Libros

Purpose: To evaluate the amount of residual cement (ECL) around the margins of zirconia crown copings after careful luting and cleaning procedures and to investigate these factors in relation to two tested luting materials. Materials and Methods: An experimental model of a maxillary arch was selected for this in vitro study. The maxillary first molar was prepared to receive an all-ceramic, single, full-crown restoration with a finish line located 1 mm below the artificial gingiva. After scanning of the prepared tooth, 20 paired zirconia coping–abutment assemblies were CAD/CAM fabricated. A slot in the model allowed for insertion and removal of the assemblies for each new test. Specimens were divided into two groups according to the cementation procedure: half (n = 10) were luted using a resin-modified glass-ionomer (RMGI) (Ketac-Cem Plus) (GI group), and the other half with a dual-curing self-adhesive resin agent (RelyX Unicem 2) (UN group). The substructures were loaded with cement, and a customized preseating device was adopted for preliminary reduction of excess. The zirconia copings were finally seated on their respective abutments located on the simulation model. A blinded investigator attempted to remove all excess cement with clinically available instruments. The amount of excess cement left in situ after cleaning procedures was weighed in grams. Dislodging forces of luted coping-abutment assemblies were obtained by using pull-off tests in a universal testing machine (crosshead speed of 0.5 mm/minute) after 24 hours of water storage. Means and standard deviations were calculated for ECL and for retention force values, and Mann-Whitney and ANOVA tests were carried out to detect significant differences (α = .05) among groups. Results: Cement remnants were found in all specimens despite the cleaning procedures, with a typical distribution in interproximal areas. Mean ECL values for the GI and UN groups were 0.0079 ± 0.0060 and 0.0107 ± 0.0081, respectively. No statistically significant differences were found between tested cements (P = .3284). Removal stress values (MPa) were significantly higher (P = .0313) for the UN group (12.4 ± 6.5) than for the GI group (6.57 ± 4.69). Conclusion: Similar amounts of undetected cement remnants were discovered around the esthetic margins of zirconia crown copings regardless of cement type. The luting procedure using the self-adhesive resin cement provided significantly higher early retention values than the RMGI material.

In dieser Studie sollte der Einfluss einer provisorischen adhäsiven Restauration auf die Wirksamkeit der Bleichreaktion gezeigt werden, und zwar unabhängig von der Konzentration des Bleichmittels. Wer auf dem Gebiet der Zahnerhaltung tätig ist, kennt die Inkompatibilität zwischen "chemischer Verbindung" und "Sauerstoff". Aus diesem Grund wählen Zahnärzte oft eine "mechanisch retinierte" provisorische Füllung, die das Entweichen von Sauerstoffionen jedoch nicht verhindern kann. Die Patienten brauchen daher mehrere Bleachingsitzungen, was auch die Gefahr von Komplikationen erhöht. Das wissenschaftliche Prinzip der hier beschriebenen Technik besteht darin, durch einen adhäsiven koronalen Verschluss die rasche Dissoziation des Wasserstoffperoxids ausschließlich in der Pulpakammer ablaufen zu lassen. So wird ein erhöhter Innendruck induziert, der die Penetration der freien Sauerstoffradikale direkt in die Dentintubuli verursacht. Tatsächlich kann das Unterdrücken einer spontanen Freisetzung freier Sauerstoffradikale nach außen deren Wirksamkeit erhöhen. Diese Studie zeigt, dass eine schnellere Bleichreaktion eintritt, wenn ein Protokoll auf Basis der "Walking-Bleach-Technik" angewendet wird, das nicht bezüglich der Mischung des Bleichmittels angepasst ist, sondern die Reaktionsausbeute der Wasserstoffperoxid-Disproportionierung gezielt und vollständig nutzt. Die Ergebnisse der dokumentierten klinischen Fallberichte belegen die Wirksamkeit dieser Methode, die in nur einer Sitzung durchgeführt wird. Somit werden die bei der klassischen Technik erforderlichen multiplen Bleichschritte vermieden.

