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

Influence of Crown Height and Width on Marginal Bone Loss and Long-Term Stability of Dental Implants: A Systematic Review

Still, a major focus of research in implantology is how crown height and width affect marginal bone loss (MBL) and the long-term durability of dental implants. Maximizing the success of implants and lowering problems depends on an awareness of these elements. Following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, this systematic review searched pertinent studies across several databases using keywords unique to databases. Studies on MBL and long-term implant stability evaluated in the review included those on crown height and width, horizontal and vertical cantilevers, and prosthesis dimensions. In the chosen studies, we found that both implant success and crestal bone loss were greatly influenced by crown height and width. Particularly in the posterior sections, horizontal cantilevers were connected to both increasing MBL and mechanical problems. Vertical cantilevers also affected MBL; however, their impacts were more obvious in circumstances with greater crown heights. Greater prosthesis widths, especially in the mandibular molar area, were linked to higher MBL. Bone density and insertion torque (IT) were the main determinants of MBL, more than the primary implant stability quotient. Early MBL was influenced by abutment height, mucosal thickness, and implant insertion depth; bone levels stabilized six months later. Short implants allow single crowns to be supported, but in some cases, a higher failure rate was seen. The success and stability of dental implants were found to be mostly dependent on crown height, width, and cantilever design. MBL and long-term stability are greatly influenced by horizontal and vertical cantilevers, which calls for careful design and planning. With specific care for bone density, IT, and early MBL stabilization, both short and standard implants can produce equivalent results. These results highlight the need for customized treatment plans to maximize implant success and lifetime.

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.

The effect of porous compliance bushings in a dental implant on the distribution of occlusal loads

Porous dental implants are clinically used, but the mechanism of load distribution for stepped implant shaft surrounded by compliance bushings is still not known, especially for different bone conditions. The aim of the study was to assess the impact of the design of a dental implant with compliance bushings (CBs) on the occlusal load distribution during primary and secondary stability using finite element simulation (FEA), with a distinction between low and high quality cervical support under primary stability. The FEA of the oblique occlusal load transfer (250 N; 45°) was carried out for implants under variable bone conditions. The stepped shaft in the intermediate part of the dental implant was surrounded by CBs with an increasing modulus of elasticity of 2, 10 and 50 GPa. With a smaller Young's modulus of the bushings the increase of stress in the trabecular bone indicated that more bone tissue can be protected against disuse. The beneficial effect for the trabecular bone derived from the reduction of the stiffness of the bushings in relation to the loss of the implant's load bearing ability can be assessed using the FEM method.

Multicentre Prospective Study Analysing Relevant Factors Related to Marginal Bone Loss: A Two-Year Evolution

INTRODUCTION

The aim of this prospective descriptive study was to analyse the possible variables associated with marginal bone loss in rehabilitated implants (Proclinic S.A.U, Zaragoza, Spain) two years after their prosthetic loading.

MATERIALS AND METHODS

Three clinical centres collaborated for a period of two years after the prosthetic rehabilitation of the implants (Proclinic S.A.U, Zaragoza, Spain), in which marginal bone loss and the possible associated variables were evaluated. The collection form comprised different variables throughout different stages of the implant procedure, from implant insertion to the subsequent prosthetic rehabilitation, over a two-year period. Data of the patients and implant characteristics were studied. Statistical analysis was performed with SPSS for qualitative (univariate logistic regressions, Chi2 test, and Haberman's corrected standardised residuals) and quantitative variables (Kolmogorov-Smirnov test).

RESULTS

The total study sample consisted of 218 implants (Proclinic S.A.U, Zaragoza, Spain). The sample presented a frequency of 99 men (45.4%) and 119 women (54.6%). The mean age of the patients among the reported cases was 58.56 ± 10.12 years. A statistically significant association was found between marginal bone loss 2 years after prosthetic rehabilitation placement and several variables, including age (under 55 years, 0.25 mm ± 0.56; 55-64 years, 0.74 mm ± 0.57; over 65 years, 0.63 mm ± 0.55; p < 0.0001), gender (female, 0.74 mm ± 0.61; male, 0.34 mm ± 0.51; p < 0.0001), bone quality (D1, 0.75 mm ± 0.62; D2, 0.43 mm ± 0.57; D3, 0.65 mm ± 0.60; p < 0.01), implant diameter (up to 4 mm, 0.49 mm ± 0.58; more than 4 mm, 1.21 mm ± 0.30; p < 0.0001), prosthetic connection type (direct to implant, 0.11 mm ± 0.58; transepithelial straight, 0.67 mm ± 0.57; transepithelial angled, 0.33 mm ± 0.25; p < 0001), implant model (internal conical, 0.17 mm ± 0.24; external conical, 0.48 mm ± 0.61; external cylindrical, 1.12 mm ± 0.32; p < 0.0001), prosthetic restoration type (full denture, 0.59 mm ± 0.59; partial denture, 0.50 mm ± 0.85; unitary crown, 0.08 mm ± 0.19; p < 0.05), and insertion torque (>35 N/cm, 0.53 mm ± 0.58; <35 N/cm, 1.04 mm ± 0.63; p < 0.01).

