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

In Vitro Reliability and Stress Distribution of Wide Diameter Extra-Short Implants as Support for Single Crowns and Fixed Partial Dentures

This study evaluated the reliability, failure mode, and stress distribution of wide-diameter extra-short dental implants (ESDI) as support for single crowns (SC) and fixed partial dentures (FPD) (3:1 crown-to-implant ratio [C:I]) for rehabilitation in the posterior atrophic mandible. For that, 126 ESDI (of 5 mm length) were allocated in four groups based on diameter (Ø4 and Ø6 mm) and prostheses (SC and FPD): SC4, SC6, FPD4, and FPD6. The fatigue test was performed by step-stress accelerated life testing (n = 21/group), failure mode by fractographic analysis, and stress distribution by finite element analysis: von Mises stress (σvM), maximum shear stress (τmax), and minimum principal stress (σmin). Reliability at 200 N was higher than 84% in both SC4 and SC6, with SC6 showing significantly higher reliability at 300 N. Failure mode involved the abutment (SC4 and SC6). The missions were suspended for the FPD groups due to 100% survival at the maximum load. The σvM showed a stress reduction of about 40% at the SC6 implant when compared to SC4 and FPD6 compared to FPD4. For the abutment, a minor decrease of at least 6.72% was observed comparing SC6 to SC4 and 2.78% for the FPD6 compared to FPD4. The τmax and σmin in the cortical bone demonstrated a stress reduction of at least 38.85% for the SC6 compared to SC4 and at least 3.78% in FPD6 compared to FPD4. The σmin in the cancellous bone showed an overall reduction of at least 8.46% for SC6 compared to SC4 and for FPD6 compared to FPD4. But, for τmax, in the cancellous bone, a 19.42% higher stress was found in SC6 compared to SC4 and 27.21% in FPD6 compared to FPD4. Finally, when splinting was used, a general stress reduction was found, about 50% in both diameters in the implant and abutment. According to the limitations of this in vitro study, it is possible to conclude that both groups (SC4 and SC6) showed high reliability in clinically relevant loads for the posterior atrophic mandible, SC6 having the lowest probability of failure at 300 N, with failure restricted to the abutment. Meanwhile, FPD6 has better stress distribution.

Clinical and radiographic outcomes of extra-short implants (≤ 6 mm) in the posterior atrophic jaws: a retrospective cohort study

OBJECTIVE

This study aimed at investigating implant survival rate and marginal bone loss (MBL) around extra-short implants. The impact of the loading protocol and of the use of an intermediate abutment was also evaluated, to explore possible differences in terms of the outcome measures.

MATERIALS AND METHODS

Patients with single or multiple mandibular or maxillary posterior edentulism rehabilitated using extra-short 5-6 mm long implants were included. Different prosthetic protocols were used. Clinical and radiological follow-up was 5 years. The outcomes measures were implant survival and MBL.

RESULTS

The analysis included 56 implants placed in 34 adults (12 males and 22 females; mean age 60 years, SD 11). Six implants failed during a median follow-up of 5 years and 4 of them were recorded in one patient at 2-year follow-up. The 5-year implant survival was 89% overall (87% in conventional and 94% in immediate loading). At univariate analysis, during follow-up immediate loading was associated with higher MBL (mean variation 0.21 mm, 95%CI 0.01 to 0.40; p = 0.02), while intermediate abutment was associated with lower MBL (mean variation -0.23 mm, 95%CI -0.39 to -0.09; p = 0.003). Multivariable analysis confirmed that immediate loading was associated with higher MBL.

CONCLUSION

Within its limitations, this study showed that extra-short implants under immediate loading conditions can be a reliable solution. The application of horizontal and vertical platform switching with the use of intermediate abutments seems to be able to contribute to the reduction of MBL.

Monolithic hybrid abutment crowns: Influence of crown height, crown morphology and material on the implant-abutment complex

PURPOSE

This in vitro study investigated the influence of material selection, crown morphology, and vertical crown height on the biomechanical behavior of screw-retained monolithic hybrid abutment crowns (HACs).

METHODS

Ninety implants were embedded in accordance with ISO standard 14801; ninety HACs were mounted (N=90). Monolithic crowns with varying group-specific designs were luted using titanium bases. HACs were fabricated from monolithic lithium disilicate ceramic (LD) or zirconia-reinforced lithium silicate ceramic (ZLS). The crown morphology was either maxillary premolar (LD_PM, ZLS_PM) or molar (LD_MO). The three groups were further divided into three subgroups of ten specimens, each designed with a small (7.5 mm), middle (10.5 mm), and high (13.5 mm) configuration of crown heights (N=10). A load-to-failure test at 30° off-axis was conducted using a universal testing machine until failure. For statistical analysis, Kolmogorov-Smirnov and Mann-Whitney U tests were conducted (P < 0.05).

RESULTS

All LD_MO groups presented the highest failure values (808.7 to 947.9 N), followed by the LD_PM (525.8 to 722.8 N) and ZLS_PM groups (312.6 to 478.8N). A comparison between LD and ZLS materials (P < 0.001) as well as the crown morphology (P < 0.001) showed significant differences in failure values. The values in the subgroups of ZLS_PM (low, middle, high) decreased as the crown height increased. The fracture modes showed no consistent patterns across the test groups.

CONCLUSIONS

Material selection, crown morphology, and vertical crown height appear to be important factors that may influence the clinical failure values and patterns of screw-retained single implant crowns.

Clinical outcomes of short dental implants supporting prostheses in the posterior region

Aim In clinically challenging scenarios with limited bone height and anatomical restrictions, the use of short implants have been proposed as a potential treatment strategy. The purpose of this retrospective study was to evaluate the clinical outcomes of short implants supporting prostheses in the posterior premolar region of the maxilla and mandible.Materials and methods A total of 30 patients requiring short 6 mm length implant placement in the posterior premolar region were included. Following a period of osseointegration, the implants were restored with either single crowns, fixed bridges or implant-supported removable overdentures. Implant and prosthetic survival with technical complications were recorded.Results In total, 45 implants were placed, with four failures reported before loading in two patients, resulting in a patient implant survival rate of 93.3% over the two-year follow-up. There was no statistically significant difference found between implant failure and arch placement. Prosthetic survival was 100% and minor technical complications recorded were low.Conclusion This study showed that short 6 mm implants could provide a viable treatment option, with high survival rates comparable with alternative bone augmentation procedures. Further research with longer observation periods would be required to validate these current findings.

Does the crown-implant ratio affect the survival and complications of implant-supported prostheses? A systematic review

STATEMENT OF PROBLEM

The use of dental implants shorter than 10 mm in length increases the crown-implant ratio. Whether an increased crown-implant ratio affects the survival rate and complications is unclear.

PURPOSE

The purpose of this systematic review was to investigate the effect of the crown-implant ratio on the survival rate and complications of implant-supported prostheses.

MATERIALS AND METHODS

Five databases (PubMed, MEDLINE, Scopus, Google Scholar, and Cochrane) were electronically and manually searched for longitudinal studies with a follow-up period of 3 years or longer. The study question was "Does the crown-implant ratio affect survival rate and complications of implant-supported prostheses?" The outcomes investigated were implant survival rate, peri-implant bone resorption rate, implant fracture rate, and other technical complications in the implant components.

RESULTS

A total of 670 studies were identified from the research in the databases. By applying the inclusion and exclusion criteria to the full texts, 17 articles were included for descriptive analysis. Qualitative data analysis showed that the survival rate of implant-supported prostheses with a crown-implant ratio greater than 2 was 97.2%, and for a ratio lower than 1, it was about 97.6%. Moreover, 9 papers reported that increasing the crown-implant ratio reduced bone resorption, while 8 other studies reported no significant association between the increase in the crown-implant ratio and bone resorption.

CONCLUSIONS

No significant relationship was found between the crown-implant ratio and implant survival rate. However, increasing the crown-implant ratio is likely to decrease bone loss around the implant. Information was insufficient to analyze the relationship between the crown-implant ratio and technical complications in implant-supported prostheses.

