Khaldoun Rifai

Nociceptive behaviour induced by dental application of irritants to rat incisors: a new model for tooth inflammatory pain.

Animal models simulating acute human pulpitis are still lacking. The rat incisors present a particular situation where most of their innervation is considered to be unmyelinated and concentrated mainly in the tooth pulp. This study reports on a new model for dental pain induced by inflammatory agents applied to the tooth pulps of incisors. In different groups of rats, artificial crowns were fixed on the lower incisors, after cutting 1–2 mm of their distal extremities. A volume of 7–10 μl of solutions of saline, capsaicin (1–10 mg/ml) or formalin (2.5% or 5%) was injected in the crown cavity, and the nociceptive behaviour was quantitated following a devised scoring method of four scales. Intradental application of capsaicin produced nociceptive scores in the form of one plateau for 1–2 h depending on the concentration used. Similar results were obtained with intradental application of formalin 2.5%. The one plateau of nociceptive scores obtained with formalin contrasts with the biphasic aspect of nociceptive behaviour described with the intradermal formalin test. This discrepancy could be attributed to a difference in the types of afferent fibres involved in each situation. Pretreatment with morphine (2 mg/kg) attenuated, in a naloxone‐reversible manner, the nociceptive behaviour observed following intradental application of capsaicin. Pretreatment with meloxicam (a cyclo‐oxygenase‐2 inhibitor) exerted a less pronounced attenuation of the nociceptive scores when compared with morphine. These results provide evidence for the validity of the described model for the simulation of tooth pulp inflammatory pain in awake animals.

Inflammatory mediators released following application of irritants on the rat injured incisors. The effect of treatment with anti-inflammatory drugs

The exchange of fluids and chemicals between the tooth pulp and the periphery, through the dentinal tubules has been well documented. Application of irritants on the open tubules produces aversion in awake rats that can be prevented by prior occlusion of these tubules. This study aims at characterizing the secretion of inflammatory mediators in tooth perfusates and assessing the effects of systemic pretreatment with anti-inflammatory drugs on the levels of these mediators. Several groups of rats (n=5-6 each) were used for intradental application of either saline, capsaicin (100 microg in 100 microl), or endotoxin (20 microg in 100 microl) for a period of 40 min followed by filling the perfusion chamber with sterile saline and collecting the perfusate every 30 min for 6h. The perfusates were used for the determination of the concentrations of cytokines by ELISA. Application of irritants produced a highly significant increase in PGE2 (peak at 2h) and NGF (peak at 4-6h). Dexamethasone antagonized the effects of endotoxin and capsaicin, while NSAID affected mainly the endotoxin-induced inflammation. Our results confirm the validity of the tooth perfusion technique and demonstrate that the efficacy of treatment with anti-inflammatory drugs depends on the type of inflammation.

A perfusion technique for the determination of pro-inflammatory mediators induced by intradental application of irritants.

INTRODUCTION Several morphological and functional features contribute to the consideration of the tooth as a separate compartment having special type of innervation and special immune mechanisms. This study describes a new method allowing the intradental perfusion of rat incisors for the in vivo assessment of pulpal reaction to inflammatory agents. METHODS Under deep anesthesia, the distal 2-3 mm of each of the rat lower incisors was cut and wrapped in a polyethylene tubing connected to a perfusion chamber made of tigone tubing (ID 1/8 in., volume 100-150 microl). Several groups of rats (n=5 each) were used for intradental application of either saline, capsaicin (100 microg in 100 microl), or endotoxin (ET, 20 microg in 100 microl) for a period of 40 min followed by filling the tooth chamber with saline and collecting the perfusate every 40 min for a period of 8 h. The collected perfusates were stored at -70 degrees C for subsequent determination of the concentration of prostaglandin E(2) (PGE(2)) and nerve growth factor (NGF) by enzyme-linked immunosorbent assay (ELISA). RESULTS Dentinal injury produced a moderate increase in the levels of NGF and PGE(2) in incisors perfused with saline. Application of ET or capsaicin, however, produced a highly significant increase in the levels of both mediators. These effects peaked at 1.5-3 h for PGE(2) and at 5 h for NGF. Capsaicin showed the most significant effects. DISCUSSION The reported results cannot be attributed to any factor other than the inflammation of the incisors pulp, because the described chamber does not allow any spread or leak of the applied irritants. Further studies using other reagents can allow the determination of the variation of the levels of the various pro-inflammatory mediators and their modulation by treatment with anti-inflammatory drugs.

