Category Archives: Orthodontics

Importance of Nutrition in Orthodontics

The importance of diet and nutrition for has been recognized in health and disease for ages. More so the history of has been to a large extent a struggle to obtain food. Continue reading Importance of Nutrition in Orthodontics

With the recognition of proteins, carbohydrates and fats as energy yielding foods and  the discovery of vitamins and minerals , great advances have been made in the knowledge of nutrition and its practical application.

Nowadays  we live in a very diet conscious society where more and more people are adopting a healthy lifestyle through a healthy diet. The  evidence for which can be obtained from knowing the fact that books written on Nutrition and diet are amongst the fastest moving books off the shelves.

But despite  these advances  malnutrition is widely prevalent in many parts of the world more so in India than anywhere else. Adequate nutrition is important for proper body growth, its development and maintenance.

Nutritional imbalances affect the normal growth and development of the individual directly or indirectly. Deficiencies resulting during the formative stages of organs results in a more severe and irreversible damage , which follows the general rule that earlier the deficiency greater is the damage. Poor nutrition reduces the resistance of the tissues to infections and increases the length of healing period after surgery or an injury.

The proper nutritional status of the patient is of utmost importance in orthodontic treatment, since success depends on the response of bone to stimulation and reformation for the accomplishment of desired results.

Only when we begin to understand these vital nutrients and the role played by each one in the normal development of orofacial region and the body as a whole can we realize its relevance in clinical application. This will facilitate a comprehensive approach to orthodontic treatment as a whole.

DEFINITIONS:

Nutrition is a dynamic process in which the food that is consumed is utilized for nourishing the body. It can be defined as the study of ingestion , digestion, absorption, transport, metabolism and excretion of the chemicals found in the food.

Diet: The term diet refers to the total oral intake of substances that furnish nourishment and/or calories to the body.

NUTRITION IN GROWTH AND DEVELOPMENT

Nutrition plays a vital role in the growth and development of an individual. Development is a process which commences at conception and continues through birth until death. The perceptible visible evidences of developmental changes is Growth.

Guilford in 1874 was amongst the first to advocate dietary deficiencies as an underlying cause of dentofacial irregularities. Important relationship exists between diet and development which can be seen during the nutrition of the foetus; placenta is the provider of the essential nutrient substrates and fetal tissue synthesizes its own proteins and nucleic acids. Therefore interferences with substrate availability results in decreased protein metabolic activity.

Miller suggested that “ critical periods” exist during the development of an organ and that stress imposed by the nutritional imbalance during critical periods can result in irreversible changes. Critical periods are defined as that time in the development of an organ system which is marked by the rapid synthesis  and accretion of protein. The critical period roughly equates with the intense hyperplastic growth phase. If imbalance occurs during hyperplastic phase then it causes irreversible damage to the tissues. If it occurs during hypertrophic phase then the growth may stop temporarily but will catch up later when adequate amounts of missing nutrients become available. Dietary deficiencies of essential nutrients during the critical periods of growth have caused retardation of growth and morphologic alterations of the orofacial area in both humans and animals.

It has been shown in animal studies that certain hormones like the pituitary hormone are sensitive to nutritional deficiencies. Animals fed on diets deficient in folic acid , riboflavin and zinc , have borne offsprings with increased risk of cleft lip and palate. Even short periods of malnutrition (7-12 months) have resulted in an increase in open bites, a reduction in dimension of dental arches with inadequate space for teeth, insufficient dental eruption, the absence of natural diastema between the front deciduous teeth and shorter roots and interosseous rotation of the permanent teeth.

Malnutrtion has also been associated with shorter mandibles in the antero posterior dimension, marked reduction in the ascending ramus, condylar region and the setting of the premolars; dentoalveolar inclination in the incisor region and reduction in the mesio-distal dimension of the third molars.

Radiologic, histologic and histo chemical studies have demonstrated such abnormalities in osseous tissues as the reduction of the cortex and enlargement of the medulary spaces and a weakening of the osteoblastic and osteoclastic activity.

A Guide To Dental Anatomy

Dental anatomy is defined  as, the study of the development, morphology, function, and identity of each of the teeth in the human dentitions, as well as the way in which the teeth relate in shape, form, structure, color, and function to the other teeth in the same dental arch and to the teeth in the opposing arch. Thus, the study of dental anatomy, physiology, and occlusion provides one of the basic components of the skills needed to practice all phases of dentistry.

Continue reading A Guide To Dental Anatomy

CHRONOLOGY OF PRIMARY TEETH

primary teeth ERUPTION

CHRONOLOGY OF PERMANENT TEETH

permanent teeth eruption

THE PERMANENT MAXILLARY INCISORS

The maxillary central incisor is larger than the lateral incisor. These teeth supplement each other in function, and they are similar anatomically.

PERMANENT MAXILLARY CENTRAL INCISOR

The maxillary central incisors are esthetically the most prominent teeth in the mouth. An ideal smile should have incisal dominance, i.e. maxillary incisors should be the most prominent teeth visible when one smiles. Any defects in the form and alignment of these teeth are easily noticed, and adversely affect the normal facial appearance

First evidence of calcification 3–4 mo
Enamel completed 4–5 yr
Eruption 7–8 yr
Root completed 10 yr

maxillary central inciser

Maxillary Lateral Incisor

Because the maxillary lateral incisor supplements the central incisor in function, the crowns bear a close resemblance. The lateral incisor is smaller in all dimensions except root length. This tooth differs from the central incisor in its development, which may vary considerably. Maxillary lateral incisors vary in form more than any other tooth in the mouth except the third molar. If the variation is too great, it is considered a developmental anomaly. A common situation is to find maxillary lateral incisors with a nondescript, pointed form; such teeth are called peg-shaped laterals.

First evidence of calcification 10–12 mo
Enamel completed 4–5 yr
Eruption 8–9 yr
Root completed 11 yr

The Permanent Mandibular Incisors

The mandibular incisors have smaller mesiodistal dimensions than any of the other teeth. The central incisor is somewhat smaller than the lateral incisor, which is the reverse of the situation in the maxilla.

Mandibular Central Incisor

Generally, the mandibular central incisor is the smallest tooth in the dental arches. The crown has little more than half the mesiodistal diameter of the maxillary central incisor; however, the labiolingual diameter is only about 1 mm less. The single root is very narrow mesiodistally and corresponds to the narrowness of the crown, although the root and crown are wide labiolingually. The length of the root is as great as, if not greater than, that of the maxillary central incisor.

mandibular central inciser

First evidence of calcification 3–4 mo
Enamel completed 4–5 yr
Eruption 6–7 yr
Root completed 9 yr

Mandibular Lateral Incisor

Direct comparison is made with the mandibular central incisor, and the variations are mentioned. The two incisors operate in the dental arch as a team; therefore their functional form is related. As with the mandibular central incisor, the shape of the lateral incisor is uniform compared with that of other teeth. Rarely, it will have a labial and lingual root division in the cervical third. Somewhat more commonly it has two canals in the single root.

First evidence of calcification 3–4 mo
Enamel completed 4–5 yr
Eruption 7–8 yr
Root completed 10 yr

The Permanent Canines: Maxillary and Mandibular

The maxillary and mandibular canines bear a close resemblance to each other, and their functions are closely related. The four canines are placed at the “corners” of the mouth; each one is the third tooth from the median line, right and left, in the maxilla and mandible. They are commonly referred to as the cornerstone of the dental arches. They are the longest teeth in the mouth; the crowns are usually as long as those of the maxillary central incisors, and the single roots are longer than those of any of the other teeth.

Maxillary Canine

Figures illustrate the maxillary canine in various aspects. The outline of the labial or lingual aspect of the maxillary canine is a series of curves or arcs except for the angle made by the tip of the cusp. This cusp has a mesial incisal ridge and a distal incisal ridge. The mesial half of the crown makes contact with the lateral incisor, and the distal half contacts the first premolar. Therefore the contact areas of the maxillary canine are at different levels cervicoincisally. (maxillary right canine)

maxillary canine

 

First evidence of calcification 4–5 mo
Enamel completed 6–7 yr
Eruption 11–12 yr
Root completed 13–15 yr

Mandibular Canine

The mandibular canine crown is narrower mesiodistally than that of the maxillary canine, although it is just as long in most instances and in many instances is longer by 0.5 to 1 mm.

