Fate of root shell after pontic/socket shield techniques,is it better to extract the whole tooth?

A series of changes occur in the remaining alveolar process after whole tooth extraction.The basic question is,why do the bony walls(especially the labial/buccal)get resorbed immediately after the tooth is removed?This could be because,with cementum of the concerned tooth and its periodontal ligament,the supporting bundle bone is dependent on the presence of the tooth.This loss can be compensated using numerous techniques,such as socket grafting using various biomaterials to preserve the alveolar bone and buccal grafting with guided tissue regeneration to increase the thickness of buccal bone or placement of implant immediately.However,none of these techniques prevent the modelling of the alveolar bone post-extraction.Few studies have demonstrated that preservation of the roots in the alveolar process maintains the bone volume and facilitates vertical bone growth.A histological study in animals and humans has shown that the retained root shell does not pose any interference in the osseointegration of the implant(if placed simultaneously).Although various names have been proposed to describe the concept of retaining full or part of the root to prevent the resorption of the ridge,socket-shield and pontic-shield are the two most commonly used terms worldwide.The extraction of the whole tooth might be the choice of therapy when socket-shield or pontic-shield is not possible due to anatomical variations,infections,or lack of clinical expertise.Irrespective of the size,when a whole root or a root fragment(is left in situ),it is the dentist’s ethical duty to advise/inform the patient and ensure repeated clinical and radiographic follow-up.The present study aimed to highlight the current status of these techniques,their benefits,and possible complications and address whether the paradigm of the teeth extraction methods should be altered.

Loss of Masticatory Function Affects Morphology of the Tooth Root in Rats

Masticatory hypofunction and soft food affect the tooth rows, occlusion, and jawbone. This study aimed to clarify the influence of tooth loss and a soft diet on morphology of the tooth root during the growth period. We divided 3-week-old Wistar rats into the following three groups: Hard diet group (rats raised on solid standard diet), Powder diet group (rats raised on powdered standard feed diet), and Extraction group (rats raised on powdered standard diet with maxillary molars extraction). Length, width, cross-sectional area, and volume of the root of the mandibular M1 and M2 were measured using micro-CT analysis. Non-decalcified thin-slice specimens of sagittal sections of the M1 were obtained at the age of 20 weeks, and the roots were observed. The root length of all roots in the Extraction group was significantly longer than that in the other groups. The root width and cross-sectional area at the apical side 1/4 of all roots in the Extraction group were significantly smaller than those in the other groups. The root volume of the M1 mesial root in the Extraction group was significantly smaller than that in the other groups. This study clarified that when masticatory stimulus in the immature teeth is reduced by the extraction of opposing teeth and a powder diet, the root length increases due to the promotion of cellular cementum addition at the apex, and the root width and cross-sectional area decrease due to the suppression of cellular cementum addition at the apical side 1/4 of the roots.

Maxillary first premolars:Ⅰ.Morphology of the apical constriction

Objective： To investigated the apical constriction morphology of maxillary first premolars in the Chinese population. Methods： Eighty recently extracted human maxillary first premolars from a native Chinese population were used. The number and shape of apical constrictions were recorded under a dental operating microscope （DOM） at 12.5 × 2.5 magnification. After access preparation, a new K-file was inserted into the canal until the tip of the file was just seen at the apical constriction under the DOM. The teeth with files in the canals were X-rayed from a mesiodistal direction using a direct digital radiography （DDR） system, and the distance between the file tip and the center of radiographic apex was directly measured from the computer screen using DDR measurement software. Results： The percentage of teeth with an apical constriction was 78.5% （102/130）. The most common apical constriction shapes were oval （55.9%） and round （35.3%）. The mean distance between the apical constriction and the anatomical tip of the root was 0.61 mm, and 84.3% （86/102） were within 1 mm. Conclusion： The most common shape of an apical constriction was oval or round, and the distance to the apex was mostly within 1 mm, indicating that root canal therapy should stop 1 mm from the radiographic apex.