Fit of pressed crowns fabricated from two CAD-CAM wax pattern process plans: A comparative in vitro study

Statement of problem. Subtractive and additive computer‐aided design and computer‐aided manufacturing (CAD‐CAM) wax pattern processing are 2 methods of fabricating a pressed ceramic crown. Whether a subtractive milled wax pattern or a pattern from the micro‐stereolithography additive process produces lithium disilicate crowns with better marginal and internal fit is unclear. Materials and methods. Ten silicone impressions were made for a prepared canine tooth. Each die received 2 lithium disilicate (IPS e.max) copings, 1 from milled wax blocks and 1 from additive wax. The replica technique was used to measure the fit by scanning electron microscopy at ×80 magnification. Collected data were analyzed using the paired Student t test for the marginal and internal fit. For the occlusal fit, the difference in scores did not follow a normal distribution, and the Wilcoxon signed rank test was used (&agr;=.05). Results. The mean marginal, axial, and occlusal fit showed no significant differences when the 2 CAD‐CAM manufacturing processes were compared (P>.05). For the marginal fit, the mean (±SD) values were 105.1 &mgr;m ±39.6 with the milled process and 126.2 &mgr;m ±25.2 for the additive process. The mean values were 98.1 &mgr;m ±26.1 for the axial fit in the milled process and 106.8 &mgr;m ±21.2 in the additive process. For the occlusal fit, median values (interquartile interval) were 199.0 &mgr;m (141.5 to 269.9) for subtractive manufacturing and 257.2 &mgr;m (171.6 to 266.0) for micro‐SLA manufacturing. Conclusions. No significant difference was found between the fit of the 2 techniques. The mean values of axial and occlusal median values were 10 and 5 to 6 times greater than machines nominal values.

Leakage evaluation of original and compatible implant–abutment connections: In vitro study using Rhodamine B

Leakage has been addressed as a major contributing factor to inflammatory reactions at the implant–abutment connection, leading to problems such as oral malodor, inflammation, and marginal bone loss. The aim of this study was to investigate in vitro the leakage at implant–abutment interface of OsseoSpeed™ implants connected to original and compatible abutments. A total of 28 OsseoSpeed implants were divided into four groups (n = 7). Each group was connected to four different abutments according to manufacturers’ recommendations: group A (TiDesign™); group B (Natea™); group C (Dual™); and group D (Implanet™) abutments. The inner volume of each implant–abutment combination was calculated and leakage was detected for each group with spectrophotometric analysis at 1 h (D0) and 48 h (D1) of incubation time using Rhodamine B. At 1 h, leakage volume was significantly lower in TiDesign and Dual than in Natea and Implanet (P < 0.001). At 48 h, however, leakage was significantly lower between TiDesign and all other systems (P < 0.005). Compatible abutments do not fit internal connection of OsseoSpeed implants perfectly, which increases the leakage of the final assembly.

