Effects of flowable liners on the shrinkage vectors of bulk-fill composites

Objectives

This investigation evaluated the effect of flowable liners beneath a composite restoration applied via different methods on the pattern of shrinkage vectors.

Methods

Forty molars were divided into five groups (n = 8), and cylindrical cavities were prepared and bonded with a self-etch adhesive (AdheSe). Tetric EvoCeram Bulk Fill (TBF) was used as the filling material in all cavities. The flowable liners Tetric EvoFlow Bulk Fill (TEF) and SDR were used to line the cavity floor. In gp1-TBF, the flowable composite was not used. TEF was applied in a thin layer in gp2-fl/TEF + TBF and gp3-fl/TEF + TBFincremental. Two flowable composites with a layer thickness of 2 mm were compared in gp4-fl/TEF + TBF and gp5-fl/SDR + TBF. TEF and SDR were mixed with radiolucent glass beads, while air bubbles inherently present in TBF served as markers. Each material application was scanned twice by micro-computed tomography before and after light curing. Scans were subjected to image segmentation for calculation of the shrinkage vectors.

Results

The absence of a flowable liner resulted in the greatest shrinkage vectors. A thin flowable liner (gp2-fl/TEF + TBFbulk) resulted in larger overall shrinkage vectors for the whole restoration than a thick flowable liner (gp4-fl/TEF + TBF). A thin flowable liner and incremental application (gp3-fl/TEF + TBFincremental) yielded the smallest shrinkage vectors. SDR yielded slightly smaller shrinkage vectors for the whole restoration than that observed in gp4-fl/TEF + TBF.

Conclusions

Thick flowable liner layers had a more pronounced stress-relieving effect than thin layers regardless of the flowable liner type.

Clinical relevance

It is recommended to apply a flowable liner (thin or thick) beneath bulk-fill composites, preferably incrementally.

Degradation Potential of Bulk Versus Incrementally Applied and Indirect Composites: Color, Microhardness, and Surface Deterioration

This study investigated the color stability and microhardness of five composites exposed to four beverages with different pH values. Composite discs were produced (n=10); Filtek Z250 (3M ESPE) and Filtek P90 (3M ESPE) were applied in two layers (2 mm, 20 seconds), and Tetric N-Ceram Bulk Fill (TetricBF, Ivoclar Vivadent) and SonicFill (Kerr) were applied in bulk (4 mm) and then light cured (40 seconds, Ortholux-LED, 1600 mW/cm²). Indirect composite Sinfony (3M ESPE) was applied in two layers (2 mm) and cured (Visio system, 3M ESPE). The specimens were polished and tested for color stability; ΔE was calculated using spectrophotometer readings. Vickers microhardness (50 g, dwell time=45 seconds) was assessed on the top and bottom surfaces at baseline, 40 days of storage, subsequent repolishing, and 60 days of immersion in distilled water (pH=7.0), Coca-Cola (pH=2.3), orange juice (pH=3.75), or anise (pH=8.5) using scanning electron microscopy (SEM). The materials had similar ΔE values (40 days, p>0.05), but TetricBF had a significantly greater ΔE than P90 or SF (40 days). The ΔE was less for P90 and TetricBF than for Z250, SonicFill, and Sinfony (60 days). Repolishing and further immersion significantly affected the ΔE (p<0.05) except for P90. All composites had significantly different top vs bottom baseline microhardnesses. This was insignificant for the Z250/water, P90/orange juice (40 days), and Sinfony groups (40 and 60 days). Immersion produced variable time-dependent deterioration of microhardness in all groups. Multivariate repeated measures analysis of variance with post hoc Bonferroni tests were used to compare the results. ΔE and microhardness changes were significantly inversely correlated at 40 days, but this relationship was insignificant at 60 days (Pearson test). SEM showed degradation (40 days) that worsened (60 days). Bulk-fill composites differ regarding color-stability and top-to-bottom microhardness changes compared with those of other composites. P90 showed better surface degradation resistance. In conclusion, bulk-fill composites are not promising alternatives to incremental and indirect composites regarding biodegradation.

Transillumination and HDR Imaging for Proximal Caries Detection

The purpose of this study was to develop an in vitro model for the validation of near-infrared transillumination (NIRT) for proximal caries detection, to enhance NIRT with high-dynamic-range imaging (HDRI), and to compare both methods, using micro-computed tomography (µCT) as a reference standard. Both proximal surfaces of 53 healthy or decayed permanent human teeth were examined using the Diagnocam (DC) (KaVo) and NIRT with HDRI (NIRT-HDRI). NIRT was combined with HDRI to improve the diagnostic performance by reducing under- and overexposed image areas. For NIRT-HDRI, an exposure series was captured and merged into a single HDR image. A classification was applied according to lesion depth. All surfaces were assessed twice by 2 trained examiners, and additionally with µCT for validation. The Kappa statistic was used to calculate inter-rater reliability and agreement between DC and NIRT-HDRI. Inter-rater reliability (weighted Kappa, wκ) showed very good agreement for the DC (0.90) and NIRT-HDRI (0.96). The overall agreement (wκ) was almost perfect (0.85). In the individual categories (0 to 4), the agreement (simple Kappa) ranged from almost perfect (category 4) to moderate (1 and 2) to substantial (categories 0 and 3). Sensitivity and specificity of sound surfaces, enamel, and dentin caries ranged from 0.57 to 0.99 and were similar for both methods in the different categories. NIRT-HDRI had a higher sensitivity for sound surfaces and enamel caries, as well as a higher specificity for dentin caries. Regarding the obtained images, HDRI allowed for the detection of caries within a greater range of luminance levels, resulting in a more detailed visualization of structures without under- or overexposure. However, HDRI this did not improve the diagnostics significantly. Distinguishing between a processed demineralized enamel and dentin lesions appears to be a problem specific to NIRT and cannot be balanced using HDRI.

