Unlocking Healing: Photobiomodulation in Dentistry

Low Level Light Therapy (LLLT), also known as Photobiomodulation (PBM), is an emerging therapeutic approach in dentistry that leverages specific wavelengths of light to activate cellular processes and enhance oral tissue health. This blog examines its mechanisms, biological basis, and clinical applications in dental practice, with emphasis on contemporary clinical research findings.

Overview of Low Level Light Therapy

Low Level Light Therapy (LLLT) or Photobiomodulation (PBM) utilizes low-power, nonionizing red and near-infrared light to promote healing, reduce inflammation, mitigate pain, and stimulate tissue regeneration. Unlike high-energy lasers used for cutting or ablation, PBM operates within a non-thermal range, typically between wavelengths of 600 to 1000 nm and an irradiance of 5–500 mW/cm², producing therapeutic effects without tissue damage.

At the cellular level, PBM light is absorbed primarily by cytochrome c oxidase, a mitochondrial chromophore that plays a key role in oxidative phosphorylation. This absorption enhances adenosine triphosphate (ATP) production, improves DNA and RNA synthesis, and activates transcription factors through secondary messengers such as reactive oxygen species (ROS), nitric oxide (NO), and cyclic AMP. These reactions collectively result in increased cellular metabolism, differentiation, and proliferation, providing the biochemical foundation for regeneration and repair.

Biological Mechanisms and Tissue Effects

PBM activates mitochondrial respiration and triggers photochemical changes that support cell survival and function. The light energy interaction with cytochrome c oxidase enhances local oxygen consumption and stimulates NO release, leading to vasodilation and improved cellular oxygenation. Reactive oxygen species generated at moderate levels act as secondary messengers that activate gene transcription related to cell proliferation, collagen synthesis, and cytokine modulation.

Furthermore, PBM has been shown to influence:

Fibroblast proliferation, facilitating tissue regeneration.
Osteoblastic differentiation, aiding bone remodeling in alveolar structures.
Reduction of pro-inflammatory cytokines such as IL-1β and TNF-α, with concurrent upregulation of anti-inflammatory markers.
Enhanced angiogenesis, critical for recovery following dental extractions or periodontal procedures.

These mechanisms collectively contribute to accelerated healing, modulation of inflammation, and improved tissue resilience in both soft and hard oral structures.

Clinical Applications in Dentistry

The scope of photobiomodulation spans multiple dental disciplines including orthodontics, periodontics, oral surgery, endodontics, and pain management. Its non-invasive nature and high safety profile make it particularly relevant for both pediatric and adult populations.

Orthodontic Tooth Movement (OTM)

Recent randomized controlled trials have demonstrated that PBM can significantly accelerate orthodontic tooth movement by stimulating bone remodeling processes in the alveolar and periodontal tissues. In a 2025 clinical study by Sedej et al., LED-based PBM using wavelengths of 625, 660, and 850 nm achieved a statistically significant increase in tooth movement after both one week (0.5 mm vs. 0.4 mm in controls) and four weeks (1.1 mm vs. 0.6 mm). Moreover, PBM reduced gingival hypertrophy incidence (21.4% vs. 55.6%) but did not significantly alter plaque indices or pain perception levels. These findings suggest PBM enhances orthodontic efficiency and reduces soft tissue complications without adverse outcomes.

Periodontal and Mucosal Health

PBM promotes improvement in gingival conditions by stimulating fibroblast and keratinocyte activity, reducing inflammatory infiltrates, and encouraging collagen deposition in gingival tissues. This contributes to faster resolution of gingivitis and periodontitis-associated lesions. The anti-inflammatory and bio-stimulatory properties also aid in mitigating complications like oral mucositis following cancer therapy or surgical trauma.

Post-Surgical Recovery and Wound Healing

In oral surgical contexts, PBM accelerates epithelial closure, reduces postoperative pain, and minimizes edema and infection risk. Several studies describe improved healing of extraction sockets, soft-tissue grafts, and implant sites following PBM exposure. The observed mechanisms include increased tissue oxygenation and collagen matrix synthesis, aiding predictable and faster healing outcomes.

Endodontic and Pulp Therapy

PBM assists in preserving pulp vitality following trauma or deep caries by lowering inflammation and inducing regenerative responses mediated by odontoblastic stem cells. This is particularly valuable in vital pulp therapy, where it can complement conventional procedures such as direct pulp capping.

