Paul Ferger

Correlation between polymerization shrinkage and marginal fit of temporary crowns

OBJECTIVES During polymerization, temporary c&b materials (t-c&b) undergo shrinkage which may lead to marginal inaccuracies of the temporary restoration. The degree of correlation between these two factors is still unknown. Hence, the objective of this study was to determine the polymerization shrinkage of t-c&bs and to evaluate, to which degree the shrinkage is correlated to the width of the marginal gap. METHODS Six different t-c&bs (2 monomethacrylates and 4 dimethacrylates) were used to fabricate temporary crowns (n = 12) on two prepared teeth (stainless steel) of different diameters (5 and 7 mm). The crown diameters and marginal discrepancy were measured at various storage times after mixing (10, 30, 60 min) using a travelling microscope. In addition, the shrinkage (bonded-disk method) and content of inorganic filler (ashing method) were recorded. The statistical analysis was carried out using parametric tests, the F-test and Pearsons correlation (p = 0.05). RESULTS The marginal discrepancies increased as a function of increasing storage time (10 min: 0.162-0.218 mm; 60 min: 0.271-0.521 mm). Lower values were recorded for monomethacrylates than for the dimethacrylates (greatest changes recorded during the first 30 min). The shrinkage values recorded 10 min after mixing varied between 3.25 and 4.10%. There was no significant relationship between the width of the marginal gap and shrinkage (p > 0.05). SIGNIFICANCE Shrinkage values are not suitable to predict the marginal accuracy of a temporary restoration. At least 30 min should elapse between fabricating and trimming temporary crowns to avoid further inaccuracies.

Bonding of acrylic denture teeth to MMA/PMMA and light-curing denture base materials: The role of conditioning liquids

OBJECTIVES The connection between resin denture teeth and the denture base is essential for the integrity of partial and full dentures. The aim of the present study was to analyse the bond strength of acrylic denture teeth to two light curing denture base materials compared to the gold-standard (MMA/PMMA) using different conditioning liquids. METHODS The ridge laps of 220 identical denture teeth were ground and pre-treated using different conditioning liquids (MMA, an experimental conditioning liquid as well as the two commercially available liquids Palabond and Versyo.bond). The denture base materials (PalaXpress, Versyo.com, Eclipse) were applied using a split mould to obtain tensile bond strength specimens of identical shape. Ten specimens per test group were either stored in water for 24h or thermocycled (5000×, 5-55°C) prior to tensile bond strength testing (cross-head speed 10mm/min). Data was subjected to parametric statistics (α=0.05). RESULTS The three-way ANOVA revealed a significant influence of the material, pre-treatment as well as the storage. PalaXpress showed the highest bond strength (24.3MPa) of all materials tested after TC, whereas the use of MMA led to the most constant results. Lower values were recorded for Versyo.com (17.5MPa) and Eclipse (10.4MPa) bonded with Versyo.bond. CONCLUSIONS The results indicate that MMA/PMMA based denture base resins provide reliable and durable bond strength to acrylic denture teeth. Using light-curing denture base materials requires the application of appropriate conditioning liquids to obtain acceptable bond strength. The use of MMA affects bond strength to light-curing denture base materials. CLINICAL SIGNIFICANCE The pre-treatment of denture teeth is critical regarding their bond-strength to denture base materials and in turn for the integrity of removable full and partial dentures. Light-curing denture base resins are more sensitive to the correct tooth pre-treatment compared to conventional MMA/PMMA materials, requiring specific conditioning liquids.

Treatment outcomes with removable partial dentures: a retrospective analysis.

