This paper proceeds from the decision to initiate

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1 Systematic Review of Conservative Operative Caries Management Strategies Dorothy McComb B.D.S., M.Sc.D., F.R.C.D.(C) Abstract: The relationship between cavity preparation extension and restoration longevity is examined through a systemic review of the available evidence on specific conservative, operative caries-management strategies. Evidence tables are provided for three specific techniques in the permanent dentition: 1) the proximal tunnel restoration, 2) the proximal box-only restoration, and 3) the preventive resin restoration. In the primary dentition, the clinical trials involving the proximal box-only restoration, most of which involved glass-ionomer materials, are reviewed. In the permanent dentition, the evidence reveals low effectiveness for tunnel restorations, limited but supportive results for proximal-only restorations, and generally favorable outcomes for the occlusal composite resin-sealant restoration. The weak link in the latter is the overlying fissure sealant, which requires adequate ongoing maintenance. Conservative operative strategies in the primary dentition have not been uniformly successful, and deleterious material effects dominate restoration performance. This systematic review concludes that operative conservatism per se does not guarantee increased restoration longevity and that all restorations are vulnerable to caries recurrence, material failures, and technical deficiencies. The more successful conservative strategies are expected to enhance tooth longevity, provided concomitant caries control is effective. Dr. McComb is Professor and Head, Restorative Dentistry at the University of Toronto. Direct correspondence to her at the Faculty of Dentistry, University of Toronto, Restorative Dentistry, 124, Edward St., Rm. 352C, Toronto, Ontario, Canada M5G 1G6; (4418) phone; fax; d.mccomb@utoronto.ca. The complete version of this paper can be viewed at Key words: conservative operative dentistry, tunnel restoration, proximal box-only restoration, slot restoration, preventive resin restoration, glass ionomer This paper proceeds from the decision to initiate operative intervention and examines the evidence for specific, conservative, operative caries-management strategies. The operative decision is a significant one as the action is irreversible and restorations have a finite lifespan. Such a decision assumes that an active caries lesion is present and that no other more conservative therapy is possible to effect a successful outcome. Traditional cavity preparation includes varying degrees of extension for prevention in an attempt to remove adjacent caries-prone tooth structure. The high rates of re-restoration performed in clinical practice, largely due to a diagnosis of recurrent caries, cast doubt on the effectiveness of this concept. In more recent years, traditional extension for prevention has been challenged, and more conservative forms of operative intervention have been recommended. Three specific techniques are 1) the proximal tunnel restoration, 2) the proximal box-only restoration, and 3) the occlusal preventive resin restoration. How do these conservative procedures perform in terms of longevity and causes of failure? Methods The clinical questions for the systematic review were developed in conjunction with the planning committee for the NIH Dental Caries Consensus Development Conference on Diagnosis and Management of Dental Caries Throughout Life. At issue is the evidence concerning the relationship between cavity preparation extension and restoration survival in 1) permanent and 2) primary teeth. A search strategy for human clinical studies since 1975 was developed in concert with a consultant. A Medline/Embase search resulted in 995/ 92 (total 1087) references for the permanent dentition and 169/116 (total 285) for the primary dentition. All abstracts were reviewed, and a final database of fiftyfour (permanent) and forty-four (primary) references was studied further. Appropriate references were included in systematic review tables for the specific interventions involved. The full report entitled The Scientific Basis for the Teaching and Practice of Conservative Operative Dentistry is available on the NIH web site at consensus.asp. The quality and nature of the literature 1154 Journal of Dental Education Volume 65, No. 10

2 were highly variable. Many clinical studies were incomplete with regard to controls, patient data, particularly caries-activity, and operator/examiner details, making definitive comparisons and analysis difficult. Study duration was often minimal. The Permanent Dentition The Proximal Tunnel Restoration The tunnel concept 1 accesses proximal dentinal caries through a sound occlusal pit and was designed to preserve the overlying proximal marginal ridge and maintain greater tooth integrity. It provides no extension for prevention. A total of nine clinical trials 2-10 in permanent teeth resulted from the search strategy and are included in Table 1. Almost all utilized a glassionomer silver-cermet cement as the restorative material. Both partial tunnel and total tunnel are described, depending on the extent of external perforation and amount of remaining demineralized enamel. Clinical reports from early usage 1,11 and the first clinical trial 2 utilized small numbers and indicated the technique to be promising. Larger clinical studies encountered higher failure rates. The most frequent causes of restoration failure were marginal ridge fracture or caries. Amalgam controls were included in only three trials. Conventional amalgam significantly outperformed tunnels over two years 10 and five years, 3 but the situation was reversed in the third trial. 2 The longest clinical study (seven years) reported a 50 percent survival time of six years 6 for the tunnel restoration, and recent multi-operator trials provide evidence of very high rates of associated caries (up to percent) as early as three years. 4,8,9 Residual caries, recurrent caries, and progression of demineralized enamel are all factors cited in failures, emphasizing the high caries risk of the interproximal area. The presence of a glassionomer was unable to overcome this ongoing caries challenge in the majority of studies. Many studies utilizing baseline radiographs reported evidence of inadequate initial caries removal 5,6,9,12 due to the blind access. The technique is clearly more difficult to execute than the traditional approach. Low restoration survival was associated with the limited preparation extension. 4,5,8,9 The low effectiveness reported reveals the difficulties involved with arresting caries in the caries-prone proximal contact area. Extremely poor performance has been documented in primary teeth. 12,13 Table 1. The proximal tunnel restoration: clinical studies October 2001 Journal of Dental Education 1155

