Hinge Articulator Research Articles

Food impaction on three-dimensional printed models with periodontal ligament simulation.

This study aims to evaluate food impaction on three-dimensional (3D) printed models with periodontal ligament simulation. Based on a commercial typodont pair, 3D maxillary and mandibular models were created with no teeth and with tooth sockets that were 1 mm wider than the original ones from 24 to 27 or 34 to 37 for periodontal ligament simulation with vinyl polysiloxane impression material. In total, 35 pairs of 7 combinations, including maxillary/mandibular typodonts in occlusion with maxillary/mandibular 3D models with/without a distal gap of canines on 3D models (tooth 23 or 33) were mounted on hinge articulators and divided into seven groups (n = 5). Each sample experienced the same manual chewing simulation on a customized device. The proximal surfaces were photographed to measure the percentage of food impaction area using ImageJ software. Group with fixed maxillary and mandibular teeth showed more food impaction than other groups with significant differences in the average of maxilla and the average of all proximal areas. The flexibility of the periodontal ligament and the degree of freedom of the teeth in their sockets may contribute to the extent of food impaction in proximal spaces.

Motion of an active bent rod with an articulating hinge: exploring mechanical and chemical modes of swimming

Swimming at the microscale typically involves two modes of motion: mechanical propulsion and propulsion due to field interactions. During mechanical propulsion, particles swim by reconfiguring their geometry. When propelled by field interactions, body forces such as phoretic interactions drive mobility. In this work, we employ slender-body theory to explore how a bent rod actuator propels due to a mechanical mode of swimming via hinge articulations and due to a chemical mode of swimming via diffusiophoretic interactions with a solute field. Although previous theoretical studies have examined mechanical and chemical modes of swimming in isolation, the simultaneous investigation of both modes has remained unexplored. For the mechanical mode of swimming, our calculations, both numerical and analytical, recover Purcell’s scallop theorem and show that the bent rod actuator experiences zero net displacement during reciprocal motion. Additionally, we calculate the trajectories traced by a bent rod actuator under a non-reciprocal hinge articulation, revealing that these trajectories are influenced by the amplitude of the hinge articulation, geometric asymmetry, and the angular velocity distribution between the two arms of the bent rod actuator. We provide intuitive explanations for these effects using free-body diagrams. Furthermore, we explore the motion induced by simultaneous hinge articulations and self-diffusiophoresis. We observe that hinge articulations can modify the effective phoretic forces and torques acting on the bent rod actuator, either supporting or impeding propulsion. Additionally, during self-diffusiophoretic propulsion, reciprocal hinge articulations no longer result in zero net displacement. In summary, our findings chart a new direction for designing micron-sized objects that harness both mechanical and chemical modes of propulsion synchronously, offering a mechanism to enact control over trajectories.

Sclerite assembly, articulation and protective system of Lower Devonian machaeridians

AbstractMachaeridians are a unique group of Palaeozoic annelids that secreted a calcitic armour consisting of dorsally interlocking sclerites running along the entire length of the animal. Preserved remains are most commonly found as disarticulated sclerites, although rare articulated specimens have also been preserved as moulds, recrystallized calcite and even pyrite replacement. These preservational modes unfortunately have obscured direct observation of the dorsal interlocking hinge, thus impeding our understanding of the functional protection offered by this biological armour. Herein, we document and describe articulated silicified lepidocoleids (Lepidocoleus caliburnus sp. nov., Lepidocoleus shurikenus sp. nov. and Lepidocoleus sp.) in association with isolated sclerites of Lepidocoleus cf. kuangguoduni from the Lower Devonian (Pragian) Garra Formation of New South Wales, Australia. Articulated specimens include straight and enrolled scleritome configurations possessing opposing and alternate dorsal hinge articulation, respectively. Silicified scleritomes were analysed using x‐ray microtomography to investigate the three‐dimensional morphology, cross‐sectional geometry and dorsal hinge articulation and configuration of individual sclerites in the armour assembly. Virtual dissection of articulated specimens alongside reconstructions of isolated sclerites reveal distinctions in sclerite morphology across opposing and alternate articulation mechanisms, including a novel system not previously observed in lepidocoleids. The combination of heterogeneous sclerite cross‐sectional geometry with sclerite overlap also serves to maintain a uniform thickness of the armour assembly and presumably improve resistance to predatory attack.

Current trends in removable partial prosthodontics education in dental colleges of Pakistan.

