Dental materials: 1978 literature review part II

Journal of Dentistry, 8, No. 3, 1980, pp. 222-248

Dental Materials: Part II D. Brown,

Printed in Great Britain

1978 literature

review

M!Sc, PhD, CEng, MIM (Editor)

Guy’s HoqCtal Dental School, London M. Braden, Dental

T. C. Tranter,

8812, PhD, FlnstP, FPRI

School, London

Hospital

Medical

College

Dental

School,

8~3, PhD Welsh National

School of Medicine,

Cardiff

B. E. Causton, Dental

School,

Bsc, PhD

London

Hospital

Medical

College

N. E. Waters, MSc, PhD, FlnstP School of Dental

E. C. Combe, Turner Dental

PhD, DSc, CChem, FRIC

Surgery,

Royal

Dental

Hospital

of London

School, Manchester

D. C. Watts, BSC, PhD, MlnstP D. W. Cruickshanks-Boyd, Eastman

Dental

Hospital,

BSc,

CEng, MIM

Turner Dental School,

D. F. Williams, c.

H. Lloyd,

Dental

Manchester

London

School and Hospital,

Bsc, PhD, CEng, MIM

School of Dental Surgery,

8Sc. PhD

University

of Liverpool

Dundee

A. D. Wilson, DSC, CChem, FRIC C. Main, Dental

School,

Laboratory

PhD

8%

of the Government

H. J. Wilson, J. F. McCabe, Dental

Chemist,

London

Glasgow

8Sc. PhD, CChem, MRIC

Dental

PhD, DSc, CChem, FRIC

School, Birmingham

School, Newcastle-upon-Tyne

M. Miller,

8Sc. CChem, FRIC

School of Dental

Surgery,

University

of Edinburgh

ABSTRACT This paper, which is presented in two parts, reviews the work on dental materials published in 1978. Included in Part I were sections on cements, amalgam, composite filling materials, endodontic materials and fissure sealants. A review of the literature relating to biomechanics, impression materials, model, die and mould materials, waxes, cast and wrought alloys, acrylic resins, tissue conditioners and soft lining materials, ceramics, implants and corrosion is presented in Part 11.

INTRODUCTION This review is the sixth in an annual series compiled by the Panel for Dental Materials Studies in the United Kingdom, and is intended as a source of reference for work on dental materials published in 1978. It covers the introduction of new materials, the evaluation of existing materials and the development and application of techniques to aid such evaluations, together with assessments of the materials-oriented problems of clinical procedures. A basic list of 37 journals was surveyed by all the contributors, but each contributor was free to include material from any other source.

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DENTAL BIOMECHANICS Masticatory forces and mandibular movement An intraoral force telemetry system for the registration of occlusal forces during function without the distorting influence of transoral linkages was described by McCall et al. (1978). The system consisted of eight strain gauges and a minaturized transmitter. This apparatus was used in a study of functional occlusal forces by De Boever et al. (1978a). The forces were related to different kinds of food and to muscle activity as recorded electromyographically. A useful comparison of these authors’ results with those of previous workers was given. A further paper dealing with functional occlusal forces under anaesthesia by the same authors was also published(De Boever et al., 1978b). A computer-graphics system was developed by Roedema et al. (1978a) to help the student understand mandibular movement patterns and to illustrate the effects of condylar and incisal guide settings on cuspal placement and ridge and groove alignment. The system simulates three-dimensional mandibular movement but this paper was restricted to interocclusal movement in the occlusal plane. In a second paper (Roedema et al., 197813) graphic representation of interocclusal movement patterns projected onto the sagittal and frontal planes was described. Lundeen et al. (1978) reported a study on 163 subjects to determine an average mandibular movement pathway. In addition the effect ofvarying anterior guidances on the cusp movement in molar teeth was examined. Chewing cycle patterns during both human and macaque mastication was recorded using an optical system attached to the mandible and an electronic tracking device by Byrd et al. (1978). When chewing the same food (carrot) human masticatory patterns were wider and the macaque patterns more vertical, symmetrical and uniform than those of the humans. Reasons for these differences were discussed in terms of intercuspal relationships and morphology of the temporomandibular joint. Human patterns of tooth displacement (upper left canine and first molar) in simulated chewing cycles were also reported by Behrend (1978a) using a two dimensional recording system described previously (Behrend, 1974). Behrend (1978b) has also investigated the variation between cusp inclination and the displacement of an upper canine with an alterable surface angulation when subject to a controlled vertical force. With the surface set at 6S” to the horizontal, displacement was approximately double in length and lower in angulation than for the surface at 25O. A theoretical analysis was presented and compared with the functional situation.

Orthodontic tooth movement A double-exposure pulsed laser holographic technique for measuring the displacements in three dimensions of maxillary central incisors was described by Burstone et al. (1978). It was claimed that this non-invasive technique had an accuracy of 0.05 urn. The ‘centre of rotation’ as well as the linear displacements of a tooth under load were calculated. Results were presented for a single case in which a tooth was subject to a 300 g load applied in a lingual-labial direction parallel to the occlusal plane for 45 seconds. In a further paper by the same authors (Pryputniewicz et al., 1978) the same technique was used on a model tooth to show the inaccuracy of predicting tooth displacement from an arbitrary force acting in a specific direction with respect to the three coordinate axes, from data of the

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displacements resulting from forces along these axes. The discrepancy was attributed to changes in geometry of the periodontal ligament. The use of suitable magnets attached to teeth to produce orthodontic tooth movement was investigated by Blechman and Smiley (1978). The possibility of tissue reactions to induced electromotive forces was examined theoretically. It was concluded that for blood vessels the induced e.m.f. would be several orders of magnitude lower than the resting potential and hence was not a hazard. This conclusion is at variance with the more cautious view of the available evidence given by Cerny (1978). Magnets made of AlNiCos were used to move the canine teeth of two cats; tissues from all oral tissues adjacent to the magnetic fields were found to be normal. As the force between two magnets of opposite polarity will be inversely proportional to the square of their distance apart, the force markedly increases as the magnets come together and may be difficult to control within the normally accepted force range for tooth movement. An examination of the use of a pulsating force for the orthodontic movement of teeth was reported by Oates et al. (1978). At the force level used, 6g, there was no obvious difference between the radiographic, histologic or linear measurement data for dog second premolar teeth subject to either a continuous or a pulsating force. The literature of headgear therapy was reviewed by Bowden (1978a, b). Mechanical principles were dealt with in Part I (Bowden, 1978a) and clinical response and usage in Part II (Bowden, 1978b). A formula by which the axis of rotation of any single-rooted tooth subject to a force on the crown perpendicular to the tooth axis may be calculated from the root length and the height of the force from the cervix was presented by Steyn et al. (1978). The analysis, which is based on certain simplifying assumptions, appeared to give results in general agreement with previous analyses.

Orthodontic wires, elastics and appliances The problems of calculating the Young’s modulus of orthodontic wires accurately from results obtained by different testing procedures was examined in detail by Brantley et al. (1978). The effect of a heat treatment on the load-deflection characteristics of loop configurations fabricated from Elgiloy Blue were reported by Williams et al. (1978). The optimum heat treatment as far as yield stress, modulus and tensile strength were concerned was 950°F (5 loot), a slightly higher temperature than that recommended by the manufacturer (900°F/482”C). By virtue of an increase in Young’s modulus the spring components made with heat-treated wire had a higher stiffness. A paper dealing with the general physical properties of the novel alloy wire Nitinol in comparison with 18/8 stainless steel was given by Andreasen and Morrow (1978). The properties considered were Young’s modulus, stiffness in both bending and torsion utilizing a Tinius Olsen stiffness test. The test was carried out to ADA Specification No. 32 for orthodontic wires. Clinical application of Nitinol were described and its limitations, viz. extremely low ductility, inability to be soldered and inherent flexibility, discussed. Force-extension characteristics of different sizes of small helical springs available from 3 manufacturers in the United States were examined by Webb et al. (1978). The springs were made from Hi T and Permachrome (Unitek Corp.), a chromium alloy (Ormco) and Elgiloy (Rocky Mountain). The results obtained appear to be in accordance with basic spring

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design. The major conclusion was that with certain springs larger forces are produced than are necessary for orthodontic tooth movement. The principles involved in the design of active and removable appliances were discussed in a general way by Eastwood and Wright (1978). The stress relaxation of orthodontic polyurethane-based elastics (Alastiks, Unitek Corp.) were measured in dry air and water at 37OC and these results compared with those obtained in vivo by Ash and Nikolai (1978). The relaxation of force with time followed the familiar pattern, the decay in force being initially very rapid and then becoming slower and slower. Relaxation was least in dry air and, although the pattern was similar for the water and in uivo results, the latter became statistically greater than those in water after 1 day for the chain and after approximately 10 days for the module examined. The forces produced by Alastik modules and their decay rate were examined under conditions simulating clinical use by Varner and Buck (1978). Ignoring the relaxation taking blace in the first 2 h, the authors concluded that with an average force decay of 26 per cent over the period 2 h to 4 weeks modules need only be changed every 4 weeks.

Stress analysis studies on teeth and amalgam restorations The development of thermal stresses in teeth subject to sudden temperature changes and the influence these stresses have on crack initiation and also propagation were considered analytically by Lloyd et al. (1978). This paper, an extension of previous work on the same subject, utilized two-dimensional axisymmetric finite difference and finite element analyses to calculate the transient temperature and stress distributions in the tooth, a model of a mandibular second molar. It was concluded that ingestion of cold food or water can result in cracks which could grow if the tooth were subsequently mechanically stressed, and conversely that cracks initiated by mechanical loading could grow under thermal stress. Estimates of the thermal stresses likely to develop in teeth during cavity preparation were undertaken by Brown et al. (1978). The energy transmitted during cutting was determined calorimetrically, the variables examined being the type of stone used (diamond or carbide), handpiece type and pressure applied. From these results the temperature and stress distributions in a model tooth were calculated using numerical finite difference and finite element computer codes. The conclusion that sufficiently high thermal stresses for fracture to occur may be generated by cutting enamel dry but not when water was sprayed were confirmed by experiment. However, whether or not it is justifiable to apply the results of an analysis on a symmetrical model of a tooth with a cavity cut solely within the enamel of the occlusal surface to the cutting of a Class V cavity, the experimental case illustrated, is open to doubt. The technique of finite stress analysis was used by Wright and Yettram (1978) to examine the effects of amalgam expansion on setting and also thermal expansion on the stress distribution within a second mandibular premolar with a Class I amalgam restoration. Lined and unlined restorations were compared with regard to the principal stresses developed and the resulting deformation. The analysis showed that: very high stresses may be developed in the region of the occlusal margin; the behaviour of the system as a whole is controlled by the ratio of the moduli for enamel and dentine; zinc phosphate, by virtue of its similar elastic modulus to dentine and low thermal diffusivity is a very good substitute for dentine both mechanically and thermally; and that values of the maximum stress under normal

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thermal loading, although transient, may be of a similar order of magniture to those produced in teeth by normal masticatory forces.

