Bonded amalgam restorations: current research and clinical procedure

This paper reviews the history of amalgam bonding; compares the results of recent clinical studies to laboratory results that report reduced microleakage, increased retention, inhibition of secondary caries, reinforcement of tooth structure, and reduced cuspal deflection; discusses conservative preparation guidelines; and presents a step-by-step clinical procedure.

A two-year randomized, controlled clinical evaluation of bonded amalgam restorations

PURPOSE

The clinical performance of adhesively bonded dental amalgam restorations was compared with that of traditionally placed non-bonded control amalgams in a randomized prospective study.

MATERIALS AND METHODS

One-hundred thirteen Class II Dispersalloy amalgams were placed in permanent molars and premolars of 31 (21 males, 10 females) human subjects with their informed consent. By random assignment, 60 amalgam restorations were adhesively bonded using ED Primer and Panavia 21 TC (both Kuraray Co, Japan), and 53 traditional non-bonded restorations were placed. Most preparations involved replacement of defective amalgam restorations. Clinical recalls were conducted by experienced evaluators using modified USPHS criteria for occlusal and proximal anatomic form, occlusal and proximal marginal adaptation, and occlusal and proximal surface roughness.

RESULTS

For the categories of anatomic form, marginal adaptation, surface quality, and temperature sensitivity, there were no significant differences between bonded and non-bonded amalgam restorations (chi-square analysis, p > 0.05). Three non-bonded restorations were lost at 4, 7, and 24 months from preparations with no deliberate retention.

CONCLUSION

After two years' clinical service, there were no failures among the amalgam restorations adhesively bonded using ED Primer and Panavia 21 TC, but three non-bonded restorations failed due to lack of retention. For traditional preparations, adhesively bonded amalgams of the type investigated perform as well as non-bonded amalgams over two years' clinical service.

Teaching of posterior composite restorations in Japanese dental schools

AIM

This study was conducted to assess the teaching programmes for Class I and II composite restorations in Japanese dental schools to obtain an overview of what is being taught, the relative teaching volume, the criteria for the provision of posterior composite restorations and the placement techniques taught.

DESIGN

Questionnaire forms mailed to the operative dentistry teaching departments in all 29 Japanese dental schools.

RESULTS

The response rate was 93 per cent, with replies from 27 of the 29 dental schools. Twenty-five (93 per cent) responding schools taught the use of Class I and two schools stated that they did not teach the use of posterior composite restorations. One of the two schools had no plan to teach posterior composites within the next five years. The other school did not answer this question. Most schools anticipated that the proportion of teaching time devoted to posterior composite restorations would increase within the next five years. Diversities and similarities between teaching programmes were noted between Japanese, North American and European dental schools, the Japanese programmes being closer to those in Europe than those in North America.

CONCLUSION

The diversities in the teaching of posterior composite restorations in Japanese dental schools are as great as in other parts of the world. Such diversities must affect the overall quality of restorations in general practice.

Influence of the isolation method on the 10-year clinical behaviour of posterior resin composite restorations

The aims of this prospective randomised clinical study were to clinically evaluate a radiopaque, highly filled, hybrid, light-activated resin-based composite for posterior teeth (Occlusin, ICI Dental, Macclesfield, UK and GC Dental, Tokyo, Japan) and compare the performance of restorations placed using rubber dam or cotton roll isolation. One clinician placed 100 (42 Class I and 58 Class II) restorations of the material under investigation. The isolation mode for each restoration was determined randomly: 52 preparations were protected from contamination with cotton rolls and aspiration, and 48 preparations were isolated under rubber dam. At baseline and periodically thereafter (0.5, 1, 2, 3, 4, 5, 6, and 10 years), each composite was evaluated by two practitioners using a modified (USPHS) rating system. After 10 years, 37 restorations were reviewed. The results showed satisfactory clinical performance with and without rubber dam after 10 years. A concern was the number of failures at 10 years due to unsatisfactory proximal contact. The evaluations for the surviving restorations were acceptable but with a large reduction in the percentage with ideal occlusal and proximal anatomy. The 10-year comparison of isolation modes showed no statistically significant differences (Kruskal-Wallis test) for each of the evaluation criteria. Furthermore, survival analysis showed no significant difference between the groups (Mantel-Haenszel method). It was concluded that the 10-year clinical behaviour of the restorations of a posterior composite placed under well-controlled, effective isolation with cotton rolls and aspiration, was not significantly different from the behaviour of restorations placed using rubber dam isolation.

