The effect of different surgical drilling procedures on full laser-etched microgrooves surface-treated implants: an experimental study in sheep

Pre-Clinical Models in Implant Dentistry: Past, Present, Future

Biomedical research seeks to generate experimental results for translation to clinical settings. In order to improve the transition from bench to bedside, researchers must draw justifiable conclusions based on data from an appropriate model. Animal testing, as a prerequisite to human clinical exposure, is performed in a range of species, from laboratory mice to larger animals (such as dogs or non-human primates). Minipigs appear to be the animal of choice for studying bone surgery around intraoral dental implants. Dog models, well-known in the field of dental implant research, tend now to be used for studies conducted under compromised oral conditions (biofilm). Regarding small animal models, research studies mostly use rodents, with interest in rabbit models declining. Mouse models remain a reference for genetic studies. On the other hand, over the last decade, scientific advances and government guidelines have led to the replacement, reduction, and refinement of the use of all animal models in dental implant research. In new development strategies, some in vivo experiments are being progressively replaced by in vitro or biomaterial approaches. In this review, we summarize the key information on the animal models currently available for dental implant research and highlight (i) the pros and cons of each type, (ii) new levels of decisional procedures regarding study objectives, and (iii) the outlook for animal research, discussing possible non-animal options.

The influence of laser-microgrooved implant and abutment surfaces on mean crestal bone levels and peri-implant soft tissue healing: a 3-year longitudinal randomized controlled clinical trial

PURPOSE

The study aimed to compare clinical and radiographic parameters of peri-implant site of laser-microgrooved implants with either laser-microgrooved or regular machined prosthetic abutment post 3 years of early loading.

METHOD

Twenty edentulous sites of systemically and periodontally healthy individuals were allocated into two groups in this prospective, two-armed, randomized double-blinded clinical trial in 1:1 ratio, wherein each site received laser-microgrooved implants with either laser-microgrooved or machined prosthetic abutments. Outcome measures included full-mouth plaque (FMPS%) and bleeding score (FMBS%), site-specific plaque (SPS%) and bleeding score (SBS%), peri-implant sulcus depth (PISD mm), and mean crestal bone loss (MCBL mm) evaluated at baseline (6 weeks), 1 and 3 years post-early loading. Mean and standard deviation of all parameters were estimated, between groups and at different time points using independent and paired t-test, respectively, Normality was checked using Kolmogorov-Smirnov test and Shapiro-Wilk test, P value ≤ 0.05 was considered as statistically significant.

RESULTS

Three-year follow-up of test group showed statistically significant reduction in SPS, SBS, PISD (P value ≤ 0.001). The MCBL reduced from 1.93 mm to 0.61 mm (P value ≤ 0.001); in other words, a bone gain of 0.15 mm was obtained in the test group.

CONCLUSION

Within the limitations of the present study, laser-microgrooved implants loaded with laser-microgrooved prosthetic abutments showed superior results clinically and radiographically when compared to loading with machined abutments.

Biomechanical and histomorphometric analysis of endosteal implants placed by using the osseodensification technique in animal models: A systematic review and meta-analysis

STATEMENT OF PROBLEM

Osseodensification, a counterclockwise drilling technique for the placement of endosseous implants is a popular clinical technique. However, the effect of the osseodensification technique on primary implant stability, bone-implant contact, and bone area frequency occupancy is unclear.

PURPOSE

The purpose of this systematic review and meta-analysis was to investigate the biomechanical and histomorphometric outcomes of endosteal implants placed by using the osseodensification technique in animal models.

MATERIAL AND METHODS

An electronic search through Medline/PubMed, Lilacs, and Science Direct databases, and an additional manual search of the reference list of included articles was conducted by using specific keywords and Medical Subject Headings (MeSH) terms for articles in the English language and published up to April 31, 2020. Only animal studies comparing the biomechanical and histomorphometric outcomes of endosteal implants placed by using the osseodensification and conventional drilling protocol were included. The SYstematic Review Center for Laboratory animal Experimentation (SYRCLE) tool was used to determine the risk of bias assessment, and the quality of included studies was assessed by using Animal Research: Reporting in Vivo Experiments (ARRIVE) guidelines.

