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Marginal adaptation
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J. Dent. 1993; 21: 265-273
Review
Marginal
adaptation
M. J. Taylor and E. Lynch* Department of Prosthetic Dentistry Hospital, UK
and *Department
of Conservative
Dentistry,
Dental School, Royal London
ABSTRACT A critical review of studies assessing the marginal adaptation of direct placement, plastic restorations is presented. The effects upon adaptation of cavity design and location of cavity margins are examined, together with the effects of differing placement and finishing techniques. Both the choice of restorative material and the use of liners/bases are shown to influence the quality of restoration margins. Techniques used in both in vivo and in vitro assessment are reviewed, however it appears that a wide variety of methodologies exist and the
establishment of standard, recommended. KEY WORDS: J. Dent. 1993)
1993;
Marginal 21:
published
adaptation,
265-273
criteria for the qualitative
Dentistry,
(Received
assessment of marginal
adaptation
is
Review
23 June
1992;
reviewed
Correspondence should be addressed to: Mr M. J. Taylor, Department School, Royal London Hospital, Whitechapel, London El 2AD, UK.
INTRODUCTION In much the same way that researchers have investigated the degree of microleakage at the tooth/restoration interface, much thought has also gone into the physical adaptation of restorative materials. This work can be broadly categorized into in vitro and in viva experimentation, although it is becoming increasingly apparent that the high degree of accuracy of modern impression materials and replication techniques allow the in viva assessment of margins to be undertaken in laboratory conditions. Thus there is much overlap between these two fields. Adaptation studies have an important role in augmenting leakage studies and the two investigations are often combined in research methodologies (Taylor and Lynch, 1992).
25 July
1992;
of Prosthetic
accepted
13 May
Dentistry and Dental
As in the case of microleakage studies, there are very many publications in the field of marginal adaptation. Although there are similarities amongst techniques used, there is not as yet a standard method for examining or measuring the adaptation of restorative .materials. Important variations exist between cavity preparation and design and the restorative technique employed. In addition, varying the restorative material may allow individual properties, such as ability to bond to dentine or postplacement water absorption, to influence marginal adaptation. Similarly, differences in finishing techniques have been shown to be an important factor, whilst perhaps the greatest variety is seen in methods of assessing marginal adaptation.
CAVITY DESIGN ADAWATION
STUDIES
Adaptation has been defined as the degree of proximity and interlocking of a filling material to the cavity wall (Jablonski, 1987). The term ‘marginal adaptation’ however is less easily defined as it has been somewhat abused as a term in the literature. The term has come to be used synonymously with adaptation at the cavosurface margin. However, it is not only at the exposed surface of the restoration that adaptation is relevant. o 1993 Butterworth-Heinemann 0300-57 12/93/050265-09
Ltd.
Cavity size Attempting to standardize cavity design within certain defined limits is possiblein vitro, especially where cavities are prepared in otherwise sound tooth substance. Cavities need to be as identical as possible to help eliminate variation between specimens. This becomes increasingly important where the behaviour of a material is influenced by its volume, as for example in the contraction which
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occurs during the polymerization of composite resins and the setting of glass polyalkenoate cements. The volumetric contraction upon curing of some composite resins and glass polyalkenoate cements has been measured by Feilzeret al. (1988) showing a range between 1.0 and 3.6% by volume after 30 s increasing to between 2.8 and 7.1% after 24 h, the smaller initial contraction being associated with the chemically setting glass polyalkenoate cements. The same workers suggest that light-curing resins demonstrate greater volumetric contraction. This may be due to the slower setting chemically activated materials allowing flow to occur within the body of the restoration as the bond to tooth substance gains strength. Subsequently absorption of oral fluids may occur and the consequent hygroscopic expansion would help compensate for polymerization contraction. Despite the obvious importance of cavity volume, few reports of adaptation studies give precise details of the cavity design used and fewer give any indication that the dimensions of the cavity are subsequently checked. Zidan et al. (1987) for example, describe the preparation of Class V cavities under a stereomicroscope and give dimensions for a ‘standard’ cavity preparation of 1.5 mm depth, 4.0 mm length and 2.5 mm width; all these dimensions are quoted as + 0.5 mm. This allows a variation in the volume of the cavity between 7.0 and 27.0 mm3. The problem of using non-standardized cavity design for in vitro research has led other workers to use mechanical devices to control cavity dimensions. Sparrius and Grossman (1989) designed a bur stop which fitted over a standard air turbine, allowing the depth of the cavity in relation to the surface contour to be controlled. More recently a similar technique using a pre-cut matrix held over the surface of the tooth (Saunders et al., 1990) has enabled workers to cut a cavity of approximately equal cavosurface dimensions. However, although approximate cavity size is quoted it is only in the research by Sparrius and Grossman that cavities were examined following preparation. In neither of the studies is any evidence given that the cavity dimensions were checked for tolerance within those quoted.
Cavity shape Whether standardized or not, cavity shape will influence adaptation. This is principally due to variations in contraction stresses within the confines of the cavity. These stresses are related both to the configuration of the cavity and the flow of unset material during the setting of the restoration. Stresses within the restoration have been shown (Davidson and Gee, 1984; Kemp-Scholte, 1989) to be related to the proportion of restoration which is in contact with tooth substance (bonded surface) compared with the surface area which is exposed (free surface). As the relative proportion of bonded surface to free surface increases so does the internal stress within the material. Thus the internal stresses within an incisal restoration are
less than in a Class II restoration, whilst the highest values would be expected within Class I and Class V cavities. Modifications of cavity design have been incorporated and tested in a number of investigations. The bevelling of enamel margins prior to etching has been shown to reduce leakage (Blunck and Roulet, 1989; Holtan et al., 1990) although standardization of enamel bevel has not been reported. Holtan ef al. have reported marginal failure in etched, bevelled enamel margins following artificial ageing of the restorative resin using a thermocycling technique. Other workers using saucer-shaped preparations with shallow depth and long bevels into both enamel and dentine (Krejci and Lutz, 1990) have shown improved adaptation to enamel, but few restorations were considered to maintain an adequate seal in dentine. Material testing using ‘standard’ wedge-shaped Class V cavities has been reported by a number of authors (Hembree and Andrews, 1978; Barkmeier and Cooley, 1989; Fitchie et al., 1990; Prati et al., 1991) in an attempt to artificially reproduce abrasion and erosion lesions. In such cavities the bonded surface area/free surface area ratio is lower than for cylindrical cavities with similar free surface areas. However, it should be considered that increasing the internal angle of the wedge will result in longer bevels to the cavosurface margin; thus standardizing this angle is essential to prevent the introduction of further variables. Unfortunately in none of the studies examined were the angles quoted nor was any indication given that reproduction of these angles was attempted. Cylindrical Class V cavities (Hansen, 1985, 1986; Munksgaard et al., 1985; Kamel et al., 1990; Chigira et al., 1991) have all been used to demonstrate the poor adaptation of composite materials, when placed in dentine cavities with butt-joint margins.
LOCATION
OF CAVITY MARGINS
Enamel and dentine
margins
An important distinction needs to be drawn between cavity designs where the cavity margins are placed in enamel only, enamel and dentine or solely dentine. As already described, use of etching techniques enable composite restorations to gain high shear bond strengths to enamel while in dentine the marginal integrity of the restoration relies upon comparatively poor micromechanical retention. Consequently contraction stresses of materials during setting are more likely to cause noticeable effects at the dentine margin where the strength of the bond will be less than that of the mechanical bond in enamel. Nevertheless, the majority of restorative material studies continue to be in test cavities cut half in enamel and half in dentine (so-called ‘mixed restorations’ -Krejci and Lutz, 1990). It must be noted that in the assessment of a material’s marginal behaviour these studies are only relevant to materials placed in this way.
Taylor and Lynch: Marginal
adaptation
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Cementum margins
INCREMENTAL PLACEMENT TECHNIQUES
Few studies of the effects of cementum on marginal adaptation exist. It appears that in vitro it is difficult to obtain specimens with an intact, exposed cemental surface (Phair and Fuller, 1985; Staninac et al., 1985). Consequently there is a largely anecdotal opinion that cementum plays little part in the sealing of restoration margins. Hargreaves et al. (1989) however have shown well-developed cementum margins in Class V cavities. The effect of this layer of tissue must therefore merit further investigation.
In the use of polymerizing resins, care must be taken during placement to minimize the effects of shrinkage whilst the maximum degree of polymerization can take place. Workers are agreed that the use of an incremental filling technique helps satisfy both these criteria, although the method of placing increments of resin varies. Studies of adaptation both in vivo and in vitro concentrate upon the analysis of Class II and Class V cavities. While adaptation of restorative materials in Class II cavities has been compared using different insertion techniques (Ciucchi et al., 1990; Eakle and Ito, 1990) and with incremental placement (Fisbein et al., 1988; Lutz et al., 1991), it is the restoration of Class V cavities which will be reviewed here. Work by Hansen (1986) has shown that the adaptation of the external surface of the restoration can be improved with the placement and curing of resins using an incremental technique. Two methods were compared by Hansen who showed that the maximum marginal gap increased when the material was placed in parallel increments rather than in layers placed obliquely (Fig. 1). It was also shown that placement and curing of the gingival increment first reduced the marginal gap formation further. This is consistent with the reduction of stress within the material caused by decreasing the bonded surface area. Work by Zidan et al. (1987) tends to support the concept of incremental placement. This study added a third oblique placement of resin in Class V cavities cut half in enamel and half in dentine. Zidan and co-workers demonstrated that the most common site for marginal failure was at the gingival wall rather than axially, supporting the principle that the cause of failure in such cavities was the differential bond strength between acidetched enamel and dentine bonding agent as the material polymerizes. Despite this evidence, the restoration of Class V cavities in dentine using a parallel incremental technique seems to have a high clinical success rate (Sheth et al., 1987) while the placement of a restorative material in one bulk continues in in vitro studies (Koike et al., 1990; Rigsby et al., 1990) as this gives a more severe test of marginal gap formation. Other workers (Blunck and Roulet, 1989; Krejci and Lutz, 1990) however prefer to use an incremental technique in laboratory studies of materials in extracted teeth. This method is therefore more representative of the dimensional changes that would be expected in the clinical situation,
RESTORATION PLACEMENT, INTERNAL AND EXTERNAL ADAPTATION Hansen (1986) points out that the methods used to measure volumetric contraction of restorative materials give no guide to the effect clinically upon wall-to-wall contraction. This discrepancy seems due to the formation of bonds between the material and cavity walls during the setting reaction. Hansen’s study also reveals one of the major oversights in the field of marginal adaptation. His study of restorations placed in cylindrical dentine buttjoint cavities has shown that the degree of contraction at the cavosurface margin was not affected by changes in the cavity depth (between 0.5 and 3.0 mm). Unfortunately no sectioning of the specimens was carried out and so it is not possible to identify where contraction gaps (if any) occurred. It seems likely that, as no increase in marginal gap occurred at the surface of the restoration, contraction shrinkage would be demonstrated elsewhere within the cavity, either by failure within the material (cohesive failure) or at the floor of the cavity or another of the internal margins (adhesive failure). It seems that this form of marginal adaptation (i.e. adaptation to the internal dimensions of the cavity form) is mostly ignored while workers concentrate upon the measurement and reduction of gaps at the external surface. While such aims are laudable, there is no doubt amongst current research that the cavosurface margins of restorations placed in dentine remain inadequate at providing a satisfactory seal. The effects of poor internal adaptation of a restorative material can therefore only further compromise the pulp-dentine complex. Recent studies which include examination of the adaptation of materials to the cavity walls exist, but these are generally either purely descriptive (Suzuki et al., 1989) or discuss adaptation findings incidental to leakage study (Davila et al., 1988). A more recent study by Hegarty and Pearson (1990) has examined closely the effects of polymerization shrinkage upon the restoration walls. However, while some time is spent upon description of the material and behaviour of tooth structure, it is only discussed in terms of the effect upon the flexing of cusps in Class II restorations.