CONCLUSIONS

At 2 years, marginal bone loss following prosthetic rehabilitation was shown to be influenced by multiple factors. Correct implantological planning is of vital importance for successful rehabilitation.

The role of folded fibular flap in patients' reconstruction of mandibular defects: a retrospective clinical study

This study has analyzed 41 patients with mandibular ameloblastoma who underwent a partial mandibulectomy and reconstruction by folding the free fibular flap. In the preoperative and postoperative (6 months and 24 months after surgery), the Quality of Life (QOL) of these patients was assessed by using the University of Washington Quality of Life Questionnaire (UW-QOL) and the medical outcome study short form-36 (SF-36) questionnaires. SPSS 20.0 statistical software was used to conduct statistical analysis on the base data of the two groups of patients. Independent sample t test was conducted for sf-36 and UW-QOL scores at two time points in each group. The SF-36 survey showed that body pain (54.54 ± 8.10), general health (55.27 ± 7.54), and health changes (58.29 ± 9.60) decreased significantly at 6 months after surgery, but the mean score at 24 months after surgery all exceeded the preoperational level. At 24 months after the surgery, the vitality (80.41 ± 3.74), social function (81.61 ± 4.07), emotional role (82.39 ± 4.07), psychological health (81.66 ± 4.37) and total score (704.00 ± 31.53) all returned to the preoperative level, which was statistically significant compared with 6 months after surgery. However, there was no significant difference compared with the preoperative level. The UW-QOL survey showed that chewing (56.68 ± 7.23), speech (54.54 ± 7.7) and taste (62.29 ± 10.15) have significantly changed at 6 months after the surgery, and the difference was statistically significant at 24 months after surgery. Saliva generation decreased slightly (80.76 ± 3.35) at 6 months after surgery, but quickly returned to the preoperative level (81.59 ± 4.06). The total score of the patients almost recovered to the preoperative level at 24 months after surgery. The folded the fibular flap can not only repair the defects of soft tissue and bone tissue, but also restore the height of the alveolar ridge to, avoid the imbalance of crown and root ratio after implantation and reduce the occurrence of peri-implant inflammation, so that a true functional reconstruction can be realized.

Short versus standard implants associated with sinus floor elevation: An umbrella review of meta-analyses of multiple outcomes

STATEMENT OF PROBLEM

Bone loss in the edentulous posterior maxilla complicates dental implant placement. In spite of the evidence available, there is continued uncertainty about the benefit of short implants for different outcomes.

PURPOSE

The purpose of this review was to evaluate the existing evidence for short and standard implants in association with sinus floor elevation regarding implant survival, marginal bone loss, and complications by using an umbrella review of the evidence across meta-analysis of interventional studies.

MATERIAL AND METHODS

Medline, Scopus, and Cochrane Library were searched to identify systematic reviews and meta-analyses comparing short implants and standard implants associated with sinus floor elevation. Data extraction and methodological quality (AMSTAR-2) was assessed by 2 authors independently. Outcomes were categorized and tabulated to assess effectiveness. Qualitative data were analyzed using thematic synthesis. The certainty of the evidence was evaluated with the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach.

RESULTS

From 2011 studies, 7 systematic reviews (66 studies) were included as per the eligibility criteria. There was no statistically significant difference between groups for implant survival (risk ratio=1.08; P=.79), and the qualitative analysis did not show differences for prosthetic outcomes. Standard implants were associated with fewer prosthetic complications in the quantitative analysis (risk ratio=3.27; P<.01), but no difference was found between the treatments in the qualitative analysis. Short implants showed reduced marginal bone loss (0.98 ±0.12 mm; mean difference=-0.22; P<.01) and better biologic outcomes (risk ratio=0.16; P<.01). Patient satisfaction was similar for both groups, whereas costs and time for the procedure favored short implants. The quality of the evidence was graded as "critically low" (57.1% of the reviews) and "low." There was a high certainty of evidence for implant survival, whereas marginal bone loss and complications had moderate certainty.