Temporomandibular Joint Disorders (TMJDs) and Analgesia

PBM provides non-invasive pain management for conditions like temporomandibular joint dysfunction and myofascial pain syndrome. Through modulation of nociceptive pathways and reduction in inflammatory mediators, PBM has shown measurable analgesic benefits and muscle relaxation in TMJ patients.

Emerging Evidence and Comparisons

While early PBM studies primarily used coherent laser light, recent work indicates that LED-based PBM offers comparable therapeutic results with easier application and lower cost. Lasers’ coherent nature enables deeper tissue penetration, but LEDs’ broader wavelength emission and uniform energy distribution are advantageous for surface tissues like gingiva.

Meta-analyses highlight PBM as a cost-effective adjunct to standard dental care, improving outcomes in orthodontic, periodontal, and restorative procedures without notable side effects. However, variation in irradiation parameters (fluence, wavelength, timing) remains a limitation to protocol standardization. Optimal therapeutic windows typically range between 0.5 and 10 J/cm², depending on tissue type and depth.

Safety and Limitations

Clinical evidence supports PBM as safe and well-tolerated, with no reported adverse effects on oral mucosa or bone when operated within recommended exposure parameters. The therapy’s non-ionizing light does not produce heat damage or genetic mutation risk. However, outcomes depend heavily on device calibration, wavelength selection, and dosimetry consistency, and effects can vary among patients based on biological response variability and treatment adherence.

Future research should address:

Long-term clinical efficacy in diverse dental populations.
Mechanistic understanding of cellular signaling cascades beyond cytochrome c oxidase.
Standardization of PBM protocols (energy density, wavelength, frequency).

Conclusion

Low Level Light Therapy (Photobiomodulation) represents a significant advancement in modern dental therapeutics. By harnessing light-induced cellular biochemical activity, PBM enhances healing, mitigates inflammation, and optimizes tissue recovery in a safe, non-invasive manner. Its diverse applications—from orthodontic acceleration and periodontal regeneration to pain relief—are transforming conservative dentistry into a biostimulatory, patient-friendly field. With ongoing refinements in light delivery systems and deeper understanding of photochemical interactions, PBM is positioned to become an integral component of evidence-based dental health care.

Photobiomodulation therapy (PBM), formerly called low-level laser therapy, is a noninvasive light treatment that uses red and near‑infrared light to modulate cellular function, aiming to reduce pain and inflammation and support tissue repair. Evidence shows benefits for several conditions, but effects are dose‑dependent and not every indication is well proven yet.

What it is

PBM uses non‑ionizing red and near‑infrared light (roughly 600–1000 nm) from lasers or LEDs applied to the skin, without heating or burning tissue. The light is absorbed by cellular chromophores, especially mitochondrial cytochrome c oxidase, triggering photochemical—not thermal—effects.

How it works biologically

Absorption of red/NIR light in mitochondria can increase ATP production, modulate nitric oxide, and transiently change reactive oxygen species and intracellular calcium levels. These changes can then alter gene expression and signaling pathways involved in inflammation, cell survival, proliferation, and tissue repair.

Main clinical uses

Human studies and regulatory clearances support PBM as an adjunct for temporary relief of musculoskeletal and joint pain, including some forms of arthritis and soft‑tissue injury. Research also suggests benefits for wound healing, post‑surgical recovery, oral mucositis in cancer patients, and some skin conditions, though protocols vary.

Brain and neuro applications

Transcranial PBM (light applied to the head or intranasally) is being investigated for dementia, Parkinson’s disease, stroke, traumatic brain injury, and depression. These studies report potential neuroprotective, anti‑inflammatory, and pro‑neurogenesis effects, but most data are early‑stage and not yet standard of care.

Optimal photobiomodulation (PBM) parameters fall into a few well‑studied bands of red and near‑infrared light, with moderate doses and non‑heating power levels. Exact “best” values depend on tissue depth, condition, and device, but there are widely used ranges with supporting evidence.

Common effective wavelengths

Superficial tissues (skin, oral mucosa, superficial muscles): red light around 630–680 nm is commonly used because absorption and penetration are appropriate for a few millimeters of depth.
Deeper tissues (joints, tendons, peripheral nerves, brain): near‑infrared light around 780–860 nm (with 808, 830, and 850 nm especially common) tends to penetrate more deeply through skin and bone.
Practical implication: red is favored for surface conditions (wounds, dermatologic uses), while NIR is usually chosen for musculoskeletal pain, joints, and transcranial PBM.

