Temporary materials used in prosthodontics: The effect of composition, fabrication mode, and aging on mechanical properties

PURPOSE

To evaluate the effect of composition, fabrication mode, and thermal cycling on the mechanical properties of different polymeric systems used for temporary dental prostheses.

MATERIALS AND METHODS

Standard bar-shaped specimens (25 × 2 × 2 mm) were fabricated of six polymeric systems of varying compositions and fabrication modes (n = 10/group): conventional PMMA (Alike, GC) - group CGC; conventional PMMA (Dêncor, Clássico) - group CD; bis-acryl (Tempsmart, GC) - group BGC; bis-acryl (Yprov, Yller) - group BY; milled PMMA (TelioCAD, Ivoclar) - group MI; 3D printed bis-acryl - (Cosmos Temp, Yller) group PY. Half of the specimens were subjected to 5000 thermal cycles (5 °C to 55 °C). Three-point bending tests were performed using a universal testing machine with a crosshead speed set to 0.5 mm/min. Flexural strength and elastic modulus were calculated from the collected data. FTIR spectra were recorded pre and post curing and after thermal cycling to evaluate material composition and degree of conversion. Energy-dispersive spectroscopy (EDS) and scanning electron microscope (SEM) were utilized to examine the composition and micromorphology of the systems, respectively. Data were analyzed using two-analysis of variance and Tukey tests (α = 0.05).

RESULTS

FTIR spectra indicated that BGC, BY and PY groups corresponded to urethane dimethacrylate systems (bis-acryl), while CGC, CD, and MI groups corresponded to monomethacrylate systems, polymethyl methacrylate (PMMA). Bis-acryl BGC system yeilded the highest flexural strength (80 MPa), followed by the milled PMMA MI system (71 MPa), both statistically significant different relative to other groups. Bis-acryl BY exhibited the lowest flexural strength (27 MPa). Thermocycling significantly increased the flexural strength of all polymeric systems (∼10-15 MPa), except for the 3D-printed PY group. Bis-acryl BGC (1.89 GPa) and conventional PMMA CGC (1.66 GPa) groups exhibited the highest elastic modulus, followed by milled PMMA MI group (1.51 GPa) and conventional PMMA CD (1.45 GPa) systems, with significant difference detected between BGC group and MI and CD groups. The 3D printed PY (0.78 GPa) and bis-acryl BY (0.47 GPa) systems presented the lowest elastic modulus. Thermocycling did not have a significant influence on the elastic modulus. FTIR spectra indicate water sorption and release of unreacted monomers as well as increased degree of conversion (∼5-12%) after thermal cycling.

CONCLUSION

Composition and fabrication mode and thermal cycling significantly affected the mechanical properties of polymeric systems used for temporary dental prostheses.

Hydrothermal degradation methods affect the properties and phase transformation depth of translucent zirconia

OBJECTIVES

To characterize the optical and mechanical properties of a commercial and in-house translucent Y-TZP before and after aging in autoclave or hydrothermal reactor.

METHODS

In-house experimental discs were obtained through uniaxial and isostatic pressing a translucent Y-TZP powder and sintering at 1,550 °C/1 h. Commercial discs were milled from pre-sintered blocks fabricated with the same powder through uniaxial and isostatic pressing and sintering. Discs were allocated into three groups according to aging condition: immediate, aged via autoclave, or reactor (134 °C, 20 h, 2.2 bar). Crystalline content and microstructure were evaluated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Residual compressive stress (CS) was determined by Raman spectroscopy. Optical properties were determined by the contrast ratio (CR) and translucency parameter (TP) using reflectance data. Mechanical properties were assessed by Vickers hardness, fracture toughness and biaxial flexural strength tests.

RESULTS

XRD and SEM revealed a typical Y-TZP crystalline content, chiefly tetragonal phase, and a dense crystalline matrix for both processing protocols. Reactor aging triggered a more pronounced t-m transformation relative to autoclave. In-house and commercial Y-TZPs demonstrated similar CR and TP, with reactor aging significantly increasing their translucency. Similarly, reactor aging influenced Vickers hardness and fracture toughness. In-house processed Y-TZP clearly demonstrated the presence of CS, whereas commercial Y-TZP showed no presence of CS. Non-aged in-house Y-TZP resulted in significantly lower characteristic strength relative to commercial Y-TZP. While aging protocols significantly increased the characteristic strength of in-house Y-TZP, reactor significantly decreased commercial Y-TZP characteristic strength. Both Y-TZP processing protocols demonstrated high reliability at high-stress missions, with no detrimental effect of aging.

CONCLUSIONS

Laboratory aging methodology significantly influenced optical and mechanical properties of a commercial and in-house translucent Y-TZP.

