To what extent does the crown-implant ratio affect the survival and complications of implant-supported reconstructions? A systematic review

The influence of crown-to-implant ratio on marginal bone levels around splinted short dental implants: A radiological and clincial short term analysis

BACKGROUND

The amount of marginal bone resorption around dental implants is considered to have a significant impact on implant stability as well as implant survival rates.

PURPOSE

The aim of this prospective study was to investigate the influence of prosthetic as well as patient specific factors on marginal bone loss around short dental implants.

MATERIALS AND METHODS

Seventy-six implants, which supported splinted crowns were included for investigation. All implants were from the same type and had an intraosseous length of 6.5 mm and a diameter of 4.0 mm. Twenty implants were additionally splinted onto longer ones. Measurements of marginal bone loss were performed at a mean of 12.38 months after prosthetic loading and the mean follow-up for clinical evaluation was 20.52 months.

RESULTS

Overall two implant failures were recorded, revealing a survival rate of 97.3%. Marginal bone resorption around 72 short implants measured 0.71 mm (SD: 0.74 mm) and was found to have a strong correlation with calculated Crown-to-Implant ratio (r = .71; P < .001). Age, gender, insertion torque, implant surface area, location, position, bone quality, and insertion torque did not influence peri-implant bone loss after one year of loading.

CONCLUSION

Within the limitations of the study, it is suggested that Crown-to-Implant ratios should not exceed 1.7 to avoid increased early marginal bone loss.

Short dental implants in the posterior maxilla: a review of the literature

The purpose of this study was to perform a literature review of short implants in the posterior maxilla and to assess the influence of different factors on implant success rate. A comprehensive search was conducted to retrieve articles published from 2004 to 2015 using short dental implants with lengths less than 10 mm in the posterior maxilla with at least one year of follow-up. Twenty-four of 253 papers were selected, reviewed, and produced the following results. (1) The initial survival rate of short implants in the posterior maxilla was not related to implant width, surface, or design; however, the cumulative success rate of rough-surface short implants was higher than that of machined-surface implants especially in performance of edentulous dental implants of length <7 mm. (2) While bone augmentation can be used for rehabilitation of the atrophic posterior maxilla, short dental implants may be an alternative approach with fewer biological complications. (3) The increased crown-to-implant (C/I) ratio and occlusal table (OT) values in short dental implants with favorable occlusal loading do not seem to cause peri-implant bone loss. Higher C/I ratio does not produce any negative influence on implant success. (4) Some approaches that decrease the stress in posterior short implants use an implant designed to increase bone-implant contact surface area, providing the patient with a mutually protected or canine guidance occlusion and splinting implants together with no cantilever load. The survival rate of short implants in the posterior edentulous maxilla is high, and applying short implants under strict clinical protocols seems to be a safe and predictable technique.

Predictability of short implants ( < 10 mm) as a treatment option for the rehabilitation of atrophic maxillae. A systematic review

BACKGROUND

Short implants (< 10 mm) are one of the treatment options available in cases of limited vertical bone. Although such implants are now widely used, there is controversy regarding their clinical reliability. The purpose of this paper is to evaluate the predictability of short implants as an alternative to technically more complex treatments in patients with atrophic maxillae, based on a systematic review of the literature and the analysis of the implant survival rates, changes in peri-implant bone level, and associated complications. It is postulated that short implants offer clinical results similar to those of longer implants.

MATERIAL AND METHODS

A Medline-PubMed search was made covering the period between January 2004 and December 2014 (both included). Studies in English published in indexed journals, involving at least 20 implants and with a follow-up period of at least 12 months were considered. A manual search in four high impact journals was also conducted.

RESULTS

A total of 37 studies meeting the inclusion criteria were included in this review. 9792 implants placed in over 5000 patients were analyzed.

CONCLUSIONS

Based on the results of this review, short implants are seen to offer clinical results in terms of survival, bone loss and complications similar to those of longer implants.

Technical and biological complications related to crown to implant ratio: a systematic review

AIM

To review the occurrence of prosthetic failure and biological complications with respect to the crown to implant (C/I) ratio.