Does crown-to-implant ratio affect marginal bone loss around a single short implant at the posterior of the mandible?

Context

Short implants are acceptable treatment options for atrophic ridges; however, they increase the crown-to-implant (C/I) ratio compared to regular length implants. The study aimed to assess the correlation between the C/I ratio and marginal bone loss (MBL) in single short implants at the posterior of the mandible.

Aims

The study aimed to assess the correlation between the C/I ratio and MBL in single short implants at the posterior of the mandible.

Settings and Design

Cross-sectional study.

Materials and Methods

This cross-sectional study assessed short implants with 6 mm lengths at the posterior of the mandible. The long-cone peri-apical digital radiographs were taken immediately after loading and 24 months later. Age, gender, implant diameter, gingival biotype, and implant brands were the study variables, and the C/I ratio was the predictive factor. The mean MBL at 2 years was considered the study outcome.

Statistical Analysis Used

The Pearson correlation test was applied to assess the correlation between MBL and C/I.

Results

Seventy implants (36 Straumann and 34 SGS implants) were studied. A significant difference was observed in the mean MBL between the two implant brands (P < 0.001). Besides, a correlation was found between MBL and the C/I ratio (P = 0.002).

Conclusions

It seems that the C/I ratio is associated with an MBL increase in single short implants at the posterior of the mandible.

Stress Distribution on Short Implants with Varying Crown Heights - An In vitro Study

The aim of this study is to determine the stress in short implants loaded with varying crown heights using a 3D finite element analysis. A total of three mandibular sectional bone blocks depicting the mandibular left first molar region were modeled. Each block carried Bicon implants of the same size and was designated B1, B2, and B3. The implant- crown ratio is 1:1.5, 1:2.5, and 1:3 respectively. The loading protocol included axial and oblique loads. The von Misses' equivalent stresses at the implant-bone interface were evaluated. Intergroup comparison was determined using one-way ANOVA analysis, and P values were calculated. Under an axial load of 600N, the models B1, B2, and B3 do not show any statistically significant P-values at the crestal module of the implant, abutment, and bone, whereas in crowns, the P-values were highly significant. Under an oblique load of 225 N at 0°, 45°, and 90°, model B3 showed the highest values in the crestal module, abutment, and crown. Based on the intergroup comparison and P value the study concluded that the variance in the crown height does not affect the bone and therefore microfracture of the bone and failure of osseointergration is not likely.

A naïve comparison to assess the success of ultra-short implants

Introduction

Conventional implants are associated with ridge augmentation/sinus lift procedures in vertically insufficient ridges, which increase morbidity and healing time. Short implants provided some hope in this context. The present study considered the use of ultra-short implants in vertically insufficient posterior mandibular ridges and evaluated their success. Hence, study was done to evaluate the success of ultra-short implants in partially edentulous posterior mandible clinically and radiographically.

Materials and Methods

The study is a "Naïve direct comparison" of ultra-short implants to conventional implants for assessing their success in vertically insufficient posterior mandibular ridges. A total of 10 ultra-short implants were placed in a partially edentulous posterior mandibular ridge with at least 8-mm horizontal (at crest) and vertical dimensions. A delayed loading was done at three-month follow-up. Data acquisition was done at baseline (immediately after loading), 6-, 9-, 12-month intervals. Parameters assessed were marginal bone loss (MBL), probing pocket depth reduction (PPDR), modified plaque index (mPI), modified gingival index (mGI).

Results

All the placed 10 implants survived, and no failure was observed. "Independent sample t-test" and "paired sample t-test" was done for intergroup and intragroup analysis, respectively. Intergroup comparison between the ultra-short and conventional implants presented a statistically insignificant difference between all the parameters at all the follow-up visits (baseline, 6-, 9-, 12 months).

Conclusions

Within the limitations, it was thus concluded that ultra-short implants may be considered as a viable treatment option for vertically insufficient mandibular ridge. Further, long-term randomized controlled trials are required to establish the evidence.

Restoratively driven planning for implants in the posterior maxilla - Part 2: implant planning, biomechanics and prosthodontic planning a proposed prosthodontic complexity index

Restoratively driven implant planning in the posterior maxilla requires a comprehensive understanding of the anatomical and physiological changes of the alveolar bone following tooth extraction and sinus augmentation. As a part of restoratively driven planning, alveolar bone, inter-arch relationships, proposed crown-implant ratio and anticipated non-axial loading should be assessed pre-operatively. This helps determine the prosthodontic and surgical aspects of implant treatment, such as prosthesis design, implant number, implant angulation, implant length and the necessity for additional bone grafting procedures. However, currently no implant planning classification is restoratively driven and include these important prosthodontic considerations. Therefore, a new index - the Posterior Maxilla Prosthodontic Index - is defined to encourage restoratively driven implant planning in the posterior maxilla.

Effects of crown-to-implant ratio on marginal bone level and bone density in non-splinted single implants: a cross-sectional study

BACKGROUND

Few studies have evaluated the effects of the crown-to-implant (C/I) ratio on the marginal bone level (MBL) and bone density in non-splinted single implants. The aim of this study was to assess the effect of C/I ratio on MBL and density of peri-implant bone in non-splinted posterior implants.

METHODS

The C/I ratio, MBL, and grayscale values (GSVs) for bone density were measured from X-rays. Four areas of interest (two at the apical area and two at the middle of the peri-implant area) and two control areas were selected for evaluation. Follow-up radiographs were calibrated according to the control areas.

RESULTS

In all, 117 non-splinted posterior implants in 73 patients followed up for a mean duration of 36.23 ± 10.40 (range 24-72) months were considered. The mean anatomical C/I ratio was 1.78 ± 0.43 (range 0.93 to 3.06). The mean change in MBL was 0.28 ± 0.97 mm. There were no significant associations between the C/I ratio and MBL changes (r = -0.028, p = 0.766). Pearson correlation showed a significant correlation between changes in GSV and the C/I ratio in the middle peri-implant area (r = 0.301, p = 0.001) and apical area (r = 0.247, p = 0.009).

CONCLUSIONS

A higher C/I ratio of single non-splinted posterior implants is associated with increased peri-implant bone density, but not correlated with changes in MBL.

Limited marginal bone loss in implant-supported fixed full-arch rehabilitations after 5 years of follow-up

PURPOSE

The aim of the present study was to evaluate the 5-year results in terms of marginal bone level (MBL) around implants supporting fixed full-arch metal-ceramic restorations in a series of cases of patients who had lost their teeth in that dental arch because of severe periodontal disease.

MATERIAL AND METHODS

A retrospective cohort study was designed to evaluate the 5-year MBL results of OsseoSpeed™ Astra Tech TX implants with internal tapered conical connection. Age, gender, bone substratum, smoking habits, history of periodontitis, and prosthetic features were recorded. Mixed linear model was used to determine the influence of the different variables on MBL.

RESULTS

In this series, a total of 160 implants placed in 19 patients were evaluated. No implant failure was reported during the 5 years of follow-up. Only 14 (8.75%) implants had more than 2 mm of MBL. Abutment height, F(3,142) = 6.917, p < .001, and implant diameter, F(1,141) = 15.059, p < .001, were determined to be statistically associated with MBL. No other effect was significant. Pairwise comparisons showed that MBL was larger for abutment height = 1 (MBL = -0.987, SE = 0.186) compared with the remaining heights [-0.335 (0.171), -0.169 (0.192) and -0.247 (0.267), 2, 4 and 6 mm, respectively]. MBL was larger for narrow (-0.510, SE = 0.169) than for wide implants (-0.364, SE = 0.190).

CONCLUSION

The current study demonstrates that the vast majority of internal conical connection implants supporting fixed full-arch metal-ceramic restorations do not suffer from relevant MBL after 5 years in function. Particularly, those implants with transmucosal abutments longer than 2 mm show less than 0.5 mm from the implant shoulder to the marginal bone.

