Soft Tissue Response and Determination of Underlying Risk Drivers for Recession and Mucositis after AMSJI Implantation in the Maxilla

PURPOSE

To evaluate the soft tissue response to the placement of additively manufactured subperiosteal jaw implants (AMSJI) in the severely atrophic maxilla and to identify possible risk factors for soft tissue breakdown.

MATERIALS AND METHODS

An international multicenter study was conducted, and 15 men (mean age: 64.62 years; SD: ± 6.75) and 25 women (mean age: 65.24 years; SD: ± 6.77) with advanced maxillary jaw resorption (Cawood and Howell Class V or more) were included in this study. General patient data were collected, and all subjects were clinically examined. Inclusion criteria were patients who underwent bilateral AMSJI placement in the maxilla at least 1 year prior. Exclusion criteria were patients who did not have patient, surgeon, or dentist consent to participate in the study before their inclusion.

RESULTS

A total of 40 patients were enrolled, with a mean follow-up period of 917 days (SD: ± 306.89 days). Primary implant stability was achieved postoperatively in all cases, and all implants were loaded with a final prosthesis. At the time of the study, only 1 patient showed mobility (> 1 mm) of the bilateral AMSJI. Due to mucosal recession, exposure of the framework was seen in 26 patients (65%) and was mainly in the left (21.43% of 26) and right (18.57% of 26) midlateral region. A thin biotype and the presence of mucositis were found to be risk factors (P < .05). Although not significant, smokers had a risk of developing a recession that was nearly seven times (odds ratio: 6.88; P = .08) greater than that of nonsmokers.

CONCLUSIONS

Twenty-six (65%) patients presented with a recession in one (or more) of the seven regions after oral rehabilitation with bilateral AMSJI placement. Several risk drivers were evaluated. The collapse of soft tissues around the AMSJI that led to caudal exposure of the arms was correlated with a thin biotype and the presence of mucositis.

A 20-year split-mouth comparative study of two screw-shaped titanium implant systems

PURPOSE

To prospectively assess marginal bone loss and implant survival with Astra Tech (Dentsply Sirona, Charlotte, NC, USA) (group A) and Brånemark (Nobel Biocare, Zurich, Switzerland) (group B) implants in a split-mouth study conducted over a 20-year follow-up period.

MATERIALS AND METHODS

A total of 95 implants (n = 50, group A and n = 45, group B) were randomly placed in the left or right side of the maxilla or mandible in 18 patients. Clinical and radiographic examinations were performed, and results were reported at 5, 10, 15 and 20 years after insertion of the prosthesis.

RESULTS

Ten patients were followed up for 20 years (n = 26 implants, group A and n = 25 implants, group B). No implant loss or prosthetic failures were observed. After 20 years of follow-up, no significant differences in marginal bone loss were found between both implant groups (P = 0.25). The proportion of marginal bone loss ≥ 0.5 mm was not significantly different between implant types (P > 0.05), and no statistically significant relationships were found between marginal bone loss and time (P ≥ 0.05). More specifically, there was no significant difference in marginal bone level between year 20 and baseline in group A (P = 0.70), whereas a difference of 0.5 to 1.0 mm was found in group B (P = 0.15).

CONCLUSIONS

After 20 years of follow-up, marginal bone loss around screw-shaped titanium implants was clinically insignificant. Furthermore, no significant differences in survival and marginal bone loss were found between group A and B implants over the follow-up period.

Radiographic Evaluation of Bone Remodeling after Additively Manufactured Subperiosteal Jaw Implantation (AMSJI) in the Maxilla: A One-Year Follow-Up Study

Additively manufactured subperiosteal jaw implants (AMSJI) are patient-specific, 3D-printed, titanium implants that provide an alternative solution for patients with severe maxillary bone atrophy. The aim of this study was to evaluate the bony remodeling of the maxillary crest and supporting bone using AMSJI. Fifteen patients with a Cawood–Howell Class V or greater degree of maxillary atrophy were evaluated using (cone beam) computed tomography scans at set intervals: one month (T1) and twelve months (T2) after definitive masticatory loading of bilateral AMSJI implants in the maxilla. The postoperative images were segmented and superimposed on the preoperative images. Fixed evaluation points were determined in advance, and surface comparison was carried out to calculate and visualize the effects of AMSJI^TM on the surrounding bone. A total mean negative bone remodeling of 0.26 mm (SD 0.65 mm) was seen over six reference points on the crest. Minor bone loss (mean 0.088 mm resorption, SD 0.29 mm) was seen at the supporting bone at the wings and basal frame. We conclude that reconstruction of the severely atrophic maxilla with the AMSJI results in minimal effect on supporting bone. Reduced stress shielding with a biomechanically tuned subperiosteal implant does not induce radiographically significant crestal bone atrophy.

Patient- and clinician-reported outcomes for the additively manufactured sub-periosteal jaw implant (AMSJI) in the maxilla: a prospective multicentre one-year follow-up study

The clinical outcomes of maxillary rehabilitation with the additively manufactured sub-periosteal jaw implant (AMSJI; CADskills BV) were evaluated in edentulous patients with a Cawood-Howell atrophy classification ≥5 in all regions of the maxilla. Fifteen consecutive patients were included in the study and followed up for 1 year. They were interviewed using a survey protocol and were examined clinically and radiographically preoperatively (T0) and at 1 (T1), 6 (T2), and 12 (T3) months after permanent upper prosthesis placement. The patients reported an increased oral health-related quality of life. The overall mean Oral Health Impact Profile-14 score at T0 was 17.20 (standard deviation (SD) 6.42). When results at T0 were compared to those at T1 (mean 8.93, SD 5.30), a statistically significant difference was seen (P = 0.001). At T3, the mean value was 5.80 (SD 4.18). Compared to T0, there was also a statistically significant difference at T3 (P = 0.001). General satisfaction based on the numerical rating scale was a mean 49.93 at T1, which was less than patient expectation prior to treatment at T0 (52.13). A higher overall value was seen at T3 (53.20) when compared to T0. Within the constraints of the short follow-up, the AMSJI appears to be a promising tool for patients with extreme jaw atrophy. The high patient expectations were met without complications.

Oral Implant Restorations By Undergraduate Students: An Up To 5-Years Clinical Outcome

PURPOSE

To clinically evaluate oral implant restorations placed by undergraduate students in the dental clinical curriculum at KU Leuven (Belgium) in terms of function and esthetics.

MATERIALS AND METHODS

A retrospective observational cohort study was designed. The esthetic and functional evaluations of implant-supported restorations placed in the framework of the undergraduate implant dentistry clinical training program using White/Pink Esthetic Score (WES/PES) and visual analog scale (VAS) scoring was performed. Furthermore, complications were registered based retrospectively on the patient's medical file. The following research questions were stipulated: (1) How well do implant-supported restorations placed by undergraduate students perform esthetically? and (2) Which complications occurred and how were these managed?

RESULTS

Between August 2008 and July 2014 (6 academic terms), 251 implants (Brånemark System Mk III, Nobel Biocare) were placed in 113 patients by 155 students (> 40% of all students enrolled in the training program). Of these implants, 228 were restored in 101 patients by 118 students with varying restoration types. Esthetic scoring of the restorations in 83 of these patients revealed a satisfying mean WES of 8.14 ± 2.09 (out of 10) and PES of 9.56 ± 3.14 (out of 14). Complications were registered in 18.9% of the cases.

DISCUSSION

Clinical training in implant dentistry for undergraduates contributes to the development of advanced skills in the dental student's Master education. Overall, patients were satisfied with their implant-supported restorations. Implant and restoration success rates and complication incidence were confirmed by long-term data in the oral implant literature.

