The Academy of Dental Materials: Providing roots and wings.

OBJECTIVES: The long history of the Academy of Dental Materials (ADM) is documented with its strategies (a) to rapidly communicate science among its members, (b) to establish special awards to stimulate new science, and (c) to develop new dental materials scientists. METHODS: We searched the history of the last 35 years of the ADM newsletters, transactions, journals, and officer notes. We document the (a) presidents, (b) meeting history, (c) membership growth, and (d) development of special awards through 2019 with the recent creation of the ADM Marshall Post-Doctoral Award. RESULTS: There are 36 years of recent ADM history, 42 international meetings, membership growth to 400 individuals from 15 countries, service of 19 presidents, Paffenbarger annual Awardees since 1989, induction of >200 fellows, and recognition of the first winner of Marshall Post-Doctoral Award in 2018. New directions for recruiting members are suggested. Three potential new thrusts for the organization are presented: artificial intelligence, genetic engineering, and intensive member mentoring. SIGNIFICANCE: These suggestions for the ADM provide a path for the ADM to continue to adapt to the ever changing scientific landscape.

Composition, phase analysis, biaxial flexural strength, and fatigue of unshaded versus shaded Procera zirconia ceramic.

STATEMENT OF THE PROBLEM: Recent interest in shaded zirconia has raised questions about the relative stability of the tetragonal phase after colorant oxide additions. PURPOSE: The purpose of this in vitro study was to evaluate the effects of fatigue cycling on the stability of a commercially available dental zirconia (Procera) in both unshaded and shaded compositions by measuring the change in biaxial flexural strength (BFS) after 500 000 cycles at 80-N loads and in phase composition as detected by x-ray diffraction (XRD). MATERIAL AND METHODS: Partially stabilized zirconia disks (NobelProcera) were fabricated in unshaded and shaded forms (12 mm diameter × 0.8 mm thick). Specimens were analyzed by energy-dispersive x-ray spectroscopy (EDS) and by wavelength-dispersive x-ray spectroscopy (WDS) for oxide compositions which indicated the presence of small amounts of Fe-O (0.13 ±0.10 wt %) in the shaded specimens. XRD focused on the tetragonal (T) and monoclinic (M) peaks in the 20 to 40 degrees 2θ range. The disks were polished on 1 side, cyclically loaded (80N, 500 000 cycles, custom 4-station fatigue test machine), and tested for residual BFS after cycling. Unshaded (U) and shaded groups (S) were compared before (U1, S1) and after (U2, S2) load cycling with XRD and residual BFS. RESULTS: Residual BFS (MPa) for specimens before (U1=856 ±99 versus S1= 842 ±40) and after fatigue (U2=772 ±65 versus S2= 718 ±68) were statistically different (U1 versus U2; S1 versus S2; U2 versus S2, P<.05). The XRD of U1 and S1 specimens revealed tetragonal and cubic zirconia. U2 and S2 specimens contained tetragonal zirconia, with the initial appearance of small amounts of monoclinic zirconia after fatigue cycling. Monoclinic detection was measured on the tension side of the tested specimens and varied between tests at the center and radially at 4 mm. CONCLUSIONS: The results indicated shaded materials more readily transform the tetragonal to the monoclinic phase during load cycling than unshaded ones. However, extrapolating the effects of any shortening of the service life of zirconia compositions is difficult. The potential mitigating effects of other factors such as the thermal postprocessing of porcelain veneers, stains on zirconia, or effects of water have yet to be investigated.

Cyclic Loading Effect on Color Stability of Unshaded versus Shaded Zirconia.

