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STATEMENT OF PROBLEM: Data on polymer materials, particularly polyetheretherketone (PEEK) used in restorative dentistry, are scarce, as is knowledge concerning the clinical efficacy of PEEK restorations produced through additive manufacturing when compared with existing indirect materials and techniques. PURPOSE: The purpose of this randomized clinical trial was to evaluate the clinical performance of additively manufactured and milled PEEK inlays compared with composite resin inlays according to modified United State Public Health Service (USPHS) criteria over a 1-year follow- up. MATERIAL AND METHODS: Participants were allocated into 3 distinct categories based on the materials and techniques used: R1 denoting teeth restored with 3 dimensionally (3D) printed PEEK inlays (N=16), R2 representing teeth restored with milled PEEK inlays (N=16), and R3 indicating the comparator group comprising teeth restored with milled composite resin inlays (N=16). After the placement of inlay restorations, evaluations were conducted at 3 time points (T): baseline (T0), 6 months (T1), and 12 months (T2) by using the modified USPHS criteria for assessing anatomic form, color match, marginal discoloration, marginal adaptation, surface texture, secondary caries, retention, and postoperative sensitivity. Ordinal data were analyzed using the Kruskal-Wallis test, followed by the Dunn post hoc test for between group comparisons, as well as the Friedman test, followed by the Nemenyi post hoc test for within group comparisons (α=.05). RESULTS: Across all parameters and intervals, most of the restorations within each group exhibited an alfa score, with no statistically significant differences noted (P>.05). However, concerning color match, all restorations within the PEEK groups received a bravo score, indicating a statistically significant difference in intergroup comparison between the milled composite resin groups and the PEEK group (P<.001). However, no significant variances were noted in the scores evaluated across different follow-up periods (P>.05). CONCLUSIONS: Subtractive and additive manufacturing techniques, as well as PEEK and composite resin materials together, offer clinically acceptable functioning restorations over 1 year. PEEK material can be used as a suitable alternative to commonly used indirect composite resin intracoronal restorations in posterior areas. Improvements in terms of surface texture and esthetics are required.

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Background: The aim was to assess the consequence of different printing orientation on the marginal misfit and internal gap of 3-unit interim fixed partial denture manufactured by two different additive manufacturing technologies compared to milling technique. Material and Methods: Three-unit interim fixed partial denture (FPD) was designed by using exocad software (Dental CAD 3.0 Galway) in the format of standard tessellation language (STL) , which was transferred to a nesting software (PreForm) and printed by A Next Dent C&B resin liquid (NextDent; Soesterberg, Neitherland) by using two printing technologies; stereolithography (SLA, n=30) and digital light processing (DLP, n=30) with 3 different orientations (occlusal direction [0°] ,buccal direction [90°] & lingual direction [270°]) for each technology (n=10). Additionally, a control group was milled (CAD/Milling, n=10) from DC PMMA A1 Disc (White peaks dental solutions; Gmbh& co., Germany). A Microcomputed tomography was used to measure the marginal misfit and internal gap for each specimen in 12 different points. The average value of the marginal and internal gaps measurements was calculated, and one-way ANOVA was used for the comparison between groups. Results: SLA printing technology showed a similar result to CAD/Milling with all different printing orientations tested. DLP printing technology showed the highest gap values within all the printing orientations with significant difference (p< 0.001) with the CAD/Milling and SLA. Conclusions: Regarding the trueness of the interim FPDs, SLA was a promising technology for its superior adaptation. Marginal misfit and Internal gap for DLP printing technology limiting the use of that technology as it exceeded the acceptable clinical range. Key words:3D Printing, Microcomputed topography, Marginal Gap, Internal Misfit.

