The International Journal of Oral & Maxillofacial Implants, 06/2012

Purpose: Dental implant therapy for posterior partial edentulism may utilize short implants. The advantages of short implants include the ability to avoid the additional surgical procedures that would be required to place longer implants. The aim of this study was to systematically review studies concerning dental implants of = 8.5 mm placed in the posterior maxilla and/or mandible to support fixed restorations. Materials and Methods: English-language articles published between 1992 and May 2011 were identified electronically and by hand search of the PubMed, Embase, and Cochrane libraries. Data were extracted and compared statistically. Forest plots were generated to compare outcomes of short versus long implants. Results: An initial screening of 1,354 studies led to direct evaluation of 401 articles. Of these, 33 met the research criteria: 5 randomized clinical studies; 16 prospective, nonrandomized, noncontrolled studies; 12 retrospective, nonrandomized studies; and 1 study with both prospective and retrospective data. These studies indicated that there is no significant difference in the reported survival of short versus long implants. Failure of 59 of 2,573 short implants at 1 year was recorded, with 71% of them failing before loading. Only 101 short implants were followed for 5 years. Conclusions: The initial survival rate for short implants for posterior partial edentulism is high and not related to implant surface, design, or width. Short implants may constitute a viable alternative to longer implants, which may often require additional augmentation procedures. Keywords: posterior partial edentulism, short dental implant, systematic review

Purpose: This study investigated the effects of a strontium-substituted nanohydroxyapatite (Sr-HA) coating, deposited onto porous implant surfaces using an electrochemical process, on implant osseointegration in a rabbit model. Materials and Methods: The surfaces were analyzed by field-emission scanning electron microscopy, x-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), a portable surface roughness tester, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Thirty implants (half HA-coated and half Sr-HA-coated) were inserted into femurs of 15 rabbits. After 2, 4, and 8 weeks, the femurs were retrieved and prepared for histomorphometric evaluation. Results: Microscopic examination showed a surface topography of rodlike crystals on both surfaces. XRD and FT-IR showed that the phase of the deposits was HA. No differences were found in surface roughness between the two groups. ICP-AES showed that the Sr/(Ca+Sr) molar ratio of Sr-HA coating was 10.1 mol%. Histologic observation showed that new bone appeared on both surfaces after 2 weeks and became mature after 8 weeks. Histomorphometric analysis showed no differences between the two groups in bone-to-implant contact at 2 weeks or in bone area within all threads at 2 and 4 weeks. The Sr-HA coated group had significantly higher bone-to-implant contact at 4 and 8 weeks. Significant differences were also found in bone area at 8 weeks. Conclusion: The present study showed that this Sr-HA coating, deposited using an electrochemical process, has the potential to enhance implant osseointegration. Keywords: dental implant, electrochemical process, hydroxyapatite coating, osseointegration, strontium

Purpose: The purpose of this study was to compare the effectiveness of three methods of cell inoculation on cell growth and bone formation: inoculation of seed cells into the scaffolds from two sides (two-side inoculation method), inoculation of seed cells from one side (single-side inoculation method), and inoculation of a compound of seed cells and type 1 collagen gel from one side (type 1 collagen inoculation method). Materials and Methods: Bone marrow stromal cells were isolated from 1-month-old male New Zealand rabbits and implanted into three-dimensional chitosan/beta-tricalcium phosphate scaffolds using the three different methods. Cultures were analyzed by various methods. Results: The type 1 collagen group expressed the best uniformity of cell distribution among all the three methods during a 1-week culture period, and the two-side group expressed the best uniformity during a 2- to 3-week culture period. The number of inoculated cells in the type 1 collagen group outpaced that of the other groups. With respect to the depth of penetration of the inoculated cells, the cells of the type 1 collagen group were concentrated on the surface of the scaffold and formed multiple layers, whereas the two-side group accounted for the deepest cell penetration. Conclusion: The two-side inoculation method improves the number and distribution of seed cells in vitro and enhances the quality and rate of bone formation in vivo. This method is the most suitable seed method for bone tissue engineering. Keywords: bone marrow stromal cells, distribution, inoculation, scaffold

Purpose: The aim of this investigation was to compare three different techniques for soft tissue closure over intraoral particulated bone grafts in a pig model: primary closure and nonprimary closure utilizing a porcine collagen matrix (Mucograft), with or without the addition of platelet-derived growth factor (PDGF). An additional aim was to determine whether the addition of PDGF to the collagen matrix would prevent the need for primary closure or later soft tissue grafting. Materials and Methods: Twenty-four bilateral mandibular alveolar defects were created in 12 minipigs. These defects were reconstructed with a mixture of autogenous bone and bovine bone and secured with a titanium mesh. The animals were randomly assigned to group A (Mucograft + PDGF), group B (Mucograft alone), or group C (primary closure and no Mucograft). In groups A and B the collagen matrix was placed directly over the mesh, and the soft tissue was closed passively. Exposure of the titanium mesh, height of new bone, and the percentage of keratinized mucosa covering the bone graft were analyzed. Results: Average new bone formation in group A was 7.0 mm, whereas groups B and C had less regenerated bone (4.7 mm and 2.5 mm, respectively). Group A had the thickest keratinized mucosa (1.6 mm), versus 0.9 mm for group B and 0.4 mm for group C. Group A had an average of 95% regenerated keratinized tissue, whereas group B had 41% and group B had 22%. Conclusion: The addition of PDGF to the collagen matrix appeared to accelerate soft tissue healing and promote bone formation. Mucograft provided an adequate alternative to autogenous soft tissue grafts or primary closure to cover bone grafts intraorally while eliminating adverse effects, namely disruption of the adjacent soft tissue architecture, loss of vestibular height, and the need for further surgery. Keywords: collagen matrix, platelet-derived growth factor, soft tissue

Purpose: The aim of the present systematic review was to address the following question: in patients treated with dental implants placed in pristine bone, what are the clinical and radiographic outcomes of bone-level (BL) implants in comparison to tissue-level (TL) implants after restoration with dental prostheses? Materials and Methods: Scanning of online literature databases from 1966 to January 2012, supplemented by hand searching, was conducted to identify relevant prospective randomized controlled trials, controlled clinical trials, and cohort studies. Sequential screenings at the title, abstract, and full-text levels were performed independently and in duplicate. A meta-analysis was conducted to compile data from the primary studies included in this systematic review. Results: The search strategy revealed a total of 5,998. Screening at the title level resulted in 752 papers, while screening at the abstract level yielded 92 publications. Full-text reading identified nine articles that fulfilled the inclusion criteria of this review. The pooled estimated difference between BL and TL implants in mean marginal bone loss was 0.05 mm (95% confidence interval [CI], -0.03 to 0.13 mm), with no statistically significant difference between the groups at 1 year after placement of the definitive prostheses. The relative risk of implant loss was estimated at 1.00 (95% CI, 0.99 to 1.02) at 1 year and at 1.01 (95% CI, 0.99 to 1.03) at 3 years after restoration, indicating no evidence of an increased risk of implant loss in BL compared to TL implants. Conclusions: No statistically significant differences in bone loss and survival rates were detected between BL and TL dental implants over a short-term observation period (1 to 3 years). Thus, both implant systems fulfill the requirements for the replacement of missing teeth in implant dentistry. Keywords: bone-level implants, bone loss, dental implants, implant outcomes, implant survival, systematic review, tissue-level implants

