Jorge L. Zeredo

Periodontal and peri-implant wound healing following laser therapy

Laser irradiation has numerous favorable characteristics, such as ablation or vaporization, hemostasis, biostimulation (photobiomodulation) and microbial inhibition and destruction, which induce various beneficial therapeutic effects and biological responses. Therefore, the use of lasers is considered effective and suitable for treating a variety of inflammatory and infectious oral conditions. The CO2 , neodymium-doped yttrium-aluminium-garnet (Nd:YAG) and diode lasers have mainly been used for periodontal soft-tissue management. With development of the erbium-doped yttrium-aluminium-garnet (Er:YAG) and erbium, chromium-doped yttrium-scandium-gallium-garnet (Er,Cr:YSGG) lasers, which can be applied not only on soft tissues but also on dental hard tissues, the application of lasers dramatically expanded from periodontal soft-tissue management to hard-tissue treatment. Currently, various periodontal tissues (such as gingiva, tooth roots and bone tissue), as well as titanium implant surfaces, can be treated with lasers, and a variety of dental laser systems are being employed for the management of periodontal and peri-implant diseases. In periodontics, mechanical therapy has conventionally been the mainstream of treatment; however, complete bacterial eradication and/or optimal wound healing may not be necessarily achieved with conventional mechanical therapy alone. Consequently, in addition to chemotherapy consisting of antibiotics and anti-inflammatory agents, phototherapy using lasers and light-emitting diodes has been gradually integrated with mechanical therapy to enhance subsequent wound healing by achieving thorough debridement, decontamination and tissue stimulation. With increasing evidence of benefits, therapies with low- and high-level lasers play an important role in wound healing/tissue regeneration in the treatment of periodontal and peri-implant diseases. This article discusses the outcomes of laser therapy in soft-tissue management, periodontal nonsurgical and surgical treatment, osseous surgery and peri-implant treatment, focusing on postoperative wound healing of periodontal and peri-implant tissues, based on scientific evidence from currently available basic and clinical studies, as well as on case reports.

Role of Occlusal Vertical Dimension in Spindle Function

Several studies have suggested the jaw-muscle spindle as the receptor responsible for regulating and maintaining the occlusal vertical dimension (OVD). However, to challenge this assumption, we hypothesized that long-term changes in OVD could affect the sensory inputs from jaw-muscle spindles. In this study, we investigated changes in masseter muscle spindle function under an increased OVD (iOVD) condition. Responses of primary and secondary endings of masseter muscle spindles to cyclic sinusoidal stretches were investigated. Twenty barbiturate-anesthetized female Wistar rats were divided into control and iOVD groups. Rats in the iOVD group received a 2.0-mm composite resin build-up to the maxillary molars. After iOVD, masseter muscle spindle sensitivity gradually decreased. Primary and secondary spindle endings were affected differently. We conclude that iOVD caused reduction in masseter muscle spindle sensitivity. This result suggests that peripheral sensory plasticity may occur following changes in OVD. Such changes may provide a basis for physiological adaptation to clinical occlusal adjustments.

Functional Adaptability of Jaw-muscle Spindles after Bite-raising

In a previous experiment, we found that masseter muscle spindles show functional plasticity after 5 to 15 days under increased occlusal vertical dimension (iOVD). In the present study, we hypothesized that spindle function would eventually recover if longer observation periods were allowed. Therefore, in this study we investigated changes in masseter muscle spindle function over periods of 1 day to 8 weeks. Masseter muscle-spindle responses to ramp-and-hold jaw stretches were recorded from the mesencephalic trigeminal nucleus in 35 barbiturate-anesthetized female Wistar rats. The rats were previously divided into Control and iOVD groups, and those in the iOVD group received a 2.0-mm composite resin build-up to the maxillary molars. In this condition, there were no statistically significant differences in masseter muscle spindle sensitivity between Control and iOVD in the six- and eight-week subgroups. Our results further indicate a high degree of adaptability in masseter muscle spindle function following changes in OVD.