CONCLUSIONS

Short implants had a better or equal performance compared with standard implants for all outcomes assessed. However, assumptions were based on reviews with low or critically low quality of the evidence, suggesting the development of high-quality systematic reviews in this field.

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.

Peri-Implant Bone Loss Measurement Using a Region-Based Convolutional Neural Network on Dental Periapical Radiographs

Determining the peri-implant marginal bone level on radiographs is challenging because the boundaries of the bones around implants are often unclear or the heights of the buccal and lingual bone levels are different. Therefore, a deep convolutional neural network (CNN) was evaluated for detecting the marginal bone level, top, and apex of implants on dental periapical radiographs. An automated assistant system was proposed for calculating the bone loss percentage and classifying the bone resorption severity. A modified region-based CNN (R-CNN) was trained using transfer learning based on Microsoft Common Objects in Context dataset. Overall, 708 periapical radiographic images were divided into training (n = 508), validation (n = 100), and test (n = 100) datasets. The training dataset was randomly enriched by data augmentation. For evaluation, average precision, average recall, and mean object keypoint similarity (OKS) were calculated, and the mean OKS values of the model and a dental clinician were compared. Using detected keypoints, radiographic bone loss was measured and classified. No statistically significant difference was found between the modified R-CNN model and dental clinician for detecting landmarks around dental implants. The modified R-CNN model can be utilized to measure the radiographic peri-implant bone loss ratio to assess the severity of peri-implantitis.

Short (6 mm) and Regular Dental Implants in the Posterior Maxilla-7-Years Follow-up Study

Short 6 mm dental implants are considered as an alternative to the maxillary sinus elevation and bone augmentation procedure where there is a reduced alveolar ridge height. The aim of this study was to compare the implant survival rate between short dental implants (6 mm) and regular length implants (11-13 mm) when placed in combination with bone grafting and loaded with a single non splinted crown, seven years after placing the implant. It was conducted as a controlled clinical study of 30 patients with partial edentulism in the posterior maxilla. The protocol included radiological and clinical evaluation of the C/I ratio (length of the superstructure divided by the length of the implant crestal part), marginal bone level (MBL), ultrasonography measurement of soft tissue surrounding implant (STT), patient-reported outcomes, and biological and technical complications. A total number of 28 implants (93%) remained integrated during follow-up period. MBL of 0.50 and 0.52 mm was observed for short implants and regular implants, respectively. MBL was checked for correlation with STT, and a negative correlation was found between MBL: STT. Our study has demonstrated a significantly lower implant survival rate for short implants compared to regular implants (87% compared to 100%). Despite the loss of several implants, good clinical results were achieved in the remaining implants in both groups. It is, therefore, worth considering short implants as an alternative to regular implants with a sinus lift surgery.

An evaluation of peri-implant marginal bone loss according to implant type, surgical technique and prosthetic rehabilitation: a retrospective multicentre and cross-sectional cohort study

To evaluate implant loss (IL) and marginal bone loss (MBL); follow-up period of up to 10 years after prosthetic loading. Retrospective multi-centre cross-sectional cohort study. Double analysis: (1) all the implants (n = 456) were analysed; (2) to allow for possible cluster error, one implant per patient (n = 143) was selected randomly. Statistical analysis: Spearman's correlation coefficient; Kruskal-Wallis (post-hoc U-Mann-Whitney); Chi-square (post-hoc Haberman). (1) Analysing all the implants (456): IL was observed in patients with past periodontitis (6 vs. 2.2%, p < 0.05), short implants (12 vs. 2.8%, p < 0.001) and when using regenerative surgery (11.3 vs. 2.9%, p < 0.001); greater MBL was observed among smokers (0.39 ± 0.52 vs. 0.2 ± 0.29, p < 0.01), maxillary implants (0.28 ± 0.37 vs. 0.1 ± 0.17, p < 0.0001), anterior region implants (0.32 ± 0.36 vs. 0.21 ± 0.33, p < 0.001), external connection implants (0.2 ± 0.29 vs. 0.63 ± 0.59, p < 0.0001), and 2-3 years after loading (p < 0.0001). (2) analysing the cluster (143): IL was observed in smokers (18.8 vs. 3.5%, p < 0.05), splinted fixed crowns (12.9%, p < 0.01), short implants (22.2 vs. 4.0%, p < 0.01) and when using regenerative surgery (19.2 vs. 3.4%, p < 0.01); greater MBL was observed in maxillary implants (0.25 ± 0.35 vs. 0.11 ± 0.18, p < 0.05), in the anterior region (p < 0.05), in the first 3 years (p < 0.01), in external connection implants (0.72 ± 0.71 vs. 0.19 ± 0.26, p < 0.01) and in short implants (0.38 ± 0.31 vs. 0.2 ± 0.32, p < 0.05). There is greater risk in smokers, patients with past periodontal disease, external connection implants, the use of short implants and when regenerative techniques are used. To prevent MBL and IL, implantologists should be very meticulous in indicating implants in patients affected by these host factors.

