Effects of screw channel angulation on the fracture resistance of one-piece zirconia crown with titanium base.

PURPOSE: The design of the angulated screw channel in implant restorations allows the possibility to correct angulation discrepancies, especially in the anterior maxilla. However, the effects of varied screw channel angulations on fracture resistances and fracture patterns of the implant restorations are still uncertain, and thus the aim of this study. MATERIALS AND METHODS: Angulated screw channel monolithic zirconia crowns (Nobel Biocare) with three different angulation groups-straight (ASC1), 15° (ASC15), and 25° (ASC25)-were digitally designed from a left central incisor prototype scan. Following fabrication, 10 samples of each group were individually mounted onto implant replicas embedded in standardized type V stone gypsum cylinder jigs (25 mm × 25 mm). All screws were manually torqued to 35 Ncm according to the manufacturer's recommendation, and screw access openings were subsequently sealed with resin composite. To mimic the off-axis loading of the central incisor, the specimens were then loaded at a cephalometric interincisal relationship of 135° between the long axis of the crown and the Instron force applicator, with crosshead speed set at 0.5 mm/min. Fractured abutment surfaces were examined, and selected specimens were further evaluated by scanning electron microscopy. Screw torque values were also measured after the catastrophic loading. One-way ANOVA was used to compare load-to-fracture values between groups, with the statistical significance set at 0.05 (p values). RESULTS: The mean load-to-fracture values in descending order were 331.24N (±34.00N) in ASC15, 325.22N (±35.50N) in ASC25, and 302.04N (±45.10N) in ASC1, with no statistically significant differences between groups. Considerable screw torque losses were found in all groups after catastrophically loading. The average torque loss was 84% in ASC1, 86% in ASC15, and 94% in ASC25. 16 out of 30 specimens experienced screw loosening; one ASC1 screw underwent slight deformation. Crowns of all tested groups exhibited cohesive fracture patterns at the screw-metallic-zirconia interfaces. CONCLUSIONS: Within the limitations of this in vitro study, one-piece monolithic zirconia implant crowns with varied screw channel angulations shared similar fracture-strength and fracture-mode characteristics. The zirconia-titanium base junctions exhibited the weakest link of all restorations.

Complete mouth rehabilitation with fixed implant-supported restoration for a patient with myasthenia gravis: A clinical report.

This clinical report describes a complete mouth fixed implant-supported rehabilitation for a patient with myasthenia gravis. Patients with myasthenia gravis may have impaired manual dexterity from progressive neuromuscular impairment. Muscle weakness and fatigue, reduced denture stability, and the inability to provide maxillary dentures with a peripheral seal have compromised the ability to wear dentures. Therefore, care is needed when providing an implant-supported prosthesis. This clinical report provides step-by-step management of a patient with myasthenia gravis, providing a complete arch implant-supported rehabilitation.

Introducing dental students to complete denture treatment in times of COVID-19: Students' responses.

OBJECTIVES: The COVID-19 pandemic required changes in the complete denture courses to comply with lock-in and social distancing requirements. The objectives were to assess (a) dental students' interest in a required complete denture course and the prosthodontics specialty, (b) how much time students spent on studying background, lab, and clinical content, and (c) how difficult and helpful course components were. Additionally, open-ended responses concerning what the students liked and what they wanted to have changed were analyzed as well. METHODS: After this "complete denture" course, 81 of 109 students responded to a web-based survey with questions about course content and design. This hybrid course consisted of weekly asynchronous virtual lectures, in-person simulated laboratory (sim lab) exercises, and synchronous virtual workshops. RESULTS: Exactly 53.7% were much/very much interested in this course, with nobody considering prosthodontics as their specialty. The students studied on average of 79.61 minutes for 1 hour (of background-related lecture, 69.92 minutes for a lab-based lecture, and 77.00 minutes for a clinical-content lecture (p < 0.001). They evaluated clinical content as most difficult, lab content as less difficult, and background material as least difficult (3-point scale with 1 = not at all difficult: means = 1.90/1.85/1.80; p < 0.001). They rated background lectures as least helpful, clinical material as more helpful, and lab content as most helpful (5-point scale with 1 = most helpful: means = 2.33/2.67/2.96; p < 0.001). Open-ended answers showed exceptionally positive responses for content and pedagogy of sim lab and clinical content. CONCLUSIONS: Gaining a better understanding of students' responses to hybrid "complete denture" courses is critical for optimally teaching this material in times of COVID-19.

A three-dimensionally printed template for locating the screw channel in a cement-retained implant-supported crown: A digital workflow.