Simultaneous placement of short implants (≤ 8 mm) versus standard length implants (≥ 10 mm) after sinus floor elevation in atrophic posterior maxillae: a systematic review and meta-analysis

Purpose

The objective of this meta-analysis was to compare the clinical outcomes of using short implants (≤ 8 mm) inserted with osteotome sinus floor elevation (OSFE) and standard implants (≥ 10 mm) inserted with sinus floor elevation (SFE) in atrophic posterior maxillae with insufficient residual bone height (RBH).

Methods

An electronic search was performed on PubMed, EMBASE, and the Cochrane Library from 1994 to July 2022, in combination with a manual search of references in relevant articles. Randomized controlled trials (RCTs) that compared the clinical results between short and standard implant placement with SFE were included. The primary outcomes were implant survival rate and marginal bone loss (MBL); the secondary outcome was complication rate.

Results

Three RCTs were included, totaling 138 short and 156 standard implants. The results of the meta-analysis showed no significant differences between the short and standard implant groups in survival rate (RR = 1.02, 95% CI   0.96–1.08, p = 0.570), MBL (MD = − 0.13, 95% CI   − 0.32 to 0.07, p = 0.190) and complication rate (intra-surgical complication: RR = 1.14, 95% CI   0.46–2.83, p = 0.770; post-operative complication: RR = 1.34, 95% CI   0.71–2.55, p = 0.370).

Conclusions

Using short implants (≤ 8 mm) combined with OSFE might be an alternative to standard implants (≥ 10 mm) with SFE when the RBH of the posterior maxilla is insufficient. Based on a short-term clinical observation, short implants with OSFE show good results in terms of survival rate, MBL, and complication incidence.

Graphical Abstract

The Biomechanical Profile of an Osseo-Integrated Rectangular Block Implant: A Pilot In Vivo Strain Analysis

Aim: To load-test the osseo-integrated rectangular block implant (RBI), measure the generated cortical peri-implant strains, and relate these findings to known human physiological parameters. Materials and methods: Two RBIs were placed into the posterior mandibular saddle in a mature greyhound dog and allowed to osseo-integrate. The half mandible (implants in situ) was mounted in a servohydraulic system. Four triple-stacked rosette gauges were placed cortically (mesial, distal, buccal, and lingual). A modified ISO-14801 protocol was used (1000 N, 300, 2 Hz, 1 h) and the generated principal strains (ep, eq) and their angular orientations (F), were calculated. Results: (1) Bucco-lingual “horizontal” dimension: dominant “horizontal” compressive stresses were on the lingual aspect and “horizontal” tensile stresses on the buccal aspect. The buccal cortex was elastically tensile-stretched, while the lingual cortex was elastically compressed. (2) Bucco-lingual “vertical” dimension: dominant vertical torsional stresses were oriented buccally and apically, with an overall buccally inclined torsional effect. This was also evidenced on the lingual aspect, where there remained high torsional rotation elements (high F and e2). (3) Mesio-distal “horizontal” dimension: dominant torsional stresses oriented as a distal-lingual “counter-clockwise” rotation. Conclusions: The applied off-axial loads generated a heterogeneous pattern of bucco-lingual and mesio-distal cortical strains, both vertically and horizontally. The short dimensioned osseo-integrated RBI design appeared to biomechanically withstand the applied loads and to maintain the strains generated to levels that were within physiological limits. More studies and statistical analyses are needed to confirm these findings.

Effect of crown-to-implant ratio and crown height space on marginal bone stress: a finite element analysis

BACKGROUND

Crown-to-implant ratio and crown height space, associated with the use of short implants, have been related with marginal bone loss. However, it is unclear which of the two entities would play the most important role on the bone remodelling process. Using a finite element analysis, the present work aims to help clarifying how those two factors contribute for the stress generation at the marginal bone level. A numerical model (reference model), with a crown-to-implant ratio of 4, was double validated and submitted to a numerical calculation. Then, it was modified in two different ways: (a) by decreasing the prosthetic height obtaining crown-to-implant ratios of 3, 2.5 and 2 and (b) by increasing the implants length obtaining a crown-to-implant ratio of 2.08. The new models were also submitted to numerical calculations.

RESULTS

The reference model showed a marginal bone stress of 96.9 MPa. The increase in the implants' length did not show statistically significant differences in the marginal bone stress (p-value = 0.2364). The decrease in the prosthetic height was accompanied with a statistically significant decrease in the marginal bone stresses (p-value = 2.2e- 16).

CONCLUSIONS

The results represent a paradigm change as the crown height space appears to be more responsible for marginal bone stress than the high crown-to-implant ratios or the implants' length. New prosthetic designs should be attempted to decrease the stress generated at the marginal bone level.

Short vs. regular length implants to rehabilitate partially edentulous mandible: a 2-year prospective split-mouth clinical study

Many studies have evaluated short implants (SIs); however, it is still unclear whether SIs are reliable and can be used to simplify surgical and prosthetic protocols with successful clinical outcomes. The aim of this non-random, conveniently sampled, prospective, split-mouth study was to compare the clinical outcomes when short (SI) (≤8 mm) or regular-length implants (RIs) (>10 mm) were used in the posterior mandible two years after the delivery of splinted reconstructions. Each participant (N=10) received four implants in the posterior mandible; two SIs were placed on one side, and two RIs were placed contra-laterally. Implants were restored with splinted, screw-retained, porcelain-fused-to-metal reconstructions. Survival and success rates, peri-implant marginal bone level (MBL), and soft tissue parameters were evaluated. No participant drop-outs were recorded. Both types of implants showed 100% success and survival rates. From prosthetic delivery to 24 months post-loading, bone remineralization of +0.40 mm for the SIs and +0.36 mm for the RIs was observed without statistically significant differences in MBL between the implant types (p=0.993). SIs showed significantly higher (p=0.001) clinical attachment level (CAL) and probing depth (PD) values. Chipping occurred in one situation in the RI group resulting in a 97.5% prosthetic success rate, which was 100% for the SIs. After 2 years, SIs with splinted reconstructions showed comparable clinical outcomes to those of RIs. Further long-term controlled clinical studies with balanced experimental designs evaluating random and larger populations are required to corroborate these findings.

The Impact of Dental Implant Length on Failure Rates: A Systematic Review and Meta-Analysis

The present review aimed to evaluate the impact of implant length on failure rates between short (<10 mm) and long (≥10 mm) dental implants. An electronic search was undertaken in three databases, as well as a manual search of journals. Implant failure was the outcome evaluated. Meta-analysis was performed in addition to a meta-regression in order to verify how the risk ratio (RR) was associated with the follow-up time. The review included 353 publications. Altogether, there were 25,490 short and 159,435 long implants. Pairwise meta-analysis showed that short implants had a higher failure risk than long implants (RR 2.437, p < 0.001). There was a decrease in the probability of implant failure with longer implants when implants of different length groups were compared. A sensitivity analysis, which plotted together only studies with follow-up times of 7 years or less, resulted in an estimated increase of 0.6 in RR for every additional month of follow-up. In conclusion, short implants showed a 2.5 times higher risk of failure than long implants. Implant failure is multifactorial, and the implant length is only one of the many factors contributing to the loss of an implant. A good treatment plan and the patient's general health should be taken into account when planning for an implant treatment.

Single-crown restorations supported by short implants (6 mm) compared with standard-length implants (13 mm) in conjunction with maxillary sinus floor augmentation: a randomized, controlled clinical trial

BACKGROUND

The purpose of the present study was to test the H0-hypothesis of no difference in the clinical and radiographical treatment outcome of single-crown restorations supported by short implants compared with standard length implants in conjunction with maxillary sinus floor augmentation (MSFA) after 1 year of functional implant loading. Forty patients with partial edentulism in the posterior part of the maxilla were randomly allocated to treatment involving single-crown restorations supported by short implants or standard length implants in conjunction with MSFA. Clinical and radiographical evaluation were used to assess survival of suprastructures and implants, peri-implant marginal bone loss (PIMBL), biological, and mechanical complications.

