Fracture Resistance of Pressed and Milled Lithium Disilicate Anterior Complete Coverage Restorations Following Endodontic Access Preparation.

PURPOSE: This in vitro study evaluated the fracture resistance and clinical prognosis of anterior lithium disilicate crowns (e.max Press and e.max CAD), following endodontic access and repair. The research design simulates intraoral loading conditions to produce clinically applicable results. MATERIALS AND METHODS: Monolithic anterior crowns, based on #8 anatomy, were fabricated from e.max Press ingots and e.max CAD blocks and adhesively bonded on identical dies milled out of a dentin analog material (NEMA G10). Specimens were divided into 4 groups: intact pressed, repaired pressed, intact milled, and repaired milled (n = 15/group). Repaired pressed and repaired milled were prepared with a standardized endodontic access and repaired using a porcelain repair system and composite resin. All crowns were cyclically loaded under simulated oral conditions and then loaded to failure in water, using a universal testing machine. Data were interpreted using ANOVA/Tukey post-hoc test (α = 0.05). RESULTS: Mean loads to failure ranged from 758.9 to 931.4 N for the 4 groups, indicating that both fabrication techniques, pressed and milled, yielded restorations that could reasonably withstand maximum masticatory forces. The pressed groups (923.7 N) exhibited significantly higher fracture resistance than the milled groups (797.5 N), p = 0.0002. When milled and pressed groups were categorized into intact and repaired subgroups, no difference was found in fracture resistance between the subgroups. Differences were noted in the modes of fracture, where the milled groups (intact and repaired) exhibited higher frequency of catastrophic fractures than the pressed groups. CONCLUSIONS: Endodontic access preparation does not appear to affect fracture resistance of an anterior lithium disilicate restoration, suggesting that replacement may not be necessary. Fabrication technique had a significant effect on fracture resistance and fracture mode of lithium disilicate restorations. The pressed fabrication technique resulted in significantly greater crown strength and fracture resistance than the milled technique.

Critical Thinking in Dental Students and Experienced Practitioners Assessed by the Health Sciences Reasoning Test.

To date, there has been a lack of published studies examining the validity of the Health Sciences Reasoning Test (HSRT) to assess critical thinking among dental students. The aim of this study was to examine the construct validity of the HSRT using a novice-expert model consisting of first-year dental students as novices and experienced general dentists as experts. Novice cohort subjects were recruited from all 105 students in the first-year dental school class at the University of Texas Health Science Center at San Antonio during a regularly scheduled course in August 2015. A total of 83 students participated, for a 79% response rate. Thirty individuals personally recruited from the same school's faculty and from private practitioners made up the expert cohort. The results showed that the adjusted mean overall score for the expert cohort (25.31) was significantly higher than that of the novice cohort (22.64) (p=0.04). The expert cohort achieved higher adjusted mean scores in all scales (Induction, Deduction, Analysis, Inference, and Evaluation), with the difference in the Analysis scale being significant (p=0.02). In this study, experienced general dentists achieved significantly better overall scores on the HSRT as compared to first-year dental students, suggesting the instrument was able to measure differences between novice and expert. Further efforts to validate the instrument in a dental education setting and to understand its correlation with strategies and practices aimed at developing critical thinking in dental students are warranted.

Marginal discrepancy of noble metal-ceramic fixed dental prosthesis frameworks fabricated by conventional and digital technologies.

STATEMENT OF PROBLEM: Studies evaluating the marginal adaptation of available computer-aided design and computer-aided manufacturing (CAD-CAM) noble alloys for metal-ceramic prostheses are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the vertical marginal adaptation of cast, milled, and direct metal laser sintered (DMLS) noble metal-ceramic 3-unit fixed partial denture (FDP) frameworks before and after fit adjustments. MATERIAL AND METHODS: Two typodont teeth were prepared for metal-ceramic FDP abutments. An acrylic resin pattern of the prepared teeth was fabricated and cast in nickel-chromium (Ni-Cr) alloy. Each specimen group (cast, milled, DMLS) was composed of 12 casts made from 12 impressions (n=12). A single design for the FDP substructure was created on a laboratory scanner and used for designing the specimens in the 3 groups. Each specimen was fitted to its corresponding cast by using up to 5 adjustment cycles, and marginal discrepancies were measured on the master Ni-Cr model before and after laboratory fit adjustments. RESULTS: The milled and DMLS groups had smaller marginal discrepancy measurements than those of the cast group (P<.001). Significant differences were found in the number of adjustments among the groups, with the milled group requiring the minimum number of adjustments, followed by the DMLS and cast groups (F=30.643, P<.001). CONCLUSIONS: Metal-ceramic noble alloy frameworks fabricated by using a CAD-CAM workflow had significantly smaller marginal discrepancies compared with those with a traditional cast workflow, with the milled group demonstrating the best marginal fit among the 3 test groups. Manual refining significantly enhanced the marginal fit of all groups. All 3 groups demonstrated marginal discrepancies within the range of clinical acceptability.

