Detection of Residual Excess Zinc Oxide–Based Cement With Laser Fluorescence (DIAGNOdent): In Vitro Evaluation

Because of its importance in the development of peri-implant mucositis and peri-implantitis, detection of residual excess cement (REC) is often the focus of studies addressing cement-retained implant-supported restorations.^1,2  Bleeding, swelling, exudation, attachment loss, and, ultimately, implant failure are the principal results of REC-caused peri-implantitis.³  Also, an overexpression of inflammatory cytokines has been observed in the crevicular fluid around the cement-retained implants.⁴  Occasionally, despite the presence of cement remnants, no tissue response develops.⁵  It has been reported that 81% of the implants restored with cement-retained restorations with signs of peri-implant disease had retained excess cement in the subgingival spaces.⁵  Also, peri-implant disease has been diagnosed in 62 of 73 implants (85%) with REC.²  The etiology of peri-implantitis is complex,^6,7  and it is believed that bacteria has a pivotal role in peri-implantitis progression. Residual excess cement is the most common reason for bacterial gathering in the implant-surrounding zone. Factors that affect REC include the amount of used cement, the procedure of cementation, cement viscosity, and the position of margin.^8,9  Detection of REC can be influenced by multiple factors, including the composition of the cement and the amount and site of cement remnant. Conventional methods for REC detection include radiography,¹⁰  dental endoscope,⁵  and the open-flap technique.¹¹  Among these, radiographic evaluation is the only noninvasive method. However, radiographic diagnoses can be affected by exposure settings and differences in evaluation methodologies, which can influence cement radiopacity.¹² 

Cementation of implant restorations can be done either with permanent or temporary cement, such as a zinc oxide (ZnO)–type cement. Provisional cement enables easy removal of the prosthesis components, and any excess can be easily removed after cementation. Provisional cements typically provide sufficient retention for implant-supported restoration.^3,13,14  A variety of temporary cements with different physical properties, biological features, and manipulation characteristics have been used in implantology. Resin-based cement can affect adjacent tissues because of its nonpolymerized superficial layer that contains formaldehyde and free monomers (both of which act as cell-damaging substances). Therefore, utmost care should be taken during the polymerization and manipulation stages of these techniques.¹⁵  On the other hand, Phan et al¹⁶  reported that zinc-containing cement inhibited production of acid and alkali by oral streptococci. Also, Pette et al reported that zinc-containing cements were the most traceable of the tested cements in radiographs.^3,17,18  Therefore, ZnO-based temporary cement is widely used as a luting agent for cementation of implant-supported restorations.

In 1998, DIAGNOdent was introduced as a detection method for occlusal caries. DIAGNOdent is also known as a complementary method introduced to aid dental practitioners for early detection of occlusal, proximal caries, and calculus.^19–21  The purpose of this study was to evaluate the sensitivity and specificity of DIAGNOdent for the detection of residual excess ZnO-based cement in the sulcus of cemented implants.

A pilot study was designed to evaluate the sensitivity of DIAGNOdent for detection of different types of cement, including resin, polycarboxylate, glass ionomer, and ZnO; ZnO was selected for the mentioned investigation. Each cement was prepared according to its manufacturer's protocol, and a drop of each was placed on a 2-mm-diameter glass slab. The DIAGNOdent probe was held perpendicularly above the cement at a distance of 2 mm. Among the examined cements, ZnO was the only cement that was detected by DIAGNOdent. Thus, subsequent tests were conducted using only the ZnO-type cement.

Fifteen tissue-level dental implants (Dentium, Korea; 4.1 × 10 mm and platform size of 4.8 mm) were embedded in acrylic resin (Acropars, Tehran, Iran). To simulate gingiva around the implants, the transgingival part of each implant was covered with a gingival mask silicon material (Zhermack, Italy). After setting, the material was trimmed with a scalpel to mimic the normal anatomical contours of gingival tissues. This gingival part was removable and could be removed and reinserted into the exact same position, guided by 3 notches in the resin model. The buccal and lingual sides of the mold were marked for the evaluation. The provisional cement (Tempbond, Kerr, Germany) was mixed according to the manufacturer's instructions and applied to 3 areas on each sample, giving a total of 30 areas (according to a random number table). Temporary cement was placed 4 mm below the gingival-mimicking line. To unify some fabricated cement, a template with a 1-mm-diameter hole was used. After cement setting, the gingival sections were placed in their positions (Figure 1).

