Effect of biologic materials on the outcomes of horizontal alveolar ridge augmentation: A retrospective study

Abstract Purpose The purpose of this study was to investigate if the addition of biologic agents to a particulate bone graft enhances horizontal ridge augmentation outcomes in terms of bone dimensions, bone density, and successful implant placement. Materials and Methods A retrospective chart review was done to assess the clinical and radiographic outcomes in 52 horizontal ridge augmentation sites in 43 patients. Information was gathered regarding surgical technique, type of graft material, biologic agents used (PRP or rhPDGF‐BB), method of space maintenance, and achieved alveolar ridge width and bone density changes as quantified on CBCT scans. Results The use of tenting screws, a resorbable membrane, and a combination of particulate allogenic and xenogenic bone graft material provided an average horizontal bone gain of 3.6 mm in the 52 augmented sites. There was no statistically significant difference observed in the amount of horizontal bone gain between sites treated with the addition of biologic agents (n = 21), or with a particulate bone graft alone (n = 31). A marginally statistically significant difference was found in the density of the grafted bone with the addition of biologics (p value = .0653). Conclusion The addition of biologic agents to the graft materials did not have a significant effect on the amount of horizontal bone gain or successful implant placement; however, it marginally enhanced the bone density of the grafted area.

Recombinant human PDGF-BB is a highly purified synthetic bioactive protein that has been credited with promoting chemotaxis, mitogenesis, and angiogenesis (Hollinger, Hart, Hirsch, Lynch, & Friedlaender, 2008). These mechanisms enhance the function of cells responsible for regeneration, including osteoblasts, cementoblasts, and fibroblasts (Bashutski & Wang, 2011;Hollinger et al., 2008;Sarment et al., 2006). Recombinant human PDGF-BB contains 1,000 times more active growth factor than either PRP or platelet-rich fibrin (Badylak et al., 2017;Nevins et al., 2005). Studies have shown that rhPDGF-BB can stimulate bone fill and the rate of clinical attachment in periodontal defects (Nevins et al., 2005), and PRP can enhance soft tissue healing during the immediate postoperative period (Albanese et al., 2013).
The use of biologic agents is relatively new in regenerative dental applications. Evidence is still limited regarding their benefit in increasing the amount of bone formation in guided bone regeneration procedures when compared to a bone graft alone and whether they critically enhance the outcomes of ridge augmentation and ultimately improve success in implant placement (Bashutski & Wang, 2011;Del Amo et al., 2015;Dohan et al., 2006;Eskan et al., 2014).
For assessment of alveolar bone dimensions and anatomical structures prior to implant placement, three-dimensional radiographs have become the standard (Deeb et al., 2017). Cone-beam computed tomography (CBCT) provides accurate information about the alveolar ridge, and can be used for evaluation of both preoperative and postoperative alveolar ridge dimensions (Aimetti et al., 2018).
The aim of this retrospective study was to evaluate if the addition of biologic agents (PRP and rhPDGF-BB) to a particulate bone graft results in a greater amount of horizontal ridge augmentation and greater augmented bone density when assessed radiographically, as well as if it improves the ability to place the implant.

| SURGICAL TECHNIQUE
Ridge augmentation procedures were performed via a crestal incision over the edentulous ridge and full-thickness mucoperiosteal flaps on the buccal and lingual aspects. Vertical releasing incisions and extensive split-thickness dissections were performed to ensure tension-free closure over bone graft and membrane. Deficient sites received a mixture of various proportions of particulate mineralized freeze-dried bone allograft 1,2,3 and bovine-derived xenograft. 4 Biologic agents (rhPDGF-BB or PRP) were mixed into the particulate bone graft in 21 cases. The bone graft was supported by 6 mm long tenting screws, 5 of which 3 mm served for intraosseous retention and 3 mm to support the particulate bone graft (Le & Rohrer, 2017). The bone graft was covered with a resorbable collagen membrane 6,7,8 or an acellular dermal matrix for guided bone regeneration. 9,10 The barriers were secured with tacks or resorbable subperiosteal sutures 11 (Urban, Lozada, Wessing, Suárez-López del Amo, & Wang, 2016). All patients received a preoperative oral dose of Amoxicillin 2 g or Clindamycin 600 mg, followed by 500 mg Amoxicillin or 300 mg Clindamycin TID for 1 week, and analgesics, as needed, to manage postoperative discomfort. Patients were advised to use 0.12% Chlorhexidine mouth rinse twice daily for 2 weeks following the surgery. Postoperative visits were scheduled at 1, 4, and 24 weeks with postoperative CBCT scheduled at 24 weeks.

| RADIOGRAPHIC ASSESSMENT
For assessment of gains in alveolar ridge bone width, the crosssections of the grafted area were measured on the preoperative CBCT scans and compared to images taken, on average, 7.3 months postoperatively (Table 1). Since this was a retrospective chart review, there was not a standardized time at which the final postoperative CBCT was taken for each patient.
CareStream CBCT scan software 12 was used for the horizontal measurements, and bone density readings were based on the grayscale ( Figure 1). The gray levels in the standard CT images were then converted into a quantitative scale of specific Hounsfield units (HU) (Mah, Reeves, & McDavid, 2010). Two independent raters measured a subset of the cases to test for accuracy of the measurements.
The intraclass correlation coefficient (ICC) of the two raters was high, at 0.94. Therefore, one rater then completed the rest of the measurements used for the analysis. The horizontal dimensions of the alveolar ridge in the desired implant sites were measured before and after augmentation of 3 mm apical to the alveolar crest at three set points 3 mm apart. The distal surface of the nearest adjacent tooth served as a reproducible reference point for the measurements. The three horizontal measurements were averaged to create a single value. These values were analyzed statistically to study bone augmentation outcomes and compare sites treated with and without biologics.

