Aim: To compare dentinal cracks incidences after root canal preparation using Hand K-files; Rotary files: Protaper NEXT (PTN), Hyflex Controlled Memory (CM); and Reciprocating files: Wave One and Wave One Gold files. Materials and Methods: Hundred extracted human mandibular first premolars with straight root canals were taken postextraction and were allocated randomly into five groups (n = 20 teeth per group). The canals were instrumented using Hand K-files, Protaper Next (PTN), Hyflex CM, Wave One, and Wave One Gold systems. Group 1-Control group comprised of canals prepared by Hand files. Further, the roots were sectioned at three levels: 3, 6, and 9?mm horizontally from the apex using a saw at a low-speed saw and under water cooling. These slices were examined under a stereomicroscope at 25× magnification and the presence of any dentinal cracks was noted. The frequency of cracks was presented in number and percentage. Intergroup comparison of crack frequency was performed using analysis of variance. Results: No cracks were observed in the control group. In all the other groups, dentinal cracks were observed. The rotary files PTN and Hyflex CM files produced significantly fewer dentinal cracks than the reciprocating Wave One and Wave One Gold files (P < 0.05). The reciprocating files significantly produced more cracks apically than the rotary files (P < 0.05). Analyses were performed on SPSS software (windows version 22.0). Conclusion: Instrumentation with file systems can cause crack formation in the dentinal wall of the root canal. Determination of which files to choose for root canal preparation is technique sensitive and each instrument type has own benefits. However, care should be taken while biomechanical preparation to avoid dentinal cracks formation.
Furthermore, the instrument used can induce cracks in the dentin, and repeated stress during endodontic or restorative instrumentation can cause vertical root fracture (VRF). Dentinal cracks cause biofilm entrapment in these cracked areas along the root surface. The biofilm is difficult to an instrument, and they are a source of potential infection and can lead to endodontic failure. Proper instrumentation and selection of instruments will reduce the iatrogenic errors caused by canal transportation. Hand files, rotary files, and nickel-titanium (Ni-Ti) files for root canal shaping have been introduced for proper shaping of a root canal.
The dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis has a key role in drug addiction susceptibility. In addition to the well-known relationship between cortisol and the HPA axis, other molecules are involved with stress response and could modify the HPA activation, such as the neuropeptide Y (NPY), which has anxiolytic proprieties. There are few studies evaluating the effect of NPY levels on addiction, especially in crack cocaine dependence.
These preliminary findings indicate that crack use influences the modulation of NPY levels and modifies stress response. The NPY pathway may play an important role in the pathophysiology of crack addiction, and the anxiolytic effect of NPY may be impaired in crack users. Future studies should consider NPY as a measurable indicator of the biological state in addiction.
Only few clinical studies have assessed the influence of peripheral NPY levels on addiction to different substances. For instance, Meng et al. found no differences in NPY plasma levels between alcohol-dependent and non-dependent individuals.1717. Meng D, Wu TC, Rao U, North CS, Xiao H, Javors MA, et al. Serum NPY and BNDF response to a behavioral stressor in alcohol-dependent and healthy control participants. Psychopharmacology (Berl). 2011;218:59-67. To the best of our knowledge, no studies have evaluated NPY levels in crack addiction. Variations in NPY levels during drug withdrawal have also not been evaluated, which precludes understanding the influence of NPY on the pathophysiology of addiction. Thus, our aim was to evaluate NPY levels among crack cocaine users during early drug withdrawal to determine their relationship with cortisol levels, time of drug use, days of hospitalization and addiction severity.
The clinical characteristics of the sample are shown in Table 1 . Serum NPY levels at admission and discharge were similar: 3.21 ng/mL (interquartile range [IQR] 2.78-4.32) and 3.40 ng/mL (IQR 3.10-3.90), with p = 0.793. Low levels of NPY at discharge were associated with higher lifetime crack use (p = 0.030; Table 2 ). No influence of recent crack use was detected, although a trend towards association was observed between NPY levels at admission and recent crack use (p = 0.057; Table 2 ). These results indicate that lower NPY levels are associated with crack use. No association was found between days of hospitalization or addiction severity and NPY levels at admission (p = 0.744 and p = 0.065, respectively), discharge (p = 0.719 and p = 0.075, respectively) or delta (p = 0.751 and p = 0.657, respectively) (data not shown).
The present study shows, for the first time, the influence of crack addiction on NPY levels during early withdrawal. These findings were strengthened by the two collection time points, which demonstrated that crack users, even without current drug consumption, could exhibit a disruptive stress response.