The objective of this study was to investigate the current trends in undergraduate teaching of removable partial prosthodontics in various dental colleges of Pakistan. A cross-sectional study was conducted in which a questionnaire was sent by email to head of Prosthodontics department of thirty-one dental institutes of Pakistan. The survey included multiple questions regarding current trends in removable partial prosthodontics education in undergraduate dental colleges. Out of thirty-one questionnaires, twenty-six were completely filled and returned. In 19 (73%) dental colleges, removable partial denture is taught over a period of at least two years of undergraduate education. Students of only six dental colleges fabricate 10-12 removable partial dentures during their Prosthodontic rotation. Lectures and live clinical demonstration for construction of removable acrylic dentures are reported to be carried out in all the dental schools. Simple hinge articulator is the articulator of choice in 22 (84.6%) colleges. Even though twenty-four out of twenty-six colleges (92.3%) teach fabrication of cast partial dentures in lectures, none of the student fabricate these dentures during their Prosthodontic rotation. This survey is the first to comprehensively report the teaching practices of removable denture Prosthodontics in undergraduate dental colleges of Pakistan. Faculty of all twenty-six colleges give clinical demonstrations of acrylic partial denture construction before students start working in the dental OPD. Most of the dental colleges report use of similar impression materials and techniques in removable partial denture fabrication. More than 90% of dental colleges teach cast partial dentures theoretically, but their construction is grossly neglected in all the dental colleges. It is important that this skill is taught and practised by students in order to have the necessary skill set, so they can provide comprehensive treatment to partially dentate patients once they graduate.

Short and mid term results of revision total knee arthroplasty with Global Modular Replacement System.

Background:The original knee megaprostheses with fixed or rotating hinge articulation were custom made and only used for reconstruction of the knee following distal femoral or proximal tibial tumor resections. The aim of the study was to analyze the short- and mid-term results of revision total knee arthroplasty with Global Modular Replacement System (GMRS) used in difficult situations not amenable to reconstruction with standard total knee replacement implants.Materials and Methods:Nine patients (9 knees) were treated with this comprehensive modular implant system, with a mean age of 73.7 years (range 56–83 years) and a mean followup of 5 years (range 3–8 years). Two patients were treated for distal femoral nonunion, five for distal femur periprosthetic fracture and two for periprosthetic joint infection.Results:The mean Knee Society Score: Knee and functional scores were 77.9 and 40 points, respectively. All demonstrated full extension and flexion was at least 90°. Recurrence of infection was present in one patient. No signs of loosening, dislocation, or implant failure were observed.Conclusions:Based on our small series of patients that represent severe cases, GMRS provides relatively good mid-term functional results, pain relief, and good implant survivorship with a low complication rate. This salvage procedure allows elderly, infirm patients to regain early ambulatory ability.

Design and Preliminary Evaluation of a Stiff Steerable Cutter for Arthroscopic Procedures

This article describes a novel and simple shaft actuated tip articulation (SATA) mechanism that allows arthroscopic instruments to articulate while remaining stiff. Since the SATA mechanism requires only independent rotation of two tubes for hinge articulation, cables, gears, or other internal components that are normally found in steerable endoscopic instruments become obsolete. The SATA mechanism was integrated in a new steerable cutter prototype and tested. Early user, mechanical strength and cadaver experiments were performed that indicate that this first prototype withstands an axial and sideways force of 100 N and 20 N, that trained users can (dis)assemble the instrument in less than 1.5 min and that a surgeon is able to reach all important locations on the menisci.

