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Meta-Analyses and Systematic Reviews

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

El-Kholey, Khalid E. DDS,*,†; Elkomy, Aamna BDS

Author Information
doi: 10.1097/ID.0000000000000917
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Abstract

Osseointegration has been believed to be the most important prerequisite for the long-term success of dental implants. Implant stability at the time of implant placement, known as primary stability, has been suggested to be the crucial factor for achieving successful osseointegration.1,2 Primary stability depends largely on the bone quality,3,4 shape of the fixture,5–7 and the drilling protocol for implant site development.8 When poor-quality bone is present at the implant site, such as in the posterior edentulous maxillary area, the achievement of proper osseointegration and consequently the long-term success can be extremely challenging9,10

Several classification systems and procedures were proposed for assessing the bone quality and predicting outcomes because mechanical behavior of the bone is a vital factor in the achievement of osseointegration.11–14 The classification suggested by Lekholm and Zarb12 in the assessment of bone density has dominated the dental literature during the past 2 decades. Although this method may provide valuable information about bone density, it has recently been considered to be subjective. Schwarz et al15,16 introduced the concept of using computerized tomography scan that was more objective for preoperative quantitative assessment of patients requiring dental implant treatment. The implant placement in low-quality bone, type IV, has a higher chance of failure compared with the other types of bone. This type of bone is often found in the posterior maxilla, and usually there is a higher implant failure rate.17,18

Surface modification of implants and their macrogeometric engineering19–23 have been the most investigated variables with respect to how implant stability can be affected. However, the effect of the drilling protocol on implant success is not clear. Several surgical protocols have been proposed to enhance survival of implants in bone of low density.24–27 One of these surgical techniques is the undersized drilling technique that has been introduced to locally optimize the bone density by using a final drill diameter considerably smaller than the implant diameter. This method has resulted in higher insertion torque values, which are an indicator of improved primary implant stability, and may increase the chance of implant success rate.28–30 This technique described previously has been mentioned in the literature under many names, for example, undersized,28 modified,24 or adapted31 drilling technique.

Another technique has been introduced that consists of first preparing a small-sized pilot hole, then gradually compressing the bone tissue laterally and apically using a hand osteotome. The goal of this technique is to place the implant with a high degree of stability without removing additional bone, which is theoretically believed to improve final bone healing.32 Recently, a similar technique to osteotome but using specially designed burs has been introduced named osseodensification for improving the integration of dental implants. The theory behind this technique is that drill designs allow for the creation of an environment that increases the initial primary stability through densification of the osteotomy site walls by means of nonsubtractive, counter-clockwise drilling, which improves bone contact with the implant and hastens bone growth.33 A relatively recent valuable alternative to the traditional drilling technique in the implant site preparation is the use of Piezoelectric surgery that has been used in implant osteotomy because of its safe, precise, less traumatic potential with soft tissue preservation and better bone healing.34,35

Considering that the drilling technique might influence the primary and secondary stability of dental implants that have been considered the crucial factor for achieving successful osseointegration, the aim of this systematic review was to investigate the influence of different surgical techniques including the undersized drilling, the osteotome, and the osseodensification on the successful osseointegration and survival of dental implants in the posterior maxilla. The present systematic review was focused on a question: Is there scientific evidence that these techniques for implant site preparation can enhance implant integration and success in low-density bone of posterior maxilla?

Material and Methods

The MEDLINE/PubMed database for articles published before April 2018 was searched. For the identification of the related studies to be considered in this review, combinations of the following keywords were used: implant site preparation, osseointegration, primary implant stability, impact of different bone quality, selection of drilling technique, osteotome technique, undersized drilling, Piezosurgery, ultrasonic implant osteotomy, modified drilling technique, low-density bone, posterior maxilla, implant survival, and osteotomy dimension. An additional manual search of reference lists from the selected manuscripts was then conducted.

Any clinical or animal studies published in English, and comparing any drilling protocol that aimed to enhance osseointegration or implant success in low-density bone with the conventional drilling technique, whatever the outcome used in evaluation, were included in our review. In vitro or ex vivo studies were excluded from our review and any study with no clear data about location of the implants in low-density bone area.

