Photobiomodulation Dose Parameters in Dentistry: A Systematic Review and Meta-Analysis.

OBJECTIVE: This systematic review and meta-analysis of published randomized controlled trials examines a possible relationship between optical spot size at surface tissue, irradiance, radiant exposure, total energy delivered, operator technique and reported clinical outcomes. BACKGROUND: Clinical photobiomodulation (PBM) therapy has achieved a high level of evidence-based acceptance in the mitigation of oral mucositis associated with cancer radiotherapy and chemotherapy, and supportive clinical research in relation to orthodontic tooth movement, oral medical conditions, including burning mouth syndrome, xerostomia and lichen planus. Inconsistent outcomes have been reported not withstanding a substantial body of primary supportive research from clinical, in vitro and animal studies. MATERIALS AND METHODS: PubMed, Cochrane Database of Reviews and Google Scholar search engines were applied to identify human clinical trials of PBM therapy in clinical dentistry. A total of 766 articles between February 2009 and June 2020 were identified and following a full text evaluation, 38 papers with sufficient data to permit analyses are included in this investigation. RESULTS: Following a detailed assessment of potential factors that may have an influence in clinical outcome, a clear trend is apparent associating optical spot size to a positive or negative effect. Furthermore, there is a clear difference in the reported results in relation to total energy applied, delivery techniques and optical parameters, which merits further investigation. Factorial statistical analyses identified an association between smaller optical surface applications and an overall lower level of reported clinical success in treating superficial and deeper targets, and correspondingly sub-surface larger target tissues were found to be more responsive to therapy by use of a larger optical surface spot size. Moreover, use of multiple small diameter probe applications was found to provide inconsistent results. CONCLUSIONS: Many factors can confound clinical success including variations in anatomy, site location, clinical condition and subject individuality. To achieve higher levels of predictable outcome, a mature appreciation of these factors, plus an expanded understanding of laser parametry, tissue volume and target depth to deliver an adequate dose within current recommended guidelines, is essential.

Systematic Review of Post-Surgical Laser-Assisted Oral Soft Tissue Outcomes Using Surgical Wavelengths Outside the 650-1350 nm Optical Window.

Objective: To explore via systematic review the validation of uneventful post-surgical healing, associated with shorter and longer laser wavelength applications in minor oral surgery procedures. Methods: From April 28 to May 11, 2020, PubMed, Cochrane Database of Systemic Reviews, and Google Scholar search engines were applied to identify human clinical trials of photobiomodulation (PBM) therapy in clinical dentistry. The searches were carried out with reference to (1) dental laser wavelengths shorter than 650 nm; (2) wavelengths localized within the 2780-2940 nm; and (3) the 9300-10,600 nm range. Selected articles were further assessed by three independent reviewers for strict compliance with PRISMA guidelines and modified Cochrane Risk of Bias to determine eligibility. Results: Using selection filters of randomized clinical trials, moderate/low risk of bias, and the applied period, and following PRISMA guidelines, 25 articles were selected and examined. A risk of bias was completed, where 11 out of 25 publications were classified as low risk of bias, and 14 out of 25 were classified as medium risk status. In total, 6 out of 13 (46% of) studies comparing the examined laser wavelengths with scalpel-based treatment showed positive results, whereas 6 out of 13 (46%) showed no difference, and only 1 out of 13 (7.7%) presented a negative outcome. In addition, 5 out of 6 (83% of) studies comparing the examined laser wavelengths with other diodes (808-980 nm) showed positive results, whereas 1 out of 6 (17%) had negative outcomes. Conclusions: A detailed and blinded examination of published studies has been undertaken, applying strict criteria to demonstrate research outcome data, which suggests positive or at worst neutral comparatives when a given laser wavelength system is used against an alternative control therapy. As such, substantiated evidence for laser surgery in delivering uneventful healing and analgesic effects, as an expression of a PBM-like (quasi-PBM) influence, has been shown.

