Mandibular single-implant overdentures: a review with surgical and prosthodontic perspectives of a novel approach

Objectives: To review the literature on mandibular single-implant overdentures (opposing complete maxillary dentures), and present surgical and prosthodontic perspectives of a novel approach for this treatment option.
Material and methods: An electronic search through the databases of Pubmed, Embase and Medline using the linked key words 'mandibular single implant overdentures' was performed. The search was limited to English language articles published up to August 2008. Hand searches through articles retrieved from the electronic search, peer-reviewed journals and recent conference proceedings were also conducted.
Results: A limited number of reports were identified on mandibular single-implant overdentures (opposing maxillary complete dentures). They comprised of case-series reports, short-term prospective trials and current randomized-controlled clinical trials. Different loading protocols with different implant systems have been used, but always with regular diameter implants. Specific anatomical and vascular dangers of the mandibular midline symphysis are identified including a novel surgical approach using a currently available short, wide diameter tapered implant. In addition, the prosthodontic rationale for using a larger attachment system (incorporating a platform switch) for mandibular single-implant overdentures is described.
Conclusion: The review reveals that there is a lack of published randomized clinical trials using mandibular single-implant overdentures, opposing maxillary complete dentures. Without the evidence from randomized clinical trials, routine use of this novel approach cannot be recommended, compared with using regular diameter implants and matching attachment systems.     

Effect of implant loading protocols on failure and marginal bone loss with unsplinted two-implant-supported mandibular overdentures: systematic review and meta-analysis

The aim of this study was to compare implant failure and radiographic bone level changes with different loading protocols for unsplinted two-implant-supported mandibular overdentures. An electronic search of two databases (PubMed, Cochrane Library) was performed, without language restriction, to identify randomized controlled trials (RCTs) comparing immediate or early versus conventional dental implant loading protocols for unsplinted two-implant-supported mandibular overdentures. Data were extracted independently by two reviewers. The Cochrane tool was used to assess the quality of included studies. A meta-analysis was performed. Eight RCTs were identified, seven of which were included; one trial was excluded because related outcomes were not measured. Four of the seven studies were considered to have a high risk of bias and three an unclear risk. Meta-analysis revealed no difference between immediate versus conventional or early versus conventional implant loading protocols regarding implant failure (risk difference (RD) ?0.02, 95% confidence interval (CI) ?0.13 to 0.10; RD 0.09, 95% CI ?0.03 to 0.20) or marginal bone loss (mean difference (MD) 0.09, 95% CI ?0.10 to 0.28; MD ?0.05, 95% CI ?0.12 to 0.02) for implants supporting mandibular overdentures. These findings should be interpreted with great caution given the serious numerical limitations of the studies included.     

The effect of loading on peri‐implant bone: a critical review of the literature

In the 90s, there was a general belief that mechanical overloading was one of the main reasons for late implant failure. This triggered research to assess the role of mechanical loading on the establishment and the maintenance of oral implant osseointegration. Animal experimental studies indeed suggested the potential detrimental effect of excessive mechanical load on peri‐implant bone, although randomised or controlled clinical trials of treatment interventions of oral implants designed to study overload are lacking. The lack of quantification of so‐called overload at the implant level in the intra‐oral setting is one of the main shortcomings in the literature. The level of evidence of the studies on bone response to implant loading is weak and does not indicate that overload can lead to peri‐implant bone loss, except in case of inflammation. Clinical and animal experimental studies on early and immediate implant loading, however, provide information on the impact of mechanical loading on the process of osseointegration. It is obvious that micromotion between the implant and host tissues compromises osseointegration. However, in case of an efficient force transfer between implant and surrounding tissues, mechanical loading might even stimulate peri‐implant bone formation and therefore osseointegration.     

Stability, marginal bone loss and survival of standard and modified sand-blasted, acid-etched implants in bilateral edentulous spaces: a prospective 15-month evaluation

