First published as Restauri diretti nei settori posteriori in 2019 by Quintessenza Edizioni in Milan, Italy.
WeRestore.it (http://www.werestore.it) is an educational project established by the authors. The project aims for excellence by developing ideas, articles, videos, texts, materials, procedures, and research projects. The authors hold regular and ad hoc training courses in English at their teaching center in Rome.
Library of Congress Cataloging-in-Publication Data
Names: Scolavino, Salvatore, author. | Paolone, Gaetano, author.
Title: Posterior direct restorations / Salvatore Scolavino, Gaetano Paolone, .
Description: Batavia, IL : Quintessence Publishing, Co, Inc, [2021] |
Includes bibliographical references and index. | Summary: “Describes
methods of performing restorations for posterior teeth, beginning with a
discussion on anatomical features of each tooth and then describing
cavity preparation to the buildup, modeling, detailing, and finishing of
restorations that closely mimic natural tooth anatomy for optimal
esthetics and function”-- Provided by publisher.
Identifiers: LCCN 2019048839 (print) | LCCN 2019048840 (ebook) | ISBN
9780867158236 (hardcover) | ISBN 9781647240042 (ebook)
Subjects: MESH: Dental Restoration, Permanent--methods | Molar
Classification: LCC RK653.5 (print) | LCC RK653.5 (ebook) | NLM WU 300 |
DDC 617.6/95--dc23
LC record available at https://lccn.loc.gov/2019048839
LC ebook record available at https://lccn.loc.gov/2019048840
© 2021 Quintessence Publishing Co, Inc
Quintessence Publishing Co, Inc
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All rights reserved. This book or any part thereof may not be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, or otherwise, without prior written permission of the publisher.
Editor: Bryn Grisham
Design: Sue Zubek
Production: Sarah Minor
Printed in China
To Mom and Dad, for the love and values they have passed on to me,
to my brothers,
to my wonderful, beloved Maria, for always being by my side,
to my children Francesco, Giuseppe, and Mariapaola, that they may live life in search of knowledge and be free to follow their dreams.
-Salvatore
To my parents,
to my sister,
to Isabella, my marvelous traveling companion,
to my children Chiara and Edoardo, that they may always be free and curious.
-Gaetano
Forewords
Preface
Contributors
1 Shape and Visual Perception
2 Anatomical Knowledge for Modeling
3 Diagnosis and Treatment of Early Caries Lesions
4 Isolation
5 Cavity Preparation
6 Restoring the Interproximal Wall
7 Occlusal Modeling
8 Detailing
9 Finishing, Polishing, and Finalizing the Occlusion
10 Clinical Cases
Index
Over the last 30 years, bonding agents and restoration materials have steadily improved. Bonding has radically changed anterior and posterior dental reconstructions, and current treatments are increasingly conservative and esthetic.
The authors of this admirable book have achieved the ambitious aim of providing dentists with state-of-the-art procedures for direct restoration of posterior teeth using composite resin. The book is masterfully illustrated and guides the reader through the various clinical stages from diagnosis to polishing and finishing of restorations. Numerous clinical tips are also described, based on their experience as methodical yet creative practitioners. The chapter on dental anatomy is particularly interesting. Such information is essential to ensure appropriate yet durable function.
Though entertaining to read, the various chapters are never trivial and always supported by scientific evidence. Different materials are widely discussed, and step-by-step clinical procedures are given to provide students and dentists with the information they need to achieve top-quality direct restorations.
Writing this foreword is a privilege and honor because I am sure this worthy text will be widely read.
Roberto C. Spreafico, DM, DMD
Private Practice
Milan, Italy
This long-awaited book is a guide for anyone who wishes to devote time to genuine conservative dentistry. Ideal anatomical reconstruction is possible through simple and effective techniques. The dominant themes of this book are diagnosis, anatomy, perception of shape, preparation, and anatomical reconstruction.
It is a great pleasure to write this foreword and advise everyone to read this work. The authors are dear friends whom I have known long enough to be able to appreciate their professional commitment and capacities. This book truly reflects the passion they pour into their daily work and their desire to improve the profession.