The root may be as long as that of the maxillary canine, but usually it is somewhat shorter. The labiolingual diameter of crown and root is usually a fraction of a millimeter less. The lingual surface of the crown is smoother, with less cingulum development and less bulk to the marginal ridges. The lingual portion of this crown resembles the form of the lingual surfaces of the mandibular lateral incisors.

The cusp of the mandibular canine is not as well developed as that of the maxillary canine, and the cusp ridges are thinner labiolingually. Usually the cusp tip is on a line with the center of the root, from the mesial or distal aspect, but sometimes it lies lingual to the line, as with the mandibular incisors.

mandibular canine

First evidence of calcification 4–5 mo
Enamel completed 6–7 yr
Eruption 9–10 yr
Root completed 12–14 yr

 The Permanent Maxillary Premolars

The maxillary premolars are developed from the same number of lobes as anterior teeth—four. The primary difference in development is the well-formed lingual cusp, developed from the lingual lobe, which is represented by the cingulum development on incisors and canines. The middle buccal lobe on the premolars, corresponding to the middle labial lobe of the canines, remains highly developed, with the maxillary premolars resembling the canines when viewed from the buccal aspect.

The buccal cusp of the maxillary first premolar, especially, is long and sharp, assisting the canine as a prehensile or tearing tooth. The mandibular first premolar assists the mandibular canine in the same manner. The second premolars, both maxillary and mandibular, have cusps less sharp than the others, and their cusps articulate with opposing teeth when the jaws are brought together; this makes them more efficient as grinding teeth, and they function much like the molars, but to a lesser degree.

The maxillary premolar crowns are shorter than those of the maxillary canines, and the roots are also shorter. The root lengths equal those of the molars. The crowns are a little longer than those of the molars. Because of the cusp development buccally and lingually, the marginal ridges are in a more horizontal plane and are considered part of the occlusal surface of the crown rather than part of the lingual surface, as in the case of incisors and canines. When premolars have two roots, one is placed buccally and one lingually.

Maxillary First Premolar

The maxillary first premolar has two cusps, a buccal and a lingual, each being sharply defined. The buccal cusp is usually about 1 mm longer than the lingual cusp. The crown is angular, and the buccal line angles are prominent. The crown is shorter than that of the canine by 1.5 to 2 mm on the average.maxillary first premolar

First evidence of calcification 11/2–13/4 yr
Enamel completed 5–6 yr
Eruption 10–11 yr
Root completed 12–13 yr

Maxillary Second Premolar

The maxillary second premolar supplements the maxillary first premolar in function. The two teeth resemble each other so closely that only a brief description of each aspect of the second premolar is necessary. Direct comparison is made between it and the first premolar, and variations are mentioned.

The maxillary second premolar is less angular, giving a more rounded effect to the crown from all aspects. It has a single root.

Considerable variations in the relative sizes of the two teeth may be seen, because the second premolar does not appear true to form as often as does the first premolar. The maxillary second premolar may have a crown that is noticeably smaller cervico-occlusally and also mesiodistally.

First evidence of calcification 2– 21/4 yr
Enamel completed 6–7 yr
Eruption 10–12 yr
Root completed 12–14 yr

The Permanent Mandibular Premolars

The mandibular first premolars are developed from four lobes, as were the maxillary premolars. The mandibular second premolars are, in most instances, developed from five lobes, three buccal and two lingual lobes.

The first premolar has a large buccal cusp, which is long and well formed, with a small, nonfunctioning lingual cusp that in some specimens is no longer than the cingulum found on some maxillary canines. The second premolar has three well-formed cusps in most cases, one large buccal cusp and two smaller lingual cusps. The form of both mandibular premolars fails to conform to the implications of the term bicuspid, a term that implies two functioning cusps.

Mandibular First Premolar

This tooth is situated between the canine and second premolar and has some characteristics common to each of them.
The characteristics that resemble those of the mandibular canine are as follows:
1. The buccal cusp is long and sharp and is the only
occluding cusp.
2. The buccolingual measurement is similar to that of
the canine.
3. The occlusal surface slopes sharply lingually in a
cervical direction.
4. The mesiobuccal cusp ridge is shorter than the
distobuccal cusp ridge.
5. The outline form of the occlusal aspect resembles the
outline form of the incisal aspect of the canine.

The characteristics that resemble those of the second mandibular premolar are as follows:
1. Except for the longer cusp, the outline of crown and
root from the buccal aspect resembles that of    the second premolar.

2. The contact areas, mesially and distally, are near the
same level.

3. The curvatures of the cervical line mesially and distally are similar.

4. The tooth has more than one cusp.

mandibular first premolar

First evidence of calcification 13/4–2 yr
Enamel completed 5–6 yr
Eruption 10–12 yr
Root completed 12–13 yr

Mandibular Second Premolar

The mandibular second premolar resembles the mandibular first premolar from the buccal aspect only. Although the buccal cusp is not as pronounced, the mesiodistal measurement of the crown and its general outline are similar. The tooth is larger and has better development in other respects.

First evidence of calcification 21/4-21/2 yr
Enamel completed 6–7 yr
Eruption 11–12 yr
Root completed 13–14 yr

The 3 elements of Dental Photography

Learning about how to get your exposure right is at the heart of good Dental photography. Its important to have a bright, sharp image to appreciate pre and post treatment conditions.  As a result we’ve written on the topic numerous times (see links below) to help our readers get their heads around it. Those elements are ISO, Aperture and Shutter Speed. Continue reading The 3 elements of Dental Photography

Often referred to as The Exposure Triangle –  these 3 elements have an impact upon exposure.

Here’s a good cheat sheet/diagram that we came across this week that gives a good explanation of these 3 elements and the impact that changing each has upon your image.

dental photography guide
dental photography guide

MUSCLES OF MASTICATION

maxresdefault

INTRODUCTION

Mastication is defined as the process of chewing food in preparation for swallowing and digestion. Four pairs of muscles in the mandible make chewing movements possible.

These muscles along with accessory ones together are termed as ‘MUSCLES OF MASTICATION’.

Continue reading MUSCLES OF MASTICATION

These muscles can be divided into:

Basic muscles:

-Lateral pterygoid

-Medial pterygoid

-Temporalis

-Masseter

Accessory muscles:

-Buccinator

-Digastric muscle (anterior belly)

-Mylohyoid

-Geniohyoid

-Orbicularis oris

DEVELOPMENT

  • The basic muscles of mastication develop from the mesenchyme of the first branchial arch.
  • So they receive all their innervations from the mandibular branch of the trigeminal nerve, all from the anterior division except the medial pterygoid which gets its nerve supply from the main trunk.
  • Also they originate from the same origin from temporal and infra-temporal fossa of the skull and are inserted in the mandible.

MOVEMENTS OF MANDIBLE

  • Movements that the mandible can undergo are:

1. Depression: as in opening the mouth.

2. Elevation: as in closing the mouth.

3. Protraction: horizontal movement of the mandible anteriorly.

4. Retraction: horizontal movement of the mandible posteriorly.

5. Rotation: the anterior tip of the mandible is “slewed” from side to side.

  • These movements of mandible are performed by various muscles involved in it. So, functionally, the muscles of mastication are classified as:

Jaw elevators:

Masseter

Temporalis

Medial pterygoid

Upper head of lateral pterygoid

Jaw depressors:

Lower head of lateral pterygoid

Anterior digastric

Geniohyoid

Mylohyoid

 

TEMPORALIS

  • It is the largest among all the masticatory muscles and is a fan shape muscle.
  • Origin; from the inferior temporal line , floor of the temporal fossa and from the overlaying temporal fascia.
  • Insertion; anterior and medial tip of the coroniod process.
  • It has been divided into 2 heads:

–     Deep head (anterior, middle and posterior fibers)

–     Superficial head (much smaller)

  • Action:

–     Elevation (anterior fibers)

–     Retraction (posterior fibers)

  • Nerve supply:

–     Anterior division of the mandibular nerve

(by 2 deep temporal nerves)

  • Its action is done by;
  • The anterior fibers during function act vertically and elevate the mandible.
  • The posterior fibers diverge and become horizontal and  retract the mandible.
  • Blood supply; from the maxillary artery (one of 2 termination of external carotid artery).

