J. Dent. 1991;

19: 199-206

199

Review

Measurement methods used for the determination of dimensional accuracy and stability of denture base materials A. Zissis, R. Huggett

and A. Harrison

Department of Prosthetic Dentistry and Dental Care of the Elderly, Dental School, Bristol, UK

ABSTRACT The literature relating to methods of measurement of dimensional accuracy and stability of denture base materials is reviewed. The papers are presented chronologically together with information on the measurement technique used and the reported level of accuracy. Most authors utilized optical measuring apparatus, with the use of calipers being the second most popular method. KEY WORDS: Denture base materials, Dimensional J. Dent. 1991; 1991)

19: 199-206

(Received

accuracy/stability,

19 July 1990;

reviewed

Measurement,

25 September

Correspondence should be addressed to: Dr A. Zissis, Department of Prosthetic Elderly, Dental School, Lower Maudlin Street, Bristol BSI 2LY, UK.

INTRODUCTION It is well established that function of a complete denture is related to the adaptation (fit) of its base to the bearing areas and that the better the adaptation of the base, the more stable and retentive is the denture. The adaptation of a denture base, however, depends on many factors which include the method and the material used for its construction. It is axiomatic that the more dimensionally accurate and stable a material is, the more retentive and stable will be the denture. The properties of the denture base material used are therefore of considerable importance in complete denture construction. There have been a number of studies concerning the dimensional accuracy and stability of denture base materials. In some, only the method of measurement of the dimensional stability is reported, while in others the reliability of the method utilized is also described. Clinical studies of strain behaviour deformation and stability of denture bases in function have been dealt with by other workers (e.g. Stafford and Griffiths, 1979; Glantz and Stafford, 1985; Ghazali et al., 1988). These studies are not included in this review as they do not evaluate the dimensional accuracy of the denture base in relation to its original cast and its stability with time. For the same reason other clinical studies which have assessed the apposition of the denture base in relation to the oral @1991 Butterworth-Heinemann 0300-5712/91/040199-08

Ltd.

Review

1990;

accepted 23 February

Dentistry

and Dental Care of the

tissues (e.g. Woelfel and Paffenbarger, 1965; Young 1970; Hosoi, 1976) are not included. Investigations of tooth movement during packing and polymerization procedures (e.g. Atkinson and Grant, 1962; Grant, 1962; Dukes et al.,1985) are also omitted since they are not strictly a measure of the dimensional accuracy and stability of the denture base material. The following review of measurement methods for the determination of dimensional accuracy and stability of denture base materials takes account of the majority of papers published during the last 30 years. They are presented in chronological order. For clarity, when the original measurements were quoted in imperial units the metric equivalent is included in parentheses.

LITERATURE

REVIEW

1958-l 969 Mowery et al. (1958) studied the dimensional changes of denture base resins and used stainless steel pins (l/8 in (3.175 mm) long and l/16 in (1.5875 mm) in diameter), polished on one end and ruled with fine cross-marks, as reference points. These were cemented in the central fossa of the last molars and in the distal-buccal peripheral flanges of the dentures. The reference distances were

