What constitutes an ideal dental restorative material?

Intense environmental concerns recently have prompted dentistry to evaluate the performance and environmental impact of existing restoration materials. Doing so entices us to explore the 'what if?' innovation in materials science to create more ideal restorative materials. Articulating a specification for our design and evaluation methods is proving to be more complicated than originally anticipated. Challenges exist not only in specifying how the material should be manipulated and perform clinically but also in understanding and incorporating implications of the skill of the operator placing the restoration, economic considerations, expectations patients have for their investment, cost-effectiveness, influences of the health care system on how and for whom restorations are to be placed, and global challenges that limit the types of materials available in different areas of the world. The quandary is to find ways to actively engage multiple stakeholders to agree on priorities and future actions to focus future directions on the creation of more ideal restorative materials that can be available throughout the world.

Tribute to Dianne Rekow-Dental "Imagineer".

Elizabeth Dianne Rekow, BSME, MSME, MBA, DDS, MS, Certificate in Orthodontics, and PhD (1944-2022), was a dental science futurist pursuing brave new paths during her career. She was one of the pivotal scientists who initiated the CAD/CAM movement in the 1980s and went on to focus on digital dentistry for the rest of her career. Her professional contributions involved seven patents, 92 peer-reviewed publications, 10 book contributions, 31 proceeding contributions, and well over 100 national and international presentations. She was an avid supporter of women in science. Her greatest contribution was her expansive imagination. She served as 35th president of the American Association for Dental, Oral, and Craniofacial Research in 2006-2007 and 88th president of the International Association for Dental Research in 2011-2012. The present article reviews key elements of her career and includes testimonies from friends about her special relationships.

The Evolution of Dental Materials over the Past Century: Silver and Gold to Tooth Color and Beyond.

The field of dental materials has undergone more of a revolution than an evolution over the past 100 y. The development of new products, especially in the past half century, has occurred at a staggering pace, and their introduction to the market has been equally impressive. The movement has mostly come in the area of improved esthetics, marked by the gradual replacement of dental amalgam with dental composite and all-metal and porcelain-fused-to-metal indirect restorations with reinforced dental ceramics, all made possible by the rapid improvements in dental adhesive materials. This article covers the time course of dental materials development over the past century in which the Journal of Dental Research has been published. While there have been advances in nearly all materials used in the field, this article focuses on several areas, including dental amalgam, dental composites and light curing, dental adhesives and dental cements, ceramics, and new functional repair materials. A few short statements on future advances will be included at the end.

Clinical studies in restorative dentistry: New directions and new demands.

Clinical research of restorative materials is confounded by problems of study designs, length of trials, type of information collected, and costs for trials, despite increasing numbers and considerable development of trials during the past 50 years. This opinion paper aims to discuss advantages and disadvantages of different study designs and outcomes for evaluating survival of dental restorations and to make recommendations for future study designs. Advantages and disadvantages of randomized trials, prospective and retrospective longitudinal studies, practice-based, pragmatic and cohort studies are addressed and discussed. The recommendations of the paper are that clinical trials should have rational control groups, include confounders such as patient risk factors in the data and analysis and should use outcome parameters relevant for profession and patients.

Fatigue characterization of nine dental amalgams.

Dental amalgams prepared from nine commercially available dental amalgam alloys, including high copper ternary, high copper blend, and a conventional alloy, were evaluated for their compressive fatigue behaviour to at least 10(6) cycles. While the fatigue behaviour of all high copper amalgams was similar, statistically significant differences in cycles to failure amongst these amgalgams were detected as a function of load, with Sybraloy demonstrating the greatest overall resistance to fatigue failure.

Review of the 1993 dental materials literature.

OBJECTIVES: Electronic databases are not sufficiently up to date to provide comprehensive notation of the most recent literature for reference in developing scientific papers. The objective of this summary was to identify and categorize the 1993 dental materials scientific literature that dealt with restorative dentistry. METHODS: 17 primary journals were manually searched via the tables of contents, and 101 secondary journals were manually or electronically searched. Dental materials citations were categorized into 15 major sections and several subsections, excluding case reports and all the literature primarily related to dental implants or biomedical materials outside of dentistry. RESULTS: This study identified 786 citations, the largest number being associated with glass ionomers and composites. SIGNIFICANCE: This citation list provides a comprehensive source for review by academicians and researchers that bridges the gap between initial publication and electronic citation.

Dental materials citations: Part B, July to December 1996.

