Medical knowledge | Dentistry » Dental materials for posterior restorations

Review article Dental materials for posterior restorations Rykke M. Dental materials for posterior restorations Endod Dent Traumatol 1992; 8: 139-148. Abstract - Assessment of the quality of dental restorations by the Ryge system is described. Generally, the quality of dental restorations is shown to be dependent on the technique sensitivity of the restorative material as well as the skill and experience of the dentist. Concerning biocompatibility, adverse reactions related to amalgam restorations are unlikely or scarce, due to small amounts of released mercury. Resin based restorative materials contain a large number of organic compounds and, as such, the toxic and allergenic potentials are unknown. Gold and ceramics turn out to be the most biotolerable dental materials Based on studies on longevity, data indicate that the median age of amalgam restorations is 1012 years, of gold castings 13-14 years and more, and of composite restorations 4 years. Data on longevity of ceramic

restorations are sparse Secondary caries appears to be the most frequent cause for replacement of the different restorations, followed by marginal degradation Secondary caries account for more failures among the resin based restorations than among amalgam. Reviewing the literature, it appears that amalgam is the best and most economic dental material for routine posterior restorations with reasonable durability. Gold is recommended for complex restorations. Resin based composites may be limited to small restorations where cosmetics is the main aspect, as wear and recurrent caries are main problems. Ceramic restorations comprise aesthetic restorations with excellent biocompatibility, however, data on longevity and marginal adaptation are not encouraging. Treatment of dental caries has traditionally been performed by removing the decayed tooth substance and replacing it with a restoration. It has been shown that there is a correlation between number of decayed tooth surfaces and oral

hygiene and plaque scores (1, 2). Moreover, there is a correlation between oral hygiene and number of new decayed tooth surfaces (3). Mjor (4) reports in a study comprising 85 dentists that of 3527 amalgam fillings inserted over a period of time, 71 % were replacement of previous restorations, and of 1960 toothcolored fillings, 79% were replacement restorations. Qyist (5, 6) reports from Denmark that of a total of 7285 dental fillings, 62% of the tooth-colored and 61 % of the amalgam fillings were replacement restorations. Despite the continuous decline in caries among children in Norway in the last decades (7), and the possibility through different prophylaxis Morten Rykke Department of Operative Dentistry, University of Oslo, Norway Key words: dental amalgams; composite resins; gold castings; operative dentistry. Morten Rykke, Department of Operative Dentistry, Faculty of Dentistry, University of Oslo, PO Box 1109, Blindern, N-0317 Oslo, Norway Accepted March 11, 1992 programs to

further reduce the caries incidence, the major work load in general dental practice is still operative procedures. The selection of the dental material is important for the longevity of a dental restoration. It may thus have biological and cost-benefit imphcations, and it may significantly affect the need for dental treatment in a population. A restoration should be durable and biologically safe, and as much as possible fulfil the demands of the patients concerning function and aesthetics. The quality of a restoration The quality of a dental restoration may be difficult to define in that it may be derived from many factors including function of the restoration, aesthetics, marginal integrity, biocompatibility, recurrent 139 Rykke caries, absence or presence of post-treatment discomfort and, importantly, the longevity of the restoration. Failure to achieve or maintain acceptable quality within one or more of these aspects of a restoration, will result in failure of the dental

treatment, and thereby necessitating a replacement of the restoration. The quality of a dental restoration may be assessed in several ways using different evaluation systems. Generally, quality assessment is carried out directly in the mouth using good light, a probe and a mirror sometimes supplemented by color guides and guides for evaluation of marginal adaptation. (8-10). Indirect assessments may comprise examination of photos, impressions and replicas of the teeth with the actual restorations (11, 12). One of the most commonly used systems for direct clinical evaluation of a restoration is presented by Ryge (10). This system consists of clinical criteria for the evaluation of 1) marginal adaptation, 2) anatomic form, 3) recurrent caries, 4)color match, 5) surface and color and 6) marginal discoloration. The rating system consists of criteria which are considered to be of clinical significance. The criteria are presented to the evaluator as questions which are to be answered by a

Yes or a No. If the answer to the first question is No, a certain rating is given. Is the answer Yes, the evaluator will be asked another Yes or No question leading to either another rating or another question. Thus, by answering one, two or three questions, the evaluator passes through a progression of bipolar decisions leading to a classification or rating of the actual dental restoration. Evaluation of the marginal adaptation of a restoration comprises the use of a mirror and a probe which is drawn across the margins. If the probe catches at the margin, the evaluator has to inspect and the question to be answered with a Yes or No is: is there evidence of a crevice along the margin into which the explorer can penetrate? If the answer is No, i.e, there is no crevice or one too small to allow the penetration of the explorer, the rating is A (Alpha). If the answer is Yes, the evaluator has to inspect visually and proceed to the next question: is dentin or base cement exposed? If the

answer is No, the rating B (Bravo) has to be recorded. If the answer is Yes, the examiner may proceed to the next question and visually inspect and test the mobility of the restoration. The question is whether the restoration is fractured, mobile or missing in part or in toto? If the answer is No the rating is C (Charlie). If the answer is Yes the rating is D (Delta). The first two ratings, A and B, designate margins of restorations which are satisfactory. A restoration with rating A has a perfect marginal adaptation, and a restoration with rating B has acceptable marginal adaptation where a crevice is 140 present, however, not extending to the dentino-en amel junction. The ratings C and D are not satisfactory and restorations with these ratings should be replaced to avoid damage of the tooth or supporting tissues. Thus, by answering these questions and making rather simple bipolar decisions it is possible to classify the quality of the marginal adaptation of a restoration. However,

