Qualitative evaluation of the adesive interface between lithium disilicate, luting composite and natural tooth

Silane Heat Treatment Could Eliminate the Hydrofluoric Acid Etching of Lithium Disilicate Overlays: A Four-Year Follow-Up

A four-year follow-up of a novel silane heat treatment method for bonding lithium disilicate overlays to tooth structures without hydrofluoric acid etching of the ceramic surface is presented in this case report. Silane heat treatment modifies the silane layer and thus enhances resin ceramic bond strength without hydrofluoric acid etching. The standard ceramic preparation technique prior to bonding silicate ceramics to tooth structure is hydrofluoric acid etching and applying a silane coupling agent, followed by dental adhesive. In this case, the micromechanical roughening of the ceramic surface was performed by air abrasion with Al₂O₃. Silane heat treatment with constant 120°C airflow, applied for 60 sec, followed by dental adhesive application enhanced the resin-ceramic bond strength. After a four-year follow-up, the restorations' clinical appearance could be defined as excellent/very good according to the FDI clinical criteria for the evaluation of direct and indirect restorations. This clinical result supports many in vitro studies regarding the resin-ceramic bond strength and durability obtained through postsilanization heat treatment.

In Vitro Fracture Strength of Teeth Restored with Lithium Disilicate Onlays with and without Fiber Post Build-Up

To our knowledge there is no data about the mechanical performance of indirect restoration adhesively cemented on teeth without an adequate build-up to provide the correct geometrical configuration. The aim of this study was to compare the fracture strength of human teeth restored with lithium disilicate onlays, with and without fiber post build-up.

METHODS

Twenty human mandibular molars were horizontally sectioned and divided into two groups (n = 10). No treatment was applied in group A. Teeth in group B were endodontically treated, built-up using fiber post and composite core and prepared with a circumferential chamfer providing a 1 mm circumferential ferrule. Lithium disilicate onlays were pressed and luted on teeth using dual-curing luting composite. Teeth were tested under static load. Failures were classified as restorable or not restorable. Failure loads were analyzed with one-way analysis of variance. Failure modes were compared using Pearson's Chi-square tests.

RESULTS

The mean fracture loads were 1383.5 N for group A and 1286.3 N for group B. No difference was found (p = 0.6). Ninety per cent of fractures were classified as not restorable in both groups, with no difference (p = 0.8).

CONCLUSIONS

For teeth restored with adhesive procedures and lithium disilicate onlays, the presence of build-up with fiber post to provide retention and resistance form does not influence the fracture strength.

Bonding to new CAD/CAM resin composites: influence of air abrasion and conditioning agents as pretreatment strategy

OBJECTIVES

Because of their industrially standardized process of manufacturing, CAD/CAM resin composites show a high degree of conversion, making a reliable bond difficult to achieve.

PURPOSE

The purpose of this experiment was to investigate the tensile bond strength (TBS) of luting composite to CAD/CAM resin composite materials as influenced by air abrasion and pretreatment strategies.

MATERIAL AND METHODS

The treatment factors of the present study were (1) brand of the CAD/CAM resin composite (Brilliant Crios [Coltene/Whaledent], Cerasmart [GC Europe], Shofu Block HC [Shofu], and Lava Ultimate [3M]); (2) air abrasion vs. no air abrasion; and (3) pretreatment using a silane primer (Clearfil Ceramic Primer, Kuraray) vs. a resin primer (One Coat 7 Universal, Coltene/Whaledent). Subsequently, luting composite (DuoCem, Coltene/Whaledent) was polymerized onto the substrate surface using a mold. For each combination of the levels of the three treatment factors (4 (materials) × 2 (air abrasion vs. no air abrasion; resin) × 2 (primer vs. silane primer)), n = 15, specimens were prepared. After 24 h of water storage at 37 °C and 5000 thermo-cycles (5/55 °C), TBS was measured and failure types were examined. The resulting data was analyzed using Kaplan-Meier estimates of the cumulative failure distribution function with Breslow-Gehan tests and non-parametric ANOVA (Kruskal-Wallis test) followed by the multiple pairwise Mann-Whitney U test with α-error adjustment using the Benjamini-Hochberg procedure and chi-square test (p < 0.05).

RESULTS

The additional air abrasion step increased TBS values and lowered failure rates. Specimens pretreated using a resin primer showed significantly higher TBS and lower failure rates than those pretreated using a silane primer. The highest failure rates were observed for groups pretreated with a silane primer. Within the Shofu Block HC group, all specimens without air abrasion and pretreatment with a silane primer debonded during the aging procedure.

CONCLUSIONS

Before fixation of CAD/CAM resin composites, the restorations should be air abraded and pretreated using a resin primer containing methyl-methacrylate to successfully bond to the luting composite. The pretreatment of the CAD/CAM resin composite using merely a silane primer results in deficient adhesion.

CLINICAL RELEVANCE

For a reliable bond of CAD/CAM resin composites to the luting composite, air abrasion and a special pretreatment strategy are necessary in order to achieve promising long-term results.