Vincenzo Musella, DMD, MDT
Adjunct Professor
Dentistry and Dental Prosthetics
University of Modena and Reggio Emilia
Modena, Italy
This book is the outcome of ideas, dreams, discussions, and debates started and continued in phone calls, messages, Skype sessions, and many companionable train journeys from Rome to Naples and back again, with the stunning Italian landscape as a backdrop.
This book also includes the essence of all the places it was written—rarely at a desk, often on a train or airplane heading to another faraway place to attend lectures and courses, next to a power outlet in an airport, in yet another hotel eating a quick meal, at a café table in a train station, or in the car waiting for our children to come out of school.
It reminds us of all the hours we spent writing, thinking, drawing, and advising one another after putting the children to bed or early in the morning in order not to steal valuable time from our families. As you read this book, we hope you will appreciate the endless hours we lavished on documentation. The work is part of ourselves.
Thank you to:
Vincenzo Musella, for encouraging and helping us to write this book. Without him, it would probably never have come to fruition.
Lauro Dusetti for his friendly support and useful advice.
Sergio Ariosto Hernández Delgado for allowing us to use his photograph on the cover.
Maciej Jùnior for supplying us with the colored composites we used to illustrate some in vitro modeling techniques.
Maria M., Maria C., Felicia, Patrizia, and Stefania—our irreplaceable assistants—because nothing would have been possible without them.
The Italian Academy of Conservative and Restorative Dentistry (AIC) for its passion, integrity, and professional diligence. The AIC remains a benchmark for those who are passionate about restorative dentistry.
The authors would like to thank the following individuals for their valuable contributions to this book, which are indicated in the text.
Tiziano Bombardelli, MD, DDS
Private Practice
Trento, Italy
Lucio Daniele
Private Practice
L’Aquila, Italy
Roberto Kaitsas, DMD
Private Practice
Rome, Italy
Giovanni Sammarco, DDS
Adjunct Professor
Restorative Dentistry
Insubria University
Varese, Italy
Private Practice
Trento, Italy
To construct occlusal morphology, it is necessary to know exactly how to observe the form to be replicated and to have a good knowledge of dental anatomy. The human brain may be considered a nearly perfect machine, but it will try to make its work simpler by expending as little energy as possible for maximum results. These mental shortcuts lead to limitations in a person’s ability to accurately observe shape. This chapter explains how to overcome these limitations through visual decomposition.
The concept of shape, concerning an object’s outward appearance, is inseparably linked with the concept of function: Objects are shaped in accordance with the function for which they were designed. For example, the hand, a tactile sensory extension of the brain, can perform prehensile functions because its thumb opposes the other fingers: Many of the fine, precise movements that can be performed with the hand, particularly the fingers, would no longer be feasible if the thumb were aligned with the forefingers. A study of shape begins with a perceptual analysis of how things are done. Visual perception is the outcome of integrating and processing an image through a series of mental processes that are influenced by the observer’s cognitive resources (cognitive processing stage). Cognitive experience is influenced by previous experiences as the brain establishes similarities between things that are currently being observed and things that are already known. Full perception of an object (shape) and the ensuing emotional experience can only come about when the various information has been assimilated.
Perception of objects is made possible by two types of stimuli: distal and proximal.1 A distal stimulus allows us to perceive an object’s physical presence. A proximal stimulus leads the observer to the information needed to arrive at the distal stimulus. In other words, we recognize an apple (distal stimulus) because it is roundish and red in color and has two depressions (proximal stimulus). Based on the proximal stimulus (characteristics of the observed object), we can perceive an object’s presence (distal stimulus) through a process that allows us to create a perceptive representation of the object by reproducing the information embedded in the proximal stimulus.
The Gestalt philosophical movement, established in Germany by Max Wertheimer (1921), Wolfgang Kohler, and Kurt Koffka (1935), adopts an interesting approach to shape. According to this philosophy, “The whole is greater than the sum of its parts.”2 The overall shape is conditioned by the perceptive capacities, which include perception of:
The perception of outlines defines an object’s visual perimeter, which essentially depends on the observation perspective: Different perspectives of observation will correspond to different visual perimeters.