Purpose: Vertical ridge augmentation is a technique to enhance alveolar bone growth or to correct bone defects. However, its long-term predictability and stability are still unknown. The aim of this study was to evaluate the impact of three alloplastic grafting materials on the retention of vertically augmented bone tissue. Materials and Methods: Four titanium caps (3 mm in radius), filled with different alloplastic materials (resorbable hydroxyapatite [HA], porous or nonporous nonresorbable HA) or peripheral blood (control) were placed on the calvaria of seven male New Zealand rabbits. Three months after implant placement, mucoperiosteal flaps were raised to expose the defect sites. The titanium caps were carefully removed and the tissue was covered by repositioned flaps. Two months later, the animals were sacrificed and the augmented new bone was retrieved and prepared for histomorphometric examination. The highest point of each augmented area was measured directly with a Boley gauge. Bone healing was evaluated by a semiquantitative bone score according to the relative proportion of newly formed bone in the cap (0%, 25%, 50%, and 75% of new bone). Results: All substitutes promoted supracranial bone augmentation. Some specimens from nonresorbable HA-augmented tissues fractured at the time of cap removal, indicating that these newly augmented tissues were fragile and less flexible. Height of the augmented tissue for nonresorbable HA, resorbable HA, and controls was 2.3, 1.5, and 1.4 mm, respectively. Most augmented tissue contained less than 25% new bone. Conclusions: Data from this experiment indicated that, while all materials conducted new bone formation predictably, new tissue augmented by resorbable hydroxyapatite and control sites were less stable. Further investigations are encouraged to search for new materials and techniques, which enhance the long-term stability of vertically augmented tissue. Keywords: bone formation, vertical ridge augmentation, alloplasts, long-term stability

Purpose: The purpose of this study was to investigate the increases in intraosseous temperature generated by a modern ultrasonic device for bone surgery (UDBS) and the influences of working pressure and cooling irrigation on this temperature. Materials and Methods: Twenty human mandibular bone specimens (20 × 15 × 5 to 7 mm) were used; three vertical cuts were performed for a duration of 12 seconds per cut. Each bone specimen was machined with a different combination of working pressure (1.5, 2.0, 3.0, 4.0, or 6.0 N) and cooling irrigation (0, 30, 60, or 90 mL/min), and intraosseous temperatures were measured. Harmful temperature development was defined as an increase of more than 10°C for the 75th percentile and/or a maximum increase of more than 15°C. Cutting performance was also measured. Results: Harmless intraosseous temperature development was identified for working pressures of 1.5 N and 2.0 N with cooling irrigations of 30, 60, and 90 mL/min and for 3.0 N at 90 mL/min. The maximum temperature observed was 72°C (6.0 N with 60 mL/min). The mean cutting performance values were 0.21 ± 0.02 mm/s for 6.0 N, 0.21 ± 0.06 mm/s for 3.0 N, 0.20 ± 0.01 mm/s for 4.0 N, 0.11 ± 0.05 mm/s for 1.5 N, and 0.08 ± 0.03 mm/s for 2.0 N. Conclusions: To prevent tissue damage in dental bone surgery, a minimum coolant amount of 30 mL/min is recommended. The working pressure should be chosen with great care because of its significant influence on intraosseous temperature. Doubling of the working pressure from 1.5 to 3.0 N requires a tripling of the coolant (30 to 90 mL/min) to prevent tissue damage. A working pressure above 3.0 N did not result in improved cutting performance. Keywords: cutting performance, intraosseous temperature development, ultrasonic bone surgery

Purpose: This study compared the bone regeneration response of different bone graft materials inside canals within anodized titanium implants in cortical and cancellous bone. Materials and Methods: Upper and lower transverse canals were created in anodic oxidized-surface titanium implants to serve as sites for cortical and cancellous bone regeneration, respectively. The canals were filled with bone graft materials- rabbit bone marrow-derived mesenchymal stem cells and platelet-rich plasma, xenograft, or alloplast (micromacroporous biphasic calcium phosphate)-or left empty (as a control). Eighty implants were surgically placed into the tibiae of 20 New Zealand white rabbits. After 4 and 12 weeks of healing, histomorphometric analysis was performed to measure the newly formed bone areas (NBs) inside the canals. Results: Inside the upper canals, the bone graft groups provided significantly higher NBs than the control (no graft). However, there was no significant difference in NBs between the bone graft groups. Inside the lower canals, no significant difference in NBs was shown among the all groups. The NBs inside the upper canals were significantly greater than those inside the lower canals in all groups after 4 and 12 weeks, respectively. Conclusions: In the cortical bone, there was significant difference in bone regeneration between the control and the bone graft groups. However, there was no significant difference among the bone graft groups in cortical and cancellous bone regeneration. There was significant difference in bone regeneration between the cortical and cancellous bone regions in the all groups using the titanium canal model. Keywords: bone graft material, bone regeneration, mesenchymal stem cell, tissue engineering, implant canal model

Purpose: Osteoporosis is a pathologic condition characterized by low bone mass and changes in the microarchitecture of the bone tissue. Although compromised bone strength and increased susceptibility to fracture have been established, little is known regarding the process of bone regeneration in osteoporotic conditions. Accordingly, this study sought to evaluate the intramembranous bone regeneration process in an ovariectomized rat model following the establishment of calvarial subcritical-size defects (sCSDs). Materials and Methods: Calvarial sCSDs were established in rats that had been ovariectomized (Ovx) or sham-operated 2 months previously and left to heal, unfilled, for 6 months. Bone regeneration was assessed by radiographic, densitometric, histologic, and histometric analyses. Results: Radiologic and histologic analyses showed reduced new bone formation in calvarial sCSDs in Ovx animals in comparison to sham animals. Densitometric analysis of radiologic images and histometric analysis showed significant quantitative differences between groups that converged to substantiate reduced bone regeneration in Ovx animals. Conclusions: The intramembranous ossification process is impaired in the Ovx rat model. This may suggest an impairment of the bone regeneration process in clinical conditions of postmenopausal osteoporosis and highlight the requirement for selective bone regenerative strategies in affected patients. Keywords: animal models, bone regeneration, osteoporosis