Photobiomodulation and Oral Mucositis: A Systematic Review.

Oral mucositis (OM) is a debilitating complication of chemotherapy, and head and neck radiotherapy. In an effort to offer the best possible advice within the limitations of published research, a systematic review with an extended discussion and commentary on dosimetry and dose delivery is presented. Using keywords as listed, Pubmed, Google Scholar and Cochrane databases were searched during a period extending from 1995 to 2019. A total of 782 abstracts were identified. A total of 50 papers were analysed, and of these, 29 satisfied criteria required for systematic review in accordance with an optimized PRISMA statement. Clinical outcome as reported was subject to analysis with respect to time of intervention, incidence and severity of oral mucositis, and pain amelioration, and a comprehensive combined univariate and multivariate statistical analysis of the methods employed was performed. Recommendations are made with respect to the timing of the intervention. Moreover, there is an extended discussion available on the treatment care rationale of photobiomodulation (PBM), and its adjunctive association with OM. In conclusion, early prophylactic application offers clear advantages in clinical management. The many studies and associated variables and covariables assessed here revealed a choice of delivery techniques, associated wavelengths and many further indices to consider with regard to the accomplishment of optical parameters. It is therefore our recommendation that clinicians use PBM as a therapy with a full and proper understanding and training in order to optimise the clinical effects achievable.

Adjunctive Use of Lasers in Peri-Implant Mucositis and Peri-Implantitis Treatment: A Systematic Review.

BACKGROUND: The aim of this systematic review is to compare the effectiveness of lasers in the treatment of implant mucositis and peri-implantitis compared to conventional treatment (non-surgical or surgical: resective or regenerative). METHODS: Sources of PubMed, Cochrane and Google Scholar search engines were used on articles published from 1997 to 2020 in English, with selected keyword criteria applied. Nine randomized controlled trials (RCTs) were selected. RESULTS: All included studies were considered of "high quality" according to the quality assessment scale. The comparative assessment of the RCTs was done twice for each RCT based on the type of treatment and according to wavelength. There is strong scientific evidence that, regarding non-surgical treatment, adjunct laser application can provide better results only in the short term (three months). Regarding the surgical approach, the method of decontamination plays a subordinate role. All wavelengths/applications presented similar results. CONCLUSION: Within the limitations of this study, the adjunctive use of lasers in the treatment of peri-implant inflammation is effective for up to three months; there is no strong evidence regarding the long term benefit compared to conventional treatment.

Systematic Review of Orthodontic Treatment Management with Photobiomodulation Therapy.

Objective: This systematic review of published research evaluates the parameters and reported outcomes in photobiomodulation therapies (PBMTs) used in management of pain and accelerated tooth movement during orthodontic treatment. Background: Consequent to positive in vitro and animal studies, there has been considerable interest in the potential applications of PBMT to ameliorate pain and to accelerate orthodontic tooth movement. Due to the lack of consistency of wavelengths and parameters applied, there is as yet no consensus in respect of guidance for clinical use. Within the limitations of the reported literature, a digest of key outcomes and parameters is presented here to assist researchers and interested clinicians. Materials and methods: Search engines, PubMed, Google Scholar, and Cochrane, were applied to identify clinical investigations into the potential benefits of PBMTs in orthodontic management. Keywords used were "low-level laser therapy," "low-level light therapy," "photobiomodulation," "orthodontics," "pain," "tooth movement," and "randomized clinical trial ≥5 years." A total of 35 articles were identified, covering the 5-year period January 2013 to December 2018. Only human clinical trials were considered. Seventeen articles were included in this investigation and the reported parameters and outcomes were assessed and presented for comparison. Results: Seven of nine studies supported the effectiveness of PBMT to reduce or prevent pain. There was no consensus on choice of wavelength and a range of parameters were found beneficial. Of the seven tooth movement studies included, four of the seven were positive, of which two used a home-use light-emitting diode (LED) device, as opposed to a clinician-applied laser. A variety of wavelengths and parameters were found to be effective in accelerating tooth movement in the range of 20-40% compared with control. Conclusions: Due to a lack of consistency in approach, further studies are required to achieve a high level of acceptance. The clinical logistics associated with frequent applications supports the concept of patient home delivery use of LED devices, although there are insufficient studies at present to make an evidence-based determination of this type of appliance. To gain more general professional acceptance of the use of PBMT in orthodontics, a continued effort to extend the number of quality human clinical trials is required. Based on the current evidence base, further positive onward progression can be regarded as inevitable.