The titles and abstracts (when available) of all articles identified through the electronic searches were scanned independently by the 2 review authors. For studies appearing to meet the inclusion criteria, or for which there were insufficient data in the title and abstract to make a clear decision, the full report was obtained and was assessed independently by the 2 review authors to establish whether they met the inclusion criteria or not. Disagreements were resolved by discussion. After an electronic and manual search, duplicated titles from different databases were merged, and titles obtained were screened for eligibility. Abstracts of the selected titles were then analyzed, and irrelevant studies were excluded. Full texts of the eligible articles were obtained for the analysis using the stated inclusion/exclusion criteria. After comprehensive full-text analysis and full agreement between reviewers, further articles were excluded, and all other remaining studies were included in this systematic review. For each study, the following data were extracted: the year of publishing, drilling technique used, sample size, number of implants, follow-up time, and study's outcome summary and results.

Results

This systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement guidelines. The workflow for the study selection is depicted in Figure 1. From the initial electronic search, 904 articles were obtained. After screening the titles independently by the 2 review authors, 794 were excluded for not being related to the review topic. After abstract analysis, more articles were excluded, and the full texts of the 68 remaining articles were obtained, plus more 5 related articles through the references of the selected papers. A total of 73 full-text articles were assessed in detail for potential inclusion/exclusion criteria. After the full-text analysis, 17 articles seemed to meet the inclusion criteria.26,36–49 Of the 17 potentially eligible studies, 2 clinical studies had to be excluded because there was no comparison to the conventional technique in their studies.24,25 Thus, a total of 7 animal studies26,36,37,40,41,47,48 and 8 clinical studies38,39,42–46,49 that met the inclusion criteria were included. An overview of the selected studies' characteristics is summarized in Table 1 for the animal study and Table 2 for the clinical study. Owing to methodological variations between studies, it was decided not to perform a meta-analysis.

Fig. 1
Fig. 1:
Flow chart illustrating the search strategy to select the eligible studies, it was done based on PRISMA guidelines.
Table 1
Table 1:
Detailed Data for the Included Animal Studies Showing Year of Study Publishing, Drilling Technique Used, Sample Size, Number of Implants, Follow-up Time, and Study' Outcome Summary and Results
Table 2
Table 2:
Detailed Data for Included Clinical Studies Showing Year of Study Publishing, Drilling Technique Used, Sample Size, Number of Implants, Follow-up Time, and Study' Outcome Summary and Results

Characteristics of the Included Surgical Drilling Techniques

Undersized implant site preparation

In this review, there were only 2 experimental studies36,37 that investigated the role of the undersized drilling technique in the low-density bone. The iliac crest bone in the sheep model was used which mainly consists of porous trabecular bone with a thin cortical layer that makes this model highly appropriate to evaluate the bone healing response in low-density bone. The histomorphometric parameters assessed were bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO). At 3 weeks of implantation, the undersized implants showed higher BIC values and less BAFO than the conventionally drilled implants. At 6 weeks, the 2 tested variables for the 2 groups seemed to be comparable. The BIC of the conventional drilling implants improved with the time.

Two prospective studies investigated the effect of the undersized drilling technique on primary implant stability and long-term implant survival rate of implants placed in the posterior maxilla area. Both of them evaluated the bone density through cone beam computed tomography and manual estimation at the first drill. The first study showed a 100% survival rate after 1 year with a comparable mean probing depth for both techniques, and although there was a higher insertion torque at implant insertion for the undersized group, there was no significant difference when compared with the standard drilling protocol.38 The survival rate in the second study was 96.6% after 3 ± 1 years, and a significant higher mean maximum insertion torque and resonance frequency analysis values were found for the undersized implant group.39