Pins and endodontic dowels A study by Fujimoto et al. (1978) of the tensile loads required to separate dentine from pin-retained amalgam and composite resin core material showed that failure generally occurred through fracture of the dentine, particularly if three of more pins were used, or because the pins pulled out of the dentine. No statistically significant difference was found between the tensile strength of retained amalgam and composite core materials. The retention of three dowel designs, viz. smooth tapered (Unitek Corp.), parallel sided and serrated (Whaledent Parapot) and parallel-sided threaded (Kurer) was examined by Standlee et aL(1978). The effects of cement type and dowel length and diameter were also investigated. Design was found to be the most important variable, the Kurer having the best and the Unitek the least retention. Increased retention was obtained with longer dowels. Cement type was only of importance with the tapered dowels when the ranking, in order of improved retention, was found to be epoxy < carboxylate < zinc phosphate.

Partial dentures A two-dimensional finite element analysis of the stresses developed around an abutment tooth, a second premolar, when the distal extension of a removable partial denture was loaded was provided by Craig and Farah (1978). The extension was connected to the abutment by an occlusal rest on the distal marginal ridge and an I-bar clasp resting on the lower third of the buccal surface at the position of maximum contour. The closer the applied load to the axis of the abutment tooth the greater the reduction in maximum stress in the bone around the tooth was found to be because of the decrease in the applied moment. The stress distribution around a fixed partial denture with a blade-vent implant abutment embedded at the site of the mandibular second molar was investigated by finite element analysis of a two-dimensional model by Takahashi et al. (1978). A model of a fiied partial denture constructed on the second premolar and second molar was used as a control. Under the assumptions made, the deflections of the implant denture to either vertical or inclined loads applied to the centre of the pontic were less than that of the natural tooth partial denture, but the stresses developed were considerably greater. Large stress concentrations were found in the pontic in both partial dentures and in the neck of the implant blade. It was concluded that occlusal loads need to be close to the premolar abutment when the distal end of the pontic is supported by an implant in order to reduce the high stresses developed in the bone surrounding the implant. Photoelastic stress analysis was used by a number of workers to evaluate the biomechanics of dental prostheses.McDowell(1978)for example, compared the magnitude and distribution of stresses within a model from a distal-extension (bilateral free-end saddle) removable partial denture with and without indirect retainer components when subject to a single vertical load in the first molar region. This three-dimensional photoelastic study showed that under the conditions used, significant stresses were placed on the indirect retainer abutment on the loaded side, whilst the opposite indirect retainer abutment was relatively free of stress. Three-dimensional photoelastic stress analysis was used by MacGregor et al. (1978) to examine the stresses produced in model systems by disjunct partial dentures which were

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either tooth-borne, mucosa-borne or tooth- and mucosa-borne. The results appear to confirm the stress distribution to be as expected on the basis of the mechanical principles involved in the designs. The stress patterns produced in a replica of the lower jaw requiring a bilateral distalextension removable appliance when Dalbo and May’s precision attachments were separately incorporated, were reported by White (1978a). A vertical load of 35 lb was applied to the central fossa of the mandibular left first molar. Contrary to the findings of Kratochvil and Caputo (1974) forces were not distributed to the abutment on the balancing side. For the other conclusions drawn by this author with regard to behaviour of the fully active or rigid Dalbo partial denture and differences between single or double abutments, the original paper should be consulted. In a further paper (White, 1978b) the abutment stress in five different overdenture retainers was examined. It was concluded that: retainer systems permitting direct contact between the denture base and the abutment behave similarly; a vertical stress-breaking system could reduce the stress concentration related to the abutment;and that vertical stress-breaking action had little effect on the stress distribution beneath the denture base. Lopuck et a1.(1978) investigated, on model systems using a photoelastic technique, the stress distribution produced within the simulated alveolar ridge when complete mandibular dentures were loaded vertically with 11, 22, 33 and 44 lb through a matching maxillary denture. Flat occlusal surfaced teeth produced a more uniform stresss pattern than teeth with cusps. The stress concentrations were less severe for plastic teeth than for porcelain teeth whether the teeth were flat or cusped. Complete dentures Calculations by Cerny (1978) showed that the magnetic properties of a recently discovered alloy of cobalt and samarium (Co5 Sm) are such that magnetically retained overlay dentures should have satisfactory retention in the mouth. The author concluded, however, that the toxicity of the alloy needs to be examined and suggested that the long term effects of magnetic fields on biological tissues need to be known before the system can be of practical use. The role of saliva in the retention of maxillary complete dentures was examined in an experimental study on patients by Kawazoe and Hamada (1978). Maximum dislodging forces were recorded for an optimum thickness of saliva between the plate and the mucosa. The dislodging force was applied to the centre of the palate. IMPRESSION MATERIALS In a review of modern impression materials Harcourt (1978) outlined the limitations of the older materials and reported the results of test on examples of six different types of elastomeric impression material, with an alginate and a zinc oxide sol eugenol for comparison. His diagrams of rheometer tracings neatly superimposed the 23 OC and 37 OC traces to show working time, setting time and stiffness on one diagram. He also showed how the thickness of material affects the rheometer traces. Two of the new type II addition curing silicones were included and found to be somewhat stiffer than thiokol rubbers, while the type I condensation curing silicones were more flexible than either. Viscoelastic recovery was also examined, and it was shown how recovery decreased with each successive repetition of loading and unloading. This confirmed the importance of avoiding jiggling movements when removing the tray,

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The type II addition curing silicones were also tested by McCabe and Wilson (1978) who found working and setting times were slower in general than for condensation curing silicones, the times being about double. There is a considerable difference between the setting times found by these workers and those of Harcourt (1978) on the same brands of material, though the working times in the two papers are not greatly different. There may be a need for closer standardization of the rheometer method. McCabe and Wilson (1978) emphasize that rheometer times, which indicate elastic properties, should be adhered to by clinicians rather than empirical estimates which tend to be 1 or 2 min shorter. This echoes previous opinions by other workers who would add as much as 50 per cent to the manufacturers’ setting times for rubber-based materials. Unlike the type I condensation curing silicones, the heavy-bodied type II addition curing materials tend to be slower than the light-bodied versions. Tear resistance comparisons by tension set tests, showed that the heavy-bodied materials could stand 50 per cent strain without tearing, hut the light-bodied could stand only 30 per cent strain. This again is precisely the opposite of what is found in the type I silicones. Dimensional stability of the type II silicones was much better than in the type I materials, the contraction being almost entirely in the first 3 min after removal from the mouth and mostly due to cooling to room temperature. Inoue and Wilson, using a torsional rheometer described previously (1978a), have compared the viscoelastic properties of elastomers in two further papers. In the first (Inoue and Wilson, 1978b) they found that the torsional shear modulus for silicones increased rapidly at first, then more slowly to reach a maximum at 20 min after mixing. Polysulphides, with one exception, reached their maximum in 11 to 12 min. This indicates that the chemical reaction in silicones, although initially faster than in polysulphides, continues longer. This paper has, therefore, thrown further light on the previously observed facts that polysulphides are apparently slower setting than silicones, yet, provided adequate time in the mouth is given, they are more accurate. The consistency of the method is confirmed by the good agreement between setting times obtained from the logarithm of the shear modulus and those obtained by the method of BS 5 199: 1975. Other plots showed the relative sensitivity of the various materials to activator : base ratio and to temperature. In their third paper (Inoue and Wilson, 1978~) these authors followed elastic recovery with time, and here again the polysulphides and silicones formed two distinct groups. The polysulphides showed more rapid decay of applied stress, i.e. more flow. After 50 per cent strain the silicones and the polyether showed more complete recovery (about 97 per cent) than the polysulphides (about 95 per cent). Recovery was completed in 3 min for all the materials tested, and the recovery of Verone Perfecting was outstanding. Results confirmed, as did those of Harcourt (1978) that impressions should be removed from the mouth as quickly as possible, especially in the case of polysulphides. Shear modulus was used also by Herfort et al. (1978) to compare silicones and polysulphides, but they calculated it from force and extension measurements on trouser-leg test pieces. The peak modulus was reached 15 min after curing for both materials, but the tear strength was 3 to 6 times greater for polysulphides than for silicones. The shear moduli indicated that ease of removal from the mouth would be in the order: light silicones; light polysulphides; heavy silicones; heavy polysulphides; polyethers. Readers of papers dealing with tear strength should consider whether a low tear strength is not more desirable since fracture at low strain is likely to induce less distortion than non-fracture at high strain. Consistencies of bases and accelerators for elastomers were studied by Combe and Moser