A Histologic and Histomorphometric Evaluation of an Allograft, Xenograft, and Alloplast Graft for Alveolar Ridge Preservation in Humans: A Randomized Controlled Clinical Trial

The aim of this study was to clinically evaluate the guided bone regeneration (GBR) potential of allograft, xenograft, and alloplastic materials in combination with resorbable membranes in extraction sockets. The qualitative and quantitative assessments of this prospective study were accomplished through histologic and histomorphometric analysis. Three experimental groups and 1 control group for comparison (n = 8) received either an allograft (human cancellous bone, freeze dried, Deutsches Institut für Zell und Gewebeersatz, Berlin, Germany), xenograft (BioOss, Geistlich Pharma AG, Wolhusen, Switzerland), or alloplast (biphasic calcium sulphate, Bondbone, MIS Implants Technologies Ltd., Charlotte, NC). The negative control group received no regenerative material. Tissue samples were then qualitatively and quantitatively evaluated as a function of percentage of new vital bone, graft particles content, soft tissue, and bone marrow over time. All 3 study groups presented bone volume suitable for the successful placement of a dental implant. The xenograft group yielded significantly less amount of vital bone compared with the allograft and alloplast groups. When comparing the percentage of residual graft particles, there was significantly greater amounts associated with the xenograft group in contrast to the allograft and alloplast groups. Similarly, a significantly increased amount of soft tissue percentage was observed within the xenograft group relative to all other groups. No significant differences were observed in the percentage of residual graft particles between the allograft and alloplast groups. There were also no significant differences detected in vital bone percentage between the allograft, alloplast, and control groups. When evaluating the bone marrow percentage, the only significant difference detected was between the xenograft and alloplast materials. Overall, no complications (ie, fever, malaise, purulence or fistula) were observed during the entirety of clinical trial among all patients. The greatest GBR potential was associated with the allograft material because of the greater degree of vital bone and the lowest percentage of residual graft particles. All studied bone substitute materials resulted in bone apposition for efficient use in alveolar ridge preservation procedures.

Ultra-translucent zirconia processing and aging effect on microstructural, optical, and mechanical properties

OBJECTIVES

To evaluate the effect of the ceramic processing and aging method on the microstructure, optical, and mechanical properties of a third generation ultra-translucent zirconia, yttria partially stabilized zirconia (5Y-PSZ).

METHODS

In-house discs were obtained through uniaxial and isostatic pressing an ultra-translucent Y-PSZ powder and sintering at 1450 °C for 2 h. As control, a commercial disc was milled from pre-sintered blocks fabricated with the same 5Y-PSZ powder through isostatic pressing and sintered under the same protocol. Discs were allocated into three groups according to aging condition as immediate (non-aged) and aged using autoclave or hydrothermal reactor at 134ºC for 20 h at 2.2 bar. Crystalline content and microstructure were evaluated using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Optical properties were determined using reflectance data to calculate the contrast ratio (CR) and translucency parameter (TP). Mechanical properties were assessed by Vickers hardness, fracture toughness and biaxial flexural strength tests.

RESULTS

XRD spectra revealed a prevalence of cubic (70%) and tetragonal (30%) phases, and the SEM images showed a dense fully crystalline ceramic matrix for both materials. Crystalline content and microstructure of the in-house and commercial 5Y-PSZs were not affected by aging. As-sintered 5Y-PSZs demonstrated similar CR (~0.6) and TP (~18) values, as well as Vickers hardness (~14 GPa) and fracture toughness (~3.8 Mpa.m^1/2), with no significant alteration after both aging methods. In-house and commercial Y-PSZs Weibull moduli ranged from 3.0 to 5.3. 5Y-PSZ processing methods resulted in similar characteristic strength after sintering (592-618 Mpa). While commercial 5Y-PSZ showed no significant influence of aging on strength, hydrothermal reactor aging significantly decreased the in-house Y-PSZ characteristic strength (474 Mpa). Both 5Y-PSZs demonstrated high reliability up to 300-Mpa strength missions, with no detrimental effect of aging (88-100%).

SIGNIFICANCE

Irrespective of the processing method, ultra-translucent 5Y-PSZ showed high aging resistance and translucency stability, as well as strength corresponding to the indication up to short-span anterior prostheses.

Survival of implant-supported resin-matrix ceramic crowns: In silico and fatigue analyses

OBJECTIVE

To evaluate the fatigue survival, failure mode, and maximum principal stress (MP Stress) and strain (MP Strain) of resin-matrix ceramic systems used for implant-supported crowns.

METHODS

Identical molar crowns were milled using four resin-matrix ceramics (n = 21/material): (i) Shofu Hard, (ii) Cerasmart (iii) Enamic, and (iv) Shofu HC. Crowns were cemented on the abutments, and the assembly underwent step-stress accelerated-life testing. Use level probability Weibull curves at 300 N were plotted and the reliability at 300, 500 and 800 N was calculated for a mission of 50,000 cycles. Fractographic analysis was performed using stereomicroscope and scanning electron microscope. MP Stress and MP Strain were determined by finite element analysis.

