Implant Stability After Graftless Motor-Driven Crestal Sinus Elevation: A Cohort Study

Introduction

The generally poor quality bone in the edentulous posterior maxillary ridge, combined with maxillary sinus pneumatization, presents a challenge for clinicians when placing dental implants.¹ As a result, this particular region of the oral cavity reportedly has a relatively high implant failure rate.^2,3 As early as 1980, Boyne and James presented the lateral window surgical technique to overcome the limitations inherent in a decreased interarch space when blade implants were planned.⁴ Several years later, Tatum recommended a modified approach requiring a U-shaped window design that is tapped in to produce a greenstick fracture of the lateral maxillary sinus wall.⁵ Once access is established, the site can be grafted. Although various bone graft materials have been suggested since the introduction of the technique, it was shown that the implant success is not linked to the type of bone graft used.^6,7 An additional modification to the surgical technique included Summer’s use of an osteotome for sinus floor elevation, advocated as a less invasive surgical approach to augment the subantral bone height for implant placement in the posterior maxilla.⁸ Summers also added bone graft material that should create a hydraulic plug to treat the perforation of the Schneiderian membrane. He referred to this technique as “bone-added osteotome sinus floor elevation (BAOSFE),” sequentially using a series of parallel-sided osteotomes in the osteotomy site.⁹ According to the author, this approach ensures the presence of bone underneath the sinus membrane and around the apex of the proposed implant. A high survival rate (96%) was reported when the technique was used in the presence of 6.0 mm or more of alveolar bone for placing a 10.0-mm long implant.¹⁰ However, because crestal sinus elevation is considered a blind surgical approach and success rates decline after elevating the sinus membrane for more than 4.0 mm, the lateral window approach is preferred when the subantral bone height is less than 6.0 mm.¹⁰ Conversely, clinical complications such as membrane perforations, injury to the arterial blood supply, and acute sinusitis can be expected with the lateral window approach. The incidence of maxillary sinus membrane perforation was reported to range between 25% and 44%.^11–15

Several techniques were later introduced to minimize the potential for perforation of the maxillary sinus. For example, blunt pressure is applied crestally, such as the “balloon technique” for greater augmentation. The aim is a safer elevation with substantial augmentation using a balloon with saline injection.¹⁶ Although the first description of the technique required the preparation of a lateral window osteotomy, subsequent modifications were reported that had similar amounts of sinus elevation but with lower perforation rates when used crestaly.^16,17 The balloon technique was later examined on human cadavers under arthroscopic evaluation and revealed that the incidence of maxillary sinus perforation ranged from 0% to 44%.¹⁸ In 2005, Chen and Cha presented the hydraulic pressure technique, which showed significant sinus augmentation with fewer complications.¹⁹ Then, in 2000, Cosci and Luccioli proposed a technique where specially designed 30° lifting drills were used to access the maxillary sinus floor gently without perforating the sinus membrane.²⁰ This technique was later tested on a randomized controlled trial basis, showing a mean vertical bone gain of 6.48 mm with a cumulative implant survival rate of 96% on an average of 48 months.²¹

Great efforts were dedicated to investigating the best grafting material to be used while attempting a crestal sinus lifting and simultaneous implant placement; however, due to the high osteogenic potential and regenerative capabilities of the Schneiderman membrane, it seems that with different grafting materials, implant possesses comparable survival outcomes.^22,23 Platelet-rich fibrin (PRF) has also been investigated with positive results.²⁴ Furthermore, a “graftless” approach (ie, without using any bone graft material) after sinus lifting has been proposed as a predictable method for bone augmentation in the maxillary sinus.^25–34 This is an encouraging alternative since the use of graft material as part of the sinus lift procedure may increase the time of surgery, cost, and risk of dislodgment of the graft material into the sinus, especially after sinus membrane perforations leading to potential infections³⁵ and/or ostium blockage.