Figure 1-1 shows the same tooth observed from two different perspectives. Marking the outlines of both teeth (in blue) establishes the differences between the visual perimeters. This demonstrates that when observing a tooth, we must observe it from all possible perspectives in order to appreciate its true morphologic variations. Each observation perspective will supply the brain with information that, when assimilated by the memory, can be processed to assemble a perceived overall form.
FIG 1-1 (a and b) Maxillary second molar from two perspectives, outlined in blue. (c and d) Viewing the outlines alone demonstrates how the visual perimeters change based on perspective.
For example, when performing a Class 2 restoration, the first step is to convert cavities to Class 1 in order to redefine the outline and make it easier to reconstruct the occlusal surface. The optical perception of a restored outline defines the peripheral limits and provides the morphologic information necessary to simplify the occlusal restoration procedure.
The perception of space and ratios defines the relationship that the object establishes with the surrounding space and other elements present in the field of observation as well as relationships established between the object’s constituent parts: everything must be in relative proportion (Fig 1-2).
FIG 1-2 Note the anatomical relationships between the constituent anatomical parts of each molar, between the two molars, and in the space surrounding and between the molars.
Perception of light and shadow plays a crucial role in perceiving an object’s 3D shape and surface details (Fig 1-3). If light is completely removed from the image of the molar shown in Fig 1-1a, only the outline of the figure can be perceived (Fig 1-4a), which is only possible due to the distinct contrast between the image and the white background. If the white background of the same image is replaced by a black background (Fig 1-4b), the shape is not perceptible. Similarly, if all the shading is removed from the molar in Fig 1-1a, only the outline can be perceived, and this is only due to the distinct contrast between the image and the black background (Fig 1-4c). If the black background of the same image is replaced by a white background, the shape is not perceptible (Fig 1-4d).
FIG 1-3 Relationship of light and shadow in an occlusal view of a maxillary molar.
FIG 1-4 (a) Molar from Fig 1-1a with all light removed. (b) Without a contrasting background, the shape is imperceptible. (c) Molar without shading. The shape can be perceived against the contrasting background. (d) Without contrast, the image is imperceptible.
All these perceptions (proximal stimuli) integrate with one another to define our perception of the whole, ie, the overall shape (distal stimulus). Visual recognition of a figure or object can be described as assimilation and alignment of a retinal image with a representation stored in our memories. Previous experiences influence visual perception so much that the shapes in Fig 1-5 look like a circle and a rectangle even if they are drawn as dashed lines.
FIG 1-5 Even though what is shown is a series of dashed lines that do not form complete shapes, the brain draws on its cognitive experience to simplify the information as a circle and a rectangle.
This happens because the data collected are organized in the simplest and most coherent way possible (law of closure). The brain is consistently wired to process observed images in accordance with a simplified process that Gestalt theory describes as the “law of past experience”: the brain associates the image of every observed object with a known shape to simplify the perceptive mechanism.3 The simpler and more regular shapes are, the less likely they are to evade perception (this is called the law of pragnanz, ie, that something should be concise and meaningful).3
In her book Drawing on the Right Side of the Brain, Betty Edwards sets out the fascinating results of her studies regarding the influence of previous experiences on perception.4 The fact that one half of the brain is dominant over the other greatly affects the perceptual capacities, especially considering that the right hemisphere expresses one’s artistic and creative side, while the left hemisphere expresses one’s analytical, rational, and logical side. According to Roger Sperry (1913–1994), if the left hemisphere dominates over the right, an individual finds it difficult to perceive, analyze, and process shape. If the opposite is true, the individual has a strong artistic bent.5 The neurosurgeon Richard Bergland made this clear when he wrote in 1985, “You have two brains: a left and a right. Modern brain scientists now know that your left brain is your verbal and rational brain; it thinks serially and reduces its thoughts to numbers, letters and words… Your right brain is your nonverbal and intuitive brain; it thinks in patterns, or pictures, composed of ‘whole things,’ and does not comprehend reductions, either numbers, letters, or words.”6 When a subject’s creative side is subdued by the left side, conditions must be created to wake up the right side.