STATEMENT OF PROBLEM: Shaded versions of dental zirconia may improve initial color matching to teeth, but might change color with cyclic mechanical loading. PURPOSE: The purpose of this study was to measure the color of unshaded and shaded zirconia dental ceramic before and after cyclic mechanical loading and calculate color differences (ΔE). MATERIAL AND METHODS: Disk-shaped specimens (N = 30, Nobel Procera, 0.8 mm thick, 12 mm diameter) of unshaded or shaded zirconia (intrinsically shaded by small oxide modifications) were fabricated by the Nobel Biocare using standard CAD-CAM processing. Milled surfaces were polished. CIE L*a*b* values were measured (Konica Minolta spectrophotometer) before and after mechanical cycling (custom modified Leinfelder test machine, biaxial flexure loading, load = 80 N × 500,000 cycles, dry), and L*a*b* individual differences and ΔE color differences were calculated and compared (ANOVA, p < 0.05). RESULTS: Mean L*a*b* values for the unshaded group before (U1 = 86.165, -0.887, 0.372) and after (U2 = 84.860, -0.805, 0.097) cyclic loading were compared to the shaded group before (S1 = 75.281, -0.679, 23.251) and after (S2 = 74.961, -1.233, 22.439) cyclic loading. All color variables for both unshaded and shaded groups were significantly different between before and after cyclic loading (p < .004) except for the L* value of the shaded group. The ΔE for unshaded (1.441 ± 0.495) versus shaded (1.252 ± 0.363) were statistically different but clinically the change would not be detectable at this point. CONCLUSIONS: The color of the unshaded and shaded zirconia specimens was influenced by cyclic loading (p < 0.05). Color changes were detectable but small at levels up to 500,000 cycles, and remained clinically acceptable at that point. CLINICAL SIGNIFICANCE: It is important to acknowledge any possible color changes that might occur in zirconia restorations, especially in the esthetic zone. Minor color changes that are individually imperceptible to the human eye within different restorative components may be compounded to produce clinically significant color change that is not aesthetically acceptable.

Evidence-based dentistry as it relates to dental materials.

Evidence-based dentistry (EBD) is reviewed in depth to underscore the limitations for evidence-based dental materials information that exist at this time. Anecdotal estimates of evidence for dental practice are in the range of 8 percent to 10 percent. While the process of evaluating the literature base for dental evidence began 20 years ago, it was not practical to implement it until high-speed wireless connections, open access to journals, and omnipresent connections via smart phones became a reality. EBD includes five stages of information collection and analysis, starting with a careful definition of a clinical question using the PICO(T) approach. Clinical evidence in randomized control trials is considered the best. Clinical trial perspectives (prospective, cross-sectional, retrospective) and outcome designs (RCTs, SCTs, CCTs, cohort studies, case-control studies) are quite varied. Aggregation techniques (including meta-analyses) allow meaningful combinations of clinical data from trials with similar designs but with fewer rigors. Appraisals attempt to assess the entire evidence base without bias and answer clinical questions. Varying intensities to these approaches, Cochrane Collaboration, ADA-EBD Library, UTHSCSA CATs Library, are used to answer questions. Dental materials evidence from clinical trials is infrequent, short-term, and often not compliant with current guidelines (registration, CONSORT, PRISMA). Reports in current evidence libraries indicate less than 5 percent of evidence is related to restorative dental materials.

Catalogue of tooth brush head designs.

PURPOSE: Manual toothbrushes (MTBs) and power toothbrushes (PTBs) are effective oral physiotherapy aids for plaque removal. End-rounded bristles are safer and reduce damage to oral tissues. Nylon bristles are more effective in plaque removal because the bristle is stiffer than natural bristles. In the last 10 years the number of options for MTBs and PTBs has expanded significantly and there is very little information providing a reference frame for the design characteristics of the heads. The present in vitro study characterized a variety of MTB and PTB heads to provide a reference library for other research comparisons which might be made. METHODS: Various commercial MTB and PTB heads were used to characterize the following: bristle size, shape, diameter, number of tufts, number of bristles per tuft and surface characteristics. Photographs were collected from the side, at 45 degrees and the top of each toothbrush (TB) head using a scanning electron microscope and digital camera. Images were analyzed (Soft Imaging System) for bristle features and designs. One-way ANOVA (p ≤ 0.05) was performed to detect differences among TB types within MTB and PTB groups and between pooled values for MTB and PTB groups. RESULTS: There were significant differences (p ≤ 0.05) in toothbrush bristle diameter and bristle shape. In contrast, there were no significant differences between PTB vs. MTB in regards to bristle diameter, bristle count and tuft count. CONCLUSION: The results suggest that although there are wide variations in toothbrush head designs, significant differences were found only in relation to bristle diameter and shape.

Framework for e-learning assessment in dental education: a global model for the future.

