Fatigue resistance of 3D printed anatomic post-and-core after mastication simulation.

STATEMENT OF PROBLEM: Rigid post-and-core systems have traditionally been used in the restoration of endodontically treated teeth and are regarded by many as the standard treatment. Flexible materials, including nanoceramic resins, are being increasingly implemented as post-and-core systems, but data supporting their use are lacking. PURPOSE: The purpose of this in vitro study was to compare the fatigue resistance of conventional cast metal and nanoceramic 3-dimensionally (3D) printed resin post-and-core systems with teeth without posts. MATERIAL AND METHODS: Thirty freshly extracted human maxillary premolars were endodontically treated and divided into 3 subgroups (n=10) according to the restorative procedure: cast metal post-and-core (CM), nanoceramic 3D printed resin post-and-core (3DR), and without a post (0P). The CM post-and-core group was fabricated conventionally, while the 3DR group was printed using a 3D resin printing material. For the 0P group, the teeth were restored with a composite resin foundation after root canal obturation. Complete coverage 3-mol% monolithic zirconia restorations were cemented on all specimens. The specimens were exposed to simultaneous mastication simulation (1.2 million cycles) and thermocycling (10 000 cycles at 5 ºC to 55 ºC) and analyzed based on the failure of specimens. Data were analyzed using the Kruskal-Wallis survival analysis and the Wilcoxon rank sum test (α=.05). RESULTS: The Kruskal-Wallis test indicated statistically significant differences among the cycles needed to reach failure for each of the 3 groups (P<.001). At 1.2 million cycles, there were no CM failures. The 3DR group failed at a median value of 950 000 cycles, while the 0P group failed at a median value of 222 500 cycles (P<.001). CONCLUSIONS: All the endodontically treated teeth that received CM survived the 1 200 000 simulated mastication cycles. Both 3DR and 0P specimens fractured at the crown cervical third during mastication simulation.

A survey on utilization and barriers of digital removable prostheses in the US dental education.

PURPOSE: Gaining knowledge on the extent of digital technology implementation in dental education and the barriers to it will help inform future directions to promote the use of such technology and will enhance dental education. This study aimed to investigate the utilization of digitally fabricated removable prostheses and the potential obstacles to implementing such technology in US dental schools. METHODS: A survey was developed and distributed to the restorative dentistry department chairs and postdoctoral prosthodontic program directors. The survey delivery protocol included follow-up emails 1 week, 3 weeks, and 4 weeks after the initial email. The collected data were analyzed descriptively. RESULTS: The response rate was 85% and 45% for predoctoral and postdoctoral prosthodontic programs, respectively. The results showed that 88.06% of the predoctoral programs and 95.65% of the postdoctoral prosthodontic programs implement digital complete dentures in the curriculum; however, the digital removable partial dentures implementation rate was recorded at 70.77% in predoctoral programs and 61.9% in postdoctoral prosthodontic programs. CONCLUSIONS: Dental schools are challenged by cost, design software limitations, IT and laboratory support, and faculty training. Multifaceted support is instrumental in further implementing digital removable prosthodontics into dental education.

Evaluation of surface roughness of differently manufactured denture base materials.

STATEMENT OF PROBLEM: The popularity of computer-aided design and computer-aided manufacturing (CAD-CAM) dentures has led to the introduction of new denture materials and resins. However, studies on the surface characteristics of these materials and how they compare to dentures fabricated by more traditional methods are lacking. PURPOSE: The purpose of this cross-sectional study was to determine whether the surface roughness (Ra) of denture base materials differed based on manufacturing technique. MATERIAL AND METHODS: Disks of Ø10×2-mm (n=10) were fabricated using 6 different manufacturing techniques, including compression molding (Lucitone 199), injection molding (Ivocap High Impact), Computer Numerical Control (CNC) milling (Ivotion Base), and additive manufacturing on the Carbon M2 (Lucitone Digital Print), the SprintRay Pro55 S (Dentca Denture Base II), and the Envision One (Flexcera Base) systems. An automatic, noncontact laser confocal microscope (VK-X1000 Series; KEYENCE) was used to analyze the Ra surface roughness of each specimen at ×5 magnification. The images were imported into a multifile analyzer, horizontal and vertical roughness profiles were inserted into each scan, and Ra values were calculated and averaged by following the International Organization for Standardization (ISO) 4287 standard. A 1-way analysis of variance (ANOVA) was performed to compare the effect of manufacturing technique on surface roughness, followed by the Tukey multiple comparisons test (α=.05). RESULTS: The additively manufactured Dentca Denture Base II (AM-DB) exhibited a statistically significantly higher Ra when compared with the other test groups (P<.001). The additively manufactured Flexcera Base (AM-FB) showed a higher Ra mean value when compared with injection molding (IM) (P=.036). No statistically significant difference in surface roughness was found among the other tested materials representing the different processing methods (P>.05). CONCLUSIONS: The manufacturing method influences the Ra of denture base materials with varying results. The injection molding method resulted in the smoothest surface compared with additively manufactured and CNC-milled denture base materials.