Our results indicate that lifetime crack use (years of frequent use) has a negative impact on NPY levels during early withdrawal. These findings suggest that crack use is associated with a putative down-regulation of peripheral NPY levels. This occurs specifically during discharge, when stress and craving could be elevated due to abstinence symptoms.2020. Sinha R, Garcia M, Paliwal P, Kreek MJ, Rounsaville BJ. Stress-induced cocaine craving and hypothalamic-pituitary-adrenal responses are predictive of cocaine relapse outcomes. Arch Gen Psychiatry. 2006;63:324-31. This could explain the increase in anxiety symptoms that may lead to early relapse.2121. Kask A, Harro J, Von Hörsten S, Redrobe JP, Dumont Y, Quirion R. The neurocircuitry and receptor subtypes mediating anxiolytic-like effects of neuropeptide Y. Neurosci Biobehav Rev. 2002;26:259-83. The variation in NPY levels may be affected primarily by drug use, since NPY levels were not associated with psychiatric comorbidities or childhood maltreatment in our sample (Table S1, available as online-only supplementary material).
Withdrawal symptoms have been associated with increased stress response, modifying cortisol levels.2020. Sinha R, Garcia M, Paliwal P, Kreek MJ, Rounsaville BJ. Stress-induced cocaine craving and hypothalamic-pituitary-adrenal responses are predictive of cocaine relapse outcomes. Arch Gen Psychiatry. 2006;63:324-31. In this sense, increased salivary cortisol levels have been correlated with short abstinence time and treatment dropout in addicted individuals.22. Sinha R. Chronic stress, drug use, and vulnerability to addiction. Ann N Y Acad Sci. 2008;1141:105-30. , 77. Daughters SB, Richards JM, Gorka SM, Sinha R. HPA axis response to psychological stress and treatment retention in residential substance abuse treatment: a prospective study. Drug Alcohol Depend. 2009;105:202-8. NPY levels have been positively correlated with cortisol following acute stress exposure in humans,2525. Morgan CA, Rasmusson AM, Wang S, Hoyt G, Hauger RL, Hazlett G. Neuropeptide-Y, cortisol, and subjective distress in humans exposed to acute stress: Replication and extension of previous report. Biol Psychiatry. 2002;52:136-42. and we observed a trend towards association between cortisol and NPY at admission. This specific response could be an attempt to balance the stress mechanism, since NPY has anxiolytic effects. In a homeostatic mechanism, increased NPY levels could aid to reestablish the negative feedback and thus prevent the dysregulation of the HPA axis. In our study, the relationship between cortisol and delta NPY levels suggests that, in crack users, during early withdrawal, there is an increased stress response leading to a physiological increase in cortisol. Nonetheless, during this period a decrease in the variation of NPY levels is also observed, which may indicate little influence of NPY on cortisol levels and on HPA axis regulation. This impaired feedback could be related to a dysfunction in the HPA axis in addictive patients. These findings are supported by Xu et al., who observed a disruptive NPY stress response in substance-dependent individuals regardless of genetic variation.2626. Xu K, Hong KA, Zhou Z, Hauger RL, Goldman D, Sinha R. Genetic modulation of plasma NPY stress response is suppressed in substance abuse: Association with clinical outcomes. Psychoneuroendocrinology. 2012;37:554-64. Furthermore, rat models of cocaine addiction presented lower NPY levels and increased NPY mRNA expression.2727. Freeman WM, Patel KM, Brucklacher RM, Lull ME, Erwin M, Morgan D, et al. Persistent alterations in mesolimbic gene expression with abstinence from cocaine self-administration. Neuropsychopharmacology. 2008;33:1807-17. , 2828. Goodman JH, Sloviter RS. Cocaine neurotoxicity and altered neuropeptide Y immunoreactivity in the rat hippocampus; a silver degeneration and immunocytochemical study. Brain Res. 1993;616:263-72. NPY infusion in the basolateral nucleus of the amygdala was found to reduce behavioral stress and increase social interaction.2323. Silveira Villarroel H, Bompolaki M, Mackay J, Miranda Tapia AP, Michaelson SD, Leitermann RJ, et al. NPY induces stress resilience via down-regulation of Ih in principal neurons of rat basolateral amygdala. J Neurosci. 2018;3528-17. In addition, NPY neutralizes the action of CRH released in the hypothalamus in response to stress, therefore preventing stress effects.2929. Reichmann F, Holzer P. Europe PMC Funders Group Neuropeptide Y: A stressful review. 2016;55:99-109.
It remains to be known why NPY is an understudied peptide in the clinical setting, considering the biological mechanisms of addiction. Scientific literature has deeply explored the reward system related to addiction, but there appear to be other valuable neurological pathways that may enhance the substrate for the discovery of new medications. There is a lack of studies evaluating serum NPY levels in humans with addictive disorder, and therefore the present findings suggesting that the NPY pathway may play an important role in the pathophysiology of crack addiction are a valid contribution. In future studies, NPY levels could be considered a measurable indicator of the biological state in addiction. 2b1af7f3a8