Malcolm Jones

Three-dimensional analysis of orthodontic tooth movement

A three-dimensional finite element model was used to investigate the biomechanical response of an upper canine tooth. The physical model was developed from ceramic replicas and X-rays, and consisted of cancellous and cortical bone, the periodontal ligament, dentine and pulp chamber. Horizontal forces were applied at the tip of the crown and at the cervical margin and a rotational force was applied at the cervical margin of the tooth crown. The resulting displacements and stress field for each load case are presented with particular emphasis being placed on the response of the periodontal ligament. The investigation shows that quantitative information on initial tooth movement can be accurately predicted and used to evaluate the response of orthodontic treatment.

The Finite Element Analysis of Stress in the Periodontal Ligament when Subject to Vertical Orthodontic Forces

In the past, vertical intrusive movement of teeth has been considered difficult and most routine clinical vertical movement of teeth has been confined to extrusion. It has been suggested that attempts at intrusion may result in an increased incidence of root resorption and also in occasional devitalization. The displacement and resulting stress fields associated with such treatment can be successfully studied using the finite element method. In the case being considered initial movements are known to be small; therefore, the assumption in the study that the material behaves linear-elastically is considered to be reasonable. This study of vertical tooth movement demonstrated that the maximum cervical margin stress in the periodontal ligament was 0·0046 N/mm2, whilst the highest apical stress was 0·00205 N/mm2 when intrusive and extrusive forces of 1 Newton were applied to the buccal surface of the crown of a tooth model. These stresses were evaluated in the light of previous studies and found to be within the suggested clinical optimum level. However, the periodontal stress distribution following orthodontic loading within this three-dimensional finite element model was found to be highly complex.

The influence of bracket base design on the strength of the bracket-cement interface.

The objectives of the study were to isolate the bracket–cement interface, and to determine the influence of bracket base morphology and orthodontic bonding agent chosen on strength of adhesion. The bracket bases evaluated included 60, 80, and 100 single mesh bases, a double mesh base, and the Dynalock™, and Mini Twin™ bases. The strength of interface provided by each of these bases with Concise™, Transbond™, Right On™, and non-encapsulated Fuji Ortho LC™ cements, was measured in tension and recorded in Mega Pascals. The single-mesh bases performed well with either Concise or Right On (11•88–22•72 MPa) and, other than the 80-mesh bracket, relatively poorly with Transbond (2•18–5•15 MPa). With Fuji Ortho LC, the single mesh bases performed well (6•05–12•19 MPa). The double mesh base performed well with Right On (13•75 MPa), and reasonably well with Concise, Transbond, and Fuji Ortho LC (6•00–9•20 MPa). The Dynalock and Mini Twin Bases performed fairly well with all cements (8•87–17•16 MPa). It was concluded that the orthodontic bonding agent selected would appear to largely determine the bond strength achieved with a particular bracket base design. A definite trend was difficult to identify in this study, and it appeared that certain combinations of bracket base and bonding agent performed optimally. Particular base designs may allow improved adhesive penetration or improved penetration of curing light. Alternatively, the dimension and distribution of resin/cement tags prescribed by one base could promote a stress distribution that is better resisted by a particular adhesive.

An Evaluation of the Quality of Orthodontic Attachment Offered by Single- and Double-Mesh Bracket Bases Using the Finite Element Method of Stress Analysis

The objective of this study was to evaluate the influence of bracket base mesh geometry on the stresses generated in the bracket-cement-tooth continuum by a shear/peel load case. A validated three-dimensional finite element model of the bracket-cement-tooth system was constructed consisting of 15,324 nodes and 2971 finite elements. Cement geometric and physical properties were held constant and bracket base geometry was varied, representing a variety of single-mesh configurations and 1 double-mesh design. For the single-mesh designs, increasing wire diameter (100-400 microm) resulted in a decrease in enamel and cement stresses. Increases in wire mesh spacing (200-750 microm) increased the major principal stress recorded in the enamel and adhesive at all wire diameters. Within the bracket, the major principal stress increased significantly at wire spacing above 400-500 microm. However, within the impregnated wire mesh (IWM), the major principal stress decreased as wire space increased. When the double-mesh bracket base was considered, the combined mesh layers resulted in a decrease in the stresses recorded in the most superficial (coarse) mesh layer and an increase in the stresses recorded in the deepest (fine mesh) layer when compared with the single-layer designs in isolation. Modification of single-mesh spacing and wire diameter influences the magnitude and distribution of stresses within the bracket-cement-tooth continuum. The use of a double-mesh design results in a reduction in the stresses recorded in the most superficial mesh. Mesh design influenced stress distribution in this study, primarily by determining the flexibility of the bracket base.

