Accuracy of digital jaw relation determination in different occlusal conditions - an in vitro study.

Objectives: In orthodontics, accurate registration of jaw relationships is essential for correct diagnosis and treatment planning. Therefore, accuracy of the digital spatial registration of maxillary and mandibular models and - for the first time-the influence of dentition stage and malocclusion type on this procedure were investigated under controlled conditions.

Materials And Methods: Eight pairs of jaw models, representing different occlusal and developmental statuses (m1-m8), were scanned using two IOS types (PS: Primescan; TR: Trios4).

Novel approach for characterizing clinical load application of superelastic orthodontic wires.

Objective: Current standardized in vitro bending experiments for orthodontic archwires cannot capture friction conditions and load sequencing during multi-bracket treatment. This means that clinically relevant forces exerted by superelastic wires cannot be predicted. To address these limitations, this study explored a novel test protocol that estimates clinical load range.

Are aligners capable of inducing palatal bodily translation or palatal root torque of upper central incisors? A biomechanical in vitro study.

Objectives: Previous studies have shown that aligners have limited ability to control root movements. The purpose of this study was to investigate which modification geometry and foil thickness are optimal for generating the force-moment (F/M) systems required for palatal root torque of maxillary central incisors.

Materials And Methods: Tooth 11 was separated from a maxillary acrylic model and connected to a movement unit via a 3D F/M sensor.

Mechanical loads exerted by different configurations of Burstone's 3-piece segmented mechanics during a simulated intrusion of the mandibular incisors.

Introduction: Burstone's segmented intrusion arch technique allows variable incisor intrusion with lingual or labial tipping, depending on the position and direction of the force vectors exerted by the intrusion springs. To date, systematic biomechanical studies are lacking. This in vitro study aimed to determine the 3-dimensional force-moment systems applied to the 4 mandibular incisors and the deactivation behavior of the appliance by different configurations of the 3-piece intrusion mechanics.

Inadvertent side effects of fixed lingual retainers : An in vitro study.

Purpose: To better understand the side effects of fixed lingual retainers by means of an in vitro study in a two-tooth model determining the three-dimensional (3D) force-moment components acting at adjacent teeth combined with different composite-wire interfaces.

Methods: Triple-stranded round retainer wires were embedded in cured disks of flowable composite. At one side the composite-wire interface was untreated and checked to be absolutely fix.

Biomechanical model registration for monitoring and simulating large orthodontic tooth movements in the maxilla and mandible.

Purpose: Superimposition of digital dental-arch models allows quantification of orthodontic tooth movements (OTM). Currently, this procedure requires stable reference surfaces usually only present in the maxilla. This study aimed to investigate the accuracy of a novel superimposition approach based on biomechanical principles of OTM and the equilibrium of forces and moments (EFM)-applicable in both jaws-for monitoring and simulating large OTM.

Force decay of polyethylene terephthalate glycol aligner materials during simulation of typical clinical loading/unloading scenarios.

Background: This in vitro study investigated the effect of three distinct daily loading/unloading cycles on force delivery during orthodontic aligner therapy. The cycles were applied for 7 days and were designed to reflect typical clinical aligner application scenarios.

Materials And Methods: Flat polyethylene terephthalate glycol (PET-G) specimens (Duran®, Scheu Dental, Iserlohn, Germany) with thicknesses ranging between 0.

Trueness of full-arch IO scans estimated based on 3D translational and rotational deviations of single teeth-an in vitro study.

Objectives: To three-dimensionally evaluate deviations of full-arch intraoral (IO) scans from reference desktop scans in terms of translations and rotations of individual teeth and different types of (mal)occlusion.

Materials And Methods: Three resin model pairs reflecting different tooth (mal)positions were mounted in the phantom head of a dental simulation unit and scanned by three dentists and three non-graduate investigators using a confocal laser IO scanner (Trios 3®). The tooth-crown surfaces of the IO scans and reference scans were superimposed by means of best-fit alignment.

Motor learning might contribute to a therapeutic anterior shift of the habitual mandibular position-An exploratory study.

Background: Passive mandibular advancement with functional appliances is commonly used to treat juvenile patients with mandibular retrognathism.

Objective: The aim of this study was to investigate whether active repetitive training of the mandible into an anterior position would result in a shift of the habitual mandibular position (HMP).

Methods: Twenty adult healthy subjects were randomly assigned to one of two groups: a training group receiving six supervised functional training sessions of 10 min each and a control group without training.

Evaluation of orthodontic loads and wire-bracket contact configurations in a three-bracket setup: Comparison of in-vitro experiments with numerical simulations.

So far, no practicable procedure exists to quantify the orthodontic loads applied to teeth in vivo. Dentists therefore rely on experience and simplified mechanical in-vitro experiments comprising deflection of orthodontic wires. Predicting the mechanical behaviour of orthodontic wires during clinical therapy requires understanding of the different contact states at multi-bracket-wire interfaces.

Effects of preventing intercuspation on the precision of jaw movements.

Background: Closing movements are among the jaw's basic physiological motor actions. During functional movements, the jaw changes position continually, which requires appropriate proprioception. However, the significance of the various proprioceptive receptors involved and how they interact is not yet fully clear.

Effect of variable periodontal ligament thickness and its non-linear material properties on the location of a tooth's centre of resistance.

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).

Experimental friction and deflection forces of orthodontic leveling archwires in three-bracket model experiments.

Objective: In vitro testing of archwires in a multibracket model may provide estimates of force-moment (F/M) systems applied to individual teeth in a realistic geometry. Such investigations have mostly been performed by continuous wire deflection, leading to frictional forces biasing the pure deflection forces. Aim of this study was to quantify this bias and the pure deflection forces for leveling archwires.

