CATEGORY AUSTRALASIAN DENTIST 93 CLINICAL at least one osteosynthesis screw (score 3), exposure of the implant with mobility (score 4). Each of these scores could be subclassified into two categories based on whether there were associated painful or inflammatory symptoms (subgroup A) or not (subgroup B). Control computed tomography (CT) scans were performed 10 days and 6 months after surgery and then annually. For the purposes of the study, the control CT scans were used to assess the extent of bone resorption beneath the abutments, as described previously for the rehabilitation of the upper jaw16. The degree of resorption for each abutment was assessed by comparing the CT scan at 10 days after surgery (T0) with those obtained at 6 months (T1), 1 year (T2), 2 years (T3), and 3 years (T4) post-surgery. Statistical analysis The statistical analysis was performed using the open-source software Jamovi, version 2.3.18.0 (accessible online at www. jamovi.org). Data are presented as the absolute number and percentage of the total (categorical variables), or as the mean ± standard deviation (quantitative variables). The differences in the amount of bone resorption beneath the abutments were assessed using the Student t-test for paired samples, with comparison of the values measured at T0 with those measured at T1, T2, T3, and T4. The level of statistical significance was set at P < 0.05 with a 95% confidence interval. Results Data from 30 implants performed in 17 patients were included and analysed retrospectively. The sample included 15 female patients and two male patients; their mean age was 60.4 years (range 48– 77 years). Supplementary Material Table S1 provides a summary of the patient characteristics. The rehabilitation was unilateral in four cases and bilateral in 13. The mean duration of surgery was 57.5 min (range 31–94 min), with a decreasing trend over time due to the surgeon’s learning curve. No major complications were encountered during the operation. In three cases, inaccurate fitting of the ridge preparation template was found, due to small bone pre-contacts not detected by the CT scan. After elimination of the precontacts with rotary instruments, it was possible to insert the guide and proceed with the preparation of the crest without any further problems. In all but one case, the implant fit was satisfactory. The main postoperative sequela was oedema, which was reported as moderate by most of the patients and regressed completely within 10 days of surgery. Temporary hypoesthesia of the innervation area of the mental nerve was reported for six implants, all passing below the nerve. This recovered completely in all cases in an average of 3.2 weeks. No infections or implant loss were detected during follow-up, which ranged from 7 to 53 months (average 22.5 months). In 10 cases, the patient reported chewing discomfort immediately after delivery of the provisional prosthesis. This problem, probably linked to the conditioning of the gingiva or to the transmission of masticatory forces to the periosteum, always regressed within a few weeks. No particular prosthetic complications were detected either during the provisional phase or final prosthetic phase. The control CBCT scans, performed at 10 days after surgery, at 6 months, and then annually in all cases, did not show displacement of the implants, or loss or loosening of the osteosynthesis screws (Fig. 4). Analysis of the gap between the implant and the bone beneath the abutments on the CT scans revealed no significant difference between the gap at 10 days postoperative and the gap at 6 months (P = 0.297), 1 year (P = 0.080), 2 years (P = 0.125), or 3 years (P = 0.166) of follow-up (Table 1). During follow-up, none of the implants presented any type of exposure of the structure (score 0 for 100% of cases). At 6 months, six out of 71 abutments (8.5%) presented BOP, which was scored as 1 (a single isolated spot) in five cases and as 2 (confluent bleeding line) in one case. At 1 year, three out of 52 abutments (5.8%) continued to present BOP, scored as 1 in all cases. BOP was present in 10% of abutments evaluated at 2 years (two abutments out of 20; score 1 in one case and score 2 in the other). Discussion Since 2017, there has been reignited interest in additively manufactured custom- made subperiosteal implants. The evidence on their safety and reliability in the treatment of severe maxillary atrophy has been corroborated by several authors15–22. However, it appears that, in recent years, only a few authors have studied the application of this new generation of implants in the mandible, despite the original history of this type of implantology being entirely oriented towards the rehabilitation of the lower jaw25,26. In an animal study, Bai et al.27 evaluated 12 custom-made subperiosteal implants placed in the mandible of six beagle dogs, by histology and microcomputed tomography. Fig. 4. Case 4 (female, age 59 years): postoperative CBCT scan obtained at 24 months after surgery showing a good fit of the implant and no evidence of bone loss below the abutments. Table 1. Results of the evaluation of the degree of bone resorption beneath the abutments.
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