In one of her experiments, Edwards invited her study participants to copy a known design, eg, the Mona Lisa, upside down. This experience disorients the participants, depriving them of any remembered reference that can be traced back to the image, thus simulating their visual perception. It would be interesting if individuals could begin to observe things with a different perceptual approach, freeing themselves from previous patterns and cultural experiences that undermine perceptive capacities and creativity.
The figure/background principle, or the relationship between the figure and the background it dominates, is known as the principle of contrast and lies at the root of visual perception; according to the Danish psychologist Edgar Rubin (1886–1951), the presence of a body is perceived only by contrasting the observed body with its background.7 When clues are few or ambiguous, our minds find it difficult to decide which shape should be the figure and which should be the background (Fig 1-6).
FIG 1-6 The image illustrates the concept of figure/background. Looking at the figure, one can perceive the face of a woman and/or see a man playing a saxophone. The information between the figure and the background is not well defined, which causes the mind to be conflicted and unable to distinguish the figure from the background.
“ Where there is bright light or no light at all, shape does not exist. The balance between light and shade allows shape to be perceived in its finest details.”
Visual decomposition, ie, dismantling each individual element making up the object from all the others, seems to make the shape clear and simple to perceive. If one observes each individual element, analyzes it in detail, and then reassembles the parts, everything acquires a new perception. In geometric terms, a figure is essentially made up of:
This holds true for teeth, which can be equated to geometric figures made up of edges, vertices, and surfaces (Fig 1-7).
FIG 1-7 Tooth surfaces, vertices, and edges.
Transition areas can be equated to rounded edges linking two or more opposing surfaces9 (Figs 1-8 and 1-9). Bearing in mind the enormous intra- and interindividual anatomical variability occurring in nature, careful observation of the occlusal surface of a posterior tooth reveals that all occlusal anatomy stems from the occlusal perimeter, ie, the set of anatomical summits representing the angle of transition from the buccal, mesial, distal, and palatal/lingual surfaces toward the occlusal surface.
FIG 1-8 Tooth surfaces and representation of transition areas.
FIG 1-9 (a and b) Graphic representations of a tooth showing that it is made up of a set of edges and transition areas, where the number of variables is infinite, and every small detail is important.
To see how the occlusal surface of a molar is constructed, its structural components must be broken down. For example, if a mesiobuccal cusp of a maxillary molar is broken down, we can see that it is made up of:
Close examination of the triangular ridge (Fig 1-10) reveals that it is defined by:
FIG 1-10 Triangular ridge broken down into the cusp crest, mesial and distal slopes, and grooves.
It therefore follows that:
The interrelationship defined between the parts of the observed object is reflected in the expressive force of the perceived image: the triangular ridge is perceived because slopes and grooves are present; one slope of the triangular ridge is perceived because this is delimited by a cusp crest and a groove; and a groove is perceived because this is contained between two slopes. Everything depends on what is being examined and the perspective of observation.
Rudolf Arnheim states that, “Perceptual shape is the outcome of an interplay between the physical object, the medium of light acting as the transmitter of information, and the conditions prevailing in the nervous system of the viewer. The shape of an object we see does not, however, depend solely on its retinal projection at a given moment. Strictly speaking, the image is determined by the totality of the visual experiences we have had with that object, or with that kind of object, during our lifetime.”11 With reference to the observation of things in general, Arnheim stresses that “detail is everything” and overall shape is nothing more than a set of details that define it: without detail there is no shape.
The take-home message is that a tooth is anatomically made up of a set of details that interact with one another to define the perceived overall shape.
1. Levitin DJ (ed). Foundations of Cognitive Psychology: Core Readings. Cambridge: MIT, 2002.
2. Ginger S. Gestalt Therapy: The Art of Contact. New York: Routledge, 2007.
3. Spagnuolo Lobb M. The Now-for-Next in Psychotherapy. Gestalt Therapy Recounted in Post-modern Society. Milan: Franco Angeli, 2013.