Locating the screw channel in a cement-retained implant-supported crown is challenging. This article describes a fully digital workflow for fabricating a 3D-printed template which can accurately guide the dentist to find the screw channel. A definitive implant cast from the patient and an implant planning software program are used in the workflow. This technique provides precise guidance for finding the location and angulation of the abutment screw access hole.

A maxillomandibular record for a removable partial denture by using polyvinyl siloxane and the metal framework: A dental technique.

The accuracy of the maxillomandibular record influences the relationship of the definitive cast and therefore the success of a prosthesis. This article describes a technique in which polyvinyl siloxane is used to both stabilize a removable partial denture on the edentulous ridge and being the recording material itself. The technique is practical and time efficient, allowing the clinician to perform this step in a single appointment.

Influence of Screw Channel Angulation on the Fracture Resistance of Zirconia Abutments: An In Vitro Study.

PURPOSE: The aim of this study was to investigate the effect of implant screw channel angulation on the fracture resistance of zirconia abutments without artificial aging. MATERIALS AND METHODS: Ten implant replicas were embedded in a jig of autopolymerizing acrylic resin. Using a surveyor and a metallic platform, the implant replicas were mounted centrally and with an angulation of 30°. A maxillary left central incisor crown was fabricated from pattern resin and scanned. The digital design of a monolithic zirconia implant abutment-crown was completed using a 3D imaging software. For all specimens of this group (ASC25 ), the screw channel was positioned at 25° to the lingual. Following fabrication, the samples were attached onto the embedded implant replicas and manually torqued to 35 Ncm as recommended by the manufacturer. The monolithic zirconia implant abutment-crowns were mounted in a metallic platform, positioned perpendicular to the indenter, and subjected to loading until failure. Crosshead speed was set at 0.5 mm/min for the universal testing machine. Data from a similar in vitro study where straight zirconia custom abutments (ASC0 ) were subjected to static load until failure was used as a control group. An unpaired Student's t-test was used to determine if fracture resistance based on load at failure and maximum load in each group were significantly different from each other (ASC25 vs ASC0 ). Statistical significance level was inferred at p ≤ 0.05 RESULTS: Group ASC25 fractured at a mean (SD) load of 215.49 (47.10) N and a mean (SD) maximum load of 420.50 (17.18) N. Group ASC0 fractured at a mean (SD) load of 534.04 (133.77) N and a mean (SD) maximum load of 762.69 (109.59) N. The difference was statistically significant for both mean load and mean maximum load at failure (p ≤ 0.05). The survival rate of 0° zirconia abutments was significantly higher than that of 25° ASC zirconia abutments. CONCLUSIONS: Within the limitations of this in vitro study the mean fracture load was significantly higher in the group with a straight channel angulation.

Bone Loss in the Posterior Edentulous Mandible with Implant-Supported Overdentures vs Complete Dentures: A Systematic Review and Meta-Analysis.

PURPOSE: To analyze the current evidence on bone loss in the posterior edentulous mandible restored with complete dentures (CDs), two-implant-supported overdentures (2-IODs), or four-implant-supported overdentures (4-IODs). MATERIALS AND METHODS: A search was conducted in the Ovid MEDLINE, Embase, Web of Science, CINAHL, and Cochrane databases for clinical studies comparing bone loss in posterior edentulous mandibles restored with CDs, 2-IODs, or 4-IODs. A meta-analysis was performed using statistical software to estimate the mean differences in bone loss with 95% CI. The level of significance was set at P < .05. RESULTS: The search strategy identified 2,806 articles, of which 14 met the inclusion criteria. The meta-analysis included 7 two-arm studies comparing CDs vs 2-IODs or 2-IODs vs 4-IODs. No statistically significant difference was found in bone loss between 2-IODs and CDs (mean difference -0.25 [95% CI -0.85 to 0.36]; P = .43), whereas bone loss was significantly lower with 4-IODs than with 2-IODs (mean difference -0.96 [95% CI -1.86 to -0.06]; P = .04). Overall, the data were highly heterogenous (I2 > 74%). CONCLUSION: 4-IODs can benefit the patient by decreasing bone loss in the posterior edentulous mandible. However, 2-IODs may not be superior to CDs in reducing bone loss in the posterior mandible. A validation of these results is needed through well-designed RCTs.

Hanau Quint Described as a Formula to Quantify Balanced Occlusion.