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(1978) who measured apparent false viscosities at various shear rates and suggested that for specification purposes these materials could be divided into four groups according to their apparent false viscosity in poise at a shear rate of 65 se? at 25°C as follows: putties, 4000-7000; heavy-bodied, 2000-3000; regular, 400- 1500; and light-bodied or wash materials, 100-700. Gunther and Walsh (1978) have reported on Neo-Plex, an impression elastomer which is unusual in that it may be manipulated with the fingers soon after mixing. Since this property depends on early development of elastic properties, as indicated by the drag felt after only 15 s mixing, impressions in this material were prone to distortion. Errors using a stock tray and single mix were 3 times as great as those using a custom tray and double mix technique. Althouth tissue conditioners are not a subject of this section of this review, their frequent use as functional impression materials bring several papers on them within our purview. In view of the controversy as to whether any material can serve this dual role McCarthy and Moser (1978a, b) have examined the mechanical properties of three such materials in two papers. They first outlined the requirements for these two functions (McCarthy and Moser, 1978a) and pointed out that materials based on polyalkylmethacrylate powder and ethanol go through a viscous phase to become a plastic gel in 1.5 to 20 min, then become an elastic gel in 20 to 30 min. To allow healing of inflamed tissues the plastic phase should be long, but for taking impressions the elastic phase is critical. In tensile tests the three materials they examined showed mutually exclusive ranges of values. In their second paper (McCarthy and Moser, 1978b) they measured creep under the range of stresses which occur on denture base fitting surfaces by loading specimens until the strain reached O-5. Although the shape of their specimens was very different from that of a lining on a denture base, and this might have some bearing on the interpretation, the differences they found were interesting. Initially Coe Comfort was softer and more plastic than FITT, though after a week there was no significant difference between them. Both this and the findings of the previous paper suggest that Coe Comfort is best used as a tissue conditioner, but FITT should be best as a functional impression material. Lynal was stiffer and less plastic than the other two and its suitability for either function could not be interpreted without further clinical research on the loads at the denture-mucosa interface. The same authors in another paper (McCarthy and Moser, 1978~) studied the ability of these materials to reproduce undercuts. Using trays giving relief spaces from 1 to 3 mm on a set of undercuts of 1 to 4 mm they found errors ranging from 0.7 to 5.5 per cent, and concluded that the relief space played the major role in undercut reproducibility. One mm thickness of material gave the greatest error and 3 mm the least. Ageing time and brand were lesser factors. Schoen et al. (1978) evaluated dental impression materials for surface replication with a view to their use in SEM work. They used a surface microanalyser to record replicates of a standard saw-tooth pattern made with 22 materials including cellulose acetate tape for comparison. They calculated a replication index which ranged from 0.83 for the tape to 0.11 for a light-bodied polysulphide. Although not intended to relate to dental performance, their results are interesting in that polyethers were in the highest range and heavy-bodied materials were better than light-bodied. Other miscellaneous work with impression materials included an improved method for duplicating dentures using alginate investment with rigid support (Heath and Basker, 1978) and the effect of freezing on dimensional stability (Arvidson and Johansson, 1978). Ultrasonic

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cleaning was shown by Loxton et al. (1978) to have no significant effect on the shrinkage of rubber base impressions, and Rowe and Forrest (1978), commenting that existing texts give no advice on the disinfection of impressions, found that treatment for 1 min with 03 per cent chlorhexidine, either as a solution or as an aerosol spray, was fully effective and had no adverse effect on the impression surface. Gettleman et al. (1978) were concerned about the toxic effects of impression materials containing lead when they become trapped beneath soft tissue. They injected 9 materials representing various types of elastic impression material into the oral mucosa of primates and observed the histological response. They found severe reactions from the materials containing lead, but less severe reactions from those without lead. They concluded that the ADA recommended practice for biological evaluation, which includes oral ingestion and mucosal surface contact, should be extended to include sub-mucosal injection of the unset material. Radio-opacity in these materials was also to be encouraged to facilitate their location, though it happened that those with high lead content were found to be radioopaque.

MODEL, DIE AND MOULD MATERIALS Products derived from gypsum find widespread use in the dental laboratory. Recent research has concentrated on the use of additives to die stones, to give improved properties. For example, Probst et al. (1978)have shown that the water substitutes increased the compressive strength of four out of five die stones which were tested. The above authors recommended vacuum spatulation for optimum properties. One of the additives they tested was also found to increase the setting expansion of gypsum die products significantly (Winters et al., 1978). This same material can increase the resistance to abrasion of a die material (Edwards and Eames, 1978).

WAXES Powers and Craig (1978) have characterized ten dental impression waxes by using penetration techniques and differential thermal analysis. They found that penetration and initial transition temperatures were directly correlated.

CAST AND WROUGHT DENTAL ALLOYS Cast alloys The papers published on casting alloys during the year were centred on casting defects which occur in non-precious alloys, and their detecton. Whilst Rostoker et al. (1978) suggested that casting porosity could not be detected by contemporary non-destructive testing procedures, Pascoe and Wimmer (1978) were of the opinion that radiography should be used routinely as a means of quality control for all Co-Cr castings supplied to the dental practitioner. Rostoker et al. (1978) were referring to hip prostheses, which have a much greater bulk and radio-opacity than the thin denture bases, of which Pascoe and Wimmer (1978) showed radiographs containing voids which were subsequently visible during the optical examination of deliberately fractured specimens. However, Lewis (1978a) in a radiographic survey of partial denture castings showed that the incidence of voids in bases cast from modern dental alloys was rare. More common was the existence of regions containing many fine, inter-dendritic pores associated with features where abrupt changes in sectional thickness took place, for example, at the entry point of a sprue on the lingual bar. When

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specimens were deliberately over-stressed, fracture took place at these points of stress concentration, but Lewis was unable conclusively to identify pores on the fracture surfaces, due to the dendritic structure of the alloys. In a second paper, Lewis (1978b) examined the failure of 41 partial dentures and found that visible voids were only positively detectable on 7 per cent of the fracture surfaces. Fatigue was identified on 32 per cent, although the criterion he employed was narrower than that set by Rostoker et al. (1978). By far the greatest proportion (46 per cent) failed because of inadequate section. Lewis (1978~) also investigated the effect of alloy composition upon the distribution of porosity. Two extremes were found: either large voids were clearly visible on radiographs or there was diffuse porosity which was barely discernable, although there was a continuum between. The amount, distribution and nature of porosity depended upon compositional variables which affected dendritic crystallization, and was found to be directly related to dendritic size. Refinement of the structure led to diffuse porosity. The nature of dendritic crystallization has been discussed by Lewis (1978d) and, in a fifth paper, Lewis (1978e) has related the derived strength of dental alloys to the size and design of test pieces and the conditions under which they may be produced. Test piece size, mould and metal temperatures, spruing patterns, casting investments and techniques of metal fusion were all shown to affect the resultant properties. In general, the sounder the cast produced by a particular combination of these variables, the more superior will be the strength and elongation. Cohen et al. (1978) have shown that post-casting heat treatment of Co-Cr surgical prosthetic alloys dramatically improves their elongation although it has little effect on the proof stress. The allergic response to base metal alloys, invariably those containing nickel, is well known, however occasionally reports have appeared in which CooCr dental casting alloys are held responsible. Fenton and Jeffrey (1978) h ave described a case in which positive reactions were obtained, not only for Co-Cr alloys but also for semi-precious and noble alloys. Rare as such cases are, possible adverse response to any dental alloy should be borne in mind, particularly if the patient has a known reaction to metals such as low carat jewellery. The pressure produced during centrifugal casting has been calculated by Nielsen (1978) by using fluid mechanics to develop a ‘reference parabola’ for each horizontal casting machine. A knowledge of the instantaneous rotational velocity, the liquid metal density and dimensions of the pattern and the casting machine are required for this. From the shape of the free surface on the solidified metal in a partially filled cavity it is possible to calculate the time to solidification. Nielsen (1978) demonstrated that for a 3 mm thick cast in a PddAg alloy this occurred 7 s after the release of the molten metal. Finally, Bergman (1978) proposed the use of X-ray diffraction patterns to derive the alloy lattice parameter and hence identify any unknown gold alloy used in crown and bridgework. Detailed tables, listing parameters obtained for 75 alloys in use in Scandanavia, are presented. Three possible limitations are apparent: the coincidence of several alloys with the same parameter; the limited availability of suitable X-ray facilities; and the practice of mixing old with new casting alloy, usually with little regard to product type. Wrought alloys During the year two papers were published which discussed the properties and uses of Nitinol (nickel/titanium) alloy (Andreasen and Morrow, 1978; Ackerman et al., 1978). Nitinol has an elastic modulus which is one sixth that of stainless steel (33 GN/m*) as compared with 197 GN sol m2, and an ultimate tensile strength some 20 per cent less. The recovery

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of Nitinol from closely similar bending moment sol angular delfection conditions is superior to that of stainless steel, as is the recovery from torsional loading. There is no overall agreement on the benefits to be gained by using Nitinol in place of stainless steel, and potential users should consult the clinical sections of both papers bearing in mind a specific application rather than a general solution to all problems. Although Nitinol has a number of potential advantages over stainless steel it is more prone to fracture at sharp bends, creates difficulties when it comes to forming particular orthodontic loops and omega bends, and requires new techniques for soldering and welding. Using empirical bending tests, Brantley et al. (1978) determined the modulus of stiffness of several wires and reported that their values were in excellent agreement with the Young’s modulus of elasticity obtained from simple tensile tests. The suitability of wrought, precipitation-hardened Co(41)-Ni(38)-Cr(l6)-Ti(4) as an implant material has been reported by Cahoon and Hill (1978). The working process applied to the cast alloy makes it a possible contender for orthodontic applications. Whilst it has a suitably high proof stress (735 MN/m2), a relatively large elongation (18 per cent) and a superior fatigue response to that for stainless steel up to lo6 cycles, it appears to suffer the same corrosion failures as 3 16L stainless steel. The use of magnets in the function currently being performed by elastomers in orthodontics has been examined by Blechman and Smiley (1978). Two cylindrical AlNiCo magnets producing an attractive force equal to 0*3N across a distance of 3-4 mm were attached to the upper arch of a cat and produced a movement in a canine tooth as effectively as a light 3/8 in latex elastomer control. Whilst AlNiCo was the subject of their report, the authors state that SmCos magnets, generating a force of lN, should be the first choice in practice. Although they conclude that the magnetic field employed is not in itself harmful, no evidence is offered as to the toxicity or otherwise of the alloys themselves. The full potential of this technique can only be assessed after this pilot study has been extended to consider the relative ease with which magnets can be placed in order to produce the required movement. Magnets, particularly those made from SmCo, which have low volume, low weight and a strong magnetic field, have continued to be used as an aid to denture retention. Cerney (1978) calculated that the use of a pair of magnets with a volume identical to that of the CEKA inter-coronal precision attachment would produce a retentive force equivalent to 2.97N when one is placed in an endodontically treated tooth root and the other in an overlay denture. The successful reconstruction of the upper jaw of a road traffic accident patient has been reported (Anon., 1978). In this case, the patient was fitted with a 3 oz prosthesis, the retention and construction of which depended upon the inclusion of 14 rareearth magnets.

