The influence of undercut depths on the accuracy of casts poured from irreversible hydrocolloid impression materials.

Abstract Background: Making accurate partial dentures is one of the greatest challenges in the treatment of patients with partial edentulous. Positional teeth movements create undercuts that must be accurately recorded in the impression material. Distortion of irreversible hydrocolloid (alginate) impressions has been reported as one of the several possible causes of an inaccurate master casts. Prostheses constructed on inaccurate master casts will not fit intraorally. Objectives: I. To measure and compare undercuts of teeth adjacent to the extraction sites and the lingual sulcus in partially dentate mandibular master casts. II. To evaluate the elastic recovery of a typical alginate impression material in terms of the amount of undercut identified and additional thickness of spacer provided prior to custom tray fabrication. III. To make recommendations of the thickness of spacer required when designing custom trays for taking definitive alginate impressions for partially dentate mandibular cast in relation undercuts depth. Materials and Methods: The undercut depths of the teeth and lingual sulci of partially edentulous mandibular dental stone casts (n=100) of adults, being routinely treated in a dental laboratory, were measured prior to the casts being digitally 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 and three custom trays were constructed for each cast with spacer thicknesses representing 20%, 30% and 50% compression of impression material against the wall of the custom tray on removal, impressions made, and casts fabricated in dental stone. Comparative measurements between the original 3D printed and stone casts were done by a single investigator. Reliability of measurements was assessed by means of Cohen’s kappa scores. Descriptive statistics were used to calculate the measurement of undercuts by age, gender and teeth surfaces. An Independent samples Mann-Whitney U test and Kruskal-Wallis test of the dataset were used to make comparisons of the undercut values between the original 3D printed casts and poured casts from the three compression impressions for each category of undercut, to establish the amount of elastic recovery of the alginate impression material. Results: For objective 1, the difference in teeth undercut depths compared by teeth surfaces and age were statistically significant ≤ 0.001). For objective 2, there was no statistical difference between the casts poured from the three compression impressions compared with the original 3D printed casts irrespective of percentage compression. Conclusion: In RPD construction, primary casts should be blocked out parallel to the path of insertion and then additional 3mm of spacer applied as a standard technique prior to custom tray fabrication to ensure elastic recovery of the alginate impression

The influence of undercut depths on the accuracy of casts poured from irreversible hydrocolloid impression materials.

Abstract Background: Making accurate partial dentures is one of the greatest challenges in the treatment of patients with partial edentulous. Positional teeth movements create undercuts that must be accurately recorded in the impression material. Distortion of irreversible hydrocolloid (alginate) impressions has been reported as one of the several possible causes of an inaccurate master casts. Prostheses constructed on inaccurate master casts will not fit intraorally. Objectives: I. To measure and compare undercuts of teeth adjacent to the extraction sites and the lingual sulcus in partially dentate mandibular master casts. II. To evaluate the elastic recovery of a typical alginate impression material in terms of the amount of undercut identified and additional thickness of spacer provided prior to custom tray fabrication. III. To make recommendations of the thickness of spacer required when designing custom trays for taking definitive alginate impressions for partially dentate mandibular cast in relation undercuts depth. Materials and Methods: The undercut depths of the teeth and lingual sulci of partially edentulous mandibular dental stone casts (n=100) of adults, being routinely treated in a dental laboratory, were measured prior to the casts being digitally 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 and three custom trays were constructed for each cast with spacer thicknesses representing 20%, 30% and 50% compression of impression material against the wall of the custom tray on removal, impressions made, and casts fabricated in dental stone. Comparative measurements between the original 3D printed and stone casts were done by a single investigator. Reliability of measurements was assessed by means of Cohen’s kappa scores. Descriptive statistics were used to calculate the measurement of undercuts by age, gender and teeth surfaces. An Independent samples Mann-Whitney U test and Kruskal-Wallis test of the dataset were used to make comparisons of the undercut values between the original 3D printed casts and poured casts from the three compression impressions for each category of undercut, to establish the amount of elastic recovery of the alginate impression material. Results: For objective 1, the difference in teeth undercut depths compared by teeth surfaces and age were statistically significant ≤ 0.001). For objective 2, there was no statistical difference between the casts poured from the three compression impressions compared with the original 3D printed casts irrespective of percentage compression. Conclusion: In RPD construction, primary casts should be blocked out parallel to the path of insertion and then additional 3mm of spacer applied as a standard technique prior to custom tray fabrication to ensure elastic recovery of the alginate impression

Effect of Enamel Bleaching on the Bond Strength of Ceramic—A Systematic Review

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

Effect of Enamel Bleaching on the Bond Strength of Ceramic—A Systematic Review

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

Wear of Modern Denture Teeth—A Systematic Review

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

Wear of Modern Denture Teeth—A Systematic Review

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