Oral mucosa - an examination map for confocal laser endomicroscopy within the oral cavity: an experimental clinical study.

OBJECTIVES: Confocal laser endomicroscopy (CLE) is an optical method that enables microscopic visualization of oral mucosa. Previous studies have shown that it is possible to differentiate between physiological and malignant oral mucosa. However, differences in mucosal architecture were not taken into account. The objective was to map the different oral mucosal morphologies and to establish a "CLE map" of physiological mucosa as baseline for further application of this powerful technology. MATERIALS AND METHODS: The CLE database consisted of 27 patients. The following spots were examined: (1) upper lip (intraoral) (2) alveolar ridge (3) lateral tongue (4) floor of the mouth (5) hard palate (6) intercalary line. All sequences were examined by two CLE experts for morphological differences and video quality. RESULTS: Analysis revealed clear differences in image quality and possibility of depicting tissue morphologies between the various localizations of oral mucosa: imaging of the alveolar ridge and hard palate showed visually most discriminative tissue morphology. Labial mucosa was also visualized well using CLE. Here, typical morphological features such as uniform cells with regular intercellular gaps and vessels could be clearly depicted. Image generation and evaluation was particularly difficult in the area of the buccal mucosa, the lateral tongue and the floor of the mouth. CONCLUSION: A physiological "CLE map" for the entire oral cavity could be created for the first time. CLINICAL RELEVANCE: This will make it possible to take into account the existing physiological morphological features when differentiating between normal mucosa and oral squamous cell carcinoma in future work.

Relevant parameters for laser surgery of soft tissue.

In recent years, the laser has become an important tool in hospitals. Laser surgery in particular has many advantages. However, there is still a lack of the understanding of the influence of the relevant parameters for laser surgery. In order to fill this gap, the parameters pulse frequency, use of an exhaustion system, air cooling, laser power, laser scan speed, laser line energy and waiting time between cuts were analysed by ANOVA using inter-animal variation as a benchmark. The quality of the cuts was quantized by a previously published scoring system. A total of 1710 cuts were performed with a [Formula: see text] laser. Of the parameters investigated, laser power and scan speed have the strongest influence. Only the right combination of these two parameters allows good results. Other effects, such as the use of pulsed or continuous wave (CW) laser operation, or air cooling, show a small or negligible influence. By modulating only the laser power and scan speed, an almost perfect cut can be achieved with a [Formula: see text] laser, regardless of the external cooling used or the laser pulse duration or repetition rate from CW to nanosecond pulses.

Practical and Statistical Considerations for the Long Term Follow-Up of Gene Therapy Trial Participants.

Study sponsors and market authorization holders are required by the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) to enroll patients administered a gene therapy product, whether in a trial setting or post-licensure, in a long term follow-up safety study to continue the safety assessments of their product. These follow-up studies range between 5 and 15 years after dosing. This unprecedented duration of engagement with patients and caregivers raises logistical challenges that will require innovation and collaboration across sponsors and regulators. In this paper we delineate some of the key considerations for designing long term follow-up protocols in the gene therapy setting, with an eye toward platform and master protocol approaches, and offer guidance for innovative operational and statistical methods that can help assess the safety profile and durability of response for these novel therapeutics.

A Treatment Approach for Carotid Blowout Syndrome and Soft Tissue Reconstruction after Radiotherapy in Patients with Oral Cancer: A Report of 2 Cases.