4. Edwards B. Drawing on the Right Side of the Brain, ed 4. New York: Penguin Group, 2012.
5. Colwyn T, Sperry RW. Brain Circuits and Functions of the Mind: Essays in Honor of Roger W. Sperry. Cambridge: Cambridge University, 2008.
6. Bergland R. The Fabric of the Mind. New York: Viking, 1985.
7. Pind JL. Edgar Rubin and Psychology in Denmark: Figure and Ground. Cham, Switzerland: Springer, 2014.
8. Brogi C, Brogi G. L’Opera di Corrado Brogi—Volume IV: La geometria descrittiva, la trigonometria sferica, solidi geometrici e la cristallografia. Scotts Valley, CA: Createspace, 2014.
9. Miceli GP. Mimesis: Imitation and interpretation of a natural tooth through shape & colour: Part I. Spectrum Dialogue 2006;5(6).
10. Scolavino S, Paolone G, Orsini G, Devoto W, Putignano A. The simultaneous modeling technique: Closing gaps in posteriors. Int J Esthet Dent 2016;11:58–81.
11. Arnheim R. Art and Visual Perception, ed 2. Berkeley: UC Press, 2004.
(PHOTOGRAPH COURTESY OF STANISLAV GERANIN, POLTAVA, UKRAINE.)
A direct bonded composite restoration must blend into the tooth structure in terms of morphology and color. Just as no two teeth are identical, one model should never be the same as another. It is essential to study dental anatomy to know how teeth are made. This allows a faithful reproduction to be constructed that fulfills two fundamental objectives: blending in with remaining healthy tooth tissue and ensuring proper function during chewing movements.
This chapter describes the anatomical principles behind modeling, paving the way for relating the model to the residual tooth anatomy through interpolation of missing parts.
The clinical anatomy of posterior teeth is characterized by certain well-defined elements explained in the following definitions and in Figs 2-1 to 2-5.
FIG 2-1 Main anatomical elements of the occlusal surface of a molar: cusp ridge (A), supplemental groove (B), central fossa (C), central developmental groove (D), marginal ridge (E), and the occlusal perimeter is A and E together.
FIG 2-2 Ridge slope (F) and cusp crest (G).
FIG 2-3 Cusp tip (blue), cusp slope (orange) cusp ridge (red), and cusp crest (purple).
FIG 2-4 Transverse ridge (H).
FIG 2-5 Oblique ridge (I).
Fossae form where grooves meet one another: If there are three, the fossa will be triangular; if there are four, the fossa will be four-sided (Fig 2-6). The distinguishing traits of maxillary molars are always present and identify them as maxillary molars (Fig 2-7). Figure 2-8 shows two maxillary left first molars; they can easily be identified as maxillary molars even though they differ completely from one another in terms of cusp morphology, mesial marginal ridge type, and number of cusps. The characteristic traits include the presence of a central fossa, buccal groove, central developmental (mesiodistal) groove, distopalatal groove, and oblique ridge in particular positions. The characteristic shape, position, and dynamic function of these all-important anatomical elements must be understood. During occlusal reconstruction, the residual anatomical details are analyzed in order to extrapolate the missing shapes and achieve an anatomical restoration that works mechanically and esthetically. This chapter covers the distinguishing elements of each tooth type that should be considered during restoration.
FIG 2-6 Four-sided and triangular fossae (red).
FIG 2-7 Main and accessory anatomical elements of a maxillary left first molar.
FIG 2-8 (a and b) Two maxillary left first molars that appear completely different from each another.
Although the maxillary premolars are very similar to one another (Fig 2-9), they possess characteristics that help distinguish and identify them so that they can be drawn and modeled:
FIG 2-9 Maxillary first (left) and second premolars.
The maxillary first premolar is bicuspid (Fig 2-10). The buccal cusp predominates over the palatal cusp, being slightly larger and higher.
FIG 2-10 (a and b) Clinical photograph and illustration of the occlusal surface of a maxillary first premolar. M, mesial.