RESULTS

Both treatment modalities were characterized by 100% survival of suprastructures and implants after 1 year. Mean PIMBL was 0.60 mm with short implants compared with 0.51 mm with standard length implants after 1 year of functional loading. There were no statistically significant differences in survival of suprastructure and implants, PIMBL, and mechanical complications between the two treatment modalities. However, a higher incidence of biological complications was associated with standard length implants in conjunction with MSFA.

CONCLUSION

Within the limitations of the present study, it can be concluded that single-crown restorations supported by short implants seems to be comparable with standard length implants in conjunction with MSFA. However, long-term studies are needed before final conclusions can be provided about the two treatment modalities.

TRIAL REGISTRATION

Clinicaltrials.Gov ID: NCT04518020 . Date of registration: August 14, 2020, retrospectively registered.

A within-subject comparison of short implants in the posterior region: retrospective study of up to 10 years

PURPOSE

This intra-patient retrospective study of up to 10 years evaluated the clinical success and risk factors of 6- and 8-mm long implants and their respective prostheses.

MATERIALS AND METHODS

The sample consisted of patients treated at a Military Polyclinic dental service, who received both 6- and 8-mm long tissue level implants in the posterior region of the same arch. Data were collected from the dental charts, clinical and radiographic exams, self-report of sleep bruxism, measurement of maximum occlusal force, and clinical crown-to-implant (C/I) ratio. Data were analyzed by descriptive and inferential statistics with univariate and hierarchical multivariate models, at the 0.05 significance level.

RESULTS

The 30 patients (27 women) had 85 implants and 83 prostheses. Two implants were lost before prosthesis installation (implant survival: 97.6%). Ten events of prosthetic complication (screw tightening loss) occurred in five patients (success rate: 87.9%) in a single moment. Only the variable C/I ratio had a significant effect for repairable prosthesis complication (P<.05).

CONCLUSION

The results suggest that 6- and 8-mm long implants have similar long-term clinical success for implants and prostheses.

Stress evaluation of different implant lengths on atrophic edentulous mandibles with fixed full-arch implant-supported prosthesis: a finite element analysis

Finite element analysis was used to compare the effect of different implant lengths on atrophic mandible with full-arch fixed prostheses. Four models were constructed with different implant lengths: 4, 6, 8 and 10 mm. A 100-N occlusal load was applied. The stress at the bone level, implant, and prosthetic components were obtained. Similar behavior was observed for all groups, except for 4 mm, which showed more discrepant values ​​for all prosthetic components. Although longer implants presented better biomechanical behavior, the 4 mm implant seems to be a viable alternative for severely atrophic mandibles, however, further studies need to be carried out.

Short Dental Implants (≤8.5 mm) versus Standard Dental Implants (≥10 mm): A One-Year Post-Loading Prospective Observational Study

Background: Recent data have shown that short dental implants can be the preferred treatment in most of cases of posterior atrophic alveolar ridges, offering higher survival and lower complication rates than long implants. The survival rates, stability, and marginal bone level changes were compared between short implants (7 and 8.5 mm) and standard-length implants (≥10 mm). Methods: Prospective observational study in which adult patients requiring ≥1 osseointegrated implants to replace missing teeth were recruited consecutively. A clinical examination was performed on the day the definitive prosthesis was placed and after 6 and 12 months. Implant stability quotient (ISQ), marginal bone level (MBL) changes, and the correlation between these parameters and the characteristics of the implants were evaluated. Results: A total of 99 implants were inserted (47 short, 52 standard) in 74 patients. The 12-month survival rate was 100%. ISQ values showed a similar pattern for both types of implants. No correlation was found between ISQ changes after one year and MBL values, nor between the latter and the characteristics of the implants. Conclusions: With clinical treatment criteria, shorter implants (7 and 8.5 mm in length) can be just as useful as standard-length implants in atrophic alveolar ridges, demonstrating similar rates of survival, stability, and crestal bone loss.

Effect of crown height on the screw joint stability of zirconia screw-retained crowns

STATEMENT OF PROBLEM

Medium- to long-term data for the performance of zirconia crowns with titanium (Ti) bases are sparse, particularly when the crown height space and occlusal loads are high.

PURPOSE

The purpose of this in vitro study was to assess the effect of the height of zirconia screw-retained implant crowns with a Ti base on the screw joint stability after cyclic loading. A secondary aim was to investigate the survival of zirconia crowns of different heights after cyclic loading.

MATERIAL AND METHODS

Twenty-one internal connection implants were secured between fiberglass-reinforced epoxy resin sleeves. Mandibular first molar monolithic zirconia crowns with 3 different heights (6 mm, 10 mm, and 14 mm) were milled and bonded to the Ti bases (n=7). The screws were tightened to 30 Ncm, and a 30-degree 120-N cyclic load was applied to the crowns at 2 Hz for 5 million cycles. After 5 million cycles, the crowns were evaluated for stability, and the same protocol was repeated for 275-N and 435-N loads for 5 million cycles each. After loading, the detorque values were recorded. Failure was characterized based on whether the crown, screw, and/or implant fracture was observed. The detorque values were analyzed by using a 1-way-ANOVA with the restricted maximum likelihood estimation. The percentage of torque loss was calculated. The LIFETEST procedure was used to analyze the survival probability of the groups (α=.05).

RESULTS

The effect of crown height on the detorque values of screws was not found to be statistically significant (P>.05). The mean detorque value for 6-mm crowns was 23.5 Ncm, 24.4 Ncm for 10-mm crowns, and 22.1 Ncm for 14-mm crowns. A significant effect of crown height was found on the survival (P=.006), and the time-to-failure survival of 14-mm crowns was significantly lower than the survival of 6 mm and 10 mm crowns (P=.020), where no failures were observed. Four 14-mm crowns failed between the 1 and 2 million cycles after the loads were increased to 435 N. The failure modes were the same for all the crowns, implants, and screws fractured.

CONCLUSIONS

When the tested internal connection implant was used, the crown height did not affect the detorque values, and 14-mm crowns performed similarly to the shorter crowns in terms of torque loss after cyclic loading. However, survival of the 14-mm crown-implant complex was lower, resulting in screw and implant fractures.

A Minimally Invasive Technique for Short Spiral Implant Insertion with Contextual Crestal Sinus Lifting in the Atrophic Maxilla: A Preliminary Report

The most recently reported techniques for the rehabilitation of the atrophic posterior maxilla are increasingly less invasive, as they are generally oriented to avoid sinus floor elevation with lateral access. The authors describe a mini-invasive surgical technique for short spiral implant insertion for the prosthetic rehabilitation of the atrophic posterior maxilla, which could be considered a combination of several previously described techniques based on the under-preparation of the implant site to improve fixture primary stability and crestal approach to the sinus floor elevation without heterologous bone graft. Eighty short spiral implants were inserted in the molar area of the maxilla in patients with 4.5–6 mm of alveolar bone, measured on pre-operative computed tomography. The surgical technique involved careful drilling for the preparation of implant sites at differentiated depths, allowing bone dislocation in the apical direction, traumatic crestal sinus membrane elevation, and insertion of an implant (with spiral morphology) longer than pre-operative measurements. Prostheses were all single crowns. In all cases, a spiral implant 2–4 mm longer than the residual bone was placed. Only two implants were lost due to peri-implantitis but subsequently replaced and followed-up. Bone loss values around the implants after three months (at the re-opening) ranged from 0 to 0.6 mm, (median value: 0.1 mm), while after two years, the same values ranged from 0.4 to 1.3 mm (median value: 0.7 mm). Clinical post-operative complications did not occur. After ten years, no implant has been lost. Overall, the described protocol seems to show good results in terms of predictability and patient compliance.

Clinical evaluation of single 4-mm implants in the posterior mandible: A 3-year follow-up pilot study

STATEMENT OF PROBLEM

Extra-short implants in the posterior mandible can increase the functional surface area and reduce the risk of implant overload. However, reports of treatment using single extra-short implants in the posterior mandible with a midterm follow-up are lacking.

PURPOSE

The purpose of this prospective pilot study was to evaluate the clinical behavior of single extra-short 4-mm implants placed in the posterior mandible during a follow-up of 3 years from implant restoration.