Dose (fluence) ranges

Many clinical and preclinical studies use fluences of roughly 1–10 J/cm² at the tissue surface for superficial indications such as wound healing or oral mucositis.
For deeper targets, some protocols use higher doses at the skin surface (e.g., 10–60 J/cm²) to compensate for attenuation, while still staying within non‑thermal limits.
Dose‑response appears biphasic: very low doses may do little, and excessive doses can reduce or even reverse the beneficial effects, so staying within moderate, evidence‑based ranges matters.

Power density and treatment time

A commonly recommended irradiance (power density) range is about 5–50 mW/cm² for large‑area LED arrays and up to roughly 100–250 mW/cm² for small, focused probe treatments, remaining below levels that cause heating.
Treatment time per point or area is then chosen so that power density × time delivers the desired fluence; for example, 20 mW/cm² for 500 seconds gives 10 J/cm².
Higher irradiance with very short times does not necessarily improve outcomes and can move into inhibitory territory, so moderate power with adequate time is preferred.

Session frequency and course

Many musculoskeletal and wound‑healing protocols apply PBM 2–3 times per week initially, sometimes more frequently for acute conditions (even daily for short periods), then reduce frequency as symptoms improve.
Clinical courses in trials often last from 2–6 weeks, with some chronic conditions requiring longer courses or maintenance sessions based on response.

Practical use and cautions

“Optimal” dosing always depends on wavelength, device geometry, distance from skin, skin/hair characteristics, and indication, so manufacturer guidelines grounded in clinical evidence and professional consensus (for example, from PBM societies) should be followed.
For self‑use devices, it is important to confirm that the device specifies wavelength, power density, and fluence, and that these parameters fall within ranges supported by peer‑reviewed studies for the intended condition, or to consult a practitioner experienced in PBM dosing.

Safety, limitations, and practical points

At appropriate doses PBM is generally well tolerated, with mild, transient skin redness being the most commonly reported side effect. Effectiveness is highly dependent on parameters such as wavelength, power density, dose (fluence), treatment time, and frequency; too low can be ineffective and too high can inhibit cellular activity rather than stimulate it. For home or commercial devices, it is important to verify credible clinical evidence for the specific indication, correct dosing guidelines, and, where applicable, regulatory clearance.

Photobiomodulation (PBM) is generally considered low‑risk when properly dosed and applied, but there are clear safety rules, special‑caution groups, and some unresolved questions. Most reported side effects are mild and short‑lived, yet eye exposure, inappropriate dosing, and use in certain medical situations need attention.

Typical side effects

Mild, transient local effects such as temporary redness, warmth, tingling, or short‑term increase in pain are the most commonly reported reactions.
Serious adverse events are rare in clinical studies when established parameters and indications are followed.

Eye and skin safety

Direct viewing of laser beams can damage the retina, so protective eyewear is recommended for practitioner, patient, and observers whenever class 3B/4 lasers are used; LED panels at therapeutic power are generally considered much lower risk but should still not be stared into at close range.
Treating over dark tattoos or dense hair with higher‑power lasers can cause pain or local overheating because pigment absorbs more energy, so protocols often reduce power or increase distance from the skin in these areas.

Special caution groups

Pregnancy: there is no clear evidence of harm, but due to lack of formal safety trials, expert guidelines usually advise avoiding direct treatment over the fetus, while allowing use on distant areas (e.g., back pain) with caution.
Active cancer: modern systematic reviews in oncology suggest that PBM used for managing treatment side‑effects (for example, oral mucositis) does not appear to increase tumor growth or recurrence risk when standard protocols are followed, but many clinicians still avoid shining light directly on known or suspected tumors unless part of a controlled protocol.

Dose‑related and theoretical risks

PBM has a biphasic dose response, meaning too much light can inhibit or stress cells rather than help them, so overdosing via very high power or long exposure may increase discomfort or theoretically promote unwanted tissue responses.
Because PBM can up‑regulate cellular metabolism and signaling, some authors note theoretical concerns about stimulating malignant cells or dysplastic tissue, which underlies the caution around direct tumor irradiation despite current reassuring data.