METHODS

Accurate search was made on the subject C/I ratio with the following criteria: (1) studies on humans with data on prosthetic failure and/or biological complications related to C/I ratio; (2) partial edentulous patients; (3) randomized clinical trials, prospective, longitudinal, retrospective, and multicenter studies with a minimum of 48 months mean follow-up; (4) language: English; (5) radiographic measurements by peri-apical x-ray; (6) implant material: titanium; and (7) no implant type selection was applied.

RESULTS

Six articles were considered eligible for full-text analysis. Unfavorable C/I ratio can be considered a potential risk factor for single crown and abutment loosening (C/I ratio ≥ 1.46) and abutment fractures in posterior areas (C/I ratio ≥ 2.01).

CONCLUSIONS

Despite the limited data, high C/I ratio may be related to some prosthetic failures. Unfavorable C/I ratio does not affect biological complications and implant failure.

Success of 6-mm Implants with Single-Tooth Restorations: A 3-year Randomized Controlled Clinical Trial

The aim of the study was to test whether implants of 6 mm in length perform equally well as 10-mm implants in terms of survival and marginal bone-level changes when supporting single crowns. Patients with a posterior single-tooth gap were randomly allocated to either the placement of a 6-mm (test) or 10-mm implant (control). The treatment protocol allowed for internal sinus lift but not for lateral bone augmentation. After a healing period of 10 wk, implants were loaded with screw-retained single crowns. Survival rates, number of pockets ≥5 mm, and bleeding-on-probing were assessed clinically. The change of marginal bone level and crown-to-implant ratios were analyzed by 2 examiners. Longitudinal intragroup analyses for marginal bone levels were performed applying the Wilcoxon signed rank test. Intergroup differences at baseline and at 3 y were compared using the Mann-Whitney U test. The effect of implant length and crown-to-implant ratio on changes of marginal bone level also was determined. Of 94 implants placed (47 test and 47 control), 78 implants (40 test and 38 control) were available for follow-up examination at 3 y of loading. One test implant was lost during the second year. Hence, implant survival was not significantly different between the 2 groups after 3 y (98% test; 100% control). We found no significant change in the crestal bone level from baseline to 3 y for test and control implants with -0.19 ± 0.62 mm and -0.33 ± 0.71 mm, respectively. The intergroup difference was not significant. Crown-to-implant ratios were not associated with a statistically significant difference in marginal bone loss. However, the number of sites with pockets ≥5 mm was significantly higher in the test group. Based on the 3-y assessment, the use of 6-mm implants can be considered a viable option when reconstructing posterior single tooth gaps (German Clinical Trials Registry: DRKS00006290).

Long-term Short Implants Performance: Systematic Review and Meta-Analysis of the Essential Assessment Parameters

<p>Lack of standard criteria in the outcome assessment makes it difficult to draw conclusions on the clinical performance of short implants and, under these circumstances, determine the reasons for implant failure. This study evaluated, through a systematic review of the literature and meta-analysis, the essential parameters required to assess the long-term clinical performance of short and extra-short implants. Electronic databases (Pubmed-MEDLINE, Cochrane Library Database, Embase, and Lilacs) were searched by two independent reviewers, without language limitation, to identify eligible papers. References from the selected articles were also reviewed. The review included clinical trials involving short dental implants placed in humans, published between January 2000 and March 2014, which described the parameters applied for outcome's measurements and provided data on survival rates. Thirteen methodologically acceptable studies were selected and 24 parameters were identified. The most frequent parameters assessed were the marginal bone loss and the cumulative implant survival rate, followed by implant failure rate and biological complications such as bleeding on probing and probing pocket depths. Only cumulative implant survival rate data allows meta-analysis revealing a positive effect size (from 0.052 (fixed) to 0.042 (random)), which means that short implant appears to be a successful treatment option. Mechanical complications and crown-to-implant (C/I) ratio measurement were also commonly described, however, considering the available evidence; no strong conclusions could be drawn since different methods were used to assess each parameter. By means of this literature review, a standard evaluation scheme is proposed, being helpful to regiment further investigations and comparisons on future studies.</p>

Posterior partially edentulous jaws, planning a rehabilitation with dental implants

AIM: To discuss important characteristics of the use of dental implants in posterior quadrants and the rehabilitation planning.