A comparison of orthodontic treatment changes as measured from study casts and cephalometric radiographs.

Orthodontic treatment change was examined for 106 consecutively referred patients using serial lateral cephalometric radiographs and study cast records. The 2-D and 3-D measurement systems used to assess the changes were compared for five variables common to both sets of records. No statistical differences were found between the study cast and radiographic records for these variables. The 3-D measurement with the Reflex Metrograph showed marginally better precision in the measurement of the treatment changes examined. However, the main advantage was that it allowed a more thorough and accurate assessment of both individual incisor position and measurement error.

A Finite Element Study of Canine Retraction with a Palatal Spring

The use of a removable appliance to retract a maxillary canine tooth into a first premolar extraction space is one of the most commonly performed orthodontic procedures. However, unwanted movements may occur, including excessive tipping, rotation, and flaring of the tooth. The present investigation by the use of a finite element model quantifies some of the initial stresses produced within the periodontal ligament when two obliquely directed forces are applied to a maxillary canine tooth. In simulating the action of a removable appliance it attempts to relate the stress patterns to the nature of the subsequent tooth movement.

The Influence of Orthodontic Adhesive Properties on the Quality of Orthodontic Attachment

The objective of this study was to determine the resilience, glass transition temperature (Tg), ultimate flexural strength (UFS), and penetration coefficient of 3 composite adhesives (Concise, Transbond, and Right On) and a glass ionomer cement (Fuji Ortho LC). For 25 minutes after initial set, the composite materials were significantly more resilient than Fuji Ortho LC (P = .000). Resilience values for all materials increased for up to 90 minutes after initial set, reflecting a continuation of their setting reaction. Right On remained the most resilient material at 90 minutes after initial set (P < or = .01). At 120 minutes, there was no significant difference in the resilience of Concise, Right On, and Fuji Ortho LC. However, Transbond was significantly less resilient than these materials (P < or = .01). The composite materials recorded significantly higher glass transition values (89-123 degrees C) than Fuji Ortho LC (54 degrees C). The composite materials were also significantly stronger (61-68 MPa) than Fuji Ortho LC (35 MPa) in flexion. The penetration coefficients of Concise and Transbond were significantly higher (P < or = .001) than Right On and Fuji Ortho LC. However, the relative penetration coefficients of the materials studied did not appear to influence the degree of bracket base penetration achieved by the cements. In conclusion, Fuji Ortho LC offered a reduced energy-absorbing capacity immediately after bracket placement and reduced cohesive and mechanical adhesive strength. In addition, the glass transition temperature of Fuji Ortho LC was low; this may result in compromised attachment at temperatures above 60 degrees C. Significant differences in the penetration coefficient of the materials studied have been recorded. However, the penetration of the 4 cements into a range of bracket base morphologies was uniformly good. Therefore, the differences in penetration coefficient recorded should not influence the quality of the bracket cement interface provided.

The Barry Project—A Further Assessment of Occlusal Treatment Change in a Consecutive Sample: Crowding and Arch Dimensions

In a further study of serially treated cases from a Welsh town, the results achieved for crowding, tooth alignment, residual spacing, tooth rotation, arch dimension, and centre line discrepancy are examined. The initial stability of the treatment change in these variables is also presented.

An initial assessment of the effect on orthodontic pliers of various sterilization/disinfection regimes.

Duplicates of six commonly used orthodontic instruments were allocated to four groups. One of the groups of instruments was stored as a control. The three other groups were exposed to different regimes of sterilization or cold disinfection over an extended period. Twenty characteristics of function, corrosion, and appearance were then judged by four observers twice using a visual analogue scale of 100 units. No statistical evidence was found of routine autoclaving causing more damage to pliers than cold disinfection; in fact, the data suggested the contrary. Chrome plated pliers appeared more resistant to damage and maintained their appearance better than stainless steel pliers.

A 'mini-typodont' for removable appliance teaching.

A simple typodont is described which may be used to demonstrate tooth movements with removable appliances.