Bonding of amalgam restorations: existing knowledge and future prospects

A number of laboratory and clinical studies over the last 15 years have explored the potential advantages of bonding amalgam to tooth surfaces. Bond strengths have been reported to range from 2 to 20 MPa, with higher bond strengths reported for filled adhesives. Most studies agree that the use of bonding results in a considerable reduction of microleakage, when compared with copal varnish or no lining. The use of bonding provides retention in vitro that is equivalent to, or better than, the use of mechanical undercuts. Most studies on strength of restored teeth report an improvement in resistance to fracture or cuspal flexing as measured by strain gauges. Penetration of secondary caries along the interface has been found to be inhibited by bonding. The mode of failure of bonded amalgams has generally been reported to be mixed, but predominantly between the resin and amalgam. In vitro studies have reported one potential problem in the incorporation of resin into amalgam, which may cause a decrease in strength of the restoration. The clinical studies of bonded amalgams that have been published to date are of short duration, indicating that when traditional preparations are used, no problems are seen with bonding, but also no advantages, as measured by clinical assessment criteria. However, some studies show that bonded amalgam may be useful for procedures where non-bonded amalgams would be expected to be lost, namely in preparations with little, if any, mechanical retention. It was concluded that, while there are various in vitro studies demonstrating that bonded amalgams have advantages of improved retention and tooth reinforcement and decreased marginal microleakage and secondary caries, the operative technique is more complicated and there are few advantages yet evident from clinical studies in conventional preparations having mechanical retentive features. However, there is evidence accruing from clinical studies that bonding of amalgam can be favorably used to extend the range of usage of amalgam to non-retentive conservative preparations, and toward the other extreme, as an adjunct to other forms of retention in large compound restorations.

Cleaning dental instruments: measuring the effectiveness of an instrument washer/disinfector

PURPOSE

To analyze the cleaning effectiveness of one type of instrument washer available for use in a dental office.

MATERIALS AND METHODS

Dental instruments were heavily contaminated with blood and specific test bacteria. They were placed in cleaning baskets or within instrument cassettes, processed through the instrument washer, and analyzed for remaining blood and viable bacteria.

RESULTS

Information obtained indicated that the washer is an effective cleaning system for dental instruments.

Effects of surface finish and fatigue testing on the fracture strength of CAD-CAM and pressed-ceramic crowns

STATEMENT OF PROBLEM

All-ceramic molar crowns can be fabricated with CAD-CAM or laboratory methods with different materials, and a polished or oven-glazed surface.

PURPOSE

This in vitro study determined the fracture strength of various all-ceramic crowns, with and without prior cyclic loading.

MATERIAL AND METHODS

Standardized molar crowns were fabricated with a CAD-CAM machine (Cerec 2), software with machinable ceramic materials (Vita Mark II and ProCAD), and also conventional heat-pressed IPS Empress crowns fabricated at 2 dental laboratories. Groups of 40 crowns of each material were manufactured with either a polished or an oven-glazed surface finish. Cyclic loading that simulated oral conditions were performed on half of each group. Afterward, all crowns were loaded until catastrophic failure.Results. Fracture loads of the polished ProCAD crowns without prior cyclic loading was 2120 +/- 231 N, significantly higher than that of the polished Vita Mark II crowns (1905 +/- 235 N), but was not significantly different from the strength of 2 laboratory-fabricated Empress crowns. Oven-glazing of ProCAD crowns improved the fracture strength significantly, up to 2254 +/- 186 N. Prior cyclic loading decreased the strength of all tested crowns significantly, but the reduction was less for the Cerec crowns than the Empress crowns.