BACKGROUND: This retrospective case series study aims to demonstrate a salvage technique for the treatment of carotid blow-out syndrome (CBS) in irradiated head and neck cancer patients with a vessel-depleted neck. METHODS: Between October 2017 and October 2021, two patients (N = 2) with CBS were treated at our institution in a multidisciplinary approach together with the Department of Vascular Surgery. Patients were characterized based on diagnoses, treatment procedures, and the subsequent postoperative course. RESULTS: Surgical emergency intervention was performed in both cases. The transition zone from the common carotid artery (CCA) to the internal carotid artery (ICA) was resected and reconstructed with a xenogic (case 1) or autogenic (case 2) interposition (end-to-end anastomosis). To allow reconstruction of the vascular defect, an additional autologous vein graft was anastomosed to the interposition graft in an end-to-side technique, allowing arterial anastomosis for a free microvascular flap without re-clamping of the ICA. Because of the intraoperative ICA reconstruction, none of the patients suffered a neurological deficit. CONCLUSIONS: The techniques presented in the form of two case reports allow for acute bleeding control, cerebral perfusion, and the creation of a vascular anastomosis option in the vessel-depleted neck.

Peculiarities in the panoramic radiograph of patients with secondary hyperparathyroidism due to terminal renal disease: a radiologic controlled comparative study.

OBJECTIVES: The present radiological observational controlled study aims to evaluate the impact of secondary hyperparathyroidism (SHPT) due to chronic kidney disease (CKD) as well as the duration of dialysis on the mineralization of the mandible by standardized qualitative evaluation of digital panoramic radiographs. METHODS: Panoramic radiographs of CKD patients with SHPT and healthy controls were used for the qualitative analysis of the mandibular cortical index (MCI), the trabecular bone pattern (TBP), and calcification and resorption foci. Radiomorphometric indices were correlated to biochemical parameters and the duration of dialysis using the Spearman Rho test. Group comparisons were conducted using the Mann-Whitney U test and Fisher's exact test at a significance level of α ≤ 0.05. Interrater reliability of two physicians was estimated using Cohen's kappa. RESULTS: Inclusion and exclusion criteria were fulfilled by N = 41 patients. Statistically significant differences in the MCI (p < 0.001) as well as the TBP (p = 0.002) could be detected for the experimental group in comparison to the healthy control group. Focusing on calcification and resorption foci, no statistically significant difference could be detected between the groups (p = 0.244). The level of the detected parathyroid hormone (PTH) significantly correlated with TBP (Rho = 0.338; p = 0.031), while no significant relationship between TBP and the duration of the dialysis could be found. CONCLUSIONS: Patients with SHPT due to CKD show statistically significant bone changes in the panoramic radiograph, whereby the grade of trabecular bone change correlates to PTH values.

Experimental Validation of Shifted Position-Diffuse Reflectance Imaging (SP-DRI) on Optical Phantoms.

Numerous diseases such as hemorrhage, sepsis or cardiogenic shock induce a heterogeneous perfusion of the capillaries. To detect such alterations in the human blood flow pattern, diagnostic devices must provide an appropriately high spatial resolution. Shifted position-diffuse reflectance imaging (SP-DRI) has the potential to do so; it is an all-optical diagnostic technique. So far, SP-DRI has mainly been developed using Monte Carlo simulations. The present study is therefore validating this algorithm experimentally on realistic optical phantoms with thread structures down to 10 µm in diameter; a SP-DRI sensor prototype was developed and realized by means of additive manufacturing. SP-DRI turned out to be functional within this experimental framework. The position of the structures within the optical phantoms become clearly visible using SP-DRI, and the structure thickness is reflected as modulation in the SP-DRI signal amplitude; this performed well for a shift along the x axis as well as along the y axis. Moreover, SP-DRI successfully masked the pronounced influence of the illumination cone on the data. The algorithm showed significantly superior to a mere raw data inspection. Within the scope of the study, the constructive design of the SP-DRI sensor prototype is discussed and potential for improvement is explored.

COVID-19 pandemic and its impact on dental education: digitalization - progress or regress? Example of an online hands-on course.