ACRYLIC RESINS The wear of acrylic resins (as used for artificial teeth) has been compared with porcelain in tests, with and without a third body (Harrison, 1978). Tests were carried out on a machine intended to simulate the conditions of masticatory function, but like many of its type the test is an arbitrary one, with the magnitude and nature of the stresses involved undefined. The results for wear between porcelain-porcelain, acrylic-acrylic and acrylic-porcelain indicated, not surprisingly, that acrylic showed a better wear resistance in the absence of a third body and against smooth surfaces. The study, which is reported in this paper, was

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carefully carried out and is interesting but highly empirical, and there was no attempt to relate the results to basic studies or principles. A very interesting study has been made on the effect of the curing cycle on poly(methy1 methacrylate) denture base material (Jagger, 1978). This inherently practical problem was studied in a very careful and fundamental way in terms of the macroscopic structure of the cured acrylic, its molecular weight distribution and residual monomer, as well as the more obvious matters of mechanical properties and water sorption. The results are discussed in a highly satisfactory way in terms of the basic parameters involved. Once again, the importance and deleterious effect of residual monomer on properties is emphasized. This depends upon the curing cycle employed and the report includes some helpful practical suggestions. It is to be hoped that, eventually, the importance of residual monomer may even percolate to standard specifications. An IADR paper by Wictorin (1978) deals with leached monomer. Harrison et al. (1978) have studied the effect of the cross-linking agent ethylene glycol dimethacrylate (EGDM) on the properties of a poly(methy1 methacrylate) based denture material. They found that even with high levels of addition (100 per cent) there was little effect on the abrasion resistance and impact strength. Discussion of these results was somewhat confused. For example, the authors expect EGDM to reduce water absorption because it is a cross-linking agent, forgetting that EGDM is a more oxygenated molecule, which on chemical grounds increases water uptake and hence its net effect is unpredictable. This confusion between the chemical and physical effects of the cross-linking agent is apparent elsewhere. Further elegant papers on the synthesis of special acrylic monomers have come from Antonucci (1978a) at the National Bureau of Standards; this time on aldehyde methacrylates. These have the merit of easy purification by crystallization, and subsequent liquefaction by admixture of isomers. The possibility of chain grafting to collagen is also discussed. In a similar vein (Antonucci, 1978b) is a paper on ascorbic acid initiators. Argentar (1978) has studied the reactivity of amine activators. Vermilyea et al. (1978) have studied the viscosity of fluid denture base resins (i.e. pourtype resins.) The measurements were highly empirical, no account being taken of the fact that the resins were almost certainly non-Newtonian. Moist et al. (1978) have established an interesting and apparently sound method for estimating the storage life of denture base resins, based on an Arrhenius-type equation.

TISSUE CONDITIONERS

AND SOFT LINING MATERIALS

Two independent groups of workers have studied the effects of denture cleansers on some soft polymers used in prosthodontics. Davenport et al. (1978) studied the effect of six types of cleanser on three conditioners (Coe Comfort, Ivoseal and Visco-Gel). Coe Comfort and Visco-Gel both suffered considerable surface degradation with an alkaline peroxide cleanser. Visco-Gel underwent hardening with acid cleansers. Coe Comfort showed surface degradation with an alkaline hypochlorite cleanser, whilst a commercial chlorhexidine solution had a similar effect on Visco-Gel. Ivoseal was not affected by any of the cleansers investigated. However, the tissue-conditioning properties of Ivoseal were not considered ideal by the authors because it is a much harder material than the other two products tested. Manderson and Brown (1978) studied the effect of two cleansers on a heat-curing acrylic soft liner (Coe Super Soft), a heat-curing silicone soft liner (Molloplast B), a self-curing silicone soft liner (Simpa) and a tissue conditioner (Soft Oryl). The heat-curing acrylic and

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silicone materials showed an increase in resilience after treatment with both acid and alkaline peroxide cleansers. A similar effect was noted after soaking in water alone. The self-curing silicone material and the tissue conditioners both underwent significant reductions in resilience after treatment with cleansers or water soaking. The most drastic effect was noted when the tissue conditioner was treated with alkaline peroxide cleaner. A large decrease in resilience and the onset of surface and sub-surface bubbling was noted. Thomas and Nutt (1978) compared the fungicidal properties of a conditioner (Visco-Gel) alone and combined with nystatin and amphotericin B. The conditioner alone had no antifungal properties but combined with nystatin became very effective. With amphotericin B only minor inhibition of fungal growth was noted despite the fact that amphotericin B has potent anti-fungal properties. McCarthy and Moser (1978a,b,c,d) published a series of papers on the mechanical properties of tissue conditioners and considered their suitability for both conditioning and functional impression taking. There were marked variations in the tensile properties between different brands of material which suggested that some materials are better suited to conditioning whilst others are more suited to impression taking (McCarthy and Moser, 1978a). Similar variations were noted when the creep characteristics were investigated (McCarthy and Moser, 1978b). The authors state that the absence of published data on the tissue loads exerted by dentures precludes making any judgments as to the absolute efficiency of any of the materials. The undercut reproducibility of three functional impression materials (McCarthy and Moser, 1978~) was most dependent on the severity of the undercut and the amount of tray relief allowed, e.g. for Coe Comfort a 3 mm undercut was best recorded using 3 mm of tray relief. The impression-taking properties of conditioners were assessed by comparing three materials with a polysulphide impression material (McCarthy and Moser, 1978d), using testing methods recommended for elastomeric impression materials. The flow, strain in compression, dimensional change and permanent deformation values were all inferior to those for the polysulphide material but the authors claim that all three conditioners can be considered adequate as functional impression materials. They state that a new standard is required for assessing the conditioners as functional impression materials. DENTAL CERAMICS The published information on dental ceramics is divisible into that concerning itself and that relating to the properties of porcelain/metal composites.

porcelain

Porcelain The decision in 1976 to remove the small traces of radioactive fluorescent materials from dental porcelain has stimulated a fresh approach to colouring it, and details are now appearing in the literature. Baran et al. (1977) evaluated a range of rare earth ions added singly and together to a glass which was similar to porcelain. They reported that many trivalent rare earth ions fluoresce strongly in U.V. light, but that the best were those of the elements dysprosium and thulium, which showed excitation wavelengths near the maximum intensity wavelength of sunlight. Although they suggest that suitable formulations are now possible, they warn that simple additive colour mixing schemes may not work, as some mixtures of rare earths give rise to absorption by energy transfer and the normal pattern of emissions can change. At the consumer level Wozniak and Moore (1978) measured the luminescence spectra of porcelain and plastic artificial teeth together with a number of porcelain powders and

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compared them with the spectrum of natural teeth when illuminated with U.V. light. They reported that many of the porcelain teeth showed maximum intensities of luminescence at wavelengths quite distant from that of natural teeth, and even in plastic teeth, where they expected the manufacturers to have used organic phosphors and fluorophors to obtain the correct characteristics, there was considerable mismatch. In a continuing attempt to improve the inherent strength of porcelain Clark et al. (1978) reported briefly on experiments in which they aimed at eliminating the internal stresses generated in porcelain when one of its components, quartz, inverts and shrinks during cooling. Two compositions, one high in silica only and the other high in silica and alumina, were found to produce glass matrices which were plastic enough to flow at the inversion temperature of 573OC, and thus the internal stresses were reduced. The result was an increased breaking stress in each case. For those situations where only part of a large porcelain restoration is fractured and lost, Newburg and Parmeijer (1978) have given details of their process for repairing porcelain, which they suggest is suitable for in vivo use. In their process the fractured porcelain was ground, cleaned with 37 per cent phosphoric acid, washed, dried and then coated with a 0.5 per cent solution of aqueous silane which had been hydrolysed with acetic acid. This was dried with a heat lamp and unfilled dimethacrylate resin was applied to this surface followed by dimethacrylate composite. This was finished in the usual way. Their in vitro measurements after thermal cycling indicated a rupture strength which was double that when no silane treatment had been given. A new shear test for porcelain was reported by Johnston and O’Brien (1978) in which porcelain cylinders were held rigidly and then slid against a hard steel edge until fracture occured. The method clearly illustrated the superiority in shear of aluminous porcelain over opaque dental enamel porcelain, the former failing at a stress of 147 MPa whereas the latter failed at 11 IMPa. Porcelain-metal composites The continuing growth in the use of restorations in which the aesthetics of porcelain are combined with the toughness of metal substrates produced both experimental and theoretical assessments of the bond between the two during the year. Caputo et al. (I 977) gave full details of their test in which a short central area of porcelain is bonded to a long metal strip. This strip is subjected to four-point flexural loading (the load being applied over the central area at the edges of the porcelain) until fracture occurs. Although no analytical solution is available to enable simple calculations of a specific bond stress value to be made, they suggest that the method does allow useful comparisons of the effects of pre-treatments. They reported that for noble alloys no significant improvements in the bond strengths was achieved by degassing the gold prior to the application of the porcelain. Another test,_which enabled alloys to be ranked for quality of their bond with porcelain, was briefly described by Younis (1978), who determined shear strain and stress by shearing porcelain from a metal button. Finite element stress analysis was used by Anusavice et al. (1978) to reveal that stress concentration effects play a significant role in reducing real ceramic-metal bond strengths. In all test systems the highest stress levels exist at the external junctions of the metal and the porcelain, and whereas flexure stress tests produce the greatest degree of non-uniform stress distributions, the pull- or push-through shear tests are the least affected by the presence of stress riser crack initiation sites. These latter tests have always produced a wide variation in results and Asgar and Giday (1978) have

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suggested that this is due to the way in which the test pieces are supported. It is customary to hold them in dental stone during the tests and they reported that if the alloy rods were coated with wax prior to embedding them, this prevented the anticipated wide variation in failure values, probably due to the elimination of the surface roughness of the alloy. The nature of the interface between the metal and the porcelain also received attention during the year. Stewart et al. (1978a), in a preliminary report, indicated that treatments other than degassing of noble alloys prior to adding the porcelain tended to remove trace surface quantities of tin and indium, which are vital for the formation of a good chemical bond. In a more complete report Stewart et al. (1978b) explained how they used scanning electron microscopy and dispersive X-ray analysis to reach their conclusions. They indicate that a degassed gold alloy had an irregular surface full of 2-3 micron diameter crevices and pits, and that during the degassing heat treatment indium and tin migrated to the surface, where they existed as particles partially fixed to the surface with no indium or tin between them. If more drastic pre-treatments were employed, such as pickling in hydrofluoric acid, these particles were removed and a second degassing treatment was not capable of reestablishing them. Alloys no longer used in the UK were the subject of two reports by Williams et al. (1978a, b). These were nickel-chromium alloys which contained up to le.5 per cent beryllium. Specimens of these alloys coated with porcelain were heated for up to 20 h in order to produce an interfacial reaction zone of considerable thickness. This zone was studied using both secondary ion mass spectroscopy and X-ray fluorescence analysis. They discovered that under such conditions a zone which was depleted in nickel and beryllium formed in the alloy and a beryllium-rich oxide at the interface. Nickel and silicon ions were reduced to form nickel silicide and silicon was seen to diffuse into the alloy. Local chromium enrichment occured in the porcelain and both sodium and lithium became depleted in the porcelain, moving by up-hill diffusion. They considered that beryllium controlled the development of the reaction zone in non-pre-oxidized samples but reported that pre-oxidation arrested the development of the nickel/beryllium-free zone, suggesting that the interfacial oxide layer is impermeable to either beryllium or oxygen.

