16 Etiological Factors There are a lot of controversies about the causes of NB. While some studies related NB to behavioral problems,17 and anxiety,18,19 others did not believe so.20,21 Anxiety in children with NB is not a trait; it is a state.22 The trait which is accompanied with NB is oral aggression.22 Oral habits including NB have an environmental etiology, and are risk factors for malocclusion development, especially in children older than preschool

years.23 Inadequate motor activity is supposed to be a cause of an increase in NB.5 Although, it was suggested that NB might reduce anxiety or tension,19 recent studies Inhibitors,research,lifescience,medical Inhibitors,research,lifescience,medical do not support the anxiety theory for NB.5,24

Nail biting usually occurs as a result of boredom or working on difficult problems rather than anxiety. Nail biter do not bite their nail when they are engaged in social interactions, or when they are reprimanded for the behavior.24 It is suspected that smoking and gum chewing in adults are substitutes for NB in childhood.3 Severe and mild NB appear to have some differences in terms of the basis of physical and social consequences, severity, frequency, and physiological mechanisms.25 Co-Morbidities or Underlying Conditions There are limited reports about co-morbidity Inhibitors,research,lifescience,medical of NB with psychiatric disorders.6 Three most common co-occurring psychiatric disorders in clinical sample children with NB are attention deficit hyperactivity disorder (74.6%), oppositional defiant disorder (36%), and separation anxiety disorder (20.6%).6 Other Inhibitors,research,lifescience,medical co-morbid disorders include enuresis (15.6%), tic disorder (12.7%) and obsessive compulsive disorder (11.1%), major

depressive disorder (6.7%), mental retardation (9.5%), and pervasive GDC-0449 molecular weight developmental disorder (3.2%).6 Co-morbidity with psychiatric Inhibitors,research,lifescience,medical disorder is not associated with gross physical damage, severity or onset age of NB. All of the boys and 81% of the girls of the clinical sample of children with NB suffer from at least one psychiatric disorder.6 Nail biting is also one of the most common (28.6%) psychiatric problems in children and adolescents with Tourette syndrome.26 Other stereotypic behavior problems are very common in children with NB, and their rate is up to 65%.6 The study,6 also did not support that NB was associated with anxiety disorders.6 The most found common co-occurring stereotypic behaviors were lip biting (33.3%) and head banging (12.7%).6 Another study reported that 70% of individuals with hair-pulling habit had other stereotypic behaviors, of which skin-picking and nail-biting were the most common ones.27 Individuals with NB have higher obsessive compulsive behaviors.2,18 Fifty six out of 509 individuals with obsessive compulsive disorder had NB.