Osteotome technique

The first experimental study about the value of osteotome in implant site preparation in low-density bone investigated the influence of the osteotome technique on insertion torque and stability values when compared with the conventional surgical drilling of the implant site in the distal femoral condyle of 52 New Zealand White rabbits. After 2 weeks, the BIC was significantly higher for the osteotome technique, and it was still significantly better at 4 weeks. Eight weeks after implant placement, the BIC was still better for the osteotome technique compared with the conventional implant placement. However, it was no longer statistically significant. The bone area ratio was also measured at different times and showed initial increase in favor of osteotome without significant difference, and at 8 weeks, it became better than conventional drilled implants.40 Another recent study with a split-mouth model was conducted in 58 mice, and for evaluation of the results, μCT and lateral stability testing, as well as histology, histomorphometric analyses, and immunohistochemistry were used. Results showed that condensation increased bone density, but it simultaneously damaged the bone and triggered a prolonged period of marginal bone resorption. Collectively, the study demonstrated that condensation does not necessarily positively contribute to implant stability.41

Five included clinical studies were designed to compare the osteotome technique and conventional drilling technique in low-density bone of the posterior maxilla.42–46 cone beam computed tomography scans were performed before surgery to assess bone density and bone volume of the planned osteotomies in all the included study except in the Sadeghi46 study, where bone quality was assessed based on the surgeon's perception of bone resistance during drilling and implant placement. The first study42 was designed to quantitatively assess the primary and secondary stability of 16 fixtures. Primary stability in the osteotome group increased from day 0 to day 30, whereas it decreased in the conventional drilling group. At 90 days, both groups showed similar results. No statistically significant difference between insertion torque and resonance frequency analysis was found across all time intervals between the 2 groups. The second included a clinical observational study;43 a total of 102 implants, 56 self-tapping and 56 non–self-tapping, were used. Implants with either macrodesign, placed after bone condensing, achieved significantly higher stability immediately after surgery and during the entire 12-week observation period compared with implants placed by the conventional drilling technique. The outcomes of this study indicated that implant stability optimization in the soft bone can be achieved by the lateral bone-condensing technique, regardless of the implant macrodesign.

The third clinical study44 with a total of 40 implants in 18 participants and 6 months of follow-up showed that the early implant success rate after placement was 100% for the osteotome and conventional drilling technique. In the fourth study's clinical trial,45 48 implants were placed into the edentulous maxillary posterior region in the same positions bilaterally. Significant higher implant stability was recorded immediately after surgery and during the whole observation period of 6 weeks for the osteotome technique compared with the bone-drilling technique. The last study46 was conducted as a controlled randomized clinical trial; 54 dental implants were placed in 32 patients; 29 implants were placed in the osteotome group and 25 in the conventional drilling group. Implant stability was assessed at 4 time intervals namely at baseline, one, 2, and 3 months after implant placement using resonance frequency analysis. Secondary stability based on the implant stability quotient was better for the osteotome group with no statistically significant difference between the 2 groups at any of the measurement times.

Osseodensification technique

The first in vivo study47 that investigated the effect of osseodensification on the initial stability and early osseointegration of conical and parallel-walled implants in low-density bone was in 2016. Five male sheep were used, where 3 implants were inserted in the ilium, bilaterally. Each animal received 3 implants of each type, the bone sites prepared by 3 techniques, regular drilling technique, clockwise osseodensification, and counter-clockwise osseodensification drilling. The last 2 techniques were considered 2 test groups where Densah Bur (Versah, Jackson, MI) was used. Insertion torque as a function of the implant type and drilling technique revealed higher values for osseodensification relative to regular drilling, regardless of implant macrogeometry. A significantly higher BIC for both osseodensification techniques was observed compared with conventional drilling. Trisi et al26 also conducted a study in sheep to compare between implants inserted by the osseodensification and implants inserted after conventional drilling. Ten implants for each technique were inserted, and after 2 months of healing, the sheep were killed, and biomechanical and histological examinations were performed. Results showed significant increase of bone volume percentage (approximately 30% higher) in the osseodensification group. Significantly better removal torque values and micromotion under lateral forces were also recorded for the test group in respect of the control group.

Piezoelectric surgery for implant site preparation

Only one animal study and one clinical study were found in the literature to evaluate the piezoelectric method in implant osteotomy in the bone with reduced quality. Zizzari et al48 used the iliac crest of the sheep as a model to compare tissue response and healing around implants placed using the piezoelectric tool versus the conventional drills. They noticed through the histological examination a more rapid healing around implants positioned using piezoelectric bone surgery and the presence of a more organized newly formed bone tissue compared with those inserted through the conventional drill technique at healing times 15 and 30 days. However, immunohistochemical analysis of iNOS and Bax showed higher expression of these in the tissues around implants prepared by conventional drills at both healing times, but without any significant difference.