it has been demonstrated that most clinicians and trained evaluators will continue to score rating A until the margins are exposed 150-175 jim (13). This value represents, in 3 years, the maximum accepted loss of restorative material due to abrasion according to the acceptance program for resin based dental materials for posterior restorations of the Scandinavian Institute for Dental Materials, NIOM (14). Assessment of recurrent caries at the margins of a restoration, is an important aspect of quality evaluation. This rating system is simple in that it has only two ratings: "no caries" with the rating A or "caries" with the rating B. However, in order to obtain consistency in the rating of "caries" or "no caries", it is obvious that a thorough calibration of the evaluators has to precede the examination of the patients. The necessity of this is stressed in a study by Merrett & Elderton (15), where 9 dentists examined 228 teeth. One of the

examiners scored "caries" in 11 teeth, whereas another scored "caries" in 54 teeth. The Ryge system (9) is recommended by FDI for clinical research programs to evaluate the quality of dental restorations. The rating system may be used to evaluate operative procedures immediately after dental treatment, or to evaluate the quality of restorative materials at intervals following the treatment. The ratings will therefore be dependent on the quality of the dental restorative material, as well as the skill and experience of the dentist. The operational decision, i.e, whether a restoration is acceptable or should be replaced, is dependent on the lowest rating within one of the five criteria evaluated. For example, if the restoration is perfect in anatomic form, surface and color, the restoration has to be replaced if there is caries along the margin, or if base cement is exposed. Dental restorative materials may in addition to clinical evaluations be subject to physical

and chemical tests. These tests are concerned with physical properties, mechanical properties and technique sensitivity of a material. Dental material institutes regularly publish test results of materials that fulfill the requirements of the ISO standards of dental restorative materials (16, 17). The ISO standards list demands about handling, storage, date of production and expiration as well as physical and chemical specifications with regard to strength, stability of dimension, light sensitivity, solubility, pu- Posterior restoration dental materials nty, and uptake of water. In addition, NIOM reouires that satisfactory documentations concerning biocompatibility and clinical properties of products for the Scandinavian market have to be available (16). Technique sensitivity The quality and longevity of a dental restoration may be dependent on the technique sensitivity of the restorative material used, and the skill and experience of the dentist. Technique sensitivity of a dental

material may be defined as the potential of the material to exhibit variations in clinical properties such as marginal adaptation, solubility, color stability and wear resistance, because of relatively small changes or alterations in manipulative procedures or material performance (Fig. 1) Resin based composite restorative materials may be defined as extremely technique sensitive materials in that moisture along the margins during insertion of the material will prevent enamel bonding with subsequent microleakage. Furthermore, composite material against dentin at the margins may also result in microleakage with the possibility of recurrent caries. Gold castings may be described as an intermediate technique sensitive material, because of difficulties in achieving accuracy in the cavity preparation and the attainment of a subsequent accurate impression. Amalgam may be described as a less technique sensitive material. The technique sensitive material is subject to more failures, appearing

earlier than when a restorative material of intermediate or low technique sensitivity is used. Allan (18) has shown that failure profiles of amal- Technique sensitivity %of failure gam restorations were different in 3 different dental practices. Since the amalgam material used exhibited the same technique sensitivity, the results may indicate different skill levels of the dentists, differences in the handling of the material, differences in opinion of the criteria for replacement, or a combination of these factors. In a study of the longevity of silicate cements, similar differences in failure profiles were seen, indicating different skill levels of the dentists or that different criteria for replacement of the restorations were applied (18). These results are supported by Eavelle (19), suggesting that the clinical skills of the dentists may be decisive for the longevity of a restoration. However, this assumption is not necessarily supported by others in that the longevity of

restorations in relation to the cause for replacement vary in different surveys. Thus, in a Swedish (20) and a Danish (6) study, fracture of amalgam restorations occurred at different times, in that after 4 years, 21% of the amalgam restorations in the Swedish study were fractured as compared to only 10% in the Danish study. Fracture of restorations was furthermore not primarily seen within the first year of service, indicating that inappropriate cavity preparation was not the primary reason for fracture, but rather progressive corrosion of the material or inadequate strength of the base cement used (21). Still, several reports conclude that proper cavity preparation and proper material performance are prerequisites for the longevity of the dental restorations (18, 19, 22). An ideal or nearly ideal restorative dental material does not exist at present, and it is unlikely that such a material will be developed in the near future due to the difficult conditions in the oral cavity with

the presence of bacteria, moisture in the dentin, sensitivity of the pulp, temperature, pressure, electrolytes in saliva, different techniques and skills of the dentists, and differences in patient comphance. However, when a restoration is to be inserted, the dentist should select the restorative material that best combines optimal biocompatibihty and longevity with function and aesthetics, and among the materials which have been tested and accepted according to acceptance programs and ISO standards. Biocompatihility 4 5 6 7 8 10 Years of service Fig. I Failure profiles (cumulative percentage of failure during time of service) for dental restorative materials of high technique sensitivity (A), of intermediate technique sensitivity (B), and of low technique sensitivity. The biocompatibility of a dental material is the first determinant of clinical acceptability. It has to be emphasized that there is no dental restorative material that can be considered as absolute safe under

all conditions, for all patients and all dental personnel. There will be some risks in any intraoral procedure which the patient has to accept Rapid changes in material specifications or withdrawal of the product may further complicate conclusions on 141 Rykke biocompatibility in surveys (23, 24). The existing acceptance programs and ISO standards of material toxicity provide a reasonable standard for the assessment of biocompatibility of a restorative material. If a material is found not to be biotolerable, all other properties of the product are only of academic interest. In the assessment of biocompatibility, reactions in the patients and the clinicians (the dentist and his team) have to be considered, and it may well be the clinicians who comprise the high-risk group. Adverse reactions to dental materials may be either toxic or allergic. Data on frequencies of adverse reactions to dental materials are scarce Kallus (25) reports of 24 complaints among 13325 patients. Only 4 of