METHODS: An electronic search of English articles was conducted on MEDLINE (PubMed) from 1990 up to the period of March 2014. The key terms were dental implants and posterior jaws, dental implants/treatment planning and posterior maxilla, and dental implants/treatment planning and posterior mandible. No exclusion criteria were used for the initial search. Clinical trials, randomized and non randomized studies, classical and comparative studies, multicenter studies, in vitro and in vivo studies, case reports, longitudinal studies and reviews of the literature were included in this review.

RESULTS: One hundred and fifty-two articles met the inclusion criteria of treatment planning of dental implants in posterior jaw and were read in their entirety. The selected articles were categorized with respect to their context on space for restoration, anatomic considerations (bone quantity and density), radiographic techniques, implant selection (number, position, diameter and surface), tilted and pterygoid implants, short implants, occlusal considerations, and success rates of implants placed in the posterior region. The results derived from the review process were described under several different topic headings to give readers a clear overview of the literature. In general, it was observed that the use of dental implants in posterior region requires a careful treatment plan. It is important that the practitioner has knowledge about the theme to evaluate the treatment parameters.

CONCLUSION: The use of implants to restore the posterior arch presents many challenges and requires a detailed treatment planning.

Short implants: are they a viable option in implant dentistry?

Short-length implants (<10 mm) can be used effectively in atrophic maxillae or mandibles even with crown/implant ratios that previously would have been considered excessive. Short implants can support either single or multiple units and can be used for fixed prostheses or overdentures. The use of short-length implants may avoid the need for complicated bone augmentation procedures, thus allowing patients who were either unwilling or unable for financial or medical reasons to undergo these advanced grafting techniques to be adequately treated.

Effect of the Parafunctional Occlusal Loading and Crown Height on Stress Distribution

The aim of this study was to assess, by the three-dimensional finite element method, the influence of crown-to-implant ratio and parafunctional occlusal loading on stress distribution in single external hexagon implant-supported prosthesis. Computer-aided design software was used to confection three models. Each model was composed of a block bone and an external hexagon implant (5x10.0 mm) with screw-retained implant prostheses, varying the height crown: 10, 12.5 and 15 mm. Finite element analysis software was used to generate the finite element mesh and to establish the loading and boundary conditions. Normal (200 N axial and 100 N oblique load) and parafunctional forces (1,000 N axial and 500 N oblique load) were applied. The results were visualized by von Mises and maximum principal stress. In comparison with the normal occlusal force, the parafunctional occlusal force induced an increase in stress concentration and magnitude on implant (platform and first threads) and screw (neck). The cortical bone showed the highest tensile stress under parafunctional force (oblique load). The stress concentration increased as the crown height increased. It was concluded that: increasing the C/I increased stress concentration in both implant components and cortical bone; parafunctional loading increased between 4-5 times the value of stresses in bone tissue compared with functional loading; the type of loading variation factor is more influential than the crown-to-implant factor.

Photoelastic analysis of fixed partial prosthesis crown height and implant length on distribution of stress in two dental implant systems

The aim of this study was to evaluate by photoelastic analysis stress distribution on short and long implants of two dental implant systems with 2-unit implant-supported fixed partial prostheses of 8 mm and 13 mm heights. Sixteen photoelastic models were divided into 4 groups: I: long implant (5 × 11 mm) (Neodent), II: long implant (5 × 11 mm) (Bicon), III: short implant (5 × 6 mm) (Neodent), and IV: short implants (5 × 6 mm) (Bicon). The models were positioned in a circular polariscope associated with a cell load and static axial (0.5 Kgf) and nonaxial load (15°, 0.5 Kgf) were applied to each group for both prosthetic crown heights. Three-way ANOVA was used to compare the factors implant length, crown height, and implant system (α = 0.05). The results showed that implant length was a statistically significant factor for both axial and nonaxial loading. The 13 mm prosthetic crown did not result in statistically significant differences in stress distribution between the implant systems and implant lengths studied, regardless of load type (P > 0.05). It can be concluded that short implants showed higher stress levels than long implants. Implant system and length was not relevant factors when prosthetic crown height were increased.