3 The evidence suggests that this conservative strategy results in a high incidence of early re-restoration and cannot be recommended for routine use. As the presence of external cavitation is becoming accepted as the earliest stage necessitating operative intervention, the tunnel technique has increasingly limited application. The low effectiveness reported argues in favor of a more direct approach that includes judicious removal of adjacent demineralized tooth structure in the proximal contact area. The Proximal Box-Only Restoration Proximal box-only or slot preparations for amalgam were introduced in and adhesive slot preparations for resin composite in They include no occlusal dovetail or extension for prevention. Only three clinical studies 3,16,17 in permanent teeth resulted from the literature search (Table 2). Two involved adhesive proximal slot restorations with resin composite. No failures were recorded for sixty-eight composite box-only restorations over five years. 16 The ten-year success rate for composite proximal saucer preparations was 68.6 percent. 17 Half of the failures were due to recurrent decay, and half were technique-related. Recurrent caries, when present, occurred only at the gingival margin, not bucco-lingually, justifying the minimal lateral and occlusal extension. Loss of retention did not occur. One clinical trial of tunnel restorations included a small number of control silver amalgam proximal slot restorations. No failures were recorded for these over a period of five to seven years. 3 Despite the limited evidence, the available clinical trials in permanent teeth support the proximal slotonly restoration as a viable treatment option, providing similar or better longevity compared to conventional Class 2 composite or amalgam restorations, combined with greater tooth preservation. The technique is superior to tunnel restorations, likely due to improved operator visibility, but also possibly due to removal of all demineralized enamel. Gingival Margin Location Gingival extension of Class 2 restorations, whether traditional or box-only design, is of particular interest as the vast majority of recurrent decay occurs in the gingival proximal location. 18,19 Shorter-length proximal restorations with gingival margins ending close to the contact area had a significantly higher rate of recurrent caries over a two-year period. 20 Although there was a trend for long proximal preparations to have less recurrent caries than intermediate at each of the three time intervals, the difference was not statistically significant. Another study 21 of the effect of cavity design concluded that recurrent caries over eight to ten years was primarily associated with gingivalproximal cavity design features of amalgam restorations, including narrow gingival extension. As a selfcleansing location for the gingival margin of proximal restorations is impossible, good patient home care is essential. There is thus some evidence that overly conservative gingival extension increases the risk of recurrent caries in the absence of good patient compliance. The Preventive Resin Restoration The preventive resin restoration (PRR) is a conservative occlusal restoration that involves replacement of discrete areas of carious tooth structure with resin composite, followed by use of an overlying fissure sealant instead of traditional extension for prevention. 22 A total of eighteen clinical studies have been published, of which fifteen were prospective and three retrospective investigations. Success rates are not Table 2. Proximal-only restorations: clinical studies in permanent teeth 1156 Journal of Dental Education Volume 65, No. 10

4 easily comparable from study to study as the definition of failure was variously reported as actual presence of caries or loss of sealant. The difficulties are compounded by the practice of replacing deficient areas of fissure sealant during the trial period. Nonetheless, a systematic review table has been produced (Table 3). All the clinical studies show generally favorable outcomes; however, all universally report total or partial loss of the sealant as a major problem. Three studies performed a direct comparison with silver amalgam. 24,25,27 The PRR was at least as successful as amalgam in two of the trials, up to five years, with the added advantage of preservation of sound tooth structure. Sealant failure was a significant problem in the other, 25 which led to an occurrence of 8.1 percent recurrent caries, with no amalgam failures recorded over the three years. No occlusal caries was reported with intact sealants in any of the clinical studies, though many did not utilize radiographs at recalls. All cases of occlusal caries, up to 24 percent at nine years, 36 were associated with sealant failure, though the incidence of sealant failure was significantly higher than the presence of caries. Loss of sealant was increased over glass ionomer restorative materials 35,33 and larger areas of composite restoration. 32 In a different but related type of study, the ability of sealed composite restorations to halt the radiographically observed progress of frank carious dentine over a period of ten years has been reported. 23 This provides some welcome reassurance concerning inadvertent sealing of dentinal caries under fissure sealants and has positive implications for the conservative treatment of deep carious dentine in the vicinity of the pulp. The apparent arrest of frank, extensive dentinal cari- Table 3. The preventive resin restoration: clinical studies October 2001 Journal of Dental Education 1157