Objectives: Chemical modification of the already proven sand‐blasted and acid‐etched (SLA) implant had increased its surface wettability and consequent early‐term osseointegration characteristics. The aim of this clinical trial was to compare the stability changes, success, survival, peri‐implant parameters and marginal bone loss (MBL) of the early‐loaded standard (SLA) and modified sand‐blasted, acid‐etched (modSLA) implants. Material and methods: A total of 96 SLA and modSLA implants were placed in a bi‐lateral, cross‐arch position to the jaws of 22 patients. Resonance frequency analysis (RFA) was used to measure the implant stability in the surgery and following healing after 1, 3 and 6 weeks. At the stage of loading, a panoramic X‐ray was obtained and RFA measurement was repeated for all implants. Implants were restored by metal–ceramic crowns and followed for 1 year to determine the success, survival rate, peri‐implant parameters and MBL. Results were compared by one‐ and two‐way ANOVA, log‐rank test and generalized linear mixed models (P<0.05). Results: One modSLA implant was lost after 3 weeks following the surgery yielding to a 100 and 97.91% success rate for SLA and modSLA implants, respectively (P=0.323). At the loading stage, modSLA implants showed significantly lower MBL (0.18 ± 0.05 mm) than SLA implants (0.22 ± 0.06 mm; P=0.002). In the loading stage, RFA value of the modSLA implants (60.42 ± 6.82) was significantly higher than the both implant types in the surgical stage (55.46 ± 8.29 and 56.68 ± 8.19), and following 1 (56.08 ± 7.01 and 55.60 ± 9.07) and 3 weeks of healing (55.94 ± 5.95 and 55.40 ± 6.50 for SLA and modSLA implants, respectively). Conclusions: modSLA implants demonstrated a better stability and a reduced MBL at the loading stage. Both SLA and modSLA implants demonstrated a favorable success and survival at the end of 15‐month follow‐up. To cite this article :
Karabuda ZC, Abdel‐Haq J. Arιsan V. Stability, marginal bone loss and survival of standard and modified sand‐blasted, acid‐etched implants in bilateral edentulous spaces: a prospective 15‐month evaluation.
Clin. Oral Impl. Res. 22 , 2011; 840–849
doi: 10.1111/j.1600‐0501.2010.02065.x     

Harvesting anterior iliac crest or calvarial bone grafts to augment severely resorbed edentulous jaws: a systematic review and meta-analysis of patient-reported outcomes

The aim of this systematic review was to compare patient-reported outcomes after harvesting calvarial or anterior iliac crest bone grafts to repair severe jaw defects and enable implant placement. The MEDLINE, Embase, Cochrane Central Register of Controlled Trials databases, and OpenGrey were searched for studies on patient satisfaction, pain, disturbances in daily functioning, sensory alterations, donor site aesthetics, and complication rates. Of the 1946 articles identified, 43 reporting 40 studies fulfilled the inclusion criteria; the studies were one randomized controlled clinical trial, one retrospective controlled clinical trial, and 23 prospective and 15 retrospective cohort studies. A meta-analysis of two studies (74 patients) showed no difference in satisfaction (mean difference (MD) ? 0.13, 95% confidence interval (CI) ? 1.17 to 0.92; P = 0.813) or postoperative pain (directly postoperative: MD ?2.32, 95% CI ?5.20 to 0.55, P = 0.113; late postoperative: MD ?0.01, 95% CI ?0.14 to 0.11, P = 0.825) between donor sites. However, the level of evidence is limited, due to the retrospective, non-randomized design of one study. Postoperative gait disturbances were highly prevalent among the anterior iliac crest patients (28–100% after 1 week). The incidence rates of sensory disturbances and other complications were low, and the donor site aesthetic outcomes were favourable for both graft types. To conclude, harvesting bone grafts from the calvarium or anterior iliac crest to augment the severely resorbed edentulous jaw results in similar patient satisfaction. However, the findings for postoperative pain and disturbances in daily living suggest a trend in favour of calvarial bone grafts if harvested using an adjusted technique.     

Treatment of severe peri‐implant bone loss using autogenous bone and a resorbable membrane. Case report and literature review.

Clinical case reports and animal studies have demonstrated that the principle of guided bone regeneration can be applied for surgical treatment of moderate to profound peri‐implant bone loss (peri‐implantitis). However, the degree of bone regeneration within the peri‐implant osseous defect was reported to be variable depending on different clinical factors and on the postoperative course. Most papers dealing with surgical treatment of peri‐implantitis advocate the use of a non‐resorbable ePTFE membrane for secluding the peri‐implant bone defect enabling bone regeneration. Additionally some surgeons fill the defects with allografts or alloplasts. The present case report demonstrates another surgical approach by using autogenous cancellous bone for grafting into the peri‐implant bone defect and placing a bioresorbable polylactide membrane as a matrix barrier. The successful out‐come of this modified surgical approach enabled the patient to maintain the implant for prosthetic reconstruction after early but severe bone loss.     

