The treatment of total or partial edentulism using dental implants has become common practice in dental surgeries and is currently considered a reliable and long-lasting surgical-prosthetic treatment, with survival rates estimated at over 90% over the first 10 years (Lekholm et al., 1999). The world market for dental implants is growing at a dizzying pace, with estimated figures in recent years exceeding 23 billion dollars (Alghamdi and Jansen, 2020).

The need for implant treatments due to edentulism increases exponentially with age and, in this sense, it has been estimated that the aging of the population during the third decade of this century will reach figures of more than 20% of the total European population and 30% of the US population (Höpflinger, 2015). However, despite all the advantages they offer, according to longitudinal studies, a certain number of implants, which the scientific literature estimates at percentages of around 15%–19% for the maxilla and 1.2% for the anterior mandibular area, fail (el Askary et al., 1999a; el Askary et al., 1999b), despite the fact that Espósito et al. reported that biology-related implant failures, out of a sample of 2,812 implants, did not reach 8% in a 5-year follow-up period (Esposito et al., 1998). For the implant to be successful, there needs to be adequate bone compression around the device and immediate fixation at the moment of insertion (primary stability), as well as long-term fixation (secondary stability) (Misch et al., 2008). Primary stability is vitally important for long-term success, as it prevents micromovements of the implant during the early stages of the healing process. The degree of primary stability can be influenced by a series of factors, such as the design of the implant, the size of the osteotomy, bone density and/or the patient’s comorbidities (Heimes et al., 2023). It has been shown that high levels of primary stability at the time of implant insertion result in rapid secondary stability. Therefore, it is necessary to take maximum care of primary stability at the moment of insertion of the endosseous implant, to increase the chances of long-term permanence (Ivanova et al., 2021). It has been reported that the peri-implant bone must have a minimum thickness of 1.5 mm for the implant to support the loads (Chiapasco et al., 2009), however, bone deficit is the main drawback faced by dental implantology, and although 3D-printed scaffold-based technologies show promise for bone regeneration (Hao et al., 2024), failure rates in bone grafts are high due to insufficient blood supply necessary for integration and regeneration. When the alveolar crests lack adequate bone volume, additional surgical procedures are necessary to reconstruct and increase the bone deficit and, in this respect, several systematic reviews have identified the most appropriate techniques to provide the quality and quantity of alveolar bone necessary to allow the placement of a dental implant and, in addition, ensure its survival over time (Aghaloo and Moy, 2007; Aghaloo et al., 2016; Chiapasco et al., 2006). These reviews conclude that there is a certain discrepancy in the results of successes and failures of implants placed in surgically modified deficient ridges, with some indicating a higher failure rate (Crespi et al., 2021), others no significant differences (Elnayef et al., 2015) and others even reporting high success rates (Waechter et al., 2017; Anitua et al., 2013). This leads to a certain degree of confusion among clinicians, which means that making decisions based on scientific evidence when it comes to gaining bone volume in atrophic alveolar ridges is a complex task that is difficult to assess and predict. Furthermore, the variables change continuously, due, above all, to technological developments, the macro and micro design of the implants and the sophisticated diagnostic (Wang et al., 2025) and surgical techniques used. On the other hand, the avalanche and the large increase in publications in recent years on bone gain in atrophic edentulous ridges make it almost impossible to keep up to date with the latest techniques and appropriate instruments (Figure 1) and for all these reasons, the clinician must have the appropriate knowledge and criteria to put into practice the necessary surgical procedures that will provide the best results.

Horizontally deficient alveolar ridges are a common clinical situation, for which various procedures are performed to increase the crestal width: guided bone regeneration (GBR), division and expansion of the alveolar ridge, block bone grafts, etc. The division of the alveolar ridge was described by Tatum (1986), although it was Simion et al. (1992) who perfected it and published it in great detail in 1992. In 1994, Scipioni described the crestal expansion technique (CET) in edentulous jaws in a 5-year retrospective study on a large sample of 170 subjects and 329 implants (Scipioni et al., 1994). Subsequently, in 1999, he published a histological study on hard tissue repair in edentulous sites treated with the CET in 20 humans, suggesting that osteoblasts differentiate from pre-existing mesenchymal cells located in the original walls of the fissure, with the consequent deposition of new bone in the surgically created intraosseous defect (Scipioni et al., 1999).