OBJECTIVE: A search was conducted in biomedical journals from July 1996 to December 1996 to identify dental materials publications and sort them into major categories. They were compared by frequency in different journals and in different categories during recent years. METHODS: Tables of contents for 16 primary and 51 secondary journals were inspected from July to December of 1996 and were divided into 17 categories. The frequencies of citations for primary journals and for different citation categories were examined over a four-year period from 1993 to 1996. RESULTS: There were 334 total citations from July to December 1996. The greatest number of citations continued to involve bonding (n = 159) and resin-based (composites; glass ionomers) restorative materials (n = 158). The numbers of articles by journal and by category were very similar over the last four years. The average number of articles per year was 531 +/- 15. SIGNIFICANCE: The literature citations compiled in this list provide a supplement for researchers and academicians to the current electronic databases.

Dental materials citations: Part A, January to June 1997.

OBJECTIVE: A search was conducted in biomedical journals published from January 1997 to June 1997 to identify all dental materials publications and sort them into major categories. METHODS: Tables of contents for 79 journals for the period of January to June, 1997 were inspected and divided into 17 categories. Citations were analyzed by both frequency in journals and in categories, as well as compared to frequencies for previous years. RESULTS: A total of 445 citations were detected in 79 journals for the period January 1997 to June 1997. Certain journals (n = 19) demonstrated a higher citation frequency (> or = 10 citations for 6 months) and represented 77.8% of all citations. The greatest number of citations continued to involve bonding (n = 97), resin-based restorative materials (composites; glass ionomers) (n = 95), prosthodontic materials (n = 51), and pulp protection/luting materials (n = 48). Frequencies by category were very similar to those for the last four years. SIGNIFICANCE: The compiled literature citations provide a supplement for researchers and academicians seeking information in existing electronic databases.

Protection hypothesis for composite wear.

Significant occlusal wear occurs on posterior composite restorations in areas without direct contact with opponent teeth (contact-free wear) in addition to wear at the contacts. Recent research has indicated that all occlusal posterior composite surfaces wear, and those surfaces show decreasing wear rates over time. This provides more evidence for an earlier theory proposed by Jørgensen et al. (1979) that composite contact-free wear is a function of access and attrition caused by small particles in the food bolus. This hypothesis is now called the "protection theory" or "protection hypothesis" for wear. Macroscopic protection or "sheltering" from wear is provided by cavity preparation walls. Microscopic protection against resin matrix wear is provided by filler particles that are close together. Clinical evidence supporting the protection hypothesis comes from recently confirmed low wear rates for microfill and hybrid composites. The objective of this work was to calculate the minimum inter-particle spacing required for microscopic protection (wear resistance) for composites based on assumptions of packing fractions (0.68) with small particles (0.02 microns radius) for dispersed versus agglomerated conditions. An inter-particle spacing (IPS) of < 0.10 microns was assumed to afford wear protection. The results are that only 1.5-6.0 volume percentage microfiller is theoretically required to generate an IPS of 0.1 micron for composite microscopic protection. However, microfiller particles are suspected to agglomerate into clusters. Modified calculations for that effect indicate that at least 35% filler is required to provide microscopic protection. This effect explains much of the 3 to 5 year clinical research results for microfills and hybrids.(ABSTRACT TRUNCATED AT 250 WORDS)

Review of dental materials citations: Part B, July to December 1995.

OBJECTIVE: A lag of many months occurs between journal issue publication and updates to electronic databases. The objective of this literature analysis was to identify and categorize all of the dental materials citations in biomedical journals that were published from July 1995 through December 1995. METHODS: Seventeen primary and 51 secondary journals were searched using their tables of contents to detect and record dental materials publications from July to December of 1995. Those journals that were typically rich in dental materials articles were classified as primary ones. Citations were categorized into 17 topics and divided into subsections. The review excluded case reports, most literature related primarily to dental implants, and most articles on biomedical materials used outside of the field of general dentistry. RESULTS: The greatest number of citations was related to topics of dentin bonding and resin-based restorative filling materials (composites and glass ionomers). There was no major change in the number of dental materials publications per year reported from 1993 (n = 786) to 1995 (n = 751). SIGNIFICANCE: This citation list provides a comprehensive resource for use by academicians and researchers to bridge the gap between initial publication and access to electronic searching methods for major databases.

Dental materials citations: Part A, January to June 1996.