A DIAGNOdent laser device (KAVO, Germany) was used to evaluate the presence or absence of residual cement in a selected area by 2 examiners blinded to the sample's nature. The indium gallium arsenide phosphide–based red laser diode used in DIAGNOdent emits a wavelength of 655 nm through optical fibers that can be absorbed by organic and inorganic components. These metabolites then emit a red fluorescence, which is second on a scale ranging from 0 to 99.^22,23  Probe No. 1, with a beveled tip designed for interproximal lesions, was selected and inserted into the device (Figure 2). The system was calibrated with the desired probe on a circular calibration disc by an expert clinician. The examiners were allowed to probe the gingival sulcus with a maximum probe penetration depth of 2 mm into the sulcus. Thus, the junctional epithelium, which is normally 2 mm beneath the gingival margin, remained intact. This procedure was applied 2 times to increase the test validity, with 5-minute intervals between tests for instrument calibration. The residual cement was recognized by gently walking the device tip around the implant (Figure 3). A DIAGNOdent score of less than 16 indicated the absence of cement, and scores of 16 or greater indicated the presence of the excess luting agent in the implant sulcus. After DIAGNOdent testing, the gingival mask was removed, and the presence of cement was assessed visually. The test's sensitivity and specificity were calculated using the following formulae:

Data were analyzed using SPSS 21 software (SPSS Inc, Chicago, Ill). The sensitivity and specificity of DIAGNOdent were measured by the receiver-operating characteristic (ROC) curve analysis. The significance level was set at less than .001 (area under the curve = .999; SE = .002; P < .001).

In this in vitro study, the sensitivity and specificity of DIAGNOdent in identifying residual cement in sulcus of implants were examined. The mean ± standard error scores reported by the 2 examiners were 50.78 ± 3.86 and 7.55 ± 0.59 in the presence and absence of cement, respectively (Table 1). The interexaminer reliability was .94 (Table 2). The sensitivity (100%) and specificity (96.677%) of DIAGNOdent for detecting residual cement are summarized in Table 3 (88.65–100 confidence interval). DIAGNOdent was able to identify the residual cement in all 30 specimens. The specificity of DIAGNOdent was 96.67%, and the confidence interval was 83.33–99.41. The area under the corresponding ROC curve was 99.5%, indicating excellent detection performance (Figure 4).

Here, we aimed to evaluate the sensitivity and specificity of DIAGNOdent for detecting residual cement in the sulcus of implants. Sensitivity is the proportion of true-positives that are correctly diagnosed by the test. DIAGNOdent was able to correctly detect the REC in all 30 specimens, thus returning a sensitivity score of 100%. The confidence interval of 88.95– 100% further confirmed that this device was capable of detecting REC. Specificity is the proportion of true-negative specimens that are properly recognized by the test. Here, the specificity of DIAGNOdent was 96.67%, with only a few cement-free specimens identified as positives.

X-ray fluorescence (XRF) is a nondestructive analytical technique that quantifies the compositional elements within materials. The XRF measurements of dental caries have revealed that the zinc content is increased in carious lesions adjacent to the untreated zone compared with intact sections.^24,25  Also, Wadhwani²⁶  evaluated various cements by XRF and found that the major spectra peaks of commonly used cements (glass ionomer cement, polycarboxylate cement, and resin cement) were zirconium, strontium, and tin, respectively. They also found that zinc was the most detected element by XRF in Tempbond cement, similar to dental caries.²⁶  In this regard, the high sensitivity of the DIAGNOdent device in the diagnosis of subgingival cement remnants, which was originally designed for dental caries detection, might be attributed to the high zinc content in both of these samples. To investigate this possibility, a pilot study was designed to evaluate the sensitivity of DIAGNOdent for detection of different types of cement. Zinc oxide was the only cement that was detected by DIAGNOdent. Thus, all subsequent tests used only the ZnO-type cement.

