERIALS AND METHODS: Seventy-five zirconia disks were divided into five groups (n = 15). Group C received no surface treatment (control). Group S was subjected to sandblasting with 50-µm aluminum oxide particles. Group B samples were coated with bioglass 45S5. Groups BL9 and BL5 received bioglass coating and laser irradiation with 9 J/cm2 and 5 J/cm2 energy density. Morphological assessment was done using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Zirconia phase transformation was assessed by XRD. Microhear bond strength testing was performed using a modified microtensile tester. The data were analyzed using the Welch test and the Games-Howell test (p < 0.05). RESULTS: The sandblasted and bioglass-coated groups showed the highest bond strengths compared to other groups (p < 0.05). Group S showed the highest surface roughness and the highest frequency of cohesive failure. In all samples, the tetragonal phase decreased after surface treatment. Groups BL9 and BL5 showed some levels of tetragonal to cubic phase transformation. CONCLUSION: Bioglass coating of zirconia surfaces (using the slurry method) can increase its microshear bond strength comparable to that of sandblasting. Surface roughness of sandblasted zirconia was the highest among all methods. Irradiation of Nd:YAG laser on bioglass-coated zirconia surfaces is not effective and decreases its bond strength compared to sandblasting and bioglass coating. Increasing the Nd:YAG laser energy density cannot increase the surface roughness of bioglass-coated zirconia surfaces. Bioglass coating results in transformation of the tetragonal to the cubic phase.

The Effect of Bioglass Coating on Microshear Bond Strength of Resin Cement to Zirconia.

Objectives: Durable bonding to zirconia is a challenging issue in dentistry. This study aimed to assess the effect of bioglass coating of zirconia on the microshear bond strength of resin cement to zirconia and to study the effect of thermocycling on this bond. Materials and Methods: This in-vitro experimental study was conducted on 60 yttria-stabilized tetragonal zirconia blocks in six groups (N=10) based on surface pretreatment and thermocycling. Surface pretreatments included no treatment control, alumina particle abrasion, and bioglass-coating of zirconia. Resin bonding was performed with Panavia F2.0 cements. Then, half of the specimens underwent a 24-hour incubation in 37°C water, while the other half were subjected to thermocycling (12000 cycles, 5-55°C, 60s for each batch) following the same incubation period. Subsequently, the microshear bond strength of the specimens was measured. Additionally, one block from each group was subjected to scanning electron microscopy and X-ray diffraction. The data were analyzed using Kruskal-Wallis and Mann-Whitney U tests. Results: There was a significant difference between the bond strength values of different groups (P<0.001). Alumina particle abrasion and bioglass coating equally increased the bond strength compared to the untreated control group (P<0.001). Thermocycling caused significant decreases in bond strength in all the groups (P<0.001); however, the bond strength value of the thermocycled bioglass-coated group was significantly higher than that reported for the thermocycled alumina particle abraded group (P=0.015). Conclusion: Despite the decrease in the bond strength values after thermocycling, the long-term efficacy of the bioglass coating of zirconia was promising.

Treatment of Peri-Invagination Lesion and Vitality Preservation in Type III Dens Invaginatus in Bilateral Immature Maxillary Lateral Incisors: A Case Report.

The superior lateral incisors are primarily affected by the developmental deformity known as dens invaginatus (DI). Oehler's type III DI has the highest complexity rendering a root canal treatment (RCT) an arduous challenge for this type, so early diagnosis and treatment before pulp involvement are important. This report presents two maxillary lateral incisors with type IIIb DI, the left one being associated with a periapical lesion and the right one with normal pulp. A nine-year-old boy was referred to our clinic complaining of mobility of the maxillary left lateral incisor (LLI) associated with gumboil throughout the previous two months. Periapical radiolucency was visible on radiographs, as well as an invagination that crosses the apical foramen from the pulp chamber in both maxillary lateral incisors. The pulp of the main canal of LLI was vital and pseudo canals were necrotized and associated with chronic apical abscess. Based on the condition of the main pulp of maxillary lateral incisors, two separate treatments were carried out. RCT was done only for the pseudo canals in the LLI, while the main root canal was preserved. The right maxillary lateral incisor (RLI) had vital pulp with normal periapical tissue So the invagination was sealed as the tooth was erupting. During the one-year follow-up period, the development of the root in LLI with a thick root wall and closed apex was observed in the periapical radiograph but pseudo canals became infected and the tooth became symptomatic, therefore retreatment for pseudo canals was carried out. The RLI root was developed and the tooth was clinically asymptomatic, so it didn't need further treatment. Maintaining pulp vitality is crucial for type III Dens invaginated young permanent teeth since it could support root formation and improve long-term prognosis, and in cases with pulp involvement, non-surgical RCT is clinically predictable.

