Faculty Bibliography

OBJECTIVE:To evaluate the reliability and failure mode of zirconia-reinforced lithium silicate (ZLS) molar crowns of different thicknesses. METHODS:Monolithic ZLS molar crowns (0.5mm, 1.0mm, and 1.5 mm thickness) were modeled and milled using a CAD/CAM system (n = 21/group). Crowns were cemented on dentin-like epoxy resin replicas with a resin cement. The specimens were subjected to single load-to-failure test for step-stress profiles designing. Mouth-motion step-stress accelerated-life test was performed under water by sliding an indenter 0.7 mm lingually down on the distobuccal cusp until specimen fracture or suspension. Use level probability Weibull curves and reliability were calculated and plotted. Polarized-light optical microscope and scanning electron microscope (SEM) were used to characterize fracture patterns. RESULTS:Irrespective of crown thickness, beta (β) values were higher than 1 and fatigue accelerated failures. While 0.5 mm ZLS crowns exhibited a significant reduction in the probability of survival at 200N, 300N and 400 N mission loads (69%, 41% and 19%, respectively), no significant difference was observed between 1.0 mm and 1.5 mm crowns. Both thicknesses have maintained the survivability at approximately 90%. Failure primarily comprised bulk fracture where radial cracks originated from the cementation surface beneath the indenter loading trail and propagated towards the cervical margin. SIGNIFICANCE/CONCLUSIONS:1.5 mm- and 1.0 mm-thickness monolithic ZLS crowns presented higher probability of survival compared to 0.5 mm crowns. Bulk fracture was the chief failure mode, regardless of thickness.

BACKGROUND:Autologous bone grafts remain a standard of care for the reconstruction of large bony defects, but limitations persist. The authors explored the bone regenerative capacity of customized, three-dimensionally printed bioactive ceramic scaffolds with dipyridamole, an adenosine A2A receptor indirect agonist known to enhance bone formation. METHODS:Critical-size bony defects (10-mm height, 10-mm length, full-thickness) were created at the mandibular rami of rabbits (n = 15). Defects were replaced by a custom-to-defect, three-dimensionally printed bioactive ceramic scaffold composed of β-tricalcium phosphate. Scaffolds were uncoated (control), collagen-coated, or immersed in 100 μM dipyridamole. At 8 weeks, animals were euthanized and the rami retrieved. Bone growth was assessed exclusively within scaffold pores, and evaluated by micro-computed tomography/advanced reconstruction software. Micro-computed tomographic quantification was calculated. Nondecalcified histology was performed. A general linear mixed model was performed to compare group means and 95 percent confidence intervals. RESULTS:Qualitative analysis did not show an inflammatory response. The control and collagen groups (12.3 ± 8.3 percent and 6.9 ± 8.3 percent bone occupancy of free space, respectively) had less bone growth, whereas the most bone growth was in the dipyridamole group (26.9 ± 10.7 percent); the difference was statistically significant (dipyridamole versus control, p < 0.03; dipyridamole versus collagen, p < 0.01 ). There was significantly more residual scaffold material for the collagen group relative to the dipyridamole group (p < 0.015), whereas the control group presented intermediate values (nonsignificant relative to both collagen and dipyridamole). Highly cellular and vascularized intramembranous-like bone healing was observed in all groups. CONCLUSION:Dipyridamole significantly increased the three-dimensionally printed bioactive ceramic scaffold's ability to regenerate bone in a thin bone defect environment.

OBJECTIVE:To compare hard-tissue healing after 3 exodontia approaches. MATERIALS AND METHODS/METHODS:Premolars of dogs were extracted: (1) flapless, (2) flap, and (3) flap + socket coverage with polytetrafluoroethylene (dPTFE) nonresorbable membrane (flap + dPTFE). Animals were euthanized at 1 and 4 weeks. Amount of bone formation within socket and socket total area were measured. RESULTS:Amount of bone formation revealed significant difference between 1 and 4 weeks; however, there was no differences among groups. Socket total area decreased after 4 weeks, and the flap + dPTFE group showed significantly higher socket total area. As a function of time and group, flap + dPTFE 4 weeks presented similar socket total area values relative to flap + dPTFE at 1 week, and significantly higher socket total area than flapless and flap. The histological sections revealed almost no bone formation within socket after 1 week, which increased for all groups at 4 weeks. CONCLUSION/CONCLUSIONS:Socket coverage with polytetrafluoroethylene (dPTFE) membrane showed to effectively preserve bone architecture. Bone formation within sockets was not influenced by tooth extraction technique.

