Resilient Layer Research Articles

Photoelastic stress patterns produced by implant-retained overdentures

Statement of problem. When 2 implants are used to support a removable overdenture, optimal stress distribution to minimize forces to the implants is desired. Purpose. This study used photoelastic analysis to compare the stress patterns generated around implants with 2 retention mechanisms. Material And Methods. Two root form implants were anchored in a photoelastic mandible and a removable overdenture was fabricated. The denture was lined with a resilient layer of impression material to simulate oral mucosa. Attachment of the denture to the implants was varied by using ball/O-ring and bar-clip attachments. Vertical and oblique occlusal forces from 10 to 200 lb were applied unilaterally to the right and left first molars. Resultant stress distributions in the photoelastic mandible were photographed and evaluated. Results. With vertical forces, the ball/O-ring attachment transferred minimal stress to both implants. Vertical forces applied to the bar-clip overdenture created immediate stress patterns of greater magnitude and concentration on both implants. A posterior oblique load resulted in similar stress patterns to both systems with slightly greater stress to the bar-clip overdenture. Conclusions. Within the limits of this study, ball/O-ring attachments transferred less stress to implants than the bar-clip attachments when the photoelastic model was subjected to a posterior vertical load. (J Prosthet Dent 1998;80:559-64.)

The Impact Sound Insulation of Pre-Loaded Timber Floating Floors on a Concrete Slab

When impact sound tests are carried out in new and refurbished flats there is not normally a load on the floor. When the flat is occupied however, loading due to furniture, appliances, people etc, will occur which compresses the resilient layer if a floating floor construction has been used. The effect this has on impact sound insulation is considered in this paper. Impact sound transmission through a chipboard floating floor on battens supported on a concrete floor has been measured when static loads were placed on the chipboard – the loads were in the range 20 kg/m3 to 160 kg/m2. Three different resilient layers under the battens were tested: 25 mm mineral wool quilt, resilient battens and resilient battens on 13 mm mineral wool quilt. The weighted standardised impact sound pressure level (L'nTw) increased by 0.5 dB to 5 dB with the larger increases for the greater loads. Further measurements were made after the floating floors had been left under a static load of 200 kg/m2 for six months: there was an additional increase in L'nTw of 1.5 dB. Finally, measurements were compared with floors where the resilient layers had been soaked to simulate water leakage from baths, pipes etc; there was no significant difference in results.

A Method for Predicting L'nT,w for Lightweight Floating Floors Comprising Low Density Flexible Polyurethane Foam on Concrete Supporting Floors

Lightweight floating floors of medium density fibreboard supported by a resilient layer of flexible polyurethane foam are increasingly being used in both new build and refurbishment projects. BS EN 29052–1 describes the Standard Method for determining the dynamic stiffness of resilient layers used under floating floors: this states that the Standard does not apply for loadings of less than 0.4 kPa, which is higher than the static load imposed by medium density fibreboard. The Standard also states that it does not apply to materials whose airflow resistivity is less than 10 kPa.s/m2 if the dynamic stiffness of the air enclosed in the material is not negligible compared with the apparent dynamic stiffness of the test specimen. Despite these restrictions it was found that, when sections of flooring were tested in the field, the Standard Method provided data which allowed the prediction of the improvement in impact sound insulation over a range of 40 dB and also the prediction of the weighted standardised impact noise level according to BS 5821. 1984. Part 2. This was achieved by taking account of the stiffness of the air in laboratory samples and the effect of the mass impedance of the hammers on the standard tapping machine used in field tests.

Diaphragm for dynamic microphones and methods of manufacturing the same

A diaphragm for microphones having a laminate structure which imparts damping characteristics to the diaphragm is disclosed. The laminate comprises upper and lower resilient layers composed of a plastic film. The upper and lower layers constrain a center layer composed of an elastomeric material having a high dissipation of vibratory shear motion. Manufacturing techniques for making such diaphragms are disclosed.

