Objectives: To evaluate the elastic recovery of a typical irreversible hydrocolloid impression material in terms of the amount of undercut identified and additional thickness of spacer provided before custom tray fabrication. Methods: This study surveyed the undercut depths of the teeth surfaces and lingual sulci of one hundred partially dentate mandibular dental casts which were subsequently scanned and the data exported as STL files. A typical cast from each undercut category (0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm) was 3D printed. Three custom trays were constructed with spacer thicknesses representing 20%, 30% and 50% compression against the wall of the custom trays on removal, impressions recorded, and casts fabricated in dental stone. Measurements for elastic recovery of irreversible hydrocolloid were done using an internal caliper and a digital caliper. All measurements were done by the principal investigator. Non-parametric analyses were used for comparisons of the undercut values between the 3D printed and poured casts to determine the amount of elastic recovery of the irreversible hydrocolloid impression material. Results: There was no statistically significant difference in measurements between the original 3D printed casts and the poured casts, irrespective of percentage compression (p > 0.05). Conclusions: In removable partial denture construction, casts should be blocked out parallel to the path of insertion and then an additional 3mm of spacer applied as a standard technique before custom tray fabrication to ensure elastic recovery of the irreversible hydrocolloid impression. Clinical implications: In severe undercut situations, accurate impressions can be taken using irreversible hydrocolloid by blocking out all undercut surfaces on the teeth and lingual sulci before adapting additional threemillimetre wax spacer on casts when constructing custom trays thereby ensuring accurate and reliable impressions for removable prosthesis construction.

The increase in aesthetic demands has increased the use of ceramic dental restorations in dentistry. Ceramic restorations are bonded to the tooth structure using adhesives. There is a lack of standard guidelines in terms of post-bleaching time intervals and bond strengths of ceramic restorations. Bleaching products have also been stated to affect the morphology of enamel. Therefore, the purpose of this systematic review is to evaluate the bond strength between ceramic and enamel and the changes in the surface roughness of enamel post teeth bleaching. An electronic search was performed in the databases PubMed, OVID MEDLINE, Scopus, and Web of Science with MESH terms: “adhesion OR bonding”, “ceramic OR ceramics OR dental porcelain”, “tooth bleaching OR teeth bleaching OR tooth whitening OR teeth whitening” and “enamel OR dental enamel OR enamels OR dental enamels”. The articles were screened, and the final selection of articles was obtained by using the inclusion and exclusion criteria. Of the 170 studies identified from the search, only 12 studies met the inclusion criteria and were selected for full-text review. A further search by hand was performed, and additional 48 studies were selected. From the 60 full-text studies, 18 studies met the inclusion criteria and were included for data extraction. The results were based on a descriptive analysis of the effect on bond strength of ceramic to enamel after a bleaching protocol and the changes in the surface roughness of enamel post bleaching protocol. In conclusion, bleaching protocols alter the surface roughness of enamel and, thus, the shear bond strength between ceramic and enamel. Bleaching treatments with a higher concentration of hydrogen peroxide reduce the bond strength between ceramic and enamel. Delaying bonding after bleaching for up to 7 days increases the bond strength between ceramic and enamel.

The purpose of this systematic review was to identify the different methods used to measure artificial teeth wear and to determine which denture teeth (or which combination of tooth types) have better wear resistance. The focused patient, intervention, comparison, and outcome (PICO) question for this review was “which available denture teeth or combination of teeth have higher wear resistance?” The method of testing and measuring the artificial teeth wear was also evaluated as a secondary outcome. We searched OVID Medline, PubMed and SCOPUS using the following terms (MeSH words) with any synonyms and closed terms: “wear”, “denture teeth”, “denture tooth”, or “artificial tooth”, “tooth wear”, or combination of “denture tooth wear”. Database searches were limited to the English language and studies published between years 1997 and 2021. Further hand searches were carried out of studies identified from the bibliographies of relevant articles. The electronic data base search identified 293 articles of which 213 were eliminated after removing duplicates and screening the titles of the articles. A further 31 articles were eliminated upon application of the exclusion criterion and full text reading because they were either not in the English language or were review articles. Only 41 articles met the inclusion criterion; along with addition of one hand search article, a total of 42 articles were included in the review. The studies showed that rate of denture teeth wear is influenced by factors such as the material and composition of the artificial teeth, the denture tooth antagonist, the tooth being replaced, patient’s age and sex, the type of removable prosthesis and the amount of the superficial layer removed during occlusal adjustments. The testing parameters were inconsistent across all studies. In conclusion, artificial teeth of same material should be used as antagonists where possible, and the superficial outer layer of the teeth must be preserved as much as possible during occlusal adjustments to enhance wear resistance. Denture teeth should be selected taking into consideration the tooth being replaced, the age and sex of the patient, and the type of prosthesis. Incorporation of nano fillers into acrylic resin teeth does not increase wear resistance; therefore, there is no evidence to favour the use of nano-filled composite teeth over micro-filled or conventional acrylic resin teeth.

Casts with a high surface hardness and abrasion resistance are essential for conventional dental prosthesis construction procedures. The water/powder ratio is a critical factor determining the physical and chemical properties of gypsum casts, and any modification to this ratio may alter these properties. This study evaluated the influence of water type and water-powder ratios on the Brinell hardness and the Compressive strength of type III & IV gypsum casts. Three groups of test samples were prepared using type III and type IV gypsum control group -recommended water/ powder ratio, and tests groups; 20% and 30% increase in water/powder ratio. The prepared samples were subjected to Compressive strength test and Brinell hardness test using the universal material testing machine. Two-way ANOVA and Tukey's test were used to analyse the data (α=5%). A significant reduction in Compressive strength and Brinell hardness was found in samples prepared with increased water-powder ratios using both the tap water and distilled water. Tap water samples showed significantly lower Compressive strength and Brinell hardness values than the distilled water samples. Chipping was observed in both type III and type IV gypsum samples prepared with an increase in the water powder ratio. Type III gypsum samples exhibited single fracture lines with the recommended water powder ratio whereas type IV gypsum samples had composite fractures. Distilled water samples exhibited higher Compressive strength and Brinell hardness values. Type III and IV gypsum samples prepared with increased water-powder ratio showed statistically significant reduction in the Compressive strength and Brinell hardness values.