BACKGROUND: Due to the SARS-CoV-2 pandemic and the accompanying contact restrictions, a new challenge arose for dental education. Despite the limited overall situation, it must be ensured that, in addition to theoretical content, practical skills in particular continue to be taught. Therefore, the aim of this study was to develop and implement an online hands-on course for dental students that ensures practical training, even during the pandemic. METHODS: The newly developed course was held from April 2020 to March 2021. A total of six groups (each consisting of approximately 40-50 students) took part in the course. The participating students were in their 3rd, 4th or 5th year of study. The course taught theoretical basics (via an online platform) and promoted the learning of practical/surgical techniques on models such as bananas, pork bellies, or chicken thighs with live demonstrations (via ZOOM) and interactive post-preparation by students at home (and in a rotating small group of 3-7 students on site). Student self-evaluation (at the beginning and end of the course) and course evaluation were performed using questionnaires. The learning success was analyzed (through self-evaluations) using Wilcoxon signed-rank tests (significance level alpha = 0.05). RESULTS: Concerning students´ self-evaluations, the theoretical knowledge, general surgical skills (such as surgical instrument handling), and specific surgical skills (such as performing a kite flap) improved during the course, with significant results (p < 0.001 for each). About 60% of the students rated the course overall as excellent (grades 9 or 10 on a Likert scale of 1 to 10). The technical implementation of the course was rated with a median of 9 (= very good, on a Likert scale of 1 to 10). 38.5% described the applicability of the skills learned for their later professional life as extremely good. CONCLUSIONS: The results of this work suggest that, within the limitations of this study, the introduced concept of an online hands-on course could be an appropriate form of teaching practical dental skills, even during a pandemic. Further research is needed in the field of digital education for dental students.

The influence of the optical properties on the determination of capillary diameters.

Various clinically applicable scores and indices are available to help identify the state of a microcirculatory disorder in a patient. Several of these methods, however, leave room for interpretation and only provide clues for diagnosis. Thus, a measurement method that allows a reliable detection of impending or manifest circulatory malfunctions would be of great value. In this context, the optical and non-invasive method of shifted position-diffuse reflectance imaging (SP-DRI) was developed. It allows to determine the capillary diameter and thus to assess the state of the microcirculation. The aim of the present study is to investigate how the quantification of capillary diameters by SP-DRI behaves in different individuals, i.e. for a wide range of optical properties. For this, within Monte-Carlo simulations all optical properties (seven skin layers, hemoglobin) were randomly varied following a Gaussian distribution. An important finding from the present investigation is that SP-DRI works when the optical properties are chosen randomly. Furthermore, it is shown that appropriate data analysis allows calibration-free absolute quantification of the capillary diameter across individuals using SP-DRI. This underpins the potential of SP-DRI to serve as an early alert system for the onset of microcirculatory associated diseases.

Optical diagnosis of oral cavity lesions by label-free Raman spectroscopy.

Oral squamous cell carcinoma (OSCC) is one of the most prevalent cancers and frequently preceded by non-malignant lesions. Using Shifted-Excitation Raman Difference Spectroscopy (SERDS), principal component and linear discriminant analysis in native tissue specimens, 9500 raw Raman spectra of OSCC, 4300 of non-malignant lesions and 4200 of physiological mucosa were evaluated. Non-malignant lesions were distinguished from physiological mucosa with a classification accuracy of 95.3% (95.4% sensitivity, 95.2% specificity, area under the curve (AUC) 0.99). Discriminating OSCC from non-malignant lesions showed an accuracy of 88.4% (93.7% sensitivity, 76.7% specificity, AUC 0.93). OSCC was identified against physiological mucosa with an accuracy of 89.8% (93.7% sensitivity, 81.0% specificity, AUC 0.90). These findings underline the potential of SERDS for the diagnosis of oral cavity lesions.

Determination of the diameter of simulated human capillaries using shifted position-diffuse reflectance imaging.