Clinician perspectives on implementation of digitally fabricated complete dentures: A national survey of prosthodontists.

STATEMENT OF PROBLEM: Research on implementation factors for digitally fabricated complete dentures is sparse. PURPOSE: The purpose of this survey of prosthodontists was to explore the current usage of conventionally and digitally fabricated complete dentures and to identify factors that may impact their use. MATERIAL AND METHODS: A confidential cross-sectional survey consisting of 20 questions was conducted in 2019 using the Qualtrics Research Suite. The survey was distributed via electronic mail to all 1820 members of the American College of Prosthodontics. Frequency distributions, chi-squared tests, and Fisher exact tests were used to analyze the data and compare subgroups (α=.05). RESULTS: The response rate was 16.8% (N=305). A total of 31.5% of respondents were implementing digitally fabricated complete dentures, 36.6% were interested in learning and/or incorporating them, 37.7% reported that they had not tried them, and 12.7% had tried them but were not interested in using them again. When asked which factors were important when considering the implementation of digitally fabricated complete dentures, 55.8% indicated laboratory costs, 72.1% total chair time spent, and 81.9% patient satisfaction. Prosthodontists who graduated from dental school after about 1991 were more interested in learning about and incorporating digitally fabricated complete dentures than earlier graduates (P=.02). CONCLUSIONS: The survey results indicate that prosthodontists are implementing digitally fabricated complete dentures in clinical practice but not at the rate that might be expected of a technology that has been available for nearly a decade. Factors reported to matter in the decision to implement this technology were decreased time, overall cost, and improved patient satisfaction.

Anatomic CAD-CAM post-and-core systems: A mastication simulation study.

STATEMENT OF PROBLEM: Few studies have investigated the differences among various post-and-core systems under mastication simulation. Comparing these systems while simulating the clinical environment should provide a more accurate assessment of their performance. PURPOSE: The purpose of this in vitro study was to evaluate the fatigue resistance of conventional cast metal and prefabricated fiber post systems with computer-aided design and computer-aided manufacture (CAD-CAM) prefabricated nonmetal post-and-core systems. MATERIAL AND METHODS: Forty freshly extracted human maxillary premolars were endodontically treated and divided into 4 subgroups (n=10) according to the material: cast metal, zirconia, fiber-reinforced composite resin, prefabricated fiber post. The post-and-core materials were manufactured either conventionally or milled with CAD-CAM technology. All specimens were exposed to simultaneous mastication simulation (1.2 million cycles) and thermocycling (10 000 cycles at 5 °C to 55 °C) and analyzed based on failure of specimens. Data were analyzed by using the Kaplan-Meier survival analysis and Cox-regression (α=.05). RESULTS: Both cast metal and zirconia post-and-core groups had similar fatigue resistance (P>.05) but significantly higher fatigue resistance than the fiber-reinforced groups (P<.05). Fiber-reinforced composite resin and prefabricated fiber post did not survive the mastication simulation, fracturing between 504 000 and 752 000 cycles, with fractures occurring in the cervical portion of the tooth. CONCLUSIONS: Cast metal and zirconia post-and-core systems had improved physical properties with high resistance to fatigue when compared with fiber-reinforced post-and-core systems.

Students' perception of digital waxing software for dental anatomy education.

