Journal of Dental Implants

REVIEW ARTICLE
Year
: 2021  |  Volume : 11  |  Issue : 1  |  Page : 4--12

Comparative evaluation of effect of three different crown to implant ratio on marginal bone loss: A systematic review


Tejhas Gobiind Agarwaal, Amit K Jagtap, Nilesh S Bulbule, Vaibhav Popat Jathar 
 Department of Prosthodontics, Dr. D Y Patil Vidyapeeth, Pune, Maharashtra, India

Correspondence Address:
Dr. Tejhas Gobiind Agarwaal
Plot No. 81, Sector 25, Next To Cosmos Bank, Pradhikaran, Nigdi, Maharashtra
India

Abstract

Partial rehabilitation in the posterior edentulous region remains a challenge due to the anatomical condition present in the area. Excessive pneumatization of the maxillary sinus and accentuated bone crest resorption following teeth extraction cause bone atrophy and may lead to impossibility of inserting standard implants. Constant efforts are aiming at the reduction of the invasiveness of implant surgery. This has led to increase the use of implants with shorter length in the posterior maxilla and mandible region which reduces the need for additional surgical procedure causing less morbidity of the site and faster healing of the region. Does crown to implant ratio has an effect on the marginal bone loss (MBL) around implants in the posterior maxillary and mandibular region? A systematic search was conducted on two databases for the studies published from January 1, 2006, to July 31, 2018. Cross-references were checked. Hand searching was done in the library. Studies were included if they were done among healthy, nonhospitalized individual, and compared for the crown-to-implant ratio and MBL. A total of 143 articles were found through search. Thirteen articles remained after removing duplicates, reading the full text and reviewing abstracts. Thirteen articles were included for the data extraction. Crown-to-implant ratio has no role in the crestal bone loss, but other factors need to be evaluated for its role along with crown-to-implant ratio that can cause the MBL.



How to cite this article:
Agarwaal TG, Jagtap AK, Bulbule NS, Jathar VP. Comparative evaluation of effect of three different crown to implant ratio on marginal bone loss: A systematic review.J Dent Implant 2021;11:4-12


How to cite this URL:
Agarwaal TG, Jagtap AK, Bulbule NS, Jathar VP. Comparative evaluation of effect of three different crown to implant ratio on marginal bone loss: A systematic review. J Dent Implant [serial online] 2021 [cited 2021 Nov 29 ];11:4-12
Available from: https://www.jdionline.org/text.asp?2021/11/1/4/318075


Full Text

 Introduction



Partial rehabilitation in the posterior edentulous region remains a challenge due to the anatomical condition present in the area. Excessive pneumatization of the maxillary sinus and accentuated bone crest resorption following teeth extraction cause bone atrophy and may lead to difficulty of inserting standard implants.[1] Constant efforts are aiming at the reduction of the invasiveness of implant surgery. This can lead to decreased patient morbidity, shorter surgical treatment time, and a minimized risk of damaging neighboring anatomical structures.[2],[3] The periodontal ligament, whose principal function is to retain a tooth in the alveolar socket, gives the natural dentition a larger range of physiologic mobility than an osseointegrated dental implant. If a force of 0.1N is applied to a tooth with a healthy periodontal ligament, the range of mobility is between 50 and 200 μm, whereas the application of the same force to a dental implant will result in mobility of 10 μm.[4],[5],[6] Such load will increase the stress transmission to the peri-implant bone, which may lead to bone resorption and implant loss. Moreover, they will increase the risk of prosthetic complication such as screw loosening, implant or abutment fracture, chipping of ceramic, and fracture of the prosthesis.[4] In the past, the use of short-length implants was related to lower success rate, with 10 mm considered as the minimum standard length for load distribution throughout the implant body.[1] Implant survival is reported to reach 97.2% after 5 years and 95.2% after 10 years (Blanes et al. 2007, Jung et al. 2012, and Benic et al. 2017). This has led to the use of fewer implants with smaller diameters and shorter implants over the last decade. These types of implants have many objective advantages. They mainly allow for less invasive interventions. They can thus minimize the risk of harming neighboring anatomic structures, accelerate preparation of the implant bed, and demand less need for remaining vertical bone height (Pistilli et al. 2013 and Thoma et al. 2015).[7],[8],[9],[10],[11] Further investigation has also demonstrated that the occlusal forces were concentrated on the cortical aspect of the bone independent of the length.[7] The benefits of using shorter implant include no need for advanced bone grafting and consequently lower risk of complications and expenses which largely increase patient's acceptance.[12],[13] Short implants have shown similar survival rates as standard (≥10 mm) implants regardless of their length and width.[14] However, a recent meta-analysis demonstrated that even with a similar long-term survival rate, shorter implants failed 2.5 years earlier than the standard ones.[15]

