Faculty Bibliography

Objectives. To test the hypothesis that there would be no differences in osseointegration by reducing the number of drills for site preparation relative to conventional drilling sequence. Methods. Seventy-two implants were bilaterally placed in the tibia of 18 beagle dogs and remained for 1, 3, and 5 weeks. Thirty-six implants were 3.75 mm in diameter and the other 36 were 4.2 mm. Half of the implants of each diameter were placed under a simplified technique (pilot drill + final diameter drill) and the other half were placed under conventional drilling where multiple drills of increasing diameter were utilized. After euthanisation, the bone-implant samples were processed and referred to histological analysis. Bone-to-implant contact (BIC) and bone-area-fraction occupancy (BAFO) were assessed. Statistical analyses were performed by GLM ANOVA at 95% level of significance considering implant diameter, time in vivo, and drilling procedure as independent variables and BIC and BAFO as the dependent variables. Results. Both techniques led to implant integration. No differences in BIC and BAFO were observed between drilling procedures as time elapsed in vivo. Conclusions. The simplified drilling protocol presented comparable osseointegration outcomes to the conventional protocol, which proved the initial hypothesis.

Lateral or vertical bone augmentation has always been a challenge, since the site is exposed to constant pressure from the soft tissue, and blood supply only exists from the donor site. Although, for such clinical cases, onlay grafting with autogenous bone is commonly selected, the invasiveness of the secondary surgical site and the relatively fast resorption rate have been reported as a drawback, which motivated the investigation of alternative approaches. This study evaluated the bone-forming capability of a novel nanoHA alloplast infused with collagen graft material made from biodegradable polylactic acid/polyglycolic acid versus a control graft material with the same synthesized alloplast without the nanoHA component and collagen infiltration. The status of newly formed bone and the resorption of the graft material were evaluated at 6 weeks in vivo histologically and three dimensionally by means of 3D microcomputed tomography. The histologic observation showed that newly formed bone ingrowth and internal resorption of the block were observed for the experimental blocks, whereas for the control blocks less bone ingrowth occurred along with lower resorption rate of the block material. The three-dimensional observation indicated that the experimental block maintained the external geometry, but at the same time successfully altered the graft material into bone. It is suggested that the combination of numerous factors contributed to the bone ingrowth and the novel development could be an alternative bone grafting choice.

Purpose: To investigate the reliability of titanium abutments veneered with indirect composites for implant-supported crowns and the possibility to trace back the fracture origin by qualitative fractographic analysis. Materials and Methods: Large base (LB) (6.4-mm diameter base, with a 4-mm high cone in the center for composite retention), small base (SB-4) (5.2-mm base, 4-mm high cone), and small base with cone shortened to 2 mm (SB-2) Ti abutments were used. Each abutment received incremental layers of indirect resin composite until completing the anatomy of a maxillary molar crown. Step-stress accelerated-life fatigue testing (n = 18 each) was performed in water. Weibull curves with use stress of 200 N for 50,000 and 100,000 cycles were calculated. Probability Weibull plots examined the differences between groups. Specimens were inspected in light-polarized and scanning electron microscopes for fractographic analysis. Results: Use level probability Weibull plots showed Beta values of 0.27 for LB, 0.32 for SB-4, and 0.26 for SB-2, indicating that failures were not influenced by fatigue and damage accumulation. The data replotted as Weibull distribution showed no significant difference in the characteristic strengths between LB (794 N) and SB-4 abutments (836 N), which were both significantly higher than SB-2 (601 N). Failure mode was cohesive within the composite for all groups. Fractographic markings showed that failures initiated at the indentation area and propagated toward the margins of cohesively failed composite. Conclusions: Reliability was not influenced by abutment design. Qualitative fractographic analysis of the failed indirect composite was feasible.

Nanostructure modification of dental implants has long been sought as a means to improve osseointegration through enhanced biomimicry of host structures. Several methods have been proposed and demonstrated for creating nanotopographic features; here we describe a nanoscale hydroxyapatite (HA)-coated implant surface and hypothesize that it will hasten osseointegration and improve its quality relative to that of non-coated implants. Twenty threaded titanium alloy implants, half prepared with a stable HA nanoparticle surface and half grit-blasted, acid-etched, and heat-treated (HT), were inserted into rabbit femurs. Pre-operatively, the implants were morphologically and topographically characterized. After 3 weeks of healing, the samples were retrieved for histomorphometry. The nanomechanical properties of the surrounding bone were evaluated by nanoindentation. While both implants revealed similar bone-to-implant contact, the nanoindentation demonstrated that the tissue quality was significantly enhanced around the HA-coated implants, validating the postulated hypothesis.

