Confirmation of Leinfelder clinical wear standards

The accuracy and precision of wear testing and wear facet analyses: The two sides of the story

A critical examination of the literature for dental wear publications highlighted three distinct areas, clinical data, laboratory data and the simulation of the clinical situation data. The imprecision of the clinical data values from direct and indirect in vivo methods renders the clinical data compromised at best. Laboratory data showed a focus on finding a correlation between simplistic laboratory abrasive wear resistance studies and established materials science laboratory techniques, but with no actual correlation identified. Replication of the masticatory cycle in the mouth in the form of an oral wear simulator has focussed more on the wear testing devices rather than the wear quantification methods. As a result, the data acquisition variables in the x- and y-planes need to be examined to consider how they can influence the accuracy and precision of the laboratory wear measurements recorded in the dental literature. The current approach was undertaken using the teaching tool outlined in "The First Three Questions".

Wear of resin composites: Current insights into underlying mechanisms, evaluation methods and influential factors

The application of resin composites in dentistry has become increasingly widespread due to the increased aesthetic demands of patients, improvements in the formulation of resin composites, and the ability of these materials to bond to tooth structures, together with concerns about dental amalgam fillings. As resistance to wear is an important factor in determining the clinical success of resin composite restoratives, this review article defines what constitutes wear and describes the major underlying phenomena involved in this process. Insights are further included on both in vivo and in vitro tests used to determine the wear resistance of resin composite and the relationships between these tests. The discussion focuses on factors that contribute to the wear of resin composite. Finally, future perspectives are included on both clinical and laboratory tests and on the development of resin composite restorations.

Wear Simulation of Resin Composites and the Relationship to Clinical Wear

Laboratory wear simulation may be useful for estimating the relative clinical wear rates of new resin composite materials.

Marginal adaptation of three-unit fixed partial dentures constructed from pressed ceramic systems

PURPOSE

This study compares the marginal accuracy of posterior metal ceramic (MC), all-ceramic IPS Empress 2 and experimental pressed ceramic (EPC-VP 1989/4) three-unit fixed partial dentures (FPD), before and after luting and after thermo-mechanical fatigue in a dual-axis chewing simulator.

MATERIALS AND METHODS

Caries-free human teeth (n=160) were used as abutments for the fabrication of eighty posterior three-unit FPD, divided into two test-groups, IPS Empress 2 and EPC, of 32 samples each and one control group of 16 samples metal ceramic FPD. All FPD were cemented with Variolink II dual-curing resin cement. Half of the samples in each group were exposed to a dual-axis chewing simulator.

RESULTS

The geometric mean marginal gap values (microm, before cementation, after cementation and after thermo-mechanical fatigue) amounted to 53, 63 and 62 for the ceramic metal FPD, 57, 71 and 68 for the Empress 2 FPD and 55, 67 and 68 for the EPC FPD. In all groups a statistically significant increase in marginal gap width was observed after cementation. The effect of functional loading in the chewing simulator on marginal gap was not significant. Marginal gap was lowest in the control group but differences with all-ceramic materials were small in all evaluation stages.

CONCLUSION

Within the limits of this investigation, it can be concluded that marginal gap values of these all-ceramic materials and conventional MC techniques are on a similar level. In particular, almost all marginal gap values observed in this study were within the limits of clinical acceptance.

Prosthodontics: achieving quality esthetic dentistry and integrated comprehensive care

BACKGROUND

Prosthodontics is the dental specialty responsible for diagnosis, rehabilitation and maintenance of patients with complex clinical conditions involving missing or deficient teeth and/or craniofacial tissues. The essence of the specialty is expert treatment planning.

OVERVIEW/LITERATURE REVIEWED

In recent years, new approaches and technology have been introduced as a result of research performed in universities and by industry. The field of prosthodontics continues to evolve owing to a better understanding of the biology of the oral cavity and the introduction of new techniques and improved biomaterials. Improvements in periodontal and oral surgical techniques, implant procedures and materials, esthetic restorative materials, and jaw tracking recorders and articulators have led to enhanced functional and esthetic oral and maxillofacial prostheses.

CONCLUSIONS AND CLINICAL IMPLICATIONS

The complexities of today's technical and clinical procedures and the higher expectations for more esthetically pleasing dentistry by the general patient population have placed a premium on teamwork involving general dentists, specialists and dental technicians.