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measured to the nearest 0.0001 in (0.00254 mm) by a toolmaker’s microscope. The mean of five readings was taken as the measurement. In their classical studies on dimensional changes occurring in dentures Woelfel et al. (1960, 1962) reported the changes in molar to molar dimension. Linear measurements were made on each denture at various times, under a controlled temperature. The reference marks were fine cross-lines ruled on polished stainless steel pins cemented in the second molars. They claimed that a skilful observer, using a calibrated toolmaker’s microscope and good reference lines, could hold the error in measurement to within f 0.0025 mm. Mirza (1961) in his study on dimensional stability of dentures used 33 heat-polymerized acrylic resin and 31 autopolymerized acrylic resin clinical dentures. Three test methods were used to evaluate the correlation of the two groups: a linear microscopic measurement; perceptible change seen on the initial cast; observation of tit in the mouth. Three pins with minute crosses on the heads were cemented into artificial stone casts and the linear dimensional changes of test dentures were measured using a Gaertner microscope (Gaertner Scientific Corp., Chicago, IL, USA: accurate to 0.0001 in (0.00254 mm)). Replicate readings were accurate to 0.0003 in (0.00762 mm). In 1962 Anthony and Peyton developed a modified comparator as a pantographic measuring device in order to measure the dimensional accuracy of different denture base materials. The contours of dentures, which were reproduced in graph form, were drawn from a series of measurements made at 0.025 in (0.635 mm) intervals, taken in parallel transversely across the upper and lower dentures in the second molar regions. The values recorded from each series were plotted on a 36 in (91.5 cm) graph. The contours of both the master impression and the dentures processed on casts poured from the master impression, were reproduced together in a relationship which permitted the distances to be measured perpendicularly to the denture surfaces. The same authors (Peyton and Anthony, 1963) carried out further studies in 1963 having modified the apparatus. Choudary et al. (1964) used a prototype contour meter to study dimensional stability and fluid sorption in porcelain-based dentures. Their instrument recorded three-dimensional changes. Barsoum et al.(1968) evaluated the accuracy of fit of aluminium cast denture bases and acrylic resin bases with a surface meter developed from a milling machine with an attached dial micrometer. The contour of the fitting surface of the denture bases was compared to a master cast. The measuring apparatus used was accurate to 0.001 in (0.025 mm). The curing of denture base resin with microwave irradiation was studied by Nishii in 1968. He measured the discrepancy between the cured base and the original metal die, a simplified pattern of the upper edentulous ridge. The adaptability was observed by lightly pressing

the cured base on the die and the discrepancy measured with a measurescope. 1970-I 979 Goodkind and Schulte (1970) studied the dimensional accuracy of pour acrylic resin and conventional processing of autopolymerized acrylic resin bases. They used a steel master die to simulate the shape of the edentulous ridge on which nine locations were selected and marked with a cross. The reference distances were measured with a Nikon optical comparator calibrated to 0.0001 in (0.00254 mm). The standard deviation of repeated measurements was 0.0007 in (0.017 mm). Kraut (1971) in his study of the comparison of denture base accuracy used 50 casts (which originated from a non-undercut edentulous maxillary cast) for each of the four tested materials, on which the denture bases were processed. The space between the base and cast was measured at 12 locations using thickness gauges 0.0015-0.025 in (0.038-0.63 mm). The space was considered equal to the thickness of the thinnest gauge that bound when inserted between the base and cast. Winkler et al. (197 l), in their study on processing changes in complete dentures constructed from pour resins, recorded the linear dimensional changes that occurred during processing. Highly polished flat-topped stainless steel pins l/8 in (3.175 mm) in diameter were cemented into the second molar regions of 20 sets of denture casts, flush with the top surface. The reference points were indentations made on the pins. Linear measurements were made by the same investigator who used a comparator microscope and read to the nearest 0.01 mm, from the exact centres of the reference point. All the readings were repeated five times. They stated that a skilful observer could minimize the measurement error to * 0.01 mm. In their research on the dimensional accuracy of dentures produced with pour type resin Grant and Atkinson (1971) also compared the changes that occurred in the flange to flange dimension. Using a Nikon measuring microscope (Nikon, Nippon Kosaku, Tokyo, Japan), measurements were made across the distal portion of the dentures, between reference points which were marks on the casts in the incisor and molar regions. The measurements between reference points were made on the models prior to processing and on the reproduction of these points on the dentures after processing. In 1972 Morris studied the effect of ultrasonic cleaning upon stability of resin denture bases. He constructed eight denture bases (five using heat-polymerized and three using fluid resin techniques). Steel pins were embedded in the wax trial bases and used as reference points. For measuring the distance from the outside of one pin to the outside of the other, a vernier caliper accurate to 0.001 in (0.0254 mm) was used. In 1973, McGivney compared the adaptation of three types of denture bases (acrylic resin, gold, gold-reinforced acrylic resin) after processing. A modified stone cast of the