Is immediate reconstruction of the mandible with nonvascularized bone graft following resection of benign pathology a viable treatment option?

PURPOSE

The purpose of this study was to address the following clinical question: Is immediate reconstruction of the mandible with a nonvascularized bone graft after resection of benign pathology a viable treatment option? Another purpose was to determine whether any variables affect the success of this treatment approach.

MATERIALS AND METHODS

The authors implemented a retrospective cohort study from a sample of patients diagnosed with a benign tumor of the mandible who were treated with segmental resection and primary reconstruction with an autogenous nonvascularized bone graft. The predictor variables were age, gender, lesion size, and diagnosis, and the outcome variable was graft success determined by re-establishment of mandibular continuity with sufficient bone for implant placement. The χ(2) test was used for statistical analysis of the categorical data and P values less than .05 were considered statistically significant.

RESULTS

Twenty patients with benign mandibular tumors were treated with transoral resection and immediate reconstruction with nonvascularized bone grafts. The mean age was 28.3 years (range, 9 to 63 yr) and 55% (11 of 20) were men. The most common lesion type was ameloblastoma (13 of 20) and all patients underwent reconstruction with autogenous anterior iliac crest bone grafting. Ninety percent of patients (18 of 20) had successful reconstruction. Ten patients underwent successful implant placement and restoration.

CONCLUSIONS

Using careful patient selection, treatment of benign pathology with transoral resection and immediate reconstruction with a nonvascularized bone graft from the anterior iliac crest can be successful. In addition, the total treatment time from implant restoration to return to preoperative function is minimized. Therefore, this method of treatment is a viable treatment option and an alternative to delayed reconstruction or reconstruction with vascularized bone flaps.

Complete arch site classification for all-on-4 immediate function

Complete arch immediate function of dental implants requires a treatment protocol that takes advantage of residual areas of cortical bone for the apical fixation of implants. A site and jaw bone classification is proposed that has been in use since 2006 for all stages of atrophy for both jaws. The use of the classification is strictly for immediate function based on specific cortical bone sites in the facial skeleton to assist practitioners in diagnosis, treatment planning, and interdisciplinary communication, as well as to reduce human error in patient management. A recent series of 100 consecutive arches that were treated according to this classification is presented.

A systematic review of the survival and complication rates of implant-supported fixed dental prostheses (FDPs) after a mean observation period of at least 5 years

OBJECTIVES

The objective of this systematic review was to assess the 5- and 10-year survival of implant-supported fixed dental prostheses (FDPs) and to describe the incidence of biological and technical complications.

METHODS

An electronic Medline search complemented by manual searching was conducted to identify prospective and retrospective cohort studies and case series on FDPs with a mean follow-up time of at least 5 years. Patients had to have been examined clinically at the follow-up visit. Failure and complication rates were analyzed using standard and random-effects Poisson regression models to obtain summary estimates of 5-year and 10-year survival and complication rates.

RESULTS

The updated search provided 979 titles and 257 abstracts. Full-text analysis was performed for 90 articles resulting in a total 32 studies that met the inclusion criteria. Meta-analysis of these studies indicated an estimated survival of implants supporting FDPs of 95.6% after 5 years and 93.1% after 10 years. When machined surface implants were excluded from the analysis and only rough surface implants included, the survival rate increased to 97.2% after 5 years. The survival rate of implant-supported FDPs was 95.4% after 5 years and 80.1% after 10 years of function. When the analysis was done exclusively for metal-ceramic FDPs, hence the old gold-acrylic FDPs were excluded, the survival rate increased significantly. The survival rate of metal-ceramic implant-supported FDPs was 96.4% after 5 years and 93.9% after 10 years. Only 66.4% of the patients were free of any complications after 5 years. The most frequent complications over the 5-year observation period were fractures of the veneering material (13.5%), peri-implantitis and soft tissue complications (8.5%), loss of access hole restoration (5.4%), abutment or screw loosening (5.3%), and loss of retention of cemented FDPs (4.7%).