Modulation of incisor eruption in rats by sympathetic efferents

INTRODUCTION Intact neural supply is necessary for tooth eruption. Sympathetic denervation accelerates or decelerates the eruption rate depending on the tooth condition (intact or injured). The aim of this study is to reexamine the role of the sympathetic innervation, through the observation of the effects of pre or post ganglionic chemical sympathectomy on the eruption of intact rat incisors. MATERIALS AND METHODS Different groups of rats were subjected to either ganglionic or peripheral chemical sympathectomy and the observed effects on incisor eruption were compared to those made on intact/sham groups or on rats subjected to inferior alveolar nerve (IAN) lesion. RESULTS The total amount of eruption in control/naïve rats, measured over a total period of 144 h, was 3 ± 0.15 mm and decreased to 2.57 ± 0.06 mm (n = 8; p < 0.01) or 2.8 ± 0.10 mm (n = 8; p < 0.05) following treatment with guanethidine and hexamethonium, respectively. This amount decreased to 1.8 ± 0.14 mm (p < 0.001 vs. control, n = 7; or p < 0.01 vs. sham, n = 5) in rats subjected to IAN lesion. CONCLUSION Sympathectomy delayed tooth eruption. Blocking the sympathetic effectors with guanethidine exerted more potent effects than ganglionic block with hexamethonium. Intact sympathetic supply is required for tooth growth under normal conditions.

Effect of Simulated Mastication on the Retention of Locator Attachments for Implant-Supported Overdentures: An In Vitro Pilot Study

PURPOSE Limited information is currently available relative to the effect of masticatory loads on the retentive properties of Locator attachments. The aims of this in vitro study were to assess and compare the effect of simulated mastication on the retention of white, pink, and blue Locator inserts for overdentures retained by 2 implants. MATERIALS AND METHODS Thirty specimens simulating a nonanatomic edentulous flat ridge with two implants and an overdenture were divided into 3 groups according to the color of the fitted insert: transparent clear group (n = 10), pink group (n = 10), and blue group (n = 10). Retention forces were measured in an axial direction initially and after 100,000 cycles of simulated masticatory loads. One-way ANOVA followed by Tukeys post hoc tests were used to compare retention values and percentage retention loss between the 3 groups with significance set at p = 0.05. RESULTS The 3 groups presented significant differences in retention at baseline (9.95 ± 1.91 N, 15.43 ± 4.08 N, and 41.73 ± 9.29 N for the blue, pink, and clear groups, respectively) and after simulated mastication (6.37 ± 2.64 N, 14.00 ± 3.89 N, 38.20 ± 5.11 N for the blue, pink, and clear groups, respectively). Within the same group, cyclic loading did not significantly affect retention in the clear and pink groups, while the blue inserts showed a significant retention loss (-37%) after loading. CONCLUSIONS The results suggest that short-term simulated mastication affects the extra-light blue inserts but not the more-retentive inserts.

Effect of rapid maxillary expansion on glenoid fossa and condyle-fossa relationship in growing patients (MEGP): Study protocol for a controlled clinical trial

Aims and Objectives: Rapid maxillary expansion (RME) is an orthodontic nonsurgical procedure aiming at increasing the width of the maxilla by opening mainly the intermaxillary suture in patients presenting a transverse maxillary skeletal deficiency. The objectives of the current prospective controlled clinical and radiographic study are to evaluate the hypothesis that RME in growing patients will result in radiographic changes at the level of interglenoid fossa distance, condyle-fossa relationship, and nasal cavity widths compared to the group who received no treatment initially and served as untreated control. Materials and Methods: In this prospective controlled clinical and radiographic study, forty healthy growing patients selected from a school-based population following a large screening campaign, ranging in age between 8 and 13 years, presenting a maxillary constriction with bilateral crossbite, and candidates for RME are being recruited. The first group will include participants willing to undergo treatment (n = 25) and the other group will include those inclined to postpone (n = 15). Results: The primary outcome is to compare radiologically the interglenoid fossa distance and the condyle-fossa relationship; nasal cavity width will be a secondary outcome. A multivariable analysis of Covariance model will be used, with the assessment of the time by group interaction, using age as covariate. The project protocol was reviewed and approved by the Ethics Committee of the Lebanese University, National Institute in Lebanon (CUEMB process number 31/04/2015). The study is funded by the Lebanese University and Centre National de Recherche Scientifique, Lebanon (Number: 652 on 14/04/2016). Conclusion: This prospective controlled clinical trial will give information about the effect of RME on the glenoid fossa and condyle-fossa relationship and its impact on the nasal cavity width. Trial Registration: Retrospectively registered in BioMed Central (DOI10.1186/ISRCTN77788053).