Zissis et al.: Accuracy

edentulous mandible was used and as reference points, slight spherical indentations about 0.25 mm in depth were made in the stone cast at selected points, and steel balls 1 mm in diameter were placed in the indentation sites. The adaptation of the dentures was evaluated on the basis of contour meter recordings. Becker et al. (1977) investigated denture base processing techniques in relation to dimensional changes and used 27 maxillary casts in which seven holes were drilled to a depth of l-l.5 mm. The reference distances were measured using a Nikon optical comparator calibrated to 0.0012 mm. In the same year Bates et al. (1977) compared the dimensional accuracy of fluid-type denture base resins to the conventional heat-polymerized resins. They used five resin bases for each of the materials tested, which were processed on stone casts prepared from a silicone mould of a master die. The differences between casts and acrylic resin bases were calculated by measuring the reference points using a Nikon optical comparator calibrated to 0.0001 in (0.00254 mm). Hardy (1978) also studied fluid resins. He compared the fluid resin and compression moulding methods in processing dimensional changes and used ten sets of complete dentures for each method. Reference points were provided for linear measurements of a molar to molar (second molars) relationship. The measurements were made by a toolmaker’s microscope accurate to 0.0001 in (0.00254 mm). Further studies on fluid resins were reported by Antonopoulos (1978) who studied dimensional and occlusal changes. He made his measurements on microscopic crosses scratched on highly polished stainless steel pins that were cemented in the central fossae of the occlusal surfaces of second molars and served as reference points. The linear dimensional changes were measured by a Gaertner microscope. Heath and Basker (1978) studied the dimensional variability of duplicate dentures by using a heatpolymerized acrylic resin complete upper denture with porcelain teeth as a master denture. Measuring points were established by grinding flats into it, in such a way that the denture could be measured in all three dimensions by a vernier caliper gauge accurate to 0.05 mm. To study the reproducibility of measurements the distances were measured on three separate occasions and three times in succession. The coefficients of variation for measurements did not exceed 0.25 per cent in any dimension. In the same year Hargreaves (1978) studied the dimensional changes of acrylic resin that occurred due to water uptake. Stainless steel pins, 0.65 mm in diameter, were inserted into the impressions (taken from patients) in the region of the tuberosities, so that the pins were transferred to the gypsum casts. The distance between the centres of the pins was measured with a travelling microscope (Olympus, STM, Tokyo, Japan) to the nearest 0.02 mm. The mean of five readings was recorded. In 1979 Barco et al. in their study of the effect of relining on the accuracy of maxillary complete dentures, developed a technique for evaluating the accuracy of denture bases

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using a low viscosity impression material to determine the space between the master die and the processed denture base. The overall lit of the dentures was compared by placing a low viscosity silicone rubber material on the denture base, seating it on the steel dies under known load and determining the volume of space between the master die and denture base by the weight of residual impression material retained. Also in 1979, Gee et al. developed a measuring procedure for the determination of the threedimensional shape of dentures. They utilized experimental complete maxillary dentures and formed a stereometrical figure by a minimum number of reference points which described the denture as fully as possible. Most of the edges of this figure had to lie in or on the denture material (left-right tuberosities, incisive papilla-midline palate). The four reference points were drilled in the casts and the holes were replicated by the resin. The x, y, z coordinates of these points were determined by an Olympus toolmakers measuring microscope (Olympus, STM, Tokyo, Japan) accurate to 0.0025 mm. Measurements were carried out four times for each sample. Soni et al. (1979) compared the accuracy of denture bases by a non-parametric method. Twenty-live maxillary stone casts were made, and five dentures for each tested resin were processed by conventional compression moulding techniques. The fit of each denture at the molarto-molar region on its cast was evaluated by five evaluators who independently ranked the 25 dentures from best to worst. The ranking data were analysed statistically by non-parametric tests. Excellent agreement among observers was obtained. Zani and Vieira (1979), in their study of silicone as a separating medium, also assessed dimensional stability by the changes which occurred in relative positions of the denture teeth during processing. Stainless steel wires embedded in the occlusal surfaces of the first molars and the incisal edge of the left central incisor were used as reference points. The reference distances were measured by a Gaertner microscope with an accuracy of 0.01 mm. 1980-I 989 In 1980, Mainieri et al. studied tooth movement and dimensional change of denture base materials using two investment methods. To evaluate the tit of resin test denture bases, a special master steel die, resembling an edentulous arch, was machined. A comparison of the weight of the residual impression material held between the denture base and the master die showed the fit of each of the ten specimens (five for each method) which was assessed five times. Windecker and Dippel (1981) in their comparative studies of the exactness of tit of maxillary complete dentures with resin and cast metal bases, used 30 hard stone casts for the determination of the gaps between surfaces, i.e. ten test dentures for each of the three test materials processed. A low viscosity impression material formed a layer between the casts and dentures at those

