Ideal orthodontic alignment load relationships based on periodontal ligament stress.

Objectives: To test the hypothesis that periodontal ligament (PDL) stress relationships that yield resistance numbers representing load proportions between different teeth depend on alignment load type.

Materials And Methods: Finite element models of all teeth, except the third molars, were produced. Four different types of loads were applied, and the third principal stresses of different teeth in standardized areas of most compression were calculated.

Axes of resistance for tooth movement: does the center of resistance exist in 3-dimensional space?

Introduction: The center of resistance is considered the most important reference point for tooth movement. It is often stated that forces through this point will result in tooth translation. The purpose of this article is to report the results of numeric experiments testing the hypothesis that centers of resistance do not exist in space as 3-dimensional points, primarily because of the geometric asymmetry of the periodontal ligament.

Polyphenylene polymers as esthetic orthodontic archwires.

Introduction: There is continuing interest in an esthetic, effective labial archwire. In this study, we evaluated the potential of new, high-strength polyphenylene polymers to fill this need.

Methods: Polyphenylene (Primospire, Solvay Advanced Polymers, Alpharetta, Ga) polymer was extruded into wires with clinically relevant round and rectangular cross sections.

Viscoelastic properties of an aesthetic translucent orthodontic wire.

The objective of this study was to evaluate the time-dependent viscoelastic properties of an aesthetic orthodontic archwire. The wire is based on a recently developed translucent polyphenylene thermoplastic, whose rigid molecular structure provides high strength. While the wire has good instantaneous mechanical properties, over time all polymers may relax so it is important to understand the potential impact of the relaxation on orthodontic force systems.

Miniscrews in orthodontic treatment: review and analysis of published clinical trials.

Introduction: A systematic review of effects related to patient, screw, surgery, and loading on the stability of miniscrews was conducted.

Methods: Reports of clinical trials published before September 2007 with at least 30 miniscrews were reviewed. Parameters examined were patient sex and age, location and method of screw placement, screw length and diameter, time, and amount of loading.

Sagittal and vertical load-deflection and permanent deformation of transpalatal arches connected with palatal implants: an in-vitro study.

Introduction: The purposes of this laboratory investigation were to (1) measure the sagittal and vertical deflection of loaded transpalatal arches (TPAs) connected to a palatal implant, (2) measure the extent of permanent deformation of the connecting TPA in the sagittal and vertical directions, (3) test various wire dimensions in terms of deflection behavior, and (4) evaluate soldering vs laser welding vs adhesive bonding of TPAs in terms of load deflection behavior.

Methods: Stainless steel wires of 6 dimensions were tested: 0.8 x 0.

Initial changes of centres of rotation of the anterior segment in response to horizontal forces.

This study investigated the changes in the initial centres of rotation (Crot) of the upper six anterior teeth in response to a horizontal load. Six upper anterior teeth were extracted, splinted as a unit, and embedded in dental stone after the roots were uniformly coated with silicone. An aluminium fixture was bonded to the anterior segment and three linear variable differential transformers (LVDTs) were attached to measure the microdisplacement of the segment.

Influence of buccal segment size on prevention of side effects from incisor intrusion.

Introduction: Deep overbite can be corrected by maxillary incisor intrusion. The purpose of this study was to determine whether the size of the maxillary buccal segment influences the amount of steepening, extrusion, or narrowing of the buccal segments, or the rate of intrusion that occurs with maxillary incisor intrusion.

Methods: Twenty patients, 9 to 14 years of age, seeking treatment at a private practice, were divided into 2 groups.

The influence of force magnitude on intrusion of the maxillary segment.

The purpose of this study was to determine whether the magnitude of intrusive force to the maxillary incisors influences the rate of incisor intrusion or the axial inclination, extrusion, and narrowing of the buccal segments. Twenty patients between the ages of nine and 14 years who needed at least two mm of maxillary incisor intrusion were assigned to one of two equal groups. In group 1 patients, the teeth in the maxillary anterior segment were intruded using 40 g, whereas in group 2 patients, 80 g was used.

The relation between the point of force application and flaring of the anterior segment.