CONCLUSION

Cerec ProCAD crowns demonstrated significantly greater strength than the Vita Mark II crowns, better resistance to cyclic loading and lower failure probability than the laboratory-fabricated IPS Empress crowns. Prior cyclic loading significantly reduced the strength of all-ceramic crowns, but had less effect on Cerec crowns than on the IPS Empress crowns. Oven-glazing of ProCAD crowns resulted in significantly higher strength and higher resistance to cyclic loading than surface polishing.

Dental materials: 1997 literature review

This review of the published literature on dental materials for the year 1997 has been compiled by the Dental Materials Panel of UK. It continues a series of annual reviews started in 1973. Emphasis has been placed upon publications, which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, ceramometallic restorations and resin-bonded bridges, ceramics, denture base resins and soft lining materials, impression materials, dental implant materials, orthodontic materials, biomechanics and image processing, resin composites, and casting investment materials and waxes). Three hundred and thirty three articles have been reviewed.

The development of resin-bonding for amalgam restorations

Adhesive techniques are now used for many dental restorative materials, including amalgam. Several generations of dentine bonding agents have been developed, mainly for bonding composite resins. When bonding is used with amalgam restorations, the need for retention and resistance form is reduced, the seal is improved, and some procedures, such as amalgam sealants, which were not previously possible, can be considered.

Surface finish produced on resin composites by new polishing systems

OBJECTIVE

There is a demand for more efficient and finer polishing of resin composite restorations. This study compared the use of some new systems, with new or reduced numbers of abrasive instruments, to polish representative resin composites.

METHOD AND MATERIALS

Super-Snap Rainbow Technique Kit, Sof-Lex Pop-On System, and Enhance Finishing and Polishing System were used to prepare the surfaces of blocks of seven different hybrid or microfilled resin composites. For each system, three instruments were used for 30 seconds each in a standard manner. The average surface roughness of the polished surfaces was determined by profilometer.

RESULTS

Visually, all surfaces were of clinically acceptable luster. By profilometer ranking, the Super-Snap Rainbow Kit produced the smoothest surfaces, followed by the Sof-Lex Pop-On System disks (which were not statistically different), and the Enhance System.

CONCLUSION

The Super-Snap Rainbow Technique Kit and Sof-Lex Pop-On System provided the smoothest surfaces for all the composites tested. For several composites, the Enhance System provided less smooth surfaces, but these were also clinically acceptable.

Single-use, disposable, presterilized light-activation probe: the future?

OBJECTIVE

The purpose of this study was to compare a single-use, disposable, presterilized light activation probe with an equivalent autoclavable probe. Light output, heat generation, and depth of cure were investigated.

METHOD AND MATERIALS

Ten disposable and two reusable probe tips were tested. Three maximum light output readings for each tip were recorded with a radiometer. Heat generation at the probe tip was recorded, at 30-second intervals over a five-minute period, with a thermocouple probe placed under a 3-mm-thick glass slide. After light-activated "compomer" was placed in a sectional two-piece stainless steel mold and cured, depth of cure was evaluated using the scrape technique.

RESULTS

With respect to light output and depth of cure, there were no statistically significant differences between probe types, but the disposable probe generated significantly less heat.

CONCLUSION

The disposable probe performed clinically as well as an autoclavable counterpart with respect to light output, heat generation, and depth of cure.

Antimicrobial activities of dental impression materials

OBJECTIVE

The aim of this study was to measure the in vitro killing effects five commercial alginate impression materials had on five test microorganisms.