Purpose: The aim of this study was to evaluate, with a new gas flow technique, leakage at the implant/abutment junction in systems with four different connections. Materials and Methods: Five Brånemark System, five One Morse, five Intra-lock System, and five Ankylos Plus implants and abutments were used. A hole was drilled in the apex of each implant to allow gas to flow through the connection from negative to atmospheric pressure. The gas flow was calculated (slope of pressure decrease, in hPa.s-1). Each connection was tested after both manual and key tightening. Statistical analysis was performed on a generalized linear model with repeated measurements. The significance level was set at α = .05. Results: A global significant difference was observed between the various systems (P = .0001). After manual tightening, gas leakage was (Ln[hPa.s-1], means ± standard deviations): One Morse: 0.20 (± 1.70); Brånemark System: -4.56 (± 2.61); Intra-lock: -4.31 (± 4.17); Ankylos Plus; -7.59 (± 0.76). After key tightening, mean values were: One Morse: -2.51 (± 2.72); Brånemark System: -7.23 (± 1.01); Intra-lock: -7.76 (± 0.50); Ankylos Plus; -7.73 (± 0.62). Conclusion: This study confirms that gas flow is an appropriate method to assess connection leakage. Ankylos Plus connection leakage was very low when the assembly was tightened manually. Among conical connection systems, low (Ankylos Plus) and high (One Morse) leakage was observed. This gas flow study suggests, therefore, that connection design is not the most important parameter for implant/abutment connection leakage. Keywords: abutment, connection, dental implant, gas flow, implant-abutment interface, leakage

Purpose: This study aimed to examine the effectiveness of a grafting technique using beta-tricalcium phosphate (ß-TCP) covered with different materials in alveolar bone defects with dehiscences. Materials and Methods: In five beagle dogs, all premolars in the mandible were extracted bilaterally. After a 12-week healing period, two bone defects (length, 5 mm; width, 5 mm; depth, 7 mm) were created on each side of the mandible, and the buccal bone plate was resected. The four bone defects were randomly assigned to one of the following treatments: group 1, ß-TCP alone (TCP group); group 2, ß-TCP graft covered with collagen sponge (TCP+collagen group); group 3, ß-TCP graft covered with free buccal mucosa (TCP+mucosa group); group 4, no treatment (control group). The microarchitecture of the regenerated bone was observed using microcomputed tomography, and the area of newly formed bone was measured. Specimens from each defect were selected and subjected to histologic and histomorphometric analysis; areas of newly formed bone and the ridge width were measured in the specimens. Results: Significant differences were found between the control group and all test groups. The median horizontal width of the ridge 2 mm from the top of the alveolar crest in the TCP+mucosa group was significantly greater than that of the TCP group. There was no significant difference between the TCP+mucosa and TCP+collagen groups in any measurement. Conclusions: Application of ß-TCP grafts to alveolar bone defects with dehiscence and covering of the open wound with free buccal mucosa or collagen sponge may be useful for ridge augmentation. Compared to no treatment or leaving the wound uncovered, these approaches resulted in more new bone formation and provided adequate horizontal mandibular width. Keywords: beta-tricalcium phosphate, canine mandible, open wound, ridge augmentation, socket preservation

Purpose: The purpose of this in vitro study was to investigate the effect of impression technique and implant angulation on the impression accuracy of external- and internal-connection implants using a novel experimental device. Materials and Methods: An experimental device was designed and fabricated to make in vitro impressions by means of open- and closed-tray techniques. Impressions of eight implants with two different connections (four external-hex and four internal-hex) at three angulations (0, 15, and 25 degrees) were made using a medium-consistency polyether material. Evaluation of implant impression accuracy was carried out by directly measuring the difference in coordinate values between the implant body/impression coping positioned on the base and the impression coping/laboratory analog positioned in the impression using a touch-probe coordinate measuring machine. Experimental data were analyzed by two-way analysis of variance. The significance level of all hypothesis testing procedures was set at P .05. Results: The results showed that: (1) for implants with external connections, impression accuracy is not significantly affected by the impression technique, implant angulation, or their interaction; and (2) for implants with internal connections, impression accuracy is significantly affected only by implant angulation: Impression inaccuracy was greater at the 25-degree implant angulation. Conclusions: Within the limitations of this in vitro study, the open- and closed-tray techniques had no effect on the accuracy of multiple implant impressions. The interaction between impression technique and implant angulation was also not significant. However, implant angulation significantly affected the impression accuracy when implants with internal connections were used. Keywords: external-connection implants, implant angulation, impression accuracy, impressions, internalconnection implants

Purpose: This review of literature was conducted to evaluate the predictability of treatment outcomes with short dental implants (SDI), ie, implants shorter than 8 mm. Materials and Methods: The review included studies, published between January 1990 and July 2011, that (1) involved SDI ( 8 mm) placed in human jaws, (2) had a minimum of 20 SDI in their analysis, (3) provided data on survival rates, and (4) reported a minimum observation period of at least 3 months after placement. Results: Forty-one studies fulfilled the above criteria; only 17 of these studies reported outcomes with microrough surface SDI. Six different lengths (4, 5, 6, 6.5, 7 and 7.5 mm) of microrough surface SDI with varying diameters (3.5 to 6 mm) were identified in the studies. A total of 1,828 microrough surface SDI were inserted and 45 failures were reported. Observation periods ranged from 3 months to 9 years. The reported survival rates for SDI ranged from 92.2% to 100%. From a total of 1,123 SDI inserted in specified jaw locations, failures were observed more often in the maxilla (n = 297, failed = 13) than in the mandible (n = 826, failed = 19). The review did not identify any correlation between implant diameter and survival for the microrough SDI. Conclusions: Microrough surface short implants (6 to 7.5 mm) appear to provide favorable survival rates and, therefore, can be predictably employed for simplification of implant therapy in situations of reduced alveolar heights in the posterior jaw segments. Keywords: dental implant, implant length (< 8 mm), literature review, short dental implants, treatment outcomes

Purpose: To assess the reliability of cone beam computed tomography (CBCT) voxel gray value measurements using Hounsfield units (HU) derived from multislice computed tomography (MSCT) as a clinical reference (gold standard). Materials and Methods: Ten partially edentulous human mandibular cadavers were scanned by two types of computed tomography (CT) modalities: multislice CT and cone beam CT. On MSCT scans, eight regions of interest (ROI) designating the site for preoperative implant placement were selected in each mandible. The datasets from both CT systems were matched using a three-dimensional (3D) registration algorithm. The mean voxel gray values of the region around the implant sites were compared between MSCT and CBCT. Results: Significant differences between the mean gray values obtained by CBCT and HU by MSCT were found. In all the selected ROIs, CBCT showed higher mean values than MSCT. A strong correlation (R = 0.968) between mean voxel gray values of CBCT and mean HU of MSCT was determined. Conclusions: Voxel gray values from CBCT deviate from actual HU units. However, a strong linear correlation exists, which may permit deriving actual HU units from CBCT using linear regression models. Keywords: accuracy, CBCT, cone beam computed tomography, Hounsfield unit