“Bone compaction” (BC) and “bone densification” or “osteodensification” (ODT) are terms used to define a series of techniques that, through the use of certain surgical instruments, such as osteotomes, expanders, or specially designed surgical drills, generate compaction of the bone trabeculae. This produces tension from the osteotomy of the bone bed towards the outside, elastically deforming the bone through the tension produced by the osteodensifying surgical device, which, unlike perforating devices, does not cause bone loss. The elastic deformation of the bone would tend to return to its original shape when the tension disappears, increasing the original bone density. (Tricio et al., 1995).

All this, together with the incorporation of new techniques and equipment into clinical practice, would mean optimal use of alveolar ridges with bone deficiency, transforming them into useful sites for implant placement.

The aim of this systematic review and meta-analysis was to evaluate the effectiveness of bone expansion, compaction, and densification methods in narrow alveolar ridges to determine their usefulness in placing long-lasting dental implants, focusing on their impact on bone density (BD), alveolar crest expansion (ACE), and implant stability quotient (ISQ).

A total of 2,464 records were originally identified (981 in PubMed/MEDLINE, 1,382 in WOS, 26 in EMBASE, 11 in Cochrane Central and 64 in Dentistry and Oral Sciences), and 2,116 duplicate records relating to clinical case reports, animal studies and in vitro studies were eliminated in an initial screening. In a second screening, a further 306 records were eliminated because they were considered irrelevant or because they reported data that was of no interest for the objectives set out in our study, leaving 47 studies to be evaluated and their eligibility determined. Of these, 37 were eliminated because they either did not provide data, or the data they did provide was in the form of graphs or figures that could not be analyzed mathematically/statistically, leaving 10 studies (Vaddamanu et al., 2024; Rizk et al., 2024; Tofan et al., 2024; Tushar et al., 2024; Ahmed et al., 2022; Salman and Bede, 2022; Yadav et al., 2022; Bergamo et al., 2021; Koutouzis et al., 2019; Anitua and Alkhraisat, 2016) to include in our systematic review and meta-analysis in synthesis, qualitative and quantitative (Figure 2).

In addition to systematically reviewing the current scientific literature, our study used a meta-analysis to evaluate the effectiveness of methods of bone expansion, compaction and densification in deficient alveolar ridges, in order to predict their usefulness when installing long-lasting dental implants. To increase the power of this systematic review, several types of studies were combined: RCTs, case series and prospective and retrospective studies. However, this particularity skews and limits the results. In fact, the studies with the worst evaluation were the prospective and retrospective ones that were not guided by randomization criteria; however, when the sample sizes of the primary studies are small, the combination of studies increases the statistical power.

The main result of our meta-analysis was that bone expansion, compaction, and densification methods in narrow alveolar ridges increase BD, ACE, and ISQ, making them useful for receiving dental implants.

A meta-analysis consists of conducting systematic reviews of quantitative and mathematical-statistical data from individual studies, using the data provided by the included studies, and calculating a statistical mean and an effect size for the event or treatment studied. Meta-analysis evaluates the need for future research (Sterne et al., 2019; Bown and Sutton, 2010), depending on the quality of the individual studies included (Straus and McAlister, 2000; Scheidt et al., 2019). Muka et al. (2020) proposed guidelines on how to conduct a systematic review and meta-analysis of observational studies and pooled RCTs, which served as a guide for our study.

Five RCTs (Vaddamanu et al., 2024; Rizk et al., 2024; Tofan et al., 2024; Tushar et al., 2024; Ahmed et al., 2022) and five observational studies (Salman and Bede, 2022; Yadav et al., 2022; Bergamo et al., 2021; Koutouzis et al., 2019; Anitua and Alkhraisat, 2016) met the inclusion criteria. The study by Tushar et al. (2024) found no differences in the ISQ between the groups comparing the motorized expanders and the osteodensifying drills; however, the motorized ridge expanders proved to be more effective in expanding the ridge, with a highly significant value (p < 0.01) and achieved, after 6 months, better primary stability than the ODT. These results would be contrary to those reported in the literature (Gaikwad et al., 2022; Lima Monteiro et al., 2024; Inchingolo et al., 2021).