MASSETER

  • It consist of 2 overlapping heads:
  • The origin of the whole muscle is mainly from the zygomatic process, in which:

-The superficial head arises from the lower border of the zygomatic arch.

-The deep head arises from the inner surface of the zygomatic arch.

  • Insertion of both the heads is into the outer surface of the ramus of the mandible.
  • The superficial head passes downwards and backwards to insert into the lower half of the lateral surface of the ramus.
    • While in the deep head, the fibers are more vertically oriented and inserted into the upper half of the lateral surface of the ramus.
    • Action of masseter is mainly to elevate the mandible (antigravity action) and also helps in protrusive movement.
    • It is the main muscle involved in the elevation of the mandible
    • Nerve supply: by the mandibular branch of the trigeminal nerve, from the anterior division(massetric nerve).
    • Blood supply is from the maxillary artery which is a terminal branch from external carotid artery.
    • One of the interesting properties of this muscle is that, internally, the muscle has many tendinous septa that greatly increase the area for muscle attachment and so increase its power.

    Masseteric Hypertrophy

    • Masseteric Hypertrophy was first described by Legg in 1880.
    • A hypertrophied muscle will alter facial symmetry, generating discomfort and negative cosmetic impact in many patients.
    • It may also produce functional  alterations like bruxism, mandibular prognathism and trismus.
    • It can be treated by using Botulinum toxin, RF  Electrocoagulation and surgical methods.
    • Botulinum toxin can reduce upto one third where as surgical methods can reduce upto two third of the muscle mass.

    MEDIAL PTERYGOID

    • It is also called as the Pterygoideus internus (Internal pterygoid muscle).
    • It consist of 2 heads which differ in origin:

    Origin:

    The deep head originates from the medial surface of lateral pterygoid plate of the sphenoid bone.

    While the superficial head originates from the maxillary tuberosity.

    The muscle inserts into the inner surface of the angle of the mandible.

    • Nerve supply  of the muscle comes from the main trunk of the mandibular nerve.
    • Blood supply is chiefly from the maxillary artery.

    Action:

    1. Elevate the mandible .
    2. Protrusion of the mandible (lateral & medial pterygoid on one side protrude the mandible to the opposite side).
    3. Side to side movement (these lateral movements are achieved by lateral & medial pterygoid on both sides acting together to produce side to side movements).

    LATERAL PTERYGOID

    • Also called as the Pterygoideus externus (External pterygoid muscle).
    • It is a short conical muscle, having 2 heads:

    upper and lower.

    • Upper head:

    –     Origin: infra-temporal surface & crest of the greater wing of sphenoid

    –     Insertion: enters the TMJ & inserted into:

    a) Pterygoid fovea of the neck of the mandible

    b) Articular disc

    c) Capsule of TMJ (anterior aspect)

    • Lower head:

    –     Origin: Lateral surface of the lateral pterygoid plate

    –     Insertion:  its insertion is same as that of the upper head, it enters the TMJ & gets inserted into:

    a) Pterygoid fovea of the neck of the mandible

    b) Articular disc

    c) Capsule of TMJ (anterior aspect)

    • The insertion of the lateral pterygoid in the articular disc occurs in the medial aspect of the anterior border of the disc and thus it plays a role in the T.M.J. diseases especially internal derangement.
      • Some of the T.M.J. diseases have been due to an attributed variation of the function and attachment of the superior head as an etiological factor in T.M.J. diseases.
      • Nerve supply is from the anterior division of the mandibular branch of trigeminal nerve(nerve to lateral pterygoid).
      • Blood supply of lateral pterygoid muscle is from maxillary artery .
      • Actions of lateral pterygoid:
      • If the Pterygoid muscles of one side act, the other side of the mandible is drawn forward while the same condyle remains comparatively fixed.
      1. Depression of the mandible .
      2. Side to side movement (lateral movement) .
      3. Protrusion of the mandible.

      ACCESSORY MUSCLES OF MASTICATION

      1. BUCCINATOR:
      • It is an accessory muscle of mastication, occupying the gap between mandible and maxilla forming important part of the cheek.
      • Its origin is from buccal plate of bone of the sockets of the upper and lower three molars and pterygomandibular ligament.
      • Course and insertion

      Upper fibers gets inserted into upper lip,

      Lower fibers gets inserted into lower lip,

      Middle fibers decussate at the angle of the mouth, the upper fibers pass to lower lip while the lower fibers pass to the upper lip .

      • Nerve supply is from buccal branch of facial nerve.
      • Blood supply is from facial artery.
      • The main action of buccinator is to prevent the accumulation of food in the vestibule of mouth.

      2. ANTERIOR BELLY OF DIGASTRIC:

      • Origin; it arises from the digastric fossa on the lower border of mandible on both sides of symphysis menti.
      • Insertion; into the intermediate tendon which is connected to the hyoid bone by a fibrous loop.
      • Nerve supply; is through anterior division of mandibular branch of trigeminal nerve.
      • Action; its main action is to depress the mandible .

      3. MYLOHYOID MUSCLE:

      • It form the floor of the mouth.
      • Origin is from mylohyoid line on the internal  aspect of mandible.
      • Insertion; The fibers slops downwards and forwards to inter-digitate with the fibers of the other side to form the median raphe.
      • This median raphe insert in the chin from above and the hyoid bone from below.
      •  Action; Elevates hyoid bone, supports and raises floor of mouth which aids in early stage of swallowing, depress the mandible.
      • Nerve  supply; by nerve to mylohyoid: which is a branch of Inferior alveolar branch of mandibular nerve, which originates before it  enters inferior alveolar canal.
      • Blood supply; by Facial artery and Lingual artery.
      • This muscle provides a separation between the submandibular and sublingual salivary glands.

      4. GENIOHYOID:

      •  Origin; from inferior genial tubercle (in the midline of inner surface of mandible).
      • Insertion; is into the hyoid bone.
      • Action; depresses the mandible.
      • Blood supply; is through lingual artery.
      • Nerve supply; is by hypoglossal nerve.

      5. ORBICULARIS ORIS:

      • It has two parts: intrinsic and extrinsic part.
      • Intrinsic part is a very thin sheet and originates from superior and inferior incisivus. It inserts into the angle of mouth.
      • The extrinsic part is actually formed by elevator and depressor muscles of the lips and their angles, and inserts into the angle of the mouth.
        • The orbicularis oris functions to close and shut the mouth and formes the most versatile types of grimaces.

        Physical Examination Of Muscles Of Mastication

        1. EXAMINATION OF MASSETER:

        • The patient is asked to clench their teeth and, using both hands, the practitioner palpates the masseter muscles on both sides, making sure that the patient continues to clench during the procedure.
        • Palpate the origin of the masseter along the zygomatic arch and continue to palpate down the body of the mandible where the masseter is attached.
        • The masseter is most often tender along the central fibers of at its insertion.
        • Masseter hypertonicity is found in patients who have premature contacts on the nonworking side.
        • Parafunctions such as bruxism and clenching also give rise to masseter pain that is frequently associated with pain in the temporalis muscle.

        2. TEMPORALIS:

        • The temporalis is palpated in much the same manner

        to detect lateral interferences.

        3. LATERAL PTERYGOID:

        •  In patients with nonworking side interferences, the lateral pterygoid muscle on the opposite of the interference is sometimes painful.
        • In addition, this muscle will be painful whenever there is a centric slide with an anterior component and the patient is bruxing or clenching in this anterior position.
        • The lateral pterygoid, despite its commonality in displaying a spasm, cannot be palpated intraorally.