Three-dimensional amplitude characteristics of masseter motor units and representativeness of extracted motor unit samples.

Objective: This study aimed to characterize amplitude topographies for masseter motor units (MUs) three-dimensionally, and to assess whether high-density surface electromyography (HDsEMG) is able to detect MU samples that represent the masseter's entire MU pool.

Methods: Ten healthy adult volunteers participated in the study, which combined three EMG techniques. A HDsEMG grid covering the entire masseter, and intramuscular fine-wire electrodes were used to obtain two independent MU samples for comparison.

Novel Method for Superposing 3D Digital Models for Monitoring Orthodontic Tooth Movement.

Quantitative three-dimensional analysis of orthodontic tooth movement (OTM) is possible by superposition of digital jaw models made at different times during treatment. Conventional methods rely on surface alignment at palatal soft-tissue areas, which is applicable to the maxilla only. We introduce two novel numerical methods applicable to both maxilla and mandible.

Forces and moments applied during derotation of a maxillary central incisor with thinner aligners: An in-vitro study.

Introduction: Recent studies have shown that therapeutic loads applied to individual teeth by aligners may substantially exceed recommended values. The primary purpose of this study was to quantify force and moment components during derotation of a maxillary central incisor when 0.3-mm-thick or 0.

Forces and moments delivered by novel, thinner PET-G aligners during labiopalatal bodily movement of a maxillary central incisor: An in vitro study.

Objective: To evaluate whether overloading of teeth can be avoided by utilizing aligners with reduced thicknesses of 0.4 mm or 0.3 mm.

Comparison of methods to determine the centre of resistance of teeth.

In orthodontic treatment, the locations of the centre of resistance (CR) of individual teeth and the applied load system are the major determinants for the type of tooth movement achieved. Currently, CR locations have only been specified for a relatively small number of tooth specimen for research purposes. Analysing cone beam computed tomography data samples from three upper central incisors, this study explores whether the effort to establish accurate CR estimates can be reduced by (i) morphing a pre-existing simplified finite element (FE) mesh to fit to the segmented 3D tooth-bone model, and (ii) individualizing a mean CR location according to a small parameter set characterising the morphology of the tooth and its embedding.

Forces and moments delivered by PET-G aligners to an upper central incisor for labial and palatal translation.

Objectives: Aligners made of polyethylene terephthalate glycol (PET-G) were tested in an experimental study for labial and palatal translation of an upper central incisor to quantify the forces and moments thus delivered and to biomechanically evaluate the capability of bodily movement.

Materials And Methods: Using a resin model of the upper dentition, tooth 21 was separated and connected to a 3D force/moment (F/M) sensor to record the forces and moments delivered by aligners for labial and palatal displacement. An impression was taken with tooth 21 in its neutral position to obtain casts for standardized thermoplastic fabrication of aligners varying in make and foil thickness (Duran® 0.

Optical 3D scans for orthodontic diagnostics performed on full-arch impressions. Completeness of surface structure representation.

Objective: The purpose of this work was to evaluate the completeness of surface structure representation offered by full-arch impression scans in different situations of tooth (mal)alignment and whether this completeness could be improved by performing rescans on the same impressions reduced sequentially to different levels of gingival height and by adding extra single scans to the number of single scans recommended by the manufacturer.

Methods: Three pairs of full-arch resin models were used as reference, characterized either by normal occlusion, by anterior diastematic protrusion (and edentulous spaces in the lower posterior segments), or by anterior crowding. An alginate impression of each arch was taken and digitized with a structured-light scanner, followed by three rescans with the impression cut back to 10, 5, and 1 mm of gingival height.

Dimensional accuracy of jaw scans performed on alginate impressions or stone models: A practice-oriented study.

Objectives: Digital jaw models offer more extensive possibilities for analysis than casts and make it easier to share and archive relevant information. The aim of this study was to compare the dimensional accuracy of scans performed on alginate impressions and on stone models to reference scans performed on underlying resin models.

Methods: Precision spheres 5 mm in diameter were occlusally fitted to the sites of the first premolars and first molars on a pair of jaw models fabricated from resin.

Comparison of orthodontic measurements on dental plaster casts and 3D scans.

Background And Objectives: Over recent years, we have witnessed a growing trend in orthodontics toward the use of three-dimensional (3D) techniques for diagnostic purposes, treatment planning, and fabricating appliances. This study was undertaken to compare the traditional manual technique of using vernier calipers to take orthodontic measurements on plaster dental casts versus an all-digital measuring technique based on virtual 3D scans of casts. In this study, we focused on the quantitative agreement between and time requirements of both methods.

Electrophysiological method to examine muscle fiber architecture in the upper lip in cleft-lip patients.

Objectives: The upper lip's musculature comprises several muscle fiber groups with different spatial orientations for various lip movements. In the past, it has not been possible to describe these various groups and their motor units in detail with traditional methods of electromyography (EMG). The purpose of this investigation was to create a viable method for studying the architecture of upper-lip muscle fibers in patients with surgically closed cleft lip by refining the design of a flexible electrode array for multichannel EMG.

Optimal placement of bipolar surface EMG electrodes in the face based on single motor unit analysis.

Locations of surface electromyography (sEMG) electrodes in the face are usually chosen on a macro-anatomical basis. In this study we describe optimal placement of bipolar electrodes based on a novel method and present results for lower facial muscles. We performed high-density sEMG recordings in 13 healthy participants.

Motor unit number estimation using high-density surface electromyography.

Objective: To present a motor unit number estimation (MUNE) technique that resolves alternation by means of high-density surface EMG.

Methods: High-density surface EMG, using 120 EMG channels simultaneously, is combined with elements of the increment counting technique (ICT) and the multiple-point stimulation technique. Alternation is a major drawback in the ICT.