Effect of Split-File Digital Workflow on Crown Margin Adaptation.

PURPOSE: Computer-aided design/computer-aided manufacturing (CAD/CAM) is becoming increasingly integrated into dental practice workflow at a pace that exceeds scientific validation. The aim of this study is to evaluate a complete digital split-file protocol relative to segmental digital and analog techniques for restoring a single maxillary anterior edentulous space with custom abutment and crown. MATERIALS AND METHODS: Four treatment workflows were assessed: complete digital (CD), segmental digital (SD), milled wax (AM), and heat pressed and hand waxed (AH) and heat pressed. The CD workflow "split" an abutment and crown into separate files to fabricate a zirconia abutment and both zirconia/lithium disilicate crown restorations. The SD workflow scanned the existing abutment for design of segmental restorations in zirconia, lithium disilicate, and milled wax (AM). The AH specimens were conventionally hand waxed. Both the AM and AH specimens were heat pressed with lithium disilicate. All restorations were evaluated with standardized measurements using scanning electron microscopy (SEM) as manufactured without internal adjustments and after manual adjustment. The number of adjustments, adjustment time, and location of adjustments were recorded. One-way ANOVA with repeated measures was used to report geometric means with 95% confidence intervals. RESULTS: The mean marginal gap after adjustment of the CD group was 69 µm, with an upper bound (UB) of 79 µm and a lower bound (LB) of 60 µm. SD group mean was 26 µm with an UB of 31 µm and LB of 22 µm. The AM group mean was 32 µm, with an UB of 49 µm and a LB of 20 µm; AH group mean of 26 µm with an UB of 34 µm and a LB of 20 µm. The SD, AM, and AH workflows were statistically similar (p = 1.000), and the CD workflow was statistically greater than the other three (p < 0.001). CONCLUSIONS: The split-file (CD) protocol results in marginal gap size within clinical standards after adjustment; however, 52 of the 60 digitally produced restorations showed a horizontal marginal offset that required adjustment for proper contours.

Marginal Gap of Milled versus Cast Gold Restorations.

PURPOSE: This in vitro study evaluated and compared the vertical marginal gap of cast and milled full coverage gold copings using two margin designs (chamfer and chamfer bevel) before and after fitting adjustments. MATERIALS AND METHODS: Ten impressions were made of two metal master dies (one chamfer margin, one chamfer-bevel margin) and poured twice in Type IV stone. The 20 subsequent casts with 40 dies were split into four groups (n = 10); cast gold bevel, cast gold chamfer, milled gold bevel, and milled gold chamfer groups. The cast specimens received approximately 40 µm die relief no closer than 1 mm from the finish line. Cast copings were hand waxed, cast in a high noble gold alloy, chemically divested, and the sprues were removed. For milled gold copings, casts were scanned and copings designed using 3shape D900 scanner and software. Parameters were set to approximate analog fabrication (cement gap = 0.01 mm; extra cement gap = 0.04 mm, drill radius = 0.65 mm). Copings were milled from the same high noble alloy. All copings were seated on their respective master die in a custom scanning jig and measured using a measuring microscope at 90× (60 measurements per specimen, 15 per surface). Following initial measurements, all copings were adjusted on stone dies. The number of adjustment cycles was recorded and post-adjustment measurements were made using the same method. Data were analyzed using independent and paired t-tests. RESULTS: Milled gold copings with a beveled margin (11.7 ± 20.4 µm) had a significantly (p < 0.05) smaller marginal gap than cast gold copings with a beveled margin (43.6 ± 46.8 µm) after adjustment. Cast gold copings with a chamfer margin (22.7 ± 24.7 µm) had a significantly (p < 0.05) smaller marginal gap than milled gold copings with a chamfer margin (27.9 ± 31.6 µm) following adjustments. Adjustments significantly decreased marginal gap for both cast groups (p < 0.05) and the milled chamfer bevel group (p < 0.05) but had no significant effect on the milled chamfer group. CONCLUSIONS: Within the limitations of this study, results indicate that gold restorations milled with the tested parameters provide a vertical marginal gap that is an acceptable alternative to traditional gold crown casting techniques.