Volar Base Fracture of the Second Phalanx: A Small Fracture a Great Challenge

Proximal interphalangeal joint (PIP) injuries can be disabling and are among the most challenging areas of hand surgery. The PIP joint is a complex, delicate and very stable hinge articulation that provides almost 100 degrees of flexion and thus serves as the cornerstone of the human hand movements. Injuries of the volar base of second phalanx (P2) deserve a special attention due to the complexity of their nature and management process. Volar plate and special cup shape geometry of the articular surface of the base of the P2 along with its volar lip prevent dorsal translation of this phalanx. For decades, volar plate arthroplasty was the preferred technique in reconstruction of comminuted and approximately irreparable volar base fracture of the P2 but there was a great concern about the re-subluxation and higher failure rate of the traditional volar plate arthroplasty. Hemi-hamate arthroplasty a novel technique introduced to the hand surgery world by Hastings in 1999 (1). In this technique the dorsal distal portion of hamate articular surface adjacent to the base of two ulnar carpometacarpal articulations bones is harvested. The bed of the volar base of the P2 is prepared by using mini oscillating saw and resection of the comminuted segments of its volar base. The harvested autograft transferred after 180 degrees rotation in two planes into the prepared bed at the volar base of the P2, and stabilized with two or three mini-fragment lag screws, the stability of pip can be restored by rebuilding the cupshaped geometry of the P2 base and palmar plate attachment. The volar overhanging lip of P2 can be reconstructed in this technique. Hemi-hamate has the capability of serving as salvage procedure after failed external fixation, open reduction and internal fixation or volar plate arthroplasty. Recently published longer term follow up of hemi-hamate arthroplasty indicates a valuable surgical procedure to address severe PIP joint fracture–dislocations (2). As the main referral orthopedic center in the country we had the same experience with this reconstruction at the department of hand surgery of Shafa Orthopedic Hospital. We do believe that managing of pip fracture dislocation has ushered in a new era with Hemi-hamate arthroplasty.

Metamorphosis in Craniiformea revisited: Novocrania anomala shows delayed development of the ventral valve

We revisited the brachiopod fold hypothesis and investigated metamorphosis in the craniiform brachiopod Novocrania anomala. Larval development is lecithotrophic and the dorsal (brachial) valve is secreted by dorsal epithelia. We found that the juvenile ventral valve, which consists only of a thin layer that was previously described as periostracal, is not a valve and is not secreted by the same epithelia as the dorsal valve. It is secreted by the attachment area of the larva at the posterior-most tip of the posterior larval lobe. The same attachment area is used by larvae of rhynchonelliform brachiopods during metamorphosis to cement their pedicle to the substrate. N. anomala is therefore not initially attached by a valve but by material corresponding to pedicle cuticle. This is different to previous descriptions, which had led to speculations about a folding event in the evolution of Brachiopoda. We show that the “brachiopod fold hypothesis,” which argues that brachiopods are transversely “folded” across the ontogenetic anterior–posterior axis, should be rejected at least with respect to the craniiforms. The data now suggest that the Craniiformea may be a derived group within the Rhynchonelliformea. This interpretation suggests that the last common ancestor of the Craniiformea has lost the pedicle and the ventral valve in early juvenile development. Characters that have previously been considered to be shared between the Craniiformea and the Linguliformea (clade Inarticulata), such as a through-gut and missing hinge articulation, may thus be secondarily derived characters of the Craniiformea within the Rhynchonelliformea.

Morphology, phylogeny, and systematic revision of genera in the Dimyidae (Mollusca, Bivalvia, Pteriomorphia)

Differences in the mineralogy of hinge teeth and inner shell layers in the family Dimyidae form the basis for a revision of genera. The stem genusAtreta(Late Triassic to Late Cretaceous) has aragonitic denticulate hinge teeth on the right valve articulating with pitted sockets on the left valve. The same arrangement is present inNeoatretan. gen. (Paleocene? Miocene to Recent) but with the appearance of extensive calcitic overarching of the resilifer. InDimyella(Eocene to Recent), aragonitic teeth and sockets are still present but are modified into hook shaped denticulate teeth with corresponding sockets. All three of these genera have inner aragonitic crossed-lamellar shell layers that extend well outside the pallial line. In contrast,Dimya(Eocene to Recent) andBasiliomya(Pliocene to Recent) comprise a second clade in which aragonitic hinge teeth are absent and hinge articulation is calcitic, derived from the calcitic rim.Dimyahas only weak hinge articulation and has an aragonitic inner shell layer delimited by the pallial line; inBasiliomyacalcitic hinge teeth are more prominent and the entire inner shell layer inside the pallial line is foliated calcite.Diploschiza(Cretaceous, Albian to Maastrichtian), here reinstated from synonymy withAtreta, is probably a precursor of theDimya-Basiliomyaclade based on incipient calcitic hinge teeth. Predation pressures probably drove the evolution of this cemented family from its original habitat on hardgrounds in moderately deep water into much greater depths or into cryptic habitats, including submarine caves.New combinations areDimyella malnatrensis(Corselli and Bernocchi),D. molokaia(Dall, Bartsch, and Rehder),D. similis(v. Koenen),Neoatreta dissimilis(Tate),N. filipina(Bartsch),N. kaiparaensis(Laws),N. phaidra(Woodring),and N. plana(Martin).