Purpose: It is unknown whether zoledronic acid (ZA) interferes with initial bone healing at implant sites. The goal of this study was to examine the effects of systemic zoledronic acid administration on osseintegration of hydroxyapatite (HA)-coated and resorbable blast material surface (RBM) implants in rabbit models. Materials and Methods: Twenty-eight male New Zealand rabbits (aged 6 to 12 months) were used in this study. Rabbits were randomly assigned to four groups. In group A, HA-coated implants were placed in the right tibia of seven rabbits. In group B, RBM-surface implants were placed in the right tibia of seven rabbits. In group C, HA-coated implants were placed in seven rabbits with intravenous (IV) administration of ZA. Finally, in group D, RBM-surface implants were placed in seven rabbits with IV administration of ZA. For groups C and D, IV zoledronic acid (0.1 mg/kg) was performed monthly during the entire osseointegration period. All of the rabbits were sacrificed 12 weeks after the implantation, and tibial specimens were harvested. Histomorphometric boneto- implant contact (BIC) analysis and the data were statistically analyzed. Results: The highest BIC percentage was detected in group D, with a mean value of 56.73% ± 1.85%, as compared with 45.80% ± 3.77% in group C, 35.11% ± 0.76% in group B, and 31.14% ± 1.04% in group A. Conclusions: Histomorphometric analyses showed significant improvement in the osseointegration of implants in the RBM-surface ZA group compared with the HA-coated ZA group. The results of this study suggest that systemic ZA administration may improve osseointegration of titanium implants in bone. Keywords: histomorphometry, implant, zoledronic acid

Purpose: To evaluate the fracture resistance of all-ceramic crowns cemented on titanium and zirconia implant abutments. Material and Methods: Customized implant abutments for maxillary right central incisors made of titanium (Ti) and zirconia (Zr) (n = 60, n = 30 per group) were fabricated for an internal connection implant system. All-ceramic crowns were fabricated for their corresponding implant abutments using the following systems (n = 10 per group): (1) monolithic computer-aided design/computer-assisted manufacture (CAD/ CAM) lithium disilicate (MLD); (2) pressed lithium disilicate (PLD); (3) yttrium stabilized tetragonal zirconia polycrystal (YTZP). The frameworks of both PLD and YTZP systems were manually veneered with a fluorapatitebased ceramic. The crowns were adhesively cemented to their implant abutments and loaded to fracture in a universal testing machine (0.5 mm/minute). Data were analyzed using two-way analysis of variance (ANOVA) and Tukey's test (α = 0.05). Results: Both the abutment material (P = .0001) and the ceramic crown system (P = .028) significantly affected the results. Interaction terms were not significant (P = .598). Ti-MLD (558.5 ± 35 N) showed the highest mean fracture resistance among all abutment− crown combinations (340.3 ± 62 − 495.9 ± 53 N) (P .05). Both MLD and veneered ceramic systems in combination with Ti abutments (558.5 ± 35 − 495.9 ± 53 N) presented significantly higher values than with Zr abutments (392.9 ± 55 − 340.3 ± 62 N) (P .05). MLD crown system showed significantly higher mean fracture resistance compared to manually veneered ones on both Ti and Zr abutments (P .05). While Ti-MLD and Ti-PLD abutment-crown combinations failed only in the crowns without abutment fractures, Zr-YTZP combination failed exclusively in the abutment without crown fracture. Zr-MLD and Zr-PLD failed predominantly in both the abutment and the crown. Ti-YTZP showed only implant neck distortion. Conclusions: The highest fracture resistance was obtained with titanium abutments restored with MLD crowns, but the failure type was more favorable with Ti-YTZP combination. Keywords: CAD/CAM, lithium disilicate, monolithic crowns, pressed ceramics, titanium, YTZP

Purpose: To determine whether a wire-guided single drill protocol could be utilized without causing an increase in bone temperature beyond those seen with the traditional techniques of sequential drilling with and without a drill guide. Materials and Methods: A bovine femoral bone model was used with thermocouples and infrared temperature measurements to record thermal increase of the bone and drills during implant site preparation. Two thermocouples, one on each side of the osteotomy, were placed 1 mm from the outer diameter of the final drill. Drilling was performed at a constant speed (2,100 rpm) and pressure (2 kg) under continuous room temperature irrigation. Infrared temperature measurements of each drill were taken immediately before and after drilling. The six study groups included standard sequential drilling protocols for 3.5-mm and 4.2-mm final drills with and without the use of a surgical guide, and cannulated single drill technique for 3.5-mm and 4.2-mm drills. Statistical analysis was performed using a Tukey post hoc one-way ANOVA test. P .05 was determined to be significant. Results: No significant difference in thermal increase was found between single drill cannulated implant site preparation and sequential drilling with or without the use of a drill guide for the 3.5-mm or 4.2-mm drilling sequences, respectively. The thermal increase was found to be significantly less for the 4.2-mm single drill compared with the 3.5-mm sequential drill with surgical guide (P = .046). Infrared temperature measurement revealed no significant difference in drill temperatures throughout the study. Conclusions: Cannulated single drill technique does not cause an increase in bone temperature greater than that seen with standard sequential drilling with or without a surgical guide. Keywords: bone, cannulation, dental implants, drill guidance

Objective: To evaluate the air powder abrasive treatment as an implant surface cleaning method for peri-implantitis based on the existing literature. Materials and Methods: A PubMed search was conducted to find articles that reported on air powder abrasive treatment as an implant surface cleaning method for peri-implantitis. The studies evaluated cleaning efficiency and surface change as a result of the method. Furthermore, cell response toward the air powder abrasive-treated discs, reosseointegration, and clinical outcome after treatment is also reported. Results: The PubMed search resulted in 27 articles meeting the inclusion criteria. In vitro cleaning efficiency of the method is reported to be high. The method resulted in minor surface changes on titanium specimens. Although the air powder abrasive-treated specimens showed sufficient levels of cell attachment and cell viability, the cell response decreased compared with sterile discs. Considerable reosseointegration between 39% and 46% and improved clinical parameters were reported after treatment when applied in combination with surgical treatment. The results of the treatment are influenced by the powder type used, the application time, and whether powder was applied surgically or nonsurgically. Conclusion: The in vivo data on air powder abrasive treatment as an implant surface cleaning method is not sufficient to draw definitive conclusions. However, in vitro results allow the clinician to consider the method as a promising option for implant surface cleaning in periimplantitis treatment. Keywords: airflow, biofilm, implant surface, peri-implantitis