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STATEMENT OF PROBLEM: Strength-gradient zirconia combining 3 zirconia formulations with different flexural strengths has been reported to have outstanding mechanical properties. However, data concerning the effect of different sintering protocols on the fracture strength of 3-unit monolithic gradient zirconia fixed partial dentures (FPDs) are sparse. PURPOSE: The purpose of this in vitro study was to test the effect of different sintering protocols on the fracture strength of 3-unit monolithic gradient zirconia FPDs. MATERIAL AND METHODS: Two custom-made stainless-steel master dies were designed to replicate a mandibular right second premolar and second molar prepared to receive a 3-unit monolithic zirconia FPD. Thirty monolithic zirconia FPDs were milled from gradient zirconia blanks and allocated to 3 groups (n=10) according to the sintering protocols: high-speed sintering, speed sintering, and conventional sintering. The FPDs were cemented onto the corresponding dies with traditional glass ionomer cement. All FPDs were cyclic loaded (600 000 cycles/49 N/1.7 Hz) in a mastication simulator. Fracture load measurements for each FPD were determined by using a universal testing machine. Scanning electron microscopy (SEM) at ×80 magnification was used to examine a fractured FPD from each group. A representative specimen from each group was examined with SEM at ×30 000 magnification to determine the grain size. One-way ANOVA, pair-wise Tukey honestly significant difference (HSD), and Pearson correlation tests were used for statistical analysis of the data (α=.05). RESULTS: The high-speed sintered FPDs recorded the highest statistically significant fracture load mean ±standard deviation value (2526 ±300 N), followed by the speed sintered FPDs (2136 ±127 N), while the lowest statistically significant fracture load mean value was recorded with the conventionally sintered FPDs (1361 ±181 N) (P<.001). In addition, the mean ±standard deviation grain size values were 488 ±272 nm for the high-speed sintered specimen, 578 ±409 nm for the speed sintered specimen, and 832 ±551 nm for the conventionally sintered specimen (P<.001). A significant negative correlation was found between fracture strength and grain size among the 3 groups. CONCLUSIONS: The fracture strength of 3-unit monolithic gradient zirconia FPDs sintered by using a high-speed protocol was significantly higher than that of speed and conventionally sintered FPDs (P<.001). The high-speed sintering protocol reduced the mean grain size of gradient zirconia FPDs compared with that of both speed and conventional sintering protocols.

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STATEMENT OF PROBLEM: Polyetheretherketone (PEEK) has been increasingly used as a framework material in prosthetic dentistry. However, data on the marginal and internal fit of PEEK restorations fabricated by using either the computer-aided design and computer-aided manufacturing (CAD-CAM) or heat-pressing technique are sparse. PURPOSE: The aim of this in vitro study was to assess the marginal and internal fit of milled and pressed PEEK single crowns by using microcomputed tomography (µCT). MATERIAL AND METHODS: A custom-made, single stainless-steel die was designed to replicate a maxillary first premolar prepared for a ceramic crown. PEEK copings (N=30) were fabricated and allocated to 3 groups (n=10) according to the fabrication technique: milled from a prefabricated PEEK blank, heat pressed from PEEK pellets, and heat pressed from PEEK granules. All copings were veneered with a composite resin material. The marginal fit was recorded at 4 predetermined points and the internal fit at 8 predetermined points on each crown by using µCT. Two-way ANOVA, pair-wise Tukey honestly significant difference (HSD), and simple main effect tests were used for statistical analysis of the data (α=.05). RESULTS: Concerning marginal fit, the milled crowns demonstrated the best marginal fit overall (44 ±3 µm), followed by those pressed from pellets (92 ±3 µm), and finally by those pressed from granules (137 ±7 µm) (P<.001). The interaction between the effects of the fabrication technique and the measurement point on the marginal fit was not statistically significant (P=.142). The milled crowns demonstrated the lowest mean gap values overall, followed by those pressed from pellets and those pressed from granules (P<.001). The interaction between the effects of the fabrication technique and the measurement point on the internal fit was statistically significant (P<.001). Except for the distal occlusal gap and mesial occlusal gap, all tested groups showed a statistically significant difference (P<.001). In addition, statistically significant differences were observed among all measurement points in different fabrication techniques (P<.001). CONCLUSIONS: The marginal and internal fit of milled PEEK crowns was significantly better than pressed crowns. However, both CAD-CAM and heat-pressing techniques produced PEEK crowns with a clinically acceptable marginal and internal fit. The mean marginal gap of the PEEK crowns pressed from granules was above the range of clinically acceptable value.