DENTAL

IMPLANTS

The pace in dental implant research seems to have slackened a little recently. The literature, in fact, contained few papers on fundamental studies of dental implants and the tissue response to them, but rather more on the use of implants in oral surgery in novel situations. Mazzocco et al. (1978) reported on the quantitation of retention of endosseous implants, using push-out tests on implants placed in dogs. They concluded that the force to displace a multi-vented blade was 6 to 12 times that for a single vented or solid implant. Baratieri et al. (1978) studied the dynamics of bone changes in relation to titanium endosseous blade vent implants, also in dogs. A vital labelling technique using intravenous injections of pyrrolidone-methyl-tetracycline and alizarin red was employed. The bone-metal interface was Seen to consist mainly of a thick layer (about 70 pm) of non-mineralized tissue, although new bone formation had begun by day 15. The authors were doubtful about the long term retention of these implants. With this difficulty of fixation in mind, Young et al. (1978) experimented with electrical

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stimulation to induce osteogenesis. A solid-core, porous-surface polymethylmethacrylate implant with a circumferential platinum-rhodium electrode was placed in the mesial socket of a canine mandibular premolar in dogs, the positive electrode being placed in the distal socket. An implantable power source supplied a 4-6 nA current stimulus. The fixation was measured mechanically and the authors claimed that the interfacial strength was increased by the electrical stimulation over a 2-6 week period. There was, however, a high degree of scatter in the results and no statistical correlation was presented. Jaffee et al. (1978) adopted a different approach by attempting to improve the anchoring of acrylic tooth implants in the dog by the use of enriched collagen solution. Second premolars were replaced by acrylic tooth replicas which had been immersed in this solution. Proliferation of connective tissue was observed and collagen fibres passed into grooves in the implant surface. Much of this had ossified by 40 days. The fixation of vitreous carbon implants was shown to be good without the aid of such stimuli by Sherman (1978) who demonstrated that conventional orthodontic treatment could not move these implants when placed in dogs. Methods of evaluation of the tissue response were studied by Wennberg (1978) and also by Baumhammers et al. (1978) who used scanning electron microscopy to observe the epithelial cells grown on various implant materials. Few new implant materials were discussed, although Adams et al. (1978) described preliminary experiments with carbon fibre-reinforced carbon for use in endosseous implant, having superior mechanical properties to unreinforced carbon. The vitreous carbon-polymethylmethacrylate composite was also discussed further by Hodosh et al. (1978) whilst Furseth and Pedersen (1978) reviewed work on porous alumina for subperiosteal implants. Takahashi et al. (1978) performed finite element stress analyses of fixed partial dentures with a blade vent implant abutment and showed that deflections were less than with a fixed partial that utilized a natural tooth abutment. However stress concentrations were found in the pontic and both the mesial and distal parts of the premolar retainer in both situatons. Mizra and Dikshit (1978) observed the use of implants following radiation therapy in cases of, for example, squamous cell carcinoma of the mandible, good results being achieved with endosseous implants if patients were selected carefully. Small (1978) surveyed his experience with the mandibular staple implant, finding 90 per cent of over 400 cases being successful, loosening of the implant being the major reason for failure. The use of diodontic implants has also been discussed by Cooke et al. (1978). Alveolar ridge augmentation was studied by Nery et al. (1978), who used 50 per cent porous, 400-500 pm tricalcium phosphate, showing the material to be well tolerated over a 7-760 day period, and by Gross and Topazian (1978) who described the use of full thickness mucosal grafts over Proplast. Mandibular reconstruction was reviewed by Terz et al. (1978) who used a wire mesh prosthesis in cases of malignant neoplasms. Implants have been used in surgery of the temporomandibular joint, with Howe et al. (1978) describing a Vitallium mesh attached to the zygoma to restrict anterior movement of the condyle in cases of hypermobility. Alpert (1978) discussed the use of Silastic tubing for interposition arthroplasty of the temporo mandibular joint whilst Lewin and Wright (1978) reported the use of Silastic ulnar head prosthesis for use in surgery of the temporo mandibular joint. Finally, Kummoona (1978) prepared cobalt-chromium prostheses to replace the condyle and glenoid fossa in monkeys and the success, measured by the retention of masticatory function and ability to open and close the mouth, led to use of such prostheses in three patients with ankylosed joints.

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CORROSION Reports on corrosion in dental materials published in 1978 can be broadly divided into studies involving dental amalgams and work concerned with base metal alloys for implant use.

Amalgam corrosion The literature on the corrosion of dental amalgam can be divided into three categories: fundamental studies and the development of new testing methods; comparative studies of proprietary amalgams; and studies related to clinical procedures. Fundamental studies and test methods Nomoto et al. (1978) used the potential sweep method of potentiostatic polarization to study the electrochemical behaviour of several commercial dental amalgams in 0.86 per cent aqueous solution of sodium chloride. Within the potential sweep range to.4 to -1.7 V (S.C.E.) there were two anodic current peaks on the anodic polarization curves. On the basis of the equilibrium potentials for the system, the cathodic current peaks were associated with reduction of Hg, Cl,, AgCl, CuCl (and/or Cu2 0), Sn(OH)4 and Sn(OH), ; the anodic current peaks were associated with the formation of Sn(OH&, and Sn(OH)* . Using the rotating ring-disc electrode, Gal-Or et al. (1978) studied the anodic dissolution of conventional dental amalgam in a 0:9 per cent aqueous sodium chloride solution. This is a powerful electrochemical technique, which allows direct identification of the soluble corrosion product species generated at the amalgam disc. Tin ions were found to be the only soluble species produced. Marek and Okabe (1978) investigated the effect of in vitro crevice corrosion on the major structural phases found in a high-copper dental amalgam. The 71(CueSns) phase exhibited good corrosion resistance, better in fact than the -yZ phase, a result in conflict with previous observations. The effects of plaque (Streptococcus mutans grown in vitro on the amalgam surface using culture media) on the polarization of conventional amalgam were reported by Onose et al. (1977). The authors found evidence of enhanced corrosion under these conditions. Darvell (1978) reported the development of an artificial saliva solution for in vitro studies of dental amalgam, The inadequacy of using simple saline solutions was demonstrated and formulation of the artificial saliva solution was based on a consideration of the components and properties of natural saliva. Test solutions included various combinations of anionic species and corrosion activity in these solutions was monitored using a photometric technique. Practical difficulties, such as the instability of the bicarbonate ion at the required pH, were discussed and a detailed formulation of the artificial saliva developed given. The author recognizes the product to be deficient in a number of respects but considers the formulation to be a firm basis for further development. Finkelstein and Greener (1978) in another artificial saliva study, attempted to simulate more accurately the electrochemical proprerties of natural saliva by the addition of albumin anodic polarization of and mucin to dilute Ringer’s solution. Using potentiostatic conventional Aristaloy amalgam, it was shown that this approach gave profiles similar to those obtained with natural saliva, and differing from those obtained using Ringer’s solution alone, in that the open circuit potential was shifted to more active values. The other major effect of the presence of these organic constituents was to delay the kinetics of the electro-

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chemical reactions; a feature not observed in the polarization profile. The corrosion medium recommended consisted of 14/ 100 diluted Ringer’s solution to. 15 g/50ml albumin to. 135 g/ 50ml mucin. Sutow et al. (1978) described a crevice corrosion test, which was used to assess the behaviour of conventional and high-copper dental amalgams. The test involves first anoditally polarizing the specimen to -50 mV(S.C.E.), followed by placement of the specimen in a crevice configuration for 3 h. Crevice currents for the conventional composition amalgam were generally greater than those of the high-copper amalgams, and remained so for the 3 h period. Comparative studies Sarkar (1978) reviewed the literature to date on the correlation between creep, corrosion and marginal fracture of dental amalgams. The author concluded that, contrary to Mahler’s hypothesis, there is no cause and effect relationship between creep and marginal failure. Instead, corrosion of the y,-phase was definitely linked with marginal breakdown. Any apparent correlation between creep and failure was thought to be coincidental, resulting from the fact that the crystallization of y1 and y2 occurs simultaneously, and that an increase in y, (associated with creep) is accompanied by an increase in y2 (i.e. corrosion). The author concluded that the adoption of creep as a measure of marginal integrity was not justified. Espevik (1977) investigated the release of copper from various copper-containing amalgams, in a study to provide information for biological reaction assessment. The dissolved copper content was determined after one month of immersion in artificial saliva. The copper amalgam released the most copper, followed by the dispersed-phase amalgams, while the single composition high-copper amalgam released the least. Vaidyanathan (1978) applied the Tuccilo-Nielsen alternative immersion tarnish test to conventional and high-copper dental amalgams. A 0.5 per cent sodium sulphide solution was used for periods of up to 16 h. The results indicated that the copper-rich phases tarnish quickly, whereas the y and yr phases tarnish more slowly. However, the -y-phase response differed significantly with the alloy composition and mode of copper alloying. A study of the effect of the in vitro corrosion of commercial dental amalgams, for up to one year, on the compressive strength revealed a loss in strength from 5 to 50 per cent (Averette et al., 1978). The smallest reduction occurred with a single composition, highcopper dental amalgam, and the largest occurred with conventional lathe-cut amalgam. Chen and Greener (1978) studied the effect on the tensile strength of galvanic coupling of conventional lathe-cut amalgam to various materials. Exposure for 7 days in Ringer’s solution at 37°C led to the following results: when coupled to non-zinc Dispersalloy or dental gold alloy plates, a significant drop of 26 per cent in tensile strength occurred; however, coupling to zinc-containing Dispersalloy led to no loss of strength. Clinical procedures Bow and Chn (1978a) investigated the corrosion behaviour of carved, burnished, burnished polished and polished specimens of a conventional spherical amalgam alloy (Spheraloy). It was demonstrated by anodic polarization and SEM studies, that carved surfaces exhibited most corrosion, polished surfaces showed intermediate behaviour, while burnished and burnished-polished surfaces corroded least. The studies including variation of the mercury