Dental anxiety in first- and final-year Indian dental students.

OBJECTIVES: The study aims to investigate dental anxiety in first- and final-year undergraduate dental students in India. DESIGN: Questionnaire Study Setting: BDS Students in four University dental colleges in India carried-out during 2013 and 2014. SUBJECTS MATERIALS AND METHODS: The students (n = 614) were assessed using a pre-tested questionnaire. We estimated the level of dental anxiety by using the Modified-Dental-Anxiety-Scale (MDAS). ANCOVA and Mann-Whitney U, and Chi-squared contingency tests were employed to analyze the extensive dataset acquired. Univariate clustering analysis and principal component regression were also applied. Students had similar demographic and lifestyle patterns. INTERVENTIONS: Assessments of the level of dental anxiety amongst undergraduate dental students. MAIN OUTCOME MEASURES: Mean ± SD MDAS scores for first- and final-year Bachelor of Dental Surgery (BDS) students were 12.96 ± 4.00 and 10.54 ± 3.41, respectively. RESULTS: Six hundred and fourteen (n = 614) students from four dental colleges were included in this study. In total 77% were female (n = 478) and 23% were male (n = 136). The mean age of the first- and final-year students were 18.31 and 21.54 years, respectively. First-year BDS students had dental anxiety score (Mean ± SD 12.96 ± 4.00) compared to that of the final year (10.54 ± 3.41), a difference which was very highly statistically significant (p < 0.0001). CONCLUSIONS: Dental anxiety was moderately higher amongst first year BDS students over that of final-year students but it is lesser than the dental phobic threshold level.

Systematic Review of Delivery Parameters Used in Dental Photobiomodulation Therapy.

Objective: This systematic review of published data critically appraises the consistency in the reported delivery parameters used in photobiomodulation (PBM) therapies research within clinical dentistry and makes reporting recommendations for future clinical protocols. Background: Key to the standardization of randomized clinical trials and associated peer-reviewed articles is the disclosure of all laser and light-emitting diode operating parameters. The current status shows a lack of full parameters and significantly impacts on the ability to integrate published data with current and future investigation into clinical PBM therapy. Materials and methods: Search engines, PubMed, Google Scholar, and Cochrane, were scanned for investigation into the effects of PBM therapy research within clinical dentistry. Key words "Low-Level-Laser," "PBM," "Photobiomodulation," "Oral" and "Therapy" were used and a total of 754 articles identified, spanning a period of 9 years and 1 month between February 2009 and March 2018. Only human clinical trials were considered. Fifty-two articles were included in this investigation and the reported basic delivery parameters used in PBM therapies research were considered for each clinical trial. Results: The overall reported basic delivery parameters used in PBM therapies research were too inadequate to be able to be replicated in further studies. These included parameters related to the power meter, beam cross-sectional dynamics, fluence, and wider aspects of dosimetry. Conclusions: The delivery parameters used in PBM therapy research within clinical dentistry, investigated in this study, presented a wide variation in their recording or nonrecording of all significant elements needed to have scientific validity. A constant inconsistency in delivering valid, reliable, PBM therapy doses, to target tissues was also identified. The lack of consensus in delivering a sound protocol for PBM therapy, is partly due to the lack of adequate reported materials and methods, which are essential for replication of individual studies. One way to resolve this problem is for Journals to insist on all comprehensive parameter records, used in PBM therapies, to be part of author guidelines in submitting articles of studies on PBM therapy in clinical dentistry.