Some drawbacks of the crestal sinus lift approach have been reported in the literature. These include: sinus membrane perforation,³⁶ generally an uncomfortable procedure for patients due to the constant tapping of osteotomes using mallets, and benign paroxysmal positional vertigo (BPPV).³⁷ BPPV is a vestibular end-organ disorder described as short, recurring episodes of vertigo provoked by specific head movements in the plane of the posterior semicircular canals.³⁸ Trauma induced by tapping using a mallet during a crestal sinus lift together with hyperextension of the neck may displace otoliths and results in BPPV.³⁹ Symptoms involved with BPPV can be very unpleasant and severe enough to dramatically limit patients from carrying routine daily activities.³⁷ The motor-driven crestal sinus lift screw system (MD-CSLS) (MIS, Dentsply, Charlotte, NC, USA) has been developed to overcome the limitations of the conventional osteotome technique for crestal approach sinus lifts and facilitate the procedure. In this system, screws with latch-type connections to motor-driven handpieces or manual ratchets are designed with a tapered geometry and concave tips. Screws come in 3 diameters: 3, 3.5, and 4 mm. Furthermore, length markings are set on 8, 10, and 13 mm.

Different methods are available for objective assessment of osseointegration. Resonance frequency analysis (RFA) is a noninvasive diagnostic technique used intra- and post-operatively to assess implant stability.^40–44 It is considered a highly objective method. Ostell (Ostell, W&H, Bürmoos, Austria) is one device that can measure RFA readings. Low-implant stability is when an implant stability quotient (ISQ) reading of less than 60 is reported; medium stability is when an ISQ reading between 60 and 70 is noted, and high stability is when an ISQ reading of more than 70 is reported.^41,44

Although different studies investigated several crestal approach sinus lift methods, the authors do not know of any studies regarding the MD-CSLS. Additionally, most studies investigating the influence of graftless crestal approach sinus lifts focused on bone formation after the procedure. To the investigators’ knowledge, no studies reported the impact of the graftless motor-driven crestal sinus elevation on implant stability.

This study aimed to evaluate the stability of implants installed using motor-driven drills simultaneously with graftless crestal sinus elevation (ie, graftless motor-driven crestal sinus elevation). The null hypothesis was that the stability of the implants, represented by RFA, installed using this technique was not significantly different than the clinically accepted level of implant stability represented by an RFA value of 65 ISQ.^41,44

Materials and Methods

This prospective cohort study was designed with the following inclusion criteria: healthy patients (ASA 1 or 2) between 21 and 70 years of age, mild smokers (less than 12 cigarettes/d), controlled diabetic patients (HbA1c < 7.5%), patients with mild sinus membrane thickening, patients requesting implant treatment in the posterior maxilla with a residual ridge height of 6 mm or more, and with elevated height not exceeding 4 mm. All implants were Straumann BLT implants (Straumann, Straumann Group) and were installed using MD-CSLS drills simultaneously with a graftless crestal sinus elevation (Figure 1). Patients with the following attributes were excluded: patients with medical conditions negating implant treatment, moderate to frequent smokers (more than 12 cigarettes/d), patients undergoing head and neck radiation, patients in need of lateral window sinus augmentation (more than 4 mm increase in vertical bone height), patients reporting active sinusitis, and patients with moderate to severe sinus membrane thickening. Ethics approval was granted from [redacted for peer review] Ethical Committee. Patients were recruited from the patient pool of the [redacted for peer review] and signed an informed consent before undergoing their surgeries. The purpose of the study and why patients were selected were included in the explanations provided to the patients.

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Furthermore, patients were assured that the benefits outweighed the risks. Confidentiality was protected by using anonymous data collection methods, and data was stored in a separate database from other study databases, which identify participants using identification numbers only. Study forms with possible identifiers were accessible to study personnel only and were stored in locked cabinets. No incentive was provided to patients, and no patients had participated in previous clinical studies.

All implant placements were performed under local anesthesia using 2% lidocaine 1:100 000 epinephrine. No antibiotic prophylaxis was given before the surgery. A full mucoperiosteal flap was reflected, and osteotomies were performed per the manufacturer’s recommendations. Implant dimensions were selected after carefully evaluating the restorative space and bone availability. The flap was repositioned using polyglactin (Vicryl, Johnson & Johnson MedTech) sutures. All patients were covered with 875 mg amoxicillin/125 clavulanate potassium (Augmentin, GlaxoSmithKline Pharmaceuticals Ltd) after surgery every 12 hours for 7 days. ISQ values were measured immediately after surgery (baseline) and after a period of healing using resonance frequency analysis (RFA) with an Ostell device (Ostell, W&H). To increase the reliability of the outcome variable, ISQ measurements were taken twice at each time point for each implant at different angles by the same clinician, and an average of the 2 measurements was used to represent implant stability.