The primary stability of dental implants has been investigated before, but a study of the influence of implant shape, size and surface morphology (machined, acid etched or anodized), surgical technique (press-fit or undersized) and substrate (natural or simulated bone) on the primary stability of dental implants has not been reported. The present work intends to fill this gap. In this work, six different dental implants were inserted into and removed from synthetic and natural bone while measuring the torque. A total of 255 dental implants with three shapes, four sizes and three surface topographies were inserted into pig rib, PTFE and polyurethane. The implant sites were prepared using straight and tapered drills. The primary stability was estimated from the maximum insertion torque. Comparisons between samples were based on the maximum insertion torque (MIT), the maximum removal torque (MRT) and the torque ratio (TR=MRT/MIT). The insertion torque into pig ribs showed larger dispersion. All parameters (shape, size and surface morphology of the implant, surgical technique and substrate type) were found to have a significant influence on primary stability. The insertion of a tapered implant requires a higher torque than the insertion of a straight implant. Surface treatments improve the primary stability. The influence of the surgical technique is smaller than that of implant size and shape. The highest insertion torque was that of anodized tapered implants inserted into undersized sites. Finally, the primary stability of dental implants is highly dependent on implant design, surgical technique and substrate type.

Purpose: To simulate coefficient of thermal expansion (CTE)-generated stress fields in monolithic metal and ceramic crowns, and CTE mismatch stresses between metal, alumina, or zirconia cores and veneer layered crowns when cooled from high temperature processing. Materials and Methods: A 3D computer-aided design model of a mandibular first molar crown was generated. Tooth preparation comprised reduction of proximal walls by 1.5 mm and of occlusal surfaces by 2.0 mm. Crown systems were monolithic (all-porcelain, alumina, metal, or zirconia) or subdivided into a core (metallic, zirconia, or alumina) and a porcelain veneer layer. The model was thermally loaded from 900 degrees C to 25 degrees C. A finite element mesh of three nodes per edge and a first/last node interval ratio of 1 was used, resulting in approximately 60,000 elements for both solids. Regions and values of maximum principal stress at the core and veneer layers were determined through 3D graphs and software output. Results: The metal-porcelain and zirconia-porcelain systems showed compressive fields within the veneer cusp bulk, whereas alumina-porcelain presented tensile fields. At the core/veneer interface, compressive fields were observed for the metal-porcelain system, slightly tensile for the zirconia-porcelain, and higher tensile stress magnitudes for the alumina-porcelain. Increasingly compressive stresses were observed for the metal, alumina, zirconia, and all-porcelain monolithic systems. Conclusions: Variations in residual thermal stress levels were observed between bilayered and single-material systems due to the interaction between crown configuration and material properties.

OBJECTIVES: The aim of this study was to assess the effect of abutment's diameter shifting on reliability and stress distribution within the implant-abutment connection for internal and external hexagon implants. The postulated hypothesis was that platform-switched implants would result in increased stress concentration within the implant-abutment connection, leading to the systems' lower reliability. METHODS: Eighty-four implants were divided in four groups (n=21): REG-EH and SWT-EH (regular and switched-platform implants with external connection, respectively); REG-IH and SWT-IH (regular and switched-platform implants with internal connection, respectively). The corresponding abutments were screwed to the implants and standardized maxillary central incisor metal crowns were cemented and subjected to step-stress accelerated life testing. Use-level probability Weibull curves and reliability were calculated. Four finite element models reproducing the characteristics of specimens used in laboratory testing were created. The models were full constrained on the bottom and lateral surface of the cylinder of acrylic resin and one 30 degrees off-axis load (300N) was applied on the lingual side of the crown (close to the incisal edge) in order to evaluate the stress distribution (s(vM)) within the implant-abutment complex. RESULTS: The Beta values for groups SWT-EH (1.31), REG-EH (1.55), SWT-IH (1.83) and REG-IH (1.82) indicated that fatigue accelerated the failure of all groups. The higher levels of sigma(vM) within the implant-abutment connection observed for platform-switched implants (groups SWT-EH and SWT-IH) were in agreement with the lower reliability observed for the external hex implants, but not for the internal hex implants. The reliability 90% confidence intervals (50,000 cycles at 300N) were 0.53(0.33-0.70), 0.93(0.80-0.97), 0.99(0.93-0.99) and 0.99(0.99-1.00), for the SWT-EH, REG-EH, SWT-IH, and REH-IH, respectively. SIGNIFICANCE: The postulated hypothesis was partially accepted. The higher levels of stress observed within implant-abutment connection when reducing abutment diameter (cross-sectional area) resulted in lower reliability for external hex implants, but not for internal hex implants.

OBJECTIVE: The aim of this study was to evaluate the use of a collagen-based membrane compared with no treatment on guided bone regeneration by 3-dimensional computerized microtomography (muCT). STUDY DESIGN: Defects were created between the mesial and distal premolar roots of the second and third premolars (beagle dogs; n = 8). A collagen-based membrane (Vitala; Osteogenics Biomedical Inc., TX, USA) was placed in one of the defects (membrane group; n = 16), and the other was left untreated (no-membrane group; n = 16). Left and right sides provided healing samples for 2 and 16 weeks. Three-dimensional bone architecture was acquired by muCT and categorized as fully regenerated (F, bone height and width) or nonregenerated (N). RESULTS: Chi-square tests (95% level of significance) showed that tooth did not have an effect on outcome (P = .5). Significantly higher F outcomes were observed at 16 weeks than 2 weeks (P = .008) and in membrane group than in no-membrane group (P = .008). CONCLUSIONS: The collagen-based membrane influenced bone regeneration at the furcation.