Randomized controlled trial comparing immediate loading with conventional loading using cone-anchored implant-supported screw-retained removable prostheses: A 2-year follow-up clinical trial

STATEMENT OF PROBLEM

Implant-based prosthetic solutions can be time consuming. If implants can be loaded immediately, treatment time can be reduced.

PURPOSE

The purpose of this prospective randomized controlled trial was to monitor the survival rate of Ankylos implants, comparing conventional with immediate loading by using abutments with the SynCone concept for screw-retained removable prostheses in the edentulous maxilla.

MATERIAL AND METHODS

A total of 90 implants were placed in 15 study participants. The participants were randomly assigned to the immediate or conventional loading treatment group. Radiographic and clinical parameters were recorded at the time of permanent prosthesis installment and at 1- and 2-year follow-up examinations, and participants' satisfaction was measured by using questionnaires before and after prosthesis installation. A linear mixed model was used to measure differences.

RESULTS

One implant in the conventional group was lost during abutment placement; hence, 89 implants could be followed for 2 years. Approximately 90% of these implants showed no bone loss or even bone gain at 1 and 2 years follow-up. Mean values for the immediate group were, respectively, 0.09 ±0.35 mm and 0.13 ±0.38 mm and 0.01 ±0.41 mm and -0.06 ±0.32 mm for the conventional method. No significant differences (P=.053) were found in bone level alterations between the groups. For all participants, the mean number of surfaces (4 per implant) with bleeding on probing (BoP) and plaque were 0.76 ±0.81 and 0.16 ±0.42 at 1 year follow-up and 0.44 ±0.66 and 0.02 ±0.15, respectively, at the second-year follow-up. The mean pocket probing depths were 2.05 ±0.54 mm at 1 year and 2.18 ±0.64 mm at 2 years. For both groups, a significant rise in satisfaction and quality of life was observed (P≤.001) at 1 and 2 years compared with pretreatment.

CONCLUSIONS

Ankylos implants placed in the edentulous maxilla, immediately or conventionally loaded by a detachable prosthesis, showed favorable bone-level preservation after 2 years of follow-up. No significant differences could be found between the immediate and conventional groups. A significant increase in quality of life was observed for both loading modes.

Effect of high-frequency loading and parathyroid hormone administration on peri-implant bone healing and osseointegration

The objective of this study is to examine the effect of low-magnitude, high-frequency (LMHF) loading, and anti-osteoporosis medications such as parathyroid hormone (PTH) and bisphosphonates on peri-implant bone healing in an osteoporosis model, and to assess their combined effects on these processes. Thirteen-week-old ovariectomized rats (n = 44) were divided into three groups: PTH, alendronate, and saline. After 3 weeks of drug administration, titanium implants were inserted into the tibiae. Each group was subdivided into two groups: with or without LMHF loading via whole-body vibration (50 Hz at 0.5 g, 15 min per day, 5 days per week). Rats were killed 4 weeks following implantation. Removal torque test, micro-CT analyses (relative gray (RG) value, water = 0, and implant = 100), and histomorphometric analyses (bone-to-implant contact (BIC) and peri-implant bone formation (bone volume/tissue volume (BV/TV))) were performed. Removal torque values and BIC were significantly differed by loading and drug administration (ANOVA). Post hoc analysis showed that PTH-treated groups were significantly higher than the other drug-treated groups. BV/TV was significantly enhanced by PTH administration. In cortical bone, RG values were significantly increased by loading. In trabecular bone, however, RG values were significantly increased by PTH administration. These findings suggest that LMHF loading and PTH can act locally and additively on the bone healing process, improving the condition of implant osseointegration.

Whole-body vibration and administration of a hormone used to treat osteoporosis can enhance bone healing at the site of a titanium implant. Toru Ogawa of Tohoku University Graduate School of Dentistry in Sendai, Japan, and colleagues gave anti-osteoporosis medications, either parathyroid hormone or the bisphosphonate drug alendronate, to female rat models of osteoporosis. After three weeks of drug administration or a saline control, the researchers inserted titanium implants into the rats’ leg bones. Half the rats were then exposed to whole-body vibration, which applies low-magnitude, high-frequency mechanical forces. A multitude of tests showed that parathyroid hormone improved bone healing at the implant more than alendronate or saline did. The vibrational stimulus further increased the healing. The findings suggest that these treatments could aid in oral bone healing for patients receiving dental implants.

Can the alendronate dosage be altered when combined with high-frequency loading in osteoporosis treatment?

Alendronate therapy has been associated with serious side effects. Altering the alendronate concentration and combining with high-frequency loading as mechanical intervention was explored in this animal study as a treatment for osteoporosis. The bone anabolic potency of high-frequency loading was overruled by the different alendronate dosages applied in the present study. Further exploration of reduced hormonal therapy associated with mechanical interventions in osteoporosis treatment should be sought.

INTRODUCTION

The aim of the present study was to investigate the effect of alendronate (ALN) administration at two different dosages, associated or not with high-frequency (HF) loading, on the bone microstructural response.

METHODS

Sixty-four female Wistar rats were used, of which 48 were ovariectomized (OVX) and 16 were sham-operated (shOVX). The OVX animals were divided into three groups: two groups were treated with alendronate, at a dosage of 2 mg/kg (ALN(₂)) or at a reduced dosage of 1 mg/kg (ALN(₁)) three times per week. A third OVX group did not receive pharmaceutical treatment. All four groups were mechanically stimulated via whole body vibration (WBV) at HF (up to 150 Hz) or left untreated (shWBV). ALN and HF were administered for 6 weeks, starting at 10-week post-(sh)OVX. Tibia bone structural parameters were analyzed using ex vivo microcomputed tomography.

RESULTS

Trabecular bone loss and structural deterioration resulting from ovariectomy were partially restored by ALN administration, demonstrated by the improvement of trabecular patter factor (Tb.Pf), trabecular separation (Tb.Sp), and structure model index (SMI) of the ALN groups compared to that of the OVX group, regardless of the applied dosage [ALN(₂) or ALN(₁)] or mechanical loading regime (shWBV or WBV). However, a significant positive effect of the ALN(₁) administration on trabecular (decrease of Tb.Sp and SMI) and cortical bone (increase of cortical thickness) microarchitecture compared to that of the OVX status group was observed for both loading regimes was not seen for ALN(₂). Furthermore, HF loading resulted in cortical bone changes, with an increased trabeculary area and endocortical perimeter. Finally, the benefits of a combined therapy of ALN with HF loading could not be discerned in the present experimental conditions.

CONCLUSIONS

The bone anabolic potency of HF loading was overruled by the ALN dosages applied in the present study. Further altering the ALN dosage combined with robust mechanical stimuli needs to be considered in osteoporosis research and eventually therapy.

Controlled Clinical Trial on the Outcome of Glass Fiber Composite Cores Versus Wrought Posts and Cast Cores for the Restoration of Endodontically Treated Teeth: A 5-Year Follow-up Study

PURPOSE

The aim of this study was to compare the 5-year outcomes of glass fiber composite with cast posts and cores for the restoration of endodontically treated teeth.

MATERIALS AND METHODS

A total of 143 patients in need of 203 full ceramic restorations on endodontically treated teeth were included. After primary stratification based on the need for post or no post, teeth were randomly allotted to test group 1 (prefabricated glass fiber posts), 2 (custom-made glass fiber posts), or 3 (composite cores without posts). The control group was treated with gold alloy-based wrought posts and cast cores. Success (original present) and survival (present after intervention) probability lifetime curves, corrected for clustering, were drawn over the entire data set.