| STATISTICAL METHODS
Patient demographics were summarized using descriptive statistics.
The effect of the biologics on the ridge augmentation outcomes and density of the grafted bone were first tested using ANCOVA, adjusting only for the time since surgery and use of biologics. Overall models for postoperative bone level were then adjusted for age, gender, jaw (maxilla, mandible), and location (posterior, anterior). Backwards elimination was used to find a parsimonious model; however, variables of interest (use of biologics and time since surgery) were maintained in all the models.  was not associated with implant site (rhPDGF-BB: 57% anterior vs. 43% posterior; p value = .3972). Augmented sites were able to receive implants in 98% of the cases (n = 51). One patient did not return for implant placement and the outcome is unknown.  The average horizontal bone gain for all cases combined was 3.6 mm (SD = 1.84), which was a statistically significant gain (p value < .0001; 95% CI: 3.04-4.07). The horizontal gain by group was nearly identical with 3.58 mm (SD = 1.96) for the biologics group and 3.60 for the non-biologics group (SD = 1.79). The postoperative width in the nonbiologic group was 9.09 mm versus 8.73 mm in the biologic group ( Figure 3). This difference was not statistically significant (Table 2; p value = .5094).

| Bone graft density
The initial model for evaluating postoperative bone density included only the healing time (defined by the time between the date of F I G U R E 3 Average baseline alveolar ridge width, bone gain, and postoperative alveolar ridge width for biologics and nonbiologics ridge augmentation groups (in mm) T A B L E 2 Initial association between bone level, bone density, and use of biologics surgery and the postoperative CBCT) and the use of biologics. The use of biologics was not associated with a significant difference in bone density (   with its more challenging anatomy. This may cause some bias in the results since the use of biologics was not randomized equally to anterior and posterior sites. A randomized controlled trial would be necessary to fully mitigate this potential confounding factor. Radiographic evaluation of all 52 sites, which involved the use of tenting screws, showed an average horizontal bone gain of 3.6 mm, which is similar to data from other ridge augmentation studies (Caldwell, Mills, Finlayson, & Mealey, 2015). Studies using resorbable membranes without tenting screws reported horizontal gains of only 1.65 mm (Sterio, Katanick, Blanchard, Xenoudi, & Mealey, 2013).
Although the use of PRP or rhPDGF-BB was not associated with significant improvements in the amount of horizontal bone gain, enhanced bone density was observed. However, the difference was only marginally statistically significant. At reentry surgery, both types of augmented sites appeared to have similar clinical characteristics and were suitable for placement of the desired number of implants of preferred dimensions in the planned positions ( Figure 3).
In clinical cases, rhPDGF-BB has been credited with increased vital bone formation and accelerated remodeling of allografts and xenografts (Wallace, Snyder, & Prasad, 2013), and with significant improvement in clinical attachment levels and bone fill in the treatment of periodontal defects (Nevins et al., 2005), which has enhanced effect on periodontal ligament cell proliferation when combined with a particulate bone allograft (Papadopoulos et al., 2003; Figure 4).
The use of PRP has consistently shown improvement in soft tissue healing, but its benefits in bone regeneration are controversial (Albanese et al., 2013;Alissa, Esposito, Horner, & Oliver, 2010). PRP may enhance bone regeneration (Eskan et al., 2014), and the grafted sites in this study showed increased bone density with both PRP and rhPDGF-BB. Although the addition of biologic agents marginally improved the mineral bone density, significant conclusions cannot be drawn from the results due to the wide confidence interval implying a great amount of variability resulting from the relatively small sample size.
This study has several limitations. The patient population presented a wide range in age, which could affect new bone formation. A variety of brands of resorbable membranes and particulate bone graft materials were used, possibly introducing slight differences that could affect the outcomes. Timelines for the radiographic bone measurements also differed among patients, introducing variability. Some CBCT scans were taken early due to postoperative complications (infection, swelling, neurosensory disturbances, and loose hardware) or late due to patients scheduling preferences, thus widening the range. The fact that teeth were needed as reference points for radiographic measurements, which eliminated all edentulous patients from the study.
Linear measurements of the augmented bone were performed rather than a volumetric analysis based on the available software.
Although linear radiographic measurements provide valuable information regarding alveolar bone width gain, and have been used in similar studies (Hong, Chen, Kim, & Machtei, 2019), these measurements provide only a two-dimensional assessment compared to a volumetric analysis achieved by superimposition of three-dimensional images (Koerich, Weissheimer, Koerich, Luz, & Deeb, 2018).
To provide better guidance for the application of biologic agents in ridge augmentation procedures, evidence to support their use should be consistent with the specific procedure. To further investigate the ability of biologic agents to improve the outcomes of guided F I G U R E 4 Clinical view of alveolar ridge augmentation using tenting screws and bone graft and platelet-rich plasma (PRP) (a), bone graft with no biologics (b), and bone graft and recombinant human platelet-derived growth factor-ββ (rhPDGF-BB) (c); before (first row images) and after augmentation (second row images) bone regeneration procedures, a prospective study with better controlled variables is indicated.

| CONCLUSION
The use of the tenting screws and resorbable membranes in combination with a mixture of particulate bone allograft and xenograft provides significant dimensional changes in alveolar ridge width for the placement of implants of the appropriate size in the desired location.