Fig. 7. Two methods of placing incremental restorations: parallel and oblique placement. (After Hansen, 1986.)
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Thus it appears that two techniques are presently used for in vitro studies. The multiple increment technique is now widely accepted in restorative dentistry and is used in research to resemble the clinical behaviour of a material. The bulk placement technique in which the cavity is restored in a single polymerization, leaving a slight excess to compensate for shrinkage to be removed at the finishing stage, unfortunately shows the greatest degree of marginal opening and is used to demonstrate the limitations of a material. In experimental situations, however, the bulk placement technique can be used to eliminate variations caused by the placement of two or more increments of material of uncontrolled volume.
CHOICE OF MATERIAL OF ACTIVATION
AND METHOD
As has already been discussed, the means by which a material hardens will determine the pattern and effect of its setting contraction. It is well known that the setting reaction of chemically curing and light-activated restorative materials differs in that chemically cured restorations set from the centre of the material’s bulk while lightactivated materials polymerize first nearer to the light source. Speed of setting will also affect the development of stresses within the restoration. The flow which occurs during the relatively slower setting of chemically cured materials is quoted as reducing the effect of polymerization contraction and hence marginal gap formation (Hansen, 1986). During the setting reaction of conventional glass polyalkenoate cements the stresses induced by contraction are more likely to be distributed by cohesive failure within the material, while in polymerizing resins the greater cohesive strength together with the reduced adhesion to dentine is more likely to induce adhesive failure and so marginal gap formation (Davidson, 1988). Dual curing materials, particularly the light/chemically cured composite resins, would be expected to show better adaptation if chemical curing were allowed to occur first. This chemical reaction would allow a more favourable flow of the unset material than the more rapid lightactivated reaction. In the case of the dual curing glass polyalkenoate cements the situation is more difficult to determine due to their complex setting chemistry. Light-activated resins polymerize more rapidly nearer to the light source and hence contraction will also be in this direction. This is contrary to the effect of chemically cured materials where contraction towards the faster setting centre of the restoration is expected. This contraction toward polymerizing resin may be used to some advantage if it is possible to cure small increments of material through the tooth. This would theoretically pull the material against the cavity margin as it polymerized, thus improving adaptation. This is supported by the work of Lutz et al. (1986).
EFFECT OF LINERS/BASES ADAPTATION
UPON
The adaptation of restorative materials will be affected by any substance with which they are in contact. The rapid development of dentine bonding agents has led to much research into their effect upon the adaptation of composite resins. However comparatively little study of the effect of liners and bases upon adaptation to the internal margins of cavities has been carried out (Al-Hamadani and Crabb, 1975, Davilaetaf., 1988).The use of conventional Class III glass polyalkenoate cements (Wilson and McLean, 1988) and their light-cured counterparts which adhere to dentine and can be bound by composite resins has significance in the adaptation of the cured restoration to the cavity floor and adjacent internal margins. Scherer et al. (1989) have suggested that the force due to polymerization contraction within composite resins exceeds the bond strength between glass polyalkenoate cement base and dentine. This may be particularly true when glass polyalkenoate liners/bases are freshly placed and their bond to dentine is not yet fully established. Because of the effect of this force, the authors question the wisdom of etching the surface of glass polyalkenoate liners/bases, implying that the failure of the composite/ base bond has less serious implications than the failure of the base/dentine bond. It is apparent that the use of a base/liner which bonds to the dentine surface less than to the restorative material will allow internal failure at the cavity floor during polymerization (Papadakou et al., 1990). Internal failure between restorative material and base/liner could
Fig. 2. Theoretical gap formation related to bond strengths between restoration, base material and tooth. a, Restoration and base prior to polymerization. Following polymerization of restoration: b, bond of restorative material to base exceeds bonding of base to dentine-gap forms between base and dentine; c, bond of base material to dentine exceeds bond to restorative material-gap forms between restorative material and base.
Taylor and Lynch: Marginal adaptation
theoretically have a substantially different effect. If an insoluble base material is used which has a high bond strength to dentine, while at the same time having a poor affinity for the restorative material, then, on contraction of the restorative material, a gap will be formed between base and restoration. As there is no bonding of the restorative material to the floor of the cavity there would be no contraction of the restorative material in this direction. Consequently the surface adaptation of the material could in theory be improved. As the internal gap formed on contraction is isolated from tooth substance by an insoluble layer, the potential for damage to the pulpdentine complex is minimized. An additional element may be the later hygroscopic expansion of the restoration, contributing to the obliteration of the contraction gap. The theoretical differences between the two situations described (i.e. where the restoration/base bond is stronger than the base/dentine bond and vice versa) are illustrated by Fig. 2.
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Kemp-Scholte (1989), concludes, however that the sealing of restoration margins with an unfilled lowviscosity resin, with adequate penetration and hardening properties can result in perfectly sealed restorations. BrSinnstr(Sm (1985) has reported the flow of such resin, with a fluorescent marker, several millimetres into restorations. Obviously such finishing techniques and their effects upon the ultimate adaptation of the restorative material justify further investigation.
ASSESSMENT OF CAVITY MARGINS There are fortunately fewer methods used in the assessment of marginal adaptation than those associated with microleakage. Effectively these methods can be classified as in vitro or in tivo, although as mentioned earlier laboratory assessment of clinical cases can be carried out. In vivo assessment
EFFECT OF FINISHING METHODS UPON MARGINAL ADAPTATION Variation in finishing techniques has been shown to affect the ability of restorative materials to resist leakage. This is likely to be due to heat generated locally during the polishing process. Dodge ef al. (1991) suggest that for at least one of the materials they investigated, the surface temperature was raised sufficiently to obtain the glass transition point for the resin tiller particles resulting in a significantly improved surface. Their results suggest that in the majority of cases a dry finishing technique is equal or superior to wet finishing when using aluminium oxidecoated finishing discs. Yu et al. (1990) examining the effects of finishing techniques upon microleakage however show an increase in leakage with a dry polishing disc technique, suggesting poorer marginal adaptation, and recommend the use of water-cooled tungsten carbide finishing burs. The discrepancy between the results may be due to the use of restorations placed in Lucite blocks in the former study, while Yu and co-workers used mixed restorations in extracted human teeth. It should be noted that the Yu study looked only at leakage present at the dentinal interface and is not a guide to the behaviour of materials in enamel. Although at least two studies have shown that the use of aluminium oxide finishing techniques can cause surface cracking of resin restorations (Lambrechts and Vanherle, 1982), this technique continues to be widely employed. Davidson et al. (1981) have shown that a dry finishing technique using Soflex (3M) discs can cause structural and chemical changes at the surface of the restoration. Lambrechts and Vanherle suggest that this may be part of the reason why, in their study of the post-finishing glazing of composites, all glazing agents applied to the surface of resins finished in this way were eventually lost.
Clinical assessments of margin quality are carried out by dentists every day, many using their individual method of subjective assessment. This explains the degree of variation between treatment planning decisions, particularly in the replacement of existing restorations (Dedmon, 1982; Elderton and Nuttall, 1983). It was early recognition of the subjective difficulties in assessing restorations that contributed to the development of a systematic approach. This was first described by McCune et al. in 1967 and has since been adopted as the US Public Health Service Criteria (Ryge Criteria, Cvar and Ryge, 1971; Ryge, 1981). Using this system, restorations are systematically evaluated using mirror and probe, and the quality of margin assessed in terms of occlusal form, cavosurface marginal discoloration and marginal adaptation. These categories are then graded according to three levels of performance ‘Clinically ideal’, ‘Clinically acceptable’ and ‘Clinically unacceptable’. Subjective assessment can however still cause problems in determining the true marginal quality. The limitations of man’s ability to detect marginal ledges using a probe has been described by Leinfelder et al. (1982), who determined that the smallest ledge which could be clinically detected measured 100 pm (0.1 mm). As restorative materials improve in quality and in their ability to adapt closely to cavity form, more sensitive methods of detecting gaps and ledges become necessary. These have included the use of cast stone study models and clinical photography (Mahler and Marantz, 1979; Osborne et al., 1980), where either rating scales were used based upon defined criteria or photographs were simply arranged in order from best to worst. Thus reproduction of the clinical situation for later assessment and comparison becomes possible. Clinical studies continue to have most relevance in dental materials testing although some clinical trials give
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little useful information. Sheth et al. (1988) report a trial of cervical restorations using a microfilled composite resin in which the results are classified as restorations lost, evidence of recurrent decay and ‘otherwise clinically acceptable’. No details of a standardized clinical assessment are given or the criteria used to reach such diagnoses. Jordan et al. (1989) in a comparable study used a modified version of the Cvar and Ryge system to classify retention, colour stability and marginal integrity, together with abrasion resistance, surface texture/staining and postoperative sensitivity. However, in their discussion of results the authors make broad assumptions that the high rates of retention of their restorations were related to the dentine bonding agents under test and their ability to resist the polymerization contraction of the composite resin. As only visual and tactile examination were used it may be possible that gaps at the margins of the restoration of less than 100 urn (Leinfelder et al., 1982) had passed unnoticed. In vitro studies in which examination of the restoration margin is conducted in the laboratory are considered in the following section. In vitro assessment In vitro assessment of marginal adaptation can be carried
out on extracted teeth either by direct observation or indirectly using a replication technique such as the production of study models, photographs or replicas for future electron microscope examination. These techniques can also be applied to the assessment of in vivo studies. Profilometery The use of profilometery in both in tivo and in vitro studies has been reported (Lambrechts and Vanherle, 1982; Roulet, 1987).These use a line stylus which is moved against the surface of a restoration. The vertical movements of the stylus can be recorded and magnified to give a picture of the surface profile of a material. This technique however is usually confined to the assessment of wear on restoration surfaces or the condition of such surfaces as they deteriorate with age. It is not generally applied to the assessment of marginal gap formation. Measurement
of coordinates
Various techniques exist by which coordinates marked on a replica can be used to compare changes in surface detail, Most systems use computerized techniques to calculate the differences involved, while the systems themselves can range in complexity from simply cutting reference points on teeth (Lambrechts et al., 1989) to complex measurements using laser scanning equipment (DeLong et al., 1989). These systems are again principally designed to compare changes such as minute losses of surface tissue;
they are not designed to measure the marginal opening of restorations. Two methods currently used in the assessment of restoration margins are light and electron microscopy.
