Unlined Cavities Research Articles

Dynamic Stress Concentration of Underground Lined Cavities in Different Distance under Incident Plane SV Wave

A series solution for dynamic stress concentration of underground lined cavities in different distance under incident plane SV waves is given by wave function expansion method. The infinite series is cut and calculated under the required precision. The lining includes rigid lining, unlined cavities, flexible lining. The numerical results show that the distance between cavities has an important impact on the dynamic stress concentration factor and the interaction between two cavities greatly amplifies the dynamic stress concentration. With the distance increases the dynamic stress concentration factor turn smaller gradually and tend to the distribution case of one cavity; The rigidity of lining also has great effect on the dynamic stress concentration which is highest for the rigid lining, second for unlined cavities and is lowest for the flexible lining.

Dynamic Stress Concentration of Underground Lined Cavities in Different Distance under Incident Plane SV Wave

A series solution for dynamic stress concentration of underground lined cavities in different distance under incident plane SV waves is given by wave function expansion method. The infinite series is cut and calculated under the required precision. The lining includes rigid lining, unlined cavities, flexible lining. The numerical results show that the distance between cavities has an important impact on the dynamic stress concentration factor and the interaction between two cavities greatly amplifies the dynamic stress concentration. With the distance increases the dynamic stress concentration factor turn smaller gradually and tend to the distribution case of one cavity; The rigidity of lining also has great effect on the dynamic stress concentration which is highest for the rigid lining, second for unlined cavities and is lowest for the flexible lining.

Research of Dynamic Stress Concentration of Lined Cavities under Incident Plane SV Waves in Different Angles

AbstractAn analytical series solution for dynamic stress concentration of lined cavities in a half space under incident plane SV waves was given by using wave function expansion method. The infinite series was cut and calculated under the required precision. The linings includes rigid lining, unlined cavities, flexible lining. The numerical result shows that (1) incident angle has great effect on the dynamic stress concentration factor; (2) the distance between two cavities has great effect on the dynamic stress concentration factor too, and the interaction between two cavities can greatly amplify the dynamic stress concentration when the distance between cavities is closer; (3) the rigidity of lining also has great effect on the dynamic stress concentration which is highest for the rigid lining second for unlined cavities and lowest for the flexible lining.

Transverse response of underground cavities and pipes to incident SV waves

AbstractThe transverse response of underground cylindrical cavities to incident SV waves is investigated. Analytical solutions are derived for unlined cavities embedded within an elastic half‐space using Fourier–Bessel series and a convex approximation of the half‐space free surface. The computed displacements at the half‐space free surface and the tangential stresses on the cavity are compared with the results of previous investigations. The analytical solutions are extended to formulate approximate solutions for assessing hoop stresses within cavity liners impinged by low‐frequency waves having wavelengths much longer than the cavity diameter. The approximate solutions are compared to existing numerical solutions, and used to evaluate the dynamic response of a flexible buried pipe shaken by the 1994 Northridge earthquake. The proposed approximate model for cavity liners is useful for the seismic analysis of underground pipes and small‐diameter tunnels. Copyright © 2001 John Wiley & Sons, Ltd.

Pulpal response to an experimental adhesion promoter

The pulpal response to an experimental adhesion promoter (PTP) used in conjunction with a composite resin material, Biogloss, is described, in lined and unlined cavities. Dycal was the lining and negative control material. Standardised Class V cavities were prepared in ferret canine teeth and the pulpal responses studied after 1, 2 and 4 weeks and 6 months post-operatively. Pre-treatment of cavities with PTP causes a reduction in pulpal inflammation at 7 and 14 days compared with Biogloss. There was no obvious difference at the longer time intervals. Pre-treatment with PTP delays the ingress of microorganisms at the cavity wall/material interface but does not prevent it in the long term in this situation. The effect of PTP is not altered if the fluid is allowed to dry naturally rather than by blow drying.

The pulpal response to dilute citric acid smear removers.

The aim of this study was to determine the pulpal response to three dilute citric acid smear removers. Forty-eight vervet monkeys (Cercopithecus aethiops pygerythrus), in three groups of sixteen animals provided 384 tooth specimens for the histological evaluation of the pulpal response at 3, 31, and 59 days post-operatively. Labial Class V cavities were prepared in the maxillary and mandibular incisor teeth. The pulpal responses elicited by 1% aqueous citric acid, 1% citric acid in 30% ethanol and 0.1% citric acid in 30% ethanol solutions, in unlined cavities and in cavities lined with Dycal after acid application, were compared with those elicited by a negative control material--(Nobetec), and a positive control material--(Syntrex). Using Stanley's criteria the most severe pulpal responses were seen in teeth treated with 1% aqueous citric acid and 1% citric acid in 30% ethanol without a subsequent liner, and by Syntrex at all three time intervals. The use of Dycal as a liner after smear removal markedly reduced the pulpal responses.

Histopathologic and bacterial evaluation of conventional and new copper amalgams.