RESULTS

The mean follow-up time was 5.8 years (range: 0.5 to 7.2 years). At 5 years, the success and survival probabilities were 85.2% and 91.5%, respectively. Lifetime curves did not show any significant differences between the test and control groups for success (P = .85) or survival (P = .57). Moreover, no significant differences for success or survival could be found among the four groups (the three test groups and the control group).

CONCLUSION

After 5 years of follow-up, cast gold and composite post-and-core systems on teeth with ceramic full restorations provided with a ferrule performed equally well.

Residual compressive surface stress increases the bending strength of dental zirconia

OBJECTIVE

To assess the influence of surface treatment and thermal annealing on the four-point bending strength of two ground dental zirconia grades.

METHODS

Fully-sintered zirconia specimens (4.0×3.0×45.0mm³) of Y-TZP zirconia (LAVA Plus, 3M ESPE) and Y-TZP/Al₂O₃ zirconia (ZirTough, Kuraray Noritake) were subjected to four surface treatments: (1) 'GROUND': all surfaces were ground with a diamond-coated grinding wheel on a grinding machine; (2) 'GROUND+HEAT': (1) followed by annealing at 1100°C for 30min; (3) 'GROUND+Al₂O₃ SANDBLASTED': (1) followed by sandblasting using Al₂O₃; (4) 'GROUND+CoJet SANDBLASTED': (1) followed by tribochemical silica (CoJet) sandblasting. Micro-Raman spectroscopy was used to assess the zirconia-phase composition and potentially induced residual stress. The four-point bending strength was measured using a universal material-testing machine.

RESULTS

Weibull analysis revealed a substantially higher Weibull modulus and slightly higher characteristic strength for ZirTough (Kuraray Noritake) than for LAVA Plus (3M ESPE). For both zirconia grades, the 'GROUND' zirconia had the lowest Weibull modulus in combination with a high characteristic strength. Sandblasting hardly changed the bending strength but substantially increased the Weibull modulus of the ground zirconia, whereas a thermal treatment increased the Weibull modulus of both zirconia grades but resulted in a significantly lower bending strength. Micro-Raman analysis revealed a higher residual compressive surface stress that correlated with an increased bending strength.

SIGNIFICANCE

Residual compressive surface stress increased the bending strength of dental zirconia. Thermal annealing substantially reduced the bending strength but increased the consistency (reliability) of 'GROUND' zirconia.

Strength, toughness and aging stability of highly-translucent Y-TZP ceramics for dental restorations

OBJECTIVE

The aim was to evaluate the optical properties, mechanical properties and aging stability of yttria-stabilized zirconia with different compositions, highlighting the influence of the alumina addition, Y₂O₃ content and La₂O₃ doping on the translucency.

METHODS

Five different Y-TZP zirconia powders (3 commercially available and 2 experimentally modified) were sintered under the same conditions and characterized by X-ray diffraction with Rietveld analysis and scanning electron microscopy (SEM). Translucency (n=6/group) was measured with a color meter, allowing to calculate the translucency parameter (TP) and the contrast ratio (CR). Mechanical properties were appraised with four-point bending strength (n=10), single edge V-notched beam (SEVNB) fracture toughness (n=8) and Vickers hardness (n=10). The aging stability was evaluated by measuring the tetragonal to monoclinic transformation (n=3) after accelerated hydrothermal aging in steam at 134°C, and the transformation curves were fitted by the Mehl-Avrami-Johnson (MAJ) equation. Data were analyzed by one-way ANOVA, followed by Tukey's HSD test (α=0.05).

RESULTS

Lowering the alumina content below 0.25wt.% avoided the formation of alumina particles and therefore increased the translucency of 3Y-TZP ceramics, but the hydrothermal aging stability was reduced. A higher yttria content (5mol%) introduced about 50% cubic zirconia phase and gave rise to the most translucent and aging-resistant Y-TZP ceramics, but the fracture toughness and strength were considerably sacrificed. 0.2mol% La₂O₃ doping of 3Y-TZP tailored the grain boundary chemistry and significantly improved the aging resistance and translucency. Although the translucency improvement by La₂O₃ doping was less effective than for introducing a substantial amount of cubic zirconia, this strategy was able to maintain the mechanical properties of typical 3Y-TZP ceramics.

SIGNIFICANCE

Three different approaches were compared to improve the translucency of 3Y-TZP ceramics.

Influence of Light Irradiation Through Zirconia on the Degree of Conversion of Composite Cements

PURPOSE

To assess the light irradiance (LI) delivered by two light-curing units and to measure the degree of conversion (DC) of three composite cements and one flowable composite when cured through zirconia or ceramic-veneered zirconia plates with different thicknesses.

MATERIALS AND METHODS

Three dual-curing composite cements (Clearfil Esthetic Cement, Panavia F2.0, G-CEM LinkAce) and one light-curing flowable composite (G-aenial Universal Flo) were investigated. Nine different kinds of zirconia plates were prepared from three zirconia grades (YSZ: Aadva and KATANA; Ce-TZP/Al2O3: NANOZR) in three different thicknesses (0.5- and 1.5-mm-thick zirconia, and 0.5-mm-thick zirconia veneered with a 1.0-mm-thick veneering ceramic). Portions of the mixed composite cements and the flowable composite were placed on a light spectrometer to measure LI while being light cured through the zirconia plates for 40 s using two light-curing units (n = 5). After light curing, micro-Raman spectra of the composite films were acquired to determine DC at 5 and 10 min, 1 and 24 h, and at 1 week.

RESULTS

The zirconia grade and the thickness of the zirconia/veneered zirconia plates significantly decreased LI. Increased LI did not increase DC. Only the Ce-TZP/Al2O3 (NANOZR) zirconia was too opaque to allow sufficient light transmission and resulted in significantly lower DC.

CONCLUSION

Although zirconia-based restorations attenuate the LI of light-curing units, the composite cements and the flowable composite could be light cured through the YSZ zirconia. LI is too low through Ce-TZP/Al2O3 zirconia, necessitating the use of self-/dual-curing composite cements.

Oral implant placement and restoration by undergraduate students: clinical outcomes and student perceptions

INTRODUCTION

Universities are developing and implementing implant dentistry training to prepare dental professionals for the growing treatment needs. This study describes how implant dentistry is taught at the KU Leuven and focuses on implant-related clinical outcomes. Perspectives of participating undergraduate students are analysed with a view to improve oral implant dentistry training.

MATERIALS AND METHODS

Implant dentistry training at the KU Leuven consists of theoretical lectures, pre-clinical hands-on workshops and clinical (surgical/prosthetic) experience. Questionnaires were used to investigate the perceptions of students on the educational programme. Radiographs were taken at implant insertion, at healing abutment connection, at restoration/prosthesis insertion and after 1 and 2 years of functional loading. The marginal bone level was measured from the implant-abutment connection to the first visible bone-to-implant contact.

RESULTS

One hundred and twelve implants were placed by 56 undergraduate students (61.5% of the total students) in 56 patients. After a follow-up time of 3 years, the cumulative implant survival rate, at implant level, was 97.1%. The mean marginal bone loss after 1 and 2 years in function was 0.35 mm and 0.39 mm, respectively. Eighty percentage of students were satisfied with the training, and they considered this sufficient preparation to perform implant placement under close supervision.

CONCLUSIONS

The clinical outcome of implant treatment performed by undergraduate students under close supervision is similar to that reported by experienced clinicians/research teams. Clinical, surgical as well as restorative experience in addition to theoretical and pre-clinical training seems beneficial when implementing implant dentistry in the undergraduate programmes.