Nevertheless, the use of short dental implants is not exempt of clinical challenging situations. Increased crown-implant (C/I) ratio is usually found when less than 10 mm implants are placed compared to the normal crown-root (C/R) ratio associated with healthy dentition. Theoretically, C/R ratio is the relationship between the length of the crown and the length of the root, taking the cementoenamel junction as the fixed point separating both. On the other hand, the clinical C/R ratio is the physical relationship between the portions of the tooth located above the alveolar bone compared to the portion embedded into the alveolar bone, as seen radio graphically.[12],[16] The importance of the C/I ratio relies on the theory that unfavorable occlusal forces, including nonaxial and overload, represent one possible explanation for biological and technical complications.[12],[17],[18] Literature exploring the influence of C/I ratio on success rate and implant marginal bone loss (MBL) is heterogeneous, with a limited number of studies reporting great variability in their findings. While some studies failed to show a correlation between C/I ratio and MBL, some others have reported higher amount of MBL with increased C/I ratios. Surprisingly, some studies have even reported an inverse relationship between C/I ratio and MBL, finding better results with higher ratios.[12],[19],[20],[21],[22]

Hence, the aim of this systematic review is to evaluate the effect and influence of different crown to implant ratio on MBL.

 Material And Methods



Eligibility criteria

Inclusion criteria

All the studies reporting randomized control trials and observational studies for crestal bone loss and crown to implant ratioAll the studies conducted in humansAll the studies evaluating MBL as an outcome parameterAll studies published in between the years 2006 and 2018All the papers written in the English language only.

Exclusion criteria

Case reportsLetter to the editorNarrative reviews.

Information sources

Literature search strategy was developed using key words – crown to implant ratio, MBL, vertical cantilever, crown height, and peri-implant bone loss crestal bone loss.

Data were searched from PubMed and Google scholar from January 1, 2006, to October 31, 2018. Cross references were checked from relevant articles. Hand searching was done for articles when the full text of articles was not available through electronic database.

Search

The comprehensive data search was done on PubMed and Google scholar. While carrying out the search filters were put for the dates of publication from January 1, 2006, to December 31, 2018. Language restriction was put to the English language only. No filters for filters for full text and for study design were kept.

Five search strategies [Table 1] and [Table 2] were formed using the primary and secondary keywords for PubMed database:

Crown to implant ratio and marginal bone lossCrown to implant ratio and crestal bone lossCrown to implant ratio and peri-implant bone lossMarginal bone loss and vertical cantileverMarginal bone loss and crown height.{Table 1}{Table 2}

Study selection process

One review author (TA) independently screened the titles and abstracts obtained by search strategy and included them if they met the inclusion criteria. Later full texts of all the included studies were obtained. After obtaining the full texts of the articles, they were screened by reading the whole article, and then, it was decided if they met the inclusion criteria. Whenever there was uncertainty regarding any study to be eligible for inclusion, the problem was resolved by discussing it with the second author (DK). For the inclusion of articles, the quality assessment of each article was done by one author (TA) independently, and later, it was crosschecked by two other authors (DK), and finally, the search yielded 13 studies to be included in both systematic reviews. All the excluded studies were recorded with reason for the exclusion for each study. None of the authors were blinded to the journal titles, study authors, or the institutions where the studies were conducted.