Light microscopy While investigating the changes in marginal gap which occur with exposure of the restoration to water, Asmussen and Jorgensen (1972) used a camera microscope fitted with a measuring eyepiece allowing calibrated measurement of the order of X 425. Using this arrangement the authors classified marginal defects between resin and tooth as: (1) extensive; (2) sporadic, and (3) with no evidence of fracture or broken enamel. The workers reported difficulties in obtaining consistency in the classification of groups (1) and (2) although group (3) produced no such problem. This kind of difficulty in subjective assessment is not uncommon. The use of a screw micrometer mounted upon a light microscope has recently been reported by one group (Koike et al., 1990; Chigira et al., 1991). This is quoted as allowing magnification to X 1024 and has been used to accurately assess marginal gaps with a view to determining the percentage volumetric contraction of a material when placed in cylindrical dentine cavities. In both papers the maximum contraction is then related to the ‘bonding efficiency’ of the resin or intermediary bonding agent. The use of stereomicroscopy has been reported by Zidan et al. (1987). In their study of mixed cavities they assessed the simple presence or absence of dye visible at the tooth/restoration interface. While this provides a qualitative assessment of the margin quality it is unfortunate that while using such magnification the authors did not report quantitative information about gap size. All the light microscope studies reported were carried out on extracted teeth rather than replicas and as such are true in vitro studies.
Scanning
electron
microscopy
The use of the scanning electron microscope (SEM) in dental research has increased dramatically in the past 20 years. One of the first dental studies carried out using SEM techniques has been reported by Lee and Schwartz (1970). This study was conducted on sectioned tooth tissue and attempted to relate marginal leakage as assessed by 45Ca autoradiography to the appearance of cavity margins as seen under SEM magnification. Unfortunately, however, the workers found no relationship between the two methods of assessment. This is likely to be due to the comparative novelty of the SEM and unfamiliarity with the techniques used. Although the authors point out that no heat or radiation damage of the specimens occurred during examination, Davila et al. (1988) point out that severe drying of specimens is required prior to SEM evaluation. As dentine has a high
Taylor and Lynch:
Table 1. Examples of criteria in the qualitative assessment of marginal quality (MCI) MQI - Excellent Margin (EM)* MQ2 - Submargination (SM)* MQ3 -Overhang (OH)* MQ4 - Marginal Opening (MO)* MQ5 - Restoration fracture (RF)* MQ6 - Enamel fracture (EF)* MQ7-MO+SM
MQ8 -MO MQ9 -MO MQIO-MO MQll -SM MQ12-SM MQ13-OH MQ14-OH
+OH +RF + EF +RF + EF + RF + EF
From Roulet et al. (199 1) *Quality criteria actually reported.
it is likely that artefactual gaps and water content distortion of the specimen will occur. Using tooth substance for analysis has major disadvantages in the electron microscope. If artefactual damage occurs due to desiccation of the specimen then original material will be lost. As with tooth sectioning in the study of microleakage, use of original material in the SEM obviates the use of longitudinal studies. Because of this most workers now favour some form of replication technique.
SEM ANALYSIS OF REPLICAS The SEM analysis of marginal adaptation using replicas is now widely accepted as an accurate method of assessment. Specimens for examination are prepared by the removal of debris using sodium hypochlorite solution to dissolve any organic material including plaque. Such techniques have been reported in tivo following rubber dam isolation of the tooth to be examined (Roulet et al., 1991). ‘Scavenging’ impressions have been used (Roulet, 1987) to remove surface debris before the final impression for replication is taken. The use of polyvinylsiloxane impression materials is widely recommended because of their high degree of dimensional stability (Pameijer, 1979). Epoxy replicas are formed using various resins which have other applications in the field of scanning electron microscopy. Stycast Resin (Emerson & Cummings, Belgium) seems particularly popular amongst investigators (Roulet et al., 1989, 1991; Krejci and Lutz, 1990; Lui et al., 1987), although examination of the literature reveals no significant differences between the quality of surface detail reproduction with this and other epoxies in common use. It seems that selection of resin may be based upon personal preference. Whatever material is used to fabricate a positive replica, it must be remembered that any inaccuracies at either stage of replication will be recorded and that technically it is not possible to produce a positive replica of the same accuracy as its original or negative. Fortunately these errors appear not to affect research on positive replicas and this difficulty is not mentioned in discussions. The examination of impression surfaces (negatives) has been reported (Suzuki et al., 1989) and the quality of reproduction has been compared with original tissue (Davila et al., 1988), suggesting that gaps on original tissue
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appeared larger than on the negative. This may however be due to change occurring within the original specimen during its preparation for viewing under the SEM, although the authors also report better detail on the surface of the original. Marginal assessment using positive replicas mainly uses a qualitative assessment technique assessing the margins as ‘Perfect/Excellent’, ‘Overfilled’, ‘Underfilled’, or as exhibiting ‘Marginal opening’ (Ciucchi et al., 1990); other scoring systems include distinctions between marginal tooth fracture and marginal restorative fracture (Krejci and Lutz, 1990). A quantitative technique for marginal analysis has been developed and described by Roulet et al. (1989) and Blunck and Roulet (1989), involving the examination of epoxy replicas with computerized image analysis. However, although using this technique the examiners record the entire circumference of the cavity, it is a qualitative assessment that is recorded for every point along the margin. Thus a percentage of each form of marginal quality can be expressed for the complete restoration. While there is much to commend this technique, including its ability to precisely compare different examiners’ assessments for any given point, the use of the term ‘Quantitative marginal analysis’ could be open to misinterpretation as it is only the length of the margin that is quantified and not the size of any opening which may exist. Use of this technique has been applied to replicas obtained from a longitudinal clinical study of Class II restorations (Roulet et al., 1991). This study assessed marginal quality using a 14-point scale based upon six criteria. The authors felt however that such a large scale did not allow the materials’ behaviour to be clearly shown and reduced this to a 6-point scale of which 5 were reported (Table I). Although criteria for assessment are frequently mentioned in qualitative studies, these are rarely described in detail even when (Table I) their definition may seem obvious. It would be interesting to compare different workers’ criteria for the classification of marginal adaptation perhaps with a view to providing standard definitions. True quantitative assessment where marginal gaps are actually measured are comparatively rare. The measurement of maximal marginal opening using epoxy replicas is described by Al-Hamadani and Crabb (1975) and Rigsby et al. (1990). Despite the 15-year interval between the studies, the techniques used remain fundamentally the same. Assessment of maximum gap is carried out under the SEM and photomicrographs are taken of the area exhibiting the greatest marginal opening. Measurements from the photomicrographs can then be later converted using the scale bars provided to give the actual gap size. There are however fundamental problems with this technique in that assessment of marginal gap is made initially by the operator from the screen of the SEM. If (as is sometimes necessary) the entire margin of the
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restoration needs to be checked, at X 2000 magnification a 3 mm diameter circular cavity can have an effective circumference of 18.85 m (ITX 3 X 1O-3 X 2 X lo3 = 18.85 m). As it is unlikely that the screen will allow more than an effective length of 30 cm to be viewed at one time, this means: 1. Observation of the entire margin will be time consuming. 2. Without some form of measuring device attached to the microscope stage it will be difficult to relocate the area of maximum opening once determined. 3. There is no detail of how the maximum gap is assessed. If this is a subjective assessment based upon visual interpretation and memory of previous gaps along the same margin then the validity of the photomicrographs providing a definitive measurement of maximum opening must be questioned. Some SEM screens now have the capability to make direct measurements which may aid the examiner. Interpretation of marginal appearance whether for quantitative or qualitative assessment will also be affected by the angle at which the margin is viewed. Wherever possible the margins should be viewed in a plane parallel to that of the cut surface of the cavity. This becomes essential when measurements are to be taken, as slight changes in angulation from this parallel axis will result in the gap appearing smaller than is actually the case. SUMMARY There is much active work in the field of marginal adaptation assessment and it is apparent that researchers must become more technically advanced as restorative materials improve. Review of the literature reveals areas which need attention. The following are suggested: 1. Recognition that marginal adaptation at the cavosurface margin is only one part of the adaptation picture. This may help to improve understanding of the behaviour of materials within the cavity including the effects of liners/bases upon adaptation. 2. Variation in studies of adaptation could be further reduced by improving methods of cutting test cavities of standard dimensions. 3. Further investigation into the role of the cemental layer upon bonding and adaptation of materials used in the restoration of cervical lesions. 4. The establishment of standard, published criteria for the qualitative assessment of marginal adaptation under the SEM (in a similar fashion to the use of the Ryge Criteria clinically) together with standard methodologies in the quantitative measurement of marginal opening. References Al-Hamadani adaptation