the complaints were assumed as "probable" and 3 as "possible". More recently, Mjor and Kallus (26) have reported an incidence of 1:700 of adverse reactions to dental materials. It is believed that this incidence may increase concomitantly with the steady introduction of new and altered restorative materials with more complex chemical compositions. Dental amalgams The safety of dental amalgams should be considered when the materials are certified and fulfill the requirements of the ISO standards. However, amalgam has gained considerable interest during the last decade, especially in USA, Sweden and Japan. In 1985 The National Board of Health and Welfare in Sweden appointed a committee to evaluate possible biological effects of low doses of mercury, with special emphasis on the effect of mercury in dentistry. The final report by Lundberg and Rubarth (27) concludes that amalgam from an ideal toxicological point of view is unsuitable as a dental restorative material,

and that new dental materials with acceptable biological and toxicological properties have to be developed. The composites or resin based restorative materials, presently available, were found to have uncertain toxicological profiles, and the biological properties of these materials should be considered and examined further. The report concludes that of the restorative materials available, gold and ceramics have acceptable biological and toxicological profiles (27). The most common exposure to mercury is through the food. The daily dose is about 10 ig, and may readily be doubled or tripled depending on dietary habits like for instance the quantity of fish eaten (28-31). However, the most important route of exposure to mercury is through the air by inhalation of mercury vapor. About 80% of the inhaled mercury vapor may be taken up by the blood stream (32). After exposure, the stored mer142 cury may be excreted with a halftime of approximately 60 days. However, the halftime of mercury

in the kidneys and the brain may be several years (33, 34). Occupational exposure to mercury vapor has a legal limit of 50 jig per m^ air, which may give doses of mercury of about 500 [ig per day. This has been shown to result in levels of mercury of about 30 |Xg/l of blood, in contrast to levels of about 3-5 jig/1 in individuals with "normal" exposure to mercury vapor. A normal level of urinary mercury is about 5 )Lig/l, and may be about 80 }Xg/l in individuals exposed to mercury in certain industries (35-38). Studies have shown that mercury vapor is released from amalgam restorations during insertion, as newly inserted, and after setting, especially during chewing (39-41). Moreover, it has been shown that there may be an increase in the level of urinary mercury concomitant with dental treatment involving the insertion of amalgam restorations, and that there is a correlation between the number of amalgam restorations in the mouth and the levels of mercury in the brain and

kidneys (42-44). Calculations have shown that the daily uptake of mercury from a medium number of amalgam restorations, may comprise urinary mercury levels of about 2-4 igjl, although great individual variations are evident (27). However, presently, there is no data suggesting that the mercury release from amalgam restorations may account for known toxic reactions Discrete effects on the central nervous system and kidneys after exposure to mercury vapor resulting in urinary mercury levels of 20-30 [O-g/l have been observed (45-47). On the other hand, exposure to mercury vapor resulting in urinary mercury levels below 10 P-g/l, is not associated with known mercury poisoning. This comprises urinary mercury levels well above levels seen as a result of dental amalgam therapy or of having amalgam restorations. Reactions or symptoms to mercury arising from dental amalgam restorations may therefore be considered unlikely or rare (48). A number of international symposia have been dealing with

toxicity and hypersensitivity to mercury related to dental amalgam. Conclusions have been reached that hypersensitivity reactions are scarce when considering the large number of individuals exposed to amalgam restorations (49). Hypersensitivity reactions to mercury in conjunction with amalgam therapy may vary from local oral symptoms with edema and ulcerations to extraoral lesions as urticaria, vesicles and dermatologic reactions without oral manifestations (50). The extraoral reactions may occur within 2-24 hours after exposure to mercury, and usually disappear within 10-14 days after exposure without removal of the amalgam restorations (50). Occasionally, oral li- Posterior restoration dental materiais chenoid lesions have been reported in connection with mercury hypersensitivity (51, 52). Oral lichenoid lesions have a characteristic histological picture with subepithelial infiltration of lymphocytes, as seen with delayed cell-mediated immune reactions. Total or partial remission

of the oral lichenoid lesions is observed following removal of the amalgam restoration and replacement with a porcelain-fused-to-metal (PFM) restoration (53). Therefore, it seems likely that low doses of mercury released from amalgam restorations may initiate and maintain hyperreactions in sensitized individuals. The Swedish report referred to above concludes that there is no epidemiologic data allowing any conclusion regarding a connection between the use of dental amalgam and the general public health (27). Reports dealing with conceivably adverse reactions to amalgam and mercury, usually contain a large number of unspecific symptoms and with no specific combination of these. Reports describing general health improvements after removal of the amalgam restorations have not been possible to control, and alleged "over-night cures" are most unlikely when considering the long half-time of mercury in the body. Recently published reports have concluded that most probably there are

no hazards related to amalgam therapy during pregnancy (54, 55). Also, no evidence has been found of any infiuence of amalgam and mercury on the immunological system (24, 54, 55) Resin based composites Concerning resin based composites the safety for dental use should be satisfactory as well, when the materials are certified and accepted according to specifications in acceptance programs (14) and ISO standards (17). Besides these requirements, there are only few data on the biocompatibility of resin based composites. Resin based composites contain a number of organic components and their long term allergenic and toxic potentials are not known. Albeit the products are certified according to an acceptance program they may release potentially toxic substances, like peroxides and free radicals, due to abrasion (56, 57). In addition, unreacted methacrylate groups may constitute as much as 30-50% of the total mass of the material, exhibiting a considerable allergenic and toxic potential (23,