CONCLUSION

It may be concluded that implant-supported fixed dental prostheses (FDPs) are a safe and predictable treatment method with high survival rates. However, biological and technical complications were frequent (33.6%). To minimize the incidence of complications, dental professionals should make great effort in choosing reliable components and materials for implant-supported FDPs and the patients should be placed in well-structured maintenance system after treatment.

Systematic review of the survival rate and the incidence of biological, technical, and aesthetic complications of single crowns on implants reported in longitudinal studies with a mean follow-up of 5 years

OBJECTIVE

To assess the 5-year survival of implant-supported single crowns (SCs) and to describe the incidence of biological, technical, and aesthetic complications. The focused question was: What is the survival rate of implants supporting single crowns and implant-supported crowns with a mean follow-up of 5 years and to which extent do biological, technical, and aesthetic complications occur?

METHODS

A Medline search (2006-2011) was performed for clinical studies focusing on implant-supported SCs with a mean follow-up of at least 5 years. The search was complemented by an additional hand search and the inclusion of 24 studies from a previous systematic review (Jung et al. 2008a). Survival and complication rates were analyzed using random-effects Poisson's regression models to obtain summary estimates of 5- and 10-year proportions.

RESULTS

Forty-six studies derived from an initial search count of 1083 titles and the complementary publications from the previous systematic review (Jung et al. 2008a) were selected and the data were extracted. Based on the meta-analysis, survival of implants supporting SCs at 5 years amounted to 97.2% (95% CI: 96.3-97.9%), and at 10 years amounted to 95.2% (95% CI: 91.8-97.2%). The survival of implant-supported SCs was 96.3% (95% CI: 94.2-97.6%) after 5 years and 89.4% (95% CI: 82.8-93.6%) after 10 years. For biological complications, a 5-year cumulative soft tissue complication rate of 7.1% (95% CI: 4.4-11.3%) and a cumulative complication rate for implants with bone loss >2 mm of 5.2% (95% CI: 3.1-8.6%) were calculated. Technical complications reached a cumulative incidence of 8.8% (95% CI: 5.1-15.0%) for screw-loosening, 4.1% (95% CI: 2.2-7.5%) for loss of retention, and 3.5% (95% CI: 2.4-5.2%) for fracture of the veneering material after 5 years. The cumulative 5-year aesthetic complication rate amounted to 7.1% (95% CI: 3.6-13.6%).

CONCLUSIONS

The outcomes of the meta-analysis demonstrated high implant survival rates for both the single tooth implants and the respective single crowns after 5 and 10 years. However, technical, biological, and aesthetic complications were frequent.

Short dental implants in reduced alveolar bone height: a review of the literature

Background

The purpose of this study was to evaluate the use of short dental implants in distally reduced alveolar bone height.

Material/Methods

MedLine (PubMed and Ovid), ISI Web of Knowledge, and Cochrane databases were used for analysis. Searching was conducted using the search equation: ‘Dental Implants’ [Majr] AND (Short[TIAB] OR Shorter[TIAB]) AND (Implant[TIAB] OR Implants[TIAB]). Abstracts were screened by 2 independent reviewers. The articles included in the analysis were published in the English language and reported data on the use of implants with lengths below 10 mm in the posterior region with reduced alveolar bone height making the placement of longer implants impossible without additional surgical interventions. Articles concerning data on orthodontic implants and post-resection surgery reconstruction were excluded from analysis. Any disagreements between the 2 reviewers were resolved by a third reviewer. No time frame was used.

Results

Of the 791 articles initially found, automatic rejection of duplicates in the Endnotes X5 software resulted in 538 articles. After the selection of studies from databases, a bibliography of 32 eligible articles was searched for other publications. Through this method, 2 more studies were added.

Conclusions

The analysis of the results of different studies on the use of short dental implants showed that this treatment could be effective and comparable to the use of standard-length implants. This study revealed that rough-surfaced implants with lengths between 6–10 mm placed in the posterior mandible are the preferred solution. However, more detailed data will require additional prospective studies.

Effect of Crown to Implant Ratio and Anatomical Crown Length on Clinical Conditions in a Single Implant: A Retrospective Cohort Study

PURPOSE

The aim of this retrospective cohort study was to evaluate the long-term influence of the crown-to-implant (C/I) ratio and anatomical crown length on clinical conditions around Astra single dental implants placed in the premolar and molar regions.