K. K. and Crabb H. S. (1975) Marginal of composite resins. .I. Oral Rehabil. 2, 21-33.
Asmussen E. and Jorgensen K. D. (1972) A microscopic investigation of the adaptation of some plastic tilling materials to dentin cavity walls. A& Odontol. Stand. 30, 3-21. Barkmeier W. W. and Cooley R. L. (1989) Resin adhesive systems: in vitro evaluation of dentin bond strength and marginal microleakage. J. Esthetic. Dent. 1, 67-72. Blunck U. and Roulet J-F. (1989) In vitro marginal quality of dentin-bonded composite resins in Class V cavities. Quintessence Int. 20, 407-412. Brannstrom M. (1985) Composite resin restorations: biological considerations with special reference to dentin and pulp. In: Vanherle G. & Smith D. C. (eds), Posterior Composite Resin Dental Restoration Materials. Minnesota, 3M, pp. 71-81. Ciucchi B., Bouillaguet S. and Holz J. (1990) Proximal adaptation and marginal seal of posterior composite resin restorations placed with direct and indirect techniques. Quintessence ht. 21, 663-669. Chigira H., Itoh K. and Wakumoto S. (1991) Marginal adaptation of nine commercial intermediate resins. Dent. Mater. 7, 103-106. Cvar J. F. and Ryge G. (1971) Criteria for the Clinical Evaluation of Dental Restorative Materials. US PHS Publication. 790-244. US Government. Darbyshire P. A., Messer L. B. and Douglas W. H. (1988) Microleakage in Class II composite restorations bonded to dentin using thermal and load cycling. J. Dent. Res. 67, 585-587. Davidson C. L. and De Gee A. J. (1984) Relaxation of polymerization contraction stresses by flow in dental composites. J. Dent. Res. 63, 146-148. Davidson C. L., Duysters P. P. E., DeLange C. et al. (1981) Structural changes in composite surface materials after dry polishing. J. Oral Rehabil. 8,431-438. Davila J. M., Gwinnett A. J. and Robles J. C. (1988) Marginal adaptation of composite resins and dentinal bonding agents. ASDC J. Dent. Child. 55,25-28. Dedmon H. W. (1982) Disparity in expert opinions on size of acceptable margin openings. Oper. Dent. 7, 97-101. DeLong R., Peterson R. and Douglas W. H. (1989) A laser profiling system for measuring wear of dental materials. lADR Abstract 328. Dodge W. W., Dale R. A., Cooley R L. et al. (1991) Comparison of wet and dry finishing of resin composites with aluminium oxide discs. Dent. Mater. 7, 18-20. Eakle W. S. and Ito R. K. (1990) Effect of insertion technique on microleakage in mesio-occlusodistal composite resin restorations. Quintessence Int. 21, 369-374. Elderton R. J. and Nuttall N. M. (1983) Variation among dentists in planning treatment. Br. Dent. J. 154,201-206. Feilzer R. J., De Gee A J. and Davidson C. L. (1988) Measuring contraction of composites and glass ionomer cements. J. Prosthet. Dent. 59, 297-300. Fisbein S., Holan G., Grajower R. et al. (1988) The effect of VLC Scotchbond and an incremental tilling technique on leakage around Class II composite restorations. ASDC .I Dent. Child. 55, 29-33. Hansen E. K. (1986) Effect of cavity depth and application technique on marginal adaptation of resins in dentin cavities. J. Dent. Res. 65, 1319-1321. Hansen E. K. (1987) Effect of Gluma in acid etched dentin cavities. Stand. J. Dent. Res. 95, 181-184. Hargreaves J. A, Grossman E. S. and Matejka J. M. (1989) Scanning electron microscope study of prepared cavities involving enamel, dentin and cementum. J. Prosthet. Dent. 61, 191-197. Hegarty S. M. and Pearson G. J. (1990) The effectiveness of dentine adhesives as demonstrated by dye penetration and SEM investigations. J Oral Rehabil. 17, 351-357.
Taylor and Lynch: Marginal adaptation
Jablonski S. (1987) Illustrated Dictionary of Dentistry, 1st edn. Philadelphia, W.B. Saunders. Kamel F. M., Retief D. H., Madras R. S. et al. (1990) A laboratory study of the Herculite XR system. Am. J. Dent. 3, 271-277. Kemp-Scholte C. M. (1989) The Marginal Integrity of Cervical Composite Resin Restorations. Doctoral Thesis, University of Amsterdam. Koike T., Hasegawa T., Manabe A et al. (1990) Effect of water sorption and thermal stress on cavity adaptation of dental composites. Dent Mater. 6, 178-180. Krejci I. and Lutz F. (1990) Mixed Class V restorations: the potential of a dentine bonding agent. J. Dent l&263-270. Lambrechts P. and Vanherle G. (1982) Observation and comparison of polished composite surfaces with the aid of SEM and profilometer. J. Oral Rehabil. 9, 169-183. Lambrechts P., Braem M., Vuysteke-Wauters M. et al. (1989) Quantitative in viva wear of human enamel. J. Dent. Res. 68, 1752-1754. Lee H. L. and Swartz M. L. (1970) Scanning electron microscope study of composite restorative materials. J. Dent. Res. 49, 149-158. Leinfelder K. F., Sockwell C. L. and Sluder T. B. (1982) Two year clinical evaluation of profile in posterior teeth. J. Dent. Res. 61, (abstr. 327), 215. Lui J. L., Masutani S., Setcos J. C. et al. (1987) Margin quality and microleakage of Class II composite resin restorations. J. Am. Dent. Assoc. 114,49-54. Lutz F., Krejci I., Luescher B. et al. (1986) Improved proximal margin adaptation of Class II composite resin restorations by use of light-reflecting wedges. Quintessence Znt 17, 659-664. Lutz F., Krejci I. and Barbakow F. (1991) Quality and durability of marginal adaptation in bonded composite restorations. Dent. Mater. 7, 107-113. McCune R. J., Johnson B. E., Cvar J. F. et al. (1967) Clinical comparison for posterior restorative materials. J. Dent. Res. 46, (spec. iss.), (abstr. 175), 546. Mahler D. B. and Marantz R. L. (1979) The effect of time on the marginal fracture behaviour of amalgam. J. Oral Rehabil. 6, 391-398. Osborne J. W., Leinfelder K. F., Gale E. N. et al. (1980) Two independent evaluations of ten amalgam alloys. J. Prosthet. Dent. 43, 622-626. Pameijer C. H. (1979) Replication techniques with new dental impression materials in combination with different negative impression materials. Scan. Electron Microsc. 2, 571-574.
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Papadakou M., Barnes I. E., Wassall R. W. et al. (1990) Adaptation of two different calcium hydroxide bases under a composite restoration. J. Dent. 18, 276-280. Phair C. B. and Fuller J. L. (1985) Microleakage of composite resin restorations with cementum margins. J. Prosthet. Dent. 53, 361-364. Prati C., Nucci C. and Montanari G. (1991) Shear bond strength and microleakage of dentin bonding systems. J. Prosthet. Dent. 65, 401-407. Rigsby D. F., Retief D. H., Russell C. M. et al. (1990) Marginal leakage and marginal gap dimensions of three dentinal bonding systems. Am. J. Dent 3, 289-294. Roulet J-F. (1987) In: Degradation of Dental Polymers, 1st edn. Basel, S, Karger AG, pp, 92-113. Roulet J-F., Reich T., Blunck U. et al. (1989) Quantitative margin analysis in the scanning electron microscope. Scan. Electron Microsc. 3, 147-159. Roulet J-F., Salchow B. and Wald M. (1991) Margin analysis of posterior composites in vivo. Dent Mater. 7, 44-49. Ryge G. (1981) Clinical criteria. Znt. Dent.1 30, 347-358. Saunders W. P., Grieve A. R., Russell E. M. et al. (1990) The effects of dentine bonding agents on marginal leakage of composite restorations. .Z. Oral Rehabil. 17, 519-527. Scherer W., Kaim J. M., Lippman X et al. (1989) Microleakage of three glass ionomer cement bases. Am. J. Dent 2, 61-63. Sparrius 0. and Grossman E. S. (1989) Marginal leakage of composite resin restorations in combination with dentinal and enamel bonding agents. J. Prosthet Dent 61, 678-684. Staninac M., Mochizuki A,Tanizaki K. et al. (1985) Effect of etching and bonding on recurrent caries in teeth restored with composite resin. J. Prosthet Dent 53, 521-525. Suzuki M., Gwinnett A. J. and Jordan R. E. (1989) Relationship between composite resins and dentine treated with bonding agents. J. Am. Dent. Assoc. 118, 75-77. Taylor M. J. and Lynch E. (1992) Microleakage. J. Dent. 20, 3-10. Wilson A. D. and McLean J. W. (1988) In: Glass Zonomer Cement, 1st edn. Quintessence. Yu X. Y., Wieczkowski G., Davis E. L. et al. (1990) The influence of finishing technique on microleakage. J. Esthetic Dent 2, 142-144. Zidan O., Gomez-Marin 0. and Tsuchiya T. (1987) A comparative study of the effect of dentinal bonding agents and application techniques on marginal gaps in Class V cavities. J. Dent. Res. 66, 716-721.
Book Review Pathobiologie Oraler Strukturen. H. H. Schroeder. Pp. 266. 199 1. Basle, S. Karger AG. Softback, f 20.00. This is an extended and revised edition of a textbook, the first edition of which appeared in 1983. It is organized in the classical way, starting with inherited and acquired developmental disturbances followed by age-related changes in the teeth, tooth fractures, discolorations, caries and erosion, root resorption, changes in the pulp and periodontal tissues, periodontal regeneration and wound healing. The text is short and clear and well supported by numerous clinical and histological illustrations as well as schematic drawings. There is an impressive collection of data and references. The wealth of information may make it hard to read but the
systematic organization of each chapter and the fact that important statements and definitions are specifically marked, facilitates reading and improves the educational value of the text. Treatment of diseases of the dental hard tissues occupies most of the working day of a practising dentist and it is surprising that there are so few books dealing with the pathology of these tissues. This is a good textbook for the dental student. For the dentist, it updates and deepens the knowledge of the tissues he or she is working with every day. A detailed knowledge of the pathobiology of the dental tissues is of fundamental importance for proper patient care today and for the development of the new treatment procedures of tomorrow. This is why this book is important. L. Hammarstrbm
J. Dent. 1993; 21: 265-273
Review
Marginal
adaptation
M. J. Taylor and E. Lynch* Department of Prosthetic Dentistry Hospital, UK
and *Department
of Conservative
Dentistry,
Dental School, Royal London
ABSTRACT A critical review of studies assessing the marginal adaptation of direct placement, plastic restorations is presented. The effects upon adaptation of cavity design and location of cavity margins are examined, together with the effects of differing placement and finishing techniques. Both the choice of restorative material and the use of liners/bases are shown to influence the quality of restoration margins. Techniques used in both in vivo and in vitro assessment are reviewed, however it appears that a wide variety of methodologies exist and the
establishment of standard, recommended. KEY WORDS: J. Dent. 1993)
1993;
Marginal 21:
published
adaptation,
265-273
criteria for the qualitative
Dentistry,
(Received
assessment of marginal
adaptation
is
Review
23 June
1992;
reviewed
Correspondence should be addressed to: Mr M. J. Taylor, Department School, Royal London Hospital, Whitechapel, London El 2AD, UK.