The BD was evaluated by two RCTs (Vaddamanu et al., 2024; Ahmed et al., 2022) highlighting the benefits of ODT on BD and the primary stability of the implant, with the distal region of the osteotomy presenting the greatest BD (Vaddamanu et al., 2024). Ahmed et al. (2022) attribute the advantages of ODT to the autograft bone particles that would function as a nucleus for faster bone development around the implant, which could reduce healing time. However, Inchingolo et al. (2021) in a recent meta-analysis highlighted what we have emphasized about the existing contradictions in this regard in the literature. Some studies provide solid results that confirm the benefits of ODT, backed up by some statistically relevant values (Padhye et al., 2020; Hindi and Bede, 2020; Pai et al., 2018) and others, on the contrary, do not provide data that demonstrate differences in relation to the conventional technique. Koutouzis et al. in a retrospective multicenter study (Koutouzis et al., 2019) found no significant differences in the mean expansion value between the groups treated with and without ODT. Two preclinical studies in experimental sheep models (Lahens et al., 2019; Trisi et al., 2016) also found no differences in the osseointegration of implants placed with or without ODT. In this respect, the conclusions of a preclinical study published in the Journal of Dental Research (Wa et al., 2017) in a murine model are striking, providing evidence that condensation can increase the density of the peri-implant bone, although it does not guarantee greater bone-implant contact, nor does it improve implant stability. Compacted bone is denser, in the sense that it has a higher bone volume/total volume (BV/TV), however, this compacted bone would be structurally damaged and weakened (Zhang et al., 2021).

Tushar et al. (2024), Ahmed et al. (2022) compared variations in implant stability (ISQ index) in expanded bones in two RCTs; the first study using motorized expanders and the ODT, and the second using manual expanders and the ODT. Tushar et al. (2024) support the use of motorized expanders over bone densification, since, according to the authors, it limits CE. These conclusions would contradict certain reviews of the scientific literature that give greater popularity to the use of osteotomes, especially in the maxillary bone, due to the lower possibility of generating heat and the greater initial stability of the implant, due to lateral bone condensation (González-García et al., 2011; Jha et al., 2017). For their part, Ahmed et al. (2022) resorted to crestal corticotomy, combined either with manual expanders or osteodensifying drills, granting the latter technique greater implant stability, with results coinciding with those of Huwais and Meyer (2017). Bergamo et al. (2021) carried out a prospective multicenter study on 56 patients and 150 implants in several institutions, with a follow-up period of 6 months, and found that the ISQ values were higher for the experimental group (osteodensifying drills) compared to the control group (threaded osteotomes). However, despite the fact that implant insertion torque is the most common criterion for assessing adequate primary stability (Gallucci et al., 2018) and that low insertion torque (≤35 N force) is a controversial factor in the survival rate of dental implants, a recent systematic review with meta-analysis by Darriba et al. (2023) who evaluated the success rates at 24 months in 326 implants with immediate loading, concluded that a low insertion torque does not have a significant effect on implant survival rates. In this respect, another systematic review and meta-analysis carried out by Be et al. (2016) which included four studies in humans and six in animals, highlighted the lack of evidence in favor of high or low torque implants for our outcomes of interest: bone resorption, implant failure and BIC.

All these conclusions from the different studies lead us to consider the discrepancies that exist in the scientific literature on insertion torque values, from those who recommend low or moderate values, which allow the formation of considerable amounts of new bone that recovers around the implant (BIC, bone to implant contact) during the first stage of osseointegration (Duyck et al., 2015), to those who propose high insertion torques (>80 N) on the grounds that these high ISQ values would not cause bone resorption or implant failure (Consolo et al., 2013; Trisi et al., 2011). An example of this is the study by Khayat et al. (2013) who reported, in a prospective controlled clinical trial in humans, that the use of a high insertion torque of up to 176 N did not prevent osseointegration of the implant and did not cause marginal bone loss. Another recent comparative study (Arpudaswamy et al., 2024) that evaluated insertion torque and ISQ at the time of implant placement, and secondary stability metrics such as ISQ 3 months after insertion, between implants inserted into osteotomy sites prepared with conventional drills and osteosynthesis drills in the femoral condyles of New Zealand white rabbits, with low-density bone (type D4), showed that implants placed using ODT exhibited superior initial stability and superior stability progression, compared to those placed using conventional drilling techniques. Clinically, this would mean that ODT shows a higher insertion torque and a higher ISQ, by improving the bone density and volume surrounding the implants. This increased stability can lead to better osseointegration and a reduction in healing times, which ultimately benefits patients with compromised bone quality. On the other hand, Schierano et al., in a preclinical study published at the beginning of 2025 (Schierano et al., 2025), highlight the advantages of piezoelectric surgery in biological and clinical responses, especially in the increase of certain osteogenic factors and the formation of new bone, as well as a possible association with an increase in the ISQ.

