Query: effect of geometric outline of tooth on periodontium

title: Effect of Geometric Dimensions and Material Models of the Periodontal Ligament in Orthodontic Tooth Movement.
abstract: The aim of the present work was set to explore the role of root diameter, root length, and thickness of periodontal ligament (PDL) and its material properties (linear and nonlinear elastic material models) on the stress and strain distribution, tooth displacement and centre of resistance (CR) location.  Both the bone and tooth were considered as rigid bodies and the PDL was modelled as a paraboloid with different geometric dimensions and material properties.  To achieve this goal, a horizontal force of 1 N was applied in the CR location and the stress and strain distribution and tooth displacement were quantified. Locations of CR were estimated through iterative finite element procedure.  It was predicted that the position of CR is in the range of 34% to 39% of the root length, slightly higher than one third of the root length reported in the literature. The geometrical dimensions of the PDL had no significant effect on the position of CR, especially in the nonlinear material model of the PDL, while the initial displacement of the tooth was found to be highly dependent on the geometrical and mechanical properties of the PDL.  The simplified PDL modelling approach with nonlinear material behaviour can be suggested for the estimation of initial tooth movement for individual clinical applications without the use of advanced 3D scans.

title: Tooth Outline Shape Analysis of the Ryukyu Wild Boar (Sus scrofa riukiuanus) and the Japanese Wild Boar (S. s. leucomystax) by Geometric Morphometrics
abstract: We examined whether the shapes of the teeth could be used to distinguish morphological differences of modern Sus scrofa between subspecies, and between regions. The occlusal outlines of the lower teeth of five populations of the Ryukyu wild boar (S. s. riukiuanus) and two populations of the Japanese wild boar (S. s. leucomystax) were photographed and digitized into landmarks. The landmark coordinates were statistically compared among the populations. As a result, correct assignment rates of the populations based on their tooth shape was the highest for the fourth deciduous premolar. Pairwise test detected significant differences in tooth outline shape between the two subspecies. In addition, the tooth outline shapes of geographically adjacent populations tended to be similar. The results in this study indicated that the evaluation of tooth outline shapes, especially that of the fourth deciduous premolar, is a powerful approach for distinguishing subspecies of S. scrofa as well as for evaluating geographic variation among them. This method is useful in archaeological and paleontological studies because of its applicability for isolated teeth, and has potential to increase our understanding about the history of macroevolution, migration, and introduction of S. scrofa in the Japanese archipelago.

title: Effect of hyperfunctional occlusal loads on periodontium: A three dimensional finite element analysis
abstract: The periodontal tissue reaction to variations in occlusal forces has been described in the literature wherein clinical and histologic changes are discussed that produced due to stresses in the periodontal structures. Unfortunately, these stresses are not quantified.  The aim of this study is to determine the stress produced on various periodontal tissues at different occlusal loads using finite element model (FEM) study.  Four FEMs of maxillary incisor were designed consisting of the tooth, pulp, periodontal ligament (PDL) and alveolar bone at the various level of bone height (25% 50% and 75% Different occlusal load (15 and 29 kg) at an angle of 50deg to the long axis of the tooth was applied on the palatal surface at the level of middle third of the crown. All the models were assumed to be isotropic, linear, and elastic, and the analysis was performed on a Pentium IV processor computer using the ANSYS software.  At normofunction load, the stresses were maximum on the mesial side near the cervical region at point D for tooth 10.93 Mpa) for PDL 4.06 Mpa) for bone 4.3 Mpa) with normal bone levels as the bone levels decreased the stresses increased and the stresses tend to concentrate at the apical region. At any given point, the stresses were increased by 90% at hyperfunctional load.  Based on the findings of the present study, there is reasonably good attempt to express numerical data of stress to be given normal occlusal and hyperfunctional loads to simulate clinical occlusal situations which are known to be responsible for healthy and diseased periodontium.

title: Effect of exogenous retinoic acid on tooth movement and periodontium healing following tooth extraction in a rat model.
abstract: To evaluate the effect of isotretinoin on orthodontic tooth movement (OTM) and wound healing following exodontia.  Sixteen 40 day old male Wistar rats were divided into two groups: (a) OTM and (b) tooth extraction (TE) of the upper 1st molar and OTM. The experimental animals were treated with isotretinoin (7.5 mg/kg) and the control animals with oil solution for 37 days.  The OTM and bone volume were evaluated by the micro CT and the periodontium healing was assessed by immunohistochemistry for VEGF C, COX 2 and IL 1ss.  The animals of both groups submitted to the TE showed a statistically significant decrease in the bone volume percentage and increase in OTM. No significant difference of OTM and bone volume was observed between the control and experimental group. However, the alveolar bone of the isotretinoin group revealed more medullary spaces with inflammatory, hematopoietic cells, blood vessels and intense immunolabeling for VEGF C. This group also showed faster gingival regeneration. No significant difference was observed in the COX 2 and IL 1ss labelings following TE between both groups.  The isotretinoin did not affect the OTM nor did it cause an alteration in maxillary bone volume. This exogenous acid may contribute to the acceleration of gingival healing.