OBJECTIVE: A search was conducted to identify the dental materials publications that appeared in biomedical journals from January 1996 to June 1996 and to compare the frequency of citations among the different categories. METHODS: The tables of contents of 16 primary journals and 48 secondary journals were examined to identify dental materials articles that were published from January to June 1996. These citations were divided into 17 categories and the numbers of citations in each category were compared. To assess the usefulness of the citation listing, a survey of Academy of Dental Materials subscribers was conducted (n = 153 of 382 or 40.1% have responded to date). RESULTS: As in previous years, the greatest number of citations were found in categories of bonding (n = 83) and resin-based restorative materials such as composites and resin-reinforced glass ionomers (n = 80). Results of the reader survey indicated that 84.3% of the respondents have used the citations lists, and 95.4% feel that its publication should be continued. SIGNIFICANCE: The literature compiled in this list serves to supplement the electronic indexing mechanisms so that academicians and researchers can have ready access to the current literature in the field of dental materials.

Review of dental materials citations: Part A, January to June 1995.

OBJECTIVE: Electronic databases are an excellent resource for identifying relevant references for research and education projects. However, these databases are not yet a substitute for direct inspection of the literature because: (a) there still is a lag of many months between journal issue publication and updates of the database, and (b) most databases selectively report a portion of the entire literature. The objective was to identify and categorize all the dental materials citations in biomedical journals that were published from January 1995 through June 1995. METHODS: Seventeen primary and 56 secondary dental journals were manually searched via their tables of contents to detect dental materials publications from January to June of 1995. Dental materials citations were categorized into 17 major sections and further divided into several subsections. The review excluded case reports and literature primarily related to dental implants or biomedical materials outside of dentistry. RESULTS: Three hundred-sixty-nine citations were identified. The greatest number of citations were associated with dentin bonding, composites, and glass ionomers. There was no significant increase in dental materials publications vs. the number reported for 1994. SIGNIFICANCE: This list provides a comprehensive source for review by academicians and researchers to bridge the gap between initial publication and electronic citation.

Comparison of direct and indirect methods for analyzing wear of posterior composite restorations.

The vast majority of recent clinical research involving wear analyses of posterior composite resin restorations have used either the direct evaluation method (USPHS) or the indirect cast comparison (Leinfelder) method. However, there has never been any established correlation of the two wear scales. The objective of this study was to determine the amount of wear for the USPHS alfa-bravo transition on the basis of cast comparison data. Clinical wear data were collected over five years by both the direct method and the indirect method. Three materials were used involving a total of 221 restorations in 61 patients. Each restoration was evaluated at baseline, six months, one, two, three, and five years by each method. Then, for those restorations which underwent a transition from an alfa to a bravo clinical rating, the absolute wear at the transition was determined by averaging the indirect ratings just before and just after the transition. The mean wear corresponding to the alfa-bravo transition was 192 +/- 60 microns. Because of the large width of the alfa category up to the alfa-bravo transition, extensive early changes and high initial wear rates cannot be detected by the USPHS system.

Bonding to resurfaced posterior composites.

Despite significant improvements in the wear resistance of posterior composite restorations, they still undergo occlusal wear, color change, and surface staining with time. One method of repairing these restorations is re-surfacing the old composite. This study investigated the bonding of new composite to the corresponding old composite material by several different mechanical conditioning steps, chemical conditioning steps, primer conditioning steps, and four posterior composites. Aged composite surfaces were conditioned, re-bonded to new composite, stored in artificial saliva for seven days at 37 degrees C, and tested in shear. The mean shear strength for unrepaired composites was 27 MPa. Optimal re-bond strengths were 88% (Estilux), 77% (Ful-Fil), 92% (Occlusin), and 102% (P-10) of original bulk shear strengths. General linear modeling revealed that the best combination tested was roughening with a D830 diamond bur, conditioning the surface with water, and priming with Scotchbond-1 dentin bonding agent.

Confirmation of Leinfelder clinical wear standards.

OBJECTIVES: Accuracy of composite wear studies based on Leinfelder standards has been disputed. There are differences with other well-calibrated systems such as the M-L and Vivadent wear standards. The objective of this study was to reevaluate the margin height at key regions along the restoration margins for each of the 6 Leinfelder standards using laser profiling techniques. METHODS: The Leinfelder standards were profiled in parallel paths 100 microns apart and measured in x-y-z position every 20 microns along those paths using a laser profilometer. RESULTS: Rounding of cavosurface enamel margins from intraoral wear greatly increased the uncertainty of the true enamel margin location and step height measurements, precluding unequivocal measurements for standards #2 and #3. Values for other standards for the original report, newly measured means and standard errors, and measured ranges were: #4 (322 microns, 333 +/- 34 microns, 171-507 microns), #5 (382 microns, 459 +/- 44 microns, 202-649 microns), and #6 (493 microns, 584 +/- 91 microns, 315-1022 microns). There were no statistically significant differences (p < or = 0.10) between these and original values. Large standard errors may have obscured small differences that may exist. The Leinfelder cast conversion scale seems to be the correct relative magnitude. SIGNIFICANCE: Differences between Leinfelder casts and other standards may be due to differences in shadow production. Clinical wear may be systematically underestimated by other cast evaluation methods that have well-defined margins. This emphasizes the need for standard casts with margin morphology similar to the clinical casts being evaluated for wear.