PURPOSE This retrospective clinical study aimed to evaluate the long-term outcomes of clasp-retained, metal-framework removable partial dentures (RPDs) and their clasped teeth, the influencing factors on survival, and the type and number of repairs needed during the observation period. MATERIALS AND METHODS The study is based on a convenience sample of 52 patients who received 65 RPDs with a total of 207 clasped teeth. The mean observation period was 3.11 ± 0.29 years (maximum: 10 years). Patient gender, prosthesis location (maxilla/mandible), number and distribution (Kennedy class) of abutment teeth, and impact of a continuous follow-up program on a favorable outcome probability were analyzed. Statistical analysis was performed using the Kaplan-Meier method (P < .05) in combination with Cox regression analysis. RESULTS During the observation period, 9.2% of the RPDs ceased to function and 5.8% of the abutment teeth were extracted. Mean RPD survival time was 8.07 ± 0.66 years, with a positive outcome probability of 90% after 5 years. Prosthesis location was the only parameter that significantly (P < .05) impacted this probability. CONCLUSION Overall, the high survival probability and low extraction rate of the abutment teeth reported in this study indicate that RPDs designed according to hygienic pronciples are clinically successful.

Effect of surface condition and storage time on the repairability of temporary crown and fixed partial denture materials

OBJECTIVES The aim of the present study was to investigate which parameters (chemical nature, time after mixing, surface characteristics) might affect the repair strength of temporary crown and bridge materials (t-c&b). METHODS Four different t-c&bs (Cool Temp Natural, Protemp 3 Garant, Structur Premium, Trim) were investigated using a shear-bond strength (SBS) setup. A cylinder (2 mm x 2.37 mm) of identical t-c&b (n=10) was bonded onto a specimen surface of either freshly set t-c&b (10 min after mixing) or onto specimens that were stored for 24h (37 degrees C, distilled water) and 7 days (thermocycling x 5,000, 5-55 degrees C=TC), respectively. The specimen surface was roughened with SiC paper (grit size 320) or left as it was (specimens stored for 10 min) prior to repair to retain the oxygen-inhibition layer. In addition, mono-block specimens were fabricated as control. The thickness of the oxygen-inhibition layer and the surface morphology was determined. Statistical analysis was carried out with an ANOVA followed by parametric tests (p=0.05). RESULTS SBS values ranged from 10 to 40 MPa. Trim showed lowest SBS values for most storage conditions. Material, surface characteristics and time after mixing significantly affected the SBS (ANOVA p<0.001). TC significantly reduced the SBS (p<0.05) for all t-c&bs except for Trim (p>0.05). CONCLUSIONS In case of monomethacrylates, storage and surface condition do not affect the repair strength. In contrast, the repair quality of dimethacrylates greatly depends on the material. In any case, roughening the surface is recommended, even if an oxygen-inhibition layer is present.

Temperature rise on dentin caused by temporary crown and fixed partial denture materials: Influencing factors

OBJECTIVES Temporary crowns and fixed partial denture materials (t-c&b) generate exothermic heat during polymerization. The amount of temperature, reaching the pulp chamber, is dependent on the residual thickness of the prepared dentin as well as the volume of the t-c&b used. Hence, the aim of this study was to investigate the influence of both factors on the temperature rise at the pulpal dentin surface as well as in the bulk of the t-c&b during polymerization. METHODS Four t-c&bs (Luxatemp AM Plus, Protemp 3 Garant, Structur Premium, Trim) were used to fabricate flat cylindrical specimens (∅ 15.5mm) of different thicknesses (1, 2 and 4mm) using an over-impression placed on top of dentin discs (thickness 0.5, 1 and 2mm). Temperature was recorded at the pulpal dentin surface as well as inside the t-c&b (n=6). Data was subjected to parametric statistics (α=0.05). RESULTS Peak temperatures inside the t-c&b varied between 37.0°C and 51.9°C and at the pulpal dentin side between 37.0°C and 50.6°C. The maximum temperatures registered depended significantly on the thickness of the dentin disc and t-c&b, respectively (ANOVA p<0.05). Peak temperatures were reached 2-3 min after start of mixing (dimethacrylates) and 6 min (mono-methacrylate), respectively, whereas Trim exhibited significantly higher peak temperatures (p<0.05). CONCLUSIONS At 4mm layer thickness of the t-c&b, temperature rise may become critical if the material is not cooled properly. Composite-based t-c&bs showed significant lower curing temperatures than Trim and should therefore be preferred in daily practice.