The aim of this study was to demonstrate the influence of an adhesive temporary restoration on the effectiveness of the bleaching reaction, regardless of the concentration of the bleaching agent used. Every clinician involved in conservative dentistry understands the incompatibility between 'chemical bond' and 'oxygen.' This awareness often influences clinicians to decide on a temporary 'mechanical retention' filling that is unable to prevent the escape of oxygen ions, forcing the patient into more sessions and therefore raising the risk of complications. The scientific rationale behind the procedure described in this article is based on the bonding capacity of the coronal seal to maintain the rapid dissociation of the hydrogen peroxide exclusively within the pulp chamber, inducing an increase in the internal pressure and a consequent penetration of the oxygen-free radicals directly inside the dentinal tubules. In fact, avoiding the spontaneous dissipation of the oxygen-free radicals in the external environment may limit their effectiveness. This study aimed specifically to prove that it is possible to obtain a rapid bleaching reaction by observing a protocol based on the 'walking bleach' technique, specifically modified not so much by the typology of the mixture used but by fully exploiting the reaction yield of the hydrogen peroxide disproportionation. The results of the documented clinical cases presented here show the effectiveness of this method, which is achieved in a single session, therefore decreasing the possibility of the several operating phases that are necessary with the traditional procedure.

Ziel: Die Randpassung gilt als eines der wichtigsten Kriterien für Qualität und Erfolg von Vollkeramikrestaurationen. Ziel dieser In-vitro-Studie war die Untersuchung der Randpassung von Lava- Zirconia-Kronengerüsten mit einer Hohlkehl- bzw. einer Schulterpräparation. Methoden: In zwei Kunststoff-Modellzähnen wurden unterschiedliche Präparationen vorgenommen: Ein Molar wurde mit einer Hohlkehle (C) und ein Prämolar mit einer abgerundeten Schulterpräparation (RS) versehen. Die Kunststoffmodelle wurden jeweils zehnmal mithilfe von silikonbasierten Abformmaterialien dupliziert und Arbeitsstümpfe mit Typ- IV-Dentalgips hergestellt. Insgesamt 20 Gerüste wurden in zwei Gruppen eingeteilt (n = 10 für die jeweilige Art der Präparationsgrenze). Nach dem Zufallsprinzip wurden an den Stümpfen 50 Messpunkte entlang der Präparationsgrenze ausgewählt. Die Randspaltmessung - die vertikale marginale Diskrepanz - erfolgte unter einem Lichtmikroskop mit 100-facher Vergrößerung, ohne dass die Kronen zementiert worden waren. Die durchschnittliche Breite des Randspalts und Standardabweichungen wurden berechnet und mithilfe der Einwegvarianzanalyse (ANOVA) die Unterschiede bei den verschiedenen Präparationsarten bestimmt (a = 0,05). Ergebnisse: Der durchschnittliche Randspalt betrug 30 ± 3 μm für die C-Gruppe und 28 ± 4 μm für die RS-Gruppe. Die Einwegvarianzanalyse (ANOVA) ergab keinen statistisch signifikanten Unterschied zwischen den beiden Gruppen (P = 0,23). Schlussfolgerungen: Innerhalb der Einschränkungen dieser Studie lagen alle Randdiskrepanzen unterhalb der festgelegten klinisch akzeptablen Grenze von 120 μm. Die Hohlkehl- und die Schulterpräparationen zeigten keine Unterschiede bezüglich der Größe des Randspalts. Klinische Signifikanz: Die Art der verwendeten Finierinstrumente ist ein leicht zu wählender Parameter vor der Präparation natürlicher Zähne. Um eine akzeptable Randpassung für die geprüften Zirkonoxidgerüste zu erreichen, erwiesen sich beide untersuchten Arten von Präparationsgrenzen als hilfreich für den Kliniker.

