Ausgabe 2/2013, Jahrgang 28 (15.03.2013)
Seite 327 - 328
Editorial: What Do You Know and How Confident Are You That You Know It?
Curtis, Donald A.
Seite 333 - 337
Thematic Abstract Review: Peri-implantitis: "Tsunami" or Marginal Problem?
Huynh-Ba, Guy
Purpose: To review the available literature on the costs and cost-effectiveness of dental implant-supported or -retained prostheses versus tooth-supported fixed partial denture restorations or mucosa-borne conventional complete or partial dentures.
Materials and Methods: A systematic literature review of the PubMed, EMBASE, and Cochrane Library databases was conducted, restricted to studies published in English between November 2000 and November 2010. The searches returned a total of 381 unique hits, and a total of 14 studies on the long-term costs or cost-effectiveness of dental implants were included in the final review. A true systemic review was complicated by the heterogeneity of the conducted studies.
Results: For single-tooth replacement, dental implants were generally either cost saving or cost-effective in comparison with tooth replacement using traditional fixed dental prostheses. For patients with mandibular edentulism, dental implants were associated with higher initial costs in comparison with conventional mucosa-borne dentures. However, the consensus among most studies was that, over the long term, dental implants represent a cost-effective treatment option. Additionally, patient acceptance, satisfaction, and willingness to pay for dental implants were high, particularly in elderly edentulous patients. A trend toward improved overall health and decreased health care costs was also reported.
Conclusions: For single-tooth replacement, a single implant was a cost-effective treatment option in comparison with a traditional three-unit fixed dental prosthesis. For the replacement of multiple teeth, dental implants (fixed or removable prostheses) were associated with higher initial costs but better improvements in oral health-related quality of life compared with other treatment options.
Purpose: To characterize the surface of implants from Brazilian companies by light interferometry and evaluate the level of control of the surface treatment process.
Materials and Methods: Oral implants from the five largest Brazilian companies were evaluated topographically. The surfaces of the implants were analyzed on the tops, valleys, and flanks of the threads, totaling nine measurements for each unit. The implants and results were separated in groups by their types of surface treatment and compared with wellknown international implants used as references.
Results: The implants examined presented a mean height deviation of less than 1 µm, which was considered minimally rough, except for the SIN-SW implant (1.01 µm) and the Vulcano Actives design (1.26 µm). The surface enlargement values varied considerably in relation to the reference implant, with lower values noted in the group of implants subjected to sandblasting and acid-etching and with higher values obtained in the group treated by acid-etching and anodizing. There were statistically significant differences between batches of implants from all companies assessed, indicative of a substantial variance in implant topography from one batch to another.
Conclusions: The low values of roughness found in the measurements and the differences between the values of the batches suggest that these companies should consider improving their surface treatments to achieve more uniform roughness.
Purpose: The relationships between three-dimensional (3D) bone-to-implant contact (BIC), cortical bone height, and trabecular bone density were measured by microcomputed tomography (micro-CT) to determine correlations with primary implant stability and peri-implant bone strain in an immediate loading scenario.
Materials and Methods: The 3D BIC ratios of artificial sawbones models with cellular foam of four densities representing trabecular bone (0.12, 0.16, 0.20, and 0.32 g/cm3) and with cortical shells of four thicknesses (0, 1, 2, and 3 mm) were evaluated by micro-CT. Statistical methods and a linear correlation model were employed to investigate the significance of the relationships between 3D BIC ratios and peak insertion torque, implant stability quotient, and Periotest value, as well as with peri-implant bone strain as measured with strain gauges.
Results: The 3D BIC ratio increased from 20.5 to 39.4 and from 27.4 to 45.2 as the height of cortical bone and the density of trabecular bone increased from 0 to 3 mm and from 0.12 to 0.32 g/cm3, respectively. A decrease in the 3D BIC ratio was associated with decreases in peri-implant bone strain and primary implant stability. In addition, there was a strong linear correlation between cortical BIC and primary implant stability (R2 > 0.8).
Conclusions: The use of an immediately loaded implant in cases with a low 3D BIC ratio (resulting from a thin cortical shell and/or low trabecular bone density) can diminish primary stability of an implant and lead to high strains in the peri-implant bone.
Purpose: One-piece dental implants are commonly used for the immediate restoration of missing teeth. In most cases, the clinician has to prepare the abutment intraorally to ensure a proper emergence profile and abutment angulation. However, this procedure might impair primary stability and thus potentially compromise osseointegration. The aim of this study was to determine the effect of abutment preparation on the primary stability of a one-piece implant system (UNO MIS).
Materials and Methods: Implant stability was assessed by resonance frequency analysis with a novel custom-made external fixation device, validated previously, developed specifically for resonance frequency measurements of this implant. Thirty 3 × 13-mm implants were inserted in porcine jawbone with insertion torque of 15 Ncm (group A, 15 implants) or 30 Ncm (group B, 15 implants). Abutments were prepared by reducing the facial aspect of the implant abutment with a high-speed dental turbine (400,000 rpm) equipped with a medium-roughness diamond bur. Implant stability quotients (ISQs) were measured before and after abutment preparation.
Results: Mean ISQs measured in group A and group B before abutment preparation were very similar (58.2 ± 1.4 and 57.4 ± 0.9, respectively; P > .05). Following abutment preparation, three implants in group A lost primary stability. The mean ISQ value in group A was reduced from 58.2 ± 1.4 to 54.9 ± 7.9 following abutment preparation (P < .05). The mean ISQ in group B was not affected by abutment preparation (57.4 ± 0.9 versus 57.3 ± 1.0; P > .05).
Conclusions: Abutment preparation of a one-piece dental implant inserted with low insertion torque might impair implant primary stability.
Purpose: A common problem with cemented crowns is inadequate retention at the crown-abutment interface. The aim of this study was to compare the retention of new laser-sintered cobalt-chromium alloy crowns to the retention of cobalt-chromium alloy crowns fabricated with a traditional casting technique with and without an alloy primer.
Materials and Methods: Twenty-four metallic crowns per casting technique were fabricated, and surface roughness values were recorded with a profilometer. Alloy primer was applied to half the specimens, and all crowns were luted with resin cement. After 24 hours, specimens were subjected to tensile force application with a universal testing machine. The effect of the cement amount was evaluated with an analytic balance. The results were compared using the Kruskal-Wallis multiple-comparison test. The Spearman correlation was used to determine correlations between crown retention and cement weight.
Results: The laser-sintered crowns (2.72 µm) were rougher than conventionally cast crowns. The mean load to failure values were as follows: 455.10 ± 192.69 Ncm for conventional crowns, 565.52 ± 112.87 Ncm for conventional crowns with alloy primer, 534.78 ± 130.15 Ncm for laser-sintered crowns, and 678.60 ± 212.83 Ncm for laser-sintered crowns with alloy primer. Laser-sintered crowns (10.10 ± 2.15 mg) showed a significant difference in terms of cement weight compared with cast crowns. In addition, negative correlations were found for retention and cement weight between all groups, except for the laser-sintered group without alloy primer.
Conclusions: Retentive forces were significantly higher for laser-sintered crowns than for conventionally cast crowns. An increase in the surface roughness and the application of alloy primers led to an increase in the adhesive bonding of resin cements to metal alloys. It was concluded that a reduction in cement weight improved retention.
