Evaluation Of The Clinical Effectiveness Of The Conometric Concept - A Systematic Review

Introduction

Edentulism is the condition of being toothless to at least some degree. Loss of some teeth is called partial edentulism, whereas loss of all teeth is called complete edentulism.Edentulism can lead directly to impairment, functional limitation, physical, psychological, and social disability, and handicap [24, 16, 26, 29, 2]. The treatment options available are complete dentures, removable partial dentures, fixed partial dentures and implant supported prosthesis [9]. The treatment given to the patient depends on physiological, anatomical, and socio-economic status of the patient. The most common treatment option for long span edentulous areas are removable appliances. However, the degree of patient satisfaction tends to decrease during the first couple of years after insertion [30, 4, 19, 23].

Endosseous implants are commonly used to achieve dental prosthesis support and retention in both partially and completely edentulous patients [21, 3]. Modern implantology marks a great treatment innovation since edentulism is a frequent situation, especially in elderly people. Different types of implant-supported prostheses are available, depending on the number and position of implants, prosthetic design and material and type of retainer. [20, 25, 15, 14].

Treatment options include removable or fixed implant-supported prosthesis. Removable implant-retained prosthesis consists in a removable prosthesis anchored to implants by different kinds of retainers [25]. On the other side, a fully stable dentition is achieved through implant-supported fixed dental prostheses only [27]. For this kind of restoration, two types of connections between implants and prostheses have been mainly used. They are screw-retained and cement retained connections. Both systems are good and predictable, but they could typically show some drawbacks. Screw-retained prosthesis offers tight retention, but shows more mechanical complications, such as screw loosening and fractures. Cement-retained prosthesis allow better aesthetics, but they showed more biological complications, such as soft tissue inflammation around the implant neck, residual cement, unretained prosthesis, dislodgement of prosthesis among a few [28, 31].

In 2018 Degidi et al, proposed using a cone-in-cone Morse taper connection between abutments and crowns to retain implantsupported de?nitive ?xed dental prostheses. This Prosthetic approach, named the �Conometric Concept� was used to retain both lithium disilicate and zirconia restorations [1, 11, 12].

The conometric concept consists of a cone-in-cone connection between an abutment and the respective coping to retain an implant supported restoration without either screws or cement. It has a tapered coping that is fixed to the prosthesis and inserted in a tapered abutment. The fit between abutment and the restoration is achieved with prefabricated components. The conical coupling abutments use the friction between the abutment and the titanium coping to retain a prosthesis without the use of cement. When an insertion force is applied, as the system is activated, the cervical margin of the coping is slightly deformed by wedge effects, causing elastic stress fields within both the coping and the abutment.

Such stresses will partially remain even if the insertion force is removed [10, 11, 6].

The use of cone-in-cone abutments to support definitive has given excellent short term prosthetic results [7]. Hence, the aim of this systematic review is to evaluate the clinical effectiveness of the conometric concept.

Aim

The aim of the current review is to evaluate the effectiveness and clinical efficiency of the conometric concept.

Structured Question

In cases requiring implants, is there a significant difference in effectiveness of the conometric abutment in comparison to conventional abutments?

Pico Analysis

Population: Healthy partially edentulous individuals with sufficient bone support for placement of implants.

Intervention: Implant crowns with conometric abutments.

Comparison: Implant crowns with conventional abutments.

Outcome Measures:

� Cumulative survival rate of the prosthesis- years
� Esthetics- Questionnaire
� Passive fit- Path of displacement(mm)
� Fracture resistance- Fatigue testing(N/cm)
� Crestal bone loss around the supporting implants
� Patient satisfaction- Questionnaire
� Vertical Fit of the framework- IOPAR
� Biofilm adherence to the crown- OHI index

Data Collection And Analysis

The data was collected from the studies that were included based on the author's name, publication year, study type, subjects, interventions, treatment time, method of measurements and outcomes assessed.

Searched Databases

The electronic databases that were included areNational Library of Medicine (PubMed), Google Scholar and the Cochrane database of systematic reviews. No limitation regarding publication date was included in the search. The electronic search was supplement by a manual search in the Journal of Prosthetic Dentistry, Journal of Prosthodontics, Clinical and Oral Implants related Research and the Clinical Oral Implant Journal.

Search Protocol

The search methodology employed was a combination of MeSH terms and Keywords.The keywords were categorized as Population, Intervention, Comparison, Outcome measures. Keywords within each group were combined using the Boolean operator(OR). The Boolean operator (AND) was used to combine all four categories together to attain the search results.

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Eligibility Criteria

The title and abstract of the entries from the initial electronic database searches were read. Full text versions of the studies that could be potentially included in this review were read and a final selection was done according to the inclusion and exclusion criteria.