Before conducting parametric analyses, the normality assumption was assessed using z-scores formed by dividing skewness by the standard error of skewness. A z-score within ±3.29 is indicative of a normal distribution.⁴⁵ Pearson correlations were conducted to rule out the significance of confounding factors that might influence the degree of postsurgical change in stability after a healing period. The effects on postsurgical and posthealing stability of registered perforations during surgery and on posthealing stability or a lack of primary stability were determined using independent samples t-tests. The effects on post-surgical and post-healing stability of the level of insertion torque were assessed using a one-way analysis of variance. The homogeneity of variances was assessed using Levene’s tests. A paired t test was used to determine the significance of the change in stability from immediately after surgery to the measurements taken after a healing period. In addition, a 1-sample t test was used to compare implant stability after healing to a known clinically acceptable ISQ value of 65. Data analysis was performed using the Statistical Package for the Social Sciences (SPSS v.26). A P value < .05 was accepted as the significance level for all comparative analyses. An independent statistician reviewed the methodology and results.

Results

To ensure independence of observations in patients where multiple implants are placed in the same patient, one of the 2 implants was excluded, and only one implant from each patient was included. Only the first implant placed in the same patient was included. This assures that each patient is represented only once in the sample.

Thirty-two patients were initially included in the study. However, 3 patients were excluded during the study due to early implant failure. The final sample of 29 patients included 17 males and 12 females ranging in age from 29 to 65 (mean: 52 ± years). Two patients were mild smokers, and 4 patients were controlled diabetics. Implant characteristics are summarized in Table 1. All variables were normally distributed (z < ± 3.29). Ten perforations were detected during surgery. Twenty-five implants achieved primary stability, while 4 did not. Twenty-three implants achieved an insertion torque equal to or exceeding 35 Ncm and were placed using a 1-stage surgical approach. Six implants achieved less than a 35 Ncm insertion torque and were placed using a 2-stage approach with cover screws.

Table 1 Summary statistics for implant characteristics

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There was a significant increase in postsurgical implant stability after a period of healing (t [28] = 2.2, P = .035). The duration of healing varied considerably, ranging from 6 to 32 weeks, but the length of healing was not significantly correlated with the amount of the increase in implant stability (r = .17, P = .373). The mean ISQ value of 77.1 after healing was significantly higher than the clinically acceptable integration value of 65 ISQ (t [28] = 14.6, P < .001). No significant relationships were found between the amount of increase in implant stability and implant length or implant width (Table 2).

Table 2 Pearson correlations between the increase in implant stability after healing and potential confounding variables

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There were no significant differences in average ISQ values measured immediately postsurgery or after healing between implants with and without registered perforations during surgery (Table 3). The posthealing stability of the 4 implants that did not achieve primary stability was not significantly less stable after the healing period than those that had achieved primary stability (Table 4). Finally, level of insertion torque (<15 Ncm, 15–20 Ncm, ≥35 Ncm) significantly impacted implant stability immediately postsurgery (P < .001), but the ISQ values measured after healing were not significantly different based on the initial insertion torque values (P = .131; Table 5).

Table 3 Comparison of implant stability immediately after surgery and after healing between implants with and without registered perforations during surgery

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Table 4 Comparison of implant stability after healing between implants with and without primary stability

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Table 5 Comparison of implant stability immediately after surgery and after healing based on the level of initial insertion torque

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Discussion

This study evaluated implant stability using a graftless motor-driven crestal sinus elevation technique. Results of this study indicated that implants placed using this technique achieved clinically acceptable stability, exceeding the benchmark of an RFA value of 65 ISQ. Hence, the null hypothesis was rejected. This result supports the use of the graftless technique, which may reduce the duration and cost of surgery and eliminates the possibility of unintentional dislodgment of graft material into the maxillary sinus, which might cause reactions by blocking sinus ostium and hence compromise patency leading to sinus infections. Moreover, using motor-driven drills will eliminate the uncontrolled force used with the conventional osteotome technique and eliminate the chances of BPPV associated with the conventional osteotome technique.