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places on the palatal surface where there was a gap. The thickness of the impression material layer was measured using an optical microscope. In a review of the properties of some denture base polymers Stafford et al. (1980) measured the dimensional accuracy of nine denture base materials. Test specimens were processed on stone casts prepared from a silicone mould of a brass master die. The casts and specimen plates were measured using a Nikon optical comparator. The measurements demonstrated a standard deviation of 0.004 mm. Using the same measuring procedure, Murphy et al. (1982a) considered dimensional accuracy in a laboratory and clinical study of Trevalon denture base material. The same measuring technique was later used by Murphy et al. (1982b), Staffordet al. (1983) and MacGregor et al. (1984). Garfunkel (1983) compared dimensional changes of dentures processed by the injection-moulding method with those that occurred during processing with the packpress method. Ten sets of complete upper and lower dentures were waxed and processed (live for each of the two methods). Small holes were drilled into several of the teeth and in specific places on the casts to be used as reference points when measuring. Every reference point was marked with red indelible paint to make it more visible. Measurements were made with a digital readout caliper and recorded to the nearest 0.01 mm. Each dimension was measured ten times to establish a mean value. In 1984 Huggett et al. evaluated the effect of different curing cycles on the dimensional accuracy of acrylic resin denture base materials, using test plates simulating mandibular complete dentures. Nine location index marks were provided. The reference points on casts and plates were measured with a Nikon optical comparator. Three readings were taken for each of the dimensions and the mean calculated. The reliability of the comparator, after repeated measurements, resulted in a standard deviation of 0.004 mm. The combination of effects associated with the processing distortion of acrylic resin maxillary complete dentures on flange adaptation, palatal base distortion and induced malocclusion was investigated by McCartney (1984). On 20 maxillary complete dentures reference notches were prepared in the lingual aspect of the most distal molar on either side of the arch. The molar to molar distance was measured by a caliper device, to the nearest 0.001 in (0.0254 mm) with an outside micrometer. Cat-ret al. (1985) compared the vertical tooth movement after denture processing procedures. They used 40 sample set-ups (with four posterior teeth) which were processed under controlled laboratory conditions. The vertical changes were measured with a comparator accurate to 0.001 mm. Polyzoisetal. (1986) evaluated the dimensional accuracy of replica dentures made from wax and autopolymerizing acrylic resin in silicone or irreversible hydrocolloid flexible moulds. They selected four duplicating methods.

Measuring points were established by grinding notches into the master maxillary denture. These points were positioned so that the denture could be measured in all three dimensions by a dial caliper to the nearest 0.05 mm. Test method accuracy was verified on the master denture by measuring 11 distances 10 times each for a total of 110 measurements. The measurements were made on, three separate occasions and also three times in succession. The coefficients of variation of measurements made on the master denture never exceeded 0.21 per cent. Johnson and Duncanson (1987) measured the dimensional changes occurring at the posterior palatal border of maxillary dentures in relation to the observed tit to the cast. They used a binocular microscope attached to a rotating micrometer transport workstage. Specimens were held on a tilt-top table of a dental surveyor and viewed at X 45 magnification. Measurements were recorded to 0.01 mm. In 1987 Ristic and Carr observed the changes in vertical measurements of 35 acrylic resin tooth-bearing samples over a period of 4 weeks of water sorption. To establish the vertical dimension an electronic digital readout micrometer and a comparator were used. Both instruments were accurate to 0.001 mm. The electronic micrometer was used to determine the maximum-minimum heights of the individual teeth. The comparator was suitable for easy and accurate repetitive measurements of all teeth on all of the samples. To assess the precision of the instruments 10 consecutive measurements of one tooth were made on each instrument. The coefficients of variation were calculated and found to be 0.103 per cent for the comparator and 0.037 per cent for the micrometer, which indicated acceptable accuracy of the instruments. In a later study, Polyzois et al. (1987) evaluated the dimensional stability of three fast boilable denture resins with a conventional and high-impact denture resin processed with a long curing cycle. Twenty-five denture wax-ups (five for each denture resin), which originated from a master complete maxillary denture with reference points, were used. The reference distances (four on the denture bases and three on the artificial teeth) were measured using a dial caliper to the nearest 0.05 mm. Measurements were made by the same operator and the mean of five readings was taken. The dimensional stability of injection and conventional processing of denture base acrylic resin was studied by Anderson et al. (1988) using a brass master die with a regular shaped squared outline to facilitate the direct comparison of linear dimensional change. Six reference marks were scribed on the die surface at regular intervals. The die was invested in 10 standard denture flasks, by using a double pour technique. This method allowed direct comparison of the sample dimensions with the master die, since the die was directly invested to make each of the samples. For the measurements a Nikon optical comparator calibrated in 0.0001 in (0.00254 mm) was used. Five measurements were made of each dimension and a mean value was calculated. The