Effects of experimentally induced inflammation on temporomandibular joint nociceptors in rats

Response properties of nociceptors in the temporomandibular joint (TMJ) and surrounding area under experimental inflammation were investigated using an in vitro TMJ-nerve preparation in the rat. Nociceptive units (receptor and innervating nerve fiber) were classified into the following subtypes: Adelta-high-threshold mechanonociceptor (HTM), Adelta-polymodal nociceptor (POLY), C-HTM and C-POLY. In the inflamed joint, mechanical thresholds tended to be lower; however, the reaction to bradykinin was not identified as clearly as in control. Experimentally induced inflammation increased the proportion of heat-sensitive units and lowered heat threshold significantly. These results suggest that inflammation may sensitize nociceptors in the temporomandibular joint, and cause hyperalgesia and allodynia.

Antinociceptive effect of Er:YAG laser irradiation in the orofacial formalin test

Low-power, soft, or low-level laser irradiation has been successfully used to provide analgesia in injured or diseased tissues. In this study, we tested the possible antinociceptive effect of laser irradiation when applied to a normal tissue before the onset of a painful stimulus. Male Wistar rats (350-380 g) were used. A 1.5% formalin solution (50 microL s.c., diluted in saline) was injected into the right upper lip of the test animals (n = 9) immediately after 10 min of low-power Er:YAG laser irradiation (wavelength: 2.94 microm; energy: 0.1 J/cm(2)/pulse at 10 Hz). Control animals (n = 9) were restrained for 10 min without laser application. The nociceptive response, i.e., the amount of time the rats spent rubbing the formalin injected area, was measured by an investigator blind to whether the animals had been laser irradiated or not. On laser irradiated rats, significantly less nociceptive behavior was observed only during the late phase (12-39 min) of the test. This result is similar to that reported for nonsteroid antiinflammatory drugs (NSAIDs) and other peripherally acting antiinflammatory agents. We conclude that low-power laser irradiation have a tonic antinociceptive effect on inflammatory pain even when applied before tissue injury.

Emotional Stress- and Pain-Related Behaviors Evoked by Experimental Tooth Movement

OBJECTIVE To investigate by behavioral methods the relationship between emotional stress and pain during experimental tooth movement in rats. MATERIALS AND METHODS Sixteen male Sprague-Dawley rats (210 to 250 g) were divided into two groups. The experimental group was treated with an active Ti-Ni appliance, and the control group received a passive appliance. A force of 20 gf was delivered by the active appliance between the maxillary first and second molars for 3 days. During this period the rats behavior was evaluated eight times by means of open-field test and resistance-to-capture test. The specific parameters of animal activity were facial grooming, rearing, and locomotor activity, movement into the center of the open field, and response to capture. RESULTS Parameters related to stress and pain were higher in the group carrying active appliance, compared to the group with a passive appliance. Statistically significant differences in stress-related behavior between control and experimental groups were found 8 hours after placing the appliance and were most evident on the second day. Pain-related behavior was significantly greater in the experimental group than in the control group at 24 hours. CONCLUSIONS The increase in emotional stress evoked by orthodontic tooth movement may precede the appearance of periodontal pain.

Cardiac nociceptors innervated by vagal afferents in rats.

It is reported that cardiac afferent information is transmitted through at least three different pathways to the CNS: sympathetic, parasympathetic, and somatic; however, there are few studies concerning the role of afferent fibers of vagus nerves for eliciting cardiac sensation including pain. Especially, receptive field properties innervated by single vagal nerve fiber and mechanical threshold of nociceptors on the cardiac surface are not yet quantitatively studied. Therefore, in this study, we systematically investigated characteristics of vagal units innervating cardiac nociceptors in rats. Using anesthetized and artificially ventilated rats, 37 single unit recordings were made from fine nerve filaments of the left vagal nerve. For quantitative mechanical stimulation, the cardiac surface was stimulated by a von Frey type device. In addition, bradykinin was used for checking the chemical sensitivity of the nociceptor. Electrical stimulation was used to estimate the conduction velocity of the recorded nerve fiber. All units recorded from the vagal nerve were either Adelta- or C-polymodal nociceptors. About 70% of the afferents had conduction velocities in the C-fiber range. In 60% of the units, the peripheral receptive field covered spot-like areas, but we also found larger and continuous receptive fields. Our results show that a majority of nociceptors innervated by vagal afferents are the C-polymodal type with spot-like receptive fields. We consider it to relate to the ambiguous and dull pain of angina pectoris.