title: A three dimensional finite element analysis of the effect of archwire characteristics on the self ligating orthodontic tooth movement of the canine
abstract: In orthodontics, the tooth movement is a biologic reaction to applied force systems, brackets, archwires, and periodontium tissue.  To investigate the effects of the various archwire characteristics like the friction coebetween bracket and archwire, the cross section shape, and the cross section dimension, on the displacement and the periodontal ligament (PDL) stresses of canine's movement in a self ligating treatment using the finite element (FE) analysis method.  Models of teeth and their supporting tissues, brackets and archwires were constructed. Ten kinds of archwires were used for the simulation.  Considering the translation movement, the maximum displacement, highest stress, and Rcr increased with an increase in the cross section area. The maximum displacement and highest stress increased with an increase in the friction coefficient. The Rcr values increased with an increase in the friction coefficient in the round archwires, while decreased with an increase in the rectangular archwires. However, these change tends were different in rotation and inclination movement.  The archwire characteristics (round archwire, rectangular archwire, cross section area, and friction coefficient) exhibited different effects on the tooth translation, rotation, and inclination. Our results can assist in the improvement of the self ligating orthodontic treatment.

title: Effect of orthodontic force associated with cigarette smoke inhalation in healthy and diseased periodontium. A histometric and immunohistochemistry analysis in rats
abstract: The aim of the present study is to evaluate the effect of orthodontic forces in healthy or diseased periodontium of rats submitted/not submitted to cigarette smoke inhalation.  Fifty six male Wistar rats were allocated into two groups of conditions: smoking and non smoking. Each group was divided into the following subgroups: control (C) orthodontic tooth movement (OTM) ligature induced periodontitis (P) and P+OTM (POTM) with n 14 each. Periodontitis was induced in the lower first molar by cotton ligature, and a 4 mm closed stainless steel spring was used for orthodontic movement. Animals were exposed to the smoke of 10 cigarettes for 8 minutes, 3 times a day for 60 days before P induction and OTM. Evaluation parameters were macroscopic analysis of dental movement, bone loss and bone density. In addition, the receptor activator of nuclear factor kappaB (RANK) immunostaining and RANK ligand/osteoprotegerin ratio in the furcation region were assessed.  There was no statistically significant difference between groups, ie, smoking and non smoking conditions (P .338) Bone loss intragroup analysis between the P and POTM groups was not significant in smoking (P 1) and non smoking (P .5) conditions; both were different from OTM and C in each condition. Regarding bone density, POTM and P were significant to C (P .05) The POTM group was significant to the P and C (P .001) regarding dental movement. The RANK ligand/osteoprotegerin ratio in the non smoking condition was higher in P and POTM compared to C and OTM and to P and POTM in the smoking condition. RANK immunostaining was significant in the smoking condition for the P and POTM groups (P .05)  Within the limitations of the present study, it was concluded that cigarette smoke inhalation had no influence on the evaluated groups, even with the presence of low levels of nicotine, carbon monoxide and tar. The POTM groups did not present greater bone loss compared to P groups, thus periodontal disease is essential for bone loss.

title: Effect of Magnification on the Precision of Tooth Preparation in Dentistry.
abstract: To evaluate the impact of magnification aids on the precision of tooth preparation under simulated clinical conditions.  Two plastic blocks marked with a geometric shape were fixed in a dental phantom head: a circle as the distal surface of tooth 16 (UNS 3) and a y shaped figure as the occlusal surface of tooth 36 (UNS 19) Sixteen dentists (mean age: 39 years; range: 26 67 years) prepared the geometric shapes from the inside to the boundary line with a cylindrical bur and water cooling. The boundary line had to be touched but not erased. Chair side assistance was provided to simulate the clinical situation. Tooth 16 was prepared under indirect vision via a dental mirror. Tooth 36 was prepared under direct vision A) without magnification aids, B) with Galilean loupes, 2.5x and light emitting diode light, and C) with a microscope, 6.4x and coaxial light. The preparation procedure was performed three times in different sequences of the magnification devices and with a break of at least 1 week between each procedure. The correctly prepared contour and the incorrectly prepared areas were evaluated in relation to the whole circumference of the geometric shapes.  For both values the precision was significantly higher when a microscope was used, followed by preparation using loupes; precision was lowest without magnification aids p<0.0001) This was true for both indirect and direct vision p<0.05)  Magnification devices improved the precision of tooth preparation under simulated clinical conditions.