Multiple diseases are associated with a wide spectrum of microvascular dysfunctions, microangiopathies and microcirculation disorders. Monitoring the microcirculation could thus be useful to diagnose many local and systemic circulatory disorders and to supervise critically ill patients. Many of the scores currently available to help identify the condition of a microcirculation disorder are invasive or leave scope for interpretation. Thus, the present study aims to investigate with Monte-Carlo simulations (as numerical solutions of the radiative transfer equation) whether shifted position-diffuse reflectance imaging (SP-DRI), a non-invasive diagnostic technique, reveals information on the capillary diameter to assess the state of the microcirculation. To quantify the SP-DRI signal, the modulation parameter K is introduced. It proves to correlate almost perfectly with the capillary diameter ( R¯2≈1 ), making it a valid parameter for reliably assessing microcirculation. SP-DRI is emerging as an important milestone on the way to early and conveniently diagnosing microcirculation associated diseases.

No Association Between DAA Treatment for HCV Infection and Herpes Zoster Infection in Analysis of Data From 37 Clinical Trials.

BACKGROUND AND AIMS: Recent case series and retrospective studies have raised concerns that patients who receive direct-acting antiviral (DAA) treatment for hepatitis C virus (HCV) infection are at increased risk of developing varicella-zoster virus infection (VZV reactivation). We investigated the relationship between DAA treatment and VZV reactivation by analyzing pooled participant-level data from 37 clinical trials of DAA agents. METHODS: We obtained demographic, adverse event, and laboratory data from 13,816 participants in 37 clinical trials submitted to the Food and Drug Administration for approval of DAA agents for treatment of HCV infection. Participants received DAAs (n = 12,249), placebo (n = 997), pegylated interferon (n = 243), or a combination of DAAs and pegylated interferon (n = 327). Occurrence of VZV reactivation was identified using systematically reported adverse event data. HCV virologic response was evaluated by measurement of HCV RNA. RESULTS: VZV reactivation occurred in 9.9 cases per 1000 person-years of DAA treatment (95% CI, 6.8-14.0 per 1000 person years) and 13.8 cases per 1000 person-years of placebo (95% CI, 3.5-37.5 per 1000 person years). No participants in the pegylated interferon or combination DAA and pegylated interferon groups experienced VZV reactivation. Within the placebo-controlled trials there was no significant difference in VZV reactivation between DAA treatment and placebo. VZV reactivation was associated with age older than 40 years, female sex, and HIV coinfection. We did not find an association between time of virologic response and time to VZV reactivation. CONCLUSION: In an analysis of data from 37 trials, we found no evidence for an association between DAA treatment for HCV infection and increased risk of VZV reactivation.

Speech intelligibility in patients with oral cancer: An objective baseline evaluation of pretreatment function and impairment.

BACKGROUND: This study seeks to identify those factors that influence the pre-therapeutic speech intelligibility in patients with oral squamous cell carcinoma (OSCC). METHOD: A group of 172 patients (125 males, 47 females, mean age = 61 ± 11 a) with different OSCC stages ranging from T1 to T4 and N0 to N2 was examined for their speech intelligibility using a computerized measuring tool, and compared to a healthy reference group (30 males, 10 females, mean age = 59 ± 12 a). RESULTS: It was found that the pre-therapeutic speech intelligibility in patients with OSCC is decreased when compared to a healthy collective. Two demographic factors that influence speech intelligibility could be identified: sex and age. It was determined that the only disease-related factor that influences speech intelligibility before therapy is the location of the tumor. CONCLUSION: The results of this study reveal that a preoperative speech intelligibility impairment in patients suffering from OSCC occurs independent of tumor stage, size of the tumor and infiltration status.

Local anaesthesia training for undergraduate students - how big is the step from model to man?