Changes of the Unique Odontogenic Properties of Rat Apical Bud Cells under the Developing Apical Complex Microenvironment

Aim To characterize the odontogenic capability of apical bud and phenotypical change of apical bud cells （ABCs） in different microenvironment.Methodology Incisor apical bud tissues from neonatal SD rat were dissected and transplanted into the renal capsules to determine their odontogenic capability. Meanwhile ABCs were cultured and purified by repeated differential trypsinization. Then ABCs were cultured with conditioned medium from developing apical complex cells （DAC-CM）. Immunocytochemistry, reverse transcriptase polymerase chain reaction （RT-PCR） and scanning electron microscope （SEM） were performed to compare the biolo- gical change of ABC treated with or without DAC-CM. Results First we confirmed the ability of apical bud to form crown-like structure ectopically. Equally important, by using the developing apical complex （DAC） condi- tioned medium, we found the microenvironment created by root could abrogate the ＂crown＂ features of ABCs and promote their proliferation and differentiation. Conclusion ABCs possess odontogenic capability to form crown-like tissues and this property can be affected by root-produced microenvironment.

Gingival unit transfer using in the Miller Ⅲ recession defect treatment

The most significant factor for the success in soft tissue grafts is the synergistic relation between vascular configuration and involved tissues. In the soft tissue graft procedures, site specific donor tissue is assumed to have improved potential for function and aesthetic survive at recipient sites. On a clinical level, using site specific gingival unit graft that placed on traditionally prepared recipient site, results in predictable root coverage. In this case report the clinical effectiveness of gingival unit transfer(GUT) technique performed on Miller Ⅲ recession was presented and a similar recession case treated with free gingival graft(FGG) technique for comparison. Probing depth, recession depth, keratinized tissue width and clinical attachment level clinical parameters were measured at baseline and postoperative 8 mo. Percentage of defect coverage was evaluated at postoperative 8 mo. Creeping attachment was assessed at postoperative 1, 3, 6 and 8 mo. The GUT revealed better defect coverage and creeping attachment results than the FGG in the treatment of Miller Ⅲ defects.

EXPERIMENTAL STUDY ON LUBRICATION BEHAVIOR OF DOUBLE ENVELOPING HOUK GLASSWOKM GEARING

The lubrication behavior of double enveloping hourglass worm gearing is studied experimently. The effects of rotational speed of the worm and load on the formation of the fluid film between engagement tooth surfaces are investigated in detail. and working angle of this worm gearing is also analyzed. Some beneficial results are obtained。

Age Estimation Using Single-Rooted Teeth of Indian Residents by Modified Kvaal’s Method:A Pilot Study

Background:This study aimed to create an age estimation formula with high sensitivity and specificity using the modified Kvaal’s dental radiographic method.The parameters for age estimation were assessed by measuring the length and width of tooth,root,and pulp with the help of a stereomicroscope and digital image analysis.Materials and Methods:Only single-rooted noncarious teeth were included.A total of 203 samples of teeth,with an age ranging from 15 to 85 years,were collected,of which only 123 samples were included in the study.Images of vertically sectioned teeth specimens were captured under a stereomicroscope(version SZ-790,×10 mm eyepiece),and parameters were measured using Adobe Photoshop.Results:Karl Pearson’s correlation coefficient was used to correlate age with the dental parameters,and step-wise regression analysis was used to derive the age estimation formula.A significant correlation of age with pulp length and root and pulp width having P<0.001 was observed,and an age estimation formula with a standard estimation error of 14 could be derived.Conclusion:Kvaal’s parameter in extracted single-rooted tooth showed a better reliability and reproducibility in age estimation.Further studies with a larger sample size and tooth-specific formula using principal component analysis should be considered to validate the accuracy of the present result.

Metallurgical concepts for optimized processing and properties of carburizing steel

Carburized steel grades are widely used in applications where high surface near hardness is required in combination with good core toughness as well as high strength and fatigue resistance. The process of carburizing lower to medium carbon containing steel can generally provide this combination of properties and has been prac- ticed for several decades. Such steel is essential in the vehicle power-train, machines and power generation equipment. However, the increasing performance demands by such applications as well as economical considerations forced steel producers to develop better alloys and fabri- cators to design more efficient manufacturing processes. The present paper describes recent concepts for alloy design optimization of carburizing steel and demonstrates the forthcoming beneficial consequences with regard to manufacturing processes and final properties.

Antrochoanal polyp derived from periapical granuloma

Antrochoanal polyp （ACP） is an infrequent, benign polypoid lesion that stems from the edematous mucosa of the maxillary sinus, grows from the natural or accessory ostium to the middle meatus, and protrudes toward the choana and nasopharynx. Although the exact causes of ACP are still unknown, chronic sinusitis, allergy, and lower respiratory tract infections are often related to ACE2 Our report is an ACP arising from a secondary infection of the periapical granuloma in the maxillary sinus. Its possible pathological mechanism, unique clinical features, and treatment are also discussed.