RESULTS

While fatigue dictated failures for Cerasmart (β > 1), material strength controlled Shofu Hard, Enamic, and Shofu HC failures (β < 1). Shofu HC presented lower reliability at 300 N (79%) and 500 N (59%) than other systems (>90%), statistically different at 500 N. Enamic (57%) exhibited a significant reduction in the probability of survival at 800 N, significantly lower than Shofu Hard and Cerasmart; however, higher than Shofu HC (12%). Shofu Hard and Cerasmart (>93%) demonstrated no significant difference for any calculated mission (300-800 N). Failure mode predominantly involved resin-matrix ceramic fracture originated from occlusal cracks, corroborating with the MP Stress and Strain location, propagating through the proximal and cervical margins.

SIGNIFICANCE

All resin-matrix ceramics crowns demonstrated high probability of survival in a physiological molar load, whereas Shofu Hard and Cerasmart outperformed Enamic and Shofu HC at higher loads. Material fracture comprised the main failure mode.

Effect of leukocyte-platelet-rich fibrin in bone healing around dental implants placed in conventional and wide osteotomy sites: A pre-clinical study

Leukocyte-platelet-rich fibrin (L-PRF) has been suggested for gap management for immediate implant placement when the distance is greater than 2 mm. However, there remains a paucity in hierarchically designed research to support this application. The present study aimed to evaluate the effect of L-PRF on the osseointegration parameters of dental implants placed after conventional osteotomy of surgically created bone defects that simulate post extraction sockets in a canine model after 3, 6, and 12 weeks in vivo. Eighty dental implants (Intra-Lock, Boca Raton, FL) were placed in the radius of 13 beagle dogs. The experiment consisted of 4 groups (n = 20 implants/group): 1) Regular osteotomy (Reg n/L-PRF); 2) Regular osteotomy and implant placement with L-PRF membrane (Reg L-PRF); 3) Wide osteotomy with no gap management performed, where an osteotomy/bony defect (6 mm of diameter and ~5 mm deep) was created to simulate immediate implant placement in post-extraction sockets, and the gap was left for spontaneous healing (Wide nL-PRF); and 4) Wide osteotomy with L-PRF gap management (Wide L-PRF). L-PRF membranes were obtained by blood drawn from each subject and centrifuged at 2700 rpm (408 RCF-clot) for 12 min. In the experimental groups where L-PRF was utilized, the membrane was inserted into the osteotomy site prior to implant placement. Six dogs had implants placed in the radius for 3 weeks; and 7 dogs had implants placed in the left radius for 6 weeks and in the right radius for 12 weeks. At the corresponding experimental time points, samples were harvested, and subjected to histological processing for qualitative and quantitative analyses, via bone-to-implant contact (BIC) and bone-area-fraction occupancy (BAFO). Qualitative analysis demonstrated increased amounts of bone formation around the implant and within the healing chambers over time for all groups. While comparable histological features were observed for both Reg groups (L-PRF and nL-PRF), the gap management performed in Wide L-PRF group resulted in effective gap filling with improved bone growth in close proximity to the implant surface. Quantitative analyses of BIC and BAFO yielded higher values for both variables at 3 weeks for Wide L-PRF (~38% and ~56% respectively) compared to Wide nL-PRF (~20% for BIC and BAFO) (p < .03). No statistical differences were detected between Wide groups at 6 and 12 weeks, neither between Reg groups, independent of the association with or without the L-PRF membrane at all healing times. L-PRF placed within wide osteotomies, prior to implant placement, resulted in increased early bone formation compared to unfilled wide osteotomies at the early healing time (3 weeks in vivo).

Effect of supplemental acid-etching on the early stages of osseointegration: A preclinical model

PURPOSE

To evaluate the effect of two surface modifications on early osseointegration parameters of conical implants in a translational pre-clinical model.

MATERIALS AND METHODS

Conical implants with progressive trapezoidal threads and healing chambers were evaluated consisting of two different surface conditions: 1) Implacil surface (IMP Sur), and 2) Implacil surface + Supplemental Acid-etching (IMP Sur + AE). Surface characterization comprised of the evaluation of roughness parameters (S_a, S_q and S_dr), surface energy and contact angle. Subsequently, implants were installed in the ilium crest of nine female sheep (weighing ~65 kg). Torque out, histological and histomorphometric analyses were conducted after 3 and 6 weeks in-vivo. The percentage of bone to implant contact (%BIC) and bone area fraction occupancy within implant threads (%BAFO) were quantified, and the results were analyzed using a general linear mixed model analysis as function of surface treatment and time in-vivo.