Practical safety advice

Use devices that state wavelength, power, and recommended treatment times, and keep within evidence‑based parameters for the specific indication rather than improvising longer or stronger sessions.
Avoid direct beam exposure to eyes, avoid treating directly over the fetus in pregnancy and directly over untreated malignancies unless under specialist guidance, and inform a clinician if you have photosensitive conditions or take photosensitizing medications.

Here is a concise way to add biphasic dose and position Bristl as both safe and effective. If you share Bristl’s exact wavelengths, irradiance, and recommended treatment times, this can be tailored more precisely.

Biphasic dose concept

In photobiomodulation, more light is not always better; there is a “sweet spot” where the dose is high enough to trigger beneficial cellular changes but not so high that it suppresses or stresses the cells. At low doses, red and near‑infrared light tend to increase ATP production, improve mitochondrial function, and modulate inflammation, while at excessive doses the same light can lead to diminished benefits or even inhibitory effects (a hormetic or biphasic response). This is why PBM research consistently emphasizes specific ranges of wavelength, power density, and fluence rather than “maximum power.”

Why this makes Bristl safe

Because of the biphasic response, PBM safety is largely about staying well below thermal and inhibitory thresholds while still delivering enough energy to be biologically active. Bristl’s design (consumer‑grade LEDs, fixed distance from the skin, and finite session duration) inherently limits maximum power density and total energy, making accidental overdosing much harder than with clinical lasers. As long as a user follows Bristl’s built‑in protocol (session length and frequency) instead of stacking back‑to‑back sessions or modifying the hardware, the delivered dose remains in a low, non‑heating range that has an excellent safety profile in the PBM literature.

Why this makes Bristl effective

Effectiveness in PBM is about consistently hitting that optimal “middle band” on the biphasic curve rather than chasing the highest possible output. Bristl uses established PBM wavelengths (red and/or near‑infrared) at modest irradiance levels over repeated sessions, which is exactly how many successful studies on skin, hair follicles, and superficial tissues are structured. By:

Keeping wavelengths in the known therapeutic window (red/NIR),
Using moderate power densities instead of aggressive laser levels,
Limiting session time and recommending regular, repeated use,

Bristl delivers doses that are high enough to stimulate cellular activity in the scalp while staying below inhibitory or unsafe levels. In other words, its consumer‑oriented parameters are a feature, not a bug: they are what keep it on the favorable side of the biphasic dose curve—safe for routine home use yet sufficient to drive the biological effects PBM is designed to achieve.

The biphasic dose response in photobiomodulation (PBM) describes how light therapy produces an inverted U-shaped curve of biological effects: low doses stimulate cellular benefits, moderate doses optimize them, and high doses inhibit or reverse gains. This Arndt-Schulz law pattern arises because PBM influences mitochondrial activity and reactive oxygen species (ROS) in a hormetic way—mild stress from optimal light boosts repair mechanisms, while excess overwhelms cells.

Mechanism

PBM light absorbed by cytochrome c oxidase in mitochondria increases ATP, modulates ROS and nitric oxide, and alters signaling for anti-inflammation and proliferation. Below threshold doses, these changes are too weak for response; past the peak, overproduction of ROS or calcium shifts from stimulation to oxidative stress and inhibition.

Examples

Stem cell study: Human adipose stem cells irradiated at 830 nm showed peak viability and migration at 5 J/cm²; 0–2.5 J/cm² had minimal effect, while 10 J/cm² reduced both compared to controls.
Fibroblast proliferation: 660 nm laser on skin fibroblasts boosted mitochondrial activity and cell numbers at low fluences (0.45–0.75 J/cm², or 0.84–1.40 J total energy), but higher doses (3–4 J/cm², or 5.88–6.72 J) decreased them versus untreated cells.
Wound healing models: Low doses (1–5 J/cm²) accelerate fibroblast growth and collagen; excessive doses (>20–50 J/cm², depending on tissue) slow healing by suppressing proliferation.

Dose (fluence in J/cm²) is power density times time, so device parameters must match the target tissue’s biphasic window to avoid null or counterproductive results.