Irregularities below the enamel-dentin junction may predispose for fissure caries

This study investigated the structure of the fissure fundus on occlusal surfaces with respect to the detection of possible irregularities below the enamel-dentin junction (EDJ). Occlusal surfaces were examined by micro-computed tomography (µCT). In total, 203 third molars with clinically sound occlusal fissures or non-cavitated lesions were selected. All specimens were scanned with µCT. Subsequently, each tooth was sectioned, and each slice was investigated by stereomicroscopy. In 7 of 203 molars (3.4%), demarcated radiolucencies below the EDJ were detected by µCT. These defects were obviously of non-carious origin, because the µCT images revealed no gradient of demineralization in the dentin. In all cases, a direct pathway between the oral cavity and the dentin was evident. The comparison of the µCT sites with conventional histological images also revealed defects in the dentin. These results demonstrate that demarcated radiolucencies below the EDJ may not necessarily be caries lesions according to µCT images and may be classified as possible developmental irregularities. To avoid misinterpreting µCT data, dental researchers should carefully consider this condition when analyzing µCT images. The clinical significance of this finding is that these defects may predispose molar teeth to early-onset caries in occlusal pits and fissures.

Two-body and three-body wear of glass ionomer cements

OBJECTIVES

Glass ionomer cements (GIC) have been modified in an attempt to improve their mechanical properties. The objective of the present paper was to compare the two-body and three-body wear of four modified GIC. The tested materials were Fuji IX (GC Corporation), Hi-Fi (Shofu) and Ketac Molar Aplicap (3M/ESPE). The cermet cement Ketac Silver Maxicap (3M/ESPE) was used as reference material.

METHODS

Two-body wear tests were carried out in the computer controlled 'artificial mouth' of the Munich Dental School, three-body wear was tested with the ACTA wear machine.

RESULTS

The resulting average two-body wear rates (in microm) were: Fuji IX 327 (SD +/- 82) < Ketac Molar 379 (SD +/- 94) < Hi-Fi 376 (SD +/- 90) < Ketac silver 449 (SD +/- 127). The differences between the materials were significant (P < 0.05, ANOVA, modified LSD-test) with the exception of Ketac Molar and Hi-Fi. The average three-body wear rates (in microm) were: Hi-Fi 30 (SD +/- 10) < Ketac Molar +/- 42 (SD +/- 12) < Fuji IX 49 (SD +/- 14) < Ketac silver 73 (SD +/- 23). The difference between Ketac silver and the three other materials was significant (P < 0.05, ANOVA, modified LSD-test). No significant difference was calculated between Hi-Fi, Ketac Molar and Fuji IX.

CONCLUSIONS

As Ketac Molar, Hi-Fi and Fuji IX show better wear resistance compared to Ketac silver both in occlusal-contact and contact-free areas, it may be assumed that the wear resistance of a glass ionomer cement may be improved more by changing the powder: liquid ratio than by incorporating silver particles into the glass powder.

Biological clearance of TEGDMA in guinea pigs

The excretion of the dental composite component triethylene glycol dimethacrylate (TEGDMA) in feces and urine in vivo and, using the pendular perfusion technique with segments of jejunum and colon, the biliary and enteric excretion in situ were investigated in anesthetized guinea pigs. In the in situ experiments guinea pigs (n = 4) received TEGDMA (0.02 mmol/kg body weight labelled with a tracer dose 14C-TEGDMA 0.7 kBq/g body weight) injected into the jugular vein. In the in vivo experiments guinea pigs (n = 4) received TEGDMA (+14C-TEGDMA; same dose as above) via a gastric tube. Urine and feces were collected for 24 h. In the in situ experiments organs were removed from the guinea pigs 60 min after the beginning of the experiment, and the 14C radioactivity measured. During the 60-min perfusion period the calculated amount of 14C radioactivity excreted into the total jejunum and colon was 0.9 +/- 0.2% and 1.9 +/- 0.1% of the dose administered, respectively (means +/- SEM). Of the 14C-TEGDMA dose, 3.7 +/- 0.2% was found in the bile. A significantly (P < 0.05) higher bile/blood concentration ratio was found 10 min after injection of TEGDMA as compared with the ratios at 20 to 60 min. The following 14C activities (percent of the dose) per total organ were found in guinea pigs (in situ experiment; means +/- SEM): 6.9 +/- 1.7 (muscle), 3.9 +/- 0.5 (kidney), 3.3 +/- 0.1 (skin), 1.4 +/- 0.1 (blood), and 1.2 +/- 0.1 (liver). The 14C activity in all other organs was < 0.4%. The total 14C recovery in all organs tested was 17.5 +/- 1.8%. Over 24 h the amounts of 14C activity excreted in the feces and urine were 0.5 +/- 0.1% and 14.7 +/- 1.8% of the dose administered, respectively (means +/- SEM). The following 14C activities (percent of the dose) per total organ or contents of organs were found (means +/- SEM): 1.4 +/- 0.3 (liver), 0.8 +/- 0.3 (muscle), 0.5 +/- 0.1 (skin), and 0.5 +/- 0.1 (contents of cecum). The 14C activity in all other organs was < 0.2%. The total 14C recovery in all organs tested was 3.9 +/- 0.9%. In a second series of in vivo experiments exhaled air from the animals was captured during the 24-h experimental period. Of the administered dose, 61.9 +/- 4.6% of the 14C (means +/- SEM; n = 4) was exhaled as 14C-carbon dioxide. The results indicate a rapid clearance of 14C-TEGDMA and/or 14C-TEGDMA metabolite(s) from the organism and exhalation is the major route of elimination.