Reconstituted Versus Virgin Open Cell Foams in Floating Floors

Sound reducing flooring systems using flexible polymer foams as a decoupling resilient layer are increasingly being used in both new build and refurbishment. Such foams have been investigated and results suggest that reconstituted polyether foam from waste products may offer some advantages over the low density open cell l.d.o.c.) foams currently used in some systems. It has been shown that reconstituted open cell (o.c.) foams have an almost linear compressive stress-strain relationship up to about 40% strain without the marked yield point observed with virgin o.c. foams. Stress strain characteristics for reconstituted o.c. and virgin l.d.o.c. foams compared in this study indicate that, for stresses below the yield point for the virgin foam, greater strain is observed in reconstituted foam. When tested according to BSEN 29052-1, systems comprising reconstituted foam exhibited lower natural frequencies than those with the lower density virgin foam.

Structural isolation of walls using elastic interlayers

Resilient layers at joints provide a practical method for reducing structureborne sound transmission. Soft materials such as cork are readily available and can provide significant improvements in performance. When such materials are introduced into buildings the nature of transmission changes. The relative importance of transmission paths changes so that the benefits may be unclear. Placing a resilient layer under a wall will reduce transmission of bending waves between the wall and floor but will have less effect on the conversion of in-plane waves to bending waves. Thus, while bending transmission may be reduced, conversion from bending to in-plane and from in-plane to bending may not be changed significantly and may become the dominant transmission path. In real situations the details of the rest of the construction are important and may reduce the expected benefits of fitting a resilient layer. It is not sufficient to calculate the change in the direct path to estimate the change in overall performance.

Comparison of the guarding capacities of mouth protectors

The guarding capacity of seven mouth protectors (Erkoflex 3.0 and 4.0, Erkoloc 3.0, 4.5 and 5.5, TranSheet/Perform and TranSheet/LiteLine) was tested mechanically on 20 plaster models, two or three tests on each mouth protector. Two tests on a plaster model without the protector served as control. An appliance was constructed to simulate the impact of an ice-hockey puck on the teeth, the plaster model was fixed onto the device and the minimum force needed to break the plaster teeth under the protector was recorded. The average total thickness and that of the soft and hard layers of the labial plates of each mouth protector were recorded along with the average thickness of the cervical and incisal hard and soft layers. The results showed that the best protection was achieved with the TranSheet/LiteLine model, followed by TranSheet/Perform and Erkoloc 5.5 and 4.5 mouthgards. All these had a resilient layer against the teeth, and it was shown in stepwise regression analysis that the only property having a statistically significant effect on the guarding capacity was the thickness of this cervical soft layer.

Vibrations of simply supported cylindrical shells isolated from an ambient acoustic medium by a compliant layer

The effect of a resilient layer isolating a finite cylindrical shell from a high-impedance acoustic medium, e.g., water, on the predominantly radial modes of the shell is explored. While the submerged, bare shell displays resonances whose natural frequencies are reduced below their in vacuo values by the kinetic energy of the entrained fluid vibrating with the same amplitude as the structure, the coated shell displays two families of radial modes: (1) predominantly structural modes whose natural frequencies are raised above those of the shell in vacuo by the coating stiffness, the coating/fluid interface remaining nearly stationary; (2) low-frequency modes embodying the compliant layer’s spring stiffness and the combined modal masses of entrained fluid and of the shell; for these modes, coating/fluid interface amplitudes are markedly enhanced above those of the coated shell and even those of the bare, submerged shell.

Resilient floor system

A resilient floor (A) is disclosed assembled on a base surface (10) to provide a resilient floor (36) which comprises a plurality of sub-floor sections (B) arranged generally side-by-side. A resilient layer of material (62) is carried generally co-extending underneath the sub-floor sections. A slot (38,74) and widened groove (40) accommodate a fastening member (51,71) which includes lateral flanges (58,60) and (78,80) which limit upward movement of sub-floor sections (B). Flooring strips (D) are nailed to the sub-floor sections so that the flooring strips move integrally together in relative vertical movements relative to the fastening strips (51,71). Resilient layer (62) urges sub-floor sections (B) and integral flooring strips (D) upwardly such that downward forces produced by activity on the floor (36) are provided with a degree of resiliency.