24). This unreacted mass may thus be responsible for local clinical manifestations like gingivitis, swollen lips and dermatological reactions with or without oral lesions (58). A topographic relationship between oral lichenoid reactions and resin based composites is sometimes evident, which are lesions similar to those reported in contact with amalgam restorations (58). Pulpal reactions to dental restorative materials, especially to the resin based composites have been reported (59, 60). However, it is reason to believe that the pulpal reactions primarily may be associated with microleakage and infections (60). Post-operative discomfort has been assumed to arise from material shrinkage during polymerization of the material, or insufficient strength and energy adsorption of the restorative material during mastication (61). Cast gold and ceramic restorations The traditional high gold alloys have been used successfully for a long time for cast dental restorations. No side-effects to

these alloys have been reported, with the exception of some unusual cases of allergy to alloy components (49). Pure gold has a certain toxic potential, as well (62, 63). However, no adverse reaction to gold has been reported, most probably because of the high stability and extreme low solubility of this material. Regarding the large number of alternative alloys containing less gold, there are few data dealing with side-effects to these materials (49). No data on adverse reactions to ceramic restorations is available. The material has turned out to be one of the most biotolerable, and as such, considered as having acceptable allergenic and toxic profiles (49, 54). A further important biological aspect of dental restorative materials is -their ability to accumulate bacterial plaque. It has been shown that resin based composite materials accumulate and retain more bacteria and plaque than dental amalgams and amalgams more than gold (64). This may explain the higher rate of recurrent

caries reported in connection with composite restorations compared to both gold castings and amalgam fillings (1,2, 22). Longevity of restorations The durability of a dental restoration may be taken as an indicator of the quality of the dental restorative material. The longevity of a restoration may be decisive for the cost-benefit of dental treatment. There are several studies concerning the longevity of dental restorations. However, data on the durability of cast gold and ceramic restorations are scarce (21). Some of the studies on longevity are longitudinal (6568), while others are transversal studying dental records retrospectively (21, 69-71). Transversal studies often take into account only restorations that need replacement due to failure, without considering the age of the restorations that remain intact and hence do not need to be replaced. This fact, as well as the lack of consistent criteria on 143 Rykke when to replace a dental restoration, complicate the studies

concerning the longevity of different restorative materials (21). Generally, it has been shown that multi-surface restorations have a shorter lifespan than single-surface restorations. Moffa (22) has shown that the percentage of amalgam restorations that remain functioning after 5 years in class I cavities is 90% and in class II cavities 75%. The corresponding data for composite restorations that remain functioning after 5 years is for class I cavities 80% and for class II cavities 50%. Thus, the study indicates that amalgam restorations last longer than resin based composite restorations and that restorations in class I cavities have a longer life-span than restorations in class II cavities. According to several transversal surveys analyzing dental records the mean life-span of amalgam restorations needing replacement, has been recorded to be between 5.5 and 11 years with a median age of 7-8 years (19, 21, 65-67, 69-72) Rytomaa et al (71) report a mean age of 73 years of amalgam

restorations in need of replacement, and Patterson (70) estimates a 50%-survival of amalgam restorations at 7.5 years These data comprise restorations in class I and class II cavities The corresponding data concerning composite restorations are 5-6 years (4, 5, 21, 70, 73). However, these data are mostly based on restorations in class HI and class IV cavities, i.e, smaller restorations It has thus been shown that amalgam restorations in need of replacement, in general, are older than composite restorations that are replaced. The composite restorations also exhibit an increase in failure after 3 years of service (22). For cast gold restorations, recent data indicate a mean age of 18 years before replacement is indicated (74, 75). Data from surveys taking into account all dental restorations, including those that do not need replacement, are best suited to calculate the efficacy of the treatment and the cost-benefit of dental res- torations. Despite the relative short life-span of

dental restorations in need of replacement, it has been reported amalgam restorations of about 40 years of age (6, 72). Preliminary data from the Scandinavian Institute of Dental Materials (NIOM) indicate a median age for functioning amalgam restorations in class II cavities of about 1012 years, for gold castings of 13-14 years and for resin based composites of 4 years (21). In a review of the literature, Maryniuk (69) finds reports on the mean longevity of amalgam restorations to vary from 5.5 to 11 years (69) In a retrospective survey, Bjertness and Sonju (76) report that about 90% of amalgam restorations are functioning after 7 years of service and 78% after 17 years. They conclude that the sample of dentists and goodquality amalgam in motivated patients, may have influenced the results in a positive manner. Similarly, Letzel et al. (77) have shown long durability of amalgam restorations in selected patients, dental students and university employees. Mean life-span of complex

amalgam restorations in military personnel has been shown to be 11.5 years (67) The data above may be influenced by the brand of amalgam alloy used. Thus, it has been shown that 30% of amalgam restorations using high-creep amalgam need replacement after 3 years, while only 3% of restorations using low-creep amalgam need replacement after that period (78). Crabb (66) claims that only 42% of gold castings are functioning after 10 years of service, whereas Bentley and Drake (65) in their study show a survival rate of 90% of the gold restorations after 10 years. The mean life-span of 3/4-gold-crown restorations in one study is 147 years (79), which is close to the results of a recent preliminary study (21). In a study of selected patients a median life-span of gold castings of 34 years is recorded (80). Furthermore, empirical calculations indicate a durability of gold castings of more than 20 years (81). Based on data on the median longevity of dental restorations and the initial cost of

the different restorations, cost-benefit calculations indicate that the long term cost of cast gold and resin based composite restorations are similar, and about 4 times more than that of amalgam restorations (75). Data on the longevity of ceramic restorations are based mainly on studies of porcelain jacket crowns, and indicate that 75% of the porcelain crowns are functioning after 10 years of service (82). Preliminary reports on the longevity of ceramic fillings are, however, not encouraging (83). Reasons for replacements Amalgam restorations Fig. 2 Porcelain-fused-to-metal inlay 144 The quality of a dental restoration may together with its durability be assessed by the reason for Posterior restoration dental materials replacement. Moffa (22) shows that recurrent caries, bulk fracture and marginal degradation each account for about 30% of the reasons for replacements of amalgam restorations. Similar findings have been presented by Qyist et al. (6), indicating that in permanent