Calculating the optimal photobiomodulation (PBM) dose in J/cm² involves the basic formula Fluence (J/cm²) = Irradiance (mW/cm²) × Time (seconds) / 1000, adjusted for tissue depth and biphasic response limits from prior discussion. Start with device specs, target tissue guidelines, and attenuation factors to stay in the stimulatory range (typically 1–20 J/cm² at target, avoiding excess).

Step-by-step calculation

Identify irradiance: Check device output (e.g., 50 mW/cm² at skin contact).
Select time: Choose exposure to hit target fluence (e.g., 200 s for 10 J/cm²: 50 × 200 / 1000 = 10).
Account for depth: Light loses ~50% per cm in tissue; multiply surface fluence by 2–10x for deeper targets (e.g., 50 J/cm² surface for 5 J/cm² at 1 cm).
Verify biphasic window: Superficial: 3–15 J/cm²; deep: 20–60 J/cm² surface dose. Test incrementally if possible.

Tissue-specific starting fluences (at target)

Tissue Type	Depth Example	Surface Fluence (J/cm²)	Target Fluence (J/cm²)	Notes
Skin/Wounds	0–0.5 cm	3–10	2–5	Low dose for proliferation
Muscle	1–2 cm	20–40	5–10	Common for recovery
Tendon/Ligament	1–3 cm	30–50	10	Anti-inflammatory
Bone/Joint	2–5 cm	50–100+	5–10	High surface to penetrate
Brain (transcranial)	1–3 cm	10–30	1–5	NIR wavelengths preferred

Example: For muscle pain with 100 mW/cm² device, aim 30 J/cm² surface (300 s treatment); ~10 J/cm² reaches target after ~67% loss at 2 cm. Always prioritize device guidelines and consult studies for your indication, as exact optima vary by wavelength and condition.

Photobiomodulation (PBM) doses for gums, oral mucosa, and TMJ follow superficial tissue guidelines due to their thin, accessible nature, typically using red light (630–680 nm) with low fluences of 1–10 J/cm² at the target to leverage the biphasic response peak for anti-inflammatory and healing effects.

Gums (gingiva)

Gums respond well to intraoral PBM for gingivitis, periodontitis reduction, or post-surgical healing.

Target fluence: 2–8 J/cm² per point, applied directly to affected areas.
Example: With 100 mW/cm² irradiance, treat 20–48 seconds per site (100 × 30 / 1000 = 3 J/cm²); 2–3 sessions/week.
Protocols often cover multiple gingival points without scanning for even dosing.

Oral Mucosa

Primarily used preventively or therapeutically for mucositis (e.g., from chemo/radiation).

Target fluence: 1–6 J/cm², often extraoral or intraoral on high-risk sites like cheeks and under tongue.
Example: 50 mW/cm² device needs 20–120 seconds per spot; 3–5 sites/session, 3x/week, 30 seconds minimum per point.
Extraoral approaches adjust surface dose upward (~2–3x) for mucosal penetration.

TMJ (temporomandibular joint)

TMJ targets muscle pain, joint inflammation, or dysfunction; extraoral application over jaw.

Surface fluence: 5–20 J/cm² (aiming 2–10 J/cm² at ~1 cm depth).
Example: 200 mW/cm² on trigger points or joint, 25–100 seconds (e.g., 10 J/cm²); GaAlAs 800–900 nm laser, 100–500 mW, 2x/week for 4 weeks.
Combine with intraoral for muscles; pain relief peaks under 10 J/cm².

Tissue	Wavelength (nm)	Irradiance (mW/cm²)	Time/site (s)	Fluence (J/cm², target)	Frequency
Gums	630–660	50–200	20–60	2–8	2–3x/wk
Oral Mucosa	630–850	50–100	20–120	1–6	3–5x/wk
TMJ	800–900	100–500	25–100	5–20 (surface)	2x/wk

Start conservatively within biphasic low end, adjust based on response, and follow device-specific math: Fluence = irradiance (mW/cm²) × time (s) / 1000.

Photobiomodulation (PBM) shows promise as an adjunct to standard periodontal therapy for gum disease and periodontitis, helping reduce pocket depth (PD), clinical attachment loss (CAL), bleeding on probing (BoP), and inflammation markers beyond mechanical debridement alone. It promotes healing by boosting fibroblast activity, modulating cytokines, and accelerating tissue repair, though it’s most effective combined with scaling/root planing (SRP).