The sound insulation of timber platform floating floors in the laboratory and field

Timber platform floors are often found to perform better in the laboratory than in the field and the reasons for this are not well understood. The main parameters that affect the sound insulation of this type of floor have been investigated and the results are reported in this paper. The parameters investigated are: density of resilient layer; effect of absorbing material; effect of joist spacing; and control of flanking transmission. The findings from the study allow advice to be given on the design of this type of floor.

Modification of osseointegrated implants for distal-extension prostheses

The use of a distal implant abutment splinted to a natural tooth by a fixed partial denture has been employed for distal-extension prostheses. There is a differential difference between the viscoelastic deflection of a natural tooth by its periodontal ligament, and the almost negligible elastic deformation of an osseointegrated implant. This difference may induce a fulcrum-like effect and overstress the implant. In this study a new modification of osseointegrated implants was proposed to counteract this problem. This modification was achieved by using a resilient layer material under the superstructure of the implant. Finite element modeling (FEM) was used to examine stresses and displacement distribution around a commercially available implant and one experimental implant with a resilient layer material. The results of this study showed that the new modification is a simple and efficient way to mimic the structural natural tooth unit. It also showed that it allowed movement of the superstructure without movement of the implant three times that of the nonresilient model.

Nonspecific Factors Involved in Attachment of Entomopathogenic Deuteromycetes to Host Insect Cuticle

The attachment of the conidia of the insect-pathogenic fungi Nomuraea rileyi, Beauveria bassiana, and Metarrhizium anisopliae to insect cuticle was mediated by strong binding forces. The attachment was passive and nonspecific in that the conidia adhered readily to both host and nonhost cuticle preparations. The hydrophobicity of the conidial wall and the insect epicuticle appeared to mediate the adhesion process. Detergents, solvents, and high-molecular-weight proteins known to neutralize hydrophobicity reduced conidial binding when added to conidium-cuticle preparations. However, these chemicals did not remove the hydrophobic components from the epicuticle or from conidial preparations. The outer surface of the conidium consists of a resilient layer of well-organized fascicles of rodlets. Intact rodlets extracted from B. bassiana conidia bound to insect cuticle and exhibited the hydrophobicity expressed by intact conidia. Both electrostatic charges and various hemagglutinin activities were also present on the conidial surface. However, competitive-inhibition studies indicated that these forces played little, if any, role in the adhesion process.

The effect of resilient layer and occlusal reactive complete dentures on the residual alveolar ridge

A technique for making resilient layer and occlusal reactive dentures was proposed. A radiographic and clinical evaluation of the effect of these dentures on the residual ridges of 17 subjects was done. The results showed that the rate of ridge reduction with these dentures was significantly less than that with conventional dentures. Therefore, the resilient layer principle is a promising clinical modality.

Wavenumber/frequency admittance of beams

Using an array of point drives, the admittance of finite beams were measured and compared to predictions. The predictions were made using an analytic model of the beam response based on Timoshenko beam theory. To drive the desired wavenumbers, the amplitudes of the point drives were weighted to produce standing wave patterns that were made up of left and right traveling waves, both of the same wavenumber. The standing wavepattern avoids the need to control the phases between the drives that would have been required for traveling single wavenumber drives. The effects of beam resonances are explored by comparing measured admittance data for beams with free ends, with and without internal damping and for beams with heavily‐damped ends. The wavenumber/frequency transfer functions of resilient layers placed between the array of drives and the beam are determined from admittance measurements made with and without the resilient layer.