In vivo pulpal responses in monkeys and in vitro bacterial inhibition studies were completed on new copper amalgams, Sybraloy, Dispersalloy, Tytin and a conventional Spheraloy amalgam. Amalgams were placed in cavities lined with ZOE and in unlined cavities. Silicate and ZOE were used as controls. A total of 165 adult monkey teeth were evaluated at 3 days, 5 and 8 weeks. At 3 days the pulpal responses elicited by the copper amalgams appeared similar to conventional Spheraloy, all showing a slight to moderate response. At 5 weeks the majority of amalgams exhibited a slight pulpar response with a tubular reparative dentin under each restoration. The 8 week pulpal response showed a reduction of the inflammatory response characterized by a tubular reparative dentin with a uniform zone of predentin. Lined ZOE controls exhibited a slight response while silicate showed a moderate response with some persistent chronic inflammation. In vitro bacterial tests revealed that the various amalgams had little to no inhibitory effect on the three serotypes of S. mutans that are most prominent in humans.

Bacteria and pulpal reactions under silicate cement restorations

Silicate cement was inserted in deep unlined cavities in 70 human teeth; 35 cavities were cleaned with an antibacterial cleanser, and the other 35 cavities in the contralateral teeth were treated with water spray only. In all teeth, invasion of bacteria from the tooth surface was prevented with a surface seal. Histologic examinations after 4 weeks revealed bacterial growth on dentinal walls in 9 of the uncleaned and in 2 cleaned cavities. Only in these 11 teeth was an inflammatory reaction seen in the pulp. Under eight cavities without bacterial growth and with silicate cement placed directly on an exposed pulp, no serious injury and no inflammatory reactions were observed. It was concluded that silicate cement per se does not seriously irritate the pulp. Infection of cavity walls should be avoided, not only by removing grinding debris and antibacterial cleansing, but also by use of a liner to prevent invasion of bacteria from the surface of the tooth.

Bacteria beneath composite restorations—a culturing and histobacteriological study

The occurrence, viability and identification of the microbial flora under composite fillings using an anaerobic technique were studied. Class V cavities were prepared on clinically healthy buccal surfaces of 7 contralateral pairs of premolars in children 11--15 years of age. After preparation, rubber dam was applied and one cavity in each pair of teeth was washed with water blasted dry with air and filled with Adaptic. The other cavity was washed with a cavity cleaner (Tubulicid) and a cavity liner (Tubulitec) was applicated prior to filling with Adaptic. The teeth were extracted after 4--6 weeks. Under anerobic conditions the tooth crown was split. From one half samples were taken from the pulpal wall under the filling and cultured on blood agar and in broth medium. The other half was examined with histobacteriological technique. No growth occurred in cultures from lined cavities but in 6 of the 7 unlined cavities. Full agreement was observed between the findings from the culturing and histobacteriological examinations concerning presence or absence of microorganisms at the pulpal wall in all 14 teeth. The flora was mixed. Gram-positive bacteria, mainly Streptococcus and Actinomyces, dominated over gram-negative bacteria including Veillonella, Fusobacterium, Campylobacter and Selenomonas. The composition of the flora was more similar to that observed in dental plaque than that found in carious dentin or in saliva in other studies.

Pulpal response to a new visible light‐cured composite restorative material: Fotofil®

A new visible light-cured composite resin, Fotofil, has been developed for the esthetic restoration of anterior teeth. The pulpal responses elicited by this material in unlined cavities and cavities lined with Dycal were compared with those elicited by a negative control consisting of modified zinc oxide-eugenol cement Notebec and a silicate cement Syntrex. The pulpal responses were evaluated in the permanent maxillary and mandibular incisors in vervet monkeys using labial Claterial in each monkey. Groups of 10 monkeys were killed at intervals of 2 days, and 2 and 8 weeks after restoration of the teeth. The most severe pulpal responses were elicited by the unlined Fotofil and Syntrex restorations at all three time intervals. The Dycal lined Fotofil restorations elicited a milder pulp response than the Nobetec at 2 days and 2 weeks. No pulpal response was elicited by the latter two materials at 8 weeks. These results clearly showed that Fotofil and Syntrex are irritant to the dental pulp up to 8 weeks. The placement of a Dycal liner beneath Fotofil restorations reduced the pulpal irritation elicited by this material to levels which were lower than those elicited by the Nobetec control at 2 days and 2 weeks.

Reaction of the human dental pulp to silver amalgam restorations: The modifying effect of treatment with calcium hydroxide

Cavities were prepared in 43 bicuspid teeth using two general categories of cavity depth. In the "deep" cavities the bottom was placed in the inner third of the dentin. In the "intermediate depth" cavities the bottom was positioned in the middle third of the dentin. The bottom of the cavities was either rubbed with calcium hydroxide, covered with calcium hydroxide, or left unlined before filling according to the wet amalgam technique. The teeth were extracted after 1 week and examined histologically. All cases, except 2 with deep and 1 with intermediate depth rubbed cavities, showed local vascular dilatation in the pulp underneath the cavity. In addition, all teeth with deep unlined cavities showed inflammatory cells as did 1 with an intermediate depth unlined cavity. There were fewer displaced odontoblast nuclei in the dentin in the calcium hydroxide-treated groups. The milder reactions in the rubbed or covered groups are probably due to the restrictive effect by calcium hydroxide on penetration of amalgam components. In the teeth with deep cavities there were only minor differences between the ones which had been rubbed and those which had been covered with calcium hydroxide.