[Influence of the removable partial denture acrylic resin on oral health and quality of life]

OBJECTIVE

This study aims to evaluate dental decay incidence and DMF index, plaque index and gingival index, and to assess the satisfaction/dissatisfaction in acrylic removal partial denture wearers (ARPD) and in partial edentate no wearers. It aims to improve the therapeutic management in prosthetic oral rehabilitation in DR Congo.

MATERIAL AND METHODS

This prospective cohort interventional randomized study on 376 patients enrolled and divided into two groups (with and without denture prosthesis) was performed in University Clinics of Kinshasa, Kinshasa Medical Center and Clinic Glory during the period August 2008 to August 2010.

RESULTS

Three hundred seventy-six patients (376) with 163 men (47 ± 16 years) and 213 women (42 ± 15 years) were followed. Of the 376 patients randomized, 189 were of "prosthesis" group and 187 were in the group "without aid". Both groups were regularly reviewed every 6 months for 2 years. Ten thousand four hundred and fifty-two (10452) teeth were examined (5149 teeth to the group "prosthesis" and 5303 for the teeth "without prosthesis" group. On hundred and twenty-nine (129) teeth that presented caries, 110 (82.96 per cent) are decayed teeth in the "prosthesis" group and 19 (17.04 per cent) are in the group "without prosthesis" (p = 0.00). The index Tooth Decayed, Missing, Filled (CAD) to start of the study for each group was 0.2. Two years after the index rose to 0.3 for the group "prosthesis" and remained steady (0.2) for the group "without prosthesis". The "prosthesis" group showed plaque index (PI) and gingival index (GI) above 0.99 (SD: ± 0.28) and 1.27 (SD: ± 0.43) than normal compared to those of the "no aid" group (0.46 ± 0.15 and 0.32 ± 0.12). The differences were statistically significant for both indices between the two groups (p = 0.00). Overall satisfaction rate for the "prosthesis" group was 26.4% while for the group "without prosthesis" satisfaction rate is 80.9%.

CONCLUSION

This study shows that improved oral hygiene and regular check of the RPD acrylic resin carriers become a concern for establishing a true oral health policy.

Bonding Effectiveness to Differently Sandblasted Dental Zirconia

PURPOSE

To evaluate the effect of different mechanical pre-treatments on the bond durability to dental zirconia.

MATERIALS AND METHODS

Fully sintered IPS e.max ZirCAD (Ivoclar Vivadent) blocks were randomly assigned to one of 4 groups: (1) kept as-sintered (control), (2) sandblasted with 50-μm Al₂O₃(Danville), or tribochemically silica sandblasted using (3) CoJet (3M ESPE) and (4) SilJet (Danville). The zirconia specimens were additionally pre-treated chemically using a 10-MDP/silane ceramic primer (Clearfil Ceramic Primer, Kuraray Noritake). Two identically pre-treated zirconia blocks were bonded together using resin-composite cement (RelyX Ultimate, 3M ESPE). The specimens were trimmed at the interface to a cylindrical hourglass shape and stored in distilled water (7 days, 37°C), after which they were randomly tested as is or subjected to additional mechanical aging involving cyclic tensile stress (10 N, 10 Hz, 10,000 cycles). Subsequently, the microtensile bond strength was determined and SEM fractographic analysis performed.

RESULTS

Weibull analysis revealed the highest Weibull scale and shape parameters when zirconia was tribochemically silica sandblasted using either CoJet or SilJet. The Weibull shape parameter of Al₂O₃-sandblasted zirconia was significantly reduced upon mechanical aging, but not when zirconia was tribochemically silica sandblasted.

CONCLUSION

The mechanical surface pre-treatment of zirconia using tribochemical silica sandblasting (CoJet, SilJet) resulted in the most favorable bond durability of a resin-composite cement (RelyX Ultimate) to dental zirconia before and after aging.

Structural and Chemical Analysis of the Zirconia–Veneering Ceramic Interface

The interfacial interaction of veneering ceramic with zirconia is still not fully understood. This study aimed to characterize morphologically and chemically the zirconia–veneering ceramic interface. Three zirconia-veneering conditions were investigated: 1) zirconia–veneering ceramic fired on sandblasted zirconia, 2) zirconia–veneering ceramic on as-sintered zirconia, and 3) alumina–veneering ceramic (lower coefficient of thermal expansion [CTE]) on as-sintered zirconia. Polished cross-sectioned ceramic–veneered zirconia specimens were examined using field emission gun scanning electron microscopy (Feg-SEM). In addition, argon-ion thinned zirconia–veneering ceramic interface cross sections were examined using scanning transmission electron microscopy (STEM)–energy dispersive X-ray spectrometry (EDS) at high resolution. Finally, the zirconia–veneering ceramic interface was quantitatively analyzed for tetragonal-to-monoclinic phase transformation and residual stress using micro-Raman spectroscopy (µRaman). Feg-SEM revealed tight interfaces for all 3 veneering conditions. High-resolution transmission electron microscopy (HRTEM) disclosed an approximately 1.0-µm transformed zone at sandblasted zirconia, in which distinct zirconia grains were no longer observable. Straight grain boundaries and angular grain corners were detected up to the interface of zirconia– and alumina–veneering ceramic with as-sintered zirconia. EDS mapping disclosed within the zirconia–veneering ceramic a few nanometers thick calcium/aluminum-rich layer, touching the as-sintered zirconia base, with an equally thick silicon-rich/aluminum-poor layer on top. µRaman revealed t-ZrO2-to- m-ZrO2 phase transformation and residual compressive stress at the sandblasted zirconia surface. The difference in CTE between zirconia– and the alumina–veneering ceramic resulted in residual tensile stress within the zirconia immediately adjacent to its interface with the veneering ceramic. The rather minor chemical elemental shifts recorded in the veneering ceramic did not suffice to draw definitive conclusions regarding potential chemical interaction of the veneering ceramic with zirconia. Sandblasting damaged the zirconia surface and induced phase transformation that also resulted in residual compressive stress. Difference in CTE of zirconia versus that of the veneering ceramic resulted in an unfavorable residual tensile stress at the zirconia–veneering ceramic interface.

Highly-translucent, strong and aging-resistant 3Y-TZP ceramics for dental restoration by grain boundary segregation

Latest trends in dental restorative ceramics involve the development of full-contour 3Y-TZP ceramics which can avoid chipping of veneering porcelains. Among the challenges are the low translucency and the hydrothermal stability of 3Y-TZP ceramics. In this work, different trivalent oxides (Al2O3, Sc2O3, Nd2O3 and La2O3) were selected to dope 3Y-TZP ceramics. Results show that dopant segregation was a key factor to design hydrothermally stable and high-translucent 3Y-TZP ceramics and the cation dopant radius could be used as a controlling parameter. A large trivalent dopant, oversized as compared to Zr(4+), exhibiting strong segregation at the ZrO2 grain boundary was preferred. The introduction of 0.2 mol% La2O3 in conventional 0.1-0.25 wt.% Al2O3-doped 3Y-TZP resulted in an excellent combination of high translucency and superior hydrothermal stability, while retaining excellent mechanical properties.

Digital versus conventional implant impressions for edentulous patients: accuracy outcomes

PURPOSE

To compare the accuracy of digital and conventional impression techniques for completely edentulous patients and to determine the effect of different variables on the accuracy outcomes.