In a randomized controlled clinical study, as a split-mouth design and with installation of 40 implants distributed equally in the posterior maxilla of the same patients using either piezoelectric drill or conventional drill, many parameters such as insertion torque, plaque and gingival indices, probing depth, and sulcular fluid collection were evaluated. They showed no difference between using the piezoelectric and conventional drills for implant site preparation in low-density bone. The survival rate of implants and crestal bone loss at 12 and 24 weeks were comparable.49

Discussion

The purpose of this systematic review was to evaluate whether there is scientific evidence to support the possible effect of the drilling techniques on achieving implant integration and enhancing its success in areas with low-quality bone. The surgical drilling techniques that were found in the literature investigating the association of successful osteointegration or the survival rate of implants placed in low-quality bone were the undersized drilling, the osteotome, the piezoelectric drill, and the osseodensification technique.

The major limitation of this study is that there were large methodological differences between the studies. Most of the selected articles had small or very small sample sizes, with relatively short follow-ups. Therefore, the studies' results could not be directly compared. For this reason, meta-analysis was not performed. There were many in vitro19,31,50–52 and ex vivo53,54 studies evaluating the association of the techniques included in our review and implant site preparation in low-quality bone, but we do not include any of these studies. We were looking for actual association between the selected drilling techniques and successful osseointegration, not the factors that help in prediction of success of implant integration or estimating absence of deleterious possible effects.

When evaluating whether the undersized drilling technique could enhance the primary implant stability, the 2 included observational clinical studies38,39 did not show a significant difference between the undersized drilling and the standard drilling techniques, but it was clearly in favor of the undersized group. The authors concluded that using thinner drills for implant placement in sites with poor bone density is beneficial in enhancing primary implant stability. The higher primary stability of implants inserted after undersized drilling compared with those inserted after standard drilling might be interpreted by considering that the implants placed in undersized beds could compress the bone and increase its density, thereby enhancing the primary implant stability. However, animal studies36,37 evaluated in a total 144 implants only divided into study and control groups showed that although the primary stability and BIC increased for implants placed after undersized preparation at 3 weeks after implantation, implants of both techniques had equal amount of BAFO and secondary stability at 6 weeks. This is in agreement with the findings of Stocchero et al28 who stated in their review about biomechanical, biologic, and clinical outcomes of undersized implant surgical preparation that biologic response in long-term healing after undersized implant placement is comparable with that in the conventional drilling protocol, and although the clinical studies indicate that performing an undersized drilling protocol in low-density bone is a safe procedure, more extensive studies with good follow-up time are needed to confirm these data.

Regarding the survival of the implants of the undersized and conventional drilling techniques, there was no significant difference, and the overall survival rate was 100% for both groups after 12 months in 1 study38 and 96.6% in other one after 3 ± 1 years.39 There was no significant difference in the mean probing depth between groups in 1 study.38 However, without any information about the amount of marginal bone loss or any other outcome evaluating the implant success criteria in any of the studies, the obtained results were of no significant difference than those that were detected between the under drilling and the conventional drilling techniques. The relatively small sample size of those 2 studies (the total number of implants is 112, divided into 2 groups) likely made them not able to demonstrate any significant difference in outcome measures between groups. Therefore, further clinical prospective studies and randomized controlled trials with larger sample sizes are required to provide compelling scientific-based evidence of the influence of the undersized drilling technique on the proper integration and success of implants in low-density bone.

