Marginal Gap Evaluation in Non-Cemented Crown Restorations

Research Article

J Dent & Oral Disord. 2020; 6(4): 1136.

Marginal Gap Evaluation in Non-Cemented Crown Restorations

Campos RE¹* and Maristela C²

¹Rua Coronel Constantino 21- Ap 603 - Tabajaras - Uberlandia – MG, Brazil

²Rua Bernardo Cupertino, 1173 - B. Daniel Fonseca - Uberlândia-MG, Brazil

*Corresponding author: Roberto Elias Campos, Rua Coronel Constantino 21- Ap 603 - Tabajaras - Uberlandia – MG, Brazil

Received: April 30, 2020; Accepted: May 19, 2020; Published: May 26, 2020


The vertical marginal gap should be regarded as the most critical in crown margin evaluation. The purpose of this study was to compare the marginal gap of crowns made from different materials and technique. Comparisons were made among six groups (n=8). Conventional metal ceramic (MCc) crowns; modified metal ceramic (MCm) crowns; lithium disilicate reinforced ceramic crowns (CDis); leucite reinforced ceramic crowns (CLeu); leucite fluorideapatite reinforced ceramic crowns (CLeuF); polymer crowns (CCer). The crowns from 48 bovine teeth were cut and 15 mm long regular and similar roots were obtained, endodontically treated and reconstructed with a metal post plus composite resin core. Impression from each specimen was made using a polyether and all restorations had the final form of a premolar with axial thickness of approximately 1 mm in the cervical and middle third and 2 mm in the occlusal surface. Each crown was fitted in its preparation and the marginal gap was measured under stereomicroscope examination (×40). A total of 16 measures were obtained from each tooth (4 in each face). Data were submitted to 1-way ANOVA statistical analysis and significant differences among the groups were not found. In conclusion, the selection of the crown restorative system should not be based on the marginal gap only as all systems presented similar results within the 100 μm limit clinically acceptable.

Keywords: Marginal gap; Cement films; Ceramic crowns


Esthetics and resistance to fracture are two of the main determinants of the success of a restoration; the third is marginal adaptation [1]. The vertical marginal gap is the space between the marginal surface of the restoration and the tooth finish line, has the most clinical relevance and should be regarded as the most critical in crown margin evaluation [2]. There is no agreement on definition of marginal gap values, [3] with reported values ranging from 3.7 to 174 μm, [1,2,4-8] nor on a common method of evaluation [3]. The American Dental Association states that the proper fit of a fixed prosthesis ranges from 25 to 40 μm, [9] but it is very difficult to reach such a goal using most of the current manufacturing technology [10]. The marginal gap level of 100 μm was defined as clinically acceptable [11] and the 120 μm was considered the maximum tolerable marginal opening [12]. The ideal gap should be small enough to prevent ingress of saliva and/or lactic acid, which is the byproduct of bacterial metabolism [13]. Gap margins of poor quality with measures higher than the 0.75 μm diameter of the Streptococcus mutans [14] might lead to cement dissolution, marginal discoloration or staining, microleakage, and secondary caries [15].

The marginal accuracy is significantly influenced by tooth preparation design, material characteristics, fabrication method, gap measuring method, and other factors [1,5,16-22]. The investigation of the marginal fit is so critical that three studies evaluating the same materials and using the same method presented three different results [4,23,24]. Concerning to the marginal fit the quality of tooth preparation and impression steps are clinicians-dependent while the quality of the indirect restoration is technicians-dependent. The fully digital fabrication method may provide better margin fit than the conventional method [2,25,26] as it eliminates most of the steps clinician/technician-dependent [27]. The challenge is to provide clinicians with a technique to asses a gap smaller than 100 μm [28] as the reading accuracy of the marginal gap was shown to be operatordependent and improved with ×4 optical magnification for clinicians [29]. In the clinical situations the marginal fit of restorations is directly evaluated by visual observation using or no an explorer [28,30,31] and through radiographs. A sharp explorer can identify an opening of 36 microns with 95% of the people using it. Dull explorers have difficulty in detecting marginal gaps of this size [32,33]. Higher marginal gaps could contribute to the zinc phosphate cement dissolution, hydrolytic degradation of resin cements or bonding hydrolysis when adhesive cementation is used [15,34-36].

Different crowns restorations obtained from different methods have been used in the search for the ideal material that would combine strength, esthetics and accurate marginal fit. As a functional property, the lower the marginal gap the lower the exposition of the cementing agent to the oral environment. The use of CAD-CAM technology significantly increased in the last decade due to their esthetic, mechanical and biocompatibility properties [2,4,24,37,38] by eliminating or reducing potential procedures for dimensional inaccuracies [20].

Thus, purpose of this study was to compare the marginal gap of crowns made from different materials and technique. The null hypothesis was that there was no difference in the marginal gap among the used materials.

Material and Methods

Comparisons were made among six groups (n=8). Conventional metal ceramic (MCc) crowns with a metal coping and feldspathic ceramic; modified metal ceramic (MCm) crowns, as in the control group, but with aluminum-reinforced ceramic in the buccal cervical area (collarless); ceramic crowns reinforced by lithium disilicate (CDis); ceramic crowns reinforced by leucite (CLeu); ceramic crowns reinforced by leucite fluoride-apatite (CLeuF); polymer crowns (CCer). All materials used were manipulated in accordance with manufacturers’ recommendations. Composition and manufacturer information are listed in Table 1. Out of 200 bovine teeth stored in 0.2% Tymol solution for up to a month, 115 with regular and similar roots were selected. They were sectioned with a double-sided diamond disc (KG Sorensen, Barueri, Brazil) to obtain roots 15-mm long.