METHODS

Two alginates with no added disinfectant, one supplemented with chlorhexidine and two others containing quaternary ammonium compounds were tested. Challenge microbes included two gram-positive cocci, two gram-negative bacilli and a yeast. Saline solutions containing standardized concentrations of test microbes were used to mix the alginates. Some set specimens were immediately homogenized and the resulting fluids diluted and spread plated. Other specimens were processed 30 or 60 min after setting. After culturing, the numbers of colonies were counted and the levels of microbial reductions determined.

RESULTS

Unsupplemented alginates had no antimicrobial effects. The quaternary-ammonium-containing alginates were completely effective against all five test microorganisms. The alginate with chlorhexidine killed all the gram-negative bacilli and the majority (95-99%) of the gram-positive cocci and yeast.

SIGNIFICANCE

Results indicated that disinfectant-containing alginate impression materials could reduce the number of soiling microorganisms present on and within test specimens.

Impression materials and techniques for crown and bridgework: a survey of undergraduate teaching in the UK

The aim of this study was to document the teaching of impression materials and techniques for crown and bridgework in the undergraduate curriculum in UK dental schools. A questionnaire sent to each school during the 1993/1994 academic year elicited fourteen replies (100% response). Addition-cured silicones were found to predominate; 71% of schools taught and used clinically a one-stage, full arch impression technique involving stock trays, and 57% of schools a full-arch custom tray technique. Routine disinfection of impressions was taught and practised in 43% of schools. The results demonstrated variation between UK dental schools in their teaching of impression materials and techniques for crown and bridgework in the undergraduate curriculum.

Dental materials: 1996 literature review. Part 2

This critical review of the published literature on dental materials for the year 1996 has been compiled by the Dental Materials Panel of the UK. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. Emphasis has been placed upon publications which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, resin-bonded bridges and ceramo-metallic restorations, ceramics, denture base resins and soft lining materials, impression materials, implants materials, orthodontic materials, biomechanics and image processing, resin composites and casting investment materials and waxes). Three hundred and thirteen articles have been reviewed.

Noise levels encountered in dental clinical and laboratory practice

PURPOSE

The aim of this study was to determine the noise levels made by different clinical hand-pieces, laboratory engines, and other significant equipment such as ultrasonic scalers, amalgamators, high-speed evacuation, and other items.

MATERIALS AND METHODS

Sound levels were measured at four dental practices and three dental laboratories selected as representative of a variety of workplaces to reveal a range of noise. The noise levels were determined using a precision sound level meter, which was positioned at ear level and also at 2 meters distance from the operator.

RESULTS

Virtually all noise levels at the dental clinics were below 85 dB(A). The noise levels in the dental laboratories had much higher maxima, with some cutting activities, steam cleaning, and sandblasting up to 90 dB(A), and compressed air blasts with a maximum of 96 dB(A).

CONCLUSIONS

The noise levels in the dental clinics are considered to be below the limit of risk of hearing loss. However, technicians and other personnel who spend many hours in noisy dental laboratories may be at risk if they choose not to wear ear protection.

Dental materials: 1996 literature review

This critical review of the published literature on dental materials for the year 1996 has been compiled by the Dental Materials Panel of the UK. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. Emphasis has been placed upon publications which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, resin-bonded bridges and ceramo-metallic restorations, ceramics, denture base resins and soft lining materials, impression materials, implants materials, orthodontic materials, biomechanics and image processing, resin composites and casting investment materials and waxes). Three hundred and thirteen articles have been reviewed.

A split-shank prefabricated post system: a critical multidisciplinary review

A multidisciplinary panel of senior academics and practitioners has evaluated a system of prefabricated threaded split-shank posts (Flexi-Post/Flexi-Flange) from published research and their own clinical use. These posts have been compared with requirements of an ideal post system in relation to clinical use, stress effects, stress distribution, retention, loosening and displacement, provision for cores, and biocompatibility. The purpose was to provide this critical review to allow interested clinicians to compare this novel design to other available post systems.