INTRODUCTION In much the same way that researchers have investigated the degree of microleakage at the tooth/restoration interface, much thought has also gone into the physical adaptation of restorative materials. This work can be broadly categorized into in vitro and in viva experimentation, although it is becoming increasingly apparent that the high degree of accuracy of modern impression materials and replication techniques allow the in viva assessment of margins to be undertaken in laboratory conditions. Thus there is much overlap between these two fields. Adaptation studies have an important role in augmenting leakage studies and the two investigations are often combined in research methodologies (Taylor and Lynch, 1992).
25 July
1992;
of Prosthetic
accepted
13 May
Dentistry and Dental
As in the case of microleakage studies, there are very many publications in the field of marginal adaptation. Although there are similarities amongst techniques used, there is not as yet a standard method for examining or measuring the adaptation of restorative .materials. Important variations exist between cavity preparation and design and the restorative technique employed. In addition, varying the restorative material may allow individual properties, such as ability to bond to dentine or postplacement water absorption, to influence marginal adaptation. Similarly, differences in finishing techniques have been shown to be an important factor, whilst perhaps the greatest variety is seen in methods of assessing marginal adaptation.
CAVITY DESIGN ADAWATION
STUDIES
Adaptation has been defined as the degree of proximity and interlocking of a filling material to the cavity wall (Jablonski, 1987). The term ‘marginal adaptation’ however is less easily defined as it has been somewhat abused as a term in the literature. The term has come to be used synonymously with adaptation at the cavosurface margin. However, it is not only at the exposed surface of the restoration that adaptation is relevant. o 1993 Butterworth-Heinemann 0300-57 12/93/050265-09
Ltd.
Cavity size Attempting to standardize cavity design within certain defined limits is possiblein vitro, especially where cavities are prepared in otherwise sound tooth substance. Cavities need to be as identical as possible to help eliminate variation between specimens. This becomes increasingly important where the behaviour of a material is influenced by its volume, as for example in the contraction which
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occurs during the polymerization of composite resins and the setting of glass polyalkenoate cements. The volumetric contraction upon curing of some composite resins and glass polyalkenoate cements has been measured by Feilzeret al. (1988) showing a range between 1.0 and 3.6% by volume after 30 s increasing to between 2.8 and 7.1% after 24 h, the smaller initial contraction being associated with the chemically setting glass polyalkenoate cements. The same workers suggest that light-curing resins demonstrate greater volumetric contraction. This may be due to the slower setting chemically activated materials allowing flow to occur within the body of the restoration as the bond to tooth substance gains strength. Subsequently absorption of oral fluids may occur and the consequent hygroscopic expansion would help compensate for polymerization contraction. Despite the obvious importance of cavity volume, few reports of adaptation studies give precise details of the cavity design used and fewer give any indication that the dimensions of the cavity are subsequently checked. Zidan et al. (1987) for example, describe the preparation of Class V cavities under a stereomicroscope and give dimensions for a ‘standard’ cavity preparation of 1.5 mm depth, 4.0 mm length and 2.5 mm width; all these dimensions are quoted as + 0.5 mm. This allows a variation in the volume of the cavity between 7.0 and 27.0 mm3. The problem of using non-standardized cavity design for in vitro research has led other workers to use mechanical devices to control cavity dimensions. Sparrius and Grossman (1989) designed a bur stop which fitted over a standard air turbine, allowing the depth of the cavity in relation to the surface contour to be controlled. More recently a similar technique using a pre-cut matrix held over the surface of the tooth (Saunders et al., 1990) has enabled workers to cut a cavity of approximately equal cavosurface dimensions. However, although approximate cavity size is quoted it is only in the research by Sparrius and Grossman that cavities were examined following preparation. In neither of the studies is any evidence given that the cavity dimensions were checked for tolerance within those quoted.
Cavity shape Whether standardized or not, cavity shape will influence adaptation. This is principally due to variations in contraction stresses within the confines of the cavity. These stresses are related both to the configuration of the cavity and the flow of unset material during the setting of the restoration. Stresses within the restoration have been shown (Davidson and Gee, 1984; Kemp-Scholte, 1989) to be related to the proportion of restoration which is in contact with tooth substance (bonded surface) compared with the surface area which is exposed (free surface). As the relative proportion of bonded surface to free surface increases so does the internal stress within the material. Thus the internal stresses within an incisal restoration are
less than in a Class II restoration, whilst the highest values would be expected within Class I and Class V cavities. Modifications of cavity design have been incorporated and tested in a number of investigations. The bevelling of enamel margins prior to etching has been shown to reduce leakage (Blunck and Roulet, 1989; Holtan et al., 1990) although standardization of enamel bevel has not been reported. Holtan ef al. have reported marginal failure in etched, bevelled enamel margins following artificial ageing of the restorative resin using a thermocycling technique. Other workers using saucer-shaped preparations with shallow depth and long bevels into both enamel and dentine (Krejci and Lutz, 1990) have shown improved adaptation to enamel, but few restorations were considered to maintain an adequate seal in dentine. Material testing using ‘standard’ wedge-shaped Class V cavities has been reported by a number of authors (Hembree and Andrews, 1978; Barkmeier and Cooley, 1989; Fitchie et al., 1990; Prati et al., 1991) in an attempt to artificially reproduce abrasion and erosion lesions. In such cavities the bonded surface area/free surface area ratio is lower than for cylindrical cavities with similar free surface areas. However, it should be considered that increasing the internal angle of the wedge will result in longer bevels to the cavosurface margin; thus standardizing this angle is essential to prevent the introduction of further variables. Unfortunately in none of the studies examined were the angles quoted nor was any indication given that reproduction of these angles was attempted. Cylindrical Class V cavities (Hansen, 1985, 1986; Munksgaard et al., 1985; Kamel et al., 1990; Chigira et al., 1991) have all been used to demonstrate the poor adaptation of composite materials, when placed in dentine cavities with butt-joint margins.
LOCATION
OF CAVITY MARGINS
Enamel and dentine
margins
An important distinction needs to be drawn between cavity designs where the cavity margins are placed in enamel only, enamel and dentine or solely dentine. As already described, use of etching techniques enable composite restorations to gain high shear bond strengths to enamel while in dentine the marginal integrity of the restoration relies upon comparatively poor micromechanical retention. Consequently contraction stresses of materials during setting are more likely to cause noticeable effects at the dentine margin where the strength of the bond will be less than that of the mechanical bond in enamel. Nevertheless, the majority of restorative material studies continue to be in test cavities cut half in enamel and half in dentine (so-called ‘mixed restorations’ -Krejci and Lutz, 1990). It must be noted that in the assessment of a material’s marginal behaviour these studies are only relevant to materials placed in this way.
Taylor and Lynch: Marginal
adaptation
267
Cementum margins
INCREMENTAL PLACEMENT TECHNIQUES
Few studies of the effects of cementum on marginal adaptation exist. It appears that in vitro it is difficult to obtain specimens with an intact, exposed cemental surface (Phair and Fuller, 1985; Staninac et al., 1985). Consequently there is a largely anecdotal opinion that cementum plays little part in the sealing of restoration margins. Hargreaves et al. (1989) however have shown well-developed cementum margins in Class V cavities. The effect of this layer of tissue must therefore merit further investigation.
In the use of polymerizing resins, care must be taken during placement to minimize the effects of shrinkage whilst the maximum degree of polymerization can take place. Workers are agreed that the use of an incremental filling technique helps satisfy both these criteria, although the method of placing increments of resin varies. Studies of adaptation both in vivo and in vitro concentrate upon the analysis of Class II and Class V cavities. While adaptation of restorative materials in Class II cavities has been compared using different insertion techniques (Ciucchi et al., 1990; Eakle and Ito, 1990) and with incremental placement (Fisbein et al., 1988; Lutz et al., 1991), it is the restoration of Class V cavities which will be reviewed here. Work by Hansen (1986) has shown that the adaptation of the external surface of the restoration can be improved with the placement and curing of resins using an incremental technique. Two methods were compared by Hansen who showed that the maximum marginal gap increased when the material was placed in parallel increments rather than in layers placed obliquely (Fig. 1). It was also shown that placement and curing of the gingival increment first reduced the marginal gap formation further. This is consistent with the reduction of stress within the material caused by decreasing the bonded surface area. Work by Zidan et al. (1987) tends to support the concept of incremental placement. This study added a third oblique placement of resin in Class V cavities cut half in enamel and half in dentine. Zidan and co-workers demonstrated that the most common site for marginal failure was at the gingival wall rather than axially, supporting the principle that the cause of failure in such cavities was the differential bond strength between acidetched enamel and dentine bonding agent as the material polymerizes. Despite this evidence, the restoration of Class V cavities in dentine using a parallel incremental technique seems to have a high clinical success rate (Sheth et al., 1987) while the placement of a restorative material in one bulk continues in in vitro studies (Koike et al., 1990; Rigsby et al., 1990) as this gives a more severe test of marginal gap formation. Other workers (Blunck and Roulet, 1989; Krejci and Lutz, 1990) however prefer to use an incremental technique in laboratory studies of materials in extracted teeth. This method is therefore more representative of the dimensional changes that would be expected in the clinical situation,
RESTORATION PLACEMENT, INTERNAL AND EXTERNAL ADAPTATION Hansen (1986) points out that the methods used to measure volumetric contraction of restorative materials give no guide to the effect clinically upon wall-to-wall contraction. This discrepancy seems due to the formation of bonds between the material and cavity walls during the setting reaction. Hansen’s study also reveals one of the major oversights in the field of marginal adaptation. His study of restorations placed in cylindrical dentine buttjoint cavities has shown that the degree of contraction at the cavosurface margin was not affected by changes in the cavity depth (between 0.5 and 3.0 mm). Unfortunately no sectioning of the specimens was carried out and so it is not possible to identify where contraction gaps (if any) occurred. It seems likely that, as no increase in marginal gap occurred at the surface of the restoration, contraction shrinkage would be demonstrated elsewhere within the cavity, either by failure within the material (cohesive failure) or at the floor of the cavity or another of the internal margins (adhesive failure). It seems that this form of marginal adaptation (i.e. adaptation to the internal dimensions of the cavity form) is mostly ignored while workers concentrate upon the measurement and reduction of gaps at the external surface. While such aims are laudable, there is no doubt amongst current research that the cavosurface margins of restorations placed in dentine remain inadequate at providing a satisfactory seal. The effects of poor internal adaptation of a restorative material can therefore only further compromise the pulp-dentine complex. Recent studies which include examination of the adaptation of materials to the cavity walls exist, but these are generally either purely descriptive (Suzuki et al., 1989) or discuss adaptation findings incidental to leakage study (Davila et al., 1988). A more recent study by Hegarty and Pearson (1990) has examined closely the effects of polymerization shrinkage upon the restoration walls. However, while some time is spent upon description of the material and behaviour of tooth structure, it is only discussed in terms of the effect upon the flexing of cusps in Class II restorations.