Purpose: To evaluate the effect of functional cyclic loading on two retrieved abutment screws used with single implant supporting cement-retained porcelain-fused-to-metal crowns by characterizing the structure, properties, and biotribologic behavior after long-term use in vivo. Materials and Methods: Two abutment screws were retrieved from the same patient and same implant at two different times. An external hex implant was used to replace a missing central incisor. A traumatic incident occurred 9 months after insertion and displaced the implant palatally by bending the screw. A second, similar incident occurred 31 months after insertion. In both cases, the abutment screws were retrieved and subjected to thorough nondestructive and destructive testing. Results: Light and scanning electron microscopic examinations revealed very minimal surface deterioration of the thread profile for the first screw (in service for 9 months) and demonstrated advanced metal adhesive wear in the form of galling for the second screw (in service for 31 months). The galling led to moderate thinning of the thread profile. Both screws were composed of Au-based alloy, where the microstructure of the matrix consisted of homogeneous equiaxed fine grains with two different second phase particles. Conclusion: It appears that the occurrence of adhesive wear on abutment screws in the form of galling is highly related to the length of in-service time in the mouth. This biotribologic behavior was inevitable and considered to be a normal consequence of long-term use in vivo. Metallurgic analysis indicated that both screws were identical in terms of composition and microstructure. Keywords: abutment screw, adhesive wear, biotribological behavior, galling, retrieval analysis, thread wear

Purpose: To assess the efficacy of a block tenting technique for reconstruction of vertical or horizontal alveolar ridge defects. Materials and Methods: Patients who underwent a block tenting graft technique between 2005 and 2010 were analyzed retrospectively. Intraoral bone blocks (ramus, chin, or tuberosity) or allogeneic blocks were fixed at 4 mm from the deficient area, and the gap was filled with bone substitutes, with or without plasma rich in growth factors (PRGF). Implants were placed simultaneously or 4 to 5 months postgrafting. Patient demographic information, amount of width/height augmentation after 4 to 5 months of healing, complications, and contributing factors were gathered and analyzed. Results: One hundred two patients were enrolled. Among the horizontal augmentations, the greatest width increase was achieved in the anterior maxilla (4.31 ± 0.93 mm). The average height increase in the vertically augmented regions was greatest in the posterior maxilla (5.75 ± 2.22 mm). Mean horizontal augmentation was the greatest with ramus (3.65 ± 0.65 mm) and allogeneic materials (3.97 ± 0.79 mm). The greatest vertical gain was achieved with tuberosity blocks (4.25 ± 3.06 mm) and a combination of allogeneic/autogenous bone particles (3.90 ± 1.05 mm). Application of PRGF showed no appreciable effect. The most common primary complications of surgery were hematoma and inflammation. The most common complication in the anterior maxilla was hematoma. Inflammation was the most common complication associated with ramus grafts, while hematoma occurred most often in cases with chin and tuberosity grafts. Total graft failure occurred in 13 patients, mainly associated with the allogeneic blocks. Most patients were followed for 11 to 38 months. Five of 237 inserted implants failed to osseointegrate. Conclusion: The block tenting technique might be effective for localized ridge augmentation and may reduce the amount of autograft required from donor sites. Keywords: allogeneic bone graft, alveolar ridge augmentation, autogenous bone graft, guided bone regeneration, tenting technique

Purpose: To compare the short-term outcome of dental implant therapy in a group of organ transplant patients with that of a control group. Materials and Methods: The study population included consecutive organ transplant patients and consecutive normal (healthy) subjects as controls. Two films were taken of all patients: one at baseline (implant placement) and one after 3 months of healing. All radiographs were analyzed twice (15 days apart) blindly by two independent trained radiologists. Crestal bone level (CBL) was measured, defined as the perpendicular distance from the reference point on the implant to the first visible apical bone-to-implant contact. Results: The study population included 10 organ transplant patients (eight hearts, two livers) and 10 control patients, who received 20 and 12 submerged dental implants, respectively. At the 3-month follow-up visit, no implants showed any exposed cover screws. CBL increased in both groups, without any significant difference between the groups (CBL increased from 0.08 ± 0.09 mm to 0.28 ± 0.20 mm in transplant patients and from 0.11 ± 0.16 mm to 0.42 ± 0.32 mm in controls). Multiple analysis of variance showed that the mean bone loss of 0.21 ± 0.18 mm observed in the group of transplant patients was not statistically different from that (0.32 ± 0.25 mm) seen in the control group and was not influenced by any of the variables considered. Conclusions: The present pilot study seems to indicate that the bone response around submerged dental implants in immunocompromised organ transplant patients does not differ from that observed in control patients and that this particular population of patients may be successfully rehabilitated with dental implants. Keywords: crestal bone loss, dental implants, longitudinal study, organ transplants, osseointegration

Purpose: The use of short implants can reduce the need for augmentative procedures prior to implant placement and, thus, morbidity and treatment time for patients with severely atrophied alveolar ridges. However, the inevitably less favorable crown-to-implant ratio is often associated with higher implant failure rates and greater marginal bone loss. The aim of this study was to evaluate the long-term survival and success rates of short implants in severely atrophic alveolar ridges retaining restorations on these short implants only. Materials and Methods: In this study, 8-mm and 9-mm implants were inserted in atrophic alveolar ridges according to the manufacturer's protocol for the respective bone quality and loaded after 3 months of healing. Prosthetic restorations were supported only by short implants (not in combination with longer implants). After a mean observation period of 10.1 years (± 1.9 years), all patients were re-examined clinically and radiographically. Results: In this study, fifty-two 8-mm and 9-mm implants were placed in 14 patients. After 10.1 years, no implants and suprastructures had been lost. A mean marginal bone loss of 0.3 mm (± 0.4 mm) was recorded. According to the Albrektsson criteria, all implants were successful; with respect to the more rigorous Karoussis et al criteria, four implants failed. Conclusions: The results of this long-term study suggest that the use of short implants results in marginal bone resorption and failure rates similar to those for longer implants. The higher crown-to-implant ratio did not seem to have any negative influence on implant success in this study. Keywords: bone atrophy, dental implants, implant success, implant survival