Purpose: The mental foramen is an important landmark during surgical procedures such as osseous grafting or the placement of dental implants. To avoid injuring the mental nerve, it is important both to carefully assess the location of the mental foramen and to determine whether an anterior loop of the mental nerve or the incisive canal lies mesial to it. The objective of this study was to quantify the ability of cone beam computed tomography (CBCT) to measure the length of the mental nerve loop, the length and diameter of the incisive nerve canals, and the incisive canal path.
Materials and Methods: The study included 352 CBCT scans that had originally been used for preoperative planning of implant placement in the interforaminal region of the anterior mandible. For each scan, the length of the mental nerve loop and the length, diameter, and path of the incisive canal were determined. Mean values were compared between groups based on sex, right versus left side, and whether the patient was edentulous.
Results: The inferior alveolar nerve loop and incisive canal had a mean length of 2.40 ± 0.93 mm and 9.11 ± 3.00 mm, respectively. The mean incisive canal diameter was 1.48 ± 0.66 mm and showed a downward path in 51.3% of CBCT images and a linear or upward path in 38.29% and 10.41% of scans, respectively.
Conclusions: CBCT provides an accurate means to identify critical anatomical features in the anterior mandible during preoperative surgical planning.
Purpose: Subsinus bone regeneration procedures are reliable and known to be effective with the use of biomaterials alone. Nevertheless, many types of biomaterials are available, and the efficacy of each in terms of bone formation and resorption rate has rarely been compared. This study aimed to compare bone formation, resorption rate, osteoconductivity, and three-dimensional volume changes of three biomaterials often used for alveolar ridge augmentation.
Materials and Methods: Rabbits underwent bilateral sinus elevation using three different types of space fillers: bovine hydroxyapatite (BHA), beta-tricalcium phosphate (ß-TCP), or biphasic calcium phosphate (BCP). Animals were sacrificed at 1 week, 5 weeks, and 6 months. Samples were subjected to microcomputed tomography and histologic examination. Qualitative analysis was performed on nondecalcified sections, and quantitative histomorphometric analysis was conducted using scanning electron microscopy. Volume differences in augmented bone were calculated at different time points.
Results: All three particulated biomaterials promoted osteogenesis in this particular animal model. At 6 months, biomaterial resorption rates were significantly different across the three groups. The highest resorption rate was found with ß-TCP, in which only 6.7% of the baseline particle surface remained. At 6 months, bone was in close contact with the BHA particles, constituting a composite network; in contrast, BCP particles were often surrounded by soft tissue. Within each group, no significant differences in volume were found at the different time points.
Conclusions: Despite the limitations of the study, the three studied biomaterials proved to be effective in promoting osteogenesis. High resorption rates and complete replacement of the biomaterials by bone seemed to withstand intrasinusal pressure. Further investigations in humans should consider longer follow-up periods.
Purpose: The present in vitro study compared the stresses transmitted to canine abutments and implants placed in either the first premolar or second molar areas for retaining removable partial overdentures in models of mandibular bilateral distal-extension with the six anterior teeth remaining. The study also compared horizontal to vertical reciprocation of bracing arms when the implants were placed mesially.
Materials and Methods: Three overdenture models were used to represent two groups. In group 1, implants were placed bilaterally in the first premolar area (claspless denture); subgroup A dentures had horizontal reciprocal arms and subgroup B dentures had vertical reciprocal arms. In group 2, the implants were placed bilaterally in the second molar areas. Ball attachments were used to retain the partial overdenture. Eight strain gauges were cemented to the facial and lingual sides of each abutment (two canines and two implants). Static unilateral (right and left) and centric loads of 70 N were applied and the stresses were measured. All measurements were repeated five times for each loading impact, and means were calculated.
Results: Group 1A showed the highest stresses around the abutments, followed by group 1B, and the lowest stresses were found in group 2. Group 1 showed statistically significant increases in the stresses induced around the implants and the abutment teeth. For group 1, although there was no statistically significant difference between subgroups, subgroup B showed lower stresses around the abutments than subgroup A in both central and unilateral loading.
Conclusion: A distally placed implant can be considered a more satisfactory solution than a mesially placed implant for retention of a mandibular distal-extension removable partial overdenture.
Purpose: Reuse of metal impression copings may be desirable for both economic and environmental reasons. When impression copings are reused, it is important to be assured that they are as accurate as new ones. The purpose of the present in vitro study was to assess the effect of multiple use of impression copings on the accuracy of direct and indirect implant transfer techniques.
Materials and Methods: An acrylic resin cast with five internal connection implants was fabricated. Forty medium-consistency polyether impressions of the cast with direct and indirect techniques were made using four sets (five each) of impression copings (square or conical). Impressions were poured with type IV dental stone. Then, the copings were subjected to a cleaning and sterilization process. The process was repeated 10 times with the same copings. Positional accuracy of the implant replica heads in x-, y-, and z-axes and also angular displacement (Δθ) were assessed using a coordinate measuring machine. These measurements were compared with the measurements made on the resin cast (control). Analysis of covariance for repeated measurements was used for the statistical analysis (α =.05).
Results: There were no significant differences among the following measurements: Δx, Δz, Δθ, and Δr (P > .05) in both techniques. Only Δy for the open tray impression technique was influenced during repeated use of impression copings (P = .02).
Conclusions: Within the limitations of this study, it could be concluded that impression copings can be successfully used, cleaned and sterilized up to 10 times without compromising the impression accuracy.
Purpose: This study aimed to evaluate the role of the implant/abutment system on torque maintenance of titanium retention screws and the vertical misfit of screw-retained implant-supported crowns before and after mechanical cycling.
Materials and Methods: Three groups were studied: morse taper implants with conical abutments (MTC group), external-hexagon implants with conical abutments (EHC group), and external-hexagon implants with UCLA abutments (EHU group). Metallic crowns casted in cobalt-chromium alloy were used (n = 10). Retention screws received insertion torque and, after 3 minutes, initial detorque was measured. Crowns were retightened and submitted to cyclic loading testing under oblique loading (30 degrees) of 130 ± 10 N at 2 Hz of frequency, totaling 1 × 106 cycles. After cycling, final detorque was measured. Vertical misfit was measured using a stereomicroscope. Data were analyzed by analysis of variance, Tukey test, and Pearson correlation test (P < .05).
Results: All detorque values were lower than the insertion torque both before and after mechanical cycling. No statistically significant difference was observed among groups before mechanical cycling. After mechanical cycling, a statistically significantly lower loss of detorque was verified in the MTC group in comparison to the EHC group. Significantly lower vertical misfit values were noted after mechanical cycling but there was no difference among groups. There was no significant correlation between detorque values and vertical misfit.
Conclusions: All groups presented a significant decrease of torque before and after mechanical cycling. The morse taper connection promoted the highest torque maintenance. Mechanical cycling reduced the vertical misfit of all groups, although no significant correlation between vertical misfit and torque loss was found.
Purpose: The objective of this study was to analyze orthotropic bone formation and remodeling of three different dental implant surfaces with and without recombinant human bone morphogenetic protein 2 derived from Escherichia coli (ErhBMP-2) in a rabbit model.