Fig. 7. Two methods of placing incremental restorations: parallel and oblique placement. (After Hansen, 1986.)
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J. Dent. 1993; 21: No. 5
Thus it appears that two techniques are presently used for in vitro studies. The multiple increment technique is now widely accepted in restorative dentistry and is used in research to resemble the clinical behaviour of a material. The bulk placement technique in which the cavity is restored in a single polymerization, leaving a slight excess to compensate for shrinkage to be removed at the finishing stage, unfortunately shows the greatest degree of marginal opening and is used to demonstrate the limitations of a material. In experimental situations, however, the bulk placement technique can be used to eliminate variations caused by the placement of two or more increments of material of uncontrolled volume.
CHOICE OF MATERIAL OF ACTIVATION
AND METHOD
As has already been discussed, the means by which a material hardens will determine the pattern and effect of its setting contraction. It is well known that the setting reaction of chemically curing and light-activated restorative materials differs in that chemically cured restorations set from the centre of the material’s bulk while lightactivated materials polymerize first nearer to the light source. Speed of setting will also affect the development of stresses within the restoration. The flow which occurs during the relatively slower setting of chemically cured materials is quoted as reducing the effect of polymerization contraction and hence marginal gap formation (Hansen, 1986). During the setting reaction of conventional glass polyalkenoate cements the stresses induced by contraction are more likely to be distributed by cohesive failure within the material, while in polymerizing resins the greater cohesive strength together with the reduced adhesion to dentine is more likely to induce adhesive failure and so marginal gap formation (Davidson, 1988). Dual curing materials, particularly the light/chemically cured composite resins, would be expected to show better adaptation if chemical curing were allowed to occur first. This chemical reaction would allow a more favourable flow of the unset material than the more rapid lightactivated reaction. In the case of the dual curing glass polyalkenoate cements the situation is more difficult to determine due to their complex setting chemistry. Light-activated resins polymerize more rapidly nearer to the light source and hence contraction will also be in this direction. This is contrary to the effect of chemically cured materials where contraction towards the faster setting centre of the restoration is expected. This contraction toward polymerizing resin may be used to some advantage if it is possible to cure small increments of material through the tooth. This would theoretically pull the material against the cavity margin as it polymerized, thus improving adaptation. This is supported by the work of Lutz et al. (1986).
EFFECT OF LINERS/BASES ADAPTATION
UPON
The adaptation of restorative materials will be affected by any substance with which they are in contact. The rapid development of dentine bonding agents has led to much research into their effect upon the adaptation of composite resins. However comparatively little study of the effect of liners and bases upon adaptation to the internal margins of cavities has been carried out (Al-Hamadani and Crabb, 1975, Davilaetaf., 1988).The use of conventional Class III glass polyalkenoate cements (Wilson and McLean, 1988) and their light-cured counterparts which adhere to dentine and can be bound by composite resins has significance in the adaptation of the cured restoration to the cavity floor and adjacent internal margins. Scherer et al. (1989) have suggested that the force due to polymerization contraction within composite resins exceeds the bond strength between glass polyalkenoate cement base and dentine. This may be particularly true when glass polyalkenoate liners/bases are freshly placed and their bond to dentine is not yet fully established. Because of the effect of this force, the authors question the wisdom of etching the surface of glass polyalkenoate liners/bases, implying that the failure of the composite/ base bond has less serious implications than the failure of the base/dentine bond. It is apparent that the use of a base/liner which bonds to the dentine surface less than to the restorative material will allow internal failure at the cavity floor during polymerization (Papadakou et al., 1990). Internal failure between restorative material and base/liner could
Fig. 2. Theoretical gap formation related to bond strengths between restoration, base material and tooth. a, Restoration and base prior to polymerization. Following polymerization of restoration: b, bond of restorative material to base exceeds bonding of base to dentine-gap forms between base and dentine; c, bond of base material to dentine exceeds bond to restorative material-gap forms between restorative material and base.
Taylor and Lynch: Marginal adaptation
theoretically have a substantially different effect. If an insoluble base material is used which has a high bond strength to dentine, while at the same time having a poor affinity for the restorative material, then, on contraction of the restorative material, a gap will be formed between base and restoration. As there is no bonding of the restorative material to the floor of the cavity there would be no contraction of the restorative material in this direction. Consequently the surface adaptation of the material could in theory be improved. As the internal gap formed on contraction is isolated from tooth substance by an insoluble layer, the potential for damage to the pulpdentine complex is minimized. An additional element may be the later hygroscopic expansion of the restoration, contributing to the obliteration of the contraction gap. The theoretical differences between the two situations described (i.e. where the restoration/base bond is stronger than the base/dentine bond and vice versa) are illustrated by Fig. 2.
269
Kemp-Scholte (1989), concludes, however that the sealing of restoration margins with an unfilled lowviscosity resin, with adequate penetration and hardening properties can result in perfectly sealed restorations. BrSinnstr(Sm (1985) has reported the flow of such resin, with a fluorescent marker, several millimetres into restorations. Obviously such finishing techniques and their effects upon the ultimate adaptation of the restorative material justify further investigation.
ASSESSMENT OF CAVITY MARGINS There are fortunately fewer methods used in the assessment of marginal adaptation than those associated with microleakage. Effectively these methods can be classified as in vitro or in tivo, although as mentioned earlier laboratory assessment of clinical cases can be carried out. In vivo assessment
EFFECT OF FINISHING METHODS UPON MARGINAL ADAPTATION Variation in finishing techniques has been shown to affect the ability of restorative materials to resist leakage. This is likely to be due to heat generated locally during the polishing process. Dodge ef al. (1991) suggest that for at least one of the materials they investigated, the surface temperature was raised sufficiently to obtain the glass transition point for the resin tiller particles resulting in a significantly improved surface. Their results suggest that in the majority of cases a dry finishing technique is equal or superior to wet finishing when using aluminium oxidecoated finishing discs. Yu et al. (1990) examining the effects of finishing techniques upon microleakage however show an increase in leakage with a dry polishing disc technique, suggesting poorer marginal adaptation, and recommend the use of water-cooled tungsten carbide finishing burs. The discrepancy between the results may be due to the use of restorations placed in Lucite blocks in the former study, while Yu and co-workers used mixed restorations in extracted human teeth. It should be noted that the Yu study looked only at leakage present at the dentinal interface and is not a guide to the behaviour of materials in enamel. Although at least two studies have shown that the use of aluminium oxide finishing techniques can cause surface cracking of resin restorations (Lambrechts and Vanherle, 1982), this technique continues to be widely employed. Davidson et al. (1981) have shown that a dry finishing technique using Soflex (3M) discs can cause structural and chemical changes at the surface of the restoration. Lambrechts and Vanherle suggest that this may be part of the reason why, in their study of the post-finishing glazing of composites, all glazing agents applied to the surface of resins finished in this way were eventually lost.
Clinical assessments of margin quality are carried out by dentists every day, many using their individual method of subjective assessment. This explains the degree of variation between treatment planning decisions, particularly in the replacement of existing restorations (Dedmon, 1982; Elderton and Nuttall, 1983). It was early recognition of the subjective difficulties in assessing restorations that contributed to the development of a systematic approach. This was first described by McCune et al. in 1967 and has since been adopted as the US Public Health Service Criteria (Ryge Criteria, Cvar and Ryge, 1971; Ryge, 1981). Using this system, restorations are systematically evaluated using mirror and probe, and the quality of margin assessed in terms of occlusal form, cavosurface marginal discoloration and marginal adaptation. These categories are then graded according to three levels of performance ‘Clinically ideal’, ‘Clinically acceptable’ and ‘Clinically unacceptable’. Subjective assessment can however still cause problems in determining the true marginal quality. The limitations of man’s ability to detect marginal ledges using a probe has been described by Leinfelder et al. (1982), who determined that the smallest ledge which could be clinically detected measured 100 pm (0.1 mm). As restorative materials improve in quality and in their ability to adapt closely to cavity form, more sensitive methods of detecting gaps and ledges become necessary. These have included the use of cast stone study models and clinical photography (Mahler and Marantz, 1979; Osborne et al., 1980), where either rating scales were used based upon defined criteria or photographs were simply arranged in order from best to worst. Thus reproduction of the clinical situation for later assessment and comparison becomes possible. Clinical studies continue to have most relevance in dental materials testing although some clinical trials give
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little useful information. Sheth et al. (1988) report a trial of cervical restorations using a microfilled composite resin in which the results are classified as restorations lost, evidence of recurrent decay and ‘otherwise clinically acceptable’. No details of a standardized clinical assessment are given or the criteria used to reach such diagnoses. Jordan et al. (1989) in a comparable study used a modified version of the Cvar and Ryge system to classify retention, colour stability and marginal integrity, together with abrasion resistance, surface texture/staining and postoperative sensitivity. However, in their discussion of results the authors make broad assumptions that the high rates of retention of their restorations were related to the dentine bonding agents under test and their ability to resist the polymerization contraction of the composite resin. As only visual and tactile examination were used it may be possible that gaps at the margins of the restoration of less than 100 urn (Leinfelder et al., 1982) had passed unnoticed. In vitro studies in which examination of the restoration margin is conducted in the laboratory are considered in the following section. In vitro assessment In vitro assessment of marginal adaptation can be carried
out on extracted teeth either by direct observation or indirectly using a replication technique such as the production of study models, photographs or replicas for future electron microscope examination. These techniques can also be applied to the assessment of in vivo studies. Profilometery The use of profilometery in both in tivo and in vitro studies has been reported (Lambrechts and Vanherle, 1982; Roulet, 1987).These use a line stylus which is moved against the surface of a restoration. The vertical movements of the stylus can be recorded and magnified to give a picture of the surface profile of a material. This technique however is usually confined to the assessment of wear on restoration surfaces or the condition of such surfaces as they deteriorate with age. It is not generally applied to the assessment of marginal gap formation. Measurement
of coordinates
Various techniques exist by which coordinates marked on a replica can be used to compare changes in surface detail, Most systems use computerized techniques to calculate the differences involved, while the systems themselves can range in complexity from simply cutting reference points on teeth (Lambrechts et al., 1989) to complex measurements using laser scanning equipment (DeLong et al., 1989). These systems are again principally designed to compare changes such as minute losses of surface tissue;
they are not designed to measure the marginal opening of restorations. Two methods currently used in the assessment of restoration margins are light and electron microscopy.
