Bacterial leakage in implants with different implant-abutment connections: an in vitro study

Background: Two‐piece implants present gaps and cavities between the implant and the abutment, and these hollow spaces can act as a trap for bacteria. The aim of the present in vitro study was to evaluate the migration of two different microbial species from the inside to the outside of the implant–abutment assembly in three different connection types. Methods: A total of 30 implants (10 implants per group) were used. The implants presented a screwed trilobed connection (group 1), a cemented connection (group 2), and an internal conical connection (group 3). The inner parts of five implants, per group, were inoculated with Pseudomonas aeruginosa suspension and the remaining five implants, per group, with Aggregatibacter actinomycetemcomitans. The penetration of bacteria into the surrounding solution was determined by the observation of turbidity of the broth. Results: In group 1, bacterial contamination was found in six of 10 implants. In group 2, no contaminated samples were found. In group 3, bacterial contamination was found in one implant of 10. Statistically significant differences were detected between group 1 versus group 3 (P <0.05) and between group 1 versus group 2 (P <0.01), whereas no significant differences were found when comparing group 2 versus group 3 (P >0.05). Conclusion: The present study confirms previous results about the hermeticity of the cement‐retained implant–abutment assembly, the very low permeability to bacteria of the conical implant–abutment connection, and the high prevalence of bacterial penetration of screw‐retained implant–abutment assemblies.     

Effect of repeated torque/mechanical loading cycles on two different abutment types in implants with internal tapered connections: an in vitro study

Objectives: Internal tapered connections were developed to improve biomechanical properties and to reduce mechanical problems found in other implant connection systems. The purpose of this study was to evaluate the effects of mechanical loading and repeated insertion/removal cycles on the torque loss of abutments with internal tapered connections.
Material and methods: Sixty-eight conical implants and 68 abutments of two types were used. They were divided into four groups: groups 1 and 3 received solid abutments, and groups 2 and 4 received two-piece abutments. In groups 1 and 2, abutments were simply installed and uninstalled; torque-in and torque-out values were measured. In groups 3 and 4, abutments were installed, mechanically loaded and uninstalled; torque-in and torque-out values were measured. Under mechanical loading, two-piece abutments were frictionally locked into the implant; thus, data of group 4 were catalogued under two subgroups (4a: torque-out value necessary to loosen the fixation screw; 4b: torque-out value necessary to remove the abutment from the implant). Ten insertion/removal cycles were performed for every implant/abutment assembly. Data were analyzed with a mixed linear model ( P ≤0.05).
Results: Torque loss was higher in groups 4a and 2 (over 30% loss), followed by group 1 (10.5% loss), group 3 (5.4% loss) and group 4b (39% torque gain). All the results were significantly different. As the number of insertion/removal cycles increased, removal torques tended to be lower. It was concluded that mechanical loading increased removal torque of loaded abutments in comparison with unloaded abutments, and removal torque values tended to decrease as the number of insertion/removal cycles increased.     

Evaluation of the marginal precision of one-piece complete arch titanium frameworks fabricated using five different methods for implant-supported restorations

Objective: The aim of the present work was to compare the marginal precision of titanium frameworks for a complete arch‐fixed prosthesis fabricated using five different methods. Methods: A prospective study was designed. Fifteen titanium frameworks for totally edentulous upper or lower jaws, each supported by five to nine implants, were assigned to five study groups, so as to have three frameworks in each group for each technique: (1) lost wax technique frameworks, (2) cast titanium sovrastructures laser welded to prefabricated titanium copings, (3) Procera ^® Implant Bridge, (4) Cresco Ti System^? and (5) CAM StructSURE^® Precision Milled Bar. The microgap between the framework and the shoulders of implant analogues was measured on the master cast with a stereomicroscope at a magnification of 100 × at four different locations, yielding a total of 364 data points on 91 implants. Data were analyzed using an ANOVA and a Tukey post hoc test (P=<0.05). Results: The mean values for the microgap were 78 μm (SD±48) for lost wax technique frameworks, 33 μm (SD±19) for cast titanium sovrastructures laser welded to titanium copyings, 21 μm (SD±10) for the Procera ^® implant bridge, 18 μm (SD±8) for the Cresco Ti System^? and 27 μm (SD±15) for the CAM StructSURE^®. The differences among the mean values were statistically significant (P<0.01 or P<0.05). The comparisons among groups 3, 4, and 5 and between groups 2 and 5 were not significant (P>0.05). Conclusion: The computer‐aided procedures analyzed in the present study were able to produce a precision‐fitting framework, with no significant differences among them and, at the same time, showed a greater precision compared with the traditional casting methods or with the use of prefabricated titanium copings. However, it should be noted that, even if group 2 frameworks were not as accurate as groups 3 and 4, cast titanium sovrastructures laser welded to prefabricated titanium copings showed significantly better marginal precision than the frameworks produced with the lost wax technique.     