MATERIALS AND METHODS

A stone cast of an edentulous mandible with five implants was fabricated to serve as master cast (control) for both implant- and abutment-level impressions. Digital impressions (n = 10) were taken with an intraoral optical scanner (TRIOS, 3shape, Denmark) after connecting polymer scan bodies. For the conventional polyether impressions of the master cast, a splinted and a non-splinted technique were used for implant-level and abutment-level impressions (4 cast groups, n = 10 each). Master casts and conventional impression casts were digitized with an extraoral high-resolution scanner (IScan D103i, Imetric, Courgenay, Switzerland) to obtain digital volumes. Standard tessellation language (STL) datasets from the five groups of digital and conventional impressions were superimposed with the STL dataset from the master cast to assess the 3D (global) deviations. To compare the master cast with digital and conventional impressions at the implant level, analysis of variance (ANOVA) and Scheffe's post hoc test was used, while Wilcoxon's rank-sum test was used for testing the difference between abutment-level conventional impressions.

RESULTS

Significant 3D deviations (P < 0.001) were found between Group II (non-splinted, implant level) and control. No significant differences were found between Groups I (splinted, implant level), III (digital, implant level), IV (splinted, abutment level), and V (non-splinted, abutment level) compared with the control. Implant angulation up to 15° did not affect the 3D accuracy of implant impressions (P > 0.001).

CONCLUSION

Digital implant impressions are as accurate as conventional implant impressions. The splinted, implant-level impression technique is more accurate than the non-splinted one for completely edentulous patients, whereas there was no difference in the accuracy at the abutment level. The implant angulation up to 15° did not affect the accuracy of implant impressions.

Aging resistance of surface-treated dental zirconia

The influence of surface treatment on the low-temperature degradation (LTD) of tetragonal zirconia polycrystalline (TZP) is still unclear.

OBJECTIVES

The effect of surface treatments on the LTD behavior of zirconia was investigated.

METHODS

Fully-sintered specimens of seven commercial dental zirconia (Aadva, GC; In-CeramYZ, VITA; IPS e.max ZirCAD, Ivoclar Vivadent; LAVA Frame and LAVA Plus, 3M ESPE; NANOZR, Panasonic; ZirTough, Kuraray Noritake) were provided by the manufacturers with specimen dimensions of approximately 10mm×5mm×3mm. For each zirconia grade, samples were kept 'as sintered' (untreated) or were subjected to one of the three surface treatments: rough polished, sandblasted with Al2O3, tribochemical silica sandblasted (n=3/group). The tetragonal to monoclinic transformation was evaluated by X-ray diffraction at several intervals during LTD testing up to 40h in steam in an autoclave (134°C, 2bar).

RESULTS

The five yttria-stabilized TZP (Y-TZP: Aadva, In-CeramYZ, IPS e.max ZirCAD, LAVA Frame, LAVA Plus) zirconia showed a similar trend in LTD behavior. The Al2O3 sandblasted zirconia showed the highest monoclinic volume fraction. The as sintered (untreated) zirconia degraded faster than the surface-treated zirconia. Although the surface-treated ceria-stabilized TZP/alumina (Ce-TZP/Al2O3: NANOZR) zirconia had a higher initial monoclinic volume fraction compared to the Y-TZP zirconia, it showed a stronger aging resistance. The as sintered (untreated) Y-TZP/alumina (Y-TZP/Al2O3: ZirTough) zirconia showed a strong aging resistance, whereas the surface-treated Y-TZP/Al2O3 zirconia degraded slightly.

SIGNIFICANCE

Surface treatment improved the aging resistance of Y-TZP zirconia. Surface treatment did not affect the LTD behavior of Ce-TZP/Al2O3 zirconia, while surface treatment decreased the aging resistance of Y-TZP/Al2O3 zirconia.

High-frequency loading positively impacts titanium implant osseointegration in impaired bone

High-frequency loading via whole body vibration promotes bone formation and increases bone strength. Whether this translates to positive titanium implant osseointegration in osteoporotic bone was explored in this animal study. An anabolic effect of not only bisphosphonate treatment but also high-frequency loading on implant osseointegration in osteoporotic bone was observed.

INTRODUCTION

The present study investigated the impact of high-frequency (HF) loading, applied via whole body vibration (WBV), on titanium implant osseointegration in healthy versus ovariectomy-induced compromised versus pharmacologically treated compromised bone.

METHODS

A custom-made Ti implant was inserted into the metaphyseal tibia of 59 rats and left to heal for either 4 or 14 days. Rats were divided into six groups according to their hormonal and mechanical status. WBV, consisting of 10 consecutive frequency steps at an acceleration of 0.3 g, was applied daily for either 4 or 14 days. Tissue samples were processed for quantitative histology at the tibial cortical and medullar level. Data were analyzed by three-way ANOVA and by post hoc pairwise comparisons.

RESULTS

The bone healing response at the interface and surrounding titanium implants was negatively influenced by osteoporotic bone conditions, mainly at the trabecular bone level. Furthermore, the administration of bisphosphonates for preventing the ovariectomy-induced impaired peri-implant response was successful. Finally, the effect of HF WBV loading on the peri-implant bone healing was dependent on the bone condition and was anabolic solely in untreated osteoporotic trabecular bone when applied for an extended period of time.

CONCLUSIONS

The bone healing response to implant installation is compromised in osteoporotic bone conditions, in particular at the trabecular bone compartment. Meanwhile, not only pharmacological treatment but also mechanical loading via HF WBV can exert a positive effect on implant osseointegration in this specific bone micro-environment. The peri-implant cortical bone, however, seems to be less sensitive to HF WBV loading influences.

Stimulation of titanium implant osseointegration through high-frequency vibration loading is enhanced when applied at high acceleration

Low-magnitude high-frequency loading, applied by means of whole body vibration (WBV), affects the bone. Deconstructing a WBV loading stimulus into its constituent elements and investigating the effects of frequency and acceleration individually on bone tissue kinetics around titanium implants were aimed for in this study. A titanium implant was inserted in the tibia of 120 rats. The rats were divided into 1 control group (no loading) and 5 test groups with low (L), medium (M) or high (H) frequency ranges and accelerations [12-30 Hz at 0.3×g (F(L)A(H)); 70-90 Hz at 0.075×g (F(M)A(M)); 70-90 Hz at 0.3×g (F(M)A(H)); 130-150 Hz at 0.043×g (F(H)A(L)); 130-150 Hz at 0.3×g (F H A H)]. WBV was applied for 1 or 4 weeks. Implant osseointegration was evaluated by quantitative histology (bone-to-implant contact (BIC) and peri-implant bone formation (BV/TV)). A 2-way ANOVA (duration of experimental period; loading mode) with α = 0.05 was performed. BIC significantly increased over time and under load (p < 0.0001). The highest BICs were found for loading regimes at high acceleration with medium or high frequency (F(M)A(H) and F(H)A(H)), and significantly differing from F(L)A(H) and F(M)A(M) (p < 0.02 and p < 0.005 respectively). BV/TV significantly decreased over time (p < 0.0001). Loading led to a site-specific BV/TV increase (p < 0.001). The highest BV/TV responses were found for F(M)A(H) and F(H)A(H), significantly differing from F(M)A(M) (p < 0.005). The findings reveal the potential of high-frequency vibration loading to accelerate and enhance implant osseointegration, in particular when applied at high acceleration. Such mechanical signals hold great, though untapped, potential to be used as non-pharmacologic treatment for improving implant osseointegration in compromised bone.

A randomized clinical trial comparing guided implant surgery (bone- or mucosa-supported) with mental navigation or the use of a pilot-drill template

AIM

To assess the accuracy of guided surgery (mucosa and bone-supported) compared to mental navigation or the use of a surgical template, in fully edentulous jaws, in a randomized controlled study.