Zissis

et al.: Accuracy and stability of denture base materials

standard deviation of repeated measurements of the die was 0.01 mm. Chen et al. (1988) evaluated the relationship between denture thickness and the dimensional stability of acrylic resin denture bases. Forty-eight maxillary complete dentures were fabricated in three different thicknesses using four processing procedures. Using an optical comparator accurate to 0.001 mm they compared discrepancies between cast and denture base. It appears that the polymerizing procedures had little effect on dimensional change, however, more distortion was observed for dentures quenched in water as compared to those that were bench cooled. It was found that thicker dentures had less molar-to-molar linear shrinkage, but more dimensional change in the posterior palatal area as compared to the thinner dentures. In 1988 Mulla et al. in their work on physical and mechanical properties of a visible light-activated material, also considered its dimensional accuracy. Seven test plates, that simulated mandibular dentures, were processed on casts originating from a brass master die. The locations of index marks (in molar-to-molar dimension) were measured using a Nikon optical comparator (to the nearest 0.001 mm) and compared to the corresponding dimension of the original stone casts on which the base plates were processed. In 1989 Takamata et al. studied the adaptation of acrylic resin dentures as influenced by the activation mode of polymerization. Forty-two specimens were tested for dimensional accuracy by placing them on the steel master die which provided four notches (three along the periphery and one on the posterior border of the palate). A low viscosity impression material was placed in the specimens and the material retained between the denture base and master die was weighed on an analytical balance to the nearest 0.00001 g. The procedure was performed three times for each specimen and the fit of each of the specimens was expressed as the weight of impression retained between the denture base and master die. Harvey and Harvey (1989) measured the dimensional changes of 50 Triad (visible light-activated) resin base plates at the posterior border before curing, when cured, after storage in room temperature water (24 h, 4 weeks) and when allowed to dry on the bench for 10 days. Three reference points were placed on the cast and resin using a marking device for making 1 mm indentations into the uncured resin at the crest of each tuberosity and on the midpalatal surface. A Gaertner measuring microscope was used for all measurements. Also in 1989 Frejlich et al. compared two methods of evaluating the accuracy of acrylic resin complete denture bases by measuring the tit of four acrylic resin materials and two processing techniques. A metal master die (with four V-shaped notches) was used. The first measurement method used a low viscosity impression material. The impression material occupying the space between the denture base and the cast was weighed on an analytical balance to the nearest 0.0001 g. To evaluate the reproducibility each

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specimen was weighed six times and a standard deviation of 0.0001 g was obtained. The second method used moire topography, an optical non-contacting technique. The reproducibility of this method was obtained by measuring the specimen ten times. A variation of 25 nm was found. Strohaver (1989) compared the changes in vertical dimension between compression and injection moulded complete dentures using 15 sets of clinical dentures for each method. The changes in vertical dimension between waxed and cured dentures were measured with a dial indicator accurate to 0.001 in (0.0254 mm). It is worth commenting that in a review article of the effect of methods of polymerization of resin denture bases, Takamata and Setcos (1989) cite several studies in the Japanese literature on polymerization shrinkage, dimensional accuracy and fitness (sic) of denture bases, e.g. Tateno (1985) Umi et al. (1986) and Nagata et al. (1987). Their review article however does not generally describe the apparatus used nor the accuracy of measurements. Latta et al. (1990) used three radiographic views, occlusal, frontal and lateral, to determine differences in three-dimensional stability of new denture base resin systems. Metal markers were luted into preselected positions in the dentures. Measurement of positional changes of the metal markers was made by examination of the radiographs with a vernier caliper accurate to 0.0005 in (0.01 mm). Sykora and Sutow (1990), in a comparison of the dimensional stability of two waxes and two acrylic resin processing techniques, used ten sets of complete dentures in which metal reference pins were inserted into the buccal cusps of the maxillary second molars, lingual cusps of the mandibular second molars and the maxillary and mandibular canines. Measurements were made using a vernier caliper accurate to 0.025 mm. In a study of the accuracy of visible light-curing denture bases Polyzois (1990) sectioned maxillary record bases on their casts and determined the space which existed between base and cast by measuring with feeler gauges at prelocated points. The gauges used were 0.05 mm to 0.5 mm in 0.05 mm increments. Burns et al. (1990) used an electronic micrometer designed to read to a precision of 0.00015 mm to study the dimensional stability of acrylic resin material in the shape of a cylinder and made the point that extrapolation of the information to complete dentures may not be valid.