Materials and Methods: Resorbable blasting media (RBM); sandblasted, large-grit, acid-etched (SLA); and magnesium-incorporated oxidized (MgO) implant surfaces were coated with ErhBMP-2 (1.5 mg/mL). The implants were placed into the proximal tibia in six New Zealand White rabbits. Each rabbit received six different implants (three coated with ErhBMP-2 in one tibia and three uncoated implants in the other tibia), and the sites were closed, submerging the implants. The animals received alizarin (at 2 weeks), calcein (at 4 weeks), and tetracycline (at 6 weeks) fluorescent bone markers, and were euthanized at 8 weeks for histomorphometric analysis.
Results: The amount of ErhBMP-2 coating was 9.6 ± 0.4 µg per MgO implant, 14.5 ± 0.6 µg per RBM implant, and 29.9 ± 3.8 µg per SLA implant. Clinical healing was uneventful. Mean bone-to-implant contact (± standard deviation) for the ErhBMP-2/RBM (35.4% ± 5.1%) and ErhBMP-2/MgO (33.4 % ± 13.2%) implants was significantly greater compared with RBM (23.6% ± 6.2%) and MgO (24.9% ± 2.7%) implants (P < .05). Considering the mean bone-to-implant contact in cortical bone, ErhBMP-2/SLA implants (32.9% ± 7.8%) showed lower bone-to-implant contact in cortical bone than all other implant variations (range, 39.9% ± 18.1% to 51.3% ± 9.2%; P < .05). There were no remarkable differences in new bone area, with minor differences between implants.
Conclusions: Within the limits of study, it was found that the absorbed ErhBMP-2 dose varied with implant surface characteristics, influencing local bone formation and remodeling.
Objective: To evaluate the effect of perforated scaffold retainers used in conjunction with dental implants and osteoinductive scaffolds to regenerate vertical supracrestal alveolar bone in an intraoral minipig model.
Materials and Methods: Three months after extraction of mandibular premolars and first molars from six adult minipigs, two titanium (Ti) custom implants were placed bilaterally in the edentulous mandibles for a total of four implants per animal. The upper 2.5 mm of the implant was left above bone level and covered with: (1) wide-neck healing caps; (2) perforated, overhanging custom scaffold retainers (umbrellas); or (3) scaffold retainers and demineralized minipig bone allograft (DBM) and nonglycosylated bone morphogenetic protein 2 (ng/rhBMP-2)-treated implants. All constructs were submerged beneath soft tissue flaps for 8 weeks. Two dental implant surfaces were compared: SLA and SLActive. Samples were retrieved after 8 weeks and analyzed by radiography, micro-computed tomography and histomorphometry.
Results: All implants were stable at the end of the experiment. Histomorphometry revealed that the use of the scaffoldretaining umbrellas led to increased, but not statistically significant, vertical bone regeneration as compared to the use of wide-neck healing caps (1.0 ± 0.4 mm vs 0.6 ± 0.3 mm). The combination of DBM and ng/rhBMP-2 released from the surface of the SLA implant resulted in the greatest amount of vertical bone regeneration (2.1 ± 0.2 mm). The bone-to-implant contact was similar for all groups. Mucosal dehiscence areas with healing cap or custom scaffold retainer exposures were reduced in the presence of ng/rhBMP-2.
Conclusions: The combined use of custom perforated Ti scaffold retainers, DBM, and ng/rhBMP-2 regenerated a substantial amount of vertical supracrestal alveolar bone around Ti implants in an intraoral minipig model.
Purpose: A bone defect model simulating an extraction socket with buccal dehiscence was designed to investigate the usefulness of a composite of beta-tricalcium phosphate (ß-TCP) and a collagen sponge, ß-TCP/ collagen (TCP/Col) for socket preservation.
Materials and Methods: Following the extraction of the maxillary second and third premolars of 13 beagle dogs, a bone defect with buccal dehiscence (5 × 3 × 7 mm) was prepared. The defects were filled with either TCP/Col, ß-TCP, collagen, or left intact (control) and evaluated at 4 and 8 weeks after surgery. A total of three micro-computed tomography (micro-CT) images were selected, and the area size occupied by the newly formed bone and residual TCP was measured. Newly formed bone and residual TCP in the bone defect site of the specimens was also measured and evaluated.
Results: No evidence of postoperative infection was found in all cases. At 4 weeks after surgery, the TCP granule was retained in the bone defects and active bone formation was observed in the TCP/Col group and the ß-TCP group, whereas in the collagen and the control groups, connective tissue grew into the defect. In the TCP/Col and ß-TCP groups, morphologically well-preserved alveolar ridges were observed; most TCP granules grafted in the defects were resorbed and only a few residuals were evident at 8 weeks after surgery.
Conclusions: These results exhibited that the TCP/Col composites could sufficiently maintain bone width and height for the preservation of the extraction socket with buccal dehiscence while preventing epithelial in-growth. In addition, TCP/Col in an easily handled spongeous form could provide a better intraoral manipulation capability than TCP granules alone and was considered to be suitable as a bone grafting material used for alveolar ridge preservation.
Purpose: The purpose of this study was to refine the Toronto Outcome Measure for Craniofacial Prosthetics (TOMCP), present evidence for its reliability and validity, and use the instrument to explore differences in quality of life between prostheses made with chlorinated polyethylene (CPE) (experimental) and silicone (control).
Materials and Methods: As part of a multicenter prospective controlled randomized double-blind singlecrossover clinical trial of the two materials, the TOMCP was administered at the start and end of two 4-month study arms, during which 42 patients wore prostheses made from one material then the other. Reliability was assessed at the crossover. To determine validity of the TOMCP, the Linear Analogue Self-Assessment (LASA-12) and the Short-Form 8 (SF-8) were also administered with the TOMCP. The TOMCP was reduced by removing items that were unreliable, had poorly distributed answers, showed increased internal consistency after their removal, or were too highly correlated with more than one other item. The tests of reliability and validity were then repeated. Finally, the reduced instrument was used to test for differences in quality of life between prostheses made of the two materials.
Results: The item reduction tactics pared the 52-item instrument down to 27 items. The correlations of both TOMCP versions with the LASA-12 and the SF-8 were found to be statistically significant, providing evidence of the validity of the TOMCP. The instrument revealed significantly better quality of life with silicone rather than CPE prostheses.
Conclusions: Both versions of the TOMCP were found to be reliable and valid. The instrument was able to show differences in quality of life between two materials.
Purpose: To assess the influence of fluoride on the adhesion of Streptococcus mutans to titanium using an experimental paradigm simulating 10 years of brushing.
Materials and Methods: Commercially pure titanium (cpTi) and titanium alloy (Ti-6Al-4V) disks (6 mm in diameter and 4 mm thick) were mirror-polished and randomly assigned to one of the following six groups (n = 6): immersion (I) or brushing (B) in deionized water (groups IW [control] and BW), fluoride-free toothpaste (groups IT and BT), or fluoridated toothpaste (groups IFT and BFT). Specimens subjected to immersion were statically submerged into the solutions without brushing. For the brushed specimens, a linear brushing machine with a soft-bristled toothbrush was used. The experiments lasted a total of 244 hours. Before and after treatment, the specimens were analyzed under an atomic force microscope to determine the mean roughness (Ra) and the mean of the maximum peak-tovalley heights of the profile (Rtm). The disks were contaminated with standard strains of S mutans in well plates with brain-heart infusion broth. Adhesion was analyzed based on the numbers of colony-forming units (CFU/mL) of adhered viable cells using scanning electronic microscopy. Differences in CFU/mL between the groups were analyzed by one-way analysis of variance.