teeth, recurrent caries is the cause for 38% of the replacements, marginal degradation 12%, and bulk fractures 27%. Mjor (4) reports that secondary caries is the reason for replacement of 58% of amalgam restorations and marginal degradation 9%. Several previous studies have suggested that 55-60% of the amalgam restorations are replaced because of secondary caries (84-88). It may thus appear, that there has been a decline in the importance of recurrent caries as the reason for replacement during the last decade, most probably due to the general decline in caries incidence (7). Generally, it may be concluded that recurrent caries and marginal degradation together are the cause for about 60% of the replacements of amalgam restorations. Thus, Boyd and Richardson (87) show a decline in recurrent caries from 68% to 50% as reason for replacement of amalgam restorations from 1972 to 1985, and with an interesting concomitant increase in the share of marginal degradation as a reason for

replacement from 5% to 2 1 % . The increase of marginal degradation as a reason for replacement of amalgam restorations is interesting, in that the marginal degradation has to be severe before a concomitant increase in secondary caries may appear (1). Resin based composites It is shown that the wear of composite materials may exceed 50 ^im/year, however, decline to about 10 |am/year after three years of service (89). Furthermore, it is shown that the resin based composites exhibit failure predominantly in the molars (90). It is, therefore, stated that three main features of posterior composites need to be improved: the physical properties (wear resistance, strength and energy adsorption), the polymerization shinkrage, and the technique sensitivity (91). The polymerization shrinkage may be 5-6% for existing resin based materials and cause marginal gaps. However, recently developed composites may contain less resin (15-20% volume) which gives a polymerization shrinkage of about 1-2%.

With regard to resin based composite restorations, Moffa (22) reports that recurrent caries is the cause for about 4 1 % of the replacements, and fractures for about 2 1 % . Although wear has been indicated as a major weakness of resin based composite restorations, it constitutes only 13% of the causes for replacement (22). This may be explained by the fact that wear is a cause of fractures and recurrent caries. Leakage as a reason for replacement of composite restorations constitutes 5%, which is 3 times as much as is reported for amalgam restorations (22). Qyist et al (5, 73) report that secondary caries is the most frequent reason for replacement of composite restorations with 32%, which is less than Moffa reports (22). However, the material presented by Qvist and co-workers mostly represents restorations in class HI and class IV cavities. Eriksen et al. (1) in a study report that 13% of the gold surfaces, 2.5% of the amalgam surfaces, and 46% of the composite surfaces were

associated with caries. The high incidence of recurrent caries reported in connection with resin based composite restorations is a matter of concern. Despite the use of preetching of the enamel, enamel bonding and rubber dam, it has been shown that the gingival-cervical area of the restorations may be subject to failure (19). This may be explained by absence of enamel at this location, entrapment of air at the margins, and the polymerisazation shrinkage. The technique may thus be described as sensitive. The use of the acid-etch technique and improved dentin bonding may infiuence the guidelines for cavity preparation. Recently introduced dentin bonding systems may give improved retention, but without seahng the cavity more effectively (92). In fact, data on optimal preparation and cavity design for different restorative materials are scarce. Cast gold and ceramic restorations For cast gold restorations it is reported that the most frequent reason for replacement of restorations is

secondary caries comprising 37%, followed by displacement with 12% (93). In a study by Mjor and Medina (74) recurrent caries constitutes 22% of the causes for replacement, and fracture of the teeth 36%. There is no data available on the reasons for replacement of ceramic restorations. This may be explained by the recent introduction of this material for this use, and hence insufficient observation time. The recently introduced CAD-CAM inlay (computer assisted design-computer assisted manufacturing) is based on an "impression" of the preparation by a 3-dimensional video camera with additional data of the external design (94). A computer analyses these data and conducts a milling of a ceramic block. The advantages of this method are a restoration with satisfactory cosmetic properties and acceptable physical properties finished in one sitting. However, marginal gaps varying from 100-150 |J.m depending on the experience of the clinician, is a most serious problem (95, 96). The

marginal gaps are meant to be eliminated by the cementation of the inlays with resin based composites. However, this makes the method highly 145 Rykke technique sensitive and dependent on the presence of enamel along the margins. Conclusions Despite recent years development of amalgam substitutes, it may appear that amalgam still remains the best, most economic and efficient dental material for routine posterior dental restorations. Amalgam is unacceptable for cosmetic reasons, but exhibits good durability, little if any microleakage, and is reasonably safe in use. The technique sensitivity is low, and it is well tolerated by the pulp and supporting tissues. The ADA Council on Ethics, Bylaws, and Judicial Affairs has, therefore, recently stated that "removing serviceable dental amalgam from nonallergenic patients because it is allegedly a toxic substance is improper and unethical". Excluded from this ruling is the removal of dental amalgams due to cosmetic reasons. The

best alternative to dental amalgams appears to be certified gold alloys, especially for complex restorations. However, the expences of cast gold restorations may be unaffordable for routine use in many patients. Gold is biotolerable, and it has been shown to be the most durable of the dental restorative materials, although the cement gap may be associated with microleakage and recurrent caries. The physical properties of gold are vastly superior to the properties of alternative restorative materials, and the cosmetic aspects may be fairly satisfactory. Resin based composites for posterior restorations have excellent cosmetic properties. The conclusion of several reports is that leakage, wear and recurrent caries still exhibit main problems of resin based composites for posterior use. However, satisfactory results using resin based composites may be achieved if the indications for use are strictly followed, i.e, that the material is used in small cavities only, that molars are avoided,