Class V lesions restored with four different tooth-colored materials--3-year results

The aim of this study was to compare the treatment results using four different types of tooth colored materials for restoring class V lesions. A total of 197 class V restorations (n = 197) were placed by one dentist in 37 patients on incisors, canines and premolars. The fillings were placed due to different indications: erosion/non-carious cervical defects (n = 69), primary carious lesions (n = 57), and for replacing defective existing fillings (n = 71). The teeth were assigned on a random basis to four groups for restoration with either a composite (group 1: n = 36; Tetric, Vivadent), or a polyacid-modified resin composite (group 2: n = 79; Dyract, Dentsply), or one of two different resin-modified glass ionomer cements (group 3: n = 51, Fuji II LC,GC; group 4: n = 31, Photac-Fil, Espe). The restorations were evaluated by a single-blind design, according to a modified USPHS system 36 months following placement. Statistical analysis was completed with the Pearson Chi-square test for comparing the results of the four groups (P < 0.05). Additionally, the survival rates were analyzed with the Kaplan-Meier estimator and the Log-rank test (P < 0.05). The Alpha ratings were as follows (Tetric/Dyract/Fuji II LC/Photac Fil): shade match (86%/77%/58%/40%), surface texture (81%/83%/16%/9%), marginal integrity (enamel) (73%/67%/61%/61%), marginal integrity (dentin) (86%/70%/55%/61%), marginal discoloration (enamel) (59%/44%/58%/52%), marginal discoloration (dentin) (82%/84%/71%/48%), anatomic contours (91%/83%/39%/35%). One Tetric restoration, five Dyract restorations, two Fuji II LC restorations and three Photac restorations were dislodged within the study period. The retention of the restorations showed no significant difference among the four materials. However, the clinical performance of the restorations retained over the 3-year period showed distinct differences for the four materials. The best clinical performance was observed for the resin composite, whereas the quality of the Dyract restorations without enamel etching was worse. The poorest results were obtained for the restorations with the resin-modified glass ionomers.

Marginal quality of tooth-colored restorations in class II cavities after artificial aging

This in vitro study compared the proximal marginal adaptation of direct composite restorations with composite and ceramic inlays inserted with different resin cements. Standardized MOD Class II inlay cavities with one proximal box extending below and the other above the CEJ were cut in 48 extracted human molars and randomly assigned to six groups (n=8). Incrementally layered direct composite restorations (P60), composite inlays (P60) and ceramic inlays (Empress; Cerec Vitablocs Mark II) were placed in the cavities. Three different resin cements (RelyX ARC; Variolink II high viscosity; Panavia 21) were used for luting the composite inlays. All ceramic inlays were cemented with RelyX ARC. After finishing and polishing, the teeth were stored for 24 hours in Ringer solution at 37 degrees C before they were subjected to thermal and mechanical loading (5/55 degrees C, 2000x; 50 N vertical load, 50000x). Margins were evaluated on epoxy replicas using a scanning electron microscope at X200 magnification. Statistical analysis was performed with non-parametric test methods (alpha=0.05). The adhesive interfaces to enamel exhibited high percentages of perfect margins for all groups (91.8% to 96%) and a maximum of 5.2% marginal gap formation. Dentin-limited cavity segments demonstrated more marginal openings and less perfect margins than enamel-bound areas; however, this was only statistically significant for direct composite restorations and composite inlays inserted with Variolink II and Panavia 21. RelyXARC showed a significantly better adaptation to P60 inlays compared with the leucite-reinforced Empress ceramic but not the Vitablocs Mark II ceramic.

Wear evaluation of MZ100 compared to ceramic CAD/CAM materials

The material and antagonist wear of two CAD/CAM ceramic materials, the laboratory-processed IPS Empress ceramic, and the composite mill block material MZ100 were tested in an artificial wear simulator with human enamel as the antagonistic material. The material samples underwent 50,000 test cycles (1 cycle per second, 50 N) in distilled water. The wear of the material samples and of the opposing enamel was documented after 30,000 and 50,000 cycles with replicas, digitized, and evaluated with a 3D evaluation system. The loss of volume and height caused by wear was calculated. No significant difference between the ceramic materials could be found either in the amount of material or in the amount of antagonist wear. The material wear of MZ100 differed significantly from Vita Mark II only in terms of volume loss. Regarding height loss, MZ100 exhibited a significantly higher wear than all ceramic materials. The wear of the enamel antagonists does not differ significantly between the ceramic materials. With MZ100, however, a significantly smaller amount of enamel wear was found when compared with Empress and Vita Mark II. Despite the highest material wear, MZ100 had the lowest material wear rate, the lowest enamel wear rate, and the lowest total wear rate. The laboratory-processed IPS Empress material had a clearly higher material wear rate than the CAD/CAM materials.

Marginal characteristics of different filling materials and filling methods with standardized cavity preparation

PURPOSE

The aim of the present study was to investigate the influence of different filling materials and methods on marginal integrity in Black Class I fillings.

MATERIALS AND METHODS

Standardized occlusal cavities were prepared in 80 extracted human molars. The preparations were filled with composite resin (1), with composite resin using the incremental technique (2), an experimental glass-fiber-reinforced (3) and polyester-reinforced (4) composite resin, a direct composite inlay (5), a ceramic insert (6), a Cerafil inlay (7), and with an experimental direct filling using Dyract AP compomer (8). Allocation of the teeth to the test groups was randomized; further processing was done on a blind basis. After the preparation of replicas, the teeth were subjected to a thermomechanical cycling process of 2,000 temperature cycles (5 degrees C/55 degrees C) and 50,000 stress cycles (50 N). This was followed by production of a second set of replicas and quantitative margin analysis by SEM (200X). A dye penetration test was then performed on the mesiodistal section.

RESULTS

Groups 1, 2, 5, 6 and 7 displayed a good primary marginal quality, with the proportion of continuous margins reaching more than 85%. Significantly poorer results were recorded for the experimental glass-fiber-reinforced composite resins and Dyract compomer, where the proportion of perfect margins was only between 36% and 73%. In groups 1, 2, 5, 6 and 7, marginal integrity remained stable after the thermomechanical stress cycles, with the Cerafil inlays recording the best values: 89% perfect margins and 3% marginal gaps. In contrast, the experimental composite resins and the compomer underwent a significant (p < 0.05) increase in the proportion of marginal gaps and a significant (p < 0.05) reduction in the proportion of continuous margin.

CONCLUSION

The results of this study show that neither Dyract compomer nor the glass-fiber-reinforced composite resins tested can be recommended for use in the occlusally stressed posterior region, whereas the other filling materials and methods were sufficiently stress resistant.

Clinical performance of a resin-modified glass-ionomer and a compomer in restoring non-carious cervical lesions. 5-year results

PURPOSE

To evaluate the 5-yr clinical performance of a resin-modified glass-ionomer cement and a polyacid-modified resin composite in restoring non-carious cervical lesions.