MATERIAL AND METHODS

Fifty-nine patients (72 jaws), requiring four to six implants (maxilla or mandible), were consecutively recruited and randomly assigned to one of the following treatment groups; guidance via Materialise Universal(®)/mucosa, Materialise Universal(®)/bone, Facilitate™/mucosa, Facilitate™/bone, or mental navigation or a pilot-drill template. The precision was assessed by matching the planning computed tomography (CT) with a post-operative cone beam CT.

RESULTS

A significant lower mean deviation at the entry point (1.4 mm, range: 0.3-3.7), at the apex (1.6 mm, range: 0.2-3.7) and angular deviation (3.0°, range: 0.2-16°) was observed for the guiding systems when compared to mental navigation (2.7 mm, range: 0.3-8.3; 2.9 mm, range: 0.5-7.4 and 9.9°, range: 1.5-27.8) and to the surgical template group (3.0 mm, range: 0.6-6.6; 3.4 mm, range: 0.3-7.5 and 8.4°, range: 0.6-21.3°). Differences between bone and mucosa support or type of guidance were negligible. Jaw and implant location (posterior-anterior, left-right), however, had a significant influence on the accuracy when guided.

CONCLUSION

Based on these findings, guided implant placement appears to offer clear accuracy benefits.

Ultrastructural characterization of the implant interface response to loading

Dynamic loading can affect the bone surrounding implants. For ultrastructural exploration of the peri-implant tissue response to dynamic loading, titanium implants were installed in rat tibiae, in which one implant was loaded while the contralateral served as the unloaded control. The loaded implants received stimulation either within 24 hrs after implantation (immediate loading) or after a 28-day healing period (delayed loading) for 4, 7, 14, 21, or 28 days. The samples were processed for histology and gene expression quantification. Compared with the unloaded control, bone-to-implant contact increased significantly by immediate loading for 28 days (p < .05), but not in case of delayed loading. No effect of loading was observed on the bone formation in the implant thread areas, on the blood vessel area, and on endosteal callus formation. Loading during healing (immediate) for 7 days induced, relative to the unloaded control, a 2.3-fold increase of Runx2 in peri-implant cortical bone (p < .01) without a change in the RANKL/Opg ratio. Loading after healing (delayed) for 7 days up-regulated Runx2 (4.3-fold, p < .01) as well as Opg (22.3-fold, p < .05) compared with the unloaded control, resulting in a significantly decreased RANKL/Opg ratio. These results indicate a stimulating effect of dynamic loading on implant osseointegration when applied during the healing phase. In addition, gene expression analyses revealed molecular adaptations favoring bone formation and, at the same time, affecting bone remodeling.

Occlusal overload and bone/implant loss

AIM

The aim of this search was to assess the biological consequences that overload might have on already osseointegrated oral implants through a systematic screening of the scientific literature.

METHOD

Detailed searches through PUBMED, OVID, EMBASE and LILACS databases were made. Articles published up to December 2011 and those reported on the clinical, radiographic and/or histological outcome of oral implants subjected to so-called overload were considered eligible for inclusion. Identified studies were assessed by one non-blinded reviewer according to well-defined inclusion and exclusion criteria. When doubt arose, the co-authors were counselled until final agreement was obtained. The PICO questions formulated was:"what is the effect of overload vs. no overload on bone/implant loss in clinically stable implants?"

RESULTS

The database searches as well as additional hand searching, resulted in 726 potentially relevant titles. Eventually, 16 clinical and 25 animal studies were considered relevant to the topic. After inclusion/exclusion criteria assessment, all clinical studies and all but three animal studies and one systematic review were considered at high risk of bias and excluded. The included animal studies did not reveal an association between overload and peri-implant bone loss in the absence of peri-implant inflammation, whereas in its presence, overload seemed to aggravate the peri-implant tissue breakdown.

CONCLUSIONS

The effect of implant overload on bone/implant loss in clinically well-integrated implants is poorly reported and provides little unbiased evidence to support a cause-and-effect relationship. The PICO question remained unanswered. At the animal level, "overload", mimicked by supra-occlusal contacts acting in an uninflamed peri-implant environment, did not negatively affect osseointegration and even was anabolic. In contrast, supra-occlusal contacts in the presence of inflammation significantly increased the plaque-induced bone resorption.

Mechanical properties and micro-morphology of fiber posts

OBJECTIVES

To evaluate flexural properties of different fiber posts systems and to morphologically characterize their micro-structure.

METHODS

Six types of translucent fiber posts were selected: RelyX Post (3M ESPE), ParaPost Taper Lux (Colthéne-Whaledent), GC Fiber Post (GC), LuxaPost (DMG), FRC Postec Plus (Ivoclar-Vivadent), D.T. Light-Post (RTD). For each post system and size, ten specimens were subjected to a three-points bending test. Maximum fracture load, flexural strength and flexural modulus were determined using a universal loading device (5848 MicroTester(®), Instron). Besides, for each system, three intact posts of similar dimensions were processed for scanning electron microscopy to morphologically characterize the micro-structure. The following structural characteristics were analyzed: fibers/matrix ratio, density of fibers, diameter of fibers and distribution of fibers. Data were statistically analyzed with ANOVA.

RESULTS

Type and diameter of posts were found to significantly affect the fracture load, flexural strength and flexural modulus (p<0.05). Regarding maximum fracture load, it was found to increase with post diameter, in each post system (p<0.001). Regarding flexural strength and flexural modulus, the highest values were recorded for posts with the smallest diameter (p<0.001). Finally, structural characteristics significantly varied among the post systems tested. However, any correlation has been found between flexural strength and structural characteristics.

SIGNIFICANCE

Flexural strength appeared not to be correlated to structural characteristics of fiber posts, but it may rather be affected by mechanical properties of the resin matrix and the interfacial adhesion between fibers and resin matrix.

Impaired osteoblastogenesis potential of progenitor cells in skeletal unloading is associated with alterations in angiogenic and energy metabolism profile

Skeletal unloading provokes bone loss. These bone alterations have been shown to be associated with impairment of osteoblastic activity. In the present study, we evaluated the effect of skeletal unloading on bone marrow progenitor cells, for exploration of the underlying mechanism. Wistar rats were randomized to be either hindlimb unloaded for 9 days or to act as controls. Micro-CT was used to detect tibial trabecular architecture changes in response to skeletal unloading. Microgravity conditions for 9 days resulted in a decreased number and an increased spacing of the bone trabeculae in the proximal tibia. The proliferative capacity of the femoral bone marrow samples was assessed (fibroblast-colony-forming assay). By using qPCR, the expression of selected markers of vascularization (Vegfa; Hif1a; Angpt1), energy metabolism (Prkaa2; Mtor), bone formation (Runx2; Alp; Bglap; Bmp2; Bmp4; Bmp7) and bone resorption (Acp5; Tnfsf11; Tnfrsf11b) in these bone marrow suspensions was measured. We demonstrated a striking decrease in the number of fibroblastic progenitors in response to hindlimb unloading. This deficit in proliferation was shown to be accompanied by altered hindlimb perfusion and cellular energy homeostasis. Ex vivo culture assays of the bone marrow-derived progenitor cells screened for osteogenic (Runx2; Alp; Bglap) and adipogenic (Pparg; Fabp4) differentiation alterations in response to microgravity. Induced progenitor cells from unloaded rats showed a delay in osteogenic differentiation and impaired adipogenic differentiation compared to control. The data of this multi-level approach demonstrate that skeletal unloading significantly affects the bone tissue and its metabolism at the progenitor stage. The molecular expressions of the bone marrow population support a role of cellular metabolic stresses in skeletal alterations induced by inactivity.