Association between oral tori, occlusal force, and mandibular cortical index.

OBJECTIVE: To assess possible associations between torus palatinus (TP), torus mandibularis (TM), occlusal force (OF), Klemetti's classes, mandibular cortical index (MCI), and sociodemographic variables in a selected sample of Jordanians. Previous studies have suggested that oral tori are benign anatomical variations probably related to several factors such as functional stress, gender predisposition, number of teeth present, and nutritional factors. METHOD AND MATERIALS: A total of 130 Jordanian adults were included. Shape, location, and appearance of tori were recorded from study casts. Size was measured using digital calipers. OF was recorded in Newtons. MCI and Klemetti's classification were assessed using panoramic radiographs. Data were statistically analyzed, and level of significance was set at P < .05. RESULTS: The mean ± SD recorded OF was 524 ± 183 N in the tori group, compared to 417 ± 172 N in controls (P = .001). OF was significantly higher in males compared to females (P < .001), and was significantly higher in subjects with TM only (543 ± 201 N) (P < .001). TP and TM were predominantly more than 6 mm in size. The average OF in subjects with Klemetti class 3 was 418 ± 174 N, while OF in Klemetti class 1 subjects amounted to 535 ± 187 N (P = .043). CONCLUSION: Average OF was significantly higher in tori subjects and in males (if compared to controls and female subjects, respectively). The presence of oral tori, Klemetti's classification, and MCI ratio seems to be positively correlated with OF.

Effect of multiple debonding sequences on shear bond strength of new stainless steel brackets.

OBJECTIVES: This in-vitro study aimed at evaluating the effect of three debonding sequences on the shear bond strength (SBS) of new stainless steel (SS) brackets. MATERIALS AND METHODS: Stainless steel twin brackets (0.022-inch, American Orthodontics, Sheboygan, WI, USA) were bonded with light cure adhesive (Transbond XT, 3M Unitek, St. Paul, MN, USA) to 80 newly extracted human premolars after acid etching with 37% phosphoric acid (30 s). Brackets were debonded with a universal testing machine, and new brackets were bonded to teeth using the same adhesive and same manner. This process was repeated twice, and brackets were debonded within 24 h after bonding. The longitudinal changes of average SBS were assessed with the repeated measures ANOVA. Post-hoc tests using the Bonferroni correction were also used to compare the average SBS at three debonding sequences. RESULT: The mean SBS decreased significantly after each debonding sequence (P < 0.01). The corresponding mean values (standard deviation, 95% CI) after the first, second, and third debonding sequences were 22.88 MPa (4.08, 21.97-22.79), 19.36 MPa (4.54, 18.62-20.64), and 16.67 MPa (4.27, 15.72-17.62), respectively. There was no significant difference among the adhesive remnant index (ARI) scores of three debonding sequences (χ(2)= 5.067, df = 6, P = 0.53). CONCLUSION: Average SBS after three debonding sequences was significantly decreased, but was above the recommended 5.9-7.8 MPa. In-vivo studies are required to validate the finding of this study.

Establishing magnetic resonance imaging as an accurate and reliable tool to diagnose and monitor esophageal cancer in a rat model.

