DISSERTATION (PH.D.)--THE UNIVERSITY OF MICHIGAN

This thesis investigated the efficacy of two techniques, digital spectrophotometry and narrow-band endoscopy, in observing and describing gingival tissue in a patient population. The efficacy of existing gingival restorative materials in mimicking the optical qualities of the participant pool was also investigated using spectrophotometric analysis. The spectrophotometric analysis examined the ability of a digital, non-contact, full-tooth spectrophotometer (Crystaleye; Olympus, Japan) to evaluate objectively gingival color, thickness, and translucency in 100 participants drawn from the patient population of a dental school. Color metrics of gingival soft tissue were obtained from all teeth in the maxillary sextant in the participant population and stratified with respect to tooth location, type, and patient sex and ethnicity. It was concluded that: • In the anterior maxillary gingiva, the luminance (brightness) of the periodontal gingival tissues decreased, whereas the chromacity (color saturation) increased, as the site progressed more posteriorly in the mouth. • Gingival color varied significantly with patient sex, with males exhibiting lower value (darker/grayer) gingiva of a more purple hue. • Gingival color varied significantly with patient ethnicity, with White participants exhibiting brighter, yet less chromatic gingiva than Black, Asian, and Hispanic participants. • Gingival thickness measured via cast analysis was found to be 13% thicker in the male population. • Gingival translucency was observed to be correlated linearly to gingival thickness calculated using two existing metrics and one novel metric. Female participants were found to have significantly more translucent gingiva than male participants. A spectrophotometric coverage error analysis investigating the efficacy with which 5 different brands of gingival acrylics replicated the optical properties of the participant population was performed. It was determined that significant differences existed in the coverage errors of different materials, with some of the shade guide sets exhibiting average best-matches outside of the range of clinical acceptability. It was observed that the coverage errors of the shade guide sets were not determined by the number of tabs in the set, but rather by the fitness of a few isolated tabs within the participant population. In a proof-of-concept analysis, a two-tab shade guide set was conceived that was optimized for the sample participant population that outperformed all other sets in coverage errors. This may have implications in the development of future spectrophotometrically guided shade sets optimized for patient populations. Lastly, using a clinical endoscope (CV-190; Olympus, Tokyo, Japan) equipped with narrow-band imaging capabilities, the microvasculature of the marginal gingiva in the esthetic zone was observed and categorized. The analysis focused on the complexity of the intrapapillary capillary loop (IPCL), a diagnostic indicator of mucosal inflammation. No significant correlations were determined between the classifications of the observed IPCLs and the spectral data obtained, suggesting that within the limitations of this study, endoscopic imaging may be limited in quantitative or diagnostic applications, although it is useful for subjective visualization of the IPCLs.

Esthetic outcomes with implants begin with proper implant placement, but the predictability of the peri-implant esthetic outcome is also affected by patient’s pre-existing or reconstructed local tissue. An unpleasant optical phenomenon where the peri-implant mucosa appears gray has been documented in the literature. However, it’s etiology and solutions have not yet been fully investigated. The overall goal of this project is to perform comprehensive optical examination and to establish the clinical guideline to achieve optimal peri-implant mucosa. A. Specific Aim 1: Assess the optical properties of the peri-implant mucosa. A total of 40 patients who has a healthy, single bone level implant in the maxillary anterior zone is recruited at HSDM. For each patient, the test site (peri-implant mucosa) and the control site (adjacent natural gingiva) are identified. Using a dental spectrophotometer, CIELAB color coordinates, translucency parameter (TP), and thickness of test and control site are measured. We found that the color of peri-implant mucosa of bone level implants is significantly different from adjacent gingiva (p=0.0003). We further found that while color of the peri-implant mucosa are significantly different from those of the adjacent gingiva, the thickness and TP do not contribute to this color difference. B. Specific Aim 2: Evaluate the vascular morphology change of the peri-implant mucosa. Studies have shown that a significant vascular reconstruction takes place around a dental implant. Therefore, using a narrow band imaging endoscope, interpapillary capillary loops (IPCL) around a dental implant are compared to those around a natural tooth. We found that there are more interpapillary capillary loops in peri-implant mucosa compared to gingiva (p=0.02). C. Specific Aim 3: Determine the threshold for soft tissue color discernment While many studies have demonstrated the color threshold for shades of teeth and restorations, there is very little information with respect to soft tissue colors. Therefore, in controlled in-vivo and ex-vivo settings, color threshold of soft tissue was investigated, and a correlation between the objective color threshold (ΔE) and subjective color threshold for soft tissue color were also determined. For soft tissue, objective threshold is found to be ΔE=6.50-6.99, and the correlation between subjective and objective evaluations is significant (r=0.67) in ex-vivo setting. D. Specific Aim 4: Evaluate the efficacy of the newly developed colored abutment on improving the optical property. In order to improve this gray optical phenomenon, a pink colored abutment system has been developed. In a randomized manner, we investigated the color of the peri-implant mucosa with pink and gray abutment. We found that this pink colored abutment can significantly improve the aforementioned optical phenomenon, especially in those with thin tissue (<2mm) (p=0.04) and those with pink neck implant (p=0.04). The clinical significance, however, still needs to be determined.

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