title: Effect of variable periodontal ligament thickness and its non linear material properties on the location of a tooth's centre of resistance.
abstract: In orthodontics, the 3D translational and rotational movement of a tooth is determined by the force moment system applied and the location of the tooth's centre of resistance (CR) Because of the practical constraints of in vivo experiments, the finite element (FE) method is commonly used to determine the CR. The objective of this study was to investigate the geometric model details required for accurate CR determination, and the effect of material non linearity of the periodontal ligament (PDL) A FE model of a human lower canine derived from a high resolution uCT scan (voxel size: 50 um) was investigated by applying four different modelling approaches to the PDL. These comprised linear and non linear material models, each with uniform and realistic PDL thickness. The CR locations determined for the four model configurations were in the range 37.2 45.3% (alveolar margin: 0% root apex: 100% We observed that a non linear material model introduces load dependent results that are dominated by the PDL regions under tension. Load variation within the range used in clinical orthodontic practice resulted in CR variations below 0.3% Furthermore, the individualized realistic PDL geometry shifted the CR towards the alveolar margin by 2.3% and 2.8% on average for the linear and non linear material models, respectively. We concluded that for conventional clinical therapy and the generation of representative reference data, the least sophisticated modelling approach with linear material behaviour and uniform PDL thickness appears sufficiently accurate. Research applications that require more precise treatment monitoring and planning may, however, benefit from the more accurate results obtained from the non linear constitutive law and individualized realistic PDL geometry.

title: Evaluation of Effect of Connector Designs in Implant Tooth supported Fixed Partial Denture: A Two dimensional Finite Element Analysis.
abstract: The aim of this study was to evaluate the effect of connector designs on scale and distribution pattern of the stress generated in the supporting bone of implant tooth supported three unit fixed partial denture in distal extension situation.  Three unit fixed partial denture geometric models with implant abutment in second molar, pontic in first molar, and second premolar as mesial abutment in distal extension situations were evaluated using a two dimensional (2D) finite element analysis. Three models were designed and constructed with mesial and distal rigid connectors, mesial nonrigid connector, and distal nonrigid connector respectively, using the software ANSYS, version 10.0 (University Intermediate) The models were analyzed to determine the maximum equivalent von Mises stress at five critical zones (maximum value) under static axial loading (240 N) after meshing and assigning the material properties.  The maximum stress concentration values at mesial and distal alveolar crest of the implant supporting bone were 60.59 and 68.57 MPa, respectively, in Model No 1. The high equivalent von Mises stress concentration values at the mesial and distal alveolar crest of the implant supporting bone were 1.65 and 0.747 MPa with 0.1 mm vertical movement and 7.88 and 9.34 MPa with 0.5 mm vertical movement of the connector respectively, in Model No 2. The high equivalent von Mises stress concentration values at mesial and distal alveolar crest of the implant supporting bone were 10.45 and 3.43 MPa with 0.1 mm vertical movement and 4.50 and 5.71 MPa with 0.5 mm vertical movement of the connector respectively, in Model No 3.  In the supporting bone around the implant in Model No 1, the maximum von Mises stress concentrations were displayed in the crestal zones. In the supporting bone around the implant abutment, the von Mises stress concentrations were minimal toward the apical third zone in all the models. The stress concentrations were minimal in the supporting bone around the implant and the natural tooth in the models with nonrigid connector.  When implant is used as distal abutment in three unit implant tooth supported fixed partial denture with pontic at first molar in distal extension situation, it is recommended to place the nonrigid connector in the mesial side of the distal implant abutment.

title: The effect of different geometric shapes and angles on the fracture strength of IPS e.max computer aided designed ceramic onlays: An in vitro study
abstract: The current ceramic onlay preparation techniques for cuspal areas involve the reduction of cusps following the cuspal anatomy and the removal of all sharp angulations. However, there is little research literature studying the effect of occlusal preparation angles. Furthermore, there is no recent literature on the effect of angulations on IPS e.max computer aided designed (CAD) (e.max) ceramic onlays.  The purpose of this study is to investigate the effect of geometric cuspal angulation and different internal preparation angles on the fracture strength of e.max CAD ceramic onlays.  Sharp (33deg and 22deg) and round (33deg and 22deg) preparations were tested, each group having 10 specimens. e.max ceramic onlays were milled, sintered, glazed, and then bonded onto geometric tooth models. Fracture strength was measured at the initial fracture with a universal testing machine. The load was applied laterally to the central fossa (2 point contact) and vertically to the cusp peak (1 point contact)  A reduced cuspal angulation of 22deg resulted in a stronger ceramic onlay than a 33deg angulation when laterally loaded (P 0.001) The presence of sharp angles weakened the ceramic significantly for both the 22deg preparation (P 0.0013) and 33deg preparation (P 0.0304)  This in vitro study found that preparation angles of 22deg resulted in superior fracture strength during central fossa loading and that rounding the preparation resulted in significantly higher fracture strength when a cusp peak load was applied. When the cusp tip loading is applied, the preparation angle does not appear to influence the fracture strength.