MATERIALS AND METHODS

Non-carious cervical lesions in 46 incisors, canines, and premolars were restored either with Fuji II LC (n=18) or with Dyract (n=28) in 16 healthy patients. The lesions were restored without cavity preparation strictly according to the manufacturer's instructions. The restorations were clinically evaluated single blind after 5 yrs using modified USPHS criteria.

RESULTS

The percentage of Alfa ratings were as follows (Dyract/Fuji II LC): color match 81.3%/28.6%, surface texture 93.8%/21.4%, anatomic form 75.0%/28.6%, marginal integrity (enamel) 62.5%/42.9%, marginal integrity (dentin) 68.8%/28.6%, marginal discoloration (enamel) 56.3%/42.9%, marginal discoloration (dentin) 68.8%/21.5%. Five-yr data revealed a significant difference between the clinical ratings of Dyract and Fuji II LC for all criteria except marginal integrity and marginal discoloration in enamel. A total of five Dyract restorations and four Fuji II LC restorations failed within the study period.

CLINICAL SIGNIFICANCE

A considerably high and almost similar overall failure rate was found for both restorative materials in restoring non-carious cervical lesions. However, retained Dyract restorations presented superior clinical performance compared to Fuji II LC restorations.

Distribution and excretion of TEGDMA in guinea pigs and mice

The monomer triethyleneglycoldimethacrylate (TEGDMA) is used as a diluent in many resin-based dental materials. It was previously shown in vitro that TEGDMA was released into the adjacent biophase from such materials during the first days after placement. In this study, the uptake, distribution, and excretion of 14C-TEGDMA applied via gastric, intradermal, and intravenous administration at dose levels well above those encountered in dental care were examined in vivo in guinea pigs and mice as a test of the hypothesis that TEGDMA reaches cytotoxic levels in mammalian tissues. 14C-TEGDMA was taken up rapidly from the stomach and small intestine after gastric administration in both species and was widely distributed in the body following administration by each route. Most 14C was excreted within one day as 14CO2. The peak equivalent TEGDMA levels in all mouse and guinea pig tissues examined were at least 1000-fold less than known toxic levels. The study therefore did not support the hypothesis.

Polymerization contraction stress in light-cured packable composite resins

OBJECTIVE

Determination of the polymerization contraction stress of packable composites (ALERT, Surefil, Solitaire, Solitaire 2) and a packable ORMOCER material (Definite) in comparison with a conventional hybrid composite (Tetric Ceram).

METHODS

Contraction force generated by the test materials (10 replications each) was measured by polymerizing the composites filled in a plastic tray between two aluminum attachments mounted in a Stress-Strain-Analyzer testing machine (specimen size: 4x4x2 mm, C-factor=0.33). Contraction force was recorded for 300s under a standard exposure condition (40s, 800mW/cm(2)). Maximum contraction stress (MPa), force rate (N/s), relative force rate (%/s) of each material were statistically analyzed by ANOVA (alpha=0.05) and post-hoc Tukey's test.

RESULTS

Maximum contraction stresses of the packable materials were 4.60 +/- 0.32MPa (ALERT), 4.16 +/- 0.18MPa (Definite), 3.36 +/- 0.08MPa (Solitaire 2), 3.33 +/- 0.23MPa (Solitaire) and 3.13 +/- 0.18MPa (Surefil), which were significantly higher than that of Tetric Ceram (2.51 +/- 0.14MPa). Tetric Ceram exhibited the significantly lowest force rate. Force/time curves were S-shaped. Solitaire especially showed a longer pre-gelation phase before contraction force was recorded.

SIGNIFICANCE

High contraction stress and rapid contraction force development can lead to failure of bond to tooth structure. This study suggested that, packable composite resins are less capable of reducing the contraction stress during the early setting stage, thus not superior in maintaining the bond with cavity walls to conventional hybrid composite Tetric Ceram.

Cytotoxicity of dental composite components and mercury compounds in lung cells

OBJECTIVE

The effect of dental composite components triethyleneglycoldimethacrylate (TEGDMA) and hydroxyethylmethacrylate (HEMA), as well as mercuric chloride (HgCl2) and methylmercury chloride (MeHgCl) was investigated on the release of lactatedehydrogenase (LDH) from alveolar epithelial lung cell lines in vitro.

METHODS

The confluent cell layers from the A549 (human, malignant) and the L2 cells (rat) were incubated with various concentrations of HEMA, TEGDMA, MeHgCl and HgCl2 at 37 degrees C in 2% (v/v) CO2 atmosphere for 8h. In further experiments the L2 cells were incubated with the same compounds for 6-48 h. LDH release was measured and the values were expressed as percentage of the LDH content. The values were plotted on a concentration log-scale and the substance concentration at the maximum slope was assessed as effective concentration (EC50).

RESULTS

A significant (p<0.05) increase in the LDH release was found in the L2 cells after 8-h incubation with HEMA (4 mmol/l), TEGDMA (2 mmol/l), MeHgCl (0.01 mmol/l) and HgCl2 (0.015 mmol/l), and in A549 cells with HEMA (14 mmol/l), TEGDMA (15 mmol/l), MeHgCl (0.15 mmol/l) and HgCl2 (0.05 mmol/l), compared to controls. The EC50 values from compounds in the L2 cells are shown in the following table (mean; sem in parentheses; n=3-6; #n=1): [see text].

SIGNIFICANCE

The toxic effect of HgCl2 and MeHgCl from the L2 cells was about 100-700-fold higher than of the dental composite components. A significant (p<0.05) time dependent increase of toxicity was observed with TEGDMA, HEMA and MeHgCl.

Simulation of dental microwear: Characteristic traces by opal phytoliths give clues to ancient human dietary behavior

In order to further evaluate the process of microwear formation on human dental enamel, microwear was experimentally produced by a chewing simulation with an Academic Center for Dentistry Amsterdam (ACTA) device. For this simulation, several cereal species were processed according to historical milling techniques, the experimental results of which were compared with those obtained from cereals processed after modern techniques, and also with natural microwear on early medieval human molars. Comparison of simulated microwear pits with natural microwear pits showed that the simulation led to traces which matched those found on the historical teeth in terms of both size and shape. Experimentally produced microwear pits were especially characteristic for the cereal species used in the simulations, and both pit morphology and enamel loss were a function of cereal phytolith content. Despite the high variability of phytolith size and shape, certain types are characteristic for certain cereals, which in turn are capable of producing cereal-specific microwear. This experimental approach is likely to further define ancient human dietary behavior, including food processing.