Composite restoration wear analysis: conventional methods vs. three-dimensional laser digitizer

The purpose of this study was to compare three-dimensional laser digitizing with subjective evaluations of wear in posterior resin-based composite restorations during a 24-month period.

BACKGROUND

The authors describe an indirect method of analyzing wear in resin-based composite restorations. A computer-driven laser was used to scan stone casts of restorations and create three-dimensional computerized surface models of the teeth. A standard computer algorithm was used to superimpose the follow-up model images over the baseline model images and to calculate the amount of wear within 10 micrometers.

METHODS

Patients were selected whose treatment plans required a Class II restoration. A total of 100 restorations were inserted at baseline and evaluated at six months, 12 months and 24 months. Polyether quadrant impressions were taken and casts were made. Twenty-one casts were selected for the three-dimensional laser digitizing technique. The same casts were evaluated via subjective evaluations using sets of 18 calibrated standard models, following the method developed by Leinfelder.

RESULTS

Statistical analysis using the Wilcoxon test revealed significant differences (P < .01) between subjective wear evaluation and the three-dimensional laser digitizing wear analysis.

CONCLUSION

The normalized three-dimensional laser digitizing technique is significantly more effective than subjective evaluations in establishing restoration wear rates.

Seventeen-year clinical study of ultraviolet-cured posterior composite Class I and II restorations

OBJECTIVES

To compare the clinical performance of four commercial ultraviolet light-cured composite materials, and to evaluate curing-system effects on long-term wear resistance of Class I and II restorations.

MATERIALS AND METHODS

Approximately 32 samples of each of four different ultraviolet light-cured composites (n = 130) were inserted into conventional Class I and II cavity preparations by two clinicians. Cavosurface margins of the preparations were not beveled. Enamel walls of the preparation were etched, and the respective bonding agent was applied. Each restoration was evaluated by two clinicians at 5, 10, and 17 years. Direct evaluations were performed using modified United States Public Health Service (USPHS) criteria. Indirect evaluations were performed using the Leinfelder cast evaluation method.

RESULTS

After 17 years, 65% of the restorations were recalled and pooled direct evaluations were conducted for color matching (94% alfa), marginal discoloration (100% alfa), marginal integrity (100% alfa), secondary caries (92% alfa), surface texture (72% alfa), and anatomic form (22% alfa). Mean occlusal wear from indirect evaluations at 5, 10, and 17 years was 197 +/- 85 microns, 235 +/- 72 microns, and 264 +/- 80 microns, respectively. For direct and indirect evaluations there were significant differences (p < or = .05) between the baseline and 5-year recall evaluations.

CLINICAL SIGNIFICANCE

This study demonstrated that the mean pooled occlusal wear of four ultraviolet light-cured posterior composites at 17 years was 264 microns (approximately 0.25 mm), and that most wear (75%) occurred in the first 5 years. Of all recalled restorations, 76% were judged clinically acceptable at 17 years, and 22% of those exhibited no clinically detectable wear.

Three-body wear of a hand-consolidated silver alternative to amalgam

Recent studies have investigated a mercury-free silver alternative to amalgam, but the silver powders required a relatively high compaction pressure to consolidate. The aim of the present study was to consolidate a precipitated silver powder into a cohesive solid using an air-driven pneumatic condenser fitted with an amalgam plugger at a clinically realistic load, and to study the mechanisms and rates of three-body wear of the consolidated silver in comparison with that of an amalgam. The silver powder was annealed, rinsed with a dilute acid, and consolidated either in a prepared tooth cavity or in a specimen mold at a load of 15 N. A four-station wear machine was used where each specimen was immersed in a slurry containing polymethyl methacrylate beads, then a steel pin was loaded and rotated against the specimen at a maximum load of 76 N. The flexural strength in MPa (mean +/- SD; n = 10) was 86 +/- 20 for amalgam, 181 +/- 45 for silver with a polished surface, and 202 +/- 21 for silver with a burnished surface. After 4 x 10(5) wear cycles, the wear scar depth in microm was 134 +/- 54 for amalgam, 143 +/- 8 for polished silver, and 131 +/- 9 for burnished silver, which were not significantly different (Tukey's multiple comparison test; family confidence coefficient = 0.95). SEM examination revealed cracks and fracture pits in the worn surface of amalgam, in contrast to a smooth surface in silver. Wear and material removal in amalgam occurred by microfracture and dislodgement of cracked segments, while wear in the silver occurred by ductile deformation and flow of materials. To conclude, the consolidated silver possesses a three-body wear resistance similar to that of amalgam, and a higher resistance to wear-induced damage and cracking than amalgam. The mechanism of wear in amalgam is microfracture and material dislodgement, while that in consolidated silver is ductile deformation and flow of material.