This study sought to qualitatively and quantitatively evaluate the effect of osteotomy preparation by conventional (control group) or OD (OD group) instrumentation on osteotomy healing. An incision of 10 cm was made in the anteroposterior direction over the hip in five sheep, and 15 osteotomies were prepared in the left ilium of the sheep (n = 3/sheep). Three different instrumentation techniques were utilized: (1) conventional/regular drilling (R [recommended by manufacturer]) in a 3-step series of a 2-mm pilot, 3.2-mm, and 3.8-mm twist drills; (2) OD clockwise (OD-CW) drilling with Densah Bur (Versah) 2.0-mm pilot, 2.8-mm, and 3.8-mm multi-fluted tapered burs; and (3) OD counterclockwise (OD-CCW) drilling with Densah Bur 2.0-mm pilot, 2.8-mm, and 3.8-mm multi-fluted tapered burs. Drilling was performed at 1,100 rpm with saline irrigation. Qualitative histomorphometric analysis of the osteotomies after 6 weeks did not show any healing impairment due to the instrumentation. Histologic analysis shows bone remodeling and growth in all samples, irrespective of osteotomy preparation technique, with the presence of bone chips observed along the length of the osteotomy wall in sites subjected to osseodensification drilling.

OBJECTIVE:To evaluate the probability of survival of monolithic and porcelain veneered lithium disilicate crowns comprised by a conventional or modified core when loaded on marginal ridges. METHODS:Lithium disilicate molar crowns (n=30) were fabricated to be tested at mesial and distal marginal ridges and were divided as follows: (1) bilayered crowns with even-thickness 0.5mm framework (Bi-EV); (2) bilayered crowns with modified core design (Bi-M-lingual collar connected to proximal struts), and: (3) monolithic crowns (MON). After adhesively cemented onto composite-resin prepared replicas, mesial and distal marginal ridges of each crown (n=20) were individually cyclic loaded in water (30-300N) with a ceramic indenter at 2Hz until fracture. The 2-parameter Weibull was used to calculate the probability of survival (reliability) (90% 2-sided confidence bounds) at 1, 2, and 3 million cycles and mean life. RESULTS:The reliability at 1 and 2 million cycles was significantly higher for MON (47% and 19%) compared to Bi-EV (20% and 4%) and Bi-M (17% and 2%). No statistical difference was found between bilayered groups. Only the MON group presented crown survival (7%) at 3 million cycles. The mean life was highest for MON (1.73E+06), lowest for Bi-M (573,384) and intermediate for Bi-E (619,774). Fractographic analysis showed that the fracture originated at the occlusal surface. The highest reliability was found for MON crowns. The modified framework design did not improve the fatigue life of crowns. SIGNIFICANCE/CONCLUSIONS:Monolithic lithium disilicate crowns presented higher probability of survival and mean life than bilayered crowns with modified framework design when loaded at marginal ridges.

OBJECTIVE:The aim of this in vivo study is to compare the osseointegration of endosteal implants placed in atrophic mandibular alveolar ridges with alveolar ridge expansion surgical protocol via an experimental osseodensification drilling versus conventional osteotome technique. METHODS:Twelve endosteal implants, 4 mm × 13 mm, were placed in porcine models in horizontally atrophic mandibular ridges subsequent to prior extraction of premolars. Implants were placed with osseodensification drilling technique as the experimental group (n = 6) and osteotome site preparation as the control group (n = 6). After 4 weeks of healing, samples were retrieved and stained with Stevenel's Blue and Van Gieson's Picro Fuschin for histologic evaluation. Quantitative analysis via bone-to-implant contact (BIC%) and bone area fraction occupancy (BAFO%) were obtained as mean values with corresponding 95% confidence interval. A significant omnibus test, post-hoc comparison of the 2 drilling techniques' mean values was accomplished using a pooled estimate of the standard error with P-value set at 0.05. RESULTS:The mean BIC% value was approximately 62.5% in the osseodensification group, and 31.4% in the regular instrumentation group. Statistical analysis showed a significant effect of the drilling technique (P = 0.018). There was no statistical difference in BAFO as a function of drilling technique (P = 0.198). CONCLUSION/CONCLUSIONS:The combined osseodensification drilling-alveolar ridge expansion technique showed increased evidence of osseointegration and implant primary stability from a histologic and biomechanical standpoint, respectively. Future studies will focus on expanding the sample size as well as the timeline of the study to allow investigation of long-term prognosis of this novel technique.