Inclusion Criteria

? Articles reporting cone in cone concept or conometric concept.
? Articles comparing conometric concept with other systems.
? Randomized control studies, Prospective clinical trials and In vitro studies.

Exclusion Criteria

? Review articles
? Case reports and series
? Animal studies

Results

The search strategy returned 22 articles from PubMed, 7 articles from Google scholar and 2 articles were handpicked. 18 clinical trials were included from the PubMed search of which 13 were excluded based on title and abstract and a total of 5 articles were selected. Of the 7 articles obtained from Google scholar, 5 were eliminated based on heading and abstract, and a total of 2 articles were selected. The total number of studies which were selected from the database were 9, of which 2 were eliminated as it did not meet the inclusion criteria and/or outcome measures and 7 articles were included based on core data. These 7 articles were reviewed and consolidated as given in the table below.

Data Extraction

The data of the selected studies were extracted using standardized abstraction tables. Information extracted from each study included the following in one table as general characteristics of the study.The outcome variables of the extracted data from the studies were interpreted in detail.The level of evidence for each included article was also tabulatedaccording to the Oxford Centre for Evidence-Based Medicine (March2009).

Analysis

Out of the 7 included studies, 8 outcome measures have been identified. However, a meta-analysis was not done as none of the included studies were randomized control studies. 2 studies have analyzed cumulative survival rate. Cumulative survival rate was in a range of 97.4%-100%[10,7]. 4 studies have analyzed mean probing depth. The range was 1.3mm-2mm [13, 11, 5]. One study analyzed mean crestal bone boss. They gave a result of 0.4mm [7]. 4 studies analysed the rate of framework fracture. The results were in a range of 0%-8.7%. 4 studies analysed the esthetic satisfaction and overall patient satisfaction and the results were in the range of 82%-91.8% and 79%-91% respectively [10, 7]. 4 studies have analyzed mean probing depth. The range was 1.3mm-2mm [13, 11, 5].

Discussion

Dental implantology is a reliable technique for treatment of partially and completely edentulous patients. The achievement of stable dentition is ensured by implant-supported fixed or removable dental prostheses. Titanium dental implants extended the treatment alternatives for edentulous patients using either implant-retained ?xed or removable prostheses([8, 25]; �Implant-Supported Rehabilitation of Completely and Partially Edentulous Patients�, 2017).

A debate still exists within dentistry over the optimal connection between a fixed restoration and an implant. Screw retained restorations have less complications overall, but the failure rate of cement retained restorations was not influenced by cement choice. The presence of excess cement in cement retained restorations has increased association with incidence of peri-implant disease and bone loss. Conversely, the screw retained prosthesis is cost effective, as it facilitates prosthesis retrieval without the risk of damaging the prosthesis [18, 28, 32, 17].

The conometric concept involves the use of cone-in-cone morse tapered connection between the abutment and the prosthesis to retain an implant supported fixed dental prosthesis. The reported advantages of this concept are absence of cement and screws, simple maintenance, favorable emergence profile, and cost effectiveness [12].

The conical coupling abutments use friction between the abutment and the coping to retain the prosthesis without the use of cement. When an insertion force is applied, the system is activated. The cervical margin of the coping is slightly deformed by wedge effect, causing elastic stress fields within both the coping and the abutment. This stress will partially remain even if the insertion force is removed. This residual stress provides the retentive capability of the system [10-12].

According to a2 year prospective study by Degidi et al showed that Cone in cone approach was successful in 2 year followup with a mean probing depth of 2�0.90, framework fracture of 8.7% and patient satisfaction of 79% [11].

In a 3 year prospective study done by Degidi et al, Titanium reinforced partial restorations with conic coupling retention supported by immediate implants provide a successful, cost effective treatment modality with a mean probing depth of 1.3�0.20, framework fracture of 0% and patient satisfaction of 91% [13].

Another 3 year prospective study by Degidi et al stated that Conical abutment prostheses coupling connections were successful within the 3-year timeframe of this study with a mean probing depth of 2 � 0.82, framework fracture of 3% and patient satisfaction of 90% [13].

A 5 year prospective study done by the same author stated that Cone in cone connections was successful in 5 year followup with a cumulative survival rate of 97.4%, framework fracture of 1.4% and patient satisfaction of 88% [10].

Bressan et al did a 2-year prospective study and noted that time and cost of treatment was reduced with conical crown concept. He noted a cumulative survival rate of 100%, mean crestal bone loss of -0.4�0.2 and a patient satisfaction of 98% [7].

Another in-vitro study done by Bressan et al showed that there was minimal bacterial invasion in both internal conical and morse taper internal connection [5]. One of the major limitations in this review is the lack of randomised control trials comparing conometric coupling with other abutment prosthetic connections. Further studies are needed in this area to determine the effectiveness of conometric coupling as a routine retention modality in commercial dental implants.