The History of Articulators: The “Articulator Wars” Phenomenon with Some Circumstances Leading up to It

At the dawn of the 20th century, all was not well with the practice of "plate prostheses." Removable prosthodontics had been degrading for several decades and was now generally in low esteem, even though there had been many significant advances. W. E. Walker had introduced adjustable condylar guides, George Snow, the facebow, and Carl Christensen, a method for clinically measuring the condylar inclines. Nevertheless, the average practicing dentist was still using simple hinge articulators and was apathetic to the deplorable state of the artificial teeth available; however, this was all going to change dramatically when two dentists, Alfred Gysi and J. Leon Williams, working together between 1910 and 1914, presented to the profession the "Trubyte Artificial Tooth System" that embodied both a typal system for selecting anterior teeth and new posterior occlusal carvings that made possible, for the first time, the articulation of artificial teeth. This incited many of prosthetic dentistry's elite to introduce their own theories of mandibular movement and the articulators that they designed to reflect those theories. The intense debates that ensued, both in the meeting halls and in the literature, were numerous and lasted for decades. At the time, the "Articulator Wars" had both positive and negative consequences. Today, with many of the "Articulator Wars" issues remaining as part of the practice of dentistry, the "Articulator Wars" can be considered a phenomenon of enlightenment.

The first scallop

Scallops (Pectinidae) are a highly diverse bivalve family with a long evolutionary history, but insufficient knowledge on the internal shell characters of initial taxa has hampered clarification of their phylogenetic roots. Here, morphological details of the shell interior of the basal pectinid Pleuronectites laevigatus from the Middle Triassic are documented for the first time. It is shown that ligament morphology, lack of internal buttresses and hinge articulation, presence of a right anterior auricular scroll, procrescent discs, and differential valve convexity of Pleuronectites link Pectinidae with Early Triassic aviculopectinoids rather than with entoliids, as recently proposed. The key adaptations of Pectinidae, i.e. the ctenolium and the alivincular-alate ligament system, probably evolved in conjunction with a marked size increase that required improvements in the shell attachment and in the system for opening the valves. Although Pleuronectites laevigatus is recognized as the earliest known member of the Pectinidae, a diphyletic origin of this family from different stocks within the Aviculopectinoidea cannot be ruled out.

Considerations for services from dental technicians in fabrication of fixed prostheses: A survey of commercial dental laboratories in Thessaloniki, Greece

Effective communication and cooperation between dentists and dental technicians are essential in providing quality services. There has been a lack of information regarding dentist-dental technician communications and current methods and materials used for the fabrication of fixed partial dentures (FPDs). This cross-sectional study identified the materials and techniques used for fabrication of FPDs, as well as the status of communication between dentists and dental technicians in Thessaloniki, Greece. A questionnaire was developed with 7 sections pertaining to procedures and materials used for the fabrication of fixed prostheses: general questions, infection control, impressions/interocclusal records, die technique/mounting, information from final casts, prostheses design/materials, and communication/shade selection. The questionnaire was anonymous and distributed by the Association of Dental Technicians of Thessaloniki to all member laboratories (228) in the wider province of Thessaloniki, Greece. Due to the absence of normal distribution of the results, frequencies and medians were reported. Ninety-six of 228 dental laboratories responded (42.1% response rate). Twenty-six percent of dental laboratories did not routinely disinfect incoming items. The dental technicians considered 30% of incoming final impressions and 20% of interocclusal registrations as inadequate. Half of the time (55%) final casts were mounted by technicians on simple hinge articulators. Only 20% of tooth preparations had adequate finish lines. The majority (70%) of fixed restorations were metal-ceramic. Fifty-seven percent of dental technicians considered the delivery time requested by dentists as insufficient. The information provided in this study indicates areas of weakness in communication between dentists and dental technicians, along with areas where both parties should use greater care during clinical and laboratory procedures.

Simplified procedure for preparing removable dies

J Prosthet Dent 2001;85:306-7.

Swallow thresholds using dentures made on different types of articulator

The purpose of this study was to determine whether edentate subjects achieved different performance when using dentures constructed on different articulators. A cross-over experimental design was employed to evaluate these swallow thresholds using complete dentures constructed on the hinge and free plane articulators. Seven subjects completed the study. Swallow threshold tests were performed 3 months after the insertion of dentures. The overall particle size distribution achieved with the dentures constructed on free plane articulators was significantly better at the end of the 3-month period (P less than 0.01 to P less than 0.0001), but significantly more strokes were used to achieve this success rate (P less than 0.04). A questionnaire revealed that the subjects had a preference for the denture constructed on the free plane articulator. It is concluded that patients performed better with dentures constructed on the free plane articulator.