RESULTS

Supplemental acid etching significantly increased S_a and S_q roughness parameters without compromising the surface energy or contact angle, and no significant differences with respect to S_dr. Torque-out testing yielded significantly higher values for IMP Sur + AE in comparison to the IMP Sur at 3- (62.78 ± 15 and 33.49 ± 15 N.cm, respectively) and 6-weeks (60.74 ± 15 and 39.80 ± 15 N.cm, respectively). Histological analyses depicted similar osseointegration features for both surfaces, where an intramembranous-type healing pattern was observed. At histomorphometric analyses, IMP Sur + AE implants yielded higher values of BIC in comparison to IMP Sur at 3- (40.48 ± 38 and 27.98 ± 38%, respectively) and 6-weeks (45.86 ± 38 and 34.46 ± 38%, respectively). Both groups exhibited a significant increase in %BAFO from 3 (~35%) to 6 weeks (~44%), with no significant differences between surface treatments.

CONCLUSION

Supplemental acid-etching and its interplay with implant thread design, positively influenced the BIC and torque-out resistance at early stages of osseointegration.

Laddec® versus Bio-Oss®: The effect on the healing of critical-sized defect - Calvaria rabbit model

The aim of this study was to evaluate the in vivo performance of two different deproteinized bovine bone (DBB) grafting materials: DBBB (Bio-Oss®) and DBBL (Laddec®), for the regeneration of critically sized (8 mm) defects in rabbit's calvaria. Three round-shaped defects were surgically created in the calvaria of 13 New Zealand White rabbits proximal to the coronal suture in the parietal bone. Two of the defects were filled with one of the grafting materials while a third was left empty to serve as a negative control. Bone regeneration properties were evaluated at 4- and 8-weeks after implantation by means of histological and histomorphometrical analyses. Statistical analyses were performed through a mixed model analysis with fixed factors of time and material. Histological evaluation of the control group evidenced a lack of bridging bone formation across the defect sites at both evaluation time points. For the experimental groups, new bone formation was observed around the defect periphery and to progress radially inwards to the center of the defect site, regardless of the grafting material. Histomorphometric analyses at 4 weeks demonstrated higher amount of bone formation through the defect for DBBB group. However, at 8 weeks, DBBL and DBBB demonstrated osteoconductivity and low resorption rates with evidence of statistically similar bone regeneration through the complete boney defect. Finally, DBBB presented lower soft tissue migration within the defect when compared to DBBL at both evaluation time points. DBBB and DBBL presented similar bone regeneration performance and slow resorption rates. Although both materials promoted bone regeneration through the complete defect, DBBB presented lower soft tissue migration within the defects at 4- and 8-weeks.

Stability of fatigued and aged ZTA compared to 3Y-TZP and Al2O3 ceramic systems

To evaluate the effect of fatigue and aging on the crystalline content and reliability of a zirconia-toughened-alumina (ZTA) composite compared to its individual counterpart materials (3Y-TZP and Al₂O₃). Thirty-six disc-shaped specimens per group were obtained to comply with ISO 6872:2015. Crystalline content, microstructure and reliability of experimental groups were evaluated in four stages: 1) immediate; 2) aged; 3) fatigued; 4) aged + fatigue. Aging was performed in autoclave and Step-Stress-Accelerated-Life-Testing (SSALT) was performed using three stress profiles. Weibull statistics were used to determine Weibull parameters and life-expectancy. A significant increase in monoclinic phase in 3Y-TZP was observed after aging (19.31%), fatigue (17.88%) and aging + fatigue (55.81%), while ZTA evidenced minimal variation among all conditions (<5.69%). 3Y-TZP presented higher reliability than ZTA at 300 and 500 MPa, and ZTA outperformed Al₂O₃ at the same stress missions. None of the ceramics yielded acceptable reliability at 800 MPa. A higher characteristic strength was observed for 3Y-TZP, followed by ZTA and Al₂O₃. While after aging ZTA and Al₂O₃ remained stable, 3Y-TZP exhibited a significant increase in the characteristic stress. Aging did not affect the reliability of ZTA and Al₂O₃. 3Y-TZP demonstrated an increase in monoclinic content and characteristic strength after aging.

Effects of relative centrifugation force on L-PRF: An in vivo submandibular boney defect regeneration study

Properties and composition of leukocyte- and platelet-rich fibrin (L-PRF) clots may be largely affected by centrifugation protocols (function of relative centrifugal force [RCF]), which may impact biological potential repair in bone regeneration. The present in vivo study sought to assess the effect of the RCF on the composition of L-PRF clots, as well as to compare the repair potential of L-PRF clots obtained with different RCF protocols in submandibular boney defects using PLGA scaffolds for bone regeneration. Complete blood count and volumetric evaluations were performed on L-PRF clots obtained through centrifugation for 12 min at 200, 400, and 600 RCF-clot centrifugation speeds. These evaluations were completed from blood collected immediately prior to any surgical procedures. The in vivo portion comprised of three submandibular unilateral, full thickness, osteotomies (~0.40cm³ ) which were created in the submandibular region of six sheep, using rotary instrumentation under continuous irrigation. Subsequently, poly(lactic-co-glycolic acid) (PLGA) scaffolds were enveloped in a L-PRF membrane from one of the three spinning speeds (n = 6/RCF) and inserted into the defect (sites were interpolated to avoid site bias). Six-weeks after surgery, the mandibles were harvested en bloc and prepared for volumetric and histomorphometric evaluations. Membranes harvested from 600 RCF produced significantly larger L-PRF clots (6.97g ± 0.95) in comparison to the lower 200 RCF (5.7g ± 0.95), with no significant differences between 600 and 400, and from 400 and 200 RCF. The three tested RCFs did not alter the platelet count of the L-PRF clot. For the in vivo component, quantitative bone regeneration analyses demonstrated significantly higher values obtained with L-PRF membranes extracted post 600 RCF (27.01 ± 8%) versus 200 RCF (17.54 ± 8%), with no significant differences regarding 400 RCF (~23 ± 8%). At the qualitative histological analyses, L-PRF membranes obtained at 600 and 400 RCFs yielded improved healing throughout the defect, where the L-PRF sourced from the lowest speed, 200 RCF, presented healing primarily at the margins along with the presence of connective tissue at the central aspect of the surgical defect. Higher 600 RCF yielded larger L-PRF clots/membranes, resulting in enhanced bone repair potential in association with PLGA scaffolds for the treatment of critical size bone defects.