Effect of ferrule and post placement on fracture resistance of endodontically treated teeth after fatigue loading

OBJECTIVES

To evaluate the influence of the ferrule effect (1) and the fibre-post placement (2) on the fracture resistance of endodontically treated teeth subjected to cyclic fatigue loading.

METHODS

40 extracted single-rooted upper pre-molars were sectioned at the CEJ (groups a and b) or 2mm above the CEJ (groups c and d), and subsequently endodontically treated. After 24-h water storage at 37°C, specimens were restored according to four build-up approaches (n=10 per group): (a) NF-NP (no ferrule, no post), (b) NF-P (no ferrule, fibre-post), (c) F-NP (ferrule, no post) and (d) F-P (ferrule, fibre post). RelyX Posts (3M-ESPE) were used in groups NF-P and F-P, and were cemented with Panavia F 2.0 (Kuraray). A standardized composite core was built, after which specimens were restored with an all-ceramic crown (IPS Empress CAD, Ivoclar-Vivadent) Specimens were fatigued by exposure to 1,200,000 cycles using a chewing simulator (Willytech). All specimens that survived fatigue loading were fractured using a universal loading device (Micro-Tester, Instron). A two-way analysis of variance was used to determine the statistical significance of the factors ferrule and post on fracture resistance.

RESULTS

Only one NF-NP specimen failed under fatigue. The ferrule effect significantly enhanced the fracture resistance of the restored teeth, regardless the use of a post (p=0.003). F-NP obtained the highest fracture resistance (758.52±121.89N), which was not significantly different from F-P (647.58±132.95N); NF-NP presented the lowest fracture resistance (361.52±151.69N). For all groups, only 'repairable' failures were recorded.

CONCLUSIONS

Avoiding extra-removal of sound tooth structure, rather than placing a fibre post, can protect endodontically treated teeth against catastrophic failure. However, when any ferrule can be preserved, a fibre-post may improve the retention and fatigue resistance of the restoration.

Bone tissue response to BMP-2 adsorbed on amorphous microporous silica implants

AIM

To evaluate bone regeneration potential of bone morphogenetic protein-2 (BMP-2) adsorbed on amorphous microporous silica (AMS).

MATERIALS & METHODS

Four implants [titanium as control (CTR); AMS-coated titanium (AMS), BMP-2 adsorbed on titanium (CTR+BMP) and AMS (AMS+BMP)] were implanted randomly in the tibiae of 20 New Zealand white rabbits. Bone specimens with implants were retrieved 2/4 weeks post implantation and analysed histologically and histomorphometrically. Bone fraction was measured in initial bone-free area (bone regeneration area, BRA) and in the area with initial bone-implant contact [bone adaptation area (BAA)] (BF(BRA) & BF(BAA) ). Bone-implant contact was measured in BRA (BIC(BRA) ). In vitro BMP-2 release profiles were determined to evaluate the impact of the carrier surface. Mixed models were used for statistical analysis.

RESULTS

BMP-2 release profiles were different for CTR+BMP and AMS+BMP. BIC(BRA) and BF(BRA) were significantly increased after 4 weeks compared to 2 weeks for AMS, CTR+BMP and AMS+BMP. However, no differences between the implant types were observed within both healing periods. BF(BAA) for CTR+BMP was smaller than that for CTR and AMS+BMP after 4 weeks. Despite slower BMP-2 release, AMS+BMP did not stimulate bone regeneration. CTR+BMP caused bone resorption at the bone-implant interface.

CONCLUSIONS

BMP-2 functionalized implant surfaces failed to stimulate bone regeneration and osseointegration.

Bone tissue response to implant surfaces functionalized with phosphate-containing polymers

OBJECTIVES

Inorganic polyphosphates are said to stimulate the activity of osteoblast-like cells in vitro. The purpose of this study was to evaluate in vivo bone regeneration around implants treated with polyphosphoric acid (PPA) and phosphorylated pullulan (PPL).

MATERIAL AND METHODS

Two types of implants with different surface roughness (R1: Sa ≈ 0.23 μm; R2: Sa ≈ 1.35 μm) were treated with three solutions (distilled water, 10%wt PPA, or 10%wt PPL) prior to implantation in both tibia of twelve female white rabbits. Each animal received six implants randomly positioned according to their surface roughness and treatment: R1 + water; R1 + PPA; R1 + PPL; R2 + water; R2 + PPA; R2 + PPL. Animals were sacrificed after 1 or 4 weeks, and samples were prepared for histological and histomorphometrical analysis. Bone regeneration areas were evaluated for bone-to-implant contact (BIC) and bone fraction (BF) in areas 100 and 500 μm remote from the implant surface. Data were statistically analyzed by means of Friedman and Wilcoxon matched-pair tests (P < 0.05).

RESULTS

After 1 week, bone tissue was rarely formed in the regeneration areas. After 4 weeks, implants treated with PPA presented higher ratios of BIC (R1 = 52.3 ± 13.1; R2 = 54.6 ± 11.0) than the ones treated with water (R1 = 24.1 ± 15.1; R2 = 32.4 ± 13.0). On the other hand, around the implant surface (100 μm), PPL-treated implants induced higher BF (R1 = 78.3 ± 34.1; R2 = 71.2 ± 21.8) as compared with the water-treated ones (R1 = 46.1 ± 22.0; R2 = 49.6 ± 21.0). At 500 μm, however, no statistically significant differences in BF were found among the groups evaluated (P > 0.05). Surface roughness influenced neither BIC nor BF.

CONCLUSIONS

Implant surface treatment with phosphate-containing polymers may positively influence osseointegration.

Enhancement of implant osseointegration by high-frequency low-magnitude loading

Background

Mechanical loading is known to play an important role in bone remodelling. This study aimed to evaluate the effect of high- and low-frequency axial loading, applied directly to the implant, on peri-implant bone healing and implant osseointegration.

Methodology

Titanium implants were bilaterally installed in rat tibiae. For every animal, one implant was loaded (test) while the other one was not (control). The test implants were randomly divided into 8 groups according to 4 loading regimes and 2 experimental periods (1 and 4 weeks). The loaded implants were subject to an axial displacement. Within the high- (HF, 40 Hz) or low-frequency (LF, 8 Hz) loading category, the displacements varied 2-fold and were ranked as low- or high-magnitude (LM, HM), respectively. The strain rate amplitudes were kept constant between the two frequency groups. This resulted in the following 4 loading regimes: 1) HF-LM, 40 Hz-8 µm; 2) HF-HM, 40 Hz-16 µm; 3) LF-LM, 8 Hz-41 µm; 4) LF-HM, 8 Hz-82 µm. The tissue samples were processed for resin embedding and subjected to histological and histomorphometrical analyses. Data were analyzed statistically with the significance set at p<0.05.

Principal Findings

After loading for 4 weeks, HF-LM loading (40 Hz-8 µm) induced more bone-to-implant contact (BIC) at the level of the cortex compared to its unloaded control. No significant effect of the four loading regimes on the peri-implant bone fraction (BF) was found in the 2 experimental periods.

Conclusions

The stimulatory effect of immediate implant loading on bone-to-implant contact was only observed in case of high-frequency (40 Hz) low-magnitude (8 µm) loading. The applied load regimes failed to influence the peri-implant bone mass.