Purpose: Marginal fit is valued as one of the most important criteria for the clinical quality and success of all-ceramic crowns. The aim of this in vitro study was to investigate the marginal fit of Lava Zirconia crown-copings on chamfer and shoulder preparations. Methods: Two acrylic model teeth were selected to simulate the clinical preparations: one molar was prepared with a chamfer finish line (C) and one premolar was prepared with a rounded shoulder finish line (RS). Each resin model was duplicated 10 times using silicon-based impression material and poured in type IV dental stone for the fabrication of working dies. A total of 20 copings were divided into two groups (n = 10 for each finish line). Fifty measuring locations were chosen randomly along the margin on the dies and the gap width - vertical marginal discrepancy - was measured under a light microscope with a magnification of x100. Measurements were made without cementation. The mean marginal gap widths and standard deviations were calculated and a one-way analysis of variance (ANOVA) was performed for different types of preparations in order to detect differences (α = 0.05). Results: The mean marginal gap was 30 ± 3 μm for the C group and 28 ± 4 μm for the RS group. The one-way ANOVA showed no statistical significant difference between the two groups (P = 0.23). Conclusions: Within the limitations of this study, the marginal discrepancies were all within the clinical acceptable standard set at 120 μm. Chamfer and shoulder preparations did not show differences regarding the gap dimension. Clinical significance: Bur design is an easily selected parameter before natural tooth preparation. Both tested finish lines are able to help clinicians in obtaining acceptable marginal fit values for the investigated zirconia copings.

Der Retentionsverlust einer Rekonstruktion aus dicht gesintertem Zirkonoxid ist ein klinisch dokumentiertes unerwünschtes Ereignis. Ein standardisiertes, erschwingliches Vorgehen für die adhäsive Befestigung von zirkonoxidgetragenen Versorgungen ist bisher nicht verfügbar. Das Ziel dieser Untersuchung war es, den Einfluss verschiedener Oberflächenkonditionierungen auf die initialen Haftwerte eines selbstadhäsiven Kompositzements auf dicht gesintertem Zirkonoxid zu bewerten. 30 Zylinder aus dicht gesintertem Zirkonoxid wurden in drei Gruppen eingeteilt (n = 10). Jede Gruppe erhielt eine unterschiedliche Oberflächenbehandlung: Kontrolle (No_T) mit einer unbehandelten Zirkonoxidoberfläche; Sandstrahlen mit niedrigem Druck (Sand_S) (50 µm, 1 bar); und Standardsandstrahlen (Sand_H) (50 µm, 2,8 bar). Drei zusätzliche oberflächenbehandelte Proben wurden unter dem Rasterelektronenmikroskop (REM) für eine qualitative Bewertung untersucht. Nach der Vorbereitung der Proben wurde die Schnittstelle zwischen Zement und Zirkonoxid mit einem SBS-Test (Scherhaftungstest) bewertet. Die durchschnittlichen Scherhaftwerte (MPa) lagen für die Sand_H-Gruppe bei 16,24 ± 2,95 und für die Sand_SGruppe bei 16,01 ± 2,68. Ein statistisch signifikanter Unterschied (P = 0,8580) zwischen den zwei sandgestrahlten Gruppen konnte nicht festgestellt werden. Das Sandstrahlen mit geringem Druck beeinflusste die initialen Haftwerte des selbstadhäsiven Zements auf dem Zirkonoxid im Vergleich zur No_T-Kontrollgruppe positiv. Trotz des geringen Drucks entstanden jedoch Kratzer und Mikrorisse auf der Keramikoberfläche.

The debonding of a densely sintered zirconia prosthesis is a clinically reported, and undesirable event. A standardized, affordable adhesive cementation protocol for zirconia-based restorations is not yet available. The aim of this investigation was to assess the influence of several surface treatments on the initial shear bond strength of self-adhesive resin cement to densely sintered zirconia ceramic. Thirty densely sintered zirconia cylinders were divided into three groups (n = 10). Each of them received a different surface treatment: control (No_T), with the zirconia surface unconditioned; low pressure air abrasion (Sand_S) (50 µm, 1 bar); and standardized air abrasion (Sand_H) (50 µm, 2.8 bar). Three more surface-treated only specimens were addressed to scanning electron microscope (SEM) for qualitative observations. After specimen fabrication, self-adhesive cementceramic interface was analyzed using SBS (shear bond strength) test. Mean shear bond strengths (MPa) obtained for Sand_H and Sand_S were 16.24 ± 2.95 and 16.01 ± 2.68, respectively; no statistically significant difference (P = 0.8580) was found between sandblasted groups. Low-pressure air abrasion positively affected the initial self-adhesive cement adhesion to zirconia with respect to the No_T control group; however it did not prevent scratches and the formation of microcracks on the ceramic surfaces.

