Evaluation of rock stability challenges affecting the formation of sustainable pit lake towards mine closure following crown pillar extraction in open pit-underground mines.

The extraction of high-grade ore from the crown pillar (CP) in open pit-underground mines poses stability challenges and potential environmental risks. While an open pit has the potential to transition into a pit lake, the extraction of CP can induce failure in the surrounding walls, preventing the formation of the lake. There is also a concern that the backfilling material may not effectively confine toxic water within the pit, thereby risking contamination of the underground environment. To address these issues, a case study was conducted using FLAC3D and 3DEC models to evaluate the extent of failure caused by CP extraction. On-site observation, along with modelling, has revealed rock damage, including deformation stretching about 4 m from the pit wall and extending vertically from the pit floor to the ramp. The study identified three primary factors leading to pit wall failure or damage: steep pit slopes reaching approximately 70° near the pit floor, an underestimated CP thickness by about 4 m, and the concurrent extraction of ore from the pit wall alongside CP. Based on these findings, rehabilitation measures are suggested, including excavation of the deformed wall and cantilever, as well as partial pit backfilling. There is a substantial increase in the volume of backfill material as the extent of failure increases, which raise concerns about the decision-making process regarding CP extraction. Therefore, this article aims to raise environmental awareness and evaluate whether the benefits of ore extraction outweigh the considerations for pit wall support and the rehabilitation efforts during mine closure.

Effects of a fluoride-containing casein phosphopeptide-amorphous calcium phosphate complex on the shear bond strength of orthodontic brackets.

The purpose of this study was to investigate the effects of enamel pre-treatment with a new fluoride-containing casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) complex on the shear bond strength (SBS) of brackets bonded with etch-and-rinse or self-etching adhesive systems. The material comprised 66 extracted human premolars randomly divided into six equal groups with respect to the enamel pre-treatment and adhesive system employed: 1. No pre-treatment and brackets bonded with the etch-and-rinse adhesive system (Transbond XT). 2. Pre-treatment with fluoride-containing CPP-ACP paste (MI Paste Plus) and Transbond XT. 3. Pre-treatment with non-fluoride CPP-ACP paste (MI Paste) and Transbond XT.4. No pre-treatment and brackets bonded with the self-etching adhesive system (Transbond Plus). 5 and 6. Enamel pre-treated as for groups 2 and 3, respectively, and the Transbond Plus. Bonded specimens were subjected to thermal cycling (×1000) before SBS testing. The residual adhesive on the enamel surface was evaluated after debonding with the adhesive remnant index (ARI). Data evaluation was made using one-way analysis of variance and Tukey test for SBS results, and Kruskal-Wallis test for ARI results. The results showed that enamel pre-treatment with either fluoride or non-fluoride CPP-ACP paste had no significant effect on the SBS of the self-etching adhesive system (P > 0.05). Enamel pre-treatment with non-fluoride CPP-ACP in group 3 significantly reduced the SBS of the etch-and-rinse adhesive (P < 0.001), while pre-treatment with fluoride-containing CPP-ACP paste (groups 2 and 5) did not affect debonding values (P > 0.05). The fluoride-containing CPP-ACP did not compromise the SBS of brackets bonded with the tested etch-and-rinse and self-etching systems, but its non-fluoride version significantly decreased the SBS of the etch-and-rinse adhesive system.

The effects of prophylactic ozone pretreatment of enamel on shear bond strength of orthodontic brackets bonded with total or self-etch adhesive systems.

OBJECTIVES: The aim of this in vitro study is to determine (1) shear bond strength (SBS) of brackets bonded with self-etch and total-etch adhesive after ozone treatment (2) bond failure interface using a modified Adhesive Remnant Index (ARI). METHODS: 52 premolars were randomly assigned into four groups (n=13) and received the following treatments: Group 1: 30 s Ozone (Biozonix, Ozonytron, Vehos Medikal, Ankara, Turkey) application + Transbond Plus Self-Etching Primer (SEP) (3M) + Transbond XT (3M), Group 2: Transbond Plus SEP + Transbond XT, Group 3: 30 s Ozone application + 37% orthophosphoric acid + Transbond XT Primer (3M) + Transbond XT, Group 4: 37% orthophosphoric acid + Transbond XT Primer + Transbond XT. All samples were stored in deionised water at 37°C for 24 hours. Shear debonding test was performed by applying a vertical force to the base of the bracket at a cross-head speed of 1 mm/min. RESULTS: The mean SBS results were Group 1: 10.48 MPa; Group 2: 8.89 MPa; Group 3: 9.41 MPa; Group 4: 9.82 MPa. One-Way Variance Test revealed that the difference between the groups was not statistically significant (P=0.267). Debonded brackets were examined by an optical microscope at X16 magnification to determine the bond failure interface using a modified ARI. The results were (mean) Group 1: 2.38; Group 2: 1.31; Group 3: 3.00; Group 4: 1.92. Multiple comparisons showed that Groups 1 and 2, 2 and 3, 3 and 4 were statistically different (P=0.014, P<.001 and P=0.025). CONCLUSIONS: Ozone treatment prior to bracket bonding does not affect the shear bond strength.

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.

Effect of acidulated phosphate fluoride and casein phosphopeptide-amorphous calcium phosphate application on shear bond strength of orthodontic brackets.

OBJECTIVE: To evaluate the effect of a recently introduced prophylactic agent, casein phosphopeptide-amorphous calcium phosphate (CPP-ACP), on shear bond strength of brackets and compare it with the effect of acidulated phosphate fluoride (APF). MATERIALS AND METHODS: Forty-eight freshly extracted mandibular bovine incisors were used. Teeth were randomly divided into four groups (n = 12) as follows: group 1 served as control, and no pretreatment was performed on the enamel; group 2, enamel was treated with 1.23% APF and CPP-ACP, respectively; group 3, enamel was treated with CPP-ACP; and group 4, enamel was treated with 1.23% APF for 4 minutes. In all groups, brackets were bonded using a conventional acid-etch and bond system (Transbond XT, 3M Unitek, Monrovia, Calif). Bonded specimens were first stored in deionized water at 37 degrees C for 24 hours, subjected to thermal cycling for 1000 cycles, and further stored in distilled water for 6 weeks before debonding procedures. After debonding, teeth and brackets were examined under a stereomicroscope at 10x magnification for any adhesive remaining, in accordance with the modified adhesive remnant index. RESULTS: The shear bond strengths of all experimental groups were significantly higher than that of the control group (P < .01). There was no significant difference between the shear bond strengths of the experimental groups (P > .05). CONCLUSION: The use of CPP-ACP either alone or combined with APF could be considered as an alternative prophylactic application in orthodontic practice since it did not compromise bracket bond strength.