Influence of Veneering Fabrication Techniques and Gas-Phase Fluorination on Bond Strength between Zirconia and Veneering Ceramics.

PURPOSE: Porcelain chipping has been one of the main problems of porcelain-fused-to-zirconia restorations. This study evaluates the bond strengths of layered, pressed, and adhesively bonded porcelain to yttria-stabilized zirconia substrates that have undergone traditional preparation or gas-phase fluorination. MATERIALS AND METHODS: A three-point bending test was used to evaluate the bond strength of the porcelain and zirconia interface. Sixty-six specimens were prepared (n = 11) following ISO 9693 and loaded until failure using an Instron testing machine. One-half of the zirconia substrates received gas phase fluorination treatment before veneering application. Three porcelain veneering methods were evaluated: layered, pressed, and adhesively bonded porcelain. Bond strength results were interpreted using a two-way ANOVA and a Bonferroni multiple comparisons test. Statistical significance was set at α = 0.05. RESULTS: ANOVA revealed a statistically significant effect of the veneering fabrication methods. No main effect was observed regarding the surface treatment to the zirconia. There was a significant effect related to the veneering method used to apply porcelain to zirconia. For untreated zirconia, layered porcelain had a significantly higher flexural strength compared to pressed or bonded, while pressed and bonded porcelains were not significantly different from one another. For zirconia specimens receiving fluorination treatment, both layered and pressed porcelains had significantly higher bond strengths than adhesively bonded porcelain. In addition, fluorinated pressed porcelain was not statistically different from the control layered or fluorinated layered porcelain. CONCLUSION: The choice of veneering fabrication technique was critical when evaluating the zirconia to porcelain interfacial bond strength. Bonded porcelain to zirconia had a lower flexural strength than layered or pressed porcelain, regardless of zirconia surface treatment. In addition, fluorination had an effect on the bond strength of pressed porcelain.

Comparison of implant and provisional placement protocols in sinus-augmented bone: a preliminary report.

PURPOSE: To evaluate preliminary data on clinical outcomes associated with timing of placement of single implant-supported provisional crowns and implants in augmented bone. MATERIALS AND METHODS: Twenty patients underwent sinus elevation bone grafting followed by a 6-month healing period before implant placement and immediate placement of a provisional crown (group [G] 1); 20 patients received sinus elevation bone grafting at the time of implant placement and immediate placement of a provisional crown (G2); 20 patients required no bone augmentation before implant placement and immediate placement of a provisional crown (G3); and 20 patients received sinus elevation bone grafting followed by a 6-month healing period before implant placement followed by a 6-month healing period before restoration (G4). The height of the crestal bone was measured and recorded to determine mean bone changes, and success rates were determined. RESULTS: Mean bone level comparisons were made between G2 and G3, G2 and G4, and G3 and G4. No statistically significant differences were found between the groups (P < .05). G1 was discontinued based on the initial results: two implants did not meet the 35-Ncm insertion test, and one implant failed within 1 month after implant placement. The 1-year implant survival rates were 86% (n = 12/14), 95% (n = 19/20), and 100% (n = 16/16) for G2, G3, and G4, respectively. Differences in survival rates between the groups were not statistically significant (P < .05). CONCLUSION: Implant survival is affected by the timing of sinus augmentation and implant placement in relation to the timing of crown placement. Implants that were restored immediately regardless of the timing of bone augmentation showed greater failure rates than implants in augmented bone with delayed restoration protocols or those that were restored immediately in sites without bone augmentation. Neither the timing of loading nor timing of implant placement in relation to bone augmentation surgery affected mean bone loss.

Investigating the association between obstructive sleep apnea and periodontitis.