Balanced occlusion is obtained through the interrelationship of the Hanau quint, which includes condylar guidance (CG), incisal guidance (IG), orientation of occlusal plane (OP), compensating curve (CC), and cuspal incline (CI). Once CG and IG are determined, the other three factors of OP, CC, and CI function among each other to balance the occlusion. This article describes a formula that is introduced to quantify a balanced occlusion within the context of the Hanau quint and discusses the limitations of the formula due to individual variabilities of mandibular movements.

Implant Angulation Effect on the Fracture Resistance of Monolithic Zirconia Custom Abutments: An In Vitro Study.

PURPOSE: To investigate the fracture resistance and performance of zirconia when employed for the fabrication of implant abutments with different angulations, simulating anterior maxillary oral rehabilitation. MATERIALS AND METHODS: Forty-five monolithic zirconia custom abutments of internal conical implant connection were CAD/CAM designed and fabricated. The specimens were divided into three groups (n = 15/group) according to implant-to-abutment angulation. The angulations used were; 0°, 15°, and 25°. The abutments were loaded until failure at 135° using the Universal Testing Machine (Instron, Canton, MA). Collected data were statistically analyzed using one-way ANOVA and post hoc Tukey test. RESULTS: Mean (±standard deviation) load at fracture of the zirconia abutments for the three groups were 962.37 ± 93.81 N (Gr15) > 718.25 ± 93.71 N (Gr25) > 534.05 ±133.77 N (Gr0). Statistically significant difference (p < 0.0001) was found between all groups; Gr0 vs. Gr15, Gr0 vs. Gr25, Gr15 vs. Gr25. CONCLUSIONS: Contrary to expectations, the non-angulated monolithic zirconia abutments presented the lowest fracture resistance values. Angulating the abutments 15 or 25 degrees, following the palatal resorption pattern of the premaxilla, significantly increased the in vitro fracture resistance.

Effect of Faculty Development Activities on Dental Hygiene Faculty Perceptions of and Teaching About Motivational Interviewing: A Pilot Study.

The aims of this pilot study were to assess dental hygiene faculty members' perceptions of the importance of motivational interviewing (MI) and their confidence in teaching students about MI and to determine the effect of MI training sessions on those perceptions. Participants were a convenience sample of all 16 dental hygiene faculty members who teach in the clinic at the University of Michigan School of Dentistry. Participants' perceptions were assessed prior to a workshop in MI (pretest), immediately after the workshop (posttest 1), and eight months after the workshop, at the end of the academic year (posttest 2). During the same period, some of the workshop participants took part in team grading sessions of audio recordings of student-patient MI interactions. The results showed that the majority of the faculty members perceived it was important to personally embrace the overall spirit of MI during patient care, and they were confident supporting students as well. Their ratings for embracing the spirit of MI increased from pretest to posttest 1, but slightly decreased at posttest 2. This trend was also seen in their assessment of the importance of and their confidence in teaching the eight MI strategies over time. Among the workshop participants, 56% were part of team grading; they reported the most helpful professional development activities overall were team grading (58%) and the workshop (25%). These results suggest the importance of making use of a variety of faculty development activities and of introducing appropriate follow-up to training sessions over time to ensure long-lasting effects. Future research using carefully designed, multi-institution, longitudinal studies is needed to determine the most effective ways to prepare dental hygiene faculty members to educate their students about MI.

Fabrication of a screw-retained restoration avoiding the facial access hole: a clinical report.

Dental implant restorations may be either screw-retained or cemented onto an abutment. While each method has its advantages and disadvantages, cemented restorations are commonly used in the maxillary arch, usually because of esthetic concerns. Available bone in the anterior maxilla dictates the placement of the implant, which may result in a facially positioned screw-access opening. Still, a growing volume of literature states that periimplant soft tissues respond more favorably to screw-retained crowns than cement-retained crowns. This clinical report outlines a treatment with a new method of fabricating a custom abutment-crown combination for a screw-retained restoration. The technique allows the channel for the screw to be placed at an angle other than parallel to the implant body. In this case, the practitioner may choose either a screw-retained or cement-retained implant restoration, where previously only a cemented restoration was possible.

The commissure line of the mouth for orienting the occlusal plane.

This study investigated the positional relation of the commissure line of the mouth to the maxillary first molars. Thirty-five volunteers, 20 to 40 years old, with normal natural dentitions were recruited. Maxillary casts with marks locating the commissure were digitally scanned to measure the vertical distance from the tip to the base of the mesiofacial cusp (CO) and from the tip to the mark (CM). There was no significant difference (t test; P > .05) between the CO (1.61 ± 0.41 mm) and CM (1.14 ± 0.68 mm). The mean distance of the commissure mark from the occlusal plane was 0.78 mm.