Purpose: The purpose of this study was to quantify and compare the retentive forces of five different prosthetic attachment designs on mandibular overdentures retained by two or three implants. Materials and Methods: Two photoelastic acrylic resin models of an edentulous mandible were cast. In one model, three implants were aligned parallel to each other and oriented perpendicular to the occlusal plane. The distal implants were placed in the canine regions, with an interimplant distance of 22 mm. In the other model, two implants were placed using the same approach, with an interimplant distance of 22 mm. Five retention mechanisms were studied on both models: a bar with yellow clips, a milled galvanoformed bar, a bar with two clear distal locator attachments, a bar with two distal Ceka attachments, and a bar with clear locator attachments. Ten dentures were fabricated in clear acrylic resin. The specimens were loaded in tension at a crosshead speed of 50 mm/min in a universal testing machine. Five hundred forty cycles of repeated insertions and removals were performed to simulate 6 months of clinical function. Results: Initial retention forces ranged from 23.33 to 54.32 N. Retentive values of the clear locator attachments on the three-implant model were higher than those for other attachments. Conclusion: All designs demonstrated a decrease in retention from the initial testing to the final pull-out test. This decrease was significant for all designs. Keywords: attachment systems, implant-retained mandibular overdentures, retention

Purpose: Clinical guidelines suggest that a minimal buccal alveolar bone thickness of 1 to 2 mm is required to maintain the tissue architecture following tooth extraction and implant placement. The aim of this study was to evaluate the thickness of buccal alveolar bone at the maxillary first premolars and anterior teeth using cone beam computed tomography (CBCT). Materials and Methods: CBCT images of the maxillae of 43 implant patients were obtained. Two examiners manually measured the distance from the cementoenamel junction (CEJ) to the buccal alveolar bone crest and the thickness of the buccal alveolar bone at the crest, midroot, and apex of the maxillary first premolars and anterior teeth. The absence of bone and presence of radiographic artifacts were recorded. Average bone thicknesses were calculated and compared. Both parametric and nonparametric statistics were used to analyze the findings. Results: The median distance from the CEJ to the buccal alveolar bone crest was 2.79 mm, and measurements were similar among tooth positions. The median buccal alveolar bone thickness 1 mm apical to the alveolar bone was 1.13 mm in the premolar area and 0.83 mm for the anterior maxillary teeth. The median buccal alveolar bone thickness at the midroot was 1.03 mm in the premolar area and 0.70 mm for the other anterior maxillary teeth. Measurements of the buccal plate at 1 mm from the tooth apex were similar in all teeth positions, with a median thickness of 0.88 mm. Conclusions: The presence or absence of buccal alveolar bone can be discerned by CBCT evaluation. Few maxillary anterior teeth displayed buccal alveolar bone thickness greater than 1 mm. The implications for implant therapy must be fully discerned regarding tissue biotypes and dental implant outcomes. Keywords: alveolar bone resorption, cone beam computed tomography, dental implant

Purpose: Intravenous (IV) sedation is commonly used in dentistry. However, no report has yet been published regarding age, hypertension, and antihypertensive drugs during implant surgery and their relationship with changes in blood pressure (BP) and heart rate in implant surgery under IV sedation with propofol and midazolam. Materials and Methods: Medical records of 252 patients who underwent implant surgery were retrospectively analyzed. Patients were classified into four groups according to their age (in years) and hypertension status: A = = 64, no hypertension; B = >= 65, no hypertension; C = = 64, hypertension; or D = >= 65, hypertension. Hypertensive patients were further characterized by their antihypertensive medications: E = calcium channel blockers (CCBs), F = angiotensin II receptor blockers (ARBs), G = CCBs+ARBs, or H = no medication. IV sedation was administered in two stages. After midazolam injection to prevent angialgia, propofol was infused at the rate of 4 mg/kg/h, followed by a dose reduction. Systolic and diastolic BP and heart rate were recorded before, during, and after surgery. Results: Systolic BP increased significantly after patients were draped in groups A, C, and D, with group D showing the most pronounced increase. Sedatives decreased BP in all groups. Diastolic BP in group F decreased significantly compared to group H after induction and before infiltration of local anesthetic. After infiltration, systolic BP decreased more significantly in group G than in group H. Intraoperative hypotension was observed in 25% of patients. The incidence of intraoperative hypertension in group D was markedly higher than in group A (23% vs 4%). Conclusion: IV sedation using midazolam and propofol reduces hypertensive risks during implant surgery. Nevertheless, care must be taken, especially in older hypertensive patients and in hypertensive patients on ARBs or ARBs+CCBs. Keywords: angiotensin II receptor blockers, dental implant, hemodynamics, midazolam, moderate sedation, oral surgery propofol

Purpose: The purpose of this study was to assess the clinical effectiveness of an experimental technique versus the conventional method for the fabrication of implant-supported fixed complete dentures. Materials and Methods: Between January 2005 and June 2010, edentulous patients who had received rehabilitation by means of nonsegmented fixed implant-supported complete dentures were identified from the pool of individuals treated at Eastman Institute for Oral Health, University of Rochester. Data collection consisted of a chart review and recording of treatment variables in a customized database. Variables of interest included number of implants per patient, time of implant placement, number of appointments required to complete prosthesis fabrication, type of appointments, manufacturing process used for creation of the framework, and fit of the framework. The number of appointments for conventional and experimental protocols was evaluated for statistical significance using two-way analysis of variance. Presence or absence of clinically acceptable prosthesis fit with the two techniques was evaluated using the Fisher exact test and exact logistic regression analysis. Results: Forty-two patients (48 arches) were included. When the experimental technique was used, prosthesis fabrication and delivery required an average of 4 appointments, whereas the conventional technique required an average of 7.8 appointments to deliver the definitive prosthesis. The prostheses fabricated with the experimental technique showed clinically passive fit on the implants in 17 of 18 arches. The frameworks fabricated with the conventional technique achieved clinically passive fit in 18 of 30 arches. Conclusions: The experimental technique significantly reduced the number of appointments required to fabricate a nonsegmented fixed implant-supported prosthesis. Moreover, this experimental technique provided clinically acceptable fit of the prosthesis in a significantly greater number of cases compared to a conventional implant elastomeric impression technique. Keywords: dental implants, edentulous mandible, edentulous maxilla, immediate loading, implant-supported prosthesis

