Biomedical subjects
Publications and source records attributed to G Schmalz.
The influence of three alloys and their amalgams on the in vitro growth of Streptococcus mutans has been estimated. Spherical, fine cut, and dispersion alloys were studied. Dispersion alloy amalgams seem to inhibit bacterial growth more than amalgams prepared from the other alloys in a similar fashion.
We will now summarize the conclusions from parts I, II and III of this study. A test procedure has been developed that provides a simple, quick, and nondestructive means of monitoring the in vitro growth of S mutans in the presence of amalgams and alloys. The spectrophotometric readings are related in a simple way to growth expressed as dry weight of bacteria and metabolic products. Results are expressed as growth relative to controls which represent bacteria growing under identical conditions but not in contact with metals. The %RA60 value that represents growth after 60 hours relative to controls is used as a measure of growth in the presence of alloys or amalgams. Spherical, fine cut, and dispersion alloys were studied as well as amalgams prepared from these alloys. The dispersion alloy inhibits growth less than the spherical alloy which in turn inhibits growth less than the fine cut alloy. The results for amalgams prepared from the alloys are reversed. At an aging time of two hours, dispersion alloy amalgams inhibit growth more than spherical alloy amalgams and fine cut alloy amalgams. Aging time of amalgams greatly influences the growth inhibition. Immediately after trituration growth is inhibited, but this inhibition is lost with aging. Different types of amalgams seem to lose growth inhibition at different rates. Hg composition in the range of 48 to 52% seems to have little effect on growth inhibition. It remains for clinical studies, which are concerned with the incidence of secondary caries associated with amalgams, to demonstrate that the age and nature of the amalgam are significant.
The purpose of the present study was to examine the marginal adaptation of ceramic veneers to dentin at the cervical margins and to enamel at the palatoincisal margins using four dual-curing composite resin cements of different viscosity with their corresponding dentin bonding systems. Thirty-six caries-free human maxillary incisors were prepared for facial ceramic veneers with cervical cavity margins located in dentin. Heat-pressed glass-ceramic veneers (IPS Empress) were inserted adhesively using one of the following luting systems: Sono-Cem (SC) with EBS; Variolink Ultra (VU), Variolink High Viscosity (VHV), and Variolink Low Viscosity (VLV) with Syntac. Both the cervical and the palatoincisal margins of the veneers (tooth/composite resin cement interface and ceramic/composite resin cement interface) were evaluated before and after thermocycling and mechanical loading (TCML) by quantitative margin analysis under a scanning electron microscope (SEM) using an image analysis system. Microleakage was assessed by dye penetration after TCML. Before TCML, SC and VU showed statistically significantly fewer marginal gaps than VHV and VLV. After TCML, SC, VU, and VHV revealed significantly fewer marginal gaps than VLV. TCML had a statistically significant influence on marginal gap formation at both the dentin and enamel margins. After TCML, the percentage of marginal gaps was not significantly different at the cervical dentin than at the palatoincisal enamel margins. Cervical dye penetration after TCML showed no statistically significant differences in microleakage among the four luting systems. In conclusion, this in vitro study showed that similarly favorable marginal adaptations of ceramic veneers to dentin and enamel can be achieved using Sono-Cem, Variolink Ultra, or Variolink High Viscosity with their corresponding dentin bonding systems.