MATERIALS AND METHODS

Seventy-six subjects were selected from patients who had been treated with single Astra implants for replacement of missing premolars and molars. The peri-implant marginal bone level change was assessed 1 year after functional loading and 6 years after functional loading. To predict the peri-implant marginal bone level change using clinical and radiographic data, a multiple linear regression model was applied. The Wilcoxon rank sum test was used to analyze difference median in technical complications.

RESULTS

The C/I ratio and anatomical crown length were not associated with peri-implant marginal bone loss or changes in the bone level at 6 years (p = .48, p = .31). However, the modified plaque index, modified sulcus bleeding index, and smoking status influenced the peri-implant marginal bone loss (p < .05, r(2)  = 0.54). In addition, the patient with technical complication group did show significantly increased anatomical crown length (p < .05) CONCLUSIONS: The higher C/I ratio and anatomical crown length did not increase the risk of peri-implant marginal bone loss during 6 years of functional loading. In addition, higher anatomical crown lengths are associated with higher technical complications.

Methodological quality and descriptive characteristics of prosthodontic-related systematic reviews

Ideally, healthcare systematic reviews (SRs) should be beneficial to practicing professionals in making evidence-based clinical decisions. However, the conclusions drawn from SRs are directly related to the quality of the SR and of the included studies. The aim was to investigate the methodological quality and key descriptive characteristics of SRs published in prosthodontics. Methodological quality was analysed using the Assessment of Multiple Reviews (AMSTAR) tool. Several electronic resources (MEDLINE, EMBASE, Web of Science and American Dental Association's Evidence-based Dentistry website) were searched. In total 106 SRs were located. Key descriptive characteristics and methodological quality features were gathered and assessed, and descriptive and inferential statistical testing performed. Most SRs in this sample originated from the European continent followed by North America. Two to five authors conducted most SRs; the majority was affiliated with academic institutions and had prior experience publishing SRs. The majority of SRs were published in specialty dentistry journals, with implant or implant-related topics, the primary topics of interest for most. According to AMSTAR, most quality aspects were adequately fulfilled by less than half of the reviews. Publication bias and grey literature searches were the most poorly adhered components. Overall, the methodological quality of the prosthodontic-related systematic was deemed limited. Future recommendations would include authors to have prior training in conducting SRs and for journals to include a universal checklist that should be adhered to address all key characteristics of an unbiased SR process.

In vitro bone strain analysis of implant following occlusal overload

OBJECTIVES

To enumerate peri-implant bone strain pattern under quantified occlusal load and verify the bone response through comparison with the critical strain thresholds defined by Frost's bone mechanostat theory.

MATERIAL AND METHODS

Mandibular unilateral recipient sites in two greyhound dogs were established with posterior teeth extractions. After 6 weeks, four titanium implants were placed in each dog mandible. Following 12 weeks of healing, successfully osseointegrated implants were placed in supra-occlusal contact via screw-retained non-splinted metal crowns. Plaque control and a dental health enhancing diet were prescribed. A bite force detection device was used to quantify in vivo occlusal load as the dogs functioned with supra-occlusal contact. After 8 weeks, the dogs were sacrificed. In vitro peri-implant bone strain under quantified occlusal load was measured using bonded stacked rosette strain gauges.

RESULTS

The average and peak in vivo occlusal load measured were 434 and 795 newton (N). When individually and simultaneously loaded in vitro (≤476 N), absolute bone strains up to 1133 and 753 microstrains (με) were measured at implant apices, respectively. Bone strain reaching 229 με was recorded at distant sites. For bone strain to reach the pathological overload threshold defined by Frost's bone mechanostat theory (3000 με), an occlusal load of 1344 N (greater than peak measured in vivo) is required based on the simple linear regression model.

CONCLUSION

Under the in vivo and in vitro conditions investigated in this study, peri-implant bone was not found to be under pathological overload following supra-occlusal contact function. Strain dissipation to distant sites appeared to be an effective mechanism by which implant overload was avoided.