Pulpal reaction to composite resin restorations

\/ omposite resin materials appear to be gaining in popularity. A report of their physical properties implied that they are superior to silicate cement and the coldcuring acrylic resins. In some situations composite resin materials are suitable for use in the restoration of posterior teeth.l Histologic studies of the effect of composite resin materials on the pulp are few and are concerned mainly with Addent 35t-the first such material to appear on the market. It has been suggested that the pulp reaction to this resin may be slightly less “severe” than to other cold-curing materials, and it was apparently difficult to find an effective liner that would prevent reactions to the Addent 35.* Stanley, Swerdlow, and Buonocore3 found that without a liner this material gave a mild response at first but that it increased in intensity with time. They considered that the proved polyvinyl cavity liner recommended for Addent 35 did not always provide adequate protection of the p~lp.~ In another study conducted by Baume and FioreDonno, pulp injury was found to be particularly severe under deep cavities with Addent 35, and the polyvinyl liner recommended by the manufacturer did not protect the pulp, though calcium hydroxide paste did. Sayegh and Reed5 studied the response beneath 36 Blendantl fillings in human teeth and, as a rule, found a mild response. No histologic examinations of the effect on the pulp of the new materials Addent 12 and Adaptics appear to have been published. The question of whether these materials are acceptable from the biologic aspect remains unanswered, and this applies to whatever kind of protection is used should damage to the pulp occur. In a separate study, 6 bacteria were detected on the walls of 56 of 66 unlined cavities restored with Adaptic, Addent 12, or DFR.11 Under 19 of these restorations, bacteria were observed in the dentinal tubules and in the pulps of three teeth. Only with

Pulp response in the rhesus monkey to “composite” dental restorative materials in unlined cavities

An investigation was carried out to compare the effects of new composite restorative materials with those of zinc oxide and eugenol and unlined silicates. The results indicate that composite materials can be considered biologically acceptable but that they are attended by a mild and persistent inflammatory response when used in deep, unlined cavities. It is recommended that the composite resins be used clinically with a protective base or liner.

Ultrastructure of odontoblasts in dentinal tubules of mice.

The presence of odontoblasts in dentinal tubules has been noted by numerous investigators. One of the first to describe their presence was B. Orban (l Dent Res 20:553-557, 1941). The cells were in tubules associated with forceps marks on the root surfaces. Odontoblasts in dentinal tubules have been reported due to various types of trauma to pulps. Cavity preparation (V. E. JAMES and I. SCHOUR, J Dent Res 34:698-699, 1955; LEFKOWITZ ET AL, Ohio State Dent Soc J 31:24-27, 1957; E. A. MARSLAND and D. S. SHOVELTON, Brit Dent J 102: 213-222, 1957; D. S. SHOVELTON and E. A. MARSLAND, Brit Dent J 105:16-26, 1958; K. LANGELAND, Odont T 65:249-386, 1957; J. J. KENNEDY ET AL, Dent Prog 3:10-16, 1962; M. BRANNSTROM, Odont Rev 14:224-253, 1963; and others) elicited this response when the cavities were cut dry or when severe trauma was provoked. Others such as I. R. H. Kramer and J. W. McLean (Brit Dent J 92:255-261, 1952), 0. Muller and B. Maeglin (Int Dent J 4:167, 1953), and K. Langeland (Odont T 68:463472, 1960) found this response under various filling materials, especially in unlined cavities. H. R. Stanley and H. Swerdlow (JADA 58: 49-59, 1959) related the appearance of aspirated odontoblasts to the degree of inflammation. Most investigators agree that this occurs soon after the toxic stimulus is applied, as noted in specimens collected 24 hours after treatment. M. B. Weiss, M. Massler, and J. M. Spence (Dent Prog 4:10-19, 1963) also found that extraction of teeth may cause this response. Thus squeezing of the pulp may force the odontoblasts into the dentinal tubules. The present observations on the teeth of mature mice prepared for electron microscopy in a study of the normal development pattern of dentin included study of the ultrastructural appearance of odontoblasts in the tubules in some of the teeth that had been extracted with forceps. The teeth were fixed in 1.33% osmic acid in s-collidine buffer at 4 C for two hours, dehydrated through graded alcohols and propylene oxide and embedded in Epon 812, sectioned at 500 to 800 A, and viewed on an Hitachi 8 electron microscope. In Figure 1 an elongated odontoblast is seen in the upper left within a tubule located partly in the predentin (lower left) and partly in the more highly calcified dentin (upper right). This electron micrograph shows the presence of the organelles within the cell as well as the dark stained