        4. MEDIAL PTERYGOID:

        • The medial pterygoid muscle is not usually involved in gnathic dysfunctions but when they are hypertonic, the patient is usually conscious of a feeling of fullness in the throat and an occasionally pain on swallowing.
        • Muscles and Malocclusion
        • Article published by T.M.Graber. in 1963 June in AJODO.
        • This study attempts  to balance orthodontic therapy and musculature philosophically
        • Orthodontist can balance them physically with appliances.
        • It deals with the role of muscles in the etiology and correction of malocclusion.
        • Muscles function is normal.
        • The teeth are in state of balance with environmental force.
        • The open bite problem may arise because of thumb and finger sucking, that gives an excellent example of applied muscles physiology.
        • With changes in tongue ,cheek, and lip muscle function, the net effect is narrowing of the maxillary arch and over eruption of post teeth.

        CLASS II, DIV I MALOCCLUSION

        • Abnormal muscle activity.
        • A change in muscle function is a requisite expansion is a treatment objective.
        • In hereditary type of class II malocclusion the teeth merely reflect the abnormal antero-posterior jaw relationship, and the excessive over jet is consequence.
        • If structural mal-relationship exists, the muscle function adapt to this pattern as best it can in line with the requirement of mastication, deglutition and speech.
        • The lip may become hypertrophic as a result.
        • The lower incisors buckle as the mandibular segment is flattened by continuously abnormal mentalis muscle activity.
        • The curve of spee increases, buccinator muscle activity.
        • Openbite also occurs in this abnormal muscle activity can cause the pseudo class II div I.
        • t/t for this should creation of normal basal bone relationship that permit muscle function properly and expansion with appliance.

        CLASS II, DIV 2 MALOCCLUSION

        • The role of musculature is more difficult to establish.
        • Activity of the cheek and lip muscles is usually normal but curve of spee is excessive that interferes with the eruption of post teeth.
        • Because of this TMJ problems arise like clicking, and pain.

        CLASS III MALOCCLUSION

        • In this we deal with dominant bone dysplasia, with adaptive muscle function and tooth irregularities reflecting a severe basal dysplasia.
        • It has got strong hereditary pattern the upper lip is short and lower lip is hypertrophic.
        • During deglutition cycle there is greater mobility of the hyoid bone as the suprahyoid and infrahyoid muscles demonstrate activity.

        CHEWING

        • Two separate acts are recognized in the chewing process.
        • First is a combination of prehension and incision in which the food is secured by the lips and bitten by the front teeth.
        • The second is mastication, the major activity during which the food is mashed between the back teeth.
        • The total chewing cycle occurs through three phases:
        1. The opening stroke during which the mandible is lowered.
        2. The beginning closing stroke during which the mandible is rapidly raised until the entrapped food is felt and
        3. The power stroke in which the food is compressed, punctured, crushed and sheared.

        CHEWING MOVEMENTS AND MECHANICS

        • The chewing process generally acts as a 2nd order lever system resulting in compression at TMJ.
        • The turning moment generated along mandibular body and ramus creates a sheer at TMJ.
        • In 2nd order lever system resistance is present between lever and fulcrum.
        • Chewing in humans is actually asymmetrical and unilateral.
        • At the working side:
          • It possesses the greatest adductor force, but articular emminence is less substantially loaded.
        • At the balancing side:
          • It possesses the less adductor force and the articular emminence is substantially loaded.
          • At the initial action, contraction of inferior head of lateral pterygoid muscle occurs to initiate mandibular deviation to working side.
        • Masticatory Muscle Disorders

        Some of the common masticatory muscle disorders involve:

        • Congenital hyperplasia/ hypoplasia
        • Hypermobility/ hypomobility of the muscle
        • Muscle pains
        • MPDS
        • Myositis ossificans etc.

        CONGENITAL HYPOPLASIA/ HYPERPLASIA

        • It occurs very rarely, and is more common in masseter and orbicularis oris.
        • Its oral symptoms include enlargement or decreased size of the affected muscle, which may show an asymmetric  facial pattern and stiffness in the temporo-mandibular joint.
        • It may or may not be associated with hypermobility/ hypomobility of the muscles.

        MUSCLE HYPERMOBILITY/ HYPOMOBILITY

        • This disorder involves extreme or diminished activity of the masticatory muscles.
        • Its etiology includes various factors such as:

        –     Decreased/ increased threshold potential of neural activity.

        –     Parkinsonism

        –     Facial paralysis

        –     Nerve decompression

        –     Secondary involvement of systemic diseases.

        Muscle Pains

        • It usually occurs as a result of reflex protective mechanism and myofacial triggers.
        • It is usually felt as a non-pulsatile variable aching sensation, with a boring quality. It may also present with tightness, weakness, swelling or tenderness.
        • It includes 3 types:

        1. local muscle soreness:

        it is a primary hyperalgesia with lowered pain threshold due to local factors such as stress, injury, infection etc.

        • This may be due to:

        1. distortion of blood vessels within the muscle or

        2. forceful or sustained contraction repeatedly.

        2. Muscle splinting pain:

        it is defined as rigidity of the muscle occuring as a means of avoiding pain caused by movement of the part.

        it is a reflex protective mechanism.

        Splinting of masticatory muscle may occur as a protective mechanism in conditions such as toothache, overstressed teeth, effect of local anaesthetics, trauma etc.

        3. Non-spastic myofacial pains:

        There is no spasm and pain is the only complaint and this is generally referred to structures outside the muscle proper.

        it may be due to atrophied muscle mass because of inactivity, illness or nutritional deficiency.

        Zones of referred pain

        • The masseter muscle pain refers to the ear, TMJ and the mandibular teeth.
        • The temporalis refers to the temple, orbit and maxillary teeth.
        • The medial pterygoid refers to the infra-auricular and post-mandibular area.
        • The lateral pterygoid always refers its pain to the TMJ.
        • Myofacial Pain Dysfunction Syndrome (Mpds)
        • Muscular Disorders (Myofascial Pain Disorders) are the most common cause of TMJ pain associated with masticatory muscles.
        • Common etiologies include:

        1. Many patient with “high stress level”

        2. Poor habits including gum chewing, bruxism, hard candy chewing

        3. Poor dentition

        • Its treatment includes 4 phases of therapy which includes muscle exercises and drugs involving NSAIDs and muscle relaxants.
        • A bite appliance is also worn by the patient in the further stages to ‘splint’ the muscle movement.

        Myositis Ossificans

        • It is a condition wherein fibrous tissue and heterotropic bone forms within the interstitial tissue of muscle, as well as in associated tendons or ligaments.
        • It is of two types: localized and generalized.

        Localized myositis ossificans:

        It is caused by trauma or heavy muscular strains or by metaplasia of pluripotential intermuscular cnnective tissue.

        • The affected site remains swollen and tender, and the overlying skin may be red and inflamed.
        • There may present a difficulty in the opening of the mouth.
        • management is done by giving sufficient rest to the muscle and excision of the involved muscle after the process has stopped.

        Generalized myositis ossificans:

        • In this, formation of bone in tendons and fascia occurs along with subsequent replacement of muscle mass by the bony tissue.
        • The masseter muscle is the most frequently involved.
        • It usually occurs in children less than 6 years of age.
        • It shows an evidence of dense osseous structures in the greater part or whole of the muscle.
        • There is a gradual increase in stiffness and limitation in the motion of masticatory muscles. Ultimately, the entire muscle may get transformed into bone resulting in no movement.

        Management: there is no specific treatment. The muscles involved are to be excised.

        Literature Reviews

        –  Nakamura, Zerado and Yoshida  concluded that the masseter muscle’s activity level was significantly lower in the malocclusion group than in normal mice. It is, therefore, suggested that malocclusion interferes with optimizing the chewing pattern and establishing appropriate masticatory function.

        –  It is also suggested that masseter muscle activity decreases following a reduction in masticatory stimulation of the periodontal ligament. Persistence of this condition might inhibit the growth and development of masticatory muscles and their function.