Data collection process

A standardized data extraction form was prepared in Microsoft Excel with the help of an expert. Initially, 3–4 entries were made in the Excel [Table 3], and it was reviewed by an expert. Any disagreement between the authors was resolved by discussion. The following criteria were predetermined for extracting the data:{Table 3}

Data items

Data items included for the data extraction were as follows:

Study id: Number given to the study for identificationAuthor's name: Name of the authorYear of publication: Year in which the study was publishedType of study: Study designIntervention and comparison baseline scores: Baseline values for different parameters such as implant system implant site, measurement on recall, crown to implant ratio and crestal bone lossPostintervention and comparison scores: Values for different parameters postprocedureRemarks: Results of the individual study.

 Results



Study selection process

One hundred and forty-three records were identified through the data search using search strategy in PubMed. Through Google Scholar, 0 articles were selected based on titles. Total article number arrived to be 143. Second step was screening through the titles and after screening 102 articles were excluded because they were not related to the objectives of the systematic review. Some articles mentioned study done on animals, whereas some mentioned various techniques for placing short implants or ridge augmentation. Forty-one articles which remained were screened for duplicates manually. Out of 41 articles, 10 articles were found to be duplicate, and hence, remaining 31 articles were screened through abstracts as a next step. Finally, 21 were articles were screened for full text. At the end, 13 studies remained which underwent qualitative synthesis. Articles yielded 13 estimates which were entered in the excel sheet.

Included studies

Two of the included studies (I; III) were randomized control trail. Five studies (II, IV, V, VI, and VII) were retrospective cohort studies. One (VIII) was a clinical study while one (IX) was literature review and one (X) was a prospective study. All the studies were carried out on the posterior partially edentulous maxillary or mandibular site. All the studies included individuals with no systemic illness, but some had a habit of smoking. Implant system used was endoossous design with no platform switch performed.

Characteristics of intervention and comparison group

All the studies there was no comparison between all the three intervention groups, the studies compared only two groups out of the three taken for intervention. Only one study (V) compared the crown-to-implant ratio clinically, while one (VIII) compared through cone-beam computed tomography, rest all the studies compared the crown-to-implant ratio through radiograph. Out of the 10 studies, only three did not mention the implant system used. The system used in the studies included Straumann (I, III); Denstply (VIII); BTI (VI); Astra (V) and nobel biocare (IX).

Duration of study

Wide variation was noted in the duration of the study period. Two studies (IV, IX) were of 1 year follow-up, three studies (II, III, and VIII) were followed up for 3 years, two studies (I, VII) were followed up for 5 years, one study (V) was followed up for 6 years, and one study (VI) was followed up for 10 years.

Between group's comparison remarks

Of all the 10 studies that provided statistical inference, 9 did not show any statistical difference between the crown-to-implant ratio and the MBL around implant placed in posterior partially edentulous maxillary and mandibular arches.

 Discussion



The aim of the systematic review was to compare three different crown-to-implant ratio, i.e., <1; =1 and > 1 and its effect on the MBL. As the crown-to-implant ratio increased, the vertical cantilever increased thus leading to increased forces on the implant restoration with a smaller length of implant for its distribution. Thirteen articles were reviewed in this systematic review which compared the various crown-to-implant ratio used for the restoration of edentulous posterior maxilla and mandible with single crowns or splinted prosthesis. Along with the MBL, long-term stability and peri-implant infection and various other factors were checked. On reviewing all the articles, it was confirmed that the crown-to-implant ratio had no correlation with the MBL. In a study comparing extra short implant, crestal bone loss and the effect of crown height space and offset placement of the forces it was found that the antagonist dentition, and the crown height space had a significant co relation in MBL when the crown-to-implant (C/I) ratio was higher than 1. Furthermore, the implant diameter was considered an important factor in reducing the MBL.