Dental materials: 1995 literature review

This critical review of the published literature on dental materials for the year 1995 has been compiled by the Dental Materials Panel of the United Kingdom. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. Emphasis has been placed upon publications which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, resin composites, dentine bonding, dental amalgam, endodontic materials, casting alloys, investment materials, resin-bonded bridges and ceramo-metallic restorations, all ceramic restorations, denture base and soft lining materials, impression materials, dental implants, orthodontic materials and biomechanics). Three hundred and thirty articles published in 68 titles have been reviewed.

Antimicrobial abilities of various dentine bonding agents and restorative materials

OBJECTIVES

The purpose of this study was to observe and measure the in vitro effect of various composite restorative materials and dentine bonding agents on the growth and adherence of oral bacterial believed to be responsible for recurrent caries in humans and on micro-organisms commonly used to evaluate the effectiveness of disinfecting agents.

METHODS

Five sets of dentine bonding agents and composite resins and ten species of micro-organisms were used. Circular disc specimens of each composite set were placed onto inoculated plates. Zones of growth inhibition around specimens were measured after incubation. On other plates, specimens were placed alone for 48 h, removed, and then the micro-organisms added. Also, the composite sets were placed into sterilized bovine incisors and suspended into sucrose-containing both inoculated with Streptococcus mutans for 3 days. Adhering materials were disclosed and scored.

RESULTS AND CONCLUSIONS

Four of the composites sets produced statistically similar (P > 0.05) inhibitory zones. The Gram-negative rods and the Staphylococcus aureus were the most resistant micro-organisms. The five composites sets produced the same (P > 0.05) reduction in bacterial accumulation (> 60%). Aging of the specimens in water for periods up to 4 weeks prior to exposure to S. mutans did not affect product activity.

Effects of pulsed Nd:YAG laser energy on human teeth: a three-year follow-up study

This study of laser use on dental hard tissues evaluated restorations and tooth vitality in teeth treated three years earlier. All teeth remained vital and asymptomatic. Restorations placed after caries removal were intact and clinically serviceable.

A worldwide survey of the teaching of glass ionomer (polyalkenoate) cements

This paper reports the findings of a worldwide survey of the teaching of glass ionomer (polyalkenoate) cements (GICs). A total of 324 questionnaires was returned from the 650 dental schools included in the study (50 per cent response), with the response ranging from 100 per cent (Australasia) to 4 per cent (USSR). The findings indicate that most primary dental degree students in the majority of countries investigated are presently taught the use of GICs in a wide range of applications using techniques which largely conform with those recommended by the manufacturers of such materials.

A new light-activated adhesive cavity liner: an in vitro bond strength and microleakage study

A new formulation of a light-activated calcium hydroxide-based cavity liner was developed for this study. Its shear bond strength and marginal microleakage in a Class V cavity preparation were compared to those of commercially available light-activated liners and conventional glass ionomer liners: GC Lining Cement (GC), Ketac-Bond (ESPE), Time Line (Caulk), Vitrabond (3M), XR lonomer (Kerr), and Zionomer (DenMat). The new formulation had significantly higher shear bond strength to dentin than the commercially available materials. Its microleakage along gingival (cemento-dentin) walls was statistically equivalent to one of the other materials and significantly better than all the others.

A new light-activated adhesive composite: shear bond strength and microleakage

A new light-activated adhesive composite has been formulated. Its shear bond strength and marginal microleakage were compared with glass ionomer cements: Fuji Ionomer Type II, Ketac-Fil and Ketac-Bond. The new material showed significantly (p < 0.05) higher bond strength to non-etched enamel (7.9 MPa) and dentin (7.3 MPa) than commercially available materials. It also performed significantly better (p < 0.05) in the microleakage test. Ease of use and the excellent marginal sealing ability of the new material are expected to allow considerable innovation in restorations of root caries, cervical erosion and other conditions where the marginal seal of the gingival cavosurface is difficult.