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There have been a number of reports on the occurrence of taper corrosion and/or fretting and some have speculated on a link to the occurrence of adverse local tissue reaction specifically in relation to total hip replacement which have a metal-on-metal bearing. As such a study was carried out to compare the magnitude of material loss at the taper in a series of retrieved femoral heads used in metal-on-polyethylene bearings with that in a series of retrieved heads used in metal-on-metal bearings. A total of 36 metal-on-polyethylene and 21 metal-on-metal femoral components were included in the study all of which were received from a customer complaint database. Furthermore, a total of nine as-manufactured femoral components were included to provide a baseline for characterisation. All taper surfaces were assessed using an established corrosion scoring method and measurements were taken of the female taper surface using a contact profilometry. In the case of metal-on-metal components, the bearing wear was also assessed using coordinate metrology to determine whether or not there was a relationship between bearing and taper material loss in these cases. The study found that in this cohort the median value of metal-on-polyethylene taper loss was 1.25 mm3 with the consequent median value for metal-on-metal taper loss being 1.75 mm3. This study also suggests that manufacturing form can result in an apparent loss of material from the taper surface determined to have a median value of 0.59 mm3. Therefore, it is clear that form variability is a significant confounding factor in the measurement of material loss from the tapers of femoral heads retrieved following revision surgery.

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BACKGROUND: Material loss at the taper junction of metal-on-metal total hip arthroplasties has been implicated in their early failure. The mechanisms of material loss are not fully understood; analysis of the patterns of damage at the taper can help us better understand why material loss occurs at this junction. METHODS: We mapped the patterns of material loss in a series of 155 metal-on-metal total hip arthroplasties received at our center by scanning the taper surface using a roundness-measuring machine. We examined these material loss maps to develop a 5-tier classification system based on visual differences between different patterns. We correlated these patterns to surgical, implant, and patient factors known to be important for head-stem taper damage. RESULTS: We found that 63 implants had "minimal damage" at the taper (material loss <1 mm3), and the remaining 92 implants could be categorized by 4 distinct patterns of taper material loss. We found that (1) head diameter and (2) time to revision were key significant variables separating the groups. CONCLUSION: These material loss maps allow us to suggest different mechanisms that dominate the cause of the material loss in each pattern: (1) corrosion, (2) mechanically assisted corrosion, or (3) intraoperative damage or poor size tolerances leading to toggling of trunnion in taper.

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Detailed visual inspection of metal hips is the first step in retrieval analysis. In this study a systematic visual inspection protocol was developed to quantify bearing surface changes and their associations with material loss was investigated. Simple and multiple linear regression models found that moderate surface scratching, discolouration, haziness and the size of visible wear scars were all significantly associated with material loss (R2 = 5%-73%, p<0.05). Visual inspection is not a substitute for measurement of material loss but an understanding of bearing surface changes may offer unique clues as to the mechanisms of failure of retrieved hips.

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Size mismatch of components used in total hip arthroplasty is a serious, preventable patient safety incident of unknown prevalence as many cases are not detected. Component size mismatch was found in 11 cases (0.9%) at our retrieval centre. All cases of mismatch were not detected on plain radiograph during routine clinical follow up and blood metal ion levels were elevated above the MHRA action level of 7 ppb. Root cause analysis identified manufacturer, hospital and surgeon factors that need to be addressed to reduce the incidence of this avoidable clinical problem. Retrieval analysis is the only method of confirming size mismatch and is likely to be under-represented in National Joint Registries that record the indication for revision at the time of revision.

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It has been speculated that material loss, either as corrosion or wear, at the head-stem taper junction is implicated in the high revision rates reported for metal-on-metal total hip replacements. We measured the volume of material loss from the taper and bearing surfaces of retrieved devices, and investigated the associations with blood metal ion levels and the diagnosis of a cystic or solid pseudotumor. The median volumes of material lost from the female and male taper surfaces were 2.0 and 0.29 mm(3) , respectively, while the median volumes of wear from the cup and head bearing surfaces were 1.94 and 3.44 mm(3) , respectively. Material loss from the female taper was similar to that from the acetabular bearing surface (p = 0.55), but significantly less than that from the femoral bearing surface (p < 0.001). Material loss from the male taper was less than that from both bearing surfaces (p < 0.001). Multivariable analysis demonstrated no significant correlations between the volume of material lost from the taper surfaces and either blood cobalt or chromium ions, or the presence of pseudotumor. While a substantial volume of material is lost at the taper junction, the clinical significance of this debris remains unclear.

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