        Angle Orthod. 2013;83:749–757

        –  Rowlerson, Raoul & Daniel concluded that there were significant differences in percentage of occupancy of fiber types in masseter muscle in bite groups with different vertical dimensions.

        –  Type I fiber occupancy increased in open bites, and conversely, type II fiber occupancy increased in deep-bites.

        –  The association between sagittal jaw relationships and mean fiber area was less strong, but, in the Class III group, the average fiber area was significantly different between the openbite, normal bite, and deepbite subjects.

        –  In the Class III subjects, type I and I/II hybrid fiber areas were greatly increased in subjects with deepbite.

        Am J Orthod Dentofacial Orthop 2005;127:37–46

        –  Keisuke, Yasuo and Kazuo employed electrophysiologic techniques (electromyogram) and found that masseter muscle activity decreases during the orthodontic treatment and this must be due to discomfort or pain and the alterations in the occlusal condition produced by the tooth movement or the ortho appliance itself.

        The Angle Orthodontist – Vol 66 no3 1996, 223-228

        –  Easton & David found that  there was an increase in action of lateral Pterigoid and Masseter muscles along with the slight increase in mandible in rats after treatment with a protrusive appliance

        AM J ORTHOD DENTOFAC ORTHOP 1990;97:149-58

        –  Carene & Steenberghe proposed that during the first phase of functional treatment ,reflexes in jaw muscles are transiently brought into imbalance. This phase of imbalance could act as a trigger for the mandible to attain a new functional position that subsequently leads to morphologic’ changes.

        AM J ORTHOD DENTOFAC ORTHOP 90: 41 O-41 9, 1986.

         

        CONCLUSION

        • The masticatory muscles include a vital part of the orofacial structure and are important both functionally and structurally.
        • The effect of muscle forces is three-dimensional although most orthodontists have considered it only one vector that is expansion.
        • A change in muscle function can initiate morphologic variation in normal configuration of the teeth and supporting bone, or it can enhance already existing malocclusion.
        • It is imperative that the orthodontist appraise muscle activity and that he conduct his ortho therapy in such a manner that the finished result reflect balance b/w structural changes obtain and the functional forces acting on the teeth an investing tissues at that time.

        REFERENCES

        • Oral diagnosis: the clinician’s guide- by Birnbaum, Dunne, 2nd ed.
        • Human anatomy by B.D. Chaurasia, 3rd ed.
        • Human anatomy by dental students by M.K.Anand, 1st ed.
        • Clinical anatomy and physiology for medical students, by Snell.
        • Essentials of oral anatomy, histology and embryology, by Avery and Chiego, 3rd ed.
        • Jco -volume 19 : number 08 : pages (584-587) 1985
        • Textbook of oral pathology by Shafers, 4th ed.
        • Textbook of oral medicine, by Avindrao ghom, 1st ed.
        • Oral anatomy and physiology, bu DuBuller
        • Burket’s oral medicine: diagnosis and treatment, 10th ed.
        • The Angle Orthodontist – Vol 66 no3 1996, 223-228
        • Virtual Journal of Orthodontics[serial online] 2011 September, 9 (2)
        • Am j orthod dentofac orthop 1990;97:149-58
        • Am j orthod dentofac orthop 90: 41 o-41 9, 1986.

IMPRESSION MATERIALS USED IN ORTHODONTICS

 

impression

INTRODUCTION:

The majority of impressions taken by orthodontists are used for pre- and post- records of dental arches.

 

“Restorations can be as true as your impressions”.

Continue reading IMPRESSION MATERIALS USED IN ORTHODONTICS

The underlying principle emphasizes the need for complete and accurate impression and highlights the importance of clinical impression procedures.

 

Purpose of impression is the formation of ‘positive’ model of the proper physical dimension, shapes and spatial relationship of these structures.

 

DEFINITIONS

 

Impression – An imprint or negative likeness of the teeth and/or edentulous areas where the teeth have been removed made in a plastic material which becomes relatively hard or set while in contact with these tissues.

 

-Boucher

 

Impression material – Any substance or Combination of substances used for making impression or negative reproduction.

 

-GPT 8

 

HISTORY

 

As early as the 17th century G. PURMAN of Breslau was said to have used wax for taking dental impressions.

 

During the late 1790s plaster was used to take impression for the famous dentures of Sir George Washington. (Dr. John Greenwood—a New York dentist)

 

In 1844-Westcott Dwinelle and Dunning started the use of PLASTER OF PARIS for taking impression for denture fabrication.

 

  • Elastic Impression first introduced to the dental profession in 1925 in the form of AGAR HYDROCOLLOID  called ‘Reversible Gel’. Since temperature changes its physical state.
  • ALGINATE HYDROCLLOID WERE DEVELOPED JUST BEFORE WORLD WAR 2(1930).
  • Since then, search for the ideal impression material has continued.

 

Historically, impression making was accomplished with inelastic materials for both soft and hard tissues.

 

Hydrocolloids ware initially introduced to make impression of hard tissues in place of inelastic materials.

 

After World War II, advances in polymer technology brought to the dental profession a group of synthetic rubbery materials called ‘ELASTOMERS’

 

They are capable of making impression of both hard and soft tissue.

 

In 1950s the rubber base material first in the form of Mercapton Polysulfide and later the Silicon began to be used as dental impression materials.

 

In 1994, Mitchell described a technique of occlusal registration for functional appliances using elastomeric bite registration materials.

 

The colloidal material used for making impression are either —-Agar or Algi dissolved in water –Hence the term Hydrocolloid impression materials.

 

Hydrocolloid impression materials can be classified as:-

 

  1. REVERSIBLE              eg. Agar
  2. IRREVERSIBLE         eg. Alginate

 

AGAR  – REVERSIBLE HYDROCOLLOID

 

In 1925, Alphous Poller of Vienna was granted a British patent for a totally different type of impression material.

 

It was later described by Skinner as colloidal sols of emulsified type.

 

Sears introduced reversible hydrocolloids in 1937

 

MODE OF SUPPLY:

 

 Supplied as gel in collapsible tube or as Cylinders in a jar.

 

COMPOSITION

 

INGREDIENT WEIGHT(%) FUNCTION
Agar 13-17 To provide dispersed phase
Borate 0.2-0.5 Provides strength
Sulfate 1-2 Gypsum hardener
Wax 0.5-1 Filler
Thixotropic materials 0.3-0.5 Thickener
Water Balance Reaction medium

 

 

 

The ADA specification No 11 sets standard properties required by agar hydro colloidal material.

 

Flow:

 

    The material should be able to record the fine details

 

Gelatin temperature:-

 

After boiling for 8 min, the material should be fluid enough to be extruded from container. After tempering the solution should be homogenous and should set between 37 and 45 when cooled.

 

The ADA specification requirement for flexibility allows a range of 4% to 15% at a stress of 14.2 psi.

 

Elasticity and elastic recovery:

 

Agar hydrocolloids are highly elastic in nature and elastic recovery occurs to the extent of 98%

 

Accuracy and dimensional stability

 

Agar impressions are highly accurate at the time of removal from mouth but shrink when stored in air and expand when stored in water.  The least dimensional change occurs when stored in 100% humidity but immediate pouring of cast is recommended.

 

Working and setting time:-

 

Working time ranges between 7-15 minutes and setting time is about 5 minutes.  They can be controlled by regulating flow of the water through cooling tubes.

 

 

 

Tear and Compressive strength

 

Tear strength is 4 psi (psi = pound per square inch)

 

Compressive strength is 800 gm/cm2.

 

MANIPULATION:

 

Conditioning unit is required for manipulation of agar. The Conditioner consists of

 

  • Boiling section
  • Storage section
  • Tempering section.

In boiling section, the material is kept for 10 min for liquefaction.

Then material is stored in storage section at 65deg.cel. in sol form until it is required.

Material is tempered at 45deg.cel. For 3 to 10 min so as to be tolerated by the patient.

Just before the tempering process for the tray material is completed, the syringe material is directly taken from the storage compartment and applied to teeth.  The water soaked on the layer of the tray hydrocolloid is removed from the container and gauge is removed.