The aim of the present in vitro study was to compare the marginal adaptation and integrity of heat-pressed glass-ceramic veneers to adjacent class 3 composite restorations and to enamel using four dual-curing composite resin cements of different viscosity with their corresponding dentin bonding agents. Thirty-six caries-free human maxillary incisors were first restored with mesial and distal class 3 composite restorations and then prepared for facial ceramic veneers. The cavity margins of the veneers were located either in the class 3 composite restorations or in the residual enamel. Heat-pressed glass-ceramic veneers (IPS Empress) were inserted adhesively using one of the following four luting systems in nine teeth: SonoCem (SC) with EBS; Variolink Ultra (VU), Variolink High-Viscosity (VHV), and Variolink Low-Viscosity (VLV) with Syntac. The veneer margins in the region of the composite restoration and in the region apical to the composite restoration (ceramic/composite resin cement interfaces, composite resin cement/composite restoration interface, and composite resin cement/enamel interface) were evaluated before and after thermo-cycling and mechanical loading (TCML) by quantitative margin analysis under a scanning electron microscope (SEM) using an image analysis system. Furthermore, microleakage was assessed in each tooth by dye penetration after TCML. For all luting systems, SEM analysis revealed excellent marginal adaptation of the ceramic veneers to the composite restorations as well as to enamel. The median percentages of marginal gap formation were 1.1% and less before TCML and 5.1% and less after TCML. The error-rates method revealed no statistical influence of the interface or of the viscosity of the luting material. Maximal values of dye penetration showed a significantly higher microleakage at veneers cemented with VU (median: 86.4%) compared to SC (median: 13.3%). In conclusion, the present data demonstrated that existing clinically acceptable class 3 composite restorations have no negative influence on the marginal adaptation of ceramic veneers. This was valid independent of the viscosity of the dual-curing composite resin cement when SC, VHV, or VLV was used.
For improving the marginal integrity of composite restorations, a total bonding method has been advocated besides the conventional selective bonding method. Total bonding avoids the placement of a base. The entire internal cavity surface is available for the adhesive bond. Selective bonding involves the placement of a base covering the pulpal floor as well as the pulpoaxial wall. In this study, five dentin/enamel bonding system/composite combinations were used to restore 60 class 2 cavities with their cervical margins below the cementoenamel junction (CEJ); six teeth per material were restored according to the total bonding and the selective bonding methods. Before and after simultaneous thermo-cycling and mechanical loading (TCML) marginal adaptation was evaluated on replicas in the SEM. Microleakage was determined by dye penetration on the original samples after TCML. The data were statistically evaluated with the Mann-Whitney U-test and the Wilcoxon test. The error rates method was applied. In SEM analysis the error rates method indicated a significant difference between the two restoration methods in general. In the pairwise comparisons, no significant differences between the selective bonding and total bonding methods were found for Syntac/Tetric, Gluma 2000/Pekafill, and Gluma/Pekafill. With Scotchbond Multi-Purpose (SBMP) and All-Bond 2 (AB2), total bonding revealed significantly (P < or = 0.01) less gap formation before and after TCML than selective bonding. Accordingly, total bonding showed significantly less (P < or = 0.01) dye penetration with Scotch-bond Multi-Purpose and All-Bond 2 compared to selective bonding. In conclusion, the reduction of microleakage by application of the total bonding method depended upon the bonding system used. Total bonding could be an alternative procedure for the adhesive restoration of class 2 cavities when their gingival margins are apical to the cementoenamel junction, provided the proper system is used and pulp damage is prevented.
Polymerization shrinkage causing marginal gap formation is still a major problem in light curing restorations. The aim of the present study was to test the influence of "softstart polymerization" (prepolymerization at a low light intensity followed by a final cure at a high light intensity) on the marginal integrity of polyacid-modified resin and composite resin restorations in Class V cavities using a commercially available curing unit with two defined curing intensities. Sixty standardized Class V cavities were prepared. Twenty cavities at a time were filled either with a composite resin [Spectrum + Prime & Bond 2.1 (SP)], or with polyacid-modified resins [Dyract + Prime & Bond 2.1 (DY); Hytac + OSB Primer (HY)]. Ten fillings of each group were either conventionally cured (40 seconds, 800 mW/cm2), or they were cured with a lower starting intensity (10 seconds, 150 mW/cm2) and then with the full intensity (30 seconds, 800 mW/cm2). Margins were evaluated before and after thermomechanical loading (TCML) by quantitative margin analysis. Microleakage was assessed by dye penetration. The softstart polymerization showed no significant influence on gap formation for each material and interface before and after TCML. Quantitative margin analysis after TCML showed significantly fewer marginal gaps at the enamel/restoration interface for SP (0%) compared to DY (15.5%) and HY (44.5%) using softstart polymerization. At the dentin/restoration interface the corresponding results for gap formation were 29.6% for SP, 8.5% for DY, and 21.0% for HY. These results were not significantly different from each other. Dye penetration was significantly higher for SP at the dentin/restoration interface. SP showed significantly more marginal swelling at the dentin/restoration interface compared to DY. In conclusion, softstart polymerization using a very low starting intensity did not improve the marginal adaptation of polyacid-modified resins or composite resins in Class V cavity preparations. The best marginal adaptation in Class V cavities at the enamel/restoration interface was achieved with SP, using the acid-etch technique. In dentin, however, the polyacid-modified resins showed a superior marginal adaptation.