MATERIAL AND METHODS

A total of 18 participants with a single extra-short 4-mm-long implant placed in the area of the mandibular first molars participated in this pilot study. The survival and success rates of implants, as well as biologic and prosthetic variables, were evaluated during a follow-up of 3 years from implant restoration.

RESULTS

The survival rate of the implants was 100%, with no implant or biologic complications recorded. One prosthetic complication (loosening of 1 screw) was observed.

CONCLUSIONS

Single extra-short (4 mm) implants in the posterior mandible showed favorable clinical behavior during the first 3-years of follow-up.

Placement of Short Implants: A Viable Alternative?

The placement of short implants, which measure less than 10 mm in length, requires the practitioner to have a thorough comprehension of implant dentistry to achieve acceptable results. Innovation of the rough-surface implant and the progression of the implant-abutment interface from an external hex to an internal connection have considerably influenced the longevity of short implants. Dentists are better equipped to serve their patients because the utilization of short implants may preclude the need for advanced surgical bone-grafting procedures.

Effect of crown-to-implant ratio on the marginal bone level changes and implant survival - A systematic review and meta-analysis

The purpose of the systematic review and meta-analysis was to analyze the existing evidence regarding the effect of crown-to-implant ratio (CIR) on the peri-implant crestal bone level change and implant survival. Randomized controlled clinical trials, prospective as well as retrospective studies with a minimum follow-up period of 12 months and 10 patients per group were included for this systematic review. Statistical analysis was performed to determine CIR effects on the peri-implant marginal bone level changes and implant survival. A total of 28 articles (14 prospective studies and 14 retrospective studies) from a database of 201 articles, with 2097 patients and 4350 implants, were included. A mean CIR ranging from 0.6 to 2.44 was presented by the study groups. A weighted mean implant loss of 0.19% per year and peri-implant marginal bone level change of 0.63 mm ± 0.55 over 46.8 ± 5.2 months was calculated from the included studies. The peri-implant marginal bone level change (p = 0.155) and the rate of implant loss (p = 0.245) showed a statistically insignificant difference between implant restorations of a high (>1.5:1) and low (<1.5:1) CIR. Within its limitations, this review concludes that a high (>1.5:1) or a low (<1.5:1) CIR does not significantly affect the peri-implant marginal bone level change and implant survival rate. However, until further evidence becomes available, extrapolation to long term clinical success cannot be ascertained.

The influence of prosthetic crown height and implant-abutment connection design selection on the long-term implant-abutment stability: A laboratory study

BACKGROUND AND AIM

Long-term edentulism associated with vertical loss of alveolar bone might lead to increased suprastructure height. This study aimed to evaluate the effect of suprastructure height on the stability of the implant-abutment connection by investigating the stability of two different two-piece titanium implants with internal hexagonal or conical connections under simulated oral loading conditions.

MATERIALS AND METHODS

A total of 48 specimens were used. The specimens were divided into 2 groups according to their implant-abutment connection (group H: internal hex connection, group C: conical connection). Each group was further divided into 3 groups according to the applied suprastructure height (H1; C1: 10 mm, H2; C2: 14 mm and H3; C3: 18 mm) (n = 8). All specimens were subjected to a cyclic loading force of 98 N for 5 million simulated chewing cycles. Then, all implants that survived the chewing simulation were quasi-statically loaded until failure. The monotonic-failure load and monotonic-bending moment at failure were evaluated.

RESULTS

After the dynamic chewing loading, the implants showed the following survival rates: group H: 95.8%; group C: 100%. The implant suprastructures revealed survival rates of 100% and 91.5% for groups H and C, respectively. After the artificial chewing simulation of 5 million cycles, some implants in the groups with higher crowns (14 mm and 18 mm) showed crack formation and plastic deformations under the light microscope. Regarding monotonic-failure load, implants with shorter suprastructures (10 mm) revealed higher resistance to failure (C1: 1496 and H1: 1201 N) than longer suprastructures (18 mm) (C3: 465 and H3: 585 N) which was expected. The mean monotonic-bending moment values at failure ranged from 400.7 Ncm to 673.3 Ncm.

CONCLUSION

Implant-supported restorations with increased crown height are considered stable for an extended time period (5 million cycles which equals approximately 20 years clinical service) and a reliable treatment option in case of increased inter-arch distance. There was no difference in stability of the two internal connections. Nevertheless, the integrity of implant components might be impaired when crowns with increased heights are applied.

Short Implants: An Answer to a Challenging Dilemma?

The purpose of this article is not to discuss the success of short dental implants versus standard/long dental implants, but to compare short dental implants with standard/long dental implants in areas that necessitated adjunctive bone grafting or augmentation procedures and as a way to avoid the need for advanced surgical procedures and their associated risks. It can be concluded that short dental implants are a viable alternative in sites that would have required additional complex and costly augmentation procedures. Short dental implants resulted in comparable survival and success rates with faster, less expensive treatment with fewer surgical complications and morbidity.

Three-dimensional finite element analysis of extra short implants focusing on implant designs and materials

AIM

When using short implants, fracture of the implant body and bone resorption are a concern because stress concentrates on and around a short implant. The purpose of this research is to investigate the differences in stress distribution between tissue level (TL) and bone level (BL) implant body designs, and between commercially pure titanium (cpTi) and the newer titanium-zirconium (TiZr) alloy in using short implants.

MATERIALS AND METHODS

Models of TL and BL implants were prepared for three-dimensional finite element analysis. The implants were produced in 10 mm, 8 mm, and 6 mm lengths, and the TL was also produced in a 4-mm length. A static load of 100 N inclined at 30° to the long axis was applied to the buccal side of the model. The largest maximum principal stress value in the cortical bone and the largest von Mises stress value in the implant body were evaluated.

RESULTS

Stress concentration was observed at the connection part of the implant, especially above the bone in TL and within the bone in BL. In the TL design, tensile stress occurred on the buccal side and compressive stress on the lingual side of the cortical bone. Conversely, in the BL design, tensile stress occurred on the lingual side of the cortical bone. CpTi and TiZr showed a similar stress distribution pattern. The maximum stress values were lower in the TL design than the BL design, and they were lower with TiZr than cpTi for both the cortical bone and implant body. The maximum value tended to increase as the length of the implant body decreased. In addition, the implant body design was more influential than its length, with the TL design showing a stress value similar to the longer BL design.

CONCLUSION

Using TiZr and a TL design may be more useful mechanically than cpTi and a BL design when the length of the implant body must be shorter because of insufficient vertical bone mass in the mandible.

Prospective, Clinical Pilot Study with Eleven 4-Mm Extra-Short Implants Splinted to Longer Implants for Posterior Maxilla Rehabilitation

In many clinical situations, rehabilitation with implants in the posterior maxillary region is complicated by limited bone availability. In this context, the use of 4 mm long implants (known as extra-short implants) may be used thanks to the concept of osseointegration enhancement. It has been demonstrated that short implants offer an alternative to the regeneration procedures involved in placing longer implants in areas where bone height is compromised. This prospective pilot study tested a treatment protocol in which 11 extra-short (4 mm) implants were splinted to 11 mesially placed longer (8 mm) implants in the posterior maxillary regions of partially edentulous patients, without using supplementary bone regeneration procedures. Eleven patients were included in this single cohort study. The clinical performance of the extra-short implants was assessed during a two-year follow-up period, obtaining a 100% survival rate and mean bone loss of 0.3 mm. Implant stability measured by resonance frequency analysis (RFA) at the time of placement was 54.9 ± 4.9, increasing to 77.0 ± 2.6 at 24 months. The study demonstrated the gradual consolidation of osseointegration in bone of less-than-ideal quality in the posterior maxillary region. The results obtained show that a partially edentulous maxilla with reduced bone height may be rehabilitated by using an extra-short implant splinted to a mesial implant of 8mm length or longer. Despite the small sample size, this pilot study observed that extra-short implants achieved adequate bone stability and clinical performance after a 24-month follow-up.

A case of effective oral rehabilitation after mandibular resection

Radical mandible resection causes significant functional and cosmetic impairment. Nonvascularized bone reconstruction and oral rehabilitation using fixed prosthesis with dental implants enabled recovery of appearance and mastication function.