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content of the amalgam (40-60 per cent) and led to the hypothesis that the reduced corrosion in burnished samples was due to lower porosity and more ready passivation because of increased yz on the surface. In a further study involving two high-copper dental amalgams (Boyer and Chan, 1978b) it was shown that burnished and polished samples had similar corrosion rates. This may be due to the lack of y,-phase in these materials. Boyer et al. (1978) also investigated the effects of different finishing procedures on two high-copper amalgams, Dispersalloy and Sybraloy. Anodic polarization in Ringer’s solution indicated that for these amalgams polished and burnished surfaces corrode at similar rates, and that a carved surface corrodes at a higher rate. Whilst the burnished surfaces are rougher than the polished surfaces, a factor which tends to increase the susceptibility to corrosion, this appears to be offset by a higher proportion of the y, -phase, which has a less active corrosion potential than the other phases present. Corrosion of screwposts in contact with amalgam was studied in vitro by Gjerdet and Espevik (1977). A substantial build-up of corrosion products was observed on the posts after immersion for 4 weeks in Ringer’s solution, in spite of the gold plating on the posts. Gjerdet and Espevik (1978) also reported on the influence that an applied tensile stress can have on the corrosion of amalgam. Using a potentiostatic technique, they showed that amalgams which had low creep, both with and without the yz-phase, revealed small increases in corrosion current with stress application, whereas alloys with high creep exhibited large increases in current. Rupture of the protective oxide film due to increased strain in the highcreep alloys may explain the phenomenon. The in vivo corrosion behaviour of high-copper amalgams was evaluated on Class I occlusal amalgam restorations placed in the posterior teeth of adult male baboons (Gettleman et al., 1978). Using the linear polarization technique, it was shown that highcopper amalgams corrode less than conventional amalgams.

Corrosion in implant alloys Several papers were published in 1978 on the corrosion alloys with improved mechanical properties.

behaviour

in vitro of new implant

Two cobalt-based alloys, a wrought Co-Ni-Mo-Ti and an air-cast Co-Cr-Mo were compared in corrosion tests with wrought 3 16L stainless steel (Sury and Semlitsch, 1978). The wrought Co-Ni-Mo-Ti alloy was found to have superior mechanical properties and was just as resistant to selective corrosion phenomena as the other two alloys. A high strength, precipitation-hardened Co-Ni-Cr-Ti alloy was evaluated for corrosion resistance by Cahoon and Hill (1978). In vitro and in vivo corrosion studies indicated that the material has a good general corrosion resistance but may be susceptible to crevice corrosion. Rostoker et al. (1978) reported on in vivo tests of alloys of cast Co-Cr-Mo, wrought Co-Cr-W, wrought Co-Ni-Cr-Mo, Ti-6 per cent Al-4 per cent V, and also of graphite. Examination of implants which had been in place for 30 months revealed that only the titanium alloy showed any degree of tarnish, and this correlated with a thicker fibrous membrane and increased vascularity. Corrosion in a new family of high strength, high ductility stainless steels, TRIP (Transformation Induced Plasticity) steels, was described in three papers in 1978, These alloys are metastable, austenitic stainless steels, which combine high yield strength (e.g. 1380 MN/m’) with high elongation (e.g. 40 per cent). In the first paper, Syrett and Wing (1978a) compared the pitting resistance of four TRIP

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steels with that of conventional 316L stainless steel and a cast Co-Cr-Mo alloy (VitaIlium). While the Vitallium exhibited the best resistance to localized corrosion, the TRIP steels showed substantially better pitting resistance than the 316L stainless steel, particularly after being cold worked. In their second paper, Syrett and Wing (1978b) compared the same alloys with respect to fretting corrosion. In this case the Vitallium performed better than the others. Jones et al. (1978) reported on studies of stress corrosion cracking and corrosion fatigue of some TRIP steels and compared them with 316L stainless steel. Immunity to stress corrosion cracking was observed in all alloys, and corrosion fatigue data led the authors to suggest that TRIP steels are capable of supporting substantially higher levels of both static and cyclic stress in saline environments than alloys in current use. Brockhurst (1978) presented a review entitled ‘Corrosion and the human body’, in which developments in ferrous and non-ferrous alloys for use in dentistry and implants were discussed with reference to corrosion and compatibility. The shortcomings of current implant test procedures, the nature of implant corrosion and failure, the circulation of corrosion products and the extent of implant ionisation within the body were discussed. REFERENCES Dental biomechanics Masticatory forces and mandicular movement Behrend D. A. (1974) A method of studying patterns of tooth displacement in simulated chewing cycles in man. Arch. Oral Biol. 19, 23-7. Behrend D. A. (1978a) Patterns of tooth displacement in simulated chewing cycles in man. Arch. Oral Biol. 23, 1089-93. Behrend D. A. (1978b) The relationship between tooth displacement and cusp inclination in man. Arch. Oral Biol. 23, 1095-8. De Boever J. A., McCall W. D., Holden S. et al. (1978a) Functional occlusal forces: an investigation by telemetry. J. Prosthet. Dent. 40, 326-33. De Boever J., McCall W. D., Holden S. et al. (1978b) Functional occlusal forces under anesthesia, J. Prosthet. Dent. 40, 402-8. Byrd K. E., Milberg D. J. and Luschei E. S. (1978) Human and macaque mastication: a quantitative study. J. Dent. Res. 57, 834-43.

Lundeen

H. C., Shryock E. F. and Gibbs C. H. (1978) An evaluation of mandibular J. Prosthet. Dent. 40, 442-52. movements: their character and significance.

border

McCall, W. D., De Boever J. A. and Ash M. M. (1978) Telemetry system to study functional occlusal forces. J. Prosthet. Dent. 40, 98- 102. Roedema W. H., Knapp J. G., Spencer J. et al. (1978a) Computer-graphic representation of mandibular movements in three dimensions. Part I. The horizontal plane. J. Prosthet. Dent.

Roedema

39, 378-83.

W. H., Knapp J. G., Spencer J. et al. (1978b) Computer-graphic

mandibular J. Prosthet.

movements in three Dent. 40, 385-91.

dimensions.

Part

II. The

sagittal

representation of and frontal planes.

Orthodontic tooth movement Blechman A. M. and Smiley H. (1978) Magnetic force in orthodontics. Am. J. Orthod. 74, 435-43. Bowden D. E. J. (1978a) Theoretical considerations of headgear therapy: A literature review. Part 1. Br. J. Orthod. 5, 145-52. Bowden D. E. J. (1978b) Theoretical considerations of headgear therapy: A literature review. Part 2. Br. J. Orthod. 5, 173-81.

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Burstone C. J., Pryputniewicz R. J. and Bowley W. W. (1978) Holographic measurement of tooth mobility in three dimensions. J. Periodont. Res. 13, 283-94. Cerny R. (1978) Magnetodontics. The use of magnetic forces in dentistry. Aus. Dent. J. 23,392-4.

Oates J. C., Moore R. N. and Caputo A. A. (1978) Pulsating forces in orthodontic

treatment.

Am. J. Orthod. 74, 577-85.

Pryputniewicz R. J., Burstone C. J. and Bowley W. W. (1978) Determination of arbitrary tooth displacement. J. Dent. Res. 57, 665-74. Steyn C. L., Verwoerd W. S., van der Merse E. J. et al. (1978) Calculation of the position of the axis of rotation when single-rooted teeth are orthodontically tipped. Br. J. Orthod. 5, 153-6. Orthodontic wires, elastics and appliances

Andreasen

G. F. and Morrow R. E. (1978) Laboratory

and clinical analyses of Nitinol wire.

Am. J. Orthod. 73, 142-51.

Ash J. L. and Nikolai R. J. (1978) Relaxation of orthodontic elastomeric chains and modules in vitro and in vivo. J. Dent. Res. 57, 685-90. Brantley W. A., Augat W. S., Myers C. L. et al. (1978) Bending deformation studies of orthodontic wires. J. Dent. Res. 57, 609- 15. Eastwood A. W. and Wright G. Z. (1978) Principles of design of active and removable appliances. Dent. Clin. N. Am. 22, 621-33. Varner R. E. and Buck D. L. (1978) Force production and decay rate in Alastik modules. J. Biomed. Mater. Res. 12, 361-6.

Webb R. I., Caputo A. A. and Chaconas S. J. (1978) closed coil springs. Am. J. Orthod. 74, 405-9.

Orthodontic

force production

by

Williams B. R., Caputo A. A. and Chaconas S. J. (1978) Orthodontic effects of loop design and heat treatment. Angle Orthod. 48, 235-g.;

Stress analysis studies on teeth and amalgam restorations

Brown, W. S., Christensen D. 0. and Lloyd B. A. (1978) Numerical and experimental evaluation of energy inputs, temperature gradients, and thermal stresses during restorative procedures. J. Am. Dent. Assoc. 96,451-8. Lloyd B. A., McGinley M. B. and Brown W. S. (1978) Thermal stresses in teeth. J. Dent. Res. 57, 571-82.

Wright K. W. J. and Yettram A. L. (1978) Finite element stress analysis of a Class I amalgam restoration subjected to setting and thermal expansion. J. Dent. Res. 57, 7 1S-23.