Performance of crowns cemented on a fiber-reinforced composite framework 5-unit implant-supported prostheses: in silico and fatigue analyses

OBJECTIVE

To characterize the biomechanical performance of fiber-reinforced composite 5-unit implant-supported fixed dental prostheses (FDPs) receiving individually milled crowns by insilico and fatigue analyses.

METHODS

Eighteen implant-supported five-unit fiber-reinforced composite frameworks with an individually prepared abutment design were fabricated, and ninety resin-matrix ceramic crowns were milled to fit each abutment. FDPs were subjected to step-stress accelerated-life testing with load delivered at the center of the pontic and at 2nd molar and 1st premolar until failure. The reliability of the prostheses combining all loaded data and of each loaded tooth was estimated for a mission of 50,000 cycles at 300, 600 and 900 N. Weibull parameters were calculated and plotted. Fractographic and finite element analysis were performed.

RESULTS

Fatigue analysis demonstrated high probability of survival at 300 N, with no significant differences when the set load was increased to 600 and 900 N. 1st and 2nd molar dataset showed high reliability at 300 N, which remained high for the higher load missions; whereas 1st premolar dataset showed a significant decrease when the reliability at 300 N was compared to higher load missions. The characteristic-strength of the combined dataset was 1252 N, with 1st molar dataset presenting higher values relative to 2nd molar and 1st premolar, both significantly different. Failure modes comprised chiefly cohesive fracture within the crown material originated from cracks at the occlusal area, matching the maximum principal strain location.

SIGNIFICANCE

Five-unit implant-supported FDP with crowns individually cemented in a fiber-reinforced composite framework presented a high survival probability. Crown fracture comprised the main failure mode.

In vitro analysis of durability of S-PRG filler-containing composite crowns for primary molar restoration

OBJECTIVE

To evaluate the reliability, maximum principal stress, shear stress, and crack initiation of a computer-aided design/computer-aided manufacturing (CAD/CAM) resin composite (RC) incorporating surface pre-reacted glass (S-PRG) filler for primary molar teeth.

METHODS

Mandibular primary molar crowns fabricated by experimental (EB) or commercially available CAD/CAM RCs (HC) were prepared and cemented to a resinous abutment tooth using an adhesive resin cement (Cem) or a conventional glass-ionomer cement (CX). These specimens were subjected to a single compressive test (n = 5/each) and the step-stress accelerated life testing (SSALT) (n = 12/each). Data was evaluated using Weibull analyses and reliability was calculated. Afterwards, the maximum principal stress and crack initiation point of each crown was analyzed by finite element analysis. To evaluate bonding of EB and HC to dentin, microtensile bond strength (μTBS) testing was conducted using primary molar teeth (n = 10/each).

RESULTS

There was no significant difference between the fracture loads of EB and HC for either cement (p > 0.05). The fracture loads of EB-CX and HC-CX were significantly lower than EB-Cem and HC-Cem (p < 0.05). The reliability at 600 N for EB-Cem was greater than that for EB-CX, HC-Cem, and HC-CX. The maximum principal stress concentrated on EB was lower than that on HC. The shear stress concentrated in the cement layer for EB-CX was higher than that for HC-CX. There was no significant difference among the μTBSs of EB-Cem, EB-CX, HC-Cem, and HC-CX (p > 0.05).

SIGNIFICANCE

The crowns fabricated with the experimental CAD/CAM RC incorporating S-PRG filler yielded greater fracture loads and reliability than the crowns manufactured with commercially available CAD/CAM RC regardless of the luting materials. These findings suggest that the experimental CAD/CAM RC crown may be clinically useful for the restoration of primary molars.

Mechanical testing of four-unit implant-supported prostheses with extensive pink gingiva porcelain: The dentogingival prostheses proof of concept

OBJECTIVE

To investigate the probability of survival and failure modes of four-unit implant-supported porcelain fused to metal (PFM) dentogingival prostheses subjected to step-stress accelerated life testing (SSALT).