Influence of Implant Length and Associated Parameters Upon Biomechanical Forces in Finite Element Analyses: A Systematic Review

PURPOSE

The aim of this systematic review is to provide an overview of finite element analyses comparing standard and short dental implants concerning biomechanical properties and to detect the most relevant parameters affecting periimplant stress concentrations.

MATERIAL AND METHODS

After screening the literature and assessment of studies, 36 studies were included in this review.

RESULTS

Eighty-three percent of the studies state that short dental implants have to bear higher stress concentrations compared with standard length implants. At the same time, 44% of articles note that implant diameter can be considered a more effective design parameter than implant length to reduce stress concentrations and to avoid an overload of periimplant bone. Regardless of implant dimension, in all studies, the highest stress concentrations are found in the cortical section around the upper part of the implant.

CONCLUSIONS

Unaffected of bone quality, implant diameter is found to play a key role to minimize periimplant stress concentrations. Concerning stress reduction implant length gains increasing relevance with decreasing bone density. Furthermore, splinting of short implants constitute an appropriate tool to avoid crestal overloading.

Short implants (≤6 mm) versus longer implants with sinus floor elevation in atrophic posterior maxilla: a systematic review and meta-analysis

OBJECTIVES

To compare the use of short implants (≤6 mm) in atrophic posterior maxilla versus longer implants (≥10 mm) with sinus floor elevation.

DESIGN

A systematic review and meta-analysis based on randomised controlled trials (RCTs).

DATA SOURCES

Electronic searches were conducted in PubMed, Embase and the Cochrane CENTRAL. Retrospective and prospective hand searches were also performed.

ELIGIBILITY CRITERIA

RCTs comparing short implants (≤6 mm) and longer implants (≥10 mm) with sinus floor elevation were included. Outcome measures included implant survival (primary outcome), marginal bone loss (MBL), complications and patient satisfaction.

DATA EXTRACTION AND SYNTHESIS

Risks of bias in and across studies were evaluated. Meta-analysis, subgroup analysis and sensitivity analysis were undertaken. Quality of evidence was assessed according to Grading of Recommendations Assessment, Development and Evaluation.

RESULTS

A total of seven RCTs involving 310 participants were included. No significant difference in survival rate was found for 1-3 years follow-up (RR 1.01, 95% CI 0.97 to 1.04, p=0.74, I²=0%, moderate-quality evidence) or for 3 years or longer follow-up (RR 1.00, 95% CI 0.97 to 1.04, p=0.79, I²=0%, moderate-quality evidence). However, short implants (≤6 mm) showed significantly less MBL in 1-3 years follow-up (MD=-0.13 mm, 95% CI -0.21 to 0.05; p=0.001, I²=87%, low-quality evidence) and in 3 years or longer follow-up (MD=-0.25 mm, 95% CI -0.40 to 0.10; p=0.001, I²=0%, moderate-quality evidence). In addition, short implant (≤6 mm) resulted in fewer postsurgery reaction (RR 0.11, 95% CI 0.14 to 0.31, p<0.001, I²=40%, moderate-quality evidence) and sinus perforation or infection (RR 0.11, 95% CI 0.02 to 0.63, p=0.01, I²=0%, moderate-quality evidence).

CONCLUSIONS

For atrophic posterior maxilla, short implants (≤6 mm) are a promising alternative to sinus floor elevation, with comparable survival rate, less MBL and postsurgery reactions. Additional high-quality studies are needed to evaluate the long-term effectiveness of short implants (≤6 mm).

TRIAL REGISTERATION NUMBER

The protocol has been registered at PROSPERO (CRD42018103531).

Occlusal overload with dental implants: a review

Controversy persists as to the role of occlusal overload in peri-implantitis. Animal studies have not revealed the biological threshold for fatigue failure in the peri-implant bone. On the other hand, clinical studies have demonstrated a link between parafunction and implant failure, although variables such as intensity and frequency of loads, as well as bone density, have led to different outcomes. The absence of specific engineering “building codes” for the clinician has relegated prosthetic design planning to intuitive guidelines for all patients. For example, higher crown to implant ratios (2–3:1), implant cantilever prostheses and non-splinted restorative designs have been avoided because of the concern for overload. However, evidence has not supported this general approach. A call for preclinical research to establish specific patient load thresholds is in order to establish a customized treatment plan.

Mechanical fatigue behaviour of different lengths screw-retained restorations connected to two designs prosthetic connection level

The aim of this work is to compare the mechanical fatigue behaviour of different crown heights of single crown implant restorations made over two different internal hexagonal titanium dental implant connection levels. Two different groups of internal hexagonal connection were studied: (a) TL group (N = 26) included implants with a transmucosal connection (12.2 mm height and 4.8 mm width) and (b) BL group (N = 26) composed by implants at a bone level connection (10 mm height and 3.8 mm width). Two subgroups (N = 13) were established for each connection level according to crown heights (TL10 = 10 mm, TL15 = 15 mm, BL12 = 12 mm, BL17 = 17 mm). Dynamic load tests were carried out according to ISO Norm 14801. Failed samples and fracture surfaces were analysed with an optical and scanning electron microscope (SEM). The fatigue limit and the fatigue strength degradation (fatigue strength exponent) decreases with increasing crown height (5 mm) in both groups of internal hexagonal titanium dental implant connection levels. Consequently, the mechanical integrity of internal hexagonal dental implants varies with the height of the crown. An increase of 5 millimetres in the crown height appears to significantly decrease the fatigue life of both types of dental implants.

A 5-year longitudinal cohort study on crown to implant ratio effect on marginal bone level in single implants

BACKGROUND

A 5-year longitudinal cohort study was carried out to evaluate the influence of anatomical crown to implant ratio (CIR) on peri-implant marginal bone level (MBL) in single implants.

MATERIALS AND METHODS

The longest possible implants, according to the availability of pristine bone, were inserted, one per patient, among periodontally healthy teeth in consecutively recruited subjects. CIR and MBL changes were measured on standardized radiographs. The relationship between MBL and multiple predictors was investigated. A statistical analysis suitable for mixed type distributions was conducted: for the discrete component a logistic regression model was used and for the continuous component the impact of the variables on MBL was examined by using robust nonparametric comparison tests.

RESULTS

Seventy-eight dental implants were inserted in 34 mandibles and 44 maxillae, with one stage procedure in 40 cases and two stage in 38 cases. Thirty-five implants were <10 mm, while 43 were ≥ 10 mm long; 28 implants had a CIR ≤1 and 50 had a CIR >1. No drop-outs or implant loss were observed. Bone loss occurred only in a few cases, measuring less than 0.5 mm and being significantly more pronounced for implant length ≥10 mm, for lower CIR values and for the two stage procedure.

CONCLUSION

Higher CIR values were not related to increased peri-implant bone loss; a <10 mm long implant insertion may be safely considered for reduced bone heights.

Is there an effect of crown-to-implant ratio on implant treatment outcomes? A systematic review

OBJECTIVES

High crown-to-implant ratios may lead to complications due to unfavorable occlusal forces, including nonaxial forces, on the bone surrounding the neck of the implant and within the connection of the crown and implant itself. The aim of this study was to perform a systematic review on the influence of crown-to-implant ratio of single-tooth, nonsplinted, implants on biological and technical complications.

MATERIALS AND METHODS

MEDLINE (1950-January 2018), EMBASE (1966-January 2018), and Cochrane Central Register of Controlled Trials database (1800-January 2018) were searched to identify eligible studies. Inclusion criteria were as follows: crown-to-implant ratio of single-tooth, nonsplinted, implant-supported restorations in the posterior maxilla or mandible and follow-up of at least 1 year. Main outcome measures were as follows: implant survival rate, marginal bone level changes, biological complications, and technical complications. Two reviewers independently assessed the articles. A meta-analysis was carried out for implant survival rate and peri-implant bone changes.