Mechanical properties of new composite restorative materials

OBJECTIVE

Determination of flexural strength, flexural modulus, fracture toughness, Vickers hardness, and wear resistance of condensable composites (Solitaire, Surefil, Alert) and an ormocer (Definite) in comparison with a hybrid composite (Tetric Ceram) and an ion-releasing composite (Ariston pHc).

METHODS

Flexural strength, flexural modulus, and fracture toughness were determined in 3-point bending. Single-edge notched-bend specimens were used to evaluate fracture toughness. Microhardness was measured with a Vickers indenter. Wear was determined in a pin-on-block-design with a Degusit antagonist at 50 N load and quantified by a replica technique after 6000, 10000, 30000, and 50000 load cycles using a 3D-laser scanner. All results were statistically analyzed with ANOVA and post hoc Tukey HSD tests.

RESULTS

Alert exhibited the highest flexural modulus, K(IC), and hardness, but lowest wear resistance. Solitaire presented the highest wear resistance, but significantly lower flexural strength, flexural modulus, K(IC), and hardness than all other materials. No significant correlation could be detected between hardness and wear of the tested composites with Pearson's correlation coefficient.

SIGNIFICANCE

The condensable composites differed significantly in their mechanical properties. This study suggested that, besides the filler content level and filler size, other factors like matrix-filler interactions highly influence the fracture and wear behavior of the materials.

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.

Tooth-colored filling materials for the restoration of cervical lesions: a 24-month follow-up study

The recently developed resin-modified glass ionomer cements and the polyacid-modified composites are promising alternatives to conventional materials for restoring cervical defects. This clinical study evaluated the clinical condition of cervical fillings 24 months following placement. The study subjects were 197 cervical restorations placed on incisors, canines and premolars in 37 patients for restoration of erosion/non-carious lesions (69 cases), primary carious lesions (57 cases) and the replacement of deficient restorations (71 cases). The teeth were randomly divided into four groups for restoration with either Tetric (composite, Group A: n = 36), Dyract (compomer, Group B: n = 79), Fuji II LC (resin-modified glass ionomer cement, Group C: n = 51) or Photac-Fil (resin-modified glass ionomer cement, Group D: n = 31). The evaluation was done single-blind at baseline, 8 and 24 months after the placement of the fillings, according to a modified USPHS rating scale. The assessment criteria were color stability, anatomical form, surface texture, marginal integrity, marginal discoloration and loss of filling. Statistical analysis was completed using Pearson chi-square and Fisher's exact test at a significance level of 5% (p < 0.05). After the 24-month period, the composite restorations showed superior results. The compomer fillings demonstrated conditions that were only slightly worse. A substantial number of the resin-modified glass-ionomer fillings were evaluated with bravo or even charlie scores in respect to at least one of the criteria assessed.

Determination of changes on tooth-colored cervical restorations in vivo using a three-dimensional laser scanning device

The present study aimed at the determination of changes of tooth-colored cervical restorations in vivo using an optical 3-dimensional laser scanning device. The study was performed on 197 cervical restorations placed on incisors, canines, and premolars. Four different tooth-colored restoration materials, a composite, a polyacid-modified resin composite, and two resin-modified glass ionomer cements, were used for the restoration of the lesions. For the determination of changes, images were taken at baseline and 15, 24 and 36 months after the placement of the fillings using a 3D-laser scanning device. The images were superimposed automatically, and digital subtraction was made by a specially developed image analysis software. The total substance loss on the entire filling surface at 36 months for the resin-modified glass ionomer Photac-Fil was 44 (+/-23) microm, for Fuji II LC 45 (+/-26) microm, for Dyract 71 (+/-47) microm and for Tetric 18 (+/-12) microm. Differentiating between the class of lesion, a higher wear rate was observed at 36 months on restorations which had been placed in erosion/non-carious cervical cavities (66 (+/-33) microm). In conclusion, the composite material demonstrated a distinctly lower surface wear rate over time in comparison to the resin-modified glass ionomer cements and the polyacid-modified resin composite.

Influence of a high-speed polymerization method on the marginal integrity of composite fillings in Class-II cavities

The aim of this study was to evaluate the effect of a rapid photopolymerization method on the marginal integrity of composite fillings. Ninety two-surface cavities were prepared in extracted human molars using the SonicSys preparation system. All cavities were bonded with one bonding agent (Syntac) and filled with a microfilled composite (Herculite XRV), a heavy filled composite (Z100 MP), and an Ormocer (Definite) in two increments. Each increment had a thickness of approximately 1.5 mm and was polymerized using either halogen light or the plasma light of Apollo 95 E. In this process, six trial groups each containing 15 fillings were created. After replicas were made, the test teeth were subjected to a thermocycling process of 2000 temperature cycles (5 degrees C/55 degrees C) followed by a wear simulation of 50,000 stress cycles each with 50 N. This was followed by the creation of a second set of replicas, quantitative margin analysis, and dye penetration. A significant (P < 0.05) influence of the thermomechanical stress and a significant (P < 0.05) influence of the factor "material" were shown for the margin criterion "continuous margin" using MANOVA. The factor "light source" produced no significant influence (P = 0.57) on the amount of continuous margin. During the dye penetration, no significant differences between the polymerization methods could be established with the materials Herculite XRV and Z100 MP (H-test according to Kruskall and Wallis). Only with the material Definite was a significantly higher dye penetration observed at the occlusal measuring point in the plasma light group. A rapid polymerization with high light intensity had no adverse effects on the margin quality within the limitations of this in vitro study. However the marginal integrity might have been influenced by the chosen adhesive system/composite resin combination, which does not represent the respective product line. Additionally, further studies ought to show which exposure time is necessary for a sufficient degree of conversion.