Comparison of two measurement techniques for clinical wear

OBJECTIVES

Clinical wear of restorations is generally evaluated by marginal integrity over time. In this study, both a subjective and an objective method for wear assessment are compared, and the relative advantages and disadvantages of each are considered.

METHODS

A surface evaluation technique for quantitative measurement of wear, as developed at the University of Minnesota (UMN) has been compared to the commonly employed method of wear assessment used by Leinfelder (LF). Measurements were made by comparing suitable casts of restored teeth before and after clinical function. Semi-quantitative wear assessment was studied in comparison with detailed quantitative information about the topology of the pre- and post-wear occlusal surfaces obtained from stylus profilometry and processed by imaging techniques. Fourteen model sets of baseline, 2, 3 and 5 year old Class II composite restorations from a Danish clinical trial were evaluated using both techniques.

RESULTS

In general, after 5 years of function, the digitizing method (UMN) generated wear values that were twice as high, indicating that general wear of restorative materials is underestimated by the LF-method.

CONCLUSIONS

The comparison clearly revealed the advantages and limitations of each technique. Evaluation of wear by means of the LF technique provides global semi-quantitative data on restoration margins relative to enamel, underestimating general wear of the restorative material. Advanced 3-D measuring techniques such as the UMN method provide extensive quantitative data regarding wear patterns of the entire occlusal surface, i.e. restoration and enamel. Such a highly accurate technique is capable of differentiation between wear behavior of restorative materials early on in clinical studies. In addition, through its digital alignment procedure, the UMN method provides data on accuracy of the replication process used in clinical studies.

In vitro abrasion using an air-powder polishing device and its quantification by radiotracer measurement

OBJECTIVES

This study was conducted to examine the assessment of abrasion of two different materials after neutron activation.

METHODS

A fissure sealant material (Fissurit F/VOCO with a compressive strength of 235 MPa) and a glass ionomer cement (Aqua Ionofil/VOCO with a compressive strength of 170 MPa) were activated by irradiation with neutrons. Subsequent measurements of the full-energy-peak (FEP) (1368.55 keV of 24Na) were made of the sample materials before and after abrasion via exposure to the air-powder polishing to accurately describe substance loss.

RESULTS

Abrasion varied more than three-fold between the two materials.

SIGNIFICANCE

Neutron activation and radiotracer measurement allows the quantification of abrasion effects in different materials. In comparison with other current methods its use may allow a superior measurement accuracy and precision in determining the abraded mass.

Effect of ion implantation of TMA archwires on the rate of orthodontic sliding space closure

A split-mouth randomized clinical trial was used to determine whether ion implantation of beta-titanium archwire would facilitate sliding space closure. After bilateral maxillary first premolar extractions, 0.19 x 0.025-inch beta-titanium arch wires, ion-implanted on one half only, were placed in 30 subjects aged 10 to 42 years wearing unimplanted 0.022 inch slot appliances. Nickel-titanium springs (150 g) were placed bilaterally to close the extraction spaces. Space closure was measured intraorally at monthly intervals until either the space on one side closed or 6 months had elapsed. The median rates of space closure were not significantly different between the ion-implanted and the unimplanted sides. The average rate of space closure on these beta-titanium wires, with or without ion implantation, was similar to the rate reported on stainless steel arch wires.

The clinical performance of CAD-CAM-generated ceramic inlays: a four-year study

The authors conducted a long-term clinical study of 50 CEREC (Siemens AG) CAD-CAM inlay restorations in 28 patients. After four years, they found the inlays to rate very highly in color matching, interfacial staining, secondary caries, anatomic contour, marginal adaptation, surface texture and postoperative sensitivity. They monitored cement loss along the occlusal margins and found it to be relatively low, with an unusual decrease in measured cement wear from the third to the fourth year. The favorable results of this long-term clinical study of these CAD-CAM restorations portend significant success for this restorative approach.