Stress distribution in implant-supported prosthesis with external and internal implant-abutment connections

Abstract

Objective. This study aimed to investigate the stress distribution in screwed implant-supported prostheses with different implant-abutment connections by using a photoelastic analysis. Materials and methods. Four photoelastic models were fabricated in PL-2 resin and divided according to the implant-abutment connection (external hexagon (EH) and Morse taper (MT) implants (3.75 × 11.5 mm)) and the number crowns (single and 3-unit piece). Models were positioned in a circular polariscope and 100-N axial and oblique (45) loading were applied in the occlusal surface of the crowns by using a universal testing machine. The stresses were photographically recorded and qualitatively analyzed using software (Adobe Photoshop). Results. Under axial loading, the MT implants exhibited a lower number of fringes for single-unit crowns than EH implants, whereas for a 3-unit piece the MT implants showed a higher number of fringes vs EH implants. The oblique loading increased the number of fringes for all groups. Conclusion. In conclusion, the MT implant-abutment connection reduced the amount of stress in single-unit crowns, for 3-unit piece crowns the amount of stress was lower using an external hexagon connection. The stress pattern was similar for all groups. Oblique loading promoted a higher stress concentration than axial loading.     

Micro-leakage at the implant-abutment interface with different tightening torques in vitro

Objectives

This study evaluated the microleakage at the implant/abutment interface of external hexagon (EH) implants and abutments with different amounts of bacteria and tightening torques.

Material and Methods

A bacterial suspension was prepared to inoculate the implants. The first phase of this study used nine EH implants and abutments that were divided into three groups with different amounts of bacterial suspension (n=3): V0.5: 0.5 µL; V1.0: 1.0 µL e V1.5: 1.5 µL, and tightened to the manufacturer''s recommended torque. The second phase of this experiment used 27 assemblies that were similar to those used in the first phase. These samples were inoculated with 0.5 µL of bacterial suspension and divided into three groups (n=9). T10: 10 Ncm; T20: 20 Ncm and T32: 32 Ncm. The samples were evaluated according to the turbidity of the broth every 24 hours for 14 days, and the bacteria viability was tested after that period. The statistical evaluation was conducted by Kruskal-Wallis testing (p<.05).

Results

During the first phase, groups V1.0 and V1.5 was presented with bacterial contamination in all samples after 24 h. During the second phase, two samples from group T10 and one from T20 presented positive results for bacterial contamination. Different amounts of bacterial solution led to overflow and contamination during the first 24 h of the experiment. The tightening torques did not statistically affect the microleakage in the assemblies. However, the group that was tightened to 32 Ncm torque did not show any bacterial contamination.

Conclusion

After 14 days of experimentation, the bacteria were proven to remain viable inside the implant internal cavity.     

Immediate loading short implants inserted on low bone quantity for the rehabilitation of the edentulous maxilla using an All‐on‐4 design

More studies evaluating the outcome of short‐length dental implants in immediate loading are needed. To evaluate the use of short‐length tapered implants in immediate loading for complete edentulous maxillae rehabilitations using an All‐on‐4 design. This retrospective clinical study included a cohort of 43 patients with 172 implants (74 short‐length implants) inserted in low bone quantity. The patients were followed between 4 months and 6 years (average = 3 years). Outcome measures were implant survival, marginal bone remodelling, biological and mechanical complications. Two patients with four short‐length implants were lost to follow‐up during the first year. Three short and three long implants failed in four patients, rendering an overall cumulative survival rate implant and patient level, respectively, of 95·7% and 95·1% for short implants, 100% for regular implants and 96·6% and 95·2% for long implants. The average marginal bone remodelling at 1 and 3 years was 0·97 and 1·25 mm for the short implants, 0·82 and 0·87 mm for regular implants and 0·87 and 0·98 mm for long implants. Three patients presented 4 short‐length implants with peri‐implant pockets (3 implants in 2 patients were pseudo‐pockets). Mechanical complications were registered in 13 patients (7 provisional prostheses fractures and 6 abutment screw loosening). All complications were treated successfully. Within the limitations of this clinical study, the short‐term outcome of fixed prosthetic complete edentulous maxillae rehabilitations supported by short‐length implants inserted in low bone quantity areas is viable. Long‐term clinical studies are necessary for evaluating the outcome of these implants.     