Mechanical properties and wear behavior of light-cured packable composite resins

OBJECTIVES

Determination of flexural strength, flexural modulus, fracture toughness and wear resistance of three packable composites (Solitaire, Surefil, ALERT) and a packable ormocer (Definite) in comparison with an advanced hybrid composite (Tetric Ceram) and an ion-releasing composite (Ariston pHc).

METHODS

Flexural strength, flexural modulus and fracture toughness of each material were determined in three-point bending (each test n = 10). Single-edge notched-bend specimens were used to evaluate the fracture toughness (K1C). Wear of the materials (n = 8) was determined in a pin-on-block-design with a spherical Degusit antagonist at 50 N vertical load and quantified by a replica technique using a 3D-laser scanner. Replicas were made after 6000, 10,000, 30,000 and 50,000 load cycles. The mean wear rate (MWR (micron 3 cycle-1)) was obtained by a linear regression analysis in the steady-state of the time-wear-curve. All results were statistically analyzed with ANOVA and post hoc Tukey HSD tests (p < 0.05).

RESULTS

ALERT exhibited the highest flexural modulus (12.5 +/- 2.1 GPa) and K1C (2.3 +/- 0.2 MN m-3/2), but the lowest wear resistance (8275 micron 3 cycle-1). Solitaire presented the highest wear resistance (1591 micron 3 cycle-1), but significantly lower flexural strength (81.6 +/- 10.0 MPa), flexural modulus (4.4 +/- 0.3 GPa), and K1C (1.4 +/- 0.2 MN m-3/2) than all other materials. Surefil revealed a significantly higher flexural modulus (9.3 +/- 0.9 GPa) and wear resistance (3028 micron 3 cycle-1) than Tetric Ceram (6.8 +/- 0.5 GPa; 5417 micron 3 cycle-1) and Ariston pHc (7.3 +/- 0.8 GPa; 7194 micron 3 cycle-1).

SIGNIFICANCE

The tested packable composite resins differed significantly in their mechanical properties. This study suggested that fracture and wear behavior of the composite resins are highly influenced by the filler system. Overall, Surefil demonstrated good fracture mechanics parameters and a low wear rate.

Bond strength of a compomer to dentin under various surface conditions

This study determined the influence of different dentin pretreatments on the shear bond strength of an adhesive system and corresponding compomer material. One hundred and twenty freshly extracted human molars were ground with wet SiC paper to expose flat oral/buccal surfaces of superficial dentin. The teeth were assigned to 12 treatment groups (n = 10) based on dentin surface finish (600-grit SiC vs. air abrasion vs. 40 microns diamond bur), surface conditioning (acid etching vs. no etching), and moisture content of the dentin (moist vs. dry). Cylinders of Compoglass F compomer were bonded to the dentin with Syntac Single-Component. After 24-h storage in distilled water, the specimens were debonded in shear mode. Bond strengths in MPa (SD) were calculated and bonding sites were analyzed for the mode of failure. Three-way ANOVA revealed significantly higher bond strength values for acid etched specimens (P = 0.001). Moisture content of the dentin surface (P = 0.614) and mechanical surface finish (P = 0.367) had no significant influence on the results. Debonding in unetched groups ranged from 94 to 100% adhesively. Acid etched groups showed adhesive failures ranging from 56 to 100%. To obtain a more reliable bond it is recommended that dentin is acid etched prior to the bonding of a compomer.

Two-year clinical evaluation of direct and indirect composite restorations in posterior teeth

STATEMENT OF PROBLEM

Few long-term clinical studies have reported data of modern posterior composites as direct and indirect restorations.

PURPOSE

This prospective, long-term clinical trial (1) evaluated direct and indirect composite restorations for clinical acceptability as posterior restoratives in single or multisurface carious teeth and (2) provided a survey on the 2-year results.

MATERIAL AND METHODS

Nine dental students placed 88 composite restorations (Tetric, blend-a-lux, Pertac-Hybrid Unifil), 43 direct composite restorations and 45 indirect inlays, under the supervision of an experienced dentist. The first clinical evaluation was performed 11 to 13 months after placement by 2 other experienced dentists, using modified USPHS criteria. A second follow-up of 60 restorations took place within 20 to 26 months after placement.

RESULTS

A total of 93% of indirect and 90% of direct composite restorations were assessed to be clinically excellent or acceptable. Two restorations (1 indirect composite inlay and 1 margin of a direct composite restoration) failed during the second year because of fracture. Indirect inlays demonstrated a significantly better "anatomic form of the surface" than direct composite restorations. Premolars revealed a significantly better margin integrity and postoperative symptoms than molars.

CONCLUSION

Posterior composite restorations provided a satisfactory clinical performance over a 2-year period when placed by relatively inexperienced but supervised students.

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.

Effect of dental materials on gluconeogenesis in rat kidney tubules

The effect of dental composite components triethyleneglycoldimethacrylate (TEGDMA) and hydroxyethylmethacrylate (HEMA) as well as mercuric chloride (HgCl(2)) and methylmercury chloride (MeHgCl) on gluconeogenesis was investigated in isolated rat kidney tubules. From starved rats kidney tubules were prepared and isolated by digestion with collagenase. Every 10 min up to 60 min 1-ml samples were drawn from the cell suspension for quantitating the glucose content. Glucose formation in controls was 3.3 +/- 0.2 nmol/mg. per min (mean +/- SEM, n=21). Relative rates of glucose formation were obtained by expressing individual rates as a percentage of the corresponding control. X-Y concentration curves (effective concentration, EC) of the substances were calculated by fitting a four-parametric sigmoid function to the relative rates of glucose formation at various test concentrations. At the end of the incubation period cell viability was assessed by trypan blue exclusion. Cell viability decreased within the 60 min interval from 90 to approx. 80% (controls), <25 (HEMA), <20 (TEGDMA), <10 (MeHgCl), and <10% (HgCl(2)). Values of 50% effective concentration (EC(50)) were calculated from fitted curves. EC(50) values were (mmol; mean +/- SEM; n=4): HEMA, 17.7 +/- 2.9; TEGDMA, 1.8 +/- 0.2; MeHgCl, 0.018 +/- 0.0005; and HgCl(2), 0. 0016 +/- 0.0005. The toxic effect of HgCl(2) was approximately 1000 or 10 000 higher than that of the dental composite components TEGDMA or HEMA, respectively.