The tray is immediately brought into position and seated with tight pressure and held with a very light force.

Gelatin is accelerated by circulating cool water (18-21deg.cel.) through the tray for 3-5 min.  After the gelatin is over, the tray is removed suddenly with a snap.

—  Advantages:

  1. Accurate dies can be prepared if handled properly.
  2. Good elastic property and reproduces undercuts  properly
  3. Well tolerated by patient
  4. Used for duplicating models.

—  Disadvantages:

1)      Flow is less Compared to recent elastic impression materials

2)      Gelatin may be painful to the patient.

3)      Tears relatively easily.

4)      Extensive equipment is required

Colloids exist as sol or gel.

A sol has the appearance and many characteristics of a viscous liquid.

A gel is a jelly-like elastic semisolid and is produced from a sol by a process called gelation.

It occurs in two ways

1) By temperature changes

2) By chemical means

TEMPERATURE CHANGES

Gelation in this case is a reversible process

Eg. Agar

The fibrils are held together by secondary molecular forces— they break at slightly elevated temperature and become re-established as the hydrocolloids cool to room temperature.

The temperature at which these changes occur is GELATION TEMPERATURE.

Gelation occurs at approx 37 deg. C temperature whereas liquifaction occurs at a higher temperature, i.e. 60-70 deg C higher than the gelation temperature.

This temp lag between liqueifaction and gelation is known as hysteresis.

 

CHEMICAL CHANGES

  • Conversion of sol           into       gel
  •  The fibrils formed are held together by primary bonds And is unaffected by  temperatures.

Hence, they are called IRREVERSIBLE HYDROCOLLOIDS

eg. ALGINATE

DIMENSIONAL EFFECTS

A majority of gel volume in hydrocolloid is made of water.

Gel may lose water by:-

a)Evaporation- from the surface

b)Syneresis- Exudation of fluid on the surface.

The exudate is not pure water, may be alkaline or acid depending on the composition of gel, both these process leads to SHRINKAGE.

Gel may absorb water if placed in water by a process called IMBIBITION causing gel to swell.

Both SYNERESIS and IMBIBITION should be avoided

As former can cause SHRINKAGE and later EXPANSION.

The dimensional changes are important in dentistry as any changes in dimension of impression after it has been removed from the mouth is a source of error.

IRREVERSIBLE HYDROCOLLOID

ALGINATE (IRREVERSIBLE HYDROCOLLOIDS)

It is extracted from certain brown seaweed.  The substance is called anhydro-beta-d mannuronic acid or alginic acid.

TYPES:-

1) Type I – Fast setting (1-2 min)

2) Type II- Normal setting ( 2-4.5 min)

COMPOSITION

INGREDIENT WEIGHT(%) FUNCTION
Potassium alginate       15% Dissolves in water and  reacts with calcium ions
Zinc Oxide        4% Acts as filler
Potassium titanium fluoride       3% Accelerator
Diatomaceous earth       60% Filler
Sodium phosphate        2% Retarder
Coloring  and Flowering agents      TRACES

 

CHEMISTRY AND SETTING REACTION

The chief ingredient of irreversible hydrocolloid is one of the soluble alginates. Reaction occurs by a chemical reaction.  Soluble alginates reacts with Calcium sulfate to produce insoluble calcium alginate as a gel.

 

The production of calcium alginate is delayed by the addition of a third soluble salt to the solution with which calcium sulfate will react in preference to the soluble alginate to form an insoluble calcium salt.

Thus, the reaction between the calcium sulfate and the soluble alginate is prevented as long as any of the added salt is left.  The added salt is called retarder.

The reactions that occur are

2Na3 PO4 + 3 CaS04 à Ca3 (Po4)2 +  3 Na2 So4  When the supply of retarder ( trisodium phosphate) is exhausted, Calcium ions begins to react with potassium alginate to produce calcium alginate.

Sod. Alg + n CaSo4 + H2Oà nNa2So4 + Cal Alg

GEL STRUCTURE

The gel structure consists of a brush heap of calcium alginate fibril network enclosing unreacted sodium alginate sol, excess water, filler particles and reaction by products.

It is a cross linked structure where calcium is responsible for cross linking.

CONTROL OF SETTING TIME:

Setting time can be altered by altering  the amount of water.

As the temperature increases, the setting time decreases.

For 10 rise of temperature 1 min reduction in setting time occurs.

Bowl and spatula also can be cooled to increase setting time.

MANIPULATION:

Gypsum can cause acceleration of setting of alginate

Alginate contamination can decrease strength of casts

For manipulations a clean bowl and metal spatula.

The First step in the manipulation is to prepare a proper mixture of water and powder.  Water is poured in to bowl and specified weight of powder  is added and powder is carefully incorporated into water with spatula.

A vigorous figure 8 motion is best with the mix being stopped against the sides of bowl with intermittent rotations of the spatula to press out air bubbles.  The final mix should be smooth creamy mixture that does not drip off the spatula when it is raised.  Mechanical devices are also available for mixing.  Their advantages are speed convenience and eliminating human errors.

   REMOVAL OF THE IMPRESSION

Alginate impression develops effective seal which can be freed by running the finger around periphery.  Impression should be removed suddenly with a jerk. Torquing or twisting should be avoided. After removal impression should be washed with water to remove saliva, covered with wet gauge to prevent synerisis and cast should be poured as soon as possible.

PROPERTIES

ADA specification No. 18 for alginate sets following standards

Mixing time:

Fast setting– 45 Sec

Normal setting – 60 Se

Working time:

Fast setting – 1.2 to 2minutes

Normal setting – 2-4.5minutes

Setting time:

Fast setting – 1.2 minutes

Normal setting – 2-4.5minutes

Over mixing Causes:

Reduction in final strength as gel fibrils are destroyed

Reduction in working time.

Under mixing Causes:

Lack of homogeneity and reduced strength

STRENGTH

—  The compressive strength of alginate ranges from 5000-8000gm/cm2.

—   The tear strength ranges between 350-700gm/cm2.

—              Both these properties are time dependent. If removal is delayed, strength increases.

—       The final strength depends on

—  W/P ratio: Too much or too little water reduces strength

—  Mixing time: Over and under mixing reduces strength

DIMENSIONAL STABILITY

—  Alginate impression lose water by evaporation and shrink in air. If placed in water it absorbs and swells. So cast should be poured immediately

Advantages

Inexpensive

Hydrophilic

Contact Angle 37 degrees (which means they will displace blood and saliva & pour well with gypsum stones)

Easy manipulation

Minimum equipment

Low cost

Accurate if properly handled

Disadvantages

Low tear strength

Poorer reproduction of surface details

Not Dimensionally stable on storage due to syneresis

RECENT ADVANCEMENTS

Zhermack advertised that the alginate impression can be kept up to 48 hours prior to pouring in their long life Hermetically sealed bags

The Vanilla flavoured Orthoprint is Anti Nausea.

Vival NF: Dimensionally stable for up to 100 hours.

High tear strength alginates: Silicone reinforced two paste system one with alginate, other with calcium reactor. It has higher tear strength

Self disinfecting alginates containing iodophor.

Dust free alginates: Organic glycol is used to agglomerate the dust particles

LAMINATE TECHNIQUE/ALGINATE AGAR METHOD

In this technique agar in the syringe is injected on to the area to be recorded, an impression tray containing chilled alginate is placed over it. 

The alginate sets by chemical reaction, where as agar gels by means of contact with cool alginate. Since agar is in contact with teeth maximum detail can be obtained.

MODIFIED ALGINATES:

Traditionally alginate is supplied in two component system, powder and water.  But other forms are also available.

In the form of a solution containing water and a reactor of plaster of Paris

As a two paste system one containing solution and other calcium reactor. These materials contain silicone and are supplied in tray viscosity and syringe viscosity.

