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Basic and Clinical Research

Correlation Between Insertion Torque and Survival Rates in Immediately Loaded Implants in the Maxilla: A Retrospective Study

Rizkallah, Nadia DMD*; Fischer, Scott DDS*; Kraut, Richard A. DDS

Author Information
doi: 10.1097/ID.0b013e3182938cf1
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Abstract

With various advances in implant microtopographic surfaces and design, practitioners have been able to modify the original Brånemark protocol to a great extent.1,2 Several studies have shown that single-stage surgery with immediate placement of dental implants after extraction and immediate loading of implants has predictable and successful results comparable to those of the traditional 2-stage protocol.3–5 However, the specific criteria for success have yet to be definitively established in the literature or are still subject to great debate. A multitude of studies have attempted to establish a correlation relating several variables and measurements, including the location of the implant (maxilla vs mandible, anterior vs posterior),5 health of the implant site (ie, presence of periapical pathology),6 bone quality (I–IV),7 peak insertion torque value,1,8–11 percentage of bone contact,12 Periotest (Medizintechnik Gulden, Modautal Germany) values,13 and resonance frequency analysis,13,14 to the successful osseointegration of implants.

The aim of this study was to evaluate the survival rates of immediately loaded implants in the maxilla placed with a wide range of insertion torque and to determine if there is any correlation between insertion torque and successful osseointegration.

Materials and Methods

390 NobelReplace Select Tapered implants (Nobel Biocare USA, Yorba Linda, CA) were placed in the maxillae of 145 patients from January 2011 to April 2012. Of the 145 patients, 83 were women and 62 were men, and the average age of all patients was 57.5 years. The implants were placed either in fresh extraction sites or in a healed ridge with or without prior socket preservation or bone graft. All implants were placed under local anesthesia or intravenous conscious sedation. Every patient received prophylactic antibiotics (2 g of ampicillin, 600 mg of clindamycin, or 500 mg of azithromycin) via IV, a corticosteroid (20 mg of intravenous Decadron), and a 5- to 10-day postoperative course of oral antibiotics (875 mg of Augmentin twice a day, amoxicillin 500 mg thrice a day, or clindamycin 300 mg 4 times a day). No strict criteria were used to exclude patients from the study (ie, certain medical conditions, bruxism, history of smoking, etc).

All of the cases were performed by the same attending surgeon or by surgical residents under direct supervision of that attending surgeon. After achieving adequate sedation and/or local anesthesia, full-thickness mucoperiosteal flaps were elevated to an extent that provided adequate visualization. For cases that required extraction with immediate implant placement, each extraction was performed atraumatically with the use of elevators, forceps, and, when needed, a Hall drill (fissure bur) under copious irrigation. The extraction sockets and surrounding tissues were curetted of all granulation tissue and debris and then thoroughly irrigated. All osteotomies were performed under copious irrigation using a NobelReplace Select Tapered system. Sequential osteotomies were performed using appropriate drill sizes. Depending on the bone type and density, underpreparation of the implant site was utilized whenever it was deemed necessary to attain adequate 35 to 45 N.cm insertion torque. The peak insertion torque was recorded using a Crane Electronics digital torque wrench with a straight driver. All implants with an insertion torque under 20 N.cm were excluded from the study and either replaced with a larger diameter implant or buried for 6 months before loading (2-stage protocol).

All implants included in the study were immediately loaded within 24 hours. Prefabricated standard (straight or angled) or temporary abutments were used and modified if required. Restorations were either prefabricated in a laboratory (metal or nonmetal reinforced temporary restorations) or fabricated chairside using a polycarbonate shell and acrylic resin or simply acrylic or composite resin. Each provisional restoration was designed to receive an occlusal load, and all eccentric contacts were relieved. Closure of all mucoperiosteal flaps was performed using 3-0 Vicryl and 3-0 Chromic Gut sutures. Postoperative recommendations were given to all patients including dietary restrictions (soft diet for 6 weeks and avoid chewing hard food on the temporary restoration for 3 months), hygiene instructions, and appropriate follow-up (1 week, 2 weeks, 1 month, 4 months, and 6 months). Impressions for the final restoration and insertion of the final prosthesis were performed between 4 and 12 months of integration. The last radiograph taken of definitively loaded implants (which consisted of panoramic, multiple intraoral periapical radiographs, or in some instances, a cone beam computed tomography) ranged between 2 weeks and 7 months after implant placement.