Long‐term,retrospective evaluation (implant and patient‐centred outcome) of the two‐implant‐supported overdenture in the mandible. Part 2: marginal bone loss

Objective: In part 2 of this long‐term, retrospective study on the two‐implant‐supported overdenture in the mandible, the annual marginal bone loss was evaluated in detail and parameters, with a significant effect on the annual bone loss, were verified. Material and methods: For all 495 patients with an overdenture in the mandible at least 5 years in function, data up to their last follow‐up visit had been collected, including long‐cone radiographs (taken at the abutment connection and after years 1, 3, 5, 8, 12 and 16 of loading) and probing data at their last evaluation. General information (medical history, implant data, report on surgery) was retrieved from the patient's file. Two hundred and forty‐eight patients had been clinically examined recently. For the others, information on bone level and probing depths were retrieved from the patient's files, as all patients had been enrolled in our annual follow‐up schedule. Results: The mean annual bone loss on a site level (without considering the first year of bone remodelling) after 3 years of loading was 0.08 mm/year (SD=0.22, n=1105), after 5 years of loading 0.07 mm/year (SD=0.14, n=892), after 8 years of loading 0.06 mm/year (SD=0.12, n=598), after 12 years 0.04 mm/year (SD=0.07, n=370) and 0.05 mm/year (SD=0.05, n=154) after 16 years of loading. Ongoing bone loss was seen in a number of implants (n=26) with the annual bone loss exceeding 0.2 mm. Some factors clearly showed a significant impact on bone loss: smoking (≥10 cigarettes/day), GBR, the presence of dehiscence and bone quantity(the latter only during the first year). The probing data showed a favourable condition, with <1.2% of the approximal pockets being ≥6 mm, and 4.1%=5 mm. Conclusions: The mean annual bone loss over the study period was <0.1 mm/year after the first year of loading. However, a small number (2.5%) of the implants showed continuing bone loss. To cite this article :
Vercruyssen M, Quirynen M. Long‐term, retrospective evaluation (implant and patient‐centred outcome) of the two‐implants‐supported overdenture in the mandible. Part 2: marginal bone loss.
Clin. Oral Impl. Res. 21 , 2010; 466–472.
doi: 10.1111/j.1600‐0501.2009.01902.x     

Volumetric osseous changes in the completely edentulous maxilla after sinus grafting and lateral bone augmentation: a systematic review

The aim of this systematic review was to evaluate the volumetric changes associated with different bone grafting techniques in the completely edentulous atrophic maxilla before dental implant placement. A search was performed according to the PRISMA guidelines. A PICO question was formed, and the PubMed, Scopus, Embase, and Cochrane Library databases were searched, covering the period 2000–2018. Relevant data were extracted from the results regarding study population, surgical details, technical information on volumetric data acquirement, and volumetric outcome after bone augmentation procedures before implant placement. Six articles with a combined population of 84 patients were included. All patients had a completely edentulous maxilla, with a crestal horizontal width of <3–4 mm or a crestal vertical height of <6–7 mm. The iliac bone and ascending ramus were most frequently used as grafts. Five of the six studies reported volumes of sinus inlay graft (SIG) and four reported volumes of lateral bone augmentation (LBA). Radiographic analyses of the augmented areas differed among the studies. Volume loss after bone augmentation procedures ranged from 5% to 50% for SIG and from 5% to 47% for LBA. All surgical augmentation techniques for the edentulous maxilla are prone to resorption; no procedure seemed to be superior, but some interesting observations were made.     

Effect of intermittent loading and surface roughness on peri-implant bone formation in a bone chamber model

Both implant surface characteristics and mechanical loading are known to affect implant osseointegration. Their interaction and the underlying mechanisms by which they affect peri-implant healing processes are still unknown. The aim of this study is therefore to investigate the influence of a turned versus a rough (Plus), Dentsply Friadent) implant surface on peri-implant bone formation in case of unloaded or loaded implant healing. Material and Methods: Bone formation was evaluated around screw-shaped implants under four experimental conditions using a repeated sampling bone chamber methodology: (1) unloaded turned implant (CU), (2) unloaded implant with a rough surface (TU), (3) loaded turned implant (CL), and (4) loaded implant with a rough surface (TL). Peri-implant tissue samples were paraffin embedded after implant removal and examined histologically and histomorphometrically. A mixed model was used for statistical analysis. Results: The surface of bone tissue relative to the total tissue area (bone area fraction) was not affected by the experimental conditions. The areas of bone trabeculae relative to the bone area (bone fraction) were significantly higher for TL compared with CU and TU. The bone fraction in the vicinity (100 microm zone) of the implant (BFZ) was significantly the highest around the loaded roughened implants (TL). Conclusion: Implant loading did not affect bone formation in the absence of surface roughness, and implant surface roughness had no effect in the absence of loading. However, a bone-stimulating effect in the implant's vicinity was assigned to the rough surface when the implant was loaded.     