One-year clinical evaluation of composite and ceramic inlays in posterior teeth

STATEMENT OF PROBLEM

There are only a few studies available that deal with the clinical behavior of composite and ceramic inlay systems as potential substitutes for amalgam restorations.

PURPOSE

This prospective clinical trial evaluated composite and ceramic inlay systems for clinical acceptability as restorative materials in single or multisurface cavities of posterior teeth and provided 1-year results.

MATERIAL AND METHODS

Forty-seven composite inlays (Tetric, Blend-a-lux, Pertac) and 24 heat-pressed ceramic inlays (IPS Empress) were placed in 45 patients by 7 student operators under the supervision of an experienced dentist. The first clinical evaluation was performed 11 to 13 months after placement of the restorations and used modified United States Public Health Services criteria.

RESULTS

Satisfactory results over this period were found, as 100% of ceramic inlays and 94% of composite inlays were assessed to be clinically excellent and acceptable. Only 3 composite inlay restorations were scored delta (unacceptable). Two inlays exhibited secondary caries and 1 demonstrated loss of pulp vitality. For the criteria "anatomic form of the surface" and "marginal integrity," ceramic inlays were significantly better than composite inlays.

CONCLUSION

Posterior tooth-colored inlays provided acceptable and excellent clinical service, even if they are placed by relatively inexperienced student operators.

A new optical 3-D device for the detection of wear

For the clinical performance of new dental restorative materials to be accurately assessed, the three-dimensional anatomical changes of the functional surfaces of the restoration must be elucidated over time. To this end, a highly accurate 3-D optical scanner has been developed that utilizes the principles of triangulation and a reference-free automated 3-D superimposition software. The aim of this study was to assess the accuracy and the precision of the new system with and without referenced positioning. Additionally, the ability of the system to determine wear of posterior fillings three-dimensionally has been shown. Gypsum replicas of restored teeth were evaluated. The tooth surfaces were scanned with a resolution of 250,000 surface points within a measuring time of 20 to 40 sec. The results show that the precision and accuracy of 3-D data acquisition depend on the surface inclination. Up to an angle of 60 degrees, the precision is better than 3 microns, and the accuracy is better than 6 microns. If exact repositioning of the object before and after occlusal loading is possible, e.g., with in vitro studies, differences on the surface can be determined with a precision of 2.2 microns. In reference-free measurements, which are a necessity in clinical studies, the 3-D data acquisition in combination with the automatic matching program can detect wear with an accuracy of 10 microns. The application of this measuring device for the detection of wear of a composite filling functioning in the mouth has been shown. Since this measuring technique is automated, and measurements of high accuracy can be attained in a short period of time, this system offers the possibility for complex analyses of three-dimensional wear to be conducted on a large number of samples in clinical studies.

Chronic ulcerative stomatitis

Chronic ulcerative stomatitis (CUS) has recently been described as a new disease entity characterized by chronic ulceration of oral mucosa which responds to treatment with hydroxychloroquine. It has a particular type of stratified epithelium-specific, antinuclear autoantibody as an immunological marker. Twelve cases have been reported in the literature. We present a 40-year-old woman with an 11-year history of chronic oral ulcerations. Other dermatological diseases, including oral lichen planus, pemphigus vulgaris and cicatricial pemphigoid, as well as bullous lupus erythematosus, were excluded. The clinical diagnosis of CUS was confirmed on the grounds of the immunological and ultrastructural findings. The lesions initially responded to high doses of systemic corticosteroids but relapsed promptly after dose reduction. Dapsone was ineffective. Hydroxychloroquine, given at a dosage of 200-400 mg/day, led to a complete and long-lasting remission.

One-year clinical evaluation of composite fillings and inlays in posterior teeth

In the course of a prospectively designed long-term clinical trial, composite fillings and inlays were evaluated for clinical acceptability as restorative materials in one, two or more surface cavities of posterior teeth over a 1-year period. In 45 patients, 88 restorations were placed by nine student operators, under the supervision of an experienced dentist, to compare the two half sides using the composite resins Tetric (Vivadent), blend-a-lux (Blend-a-med), and Pertac-Hybrid Unifil (Espe). The first clinical follow-up check took place within a time period of 11-13 months after placement of the restorations using modified USPHS criteria. The interpretation of the clinical criteria showed satisfactory results over this time period: more than 85% of the inlays and direct fillings were rated "alpha" or "bravo", using the parameters of assessment defined in this study. Only three restorations (two fillings, one inlay), all in molars, were rated "delta", i.e., unacceptable. The reasons for their replacement were marginal opening, secondary caries, and loss of sensitivity. For the criteria "surface texture", "anatomical form of the surface", and "occlusion", composite inlays were significantly better than composite fillings. These results indicate that posterior composite restorations provide acceptable and excellent clinical service, even if they are placed by relatively inexperienced student operators.

Physical properties and gap formation of light-cured composites with and without 'softstart-polymerization'

OBJECTIVES

Recently it has been pointed out that light-initiated prepolymerization at low intensity followed by a post-light-cure at full intensity ('softstart-polymerization') may lead to light-cured composite fillings with improved marginal adaptation. The aim of this study was to examine the influence of this procedure with different initial cure conditions on physical material properties like flexural modulus, flexural strength and Vickers microhardness of different composites. Additionally, an in vitro study was carried out to investigate the influence of different initial cure conditions on the marginal quality of composite restorations in cases of Class V cavities with a cemento-enamel junction.

METHODS

Physical properties of composite materials Tetric (Vivadent, Liechtenstein) and Charisma (Kulzer, Germany) were evaluated. Three hundred specimens were made for the flexural tests performed similar to EN 24049:1993. Microhardness was measured with a Vickers indenter. For the in vitro study of Class V composite fillings, cavities of 32 extracted teeth were filled with Tetric and analysed by quantitative marginal gap analysis and dye penetration test before and after thermocycling.