Results: Immersion did not affect either surface. As suggested by Ra and Rtm, BW, BT, and BFT induced changes on the surface of cpTi, whereas only BT and BTF induced changes on the surface of Ti-6Al-4V. No significant differences were observed regarding CFU/mL among the cpTi or Ti-6Al-4V groups. S mutans adhesion was similar for all surfaces.
Conclusions: The changes in titanium induced by 10 years of simulated brushing with fluoride toothpaste did not increase the adhesion of S mutans.
Purpose: To investigate the adequacy of potential sites for insertion of orthodontic mini-implants (OMIs) in the anterior alveolar region (delimited by the first premolars) through a systematic review of studies that used computed tomography (CT) or cone beam CT (CBCT) to assess anatomical hard tissue parameters, such as bone thickness, available space, and bone density.
Materials and Methods: MEDLINE, EMBASE, and the Cochrane Database of Systematic Reviews were searched to identify all relevant papers published between 1980 and September 2011. An extensive search strategy was performed that included the key words "computerized (computed) tomography" and "mini-implants." Information was extracted from the eligible articles for three anatomical areas: maxillary anterior buccal, maxillary anterior palatal, and mandibular anterior buccal. Quantitative data obtained for each anatomical variable under study were evaluated qualitatively with a scoring system.
Results: Of the 790 articles identified by the search, 8 were eligible to be included in the study. The most favorable area for OMI insertion in the anterior maxilla (buccally and palatally) and mandible is between the canine and the first premolar. The best alternative area in the maxilla (buccally) and the mandible is between the lateral incisor and the canine, while in the maxillary palatal area it is between the central incisors or between the lateral incisor and the canine.
Conclusions: Although there is considerable heterogeneity among studies, there is a good level of agreement regarding the optimal site for OMI placement in the anterior region among investigations of anatomical hard tissue parameters based on CT or CBCT scans. In this context, the area between the lateral incisor and the first premolar is the most favorable. However, interroot distance seems to be a critical factor that should be evaluated carefully.
Purpose: To evaluate the marginal discrepancy of monolithic and veneered all-ceramic crown systems cemented on titanium (Ti) and zirconia implant abutments.
Material and Methods: Sixty customized implant abutments for a maxillary right central incisor were fabricated of Ti and zirconia (n = 30 of each) for an internal-connection implant system. All-ceramic crowns were fabricated using the following systems (n = 10 per group): monolithic with computer-aided design/computer-assisted manufacture (CAD/CAM) lithium disilicate (MLD), pressed lithium disilicate (PLD), or CAD yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP). The frameworks of the PLD and Y-TZP systems were manually veneered with a fluorapatite-based ceramic. The crowns were cemented to their implant abutments, and the absolute marginal discrepancy of the gap was measured before and after cementation. Data were analyzed statistically.
Results: Marginal discrepancies were significantly influenced by the crown system and by cementation, but the material did not significantly affect the results. Interaction terms were not significant. Y-TZP crowns on both Ti and zirconia abutments presented the smallest mean marginal discrepancies before (52.1 ± 17 µm and 56.2 ± 11 µm, respectively) and after cementation (98.7 ± 17 µm and 101.8 ± 16 µm, respectively). Before cementation, MLD crowns showed significantly larger mean marginal openings than PLD crowns on both Ti and zirconia abutments (75.2 ± 12 and 77.5 ± 13 µm for MLD, 52.1 ± 17 µm and 69.7 ± 8 µm for PLD, respectively). After cementation, both Ti and zirconia abutments with MLD crowns (113.5 ± 12 µm and 118.3 ± 14 µm, respectively) showed significantly larger values than with PLD crowns (98.7 ± 17 µm and 109.4 ± 9 µm, respectively).
Conclusions: Manually veneered Y-TZP crowns demonstrated more favorable marginal fit on both Ti and zirconia implant abutments before and after cementation compared to those of MLD and PLD.
Purpose: The purpose of this study was to determine the fatigue and fracture strength of zirconia implant abutments connected to titanium cores (ZrTi) and one-piece zirconia implant abutments (Zr).
Materials and Methods: Thirty-two implants were secured into epoxy resin blocks and connected with abutments. Eight specimens of each group (Zr with a diameter of 3.75 mm [Zr3.75] or 5.5 mm [Zr5.5] and ZrTi with a diameter of 3.75 mm [ZrTi3.75] or 5.5 mm [ZrTi5.5]) were thermally cycled from 5°C to 55°C and loaded with 100,000 cycles at 120 N at 30 degrees off-axis. All specimens were then tested for fracture resistance using a compressive load at 30 degrees off-axis.
Results: Abutment fracture or screw loosening was not observed during thermal cycling and cyclic loading. The median fracture resistance values and standard deviations were 526 N (± 32 N) for group Zr3.75, 1,241 N (± 269 N) for group ZrTi3.75, 1,894 N (± 137 N) for group Zr5.5, and 2,225 N (± 63 N) for group ZrTi5.5. Statistically significant differences in fracture strength were found between Zr and ZrTi for each implant diameter.
Conclusions: Zirconia implant abutments connected to titanium cores showed higher fracture strength compared to one-piece zirconia abutments. Hence, they might be preferable for clinical use.
Purpose: To evaluate the biologic width dimensions around implants with nonmatching implant-abutment diameters.
Materials and Methods: Five canines had their mandibular premolars and first molars removed bilaterally and replaced with 12 implants that had nonmatching implant-abutment diameters. On one side, six implants were placed in a submerged surgical approach, and the other side utilized a nonsubmerged approach. Two of the implants on each side were placed either 1 mm above, even with, or 1 mm below the alveolar crest. Two months later, gold crowns were attached, and the dogs were sacrificed 6 months postloading. Block sections were processed for histologic and histomorphometric analyses.
Results: The bone level, connective tissue length, epithelial dimension, and biologic width were not significantly different when the implants were initially placed in a submerged or nonsubmerged surgical approach. The bone level was significantly different around implants placed 1 mm above the crest compared to implants placed even with or 1 mm below the alveolar crest. The connective tissue dimension was not different for any implant level placement. The epithelial dimension and biologic width were significantly greater for implants placed 1 mm below the alveolar crest compared to implants placed even with or 1 mm above the alveolar crest. For five of six implant placements, connective tissue covered the implant/abutment interface.
Conclusions: This study reveals a fundamental change in the biologic response to implants with nonmatching implant-abutment diameters. Unlike implants with matching implant-abutment diameters, the connective tissue extended coronally past the interface (microgap). This morphologic tissue alteration represents a significant change in the biologic reaction to implant-abutment interfaces and suggests that marginal inflammation is eliminated or greatly reduced in these implant designs.
Purpose: The aim of this systematic review was to evaluate the long-term clinical performance of one-piece implants.
Materials and Methods: An electronic MEDLINE search complemented by a manual search was conducted to identify randomized and prospective cohort studies on one-piece implants. Additional inclusion criteria were: a mean follow-up period of at least 5 years and an inception cohort where more than 80% of the enrolled patients remained in the study at the 5- or 10-year observation point.