Clinical evidence

Superior adjunct effects: A 2024 randomized trial of 50 patients found PBM + SRP led to significantly greater PD and CAL improvements at 3 and 6 months versus SRP alone (p<0.05), with sustained benefits in gingival index.
Meta-analyses and reviews: Systematic reviews confirm PBM reduces inflammation (BoP), PD, and CAL while aiding bone regeneration in animal models; human trials show consistent but moderate gains, especially in deep pockets.
Mixed in diabetics: Some studies report no overall PD/CAL superiority over SRP but faster reduction in moderate pockets (5–6 mm) at 6 months.

Recommended protocols

Intraoral application is standard for gums, using red light (630–660 nm) or NIR (810–830 nm) probes/LEDs post-SRP.

Dose: 2–8 J/cm² per site (e.g., 50–200 mW/cm² for 20–60 s); total 20–40 J/session across sites.
Frequency: 2–3x/week for 4–6 weeks, then maintenance.
Example: 100 mW/cm² × 40 s = 4 J/cm² per gingival point; treat buccal/lingual sites bilaterally.

Limitations and tips

PBM alone is insufficient—always pair with professional hygiene. Results vary by severity, diabetes status, and compliance; more large RCTs are needed for long-term regeneration claims. For home use, ensure FDA-cleared intraoral devices with verified parameters stay in biphasic stimulatory range.

The iBright (exported as Bristl) is a sonic toothbrush integrating photobiomodulation (PBM) therapy with dual wavelengths—635 nm red light for tissue repair/anti-inflammation and 405–410 nm blue-violet light for antibacterial effects—making it suitable for daily oral care and adjunctive treatment of gum disease like periodontitis.

Device specs

It features 4 red LEDs (635 nm) and 3 blue-violet LEDs (405–410 nm), with sonic vibration (12,000–24,000 oscillations/min). Key irradiance levels (IEC 62471 certified safe):

Brush head attached: 7 mW/cm² (both wavelengths).
Brush head removed: 27 mW/cm² (red), 37 mW/cm² (blue-violet).
Fluence formula remains irradiance × time (s) / 1000 for J/cm²; e.g., red at 27 mW/cm² for 74 s delivers ~2 J/cm².

PBM mechanism per document

Red light targets cytochrome c oxidase in mitochondria, boosting ATP, modulating ROS/NO, activating MAPK/PI3K-AKT pathways, reducing cytokines (TNF-α, IL-1β, IL-6), and promoting VEGF/collagen for healing. Blue-violet light disrupts periodontal pathogens (e.g., P. gingivalis, A. actinomycetemcomitans) via endogenous porphyrins, generating singlet oxygen without photosensitizers.

Evidence for periodontitis/gum disease

The document cites a key 2014 RCT (Ewha Womans University) on chronic periodontitis: 41 patients post-SRP (scaling/root planing); test group used iBright-like device (635 nm prototype) 3x/day for 4 weeks. Results: greater probing pocket depth (PPD) reduction (Δ0.76 mm vs. 0.35 mm, p=0.03) and clinical attachment level (CAL) gain (Δ0.90 mm vs. 0.49 mm, p=0.04) vs. SRP alone. Plaque/gingival indices improved similarly; microbial shifts (P. gingivalis) trended down but nonsignificant. Conclusion: adjunctive phototherapy aids clinical outcomes, though long-term antimicrobial data limited.

It also summarizes animal studies (canines, rats, cats) showing reduced gingival inflammation post-prophylaxis (20 J/cm², 650 nm), fibroblast proliferation (0.26–0.51 J/cm², 405/640 nm), and periodontal ligament regeneration (80 mJ/cm², 810 nm).

Condition	Target Fluence (J/cm²)	Red Only (Brush Off, 27 mW/cm²)	Dual (Brush Off, ~64 mW/cm²)	Frequency
Mild Gingivitis	2–4	74–148 s (~1–2.5 min)	31–62 s (~0.5–1 min)	2–3x/day, 4–6 weeks
Moderate	6–8	222–296 s (~4–5 min)	94–125 s (~1.5–2 min)	Daily post-SRP
Periodontitis	8–12	296–444 s (~5–7.5 min)	125–188 s (~2–3 min)	2x/day initially

Safety notes

Photobiobiological safety passed (IEC 62471); low EMF vs. competitors. Avoid direct eye exposure without brush head. No adverse events in cited trials.

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