One interesting feature, particularly for reconstructive purposes, is an interradicular concavity on the mesial side. This continues along the mesial wall and very often along the occlusal surface, causing a break in the marginal ridge. The central developmental groove runs along the premolar mesiodistally and is longer on the first premolar compared with the second premolar. Also in comparison with the second molar, the first premolar also displays a more uniform occlusal anatomy, featuring fewer secondary grooves, and the palatal cusp tip is often positioned more mesially (Fig 2-11). Figure 2-12 shows anatomical references whose specificities and variants should be considered when modeling. Figures 2-13 and 2-14 provide additional views of the occlusal surfaces of maxillary premolars, highlighting the variations that occur naturally.
FIG 2-11 Maxillary left first (left) and second premolars.
FIG 2-12 Maxillary right first premolar. (a) The central developmental groove is centered mesiodistally but located slightly palatally. The buccal cusp is slightly larger than the palatal cusp. In subtractive techniques, this will be the first groove to be defined; in additive techniques, the cusps will be defined as the result of moving masses closer together. M, mesial. (b) The central developmental groove extends in a buccal direction both mesially and distally, separating the buccal ridges from the palatal cusp as well as from the mesial and distal marginal ridges. Two small supplemental grooves sometimes extend from the primary groove toward the palatal cusp. (c) The mesial interradicular concavity can extend to the mesial marginal ridge, creating a depression or break in the ridge. (d) Sometimes this break in the marginal ridge continues into the central developmental groove. (e) The triangular ridges of the cusps are not usually accentuated. When they are, the associated supplemental grooves must be exaggerated accordingly.
FIG 2-13 Maxillary right first (right) and second premolars.
FIG 2-14 Maxillary left first (left) and second premolars.
The maxillary second premolar is very similar to the first (Fig 2-15). However, the central developmental groove is shorter, and there are many more supplemental grooves extending from it than in the first premolar. This tooth is much more symmetric than the first premolar and significantly more rounded. Figure 2-16 shows anatomical references whose specificities and variants should be considered when modeling. Figures 2-17 and 2-18 provide additional views of the occlusal surfaces of maxillary premolars, highlighting the variations that occur naturally.
FIG 2-15 (a and b) Clinical photograph and illustration of the occlusal surface of a maxillary right second premolar. M, mesial.
FIG 2-16 Maxillary right second premolar. (a and b) The position of the central developmental groove is approximately centered mesiodistally and buccopalatally; its mesiodistal extension is shorter than on the first premolar. (c) The space occupied by the marginal ridges is accordingly greater. (d) The quantity of supplemental ridges and grooves is extremely variable; the anatomy ranges from only slightly to very accentuated depending on individual tooth characteristics.
FIG 2-17 (a to c) Maxillary right first and second (left) premolars.
FIG 2-18 (a and b) Maxillary second premolars.
Compared with the maxillary premolars, the maxillary molars are relatively dissimilar to one another (Fig 2-19). The first molar is very bulky; it is often accompanied by an accessory cusp (cusp of Carabelli), which is located palatal to the mesiopalatal cusp. A distinctive oblique ridge joins the mesiopalatal and distobuccal cusps. The buccopalatal diameter of the maxillary molars is wider than the mesiodistal diameter. On the maxillary second molars, the smallest cusp (distopalatal) may be missing.
FIG 2-19 Maxillary left first (left) and second molars.
The maxillary first molar has four cusps (five if the cusp of Carabelli is included) (Fig 2-20). The mesiopalatal cusp is the largest. Specific features include:
FIG 2-20 (a and b) Clinical photograph and illustration of the occlusal surface of a maxillary left first molar. M, mesial.
The oblique ridge is characterized by a slight depression (groove) in the center. Figure 2-21 shows anatomical references whose specificities and variants should be considered when modeling. Figure 2-22 provides additional views of the occlusal surfaces of maxillary first molars, highlighting the variations that occur naturally.