Pins and endodontic dowels

Fujimoto J., Norman R. D., Dyeema R. W. et al. (1978) A comparison of pin-retained amalgam and composite resin cores. J. Prosthet. Dent. 39, 5 12- 19. Standlee J. P., Caputo A. A. and Hanson E. C. (1978) Retention of endodontic dowels: Effects of cement, dowel length, diameter and design. J. Prosthet. Dent. 39, 401-S. Partial dentures

Craig R. G. and Farah J. W. (1978) Stresses from loading distal-extension dentures. J. Prosthet. Dent. 39, 274-7.

removable partial

Brown et al.: Review of dental materials

243

Kratochvil F. J. and Caputo A. A. (1974) Photoelastic analysis of pressure on teeth and bone supporting removable partial dentures. J. Prosthet. Dent. 32, 52-6 1. Lopuck S., Smith J. and Caputo A. A. (1978) Photoelastic comparison of posterior denture occlusions. J. Prosthet. Dent. 40, 18-22. MacGregor A. R., Miller T. P. G. and Farah J. W. (1978) Stress analysis of partial dentures. J. Dent. 6, 125-32. McDowell G. C. (1978) Force transmission by indirect retainers during unilateral loading. J. Prosthet. Dent. 39, 616-21. Takahashi N., Kitagami T. and Komori T. (1978) Analysis of stress on a fixed partial denture with a blade-vent implant abutment. J. Prosthet. Dent. 40, 186-91. White J. T. (1978a) Visualization of stress and strain related to removable partial denture J. Prosthet. Dent. 40, 143-51. abutments. White J. T. ( 1978b) Abutment stress in overdentures. J. Prosthet. Dent. 40, 13- 17. Complete

dentures

Cerny R. (1978) Magnetodontics. The use of magnetic forces in dentistry. Aust. Dent. J. 23, 392-4. Kawazoe Y. and Hamada T. (1978) The role of saliva in retention of maxillary complete dentures. J. Prosthet. Dent. 40, 131-6.

Impression materials Arvidson K. and Johansson E. G. (1978) The freezing effect on the dimensional stability of impression materials. Swed. Dent. J. 2, 6 l-5. Combe E. C. and Moser J. B. (1978) The rheological characteristics of elastomeric impression materials. J. Dent. Res. 57, 221-6. Gettleman L., Nathanson D., Shklar G. et al. (1978) Preliminary evaluation of the histotoxicity and radio-opacity of lead-containing elastic impression materials. J. Am. Dent. Assoc. 96, 987-93. Gunther G. and Walsh S. L. (1978) Evaluation of a rubber-base impression material. J. Prosthet. Dent. 39, 95-9. Harcourt J. K. (1978) A review of modern impression materials. Aust. Dent. J. 39, 178-86. Heath J. R. and Basker R. M. (1978) The dimensional variability of duplicate dentures produced in an alginate investment. Br. Dent. J. 144, 11 l-4. Herfort T. W., Gerberich W. W., Macosko C. W. et al. (1978) Tear strength of elastomeric impression materials J. Prosthet. Dent. 39, 59-62. Inoue K. and Wilson H. J. (1978a) Viscoelastic properties of elastomeric impression materials I: A method of measuring shear modulus and rigidity duringsetting. J. OralRehabil. 5, 89-94. Inoue, K. and Wilson H. J. (1978b) Viscoelastic properties of elastomeric impression materials II: Variation of rheological properties with time, temperature, and method of mixing. J. Oral Rehabil. 5, 261-7. Inoue K. and Wilson H. J. (1978~) Viscoelastic properties of elastomeric impression materials III: The elastic recovery after removal of strains applied at the setting time. J. Oral Rehabil. 5, 323-7. Loxton L., Phillips R. W. and Swartz M. L. (1978) The effect of ultrasonic cleaning methods on rubber base impression materials. J. Dent. Res. 57, 939. McCabe, J. F. and Wilson H. 3. ( 1978) Addition curing silicone rubber impression materials. Br. Dent. J. 145, 17-20.

244

Journal of Dentistry, Vol. ~/NO. 3

McCarthy .I. A. and Moser J. B. (1978a) Mechanical properties of tissue conditioners. Part I: Theoretical considerations, behavioral characteristics, and tensile properties. J. Prosthet. Dent. 40, 89-97.

McCarthy J. A. and Moser J. B. (1978b) Mechanical properties of tissue conditioners. Part II: Creep characteristics. J. Prosthet. Dent. 40, 334-42. McCarthy J. A. and Moser J. B. (1978~) Undercut reproducibility of functional impression materials (tissue conditioners). J. Oral Rehabil. 5, 287-92. Rowe A. H. R. and Forrest J. 0. (1978) Dental impressions, the probability of contamination and a method of disinfection. Br. Dent. J. 145, 184-6. Schoen F. J., Mohammed H., Fischlschweiger W. et al. (1978) Objective evaluation of surface microreplication by dental impression materials. J. Dent. Res. 57, 283-90.

Model, die and mould ma tarials

Edwards C. R. and Eames W. B. (1978) A comparison of scraping resistance of dental die materials. J. Dent. Res. 57, Special issue A, abstr. 713. Probst R. T., Duncanson M. G. and Winters F. G. (1978) Comparison of two water substitutes on die stone compressive strength. J. Dent. Res. 57, Special issue A, abstr. 884. Winters F. G., Duncanson M. G. and Probst R. T. (1978) Gypsum hardeners and spatulation techniques affecting die stone setting expansion. J. Dent. Res. 57, Special issue A, abstr. 883.

Dental waxes

Powers J. M. and Craig R. G. (1978) Thermal analysis of dental impression

waxes. J. Dent.

Res. 57, 37-41.

Cast and wrought dental alloys

Cast alloys Bergman M. (1978) Powder data file as a tool for identification

of dental gold alloys. Acta

Odontol. Stand. 36, 339-44.

Cohen J., Rose R. M. and Wulff J. (1978) Recommended heat treatment and alloy additions for cast Co-Cr surgical implants. J. Biomed. Mater. Res. 12, 935-7. Fenton A. H. and Jeffrey J. D. (1978) Allergy to a partial denture casting: case report. J. Can. Dent. Assoc. 10, 466-8. Lewis A. J. (1978a) Radiographic evaluation of porosities in removable partial denture castings. J. Prosthet. Dent. 39, 278-81. Lewis A. J. (1978b) Failure of removable partial denture castings during service. J. Prosthet. Dent. 39, 147-9.

Lewis A. J. (1978~) The effect of alloy composition on the development of internal porosity in cast structures. Aust. Dent. J. 23, 192-5. Lewis A. J. (1978d) Dendritic crystallisation. Aust. Dent. J. 23, 356-8. Lewis A. J. (1978e) The influence of design and production on the surgical integrity of tensile test specimens and stated values for mechanical properties. Aust. Dent J. 23, 275-8. Nielsen J. P. (1978) Pressure distribution in centrifugal dental casting. J. Dent. Res. 57, 261-9.

Pascoe D. F. and Wimmer J. (1978) A radiographic technique for the detection of internal defects in dental castings. J. Prosthet. Dent. 39, 150-7. Rostoker W., Chao E. Y. S. and Galante J. 0. (1978) Defects in failed stems of hip prostheses. J. Biomed. Mater. Res. 12, 635-S 1.

245

Brown et al.: Review of dental materials

Wrought

alloys

Ackerman

J. L., Chandra

L. H., Creekmore

T. D. et al. (1978)

Round

table-Nitinol

wire.

J. Clin. Orthod. 12, 479-85. Andreasen

G. F. and Morrow

R. E. (1978)

Laboratory

and clinical analysis

of Nitinol

wire.

Am. J. Orthod. 73, 142-51. Anon. (1978) Prosthetic devices held by magnets. Blechman A. M. and Smiley H. (1978) Magnetic

Dent. Technol. 31, 4. force in orthodontics. Am. J. Orthod. 74,

435-43. Brantley W. A., Augat W. S., Myers C. L. et al. (1978) Bending deformation studies of orthodontic wires. J. Dent. Res. 57, 609- 15. Cahoon J. R. and Hill L. D. (1978) Evaluation of precipitation hardened Co-Ni-Cr-Ti alloy for surgical implants. J. Biomed. Mater. Res. 12, 805-2 1. Cerney R. (1978) Magnetodontics: the use of magnetic forces in dentistry. Aust. Dent. J.

23, 392-4. Acrylic resins Antonucci J.

( 1978a)

Aldehyde

me thacrylates

derived

from

J.

hydroxybenzaldehyde.

Dent. Rex 57, 500-S. Antonucci

J. (1978b)

New initiating

systems

for dental

resins

based

on ascorbic

acid. J.

Dent. Rex 57, Special issue A, abstr. 704. Argentar H. (1978) Reactivity of amine polymerisation accelerators at low concentrations under aerobic conditions. J. Dent. Res. 57, Special issue A, abstr. 705. Harrison A. (1978) Wear combinations of acrylic resin and porcelain on an abrasion testing machine. J. Oral Rehabil. 4, 11 l-5. Harrison A., Huggit R. and Jagger R. C. (1978) The effect of a cross-linking agent on the abrasion resistance and impact strength of an acrylic denture base material. J. Dent.

6, 299-303. Jagger R. C. (1978) Effect of the curing cycle on some properties methacrylate) denture base material. J. Oral Rehabil. 4, 15 1-9. Moist K. F., Koblitz F. F. and Glenn J. F. (1978) Predicting the shelf J. Dent. Res. 57, Special issue A, abstr. 706. Vermilyea S. G., Powers J. M. and Koran A. (1978) The rheological denture base resins. J. Dent. Res. 57, 227-3 1. Wictorin L. (1978) The leaching of residual monomer from acrylic based Res. 57, Special issue A, abstr. 204.

of a Poly(methy1 life of base resins. properties materials.

of fluid

J. Dent.

Tissue conditioners and soft lining materials Davenport J. C., Wilson H. J. and Basker R. M. (1978) The compatability of tissue conditioners with denture cleaners and chlorhexidine. J. Dent. 6, 239-46. Manderson R. D. and Brown D. (1978) A clinical and laboratory investigation of a new denture cleanser. J. Dent. 6, 222-28. McCarthy J. A. and Moser J. B. (1978a) Mechanical properties of tissue conditioners. Part I. Theoretical considerations, behavioural characteristics and tensile properties. J. Prosthet.

Dent. 40, 89-97. McCarthy J. A. and Moser J. B. (1978b) Mechanical properties of tissue conditioners. Part II. Creep characteristics. J. Prosthet. Dent. 40, 334-42. McCarthy J. A. and Moser J. B. (1978~) Undercut reproducibility of functional impression materials. J. Oral Rehabil. 5, 287-92. McCarthy J. A. and Moser J. B. ( 1978d) Tissue conditioners as functional impression materials. J. Oral Rehabil. 5, 357-64.