Maxillary sinus floor elevation combined with a vertical onlay graft

We performed maxillary sinus floor elevation combined with a vertical onlay graft for a total of 11 sides of nine patients (1 woman and 8 men) in our Hospital. On CT, the preoperative minimum alveolar bone thickness with a mean of 1.8 mm was improved to 15.3 mm within a month after this surgery. A total of 20 dental implants were placed and there was only one failed implant. With the average follow-up of 15.6 months, an average of 3.4 mm of bone absorption was found in the site of the maxillary sinus and 1.1 mm in the site of the onlay graft. The crown-implant ratio in all cases was within the permissible range. Consequently, this bone augmentation surgery was considered to be useful.

Short implants: A systematic review

BACKGROUND

Short implants are manufactured for use in atrophic regions of the jaws. Although many studies report on short implants as ≤10 mm length with considerable success, the literature regarding survival rate of ≤7 mm is sparse.

PURPOSE

The purpose of this study was to systematically evaluate the publications concerning short dental implants defined as an implant with a length of ≤7 mm placed in the maxilla or in the mandible.

MATERIALS AND METHODS

A Medline and manual search was conducted to identify studies concerning short dental implants of length ≤7 mm published between 1991 and 2011. The articles included in this study report data on implant length ≤7 mm, such as demographic variables, implant type, location in jaws, observation time, prostheses and complications.

RESULTS

The 28 included studies represent one randomized controlled trial, 12 prospective studies and 10 retrospective studies. The survival rate of short implant was found to be increased from 80% to 90% gradually, with recent articles showing 100%.

CONCLUSION

When severe atrophy of jaws was encountered, short and wide implants can be placed successfully.

Esthetic evaluation of single-tooth implants in the anterior maxilla following autologous bone augmentation

OBJECTIVES

Autologous bone augmentation to rebuild compromised alveolar ridge contour prior to implant placement allows for favorable three-dimensional implant positioning to achieve optimum implant esthetics. The aim of the present study was to evaluate peri-implant soft tissue conditions around single-tooth implants following bone grafts in the esthetic zone of the maxilla.

MATERIALS AND METHODS

Sixty patients underwent autologous bone augmentation of deficient maxillary sites prior to placement of 85 implants in the esthetic zone. In case of multiple implants per patient, one implant was randomly selected. Objective evaluation of 60 single-tooth implants was performed using the Pink-Esthetic-Score (PES) and Papilla Index (PI) and supplemented by subjective patient evaluation, as well as clinical and radiologic examination.

RESULTS

Objective ratings of implant esthetics were satisfactory (median PES: 11, median PI: 2) and significantly correlated with high patient satisfaction (mean VAS score: 80%). Both esthetic indices demonstrated respectable levels of inter- as well as intra-observer agreement. Poor implant esthetics (low PES and PI ratings) were significantly associated with increased anatomic crown height, while no influence of horizontal implant-tooth distance could be found.

CONCLUSIONS

The present investigation indicates that favorable esthetic results may be achieved in the augmented anterior maxilla. However, bony reconstruction of compromised alveolar ridges does not guarantee optimum implant esthetics.

Influence of the crown-to-implant length ratio on the clinical performance of implants supporting single crown restorations: a cross-sectional retrospective 5-year investigation

PURPOSE

The aim of this study was to investigate the influence of the crown-to-implant length ratio (c/i ratio) on the implant survival, changes of the marginal bone level (MBL) and the occurrence of biological and technical complications.

MATERIAL AND METHODS

This cross-sectional retrospective study included all patients with implants in the posterior segments supporting single crown restorations with a minimum follow-up of 5 years. All patients were questioned and examined clinically and radiographically. The technical and biological c/i ratio and the MBL were measured on digitized periapical radiographs. The following outcome parameters in relation to the c/i ratio and the co-factors were statistically analyzed: implant survival rate, MBL, occurrence of technical and biological complications. For statistical analysis, regression, correlation and survival analyses were applied (P<0.05).