The speed of sound correlates with implant insertion torque in rabbit bone: an in vitro experiment

Objectives: This study investigated the correlation of quantitative ultrasound with bone quality as evaluable from implant final insertion torque. Material and methods: Implants were planned at diaphyses (group 1) and epiphyses (group 2) of 16 rabbit femurs where amplitude‐dependent speed of sound (Ad‐SOS) was measured. The insertion torque from 7‐mm‐long implants placed at planned sites was recorded. The correlation between cutting torque and Ad‐SOS was evaluated using Spearman's coefficient. Results: Statistics were based on data from 15 diaphyses and 13 epiphyses. The mean insertion torque was 8.8 N cm while the mean Ad‐SOS was 1710.9 m/s. A negative correlation resulted between insertion torque and Ad‐SOS. Conclusions: In the rabbit bone model investigated, quantitative ultrasound correlates inversely with implant insertion torque. Although this correlation remains to be verified in humans because rabbit femur does not convincingly represents different human bone qualities, it seems that ultrasound could convey potentially useful, pre‐surgical, site‐specific, non‐invasive information on bone mechanical characteristics therefore deserving further research efforts. To cite this article:
Veltri M, Valenti R, Ceccarelli E, Balleri P, Nuti R, Ferrari M. The speed of sound correlates with implant insertion torque in rabbit bone: an in vitro experiment.
Clin. Oral Impl. Res. 21 , 2010; 751–755.
doi: 10.1111/j.1600‐0501.2009.01873.x     

Cross-sectional analysis of the implant-abutment interface

The purpose of this study was to develop a technique to evaluate the implant-abutment gap of an external hexagon implant system as a function of radius. Six implants of 3.75 mm in diameter (Conexao Sistema de Protese Ltda, Sao Paulo, Brazil) and their respective abutments were screw connected and torqued to 20 N cm(-1). The implants were mounted in epoxy assuring an implant long-axis position perpendicular to the vertical axis. Each implant was grounded through its thickness parallel to implant long-axis at six different distance interval. Implant-abutment gap distances were recorded along the implant-abutment region for each section. Individual measurements were related to their radial position through trigonometric inferences. A sixth degree polynomial line fit approach determined radial adaptation patterns for each implant. Micrographs along implant sections showed a approximately 300 mum length implant-abutment engagement region. All implants presented communication between external and internal regions through connection gaps and inaccurate implant-abutment alignment. Average gap distances were not significantly different between implants (P > 0.086). Polynomial lines showed implant-abutment gap values below 10 mum from 0 mum to approximately 250 mum of the implant-abutment engagement region. Gap distances significantly increased from approximately 250 mum to the outer radius of the implant-abutment engagement region. The technique described provided a broader scenario of the implant-abutment gap adaptation compared with previous work concerning implant-abutment gap determination, and should be considered for better understanding mechanical aspects or biological effects of implant-abutment adaptation on peri-implant tissues.     

Anti-inflammatory effects of the prostacyclin analogue iloprost in an in vitro model of inflamed human dental pulp cells

Iloprost's anti-inflammatory effects on human dental pulp stem cells (HDPCs) are currently unknown. We hypothesized that iloprost could downregulate the expression of inflammatory-related genes and protein in an inflamed HDPC in vitro model. To induce inflammation, the HDPCs were treated with a cocktail of interleukin-1 beta, interferon-gamma, and tumour necrosis alpha, at a ratio of 1:10:100. Iloprost (10⁻⁶ M) was then added or not to the cultures. Interleukin-6 (IL-6) and interleukin-12 (IL-12) mRNA expression were assessed by real-time polymerase chain reaction. IL-6 protein expression was assessed by enzyme-linked immunosorbent assay. The results were analysed using one-way ANOVA or the Kruskal–Wallis test. The cytokine cocktail induced more robust IL-6 expression than LPS treatment. Iloprost slightly, yet significantly, downregulated IL-6 and IL-12 mRNA expression. These findings suggest that iloprost might be used as a beneficial component in vital pulp therapy.     

