Till N. Göhring

Clinical and scanning electron microscopic evaluation of fiber-reinforced inlay fixed partial dentures: Preliminary results after one year

STATEMENT OF PROBLEM Restorative dentistry searches for nonmetal reinforcement of esthetic fixed partial dentures (FPDs). PURPOSE This clinical study evaluated conservative fiber-reinforced composite FPDs bonded to inlay abutments. MATERIAL AND METHODS Twenty fiber-reinforced composite inlay FPDs were made for 15 patients. Restorations were manufactured with the Targis Vectris glass-fiber-reinforced composite system and a simplified laboratory technique. The 20 bonded inlay FPDs were examined clinically and by SEM after 1 year. RESULTS All 20 FPDs were intact at the 1-year examination. There were no signs of fracture, surface defects, or excessive wear with SEM. SEM marginal analysis exhibited 91.6% +/- 5% excellent margins at the tooth-luting composite interface and 86. 1% +/- 8% excellent margins at luting composite/restoration interface. CONCLUSION On the basis of the results of this descriptive study, bonded glass-fiber-reinforced composite inlay FPDs were considered clinically successful at the 1-year examination.

Attritional wear and abrasive surface alterations of composite resin materials in vitro

OBJECTIVES A laboratory study was performed with 232 specimens and 72 human enamel, 24 gold, 24 ceramic and 12 composite antagonists in 22 groups to test attritional and abrasive wear behavior of composite materials compared to wear behavior of human enamel. METHODS Belleglass HP, Concept Inlay/Onlay, Targis and Targis Upgrade 99 composite resin for lab-made restorations was tested as well as Tetric Ceram and FHC Merz light as resins for direct restorations. Natural human enamel specimens served as control. All specimens were subjected to long-term thermo-mechanical loading in a computer-controlled masticator, chemical degradation and toothbrush/toothpaste abrasion. Wear of specimen in occlusal contact area (OCA), contact-free occlusal area and wear of natural enamel cusps as well as antagonists made of gold, ceramic and composite in identical form was measured after 120,000, 240,000, 640,000 and 1200,000 load cycles. A qualitative SEM analysis was performed to support quantitative data. RESULTS Belleglass HP and Targis Upgrade 99 restorative materials showed wear resistance comparable to human enamel when loaded with enamel cusps. Wear of Targis versus composite and gold antagonists was significantly higher (p<0.0001). Analysis of surface alterations showed hygroscopic expansion in all composite resins during the test. CONCLUSIONS As a consequence of this study, necessity to further improve physical properties of composites for long lasting restorations was obvious. Beside of attritional wear in OCA, attention must be given to stable filler-matrix interfaces and prevention of water sorption.

Influence of the type of post and core on in vitro marginal continuity, fracture resistance, and fracture mode of lithia disilicate-based all-ceramic crowns

STATEMENT OF PROBLEM The influence of different crown foundations on marginal seal and fracture resistance of ceramic crowns placed on endodontically treated teeth has not been clearly established. PURPOSE The purpose of this study was to evaluate the marginal continuity and fracture behavior of high-strength all-ceramic crowns with different substructures in endodontically treated premolars. MATERIAL AND METHODS Forty-eight human mandibular premolars were assigned to 6 groups, including a no-treatment group (UNTREATED) and a group for which the access cavity was restored with composite resin (Tetric Ceram) (COMP). In the remaining 4 groups, teeth were prepared to receive all-ceramic crowns with 0.8-mm-wide shoulders and axial dentin heights of 2 mm. No posts were used in the ENDOCROWN group. Glass fiber posts (FRC Postec) were used in group FRC-POST. Group ZRO-POST received zirconia ceramic posts (CosmoPost), and group GOLD-POST received cast gold posts (CM). Experimental lithia disilicate ceramic crowns were made and adhesively cemented (Variolink). All teeth were subjected to thermal cycling and mechanical loading (TCML) in a masticatory simulator (1,200,000 loads, 49 N, 1.7 Hz, 3000 temperature cycles of 5 degrees C-50 degrees C-5 degrees C). Marginal continuity was evaluated with scanning electron microscopy at x200. All specimens were loaded to failure in a universal testing machine at 0.5 mm/min after TCML. Data were analyzed using 1-way ANOVA and post hoc t tests with Bonferroni correction (alpha=.05). RESULTS Initially, mean values (SD) between 72.4 (15.8)% (ENDOCROWN) and 94.8 (3)% (FRC-POST) for continuous margins were found. With TCML, marginal continuity decreased significantly only in FRC-POST, to 75.5 (8.4)%, and in ENDOCROWN, to 44.7 (14.5)%. Mechanical load testing measured mean loads to failure between 1092.4 (307.8) N (FRC-POST) and 1253.7 (226.5) N (ZRO-POST) without significant differences between groups. Deep root fractures were observed in half of the specimens, irrespective of their groups. CONCLUSIONS Marginal continuity of the crowns studied was better and more stress resistant when posts and cores were included in the restoration of endodontically treated teeth with complete ceramic crowns. The placement of a post-and-core foundation did not influence the pattern of failure.