The purpose of this study was to determine whether application of an intrusive force by an intrusion arch at the distal wings of the lateral incisor brackets causes a change in the axial inclination of the anterior segment. Maxillary incisor intrusion was performed, and records were taken from 40 adolescent patients at the beginning and end of intrusion. Intrusion of the maxillary anterior segment caused a statistically significant mean increase in axial inclination of the central incisor of 8.

The role of a high pull headgear in counteracting side effects from intrusion of the maxillary anterior segment.

Intrusion of incisors is often the preferred treatment of a deep overbite. This study focuses on deep overbite correction by intrusion of maxillary incisors. The purpose of this study is to determine whether high-pull headgear wear can prevent steepening of the buccal segment, extrusion of the buccal segment, maintain arch width, and increase the rate of incisor intrusion.

Shear in flexure of fiber composites with different end supports.

The integrity of fiber-reinforced composite (FRC) prostheses is dependent, in part, on flexural rigidity. The object of this study was to determine if the flexure behavior of uniform FRC beams with restrained or simply supported ends and various length/depth (L/d) aspect ratios could be more accurately modeled by correcting for shear. Experimental results were compared with three analytical models.

Controlled space closure with a statically determinate retraction system.

We designed a variant of a cantilever spring, the statically determinate retraction system, and studied its mechanical characteristics. This novel system consisted of a single-force cantilever arm made of 0.017 x 0.

Bond strength of fiber-reinforced composite bars for orthodontic attachment.

Long fiber-reinforced composites (FRC) have been shown to have enhanced mechanical properties that allow their use in orthodontic appliances as bars that join teeth to form either anchorage or active units. This study was designed to determine if the bonding of an orthodontic attachment has sufficient strength to withstand loading during clinical use. The experimental model consisted of a hydroxyapatite stone that simulated enamel, FRC bars, and a bonded metal hook.

[Stability of orthodontic treatment of occlusal asymmetry].

A common finding in orthodontic patients is asymmetric occlusion. These asymmetries can be dental, skeletal, or functional in origin. Since many patients have typical posterior overjet the use of Class II-Class III and anterior crisscross elastics are contra-indicated.

Effect of root and bone morphology on the stress distribution in the periodontal ligament.

To achieve predictable and physiologic orthodontic tooth movement, estimating the axis of rotation of a tooth and the level and location of maximum stress distributed in the periodontal ligament is essential. An extracted upper canine was scanned into a computer 2-dimensionally and divided into 80 nodes along the long axis of the tooth. A mathematical formula was derived, and stress was calculated on each node.

Force characteristics of nickel-titanium tension coil springs.

Nickel-titanium closed coil springs are commonly used for space closure. The springs possess a high resistance to permanent deformation and the potential for relatively constant force delivery. A study was designed to determine whether relatively constant forces can be delivered and whether the force magnitudes approach the manufacturer's targeted force values.

Diagnosis and treatment planning of patients with asymmetries.

The diagnosis, treatment planning, and design of mechanics for the asymmetric patient requires the differentiation between problems of dental and skeletal origin. Although much information can be gleaned from a cephalometric analysis, the clinical examination and study models offer important clues in establishing the diagnosis of skeletal discrepancy. Abnormal and asymmetric axial inclinations can either produce a dental asymmetry or, if compensatory in nature, may mask an underlying skeletal problem.

Development and clinical applications of a light-polymerized fiber-reinforced composite.

Statement Of Problem: After 0 years of intermittent reports in the literature, the use of fiber reinforcement is just now experiencing rapid expansion in dentistry.

Purpose: This article describes the development and use of a continuous, unidirectional fiber reinforced composite as a framework for the fabrication of fixed prostheses.

Methods: By using various matrix materials and fibers, a number of fiber-reinforced composite formulations were evaluated with the goal of creating a system with optimized mechanical properties and handling characteristics.

T-loop position and anchorage control.

The effect of off-center positioning on the force system produced by segmented 0.017 x 0.025-inch TMA T-loops was measured.

Class II subdivision treatment with tip-back moments.

Unilateral tip-back mechanics are challenging because of a number of undesirable side-effects associated with their use during orthodontic treatment. The purpose of this paper is to review the differential diagnosis and treatment planning of Class II subdivision malocclusions and present a treatment strategy based on a careful biomechanical analysis of the clinical situation. Emphasis is placed on the correction of molar axial inclination using unilateral tip-back moments in the treatment of dental asymmetries.