Results

The 390 implants included in the study were placed in 15 different groups of peak insertion torque (by increments of 10 N.cm). Table 1 shows the number of successful and failed implants recorded for each group. The average insertion torque for all 390 implants was 72.0 N.cm, with a range from 23.8 to 178 N.cm. The 381 successful implants had an average insertion torque of 72.1 N.cm. The 9 failures had an average insertion torque of 69.2 N.cm.

Table 1
Table 1:
Success and Failures by Insertion Torque Value

The average insertion torque for each tooth number (Table 1; Fig. 1) and for each implant size (Table 2; Fig. 2) was also evaluated. By tooth number, the average insertion torques were fairly consistent, with site #10 having the lowest average insertion torque of 62.9 N.cm (n = 40) and site #12 having the highest average insertion torque of 78.3 N.cm (n = 32). When analyzing the average insertion torque by different implant sizes, a positive correlation was made between increasing implant diameter and increased insertion torque. Only five 6.0-mm-diameter implants were placed and, due to the small sample size, they were not included in this discussion. The average insertion torque for 3.5-mm-diameter implants was 57.0 N.cm (n = 52); for 4.3-mm-diameter implants, it was 72.3 N.cm (n = 278), and for 5.0-mm-diameter implants, it was 84.1 N.cm (n = 55). Overall, three 3.5-mm implants failed, five 4.3-mm implants failed, and one 5.0-mm implant failed. Finally, there seems to be no significant correlation between the type of abutment and the survival of the implant, as failures included 6 standard abutments and 3 temporary abutments.

Fig. 1
Fig. 1:
Average insertion torque (N.cm) of implants placed for each tooth site (3–14). Refer toTable 2 for more information regarding number of implants placed and number of failures for each tooth site.
Table 2
Table 2:
Number of Implants Placed, Average Insertion Torque, and Failures by Tooth Number
Fig. 2
Fig. 2:
Average insertion torque (N.cm) for each implant size (diameter and length). The figures are grouped together based on implant length (10, 11.5, 13, 16 mm) and are color coded to reflect the diameter of each implant.

Overall, 6 patients experienced failures with 9 (2.3%) total implants failing, with insertion torques ranging from 45.8 to 134 N.cm. One failure was a single-unit implant, and the other 8 failures served as abutments in multiple-unit implant-supported prostheses. One patient accounted for 4 of the failed implants, with all 4 implants placed into this patient having failed before the insertion of the final prosthesis. At the time of implant placement, the bone quality of this patient was noted to be poor (type IV), but adequate insertion torques (51.4, 61, 88.1, and 94 N.cm) were still attained by “underprepping” of the implant sites. One patient had a single failure in which the implant was placed next to a preexisting implant (already restored) that was later found to be failing due to periodontal sequelae from retained excess cement. The other 4 failed implants had no identifiable cause for failure. Seven of the failures had natural mandibular dentition opposing them, and the other 2 failures were opposed by dentition with crowns. Addressing the medical conditions of the 6 patients with failures, 2 had gastroesophageal reflux disease, 1 had hypertension (controlled), 1 was a smoker (1/2 pack per day), 1 had hyperlipidemia, and 1 had osteoporosis with a history of bisphosphonate use (Actonel for 6 months) (Table 3).

Table 3
Table 3:
Total Number of Implants Placed and Number of Failures by Implant Size

Discussion

As implant technologies and surgical techniques progress, so do the expectations of the patient. Patients are becoming more educated about treatment options, and their demands for immediate prostheses can only be expected to increase in the future. Patients also understand that implant therapy is a time-consuming and costly endeavor, and thus failures can be very disappointing for both the patient and practitioner. A multitude3–6,8–10,15–21 of studies have been published aimed at identifying certain criteria that can help guide the practitioner in achieving predictable results when placing immediately loaded implants.