RESULTS

Nine studies were included. The results of the meta-analysis showed that the pooled weighted mean difference of the insertion torque value for the primary implant stability of endosseous dental implants placed by using the osseodensification technique was 2.270 (95% confidence interval [CI]=1.147 to 3.393; P<.001), the weighted mean difference of the percentage of bone-implant contact at 3 weeks was 0.487 (95% CI=0.220 to 0.754; P=.114), the weighted mean difference of the percentage of bone-implant contact at 6 weeks was 0.565 (95% CI=0.219 to 0.911; P=.448), the weighted mean difference of the percentage of bone area frequency occupancy at 3 weeks was 0.679 (95% CI=0.265 to 1.093; P=.073), and the weighted mean difference of the percentage of bone area frequency occupancy at 6 weeks was 0.391 (95% CI=-0.204 to 0.986; P=.027).

CONCLUSIONS

Limited data from animal studies suggest that the primary implant stability, bone-implant contact, and bone area frequency occupancy significantly improved for the endosteal implants placed by using the osseodensification technique compared with conventional drilling protocol. However, additional laboratory and clinical studies are recommended to provide stronger evidence.

Impact of salivary contamination during placement of implants with simultaneous bony augmentation in iliac bone in sheep

Our aim was to investigate the possible impact of contamination with saliva on osseointegration during placement of implants with simultaneous bone augmentation. Six hemispheric shape bone defects (8mm in diameter×4mm deep) were prepared in each iliac bone of six sheep. A dental implant (2.9mm in diameter×10mm long) was placed in the centre of each defect, and then pairs of defects were filled with one of the following bone augmentation materials: autogenous bone, autogenous bone plus bovine bone, or resorbable biphasic ceramic bone substitute. One site in each augmentation group was impregnated with saliva (contaminated group), while the other was not (non-contaminated group). Bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO) within implant threads were measured after a healing period of five weeks, both in respect of the implant inserted in the augmented bone and in that inserted in the residual bone. Overall results showed that there was a significant difference between the contaminated and non-contaminated group for BIC in the augmented implant (p=0.028), while there were no significant differences in the implant in residual bone (p=0.722). For BAFO, there were no significant differences between the contaminated and non-contaminated groups among the different augmentation materials. The results showed that contamination with saliva during placement of an implant with simultaneous bone augmentation had a serious deleterious effect on osseointegration of the aspect of the implant within the augmented defect. Contamination with saliva during placement of an implant with simultaneous bone augmentation should therefore be avoided.

Does the Drilling Technique for Implant Site Preparation Enhance Implant Success in Low-Density Bone? A Systematic Review

PURPOSE

The objective of this systematic review was to investigate the possible association between the drilling technique and proper implant integration and survival in areas with low bone density.

MATERIALS AND METHODS

An electronic search using the MEDLINE/PubMed database was performed including studies published up to April 2018. Animal and clinical studies that evaluated the association between the drilling technique and proper implant integration and survival in low-density bone were included.

RESULTS

Fifteen studies met the inclusion criteria, including 7 experimental and 8 clinical. Undersized, osteotome, Piezosurgery, and osseodensification drilling were the 4 techniques found in the literature to enhance osseointegration of implants in low-density bone. Owing to the methodological variation, meta-analysis was not performed. The 4 drilling protocols were effective in increasing primary stability, but the long-term outcome is comparable with that of the conventional surgical drilling protocol.

CONCLUSION

There is weak evidence suggesting that any of the previously mentioned surgical techniques could enhance successful osseointegration and survival of the implants placed in low-density bone.

Atemporal osseointegration: Early biomechanical stability through osseodensification

Osseointegration, the direct functional and structural connection between device and bone is influenced by multiple factors such as implant macrogeometry and surgical technique. This study investigated the effects of osseodensification drilling techniques on implant stability and osseointegration using trabecular metal (TM) and tapered-screw vent (TSV) implants in a low-density bone. Six skeletally mature sheep were used where six osteotomy sites were prepared in each of the ilia, (n = 2/technique: Regular [R] (subtractive), clockwise [CW], and counterclockwise [CCW]). One TM and one TSV implant was subsequently placed with R osteotomy sites prepared using a conventional (subtractive) drilling protocol as recommended by the implant manufacturer for low density bone. CW and CCW drilling sites were subjected to osseodensification (OD) (additive) drilling. Evaluation of insertion torque as a function of drilling technique showed implants subjected to R drilling yielded a significant lower insertion torque relative to samples implanted in OD (CW/CCW) sites (p < 0.05). Histomorphometric analysis shows that the osseodensification demonstrates significantly greater values for bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO). Histological analysis shows the presence of bone remnants, which acted as nucleating surfaces for osteoblastic bone deposition, facilitating the bridging of bone between the surrounding native bone and implant surface, as well as within the open spaces of the trabecular network in the TM implants. Devices that were implanted via OD demonstrated atemporal biomechanical stability and osseointegration. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2516-2523, 2018.