Effect of Celecoxib on Emotional Stress and Pain-Related Behaviors Evoked by Experimental Tooth Movement in the Rat

OBJECTIVE To test the efficacy of an animal model of pain and stress and evaluate the effects of celecoxib administered when orthodontic force is applied. MATERIALS AND METHODS A 20-g reciprocal force was applied via an orthodontic appliance to the maxillary left first and second molars of 7-week-old male Sprague-Dawley rats. Rat behavior was evaluated at 5, 24, and 48 hours after the appliance was set. Behavior was assessed in a test field by the number of lines crossed in the first 30 seconds and 5 minutes following force application; number of lines crossed to the center; rearing time; and facial grooming time. Experimental group 1 received intraperitoneal administration of 30 mg/kg celecoxib before every behavioral test. Experimental group 2 received 90 mg/kg before the first behavioral test, and physiologic saline was administered before the remaining behavioral tests. Control groups received saline before every behavioral test and were given passive (passive control group) and active (active control group) appliances, respectively. RESULTS Parameters related to pain increased in the active controls, whereas the parameters in the experimental groups decreased to the level seen in the passive controls. Statistically significant differences in pain-related behavior between control and experimental groups were found at 5 and 24 hours after placing the appliance. Stress-related behavior was significantly less in the experimental groups compared to the active control group during experimental periods. CONCLUSIONS The administration of celecoxib relieves pain- and stress-related behavior evoked by orthodontic tooth movement in the rat. This model might be a useful tool for the evaluation of pain and stress.

Effects of traditional “Juci” (contralateral acupuncture) on orofacial nociceptive behavior in the rat

Purpose“Juci”, one of the traditional acupuncture techniques, means contralateral acupuncture; i.e., implanting a needle into an acupoint to treat a given disease or disorder, but on the side of the body opposite to the diseased side. The aim of this study was: (1) to assess acupuncture effects on formalin-induced nociceptive behavior in the orofacial region in the rat, and (2) to evaluate the efficacy of Juci in the orofacial formalin test.MethodsForty-four adult male Wistar rats were used in the present study. A 1.0% formalin solution (25 µl s.c., diluted in saline) was injected into the right upper lip. The rats were randomly assigned to five groups. (1) The control group (n = 9), which received formalin injection without acupuncture pretreatment; (2) the ipsilateral Ho-ku (see note below) acupuncture group (n = 10); (3) the contralateral Ho-ku acupuncture group (n = 11); (4) the acupuncture plus naloxone group (n = 9), where intraperitoneal naloxone (1.0 mg·kg−1) was injected immediately before acupuncture pretreatment; and (5) the sham acupuncture group (n = 5). “Ho-ku” is the term used for the “Large Intestine 4” acupoint, located between the first and second metacarpal bones.ResultsThe injection of formalin produced the characteristic biphasic behavioral response. Acupuncture significantly inhibited the response in the early and late phases. Naloxone significantly reversed these effects. There were no statistically significant differences between the ipsilateral and Juci acupuncture groups. Sham acupuncture did not exert any significant effect on the formalin-induced behavior.ConclusionOur results showed that the degree of effectiveness of Juci was similar to that of the ipsilateral acupuncture technique. Therefore, the Juci technique is also useful for the treatment of orofacial pain.

Response Properties of Nucleus Reticularis Lateralis Neurons After Electroacupuncture Stimulation in Rats

A descending inhibitory mechanism from the periaqueductal gray (PAG) to the spinal cord through the nucleus raphe magnus (NRM) is strongly involved in endogenous analgesic system produced by acupuncture stimulation. In addition to the PAG to NRM system which descends in the medial pathway of the brain stem, the nucleus reticularis lateralis (NRL) situated in the lateral part of the brain stem is reported to play an important role in modulating centrifugal antinociceptive action. In the present study, to clarify the role of NRL in acupuncture analgesia, we investigated the response properties of NRL neurons to acupuncture stimulation. The majority of NRM-projecting NRL neurons were inhibited by electroacupuncture stimulation. This effect was antagonized by ionophoretic application of naloxone, indicating that endogenous opioids act directly onto these NRL neurons. By contrast, about half of spinal projecting NRL neurons were excited by electroacupuncture stimulation, suggesting that part of the NRL neurons may modulate pain transmission directly at the spinal level.