Inhibition of microbial adherence and growth by various glass ionomers in vitro

This study measured the in vitro inhibition of growth and adherence of five oral bacteria by glass-ionomer materials. Disks were prepared from two cavity liners and four restorative class materials, by use of Teflon plates with circular wells, five mm wide and two mm deep. The bacterial species tested included: A. viscosus, S. mitis, S. mutans, L. casei, and S. sanguis. Growth inhibition studies were performed by the spreading of 0.1 mL of standardized inocula over agar plates produced with selective media, followed by the direct application of glass-ionomer disks onto the agar. On other plates, disks were placed onto uninoculated agars for 48 h, followed by bacterial inoculation. All agar plates were incubated under optimal growth conditions for each bacterial species. The four restorative materials were also placed aseptically into sterilized bovine incisors and placed into sucrose containing broth media, inoculated with S. mutans for three days. Adhering materials were disclosed and scored. An ion-exchange electrode was used to measure fluoride release over a seven-day period for all six glass ionomers. The two cavity liners and two of the restorative materials produced the largest growth inhibition zones by direct contact. No growth inhibition occurred when the specimens were allowed to come into contact with the agars prior to inoculation. All four restorative materials reduced bacterial accumulations on enamel surfaces by over 80%. Elevations in short-term fluoride release levels were positively correlated with growth inhibition.

Connective tissue reactions to glass ionomer cements and resin composites

This study evaluated the histopathologic reactions of rat connective tissue to two glass-ionomer cements (Fuji Cap II, Fuji Ionomer Type III) and two microfilled light-cured composite resins (Helio-molar Radiopaque and Helioprogress). IRM (zinc oxide-eugenol cement) was used as a control. Discs of the materials, 5 mm in diameter and 2 mm thick, that had set for 15 minutes were implanted under the dorsal skin of 75 Sprague-Dawley rats. There were 15 rats in each group and each animal received two identical implants. Five rats from each group were terminated at 7, 28 and 85 days after implantation. Histologic sections of the implant sites were stained with hematoxylin and eosin. Findings at all study periods indicated that Fuji Ionomer Type III elicited more intense reactions than the other materials. Reactions to Fuji Cap II, Heliomolar Radiopaque and Helioprogress, at all study periods, were comparable to each other and to IRM.

Treatment selections for fissured grooves of permanent molar teeth

Twenty dentists from selected dental school departments were asked to examine thirteen areas of fissured grooves or pits in extracted molars, and select a treatment from a list of options for each designated groove area, as if each was on a separate tooth. There was a wide variation in initial treatment selections with (29 percent) amalgam and (25 percent) resin sealants being the most common. Pediatric dentists were significantly more conservative in both their original and later diagnoses than were the other dentists in this study.

Resin denture bases: review of accuracy and methods of polymerization

Traditional compression molding and heat-activation methods for polymerization of denture base resins have been widely used. Studies have shown that stresses introduced during processing can lead to the distortion of denture bases. Chemical-, microwave-, and light-energy activation, and various combinations (including polymerization under pressure) have been offered as alternative ways to make dentures. These methods have been attempts to improve the accuracy of fit of the dentures, but sometimes the goal has also been to provide a more convenient laboratory technique. This extensive review covers studies that have investigated the accuracy of acrylic and other types of resins for making dentures using the known range of fabrication methods.

Adaptation of acrylic resin dentures as influenced by the activation mode of polymerization

With the advent of newer methods of activation of the polymerization of denture base resins, there is a need to compare dentures constructed using various modes of activation such as heat, light, and microwave energy. This study compares the dimensional accuracy of a conventional heat-activated acrylic resin poly (methyl methacrylate) with a new pour resin, a visible light-activated resin, and microwave-activated acrylic resin, all polymerized for denture bases. All groups showed a processing contraction; the poorest-fitting group was processed in a brass flask and a water bath at 70-100 C, using a heat-activated resin (Acron); the relatively new light-activated resin (Triad) produced dentures of intermediate accuracy, as did Acupac 20, when either heat- or microwave-activated. The two best-fitting groups were prepared from an autopolymerizing resin (PERform) and the microwave-activated resin (Acron MC).