DISCUSSION From the foregoing it is apparent that the apparatus used can be divided into three groups. Optical comparators based on the travelling microscope were used in 60 per cent of studies reviewed, whereas 25 per cent of studies employed a simple hand-held caliper instrument. The remainder of studies employed a variety of techniques

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ranging from subjective non-parametric techniques and simple measurement determination using feeler gauges to the sophisticated moire topography. Surprisingly, in the majority of studies presented, the accuracy and reproducibility of the measuring techniques are not detailed. It has been shown that contraction in denture base systems averages - 0.5 per cent. It is perhaps worth commenting that 1 per cent shrinkage represents approximately 0.5 mm across a 50 mm denture span. This amount of contraction measured should be readily detectable using apparatus such as calipers, accurate to 0.05 mm. The use of a measurescope accurate to 0.001 mm will obviously be more discerning but perhaps not of significantly greater value in linear determination. What is important is the effect of contraction on denture shape and contour which is unlikely to be linear. With this in mind, it is perhaps appropriate that measuring techniques should evaluate surface contour change between cast and denture base rather than simple linear contraction measurement. Several attempts have been made, in the past, to evaluate contour change. For example, Anthony and Peyton (1962) appreciated the necessity of assessing dimensional change by measuring surface contour. Similarly, Choudharyefal. (1964), Barsoumetal. (1968) and Frejlich ef al. (1989) used apparatus capable of assessing contour change. The technique of using feeler gauges has the obvious advantages of simplicity and availability. However, it will be appreciated that the determination of quantifying the gap with the feeler gauge will be influenced by the shape of the gauge relative to the height, depth and width of the gap space. Also, the force applied by the operator when inserting the gauge into the gap could foreseeably lift the base place from the cast unless a uniform weight was applied to the baseplate to prevent movement. The ‘weight of impression material technique’ may be capable of assessing volume of space between baseplate and cast. However, it fails to indicate the precise nature and location of the changes that may have occurred. Further, the technique is sensitive to the viscosity of material, the load applied when placing the base plate in situ and the precise removal of excess impression material. All of these factors can contribute to measurement error. A subjective evaluation analysed by a non-parametric statistical method, although possibly showing good agreement between the assessors, at best can only rank between best fit and worst fit, the fit being assessed visually in the molar-to-molar region of each denture based on its cast. Once again this fails to quantify or indicate the precise nature of the dimensional changes. In the technique known as Moire topography light is passed through a grid and a shadow is cast onto the surface of the object studied. The object is thus overlaid with light and dark fringes and these fringes are interpreted as lines of equal height. By applying the phase shift method on the Moire topogram three-dimensional plots can be obtained and measurements of the different

surfaces can be compared. The apparatus is relatively complex and not readily available. However, it is claimed that it can provide cross-sectional determination of denture base fit in addition to an overall fit value without sectioning the denture and cast. Recent developments in coordinated measuring systems, such as the Mitutoyo BX 303 air bearing apparatus (Mitutoyo (UK) Ltd, Andover, Hampshire, UK), originally developed for applications in engineering, would appear to have considerable potential in studies on dimensional accuracy and stability of prosthetic appliances. This system offers the advantages of threedimensional measuring linked with sophisticated computer technology. References to this type of measurement system used in the evaluation of denture bases can be found in the Japanese literature (Inanaga et al., 1982; Habu et al., 1985). Work is’currently being undertaken using this type of apparatus and it is our intention to present the outcome of these studies in future reports. SUMMARY