SPECT/CT characterization of oral activity on radioiodine scintigraphy.

CONTEXT: Oral activity on radioiodine scintigraphy is commonly seen and may cause diagnostic dilemma. Determining the precise mechanism of oral uptake on radioiodine scintigraphy will increase the accuracy and confidence of interpretation and avoid possible misinterpretation. OBJECTIVE: To determine the etiology of focal persistent radioiodine oral uptake seen on radioiodine scans. DESIGN: Retrospective sequential series at a university clinic and a phantom study experiment. METHODS: Preablation iodine-131 planar and single photon emission computed tomography/computed tomography (SPECT/CT) scans of 216 patients after total thyroidectomy were reviewed. Planar images were inspected for the presence of oral activity above the salivary gland background and SPECT/CT was reviewed to determine the location and nature of oral activity. A post-hoc phantom study was designed using typodont stone models fitted with various dental materials, immersed in a diluted iodine-131 solution, and imaged with SPECT/CT to characterize radioiodine uptake by high-attenuation dental materials. RESULTS: Oral activity was seen on planar images in 123 of 216 (57%) patients; 12 patients were excluded from analysis because the SPECT/CT field of view did not cover the entire oral cavity. In the remainding 111 patients SPECT/CT images demonstrated focal uptake localizing to high-attenuation dental material on the CT in 95 of 111 (86%) patients. All cases of oral activity on planar imaging were interpreted as benign etiology on SPECT/CT. The phantom study confirmed focal in vitro uptake within high-attenuation dental materials representing a range of commonly used metal alloys. CONCLUSION: Focal oral activity on diagnostic radioiodine scans frequently localizes to high-attenuation dental material on SPECT/CT. We postulate that an affinity between negatively charged iodide ions (I(-)) in saliva and positively charged metal ions (eg, Ag(+), Hg(+), Au(2+), Pd(2+)) within the dental materials is at the basis of persistent focal radioiodine uptake in the oral cavity. This represents a new mechanism underlying benign radioiodine activity not previously described in the medical literature.

Modified record base featuring postpalatal seal using silicone bite registration material.

This article describes a simple method of fabricating a stable and retentive record base to ensure an accurate registration of the maxillomandibular relationship. A postpalatal seal is established along the posterior end of the record base on the definitive cast using a silicone bite registration material to create a border seal along with the lip/cheek draping actions and to evaluate adequacy of the post dam.

Maxillary implant-supported bar overdenture and mandibular implant-retained fixed denture using CAD/CAM technology and 3-D design software: a clinical report.

The implant-supported bar overdenture and the implant-retained fixed complete denture are appropriate treatment choices for patients with inadequate bone volume in the posterior maxilla and mandible, respectively. Computer-aided design/computer-aided manufacturing (CAD/CAM) technology has broadened the scope and application of those treatment options, allowing for prosthodontically-driven implant placement and ideal substructure design for optimal esthetics and biomechanics. This report describes the fabrication of a maxillary implant-supported milled titanium bar with attachments and an overdenture, and a mandibular implant-retained fixed complete denture with milled titanium substructure.

Acrylic strengthened casts for removable partial denture for occlusion equilibration.

A removable partial denture (RPD) remount cast must resist wear or breakage, present a rigid surface, and ensure a solid support for an accurate equilibration of the occlusion for a RPD. This article describes a procedure of processing a thin layer of tooth colored acrylic resin over the dental plaster to present wear- and fracture-resistant incisal/occlusal surfaces without involving a third material.

Tooth reduction guide using silicone registration material along with vacuum-formed thermoplastic matrix.

Adequate tooth reduction is a prerequisite for function, esthetics, and longevity of fixed restorations. A tooth reduction guide may be useful for establishing the proper angulation of the tooth and maximizing periodontal health and restorative success. This article describes a simple and versatile technique for an accurate evaluation of tooth reduction for fixed restorations by using a color-contrasting positive guide of a silicone occlusal registration material processed inside a vacuum-formed clear thermoplastic matrix.

Provisional prosthetic management of mobile teeth in conjunction with a removable partial denture using orthodontic wire.

Precision attachment-retained removable partial dentures eliminate the use of visible clasps and improve the esthetic appearance of the smile; however, terminal abutment teeth may be subject to unfavorable stresses under function when misused. A provisional prosthetic management technique that incorporates an orthodontic wire to assist cross-arch support and stability of the periodontally weakened abutment teeth is described. This technique is simple, reversible, does not alter the esthetic appearance of the smile, and controls the mobility of the abutment teeth until a definitive treatment plan is established.