Clinical Behavior of Short Dental Implants: Systematic Review and Meta-Analysis

Short implants are an increasingly common alternative to other surgical techniques in areas where bone availability is reduced. Despite the advantages they offer, a variety of biological repercussions have been described in the literature that can even lead to the loss of these. The aim of this systematic review and meta-analysis was to analyze the impact of the use of short implants on their survival and on peri-implant bone loss, evaluating the influence that length, diameter, and crown-to-implant ratio (C/I) have on these parameters. This systematic review was based on guidelines proposed by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). An electronic search was conducted using terms related to the use of short implants in partially or totally edentulous patients. A total of five databases were consulted in the literature search: PubMed, Embase, Cochrane, Scopus, and Web of Science. After eliminating the duplicate articles and assessing which ones met the inclusion criteria, 15 articles were included for the qualitative analysis and 14 for the quantitative study. Through meta-analysis, the percentage of implant loss and peri-implant bone loss was estimated. Relating these parameters to length, diameter, and C/I ratio, no significant differences have been found for implant loss (values of p = 0.06, 0.10, and 0.9, respectively for length, diameter, and C/I ratio), nor for peri-implant bone loss (values of p = 0.71, 0.72, and 0.36, respectively for length, diameter, and C/I ratio). In conclusion, the use of short implants does not seem to have a significant influence on marginal bone loss or the survival rate of implants.

CT-based dentulous mandibular alveolar ridge measurements as predictors of crown-to-implant ratio for short and extra short dental implants

The purpose was to predict the crown-to-implant ratio variation in the edentulous posterior mandibles rehabilitated with short dental implants. Hence, vertical and horizontal dimensions of dentulous posterior mandibles in a sample of 18- to 25-year-olds were measured, and correlations of these dimensions with sex and site were investigated. Mandibular computed tomography scans from 100 subjects were considered. Vertical and horizontal bone and tooth measurements were taken at the sites of the second premolar (PM), and the mesial and distal roots of the first and second molars (M1m, M1d, M2m and M2d, respectively). A hypothetical crown-to-implant ratio (C/I R) was calculated assuming the insertion of short and extra short implants (5, 6 or 7 mm), at 1.5 mm from the inferior alveolar canal, maintaining the position of the existing occlusal plane. All vertical bone dimensions decreased from the PM to the M2d. Width measurements increased from the mesial (PM) to the distal sites (M1m, M1d, M2m and M2d). Males had significantly greater vertical and horizontal measurements than females at all sites. The mean C/I R was higher than 2 for all sizes of implant. The C/I R was lower for the second molar than for the second premolar, while it was similar for the first molar and the second premolar. Males had a higher C/I R than females. Computed tomography can be used to study the anatomical features of alveolar bone, and to predict some clinical aspects of prosthetic rehabilitation with implants, such as the crown-to-implant ratio in conditions of serious bone atrophy.

Annual review of selected scientific literature: A report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

This comprehensive review of the 2018 dental literature is provided to inform busy dentists about progress in the profession. Developed by the Committee on Scientific Investigation of the American Academy of Restorative Dentistry, each author brings discipline-specific expertise to one of the 8 sections of the report including (1) prosthodontics; (2) periodontics, alveolar bone, and peri-implant tissues; (3) implant dentistry; (4) dental materials and therapeutics; (5) occlusion and temporomandibular disorders; (6) sleep-related breathing disorders; (7) oral medicine and oral and maxillofacial surgery; and (8) dental caries and cariology. The report targets important information that will likely influence day-to-day treatment decisions. Each review is not intended to stand alone but to update interested readers so that they may visit source materials if greater detail is desired. As the profession continues its march toward evidence-based clinical decision-making, an already voluminous library of potentially valuable dental literature continues to grow. It is the intention of this review and its authors to provide assistance in navigating the extensive dental literature published in 2018. It is our hope that readers find this work useful in the clinical management of patients moving forward.