and that the cavity in toto is bordered by enamel. It is suggested that resin based composites are used only in small class I and class II cavities where the cosmetic aspect of the restoration is important. Little is known about the safety of the use of resin based composites. They contain a number of organic compounds whose long-term allergenic and toxic potentials are not known. Ceramic restorations are cosmetically satisfactory, and exhibit wear resistance comparable to that of amalgam and enamel. The marginal adaptation has been reported to be satisfactory in in vitro studies. Other studies indicate that ceramic inlays are associated with marginal gaps and marginal degradation due to marginal fractures. The biological and toxicological properties are satisfactory A drawback may be that it is necessary to remove more tooth 146 substance than usual to achieve sufficient dimensional strength of the restoration. Finally, one should keep in mind the possibility to select a

porcelain-fused-to-metal inlay, which may combine the cosmetic properties of porcelain with the excellent marginal adaptability and durability of gold (Fig. 2) References 1. 2. 3. 4. 5. 6. 7. ERIKSEN HM, BJERTNESS E, HANSEN BF. Cross-sectional clinical study of quality of amalgam restorations, oral health and prevalence of recurrent caries. Community Dent Oral Fpidemiol 1986; 14: 15-8. BJERTNESS E, ERIKSEN HM, HANSEN BF. Caries prevalence of 35-year-old Oslo citizens in 1973 and 1984. Community Dent Oral Fpidemiol 1986; 14: 277-82. AxELSsoN P, LINDHE J. Effect of controlled oral hygiene procedures on caries and periodontal disease in adults. J Clin Periodontol 1978; 5.- 133-51 MJOR IA. Placement and replacement of restorations Operative Dent 1981; 6: 49-54 QyiST V, QyiST J, MJOR IA. Placement and longevity of tooth-colored restorations in Denmark. Acta Odontol Scand 1990; 48: 305-11. QyiST J, QyiST V, MJOR IA. Placement and longevity of amalgam restorations in Denmark. Acta

Odontol Scand 1990; 48: 297-303. VON DER FEHR F R . Caries decline in Norway in 12-year-old children expressed by various parameters. Caries Res 1991; 25: 215 -Abstr. No 8 8. CHANDLER H H , BOWEN RL, 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. PAFFENBARGER GC, MULLI- NEAUX AL. Clinical evaluation of a radiopacque composite restorative material after three and a half year. J Dent Res 1973; 52: 1128-37. RYGE G, SNYDER M . Evaluating the clinical quality of restorations J Am Dent Assoc 1973; 87: 369-77 RYGE G. Clinical criteria Int Dent J 1980; 30: 347-58 OsBORNE JW, GALE EN, CHEW C L , RHODES BF, PHILLIPS RW. Clinical performance and physical properties of twelve amalgam alloys. J Dent Res 1978; 57: 983-8 LEINEELDER K F . Methodological aspects of clinical research Proceding of the international symposium on amalgam and tooth-colored restorative materials. The Netherlands: University of Nijmegen, 1975; 87-103 TAYLOR DF, TURNBULL CD, LEINEELDER KF. Comparative evaluation

of casts for the measurement of composite wear. J Dent Res 1984; 63: 293 - Abstr. No 1104 Acceptance program for resin based dental filling materials for use in occlusal class I or class II restorations. NIOMs testing program for resin based dental filling materials, 1990. MERRETT M C W , ELDERTON RJ. An in vitro study of restorative dental treatment decisions and dental caries Br Dent J 1984; 157: 128-33. NIOM. Lister over sertifiserte produkter, 1991 ISO 4049. International Standard Organization, 1988 ALLAN D N . A longitudinal study of dental restorations Brit Dent J 1977; 143: 87-9. LAVELLE C L B . A cross-sectional longitudinal survey into the durability of amalgam restorations. J Dentistry 1976; 4: 139-43. MJOR IA. Revisjon av fyllingar Tandldkartidningen 1980; 72: 375-80. MJOR I A, JOKSTAD A, QVIST V. Longevity of posterior restorations Int Dent J 1990; 40: 11-7 MOFFA JP. Comparative performance of amalgam and composite restorations and criteria for their use In: ANUSAVICE

Posterior restoration dental materials 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. KJ, ed. Quality evaluation of dental restorations Chicago: Quintessence Publ Co, 1989; 125-38. RuYTER E, SVENDSEN S A . Remaining methacrylate groups in composite restorative materials. Acta Odontol Scand 1978; 36: 75-81. RuYTER E. Kompositte tannfyllingsmaterialer Tandldkartidningen 1984; 76: 1207-10 KALLUS T. Incidence of adverse reactions from dental materials J Dent Res 1985; 64: 758 - Abstr No 21 KALLUS T, MJOR IA. Incidence of adverse effects of dental materials. Scand J Dent Res 1991; 99: 236-40 LUNDBERG PO, RUBARTH L . Kvicksilver/amalgam halsorisker Rapport fran socialstyrelsens ekspertgrupp, 1987 Uppsala, Sverige ScHUTZ A. Mercury In: BORGSTROM B, NORDEN A, KESSON B, ABDULLA M , eds. Nutrition and old age Vol 14 Stockholm: Scand J Gastroenterol, 1979; 223-31 DENCKER I, ScHiJTZ A. Kvicksilverinnehallet i kosten Ldkartidningen 1972; 68: 4031 JoNssoN E, NiLssoN T, SKERFVING S, SVENSSON