A method to detect distinctive features from boundary data

AbstractRecently, attempts have been made regarding automatic learning of models of objects with two‐dimensional shapes from their multiple number of images and recognizing objects using pregiven models by partial features of shapes. Both are based on a principle of extracting the local features of a figure and using them as distinctive features for both learning and recognition.This paper proposes a method of feature extraction from a boundary pattern intended to be applied for such purpose. A hinge articulation is considered as a basic component of two‐dimensionally shaped objects, and for each one of the hinge representative shapes—a circle, linked bars and crossed bars—a simple but robust detection method is presented. Since extraction of line segments is necessary as a preprocess for detecting linked and crossed bars, a line‐segment detection method applying Hough transformation is developed for boundary patterns.

Complete denture construction in general dental practice: an update of the 1970 survey

A survey was carried out on materials and techniques used for complete denture construction in general dental practice, by means of a postal questionnaire sent to a random sample of 1000 dentists whose names were taken from the BDA membership. There was a 71.5% response. The results obtained are compared with a similar survey undertaken in 1970. The majority of practitioners still provided dentures totally or mainly within the NHS. Whilst the demand for complete dentures was reported as having remained stable, there has been considerable reduction in the numbers of dental technicians employed by general dental practitioners. Alginate remains the impression material of choice and the majority of impressions were sent to a commercial laboratory for pouring. Although still the most popular, the use of the plane-line hinge articulator has reduced and there has also been a continued reduction in the use of porcelain teeth. The importance of a cross-infection policy is highlighted. There were conflicting opinions expressed on the role of implants in general dental practice. Many respondents took the opportunity to comment on the status of dental prosthetics under the NHS and most criticised the fee structure.

At Last—A Disposable Articulator!

A simple disposable hinge articulator is described and its advantages in orthodontic clinical practice discussed.

Equilibrium rigidity of macromolecules of poly(4,4′-phenylene)pyromellitamido acid

From the value of the intrinsic viscosity in θ conditions and from the value of reduced dynamic birefringence the authors determine the equilibrium rigidity of non-hinge macromolecules of poly(4,4′-phenylene)pyromellitamido acid. They obtain the size of the statistical segment A=(60±10) × 10 −10 which is twice the size of the segment of the macromolecules of poly(4,4′-oxydiphenylene)pyromellitamido acid similar in structure but with hinge articulation.

A simple appliance for continuous jaw exercise

Impressions of the upper and lower occlusal surfaces of the teeth anterior to the molars are obtained in the traditional manner. The models are mounted on a hinge articulator. The exerciser is made of a 5 in. X 5 in. clear sheet of resin that is normally used for mouth guards. It is 0.15 in. thick, which gives the material resilience. The sheet is heated over a flame and then applied to the lower arch where the markings of the lower occlusal surfaces are imprinted. Following that, the sheet is chilled and folded over in the premolar or first molar region. The part that faces the maxillary teeth is now heated, and the markings of the maxillary occlusal surfaces are registered (Fig. 1). The sheet is again chilled, and a heavy pair of scissors is used to trim the outer part and to remove the middle section (Fig. 2). The sharp edges at the periphery are then smoothed with an acrylic bur. The final product is a thin, soft appliance that can be inserted between the arches, provided the patient’s mouth is not completely closed (Fig. 3). We recommend that the patient begin by wearing the appliance day and night for 2 weeks. The severity of the condition dictates the length of its use; in some cases, this may be for several months.

Simple hinge and semiadjustable articulators in orthognathic surgery

Model surgery, an integral part of the planning of orthognathic surgical cases, can in some cases be performed on a simple hinge articulator, while in other cases a face-bow and semiadjustable articulator is required. Careful geometric and mathematic analyses of both simple hinge (for example, the Galetti) and semiadjustable articulators (for example, a Hanau) will yield definite indications for their use. The purpose of this article is fourfold: to discuss the theoretic errors inherent in the use of the face-bow record, to derive error formulas that calculate the errors inherent in the use of all articulators, to determine the indications for the use of simple vs. adjustable articulators, and to describe the use of a semiadjustable articulator and intermediate splint in two-jaw surgery. The error formulas show that, although a simple hinge articulator can be used in many cases, its use should be restricted to mandibular surgery, anterior subapical surgery, and transverse maxillary surgery. However, to err on the side of overuse of a semiadjustable articulator will not create difficulties in any orthognathic surgery case.