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Journal of Dentistry, Vol. ~/NO. 3

Thomas C. J. and Nutt G. M. (1978) The in vitro fungicidal properties of V&o-gel, and combined with nystatin and amphotericin B. J. Oral Rehabil. 5, 167-72.

alone

Dental ceramics

Anusavice K. J., De Hoff P. H. and Fairhurst C. W. (1978) Comparative evaluation of ceramic-metal bond tests using finite element stress analysis. J. Dent. Res. 57, Special issue A, abstr. 869. Asgar K. and Giday Z. (1978) Refinement on testing of the porcelain to metal bond. J. Dent. Res. 57, Special issue A, abstr. 870. Baran G. R., O’Brien W. J. and Tien T. Y. (1977) Coloured emission of rare earth ions in a potassium feldspar glass. J. Dent. Res. 56, 1323-9. Caputo A. A., Dunn, B. and Reisbick M. H. (1977) A flexural method for evaluation of metal-ceramic bond strengths. J. Dent. Res. 56, 1501-6. Clark A. E., Lazear J. and Mohammed H. (1978) Compositional influence on the strength of dental porcelain. J. Dent. Res. 57, Special issue A, abstr. 867. Johnston W. M. and O’Brien W. J. (1978) Shear strength of dental porcelain. J. Dent. Res. 57, Special issue A, abstr. 868. Newburg R. and Parmeijer C. H. (1978) Composite resins bonded to porcelain with silane solution. J. Am. Dent. Assoc. 96, 288-91. Stewart G. P., Maroso D. and Schmidt J. R. (1978a) Effect of surface treatment on alloy surfaces. J. Dent. Rex 57, Special issue A, abstr. 875. Stewart G. P., Maroso D. and Schmidt J. R. (1978b) Topography and distribution of trace surface metals (tin and indium) on alloys for porcelain-metal restoration: influence of surface treatments. J. Dent. Res. 57, 237-43. Williams T. R. P., Johnson C. E., Winchell P. G. et al. (1978a) Beryllium, lithium and sodium distribution near a porcelain/nickel alloy interface shown by ion microprobe mass analysis. J. Dent. Res. 57, 233-6. Williams T. R. P., Winchell P. G. and Phillips R. W. (1978b) Dental porcelain/nickel alloy interface reactions and their effective prevention. J. Dent. Res. 57, 583-91. Wozniak W. T. and Moore B. K. (1978) Luminescence spectra of dental porcelains. J. Dent. Res. 57, 971-4.

Younis 0. (1978) A method for determining shear strain at failure of porcelain/ceramic alloy systems. .I. Dent. Res. 57, Special issue A, abstr. 87 1.

Den tal imp Ian ts

Adams D., Williams D. F. and Hill J. (1978) Carbon-fibre reinforced carbon as a potential implant material. J. Biomed. Mater. Res. 12, 35-42. Alpert B. (1978) Silastic tubing for interpositional arthroplasty. J. Oral Surg. 36, 153. Baratieri A., Sacchi A. and Miari C. (1978) Bone changes incident to blade vent implants. J. Biol. Buccale. 6, 121-8. Baumhammers A., Langkamp H. H., Matta R. K. et al. (1978) Scanning electron microscopy of epithelial cells grown on enamel, glass and implant materials. J. Periodontal 49, 39-42.

Cooke M. S., Heslop I. H., Smith B. G. N. et al. (1978) A two-stage bonded canine transplantation and diodontic implant. Br. Dent. J. 144, 108. Furseth R. and Pedersen K. N. (1978) Ultrastructure of tissue in intrabony and subperiosteal porous ceramic implants. Znt. J. Oral Surg. 7, 47 l-8. Gross B. D. and Topazian R. G. (1978) Mucosal grafting over Proplast augmented edentulous ridges. J. Oral Surg. 36, 948-9.

Brown et al.: Review of dental materials

247

Hodosh M., Gettleman L., Shklar G. et al. (1978) Surface texture of vitreous carbonpoly(methylmethacrylate) dental implant material. J. Biomed. Mater. Res. 12, 16780. Howe A. G., Kent J. N., Farrell C. D. et al. (1978) Implant of articular eminence for recurrent dislocation of the temporomandibular joint. J. Oral. Surg. 36, 523-6. Jaffee A., Ehrlich J. and Shoshan S. (1978) Biological anchoring of acrylic tooth implants in the drug using enriched collagen solution. Arch. Oral Biol. 23, 4 15-l 8. Kummoona R. (1978) Functional rehabilitation of ankylosed temporomandibular joints. Oral Surg. Oral Med. Oral Pathol. 46, 495-505. Lewin R. W. and Wright J. A. (1978) Silastic ulna head prosthesis for use in surgery of the temporomandibular joint. J. Oral Surg. 36, 906. Mazzocco D. M., Ceravolo F. J., Baumhammers A. et al. (1978) Quantitation of retention of endosseous dental blade implants in dogs. J. Periodontal. 49, 39-42. Mizra F. 0. and Dikshit J. V. (1978) The use of implant prostheses following radiation therapy. J. Prosthet. Dent. 40, 663-7. Nery E. B., Lynch K. L. and Rooney G. F. (1978) Alveolar ridge augmentation with tricalcium phosphate ceramic. J. Prosthet. Dent. 40, 668-74. Sherman A. J. (1978) Bone reaction to orthodontic forces on vitreous carbon dental implants. Am. J. Orthod. 74, 79-87. Small I. A. (1978) Survey of experience with the mandibular staple bone plate. J. Oral Surg. 36, 604-7. Takahashi N., Kitagami T. and Komori T. (1978) Analysis of stress on a fixed partial denture with a blade vent implant abutment. J. Prosthef. Dent. 40, 186-91. Ten. J. J., Bear S. E., Brown P. W. et al. (1978) Primary reconstruction of the mandible with a wire mesh prosthesis. J. Max. Fat. Surg. 6, 105-8. Wennberg A. (1978) A method for the evaluation of the initial tissue response to biomaterials. Acta Odontol. Stand. 36, 57-63. Young S. O., Park J. B., Kenner G. H. et al. (1978) Dental implant fixation by electrically mediated process: interfacial strength. Biomat. Med. Dev. Art. Org. 6, 1 1 l-26. Corrosion Amalgam

corrosion

Averette D. F., Hochman R. F. and Marek M. (1978) The effects of corrosion in vitro on the structure and properties of dental amalgam. J. Dent. Res. Special Issue A, abstr. 361. Boyer D. B. and Chan K. C. (1978a) The effect of surface finish on the anodic polarisation of a conventional spherical amalgam. J. Biomed. Mater. Res. 12, 541-55. Boyer D. B. and Chan K. C. (1978b) Effect of finish on the anodic polarisation of amalgam. J. Dent. Res. Special Issue A, abstr. 354. Boyer D. B., Chan K. C., Svare C. W. et al. (1978) The effect of finishing on the anodic polarisation of high-copper amalgams. J. Oral Rehabil. 5, 223-8. Chen C. P. W. and Greener E. H. (1978) The effect of galvanic corrosion on the axial tensile strength of amalgam. J. Dent. Res. Special Issue A, abstr. 360. Darvell B. W. (1978) The development of an artificial saliva for amalgam corrosion studies. J. Oral Rehabil. 5, 41-9. Espevik S. (1977) In vitro corrosion of dental amalgams with different Cu content. Stand. J. Dent. Res. 85, 631-6. Finkelstein G. F. and Greener E. H. (1978) Role of mucin and albumin in saline polarisation of dental amalgam. J. Oral Rehabil. 5, 95- 100. Gal-Or L., Bruckenstein S. and Carter J. M. (1978) A study of the corrosion of amalgam using the ring-disc electrode. J. Biomed. Mater. Res. 12, 1- 12.

Journal

248

of Dentistry,

Vol. S/No.

3

of Gettleman L., Cocks F. H., Darmiento L. et al. (1978) I n viva corrosion determination high-copper dental amalgams. J. Dent. Res. Special Issue A, abstr. 357. Gjerdet N. R. and Espevik S. (1977) In vitro corrosion of screw posts and amalgam placed in contact. Swed. Dent. Res. 1, 193-5. Gjerdet N. R. and Espevik S. (1978) Corrosion and creep of dental amalgam. J. Dent. Res. 57, 21-6.

Marek M. and Okabe T. (1978) Corrosion behaviour of structural phases in high-copper dental amalgam. J. Biomed. Mater. Res. 12, 857-66. Nomoto S., Kobayashi K. and Onose H. (1978) Potentiostatic polarisation curves for dental amalgams by means of a potential sweep method. J. Nihon Univ. Sch. Dent. 18,47-62. Onose H., Audo S., Nomoto S. et al. (1977) Corrosion of dental amalgam in culture media. J. Dent. Res. 56, 1336.

Sarkar N. K. (1978) Rehabil.

Creep, corrosion

and marginal

fracture

of dental

amalgams. J. Oral

5, 413-23.

Sutow E. J., Jones D. W. and Bezanson R. H. (1978) Crevice corrosion of dental amalgam. J. Dent. Res. Special Issue A, abstr. 359. Vaidyanathan T. K. (1978) In vitro tarnish characterisation of dental amalgams. J. Dent. Res. Special Issue A, abstr. 355. Corrosion in implant alloys

Brockhurst P. J. (1978) Corrosion and the human body. Met. Australas. 10, 18-20. Cahoon J. R. and Hill L. D. (1978) Evaluation of a precipitation-hardened, wrought cobaltnickel-chromium-titanium alloy for surgical implants. J. Biomed. Mater. Res. 12, 805-21. Jones R. L., Wing S. S. and Syrett B. C. (1978) Stress-corrosion cracking and corrosion fatigue of some surgical implant materials in a physiological saline environment. Corrosion-NACE

34, 226.

Rostoker W., Galante J. 0. and Leveim P. (1978) Evaluation of couple/crevice corrosion by prosthetic alloys under in vivo conditions. J. Biomed. Mater. Res. 12, 823-9. Sury P. and Semlitsch M. (1978) Corrosion behaviour of cast and forged cobalt-based alloys for double-alloy joint endoprostheses. J. Biomed. Mater. Res. 12, 723-41. Syrett B. C. and Wing S. S. (1978a) Pitting resistance of new and conventional orthopaedic implant materials - effect of metallurgical condition. Corrosion-NACE 34, 138. Syrett B. C. and Wing S. S. (1978b) An electrochemical investigation of fretting corrosion of surgical implant materials. Corrosion-NACE 34, 379.