Results: Sixty-six studies from an initial yield of 597 titles were selected, and the data were extracted. Of the full-text articles examined, 46 were excluded from the final analysis. A total of 20 articles were finally selected. All studies were published between 1995 and 2011. Two different study designs were included: 4 randomized controlled trials and 16 prospective cohort studies. The studies were analyzed and classified according to the follow-up period, the type of implant surface, the type of edentulism, the type of loading protocol, and the type of setting. The meta-analysis of the included studies showed an implant survival rate for one-piece, one-part implants of 96.79% (95% CI: 94.04% to 98.71%) after 5 years. In one-piece, two-part implants, the survival rate was slightly higher: 98.16% (95% CI: 96.48% to 99.31%) after 5 years and 96.83% (95% CI: 93.12% to 99.24%) after 10 years.
Conclusion: Within the limits of this systematic review, it can be concluded that high longterm survival rates can be observed with one-piece implants. Further randomized clinical trials are needed to provide more information about the outcome of different variables associated with one-piece implants.
Purpose: To determine the optimal dilation pixel size distance from the mini-implant interface needed to compensate for the metal artifact on micro-computed tomography (micro-CT) for bone morphometric analysis.
Materials and Methods: A total of 72 self-drilling mini-implants were placed into the buccal alveolar bone of six male beagle dogs. After 12 weeks of orthodontic loading, specimens were harvested and scanned with micro-CT (Skyscan 1076) at a resolution of 9 µm. Using the reload plug-in and dilation procedure of CTAn, the percentage of bone-implant contact (BIC) and bone volume density (BV/TV, bone volume/total volume), respectively, were measured from one to seven pixels from the metal implant surface. Each pixel size of dilation (PSD) were compared with that of a ground histologic section, and the optimal PSD for bone morphometric analysis using micro-CT was determined.
Results: BIC values from micro-CT analysis decreased when the PSD increased (P < .05). BIC from micro-CT showed the highest correlation coefficient with BIC from histologic slides when the PSD was 5 to 7 (P < .05), whereas BV/TV from micro-CT showed a very high correlation with BV/TV from histologic slides in all ranges (P < .0001).
Conclusion: To measure BIC and BV/TV using micro-CT, at least 5 PSD from the metal implant surface is needed.
Purpose: The purpose of this study was to evaluate changes in alveolar bone height after direct sinus elevation and simultaneous implant placement in the posterior edentulous maxilla.
Materials and Methods: A prospective clinical study was conducted of patients undergoing sinus elevation for implant placement in the posterior maxilla to replace missing teeth. Residual alveolar bone height was between 4 and 7.5 mm. Lateral osteotomy of the maxillary sinus, followed by simultaneous implant placement without bone grafting, was performed under local anesthesia. Prosthetic restoration was completed 9 months later. The changes in alveolar bone height at the sinus floor were assessed radiographically after 1 week and 6, 9, 18, and 28 months after implant placement. Probing depths, implant mobility, and crestal bone loss were assessed at the same intervals.
Results: Twenty-eight patients (17 women and 11 men) participated in the study. Forty-five implants were placed and followed after prosthetic rehabilitation. At 18 months after loading of the implants, alveolar bone height in the area of sinus elevation ranged from 7.40 to 11.55 mm. Increases in alveolar bone height at the sinus floor ranged from 2.05 to 5.40 mm at a minimum of 18 months after loading, a statistically significant gain. Crestal bone loss and changes in probing depths were not significant in any patients, and all implants remained clinically stable. The implant success rate was 100% without any complications after 18 to 28 months of follow-up.
Conclusion: Placement of endosseous implants in the atrophic posterior maxilla in conjunction with sinus elevation without bone grafting resulted in a significant amount of bone formation around the implants at the sinus floor, resulting in successful restorations and eliminating the need for bone grafting.
Purpose: To investigate the change in 89 patients' pain and anxiety following implant surgery and to evaluate the correlation among anxiety, pain, and influencing factors.
Materials and Methods: Eighty-nine patients were included in this study. Subjective factors influencing pain perception included anxiety from the overall dental treatment (scored on the Dental Anxiety Scale [DAS]) and anxiety relative to the time from implant surgery. Objective factors were sex, age, and implant location and number. Patients completed questionnaires just before surgery (T0), immediately after surgery (T1), 1 day after surgery (T2), and 1 week after surgery (T3).
Results: The average pain perception was highest at T2, followed by T1 and T3. Pain perception at T1 was significantly higher in women and for a larger number of implant placements. Pain perception at T2 was significantly higher in women and when DAS and anxiety scores were high. The pain score at T3 was significantly higher in women and when anxiety scores were high. The results from multiple linear regression analysis showed that pain perception was significantly higher at T1 in women and for a larger number of implant placements, and at T3 when the dental anxiety score was high.
Conclusion: Within the limitations of this study, a patient's anxiety represented by dental anxiety score and state of anxiety scores affected pain intensity 1 day after implant surgery. Sex and the number of implants affected pain intensity immediately after implant surgery. Patients who have high pain intensity 1 week after implant surgery showed high pain intensity at each time point.
Purpose: This study compared the accuracy of cone beam computed tomography (CBCT) and medicalgrade CT in the context of evaluating the diagnostic value and accuracy of fiducial marker localization for reference marker-based guided surgery systems.
Materials and Methods: Cadaver mandibles with attached radiopaque gutta-percha markers, as well as glass balls and composite cylinders of known dimensions, were measured manually with a highly accurate digital caliper. The objects were then scanned using a medical-grade CT scanner (Philips Brilliance 64) and five different CBCT scanners (Sirona Galileos, Morita 3D Accuitomo 80, Vatech PaX-Reve3D, 3M Imtech Iluma, and Planmeca ProMax 3D). The data were then imported into commercially available software, and measurements were made of the scanned markers and objects. CT and CBCT measurements were compared to each other and to the caliper measurements.
Results: The difference between the CBCT measurements and the caliper measurements was larger than the difference between the CT measurements and the caliper measurements. Measurements of the cadaver mandible and the geometric reference markers were highly accurate with CT. The average absolute errors of the human mandible measurements were 0.03 mm for CT and 0.23 mm for CBCT. The measurement errors of the geometric objects based on CT ranged between 0.00 and 0.12 mm, compared to an error range between 0.00 and 2.17 mm with the CBCT scanners.
Conclusions: CT provided the most accurate images in this study, closely followed by one CBCT of the five tested. Although there were differences in the distance measurements of the hard tissue of the human mandible between CT and CBCT, these differences may not be of clinical significance for most diagnostic purposes. The fiducial marker localization error caused by some CBCT scanners may be a problem for guided surgery systems.
Purpose: Sinus elevation via the lateral approach for implant rehabilitation of atrophic posterior maxillae is considered a safe and predictable therapy. Several xenogeneic biomaterials of different biologic origin have been used as valid and predictable alternatives to autogenous bone. This multicenter randomized controlled double-blind prospective clinical trial aimed to compare histomorphometrically two xenogeneic grafting materials used for sinus elevation with simultaneous implant placement.
Materials and Methods: Seven private practices in Italy were involved. Patients presenting at least one site with a residual bone crest height between 2 and 4 mm were treated. Control sites were grafted with 100% deproteinated particulated bovine bone (DPBB), while test sites were grafted with prehydrated corticocancellous porcine bone (PCPB). Root-form implants were placed simultaneously. Insertion torque and clinical stability were assessed and recorded. At 6 months, a biopsy specimen was harvested from each site, and histomorphometric analyses were performed.