OBJECTIVE: To assess the reliability of magnetic resonance imaging (MRI) for detection of esophageal cancer in the Levrat model of end-to-side esophagojejunostomy. BACKGROUND: The Levrat model has proven utility in terms of its ability to replicate Barrett's carcinogenesis by inducing gastroduodenoesophageal reflux (GDER). Due to lack of data on the utility of non-invasive methods for detection of esophageal cancer, treatment efficacy studies have been limited, as adenocarcinoma histology has only been validated post-mortem. It would therefore be of great value if the validity and reliability of MRI could be established in this setting. METHODS: Chronic GDER reflux was induced in 19 male Sprague-Dawley rats using the modified Levrat model. At 40 weeks post-surgery, all animals underwent endoscopy, MRI scanning, and post-mortem histological analysis of the esophagus and anastomosis. With post-mortem histology serving as the gold standard, assessment of presence of esophageal cancer was made by five esophageal specialists and five radiologists on endoscopy and MRI, respectively. RESULTS: The accuracy of MRI and endoscopic analysis to correctly identify cancer vs. no cancer was 85.3% and 50.5%, respectively. ROC curves demonstrated that MRI rating had an AUC of 0.966 (p<0.001) and endoscopy rating had an AUC of 0.534 (p = 0.804). The sensitivity and specificity of MRI for identifying cancer vs. no-cancer was 89.1% and 80% respectively, as compared to 45.5% and 57.5% for endoscopy. False positive rates of MRI and endoscopy were 20% and 42.5%, respectively. CONCLUSIONS: MRI is a more reliable diagnostic method than endoscopy in the Levrat model. The non-invasiveness of the tool and its potential to volumetrically quantify the size and number of tumors likely makes it even more useful in evaluating novel agents and their efficacy in treatment studies of esophageal cancer.

Xerostomia in complete denture wearers: prevalence, clinical findings and impact on oral functions.

OBJECTIVES: To investigate the prevalence of dry mouth in a select sample of edentulous Jordanian older population wearing complete dentures and to evaluate its impact on oral functions. BACKGROUND: The prevalence and impact of Xerostomia as a cofactor in causing denture problems in Jordanians have not been previously investigated. MATERIALS AND METHODS: This study included 455 participants (253 men and 202 women). Perception of dry mouth was measured by a pilot-tested questionnaire. Xerostomic status was confirmed clinically. Complete denture function was also assessed. RESULTS: One hundred and thirty six subjects (29.9%) had reported a subjective feeling of dry mouth with a prevalence of 24.9% in men (n = 63) and 36.1% in women (n = 73) (p < 0.01). 136 of the 145 subjects with satisfactory dentures showed one or more signs suggestive of Xerostomia. The majority of xerostomic participants with different sets of complete dentures were dissatisfied with oral functions (p < 0.05). There was a significant association between dry mouth and increasing age, female gender and smoking status (p < 0.05). CONCLUSION: Among complete denture wearers, Xerostomia is significantly more prevalent in women and associated with increased age and smoking. Xerostomia adversely affects oral functions and overall satisfaction with dentures.

Awareness, attitude, and expectations toward dental implants among removable prostheses wearers.

PURPOSE: To assess removable denture patient awareness, expectations, and source of information about dental implants (DIs). MATERIALS AND METHODS: Three hundred patients [150 removable partial denture (RPD) wearers and 150 complete denture wearers (CDWs)] attended the removable prosthodontic clinic at Faculty of Dentistry, Jordan University of Science and Technology. Patients were evaluated using a pilot-tested, 21-question questionnaire. RESULTS: Ninety-six percent of participants were aware of DIs, with no difference between CDWs and RPD wearers (p > 0.05). The participants' friends and relatives were the main source of information (63.4%), followed by dentists (32.4%). Improvement in function was the predominant reason (55.7%) for patients to consider DIs. Fear of unknown side effects was the major factor in preventing patients from choosing DIs (11.7%), followed by high cost (9.7%) and surgical risk (8.7%). Approximately 89% had no information or were poorly informed about DIs. Over two-thirds of patients did not know about the care (78.3%) of DIs, causes of DI failure (69.7%), or DI duration of service (80.7%). Only 24.7% knew that DIs would be anchored to the jawbone; however, 27.3% and 56.7% of CDWs and RPD wearers, respectively, preferred (p < 0.05) to have their teeth replaced with DIs. High costs were considered the major disadvantage of DIs in 45% of participants, followed by fear of surgery (27.3%), and long treatment times (24.7%). CONCLUSIONS: There was a high awareness about DIs among removable denture patients; however, this awareness was associated with a low level of accurate information.

