Research on Cervical Margin Relocation
The Cervical Margin Relocation (CMR) was proposed more than 15 years ago, and in the last decade became more and more popular among dental practitioners [1-2].
CMR is indicated when the gingival margin of a Class II interproximal cavity cannot be isolated with rubber dam alone, in alternative to perform surgical crown lengthening. CMR consists on placing a base of direct resin composite using a metal interproximal matrix to elevate the interproximal underneath indirect bonded restorations. Consequently, margins can be predictably caught by a conventional impression and/or intraoral optical scanning (IOS) . Different papers described clinical procedures of CMR and evaluated in the lab this technique. [4-10]
Location of a subgengival margin can affect the periodontal health and therefore healthy periodontal tissues, defined by a Probing Pocket Depth (PPD) less/equal than 4mm without Bleeding on Probing (BoP).
Unfortunately, no clinical trial evaluating periodontal tissue response on indirect adhesive restorations placed on posterior teeth with CMR are available till now .
Also, the literature reports about the influence of approximal restorations extension on the development of secondary caries, showing that restorations ending below the CEJ showed significantly increased risk for failure [12-13].
The primary aim of this clinical trial was to evaluate BoP on single adhesive indirect restorations made on posterior teeth with one interproximal margin relocated cervically; and secondary, to analyse the correlation between depth of the interproximal margins and BoP. The null hypothesis tested was that there is no statistically significant difference between margins with or without CMR regarding periodontal tissue inflammation (BoP).
Materials and methods
A consecutive sample of 35 restorations in 35 patients in need of one single partial crown (onlay) on posterior teeth was placed between January and April 2016. A partial restoration was performed from the pool of patients accessing the Department of Prosthodontics and Dental Materials of the University of Siena, Italy. All of them had an old restoration and some carious tissue to be replaced (Fig. 1a-1e).
Patients written consent to the trial was obtained after having provided a complete explanation of the aim of the study. Ethical approval was achieved beforehand by the University of Siena, Italy.
Caries cleaning of the affected area was performed after placing a first matrix band to retract and simultaneously protect the soft tissue, the curvature of the metal matrix was properly adapted to the curvature of the tooth to achieve the best cervical fit was possible . In one proximal box CMR procedure was performed using G-Premio Bond, simultaneously used to perform hybridization of entire exposed dentin, and universal flow resin composite applied in two or three thin layers depending the depth and size of the cavity (GC Co. Tokyo, Japan) (Figs. 2a-2d). After final cavity’s preparation, an impression was taken (Ex’lance, GC Co., Tokyo, Japan)(Fig. 2e) and sent to the laboratory in order to make the restoration using lithium disilicate (LS2) press material (LiSi Press, GC Co. Tokyo, Japan) (Fig. 3a). A temporary restoration was made with heat-polymerizing polymethylmethacrylate (PMMA) acrylic resin and luted. Patients were instructed to use a 0.2 % chlorhexidine gluconate solution for 7 days until they could perform regular oral hygiene and returned 2 weeks later for the impression procedures, giving enough time for soft tissue adaptation and maturation after teeth preparation. The restorations were made in the laboratory, then tried-in, and margins were examined and carefully verified for fit and extension. Rubber dam was always placed to isolate the abutment (Fig. 3b). The restorations were luted following manufacturer’s instructions using proprietary’s cement (Link Force, GC Co., Tokyo, Japan) after being sandblasted, etched with fluoridric acid at 5 % for 60 seconds and a coat of multi primer being applied and left to evaporate for 1 minute.
Cement excess was carefully removed, and occlusion was slightly adjusted when needed. Intra-sulcular margin position was verified, and oral hygiene instructions were given to the patients.
The restorations were placed in the time period between January 2016 and April 2016 and examined for (BoP) at baseline (cementation of the restorations), and after 12 months by two calibrated operators (Figs. 4a-4b and video).
At baseline, the restorative margin position in relation to the gingival margin was recorded quantifying by probing in mm , and the linear distance from the bone crest was calculated in mm by intraoral x-ray. In addition, intraoral x-rays were made at the 12-month recall as well.
All clinical procedures were made using ~ 3.5/4.5 magnification.
The CMR was associated with statistically significant increased scores for BoP. Gingival Index (GI) and Plaque Index (PI) were not statistically different between the groups. At the end of the experimental period, 53% and 31.5% of sites (Group 1 and 2 respectively) were positive to BoP: this difference was statistically significant (p=0.10). The linear distance between the bone crest and the restorative margin, assessed by a radiographic analysis, was 2 mm in 13 out of 19 experimental sites of group 1 and 6 out of 11 of group 2.
Old indirect restoration made with porcelain fused to metal in need to be replaced because secondary decay.
Removal of the old restoration
X-ray of the cavity after the old restoration was removed.
The cavity after decay removal.
The cavity after decay removal, lateral view.
The application of a metal matrix protected the soft tissue, although after removing the matrix the tissue is slightly bleeding. Under rubber dam and after adaptating metal matrix and wedge to the emergence profile of the tooth, the procedure of immediate dentin sealing and cervical margin relocation are perfomed: the first layer of flowable resin composite is already light-cured.
Complete build-up of the cavity.
Immediately after the build up, still under rubber dam, the final preparation was made.
The final preparation.
The traditional impression.
The final LiSi Press partial crown
The crown after being luted under rubber dam.
Recall after 12 months; clinical view.
Recall after 12 months; radiographic views.
Within the limitations of this study, higher incidence of BoP can be expected around CMR margins and in coincidence with margins. CMR of margins is a sensitive-technique, especially when deep subgingival margin is selected and bonding restorative procedures are performed below the cementum enamel margins.