BACKGROUND: Local anesthesia is an important skill and a prerequisite for most dental treatments. However, the step from theory to application on the patient is huge for the novice. Hence, a mannequin training model course was developed and implemented into the existing local anesthesia curriculum in undergraduate dental students. It was the aim of this study to evaluate the relation between training-model and real-life anesthesia performance and to measure whether a gain in skill on the model translates to the actual patient situation. METHODS: Thirty-six third-year students (14 males, 22 females, age 24 years±2.98) attended the four-day course comprising each 4 h of lectures and practical training. The student cohort gave subjective ratings about the didactical components of the course after attendance by using the TRIL questionnaire (TRIL-mod; University of Trier). At the end of the course the performance of each student in administering an inferior alveolar nerve (IAN) block on the training model as well as on a fellow dental student was investigated using a standardized checklist. To evaluate the successful performance, the in vivo IAN-block was assessed using subjective patient-feeling, the sharp-blunt test and an objective pain- and thermal sensitivity tester (PATH). RESULTS: The course was rated with an average score of 5.25 ± 0.44 (range 1-6; 6 = best). On the training model, 69.4% of the students successfully performed an IAN-block. The in vivo assessment, objectified by the PATH test, showed a successful anesthesia in 36.9% of the cases. The assessment of local anesthesia by using the sharp blunt test and the subjective patient feeling significantly correlated with these findings (k = 0.453-0.751, p < 0.05). The model performance did not correlate with the performance on the patient (k = 0.137, p = 0.198). CONCLUSIONS: Although subjective ratings of the course were high, the anesthesia success rate on mannequin models did not imply an equal performance on the in vivo setting. As local anesthesia training models are a valuable didactic complement, the focus of the training should be on to the actual real life situation. Chair side feedback should be offered to the students using one of the presented evaluation methods.

Long-term Outcome of Speech Intelligibility in Maxillary Dental Rehabilitation with Full Dentures: A Prospective Study Using Automatic Speech Quantification.

AIMS: Complete maxillary edentulism and prosthetic rehabilitation with removable full dentures are known to affect speech intelligibility. The aim of this study was to prospectively investigate the long-term effect of time on speech intelligibility in patients being rehabilitated with newly fabricated full maxillary dentures. MATERIALS AND METHODS: Speech was recorded in a group of 14 patients (male = 9, female = 5; mean age ± standard deviation [SD] = 66.14 ± 7.03 years) five times within a mean period of 4 years (mean ± SD: 47.50 ± 18.16 months; minimum/maximum: 24/68 months) and in a control group of 40 persons with healthy dentition (male = 30, female = 10; mean age ± SD = 59 ± 12 years). All 14 participants had their inadequate removable full maxillary dentures replaced with newly fabricated dentures. Speech intelligibility was measured by means of a polyphone-based speech recognition system that automatically computed the percentage of accurately spoken words (word accuracy [WA]) at five different points in time: 1 week prior to prosthetic maxillary rehabilitation (both with and without inadequate dentures in situ) and at 1 week, 6 months, and a mean of 48 months after the insertion of newly fabricated full maxillary dentures. RESULTS: Speech intelligibility of the patients significantly improved after 6 months of adaptation to the new removable full maxillary dentures (WA = 66.93% ± 9.21%) compared to inadequate dentures in situ (WA = 60.12% ± 10.48%). After this period, no further significant change in speech intelligibility was observed. After 1 week of adaptation, speech intelligibility of the rehabilitated patients aligned with that of the control group (WA = 69.79% ± 10.60%) and remained at this level during the examination period of 48 months. CONCLUSION: The provision of new removable full maxillary dentures can improve speech intelligibility to the level of a healthy control group on a long-term basis.

Autofluorescence spectroscopy for nerve-sparing laser surgery of the head and neck-the influence of laser-tissue interaction.