RESULTS

Of 154 primarily selected articles, eight studies fulfilled the inclusion criteria. Study groups presented a mean crown-to-implant ratio varying from 0.86 (with 10-mm implants) to 2.14 (with 6-mm implants). The meta-analysis showed an implant survival of more than 99% per year and mean peri-implant bone changes of <0.1 mm per year. Limited biological and technical complications were reported.

CONCLUSION

Data reviewed in the current manuscript on crown-to-implant ratio, ranging from 0.86 to 2.14, of single-tooth, nonsplinted, implants did not demonstrate a high occurrence of biological or technical complications.

Short implants in the posterior maxilla to avoid sinus augmentation procedure: 5-year results from a retrospective cohort study

BACKGROUND

Short implants present a promising approach for patients with advanced atrophy to avoid augmentative procedures. However, concerns about increased biological and technical complications due to an unfavorable implant-crown ratio are still present.

PURPOSE

The aim of the present retrospective study was to evaluate whether a reduced implant length has any impact on implant success and peri-implant hard and soft tissue health in implants placed in the posterior maxilla to avoid sinus augmentation procedures.

MATERIALS AND METHODS

Fourteen patients received a total of 30 implants of 7-mm length in the posterior maxilla. Implants with a mean loading period of 5 years (range 2-7 years) were followed up clinically and radiologically, with a focus on the peri-implant soft tissue parameters probing pocket depth (PPD), bleeding on probing (BoP), and the stability of the marginal peri-implant bone level.

RESULTS

None of the implants were lost, and no technical failures occurred. A mean PPD of 2.5 mm, a mean BoP of 13.3%, and a mean marginal bone loss (MBL) of 0.5 mm indicate healthy peri-implant hard and soft tissue conditions without signs of peri-implantitis.

DISCUSSION

The present results indicate the suitability of implants of 7-mm length to replace missing teeth in the posterior maxilla. An unfavorable implant-crown ratio or reduced bone-implant contact length seems to have no negative influence on midterm implant success or on peri-implant hard and soft tissue health.

Long-term follow-up of single crowns supported by short, moderately rough implants-A prospective 10-year cohort study

OBJECTIVES

To evaluate prospectively the clinical and radiographic outcomes after ten years of short (6 mm) implants with a moderately rough surface supporting single crowns in the posterior region.

MATERIAL AND METHODS

Forty 6 mm modified sandblasted large-grit acid-etched (mod-SLA), soft tissue level implants were installed in the distal segments of 35 consecutive patients. After 6 weeks of healing, abutments were tightened, and single porcelain-fused-to-metal crowns were cemented. Implant survival, marginal bone loss, and clinical crown/implant ratio were evaluated at various time intervals up to 10 years after loading.

RESULTS

Two out of the 40 implants were lost before loading, one implant was lost after 7 years because of peri-implantitis. One patient with two implants died and was excluded from analysis. Two patients did not come at the 10-year follow-up and were considered as drop out (2 implants). The survival rate was 91.7% (n = 36). Thirty-three implants were available for marginal bone loss evaluation. A mean marginal bone loss after 10 years of function was 0.8 ± 0.7 mm. Between 5 and 10 years, the loss was 0.2 ± 0.4 mm. No technical complications were registered during the 10-year period. The clinical crown/implant ratio increased with time from 1.6 at the delivery of the prosthesis to 2.0 after 10 years of loading with no increase between 5 and 10 years.

CONCLUSION

Short (6 mm) implants with a moderately rough surface supporting single crowns in the posterior region and loaded after 6-7 weeks maintained full function for at least 10 years with low marginal bone resorption.

Evaluation of the Surrounding Ring of Two Different Extra-Short Implant Designs in Crestal Bone Maintanence: A Histologic Study in Dogs

The aim of this study was to compare the implant stability and bone resorption and formation of two different extra-short implant designs with different diameter rings placed in a dog´s maxilla. Thirty-six extra-short, 5 mm diameter × 4 mm length (Short DM^®, Bioner Sistemas Implantológicos, Barcelona, Spain), delayed implants were placed in each hemimaxilla of six dogs at the bone crest level. Eighteen implants of each design (wide and narrow ring) were installed. After 8 and 12 weeks of healing, histomorphometric analyses of the specimens were carried out to measure the crestal bone level values and the tissue thickness around the wide and narrow ring implant designs. In the microscopic analysis, less buccal bone resorption was observed in the narrow ring implants with a statistical significance (p < 0.001). For the peri-implant tissue thickness, the distance from the implant shoulder to the external portion of the epithelium was significantly higher for the implants installed with a wide ring with statistical significance (p < 0.001). Our findings suggest that the amount of peri-implant tissues (crestal bone loss) after remodeling over a period of 12 weeks was smaller in the narrow ring extra-short implant installed in the healed maxilla, compared with the wide ring extra-short implants.

Short Implants Versus Standard Implants: Midterm Outcomes of a Clinical Study

INTRODUCTION

The aim of this study was to evaluate the midterm survival rate, marginal bone resorption (MBR), and stability of short implants and to compare the results with standard length implants.

MATERIALS AND METHODS

A total of 38 patients were included. In total, 147 implants (Nucleoss Implants, Izmir, Turkey) were placed (86 short implants and 61 standard implants). Cement-retained metal-ceramic prostheses were fabricated. MBR was evaluated on periapical radiographs taken at implant placement, at the time of crown insertion and annually thereafter. The stability of the implants was evaluated by resonance frequency analysis.

RESULTS

The 3- and 5-year cumulative survival rates for standard implants was 98.4% and for short implants was 96.5% (P = 0.644). The MBR of the short implants was significantly lower than that of the standard implants after 1, 2, and 3 years of loading (P < 0.05). No significant differences were found between 2 groups after 6 and 12 months of loading in terms of implant stability (implant stability quotient values) (P > 0.05).

CONCLUSION

Within the limits of this study, it is concluded that short implants achieved similar results as standard implants after 3 to 5 years of loading.

Short vs. Standard Laser-Microgrooved Implants Supporting Single and Splinted Crowns: A Prospective Study with 3 Years Follow-Up

PURPOSE

The aim of this study was to compare survival rates, marginal bone loss (MBL), and peri-implant soft tissue parameters between short and standard laser-microgrooved implants supporting single or splinted crowns 3 years after loading.

MATERIALS AND METHODS

30 subjects received 1 short ( ≤ 7 mm ) and 1 standard length ( ≥ 9 mm ) laser-microgrooved implant in adjacent sites of the premolar and molar regions of the mandible or maxilla. Peri-implant soft tissue parameters and intraoral radiographs were recorded at the delivery of definitive crowns (baseline) and 3 years later. Cumulative survival rate (CSR) and marginal bone loss (MBL) in relation to crown/implant (C/I) ratio, implant length, location, type of antagonist, and type of prosthetic design (single or splinted), were evaluated.

RESULTS

CSR of short implants was 98%, compared to 100% for standard implants, without significant statistical difference. MBL was not significantly different over the observation period, with an average of 0.23 ± 0.6 mm and 0.27 ± 0.3 mm for short and standard implants, respectively. No statistical differences were found between short and standard implants regarding plaque (14.7% vs. 15.7%), number of sites BOP (8.3% vs. 5.9%), probing depth (1.13 ± 0.6 mm vs. 1.04 ± 0.8 mm), and mean mucosal recession (0.18 ± 0.3 mm vs. 0.22 ± 0.3 mm). Analyzing MBL in relation to the C/I ratio, implant length, location, type of antagonist, and type of prosthetic design, no statistically significant differences were found.

CONCLUSION

Regardless of C/I ratio, implant length, location, type of antagonist, and type of prosthetic design, short and standard laser-microgrooved implants had similar survival rates, MBL, and peri-implant soft tissue conditions over the observation period of 3 years.