RESULTS

Seventy patients (mean age of 50.7 years [range 19.8-76.6 years]) with a total of 100 implants (24 Straumann type, 76 Brånemark type) were included in this study. The mean follow-up period was 6.2 years (range 4.73-11.7 years). Six implants failed during the follow-up period, yielding a cumulative survival rate of 95.8% at 5 years in function. The mean technical c/i ratio was 1.04 (±0.26, range 0.59-2.01). The mean biological c/i ratio was 1.48 (±0.42, range 0.82-3.24). No statistically significant influence of the technical and biological c/i ratio was found on the implant survival, MBL and occurrence of technical and biological complications. When adjusted for the biological c/i ratio, smoking was the only co-factor significantly associated with implant failure and biological complications.

CONCLUSION

In the present study, the c/i ratio did not influence the clinical performance of implants supporting single crown restorations in the posterior segments of the jaw within the range tested.

Four-millimeter implants supporting fixed partial dental prostheses in the severely resorbed posterior mandible: two-year results

BACKGROUND

Reduced alveolar bone volume complicates implant dentistry.

PURPOSE

In this prospective multicenter study, a new, 4-mm long Straumann SLActive implant (Ø 4.1 mm) supporting a fixed dental prosthesis (FDP) in the severely resorbed posterior mandible was evaluated for two years.

MATERIAL AND METHODS

Thirty-two patients (11 men, 21 women; mean age 64.1 years) participated. Ten to 12 weeks after single-stage surgery, a screw-retained FDP was attached to three or four 4-mm implants.

RESULTS AND DISCUSSION

One hundred implants were inserted. Three failed at surgery and four were lost before loading. Twenty-eight patients received FDPs (93 implants). Two patients were discontinued because of secondary exclusion criteria; therefore, 26 patients were followed up from baseline (BL). After 1 year, one patient insisted on removal of all implants and one patient died because of nonstudy-related complications. Twenty-four patients (87 implants) were eligible for examination 2 years post-loading. All implants were found to be stable [survival rate 95.7% (confidence interval, CI 88.8-98.3) after 1 year and 92.3% (CI 84.5-96.2) after 2 years]. The mean change from BL to 12 months was - 0.43 mm (CI 0.31-0.59; p < .001) and from 12 to 24 months - 0.11 mm (CI -0.01-0.23; p = .056). The survival rate is only slightly lower than in similar studies on 6 to 8.5 mm implants. This may be related to high initial stability and effective use of the residual bone volume with high primary bone-to-implant contact in dense bone structures. The surgical handling of the tested implant was found to be similar to that of implants of common length. However, the preparation procedure must be done with great care to avoid overdrilling. Careful planning and design of the prosthetic construction is mandatory to prevent unfavorable occlusion and avoid harmful shear forces.

CONCLUSION

This study showed that 4 mm implants can support an FDP in severely resorbed posterior mandibles for at least 2 years and with healthy peri-implant conditions.

Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study

AIM

To evaluate prospectively the clinical and radiographic outcomes after 2 years of loading of 6 mm long moderately rough implants supporting single crowns in the posterior regions.

MATERIAL AND METHODS

Forty SLActive Straumann short (6 mm) implants were placed in 35 consecutively treated patients. Nineteen implants, 4.1 mm in diameter, and 21 implants, 4.8 mm in diameter, were installed. Implants were loaded after 6 weeks of healing. Implant survival rate, marginal bone loss and resonance frequency analysis (RFA) were evaluated at different intervals. The clinical crown/implant ratio was also calculated.

RESULTS

Two out of 40 implants were lost before loading. Hence, the survival rate before loading was 95%. No further technical or biological complications were encountered during the 2-year follow-up. The mean marginal bone loss before loading was 0.34+/-0.38 mm. After loading, the mean marginal bone loss was 0.23+/-0.33 and 0.21+/-0.39 mm at the 1- and 2-year follow-ups. The RFA values increased between insertion (70.2+/-9) and the 6-week evaluation (74.8+/-6.1). The clinical crown/implant ratio increased with time from 1.5 at the delivery of the prosthesis to 1.8 after 2 years of loading.

CONCLUSION

Short implants (6 mm) with a moderately rough surface loaded early (after 6 weeks) during healing yielded high implant survival rates and moderate loss of bone after 2 years of loading. Longer observation periods are needed to draw more definite conclusions on the reliability of short implants supporting single crowns.