Furthermore, treatment costs will decrease due to eliminating graft expenses. A graftless technique provides similar stability of implants compared to the conventional method by promoting de novo bone formation (Figure 2), which will eliminate a variable contributing to intraoperative and postoperative complications. Although the results of this study are promising, they should be interpreted carefully due to the relatively small sample size. However, since this is the first study investigating such a technique and its influence on implant stability, it may be the foundation for further studies with larger sample sizes to be conducted.

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There was a significant increase in implant stability after healing (P =.035). This is similar to other studies and was expected due to secondary stability achieved after osseointegration.⁴⁶ Moreover, posthealing implant stability was significantly higher than the clinically acceptable integration value of 65 ISQ (P <.001).

There was no significant difference between the level of implant stability either immediately after surgery or after healing between implants with registered perforations during surgery and those with no perforations detected (P = .118 and P = .366, respectively). The perforation rate in this study was calculated to be 34%. A systematic review conducted by Tan et al reported that intraoperative perforations were the most common surgical complication during the transalveolar sinus lift technique, with a rate of up to 21.4%.⁴⁷ Furthermore, a cadaver study conducted by Garbacea et al using real-time sinus endoscopy reported an overall sinus perforation rate of 40%.³⁶ Hence, this study’s 34% sinus perforation rate falls within the range reported in the literature. However, this rate might be understated since microscopic perforations are relatively challenging to detect visually in the surgical field.³⁶ Sinus perforations in this study were repaired using cross-linked collagen membranes without adding a bone graft.

In this study, the level of insertion torque significantly impacted implant stability immediately postsurgery (P < .001), but the ISQ values measured after healing were not significantly different based on the initial insertion torque values (P = .131). In a study conducted by Silva et al, it was reported that there was no correlation between insertion torque and ISQ values.⁴⁸ The systematic review also reported that ISQ and insertion torque are independent.⁴⁹ Nonetheless, in a study published by Turkyilmaz et al, ISQ and insertion torque were correlated.⁵⁰ However, in their study, ISQ values were only recorded after surgery as a measure of primary stability, as opposed to our study, which recorded ISQ values immediately after surgery and after a healing phase. It is noteworthy to mention that in our study, implants achieving insertion torques lower than 35 Ncm received cover screws, and a 2-stage approach was followed.

In this study, healing duration was not correlated with posthealing implant stability (P = .373). This aligns with the findings documented in the literature.⁴⁶ It is noteworthy that the minimum healing duration in our study was 6 weeks. In our study, implants achieving insertion torque lower than 35 Ncm were left longer to heal than those achieving insertion torque higher than 35 Ncm. Our study’s mean healing duration (15.52 weeks) was similar to common practice (approximately 4 months) before implant restoration. This reflects early healing (short-term) patterns and should not be interpreted as implant performance in the long term. Further studies are needed to validate the short-term results of this study on long-term healing.

In our study, implant length and width did not play a significant role in the increase in stability during the healing period (P = .764 and P = .085, respectively). Balleri et al evaluated implant stability using Osstell in partially edentulous patients with a mean implant length of 11.9 mm and concluded no correlation between implant length and ISQ values.⁵¹ The effect of implant width on ISQ values reported in our study is not aligned with what is reported in the literature. Garcia et al reported that wider implants increased ISQ values after surgery and healing.⁵² Likewise, Ostam et al reported that wider diameter platforms could positively correlate with higher ISQ values.⁵³ This may be explained by the fact that implants included in other studies were placed in healed sites with no sinus augmentation involved, as in our study. Moreover, poor bone quality in the posterior maxilla in our study may have provided less cortical bone for engagement, which may have minimized the advantage gained from wider implants.

Limitations of this study include the relatively small sample size, the short-term nature of the healing pattern, and the absence of a control group. The authors suggest areas of future investigations should include larger sample sizes, long-term healing durations with at least a 1-year follow-up, and other groups including more variables (such as platelet-rich fibrin and particulate bone graft regeneration) and using different implant systems.

Conclusion

The results of this study suggest that implants placed using a graftless motor-driven crestal sinus elevation achieved clinically acceptable stability, exceeding the stability value of 65 ISQ. Implant stability significantly increased after placement with no significant correlations with the healing duration or implant width or length.

Abbreviations

BPPV

benign paroxysmal positional vertigo

ISQ

implant stability quotient

MD-CSLS

motor-driven crestal sinus lift screw system

PRF

platelet-rich fibrin

RFA

resonance frequency analysis