On a micro level, Liu et al12 inserted implants into artificial bone and found a positive correlation between the insertion torque value and the bone-implant contact percentage. Trisi et al7 placed implants into fresh bovine bone and determined that increasing the peak insertion torque reduces the amount of micromotion at the implant-bone surface, producing an implant with a higher degree of primary stability. In a follow-up article, Trisi et al11 placed implants into sheep in 2 groups of insertion torque: high torque (110 N.cm) and low torque (10 N.cm). They found that not only did the high-torque implants have a greater degree of primary stability, but also they produced microcracks in the bone that led to a greater degree of bone remodeling as compared to the low torque group. Contrary to the previous literature stating that high insertion torque leads to disruption of microcirculation with subsequent bone necrosis, the authors’ histological examination did not reveal any areas of bone necrosis caused by compression forces during the insertion of high-torque implants. This study corroborates this finding, as there was no increase in failure rates of implants that were placed with very high levels of insertion torque. This study included 68 implants that were placed with greater than 100 N.cm of insertion torque, and of this group, only 1 implant failed (1.5%).

On a macro level, Ottoni et al1 found a significantly higher failure rate in implants placed with minimal insertion torque (20 N.cm) compared to implants placed with an adequate insertion torque (32 N.cm) and recommended that single-tooth implants should be considered for immediate loading only if they are placed with an insertion torque greater than 32 N.cm. Norton10 called into question the importance and predictive value of insertion torque in their study as they found that of 68 implants placed with minimal peak insertion torque (≤25 N.cm), only 3 failed. Degidi et al9 compared implants inserted with low insertion torque (≤20 N.cm) and implants inserted with higher torque (25–50 N.cm) and found no statistically significant difference in survival rates after 1 year. Additionally, Becker et al17 analyzed 100 immediately loaded implants placed with low insertion torque (15 N.cm or an implant stability quotient of 50 using resonance frequency analysis) and found only 1 failure at the 1-year recall appointment.

The current study had only 4 implants placed with insertion torques between 20 and 30 N.cm, with no failures in this group. Although this sample size is too low to be able to draw any conclusions that would relate minimal insertion torque and implant survival, this study had an abundance of data pertaining to implants inserted with high insertion torque. Contrary to the findings of Walker et al,8 this study was unable to show any apparent correlation between increased insertion torque and higher success rates of osseointegration. The 381 successful implants had an average insertion torque of 72.1 N.cm, and the 9 failures had an average insertion torque of 69.2 N.cm. However, it is evident that high insertion torque produces high success rates. The author showed that by modifying the osteotomy technique (“underprepping”), it is possible to routinely achieve high insertion torque when placing maxillary implants. This can be reflected by the correlation between implant diameter and the average insertion torques achieved (3.5 mm and 57.0 N.cm, 4.3 mm and 72.3 N.cm, 5.0 mm and 84.1 N.cm). This correlation reflects the effectiveness of “underprepping” the implant osteotomy in attaining high insertion torque,22 as the 4.3-mm-diameter and 5.0-mm-diameter implants can benefit from an underprepped osteotomy, whereas the 3.5-mm-diameter implant cannot (smallest diameter drill in the set).

Conclusions

One conclusion that can be drawn from this study is that immediate loading of implants in the maxilla is indeed a successful and predictable treatment option. This study confirms the findings of Esposito et al,18 Grandi et al,19 and Capelli et al,20 who found no statistically significant difference in prosthesis success, implant success, or marginal bone levels when comparing different loading regimens (immediate [<1 week], early [1 week–2 months], and traditional [>2 months]). Additionally, similar to the findings of Lindeboom et al,21 this study showed that maxillary implants subjected to immediate functional loading can achieve high rates of osseointegration. Of the 390 immediately loaded implants in this study, only 2.3% failed. This is a failure rate that is acceptable by any criteria and approaches that of the traditional 2-stage protocol.

There is no question that more randomized, controlled, clinical trials are needed to evaluate immediately loaded implants and determine what the exact criteria for success should include. In particular, more research is needed to elucidate the relationship between minimal insertion torque and the osseointegration of immediately loaded implants. The goal of future studies should be to evaluate, prospectively, what is the minimum level of insertion torque that produces acceptable success rates of osseointegration according to the design and microstructure of any specific implant. Before this is clarified, each individual practitioner must determine what is the acceptable minimum level of insertion torque for any given case when immediately loading implants.

Disclosure

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

References

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Keywords:

immediate load; insertion torque

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