Resistance of an enamel-bonding agent to saliva and acid exposure in vitro assessed by liquid scintillation

OBJECTIVES To determine the leakage and resistance of a bonding agent and a light-curing fine hybrid composite when exposed to saliva or lactic acid (pH 4) in vitro. METHODS Twenty discs in each of four groups of selected irradiated bovine lower central incisors were treated with one of three sealing options: an enamel bond (Heliobond, Vivadent, Schaan, Liechenstein) in a single-step application; Heliobond in a two-step application; and Tetric Flow (Vivadent) as the negative control. One group served as the positive control and remained unsealed. Loss of apatite was determined using the radiochemical method of liquid scintillation. The Cherenkov radiation was assessed in order to evaluate the acid resistance and leakage of smooth surface enamel bonding after exposure to saliva and lactic acid. In addition, replicas were made for SEM analysis of micromorphologic surface changes. RESULTS A mean loss of 416.5 g (s.d. 57.0) apatite was observed over the unsealed sites following 14 days of exposure to lactic acid. The application of Heliobond in a one- and two-step application still revealed a remarkable degree of leakage, and substance losses of 196.5 g (s.d. 38.9) and 161.8 g (s.d. 39.7), but a protective potential was evident. In saliva, untreated, as well as sealed teeth, showed a modest leakage that was less than 20 g. When Tetric Flow was used (negative control) leakage was reduced to a minimum of 2.4 g (s.d. 1.0) in saliva and 12.8 g (s.d. 19.6) in lactic acid. These results were confirmed by SEM analysis. SIGNIFICANCE The method of liquid scintillation was revealed to be of considerable value in evaluating leakage and acid resistance of potential smooth enamel sealing options. Sealing with an unfilled resin still demonstrated remarkable levels of acid dissolution, although a protection tendency could be observed. This leads to the conclusion that there is a need for further investigation to establish more acid-resistant enamel sealing agents.

Interface evaluation after manual and ultrasonic insertion of standardized class I inlays using composite resin materials of different viscosity

Objective. The aim of the present study was to investigate the effect of manual and ultrasonic insertion of standardized class I inlays (Cerana®) using three composite resin materials of different viscosity (Tetric Flow®, Tetric®, and Tetric Ceram®) on time to seat inlays, film thickness, and filler distribution within the materials. Methods. In a preliminary test, mean loads for manual and ultrasonic insertion were measured using the high viscosity composite resin material (Tetric Ceram). These loads were then applied with all composite resin materials to evaluate the times required to seat the inlays. In addition, film thickness was assessed using scanning electron microscopy, and filler distribution (wt% silicon, barium, ytterbium) was monitored using energy-dispersive spectroscopy. Results. Ultrasonic insertion significantly reduced mean load applied to seat inlays (6.4±1.4 N; mean±SD) as compared to manual insertion (18.9±3.1 N; p<0.001). Using an ultrasonic device, times for insertion values were significantly lower in the high and medium viscosity composite resin material groups compared to manual insertion (p<0.05). The widest film thickness was recorded for the high viscosity composite resin material in combination with manual insertion (p<0.05). However, when ultrasound was applied, there was no difference in film thickness between the three materials at any levels. Furthermore, the analysis of filler distribution revealed no significant differences between groups. Conclusion. Highly filled viscous composite resin materials may be used in combination with the ultrasonic insertion technique without untoward effects on film thickness or filler distribution.

Wear Resistance and Surface Roughness of a Newly Devised Adhesive Patch for Sealing Smooth Enamel Surfaces

A laboratory study assessed the wear resistance and surface roughness after chemical and mechanical wear of a newly devised adhesive patch when used as a smooth surface sealant. Forty-eight enamel discs were prepared from bovine lower central incisors. Sixteen specimens were treated with one of two sealing options: the prototype of an adhesive patch or a flowable resin. Unsealed enamel served as the positive control. Wear and surface roughness was measured at baseline and after all the samples were immersed in saliva or lactic acid (n=8 per treatment group) for up to 21 days, during which the experimental and control enamel surfaces were exposed to 10 double-stroke toothbrush cycles per day. In saliva and lactic acid, the sealed specimens showed no significant wear during the observation period (p=0.1841). Only untreated specimens exposed to lactic acid showed a significant substance loss after 14 and 21 days (p=0.0186). The patch and flowable resin showed no differences in surface roughness values at respective times (p=0.385); whereas the surface roughness of the unsealed specimens in lactic acid was significantly higher (p<0.0001). It was concluded that the adhesive patch under investigation merits further study to assess its potential as a sealant for smooth enamel surfaces.

Influence of a proximal margin elevation technique on marginal adaptation of ceramic inlays

PURPOSE Evaluating the effect of a proximal margin elevation technique on marginal adaptation of ceramic inlays. METHODS Class II MOD-cavities were prepared in 40 human molars and randomly distributed to four groups (n = 10). In group EN (positive control) proximal margins were located in enamel, 1 mm above the cementoenamel junction, while 2 mm below in groups DE-1In, DE-2In and DE. The groups DE-1In, DE-2In and DE simulated subgingival location of the cervical margin. In group DE-1In one 3 mm and in group DE-2In two 1.5 mm composite layers (Tetric) were placed for margin elevation of the proximal cavities using Syntac classic as an adhesive. The proximal cavities of group DE remained untreated and served as a negative control. In all groups, ceramic inlays (Cerec 3D) were adhesively inserted. Replicas were taken before and after thermomechanical loading (1.200.000 cycles, 50/5°C, max. load 49 N). Marginal integrity (tooth-composite, composite-inlay) was evaluated with scanning electron microscopy (200×). Percentage of continuous margin (% of total proximal margin length) was compared between groups before and after cycling using ANOVA and Scheffé post-hoc test. RESULTS After thermomechanical loading, no significant differences were observed between the different groups with respect to the interface composite-inlay and tooth-composite with margins in dentin. The interface tooth-composite in enamel of group EN was significantly better compared to group DE-2In, which was not different to the negative control group DE and DE-1In. CONCLUSION Margin elevation technique by placement of a composite filling in the proximal box before insertion of a ceramic inlay results in marginal integrities not different from margins of ceramic inlays placed in dentin.