P G . Consumption of fish and exposure to methylmercury through fish in Swedish males. Vdr Foda 1972; 72: 59-70 SVENSSON BG, ANDERSSON P, BENGTSSON L . et al Forsurning och upptag av tungmetaller. Hygiea 1985; 94: 124-5 TEISINGER J , FISEROVA-BERGEROVA V. Pulmonary retention and excretion of mercury vapors in man. Ind Med Surg 1965; 34: 580. KosTA L, VYRNE A R , ZELENKO V. Correlation between selenium and mercury in man following exposure to inorganic mercury. Nature 1975; 254: 238-9 WANTABE S. Mercury in the body 10 years after long term e x p o s u r e to m e r c u r y . Proc Int Congr Occup Health 1971; 16: 553-4. 35. SKERFVING S "Normal" concentration of mercury in human tissue and urine. In: FRIBERG L, VOSTAL J, eds Mercury in the environment. Ohio: CRC Press, 1972; 109-12 36. LANGWORTH S, ELINDER CG, GOTHE CJ, VESTERBERG O , KESSON A. Kvicksilverhalter i blod och urin - inverkan av yrkesmassig exponering respektive fiskintag och amalgamfyllningar. Hygiea 1986; 95:

122 37. SKERFVING S, BERLIN M Nordiske expertgruppen for gransevardesdokumentation: 59 Organiskt kvicksilver Arbete & Halsa 1985; 20: 80-5. 38. LiNDSTEDT G, KARLSSON G . 39. 40. 41. 42. 43. 44. 45. GOTTBERG I, HoLMGREN B, JONSSON T, Individual mercury exposure of chloralkali workers and its relation to blood and urinary mercury levels. Scand J Work Fnviron Health 1979; 5: 59-69. ViMY MJ, LoRSCHEiDER FL. Serial measurements of intraoral air mercury: estimation of daily dose from dental amalgam J Dent Res 1985; 64: 1072-8 LANGWORTH S, KOLBECK K C , KESSON A. Mercury exposure from dental fillings. II Release and absorption Swed Dent J 1988; 12: 71-84. BERGLUND A, POHL L , OLSSON S, et al. Determination of the rate of release of intra-oral mercury vapor from amalgam. J Dent Res 1988; 67: 1235-41. OLSTAD M L , HOLLAND RI, WANDEL N , et al. Correlation between amalgam restorations and mercury concentrations in blood and urine. J Dent Res 1987; 66: 1179-84 LANGWORTH S,

ELINDER CG, KESSON A, et al. Mercury exposure from dental fillings. I Mercury concentration in urine. Swed Dent J 1988; 12: 69-74 MoLiN M, MARKLUND S, BERGMANN B, et al. Plasmaselenium, glutathioneperoxidase in erythroeytes and mercury in plasma in patients allegedly subject to oral galvanism. Swed Dent J 1987; 95: 328-32. PiiKivi L, HANNINNEN H , MARTELIN T, MANTERE P. Psychological performance and long-term exposure to mercury vapors Scand J Work Fnviron Health 1984; 10: 35-41 46. RoELS H, LAUWERYS R , BUCHET JP, et al Comparison of renal function and psychomotor performance in workers exposed to elemental mercury. Int Arch Occup Fnviron Health 1982; 50: 77-93. 47. HANNINEN H Behavioral methods in the assessment of early impairments in central nervous function. In: AITIO A, RimiMAKE V, VAINIO H , eds Biological monitoring and surveillance of workers exposed to chemicals Washington DC: Hemisphere Publ Co, 1983; 115-23. 48. NEWMAN SM Amalgam alternatives: What can compete? J Am Dent

Assoc 1991; 122: 67-71. 49. BERGMAN M Side-effects of amalgam and its alternatives: local, systemic and environmental. Int Dent J 1990; 40: 4-10 50. HENSTEN-PETTERSEN A Allergiske reaksjoner pa dentale materialer Den norske tannlegefor tidende 1984; 94: bl2>l 51. FiNNE K, GoRANssoN K, WiNCKLER L Oral lichen planus and contact allergy to mercury. Int J Oral Surg 1982; 11: 573-7. 52.LuNDSTROM IM Allergy and corrosion of dental materials in patients with oral lichen planus. Int J Oral Surg 1984; 13: 16-9. 53. LYBERG T, LIND PO Oral lichen planus Den norske tannlegefor tidende 1984; 94: 561-9. 54. MACKERT J R Dental amalgam and mercury J Am Dent Assoc 1991; 122: 54-61. 55. MANDEL I D Amalgam hazards An assessment of research J Am Dent Assoc 1991; 122: 62-5. 56. EAMES WB, STRAIN JD, WEITMAN RT, et al Clinical comparison of composite, amalgam and sihcate restorations J Am Dent Assoc 1974; 5.9- 1111-5 57. LEINEELDER KF, SLYDER T B , SOCKWELL CL Clinical evaluation of composite

resins as anterior and posterior restorative materials. J Prosthet Dent 1975; 33: 407-11 58. LIND PO Oral hchenoid reactions related to composite restorations Preliminary report Acta Odontol Scand 1988; 46: 63-5. 59. QVIST V, THYLSTRUP A Pulpal reactions to resin restorations In: ANUSAVIGE KJ, ed. Quality evaluation of dental restorations Chicago: Quintessence Publ Co, 1989; 291-9 60. TRONSTAD L Clinical endodontics New York: Thieme 1991; 10-31. 61. JENSEN ME, CHAN D C N Polymerization shrinkage and microleakage. In: VENHERLE G, SMITH DC, eds Posterior composite resin dental restorative materials. Amsterdam: Peter Szulc Publ, 1985; 243-62 62. YOUNG E Contact hypersensitivity to metallic gold Dermatologica 1974; 149: 294-8 63. FREGERT S, KOLLANDER M , POULSEN J Allergic contact stomatitis from gold dentures. Contact Dermatitis 1979; 5- 63-4 64. SKJORLAND K K Plaque accumulation on different dental fining materials. Scand J Dent Res 1973; 81: 538-42 65. BENTLEY C, DRAKE C W Longevity