The use of remote optical feedback systems represents a promising approach for minimally invasive, nerve-sparing laser surgery. Autofluorescence properties can be exploited for a fast, robust identification of nervous tissue. With regard to the crucial step towards clinical application, the impact of laser ablation on optical properties in the vicinity of structures of the head and neck has not been investigated up to now. We acquired 24,298 autofluorescence spectra from 135 tissue samples (nine ex vivo tissue types from 15 bisected pig heads) both before and after ER:YAG laser ablation. Sensitivities, specificities, and area under curve(AUC) values for each tissue pair as well as the confusion matrix were statistically calculated for pre-ablation and post-ablation autofluorescence spectra using principal component analysis (PCA), quadratic discriminant analysis (QDA), and receiver operating characteristics (ROC). The confusion matrix indicated a highly successful tissue discrimination rate before laser exposure, with an average classification error of 5.2%. The clinically relevant tissue pairs nerve/cancellous bone and nerve/salivary gland yielded an AUC of 100% each. After laser ablation, tissue discrimination was feasible with an average classification accuracy of 92.1% (average classification error 7.9%). The identification of nerve versus cancellous bone and salivary gland performed very well with an AUC of 100 and 99%, respectively. Nerve-sparing laser surgery in the area of the head and neck by means of an autofluorescence-based feedback system is feasible even after ER-YAG laser-tissue interactions. These results represent a crucial step for the development of a clinically applicable feedback tool for laser surgery interventions in the oral and maxillofacial region.

The differentiation of oral soft- and hard tissues using laser induced breakdown spectroscopy - a prospect for tissue specific laser surgery.

Compared to conventional techniques, Laser surgery procedures provide a number of advantages, but may be associated with an increased risk of iatrogenic damage to important anatomical structures. The type of tissue ablated in the focus spot is unknown. Laser-Induced Breakdown-Spectroscopy (LIBS) has the potential to gain information about the type of material that is being ablated by the laser beam. This may form the basis for tissue selective laser surgery. In the present study, 7 different porcine tissues (cortical and cancellous bone, nerve, mucosa, enamel, dentine and pulp) from 6 animals were analyzed for their qualitative and semiquantitative molecular composition using LIBS. The so gathered data was used to first differentiate between the soft- and hard-tissues using a Calcium-Carbon emission based classifier. The tissues were then further classified using emission-ratio based analysis, principal component analysis (PCA) and linear discriminant analysis (LDA). The relatively higher concentration of Calcium in the hard tissues allows for an accurate first differentiation of soft- and hard tissues (100% sensitivity and specificity). The ratio based statistical differentiation approach yields results in the range from 65% (enamel-dentine pair) to 100% (nerve-pulp, cancellous bone-dentine, cancellous bone-enamel pairs) sensitivity and specificity. Experimental LIBS measuring setup.

Development and validation of a classification and scoring system for the diagnosis of oral squamous cell carcinomas through confocal laser endomicroscopy.

BACKGROUND: Confocal laser endomicroscopy (CLE) is an optical biopsy method allowing in vivo microscopic imaging at 1000-fold magnification. It was the aim to evaluate CLE in the human oral cavity for the differentiation of physiological/carcinomatous mucosa and to establish and validate, for the first time, a scoring system to facilitate CLE assessment. METHODS: The study consisted of 4 phases: (1) CLE-imaging (in vivo) was performed after the intravenous injection of fluorescein in patients with histologically confirmed carcinomatous oral mucosa; (2) CLE-experts (n = 3) verified the applicability of CLE in the oral cavity for the differentiation between physiological and cancerous tissue compared to the gold standard of histopathological assessment; (3) based on specific patterns of tissue changes, CLE-experts (n = 3) developed a classification and scoring system (DOC-Score) to simplify the diagnosis of oral squamous cell carcinomas; (4) validation of the newly developed DOC-Score by non-CLE-experts (n = 3); final statistical evaluation of their classification performance (comparison to the results of CLE-experts and the histopathological analyses). RESULTS: Experts acquired and edited 45 sequences (260 s) of physiological and 50 sequences (518 s) of carcinomatous mucosa (total: 95 sequences/778 s). All sequences were evaluated independently by experts and non-experts (based on the newly proposed classification system). Sensitivity (0.953) and specificity (0.889) of the diagnoses by experts as well as sensitivity (0.973) and specificity (0.881) of the non-expert ratings correlated well with the results of the present gold standard of tissue histopathology. Experts had a positive predictive value (PPV) of 0.905 and a negative predictive value (NPV) of 0.945. Non-experts reached a PPV of 0.901 and a NPV of 0.967 with the help of the DOC-Score. Inter-rater reliability (Fleiss` kappa) was 0.73 for experts and 0.814 for non-experts. The intra-rater reliability (Cronbach's alpha) of the experts was 0.989 and 0.884 for non-experts. CONCLUSIONS: CLE is a suitable and valid method for experts to diagnose oral cancer. Using the DOC-Score system, an accurate chair-side diagnosis of oral cancer is feasible with comparable results to the gold standard of histopathology-even in daily clinical practice for non-experienced raters.