The teaching of posterior composites: a worldwide survey

The findings of a worldwide survey of the teaching of posterior composites have been reported. In most schools in at least Africa, Australasia, Europe, North America and Japan (mean response, 70 per cent) the undergraduate course in operative dentistry includes some consideration of posterior composites. However, the teaching in relation to these materials is typically limited and rarely includes practical exercises let alone requirements to gain clinical experience of the use of these materials. The data collected in respect of the materials and techniques considered appropriate for posterior composites was essentially consistent and in keeping with most of the recent authoritative literature in this field. It is concluded that many schools should review their approach to the teaching of posterior composites.

Marginal fracture of posterior composite resins

This study assesses the early cavomarginal breakdown of the newer posterior composite resin restorations compared with that of amalgam restorations. A total of 432 posterior composite restorations and 73 amalgam restorations were examined: 121 composite restorations (28%) and 44 amalgam restorations (60%) clinically showed a marginal crevice at some point on the cavosurface margin of the restoration at 6-month, 1-year, and 2-year recalls. The largest single reason for poor marginal adaptation was marginal fracture. Up to 2 years, the marginal integrity of the studied posterior composites was superior to that of an amalgam alloy. It was determined that smaller cavities, greater bulk of resin at the margin (especially at functional cusp areas), and well-finished margins without overfiling seem to reduce the occurrence of marginal fracture on composite resin restorations.

Margin quality and microleakage of Class II composite resin restorations

Margin quality and isotope microleakage analyses of Class II restorations placed in extracted human molars were compared using various composite resins and placement techniques. At occlusal margins, the traditional (experimental) composite resin restoration placed by the incremental technique showed less microleakage than did the traditional (commercial) [corrected] composite resin restoration placed by the bulk technique. In each group, the occlusal and proximal adaptations had significantly higher "excellent margin" than did the cervical adaptation. Thus, the marginal adaptation at the cervical aspect of conventional Class II composite resin restorations may present a problem with respect to microleakage.

The sealed composite resin restoration

This composite restoration-sealant combination is only to be considered for the small pit and fissure caries lesion. Bitewing radiographs should indicate no smooth surface interproximal caries in the teeth to be restored in this manner. All teeth treated with the composite restoration-sealant combination should be carefully evaluated at periodic recall visits. There is no single perfect conservative restoration for the young patient. Each of us must decide, on an individual basis, the appropriate type of procedure we elect to use. The sealed composite resin restoration can be very effective in carefully selected cases.

In vivo and in vitro wear of potential posterior composites

The influence of cavity size, material composition, and curing mechanism on wear resistance of Class II MOD resin restorations was analyzed quantitatively. Wear resistance tends to increase both as cavity size decreases, and also from chemical- to light- to heat-cured. As to wear, among the composite resins tested, there was no acceptable resin-based amalgam substitute.

New finishing instruments for composite resins

The trimming of composite resin restorations encompasses gross finishing, contouring, fine finishing, and polishing. A series of aluminum oxide-coated flexible disks have been marketed and are suitable for that purpose. However, their use is confined to directly accessible convex surfaces. For precise finishing of small delineated areas, and for concave and occlusal surfaces, rigid rotary instruments are necessary. The currently used stones and tungsten carbide burs are ineffective with microfilled composite systems. Thus, a series of finishing burs coated with 40- and 15-microns diamond chips were evaluated because of the superior grinding effectiveness as compared with existing instruments. Surface roughness measurements, and qualitative and quantitative SEM evaluations, indicate that these fine and superfine diamond finishing burs produce surfaces on composite resins as smooth as tungsten carbide burs and stones. At the same time, they cause less surface and subsurface damage or marginal fractures on composite resin restorations. The three-year clinical experience is generally favorable. Further quantitative clinical studies are warranted.