of restorations in a dental school clinic. J Dent Fduc 1986; 50: 594-600 66. CRABB H S M The survival of dental restorations in a teaching hospital Brit Dent J 1981; 150: 315-8 67. RoBBiNS JW, SuMMiTT JB Longevity of complex amalgam restorations. Operative Dentistry 1988; 13: 54-7 68. OsBORNE JW, BiNON PP, GALE EN Dental amalgam: clinical behavior up to eight years. Operative Dentistry 1980; 5: 24-8 69. MARYNIUK GA In search of treatment longevity - a 30-year perspective. J Am Dent Assoc 1984; 109: 739-44 70. PATERSON N The longevity of restorations Brit Dent J 1984; 157: 23-5. 71. RYTOMAA I, MuRTOMAA H, TuRTOLA L, LiND K Clinical assessment of amalgam fillings. Comm Dent Oral Fpidemiol 1984; 12: 169-72. 72. QyisT V, THYLSTRUP A, MJOR IA Restorative treatment pattern and longevity of amalgam restorations in Denmark. Acta Odontol Scand 1986; 44: 343-9. 147 Rykke 73. QVIST V, THYLSTRUP A, MJOR IA Restorative treatment pattern and longevity of resin restorations in Denmark. Acta

Odontol Scand 1986; 44: 351-6. 74. MJOR IA, MEDINA J E Reasons for placement, replacement and age of gold restorations in selected practices. Scand J Dent Res 1992; 100: In press. 75. MJOR IA The long term cost of restorative therapy using different materials. Scand J Dent Res 1992; 100: In press 76. BJERTNESS E, SONJU T Survival analysis of amalgam restorations in long-term recall patients Acta Odontol Scand 1990; 48: 93-7. 77. LETZEL H , VANT HOF MA, VRIJHOEF MM A, MARSHALL GW, MARSHALL SJ. Failure, survival, and reasons for replacements of amalgam restorations In: ANUSAVICE KJ, ed 78. 79. 80. 81. Quality evaluation of dental restorations. Chicago: Quintessence Publ Co, 1989; 83-94 MJOR I A, ESPEVIK S. Assessments of variables in clinical studies of amalgam restorations. J Dent Res 1980; 59 (9): 1511-5. MARYNIUK GA, KAPLAN S H . Longevity of restorations: survey results of dentists estimates and attitudes J Am Dent Assoc 1986; 112: 39-45. NoRDBO H, LYNGSTADAAS SP. The clinical

performance of class II cast gold inlays. Scand J Dent Res 1992; 100: In press CHRISTENSEN G . The practicability of compacted gold foils in general practice - A survey. J Am Acad Gold Foil Oper 1971; 14: 57-65. 82. LEEMPOEL P J B , ESGHEN S, DEHAAN A F J , VANT HOF MA. An evaluation of crowns and bridges in a general dental practice. J Oral Rehabil 1985; 12: 515-28 83. CHRISTENSEN R , CHRISTENSEN G , VOGL S, BAGERTER V 2- year clinical comparison of 6 inlay systems. J Dent Res 1991; 70: 561 - Abstr. No 2360 84. DAHL JE, ERIKSEN HM Reasons for replacement of amalgam dental restorations Scand J Dent Res 1978; 86: 404-7 85. KLAUSNER L H , CHARBENEAU GT Amalgam restorations: a cross-sectional survey of placement and replacement. J Mich Dent Assoc 1985; 67: 249-52. 148 86. KLAUSNER LH, GREEN TG, CHARBENEAU GT Placement and replacement of amalgam restorations: a challenge for the profession. Oper Dent 1987; 12: 105-12 87. BOYD MA, RICHARDSON AS Frequency of amalgam replacement in

general dental practice J Can Dent Assoc 1985; 51: 763-6. 88. BOYD MA Amalgam replacement: are decisions based on fact or tradition? In: ANUSAVICE KJ, ed. Quality evaluation of dental restorations. Chicago: Quintessence Publ Co Int, 1989; 73-82. 89. QVIST V, PALLESEN U Clinical evaluation of three posterior composite resins: five-year report. J Dent Res 1990; 69; 307 -Abstr. No 1589 90. PETERS MCRB, LETZEL H , VANT HOF MA Process influence on the survival of amalgam and composite restorations J Dent Res 1990; 69: 287 - Abstr. No 1427 91. ROBERTS T A Composites, current status and future developments, reaction paper International state-of-the-art conference on restorative materials Bethesda: National Institutes of Health, 1986; 1-33. 92. ANUSAVICE KJ Criteria for selection of restorative materials: properties versus technique sensitivity. In: ANUSAVICE KJ, ed. Quality evaluation of dental restoration Chicago: Quintessence Publ Co Inc, 1989; 15-59 93. SCHWARTZ N L , WHITSET L D , BERRY

TG, STEWART JL Un- serviceable crowns and fixed partial dentures: life-span and causes for loss of serviceability. J Am Dent Assoc 1979; 81: 1395-1401. 94. MoRMANN WH, BRANDESTINI M , LUTZ F, BARBAKOW F Chairside computer-aided direct ceramic inlays. Operative Dentistry 1989; 20: 329-39. 95. GoETSCH T, MoERMANN W, KREJCI I, LuTZ F Cerec ceramic inlays clinically assessed using modified USPHS criteria. J Dent Res 1990; 69: 162 - Abstr. No 425 96. ISENBERG BP, ESSIG M E , MUENINGHOFF L M , LEINFELDER KF. Clinical evaluation of Cerec CADCAM restorations J Dent Res 1990; 69: 308 - Abstr. No 1597