FIG 2-21 Maxillary left first molar. (a) The central fossa is approximately centered in the occlusal surface. M, mesial. (b) The pit of the central fossa can be approximately positioned by drawing a line joining the mesiobuccal and distobuccal cusp tips and extending a perpendicular line starting from the intercuspal groove. (c) The occlusomesial and occlusobuccal grooves run from the central fossa (generally perpendicular to one another). The distal fossa is located approximately at the buccopalatal midpoint and 1.5 to 2 mm from the distal margin. (d) The distopalatal groove extends from the distal fossa in a mesiopalatal direction. This oblique groove generally runs parallel to the distal portion of the mesiopalatal cusp crest. (e) The mesial marginal ridge invades the occlusal surface to a greater or lesser extent, determining the length of the mesial groove. (f) The oblique ridge is defined by two opposing cusp crests. The mesial slopes of the ridge are broader and shallower than the distal slopes. (g) The supplemental grooves can be more or less pronounced. (h) Sometimes the mesial marginal ridge is clearly interposed between the mesiopalatal and mesiobuccal cusps, almost reaching the central fossa. (i) The mesial marginal ridge can be a single ridge or sometimes has breaks that divide it into several segments invading the occlusal surface. (j) Sometimes, as with the first premolar, the break in the mesial marginal ridge is pronounced enough to mark a distinct separation from the mesiopalatal cusp.
FIG 2-22 Maxillary right (a) and left (b) first molars.
The maxillary second molar is not as bulky as the first molar (Fig 2-23). The normal geometry of this tooth is somewhat more diamond-shaped than the first molar, which is much squarer. Sometimes this tooth also has an oblique ridge, almost always divided by a relatively pronounced groove. Figures 2-24 and 2-25 shows anatomical diagrams of both the four- and three-cusp variants. Sometimes, it is more triangular than square due to the absence of a distopalatal cusp.
FIG 2-23 Maxillary right second molar.
FIG 2-24 (a and b) Clinical photograph and illustration of the occlusal surface of a four-cusp variant of a maxillary left second molar. M, mesial.
FIG 2-25 (a and b) Clinical photograph and illustration of the occlusal surface of a three-cusp variant of a maxillary left second molar. M, mesial.
Mandibular molars (Fig 2-26) differ from maxillary molars because their mesiodistal diameter is greater than their buccopalatal diameter. The first molar has five cusps, and the second has four. The occlusal anatomy of the second molar is defined by grooves that form a cross that separates the four cusps in a relatively equally proportioned manner.
FIG 2-26 Mandibular right first (left) and second molars.
The occlusal surface of the mandibular first molar (Fig 2-27) consists of five cusps—three buccal and two lingual. In order of magnitude they are as follows: mesiolingual, distolingual, mesiobuccal, centrobuccal, and distobuccal. The latter is absent in the four-cusp variant. Because an occlusal view of the tooth shows a large amount of the tooth’s buccal surface, the occlusal surface looks as though it has shifted lingually. Figure 2-28 shows anatomical references whose specificities and variants should be considered when modeling. Figure 2-29 provides an additional occlusal view.
FIG 2-27 (a and b) Illustration and clinical photograph of the occlusal surface of a mandibular left first molar. M, mesial.
FIG 2-28 Mandibular left first molar. (a) The central fossa is approximately centered mesiodistally but displaced slightly lingually. (b) The central fossa is the point of confluence of three grooves, forming a Y. The two buccal grooves house the centrobuccal cusp crest, while the lingual groove separates the lingual cusp crests. (c and d) Both buccal portions of the Y-shaped groove end in fossae. The other grooves, separating the mesiobuccal and distobuccal ridges, branch off from these. The buccolingual developmental grooves, together with the supplemental grooves, separate the cusps from one another. (e) The mesiodistal developmental grooves extend toward the mesial and distal marginal ridges. (f) The mesial marginal ridge extends toward the occlusal surface. (g) Sometimes there is a mesial fossa from which two supplemental grooves run toward the margin. (h) On other occasions, these supplemental grooves traverse the entire marginal ridge, creating breaks. These characteristics can be appropriately recreated to break up a marginal ridge that would otherwise look artificial.
FIG 2-29 Occlusal surface of a mandibular left first molar.
The mandibular second molar has four cusps (Fig 2-30). The occlusal surface looks quite simple as it is only slightly lingualized and features cross-shaped developmental grooves separating the four cusps. Figure 2-31 shows anatomical references whose specificities and variants should be considered when modeling. The simplicity of a cross-shaped occlusal growth pattern is difficult to replicate in a natural-looking way during restoration. Sometimes the cross-shaped pattern is more complex, and there are two triangular fossae from which the grooves run (Fig 2-32).