In vivo assessment of the effect of controlled high- and low-frequency mechanical loading on peri-implant bone healing

The aim of this study was to investigate the effect of controlled high- (HF) and low-frequency (LF) mechanical loading on peri-implant bone healing. Custom-made titanium implants were inserted in both tibiae of 69 adult Wistar rats. For every animal, one implant was loaded by compression through the axis of tibia (test), whereas the other one was unloaded (control). The test implants were randomly distributed among four groups receiving different loading regimes, which were determined by ex vivo calibration. Within the HF (40 Hz) or LF (2 Hz) loading category, the magnitudes were chosen as low- (LM) and high-magnitude (HM), respectively, leading to constant strain rate amplitudes for the two frequency groups. This resulted in the four loading regimes: (i) HF-LM (40 Hz-0.5 N); (ii) HF-HM (40 Hz-1 N); (iii) LF-LM (2 Hz-10 N); and (iv) LF-HM (2 Hz-20 N) loading. Loading was performed five times per week and lasted for one or four weeks. Tissue samples were processed for histology and histomorphometry (bone-to-implant contact, BIC; and peri-implant bone fraction, BF) at the cortical and medullar level. Data were analysed statistically with ANOVA and paired t-tests with the significance level set at 0.05. For the one-week experiments, an increased BF adjacent to the implant surface at the cortical level was exclusively induced by the LF-HM loading regime (2 Hz-20 N). Four weeks of loading resulted in a significant effect on BIC (and not on BF) in case of HF-LM loading (40 Hz-0.5 N) and LF-HM loading (2 Hz-20 N): BIC at the cortical level significantly increased under both loading regimes, whereas BIC at the medullar level was positively influenced only in case of HF-LM loading. Mechanical loading at both HF and LF affects osseointegration and peri-implant BF. Higher loading magnitudes (and accompanying elevated tissue strains) are required under LF loading to provoke a positive peri-implant bone response, compared with HF loading. A sustained period of loading at HF is needed to result in an overall enhanced osseointegration.

Model-based guided implant insertion for solitary tooth replacement: a pilot study

OBJECTIVE

The impact of the implant position on the restorative outcome could justify guided surgery even for the single implants particularly in the aesthetic zone and especially when a simplified concept is available.

MATERIAL AND METHODS

Based on a plaster model, on which the soft tissues were mimicked (according to the thickness measured on a Cone-Beam CT), a tooth-supported, surgical template was prepared. The latter guided all drills so that even flapless implant insertion became possible. All implants were placed by students of the master-after-master training program in Periodontology.

RESULTS

The prospective cohort included a total of 34 implants, all of AstraTech (Osteospeed(®)) type, which were successfully inserted in 29 patients, 16 flapless, 32 onestage. The marginal bone along the integrated implants remained stable over time, with 0.13 mm loss during the first year. The aesthetic parameters were reassuring.

CONCLUSIONS

This simple model-based concept seems to be reliable for the guided placement of single implants and the pre-operative preparation of their restorations.

An up to 3-Year Controlled Clinical Trial Comparing the Outcome of Glass Fiber Posts and Composite Cores with Gold Alloy-Based Posts and Cores for the Restoration of Endodontically Treated Teeth

PURPOSE

This controlled clinical trial aimed to compare the 3-year outcomes of glass fiber posts and composite cores with gold alloy-based posts and cores for the restoration of endodontically treated teeth.

MATERIALS AND METHODS

One hundred forty-four patients in need of 205 restorations on endodontically treated teeth were selected and followed for 7 to 37 months (mean: 21 ± 9 months). The teeth were primarily stratified based on the remaining tissue available to restore the tooth core with or without a post. Then, randomization allocated the teeth to either test group 1 (prefabricated glass fiber posts), test group 2 (custom-made glass fiber posts), or test group 3 (composite cores without posts). The control group consisted of gold alloy-based posts and cores. All posts/cores were covered with all-ceramic single crowns. Failures were either absolute, such as root fractures or irreparable fractures of the post/core, or relative, such as loss of post retention or reparable fractures of the core. Success and survival probability lifetime curves, corrected for clustering, were drawn for the entire data set.

RESULTS

The recall rate at 3 years was 97.1%. Absolute failures consisted of two root fractures and one endodontic failure, while relative failures included three instances of retention loss of the post/core and one post fracture. Because of the low number of events, no statistical tests were performed. The success and survival probabilities over all groups together at 3 years amounted to 91.7% and 97.2%, respectively.

CONCLUSIONS

After being followed for up to 3 years, both cast gold and composite post and core systems performed well clinically. Longer follow-up times are needed to detect possible significant differences. Int J Prosthodont 2011;24:363-372.

A double-blind randomized controlled trial (RCT) of Titanium-13Zirconium versus Titanium Grade IV small-diameter bone level implants in edentulous mandibles--results from a 1-year observation period

BACKGROUND

The use of endosseous dental implants has become common practice for the rehabilitation of edentulous patients, and a two-implant overdenture has been recommended as the standard of care. The use of small-diameter implants may extend treatment options and reduce the necessity for bone augmentation. However, the mechanical strength of titanium is limited, so titanium alloys with greater tensile and fatigue strength may be preferable.

PURPOSE

This randomized, controlled, double-blind, multicenter study investigated in a split-mouth model whether small-diameter implants made from Titanium-13Zirconium alloy (TiZr, Roxolid™) perform at least as well as Titanium Grade IV implants.

METHODS AND MATERIALS

Patients with an edentulous mandible received one TiZr and one Ti Grade IV small-diameter bone level implant (3.3 mm, SLActive®) in the interforaminal region. The site distribution was randomized and double-blinded. Outcome measures included change in radiological peri-implant bone level from surgery to 12 months post-insertion (primary), implant survival, success, soft tissue conditions, and safety (secondary).

RESULTS

Of 91 treated patients, 87 were available for the 12-month follow-up. Peri-implant bone level change (-0.3 ± 0.5 mm vs -0.3 ± 0.6 mm), plaque, and sulcus bleeding indices were not significantly different between TiZr and Ti Grade IV implants. Implant survival rates were 98.9 percent and 97.8 percent, success rates were 96.6 percent and 94.4 percent, respectively. Nineteen minor and no serious adverse events were related to the study devices.

CONCLUSION

This study confirms that TiZr small-diameter bone level implants provide at least the same outcomes after 12 months as Ti Grade IV bone level implants. The improved mechanical properties of TiZr implants may extend implant therapy to more challenging clinical situations.

Peri-implant bone tissue assessment by comparing the outcome of intra-oral radiograph and cone beam computed tomography analyses to the histological standard

OBJECTIVES

The present study aims to identify radiographic methods revealing data that are most representative for the true peri-implant bone as assessed by histology.

MATERIALS AND METHODS

Eighty implants were placed in 10 minipigs. To assess matching between different image modalities, measurements conducted on intra-oral digital radiographs (IO), cone beam computer tomography (CBCT) and histological images were correlated using Spearman's correlation. Paired tests (Wilcoxon test) were used to determine changes in the bone parameters after 2 and 3 months of healing.

RESULTS

Significant correlations between bone defect depth on IO and histological slices (r= + 0.7, P<0.01), as well as on CBCT images and histological slices (r= + 0.61, P<0.01), were found. CBCT and IO images deviate, respectively, 1.20 and 1.17 mm from the histology regarding bone defects. No significant correlations were detected between fractal analysis on CBCT, intra-oral radiography and histology. For bone density assessment, significant but weaker correlations (r= + 0.5, P<0.01) were found for intra-oral radiography vs. histology. Significant marginal bone-level changes could be observed after 3 months of healing using intra-oral radiography.

CONCLUSIONS

This study allowed linking radiographic bone defect depth to the histological observations of the peri-implant bone. Minute bone changes during a short-term period can be followed up using digital intra-oral radiography. Radiographic fractal analysis did not seem to match histological fractal analysis. CBCT was not found to be reliable for bone density measures, but might hold potential with regard to the structural analysis of the trabecular bone.