When evaluating the osteotome technique, 2 experimental studies40,41 compared 110 implants installed with the osteotome technique to equal number placed with the conventional drilling technique. The result was contradictory, where the first study concluded that the osteotome technique was superior to the traditional drilling technique in enhancing the primary stability;40 the second study demonstrated that condensation did not positively contribute to implant stability. The last study explained in detail that the high primary stability comes from the smaller osteotomy site that increases interfacial bone density but simultaneously damages the bone, which triggered an immediate and protracted period of bone resorption.41 In the conventional drilling sites, where a closed chamber is created in between the implant thread and the surrounding bone, blood can be sustained within the chamber resulting in bone formation that by time produces a gradual increase in implant stability.7,55 This is in agreement with the findings of Jimbo et al56 who stated that the overall stability of the implant with the osteotome technique has been suggested to decrease the most during the stability transition stage from primary mechanical to secondary biologic stability, and this is one of the critical stages where the implant could disintegrate. On the other hand, with the conventional drilling, implants show lower primary stability; however, because most of the implant surface is contacting the blood, bone remodeling will not undergo resorption but induces contact osteogenesis.57

Regarding the 5 clinical studies included in our review, although they found a positive association between using the osteotome technique and the primary implant stability but in respect of the influence of the osteotome technique on secondary implant stability, Xing et al42 found no significant influence of using osteotome on secondary implant stability when compared with the conventional drilling technique. Another 2 different studies found that there was significantly higher mean stability levels for implant sites prepared by bone condensing compared with bone drilling at all time points during the observation period.43,45 In a total of 260 implants that were included in these studies, the survival rate was 100% for both osteotome and conventional drilling techniques. However, the follow-up was very short ranging from 1.5 to 6 months. The too total small sample size in 4 of the included studies42,44–46 (16, 40, 48, and 54 implants) and relatively small sample size in one of them43 (102 implants) to provide any reliable evidence and methodological differences might be responsible for these contrasting results. Absence or short follow-up time is another shortcoming in these studies.

In evaluating the osseodensification technique, the 2 in vivo studies26,47 demonstrated that this technique is able to increase the implant primary stability and maintain implant secondary stability and to increase the bone volume around dental implants inserted in low-density bone in respect of conventional implant drilling procedures. Osseodensification avoided bone sacrifice that seems unavoidable with conventional drilling procedures and prevented fractured trabeculae causing a delayed bone growth, as with the osteotome technique.41 These encouraging results in animal studies showed the need for more studies to confirm the results showed in these 2 studies and to start trials in human applications. Regarding the piezoelectric for implant site preparation, although rapid healing and more organized new bone formation around implants inserted using piezoelectric drill was demonstrated in the experimental study,48 there were no differences in the clinical outcomes for the implants installed in the posterior maxilla by the conventional or piezoelectric technique. The probing depth, plaque and gingival indices, and crestal bone loss were comparable for both techniques in the only clinical study included in our review. This is in addition to the similar survival rate of the implants in both techniques in the 6-month observation time.49

During preparation of this article, a similar systematic review about the effect of instrument used for implant site preparation on the bone implant interface was published and the authors did not find great effect for the instrument in the investigated aspect, and they stated that the influence of the instrument depends on the property evaluated.58 In his review about methods to improve osseointegration of dental implants in low-quality bone, Alghamdi59 investigated different factors including effect of drilling technique, and concluded that developments regarding implant surface modifications seem more critical for bone healing and improving osseointegration at sites that lack sufficient quantity or quality of bone than the drilling technique or other factors. In contrast to that, Toia et al60 in their recent study about the adapted drilling protocol stated that “a presurgical radiographic assessment and the perception of bone quality are necessary to select an optimal drilling protocol and to minimize surgical trauma.”

The number of implants considered in the studies included in the present review is generally few and with short follow-up times and no comment on marginal bone status in most studies; it must be disclosed that available data are limited before drawing definitive conclusions. Also, included clinical studies did not show a high level of evidence because no randomized clinical trial with good follow-up time was found on this topic. From the biomechanical standpoint, the drilling protocol included here to enhance osseointegration of the implants in low-density bone is effective in increasing insertion torque, but the biologic response in long-term healing after them is comparable with that in the conventional surgical drilling protocol.

Conclusion

Studies indicate that using these protocols on low-density bone is a safe procedure but with weak evidence suggesting that any of previously mentioned surgical techniques could improve osseointegration and survival of the implants placed in low-density bone. More extensive studies are needed to confirm these data.

Disclosure

The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.

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Keywords:

posterior maxilla; osseointegration; implant drilling protocol; implant survival; low-quality bone

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