This paper has reviewed the literature and detailed the apparatus utilized by workers in evaluating the dimensional stability and adaptability of denture bases. Most workers have used either optical measuring apparatus or calipers, whilst a variety of other methods have found less use. Sophisticated computerized coordinate measuring systems, which permit contour comparisons between cast and base, would seem to offer interesting potential in future research. References Anderson G. C., Schulte J. K. and Arnold T. G. (1988) Dimensional stability of injection and conventional processing of denture base acrylic resin. J. Prosthet Dent. 60, 394-398. Anthony D. H. and Peyton F. A. (1962) Dimensional accuracy of various denture base materials. J. Prosthet. Dent. 12, 67-81. Antonopoulos A. (1978) Dimensional and occlusal changes in fluid resin dentures. J. Prosthet. Dent. 39, 605-608. Atkinson H. F. and Grant A. A (1962) An investigation into tooth movement during the packing and polymerizing of acrylic resin denture base materials. Aust. Dent. J. 7, 101-108. Barco M. T., Moore B., Swartz M. et al. (1979) The effect of relining on the accuracy and stability of maxillary complete dentures. An in vivo and in vitro study. J. Pro&et. Dent. 42, 17-23. Barsoum W. M., Eder J. and Asgar K. (1968) Evaluating the accuracy of fit of aluminium-cast denture bases and acrylic resin bases with the surface meter. J. Am. Dent. Assoc. 76, 82-88. Bates J. F., Stafford G. D., Huggett R. et aZ. (1977) Current status of pour type denture base resins. J. Dent. 5, 177-189. Becker C., Smith D. and Nicholls J. (1977) The comparison of denture base processing techniques. Part II Dimensional changes due to processing. J. Prosthet. Dent. 38,450-458. Burns D. R., Kazanoglu A., Moon P. C. et al. (1990) Dimensional stability of acrylic resin materials after microwave sterilization. Int. J. Prosthodont. 3, 489-493.

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Carr L., Cleaton Jones P., Fatti P. et al. (1985) An experimental comparison of vertical tooth movement of 33 degrees and 0 degree teeth after denture processing procedures. J. Oral Rehabil. 12,263-278. Chen J. C., Lacefield W. R. and Castlebury D. J. (1988) Effect of denture thickness and curing cycle on the dimensional stability of acrylic resin denture bases. Dent. Mater. 4, 20-24. Choudhary S. C., Terry J. M., Gehl D. H. et al. (1964) Dimensional stability and fluid sorption in porcelain base dentures. J Prosthet. Dent. 14, 442-455. Dukes B. S., Fields H., Olson J. W. et al. (1985) A laboratory study of changes in vertical dimension using a compression moulding and a pour resin technique. J. Prosthet. Dent. 53, 667-669. Frejlich S., Dir&x J. J. J., Goodacre C. J. et al. (1989) Moire topography for measuring the dimensional accuracy of resin complete denture bases. Znt. .Z.Prosthodont. 2, 272-279. Garfunkel E. (1983) Evaluation of dimensional changes in complete dentures processed by injection-pressing and pack-press technique. .Z Prosthet. Dent. 50, 757-761. Gee A., Harkel E. and Davidson C. (1979) Measuring procedure for the determination of the three dimensional shape of dentures. _ZProsthet. Dent. 42, 149-153. Ghazali El. S., Glantz P-O. and Randow K. (1988) On the clinical deformation of maxillary complete dentures. Influence of the processing techniques of acrylate-based polymers. Acta Odontol. Stand. 46, 287-295. Glantz P-O. and Stafford G. D. (1985) Bite forces and functional loading levels in maxillary complete dentures. Dent. Mater. 1, 66-70. Goodkind R. J. and Schulte R. C. (1970) Dimensional accuracy of pour acrylic resin and conventional processing of coldcuring acrylic resin bases. J. Prosthet. Dent. 24, 662-668. Grant A. A. (1962) Effect of the investment procedure on tooth movement. J. Prosthet. Dent. 12, 1053-1058. Grant A. and Atkinson H. (1971) Comparison between dimensional accuracy of dentures produced with pour type resin and with heat-processed materials. .Z Prosthet. Dent. 26, 296-301. Habu T., Inanaga A., Takenchi T. et al. (1985) Studies on dimensional change of dentures during polymerizing process: Part 1. Three dimensional investigation in the denture base area of maxillary complete dentures. J. Jpn. Prosthodont. Sot. 29,310-318 (in Japanese). Hardy F. (1978) Comparison of fluid resin and compression moulding methods in processing dimensional changes. J. Prosthet. Dent. 39, 375-380. Hargreaves A S. (1978) Equilibrium, water uptake and denture base resin behaviour. J. Dent. 6, 342-352. Harvey W. and Harvey E. V. (1989) Dimensional changes of the posterior border of base plates made from a visible light activated composite resin. .Z Prosthet. Dent. 62, 184-189. 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-l 14. Hosoi N. (1976) Studies on the fitness test for the denture base. Tsurumi Shigaku 2, 111-134 (in Japanese). Huggett R., Brooks S. C. and Bates J. F. (1984) The effect of different curing cycles on the dimensional accuracy of acrylic resin denture base materials. Quintessence Dent. Technol. 8, 81-86. Inanaga A., Miyaguchi H., Oka K. et al. (1982) Studies on denture base resin: Part 2. The dimensional accuracy of Intopress (injection type cold curing acrylic resin) in a denture base area. J. Fukuoka Dent. Coll. 9,215-226 (in Japanese).