Light microscopy While investigating the changes in marginal gap which occur with exposure of the restoration to water, Asmussen and Jorgensen (1972) used a camera microscope fitted with a measuring eyepiece allowing calibrated measurement of the order of X 425. Using this arrangement the authors classified marginal defects between resin and tooth as: (1) extensive; (2) sporadic, and (3) with no evidence of fracture or broken enamel. The workers reported difficulties in obtaining consistency in the classification of groups (1) and (2) although group (3) produced no such problem. This kind of difficulty in subjective assessment is not uncommon. The use of a screw micrometer mounted upon a light microscope has recently been reported by one group (Koike et al., 1990; Chigira et al., 1991). This is quoted as allowing magnification to X 1024 and has been used to accurately assess marginal gaps with a view to determining the percentage volumetric contraction of a material when placed in cylindrical dentine cavities. In both papers the maximum contraction is then related to the ‘bonding efficiency’ of the resin or intermediary bonding agent. The use of stereomicroscopy has been reported by Zidan et al. (1987). In their study of mixed cavities they assessed the simple presence or absence of dye visible at the tooth/restoration interface. While this provides a qualitative assessment of the margin quality it is unfortunate that while using such magnification the authors did not report quantitative information about gap size. All the light microscope studies reported were carried out on extracted teeth rather than replicas and as such are true in vitro studies.
Scanning
electron
microscopy
The use of the scanning electron microscope (SEM) in dental research has increased dramatically in the past 20 years. One of the first dental studies carried out using SEM techniques has been reported by Lee and Schwartz (1970). This study was conducted on sectioned tooth tissue and attempted to relate marginal leakage as assessed by 45Ca autoradiography to the appearance of cavity margins as seen under SEM magnification. Unfortunately, however, the workers found no relationship between the two methods of assessment. This is likely to be due to the comparative novelty of the SEM and unfamiliarity with the techniques used. Although the authors point out that no heat or radiation damage of the specimens occurred during examination, Davila et al. (1988) point out that severe drying of specimens is required prior to SEM evaluation. As dentine has a high
Taylor and Lynch:
Table 1. Examples of criteria in the qualitative assessment of marginal quality (MCI) MQI - Excellent Margin (EM)* MQ2 - Submargination (SM)* MQ3 -Overhang (OH)* MQ4 - Marginal Opening (MO)* MQ5 - Restoration fracture (RF)* MQ6 - Enamel fracture (EF)* MQ7-MO+SM
MQ8 -MO MQ9 -MO MQIO-MO MQll -SM MQ12-SM MQ13-OH MQ14-OH
+OH +RF + EF +RF + EF + RF + EF
From Roulet et al. (199 1) *Quality criteria actually reported.
it is likely that artefactual gaps and water content distortion of the specimen will occur. Using tooth substance for analysis has major disadvantages in the electron microscope. If artefactual damage occurs due to desiccation of the specimen then original material will be lost. As with tooth sectioning in the study of microleakage, use of original material in the SEM obviates the use of longitudinal studies. Because of this most workers now favour some form of replication technique.
SEM ANALYSIS OF REPLICAS The SEM analysis of marginal adaptation using replicas is now widely accepted as an accurate method of assessment. Specimens for examination are prepared by the removal of debris using sodium hypochlorite solution to dissolve any organic material including plaque. Such techniques have been reported in tivo following rubber dam isolation of the tooth to be examined (Roulet et al., 1991). ‘Scavenging’ impressions have been used (Roulet, 1987) to remove surface debris before the final impression for replication is taken. The use of polyvinylsiloxane impression materials is widely recommended because of their high degree of dimensional stability (Pameijer, 1979). Epoxy replicas are formed using various resins which have other applications in the field of scanning electron microscopy. Stycast Resin (Emerson & Cummings, Belgium) seems particularly popular amongst investigators (Roulet et al., 1989, 1991; Krejci and Lutz, 1990; Lui et al., 1987), although examination of the literature reveals no significant differences between the quality of surface detail reproduction with this and other epoxies in common use. It seems that selection of resin may be based upon personal preference. Whatever material is used to fabricate a positive replica, it must be remembered that any inaccuracies at either stage of replication will be recorded and that technically it is not possible to produce a positive replica of the same accuracy as its original or negative. Fortunately these errors appear not to affect research on positive replicas and this difficulty is not mentioned in discussions. The examination of impression surfaces (negatives) has been reported (Suzuki et al., 1989) and the quality of reproduction has been compared with original tissue (Davila et al., 1988), suggesting that gaps on original tissue
Marginal
adaptation
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appeared larger than on the negative. This may however be due to change occurring within the original specimen during its preparation for viewing under the SEM, although the authors also report better detail on the surface of the original. Marginal assessment using positive replicas mainly uses a qualitative assessment technique assessing the margins as ‘Perfect/Excellent’, ‘Overfilled’, ‘Underfilled’, or as exhibiting ‘Marginal opening’ (Ciucchi et al., 1990); other scoring systems include distinctions between marginal tooth fracture and marginal restorative fracture (Krejci and Lutz, 1990). A quantitative technique for marginal analysis has been developed and described by Roulet et al. (1989) and Blunck and Roulet (1989), involving the examination of epoxy replicas with computerized image analysis. However, although using this technique the examiners record the entire circumference of the cavity, it is a qualitative assessment that is recorded for every point along the margin. Thus a percentage of each form of marginal quality can be expressed for the complete restoration. While there is much to commend this technique, including its ability to precisely compare different examiners’ assessments for any given point, the use of the term ‘Quantitative marginal analysis’ could be open to misinterpretation as it is only the length of the margin that is quantified and not the size of any opening which may exist. Use of this technique has been applied to replicas obtained from a longitudinal clinical study of Class II restorations (Roulet et al., 1991). This study assessed marginal quality using a 14-point scale based upon six criteria. The authors felt however that such a large scale did not allow the materials’ behaviour to be clearly shown and reduced this to a 6-point scale of which 5 were reported (Table I). Although criteria for assessment are frequently mentioned in qualitative studies, these are rarely described in detail even when (Table I) their definition may seem obvious. It would be interesting to compare different workers’ criteria for the classification of marginal adaptation perhaps with a view to providing standard definitions. True quantitative assessment where marginal gaps are actually measured are comparatively rare. The measurement of maximal marginal opening using epoxy replicas is described by Al-Hamadani and Crabb (1975) and Rigsby et al. (1990). Despite the 15-year interval between the studies, the techniques used remain fundamentally the same. Assessment of maximum gap is carried out under the SEM and photomicrographs are taken of the area exhibiting the greatest marginal opening. Measurements from the photomicrographs can then be later converted using the scale bars provided to give the actual gap size. There are however fundamental problems with this technique in that assessment of marginal gap is made initially by the operator from the screen of the SEM. If (as is sometimes necessary) the entire margin of the
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restoration needs to be checked, at X 2000 magnification a 3 mm diameter circular cavity can have an effective circumference of 18.85 m (ITX 3 X 1O-3 X 2 X lo3 = 18.85 m). As it is unlikely that the screen will allow more than an effective length of 30 cm to be viewed at one time, this means: 1. Observation of the entire margin will be time consuming. 2. Without some form of measuring device attached to the microscope stage it will be difficult to relocate the area of maximum opening once determined. 3. There is no detail of how the maximum gap is assessed. If this is a subjective assessment based upon visual interpretation and memory of previous gaps along the same margin then the validity of the photomicrographs providing a definitive measurement of maximum opening must be questioned. Some SEM screens now have the capability to make direct measurements which may aid the examiner. Interpretation of marginal appearance whether for quantitative or qualitative assessment will also be affected by the angle at which the margin is viewed. Wherever possible the margins should be viewed in a plane parallel to that of the cut surface of the cavity. This becomes essential when measurements are to be taken, as slight changes in angulation from this parallel axis will result in the gap appearing smaller than is actually the case. SUMMARY There is much active work in the field of marginal adaptation assessment and it is apparent that researchers must become more technically advanced as restorative materials improve. Review of the literature reveals areas which need attention. The following are suggested: 1. Recognition that marginal adaptation at the cavosurface margin is only one part of the adaptation picture. This may help to improve understanding of the behaviour of materials within the cavity including the effects of liners/bases upon adaptation. 2. Variation in studies of adaptation could be further reduced by improving methods of cutting test cavities of standard dimensions. 3. Further investigation into the role of the cemental layer upon bonding and adaptation of materials used in the restoration of cervical lesions. 4. The establishment of standard, published criteria for the qualitative assessment of marginal adaptation under the SEM (in a similar fashion to the use of the Ryge Criteria clinically) together with standard methodologies in the quantitative measurement of marginal opening. References Al-Hamadani adaptation
