Stress Induced in Periodontal Ligament under Orthodontic Loading (Part II): A Comparison of Linear Versus Non-Linear Fem Study.

BACKGROUND: Simulation of periodontal ligament (PDL) using non-linear finite element method (FEM) analysis gives better insight into understanding of the biology of tooth movement. The stresses in the PDL were evaluated for intrusion and lingual root torque using non-linear properties. MATERIALS AND METHODS: A three-dimensional (3D) FEM model of the maxillary incisors was generated using Solidworks modeling software. Stresses in the PDL were evaluated for intrusive and lingual root torque movements by 3D FEM using ANSYS software. These stresses were compared with linear and non-linear analyses. RESULTS: For intrusive and lingual root torque movements, distribution of stress over the PDL was within the range of optimal stress value as proposed by Lee, but was exceeding the force system given by Proffit as optimum forces for orthodontic tooth movement with linear properties. When same force load was applied in non-linear analysis, stresses were more compared to linear analysis and were beyond the optimal stress range as proposed by Lee for both intrusive and lingual root torque. To get the same stress as linear analysis, iterations were done using non-linear properties and the force level was reduced. CONCLUSION: This shows that the force level required for non-linear analysis is lesser than that of linear analysis.

Stress Induced in the Periodontal Ligament under Orthodontic Loading (Part I): A Finite Element Method Study Using Linear Analysis.

BACKGROUND: Orthodontic tooth movement is a complex procedure that occurs due to various biomechanical changes in the periodontium. Optimal orthodontic forces yield maximum tooth movement whereas if the forces fall beyond the optimal threshold it can cause deleterious effects. Among various types of tooth movements intrusion and lingual root torque are associated with causing root resoprtion, especially with the incisors. Therefore in this study, the stress patterns in the periodontal ligament (PDL) were evaluated with intrusion and lingual root torque using finite element method (FEM). MATERIALS AND METHODS: A three-dimensional (3D) FEM model of the maxillary incisors was generated using SOLIDWORKS modeling software. Stresses in the PDL were evaluated with intrusive and lingual root torque movements by a 3D FEM using ANSYS software using linear stress analysis. RESULTS: It was observed that with the application of intrusive load compressive stresses were distributed at the apex whereas tensile stress was seen at the cervical margin. With the application of lingual root torque maximum compressive stress was distributed at the apex and tensile stress was distributed throughout the PDL. CONCLUSION: For intrusive and lingual root torque movements stress values over the PDL was within the range of optimal stress value as proposed by Lee, with a given force system by Proffit as optimum forces for orthodontic tooth movement using linear properties.

Estimation of Release of Nickel and Chromium by Indian Made Orthodontic Appliance in Saliva.

INTRODUCTION: With increasing use of Indian made orthodontic materials, need was felt to know nickel and chromium release from these material. MATERIALS AND METHODS: This study was conducted on simulated appliances consisting of brackets (022″Roth, Modern orthodontics, Ludhiana, India), from second premolar to central incisor, buccal tube and 0.019×0.025- inch SS arch wires secured with SS ligatures. Immersion was done in artificial saliva. Samples were analysed to using Atomic Absorption Photospectrometer (GVC ScientificEquipment Pvt. Ltd Australia) at AES Laboratories (P) Ltd., Noida India on 1(st), 7(th), 14(th) and 28(th) day. RESULTS: SPSS (ver 17, Inc., Chicago, Illinois, USA) was used toperform the statistical analysis. Descriptive statistics i.e. median and 25 and75 percentiles were used. Peak nickel release was on 7(th) day and subsequently declined over 14(th) and 28(th) day. The peak level of chromium concentration was on 14(th) day, which declined thereafter. CONCLUSION: Average daily release of nickel and chromium over a period of one month was 97.368 µg/day and 47.664 µg/day respectively. The estimated release rates were approximately 32% and 16% of the reported average daily dietary.

Traumatic impact loading on human maxillary incisor: A Dynamic finite element analysis.

BACKGROUND: The most vulnerable tooth is the maxillary incisor, which sustains 80% of dental injuries. Dynamic Finite element analysis is used to understand the biomechanics of fracture of maxillary incisor under traumatic impact loading. AIM: The aim was to investigate the stress patterns of an upper incisor in a three-dimensional (3D) model under traumatic impact loading in various directions. MATERIALS AND METHODS: A 3D finite element model of the upper incisor and surrounding tissues was established. A sinusoidal force of 800N was applied over a period of 4 ms. RESULTS: Software performs a series of calculations and mathematical equations and yields the simulation results. During the horizontal impact (F1), stresses were concentrated in the cervical area of the crown, reaching peak stress of 125 MPa at 2 ms. CONCLUSION: A horizontal force exerted on the labial surface of the tooth tends to cause cervical crown fractures, oblique crown root fractures, and oblique root fractures.

Mandibular incisor extractions in orthodontics: pitfalls and triumphs: a report of three cases.

Mandibular incisor extraction therapy has been used as a treatment option since the early 1900s to relieve tooth size-arch length discrepancies in the anterior segment of the mandible. The advantages of this therapy include potential reduction in treatment time, possibility of achieving better long-term stability in the mandibular anterior segment since inter canine width is not increased and maintenance of the soft-tissue profile because retraction of the mandibular incisors is less compared with mandibular premolar extractions These advantages are counterbalanced, however, by some potential disadvantages. The most significant of these is the possibility of the space reopening in the long term, an occlusal result less than ideal because of a significant tooth-mass reduction in the anterior mandibular region, development of an open gingival embrasure and the need for permanent or long term retention. We present three cases with three different indications for mandibular incisor extraction where the patient was benefited despite this atypical extraction pattern.

Drug utilization pattern in dental outpatients in tertiary care teaching hospital in western Nepal.

A high incidence of dental disease has been reported in Nepal. Previous studies, both in the Manipal Teaching Hospital, Pokhara, Nepal, and other centers revealed problems in the use of medicines in dentistry. A number of initiatives to improve prescribing have been carried out. The study presented here was undertaken to assess the impact of these initiatives on drug utilization among dental outpatients. The study was conducted among patients attending the dental outpatient department of the hospital over a six-month period. Demographic details were studied. The drug classes and individual drugs prescribed were recorded. The cost of drugs was calculateS using the outpatient pharmacy price list. The prescriptions were analyzed using the WHO/INRUD prescribing indicators. Anomalies were noted in prescribing. Improvement was noted in certain parameters compared to previous studies. The educational initiatives should be strengthened. Managerial interventions can be considered. Further studies are required.