The effect of osseodensification drilling for endosteal implants with different surface treatments: A study in sheep

This study investigated the effects of osseodensification drilling on the stability and osseointegration of machine-cut and acid-etched endosteal implants in low-density bone. Twelve sheep received six implants inserted into the ilium, bilaterally (n = 36 acid-etched, and n = 36 as-machined). Individual animals received three implants of each surface, placed via different surgical techniques: (1) subtractive regular-drilling (R): 2.0 mm pilot, 3.2 and 3.8 mm twist drills); (2) osseodensification clockwise-drilling (CW): Densah Bur (Versah, Jackson, MI) 2.0 mm pilot, 2.8, and 3.8 mm multifluted tapered burs; and (3) osseodensification counterclockwise-drilling (CCW) Densah Bur 2.0 mm pilot, 2.8 mm, and 3.8 mm multifluted tapered burs. Insertion torque was higher in the CCW and CW-drilling compared to the R-drilling (p < 0.001). Bone-to-implant contact (BIC) was significantly higher for CW (p = 0.024) and CCW-drilling (p = 0.006) compared to the R-drilling technique. For CCW-osseodensification-drilling, no statistical difference between the acid-etched and machine-cut implants at both time points was observed for BIC and BAFO (bone-area-fraction-occupancy). Resorbed bone and bone forming precursors, preosteoblasts, were observed at 3-weeks. At 12-weeks, new bone formation was observed in all groups extending to the trabecular region. In low-density bone, endosteal implants inserted via osseodensification-drilling presented higher stability and no osseointegration impairments compared to subtractive regular-drilling technique, regardless of evaluation time or implant surface. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 615-623, 2019.

Nanomechanical Assessment of Bone Surrounding Implants Loaded for 3 Years in a Canine Experimental Model

PURPOSE

This work evaluated the nanomechanical properties of bone surrounding submerged and immediately loaded implants after 3 years in vivo. It was hypothesized that the nanomechanical properties of bone would markedly increase in immediately and functionally loaded implants compared with submerged implants.

MATERIALS AND METHODS

The second, third, and fourth right premolars and the first molar of 10 adult Doberman dogs were extracted. After 6 months, 4 implants were placed in 1 side of the mandible. The mesial implant received a cover screw and remained unloaded. The remaining 3 implants received fixed dental prostheses within 48 hours after surgery that remained in occlusal function for 3 years. After sacrifice, the bone was prepared for histologic and nanoindentation analysis. Nanoindentation was carried out under wet conditions on bone areas within the plateaus. Indentations (n = 30 per histologic section) were performed with a maximum load of 300 μN (loading rate, 60 μN per second) followed by a holding and unloading time of 10 and 2 seconds, respectively. Elastic modulus (E) and hardness (H) were computed in giga-pascals. The amount of bone-to-implant contact (BIC) also was evaluated.

RESULTS

The E and H values for cortical bone regions were higher than those for trabecular bone regardless of load condition, but this difference was not statistically significant (P > .05). The E and H values were higher for loaded implants than for submerged implants (P < .05) for cortical and trabecular bone. For the same load condition, the E and H values for cortical and trabecular bone were not statistically different (P > .05). The loaded and submerged implants presented BIC values (mean ± standard deviation) of 57.4 ± 12.1% and 62 ± 7.5%, respectively (P > .05).

CONCLUSION

The E and H values of bone surrounding dental implants, measured by nanoindentation, were higher for immediately loaded than for submerged implants.

Biomechanical and histologic basis of osseodensification drilling for endosteal implant placement in low density bone. An experimental study in sheep

A bone drilling concept, namely osseodensification, has been introduced for the placement of endosteal implants to increase primary stability through densification of the osteotomy walls. This study investigated the effect of osseodensification on the initial stability and early osseointegration of conical and parallel walled endosteal implants in low density bone. Five male sheep were used. Three implants were inserted in the ilium, bilaterally, totaling 30 implants (n=15 conical, and n=15 parallel). Each animal received 3 implants of each type, inserted into bone sites prepared as follows: (i) regular-drilling (R: 2mm pilot, 3.2mm, and 3.8mm twist drills), (ii) clockwise osseodensification (CW), and (iii) counterclockwise (CCW) osseodensification drilling with Densah Bur (Versah, Jackson, MI, USA): 2.0mm pilot, 2.8mm, and 3.8mm multi-fluted burs. Insertion torque as a function of implant type and drilling technique, revealed higher values for osseodensification relative to R-drilling, regardless of implant macrogeometry. A significantly higher bone-to-implant contact (BIC) for both osseodensification techniques (p<0.05) was observed compared to R-drilling. There was no statistical difference in BIC as a function of implant type (p=0.58), nor in bone-area-fraction occupancy (BAFO) as a function of drilling technique (p=0.22), but there were higher levels of BAFO for parallel than conic implants (p=0.001). Six weeks after surgery, new bone formation along with remodeling sites was observed for all groups. Bone chips in proximity with the implants were seldom observed in the R-drilling group, but commonly observed in the CW, and more frequently under the CCW osseodensification technique. In low-density bone, endosteal implants present higher insertion torque levels when placed in osseodensification drilling sites, with no osseointegration impairment compared to standard subtractive drilling methods.