DISINFECTION

Rinse the impression

Place in zip lock bag, pour in disinfectant to cover all surfaces

Seal for 10 minutes

Remove and rinse prior to pouring stone

Chlorhexidine has also been incorporated to limit cross infection (Hydrogum + CHX- Zhermack)

ELASTOMERS

Polysulfide

Condensation polymerizing silicone

Addition polymerizing silicone

Polyether

Each type is further divided into four viscosity classes

Light body

Medium / regular body

Heavy body

Putty

GENERAL PROPERTIES

Excellent reproduction of surface details. The low viscosity is able to record fine details

They are hydrophobic. So oral tissues in the area of impression should be dry.

Co-efficient of thermal expansion of elastomers is high.  So thermal contraction of set material occurs when transferred to room temperature

Tear strength is excellent. So impressions can be removed from thin areas.

The elastomeric materials can be copper/silver plated

Shelf life of elastomers is good

Dimensional stability

For visco-elastic material slow elastic recovery may control for sometime after withdrawal of the impression, producing dimensional change. In this case the dimensional change results in more accurate impression.

But many impression materials contain volatile substances either as primary components or as by products of setting reaction. Loss of such volatile materials results in shrinkage of impression material resulting in decrease in accuracy. So for majority of materials, accuracy can be maintained by pouring the cast soon after the removal of impression.

Curing shrinkage

Loss of byproducts

Polyether being hydrophilic absorbs water and loses soluble plasticizers causing change in dimension

Thermal contraction when transferred from mouth to room temperature

Incomplete elastic recovery after deformation during removal

Amount of filler

Uniform thickness of material gives more accurate impression

Time of pouring of impression. Impression should be powered after elastic recovery and before dimensional change

POLYSULFIDES

Also called as Mercaptan or Thiokol

MODE OF SUPPLY

It is supplied in tubes as base and accelerate in paste form

Available in three viscosities

Light bodied

Medium bodied

Heavy bodied

COMPOSITION

 

     BASE PASTE     FUNCTION
Polysulfide polymer – 80-85% This is further polymerized and cross linked to form rubber
Filler (Titanium dioxide zinc sulfate) – 16-18% To provide required strength
Plasticizer (Dibutyl Phthalate) To provide appropriate viscosity
Small quantity of sulphur – 0.5% To accelerate the reaction

 

Accelerator paste

Lead dioxide – 60-68% To react with thiol group causing setting and give brown colour
Filler and plasticizer To provide strength and to give adequate viscosity
Oleic / stearic acid Act as retarder to control rate of setting reaction

 

CHEMISTRY AND SETTING REACTION

The main component of polysulfide is a multifunctional mercaptan (-SH) or polysulfide polymer. These linear polymer contains pendent –SH groups

Reaction yields water as by product

PROPERTIES

Unpleasant odour and colour

It has a long Setting time of 8 to 12minutes

Mixing time is 45 seconds

Excellent reproduction of surface detail

Dimensional stability:

The curing shrinkage is high (0.45%)

Has the highest permanent deformation (3.5%)

This improves with time.  So pouring of model should be delayed by half an hour

Tear strength is 4000 gms/cm2

It has good flexibility.  A 2mm spacing in the tray is sufficient to make the impression.

It is hydrophobic.  So impression area should be dry

Shelf life is good i.e. 2 years

SILICONE RUBBER IMPRESSION MATERIALS

            Types:

            Two types of silicone impression materials are available based on the type of polymerization reaction occurring during setting

Condensation silicone

Addition silicone

MODE OF SUPPLY

Available as base and catalyst in paste form. The condensation silicone catalyst can also be supplied as a liquid. The putty is supplied in jars.

Condensation silicone is available in three viscosities.

Light bodied

Medium bodied

Putty

CONDENSATION SILICONES

BASE PASTE

Hydroxyl terminated polydimethyl siloxane Undergoes cross linking to form rubber
Colloidal silica Filler

REACTOR PASTE

Tetraethyl orthosilicate Cross linking agent
Stannous octate Catalyst

 

CHEMISTRY AND SETTING REACTION

It is a condensation reaction

Polymerization occurs as a result of cross linkage between orthoethyl silicate and terminal hydroxyl group of dimethyl siloxane to form a three dimensional network

Stannous octate acts as a catalyst

Ethyl alcohol is by product. Its evaporation probably accounts for much of the condensation taking place in set silicone impression

     PROPERTIES

Pleasant colour and odour

Setting time is 6-8 minutes, mixing time is 45 seconds

Excellent reproduction of surface details

Dimensional stability is low due to high curing shrinkage (0.4-0.6%) and shrinkage due to evaporation of ethyl alcohol. To avoid this cast should be poured immediately.

Tear strength is 3000gm/cm2

It is hydrophobic.  So impression field should be dry

Can be electroplated with silver or copper

Evaporation of alcohol can lead to dimensional instability

Production of hydrogen can lead to pitting of dental stone surfaces.

ADDITION SILICONES

Superior to condensation silicones

Also called polyvinyl silioxane impression materials.

COMPOSITION

            Base:

Polymethyl hydrogen siloxane

Other siloxane prepolymers

Fillers

            Accelerator

Divinylpolydimethyl  siloxane

Other siloxane prepolymers

Fillers

Platinum salt-catalyst

CHEMISTRY AND SETTING REACTION

It is an addition reaction

In this case polymer is terminated with vinyl groups and it is cross linked with silane (hydride group). The reaction is activated by platinum salt

No reaction byproduct develops as long as correct proportions of vinyl siloxane and silane siloxane are maintained

-Sulfur compounds retard the setting of addition silicone.

PROPERTIES

Pleasant colour and odour

Good reproduction of surface details

Setting time is 4-7 minutes and mixing time is 45 seconds

It has the best dimensional stability among all elastomers. It has low curing shrinkage (0.17%) and low permanent deformation (0.05-0.3%)

Good tear strength (3000gm/cm2)

It is hydrophobic with contact angle 80deg. – 100deg. so impression field should be dry

Can be electroplated with copper/silver

Shelf life ranges from 1-2 years

POLYETHER

Mode of Supply:

Available as base and accelerate paste in tubes

Available in three viscosities

Light bodied

Medium bodied

Heavy bodied

COMPOSITION

Base:

Polyether polymer                   Cross linked to form rubber

Colloidal silica                        Acts as filler

Glycol ether (or) phthalate     Plasticizer

Accelerator Paste:

Alkyl aromatic sulfonate         Initiates cross linking

Colloidal silica                        Filler

Phthalate                                 Plasticizer

PROPERTIES

Pleasant odour and taste

Setting time is short 3.5minutes, mixing time is 30 seconds

Good dimensional stability

Curing shrinkage is 0.24%

Polyether absorbs water and can change in dimension. So should not be stored in contact with water or in humid climates

It is extremely stiff

Tear strength is 3000gm/cm2

Hydrophilic, has good compatibility with stone

Can be electroplated

Good shelf life i.e., more than 2 years.

IMPRESSION MAKING WITH ELASTOMERS

It involves five steps:::

  1. Preparing a tray
  2. Preparing the material
  3. Making impression
  4. Removing the impression
  5. Preparing stone casts and dies

            PREPARING A TRAY:

Impressions are usually made with custom trays. Perforated stock trays are used for making impression in putty.

To prepare a custom tray, an alginate impression is made and stone cast is constructed

Teeth are covered with modeling wax (1 or 2 sheets approximately 3-4mm) to act as spacer and stops are provided

Custom tray is prepared with tray material

Slightly roughened surface of tray inside improves retention.

PREPARING THE MATERIAL:

Materials are provided in two paste tubes

Same length of materials should be dispensed on to mixing pad

Catalyst paste is first collected on to spatula and then distributed over the base

Mixing should be thorough, uniform in colour with no streaks of base of catalyst

If one of the components is in liquid form such as catalyst for condensation silicone, a length of base is dispensed from tube onto the mixing pad and a drop of catalyst is added for each unit length of base.

Putty consistence are dispensed by volume using equal number of scoops and kneaded.

Automatic mixing and dispensing devices are available used for light, medium and heavy body consistencies.

It consists of a double barrel gun with mixing tip. The tip consists of spiral inside.   The mixing tips vary in diameter length and size of the tip opening for specific consistency.