MATERIALS AND METHODS

Eighteen implant-supported PFM dentogingival prostheses with thin metallic infrastructures, which provided minimal ceramic support and improved esthetics were fabricated over external hexagonal connection UCLA abutments. SSALT was performed until specimen failure. Use level probability Weibull curve and reliability were calculated and plotted. Weibull modulus (m) and characteristic strength (η) were also calculated. Polarized light microscope and scanning electron microscope were used to characterize fractures.

RESULTS

Failures were dictated by material strength rather than fatigue damage accumulation. The probability of survival for loads reaching 100 and 150 N in 100,000 cycles was 92 and 61%, respectively. No cracks or fractures were identified in the veneered porcelain, whereas abutment fixation screw fracture was the chief failure mode.

CONCLUSION

Implant-supported PFM four-unit dentogingival prostheses with minimum metal framework dimensions presented favorable lifetime prediction under fatigue testing. Fractures were restricted to fixation screws.

CLINICAL SIGNIFICANCE

In-vitro fatigue testing and failure mode analyses evidenced favorable lifetime prediction for 4-unit implant-supported dentogingival prostheses with minimum metal frameworks. Abutment fixation screw fracture might be the most frequent clinical complication. Since this proof of concept has been tested in-vitro, further studies including different restorative materials, as well as long-term clinical trials are warranted.

In vitro assessment of the effect of luting agents, abutment height, and fatigue on the retention of zirconia crowns luted to titanium base implant abutments

STATEMENT OF PROBLEM

The bonding of implant-supported prostheses is determined by abutment material, convergence angle, height, surface treatment, and luting agents. However, studies evaluating the bonding of luting agents to titanium base abutments with different heights under fatigue conditions are scarce.

PURPOSE

The purpose of this in vitro study was to evaluate the retention of zirconia crowns bonded with different luting agents to titanium base abutments of different heights before and after fatigue testing.

MATERIAL AND METHODS

Zirconia crowns were designed, milled, and distributed into 4 experimental groups according to the luting agents (G-Multi Primer/G-Cem LinkForce [MP/GC] and Scotchbond Universal/RelyX Ultimate [SU/RU]) and titanium base abutment heights (2.5 mm and 4 mm) (n=10). Pull-out testing was performed in a universal testing machine at a crosshead speed of 1 mm/min until crown displacement. Fatigue testing was performed by an electric precision fatigue simulator (1×106 cycles; 100 N; and 15 Hz), followed by pull-out testing of fatigued specimens. Collected data were statistically evaluated by using a linear mixed model after post hoc comparisons by the least significant difference test (α=.05).

RESULTS

Luting agents, abutment heights, and fatigue influenced the bonding retention of zirconia crowns to titanium base abutments. SU/RU agents promoted higher pull-out compared with MP/GC for both abutment heights before and after fatigue. Higher abutment height increased pull-out regarding lower abutment height for SU/RU materials before and after fatigue testing. Although fatigue had no significant effect on the pull-out of MP/GC, lower bond retention was observed for SU/RU after fatigue, regardless of abutment height.

CONCLUSIONS

Luting agent composition and the interaction with abutment height and fatigue influenced the retention of zirconia crowns to titanium base abutments.

Probability of survival and failure mode of endodontically treated incisors without ferrule restored with CAD/CAM fiber-reinforced composite (FRC) post-cores

PURPOSE

This study evaluated the probability of survival and failure mode of endodontically treated incisors without ferrule restored with CAD/CAM FRC post-cores.

METHODS

Root canals of bovine incisors were treated, leaving post preparations of ∼10 mm. Teeth were allocated into three groups: (i) cast metal post-core, (ii) FRC prefabricated post with a direct resin core build-up, and (iii) CAD/CAM FRC post-core. Posts and zirconia crowns were cemented using resin cement. Specimens were subjected to step-stress accelerated-life fatigue testing in water. Use level probability Weibull curves, probability of survival for a mission of 100,000 cycles at 25, 50, and 100 N, Weibull modulus, and characteristic strength were calculated and plotted. Failure mode was examined under a stereomicroscope.

RESULTS

Restored incisors demonstrated high probability of survival (93-100%) for missions estimated at 25 and 50 N, irrespective of post-core foundation. At 100 N, incisors restored with metal posts presented significantly higher probability of survival (99%) relative to CAD/CAM posts (79%), whereas FRC groups demonstrated no significant difference. Weibull analysis indicated no significant difference on the Weibull modulus (m = 3.38-5.92). Incisors reconstructed with metal post-cores (431 N) presented significantly higher characteristic strength relative to prefabricated (200 N) and CAD/CAM (202 N) FRC post-cores. While post fracture was the chief failure mode for prefabricated and CAD/CAM FRC post-cores, post and/or root fracture were the main event for metal post-cores.