Relationship Between Crestal Bone Levels and Crown-to-Implant Ratio of Ultra-Short Implants With a Microrough Surface: A Prospective Study With 48 Months of Follow-Up

The aim of this cohort study was to investigate the relationship between crestal bone levels and crown-to-implant ratio of ultra-short implants, after functional loading. Sixty patients with single or partial edentulism and alveolar bone atrophy were enrolled and treated between December 2009 and January 2016. Without using bone-grafting procedures, patients were rehabilitated with ultra-short implants characterized by a microrough surface and a 6-mm length. Clinical and anatomical crown-to-implant (C/I) ratios and crestal bone levels (CBL) were measured after a follow-up period ranging from 12 to 72 months; all peri-implant and prosthetic parameters were recorded. The data collected were statistically analyzed ( P = .05). A total of 47 patients with 66 ultra-short implants were completely followed up according to described protocol. The mean follow-up was 48.5 ± 19.1 months. The mean anatomical C/I ratio was 2.2, while the mean clinical C/I ratio was 2.6 ± 0.6 at baseline and 2.8 ± 0.6 at the last follow-up appointment. Mean CBL as calculated at the baseline was 0.7 ± 0.5 mm, while at the last appointment it measured 1.0 ± 0.5 mm. The overall implant-based success rate was 96.9%, and the mean peri-implant bone loss (PBL) was 0.3 ± 0.3 mm. No statistically significant relationship was found between anatomical or clinical C/I ratio and PBL. Ultra-short implants appear to offer a predictable solution for implant-prosthetic rehabilitation in patients with edentulism and bone atrophy. A high percentage of implants were successful, with minimal crestal bone loss. The high C/I ratio did not appear to influence either peri-implant bone loss or prosthetic complication rates.

Prosthetic Rehabilitation of the Partially Edentulous Atrophic Posterior Mandible with Short Implants (≤ 8 mm) Compared with the Sandwich Osteotomy and Delayed Placement of Standard Length Implants (> 8 mm): a Systematic Review

Objectives

Test the hypothesis of no difference in prosthetic rehabilitation of the partially edentulous atrophic posterior mandible with short implants (≤ 8 mm) compared with the sandwich osteotomy and delayed placement of standard lengths implants (> 8 mm).

Material and Methods

A MEDLINE (PubMed), Embase and Cochrane library search in combination with a hand-search was conducted by including studies published in English. No year of publication restriction was applied.

Results

Six randomized controlled trials characterized by low or moderate risk of bias fulfilled the inclusion criteria. There were no statistically significant differences (P > 0.05) in the survival rate of suprastructures and implants between the two treatment modalities after one year. Sandwich osteotomy and delayed implant placement demonstrated statistically significant higher long-term peri-implant marginal bone loss as well as biological and technical complications compared with short implants (P < 0.0001). Moreover, patients significantly favoured prosthetic rehabilitation with short implants (P < 0.0001).

Conclusions

Short implants and the sandwich osteotomy with delayed placement of standard length implants appear to result in predictable outcomes in terms of high survival rate of suprastructures and implants after prosthetic rehabilitation of the partially edentulous atrophic posterior mandible. However, further long-term randomized controlled trials assessing donor site morbidity, an economic perspective, professional and patient-related outcome measures with the two treatment modalities are needed before definite conclusions can be provided about the beneficial use of short implants for prosthetic rehabilitation of the partially edentulous atrophic posterior mandible compared with the sandwich osteotomy and delayed placement of standard length implants.

The Influence of the Crown-Implant Ratio on the Crestal Bone Level and Implant Secondary Stability: 36-Month Clinical Study

Introduction

When the era of dental implantology began, the pioneers defined some gold standards used in dental prosthetics treatment for implant-supported restorations. Referring to traditional prosthetics, it was taken for granted that the length of an implant placed in the alveolar bone (the equivalent of the root) should exceed the length of the superstructure.

Aim of the Study

The aim of the study was to determine whether implant length and the crown-to-implant (C/I) ratio influence implant stability and the loss of the surrounding marginal bone and whether short implants can be used instead of sinus augmentation procedures.

Material and Methods

The patients participating in the study (n = 30) had one single tooth implant, a short (OsseoSpeed™ L6 Ø4 mm, Implants) or a regular implant (OsseoSpeed L11 and L13 Ø4 mm, DENTSPLY Implants), placed in the maxilla. The evaluation was based on clinical and radiological examination. The crown-to-implant ratio was determined by dividing the length of the crown together with the abutment by the length of the implant placed crestally. Mean crown-to-implant ratios were calculated separately for each group and its correlation with the MBL (marginal bone loss) and stability was assessed. The authors compared the correlation between the C/I ratio values, MBL, and secondary implant stability.

Results

Positive results in terms of primary and secondary stability were achieved with both (short and conventional) implants. The MBL was low for short and conventional implants being 0.34 ± 0.24 mm and 0.22 ± 0.46 mm, respectively. No significant correlation was found between the C/I ratio and secondary stability as well as the C/I ratio and the marginal bone loss.

Conclusions

Short implants can be successfully used to support single crowns. The study has revealed no significant differences in the clinical performance of prosthetic restorations supported by short implants. Clinical trial registration number is NCT03471000.

Clinical and Radiographic Evaluation of Short Implants Placed in the Posterior Mandible: A 1-Year Pilot Split-Mouth Study

In many cases, due to anatomical limitations, the placement of regular-length implants cannot be facilitated without the performance of advanced surgical procedures. However, these are associated with morbidity, prolonged treatment time, and costs. To overcome such disadvantages, short implants were introduced. The aim of this prospective pilot split-mouth study was to compare the clinical outcome between short implants (7 mm) and regular-length (≥10 mm) implants placed in the posterior mandible after 1 year of prosthetic delivery. Ten patients received 4 implants in the posterior mandible. Two short implants were placed in one side and 2 regular-length implants were placed contralaterally. These were restored by means of splinted screw-retained metal-ceramic crowns. Marginal bone loss (MBL) and soft-tissue parameters were compared. No implant failed. Both types of implants showed success rates of 90% and survival rates of 100%. From prosthetic delivery to 1 year post-loading a bone gain of +0.29 mm for short implants and +0.19 mm for regular-length implants was present without showing any statistically significant differences in MBL between the 2 implant types ( P > .05). Bleeding on probing, clinical attachment level, probing depth, and crown-to-implant ratio did not show any statistically significant differences between the 2 implant lengths ( P > .05). One case of chipping occurred in the regular-length implant group, leading to a prosthetic survival rate of 95%. Short implants showed a prosthetic survival rate of 100%. After 1 year, short implants showed comparable clinical outcomes to that of regular-length implants, making them a viable treatment option in the posterior mandible.

Five-Year Survival of Short Single-Tooth Implants (6 mm): A Randomized Controlled Clinical Trial

The aim of the present study was to evaluate whether 6-mm dental implants in the posterior segments of either jaw perform equally well in terms of clinical and radiographic outcomes when compared with 10-mm implants after 5 y of loading. Patients with single-tooth gaps in the posterior area who were scheduled for implant therapy were randomly assigned to a group receiving either a 6- or 10-mm implant. After a healing period of 10 wk, implants were loaded with a screw-retained single crown and followed up at yearly intervals. Of 96 patients, 86 could be recalled after 5 y. The implant survival rates amounted to 91% (95% confidence interval: 0.836 to 0.998) for the 6-mm group and 100% for the 10-mm group ( P = 0.036). Median crown-to-implant (C/I) ratios were 1.75 (interquartile range [IQR], 1.50 to 1.90) for the 6-mm group and 1.04 (IQR, 0.95 to 1.15) for the 10-mm group, whereas the median marginal bone levels measured −0.29 mm (IQR, −0.92 to 0.23) for the 6-mm group and −0.15 mm (IQR: −0.93 – 0.41) for the 10-mm group after 5 y. The C/I ratio turned out to be statistically significant ( P < 0.001), whereas marginal bone levels showed no significant difference between the groups. The 6-mm implants exhibited significantly lower survival rates than the 10-mm implants over 5 y, whereas there was no difference between upper and lower jaws in terms of survival ( P = 0.58). Lost implants did not show any sign of marginal bone loss or peri-implant infection previous to loss of osseointegration. High C/I ratio and implant length had no significant effect on marginal bone level changes or technical and biological complications (German Clinical Trials Registry: DRKS00006290).