K. K. and Crabb H. S. (1975) Marginal of composite resins. .I. Oral Rehabil. 2, 21-33.
Asmussen E. and Jorgensen K. D. (1972) A microscopic investigation of the adaptation of some plastic tilling materials to dentin cavity walls. A& Odontol. Stand. 30, 3-21. Barkmeier W. W. and Cooley R. L. (1989) Resin adhesive systems: in vitro evaluation of dentin bond strength and marginal microleakage. J. Esthetic. Dent. 1, 67-72. Blunck U. and Roulet J-F. (1989) In vitro marginal quality of dentin-bonded composite resins in Class V cavities. Quintessence Int. 20, 407-412. Brannstrom M. (1985) Composite resin restorations: biological considerations with special reference to dentin and pulp. In: Vanherle G. & Smith D. C. (eds), Posterior Composite Resin Dental Restoration Materials. Minnesota, 3M, pp. 71-81. Ciucchi B., Bouillaguet S. and Holz J. (1990) Proximal adaptation and marginal seal of posterior composite resin restorations placed with direct and indirect techniques. Quintessence ht. 21, 663-669. Chigira H., Itoh K. and Wakumoto S. (1991) Marginal adaptation of nine commercial intermediate resins. Dent. Mater. 7, 103-106. Cvar J. F. and Ryge G. (1971) Criteria for the Clinical Evaluation of Dental Restorative Materials. US PHS Publication. 790-244. US Government. Darbyshire P. A., Messer L. B. and Douglas W. H. (1988) Microleakage in Class II composite restorations bonded to dentin using thermal and load cycling. J. Dent. Res. 67, 585-587. Davidson C. L. and De Gee A. J. (1984) Relaxation of polymerization contraction stresses by flow in dental composites. J. Dent. Res. 63, 146-148. Davidson C. L., Duysters P. P. E., DeLange C. et al. (1981) Structural changes in composite surface materials after dry polishing. J. Oral Rehabil. 8,431-438. Davila J. M., Gwinnett A. J. and Robles J. C. (1988) Marginal adaptation of composite resins and dentinal bonding agents. ASDC J. Dent. Child. 55,25-28. Dedmon H. W. (1982) Disparity in expert opinions on size of acceptable margin openings. Oper. Dent. 7, 97-101. DeLong R., Peterson R. and Douglas W. H. (1989) A laser profiling system for measuring wear of dental materials. lADR Abstract 328. Dodge W. W., Dale R. A., Cooley R L. et al. (1991) Comparison of wet and dry finishing of resin composites with aluminium oxide discs. Dent. Mater. 7, 18-20. Eakle W. S. and Ito R. K. (1990) Effect of insertion technique on microleakage in mesio-occlusodistal composite resin restorations. Quintessence Int. 21, 369-374. Elderton R. J. and Nuttall N. M. (1983) Variation among dentists in planning treatment. Br. Dent. J. 154,201-206. Feilzer R. J., De Gee A J. and Davidson C. L. (1988) Measuring contraction of composites and glass ionomer cements. J. Prosthet. Dent. 59, 297-300. Fisbein S., Holan G., Grajower R. et al. (1988) The effect of VLC Scotchbond and an incremental tilling technique on leakage around Class II composite restorations. ASDC .I Dent. Child. 55, 29-33. Hansen E. K. (1986) Effect of cavity depth and application technique on marginal adaptation of resins in dentin cavities. J. Dent. Res. 65, 1319-1321. Hansen E. K. (1987) Effect of Gluma in acid etched dentin cavities. Stand. J. Dent. Res. 95, 181-184. Hargreaves J. A, Grossman E. S. and Matejka J. M. (1989) Scanning electron microscope study of prepared cavities involving enamel, dentin and cementum. J. Prosthet. Dent. 61, 191-197. Hegarty S. M. and Pearson G. J. (1990) The effectiveness of dentine adhesives as demonstrated by dye penetration and SEM investigations. J Oral Rehabil. 17, 351-357.
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Jablonski S. (1987) Illustrated Dictionary of Dentistry, 1st edn. Philadelphia, W.B. Saunders. Kamel F. M., Retief D. H., Madras R. S. et al. (1990) A laboratory study of the Herculite XR system. Am. J. Dent. 3, 271-277. Kemp-Scholte C. M. (1989) The Marginal Integrity of Cervical Composite Resin Restorations. Doctoral Thesis, University of Amsterdam. Koike T., Hasegawa T., Manabe A et al. (1990) Effect of water sorption and thermal stress on cavity adaptation of dental composites. Dent Mater. 6, 178-180. Krejci I. and Lutz F. (1990) Mixed Class V restorations: the potential of a dentine bonding agent. J. Dent l&263-270. Lambrechts P. and Vanherle G. (1982) Observation and comparison of polished composite surfaces with the aid of SEM and profilometer. J. Oral Rehabil. 9, 169-183. Lambrechts P., Braem M., Vuysteke-Wauters M. et al. (1989) Quantitative in viva wear of human enamel. J. Dent. Res. 68, 1752-1754. Lee H. L. and Swartz M. L. (1970) Scanning electron microscope study of composite restorative materials. J. Dent. Res. 49, 149-158. Leinfelder K. F., Sockwell C. L. and Sluder T. B. (1982) Two year clinical evaluation of profile in posterior teeth. J. Dent. Res. 61, (abstr. 327), 215. Lui J. L., Masutani S., Setcos J. C. et al. (1987) Margin quality and microleakage of Class II composite resin restorations. J. Am. Dent. Assoc. 114,49-54. Lutz F., Krejci I., Luescher B. et al. (1986) Improved proximal margin adaptation of Class II composite resin restorations by use of light-reflecting wedges. Quintessence Znt 17, 659-664. Lutz F., Krejci I. and Barbakow F. (1991) Quality and durability of marginal adaptation in bonded composite restorations. Dent. Mater. 7, 107-113. McCune R. J., Johnson B. E., Cvar J. F. et al. (1967) Clinical comparison for posterior restorative materials. J. Dent. Res. 46, (spec. iss.), (abstr. 175), 546. Mahler D. B. and Marantz R. L. (1979) The effect of time on the marginal fracture behaviour of amalgam. J. Oral Rehabil. 6, 391-398. Osborne J. W., Leinfelder K. F., Gale E. N. et al. (1980) Two independent evaluations of ten amalgam alloys. J. Prosthet. Dent. 43, 622-626. Pameijer C. H. (1979) Replication techniques with new dental impression materials in combination with different negative impression materials. Scan. Electron Microsc. 2, 571-574.
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Papadakou M., Barnes I. E., Wassall R. W. et al. (1990) Adaptation of two different calcium hydroxide bases under a composite restoration. J. Dent. 18, 276-280. Phair C. B. and Fuller J. L. (1985) Microleakage of composite resin restorations with cementum margins. J. Prosthet. Dent. 53, 361-364. Prati C., Nucci C. and Montanari G. (1991) Shear bond strength and microleakage of dentin bonding systems. J. Prosthet. Dent. 65, 401-407. Rigsby D. F., Retief D. H., Russell C. M. et al. (1990) Marginal leakage and marginal gap dimensions of three dentinal bonding systems. Am. J. Dent 3, 289-294. Roulet J-F. (1987) In: Degradation of Dental Polymers, 1st edn. Basel, S, Karger AG, pp, 92-113. Roulet J-F., Reich T., Blunck U. et al. (1989) Quantitative margin analysis in the scanning electron microscope. Scan. Electron Microsc. 3, 147-159. Roulet J-F., Salchow B. and Wald M. (1991) Margin analysis of posterior composites in vivo. Dent Mater. 7, 44-49. Ryge G. (1981) Clinical criteria. Znt. Dent.1 30, 347-358. Saunders W. P., Grieve A. R., Russell E. M. et al. (1990) The effects of dentine bonding agents on marginal leakage of composite restorations. .Z. Oral Rehabil. 17, 519-527. Scherer W., Kaim J. M., Lippman X et al. (1989) Microleakage of three glass ionomer cement bases. Am. J. Dent 2, 61-63. Sparrius 0. and Grossman E. S. (1989) Marginal leakage of composite resin restorations in combination with dentinal and enamel bonding agents. J. Prosthet Dent 61, 678-684. Staninac M., Mochizuki A,Tanizaki K. et al. (1985) Effect of etching and bonding on recurrent caries in teeth restored with composite resin. J. Prosthet Dent 53, 521-525. Suzuki M., Gwinnett A. J. and Jordan R. E. (1989) Relationship between composite resins and dentine treated with bonding agents. J. Am. Dent. Assoc. 118, 75-77. Taylor M. J. and Lynch E. (1992) Microleakage. J. Dent. 20, 3-10. Wilson A. D. and McLean J. W. (1988) In: Glass Zonomer Cement, 1st edn. Quintessence. Yu X. Y., Wieczkowski G., Davis E. L. et al. (1990) The influence of finishing technique on microleakage. J. Esthetic Dent 2, 142-144. Zidan O., Gomez-Marin 0. and Tsuchiya T. (1987) A comparative study of the effect of dentinal bonding agents and application techniques on marginal gaps in Class V cavities. J. Dent. Res. 66, 716-721.
Book Review Pathobiologie Oraler Strukturen. H. H. Schroeder. Pp. 266. 199 1. Basle, S. Karger AG. Softback, f 20.00. This is an extended and revised edition of a textbook, the first edition of which appeared in 1983. It is organized in the classical way, starting with inherited and acquired developmental disturbances followed by age-related changes in the teeth, tooth fractures, discolorations, caries and erosion, root resorption, changes in the pulp and periodontal tissues, periodontal regeneration and wound healing. The text is short and clear and well supported by numerous clinical and histological illustrations as well as schematic drawings. There is an impressive collection of data and references. The wealth of information may make it hard to read but the
systematic organization of each chapter and the fact that important statements and definitions are specifically marked, facilitates reading and improves the educational value of the text. Treatment of diseases of the dental hard tissues occupies most of the working day of a practising dentist and it is surprising that there are so few books dealing with the pathology of these tissues. This is a good textbook for the dental student. For the dentist, it updates and deepens the knowledge of the tissues he or she is working with every day. A detailed knowledge of the pathobiology of the dental tissues is of fundamental importance for proper patient care today and for the development of the new treatment procedures of tomorrow. This is why this book is important. L. Hammarstrbm