Sun et al. compared C/I ratio and anatomic crown length in single crowns and found that the anatomic crown length and the soft tissue health to be more significant in MBL than the C/I ratio.[23] In a retrospective study of short and extra-short implants placed in the posterior regions by Aniuta et al., there no correlation of C/I ratio and MBL, but it was found that the use of cantilevers, which represents a challenging biomechanical situation, is related with an increased MBL during the 1st year postloading.[24]

Lee et al. compared the influence of crown-to-implant ratio on peri-implant MBL in the posterior region and found that that implants with a higher C/I ratio showed statistically significantly less peri-implant MBL than implants with a lower C/I ratio.[22] The author also suggested that the C/I ratio and implant system were the factors that should be considered as affecting MBL around the implant in the posterior region more than implant diameter, prosthesis type, implant location, or GBR procedure, especially in the maxilla. Furthermore, the implant location had an influence on peri-implant MBL related to the C/I ratio. Implants with a lower C/I ratio had more peri-implant MBL than implants with a higher C/I ratio in the maxilla, while the C/I ratio had no influence on peri-implant MBL in the mandible. Bone density is directly related to the elastic modulus of bone. Due to its lower elastic modulus, the cancellous bone exhibited a lower stress concentration and less variation than the cortical bone.[22] In a systematic review by Blanes is was seen that that implant supported prostheses with higher C/I ratios experienced less crestal bone loss than those with lower C/I ratios. These observations may be explained by the stimulatory nature of bone stress. It has been suggested that the stress concentration at the bone crest induced by the masticatory forces may stimulate bone formation around some fixtures. This biological response is further supported by the “stress-shielding” effect described in previous publications.[17]

Hingsammer et al. checked the influence of crown-to-implant ratio on marginal bone levels around splinted short dental implants and found that Crown to implant ratio (C/I) ratio has a high impact on early peri-implant bone loss as an increase of Crown implant ratio (CIR) is associated with higher Marginal bone loss (MBL). It was also found that there was a positive correlation between MBL and the proportion of cortical bone exists. Significantly, less resorption around implants inserted in sites with a higher proportion of cancellous bone. In smokers, a significant higher MBL compared to nonsmokers was recorded. This supports the findings of several studies that prove the association between smoking and MBL. It was concluded that a CIR of 1.7 can be considered as a benchmark for clinicians and to avoid increased early MBL it is suggested not to be exceeded.[25]

Esfahrood et al. in their literature review on short dental implants in the posterior maxilla concluded that C/I ratio of short implants might increase the risk of biomechanical complication because of overloading non axial loading and can eventually result in crestal bone loss. Increasing the implant number and splinting short implants together or to long implants could increase the survival rate he also stated some risk factors that may increase stress when using short implants (1) increased crown height, (2) high bone density in the region, and (3) higher bite force. Some methods available to decrease stress include (1) minimizing the lateral force on the prosthesis, (2) lack of cantilevers on the prostheses, and (3) splinting multiple implants together.[26]

Tolentino da Rosa de Souza et al. in their systematic review on short implants having similar survival rates compared to standard implants in posterior single crown found no difference in the survival rate between the two groups of implants. The survival rates of the short implants were similar to the standard implants in posterior single crowns, for the 1-year follow-up period. In the qualitative analysis, the short implants presented low MBL, prosthetic failure, and surgical complications, in addition to a good survival rate, being a predictable treatment for single rehabilitation in posterior tooth loss.[27],[28]

Limitations

This review had the following limitations:

As all the databases were not open access, the inclusion of the studies is smallUnpublished data were not included in this reviewNot all the studies provided baseline and end scores so those studies were excluded from the calculation of statistical and clinical significance.

 Conclusion



The review concludes that on the basis of the factors used for assessing clinical significance, showed that although the studies gave statistically significant results, but they did not match clinical significance. Thus, the crown-to-implant ratio has no relation with the MBL around short dental implants. Very few studies with crown-to-implant ratio < 1 had more crestal bone loss than studies which had crown-to-implant ratio greater than 1 on a short-term follow-up. Crown-to-implant ratio equal to 1 had no significant role in crestal bone loss. If the crown to implant ratio was more than 1, also it did not show any MBL on a long-term follow-up. Thus, there was no statistical significance of crown-to-implant ratio and MBL. Although the location of the implant, density of the bone, smoking status, and gender had an important role regarding the MBL around the short dental implant requiring further studies on the same.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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