Results: Thirty-seven patients received 42 sinus elevations (24 test and 18 control). Eighty-two implants with adequate primary stability were placed. Fifty-five implants were placed in residual bone crests greater than 2 mm but less than 4 mm (average 2.7 mm) and achieved an average insertion torque of 22.8 ± 11.3 N/cm. Nineteen implants were placed in ridges greater than 3 mm but less than 5 mm, and eight were placed in ridges with more than 5 mm remaining. After 6 months, three implants had failed to integrate, leading to a survival rate of 96.34%. Forty-two specimens were analyzed histomorphometrically. No significant differences in total bone volume (PCPB 37.43%, DPBB 37.52%) or residual grafting material (PCPB 13.55%, DPBB 16.44%) were detected.
Conclusions: In this study, PCPB compared well with DPBB as a grafting material for lateral sinus elevation.
Purpose: Scalloped implants were developed to better maintain marginal bone. Therefore, this study evaluated marginal bone levels (MBLs) and soft tissue around single implants with scalloped necks in the esthetic zone prospectively over a 3-year period. MBLs were compared to those of conventional flat-platform implants at 1 and 3 years.
Materials and Methods: Patients received anterior single-tooth implants and were divided into two groups; the test group included implants with a scalloped neck design and the control group included conventional rough-surface implants with external hex. MBLs were compared radiographically at 1 and 3 years after crown insertion. For the test group, soft and hard tissue assessments were made at six different time points, beginning at abutment connection. Mesial and distal interproximal papillae and probing depths were assessed clinically. Data were analyzed with the Student t test and repeatedmeasures analysis of variance on ranks (P < .05).
Results: Twenty-four patients (17 men, 7 women) took part; each group included 12 implants. The test group had significantly more marginal bone resorption than the control group at each time point (P < .001). With respect to changes in MBL values over time, a significant difference was detected between groups mesially (P < .001) but not distally. Statistical analyses demonstrated obvious significant increases with time (P < .001) in bone resorption and mesial papilla index. A significant increase over time in probing depths was demonstrated distally (P = .003) but not mesially.
Conclusions: The scalloped implant did not stabilize interproximal bone remodeling and caused more bone loss than conventional implants. Soft tissue levels were not maintained around the scalloped implants.
Purpose: To evaluate the clinical outcome of a novel open-tray impression technique for fabrication of a provisional prosthesis supported by immediately loaded implants in a completely edentulous arch.
Materials and Methods: An open-tray impression technique was evaluated in this retrospective study that included patients treated between March 2006 and October 2009. Preoperatively, a diagnostic prosthesis was delivered, and a novel open tray was fabricated based on this prosthesis. After implant placement, the impression and interocclusal record were taken simultaneously using the novel open tray. Laboratoryfabricated, screw-retained, all-acrylic resin provisional restorations were delivered on the same day of surgery. The prosthesis was assessed from the day of surgery until replacement with a definitive prosthesis.
Results: The study included 21 patients (mean age, 64.5 years) and a total of 125 implants. Of these, 104 implants were immediately loaded. In all patients, well-fitting provisional restorations supported by a minimum of four implants were delivered. Fracture of the first molar cusp was observed in one case after 30 days. However, there was no extensive fracture in the framework or functional disorder of the prosthesis. No implant failed during the follow-up after implant surgery.
Conclusion: This protocol enabled fabrication of a well-fitting acrylic resin provisional prosthesis supported by immediately loaded implants because the impression was taken while in centric occlusion and an occlusion identical to the diagnostic prosthesis could be reconstructed.
Purpose: Recent clinical studies have shown that implant placement is highly predictable with computergenerated surgical guides; however, the reliability of these guides has not been compared to that of conventional guides clinically. This study aimed to compare the accuracy of reproducing planned implant positions with computer-generated and conventional surgical guides using a split-mouth design.
Materials and Methods: Ten patients received two implants each in symmetric locations. All implants were planned virtually using a software program and information from cone beam computed tomographic scans taken with scan appliances in place. Patients were randomly selected for computer-aided design/computer-assisted manufacture (CAD/CAM)-guided implant placement on their right or left side. Conventional guides were used on the contralateral side. Patients underwent operative cone beam computed tomography postoperatively. Planned and actual implant positions were compared using three-dimensional analyses capable of measuring volume overlap as well as differences in angles and coronal and apical positions. Results were compared using a mixed-model repeated-measures analysis of variance and were further analyzed using a Bartlett test for unequal variance (α = .05).
Results: Implants placed with CAD/CAM guides were closer to the planned positions in all eight categories examined. However, statistically significant differences were shown only for coronal horizontal distances. It was also shown that CAD/CAM guides had less variability than conventional guides, which was statistically significant for apical distance.
Conclusion: Implants placed using CAD/CAM surgical guides provided greater accuracy in a lateral direction than conventional guides. In addition, CAD/CAM guides were more consistent in their deviation from the planned locations than conventional guides.
Purpose: To evaluate biologic and prosthetic outcomes of titanium-zirconia alloy implants supporting fixed prostheses.
Materials and Methods: A total of 52 titanium-zirconia alloy implants were placed in 23 consecutive patients with partial edentulism. All implants were subjected to an early loading protocol by means of single-unit or up-to-four-unit fixed partial prostheses and observed between 7 and 24 months. The radiographic marginal bone loss and peri-implant soft tissue scores (Plaque Index, Bleeding Index, and Calculus Index) were recorded. In addition, prosthetic complications were recorded during the period of the study.
Results: Early or late implant failures were not observed, resulting in 100% implant survival and success of the implants. No prosthetic complications were observed. The mean (standard deviation) of marginal bone loss for 52 implants was 0.315 mm (0.24 mm). There were no signs of excessive bone loss with or without swelling or suppuration of the peri-implant soft tissue, and the soft tissue scores indicated good soft tissue integration.
Conclusions: Titanium-zirconia alloy implants supporting fixed prostheses showed optimum radiographic, clinical, and prosthetic outcomes in an up-to-24-month assessment period.
Purpose: To compare three different lateral sinus elevation procedures concerning new bone formation by using micro-computed tomography (micro-CT) of retrieved implants.
Materials and Methods: Twenty-four consecutive partially dentate patients with a mean age of 64 years were included in the study and provided with 30 sinus elevation procedures. Three procedures for lateral sinus elevation were used: lateral sinus elevation with replacement of bone window and without bone graft (BW), lateral sinus elevation and covering osteotomy site with a collagen membrane and without bone graft (CM), and lateral sinus elevation with autogenous bone graft (ABG). Experimental implants were retrieved after 7 months of healing and analyzed by micro-CT.
Results: One implant was found not to be integrated at the time of implant retrieval. This implant belonged to group CM and was excluded when calculating bone-to-implant contact (BIC) and intrasinus bone levels. The integrity of the lateral sinus bony wall was determined at the time of implant removal. In group ABG, all lateral sinus walls were ossified. In group BW, one lateral sinus wall was not completely ossified and in group CM, two lateral sinus walls. There were no statistical differences in %BIC between the groups: 93.5% (BW), 92.0% (CM) and 93.5% (ABG). Additionally, no statistical differences were found in apical intrasinus bone levels between the groups. When surfaces were compared within the same implant, a statistical difference was found between the apicobuccal distance and the apicolingual distance. The mean apicobuccal distances/apicolingual distances were 0.6 mm/1.2 mm for the BW group, 0.5 mm/0.8 mm for the CM group, and 0.6 mm/0.8 mm for the ABG group (P = .003).