Antonijevic et al²⁷  compared the ability of conventional and digital radiography to detect residual cement around implant abutments. They concluded that the small amount of cement that overhangs adjacent to implant restorations could be easily detected in high-resolution images. Thus, digital radiography, which allows the clinician to adjust the magnification, resolution, and contrast of images, led to a more accurate diagnosis of cement. Wadhwani et al²⁸  showed that the radiodensity of implant restorative cement was dependent on the thickness and material of the specimens and that smaller pieces might remain unseen. Zinc cement could be detected at either 1- and 2-mm portion thickness using an X-ray machine. However, Linkevicius et al²⁹  revealed that dental radiography is an unreliable method for detection of residual cement in the implant-crown interface. They found that excess cement located on the mesial and distal aspect of teeth was detectable in 7.5% and 11.3% of cases, respectively. Also, only interproximal areas, not palatal/lingual and facial areas of implants, could be visualized in radiographs. An advantage of the fluorescence laser approach is its potency for exploration of all dental aspects to notice the residual cement as soon as the laser beam encountered the target, especially for buccal and lingual surfaces, which cannot be recognized in radiographs. Similarly, Shakibaie and Walsh²¹  compared the efficiency of DIAGNOdent for identification of subgingival deposits with conventional periodontal probing under controlled laboratory conditions. They mounted 30 extracted teeth using a silicone impression material. The prepared casts were then examined by both laser fluorescence radiation and tactile assessment. These authors reported a threshold level of 7 for diagnosis of subgingival calculus, and they classified as gold standard samples those samples that had a score greater than 7 by laser and visual confirmation of the presence of calculus after exposure of root surfaces. These authors found that DIAGNOdent was more sensitive and precise than tactile probing. In addition to diagnostic devices, which help recognize foreign debris in the subgingival sulcus, the depth of the residual cement or calculus is of great importance. Wadhwani et al¹  reported that 1- to 3-mm subgingival REC was undetectable in dental intraoral radiographs, while exploratory surgery revealed the presence of excess cement in those clinical reports. DIAGNOdent can detect REC irrespective of thickness, depth, and site of cement. In the present study, DIAGNOdent sensitivity was analyzed for identification of excess cement (1-mm thickness and located 4 mm subgingivally around implant surfaces). More research is required to evaluate the applicability of this device in detecting deeper-placed cement and in clinical situations.

Although we found that DIAGNOdent could successfully detect REC in an artificial gingiva, we anticipate that this will be more difficult in a clinical setting. This is because the anatomical structures of the gingiva (eg, cellular and morphological structures, the thickness of the soft tissue, and the keratinized mucosa) differ from person to person. Also, situations such as edema or inflammation due to REC might also make it difficult to determine the REC using DIAGNOdent. Thus, it is difficult to standardize the gingiva because of its various biological and morphological structures and the tissues around it. Therefore, a clinical study is now needed to determine the effectiveness of DIAGNOdent when adapted to the clinic.

Zinc oxide was the only cement that was detected by DIAGNOdent. The sensitivity and specificity of DIAGNOdent for detecting Tempbond REC in gingival sulcus dental implants were 100% and 96.67%, respectively. Although a clinical investigation is now required, and it is difficult to transfer in vitro results to the clinical anticipation, our data suggest that DIAGNOdent is useful for the detection of REC around the implant-crown interface.

Abbreviations

REC

residual excess cement

ROC

receiver-operating characteristic

XRF

X-ray fluorescence

ZnO

zinc oxide

This study was supported by grant 95-02-70-29136 by the Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences.

The authors report no conflicts of interest related to this study.