5 ous lesions under modest sealed restorations, however, requires further study. In summary, the preventive resin restoration is an effective conservative treatment for localized areas of occlusal dentinal decay. The weak link is the overlying fissure sealant, and loss of sealant was variously reported from 13 to 70 percent. As the sealant replaces extension for prevention, it is an integral part of the restoration and requires regular monitoring and maintenance. The Primary Dentition Longevity of restorations is very low in the primary dentition. 41 Generally, the earlier the age at restoration, the lower the longevity. 42,43 The predicted life span of re-restorations is even shorter. 42 The vast majority of clinical research on the primary dentition from the systematic review involves relatively short-term comparisons of dental materials, particularly newer proprietary materials, as they enter the marketplace. Qvist et al. 44 found that the major reasons for replacement of restorations in the primary dentition were restoration fracture or total loss. There is a continuing search, to the present day, for improved materials as a restorative solution to caries management in the primary dentition. Only one consistent conservative restorative strategy resulted from the search. Twelve clinical studies involved proximal box-only conservative restorations, and the results of these have been summarized in a systematic review table (Table 4). Almost all clinical studies involving glass ionomer materials in the posterior primary dentition involved proximal-only restorations. For completeness, the few other clinical studies of glass ionomer performance in primary molars are included. The first four references in Table 4 involve glass ionomer-type materials in traditional Class 2 restorations in comparison with silver amalgam. The remaining references in the table all involve box-only proximal restorations, with the last three involving poly-acid-modified-composites or compomers, a relatively new class of dental materials. No clinical studies resulted involving silver amalgam or composite proximal box-only restorations in the primary dentition. A significant omission in many of the trials is the presence of a control amalgam or resin-composite traditional restoration. The varying success rates reported with use of these more established materials in the primary dentition reveal the significant operator and/or patient factors involved in restoration failure, which must be controlled in any clinical trial. The results of the uncontrolled studies are therefore difficult to compare, and only generalized conclusions can be made. Material effects dominate the performance of primary molar restorations. Both conventional and silver-cermet glass-ionomers provided consistently poor results in both traditional and box-only restorations, generally due to their strength limitations. Failures involved mostly restoration fracture, bond breakdown, and total loss of restoration. Recurrent caries was recorded in association with a significant proportion of failed restorations. Due to the high failure rates, it has been stated that conventional and silver-cermet glassionomers are not suitable for the permanent restoration of primary molars. 46 They may be useful as a shortterm solution only for Class 1 restorations. 53 Deleterious material effects therefore overwhelmed the assessment of the conservative preparation per se on tooth longevity, pulpal response, and recurrent caries. The minimal preparation may even have increased failure rates due to technical and material limitations. Better results 45 have been reported for resinmodified glass-ionomer materials in proximal box-only restorations. Improved, but varying, results are reported for the newer acid-modified composite materials or compomers in conservative proximal restorations In summary, conservative operative procedures in the primary dentition have not been uniformly successful to date. Initial trials of innovative non-traumatic caries-management strategies, which involved incomplete caries removal, have been reported. 61 Cariostasis occurred over a period of eighteen months in the primary dentition, which parallels somewhat the results for the permanent dentition. 23 Further research is required in this area. Conclusions This systematic review of conservative interventions has revealed that conservatism per se does not guarantee increased restoration longevity. All restorations are vulnerable to caries recurrence, material failures, and technical deficiencies. Indeed, misguided conservatism in some cases may accelerate restoration demise due to the technical difficulties involved, the materials used, and the absence of disease control. This is particularly evidenced by the poor effectiveness of the tunnel restoration for the treatment of proximal caries. On the other hand, more successful conservative strategies, such as the preventive resin and proximal slot restorations, which can provide equivalent longevity to traditional restorations in the permanent denti Journal of Dental Education Volume 65, No. 10

6 Table 4. Glass ionomer and modified restorations in primary teeth tion, should enhance tooth longevity over larger-sized restorations, due to the initial reduction in tooth structure removal. Concomitant and future caries control is essential. Acknowledgments The text of this paper is a summary version of a full evidence report prepared for the NIH Consensus Development Conference on Diagnosis and Management of Dental Caries Throughout Life, The invaluable role of the search consultant in the process (P.F. Anderson, Dentistry Library, University of Michigan) is acknowledged. The assistance of a second reviewer (Dr. P.R. Walshaw, Assistant Professor, Clinical Sciences, Faculty of Dentistry, University of Toronto) for the assessment of the clinical research on specific October 2001 Journal of Dental Education 1159

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