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Book Review Tylman’s Theory and Practice of Fixed Prosthodontics, 8th edition. Edited by William F. P. Malone and David L. Koth. Pp. 461. 1989. lshiyaku EuroAmerica (distributed by Gazelle Book Services, Lancaster). Hardback, f 39.95. Earlier editions of Tylman’s textbook were considered by some benchmarks of North American fixed prosthodontics. The eighth is multiauthored and dedicated to crown and bridgework. My initial impressions were not favourable, due, fundamentally, to the failure of the editors to do their job. As a textbook it is impossible to read from beginning to end since the ordering of the chapters is, in general, illogical. For example, there is an excellent chapter discussing pontics but this is four chapters away from anything else to do with fixed bridgework. The text starts by dealing, in a sound fashion, with treatment planning and periodontal considerations before moving on to tooth preparation. The restoration of dentitions which are also periodontally compromised is dealt with in the manner of Schluger, Yuodelis and Page but is none the worse for that. There are chapters describing the use of indirect adhesive restorations, including porcelain veneers. The latter is of interest as little has been published on this topic in textbooks. Tissue management in fixed prosthodontics is almost exclusively based on the use of electrosurgery. While permissible in a postgraduate text this is ill-advised in one directed at undergraduates. On the other hand, the description of impression materials and techniques is basic to the point where my insomnia was cured for that evening. In contrast, the subsequent chapter describing provisional restorations and temporary coverage is

stimulating. The next five chapters deal with, in an order that is hard to fathom, ‘Inter-occlusal records’, ‘Laboratory support for fixed partial dentures’, ‘Occlusion’, ‘Occlusal adjustment’ and ‘Articulators’. All are disappointing, the occlusion discussions particularly; the authors lack discrimination in considering occlusal adjustment and there is a disturbing absence of rationale. The subsequent order is bewildering, cements followed by pontics followed by more cement! The discussion of glass ionomer cement, including fissure sealing and tunnel preparations, must surely be an editorial oversight in a book on fixed prosthodontics. Their views on the restoration of the endodontically treated tooth are handicapped by the concept that posts reinforce. The authors of the potentially interesting chapter on ‘Stomatognathic dysfunction’ (yet another term for this well-know problem) take a broad view but their discussion of management is cursory to the point where the whole chapter would have been better omitted. The inclusion of Cerestore crowns, despite the fact that they are virtually redundant, can be forgiven if the time required to produce a text of this size is taken into account. The bibliographies at the end of each chapter are comprehensive and the illustrations are generally clear, although there is marked variability in the quality of the line diagrams. This is not a book which gives comprehensive details of procedures in fixed prosthodontics but is more for selective perusal of the useful information that can be found. Although the price is competitive, it should be borrowed rather than bought. I hope that the ninth edition is not far away as the ‘end of term report’ on the editors would have to be ‘tried hard but could have done better’. R. J. lbbetson