Rescuing failed oral implants via Wnt activation

AIM

Implant osseointegration is not always guaranteed and once fibrous encapsulation occurs clinicians have few options other than implant removal. Our goal was to test whether a WNT protein therapeutic could rescue such failed implants.

MATERIAL AND METHODS

Titanium implants were placed in over-sized murine oral osteotomies. A lack of primary stability was verified by mechanical testing. Interfacial strains were estimated by finite element modelling and histology coupled with histomorphometry confirmed the lack of peri-implant bone. After fibrous encapsulation was established peri-implant injections of a liposomal formulation of WNT3A protein (L-WNT3A) or liposomal PBS (L-PBS) were then initiated. Quantitative assays were employed to analyse the effects of L-WNT3A treatment.

RESULTS

Implants in gap-type interfaces exhibited high interfacial strains and no primary stability. After verification of implant failure, L-WNT3A or L-PBS injections were initiated. L-WNT3A induced a rapid, significant increase in Wnt responsiveness in the peri-implant environment, cell proliferation and osteogenic protein expression. The amount of peri-implant bone and bone in contact with the implant were significantly higher in L-WNT3A cases.

CONCLUSIONS

These data demonstrate L-WNT3A can induce peri-implant bone formation even in cases where fibrous encapsulation predominates.

Osseointegration: hierarchical designing encompassing the macrometer, micrometer, and nanometer length scales

OBJECTIVE

Osseointegration has been a proven concept in implant dentistry and orthopedics for decades. Substantial efforts for engineering implants for reduced treatment time frames have focused on micrometer and most recently on nanometer length scale alterations with negligible attention devoted to the effect of both macrometer design alterations and surgical instrumentation on osseointegration. This manuscript revisits osseointegration addressing the individual and combined role of alterations on the macrometer, micrometer, and nanometer length scales on the basis of cell culture, preclinical in vivo studies, and clinical evidence.

METHODS

A critical appraisal of the literature was performed regarding the impact of dental implant designing on osseointegration. Results from studies with different methodological approaches and the commonly observed inconsistencies are discussed.

RESULTS

It is a consensus that implant surface topographical and chemical alterations can hasten osseointegration. However, the tailored combination between multiple length scale design parameters that provides maximal host response is yet to be determined.

SIGNIFICANCE

In spite of the overabundant literature on osseointegration, a proportional inconsistency in findings hitherto encountered warrants a call for appropriate multivariable study designing to ensure that adequate data collection will enable osseointegration maximization and/or optimization, which will possibly lead to the engineering of endosteal implant designs that can be immediately placed/loaded regardless of patient dependent conditions.

Are insertion torque and early osseointegration proportional? A histologic evaluation

OBJECTIVES

The objective of this histologic study was to determine the effect of three drilling protocols (oversized, intermediate, and undersized) on biologic responses to a single implant type at early healing periods (2 weeks in vivo) in a beagle dog model.

MATERIALS AND METHODS

Ten beagle dogs were acquired and subjected to surgeries in the tibia 2 weeks before euthanasia. During surgery, each dog received three Unitite implants, 4 mm in diameter by 10 mm in length, in bone sites drilled to 3.5, 3.75, and 4.0 mm in final diameter. The insertion torque was recorded during surgery, and bone-to-implant contact (BIC), and bone area fraction occupied (BAFO) measured from the histology. Each outcome measure was compared between treatment conditions with the Wilcoxon signed-rank test. Bonferroni-corrected statistical significance was set to 95%.

RESULTS

Insertion torque increased as an inverse function of drilling diameter, as indicated by significant differences in torque levels between each pair of conditions (P = 0.005). BIC and BAFO levels were highest and statistically similar in the recommended and undersized conditions and significantly reduced in the oversized condition (P < 0.01).

CONCLUSIONS

Reduced drilling dimensions resulted in increased insertion torque (primary stability). While BIC and BAFO were maximized when drilling the recommended diameter hole, only the oversized hole resulted in evidence of statistically reduced integration.