From 15 September to 15 October 1991, 102 dentists practicing in a rural area of Germany provided information on 3375 composite resin fillings. The purpose of this cross-sectional study was to record the reasons for placement and replacement of composite resin restorations, including any change of material when replacing a filling, and to register the age of any failed restoration. First placements because of primary caries were made in 50.6% of all cases; 49.4% were replacements of failed restorations. Composite resins were used as a material for the first placement of a restoration in 19.2% of primary teeth and in 47.8% of permanent teeth. More amalgams were replaced by composites than vice versa. Secondary caries was the most frequent reason for replacement in permanent teeth and in restorations with less than four surfaces, whereas fracture caused most failures in primary teeth and in fillings with four surfaces. The median age of the replaced restorations was 43.5 months. Failed restorations with four surfaces had the lowest median age.
From 15 September to 15 October 1991, 102 dentists practicing in a rural area of Germany provided information on 5240 amalgam restorations. The aim of the present cross-sectional study was to investigate the reasons for placement and replacement of amalgam fillings and to register the age of the failed restorations. First placements because of primary caries were made in 47.1% of all cases; 52.9% were replacements of failed restorations. The most frequently recorded reason for replacement was secondary caries, irrespective of size of the filling, dentition, and age group. The second most frequently recorded reasons for replacement depended on the size of the filling, the age and the dentition of the patient: Bulk fractures were predominant in primary teeth and in fillings with three or four surfaces, primary caries in permanent teeth of patients 16 years old or younger and marginal gaps in adults and in fillings with one or two surfaces. The median age of replaced amalgam restorations in adults was 60 months.
The aim of this in vitro study was to compare the approximal marginal quality of composite fillings using a dentin bonding system to the marginal quality of hybrid ionomer/composite sandwich restorations. Forty-eight standardized class 2 cavity preparations were prepared in caries-free, human third molars. Twelve preparations at a time were filled either with a composite using the matching dentin bonding system, SZ (Scotchbond MP/Z100) or PP (PROBOND/Prisma TPH) or with hybrid ionomer/composite sandwich fillings VZ (Vitremer/Z100) or DP (Dyract/Prisma TPH). Margins were evaluated before and after thermomechanical loading (TCML) (5000 cycles [+5 degrees C/+55 degrees C], 72.5 N [1,7 Hz]) by quantitative scanning electron microscope analysis using an image analyzing system. Furthermore, microleakage was assessed by dye penetration before and after TCML. Statistical analysis was performed using the Mann-Whitney test at the 0.05 level of significance. SEM analysis after TCML showed significantly fewer marginal gaps at the material/dentin interface with VZ (2.2%), DP (7.3%), and PP (6.0%) compared to SZ (29.6%). After TCML, SZ showed significantly more marginal gaps at the material/dentin interface, whereas VZ, DP, and PP were not susceptible to TCML. PP showed the highest percentage in marginal swelling before (18.2%) and after TCML (15.9%), while VZ showed no marginal swelling at all. VZ showed significantly fewer marginal gaps at the composite/hybrid ionomer interface than DP. After TCML there was no significant difference in marginal gaps between the hybrid ionomer/enamel and the hybrid ionomer/dentin interface for both Vitremer and Dyract. Using the sandwich technique the Z100/enamel interface had significantly more marginal gaps than all other composite/enamel interfaces after TCML. There was no significant difference in microleakage between the test groups at the material/dentin interface. SEM analysis and dye penetration showed that hybrid ionomer/composite sandwich restorations have good marginal qualities and may be an alternative to composite restorations using a dentin bonding system.