The purpose of this study is to assess students' perception of digital waxing software for dental anatomy education. Dental students were introduced to digital waxing during a dental anatomy course, and were requested to finish a voluntary survey. Students strongly agreed (18.2%) or agreed (48.0%) with the statement "digital waxing contributed to my learning of dental anatomy", and strongly agreed (29.9%) and agreed (55.8%) with the statement "The digital waxing software helped develop my wax-up skills". The digital waxing software may be effective for dental anatomy education, but students do not believe digital waxing can be a replacement for conventional wax-up practice.

A Comparison of Conventionally Versus Digitally Fabricated Denture Outcomes in a University Dental Clinic.

PURPOSE: The purpose of this retrospective, cross-sectional study is to evaluate if there is a difference in number of visits (including fabrication and postoperative) and remake rate when comparing conventionally fabricated and digitally fabricated complete dentures by dental students in a predoctoral student dental clinic. MATERIALS AND METHODS: This two-year retrospective cross-sectional study consisted of a chart review for patients receiving maxillary and/or mandibular complete dentures between 2017 and 2019 (n = 314) at the UNC Adams School of Dentistry predoctoral student clinic. No control group was determined for this study. Data were extracted for 242 conventional dentures and 39 digital dentures. Objective treatment outcomes were obtained for each included denture: the number of patient appointments from preliminary impressions to denture placement, the number of postoperative visits, any complications noted, and any need for remakes. Fisher's Exact Test and Cochran-Mantel-Haenszel analysis were completed with statistical significance set at p < 0.05. RESULTS: For the number of visits from preliminary impression to placement, 50% of conventionally fabricated dentures had 6 or more visits, while only 5% of digitally fabricated dentures had 6 or more visits. This difference for the number of patient visits was statistically significant (p < 0.05). Additionally, conventionally fabricated dentures required an average of 2-3 postoperative visits, whereas digitally fabricated dentures required 1-2 postoperative visits. This difference was also statistically significant (p < 0.05). For the number of dentures requiring remake, there was no statistical difference (p = 0.1904). CONCLUSIONS: When comparing conventionally fabricated and digitally fabricated dentures in the predoctoral clinic, the digitally fabricated dentures required fewer patient appointments from start to finish, and fewer postoperative appointments than conventionally fabricated dentures. Fewer visits may be an important consideration for patients, especially those with limited access to care.

Laboratory Trends for Removable Prosthodontics: A Comparison of Two Surveys.

PURPOSE:  The purpose of this survey was to assess dental laboratory technicians' perceptions of the quality of communication and techniques used when receiving removable prosthodontic cases. Additionally, responses were compared to a 2009 survey and changes in trends were evaluated. MATERIALS AND METHODS:    An eleven-question anonymous response survey was developed based on a 2009 survey that assessed dental laboratory technicians' perceptions.  The survey was distributed via Qualtrics to members of the National Association of Dental Laboratories (NADL) The survey included questions related to detail of instruction, quality of work received, design of the prosthesis, and type of articulator used.  Responses were compared to those received in 2009. RESULTS:  Fifty-two survey responses were received from dental laboratory technicians. Of these, 12 did not provide removable prosthodontics services and were excluded. The remaining 40 responses were analyzed. Of these, only 3.7% of the responding laboratory technicians reported receiving work authorizations from dentists that were complete enough to do their best work. While roughly half of the respondents (48.49%) expected a dentist to send a design for a cast partial denture framework, most respondents (72.5%) answered that they designed the majority of the partial denture frameworks they fabricated. The majority of respondents reported that complete denture impressions were not border molded in custom trays, and that most dentists did not rearrange or modify a wax setup for complete or partial dentures. These findings were consistent with the trends reported in the 2009 survey. CONCLUSIONS:  Most dental laboratory technicians answered that based on their selected techniques, dentists tend to complete clinical procedures that minimize patient chair time. While the surveyed technicians appeared satisfied with the quality of work they received, there was a consistent message that communication was frequently inadequate, limiting the technicians ability to fabricate their best work.

Time-lasting ceramic stains and glaze: A toothbrush simulation study.