Purpose: Extractions in partially edentulous patients often lead to insufficient stability of an existing partial prosthesis and a need for additional anchorage. Implants may therefore be placed as supplementary abutments to increase patient comfort and satisfaction. The aim of this study was to evaluate the longterm clinical outcome of implants combined with teeth to support telescopic abutment-retained removable full-arch prostheses under an immediate functional loading protocol. Materials and Methods: The present retrospective study included implants placed and connected via removable prostheses with periodontally healthy teeth immediately postplacement using prefabricated abutments. Secondary copings, precisely fit to the abutments, were placed and the partial dentures were relined chairside. The prosthetic restorations were not removed for 10 days. Clinical and radiographic evaluations of implants loaded for at least 2 years were performed. Results: One hundred ten implants with a progressive thread design (Ankylos, Dentsply) were placed in 55 patients (mean age, 63.51 ± 9.95 years). Twenty-five implants were placed in fresh extraction sockets (22.73%) and 85 implants were placed in healed ridges. All implants were placed 2 to 3 mm subcrestally (measured from the midfacial bone level). After a mean follow-up of 61.58 ± 28.47 months (range, 24 to 125 months), there were only three failures (2.73%); another six implants (5.45%) displayed crestal bone loss greater than 2 mm but remained stable. Therefore, the failure rate was 8.18% for the entire observation period of 5.13 years. The success rate was 91.82% and the cumulative survival rate was 97.27%. All patients were satisfied with the stability of their prostheses, and no prosthetic, peri-implant, or abutment tooth problems were observed. Conclusions: Telescopic tooth-implant-supported mandibular restorations with immediate loading present an alternative prosthetic solution for partially edentulous patients, providing a long-term predictable clinical outcome. Keywords: dental implants, partial edentulism, prosthesis, telescopic attachments

Purpose: To evaluate whether adding bone substitute materials to autogenous particulated bone (PAB) might have an effect on the density of the grafted bone after maxillary sinus augmentation. Materials and Methods: Thirty healthy patients undergoing lateral antrostomy were included. Sinuses were augmented at random with PAB (n = 10) (control group); a mixture of PAB and beta-tricalcium phosphate (ß-TCP) (n = 10) (experimental group); or a mixture of PAB, ß-TCP, and hydroxyapatite (HA) (n = 10) (experimental group). A sample of each graft material was obtained at time of maxillary sinus augmentation, and microcomputed tomography (µ-CT) analyses were performed. Five months later, samples of the augmented areas (n = 23) were harvested by means of a trephine bur, and µ-CT analyses of these samples were performed. Density values for the bone were compared to the data obtained 5 months before from the original material. Results: All groups showed increasing density values after a healing time of 5 months. Because of a high dropout rate, the sample size was too small to compare the groups statistically. Conclusions: Bone density increased after maxillary sinus augmentation for both PAB alone or in combination with substitute materials based on HA and/or ß-TCP particles. A larger sample size and a split-mouth design would help to reliably reveal significant differences between the single materials. Keywords: bone mineral density, bone replacement materials, maxillary sinus floor augmentation, microcomputed tomography

Purpose: To review a series of 454 pterygoid implants placed more vertically than the previous standard angle (45 degrees) over a functional loading period ranging from 2 months to 14 years with a mean follow-up period of 6 years. Materials and Methods: A retrospective study was made. The sample was composed of patients rehabilitated with pterygoid implants between January 1997 and December 2010. Patient selection criteria included: edentulism on the posterior area of an atrophic maxilla, with less than 8 mm remaining from the sinus floor to the alveolar crest, and the presence of an anterior implant or tooth to ensure mesial support for a partial denture. After a healing period between 2 and 7 months, panoramic x-rays were taken at the time of loading. The implant length, implant diameter, implant success, and the angulation of the pterygoid implants were measured. Results: Three hundred ninety-two patients (206 women and 186 men) ranging in age from 34 to 75 years were fitted with 454 pterygoid implants and followed up. The 18-mm implant length was the most favored implant to fit in the pterygoid area. Implant diameter was 3.75 mm in 448 cases (98.6%). The mean mesiodistal angulation of the pterygoid implants was 70.4 degrees ± 7.2. After a mean follow-up period of 6 years, 96.5% of the implants placed were successfully osseointegrated. Conclusions: The findings indicate that a mesiodistal inclination of the pterygoid implant at 70 degrees relative to the Frankfort plane following the bony column of the pterygoid region decreases the non-axial loads of the rehabilitations and exhibits good long-term survival; however, further studies are needed to assess the long-term survival of implants in the pterygomaxillary region. Keywords: atrophic maxilla, follow-up period, pterygoid buttress, pterygoid implant

Purpose: The objective of this study was to compare the biologic and prosthetic outcomes of early- and conventionally-placed implants supporting fixed prostheses. Materials and Methods: Using inclusion/ exclusion criteria, early- and conventionally-placed implant patient groups, rehabilitated with Brånemark System implants supporting fixed prostheses for 2 years, were selected from the patient archives. Kaplan- Meier survival estimates, time-dependent marginal bone loss, Plaque Index, peri-implant infection, Bleeding Index scores, and prosthetic complications data of the groups were compared. Results: A total of 212 implants were placed in early-placed (n = 42, 101 implants) and conventionally-placed (n = 45, 111 implants) patient groups and 5 implants failed during the 2-year follow-up. The 1- and 2-year Kaplan-Meier survival probabilities of early-placed (0.98) and conventionally-placed (0.973) groups were comparable (P =.735). The 6-month to 2-year marginal bone loss in the conventionally-placed group was higher than in the earlyplaced group (P .05). There were differences between groups on soft tissue scores between the 2 years of function (P .05). The frequency of prosthetic complications was very low and comparable in both groups (P = .476). Conclusions: Early- and conventionally-placed implants supporting fixed prostheses showed comparable clinical outcomes during the 2-year follow-up, although the marginal bone loss was higher in the latter group. Keywords: conventional implant placement, early implant placement, marginal bone loss, peri-implant soft tissue, prosthetic complication

Purpose: To determine patient satisfaction and preference for implant-supported mandibular overdentures (IOD) retained with ball or Locator attachments. In addition, peri-implant conditions and prosthodontic maintenance efforts for the final attachments were evaluated after 1 year of function. Material and Methods: In this crossover clinical trial, 20 edentulous patients were recruited to receive two mandibular implants in the canine region and were provided with implant-retained mandibular overdentures and new complete maxillary dentures. Implant-retained mandibular overdentures were stabilized with either ball attachments or Locator attachments, in random order. After 3 months of function, the attachments in the existing denture were changed. Questionnaires on satisfaction/complaints with the prostheses were administered at baseline (with the old dentures) and after 3 months of function with each attachment, thus providing for an intraindividual comparison. The decision for the final attachment chosen was based on the patient's preference. For the definitive attachment, peri-implant conditions (peri-implant marginal bone resorption, pocket depth, and Plaque Index, Gingival Index, and Bleeding Index) as well as prosthodontic maintenance efforts and satisfaction score were evaluated after an insertion period of 1 year. Results: Nineteen (95%) patients completed the study (1 dropout). Patient satisfaction improved significantly (P .05) from baseline (old dentures) to the new prostheses retained with each of the two attachment types for all domains of satisfaction. However, there were no differences between ball or Locator attachment for any items of satisfaction evaluated and neither attachment had a significant patient preference. No differences for peri-implant parameters or for patient satisfaction were noted between the definitive attachments (ball, n = 10; Locator, n = 9) after 1 year. Although the overall incidence rate of prosthodontic maintenance did not significantly differ between both retention modalities, the Locator attachment required more postinsertion aftercare (activation of retention) than the ball anchors. Keywords: ball-locator attachment, crossover trial, mandibular overdenture