Sound absorbing wall lining

It should be possible to manufacture, in a simple manner, a sound-absorbing wall-lining (3) consisting of a material to be applied to the wall which needs lining, and a resilient layer (4, 5) of foam, e.g. foam rubber, felt, or similar material, having locally distinctive sound-absorbing capacities, and whose thickness will possibly remain uniform, provided the resilient layer (4, 5) contains a filler with locally distinctive degrees of cross-linking--corresponding to distinctive sound-absorbing capacities.

Flexible drive coupling

A flexible drive coupling for innerconnecting a pair of rotatable shafts includes a hub and an outer member. The outer member has formed in it a central opening and is disposed so as to circumscribe the hub and to be generally concentric with the central axis of the hub. Secured to and disposed between the hub and the outer member is a flexing section. The flexing section includes a plurality of helically wound, radially alternating layers of a resilient material and a substantially inextensible material. The layers of the flexing section, when viewed in section taken transversely through the layers and generally parallel to the central axis of the hub, have widths that diminish with increasing radial distance from the hub. The widths of successive resilient layers, however, diminish with increasing radial distance from the hub at a faster rate than the widths of successive and intervening inextensible layers. As a result, the strains experienced by the resilient layers are more uniformly distributed throughout the layers and the coupling has an increased capablility for permitting angular misalignment between the shafts joined by the coupling.

Effect of a resilient layer in a removable partial denture base on stress distribution to the mandible

The results of two-dimensional finite element analyses of a mandible indicate that a resilient layer within a denture base can act as an effective "shock absorber" and may slow down ridge resorption. Finite element models of similar types can easily be used to further investigate various applications of resilient layers. The magnitudes and distributions of stresses generated in the mandible by force application to two types of a distal extension denture base were determined and compared. The results were obtained by using the finite element method of stress analysis. In the first analysis, a conventional distal extension denture base resting on the mandible was simulated. In the second analysis, the same testing force was applied to a distal extension denture base with a resilient layer between the teeth and the basal seat. The results indicated that the stress distribution was more uniform during occlusal loading through a resilient layer. The vertical displacement of the alveolar ridge under the denture base with a resilient layer was far less than that of the conventional denture base.

The sound insulation of wood joist floors in timber frame constructions

The results of an investigation of the sound insulation provided by wood joist floors between timber frame dwellings are described. The investigation was mainly concerned with impact transmission since available field data showed that the impact performance was, in general, worse than the airborne performance. The effects of changing various aspects of the floor design are discussed and limited guidance is given on the values of some floor parameters. Some tests have been carried out with the resilient layer bridged by nails and with the floor loaded. Suggestions are given for further research which is required to improve the understanding of sound transmission processes in wood joist floors.

Analysis of a Journal Bearing with Self-Boosted Pressure Generation

The shaft of a journal bearing is covered with a resilient layer containing perforations. These act as varying volume pockets, owing to the elasticity of the material, and force lubricant into the film as the shaft rotates. An improvement in load capacity is given for eccentricity ratios greater than 0.7 which is accompanied by a proportional increase in flow and a slight increase in friction. A range of suitable lining materials is considered.

Discussion of “impact reduction in complete and partial dentures, a pilot study”

I wish to commend Dr. Parker for his original approach to the problem of impact reduction to denture foundation tissues. Most discussions allow for a review of the literature so that personal opinions can be reinforced or refuted. In discussing this pilot study no such comforting references were available. The study has appealing ideas. Is it a better answer than we have in the soft liner? For complete dentures, the resilient layer does not solve the problem of undercut areas, nonresilient mucosa, relief for exostosis, isolated bony prominences, and sensitivity to acrylic resin. The soft liner seems to have merit for complete dentures. For partial dentures with distal extension bases, the principle of the resilient layer has merit and is practical. More relief from soreness can be provided today for the chronically affected than was possible a decade ago. New techniques will be proposed for new materials that will be developed. Studies such as this give stimulation and impetus to dentistry's search for a better way to treat patients.