Review of the 1994 dental materials literature.

OBJECTIVES: Electronic databases provide strong support for research and education literature searches. However, there is still some lag in time between publication and updates of the database. The objective of this summary was to identify and categorize the 1994 dental materials scientific literature that dealt with restorative dentistry. METHODS: Seventeen primary journals were manually searched via the Tables of Contents and 88 secondary journals were manually or electronically searched. Dental materials citations were categorized into 15 major sections and several subsections, excluding case reports and literature primarily related to dental implants or biomedical materials outside of dentistry. RESULTS: Nearly twelve hundred citations were identified, the largest number being associated with composites and glass ionomers. SIGNIFICANCE: This list provides a comprehensive source for review by academicians and researchers to bridge the gap between initial publication and electronic citation.

Correlation of M-L, Leinfelder, and USPHS clinical evaluation techniques for wear.

Most recent clinical research studies on wear of posterior composite restorations have used the USPHS and Leinfelder measuring techniques. New studies are adopting the Moffa-Lugassy (M-L) technique. However, to date there has been no means of comparing results of the different techniques. The objective of this study was to correlate the M-L scale wear values to Leinfelder scale wear values and to USPHS scale alfa-bravo transitions, so that data can be pooled across studies for comparisons. M-L evaluations were made for 221 restorations previously evaluated by the USPHS and Leinfelder methods. The M-L wear values were determined as the mean of three independent evaluators' values. At the USPHS alfa-bravo transition, the mean Leinfelder wear value was 192 microns, and the mean M-L value was 97 microns. The correlation coefficient for the linear regression of M-L values vs. Leinfelder values was 0.87. The scales were linearly related, with a slope of 0.52. The average values for M-L readings of wear were statistically different and approximately half the Leinfelder values.

Three-year clinical evaluation of a self-cured posterior composite resin.

A study was conducted to determine whether the wear resistance of a posterior composite could be improved by maximizing filler particle-to-particle contacts. This was expected to reduce stress concentrations on the resin matrix and thus reduce occlusal wear. A self-curing quartz-filled composite with this design, P-10, was used to restore 90 Class I and II cavity preparations in adult teeth. Restorations were recalled after baseline at six months, one year, two years, and three years to measure wear by direct and indirect evaluation methods. There was no apparent advantage for this material compared with other previously evaluated posterior composites. The average cumulative wear for P-10 after three years was 145 microns. In addition, the restorations were evaluated for color-matching, interfacial staining, secondary caries, marginal adaptation, surface texture, and postoperative sensitivity. This material was not significantly different in those ways from other posterior composite products except in terms of more rapid color change, because it is self-cured.

3D-FEA of osseointegration percentages and patterns on implant-bone interfacial stresses.

OBJECTIVES: The degree of osseointegration and its patterns are important for the success of implants. 3D-FEA was used to determine interfacial stresses on a single tooth implant (IMZ) for four degrees of osseointegration (100, 75, 50 and 25%), and five patterns at 50% osseointegration (locally alternating, coronal only, apical only, facial only and lingual only). METHODS: The implant was restored with a metal-ceramic crown and subjected to 10 MPa axial or oblique applied stress. Resolved stresses were examined at four heights along the implant-bone interface. RESULTS: The degree of osseointegration did not affect resolved stress levels or distributions. Oblique loads elevated interfacial stresses 5 to 20 times. Stresses were always higher at the bone crest. CONCLUSIONS: Osseointegration patterns with crestal bone reduced both crestal and apical stresses. Apical only osseointegration produced much higher apical stresses. Crestal osseointegration and axial loads minimized overall stress.

Five-year clinical study of u.v.-polymerized posterior composites.

Four u.v.-polymerized composites (Estilux, Nuva-Fil, Nuva-Fil P.A. and Uvio-Fil) were clinically evaluated in Class I and II cavity preparations in permanent teeth. The restorations were evaluated at baseline, 1, 2, 3, 4 and 5 years using USPHS criteria for direct evaluation and at 3, 4 and 5 years using the Leinfelder method for indirect evaluation of wear. The wear measured by the USPHS method showed increasing wear rates in earlier reports, apparently due to the limited sensitivity of the scale to early wear. The wear by the Leinfelder method showed gradually decreasing wear rates. There were no statistically significant differences among the wear values for the four u.v.-cured materials or between these materials and the self-cured and visible light-cured controls.