Purpose: To evaluate implant and patient characteristics in a prospective clinical study involving immediate fixed restoration of delayed placement of dental implants. Materials and Methods: Patients diagnosed with generalized chronic periodontitis and previously treated were accepted into the study when they expressed a wish to receive immediate restoration of dental implants. Treatment planning and implant placement were computer assisted, using computerized tomography, planning software, and a surgical template. Patients received abutments and cemented provisional prostheses no later than 72 hours following implant surgery. Patients were followed at 2 and 4 weeks, and 3, 6, and 12 months. Results: Eighteen patients were accepted and completed the study, ages ranged from 34 to 69 years (mean 54.5 ± 8.5 years). Five patients (27.8%) were smokers (2.5 to 60 pack years). Fifty implants were placed, ranging between 1 to 8 implants per patient. Median implant length was 13 mm (range, 10 to 13 mm) and median implant diameter was 3.75 mm (range, 3.75 to 5 mm). Mean insertion torque was 43 NCm ± 6.2 SD (range 30 to 50 NCm). Mean implant stability quotient was 71 ± 11 (range 37 to 85). One implant in a patient who smoked and three implants in another patient who smoked failed for a total of four failed implants. At 12 months, the overall survival rate was 92% (100% and 73% among nonsmokers and smokers, respectively). Conclusions: The survival of immediately restored dental implants in periodontally treated patients is greater than 90%. Smokers with a past history of chronic periodontitis seem to have a lower implant survival rate. Keywords: bone loss, implant failure, implant success, implant survival, periodontitis

Purpose: The primary aim of this systematic review was to compare the amount of marginal bone loss around tilted and straight implants. As the secondary aim, the incidence of biomechanic complications was compared. Materials and Methods: An electronic literature search from five databases, for the years 2000 to 2011, and a hand search in implant-related journals were conducted. Clinical human studies in the English language that had reported marginal bone loss in tilted and straight implants at 12-months followup or longer were included. Mean marginal bone loss and the number of implants that were available for analysis were extracted from original articles for meta-analyses. Results: Eight (six prospective and two retrospective) studies were included. One-year data were available in seven articles, which included 1,015 (451 tilted) implants. Three articles provided 3- to 5-year data from 302 (164 tilted) implants. No significant difference in weighted mean marginal bone loss was found between the tilted and straight implants in the short and medium terms. Three articles reported the incidence of biomechanic complications. There was not enough information to make a comparison. Conclusions: This meta-analysis failed to support the hypothesis that tilted implants that were splinted for the support of fixed prostheses had more marginal bone loss. Additionally, there was not enough evidence to claim a higher incidence of biomechanic complications in tilted implants. However, due to the nature of the study design of the included articles, caution should be exercised when interpreting the results of this review. Keywords: edentulous, immediate dental implant loading, marginal bone loss, nonaxial loading, splinting, tilted implant

Purpose: Full-arch implant rehabilitation with four implants has become an accepted modality of treatment for fixed restorations in totally edentulous mandibles or maxillas; however, there is little scientific evidence on the outcome for the same treatment with three implants. The purpose of this study was to evaluate a protocol for three implants (all-on-three) supporting a delayed loaded fixed prosthesis in the completely edentulous maxilla, mandible, or both. Materials and Methods: This retrospective clinical study included 17 patients with 72 implants to restore 24 fully edentulous arches. The implants were loaded 4 months after surgery with fixed zirconia prostheses. A 5-year follow-up was performed. Results: No implants were lost, giving a 100% success rate. The marginal bone loss was, on average, 0.53 mm (SD, 0.32 mm) for the internal connection implants and 0.84 mm (SD, 0.62 mm) for the external connection implants. Conclusions: Within the limits of this small group clinical study, the high survival rate of the all-on-three protocol with delayed loading may be a viable concept. Keywords: all-ceramic prosthesis, full arch, three implants, zirconia prosthesis

Purpose: To detect the differences in the distribution of micromotion within implants and alveolar bone with different implant thread designs during immediate loading. Materials and Methods: A three-dimensional finite element model with contact elements was used to simulate the contact behavior between the implant and alveolar bone. Implants with four different thread designs were created: Acme (trapezoidal) thread (AT), buttress thread (BT), square thread (ST), and a standard V-thread (VT). To simulate immediate loading, the model was designed without osseointegration between the implant and alveolar bone. A load of 300 N was applied axially to the model, and the micromovements were measured. Results: The maximum micromotion values of the ST, AT, VT, and BT models were 8.53, 9.57, 11.00, and 15.00 µm, respectively. All micromotion was located near the interface of cortical and cancellous bone. Different thread designs showed different distribution of micromotion during loading. This indicates that initial stability in immediate loading may be affected by thread design. Conclusion: The ST profile showed the most favorable result in the study. An implant with an ST profile might provide the best primary stability in an immediate loading situation.

Purpose: The present study investigated the biomechanical interactions of a monocortically or bicortically engaged short and wide implant in the atrophic posterior maxilla and compared them to those of a long implant in the augmented sinus under different loading conditions via a nonlinear finite element (FE) approach. Materials and Methods: Nonlinear FE models of a single implant in the posterior maxilla were constructed for the following conditions: (1) A monocortically engaged 5-mm-long, 7-mm-wide implant with an internal tripodgrip abutment connection (SIT-1), (2) a bicortically engaged 6-mm-long, 7-mm-wide implant with internal tripod-grip abutment connection (SIT-2), and (3) a 13-mm-long, 4.5-mm-wide implant with an internal-hexagon abutment connection in an augmented sinus. Simulated loads of 150 N were applied axially at the central fossa, off-axis at the buccal and palatal cusps, and toward the axis at the buccal and palatal cusps. Results: The simulated results showed that loading condition was the main factor influencing the mechanical responses. Oblique occlusal forces increased implant stress and stress/strain values for the surrounding bone. The use of a long implant decreased the implant stress but increased the bone stress/strain values relative to a short and wide implant. The SIT-1 and SIT-2 implants increased the implant stress on average by 2.94 and 2.67 fold, respectively. However, the SIT-2 implant reduced the average stress and strain in bone by 37%, and the SIT-1 implant reduced average stress by 33% and average strain by 32%. Conclusions: Placement of a short and wide implant in the atrophic posterior maxilla may be a possible alternative for reducing the strain/stress on the surrounding bone. Detrimental off-axis loads should always be minimized to prevent extraordinarily high bone strain and stress.