RESULTS

The results indicate that initial cure with decreased light intensity followed by final cure with high light intensity has no influence on microhardness and increases flexural modulus and flexural strength. With the low-level initial cure/high-level final cure regime the marginal integrity was significantly better compared with the high light intensity curing system.

CONCLUSION

Therefore, initial cure with low light intensity followed by final cure with high light intensity significantly improves the marginal integrity of light-cured composite fillings and also the material properties.

Experience with midazolam as sedative in the dental treatment of uncooperative children

Shortage of capacity, and the limited range of therapies available for dental treatment of uncooperative children involve obvious problems which have given rise to new developments in treatment. Over the last two years, 83 children have been treated in 181 sessions after sedation with Midazolam. Rectal application is clearly superior to giving the drug orally. The results, and the good amnestic effect of Midazolam show that sedation employing this drug, while not a substitute for general anaesthesia in every case, does constitute an important alternative in the treatment of uncooperative children.

[Treatment of deciduous teeth under rectal Midazolam sedation]

Individual controlled sedation using Midazolam proves to be a valuable addition to the range of therapeutic options for non-cooperative children. In a clinical study the oral and rectal routes of administration were compared with each other. Rectal application allowed considerably better dose adjustment. While the quality of sedation and the therapeutic range were equal with both routes, rectal application had the advantage that treatment can be commenced sooner. The sedation was of shorter duration and left the patient with less unpleasant memories. Rectal application was easier and required a smaller amount of Midazolam than oral administration.

[Individually controlled sedation using Midazolam]

Midazolam might be an alternative to general anesthesia for noncooperative children. 40 children were treated during 94 midazolam sedations to evaluate the potential dental therapy. An average of 2 fillings and 1 endodontic treatment was possible per sedation. The initial Midazolam dosage was 0.6 mg/kg. Every 15 min another 0.3 mg Midazolam/kg were administered to maintain the treatability of the children. 30 min after the initial Midazolam dosage dental treatment could be started. The average duration of a sedation was 76 min. Our results suggest that sedations complement under dental treatment general anesthesia.

[Middle course between group and individual preventive programs]

A pilot study was initiated to prove the effectivity of a prophylaxis programme for small groups of preschool children. A total number of 190 children was examined twice a year at the Dental School of Erlangen. The dental examination included df-s index and plaque index according to Quigley-Hein. Tooth cleaning was performed in small groups under professional supervision. Professional plaque removal and local fluoridation concluded each session. Twice a year the parents were offered oral hygiene instructions and informed about the relationship between sugar and caries. After two years the dfs-values were significantly lower in the test group than in the control group. Mean dfs scores ranged from 1.9 for the experimental to 3.8 for the control group. These comparatively low recordings--as against other investigations--may be due to the relatively high social standing of the children.

Dental fear and pain: effect on patient's perception of the dentist

A questionnaire was developed including the Dental Anxiety Scale (DAS) and the Dental Beliefs Survey (DBS) as subscales to examine the epidemiology of dental fear and dental beliefs in Germany. The survey was administered before treatment to a sample of 474 dental patients. Of the respondents 56% were female. The mean age was 34.3 yr (SD 12.4 yr). The mean DAS score was 8.6 (SD 3.7). Mean DBS score ranged from 1.73 to 2.75 for single items. The correlation between DAS and DBS scores was highly significant (rs = 0.39, P less than 0.001). Absence or presence of dental pain revealed significant differences for DAS and DBS scores (P less than 0.001). Both tests are valid screening forms for the German linguistic context and easy to implement in daily dental routine.

[The influence of cavity preparation on the width of marginal gaps in Cerec inlays]

In a study of the influence of the proximal box shape on the marginal fit of Cerec inlays, MOD cavities were prepared in 10 extracted teeth. One box was prepared with sharp edges as recommended by Mörmann (1989), the other was conventionally U-shaped. The width of the marginal gap was measured with a microscope at five different points. The results showed with high significance that the marginal gap of the U-shaped box preparation is smaller. It is recommended to use conventional U-shaped proximal box preparations for Cerec-inlays, too.

[Interaction of dental treatment anxiety and oral health]

Measurements of oral health (PBI, DMFS), dental treatment anxiety (DAS) and frequency of dental utilization were taken in a sample of 474 dental patients. Regression analysis shows that DAS scores are significantly correlated with DS, but not with MS and FS. Dental anxiety has a negative impact on the frequency of dental utilization, which is a predictor variable of oral health status. These results permit the conclusion that our attention should be focussed on reducing dental treatment anxiety to improve oral health.

[Fine polishing of Cerec inlays using diamond polishing systems]

The surface roughness of Cerec-inlays after polishing with diamond polishing pastes or Diafinish-disks was compared to polishing with aluminium oxide disks (AOD). SEM evaluation of the occlusal surface of extracted teeth revealed that diamond polishing pastes or Diafinish-disks produced smoother surfaces than AOD. The pastes, however, damaged the bonding resin. It is recommended to use AOD and diamond polishing systems for the approximal surfaces of the inlays extraorally. Intraorally AOD or Diafinish-disks are recommended.

[Precision of the Cerec-System: the milling unit]

The Cerec-System is a computer-assisted method for fabrication of customized ceramic inlays. Until now there are no data available to judge the precision of this system, which is a function of several variables. This study investigated the tolerance of the milling unit by using computer-constructed data sets for test purposes. REM pictures show how the diamond bur is affected by several milling cycles. Overall precision along the x- or z-axis is largely independent of the inherent properties of the milling instrument used, such as wear. Precision along the y-coordinate, however, is dependent on the number of milling cycles and the feed along the horizontal axis. Best results can be obtained by using a new bur and slow feed.

[The patient--his anxiety and his assessment of the dentist as variables in the compliance model]

The publication concerns the relationship between the two variables "patient anxiety" and "assessment of the dentist by the patient". Two instruments were used: the German versions of the "Dental Anxiety Scale" and the "Dental Belief Survey". The answers of 383 patients, age 18 to 80 years, demonstrated that both tests are highly age dependent. There is no difference between males and females in either test in the overall population nor in the individual age categories. Patient anxiety and assessment of the dentist by the patient show a highly significant correlation.