BACKGROUND: Obstructive sleep apnea (OSA) is a sleep disorder characterized by disruptions of normal sleep architecture. Chronic periodontitis is a chronic disease of the periodontium that elicits a general inflammatory response to local dental plaque. It has been suggested that periodontal disease may increase in severity with increasingly severe OSA because both disease entities share common inflammatory pathways, acting synergistically to alter the host response. The aim of this study is to analyze the association between severity of OSA and the prevalence/severity of periodontitis. METHODS: One hundred patients from a large veterans administration sleep study center (n = 26 normal, n = 21 mild, n = 19 moderate, n = 34 severe) diagnosed with an overnight polysomnogram underwent a comprehensive periodontal examination. Periodontal parameters measured included the following: 1) mean periodontal probing depth (PD); 2) clinical attachment level (CAL); 3) gingival recession; and 4) percentage of sites with bleeding on probing, plaque, PD ≥5 mm, and CAL ≥3 mm. RESULTS: Seventy-three percent of the sampled population had moderate/severe periodontal disease. χ(2) analyses revealed no significant differences in the prevalence of periodontal disease between the apnea-hypopnea index (AHI) groups, with a negligible Spearman correlation coefficient of 0.246 between AHI severity and periodontal disease severity categories. Analysis of covariance indicated a significant association between AHI severity categories and percentage of sites with plaque, after adjusting for age. Multivariable logistic regression analysis predicting moderate/severe periodontitis with AHI score, age, and smoking status indicated a significant association with age (P = 0.028) but no significant association with the other two predictors. CONCLUSION: OSA was not significantly associated with the prevalence of moderate/severe periodontitis and the periodontal parameters examined, except percentage plaque.

A randomized crossover study comparing two mandibular repositioning appliances for treatment of obstructive sleep apnea.

PURPOSE: The purpose of this study was to determine whether treatment outcomes vary according to the design of the mandibular repositioning appliance (MRA). Two titratable MRA's were compared. The designs differ in advancement hardware and configuration of acrylic both in bulk and interocclusal contact. MATERIALS AND METHODS: The primary treatment outcome was the Respiratory Disturbance Index (RDI). Other outcomes that were compared included Sleep Apnea Quality of Life Index (SAQLI), Epworth Sleepiness Scale, oxygen saturation, and subjective feedback regarding experiences with the appliances. Twenty-four subjects were recruited from consecutive referrals for MRA therapy following diagnosis of obstructive sleep apnea (OSA) by polysomnography. Subjects were randomly assigned to a treatment arm of the crossover study. Each subject underwent an initial sleep study with a type III home monitor to establish a baseline RDI. Subjects were then treated with one of the two MRAs determined by random assignment. The MRA self-titration phase was monitored until a treatment position was determined, and the home sleep study was repeated. After a 2-week period without any OSA treatment, subjects received the second MRA and the self-titration treatment protocol was repeated. At completion of treatment with each appliance, subjects answered questionnaires and underwent a sleep study with the type III monitor. The outcome data for each appliance were compared using analysis of variance. RESULTS: Eighteen subjects completed the treatment protocol. There were no significant statistical differences in treatment outcomes between the two appliances. There was a statistically significant (p ≤ 0.05) preference for a MRA design with minimal coverage of teeth and palate. The subjects' appliance selection was consistent with a corresponding reduction in SAQLI score for the selected appliance. CONCLUSION: Although no statistically significant difference was observed between the two appliances in the outcomes measured, there was a trend toward greater improvement with the appliance with less acrylic resin bulk and less interocclusal contact. MRA selection should favor titratable, unobtrusive designs with appropriate construction to promote acceptance and adherence to MRA therapy.

Immediate restoration of single tapered implants with nonoccluding provisional crowns: a 5-year clinical prospective study.

BACKGROUND: Dental literature has limited number of publications regarding long-term outcome data of immediate restoration of single missing teeth with an implant-supported provisional crown. PURPOSE: This 5-year study evaluated hard and soft tissue responses to the immediate placement of single implant-supported provisional crowns. MATERIALS AND METHODS: Twenty patients received one dental implant restored immediately with a provisional acrylic resin screw-retained crown. Crestal bone loss was evaluated from standardized periapical radiographs collected at 3-month intervals for the first 21 months followed by a 5-year evaluation. Historical controls acquired from available dental literature were used for comparison. RESULTS: One implant failed within 2 months of surgical placement, presenting with pain and mobility. The remaining implants demonstrated no infection, pain, or radiolucencies. Nineteen implants were clinically immobile, osseointegrated, and asymptomatic at 21 months. At 5 years, one patient died, three patients were noncompliant, and 15 implants were evaluated as functional. Mean bone loss (MBL) at 1 year and 21 months was approximately 0.5 ± 0.5 mm and 0.70 ± 0.26 mm at 5 years. There was no statistically significant difference between MBLs at p < 0.05. CONCLUSIONS: Immediate provisionalization of single dental implants compares favorably with conventional loading protocols. Long-term data suggest that immediate provisionalization of single dental implants is a viable treatment option.

Evaluation of a novel device for measuring patient compliance with oral appliances in the treatment of obstructive sleep apnea.