The framework presented in this article demonstrates strategies for a global approach to e-curricula in dental education by considering a collection of outcome assessment tools. By combining the outcomes for overall assessment, a global model for a pilot project that applies e-assessment tools to virtual learning environments (VLE), including haptics, is presented. Assessment strategies from two projects, HapTEL (Haptics in Technology Enhanced Learning) and UDENTE (Universal Dental E-learning), act as case-user studies that have helped develop the proposed global framework. They incorporate additional assessment tools and include evaluations from questionnaires and stakeholders' focus groups. These measure each of the factors affecting the classical teaching/learning theory framework as defined by Entwistle in a standardized manner. A mathematical combinatorial approach is proposed to join these results together as a global assessment. With the use of haptic-based simulation learning, exercises for tooth preparation assessing enamel and dentine were compared to plastic teeth in manikins. Equivalence for student performance for haptic versus traditional preparation methods was established, thus establishing the validity of the haptic solution for performing these exercises. Further data collected from HapTEL are still being analyzed, and pilots are being conducted to validate the proposed test measures. Initial results have been encouraging, but clearly the need persists to develop additional e-assessment methods for new learning domains.

Wear of a dental composite in an artificial oral environment: A clinical correlation.

The study objective was to correlate wear between an in vitro method for simulating wear and in vivo wear of a posterior dental composite. Ten subjects (12 restorations) were selected from a five-year clinical study (University of North Carolina, School of Dentistry) that assessed wear of SureFil composite (Caulk, Dentsply). Subject casts were digitized and changes in volume and mean depth with time were calculated from the 3D digital models for contact and contact-free wear. SureFil composite disks were mounted in the University of Minnesota's Artificial Oral Environment, opposed by natural enamel, subjected to mandibular-like movements for 150 K, 300 K, 600 K, 1.2 M, and 1.5 M cycles, and loaded with peak forces of 13 N (n = 7) or 30 N (n = 3). Wear rates were calculated as the slope of the linear regressions fitting the wear data. Data were analyzed using one-way ANOVAs and post hoc t-tests where appropriate (p = 0.05). Clinical restorations included contact wear on seven restorations and contact-free wear on all restorations. Contact-free wear was less than contact wear (p < 0.01). SureFil clinical wear rates were 0.012 mm/year (mean depth) and 0.023 mm(3)/year (volume). Clinical restorations expanded slightly during the first year. Using a conversion rate of one year equals 3 × 10(5) cycles, there were no significant differences between the clinical and simulated data except depths at Year 5 and 13 N volume at Year 4. The 30 N simulation reproduced the clinical data if contact-free wear was taken into account. Good agreement between simulated and clinical wear implies that in vitro simulation can screen new composite formulations.

Correlation of clinical performance with 'in vitro tests' of restorative dental materials that use polymer-based matrices.

OBJECTIVE: Review correlations of in vivo clinical performance with in vitro laboratory tests of restorative dental materials involving polymer-based matrices. Identify those factors interfering with the process. MATERIALS AND METHODS: An evidence-based dentistry approach was used to identify clinical trials, critical reviews, and meta-analyses involving correlations. Factors impacting meaningful correlations were reviewed. The limited bona fide correlations were reviewed. RESULTS: In vitro tests include physical, chemical, mechanical, and biological properties. Clinical research measurements routinely include 10-15 categories of clinical observations of performance such as color match, caries resistance, marginal integrity, surface texture, and others, but do not correspond well with laboratory properties. Clinical trials of restorative dental materials represent a small fraction of the total research in this arena (typically <10% of dental materials research over many years). Trials are generally short-term (2-5 years) and are designed primarily to test product "safety and efficacy." A large number of risk factors (operator, design, material, intraoral location, patient) affect clinical outcomes and are not simulated well in laboratories. Little long-term information exists for clinical performance other than on composite wear. Very few meaningful correlations of laboratory tests and clinical results are demonstrated. CONCLUSIONS/RECOMMENDATIONS: New studies should be focused on recovering restorations from service and characterizing them with the same tests as normally conducted in the laboratory. Many more long-term clinical trials that involve 10-20 years of observations are needed. Those trials should include planned restoration recovery to assess changes in laboratory properties of interest.