The effect of smoking on survival and bone loss of implants with a fluoride-modified surface: a 2-year retrospective analysis of 1106 implants placed in daily practice

Aim: To compare the survival and peri‐implant bone loss of implants with a fluoride‐modified surface in smokers and nonsmokers. Materials and methods: Patient files of all patients referred for implant treatment from November 2004 to 2007 were scrutinized. All implants were placed by the same experienced surgeon (B. C.). The only inclusion criterion was a follow‐up time of at least 2 years. Implant survival and bone loss were assessed by an external calibrated examiner (S. V.) comparing digital peri‐apical radiographs taken during recall visits with the post‐operative ones. Implant success was determined according to the international success criteria ( Albrektsson et al. 1986 ). Survival of implants installed in smokers and nonsmokers was compared using the log‐rank test. Both nonparametric tests and fixed model analysis were adopted to evaluate bone loss in smokers and nonsmokers. Results: One‐thousand one‐hundred and six implants in 300 patients (186 females; 114 males) with a mean follow‐up of 31 months (SD 7.15; range 24–58) were included. Nineteen implants in 17 patients failed, resulting in an overall survival rate of 98.3% at the implant level and 94.6% at the patient level. After a follow‐up period of 2 years, the cumulative survival rates was 96.7% and 99.1% with the patient and implant as the statistical unit, respectively. Implant survival was significantly higher for nonsmokers compared with smokers (implant level P=0.025; patient level P=0.017). The overall mean bone loss was 0.34 mm (n=1076; SD 0.65; range 0–7.1). Smokers lost significantly more bone compared with nonsmokers in the maxilla (0.74 mm; SD 1.07 vs. 0.33 mm; SD 0.65; P<0.001), but not in the mandible (0.25 mm; SD 0.65 vs. 0.22 mm; SD 0.5; P=0.298). Conclusion: The present study is the first to compare peri‐implant bone loss in smokers and nonsmokers from the time of implant insertion (baseline) to at least 2 years of follow‐up. Implants with a fluoride‐modified surface demonstrated a high survival rate and limited bone loss. However, smokers are at a higher risk of experiencing implant failure and more prone to show peri‐implant bone loss in the maxilla. Whether this bone loss is predicting future biological complications remains to be evaluated.     

Simultaneous implant placement and bone grafting with particulate mineralized allograft in sites with buccal wall defects,a three-year follow-up and review of literature

ObjectivesTo assess the relationship between the vertical buccal defect size and the outcome of single-stage (non-submerged) implant placement and simultaneously augmentation of sites with mineralized particulate allograft (Puros Cancellous) using collagen membranes (Ossix Plus).Subjects and methodsRecords of 108 partially edentulous patients with localized, buccal bone defects in the posterior maxilla and/or mandible [156 tissue-level Straumann implants, 38 male, 70 female, average age = 46.7 (6.4) years] were used for this study. Sectional CBCT scans were used to evaluate ridge forms before implant placement and after bone grafting (36 ± 2.2 months). The initial vertical buccal wall defect was recorded by measuring the amount of vertical Implant Platform's Rough Surface Exposure (IPRSE) when implants were placed [small (<3 mm), medium (3–5 mm), and large (>5 mm)]. The ridge contour at 36 (±2.2) months was classified into 3 categories [completely corrected (no IPRSE seen on CBCT), partially improved (some IPRSE seen on CBCT), no difference/worse].ResultsComplete defect correction occurred in 66 (61.1%) patients followed by improved ridge contours in 38 patients. Significant differences were observed in the outcome of simultaneous grafting of sites with different pre-treatment vertical defect sizes (chi-square = 69.394, df = 4, P < 0.001). Two graft failures (one needed regrafting) and 2 implant failures were also seen. Treatment was effective in complete correction of 100% and 79.3% of small and medium-sized vertical defects, respectively. Large-sized defects showed only partial improvement in 90% of cases, without any complete correction. Cumulative implant and graft survival was 98.1%.ConclusionsSingle-stage implant placement and simultaneous grafting with mineralized particulate allograft showed promising outcome in correcting small and medium sized vertical buccal wall bone defects (<5 mm).