The effect of subgingival ozone and/or hydrogen peroxide on the development of peri-implant mucositis: a double-blind randomized controlled trial.

PURPOSE: This double-blind randomized controlled trial assessed the effect of subgingival ozone (O3, gaseous ozone, HealOzone MK II, KaVo) and/or hydrogen peroxide (H2O2) on the development of peri-implant mucositis. MATERIALS AND METHODS: Twenty subjects (mean age, 60 ± 7.7 years) with 80 implants (4 implants each) were recruited. First, a 2-week pretrial phase took place to achieve healthy gingiva. Subsequently, partial gum shields were constructed for the experimental area (around the 4 implants); subjects were asked to refrain from brushing in that area by wearing the gum shield. The following treatments were randomly applied (for 60 seconds) to implant sites on days 0, 7, and 14: (1) air (O2) and saline (0.9% NaCl) (control group), (2) O2 and H2O2 (3%), (3) O3 and saline, and (4) O3 and H2O2. Plaque, gingival, and bleeding indices were recorded on days 0, 7, 14, and 21. RESULTS: Significant differences were seen among the treatments (P < .01) in plaque (F = 16.68), modified gingival (F = 7.86), and bleeding (F = 18.42) indices. O3 + saline and O3 + H2O2 produced optimum gingival health scores and were equally effective and the most effective in controlling bleeding (mean score = 0.05), while O2 + saline was the least effective (mean score = 0.56). CONCLUSION: Ozone showed great potential for management of peri-implant mucositis.

High-resolution 1H NMR investigations of the oxidative consumption of salivary biomolecules by oral rinse peroxides.

BACKGROUND: A multicomponent evaluation of the oxidative consumption of salivary biomolecules by a tooth-whitening oral rinse preparation has been performed using high-resolution proton ((1)H) nuclear magnetic resonance spectroscopy (NMR). METHODS: Unstimulated human saliva samples (n = 12) were treated with aliquots of the oral rinse tested and 600 MHz (1)H NMR spectra acquired on these samples demonstrated that hydrogen peroxide (H(2)O(2)) and/or peroxodisulphate (S(2)O(8) (2-)) present in this product gave rise to the oxidative decarboxylation of the salivary electron-donor pyruvate (to acetate and CO(2)), and also oxidized methionine (a precursor to volatile sulphur compounds responsible for oral malodour), and malodourous trimethylamine to methionine sulphoxide and trimethylamine-N-oxide, respectively (reductions observed in the salivary concentrations of each biomolecular peroxide-scavenging agent were all extremely statistically significant, p < 0.005). RESULTS: Experiments conducted on chemical model systems confirmed the consumption of pyruvate by this product, and also revealed that the amino acids cysteine and methionine were oxidatively transformed to cystine and methionine sulphoxide, respectively. CONCLUSIONS: High-field (1)H NMR analysis provides much valuable molecular information regarding the fate of tooth-whitening oxidants in human saliva and permits an assessment of the mechanisms of action of oral healthcare products containing these agents. The biochemical and potential therapeutic significance of the results obtained are discussed.

Undesirable and adverse effects of tooth-whitening products: a review.