A review of adhesion science.

OBJECTIVE: Adhesion or cohesion includes an adherend, adhesive, and intervening interface. Adhesive joints may include one or more interfaces. Adhesion science focuses on understanding the materials properties associated with formation of the interfaces, changes in the interfaces with time, and events associated with failure of the interfaces. METHODS: The key principles for good interface formation are creation of a clean surface, generation of a rough surface for interfacial interlocking, good wetting of the substratum by the adhesive/cohesive materials, adequate flow and adaptation for intimate interaction, and acceptable curing when phase changes are required for final joint formation. RESULTS: Much more effort is needed in the future to carefully assess each of these using available testing methods that attempt to characterize the energetics of the interfaces. Bonding involves potential contributions from physical, chemical, and mechanical sources but primarily relies on micro-mechanical interaction for success. Characterization of the interface before adhesion, during service, and after failure would be much more useful for future investigations and remains as a great challenge. SIGNIFICANCE: Scientists should more rigorously apply techniques such as comprehensive contact angle analysis (rather than simple water wettability) for surface energy determination, and AFM in addition to SEM for surface texture analysis.

A 12-year clinical evaluation of a three-step dentin adhesive in noncarious cervical lesions.

BACKGROUND: The authors conducted a study to evaluate the clinical performance of a dual-cured, three-step dentin adhesive (OptiBond Dual Cure, Kerr, a subsidiary of Sybron Dental Specialties, Orange, Calif.; no longer on the market) at 12 years. METHODS: The authors restored 100 noncarious cervical lesions without use of macromechanical retention or enamel bevels. In one-half of the lesions (group A), the authors etched only the enamel; in the other half (group B), they etched both enamel and dentin. After etching, they applied a light-cured primer and dual-cured adhesive to enamel and dentin in both groups. They restored the preparations with a resin-based composite. They performed direct evaluations by using modified U.S. Public Health Service criteria at insertion (baseline) and at one year and 12 years after insertion. RESULTS: The 12-year retention rates were 93 percent in group A and 84 percent in group B, for an overall retention rate of 89 percent. Except for marginal discoloration in both groups and retention in group B, the restorations in both groups had Alfa ratings of 88 percent or greater in all of the direct clinical evaluation categories. CONCLUSIONS: The 12-year clinical performance, including retention rate, of a dual-cured dental adhesive was excellent and was not affected by dentin acid-etching. CLINICAL IMPLICATIONS: This clinical study provides additional evidence for the long-term durability of a three-step etch-and-rinse adhesive in non-carious cervical lesions.

Fracture resistance of yttria-stabilized zirconia dental implant abutments.

PURPOSE: An in vitro study was performed to assess the effect of different degrees of clinical reduction of zirconia abutments on the failure load of clinical assemblies. MATERIALS AND METHODS: Zirconia abutments (Y-TZP Ceramic Abutment, Astra Tech) were prepared with 0, 0.5, or 1 mm of external axial reduction starting 1 mm above the height-of-contour. Abutments (n = 10) were attached to implant analogs (25 Ncm torque) embedded in a stainless steel cylinder using Field's metal. Fracture loads (N) were determined when assemblies were loaded at 60 degrees off-axis until failure (Instron, CHS = 0.1 mm/min). Groups were statistically compared using ANOVA (p < 0.05). RESULTS: Fracture loads for all assemblies displayed large variations within groups. There were no statistically significant differences (p > 0.05) among different abutment groups with a mean fracture load of 429 N (+/-140) for the control group, 576 N (+/-120) for 0.5-mm margins, and 547 (+/-139) for 1.0-mm margins. All fractures occurred at the interface where the abutment was connected to the analog. CONCLUSION: In this in vitro study of simulated ultimate assembly strength, the preparation of zirconia abutments did not significantly impair the fracture resistance of simulated implant assemblies. All implant abutments fractured at rates higher than the maximum incisal forces (90-370 N) estimated to occur in the anterior region of the mouth.

Effect of power toothbrushing on simulated wear of dental cement margins.