Immediate loading in the completely edentulous mandible: technical procedure and clinical results up to 3 years of functional loading

Objectives: This prospective mono‐center study describes a clinical technique to provide dental implants with a temporary cross‐arch cantilever bridge functionally loaded on the day of fixture insertion and discusses the 3‐year follow‐up of four to six machined surface Brånemark implants installed in the interforamina area. Material and methods: Ninety Brånemark implants were installed in 18 edentulous mandibles. Five patients were heavy smokers and one had Down syndrome. The day of surgery, a 10 unit provisional glassfiber‐reinforced cantilever bridge was installed. The final 12 unit bridge was in place after an average of 144 days (range 10–332). Bone‐to‐implant level was assessed radiologically from the day of surgery up to 3 years. Results: Two out of five fixtures were lost within 3 months in the Down syndrome patient but the provisional bridge continued to function on the three remaining implants until the patient was successfully reoperated. Another implant was lost after 11 months due to a non‐detected fracture in the metal framework, resulting in overloading of the cantilever part. As no additional losses occurred during the follow‐up time (range 57–26 months), the total failure rate is 3/91 (3.3%). Seventeen of the 18 patients are loading their implants more than 3 years and nine have moved beyond the 4‐year period. Average bone remodelling as measured on the apical radiographs from 12 patients at 0, 12 and 36 months revealed a statistically significant bone loss from the initial 0.1 mm [standard deviation (SD) 0.2; range 0–0.7] toward 1.8 mm (SD 0.2; range 1.6–2.2) during the first year of function. (Wilcoxon's signed rank test; P<0.002). After 3 years, no further significant bone loss occurred. Conclusion: This 3‐year study shows that machined surface Brånemark implants can be immediately loaded with cross‐arch cantilever bridges with an average bone‐remodelling pattern indicative of a steady state after 1 year of loading.     

Immediate loading of dental implants in partially edentulous patients: A clinical report

Immediate loading of dental implants offers attractive advantages for patient and prosthodontist alike. Current data support immediate loading of splinted screw-shaped implants in the parasymphysis region. This report presents a case of a partially edentulous patient successfully restored with a fixed implant prosthesis following an immediate loading protocol.     

Relationship between dental implant stability determined by resonance frequency analysis measurements and peri-implant vertical defects: an in vitro study

Resonance frequency (RF) analysis is a non-invasive and objective technique developed for implantology, where it measures the stability of the implant in the bone socket. A limited number of studies were performed to compare different stability measurement devices. The aim of the study was to evaluate the association between the implant stability and peri-implant vertical defect by using the new wireless RF analyser. Micro-textured rough-surfaced implants with diameters of 3.7 and 4.8 mm and with a length of 12 mm were used. The peak insertion torque was recorded with the help of the torque control system only during the implant placement. The peri-implant defects were created in millimetre increments ranging between 0 and 5 mm to the same extent on all implants. The RF analysis values were measured by using the RF analyser. Significant correlation was found between insertion torque (44.3 +/- 3 N cm) and implant stability quotient (ISQ) (all implants: r = 0.76, 3.7 mm diameter: r = 0.65, 4.8 mm diameter: r = 0.80). For 3.7 x 12-mm(2) implants, the mean ISQ values were 72.6 +/- 2.4, 69.8 +/- 2, 67.2 +/- 1.8, 64.3 +/- 1.9, 61.2 +/- 2 and 57.2 +/- 2.5 when peri-implant vertical defects were 0, 1, 2, 3, 4 and 5 mm; and the corresponding values were 76.5 +/- 2.2, 74.5 +/- 2.2, 72.3 +/- 2, 70 +/- 1.9, 67 +/- 1.9 and 63.4 +/- 2.3, respectively, for 4.8 x 12-mm(2) implants. All values were significantly different when compared with each other. The wireless RF analyser seems to be a suitable and reliable device to determine the implant stability. Peri-implant bone loss simulated by using acrylic models may result with a decrease in ISQ values for osseo-integrated implants measured by the RF analyser.     