OBJECTIVE: To evaluate and compare color stability and gloss retention of ceramic stains and glaze under simulated toothbrushing using dentifrices with different relative dentin abrasion (RDA). MATERIALS AND METHODS: Feldspathic porcelain, lithium disilicate, 3 mol% yttria partially stabilized zirconia, and 5 mol% yttria partially stabilized zirconia were evaluated. Ceramics were externally stained, glazed and mounted in the toothbrush simulator. A toothbrush with 300 g force was applied. Regular toothpaste (72 RDA) and charcoal toothpaste (RDA <200) were used. Linear brushing motion with cycle intervals: 5 k, 10 k, 30 k, and 50 k was achieved. Change in color (CIEΔE2000) and gloss measurements were collected using a reflection spectrophotometer (Ci 7600, X-rite) at baseline and cycle intervals. Repeated measures analysis of variance within specimen factors (ceramic type, toothpaste and cycles) was performed. RESULTS: ΔE00 was significantly different at 50 k cycles and with zirconia ceramics (P < .0001). Charcoal toothpaste was significantly different in ΔE00 compared to regular toothpaste (P > .0001). Loss of gloss was observed at 5 k and 30 k (charcoal and regular toothpaste respectively) regardless type of ceramic (P > .0001). CONCLUSION: Glass-phase ceramics retain stains longer than zirconia ceramics. Charcoal toothpaste affect color and gloss stability. Ceramic glaze maybe lost within the first 6 months in patients' mouth. CLINICAL SIGNIFICANCE: Long-term color and gloss stability of externally stained and glazed ceramics maybe a clinical concern. Charcoal toothpastes enhance loss of color and gloss of ceramic restorations.

A Novel, Minimally Invasive Approach to Replacing Missing Teeth: Two Case Reports.

For the replacement of missing teeth, resin-bonded fixed partial dentures (RBFPDs) are a routine, minimally invasive option clinicians can use on patients who either cannot or will not move forward with surgical interventions. Advances in materials and design have greatly improved the longevity and prognoses for these prostheses. In some patients, however, debonding remains a clinical problem. In this clinical report, novel RBFPD designs are presented with the aim of improving retention and esthetics while offering short treatment time and minimal preparation without the need for local anesthesia.

The digitally replicated denture technique: A case report.

OBJECTIVE: Conventional complete denture protocols require several patient appointments with multiple laboratory procedures. There are multiple workflows incorporating digital technology that can expedite the process, whereas increasing predictability. The proposed digitally replicated denture technique (DRDT) demonstrates a predictable workflow for fabricating complete dentures for patients with existing dentures. CLINICAL PROCEDURE: A patient's existing maxillary and mandibular complete dentures were scanned with an intraoral scanner. The generated STL was then printed using a desktop 3D printer. This served as a custom tray and record base to decrease patient chair time and associated laboratory procedures. CONCLUSION: The DRDT workflow incorporates digital technology into a complete denture protocol to minimize laboratory steps and chair time when fabricating complete dentures for patients with existing prostheses. CLINICAL SIGNIFICANCE: The use of a digitally replicated denture using rapid prototyping can streamline the process of complete denture fabrication for patients with existing dentures.

The "Scalloped Guide": A Proof-of-Concept Technique for a Digitally Streamlined, Pink-Free Full-Arch Implant Protocol.

Inadequate restorative space can result in mechanical, biologic, and esthetic complications with full-arch fixed implant-supported prosthetics. As such, clinicians often reduce bone to create clearance. The aim of this paper was to present a protocol using stacking computer-aided design/computer-assisted manufacturing (CAD/CAM) guides to minimize and accurately obtain the desired bone reduction, immediately place prosthetically guided implants, and load a provisional that replicates predetermined tissue contour. This protocol can help clinicians minimize bone reduction and place the implants in an ideal position that allows them to emerge from the soft tissue interface with a natural, pink-free zirconia fixed dental prostheses.

The clinical management of awake bruxism.

BACKGROUND: Awake bruxism is a common clinical condition that often goes undetected, often leading to pain or damaged teeth and restorations. METHODS: The authors searched electronic databases regarding the treatment and effects of awake bruxism compared with those of sleep bruxism. The authors used the search terms diurnal bruxism and oral parafunction. The authors combined information from relevant literature with clinical experience to establish a recommended protocol for diagnosis and treatment. RESULTS: The authors found articles regarding the diagnosis and treatment of bruxism. The authors combined information from the articles with a review of clinical cases to establish a treatment protocol for awake bruxism. CONCLUSIONS: Literature and clinical experience indicate a lack of patient awareness and, thus, underreporting of awake bruxism. As a result, myriad dental consequences can occur from bruxism. The authors propose a need for increased awareness, for both patients and professionals, particularly of the number of conditions related to awake bruxism. PRACTICAL IMPLICATIONS: Clinicians should look for clinical signs and symptoms of awake bruxism and use minimally invasive treatment modalities.