UNLABELLED: Power toothbrushes (PTBs), in combination with abrasive dentifrices, may encourage wear of dental cements at crown margins. PURPOSE: The objective of this in vitro simulation was to control the clinical variables associated with PTB use and measure the potential side effects of PTBs with mild and abrasive dentifrices. METHODS AND MATERIALS: Four PTBs ( Braun-Oral-B-Professional Care at 150 g brushing force, Sonicare-Elite at 90 g, Colgate-Actibrush at 200 g and Crest-Spinbrush-Pro at 250 g) and 2 dentifrices mixed 1:1 with tap water (Mild= Colgate-Total, Colgate-Palmolive; Abrasive= Close-up, Chesebrough-Ponds) versus tap water alone (control) were used to abrade 2 cements (Fleck's Mizzy Zinc Phosphate [ZP]; 3M-ESPE Unicem universal cement [UC]) using cement-filled slots (160 m wide) cut into wear-resistant ceramic blocks. A custom fixture controlled PTB/block alignment, PTB loads, and other testing variables. Wear was measured (3 profilometer traces/slot, 5 slots/block/group, baseline to 5-year differences) and analyzed (3-way ANOVA, p < or = 0.05, Bonferroni). RESULTS: Wear for ZP was much greater than UC (p<0.05) for all 4 PTBs and both dentifrices. Brushing with water showed no effects (p<0.05). Cement-PTB-dentifrice interactions did occur. Only minor differences occurred among PTBs. Pooled 5y-wear levels for ZP for both dentifrices approximately 21 microm /5y) were similar to values for current-day posterior composite materials. CONCLUSIONS: Combinations of PTBs with mild and abrasive dentifrices produced significant wear with ZP but not UC; thus, resin-composite cements seem to represent a better choice for wear resistance.

Shear bond strength of self-etching bonding systems in combination with various composites used for repairing aged composites.

PURPOSE: Repair of worn, broken or discolored composite restorations can be accomplished using new composite material and dentin bonding systems. The purpose of this study was to investigate the effectiveness of self-etching adhesive systems for composite re-bonding procedures onto different composite substrates that had been aged for 6 years prior to testing. MATERIALS AND METHODS: Two hundred cylinders (4 mm x 5 mm) of composite were fabricated using 4 hybrid composites [AeliteFil (Bisco), Prodigy (SDS Kerr), TPH (Dentsply Caulk), and Z100 (3M ESPE)] following manufacturers' directions and stored for 6 years in 1% NaCl solution. After aging, each specimen was wet polished through 600-grit SiC and randomly assigned to a self-etching bonding system (Adper Prompt L-Pop/Z100 [3M ESPE]; Tyrian One-Step Plus/AeliteFil [Bisco]; OptiBond Solo Plus SE/Prodigy [SDS Kerr], Xeno III/TPH [Dentsply Caulk]) or a total-etch control (Prime&Bond NT/TPH [Dentsply Caulk]) (n = 10 per group). Shear bond strengths (SBS) for repairs were evaluated after 48 h (crosshead speed = 0.5 mm/min) and were compared by two-way ANOVA (p = 0.05) with Tukey post-hoc tests. RESULTS: Significant differences (p < or = 0.05) were detected for the main effects (substrates and bonding systems), but the interaction was not significant. SBS for bonding systems were from highest to lowest: (1) Prime&Bond NT, (2) OptiBond Solo Plus SE, (3) Adper Prompt L-Pop, (4) Xeno III, (5) Tyrian One-Step Plus. SBS of the repair systems to Z100 were significantly lower than those to the other composite substrates. CONCLUSION: Self-etching systems can be used to repair aged composite, but the efficacy of repair of aged composite is system dependent.

Dental biomaterials: where are we and where are we going?

This article reviews the current state of the art for restorative biomaterials by examining the roles of 1) truly biological biomaterials, with respect to the "near-future" of five to ten years, 2) traditional synthetic biomaterials, and 3) performance outcomes for biomaterials. Biological biomaterials are discussed in terms of tissue engineering and stem cell research, self-assembling system opportunities, and nanotechniques or technologies. Future developments for major areas of synthetic biomaterials are considered for bonding systems, composites, VLC curing, ceramics, and cements. Performance outcomes are discussed for all biomaterials in terms of safety, efficacy, and longevity of materials.