Comparative Evaluation of Canal Transportation and Centering Ratio in Curved Canals: A Study of Cone-beam Computed Tomography and Micro-computed Tomography.

Introduction: This study aimed to compare the accuracy and agreement between cone-beam computed tomography (CBCT) and micro-computed tomography (micro-CT) in the assessment of canal transportation and centering ratio following root canal instrumentation with rotary files. Material and Methods: Twenty mesiobuccal canals of mandibular molars were prepared using the 2Shape sequential rotary system. CBCT and micro-CT scans were performed before and after instrumentation, and the magnitude of transportation and centering ratio were measured. The acceptable transportation was set at ≤0.15 mm. The accuracy and agreement between CBCT and micro-CT were calculated, and the intra-class correlation coefficient (ICC) and kappa coefficient were determined to assess the agreement between the two modalities. Statistical analyses were performed using repeated measures ANOVA. Results: Transportation was detected by both modalities at all distances from the apex after instrumentation. The agreement between CBCT and micro-CT in assessing canal transportation was observed in 80%, 85%, 75%, and 75% of specimens at 1-, 3-, 5-, and 7-mm from the apex, respectively. The ICC for transportation and centering ratio was much lower than 0.75, indicating poor agreement between the modalities. The kappa coefficient did not show acceptable agreement between the methods. Conclusions: CBCT and micro-CT demonstrated poor agreement in assessing canal transportation and centering ratio. Micro-CT remains the preferred modality for in vitro investigations, while CBCT should be limited to clinical settings.

Micro-computed tomography assessment of dentinal microcracks after the preparation of curved root canals with rotary and reciprocal systems.

BACKGROUND: Root canal preparation with nickel-titanium (NiTi) instruments may lead to the formation of microcracks in the root canal wall. Vertical root fractures may initiate from dentinal cracks, and eventually necessitate tooth extraction. OBJECTIVES: This study aimed to assess the effect of the instrumentation of curved root canals of mandibular molars with the 2Shape (2S) sequential rotary, EdgeFile® X1 (EFX1) reciprocating and NeoNiTi (NN) rotational single-file systems on the formation of dentinal microcracks with the use of micro-computed tomography (micro-CT). MATERIAL AND METHODS: Thirty curved mandibular molar root canals were instrumented with the 2S, EFX1 and NN systems (10 in each group). The teeth underwent micro-CT before and after instrumentation. Next, the pre-instrumentation and post-instrumentation cross-sectional images were evaluated and compared for the detection of dentinal microcracks. The number of microcracks in each group was calculated and reported as percentage. The data was analyzed using the McNemar's test with the IBM SPSS Statistics for Windows software, v. 25.0 (α = 0.05). RESULTS: Out of the 29,280 cross-sectional images evaluated in this study, 11.5% showed dentinal microcracks (n = 3,362). On the post-instrumentation images, the frequency percentage of microcracks was 12.0% (n = 585) in the 2S group, 8.8% (n = 402) in the EFX1 group and 13.3% (n = 694) in the NN group. All of the microcracks detected on the post-instrumentation images were also present on the preinstrumentation images and no new microcracks were formed after root canal instrumentation with the aforementioned systems. CONCLUSIONS: Root canal instrumentation with the 2S, EFX1 and NN systems did not result in the formation of new dentinal microcracks.

Comparison of Canal Transportation and Centering Ability of One-G, EdgeGlidePath, and Neolix: A MicroComputed Tomography Study of Curved Root Canals.

AIMS: A glide path is created prior to root canal instrumentation by nickel-titanium (NiTi) rotary files to increase the efficiency and safety of cleaning and shaping. This study aimed to assess root canal transportation in use of different glide path files in curved canals. MATERIALS AND METHODS: 30 sound mesiobuccal root canals of mandibular molars with 20° to 40° curvature were selected and randomly assigned to 3 groups of EdgeGlidePath (EGP, EdgeEndo), One-G (Micro-Mega), and Neolix (Neoniti). The specimens were scanned before and after glide path creation by microcomputed tomography (micro-CT). The pre- and postoperative micro-CT scans were superimposed, and the degree of canal transportation and centering ratio were measured at 1, 3, 5, and 7 mm distances from the apical foramen. Statistical Analysis. The data were analyzed by two-way and one-way ANOVA. RESULTS: The effects of distance from the apical foramen and instrument type and the interaction effect of the two were not significant on the centering ability of the files or canal transportation. CONCLUSION: EdgeGlidePath, One-G, and Neolix files fabricated from the conventional NiTi alloy or heat-treated M-Wire alloy showed similar performance regarding centering ability and canal transportation in glide path preparation in curved canals.