FIG 2-30 (a and b) Clinical photograph and illustration of the occlusal surface of a mandibular left second molar.
FIG 2-31 Mandibular left second molar. (a) The occlusal surface looks relatively square-shaped. M, mesial. (b) The position of the central fossa is relatively centered in the occlusal surface, which looks slightly lingualized from an occlusal viewpoint. (c) Grooves defining the four cusps originate in the central fossa. (d) Mesial and distal marginal fossae, from which the supplemental grooves run, are located approximately 1.5 mm from the marginal ridge.
FIG 2-32 (a and b) Two mandibular second molars in which two opposing cusp crests meet to create two central fossae separated by a groove.
Unlike their maxillary counterparts, the mandibular premolars are very different from one another (Fig 2-33). They have one feature in common: The lingual cusps are much lower than the buccal cusps (particularly on the first premolar), causing the center of the occlusal surface to be highly lingualized from an occlusal viewpoint. The mandibular second premolar shows great occlusal anatomical variability.
FIG 2-33 Mandibular first (right) and second premolars.
The mandibular first premolar is mainly composed of its buccal cusp; the lingual cusp is reduced in both volume and height (Fig 2-34). There is one developmental groove, and the occlusal surface is lingually displaced (Fig 2-35). Figure 2-36 shows anatomical references whose specificities should be considered when modeling.
FIG 2-34 (a and b) Illustration and clinical photograph of the occlusal surface of a mandibular right premolar.
FIG 2-35 Premolar comparison. The occlusal plane of the first premolar (left) is very angled compared with that of the second premolar.
FIG 2-36 Mandibular right first premolar. (a and b) The central developmental groove is positioned lingually, creating a buccal portion that is two-thirds or three-quarters of the occlusal surface. The surface may be concave, convex, or straight. The central developmental groove often continues to cut into the marginal ridge (both mesially and distally). M, mesial. (c) Supplemental grooves originating from the developmental groove delimit the occlusal extensions of the marginal ridges.
The lingual portion of the mandibular second premolar is more pronounced than that of the first premolar and may consist of one or two cusps. This variability is the result of differences in the central developmental groove, giving this tooth an H, U, or Y configuration (Fig 2-37). Figure 2-38 shows anatomical references whose specificities and variants should be considered when modeling. Figure 2-39 provides additional views of the occlusal surfaces of mandibular premolars, highlighting the variations that occur naturally.
FIG 2-37 Mandibular right second premolar. (a) Diagram showing the Y variant. (b and c) H variant.
FIG 2-38 Mandibular right second premolar. M, mesial. (a to c) H variant. The central developmental groove (slightly lingually positioned in all mandibular premolars) is horizontal and confers an H-shaped appearance once the supplemental grooves delimiting the marginal ridges have been defined. (d to f) U variant. If the buccal cusp is very pronounced, it extends toward the lingual portion to assume a U shape. (g to i) Y variant. Two lingual cusps are present, giving a Y shape to the central developmental groove.
FIG 2-39 (a to d) Extreme anatomical variability of mandibular premolars.
A study of anatomy is extremely useful in order to grasp anatomical basics. However, it is one thing to talk about anatomical fundamentals and quite another thing to talk about shape and its perception (see chapter 1). Observing a natural tooth from an occlusal viewpoint allows one to check the basic anatomical theories described (Fig 2-40a), but the only way to perceive the anatomical details that will be very useful to clinicians in constructing a natural-looking model is to change the observation perspective (Fig 2-40b). Many of these details, even those imperceptible from a particular observation perspective, are still always present and play a crucial role in shape perception. A shape is a set of details, with each one making an intrinsic contribution to the overall shape; without any particular detail the perceived shape will no longer be the same.
FIG 2-40 (a) Occlusal view of a maxillary first molar. (b) Occlusal view with a slightly palatal angle. Different anatomical features are identified according to the observation point.
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