Influence of Different Tightening Forces Before Laser Welding to the Implant/Framework Fit

Purpose: The aim of the present study was to evaluate the influence of abutment screw tightening force before laser welding procedures on the vertical fit of metal frameworks over four implants.
Materials and Methods: To construct the frameworks, prefabricated titanium abutments and cylindrical titanium bars were joined by laser welding to compose three groups: group of manual torque (GMT), GT10 and GT20. Before welding, manual torque simulating routine laboratory procedure was applied to GTM. In GT10 and GT20, the abutment screws received 10 and 20 Ncm torque, respectively. After welding, the implant/framework interfaces were assessed by optical comparator microscope using two methods. First, the single screw test (SST) was used, in which the interfaces of the screwed and non-screwed abutments were assessed, considering only the abutments at the framework extremities. Second, the interfaces of all the abutments were evaluated when they were screwed.
Results: In the SST, intergroup analysis (Kruskal Wallis) showed no significant difference among the three conditions of tightening force; that is, the different tightening force before welding did not guarantee smaller distortions. Intragroup analysis (Wilcoxon) showed that for all groups, the interfaces of the non-screwed abutments were statistically greater than the interfaces of the screwed abutments, evidencing distortions in all the frameworks. ANOVA was applied for the comparison of interfaces when all the abutments were screwed and showed no significant difference among the groups.
Conclusions: Under the conditions of this study, pre-welding tightness on abutment screws did not influence the vertical fit of implant-supported metal frameworks.     

Variation in the total lengths of abutment/implant assemblies generated with a function of applied tightening torque in external and internal implant-abutment connection

Aim: Settling (embedment relaxation), which is the main cause for screw loosening, is developed by microroughness between implant and abutment metal surface. The objective of this study was to evaluate and compare the relationship between the level of applied torque and the settling of abutments into implants in external and internal implant–abutment connection. Material and methods: Five different implant–abutment connections were used (Ext, External butt joint+two‐piece abutment; Int‐H2, Internal hexagon+two‐piece abutment; Int‐H1, Internal hexagon+one‐piece abutment; Int‐O2, Internal octagon+two‐piece abutment; Int‐O1, Internal octagon+one‐piece abutment). All abutments of each group were assembled and tightened with corresponding implants by a digital torque gauge. The total lengths of implant–abutment samples were measured at each torque (5, 10, 30 N cm and repeated 30 N cm with 10‐min interval) by an electronic digital micrometer. The settling values were calculated by changes between the total lengths of implant–abutment samples. Results: All groups developed settling with repeated tightening. The Int‐H2 group showed markedly higher settling for all instances of tightening torque and the Ext group was the lowest. Statistically significant differences were found in settling values between the groups and statistically significant increases were observed within each group at different tightening torques (P<0.05). After the second tightening of 30 N cm, repeated tightening showed almost constant settling values. Conclusions: Results from the present study suggested that to minimize the settling effect, abutment screws should be retightened at least twice at 30 N cm torque at a 10‐min interval in all laboratory and clinical procedures. To cite this article:
Kim K‐S, Lim Y‐J, Kim M‐J, Kwon H‐B, Yang J‐H, Lee J‐B, Yim S‐H. Variation in the total lengths of abutment/implant assemblies generated with a function of applied tightening torque in external and internal implant–abutment connection.
Clin. Oral Impl. Res. 22 , 2011; 834–839
doi: 10.1111/j.1600‐0501.2010.02063.x     

Levels of glycosaminoglycans in peri‐implant sulcus fluid as a means of monitoring bone response to endosseous dental implants

The presence of certain glycosaminoglycans in peri‐implant sulcus fluid may be an effective means of monitoring changes in bone metabolic activity following initial loading of implant abutments. This study has investigated levels of chondroitin 4 sulphate and hyaluronan in peri‐implant sulcus fluid from titanium osseointegrated implants following initial abutment placement and exposure to masticatory stresses. Abutments were placed after a 3-month osseointegration period post‐initial surgical placement of the interosseous stage. 10 edentulous patients, each with 5 mandibular implants were reviewed at 2, 4, 6 and 8 days after abutment placement. Clinical details were assessed and recorded and sulcus fluid collected in microcapillary tubes for a 5‐min period for each abutment. Levels of glycosaminoglycans were assessed using cellulose acetate electrophoresis and densitometric scanning of alcian blue stained strips against known glycosaminoglycan standards. Maximum levels of sulcus fluid (0.3–1.25 /5 min) were evident at 4 days with a decrease towards 8 days. Levels of sulphated glycosaminoglycans were also maximal at 2–4 days (range 0.03–0.126 μg/5 min) and decreased at 6-8 days. Hyaluronan was detected within a similar range of values reaching maximal levels at 4 days and decreasing by 8 days. The results indicate that glycosaminoglycan levels of peri‐implant sulcus fluid is an effective means of measuring and maintaining changes in bone metabolism. The absence of proteodermatan sulphate precludes 1 soft tissues being a source of these markers.