The effect of autopolymerizing acrylic resin thickness on the bond strength of a repaired denture tooth.

PURPOSE: This study analyzed the conventional method of rebonding a denture tooth, evaluating the effect of varied thickness of autopolymerizing acrylic resin on the bond strength and the failure mode. MATERIALS AND METHODS: A total of 52 heat-polymerizing acrylic resin specimens were fabricated with an anterior denture tooth. A cantilever-type bending force was applied with a universal testing machine to each specimen until failure. The failure mode was determined, and cohesive failures were excluded from part II. Thirty specimens were randomly selected and divided into three groups (n = 10). For each group, resin was relieved from the bonding area to create a 0, 1, or 3 mm space. The tooth was repositioned using its matrix and reattached to its base, filling the relieved space with autopolymerizing acrylic resin. The repaired specimens were tested using the same parameters. Data were analyzed with paired t-tests, one-way ANOVA, and post hoc test. Statistical significance was determined at p < 0.05. RESULTS: The mean peak load to failure for the part I group was 88.91 N. While the peak load to failure decreased to 71.96 N (19.69% loss of original bond strength), statistical analysis revealed no difference between the bond strength of the specimens repaired with a 0 mm thickness of autopolymerizing acrylic resin and the original (part I) group (p > 0.05). The bond strength was lower for the group repaired with a 1 mm thickness compared to the original (part I) group (p < 0.05), with 65.8 N load to failure (29.63% loss). The bond strength was even lower for the group repaired with a 3 mm thickness (p < 0.05), with 58.64 N load to failure (33.07% loss). Post hoc analysis revealed a significant difference between the 0 and 3 mm groups (p = 0.04). The most common failure mode in the original group was adhesive (56%), then combination (34%), then cohesive (9.8%). The repaired group (n = 30) had similar results, with 56.7% adhesive, 36.7% combination, and 6.7% cohesive failures. CONCLUSIONS: The bond strength of a replaced denture tooth is affected by the thickness of the autopolymerizing acrylic resin. The failure mode of a rebonded denture tooth follows the same trend of the original failure. If possible, replace teeth with no relief. If combination failure occurs, leave residual base acrylic resin on the ridge lap.

Ambulatory surveillance of patients referred for cardiac rehabilitation following cardiac hospitalization: a feasibility study.

BACKGROUND: Our purpose was to examine the feasibility of implementing an ambulatory surveillance system for monitoring patients referred to cardiac rehabilitation following cardiac hospitalizations. METHODS: This study consists of 1208 consecutive referrals to cardiac rehabilitation between October 2007 and April 2008. Patient attendance at cardiac rehabilitation, waiting times for cardiac rehabilitation, and adverse events while waiting for cardiac rehabilitation were tracked by telephone surveillance by a nurse. RESULTS: Among the 1208 consecutive patients referred, only 44.7% attended cardiac rehabilitation; 36.4% of referred patients were known not to have attended any cardiac rehabilitation, while an additional 18.9% of referred patients were lost to follow-up. Among the 456 referred patients who attended the cardiac rehabilitation program, 19 (4.2%) experienced an adverse event while in the queue (13 of which were for cardiovascular hospitalizations with no deaths), with mean waiting times of 20 days and 24 days among those without and with adverse events, respectively. Among the 440 referred patients who were known not to have attended any cardiac rehabilitation program, 114 (25.9%) had adverse clinical events while in the queue; 46 of these events required cardiac hospitalization and 8 patients died. CONCLUSIONS: Ambulatory surveillance for cardiac rehabilitation referrals is feasible. The high adverse event rates in the queue, particularly among patients who are referred but who do not attend cardiac rehabilitation programs, underscores the importance of ambulatory referral surveillance systems for cardiac rehabilitation following cardiac hospitalizations.

Time to take stand on non-meat eating.

I agree with the points raised by Lynn Sawyer (Letters, May 10) regarding meat eating, BSE and the adoption of a vegan diet. How refreshing to see the issue raised positively.