CONCLUSION

Endodontically treated incisors without ferrule restored with CAD/CAM FRC post-cores presented promising probability of survival for loads compatible with anterior masticatory forces and favorable failure modes.

Effects of local single dose administration of parathormone on the early stages of osseointegration: A pre-clinical study

The present study aimed to evaluate the effect of parathormone (PTH) administered directly to the implant's surface prior to insertion, using a large translational animal model. Sixty titanium implants were divided into four groups: (i) Collagen, control group, where implants were coated with Type-I Bovine-collagen, and three experimental groups, where implants received varying doses of PTH: (ii) 12.5, (iii) 25, and (iv) 50 μg, prior to placement. Fifteen female sheep (~2 years old, weighing ~65 kg) received four implants in an interpolated fashion in C3, C4 or C5 vertebral bodies. After 3-, 6- and 12-weeks, samples were harvested, histologically processed, qualitatively and quantitatively assessed for bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO). BIC yielded lower values at 6-weeks for 50 μg relative to the control group, with no significant differences, when compared to the 12.5- and 25-μg. No significant differences were detected at 6-weeks between collagen, 12.5- and 25-μg groups. At 3- and 12-weeks, no differences were detected for BIC among PTH groups. With respect to BAFO, no significant differences were observed between the control and experimental groups independent of PTH concentration and time in vivo. Qualitative observations at 3-weeks indicated the presence of a more mature bone near the implant's surface with the application of PTH, however, no significant differences in new bone formation or healing patterns were observed at 6- and 12-weeks. Single local application of different concentrations of PTH on titanium implant's surface did not influence the osseointegration at any time-point evaluation in low-density bone.

3D Printing Applications for Craniomaxillofacial Reconstruction: A Sweeping Review

The field of craniomaxillofacial (CMF) surgery is rich in pathological diversity and broad in the ages that it treats. Moreover, the CMF skeleton is a complex confluence of sensory organs and hard and soft tissue with load-bearing demands that can change within millimeters. Computer-aided design (CAD) and additive manufacturing (AM) create extraordinary opportunities to repair the infinite array of craniomaxillofacial defects that exist because of the aforementioned circumstances. 3D printed scaffolds have the potential to serve as a comparable if not superior alternative to the "gold standard" autologous graft. In vitro and in vivo studies continue to investigate the optimal 3D printed scaffold design and composition to foster bone regeneration that is suited to the unique biological and mechanical environment of each CMF defect. Furthermore, 3D printed fixation devices serve as a patient-specific alternative to those that are available off-the-shelf with an opportunity to reduce operative time and optimize fit. Similar benefits have been found to apply to 3D printed anatomical models and surgical guides for preoperative or intraoperative use. Creation and implementation of these devices requires extensive preclinical and clinical research, novel manufacturing capabilities, and strict regulatory oversight. Researchers, manufacturers, CMF surgeons, and the United States Food and Drug Administration (FDA) are working in tandem to further the development of such technology within their respective domains, all with a mutual goal to deliver safe, effective, cost-efficient, and patient-specific CMF care. This manuscript reviews FDA regulatory status, 3D printing techniques, biomaterials, and sterilization procedures suitable for 3D printed devices of the craniomaxillofacial skeleton. It also seeks to discuss recent clinical applications, economic feasibility, and future directions of this novel technology. By reviewing the current state of 3D printing in CMF surgery, we hope to gain a better understanding of its impact and in turn identify opportunities to further the development of patient-specific surgical care.

Hydrothermal aging affects the three-dimensional fit and fatigue lifetime of zirconia abutments

OBJECTIVE

Evaluate the effect of aging using two different methods on the three-dimensional fit of zirconia abutments at the implant-abutment connection and estimate the probability of survival of anterior crowns supported by straight and 17-degree angled abutments.

MATERIALS AND METHODS

Two different zirconia abutment designs, straight and 17-degree angled abutments (n = 63/group), were evaluated in the current study. The abutments were randomly allocated into three experimental groups according to laboratory aging condition (134°C, 2.2 bar, 20 h): (i) control, (ii) autoclave aging, and (iii) hydrothermal reactor aging. Crystalline content was determined by X-Ray diffraction (XRD) and Raman spectroscopy, and microstructure was analyzed using field-emission gun scanning electron microscope (FEG-SEM). Implant-abutment volume misfit was determined in the straight abutments by micro-computed tomography using the silicone replica technique. For fatigue testing, abutments were torqued to the implants and connected to standardized maxillary incisor zirconia crowns. The assemblies were subjected to step-stress accelerated life testing (SSALT) in water until fracture or suspension. The use level probability Weibull curves and probability of survival for a mission of 50,000 cycles at 50, 100, 150 and 200 N were calculated and plotted. Fractured samples were analyzed using a stereomicroscope and scanning electron microscope.