Hydrogen peroxide (H(2)O(2)) is a powerful oxidising agent. It gives rise to agents known to be effective bleaching agents. The mechanisms of bleaching involve the degradation of the extracellular matrix and oxidation of chromophores located within enamel and dentin. However, H(2)O(2) produces also local undesirable effects on tooth structures and oral mucosa. In clinical conditions, the daily low-level doses used to produce tooth whitening never generate general acute and sub-acute toxic effects. Genotoxicity and carcinogenicity only occur at concentrations that are never reached during dental treatments. Some transient adverse effects have been reported on the oral mucosa and the digestive tract if the product is swallowed. Local effects may occur on the oral mucosa and dental tissues during whitening, namely, pulp sensitivity, cervical resorption, release of selected components of dental restorative materials, and alteration of the enamel surface. Most of the local effects are dependent of the technique and concentration of the product so far used, but as the results of bleaching obtained are not stable, repeated treatments add to the adverse effects. The informed decision to administer or not and the control of bleaching effects should stand in the hand of dental surgeons and certainly not as it appears at present, as cosmetics sold without any restriction despite the potential health hazards of peroxides.

A rare peripheral nervous system tumor: soft tissue perineurioma of the hallux.

UNLABELLED: Perineuriomas are rare tumors of the peripheral nervous system that occur as either intraneural or extraneural lesions. Intraneural perineuriomas generally affect the major nerve branches in the upper extremity, whereas extraneural perineuriomas have a predilection for the subcutaneous tissues of the lower extremities. In this article, we describe the case of an adult patient who had a perineurioma localized to the foot. LEVEL OF CLINICAL EVIDENCE: 4.

The effects of ozone gas application on shear bond strength of orthodontic brackets to enamel.

PURPOSE: To investigate the possibility that ozone may have an adverse effect on the bond strength of orthodontic brackets and to determine the area of residual adhesive on teeth after the debonding of brackets. METHODS: 60 extracted premolars teeth were used in this study. Resin coated APC brackets (3M) were bonded according to the manufacturers' instructions. Bonded teeth were randomly divided into two groups. The teeth in Group 1 were subjected to a 10-second dosage of ozone from the HealOzone unit (Kavo) after etching and to a further 10 seconds of ozone after bonding the brackets using a 5 mm delivery cup. Teeth in Group 2 were used as a control. Debonding was carried out using a testing instrument at a cross-head speed of 1 mm/minute. RESULTS: The Mann-Whitney test revealed no significant differences in shear bond strength between the two groups (P = 0.337). The mean shear bond strength (11.66 MPa) of Group 1 (subjected to ozone) was not significantly different than the mean shear bond strength (10.88 MPa) of Group 2 (not subjected to ozone). A Pearson Chi-square test of the Adhesive Remnant Index (ARI) revealed no significant difference in residual adhesive among the groups tested.

Effect of ozone on the oral microbiota and clinical severity of primary root caries.

PURPOSE: To assess the effect of ozone on the microbial flora and clinical severity of primary root caries. METHODS: 26 patients with 70 primary root carious lesions (PRCLs) were entered. Each PRCL was classified in terms of color, cavitation, size, hardness, distance from the gingival margin and severity. Overlying plaque was then removed and each lesion dried. A biopsy was taken from half of each PRCL using a sterile excavator. Subsequently, the remaining lesions were exposed to ozone gas for a period of either 10 seconds (n = 35) or 20 seconds (n = 35) and a further biopsy was taken. RESULTS: Using a paired Student t-test, a significant (P < 0.001) difference (mean +/- SE) in total micro-organisms was observed in the ozone-treated samples after either a 10 seconds (log10 4.35 +/- 0.49) or 20 seconds (log10 0.46 +/- 0.26) ozone application compared with the control samples (log10 7.00 +/- 0.24) and (log10 6.00 +/- 0.21) respectively. Using Pearson's correlation tests, there were significant correlations for the reduction in total micro-organisms after 10 seconds of ozone application with cavitation, size, distance from gingival margin and severity of PRCLs (P < 0.05). In conclusion, ozone application either for 10 or 20 seconds dramatically reduced most of the micro-organisms in PRCLs without any side effects recorded at recall intervals between 3 and 5.5 months. Out of the 65 PRCLs reviewed, 33 lesions had become hard, 27 lesions reversed to severity index 1 from severity index 2, and five lesions remained the same following ozone application for a period of either 10 or 20 seconds.