Aim: The objective of this study was to assess, by means of a scanning electron microscope (SEM), the cleanliness of canal dentine surfaces after post space preparation with the aid of two different magnification devices, either dental loupes or an operating microscope. Materials and methods: Twenty extracted single-rooted human teeth (18 canines and 2 premolars) were selected. Root canals were cleaned, shaped using nickel-titanium instruments and filled with gutta-percha. Samples were divided into two groups (n = 10), according to the device used by the operator: A (microscope) and B (loupes). Gutta-percha/sealer fillings were removed using a sequence of low-speed post drills; root canal walls were also cleaned by means of tips for ultrasound and microbrush. SEM images of post spaces were taken, and the presence of both debris and open dentine tubules was evaluated using a three-step scoring system. Mean scores were calculated at three depth levels of post space. Results: Residual debris was observed in all specimens. Statistically significant differences (P 0.05) between groups were found at both coronal and apical levels, and better scores for debris and open tubules were obtained by group A. Conclusions: The use of an operating microscope allowed the authors to achieve superior debridement scores at specific levels (coronal and apical levels) of the post space area, compared with the use of dental loupes. Palabras clave: debridement, dental microscope, dentinal surface, magnification, post space

Introduction: The aim of the present study was to compare two obturation techniques, i.e. Thermafil® and cold lateral condensation, in order to determine which one was most easily and rapidly learnt and applied by dental students. Methods: Fifty single-rooted teeth were instrumented by the crown-down technique. Five students were requested to obturate five teeth using the Thermafil technique and five using lateral condensation. A microleakage study was performed using a 2% aqueous methylene blue dye solution. The apical portion of teeth was sectioned into six sections and evaluated under a stereomicroscope. The presence of dye microleakage was considered when assessing every section. Results: Results were processed statistically by frequence of distribution and the Mann-Whitney test. A highly significant difference (P 0.0001) was observed between Thermafil and cold lateral condensation techniques, the former resulting in lower leakage. Conclusion: The present study, though limited and only referring to a small group, suggested that characteristics of operators and the early repeated use of a technique may influence performance. Palabras clave: education, filling techniques, lateral condensation, Thermafil

The purpose of the study was to evaluate the shear bond strengths (SBS) of two resin cements to intaglio surfaces of zirconia from two manufacturers after three surface treatment methods. Forty zirconia specimens from one manufacturer (Lava, 3M ESPE) and 40 zirconia specimens from another manufacturer (Cercon, Dentsply), each with system-specific intaglio surfaces, were randomly divided into four treatment groups (20 samples per group, 10 for each manufacturer): no treatment (No_T), sandblasting with 50µm Al₂O₃ (S_50), sandblasting with 110µm Al₂O₃ (S_110), and Rocatec silica coating and silanization (ESPE-Sil, 3M ESPE) (Roc). A 5-mm metal ring was fixed upon the zirconia and was filled with one of two different resin composite cements (RelyX Unicem, 3M ESPE and Panavia F 2.0, Kuraray). Samples were stored in distilled water at 37°C for 7 days; SBS was evaluated using a universal testing machine. Values were calculated in MPa and the data were analyzed by ANOVA and Tukey HSD test (P < .05). In the Lava specimens, the three surface treatment methods tested did not increase the bond strength of Panavia compared to the control group (P = .195); using RelyX Unicem, S_50 and Roc, mean SBS values were significantly higher than values for No_T (S_50 P = .0048; Roc P < .001). For Lava surfaces treated with Rocatec, there was a statistically significant difference between the two luting cements used (Unicem 11.39 ± 2.19; Panavia 8.56 ± 1.17; P = .002). Regarding the Cercon specimens, there was a significant difference between the Unicem and the Panavia control groups (No_T Unicem 1.48 ± 1.19, No_T Panavia 4.60 ± 2.75, P = .004). In conclusion, all surface treatments increased the bond strength of RelyX Unicem resin cement to both zirconia substrates. No statistically significant changes were found using Panavia on Lava. Sandblasting with 110µm Al₂O₃ provided the highest bond strength for Panavia on Cercon.