RESULTS

The crystalline spectra depicted a zirconia system primarily composed of the tetragonal phase. Laboratory aging yielded a 20%- and 37%-increase in the monoclinic content for abutments aged in autoclave and hydrothermal reactor relative to control, respectively. A fully crystalline matrix with a regular grain size was observed in the FEG-SEM for control abutments, with a considerable presence of intergranular defects. While autoclave aging triggered no significant alteration to the microstructure, defect population was reduced after hydrothermal reactor aging. Control abutments presented a significantly higher volume misfit (2.128 ± 0.54 mm3) relative to aged abutments using autoclave (1.244 ± 0.48 mm3) or hydrothermal reactor (1.441 ± 0.41 mm3). The beta (β) values indicated that failures were predominantly controlled by material strength rather than fatigue damage accumulation for all groups, except for straight control abutments. Irrespective of aging, the probability of survival of straight and angled zirconia abutments was up to 95% (95-100%) at 50 and 100 N. A 50N-increase in the load resulted in wider range of survival estimate, with straight autoclave abutments percentage significantly lower probability of survival (77%) than angled hydrothermal reactor abutments (99%). At 200N, angled hydrothermal reactor (97%) or autoclave (82%) aged abutments demonstrated the highest probability of survival, angled control (71%) and straight hydrothermal reactor (69%) abutments intermediate values, and straight autoclave (23%) and control (7%) abutments the lowest estimate. The failure mode predominantly involved abutment and/or abutment screw fracture for both straight and angled abutments.

CONCLUSIONS

Hydrothermal aging significantly influenced volume misfit, as well as the probability of survival of zirconia abutments at higher loads for both angled and straight abutments.

Análise da Retenção de Coroas CAD/CAM Cimentadas em Pilares do Tipo Ti-Base por Meio do Teste de Tração Pull-Out

Este estudo avaliou a resistência ao pull-out de coroas implantossuportadas confeccionadas em CAD/CAM e cimentadas em pilares de implante do tipo ti-base. Quarenta e cinco coroas foram fresadas para uso no pilar de implante ti-base (SIN Implante) e divididas (n15) de acordo com o material: Zircônia, Co-Cr ou Titânio. A cimentação foi realizada com cimento provisório Temp Bond NE (Kerr) ou cimento resinoso RelyX U200 (3M – Oral Care), sob carga de 50N por 10 minutos. As coroas foram submetidas ao   teste de tração em máquina de teste universal a 1,0 mm/min. Os testes foram feitos de acordo com a condição de cimentação: sem cimento (SC), cimentação provisória (CP, TempBond NE), sem cimento após a cimentação provisória (SCSP) e cimentação definitiva (CD, RelyX U200). Os resultados obtidos foram analisados por análise de variância e teste Tukey (p<0,05). Os valores médios de resistência (N) e desvio padrão foram: ZirSC (104,90/51,23) ZirCP (154,26/43,53) ZirSCCP (66,38/40,81) ZirCD (300,01/82,65) CoCrSC (72,38/43,07) CoCrCP (40,43/17,46) CoCrCD (900,35/133,63) TiSC (61,13/30,01) TiCP (158,85/22,18) TiSCCP (60,92/26,11) TiCD (566,66/75,82). Os materiais Co-Cr e titânio apresentaram maiores níveis de retenção ao pilar ti-base, na cimentação definitiva. O cimento RelyX U200 apresentou comportamento superior quando comparado ao cimento Temp Bond NE, independente do material da coroa.Palavras-chave: Implante Dentário. Cimentação. Coroa.

The Influence of Surface Treatment on Osseointegration of Endosteal Implants Presenting Decompressing Vertical Chambers: An In Vivo Study in Sheep

PURPOSE

To qualitatively and quantitatively evaluate histologic osseointegration parameters of implants designed with decompressing vertical chambers between the threads with two different surface treatments (TiO₂ blasting + maleic acid vs TiO₂ blasting + maleic + HCl) in a large translational animal model at 3 and 6 weeks in vivo.

MATERIALS AND METHODS

Nine female sheep were used, and 72 implants with trapezoidal threads and decompressing vertical chambers of 0.6 mm in diameter and 0.2 mm in depth were placed in the ilium crest. After 3 and 6 weeks, the animals were euthanized, and biomechanical and histomophometric analyses were performed.

RESULTS

Survey histologic evaluation indicated intimate contact between the bone and the implants independent of surface treatment at both times in vivo. Bone formation at both time points depicted an intramembranous-type healing pattern between the implant threads. The mean removal torque values for all groups showed a relative increase in removal torque from 3 to 6 weeks. In terms of bone area fraction occupancy analysis, significant differences were found at 6 weeks between surface treatments (P = .046), where the experimental surface yielded higher degrees of bone area fraction occupancy.

CONCLUSION

Conical implants with decompressing vertical chambers between threads presented similar osseointegration parameters regarding bone-toimplant contact and torque-out test values irrespective of surface treatment. However, shifting from a minimally rough to a moderately rough surface (experimental surface with supplemental acid-etching) resulted in significantly improved bone area fraction occupancy at 6 weeks.