Oral squamous cell carcinoma of the tongue: Prospective and objective speech evaluation of patients undergoing surgical therapy.

BACKGROUND: Prospective speech intelligibility assessments lack objectivity in patients undergoing surgery for oral squamous cell carcinoma (OSCC) of the tongue. METHODS: Speech intelligibility was measured based on word recognition by means of an automatic and objective speech recognition system preoperatively, and 14 to 20 days, and 3 months, 6 months, and 12 months postoperatively. The study comprised 25 patients with OSCC of the tongue and a healthy control group (n = 40). RESULTS: Patients yielded significant speech impairments compared to the healthy control group both before surgery and after 12 months (p ≤ .002). The speech intelligibility of the patients decreased significantly 14 to 20 days after surgery (p < .001) but realigned to preoperative values after 12 months (p = .159). Preservation of the tip of the tongue resulted in significantly higher word recognition after 12 months (p = .007; Δword recognition = 16.29). CONCLUSION: Having OSSC of the tongue results in a significant impairment of speech intelligibility. The preservation of the tip of the tongue seems to be a central factor concerning the recovery of speech. © 2015 Wiley Periodicals, Inc. Head Neck 38: 993-1001, 2016.

Does Laser Surgery Interfere with Optical Nerve Identification in Maxillofacial Hard and Soft Tissue?--An Experimental Ex Vivo Study.

The protection of sensitive structures (e.g., nerves) from iatrogenic damage is of major importance when performing laser surgical procedures. Especially in the head and neck area both function and esthetics can be affected to a great extent. Despite its many benefits, the surgical utilization of a laser is therefore still limited to superficial tissue ablation. A remote feedback system which guides the laser in a tissue-specific way would provide a remedy. In this context, it has been shown that nerval structures can be specifically recognized by their optical diffuse reflectance spectra both before and after laser ablation. However, for a translation of these findings to the actual laser ablation process, a nerve protection within the laser pulse is of utmost significance. Thus, it was the aim of the study to evaluate, if the process of Er:YAG laser surgery--which comes with spray water cooling, angulation of the probe (60°) and optical process emissions--interferes with optical tissue differentiation. For the first time, no stable conditions but the ongoing process of laser tissue ablation was examined. Therefore, six different tissue types (nerve, skin, muscle, fat, cortical and cancellous bone) were acquired from 15 pig heads. Measurements were performed during Er:YAG laser ablation. Diffuse reflectance spectra (4500, wavelength range: 350-650 nm) where acquired. Principal component analysis (PCA) and quadratic discriminant analysis (QDA) were calculated for classification purposes. The clinical highly relevant differentiation between nerve and bone was performed correctly with an AUC of 95.3% (cortial bone) respectively 92.4% (cancellous bone). The identification of nerve tissue against the biological very similar fat tissue yielded good results with an AUC value of 83.4% (sensitivity: 72.3%, specificity: of 82.3%). This clearly demonstrates that nerve identification by diffuse reflectance spectroscopy works reliably in the ongoing process of laser ablation in spite of the laser beam, spray water cooling and the tissue alterations entailed by tissue laser ablation. This is an essential step towards a clinical utilization.