PURPOSE: The purpose of this study was to evaluate a novel intraoral monitor for measuring patient compliance of oral appliances for the treatment of obstructive sleep apnea. MATERIALS AND METHODS: A clinical trial was conducted to compare objective recording by an intraoral compliance monitor and self-reporting by participants using a mandibular repositioning device (MRD). Ten participants were fitted with a Thornton Adjustable Positioner (TAP III) with an embedded compliance monitor. The participants were asked to wear the test appliance for seven nights and to record their usage of the appliance and any adverse effects in a treatment journal. The data were downloaded to a dedicated computer using radio-frequency identification (RFID) technology, and the information was compared to the data in the participant's journal. RESULTS: The mean objective wearing time, as detected by the compliance monitor, was found to be 6.6 ± 1.6 hours/night. The mean subjective wearing time, as recorded by the participants, was 6.5 ± 1.5 hours/night. The correlation between subjective and objective times was 0.9985. The use of the test appliance by this sample population was 68.7% with a range of 24% to 100%. Participants reported a range of adverse outcomes related to the MRD consistent with those reported in the literature and were found to be transient in nature. CONCLUSIONS: This study supports previously reported usage times and adverse outcomes. The compliance monitor showed a very high linear correlation between subjective and objective data, validating its use in future compliance studies.

Relationship between clinical periodontal biotype and labial plate thickness: an in vivo study.

The primary aim of this study was to evaluate the differences in labial plate thickness in patients identified as having thin versus thick/average periodontal biotypes. The association between biotype and labial plate thickness was evaluated by correlating information obtained from cone beam computed tomographs, diagnostic impressions, and clinical examinations of the maxillary anterior teeth (canine to canine) in 60 patients. Compared to a thick/average biotype, a thin biotype was associated with thinner labial plate thickness (P < .001), narrower keratinized tissue width (P < .001), greater distance from the cementoenamel junction to the initial alveolar crest (P = .02), and probe visibility through the sulcus. There was no relationship between biotype and tooth height-to-width ratio or facial recession. Periodontal biotype is significantly related to labial plate thickness, alveolar crest position, keratinized tissue width, gingival architecture, and probe visibility but unrelated to facial recession.

Customizing a nasal CPAP mask using a silicone elastomer.

Nasal continuous positive airway pressure (CPAP) is an effective treatment for obstructive sleep apnea (OSA). Airway obstruction is prevented by delivering air at a constant pressure via a nasal mask worn during sleep. Small nares may cause difficulty in wearing even the smallest standard nasal mask, with wear resulting in discomfort and air leaks. This article describes a method for fabricating a custom nasal CPAP mask using maxillofacial prosthodontic laboratory techniques.

Microabrasion of cast metal margins--a warning.

Plastic test patterns were milled to simulate casting margins and were cast in a variety of dental alloys. The cast specimens were exposed to horizontal and vertical streams of low-pressure microabrasion with 50 microm aluminum oxide particles. Post-exposure measurements show all specimens were affected by microabrasion. Dentists and laboratory technicians who use microabrasion must be aware of the potential damage to casting margins.

Fabrication of a stable surgical template using staged tooth extraction for immediate implant placement.

When a patient with a nonrestorable dentition desires an immediate restoration, fabrication and use of a stable surgical template can be challenging. Conventionally made surgical templates may lack stability and may, therefore, be less predictable. This article describes the fabrication of a surgical template that permitted the use of staged tooth extraction to facilitate predictable immediate implant placement in a patient with a nonrestorable dentition.

Fracture of a fixed partial denture abutment: a clinical report.

Commonly observed complications associated with a conventional fixed partial denture (FPD) include loss of retention and tooth fracture. This report describes the occurrence of an unusual FPD abutment fracture and subsequent treatment. The distal abutment of an FPD developed severe periodontal disease with mobility. The anterior abutment fractured in the middle of the clinical crown and experienced cement failure.

Removal of a metal-ceramic fixed partial denture with a loose retainer.

In clinical practice, it is necessary to remove a ceramic-veneered fixed partial denture when an abutment becomes loose. When possible, the fixed partial denture is removed in a single piece, allowing recementation when appropriate. A 1-piece removal is challenging, often putting the veneer and abutment teeth at risk for damage. This article describes a technique for fabricating and using a 2-piece matrix that both protects the prosthesis and better directs removal forces along the long axis of the abutments.

The single-unit crown: factors for clinical success.

Application of the crown preparation guidelines obtained through theoretical models, laboratory testing and clinical studies provide an evidence-based rationale for clinical practice procedures. The evidence-based rationale has been presented to support basic day-to-day techniques in clinical practice. As new techniques and materials are developed, each should be evaluated carefully prior to clinical use and acceptance.