CE was a clinical parameter evaluated in eight studies (Rizk et al., 2024; Tofan et al., 2024; Tushar et al., 2024; Ahmed et al., 2022; Salman and Bede, 2022; Yadav et al., 2022; Koutouzis et al., 2019; Anitua and Alkhraisat, 2016), resulting in the most highly valued of the three analyzed. Four of them were RCTs (Rizk et al., 2024; Tofan et al., 2024; Tushar et al., 2024; Ahmed et al., 2022) and four more (Salman and Bede, 2022; Yadav et al., 2022; Koutouzis et al., 2019; Anitua and Alkhraisat, 2016) were observational studies. Within the context of RCTs, Rizk et al. (2024), Tushar et al. (2024) and Ahmed et al. (2022) compared ODT with CE techniques, such as threaded expanders, either manual (Rizk et al., 2024), motorized (Tushar et al., 2024) or crestal corticotomy (“split”) (Ahmed et al., 2022). The results reported by these studies are completely contradictory. Rizk et al. (2024) analyzed fourteen implants placed in eight patients, seven using the osteodensifying drill technique and seven using expansion with manual threaded expanders. The analysis was carried out at three points: point 0 (below the implant cover screw), point A (1 mm below the level of the cover screw) and point B (2 mm below the level of the cover screw), in the immediate postoperative period and 6 months after placement. In the immediate postoperative period, they found a statistically significant difference between the two groups at points 0 and A in the experimental group (ODT) with the control group (manual expansion); however, the difference at point B was not statistically significant. Six months after insertion they found that the crest was undergoing continuous remodeling and, in some implants, the width of the alveolar crest was slightly less than the width of the preoperative alveolar crest. They even attribute the failure of three implants (despite the normal radiographic image of the surrounding bone) to the increase in bone density in the narrow alveolar crest, which could have caused a decrease in blood supply and an increase in temperature during surgery, for which reason they recommend using expansion techniques only in cases where other more predictable methods for horizontal bone augmentation are not feasible, such as GBR, bone blocks and crestal splitting. The conclusions of Rizk et al. (2024) are contradicted by those of Tushar et al. (2024), Ahmed et al. (2022) who propose expansion techniques (motorized expanders, ODT and split techniques) as effective methods for the expansion of narrow ridges. A systematic review carried out by Padhye et al. (2020) concluded by stating that, through ODT, bone expansion is achieved at the osteotomy site, although they recognize the need for well-designed prospective cohorts and randomized controlled trials to definitively establish the credibility of these techniques, both in the biological aspect and in clinical success. Similar conclusions are proposed by Inchingolo et al. (2021) who recommend thorough training of professionals before resorting to these techniques, considering them, from a practical point of view, complex to perform in inexperienced hands, describing the studies carried out to date as” modest and immature”, something we do not agree with, since the three studies discussed (Rizk et al., 2024; Tushar et al., 2024; Ahmed et al., 2022) achieved an adequate score on the JBI MAStARI scale of methodological quality, especially the study by Rizk et al. (2024) which achieved almost the maximum score.

The observational studies included (Salman and Bede, 2022; Yadav et al., 2022; Koutouzis et al., 2019; Anitua and Alkhraisat, 2016) evaluated 86 patients who received 119 implants with different conclusions that are presented and discussed below: Salman and Bede (2022) in a prospective study of 23 subjects, evaluated CE in narrow alveolar ridges, with low BD, before and after the use of osteodensifying drills, reaching the conclusion that the use of this type of device produced bone expansion without dehiscence or fenestration, increasing the width of the alveolar crest between 4 and 5.3 mm and allowing the simultaneous placement of implants with high primary and secondary stability. These results would be consistent with those obtained by Koutouzis et al. (2019) who, in a retrospective multicenter study of 21 subjects, also concluded that ODT allowed for an expansion of the alveolar crests in the coronal area of 3–8 mm (average 5.2 mm). Other studies (Tricio et al., 1995) also coincided in their results with the previous ones, reporting, through these expansion techniques, increases in crestal width ranging from 1.1 to 2.4 mm. Jarikian et al. (2021) in a non-randomized clinical study of 11 patients who had received 28 implants, compared ODT with bone densifying drills in narrow alveolar ridges (4–5 mm), obtaining similar results with an average of 2.36 mm of expansion, compared to the 1.5 mm achieved with threaded expanders. However, some preclinical studies have reported different results with regard to bone expansion, using ODT. Yeh et al. (2021) found that the ODT increased bone mineral density and primary contact between bone and implant in bovine rib segments; they also suggested that implant placement using ODT, compared to conventional drilling, can increase ridge dimensions in narrow alveolar ridges. Similarly, Li et al. (2023) demonstrated ex vivo that ODT increases the primary stability of cylindrical implants without overheating the bone and significantly increases the width of the crest. However, Tian et al. (2019), in atrophic mandibular ridges, in a porcine model, compared the ODT with the conventional osteotome technique, finding no significant differences between the two with regard to the degree of crestal CE. Yadav et al. (2022) assessed the stability of twenty-two implants placed in the maxilla and mandible of as many subjects after narrow ridge augmentation (assessed by CBCT), using the crestal split corticotomy technique. The preoperative bone width had an average value of 3.64 ± 0.41. After the operation, the bone width increased to an average value of 5.62 ± 0.45 mm, with a statistically significant postoperative period (p < 0.001). In this respect, a recent systematic review (Manekar et al., 2023) that analyzed twenty-two cohort studies and two randomized controlled trials, with 634 patients and 1,287 implants placed after alveolar ridge splitting and expansion, found an overall survival rate of 98.07% at 3 months of follow-up. They also showed that motorized expanders, as well as being a minimally invasive procedure, reduce the number of surgical procedures and the total duration of treatment and are recommended for osteocondensation. It should be noted, however, that the study by Yadav et al. (2022), together with Bergamo et al. (2021), Koutouzis et al. (2019) were the lowest rated in terms of methodology (5 points), as they did not report or left unclear issues of great relevance such as the randomization and blinding of participants and personnel involved in the study, which greatly limits the analysis of their results.