Conclusions: All three procedures were statistically equal when new bone formation was compared. Most of the examined implants' apices were not covered with bone at the time of retrieval.
Purpose: The purpose of the present study was to evaluate the thickness and anatomic characteristics of the sinus membrane using cone beam computed tomography (CBCT) in patients evaluated for implant surgery in the posterior maxilla.
Materials and Methods: The study included 131 consecutive patients referred for dental implant placement in the posterior maxilla. A total of 138 CBCT images was obtained using fields of view of 4 × 4 cm, 6 × 6 cm, or 8 × 8 cm. Reformatted sagittal CBCT slices were analyzed with regard to the thickness and characteristics of the sinus membrane at single-tooth gaps in the posterior maxilla. Factors that might influence the dimensions of the sinus membrane, such as age, sex, endodontic status, and the season, were analyzed.
Results: The mean thickness of the maxillary sinus mucosa varied between 2.1 and 2.69 mm in the three locations analyzed. Fewer than half of the evaluated sinuses exhibited a healthy mucosa (49 of 138, or 35.51%). Most of the pathologic findings were flat, shallow thickenings (63 of 138, or 45.65%). Sex did not influence the thickness of the sinus membrane at the root tips of the premolars or at single-tooth gaps, but there was a statistically significant correlation in the region of the maxillary molars. No other evaluated factors had a statistically significant effect on the dimensions of the antral mucosa.
Conclusions: In the present study, sex was the only factor influencing the dimension of the sinus membrane, whereas patient age, season, and the endodontic status of neighboring teeth had no significant effect on the thickness of the antral mucosa. Future studies should address which types of mucosal thickening require interdisciplinary therapy.
Purpose: The aim of this study was to evaluate the efficacy and morbidity of two periodontal releasing incision techniques in vertical ridge augmentation.
Materials and Methods: Twenty-three vertical and horizontal defects (Seibert Class III) were selected to compare the double-flap incision (DFI) to the conventional periosteal releasing incision (PRI). An incision technique was randomly assigned for flap advancement. The amount of flap advancement, the incidence of postsurgical complications, and the level of patient discomfort were compared. Flap advancement was measured with a UNC-15 probe as the difference between the initial elevated flap and the final advanced flap. Postsurgical complications including premature membrane exposure, infection, paresthesia, and continuous discomfort were noted at follow-up visits. A visual analog scale (VAS) was used to quantify the amount of pain, swelling, and bleeding in the patients.
Results: An average of 9.64 ± 0.92 mm flap advancement was accomplished for DFI, whereas PRI advancement averaged 7.13 ± 1.45 mm (P < .001). Premature membrane exposures occurred in two sites in the PRI group and one site in the DFI group. Paresthesia, infection, and continuous discomfort were noted in one site each in the PRI group. The difference between groups in the incidence of postoperative complications (PRI, 5; DFI, 1) was not significant (P < .082). The mean pain, swelling, and bleeding scores for DFI (1.55 ± 1.21, 1.91 ± 0.94, and 0.40 ± 0.12, respectively) were lower than those of the PRI group (3.75 ± 2.63, 3.25 ± 1.29, and 1.16 ± 0.34, respectively) (P = .019, P = .010, and P = .061, respectively).
Conclusions: Flap advancement was facilitated and morbidity was decreased in the DFI group. The technique may have potential to serve as an alternative to PRI to overcome some of the latter's limitations.
Purpose: To evaluate the retention of bone around implants placed immediately following tooth extraction and used to support dental prostheses.
Materials and Methods: Patients from a previous study of implants placed immediately following tooth extraction were recalled to the original practice to obtain dental radiographs, which were then used to compare bone levels after 1 to 22 years of clinical function supporting dental prostheses. All radiographs were evaluated by measuring the bone within the implant threads. Implant bone maintenance was correlated with smoking history, type of implant surface, antibiotics used in conjunction with surgery, bisphosphonate use, presence of splinted restorations, anatomical location (mandible or maxilla and anterior or posterior), sex, and past periodontal disease status. Statistical analysis was performed using the Mann-Whitney test for statistical significance of differences in mean bone loss.
Results: A total of 1,187 implants were identified, with mean bone loss of 0.52 ± 0.79 mm. Overall bone loss was less than 1.5 mm in 90% of the implants studied. Bone loss was greater in women (0.61 ± 0.91 mm vs 0.44 ± 0.69 mm in men; P = .002). There was a correlation between bone loss and patient age at the time of tooth loss, with patients below the age of 50 experiencing significantly more loss (mean loss, 0.76 ± 1.07 mm at age < 50 and 0.46 ± 0.71 mm at age > 50; P = .008). Other significant differences were seen with implant surface (machined surface, 0.57 ± 0.77 mm; roughened surface, 0.44 ± 0.84 mm; P = .0049), maxilla vs mandible in molar areas (maxilla, 0.68 ± 0.83 mm; mandible, 0.43 ± 0.80 mm; P = .0001), and platform width (regular, 0.46 ± 0.77; wide, 0.83 ± 0.94 mm; P <= .0001). None of the other factors demonstrated significant differences.
Conclusions: Bone loss of 1.5 mm or less was observed in 90% of the patients followed. Bone loss was correlated with age, sex, implant surface, anatomical location, and platform width. There was no statistical correlation between bone loss and any other factors evaluated.
Purpose: The biomechanical performance of a novel engineered porous-structure implant (EPSI) with various porosities and a conventional solid-structure implant (CSSI) was investigated and compared.
Materials and Methods: The three-dimensional finite element method was applied to titanium dental implant models placed in a block of bone that included both cortical and medullary bone. Five different pore sizes and porosities of the EPSI (58% porosity [PSI-58], 62% porosity [PSI-62], 71% porosity [PSI-71], 75% porosity [PSI-75], and 79% porosity [PSI-79]), were compared with the CSSI. Equivalent von Mises (EQV) stress, strain energy density, and displacement were examined for each implant design.
Results: The maximum EQV stresses exhibited in cortical bone of the EPSI models were lower than those of the CSSI model. Higher EPSI porosity tended to increase the EQV stress. The EPSI appeared to share the load with the cortical bone, as evidenced by lower strain energy density in the cortical bone of EPSI models. High values for displacement were observed at the coronal part of the implant in all models. Slight differences in maximum displacement values were seen between EPSI and CSSI models.
Conclusion: The EPSI effectively reduced the maximum EQV stress in the cortical bone and enhanced the load-sharing capacity. A significant amount of energy was absorbed by the implant instead of being transferred to the surrounding cortical bone. Varying the porosity of an implant had less effect on implant displacement.
Purpose: To compare biomechanical outcomes of immediately and conventionally loaded bar-retained implant-supported maxillary overdentures using finite element stress analysis.
Materials and Methods: Finite element models were created to replicate the spatial positioning of four 4.1 × 12-mm implants in the completely edentulous maxillae of four cadavers to support bar-retained overdentures with 7-mm distalextension cantilevers. To simulate the bone-implant interface of immediately loaded implants, a contact situation was defined at the interface; conventional loading was simulated by "bonding" the implants to the surrounding bone. The prostheses were loaded with 100 N in the projected molar regions bilaterally, and strain magnitudes were measured at the buccal aspect of bone.