 POLYETHER IMPRESSION MATERIALS

It has the advantages over hand mixing

Less air bubbles

Reduced working time

More uniform mix

A recent development in the automatic mixing and dispensing device is a dynamic mechanical mixer. Materials are supplied in plastic bags housed in a cartridge. Device uses a motor to drive parallel plunger that force the materials into a mixing tip and the spiral inside the mixing tip rotates as the materials are extruded through the tip.  With this uniform mix of even higher viscosity material can be achieved

       Making of impression

Initially tray is coated with adhesive that forms bond between tray and impression material. Slightly roughened surface of tray increases adhesion.

      METHODS OF MAKING IMPRESSION

Three techniques

Single mix technique

Multiple mix technique

Reline technique

Single Mix technique:

Viscosity used is regular body

Method:

The paste is mixed and part of it is loaded into tray and part into syringe.  The syringe material is then injected on to the prepared area.  Then tray is seated over it.

Multiple mix technique

Viscosity used is heavy body and light body

Method

            The two viscosities are mixed simultaneously on separate pads. Heavy body is loaded onto the tray and light body in to syringe. The syringe material is injected into area of preparation. Tray with heavy body is seated over it.

Reline technique:      

Viscosity used is putty and light body

Two approaches are present

Two stage procedure

Single stage procedure

—  For two stage procedure, thick putty material is placed in stock tray and a preliminary impression is made.  This forms an intra oral custom tray.  Space for light body or was is provided whether by cutting away some of the putty or by using thin polyethelene sheet as a spacer between putty and prepared teeth.

—  A mix of thin wash material is placed into putty and putty with combination tray is seated finally to make impression.

For single stage procedure,  material is syringed into place and then unset putty is seated over light body but the disadvantage is that putty may displace light body.

Removal of the impression:

The material is checked for set by probing with the blunt instrument.  Then impression is dislodged from the mouth with a steady pressure

APPLICATIONS:

  1. Impressions for fixed partial dentures
  2. Impressions for removal partial dentures
  3. Impressions for complete dentures
  4. polyether is used for Border moulding
  5. To make impressions for implant procedure
  6. In maxillofacial prosthesis
  7. To make impression in orthodontic cases for study model

REVIEW OF LITERATURE

# Andree, Alfred and Christoph evaluated the dimensional accuracy of monophase elastic impression making with addition silicone and polyether and found no significant change.

 int J Prosthodont . 2002;15:168–174

# Steven O Hondrum assessed the shelf life of different elastomers like polyether, polysulfide, additive silicone and found all the materials were fairly efficacious. But addition silicone showed better value during 72 month period and polysulfide with a little change.

Journal of prosthodontics 2001 Jan;85(1):73-81.

#  The influence of mixing methods and disinfectant on the physical properties of alginate impression materials.

The European Journal of Orthodontics Advance Access published May 10,2012

# Ohn Chai, Yutaka investigated modulus of elasticity, strain and tear energy of VPS, polysulfide and polyether and concluded that high strain tolerance of PVS allows their removal without distortion from undercuts. The high tear energy of polysulfides indicates their superior resistance to tear in thin sections

Volume 15, Number 2, 2002 183 The International Journal of Prosthodontics.

# Alvin G. Wee evaluated the accuracy of solid implant casts fabricated from different impression materials (Polyether, AS, CS, polysulfide) and concluded that polyther (medium) was recommended for direct implant impression

# Shirley, John H Park and Daneil E. Tira compared  the accuracy of one step putty wash with two step putty wash of addition silicone impression. They found different was not significant.

J Prostho Dent 2010;103:228-239;

# Kern and Reinhold tested the influence of disinfectants (MD/520 and impresept) on the accuracy of reversible hydrocolloid and found accuracy change was not significant.

j.of prostodontic 1993 Nov;70(5):449-56

# Willium Heisler and Anthony evaluated for dimensional accuracy and bond strength of irreversible hydrocolloid with reversible hydrocolloid system and found that accuracy was suitable for clinical use and bond strength was similar to tear strength of reversible hydrocolloid.

J Prosthet Dent. DOI:10.1016/0022-3913(92)90369-L

# L.W. Carlyle evaluated compatibility of irreversible hydrocolloid with three dental stones (Die keen, Quick stone, Hemihydrate). Results showed that Die keen was most compatible.

J Prosthet Dent. 1983 Mar;49(3):434-7.

# Paul, Gardener and Steven conducted a study to evaluate the effect of storage time in a 100% humid environment on the accuracy of gypsum casts poured from reversible hydrocolloid impression and concluded that reversible hydrocolloid can be stored in 100% humidity for 60 minutes before pouring.

(J Prosthet Dent 2001;86:244-50.)

 

 

 

 

REFERENCES

  • Anusavice. Dental Material, 11th edition
  • Robert G. Craig. Restorative Dental Material
  • Smith. The clinical handling of Dental material
  • International Journal of Prosthodontics, 2002; 15: 168-174.
  • Journal Prosthet Dent, 2000; 83: 161-165
  • Journal Prosthet Dent, 2001; 85: 73-81.
  • International Journal of Prosthodontics, 1998; 11: 219-23
  • Journal Prosthet Dent, 2000; 83: 323-31.
  • Journal Prosthet Dent, 2003; 90: 354-64.
  • International Journal of Prosthodontics, 1992; 5: 55-8.
  • Journal Prosthet Dent, 1990; 63: 12-15
  • J Prosthet Dent, 1993; 70: 449-53
  • BJO mayed.1998VOL25 NO.2

 

Want to avoid a hangover? Drink Sprite

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Put aside that tomato juice and greasy breakfast for a moment: A new hangover cure is on the scene, backed by some chemical evidence — and chances are you’re already familiar with this beverage.

The carbonated lemon-lime drink Sprite emerged as a potential reliever of alcohol-related symptoms in a study published late last month in the journal Food & Function. Researchers in China conducted the research on the chemical causes and effects of a hangover, and how best to disrupt them.

Continue reading Want to avoid a hangover? Drink Sprite

Hangovers are commonly thought to be caused not by the alcohol itself in a drink, but by one of the chemical byproducts produced when our bodies metabolize ethanol. When we drink a boozy beverage, ethanol is broken down first into acetaldehyde, which causes the feelings of a hangover, and then into acetate, which is not only thought to be harmless in terms of hangover symptoms, but also may contain some of the health benefits of alcohol consumption, such as a jolt of energy for the brain.

Acetaldehyde, on the other hand, was the enemy in the China study, and researchers focused on how best to limit the body’s exposure to it in the process of digesting alcohol. They hypothesized that by acting on two key enzymes — one that breaks down ethanol into acetaldehyde (alcohol dehydrogenase), and subsequently the one that breaks acetaldehyde into acetate (aldehyde dehydrogenase) — that they could shorten the entire process and limit the effects of a hangover.

Hua-Bin Li and colleagues at Sun Yat-Sen University in Guangzhou systematically tested the effect a variety of common carbonated beverages and herbal teas had on ADH and ALDH, and measured levels and activity of the enzymes accordingly.

Some of the drinks tested, including a herbal infusion known as Huo ma ren (a hemp-seed based beverage), were found to increase the activity of alcohol dehydrogenase, hastening metabolism of ethanol into toxic acetaldehyde, while interestingly also inhibiting aldehyde dehydrogenase in the process, reducing acetaldehyde removal and possibly prolonging or worsening hangover and other alcohol-withdrawal symptoms.

By contrast, some drinks studied markedly increased aldehyde dehydrogenase activity, thus promoting rapid breakdown of acetaldehyde, possibly helping to minimize the harmful effects of drinking alcohol. Among these drinks were Xue bi and Hui yi su da shui, fizzy drinks better known in North America by their English names: Sprite and soda water, respectively.

Edzard Ernst, a medical expert at the University of Exeter in the U.K., says the results are interesting, but cautioned against an over-reliance on this “cure,” especially before the results can be independently replicated.

“These results are a reminder that herbal and other supplements can have pharmacological activities that can both harm and benefit our health,” he said.

Source – NationalPost