In a retrospective cohort study involving 20 patients and 31 implants (26 of which were placed in the posterior mandibular area), Anitua and Alkhraisat (2016) proposed the placement of transitional implants with a diameter of 2.5 and 3 mm, following CE with motorized threaded expanders, in crests with horizontal bone atrophy. In the second surgery, the transitional implant was removed, and the definitive dental implant was placed. Using CBCT, they verified that the preoperative width of the alveolar crest was originally 3.1 mm and the “guided bone augmentation” increased this width to 5.1 mm. This study reinforces the indication of crestal split in the treatment of horizontally atrophic jaws. Recently, a meta-analysis evaluated alveolar ridge splitting in implant surgery. This study by Lin et al. (2023) included twenty-four observational studies and one RCT; fourteen of the included studies investigated horizontal bone gain and seventeen examined implant survival. This meta-analysis found that the width obtained by crestal division was 3.633 mm within the range of 2.0–5.3 mm, which is consistent with what was reported by Anitua and Alkhraisat (2016). In addition, they found that the implant survival rate exceeded 98%, similar to the rate obtained with standard implant placement procedures. However, Crespi et al. (2021) in a retrospective study of thirty-eight patients, reported significantly lower incremental crestal values in the mandible than in the maxilla; nevertheless, the survival rates of the implants placed were 100% for the mandibles and 95.5% for the maxillas. The different expansion achieved in the mandible and maxilla could be explained by the fact that the buccal bone in the maxilla is highly viscoelastic and flexible, and this minimizes bone trauma. In contrast, the buccal wall of the mandible is made of harder, corticalized bone, which makes crestal division difficult. On the other hand, Altiparmak et al. (2017) had already reported that crestal splitting had a higher survival rate than onlay bone grafting (100% and 92%, respectively) and Mahmoud et al. (2020) had previously reported that there were no significant differences in the increase in crestal width between autologous bone block grafting and ridge splitting with flapless piezoelectric surgery. All of this would mean that the ridge splitting technique could shorten the treatment period, reduce postoperative inflammation and pain, eliminate the need for second surgeries, shorten treatment times and reduce costs. These considerations are at odds with the technique proposed by Anitua and Alkhraisat (2016) which, in addition to being complex and unsuitable for professionals without a certain level of experience, since the removal of the transitional devices can lead to bone fractures, lengthens the treatments and raises their cost, not exactly facilitating patient collaboration. Studies on new drilling techniques will help to alleviate many of these drawbacks (Fan et al., 2023).

Our study revealed a number of limitations that are worth highlighting: In terms of methodology, the heterogeneity of the studies included (RCTs and observational studies), together with publication and selection biases. Regarding the clinical aspect, the different surgical techniques and instruments used, the different methods of measuring the parameters analyzed, the different anatomical locations for expansion, and the follow-up periods.

All of this makes it hard to do a proper evaluation and means that the conclusions we present should be taken with some caution.

i) The two studies that evaluated BD were homogeneous, with a significant trend toward the intervention group.

Despite the limitations, all this would mean that expansion, compaction and ODT in narrow alveolar ridges could be useful and reliable for clinicians when placing long-lasting dental implants, but more well-designed studies are needed to corroborate these results.