Results: The amplitude of axial and lateral strains, the overall strain magnitudes, and the strain magnitudes around anterior and posterior implants in the immediate loading group were comparable to those seen in the conventional loading group, suggesting that the loading regimens created similar stress/strain fields (P > .05).
Conclusions: Conventional and immediate loading of maxillary implants supporting bar-retained overdentures resulted in similar bone strains.
Purpose: Bone stress and interfacial sliding at the bone-implant interface (BII) were analyzed in zirconia and titanium implants with various thread designs and interface conditions (bonded BII and contact BIIs with different frictional coefficients) for both conventional and immediately loaded treatments.
Materials and Methods: A total of 18 finite element models comprising two implant materials (zirconia and titanium), three thread designs (different shapes and pitches), and three interface conditions (bonded and contact BIIs) were analyzed to assess the effects on bone stresses and on sliding at the BII. The material properties of the bone model were anisotropic, and a lateral force of 130 N was applied as the loading condition.
Results: In the immediately loaded implant, the stress was highly concentrated at one site of the periimplant bone. The peak bone stress was more than 20% lower in zirconia implants than in titanium implants for a bonded BII and 14% to 20% lower for a contact BII. The bone stresses did not differ significantly between implants with V-shaped threads and square threads. However, sliding at the BII was more than 25% lower with square-thread implants than with V-shaped-thread implants for titanium implants and 36% lower for zirconia implants. Reducing the thread size and pitch in cortical bone (via two V-shaped threads with different pitches) decreased the bone stress by 13%. Increasing the frictional coefficient reduced sliding at the BII in both zirconia and titanium implants.
Conclusions: As an implant material, zirconia can reduce the bone stress in the crestal cortical region. Bone stress and sliding at the BII are heavily dependent on the thread design and the frictional coefficient at the BII of immediately loaded implants.
Purpose: Misfit in the conical implant-abutment interface plays an important role on the mechanical behavior of the implant when masticatory forces are applied. The origin of the misfit adopted in this work is a conical angle difference between implant and abutment, which can be due to a combination of design decisions and manufacturing tolerances. The goal of this work was to investigate the effects of the implant-abutment conical angle difference in the following mechanical features: interfacial microgap, preload loss on the bolt, stress level in the bone, and abutment removal force and/or torque.
Materials and Methods: A simplified three-dimensional nonlinear monoparametric finite element model of an OsseoSpeed TX 4.5 S 9-mm implant (Astra Tech) with a tapered implant-abutment interface was built to evaluate the variability of the mechanical features cited above with the conical angle difference, keeping constant the overall geometry, load and boundary conditions, material properties, frictional behavior, and mesh structure.
Results: As the conical angle difference increased, the following effects were observed: the microgap decreased and remained almost constant for values over a given positive angle difference, the stress level in the bone increased sensitively, the removal force and/or torque needed to separate the abutment from the implant varied slightly, and the bolt preload loss increased.
Conclusions: In light of the results provided, the conical angle difference in the implant-abutment interface had a significant influence on the overall mechanical behavior of the implant. Among the four mechanical features considered, the interfacial microgap and the bone stress were demonstrated to be the most sensitive to the conical angle difference, and therefore the most relevant when selecting an optimum value in the design process of a conical interface.
Purpose: The aim of this study was to compare the influence of abutment screw preload on the marginal bone stress around a conventional external-hex implant system and one with a new implant/abutment joint design.
Materials and Methods: Two implant/bone models, each consisting of three parts and fabricated of titanium and bone (cortical), were built and arranged with computer-aided design software. The first model represented an external-hex implant system, while the second had a tapered extension over the external hex, 1.5 mm high, so that the apical extension of the abutment screw in the assembly did not go beyond the lower level of the implant shoulder. Meshing and generation of boundary conditions, loads, and interactions were performed for the two models. All parts were meshed independent of each other. The sole load applied on the model was a torque of 32 Ncm on the abutment screw about its axis of rotation.
Results: The first model showed deformation of the implant collar, and the resulting von Mises stress was 60 MPa in the marginal bone. In contrast, no deformation was observed in the second model.
Conclusions: The new implant/abutment joint eliminated the deformation at the implant collar area caused by the application of tightening torque and thus eliminated the resulting stresses in the marginal bone.
Purpose: To identify from a biomechanical point of view the optimal parameters for an expandable implant in the osteoporotic mandible, a three-dimensional finite element model (FEM) of an expandable implant was created with variations in expansion angle and expansion length.
Material and Methods: FEMs of osteoporotic posterior mandibular segments with an expandable implant were created. An axial load of 100 N and a buccolingual load of 30 N were applied to the implant. The expansion angle ranged from 0 to 4 degrees, and the expansion length ratio ranged from 1/6 to 5/6. The maximum equivalent stress (max EQV stress) in jawbone and the implant-abutment complex and the maximum displacement in the implantabutment complex were evaluated.
Results: With changes in the expansion angle and expansion length ratio, the max EQV stress in cortical and cancellous bone increased by 12.4% and 73.9%, respectively, under axial loading, respectively, and by 38.6% and 69.1%, respectively, under buccolingual loading. The max EQV stress in the implant-abutment complex increased by 65.3% and 160% under axial and buccolingual loading, respectively. Maximum displacement in the implant-abutment complex increased by 3.66% and 19.73% under axial and buccolingual loading, respectively.
Conclusion: Expansion angles and the expansion length ratio favored stress distribution in jawbone under axial and buccolingual loads, respectively. An expansion angle between 1.5 and 2.5 degrees and an expansion length ratio between 2/6 and 3/6 provided optimal biomechanical properties for an expandable implant in the osteoporotic mandible.
Purpose: To verify the effectiveness of a countertorque device in dental implants in redistributing stress to the bone-implant interface during tightening of the abutment screw.
Materials and Methods: Two prismatic photoelastic samples containing implants were made, one with a 3.75-mm-diameter implant and the other with a 5.0-mm-diameter implant (both implants had an external-hexagon interface) and the respective abutments were attached (CeraOne). The samples were placed in a support and submitted to torques of 10, 20, 32, and 45 Ncm with an electronic torque meter. The torque application was repeated 10 times on each sample (n = 10) with and without a countertorque device. Photoelastic patterns were detected; thus, a photographic register of each test was selected. The fringe patterns were analyzed at discrete points near the implants' external arch.
Results: In both implants analyzed, a stress gradient reduction was observed through the implant with the countertorque device.
Conclusions: The countertorque device used in this study proved to be effective in reducing the stresses generated in the peri-implant bone tissue during torque application.
Anteroposterior (AP) deficiencies present a restorative treatment challenge. Complex, multidisciplinary planning is necessary for the success of the treatment. This clinical report describes an approach to managing a complex complete oral rehabilitation of an edentulous patient with skeletal transverse and AP deficiencies with a history of facial trauma to the left zygomaticomaxillary complex. This was further complicated by a hopeless remaining dentition and pneumatization of the maxillary sinuses. Treatment included initial bony augmentation of the vertically and horizontally deficient maxilla, dental implant placement, provisional restoration in a Class III malocclusion with bilateral posterior crossbite, and Le Fort I osteotomy with transverse widening and advancement to correct the skeletal deficiency. Definitive restoration was accomplished with implant-supported fixed prostheses that provided ideal facial balance and occlusion.
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