Jose Johann Chidiac

Impression Materials in Fixed Prosthodontics: Influence of Choice on Clinical Procedure

The purpose of this article is to review impression materials used for fabricating fixed restorations in dentistry. Their compositions, properties, advantages, and disadvantages are presented and compared. How these properties influence clinical decisions is also described. This review helps the clinician choose which material is more suitable for a specific case. A broad search of the published literature was performed using Medline to identify pertinent current articles. Textbooks, the Internet, and manufacturers’ literature were also used to supplement this information. It is limited to impression materials used in fixed prosthodontics. The review gives basic knowledge of ideal impression material properties and discusses traditional and, primarily, more recently developed products, such as polyethers, poly(vinyl siloxane), polysulfides, and condensation silicone materials. Clear advantages and disadvantages for these impression materials are provided along with the role that compositional variations have on the outcome of the impression. This should enable clinicians and technicians to easily identify the important physical properties of each type of impression material and their primary clinical indications.

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.

Prosthetic Requirements for Immediate Implant Loading: A Review

Purpose: The aim of this article is to review the current literature with regard to prosthetic considerations and their influence on the outcome of immediately loaded implants. Materials and Methods: A broad search of the published literature was performed using MEDLINE and PubMed to identify pertinent articles. Results: One hundred fifty six references were selected. They were mainly descriptive, prospective, follow-up studies. They were reviewed and were categorized with respect to 6 factors that influence immediate loading: cross-arch stability and micromovements, interim prostheses, definitive restorations inserted immediately, screw- or cement-retained prostheses, occlusion, and number and distribution of implants in overdentures and fixed prostheses. Conclusion: Immediate loading seems to be a relatively safe procedure. From the prosthodontic point of view, there are specific guidelines to follow. They are: implants should be splinted with a metallic bar and acrylic interim prostheses until full osseointegration occurs. To have a successful outcome, screw-retained interim prostheses are recommended. CAD/CAM systems can improve the placement of implants with minimum risk. Regarding occlusion, there is a disagreement on when and how to provide occlusal contacts, but all authors agree on keeping centric contacts only. Finally, concerning the number of implants required for an immediate overdenture, no conclusive evidence could be found.PURPOSE The aim of this article is to review the current literature with regard to prosthetic considerations and their influence on the outcome of immediately loaded implants. MATERIALS AND METHODS A broad search of the published literature was performed using MEDLINE and PubMed to identify pertinent articles. RESULTS One hundred fifty six references were selected. They were mainly descriptive, prospective, follow-up studies. They were reviewed and were categorized with respect to 6 factors that influence immediate loading: cross-arch stability and micromovements, interim prostheses, definitive restorations inserted immediately, screw- or cement-retained prostheses, occlusion, and number and distribution of implants in overdentures and fixed prostheses. CONCLUSION Immediate loading seems to be a relatively safe procedure. From the prosthodontic point of view, there are specific guidelines to follow. They are: implants should be splinted with a metallic bar and acrylic interim prostheses until full osseointegration occurs. To have a successful outcome, screw-retained interim prostheses are recommended. CAD/CAM systems can improve the placement of implants with minimum risk. Regarding occlusion, there is a disagreement on when and how to provide occlusal contacts, but all authors agree on keeping centric contacts only. Finally, concerning the number of implants required for an immediate overdenture, no conclusive evidence could be found.

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.

Modified technique for the exposure of the inferior alveolar nerve in rats

The inferior alveolar nerve (IAN), a branch of the mandibular division of the trigeminal nerve, is a major component of the neurovascular bundle along with the inferior alveolar artery and vein. In rats, when exposed using an external oral approach while remaining intact, it can serve as an important tool to study the different effects of neuromediators and assess the role of different groups of nerve fibers. This paper describes a new technique to expose this nerve giving some experimental results to support its usefulness.

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.

Considerations for Altering Preparation Designs of Porcelain Inlay/Onlay Restorations for Nonvital Teeth

PURPOSE The aim of this study was to compare all ceramic inlay/onlay survival rates in vital and nonvital teeth having the same cavity design. Filling the pulp chamber with ceramic materials or not was also discussed. MATERIALS AND METHODS Ceramic class II inlays/onlays were made on 11 premolars and 30 molars: 14 vital, 27 endodontically treated. The same tooth preparation design was performed on vital and nonvital teeth: In nonvital teeth the pulp chambers were covered by a glass ionomer cement until the pulpal floor depths were between 2 and 2.5 mm, more likely similar to the vital teeth preparations. In vital teeth, glass ionomer was used as a liner to achieve pulpal floor depths between 2 and 2.5 mm when needed. The restorations were assessed (at baseline, 6 months, 1 and 2 years) according to three criteria: marginal discoloration, marginal integrity, and fracture of teeth/restorations, consistent with United States Public Health Service (USPHS) criteria. RESULTS Eight teeth (19%) showed minor marginal discolorations, while three molars (7%) had loss of marginal integrity. These margins were adjusted using rubber polishing cups and were then judged clinically acceptable. From these three molars, one was vital and two were endodontically treated. No fracture of teeth or restorations was observed. Chi square and exact probability tests were used. There was no statistical difference between vital and nonvital teeth (p = 0.719 chi-squared and Fisher) or between premolars and molars (p = 0.564 chi-squared; 1.000, Fisher). CONCLUSION Within the limitations of this study there was no difference for the same inlay/onlay cavity design between vital and nonvital teeth. In nonvital teeth, it seems that filling the pulp chamber with a ceramic core material is not important. Long-term observation periods are needed to reinforce the clinical behavior outcome.